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Russian Chemical Reviews 69 (2) 95 ± 104 (2000) Thermodynamic properties of C60 and C70 fullerenes V V Diky, G J Kabo Contents I. Introduction II. Behaviour of fullerenes in thermodynamic studies III. Enthalpies of formation of C60 and C70 IV. Heat capacities in the condensed state and thermodynamics of phase transitions in C60 and C70 V. Saturated vapour pressures and enthalpies of sublimation of fullerenes VI. Thermodynamic properties of C60 and C70 in the ideal gas state VII. Conclusion Abstract. thermodynamic basic the of values reliable most The The most reliable values of the basic thermodynamic parameters based recommended are C the of parameters of the C60 and and C70 fullerenes fullerenes are recommended based on original and data published the of analysis the on the analysis of the published data and original calculations, calculations, viz states, gaseous and solid the in formation of enthalpies ., ., enthalpies of formation in the solid and gaseous states, saturated sublimation, of enthalpies pressures, vapour saturated vapour pressures, enthalpies of sublimation, enthalpies enthalpies of the in entropies capacities, heat transitions, phase of phase transitions, heat capacities, entropies in the condensed condensed state state.gas ideal the in entropies and capacities heat and state and heat capacities and entropies in the ideal gas state. The The factors of studies thermodynamic of results the influencing factors influencing the results of thermodynamic studies of full- full- erenes structure crystal of aspects Various discussed.are erenes are discussed. Various aspects of crystal structure determi- determi- nation, of modes normal of frequencies and PVT-relationships nation, PVT-relationships and frequencies of normal modes of the the C and interpret to order in considered are C 60 and and C70 fullerenes fullerenes are considered in order to interpret and correlate the thermodynamic data and extend them to a wide correlate the thermodynamic data and extend them to a wide temperature range. The bibliography includes 135 references. temperature range. The bibliography includes 135 references. I. Introduction The need for the knowledge of thermodynamic properties of fullerenes arises not only from the interest in this unusual class of compounds or the quest for efficient ways of their preparation and practical use.The fullerenes have now become the `proving ground' for testing virtually all the modern methods of predicting the structure and properties of solids, fluids and ensembles of particles. Therefore, the well-grounded and reliable values of the basic thermodynamic parameters of these compounds are of great importance. Although the extensive literature on fullerenes is available (including reviews 1± 5), their thermodynamic properties are known less reliably than those of many other `ordinary' compounds. The publication of a specialised review 6 devoted to the studies of thermodynamic properties of fullerenes was fol- lowed by the appearance of many new communications.However, their results were often contradictory. The main reason for the contradictions seems to lie in the specific properties of fullerenes, which are more sensitive to the sample prehistory and conditions of the experiment than the properties of ordinary organic sub- stances. Understanding of this fact came gradually in the course of thermodynamic and other studies, so that the lack of information at the time of publication of an article often did not enable the V V Diky, G J Kabo Department of Chemistry, Belarus State University, ul. Leningradskaya 14, 220050 Minsk, Belarus. Fax (375-17) 220 39 16. E-mail: diky@chem.bsu.unibel.by Received 20 May 1999 Uspekhi Khimii 69 (2) 107 ± 117 (2000); translated by E Kravchenko #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v069n02ABEH000535 95 95 96 97 100 100 102 authors to assess the influence of various factors on the final result of their measurements.Therefore, any report on thermodynamic properties of fullerenes should be considered in the light of the overall information available on these compounds with the details of the experiment taken into account. Based on such an analysis (the experimental data published between 1987 and 1998 have been surveyed), the present review recommends values for the most important thermodynamic parameters of the C60 and C70 fullerenes. The following criteria were used in selecting the experimental data and establishing the recommended values.The characterisation of samples and exper- imental procedures should be exhaustive in order to rule out the influence of known factors affecting the results of measurements. Preference was given to the results available for the sublimates whose purity and stability were confirmed by independent studies. The precision of the techniques used and reproducibility of the results were taken into account. Thus the heat capacity values measured by adiabatic calorimetry (AdC) were considered to be the most reliable. An agreement between the results obtained by various authors as well as between the thermodynamic parameters of each of the fullerenes were also taken into consideration. II. Behaviour of fullerenes in thermodynamic studies The effect of impurities and chemical instability of fullerenes are the factors that hamper the determination of their thermodynamic properties most seriously.Conventional purification procedures and methods of purity control applied to organic compounds appeared to be inefficient for fullerenes which show a tendency towards co-crystallisation with the solvent molecules. Even small amounts of impurities significantly affect various properties of fullerenes. Thus, the phase transition temperature 7 (Ttr) of C60 shifts from 260.7 K to 243 K or to 245 K in the presence of benzene 8 or toluene admixtures. Also an additional heat capacity anomaly appears at 232 or 239 K, respectively. Two additional heat capacity anomalies,9 at 185 and 425 K appear in the C60 sample crystallised from carbon disulfide due seemingly to the presence of a CS2 impurity.The anomaly observed at 185 K disappears after annealing the sample at 425 ± 500 K. The C60 crystals grown from a solution of fullerene in carbon disulfide are monoclinic, the temperature of the `ordinary' phase transition being shifted in such crystals to 242 K.10 The rhombohedral C60 crystals grown from a toluene ± hexane solution (the purity is 99.9% from mass spectrometric measurements) undergo a phase96 transition associated with a diffuse anomaly of the heat capacity at 239 K.11 It was found that an adduct of the C70 fullerene with toluene (C70 .C7H8) exhibits heat capacity anomalies at 195 and 430 K (the latter is due to an irreversible decomposition of the adduct).12 After the decomposition of the adduct, a heat capacity anomaly 12 at 304 K and two phase transitions 13 at 277.4 and 340.0 K were observed in the sample.It was also found out that several heat capacity peaks observed upon phase transition in C60 are due to the C70 impurity present in the sample.14 It was found that fullerenes absorb (or adsorb) large amounts of oxygen and, probably, water.15 Pellet-like samples were kept in a moist oxygen atmosphere under pressure of 30 bar. It was measured that C60 absorbs 30 ± 60 g mol71 in 0.5 h and C70, more than 150 g mol71 in *24 h. Although these estimates 15 are seemingly overstated (the specific surface of the C60 samples measured with liquid nitrogen 16 was *3 m2 g71), the uncon- trolled adsorption could affect the results of combustion experi- ments.Two maxima on the temperature curve of desorption of oxygen and other substances plotted for a C60 sample indicate 17 that impurities are absorbed by both the surface and the bulk of a substance. The location of impurities in polycrystalline fullerene C60 has been studied in detail;16 it was found that the solvent molecules were mainly adsorbed on the surface of microcrystals, whereas upon thermal treatment, they could be fixed in cavities of the baked crystals. This may be a reason why it is difficult to purify fullerenes by heating in vacuo. The thermodynamic properties of fullerenes were reported to depend on the size of crystals in a sample.18 ± 21 A finely crystalline C60 sample (1) of brown colour which contained 0.004 mol of C70 (from HPLC measurements) exhibited a fall in the phase tran- sition temperature (Ttr=258.6 K), a decrease in the enthalpy of combustion (DcU8=735 896 J g71) and incomplete yield of CO2 in the combustion products (approximately 99.8%) as compared to similar characteristics (Ttr=260.9 K; DcU8= 736 030 J g71; the yield of CO2 upon combustion is 100.000.04%) exhibited by a chromatographically pure coarsely crystalline C60 sample (2) of black colour.21 Both samples were dried under the same condi-tions: for several hours at 440 ± 520 K and a pressure of 0.001 Pa.Kolesov et al.21 suggest however that the changes in the properties of the sample 1 could be caused by impurities either occluded upon its fast crystallisation or adsorbed by its developed surface.It was found 19, 20 that the C60 crystals become progressively less capable of solid-state transitions as they are ground. Skokan et al.16 examined this phenomenon in detail to conclude that this results from the defects accumulated in the crystals, the effect of solvent impurity not being involved. At fairly high temperatures (700 K and above) at which most of the reported effusion measurements have been made, partial decomposition of samples can occur. Thus, a nonvolatile residue (8%) was detected in C60 after it had been sublimed at 1273 K in a nitrogen atmosphere and dried in vacuo at 700 K.22 A sample of C60 purified by sublimation at 673 K (the sample purity was 99% from mass spectrometric measurements 23) yielded 5% of a non- volatile residue after it had been sublimed at 973 ± 1073 K in a nitrogen or an argon atmosphere.After sublimation of the 99.98% pure C60 fullerene, 0.1% ± 0.3% of the substance still remained nonvolatile, the evaporation of the first half of the sample being followed by a not fully understood fall of the saturated vapour pressure.24 It is suggested that partial trans- formation of fullerenes into nonvolatile amorphous carbon at 700 ± 740 K may result from contamination of the initial sample with remains of organic solvents.25 Fullerene C70 (98.5% pure, the main impurity being C60) contained 6%± 8% of nonvolatile deposit (amorphous carbon) after mass loss of 1% had been detected at 450 K and a cycle of effusive measurements had been performed.26 A sublimed sample was evaporated nearly com- pletely in a repeat run, although some pressure fall was observed in the effusive measurements in carbon cells at 800 ± 900 K and a small amount of nonvolatile deposit was still detected.Destruc- V V Diky, G J Kabo tion of the C60 and C70 fullerene molecules in the vapour phase 27 begins at 2650 and 2440 K, respectively, and in the condensed state,28, 29 above 1000 ± 1073 K, the temperature limits depending on the nature and content of impurities.25 Therefore, the following strategies appear to be efficient in the preparation of pure specimens suitable for thermodynamic stud- ies: growth of large-sized crystals 16, 21 and sublimation of full- erenes in vacuo.24, 26, 30, 31 If, prior to sublimation, a sample is dried at a gradually increasing temperature, the major portion of the solvent is probably removed before the degradation (amorphisa- tion) of the basic substance begins.Experience gained by various researchers suggests 15, 17 that the protection from traces of oxygen is particularly necessary in the sublimation. Fullerenes are known to be vigorously oxidised by oxygen at elevated (>500 K) temperatures.23, 32 ± 34 However, under exposure to either high-energy photons or visible light (0.5 ± 5.0 eV), the photoinduced oxidation of the fullerenes by atmospheric oxygen becomes possible at room and even low (20 K) temperatures.35 This imposes additional requirements for the preparatory conditions and purification of fullerenes intended for thermodynamic studies.Methods of purity control of the samples used for thermody- namic measurements are of principal importance. HPLC is a traditional method which allows determination of the degree of separation of fullerenes with different compositions and the C60O content.15 It is significant to establish to what extent the organic solvents used for the sample preparation (benzene, toluene, xylene, carbon disulfide, diethyl ether, etc.) have been removed. The presence of benzene impurity is determined using 1HNMR,36 although the sensitivity of the method may be insufficiently high.37 The hydrogen content in a C60 sample is measured by activation analysis.38 The C60 sample was heated in a sealed tube in a nitrogen atmosphere (673 K, 10 min) and the vapour phase was then analysed by GLC.39 Unfortunately, total removal of impurities as well as their constant chemical composition are questionable under such conditions.Volatile substances released upon gradual heating of a C60 sample were analysed by mass spectrometry,17 but no quantitative estimates of the impurity content were made. The phase transition temperatures and a proportion of nonvolatile deposit found after the sublimation may serve as indirect criteria of the sample purity. The lack of details in some papers describing the prehistory of samples and methods of their study does not enable one to evaluate the effect of the above-listed factors on the results of measurements of thermodynamic properties. III.Enthalpies of formation of C60 and C70 The measured enthalpies of combustion and formation of C60 are listed in Table 1. The scatter in the standard combustion energies amounts to *0.6% (from 735 914 to 736 124 J g71) which is Table 1. The enthalpies of combustion and formation of C60. Ref. 7DcH8 /kJ mol71 DfH8 /kJ mol71 7DcU8 /J g71 2273.0(13.0) 2278.1(14.4) 228216 232744 25 881.8(13.0) 25 888.7(12.1) 25 893.014.0 25 93844 36 38 43 15 42 21 39 37 2336.5(8.5) 235515 236016 2422.3(14.0) 25 947.1(8.5) 25 96512 25 97012 26 032.9(14.0) 35 914.0(18.0) 35 923.6(16.8) 35 929.519.4 35 99261 36 004.6(11.8) 36 03016 36 036.716.7 36 123.7(19.4) 36 01717 25 95612 234612 Note.Here and in Table 2, the recommended values are printed in bold face. We estimated the uncertainties within the reliability interval of 95%. The errors given in parentheses are taken from the reference cited; they are most commonly twice the standard deviation.Thermodynamic properties of C60 and C70 fullerenes Table 2. The enthalpies of combustion and formation of C70. Ref. DfH8 /kJ mol71 7DcH8 /kJ mol71 7DcU8 /J g71 36 42 44 15 45 2375(36) 2410.4(8.9) 243937 a 249735 b 255522 2577.816.2 255522 29 921(36) 29 956.1(8.9) 29 98537 a 30 042.835.3 b 30 10122 30 123.513.4 30 10122 35 587(25) 35 629.4(10.6) 35 66444 a 35 73342 b 35 80226 35 828.415.8 35 80226 a From the mass of a substance; b from the mass of CO2.more than an order of magnitude higher than the experimental error of measurement by combustion calorimetry of organic substances without heteroatoms. The reasons for such a scatter may be the factors that counteract each other, e.g., organic solvent impurities like toluene which are characterised by the heats of combustion of large absolute values (742382 J g71) and adsorbed oxygen and water which increase the apparent weight of a sample. The problems of precise determination of the enthalpies of combustion of fullerenes are discussed in a review,40 and the enthalpies of formation of carbon clusters in relation to their structures and sizes are analysed in a review.41 The scatter of the reported enthalpies of combustion DcH8 lies within 0.12%.15, 21, 39, 42 The results of earlier publications lie outside this interval.Five experiments performed on presumably one of the best C60 samples (purified by sublimation) 15 gave, for unclear reasons, a wide dispersion of the results. Kolesov et al.21 examined a specially prepared coarsely crystalline sample; an analysis of the combustion products gave the CO2 yield of 100.000.04%. A similar result was obtained 39 (see Table 1) using large samples (of approximately 0.5 g) and an original GLC-analysis of organic solvent contaminations in fullerene (0.013 mass%of diethyl ether and 0.007 mass%of o-xylene).Later, An et al.42 gave the enthalpy ofC60 combustion which was slightly different from their previous result.39 Therefore, the value DfH8(cr)= 234612 kJ mol71 which is an average of the published data 21, 42 is recommended for the enthalpy of formation of C60 in the crystalline state. The enthalpy of formation in the gaseous state is DfH8(g)= 253013 kJ mol71, the enthalpy of sublimation of C60 (DsubH8=183.75.1 kJ mol71) being taken into account. The measured combustion energy values DcU for the C70 fullerene (Table 2) are scattered even wider, over more than 0.7% (from 735 587 to 735 828 J g71). The reasons for the scatter are evidently similar to those for C60. The uncertainty of the crystal composition of C70 at 298.15 K which is discussed Table 3.Thermodynamic characteristics of a solid-state transition in C60. Ttr /K DtrH /kJ mol71 Sample purity 99.5% dried in vacuo at 700 K 4.8 6.7 249 255 dried in vacuo at 475 K, purity 99.5% a 256 257.6 258 259 ±±± 7.0 7.54 6.2 3.20.2 dried at 440 K (13 Pa, 5 days) DSC dried in vacuo at 400 K, purity 99.98% b AdC DSC 260 260.7 261.4 sublimed, single crystal 77.460.15 9.00.5 Note. DSC is differential scanning calorimetry, AdC is adiabatic calorimetry. a From mass spectra and Raman spectra; b from HPLC measurements; c the remaining part of the heat effect (2.2 kJ mol71) was found by integrating the difference between the heat capacity of a sample and the baseline in the temperature interval 150 ± 290 K.97 below cannot have a notable effect on the error in determination of the enthalpy of formation, because the energy difference between different crystal modifications of C70 is two orders of magnitude smaller. It is likely that the best sample of this fullerene purified by sublimation was studied by Beckhaus et al.,15 therefore their results are recommended as most reliable. Only in one publication 44 was the amount of CO2 in the combustion products measured to find a yield of 99.810.02%. Assuming that the material balance on carbon 44 was upset due to the presence of inert impurities (adsorbed gases or water) in the C70 finely crystalline sample and relating the heat of combustion to the appropriate amount of CO2, one obtains the value DcU8= 735 732.542 J g71, which is close to that given by Beckhaus et al.15 The data by Diogo et al.45 are also close to the latter value 15, but one cannot say, judging from the results of HPLC analysis of C70 fullerene,45 whether toluene was completely removed from the sample.We cannot offer an explanation of a low absolute value of the enthalpy of C70 combustion reported by An et al.42 Thus, the recommended value for the enthalpy of formation 15 of C70 is DfH8(cr)=255522 kJ mol71. With the enthalpy of sublimation of C70 DsubH298:15=200.36.1 kJ mol71 taken into account, the enthalpy of formation in the gaseous state at 298.15 K is DfH8(g)=275523 kJ mol71. IV. Heat capacities in the condensed state and thermodynamics of phase transitions in C60 and C70 It is now commonly accepted that the C60 fullerene crystallises at T=298.15 K and pressure P=1 atm in a face-centred cubic lattice with a=14.152A and d=1.69 g cm73 (see Ref.17). Molecular rotation in such a crystal results in an orientational disorder. Upon cooling below 260 K, a solid-state transition occurs. In the low-temperature modification,46, 47 the C60 mole- cules have four different orientations in space making a simple cubic lattice. Some rotational degrees of freedom are retained in this case. The remaining rotational degrees of freedom freeze upon vitrification of the crystal 48 at around 90 K. From calorimetric measurements, the vitrification temperatures are Tg=86.8 (see Ref. 49) and 86.0K(see Ref.7). The residual entropy ofC60 at 0K was estimated to be 4.70.5 (see Ref. 50) and 4.9 J K71 mol71 (see Ref. 7). Although the estimation procedures are not indis- putable, we see little reasons for revising the results. As reported by Willart et al.,51 no other transitions occur in an impurity-free C60 sample at atmospheric pressure. Table 3 lists the measured enthalpies of phase transition DtrH in C60 around 260 K. Probable reasons for the scatter in Ttr and Ref. Note Method 52 22 DSC AdC sample of small weight, 8% of a deposit detected after sublimation in nitrogen at 700 K 53 49 54 27 DSC AdC DSC DSC three peaks at 253, 258 (90%) and 260 K peaks at 240 K (due to impurities) and 259 K; difficulty in baseline location 477 19 sample of small weight, the heat effect under the peak is 6.8 kJ mol71 (see c)98 Table 4.Details of heat capacity measurements of C60 in the condensed state. Sample Not completely solvent-free Extracted with benzene, chromatography, dried at 700 K, 8% of a deposit detected after sublimation Extracted with a benzene ± hexane mixture, chromatography, washed with ether, dried at 475 K, 99.5% pure a Extracted with toluene, washed with ether, chromatography, dried at 450 K for 50 h, purity 99.99 mol.% c ±±Extracted with a benzene ± hexane mixture, chromatography, dried at 523 K for 24 h, single crystal Extracted with toluene, chromatography, dried at 400 K, 99.98%pure d Note.MCis modulation calorimetry. a From mass spectra and Raman spectra; b no phase transitions occur upon further heating to 950 K; c from HPLC measurements; d from HPLC and X-ray diffraction. DtrH values were discussed in Section II.In addition, the tran- sition is not isothermal (2N-type according to the classification of Westrum and McCullough 55), which makes difficult both the interpretation of the calorimetric data and the choice of the heat capacity baseline in the calculation of the enthalpy of phase transition. This seems to account for the large value of DtrH reported by Dworkin et al.19 The values 7, 49 of DtrH measured by an adiabatic calorimetry are in good agreement with each other. The values measured in 1993 using differential scanning calorimetry (DSC) are fairly close to them.19, 47, 54 For the calculation of the entropy of the crystalline C60, one should know the value of DtrH together with the heat capacity values, which rules out the use of DtrH averaged over several published data. Therefore, we recommend the values 7 Ttr=260.7 K and DtrH=7.460.15 kJ mol71 which are consistent with the heat capacity values recommended in the same publication.7 The heat capacities of C60 samples of different qualities measured by various methods are listed in Table 4.All the published results except for the data given in Refs 7, 37, 53 were presented only in a graphical form to show a fairly good agree- ment with each other (except for the data 37). Thus, the recom- mended values of thermodynamic parameters for the solid C60 in the interval 0 ± 1000 K (Table 5) were listed based on the heat capacities measured by AdC7 in the range 5 ± 340 K and by DSC53 in the range 340 ± 560 K.Because the Debye characteristic temperature of fullerenes is low, it is important to know their heat capacity below 5 K. Allowance is made in Table 5 for the heat capacities of C60 in the range 0 ± 10 K which were measured by a thermal relaxation method (the graphical data 56). We extended the heat capacity values to the interval 560 ± 1000 K by a proce- dure described by Jin et al.53 The heat capacity CV of a crystal was represented by a sum of contributions of the lattice (Clat) and intramolecular (Cint) vibrations CV=Clat+Cint .The contribution of the intramolecular vibrations was calcu- lated by methods of statistical thermodynamics using the set of normal modes chosen as described in Section VI. The contribu- tion of the lattice translational modes at T>298.15 K was taken to be 3R, whereas that of the librational modes (or molecular rotation in a crystal) was calculated for the hindered rotation of the C60 molecules using a harmonic potential. The effective value of the potential barrier to molecular rotation (5 kJ mol71) was chosen to provide the best fit of the calculated heat capacities with their measured values in the range 300 ± 560 K. A relatively low value of the potential barrier is qualitatively consistent with both Method AdC AdC DSC DSC thermal relaxation AdC MC AdC the spherical shape of the C60 molecule and the absence of heat capacity jump upon the solid-phase transition.57 Table 5.Recommended values of the thermodynamic parameters [CP, S and7(G7H0)/T in J K71 mol71; H7H0 in kJ mol71] of the crystalline C60. T /K CP Vitreous crystal II 02.37 13.78 33.41 49.72 76.62 76.62 96.60 185.5 303.3 423.1 446.8 05 10 20 50 86.0 Crystal II 86.0 100 150 200 250 260.7 Crystal I 260.7 298.15 300 350 400 450 500 550 600 650 700 750 800 850 860 900 950 1000 446.8 525.6 529.6 633.6 720.5 801.9 877.7 947.8 1009 1062 1107 1147 1180 1210 1215 1236 1259 1281 Temperature range /K 10 ± 300 4.2 ± 300 120 ± 560 b 300 ± 800 1.4 ± 20 13 ± 300 120 ± 300 5 ± 339 S4.9 5.7 10.4 26.9 65.5 97.4 97.4 110.6 165.4 234.5 315.1 333.3 361.9 427.1 430.3 520.1 610.4 700.0 788.5 875.5 960.6 1044 1124 1202 1277 1349 1363 1419 1487 1552 V V Diky, G J Kabo Ref.8 22 53 37 56 49 117 7(G7H0)/T H7H0 00.0030 0.0399 0.2887 1.586 3.744 4.9 5.1 6.4 12.4 33.8 53.8 3.744 4.974 11.88 24.04 42.20 46.85 53.8 60.8 86.2 114.3 146.3 153.6 54.31 72.52 73.50 102.7 136.6 174.6 216.6 262.3 311.3 363.1 417.3 473.7 531.9 591.6 603.8 652.8 715.2 778.7 153.6 183.8 185.3 226.7 269.0 311.9 355.2 398.5 441.8 485.0 527.7 570.1 611.9 653.2 661.4 693.8 733.8 773.0Thermodynamic properties of C60 and C70 fullerenes Table 6.The a and b parameters of the C60 fullerene. T /K 105a /K71 298 ¡À 323 ¡À 523 27 a 298.15 260 ¡À 300 ¡À4 298 6.20.2 3.5 298 300 ¡À 900 4.570.04 298 ¡À a A 3 : 1 mixture of C60 and C70. CP was calculated from CV by the relationship CP ¡¦ CV �� a2 b VmT , where a is the volume expansion coefficient, b is the isothermal compressibility coefficient, Vm is the molar volume. The following values were accepted for a and b at 300 K: a=4.661075 K71, b=1.55610710 Pa71 (Table 6). At this temperature, the differ- ence CP7CV was as low as 1.8 J K71 mol71, which appeared to be much less than the value estimated by Jin et al.53.The difference CP7CV was extended to T=1000 K using the procedure described by the same authors CP7CV=kCVT, the value of k (1.1661075 K71) was calculated from the data at 300 K. The calculated heat capacities of the C60 crystal (Fig. 1) are in good agreement with those measured by DSC53 in the interval 500 ¡À 550 K, whereas at 300 K, they are 11 J K71 mol71 (or *2%) less than the values measured by AdC.7 We estimate the error of the entropy determination of C60 to be 2 and 13 J K71 mol71 at 298.15 and 860 K, respectively. The Debye characteristic temperature of C60 estimated from the heat capacity measurements in the interval 0 ¡À 5 Kamounts to *46 K, which is close to the value predicted based on the law of corresponding states with the inert gases (40 K).5 CP /J K71 mol71 1200 800 4000 200 Figure 1.The heat capacity of the C60 fullerene vs. temperature. (1) the DSC data;53 (2) the AdC smoothed data;7 (3) our calculations. Ref. Method 1010 b /Pa71 58 0.7 X-ray structural analysis 59 1.4 ¡À 2.5 a dilatometry of powder 60 48 1.47 ¡À dilatometry capacitance dilatometry 61 ¡À X-ray structural analysis 62 0.70 calculation 63 ¡À X-ray structural analysis 64 1.5 the same (1) D1 D2 D3 800 600 400 T /K 99 In a recent paper,13 the data reported on the heat capa- city 65 ¡À 67 and thermodynamics of phase transitions 12, 68 in C70 were compared and commented.We are also aware of reports 69 ¡À 72 the results of which require no revision.13 The phase state of C70 fullerene is influenced by the sample prehisto- ry.73 ¡À 79Acrystal I in the high-temperature phase characterised by an isotropic molecular rotation can form either a hexagonal or a face-centred lattice. With time, it transforms to a crystal having a face-centred lattice which however comprises 10% ¡À20% of a hexagonal phase. Upon cooling, the crystal I converts to the crystal II characterised by partially frozen rotational degrees of freedom and having either a rhombohedral or a distorted hexa- gonal (c/a=1.82) structure with considerable admixture of hexa- gonal or rhombohedral phases, respectively. Upon further cooling, a monoclinic phase III arises which, unlike the low-tem- perature C60 fullerene crystal, does not undergo transition to the vitreous state.At increased pressure, the transition to the phase III splits into two phase transitions. Some researchers report that the double peak on the heat capacity curve is observed also at atmospheric pressure and explain this phenomenon by either a mixture of the crystal phases present in a sample or successively proceeding phase transitions. It might be suggested from the aforesaid that two modifications of the low-temperature mono- clinic crystal are available and the residual entropy of C70 is not zero at 0 K. Unfortunately, the latter could not be estimated. Note that according to Ref. 13, the transformation of the crystal III to II (Table 7) is associated with one peak on the heat capacity curve.We calculated the thermodynamic parameters of solid C70 in the range 0 ¡À 340 K (Table 8) based on the heat capacities meas- ured by AdC.13 To our knowledge, the report 13 is the only one which gives the numerical values of heat capacities of C70 in this temperature range. In the range 340 ¡À 560 K, we used the heat capacities measured by DSC.13, 65 The heat capacity of C70 was earlier extended to T=1000 K (see Refs 26 and 65); we made an extension by a procedure identical to that for C60. The contribu- tion of intramolecular vibrations was calculated using the same set of frequencies as that accepted for the calculation of the thermo- dynamic properties in the ideal gas state (see Section VI). The translational contribution of the lattice heat capacity was accepted to be 3R, the librational one was calculated for the hindered rotation of the C70 molecules using the harmonic potential.To give the calculated heat capacity the best fit to its measured values in the range 300 ¡À 560 K, the effective potential barrier to molec- ular rotation was chosen to be 3 kJ mol71. The differenceCP7CV was estimated to be 2.6 J K71 mol71 at T=365 K assuming a=4.661075 K71 and b=1.25610710 Pa71 (see Ref. 80). It was extended to a high-temperature region using Eqn (1). The value of k (9.4461076 K71) was calculated from the data at 365 K. The calculated heat capacities of crystalline C70 (Fig. 2) are close to their experimental values at all the temperatures except for those around 400Kwhere they are 30 J K71 mol71 (*4%) larger than those measured by DSC.65 In that region, the curve lies below the line connecting the adjacent regions, the reason being as yet unexplained.We estimate the error in the entropy determination of C70 to be 3 and 15 J K71 mol71 at 298.15 and 843.5 K, respectively. Note that in the interval 100 ¡À 1000 K, excluding the phase transition areas, the heat capacities per carbon atom of the C60 Table 7. The thermodynamic characteristics of solid-state transitions in C70 (see Ref. 13). T /K Note DtrH /kJ mol71 DtrS J K71 mol71 non-isothermal non-isothermal cr. III ?cr. II cr. II ?cr. I 0.54 0.47 11.6 8 29 38 277.4 340 0.0139 0.0176 3.22 2.70.4100 Table 8.Recommended values of the thermodynamic parameters [CP, S and7(G7H0)/T in J K71 mol71;H7H0 in kJ mol71] of crystallineC70. T /K Crystal III 0 03.71 16.46 34.38 52.77 105.7 207.1 337.7 485.4 566.9 5 10 20 50 100 150 200 250 277.40 Crystal II 277.40 298.15 300 340 Crystal I 340 350 400 450 500 550 600 650 700 750 800 843.5 850 900 950 1000 and C70 fullerenes are similar to those of graphite, although these are markedly different in the molecular composition and the crystal structure. It is noteworthy that unlike most organic substances, the temperature dependence of the heat capacities of fullerenes exhibits two inflections, which are caused by low Debye teatures (*46 K and *40 K for C60 and C70 , respectively) and low libration frequencies.When temperature increases from 0 to *30 ± 50 K, both the Debye and librational contributions to the fullerene lattice heat capacity approach their limiting values 3R, whereas the intramolecular contributions still remain small in CP /J K71 mol71 1200 800 4000 Figure 2. The heat capacity of the C70 fullerene vs. temperature; (1) the DSC data;65 (2) the AdC smoothed data;13 (3) our calculations. S CP 01.17 7.44 25.08 65.74 114.5 175.4 252.4 343.4 398.1 409.7 452.7 456.6 541.7 566.9 625.6 630.7 727.0 549.6 571.0 675.0 777.6 882.3 985.0 1085 1183 1277 1368 1456 1531 1542 1624 1703 1779 727.0 746.2 813.0 940.5 1040 1116 1186 1247 1300 1346 1386 1417 1421 1451 1478 1502 400 200 7(G7H0)/T H7H0 00.00448 0.0533 0.318 1.691 5.351 13.04 26.56 47.10 61.52 00.274 2.109 9.175 31.92 60.95 88.52 119.6 155.0 176.3 64.74 77.12 78.28 105.5 176.3 194.0 195.6 231.3 108.2 115.6 154.6 198.2 247.9 301.8 359.4 420.2 483.9 550.1 618.5 679.5 688.7 760.5 833.8 908.3 231.3 240.7 288.6 337.2 386.5 436.3 486.2 536.0 585.6 634.7 683.4 725.2 731.4 778.7 825.2 871.0�1 �2 �3 600 1000 800 T /K V V Diky, G J Kabo this temperature range.In the range 30 ± 50 K, the heat capacity remains relatively stable varying within 40 ± 50 J K71 mol71 (close to 6R), which indicates that the Debye and librational contributions to the heat capacity are saturated.For most of organic substances, such a saturation occurs at higher temper- atures being masked by an increasing contribution of the intra- molecular vibrations. Various computational approaches, from the Debye models with adjustable parameters 22, 56 to those based on the examina- tion 81, 67 and integration 53, 82 of phonon spectra of crystals may give a key to a more comprehensive interpretation of the heat capacities of fullerenes in the condensed state. Both theoreti- cal 83 ± 87 and experimental 88, 89 data on the fullerene lattice vibrations can be found in the literature.V. Saturated vapour pressures and enthalpies of sublimation of fullerenes The results of a recent extensive study by Piacente et al.24 gave the saturated vapour pressure (P) and the enthalpy of sublimation of C60 measured by the Knudsen method, which is one of the most precise methods for measuring low vapour pressures. The prob- lems of sample purity and stability (see Section II) were closely examined, and earlier publications 23, 25, 90 ± 96 were surveyed.24We are also aware of other reports.97 ± 103 Most of the results are merely consistent with those by Piacente et al.24 in order of magnitude. The methods of measurement and preparatory proce- dures described 24 suggest that the following values of saturated vapour pressure and enthalpy of sublimation are most reliable: ln P(kPa)=(19.070.46) ± (21 078350)/T (T=730 ± 990 K), DsubH860 =175.32.9 kJ mol71. It follows from these values and the data listed in Table 5 that at T=860 K and P=1 bar, the experimental magnitude of entropy of C60 in the gaseous state amounts to S860(g)= 148114 J K71 mol71.With the heat capacity of the crystal (see Section IV) and the results of statistical calculations of the heat capacity of a gas (see Section VI) taken into account, the enthalpy of sublimation of C60 at T=298.15 K was recalculated: DsubH8=183.75.1 kJ mol71. The saturated vapour pressure and enthalpy of sublimation of C70 were determined by Piacente et al. in their extended research.26 In addition to the reports 25, 92 ± 94, 104 discussed in Ref.26, we are also aware of other publications (Refs 101 and 105). The values ln P(kPa)=(19.300.35)7(22 835370)/T (T=783 ± 904 K), DsubH843.5=189.93.1 kJ mol71, determined for the freshly sublimed C70 sample 26 are recom- mended as most reliable by the same reasoning as those for C60. Based on these values and the data listed in Table 8, one can deduce that the experimental value of the entropy of C70 in the gaseous state amounts to S843.5(g)=165316 J K71 mol71 at T=843.5 K and P =1 bar. With the crystal heat capacity (see Section IV) and the results of statistical calculations of the heat capacity of a gas (see Section VI) taken into account, the enthalpy of sublimation of C70 at T=298.15 K was recalculated to be DsubH8=200.36.1 kJ mol71.VI. Thermodynamic properties of C60 and C70 in the ideal gas state Thermodynamic properties of fullerenes in the gaseous state were calculated by the methods of statistical thermodynamics.6, 24, 26 All the calculated entropy values of C60 appeared to be lower than the experimental ones (see Section V). In our opinion, the most reasonable set of frequencies of normal modes was used byThermodynamic properties of C60 and C70 fullerenes Piacente et al.24 They averaged the values measured using IR 106 and Raman spectroscopy,107 ± 109 inelastic neutron scatter- ing 110, 111 and those derived from the calculations of the normal modes.112 It appeared that the statistical calculation carried out using the average frequencies of normal modes gives the entropy of gaseous C60 which is closest to its experimental value.Schettino et al.106 gave also a short survey of the spectroscopy and assign- ment of the C60 vibration frequencies. Later, other reviews on IR spectroscopy of fullerenes 113 and assignment of the C60 vibration frequencies 114 ± 121 were published. To our knowledge, no contra- dictions exist at present as to the interpretation of the C60 molecular vibration frequencies. In the present review, the thermodynamic parameters of 860 fullerenes in the ideal gas state were calculated as described by Frenkel et al.122 The translational contributions of C60 and C70 were calculated using their molecular masses equal to 720.66 and 840.77, respectively. In the calculation of rotational contributions, the symmetry numbers 60 and 10 and the products of the principal moments of inertia (IAIBIC) equal to 1.006107129 and 2.506107129 kg3 m6 were used for C60 and C70, respectively. The two latter values were calculated by the models fairly consistent with the X-ray structural results 123 (for C60) and the electron diffraction data 124 (for C70).The scatter in the entropy values of C60 in the gaseous state does not exceed 0.2 J K71 mol71, although different estimates of the moments of inertia are available in different publications. The frequencies of normal modes of C60 (Table 9) were averaged over the measured values.106 The contribution of the excited electronic states (assuming that all the remaining contributions are inde- pendent on the electronic state of molecules) was estimated from the relative energies of one-electron states (Table 10).According to the model used, the contribution of the excited electronic states to the heat capacity of C60 at temperatures above 3000 Kamounts to 5 J K71 mol71, whereas a similar contribution to the entropy is reached at 4500 K. The calculated value of S (1463.8 J K71 mol71, Table 11) is 17 J K71 mol71 smaller than that determined experimentally (148114 J K71 mol71). Therefore, 17 J K71 mol71 can be considered as the error in calculation of the entropy of C60 in the gaseous state. This comprises *1.5% of the vibrational contribution to the entropy, as in the case of the cage hydrocarbons C11H14 and C14H16 with rigid carbon skeletons.129, 130 To make both the entropy of full- erenes in the gaseous state and the heat capacity of a crystal (see Section IV) consistent with the experimental data, we examined a possibility to revise the C60 vibration frequencies.In order for the calculated entropy of C60 in the gaseous state to be equal to its measured value, one has to reduce the wave numbers hence breaking the agreement of the calculated heat capacity of a crystal Table 9. The frequencies of the C60 normal modes used in statistical calculations. Wave number /cm71 Degeneracy Type Ag Hg T1g T2g Gg Au T1u T2u Hu Gu 491, 1458 266, 429, 710, 768, 1095, 1254, 1437, 1570 565, 850, 1289 535, 764, 805, 1334 484, 570, 738, 1135, 1314, 1515 973 527, 578, 1184, 1439 355, 714, 1040, 1187, 1565 403, 486, 669, 740, 1211, 1342, 1530 344, 760, 771, 967, 1321, 1415 1554 Table 10.The low-lying excited electronic states of the C60 molecule. Type Energy /eV III II I 1.88 2.29 2.33 2.34 2.76 3.01 2.65 3.11 3.70 3.38 3.36 4.00 4.26 1.6 2.58 2.61 2.70 2.89 3.15 3.15 3.21 3.89 3.90 4.08 4.12 4.37 4.39 4.41 4.51 6.19 2.06 2.40 2.58 2.59 2.59 2.61 2.66 2.98 3.66 3.81 3.84 4.26 4.28 4.29 4.32 4.32 4.34 1 1T2g 1 1T1g 1 1Gg 1 1T2u 1 1Hu 1 1Hg 1 1Gu 2 1Hu 2 1Gu 1 1T1u 2 1T2u 3 1Gu 3 1Hu 2 1T2g 2 1T1u 3 1T1u 1 3T2g 1 3T1g 1 3Gu 1 3Hg 1 3T2u 1 3T1u 1 3Gg 1 3Hu 2 3T2u 2 3Hu 2 3Gu 2 3Gg 2 3Hg 3 3Gu 2 3T2g 3 3Hu 3 3T1u Note.I, see Ref. 125; II, see Ref. 126; III, see Refs 127 and 128; IV, the energies used in the calculations of contributions of the excited electronic states to the thermodynamic parameters (Table 11). with the experiment. Therefore, the agreement currently available between the thermodynamic and molecular data on the C60 fullerenes seems to be the best at present. The set of frequencies of the C70 normal modes (Table 12) was obtained by averaging the experimental values (the IR 114, 131, 132 and Raman 114, 131 spectroscopic data) based on the reported frequency assignment 133, 134 (see Ref.26). The report 133 was followed by publication of the data 113 on IR spectroscopy of fullerenes and assignments of frequencies of the C70 normal modes 115, 117, 118, 121 which require no revision.133, 134 The calculated value of S 843:5 (1669.2 J K71 mol71) is 16 J K71 mol71 larger than the experimental one (165316 J K71 mol71). This difference can be considered as the uncer- tainty in the calculated entropy of C70 in the gaseous state. Unfortunately, we have no information on a reasonably complete set of the excited electronic state energies for theC70 molecule. The experiments 127, 135 provide evidence that the low-lying electroni- cally excited states are expected to have slightly lower energies than those of C60.Nevertheless, it is believed that only at temper- atures above 3000 Kdoes the neglect of the excited electronic state contributions increase significantly the error in the calculation of the entropy of C70 in the gaseous state. 101 Degener- acy IV 1.88 2.33 2.34 2.76 3.01 2.65 3.11 3.70 3.38 3.36 4.12 4.37 4.39 4.41 4.00 4.26 1.60 2.40 2.58 2.59 2.59 2.61 2.66 2.98 3.66 3.81 3.84 4.26 4.28 4.29 4.32 4.32 4.34 334355454334533333453345354454353102 Table 11. The thermodynamic properties of the C60 and C70 fullerenes [S8, C P, (H7H0)/T and 7(G7H0)/T in J K71 mol71; DfH8 and DfG8 in kJ mol71] in the ideal gas state at 101 325 Pa.T /K C S8 P H ¡¦ H0 T ¡¦G ¡¦ H0 T Fullerene C60 0 50 100 150 200 300 400 500 0 221.2 245.9 266.6 290.2 331.9 348.0 349.2 420.1 497.8 578.6 659.9 740.4 787.9 819.2 895.8 969.9 1041.5 1110.5 1177.0 1241.2 1391.8 1529.8 1774.6 1986.1 2171.9 2337.7 2487.2 2623.4 0 33.4 41.0 65.1 102.6 170.8 196.0 197.8 300.3 398.6 488.1 567.8 638.0 675.9 699.5 753.6 801.3 843.6 881.1 914.7 944.9 1008.3 1058.5 1133.1 1185.8 1225.3 1256.5 1282.2 1303.9 0 34.8 72.3 160.2 272.0 442.3 498.5 502.6 706.3 870.2 996.1 1091.3 1163.3 1198.0 1218.3 1260.9 1294.3 1320.9 1342.3 1359.8 1374.2 1400.9 1418.9 1441.5 1456.2 1468.8 1481.3 1493.6 1504.2 0 254.7 286.9 331.6 392.7 273.15 502.8 298.15 543.9 547.0 720.4 896.4 600 1066.7 700 1227.8 800 1378.4 860 1463.8 900 1518.7 1000 1649.4 1100 1771.2 1200 1885.0 1300 1991.6 1400 2091.7 1500 2186.1 1750 2400.0 2000 2588.4 2500 2907.6 3000 3171.8 3500 3397.2 4000 3594.2 4500 3769.4 5000 3927.3 Fullerene C70 0 50 100 150 200 300 400 0 241.9 267.6 290.8 318.1 366.6 385.3 386.7 469.7 560.8 655.7 751.3 845.9 886.5 938.5 1028.5 1115.6 1199.7 1280.7 1358.9 1434.2 1610.9 1772.8 2059.6 2307.3 2524.8 2718.5 2893.0 3051.7 0 33.7 44.9 74.5 118.8 199.0 228.5 230.8 351.7 467.9 573.7 667.6 750.0 782.6 822.3 885.6 941.4 990.7 1034.6 1073.8 1108.9 1182.7 1241.1 1327.6 1388.2 1433.1 1467.6 1494.9 1517.1 0 36.4 86.2 188.3 317.7 518.3 585.1 589.9 831.9 1025.4 1172.8 1283.5 1366.9 1396.6 1430.4 1479.3 1517.7 1548.1 1572.6 1592.6 1609.1 1639.4 1659.7 1684.2 1697.8 1706.1 1711.5 1715.2 1717.9 0 275.6 312.5 365.4 436.9 273.15 565.6 298.15 613.9 617.5 821.4 500 1028.7 600 1229.4 700 1418.9 800 1596.0 843.5 1669.1 900 1760.8 1000 1914.1 1100 2057.0 1200 2190.4 1300 2315.3 1400 2432.6 1500 2543.1 1750 2793.6 2000 3013.9 2500 3387.2 3000 3695.5 3500 3957.9 4000 4186.1 4500 4387.9 5000 4568.8 Table 12.The frequencies of the C70 normal modes used in statistical calculations. Type DfH8 DfG8 A012 A0 E01 E02 A00 1 A00 2 E00 1 E00 2 VII. Conclusion Based on the analysis of the published data, the values of the most important thermodynamic parameters are recommended for the C60 and C70 fullerenes in the crystalline state in the temperature range 0 ¡À 1000 K and in the gaseous state in the range 100 ¡À 5000 K. We believe that their further refinement will be made within the limits of error outlined in the present review. References 2538.6 2527.8 2516.2 2505.0 2494.4 2479.5 2474.5 2474.2 2454.3 2434.6 2415.0 2395.7 2376.6 2365.3 2357.9 2339.6 2321.6 2304.0 2287.0 2269.5 2252.8 2214.0 2176.9 2110.7 2058.1 2008.3 1968.1 1964.7 1943.1 2534.6 2535.8 2535.2 2533.6 2532.0 2530.4 2530.0 2530.0 2529.4 2528.9 2527.8 2526.1 2523.7 2522.0 2520.8 2517.5 2513.7 2509.4 2505.0 2499.4 2493.5 2477.1 2456.7 2406.5 2350.4 2266.0 2172.9 2086.0 1970.0 1. A V Eletskii, B M Smirnov Usp.Fiz. Nauk 161 173 (1991) a 2. A V Eletskii, B M Smirnov Usp. Fiz. Nauk 163 33 (1993) a 3. V I Sokolov, I V Stankevich Usp. Khim. 62 455 (1993) [Russ. Chem. Rev. 62 419 (1993)] 4. A V Eletskii, B M Smirnov Usp. Fiz. Nauk 165 977 (1995) a 5. V N Bezmel'nitsyn, A V Eletskii, M V Okun' Usp. Fiz. Nauk 168 1195 (1998) a 6. M V Korobov, L N Sidorov J. Chem. Thermodyn. 26 61 (1994) 7.B V Lebedev, K B Zhogova, T A Bykova, B S Kaverin, V L Karnatsevich, M A Lopatin Izv. Akad. Nauk, Ser. Khim. 2229 (1996) b 8. T Atake, T Tanaka, H Kawaji, K Kikuchi, K Saito, S Suzuki, Y Achiba, I Ikemoto Chem. Phys. Lett. 196 321 (1992) 9. N A Fortune, K Murata, F Iga, Y Nishihara, K Kikuchi, S Suzuki, I Ikemoto, Y Achiba Physica C, Pt. 1 185 ¡À 189 425 (1991) 10. X D Shi, A R Kortan, J M Williams, A M Kini, B M Savall, M Chaikin Phys. Rev. Lett. 68 827 (1992) 11. M Chung, Y Wang, J W Brill, X-D Xiang, R Mostovoy, J G Hou, A Zettl Phys. Rev. B, Condens. Matter 45 13 831 (1992) 12. J Sworakowski, K Palewska, M Bertault Chem. Phys. Lett. 220 197 (1994) 13. K B Zhogova, B V Lebedev Izv. Akad. Nauk, Ser. Khim. 647 (1998) b 14. A K Gangopadhyay, T Kowalewski, J S Schilling Chem.Phys. Lett. 239 387 (1995) 15. H-D Beckhaus, S Verevkin, C Ru�� chardt, F Diederich, C Thilgen, H-U ter Meer, H Mohn,W Mu�� ller Angew. Chem. 106 1033 (1994) 16. E V Skokan, V I Privalov, I V Arkhangelsky, V Ya Davydov, N B Tamm J. Phys. Chem. B 103 2050 (1999) 17. H Werner, D Bublak, U Go�� bel, B Henschke, W Bensch, R Schlo�� gl Angew. Chem. 104 909 (1992) 18. A Dworkin, C Fabre, D Schu�� tz, G Kriza, R Ceolin, H Szwarc, P Bernier, D Jerome, S Leach, A Rassat, J P Hare, T J Dennis, H W Kroto, R Taylor, D R M Walton C. R. Hebd. Seances Acad. Sci., Ser. B 313 1017 (1991) 2760.4 2748.6 2736.2 2724.3 2712.9 2697.1 2691.8 2691.4 2670.3 2649.1 2627.8 2606.7 2585.8 2576.8 2565.1 2544.8 2524.7 2505.1 2486.2 2466.5 2447.8 2404.2 2362.5 2287.9 2229.0 2173.6 2129.7 2130.0 2110.4 2760.4 2761.5 2760.8 2759.0 2757.2 2755.3 2755.0 2755.0 2754.9 2755.3 2755.0 2754.0 2752.3 2751.3 2749.8 2746.8 2743.2 2739.0 2734.4 2728.6 2722.3 2704.5 2681.8 2625.1 2560.0 2459.5 2344.9 2232.6 2081.1 V V Diky, G J Kabo Degeneracy Wave number /cm71 11221122 258, 357, 457, 573, 678, 728, 1061, 1175, 1189, 1363, 1433, 1522 501, 550, 651, 742, 817, 958, 1208, 1325, 1432 310, 341, 424, 509, 535, 578, 642, 683, 750, 792, 820, 904, 1073, 1135, 1222, 1254, 1280, 1318, 1384, 1454, 1569 227, 305, 426, 491, 519, 643, 697, 711, 728, 765, 785, 792, 933, 1069, 1164, 1224, 1280, 1314, 1336, 1452, 1496, 1570 333, 545, 612, 768, 807, 917, 1223, 1322, 1536 322, 458, 566, 716, 843, 1099, 1179, 1292, 1414, 1501 232, 409, 479, 505, 537, 665, 703, 739, 771, 793, 1050, 1088, 1186, 1259, 1298, 1332, 1377, 1470, 1515 300, 384, 471, 588, 641, 690, 738, 748, 780, , 1231, 1301, 1328, 1384, 1442, 1500, 1548Thermodynamic properties of C60 and C70 fullerenes 19. J De Bruijn, A Dworkin, H Szwarc, J Godard, R Ceolin, C Fabre, A Rassat Europhys. Lett.24 551 (1993) 20. E V Skokan, V E Alioshina, F M Spiridonov, I V Arkhangelsky, V Ya Davydov, N B Tamm, L N Sidorov J. Phys. Chem. 99 16 116 (1995) 21. V P Kolesov, S M Pimenova, V K Pavlovich, N B Tamm, A A Kurskaya J. Chem.Thermodyn. 28 1121 (1996) 22. T Atake, T Tanaka, H Kawaji, K Kikuchi, K Saito, S Suzuki, I Ikemoto, Y Achiba Physica C, Pt. 1 185 ± 189 427 (1991) 23. H S Chen, A R Kortan, R C Haddon, D A Fleming J. Phys. Chem. 96 1016 (1992) 24. V Piacente, G Gigli, P Scardala, A Giustini, D Ferro J. Phys. Chem. 99 14 052 (1995) 25. A Popovic, G Drazic, J Marsel Rapid Commun. Mass Spectrom. 8 985 (1994) 26. V Piacente, G Gigli, P Scardala, A Giustini, G Bardi J. Phys. Chem. 100 9815 (1996) 27. T Sommer, T Kruse, P Roth J. Phys. B 29 4955 (1996) 28. J S Tse, D D Klug, D A Wilkinson, Y P Handa Chem. Phys. Lett. 183 387 (1991) 29. I Mochida,M Egashira, Y Korai, K Yokogawa Carbon 35 1707 (1997) 30. R D Averitt, J M Alford, N J Halas Appl. Phys. Lett.65 374 (1994) 31. M Haluska,M Vybornov, P Dolinar, H Kuzmany, in International Workshop Fullerenes and Atomic Clusters (Abstracts of Reports), St. Petersburg, 1993 p. 37 32. A M Vassalo, L S K Pang, P A Cole-Clarke, M A Wilson J. Am. Chem. Soc. 113 7820 (1991) 33. D W McKee Carbon 29 1057 (1991) 34. H S Chen, A R Kortan, R C Haddon,M L Kaplan, C H Chen, A M Mujsce,H Chou,D A Fleming Appl. Phys. Lett. 59 2956 (1991) 35. G H Kroll, P J Benning, Y Chen, T R Ohno, J H Weaver, L P F Chibante, R E Smalley Chem. Phys. Lett. 181 112 (1991) 36. T Kiyobayashi,M Sakiyama Fullerene Sci. Technol. 1 269 (1993) 37. W V Steele, R D Chirico, N K Smith, W E Billups, P R Elmore, A E Wheeler J. Phys. Chem. 96 4731 (1992) 38. H P Diogo,M E Minas da Piedade, T J S Dennis, J P Hare, H W Kroto, R Taylor, D R M Walton J.Chem. Soc., Faraday Trans. 89 3541 (1993) 39. X An, J He, Z Bi J. Chem. Thermodyn. 28 1115 (1996) 40. H P Diogo,M E Minas da Piedade Proc. Electrochem. Soc. 98-8 627 (1998) 41. T Kiyobayashi Proc. Electrochem. Soc. 98-8 76 (1998) 42. X An, B Chen, J He Sci. China, Ser. B 41 543 (1998); Chem. Abstr. 130 57 790 (1998) 43. H-D Beckhaus, C RuÈ chardt,M Kao, F Diederich, C S Foote Angew. Chem. 104 69 (1992) 44. S M Pimenova, V P Kolesov, Yu A Volkov, V Ya Davydov, N B Tamm, S V Mel'khanova Zh. Fiz. Khim. 71 1937 (1997) c 45. M E Minas da Piedade, H P Diogo, A D Darwish, T J S Dennis J. Phys. Chem. Solids 58 1965 (1997) 46. R Sachidanandam, A B Harris Phys. Rev. Lett. 67 1467 (1991) 47.E Grivei, M Cassart, J P Issi, L Langer, B Nysten, J-P Michenaud, C Fabre, A Rassat Phys. Rev. B, Condens. Matter 48 8514 (1993) 48. F Gugenberger, R Heid, C Meingast, P Adelmann, M Braun, H WuÈ hl, M Haluska, H Kuzman Phys. Rev. Lett. 69 3774 (1992) 49. T Matsuo, H Suga, W I F David, R M Ibberson, P Bernier, A Zahab, C Fabre, A Rassat, A Dworkin Solid State Commun. 83 711 (1992) 50. G P Johari J. Chem. Phys. 100 2220 (1994) 51. J F Willart, L Carpentier, M Descamps, H G Krane, J L Sauvajol Solid State Commun. 101 319 (1997) 52. P A Heiney, J E Fischer, A R McGhie, W J Romanow, A M Denenstein, J P McCauley Jr , A B Smith III, D E Cox Phys. Rev. Lett. 66 2911 (1991) 53. Y Jin, J Cheng,M Varma-Nair, G Liang, Y Fu, B Wunderlich, X-D Xiang, R Mostovoy, A K Zettl J.Phys. Chem. 96 5151 (1992) 54. V M Egorov, V V Shpeizman, I N Kremenskaya Pis'ma v Zh. Eksp. Teor. Fiz. 19 49 (1993) 55. E Westrum, J McCullough, in Physics and Chemistry of the Organic Solid State (Eds D Fox,M MLabes, A Weissberger) (New York: Wiley, 1965) 103 56. W P Beyermann,M F Hundley, J D Thompson, F N Diederich, G GruÈ ner Phys. Rev. Lett. 68 2046 (1992) 57. G J Kabo, A V Blokhin, A A Kozyro, V V Diky, L S Ivashkevich, A P Krasulin, V M Sevruk,M Frenkel Thermochim. Acta 313 111 (1998) 58. J E Fischer, P A Heiney, A R McGhie, W J Romanow, A M Denenstein, J P McCauley Jr , A B Smith III Science 252 1288 (1991) 59. W Li, R D Sherwood, D M Cox, M Radosz J. Chem. Eng. Data 39 467 (1994) 60.A Lundin, B Sundqvist Europhys. Lett. 27 463 (1994) 61. P A Heiney, G B M Vaughan, J E Fischer, N Coustel, D E Cox, J R D Copley, D A Neumann, W A Kamitakahara, K M Greegan, D M Cox, J P McCauley Jr , A B Smith III Phys. Rev. B, Condens. Matter 45 4544 (1992) 62. L N Yakub Fiz. Nizk. Temp. 19 726 (1993) 63. W Vogel Appl. Phys. A 62 295 (1996) 64. R Komori, Y Miyamoto J. Phys. Chem. Solids 56 535 (1995) 65. Y Jin, A Xenopoulos, J Cheng,W Chen, B Wunderlich,M Diack, C Jin, R L Hettich, R N Compton, G Guiochon Mol. Cryst. Liq. Cryst. 257 235 (1994) 66. E Grivei, M Cassart, B Nysten, A Demain, J-P Issi Solid State Commun. 85 73 (1993) 67. T Tanaka, T Atake J. Phys. Chem. Solids 57 277 (1996) 68. G B M Vaughan, P A Heiney, J E Fischer, D E Luzzi, D A Ricketts-Foot, A R McGhie, Y-W Hui, A L Smith III, D E Cox, W J Romanow, B H Allen, N Custel, J P McCauley, B Smith Science 254 1350 (1991) 69.T Tanaka, H Kawaji, T Atake, K Kikuchi, K Saito, S Suzuki, Y Achiba, I Ikemoto Fullerene Sci. Technol. 2 121 (1994) 70. E Grivei, B Nysten, M Cassart, J P Issi, C Fabre, A Rassat Phys. Rev. B, Condens. Matter 47 1705 (1993) 71. A Soldatov, B Sundqvist J. Phys. Chem. Solids 57 1371 (1996) 72. D P H Hasselman, K Y Donaldson, J Withers, R O Loutfy Carbon 31 996 (1993) 73. S K Ramasesha, A K Singh, R Seshadri, A K Sood, C N R Rao Chem. Phys. Lett. 220 203 (1994) 74. C Meingast, F Gugenberger, G Roth,M Haluska, H Kuzmany Z. Phys. B, Condens. Matter 95 67 (1994) 75. M C Valsakumar, N Subramanian, M Yousuf, P Ch Sahu, Y Hariharan, A Bharathi, V Sankara Sastry, J Janaki, G V N Rao, T S Radhakrishnan, C S Sundar Phys.Rev. B, Condens. Matter 48 9080 (1993) 76. L Jiang, J Li, L A Nagahara, N Kino, K Kitazawa, T Iyoda, K Hashimoto, A Fujishima Appl. Phys. A 61 17 (1995) 77. J Janaki, G V N Rao, V Sankara Sastry, Y Hariharan, T S Radhakrishnan, C S Sundar, A Bharati,M C Valsakumar, N Subramanian Solid State Commun. 94 37 (1995) 78. L Jiang, T Iyoda, N Kino, K Kitazawa, K Hashimoto, A Fujishima Jpn. J. Appl. Phys., Pt. 2 35 L48 (1996) 79. T Mitsuki, Y Ono, H Horiuchi, J Li, N Kino, K Kishio, K Kitazawa Jpn. J. Appl. Phys., Pt 1 33 6281 (1994) 80. A Lundin, A Soldatov, B Sundqvist Europhys. Lett. 30 469 (1995) 81.A Cheng,M Klein J. Phys. Chem. 95 6750 (1991) 82. B Wunderlich, Y Jin Thermochim. Acta 226 169 (1993) 83. E Burgos, E Halac, H Bonadeo Phys. Rev. B, Condens. Matter 47 13903 (1993) 84. T F Nagy, K J Conley, D Tomanek Phys. Rev. B, Condens. Matter 50 12207 (1994) 85. Yu I Prilutskii, V A Andreev, G G Shapovalov Ukr. Fiz. Zh. 42 195 (1997) 86. E I Mukhtarov, Yu N Krasyukov Zh. Fiz. Khim. 70 464 (1996) c 87. Yu I Prilutskii Ukr. Fiz. Zh. 42 1128 (1997) 88. G Kato, C Yokomizo,H Omata,M Sato, T Ishii,K Nagasaka Solid State Commun. 93 801 (1995) 89. L Pintschovius, S L Chaplot Z. Phys. B, Condens. Matter 98 527 (1995) 90. S Dai, L Mac Toth, G D Del Cul, D H Metcalf J. Chem. Phys. 101 4470 (1994) 91. C K Mathews, M Sai Baba, T S Lakshmi Narasimhan, R Balasubramanian, N Sivaraman, T G Srinivasan, P R Vasudeva Rao J.Phys. Chem. 96 3566 (1992) 92. J Abrefah, D R Olander,M Balooch, W J Siekhaus Appl. Phys. Lett. 60 1313 (1992)104 93. C Pan,M P Sampson, Y Chai, R H Hauge, J L Margrave J. Phys. Chem. 95 2944 (1991) 94. M Sai Baba, T S Lakshmi Narasimhan, R Balasubramanian, N Sivaraman, C K Mathews J. Phys. Chem. 98 1333 (1994) 95. R E Haufler, J Conceicao, L P F Chibante, Y Chay, N E Byrne, S Flanagan, M M Haley, S C O'Brien, C Pan, Z Xiao, W E Billups, M A Ciufolini, R H Hauge, J L Margrave, L J Wilson, R F Curl, R E Smalley J. Phys. Chem. 94 8634 (1990) 96. A Tokmakoff, D R Haynes, S M George Chem. Phys. Lett. 186 450 (1991) 97. M V Korobov, E V Skokan, D Yu Borisova, L M Khomich Zh.Fiz. Khim. 70 999 (1996) c 98. K Yase, Y Takahashi,N Ara-Kato, A Kawazu Jpn. J. Appl. Phys., Pt. 1 34 636 (1995) 99. K Yase, Y Yoshida, T Uno N Okui J. Cryst. Growth 166 942 (1996) 100. D M Poirier, D W Owens, J H Weaver Phys. Rev. B, Condens. Matter 51 1830 (1995) 101. M Moalem,M Balooch,A V Hamza, R S Ruoff J. Phys. Chem. 99 16736 (1995) 102. H Richter, A Dereux, J M Gilles, C Guillaume, P A Thiry, A A Lucas, R Rozenberg, A Spote, E de Hoffmann Ber. Bunsenges. Phys. Chem. 98 1329 (1994) 103. R Pankajavalli, C Mallika, O M Sreedharan, M Premila, P Gopalan Thermochim. Acta 316 101 (1998) 104. Y Guo, N Karasawa,W A Goddard Nature (London) 351 464 (1991) 105. C K Mathews, M Sai Baba, T S L Narasimhan, R Balasubramanian, N Sivaraman, T G Srinivasan, P R V Rao Fullerene Sci.Technol. 1 101 (1993) 106. V Schettino, P R Salvi, R Bini, G Cardini J. Chem. Phys. 101 11 079 (1994) 107. M Matus, H Kuzmany Appl. Phys. A 56 241 (1993) 108. P H M van Loosdrecht, P J M van Bentum, M A Verheijen, G Meijer Chem. Phys. Lett. 198 587 (1992) 109. S P Love, D McBranch,M I Salkola,N V Coppa, J M Robinson, B I Swanson, A R Bishop Chem. Phys. Lett. 225 170 (1994) 110. C Colombeau, H Jobic, P Bernier, C Fabre, D SchuÈ tz, A Rassat J. Phys. Chem. 96 22 (1992) 111. K Prassides, T J S Dennis, J P Hare, J Tomkinson, H W Kroto, R Taylor, D R M Walton Chem. Phys. Lett. 187 455 (1991) 112. P Giannozzi, S Baroni J. Chem. Phys. 100 8537 (1994) 113. H Kuzmany, R Winkler, T Pichler J. Phys., Condens. Matter 7 6601 (1995) 114. P Bowmar, W Hayes,M Kurmoo, P A Pattenden,M A Green, P Day, K Kikuchi J. Phys., Condens. Matter 6 3161 (1994) 115. D Inomata, N Kurita, S Suzuki, K Nakao Phys. Rev. B, Condens. Matter 51 4533 (1995) 116. N V Khokhryakov, S S Savitskii Fiz. Tv. Tela 36 3524 (1994) 117. W Brockner, F Menzel J. Mol. Struct. 378 147 (1996) 118. S H Gallagher, R S Armstrong, R D Bolskar, P A Lay, C A Reed J. Mol. Struct. 407 81 (1997) 119. M Fanti, G Orlandi, F Zerbetto J. Phys. B 29 5065 (1996) 120. M C Martin, X Du, J Kwon, L Mihaly Phys. Rev. B, Condens. Matter 50 173 (1994) 121. Yu I Prilutskii, V O Gubanov, S S Durov Ukr. Fiz. Zh. 42 1143 (1997) 122. M L Frenkel, G J Kabo, K N Marsh, G N Roganov, R C Wilhoit Thermodynamics of Organic Compounds in the Gas State (College Station, TX: Thermodynamic Research Center, 1994) 123. F Leclercq, P Damay,M Foukani, P Chieux,M C Bellissent- Funel, A Rassat, C Fabre Phys. Rev. B, Condens. Matter 48 2748 (1993) 124. K Hedberg, L Hedberg,M BuÈ hl, D S Bethune, C A Brown, R D Johnson J. Am. Chem. Soc. 119 5314 (1997) 125. F Negri, G Orlandi, F Zerbetto Chem. Phys. Lett. 144 31 (1988) 126. F Negri, G Orlandi, F Zerbetto J. Chem. Phys. 97 6496 (1992) 127. M Lee, O-K Song, J-C Seo, D Kim, Y D Suh, S M Jin, S K Kim Chem. Phys. Lett. 196 325 (1992) 128. B S Razbirin, A N Starukhin, A V Chugreev, D K Nel'son, Yu S Grushko, S N Kolesnik, V N Zgonnik, L V Vinogradova, L A Fedorova Fiz. Tv. Tela 38 943 (1996) V V Diky, G J Kabo 129. G J Kabo, A A Kozyro, V V Diky, V V Simirsky, L S Ivashkevich, A P Krasulin, V M Sevruk, A P Marchand, L M Frenkel J. Chem. Thermodyn. 27 707 (1995) 130. G J Kabo, A A Kozyro, A P Marchand, V V Diky, V V Simirsky, L S Ivashkevich, A P Krasulin, V M Sevruk, M L Frenkel J. Chem. Thermodyn. 26 129 (1994) 131. D S Bethune, G Meijer, W C Tang, H J Rosen,W G Golden, H Seki, C A Brown,M S de Vries Chem. Phys. Lett. 179 181 (1991) 132. P H M van Loosdrecht,M A Verheijen, H Meekes, P J M van Bentum, G Meijer Phys. Rev. B, Condens. Matter 47 7610 (1993) 133. X Q Wang, C Z Wang, K M Ho Phys. Rev. B, Condens. Matter 51 8656 (1995) 134. G Onida,W Andreoni, J Kohanoff,M Parrinello Chem. Phys. Lett. 219 1 (1994) 135. B S Razbirin, A N Starukhin, A V Chugreev, Yu S Grushko, S N Kolesnik Pis'ma Zh. Eksp. Teor. Fiz. 60 435 (1994) a�Physics-Uspekhi (Engl. Transl.) b�Russ. Chem. Bull. (Engl. Transl.) c�Russ. J. Phys. Chem. (Engl. Tr

ISSN:0036-021X    

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Russian Chemical Reviews 69 (2) 105 ± 120 (2000) Alkenyliodonium salts N Sh Pirkuliev, V K Brel, N S Zefirov Contents I. Introduction II. Synthesis of alkenyliodonium salts III. Reactions of alkenyliodonium salts IV. Conclusion Abstract. transformations chemical and synthesis the on data New New data on the synthesis and chemical transformations of analysed. and summarised are salts alkenyliodonium of alkenyliodonium salts are summarised and analysed. The The bibliography includes 146 references. bibliography includes 146 references. I. Introduction The first synthesis of a three-coordinated iodine with at least one C7I bond was reported by Willgerodt in 1886.1 Following preparation of (dichloro-l3-iodanyl)benzene { (1) by chlorination of iodobenzene, Willgerodt soon synthesised (diacetoxy-l3-ioda- nyl)benzene (2) and other organic derivatives of three- and poly- coordinated iodine.By the time of the publication by Willgerodt in 1914 of his comprehensive treatise 2 on the chemistry of hyper- valent iodine that summarised the data on the synthesis of tri- and pentavalent iodine-containing organic compounds, about 500 such compounds were already known. Among them, diaryliodo- nium salts 3 were examined most thoroughly.+ Ar2I X7 I(OAc)2 ICl2 3 2 1 The chemistry of organic compounds of polyvalent iodine was the subject of several reviews (see, for example, Refs 3 ± 5). However, because of rapid development of this chemistry, it is nearly impossible at the moment to consider all its aspects in the framework of only one publication.A brief review 6 has been published on iodonium salts; they were also considered in a chapter of a monograph 7 devoted to organic compounds of polyvalent iodine. The chemistry of { This naming is given in accord with IUPAC Nomenclature of Organic Compounds (Recommendations 1993). Furthermore, symbol l3 can be omitted from the names of iodine-containing compounds. N Sh Pirkuliev, V K Brel Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax (7-095) 913 21 13. Tel. (7-095) 939 51 55. E-mail: prnmsh@chem.org.msu.su (N Sh Pirkuliev), Tel. (7-095) 524 50 62. E-mal: brel@ipac.ac.ru (V K Brel) N S Zefirov Department of Chemistry, MV Lomonosov Moscow State University, Leninskie Gory, 119899 Moscow, Russian Federation.Fax (7-095) 932 88 46. Tel. (7-095) 939 16 20 Received 8 October 1999 Uspekhi Khimii 69 (2) 118 ± 133 (2000); translated by S V Chapyshev #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v069n02ABEH000557 105 106 111 118 diacyloxyiodanylarenes was treated in a special review 8 and the application of these compounds as oxidising reagents is described in a monograph.9 A review 10 devoted to the use of compounds of polyvalent iodine, mostly organic compounds, has also been published. Interesting data on the chemistry of iodonium salts can be found in the book `The Problems of Organic Chemis- try' 11, 12 and those on the chemistry of diacyloxyiodanylarenes in two other books;13, 14 derivatives of iodosylarenes are discussed in a separate review.15 Organic compounds of three- and poly-coordinated iodine are widely used as reagents in modern organic chemistry.Particular areas of synthetic application of these compounds vary depending on their structures, viz., on the number of organic ligands at the iodine atom 4, 7 and on the electronegativity and nucleofugality of their heteroatomic ligands. All compounds of polyvalent iodine can be conventionally divided into several groups. The first one comprises compounds with one carbon ligand (RIX2 and RIX4), viz., hydroxy(sulfonyl- oxy)-l3-iodanylarenes, periodinanes, substituted benzoiodoxols and azides of trivalent iodine.8, 10, 16 ± 30 Compounds of this group are employed for selective oxidation of various organic substrates.The second group of polyvalent iodine compounds includes iodonium salts R2I+X7 with two carbon ligands.8, 10, 16 ± 30 Iodo- nium salts do not possess strong oxidising properties and are mainly employed as precursors of nucleophilic species resulting from transformations of an organic ligand. Depending on the nature of the organic ligand R, iodonium salts, in turn, can be conventionally classified as alkyl-, polyfluo- roalkyl-, alkenyl- and alkynyl-iodonium salts. Most of alkyliodo- nium salts Alk2I+X7 or Alk(Ph)I+X7, with a few exceptions,31 are unstable and therefore have not been exploited in organic synthesis.On the contrary, polyfluoroalkyliodonium salts Rf(Ph)I+X7 are stable and represent effective electrophilic poly- fluoroalkylating reagents.32 Compounds of three-coordinated iodine with three organic ligands are, as a rule, unstable at room temperature; only a few stable representatives of this class are known to date.33 ± 35 Derivatives of the type 4 containing an alkynyl group as a substituent were unknown until recently. The intense develop- ment of the chemistry of alkenyliodonium salts 5 began only recently, although the first representative of this class of com- pounds was described back in 1914.2 + + R1R2C CI X7 R1C4 C(R3)IAr X7 5 R2 At the moment, synthetic aspects of the chemistry of alkynyl- iodonium salts are well developed and discussed in detail, for106 example, in monographs 36 ± 38 and reviews 25, 39, 40 One of these reviews 25 contains a section treating the chemistry of alkenyl- iodonium salts.This chemistry was also briefly considered in another review 41 devoted to organic compounds of polyvalent iodine. However, new important results obtained recently in this field deserve generalisation. It is the purpose of this review to systematise and analyse the data on the synthesis and properties of alkenyliodonium salts which were mainly published over the last 10 ± 15 years. Earlier publications are cited only as may be necessary for the better elucidation of the issues in question. II. Synthesis of alkenyliodonium salts In recent decades, the interest in alkenyliodonium salts has sharply increased.Alkenyliodonium salts bearing not only alkyl, but also aryl, triflate, mesylate and other substituents at the double bond were synthesised. These compounds were demon- strated to be very promising intermediates for organic synthesis. At present, several types of alkenyliodonium salts are known, viz., those with one (5) or two (6 ± 8) alkenyl groups and also cyclic alkenyliodonium salts of the type 9 and 10. + + + PhI I I 2BF¡4+ R1 R1 (CH2)n R3 (XCH CH)2I X7 6 R2 R2 + 7 IPh R3 2 X7 8 X R Y7 + + IAr X7 H I O R1 O 9 R2 10 Several methods for the synthesis of alkenyliodonium salts have been described earlier.7 However, none of them has been really convenient until recently.At present, a number of new methods have been developed, however, these did not receive much attention in relevant reviews.25, 41 Taking this fact into account, we systematise in this Section the published data on the synthesis of alkenyliodonium salts. These syntheses are based on the use of electrophilic l3-iodanes. Among compounds of polyvalent iodine, the Koser reagent 11, complexes of iodosylbenzene 12 and 13, alkynyliodo- nium salts 4, the iodosylbenzene trifluoromethanesulfonic acid complex 14, cyano(hydroxy)-l3-iodanylbenzene triflate and tosy- late (15a,b), fluoro(hydroxy)-l3-iodanylarene sulfonates (16a,b) are the key reagents. + PhIO . HOTf PhI(OH)OTs PhIO . BF3 PhIO . Et3O. BF¡4 14 12 13 11 + ArIF ZO7 PhI(CN)OY 16a,b [Z=Tf (a), Ms (b)].15a,b [Y=Tf (a), Ts (b)]. 1. Syntheses starting from dichloro-l3-iodanylbenzene and dichloro-l3-iodanylalkenes Early methods for the synthesis of alkenyliodonium salts were based on the reactions of organometallic derivatives of alkynes with dichloroiodanylarenes. Using this approach, alkenyliodo- nium salts 17a,b have been synthesised.2 However, on the whole, this method was rather ineffective and had a number of limita- tions. + H2O Cl(R)C C(Cl)IAr Cl7 RC CAg . AgCl +ArICl2 17a,b R=H, Ar=Ph (17a); R=Me, Ar=C6H4Me-2 (17b). N Sh Pirkuliev, V K Brel, N S Zefirov Later, the reactions of organomercuric derivatives of alkenes with dichloroiodanylarenes were proposed to synthesise alkenyl- iodonium salts.42 ± 44 Thus the treatment of trans-chlorovinylmer- curic chloride with various dichloroiodanylarenes in dilute hydrochloric acid results in arylvinyliodonium mercurates 19 in 5%± 53% yields. The latter can be converted into the correspond- ing arylvinyliodonium chlorides 17a,c ± k upon treatment with hydrogen sulfide.H Cl + H2S 3% HCl +ArICl2 ClHC CClIAr X7 19 HgCl H 18 + ClHC CClIAr Cl7 17a,c ± k Ar=Ph (a), 2-MeC6H4 (c), 3-MeC6H4 (d), 4-MeC6H4 (e), 2-ClC6H4 (f), 3-ClC6H4 (g), 4-C6H4 (h), 2-MeOC6H4 (i), 4-MeOC6H4 ( j ), 3-NO2C6H4 (k); X=Cl . HgCl2, Cl . 2HgCl2 . The reaction of vinyl- or styryltrichlorostannane with dichlo- roiodanylbenzene (1) leads to alkenyliodonium salts 20 or 21.45, 46 1, THF,720 8C H2C CHSnCl3 (H2C CHIPh)2SnCl6 20 + 1) 1, HCl, H2O 2) KI, H2O PhHC CHSnCl3 PhHC CHIPh I7 21 1-Chloro-2-dichloroiodanylethylene 22 has been synthesised for the first time by the reaction of trans-chloroiodoethylene with chlorine.47 Later, compound 22 was obtained in high yield by the reaction of acetylene with iodine trichloride.48 Compound 22 is unstable at room temperature, but can be stored below 720 8C for two months without noticeable changes.This reagent is employed for the synthesis of alkenyliodonium salts. Thus its reactions with silver acetylenide or phenyltrichlorostannane afford compounds 23 and 24.46 + HC CAg . AgCl H ICl2 (ClHC CH)2I Cl7 23 + PhSnCl3 H Cl 22 ClHC CHIPh Cl7 24 (31%) Diphenyliodonium chloride rather than a vinyliodonium salt of the type 24 is formed from 1-dichloroiodanyl-2-iodoethylene in 50% yield.43 Organolithium derivatives react with compound 22 to give cyclic iodonium salts 25 and 26.49 Ph Bu Bu 22 Li + Li Ph I Cl7 25 (26%)Cl7 Ph I Ph Ph Ph + Li 1) 22 2) Et2O, HCl Li Ph Ph Ph Ph 26 (2.5%) It should be noted that the reaction of dichloroiodanylben- zene with an equivalent amount of vinyllithium inTHFat770 8C affords diphenyliodonium chloride in low yield (5%).49 2.Syntheses starting from dihydroxy-l3-iodanylbenzene tosylate The availability of iodanylbenzene derivatives, their reasonable stabilities on storage and fair solubilities enable the use of these compounds in the synthesis of alkenyliodonium salts.The reac-Alkenyliodonium salts tions of dihydroxy-l3-iodanylbenzene tosylate (11) with 3-amino- and 3-ethoxy-5,5-dimethylcyclohex-2-enone in chloroform result in the formation of vinyliodonium salts 27a,b in 87% and 40% yields, respectively.50 The reaction mechanism presumably involves the initial attack by the hydroxy(phenyl)iodonium ion on the double bond followed by the deprotonation of the intermediate 28 and the exchange reaction of aryl(vinyl)iodonium hydroxide 29 with p-toluenesulfonic acid. TsO7 + +PhI(OH)OTs 11 O X O X I(OH)Ph H 28 TsOH 7H2O O X O X +IPh TsO7 29 I(OH)Ph 27a,b X=NH2 (a), OEt (b). The condensation of uracil with diacetoxyiodanylbenzene in DMF in the presence of TsOH .H2O leads to compound 30 in 78% yield.51 The reaction apparently involves the intermediate formation of the tosylate 11.O +IPh TsO7 HN O 30 NH More general and simple procedure for the synthesis of (b-tosyloxyvinyl)iodonium tosylate 31 includes the reactions of dihydroxyiodanylbenzene tosylate (11) with terminal alkynes.52 ± 56 + + D, CHCl3 RC CH+11 R(TsO)C CHIPhTsO7+RC CIPhTsO7 32a ± i 31a ± i (40% ± 60%) R=Prn (a), Bun (b), n-C5H11 (c), Pri (d), sec-C4H9 (e), Bui (f), cyclo-C6H11 (g), But (h), Ph (i). Depending on the nature of the substituent in terminal alkynes, either alkenyl- or alkynyliodonium salts or their mixture are formed.54 Thus pent-1-yne yields the alkenyliodonium salt 31a exclusively (58%), 3,3-dimethylbut-1-yne gives alkynyliodonium tosylate 32h (74%), while 3-methylbut-1-yne affords a mixture of alkenyl- (31d) (11%) and alkynyl-iodonium salts 32d (15%).A correlation was found between the degree of branching in the substituent and the direction of the reactions. Thus alkynyliodo- nium salts are formed if the substituent is more branched than the isopropyl group (e.g., But and cyclo-C6H11). Mixtures of both salts are obtained from 3-methylbut-1-yne and 4-methylpent-1- yne, which are branched in the b-position. Trimethylsilylacetylene reacts with compound 11 with the elimination of the trimethylsilyl group to give phenyl(2-tosyl- oxyvinyl)iodonium tosylate.54 Disubstituted acetylenes react with compound 11 producing vinyliodonium salts in up to 62% yield.53 +IPh TsO7 Me3SiC CH TsO D, CHCl3 (22%) + TsO IPh TsO7 PhI(OH)OTs 11 R1C CR2 R2 R1(32% ± 62%) R1, R2=Me, Bun, n-C5H11, Ph.107 The reactions of compound 11 with alkenes were also studied.53 Alkenyliodonium salt 33 (5%) was found to be a product of the reaction with 1,1-diphenylethylene. + 11+Ph2C CH2 PhC(O)CH2Ph+Ph2C CHIPhTsO7+TsOH 33 Methyl 3-aminocrotonate 34 reacts with the tosylate 11 at 20 8C to give [2-amino-1-methoxycarbonyl-(E)-prop-1-enyl]phe- nyliodonium tosylate (35) as the major product.57 + Me H IPh TsO7 Me 11 H2N CO2Me H2N CO2Me 35 (73%) 34 3. Syntheses starting from iodosylbenzene in the presence of Lewis acids The first general method for the synthesis of alkenyliodonium salts was suggested in the mid-1980s.58, 59 It was based on the reactions of silylated alkenes with iodosylbenzene in the presence of Lewis acids.These reactions proceed stereoselectively in the presence of boron trifluoride diethyl etherate to afford alkenylio- donium tetrafluoroborates 36 in high yields. The preparation of a wide range of diverse alkenyliodonium salts has demonstrated the versatility of this procedure. The yields of the reaction products reached 89%. + R1 R1 IPh BF¡ SiMe3 4 PhIO, Et2O.BF3 H R2 H R2 36 R1=H, Me, n-C8H17 , Ph(CH2)2; R2=H, Me, n-C8H17, Ph, PhCH2 , Ph(CH2)2 , p-BrC6H4OCH2 , p-ClC6H4(CH2)2 . Using this approach, cyclic alkenyliodonium salts, viz., 4-R- cyclohex-1-enyl(phenyl)iodonium tetrafluoroborates 37a,b, were synthesised.58, 59 + R IPh BF¡4 37a,b R = H (a), But (b).The reaction of 1-trimethylsilyldec-1-ene with iodosylbenzene in the presence of boron trifluoride diethyl etherate yields dec-1- yne.60, 61 UsingNMRspectroscopy, it was shown that the reaction with the alkene 38a occurs via unstable alkenyl(phenyl)iodonium salt 39a.58 Treatment of salts 39a ± e with an aqueous solution of KClO4 allowed the synthesis and characterisation of stable (Z)- alkenyliodonium perchlorates 39a ± e.61 PhIO, Et2O. BF3 + R R 4 SiMe3 38a ± e IPh BF¡ 7HBF4,7PhI 39a ± e CH RC R=n-C8H17 (a), Me2CH(CH2)4 (b), cyclo-C5H9CH2 (c), Ph (d), Ph(CH2)3 (e). Electrophilic addition of the complex of PhIO with BF3 . Et2O to allenes was used to synthesise alkenyliodonium salts.Thus salt 40a was obtained by the reaction of diethyl 1-methoxy-4- methylpenta-2,3-dien-2-ylphosphonate (41) with 2 equivs of iodosylbenzene in the presence of boron trifluoride diethyl ether- ate.62 The respective perchlorate 40b was obtained in 48% yield upon treatment of the reaction mixture with a saturated aqueous solution of LiClO4. The salt 40 is also formed in the reaction of the allene 41 with a system PhIF2±BF3 . Et2O.62108 OMe Me C C C Me (EtO)2(O)P 41 F7 Me Me O+ Me I(Ph) (EtO)2(O)P 42 X=BF4 (a), ClO4 (b). The unusual reaction course is explained by a Z-orientation of the electrophilic fragment I(Ph)F relative to the phosphoryl group in the intermediate 42. In all the structures examined so far,63 ± 71 resulting from electrophilic additions to allenylphosphonates, E-orientation of the substituents at the double bond was mainly observed, which favoured the formation of oxaphospholenes. The reactions of alkynyltrimethylsilanes with iodosylbenzene in the presence of BF3 or Et3O+.BF4 lead to alkynyliodonium compounds.72 ± 77 12, CH2Cl2, 20 8C 1) 13, CH2Cl2, 20 8C 2) NaBF4, H2O RC CSiMe3 1) 13, CHCl3, 20 8C 2) NaOSO2Ar, H2O R=Ph, But, Bun, Me3Si (PhIOTf)2O (in situ), CH2Cl2, 0 8C R=Ph, PhCH2, PhCH2CH2, n-C8H17, cyclo-C6H11; Ar=4-MeC6H4, 4-NO2C6H4. The addition of PhIO to trimethylsilylacetylene in the pres- ence of triethyloxonium tetrafluoroborate or boron trifluoride diethyl etherate results in the formation of (E)-(2-ethoxyvinyl-1- trimethylsilyl)phenyliodonium tetrafluoroborate in 68% yield.78 Treatment of compound 43 with tetra-n-butylammonium fluoride or triethylamine leads to vinyliodonium salt 44. The reaction presumably occurs via an intermediate ylide 45.78 + PhIO, Et3OBF¡4 or HC CSiMe3 BF3 .Et2O C IPh EtO A method allowing the stereoselective synthesis of alkenylio- donium salts from boronic acids or their esters has been described.79 The reactions of (Z)-2-bromovinyl(diisopropoxy)- boranes with diacetoxyiodanylbenzene in dichloromethane at 0 8C under nitrogen followed by the anion exchange led to (Z)- phenyl(vinyl)iodonium tetrafluoroborates. In addition to the iodonium salt 46b, (Z)-2-bromodec-2-enal (9%), 2,2-dibromode- cenal (3%) and (Z)-1,2-dibromodec-1-ene (5%) were also formed.O Me Me 1) PhIO, BF3 . Et2O 2) MX +IPh X7 (EtO)2(O)P 40a,b Me 4 + BF¡ Me MeOCH2 PhIF2, BF3 . Et2O I(Ph)F (EtO)2(O)P Me +O Me BF¡4+ 7MeF IPh BF¡ (EtO)2(O)P 4 40a F + 4 RC CIPh BF¡ (56% ± 75%) + 4 RC CIPh BF¡ (62% ± 85%) + 3 RC CIPhAr SO¡ (62% ± 89%) + RC CIPh TfO7 (67% ± 88%) +IPh BF¡4Bu4NF or Et3N THF EtO SiMe3 43 +IPhBF¡4+ C7 IPh EtO EtO 44 45 N Sh Pirkuliev, V K Brel, N S Zefirov If the reactions are carried out in the presence of boron trifluoride etherate, the yields of alkenyliodonium salts are increased to 85%. R R + 1) PhI(OAc)2, BF3 . Et2O, CH2Cl2 , 0 8C 2) NaBF4, H2O Br Br IPh BF¡ B(OPri)2 4 46a,b R=Bun (a), n-C8H17 (b).The yields of the salts 46 also depend on the nature of the solvent; in dichloromethane, benzene, ethyl acetate and methanol, they are higher (>80%) than in acetonitrile and diethyl ether. Alkoxyboranes also produce alkenyliodonium salts in reac- tions with other derivatives of I(III), viz., with PhIO in the presence of boron trifluoride etherate, dihydroxyiodanylbenzene tosylate (11) or PhI(OCOCF3)2.79 When (Z)-2-bromohex-1-enyl(diisopro- poxy)borane reacted with bis(trifluoroacetoxy)iodanylbenzene, [(Z)-2-bromohex-1-enyl]phenyliodonium trifluoroacetate was isolated from the reaction mixture together with the respective tetrafluoroborate as the major product. The reaction of (E)-(diisopropoxy)hex-1-enylborane (47a) with PhI(OAc)2±BF3 .Et2O results in the stereoselective forma- tion of (E)-vinyliodonium salt 48 (47%) and hexenal as a side- product (12%). Bun Bun PhI(OAc)2, + BF3 . Et2O 48 47a ± c IPh BF¡ BR2 4 O (c). R2=(OPri)2 (a), 7OCMe2CMe2O7(b), O Vinylboronic acids 49 react with PhI(OAc)2±BF3 . Et2O in dichloromethane at 0 8C under nitrogen to form vinyliodonium salts 36.79 This procedure allows the synthesis of not only mono-, but also bis(vinyliodonium) salts from the corresponding vinyl- boronic acids.79 R1 R1 + 1) PhI(OAc)2, BF3 . Et2O, CH2Cl2, 0 8C 2) NaBF4, H2O R2 R2 IPh BF¡ B(OH)2 4 36 49 R1=n-C4H9, n-C8H17, Ph(CH2)3, Cl(CH2)3, NC(CH2)3, cyclo-C5H9CH2, Me2CH(CH2)2, But, Ph; R2=H, Me, Ph.(HO)2B (CH2)4 1) PhI(OAc)2, BF3 . Et2O, CH2Cl2, 0 8C 2) NaBF4, H2O B(OH)2 PhI+BF¡4 (CH2)4 +IPh BF¡4 4. Syntheses based on the activation of iodosylbenzene with trifluoromethanesulfonic acid or its derivatives Yet another method for the synthesis of alkenyliodonium salts is based on the reactions of alkynes with PhIO ±HOTf (14), PhIO ± Tf2O or PhIO ±Me3SiOTf systems.80 ± 82 These reactions occur stereoselectively yielding (E)-alkenyliodonium salts 50. Complex 14 is generated in situ either from a 1 : 1 mixture of iodosylbenzene and trifluoromethanesulfonic acid or from a 1 : 2 mixture of diacetoxyiodanylbenzene and TfOH .H2O. PhIO+HOTf RC CH [PhIO .HOTf] PhI(OAc)2+2 TfOH .H2O 14Alkenyliodonium salts +IPh TfO7 R H TfO 50 (62% ± 100%) R=H, Prn, Bun, n-C6H13, Ph.Disubstituted acetylenes also react with the complex 14 stereoselectively to form (E)-alkenyliodonium salts.82 +IPh TfO7 R 14+ RC CR R TfO (67% ± 80%) R=Me, Et. However, only alkynyliodonim triflate 51 is formed in 42% yield in the reaction of sterically hindered 3,3-dimethylbut-1-yne with PhIO ± HOTf.82 + 14+ ButC CH ButC CIPh TfO7 51 Activation of bis(iodosyl)benzene with trimethylsilyl triflate followed by treatment with appropriate terminal alkynes afford bis(alkenyliodonium) salts 52 in 50% ±66% yields.83 + + I I 2TfO7 1) Me3SiOTf R R OI IO 2) RC CH, CH2Cl2, 40 8C, 10 h 52 OTf OTf R=H, Me, Et, Ph. The reaction of iodosylbenzene with 2 equivs of trifluorome- thanesulfonic acid or with an equimolar amount of Tf2Oproduces the iodanyl-iodonium derivative 53.The latter readily reacts with terminal alkynes to give the corresponding E-alkenyliodonium salts 54.84, 85 CH2Cl2, 20 8C, 12 h PhIO+Tf2O (76%) CH2Cl2, 20 8C, 4 h PhIO+2 TfOH (94%) RC CH 7 I(OH)OTf OTf PhI + 53 + R 7OTf PhI +ITfO7 H 54 (61% ± 70%) OTf R=Prn, Bun, n-C6H13 . It should be noted that 1-trimethylsilylalkynes react with the reagent 53 with the elimination of the trimethylsilyl group to form the corresponding mono(alkynyl)iodonium salts.85 5. Syntheses starting from cyano(hydroxy)-l3- iodanylbenzene triflate A more versatile method for the synthesis of alkenyliodonium salts that allows the introduction of a wide range of different substituents at the double bond is based on the reactions of cyano(hydroxy)-l3-iodanylbenzene sulfonates 15a,b with tin-sub- stituted alkenes.86 ± 88 R1 R1 + CH2Cl2,723 8C + 7Bu3SnCN +PhI(CN)X7 15a,b R2 R2 SnBu3 IPh X7 (55% ± 90%) R1, R2=Me, Bun, Et, Ph; X=OTf (a), OTs (b).109 The reactions proceed under mild conditions and stereoselec- tively afford alkenyliodonium salts in high yields. Using this approach, phenyl(vinyl)iodonium triflate was synthesised starting from tributyl(vinyl)stannane.88 + 15a H2C CHSnBu3 H2C CHIPh TfO7 (75%) 6. Syntheses starting from alkynyliodonium salts The reactions of alkynyliodonium salts with nucleophiles in protic solvents represent a convenient approach to stereoselective syn- thesis of (Z)-b-functionalised alkenyliodonuim salts. The ratio between the substitution and addition products depends on the nature of the counterion and nucleophile.When trimethylsilyl azide is used as a source of nucleophilic species (in the presence of water), the addition products are formed in high yields, and it is employed for the preparation of (Z)-(b-azidoalkenyl)iodonium salts 55.89 +IPh BF¡ N3 4 + CH2Cl2, H2O, RHC CHIPh BF¡4 +Me3SiN3 778 to 20 8C R H 55 (50% ± 91%) R=Me, But, n-C8H17, cyclo-C5H9CH2. However, the reactions of alkynyliodonium tosylates with sodium azide in the presence of methanol result in the correspond- ing (Z)-(b-azidoalkenyl)iodonium tosylates in relatively low yields.90 1-(Z)-(b-Azidovinyl)-3H-2,1l3-benzooxaiodol-3-one triflates 57 have been obtained by the reactions of alkynyliodonium salts 56 with sodium azide in the presence of 18-crown-6.91 The initial intramolecular hydrogen transfer followed by cyclisation involv- ing the ortho-carboxy group may account for such unusual syn- stereochemistry of the azide addition.N3 + C R CI TfO7 + R I CO2H a O TfO7 56 O 57 (57% ± 63%) R=Bun, n-C6H13, n-C8H17, n-C10H21; (a) NaN3, 18-C-6, CH2Cl2,780 to 20 8C. Stereoselective synthesis of (Z)-(b-halogenovinyl)iodonium salts 58 by the reactions of alkynyliodonium tetrafluoroborates with halide anions in an acid medium has been effected.92, 93 Fluoride anion does not react under these conditions, while the addition of iodide anion results in a complex mixture of products probably due to the low stability of the primary addition prod- ucts.92 (Z)-(b-Halogenovinyl)iodonium salts 58 are useful precur- sors for halogenoalkylidene carbenes.93 +IPh X7 X + LiX, AcOH or HX, AcOH RC CIPh BF¡4 H R58 (66% ± 100%) R=PhCH2, PhCH2CH2, But, n-C8H17, cyclo-C5H9CH2; X=Cl, Br.The conjugate addition of sulfinic acids in methanol affords stereoselectively (Z)-(b-sulfonylvinyl)iodonium salts.94, 95110 +IPh BF¡ R2SO2 4 + R2SO2H, 0 8C, MeOH R1C CIPhBF¡4H R1 (64% ± 100%) R1=Me, Ph(CH2)3, n-C8H17, cyclo-C5H9CH2, HO(CH2)2, cyclo-C6H11(CH2)2; R2=Ph, 4-NO2C6H4, 4-MeOC6H4, Bun. Recently, a similar approach was used to synthesise (Z)-(b- acetoxyvinyl)phenyliodonium bromides 59.96 The reaction sequence includes the conjugate addition of sodium acetate to alkynyliodonium salts in acetic acid and anion exchange in an aqueous solution of sodium bromide.The yields of the products 59 depend on the amount of sodium acetate added. The use of 0.1 equiv. of sodium acetate is optimum; the addition of a greater amount of sodium acetate decreases the yields of the targeted products considerably.96 + 1) NaOAc, AcOH, 20 8C AcO IPh Br7 + 2) NaBr, H2O RC CIPh BF¡4H R 59 (69% ± 76%) R=Me, But, n-C8H17 . Alkynyliodonium salts represent activated electron-deficient alkynes with a highly polarised triple bond. Owing to their dipolar structures, these compounds can be used as dipolarophiles in a variety of cycloaddition reactions.This provides a way to the synthesis of diverse alkenyliodonium salts. Thus (arylethynyl)iodonium tosylates react with nitrile oxides 60a,b to form cycloadducts in high yields.97 The reaction of [(4- methoxyphenyl)ethynyl]iodonium tosylate under similar condi- tions leads to a 1 : 1 mixture of two isomeric adducts 61a and 61b in 60% overall yield.97 Ar1 +IPh + + CH2Cl2, 20 8C TsO7 O Ar1C CIPh TsO7+ Ar2C N O7 N 60a,b Ar2 (71% ± 76%) Ar1=Ph, 2-ClC6H4; Ar2=Mes (a), 2,6-Cl2C6H3 (b). + 4-MeOC6H4C CIPh TsO7 60a CH2Cl2, 20 8C +IPh TsO7 4-MeOC6H4 +IPh TsO7 4-MeOC6H4 O O + N N Mes Mes 61b 61a Nitrone 62 reacts with (phenylethynyl)iodonium tosylate to give adduct 63.97 + 7 + CH2Cl2, 20 8C PhC CIPh TsO7+ O N CHC6H4CN-4 62 Me Ph +IPh TsO7 O N C6H4CN-4 63 (37%) Me Diazocarbonyl compounds 64 form the corresponding cyclo- adducts 65 in the reactions with phenyl(2-trimethylsilylethynyl)- iodonium triflate.98 N Sh Pirkuliev, V K Brel, N S Zefirov O N2 + CH2Cl2, 20 8C Me3SiC CIPh TfO7+ H R 64 Me3Si +IPh TfO7 HN N C(O)R 65 (14% ± 49%) R=OMe, OEt, Ph, But.Methyl and phenyl azides react with alkynyliodonium triflates on heating in tetrahydrofuran or acetonitrile to give triazolyl- iodonium salts 66.98 RN2 R1 N + THF, 85 8C or MeCN, 75 8C R1C CIPh TfO7+R2N3 + N PhI TfO7 66 (17% ± 26%) R1=H, But; R2=Me, Ph. Alkynyliodonium salts can add not only to 1,3-dipolarophiles, but also to 1,3-dienes.99 Adducts 67 ± 69 are obtained as stable, crystalline compounds.Owing to the presence of two functional groups, these adducts can then be used in further reactions. +IPh TfO7 R 67 (55% ± 91%) +IPh TfO7 + RC CIPh TfO7 MeCN 20 8C 68 (45% ± 74%) R Me +IPh TfO7 Me Me R Me 69 (73% ± 88%) . R=CN, Ts, PhCO, C(O) C(O) , O S The reactions of alkynyliodonium salts with unsymmetrically substituted dienes 70 lead to mixtures of two regioisomeric cyclo- hexadienes 71 and 72 in 62%± 84% overall yields.100 Usually, the regioselectivity of the reactions with 2-substituted dienes is low, whereas 1-substituted dienes react more regioselectively. Thus the reaction of penta-1,3-diene with the alkynyliodonium salt 73 leads exclusively to the regioisomer 74, the structure of which was unequivocally established by X-diffraction analysis.100 + MeCN, 20 8C (62% ± 84%) R1C CIPh TfO7+R2 70 R3 R3 + +IPh TfO7 R2 IPh TfO7 + R1 R1 R2 72 71 R3 , R1=CN, Ts, PhCO, C(O) C(O) , Me2NC(O); S O R2, R3=H, Me, Et, But.Alkenyliodonium salts +IPh TfO7 + MeCN, 20 8C ButC(O)C CIPh TfO7+ C(O)But 73 74 (76%) Me Me Acetylene bisiodonium salt 75 is more reactive and readily enters into reactions with cyclopentadiene, furan and 1,3-diphe- nylisobenzofuran in acetonitrile under mild conditions.101 The adducts 76a,b and 77 are stable and can be used in further reactions with various nucleophiles or in cross-couplings with alkynes.102 ± 104 X + X + + IPh TfO7 PhIC CIPh 2 TfO7+ MeCN,735 8C (69% ± 73%) 75 + 76a,b IPh TfO7 X=CH2 (a), O (b).Ph Ph O +IPh TfO7 75 O MeCN, 735 8C + Ph IPh TfO7 Ph 77 (47%) 7. Synthesis starting from fluoro(hydroxy)-l3-iodanylarene sulfonates Most of trivalent iodine organic derivatives employed in the synthesis of stable vinyliodonium salts are insufficiently reactive. Their electrophilicity can be enhanced if these compounds are converted into derivatives of strong acids containing highly nucleofugal groups as ligands. In this approach, reactive iodo- nium compounds are obtained in two steps, and the first step is the synthesis of readily available I(III)-derivatives from aryl iodides.A new one-step procedure for the generation of iodanylarenes directly from aryl iodides has been proposed recently.105 ± 108 It was found that oxidation of aryl iodides with fluoroxenon sulfonate results in the formation of iodonium salts 16a,b. The latter represent convenient starting compounds for the synthesis of diverse diaryl- and alkenyl-iodonium sulfonates. Compounds 16a,b can also be obtained by the reactions of difluoroiodanylar- enes with the respective sulfonic acid, its anhydride or trimethyl- silyl ester.105 HOTf or Tf2O or Me3SiOZ ArIF2 ArI+XeF2 + 7Xe [ArIF ZO7] ArI FXeOZ XeF2+HOZ 16a,b 7HF Z=Tf (a), Ms (b). The fact that the reagents 16a,b contain the highly nucleofugal sulfonate group makes them important.These compounds prob- ably have an ionic structure. It is worth noting that the reagents 16 represent only a specific example of compounds of the general formula [ArI+X Z7] where X and Z denote a heteroatomic substituent and a nucleofugal group, respectively. For example, derivatives with X=OH, Z=OTf;82 X=OH, Z=FSO3;41 X=OH, Z=HSO4;7 X=OH, Z=BF4;41 X=F, Z=BF4 (Refs 41, 62) are also known. In most instances, the structures of these compounds have not been strictly established. Several of them were deduced on the grounds of chemical transformations of these intermediates in reactions with various organic substrates. For example, the reactions with alkynes, aromatic compounds and enol silyl ethers gave rise to iodonium salts 41, 58, 59, 62, 82 and b-diketones.41 Fluoro(hydroxy)iodanylarene sulfonates 16 react stereoselec- tively with terminal alkynes to form (E)-[b-(sulfonyloxy)alk-1- 111 enyl](aryl)iodonium sulfonates 78;105, 109 the structure of one of these compounds was proved by X-diffraction analysis.108 +IAr ZO7 R CH2Cl2 16a,b+RC CH +ArIF2 778 to 20 8C H ZO 78 Z=Tf, Ms; Ar=Ph, 4-MeC6H4, 2-MeC6H4, 4-NO2C6H4 ; R=H, Prn, Bun, n-C8H17, CH2OH, CH2OMe, CH2Cl,CH2CH2OH.Earlier, (E)-(2-trifluoromethylsulfonyloxyvinyl)(aryl)iodo- nium sulfonates 78 were obtained by the electrophilic addition of the [PhIO ± HOTf] reagent to alkynes.82 However, the synthesis of b-functionalised vinyliodonium salts by this method required an additional step including the conversion of iodobenzene into iodosobenzene followed by the activation of the latter with methanesulfonic acid.Compared with this procedure, the use of a novel oxidant, viz., fluoroxenon sulfonate, which already con- tains the sulfonate group, allows a one-step preparation of b-functionalised vinyliodonium salts directly from iodobenzene and terminal alkynes. In addition, the reagents 16 are more reactive towards alkynes than the system [PhIO ± HOTf], and readily enter into reactions even at 770 8C. This method was shown to be suitable for the synthesis of bis(alkenyl)-p-phenyl- eneiodonium salts 52.110 + +RC CH 2 FXeOTf FI I I 72 Xe IF 2 TfO7 +I +I2 TfO7 R R 52 OTf OTf R=H, Me, Et, Ph, Prn, n-C8H17, CH2Cl. It is important to note that exclusively Z-alkenyliodonium salts are formed in the reactions with phenyl(trimethylsilyl)acety- lene.106, 109 The structure of one of such salts has definitively been established by means of X-diffraction analysis.106 This stereo- chemical result differs in principle from other cases where adducts of iodosobenzene with fluorosulfonic or trifluoromethanesulfonic acid 81, 82 reacted with alkynes to give E-b-substituted iodonium salts.It should also be noted that the reactions of other alkynyl- trimethylsilanes with the reagents 16a,b give rise to the corre- sponding alkynyliodonium salts. Ph H a + + ZO IAr ZO7 [ArIF ZO7] + RC CSiMe3 + b RC CIAr ZO7 (37% ± 67%) Z=Tf: Ar=Ph (58%), p-MeC6H4 (53%); Z=Ms, Ar=Ph (56%); (a) R=Ph, HOZ, CH2Cl2,778 to 20 8C; (b) R=H, Bun, But, MeOCH2, CH2Cl; CH2Cl2,778 to 20 8C.III. Reactions of alkenyliodonium salts Exploration of chemical properties of alkenyliodonium salts was begun only in the mid-1980s. Although the majority of alkenylio- donium salts are rather stable compounds and can be stored for a relatively long time without any noticeable changes, most of them undergo thermal destruction on heating. As a rule, the thermal decomposition of alkenyliodonium salts involves the cleavage of a bond between I+ and the carbon atom of the alkenyl fragment. Thermolysis of trans-chlorovinyliodonium salts is accompanied by the formation of acetylene.42, 43, 46 Iodobenzene and vinyl bromide in the ratio of 1 : 1 are formed upon thermal decom-112 position of solid phenyl(vinyl)iodonium bromide 79; no other products have been detected.46 Thermal decomposition of a cyclic iodonium salt 80, which occurs at a melting temperature, leads to a mixture of substituted cis- and trans-stilbenes 81.49 + H2C CHIPh Br7 79Bun +I 80 Cl7 Alkenyliodonium salts undergo solvolysis and fragmentation. The mechanism of solvolysis of (4-tert-butylcyclohex-1-enyl)phe- nyliodonium tetrafluoroborate (37b) in ethanol and aqueous solutions was examined.111 It was shown that the phenyliodonio group is about 106 times as good a leaving group as the triflate.In addition to the expected products, viz., 82 and iodobenzene, the solvolysis also yielded the internal return product 83 and a small amount of 4-tert-butylcyclohexene (84) resulting from a single- electron transfer.A mechanism involving initial heterolysis to form a contact ion pair 85 followed by a single-electron transfer to lead to an intermediate 86 was suggested. However, a possibility that the species 86 is formed upon homolysis of the C7I+ bond is also not excluded. But 37b d 86 eg 85 e (a) C7I+ bond heterolysis; (b) C7I+ bond homolysis; (c) single- electron transfer; (d ) ROH (solvolysis); (e) internal return; (g)7PhI. Fragmentations of 2,2-disubstituted alkenyliodonium salts 87a,b in CDCl3 follow a similar mechanism. However, in this case, triflates 91 and 92 are formed as the products of a cationic rearrangement of an intermediate 90 together with the solvolysis products 88 and 89.112 R1 TfO7 + R2 IC6H4X-4 87a,b R1 90 R2 R1=R2=Me, X=CF3 (87a); R1=Ph, R2=Et, X=H (87b).D H2C CHBr+PhI Bun Ph D Ph Cl I 81 a But + c IPh b But But OR 82 But 83 I But 84 86 CDCl3 4-XC6H4I + 88 H R2 H + + TfO OTf R1 91 89 +. . IPh 85 + IPh 86 R1 + R2 90 H TfO R1 R2 92 Obviously, the presence of the I+ArX7 fragment significantly affects the electron density distribution not only in the groups vicinal to this fragment, but also in the molecule as a whole. Thus according to the 1H NMR spectra of E- and Z-alkenyliodonium salts, the a-proton of the alkenyl group (with respect to the I+Ar fragment) is rather acidic.58, 61 The I+ArX7 group is also respon- sible for the substantially enhanced C7H acidity of some other compounds.113 Being highly acidic, the a-hydrogen atom can readily be removed from alkenyliodonium salts even by such weak bases as amines.78, 114 An exchange of deuterium for the a-vinylic proton and to form deuterio-derivative 94 takes place upon treatment of (E)-(2-ethoxyvinyl)phenyliodonium salt 93 with triethylamine and D2O in THF.The reaction presumably involves the inter- mediate formation of a vinyliodonium ylide 45.114 EtO + D2O, 20 8C 93 IPh BF¡4 1. Generation of alkylidenecarbenes from vinyliodonium salts Owing to the high nucleofugality of the I+ArX7 group, vinyl- iodonium salts readily undergo reductive elimination of iodoben- zene generating thereby highly reactive alkylidenecarbenes.The latter can further transform into cyclopentenes through an intra- molecular regioselective insertion into the C7H bond (1,5- insertion). Thus a-elimination in the iodonium salt 95 followed by the 1,5-insertion in the species 96 proceed under mild con- ditions (Et3N, 25 8C) yielding 2-methylbicyclo[3.3.0]oct-1-ene (97). Similarly, the ketone 99 is obtained from the iodonium salt 98.115 This procedure can also be applied to alkenyliodonium salts bearing the OH group. Thus compound 100 eliminates iodoben- zene to produce carbene 101, which then inserts into the O7H bond to form 2,3-dihydrofuran derivative 102.95 Me +IPh BF¡ THF, 20 8C 95 HH O Me +IPh BF¡ 98 HH HO(CH2)2 +IPh BF¡ THF, 20 8C PhSO2 100 O 102 SO2Ph Reactions of deuterated alkenyliodonium salts 103 with triethylamine at 0 8C lead to terminal alkynes 104 (10% deute- rium) and 105 (89% deuterium) in quantitative yields.The compositions of the reaction products indicate that alkylidene- carbenes predominantly arise through a-elimination and subse- quent 1,2-hydrogen shift rather than through a syn-b-elimination process.115 The absence, in the reaction mixture, of cyclopentene N Sh Pirkuliev, V K Brel, N S Zefirov D EtO EtO 7 Et3N + + 94 IPh IPh BF¡4 Me Et3N 4 96 H Me 97 (84%) O Me ButOK THF, 778 8C 4 H O Me 99 (61%) HO(CH2)2 SO2Ph Et3N 4 101Alkenyliodonium salts derivatives suggests that the 1,2-a-hydrogen shift following 1,5- insertion of alkylidenecarbenes into the C7H bond is very unfavourable.116 n-C8H17 D n-C8H17 Et3N + THF, 0 8C H IPh BF¡ a-D-103 4 n-C8H17C CH 104 n-C8H17 n-C8H17 Et3N + THF, 0 8C D IPh BF¡4 Db-D-103 n-C8H17C CD 105 Elimination of iodobenzene from iodonium salts 106a,b under the action of potassium tert-butoxide leads to alkynes 107a,b as the main products.The a-phenylthio and a-phenylsulfinyl groups in alkylidenecarbenes 108a,b are good leaving groups. Their migration apparently occurs via sulfonium ylides.95 In contrast to compounds 106a,b, an iodonium salt with the a-phenylsulfonyl group gives predominantly 2-phenylsulfonylbicyclo[3.3.0]oct-1- ene (109) (the ratio 109 : 110=4 : 1).This shows that the carbene 111 preferentially inserts into the C7H bond rather than under- goes migration of the sulfur-containing substituent despite the very good migrating ability of this group.116 S(O)nPh S(O)nPh ButOK +IPh BF¡ 778 8C 4 106a,b 108a,b CS(O)nPh CH2C +S(O)nPh 7 107a,b (72% ± 84%) n = 0 (a), 1 (b). SO2Ph SO2Ph Et3N + 20 8C IPh BF¡4111 (89%) H CH2C CSO2Ph SO2Ph+ 110 109 H Reactions of halogen-containing alkenyliodonium salts of similar structures yield different products depending on the nature of the halogen atom in these salts. Thus chlorine-substituted salt 112a gives a 38 : 62 mixture of the product of 1,5-insertion of a carbene into the C7H bond (113a) and the rearrangement product (114a).Only bromoalkyne 114b is formed from the bromine-substituted salt 112b due to the more preferable migra- tion of the bromine atom in the carbene 115b.93 X X NaHCO3 + 0 8C IPh BF¡4112a,b 115a,b (87% ± 95%) H CX CH2C X+ 114a,b 113a,b H X=Cl (a), Br (b). 113 a-Halogenoalkylidenecarbenes are generated in the a-elimi- nation of iodobenzene from (Z)-(2-halogenoalkenyl)iodonium salts (route a). However, in this case the reaction apparently also involves the more stereoelectronically favourable base-induced anti-b-elimination of HX giving rise to alkynyliodonium salts (route b). The Michael addition of a halide ion and subsequent reductive elimination of iodobenzene lead to the final pro- ducts.93, 117, 118 R R route a 7PhI,7BF¡4X + X7 + X IPh BF¡4RC CIPh BF¡4 route b 7HX R R 7+ 7PhI X X IPh BF¡4 Possible transformations of the carbene formed were eluci- dated in a cross-reaction of (Z)-(2-bromoalkenyl)iodonium 116 and alkynyliodonium tetrafluoroborates 117 with sodium hydro- gencarbonate.Alkynes 118 and 114b were formed in the ratio 7 : 3, thus indicating that a-bromoalkylidenecarbene is generated through both a-elimination of the phenyliodonio group and anti- b-elimination of hydrogen bromide.93 + CIPh BF¡ CH2C 4 n-C8H17 NaHCO3 + 0 8C + IPh BF¡ Br 4 116 117 n-C8H17C CBr+114b 118 2-Bromovinyliodonium salt 116 more readily undergoes anti- b-elimination than the 2-chlorovinyliodonium salt 119.This follows from the fact that a 78 : 13 : 9 mixture of compounds 118, 120 and 121 is formed in the cross-reaction of both salts with NaHCO3.93 n-C8H17 NaHCO3 + 116+ IPh Cl7 Cl 119 C5H11-n 118+n-C8H17C CCl+ 120 121 Cl The direction of reactions involving the intermediacy of alkylidenecarbenes was found 119 ± 121 to be also dependent on the nature of solvent employed. In diethyl ether or THF, the complexation of alkylidenecarbenes with these solvents, viz., the formation of oxonium ylides, was observed. Thus treatment of alkenyliodonium salt 122 with triethylamine in THF yields a mixture of products 123 ± 125 formed as the result of 1,5-insertion of the carbene 127 into the C7H bond, 1,2-migration of the butyl group and also the reaction of salt 122 with triethylamine.In addition, a nucleophilic attack of the intermediate carbene 127 on tetrahydrofuran to form oxonium ylide 128 and further trans- formation of the latter into compound 126 via oxonium salt 129 also occur.122 Bun Me NEt3 + BunC CBun + + Bun IPh BF¡ THF 4 124 123 122 BunBun Bun + + + + Bun Bun O(CH2)4NEt3 BF¡ NEt3 BF¡ 4 4 126 125N Sh Pirkuliev, V K Brel, N S Zefirov 114 Bun NEt3 122 + 7PhI, 7Et3NH BF¡4 ipation of the alkylidenecarbene as an intermediate species in this reaction.115 Bun Bun C8H17-n 127 + 123 (E )-132 BF¡4 PhI ButOK 124 Bun C8H17-n + Bun Et3N 7 4 125 + + Et3NH BF¡ 7Et3N (Z)-132 IPh BF¡4Bun NEt3 Bun C8H17-n + Bun 7 THF + Et3NH BF¡4127 + 7NEt3 7THF 134 133 Me C5H11-n O Bun 128 Bun BF¡4NEt3 Complete loss of regioselectivity testifies that this intermediate species represents a `true' carbene (structure A) rather than a carbenoid (structure B) in which the `memory effect' would be preserved to some extent.126 + Bun O Bun +IPh Me H H H C5H11-n n-H11C5 129 H B A B The course of the reactions is also controlled by the temper- ature (Table 1). On lowering the reaction temperature, the yields of the products 123 ± 125 derived from alkylidenecarbene 127 are decreased, and the yield of the ether 126 derived from vinyl- oxonium ylide 128 is increased. These effects were explained as the reversibility of the process of oxonium ylide 128 formation, although no solid proof for the existence of an equilibrium between free alkylidenecarbenes and oxonium ylides was obtained.In the presence of sulfides, alkylidenecarbenes give vinyl- sulfonium salts as the products of onium species transformations. An assumption that these reactions occur via free alkylidenecar- benes was put forward on the grounds of stereochemical stud- ies.122 Thus (E)-vinylsulfonium salt (E)-136 was the major product [the ratio (E)-136 : (Z)-136 is 69 : 31] in the reactions of both E- and Z-iodonium salts 135 with diisopropylamine in the presence of diphenyl sulfide. Such stereoselectivity most likely results from different bulkiness of two a-substituents in the alkylidenecarbenes formed. Table 1. The ratio of the reaction products of compound 122 with Et3N in THF.+SPh2 BF¡ Bn Bn Bn 4 Pri2NEt + + + Tempera- Time Overall Yields of reaction products (%) Ph2S ture /8C /h Me Me IPh BF¡ SPh2 BF¡44 Ratio (123+124+125) : : 126 yield (%) 135 Me(E )-136 (Z)-136 123 124 125 126 98 : 2 90 : 10 85 : 15 74 75 75 90 95 99 10 10 10 60 40 20 29 15 1 14 <1 11 <1 8 0 10 98 71 3 1 23 77:23 223 65 : 35 54 : 46 54 : 46 27 40 42 48 44 44 78 87 92 10 10 10 0 a 0 b 0 c 113 The r constants for the reactions of 2-methyl-1-propylidene, generated from the salt 130, with different styrene derivatives in the presence of Et3N and ButOK have been determined (70.56 and 70.55, respectively) by measuring relative rates for these reaction.123 Since free alkylidenecarbenes are relatively `soft' nucleophiles, their reactions usually have small negative r values.In contrast, carbenoids generated from other precursors possess much more pronounced electrophilic properties and therefore their reactions have high negative r values. Note. The reaction mixture was preliminarily kept for 2 days at: a720 8C; b740 8C; c760 8C. 2. Vinylic nucleophilic substitution in alkenyliodonium salts. An alkylidenecarbene generated from the alkenyliodonium salt 130 adds to alkenes to give alkylidenecyclopropanes 131.123 Its addition to cis- and trans-4-methylpent-2-enes occurs stereo- spesifically. R Me H Me RHC CH2 + Me Me IPh BF¡4 ButOK or Et3N 3 8C, CH2Cl2 131 130 The ratio of isomeric cyclopentenes 133 and 134 formed upon treatment of both Z- and E-isomers of the iodonium salt 132 with ButOK is 1 : 1 and is independent of the geometry of the starting compounds or the reaction conditions.This suggests the partic- The aryliodonio group is known to be one of the best leaving groups in nucleophilic substitution reactions.111, 124 Owing to the capability of aryl(vinyl)iodonium salts to generate vinylic cations under remarkably mild conditions, these salts can formally be considered as vinylic cation equivalents. The reactions of (4-tert- butylcyclohex-1-enyl)phenyliodonium tetrafluoroborate 37b with various nucleophiles 58, 59 are exemplified in Scheme 1. Alkylation of alkenyliodonium salts with organometallic compounds to give substituted cyclohexenes 137 occurs success- fully only with lithium organocuprates; other organometallic compounds are oxidised by the iodonium salt 37b.Substitutions by halide ions in the presence of the respective copper(I) halides in DMF at 20 8C result in nearly quantitative yields of products. Good product yield is also obtained in the reaction with cyanide ion. The salt 37b reacts with sodium nitrite in the presence of copper(II) sulfate to give nitroalkene 138 without any traces ofAlkenyliodonium salts CO2Me MeOH, CO Pd(OAc)2 But 141 (84%) X CuX, KX, DMF X=Hal But SPh PhSNa But 139 (81%) 137: R=Me, Ph, Bu. nitrite. The reaction with sodium benzenethiolate yields (4-tert- butylcyclohex-1-enyl) phenyl sulfide (139), while with indandione enolate it leads to the C-vinylation product 140 (see also Ref.125). Vinyliodonium salt 37b is carbonylated in methanol in the presence of palladium salts as catalysts to afford ester 141. Reactions of several nucleophiles with 2-azidoalkenyl- iodonium salts 142 prepared in situ by the addition of sodium azide to alkynyliodonium salts have been studied.90 In all cases, the iodine-containing fragment was substituted by nucleophiles. Ph H+IPh TsO7 N3 142 Nucleophilic substitutions of vinyliodonium salts in the pres- ence of copper compounds occur stereospecifically with retention of the initial configuration.126, 127 This was the reason to reject an idea of a free-radical mechanism for such reactions.Instead, a mechanism involving the intermediacy of three-coordinated iodine species 143 and three-coordinated copper 144 was sug- gested.102, 126, 127 n-C8H17 KCuX2 +IPh BF¡4 Scheme 1 R R2CuLi But 137 (73% ± 90%) + CN IPhBF¡4 KCu(CN)2 But But 37b (92%) NO2 NaNO2, CuSO4 O But Me 138 (55%) O7 O Me O 140 (86%) But H Ph Et3SiH, CH2Cl2 20 8C N3 SiEt3 (61%)H Ph MeOH 20 8C N3 OMe (20%)H Ph ButOK, HO(CH2)2OMe 770 8C N3 O(CH2)2OMe (51%) n-C8H17 7PhI 143 I(Ph)CuX2 115 n-C8H17 n-C8H17 7CuX 144 X CuX2 X= Cl, Br. The stereochemistry of vinylic nucleophilic substitution has been studied in detail in the reactions of alkenyl(phenyl)iodonium salts 36a,b with Ph2CuLi in tetrahydrofuran.It was found that compound 36a gives the products in high yields and with complete retention of the initial configuration. By contrast, the reactions of compound 36b are accompanied by elimination to form the corresponding alkyne.58 + Ph IPh BF¡ Ph(CH2)2 Ph(CH2)2 4 Ph2CuLi THF, 730 8C, 4 h Me Me 36a (E:Z=97 : 3 or 12 : 88) [82% (E:Z=97 : 3)] [82% (E:Z=12 : 88)] n-C8H17 Ph2CuLi, THF + 740 8C, 3.5 h 36b IPh BF¡4 n-C n-C8H17 17 CH +n-C8H17C(7%) Ph (72%) The substitution of the iodine-containing fragment in vinyl- iodonium salts by halide, under the action of tetrabutylammo- nium halides in dichloromethane in the absence of copper(I) halides, occurs with inversion of configuration, which competes with elimination and the formation of alkynes.128 Transforma- tions of a- and b-deuterated substrates were examined in order to elucidate the mechanism of these reactions.Based on the results obtained 128 it was concluded that elimination in the reactions with Bun4 NF results from the initial attack by the fluoride ion on the a-hydrogen atom followed by rearrangement of the carbene formed. + F7 H R R R Bun4 NF7 RC CH + + IPh BF¡ IPh BF¡ H 4 4 By contrast, other halide ions react through the b-elimination mechanism. The yields of elimination products are increased in the series: I7<Br7<Cl7<F7; the dependence on the nature of a substituent at the C(2) atom has the order: n-alkyl<benzyl< phenyl.Stereoselectivity of the reactions decreases in the same order. With an increase in the excess of tetrabutylammonium halide in the reaction, a noticeable drop in the ratio alkyne : vinyl halide is observed, thus indirectly confirming the proposed reaction scheme.128 + X R Bun4 NX7 + R R Bun4 NX7 b-elimina- tion + + RC CH H IPh X7 IPh BF¡4 R=n-C8H17, Ph(CH2)3, Ph; X=Cl, Br, I. Nucleophilic substitutions of the iodine-containing fragment in the iodonium salt 35 occur, as a rule, in good yields (Table 2); the ratio of stereoisomers depends on the nature of the nucleophile and the reaction conditions.57 + X IPh TsO7 Me Me X7 or HX H2N CO2Me H2N CO2Me 145a ± f 35116 Table 2. Nucleophilic substitution of the iodine-containing fragment in compound 35.Reaction conditions X Yield (%) Product 145 time /h solvent reagent 12 CH2Cl2 12 DMF Bu4N+Br7 NaNO2, CuSO4 TsONa KCN abcde 78 DMF, H2O 12 20 25 DMF, H2O 12 60 4 80 Br NO2 TsO CN Et2N Et2 NH CH2Cl2 f 4 83 CH2Cl2 NH O N O Bisiodonium salts 76a,b react with anionic nucleophiles to form the nucleophilic substitution products of the phenyliodonio group (146 and 147).102 ± 104 Z CR C a Z C +IPh TfO7 CR 146 (40% ± 69%) + 76a,b IPh TfO7 Z X b 147 X Z=O (a), CH2 (b); (a) CH:CR, BuLi, CuCN, CH2Cl2,778 to 25 8C, 12 h, R=SiMe3, But, Bun, Ph; (b) NaX, CuX; X=Br, I, CN, PhCOO. Nucleophilic substitutions in (Z)-(2-phenylsulfonyl)alkenyl- iodonium salts 148 with tetrabutylammonium halides or sodium benzenesulfinate proceed with retention of configura- tions.94, 129 ± 132 + R Bun4 N X7 R X PhO2S + R IPh BF¡ PhO2S PhSO2Na 4 148 PhO2S SO2Ph X=Cl, Br, I.Heterocyclic iodonium salts also undergo nucleophilic sub- stitution. Thus the reactions of compound 40b with nucleophiles lead to the corresponding cyclic adducts through a two-step addition ± elimination process and/or reductive elimination fol- lowing attack by a nucleophile on the iodine atom (Scheme 2).62 Perchlorate 40b reacts with sodium azide in acetonitrile to give vinyl azide 149 in nearly quantitative yield. The reactions of compound 40b with sodium methoxide and sodium ethoxide in the respective alcohol afford vinyl ethers 150 in 83% and 91% yields, respectively. Compound 40b reacts with a mixture of equimolar amounts of potassium and copper(I) iodides to give vinylic iodide 151 in 67% yield.In the reaction with triphenyl- phosphine, vinylic iodide 151 and the phenylation product of triphenylphosphine, viz., tetraphenylphosphonium perchlorate (22% yield), are formed along with the expected vinylphospho- nium salt 153 (20% yield). Me O Me N3 (EtO)2(O)P 149 (98%) NaN3, MeCN Me O Me +IPh ClO¡ (EtO)2(O)P 4 40bPPh3, MeCN Me O +Ph4PClO¡4 +151 Me +PPh3 (EtO)2(O)P 4 ClO¡ 153 3. Vinylation of aromatic compounds with vinyliodonium salts As is known, direct introduction of the vinylic group into aromatics by electrophilic substitution is rather inefficient because of the low reactivities of vinyl halides.Unlike vinyl halides, vinyliodonium salts do enter into the reactions of electrophilic aromatic substitution. These substitutions can proceed as an intramolecular process to lead to cyclic systems, if vinyliodonium salts have suitable structures.133 Compared with Friedel ± Crafts reactions they proceed under milder conditions and in the absence of catalysts. X R2 R1 +IPh BF¡4 X=CH2, O;R1, R2=H, Me, Cl, Br. +IPh BF¡4 PhH 80 8C, 1 h But 37b (Z)-Alkenyliodonium salts do not cyclise under the same conditions. An SE(Ar)-substitution mechanism was suggested 133 in which iodobenzene is eliminated from the intermediate iodocy- clopropane, though other mechanisms cannot be ruled out.4. Palladium-catalysed cross-coupling Vinyliodonium salts were found to undergo cross-couplings with activated alkenes. The reactions conditions are milder than those used in the Heck reaction. Thus salts 154 and 36c are carbonylated in the presence of palladium at 20 8C with complete retention of configurations to form a,b-unsaturated esters 155 and 156.58, 134 N Sh Pirkuliev, V K Brel, N S Zefirov Scheme 2 Me O Me RONa, ROH R=Me, Et OR (EtO)2(O)P 150 Me O CuI, KI Me I (EtO)2(O)P 151 (92%)Me O P(OEt)3, MeCN +151 Me P(O)(OEt)2 (EtO)2(O)P 152 + X CD3OD 40 ± 60 8C R2 R1 Ph ButAlkenyliodonium salts Ph(CH2)2 Me Ph 36c Enynones 157 were synthesised from alkenyliodonium salt 36c and terminal alkynes under similar conditions in the presence of copper iodide.135 Ph + 36c IPh BF¡ R=Bu (76%), Ph (88%).A highly stereoselective synthesis of conjugated dienes 158 is accomplished at 20 8C.136R3 R1 R2 R1=H, Bun, OTs; R2=Bun, Ph, OTs, R3=Ph, COMe, CO2Me, CHO; X =OTs, BF4. An asymmetrical version of the Heck reaction was imple- mented in the presence of a chiral ligand, viz., (R)-2,20-bis(diphe- nylphosphino)-1,10-binaphthyl [(R)-BINAP].137 +IPh BF¡ 37a Furthermore, in the presence of palladium, alkenyliodonuim salts react under mild conditions with alkynyl-,86 allyl- 138 and alkenyl-stannanes.86, 138 The reactions with alkenylstannanes occur faster but less selectively to give various unidentified compounds along with the major product.R1 R2 R2 R1 Bun Et Me Bun Et Bun Me Et Bun BunR1 R2 Ph(CH2)2 + Pd(OAc)2, CO, Bu3N, MeOH 20 8C Me IPh BF¡ CO2Me 4 155 154 Ph Pd(OAc)2, CO, ROH +IPh BF¡ CO2Me 4 156 Ph +HC CR 157 C(O)C CR 4 Pd(OAc)2, CuI, NaHCO3 CO (1 atm), DME, H2O R3 + R1 Pd(OAc)2, NaHCO3 IPh X7+ DMF, 20 8C, 0.5 ± 6 h H R2 H 158 (60% ± 85%) ; 4 Pd(OAc)2 + O (R)-BINAP CH2Cl2, 208C O159 H +Bu3SnC CR3 + 5 mol.% Bu(PPh3)2PdCl 8 mol.% CuI, DMF, 20 8C IPhTfO7 H C R3C R1 160 R2 Yield of 160 (%) R3 77 64 66 66 67 Ph Ph Ph ButCO C(O)N(CH2)4 PriO O H 5 mol.% Bu(PPh3)2PdCl + + 8 mol.% CuI, DMF, 20 8C IPhTfO7 Bu3Sn O 117 O PriO O PriO + O Ph O 162 R2 R1 161 R1=R2=Me (70%), R1=Bun, R2=Et (60%); R1=R2=Bun (65%); R1=Et; R2=Bun (76%).Terminal alkynes readily react with alkenyl(aryl)iodonium salts bearing the TfO group in the b-position at 30 ± 40 8C in DMF:H2O (6 : 1) to form enynes 163 in high yields.139 TfO H TfO H R2C:CH, PdCl2(PPh3)2, CuI + K2CO3, DMF, H2O, Et3N C CR2 IPh TfO7 R1 R1 163 (59% ± 77%) R1=Bun, H, CH2OMe, Ph; R2=n-C8H17, Ph, CH2OMe, SiMe3, CH2Cl, Prn. The reaction rates were found to be higher in polar solvents.139 Small variations in the basicity of amines almost do not affect the reaction rates and the yields of the coupling products. Complexes of palladium with triphenylphosphine ligands were found to be the most efficient.The addition of CuBr instead of CuI does not affect the reaction rates. An induction period (*1 ±2 h) is observed in the CuCl-catalysed reactions, after which the reaction rates become the same as in the case of CuI. The optimum ratio of PdCl2(PPh3)2 to CuI is 2 : 3. The reaction rates are increased on addition of water to the system DMF±Et3N± [Pd], this effect depending on the palladium catalyst employed. Thus the max- imum rate acceleration on addition of water is observed in the presence of PdCl2(PPh3)2. In aqueous media in the presence of ligand-free palladium catalysts, unsubstituted alkenyliodonium salts also enter into reactions with terminal alkynes.140 Alkenyliodonium salts react with allylic alcohols [in the presence of Pd(OAc)2 (see Ref.141) or a polymeric palladium catalyst 142] and allylic cyclic carbonates.143 OH + Pd(OAc)2, NaHCO3 IPh BF¡ + 4 Ph R DMF or MeCN:H2O (5 : 1), 20 8C R OH Ph R=H, n-C5H11. + Pd(OAc)2, NaHCO3 O IPh BF¡4BnO +Ph DMF or MeCN:H2O (5 : 1), 20 8C O O O Ph BnO O O In the presence of palladium catalysts, alkenyliodonium salts also undergo the cross-coupling reactions with organoelement compounds.144 ± 146 Thus, in the reaction of phenyl(styryl)- iodonium tetrafluoroborate 36c with vinylfluorosilanes, only the b-styryl group was transformed to afford the cross-coupling products, dienes 164, in high yields.145118 Ph R1 a Ph + + R1 164 (41% ± 81%) 36c SiR2 IPh BF¡ 3 4 R1=Bun, Ph; R23 =MeF2, F3, Me2F; (a) Z3-C3H5PdCl2, KF or Bun4 N+F7, DMF, 20 8C, 5 min.To account for the palladium-catalysed reactions of vinyl- fluorosilanes with alkenyliodonium salts, a mechanism involving the interaction of an electrophilic alkenyliodonium salt with catalytically active Pd(0), the reductive elimination of iodoben- zene to form alkenylpalladium tetrafluoroborate and the trans- metallation reaction with vinylfluorosilanes was proposed.145 Carbonylation of alkenyliodonium salts in the presence of Pd complexes 145, 146 can serve as a convenient procedure for the synthesis of unsaturated ketones, viz., 165 and 166. Enyne 167 is smoothly obtained on coupling of alkynylfluoromethylsilane with the iodonium salt 36c.145 Ph Ph b Ph Ph + + 36c IPh BF¡ SiMe2F 4 O 165 (72%) (b) Z3-C3H5PdCl2, Bun4 N+F7, DME, CO (1 atm), 20 8C, 5 min.c Ph C PhC Ph 167 (81%) +PhC CSiMe2F + 36c IPh BF¡ Ph d 4 CC(O) PhC 166 (78%) (c) Z3-C3H5PdCl2, KF or Bun4 N+F7, DMF, 20 8C, 5 min; (d ) Z3-C3H5PdCl2, Bun4 N+F7, DME, CO (1 atm), 20 8C, 5 min. The cross-coupling of alkenyliodonium salt 36c with a large series of boronates in the system Pd(PPh3)4±Na2CO3 ± DMF±H2O has been effected and in all cases the cross-coupling product 168 was obtained in virtually quantitative yield.144 Ph Ph a Ph O + Ph + IPh BF¡ 36c B 4 168 (98%) O (a) [Pd(PPh3)4], Na2CO3, DME:H2O=4 : 1, 20 8C, 10 min. IV. Conclusion From the data presented in this review one can see that alkenylio- donium salts are of interest for synthetic organic chemistry.These compounds are rather effective oxidants and can readily undergo free-radical transformations. They also possess high electrophi- licities, which can be changed within a wide range by varying the ligands at the iodine atom, and are featured by the presence of the highly nucleofugal iodine-containing group. Alkenyliodonium salts with several functional groups attract ever-growing interest. Such reagents allow the introduction into substrates of rather complex fragments under mild conditions. References 1. C Willgerodt J. Prakt. Chem. 33 155 (1886) 2. C Willgerodt Die Organischen Verbindungen mit Mehrerwertigem Iod (Sttutgart: Enke, 1914) 3. R B Sandin Chem.Rev. 32 249 (1943) 4. D F Banks Chem. Rev. 66 243 (1966) 5. F M Beringer, E M Gindler Iodine Abstr. Rev. 3 70 (1956) 6. O Ya Neiland Uch. Zap. Rizhsk. Politekh. In-ta 16 131 (1956) 7. G F Koser, in The Chemistry of Functional Groups. Suppl. D (Eds S Patai, Z Rappoport) (New York: Wiley, 1983) Ch. 18, p. 721; Ch. 25, p. 1265 N Sh Pirkuliev, V K Brel, N S Zefirov 8. A Varvoglis Chem. Soc. Rev. 10 377 (1981) 9. H Kuppers, in Methoden der Organischen Chemie (Houben-Weyl) Vol. 4/1b (Stuttgart: Georg Thieme Verlag, 1975) p. 935 10. A Varvoglis Synthesis 709 (1984) 11. O A Ptitsyna, in Problemy Organicheskoi Khimii (Problems of Organic Chemistry) (Ed. A N Kost) (Moscow: Moscow State University, 1970) p. 73 12. N A Nesmeyanov, T P Tolstaya, in Problemy Organicheskoi Khimii (Problems of Organic Chemistry) (Ed.A N Kost) (Moscow: Moscow State University, 1970) p. 29 13. E B Merkushev, M S Shvartsberg Iodistye Organicheskie Soedine- niya i Sintezy na Ikh Osnove (Iodine Organic Compounds and Syntheses Based on Them) (Tomsk: Tomsk State Pedagogical Institute, 1978) 14. E B Merkushev Preparativnye Sintezy Iodaromaticheskikh Soedinenii (Preparative Syntheses of Iodoaromatic Compounds) (Tomsk: Tomsk State Pedagogical Institute, 1985) 15. E B Merkushev Usp. Khim. 56 1444 (1987) [Russ. Chem. Rev. 56 826 (1987)] 16. A Varvoglis The Organic Chemistry of Polycoordinated Iodine (New York: VCH, 1992) 17. A Varvoglis Hypervalent Iodine in Organic Synthesis (London: Academic Press, 1997) 18.A Varvoglis Tetrahedron 53 1179 (1997) 19. T Umemoto Yuki Gosei Kagaku Kyokaishi 41 251 (1983); Chem. Abstr. 98 214 835 (1983) 20. R M Moriarty, O Prakash Acc. Chem. Res. 19 244 (1986) 21. M Ochiai, Y Nagao Yuki Gosei Kagaku Kyokaishi 44 660 (1986); Chem. Abstr. 106 84 682 (1987) 22. M Ochiai Rev. Heteroatom. Chem. 2 92 (1989) 23. R M Moriarty, R K Vaid Synthesis 431 (1990) 24. R M Moriarty, R K Vaid, G F Koser Synlett 365 (1990) 25. P J Stang Angew. Chem., Int. Ed. Engl. 31 274 (1992) 26. O Prakash, N Saini, P K Sharma Synlett 221 (1994) 27. O Prakash, N Saini, P K Sharma Heterocycles 38 409 (1994) 28. O Prakash, S P Singh Aldrichim. Acta, 27 15 (1994) 29. O Prakash Aldrichim. Acta 28 63 (1995) 30. V V Zhdankin Rev.Heteroatom. Chem. 17 133 (1997) 31. V V Zhdankin, S A Erickson, K J Hanson J. Am. Chem. Soc. 119 4775 (1997) 32. T Umemoto Chem. Rev. 96 1757 (1996) 33. G Wittig, M Rieber Liebigs Ann. Chem. 562 187 (1949) 34. H J Reich, C S Cooperman J. Am. Chem. Soc. 95 5077 (1973) 35. V V Zhdankin, R Tykwincki, B L Williamson, P J Stang, N S Zefirov Tetrahedron Lett. 32 733 (1991) 36. G F Koser, in The Chemistry of Halides, Pseudo-Halides and Azides. Suppl. D2 (Eds S Patai, Z Rappoport) (Chichester: Wiley-Interscience, 1995) p. 1173 37. P J Stang, in Modern Acetylene Chemistry (Eds P J Stang, F Diederich) (Weinheim: VCH, 1995) p. 67 38. P J Stang, in The Chemistry of Triple-Bonded Functional Groups. Suppl. C2 Vol. 2 (Ed. S Patai) (Chichester: Wiley, 1994) p.1164 39. V V Zhdankin, P J Stang Tetrahedron 54 10927 (1998) 40.P J Stang Izv. Akad. Nauk, Ser. Khim. 20 (1993) a 41. P J Stang, V V Zhdankin Chem. Rev. 96 1123 (1996) 42. R Kh Freidlina, E M Brainina, A N Nesmeyanov Izv. Akad. Nauk SSSR, Otd. Khim. Nauk 647 (1945) 43. E M Brainina, R Kh Freidlina Izv. Akad. Nauk SSSR, Otd. Khim. Nauk 623 (1947) 44. E L Colichman, J T Matschiner J. Org. Chem., 18 1124 (1953) 45. A N Nesmeyanov, T P Tolstaya, N F Sokolova, V N Varfolomeeva, A V Petrakov Dokl. Akad. Nauk SSSR 198 115 (1971) b 46. A N Nesmeyanov, T P Tolstaya, A V Petrakov Dokl. Akad. Nauk SSSR 197 1337 (1971) b 47. J Thiele, H Haakh Liebigs Ann. Chem. 369 131 (1909) 48. J B Howell, W A Noyes J. Am. Chem. Soc. 42 991 (1920) 49.F M Beringer, P Ganis, G Avitabile, H Jaffe J. Org. Chem. 37 879 (1972) 50. O Ya Neiland, B Ya Karele Zh. Org. Khim. 6 885 (1970) c 51. B Ya Karele, S V Kalnin', I P Grinberga, O Ya Neiland Khim. Geterotsikl. Soedin. 553 (1973) d 52. J S Lodaya, G F Koser J. Org. Chem. 55 1513 (1990) 53. G F Koser, L Rebrovic, R H Wettach J. Org. Chem. 46 4324 (1981) 54. L Rebrovic, G F Koser J. Org. Chem. 49 4700 (1984)Alkenyliodonium salts 55. G F Koser, R H Wettach J. Org. Chem. 45 1542 (1980) 56. A J Margida, G F Koser J. Org. Chem. 49 4703 (1984) 57. I Papoutsis, S Spyroudis, A Varvoglis Tetrahedron 54 1005 (1998) 58. M Ochiai, K Sumi, Y Takaoka,M Kunishima, Y Nagao,M Shiro, E Fujita Tetrahedron 44 4095 (1988) 59. M Ochiai, K Sumi, Y Nagao, E Fujita Tetrahedron Lett.26 2351 (1985) 60. M Ochiai, K Sumi, Y Nagao, E Fujita, H Arimoto, H Yamaguchi J. Chem. Soc., Chem. Commun. 697 (1985) 61. M Ochiai, K Oshima, Y Masaki J. Chem. Soc., Chem. Commun. 869 (1991) 62. N S Zefirov, A S Koz'min, T M Kasumov, K A Potekhin, V D Sorokin, V K Brel, E V Abramkin, Yu T Struchkov, V V Zhdankin, P J Stang J. Org. Chem. 57 2433 (1992) 63. V M Ignat'ev, Kh M Angelov, B I Ionin, A A Petrov Zh. Obshch. Khim. 45 2342 (1975) e 64. Kh M Angelov,M Kirilov, B I Ionin, A A Petrov Zh. Obshch. Khim. 49 2225 (1979) e 65. R S Macomber J. Org. Chem. 42 3297 (1977) 66. R S Macomber, G A Krudy, K Sefft, L E Rendon-Diazmicon J. Org. Chem. 48 1425 (1983) 67. Kh Angelov, K Vachkov Phosphorus Sulfur Relat.Elem. 21 237 (1984) 68. Kh M Angelov, Kh Zh Khristov Zh. Obshch. Khim. 50 1891 (1980) e 69. Kh M Angelov, Ch Tancheva Zh. Obshch. Khim. 55 53 (1985) e 70. Kh Angelov, Kh Khristov Phosphorus Sulfur Relat. Elem. 15 373 (1983) 71. C Tancheva, Kh Angelov, D Mondeshka Heterocycles 23 843 (1985) 72. M Ochiai, M Kunishima, K Sumi, Y Nagao, E Fujita, M Arimoto, H Yamaguchi Tetrahedron Lett. 26 4501 (1985) 73. M Ochiai, T lto, Y Takaoka, Y Masaki,M Kunishima, S Tani, Y Nagao J. Chem. Soc., Chem. Commun. 118 (1990) 74. T Kitamura, P J Stang J. Org. Chem. 53 4105 (1988) 75. P J Stang, T Kitamura Org. Synth. 70 215 (1992) 76. P J Stang, A M Arif, C M Crittell Angew. Chem., Int. Ed. Engl. 29 287 (1990) 77. M D Bachi, N Bar-Ner, C M Crittell, P J Stang, B L Williamson J.Org. Chem. 56 3912 (1991) 78. M Ochiai, M Kunishima, K Fuji,M Shiro, Y Nagao J. Chem. Soc., Chem. Commun. 1076 (1988) 79. M Ochiai, M Toyonari, T Nagaoka, D-W Chen, M Kida Tetrahedron Lett. 38 6709 (1997) 80. T Kitamura, R Furuki, K Nagata, H Taniguchi, P J Stang J. Org. Chem. 57 6810 (1992) 81. T Kitamura, R Furuki, H Taniguchi, P J Stang Tetrahedron Lett. 31 703 (1990) 82. T Kitamura, R Furuki, H Taniguchi, P J Stang Tetrahedron 48 7149 (1992) 83. P J Stang, V V Zhdankin, N S Zefirov Mendeleev Commun. 159 (1992) 84. T Kitamura, R Furuki, H Taniguchi, P J Stang Mendeleev Commun. 148 (1991) 85. T Kitamura, R Furuki, K Nagata, L Zheng, H Taniguchi Synlett 193 (1993) 86. R J Hinkle, G T Poulter, P J Stang J.Am. Chem. Soc. 115 11626 (1993) 87. R J Hinkle, P J Stang Synthesis 313 (1994) 88. P J Stang, J Ullmann Angew. Chem., Int. Ed. Engl. 30 1469 (1991) 89. M Ochiai, M Kunishima, K Fuji, Y Nagao J. Org. Chem. 53 6144 (1988) 90. T Kitamura, P J Stang Tetrahedron Lett. 29 1887 (1988) 91. T Kitamura, T Fukuoka, Y Fujiwara Synlett 659 (1996) 92. M Ochiai, K Uemura, K Oshima, Y Masaki, M Kunishima, S Tani Tetrahedron Lett. 32 4753 (1991) 93. M Ochiai, K Uemura, Y Masaki J. Am. Chem. Soc. 115 2528 (1993) 94. M Ochiai, K Oshima, Y Masaki Tetrahedron Lett. 32 7711 (1991) 95. M Ochiai, M Kunishima, S Tani, Y Nagao J. Am. Chem. Soc. 113 3135 (1991) 96. M Ochiai, Y Kitagawa, S Yamamoto J. Am. Chem. Soc. 119 11598 (1997) 97. E Kotali, A Varvoglis, A Bozopoulos J.Chem. Soc., Perkin Trans. 1 827 (1989) 119 98. G Maas,M Regitz, U Moll, R Rahm, F Krebs, R Hector, P J Stang, C M Crittell, B L Williamson Tetrahedron 48 3527 (1992) 99. B L Williamson, P J Stang A M Arif J. Am. Chem. Soc. 115 2590 (1993) 100. P Murch, A M Arif, P J Stang J. Org. Chem. 62 5959 (1997) 101. P J Stang, V V Zhdankin J. Am. Chem. Soc. 113 4571 (1991) 102. P J Stang, T Blume, V V Zhdankin Synthesis 35 (1993) 103. P J Stang, A Schwartz, T Blume, V V Zhdankin Tetrahedron Lett. 33 6759 (1992) 104. J H Ryan, P J Stang J. Org. Chem. 61 6162 (1996) 105. T M Kasumov, N Sh Pirguliyev, V K Brel, Yu K Grishin, N S Zefirov, P J Stang Tetrahedron 53 13139 (1997) 106. T M Kasumov, V K Brel, K A Potekhin, E V Balashova, N S Zefirov Dokl.Akad. Nauk 351 644 (1996) b 107. T M Kasumov, V K Brel, K A Potekhin, A S Koz'min, E V Balashova, Yu S Struchkov, N S Zefirov Dokl. Akad. Nauk 349 634 (1996) b 108. T M Kasumov, V K Brel, K A Potekhin, E V Balashova, N S Zefirov, P J Stang Dokl. Akad. Nauk 353 770 (1997) b 109. N Sh Pirkuliev, V K Brel, T M Kasumov, N G Akhmedov, N S Zefirov Zh. Org. Khim. 1633 (1999) c 110. N Sh Pirguliyev, V K Brel, T M Kasumov, Yu K Grishin, N S Zefirov, P J Stang Synthesis 1297 (1999) 111. T Okuyama, T Takino, T Sueda,M Ochiai J. Am. Chem. Soc. 117 3360 (1995) 112. R J Hinkle, D B Thomas J. Org. Chem. 62 7534 (1997) 113. O Ya Neiland, B Ya Karele Zh. Org. Khim. 7 1611 (1971) c 114. P J Stang,H Wingert, A M Arif J. Am. Chem. Soc. 109 7235 (1987) 115. M Ochiai,Y Takaoka,Y Nagao J. Am. Chem. Soc. 110 6565 (1988) 116. J C Gilbert, D H Giamalva, U Weerasooriya J. Org. Chem. 48 5251 (1983) 117. M Ochiai, Y Kitagawa,M Toyanari, K Uemura, K Oshima, M Shiro J. Org. Chem. 62 8001 (1997) 118. T Okuyama, M Ochiai J. Am. Chem. Soc. 119 4785 (1997) 119. J C Gilbert, U Weerasooriya Tetrahedron Lett. 21 2041 (1980) 120. A Oku, T Harada, Y Nozaki, Y Yamaura J. Am. Chem. Soc. 107 2189 (1985) 121. A Oku, K Kimura, S Ohwaki Acta Chem. Scand. 47 391 (1993) 122. T Sueda, T Nagaoka, S Goto, M Ochiai J. Am. Chem. Soc. 118 10141 (1996) 123. M Ochiai, T Sueda, K Uemura, Y Masaki J. Org. Chem. 60 2624 (1995) 124. T Okuyama, T Takino, K Sato, M Ochiai J. Am. Chem. Soc. 120 2275 (1998) 125. F M Beringer, S A Galton J. Org. Chem. 30 1930 (1965) 126. M Ishikura,M Terashima J. Chem. Soc., Chem. Commun. 727 (1989) 127. M Ishikura,M Terashima Heterocycles 27 2619 (1988) 128. M Ochiai,K Oshima, Y Masaki J. Am. Chem. Soc. 113 7059 (1991) 129. M Ochiai, in Chemistry of Hypervalent Compounds (Ed. Kin-ya Akiba) (New York: Wiley-VCH, 1999) p. 359 130. M Ochiai, K Oshima, Y Masaki,M Kunishima, S Tani Tetrahedron Lett. 34 4829 (1993) 131. M Ochiai, K Oshima, Y Masaki Chem. Lett. 871 (1994) 132. M Ochiai, Y Kitagawa,M Toyonari, K Uemura Tetrahedron Lett. 35 9407 (1994) 133. M Ochiai, Y Takaoka, K Sumi, Y Nagao J. Chem. Soc., Chem. Commun. 1382 (1986) 134. S-K Kang, T Yamaguchi, P-S Ho, W-Y Kim, H-Ch Ryu J. Chem. Soc., Perkin Trans. 1 841 (1998) 135. S-K Kang, K-H Lim, P-S Ho, W-Y Kim Synthesis 874 (1997) 136. R M Moriarty, W R Epa, A K Awasthi J. Am. Chem. Soc. 113 6315 (1991) 137. Y Kurihara,M Sodeoka,M Shibasaki Chem. Pharm. Bull. 42 2357 (1994) 138. R M Moriarty, W R Epa Tetrahedron Lett. 33 4095 (1992) 139. N Sh Pirquliyev, V K Brel, N S Zefirov, P J Stang Tetrahedron 55 12377 (1999) 140. S-K Kang, S-B Lee, S-B Jang, P-S Ho J. Chem. Soc., Chem. Commun. 835 (1996) 141. S-K Kang, H-W Lee, S-B Jang, T-H Kim, S-J Pyun J. Org. Chem. 61 2604 (1996)120 142. S-B Jang Tetrahedron Lett. 38 4421 (1997) 143. S-K Kang, K-Y Jung, C-H Park, S-B Jang Tetrahedron Lett. 36 144. S-K Kang, H-W Lee, S-B Jang, P-S Ho J. Org. Chem. 61 4720 145. S-K Kang, T Yamaguchi, R-K Hong, T-H Kim, S-J Pyun 146. S-K Kang, T Yamaguchi, P-S Ho, T-H Kim Tetrahedron Lett. 38 8047 (1995) (1996) Tetrahedron 53 3027 (1997) 1947 (1997) a�Russ. Chem. Bull. (Engl. Transl.) b�Dokl. Chem. Technol., Dokl. Chem. (Engl. Transl.) c�Russ. J. Org. Chem. (Engl. Transl.) d�Chem. Heterocycl. Compd. (Engl. Transl.) e�Russ. J. Gen. Chem. (Engl. Transl.) N Sh Pirkuliev, V K Brel, N

ISSN:0036-021X    

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Russian Chemical Reviews 69 (2) 121 ± 135 (2000) Metal complex catalysis in the synthesis of organoaluminium compounds UMDzhemilev, A G Ibragimov Contents I. Introduction II. Catalytic hydroalumination of alkenes III. Catalytic hydroalumination of alkynes IV. Carboalumination of alkenes catalysed by titanium and zirconium complexes V. Carboalumination of alkynes catalysed by transition metal complexes VI. Cycloalumination of alkenes in the presence of zirconium- and titanium-containing catalysts VII. Catalytic cycloalumination of alkynes VIII. Conclusion Abstract. organo- of synthesis the on data published The The published data on the synthesis of organo- aluminium catalysts complex metal involving compounds aluminium compounds involving metal complex catalysts are are generalised and carbo- Hydro-, systematised.and generalised and systematised. Hydro-, carbo- and cycloalumina- cycloalumina- tion reactions of alkenes, conjugated dienes and alkynes catalysed tion reactions of alkenes, conjugated dienes and alkynes catalysed by use The detail. in considered are complexes Zr and Ti by Ti and Zr complexes are considered in detail. The use of of organoaluminium novel and synthesis organic in reagents organoaluminium reagents in organic synthesis and novel reac- reac- tions The discussed. are compounds these involving tions involving these compounds are discussed. The bibliography bibliography includes 240 includes 240 references. references. I. Introduction About 40 years have passed since the discovery by Ziegler et al.1 of a direct method for the synthesis of trialkylalanes based on the reaction of alkenes with activated aluminium and hydrogen. In this period, organoaluminium compounds (OAC) have become indispensable tools in practical synthetic and organometallic chemistry.Fundamental studies into the chemistry of OAC carried out in the 1960's 2±8 have formed the basis for the development of industrial methods for their synthesis. Special mention should be made of the investigations carried out by prominent Soviet specialists Zakharkin,9, 10 Zhigach 11, 12 and Korneev 13, 14 who have developed and industrialised a wide range of practically important OAC including co-catalysts for polymerisation and oligomerisation of alkenes and dienes.15 The manufacture of OAC has considerably stimulated the interest of investigators in these compounds as promising reagents for fine organic and organometallic synthesis.The most important fields of their application include thermal hydroalumination of alkenes, dienes and alkynes; reduction of carbonyl compounds, esters and nitriles; synthesis of higher OAC and selective function- alisation of unsaturated compounds. The results of these studies are summarised in numerous reviews and monographs (see, e.g., Refs 16 ± 20). UMDzhemilev, A G Ibragimov Institute of Petrochemistry and Catalysis, Academy of Sciences of the Republic of Bashkortostan, prosp. Oktyabrya 141, 450075 Ufa, Russian Federation. Fax (7-347) 231 27 50 Received 11 March 1999 Uspekhi Khimii 69 (2) 134 ± 149 (2000); translated by R L Birnova #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v069n02ABEH000519 121 121 124 125 127 128 131 132 Studies by Tolstikov et al.(see Refs 18 and 19) deserve special mention, since they generalise the data on OAC as efficient reagents for organic synthesis. Thus the recently published mono- graph by Kouchin and Tolstikov 19 provides a systematic descrip- tion of the published data concerning the synthesis and conversions of OAC since 1970; however, more recent studies carried out in the last decade have not been cited in this book. Meanwhile, the fact that modern studies into the chemistry of OAC widely employ metal complex catalysis has made it possible not only to alter the strategy of organoaluminium synthesis but also to develop chemo-, regio- and stereoselective synthetic procedures for obtaining novel classes of OAC under mild conditions; these methods compete favourably with traditional approaches which utilise elevated pressures and temperatures.The most efficient and widely employed catalysts for the reactions with OAC include Ti and Zr complexes and, in a lesser degree, Hf-, Co-, Ni-, V- and rare-earth element-containing compounds. About ten years have passed since the publication of the reviews 16, 17 dealing with the application of metal complex cata- lysts based on Ti and Zr complexes in the synthesis and trans- formations of OAC. Numerous publications appeared in this decade and they were devoted to non-traditional catalytic meth- ods for the synthesis of OAC.The present review summarises the most important published data on the application of metal complex catalysts in the synthesis of OAC by catalytic hydro-, carbo- and cyclo-metallation of alkenes, dienes and alkynes using the simplest alkylaluminium compounds and aluminium hydrides and systematises the data on the synthetic conversions of OAC in the presence of transition metal complexes. II. Catalytic hydroalumination of alkenes Thermal hydroalumination of mono-, di-and trisubstituted alkenes with OAC containing an Al ±H bond is still one of the most popular methods for the synthesis of higher OAC.18 ± 20 Unfortunately, this method suffers from a number of disadvan- tages which considerably restrict its application, viz., hydroalumi- nation has to be carried out at elevated temperatures (70 ± 150 8C); moreover, this reaction is not suitable for all types of alkenes, since the presence of functional groups strongly complicates the results of reactions. The reaction of LiAlH4 with a-alkenes in the presence of Ti and Zr complexes is one of the first examples of catalytic hydro-122 alumination under mild conditions (0 ± 20 8C).21 This novel procedure allows the synthesis of lithium tetraalkylalanates in 60% to 100% yields.Sato et al.21 who studied the mechanism of catalytic hydroalumination of alkenes with LiAlH4 in the presence of Zr complexes suggested that this reaction generates active hydride zirconium complexes 1, which hydrozirconate alkenes with the formation of alkylzirconium complexes 2.Transalkyla- tion of the latter with LiAlH4 gives lithium tetraalkylalanates 3. R LiAlH4 ZrCl4 LnZr R LiAlH4 2 LnZrH 1al R LnZrH+ 3 al=1/4 Al. Using hydroalumination of hex-1-ene with lithium aluminium hydride as an example, it was shown 22 that TiCl4, VCl4, Cp2TiCl2 and Cp2ZrCl2 manifest high catalytic activity comparable with that of ZrCl4. In the case of VCl4 and Cp2TiCl2, hydroalumination products were formed together with hex-2-ene resulting from isomerisation of the original hex-1-ene. The isomerisation of terminal alkenes in the presence of Cp2TiCl2 is shown in Scheme 1.The coordination of the central atom of the catalyst with an alkene results in the corresponding alkyltitanium s-com- plex 4 in which the transfer of the hydride ion is accompanied by the formation of a complex 5 in the presence of an excess of the a-alkene. Decomposition of the complex 5 yields a mixture of stereoisomeric hex-2-enes.23 Scheme 1 Cp2TiCl2+2 LiAlH4 2 LiCl+H2 Cp2Ti(AlH3)2 RHC CHMe RCH2CH CH2 Cp2Ti(AlH3)2 Cp2Ti(AlH3)2 RCH2CH CH2 RCH CHMe 5 Cp2Ti(Al2H5) RCH2CHMe 4 In their reactivities in the hydroalumination reaction, alumi- nium hydrides and alkenes can be arranged in the following orders: 24 LiAlH4 > AlH3 > AlH2Cl > AlHCl2; RCH=CH2 > R2C=CH2>RCH=CHR. Co, Ni and Fe chlorides,25, 26 Cr 27 and U28 salts and tran- sition metal complexes immobilised on inorganic 29 or polymeric supports 29, 30 can be used as catalysts in hydroalumination reactions.In contrast with thermal hydroalumination, catalytic hydroalumination in the presence of Zr and Ti complexes can also be performed in the presence of such functionally substituted alkenes as allylic alcohols and ethers.31 ± 33 [M] al(CH2)2CH(OR1)R2 LiAlH4+H2C CHCH(OR1)R2 R1, R2=Alk, Ph; al =1/4 Al. Subsequent one-pot conversions of lithium tetraalkylalanates are of considerable practical interest. Thus cross-coupling of lithium tetraalkylalanates formed in situ with allyl halides in the presence of copper salts [CuBr, CuI, CuCN, CuCl2, Cu(OAc)2] yields alkenes which are three carbon atoms longer than the starting compounds;34 the CuCl-catalysed reaction with prop- argyl bromide yields terminal allenes in high yields.35 This reaction is one of the simplest and most convenient procedures for one-step conversion of alkenes into the corresponding allenes.U MDzhemilev, A G Ibragimov Later, cross-coupling was successfully extended to allenyl bro- mide,36 carboxylic acid halides,37 acrolein 38 and methyl vinyl ketone.38, 39 Catalytic hydroalumination with LiAlH4 and subse- quent functionalisation of the alkylalanes formed makes it possi- ble to convert the starting alkenes into the corresponding organic halides,40 acetates 41 or organoboron compounds 42 in one step. Unlike reactions with terminal alkenes, hydroalumination of 1,3-dienes with LiAlH4 or NaAlH4 in the presence of catalysts, such as Cp2TiCl2 or TiCl4 occurs less selectively and affords 1,2-, 1,4- and 3,4-addition products.43, 44 H+ al al D D2O al + D al D D2O + al D al=1/4 Al.Along with complex aluminium hydrides, readily available alkylaluminium hydrides are also used for catalytic hydroalumi- nation of alkenes. In the example of hydroalumination of a mixture of isomeric decenes with Bui2AlH in the presence of catalytic amounts of Ti(OBu)4, it was established that the terminal double bond enters into the reaction 154 times faster than the cis- disubstituted bond and 241 times faster than the trans-disubsti- tuted bond.45 Hydroalumination of hexa-1,5-dienes with Bui2AlH has a number of specific features.In the presence of Ti(OBu)4 as a catalyst (1.5 mol.%) 46 and without it 5 hydroalumination occurs, which is followed by intramolecular cyclisation. However, when the reaction is carried out in solvents containing electron-donor atoms (N, O, S, P), no cyclisation takes place and the a,o- dialuminium compound 6 is formed instead.46 These data suggest that in the course of hydroalumination the starting hydrometal- lating reagent readily forms donor-acceptor complexes with the solvent owing to the lone electron pair of the heteroatom, which prevents the intramolecular cyclisation. Bui2AlH [Ti], THF CH2al al(CH2)6al 6 Bui2AlH al(CH2)4CH CH2 [Ti] [Ti]=Ti(OBu)4 , al=1/3 Al. Commercially available diisobutylaluminium hydride can be used as an efficient hydroaluminating reagent for linear and cyclic mono-, di- and trienes including those containing functional groups.Zirconium complexes proved to be the most active catalysts in these reactions.16, 47 Thus Bui2AlH hydroaluminates a-, a,b-disubstituted and cyclic alkenes in high yields in the presence of ZrCl4 even at *20 8C (3 ± 6 h).48 The use of titanium-containing catalysts results in the formation of side products as a result of isomerisation of the original alkenes.23 This reaction virtually does not occur in the absence of the catalysts. An analysis of the literature data on hydrozirconation of alkenes 49 prompts a conclusion that hydroalumination yields reactive zirconium hydride intermediates able to hydrozirconate alkenes; further transmetallation of alkyl and cycloalkyl zirco- nium complexes results in higher OAC.48 Cp2ZrCl2 Bui2Al Bui2AlH Bui2Al Cp2ZrCl2Metal complex catalysis in the synthesis of organoaluminium compounds Studies by Tolstikov et al.50 have shown that zirconium chloroalkoxides (RO)nZrCl4± n are more reactive catalysts of the hydroalumination reaction than ZrCl4 or Zr(OBu)4.Therefore, a mixture of ZrCl4 with BunOH, MeOH, EtOH and PrnOH is used to obtain a reactive catalyst. The rate of cycloalkene hydro- alumination depends on the ring size and decreases in the follow- ing order: C5>C6>C7>C12>C8. (CH2)n (CH2)n +Bu2 iAlH [Zr] AlBui2 at of presence ZrCl4 (RO)nZrCl4±n Hydroalumination of the C60 fullerene with Bui2AlH in the *20 8C or {C60 : [Al]=1 : (100 ± 300), 24 h, toluene} was carried out by Ibragimov et al.51, 52 Data from hydrolysis and deuteriolysis of fullerene-containing OAC suggest that these reaction conditions favour the formation of both hydro- and carboalumination products (total yield*90%).ZrCl4 (2 mol.%) Bui2AlH+C60 PhMe, 20 8C H HH3O+(D3O+) al H(D) Bui Bui H3O+(D3O+) al H(D) al=1/3 Al. Bis(dialkylamino)alanes manifest high reactivity in hydro- alumination of alkenes, however, only in the presence of Cp2TiCl2.53, 54 These compounds hydroaluminate a-alkenes, methylidenealkanes and aliphatic disubstituted alkenes in practi- cally quantitative yields.Cycloalkenes are less reactive in this reaction. Tri- and tetrasubstituted alkenes cannot be involved in this reaction. Cp2TiCl2 Al(NR12 )2 R2 (R12 N)2AlH+R2 *20 8C The advantage of bis(dialkylamino)alanes over dialkylalanes is in the feasibility to use them for catalytic hydroalumination of conjugated dienes; however, the selectivity of these reactions is rather low as in the case of complex hydrides.55, 56 a, b + + (a) (Pri2N)2AlH, Cp2TiCl2, THF, 12 h, 20 8C; (b) H2O (55%). Dichloroalane which reacts with alkenes in the presence of boron derivatives to give the corresponding higher alkyldichloro- aluminium compounds 7, is used as a reactive hydroaluminating reagent.57 ± 60 [B] C C HC CAlCl2 +Cl2AlH 7 [B]=PhB(OH)2, B(OH)3, Et3B, B(OMe)3, 9-borabicyclo[3.3.1]- nonane (9-BNN), BF3OEt2.123 Hydroalumination of disubstituted alkenes with Bui3Al in the presence of Ti4+ or Zr4+ salts at 110 ± 120 8C gives predom- inantly OAC 8.61 Apparently, the catalyst induces the isomer- isation of the disubstituted double bond in the original alkenes into the terminal bond which is much more readily hydroalumi- nated with Bui3Al. Prn +AlBui Prn 3 [Ti], 120 8C 7Me2CH CH2 1) O2 Me(CH2)7OH Al[(CH2)7Me]3 2) H3O+ 8 The yield of reaction products in hydroalumination of alkenes with Bui3Al strongly depends on the nature of the catalyst. Thus in the presence of catalytic amounts of Cp2ZrCl2, higher trialkyl- alanes can be synthesised from terminal alkenes and AlBui3 in high yields (0 8C, 6 h).62 This reaction does not take place in the absence of the catalyst.Such a high reactivity of Bui3Al in the presence of Cp2ZrCl2 can be attributed to the formation of zirconium hydrides 9,63, 64 which hydrometallate alkenes at low temperatures to give the complex 10. Subsequent transmetallation of alkyzirconium complexes results in alkylalanes 11. Bui2Al(CH2)7Me Bui3Al 11 Cp2ZrCl2 Bui2AlCl Bui2AlCl Bui Me(CH2)7 ZrCp2 ZrCp2 Cl Cl 10 H Me2CH CH2 ZrCp2 Me(CH2)5CH CH2 9 Cl Hydroalumination of terminal alkenes with yet another hydroaluminating reagent, viz., AlEt3 in the presence of Cp2TiCl2, follows a similar path and yields alkyl(diethyl)alanes 12.65 Cp2TiCl2 Et2Al(CH2)2R AlEt3+ R 7C2H4 12 Higher dialkylaluminium chlorides cannot be synthesised by thermal transalkylation with Bui2AlCl; therefore, the use of Bui2AlCl for Cp2ZrCl2-catalysed hydroalumination of alkenes 66 which gives nearly quantitative yields should be regarded as a significant breakthrough.R [R(CH2)3]2AlCl Cp2ZrCl2 Bui2AlCl (cyclo-C6H11)2AlCl Cp2ZrCl2 This reaction involves non-conjugated di- and trialkenes (including cyclic and functionally substituted ones).67 Hydro- alumination of norbornenes with Bui2AlCl is stereoselective and affords the corresponding cycloalkylhalogenoalanes.68 The reac- tions involving 4-vinylcyclohexene and dicyclopentadiene result in bi- and tri-cyclic halogenoalanes. ClAl Bui2AlCl Cp2ZrCl2124 Al(Cl)Bui Bui2AlCl Cp2ZrCl2 The Cp2ZrCl2-catalysed hydroalumination of cyclohexene with Bui2AlCl was successfully employed to obtain tricyclohex- yltin chloride (13).69 SnCl4 Bui2AlCl, [Zr] (cyclo-C6H11)3SnCl (cyclo-C6H11)2AlCl 13 (2,6-Di-tert-butyl-4-methylphenoxy)diisobutylaluminium (14) was recommended for use as a regio- and stereoselective reagent for hydroalumination of alkenes and carbonyl compounds in the presence of a two-component catalyst, Cp2ZrCl2 ± aluminium hydride (1:1).70 Cp2ZrCl2 Bui2AlOAr +ButCH2(Me)C CH2 14 BuiAl(OAr)CH2CH(Me)CH2But But Me Ar=But Because of the low reactivity of reagent 14, hydroalumination should be performed at high temperature (145 8C); however, the presence of a bulky aryloxy substituent ensures high regioselec- tivity of this reaction.It was shown 71, 72 that the exchange reaction between opti- cally active solvates (L* . Bui3Al) and disubstituted terminal alkenes in the presence of a nickel(II) ±N-methylsalicylidenamine complex 15 gives optically active trialkylalanes; their further oxidation or hydrolysis results in optically active alcohols or hydrocarbons. (7)-N,N-Dimethylmenthylamine, (+)-(S,S)-2,3- dimethoxy-1,4-bis(N,N-dimethylamino)butane, (+)-N,N-dime- thylbornylamine, (+)-(R)-N,N-dimethyl-1-phenylethylamine, etc. were used as chiral ligands which form solvates with AlBui3.71, 72 Bui3AlL*, 15 R1R2C CH2 H3O+ * R1R2CHMe * (R1R2CHCH2)3AlL O2, H2O * R1R2CHCH2OH O 15= Ni N CH Me 2 Hydroalumination of oxabicycloalkenes with Bui2AlH can be carried out in the presence of Ni(COD)2 (COD is cyclooctadiene) or its derivatives with phosphines;73 the regio- and enantioselec- tivity of this reaction largely depend on the ligand environment of the central atom of the catalyst.III. Catalytic hydroalumination of alkynes Non-catalysed hydroalumination of disubstituted acetylenes can be achieved by using Bui2AlH, Et2AlH or Bui3Al under sufficiently mild conditions but is characterised by low selectivity, since the vinylalanes formed in this reaction undergo further transforma- tions.20 Hydrolysis of vinylalanes results in 1,2-disubstituted alkenes with a Z- or an E-configuration depending on the nature of the starting hydroaluminating reagent,74 the structure of the alkyne 75 and the solvent.76 U MDzhemilev, A G Ibragimov R23 N R1HC C(SiMe3)AlBui2 .NR23C6H14 R1C CSiMe3+Bui2AlH C6H14 R1HC C(SiMe3)AlBui2 In the presence of transition metal complexes, hydroalumina- tion of alkynes sometimes occurs with higher selectivity and in higher yields.For example, the reaction of oct-1-yne with Bui2AlH in the presence of stoichiometric amounts of methylcuprate (1.25 h, 20 8C) and subsequent hydrolysis of the reaction mixture give oct-1-ene in a quantitative yield.77 a, b CH2 C6H13CH C6H13C CH (a) Bui2AlH, MeMgBr, CuCl, LiCl, THF; (b) H2O (100%). Hydroalumination of monosubstituted acetylenes normally yields a mixture of alkenes and alkanes, since mono- and dihy- droalumination of the triple bond occur simultaneously.Selective mono- or dihydroalumination of alkynes can be carried out in the presence of Fe or Ni salts.26 a, b PhCH CH2 PhC CH c, d PhCH2Me (a) LiAlH4, FeCl2,*20 8C, 24 h; (b) H2O (94%); (c) LiAlH4, NiCl2,*20 8C, 24 h ; (d) H2O (99%). Hydroalumination of mono- and disubstituted acetylenes with LiAlH4 in the presence of TiCl4 or Cp2TiCl2 can be carried out with high selectivity. Thus the reaction of oct-4-yne or hex-2- yne with hydride aluminium complexes [LiAlH4, NaAlH4, LiAlMe3H, NaAlMe3H, NaAl(OCH2CH2OMe)2H2] in the pres- ence of catalytic amounts of Cp2TiCl2 inTHFyields alkenylalanes after 2 h at 20 8C; hydrolysis of the latter results in cis-oct-4-ene and cis-hex-2-ene, respectively (yields *100%).78 Aminoalanes can also be used for hydroalumination of alkynes.53 In this case, hydroalumination of disubstituted acetylenes occurs with high selectivity and under milder conditions than that of terminal alkynes.Thus in the presence of 5 mol.% of Cp2TiCl2, the reaction of methylphenylacetylene with (PrN)2AlH gives alkenylalanes in a total yield of >95%.54 The reaction of aminoalanes with disub- stituted acetylenes predominantly occurs as the cis-addition, which makes it possible to use this method for the synthesis of Z-alkenes. 1) Cp2TiCl2, PhH, THF, 20 8C, 2 h R1C CR2+(Pri2N)2AlH 2) D2OH D D R1 + R1 R2 R2 (90% ± 96%) H(1% ± 4%) R1=Me: R2=Bun, n-C6H13, Ph; R1=R2=Ph. The composition of the reaction mixture depends on temper- ature, solvent and reaction time.Thus hydroalumination of hex-2- yne with (PrN)2AlH in benzene at 0 8C yields a mixture of alkenylalanes with trans- and cis-configurations of the substitu- ents. Their hydrolysis yields a mixture of isomeric hex-2-enes.54 1) 10 mol.% Cp2TiCl2, 0 8C, PhH MeC CPrn+(Pri2N)2AlH 2) H3O+ Prn Me Prn + Me (26%) (47%) The aluminium-magnesium reagent 16 (Bui3Al ± BuiMgBr) 79 the efficiency of which is comparable with that of 9-BBN wasMetal complex catalysis in the synthesis of organoaluminium compounds recommended for stereoselective hydrometallation of disubsti- tuted acetylenes. This method is especially efficient in the con- versions of disubstituted acetylenes into Z-alkenes.In the presence of 2 mol.% Cp2TiCl2, the reaction with an excess of this reagent (3 ± 10 equiv.) occurs at 20 8C and is completed within 20 min. Z-Alkenes are formed in 95%± 98% yields and with *98%± 100% selectivity. D RC CR+Bui3Al . BuiMgBr 1) Cp2TiCl2 2) D2O R R 16 The recently synthesised reagents Bui2AlCl ±Cp2TiCl2 and Et3Al ±Cp2TiCl2, designed for selective hydroalumination of disubstituted acetylenes into the corresponding unsaturated OAC 17 and 18 the stereoselectivity of which is close to 100%, deserve special attention.80 ± 82 Hydrolysis of OAC 17 and 18 results in Z-alkenes. Depending on the structure of the original alkynes and reaction conditions, 5% to 30% of alkadienylalanes are formed together with alkenylalanes.The structure of the unsaturated OAC 17 and 18 has been established by spectral methods.83 R R Al(Cl)Bui Bui2AlCl + Cp2TiCl2 R R R R Al(Cl)Bui 17 RC CR R R Et2Al Et3Al + Cp2TiCl2 R R R R 18 AlEt2 R=Ph, Prn, Bun. Hydroalumination of disubstituted acetylenes with Bui3Al in the presence of catalytic amounts of Cp2ZrCl2 is accompanied by the formation of isomeric alkenylalanes, their hydrolysis affords alkenes 19 and 20 (*1:1).84, 85 Under analogous conditions, terminal alkynes yield a mixture (*1:1) of mono- and 1,1- dialuminium compounds in practically quantitative yields.84 Bun Prn Bun C5H11 a, b + BunC CBun (87%) D H H D 20 19 H C8H17 a, b +C10H21D2 C8H17C CH (*100%) D H (a) Bui3Al, Cp2ZrCl2; (b) D2O.In contrast with hydroalumination with Et3Al ±Cp2TiCl2,81 the reaction of disubstituted acetylenes with Prn3 Al in the presence of Cp2ZrCl2 occurs less selectively and gives a mixture of isomeric alkenylalanes (total yield 63%) and alumacyclopentadiene (38%).84 Cp2ZrCl2 BunC CBun+AlPrn3 Prn Prn Prn Bun Bun C5H11 + + H AlPrn H AlPrn 2 2 Prn Prn (33%) (30%) Al Prn (38%) It should be noted that selective hydroalumination of terminal alkynes with trialkylalanes R3Al [R=Et, Bui, EtCH(Me)CH2] does not take place if Fe or Ni complexes substituted titanium- or zirconium-containing catalysts. In this case, the alkenylalanes formed undergo further conversions; subsequent hydrolysis results in a complex mixture of alkenes, 1,3-dienes and trialkyl- substituted benzenes.86, 87 125 Hydroalumination of mono- and disubstituted acetylenes has found wide application in synthetic organic chemistry, particu- larly in the synthesis of practically valuable trisubstituted alkenes,76 substituted 1,3-dienes,88 alk-1-en-3-ynes,89 alkenylsi- lanes and alkenyl sulfones,90, 91 1-alkyl-2-halogenocyclopro- panes,92 Z-alkenes,93 etc.Hydroalumination of allenes (both thermal with Bui2AlH,94 and that with the use of LiAlH4 in THF in the presence of catalytic amounts of Ti or Zr complexes, e.g., Cp2TiCl2, TiCl4, TiCl3, ZrCl4 or Cp2ZrCl2) is non-selective.95 This reaction may be highly regioselective with the use of HAlCl2 in the presence of catalytic amounts of organoboranes.95, 96 C6H13 1) PhB(OH)2 C H2C CHCH(D)C6H13 +Cl2AlH 2) D3O+ Thus in the majority of cases, stereoselective hydroalumina- tion of alkynes and allenes occurs under mild conditions.Hydro- lysis of the resulting higher alkenylalanes affords Z-alkenes in high yields. IV. Carboalumination of alkenes catalysed by titanium and zirconium complexes Catalytic carboalumination of unsaturated compounds gives an access to novel types of higher OAC. It is known 97 that carbo- alumination of terminal alkenes in the absence of catalysts usually occurs under drastic conditions and is accompanied by side reactions of hydro- and dehydroalumination. In the presence of metal complex catalysts, carboalumination proceeds under milder conditions and with higher selectivity.The first examples of catalytic carboalumination of alkenes aimed at the synthesis of higher dialkylhalogenoalanes were described in 1979.98 This method is based on a consecutive insertion of ethylene at the Al ±C bond in the presence of low- valent Ti complexes. This reaction results in the formation of higher OAC (dialkylaluminium chlorides) with the number of carbon atoms from 4 to 30. The reaction of terminal alkenes with Et2AlCl in the presence of 0.3 mol.% ± 3.0 mol.% Ti(OBu)4 or TiCl4 was studied by Dzhemilev et al.99 It was found that Et2AlCl carboaluminates alkenes even at*20 8C; this reaction proceeds with high regiose- lectivity and affords the corresponding higher dialkylaluminium chlorides 21 in high yields.D2O, DCl RCH2CH(Et)CH2Al(Et)Cl RCH2CH CH2 Et2AlCl [Ti] 21 RCH2CH(Et)CH2D This reaction is of general character and is successfully employed in the synthesis of OAC and in directed synthesis of natural compounds.99 ± 101 Carboalumination of terminal alkenes with 3-alkyl-1-chloro- alumacyclopentanes was used to obtain other cyclic OAC, e.g., 1-chloro-3,6-disubstituted alumacycloheptanes.102 CH2R TiCl4 ClAl RCH2CH CH2+ClAl CH2R CH2R Dialkylhalogenoalanes, such as Et2AlCl and Me2AlCl, car- boaluminate substituted norbornenes in the presence of catalytic amounts of Ti complexes [Cp2TiCl2, Ti(acac)2Cl2, TiCl4] with high stereoselectivity; subsequent hydrolysis results in alkylated norbornanes.103, 104126 , [Ti] 1) Et D 2) D3O+ Et2AlCl , [Ti] 1) Et 2) D3O+ D Carboalumination of terminal alkenes with Me3Al in the presence of chiral derivatives of zirconocene, e.g., bis(1-neomen- thylindenyl)zirconium dichloride, bis(1-neo-isomenthyl-4,5,6,7- tetrahydroindenyl)zirconium dichloride, etc.with subsequent oxidation of alanes is used in a highly enantioselective synthesis of optically active alcohols.105 R R * 1) Me3Al, [Zr] 2) O2 OH [62% ± 92% (65% ±85% ee)] R=C6H13, PriCH2, Ph, PhCH2, HO(CH2)4, Et2N(CH2)3; Me [Zr]= ZrCl2 Pri 2 The direction of the reaction of trialkylalanes with alkenes depends on the solvent used. Thus carboalumination in 1,1- dichloroethane proceeds with high enantioselectivity in the pres- ence of catalytic amounts of chiral zirconium catalysts.106 C8H17 1) Et3Al, [Zr] OH 2) [O] H Et [63% (92% ee)] C8H17 C8H17 1) Prn3 Al, [Zr] OH Prn H 2) [O] [62% (91% ee)] [Zr], bis(1-neomenthylindenyl)zirconium dichloride.Carboalumination of terminal alkenes with Me3Al is selective when a two-component catalyst Cp2*ZrMe2 ± B(C6F5)3 (Cp* = Z5-C5Me5) (toluene, 0 8C,*3 h) is used.107 Me3Al, [Zr], 0 8C RCH2CH CH2 O2 RCH2CH(Me)CH2OH RCH2CH(Me)CH2AlMe2 (71% ± 82%) R=H2C C(Me)(CH2)2, Me(CH2)2. In contrast with terminal alkenes, hexa-1,5-diene, hepta-1,6- diene, octa-1,7-diene and their N-, O- and Si-containing deriva- tives react with trialkylalanes 107 or dialkylhalogenoalanes 108 in the presence of Zr- or Ti-containing complex catalysts to give, as a rule, cycloalkylmethylalanes or their heterocyclic analogues.Me a AlMe2 X H CH2OH X b, c H R X (a) Me3Al, Cp2 ZrMe2, B(C6F5)3, 0 8C; Cp*=Z5-C5Me5; X=(CH2)n, R2Si, PhN, CHOSiR3 (51% ± 88%); (b) R2AlCl, Ti(OPri)4; R=Et, Prn, Bui; X=CH2; (c) [O]. Negishi et al.108 carried out cascade carboalumination of 5-vinylnona-1,8-diene in the presence of Et2AlCl and Ti(OPri)4 as a catalyst. +Et2AlCl 1) Ti(OPri)4 2) O2 (83%) Et CH2OH Catalytic carboalumination of non-conjugated dienes in the presence of Zr, Cp2ZrX2 or Cp2*ZrX2 complexes (X=Cl, Me; Cp*=Z5-C5Me5) and methylalumoxane was used for diastereo- and enantioselective cyclopolymerisation of hexa- 1,5-diene.The diastereoselectivity of this reaction depends on the original catalyst. Catalysis with Cp2ZrMe2 at778 8C results in a polymer trans-22 (yield 91%), whereas in the case of Cp2*ZrCl2 the yield of trans-22 is 14% at725 8C.109 Cyclopolymerisation of hexa-1,5-diene in the presence of a chiral zirconium catalyst, (+)- (S)-23, and methylalumoxane gives the chiral polymer (7)-22 {trans-isomer (68%), [a]= 749.3 8}.110, 111 [Zr] Al(Me)O n (7)-22 O Zr [Zr]= O (+)-(S )-23 In the presence of Zr(OBu)4, terminal alkenes are alkylated with Et2AlCl into position 2; alkenes 24 are formed in one step and with high selectivity.112 Zr(OBun)4 Et2AlCl+RCH2CH CH2 Ethylation of ethylene with Et2AlCl in the presence of zirconium catalysts, e.g., Zr(OBun)4, Zr(OR)nCl4±n, served as the basis for the synthesis of but-1-ene.113 Et+MeCH2Al(Et)Cl Et2AlCl H2C CH2 Zr(OBun)4 The reaction of dec-1-ene with AlEt3 in the presence of Cp2ZrCl2 yields hydro- (26) and carboalumination (27) products as well as 1,1-dialkylethylenes 25.106 C8H17CH CH2 1) Et3Al, Cp2ZrCl2 2) DCl, D2O (CH2Cl)2 +C9H19CH2D+C8H17CH(Et)CH2D H17C8 26 (20%) 25 (20%) Et Reactions of trialkylalanes with terminal alkenes (including functionally substituted ones) in the presence of 2 equivalents of Cp2TiCl2 and trialkylaluminium in CH2Cl2 also result in 1,1-disubstituted alkenes.According to Barber et al.,114 carbo- alumination of alkenes under these conditions affords trialkyl- alanes which contain hydrocarbon radicals with an iso-structure; U MDzhemilev, A G Ibragimov Et + CH2OH Al(Me)O n n Et R +R(CH2)3Al(Cl)Et 24 27 (37%)Metal complex catalysis in the synthesis of organoaluminium compounds they undergo b-hydride elimination by titanium complexes to give the corresponding alkenes in sufficiently high yields (45% ± 85%).R2 CH2Cl2 R1 +2Cp2TiCl2+2 AlR2323 8C, 1 ± 24 h R1 R1=C8H17, MeCO2(CH2)4, Br(CH2)4, NC(CH2)4; R2=Me, Et, Bun. Homoallylic alcohols react with Et2AlCl in a non-selective manner. This reaction can be accomplished only in the presence of stoichiometric amounts of Ti-containing compounds, e.g., Cp2TiCl2, TiCl4, Ti(acac)2Cl2.114 ± 117 Carbometallation results in two regioisomeric products (28 and 29) and is accompanied by side reactions, such as hydrometallation, hydrogenation, isomer- isation and b-hydride elimination. H2O HO(CH2)2CH CH2+TiCl4 Et2AlCl+ Et+ HO(CH2)2CH(Me)Et+HO(CH2)5Me + HO(CH2)2 29 28 +HO(CH2)3Me +HO(CH2)2CH CH2 It is believed 114 ± 117 that the reaction of Et2AlCl with titanium compounds results in the formation of the corresponding ethyl- titanium complexes which are active in further carbometallation of terminal alkenes.Subsequent hydrolysis affords isomeric alcohols 28 and 29. Prn Et H+ 28+29 Ti + Ti EtTi O O O In a continuation of these studies, the reaction of intra- molecular carbotitanation in the presence of EtAlCl2 was further extended to the selective synthesis of substituted cyclopentanes from 1-bromohex-5-enes.118 ± 120 The role of EtAlCl2 complexes consists in the activation of the intermediate titanium complex 30.R2 R2 BrMg R3 Br R3 Cp2TiCl2 Mg THF R1 R1 R4 R4 R2 R3 Cp2(Cl)Ti EtAlCl2 R1 778 8C R4 30 d7 EtAlCl2 R2 Cl R1 d+ R3 7AlCl2Et Cp2Ti R4 R2 R1 R2 R1 HCl Cp2(Cl)Ti Me R3 R3 R4 R4 Thus the carboalumination of alkenes with the simplest organoaluminium compounds catalysed by transition metal com- plexes permits simultaneous formation of C±C and Al ±C bonds with high regio- and stereoselectivities. Further transformations of the organoaluminium compounds formed in the process make it possible to obtain alcohols, aldehydes, acids and other com- pounds. 127 V. Carboalumination of alkynes catalysed by transition metal complexes The reaction of gaseous acetylene with trialkylalanes occurs under mild conditions (40 ± 60 8C) with high stereoselectivity and results in Z-alkenyldialkylalanes, this being one of the simplest examples of carboalumination of alkynes with OAC.74 The features of this non-catalytic reaction and alkenylalane conversions are docu- mented in a substantial body of literature (see, e.g., Refs 18 ± 20 and 121).Catalytic carboalumination of alkynes has been exten- sively generalised (cf., e.g., Refs 17, 47, 122 ± 125). The present review considers the synthesis of alkenylalanes by catalytic carboalumination of alkynes with trialkyl- and halogenoalkyl- alanes. Carboalumination of mono- and disubstituted acetylenes is carried out in the presence of transition metal compounds derived from Fe,86 Mn, Ni, Ti,126 ± 130 Zr 131 and Cu salts and com- plexes;132 ± 134 this reaction utilises trialkylalanes (Et3Al, Bui3Al, [EtCH(Me)CH2]3Al),86 chlorodialkylalanes (Me2AlCl,135 Et2AlCl,131 Prn2 AlCl),131 allyl-, benzylalanes 136 and alumocup- rates 132 ± 134 as carbometallating reagents.Such reactions are gen- erally non-selective and yield a complex mixture of regioisomers. A two-component system proposed by Negishi et al.137 ± 139 which contains AlMe3 and catalytic amounts of Cp2ZrCl2 is one of the most efficient reagents for acetylene carbometallation presently available. Later, this system was modified by addition of H2O.140 Yoshida and Negishi 141 have initially proposed that Cp2ZrCl2-catalysed carboalumination of alkynes involved meth- ylation of Cp2ZrCl2 with trimethylaluminium to give MeZrCp2Cl and Me2AlCl.Subsequent carbozirconation of the alkyne yields the corresponding alkenylzirconium derivatives; their transmetal- lation with Me2AlCl results in alkenyldimethylalanes with simul- taneous regeneration of the catalyst. The reaction mechanism included the existence of a reversible reaction where the methyl group or the methyl radical is transferred from the Al atom to the Zr atom as can be evidenced from the NMR data. However, further investigations 142, 143 showed that this reaction involves direct carboalumination of alkynes.Cl RC CR Me3Al +Cp2ZrCl2 ZrCp2Me Me2Al Cl RC CR R R d7 d+ Cl Me2Al Cl ZrCp2Me Al Me ZrCp2Me Cl Me Cl R R +Cp2ZrCl2 AlMe2 Me Carboalumination of alkynes resulted in a great number of practically important organoaluminium and organic compounds. Thus an elegant method was proposed for the synthesis of isoprene linear trimers 31 and 32 by stereo- and regiospecific cross-coupling of geranyl and neryl chlorides with alkadienylalu- minium 33.144 The reagent 33 was synthesised by carboalumina- tion of vinylacetylene with trimethylaluminium in the presence of catalytic amounts of Cp2ZrCl2.Cp2ZrCl2 C CH +Me3Al AlMe2 33 Cl 31 Pd(PPh3)4, THF Cl 32 Pd(PPh3)4, THF128 Catalytic carboalumination of terminal alkynes with AlMe3 with subsequent functionalisation of the alkenylalanes formed was used for the synthesis of natural isoprenoids, e.g., geraniol,145 monocyclofarnesol 146 and farnesol.147 An efficient procedure has been developed for the synthesis of polyenic hydrocarbons of different structure (including those containing conjugated double bonds) using alkenylalanes and catalytic amounts of phosphine complexes of Ni or Pd.148 1) Me3Al Cl2ZrCp2 C CH 2) H2C CHBr, ZnCl2, Pd(PPh3)4 (70%) A similar approach was used in the synthesis of cyclic and acyclic functionally substituted unsaturated compounds.149, 150 Alk Me3Al, Cp2ZrCl2 AlkC CH AlMe2 Me OAc Alk OAc Pd(PPh3)4 Me CO2Me Alk CH(OMe)2 CHO Pd(PPh3)4 Me The ability of alkenylalanes to enter into the cross-coupling reactions with organic halides was used as the basis for a new method of synthesis of substituted cyclobutenes.Thus carboalu- mination of silylated alkynes 34 with trimethylaluminium under mild conditions yields alkenylalanes 35 containing a good leaving group X. Intramolecular cyclisation of the intermediates 35 results in 1-methyl-2-(trimethylsilyl)cyclobutene (36).151 Me3Al Cp2ZrCl2, 24 h X(CH2)2C CSiMe3 34 SiMe3 SiMe3 X(CH2)2 Me AlMe2 Me 36 35 (30% ± 100%) X=Cl, Br, I, OTs. Carbometallation of o-halogen-substituted 1-trimethylsilyl- alk-1-ynes or enynes with alkyl derivatives of Al, Zn or Li followed by intramolecular cyclisation of the organometallic compounds formed allows one to synthesise substituted cyclo- alkenes in high yields.152 ± 154 5-Bromo-1-trimethylsilylpent-1-yne (37) is the least prone to intramolecular cyclisation; it generates alkenylalane 38 in 60% yield.The iodo-substituted alkynylalane 39 enters into the carboalumination reaction to give the dialumi- nium derivative 40; treatment of the latter with I2 gives iodo- substituted cyclopentene.155 Br(CH2)3C CSiMe3 Me3Al Cp2ZrCl2 37 Me Me2Si SiMe3 + Br(CH2)3 AlMe2 38 (60%) trace amounts U MDzhemilev, A G Ibragimov Me3Al I(CH2)3C CAlMe2 Cp2ZrCl2 39 Me I Me AlMe2 I2 AlMe2 I(CH2)3 40 (78%) Cp2ZrCl2-Catalysed carboalumination of mono- and disub- stituted acetylenes or 1,3-diynes is an example of an efficient regio- and stereoselective synthesis of trisubstituted alkenes, homoallylic alcohols, esters of a,b-unsaturated acid and 1,4-disilylated 1,3-enynes.156 ± 159 Me Me3Si Me3SiC C C CSiMe3 1) Me3Al, Cp2ZrCl2 2) E+ C E CSiMe3 E=H (69%), D (60%), Br (56%), Cl (47%), Ac (44%).Alkenylalanes obtained by carboalumination of alkynes are extremely useful for introducing alkenyl groups into the b-position of cyclic enones. This approach was used, for example, in the preparation of key compounds for the synthesis of prosta- glandins.160, 161 O Me H HO(CH2)2 Me3Al HC C(CH2)2OH Cp2ZrCl2 CuCN± 2 LiCl Me AlMe2 O Me Me (CH2)2OH Transmetallation of alkenylalanes with organoboron or organozirconium compounds occurs under mild conditions (25 8C, 1 h) and affords the corresponding alkenylboron- (41) or -organozirconium (42) compounds which can further be used in terpenoid syntheses.162 H R1 Cp2ZrCl2 R1C CR1+Me3Al Me AlMe2 H R1 MeOBR22 Me BR2241 H R1 1) BunLi 2) X2ZrCp2 X=Cl, I Me ZrCp2X 42 In recent years, catalytic carboalumination of alkynes has found wide application in the synthesis of natural and biologically active compounds, e.g., brassinolide,163 milbemycin,164 ± 166 zoa- patanol,167 macbecin fragments,168 synthetic precursors of lopho- toxin and pukalide,169 mokupalide,170 trichoverrol B,171 verrucarin,172 etc.VI. Cycloalumination of alkenes in the presence of zirconium- and titanium-containing catalysts The methods developed in the late 1980's dealt mainly with the synthesis of alkyl-, cycloalkyl-, alkenyl- and vinylalanes.Data on the possibility of preparative synthesis of stable three- and five- membered OAC were practically absent in the literature. The first report on a regioselective synthesis of previously unknown five-Metal complex catalysis in the synthesis of organoaluminium compounds membered OAC (alumacyclopentanes, ACP) was published as late as in 1989.173 R Cp2ZrCl2 (3 mol.% ± 5 mol.%) R +AlEt3 20 8C Al Et (98%) Later, it was found that this reaction is versatile and allows one to perform a one-step synthesis of five-membered OAC from AlEt3 and terminal alkenes in nearly quantitative yields. This reaction was termed as `catalytic cycloalumination of unsaturated compounds' 174 ± 177 or `cyclic carboalumination'.84, 178 O-, N- and S-containing alkenes and norbornenes also undergo cycloalumination to give the corresponding ACP.179, 180 The cycloalumination of norbornenes is highly selective and results in the formation of five-membered metallocycles 43 having an exo-configuration.179 CH2XR Cp2ZrCl2 X Al Et AlEt3 R2 R2 R2 Cp2ZrCl2 EtAl 43 R2 X=OR1, SR1, NR12 .Substitution of higher OAC for AlEt3 affords predominantly trans-3,4-disubstituted ACP 44 ± 46.181 R2 Cp2ZrCl2 [R1(CH2)3]3Al+ THF, 20 8C (>98%) R2 R2 R1 R2 R1 R1 + + Al (CH2)3R2 Al (CH2)3R2 Al (CH2)3R2 46 45 44 This is accompanied by the formation of 2,4-dialkyl-substi- tuted alumacyclopentanes (5% ± 12%); the latter undergo intra- molecular b-hydride conversions into E-alkenylalanes 47 and, after hydrolysis, into E-alkenes 48.181 R1 R1 R1 H3O+ R1 H RAl2 AlHR2 47 Me R1 R1 48 After substitution of dihalogenoalanes for higher trialkyl- alanes, the cycloalumination of terminal alkenes occurs more selectively and gives trans-3,4-dialkyl-substituted ACP.In con- trast with previously developed procedures;173, 179, 180 the reactive catalytic intermediate, viz., Cp2Zr, is generated in these reactions by reduction of Cp2ZrCl2 in THF by Mg activated with RAlCl2. This approach enables the synthesis of 1-alkyl-, 1-alkoxy-, 1-di- alkylamino- and 1-halogeno-trans-3,4-dialkyl-substituted aluma- cyclopentanes 49 from a-alkenes, dihalogenoalanes and metallic magnesium (which is a halogenide ion acceptor) in the presence of catalytic amounts of Cp2ZrCl2 or ZrCl4 (yields 70%± 90%).182 ± 184 The structure of substituted alumacyclopentanes, the position of substituents and their configuration were estab- lished by spectral methods.185, 186 R1AlCl2+2R2 Mg, [Zr] 7MgCl2 R1=Alk, RO, R2N; R2=Alk(C37C20); [Zr]=Cp2ZrCl2, ZrCl4.The incorporation of an alkene molecule into the Al ±C bond of 3-alkyl-substituted ACP in the presence of Ti complexes is an efficient procedure for obtaining 1-ethyl-3,6-dialkyl-substituted alumacycloheptanes 50.102 The cleavage of the Al ±C bond in ACP in the presence of nickel catalysts results in the unsaturated OAC 51187 or 2-alkyl-substituted 1,3-dienes 52 in quantitative yields (Scheme 2).188 R1 R2 a Al Et 50 b Et(Cl)Al R1 51 R1 c 52 R1 d OH HO 53 R1 e SO 54 R1 f 55 Cl R2, [Ti]; (b) (a) , [Ni]; (c) Cl , [Pd]; (g) (e) SOCl2; (f) (j) R2PCl2; (k) Zr ± L*.ACP was used in the synthesis of different classes of com- pounds (see Scheme 2). They are active co-catalysts in co-telomer- isation reactions as well as in one-pot conversions of a-alkenes into 1,4-butanediols 53,189 thiolane 1-oxides 54,190 cyclobutanes 55,191, 192 cyclopropanes 56,193 thiophanes 57, selenophanes 58,194, 195 phospholanes 59,196 a,o-dienes 197 and optically active hydrocarbons 60.198 ACP were used as intermediates in preparative syntheses of 2-alkyl-substituted 1,3-dienes 52 (b-vinylation 188), 1,1-dialkyl- ethylenes 61 (reductive b-vinylation 187, 199), branched hydrocar- bons 62 (reductive b-ethylation 200) and iodo-derivatives 63 (reductive b-iodoethylation 201) from alkenes (Scheme 3).The use of ACP offers a simple approach to the synthesis of linear E-isoprenoids 64 and 65 with a definite number of the C5 fragments.202 Alumacyclopentanes can be used in the synthesis of biologically active compounds, e.g., pheromones of pine sawfly, German cockroach and mealworms Tribolium confusum and Tribolium castaneum (Scheme 4).203 ± 206 129 R2 R2 Al R1 49 Scheme 2 g R1 56 R1 h S 57R1 R1 i Al Et Se 58 R1 j 59 R P2 R1 * k 60 Me OAc , [Ni]; (d) O2; Cl , [Ni]; (h) S8; (i ) Se;130 Scheme 3 R [Zr] AlEt3 R R OAc H3O+ R Et Me 62 52 R R (CH2I)2 [Ni] Al Et Et Me CH2I 61 63 A method for the synthesis of 3-alkyl-substituted ACP from a-alkenes and AlEt3 (see Refs 173, 179, 180) was recently modified through the application of more readily available and less pyro- phoric reagents.This novel procedure is also based on the in situ generation of an active catalytic species, viz., Cp2Zr, from Cp2ZrCl2 and simultaneous introduction of a-alkene and ethylene molecules, synthesised in situ from dichloroethane and metallic Mg, into the coordination sphere of the central atom of the catalyst.207, 208 The main product of this reaction is 3-alkyl- substituted ACP; 1-ethyl-trans-3,4-dialkyl-substituted ACP 66 is formed as a by-product (*6 : 1).R1 R1 R2 + R1AlCl2+R2 a 7MgCl2 Al Et 66 Al R1 (95%) (a) Cp2ZrCl2, Mg, C2H4Cl2, THF, 20 8C. Substitution of R2AlCl for RAlCl2 gives substituted 1,4- dialuminiobutanes 67 and 68 which represent a novel class of acyclic OAC. This reaction was studied rather comprehensively for numerous a-alkenes and structurally different OAC.209 R2 Mg, C2H4Cl2,R2 Cp2ZrCl2, THF, 20 8C AlR12 R12 Al 67 R12 AlCl R2 R2 , Mg 2R2 Cp2ZrCl2, THF, 20 8C AlR12 R12 Al 68 R1=OR3, NR32 , R3S, Alk(C3±C20). In 1997, Dzhemilev et al. developed a method for the synthesis of a previously unknown class of metallacycles, viz., alumacyclo- propanes. Cycloalumination of arylalkenes (styrene, o- and p-methylstyrene and 1,4-diphenylbuta-1,3-diene) with ethylalu- minium dichloride in the presence of metallic magnesium as a chloride ion acceptor and Cp2TiCl2 yielded alumacyclopropanes (yields 80%).210 Me Me Me c a b Cl Me Me Me d Me Me EtAl Me Me Me e Me MgHal OAc (a) HCl; (b) , Ni(acac)2; (e) (CH2I)2. , CuCl; (c) AlEt3, Cp2ZrCl2; (d ) RAlCl2, Cp2TiCl2 ArHC CH2 Mg, THF, 20 8C RAlCl2, Cp2TiCl2 Ph Ph Mg, THF, 20 8C Treatment of the C60 fullerene with EtAlCl2 in the presence of Cp2TiCl2 and Mg yielded the organometallic compounds 69 containing alumacyclopropane fragments.207, 211 Cycloalumina- tion of C60 probably involves titanacyclopropane intermediates, Cp2Ti(Z2-C60);212 transmetallation of the latter with EtAlCl2 results in fullerenic alumacyclopropanes 69.Cp2TiCl2, Mg C60+EtAlCl2 MePh, THF, 20 8C AlEt 69 n=1±6. Cp2ZrCl2-Catalysed cycloalumination of the C60 fullerene with AlEt3 recently carried out by Dzhemilev et al.213, 214 gave the organometallic derivatives of C60 containing alumacyclopen- tane fragments. Organometallic fullerene derivatives containing two alumacyclopentane fragments are formed in toluene (*22 8C, 36 h) at the C60 : AlEt3 ratio of 1 : 30 (total yield *80%). At the C60 : AlEt3 ratio of 1 : 300, up to 12 alumacyclo- pentane fragments can be introduced into the C60 molecule. Cp2ZrCl2 C60+n AlEt3 n=30, 300; m=2 ± 12. Me Me 4 steps Me 64 Me 3 steps I Me U MDzhemilev, A G Ibragimov Ar AlR Ph Ph AlR H H3O+ H n n D D3O+ D n H3O+ (D3O+) Al Et m H H (D) (D) m Scheme 4 Me Me I 65Metal complex catalysis in the synthesis of organoaluminium compounds In contrast with aliphatic alkenes, cycloalumination of termi- nal aryl-substituted alkenes with AlEt3 in the presence of Cp2ZrCl2 occurs less selectively. Thus a mixture of mono- and disubstituted arylalumacyclopentanes and 2-aryl-1-ethylaluma- cyclopropane are formed in a total yield >90% (70 : 71 : 72 : 73 : 74*50 : 25 : 15 : 3 : 7).207, 215 R Cp2ZrCl2 R +AlEt3 THF, 20 8C R D + + Al Al Et 70 71 Et R R + + + R R R Al Et Al 73 Et Al Et 72 74 R=Ph, 2-MeC6H4, 4-MeC6H4.The reaction of R2AlCl with arylalkenes catalysed by Cp2TiCl2 was used in the synthesis of 1,2-dialuminiomethanes 75.215 R2 Mg, Cp2ZrCl2 Cp2Ti R12 AlCl+R2 THF, 20 8C AlR12 R12 Al 75 R2 (*85%) VII.Catalytic cycloalumination of alkynes Simple procedures have been developed for the synthesis of unsaturated cyclic OAC from saturated three- and five-membered cyclic OAC in the presence of titanium- and zirconium-containing metal complex catalysts. Thus cycloalumination of disubstituted acetylenes with triethylaluminium in the presence of catalytic amounts of Cp2ZrCl2 gave 2,3-dialkyl(aryl)-substituted aluma- cyclopent-2-enes 77.216, 217 Carboalumination of disubstituted acetylenes in halogen-containing solvents yields acyclic alkenyl- alanes.84 The nature of the solvent plays a crucial role in the formation of intermediate titanium- and zirconium-containing metallacycles 76, the key intermediates in the synthesis of aluma- cyclopentenes 77.84, 218 R R RC CR R AlEt3 Cp2ZrCl2 7Cp2ZrEtCl R 7 + Cp2Zr AlEt2 Al Et 77 Cl 76 The structure of alumacyclopentenes 77 was established by spectral methods 217 and by their conversions.Thus hydrolysis of compounds 77 with D2O gave trisubstituted alkenes 78 (Scheme 5).217 Dealumination of OAC 77 in the presence of catalytic amounts of palladium phosphine complexes results in 1,2-disubstituted cyclobutenes 79.219 In the presence of an excess of dimethyl sulfate, compounds 77 are readily transformed into 1,1-dialkyl-substituted cyclopropanes 81. Cross-coupling of OAC 77 with allyl halides results in 4,5-disubstituted 1,(4Z),9-deca- trienes 80 (see Scheme 5).220 In 1998, Negishi et al.178 carried out the synthesis of bicyclic alumacyclopentenes 82 by intramolecular cycloalumination of enynes 83 in the presence of catalytic amounts of Cp2ZrCl2. R [Zr] RC CR+AlEt3 R 77 (CH2)2D D3O+ R [Cu] R 78 77 R Cl Me2SO4 [Pd] 79 R Subsequent treatment of OAC 82 with CO2 or BrCH2OMe resulted in the corresponding cyclopentenones 84 and vinylcyclo- propanes 85.CSiMe3 AlEt3, [Zr] C (CH2)n CH CH2 83 SiMe3 AlEt (CH2)n82 n=1, 2. A modified procedure for the synthesis of 1-ethyl-2,3-dialkyl- (aryl)alumacyclopent-2-enes 77 from disubstituted acetylenes and ethylene generated in situ from dichloroethane and activated metallic magnesium has been recently developed by Ramazanov et al.221, 222 This reaction yields the corresponding alumacyclo- propenes 86 and alumacyclopentadienes 87 as by-products (5% ± 30%).RC CR+EtAlCl2 (CH2)2Cl2, Mg, Cp2ZrCl2 THF, 20 8C R + EtAl R 86 77 Al Et The synthesis of alumacyclopropenes 88 by cycloalumination of 1,2-disubstituted acetylenes using alkyldichloroalanes 223 in the presence of Ti complexes is one of the most substantial achieve- ments in the synthesis of small alumacycles. Presumably, these reaction conditions favour the generation of titanacyclopropene intermediates,224 ± 235 their transmetallation with dihalogeno- alanes results in the corresponding trisubstituted alumacyclopro- penes 88.223, 236 ± 238 Cp2TiCl2, Mg R1C CR1+R2AlCl2 THF, 20 8C R1=Alk, Ph; R2=Alk, OR3, NR32 .131 Scheme 5 Al Et R R Hal 80 R Me R Me 81 SiMe3 CO2 O (CH2)n84 Me3Si BrCH2OMe (CH2)n85 R R R + R R87 Al Et R R1 R2Al 88 R1132 In contrast with 1,2-disubstituted acetylenes, terminal alkynes react with RAlCl2 in the presence of Ti complexes less selectively. This reaction yields alumacyclopentadienes 87 along with aluma- cyclopropenes 88. The synthesis of 1,2-dialuminioethylenes 89 by the reaction of 1,2-disubstituted acetylenes with R2AlCl under the action of catalytic amounts of Cp2TiCl2 in the presence of a chloride ion acceptor (activated Mg) has been carried out byDzhemilev et al.239 Mg Cp2TiCl2 MgCl2 AlR22 R22 Al R1 R1 Cp2Ti 89 R1C CR1 R1 R22 AlCl Cp2Ti R1 1-Ethyl-2,3,4,5-tetraalkyl-1-alumacyclopenta-2,4-dienes 87 were synthesised with high selectivity by cycloalumination of 1,2-dialkyl-substituted acetylenes using EtAlCl2 in the presence of Cp2ZrCl2 (5 mol.%, *23 8C, TTF).221, 240 The content of alumacyclopropenes in the reaction mixture does not exceed 5%± 7%.R R Cp2ZrCl2, Mg 2 RC CR+EtAlCl2 THF R R Al Et 87 (>93%) R=Alk(C3±C10). VIII. Conclusion In the past 10 ± 15 years, organoaluminium compounds have gained popularity in the practice of synthetic organic and organo- metallic chemistry along with organomagnesium reagents. The catalytic reactions of hydro-, carbo- and cycloalumina- tion of alkenes, dienes and alkynes are carried out under mild conditions and yield OAC with high regio- and stereoselectivity.Thus OAC were used in the synthesis of the major classes of natural compounds, such as vitamins, antibiotics, alkaloids, steroids, carbohydrates, prostaglandins, isoprenoids, drugs, etc. We are convinced that future syntheses will widely employ organoaluminium compounds and will be aimed at obtaining novel co-catalysts for oligomerisation and polymerisation reac- tions and efficient reagents for regio- and stereoselective reduction and alkylation of unsaturated compounds as well as at the development of non-traditional approaches to the design of organic and organometallic compounds and most advanced chemical technologies.References 1. K Ziegler, H G Gellert, H Lehmkuhl,W Pfohl, K Zosel Liebigs Ann. Chem. 629 1 (1960) 2. R Polster Liebigs Ann. Chem. 654 20 (1962) 3. G Hata, A Miyake J. Org. Chem. 28 3237 (1963) 4. R Rienacker, G F GoÈ thel Angew. Chem. 79 862 (1967) 5. R Schimpf, P Heimbach Chem. Ber. 103 2122 (1970) 6. W R Kroll, B E Hudson Jr J. Organomet. Chem. 28 205 (1971) 7. K Ziegler, H Martin, F Krupp Liebigs Ann. Chem. 629 14 (1960) 8. E Marcus, D L MacPeek, S W Tinsley J. Org. Chem. 36 381 (1971) 9. L I Zakharkin, V V Gavrilenko Dokl. Akad. Nauk SSSR 118 713 (1958) a U MDzhemilev, A G Ibragimov 10. N M Alpatova, V V Gavrilenko, Yu M Kessler, O R Osipov, D N Maslin, in Kompleksy Metalloorganicheskikh, Gidridnykh i Galoidnykh Soedinenii (Complexes of Organometallic, Hydride and Halide Compounds) (Ed. L I Zakharkin) (Moscow: Nauka, 1970) 11.A F Zhigach, D S Stasinevich, in Reaktsii i Metody Issledovaniya Organicheskikh Soedinenii (Reactions and Methods of Investigation of Organic Compounds) Vol. 10 (Moscow: Goskhimizdat, 1961) 12. A F Zhigach Alyuminiiorganicheskie Soedineniya (Organoaluminium Compounds) (Moscow: Izd. Inostr. Lit., 1962) 13. N N Korneev Khimiya i Tekhnologiya Alyuminiiorganicheskikh Soedinenii (Chemistry and Technology of Organoaluminium Compounds) (Moscow: Khimiya, 1979) 14. N N Korneev, N N Govorov, M V Tomashevskii Alyuminiiorgani- cheskie Soedineniya (Svoistva, Sposoby Polucheniya, Primenenie, Metody Analiticheskogo Kontrolya, Osnovnye Pravila Obrashcheniya) [Organoaluminium Compounds (Properties, Methods of Synthesis, Application, Methods of Analytical Control, Main Rules of Handling)] (Moscow: NIITEKhim, 1988) 15.Yu B Monakov, G A Tolstikov Kataliticheskaya Polimerizatsiya 1,3-Dienov (Catalytic Polymerisation of 1,3-Dienes) (Moscow: Nauka, 1990) 16. U M Dzhemilev,O S Vostrikova, A G Ibragimov Usp. Khim. 55 191 (1986) [Russ. Chem. Rev. 55 66 (1986)] 17. U M Dzhemilev, O S Vostrikova, G A Tolstikov Usp. Khim. 59 1972 (1990) [Russ. Chem. Rev. 59 1157 (1990)] 18. G A Tolstikov, V P Yur'ev Alyuminiiorganicheskii Sintez (Organoaluminium Synthesis) (Moscow: Nauka, 1979) 19. A V Kuchin, G A Tolstikov Preparativnyi Alyuminiiorganicheskii Sintez (Preparative Organoaluminium Synthesis) (Syktyvkar: Komi Scientific Centre of Ural Branch, Russian Academy of Sciences, 1997) 20.J R Zietz, G C Robinson, K L Lindsay, in Comprehensive Organometallic Chemistry V. 7 (Eds A F G A Stone, G Wilkinson) (Oxford: Pergamon Press, 1982) p. 384 21. F Sato, S Sato, M Sato J. Organomet. Chem., 122 C25 (1976) 22. F Sato, S Sato, M Sato J. Organomet. Chem. 131 C26 (1977) 23. K Isagawa, K Tatsumi, H Kosugi, Y Otsuji Chem. Lett. 1017 (1977) 24. F Sato, S Sato, H Kodama,M Sato J. Organomet. Chem., 142 71 (1977) 25. Jpn. P. 53 103 426; Ref. Zh. Khim. 13 N 90P (1978) 26. E C Ashby, J J Lin J. Org. Chem. 43 2567 (1978) 27. F Sato, in Fundamental Research in Homogeneous Catalysis (Eds Y Ishii, MTsutsui) (New York: Plenum Press, 1977) p.81 28. J-F Le Marechal, M Ephritikhine, G Folcher J. Organomet. Chem. 309 C1 (1986) 29. F Sato, H Ishikawa, Y Takahashi, M Miura, M Sato Tetrahedron Lett. 3745 (1979) 30. O S Vostrikova, N M Shishlov, V V Savrasov, in Primenenie Metallokompleksnogo Cataliza v Organicheskom Sinteze (Tez. Dokl.), Ufa, 1989 [Application of the Metallocomplex Catalysis for Organic Synthesis (Abstracts of Reports), Ufa, 1989] p. 5 31. F Sato, Y Tomuro, H Ishikawa,M Sato Chem. Lett. 99 (1980) 32. J Tsuji, T Mandai Chem. Lett. 975 (1977) 33. J Tsuji, T Yamakawa, T Mandai Tetrahedron Lett. 565 (1978) 34. F Sato, H Kodama,M Sato J. Organomet. Chem. 157 C30 (1978) 35. F Sato, K Oguro,M Sato Chem. Lett. 805 (1978) 36. F Sato, H Kodama,M Sato Chem. Lett.789 (1978) 37. F Sato, H Kodama, Y Tomuro M Sato Chem. Lett. 623 (1979) 38. F Sato, T Oikawa, M Sato Chem. Lett., 167 (1979) 39. F Sato, Y Mori,M Sato Chem. Lett. 1337 (1978) 40. F Sato, Y Mori,M Sato Chem. Lett. 833 (1978) 41. F Sato, Y Mori,M Sato Tetrahedron Lett. 1405 (1979) 42. F Sato, S Haga, M Sato Chem. Lett. 999 (1978) 43. S Nagahara, T Uchimoto,W Yano,Y Doi J. Chem. Soc. Jpn., Chem. Ind. Chem. 2246 (1985) 44. L I Zakharkin,M I Vinnikova, V V Gavrilenko Metalloorg. Khim. 1 101 (1988) b 45. F Asinger, B Fell, F Theissen Chem. Ber. 100 937 (1967) 46. B Fell, S Warwel, F Asinger Chem. Ber. 103 855 (1970) 47. U M Dzhemilev, O S Vostrikova, G A Tolstikov J. Organomet. Chem. 304 17 (1986) 48. U M Dzhemilev, O S Vostrikova, A G Ibragimov, G A Tolstikov Izv.Akad. Nauk SSSR, Ser. Khim. 2134 (1980) a 49. J Schwartz Pure Appl. Chem. 52 733 (1980)Metal complex catalysis in the synthesis of organoaluminium compounds 50. G A Tolstikov, U M Dzhemilev, O S Vostrikova, A G Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 669 (1982) a 51. A G Ibragimov, Z A Yusupov, M F Akhmetov, I V Zagrebel'naya, L M Khalilov, U M Dzhemilev, in The IWFAC' 97 `Fullerenes and Atomic Clusters' (Abstracts of Reports), St. Petersburg, 1997 p. 121 52. Yu V Vasil'ev, R F Tuktarov, M F Chegodaeva, A G Ibragimov, L M Khalilov, U M Dzhemilev, in The IWFAC' 97 `Fullerenes and Atomic Clusters' (Abstracts of Reports), St. Petersburg, 1997 p. 216 53. E C Ashby, S A Noding Tetrahedron Lett. 4579 (1977) 54.E C Ashby, S A Noding J. Organomet. Chem. 177 117 (1979) 55. E C Ashby, S A Noding J. Org. Chem., 44 4364 (1979) 56. G Dozzi, S Cucinella, A Mazzei J. Organomet. Chem. 164 1 (1979) 57. K Maruoka, H Sano, K Shinoda, S Nakai, H Yamamoto J. Am. Chem. Soc. 108 6036 (1986) 58. K Maruoka, H Sano, K Shinoda, H Yamamoto Chem. Lett. 73 (1987) 59. K Maruoka, K Shinoda, H Yamamoto Synth. Commun. 18 1029 (1988) 60. K Maruoka, H Yamamoto Tetrahedron 44 5001 (1988) 61. F Asinger, B Fell, R Osberghaus Chem. Ber. 104 1332 (1971) 62. E -i Negishi, T Yoshida Tetrahedron Lett., 21 1501 (1980) 63. P C Wailes, H Weigold, A P Bell J. Organomet. Chem., 43 C32 (1972) 64. P C Wailes, H Weigold J. Organomet. Chem. 24 405 (1970) 65. A G Ibragimov, I V Zagrebel'naya, K G Satenov, L M Khalilov, U M Dzhemilev Izv.Akad. Nauk, Ser. Khim. 712 (1998) a 66. U M Dzhemilev, O S Vostrikova A G Ibragimov, G A Tolstikov, L M Zelenova Izv. Akad. Nauk SSSR, Ser. Khim. 476 (1981) a 67. U M Dzhemilev, A G Ibragimov, O S Vostrikova, E V Vasil'eva, G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 1089 (1987) a 68. A G Ibragimov, D L Minsker, A A Berg, O V Shitikova, S I Lomakina, U M Dzhemilev Izv. Akad. Nauk, Ser. Khim. 2791 (1992) a 69. V V Gavrilenko, L A Chekulaeva, L I Zakharkin Izv. Akad. Nauk SSSR, Ser. Khim. 1171 (1984) a 70. A V Kuchin, R A Nurushev, L I Umanskaya, G A Tolstikov Zh. Obshch. Khim. 57 1334 (1987) c 71. G Giacomelli, L Bertero, L Lardicci Tetrahedron Lett. 22 883 (1981) 72. K Fischer, K Jonas, A Mollbach, G Wilke Z.Naturforsch., B Anorg. Chem. Org. Chem. 39 1011 (1984) 73. M Lantens, P Chin, S Ma, T Rovis J. Am. Chem. Soc. 117 532 (1995) 74. G Zweifel, R B Steele J. Am. Chem. Soc. 89 5085 (1967) 75. J J Eisch, R Amtmann J. Org. Chem., 37 3410 (1972) 76. J J Eisch, G A Damasevitz J. Org. Chem. 41 2214 (1976) 77. D Masure, P Coutrot, J F Normant J. Organomet. Chem. 226 C55 (1982) 78. E C Ashby, S A Noding J. Org. Chem. 45 1035 (1980) 79. O S Vostrikova, A R Gimaeva, in Primenenie Metallokompleksnogo Cataliza v Organicheskom Sinteze (Tez. Dokl.), Ufa, 1989 [Application of the Metallocomplex Catalysis for Organic Synthesis (Abstracts of Reports), Ufa, 1989] p. 44 80. U M Dzhemilev, A G Ibragimov, I R Ramazanov, R M Sultanov, L M Khalilov, R R Muslukhov Izv.Akad. Nauk, Ser. Khim. 2751 (1996) a 81. A G Ibragimov, I R Ramazanov, L M Khalilov, R M Sultanov, U M Dzhemilev Mendeleev Commun. 231 (1996) 82. U M Dzhemilev, A P Zolotarev, I R Ramazanov, R R Muslukhov, A G Ibragimov, in VI Vseros. Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Nizhnii Novgorod, 1995 [The VIth All-Russian Conference on Organometallic Chemistry (Abstracts of Reports), Nizhnii Novgorod, 1995] p. 16 83. R R Muslukhov, L M Khalilov, I R Ramazanov, A Z Sharipova, A G Ibragimov, U M Dzhemilev Izv. Akad. Nauk, Ser. Khim. 2194 (1997) a 84. E-i Negishi, D Y Kondakov, D Choueiry, K Kasai, T Takahashi J. Am. Chem. Soc. 118 9577 (1996) 85. H Makabe, E-i Negishi Eur. J. Org. Chem. 969 (1999) 86.A M Caporusso, G Giacomelli, L Lardicci J. Chem. Soc., Perkin Trans. 1 3139 (1979) 87. G Giacomelli, A M Caporusso, L Lardicci J. Org. Chem. 44 231 (1979) 88. G Zweifel, R L Miller J. Am. Chem. Soc. 92 6678 (1970) 89. J A Miller,W Leong, G Zweifel J. Org. Chem. 53 1839 (1988) 133 90. G Zweifel, W Lewis J. Org. Chem. 43 2739 (1978) 91. J J Eisch, M Behrooz, S K Dua J. Organomet. Chem. 285 121 (1985) 92. G Zweifel, G M Clark, C C Whitney J. Am. Chem. Soc. 93 1305 (1971) 93. N I Andreeva, A V Kuchin, G A Tolstikov Zh. Obshch. Khim. 55 1316 (1985) c 94. M Montury, J Gore Tetrahedron Lett. 21 51 (1980) 95. S Nagahara, K Maruoka, H Yamamoto Bull. Chem. Soc. Jpn. 66 3783 (1993) 96. S Nagahara, K Maruoka, Y Doi, H Yamamoto Chem.Lett. 1595 (1990) 97. J N Hay, P G Hooper, J C Robb Trans. Faraday Soc. 66 2045 (1970) 98. USSR P. 687 076; Byull. Izobret. (35) 108 (1979) 99. U M Dzhemilev, A G Ibragimov, O S Vostrikova, G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 207 (1985) a 100. U M Dzhemilev, O S Vostrikova J. Organomet. Chem. 285 43 (1985) 101. UMDzhemilev, A G Ibragimov, O S Vostrikova, G A Tolstikov, L M Zelenova Izv. Akad. Nauk SSSR, Ser. Khim. 361 (1981) a 102. U M Dzhemilev, A G Ibragimov, A B Morozov, G A Tolstikov, in V Vseros. Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Riga, 1991 [The Vth All-Russian Conference on Organometallic Chemistry (Abstracts of Reports), Riga, 1991] p. 101 103. H G Richey, L M Moses, J J Hangeland Organometallics 2 1545 (1983) 104.U M Dzhemilev, A G Ibragimov, D L Minsker, G A Tolstikov, in V Vseros. Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Riga, 1991 [The Vth All-Russian Conference on Organometallic Chemistry (Abstracts of Reports), Riga, 1991] p. 100 105. D Y Kondakov, E-i Negishi J. Am. Chem. Soc. 117 10771(1995) 106. D Y Kondakov, E-i Negishi J. Am. Chem. Soc. 118 1577 (1996) 107. K H Shaughnessy, R M Waymouth J. Am. Chem. Soc. 117 5873 (1995) 108. E-i Negishi, M D Jensen, D Y Kondakov, S Wang J. Am. Chem. Soc. 116 8404 (1994) 109. L Resconi, R M Waymouth J. Am. Chem. Soc. 112 4953 (1990) 110. G W Coates, R M Waymouth J. Am. Chem. Soc. 113 6270 (1991) 111. G W Coates, R M Waymouth J. Am. Chem. Soc. 115 91 (1993) 112. U M Dzhemilev, O S Vostrikova, G A Tolstikov, A G Ibragimov Izv.Akad. Nauk SSSR, Ser. Khim. 2626 (1979) a 113. UMDzhemilev, A P Zolotarev, I R Ramazanov, A G Ibragimov, in International Symposium on Recent Advances in Organometallic Chemistry in Organic Synthesis (Pre-OMCOS-8) (Abstracts of Reports), Davis, 1995 p. 26 114. J J Barber, C Willis, G M Whitesides J. Org. Chem. 44 3603 (1979) 115. H E Tweedy, P E Hahn, L C Smedley, A V Youngblood, R A Coleman, D W Thompson J. Mol. Catal. 3 239 (1978) 116. A V Youngblood, S A Nichols, R A Coleman, D W Thompson J. Organomet. Chem. 146 221 (1978) 117. T V Harris, R A Coleman, R B Dickson, D W Thompson J. Organomet. Chem. 69 C27 (1974) 118. P Rigollier, J R Young, L A Fowley, J R Stille J. Am. Chem. Soc. 112 9441 (1990) 119.J R Young, J R Stille Organometallics 9 3022 (1990) 120. J R Young, J R Stille J. Am. Chem. Soc. 114 4936 (1992) 121. A V Kuchin, Doctoral Thesis in Chemical Sciences, Institute of Chemistry of Bashkir. Scientific Centre, Ural Branch of Academy of Sciences, USSR, Ufa, 1989 122. J F Normant, A Alexakis Synthesis 841 (1981) 123. E-i Negishi Pure Appl. Chem. 53 2333 (1981) 124. E-i Negishi, T Takahashi Aldrichim. Acta 18 31 (1985) 125. E-i Negishi Acc. Chem. Res. 20 65 (1987) 126. M D Schiavelli, J J Plunkett, D W Thompson J. Org. Chem. 46 807 (1981) 127. J C Ewing, G S Ferguson, D W Moore, F W Schultz, D W Thompson J. Org. Chem. 50 2124 (1985) 128. T J Zitzelberger,M D Schiavelli, D W Thompson J. Org. Chem. 48 4781 (1983) 129.F W Schultz, G S Ferguson, D W Thompson J. Org. Chem. 49 1736 (1984) 130. E-i Negishi, D Y Kondakov, D E Van Horn Organometallics 16 951 (1997)134 131. T Yoshida Chem. Lett. 293 (1982) 132. J Hibino, S Matsubara, Y Morizawa, K Oshima, H Nozaki Tetrahedron Lett. 25 2151 (1984) 133. S Matsubara, J-i Hibino, Y Morizawa, K Oshima, H Nozaki J. Organomet. Chem. 285 163 (1985) 134. S Sharma, A C Oehlschlager Tetrahedron Lett. 27 6161 (1986) 135. B B Snider, M Karras J. Organomet. Chem. 179 C37 (1979) 136. J A Miller, E-i Negishi Tetrahedron Lett. 25 5863 (1984) 137. D E Van Horn, E-i Negishi J. Am. Chem. Soc. 100 2252 (1978) 138. D E Van Horn, L F Valente,M J Idacavage, E-i Negishi J. Organomet. Chem. 156 C20 (1978) 139. C L Rand, D E Van Horn, M W Moore, E-i Negishi J.Org. Chem. 46 4093 (1981) 140. P Wipf, S Lim Angew. Chem., Int. Ed. Engl. 32 1068 (1993) 141. T Yoshida, E-i Negishi J. Am. Chem. Soc. 103 1276 (1981) 142. T Yoshida, E-i Negishi J. Am. Chem. Soc. 103 4985 (1981) 143. E-i Negishi,D E Van Horn, T Yoshida J. Am. Chem. Soc. 107 6639 (1985) 144. H Matsushita, E-i Negishi J. Am. Chem. Soc. 103 2882 (1981) 145. N Okukado, E -i Negishi Tetrahedron Lett. 2357 (1978) 146. E-i Negishi, A O King, W L Klima J. Org. Chem. 45 2526 (1980) 147. E-i Negishi, L Valente,M Kobayashi J. Am. Chem. Soc. 102 3298 (1980) 148. E-i Negishi, N Okukado, A O King, D E Van Horn, B J Spiegel J. Am. Chem. Soc. 100 2254 (1978) 149. S Chatterjee, E-i Negishi J. Org. Chem.50 3406 (1985) 150. H Matsushita, E-i Negishi J. Chem. Soc., Chem. Commun. 160 (1982) 151. E-i Negishi, L D Boardman, J M Tour, H Sawada, C L Rand J. Am. Chem. Soc. 105 6344 (1983) 152. L D Boardman, V Bagheri, H Sawada, E-i Negishi J. Am. Chem. Soc. 106 6105 (1984) 153. E-i Negishi, L D Boardman, H Sawada, V Bagheri, A T Stoll, J M Tour, C L Rand J. Am. Chem. Soc. 110 5383 (1988) 154. J A Miller, E-i Negishi Isr. J. Chem. 24 76 (1984) 155. E -i Negishi, H Sawada, J M Tour, Y Wei J. Org. Chem. 53 913 (1988) 156. T Kusumoto, K Nishide, T Hiyama Bull. Chem. Soc. Jpn. 63 1947 (1990) 157. E -i Negishi, F Luo, C L Rand Tetrahedron Lett., 23 27 (1982) 158. M Kobayashi, L F Valente, E-i Negishi Synthesis 1034 (1980) 159. T Kusumoto, K Nishide, T Hiyama Chem.Lett. 1409 (1985) 160. R E Ireland, P Wipf J. Org. Chem. 55 1425 (1990) 161. B H Lipshutz, S H Dimock J. Org. Chem. 56 5761 (1991) 162. E-i Negishi, L D Boardman Tetrahedron Lett. 23 3327 (1982) 163. S Fung, J B Siddall J. Am. Chem. Soc. 102 6580 (1980) 164. K Mori,M Sakakibara, K Okada Tetrahedron 40 1767 (1984) 165. D R Williams, B A Barner,K Nishitani, J G Phillips J. Am. Chem. Soc. 104 4708 (1982) 166. P J Kocienski, S D A Street,C Yeates, S F Cambell J. Chem. Soc., Perkin Trans. 1 2189 (1987) 167. R C Cookson, N J Liverton J. Chem. Soc., Perkin Trans. 1 1589 (1985) 168. R Baker,W J Cummings, J F Hayes, A Kumar J. Chem. Soc., Chem. Commun. 1237 (1986) 169. I Paterson, M Gardner, B J Banks Tetrahedron 45 5283 (1989) 170.M Kobayashi, E-i Negishi J. Org. Chem. 45 5223 (1980) 171. W R Roush, A P Spada Tetrahedron Lett. 24 3693 (1983) 172. W R Roush, T A Blizzard J. Org. Chem. 48 758 (1983) 173. U M Dzhemilev, A G Ibragimov, A P Zolotarev, R R Muslukov, G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 207 (1989) a 174. O S Vostrikova, A G Ibragimov, R M Sultanov, U M Dzhemilev Metalloorg. Khim. 5 782 (1992) b 175. U M Dzhemilev,A G Ibragimov J. Organomet. Chem. 466 1 (1994) 176. U M Dzhemilev Tetrahedron 51 4333 (1995) 177. U M Dzhemilev, A G Ibragimov Izv. Akad. Nauk, Ser. Khim. 816 (1998) a 178. E-i Negishi, J-L Montchamp, L Anastasia, A Elizarov, D Choueiry Tetrahedron Lett. 39 2503 (1998) 179. U M Dzhemilev, A G Ibragimov, A P Zolotarev, R R Muslukov, G A Tolstikov Izv.Akad. Nauk SSSR, Ser. Khim. 2831 (1990) a 180. U M Dzhemilev, A G Ibragimov, A P Zolotarev, L M Khalilov, R R Muslukhov Izv. Akad. Nauk, Ser. Khim. 386 (1992) a U MDzhemilev, A G Ibragimov 181. U M Dzhemilev, A G Ibragimov, A B Morozov, L M Khalilov, R R Muslukhov,G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 1141 (1991) a 182. U M Dzhemilev, A G Ibragimov, A B Morozov, R R Muslu- khov, G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 1607 (1991) a 183. U M Dzhemilev, A G Ibragimov, A B Morozov Mendeleev Commun. 26 (1992) 184. U M Dzhemilev, A G Ibragimov, A B Morozov, R R Muslu- khov, G A Tolstikov Izv. Akad. Nauk, Ser. Khim. 1393 (1992) a 185. R R Muslukhov, L M Khalilov, A P Zolotarev, A B Morozov, A G Ibragimov, U M Dzhemilev, G A Tolstikov Izv.Akad. Nauk, Ser. Khim. 2110 (1992) a 186. R R Muslukhov, L M Khalilov, A G Ibragimov, A P Zolotarev, U M Dzhemilev Izv. Akad. Nauk, Ser. Khim. 2742 (1992) a 187. U M Dzhemilev, A G Ibragimov, A P Zolotarev, R R Muslu- khov Izv. Akad. Nauk, Ser. Khim. 382 (1992) a 188. A G Ibragimov, A P Zolotarev, R R Muslukhov, S I Lomakina, U M Dzhemilev Izv. Akad. Nauk, Ser. Khim. 118 (1995) a 189. U M Dzhemilev, A G Ibragimov, A P Zolotarev, in Primenenie Metallokompleksnogo Cataliza v Organicheskom Sinteze (Tez. Dokl.), Ufa, 1989 [Application of Metallocomplex Catalysis to Organic Synthesis (Abstracts of Reports), Ufa, 1989] p. 41 190. USSR P. 1 735 294; Byull. Izobret. (19) 103 (1992) 191. UMDzhemilev, A G Ibragimov, A P Zolotarev, R R Muslukhov, G A Tolstikov Izv.Akad. Nauk SSSR, Ser. Khim. 2152 (1989) a 192. U M Dzhemilev, A G Ibragimov,M N Azhgaliev, A P Zolotarev, R R Muslukhov Izv. Akad. Nauk, Ser. Khim. 273 (1994) a 193. UMDzhemilev, A G Ibragimov, A P Zolotarev, R R Muslukhov, G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 1190 (1990) a 194. UMDzhemilev, A G Ibragimov,MN Azhgaliev, R R Muslukhov Izv. Akad. Nauk, Ser. Khim. 276 (1994) a 195. U M Dzhemilev, A G Ibragimov, A P Zolotarev, G A Tolstikov Izv. Akad. Nauk SSSR, Ser. Khim. 1444 (1989) a 196. USSR P. 1 747 452; Byull. Izobret. (26) 79 (1992) 197. Russ. P. 2 109 718; Byull. Izobret. (12) 222 (1998) 198. UMDzhemilev, A P Zolotarev, I R Ramazanov, A G Ibragimov, in International Symposium on Recent Advances in Organometallic Chemistry in Organic Synthesis (Pre-OMCOS-8) (Abstracts of Reports), Davis, 1995 p.24 199. U M Dzhemilev, A G Ibragimov, A P Zolotarev Mendeleev Commun. 28 (1992) 200. A P Zolotarev, Candidate Thesis in Chemical Sciences, Institute of Petrochemistry and Catalysis, Academy of Sciences, Republic Bashkortostan, Ufa, 1994 201. UMDzhemilev, A P Zolotarev, I R Ramazanov, R R Muslukhov, A G Ibragimov, in VI Vseros. Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Nizhnii Novgorod, 1995 [The VIth All-Russian Conference on Organometallic Chemistry (Abstracts of Reports), Nizhnii Novgorod, 1995] p. 14 202. UMDzhemilev, A P Zolotarev, I R Ramazanov, A G Ibragimov, in The XVIth International Conference on Isoprenoids (Abstracts of Reports), Prague, 1995 p.39 203. VNOdinokov,GYu Ishmuratov,RYa Kharisov,UMDzhemilev, A G Ibragimov, in IV Vsesoyuz. Simp. po Khemoretseptsii Naseko- mykh (Tez. Dokl.), Vil'nyus, 1988 [The IVth All-Union Symposium on Chemoreception of Insects (Abstracts of Reports), Vilnius, 1988] p. 39 204. U M Dzhemilev, V N Odinokov, A P Zolotarev, I R Ramazanov, A G Ibragimov, in International Symposium on Recent Advances in Organometallic Chemistry in Organic Synthesis (Pre-OMCOS-8) (Abstracts of Reports), Davis, 1995 p. 25 205. VNOdinokov,GYu Ishmuratov, AGIbragimov,MP Yakovleva, A P Zolotarev, U M Dzhemilev, G A Tolstikov Khim. Prir. Soedin. 567 (1992) d 206. V N Odinokov, G Yu Ishmuratov, R Ya Kharisov, A G Ibragimov, R M Sultanov, U M Dzhemilev, G A Tolstikov Khim.Prir. Soedin. 272 (1989) d 207. L O Khafizova, Candidate Thesis in Chemical Sciences, Institute of Petrochemistry and Catalysis, Academy of Sciences, Republic Bashkortostan, Ufa, 1998 208. A G Ibragimov, L O Khafizova, L G Yakovleva, E V Nikitina, K G Satenov, L M Khalilov, U M Dzhemilev Izv. Akad. Nauk, Ser. Khim. 778 (1999) aMetal complex catalysis in the synthesis of organoaluminium compounds 209. UMDzhemilev, A G Ibragimov,MN Azhgaliev, R R Muslukhov Izv. Akad. Nauk, Ser. Khim. 1561 (1995) a 210. U M Dzhemilev, A G Ibragimov, L O Khafizova, S V Rusakov, L M Khalilov Mendeleev Commun. 198 (1997) 211. U M Dzhemilev, A G Ibragimov, L O Khafizova, L M Khalilov, Yu V Tomilov, O M Nefedov, in The IWFAC' 99 `Fullerenes and Atomic Clusters' (Abstracts of Reports), St.Petersburg, 1999 p. 31 212. A V Usatov, V V Bulgakov, K A Lyssenko, M Yu Antipin, V B Shur, Yu N Novikov, in The IWFAC' 99 `Fullerenes and Atomic Clusters' (Abstracts of Reports), St. Petersburg, 1999 p. 284 213. U M Dzhemilev, A G Ibragimov, Z A Yusupov, M F Akhmetov, L M Khalilov, R V Kunakova, in The IWFAC' 97 `Fullerenes and Atomic Clusters' (Abstracts of Reports), St. Petersburg, 1997 p. 204 214. U M Dzhemilev, A G Ibragimov, L O Khafizova, L M Khalilov, Yu V Vasil'ev, R F Tuktarov, Yu V Tomilov, O M Nefedov Izv. Akad. Nauk, Ser. Khim. 572 (1999) a 215. A G Ibragimov, L O Khafizova, K G Satenov, L M Khalilov, L G Yakovleva, S V Rusakov, U M Dzhemilev Izv.Akad. Nauk, Ser. Khim. 1594 (1999) a 216. In Vazhneishie Rezul'taty v Oblasti Estestvennykh i Obshchestven- nykh Nauk za 1990 god (Otchet Akad. Nauk SSSR), Moskva, 1991 [Major Results in the Field of Natural and Social Sciences for 1990 (Report of Academy of Sciences of the USSR), Moscow, 1991] p. 44 217. U M Dzhemilev, A G Ibragimov, A P Zolotarev Mendeleev Commun. 135 (1992) 218. E-i Negishi, D Y Kondakov Chem. Soc. Rev. 26 417 (1996) 219. UMDzhemilev, A P Zolotarev, I R Ramazanov, R R Muslukhov, A G Ibragimov, in International Symposium on Recent Advances in Organometallic Chemistry in Organic Synthesis (Pre-OMCOS-8) (Abstracts of Reports), Davis, 1995 p. 23 220. UMDzhemilev, I R Ramazanov, A P Zolotarev, R R Muslukhov, A G Ibragimov, in VI Vseros.Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Nizhnii Novgorod, 1995 [The VIth All-Russian Conference on Organometallic Chemistry (Abstracts of Reports), Nizhnii Novgorod, 1995] p. 15 221. I R Ramazanov, Candidate Thesis in Chemical Sciences, Institute of Petrochemistry and Catalysis, Academy of Sciences, Republic Bashkortostan, Ufa, 1998 222. A G Ibragimov, I R Ramazanov, MP Luk'yanova, LMKhalilov, U M Dzhemilev, in VII Vseros. Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Moskva, 1999 [The VIIth All-Russian Confer- ence on Organometallic Chemistry (Abstracts of Reports), Moscow, 1999] p. 33 223. U M Dzhemilev, A G Ibragimov, I R Ramazanov, L M Khalilov Izv. Akad. Nauk, Ser. Khim. 2269 (1997) a 224. V B Shur, S Z Bernadyuk, V V Burlakov, V G Andrianov, A I Yanovsky, Yu T Struchkov,M E Vol'pin J. Organomet. Chem. 243 157 (1983) 225. V B Shur, V V Burlakov, A I Yanovskii, Yu T Struchkov, M E Vol'pin Izv. Akad. Nauk SSSR, Ser. Khim. 1212 (1983) a 226. V B Shur, V V Burlakov, M E Vol'pin Izv. Akad. Nauk SSSR, Ser. Khim. 1929 (1983) a 227. V B Shur, V V Burlakov, A I Yanovsky, P V Petrovsky, Yu T Struchkov,M E Vol'pin J. Organomet. Chem. 297 51 (1985) 228. V B Shur, V V Burlakov, A I Yanovskii, Yu T Struchkov, M E Vol'pin Metalloorg. Khim. 1 475 (1988) b 229. V B Shur, V V Burlakov,M E Vol'pin J. Organomet. Chem. 347 77 (1988) 230. V V Burlakov, U Rozental', P V Petrovskii, V B Shur, M E Vol'pin Metalloorg. Khim. 1 953 (1988) b 231. V V Burlakov, U Rozental', A I Yanovskii, Yu T Struchkov, O G Ellert, V B Shur, M E Vol'pin Metalloorg. Khim. 2 1193 232. U Rosenthal, G Oehme, V V Burlakov, P V Petrovskii, V B Shur, 233. U Rosenthal, H GoÈ rls, V V Burlakov, V B Shur, M E Vol'pin 234. V V Burlakov, U Rozental', F M Dolgushin, A I Yanovskii, (1989) b M E Vol'pin J. Organomet. Chem. 391 119 (1990) J. Organomet. Chem. 426 C53 (1992) Yu T Struchkov, O G Ellert, V B Shur,M E Vol'pin Metalloorg. Khim. 5 1213 (1992) b 235. V V Burlakov, A V Polyakov, A I Yanovsky, Yu T Struchkov, V B Shur,M E Vol'pin, U Rosenthal, H GoÈ rls J. Organomet. Chem. 476 197 (1994) 135 236. UMDzhemilev, A G Ibragimov, L O Khafizova, I R Ramazanov, I V Zagrebel'naya, L G Yakovleva, K G Satenov, in XVI Mende- leevskii S'ezd po Obshchei i Prikladnoi Khimii (Tez. Dokl.), Moskva, 1998 [The XVIth Mendeleev Congress on General and Applied Chemistry (Abstracts of Reports), Moscow, 1998] Vol. 1, p. 81 237. L M Khalilov, L V Parfenova, S V Rusakov, A Z Sharipova, I R Ramazanov, A G Ibragimov, U M Dzhemilev, in XVI Men- deleevskii S'ezd po Obshchei i Prikladnoi Khimii (Tez. Dokl.), Moskva, 1998 [The XVIth Mendeleev Congress on General and Applied Chemistry (Abstracts of Reports), Moscow, 1998] Vol. 1, p. 318 238. U M Dzhemilev,A G Ibragimov, I R Ramazanov, L M Khalilov, R V Kunakova, in The XIth International Symposium on Homogeneous Catalysis (Abstracts of Reports), London, 1998 p. 85 239. UMDzhemilev, AGIbragimov, LGDudoladova, RV Kunakova, L M Khalilov, in The IXth International Symposium on Organo- metallic Chemistry (IUPAC) (Abstracts of Reports) GoÈttingen, 1997 p. 76 240. AGIbragimov, IRRamazanov,MP Luk'yanova,UMDzhemilev, in VII Vseros. Konf. po Metalloorganicheskoi Khimii (Tez. Dokl.), Moskva, 1999 [The VIIth All-Russian Conference on Organo- metallic Chemistry (Abstracts of Reports), Moscow, 1999] p. 34 a�Russ. Chem. Bull. (Engl. Transl.) b�Russ. Organomet. Chem. (Engl. Transl.) c�Russ. J. Gen. Chem. (Engl. Transl.) d�Chem. Nat. Compd. (Engl.

ISSN:0036-021X    

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Russian Chemical Reviews 69 (2) 137 ± 151 (2000) Dehydrocondensation of organylsilanes giving Si7Si bonds V B Pukhnarevich,MG Voronkov, L I Kopylova Contents I. Introduction II. Catalytic dehydrocondensation of organylhydrosilanes III. Electrochemical dehydrocondensation of organylhydrosilanes IV. Other reactions V. Conclusion Abstract. organ- of dehydrocondensation catalytic on data The The data on catalytic dehydrocondensation of organ- ylsilanes and systematised are bonds of formation the with ylsilanes with the formation of Si Si7Si Si bonds are systematised and generalised. effects (the features general and mechanism The generalised. The mechanism and general features (the effects of of the and solvent the catalyst, the and reactants the of nature the nature of the reactants and the catalyst, the solvent and the the reaction by catalysed reactions these of conditions) reaction conditions) of these reactions catalysed by cyclopenta- cyclopenta- dienyl considered.are metals transition of complexes dienyl complexes of transition metals are considered. Electro- Electro- chemical dehydrocondensation the for procedures other and chemical and other procedures for the dehydrocondensation of of organylsilanes includes bibliography The discussed. are organylsilanes are discussed. The bibliography includes 220 220 references. I. Introduction Organosilicon compounds with Si7H bonds, in particular, organylsilanes of the R47n SiHn type (n=1 ± 3), are highly reactive substances.1 In this connection, these compounds are of considerable theoretical and practical interest.Thus addition of silanes to unsaturated substrates containing the C=C, C=N, N=N, C=O, C:C or N:N bonds, viz., hydrosilylation,2 is one of the most important procedures for the synthesis of various organosilicon compounds.1±8 This unique reaction makes it possible to form Si7C bonds as well as Si7O7C and Si7N7C groups in one stage. SiY CH Si H+Y C Y=R2C, O, HN etc. Organylsilanes, unlike their formal analogues, viz., hydro- carbons, readily enter into dehydrocondensation reactions with OH, NH, SH and CH acids. Dehydrocondensation reactions with different compounds, such as water, alcohols, phenols, inorganic and carboxylic acids, amines, thiols, etc., have been well studied.V B Pukhnarevich, L I Kopylova Irkutsk State Pedagogical University, ul. Nizhnyaya Naberezhnaya 6, 664011 Irkutsk, Russian Federation. Fax (7-395) 224 05 59. Tel. (7-395) 246 31 22 (V B Pukhnarevich), (7-395) 246 31 23 (L I Kopylova) MG Voronkov Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1, 664033 Irkutsk, Russian Federation. Fax (7-395) 235 60 46. Tel. (7-395) 246 24 00. E-mail voronkov@irioch.irk.ru Received 8 December 1998 Uspekhi Khimii 69 (2) 150 ± 165 (2000); translated by T N Safonova #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v69n02ABEH000498 137 138 147 148 148 Si H+H YR Si YR+H2 Y=O, S, NH; R=H, Alk, Ar, Ac etc. Hydrosilylation and dehydrocondensation are most often catalysed by transition metal compounds and nucleophiles. Examples of the use of dehydrocondensation of organylsilanes for the preparation of organosilicon compounds are shown in Scheme 1.Scheme 1 HOH R13 SiX HX X=Cl, Br, I R13 SiOH, R13 SiOSiR13 HOR2 R2CH CH2 R13 SiOR2 R13 SiCH CHR2 R2CH CHR3 R2C CH R13 SiC CR2 OH OH CHR3 R2CH HSR2 R13 SiH R13 SiSR2 OSiR13 R13 SiO HOC(O)R2 R23 SiOH R13 SiOC(O)R2 R13 SiOSiR23 HON CR2 HNR2 2 2 R13 SiON CR22 R13 SiNR22 Synthetic applications of dehydrocondensation of silanes with hydroxy-containing organic compounds and the mechanism of this reaction have been adequately surveyed in the reviews.1, 9 ± 14 Of more recent investigations, studies on alcoholysis of mono-, di- and trisubstituted silanes with saturated and unsaturated primary and secondary alcohols and diols in the presence of complexes of copper {[Ph3PCuH]6},15 titanium 16 and manganese {[Mn(CO)4Br]2} 17 as well as in the presence of soluble platinum, palladium, nickel, ruthenium and rhodium complexes fixed on silica gel,18 ± 20 and studies on alcoholysis of disilanes in the presence of tetrabutylammonium fluoride 21 are worthy of note.Dehydrocondensation of silanes with phenols, ammonia, amines, thiols and carboxylic acids are less well understood.11 Of the recent advances, phenolysis catalysed by potassium fluo- ride 22, 23 and ammonolysis (with ammonia or hydrazines) of phenylmethyl-, diphenylmethyl- and methyldichlorosilanes in the presence of dimethyltitanocene 24 ± 27 should be mentioned. The synthesis of quaternary ammonium difluorosilicates by the reactions of R12 R2SiH with R32 R4N+HF¡2 was reported.28 The reactions of unsaturated organic acids with dimethylchlorosilane followed by intramolecular hydrosilylation of the resulting b,g- unsaturated acyloxysilanes catalysed by Pt(II) 1,5-cyclooctadiene (COD) complexes afford silaoxacyclopentanones. The latter can138 be converted into esters of hydroxycarboxylic acids. This method was used in the stereoselective synthesis of methyl ester of (2S,3R)- 3-hydroxy-N-Boc-proline.29 Products of hydrosilylation of styr- ene, 1-octyne and phenylacetylene with phenyl- and diphenylsi- lane enter into dehydrocondensation reactions with arenethiols ArSH (Ar=Ph, 4-MeC6H4 or 4-MeOC6H4) in the presence of rhodium tris(triphenylphosphine) chloride.30 Dehydrocondensation of octacarbonyldicobalt complexes of mono-, di- and triethynylsilanes (1 ± 3) in the absence of nucleo- philic or metal complex catalysts occurs through interactions between the Si7H bond and water, alcohols, carboxylic acids, primary amines, etc.31, 32 CMe CSi(R)HC MeC RC CSiMe2H Co2(CO)6 Co2(CO)6 (CO)6Co22 (R=Me) 1 (R=Ph, Me2SiH) CMe CSi(R)HC MeC Co2(CO)6 (CO)6Co2 3 (R=MeC C) Dehydrocondensation of silanes with CH acids (alkanes, alkenes, alkynes and their derivatives) has been studied in suffi- cient detail.11, 33 ± 39 Dehydrocondensation of organosilicon compounds contain- ing Si7Hbonds to form disilanes has remained poorly studied for a long time and attracted considerable attention only recently.Si H+H Si Si Si +H2 Organosilicon compounds containing Si7Si bonds have attracted growing interest because they can be used as starting compounds in the synthesis of organic and inorganic derivatives of oligo- and polysilanes possessing specific structural, electronic, optical and chemical properties.40, 41 These oligo- and polysilanes find use in the production of ceramic materials,42 ± 64 semiconduc- tors,4, 42, 48, 49, 65 ± 69 photoresistors,42, 44, 46, 48, 49, 70 ± 77 photoinitia- tors of polymerisation of alkenes, etc.42 In this review, studies on dehydrocondensation of organylsi- lanes (which is sometimes wrongly called `dehydropolymerisa- tion' 42) accompanied by the formation of Si7Si bonds are surveyed.II. Catalytic dehydrocondensation of organylhydrosilanes 1. Catalysis by compounds of Group IIIB elements The data on the use of complex compounds of Group IIIB elements as catalysts of dehydrocondensation of silanes are scarce. The activation energies and the enthalpies of dehydroconden- sation of monosilane in the presence of complexes of lanthanides M(M=Sc, Y, La, Lu or Sm), which were calculated in a study,78 indicate that this reaction can in principle proceed. It is believed that the first stage of the process involves silylation of intermediate 4. The second stage leads to the formation of disilane and regeneration of intermediate 4.LnMSiH3+ H2 , LnMH+SiH4 4 LnMSiH3+SiH4 Si2H6+LnMH. 4 Of Group IIIB elements, only derivatives of lanthanides and actinides, as far as is known, are active in dehydrocondensa- tion.78 ± 80 Thus PhSiH3 in the presence of Cp2 NdCH(SiMe3)2 (Cp*=Z5-C5Me5) was converted into oily polyphenylsilane with a molecular weight (M) of 600 at 80 8C during two days.80 The dimeric hydride complex of lanthanocene [Cp2 LaH]2 is also an active catalyst of dehydrocondensation of phenylsi- V B Pukhnarevich,M G Voronkov, L I Kopylova lane.80, 81 In this case, a mixture of PhSiH2SiH2Ph and (PhSiH2)2- SiHPh was formed from PhSiH3. Cyclopentadienyl complexes of actinides also catalyse dehy- drocondensation of organylsilanes.Thus cyclopentadienyl deriv- atives of dimethyluranium and dimethylthorium converted phenylsilane into 1,2-diphenyldisilane (M=Th) or an oligomer (M=U) in 70% and 30% yields, respectively, even at room temperature during 6 h.82 Cp2 MMe2 H(PhSiH)nH+H2 n PhSiH3 M=U, Th. Dimethylmetallocenes, which are actinide derivatives, rank below isostructural titanocenes and zirconocenes in the catalytic activity.82 type Dehydrocondensation of silanes of the SiaHbR1c[R1=Alk, Ar, alkenyl, AlkO, Hal or NHR2; a52; b51; (b+c)=(2a+2)] occurs under an inert atmosphere in the presence of Cp2MR32 (M=Th or U).83 ± 85 2. Catalysis by compounds of Group IVB elements a. Catalysis by alkyl- and arylmetallocenes CpMR3, Cp2MR2 and Cp2MPh2 Dehydrocondensation of silanes, such as PhSiH3, MeSiH(OR)2 and HSi(OR)3, in the presence of dimethyltitanocene was first reported by Harrod and coworkers in 1984.86 The above-men- tioned silanes react with dimethyltitanocene in a hydrocarbon solvent or without a solvent at room temperature to give the titanium hydride complex and the corresponding disilane deriva- tives.4Cp2TiMe2+8R3SiH 2 [(Cp2TiH)2H]+R3SiSiR3+6R3SiMe+2CH4 Trialkyl- and triarylsilanes as well as chlorosilanes do not undergo dehydrocondensation even at 80 ± 120 8C.82, 86, 87 More recently, Harrod and coworkers published a series of studies 82, 88 ± 100 on dehydrocondensation of monosubstituted silanes (RSiH3, where R=Ph, Bn or C6H13), disubstituted silanes (R1R2SiH2 , where R1=R2=Ph or R1=Ph and R2=Bu), trialkoxysilanes (RO)3SiH (R=Me or Et), Me(EtO)2SiH and 1,3,5,7-tetramethylcyclotetrasilane catalysed by dialkyltitano- cenes Cp2MR2 (M=Ti or Zr; R=Me or Bn but not Ph).Later on, the series of catalysts of dehydrocondensation of silanes was substantially extended. It was demonstrated 82, 89 ± 91 that mono- (cyclopentadienyl)trialkyl and di(cyclopentadienyl)dialkyl deriv- atives of Group IVB metals (Ti, Zr and Hf) exhibit a high catalytic activity in this reaction. The most important advantage of the above catalysts over inorganic compounds,24, 29, 101 ± 107 complex and organometallic compounds 108, 109 is their ability to catalyse the formation of oligomers containing 10 ± 20 silicon atoms in the chains under rather mild conditions (Table.1). The catalytic activity of sterically hindered (cyclopentadien- yl)trimethyltitanium as well as of its zirconium analogue in dehydrocondensation of phenylsilane is low.82 Attempts to per- form dehydrocondensation of phenylsilane in the presence of Cp2HfMe2 at 20 or 90 8C (12 h) were unsuccessful. Generally, dehydrocondensation of silanes RSiH3 catalysed by dimethyltitanocene or dimethylzirconocene affords a mixture of linear and cyclic oligomers the ratio of which depends on the nature of the initial silane and the reaction conditions.92, 93, 112 (n+m)RSiH3 H(RSiH)nH+(RSiH)m+(n+m71)H2 Thus phenylsilane forms predominantly linear oligomers, whereas hexylsilane produces a mixture of linear and cyclic oligomers.In the presence of dimethyltitanocene, benzylsilane was converted predominantly into hexabenzylcyclohexasilane (the yield was*35%).92Dehydrocondensation of organylsilanes giving Si7Si bonds Table 1. Comparative catalytic activities of metallocenes of derivatives of Groups IV ± VII elements in dehydrocondensation of organylhydrosilanes RSiH3 and R2SiH2 . Catalyst R47nSiHn PhSiH3 (MeCp)2TiMe2 (MeCp)2ZrMe2 CpCp*TiMe2 [CpCp*ZrH2]2 [CpCp*ZrH2]2 CpCp*ZrMe2 CpCp*ZrMe2 CpCp*ZrMe2 Cp2TiMe2 Cp2TiPh2 Cp2TiPh2 Cp2TiPh2 Cp2Ti(OPh)2 Cp2Ti(OC6H4OMe-4)2 Cp2Ti(OC6H4Cl-4)2 Cp2Ti(OC6H4CN-4)2 Cp2Ti(OC6H4Me-4)2 Cp2TiMe2 Cp2Zr(OPh)2 CpCp*Zr[Si(SiMe3)3]Me CpCp*Zr[Si(SiMe3)3]Me CpCp*Zr[Si(SiMe3)3]Me Cp*(C5H4Me)Zr[Si(SiMe)3]3Me (Z5-C5H4SiMe3)2ZrMe2 Cp*(Z5-C6H4SiMe3)ZrH2 CpSiMe2CpZr[Si(SiMe3)3]Me CpSiMe2CpZr[Si(SiMe3)3]Me CpSiMe2CpZrMe2 CpSiMe2CpZrMe2 Cp2V Cp2VMe2 Cp2TiMe2 Cp2ZrMe2 Ph2SiH2 9,10-Dihydro-9-sila- anthracene (5a) 10,11-Dihydro-5H-di- Cp2ZrMe2 benzo[b, f ]silepine (5b) Ph2SiH2 Cp2TiPh2 Cp2TiPh2 Cp2TiPh2 Cp2Ti(OPh)2 Cp2TiPh2 MePhSiH2 Cp2TiPh2 Cp2TiPh2 a In the presence of a hydrogen acceptor; b the highest degree of polymerisation; c in the presence of cyclooctene; d 52% of unidentified oligomers; e in the presence of dec-1-ene.The reactivity of RSiH3 upon catalysis by dimethyltitanocene decreases in the following series (the relative reaction rates at 20 8C are given in parentheses): Ph (13)>Bn (1)=C6H13 (1).In the reactions catalysed by dimethylzirconocene, the reactivity changes in the following order: Ph (100)>Bn (15)>C6H13 (5).91 Zirconocenes catalyse dehydrocondensation of substituted phenylsilanes XC6H4SiH3 containing the fluoroalkyl, alkoxy, aryloxy, acyloxy, hydroxy or alkylamino groups in the benzene t /h T /8C 66 400.25 15 40 24 54 168 24 24 24 24 48 72 72 72 15 720.4 24 48 48 24 14 24 48 20 20 20 23 23 20 23 23 20 110 110 110 20 20 25 25 25 20 20 23 23 23 23 23 23 23 23 23 23 100 ± 120 3 48 40 100 ± 120 40 25 90 29 10 105 72 24 24 24 110 110 110 80 110 5 24 110 24 110 24ring.110 Thus a polymer with the molecular weight of 1330 was prepared from 4-(dimethylamino)phenylsilane.110 The only convenient procedure for the synthesis of polyme- thylsilane involves dehydrocondensation of methylsilane cata- lysed by dimethyltitanocene or dimethylzirconocene at 50 8C and 10 atm.92 The molecular weight of the resulting cross-linked polymethylsilane is rather high (*10 000).Disubstituted silanes, such as MeSiH2Ph and Ph2SiH2, are less reactive than RSiH3 . In the presence of dimethyltitanocene or Average molecular weight Yield (%) Reaction products Mn H(SiHPh)nH 7 7 82 2430 2300 1700 2340 H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)10Ha H(SiHPh)160Hb H(SiHPh)30Hb H(SiHPh)40Hb, c 730 620 620 H(SiHPh)nH 85 7 7 82 100 H(SiHPh)nH 80 7 7 82 48 48 7 7 82 48 48 110 49 49 49 110 110 110 110 110 110 110 48 48 48 48 48 48 48 48 48 48 82 11 14 100 7788 83 99 40 H(SiHPh)nH 25 7 H(SiHPh)nH 25 7 H(SiHPh)nH 30 7 H(SiHPh)nH 30 7 H(SiHPh)nH 30 7 H(SiHPh)nH 25 7 H(SiHPh)nH 10 7 1720 1990 2240 1560 1270 1660 1910 1730 1880 1570 777777777740 H(SiHPh)2H, H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)nH H(SiHPh)2H, H(SiHPh)3H 2040 H(SiHPh)3H 20100 12 87 20 d [Ph2SiH]4 dimer, trimer dimer [Ph2SiH]2 [Ph2SiH]2 [Ph2SiH]2 [Ph2SiH]2 e 72 66 e 72 c 10 (MePhSiH)2, 14 H(MePhSi)3H 32 (MePhSiH)2, 15 H(MePhSi)3H 23c (MePhSiH)2, 7 H(MePhSi)3H 88 139 Ref.Mw 8360 11 950 6100 8250 960 700 780 2400 3100 2200 2200 2300 2700 3200 4750 7660 10 150 6110 3080 8630 5090 5250 3770 3890 82 111 111 111 49 49 49 110494949140 dimethylzirconocene at 60 ± 80 8C, these silanes form predomi- nantly dimers and trimers, viz., RH2SiSiH2R and (R2SiH)2. .SiHR.91, 92 The catalytic activity of metallocenes Cp2MMe2 in this reaction decreases in the series Zr>Ti Hf.89, 91, 92 When zirconocene, which was prepared in situ by the reaction of Cp2ZrCl2 with BuLi, was used as a catalyst, methylphenylsilane was converted into the linear H(MePhSi)nH oligomer, where n=5 or 6.113 Unlike methylphenylsilane, butylmethylsilane 91, 92 as well as other silanesR3SiH (see Ref.42) remained unchanged in the presence of dimethyltitanocene or dimethylzirconocene even at 100 8C. Dehydrocondensation of dibenzosilaheterocycles 5a ± d was studied.112 (CH2)n R Si R H H R=H: n=1 (a), 2 (b), 0 (c); R=But, n=0 (d). 5a ± d Dehydrocondensation of 9,10-dihydro-9-silaanthracene 5a in the presence of dimethyltitanocene at 20 8C does not occur. In the reaction catalysed by dimethylzirconocene at 90 8C, the corre- sponding trimer is formed in high yield. Under analogous con- ditions in the presence of the same catalysts, 10,11-dihydro-5H- dibenzo[b, f ]silepine (5b) remains unchanged.Silafluorene (5c) is converted into a pentamer, which is insoluble in the usual organic solvents, upon catalysis by dimethyltitanocene in toluene in the absence of oxygen for 29 h. Titanium and zirconium complexes with the [2-(diisopropyl- 2]2MMe2 2]2TiBr2 and [Cp(CH2)2. 2]2Ti(OPh)2, were suggested as efficient catalysts of dehydro- amino)ethyl]cyclopentadienyl ligand, viz., [Cp(CH2)2NPri (M=Ti or Zr), [Cp(CH2)2NPri .NPri condensation of phenylsilane.114 Binary mixtures of dimethyltitanocene with one equivalent of trialkyl- or alkylarylphosphine are used as catalysts of dehydro- condensation of PhSiH3, MePhSiH2, Ph2SiH2 and BnSiH3.97 ± 99 In these cases, microcrystalline products are formed.Nakano and coworkers 49 succeeded in performing dehydro- condensation of triphenyl-, diphenyl- and methylphenylsilanes in the presence of Cp2TiPh2 (under an argon atmosphere, 110 8C, 24 h). In this case, 1,1,2,2-tetraphenyldisilane (72%) formed from diphenylsilane, whereas 1,2,3-trimethyl-1,2,3-triphenyltrisilane (32%) and 1,2-dimethyl-1,2-diphenyldisilane (14%) were obtained from methylphenylsilane. When cyclooctene was used as an acceptor of hydrogen, which was eliminated upon dehydro- condensation, the yield of trisilane was increased to 80%. Dehydrocondensation of phenylsilane under analogous condi- tions proceeds more readily to yield polyphenylsilanes containing terminal hydrogen atoms (M=340 ± 17 300). The reaction of phenylsilane in the presence of Cp2TiPh2 at 140 8C for 3 h afforded a cyclic six-membered silane.115 Under analogous con- ditions, triethylsilane generates hexaethyldisilane in insignificant yield (0.6%).Dehydrocondensation of 1,2-diphenyldisilane catalysed by dimethyltitanocene or dimethylzirconocene proceeds very rap- idly. Thus the H(PhSiH)4 tetramer was obtained in 40%yield after 30 min.91 Apparently, the presence of PhSiH3 and H(PhHSi)2. .SiH2Ph among the reaction products results from competitive disproportionation of the initial 1,2-diphenyldisilane PhSiH3+H(PhHSi)2SiH2Ph. 2 PhH2SiSiH2Ph The enhanced reactivity of 1,2-diphenyldisilane is determined by the lower energy of the Si7H bonds in the 7H2Si7SiH27 fragment compared to their energy in the SiH3 group.Dehydrocondensation of silanes of the SiaHbRc type [R=Alk, Ar, alkenyl, AlkO, Hal or NR2 ; a52; b51; (b+c)=(2a+2)] catalysed by dialkylmetallocenes Cp2MAlk2 (M = Ti, Zr or Hf) afforded liquid linear polymers containing from three to seven monomer units.83 ± 85 V B Pukhnarevich,M G Voronkov, L I Kopylova Dehydrocondensation of phenylsilane with 1,2-dimethyldisi- lane in the presence of Cp2MMe2 (M=Ti or Zr) yielded the H[(MeSiH)x(PhSiH)y]nH oligomer.116 The reaction of Me2HSiSiH2Me with 1,2-dimethyldisilane afforded the H[(MeSi)x(Me2Si)y]nH oligomer. The structures of these oligomers were established by GLC-mass spectrometry.116 b. Catalysis by alkoxy- and aryloxymetallocenes and titanium alkoxides Dehydrocondensation of phenyl-, diphenyl- and dibutylsilane catalysed by dialkoxy-, diphenoxytitanocene, its derivatives Cp2Ti(OR)2 (R=Alk, Ph, 4-MeC6H4, 4-MeOC6H4 , 4-ClC6H4 or 4-CNC6H4) or diphenoxyzirconocene Cp2Zr(OPh)2 was studied.117 ± 120 Dehydrocondensation of PhSiH3 afforded a mix- ture of linear and cyclic oligomers (15 min, 50 8C, the total yield was 25%).In this case, the reaction rate and the compositions of the resulting oligomers are comparable with those observed in the reactions with the use of Cp2TiMe2 (see Ref. 87) or the Cp2TiCl2 ± 2 BuLi binary mixture 113 as catalysts. In the presence of Cp2Ti(OPh)2 at 100 8C, diphenylsilane formed the Ph2SiHSiHPh2 dimer in 10% yield.111 In the presence of 5 mol.% of Cp2Ti(OPh)2 at 110 8C, dibutylsilane gave mono- and diphenoxy derivatives due to the interaction with the catalyst. Bu2SiH2+Cp2Ti(OPh)2 Bu2SiH(OPh)+Bu2Si(OPh)2+Bu2HSiSiHBu2+Cp2TiH2 For the reaction to start, preliminary heating of the reaction mixture is required. In this case, an induction period from 15 to 120 min was observed.Probably, the reduction of the Ti7OPh bonds in the catalyst to form an intermediate hydride complex occurs in one of the initial stages.119 Diphenoxytitanocene deriv- atives containing substituents in the benzene ring, viz., Cp2Ti(OC6H4X-4)2 (X=Me, Cl, CN or OMe), exhibit higher catalytic activity. In the presence of these complexes even at 20 8C, phenylsilane yielded products identical to those obtained at 50 8C in the presence of diphenoxytitanocene (see Table 1).119 Dehydrocondensation of diphenylsilane catalysed by diphen- oxyzirconocene occurs at 20 8C with elimination of hydrogen.However, an induction period was also observed and prior heating (50 8C, 15 min) of the reaction mixture is required. In this case, the amount of cyclic oligomers among the reaction products is smaller than that obtained with the use of diphenoxytitanocene.119 Dehydrocondensation of phenylsilane in the presence of dicyclopentadienylzirconium dimethoxide as a catalyst was reported.121 Dehydrocondensation of 1,4-disilapentane catalysed by diphenoxytitanocene was described.119 The rate of this reaction is smaller than that in the case of phenylsilane and is close to that observed with the use of dimethyltitanocene or the Cp2TiCl2 ± 2 BuLi system as catalysts.122 Initially, the catalyst was activated at 0 8C and then the reaction was performed at 20 8C.In this case, exclusively SiH3 groups reacted resulting in a linear oligomer containing the SiMeH2 fragments. This oligomer was converted into an insoluble cross-linked polymer upon heating.119 n MeSiH2CH2CH2SiH3 H(MeSiHCH2CH2SiH2)nH + (n71)H2 Alkoxy derivatives of titanium, which do not contain cyclo- pentadienyl ligands, such as Ti(OPri)4 or MeTi(OPri)3, were also used as catalysts of dehydrocondensation of alkyl- and arylsi- lanes.117 c. Catalysis by metallocene chlorides and the Cp2MHal2 ± RLi(RMgX) systems Metallocene dichlorides Cp2MCl2 are similar to Cp2MMe2 (M=Ti or Zr) in catalytic activity.90, 123 The activity of Cp2HfCl2 is substantially lower than that of Cp2HfMe2, but it can be enhanced by adding MeLi in a molecular ratio of 1 : 2.In this case, both chlorine atoms are apparently completely replaced byDehydrocondensation of organylsilanes giving Si7Si bonds the methyl groups. Dehydrocondensation of phenylsilane in the presence of a mixture of Cp2HfCl2 and MeLi afforded cyclo- phenylsilanes in 15% yield.90 When the reagents were taken in a ratio of 1 : 3 or 1 : 4, the yield of (PhSiH)n was only 25%; the molecular weights of the resulting phenylcyclosilanes were larger than those obtained with the use of dimethyltitanocene or dimethylzirconocene as a catalyst.90 When a mixture of [1,2- bis(tetrahydroindenyl)ethane]dichlorozirconium with MeLi taken in a ratio of 1 : 2 was used, cyclophenylsilanes were formed in 42% yield.123 Dehydrocondensation of phenylsilane catalysed by zircono- cene derivatives of the Cp2ZrX(Y) type (X=H or Cl and Y=Cl or Alk) yields stereoregular polyphenylsilane in good yields.124 ± 126 H H Ph H Ph Ph Si Si Si PhSiH3 7H2 Si Si H H Ph Ph n It was expected 90 that dehydrocondensation of phenylsilane catalysed by Zr complexes containing ethylenebis(tetrahydro- indenyl) or -indenyl ligands would also afford stereoregular polyphenylsilanes, unlike the reactions catalysed by biscyclopen- tadienyl complexes of Ti and Zr, which yield atactic polymers.According to the data of 1H NMR spectroscopy and gel-perme- ation chromatography, this reaction afforded a mixture of linear and cyclic oligomers, which hindered the interpretation of the microstructure of the resulting polymer.It should be remembered that, for example, nine stereoisomers of hexaphenylcyclohexa- silane possessing 23 chiral centres can exist.90 Dehydrocondensation of hydrosilanes RSiH3 (R=Bun, C6H13 or Ph) catalysed by the Cp2MCl2 ± 2 BuLi system (M=Ti, Zr or Hf) was studied in detail.127 ± 130 The course of the reaction was monitored by gas chromatography and GLC- mass spectrometry. Dehydrocondensation of phenylsilane afforded linear oligomers with M=1775 and 614 (Mw :Mn= 1.17 and 1.01, respectively, when Cp2ZrCl2 was used) and M=1308 and 600 (Mw :Mn=1.09 and 1.03, respectively, when Cp2TiCl was used).Therefore, the molecular weight of the dehydrocondensation products of phenylsilane is affected by the nature of the catalyst. The molecular weight increases in the series Hf Ti Zr, as in the case of the use of individual metal- locenes.82 Dehydrocondensation of diphenylsilane catalysed by the Cp2HfCl2 ± 2 BuLi system at 20 8Cfor 1 h yielded only 1,1,2,2- tetraphenyldisilane. When the temperature was increased to 50 8C, higher oligomers up to decaphenylpentasilane (the yield was 17%) were also obtained after 5 h. Under analogous con- ditions, butylsilane in the presence of the Cp2MCl2 ± 2 BuLi system (M=Ti or Zr) was converted into a mixture of linear and cyclic oligomers containing up to 11 silicon atoms.Two individual diastereomers of tetrabutyltetrasilane were isolated from this mixture. It is remarkable that the ratio of the diaster- eomers remained unchanged in the course of the reaction if M=Ti, whereas in the case of M=Zr, the diastereomers were formed at different rates. Hexylsilane in the presence of the Cp2ZrCl2 ± 2 BuLi system forms linear and cyclic tetra- and heptamers.127 Dehydrocondensation of R1R2SiH2 (R1=Ph and R2=Me; R1=R2=Ph; or R1=3-MeC6H4 and R2=Me) and dibenzosi- laheterocycles 5a,b,d in the presence of the Cp2MCl2 ± 2 BuLi system (M=Ti, Zr or Hf) was studied.113 In the case of dehy- drocondensation of MePhSiH2 (90 8C, 24 h), the activity of these catalysts increases in the series Hf< Ti<Zr. Linear oligomers containing from 2 to 8 silicon atoms are the major reaction products.At 20 ± 90 8C, more sterically hindered diphenylsilane yields only tetraphenyldisilane. Silafluorene (5d) reacted analo- gously to give (after 2 h) the corresponding disilane in 82% yield. Dehydrocondensation of 9,10-dihydro-9-silaanthracene (5a) in the presence of the binary catalyst proceeds substantially more slowly than the reaction with the use of dimethyltitanocene. 141 Dibenzosilepine (5b) remained unchanged at 90 8C in the presence of any catalytic system based on zirconium. The use of ethyl-, isopropyl- or butylmagnesium chlorides instead of BuLi (90 8C, 24 h, toluene) led to a substantial decrease in the propor- tion of tri- and tetramers. The binary Cp2ZrCl2 ± BuLi system is an efficient catalyst of dehydrocondensation of diorganylsilanes, but its use, unlike dimethyltitanocene, leads predominantly to the formation of short-chain oligomers.113 Syndiotactic polyphenylsilanes with highMw (>10 000) were prepared by dehydrocondensation of phenylsilane in the presence of a mixture of the zirconium complex {Cp*[Cp(CH2)n..NMe2]ZrCl2 (n=2 or 3) or Cp*[Cp(CH2)nCHMe2]ZrCl2 (n=1 or 2)} with two equivalents of BuLi.131, 132 The catalytic activity of pure dimethyltitanocene as well as of its mixture with butyllithium decreases substantially in the pres- ence of atmospheric oxygen.122 Dehydrocondensation of silanes [both symmetrical, viz., H(PhMeSi)2H and H(BuMeSi)2H, and unsymmetrical, viz., HPh2SiSiPhMeH, HPhMeSiSiMe2H, HPhMeSiSiPrMeH and HPh2SiSiPhH2] catalysed by the Cp2MCl2 ± 2 BuLi system (M= Ti or Zr) in the presence of cyclooctene was studied.133, 134 When the disilane : cyclooctene :Cp2MCl2 ratio was 30 : (>30) : 1, tri- silanes were rapidly formed from HPh2SiSiPhMeH and HPhMe..SiSiMe2H. The products were identified by GLC-mass spectrometry. Dehydrocondensation of HPh2SiSiPhH2 afforded Ph2SiH2 and PhSiH3, which were subsequently converted into a mixture of linear and cyclic polysilanes. These data indicate that dehydrocondensation is accompanied by the cleavage of the Si7Si bond in the initial disilane. Dehydrocondensation of RSiH3 and RH2SiSiH2R, where the R substituent is the Cp(CO)2Fe metallocene group, was per- formed in the presence of the Cp2MCl2 ± BuLi system (M=Ti or Zr).Dehydrocondensation of Cp(CO)2FeSiH3 and Cp(CO)2. .FeSiH2SiH2Fe(CO)2Cp gave organometallic oligosilanes charac- terised by spectroscopic and chromatographic methods.135 Dehydrocondensation of 2,4-disilapentane catalysed by the Cp2ZrCl2 ± 2 BuLi or Cp2TiCl2 ± 2 MeLi system afforded new poly(silacarbo)silanes containing the SiCH2Si fragments in the main chain.43, 128 a or b nMeH2SiCH2SiH2Me SiH(Me)CH2SiH(Me) n +H2 (a) Cp2ZrCl272 BuLi; (b) Cp2ZrCl272 MeLi. This reaction yielded predominantly oligomers (50% ± 80%), while di- and trimeric products were formed in insignificant amounts. The yields of oligomers depend substantially on the nature of the metal atom in the metallocene, the duration of the reaction and the concentration of the monomer.The Cp2ZrCl2 ± 2 BuLi catalytic system is more efficient than the Cp2TiCl2 ± 2 MeLi system (the yields of oligomers are 80% and 50%, respectively). The degree of condensation of these mono- mers is somewhat higher than that of PhMeSiH2; the resulting polymers are characterised by moderateMvalues, which indicates that they are partially cross-linked.86, 89, 113 The higher reactivity of 2,4-disilapentane compared to phenylmethylsilane is attribut- able to the favourable steric factors. d. Catalysis by the Cp2MCl2 ±Al system Dehydrocondensation of 3-arylpropylsilanes 6a ± g as well as of 2-phenyl-1,3-disilapropane [H3SiCH2CH(Ph)CH2SiH3, 7] cata- lysed by the Cp2MCl2 ±Al system (M=Ti or Hf) was per- formed.44, 45 7H2 H[ArCH(Me)CH2SiH2]nH 8a ± g ArCH(Me)CH2SiH3 6a ± g Ar=Ph (a), 4-MeC6H4 (b), 2,5-Me2C6H3 (c), ClC6H4 (d, mixture of isomers), 4-MeC6H3Cl (e, mixture of isomers), PhOC6H4 (f, mixture of isomers), C10H7 (g, mixture of isomers).142 Substituted polysilanes 8a ± g prepared from compounds 6a ± g have predominantly linear structures and molecular weights from 800 to 1028 (the degree of polymerisation is 3 ± 7, M=Hf) and from 800 to 1300 (the degree of polymerisation is 6 ± 16, M=Ti), i.e., the molecular weights are higher than those of the analogous polyarylalkylsilanes synthesised in the presence of other catalytic systems.42, 46 The catalytic activity of the Cp2HfCl2 ±Al system is lower than that of its titanium analogue (the yields of polysilanes are 31%± 84% and 79%± 99%, respec- tively).The reaction rate increases both as the concentration of the catalyst increases [from 0.5 mol.% to 10 mol.% (M=Ti) or from 1.0 mol.% to 6.5 mol.% (M=Hf )] and as the reaction temperature increases to 90 8C. Dehydrocondensation of com- pound 7 catalysed by the Cp2TiCl2 ±Al system proceeded smoothly and the total yield of polysilanes reached 90%.44 Two polymeric reaction products were isolated from the resulting mixture by column chromatography. One of these products is a viscous weakly cross-linked soluble polysilane (Mw=1046, Mn=819, n=11) and the second product is a completely cross- linked insoluble white solid polymer. Dehydrocondensation of organylsilanes 6b and 6d, 6b and 6f or 6d and 6f catalysed by the Cp2TiCl2 ±Al system afforded the corresponding cooligomers (the yields were 51%± 86%) with Mw=678 ± 994 andMn=405 ± 538 (the degree of copolymerisa- tion was 7).44 e.Catalysis by the ternary Cp2MCl2 ± RLi ± B(C6F5)3 system and by the cationic bis(cyclopentadienyl) complexes of zirconium and hafnium Dehydrocondensation of phenylsilanes in the presence of the ternary Cp2MCl2 (CpCp*MCl2) ± 2 BuLi ± B(C6F5)3 catalytic sys- tem (M=Ti, Zr or Hf) afforded polyphenylsilanes with M=10 910 ± 13 790.47, 95, 96 It is remarkable that when the reac- tion was performed in the presence of only B(C6F5)3 at 20 8C for 10 days, the molecular weight of the resulting polyphenylsilane reached only 2450.In both cases, the ratio between linear and cyclic polymers remained the same.47 The addition of B(C6F5)3 to the Cp2MCl2 ± BuLi catalytic system changes the ratio between the cyclic and linear dehydrocondensation products from 45 : 55 to 15 : 85. The catalytic activity of zirconocenes both in the presence of B(C6F5)3 and in its absence increases in the series Cp2 Zr Cp2Zr&(MeC5H4)2Zr<CpCp*Zr (cf. Ref. 136). The Cp2TiMe2 ± B(C6F5)3 and [Cp2ZrMe(THF)](BPh4) systems, which are successfully used for the polymerisation of alkenes,137 do not catalyse dehydrocondensation of phenylsilane.47 Dehydrocondensation of organylsilanes in the presence of the ternary catalytic system, which contains Group IVB metallocene, a trimethylsilyl derivative of alkali metal and THF, has been described.138 Thus a polymer with M=6800 was prepared from phenylsilane in the presence of the Cp2HfCl2±Me3SiLi ±THF system.Dehydrocondensation of phenylsilane in the presence of cationic bis(cyclopentadienyl) complexes of Zr and Hf was studied. These complexes were prepared in situ by the reactions of Cp2MMe2 (M=Zr or Hf) with [Bu3NH]+[B(3,5- Me2C6H3)4]7 or [PhMe2NH]+[B(C6F5)4]7.48 The activity of these catalysts appeared to be low. The total yield of cyclo- phenylsilanes at 23 8C is no higher than 13%. Dehydro- condensation with the use of the CpCp*ZrMe2 ± [Bu3NH]+. .[B(3,5-Me2C6H3)4]7 system as a catalyst (23 8C, 1 h) affords linear and cyclic polyphenylsilanes with rather low M values (up to 2810).In this case, variations in the anion and the metal atom in the metallocene (Zr or Hf) have no substantial effect on the course of the process.48 f. Catalysis by metallocenes containing organosilicon groups at the metal atom Metallocenes (Ti, Zr or Hf) containing organosilicon groups at the metal atom were also suggested as catalysts of dehydrocon- V B Pukhnarevich,M G Voronkov, L I Kopylova densation of organosilanes. In the presence of these catalysts, di- and trisubstituted silanes form linear (at 460 8C) or cyclic (at 580 8C) polysilanes.48, 65, 91, 94, 100, 139 ± 147 For example, dehydro- condensation of phenylsilane catalysed by Cp2Ti(CH2SiMe3)2 afforded linear polysilane (92%, M=1890) and cyclic oligophe- nylsilane (95%, M=738) at 30 8C (24 h) and 80 8C, respec- tively.139 Dehydrocondensation of arylsilanes RC6H4SiH3 (R=H, 4-Me, 3-Me, 2-Me, 4-CF3, 3-CF3 or 2-CF3) in the presence of Cp2Zr[Si(SiMe3)3]Me yielded poly(trifluoromethylphenyl)-, poly(methylphenyl)silanes and polyphenylsilane.65 In the de- hydrocondensation process, the reactivity of RC6H4SiH3 decreases depending on the radical R in the series (the relative reaction rates are given in parentheses) 4-CF3 (1.34)&3-CF3 (0.95)&3-Me (1.33)>H (0.93) 2-Me (1.00)>4-Me (0.18)&2-CF3 (0.14).These data indicate that the reaction rate is influenced both by the electronic and steric effects of the substituents in the aromatic core. 2-Substituted phenylsilanes exhibit the lowest activities.The molecular weights of poly(tri- fluoromethyl)phenylsilanes and polyphenylsilanes obtained under analogous conditions are much the same. Silyl complexes of zirconocene and hafnocene of the CpCp0M(SiR13 )R2 type (Cp0=Cp or Cp*; M=Zr or Hf; R1= Me, Ph or SiMe3; R2=Alk, SiMe3 or Cl) are also efficient catalysts of dehydrocondensation of arylsilanes. In these cases, the molecular weights of linear and cyclic polymers vary over wide ranges depending on the nature of the catalyst and the reaction conditions.48, 140 ± 142 Phenylsilane in the presence of Cp2Zr[Si(SiMe3)3]Me or Cp2Zr[Si(SiMe3)3]Cl formed polymers with M=990 and poly- mers with M=1240 containing from 10 to 20 SiHPh monomer units after 15 min and 7 h, respectively.Phenylcyclosilane (con- taining from 5 to 8 silicon atoms) was identified among these polymers.14, 48 It should be noted that polyphenylsilane with Mn=560 was obtained upon catalysis by dimethylzirconocene during 24 h. Zirconocenes with mixed cyclopentadienyl ligands (nonsubstituted or partially or completely methylated) appeared to be more active catalysts in these reactions. The molecular weight of the linear polymer H(PhHSi)nH formed in the presence of CpCp*Zr[Si(SiMe3)3]Me reached 3000 and 5260 after 15 min and 48 h, respectively. Linear and cyclic polymers contain about 70 silicon atoms in the polysilane chains (see Table 1).48 Dehydrocondensation of methylphenyl- and diphenylsilanes catalysed by alkyne zirconocene and titanocene complexes of the Cp2M(L)(RC:CSiMe3) type (M=Ti or Zr; L=THF or Py) affords oligomers. Under these conditions, phenylsilane forms polymers.148, 149 The catalytic activities of the zirconium and titanium com- plexes, viz., (Z5-C5H4SiMe3)2Zr[Si(SiMe3)3]Cl (9) and Cp2Ti[Si..(SiMe3)3]Cl (10), respectively, in dehydrocondensation of phenylsilane and dibutylstannane were studied.143 According to the data of GLC-mass spectrometry, a viscous mixture of linear H(PhHSi)nH and cyclic (PhSiH)n (n=5 or 6) oligomers (Mn= 900,Mw=1810) was formed from phenylsilane in the presence of the complex 9 after 24 h. Under analogous conditions, a mixture of linear and cyclic polysilanes with Mn=1870 and Mw=3280 was formed upon catalysis by the CpCp*Zr[Si(SiMe3)3]Cl com- plex, which does not contain the trimethylsilyl group in the cyclopentadienyl ring. Dehydrocondensation of dibutylstannane in the presence of the complex 9 affords polybutylstannanes with a broad molecular weight distribution spectrum (Mw=4800, Mn=1420).The reaction of the complex 10 with an equivalent amount of phenylsilane in C6D6 gave a mixture of the metathesis product 11 and the reductive elimination product 12 in a ratio of 2 : 1 in quantitative yield.143 HSi(SnMe3)3+ClSi(SnMe3)3 12 Cp2Ti[Si(SnMe3)3]Cl+PhSiH3 10 11 Dehydrocondensation of 1,4-RH2SiC6H4SiH2R (R=Me, Et or C6H13) catalysed by CpCp*Zr[Si(SiMe3)3]Me under mildDehydrocondensation of organylsilanes giving Si7Si bonds conditions (20 8C) afforded linear oligomers RH2Si(C6H4SiHR..SiHR)nC6H4SiH2R.150 Further heating of the resulting mixture of oligomers (R=Me or Et) led to an increase in the molecular weight due to partial cross-linking of the polymer chains through free Si7H groups. Thermolysis of the insoluble cross-linked polymer EtH2Si(C6H4SiHEtSiHEt)nC6H4SiH2Et at 1100 8C afforded ceramics in higher yield (67%) than that with the use of the corresponding low-molecular-weight oligomers (35%).150 It was reported that the Cp2Zr(OMe)2 ± (Me3Si)3SiLi ± 3THF ternary system was used as a catalyst of dehydrocondensation of phenylsilane.121 g. Catalysis by ansa-metallocenes Dehydrocondensation of phenyl- and methylphenylsilane cata- lysed by ansa-metallocenes (13a ± f ),144, 145, 151, 152 which are used for the preparation of iso- and syndiotactic polypropylenes, was studied.153, 154 MCl2 Me2E E=Si:M=Ti (a), Zr (b), Hf (c); E=C:M=Ti (d), Zr (e), Hf (f ).13a ± f Methylphenylsilane in the presence of ansa-metallocenes with a BuLi cocatalyst (the ratio is 22 : 1 : 2) in toluene at 90 8C formed low-molecular-weight oligomers, viz., the corresponding di-, tri- and tetrasilanes. In this case, tetramers existed in the reaction mixture in insignificant amounts (1.8% ± 5.5% according to the GLC data). In the presence of ansa-hafnocene, tetrasilane is not formed at all. The activity of ansa-metallocenes, which was estimated from the yield of disilane after 24 h, decreases in the series Ti>Hf>Zr. 13d 13f 13e 25 13c 13b 22 13a 36 37 58 30 Catalyst Yield of disilane according to GLC (%) The activity of metallocene dichlorides in dehydrocondensa- tion of methylphenylsilane decreases in the series Hf (37)>Ti (32)>Zr (15) (the yields of disilane according to the GLC data are given in parentheses).1,2-Dimethyl-1,2-diphenyldisilane and 1,2,3-trimethyl-1,2,3-triphenyltrisilane prepared from methylphe- nylsilane exist as mixtures of diastereomers. Dehydrocondensa- tion of phenylsilane catalysed by ansa-metallocenes (Ti, Zr or Hf) in the absence of a solvent affords a mixture of linear and cyclic polyphenylsilanes. In this case, the molecular weight of the linear polymer increases in the series Ti<Zr<Hf.144 Under analogous conditions (the silane : complex : BuLi ratio is 24 : 1 : 2, 13 ± 24 h, 20 8C), the molecular weight of polyphenylsilanes prepared in the absence of ansa-metallocenes is always lower than that obtained with the use of usual metallocenes.e. Catalysis by binuclear titanium and zirconium complexes Dehydrocondensation of phenyl-, benzyl-, hexyl- and diphenylsi- lanes catalysed by the binuclear titanium complexes Cp2Ti(m- HSiHPh)2TiCp2 and Cp2Ti(m-H)(m-HSiHPh)TiCp2 generally affords oligomers.100 Alkenes, the activating action of which increases in the series cyclohexene < 2-pentene < 1-pentene * norbornene * styrene, are used as cocatalysts, which substan- tially enhance the rate of this reaction. It was reported 146 that binuclear titanocene complexes can be used as catalysts of dehydrocondensation of phenylsilane, for example CpTiCl2CpSi(Me)(R)CpTiCl2Cp (R=H, Me, Ph), CpTiCl2CpSiMe2(CH2)nSiMe2CpTiCl2Cp, 143 Me2Si CpTiCl2 (a mixture of cis and trans isomers) Cp2TiCl2Cp Si(Me)R These reactions give mixtures of linear and cyclic polyphenylsi- lanes;146 BuLi is used as a cocatalyst.3. Catalysis by compounds of Group VB± VIIB elements The data on the use of compounds of Group VB± VIIB metals as catalysts of dehydrocondensation of organylsilanes are scarce. Vanadocene Cp2V and dimethylvanadocene Cp2VMe2 do not catalyse this reaction at 20 8C.82 However, phenylsilane in boiling toluene in the presence of these compounds was converted into a mixture of the PhH2SiSiH2Ph dimer (40%) and the (PhSiH2)2..SiHPh trimer (20%). Under analogous conditions (100 ± 120 8C, 123 h), higher metallocenes Cp2M (M=Nb or Ta) do not catalyse dehydrocondensation of phenylsilane. Neither at high temperature (115 ± 120 8C) nor upon UV irradiation is this reaction catalysed by hydride complexes of niobium or tantalum Cp2MH3 (M=Nb or Ta),82 whereas phenylsilane actively under- goes dimerisation in the presence of trimethylsilyl derivatives of tantalocene Cp*Ta(SiMe3)Cl3. In this case, reduction products of the catalyst, viz., trimethylsilane and the tantalum hydride com- plex [Cp*TaHCl3]n , are formed along with 1,2-diphenyldisilane.46 Cyclopentadienyl complexes of chromium, molybdenum and tungsten, viz., Cp2Cr, Cp2MoH2 and Cp2WH2, do not catalyse dehydrocondensation of PhSiH3 at room temperature as well as under irradiation.82 Cyclopentadienyl chromium complexes, such as (Z6-H3SiC6H5)Cr(CO)3, act as catalysts of dehydrocon- densation of silanes.In this case, the corresponding polysilanes containing chromium carbonyls in the side chain are formed.155 Some binary carbonyl complexes of manganese catalyse dehydrocondensation of phenylsilane at 100 8C.68 4. Catalysis by compounds of Group VIIIB elements The use of platinum complexes as catalysts of dehydro- condensation of pentamethyldisilane and symmetrical tetra- methyldisilane was reported for the first time in 1970.156 Later on, these reactions were described as disproportionations cata- lysed by phosphine complexes of platinum metals.157 It was found that penta- and tetramethyldisilanes were con- verted into the (Me3SiSiMe2)2 dimer or a mixture of H(Me2Si..SiMe2)nH oligomers (n=2 ± 6), respectively, in the presence of platinum bis(triethylphosphine) dichloride at 90 8C (18 h).156 ± 158 cat R(Me2Si)nH RMe2SiSiMe2H R=H, Me; n=2 ± 6; cat=trans-[PtCl2(PEt3)2], [NiCl2(PEt3)2] etc. of complex platinum ethylenebisphosphine The [C2H4Pt(PPh3)2] at room temperature does not induce dehydro- condensation of silanes, such as Ph3SiH, Me2PhSiH, Et3SiH and (EtO)3SiH.109, 112 However, MePhSiH2 and Et2SiH2 in the pres- ence of this complex were converted into the corresponding dimers in 27% and 95% yields, respectively.109 It is remarkable that in the case of Et2SiH2, dehydrocondensation occurs more readily than hydrosilylation of 1-hexene.In attempting to perform hydrosilylation of 1-hexene with a mixture of Et3SiH and Et2SiH2, only dehydrocondensation products Et2HSiSiHEt2 and Et2HSi ± SiEt3 were obtained in a ratio 7 : 1. In this case, hexaethyldisilane was not formed. The dehydrocondensation product, viz., tetra- ethyldisilane, was also not detected upon hydrosilylation of 1-hexene with diethyldisilane in the presence of H2PtCl6 (Spier's catalyst) or Ph2PtCl2.109 Dehydrocondensation of acyclic and cyclic disubstituted silanes R1R2SiH2 [R1 and R2=Alk, (CH2)n (n=3 ± 5) or 1,2-C6H4] catalysed by the Pt(COD)2 or Me2Pt(COD) complexes affords polysilanes with high molecular weights (Mw up to 40 000; Mn up to 39 000) in 60% ±95% yields.159 Dehydrocondensation of dimethylphenylsilane in the pres- ence of platinum complexes with different phosphine ligands was144 studied.160 Their catalytic activities are rather low.The exception is the Pt(PPhMe2)4 complex in the presence of which the yield of 1,1,2,2-tetramethyl-1,2-diphenyldisilane reaches 50%. Methyldi- phenylsilane in the presence of Pt(PPhMe2)4 forms 1,2-dimethyl- tetraphenyldisilane in low yield.160 Platinum black as well as PtO2, H2PtCl6 .6H2O and (PhCN)2PtCl2 do not catalyse dehy- drocondensation of dimethylphenylsilane.160 A procedure for the dehydrocondensation of substituted oligosilanes of the general formula Ha SibRc [R=Alk, Ar, alkenyl, AlkO, Hal or R2N; a51; b52; (a+c)=(2b+2)] in the presence of dialkyldicyclopentadienyl Pt or Rh complexes was covered by a patent.83 In 1973, (Ph3P)3RhCl (Wilkinson's complex) was suggested as a catalyst of dehydrocondensation of hydrosilanes.108 In its presence, methylphenylsilane was converted into a mixture of 1,2-dimethyl-1,2-diphenyldisilane (14%) and 1,2,3-trimethyl- 1,2,3-triphenyltrisilane (30%) at 70 8C for 1 h.Under analogous conditions, 1,1,2,2-tetraphenyldisilane was formed from diphe- nylsilane in 38% yield. 1,2-Diphenylsilane and 1,2,3-triphenyltri- silane were obtained from phenylsilane. 1,1,2,2-Tetraethyldisilane and 1,1,2,2,3,3-hexaethyltrisilane were obtained from diethylsi- lane. Dehydrocondensation of dibenzosilaheterocycles 5a ± d in the presence of (Ph3P)3RhCl proceeds according to the following scheme 108, 112, 161 H Si H SiH2 m m=2, 3.The drawback of Wilkinson's catalyst is the fact that it promotes oxidation of Si7Si bonds to Si7O7Si groups when the reaction is performed in air.109, 113 The possible reaction mechanism involves the formation of the silylene rhodium(II) complex 14 as an intermediate, which appears as a result of b-elimination of the hydrogen molecule from the rhodium(I) complex 15. [Rh] R2SiH2 7H2 R2SiH [Rh]H 15R2SiH2 R2HSiSiHR2 7[Rh] R2Si [Rh] 14 The results of dehydrocondensation of disubstituted silanes in the presence of (Ph3P)3RhCl are given in Table 2.112 The con- version of R2SiH2 decreases in the series 5c,d (100%)>5a (83%)>Ph2SiH2 (59%)>5b (10%).113 The addition of cyclo- hexene as an acceptor of hydrogen does not affect the activity of silanes.In attempting to perform dehydrocondensation of di- hydrosilaanthracene (5a) in the presence of the [Rh(COD)(PPh3)2]PF6 complex (37 8C, 25 h), only the corres- ponding disiloxane was isolated in 33% yield.112 Dehydrocondensation of methylphenylsilane catalysed by different rhodium complexes has been studied. In these reactions, a dimer and a trimer were obtained as by-products (Table 3).50 Table 2. Dehydrocondensation of diorganylsilanes in the presence of Wilkinson's catalyst (0.4 mol. %, 10 h, 25 8C).112 Yield of the reaction products (%) R2SiH2 trimer dimer R2SiH2 other products disil- oxane 11% (Ph3SiH) 3 42 48 38 10 41 17 90 oligomer oligomer Ph2SiH2 5a 5b 5c 5d V B Pukhnarevich,M G Voronkov, L I Kopylova Table 3.Dehydrocondensation of methylphenylsilane in the presence of rhodium complexes (0.1 mol. %).50 Catalysts t /h T /8C Yield (%) Cocatal- yst MePhSiH2 di- tri- mer mer RhCl(PPh3)3 PPh3 RhH(PPh3)4 PPh3 PPh2Me 16.3 3.9 15.4 6.9 14.3 4.0 10.3 4.1 16.7 3.7 3.3 0 25.8 8.8 65.5 29.3 58.5 29.3 19.2 69.0 31.2 100 1 80 1.5 90 2 100 2 100 2 100 2 100 2 Rh2(OAc)4 [RhCl4(H2O)2]7X+ (see a) aX=NH(C8H13)3 . Dehydrocondensation of diphenylsilane catalysed by carbene rhodium complexes (20 8C, 18 h) afforded predominantly 1,1,2,2- tetraphenyldisilane.162 The reaction was monitored by GLC.It was demonstrated that the disilane Ph2HSiSiHPh2, which was initially formed, was then oxidised by atmospheric oxygen to the corresponding disiloxane. L12 L2RhCl, O2 L12 L2RhCl, N2 Ph2SiH2 Ph2HSiSiHPh2 Ph2HSiOSiHPh2 MeN L1=COD, L2= MeN Hydrosilylation with diethylsilane catalysed by complexes of Group VIII metals involves the dimerisation of diethylsilane as a competitive process. The relative rate constants of dehydrocon- densation of diethylsilane (18 8C, 75 h) depending on the catalyst were determined.109 These constants change in the following order (krel are given in parentheses): (Ph3P)3RhCl (31)>[Pd(Z3-C3H5)Cl2] (12)>[Rh(CO)2Cl]2 (5)> >(Ph3P)2Pt(C2H4) (1)*[Rh(COD)Cl]2 (1)>Pt(COD)Cl2 (0.7)> >RhCl3 (0.3)>CpRh(C2H4) (0.2)*[Ir(COD)Cl]2 (0.2)> >H2PtCl6 (0.1)*(Ph3P)2PtCl2 (0.1).The reactivity of silanes in dehydrocondensation decreases in the series RSiH3>R2SiH2 R3SiH. Dimethylphenylsilane in the presence of platinum complexes undergoes only dimerisation. Dehydrocondensation of compounds of the A(SiH3)2 type [A=CH2, Alk(CH2)n, Me3Si(CH2)n (n=2±7) or Me3Si(CH2)m (m=3 ± 8)] catalysed by HRh(CO)(PPh3)3 was studied. The reactions afforded polysilanes, which were further converted into silicon carbide.163 Dehydrocondensation of 1,4-bis(trihydrosilyl)benzene in the presence of RuCl2[P(C6H4Me-4)3]3 afforded a white polymer (M=1170) containing alternating SiH2C6H4 groups.164, 165 5. Reaction mechanism Dehydrocondensation of organylsilanes is a promising procedure for the formation of Si7Si bonds.This procedure is suitable for the preparation of polyorganylsilanes with the controlled chain length. However, the majority of the published studies generally dealt with the preparative aspects of this reaction. The difference in the reaction conditions and sometimes the contradictory results do not allow one to propose the mechanism of catalytic dehydro- condensation of organylhydrosilanes with assurance. Presently, three rather justified schemes of the process pro- ceeding in stages are available. These schemes are interrelated and complement each other. 1. Harrod's mechanism involves oxidative addition of organ- ylsilanes to complex-forming metal followed by a-elimination ofDehydrocondensation of organylsilanes giving Si7Si bonds the RH molecule (R=Alk or Ar) to form a silylene complex of the Cp2M=SiHR type (M=Ti or Zr) as an active catalytic intermediate. The latter forms polyorganylsilanes through a series of successive conversions with the participation of organylsilane.2. Tilley's mechanism is based on the metathesis of the s-bond. The reaction proceeds through a four-centre transition state containing the M7H, M7Si, Si7H and Si7Si bonds followed by the metathesis of the M7Si s-bond and the for- mation of dehydrocondensation products H(SiHR)nH. 3. Hengge's mechanism involves silylene Me2Si:, which is formed in a four-centre transition state according to a b-elimi- nation reaction of a new type, as an active catalytic intermediate.Dimethylsilylene is then inserted into the Si7Hor Si7Si bonds to form linear or branched oligomers, respectively. Let us consider these mechanisms in more detail. Harrod and coworkers 68, 87, 89, 93 suggested two schemes of the dehydrocondensation mechanism for organylsilanes (Scheme 2). One of the schemes 87 assumes that the bridging hydride complex 16 is formed as an active catalytic intermediate. This scheme involves oxidative addition of silane to metallocene to form the complex 17 followed by a-elimination of MeRSiH2. The resulting Cp2Ti reacts with silane to give the complex 16, which accomplishes the chain growth (Scheme 2, pathway a). Scheme 2 Pathway a Me Cp2M Cp2TiMe2+RSiH3 7MeRSiH2 7CH4 17 SiH2R H Cp2Ti RSiH3 Cp2Ti Cp2Ti 7Cp2Ti SiH2R H H RSiH3 2Cp2Ti TiCp2 Cp2Ti SiH(R)SiH2R SiHR 16 Pathway b H RSiH3 17 Cp2M Cp2M SiHR 7CH4 7H2 20 18 SiH(R)SiH2R H R RSiH3 Si Cp2M Cp2M19 Si(R)(SiH2R)2 SiH2R H Cp2M SiH(R)SiH(R)SiH2R 7H2 R RSiH3 Si etc.Cp2M SiH(R)SiH2R However, the high catalytic activity of possible intermediates of dehydrocondensation, viz., the Ti and Zr complexes of type 17 containing m-H and m-Si bonds, was not confirmed.87, 89, 91, 94 ,100 Later on, Harrod and coworkers93 suggested that the silylene complexes 18 and 19 are intermediates in dehydrocondensation. The complex 19 can be formed upon elimination of hydrogen from the hydride complex 20. The chain growth occurs through the repeated insertion of the newly formed silylene complex into the M7Si bond (Scheme 2, pathway b).This scheme adequately describes the formation of the linear polyphenylsilanes H(PhSiH)nH and H(Ph2Si)2H from PhSiH3 and Ph2SiH2, respec- tively. The formation of cyclic products upon dehydrocondensation of PhSiH3 and PhCH2SiH3 in the presence of dimethyltitanocene or dimethylzirconocene proceeds through the intermolecular metathesis of the terminal SiH2 group and the M7Si bond of the growing terminus of the chain.68 This process is most probable when the chain contains six Si atoms. 145 SiHR RHSi Cp2(H)MSi(R)HSiRH SiHR RHSi H2SiR 7Cp2MH2 SiRH Si(R)HSiRH SiHR RHSi M=Ti, Zr. The second pathway, which involves the cleavage of the Si7Si bond by a particular reactive intermediate and intermolecular metathesis, is also possible.Cp2(H)MSi(R)HSiRH H ( HSiR )n H(R)Si SiRH Si(R)HSiRH SiHR RHSi H Cp2M SiHR RHSi + (SiHR)nH SiHR RHSi M=Ti, Zr. The scheme proposed by Harrod does not explain why only tetraorganyldisilanes rather than higher oligomers are formed from diorganyldisilane. An alternative reaction mechanism was proposed 112 to account for the formation of cyclic oligomers, for example, of 1,2,3-triphenyltrisilane from Ph2SiH2 in the presence of titanocene or zirconocene complexes. This mechanism involves either dehy- drocondensation of Ph2SiH2 with the resulting Ph2SiHSiHPh2 (which is formed, probably, through a silylene complex) or disproportionation of 1,1,2,2-tetraphenyldisilane.However, it was established 161 that the dimeric product of dehydrocondensation of 9,10-dihydro-9-silaanthracene in the presence of Wilkinson's catalyst formed the corresponding trimer only in 7% yield, i.e., disproportionation is not the major process. Silylene complexes of type 18 or 19 are very attractive compounds for explaining the mechanism of dehydrocondensa- tion of silanes. These compounds have been extensively studied in the last decade.166 Base-stabilised silylene complexes of transition metals, which are used in different catalytic (hydrosilylation 108) and photochemical 167 reactions, are known. Nevertheless, it is believed 46 that silylene metal complexes cannot be intermediates of dehydrocondensation for two reasons.First, during catalytic dehydrocondensation of organylsilanes, complexes of the CpCp*M[Si(SiMe3)3]Cl type are quantitatively converted into the corresponding polymeric complexes [CpCp*MHCl]n.142 Only one s-bond of complex-forming metal is used in the course of dehydrocondensation. At the same time, the participation of at least two s-bonds is necessary for the formation of the silylene complex followed by its reaction. Second, the formation of silylene complexes through a-elimina- tion of the RH molecule should result in complexes of the M(SiHR1R2)R3 type (R1, R2 and R3=H or Alk). Several mixed alkylsilyl complexes containing Si7H bonds were isolated. How- ever, the latter do not undergo decomposition with a-elimination of substituents at the silicon atom.Only one instance where decomposition proceeds through a-elimination of the hydrogen atom from the alkyl group at the silicon atom is known.168 This reaction afforded dimesitylsilane in quantitative yield along with an unidentified zirconium-containing compound. Methane was not detected among the reaction products. decomposition Cp2 Zr(Me)SiHMes2 7Mes2SiH2 [Cp2 Zr CH2] Tilley 136 suggested an alternative mechanism of dehydrocon- densation of organylsilanes, which was called the metathesis of the s-bond. This mechanism was confirmed by the kinetic data obtained by monitoring the process by 1H NMR spectroscopy in C6D6.46, 48, 142, 169 In this case, the cyclopentadienyl tris(trimethyl- silyl) hafnium complex 21, which exhibits lower reactivity and higher stability compared to the isostructural titanium and zirconium complexes, was used as a catalyst.146 CpCp*Hf[Si(SiMe3)3]Cl+PhSiH3 21 CpCp*Hf(SiH2Ph)Cl+HSi(SiMe3)3 These authors also synthesised and studied the behaviour of other silylated cyclopentadienyl hafnium complexes, viz., CpCp*Hf(SiHR1R2)Cl (R1=H and R2=Ph, 4-MeC6H4 , Mes, Bn or cyclo-C6H11; R1=R2=Ph; or R1=Me and R2=Ph), in dehydrocondensation of PhSiH3.141, 170 The general second order of the reaction, first order with respect both to the catalyst and the organylsilane, were established. The activation parameters of the process (DH6à=68.5 kJ mol71, DS 6à=727 kJ mol71 K71) and the kinetic isotopic effect (kH/kD=2.5) correspond to the values observed for the reactions of hydrocarbons proceeding through the metathesis of the s-bond.170, 171 d+ d7 6à R2 H LnMR2+HR1 LnMR1+HR2 R1 LnM d7 d+ R1, R2=H, Alk, Ar; LnM=Cp2 Sc, Cp2 Y, Cp2 Lu, [(Me3Si)2N]3U, etc.The kinetics of thermal decomposition of CpCp*. .Hf(SiH2Ph)Cl, which obeys a second-order equation with DH6à=81.5 kJ mol71 and S 6à=721 kJ mol71 K71, was studied.142 The four-centre transition state A was suggested for the dehydrocondensation process. 6à Si(M)PhH H 2 HfSiH2Ph HfSiH2Ph 7HfH Hf SiH2Ph A HfSiH2Ph Hf(SiHPh)2SiH2Ph, etc. HfSi(Ph)HSiH2Ph 7HfH Decomposition of the hafnium complex was performed in the presence of efficient traps of silylene, such as Et3SiH, (cyclo- C6H11)3SiH, Ph2SiH2 or MePhSiH2, which had no effect on the reaction rate.It is suggested that a hydride complex, which reacts predominantly with the sterically most accessible terminal SiH2R group of the polysilane chain, is an active catalytic species in the reaction. This leads to the appearance of the polysilyl group in the coordination sphere about the metal atom. The formation of the Si7Si bonds (chain growth) occurs through the two-stage meta- thesis of the s-bond via the four-centre transition states B and C.142 L2MH H(SiHR)m(SiHR)nH H(SiHR)nH H R 6à 6à H R H Si(SiHR)m71H H H(SiHR)n71Si L2M Si(SiHR)n71H L2M H R H C B H(SiHR)mH 7H2 L2M(SiHR)nH Slow oligomerisation of phenylsilane catalysed by CpCp*..Hf(SiH2Ph)Cl was used as a model reaction. In this process, intermediates of dehydrocondensation, for example, CpCp*Hf(SiHPhSiH2Ph)Cl, were identified. This complex was prepared by independent synthesis from CpCp*Hf[Si(SiMe3)3]Cl as two diastereomers, which were detected in the course of the reaction by 1H NMR spectroscopy. The addition of two equiv- alents of phenylsilane to CpCp*Hf(SiH2Ph)Cl afforded (after V B Pukhnarevich,M G Voronkov, L I Kopylova (33%) and a mixture 24 h) of [CpCp*HfHCl]n CpCp*Hf[SiH(Ph)SiH2Ph]Cl, PhH2SiSiH2Ph and PhH2Si ± SiH(Ph)SiH2Ph in a ratio of 3 : 2 : 3. Dehydrocondensation of PhSiH3 catalysed by Cp*HfH2 afforded also free oligophenylsi- lanes. Due to steric hindrance, this hafnium hydride reacts with the Si7Hbond very slowly, which makes it possible to observe the conversion of phenylsilane into 1,2-diphenyldisilane.The latter is even more slowly converted into 1,2,3-triphenyltrisilane, and apparently, finally into 1,2,3,4-tetraphenyltetrasilane. The corre- lation between the concentration of the silane and the reaction time indicates that the cleavage of the Si7Si bond is an important stage of the process. Within the framework of this mechanism, the formation of cyclic oligomers is attributed to the intramolecular metathesis of R(RSiH)nH, where n=5 (Scheme 3).127 The meta- thesis with the participation of the terminal Si7H (pathway a) or Si7Si (pathway b) bonds affords five- or six-membered rings. The metathesis with the participation of the exocyclic Si7H bonds (pathway c) can lead to rings containing organosilicon substitu- ents.Scheme 3 Si Si Si Si Si M Si a 7MH Si Si Si H Si Si Si Si Si Si Si M b Si Si H M Si 6 HSi Si Si MSiH Si Si Si Si Si Si M c SiSiH Si 7MH Si Si H Si Si SiH The suggested multistage mechanism of dehydrocondensation of organylsilanes can serve as the basis for the design of new catalysts, viz., coordinatively unsaturated electrophilic metal hydride complexes, which can participate in the concerted process of metathesis of the s-bond. The proposed mechanism explains many aspects of dehydro- condensation, including steric requirements imposed on the catalyst and the substrate as well as the formation of rather short polymer chains.However, this mechanism inadequately explains the difference in the behaviour of, on the one hand, the silyl complexes of zirconium and hafnium and, on the other hand, of the titanium complexes. The mechanism of metathesis of the s-bond was also used for the explanation of the regularities of other dehydrocondensation reactions, viz., the reaction of RSiH3 catalysed by the Cp2MCl2 ± 2BuLi binary system or Cp2MMe2,129 the reaction of R1R2SiH2 in the presence of Wilkinson's complex 112 and the reaction of 2,4-disilapentane in the presence of titanocene or zirconocene.43 Hengge and Weinberger 172 suggested yet another mechanism of dehydrocondensation of organylsilanes in the presence of dimethylzirconocene with the use of autocondensation of 1,2,3- trimethyltrisilane and a mixture of diastereomers of 1,2,3,4- tetramethyltetrasilane as a model reaction.The conversions of these oligomers cannot be explained in the context of Harrod's mechanism 87, 89 because a-elimination should be accompanied by evolution of CH4. Dimethylsilylene Me2Si: was suggested as an intermediate in dehydrocondensation of Me3SiSiMe2H and HMe2SiSiMe2H in the presence of Cp2ZrMe2 (22, Scheme 4). This intermediate is formed from the intermediate silyl metal complex 23 as a result of b-elimination. This process is not the classical elimination of an organic substituent at the b position with respect to the metal atom. This mechanism can more likely be considered as b-bonding147 Dehydrocondensation of organylsilanes giving Si7Si bonds Scheme 4 Pathway a.Formation of the active catalytic L2Mmolecule R L2M L2MR2+Me3SiSiMe2H 7RH SiMe2SiMe3 6�� R SiMe3 L2M SiMe2 7RSiMe3 (Scheme 5, pathway a) or the b-elimination with evolution of MeSiH3 (Scheme 5, pathway b) to form a branched polymer. We believe that the mechanism suggested by Tilley,46 which is based both on the kinetic data and on the identification of the intermediate reaction products, is the most probable one among the above-considered mechanisms of catalytic dehydro- condensation of organylsilanes. The mechanism suggested by Hengge 172 attracts attention because it involves a new type of elimination reactions, viz., the elimination of the b-bond.L2M+ SiMe2 22 L2M SiMe2 23 Pathway b. Dehydrocondensation III. Electrochemical dehydrocondensation of organylhydrosilanes Me3SiSiMe2H L2M SiMe2 22 H L2M L2M SiMe2 SiMe2SiMe3 6�� H SiMe3 HSiMe3 L2M SiMe2 Pathway c. Insertion of silylene into the Si7H bond Me Me SiMe2 Me3SiSi SiH Me3SiSiHMe2 Electrochemical reactions are used for the synthesis of various organosilicon compounds, including functionally substituted compounds.173 Methods for the cathodic electroreduction of organylchlorosilanes to form substituted disilanes 174 ¡À 177 and oligo- and polysilanes 178 ¡À 182 have been developed. Since organ- ylchlorosilanes are difficult to reduce, cathodic processes with their participation generally require preliminary electrogeneration of carbanions (or other nucleophiles), which then replace the chlorine atoms bound to the silicon atoms.173 Most of cathodic reactions based on organylchlorosilanes are variations of this process.Anodic reactions of organosilicon compounds are more diversified, though less well studied, than cathodic reduction processes.173, 183 ¡À 186 Me Me 24 Pathway d. Insertion of silylene into the Si7Si bond SiMe2 24 Me3SiSiHMe2 Electroreduction of mono-, di- and triorganylsilanes RSiH3 (R=Ph or n-C6H13), R1R2SiH2 (R1 and R2=Me or Ph) and R3SiH (R=Et or EtO) on metallic (Pt, Au or Hg)187 ¡À 190 and nonmetallic (glassy-carbon) 191 electrodes was studied. The reac- tions were performed in acetonitrile in the presence of Bu4NBF4 (see Refs 187 ¡À 190) or LiClO4.191 Organylsilanes have low oxida- tion potentials on metallic electrodes (the ERed/Ox value varies from70.05 to 0.7 V).On the contrary, the oxidation potential of dimethylphenylsilane on a glassy-carbon electrode is rather high (ERed/Ox=2.2 V). Preparative electrooxidation of Me2PhSiH in the DME¡À Bu4NClO4 system (DME is dimethoxyethane) in the presence of CuCl or CuCl2 affords a mixture of compounds. The formation of the latter can be described by the following scheme.191 Cl7 Me2PhSiCl Cl7 72e Me2PhSiCl upon destruction of a four-centre transition state accompanied by elimination of the resulting residue, viz., the so-called elimination of the b-bond (S pathways a,b). The resulting dimethyl- silylene can be inserted both into the Si7H bond (Scheme 4, pathway c) and into the Si7Si bond (Scheme 4, pathway d ) of the initial pentamethyldisilane to form the heptamethyltrisilane 24.Two pathways of dehydrocondensation of diorganylsilanes and higher silanes are possible, viz., the metathesis of the s-bond resulting in the formation of linear polymers with evolution of H2 Me2PhSiH ClO¡¦4 e Me2PhSiClO4 Me2PhSiSiPhMe2 72e, 7H+ Scheme 5 H2O Pathway a. Linear metathesis of the s-bond of H(MeHSi)3H Me2PhSiOSiPhMe2 SiSiSi Cp2MH2 (SiSiSi)2 Cp2M H SiSiSi H SiSiSi SiSiSi H MCp2 H2 SiSiSi Chlorodimethylphenylsilane is formed in a yield from 46% to 95% depending on the degree of oxidation of copper and the quantity of electricity passed.Under these conditions, 1,1,2,2- tetramethyl-1,2-diphenyldisilane is formed in insignificant yield. When the supporting electrolyte was changed for Bu4NBF4, fluorodimethylphenylsilane predominantly formed (the yield was 90%). In this case, the exchange reaction of the initially formed Me2PhSiCl with BF¡¦ Cp2MSiSiSi 4 apparently proceeded.180, 192 ¡À 194 The oxidation potentials of the initial monomeric organylsi- H Pathway b. Branched metathesis of the s-bond of H(MeHSi)3H Si lanes 190 are *200 mV lower than the oxidation potentials of polyorganylsilanes, which hinders oxidation of the latter with the cleavage of the Si7Si bond.173 (SiSiSi)2 SiSiSi Cp2MH2 Si Electrolysis of methylphenyl- and diphenylsilane in the DME¡À Bu4NBF4 system with the use of a platinum cathode and a platinum anode for 5.3 h afforded the corresponding oligo- mers.195, 196 Cp2M H SiSiSi H H(RPhSi)nH n RPhSiH2 Si Si H R=Me: n=2¡À6; R=Ph: n=2¡À5. MCp2 Si Si Si Si H H2 Cp2MSiSi SiSiSi Si According to GLC data, the dehydrocondensation product of methylphenylsilane, which is characterised by Mn=454 and the molecular distribution coefficient Mw/Mn=1.05, is a mixture of at least five compounds.1,2-Dimethyl-1,2-diphenyldisilane148 (n=2, M=242, the yield was 10%) and 1,2,3-trimethyl-1,2,3- triphenylsilane (n=3, M=362, the yield was 14%) were identi- fied in the reaction mixture by mass spectrometry. The yields of methylphenyloligosilanes with n=4 and 5 were 16% and 6%, respectively.185 Under analogous conditions, diphenylsilane was predominantly converted into the dimer, viz., 1,1,2,2-tetraphenyl- disilane (the conversion was 38%), in 23% yield.Apparently, silyl radical cations are intermediates in this anodic reaction. Then these radical cations attack the corresponding monomers or oligomers to form the Si7Si bond. Polyorganylsilanes of the H(RHSi)nH type are formed upon electrolysis of organylsilanes R1SiH3 (R1=Alk, Ar or CH2CH2R2, where R2 is a perfluoroalkyl group) in an organic solvent containing an appropriate electrolyte. Previously unknown oligo- and polyfluoroalkylsilanes with M=200 ± 5000 were synthesised according to this procedure in high yields.197 Electrolysis of organylchlorosilanes RSiHnCl37n (n=1 or 2) in the THF± Bu4NBF4 system in an undivided cell yields two different condensation products depending on the metal of the electrodes.198 Electrolysis of methylphenylchlorosilane with the use of a stainless steel cathode and a subcritical anode affords predominantly 1,2-dimethyl-1,2-diphenyldisilane, which is formed upon cathodic reduction with elimination of chlorine.e MePhHSiSiHPhMe 2 MePhSiHCl 72 Cl7 When platinum electrodes are used, the cathodic reduction is suppressed and the anodic oxidation becomes the predominant reaction. In this case, the Si7Si bond is formed through the elimination of the proton on an anode. e ClMePhSiSiPhMeCl 2 MePhSiHCl 72 H+ Radical cations formed upon electrochemical oxidation of triorganylsilanes R3SiH were identified as adducts with tetracya- noethylene 199 or cyclohexene.188, 189, 200 The lifetime of the radical cation Et3SiH+., which was detected by the rotating disk-ring electrode method, is 0.003 ± 0.006 s.188, 189 In the absence of radical traps, these radical cations decom- pose with liberation of the hydrogen atom.7e Et3Si++H. [Et3SiH]+. Et3SiH +e IV. Other reactions Dehydrocondensation of organylsilanes can also occur under the action of di-tert-butyl peroxide.201 ± 203 Thus the reaction of dimethylcyclopropylsilane with di-tert-butyl peroxide afforded tetramethyl-1,2-di(cyclopropyl)disilane in small yield,202 whereas the reaction of dimethylphenylsilane gave a mixture of PhMe2Si ± SiMe2H (2%), PhMe2SiSiMe3 (6%), Ph2MeSiSiMe3 (3%) and PhMe2SiSiMe2Ph (3%) in insignificant yield.203 Disilane was prepared by the reaction of di-tert-butyl peroxide with dimethyl(2-thienyl)silane in noticeable yield (26%).203 Recently, it was found that triethylsilane underwent dehydro- condensation to form hexaethyldisilane in the reaction with germanium or tin dihalides.204 ± 206 CD2Cl2 or CD3CN Et3SiSiEt3+(GeX)n+2 HX, Et3SiH+GeX2 CD3CN Et3SiH+SnX2 Et3SiSiEt3+Sn + 2HX X=Cl, I.The reaction of triethylsilane with tetrachlorogermanium affords a mixture of hexaethyldisilane and triethylchlorosilane in a ratio of 1 : 3.204, 205 V B Pukhnarevich,M G Voronkov, L I Kopylova CD3CN 4Et3SiH+2 GeCl4 Et3SiSiEt3+2Et3SiCl+2/n (GeCl)n+4 HCl The reactions of germanium dichloride with Et3SiH proceed readily in more or less polar solvents (CD3CN or CD2Cl2) but do not proceed in nonpolar solvents (C6D6).Tetrachlorogermanium reacts with Et3SiH only in a polar solvent (CD3CN). It is believed that electron transfer to form the [Et3SiH+.GeCl¡2 .] and [Et3SiH+.GeCl¡4 .] radical ion pairs, respectively, is the key stage of these reactions. Thermal and photochemical decomposition of bis(triorganyl- silyl)mercury and -cadmium 22a,b can be considered as a two- stage procedure for the dehydrocondensation of triorganylsilanes to form hexaorganyldisilanes.207 ± 212 The compounds 22a,b were prepared by the reactions of triorganylsilanes with dialkyl deriv- atives of mercury and cadmium.207, 209, 213D or hn R13 SiSiR13 +M R13 SiMSiR13 2R13 SiH+MR2272R2H 22a,b M=Hg (a), Cd (b).The reaction proceeds according to the radical mechanism through intermediate formation of the R3Si. radicals.214 ± 217 The latter not only can undergo recombination but also can react with the solvent (particularly, in a photochemical process).213, 218 ± 220 Hg, .HgSiMe3 (Me3Si)2Hg 7Me3Si. 7Me3Si. Hg+Me3SiSiMe3+.SiMe3 . Me3Si.+Hg(SiMe3)2 Thermolysis of bis(triphenylsilyl)mercury, -zinc and -barium derivatives proceeds with elimination of free metal.210 Hexaphe- nyldisilane is formed from the mercury derivative. The barium and zinc compounds give tetraphenylsilane and diphenylsilylene. The latter undergoes subsequent oligomerisation.212 M=Hg Ph3SiSiPh3+M D Ph3SiMSiPh3 M=Ba, Zn 1/n (Ph2Si)n+SiPh4+M D Bis(methyldichlorosilyl)- and bis(dimethylchlorosilyl)-mer- cury, which were prepared under UV irradiation of a mixture of bis(trimethylsilylmethyl)mercury and the corresponding methyl- dichloro- or dimethylchlo-rosilane, spontaneously decompose above 779 8C with elimination of mercury to form substituted disilanes.212 V.Conclusion To summarise, dehydrocondensation of organosilicon com- pounds containing Si7H bonds is a promising procedure for the preparation of linear and cyclic oligo- and polyorganylsilanes H(R1R2Si)nH and SiR1R2 n , which find use as precursors of ceramics, semiconductors, photoresistors, photoinitiators of poly- merisation of alkenes, etc.Group IVB metallocenes Cp2ML2 (M=Ti, Zr or Hf; L=H, Alk, OAlk, Ar or Hal ) and their binary systems with promoters, such as alkyllithium, triorganylphosphines, aluminium, etc., are the most efficient catalysts of dehydrocondensation. These com- pounds allow one to prepare linear and cyclic polysilanes under rather mild conditions. The catalytic activity of metallocenes decreases in the Zr>Ti Hf series depending on the nature of the central metal atom. When heteronuclear metallocenes are used, monosilanes RSiH3 are more active than diorganylsilanes R2SiH2, while triorganylsilanes R3SiH do not undergo dehydro- condensation.Dehydrocondensation of organylsilanes giving Si7Si bonds As for the mechanism of dehydrocondensation, it is evidently nontrivial and complicated.Apparently, further studies will be aimed at elucidating details of the mechanism, which can allow one to elaborate an approach to the choice of catalysts for the purpose of enhancing the selectivity of a procedure for the preparation of polysilanes with the desired structures. References 1. M G Voronkov, V B Pukhnarevich Izv. Akad. Nauk SSSR, Ser. Khim. 1056 (1982) a 2. E Ya Lukevics,M G Voronkov Gidrosililirovanie, Gidrogermiliro- vanie i Gidrostannilirovanie (Hydrosilylation, Hydrogermylation and Hydrostannylation) (Riga: Izd. Akad. Nauk Latv. SSR, 1964) 3. E Lukevics, M G Voronkov Organic Insertion Reactions of Group IVB Elements (New York: Consultants Bureau, 1966) 4.E Lukevics, Z V Belyakova,M G Pomerantseva, M G Voronkov J. Organomet. Chem. Library 5 1 (1977) 5. T Hiyama, T Kusumoto, in Comprehensive Organic Synthesis (Ed. BM Trost) (Oxford: Pergamon Press, 1991) Vol. 8, p. 763 6. B Marciniec, J Gulinski, W Urbaniak, Z Kornetka, in Comprehen- sive Handbook on Hydrosilylation (Ed. B Marciniec) (Oxford: Pergamon Press, 1992) 7. V B Pukhnarevich, E Lukevics, L I Kopylova, M G Voronkov Perspektivy Gidrosililirovaniya (Perspectives of Hydrosilylation) (Riga: Zinatne, 1992) 8. L N Lewis, J Stein, K A Smith, R P Messmer, D G Legrand, R A Scott, in Progress in Organosilicon Chemistry (New York: Gordon and Breach, 1995) p. 263 9. E Lukevics, M Dzintara Alkogoliz Gidrosilanov (Alcoholysis of Hydrosilanes) (Riga: Zinatne, 1985) 10.E Lukevics, M Dzintara J. Organomet. Chem. 295 265 (1985) 11. J Y Corey, in Advances in Silicon Chemistry Vol. 1 (New York: Academic Press, 1991) p. 327 12. Th C Bedard, J Y Corey J. Organomet. Chem. 428 315 (1992) 13. H Matsumoto Organomet. News (2) 34 (1995); Chem. Abstr. 127 51 016 (1997) 14. K Kim, K-D Kim Kobunja Kwahak Kwa Kisul 8 269 (1997); Chem. Abstr. 127 109 203 (1997) 15. C Lorenz, U Schubert Chem. Ber. 128 1267 (1995) 16. S Xin, J F Harrod J. Organomet. Chem. 499 181 (1995) 17. B T Gregg, A R Cutler Organometallics 13 1039 (1994) 18. N K Skvortsov, L N Burova, A E Trofimov, E B Vasil'eva, V O Reikhsfel'd Zh. Obshch. Khim. 60 1087 (1990) b 19. N A Lasitsa, Candidate Thesis in Chemical Sciences, St Petersburg Technological Institute, St Petersburg, 1993 20.G G Zhigareva, L S Podvisotskaya Zh. Obshch. Khim. 64 619 (1994) b 21. Y Tanabe, H Okumura, A Maeda,M Murakami Tetrahedron Lett. 35 8413 (1994) 22. Z Zhang, Z Xia Youji Huaxue 13 63 (1993); Chem. Abstr. 119 49 436 (1993) 23. Z Zhang, Z Xia Cuihua Xuebao 16 131 (1995); Chem. Abstr. 123 286 149 (1995) 24. J F Harrod, in Progress in Catalysis (Eds K J Smith, E C Sanford) (Amsterdam: Elsevier, 1992) p. 147 25. H Q Liu, J F Harrod Organometallics 11 822 (1992) 26. M Scarlete, J He, J F Harrod, I S Butler NATO ASI Ser., Ser. E 297 125 (1995); Chem. Abstr. 125 426 549 (1996) 27. J He, H Q Liu, J F Harrod, R Hynes Organometallics 13 336 (1994) 28. D Albanese, D Landini, M Penso Tetrahedron Lett.36 8865 (1995) 29. M P Sibi, J W Christensen Tetrahedron Lett. 36 6213 (1995) 30. Y B Baruah, K Osakada, T Yamamoto J. Mol. Catal. A101 17 (1995) 31. R J P Corriu, J J E Moreau, H Praet J. Organomet. Chem. 376 C39 (1989) 32. R J P Corriu, J J E Moreau, H Praet Organometallics 9 2086 (1990) 33. MG Voronkov, N I Ushakova, I I Tsykhanskaya, V B Pukhnarevich J. Organomet. Chem. 264 39 (1984) 34. MGVoronkov, V B Pukhnarevich,NI Ushakova, I I Tsykhanskaya, A I Albanov, V Yu Vitkovskii Zh. Obshch. Khim. 55 94 (1985) b 35. Y Seki, K Takeshita, K Kawamoto J. Organomet. Chem. 369 117 (1989) 36. J Y Corey, X-H Zhu Organometallics 11 672 (1992) 149 37. M L Christ, S Sabo-Etienne, B Chaudret Organometallics 14 1082 (1995) 38. R Takeuchi, H Yasue Organometallics 15 2098 (1996) 39.A M LaPointe, F C Rix,M Brookhart J. Am. Chem. Soc. 119 906 (1997) 40. R Walsh Acc. Chem. Res. 14 246 (1981) 41. S Patai, in The Chemistry of Functional Groups. The Chemistry of Organic Silicon Compounds (Eds Z Rappoport, J Apeloig) (New York: Wiley,1998) Vol. 2, Pt. 3, p. 2177 42. T D Tilley, in The Chemistry of Organic Silicon Compounds (Eds S Patai, Z Rappoport) (New York: Wiley, 1989) p. 1415 43. Ph Roux, J-P Pillot,M Birot, J Dunogues, P Lapouyade J. Organomet. Chem. 499 199 (1995) 44. H-G Woo, S-Y Kim, M-K Han, E J Cho, I N Jung Organometallics 14 2415 (1995) 45. H-G Woo, S-J Song, H You, E J Cho, I N Jung Bull. Korean Chem. Soc. 17 475 (1996); Chem. Abstr. 125 34 228 (1996) 46.H-G Woo, T D Tilley, in Ultrastructure Processing of Advanced Materials (EdsDRUhlmann,DR Uhlrich) (New York: Wiley, 1992) p. 651 47. V K Dioumaev, J F Harrod Organometallics 13 1548 (1994) 48. T Imori, T D Tilley Polyhedron 13 2231 (1994) 49. T Nakano, H Nakamura, Y Nagai Chem. Lett. 83 (1989) 50. M J Morris, V E McGrath, S Norris, W G Stibbs, R J P Emsley, J H Sharp, in Proceedings of the 11th European Conference on Advances Materials Processes, 1992 Vol. 3, p. 259; Chem. Abstr. 119 97 791 (1993) 51. R West, L L Hench, D R Ulrich (Eds) Ultrastructure Processing of Ceramics, Glasses and Composites (New York: Wiley-Interscience, 1984) 52. J P Wesson, T C Williams J. Polym. Sci., Polym. Chem. Ed. 19 65 (1981) 53. C L Schilling, J P Wesson, T C Williams Am.Ceram. Soc. Bull. 62 912 (1983) 54. R West, L D David, P J Djurovich, H Yu Am. Ceram. Soc. Bull. 62 899 (1983) 55. P S Yajima Am. Ceram. Soc. Bull. 62 893; 903 (1983) 56. K W Wynne, R W Rise Ann. Rev. Mater. Sci. 14 297 (1984) 57. S Yajima, J Hayashi, M Omori Nature (London) 261 683 (1976) 58. K S Mazdiyashi, R West, L D David J. Am. Ceram. Soc. 61 504 (1978) 59. S Yajima Trans. Jpn. Soc. Compos. Mater. 3 6 (1977); Chem. Abstr. 89 130 854 (1978) 60. S Yajima, J Hayashi, M Omori, K Okamura Chem. Lett. 931 (1975) 61. Y Hasegawa, K Okamura J. Mat. Sci. 20 321 (1985) 62. Y Mu, J F Harrod Inorganic and Organometallic Polymers and Oligomers (Eds J F Harrod, R MLainet) (Dordrecht: Kluwer Academic, 1991) p. 23 63. Y Mu, R M Lainet, J F Harrod Appl.Organomet. Chem. 8 95 (1994) 64. D Seyferth NATO ASI Ser., Ser. E, Appl. Sci. 141 133 (1988) 65. J P Banovetz, H Suzuki, R M Waymouth Organometallics 12 4700 (1993) 66. R G Kepler, J M Ziegler, L A Harrah, S R Kurtz Bull. Am. Phys. Soc. 28 362 (1983) 67. R West, L D David, P I Djurovich, K L Stearley, K S V Srinivasan, H Yu J. Am. Chem. Soc. 103 7352 (1981) 68. J F Harrod, Y Mu, E Samuel Polyhedron 10 1239 (1991) 69. Jpn. P. 07 247 437; Chem. Abstr. 124 13 308 (1996) 70. J M Ziegler, L A Harrah, A W Johnson Proc. SPIE-Adv. Resist. Technol. 539 166 (1985) 71. D C Hofer, R D Miller, G C Wilson Proc. SPIE-Adv. Resist. Technol. 469 108 (1984) 72. P Trefonas III, R West, R D Miller J. Am. Chem. Soc. 107 72737 (1985) 73.R West J. Organomet. Chem. 300 327 (1986) 74. L A Harrah, J M Ziegler Macromolecules 20 601 (1987) 75. J V Beach, D A Loy, Yu-L Hsiao, R M Waymouth, in Proceedings of the XXVIIIth Organosilicon Symposium (Gainesville, FL: University of Florida, 1995) P-64 76. P Trefonas, R West, R D Miller, D Hofer J. Polym. Sci., Polym. Lett. Ed. 21 823 (1983) 77. S J Holder, R G Jones, J J Murphy J. Mater. Chem. 7 1701 (1997) 78. T Ziegler, E Folga J. Organomet. Chem. 478 57 (1994) 79. Jpn. P. 0 532 785; Chem. Abstr. 119 73 370 (1993)150 80. T Sakakura, H J Lautehschlager,M Nakajima, M Tanaka Chem. Lett. 913 (1991) 81. C M Forsyth, S P Nolan, T J Marks Organometallics 10 2543 (1991) 82. C Aitken, J-P Barry, F Gauvin, J F Harrod, A Malek, D Rousseau Organometallics 8 1732 (1989) 83.BRD P. 4 110 917; Chem. Abstr. 118 255 522 (1993) 84. E Hengge, M Weinberger, Ch Jammegg J. Organomet. Chem. 410 C1 (1991) 85. E Hengge, M Weinberger J. Organomet. Chem. 433 21 (1992) 86. E Samuel, J F Harrod J. Am. Chem. Soc. 106 1859 (1984) 87. C Aitken, J F Harrod, E Samuel J. Am. Chem. Soc. 108 4059 (1986) 88. C Aitken, J F Harrod, E Samuel J. Organomet. Chem. 279 C11 (1985) 89. C Aitken, J F Harrod, E Samuel Can. J. Chem. 64 1677 (1986) 90. F Gauvin, J F Harrod Can. J. Chem. 68 1638 (1990) 91. Y Mu, C Aitken, B Cote, J F Harrod, E Samuel Can. J. Chem. 69 264 (1991) 92. J F Harrod NATO ASI Ser., Ser. E. (Inorg. Organomet. Polym. Spec. Prop.), 206 87 (1992); Chem. Abstr. 118 7409 (1993) 93.C Aitken, J Harrod, U S Gill Can. J. Chem. 65 1804 (1987) 94. J F Harrod, Y Mu, E Samuel Can. J. Chem. 70 2980 (1992) 95. V K Dioumaev, J F Harrod Organometallics 15 3859 (1996) 96. V K Dioumaev, J F Harrod J. Organomet. Chem. 521 133 (1996) 97. E Samuel, Y Mu, J F Harrod, Y Dromzee, Y Jeannin J. Am. Chem. Soc. 112 3435 (1990) 98. H-G Woo, J F Harrod, J Henique, E Samuel Organometallics 12 2883 (1993) 99. Sh Xin, H-G Woo, J F Harrod, E Samuel, A-M Lebis J. Am. Chem. Soc. 119 5307 (1997) 100. J F Harrod, S S Yun Organometallics 6 1381 (1987) 101. R West, A R Wolff, D J Peterson J. Rad. Curing 13 35 (1986) 102. R B Ganey, J H Gaul Jr, T K Hilty Organometallics 2 859 (1983) 103. R D Miller, E J Ginsburg, D Thompson Polym. J. (Tokyo) 25 807 (1993); Chem.Abstr. 119 203947 (1993) 104. R G Jones, R E Benfield, R H Gragg, Ph J Evans, A C Swain Polymer 35 4924 (1994) 105. R D Miller, P K Jenkner Macromolecules 27 5921 (1994); Chem. Abstr. 121 180 283 (1994) 106. Z Pawelec,W Wojnowski J. Inorg. Organomet. Polym. 5 163 (1995); Chem. Abstr. 123 144 806 (1995) 107. W Koll, K Hassler, in Proceedings of Organosilicon Symposium (Gainesville, FL: University of Florida, 1995) P-34 108. I Ojima, S Inaba, T Kogure, Y Nagai J. Organomet. Chem. 55 C7 (1973) 109. H Li, I S Butler, J F Harrod Organometallics 12 4553 (1993) 110. K A Brown-Wensley Organometallics 6 1590 (1987) 111. Jpn. P. 07 300 529; Chem. Abstr. 124 177 277 (1996) 112. L S Chang, J Y Corey Organometallics 8 1885 (1989) 113.J Y Corey, X-H Zhu, T C Bedard, L D Lange Organometallics 10 924 (1991) 114. P Jutzi, T Redeker, B Neumann, H-G Stammler Organometallics 15 4153 (1996) 115. Jpn. P. 05 262 879; Chem. Abstr. 120 165 302 (1994) 116. E Hengge, M Weinberger J. Organomet. Chem. 441 397 (1992) 117. T Sakakura,R Le Lagadec,M Tanaka Nippon Kagaku Kaishi 1067 (1996); Chem. Abstr. 126 118 007 (1997) 118. Jpn. P. 08 208 843; Chem. Abstr. 125 276 906 (1996) 119. S Bourg, R J P Corriu,M Enders, J J E Moreau Organometallics 14 564 (1995) 120. P Jutzi, T Redeker, B Neumann, H-G Stammler Chem. Ber. 129 1509 (1996) 121. Jpn. P. 07 252 363; Chem. Abstr. 124 88 253 (1996) 122. R J P Corriu, M Enders, S Huille, J J E Moreau Chem. Mater. 6 15 (1994) 123.H Li, F Gauvin, J F Harrod Organometallics 12 575 (1993) 124. J P Banovetz, Y-L Hsiao, R M Waymouth J. Am. Chem. Soc. 115 2540 (1993) 125. J P Banovetz, K M Stein, R M Waymouth Organometallics 10 3430 (1991) 126. WO PCT 9 702 322; Chem. Abstr. 126 186 889 (1997) 127. J Y Corey, X-H Zhu J. Organomet. Chem. 439 1 (1992) V B Pukhnarevich,M G Voronkov, L I Kopylova 128. R M Shaltout, J Y Corey, in Proceedings of the XXVIIIth Organosilicon Symposium (Gainesville, FL: University of Florida, 1995) P-24 129. J Y Corey, J L Huhmann, R M Shaltout, D M Kraichely, in Progress in Organosilicon Chemistry Vol. 10 (Eds B Marciniec, J Chojnowski) (Basel, 1995) p. 387 130. J Y Corey, S M Rooney J. Organomet. Chem. 521 75 (1996) 131. N Choi, S Onozawa, T Sakakura,M Tanaka Organometallics 16 2765 (1997) 132.N Choi, S Onozawa, T Sakakura,M Tanaka, in Proceedings of the 11th International Symposium on Organosilicon Chemistry Vol. 2 (Montpellier: Universite Montpellier, 1996) PB 12 133. J Y Corey, S M Rooney, in Proceedings of the 11th International Symposium on Organosilicon Chemistry Vol. 2 (Montpellier: Universite Montpellier, 1996) PA 95 134. S M Rouney, J Y Corey, in Proceedings of the XXVIIIth Organosilicon Symposium (Gainesville, FL: University of Florida, 1995) P-23 135. F Lunzer, Ch Marschuer, E Hengge, in Proceedings of the 11th International Symposium on Organosilicon Chemistry Vol. 2 (Montpellier: Universite Montpellier, 1996) PA 85 136. T D Tilley Acc. Chem. Res. 26 22 (1993) 137.R F Jordan, C S Bajgur, R Willett, B Scott J. Am. Chem. Soc. 108 7410 (1986) 138. Eur. P. 551 771; Chem. Abstr. 120 108 031 (1994) 139. Jpn. P. 04 334 551; Chem. Abstr. 119 96 399 (1993) 140. H-G Woo, J F Walzer, T D Tilley J. Am. Chem. Soc. 114 7047 (1992) 141. H-G Woo, T D Tilley J. Am. Chem. Soc. 111 3757 (1989) 142. H-G Woo, T D Tilley J. Am. Chem. Soc. 111 8043 (1989) 143. T Imori, R H Heyn, T D Tilley, A L Rheingold J. Organomet. Chem. 493 83 (1995) 144. R M Shaltout, J Y Corey Tetrahedron 51 4309 (1995) 145. R M Shaltout, J Y Corey, N P Rath J. Organomet. Chem. 503 205 (1995) 146. J L Huhmann, J Y Corey, N P Rath, in Proceedings of the XXVIIIth Organosilicon Symposium (Gainesville, FL: University of Florida, 1995) P-21 147.E Hengge, P Gspaltl J. Organomet. Chem. 521 145 (1996) 148. N Peulecke, P Kosse, A Ohff,W Baumann, U Rosenthal, in Proceedings of the 11th International Symposium on Organosilicon Chemistry Vol. 2 (Montpellier: Universite Montpellier, 1996) PB 53 149. N Peulecke, D Thomas, W Baumann, Ch Fischer, U Rosenthal Tetrahedron Lett. 38 6655 (1997) 150. T Imori, H-G Woo, J F Walzer, T D Tilley Chem. Mater. 5 1487 (1993) 151. R M Shaltout, J Y Corey Main Group Chem. 1 115 (1995) 152. Sh Xin Ph.D. Thesis, Diss. Abstr. Int. 57 2561 (1996); Chem. Abstr. 125 222 047 (1996) 153. J A Even, in Catalytic Polymerization of Olefins (Eds T Keil, K Soga) (New York: Wiley, 1986) p. 271 154. J A Even, R L Jones, A Razavi J. Am. Chem. Soc. 110 6255 (1988) 155. T D Tilley, H-G Woo Polym.Prepr. 31 228 (1990) 156. K Yamamoto, H Okinoshima, M Kumada J. Organomet. Chem. 23 C7 (1970) 157. M Kumada J. Organomet. Chem. 500 195 (1995) 158. K Yamamoto, H Okinoshima, M Kumada J. Organomet. Chem. 27 C31 (1971) 159. Bh P S Chauhan, T Shimizu, M Tanaka Chem. Lett. 785 (1997) 160. M Tanaka, T Kobayashi, T Hayashi, T Sakakura Appl. Organomet. Chem. 2 91 (1988) 161. J Y Corey, L S Chang, E R Corey Organometallics 6 1595 (1987) 162. M F Lappert, R K Maskell J. Organomet. Chem. 264 217 (1984) 163. Jpn. P. 05 209 056; Chem. Abstr. 120 55 345 (1994) 164. T Sakakura, O Kumberger, R P Tan, M-P Arthur,M Tanaka J. Chem. Soc., Chem. Commun. 193 (1995) 165. Jpn. P. 06 256 526; Chem. Abstr. 122 161 773 (1995) 166.C Zybill, D L Wilkinson, G MuÈ ller Angew. Chem. 100 574 (1988) 167. T H N Huy, F Mathey Organometallics 6 207 (1987) 168. D M Roddick,R H Heyn, T D Tilley Organometallics 8 324 (1989) 169. T D Tilley Commun. Inorg. Chem. 10 37 (1990) 170. M E Thompson, S M Baxter, A R Bulls, B J Burger,M C Nolan, B D Santarsiero,W P Schaefer, J E Bercaw J. Am. Chem. Soc. 109 203 (1987)Dehydrocondensation of organylsilanes giving Si7Si bonds 171. K H den Haan, Y Wielstra, J H Teuben Organometallics 6 2053 (1987) 172. E Hengge, M Weinberger J. Organomet. Chem. 443 167 (1993) 173. V V Jouikov Usp. Khim. 66 564 (1997) [Russ. Chem. Rev. 66 509 (1997)] 174. E Hengge, H Firgo J. Organomet. Chem. 212 155 (1981) 175. T Shono, S Kashimura,M Ishifune, R Nishida J.Chem. Soc., Chem. Commun. 1160 (1990) 176. A Kunai, T Kawakami, E Toyoda,M Ishikawa Organometallics 10 893 (1991) 177. A Kunai, T Kawakami, E Toyoda,M Ishikawa Organometallics 10 2001 (1991) 178. M Bordeau, C Biran,M P Leger-Lambert, F Sparau, D Deffieux, in Inorganic, Organometallic Polymers II. Advanced Materials, Intermediates (Eds P Wisian-Nelson, H R Allcock, K J Wynne) (Washington, DC: American Chemical Society, 1994) p. 18 179. T Shono Kino Zairyo 12 15 (1992); Chem. Abstr. 117 7964 (1992) 180. A Kunai, E Toyoda, T Kawakami,M Ishikawa Electrochem. Acta 39 2089 (1994) 181. A Watanabe,K Komatsubara,M Matsuda,Y Yoshida, S Tagawa J. Polym. Sci. Technol. 5 545 (1992) 182. S Kachimura, M Ishifune, H-B Bu, M Takebayashi, S Kitajima, D Yoshihara, R Nishida, Sh-i Kawasaki, H Murase, T Shono Tetrahedron Lett. 38 4607 (1997) 183. S G Mairanovskii Usp. Khim. 45 604 (1976) [Russ. Chem. Rev. 45 298 (1976)] 184. Yu M Kargin, V V Zhuikov, Yu G Budnikova, D S Fattakhova Elektrokhimiya 28 615 (1992) c 185. J Yoshida Kagaku to Kogyo (Osaka) 67 151 (1993); Chem. Abstr. 119 72 640 (1993) 186. J Yoshida Top. Curr. Chem. 170 39 (1994); Chem. Abstr. 125 58 557 (1996) 187. N T Berberova, O Yu Okhlobystin Zh. Obshch. Khim. 51 244 (1981) b 188. A A Khapicheva,N T Berberova, E S Klimov,O Yu Okhlobystin Zh. Obshch. Khim. 55 1533 (1985) b 189. N T Berberova, Doctoral Thesis in Chemical Sciences, Rostov State University, Rostov-on-Don, 1991 190. Y Kimata, H Suzuki, S Satoh, A Kuriyama Organometallics 14 2506 (1995) 191. A Kunai, T Kawakami, E Toyoda, T Sakurai, M Ishikawa Chem. Lett. 1945 (1993) 192. C Duprat Ph. D. Thesis, University Bordeaux I, Bordeaux, 1995 193. A Kunai, E Toyoda, T Kawakami,M Ishikawa Organometallics 11 2899 (1992) 194. G K S Prakash,H A Buchholz,D Deffieux,G A Olah Synlett 819 (1994) 195. Jpn. P. 06 100 696; Chem. Abstr. 121 180 523 (1994) 196. Y Kimata, H Suzuki, Sh Satoh, A Kuriyama Chem. Lett. 1163 (1994) 197. Jpn. P. 0 849 088; Chem. Abstr. 124 273 117 (1996) 198. S Graschy, Ch Grogger, E Hengge, in Proceeding of the XXVIIIth Organosilicon Symposium (Gainesville, FL: University of Florida, 1995) P-37 199. R J Klinger, K Mochida, J K Kochi J. Am. Chem. Soc. 101 6626 (1979) 200. O Yu Okhlobystin, N T Berberova Dokl. Akad. Nauk 332 599 (1993) d 201. R A Jackson, C J Rhodes J. Organomet. Chem. 336 45 (1987) 202. H Sakurai, A Hosomi, M Kumada Bull. Chem. Soc. Jpn. 40 1551 (1967) 203. E Lukevics, O A Pudova, L I Borisova, V N Gevorgyan Izv. Akad. Nauk Latv. SSR, Ser. Khim. 597 (1989) 204. K S Nosov, Candidate Thesis in Chemical Sciences, Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 1997 205. K S Nosov, A V Lalov,M P Egorov, O M Nefedov, in Proceed- ings of the 9th IUPAC Symposium on Organometallic Chemistry Directed Towards Organic Synthesis, Goettingen, 1997 p. 400 206. K S Nosov, A V Lalov,M P Egorov, O M Nefedov, in Proceed- ings of the 9th IUPAC Symposium on Organometallic Chemistry Directed Towards Organic Synthesis, Goettingen, 1997 p. 399 207. N S Vyazankin, O A Kruglaya Usp. Khim. 35 1388 (1966) [Russ. Chem. Rev. 35 593 (1966)] 151 208. N S Vyazankin, O A Kruglaya, G A Razuvaev, G S Semchikova Dokl. Akad. Nauk SSSR 166 99 (1966) d 209. M G Voronkov, N F Chernov Usp. Khim. 48 1804 (1979) [Russ. Chem. Rev. 48 964 (1979)] 210. E Wiberg, O Stecher, H-J Andrascheck, L Kreuzbichler, E Staude Angew. Chem. 75 516 (1963) 211. G A Marano, A G MacDiarmid Inorg. Nucl. Chem. Lett. 5 621 (1969) 212. C R Bettler, J C Sendra, G Urry Inorg. Chem. 9 1060 (1970) 213. N S Vyazankin,G A Razuvaev, E N Gladyshev Dokl. Akad. Nauk SSSR 155 830 (1964) d 214. A G Beaumont, C Eaborn, R A Jackson, R W Walsingham J. Organomet. Chem. 5 297 (1965) 215. C Eaborn, R A Jackson,M T Rahman J. Chem. Soc., Perkin Trans. 2 55 (1972) 216. C Eaborn, R A Jackson, R W Walsingham J. Chem. Soc. Perkin Trans. 2 366 (1973) 217. C Eaborn, R A Jackson, D J Tune, D R M Walton J. Organomet. Chem. 63 85 (1973) 218. T N Mitchell Tetrahedron Lett. 2281 (1972) 219. T N Mitchell J. Organomet. Chem. 71 27 (1974) 220. M Lehnig, F Werner, W P Neumann J. Organomet. Chem. 97 375 (1975) a�Russ. Chem. Bull. (Engl. Transl.) b�Russ. J. Gen. Chem. (Engl. Transl.) c�Russ. J. Electrochem. (Engl. Transl.) d�Dokl. Chem. Technol., Dokl. Chem. (Engl.

ISSN:0036-021X    

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Russian Chemical Reviews 69 (2) 153 ± 164 (2000) Free radical addition: factors determining the activation energy E T Denisov Contents I. Introduction II. Enthalpy and entropy of radical addition III. Empirical correlation equations IV. Quantum-chemical calculations of the activation energy V. The parabolic model of radical addition VI. The contribution of enthalpy of an addition reaction to its activation energy VII. Force constants of reacting bonds VIII. Triplet repulsion in addition reactions IX. The influence of neighbouring p bonds on the activation energy of radical addition X. The role of the radius of the atom carrying the free valence XI. Interaction of two polar groups XII. Multidipole interaction in addition reactions XIII. Steric hindrance XIV. Competition between the addition of free radicals to the carbon and oxygen atoms of the carbonyl group XV.Comparison of radical addition and radical abstraction reactions XVI. Conclusion Abstract. reagents of reactivity the describing relations Empirical Empirical relations describing the reactivity of reagents in of results the and reactions addition radical in radical addition reactions and the results of quantum-chemical quantum-chemical calculations processes these of energy activation the of calculations of the activation energy of these processes are are considered. The experimental data obtained for the addition of considered. The experimental data obtained for the addition of atoms are bonds multiple with molecules to radicals and atoms and radicals to molecules with multiple bonds are analysed analysed in characteristics following The model.parabolic the of terms in terms of the parabolic model. The following characteristics and and factors of energy activation the affect to shown are factors are shown to affect the activation energy of radical radical addition: the reaction enthalpy, the strength of the arising bond, addition: the reaction enthalpy, the strength of the arising bond, the of presence the valence, free a having atom the of radius the radius of the atom having a free valence, the presence of a p bond two of interaction the centre, reaction the to adjacent bond adjacent to the reaction centre, the interaction of two polar polar groups, the factor, steric the interaction, multidipole the groups, the multidipole interaction, the steric factor, the non- non- linearity of constants force the and centre, reaction the of linearity of the reaction centre, and the force constants of the the reacting bonds.The bibliography includes 85 references reacting bonds. The bibliography includes 85 references. I. Introduction Radical addition to unsaturated compounds underlies the modern technology for production of polymers, copolymers and oligom- ers.1± 5 These reactions proceed during pyrolysis of hydrocarbons, halogenation of alkenes or oxidation of unsaturated com- pounds.6± 9 They are widely used in the synthesis of diverse medicines.10 ± 14 The addition of hydrogen atoms and hydroxyl radicals to unsaturated, aromatic and heterocyclic compounds is involved in the photolysis and radiolysis of organic materials and biological objects.7 The problem of reactivity of compounds in the addition of atoms and radicals to double C=C bonds has been widely discussed and is still debated.3, 6, 8, 15 ± 24 Two factors which exert substantial influence on these processes have been noted, E T Denisov Institute for Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federa- tion.Fax (7-096) 515 35 88. E-mail: denisov@icp.ac.ru Received 1 November 1999 Uspekhi Khimii 69 (2) 166 ± 177 (2000); translated by Z P Bobkova #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v069n02ABEH000560 namely, heat (enthalpy) of the reaction and the interaction of polar groups of the reactants in the transition state (the so-called polar factor).Quantum-chemical calculations showed that the reaction centre in the transition state is non-linear.16 When interpreting the results of these calculations, researchers restricted themselves to consideration of only three factors influencing the activation energy of addition, namely, the reaction enthalpy, the interaction of polar groups and the steric effect.25 ± 39 Analysis of the experimental data (on activation energies) obtained in the studies of radical abstraction reactions in terms of the parabolic model showed that, apart from the factors men- tioned above, there is a whole series of other factors that determine the activation energy of an elementary step.40 ± 42 The author of this review has analysed an extensive array of experimental data concerning radical addition reactions in terms of the parabolic model for this type of reaction.43 ± 53 The results of this analysis are presented in detail in this review.II. Enthalpy and entropy of radical addition The radical addition reactions XCH2C.HY X.+CH2=CHY involve the rupture of the C=C p bond and the formation of a C7X s bond. A s bond is normally stronger than a p bond; hence, radical addition is an exothermic reaction. This can be clearly seen when comparing the reaction enthalpies DH and the strengths of the bonds being formed D(Et7X) given in Table 1; the stronger the Et7X bond, the larger the 7DH value. Yet another important factor influencing the reaction enthalpy is the energy of stabilisation of the radical XCH2C.HY formed: the higher this energy, the greater the heat of the addition of the X.radical to an alkene. Stabilisation energy can be characterised as the difference between the strengths of the C7H bonds in Pr7H and EtYHC7H. Below we present the data characterising the contribution to the enthalpy of this reaction of the stabilisation 153 153 154 155 155 157 158 158 159 160 160 160 161 161 162 163154 Table 1. Bond strength (kJ mol71), enthalpy (kJmol71), entropy (Jmol71K71) and Gibbs energy (kJ mol71) for the addition of atoms and X. radicals to ethylene (T=298 K). X. 7DG 7DS 7DH D(Et7X) H. Cl. C.H3 Me2C.H PhC.H2 N.H2 HO. CH3O. 84 88 122 134 122 109 100 118 134 422 352 370 364 318 353 343 352 327 150 82 100 92 63 81 122 82 63 125 56 64 52 27 49 93 46 23 HO2 . energy of the MeCH2C.HY radical, resulting from the addition of a methyl radical to the monomer CH2=CHY.Cl Ph CN C(O)OMe H Y 57.9 33.6 24.1 23.2 0.0 DPr7H7DEtYHC7H 143.0 129.7 104.3 102.0 95.8 /kJ mol71 7DH /kJ mol71 It can be seen that the greater the energy of radical stabilisa- tion, the smaller the reaction enthalpy. All the addition reactions are accompanied by a decrease in entropy (two species are combined to give one species, see Table 1). Therefore, for addition reactions, DG<DH (DG is the Gibbs energy) and, when the temperature is sufficiently high, exothermic addition is reversible because DG=DH7TDS. Free radical addition can be considered to be reversible if the equilibrium concentration of the X. radicals is commensurate with the concentration of the XCH2C.HY radicals formed, i.e.if the CH2=CHOEt [X.] : [XCH2C.HY] ratio in the equilibrium state is not smaller than 0.05. When [CH2=CHY]=10 mol litre71 and T=300K, this condition results in the inequality K5200 (K is the equilibrium constant). In turn, 7RTlnK=DG; therefore, DG4 47RTln 200=713 kJ mol71. For addition reactions, DS&7100 J mol71 K71; therefore, the enthalpy of irreversible addition of X. to an alkene DH=DG+TDS should be smaller than743 kJ mol71 (at T=300 K). The DH values for radical addition reactions listed in Table 1 comply with this condition. Naturally, as the temperature rises, the boundary value of DH increases in absolute magnitude. III. Empirical correlation equations Activation energy and heat of reaction. A linear correlation between the change in the activation energy (DE) of the monomer addition to a macroradical and the change in the heat of the reaction (Dq) of the type (1) DE=7a0Dq, where a 0 is an empirical factor of proportionality, was found by Evans et al.54 Later, N N Semenov confirmed this correlation and extended it to a wider range of addition reactions.15 However, even for a narrow series of reactions, for example, for the addition of methyl radical to CH2=CHY, this correlation is nothing but a trend.Indeed, the correlation coefficient for the variation of Dlog k as a function of Dq is 0.85 (k is the reaction rate constant).55 Evidently, apart from the heat of reaction, other factors also influence the activation energy. The Alfrey and Price Q± e scheme 56 takes account of two factors affecting activation energy, namely, the energy of stabili- E T Denisov sation of the radical formed in the reaction and the interaction between polar groups in the radical and the monomer.This scheme was based on the analysis of empirical rate constants for copolymerisation. The rate constant for the reaction of a radical with a monomer is postulated to have the following form: (2) k12=P1Q2exp(7e1e2), where the factors P1 and Q2 reflect the reactivity and e1 and e2 are the charges of the radical and the monomer, respectively. The Q and e parameters are calculated from the corresponding rate constants for copolymerisation. When developing the Q7e scheme, the researchers assumed that the charges on the molecule and on the radical are equal and constant (polarisation in the transition state was not taken into account) and that the copoly- merisation rate constants do not depend on the dielectric constant of the medium.Subsequently, these assumptions have been critisised.2 The Q7e scheme made it possible to systematise the vast experimental information on radical copolymerisation of various monomers. It permits rough prediction of the rate constants for copolymerisation. TheQand e values for monomers in radical polymerisation are listed in Table 2. Table 2. Correlation parameters for the reactivity of monomers towards radical polymerisation in terms of the Alfrey ± Price (Q, e), Bamford ± Jenkins (a, b) and Ito ± Matsuda (K, P) schemes.56 ± 62 Monomer Q e a b K P 1.00 70.80 2.28 1.30 4.85 4.21 5.20 CH2=CHPh CH2=CHSEt CH2=CHSO2Et CH2=CHCO2Me CH2=CHOCOMe CH2=CHCN 1.29 74.0 0.60 73.0 0.0 0.12 73.0 0.0 4.72 4.90 0.78 1.00 2.78 4.62 71.40 70.26 0.58 0.81 0.89 71.00 1.63 1.69 0.25 1.00 1.09 0.10 1.00 0.00 0.27 71.33 70.50 0.07 0.45 0.03 70.88 0.48 0.02 71.17 0.98 70.81 71.0 0.40 1.70 70.50 1.99 70.55 10.52 0.45 CH2=CMePh CH2=CMeCO2Me CH2=CHCH=CH2 CH2=CMeCH=CH2 CH2=CClCH=CH2 CH:CPh 70.0 0.0 1.20 71.5 0.5 0.5 0.00 3.00 71.36 5.30 2.97 70.59 1.30 1.89 5.03 7 4.92 7 5.82 7 4.41 7 The Bamford and Jenkins a7b scheme.57 These researchers suggested that the reactivities of a radical and a monomer should be described by three parameters, namely, rate constant for the reaction of the macroradical (for example, R1.) with toluene (kT) R1.+PhMe R1H+PhCH2 .; the product of coefficient a with the Hammett constant s, which takes into account the polar effect, and the coefficient b, reflecting the difference between the radical reactivities towards the mono- mer and towards toluene.Thus the equation for the rate constant for the addition of R1. to the monomer M1 is represented as follows: (3) ln k11=lnkT+a1s1+b1; the coefficients s1 and b1 are calculated from the dependence of ln(k11/kT) on s, and the rate constant kT is determined experi- mentally at T=333 K. The values of a and b for a number of monomers are listed in Table 2. The relationship between the parameters of the Alfrey ± Price and Bamford ± Jenkins schemes is expressed by the following equations:58 (4) 7e1(e17e2)=s1(a17a2), lnQ17lnQ2=b17b2.Free radical addition: factors determining the activation energy The Ito and Matsuda K±P scheme.59 ± 62 In terms of this scheme, the activation energy of an addition reaction is repre- sented as the sum of two terms, E1 and E2.The first term E1 is proportional to the change in the Gibbs energy in the reversible addition of the thiyl radicalXC6H5S. to the monomer, E1*logK, where K is the equilibrium constant of the reaction PhSCH2C.HY. PhS.+CH2=CHY The second term E2 reflects the contribution of the polar interaction between the radical and the monomer to the activation energy. The contribution of the Gibbs energy to the activation energy is determined by the coefficient present in the linear dependence on logK of the logarithm of the rate constant (kX) for the addition of the XC6H4S. radical to the monomer CH2=CHY (5) Dlog kX=aYDlogK. The aY value depends on the nature of the substituent Y in the monomer, this dependence being used to estimate the contribu- tion of the polar effect to the activation energy.This contribution is characterised by the increment P (6) P=aY+2(aY7astyrene). The parameters K and P are listed in Table 2. Parameters of the Ito ± Matsuda scheme are related to the parameters of the Alfrey ± Price approach by simple relations:62 (7) logQ=0.49K70.93, e=0.91 P+0.95. All the above schemes include, in essence, different variants of empirical linear equations in which the rate constants for chain propagation in the free radical polymerisation are brought into correlation with thermodynamic [heat, Hammett constant (s), the change in the Gibbs energy in the equilibrium reaction] and kinetic (logarithms of the rate constants of the reference reaction and the reaction under study) characteristics of the addition reaction.IV. Quantum-chemical calculations of the activation energy Quantum-chemical methods are widely used to study addition reactions.26 ± 39 The results obtained, in particular, the activation energies, depend significantly on the programme chosen for calculations. For example, Wong et al.38 calculated the activation energy of the methyl radical addition to ethylene using the QCISD(T) programme package. The results of calculations by this programme are in good agreement with experimental data. When atoms approach one another and a transition state is formed, the bond angles at the carbon atom attacked by an atom or radical substantially change. Figure 1 shows the configuration of atoms in the transition state for the addition of substituted methyl radicals XC.H2 to substituted ethylenes CH2=CHY.38 The geometry of the transition state is characterised by the distance r(C7C), the angle of attack jat=j(CCC) and the pyramidal angle jpyr=j(HCC).The last-mentioned parameter HH X C jat r(C7C) C C HY jpyr H H Figure 1. Geometry of the reaction centre in the transition state for the addition of substituted methyl radicals (XC.H2) to substituted ethylenes (CH2=CHY).38 155 Table 3. Interatomic distances and bond angles in the reaction centre and the activation energies for the addition of the XC.H2 radicals to ethylene (quantum-chemical calculations).38 E/ kJ mol71 X jpyr/ deg r (C7C) /AÊ jat/ deg 39.8 35.0 42.3 25.0 25.9 28.0 109.9 108.2 109.3 2.246 2.226 2.173 HOH CN is the angle of deviation of the two C7H bonds of ethylene from the plane in which they have been located in the initial molecule (the four hydrogens and both carbons of ethylene lie in one plane).Table 3 presents the values of the three above parameters and the activation energies for the addition of methyl radicals and the C.H2OH and C.H2CN radicals to ethylene.38 The energy profile of the addition reaction is calculated using specific quantum-chemical programmes as a superposition of four different electron configurations of the reactants, namely,38, 39 DA[XC.H2(:)CH2=CHY(:;)], D3A*[XC.H2(;)CH2=CHY(::)], D+A7[XCH2(+)CH2=CHY(7)], D7A+[XCH2(7)CH2=CHY(+)], where D is the radical, A is the molecule, the arrows mark the orientation of the electrons involved in the reorganisation, and (+) and (7) are the charges on the radical and on the molecule.The results (the activation energies) thus obtained are considered with allowance for the influence of two values, namely, the reaction enthalpy and the polar effect. V. The parabolic model of radical addition Within the framework of the parabolic model, radical addition XCH2C.HY X.+CH2=CHY is represented 43 as a result of intersection of two potential curves, each of them describing the potential energy of the stretching vibrations of atoms as a parabolic function of the amplitudes of vibrations of atoms in the outgoing (i) and incoming (f ) bonds. In terms of the parabolic model, radical addition can be character- ised by the following parameters (Fig.2). 1. Reaction enthalpy DHe DHe=Di7Df+0.5hL(ni7nf)=DH+0.5hL(ni7nf), (8) U C=C Ee C7H E0 0 E 00 7He r 0 r= re Figure 2. Diagram of the transition state for the hydrogen atomaddition to ethylene in the coordinates of the amplitude of the stretching vibration of atoms in the reaction centre (r) and the potential energy of the stretching vibration (U) in terms of the parabolic model.43 E0, E 00 are the zero-point energies of the corresponding bonds.156 Table 4. Parameters of various classes of addition of atoms and radicals to multiple bonds used in the parabolic model.44 ± 50 Reaction a CH3C.HR CH2=C.R DCH2C.HR ClCH2C.HR H.+CH2=CHR H.+CH:CR D.+CH2=CHR Cl.+CH2=CHR BrCH2C.HR RCH2C.HR RCH=C.R NCH2C.HR Br.+CH2=CHR R.+CH2=CHR R.+CH:CR N.H2+CH2=CHR ROCH2C.HR ROOCH2C.HR RO.+CH2=CHR RO2 .+CH2=CHR R3 1SiCH2C.HR2 PhSCH2C.HR HOC.R1R2 ROC.R1R2 R3 1Si.+CH2=CHR2 PhS.+CH2=CHR H.+O=CR1R2 R.+O=CR1R2 1.440 1.847 1.461 1.591 1.844 1.202 1.542 1.410 1.413 1.737 2.012 2.282 1.600 1.570 2.518 R3SiOC.R1R2 R3Si.+O=CR1R2 Table 5.Parameters DHe, Ee, bre and DEH for the hydrogen atom addition to multiple bonds in the gas and liquid phases calculated from Eqns (8) ± (10).64 ± 79 Alkene DHe/ kJ mol71 162.1 162.1 165.3 165.3 166.2 166.2 168.9 165.7 165.7 158.5 154.2 158.5 173.3 173.3 169.5 173.3 168.9 165.9 158.5 177.7 158.5 163.1 165.7 165.7 165.7 158.3 161.7 161.7 163.6 166.5 182.0 184.3 184.3 189.1 184.9 161.7 179.5 174.3 a The value in parentheses is the number of determinations. CH2=CH2 CH2=CH2 CH2=CHMe CH2=CHMe CH2=CHEt CH2=CHEt CH2=CMe2 CH2=CHPr CH2=CHPr cis-MeCH=CHEt trans-MeCH=CHEt cis-MeCH=CHEt CH2=CMeEt CH2=CMeEt MeCH=CMe2 CH2=CMePr CH2=CEt2 EtCH=CMe2 MeCH=CHPr Me2C=CMe2 MeCH=CHBu MeCH=CEt2 CH2=CH(CH2)4Me CH2=CH(CH2)5Me CH2=CH(CH2)7Me cyclo-C5H8 cyclo-Ê 6H10 cyclo-C6H10 cyclo-C6H11CH=CH2 CH2=CHCH2OH CH2=CHCOOH trans-HO2CCH=CHCO2H trans-MeO2CCH=CHCO2Me cyclo-[C(CO2H)=CH(CH2)3] cyclo-[C(CO2H)=CH(CH2)4] cyclo-[CH=CHCH2CH(CO2H)(CH2)2] CH2=CHCl CH2=CHF 10711b / kJ1/2 mol71/2m71 0.5hLv/ kJ mol71 9.9 12.7 9.9 9.9 9.9 9.9 12.7 9.9 9.9 9.9 9.9 9.9 10.3 10.3 10.3 5.389 6.912 5.389 5.389 5.389 5.389 6.912 5.389 5.389 5.389 5.389 5.389 5.991 5.991 5.991 Phase a Ee/ kJ mol71 22.5 22.6 21.6 20.3 20.2 19.6 18.0 20.6 24.3 23.9 24.1 26.9 20.3 23.5 24.4 23.3 23.3 24.7 25.3 25.1 25.3 24.5 24.2 24.3 24.2 25.2 23.6 22.9 24.3 19.5 21.3 18.8 18.2 20.9 27.3 21.3 19.8 19.7 gas (4) liq (2) gas (1) liq (1) gas (1) liq (1) gas (1) gas (1) liq (1) gas (1) gas (1) liq (1) gas (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (1) liq (2) gas (3) liq (4) liq (1) liq (1) liq (2) liq (1) liq (1) liq (1) liq (1) liq (1) gas (1) gas (1) DDHe/ 10 kJ mol71 litre mol71 s71 77.5 74.7 72.7 4.8 5.8 1.7 3.8 3.1 3.3 4.6 4.1 6.3 711.4 3.7 7.0 bre/ kJ1/2 mol71/2 24.26 24.32 24.34 24.08 24.15 24.01 23.93 24.19 24.73 24.34 24.13 24.34 24.55 25.00 24.94 24.97 24.75 24.80 24.50 25.48 24.51 24.63 24.71 24.74 24.72 24.48 24.47 24.34 24.63 24.06 25.09 24.82 24.72 25.39 25.20 24.05 24.79 24.50 E T Denisov 710A / 10 40 10950.1 0.1 0.008 0.05 0.1 0.1 0.07 100.05 0.08 7DEH/ kJ mol71 79.1 79.0 80.0 81.3 81.4 82.0 83.6 81.0 77.3 77.7 77.5 74.7 81.3 78.1 77.2 78.3 78.3 76.9 76.3 76.5 76.3 77.1 77.4 77.3 77.4 76.4 78.0 78.7 77.3 82.1 80.3 82.8 83.4 80.7 76.4 80.3 81.8 81.9Free radical addition: factors determining the activation energy whereDi andDf are dissociation energies, h is the Planck constant, L is the Avogadro number, and ni and nf are the stretching vibration frequencies of bonds i and f, respectively.The second term is the difference between the zero-point energies of the reacting bonds. 2. Activation energy Ee, which includes the zero-point energy of the bond being attacked (0.5hLni) and depends on the exper- imentally determined activation energy E (9) Ee=E+0.5(hLni7RT). 3.Distance re, which is equal to the sum of the amplitudes of vibrations of the atoms of the reacting bonds in the transition state. 4. Parameters bi and bf, which are dynamic characteristics (2b2 is the force constant) of the outgoing bond bi=pni(2mi)1/2 and the incoming bond bf=pnf(2mf)1/2, where mi and mf are the reduced masses of atoms forming the bonds. The above parameters are related to one another by the following expression:42 (10) bre=a(Ee7DHe)1/2+E1e =2. By using the parameter bre, one can calculate characteristics of a whole group of reactions with bre=const, for example, the activation energy of the thermally neutral reaction Ee0 for DHe=0 (11) (Ee0)1/2=bre(1+a)71 and the position of the transition state r= in the segment re r6a (12) re a 1 a a .1 As a rule, each reaction within one group is characterised by the same pre-exponential factor A (determined in relation to one reaction centre). This allows the activation energy to be expressed in terms of the rate constant k using the Arrhenius equation (13) E a RTlnAk . Since for any elementary reaction,E >0, relation (13) holds when DHe>DHemin, whereas for DHe<DHemin, the activation energy is very small and amounts to 0.5RT. In accordance with the parabolic model,DHemin is related to bre and a by the expression 63 a2DHemin=7(bre)2+2bre (0.5hLni)1/2 +0.5hLni(a271). (14) The physical, thermodynamic and kinetic parameters for 15 classes of reactions involving addition of atoms and radicals to carbon7carbon and carbon7oxygen multiple bonds are listed in Table 4.The parabolic model makes it possible to develop an empirical hierarchy of addition reactions. All the known addition reactions are divided a priori into classes in accordance with the atomic structure of the reaction centre in the transition state. Each class is characterised by a pair of force constants of the outgoing and incoming bonds or by the parameters b=bi and a=bi/bf (see above). Subclasses are distinguished in each class. Each subclass is characterised by re=const or bre=const, which is confirmed by analysis of a large array of experimental results. This fact is illustrated, for example, by the data on the addition of a hydrogen atom to alkenes with various structures (Table 5). For thirty two reactions, bre=24.500.40 kJ1/2 mol71/2.Each subclass of reactions can be described additionally by the energy of the thermally neutral reaction Ee0 [see Eqn (11)] and by the threshold value DHemin, for which E=0.5RT provided that Table 6. Kinetic parameters Ee0 (kJ mol71), b(1+a)71610711 (kJ1/2 mol71/2m71), re61011 (m), (r6a/re)0 and 7DHe min (kJ mol71) calculated from Eqns (10) ¡¾ (12) and (14) for addition reactions of various subclasses.44 ¡¾ 50 X. Ee0 b(1+a)71610711 re61011 (r6a/re)0 Reaction X.+CH2=CHY H. D. Cl. Br. C.H3 C6H5. N.H2 RO. 101.6 99.6 50.5 31.2 82.6 105.3 61.0 65.2 90.5 76.6 31.4 RO2 . R3Si. PhS. 125.1 97.7 H. C.H3 102.9 2.21 2.19 1.86 1.69 2.45 2.45 2.24 2.23 1.97 1.78 1.64 Reaction X.+HC:CY 2.43 2.72 Reaction X.+O=CR1R2 2.30 2.33 1.70 H. C.H3 72.9 R3Si. 114.5 DHe<DHemin [see Eqn (14)].The kinetic parameters for various subclasses of addition reactions are listed in Table 6. It can be seen that each subclass is characterised by individual values of these parameters. For instance, Ee0 varies from 31.4 kJ mol71 for the addition of PhS. to 105.3 kJ mol71 for the addition of the phenyl radical to an alkene double bond. VI. The contribution of enthalpy of an addition reaction to its activation energy DE The parabolic model postulates a non-linear relationship between the activation energy and the enthalpy of a reaction [see Eqn (10)]. The contribution of enthalpy to the activation energy DEH can be estimated as the difference DEH=Ee7Ee0 . Transformation of Eqn (10) gives the following equation for DEH as a function of DHe 42

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出版商:RSC    

年代:2000

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Russian Chemical Reviews 69 (2) 165 ± 177 (2000) Effects of ultrasound on catalytic processes MG Sulman Contents I. Introduction II. Pre-reaction conditioning of catalysts III. Sonochemical catalysis IV. Regeneration of catalysts V. Conclusion Abstract. reac- catalytic sonochemical on studies of results The The results of studies on sonochemical catalytic reac- tions processes on ultrasound of effects The generalised. are tions are generalised. The effects of ultrasound on processes of of preparation, as well as catalysts of regeneration and activation preparation, activation and regeneration of catalysts as well as its its influence on the course of catalytic reactions are considered. The influence on the course of catalytic reactions are considered. The advisability of ultrasonic treatment in different stages of catalytic advisability of ultrasonic treatment in different stages of catalytic processes 143 includes bibliography The discussed.is processes is discussed. The bibliography includes 143 references. references. I. Introduction The effect of ultrasonic waves on chemical reactions was first revealed in 1927.1 The number of publications devoted to studies of reactions which change considerably their rates or direction in an ultrasonic field is increased every year. As regards their sensitivity to acoustic vibrations, all sonochemical reactions may be divided into two groups: some reactions are accelerated in an ultrasonic field and can also occur in its absence, though at a lower rate, whereas others cannot occur at all without the action of ultrasound vibrations. For both groups of reactions, high-fre- quency (2 ± 10 MHz), medium-frequency (20 ± 100 kHz) and low- frequency (from 10 Hz) vibrations are applied.1 ±7 The classifica- tion of sonochemical reactions proposed by Margulis 2 envisages their following division: � redox reactions in aqueous solutions between solutes and the products resulting from ultrasonic degradation of water (H, OH, H2, H2O2); � reactions between dissolved gases and substances in the vapour state under high pressure inside cavitation bubbles; � chain reactions induced not by radical products obtained upon ultrasonication of water, but rather by another compound present in the system which is split upon cavitation; � reactions involving macromolecules, including oscillatory reactions which acquired wide popularity in recent years;1, 8 �sonochemical reactions in non-aqueous systems; �initiation of explosion in liquid and solid explosives.According to this classification, nearly all the catalytic proc- esses can be referred to the reactions in non-aqueous systems, because the main solvent or reagent in them is an organic substance, although water can also participate. For this reason, it seems more appropriate to divide catalytic processes with regard MG Sulman Tver State Technical University, Naberezhnaya A Nikitina 22, 170026 Tver, Russian Federation. Fax (7-082) 244 93 17. E-mail: sulman@online.tver.ru Received 16 June 1999 Uspekhi Khimii 69 (2) 178 ± 191 (2000); translated by V D Gorokhov #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v069n02ABEH000543 165 166 170 174 175 to the type of catalysis (e.g., homogeneous, heterogeneous) and also to classify them by the type of catalyst and the kind of reaction (hydrogenation, oxidation, etc.).This approach has been used in fundamental studies on sonochemistry 1±5, 9 and has become classical in the theory of catalysis.10, 11 It was proposed to divide the results of the impact of acoustic vibrations on chemical processes into the so-called effects of the first and the second order.12 ± 14 These are non-linear effects developing in a liquid upon propagation of high-intensity acoustic waves.How- ever, this approach does not allow estimation of the extent of the influence of individual parameters of ultrasound on chemical reactions. Nonetheless, the equations describing each of these parameters and effects can be used for formalising the problems of mathematical simulation of the corresponding chemical proc- esses.9, 15 The action of acoustic vibrations is highly diverse.16 Ultra- sonic waves can accelerate chemical reactions owing to emulsifi- cation of liquid components,17 dispersion of solid components and catalysts, erosion of their surfaces, degassing, prevention of sedimentation or coagulation of the products, intense mixing, etc.18 ± 20 The action of ultrasound on solid catalysts is far from being always reduced solely to dispersion, since under definite conditions their activities are much higher than those which could be expected after mere grinding of particles.1± 3 Dispersion results in the increased interface area of reactants and occurs due to both the fragmentation of solid phase particles and the surface friction between the solid and liquid phases.21, 22 As the thickness of the diffusion boundary layer is decreased, the number of effective collisions between the molecules of reactants is increased.23 Erosion of solids under the action of low acoustic frequencies has the following feature: the use of medium- and high-frequency acoustic fields crumbles out rather large particles from the surface and it becomes rough, whereas low frequencies cause smoothing and `polishing' of the surface, apparently owing to the crumbling out of microscopic particles.2, 24, 25 The increase in the rates and selectivities of most chemical reactions in ultrasonic fields appears to be due to the occurrence of cavitation:26 ± 29 acoustic waves induce the formation and growth of vapour/gas bubbles in a liquid, which oscillate, pulsate and coalesce.There are two basic approaches to the explanation of high-energy effects caused by cavitation, viz., the thermal and electrical ones. In the thermal approach, these effects are associ- ated with high temperature inside a cavitation bubble upon its adiabatic compression at a continuously increasing rate, whereas in the electrical approach these are related to a discharge inside the bubble resulting from the accumulation of electric charges on its walls.1, 2, 6, 12 The electrical action of ultrasound can be exempli-166 fied in the formation of hydrogen peroxide.1 H2O2 is generated in microbubbles upon electric discharge in water vapour.First, the elementary processes of ionisation and excitation take place: H2O++2e7, H2O+e7 H2O* + e7, H2O+e7 H++OH , H2O+ H2O* H +OH . Hydrogen peroxide is formed upon recombination: OH +OH H2O2. Hydrogen peroxide cannot be obtained by adiabatic compres- sion of water vapour and a noble gas since this process occurs at high temperature. Hydrogen peroxide decomposes at a lower temperature than does water and therefore is not accumulated to an appreciable extent if only the thermal factors are involved in the adiabatic compression of a cavitation bubble under the action of ultrasound.The effects of ultrasonic action are the reason for the ever- increasing interest in the use of sonochemical methods in organic synthesis and catalysis.30 ± 37 Clearly, the necessity of joint inves- tigation of such complex phenomena as catalysis and sonochem- ical effects does not promise rapid advances in the elucidation of the mechanism of catalysis in an ultrasonic field. Nonetheless, in some instances the action of ultrasound on catalytic processes has been studied in sufficient detail and the number of publications devoted to catalytic reactions in ultrasonic fields is rather large.38 ± 46 Most experimental studies merely state the facts of intensification of processes, increased yields of products and higher catalytic activity without considering the mechanisms underlying the ultrasonic impacts leading to the above-mentioned effects.As organic liquids are widely used as solvents or reagents, studies of sonochemical reactions in non-aqueous systems are of special significance. In most cases, the use of acoustic vibrations intensifies drastically chemical reactions in such sys- tems.9, 21, 22, 47 ± 49 Investigations into the mechanisms of sono- chemical reactions in non-aqueous systems are cor the following three reasons: the results of these reactions are simultaneously affected by usual thermal and sonochemical effects; such processes occur in rather diverse systems; the action of ultrasound also leads to other concomitant physicochemical and colloidal-chemical effects, e.g., emulsification, dispersion of solids, formation of microscopic bubbles, etc.The present review is devoted to the consideration of the effects of ultrasonic vibrations on catalytic systems and catalysts in different stages of preparation for, and implementation of, chemical reactions. II. Pre-reaction conditioning of catalysts 1. Ultrasonic treatment in the process of catalyst preparation Acoustic vibrations are applied to the process of catalyst prepa- ration in order to enhance its activity.50 Ultrasound influences substantially the properties of platinum and palladium blacks.51 ± 53 The blacks prepared by the reduction of H2PtCl6 or PdCl2 with 40% formaldehyde under the action of ultrasonic waves (USW) of different frequencies in the presence of various gases increased their activities 1.5 ± 2-fold compared to that of USW-nontreated blacks.The surface areas of platinum catalysts increased on the average from 15 to 18m2 g71. The basic characteristics of Pt and Pd blacks are listed in Table 1. Magnetic susceptibility of catalysts is enhanced under the action of ultrasound. Paramagnetism of `ultrasonic' blacks obtained under nitrogen is increased appreciably (about twofold), and it is almost not changed in the course of further training of these catalysts in vacuum. X-ray patterns of `ultrasonic' blacks exhibit noticeable enhancement of the background, which points to the presence of a substantial amount of the atomic metal phase.M G Sulman Table 1. Relative activity of platinum and palladium blacks prepared by ultrasonication in an atmosphere of different gases. Activity in reactions a (%) Preparation conditions gas of H2O2 de- of hex-1-ene of EtOH composition hydrogenation oxidation frequency medium /kHz Pt black H2 N2 Air 69 74 84 140 118 110 125 119 113 104 138 90 87 79 195 135 175 260 226 226 116 3000 20 548 3000 20 548 3000 Pd black H2 N2 82 240 135 Air 150 130 140 175 84 79 70 3000 20 548 3000 20 548 3000 79 7 173 30 150 320 200 100 7 158 58 a The activity of USW-nontreated black in the corresponding reaction is taken as 100%.The increase in the activity of Pt black in hydrogenation of hex-1- ene and oxidation of ethanol may be explained by the catalyst's increased surface. It is noteworthy that in the process of decom- position of H2O2 the effect due to USW is *2.5 times stronger than that related to the increased surface. Consequently, ultra- sound has a specific effect on the active centres of the catalyst. In the oxidation of ethanol, the Pt and Pd blacks prepared under definite conditions in an ultrasonic field proved to be less active than the control catalysts. Probably, the application of an ultrasonic field induces the formation, on the surface of crystals, of the most disordered amorphous phase which contains active centres for decomposi- tion of H2O2, whereas in the reactions of hydrogenation of hex-1- ene and oxidation of ethanol the amorphous phase possesses a decreased catalytic activity.51 The reason for enhanced activities of the ultrasonicated Pt blacks in the catalytic decomposition of hydrogen peroxide and their relatively low activities in the reactions of hydrogenation and oxidation consists in virtually all the amorphous phase being active in the reaction of decomposi- tion of H2O2 since this simplest reaction can occur on active centres of any type.On the contrary, hydrogenation or oxidation require active centres with a more ordered structure which are not formed abundantly under the action of ultrasound.The increase of the reaction order 1 of hydrogenation of hex-1-ene on the ultrasonicated Pt black from zero to first order points to changes in the reaction mechanism. Thus, when discussing an increase or a decrease in the activity of a heterogeneous metal catalyst under the action of ultrasound, it should be indicated to what kind of reaction these changes are referred. This circumstance first established by Kobozev et al.51 should be taken into account in studies of heterogeneous catalytic systems. As can be seen from Table 1, the nature of gases used in the preparation of blacks has a similar influence on different catalysts. Thus in the decomposition of H2O2, the blacks obtained under nitrogen are the most active. The blacks prepared in an ultrasonic field in air are noticeably deactivated possibly due to the adsorp- tion on their surface of nitrogen oxides formed with the partic- ipation of the water sonolysis products.53 Deactivation of `ultrasonic' catalysts prepared in air is most strongly manifested in the hydrogenation reactions.Apparently, the enhanced chemi- sorption of nitrogen oxides and oxygen in an ultrasonic fieldEffects of ultrasound on catalytic processes Table 2. Activity of platinum blacks (mmol s71 g71) prepared by the reduction of H2PtCl6 solutions of different concentrations with hydrogen using ultrasonic fields and mechanical stirring.Hydrogenation of hex-1-1ene Concentration Decomposition of H2O2 of H2PtCl6 (mass %) I II I II 0.72 0.14 0.065 0.062 0.37 0.28 0.21 0.27 0.05 0.10 0.25 0.50 7 70.25 0.071 0.049 0.19 0.17 0.068 Note.I, mechanical stirring; II, ultrasonication. prevents the hydrogen uptake by the catalyst and reduces its hydrogenation activity. It is noteworthy that the catalysts obtained from dilute solutions in an ultrasonic field are more active in the reactions of decomposition ofH2O2 and hydrogenation of hex-1-ene (Table 2) than those prepared in the absence of USW. It appears that upon reduction of dilute solutions of H2PtCl6 in an ultrasonic field the dispersive action of ultrasound is better manifested, whereas upon reduction of concentrated solutions the effects of acceleration of crystallisation and coagulation under the action of ultrasound are predominant.51 One should, however, bear in mind that the results of studies 51 ± 53 were interpreted in terms of N I Kobozev's theory of active ensembles, which was not fully confirmed subsequently in the theory and practice of catalysis.Some specific effects appear under the action of ultrasound in the process of preparation of adsorption catalysts.52, 53 For example, ultrasonication (frequency 550 kHz, flux density 5.4 W cm72) of a system H2PtCl6 ± silica gel, in which the support does not virtually adsorb H2PtCl6, in a hydrogen atmosphere leads to the formation of a mechanical mixture of platinum black and silica gel, whereas in a system H2PtCl6 ± alumogel, in which the support adsorbs H2PtCl6 well, the latter is reduced directly on alumogel under the action of ultrasound.The catalyst thus obtained is active in the hydrogenation of hex-1-ene, whereas the alumogel adsorption catalyst prepared without ultrasonication is inactive. Ultrasound is successfully used for the preparation of cata- lysts supported on silica gel, alumina or lamellar inorganic materials. Thus the reduction of ammonium hexachloroplatinate in an acoustic field (frequency 440 kHz, intensity 5W cm72) in the presence of suspended silica gel leads to an 80% increase in the surface of the metal compared to that of a sample obtained by mechanical stirring. This may rationalise the increase in the activity of highly dispersed catalysts Pd/Al2O3 or Pd/C in the reaction of reduction of acetophenone by hydrogen.54 One of the stages in the proposed mechanism of catalytic hydrogenation is migration (spillover) of hydrogen to the adsorbed substrate molecules.55 This explains the enhancement of the activity of a Pd/C catalyst obtained by the reduction of a palladium salt with formaldehyde under the action of ultrasound in the reaction of hydrogenation of nitrobenzene at 303 K.56 In the case of ultrasonic treatment, the amount of hydrogen capable of participating in the spillover increases appreciably: after ultra- sonication of the Pd/C catalyst (0.8 mass% Pd) the H: Pd ratio may reach 6.8.Preliminary ultrasonic treatment of a Pt/SiO2 catalyst intended for the hydrogenation of cinnamaldehyde resulted in a considerable increase in the selectivity of formation of cinnamic alcohol (up to 80%) and a twofold increase in the reaction rate.This effect is explained 57 by the formation on the support of effective metal centres providing for stronger substrate adsorption involving the C=O bond. Comparative studies of the profound reduction of the C=O groups onH2SO4-unmodified and -modified Pt catalysts with and without ultrasonic treatment also confirmed the activating action 167 CO(CH2)8COOEt of USW.58, 59 This conclusion was drawn from the results of hydrogenation of the carbonyl group of ethyl 9-(2,3,4-trime- thoxy-6-methylbenzoyl)nonanoate on a Pt/sibunit catalyst. (CH2)9COOEt OMe Me Me OMe H2 OMe OMe OMe OMe In the course of the experiment, the extent of the catalyst dispersion was monitored by a conductometric method.Analysis of the results obtained allowed one to conclude that the granulo- metric composition of the catalyst remained invariant under the action of USW with the intensity of up to 1 W cm72, while the reaction rate increased as the duration of ultrasonic pretreatment was prolonged from 15 to 30 s. The catalyst subjected to theUSW action for 60 and 120 s exhibited lower activity. The increase in the ultrasonic flux density from 0.1 to 1 W cm72 favoured the catalyst's activity, while its further increase to 3 W cm72 resulted in the decrease in activity (Fig. 1). Deactivation of the catalyst upon increase in the duration and intensity of sonication may be explained by the restructuring of active centres associated with an appreciable modification of the morphology of the catalyst's surface.Examination of the catalyst's samples before and after sonication by electron microscopy confirmed this conclusion, which is in full agreement with the data reported by Garibyan et al.25 X-Ray photoelectron spectroscopic data showed that the Pd(II) : Pd(0) ratio increased after ultrasonic treatment. Assuming that the hydrogenation of the C=O group proceeds on a bifunc- tional active centre Pd(0) ± Pdd+, the higher catalyst activity may be explained by the increased proportion of Pd(II) under the action of USW.31, 32 Yield (%) 2 4 1 3 80 400 120 80 40 t /min Figure 1.Dependence of the yield of the hydrogenation product of ethyl 9-(2,3,4-trimethoxy-6-methylbenzoyl)nonanoate on a Pt/sibunit catalyst on the reaction time (t) and the USW intensity (W cm72): (1) 0.1; (2) 1; (3) 3; (4) without USW. The duration of ultrasonication was 30 s. Systematic investigations of the impact of ultrasound on novel polymeric palladium catalytic systems containing metal colloids have led to a conclusion about an appreciable effect of acoustic vibrations on the activity of these catalysts in the selective hydro- genation of the triple bond of acetylenic alcohols to the double bond.60, 61 High dispersion of the catalyst's active phase was attained also by ultrasonication in the stage of preparation of supported ruthenium catalysts.62 Ultrasound has a strong effect on the genesis and properties of alumogel,63 which is widely used as the support for hydrogenation and dehydration catalysts and also as the support for the active phases of adsorption catalysts. The application of an ultrasonic field accelerates crystallisation of alumogel and its surface is increased by 40% compared to that of ultrasound-nontreated samples.This results in the formation of a secondary structure consisting of smaller aggregates with a168 strongly developed surface and in higher hydrophilicity of par- ticles, which prevents their aggregation. The relevant literature carries a suggestion that cleavage of the carbon ± carbon bonds occurs after their activation on `metal' active centres.55 The number of such centres appears to increase as a result of changes in the dispersion under the action of ultrasound leading to the acceleration of hydrogenolysis. Supported palla- dium and rhodium catalysts prepared on the base of TiO2 ± SiO2 gels under ultrasonic treatment possess higher activity than analogous systems non-treated with ultrasound and ensure the required selectivity in the hydrogenolysis of n-butane.64 The catalytic activity of nickel obtained by the reduction of nickel oxalate at 583 K under the action of acoustic vibrations with a frequency of 25 kHz and an intensity of 3000 W cm72 is increased by 87% in the reaction of hydrogenation of benzene (see Ref. 9).Probably, as in the case of Pt and Pd,5, 59 this is related to the modification of the structure of the catalyst's surface under the action of ultrasound.Similar effects were also observed when other nickel catalysts were used. Sonication in the course of reduction of nickel iodide with lithium has led to activated nickel which catalysed 1,4-addition of phenylsilane to a,b-unsaturated ketones and nitriles providing high yields (after hydrolysis) of hydrogenation products.65 Activated nickel powder is also used in the synthesis of aminoarenes by reduction of nitroarenes. This catalyst is prepared by the reduction of anhydrous nickel chloride with potassium subjected to dispersion by ultrasound.66 Ultrasonication gives a positive effect in the preparation of promoted and supported oxide catalysts which are used in the oxidative addition of methane (Na2O± ZnO, Li2O± MgO, La2O3 ± MgO, Sm2O3 ± MgO), oxidation of propylene (Na2O± ZnO) and total oxidation of methanol to CO2 (CuO ± SiO2).67 Application of USW in the stage of impregnation increases the catalytic activity of oxides in oxidative processes.The use of the 10% Na2O±ZnO catalyst thus obtained increases the methane conversion from 14% to 18% and raises the selectivity from 40% to 54%. On the activated 1% La2O3 ±MgO catalyst, the degree of conversion is increased insignificantly, whereas the selectivity is increased from 54% to 60%. The C2H4: C2H6 ratio is changed in favour of ethylene. A similar effect of an increase in the catalytic activity of manganese and chromium oxides was also observed in the heterogeneous oxida- tion of 1-hydroxyphosphonates.68 According to Garibyan et al.,67 the improvement of catalytic properties of oxides upon sonication may be due to changes in the number and structure (composition) of active centres, which is in agreement with the conclusions 52 drawn from the study of oxidation of ethanol on platinum and palladium.The electron microscopy analysis of samples prepared with and without application of USW has shown that the application of ultrasound provided a more uniform distribution of components. This inference is consistent with the results of analysis of palladium catalysts.24, 25 Promoter oxides present on ZnO or MgO in the form of agglomerates are dispersed on the support surface.The promoter increases the efflux of CH3 and C2H5 radicals to the gas phase;69 consequently, a uniform distribution of sodium and lanthanum ions reached under the action of USW favours the formation of radicals and prevents their capture by the surface. This results in an increased yield of C2 hydrocarbons. The use of the EPR method has shown that the activation of methane and ethane on ultrasound-treated catalysts provides higher concentrations of free radicals in the gas phase. On the USW-nontreated Sm2O3 ±MgO catalyst, the ratio of desorbed radicals [ CH3] : [ C2H5] is equal to 0.9, whereas upon ultrasoni- cation it increases to 1.75. This implies that in the latter case additional disintegration processes with the release of C2H4 take place in the course of formation of C2H5 radicals.Experiments on CH4 conversion under atmospheric pressure showed that under the action of USW the [C2H6] : [C2H4] ratio is shifted in favour of ethylene. The ethyl radicals are decomposed either on the surface M G Sulman or in the gas phase, i.e., a radical mechanism without participation of a solvent is realised: C2H4+H , C2H5 (ads) C2H4+CH4, C2H5 (ads)+CH3 (gas) C2H4+CH4. C2H5 (gas)+ CH3 (ads) Incorporation of ions of a different valence (M+) into the lattice of alkaline-earth metal oxides leads to changes in the defect structure of the catalyst and its higher activity in the process under study. Ultrasonication results in the enhancement of this effect. The extent of oxidation of propylene on the Na2O± ZnO catalyst activated by 60-min ultrasonication increased by 4% compared to that on the USW-nontreated catalyst; the composi- tion of products also changed:67 the yield of hexadiene increased, while the amount of hydrogen and benzene decreased (Table 3).The Na2O± ZnO system contains numerous unprotected ZnO centres on which oxidation does take place. Considerable content of hydrogen in the products is related to the possible dehydro- aromatisation of hexadiene on zinc oxide. In the catalyst subjected to the action of USW, sodium oxide covers the surface of zinc oxide uniformly and suppresses this process thus increasing the yield of hexadiene. Table 3. Composition of the propylene oxidation products on a 10% Na2O± ZnO catalyst.Reaction conditions: temperature, 843 K; contact time, 5.5 s; pressure, 1 atm. [C3H6] Con- Conditions Composition of products (vol.%) ver- of catalyst (vol.%) sion treatment (%) (C3H5)2 MeOH C2H6 CO+CO2 H2 0.081 2.7 0.112 0.01 30 3.5 0.103 0.5 0.082 0.08 9.00 3.9 mechanical 8.32 stirring 33.9 ultra- sonication The same approaches were used in studies of the total oxidation of methanol on the 5% CuO ± SiO2 catalyst. The data on the temperature dependence of conversion of methanol in this system are listed in Table 4. The selectivity of CO2 formation was found to be equal to 100% at all the temperatures studied. As can be seen from Table 4, irrespective of the SiO2 porosity (catalysts 1 and 2 have the pore size 102± 105 and 10 ± 100 A, respectively), the ultrasonic treatment in the stage of catalyst preparation increased the degree of conversion, which reached 86% at 668 K.The ultrasound-treated catalysts preserve their activities for a pro- longed time. The phase composition of catalysts prepared by the method of thermal treatment at 623 K with and without sonica- tion was also studied. The diffractograms of the catalysts of oxidation of methanol that have operated for the same time period point in both cases to the presence of only CuO phase, Table 4. The temperature dependence of the methanol conversion into CO2 on the 5% CuO± SiO2 catalyst (1.5 vol.% MeOH in air). Conditions of treatment Conversion (%) at the temperature /K 668 648 623 598 573 Sample No.1 75 86 56 65 20 43 Mechanical stirring Ultrasonication 66 77 43 60 Sample No. 2 73 86 48 66 33 40 Mechanical stirring Ultrasonication 67 70 43 50Effects of ultrasound on catalytic processes although the activity of the ultrasound-treated catalyst remains at a high level. The sonication favours uniform distribution of the CuO phase over the SiO2 surface. The CuO ± SiO2 samples prepared at 623 K with and without ultrasonication were studied before and after the reaction by the EPR method. The concen- tration of paramagnetic Cu2+ ions in the catalyst ultrasonicated before the reaction was one order of magnitude higher than that in the catalyst prepared in the usual manner. After the reaction, nearly equal low concentrations of copper ions were found on both catalysts.This may be explained by the degradation of the intermediate Cu2(OH)3NO3 phase into CuO during the reaction. Thus, the application of ultrasound for the preparation of promoted and supported catalysts enhances appreciably the efficiency of catalytic systems. Ultrasonication of a suspension in the co-precipitation and ageing of copper, zinc and aluminium oxides enhanced noticeably the activity of the catalyst of methanol synthesis.70 It was suggested that under the action of ultrasound the Cu :Zn : Al ratio in the catalyst precursor becomes the same as in the compound Cu3Zn3Al2(OH)16CO3 . 4H2O, i.e., 3 : 3 : 2. The specific surface of the thus obtained highly dispersed Cu(Cu+), ZnO and Al2O3 particles as well as the yield of methanol depend linearly on the content of this hydrate-like phase.Ultrasound is also used in the stage of precipitation in the preparation of catalysts and their precursors.71 Formation of agglomerates in mixed half-precipitated suspensions of (Cu/Zn)2(OH)2CO3 under the action of acoustic waves of different intensity was studied. The application of ultrasound influences substantially the size of particles and the surface of agglomerates. The precursors precipitated by the low-intensity ultrasonication have basically small specific surface and are composed of small agglomerates. The precursors prepared using high-intensity USW are characterised by a more developed sur- face and formation of larger agglomerates.The MnO2 catalyst prepared under the conditions of high-intensity ultrasonic treat- ment possesses higher activity as regards evolution of oxygen from H2O2 than that of an analogous but USW-nontreated catalyst. The ultrasound treatment is also used for the preparation of electrode catalysts of the solid-oxide fuel cell.72 For example, the anode catalyst La1.8Al0.2O3 is prepared by pyrolysis of an aqueous mixture of lanthanum and aluminium nitrates. This technique provides higher activity of the anode catalyst than that attained using other methods. The optimum conditions for the ultrasonic treatment are determined experimentally by monitoring the particle size and from the dependence of the quantity of deposited particles and their size on the concentration of an aqueous solution and temperature.There is a possibility of sonochemical synthesis of various nanostructured materials using high-intensity ultrasound.73 In the decomposition of organometallic compounds under the action of ultrasound, the specific surface of the solid phase composed of agglomerates and nanoclusters is increased. This technique was used to synthesise nanostructured metals and alloys from iron pentacarbonyl and cobalt tricarbonylnitrosyl; molybdenum car- bide was prepared in this way from molybdenum hexacarbonyl. These materials represent active heterogeneous catalysts for reforming of hydrocarbons and hydrogenation of CO. The use of surface acoustic waves and resonance vibrations makes it possible to prepare heterogeneous catalysts with artifi- cially controllable functions.74 For instance, thin films of catalysts were precipitated using horizontal surface-active waves generated on ferroelectric single crystals of LiNbO3 and LiTaO3.This resulted in an appreciable increase in the activities of Ag, Pd and Ni catalysts in the oxidation of ethanol and of Pd catalyst in the oxidation of CO. The enhancement of catalytic activity is related to the modification of the coefficients of electromechanical adhesion of ferroelectrics and to the state of the catalyst surface. It should be noted that ultrasound not only influences the process of catalyst preparation but also enhances the activities of ready-to-use catalysts in various reactions.59 169 2.The action of ultrasound on ready-to-use catalysts Ultrasonication influences the genesis of crystalline catalysts, their properties and catalytic activities in various reactions and favours the increase in the size of solid particles irrespective of the nature of the material used.75 An appreciable decrease in the particle size is particularly noticeable at a low metal content.76 The removal of impurities from the metal surface makes an additional contribution to the enhancement of the catalyst's activity.59 Asymmetric catalysis on metals implies the interaction of a substrate with an active centre formed as a result of coordination of a chiral modifier with the metal component of the catalyst.77 Ultrasonic treatment of catalysts leads to an increased enantiose- lectivity of many processes, e.g., hydrogenation of ethyl pyruvate to ethyl lactate on various platinum catalysts (Pt/C, Pt/Al2O3, Pt/SiO2 and Pt/montmorillonite).78 After the action of USW on the Pt/SiO2 and Pt/montmorillonite catalysts, the enantioselectiv- ity is enhanced substantially, the hydrogenation rate is increased by an order of magnitude compared to that on the untreated catalyst, while the yield of the target product reaches 100%.The enhanced activity can be due to the decreased size of the catalyst's particles (Table 5) and changes in their morphology. Initially, the size of platinum crystals ranges from 5 to 60 nm. After ultra- sonication, small particles (3 ± 5 nm) become predominant and their distribution is almost uniform.Apparently, this favours the formation of a large number of reactive different-ligand com- plexes and, consequently, enhances the catalyst's activity. Analo- gous results were obtained in the sonochemical treatment of a catalytic system Pt/Al2O3 ± quinidine in acetic acid.79 In addition, sonication made possible the repeated use of the catalyst without its regeneration, i.e., made the catalyst more stable. Table 5. Mean diameter of metal particles in supported platinum catalysts before and after 30-min ultrasonication.78 Catalyst after treatment Diameter of particles /nm before treatment 2.5 4.2 3.8 12.6 3.0 6.7 3.7 23.1 5% Pt/C 3% Pt/SiO2 5% Pt/montmorillonite 5% Pt/Al2O3 A number of studies were devoted to the investigation of the ultrasonic treatment of Raney nickel.22, 80 ± 87 Sonication in water 80 with subsequent asymmetric modification yielded a highly efficient catalyst of enantioselective hydrogenation.The complex tartaric acid ± NaBr ± modified Raney nickel exhibits high enantioselectivity and catalytic activity in the hydrogenation of b-diketones and b-keto esters.81, 82 According to Suslick and Casadonte,22 ultrasonic treatment (20 kHz, 50 W cm72) of a nickel powder (particle size 5 mm) in octane increased 105 times its ability to catalyse hydrogenation of alkenes. Though, such a strong effect is in part due to the fact that the results were compared with an inactive form of nickel.The application of an acoustic field simplifies considerably the prep- aration of the catalyst. The initial hydrogenation rate reaches its maximum after preliminary 60-min ultrasonication of a sample, whereas further action of ultrasound decreases its catalytic activity (Fig. 2). The use of scanning electron microscopy showed that the acoustic field does not modify the particle size but influences noticeably the surface morphology. Sonolysis allows preparation of nickel with a specific surface close to that of Raney nickel. Initially, the surface of the crystalline structure is smoothed under the action of ultrasound and then the particles `stick' to each other,22, 86 which is presumed to be the main reason for the decrease in the hydrogenation rate upon prolonged action of ultrasound.However, the effect of particle sticking is difficult to explain from the physical viewpoint, since for this process to occur, the particles should be heated to their melting temperature,170 w0 /mmol min71 2.0 1.0 0.5 120 60 0 180 t /min Figure 2. Dependence of the initial rate of hydrogenation of non-1-ene (w0) on the duration of ultrasonic activation (t) of nickel powder; temper- ature 273 K, pressure 1 atm. which is possible if their minimal relative speed at the moment of collision 1 is 15 000 m s71, which is 30 times as high as the really observed one (500 m s71) and almost 10 times higher than the velocity of sound propagation in the liquid. The ultrasound-treated platinum (mainly Pt/C), nickel and palladium catalysts are successfully used in reactions of hydro- genation and hydrosilylation of alkenes.83 ± 85 A catalytic system metal hydride ± dialkylzinc activated by ultrasound is effective in the reduction of carbonyl compounds and epoxides (like the ultrasound-nontreated system) and in reactions of partial reduction of carboxylic acids to aldehydes.88 This system is highly attractive owing to its accessibility, inex- pensiveness and simplicity of handling and, hence, it may be particularly useful for the implementation of large-scale reduction processes.The possibility of ultrasonic activation of polymerisation, aldol condensation, allylation and oxidation catalysts should also be noted.Ultrasonic treatment (20 ± 500 kHz, 4 ± 20 W cm72) of octane-suspended titanium trichloride, belonging to the group of the Ziegler ± Natta catalysts, led to the decrease in the particle size from 15 ± 40 to 0.1 ± 5 mm. Crystalline polymers formed in the presence of this catalyst are more uniform with regard to their molecular mass than are polymers obtained on the ultrasound-nontreated catalyst. Similar results were also derived using other Ziegler ± Natta catalysts.5 The application of ultra- sound enhances the catalytic activity of the metal iodide-pro- moted BiCl3 used as the catalyst of the Mukaiyama and Mukaiyama ± Michael reactions.89 The ultrasound has an accel- erating effect on the systems BiCl3 ± 1.5 ZnCl2 or BiCl3 ± 1.5 SnI2 (5 mol.%), which catalyse the crossover aldolisation of acetophe- none and benzaldehyde.Ultrasound-activated palladium catalyses the heterogeneous allylation of carbonyl compounds with g-substituted allyl alcohols in the presence of SnCl2 in non-polar solvents (diethyl ether, diisopropyl ether and toluene).90 The reaction proceeds regiose- lectively with high yields of 1,4-disubstituted but-3-en-1-ols; the regioselectivity (a-selectivity) of the reaction on ultrasound-acti- vated palladium is the opposite of the regioselectivity (g-selectiv- ity) of the palladium-catalysed homogeneous carbonyl allylation in polar solvents. Garibyan et al.25 studied the effect of ultrasound in the stage of preparation of catalysts on their activities and selectivities in the oxidative condensation of methane, oxidation of propylene on Na2O/ZnO and profound oxidation of MeOH on CuO/SiO2.It is noteworthy that the most interesting results were obtained when the ultrasound was involved in catalytic processes. III. Sonochemical catalysis 1. Homogeneous catalysis The application of ultrasound with the intensity sufficient for inducing cavitation leads to the acceleration of chemical reactions, which appears to be determined by the formation of free radi- cals.91 M G Sulman An extensive series of homogenous catalytic processes carried out under sonication have been studied. Thus MuÈ ller et al.92 demonstrated the possibility of the ultrasound-induced highly effective enantioselective chain elongation of labile fluorenylme- thoxycarbonyl-protected amino acids by means of Wolf rear- rangement of the corresponding a-diazo ketones at room temperature catalysed by silver ions.Donatti and Vollet 93 inves- tigated hydrolysis of tetraethoxysilane at 312 K and mixtures of tetramethoxysilane and tetraethoxysilane at 308 K catalysed by hydrochloric or oxalic acid in an ultrasound field. It was shown that Lewis acids or sonication catalyse the condensation of imines with H-phosphonates bound to the Wang resins resulting in high yields of the corresponding a-aminoalkylphosphonates.94 A num- ber of diterpenoids were obtained by highly regioselective cyclo- addition of styrenes to substituted 1,4-benzoquinones under the action of ultrasound in the presence of Lewis acids as catalysts.95 The application of ultrasound increased appreciably the rate of addition of aldehydes to methyl acrylates catalysed by 1,4- diazabicyclooctane.96 Ultrasonic waves with an amplitude of 120 mm accelerate decomposition of 2-chlorophenol in the pres- ence of 200 mg litre71 of H2O2.97 Under the action of ultrasonic vibrations, the condensation of indene or 2-nitrofluorene cata- lysed by bis(p-methoxyphenyl) telluroxide leads to the corres- ponding fulvenes in high yields.98 Ultrasound is also used in the re- actions involving fatty acids.99 For example, an isomer of methyl 8-(5-hexyl-4,5-dihydro-3H-pyrrol-2-yl)octanoate can be synthes- ised from methyl ricinoleate in several ways.The highest yield (42%) is achieved and the minimum reaction time is necessary in the case where USW (20 kHz, 53W cm72) are applied. Let us consider in more detail oxidation and isomerisation reactions occurring under the action of USW. The results of studies of the effect of ultrasound on the liquid-phase oxidation of hydrocarbons by the radical-chain mechanism in the presence of 0.3% cobalt stearate are presented in Table 6. It is seen that the accumulation of oxygenated compounds is increased by 15%± 30% under the action of USW. As the pressure increases, the oxidation rate also increases. The maximum acceleration of the process is reached at a frequency of*300 kHz. It is of essence that in an ultrasonic field the oxidation rate remains invariant for a long time, whereas without ultrasonic treatment it reaches a maximum and then decreases appreciably. In the process of oxidation, cobalt stearate usually forms a micelle with the hydro- carbon, which is a reason for the decrease in the catalyst's activity. In an ultrasonic field, complexes of this type decompose or are not formed at all, and this prevents shielding of the catalyst by hydrocarbon molecules and enhances their stabilities because of which the reaction rate remains constant.Table 6. Characteristics of the product of n-tetradecane oxidation at 385 K in the presence of cobalt stearate catalyst. Characteristic Without ultrasonic treatment Under the action of ultra- sound with a frequency of /kHz 1000 600 300 25.0 13.7 27.4 5.5 71.6 27.2 14.2 26.4 6.2 73.9 29.2 14.9 28.1 7.5 79.1 21.0 10.6 22.4 7.2 61.2 Acid number a Ester number Carbonyl number Hydroxyl number Sum of oxygenated compounds a In mg KOH per 100 g product.It is of note that the oxidation rate decreases appreciably at an USWfrequency of 16 kHz. This effect may be explained by several reasons: intense degasification of the hydrocarbon at low frequen- cies and high intensity of irradiation; chemical modification of theEffects of ultrasound on catalytic processes catalyst's molecules; higher decomposition rate of peroxide com- pounds formed in the oxidation. Oxidation of alkenes by oxygen in the presence of Mo(CO)6 with the formation of enols and epoxides was performed under the action of ultrasound.5 The primary sonochemical act in this process is presumed to be homolysis of the allylic C7H bond under the action of cavitation.))) +H ,O2 ., +O2 O2 .+ O2H+ , OH O2H + + . O Under ultrasonic stirring, the homogeneous cationic ferro- porphyrins become effective catalysts of cyclohexane oxidation in the presence of MeCN. At a total yield of 93%, the ratio of selectivities of the formation of epoxide, alcohol and ketone is 77 : 12 : 11.100 Margulis 26 investigated the catalytic isomerisation of alk-1- enes into alk-2-enes in an ultrasonic field in the presence of metal carbonyls. In the presence of Fe(CO)5, isomerisation of pent-1-ene under the USW action (frequency 20 kHz, intensity 100W cm72) proceeds at a constant rate for 1 h, then the catalyst's activity drops for a period of several hours due to the formation of dispersed metallic iron and a small amount of Fe3(CO)12.High initial activity of carbonyl Fe2(CO)9 decreases rapidly, since under the conditions of sonolysis it is transformed at a high rate into the complex Fe(CO)5 . Fe3(CO)12; however, even under prolonged exposure to ultrasound the complex does not undergo degrada- tion with the liberation of metallic iron. The initial rate of catalytic isomerisation of pent-1-ene measured 5 min after the beginning of sonication is increased more than 106 times compared to the rate in the control experiment (without ultrasound). It was shown that the efficiency of isomerisation decreases when alk-1-enes have substituents creating steric hindrances (Table 7).Therefore, isomerisation of 2-ethylpent-1-ene and allylbenzene is appreciably slower than that of pent-1-ene. Isomer- isation of cis-stilbene virtually does not occur because of either the non-terminal position of the double bond or the difficulty of forming an intermediate complex with Fe(CO)5. According to the data from Table 7, the isomerisation rate of linear alk-1-enes changes in the order: pent-1-ene & hex-1-ene 44 oct-1-ene > dec-1-ene. Isomerisation of alkenes in an ultrasonic field in the presence of other metal carbonyls, not only iron carbonyls, was also studied. It is seen from Table 7 that in the presence of iron carbonyl trans- and cis-pent-2-enes are formed in the ratio Table 7.Isomerisation of alk-1-enes in an ultrasonic field in the presence of Fe(CO)5. Products a Initial alkene Relative isomerisa- tion rate 1.0 Pent-1-ene 1.1 Hex-1-ene trans-pent-2-ene (77%) cis-pent-2-ene (23%) trans-hex-2-ene (74%) cis-hex-2-ene (26%) 2-Ethylpent-1-ene 2-ethylpent-2-ene Oct-1-ene Dec-1-ene Allylbenzene cis-Stilbene 0.31 0.17 0.05 0.02 0.02 trans- and cis-oct-2-enes trans- and cis-dec-2-enes b-methylstyrene trans-stilbene a Yields are indicated in parentheses. 171 virtually close to the thermodynamic equilibrium. This ought to be expected, since irrespective of the presence or the absence of the ultrasonic field the same species remain catalytically active.However, in the presence of Ru(CO)5 and Ru3(CO)12 other ratios of cis- and trans-isomers are obtained, which points to a different mechanism of catalytic action of ruthenium carbonyls and to the participation of different intermediates in the reaction. The catalytic activities of carbonyls in the isomerisation reaction under the action of USW decrease in the series: Ru3(CO)12 > Fe(CO)5>Mo(CO)6>Fe3(CO)12 44 W(CO)6&Cr(CO)6. The rates of photocatalytic isomerisation change in a different sequence: Fe(CO)5 > Fe3 (CO)12 > Ru3 (CO)12 > W(CO)6 & Mo(CO)6 44 Cr(CO)6. In many cases, the ratios of trans- and cis- isomers in the sonocatalytic and photochemical isomerisations are similar; however, when Ru3(CO)12 is used, they differ consider- ably and amount to 2.8 and 6.0, respectively.These results suggest the existence of substantial differences in the mechanisms of sonochemical and photochemical initiation of the catalytic processes, the catalytic activity being higher in the first case. Experimental data support the suggestion that in both cases the stages in which hydrogen migrates from the b-position of the alkene to form an intermediate hydride, viz., p-allyllic com- plex, are analogous. In accordance with the commonly accepted scheme, sonolysis of Fe(CO)5 in the presence of an excess of pent- 1-ene yields [Fe(CO)4(C5H10)], which is confirmed by IR spectro- scopy. Exposure to ultrasound not only enhances the rates of homogeneous catalytic reactions, but also increases the number of catalytic cycles.Ultrasound is a factor which influences the catalytic activity of iron(III) meso-tetrakis(2,6-dichlorophenyl)- porphyrin chloride [Fe(TDCPP)Cl] in a homogeneous system 101 where cyclohexanol is formed from cyclohexane by a classical mechanism of hydroxylation with the participation of iodosyl- benzene: PhIO is reduced to iodobenzene with the oxidation of Fe(TDCPP)Cl resulting in the formation of catalytically active species of iron(IV)oxoporphyrin radical, which directly hydrox- ylate cyclohexane. The optimum conditions of this reaction have been established: [Fe(TDCPP)Cl]=361074 mol litre71 in 1,2- dichloroethane, ultrasonic stirring at 273 K in an excess of PhIO.Ultrasound makes it possible to achieve an unusually high yield of cyclohexane (96%) and to increase more than twofold (from 45 to 96) the number of reaction cycles. The catalyst [Fe(TDCPP)Cl] acting in an ultrasonic field may be regarded as a good biomimetic model. This is a stable and selective catalyst allowing the prepa- ration of cyclohexanol as the single product. Application of an ultrasonic field (35 ± 40 kHz) increases considerably the number of catalytic cycles involving a water- soluble rhodium catalyst for the hydroformylation of alkenes.5 The number of such cycles in the preparation of aldehydes under a pressure of 2.5 MPa in an aqueous solution containing a 1 : 1 mixture of carbon monoxide and hydrogen, hex-1-ene and the rhodium complex HRhCl(CO)[P(C6H4SO3H)3]3 under the action of ultrasound is 11.34, whereas with mechanical stirring at a rate of 500 rpm it is 3.24.Thus, ultrasound accelerates homogeneous catalytic reactions by modifying in some cases their mechanisms and increases the stability of homogeneous catalysts. 2. Heterogeneous catalysis Acoustic vibrations can exert a dual effect on heterogeneous catalytic reactions. On the one hand, they favour mass transfer and, on the other hand, enhance the activity of catalysts.51, 102, 103 The use of ultrasound in heterogeneous reactions opens broad possibilities for the application of physical and chemical factors of acoustic impact. Difficulties of studying such factors are related to the absence of unequivocal and clear-cut concepts of the nature of the ultrasound effect on heterogeneous catalytic processes.At present, several tentative mechanisms of the effects observed may be discussed, but there is no answer so far to the question about which of them is predominant.26172 Table 8. Rates ofNH3 formation (mmol litre71 min71) in the sonolysis of water saturated with a mixture of N2 and H2 in the presence of metal catalysts.51 Catalyst Catalyst Rate of NH3 formation a Rate of NH3 formation a 1.4, 1.3 1.0, 0.9 0.73, 0.80 0.00 Rh (from RhCl3) 2.5, 3.0 Pt (from H2PtCl6) 1.6, 2.0 Pd (from PdCl2) 1.3, 1.5 Without catalyst 0.4 Rh black Pt black Pd black Rh black (without USW) a In most cases, there are two values derived from parallel experiments.Let us consider the mechanism { of a heterogeneous catalytic reaction in an ultrasonic field exemplified in the synthesis ofNH3. A remarkable effect has been observed: in water saturated with a mixture of N2 and H2 in the stoichiometric proportion, the rate of NH3 formation under ultrasonic irradiation in the presence of platinum group metals as catalyst is rather high, whereas without ultrasound no reaction occurs whatsoever.51 Table 8 lists the rates of the NH3 formation in the presence of different catalysts in the sonolysis (550 kHz, 4 ± 5 W cm72) of water saturated with a mixture of N2 and H2. The rate of NH3 formation in the absence of catalysts is close to the rate of HNO2 formation in the sonolysis of water in the nitrogen atmosphere (in addition to nitrous acid, H2O2 and HNO3 are also formed as the reaction products).104 Accordingly, it may be presumed that NH3 is synthesised in an ultrasonic field non-catalytically in the gas phase with cavitation bubbles involving the excited nitrogen N+NH.N2 +H molecules, e.g., the long-living metastable term N2 (A3Páu ) In this case, ammonia is formed according to the following scheme: NH+H, NH3, NH2, NH3+H. N+H2 NH+H2 N+H2 NH2+H2 It is possible 105 that, as in the case of the reaction in an electric discharge, the primary act in the sonochemical synthesis ofNH3 is the ionisation of nitrogen followed by the stage N2H++H N2++H2 and then by the stage which ultimately leads to the formation of ammonia. Ultrasonic fields accelerate appreciably hydrogenation of unsaturated compounds,81 e.g., indene, acenaphthylene, non-1- ene, a-methylstyrene and trans-benzylideneacetone.Hydrogenation was carried out on a catalyst obtained by deposition of 10% Pd on activated carbon in the presence of formic acid as the hydrogen carrier. In an ultrasonic field, 100% hydrogenation of the double bonds at 298 K was reached within 1 h, whereas the aromatic rings remained intact. Without ultra- sound, the reaction was considerably slower and the yield was 70% after 1 h and 90% after 2 h. Ultrasonic field increased appreciably the hydrogenation rate of alkenes in anhydrous media in the presence of platinated carbon.It should be noted that the hydrogenation of acyclic { Unfortunately, the mechanism of catalytic synthesis of NH3 in an ultrasonic field is not considered in the relevant literature; therefore, only some suggestions may be discussed. M G Sulman alkenes is accelerated to a greater extent than that of unsaturated cyclic hydrocarbons.26 The rate of hydrogenation of acrylic acid on Pt black at 298 K in an acoustic field (440 kHz, 5W cm72) is three times as high as that under mechanical stirring at 1000 rpm (see Ref. 106). The use of ultrasound (1 MHz, 3W cm72) in the catalytic hydrogenation of olive oil on Raney nickel made it possible to reduce appreciably the residual concentration of unsaturated compounds in the product (the iodine number was 77.0 after hydrogenation for 3 h and 50.0 after hydrogenation in the ultrasonic field).107 Under the action of ultrasound, anthracene can be reduced by lithium to its dianion.Addition of water leads to the formation of 9,10-dihydroanthracene. Under similar conditions, diphenylace- tylene yields a radical anion which then dimerises. This dianion may be captured by some species,5 as is shown in the scheme: Li [PhC CPh]7. PhC CPh USW Ph Ph Ph Ph MeHSiCl2 Ph Ph Ph Ph Si Li Li Me H Ultrasonic waves speed up not only hydrogenation, but also dehydrogenation, which seems to be due to the fact that both reactions occur by the same mechanism. For example, the degree of dehydrogenation of tetrahydronaphthalene to naphthalene in the presence of 3% Pd/C as a catalyst in diethylene glycol at 473K reaches 55% after 6 h.108 The use of ultrasound makes it possible to decrease the temperature to 453 K and to achieve the total conversion within the same time.The use of pulse ultrasound is as effective as continuous ultrasound. Dehydrogenation of triethy- lene glycol in dimethyl ether is much less sensitive to ultrasound. Ultrasound makes it possible to increase the efficiency of the preparation of deuterium-labelled compounds.109 The Raney nickel-catalysed hydrogen exchange for deuterium in a monosac- charide was performed in different solvents under the action of ultrasound. Deuterium was introduced with a high stereospecific- ity and regioselectivity.Ultrasonication of a reaction mixture containing barium hydroxide increased the rates of the reactions and the yields of products involving aromatic aldehydes. For example, 4-chloro- benzaldehyde does not enter into the Cannizzaro reaction in the absence of ultrasound. The use of catalytic poisons which affect selectively the oxidative active centres made it possible to establish that this reaction occurs on the reduction centres, the catalytic cycle being initiated by a single-electron transfer from the catalyst to the substrate.5 Acceleration of the aldol condensation of ketones in an ultrasonic field in the presence of Al2O3 is confirmed by the following data:110 sonolysis of 1-tetralone in an argon atmosphere at 353 K for 24 h produces the hydroxy ketone in 80% ±90% yield, whereas in the absence of ultrasound its yield is not more than 52% after 144 h.The rate of the Ullmann coupling of 2-iodonitrobenzene in dimethylformamide in the presence of copper bronze at 333 K is increased 64-fold upon sonication.111 If this process is performed in the usual manner, but using the pre-sonicated copper bronze, its rate also increases compared to the reaction rate on the ultra- sound-nontreated copper bronze, though to a much lesser extent. This effect may be easily explained by the decrease in the size of metal powder particles under ultrasonic treatment. An appreci- able acceleration of the reaction under the direct action of ultra- sound results from the constant activation of the metal surface. In addition, the sonochemical process has two other advantages: it requires a considerably smaller excess of copper and excludes sticking of metal powder to the walls of the reaction vessel.Sonication was also employed in the synthesis of a-amino acids using amino acid g-anion equivalents.112 The reaction ofEffects of ultrasound on catalytic processes activated zinc with a iodohomoalanine derivative yields alkylzinc iodide, which reacts in the presence of palladium catalysts with a number of electrophiles (aryl iodides and acid chlorides) produc- ing the corresponding a-amino acid derivatives. Sufficiently high yields are obtained using tetrahydrofuran as the solvent in the former case; to reach high yields in the reactions with acid chlorides under the action of ultrasound, it is necessary to use a combination of toluene and dimethylacetamide.Furthermore, alkylzinc iodide may be transformed into a zinc ± copper couple, which reacts with allyl halides and reactive acid chlorides to give sufficiently high yields of the corresponding adducts. The accelerating effect of ultrasonic treatment was exempli- fied in the liquid-phase alkylation of benzene by cyclohexene yielding cyclohexylbenzene.113 The reaction was conducted on an AlCl3 catalyst prepared by the method of chemical deposition on SiO2 from the vapour phase. These catalysts are active below 273 K and can be regenerated. Despite the fact that the activity of the catalysts becomes lower in successive experiments, they can be used repeatedly.At least until the sixth cycle, the turnover number was 110. Apparently, reactions on solid catalysts are limited by the diffusion of reagents and/or products into the catalyst's pores. The ultrasonic impact in the course of catalytic reaction provides an accelerating effect, so that, depending on the size of the catalyst's particles, the reaction rate can increase by even one order of magnitude. It is of note that the action of surface acoustic waves changes appreciably the activation energy and the reaction orders on oxidised catalytic surfaces, whereas on the reduced surfaces these changes prove to be much smaller. At a resonance frequency, oxidation of ethanol on palladium is accelerated 140 ± 160 times, which may be explained by a stronger distortion of the lattice under these conditions.72 The application of USW speeds up substantially b-hydrox- ylation of acrylonitrile at room temperature (the same effect was also revealed in a homogeneous reaction 101) on a catalytic system comprising copper(I) oxide and tetramethylethylenediamine. With the use of USW, the yield of the b-adduct also increases from 30% (stirring) to 70%± 75%.114 Ultrasonic acceleration of reactions on non-metal catalysts (using HSiCl3 as the silylation agent) was not studied as thoroughly as that on metals;115, 116 nonetheless, in these cases too the increase in the reaction rate is related to the increase in the specific surface of the solid reagent due to the decrease in the particle size upon cavitation and the improvement in the mass transfer of a liquid reagent to the solid phase surface.The reaction route can also be changed under the action of ultrasound.5 Stirring aluminium oxide with KCN in a mixture of p-methylbenzyl bromide and toluene leads to the formation of products of the Friedel ± Crafts reaction (in this case, aluminium oxide acts as a catalyst). Under the action of ultrasound, this reaction follows a different route: p-methylbenzyl cyanide is formed as a result of direct substitution of CN for Br. KCN, Al2O3 Me CH2Br + Me USW Me CH2CN Me stirring Me CH2 The change in the composition of products upon sonication is presumed to be due to the saturation of the Lewis acid centres on the aluminium oxide surface with CN7 ions, which induces nucleophilic substitution.5 The reaction of aryl iodides with zinc powder accelerated by ultrasound yields arylzinc compounds which contain the electron- withdrawing groups, viz,.CO2Me, C(O)NMe2, CN, Br, Cl and CF3. The presence of these groups provides fairly good yields of 173 asymmetric multifunctional biaryls in the catalytic synthesis with participation of Pd(0).117 Ultrasonication is also employed in electrochemical processes for intensifying the electrode reactions, which may be exemplified in the sonovoltammetric reduction of nitrobenzene on glassy carbon and gold electrodes.118 The four-electron reduction of nitrobenzene in an alkaline solution (pH 13) was studied as a model.The mechanism of electrochemical reduction is known to be complex; it includes protonation and dehydration, the proc- esses proceeding both on the surface and in bulk depending on the nature and the state of the electrode. In the absence and in the presence of ultrasound, the reduction of nitrobenzene on the glassy carbon electrodes includes a chemically reversible process followed by the irreversible three-electron reduction. The com- bined use of a rotating disc and sonovoltammetry permits one to decrease the capacity of the double layer. Electrochemical dehalogenation of organic compounds in microemulsions of a system didodecyldimethylammonium bro- mide ± water ± dodecane under the action of ultrasound in the presence of zinc phthalocyanine as a catalyst proceeds faster than in a homogeneous system including toxic and expensive organic solvents.119 Thus, ultrasound accelerates the heterogeneous catalytic reac- tions owing to a better mass transfer, smaller size of the surface particles and creation of active centres on which the substrate undergoes specific transformation. 3.Phase-transfer catalysis Ultrasound initiates and accelerates reactions in phase-transfer catalysis.120, 121 The chemical effect of ultrasound in this case is also explained by the coalescence of cavitation bubbles, whereas its mechanical impact is associated with the formation of a highly dispersed emulsion which increases appreciably the interface area.The mechanism of a typical phase-transfer reaction resembles the substitution mechanism. The overall equation RY(org)+MX(aq) RX(org) +MY(aq) includes the catalytic cycle (organic phase) RY+[Q+X7] RX+[Q+Y7] M+X7 + [Q+Y7] M+Y7 + [Q+X7] (aqueous phase), where Q+ is the cation of the phase-transfer catalyst (PTC). Combined action of PTC and ultrasound in heterogeneous reactions can be exemplified in the reaction of benzyl chloride with solid sodium sulfide in the presence of tetrabutylammonium bromide as PTC and acetonitrile as the solvent.122 Na2S S CH2 CH2 CH2Cl The proposed mechanism includes two phase-transfer ion- exchange stages and the main reaction in the organic phase: 2NaBr(sol)+Q+S27Q+(org) , Na2S(sol)+2Q+Br7(org) Q+S27Q+(org)+2 PhCH2Cl(org) PhCH2SCH2Ph(org)+2Q+Cl7(org), 2NaCl(sol)+Q+S27Q+(org).Na2S(sol)+2Q+Cl7(org) The results obtained upon the use of PTC and ultrasound and upon their combined action are shown in Fig. 3. The catalytic cycle of transformation of benzyl chloride includes the transfer of sulfide anions to the organic phase. The influence of ultrasound on the molecular diffusion and dissolution of sodium sulfide in acetonitrile is minimal, whereas a slight increase in the conversion occurs owing to the development of174 Conversion (%) 50 30 1� 2� 3� 4� 100 5 15 10 t /min Figure 3. Results of the use of PTC and ultrasound in the reaction of benzyl sulfide formation (USW intensity, 150W cm72): (1) without USW and PTC; (2) with USW; (3) 0.4% PTC; (4) 0.4% PTC+USW.the interface where the reaction takes place, facilitation of mass transfer and effective stirring of the reagents as a result of cavitation. Combination of PTC and ultrasound gives a max- imum increase in the conversion owing to the additive effect of their individual impacts on the system. Ido et al.123 investigated the possibility of the multiple use of phase-transfer catalysts. The catalyst (hexadecyltri-n-butylphos- phonium bromide) is concentrated in the third phase formed between the organic (dodecane) and the aqueous (saturated KBr solution) phases. This interface catalyses substitution in benzyl chloride by bromide, the former being in the organic phase and the latter, in the aqueous phase.After completion of the reaction, the organic phase was removed and a new phase was introduced. The application of USW made it possible to avoid direct contact between the organic and the aqueous phase. The three phases were not mixed, the reagents were transferred across the interface under the impact of ultrasonic vibrations. According to the theoretical concepts,48 the chemical action of ultrasound is limited by the unpaired electron transfer. In this case, the reaction mechanism includes only ionic species; there- fore, the effect of ultrasound is of physical nature. Ultrasound in fact increases the catalyst surface area since cavitation prevents agglomeration of particles. Sonochemical acetylation of tertiary alkyl halides in the presence of zinc acetate was accomplished in the presence of PTC and under the action of ultrasound.124 Alkylation of a glycine derivative by activated organohalogen compounds under the conditions of ultrasonic acceleration of phase transfer and subsequent hydrolysis of the products yielded aminoacylsultams and then, upon mild saponification, pure a-amino acids in a rather high overall yield.125 In the example of the addition of ethyte to chalcone in the presence of KOH and trimethylbenzylammonium chloride as PTC (the Michael reaction) it was shown that with ultrasonic stirring the reaction is complete in 2 min, instead of 1 h.89 Ar EtO EtO Ar + COAr OEt OEt O O COAr O O Allylation and benzylation of sodium 5-b-D-glucopyranosyl- 1,3-dimethylbarbiturate in water were carried out with benzyl bromide inMe2SO or allylic and benzylic bromides in the presence of PTC under sonication.126 The application of ultrasound in combination with phase- transfer catalysts, crown-ethers and lithium chloride accelerated the transformation of 6-methoxytetralins into 8-methoxytetralins including the stages of cleavage and cyclisation by the intermo- lecular Friedel ± Crafts alkylation.127 M G Sulman It is noteworthy that in many cases the application of ultra- sound makes it possible to avoid PTC.An example is the cyclo- propanation of styrene in which the yield of 96% was reached within 1 h without PTC.128 Cl Cl NaOH, CHCl3 In the control reaction carried out under mechanical mixing the yield was only 30% after 16 h. 4.Enzymic catalysis Recent studies show the possibility of the ultrasonic influence on enzymic reactions. Acoustic vibrations increase substantially the activity and decrease the size of subtilisin particles which catalyse trans-esterification in organic solvents, the changes in the USW amplitude having no effect on the reaction rate.129 It was shown that the activity of enzymes depends on the duration of sonication. Thus a short-term action of ultrasound activates butyryl chol- inesterase, whereas a prolonged action brings about partial dissociation of the tetrameric enzyme and its irreversible inactiva- tion.130 Total inactivation of peroxidases (lipoxenases and phenol oxidases) under the action of ultrasound and elevated temper- atures is used in food technologies.131 Ultrasound was shown to influence hydrolysis of sucrose catalysed by invertase.132 The effect of ultrasound was studied over a wide range of changes in biochemical and physical conditions, such as pH, sucrose concentration andUSWintensity.It was found that the reaction rate increases at low sucrose concentrations. At high concentrations, continuous ultrasonic vibrations have a more substantial influence on this enzymic reaction. The rate of reactions catalysed by lipase from porcine pan- creas is increased 3 ± 60 times under the conditions of azeotropic distillation and 7 ± 83 times under the action of ultrasound, the enantioselectivity being preserved in both cases.133, 134 IV.Regeneration of catalysts Traditional techniques for the regeneration of catalysts include their high-temperature calcination in the atmosphere of oxygen to remove organic residues.135 However, the initial catalyst's activity is not recovered completely. The physical components of the ultrasonic action make it possible to use acoustic treatment for the effective regeneration of catalysts. Thus the initial activity of a brass catalyst used for the preparation of acetone from propan-2- ol recovered to 83% under the action of ultrasound (18 ± 22 kHz, 6 ± 20 W cm72) in a solution of sulfuric and nitric acids and sodium bichromate.5 Without ultrasound, the activity of this catalyst recovered only to 63%. Ultrasound intensifies considerably the oxidative regenera- tion of the deactivated rhodium triphenylphosphine catalyst used in the hydroformylation of alkenes.136 Anickel-molybdenum catalyst used for the cracking of hydro- carbons was regenerated by oxidation in air with the subsequent action of USW in low-viscosity oils.5 Similarly, a 30-min action of an acoustic field in water led to the regeneration of the activity of a catalyst of denitrification of waste gases (TiO2±V2O3).Ultrasound restores totally the specific surface, porosity and activity of the palladium ± aluminium catalyst APK-Z, which is used for the removal of nitrogen oxides from exhaust gases.137 The activity of the 3% Pd/C catalyst in diethylene glycol used for the dehydrogenation of tetrahydronaphthalene and studied earlier in an analogous reaction without ultrasound 138 decreases in the course of the reaction, but it can be restored with the aid of ultrasound.108 A series of studies 24, 139 ± 143 were devoted to the regeneration of the industrial ShPAK-0.5 catalyst (0.5% Pd/Al2O3) modified by zinc acetate, pyridine and KOH.This catalyst is used for the selective hydrogenation of the triple bond of acetylenic alcohols toEffects of ultrasound on catalytic processes Zn : Pd (mass %) 431 1� 2� 3� 0 1 2 5 6 3 4 Point number Figure 4. Changes in the Zn : Pt ratio across the granule in subsurface layers of a fresh catalyst (1), exhausted catalyst (2) and a catalyst following sonication (3). The distance between the points is 0.05 mm.the double bond in the synthesis of vitaminAand E intermediates. In the course of hydrogenation, the catalyst loses its activity and its selectivity is decreased. Besides, the use of physicochemical methods (X-ray spectral microanalysis, electron microscopy and X-ray photoelectron spectroscopy) showed that the catalyst's surface is changed substantially. The ultrasonic treatment with an intensity of 1 W cm72 and a 3-min duration leads to the total recovery of the initial properties of the catalyst (Fig. 4).54 After the ultrasonic treatment, the content of zinc and palladium in the surface layers of the regenerated catalysts becomes the same as that in the fresh sample. Probably, this is explained by the purification of the surface from coke deposits and the diffusion of the zinc atoms into the subsurface layer.The XPES data also point to a possible amorphisation of the structure of the catalyst's surface, which is at variance with the conclusions made in Refs 54 and 66. V. Conclusion The application of ultrasound in chemistry, particularly in catal- ysis, is one of the most fortunate examples of the use of non- conventional physical methods influencing a reaction system. The present review reflects only the basic results of studies of the applicability of USW for the preparation, activation and regener- ation of various catalytic systems as well as for conducting catalytic reactions. The unique results of the action of ultrasound make rather attractive the prospects of its technological uses and are also of appreciable interest for fundamental research.Sum- ming up the above considerations, let us emphasise the following most important moments. It has been established that ultrasound increases the specific catalyst's surface, because cavitation prevents the agglomeration of particles. The action of ultrasound on solids, including cata- lysts, increases the content of small particles (3 ± 5 nm) and modifies their lyophilicity. Under ultrasonic treatment, the increase in the activity of catalysts is often several orders of magnitude larger than the increase in their specific surface. This may be associated with a specific action of ultrasound on the nature of the active centres.The change in the nature of the active centres influences not only the catalytic activity but also the reaction selectivity, including enantioselectivity. In an ultrasonic field, the rate of catalytic reactions remains constant for a long time, i.e., the stability of a catalyst is enhanced. In addition, the acoustic waves can change the activation energy and the reaction orders. The combined use of phase-transfer catalysts and ultra- sound provides a maximum increase in the degree of conversion owing to the addition of their individual impacts on the system. In a number of cases, the application of ultrasound makes it possible to conduct reactions without phase-transfer catalysts. A topical problem is the use ofUSW and resonance vibrations for the creation of heterogeneous catalysts with adjustable func- tions.Heterogeneous reactions in a liquid phase are limited by the diffusion of the reagents and/or the product in the catalyst's pores. 175 The application of ultrasonic vibrations in the course of a catalytic reaction leads to a several-fold increase in its rate depending on the f the catalyst particles. The optimum USW parameters are individual for each catalyst and catalytic reaction. The ultrasonic treatment increases appreciably the spillover of hydrogen which explains higher activity of ultrasound-treated catalysts in hydrogenation reac- tions. The phenomenon of catalyst's deactivation, which is some- times observed at a longer duration and a higher intensity of ultrasonic treatment, may be explained by the rearrangement of active centres, which is in turn related to the modification of the catalyst's surface.The fundamental question about a detailed mechanism of catalysis in an ultrasonic field remains still open to debate. Solution of this problem is a priority issue in the catalysis and determines the prospects of the technological use of USW. References 1. M A Margulis Sonochemistry and Cavitation (Luxemburg: Gordon and Breach, 1995) 2. M A Margulis Osnovy Zvukokhimii (Khimicheskie Reaktsii v Akus- ticheskikh Polyakh) [Foundation of Sonochemistry (Chemical Reactions in Acoustic Fields)] (Moscow: Vysshaya Shkola, 1984) 3. T J Mason, J Ph Lorimer Sonochemistry. Theory, Application and Uses of Ultrasound in Chemistry (London: Ellis Horwood, 1988) 4.K S Suslick (Ed.) Ultrasound, Its Chemical, Physical and Biological Effects (New York: VCH, 1988) 5. T J Mason (Ed.) Chemistry with Ultrasound (New York: Elsevier, 1990) 6. M A Margulis Zh. Vses. Khim. O-va im. D I Mendeleeva 35 579 (1990) a 7. R L Hunicke Ultrasonics 28 291 (1990) 8. M A Margulis, G P Los', O I Zinov'ev Zh. Fiz. Khim. 65 3054 (1991) b 9. B G Novitskii Primenenie Akusticheskikh Kolebanii v Khimiko-Tekh- nologicheskikh Protsessakh (Application of Acoustic Vibrations for Chemical Technological Processes) (Moscow: Khimiya, 1983) 10. V I Ivanskii Kataliz v Organicheskoi Khimii (Catalysis in Organic Chemistry) (Leningrad: Leningrad State University, 1985) 11.B C Gates Catalytic Chemistry (London: Wiley, 1992) 12. I P Golyamina (Ed.) Ul'trazvuk. Malen'kaya Entsiklopediya (Ultrasound. Small Encyclopedia) (Moscow: Sov. Entsiklopediya, 1979) 13. I E El'piner Ul'trazvuk. Fizikokhimicheskoe i Biologicheskoe Deistvie (Ultrasound. Physicochemical and Biological Effect) (Moscow: Fizmatgiz, 1963) 14. G A Kardashev, in Akusticheskaya Kavitatsiya i Primenenie Ul'tra- zvuka v Khimicheskoi Tekhnologii (Tez. Dokl. Vsesoyuz. Nauch. Konf.), Slavskoe, 1985 [Acoustic Cavitation and Application of Ultrasound in Chemical Technology (Abstracts of Reports of the All-Union Research Conference), Slavskoe, 1985] p. 66 15. M G Sulman, I Yu Yanov, Yu Yu Kosivtsov, in Programmnye i Tekhnicheskie Sredstva Mediko-Biologicheskikh i Tekhnicheskikh Sistem, Tver', 1998 (Software and Technical Hardware of Medical Biological and Technical Systems, Tver', 1998) p.108 16. D Bremner Adv. Sonochem. 1 1 (1990) 17. B Abismail, J P Canselier, A M Wilhelm,H Delmas, C Gourdon, in Applications of Power Ultrasound in Physical and Chemical Processing (Abstracts of Reports), Toulouse, 1997 p. 151 18. M A Margulis, in Applications of Power Ultrasound in Physical and Chemical Processing (Abstracts of Reports), Toulouse, 1997 p. 87 19. K V Patel, K Ethirajulu, N Subrahmanyam Chem. Age India 35 29 (1984) 20. A N Kotyusov Akust. Zh. 38 179 (1992) 21. J Lindley, T J Mason, J P Lorimer Ultrasonics 25 45 (1987) 22. K S Suslick, D J Casadonte J. Am. Chem. Soc. 109 3459 (1987) 23.V M Fridman Fiziko-Khimicheskoe Deistvie Ul'trazvuka i Ul'trazvu- kovaya Apparatura dlya Intensifikatsii Khimiko-Tekhnologicheskikh Protsessov (Physicochemical Effect of Ultrasound and Ultrasound Equipment for Intensification of Chemical Technological Processes) (Moscow: NIIKhM, 1965)176 24. M G Sulman, V G Matveeva, E M Sulman, N I Komarova, S P Kobeleva Kinet. Katal. 39 635 (1998) c 25. T A Garibyan, A A Muradyan, R R Grigoryan, N S Manukyan Kinet. Katal. 34 742 (1993) c 26. M A Margulis Zvukokhimicheskie Reaktsii i Sonolyuminestsentsiya (Sonochemical Reactions and Sonoluminescence) (Moscow: Khimiya, 1986) 27. K S Suslick Science 247 1439 (1970) 28. E A Neppiras Phys. Rep. 61 159 (1980) 29. I Anton Cavitatia Vol. 2 (Bucuresti, Academia RSR, 1985) 30.C Einhorn, J Einhorn, J L Luche Synthesis 787 (1989) 31. E M Sulman,M G Sulman, D N Pirog, N V Semagina, in Organ- icheskii Sintez i Kombinatornaya Khimiya (Tez. Dokl. Mezhdunar. Nauch. Konf.), Moskva, Zvenigorod, 1999 [Organic Synthesis and Combinatorial Chemistry (Abstracts of Reports of International Research Conference), Moscow, Zvenigorod, 1999] p. 153 32. M Sulman, E Sulman, D Pirog, N Semagina, in The 13th Inter- national Congress of Chemical and Process Engineering (Abstracts of Reports), Prague, 1998 Vol. 2, p. 33 33. J L Luche, C Einhorn, J Einhorn, J C de Souza Barboza, C Petrier, C Dupuy, P Delair, C Allavena, T Tuschl Ultrasonics 28 316 (1990) 34. P G Manzo, S M Palacios, R A Alonso Tetrahedron Lett.35 677 (1994) 35. I Hua, R H HoÈ chemer, M R Hoffmann J. Phys. Chem. 99 2335 (1995) 36. G Gopalakrishnan, S Anandhi, N S Narasimhan Indian J. Chem. B, Org. Chem. Incl. Med. 35 1194 (1996) 37. G Gopalakrishnan, S Anandhi, N S Narasimhan Indian J. Chem. B, Org. Chem. Incl. Med. 35 1197 (1996) 38. A-S Y Lee, C-L Cheng Tetrahedron 53 14255 (1997) 39. MWoltersdorf,RKranich, H-G Schmalz Tetrahedron 53 7219 (1997) 40. R SanMartin, R Olivera, E Martinez de Marigorta, E Domingues Tetrahedron 51 5361 (1995) 41. H C Chou, J O Stoffer J. Appl. Polym. Sci. 72 797 (1999) 42. E A Mistryukov Mendeleev Commun. 6 251 (1993) 43. M T Molina, C del Valle, A M Escribano, J Ezquerra, C Pedregal Tetrahedron 49 3801 (1993) 44. M A Margulis, A N Mal'tsev Vestn.Mosk. Univ., Ser. 2, Khim. (5) 540 (1971) d 45. M A Margulis, A V Sokol'skaya, I E El'piner Akust. Zh. 10 370 (1964) 46. D M Kolosov, V A Nikulin, S P Chernykh Zh. Fiz. Khim. 64 355 (1990) b 47. K S Suslick, D A Hammerton, R E Cline J. Am. Chem. Soc. 108 5641 (1986) 48. J L Luche, C Einhorn, J Einhorn, J V Sinisterra-Gago Tetrahedron Lett. 31 4125 (1990) 49. Yu I Skorik, K G Gileva, E V Kukharskaya Izv. Akad. Nauk SSSR, Ser. Khim. 932 (1963) e 50. A N Mal'tsev Zh. Fiz. Khim. 50 1641 (1976) b 51. Li Wen-zhou, A N Mal'tsev, N I Kobozev Zh. Fiz. Khim. 38 80 (1964) b 52. Li Wen-zhou, A N Mal'tsev, N I Kobozev Vestn. Mosk. Univ., Ser. 2, Khim. (1) 39 (1964) d 53. A N Mal'tsev, I V Solov'eva Zh. Fiz. Khim. 44 1092 (1970) b 54.C L Bianchi, R Carli, C Fontaneto, V Ragaini Stud. Surf. Sci. Catal. 91 1095 (1995) 55. E M Sulman Usp. Khim. 63 981 (1994) [Russ. Chem. Rev. 63 923 (1994)] 56. Z X Cheng, S B Yuan, J W Fan, J W Zhu,M S Zhen Stud. Surf. Sci. Catal. 112 261 (1997) 57. G SzoÈ lloÈ si, B ToÈ roÈ k, G Szakonyi, I Kun,M Barto k Appl. Catal. A, Gen. 172 225 (1998) 58. E M Sulman, I P Shkileva,M G Sulman, O B Sannikov Kinet. Katal. 36 865 (1995) c 59. Russ. P. 2 102 136; Byull. Izobret. (2) 191 (1998) 60. M G Sulman, V G Matveeva, D N Pirog, N V Semagina, L M Bronshtein, D M Chernyshov, in XVI Mendeleevskii S'ezd po Obshchei i Prikladnoi Khimii (Tez. Dokl.), Moskva, 1999 [The XVIth Mendeleev Congress on General and Applied Chemistry (Abstracts of Reports), Moscow, 1999] Pt.2, p. 496 61. M G Sulman, D N Pirog, V G Matveeva, E M Sulman, in Applications of Power Ultrasound in Physical and Chemical Proc- essing (Abstracts of Reports), Toulouse, 1997 p. 139 M G Sulman 62. C L Bianchi, R Carli, S Lanzani, D Lorenzetti, G Vergani, V Ragaini Catal. Lett. 22 319 (1993) 63. T V Paryichak,A N Mal'tsev,N I Kobozev Zh. Fiz. Khim. 41 1206 (1967) b 64. S Bernal, J J Calvino, M A Cauqui, J M Rodriguez Izquierdo, H Vidal Stud. Surf. Sci. Catal. 91 461 (1995) 65. P Boudjouk, S-B Choi, B J Hauck, A B Rajkumar Tetrahedron Lett. 39 3951 (1998) 66. H B Li, R Zhang, H Wang, Y Pan, Y Z Shi Synth. Commun. 27 3047 (1997) 67. T A Gharibyan, A A Muradyan, R R Grigoryan, V T Minasyan, in Applications of Power Ultrasound in Physical and Chemical Processing (Abstracts of Reports), Toulouse, 1997 p.45 68. Y Liao, H Shabany, C D Spilling Tetrahedron Lett. 39 8389 (1998) 69. A A Muradyan, T A Garibyan, A B Nalbandyan Kinet. Katal. 30 824 (1989) c 70. J L Li, T Inui Appl. Catal. A, Gen. 139 87 (1996) 71. U Kunz, C Binder, U Hoffmann Stud. Surf. Sci. Catal. 91 869 (1995) 72. K K Moe, T Tagawa, S Goto J. Ceram. Soc. Jpn. 106 242 (1998) 73. K S Suslick, T Hyeon,M Fang Chem. Mater. 8 2172 (1996) 74. Y Inoue, Y Watanable, Y Ohkawara Nippon Kagaku Kaishi 317 (1996); Chem. Abstr. 124 271 550 (1997) 75. J Lindley, in Chemistry with Ultrasound Vol. 28 (London; New York: Elsevier, 1990) p. 27 76. C L Bianchi, R Carli, S Lanzani, D Lorenzetti, G Vergani, V Ragaini Ultrason.Sonochem. 1 S47 (1994) 77. E I Klabunovskii, A A Vedenyapin Asimmetricheskii Kataliz. Gidrogenizatsiya na Metallakh (Asymmetric Catalysis. Hydrogenation on Metals) (Moscow: Nauka, 1980) 78. B ToÈ roÈ k, K FelfoÈ ldi, G Szakonyi, A'Molna r,M Barto k, in Catalysis of Organic Reactions (Ed. F E Herkes) (New York: Marcel Dekker, 1998) p. 129 79. B ToÈ roÈ k, K FelfoÈ ldi, G Szakonyi, K Balazsik, M Bartok Catal. Lett. 52 81 (1998) 80. A Tai, T Kikukawa, T Sugimura, Y Inoue, S Abe, T Osawa, T Harada Bull. Chem. Soc. Jpn. 67 2473 (1994) 81. A Tai, T Kikukawa, T Sugimura, Y Inoue, S Abe, T Osawa, T Harada Stud. Surf. Sci. Catal. 75 2443 (1993) 82. A Tai, T Kikukawa, T Sugimura, Y Inoue, T Osawa, S Fujii J. Chem.Soc., Chem. Commun. 795 (1991) 83. B H Han, P Boudjouk Organometallics 2 769 (1983) 84. P Boudjouk, B-H Han J. Catal. 79 489 (1983) 85. P W Cains, L J McCausland, D M Bates, T J Mason Ultrason. Sonochem. 1 S45 (1994) 86. K S Suslick, S J Doktycz Adv. Sonochem. 1 197 (1990) 87. J-P Mikkola, T Salmi Chem. Eng. Sci. 54 1583 (1999) 88. M Uchiyama, S Furumoto,M Saito, Y Kondo, T Sakamoto J. Am. Chem. Soc. 119 11425 (1997) 89. C Le Roux, H Gaspard-Iloughmane, J Dubac, J Jaud, P Vignaux J. Org. Chem. 58 1835 (1993) 90. Y Masuyama, A Hayakawa, M Kishida, Y Kurusu Inorg. Chim. Acta 220 155 (1994) 91. N Ratoarinoro, A M Wilhelm, J Berlan, H Delmas Chem. Eng. J. 50 27 (1992) 92. A MuÈ ller, C Vogt, N Sewald Synthesis 6 837 (1998) 93. D A Donatti, D R Vollet J.Non-Cryst. Solids 208 99 (1996) 94. C Zhang, A M M Mjalli Tetrahedron Lett. 37 5457 (1996) 95. Z-r Zhang, F Flachsmann, F M Moghaddam, P RuÈ edi Tetrahedron Lett. 35 2153 (1994) 96. G H P Roos, P Rampersadh Synth. Commun. 23 1261 (1993) 97. J G Lin, C N Chang, J R Wu, Y S Ma Water Sci. Technol. 34 41 (1996) 98. M Zheng, L C Wang, J G Shao,Q Zhong Synth. Commun. 27 1751 (1997) 99. M S F L K Jie, M S K Syedrahmatullah, C K Lam, P Kalluri Lipids 29 889 (1994) 100. Y Iamamoto, Y M Idemori, S Nakagaki J. Mol. Catal. A, Chem. 99 187 (1995) 101. Y Iamamoto,M D Assis, K J Ciuffi, H C Sacco, L Iwamoto, A J B Melo, O R Nascimento, C M Prado J. Mol. Catal. A, Chem. 109 189 (1996) 102. W Lintner, D Hansian Ultrasonics 15 21 (1977)177 Effects of ultrasound on catalytic processes 142.M G Sulman, V G Matveeva, I P Shkileva, in Naukoemkie Khimi- cheskie Tekhnologii (Tez. Dokl. III Mezhdunar. Konf.), Tver', 1995 [Science-Dependent Chemical Technologies (Abstracts of Reports of the IIIth International Conferences), Tver', 1995] p. 174 143. M G Sulman, V G Matveeva, T V Ankudinova, N I Komarova, in Sintez Biologicheski Aktivnykh Veshchestv (Synthesis of Biologically Active Substances) (Tver': Tver' State Technological Institute, 1996) p. 51 103. P Boudjouk, in Ultrasound, Its Chemical, Physical and Biological Effects (Ed. K S Suslick) (New York: VCH, 1988) p. 165 104. M A Margulis, Yu T Didenko Zh. Fiz. Khim. 54 1587 (1980) b 105. V N Kondrat'ev, E E Nikitin Khimicheskie Protsessy v Gazakh (Chemical Processes in Gases) (Moscow: Nauka, 1981) 106. H BoÈ nnemann, B Bogdanovic, R Brinkmann, D-w He, B Spliethoff Angew. Chem., Int. Ed. Engl. 22 728 (1983) 107. T Ando, T Kawate, J Yamawaki, T Hanafusa Synthesis 637 (1983) a�Mendeleev Chem. J. (Engl. Transl.) b�Russ. J. Phys. Chem. (Engl. Transl.) c�Kinet. Catal. (Engl. Transl.) d�Moscow Univ. Bull. (Engl. Transl.) e�Russ. Chem. Bull. (Engl. Transl.) 108. T J Mason, J P Lorimer, L Paniwnyik, P W Wright, A R Harris J. Catal. 147 1 (1994) 109. E A Cioffi Tetrahedron Lett. 37 6231 (1996) 110. B C Barot, D W Sullins, E J Eisenbraun Synth. Commun. 14 397 (1984) 111. J Lindley, J P Lorimer, T J Mason Ultrasonics 24 292 (1986) 112. R F W Jackson, J L Fraser, N Wishart, B Porter, M J Wythes J. Chem. Soc., Perkin Trans. 1 1903 (1998) 113. S Sato, F Nozaki, S J Zhang, P Cheng Appl. Catal. A, Gen. 143 2 271 (1996) 114. A B Rajkumar, P Boudjouk Organometallics 8 549 (1989) 115. S Raucher, P J Klein J. Org. Chem. 46 3558 (1981) 116. B H Han, P Boudjouk Tetrahedron Lett. 23 1643 (1982) 117. K Takagi Chem. Lett. 469 (1993) 118. F Marken, S Kumbhat, G H W Sanders, R G Compton J. Electroanal. Chem. 414 95 (1996) 119. J F Rusling, S Schweizer, S P Zhang, G N Kamau, P Lo Nostro, S H Chen, Y C Liu, J Teixera, L Kevan Colloid Surf. A, Physicochem. Eng. Aspects 88 41 (1994) 120. E Diez-Barra, A de la Hoz, A Diaz-Ortiz, P Prieto Synlett 893 (1992) 121. S Deshayes, M Liagre, A Loupy, J-L Luche, A Petit Tetrahedron 55 10851 (1999) 122. L C Hagenson, S D Naik, L K Doraiswamy Chem. Eng. Sci. 49 4787 (1994) 123. T Ido, K Yamaguchi, T Yamamoto, S Goto Kagaku Kogaku Ronbunshu 21 804 (1995) 124. J Jayasree, J M Rao Synth. Commun. 26 1103 (1996) 125. W Oppolzer, R Moretti, C Y Zhou Helv. Chim. Acta 77 2363 (1994) 126. G Wulff, G Clarkson Carbohydr. Res. 257 81 (1994) 127. D C Harrowven, R F Dainty Tetrahedron 53 15771 (1997) 128. O Repic, C Vogt Tetrahedron Lett. 23 2729 (1982) 129. E Bracey, R A Stenning, B E Brooker Enzyme Microb. Technol. 22 147 (1998) 130. M-T Froment, O Lockridge, P Masson Biochim. Biophys. Acta (Protein Structure and Molecular Enzymology) 1387 53 (1998) 131. L De Gennaro, S Cavella, R Romano, P Masi J. Food Eng. 39 401 (1999) 132. M Sakakibara, D Wang, R Takahashi, K Takahashi, S Mori Enzyme Microb. Technol. 18 444 (1996) 133. G Lin, H-C Liu Tetrahedron Lett. 36 6067 (1995) 134. G Lin, H-C Liu, S H Liu J. Chin. Chem. Soc. 42 957 (1995); Chem. Abstr. 124 201 511 (1995) 135. R A Buyanov Sib. Khim. Zh. 1 5 (1991) 136. Y V Slivinskii, V I Kurkin,M M Ali, G A Korneyeva, R A Aronovich,O Y Pesin,M A Margulis,Y I Solovetskii Petrol. Chem. 35 154 (1995) 137. A V Romenskii, A Ya Loboiko, V I Atroshchenko Khim. Tekhnol. 6 39 (1986) 138. R E Malz, H Greenfield, in Catalysis of Organic Reactions (Eds P N Rylander, H Greenfield) (New York: Marcel Dekker, 1990) p. 262 139. Russ. P. 2 080 921; Byull. Izobret. (16) 77 (1997) 140. E M Sulman,M G Sulman, O B Sannikov, V G Matveeva, M V Gridneva, N I Komarova, in The 18th International Conference on Science and Technology (Abstracts of Reports), New Delhi, India, 1995 p. 18 141. E M Sulman,M G Sulman, V G Matveeva, I P Shkileva, T V Ankudinova, in XV Mendeleevskii S'ezd po Obshchei i Prikladnoi Khimii (Tez. dokl.), Minsk, 1993 [The XVth Mendeleev Congress on General and Applied Chemistry (Abstracts of Reports), Minsk, 1993] Vol.

ISSN:0036-021X    

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Russian Chemical Reviews 69 (2) 179 ± 186 (2000) Heat-accumulating properties of melts AMGasanaliev, B Yu Gamataeva Contents I. Introduction II. Methods of the thermal energy accumulation with the use of melts III. Criteria for the estimation of the heat-accumulating properties of melts IV. Principles for the development of heat-accumulating materials based on multi-component systems V. Conclusion Abstract. are melts of properties heat-accumulating the on Data Data on the heat-accumulating properties of melts are generalised. The principles and methods of thermal energy accu- generalised. The principles and methods of thermal energy accu- mulation problem The considered. are melts of use the with mulation with the use of melts are considered. The problem of of search for heat-accumulating materials with the required proper- search for heat-accumulating materials with the required proper- ties anhydrous of systems multi-component on based ties based on multi-component systems of anhydrous inorganic inorganic compounds references 57 includes bibliography The discussed.is compounds is discussed. The bibliography includes 57 references. I. Introduction One of the major problems of the national economy, viz., decreasing power consumption of production, can be solved by two methods. The first one is more efficient transformation of primary energy into electrical and thermal energy. This can be done by increasing the efficiency factor of power stations, by using cheaper fuel types or renewable energy sources, such as wind, geothermal sources, tides, sea waves, etc.The second method of ever-growing importance involves increasing the efficiency of the energy utilisation by the consumer. The expenses for saving fuel and electric power are two to three times lower than those required for expanding the fuel and energy base. The following measures for improving the efficiency of energy usage by the consumers can be listed: transition to more perfect and less power-consuming technologies; use of secondary power resources; smoothing the time differences between the energy generation and energy demand schedules by means of accumulation. Accumulation of electric energy is a difficult problem. The capacities of the existing electrochemical accumulators are insuf- ficient for their use on an industrial scale.The promising super- conducting electric power accumulators are still under develop- ment. The hydraulic methods for energy storage make it possible to accumulate significant amounts of energy; however, this involves large capital investment and impact on the environment (not always favourable). Methods for the thermal energy accumulation have been developed in detail and tested under various conditions. The world energy crisis of the 1970s has confirmed once again the AMGasanaliev, B Yu Gamataeva Dagestan State Pedagogical University, ul. 26 Bakinskikh Komissarov 57, 360219 Makhachkala, Russian Federation. Fax (7-872) 267 06 03. Tel. (7-872) 268 44 80 Received 19 March 1999 Uspekhi Khimii 69 (2) 192 ± 200 (2000); translated by S S Veselyi #2000 Russian Academy of Sciences and Turpion Ltd DOI 10.1070/RC2000v069n02ABEH000490 179 180 183 184 185 urgency of the problem of the thermal energy accumulation followed by heat recovery and transformation into useful work.1 Studies along these lines include two aspects, namely, the chemical-technological and technical-physical ones.2, 3 The chem- ical-technological aspect includes choosing the heat-accumulating materials (HAM), studying their properties and selecting the accumulation method.The thermal energy accumulation and recovery methods involving melts are based on the following processes: heating compounds to a high temperature followed by heat release on cooling (heat accumulation due to the heat capacity of the solid and liquid phases); reversible first-order phase transitions (accumulation due to latent heat of phase transitions); reversible chemical reactions (chemical accumula- tion). The technical-physical aspect examines selection of the processes for the transformation and use of the stored energy.National programmes on the thermal energy accumulation with the use of reliable and inexpensive accumulators have been developed in different countries and are now being implemented. The use of such accumulators enables one to replace the tradi- tional fuel types (coal, natural gas) by non-traditional renewable energy sources 4, 5 as well as allows one to use the spent heat in chemical-technological processes or for heat supply.However, an important drawback of heat accumulators is the high cost of accumulated energy, mainly because of the cost of the HAM. For this reason, the development of heat accumulators starts from the search for cheapHAMwith high heat capacity and predetermined properties. Synthesis of novel inorganic materials with predetermined properties requires complex studies of fusibility diagrams and physicochemical properties of multi-component systems by mod- ern physicochemical methods, primarily those using computer 3D simulation methods.2, 6 ± 8 Recent studies on HAM mostly deal with crystal hydrates of inorganic salts, salt eutectics and metal alloys traditionally used in this field.The present review generalises the data regarding the methods and principles of the thermal energy accumulation using melts of anhydrous inorganic compounds as the HAM. Criteria for the estimation of the heat-accumulating ability of melts and a new methodological approach to the development ofHAMbased on multi-component systems and study of their physicochemical properties are considered. Special attention is given to the system- atisation of experimental data on the fusibility diagrams of multi- component systems.180 II. Methods of the thermal energy accumulation with the use of melts The most popular heat accumulators use melts as the HAM. They can accumulate thermal energy either due to the heat capacity of solid or liquid media or due to the latent heat of phase transitions and chemical reactions.Non-isothermal and isothermal accumu- lators are distinguished, depending on the mode of heat storage. 1. Heat accumulation due to the heat capacity of solid and liquid media The most popular method of heat accumulation is that due to the heat capacity of liquid and solid media. A compound which accumulates heat due to the heat capacity of its different phases is called a heat-capacity compound. Heat accumulators with such a compound as the working medium are non-isothermal. They are used for the heat accumulation over a broad temperature range (several hundred degrees). The allowed temperature variation in an accumulator is normally specified (it is determined by the temperature of the heat source, the temperature of the heat- carrier, the temperature required by the consumer, and the temperature differences controlling the intensity of heat exchange during the accumulator charge and discharge phases).Water (for temperatures up to 100 8C), air, noble gases, melts of simple and complex inorganic compounds and technical oils can serve as heat-carriers. If melts are used as heat-capacity HAM, it has to be taken into account that the specific heat is generally independent of temper- ature and is a constant. The specific energy stored by a heat- capacity heat accumulator is determined by the formula Q=Cp DT , where Cp is the specific heat of the accumulator working medium at constant pressure; DT is the difference between the starting and final accumulation temperatures. It is known from thermodynamics that the specific heat is the higher the smaller the relative molecular mass of the compound.Therefore, compounds with small molecular masses are used as working media for heat-capacity accumulators. Of anhydrous inorganic compounds, systems based on oxides, the so-called refractory compounds, are used as the HAM most commonly. The properties of the most promising oxide-based HAM are analysed in Ref. 9. A great many experimental studies relate to the determination of the dependences of Cp, thermal con- ductivity factor (l) and apparent density (r) on temperature and open porosity (Op). In some cases, natural minerals and anhyd- rous inorganic compounds obtained from them are used, e.g.granite, sand, pebbles, gravel, cobble-stone, macadam, sand ± pebble mixture, etc. Such heat-capacityHAMare inexpensive and readily accessible, are not corrosive with respect to construction materials, but have low effectiveness in terms of their thermal properties, which results in the low density of the accumulated energy. The increase in the specific density of the heat-capacity HAM increases the specific heat, and hence the amount of accumulated heat in the bulk material. The materials based on magnesia have the highest heat capacity; these materials have sufficient thermal Table 1. Heat-accumulating properties of oxide heat-capacity HAM in the temperature range 100 ± 900 8C. Refractory compounds (mass %) Op (%) 20 ± 24 24 ± 30 20 ± 30 3 ± 10 0 ± 3 18 ± 21 Chamotte, 284Al2O3445 Periclase-chromite, 65.5MgO± 14.2 Cr2O3 Forsterite, 58.3MgO± 38.9 SiO2 Periclase-spinel, 75.6MgO± 18.2 Al2O3 Periclase Magnesian limestone, 70MgO± 26.2 CaO AMGasanaliev, B Yu Gamataeva conductivity in the temperature range 100 ± 900 8C to be used as heat-capacity HAM (Table 1).As the proportion of magnesia and the material apparent density increase, the thermal conductivity increases. The thermal conductivity of hyperdense heat-capacity HAM (3.55 ± 3.97 kg m73) exceeds 30 W m71 K71 at 100 8C, while it is less than 5 W m71 K71 for dense (3.00 ± 3.50 kg m73) and medium- density ones (1.83 ± 2.96 kg m73).9 Medium-density materials containing mixtures of magnesia with SiO2, Al2 O3, Cr2 O3, or CaO and having an open porosity of 20%± 30% are most efficient in terms of thermal conductivity (l changes from 0.74 ± 3.93 at 100 8C to 1.07 ± 1.80 at 900 8C).Magnesia-based materials con- taining chromium oxide are the most heat-resistant (see Table 1). 2. Heat accumulation owing to the latent heat of phase transitions The accumulation of heat with the use of the latent heat of phase transitions of anhydrous inorganic compounds is possible in the following changes in the state of aggregation:3, 8 melting>crys- tallisation, vapourisation>condensation, sublimation and decomposition. The heat-accumulating materials which accumulate heat due to phase transitions are called phase-transition HAM.The accu- mulators with such materials as the working media are isothermal. The accumulators in which the latent heat of the melting> crystallisation phase transition is used have good energetic char- acteristics. The principle of such an accumulator is based on the thermal energy absorption accompanying the crystal lattice destruction upon heating of a compound and energy liberation upon crystallisation of the melt on cooling. In many technological processes, the only useful thermal energy is that accumulated due to the heat of phase transitions and due to the heat capacity of the material in the liquid phase.10 ± 14 These processes include: maintaining the given oper- ating temperature of steam at thermal and nuclear power plants; transformation of thermal energy into electrical energy through the Brighton cycle; thermal energy accumulation and transfer with the use of molten phase-transition HAM as heat-carriers; increas- ing the efficiency of non-traditional systems by compensating for the intermittent and non-steady nature of renewable energy sources (solar, wind, geothermal, etc.).The type of the thermodynamic cycle and the nature of the HAM are determined by the operating temperature range of the heat accumulator. This primarily assumes a relationship between the characteristics of the main power system, the accumulator and the parameters of the cycle in which the mass and heat transfer occur. For example, Table 2 lists the efficiency values of three cycles. Yet another example: the maximum temperature of the hot source at a solar power station without radiation concentrating by local concentrators is about 100 8C.In this case, it is only possible to speak about a cycle with evaporation of the working media such as freons. However, these working media cause ecological prob- lems if they leak. In this case, a perfect HAM would consist of eutectic compositions based on n-component mixtures of hydrates and anhydrous compounds with m.p.4100 8C. The thermal characteristics of the most promising systems based on aluminium chloride and alkali metals with the heat- accumulating ability above 0.3 GJ m73 are presented in Table 3. Cp /MJ m73 K71 l/W m71 K71 r /kg m73 0.74 ± 1.07 2.42 ± 2.08 3.93 ± 1.80 2.04 ± 3.33 34.82 ± 7.52 1.74 ± 2.72 1.5874 ± 2.4232 2.3575 ± 3.5011 2.2115 ± 3.5409 3.1617 ± 4.0219 3.6954 ± 4.5683 3.2217 ± 3.4232 2.05 ± 1.85 2.81 ± 2.52 2.69 ± 2.29 3.15 3.55 ± 3.37 2.80 ± 2.68Heat-accumulating properties of melts Table 2.Characteristics of thermodynamic cycles. Efficiency Characteristic cycle parameter Cycle Temperature range 40 ± 268 8C 0.420 0.365 ±steam under a pressure of 5 MPa Carnot Rankin Temperature range 40 ± 450 8C Chirn Carnot 0.380 0.567 evaporation at 268 8C ± Table 3. Characteristics of phase-transition HAM for accumulation of low-potential thermal energy (m.p.4100 8C). System (mass%) DHm (see a) M.p. r /8C /kg m73I II 77 AlCl3 ± 5 BaCl2 ± 18 NaCl 88.5 AlCl3 ± 11.5 LiCl 50 1786 80 1645 22.2 LiNO3 ± 10.9NaNO3 ± 66.9NH4NO3 81 7 26.4 LiNO3 ± 58.7NH4NO3714.9KNO3 78.1 AlCl3 ± 5.5 KCl ± 16.4 LiCl 77.9 AlCl3 ± 11.3 KCl ± 10.8 NaCl 73.8 AlCl3 ± 21.8 NaCl ± 4.4 TlCl3 73.7 AlCl3 ± 22.2 KCl ± 4.1 TlCl3 63.8 AlCl3 ± 18.1 KCl ± 18.1 TlCl3 85 1631 88 1653 98 1659 100 1650 100 1743 168.5 0.3009 199 0.3274 127 7 81.57 7 0.234 196 0.3207 191 0.3185 192 0.3185 184.2 0.3039 156.1 0.2756 a The accumulated energy is usually expressed as enthalpy/weight ratio DH/Mor enthalpy/volume ratio DH/V, therefore the dimensionalities are: (I) kJ kg71; (II) GJ m73.Judging by the data listed, the choice of phase-transitionHAMfor the accumulation of low-potential thermal energy is limited, particularly if one takes the cost of the accumulated energy into account.7 Studies of movement of the solidification (melting) frontier of HAM on a planar unit cell model of a heat accumulator 15 were carried out using an eutectic three-metal alloy with composition (mass %) 50 Bi ± 31 Pb ± 19 Sn and the parameters: T=94.5 8C, r=9590 kg m73, DHm=26.4 kJ kg71, Cp= 0.138 kJ kg71 K71, l=16.5 W m71 K71 as a phase-transfer heat-accumulating material.The heat-accumulating ability of metal alloys (>0.2 GJ m73) is ensured by their high densities, unlike the case of salt melts where this ability is ensured by the enthalpy of melting (see Table 3). It has been shown (see, e.g., Refs 8 and 16) that an efficient short-term accumulator of average-potential thermal energy can be represented by an accumulator that uses the heat of phase transitions (melting>crystallisation) of mixtures of anhydrous inorganic compounds.These mixtures represent mainly n-compo- nent eutectic compositions of molten alkaline and alkaline-earth metal salts with melting points of 100 ± 500 8C. The ranges of the melting points (m.p.) and DHm for the recommended phase- transition HAM and the most promising eutectic compositions are given in Table 4. Thermodynamic analysis of such systems shows 8, 19 that the highest heat-accumulating ability is characteristic of salt eutectics based on lithium nitrate possessing high heats of phase transition (370 kJ kg71) and thermal stability up to 500 8C and a melting point of 256 8C; in addition, these are not corrosive with respect to many structural materials and their alloys.Eutectic compositions containing only alkali and alkaline-earth metal nitrates (except for LiNO3) can be used at operating temperatures only 30 ± 50 8C higher than their melting points (due to decomposition). Table 4. Characteristics of phase-transition HAM for accumulation of medium-potential (100<m.p.<500 8C) thermal energy.6, 16 ± 18 System (mass%) M.p. /8C 105 114 128 135 160 166 180 193 200 208 220 255 368 419 420 29 LiNO3 ± 17NaNO3 ± ± 49.4KNO3 ± 4.6 Sr(NO3)2 17.5 LiCl ± 82.5 AlCl3 21.6 KCl ± 78.4 AlCl3 31.7 LiNO3 ± 68.3KNO3 55.4 LiNO3 ± 4.5NaNO3 ± ± 40.1 KCl 58.1LiNO3 ± 41.9 KCl 47.9 LiNO3 ± 1.4 LiCl ± ± 50.7NaNO3 57 LiNO3 ± 43NaNO3 45 LiNO3 ± 47NaNO3 ± ± 8 Sr(NO3)2 87 LiNO3 ± 13 NaCl 93.6 LiNO3 ± 6.4 NaCl 98 LiNO3±2Li2SO4 1.8 LiF ± 39.9 LiCl ± ± 8.3 NaCl ± 50 KCl 29 LiCl ± 24 LiF ± ± 21Li2CO3 ±26Li2SO4 29.6 KCl ± 53.8 Li2SO4 ± ± 16.6NaCl 26.9 NaCl ± 73.1 Sr(NO3)2 424 a The dimensionalities are: (I) kJ kg71; (II) MJ m73.High DHm values are characteristic of alkali metal chlorides and sulfates, and hence intense heat liberation is observed on the DTA (or DSK) cooling curves for eutectic mixtures with lithium nitrate.16 Addition of alkali metal nitrates to halide-, sulfate- and carbonate-containing mixtures of alkali and alkaline-earth metals allows not only reduction of the operating temperature but also an increase in the heat-accumulating ability, as well as a decrease in the corrosive effect of these mixtures on structural materials.The number of components in promising eutectic systems (n) ranges from 1 to 4. If n>4, degeneration with respect to both the melting points and the physicochemical properties occurs; this increases the cost of the accumulated energy with the heat- accumulating ability being the same. Technical and economic analysis showed that accumulators with high-temperature phase-transition HAM (m.p.> 500 8C) as the heat-carriers, particularly eutectic compositions of salt and metal multi-component systems, are most suitable for non-tradi- tional energy sources.5 However, the development of such accu- mulators entails the solution of a number of complex technical problems (for example, the corrosion compatibility of the HAM with structural materials, intensification of heat exchange in the charge and discharge modes, regeneration of the HAM, etc.).Of the phase-transition HAM used for the thermal energy accumulation, eutectic metal alloys possess the best thermal conductivities and stabilities. Analysis of published data on thermodynamic parameters of metal-based multi-component sys- tems 17, 19 made it possible to single out the most promising ones for use as the working materials in heat accumulators (Table 5). Of ionic compounds, alkali and alkaline-earth metal fluorides, chlorides, carbonates, and sulfates have the best thermal proper- ties for the accumulation of high-potential thermal energy.Salt eutectics are the most power-intensive (due to the enthalpy of melting, see Table 6). The DHm values were found experimentally or calculated using the additivity principle. The experimental studies of heat capacity were carried out using a continuous- heating calorimeter.17 181 DHm (see a) r/kg m73 I II229.6 110 2087 596 595 241.4 507 251 254 135.6 266 2376 2343 1780 1905 522 530 272 267 1918 1986 467 397 248.3 199 1880 1993 697 675 834.4 1071 369 363 354 523 1889 1850 2357 2048 871.4 387 2252 1209 586.2 2062 252 244 2152182 Table 5. The characteristics of phase-transition HAM from metal alloys.System (mass%) r/kg m73 M.p. /8C 78.55 Ga ± 21.45 In 86.5 Ga ± 13.5 Sn 96.5 Ga ± 3.5 Zn 67 Ga ± 20.5 In ± 12.5 Zn 82 Ga ± 12 Sn ± 6 Zn 74 Ga ± 22 Sn ± 4Cd 93 Ga ± 5 Zn ± 2 Cd 13.3 Sn ± 50 Bi ± 10 Sd ± 26.7 Pb 46.3Mg± 53.7 Zn 96 Zn ± 4 Al 34.65Mg± 65.35Al 60.8 Al ± 33.2 Cu ± 6.0Mg 68.5 Al ± 5.0 Si ± 26.5 Cu 64.3 Al ± 34.0 Cu ± 1.7 Sb 66.92 Al ± 33.08 Cu 83.14 Al ± 11.7 Si ± 5.16Mg 87.76 Al ± 12.24 Si 46.3Al ± 4.6 Si ± 49.1 Cu 86.4 Al ± 9.4 Si ± 4.2 Sb 6197 5885 5946 6170 5961 5983 6020 8974 4600 6630 2155 3050 4400 2938 4000 3600 2500 2540 5560 2700 a The dimensionalities are: (I) kJ kg71; (II) GJ m73. 15.7 20.55 25.0 10.7 18.8 20.2 24.6 70 340 381 497 506 64.6 Al ± 5.2 Si ± 28Cu ± 2.2Mg 507 525 545 548 555 557 571 575 Table 6.Enthalpy of melting of salt eutectics with m.p.> 500 8C.16, 17, 20, 21 System (mass%) M.p. /8C DHm /kJ m73 505 510 528 536 540 556 593 595 602 622 651 652 680 746 750 832 996 1006 50 Li2CO3± 50K2CO3 64.25 LiCl ± 35.75 Li2CO3 56.4 Na2SO4 ± 12.9NaCl ± 30.7 KCl 56.7 Li2SO4 ± 10.3 Na2SO4 ± 33 KCl 26.2 LiF ± 73.8 Li2SO4 64.5 LiCl ± 35.5 NaCl 25.7 LiF ± 36.5 NaF± 10.6MgF2 ± 27.2 CaF2 24.8 LiF ± 75.2 Li2CO3 10.4 NaF ± 39.4NaCl ± 50.2 KCl 32.6 LiF ± 50.4 NaF± 17MgF2 34.7 LiF ± 3.3 NaF ± 37.5MgF2 ± 24.5 CaF2 48 LiF ± 52 NaF 24 LiF ± 76 NaCl 67 LiF ± 33MgF2 46 LiF ± 54MgF2 75 NaF ± 25MgF2 31 NaF ± 69MgF2 29.5KF± 70.5MgF2 From the viewpoint of thermal accumulation, salt systems have drawbacks such as rather low thermal conductivities and undesirable volume increase by 10%± 30% upon melting; because of this, it is necessary to provide free volume for thermal expansion of the melt in the accumulators.Prediction of the properties of ionic systems without exper- imental studies was carried out using the equation17 DHm=DHadd +DDHm , m where DHadd m =SxiDHmi (Te); xi is the mole fraction of the ith component; DHmi (Te) is the enthalpy of melting of the ith component referred to the temperature of the eutectic. DHm (see a) I II0.4429 0.4942 0.5415 0.4185 0.5255 0.4571 0.5246 0.412 0.851 0.916 0.615 1.113 1.644 1.069 1.324 1.339 1.213 1.265 2.260 1.272 69.7 81.9 88.5 67.2 86.5 75.2 85.03 45.8 185 138 285 365 374 364 331 372 485 498 406 471 335 339.7 410 514.6 348.9 414.5 510 594.5 370.3 625 470 711 476.9 708 847 649 710 770 AMGasanaliev, B Yu Gamataeva Comparison of the DDHm values and the enthalpy of mixing of melts DHmix showed 17 that DDHm=DHmix .Eutectic mixtures containing salts of stable intersecting ele- ments of mutual systems have the highest heat content.16 Several papers report on the finding of stable intersecting elements in three-, four- and five-component mutual systems and studying their heat-accumulating properties.20, 22 3.Chemical accumulation Chemical accumulation implies the energy accumulation and release by virtue of chemical reactions. The accumulated energy can be released as heat, electrical energy, light, or mechanical energy. Depending on the type of the accumulated energy, one distinguishes thermochemical (energy is accumulated as heat) and electrochemical accumulators (energy is accumulated as electrical energy sometimes supplemented with some heat). Both natural organic (coal, oil products, natural gas, etc.) and synthetic fuels (organic and inorganic) can serve as chemical accumulators. A special place among the compounds used as heat accumulators in thermochemical accumulators belongs to melts and alloys of naturally abundant compounds, such as metals, oxides, hydroxides, salts, etc.Simulation of the thermody- namics and thermochemistry of reactions involving these com- pounds facilitates essentially the selection of the HAM and the calculation of parameters of chemical accumulators. The state-of-the-art in this field was considered in Ref. 8. Accumulation can be based on three main reaction types involving melts of inorganic compounds: (1) synthesis of complex coordi- nation compounds,23 ± 25 inclusion compounds 26 and ammonia complexes,27, 28 hydration of alkaline-earth metal oxides (CaO, MgO);29, 30 (2) decomposition of carbonates,31 sulfates,32 alka- line-earth metal hydroxides, ammonium hydrogensulfate (NH4HSO4),33 metal hydrides;34 (3) exchange decomposition in full conversion points in mutual multi-component systems formed by ionic melts of inorganic compounds (hydroxides, salts).4 Of interest are chemical reactions that involve ionic compounds 35 capable of reversible accumulation (Table 7).The following scheme of exchange reactions in mutual multi- component systems serves as the basis of heat accumulation: nAX+mBY+...=cAY+dBX+...+Q , where AX, BY, AY, and BX are ionic compounds; n, m, c, d are the stoichiometric factors in the exchange reaction; Q is the heat effect of the reaction. This type of processes is also used for the synthesis of diverse compounds. For instance, exchange decomposition occurring to the full conversion point of ternary mutual system Na,Ca/F,Cl is, on the one hand, the most efficient method to obtain calcium fluoride; on the other hand, this is a process that can be used in thermochemical accumulators (Q=519.72 kJ mol71).36 It is recommended to use a powder mixture of equivalent quantities of calcium chloride and sodium fluoride for reversible accumulation.37 The thermochemical equation of the reaction is CaCl2+2NaF=CaF2+2NaCl7101.28 kJ mol71.The reaction starts at 490 8C. The mixture can be heated to a maximum temperature of 600 8C. If the specific heat effect of the exchange reaction is within 304Q<250 kJ kg71, accumulation of thermal energy is an efficient side process to save energy in chemical technology. If Q>250 kJ kg71, the reaction is applicable as a working process in thermochemical accumulators.The major problem in the development of chemical heat accumulators is the choice of chemical reactions that meet the following requirements:3 the heat effects of the reaction should beHeat-accumulating properties of melts Table 7. Thermodynamic characteristics of some exchange decomposition reactions in ternary mutual systems.35 M.p. /K (see a) Reaction 2NaOH + CaCl2=2 NaCl + Ca(OH)2 2NaOH + CaSO4=Na2SO4 + Ca(OH)2 Na2CO3 + CaCl2=2 NaCl + CaCO3 Na2CO3 + Ca(NO3)2=2NaNO3 + CaCO3 Na2SO4 + CaCl2=2 NaCl + CaSO4 Na2SO4 + Ca(NO3)2=2NaNO3 + CaSO4 Na2S + CaCl2=2 NaCl + CaS Na2S + CaSO4=Na2SO4 + CaS 2(KOH + NaCl=KCl + NaOH) 320 320 782 310 782 310 782 890 320 a The melting point of the lowest-melting reaction component.no less than ca. 250 kJ kg71 or ca. 1800 kJ litre71 if gaseous products are taken into account; the volume density of the accumulated energy should be as high as possible at a minimum possible volume of the reaction products. 4. Comparative analysis of the properties of heat-accumulating materials The prospects of the development of heat accumulators in which accumulation and liberation of energy occur due to the heat- accumulating properties of melts of inorganic compounds are estimated using the following HAM parameters: specific volume, heat capacity, heat and phase transition temperature (in chemical reactions, in solid and liquid phases). The heat-capacity heat accumulators are less thermally effi- cient in comparison with phase-transfer and thermochemical ones, because the considerable `heat storage capacities' needed despite the HAM temperature increase in them requires a mini- mum quantity of thermal energy consumed.1 However, heat- capacity heat accumulators are characterised by low cost and simplicity and hence they have found wide use.The accumulators with the use of the heat effects of reversible phase transitions are characterised by high energy density, small HAM mass and virtually constant operating temperature; the temperature difference of the heat-carrier transferring heat to the consumer and the heat source charging the accumulator is determined only by the required heat transfer intensity. In heat- capacity accumulators, in most cases this difference also depends on the change in the working medium temperature. The drawback of the isothermal phase-transfer accumulators is that one has to use a different working medium with a specific phase transition (melting) temperature for each required temper- ature.In practice, phase-transfer heat accumulation is partially combined with accumulation of physical heat, i.e. with heat- capacity accumulation. These are called hybrid accumulators; they are most popular for high-temperature short-term accumu- lation.20 The thermochemical heat accumulators ensure the compact- ness of the accumulator for long-term heat storage and the absence of losses, as well as the possibility of accumulation at ambient temperature without recourse to thermal insulation.However, the limited number of cheap chemical compounds that meet the requirements for HAM is the main obstacle for the development of such accumulators.38 Comparative analysis shows that phase-transition HAM accumulate an order of magnitude more heat than materials that do not undergo phase transitions. This stems from the fact that the phase transition enthalpies of many compounds are much higher than the heat-capacity effect, particularly upon accumulation of medium- and low-potential thermal energy where the operating temperature range is not very wide. The evaporating and sub- limating HAM accumulate 3 ± 5 times more heat than the melting 183 7DG /kJ mol71 7DH /kJ mol71 DG DG DHT DH T 298 298 157.9 76.4 89.5 67.6 62.2 45.7 124.7 59.6 31.1 163.4 89.9 100.8 73.1 73.5 45.8 136.5 62.6 43.7 175.6 138.6 108.8 64.3 76.4 40.3 141.5 65.1 55.9 162.5 83.5 104.6 74.3 77.3 47.0 138.6 61.3 53.3 ones, while the HAM in thermochemical accumulators accumu- late an order of magnitude more than the evaporating ones.18 The basic obstacles preventing the wide use of heat accumu- lators include insufficient development of problems regarding good thermal insulation from the environment, the absence of well-developed models for the calculation of heat and mass trans- fer in heterogeneous systems and for increasing the efficiency of electric power reproduction and accumulator power rating.In view of this, studies of the thermal, thermodynamic and techno- logical characteristics of the available HAM as well as develop- ment of novel power-intensive materials with a wide operating temperature range are required.Solution of the above problems would ensure the effectiveness, high performance and low cost of energy accumulation. The hybrid (phase-transition and thermo- chemical) heat accumulators with melts of inorganic compounds as the HAM can prove to be the most promising for the develop- ment of durable heat-accumulating systems. The increase in the efficiency of power system can amount from 15%± 25% (with heat-capacity accumulators) to 80% ±85% (with thermochemical accumulators); in these cases, the cost of the heat accumulator is about 5% of the total power system cost.39 For each power system, the choice of particular methods for the thermal energy accumulation is determined by both local conditions and the results of actual technical and economic calculations.III. Criteria for the estimation of the heat- accumulating properties of melts When choosing the accumulator type, one has to consider such factors as the methods for the supply and removal of energy, the amount of the stored energy, the operating temperature levels, the storage period, the heat transfer intensity, the investment and working costs, and the requirements for operational reliability and safety. In the design of a heat accumulator, the prime thing is the search for a HAM the properties of which affect the majority of the above-mentioned factors.The choice of the material is primarily determined by the operating temperature level and the amount of the thermal energy to be accumulated. The basic requirements for the melts which can be used as the HAM are as follows: an acceptable melting point determining the accumulator operating temperature; high values of such specific quantities as the heat effect (which eventually determines the volume of the material used, and hence, the accumulator compactness and cost), the heat capacity, the thermal conductivity, the density; low viscosity in liquid phase and low thermal expansion coefficient; stability of the physicochemical parameters in the operating temperature range, i.e.the absence of chemical transformations; stability of the thermal and thermodynamic characteristics of the HAM; low vapour density; abundance in nature; low cost.2, 17184 There are also a number of operational requirements for melts, such as operating safety (the absence of explosion hazard or the presence of gaseous products easy to detect, environmental safety, the absence of hazardous pollution), easy heat absorption and liberation (the absence of supercooling and segregation), stability of physicochemical properties in multiple duty cycles, low corrosivity toward structural materials. The performance of accumulators employing melts of inor- ganic compounds as the phase-transition HAMmuch depends on the extent of their supercooling (below the phase transition temperature) and on whether phase stratification occurs.In order that the heat of phase transition are used more completely, it is necessary to ensure minimum overcooling when the HAM crystallises.1 This means that liberation of the accumulated energy occurs at a lower temperature than the HAM melting point; as a result, the accumulator may fail to operate at this temperature. Therefore, one of the major requirements for phase-transition HAMis that they should have an equilibrium crystallisation point where the fluid phase is transformed into solid one, avoiding a metastable supercooled state. This requires creating conditions where crystallisation occurs quickly, for example, by using an additive that accelerates this process.40 Supercooling in the crystallisation is a minimum if the difference between the HAM melting points and the heat source temperature is 5 ± 10 8C.This temperature range makes it possible to reduce thermal losses and the extent of supercooling of the melt; on the other hand, it is sufficient to provide good heat transfer when withdrawing heat from the HAM. If the supercooling of the melt is 5 ± 10 8C, heat dissipation virtually stops, hence increasing the crystallisation rate is of importance. Of anhydrous inorganic compounds that can be utilised for heat accumulation, only certain chlorides and nitrates (e.g., calcium chloride and nitrate) and eutectic compositions contain- ing more than 40 mass% of these compounds crystallise with supercooling.Borax, sodium silicate, and strontium and barium fluorides and chlorides can be used as the crystallisation stabil- isers. Segregation decreases the heat exchange between the solid and liquid phases, which necessitates continuous stirring of the HAM during crystallisation.17 When designing heat-accumulating systems, a comprehensive approach is required, including the development of a procedure for numerical solution of multi-parameter heat exchange prob- lems with the use of thermodynamic analysis methods, theoretical and experimental simulation for optimisation and studies of the thermal and thermodynamic properties of HAM and operating parameters of the accumulators. The final stage of studies involves the development of methods for optimisation of the design of heat-accumulating systems as regards the thermal and economic efficiencies and environmental safety. IV.Principles for the development of heat- accumulating materials based on multi-component systems Development of promising HAM calls for search for specific compounds or eutectic compositions that combine the above- mentioned properties in the optimum way. The search for such compounds is a complex problem, as certain properties can be combined in a material, while others cannot. Therefore, prelimi- nary estimation of the thermal characteristics of the knownHAM and the selection of physicochemical systems which can serve as a basis for creating new materials should be carried out with regard to the most important thermal accumulation parameters, such as temperature, specific enthalpy (heat capacity) and density.AMGasanaliev, B Yu Gamataeva Pure anhydrous inorganic compounds and their eutectic mixtures are promising as the HAM.23 Unlike crystal hydrates, eutectic mixtures undergo melting and crystallisation at constant temperature, irrespective of the number of components. The search for eutectic compositions is carried out with the use of reference data bases on the physicochemical properties of com- pounds and the fusibility diagrams. The starting components of eutectics include metals, alkali and alkaline-earth metal oxides, hydroxides, nitrites, nitrates, halides, carbonates, sulfates and phosphates, which belong to traditional HAM, as well as tran- sition metal compounds.At present, the choice of compositions that meet the require- ments for theHAMis limited, especially from the viewpoint of the accumulated energy cost. Therefore, directed development of HAM and study of their properties and technological character- istics are topics of current interest.41 Novel materials can be created using the results of studies of the phase diagrams and composition ± property diagrams for various physicochemical systems as their theoretical base. The trend of an increase in the information output with minimisation of experiment is characteristic of modern research in the field of multi-component systems. This is achieved by using: (1) experi- ment planning with the use of modern rapid methods;42 (2) computer simulations with modern solid modelling methods;42 ± 50 (3) development of fast methods and measuring instruments for studying the composition ± property diagrams that require the use of automatic recording systems, systems for data collection and processing and those for controlling the experiment.51, 52 The development of methods and measuring instruments that enable the study of a set of properties in one experiment improves not only the information output but also the quality of the exper- imental data, since the results of measuring the different proper- ties refer to the same sample in the same state.53, 54 The above ways of optimisation in the study of the composi- tion ± property diagrams can be used independently of each other, but combining them is the most efficient.This is taken into account in the development of algorithms for computer programs required for the simulation and automation of the physicochem- ical analysis of multi-component systems.55 ± 57 Algorithmisation and programming imply the wide use of modern methods for the calculation, prediction and analysis, both for preliminary estimation of the physicochemical properties and composition ± property diagrams and for subsequent processing of experimental data with the use of computer programs. Then the confirming experiments performed on the basis of complex methodology for the study of multi-component systems are minimised.40 This approach allows one to establish the logical sequence of steps (from the choice of the starting components to the develop- ment of recommendations on the design of heat accumulators), to reduce the laboriousness of experimental studies, and to carry out directed, efficient and cost-effective choice of systems with pre- determined properties applicable as multi-purpose HAM.A five-level algorithm has been suggested (Scheme 1) as a methodological basis forHAMdevelopment from melts 2 consist- ing of: zero level, statement of work (stage 0); first level, data analysis (stages 1 and 2); mathematical analysis level (stages 3 and 3a); experimental and theoretical level (stages 4 ± 9); analytical level (stages 10 and 11). The results of studies are presented graphically as the compo- sition ± property and property ± property fusibility diagrams and in tabulated form.The three basic rules should be observed in studies with the use of the algorithm suggested: (1) first, theoretical analysis as thorough as possible should be performed in each of the eleven stages; (2) a computer is used for work optimisation; (3) justified choice of compositions for subsequent studies is made in each level.Heat-accumulating properties of melts Scheme 1 0. Statement of work 1. Selection of specific compounds 2. Multi-component system formation and analysis 3. Building the phase tree 3a. Description of chemical ex- change reactions 4. Derivation of the crystallisation tree for the system 4a. Description of chemical synthesis reactions 5. Localisation of eutectics with the given m.p.5a. Confirmation (X-ray diffraction analysis) 6. Thermodynamic analysis 7. Thermophysical analysis 8. Chemical analysis 9. Technological analysis 10. Economical aspects 11. Social and ecological aspects V. Conclusion Power plants used in various branches of industry are expensive, hence the increase in their efficiencies is a problem of vital importance. This problem can partially be solved by using accumulated energy. Presently, directed development and perfec- tion of both heat accumulators and power-intensive working materials for them are under way. The development of HAM implies not only the estimation of their chemical (corrosion activity), thermal (heat and mass trans- fer) properties and environmental safety but also the search for the optimum heat accumulator design with the use of simulation methods, calculation of its technical and cost efficiency and selection of structural materials.22 ± 35 The basic directions of chemical research on cost-effective HAM based on melts and their efficient operations include development of new and perfection of the existing methods of energy transformation and storage, search for new materials with controlled properties capable of serving as structural materials, heat accumulators and heat-carriers of heat accumulators, devel- opment of computerised methods for the simulation of the thermodynamics of heat and mass transfer in accumulators of particular design, optimisation of research and development efforts with the use of computers.185 Depending on the required energy storage time period, buffer (15 ± 60 min), short-term (up to 2 ± 3 days) and long-term (week, month, season) accumulation types are distinguished. Accumu- lation of this duration is used in production of energy during `peak hours' (hydroelectric, nuclear power plants), during cloudy hours (solar power plants), for supply of heat to stand-alone consumers and so on. It cannot be ruled out that development of power- intense heat-accumulating systems using direct chemical trans- formation methods will result in considerable progress in heat and energy supply. In order to select energetically and economically advanta- geous HAM, one has to know their thermal characteristics.Since an experimental study on the complex of properties that is required for estimating the heat-accumulating ability of a melt is commonly a complex task (in particular, reference equipment operated by skilled personnel and long measurements are neces- sary), it is very important to have methods for the prediction of the heat-accumulating properties of melts based on incomplete or indirect data. An important place in obtaining the required information on the properties of HAM belongs to approximate calculation methods and prediction with the use of the system approach for discovering the relationship between the thermal properties (reac- tion heats) and the nature of the components.The most efficient methods of HAM research are the calcu- lation-experimental ones which combine theoretical calculations with experimental studies. In particular, the HAM properties can be determined with the use of the experimentally studied phase diagrams of multi-component systems. It is this methodological approach that is implied by algorithm considered above (see Scheme 1). References 1. G Beckmann, P V Gilli Thermal Energy Storage (Translated into Russian; Moscow: Mir, 1987) 2. A M Gasanaliev, B Yu Gamataeva Metodologicheskie Osnovy Teplovogo Akkumulirovaniya s Ispol'zovaniem Rasplavov, S.-Peterburg, 1999 (Methodological Foundation of Thermal Storage with the Use of Melts, St. Petersburg, 1999); article deposited at the VINITI 1969-V (Moscow, 1999) 3.L A Reznitskii Zh. Neorg. Khim. 43 1288 (1998) a 4. R K Rokhas, Candidate Thesis in Technical Sciences, Moscow Energy Institute, Moscow, 1993 5. A M Magomedov Netraditsionnye Istochniki Energii (Non- Traditional Sources of Energy) (Makhachkala: Yupiter, 1996) 6. Teplofizicheskie Svoistva Teploakkumuliruyushchikh Materialov. Kristallogidraty (Thermal Properties of Heat-Storage Materials. Crystal Hydrates) (Moscow: Institute of High-Temperature of Academy of Sciences of the USSR, Scientific Information Centre on Thermal Properties of Pure Substances, 1990) 7. M A Dibirov, in Fiziko-Khimicheskii Analiz Mnogokomponentnykh Sistem (Tez. Dokl. Vseros. Konf.) [Physicochemical Analysis of Multi-Component Systems (Abstracts of Reports of All-Russian Conference)] (Makhachkala: Dagestan State Pedagogical University, 1997) p.19 8. B Yu Gamataeva, Candidate Thesis in Chemical Sciences, Dagestan State Pedagogical University, Makhachkala, 1995 9. V I Dauknis, A I Kuklyauskas, in Akkumulirovanie Energii i Puti, Povysheniya Effektivnosti Raboty Elektrostantsii i Ekonomii Energii. Akkumuliruyushchie Energoustanovki, Teplovye Protsessy i Teploak- kumuliruyushchie Materialy (Energy Storage and Ways of Increasing the Efficiency of Operation of Power Plants and Economy of Energy. Stored Power Plants, Thermal Processes and Heat-Storage Materials) (Moscow: Khimiya, 1986) Pt. 2, p. 182 10. C Etievant, J L Peube,A Vialarou, J P Allard, J Bounin, F Pharabod, in Solar Electricity (Proceedings of International Conference), Toulouse, 1976 11.L J Radosevich, C E Wyman J. Sol. Energy Eng. 105 111 (1983) 12. R H Carthy,W L Conger Int. J. Hydrogen Energy 5 7 (1980)186 13. R J Copeland, R E West, F Kreith, in Proc. Intersoc. Energy Convers. Eng. Conf. 19th Vol. 2 (Golden: Sol. Energy Res. Inst., 1984) p. 1171; Chem. Abstr. 101 233 183 (1984) 14. R B Akhmedov Energiya 4 22 (1985) 15. T B Voronina, V I Gudkov, O V Shimanskii, in Akkumulirovanie Energii i Puti, Povysheniya Effektivnosti Raboty Elektrostantsii i Ekonomii Energii. Akkumuliruyushchie Energoustanovki, Teplovye Protsessy i Teploakkumuliruyushchie Materialy (Energy Storage and Ways of Increasing the Efficiency of Operation of Power Plants and Economy of Energy.Stored Power Plants, Thermal Processes and Heat-Storage Materials) (Moscow: Khimiya, 1986) Pt. 2, p. 151 16. N A Vasina, E S Gryzlova, S G Shaposhnikova Teploakkumulir- uyushchie Svoistva Mnogokomponentnykh Solevykh Sistem (Heat-Storage Properties of Multi-Component Salt Systems) (Moscow: Khimiya, 1984) 17. N M Martynova, E K Rodionova, T A Tishura, L I Cherneeva, in Akkumulirovanie Energii i Puti, Povysheniya Effektivnosti Raboty Elektrostantsii i Ekonomii Energii. Akkumuliruyushchie Energousta- novki, Teplovye Protsessy i Teploakkumuliruyushchie Materialy (Energy Storage and Ways of Increasing the Efficiency of Operation of Power Plants and Economy of Energy. Stored Power Plants, Thermal Processes and Heat-Storage Materials) (Moscow: Khimiya, 1986) Pt.2, p. 167 18. Y Takahashi , M Kamimoto , Y Abe, K Sakamoto Thermochim. Acta, 123 233 (1988) 19. V N Danilin, P E Shurai I T Sryvalin Tr. Krasnodar. Politekh. In-ta 65 (1969) 20. MA Dibirov, AMGasanaliev, B Yu Gamataeva,MMMagomedov, in Fiziko-Khimicheskii Analiz Mnogokomponentnykh Sistem (Tez. Dokl. Vseros. Konf.) [Physicochemical Analysis of Multi-Component Systems (Abstracts of Reports of All-Russian Conference)] (Makhachkala: Dagestan State Pedagogical University, 1997) p. 19 21. A S Trunin Kompleksnaya Metodologiya Issledovaniya Mnogokom- ponentnykh Sistem (Complex Methodology of Investigation of Multi-Component Systems) (Samara: Samara State Technological University, 1997) 22.I K Garkushin, A S Trunin, A I Sechnoi, MA Dibirov, N N Verdiev Eksperimental'noe Opredelenie Oblastei Sostavov na Diagrammakh Sostoyaniya pri Poiske Teploakkumuliruyushchikh Sostavov, Moskva, 1988 (Experimental Determination of Regions of Composition on State Diagram in Search for Heat-Storage Compositions, Moscow, 1988); article deposited at the VINITI 1029-V (1988) 23. L A Reznitskii, S E Filippova Usp. Khim. 62. 474 (1993) [Russ. Chem. Rev. 62 437 (1993)] 24. L A Reznitskii Zh. Fiz. Khim. 67 2379 (1993) b 25. L A Reznitskii, S E Filippova Vest. Mosk. Univ., Ser. 2, Khim. 38 132 (1997) c 26. P Touzain, J Michel, P Blum Synth. Met. 8 313 (1983) 27. J Villermaux Recherche 14 1346 (1983) 28. I Fujiwara, Y Nakashima, T Goro Energy Convers.Manage. 21 157 (1981) 29. M Tmar, C Bernard, M Ducaroir Sol. Energy 26 529 (1981) 30. G Flamant, D Herlandez, C Bonet, J P Traverse Sol. Energy 24 385 (1980) 31. O Abu Leiych Ber. Kernforshungsanlage Juelich, Juel-1847 157 (1983); Chem. Abstr. 99 91 062 (1983) 32. N El Ghandour, R Valls,M Ducaroir Bull. Soc. Chim. Fr. (5-6, Pt. 1) 133 (1983) 33. S M Ranade, M Ch Lee, H W Prengle Jr Sol. Energy 37 375 (1986) 34. H Buchner Energy Storage, Trans. Int. Assem., 1st (Oxford: Pergamon Press, 1980) p. 327; Chem. Abstr. 94 194 868 (1981) 35. A P Protsyuk O Nekotorykh Zakonomernostyakh Napravlenii Reakt- sii v Solevykh i Okisno-Solevykh Sistemakh pri Nagrevanii, Moskva, 1977 (Some Regularities of Reaction Routes in Salt and Oxide Salt Systems at Heating, Moscow, 1977); article deposited at the VINITI 2492-77 (1977) 36.V N Danilin Fizicheskaya Khimiya Teplovykh Akkumulyatorov (Physical Chemistry of Heat Accumulators) (Krasnodar: Krasnodar Polytechnic Institute, 1981) 37. I K Garkushin, B V Anipchenko, in Ftoridnye Materialy (Tez. Dokl. X Simp. po Khimii Ftoridov) [Fluoride Materials (Abstracts of Reports of the Xth Symposium on Chemistry of Fluorides)] (Moscow: Moscow State University, 1998) p. 36 AMGasanaliev, B Yu Gamataeva 38. V V Ershevich, V Ya Peisakhovich, A N Kir'yanova Elektr. Stantsii 4 37 (1985) 39. A G Chukaev, A M Kuks Izv. Vyssh. Uchebn. Zaved., Mashinostroenie (1) 67 (1984) 40. A M Gasanaliev, Doctoral Thesis in Chemical Sciences, Institute of Chemistry, Academy of Sciences, Uzb.SSR, Tashkent, 1989 41. Zh A Koshkarov, A M Gasanaliev, M V Mokhosoev Zh. Neorg. Khim. 35 1254 (1990) a 42. A M Gasanaliev, K D Kurbanmagomedov, A S Trunin, G E Shter Modelirovanie Khimicheskikh Reaktsii v Mnogokomponentnykh Sistemakh na Personal'noi EVM, Cherkassy, 1988 (Modelling of Chemical Reactions in Multi-Component Systems on a Personal Computer, Cherkassy, 1988); article deposited at the ONIITEKhIM 01154-88 (1988) 43. Zh A Koshkarov,M V Mokhosoev , A M Gasanaliev Dokl. Akad. Nauk SSSR 308 889 (1989) d 44. A M Gasanaliev, Zh A Koshkarov Dokl. Akad. Nauk SSSR 311 892 (1990) d 45. V I Posypaiko, S A Tarasevich, E A Alekseeva Prognozirovanie Khimicheskikh Vzaimodeistvii v Sistemakh iz Mnogikh Komponentov (Prediction of Chemical Interaction in Multi-Component Systems) (Moscow: Nauka, 1984) 46.Ya L Kharif Metody Teoreticheskogo Analiza i Rascheta Diagramm Sostoyaniya (Methods of Theoretical Analysis and Calculation of State Diagrams) (Moscow: Moscow Chemical Technological Institute, 1986) 47. P L Kapitsa Eksperiment, Teoriya, Praktika (Experiment, Theory and Practice) (Moscow: Nauka, 1987) 48. A G Morachevskii, I B Sladkov Fiziko-Khimicheskie Svoistva Mole- kulyarnykh Neorganicheskikh Soedinenii (Physicochemical Properties of Molecular Inorganic Compounds) (St Petersburg: Khimiya, 1996) 49. Zh A Koshkarov, S M Lok'yaeva, in Fiziko-Khimicheskii Analiz Mnogokomponentnykh Sistem (Tez. Dokl. Vseros. Konf.) [Physicochemical Analysis of Multi-Component Systems (Abstracts of Reports of All-Russian Conference)] (Makhachkala: Dagestan State Pedagogical University, 1997) p. 21 50. A M Gasanaliev, K D Kurbanmagomedov, in Vseros. Konf. po Termicheskomu Analizu i Kalorimetrii (Tez. Dokl.) [All-Russian Conference on Thermal Analysis and Calorimetry (Abstracts of Reports)] (Kazan': Kazan' State University, 1996) p. 53 51. V P Meshalkin Ekspertnye Sistemy v Khimicheskoi Tekhnologii. Osnovy Teorii, Opyt Razrabotki i Primenenie (Expert Systems in Chemical Technology. Foundations of Theory, Experience in the Development and Application) (Moscow: Khimiya, 1995) 52. A M Gasanaliev, K D Kurbanmagomedov, in Fiziko-Khimicheskii Analiz Mnogokomponentnykh Sistem (Tez. Dokl. Vseros. Konf.) [Physicochemical Analysis of Multi-Component Systems (Abstracts of Reports of All-Russian Conference)] (Makhachkala: Dagestan State Pedagogical University, 1997) p. 68 53. V P Egunov Vvedenie v Termicheskii Analiz (Introduction in Thermal Analysis) (Samara: Samara State Technology University, 1996) 54. T G Lupeiko, S P Vydrenok, in Vseros. Konf. po Termicheskomu Analizu i Kalorimetrii (Tez. Dokl.) [All-Russian Conference on Thermal Analysis and Calorimetry (Abstracts of Reports)] (Kazan': Kazan' State University, 1996) p. 46 55. V I Lutsyk, Doctoral Thesis in Chemical Sciences, Irkutsk State University, Irkutsk, 1997 56. A E Rozhanskaya, Candidate Thesis in Chemical Sciences, Samara State Technology University, Samara, 1995 57. AMGasanaliev, N N Verdiev, A S Trunin, G E Shter, Yu I Sultanov Algoritm Opisaniya Khimizma v Mnogokomponentnykh Vzaimnykh Solevykh Sistemakh s Razvitym Kompleksoobrazovaniem, Cherkassy, 1988 (Algorithm of Description of Chemism in Multi-Component Mutual Salt Systems with Extensive Complex Formation, Cherkassy, 1988); article deposited at the ONIITEKhIM 834-KhP88 (1988) a�Russ. J. Inorg. Chem. (Engl. Transl.) b�Russ. J. Phys. Chem. (Engl. Transl.) c�Moscow Univ. Bull. (Engl. Transl.) d�Dokl. Chem. Technol., Dokl. Chem. (Engl.

ISSN:0036-021X    

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年代:2000

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