摘要:

Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Raman and UV-VIS study of the conformational polymorphism of solid tetramesityldisilene Mes2Si=SiMes2 Larissa A. Leites,*a Sergey S. Bukalov,a John E. Mangette,b Thomas A. Schmedakeb and Robert Westb a Scientific and Technical Centre on Raman Spectroscopy, A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation.Fax: +7 095 135 5085 b Department of Chemistry, University of Wisconsin, Madison WI, USA All three modifications of tetramesityldisilene 1 reported to date (orange unsolvated 1a and two yellow 1:1 solvates with toluene 1b and THF 1c) have been shown to readily transform to a new form, yellow unsolvated 1d, for which a quasi-trans conformation with two mesityl rings nearly orthogonal and the other two nearly coplanar to the double bond plane, is tentatively proposed.Form 1d appears to be the most stable conformational polymorph, but can be converted to the orange form upon illumination in the region 514–457 nm. Tetramesityldisilene 1, the first stable Si=Si doubly-bonded compound, was synthesized in 1981.1 However, details of its structure and especially its conformation are not completely understood.Three different crystalline modifications of 1 have been reported to date and characterized by X-ray diffraction: an unsolvated orange modification 1a obtained from solution in hexane,2 and two yellow 1:1 solvates: 1b with toluene3 and 1c with THF,4 obtainable from the corresponding solutions.In this paper yet a fourth, unsolvated, yellow modification 1d is reported and interconversions of 1a–d are described.† The X-ray data for 1a–c, summarized in ref. 4, demonstrate that both the crystal and the molecular structures of 1a–c differ significantly. The Si=Si moiety is slightly distorted from planarity in all three forms but in a different way. The aromatic rings are twisted out of the double bond plane in all structures but again, in quite different ways.In addition, there is no specific interaction between 1 and solvent molecules in the solvates 1b–c, both being typical ‘packing crystals’.5 Figure 1 presents the Raman spectra of solid samples of 1a–c in the most informative region, i.e. 15–750 cm–1.‡ According to a recently published paper6 in which the normal vibrations of disilenes were analysed by normal coordinate analysis (NCA), the Si=Si stretching vibration n(Si=Si) is not localized, the Si=Si and Si–C stretching coordinates of the C2Si=SiC2 moiety being heavily mixed.Their in-phase combination (n1) results in a normal mode in the region 460–550 cm–1 while their out-of-phase combination (n2) gives a normal mode near 700 cm–1.Particular contributions of the Si=Si and Si–C stretching coordinates to the eigenvectors of n1 and n2, the modes of principal interest, depend on the particular molecular structure but both are always significant. Therefore, the assignment of the n1 mode to the n(Si=Si) stretch and of the n2 mode to the totally symmetric ns(Si–C) stretch is in essence arbitrary.For mesityl-substituted disilenes, the results of NCA6 predict that two of the symmetric vibrations localized in the mesityl group should fall in the same frequency range as n1, i.e. 500–550 cm–1. In good accord with the data,6 Figure 1 demonstrates that the Raman spectra of 1a–c all exhibit a triplet in the region 520–550 cm–1, which is the result of superposition of three lines, corresponding to two mesityl vibrations and to n1, as well as an intense line of n2 at ca. 680 cm–1. However, the precise frequency values and intensity ratios for 1a–c differ slightly but distinctly, in accord with their different molecular structures, allowing identification of each modification by its Raman spectrum. † Experimental. The synthesis of 1 was accomplished according to the method reported previously.1 All experiments were carried out in a high vacuum or in a strictly inert atmosphere to prevent sample decomposition.To control sample purity, the spectra of the products of degradation were specially studied. ‡ For Raman studies, the samples were sealed in capillaries in vacuo. To record the Raman spectra, Jobin-Yvon HG2S and U-1000 laser Raman spectrometers were used, excited by the 514.5 nm line of an SP-2020 Ar+ laser.In the course of experimenting with the orange crystals 1a (in an inert atmosphere or in a high vacuum) we found that, when slightly heated, sublimed or ground in a mortar, they readily transform to a yellow powder 1d whose UV band at ca. 425 nm confirms that it is also a disilene.1,7 The same substance 1d was obtained when solvates 1b or 1c were exposed to high vacuum and heated to remove the solvent.The identity of 1d, obtained from unsolvated 1a and from the solvates 1b–c, was confirmed from its Raman and UV-VIS spectra.§ In the low-frequency region of the Raman spectra, 15–150 cm–1, the crystal lattice modes are situated. This region demonstrates that the crystal structure of 1d differs from those of 1a–c.The Raman spectrum of 1d in the region 450–750 cm–1 presented in Figure 1 resembles the spectra of 1a–c but exhibits minor and quite expected changes in position and intensity of the diagnostic lines, allowing the conclusion that the molecular structure of 1d also differs from those of 1a–c. The different colours of 1a and 1d suggest that they should also differ in electronic absorption.Indeed, the UV-VIS spectrum of solid 1a exhibited a band at ca. 460 nm which is ca. 35 nm red-shifted compared to that of 1d (see Figure 2). It is important to note that to obtain a real UV spectrum of 1a one should not expose the sample to any mechanical or thermal stress, otherwise spectra of mixtures of 1a and 1d in various § The UV-VIS spectra of solid 1a and 1d samples were obtained using Nujol, apiezon or silicone grease mulls or suspensions prepared in an inert atmosphere.The UV-VIS spectrum of 1d was also obtained when either 1a or 1d were sublimed slowly onto the cooled quartz window of a cryostat in a high vacuum. The UV-VIS absorption spectra were recorded on Carl Zeiss M-40 and Perkin-Elmer Lambda Array 3280 spectrophotometers. (d) (c) (b) (a) 100 200 300 400 500 600 700 n/cm–1 Figure 1 Raman spectra in the region 15–750 cm–1 of the four conformational polymorphs of solid Mes2Si=SiMes2 (solid samples sealed in vacuo), 514.5 nm excitation. (a) Orange crystals; (b) 1:1 toluene solvate; (c) 1:1 THF solvate; (d) unsolvated yellow form.Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) proportions are obtained. The best way is to simply press a small amount of 1a in Nujol, apiezon or silicon grease between quartz plates in a dry box. Unsolvated forms 1a and 1d were found to interconvert upon laser irradiation, provided the laser light density overcomes a certain threshold. Moreover, the yellow solvates 1b and 1c can also, sometimes, be converted to orange 1a.For instance, prolonged exposure to a 514.5 nm laser beam produced an orange spot in the yellow sample of 1c sealed in a capillary. The spot persisted when the capillary was removed from the light. When exposed to light of the same wavelength but of higher intensity, the crystals of 1b, sealed in vacuo in a quartz cell, suddenly emitted a yellow ‘cloud’, a solid part of which settled on the upper wall of the cell, well separated from the initial crystals.According to the Raman spectrum, this solid film appeared to be a mixture of 1a and 1d with 1a predominant. Thus, solid 1 exists in at least four forms: two yellow crystalline 1:1 solvates with toluene and THF (1b and 1c) and two solvent-free forms: orange crystals 1a and a yellow powder 1d.The spectral data reported here clearly show that the crystal and molecular structure of 1d differ from those of 1a–c. Bernstein8 proposed the term ‘conformational polymorphism’ for an analogous phenomenon, i.e., the existence of several forms of a conformationally flexible molecule, depending on crystallization conditions. Theoretical (ab initio) calculations for model disilenes9 predicted a very flat molecular potential energy surface for the C2Si=SiC2 moiety.The existence of conformational polymorphs of 1 is evidently the result of interplay between the steric hindrance of the bulky mesityl groups, the tendency of the whole molecule towards planarity which would maximize p-p conjugation, and the crystal forces favouring close packing. The fact that unsovated 1a as well as both solvates 1b and 1c readily convert to yellow form 1d indicates that forms 1a–c are metastable while form 1d is the most thermodynamically stable.In spite of the fact that we still have no X-ray data for 1d, there are some reasons to speculate about its structure. For disilenes of the type RR' Si=SiR' R, photochemical cis–trans isomerization in solution was shown to occur,10 the trans isomer being predominant under equilibrium conditions.Of course, symmetrically substituted 1 cannot have real cis–trans isomers, but, by analogy, a similar equilibrium with predominance of the quasi-trans conformer seems likely in solution. This assumption is confirmed by our Raman polarization measurements for a solution of 1 in hexane,11 because the selection rules observed for the conformer predominant in solution are consistent with C2h symmetry, i.e., with a quasi-trans structure of this conformer.As both the Raman and UV-VIS absorption spectra of solid 1d are very similar to those of 1 in solution,1,7,11 we can also suggest for 1d a quasi-trans structure shown in Figure 3. The Russian authors acknowledge partial financial support from the Russian Foundation for Basic Research (grant no. 96-03-34079). References 1 R. West, M. J. Fink and J. Michl, Science, 1981, 214, 1343. 2 B. D. Shepherd, C. F. Campana and R. West, Heteroatom Chem., 1990, 1, 1. 3 M. J. Fink, M. J. Michalczyk, K. J. Haller, R. West and J. Michl, Organometallics, 1984, 3, 793. 4 M. Wind, D. R. Powell and R. West, Organometallics, 1996, 15, 5772. 5 A. I. Kitaigorodsky, Smeshannye Kristally (Mixed Crystals), Nauka, Moscow, 1983, p. 198 (in Russian). 6 L. A. Leites, S. S. Bukalov, I. A. Garbuzova, R. West, J. Mangette and H. Spitzner, J. Organomet. Chem., 1997, 536, 425. 7 R.West, Pure Appl. Chem., 1984, 56, 163. 8 J. Bernstein, J. Phys. D. Appl. Phys., 1993, 26, B66. 9 K. Krogh-Jespersen, J. Am. Chem. Soc., 1985, 107, 537. 10 (a) M. J. Michalczyk, R. West and J. Michl, J. Am. Chem. Soc., 1984, 106, 821; (b) M. J. Michalczyk, R. West and J. Michl, Organometallics, 1985, 4, 826. 11 L. A. Leites, S. S. Bukalov, R.West, J. E. Mangette, T. A. Schmedake, J. Michl and G. J. Radziszewsky, to be published. Absorbance (arbitrary units) 460 nm 428 nm (a) (b) 30000 25000 20000 15000 n/cm–1 Figure 2 UV-VIS spectra of solid samples of Mes2Si=SiMes2: (a) orange crystals as an apiezon mull (almost without grinding); (b) unsolvated yellow form sublimed on a quartz window. Si Me Me Me Me Me Me Me Me Me Si Me Me Me Figure 3 The structure proposed for the unsolvated yellow form of Mes2Si=SiMes2. Received: Moscow, 2nd December 1997 Cambridge, 11th February 1998; Com. 7/08972D

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Ionisation of lanthanum monoxide molecules by two-step excitation Alexander A. Gorbatenko,* Raisa D. Voronina, Nikita B. Zorov, Yurii Ya. Kuzyakov and Elena I. Revina Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846; e-mail: gorby@laser.chem.msu.ru Ionisation of lanthanum monoxide molecules by a two-step scheme, in which the first-step radiation transfers a molecule into an excited electronic state, and the second-step radiation excites the molecule to the ionisation potential, is proposed; this makes it possible to increase the ionisation signal in comparison with one-step excitation.Laser-induced ionisation (LII) flame spectrometry is based on the detection of electric charges that result from the ionisation of atoms of the element to be determined due to resonance absorption of the laser radiation by these atoms.1 Using this method, detection limits lower than those provided by other spectroscopic flame methods have been achieved for more than 35 elements, including rare-earth elements.2 The analytical form of the elements determined by LII spectrometry is usually the atoms formed on heating a specimen to be analysed in a flame.The fraction of free atoms depends on the element nature, the temperature of the analytical zone, the flame composition and a number of other factors. Readily accessible low-temperature flames have been used in the majority of studies employing LII spectrometry.However, the efficiency of such flames for the determination of rare-earth elements due to the small fraction of free atoms formed is low. On the other hand, the concentration of molecules of rare-earth element monoxides in the flame is rather high. It therefore seems sensible to use such molecules as an analytical form. However, there is almost no published work dealing with this problem. Only one study is known3 in which LII spectra of SrO, YO and LaO were obtained. The use of monoxide molecules as an analytical form in LII spectrometry was reported in a communication4 dealing with phosphorus determination.The unique potential for enhancing the sensitivity and selectivity of the LII method lies in the use of a two-step scheme for the excitation of atoms in a flame.5 Two-step schemes have hardly ever been used for excitation of molecules.Lanthanum was selected as the object of this study because of: i, the availability of spectral and thermodynamic data for its compounds in the literature and ii, the physical and chemical properties of rare-earth elements are rather similar and lanthanum is a typical representative of this family of elements.The purpose of this work was to find optimum two-step schemes for the excitation of lanthanum monoxide molecules. The experimental set-up consists of a laser spectrometer based on an exciting excimer laser (Figure 1). The radiation of an excimer XeCl laser (l = 308 nm, mean pulse energy 31 mJ, pulse repetition rate 10 Hz) was used for the excitation of two DL-mini dye lasers (ESTLA, Tartu, Estonia). The mean energy of the dye laser pulses was 0.58 mJ (coumarin-540A dye) and 0.64 mJ (coumarin-47 dye).The dye laser radiation was directed by a set of mirrors and prisms into the flame of a preliminary mixing burner and focused by lenses. A water-cooled cathode was located in the flame. A ground burner nozzle served as an anode.Weakly focused dye laser radiation (beam diameter 2.5 mm) was directed into the flame at a distance of 2.5 mm from the cathode and parallel to it. The maximum spatial coincidence of both rays (l1, l2) was striven for. Using a pneumatic nebuliser, the solutions studied were aspirated into a natural gas air flame. Continuous recording of the ionisation signal of the LaO molecule was started simultaneously with the start of the dye laser scan. The ionisation signal was fed through a blocking capacitor to the input of a broad-band amplifier and then to a RIFF-016 gating integrator (Mozaika, Moscow). The digital signal from the integrator was read by a digital voltmeter and simultaneously recorded by a strip chart recorder.The burner and the cathode were protected from electromagnetic interference by a copper jacket.A diagram of energy levels for the LaO molecule is presented in Figure 2. First, a spectrum of the LaO molecule was recorded at 535–565 nm (excitation by the first dye laser, coumarin-540A dye). The wavelengths corresponding to the X2S+ ® B2S+ transition (oscillator strength 0.16)6 are known from the literature,3 which made it possible to assign the observed bands.It is known from the same source that the excitation wavelength which we intended to use for second-step excitation also corresponds to the X2S+ ® C2Pr transition (oscillator strength 0.21).6 Therefore, in order to choose the wavelength for second-step excitation, the spectrum of the LaO molecule was recorded in the 440–470 nm range corresponding to this transition.The spectrum is presented in Figure 3(a). The ionisation signal obtained from the transition at 440–470 nm is by one order of magnitude smaller than that at 535–565 nm. Since this observation contradicts the transition probabilities, it may be assumed that the molecules at the higher C2P level more easily undergo collision deactivation than those at the B2S+ level. In order to choose the second-step excitation wavelength, the spectrum of the LaO molecule was recorded in the 440–470 nm region with additional excitation by radiation with a wavelength of l = 561 nm (this corresponds to the maximum signal in the 535–565 nm range, 0–0 band of the X2S+ ® B2S+ transition). The spectrum obtained with such two-step excitation is presented in Figure 3(b). The shapes of both spectra are almost similar, but the signal obtained from the radiation of two lasers is considerably stronger.The reason for this phenomenon is that with laser radiation wavelength of 561 nm, a strong ionisation signal is observed, which adds to the signal formed on excitation of a LaO molecule by the 1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 5 H2O Trigger l1 l2 Figure 1 Block diagram for the experimental set-up: 1, XeCl excimer laser; 2 and 3, dye lasers; 4, ground burner nozzle; 5, flame; 6, cooled cathode; 7, analysed solution; 8, high voltage power supply; 9, broad-band preamplifier; 10, RIFF-016 gating integrator; 11, strip chart recorder; 12, blocking capacitor; 13–16, mirrors; 17 and 18, rotating prisms; 19 and 20, lenses; 21, digital voltmeter.Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) second dye laser in the region of 440–470 nm. This simple addition of signals does not cause an enhancement typical of two-step schemes, when the signal is much stronger than the sum of signals resulting from each of the excitation steps. A comparison with the spectrum without first-step excitation [Figure 3(a)] makes it possible to determine the wavelength at which enhancement of the first-step signal occurs.This corresponds to an additional maximum in Figure 3 and equals 448 nm. In this case, the signal from first-step excitation (l = 561 nm) increases by 25%. A simple consideration of the energy level structure for the LaO molecule shows that, within the error of wavelength measurement, the total excitation energy over the two steps equals the ionisation potential of the molecule and does not excite the molecule into any bound state.This is one of the reasons for the small signal enhancement in the second step. Similarly, the spectrum of the LaO molecule was recorded in the region of 567–600 nm, also with additional excitation by radiation of l = 561 nm.This did not result in any extra bands. Radiation of l = 441.8 nm was then used as the first excitation step and radiation of l = 567–600 nm was used in the second step. The wavelength at which signal enhancement occurs, determined from the spectrum obtained under these conditions, was found to be 578.6 nm. In this case, the signal from excitation in the first step only (l = 441.8 nm) increases by 20%.As in the first case, the total excitation energy equals the ionisation potential of the molecule, within the error of wavelength measurement, and does not correspond to any bound state. In order to enhance the ionisation signal, an attempt at direct photoionisation of the LaO molecule from the B2S+ excited state was made.For this purpose, part of the radiation from the exciting excimer laser (l = 308 nm) with an energy of ca. 15 mJ was used as a photoionising step. The energy of the excimer laser quantum is sufficient for photoionisation of the B2S+ state. However, irradiation of the flame, even without focusing, gave an intense ionisation signal not related to the presence of lanthanum compounds in the flame.The study performed revealed no excited states of the LaO molecule close to the ionisation potential (ca. 0.7 eV). Therefore, the use of two-step laser excitation schemes for ionisation of the LaO molecule does not give a considerable gain in the signal in comparison with the one-step scheme. The observed signal enhancement is explained by the fact that the total energy of the photons in the two excitation steps equals the ionisation potential of the lanthanum monoxide molecule.Since the crosssection of direct ionisation into the continuum is lower, the higher the photoelectron energy (i.e. the excess of excitation energy over the ionisation potential),7 excitation of a molecule directly to the ionisation potential is most efficient. If higher intensity lasers are used for this purpose, the enhancement in such a two-step scheme is significant.This study was financially supported by the Russian Foundation for Basic Research (grant no. 96-03-33325a). References 1 N. B. Zorov, Yu. Ya. Kuzyakov, O. A. Novodvorsky and V. I. Chaplygin, in Khimiya plasmy (Plasma Chemistry), ed. B. M. Smirnov, Energoatomizdat, Moscow, 1987, vol. 13, p. 131 (in Russian). 2 G. C. Turk, in Laser-Enhanced Ionization Spectrometry, eds. J. C. Travis and G. C. Turk, John Wiley, New York, 1996, p. 161. 3 P. K. Schenk, W. G. Mallard, J. C. Travis and K. C. Smith, J. Chem. Phys., 1978, 69, 5147. 4 G. C. Turk, Anal. Chem., 1991, 63, 1607. 5 A. S. Gonchakov, N. B. Zorov, Yu. Ya. Kuzyakov and O. I. Matveev, Anal. Lett., 1979, 12A, 1037. 6 L.A. Kuznetsova, N. E. Kuz’menko, Yu. Ya. Kuzyakov and Yu. A. Plastinin, Veroyatnosti opticheskikh perekhodov dvukhatomnykh molekul (Optical transitions probabilities for diatomic molecules), Nauka, Moscow, 1980, p. 150 (in Russian). 7 V. S. Letokhov, V. I. Mishin and A. A. Puretsky, in Khimiya plasmy (Plasma Chemistry), ed. B. M. Smirnov, Atomizdat, Moscow, 1977, vol. 4, p. 18 (in Russian). 5 4 3 2 1 0 E/eV 1.82 1.84 1.86 re/10–10 m IP = 4.95 eV 578.6 567 600 440 470 441.8 (0.21) 561.0 (0.16) 600 567 448.0 C2Pr A2Pr X2S+ A' 2Dr B2S+ Figure 2 Simplified diagram of the energy levels of the LaO molecule. The numbers on the arrows indicate the wavelengths of the corresponding transitions in nm; the numbers in parentheses are the oscillator strengths of these transitions. The ranges of excitation energy scanned by laser radiation of the second excitation step are crosshatched. 350 300 250 200 150 100 50 0 440 450 460 470 l/nm Intensity (arbitrary units) Figure 3 Molecular-ionisation spectrum of LaO molecule in the region of 440–470 nm: (a) using one dye laser; (b) with additional radiation of a second dye laser (561 nm). (a) (b) Received: Moscow, 5th November 1997 Cambridge, 3rd February 1998; Com. 7/08306H

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) The anomalous influence of water on the intensity and lifetime of fluorescence in tris(benzoyltrifluoroacetonate)europium(III) Valerii P. Kazakov,* Alexander I. Voloshin, Sergey S. Ostakhov and Nail M. Shavaleev Institute of Organic Chemistry, Ufa Scientific Centre of the Russian Academy of Sciences, 450054 Ufa, Russian Federation.Fax: +7 3472 35 6066; e-mail: chemlum@ufanet.ru Addition of H2O (D2O) to a Eu(btfa)3 toluene solution enhances the luminescence intensity and lifetime of Eu(btfa)3, a phenomenon due to the formation of associates Eu(btfa)3·nH2O [Eu(btfa)3·nD2O]. It is well known that water and other hydroxyl-containing molecules effectively quench the fluorescence of rare-earth ions.The quenching occurs through the exchange of rare-earth ion electronic excitation energy with the high-frequency vibrational overtones of the O–H bond. The quenching efficiency is sharply decreased upon deuteration of the O–H bond.1 However, we have observed that addition of water to toluene solutions of fluorinated europium b-diketonate Eu(fod)3 (fod = [C3F7COCHCOCF3]–) enhances the fluorescence quantum yield and lifetime of this complex.This unexpected result was explained by assuming that outer-sphere associates are formed between water and fluorine atoms in the chelate ligand.2 Here we report results on the influence of water on the photoluminescence of tris(benzoyltrifluoroacetonate)europium(III), Eu(btfa)3, toluene solutions. Complex Eu(btfa)3 was prepared according to the literature.3 Toluene was dried by boiling over metallic sodium for 4 h and distilled.Fluorescence spectra and intensity of Eu(btfa)3 were recorded on a MPF-4 ‘Hitachi’ spectrofluorimeter after excitation with radiation l = 390 nm in the temperature range 60–80 °C. Fluorescence lifetime was measured with a laser impulse fluorimeter LIF-200 at 65 °C. The fluorescence quantum yield of Eu(btfa)3 in toluene was determined relative to Eu(TTA)3·phen (10–4 M in toluene). Addition of H2O (D2O) to a toluene solution of Eu(btfa)3 leads to formation of an emulsion.However, in a short period of time (5 min) the drops of the emulsion are transformed into crystals and then a rather lengthy process of dissolution of these crystals takes place (20–30 min).All measurements were carried out for optically homogeneous solutions in which all transformations had finished. Addition of H2O (D2O) enhances the photoluminescence intensity and lifetime of Eu(btfa)3 upon excitation into the absorption band of the ligand (Figures 1 and 2). In our experimental conditions, when the water concentration was one order of magnitude greater than that of Eu(btfa)3, we obtained inner-sphere complexes between H2O (D2O) and Eu(btfa)3 at each water concentration studied, since in solvents with low donor number, such as toluene, water molecules coordinate to the rare-earth ion in the inner coordination sphere.4 The observed increase in fluorescence intensity and lifetime of Eu(btfa)3 could not be explained by the generally accepted point of view of the strong quenching effect of H2O on the luminescence of rare-earth ions.The suggestion that Eu(btfa)3 undergoes hydrolysis on addition of water was rejected based on the similarity of the Eu(btfa)3 luminescence spectra obtained in the absence and in the presence of H2O (D2O) in the concentration range of H2O (D2O) studied (10–2–5×10–2 M), although it is known that hydrolysis of chelates is accompanied by a change in the fluorescence spectra and usually leads to a decrease in the fluorescence intensity of the rare-earth ion.The addition of water results in a slight decrease of the optical density at 390 nm in the absorption spectrum of Eu(btfa)3 which could not explain the observed increase in fluorescence intensity. The luminescence decay of Eu(btfa)3 in the presence of water was non-exponential, consisting of two parts with different lifetimes: t1 and t2, where t2 was 2–4 times greater than t1.However, recording of t2 was impossible because of the small luminescence yield (5–10% of the total luminescence), causing a large error in the measurement of t2. For this reason the following conclusions were drawn by considering the dependence of luminescence with lifetime t1 on the concentration of H2O (D2O).t1 is subsequently abbreviated as t. We assume that the increase in fluorescence intensity and lifetime of Eu(btfa)3 is caused by the associates Eu(btfa)3·nH2O [Eu(btfa)3·nD2O] formed through hydrogen bonds arising between the fluorine atoms or aryl substituent present in the ligand and hydrogen or deuterium atoms in water.† The formation of complexes between molecules able to form hydrogen bonds (HF, HCl, H2O, H2S, NH3) and aromatic molecules (serving as H acceptor) is well established.5 This process is accompanied by significant redistribution of electronic charge.5 We should therefore expect that the Eu3+–O bond in † Evidence for associate formation involving the aryl substituent in the chelate can be found in ref. 1 where the authors observed that addition of D2O to a cyclohexane solution of europium benzoylacetonate [Eu(CH3COCHCOPh)3] enhances the fluorescence lifetime of this complex. Although the authors gave no explanation for this phenomenon we think that it is caused by the formation of associates similar to those discussed in this paper.O O F F F Eu3+/3 Eu(btfa)3 400 350 300 250 200 150 100 50 0 1 2 3 4 5 6 Intensity (relative units) [L]/102 M 1 2 3 4 1' 2' 3' 4' Figure 1 Dependence of 10–3 M Eu(btfa)3 photoluminescence on concentration of H2O (1–4) and D2O (1'–4') at 60 °C (1, 1'), 65 °C (2, 2'), 70 °C (3, 3'), 80 °C (4, 4').Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) the associates Eu(btfa)3·H2O [Eu(btfa)3·D2O] will be much more ionic than in free Eu(btfa)3, since less electron density will be donated from the aryl substituent to the oxygens of the ligand.Taking into account the fact that enhancement of the ionic character of that bond results in lower nonradiative degradation of the electronic excitation of Eu3+ through the vibrational overtones of the surrounding molecules6 we obtain a reasonable explanation for the observed ‘anomalous’ influence of water on the luminescent properties of Eu(btfa)3.An alternative explanation for the observed phenomenon might be an increase in the energy of the triplet level of the ligand caused by the formation of associates. This would result in diminished radiationless losses of energy from the resonant excited 5D0 level of Eu3+ through the triplet level of the ligand.However, the observed activation energy of the temperature dependence of the Eu3+ luminescence intensity in Eu(btfa)3 Ea = 4.5±0.7 kcal mol–1 coincides with the value of the energy gap between the 5D1 and 5D0 levels of europium (DE = 4.9 kcal mol–1). Apparently the deactivation of the resonant excited 5D0 level of Eu3+ in Eu(btfa)3 takes place through the population of the higher lying 5D1 level of Eu3+ but not through the triplet level of the ligand.The formation of associates is further proved by the fact that water does not enhance the luminescence intensity or lifetime of another b-diketonate, Eu(dpm)3 (dpm = [ButCOCHCOBut]–), which contains neither fluorine atoms nor aryl groups.2 With an increase in the H2O (D2O) concentration the fluorescence lifetime (t) and intensity (I) reach a maximum value (Figures 1 and 2).These dependences were linearised in the inverse coordinates [H2O–1 (D2O–1) vs. I –1 or t–1]. This empirical approach does not reflect the complicated processes involved in associate formation with more than one molecule of water taking place in the system.It does nevertheless permit the determination of the maximum values of Eu3+ luminescence intensity and lifetime. From the intercepts on the I –1 or t–1 axes the maximum values for I and t were obtained (Imax and tmax, respectively, Table 1). The quantum yield for Eu(btfa)3·H2O [Eu(btfa)3·D2O] fmax corresponding to Imax was obtained from the equation fmax = f0(Imax /I0)–1 where f0 and I0 are the photoluminescence quantum yield and intensity for an anhydrous toluene solution of Eu(btfa)3.Using fmax and tmax we calculated the values of radiative and non-radiative decay rate constants (kem and kd, respectively) for the associates from equations kem = fmax t–1 max and kd = = (1 – fmax) t–1 max (Table 2). As can be seen from Figures 1 and 2 the increase of fluorescence intensity and lifetime of Eu(btfa)3 for D2O is much larger than for H2O.This fact is in accordance with the theory of radiationless energy transfer.1 The observed isotope effect clearly shows that in the system consisting of europium chelate containing potential H-accepting groups in the ligand and in water, two opposing effects exist. The first is quenching of rare-earth ion luminescence by the water molecules coordinated in the inner sphere of Eu3+; and the second is a luminescence increase due to the formation of outer-sphere associates between water and the chelate ligand.Assuming that H2O and D2O form similar associates we can estimate the average number of water molecules coordinated in the inner sphere of Eu3+ in the presence of water.The difference between non-radiative decay rate constants for Eu(btfa)3·nH2O and Eu(btfa)3·nD2O is 2300 s–1. Taking into account the fact that the rate constant for quenching of the 5D0 excited state of Eu3+ by a single O–H bond7 is 450–650 s–1 we deduce that 2 or 3 molecules of H2O (D2O) are present in the inner coordination sphere of Eu3+ in the presence of water (4 or 6 O–H bonds, respectively).This is a reasonable estimate because the coordination number for Eu3+ is 8–9 and only 6 coordination sites are occupied in the tris-b-diketonates of Eu3+. The reactions for associate formation can thus be represented by Scheme 1: where L = H2O (D2O), reaction (1) represents formation of an inner-sphere complex (x = 2 or 3) and reaction (2) represents formation of outer-sphere associates.The larger increase of quantum yield for Eu(btfa)3 (fmax /f0 = 10–15) compared to Eu(fod)3 (fmax/f0 = 2–4)2 can be explained by considering that besides fluorine atoms the (btfa) ligand also contains an aryl substituent. The aryl substituent (being the chromophore) and the H-accepting group form a system of conjugated bonds in the b-diketonate which helps the redistribution of the electronic density caused by the formation of associates.Thus, based on these and previous2 results we should expect that addition of water to a rare-earth b-diketonate containing H-accepting groups in the ligand will lead to an ‘anomalous’ influence of water on the fluorescence intensity and lifetime of the rare-earth b-diketonate.The same influence on the luminescence of rare-earth b-diketonates should be expected from other compounds able to form hydrogen bonds, e.g. alcohols. This work was financially supported by the Russian Foundation for Basic Research (grant no. 96-03-33871). N. M. 120 110 100 90 80 70 60 50 40 t/ms [L]/102 M 0 1 2 3 4 1 2 Figure 2 Dependence of 10–3 M Eu(btfa)3 photoluminescence lifetime on the concentration of water at 65 °C: 1, H2O; 2, D2O.aI0 and t0 are the photoluminescence intensity and lifetime of a Eu(btfa)3 anhydrous toluene solution. Errors of measurement of I and t are 5% and 10%, respectively. Table 1 Maximum values for the relative increase of Eu(btfa)3 photoluminescence intensity (Imax/I0) and lifetime (tmax/t0) in the presence of H2O (D2O).a T/K t0 /ms Imax/I0 H2O tmax/t0 H2O Imax/I0 D2O tmax/t0 D2O 333 7.0 16 338 42 7.7 2.2 12 2.9 343 10.0 16 353 10.0 15 aErrors in the calculation of the photophysical constants are 30%.Table 2 Photophysical constants for Eu(btfa)3 toluene solutions: (f0, k0 em, k0 d) and in the presence of H2O (D2O) (fmax, kem, kd) at 65 °C.a f0 (%) k0 em /s–1 k0 d /s–1 fmax H2O kem H2O kd H2O fmax D2O kem D2O kd D2O 2.7 640 23000 21 2000 7700 32 2700 5400 Eu(btfa)3 + xL [Eu(btfa)3 xL] [Eu(btfa)3 xL] + nL [Eu(btfa)3 xL] nL (1) (2) Scheme 1Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Sh. is grateful for financial support from the International Soros Science Education program (grant no. s97-62). References 1 J. L. Kropp and M. W. Windsor, J. Chem. Phys., 1965, 42, 1599. 2 S. S. Ostakhov, A. I. Voloshin, V. P. Kazakov and N. M. Shavaleev, Izv. Akad. Nauk, Ser. Khim., in press (Russ. Chem. Bull., in press). 3 H. Bauer, J. Blanc and D. L. Ross, J. Am. Chem. Soc., 1964, 86, 5125. 4 V. L. Ermolaev, E. B. Sveshnikova and T. A. Shakhverdov, Usp. Khim., 1976, 45, 1753 (Russ. Chem. Rev., 1976, 45, 896). 5 B. V. Cheney, M. V. Schulz, J. Cheney and W. G. Richards, J. Am. Chem. Soc., 1988, 110, 4195. 6 V. E. Karasev, A. G. Mirochnik and E. N. Murav’ev, Zh. Neorg. Khim., 1984, 29, 259 (Russ. J. Inorg. Chem., 1984, 29, 148). 7 V. L. Ermolaev and E. B. Sveshnikova, Usp. Khim., 1994, 63, 962 (Russ. Chem. Rev., 1994, 63, 905). Received: Moscow, 23rd September 1997 Cambridge, 8th January 1998; Com. 7/07579K

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年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Chemiluminescence occurring upon decomposition of dimethyldioxirane adsorbed from the gas phase onto a silipor surface in the presence of tris(bipyridine)ruthenium(II) and 9,10-diphenylanthracene Dmitri V. Kazakov, Alexander I. Voloshin, Natal’ya N. Kabal’nova, Valerii V. Shereshovets and Valerii P. Kazakov* Institute of Organic Chemistry, Ufa Scientific Centre of the Russian Academy of Sciences, 450054 Ufa, Russian Federation.Fax: +7 3472 35 6066; e-mail: chemlum@ufanet.ru Chemiluminescence arising upon decomposition of dimethyldioxirane adsorbed from the gas phase onto a silipor surface containing tris(bipyridine)ruthenium(II) and 9,10-diphenylanthracene has been found and some mechanisms of activation have been suggested.One of the most attractive and interesting properties of such powerful oxidizing reagents as dioxiranes (for example, see refs. 1–3) is their chemiluminescence. Indeed, it was previously assumed that upon isomerization of dioxiranes (DH0 > 356 kJ mol–1) the formation of a triplet excited ester was possible.4 Recent experimental investigations have completely confirmed this assumption.Thus, it was found that decomposition of dimethyldioxirane (DMD) in an oxygen-free acetone solution was accompanied by light emission.5 The same phenomenon was observed upon interaction of dioxiranes with tris(bipyridine)ruthenium(II) [Ru(bipy)3]6 and some aromatic hydrocarbons.2,7 In addition, dioxirane as intermediate has been postulated as a source of chemiluminescence in a number of chemical8,9 and biochemical10 systems.Recently, we were able to show that isomerization of DMD adsorbed from the gas phase onto a silipor surface is also accompanied by chemiluminescence.11 Since the adsorption of luminescent compounds is known to substantially change their photophysical properties,12 the latter observation offers a quite new and promising direction in the investigation of the luminescent properties of dioxiranes.In this connection, in the present work some features of chemiluminescence in the system DMDabs–silipor are considered and the significant increase in chemiluminescence intensity in the presence of Ru(bipy)3 and 9,10-diphenylanthracene (DPhA) placed on the silipor surface is reported for the first time.The luminescence was recorded as follows. DMD solution (2 ml) in acetone ([DMD]0 = 6×10–2 mol dm–3) was introduced into a cell connected to another cell (V = 27 ml) containing 100 mg of silipor (Silipor 400, Chemapol, 0.125–0.160 mm, 400 m2 g–1) and placed above the photocathode of a FEU-140 photomultiplier. An argon flow entering the first cell captured the acetone vapour with the DMD, and this mixture entered the second cell, which was thermostatted at the required temperature. The argon flow was then stopped and chemiluminescence was recorded under static conditions.DPhA and Ru(bipy)3 were sorbed on silipor as described in ref. 13. Thus, upon decomposition of DMD on a silipor surface chemiluminescence is observed (maximum intensity of chemiluminescence at 75 °C is equal to 5.7×106 photon s–1).The chemiluminescence emitter (estimated by means of light filters) was found to be triplet excited methyl acetate (MA*T , lmax = 390 nm, see ref. 14). The kinetics of chemiluminescence decay follow an exponential law. It is interesting to note that the rate constant of luminescence decay kcl = 0.01 s–1 hardly depends on temperature (65–90 °C).From our point of view this is associated with the fact that kcl is an effective value, which depends [apart from reaction (1)] on the adsorption– desorption equilibrium of DMD. An increase in the efficiency of DMD desorption from the silipor surface with an increase in temperature obviously compensates for the increase in the rate constant of isomerization reaction (1), which results in a constant value for kcl. The chemiluminescence yield (hcl)† upon decompostion of DMD (the light sum S = 7×108 photons, 75 °C) adsorbed from the gas phase on the silipor surface is equal to 4×10–9 Einstein mol–1 and the excitation yield (h*)‡ of MA*T is 10–4. It should be pointed out that hcl, estimated by us, is the lowest possible, because we have assumed that the whole quantity of DMD is adsorbed on a sorbent surface.However, this part can amount to only several percent and in reality the value of hcl should be much higher. One can assume that decomposition of chromophore-containing dioxiranes15,16 (for example, dimesityldioxirane or diphenyldioxirane), whose phenyl derivatives possess a greater radiation efficiency, can give us the possibility of observing much brighter chemiluminescence. The value of chemiluminescence yield in the system DMDabs–silipor is nearly two orders of magnitude higher than that obtained by us when investigating DMD decomposition in † DMD exists only as an acetone solution.1–3 Since DMD solutions in acetone are distilled with hardly any fractionation,1 in order to calculate the DMD concentration in the gas phase we have assumed that the density of DMD and acetone vapours are equal to each other.‡ There are no data in the literature concerning the radiative efficiency of MA*T . Therefore, to calculate its excitation yield we have assumed that the phosphorescence yield of methyl acetate (hrad) is at least no higher than that of related compounds, i.e. ketones: 10–5.C R1 R2 O O R1 C O O R2 * R1 C O O R2 + hn (1) 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 1.0 2.0 3.0 4.0 5.0 6.0 20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 0.0 k'c l /s–1 s/1010 photons [Ru(bipy)3]/10–6 mol g–1 0.0 Figure 1 The dependence of k'cl and the light total on Ru(bipy)3 concentration (75 °C) during DMDabs decomposition on a silipor surface.Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) oxygen-free acetone solutions.5 Obviously, this is associated with the favourable conditions for chemiluminescence on a sorbent surface (for example, the absence of quenching by solvent and different impurities in solution). The other reason obviously lies in the mechanism of DMD decomposition itself. In fact, in solution (without oxygen) DMD is mainly decomposed by a radical-chain mechanism5,17 (‘dark’ reaction).That part of chemiluminescent reaction (1) is negligible.5 Instead, on a sorbent surface the radical-chain processes are not so effective and the isomerization reaction plays a major role in DMD decomposition, which results in a significant increase in chemiluminescence yield. In the presence of Ru(bipy)3 adsorbed on the silipor surface, a significant increase in chemiluminescence intensity is observed.Thus, at 75 °C and [Ru(bipy)3]0 = 1×10–6 mol g–1 the maximum intensity of luminescence increases by a factor of 100. The luminescence emitter was found to be Ru(bipy)3. However, in contrast to the DMD decomposition on nonactivated silipor, the kinetics of chemiluminescence damping in the presence of Ru(bipy)3 have a more complicated character: a rapid exponential drop in the chemiluminescence intensity followed by a much slower exponential decay.The maximum luminescence intensity on the second (slow) part is about 10% of that on the first (rapid) one. One can suppose that it is the rapid part of the kinetic curve that reflects DMD decomposition, whereas luminescence on the slow part is obviously caused by decomposition of labile compound, formed during oxidation of the complex by the dioxirane.Ru(bipy)3 considerably increases the rate of DMD decomposition. The dependence of the rate constant of chemiluminescence damping on the first part of the kinetic curve on Ru(bipy)3 concentration is linear (see Figure 1): k'cl = a + b[Ru(bipy)3], where a and b are constant values.From Figure 1 it follows that a = (1.7±0.6)×10–2, b = (9.6±1.8)×103. As we anticipated, the light total of the reaction in the system DMDabs–silipor–Ru(bipy)3 (see Figure 1), as well as chemiluminescence yield (ª3×10–7 Einstein mol–1) is considerably higher then that on non-activated silipor. However, the yield of chemiexcitation of Ru(bipy)3 (ª3×10–5) is one order of magnitude lower than the corresponding value for methyl acetate.Obviously, the increase in chemiluminescence in the presence of Ru(bipy)3, adsorbed on silipor, is caused by the higher radiation yield of the complex (0.0095), which is three orders of magnitude higher than hrad for methyl acetate. One can suppose that the activation of luminescence by Ru(bipy)3 in the course of the decomposition of DMD on the silipor proceeds via a chemically induced electron exchange luminescence mechanism (CIEEL), which is akin to that observed in solution:6 Taking into account the fact that dioxiranes possess a high enough electron affinity (2 eV)18 and readily participate in electron-transfer reactions,19 the CIEEL mechanism seems to be very possible.It is of interest that the samples of silipor containing DPhA also give more intense chemiluminescence and accelerate the rate of DMD decomposition compared with that on the non-activated silipor. Thus, at 75 °C and [DPhA] = = 1×10–6 mol g–1 the rate constant observed and the maximum intensity of luminescence increase by 2 and 10 times, respectively. This was previously reported1,20,21 for the oxidation of some polycyclic aromatic hydrocarbons (PAH) (such as chrysene, pyrene and others) adsorbed on a sorbent surface, by DMD.The main principle of the method was very close to that used by us in the present work, namely, DMD was supplied on a sorbent surface from the gas phase. Since DPhA is also related to PAH, it seems very possible that the interaction of the DMDabs with the other PAH, adsorbed on the surface, will give us a very useful method for studying the kinetics of such reactions by following the chemiluminescence.However, this is the subject of further investigations. Valerii P. Kazakov and Alexander I. Voloshin are grateful to the Russian Foundation for Basic Research (grant no. 96-03-33871) for making this work possible.References 1 R. W. Murray, Chem. Rev., 1989, 89, 1187. 2 W. Adam, L. P. Hadjiarapoglou, R. Curci and R. Mello, in Organic Peroxides, ed. W. Ando, J.Wiley, New York, 1992, ch. 4, p. 195. 3 R. Curci, A. Dinoi and M. F. Rubino, Pure Appl. Chem., 1995, 67, 811. 4 W. Adam and R. Curci, Chim. Ind. (Milan), 1981, 63, 20. 5 D. V. Kazakov, A. I. Voloshin, N. N. Kabal’nova, S.L. Khursan, V. V. Shereshovets and V. P. Kazakov, Izv. Akad. Nauk, Ser. Khim., 1997, 477 (Russ. Chem. Bull., 1997, 46, 456). 6 D. V. Kazakov, A. I. Voloshin, N. N. Kabal’nova, V. V. Shereshovets and V. P. Kazakov, Izv. Akad. Nauk, Ser. Khim., 1997, 1138 (Russ. Chem. Bull., 1997, 46, 1089). 7 D. V. Kazakov, N. N. Kabal’nova, A. I. Voloshin, V. V. Shereshovets and V. P. Kazakov, Izv.Akad. Nauk, Ser. Khim., 1995, 2286 (Russ. Chem. Bull., 1995, 44, 2193). 8 M. F. D. Steinfatt, J. Chem. Res. (S), 1985, 140. 9 A. M. Nazarov, A. I. Voloshin, G. A. Yamilova, V. D. Komissarov and V. P. Kazakov, Izv. Akad. Nauk, Ser. Khim., 1996, 2593 (Russ. Chem. Bull., 1996, 45, 2462). 10 F. M. Raushel and T. O. Baldwin, Biochem. Biophys. Res. Commun., 1989, 164, 1137. 11 D. V. Kazakov, A. I. Voloshin, N. N. Kabal’nova, V. V. Shereshovets and V. P. Kazakov, Izv. Akad. Nauk, Ser. Khim., 1996, 2582 (Russ. Chem. Bull., 1996, 45, 2452). 12 Y. S. Lin, P. de Mayo and W. R. Ware, J. Phys. Chem., 1993, 97, 5995. 13 V. P. Kazakov, A. I. Voloshin, S. S. Ostakhov and N. Sh. Ableeva, Izv. Akad. Nauk, Ser. Khim., 1995, 447 (Russ. Chem. Bull., 1995, 44, 432). 14 D.V. Kazakov, A. I. Voloshin, N. N. Kabal’nova, V. V. Shereshovets and V. P. Kazakov, Izv. Akad. Nauk, Ser. Khim., 1997, 938 (Russ. Chem. Bull., 1997, 46, 898). 15 A. Kirschfeld, S. Muthusamy and W. Sander, Angew. Chem., Int. Ed. Engl., 1994, 33, 2212. 16 W. Sander and A. Kirschfeld, in Advances in Strain in Organic Chemistry, JAI Press Inc., London, 1995, vol. 4, p. 1. 17 M. Singh and R. W. Murray, J. Org. Chem., 1992, 57, 4263. 18 M. Cantos, M. Merchan, F. Tomas-Vert and B. O. Ross, Chem. Phys. Lett., 1994, 229, 181. 19 W. Adam, G. Asensio, R. Curci, M. E. Gonzalez-Nuñez and R. Mello, J. Am. Chem. Soc., 1992, 114, 8345 (and references cited therein). 20 R. W. Murray, M. K. Pillay and M. J. Snelson, in Polynuclear Aromatic Hydrocarbons: Measurements, Means, and Metabolism, eds. M. Cooke, K. Loening and J. Merritt, Battelle Press, Columbus, Ohio, 1991, p. 615. 21 R. W. Murray and W. Kong, Polycyclic Aromat. Compd., 1994, 5, 139. C CH3 CH3 O O H3C C OCH3 O RuII + C CH3 CH3 O O RuII ... C CH3 CH3 O O RuIII ... RuIII ... H3C C OCH3 O Ru*II ... RuII + MA RuII + MA + hn Received: Moscow, 10th July 1997 Cambridge, 20th November 1997; Com. 7/05300B

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Topological anchoring of metal complexes on zeolites Alexander N. Zakharov* and Nikolai S. Zefirov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846; e-mail: zefirov@synth.chem.msu.su The supporting of copper(II) benzoylacetonate on a NaY zeolite by means of ‘anchor fragments’ (derivatives of benzidine, benzophenone or anthraquinone) sterically retained within supercages of the crystal framework is reported.The supporting of metal complexes on zeolites is of growing interest due to the catalytic properties the co-ordination compounds exhibit for a number of reactions.1–4 Steric retention based on the difference between the sizes of the complex molecule and the entrance into the supercage of the zeolite crystal structure was shown1 to be the most effective way of arranging this support. The topologically-encapsulated metal complexes operate as pseudohomogeneous catalysts owing to the molecular stochastic dispersion throughout the bulk of the crystallites.It is evident, however, that the introduction of metal complexes into the zeolite pores inhibits diffusion through the canals of the support. The catalytically-active metal centres appear to be screened by the zeolite lattice, i.e., they become inaccessible for the substrate molecules which usually leads to an apparent decrease in the effective rate constant of the reaction.This paper reports the supporting of copper(II) benzoylacetonate on the external surface of the NaY zeolite via anchor fragments providing a topological linkage between the chelate and the solid.The problems connected with the zeolite sieve effect are surely complicated by introducing ‘guest’ molecules into the large cavities of the ‘host’ framework. The number of metal complex molecules actually operating as catalysts decreases drastically for those species which are localized in the ‘inner’ supercages, remote from the external surface of the crystallites.Taking into consideration the fact that the ‘external’ metal complexes are those that actually operate as catalysts, this work reports the synthesis of samples in which, with the aim of eliminating the diffusion hindrances, the metal centres of the complexes are dragged out of the zeolite pores on to the external surface in contact with the bulk of the reaction medium.At the same time, this retains the topological cohesion with the support via a sterically hindered segment of the ligand.5 The same effect is known6 to take place by supporting the metals by means of the branch functional groups of the solid. Polymer materials, silica gels and some oxides bearing surface OH groups are usually used as supports in these cases.However, there are no examples showing the use of the alkaline forms of zeolites for these aims. At the same time, based on their chemical and physico-mechanical properties, the crystal silica–alumina supports are in no way inferior to, but in fact exceed the polymers, silica gels and oxides in terms of swelling restriction in organic media, wetting, stability at elevated temperatures, and so on.Moreover, surface functionalization can lead to changes in the properties of the solid material. Figure 1 shows schematically the mode of support of the metal complex C by means of the fragment A which plays the role of an anchor providing irreversible retention on the zeolite.The fragment A is evidently sterically entrapped by the supercage B of the NaY zeolite so that the external part of the catalyst molecule containing the metal centre is also supported on the solid. The anchoring obviously becomes possible under the same conditions that are required for the steric retention. However, there is a significant difference between the steric retention and the topological anchoring.5 Steric retention is known to be achieved for those species for which all dimensions exceed the effective diameter of the supercage entrance b.At the same time, such species which possess only one parameter which exceeds the value b, i.e., possess pronounced non-spherical shape, are available for the topological anchoring. Thus, a linear-chain precursor can be used for the topological anchoring.The anchor precursor should consist of roughly cylinder-shaped particles with an effective base diameter a1 less than that of the entrance into the NaY supercage and with the length a2 more than the value b, i.e., a1 < b < a2 (see Figure 1). In order that a molecule can be the precursor for the anchoring of the metal complex by providing the topological linkage with the zeolite, the above conditions should be obeyed with one additional requirement.The precursor has to bear an appropriate functional group in the middle of the molecular chain to form a cross linkage with the ligand. The molecules of benzophenone and anthraquinone clearly meet the above requirements. These compounds can penetrate the large cavities of the NaY zeolite owing to their asymmetric shape in the direction of their main axes.However, they are unable to leave the zeolite supercages by a route perpendicular to the same axis of the molecule. After sorption on the zeolite, the precursor molecules located in the large cavities undergo reaction with benzidine to give the T-shaped products of condensation as shown in Scheme 1.Having been formed in situ the condensation products will become topologically retained within the supercages of the NaY zeolite owing to the rigidity of the benzidine molecule. They cannot be drawn out from the zeolite without destruction of the crystal network. For the same reason, the condensed T-shape derivatives also cannot be drawn into the zeolite void space more than by the depth of one supercage.Thus, after being formed in the zeolite, the anchor compounds 1 and 2† (see Scheme 1) seem to be irreversibly entrapped by the crystal lattice. As these compounds bear one functional group which is located aside the external surface of the crystallite, they can react with other substances. The amino group of benzidine susceptible to reaction is accessible for the reagents from solution or gas phases outside the zeolite.The samples of NaY zeolite containing the anchor compounds † 1 g of the NaY zeolite (SiO2:Al2O3 = 4.1) calcined in air at 550 °C for 4–5 h was treated with benzophenone or anthraquinone vapour. Excess of a solution of benzidine in chloroform was added and the mixtures were refluxed for 30–40 min.The samples were extracted with warm chloroform followed by removal of excess solvent in vacuo at 50–60 °C. The products were identified by IR-spectroscopy and elemental analysis. a2 b c A B C a1 Figure 1 Topological anchoring of the complex C with effective diameter c in the NaY zeolite supercage B (effective diameter of the entrance is b) by means of the cylinder-shape anchor A (conventional dimensions are a1 and a2).Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) 1 and 2 were extracted with chloroform to remove unreacted substances and were treated with a solution of copper(II) benzoylacetonate.The resulting samples formulated as 3 and 4‡ (see Scheme 2), respectively, do not lose colour after subsequent extraction with the solvent.This observation provides indirect but important evidence in favour of the irreversible support of the copper(II) chelate molecules on the zeolite. Indeed, the molecules of copper(II) benzoylacetonate are too large to enter into the supercages of the NaY zeolite and, therefore, could be adsorbed only on the external surface of the crystallites. If this were the case, the subsequent extraction with boiling solvent would result in total removal of the sorbate from the zeolite.On the contrary, if the copper(II) chelates do react with functional NH2 groups, the metal centres are chemically fixed and the metal complexes remain on the support even after solvent extraction. Thus, the samples 3 and 4 containing the resulting complexes anchored by the fragment of benzidine appear to be topologically supported on the NaY zeolite.According to the SEM data, the external surface concentration of copper(II) is quite comparable with the amount of precursor adsorbed on the zeolite, which is indicative that the condensation of benzophenone or anthraquinone with benzidine takes place more rapidly than desorption from the zeolite.It should be noted that the topological anchoring of the metal complexes on porous supports reveals pronounced advantages in comparison with the intracrystalline synthesis. The catalytically-active centres are not hidden within the silica– alumina skeleton but are localized in the phase in contact with the zeolite. They are therefore accessible to any substrate from the side of the reaction medium independently of its shape and dimensions.This method of support eliminates the influence of the intrapellet diffusion gradients which results in an increase in the observed rate constant. Moreover, the topological anchoring allows support of complexes of various shapes and sizes which ‡ The samples 1 and 2 were treated with excess solutions of copper(II) benzoylacetonate under reflux in ethanol for 1 h.The resulting products 3 and 4, respectively, were loaded into an extractor for removal of excess reagents and unreacted substances with warm ethanol. The excess of the solvent was then removed in vacuo at 70 °C. The samples 3 and 4 were characterized by elemental analysis and SEM, and FTIR-spectroscopy. cannot be geometrically situated at all in the supercages of the zeolite.According to the diffuse reflectance spectra for 3 and 4, the nature of the anchor fragment of the ligand hidden in the zeolite framework is not reflected on d–d transitions of the copper(II) complex and, therefore, does not affect the chelate catalytic activity.7 This enables us to use different precursors with respect to the character and features of the zeolite without undesirable changes in the catalytic properties of the coordination compound.The matrix synthesis of metal complexes is known to be hindered in the presence of solvent molecules which compete for the adsorption sites in the large cavities of the zeolite. In the case of topological anchoring, the filling of supercages with the solvent molecules surprisingly favours the retention of the anchor segment by the solid and, at the same time, does not inhibit the reaction between the metal complex and the amino group on the external surface of the zeolite crystallites.This feature permits the reaction between the metal complex and the zeolite-encapsulated anchor to proceed in solution rather than in vacuo. Thus, topological anchoring provides for the development of zeolite-supported systems and allows an expansion of the application of chelate metal complexes to the solution of catalytic problems.References 1 B. V. Romanovskii and A. N. Zakharov, Kataliz. Fundamental’nye i prikladnye issledovaniya (Catalysis. Fundamental and applied investigations), Izdatel’stvo Moskovskogo Universiteta, Moscow, 1987, p. 125 (in Russian). 2 A. N. Zakharov, Mendeleev Commun., 1991, 80. 3 A. N. Zakharov, Kinet. Katal., 1991, 32, 1377 [Kinet. Catal. (Engl. Transl.), 1991, 32, 1230]. 4 A. N. Zakharov and D. Louca, Kinet. Katal., 1993, 34, 662 [Kinet. Catal. (Engl. Transl.), 1993, 34, 589]. 5 A. N. Zakharov and N. S. Zefirov, Dokl. Ross. Akad. Nauk, 1997, 357, 60 [Dokl. Chem. (Engl. Transl.), 1997, 357, 241]. 6 F. R. Hartley, Supported Metal Complexes. A New Generation of Catalysts, D. Reidel Publishing Company, Dordrecht–Boston–Lancaster– Tokyo, 1985. 7 A. N. Zakharov and N. S. Zefirov, Kinet. Katal., 1997, 38, 69 [Kinet. Catal. (Engl. Transl.), 1997, 38, 58]. N H2N N H2N O 1 2 Scheme 1 Cu O O N O N R Me Me Cu O 3 R = 4 R = Scheme 2 Received: Moscow, 24th December 1997 Cambridge, 9th March 1998; Com. 8/00166I

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Activation of the H–H bond by Ni2-porphyrinate Victor M. Mamaev,* Igor P. Gloriozov and Andrew V. Prisyajnyuk Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846; e-mail: vmam@nmr.chem.msu.su The H–H bond is activated without any barrier by Ni2-porphyrinate, based on calculations in terms of the reaction-path Hamiltonian approximation. The creation of catalytic cycles for selective alkane functionalization is one of the most important chemical problems.The reactions leading to H–H, C–H and C–C bond breaking (i.e., H–H, C–H and C–C bond activation) are the key processes in such catalytic cycles.1–4 We have performed a theoretical study of H–H bond activation by bimetallic singlet coordinately unsaturated porphyrin complexes (Por–M1–M2, where M1,2 = Ni).Presently, there is no practical evidence that such a complex exists. We studied the reaction in terms of the reaction-path Hamiltonian approximation.5 The potential-energy surface (PES) was computed by the semiempirical CNDO/S2 method that is aimed at an evaluation of the reaction PESs with participation of Pd and Ni atoms, Pd2 and Ni2 clusters, as well as their complexes.6 Three stationary points have been found on the PES of the activation.These are: precursor complex (PC), transition state (TS) and product (PR) (all the energies are given with respect to the separate reactants). Data on the geometry structure (R, r, a) and the charges (q) on the atoms of the structures of the stationary points of the PESs are presented in Table 1.Analysis of the eigenvalues and eigenvectors of the Hessian matrices showed that in the TS–PR range displacements of the atoms corresponding to the vector directed along the reaction path (RP) were determined mainly by variation in the only internal coordinate, namely, a(H–Ni–H).We have obtained a similar result for oxidative dihydrogen addition to the Pd atom.7 Thus, the catalytic activity of a Por–M1–M2 system is determined by the M2 atom lying above the plane of the porphyrin. We have found only a PC minimum for the Por–Pd–Pd + H2 reaction. The other stationary points are absent. In order to verify our results, we calculated the geometry structures of Por–Ni–Ni–H2, Por–Pd–Pd–H2 and Por–Ni–Pd–H2 using the DFT program in ref. 8. These calculations confirmed our conclusions made earlier from the results of the CNDO/S2 method, namely: the product Por–Ni–Ni–H2 [r(Ni–H) = 1.45 Å, E = –15.9 kcal mol–1] was found, while in the other two systems only molecular adsorption complexes were found to be formed [r(Pd–H) = 1.78 Å]. We think that complexes may exist in which the transition metal atoms would be as active as bare metal atoms (or, possibly, bare clusters), and such complexes would allow us to create real catalytic cycles.This work was supported by the Russian Foundation for Basic Research (RFBR) (grant no. 96-03-32536a) and INTAS– RFBR (grant no. 95-0163). References 1 R. James, Homogeneous Hydrogenation, Wiley, New York, 1973. 2 E.Shilov, The Activation of Saturated Hydrocarbons by Transition Metal Complexes, Riedel, Dordrecht, 1984. M2 M1 N N N N Table 1 Geometry data and atomic charges of the structures of the stationary points of the PES of H–H bond activation by Ni2-porphyrinate. R, r are the distances between the Ni–Ni and Ni–H atoms, a is the H–Ni–H angle and q are nuclear charges.Structure R/Å r/Å a/° qNi1 /e qNi2/e qH/e PC 2.71 2.04 22 0.82 0.04 0.00 TS 2.98 1.50 39 0.82 0.02 –0.02 PR 2.92 1.45 92 0.80 0.45 –0.23 H H M2 M1 N N N N M1 N N N N M2 M1 N N N N H H H H M2 PC,E= –6.1 kcal mol–1 TS,E= –0.4 kcal mol–1 PR,E= –13.2 kcal mol–1Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) 3 S. P. Daley, A. L. Utz, T. R. Trautman and S. T. Ceyer, J. Am. Chem. Soc., 1994, 116, 6001. 4 M. L. Burke and R. J. Madix, J. Am. Chem. Soc., 1991, 113, 1475. 5 W. H. Miller, J. Phys. Chem., 1983, 87, 3811. 6 M. J. Filatov, O. V. Gritsenko and G. M. Zhidomirov, J. Mol. Catal., 1989, 54, 452. 7 V. M. Mamaev, I. P. Gloriozov, V. A. Khmara, V. V. Orlov and Yu. A. Ustynyuk, Dokl. Ross. Akad. Nauk, 1994, 338, 65 [Dokl. Chem. (Engl. Transl.), 1994, 338, 171]. 8 D. N. Laikov, Chem. Phys. Lett., 1997, 281, 151. Received: Moscow, 25th November 1997 Cambridge, 8th January 1998; Com. 7/08940F

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Stereospecific synthesis of bicyclic diaziridines: 4a-chloro-; 4e,6a- and 4a,6e-dichloro-5-methoxycarbonyl-1,6-diazabicyclo[3.1.0]hexanes Sergey N. Denisenko,a Paul Rademacherb and Remir G. Kostyanovsky*c a Ukrainian State University of Chemistry and Technology, 320005 Dnepropetrovsk, Ukraine. E-mail: denisenk@chem.ufl.edu b Institute of Organic Chemistry, University of Essen, D-45117 Essen, Germany. Fax: +49 201 183 3082; e-mail: radem@ocl.orgchem.uni-essen.de c N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Russian Federation. Fax: +7 095 938 2156; e-mail: kost@center.chph.ras.ru Amination of 2-methoxycarbonyl-3-chloro-1-pyrroline 1 with H2NOSO3H occurs predominantly from the anti side with respect to chlorine to afford the bicyclic diaziridine 2 with axial orientation of the 4-chloro substituent.Chlorination of 2 takes place exclusively in the 6-endo position to give 3a. 4,6-Dichlorodiaziridine is transformed from chair 3a into boat 3b as a result of endo–exo isomerization. Similarly to a-chloroalkylamines, N-chlorohydrazines have an ionic state and exist in the form of diazenium salts A.1–5 This can be explained by kinetic destabilizing n(N) ® s*(NCl) and n(N)–n(N) interactions.3–5 These interactions can be eliminated by: i, quaternization of the donor N atom to give a stable N-chlorohydrazinium salt B;4 ii, transformation of the nitrogen atom into a bridgehead position of bicyclic N-chlorohydrazine C4,6 or N-chlorodiaziridines D and E,7–16 or iii, attaching a strong electron-withdrawing group to the N atom to form a stable monocyclic N-chlorodiaziridine F.17 In the strained bicyclic compounds the nitrogen atom in the bridgehead position is forced to re-hybridize to accommodate bond angle variations.For example, the donor capacity of the bridgehead nitrogen in bicyclic compounds D,E is greatly reduced due to the decrease of p-character of the lone-pair.Therefore, the contribution of destabilizing n(N) ® s*(NCl) interactions is less pronounced.5 In contrast, the geometry of the donor nitrogen atom in bicyclic diaziridine G is ‘flattened’. Therefore, n(N) ® s*(NCl) interaction is still significant, and N-chloro derivatives of this type cannot be obtained.11 Additional stabilization of structures D,E by electron-withdrawing substituents R16 in position 5 allows the isolation of endo-6-Cl isomers D in quantitative yield.The properties, including molecular and electronic structures, of bicyclic 6-chlorodiaziridines D,E7–16 and their 6-H-precursors7 –16,18–25 have been studied in detail. The boat conformation of 6-exo isomers of type E, e.g. 6-bromodiaziridine (R = CONHMe)9 and the ephedrinium salt of 6-H-derivative (R = CO2 –), was confirmed using X-ray diffraction.23 Reliable 1H, 13C and 15N NMR criteria for the conformational analysis of D,E have been developed, e.g., the downfield chemical shift of the C(3) atom with a conformational change from boat E to chair D (i.e. 21 to 28 ppm).11 A quadrant rule for the N–Hal chromophore of optically active 6-chlorodiaziridines D,E and 6-bromo derivatives of type E has been proposed.14 Although the vicinal interaction n(N) ® s*(N-Hal) is diminished it is still sufficient to ensure N–Hal bond ionization.Therefore, the isomerization of D to E occurs via an intermediate ion pair H (Scheme 1). In our opinion, this intermediate H is also involved in other chemical transformations of D such as nucleophilic substitution of the chlorine atom and thermal decomposition at T � 40 °C, etc.(Scheme 1). We believe that introducing an additional electronegative substituent into position 4 of bicyclic diaziridines 2 will further inhibit the formation of ion pair H. For example, 1-fluoro- 2-tert-butyl-3,3-pentamethylenediaziridine rearranges spontaneously into the corresponding a-fluoroalkyldiazene26 whereas perfluorinated N-fluoro diaziridines are quite stable.27,28 Thus, we have prepared a new bicyclic diaziridine 2 from 2-methoxycarbonyl- 3-chloro-1-pyrroline (Scheme 2).The intermediate 1 was obtained by a known chlorination procedure.29 Surprisingly, the amination of pyrroline 1 by treatment with H2NOSO3H in the presence of a phase-transfer catalyst according to a previously developed methodology15 gave almost exclusively only one isomer of diaziridine 2 (Scheme 2).The stereospecificity of amination of pyrroline 1 can be explained as follows (Scheme 3). Two conformers with an R N N R R R TsO– Me3N N H Cl Cl– N N Cl N N Hal R N N Hal F N N F3C Cl F R N N H A B C D E F G R = CONHMe, CO2Me, CF3 R = CONHMe, CO2Me, CF3, Me, H 1 2 3 4 5 6 R N N Cl R N N Cl R N N Cl R N N OMe N N Cl R R Cl + N2 + C2H4 D H E Scheme 1 MeO– D Table 1 Spin coupling constants 3JHH/Hz of diaziridine 2 and calculated values for 2b,2c. Coupled protons Experiment 2 Calculated by PCMODEL 2b (axial 4-Cl) 2c (equatorial 4-Cl) 2a3a 10.9 11.8 11.9 2a3e 6.3 6.1 6.2 2e3a 7.8 7.0 6.9 2e3e 1.0 0.5 0.5 3a4 5.4 6.0 10.1 3e4 0.0 1.3 7.3 CO2Me N NH N CO2Me N CO2Me ButOCl Cl Cl 1 2 Scheme 2 H2NOSO3 – – HOSO3 –Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) axial (1a) or equatorial (1b) 3-Cl atom are possible. Molecular mechanics calculations by the MMX method predict a slight preference of axial conformer 1a compared to 1b. The calculated dihedral angle of the p-bond fragment N=C–C=O is 180° for 1a.At the same time, steric 1,2-repulsion between the equatorial Cl atom and the CO2Me group in conformer 1b changes the N=C–C=O dihedral angle to 155°. Comparison of experimental and calculated coupling constants 3JHH for both conformers confirms the predomination of the envelope conformation 1a with an axial chlorine atom.† However, the energy difference of the conformers is rather small, and therefore both of them might undergo amination (Scheme 3).Nevertheless, the approach of the aminating agent to the C=N bond of 1 from the opposite side of the chlorine atom seems to be preferable owing to steric and dipole–dipole interactions. This leads to the formation of a single isomer 2, which assumes the boat conformation 2b.Comparison of 13C, 1H chemical shifts and spin coupling constants 3JHH with those described earlier19 unambiguously confirmed the axial orientation of the 4-Cl substituent in boat 2b.‡ The axial orientation of the 4-Cl atom in 2b is also convincingly confirmed by comparison of experimental and calculated values of 3JHH for isomers with axial or equatorial 4-Cl substituents (PCMODEL molecular mechanics program, QCPE 395) (Table 1).Hence, equatorial orientation of the hydrogen and accordingly axial orientation of the Cl-atom follow. The 4-Cl substituent in diaziridine 2b leads to a reduction of the energies of the two highest occupied MOs, but is not however, as efficient as a CF3 group in the 5-position.16 Therefore, the configurational and thermal stabilities of 4,6-dichlorodiaziridines 3a,b, derived from 2b, are similar to those of 6-chlorodiaziridines D,E (R = CO2Me).Like in cases reported earlier,11,15 chlorination of 2 with ButOCl occurs stereospecifically to form the 6-endo isomer 3a in quantitative yield. † 1, yield 77%, yellowish oil, bp 40–48 °C (0.1 torr) (chromatographic purity 98%); 1H NMR (300 MHz, CDCl3) d: 2.32 (m, 4-He, 2J = –14.8 Hz, 3J = 5.7, 3.6, 2.2 Hz), 2.47 (m, 4-Ha, 2J = –14.8 Hz, 3J = 7.6, 7.2 Hz), 3.94 (s, MeO), 4.0–4.45 (m, 5-CH2), 5.12 (m, 3-H, 3J = 7.6, 2.2 Hz, 4J = 1.4 Hz); 13C NMR (75 MHz, CDCl3) d: 34.6 (t, 4-C), 53.0 (q, MeO), 58.7 (d, 3-C), 60.8 (t, 5-C), 161.3 (s, 2-C), 165.7 (s, CO); MS, m/z (%): 163, 164 (4) [M+], 133, 131 (48), 126 (30), 105, 103 (100), 99 (36), 94 (26), 78, 76 (90), 67 (31), 66 (38), 59 (37), 54 (37), 45 (29), 41 (95).‡ 2, yield 56%, bp 74.8 °C (0.5 torr); 1H NMR (300 MHz, CDCl3) d: 1.9 (ddd, 3-He, 2J = –14.0 Hz, 3J3e2a = 6.3 Hz, 3J3e2e = 1.0 Hz), 2.3 [m, 3-Ha, 2J = –14.0 Hz, 3J3a2a = 10.9 Hz, 3J3a2e = 7.8 Hz, 3J3a4e = 5.4 Hz,J3a6H = 0.8 Hz, spin–spin coupling constants 5J were observed earlier only in similar systems with a boat conformation, such as 1,5-diazabicyclo[ 3.1.0]hexanes (5J3a6e = 0.7 Hz, 5J3e6e = 0.5Hz)19], 2.51 (br.m, NH), 3.2 (m, 2-He, 2J = –12.8 Hz, 3J2e3a = 7.8 Hz, 3J2e3e = 1.0 Hz), 3.3 (m, 2-Ha, 2J = –12.8 Hz, 3J2a3a = 10.9 Hz, 3J2a3e = 6.3 Hz), 3.86 (s, MeO), 4.82 (d, 4-He, 3J4e3a = 5.4 Hz); 13C NMR (75 MHz, CDCl3) d: 31.1 (t, 3-C), 51.9 (t, 2-C), 53.1 (q, MeO), 57.4 (d, 4-C), 67.9 (s, 5-C), 167.2 (s, CO); MS, m/z (%): 147, 145 (4) [M–MeO], 141 (100), 114 (13), 109 (17), 85 (43), 81 (38), 59 (26), 54 (24), 53 (80).The chair conformation of 3a is sterically inconvenient,19 therefore, 3a transforms quantitatively to the boat conformer 3b within a few hours at room temperature in CDCl3 solution. Conformational change from boat 2b to chair 3a and to boat 3b (Scheme 4) was confirmed by the characteristic chemical shifts of C(3).§ It is noteworthy that the new diaziridines 2 and 3 are of interest as potential inhibitors of monoaminooxidase.30 This work was accomplished with financial support from INTAS (grant no. 94-2839). References 1 (a) V. Ya. Bespalov and M. A. Kuznetzov, Zh. Strukt. Khim., 1974, 15, 740 (in Russian); (b) V. Ya. Bespalov and M.A. Kuznetzov, Teor. Eksp. Khim., 1979, 15, 557 (in Russian). 2 (a) M. A. Kuznetzov, Usp. Khim., 1979, 48, 1054 (Russ. Chem. Rev., 1979, 48, 563); (b) M. A. Kuznetzov, Zh. Org. Khim., 1979, 15, 1793 [J. Org. Chem. USSR (Engl. Transl.), 1979, 1612]. 3 G. V. Shustov, N. B. Tavakalyan, L. L. Shustova, I. I. Chervin and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1980, 1058 (Bull.Acad. Sci. USSR, Div. Chem. Sci., 1980, 29, 765). 4 (a) G. V. Shustov, N. B. Tavakalyan and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1981, 1677 (in Russian); (b) G. V. Shustov, N. B. Tavakalyan and R. G. Kostyanovsky, Tetrahedron, 1985, 41, 575. 5 G. V. Shustov, M. A. Shochen, S. V. Barmina, A. V. Yeremeev and R. G. Kostyanovsky, Dokl. Akad. Nauk SSSR, 1986, 287, 689 (in Russian). 6 J. W. Davies, J. R. Malpass and R. E. Moss, Tetrahedron Lett., 1985, 26, 4533. 7 G. V. Shustov, S. N. Denisenko and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1983, 1930 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1983, 32, 1754). 8 S. N. Denisenko, G. V. Shustov and R. G. Kostyanovsky, J. Chem. Soc., Chem. Commun., 1983, 1275; corrigendum: J. Chem.Soc., Chem. Commun., 1985, 680. 9 G. V. Shustov, S. N. Denisenko, I. I. Chervin, A. B. Zolotoi, O. A. D’yachenko, S. V. Konovalikhin, G. V. Shilov, L. O. Atovmyan and R. G. Kostyanovsky, Khim. Geterotsikl. Soedin., 1986, 1330 [Chem. Heterocycl. Compd. (Engl. Transl.), 1986, 1076]. 10 G. V. Shustov, V. V. Starovoytov and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1986, 1205 (Bull.Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 1096). 11 G. V. Shustov, S. N. Denisenko, V. V. Starovoytov, I. I. Chervin and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1599 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 1415). 12 G. V. Shustov, S. N. Denisenko, M. A. Shochen and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1862 (Bull. Acad. Sci.USSR, Div. Chem. Sci., 1988, 37, 1665). 13 G. V. Shustov, S. N. Denisenko, A. Yu. Shibaev, Yu. V. Puzanov, I. K. A. Romero Maldonado and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, § 3a, obtained from 2 under the action of ButOCl in Et2O followed by evaporation in vacuo (0.5 torr, 0 °C), in quantitative yield; 1H NMR (300MHz, CDCl3) d: 2.46 (m, 3-He, 2J = –14.7 Hz, 3J = 10.7, 3.0, 2.1 Hz), 2.76 (m, 3-Ha, 2J = –14.7 Hz, 3J = 9.2, 7.9, 7.6 Hz), 3.38 (m, 2-He, 2J = = –15.3 Hz, 3J = 9.2, 3.7 Hz), 4.1 (m, 2-Ha, 2J = –15.3 Hz, 3J = 10.7, 7.6 Hz), 3.89 (s, MeO), 4.9 (dd, 4-He, 3J = 7.9, 2.1 Hz); 13C NMR (75 MHz, CDCl3) d: 40.1 (t, 3-C), 53.7 (q, MeO), 53.8 (t, 2-C), 56.9 (d, 4-C), 76.3 (s, 5-C), 162.6 (s, CO). 3b, obtained from 3a by keeping its solution in CDCl3 (6 hrs, 20 °C), in quantitative yield; 1H NMR (300 MHz, CDCl3) d: 1.97 (m, 3-He, 2J = = –14.1 Hz, 3J = 7.3, 1.0 Hz), 2.21 (m, 3-Ha, 2J = –14.1 Hz, 3J = 11.3, 8.0, 5.9 Hz), 3.43 (ddd, 2-Ha, 2J = –13.3 Hz, 3J = 11.3, 7.3 Hz), 3.66 (ddd, 2-He, 2J = –13.3 Hz, 3J = 8.0, 1.0 Hz), 3.99 (s, MeO), 4.96 (d, 4-He, 3J = 5.9 Hz); 13C NMR (75 MHz, CDCl3) d: 31.6 (t, 3-C), 53.5 (q, MeO), 54.0 (t, 2-C), 57.4 (t, 4-C), 78.8 (s, 5-C), 164.3 (s, CO).MeO 2C N N H Cl H N CO2Me Cleq H MeO 2C N N H Cl H i i NCO2Me H Clax MeO 2C N N H H Cl MeO 2C N N H H Cl i i 2c (chair, Cl equatorial) 1b 2a (boat, Cl equatorial) 2d (chair, Cl axial) minor product 1a 2b (boat, Cl axial) major product Scheme 3 Reagents and conditions: i, H2NOSO3H/K2CO3 as described.22 N N H H Cl MeO2C N N Cl Cl H MeO2C N N Cl H Cl MeO O i ii 2b 3a 3b Scheme 4 Reagents and conditions: i, ButO Cl in Et2O at 20 °C; ii, 6 h at 20 °C in CDCl3 or 15–20 min in pure form.Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Ser. Khim., 1988, 2358 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 2123). 14 G. V. Shustov, G. K. Kadorkina, R. G. Kostyanovsky and A. Rauk, J. Am. Chem.Soc., 1988, 110, 1719. 15 G. V. Shustov, S. N. Denisenko, A. Yu. Shibaev, Yu. V. Puzanov and R. G. Kostyanovsky, Khim. Fiz., 1989, 8, 366 (in Russian). 16 S. N. Denisenko, P. Rademacher, K. Kowski, G. V. Shustov and R. G. Kostyanovsky, J. Mol. Struct., 1995, 350, 49. 17 Y. Y. Zheng, C. W. Bauknight and D. D. Des Marteau, J. Org. Chem., 1984, 49, 3590. 18 O. G. Khvostenko, B. G.Zykov, N. L. Asfandiarov, V. I. Khvostenko, S. N. Denisenko, G. V. Shustov and R. G. Kostyanovsky, Khim. Fiz., 1985, 4, 1366 (in Russian). 19 G. V. Shustov, S. N. Denisenko, I. I. Chervin, N. L. Asfandiarov and R. G. Kostyanovsky, Tetrahedron, 1985, 41, 5719. 20 G. V. Shustov, S. N. Denisenko, H. L. Asfandiarov, L. R. Chusnutdinova and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser Khim., 1986, 1824 (Bull.Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 1655). 21 G. V. Shustov, S. N. Denisenko and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1986, 1831 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 1662). 22 G. V. Shustov, S. N. Denisenko, A. B. Zolotoi, O. A. D’yachenko, L. O. Atovmyan and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1986, 2266 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 2071). 23 A. B. Zolotoi, O. A. D’yachenko, L. O. Atovmyan, G. V. Shustov, S. N. Denisenko and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1986, 2441 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 2232). 24 G. Kaupp, S. N. Denisenko, G. V. Shustov and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1991, 2496 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1991, 40, 2173). 25 G. Kaupp and S. N. Denisenko, Magn. Reson. Chem., 1992, 30, 637. 26 W. H. Graham, J. Am. Chem. Soc., 1966, 88, 4677. 27 R. A. Mitsch, J. Org. Chem., 1968, 33, 1847. 28 W. C. Firth, J. Org. Chem., 1968, 33, 3489. 29 J. Häusler, Lieb. Ann. Chem., 1981, 1073. 30 R. G. Kostyanovsky, G. V. Shustov, O. G. Nabiev, S. N. Denisenko, S. A. Sukhanova and E. F. Lavretskaya, Khim.-Farm. Zh., 1986, 20, 671 (in Russian). Received: Moscow, 8th December 1997 Cambridge, 8th January 1998; Com. 7/08974K

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摘要:

Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) The -hydroxyethyl radical as a model system for two-pathway electroreduction in the presence of proton donors Alexander G. Krivenko, Alexander S. Kotkin and Vladimir A. Kurmaz* Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 096 515 3588; e-mail: kurmaz@icp.ac.ru The mechanism of electrode reactions of the b-hydroxyethyl radical has been found experimentally to depend on pH, and a general kinetic scheme of organic radical electroreduction is suggested which includes two parallel pathways of electron transfer, either to adsorbed radical Rads or to its metastable protonated complex [Rads·BH+]; the competition between these pathways is determined by the capacity of Rads for complex formation, the concentration of the proton donor, and electron transfer rates to Rads and [Rads·BH+].The problems of electron transfer in electrochemical systems have received much attention.1 Two-electron electrochemical reduction (subsequently called electroreduction or reduction) of electroactive depolariser A may be represented by the following sequence of one-electron steps:2 where IS is an intermediate and W3 and W2 are its electroreduction and electrooxidation rate constants, respectively.If A is an organic depolariser, e.g., an organic halide, IS is usually a radical which is adsorbed on the electrode surface.2 It has been demonstrated previously by the laser photoemission method2 (LPE) that the dependence of W3 on the electrode potential E for organic radicals follows the slow discharge equation with a transfer coefficient a ca. 0.5 at W3 within 1–107 s–1. According to refs. 2–6, W3 does not depend on the concentration of proton donors BH+ for certain radicals (linear ether and a-hydroxy alkyl radicals; alkyl, aryl and their halogen derivatives, i.e.group I), whereas W3 is proportional to [BH+] for group II (a-radicals of cyclic ethers and glycols; b-radicals of alkylcarboxylic acids; HCO·). The nature of these differences is not clear. Therefore, it seems important to perform a comparative study of the electrochemistry of radicals which have the same (or similar) chemical composition but differ in structure, e.g. in the localisation of the free valence. The a- and b-hydroxyethyl radicals were chosen for the study (radicals I and II, respectively).The former has been thoroughly studied by photoemission methods,6,7 but the electrochemistry of radical II has not been studied in detail before, see refs. 2 and 8. We generated radical II by the reaction of solvated electron e– aq † with an acceptor, namely, 2-chloro- or 2-bromoethanol XCH2CH2OH (X = Cl, Br): where ka = 6.4×108 dm3 mol–1 s–1 for X = Cl.9‡ Radical I is formed upon elimination of an H-atom by an OH radical from the a-carbon of ethanol.The OH radical is generated from aqueous solutions of N2O by a process such as reaction (2). The radicals formed by a dissociative electron transfer1 reaction (2) diffuse to an electrode and are adsorbed on it and are involved in electrode reactions to yield photocurrent j.The values of j were obtained by recording and digital Fouriertransformation of the signal from a photoelectrochemical cell at 1.0–1100 Hz frequencies n of electrode illumination. The position of the voltammetric wave on the E axis is determined by a competition between the irreversible reduction of a radical with rate constant W3 and the duration of electrode illumination.W3 is derived from W3 = 5.31n at E = E1/2 under the same experimental conditions as those which provide † e– aq are generated by the LPE method at distances of ca. 10–100 Å from the electrode by its irradiation with a UV-laser pulse (l 337 or 265 nm). ‡ kd values for such reactions are usually � 108–109 s–1, see ref. 10. the measurement of W3 values in the range 5–5.8×103 s–1. The values of W3 in the range 3×103–6×106 s–1 were determined by measurement of the kinetics of emitted charge Q(t). The experimental setup and measurement technique have been described in detail elsewhere.2–4 The electrochemical behaviour of a- and b-hydroxyethyl radicals was found to differ fundamentally.W3 does not depend on pH in the range 3–12 for radical I,6 whereas the W3(E) dependences for radical II are different in acidic and basic solutions and consist of three characteristic sections (Figure 1). The first (a) and third (c) sections follow the equation of slow discharge with a transfer coefficient a of ca. 0.4, while W3 decreases in the first section of the curve as pH increases.These sections are separated by an intermediate second section (b), where W3 hardly depends on E; the lower the pH the higher the position of this region on the Y-axis. All three sections (a)–(c) are most pronounced at low-acid pH values. W3 decreases in the first section as pH changes from acidic to low-basic values (Figure 2); the slope of (dEW3 = 10 s–1/dpH) dependence (0.14±0.02 V) at pH £ 8.1 is close to the corre- b A IS B W1 W2 W3 W4 (1) XCH2CH2OH + e– aq XCH2CH2OH–· ·CH2 CH2OH· + X– ka kd (2) ·CH2CH2OH pH 2.20 pH 3.60 pH 4.85 pH 6.70 pH 10.60 pH 11.90 pH 13.50 (a) (b) (c) CH3CHOH · pH 3–12 7 6 5 4 3 2 1 0.4 0.8 1.2 1.6 log W3 –E/VSCE Figure 1 W3(E) dependences for the radicals I (dashed line, data from refs. 6 and 7) and II (solid lines) at various pH. 0.045–0.27 M 2-chloroethanol or 0.01 M 2-bromoethanol are used as acceptors. Stationary mercury electrode. Supporting electrolytes are aqueous buffer solutions with the addition of 0.5 M KCl. 0Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) sponding (2.3RT/F)/a value that characterises electroreduction as a first-order reaction with respect to BH+ concentration.Similar W3(E, pH) dependences were observed earlier for electroreduction of H atoms,11 bromate anions,2,12 radicals of 1,4-dioxane3 and dihydroxyethyl radicals.4 We believe that their shape is evidence for two parallel electron transfer pathways. The first one involves electron transfer to Rads with the formation of an R– carbanion (W3 does not depend on [BH+]). The second pathway involves electron transfer with a preceding chemical step, which is the formation of a metastable complex of the radical with a proton donor [Rads·BH+].3,4 The general scheme of the process may be written as follows: where Ve' and Ve are the rate constants of electron transfer to Rads and to a metastable complex [Rads·BH+], and k1, k2 are rate constants of its formation and dissociation, respectively; kpr is the rate constant of R– protonation.The lifetime of the carbanions is very small13 in aqueous solutions for simple organic radicals, which makes electron transfer irreversible. The W3 value measured by the LPE method is described by the following expression in terms of this scheme (see, e.g., refs. 2 and 4): Let us consider the dependence of W3 on E and pH and compare it with the experimental results.(a) Strongly acidic solutions, not too negative potentials: k1 � k2; Ve, and W3 = Ve. Apparently, this case cannot occur because the dark H3O+ discharge makes the measurements impossible at the required BH+ concentrations. (b) Moderately acidic solutions, the same E: k2 > k1; Ve; W3 = (k1/k2)Ve. Quasi-reversible complex discharge. W3 is proportional to [BH+] and depends on E as an exponent [section (a) of the W3(E, pH) dependences at pH < 6.7, Figures 1, 2].(c) Low-acidic and neutral solutions: Ve > k1,k2; W3 = k1. The limiting step is complex formation. W3 µ [BH+] but does not depend on E [section (b) of W3(E, pH) dependences, Figures 1, 3). It follows from equation (5) that the potential of transfer EQC from a ‘quasi-reversible discharge’ to that controlled by a chemical step is defined by Ve @ k2 and does not depend on pH; this is also observed experimeny (Figure 1).(d) Neutral and basic solutions, more negative potentials. Ve' > k1; W3 = Ve ' . The rate of electron transfer to Rads is higher than that of complex discharge [section (c) of W3(E, pH) dependences; it is observed in the electroreduction of radical I as well as in the electroreduction of radical II at pH > 10, Figure 1].In this model, the particular method of electroreduction [i.e. (b), (c) or (d)] at the given E and pH is determined both by the difference in overvoltages of electroreduction of Rads and [Rads·BH+] and the free energy DfG0 of complex formation, where DfG0 µ log(k1/k2).For example, only the reduction of [Hads·BH+] is observed for H atoms, since their direct electroreduction to H– is energetically unfavourable. And vice versa, reduction of radicals of group I occurs only through the first pathway, probably due to their relatively low capacity for complex formation. The value of k0 may be a quantitative characteristic of such ability and is determined by the extrapolation of the k1, pH-dependence (Figure 3) to pH = 0.This is close to the diffusion-controlled rate constant for the H atom,11 for radical II and for the dihydroxyethyl radical4 and equals (6–8)×109 mol–1 s–1, whereas k0 for the 1,4-dioxane radical3 is somewhat lower, (1.5–2.0)×107 mol–1 s–1. For radicals of group I k0 < (103–102) mol–1 s–1.Assuming that k2 constants for the complex decay are similar in both groups, this implies that for radicals of groups I and II the DfG0 values differ by no less than 0.4–0.45 eV.§ The reason for such differences may lie in the structural features of the radicals. Probably, the free valence is blocked upon adsorption of radicals of group I, and formation of the [Rads·BH+] complex is hindered.However, if a radical is bifunctional, the reactivity is provided by the second active centre, e.g., the remote functional group (radicals of group II). This may lead to differences in the products of reactions (3) and (4), as is the case in redox reactions of a- and b-radicals of aliphatic alcohols and ethers with ions of variable valences, see ref. 14 and references therein.Conjugated elimination of active groups with the formation of an olefin in such reactions is more characteristic of b-radicals.14 Thus, the model suggested is in accordance with the experimental results. This approach may be applied to the description of electroreduction of stable compounds, with the only difference that the respective intermediates are formed not only on the electrode surface but in the bulk of the solution.§ In this case the EQC values define the respective positions of W3(E) dependences for reduction of complexes of BH+ with various radicals. 1.2 0.8 0.4 0.0 4.0 8.0 12.0 –EW3 = 10 s–1/VSCE pH Figure 2 E, pH-dependences obtained by a cross-section method from W3(E) plots for radical II at W3 = 10 s–1. Rads R– RH Rads + BH+ RadsH+ products Ve' kpr k1 k2 Ve (3) (4) W3= +Ve ';kpr >> W3; k1 = k0[BH+] k1Ve k1 + k2 + Ve (5) 8 4 0 8.0 4.0 0.0 pH log k1 Figure 3 k1, pH-dependences obtained in terms of kinetic scheme (3)–(4) for radical II ( ), the radical of 1,4-dioxane3 ( ), H-atoms11 ( ) and dihydroxyethyl radical4 ( ).Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) This work was supported by the Russian Foundation for Basic Research (grant no. 97-03-32265). References 1 J.-M. Savéant, Acc. Chem. Res., 1993, 26, 455. 2 V. A. Benderskii and A. G. Krivenko, Usp. Khim., 1990, 59, 3 (Russ. Chem. Rev., 1990, 59, 1). 3 V. A. Benderskii, A. G. Krivenko, A. S. Kotkin and V. A. Kurmaz, Elektrokhimiya, 1993, 29, 246 (Russ. J. Electrochem., 1993, 29, 221). 4 A. G. Krivenko, V.A. Benderskii, A. S. Kotkin and V. A. Kurmaz, Elektrokhimiya, 1993, 29, 869 (Russ. J. Electrochem., 1993, 29, 741). 5 A. G. Krivenko and V. A. Kurmaz, Extended Abstracts of the 46th Annual ISE Meeting, Xiamen, China, 1995, vol. 1, p. 47. 6 V. A. Benderskii, A. G. Krivenko and V. A. Kurmaz, Elektrokhimiya, 1986, 22, 644 [Sov. Electrochem. (Engl. Transl.), 1986, 22, 607]. 7 Z. A. Rotenberg and N. M. Rufman, J. Electroanalyt. Chem., 1984, 175, 153. 8 P. Toffel and A. Henglein, Disc. Faraday Soc., 1978, 63, 124. 9 G. V. Buxton, C. L. Greenstock, W. Ph. Helman and A. R. Ross, J. Phys. Chem. Ref. Data, 1988, 17, 513. 10 L. G. Feoktistov, in Organic Electrochemistry, eds. M. M. Baizer and H. Lund, Marcel Dekker, Inc., New York and Basel, 1983. 11 A. V. Benderskii, V. A. Benderskii and A. G. Krivenko, J. Electroanalyt. Chem., 1995, 380, 7. 12 V. A. Benderskii, A. G. Krivenko and N. V. Fedorovich, J. Electroanalyt. Chem., 1988, 241, 247. 13 R. A. McClelland and S. Steenken, J. Am. Chem. Soc., 1988, 110, 5860. 14 H. Cohen and D. Meyerstein, Inorg. Chem., 1987, 26, 2342. Received: Moscow, 29th December 1997 Cambridge, 11th February 1998; Com. 8/00174J

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Self-quenching in the stepwise photocyclization of 1,4-bis(diphenylamino)butane to 1,4-dicarbazolylbutane Mikhail F. Budyka,* Olga D. Laukhina and Tatyana N. Gavrishova Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 096 515 3588; e-mail: budyka@icp.ac.ru The quantum yields of stepwise cyclization of the first and second diphenylamino groups in 1,4-bis(diphenylamino)butane are 0.3 and 0.02, respectively, which indicates quenching of the excited diphenylamino group by a carbazole unit in the asymmetric semicyclized compound.On irradiation, diphenylamine and derivatives are known to form the corresponding carbazoles by an intramolecular cyclization reaction.1–5 The cyclization has been shown to proceed in the excited triplet state followed by oxidation of intermediate dihydrocarbazole to carbazole by oxygen.In this communication we report the peculiarities of the photocyclization of the bichromophoric derivative of diphenylamine, namely, 1,4-bis(diphenylamino)butane 1. The photochemical properties of the model compounds, N-butyldiphenylamine 2 and 1-(N-diphenylamino)-4-(N-carbazolyl)butane 3 are also considered for comparison.An air-saturated acetonitrile solution of 1 (5.08×10–6 M) was irradiated at 313 nm (light intensity 3×10–6 einstein dm–3 s–1). Spectrum (1) in Figure 1 belongs to pure 1, whereas the final spectrum (7) coincides with the spectrum of 1,4-dicarbazolylbutane 4.This compound was identified by its characteristic absorption (labs ~ 240, 260, 290 and 340 nm) and fluorescence (lfl ~ 350 and 365 nm) spectra and by comparison (thin layer chromatography) with a thermally synthesized sample. Therefore, 4 is the final product of the photocyclization of 1. Aminocarbazole 3, which is a semi-cyclized compound with a diphenylamino group on one side of the methylene bridge and a carbazole group on the other, is a possible intermediate in the diamine cyclization reaction.The model asymmetric compound 3 was synthesized. The absorption spectrum of 3 was proved to be the half-sum of the spectra of 1 and 4, and to coincide with spectrum (4) in Figure 1. Investigation of the kinetics of photocyclization (see insert in Figure 1) shows clearly that the reaction proceeds in two stages, with a fast first stage, spectra (1) ® (4), and a slow second stage, spectra (4) ® (7).Based on this fact, and on the coincidence between the intermediate spectrum (4) in Figure 1 and the absorption spectrum of aminocarbazole 3, the following two-step scheme for the photochemical reactions can be proposed (Scheme 1).The rate of photochemical transformation of substance X is expressed by equation (1): where jX and DX are, respectively, the quantum yield of the reaction and optical density of the substance X at the irradiation wavelength, D is the optical density of the reaction mixture at the same wavelength and I0 is the intensity of incident light (einstein dm–3 s–1). In the case of a thin optical layer (D < 0.1) and monitoring the reaction kinetics at the irradiation wavelength, equation (1) can be integrated and gives for time t: where eX is the absorption coefficient (M–1 cm–1) of X at the irradiation wavelength and l is the optical path (cm). In addition to diamine photocyclization, reaction kinetics of the model compounds 2 and 3 were investigated.All kinetic data are treated in terms of equation (2) and are compared in Figure 2. One can see that, firstly, the kinetics of diamine photocyclization, curve (1), in the initial stage of the reaction are similar to those of the monoamine photocyclization, straight D 0.3 0.2 0.1 0.0 240 280 320 360 l/nm D313 0.08 0.06 0.04 0 500 1000 1500 t/s Figure 1 Spectral changes during irradiation of a 5.08×10–6 M acetonitrile solution of 1: irradiation time (1)–(7)/s: 0, 10, 30, 80, 270, 600, 1560.Insert: kinetics of the optical density decrease at the wavelength of irradiation (313 nm). 1 7 7 1 N (CH2)4 N N (CH2)4 N N (CH2)4 N 1 3 4 Scheme 1 hn j1 hn j2 d[X]/dt = –jX(DX/D)(1 – 10–D)I0 (1) ln[(Dt – D•)/(D0 – D•)] = –2.3eXjXlI0t (2) ln[(Dt – D•)/(D0 – D•)] 0.0 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 0 200 400 600 800 t/s 1 2 3 Figure 2 Semilogarithmic plots for the photocyclization reactions: (1) 1; (2) 2; (3) 3 (in all cases D0 < 0.1).Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) line (2), whereas the kinetics of the final stage of the diamine reaction are similar to those of the aminocarbazole photocyclization, straight line (3); and, secondly, the slopes of both lines differ markedly.The quantum yields for the first (j1) and the second (j2) diphenylamino groups cyclization in 1 are calculated to be 0.3 and 0.02, respectively. Thus, an investigation of the photocyclization reaction of diamine 1 in comparison with reactions of the model monoamine 2 and aminocarbazole 3 shows that the presence of the second diphenylamino group has no effect on the photocyclization of the first diphenylamino group, whereas the photocyclization of the second diphenylamino group is retarded after the photocyclization of the first diphenylamino group.Therefore, the carbazole group is a quencher for the photocyclization reaction of the diphenylamino group in semicyclized compound 3.Symmetrically a,w-disubstituted alkanes have attracted many researchers in connection with an investigation of the problem of functional group interaction.6–11 In the case of alkanes with carbazole6 and diphenylamino11 groups no intramolecular interaction of functional groups was observed, provided the number of linking CH2 groups exceeded 3 (number of linking s-bonds exceeded 4).In this respect, the properties of bifunctional compounds with flexible polymethylene chains differ markedly from those with rigid polynorbornyl bridges, where interaction has been observed through up to 6 s-bonds.12 The absence of any diphenylamino group interaction in 111 agrees with our finding that the quantum yield of the first diphenylamino group photocyclization in 1 (j1 = 0.3) is equal to that of monoamine 2 photocyclization.However, the small value of j2 = 0.02 points to the stronger interaction of the two functional groups in asymmetrically disubstituted butane 3 compared to symmetrically substituted butanes 1 and 4. The data obtained can be explained as follows. Singlet (S1) and triplet (T1) levels of diphenylamine lie at 31100 and 25140 cm–1, and those of carbazole lie at 29500 and 24690 cm–1, respectively.13 The interchromophoric edge-to-edge distance in 3 does not exceed 5.1 Å and in such compounds the energy transfer proceeds on a time scale of several picoseconds for the singlet-singlet transfer14 and of tens of nanoseconds for the triplet-triplet one.15 Taking into account the lifetimes of the lowest excited states of the diphenylamine chromophore, i.e. 4.0×10–9 s for the singlet and 2.7×10–5 s for the triplet state,16 one should expect effective quenching of both singlet and triplet excited diphenylamine groups by a carbazole group. So, on irradiation of 3 the excitation appears to be localised at the carbazole group thus preventing cyclization of the diphenylamino group. The possibility of quenching by an electron transfer mechanism should not be neglected either.The work was supported by the Russian Foundation for Basic Research (grant no. 97-03-32342). References 1 E. W. Forster, K. H. Grellmann and H. Linschitz, J. Am. Chem. Soc., 1973, 95, 3108. 2 K. H. Grellmann, W. Kuhnle, H. Weller and T. Wolff, J. Am. Chem. Soc., 1981, 103, 6889. 3 H. Shizuka, Y. Takayama, I. Tanaka and T.Morita, J. Am. Chem. Soc., 1970, 92, 7270. 4 K. Amano, T. Hinohara and M. Hoshino, J. Photochem. Photobiol. A: Chem., 1991, 59, 43. 5 T. Suzuki, Y. Kajii, K. Shibuya and K. Obi, Bull. Chem. Soc. Jpn., 1992, 65, 1084. 6 G. E. Johnson, J. Chem. Phys., 1974, 61, 3002. 7 K. Zachariasse and W. Kuhnle, Z. Phys. Chem., 1976, 101, 267. 8 R. A. Beecroft, R. S. Davidson and T. D.Whelan, J.Chem. Soc., Perkin Trans. 2, 1985, 1069. 9 F. C. Deschryver, P. Collart, R. Goedeweeck, A. M. Swinnen, J. Vandendriessche and M. Vanderauweraer, Acc. Chem. Res., 1987, 20, 159. 10 J. J. Cai and E. C. Lim, J. Phys. Chem., 1994, 98, 2515. 11 M. F. Budyka, T. N. Gavrishova, O. D. Laukhina and E. M. Koldasheva, Izv. Akad. Nauk, Ser. Khim., 1995, 1725 (Russ. Chem. Bull., 1995, 44, 1656). 12 G. D. Scholes, K. P. Ghiggino, A. M. Oliver and M. N. Paddon-Row, J. Am. Chem. Soc., 1993, 115, 4345. 13 J. E. Adams, W. W. Mantulin and J. R. Huber, J. Am. Chem. Soc., 1973, 95, 5477. 14 M. Kaschke, B. Valeur, J. Bourson and N. P. Ernsting, Chem. Phys. Lett., 1991, 179, 544. 15 G. H. Haggquist, H. Katayama, A. Tsuchida, S. Ito and M. Yamamoto, J. Phys. Chem., 1993, 97, 9270. 16 H. Shimamori and A. Sato, J. Phys. Chem., 1994, 98, 13481. Received: Moscow, 11th November 1997 Cambridge, 15th December 1997; Com. 7/08310F

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43–82) Synthesis of tetracoordinated rhodium(I) complexes with chiral Shiff bases prepared from dehydroabietic acid Aleksander G. Tolstikov,*a Nikolay N. Karpyshev,a Yurii I. Amosov,a Olga V. Tolstikova,a Tatiana B. Khlebnikova,a Genrikh A. Tolstikov,b Victor I. Mamatyukb and Georgii E. Salnikovb a G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation.Fax: +7 3832 35 5756 b Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 35 4752 New optically active Shiff bases 16–19 have been prepared from dehydroabietic acid 1 and have been used as ligands to synthesize tetracoordinated rhodium(I) complexes 20–27.Synthesis of numerous pharmacologically valuable compounds is based on catalytic enantioselective reduction of prochiral ketones to optically active carbinols. Apart from direct hydrogenation, reactions of hydrosilylation and hydrogen transfer promoted by transition metal complexes with chiral P,N-donor ligands can be used to achieve the transformation under discussion.1–3 The use of tetra- and pentacoordinated rhodium(I)- and iridium(I)-complexes with Shiff bases, prepared by interaction between optically active amines and heteroaromatic aldehydes, provided high chemical and optical yields of the products of reduction of acetophenone and its homologues.4,5 Having defined the synthesis of chiral ligands as the key objective in the concept we are developing for the various uses of natural higher terpenoids, we notice that resin acids have been studied only slightly in this respect.The adducts of levopimaric acid with maleic anhydride and p-quinone were shown to be promising starting compounds for the synthesis of optically active phosphorus-containing ligands.6,7 The purpose of the present work was to synthesize tetracoordinated rhodium(I) complexes with chiral Shiff bases prepared from dehydroabietic acid 1.8 The treatment of its acyl chloride 29 with a saturated NH3 solution in methanol at 0 °C produced amide 3 (92%), which was then reduced using a three-fold excess of LiAlH4 to dehydroabietylamine 4 (75%).The latter compound is the same as that described in refs. 10 and 11.The interaction of acyl chloride 2 with NaN3 and thermal rearrangement of the intermediate azide 5 resulted in dehydroabietyl isocyanate 6,9 which was heated with concentrated hydrogen chloride in benzene to obtain amine hydrochloride 7 (65%). Amine 11 was synthesized according to the following procedure (Scheme 2). Methyl dehydroabietate 8 was oxidized by KMnO4 immobilized on Al2O3 to produce methyl-7- ketodehydroabietate 9,12 which was readily transformed to the corresponding oxime 10 (75%) under the action of NH2OH·HCl.This compound was hydrogenated over a PtO2 catalyst in the presence of an equimolar quantity of HCl in methanol to produce a mixture of products, from which the target compound, methyl 7-aminodehydroabietate 11 (80%) was isolated after neutralization using column chromatography on SiO2.A comparative analysis of 1H and 13C NMR spectra recorded for hydrochloride 7 and amines 4, 11† suggested that the b-configuration of the NH2 group in compound 11 was favoured. A similar example of the selective reduction of oximes is the preferential formation of b-amines in the catalytic (PtO2) hydrogenation of some oximino-derivatives of monoterpenes and steroids.13,14 Oxidation of methyl 12-bromodehydroabietate 12 with KMnO4/Al2O3 in acetone gave methyl 12-bromo-7-ketodehydroabietate 13 (85%).Oxime 14 synthesized from this was hydrogenated over PtO2 under the same conditions as oxime 10. A mixture of products was obtained, among which methyl 7(b)-amino-12-bromodehydroabietate 15 (56%) was isolated.The reaction between pyridine-2-carboxaldehyde and amine 4 was conducted in benzene in the presence of anhydrous Na2SO4 and gave azomethine 16 (67%).‡ Chiral Shiff bases 17 (52%), 18 (60%) and 19 (54%) were synthesized in the same way from amines 7, 11 and 15, respectively. Chiral rhodium(I) complexes 20–27 were prepared through interaction of ligands 16–19 with di-m-chlorobis(cyclooctadiene) dirhodium and NaClO4 or NaBF4 in methanol.Reduction of acetophenone to phenethyl alcohol by means of a hydrogen transfer reaction under the conditions given elsewhere4 was used as an example for the preliminary R = RCOOH RCOCl RCONH2 RCH2NH2 [RCON3] RNCO RNH2·HCl 1 2 3 4 5 6 7 i ii iii iv Scheme 1 Reagents and conditions: i, NH3, MeOH, 0 °C, 2 h; ii, LiAlH4, Et2O, 35 °C, 8 h; iii, NaN3, Me2CO, 0 °C, 1 h, then MePh, 100 °C, 1.5 h; iv, HCl, C6H6, 80 °C, 5 h.R CO2Me R CO2Me O R CO2Me NOH R CO2Me H NH2 i ii iii 8 R = H 12 R = Br 9 R = H 13 R = Br 10 R = H 14 R = Br 11 R = H 15 R = Br Scheme 2 Reagents and conditions: i, KMnO4/Al2O3, Me2CO, 20 °C, 12 h; ii, NH2OH·HCl, AcONa, EtOH, 78 °C, 3 h; iii, H2, PtO2, MeOH/HCl, 20 °C, 1.5 h, then Et3N, Et2O, 20 °C.Mendeleev Communications Electronic Version, Issue 2, 1998 (pp. 43-82) estimation of the catalytic activity and enantioselectivity of the new complexes. For example, at [cat.] = 1.6×10–4 M and ratios of [sub.]/[cat.] = 1000, [propan-2-ol]/[sub.] = 80, the transformation of acetophenone in boiling propan-2-ol catalysed by complex 20‡ produced (+)-(R)-phenethyl alcohol at 50% conversion and a moderate optical yield (12%) {[a]D 20 +5.1° (neat), lit.,4 [a]D 20 +43.6° (neat)}.† A Bruker DRX 500 spectrometer was used to record 1H and 13C NMR spectra for compounds 7 and 11, and a Bruker AC-200 for compounds 16 and 20. 7: mp 250 °C (decomp.), [a]D 20 +49.6° (c 0.74, in CHCl3); 1H NMR (CDCl3) d: 1.19 (s, 3H, 18-H3), 1.22 (d, 6H, 16-H3, 17-H3, J = 7 Hz), 1.46 (s, 3H, 19-H3), 1.52 (m, 1H, 1-Ha, Jhem = 13 Hz, J = 13 Hz, J = 4 Hz), 1.73 (m, 1H, 3-Ha), 1.76–1.87 (m, 3H, 2-H2, 6-Ha), 1.99 (d, 1H, 5-H, J = 13 Hz), 2.19–2.30 (m, 3H, 3-Hb, 6-Hb, 1-Hb), 2.81 (septet, 1H, 15-H, J = 7 Hz), 2.93 (m, 1H, 7-Ha, Jhem = 17 Hz, J = 7 Hz), 3.00 (m, 1H, 7-Hb, Jhem = 17 Hz, J = 11.5 Hz, J = 6.5 Hz), 6.88 (d, 1H, 14-H, J = 1.5 Hz), 6.98 (dd, 1H, 12-H, J = 8Hz, J = 1.5 Hz), 7.13 (d, 1H, 11-H, J = 8 Hz), 8.4 (br.s, 3H, NH2·HCl); 13C NMR (CDCl3) d: 18.72, 18.77 (C-2, C-6), 19.89 (C-19), 23.83 (C-16, C-17), 24.74 (C-18), 29.74 (C-7), 33.38 (C-15), 37.18 (C-1), 37.86 (C-10), 37.89 (C-3), 48.49 (C-5), 58.44 (C-4), 124.01 (C-12), 124.35 (C-11), 126.77 (C-14), 134.10 (C-8), 145.05 (C-9), 145.87 (C-13). 11: oil, [a]D 18 +13.9° (c 1.50, in CHCl3); 1H NMR (CDCl3) d: 1.21 (d, 6H, 16-H3, 17-H3, J = 7 Hz), 1.24 and 1.26 (s, 6H, 18-H3, 19-H3), 1.31–1.93 (m, 8H, 1-H2, 2-H2, 3-H2, 6-H2), 2.25 (dd, 1H, 5-H, J = 12 Hz, J = 2 Hz), 2.84 (septet, 1H, 15-H, J = 7 Hz), 3.64 (s, 3H, OCH3), 4.01 (dd, 1H, 7-H2, J = 10.5Hz, J = 7.2 Hz), 7.03 (dd, 1H, 12-H, J = 8.0 Hz, J = 2.0 Hz), 7.13 (d, 1H, 11-H, J = 8.0 Hz), 7.28 (d, 1H, 14-H, J = 2.0 Hz); 13C NMR (CDCl3) d: 16.24 (C-19), 18.27 (C-2), 23.69, 23.84 (C-16, C-17), 25.41 (C-18), 33.21 (C-6), 33.47 (C-15), 36.32 (C-1)*, 37.31 (C-10), 37.90 (C-3)*, 43.77 (C-5), 47.12 (C-4), 51.47 (C-7), 51.77 (OCH3), 123.98 (C-12)*, 124.92 (C-11), 125.14 (C-14)*, 138.24 (C-8), 146.14 (C-13), 146.55 (C-9), 178.54 (CO2CH3).Signal assignments follow the assumed formula.‡ 16: mp 107–108 °C (C2H5OH), [a]D 24 +29.1° (c 0.48, CHCl3); 1HNMR (CDCl3) d: 1.07 (s, 3H, 18-H3), 1.24 (d, 6H, 16-H3, 17-H3, J = 7 Hz), 1.26 (s, 3H, 19-H3), 1.32–2.05 (m, 8H, 1-H2, 2-H2, 3-H2, 6-H2), 2.30 (d, 1H, 5-H, J = 13 Hz), 2.85 (m, 3H, 7-H2, 15-H), 3.45 (d, 1H, 20-Ha, J = 12 Hz), 3.55 (d, 1H, 20-Hb, J = 12 Hz), 6.88 (s, 1H, 14-H), 7.01 (d, 1H, 12-H, J = 8 Hz), 7.19 (d, 1H, 11-H, J = 8 Hz), 7.30 (m, 1H, 5'-H, J = 8.5Hz, J = 2 Hz), 7.70 (t, 1H, 4'-H, J = 8 Hz), 8.02 (d, 1H, 3'-H, J = 8 Hz), 8.36 (s, 1H, 1'-H), 8.60 (d, 1H, 6'-H, J = 5 Hz). 20: mp 210–220 °C (decomp.); 1H NMR (CDCl3) d: 1.15 (d, 6H, 16-H3, 17-H3, J = 7 Hz), 1.19 (s, 3H, 18-H3), 1.21 (s, 3H, 19-H3), 1.31– 2.15 [m, 8H, 1-H2, 2-H2, 3-H2, 6-H2, 4H (1,5-COD)], 2.27 (m, 1H, 5-H), 2.38–2.62 [m, 4H (1,5-COD)], 2.72–3.05 (m, 3H, 7-H2, 15-H), 3.15 (d, 1H, 20-Ha, J = 11 Hz), 3.41 (d, 1H, 20-Hb, J = 11 Hz), 4.45 [m, 4H (1,5- COD)], 6.88 (s, 1H, 14-H), 6.94 (d, 1H, 12-H, J = 8 Hz), 7.11 (d, 1H, 11-H, J = 8 Hz), 7.68 (m, 1H, 5'-H), 7.85 (d, 1H, 6'-H, J = 5 Hz), 8.09 (m, 1H, 4'-H), 8.20 (d, 1H, 3'-H, J = 7.5 Hz), 8.55 (s, 1H, 1'-H).A further communication concerned with a detailed study of the catalytic activity and enantioselectivity of new rhodium(I)- complexes in hydrogen transfer reactions will follow.This work was supported by the Russian Foundation for Basic Research (grant no. 96-15-97013). References 1 V. V. Dunina and I. P. Beletskaya, Zh. Org. Khim., 1992, 28, 1929 (Russ. J. Org. Chem., 1992, 28, 1547). 2 R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New York, 1994. 3 P. Gamez, B. Dunjic and M. Lemaire, J. Org. Chem., 1996, 61, 5196. 4 G. Zassinovich, R. Bettela, G. Mestroni, N. Brescian-Pahor, S. Geremia and L.Randaccio, J. Organomet. Chem., 1989, 370, 187. 5 H. Brunner, B. Reiter and G. Riepl, Chem. Ber., 1984, 48, 4351. 6 A. G. Tolstikov, O. V. Tolstikova, T. B. Khlebnikova, K. I.Zamaraev, V. G. Kasradze, O. S. Kukovinets and L. V. Spirikhin, Mendeleev Commun., 1996, 215. 7 A. G. Tolstikov, O. V. Tolstikova and K. I. Zamaraev, 2nd Conference on ‘Modern Trends in Chemical Kinetics and Catalysis’, Book of Abstracts, Part II, Novosibirsk, 1995, p. 399. 8 Le-Van-Thoi and A. Belloc, Industr. Plast. Mod., 1954, 6, 90. 9 H. H. Zeiss and W. B. Martin, J. Am. Chem.Soc., 1953, 75, 5935. 10 W. J. Gottstein and L. G. Cheney, J. Org. Chem., 1965, 30, 2072. 11 L. G. Cheney, US Patent 2, 585, 436, 1952 (Chem. Abstr., 1952, 46, 5269f). 12 G. F. Chernenko, E. N. Shmidt and B. A. Radbil, Khim. Prir. Soedin., 1995, 229 [Chem. Nat. Compd. (Engl. Transl.), 1995, 31, 187]. 13 R. Rausser, L. Weber, E. B. Hershberg and E. P. Olivetto, J. Org. Chem., 1966, 31, 1342. 14 D. V. Banthorpe, D. G. Morris and C. A. Bunton, J. Chem. Soc., (B), 1971, 687. H2C N C H N 4 16 i N C H N 7 17 i CO2Me N C H N 11, 15 18 R = H 19 R = Br i R H Scheme 3 Reagents and conditions: i, pyridine-2-carboxaldehyde, Na2SO4, C6H6, 20 °C, 2 h. H2C N CH N 16 20, 21 i Rh An– 17, 18, 19 [Rh(C8H12) 17, 18, 19]+An– 20, 22, 24, 26 An– = ClO4 – 21, 23, 25, 27 An– = BF4 – 22–27 Scheme 4 Reagents and conditions: i, [Rh(C8H12)Cl]2, NaClO4 or NaBF4, MeOH, 20 °C, 0.5 h. C CH3 O i CH OH CH3 Scheme 5 Reagents and conditions: i, PriOH, 20, 83 °C, 24 h. Received: Moscow, 27th November 1997 Cambridge, 8th January 1998; Com. 7/08971J

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC