摘要:

Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Generation of platinum(III) species by mechanical treatment of solid K2PtX6 (X = Cl, Br) salts Sergey A. Mitchenko,*a Eugenii V. Khomutov,b Vitalii V. Kovalenko,b Anatolii F. Popovb and Irina P. Beletskayac a A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation.Fax.: +7 095 135 5085; e-mail: mitchen@samit.donetsk.ua b Institute of Physico-Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 340114 Donetsk, Ukraine c Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 3618 A mechanical treatment of the solid salts K2PtX6 containing a small admixture of K2PtX4 (X = Cl, Br) in the atmosphere of air or argon leads to the formations of paramagnetic platinum d7-complexes.The most stable platinum complexes are diamagnetic and contain platinum in the +2 and +4 oxidation states. Paramagnetic compounds in the intermediate +3 oxidation state are much rarer1 than species containing platinum ions in the even-electron configurations. Probably, owing to this reason the information on PtIII compounds with simple inorganic ligands is limited.A number of compounds and complexes which were originally thought to involve the trivalent metal are now known to contain two platinum atoms, one in the +2 oxidation state and the other in the tetravalent state (see, for example, ref. 2). Therefore, the existence of paramagnetism with the magnetic moment close to the spin only value and hyperfine structure in the EPR spectra due to 195Pt nuclei (nucleus spin I = 1/2; natural abundance, 33.7%) may be considered as evidence† for PtIII compound formation.One of the first unequivocal evidence for the formation of platinum(III) complexes has been obtained4 in the case of cis-Pt(NH3)2(SCN)2 oxidation by iodine into Pt(NH3)2(SCN)2I. The EPR spectrum of the latter is a broad intense signal with gef = 2.18 and the line width DH = 56 mT at 20 °C.The formation of platinum(III) complexes has also been observed5 under H2PtCl6·6H2O thermolysis. The EPR spectrum of the species obtained corresponds to the spin-Hamiltonian of the axial symmetry with the parameters g|| = 1.98, g^ = 2.18, A|| = 14 mT, and A^ = 6mT, where A|| and A^ are the hyperfine splitting constants on 195Pt nuclei in the parallel and perpendicular orientations, respectively.The interaction of H2PtCl6·6H2O with concentrated sulfuric acid leads6 to the formation of the platinum(III) sulfate complex [PtO(SO4)]–. The platinum(III) dithiolate complexes [Pt(S2C2R2)2]– (R = CN,7,8 Ph9) have also been studied.For these compounds, the hyperfine structures have been resolved, and the EPR spectra may be fitted to the spin-Hamiltonian of the rhombic symmetry. The paramagnetic resonance of Pt3+ ions in Al2O3,10 BaTiO3,11 and YAl garnets12 has been investigated. The EPR spectra correspond to the spin-Hamiltonian of the axial symmetry for the first two cases, and the spin-Hamiltonian is of the rhombic symmetry in the third case.In the latter two cases, the hyperfine structure due to 195Pt nuclei has been observed. To our best knowledge this is the only information on the paramagnetic platinum(III) complexes with simple inorganic ligands. It is well known that mechanical treatment in mills (where destruction is accompanied by the friction of particles with each other) of covalent crystals such as diamond, graphite, silica, etc., generates free radicals predominantly located at the surface13 of particles.The mechanical treatment of magnesium oxide ionic crystals under frictional conditions also leads to electron transfer from an anionic lattice point to a cationic one with the formation of reactive radical-ion pairs13 {Mg2+O2–} ® {Mg+· O–·}.By analogy with the above data, we may expect that cooperative lattice vibrations can induce oscillations of separate atoms that constitute the complex anion [PtCl6]2–. If the intensity of † The platinum(III) complexes can also form dimeric complexes with a Pt–Pt bond, which are diamagnetic due to this bonding.3 the vibrations is sufficiently large, it results in the Pt–Cl bond cleavage with the loss of a chlorine atom and the formation of the trivalent platinum ion [PtCl5]2– at an anionic lattice point: The aim of this study was to prove this hypothesis.Platinum(II) can serve as a trap for chlorine and shift equilibrium (1) to the right. Thereby, the formation of platinum(III) in appreciable amounts should be expected in the presence of platinum(II) salt admixtures to the treated K2PtCl6.The samples were activated in a dry air atmosphere‡ for 1 h at room temperature in a closed glass vibroreactor containing K2PtCl6 K2PtCl5 + Cl· mechanical treatment (1) 260 300 340 H/mT 240 280 320 (a) (b) 1 2 1 2 H/mT Figure 1 EPR spectra, measured at (a) room temperature and (b) 77 K, of Pt3+ complexes generated by mechanical treatment of a K2PtCl6–K2PtCl4 mixture.(1) The experimental spectrum and (2) the simulated spectrum. The arrow indicates the EPR signal with g = 2.0036.Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) grinding bodies of glass. The working frequency used in an MMVE 0.005 vibratory micromill was 50 Hz. The amplitude was 5.5 mm. The specific energy intensity was 15 W kg–1.The K2PtX6 and K2PtX4 (X = Cl, Br) salts were prepared according to the standard procedure14 and carefully dried. The EPR measurements were performed using an SE/X-2544 spectrometer with the working frequency 9.4 GHz. An MnII sample in an MgO matrix was used as a standard for quantitative measurements. The spectra were taken in the solid polycrystalline samples at room temperature and 77 K. We have found that mechanical treatment of the K2PtCl6 salt results in the appearance of a relatively weak EPR signal with the resolved hyperfine structure due to 195Pt nuclei.As we expected, more intense signals were observed in the samples obtained by mechanical treatment of a K2PtCl6 powder which contained a small K2PtCl4 additive (5–15 mol%). The mechanical activation of K2PtCl6 in an atmosphere of Cl2 does not lead to ‡ The reaction also takes place in an argon atmosphere.the appearance of the characteristic EPR signal. Analogous effects occurred when K2PtBr6 with an admixture of K2PtBr4 was treated. The observed spectra can be fitted to the spin- Hamiltonian of the axial symmetry: where S = 1/2 and I = 1/2 are electron and nucleus spins, respectively; b is the Bohr magneton; the other parameters are given in Table 1.The EPR spectra parameters for other known platinum(III) compounds, which are characterised by the spin- Hamiltonian of the axial symmetry, are also presented in Table 1. The EPR spectra for the case of the axial symmetry of the spin-Hamiltonian have been simulated. The values of g-factors and hyperfine interaction constants were obtained by using the perturbation theory of the second order (Figures 1 and 2). The good agreement between experimental and simulated spectra confirms the correctness of the spectra interpretation.The occurrence of hyperfine structures in the perpendicular orientation due to 195Pt isotope proves that the spectra correspond to PtIII compounds.We have observed an appreciable temperature dependence of the line width [Figure 1(b)]. This can be attributed to the temperature-dependent spin–lattice relaxation time. No hyperfine splitting can be detected for the parallel orientation of the magnetic field even at 77 K. Hence, the hyperfine parameter A|| must be smaller than the line width. This gives a value of (0±35)×10–4 cm–1 at 77 K or <65×10–4 cm–1 at room temperature. Let us compare the spectra parameters for different PtIII compounds with the axially symmetric spin-Hamiltonian (Table 1).For these complexes, the g|| values are close to 2, and the values of g^ are higher than 2. The axial character of the spectra and the g-values point10 to the localisation of an unpaired electron at the 5dz2 orbital, and hence to a square-pyramidal structure of the complex.Unusually high values found for the hyperfine constants of PtIII compounds formed in the K2PtCl6 matrix probably arise from the appreciable admixture of the 6s orbital to the 5dz2 orbital.10 The initial amount of Pt3+ was estimated§ at 1×1018 spin g–1 from the EPR spectra. The intensity of the EPR signals corresponding to the Pt3+ ions decreased with time.The decrease of the Pt3+ signal intensity was accompanied by the appearance and intensity growth of the singlet with g = 2.000 and DH = 3mT (Figure 3). The decrease in the amount of paramagnetic platinum( III) ions and the simultaneous accumulation of paramagnetic centres with the g-factors close to the inherent values for free electrons apparently means that the decay of Pt3+ proceeds through electron transfer from platinum(III) to regenerate diamagnetic platinum(IV) and to form structural defects in the K2PtCl6 ion crystal matrix of the F-centre type.Taking into account the absence of ‘free’ chloride ions in the system and the diffusively retarded mobility in solids, the stoichiometric consequence of the reaction should be the formation of a coordinatively unsaturated platinum(IV) anion. As a result, the creation of the single-charged anion as a point defect in an anionic point of the lattice should be expected: § The concentration of Pt3+ was measured immediately after the mechanical treatment (for 1 h) of K2PtCl6 with a K2PtCl4 additive (15 mol%).The yield of platinum(III) formed under the same conditions but in the absence of K2PtCl4 was approximately equal to 2×1017 spin g–1. 1 2 260 340 H/mT Figure 2 The EPR spectra of Pt3+ complexes generated by mechanical treatment of a K2PtBr6–K2PtBr4 mixture. (1) The experimental spectrum and (2) the simulated spectrum. The arrow indicates the EPR signal with g = 2.0036. 1 2 3 4 5 250 300 350 H/mT Figure 3 EPR spectra of the mechanically treated K2PtCl6 solid salt with the additives of K2PtCl4 (5 mol%).The spectra were measured (1) 1, (2) 14, (3) 134, (4) 157 and (5) 189 h after the completion of mechanical treatment at room temperature. The arrow indicates the EPR signal with g = 2.0036. H = g|| bHzSz + g^b(HxSx + HySy) + A||Sz Iz + A^(Sx Ix + Sy Iy), (2) aHyperfine splitting constant/mT. bAt room temperature.cAt 77 K. Table 1 The EPR spectra parameters for platinum(III) complexes with the axially symmetric spin-Hamiltonian. Compound g^ g|| A^/ 10–4 cm–1 A|| / 10–4 cm–1 Reference Pt3+ in PtCl4 2.18 1.98 6a 14a 5 Pt3+ in Al2O3 2.328 2.011 — — 10 Pt3+ in BaTiO3 2.459 1.950 135 0 11 Pt3+ in K2PtCl6 2.371b 1.983b 500b <65b This work 2.385c 2.000c 511c 0±35c This work Pt3+ in K2PtBr6 2.45 1.95 317 <420 This work [PtCl5]2– [PtCl5]·– + e– (F-centre).(3)Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) The electron transfer in reaction (3) to the point of localisation of a structural defect that is able to accept it, probably, proceeds as a relay-race charge-transfer process through the neighbouring platinum(IV) complex anions with intermediate platinum(III) formation.The time dependence of the concentration of paramagnetic centres with g = 2.000 exhibits a maximum. In this case, the platinum(III) can probably serve as a sink for defects of the F-centre type: reduction of platinum(III) by free electrons should give platinum(II). In other words, despite the low mobility and a relatively low concentration of Pt3+ ions, the effective reaction of diffusively forbidden platinum(III) disproportionation into PtII and PtIV reaction should be expected in the K2PtCl6 solid matrix.Thus, mechanical treatment of the solid salts K2PtX6 (X = = Cl, Br) leads to the formation of metastable and hence potentially reactive species: platinum(III) complexes and, possibly, coordinatively unsaturated platinum(IV) complexes.The reactivity of these compounds towards organic substrates of different nature is under study in our laboratories. This work was supported by INTAS (grant no. 97-1874). References 1 F. R. Hartley, The Chemistry of Platinum and Palladium, Wiley, New York, 1973, p. 573. 2 T. D. Ryan and R. E. Rundle, J. Am. Chem. Soc., 1961, 83, 2814. 3 G. S. Muravejskaya, G.A. Kuksha, V. S. Orlova, O. N. Evstaf’eva and M. A. Porai-Koshits, Dokl. Akad Nauk SSSR, 1976, 226, 596 [Dokl. Chem. (Engl. Transl.), 1976, 226, 76]. 4 G. S. Muravejskaya, G. M. Larin and V. F. Sorokina, Zh. Neorg. Khim., 1968, 13, 1466 (Russ. J. Inorg. Chem., 1968, 13, 771). 5 L. K. Shubochkin, V. I. Gushchin, G. M. Larin and V. A. Kolosov, Zh. Neorg. Khim., 1974, 19, 460 (Russ.J. Inorg. Chem., 1974, 19, 249). 6 G. M. Larin, Zh. Neorg. Khim., 1997, 42, 1163 (Russ. J. Inorg. Chem., 1997, 42, 1048). 7 P. A. Koz’min, T. B. Larina and M. D. Surazhskaya, Koord. Khim., 1979, 5, 591 [Sov. J. Coord. Chem. (Engl. Transl.), 1979, 5, 464]. 8 G. M. Larin, G. A. Zvereva and P. A. Koz’min, Neorg. Mater., 1990, 26, 2584 [Inorg. Mater. (Engl. Transl.), 1990, 26, 2223]. 9 A. V. Ryzhmanova and N. S. Gafriyanov, Zh. Neorg. Khim., 1970, 15, 3095 (Russ. J. Inorg. Chem., 1970, 15, 1613). 10 S. Geschwind and J. P. Remeika, J. Appl. Phys., 1962, 33, 370. 11 E. Simanek, Z. Sroubek, K. Zdansky, J. Kaczer and L. Novak, Phys. Status Solidi, 1966, 14, 333. 12 J. A. Hodges, R. A. Serway and S. A. Marshall, Phys. Rev., 1966, 151, 196. 13 P. Yu. Butyagin, Usp. Khim., 1994, 63, 1031 (Russ. Chem. Rev., 1994, 63, 965). 14 Sintez Kompleksnykh Soedinenii Metallov Platinovoi Gruppy (Synthesis of Complex Compounds of Platinum Group Metals), ed. I. N. Chernyaev, Nauka, Moscow, 1964, p. 239 (in Russian). 15 S. A. Mitchenko, Yu. V. Dadali and V. V. Kovalenko, Zh. Org. Khim., 1998, 34, 1293 (Russ. J. Org. Chem., 1998, 34, 1233). Received: 19th February 1999; Com. 99/1445

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年代:1999

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Complexation of ruthenium with glucose oxidase modified by 4-pyridineacetic and 4-imidazoleacetic acids Vasily N. Goral,a Elisabeth Csöregi,b Bo Mattiassonb and Alexander D. Ryabov*a,c a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 5417; e-mail: ryabov@enzyme.chem.msu.su b Department of Biotechnology, Centre for Chemistry and Chemical Engineering, Lund University, P.O.Box 124, S-221 00 Lund, Sweden. Fax: +46 46 222 4713 c G. V. Plekhanov Russian Economic Academy, 113054 Moscow, Russian Federation. E-mail: ADR@enzyme.chem.msu.ru Glucose oxidase (GO) conjugated with 4-pyridineacetic and 4-imidazoleacetic acids reacted with cis-[Ru(bpy)2Cl2] to afford the Ru-containing catalytically active species Ru–X–GO (X = pyridine or imidazole) capable of the intramolecular electron transfer from reduced FAD to an electrochemically generated RuIII centre.Our current interests are aimed at understanding the intimate mechanistic features of the interaction between redox enzymes and transition metal species.1–6 Recently,7 it has been demonstrated that the coordination of bis(2,2'-bipyridine) or bis(1,10- phenanthroline) ruthenium(II/III) complexes with glucose oxidase (GO) from Aspergillus niger presumably via histidine residues affords the biocatalyst (Ru–GO) capable of an efficient Ru-mediated electron exchange between the active site of the modified enzyme and an electrode.Thus, the intrinsic natural donor ligands of the enzyme served as traps for the ruthenium centres.Searching for more efficient electron transfer relays and with the goal to compare the electrocatalytic properties of different preparations of modified GO, we have prepared and investigated the properties of the enzyme first covalently conjugated with 4-pyridineacetic or 4-imidazoleacetic acid via surface amino groups of the protein using a water-soluble carbodiimide followed by the complexation of cis-[Ru(bpy)2Cl2] to the introduced pyridine or imidazolyl moieties (Scheme 1).Glucose oxidase (Serva, 220U) was modified by 4-pyridineacetic acid (PAA) (Aldrich) as described elsewhere.8 PAA (4.3 mg), NaHEPES (20 mg), and urea (48 mg) were dissolved in water (400 ml). The solution was adjusted to pH 7.0. Next, GO (10 mg) was introduced, and 5 mg of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC, Sigma) was added.The solution was readjusted to pH 7.0 and allowed to stand overnight (16 h) in an ice bath. The chemically modified enzyme was separated by gel filtration chromatography on a Sephadex G-50 (fine) column equilibrated with a 0.1 M phosphate buffer (pH 7.0).The same buffer was used as an eluent. The first eluted yellow fraction contained the modified enzyme (py–GO), which was then concentrated to 600 ml by ultrafiltration using a 100000 cut-off membrane (Amicon). The modification of GO by 4-imidazoleacetic acid (IAA) (ACROS) to afford im–GO was carried out similarly using 3.9 mg (2.45×10–5 mol) of IAA, 10 mg (6.25×10–8 mol) of GO, 5 mg (2.6×10–5 mol) of EDC, 48 mg (8×10–4 mol) of urea and 20 mg (7.68×10–5 mol) of NaHEPES in 400 ml of H2O.To prepare the ruthenium-modified enzyme (Ru–py–GO), the complex cis-[Ru(bpy)2Cl2] (1 mg) was dissolved in 200 ml of a phosphate buffer (pH 7.0), and 180 ml of this solution was added to 600 ml of the yellow solution of py–GO. Urea necessary to yield a 2 M solution was added, and the resulting solution was kept at room temperature for 4 h.Ru–py–GO was then separated on a Sephadex G-50 (fine) column. Two fractions were collected. A comparison of the UV–VIS spectra recorded at pH 7.0 (0.1 M phosphate) with that obtained for cis-[Ru(bpy)2Cl2] showed that the second fraction contained the unbound ruthenium complex. The enzyme-containing first fraction was concentrated to 600 ml by ultrafiltration to yield a 12.3 mg ml–1 solution of Ru–py–GO.The protein concentration was determined by the Lowry procedure9 using native GO as a standard. The enzymatic activities of native GO and Ru–py–GO solutions were determined colorimetrically by measuring the rate of bleaching of 2,6-dichlorophenol –indophenol.10 The activity of Ru–py–GO was 70% with respect to the native enzyme.Ru–im–GO was prepared similarly; its catalytic activity toward 2,6-dichlorophenol–indophenol was 65%. The UV–VIS spectra of GO and py–GO clearly show that the enzyme surface is modified with PAA (Figure 1). The spectra of im–GO and Ru–im–GO presented in Figure 2 (curves 1 and 2) clearly demonstrate that the coordination of ruthenium species with the modified enzyme provides noticeable spectral changes. The addition of an excess of D-glucose to Ru–py–GO and Ru–im–GO induces the expected spectral changes in both cases FAD H2N NH2 GO EDC N COOH FAD H2N NHCO GO N [Ru(bpy)2Cl(OH)2]+ FAD H2N NHCO GO N Ru(bpy) 2 Cl+ Scheme 1 0.5 0.4 0.3 0.2 0.1 0.0 300 350 400 450 500 550 Absorbance l/nm Figure 1 UV–VIS spectra of native GO (solid line) and GO covalently conjugated with 4-pyridineacetic acid (py–GO) (broken line) recorded at pH 7.0 (0.1 M phosphate) and 22±2 °C. Concentrations of the enzyme preparations were about 4 mg ml–1.Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) associated with the reduction of flavine adenine dinucleotide (FAD) into FADH2 and with partial conversion of RuIII into RuII (Figure 2, curve 3).As can be seen, the intensity of the broad band at 465 nm, where the contribution from FAD is dominant, drops due to reduction of the latter into FADH2. Thus, there is a maximum shift since a new band at 482 nm corresponds predominantly to RuII species. The reduction of RuIII, which is most likely generated during the gel filtration, occurs due to the glucose oxidase–catalysed oxidation of b-D-glucose into d-D-gluconolactone, which is accompanied by the reduction of the oxidised FAD into FADH2 (equation 1)11 followed by the intramolecular reoxidation of the reduced enzyme into its catalytically active form by RuIII (equation 2):7 Assuming that RuII is the only species absorbing at 482 nm, the amount of the ‘catalytically active’ ruthenium, viz.involved in reaction (2), can be estimated from the spectral changes in Figure 2 (curves 2 and 3) using the molar absorption coefficient obtained for cis-[Ru(bpy)2Cl2] in the presence of 4-imidazoleacetic acid (e = 5660 dm3 mol–1 cm–1 at 475 nm). The calculations performed according to the procedure in ref. 7 taking into account the independently determined catalytic activity of the enzyme samples suggest that the Ru–im–GO preparation contains 1.8 active ruthenium centres per protein molecule.The same approach applied to Ru–py–GO gives practically the same value (1.5). The electrochemical properties of Ru–py–GO and Ru–im–GO were investigated by cyclic voltammetry both in the presence and in the absence of D-glucose.The representative data are shown in Figures 3 and 4. As can be seen in Figures 3 (curve 1) and 4 (curve 1), the cyclic voltammograms of Ru–py–GO and Ru–im–GO are characterised by weak signals from coordinated ruthenium around 300 mV versus Ag/AgCl (288 and 305 mV, respectively). The addition of D-glucose to both preparations leads to a current increase indicative of the coupling between the electrochemically generated RuIII species and FADH2 of reduced glucose oxidase.Therefore, in addition to reactions (1) and (2), the third step should be added to accomplish the electrocatalytic cycle which accounts for the origin of catalytic currents in Figures 3 (curve 2) and 4 (curve 2). As in the previous work,7 the rate constants for the intramolecular electron transfer according to reaction (2) were estimated using computer simulation of the data displayed in Figures 3 and 4 as described elsewhere.12 The model applied is given below: The following assumptions have been made: k1 = k2 and E0 1 = = E0 2; k3 = 800 s–1 (saturating glucose concentration).13 The rate constants thus obtained are equal to 0.55 and 2 s–1 for Ru–py–GO and Ru–im–GO, respectively, at 22±2 °C and pH 7.These should be compared with the rate constant of 12 s–1 previously obtained7 for native glucose oxidase modified by cis-[Ru(bpy)2Cl2]. The comparison suggests that the coordinative loading of Ru complexes onto the enzyme surface without pretreatment with artificial donor centres is more advantageous for the preparation of bioelectrocatalysts capable of the intramolecular electron transfer from the reduced cofactor (FADH2) at the metal centre.Note that the rate constants obtained in this work are very close to those reported for GO randomly modified with ferrocenecarboxylic acid residues.14 The highest rate constant of 3.6 s–1 was calculated for the enzyme with 13 ferrocene units.14 In conclusion, the procedure for loading electroactive ruthenium species onto glucose oxidase involving covalent attachment of Absorbance l/nm 1 2 3 1 0 300 400 500 600 Figure 2 UV–VIS spectra of (1) im–GO, (2) Ru–im–GO and (3) the product obtained after addition of D-glucose (0.02 M) to the Ru–im–GO at 22±2 °C.Concentrations of the enzyme preparations were 10 mg ml–1; pH (1) 5.5 and (2,3) 7.0. I/nA E/mV 1 2 Figure 3 Cyclic voltammograms of Ru–py–GO (1) in the absence and (2) in the presence of D-glucose (0.033 M); [Ru–py–GO], 10 mg ml–1, pH 7, 0.01 M phosphate, scan rate 2 mV s–1, 22±2 °C. 450 400 350 300 250 200 150 100 50 0 –50 –100 –150 –100 0 100 200 300 400 500 600 700 RuIII–im–GO(ox) + b-D-glucose RuIII–im–GO(red) + d-D-gluconolactone; RuIII–im–GO(red) RuII–im–GO(ox). (1) (2) k RuII–im–GO(ox) – 1e RuIII–im–GO(ox).(3) I/nA E/mV 1 2 Figure 4 Cyclic voltammograms of Ru–im–GO (1) in the absence and (2) in the presence of D-glucose (0.033 M); [Ru–im–GO], 10 mg ml–1, pH 7, 0.01 M phosphate, scan rate 2 mV s–1, 22±2 °C. 400 300 200 100 0 –100 0 100 200 300 400 500 600 700 FADH2–MII FADH2–MIII + e (E0 1 electrode); FADH2–MIII FADH–MII + H+ (k1); FADH–MII FADH–MIII + e (E0 2 electrode); FADH–MIII FAD–MII + H+ (k2); FAD–MII FADH2–MII (k3).Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) 4-pyridineacetic and 4-imidazoleacetic acids followed by the complexation with cis-[Ru(bpy)2Cl2] affords biocatalysts the efficacy of which in the intramolecular electron transfer reaches the same level as in the case of GO covalently modified with ferrocenecarboxylic acid, but somewhat lower than in the case of native GO coordinatively enriched with cis-[Ru(bpy)2Cl2].This work was supported in part by the Russian Foundation for Basic Research (grant no. 99-03-33070a), INTAS (grant no. 96-1432), the Wenner–Gren Foundation and the Swedish Medical Research Council/MFR. References 1 A. D. Ryabov, Y. N. Firsova and M. I. Nelen’, Appl.Biochem. Biotechnol., 1996, 61, 25. 2 A. D. Ryabov and V. N. Goral, J. Biol. Inorg. Chem., 1997, 2, 182. 3 A. D. Ryabov, Y. N. Firsova, V. N. Goral, E. S. Ryabova, A. N. Shevelkova, L. L. Troitskaya, T. V. Demeschik and V. I. Sokolov, Chem. Eur. J., 1998, 4, 806. 4 A. D. Ryabov, V. S. Kurova, V. N. Goral, M. D. Reshetova, J. Razumiene, R. Simkus and V. Laurinavicius, Chem.Mater., 1999, 11, 600. 5 A. D. Ryabov, V. N. Goral, L. Gorton and E. Csöregi, Chem. Eur. J., 1999, 5, 961. 6 A. D. Ryabov, Y. N. Firsova, A. Y. Ershov and I. A. Dementiev, J. Biol. Inorg. Chem., 1999, 4, 182. 7 E. S. Ryabova, V. N. Goral, E. Csoregi, B. Mattiasson and A. D. Ryabov, Angew. Chem., Int. Ed. Engl., 1999, 38, 804. 8 Y. Degani and A. Heller, J. Am. Chem. Soc., 1988, 110, 2615. 9 O. H. Lowry, N. J. Rosebrough, A. L. Farr and R. J. Randall, J. Biol. Chem., 1951, 193, 265. 10 T. Yoshimura and T. Isemura, J. Biochem., 1971, 69, 839. 11 R. Wilson and A. P. F. Turner, Biosensors Bioelectronics, 1992, 7, 165. 12 D. K. Gosser, Jr., Cyclic Voltammetry. Simulation and Analysis of Reaction Mechanisms, VCH, Weinheim, 1993. 13 M. K. Weibel and H. J. Bright, J. Biol. Chem., 1971, 246, 2734. 14 A. Badia, R. Carlini, A. Fernandez, F. Battaglini, S. R. Mikkelsen and A. M. English, J. Am. Chem. Soc., 1993, 115, 7053. Received: 12th May 1999; Com. 99/1488

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Alkylation and phenylation of [60]- and [70]-fullerenes by the reaction with ketones in the ionization chamber of a mass spectrometer Elena A. Shilova, Yury I. Lyakhovetsky,* Boris L. Tumanskii, Alexander I. Belokon’ and Yurii S. Nekrasov A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation.Fax: +7 095 135 5085; e-mail: yulyakh@ineos.ac.ru The title reactions proceed under electron impact (EI) and are accompanied by hydrogen addition and loss; the reaction of C60 with acetone has been shown to occur at least partly at the walls of the ionization chamber and experimental evidence suggests a radical path process involving EI generation of methyl radicals from acetone.The reactions of fullerenes with other species in a mass spectrometer, though proceeding under special conditions (high energy of the ionising electrons, the absence of solvent etc.), provide valuable information on what can be successfully achieved in a flask and in what manner this can be done. The advantages of such a test for fullerene reactivity consist in that it requires only traces of reagents, the results can be obtained from relatively quick runs, and products are identified simultaneously.Recently we found that the reactions of C60 and C70 with the Scherer radical C9F19 1 in the EI ion source of a mass spectrometer resulted in trifluoromethylated fullerenes. The reaction substantially occurs at the walls of the ionization chamber by a radical mechanism involving the intermediate triflluoromethyl radicals formed from 1 by thermal dissociation and under EI.Accordingly, C60 attached up to 18 CF3 addends when dissolved in 1,2,4- trichlorobenzene and reacted with 1 at 200 °C.1 Here, we report on the C60 and C70 reactions with ketones in the ionization chamber. We decided on ketones as reactants because of the fact that their molecular ions dissociate predominantly with the elimination of organic radicals to afford acyl cations.Thus, by analogy with the previous work,1 radical reactions between fullerenes and ketones could also be anticipated to occur. The experiments were performed on a ‘Kratos MS890’ mass spectrometer at an electron energy of 70 eV and an ionization chamber temperature of 300 °C (in some cases, 270 °C) by two procedures.Procedure A involved evaporation of a fullerene in the ionization chamber from a quartz needle, while a ketone was introduced via the GLC inlet. With procedure B, the ketone was evaporated from a capillary ampoule with the fullerene applied onto the outer surface of it (see ref. 1 for details). The mass spectra obtained at the combined evaporation of C60 and acetone 2 by both of the procedures displayed the groups of ion peaks due to products of the methyl group addition to the fullerene core. These groups also contained ions formed by both hydrogen addition to the methylation products and hydrogen loss from them and/or their ions (Scheme 1 and Figure 1).The interaction of ketone 2 with C60, C70 and endohedral metallofullerenes under conditions of the self-chemical ionization (self-CI) of 2 was studied.2,3 The main products of these processes were identified as acetylfullerene cations.This difference can be attributed to the fact that the experiments were performed at a relatively high pressure in the ionization chamber (ca. 10 Pa) and at a rather low temperature (200 °C); at this temperature, fullerenes and their derivatives did not vaporise from the ionization chamber surface. Thus, only the products of gas-phase ion–molecule reactions were detected.By contrast, our experiments performed at a chamber temperature of 190 °C followed by an increase in the temperature up to 270 °C† and experiments performed at 300 °C with the ‘filament switched off’1 showed that the reaction occurred, at least partly, at the metal surface of the ionization chamber.A considerable amount of the products detected as ions (> 60%‡) vaporised from the walls of the ionization chamber, and EI was required for the process to proceed. The observed polyaddition, especially in the case of procedure B, agrees better with a surface process than with a gas-phase reaction.Furthermore, special runs were carried out with the ion-repelling electrode potential set to zero with respect to the ionization chamber, and the accelerating voltage (AV) turned off. If cation-involving reactions contribute significantly to the overall process, the amount of products can be expected to increase under these conditions.§ Indeed, cations are forced out (extracted) from the ionization chamber to a lesser extent and more evenly distributed within the ionization chamber; thus, they attack the surface more evenly.However, only a small decrease (on the average, by about 20%) in the amount of the products evaporated from the ionization chamber surface and detected as the integral peak intensity of the first two ion groups (734–738 and 748–752 a.m.u.) was observed after switching AV on and returning the repeller potential to a standard value of +30 V.The decrease can be attributed to the alteration of the conditions under which a substance interacts with the electron beam. The aforesaid counts in favour of a radical path for the reaction involving the formation of intermediate methyl radicals from 2 under EI.¶ The observed hydrogen addition and loss can be easily explained in terms of this mechanism.The addition of methyl radicals to the fullerene core accompanied by hydrogen addition and loss was also found in the reaction between C60 and dibutyl ketone 3. However, the monoisotopic (12C) mass spectra derived from the aggregated magnet † C60 was applied to the inner surface of the ionization chamber at 270 °C using a quartz needle.Next, the temperature of the ionization chamber was reduced to 190 °C, and 2 was introduced via the GLC inlet. After 30 min, the temperature was again raised up to 270 °C. From the moment of the first appearance of the products until the main body of them had evaporated from the chamber surface, the peak intensities of the first two groups of ions (734–738 and 748–752 a.m.u.) were summarised over the magnet scans and then over the components of both of the groups.The integral intensity thus obtained was related to the similar value from the method A run performed subsequently on the same day at 270 °C. ‡ This value may include a contribution from the products formed in the gas phase and condensed onto the surface of the chamber in the course of the reaction.§ The processes involving negative ions that could afford the detected products seem to be unlikely here. ¶ Three possibilities may be taken into consideration for the formation of methyl radicals: (i) via dissociation of the molecular ion of 2, (ii) via homolytic dissociation of acetone molecules in a superexcited state (the excited state with the energy higher than the first ionization potential),4 (iii) the generation in the self-CI plasma of 2 because the pressure in the ionization chamber could be 10–2 Pa or higher when ketone 2 was introduced. 2, 300 ºC, (H) EI Men (– rH) Hk n = 1, ..., 16, ... Scheme 1Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) scans and averaged over several runs performed by procedures A or B showed an ion peak at m/z 778 to be one of the most abundant peaks in the 776–784 a.m.u.group. This peak was considerably less abundant in the analogous spectra for the reaction between C60 and 2, whereas a peak at m/z 780 (C60Me4 +·) was among the dominant ones in the above group. This indicates that the butyl radical adds to C60 in the reaction of the latter with ketone 3.In addition, the mass spectra display ion peaks (of low intensities) at m/z 834 and 836, which can be ascribed to the C60Bu2 + · and C60Bu2H2 + · ions (at least, these ions may contribute to the peak intensities). The aforesaid is in good agreement with the finding that, in the reaction of C60 with phenylacetone 4, the ions due to the addition of both methyl radicals and a benzyl group (toluene) were detected.The reaction between C60 and acetophenone 5 gave rise to the ions of fullerene derivatives bearing up to four methyl groups and ions containing up to three phenyl groups. The ions of mixed derivatives (Figure 2) were also present in the spectra. Analogously, C70 reacts with ketones 2 and 5 adding methyl and phenyl radicals.The EI–MS analysis of the reaction products obtained by UV irradiation of a mixture of C60 with 5 during 13.5 h allowed us to detect fullerene derivatives containing from one to at least three methyl groups (some of the products had attached or lost hydrogen atoms) and that with a phenyl group (benzene) attached.†† This agrees closely with the results obtained for the reaction with the same reactants in the ionization chamber.††Other products will be discussed in a subsequent publication. This work was supported by the Russian Foundation for Basic Research (grant no. 99-03-33067), the Federal Special Program ‘Integration’ (project no. K0559) and the Russian Interdisciplinary Scientific and Technical Program ‘Fullerenes and Atomic Clusters’.References 1 Yu. I. Lyakhovetsky, E. A. Shilova, B. L. Tumanskii, A. V. Usatov, E. A. Avetisyan, S. R. Sterlin, A. P. Pleshkova, Yu. N. Novikov, Yu. S. Nekrasov and R. Taylor, Fullerene Sci. Technol., 1999, 7, 263. 2 Z. Liu, G. Hao, H. Wang, W. Xu, X. Guo, G. Ma, D. Ma and Sh. Liu, Wuli Huaxue Xuebao, 1995, 11, 751 (Chem. Abstr., 1995, 123, 169042j). 3 D.Sun, Zi. Liu, Zh. Liu. X. Guo, C. Hao, W. Xu and S. Liu, Fullerene Sci. Technol., 1997, 5, 1461, and refs. 25, 29 and 30 therein. 4 V. I. Makarov and L. S. Polak, Khim. Vys. Energ., 1970, 4, 3 [High Energy Chem. (Engl. Transl.), 1970, 4, 1]. Intensity (arbitrary units) 1200000 1000000 800000 600000 400000 200000 0 750 850 900 950 1000 m/z 800 35000 25000 15000 5000 800 900 1000 766 782 796 814 841 858 872 901 916 929 957 969 721 736 752 782 814 827 858 872 901 916 946 957 982 m/z 1Me 3Me 16Me Scan 41 (1.722 min) Figure 1 Mass spectrum recorded in the course of a run with C60 and acetone 2 performed by procedure B. 900000 700000 500000 300000 100000 0 720 760 800 840 880 920 960 1000 m/z Intensity (arbitrary units) 50000 30000 10000 0 800 900 1000 m/z Scan 43 (1.808 min) 722 736 773 798 810 842 876 890 929 952 967 999 736 750 769 798 810 842 876 890 929 952 967 999 1Me 2Me 1Ph 1Me 1Ph 2Ph 2Ph 1Me 3Ph 3Ph 1Me Figure 2 Mass spectrum from a run with C60 and acetophenone 5 by procedure A (the ion peaks due to the products bearing three and four methyl groups are more pronounced in the spectra from other magnet scans).Higher intensities of the ion peaks due to phenyl derivatives than those of the corresponding methyl species can indicate that the former compounds are more stable (thermally and/or under EI). Received: 16th June 1999; Com. 99/1505

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年代:1999

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Manganese tetraazaporphines as effective catalysts for the nuclear oxidation of aromatics by peracetic acid Svetlana V. Barkanova,* Elena A. Makarova, Oleg L. Kaliya and Eugene A. Luk’yanets Institute of Organic Intermediates and Dyes, 103787 Moscow, Russian Federation. Fax: +7 095 254 1200; e-mail: jerrik@cityline.ru Manganese tetranitrotetra-tert-butyltetraazaporphine at low concentrations (0.02 mol%) effectively catalyses the oxidation of 2-methylnaphthalene by peracetic acid to give 2-methyl-1,4-naphthoquinone in 65% yield with a catalyst turnover number of 3100.The problem of the nuclear oxidation of non-activated aromatics is noteworthy in terms of both its mechanistic study and practical applications. Thus, 2-methyl-1,4-naphthoquinone (vitamin K2, menadione, MD) can be produced in moderate yields (~45%) in 2-methylnaphthalene oxidation catalysed by transition metal complexes such as Re(Me)O3 with hydrogen peroxide1 and watersoluble Mn or Fe tetraphenylporphyrins with KHSO5.2 Earlier,3 we have described the oxidation of naphthalene and its methyl derivatives to the corresponding 1,4-quinones (~60% yield) with peracetic acid catalysed by manganese and iron complexes of 3,5-octanitrophthalocyanine.Here, we report the use of a new class of catalysts, manganese complexes of tetraazaporphines (porphyrazines), in particular, Mn3+ tetra-R-tetra-tert-butyltetraazaporphines (1–3, Figure 1) in this reaction; we also compared the catalytic activity of these complexes and their carboanalogues, Mn meso-tetra(o,o'-dichloro-p-R-phenyl)porphyrins (4 R =H; 5 R = NO2).Complexes 2 and 3 [m/z 892 (M – Me, 100%) and 771 (100%), respectively] were obtained in 91 and 80% yields, respectively, from the corresponding free bases4 by Mn(OAc)3 treatment (DMFA, 70 °C) followed by chromatography (SiO2, CHCl3). In acetonitrile solutions of 1–5 both naphthalene and 2-methylnaphthalene are fully and quickly (5–30 min) oxidised with a three-to-five fold excess of peracetic acid (AcOOH, a solution in acetic acid5) yielding 1,4-naphthoquinone and menadione, respectively; oligomeric by-products derived from originally formed 1-naphthols were also detected.The reaction product of the oxidation of 2-methylnaphthalene isolated by column chromatography [petroleum ether–benzene (1:1)] is pure menadione (mp 106.3 °C) and does not contain isomeric 6-methyl- 1,4-naphthoquinone (HPLC and 1H NMR data), indicating that the described catalytic systems are more selective in menadione production than those reported in refs. 1 and 2, where with a similar isolation procedure the isomeric quinone was obtained in 7 and 58% yields, respectively.Quinone yields† determined at the end of the reaction (initial yield, hin) can be significantly enhanced by heating (15 min, 50 °C) the neutralised (Na2CO3) reaction mixture (thermal yield, htherm, Table 1). A similar phenomenon was observed earlier3 in the reactions catalysed by 3,5-octanitrophthalocyanine 6. It seems that the mechanism † Molar yield values were calculated as [product]formed/[substrate]reacted. At exhaustive substrate oxidation, [substrate]reacted = [substrate]0. of oxidation of the aromatic nucleus includes the formation of a thermally unstable quinone precursor and is common for all the Mn3+ porphinoid complexes (PMnX) used here.In our studies of naphthalene oxidation catalysed by 63,6 and of olefin epoxidation catalysed by 1–5,7–9 we have supposed that two types of highly reactive oxygen-containing complex are generated by the interaction of PMnX with AcOOH: the MnV–oxene [PMn5+(O)(L)] and Mn–peroxo [PMn(O2)(L)] complexes.The latter is thought to play a key role in the oxidation of naphthalene to quinone via the formation of intermediate 7, which in turn produces intermediate 8 by the interaction with PMn5+(O)(L).‡ Competitive naphthalene and olefin oxidation has revealed6 that both types of oxygencontaining Mn complexes are generated from the firstly formed molecular ‘catalyst–oxidant’ complex. Based on these data, Scheme 1 has been proposed for the mechanism of the nuclear oxidation of aromatics in these catalytic systems.Experimental results reported here allow us to detail some stages of this Scheme.§ As shown in Figures 2 and 3 and in Table 1, the quinone yield strongly depends on the concentrations of both the catalyst and AcOOH even at full substrate conversion.¶ The growth of menadione yield with increasing the [AcOOH]:[2-methylnaphthalene] ratio up to 5:1 (higher than it is necessary for ‡ The indirect proof of the structure of intermediate 8 as reported earlier;3,6 additional data for the affirmation of the structure of 8 will be published later.§ The rate of the reaction catalysed by 3 is too high to be measured by common methods. Assuming that the sum of ‘oxenoid’ and ‘peroxide’ pathways describes all possible transformations of aromatic molecules in the reaction studied, the menadione yield may be considered to be proportional to the rate of menadione formation.¶ Catalysts 1 and 4 at low content (< 0.1 mol%) do not produce quinones; exhaustive naphthalene oxidation by AcOOH leads in these cases to oxygen-containing oligomers derived from originally formed 1-naphthol. N N N N N N N N But R But R But R But R Mn Cl 1 R = H 2 R = Br 3 R = NO2 Figure 1 The structure of Mn3+ tetra-R-tetra-tert-butyltetraazaporphines 1–3.aHPLC data (Separon C18 reversed phase column; mobile phase, 10–100% aqueous MeCN; lanal, 250 nm; quinone yields are calculated with an accuracy of 10 rel.%, Q refers to 1,4-naphthoquinone. bTNMD = [MD]formed:[Cat]. cFivefold excess of AcOOH. dFrom ref. 3. Table 1 ‘Initial’ and ‘thermal’ menadione (MD) molar yields† in the exhaustive oxidation of 2-methylnaphthalene (0.004 M) with AcOOH (0.016 M) catalysed by 1–6.MeCN + AcOH (~1%, v/v); reaction time, 5–30 min. Catalyst (Cat) [lmax/nm, e/dm3 cm–1 mol–1 in MeCN] [Cat]:[2-methylnaphthalene] (mol%) hMD therm (hin MD)a (mol%) hQ therm (hin Q)a (mol%) TNb MD 1 [616, 4.6×104] 0.82 25.0 (20) 30.5 1 2.5 29.0 (15) 12 1 5.0 36.0 (7) 16.0 (9.5) 7 2 [634, 3.8×104] 0.21 31.5 (3) 150 2 0.41 40.5 (4) 99 2 0.82 46.0 (4) 56 2 1.65 45 (3.5) 27 3c [620, 3.2×104] 0.02 62 (2) 45.0 (5.0) 3100 4 5.0 11 (2) 9.0 (1.0) 2.2 5 2.5 14 (3) 5.6 5 5.0 12 (3) 11.5 (1.5) 2.4 6d 4.3 55 (20) 51.7 (10.6) 13Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) quinone formation, 3:1)†† together with the relationship shown in Figure 2 (curve 1) evidence the participation of second molecules of both AcOOH and the catalyst in the quinone formation at the rate-determining step (or before it), i.e., at macro stage (4).It seems that the reaction of the molecular complex PMn(AcOOH)(L) with the second AcOOH molecule followed by the formation of a Mn peroxo complex is catalysed by PMnX. The dependence of hin MD on catalyst concentration (Table 1; Figure 2, curve 2) agrees with the hypothesis on the participation of Mn5+–oxene in quinone formation at stage (6), which we have proposed earlier6 in competitive naphthalene and olefin oxidation catalysed by 6.6 Indeed, according to Scheme 1, as the catalyst content was increased, the contribution of stage (7) to the overall transformations of intermediate 7 diminishes because of an increase in the stationary concentration of Mn–oxene, which in turn leads to a decrease in the hin MD value.At high catalyst contents (> 0.02 mol% for 3; Figure 2, curve 1) the promotion of reaction (4) with catalyst concentration may be lowered by a competitive reaction of catalyst degradation with the Mn peroxo complex (8). Equation (1) for the relative share of menadione formation calculated from Scheme 1 is in qualitative agreement with the experimental data presented here and reported earlier.For Mn complexes of porphyrins and tetraazaporphines, we have shown8,9 that the transformation of molecular complex to Mn–oxene(s) [reaction (2)] is enhanced by electronegative substitution in the porphinoid macrocycle. The data described †† The decrease of menadione yield at [AcOOH]:[2-methylnaphthalene] > > 5:1 can be explained by competitive radical decomposition of excess AcOOH followed by 2-methylnaphthalene oxidation with the radicals formed without menadione formation.here allow us to conclude that electron-withdrawing substituents stimulate the formation of Mn peroxo complexes even more: for 1–3, the maximum value of the yield of menadione (and hence the contribution of the ‘peroxide’ pathway) increases in the order 1 > 2 > 3 (25, 45 and 65%, respectively).This means that in the azaporphine molecule, the ‘peroxide’ pathway is more sensitive to electronegative peripheral substitution than the ‘oxenoid’ one. It is noteworthy that Mn porphyrins 4 and 5 exhibit slight efficiency in menadione production and provide very low turnover numbers; the reason for the different reactivity of Mn3+ porphyrins and azaporphines in the production of para-quinone is now under study.Thus, within the group of Mn porphinoids studied here, Mn tetraazaporphine 3 was found to be the most effective catalyst in the production of para-quinone from non-activated (or slightly activated) aromatics not only due to the well-known effect of catalyst stabilization by electronegative peripheral substitution, but also due to the highest reactivity in the formation of the Mn peroxo complex.This catalyst at low content (£ 0.02 mol%) produces a yield of 60–65% menadione in the oxidation of 2-methylnaphthalene with an extremely high catalyst turnover number (3100).This work was supported by the Russian Foundation for Basic Research (grant no. 97-03-32327). We are grateful to Professor S. Banfi and L. Pozzi (University of Milan) for the provision of samples of compounds 4 and 5. References 1 W. Adam, W. A. Herrmann, J. Lin, C. R. Saha-Mëller, R. W. Fischer and J. D. G. Correia, Angew. Chem., Int. Ed. Engl., 1994, 33, 2475. 2 R. Song, A. Sorokin, J.Bernadou and B. Meunier, J. Org. Chem., 1997, 62, 673. 3 S. V. Barkanova, V. M. Derkacheva, O. V. Dolotova, V. D. Li, V. M. Negrimovski, O. L. Kaliya and E. A. Luk’yanets, Tetrahedron Lett., 1996, 37, 1637. 4 (a) V. N. Kopranenkov, I. D. Mundshtukova and E. A. Luk’yanets, Khim. Geterotsikl. Soedin., 1994, 30 [Chem. Heterocycl. Compd. (Engl. Transl.), 1994, 26]; (b) E. A.Makarova, V. N. Kopranenkov and E. A. Luk’yanets, Khim. Geterotsikl. Soedin., 1994, 1206 [Chem. Heterocycl. Compd. (Engl. Transl.), 1994, 1043]. 5 S. Banfi, F. Montanari, S. Quici, S. V. Barkanova, O. L. Kaliya, V. N. Kopranenkov and E. A. Luk’yanets, Tetrahedron Lett., 1995, 36, 2317. 6 S. V. Barkanova and O. L. Kaliya, J. Porph. Phthal., 1999, 180. 7 S. Banfi, F. Montanari, S.V. Barkanova and O. L. Kaliya, J. Chem. Soc., Perkin Trans. 2, 1997, 8, 1577. 8 S. Banfi, L. Pozzi, S. Quici, S. V. Barkanova and O. L. Kaliya, J. Chem. Soc., Perkin Trans. 2, in press. 9 S. V. Barkanova, E. A. Makarova, O. L. Kaliya and E. A. Luk’yanets, J. Chem. Soc., Perkin Trans. 2, submitted. hQ therm 100 – hQ therm ~ WQ WNfOH ~ [PMnL]0[AcOOH]0[R-naphtalene]0 k5[R-naphthalene]0 + kd[PMnL]0 (1) PMn3+(L) + AcOOH PMn3+(HOOAc)(L) PMn5+(O)(L) [ ] k1 k2 (1) (2) (3) (4) (5) (6) (7) (8) PMn(O2)(L) + AcOOH + PMn3+(L) R OH R oligomers catalyst degradation kd + PMn3+(L) R k5 O O R 7 O O R 8 PMn5+(O)(L) O O R 50 ºC – H2O 20 ºC, AcOOH O L = AcOH, R = H,Me counterion is not shown 50 25 0 0.05 0.10 0.15 0.20 0.25 0.30 0.6 0.8 1 2 [3] (mol%) hMD (%) Figure 2 The dependencies of ‘thermal’ (1) and ‘initial’ (2) menadione yields on the concentration of 3 at full substrate conversion. [AcOOH]: [2- methylnaphthalene] = 5:1.[2-methylnaphthalene]: ( ) 0.004, ( ) 0.008, ( ) 0.024 and ( ) 0.05 M. (At [3] = 0.005 mol% the substrate conversion was 75%, and the menadione yields were calculated on the reacted 2-methylnaphthalene.) 75 50 25 0 2.5 5.0 7.5 10.0 [AcOOH]:[2-methylnaphthalene] hMD therm (%) Figure 3 The dependence of the ‘thermal’ menadione yield on the oxidant excess. [3] = 0.02–0.1 mol%, [2-methylnaphthalene]: ( ) 0.004, ( ) 0.008, ( ) 0.024 and ( ) 0.05 M. Received: 25th May 1999; Com. 99/1491

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年代:1999

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Supercritical carbon dioxide extraction of caesium from aqueous solutions in the presence of macrocyclic and fluorinated compounds Chen M. Wai,a Yuriy M. Kulyako*b and Boris F. Myasoedovb a Department of Chemistry, University of Idaho, Moscow, ID, 83844-2343, USA. Fax: +1 208 885 6173 b V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow, Russian Federation.Fax: +7 095 938 2054 Supercritical fluid extraction of caesium, potassium and sodium from aqueous solutions in the presence of dicyclohexano- 21-crown-7, pentadecafluoro-n-octanoic acid (PFOA) and tetraethylammonium perfluoro-1-octanesulfonate (TPFOS) has been investigated at different temperatures of supercritical carbon dioxide, ratios between reagent concentrations and initial concentrations of caesium in the solution.The long-lived fission products of nuclear fuel 137Cs and 90Sr are among the most hazardous components of radioactive high-level wastes (HLW). Current extraction technology for the recovery of caesium and strontium from HLW involves macrocyclic polyethers (crown ethers) as extractants and paraffinic or halogenated hydrocarbons as solvents.One of the main drawbacks of these processing systems is the generation of large amounts of harmful organic wastes. In connection with increased environmental requirements restricting the use of conventional solvents, the development of alternative extraction methods that exclude or decrease drastically the amount of wastes has been carried out very intensively in recent years. Supercritical fluid extraction (SFE) with CO2 is one of the most promising techniques capable of solving environmental problems because fluid carbon dioxide as a solvent precludes the use of toxic organic liquids.Since Laintz et al.1 have demonstrated the possibility of metal (copper) chelate extraction with supercritical CO2, this method has attracted interest of researchers involved in the extraction of actinides.2–5 Until recently, no data on the SFE of caesium were published.It is well known that crown ethers are primarily used for the extraction of alkali and alkaline earth metals, which do not form complexes with other types of reagents. Crown ethers extract metals as ion pairs in which the metal enters into the cationic part of the complex.Counteranions are usually required for creating these ion pairs capable of being transferred through a phase boundary. Under SFE conditions, when a crown ether is in the aqueous phase, the solubility of compounds that serve as a source of counteranions in such a non-polar solvent as supercritical CO2 is crucial for the transport of the resulting complex into the CO2 phase.Fluorinated organic compounds and metal complexes with fluorinated ligands are known to be highly soluble in supercritical CO2. The solubility of the compounds increases with increasing number of fluorine substituents. 6 Therefore, pentadecafluoro-n-octanoic acid (PFOA) and tetraethylammonium perfluoro-1-octanesulfonate (TPFOS) have been chosen as a source of counteranions.In this work, we report on the first results of the SFE of caesium with crown ethers in the presence of the above compounds. The experiments were performed on an SFE unit involving a high-pressure pump, a thermostatted oven and a 10 ml stainless steel extraction cell. Certain amounts of dicyclohexano-21- crown-7 (DCH21C7), PFOA or TPFOS dissolved in chloroform were introduced into the cell.The contents of the cell were evaporated to dryness on a water bath (T = 60 °C) in a nitrogen flow. Next, 2 ml of an aqueous solution containing a mixture of alkali metal ions (Cs+, K+ and Na+) was added to the cell. The cell was placed in the oven connected to the CO2 line and heated to a required temperature.Next, the system was pressurised by CO2 to 100 atm. The contents of the cell was held under static conditions for 20 min. Thereafter, the dynamic stage of the extraction was conducted at a fluid CO2 flow rate of 1.0–2.0 ml min–1 (the total CO2 volume was 50 ml). The CO2 flow leaving the cell passed through a restrictor dipped into a vessel with chloroform (a trap for the collection of extracted solutes).On completion of the extraction process, the cell was depressurised to 1 atm. The extraction efficiency was calculated by difference between the metal concentrations in the aqueous phase before and after extraction. The metal concentration was determined by ICP–MS. Each series of test solutions included samples with known Cs+, K+ and Na+ concentrations for controlling the accuracy of determination.It was found that PFOA, TPFOS and DCH21C7 caused no interference in the ICP–MS determination of the elements. It is considered that the selectivity of crown ethers for metal ions is primarily determined by the so-called ionic diameter– cavity size comparability concept.7,8 For example, the 21-crown-7 host with a cavity diameter of 3.4–4.3 Å was found to be selective for caesium (the cationic diameter 3.34 Å) under conventional liquid–liquid extraction conditions.To be certain in the validity of this concept for SFE, we examined the effect of the crown ether structure on the efficiency of caesium extraction. The experimental results are presented in Table 1. The data in Table 1 show that, in general, the extraction efficiencies are maximum for cations whose ionic diameters are closest to the cavity size of the crown ether; this fact is consistent with the above-mentioned concept.Thus, DCH18C6 exhibits appreciable selectivity for K+ ions, and DCH21C7 removes caesium most effectively in comparison with the other crown ethers. Therefore, the latter was chosen for the further investigation. As can be seen in Table 1, the efficiency of caesium extraction is no higher than 50% even with a large excess of reagents.Table 1 Extraction of alkali metals with various crown ethers in the presence of PFOA. Initial alkali metal concentrations: [Cs+] = 1.67×10–4 mol dm–3 (22.2 mg ml–1); [K+] = 1.73×10–4 mol dm–3 (6.8 mg ml–1); [Na+] = = 1.76×10–4 mol dm–3 (4.1 mg ml–1); P = 100 atm; T = 40 °C; the molar ratio [Cs+]:[crown ether]:[PFOA] = 1:100:100.Crown ether Cavity size/Å Extraction efficiency, E (%) Cs+ (3.34 Å) K+ (2.66 Å) Na+ (1.90 Å) 18C6 2.67–2.86 4 0 0 DCH18C6 2.67–2.86 28 68 7 DCH21C7 3.40–4.30 42 46 0 DB24C8 >4.3 27 17 0 Table 2 Effect of temperature on the extraction efficiency of alkali metals in the presence of PFOA or TPFOS.Initial concentrations of alkali metals: [Cs+] = 1.67×10–4 mol dm–3 (22.2 mg ml–1); [K+] = 1.73×10–4 mol dm–3 (6.8 mg ml–1); [Na+] = 1.76×10–4 mol dm–3 (4.1 mg ml–1). The molar ratio [Cs+]:[DCH21C7]:[counteranion] = 1:100:100. P = 100 atm. T/°C Counteranion Extraction efficiency, E (%) Cs+ K+ Na+ 21 60 72 0 40 PFOA 43 53 0 60 16 19 0 21 67 73 0 40 TPFOS 63 69 0 60 55 39 0Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) The solubility of the resulting complexes in the CO2 phase, which mainly depends on temperature and pressure,6 is a primary prerequisite to the effective extraction with supercritical CO2. We examined the temperature effect on the extraction of alkali metals (Table 2). As a rule, the solubility of a compound in supercritical CO2 increases with temperature.6 However, in our case (Table 2), the opposite dependence is observed, i.e., an increase in the temperature results in a decrease of the caesium extraction efficiency.Note that this dependence is more clearly pronounced with the use of PFOA. The extraction of caesium with supercritical CO2 was found to depend on the initial concentration in the solution.Table 3 shows that in the recovery of caesium from solution with a concentration of 5 mg ml–1 the caesium extraction efficiency decreases markedly as compared to the case with a concentration of caesium of about 22 mg ml–1. In studies of the dependence of the extraction efficiency for alkali metals on the ratio between reagents, we found that an excess of counteranions rather than the crown ether is a more important factor affecting the extraction efficiency (Table 4).Thus, the SFE of caesium can be performed with the crown ether DCH21C7 in the presence of fluorinated compounds as counteranions. The SFE temperature, the concentration of counteranions and the initial caesium concentration in the solution were found to be crucial factors determining the extraction behaviour of caesium.This work was supported by a grant from the USA National Research Council’s Radioactive Waste Management Program. References 1 K. E. Laintz, C. M. Wai, C. R. Yonker and R. D. Smith, Anal. Chem., 1992, 64, 2875. 2 C. L. Phelps, N. G. Smart and C. M. Wai, J. Chem. Educ., 1996, 73, 1163. 3 Yuche Lin, N. G. Smart and C. M. Wai, Trends Anal.Chem., 1995, 14, 123. 4 Yuche Lin, N. G. Smart and C. M. Wai, Environ. Sci. Technol., 1995, 29, 2706. 5 Yuche Lin, C. M. Wai, F. M. Jean and R. D. Brauer, Environ. Sci. Technol., 1994, 28, 1190. 6 N. G. Smart, T. Carleson, T. Kast, A. A. Clifford, M. D. Burford and C. M. Wai, Talanta, 1997, 44, 148. 7 Makrotsiklicheskie soedineniya v analiticheskoi khimii (Macrocyclic compounds in analytical chemistry), eds.Yu. A. Zolotov and N. M. Kuz’min, Nauka, Moscow, 1993, p. 41 (in Russian). 8 Separation Techniques in Nuclear Waste Management, eds. T. E. Carlson, N. A. Chipman and C. M. Wai, 1996, p. 47. Table 3 Comparison of the extraction behaviour of caesium in the recovery from solutions containing equal molar (about 1.7×10–4 mol dm–3; solution I) and weight amounts (about 5 mg ml–1; solution II) of alkali metals.P = 100 atm. The molar ratio [Cs+]:[DCH21C7]:[PFOA] = 1:100:100. Initial concentrations: (I) [Cs+] = 1.67×10–4 mol dm–3 (22.2 mg ml–1); [K+] = = 1.73×10–4 mol dm–3 (6.8 mgml–1); [Na+] = 1.76×10–4 mol dm–3 (4.1 mgml–1). (II) [Cs+] = 4.87 mg ml–1; [K+] = 5.0 mg ml–1; [Na+] = 5.1 mg ml–1. Counteranion T/°C Extraction efficiency, E (%) I II Cs+ K+ Na+ Cs+ K+ Na+ 21 60 72 0 36 29 0 PFOA 40 43 53 0 21 12 0 60 16 19 0 0 0 0 TPFOS 40 63 69 0 40 56 0 60 55 39 0 25 32 0 Table 4 Effect of the ratio between crown ether (DCH21C7) and counteranion (TPFOS) concentrations on the efficiency of alkali metal extraction. P = 100 atm; T = 60 °C. Molar ratio [Cs+]:[DCH21C7]:[TPFOS] Extraction efficiency, E (%) Cs+ K+ Na+ 1: 0:100 7 2 0 1: 10:100 24 32 0 1: 50: 50 14 20 0 1: 50:100 25 37 0 1:100:100 25 32 0 Received: 24th February 1999; Com. 99/1446

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年代:1999

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Close contact distance between hexacyanometallate ions in the course of electron transfer Vitalii Yu. Kotov*a and Galina A. Tsirlinab aHigher Chemical College, Russian Academy of Sciences, 125047 Moscow, Russian Federation. Fax: +7 095 200 4204 bDepartment of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation.Fax: +7 095 939 0171; e-mail: tsir@elch.chem.msu.ru On the basis of rate constants of redox reactions and stability constants of anion pairs, the contact distances between hexacyanometallate ions in the course of electron transfer were estimated as 6.7–7.1 Å, these values are comparable with the contact anion– anion distances in solids and subtantially lower than the sum of radii of nonhydrated ions.The charge-transfer distance (d) is the most important model parameter in the quantitative examination of the kinetics of a wide range of redox reactions. For estimating it, the sum of the reactant radii is frequently used, which is considered as the closest possible contact distance (d*) of the formation of intermediates (ion pairs).This work compares the contact distances between hexacyanometallate ions, which are calculated from the rates of bimolecular redox reactions (kobs) and stability constants of anion pairs (KIP). We consider anion pairs as the products of cooperative interactions of ions in bulk solution; these interactions are accompanied by the contact between anions participating in electron transfer.When two ions interact, the value of kobs is determined by the equation1,2 where ket is the rate constant of electron transfer, and KIP can be estimated within an approximation of spherical particles from the Fuoss3 equation where N is the Avogadro number, z1 and z2 are ionic charges, e is the elementary charge, Ds is the static dielectric constant, I is the solution ionic strength, T is the absolute temperature, and k is the Boltzmann constant.As we have demonstrated earlier,4 the Fuoss equation is also suitable for the quantitative description of associates containing two anions. According to the Marcus theory, ket is determined by the equation1 where the preexponential factor Hd,a (cm–1) can be expressed in terms of charge-transfer spectral bands as follows: where is Planck’s constant, R is the molar gas constant, DE is the standard free energy of the reaction and d is the chargetransfer distance (Å).The values of the optical transition energy (nmax/cm–1), the half-width of the absorption band (n1/2/cm–1), and the reorganization energy (c) can be found from the experimental absorption spectra of ion pairs.5,6 The reorganization energy can be either calculated from a particular model7 or assessed by taking into account the additive nature of ion contributions to the sought values.8 The molar absorption coefficients (emax/dm3 mol–1 cm–1) and the stability constants of ion pairs can be found from the concentration dependences of the absorption.4–6 It is possible to accurately determine the close-contact distances during the interaction of anions using equations (2) and (3) because of the fact that the dependence of KIP on d* at z1, z2 < 0 is clearly pronounced.The estimation of the contact distance in an ion pair from equation (4) presents the major problem because, in the general case, d � d*. However, inasmuch as the electron transfer in hexacyanometallate ions proceeds between nonbinding t2g orbitals localised predominantly at the transition-metal atoms, which, at the same time, are the charge centres of effective spheres, we can expect the distances obtained from equations (1)–(4) under comparable experimental conditions be equal.A comparison of the rate constants of bimolecular redox reactions between different hexacyanometallate ions (Table 1) shows that the experimental values9,10 and those calculated using the data5,6 and equation (1) are equal at a distance of 6.7 Å for the [Fe(CN)6]3–, [Fe(CN)6]4– pair and of 6.8±0.2 Å for the [Fe(CN)6]3–, [Os(CN)6]4– pair.An independent calculation of close-contact distances from the stability constants of the anion pairs [Fe(CN)6]3–, [M(CN)6]4– (M = Fe or Os) was carried out by equation (2).In accordance with the spectroscopic data,6 at a constant total concentration of potassium ions equal to 2.5 mol dm–3, the stability constants of the [Fe(CN)6]3–, [M(CN)6]4– (M = Fe or Os) ion pairs are equal to 0.055±0.006 dm3 mol–1. Inasmuch as Billing and Khostariya6 determined the stability constants in solutions containing high concentration of multicharged ions, we found the ionic strengths of solutions in accordance with the equation11 I = 0.5SCi|zi|.In this case, the contact distance for hexacyanometallate ions is 6.9±0.1 Å. This value is consistent with the above results. The use of the classical equation I = 0.5SCi|zi|2 results in still lower values of d. The third way to estimate the sought values is based on the use of the dependence of the rate constants of redox reactions kobs = KIPket (1) KIP = K0 IP f, K0 IP= exp– , 4pN(d*)3 3000 z1z2e2 Dsd*kT f = exp , K= , z1 z2 e2K Ds kT(1 + Kd*) 8pNe2I 1000DskT 1/2 (2) (3) ak–1 is the rate constant of the reverse redox reaction.Table 1 Contact distances in [Fe(CN)6]3–, [M(CN)6]4– anion pairs and parameters used in the calculations. M T/K I/mol dm–3 DE/V c/V nmax/cm–1 n1/2/cm–1 emax/dm3 mol–1 cm–1 ka –1/dm3 mol–1 s–1 kobs/dm3 mol–1 s–1 D/Å Fe 293 0.01 KOH 0 1.47 12200 7900 28 — 4.8×101 6.7 Os 298 0.03 KCl 0.25 1.47 16400 10100 45 4.7×104 2.8×100 6.6 Os 298 0.075 KCl 0.25 1.47 16400 10100 45 4.1×105 2.4×101 7.1 Os 298 0.24 KCl 0.25 1.47 16400 10100 45 1.5×106 8.8×101 6.8 Os 298 0.44 KCl 0.25 1.47 16400 10100 45 2.9×106 1.7×102 6.6 ket= exp– , 2p h H2 d,a (4pcRT)1/2 (DE + c)2 4cRT (4) Hd,a = 0.0206 , (emaxnmaxn1/2)1/2 d hMendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) on the ionic strength of solution in accordance with equation (3). The results of processing the data9 (KCl, I = 0.03–0.44) by the least-squares technique agree with the theoretical dependence at a contact distance of 6.9 Å in the [Os(CN)6]3–, [Fe(CN)6]4– and [Ru(CN)6]3–, [Fe(CN)6]4– ion pairs and of 7.1 Å in the [Ru(CN)6]3–, [Os(CN)6]4– ion pair.Thus, the calculated contact distances agree with one another and with a contact distance of 6.673 Å between anions in solid K3[Fe(CN)6],12 in which the contact between anions also takes place because of cooperative interactions of all ions. These distances are substantially lower as compared not only with the estimated value of 14 Å accepted in ref. 6 but also with the sum of ionic radii (according to different estimations,13,14 about 8.6–9.4 Å). The relative positions of low-spin octahedral complexes with t5 2g and t6 2g electron configurations along the axes of the second order during the formation of an anion pair (like the positions of ions in a crystal) facilitate the most effective overlapping of the orbitals of complex ions participating in the electron transfer.Undeniably, all of the d values obtained should be considered as effective, bearing in mind that approximations introduced in the derivation of equations (1)–(4) adequately correspond to the geometry and the charge distribution in real systems, and also that we are operating with parameters dependent on ionic strength.The agreement between contact distances determined by different methods can be partly caused by the fact that different approximations were used when we considered equilibrium [equations (2) and (3)] and kinetic [equation (4)] characteristics. This work was supported by the Russian Foundation for Basic Research (grant no. 99-03-32367a). References 1 P. Chen and T. J. Meyer, Chem. Re, 1998, 98, 1439. 2 D. M. Stanbury, W. K. Wilmarth, S. Khalaf, H. N. Po and J. E. Byrd, Inorg. Chem., 1980, 19, 2715. 3 R. M. Fuoss, J. Am. Chem. Soc., 1958, 80, 5059. 4 A. B. Nikol’skii and V. Yu. Kotov, Mendeleev Commun., 1995, 139. 5 J. C. Curtis and T. J. Meyer, Inorg. Chem., 1982, 21, 1562. 6 R. Billing and D. E. Khostariya, Inorg. Chem., 1994, 33, 4038. 7 A. M. Kuznetsov, Charge Transfer in Physics, Chemistry and Biology. Physical Mechanisms of Elementary Processes and Introduction to the Theory, Gordon and Breach Science Publishers, Berkshire, 1995. 8 S. I. Gorelsky, V. Yu. Kotov and A. B. P. Lever, Inorg. Chem., 1998, 37, 4584. 9 K. C. Cho, P. M. Cham and C. M. Che, Chem. Phys. Lett., 1990, 168, 361. 10 R. G. Campion, C. F. Deck, P. King and A. C. Wahl, Inorg. Chem., 1967, 6, 672. 11 L. Johansson, Acta Chem. Scand., 1975, A29, 365. 12 N. G. Vannerberg, Acta Chem. Scand., 1972, 26, 2863. 13 B. M. Gordon, L. L. Williams and N. Sutin, J. Am. Chem. Soc., 1961, 83, 2061. 14 R. D. Cannon, Adv. Inorg. Chem., 1978, 21, 179. Received: 24th March 1999; Com. 99/1465

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年代:1999

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Systematic estimation of isotropic hyperfine coupling constants for protons in free radicals Nikolai D. Chuvylkin*a and Andrei M. Tokmachevb a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation. Fax: +7 095 135 5328 b Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation.Fax: +7 095 939 4575 Modified formalism of consistent quantum-chemical estimations of contact interactions between magnetic moments of an unpaired electron and protons, when the spin populations of atoms are determined in the basis of symmetrically orthogonalised atomic orbitals, is presented and examined using the H2C=CH·a test free radical as an example.Radiospectroscopic investigations provide a wealth of information on the structures of molecular compounds. Thus, a simple EPR technique is widely used for studying radical systems. Experimental EPR spectra are often difficult to interpret.1 Current methods of quantum chemistry can give useful assistance in identifying spectra.2–5 Successful applications of these approaches require reliable techniques for computation of magnetic resonance parameters of radical systems.Bulky radical systems are of current practical interest. Thus, radical probes such as 2,2,6,6-tetramethylpyperidin-N-oxyl and 2-octyl-2,4,5,5-tetramethyl-3-imidazolin-N-oxyl at the surfaces of various catalysts were systematically examined.6 Analogous radical probes were added to protein molecules for investigating their conformational transformations.7 The commonly used ab initio methods even of relatively low levels are usually inapplicable in practice to these bulky systems because of technical difficulties. In the circumstances, alternative quantumchemical approaches to estimate the EPR spectra parameters of free radicals deserve special consideration. The reliable and rapid identification of highly informative EPR spectra is presently associated, as a rule, with the future progress and applications of the density functional theory8–11 or adequate semi-empirical quantum-chemical ZDO approaches,2,3,12,13 which are believed to be theoretically well-founded in the basis of Löwdin symmetrically orthogonalised atomic orbitals ( s).14 In the framework of semi-empirical ZDO approaches, when establishing structure–property correlations, the confusing problems of ascertaining the interrelations between the calculated wave functions and experimental radiospectroscopic parameters inevitably arise.Thus, to relate the isotropic hyperfine coupling (ihfc) constant aZn iso found by EPR to the quantum-chemically calculated spin population rs Zn of a valence s-AO of the particular n-th atom Zn, the following well-known expression is commonly used:2 Over a long period of time it was assumed that the proportionality coefficient K(Z) in this expression was dependent on only the type of the atom regardless of its chemical environment, i.e., of the compound in which it occurred.However, afterwards in calculations of proton ihfc constants by ZDO semi-empirical methods tremendously unlike values of the proportionality coefficient K(H) were suggested.15,16 Keeping this in mind, the opinion was expressed3 that for description of two fundamentally alternate mechanisms of spin density distribution (i.e., polarization and delocalization) the use of two corresponding highly different Ka(H) and Kb(H) values was reasonable.Regardless of the qualitative explanation3 of a need for using two proportionality coefficients Ka(H) and Kb(H), which diminishes the contradiction between recommendations of different authors,15,16 it was necessary to determine theoretically each of the coefficients using an adequate mathematical expression that takes into account the specificity of both mechanisms of spin distribution and conventional quantumchemical approximations.Recently, using model p- and s-electron hydrocarbon fragments as an example, the scheme of consistent quantum-chemical calculations of the proton ihfc constants aH iso for free radicals was considered,12 when the spin populations rs H were determined in the basis of Löwdin symmetrically orthogonalized s.Keeping in mind the fact that in a purely p-electron radical the ihfc with a proton results only from the exchange spin polarization, the expression was deduced in the framework of a valence bond (VB) approach with the inclusion of s–p- configuration interaction: where d(H) is the Hartree–Fock value (508 G) of the proportionality coefficient, and Shs is the overlap integral of a hybrid h-AO of a heavy atom (C) and 1s-AO of an H atom.From equation (2) it follows that for Shs ª 0.75 (typical case) the values of the Ka(H) and d(H) are practically indistinguishable. At the same time, it was shown12 that in the framework of the MO LCAO theory when passing from overlapping AOs to symmetrically orthogonalized s the expression for the ihfc constant aH iso did not undergo any changes in the case of p-electron radicals.At the same time, it was established12 that the ihfc constants for protons in typical s-electron radicals, resulting predominantly from spin delocalization, were to be computed with the proportionality coefficient Kb(H) higher than the Hartree–Fock coefficient because its expression with even reduced account of only the one-electron contribution r0 H into the spin population of hydrogen 1s-AO assumed the substantially modified form in the basis of symmetrically orthogonalised s: For typical values of the overlap integral Shs the proportionality coefficient Kb(H) is within the range 700–800 G.This AO aZn iso = K(Z)rs Zn (1) AO Ka(H) = d(H) (1+S2 hs), 2 3 (2) AO 60 50 40 30 20 10 0 90 100 110 120 130 140 150 160 170 180 1 2 DE/kcal mol–1 qa/° Figure 1 Relative total energies of the vinyl s-electron radical as functions of the angle CCHa: (1) MNDO/UHF, (2) UHF/6-31G**.AO Kb(H) = d(H) 2 . 1 2 1 1 – Shs 1 1 + Shs + (3)Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) is consistent with the data of ref. 17 wherein it has been found that the best coincidence of semi-empirically calculated ihfc constants and experimental ones for protons of a number of s-radicals is observed when Kb(H) = 743 G.With the use of the restricted Hartree–Fock (RHF) method, the calculated one-electron spin densities RHFr0( ) are always not negative whereas real physical experiments also detect the negative total spin densities r( ).The appearance of negative r( ) values is owing to the additional polarization contribution rp( ) caused mainly by exchange electronic correlation.2 This correlation suggests that the electrons with different spins become differently distributed in the space. In practical quantum-chemical calculations of magnetic resonance parameters of free radicals with allowance for electron correlation effects, the UHF method is most widely used.In this method, the one-electron (delocalization) and polarization contributions to the spin density are not partitioned.2 Note that because of proper symmetry properties of wave functions the polarization component rp( ) is usually overestimated in UHF calculations. The separation of the UHF spin densities into the delocalization and polarization contributions is possible by the natural orbital analysis within the scope of UHF method.2,18,19 At the same time, a simple relation between the UHF and projected unrestricted Hartree–Fock (PUHF) wave functions is well known.18,19 From these considerations a simple way was found to partition the spin density calculated by the UHF method into contributions from the spin polarization and spin delocalization mechanisms.For doublet radicals, the polarization correction takes the form:18 The delocalization contribution is then approximated as the difference: The validity of this approach was confirmed18 by comparing the delocalization components UHFr0 calculated by equation (5) with those (RHFr0) obtained by the open-shell RHF method.2 The result is that equation (5) becomes: Because of the physical simplicity, equation (6) can be quite useful in systematic analysis of the ihfc constants for protons in bulky radical systems. In the case of the RHF approach (e.g., CNDO/SP variant2) the polarization correction is estimated, as a rule, with the use of the perturbation theory.For convenience, we used expression (6).However, it was taken into account that the polarization component rp( ) of the total spin density can be partitioned into contributions of so-called spin [rsp( )] and exchange [rep( )] polarizations,2 and the component rep( ) is the only one for p-radicals and much more significant than rsp( ) for s-radicals. Consequently, supposing the correction sprs H to be negligible for s-radicals and not entering into a contradiction with the results,12 we have, when estimating the polarization contribution paH iso with equation (1), to multiply the spin population prs H obtained using equation (6) by the Hartree–Fock proportionality coefficient Ka(H) = 508 G.With the aim to test the presented approach to evaluating the ihfc constants for protons, in the framework of the MNDO approximation,20 we consider the vinyl radical, which is commonly regarded as a ‘criterion’.2,3,17,18 This approach based on equations (1)–(3) and (6), the standard MNDO parametrization, and the Dewar half-electron method21 is below referred to as MNDORU.When the geometry of free radicals is inadequately known, the magnetic-resonance parameters are evaluated by quantumchemical methods with great errors.3 Unfortunately, experimental data on the geometry of free radicals are either absent at all or often ambiguous.2 At the same time, because of the high sensitivity of calculated magnetic-resonance characteristics to changes in the structural parameters and the ability of NDO approaches to interpret radiospectroscopic data with acceptable accuracy, if the supposed structures of free radicals are close to the real ones, these methods make it possible to predict the electronic structure and geometry of free radicals more exactly than an energy optimization procedure.3 Like the majority of other radicals, the geometry parameters of a vinyl radical were not determined experimentally.Table 1 contains these parameters computed by us using both semiempirical MNDO and ab initio methods in the 6-31G** basis. The two sets of structural characteristics are similar; however, the data for the CCHa angle are dramatically different.The procedure of energy variation can reliably determine the gasphase geometries of free radicals only at a level of nonempirical calculations in extended basis sets in quality comparable to the 6-31G** basis.Therefore, we can believe that real structural parameters of the vinyl radical are closer to the ab initio calculated data (Table 1). Table 2 includes, together with the experimental aH iso values, the delocalization (0aH iso) and spin-polarization (paH iso) contributions and total (aH iso = 0aH iso + paH iso) ihfc constants estimated according to the above scheme for the specified (ab initio optimised) radical geometry.As can be seen, the MNDO/RHF method did not reproduce the recorded ihfc constants for the protons in the vinyl radical even qualitatively. After taking into account the polarization contribution, the great discrepancies between theoretical and experimental values for cis- and transprotons became much lower, but for the proton Ha calculated ihfc constant was found to have a wrong sign.It is problematic that the reversed sign [aH iso(a) = –1.3 G] was also obtained in ab initio calculations, whereas the INDO and CNDO/SP methods led to a satisfactory quantitative description of this constant [aH iso(a) = 10.7 G and aH iso(a) = 13.4 G, respectively].22 The contradiction with the experiment can be removed by a change in geometry parameters.Taking into account the data in Table 1, it is reasonable to remove the strong discrepancy between the calculated and experimental values by variation of the valence angle CCHa º qa keeping in mind the pronounced angular dependence of the calculated ihfc constant for the a-proton in the vinyl radical.2,3,17 The remaining (more ‘rigid’) structural parameters may be fixed in the course of this variation.Relative total energies of the vinyl radical calculated by MNDO/UHF and UHF/6-31G** methods are plotted in Figure 1 as functions of angle qa. As can be seen in Figure 1 (curve 1), DE remains practically constant over a wide range of qa. Hence, it is reasonable to accept the degree of agreement of theoretical r r r r r Table 1 Bond lengths (Å) and angles (°) in the vinyl radical, optimised by semi-empirical and ab initio methods. Parameter Method MNDO 6-31G** CHa 1.049 1.070 CHcis 1.091 1.075 CHtrans 1.091 1.078 CC 1.307 1.341 CCHa 180.0 135.6 CCHcis 122.9 121.4 CCHtrans 122.9 122.0 UHFrp(r) = [UHFr(r) – PUHFr(r)] 3 2 (4) UHFr0(r) = UHFr(r) – UHFrp(r) (5) UHFr(r) – RHFr0(r) = UHFrp(r) (6) r r r r r aEquations (1)–(3).Table 2 Experimental data23 and theoretical quantitiesa estimated for ab initio optimised radical geometry. Nucleus Shs K(H) MNDORU Exp. 0aH iso paH iso aH iso aH iso Ha 0.661 791 28.3 –31.4 –3.1 13.4 Hcis 0.648 773 18.3 12.2 30.6 37.0 Htrans 0.649 774 52.6 9.2 61.8 65.0 C C Htrans Hcis HaMendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) and experimental magnetic-resonance parameters for one or another radical geometry as an adequate test of authenticity of the vinyl radical geometry. Figure 2 depicts the calculated angular dependence of oneelectron (curve 1) and spin-polarization (curve 2) components and the total ihfc constant (curve 3) for the vinyl s-radical. Curve 3 in Figure 2 decays monotonically as the varied angle increases, whereupon a fair agreement with the experiment is achieved for qa ª 110–125° rather than qa ª 135°. The former value is energy-acceptable (Figure 1) and permissible from the point of view of computing errors of the ab initio method24 and a possible matrix effect on the constant under discussion.Anyhow, the qa angle estimated roughly in this manner proved to be much closer to the ab initio calculated one than the qa angle optimised by the MNDO/UHF method.The evaluated ihfc constants for the cis- and trans-protons distant from the radical centre in the vinyl radical range from 23.8 to 27.1 G and from 62.1 to 61.8 G at qa ª 110–125°, respectively. Therefore, with the account of spin polarization in the MNDORU approximation, all above experimental values of ihfc constants can be, in principle, reproduced with the use of geometry parameters of the vinyl radical, which are different only slightly from those fully optimised by us with the UHF/6-31G** method and accepted as authentic (Table 1).The same has been recently demonstrated13 by the results of similar MNDORU calculations carried out for a test representative sample of 17 p- and s-electron free radicals.Thus, the modified scheme12 of logically consistent quantumchemical calculation of ihfc constants for protons in free radicals when the spin populations of atoms are determined in the basis of Löwdin symmetrically orthogonalised s quite naturally removes the seeming contradiction in the applications15,16 of two tremendously different proportionality coefficients in equation (1) for estimating these constants by most commonly used semi-empirical methods of quantum chemistry.We can also conclude that in calculations of ihfc constants for protons even in s-electron radicals the spin-polarization effects must be borne in mind. Reliable determinations of geometry parameters of free radical systems by modern quantum-chemical methods require not only findings of a minimum on the potential energy surface but also concurrent comparisons of theoretical and experimental radiospectroscopic characteristics.References 1 Yu. V. Rakitin, G. M. Larin and V. V. Minin, Interpretatsiya spektrov EPR koordinatsionnykh soedinenii (Interpretation of EPR spectra of coordination compounds), Nauka, Moscow, 1993, p. 399 (in Russian). 2 G. M. Zhidomirov, P. V. Schastnev and N. D. Chuvylkin, Kvantovokhimicheskie raschety magnitno-rezonansnykh parametrov (Quantumchemical calculations of magnetic resonance parameters), Nauka, Novosibirsk, 1978, p. 368 (in Russian). 3 N. D. Chuvylkin, I. Yu. Shchapin, V. L. Klochikhin, V. A. Tikhomirov and V. I. Feldman, Vestn.Mosk. Univ., Ser. 2, Khim., 1992, 33, 307 (in Russian). 4 N. D. Chuvylkin, A. M. Tokmachev, A. V. Fionov and E. V. Lunina, Izv. Akad. Nauk, Ser. Khim., 1997, 1743 (Russ. Chem. Bull., 1997, 46, 1649). 5 N. D. Chuvylkin, A. M. Tokmachev, A. V. Fionov and E. V. Lunina, Mendeleev Commun., 1997, 191. 6 E. V. Lunina, in Kataliz (Catalysis), eds. O. A. Petrii and V. V. Lunin, Izdatel’stvo MGU, Moscow, 1987, p. 287 (in Russian). 7 E. G. Rosantsev and V. D. Sholle, Organicheskaya khimiya svobodnykh radikalov (Organic chemistry of free radicals), Khimiya, Moscow, 1977, p. 344 (in Russian). 8 C. Adamo, V. Barone and A. Fortunelli, J. Chem. Phys., 1995, 102, 384. 9 J. M. Martell, R. J. Boyd and L. A. Ericsson, J. Phys. Chem., 1995, 99, 623. 10 P. J. O’Malley and D. A. Ellson, Chem.Phys. Lett., 1996, 260, 492. 11 P. J. O’Malley, Chem. Phys. Lett., 1996, 262, 797. 12 N. D. Chuvylkin and A. M. Tokmachev, Izv. Akad. Nauk, Ser. Khim., 1999, 245 (Russ. Chem. Bull., 1999, 48, 245). 13 N. D. Chuvylkin and A. M. Tokmachev, Izv. Akad. Nauk, Ser. Khim., 1999, 1459 (in Russian). 14 R. D. Brown and K. R. Roby, Theor. Chim. Acta, 1970, 16, 175. 15 P. Bischof and G. Friedrich, J. Comput. Chem., 1982, 3, 486. 16 C. Glidewell, J. Chem. Soc., Perkin Trans. 2, 1983, 1285. 17 T. Yonezawa, H. Nakatsuji, T. Kawamura and H. Kato, Bull. Chem. Soc. Jpn., 1969, 42, 2437. 18 T. Yonezawa, H. Nakatsuji, T. Kawamura and H. Kato, J. Chem. Phys., 1969, 51, 669. 19 H. Nakatsuji, J. Chem. Phys., 1973, 59, 2586. 20 M. J. S. Dewar and W. Thiel, J. Am. Chem. Soc., 1977, 99, 4899. 21 M. J. S Dewar, J. A. Hashmall and C. G Venier, J. Am. Chem. Soc., 1968, 90, 1953. 22 G. M. Zhidomirov and N. D. Chuvylkin, Theor. Chim. Acta (Berl.), 1973, 30, 197. 23 R. W. Fessenden and R. H. Schuler, J. Chem. Phys., 1963, 39, 2147. 24 W. J. Hehre, L. Radom, P. R. Schleyer and J. A. Pople, Ab initio Molecular Orbital Theory, WIP, New York, 1986. 60 50 40 30 20 10 0 –10 –20 –30 –40 100 110 120 130 140 150 160 170 180 qa/° aiso(a)/G 1 2 3 Figure 2 Delocalization (1) and spin-polarization (2) contributions and the total (3) ihfc constant for the a-proton in the vinyl s-electron radical as functions of the angle CCHa. AO Received: 5th January 1999; Com. 99/1421

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Dynamic structure of the reaction product of the H–H bond activation by a Ni2 cluster Viktor M. Mamaev,* Sergei Ya. Ishchenko, Igor P. Gloriozov and Elena V. Zernova 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 activated H–H bond was theoretically found to occupy a considerable space characterised by the distances between the centres of mass of H–H and Ni–Ni within the range from –0.5 to +0.5 Å.The development of catalytic cycles for selective conversion of hydrocarbons is one of the most important chemical problems. Key steps of these cycles are reactions of activation of H–H, C–H and C–C bonds.1 As a rule, theoretic studies of these reactions are limited by a static quantum-chemical model when the mechanism of a chemical reaction is judged from the calculations of energy and structure geometry of stationary points in potential energy surfaces by solving the Schrödinger electronic equation.On the other hand, the wave nature of not only electrons but also atoms, molecules, and nuclei was clearly demonstrated using a molecular-beam technique.2 Thus, from the experimental standpoint, wave properties of not only electrons but also nuclei should be taken into account in theoretical studies of the geometry of molecular systems.In this connection, it is evident that only an optimisation process is insufficient for the analysis of molecular systems.To examine the structure of molecular systems, at the first step, it is necessary to construct a potential energy surface. Next, at the second step, the Schrödinger nuclear equation is solved on the basis of the potential energy surface. This technique for studying the dynamic structure is most popular for three- and four-particle molecular systems.3 We examined the dynamic structure of the reaction product of H–H bond activation by a Ni–Ni cluster.The calculations of potential energy surfaces were performed by the density functional technique (DFT).4 An important advantage of the computer program used was that the Coulomb and exchangecorrelation energy components were approximately represented using the expansion of the electron density in an auxiliary basis.5 The main basis consists of the grouped Gaussian functions {311} for H and {842111/63111/411} for Ni; the auxiliary basis for the representation of electron density, of the ungrouped functions (4s1p) for H and (7s5p4d4f5g) for Ni.The general system of coordinates for the interaction of two diatomic molecules has the following form:3(b),(c) In our case, C,D º Ni and A,B º H.Here, z', r' and R' are the Jacobi vectors for the four-particle reaction. The mass-scaled vectors z, r and R are represented as follows: where mA, mB, mC and mD are the particle masses. The equivalent mass m is expressed as The quantum-mechanical Hamiltonian on mass-weighted coordinates results from transformation of classical kinetic energy with the addition of a potential function: An analysis of the reaction mechanism of H–H bond activation by the Ni2 cluster in the reaction-path Hamiltonian approximation6 demonstrated that the movement along the reaction path is associated with a change in the R' distance between the centres of mass of H–H and Ni–Ni (with the retention of the C2v symmetry).In this case, the barrierless formation of a pseudo-rhombic product with a minimum energy at R' ~ 0.2 Å. Note that the singlet state of the molecular system is lower than the triplet state by 6.6 kcal mol–1.The classical structure of the molecular system is shown below. We examined the displacement of the molecular system within the range R' = 0–1.5 Å with the retention of the C2v symmetry (the D2h symmetry at R = 0). In this case, only the two coordinates z' and r' (the Ni–Ni and H–H distances) are changed (except for R').Because z' changed insignificantly (to within 4%), we plotted the two-dimensional potential function V(r', R') at the fixed coordinate z' = 2.294 Å with the retention of the C2v symmetry (Figure 1). In this case, the r' and R' A B C D r' R' z' z = z' r = r' R = R' (mCmD) m(mC + mD) (mAmB) m(mA + mB) (mA + mB)(mC + mD) m(mA + mB + mC + mD) m = mAmBmCmD mA + mB + mC + mD 3 H = – + + + V(z, r, R) h2 2m z2 2 ¶ ¶ è ç æ r2 2 ¶ ¶ R2 2 ¶ ¶ ø ÷ ö Ni 2.294 Å 1.577 Å Ni V/ev 1.5 1.0 0.5 1.5 2.0 –0.5 –0.25 0.0 0.25 0.5 r' R' Figure 1 Two-dimensional potential energy surface in the neighbourhood of the reaction product of the H–H bond activation by the Ni2 cluster as a function V(R', r') of the distance (R'/Å) between the centres of mass of H–H and Ni–Ni and the H–H distance (r'/Å).Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) coordinates varied from 1.0 to 2.9 and from 0 to 1.5 Å, respectively, at a step of 0.1 Å. The 300 points obtained in this manner were used as nodes in the interpolation of the final function V(r', R') by cubic spline functions.Note that the energy of the molecular system varied to within 0.6 kcal mol–1 as the R' coordinate along the reaction path changed within the range from –0.5 to +0.5 Å (Figure 2). In our case, the equivalent mass is equal to 3.0725mH, and the mass-scaled coordinates are R = 0.800R' and r = 0.403r'. The wave functions yi(r, R) were obtained by solving the twodimensional Schrödinger equation The two-dimensional Schrödinger equation was solved by the Rietz method on the basis of 100×100 trigonometric functions with an accuracy of 10–5 cm–1 or better7 in the calculations of eigenvalues.Table 1 summarises the vibrational energy levels and their population at T = 300 K according to the Maxwell–Boltzmann statistics. It can be seen that only the first three vibrational levels are occupied.Figure 3 demonstrates the probability densities of the spatial distribution of an activated H–H bond at a temperature of 300 K. The probability densities were obtained after considering the population of the vibrational energy levels En according to Maxwell–Boltzmann. A significant difference between the dynamic (quantum) and classical structures of the product is obvious.In the classical approach, the activated H–H bond is located at the fixed distance R' ~ 0.2 Å from the Ni–Ni cluster. The results of the dynamic study allowed us to conclude that, with a considerable probability density (~0.8), the activated H–H bond occupies a great deal of space within the R' and r' ranges from –0.5 to +0.5 and from 1.9 to 2.4 Å, respectively. These data are of paramount importance for the development of catalytic cycles of hydrocarbon conversion, for example, olefin hydrogenation, by not only transition metal clusters but also bimetallic complexes.References 1 (a) J. J. Carroll, K. L. Haug, J. C. Weisshaar, M. R. A. Blomberg, Per E. M. Siegbahn and M. Swensson, J. Phys. Chem., 1995, 99, 13955; (b) S.P. Daley, A. L. Utz, T. R. Trautman and S. T. Ceyer, J. Am. Chem. Soc., 1994, 116, 6001; (c) M. L. Burke and R. J. Madix, J. Am. Chem. Soc., 1991, 113, 1475; (d) Homogeneous Transition Metal Catalysed Reactions, eds. W. R. Moser and D. W. Slocum, American Chemical Society, Washington, D.C., 230, 1992. 2 K. F. Smith, Molecular Beams, Methuen, London, 1955. 3 (a) A. Kuppermann, Theoretical Chemistry.Advances and Perspectives, 1981, 6A, 79; (b) J. Echave and D. C. Clary, J. Chem. Phys., 1994, 100, 402; (c) D. C. Clary, J. Chem. Phys., 1991, 95, 7298. 4 (a) A. D. Becke, Phys. Rev., 1988, A38, 3098; (b) C. Lee, W. Yang and R. G. Parr, Phys. Rev., 1988, B37, 785. 5 D. N. Laikov, Chem. Phys. Lett., 1997, 281, 151. 6 W. H. Miller, J. Phys. Chem., 1983, 87, 3811. 7 S. Ya. Ishchenko, V. M. Mamaev, M. S. Topaler and L. N. Alekseiko, Dokl. Ross. Akad. Nauk, 1992, 324, 815 [Dokl. Phys. Chem. (Engl. Transl.), 1992, 324, 282]. E/kcal mol–1 R'/Å 25 20 15 10 5 0 –1.5 –1.0 –0.5 0.0 0.5 1.0 1.5 Figure 2 Minimum energy path in the neighbourhood of the reaction product of the H–H bond activation by the Ni2 cluster as a function of the distance (R'/Å) between the centres of mass of H–H and Ni–Ni. – + +V(r, R) y(r, R) = Ey(r, R) h2 2m r2 2 ¶ ¶ è ç æ R2 2 ¶ ¶ ø ÷ ö Table 1 Energies (E) of vibrational levels (n) of the product of oxidative addition of a hydrogen molecule to a Ni2 cluster and their Maxwell– Boltzmann populations (MB) at T = 300 K. n E/eV MB (%) 0 0.140 74.2 1 0.171 22.4 2 0.222 3.0 3 0.279 0.3 4 0.342 0.03 5 0.395 ~0.0 –0.5 0.0 0.5 R'/Å r'/Å 2.4 2.2 2.0 1.8 0.1 0.2 0.4 0.6 0.8 Figure 3 Dynamic structure of the reaction product of the H–H bond activation by the Ni2 cluster, represented by the probability density distribution. The figures at each of the contour lines represent the total probability of the molecular structure occurring within the given contour. Received: 1st March 1999; Com. 99/1452

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Thermogravimetric determination of amorphous and crystalline phases in superdispersed diamond Irina S. Larionovaa and Alexander L. Vereshchagin*b a “Altay” Federal Research and Production Centre, 659322 Biysk, Russian Federation b Biysk Technological Institute, Altay State Technical University, 659305 Biysk, Russian Federation.Fax: +7 3854 25 2486; e-mail: val@bti.secna.ru Amorphous and crystalline phases in superdispersed diamond have been determined by thermogravimetric analysis at a heating rate 1.25 K min–1 or lower, and the kinetic parameters of oxidation of different carbon species have been calculated. Superdispersed diamonds are formed under non-equilibrium conditions of detonation at high temperature gradients and rates of cooling.1 This process results in the occurrence of several carbon phases in the primary particles of condensed products of detonation2,3 or detonation carbon.It is well known4 that the structure of detonation carbon depends on the conditions of synthesis and, in the general case, can contain several types of primary particles, namely, amorphous, graphite-like and diamond carbon.The following three carbon phases were detected by X-ray diffraction analysis of detonation carbon:2 diamond (a set of 5 reflections), amorphous carbon and dispersed carbon (a 002 reflection). The aim of this work was to examine the structure and distribution of carbon phases in the detonation product of a trinitrotoluene–cyclotrimethylenetrinitramine (40:60) mixture.5 The experimental procedure involved consecutive selective oxidation of carbon phases under special conditions.The detonation carbon was oxidised by oxygen of the air and by nitric acid solutions. The kinetics of oxidation of detonation carbon by oxygen of the air was investigated by dynamic thermogravimetry on a Q-derivatograph (F. Paulik, J. Paulik and I.Erdey, Hungary) in the temperature range 603–893 K. The experimental conditions provided selective oxidation of the carbon phases. The DTA and TGA curves measured at a heating rate of 10 K min–1 exhibited only two stages of oxidation:6 one of them refers to the oxidation of dispersed carbon with nondiamond structure and the other, to the oxidation of superdispersed diamonds.The DTA and TGA curves of superdispersed diamond measured under the same conditions exhibited one stage of oxidation.6 A decrease in the heating rate down to 1.25 K min–1 resulted in the appearance of three and two stages of oxidation in the cases of detonation carbon and superdispersed diamond, respectively (Figure 1). A sample of superdispersed diamond was separated from detonation carbon by thermal liquid-phase oxidation.7 The kinetic parameters of oxidation for detonation carbon and superdispersed diamond were calculated by the Freeman and Carroll method.8 Table 1 summarises the results.The mass fractions of each individual phases in a number of the detonation carbon samples were determined from the thermogravimetric data. These data indicate that 40–45, 20–25, and 30–35% dispersed carbon was oxidised at stages I, II and III, respectively.While the loss of mass at the first stage in superdispersed diamond prepared by the treatment with a mixture of sulfuric and nitric acids varied from 3 to 7%, the residual carbon was oxidised as a structurally homogeneous material. Note that the Ea and A0 values are similar for the last two stages of oxidation of detonation carbon and superdispersed diamond.Thus, we can assume that the phase that is oxidised immediately before the diamond phase is an amorphous phase of diamond. Next, using thermogravimetry at a heating rate of 1.25 K min–1, it is possible to determine a loss of the amorphous diamond phase in the course of oxidation of a nondiamond carbon phase.Thus, for the cited example, these data indicate that approximately 2/3 of the amorphous diamond phase was lost in the course of purification. An analysis of the kinetics of the liquid-phase oxidation of detonation carbon by nitric acid solutions at 366 K has also shown the occurrence of three stages in the oxidation. The first stage corresponds to the removal of the easiest oxidisable carbon.The degree of oxidation depends on the oxidation potential of the system and on the duration of exposure; however, it is characterised by a limiting value of the conversion of a nondiamond phase. The first-order rate constant of this reaction in the oxidation by 65% HNO3 solution is 2.5×109 s–1. The second stage differs from the first by a lower rate of reaction. For 65% HNO3, the first-order rate constant of this stage is 0.5×109 s–1.The third stage occurs in systems with high oxidation potentials (mixtures of CrVI compounds, sulfuric and nitric acids etc.) Table 1 Kinetic parameters of gas-phase oxidation for detonation carbon and superdispersed diamond. Stage Detonation carbon Superdispersed diamonds Temperature/K Activation energy Ea/KJ mol–1 Preexponential factor A0 /s–1 Temperature/K Activation energy Ea/KJ mol–1 Preexponential factor A0 /s–1 I 633–698 114.1 0.04×104 — — — II 698–723 73.5 0.34 693–803 115.4 0.28 III >723 193.5 5.5×108 >803 194.4 0.51×108 0 603 653 703 753 803 853 T/K 1 2 T dm/dt Figure 1 DTG curves for (1) detonation carbon and (2) superdispersed diamond oxidation by oxygen of the air at a heating rate of 1.25 K min–1 (sample mass of 5.0 mg).Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) under long exposures and corresponds to the conditions of etching diamond structures. A comparison of these results with each other and with the published data5,7,10 allowed us to suggest that stages I, II and III in both gas-phase and liquid-phase oxidation of detonation carbon characterise the structural inhomogeneity of this material and are responsible for the step-by-step removal of amorphous nondiamond carbon, the amorphous surface structure of diamond particles and then the diamond phase of carbon.We are grateful to I. N. Molostov for his experimental assistance. References 1 A. I. Lyamkin, E. A. Petrov, A. P. Ershov and G. V. Sakovich, Dokl. Akad.Nauk SSSR, 1988, 302, 611 (Soviet Physics, Doklady, 1988, 33, 705). 2 A. L. Vereshchagin, V. F. Komarov and V. M. Mastikhin, Sbornik dokladov V Vsesoyuznogo soveshchaniya po detonatsii (Proceedings of the Fifth All-Union Conference on Detonation), Krasnoyarsk, 1991, vol. 1, p. 99 (in Russian). 3 V. F. Tatsii, A. V. Anan’in, O. N. Breusov, V. N. Drobyshev, A. N. Dremin, A.I. Rogacheva and N. P. Shcherbakova, Sbornik dokladov V Vsesoyuznogo soveshchaniya po detonatsii (Proceedings of the Fifth All-Union Conference on Detonation), Krasnoyarsk, 1991, vol. 2, p. 305 (in Russian). 4 I. Yu. Mal’kov and V. M. Titov, Proceedings of the American Physical Society Conference ‘Shock Compression of Condensed Matter’, Seattle, 1995, part 2, p. 783. 5 A. L. Vereshchagin, E. A. Petrov, G. V. Sakovich, V. F. Komarov, A. V. Klimov and N. V. Kozyrev, US Patent 5861349, 1999. 6 A. L. Vereshchagin, G. M. Ul’yanova and V. V. Novoselov, Sverkhtverdye Materialy, 1990, 5, 20 (in Russian). 7 T. M. Gubarevich, I. S. Larionova, R. R. Sataev, V. Yu. Dolmatov and V. F. Pyaterikov, USSR Inventor’s Certificate 1819851, 1992. 8 E. S. Freeman and P. J. Carroll, Phys. Chem., 1958, 62, 394. 9 T. M. Gubarevich, I. S. Larionova and N. M. Kostyukova, Zh. Prikl. Khim., 1991, 66, 113 (Russ. J. Appl. Chem., 1991, 66, 65). 10 A. L. Vereshchagin, L. A. Petrova and P. M. Brylyakov, Sverkhtverdye Materialy, 1992, 1, 14 (in Russian). Received: 26th February 1999; Com. 99/1451

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Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Induced oxidative rearrangement of non-terminal alkynes by [fluoro(trifluoromethanesulfonyloxy) iodo]benzene to esters of 2-alkyl- and 2-arylalkanoic acids Namig Sh. Pirguliyev,a Valery K. Brel,*b Nikolai S. Zefirova,b and Peter J. Stangc a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation.Fax: +7 095 939 0290; e-mail: prnmsh@org.chem.msu.su b Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 095 913 2113; e-mail: brel@ipac.ac.ru c Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA. Fax: +1 801 581 8433 The oxidation of non-terminal acetylenes by [fluoro(trifluoromethanesulfonyloxy)iodo]benzene in methanol causes oxidative rearrangement to esters of 2-alkyl- and 2-arylalkanoic acids.Hypervalent iodine reagents react with alkynes to give various products depending upon the type of reagent, the structure of alkynes and the reaction conditions. Terminal alkynes react with [hydroxy(tosyloxy)iodo]benzene to yield alkynyl iodonium tosylates,1 which are important intermediates for the syntheses of alkynyl carboxylates,2 phosphates2 and triflates.3 Reactions of (perfluoroalkyl)phenyliodonium salts with terminal alkynes yield a mixture of substitution and addition products.4 Nonterminal alkynes are converted to a-diketones by oxidation with iodosobenzene in the presence of ruthenium,5 while terminal alkynes afford carboxylic acids.5 Oxidation of alkynyl ethers and alkynyl amines with PhIO in the presence of RuII catalysts yields a-ketoesters and a-ketoamides,6 respectively.Bis-trifluoroacetoxyiodobenzene (PIFA) reacts with non-terminal alkynes to give a-diketones,7 while terminal alkynes yield a-hydroxyketones. 7,8 The cleavage of alkynes to carboxylic acids has been accomplished using PIFA/C6H6/H2O under reflux conditions.9 Oxidative rearrangement of terminal and non-terminal alkynes by [hydroxy(tosyloxy)iodo]benzene affords carboxylic acid esters.10 Recently, a new approach was suggested for the one-pot generation of aryliodoso derivatives directly from iodoarenes.11 The iodonium triflate with the general formula [ArI+F–OTf] is assumed to result from the oxidation of iodoarenes upon treatment with xenon fluorotriflate.It was shown that the reactions of these reagents with terminal acetylenes are accompanied with anti-addition to afford (E)-[b-(trifyloxy)alkenyl]- (aryl)iodonium triflates in moderate to excellent yields.11 In a continuation of our investigation on hypervalent iodine chemistry, we now report the results of reaction of [fluoro- (trifluoromethanesulfonyloxy)iodo]benzene with non-terminal alkynes in methanol.It is interesting to note that this reaction is accompanied by oxidative rearrangement of non-terminal alkynes to esters of alkyl and arylalkanoic acids (Table 1). A great attention directs towards the synthesis of arylalkanoic acids due to their anti-inflammatory properties.10,12,13 A likely mechanism for these oxidative rearrangements entails the initial formation of 2-methoxy-1-alkenyl(phenyl)iodonium triflates A analogous to the production of (2-trifyloxy-1- alkenyl)iodonium salts from terminal alkynes with PhI+F–OTf in non-hydroxylic solvents.11 Michael addition followed by a 1,2-shift of the R group in B with dissociative reductive elimination of iodobenzene would ultimately afford 2a–g.† In summary, iodine(III)-induced oxidative rearrangement of non-terminal acetylenes by [fluoro(trifluoromethanesulfonyloxy) iodo]benzene offers an efficient procedure for the specific transformation of alkynes to alkyl- and arylalkanoic acids. This work was supported by FIRCA of NIH (grant no. 5RO-TW00437). XeF2 + HOTf FXeOTf [PhIF]+[TfO]– i ii iii iv – HF – Xe [PhIF]+[TfO]– + R R' R' R OMe O R' R OH O 1a–g 2a–g 3a–g Scheme 1 Reagents and conditions: i, CH2Cl2, –78 °C; ii, PhI, CH2Cl2; iii, MeOH; iv, aqueous NaOH, then 5% aqueous HCl.a R = Ph, R' = Me b R = Ph, R' = Et c R = R' = Ph d R = p-NO2C6H4, R' = Me e R = p-MeCOC6H4, R' = Me f R = R' = Et g R = Pr, R' = Me R R' [PhIF]+[TfO]– R C R' I Ph F OTf MeOH – HF R MeO I+Ph–OTf R' A MeOH MeO MeO R I+Ph–OTf R' R R' MeO MeO OTf B 1a–g R' R OMe O 2a–g Scheme 2 Table 1 Oxidative rearrangement of non-terminal acetylenes with [PhI+F–OTf] in methanol.Starting compound Reaction time/h Product Yield (%) Characteristic 1a 22 3a 52 nD 20 1.523114 1b 28 3b 42 mp 43–44 °C 1c 28 3c 47 mp 147 °C14 1d 28 3d 44 mp 89 °C14 1e 30 3e 53 mp 57 °C15 1f 25 3f 39 nD 20 1.412914 1g 25 3g 40 nD 20 1.414214Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) References 1 (a) F. M. Beringer and S. A. Galton, J. Org. Chem., 1965, 30, 1930; (b) G. F. Koser, L. Rebrovic and R. H. Wettach, J. Org. Chem., 1981, 46, 4324; (c) L. Rebrovic and G. F. Koser, J. Org. Chem., 1984, 49, 4700; (d) A. J. Margida and G. F. Koser, J. Org. Chem., 1984, 49, 4703. 2 P. J. Stang, M. Boehshar and J. Lin, J. Am. Chem. Soc., 1986, 108, 7832. 3 P. J. Stang, B.W. Surber, Z. C. Chen, K. A. Robert and A. G. Anderson, J. Am. Chem. Soc., 1987, 109, 228. 4 T. Umemoto, Y. Kuriu and O. Miyano, Tetrahedron Lett., 1982, 23, 3579. 5 P. Müller and J. Godoy, Helv. Chim. Acta, 1981, 64, 2531. 6 P. Müller and J. Godoy, Tetrahedron Lett., 1982, 23, 366.† Typical procedure. A solution of iodobenzene (1.3 mmol) in CH2Cl2 (5 ml) was added dropwise at –78 °C to a solution of FXeOTf (1.3 mmol)16 in dry CH2Cl2 (20 ml). The mixture was stirred for 0.5 h at –78 °C. Next, an appropriate alkyne (10 mmol) was added dropwise to a solution of [PhIF]+[TfO]– in CH2Cl2 at –78 °C. The mixture was allowed to warm to –30 °C, and the stirring was continued for 0.5–1 h.Then, the mixture was cooled to –78 °C, and methanol (15 ml) was added dropwise to the solution. After being warmed to room temperature over 3 h, the stirring was continued for 20–30 h. Next, the mixture was treated with a saturated NaHCO3 solution. Extraction with CH2Cl2 (3×15 ml) followed by drying (MgSO4) and concentration at a reduced pressure gave a mixture of ester 2a–g and iodobenzene.The ester was purified by column chromatography on silica gel using heptane–diethyl ether (6:1) as an eluent. Hydrolysis in a 2 M NaOH solution yielded corresponding carboxylic acids 3a–g in good yields. All known products were identified by the IR and 1H NMR spectral data (Table 1). 7 E. B. Merkushev, L. G. Karpitskaya and G. I. Novosel’tseva, Dokl. Akad.Nauk SSSR, 1979, 245, 607 (Chem. Abstr., 1979, 91, 39072d). 8 Y. Tamura, T. Yakura, J.-J. Haruta and Y. Kita, Tetrahedron Lett., 1985, 26, 3837. 9 R. M. Moriarty, R. Penmasta, A. K. Awasthi and I. Prakash, J. Org. Chem., 1988, 53, 6124. 10 R. M. Moriarty, R. K. Vaid, M. P. Duncan and B. K. Vaid, Tetrahedron Lett., 1987, 28, 2845. 11 T. M. Kasumov, N. Sh. Pirguliyev, V. K. Brel, Yu. K. Grishin, N. S. Zefirov and P. J. Stang, Tetrahedron, 1997, 53, 13139. 12 J. Rieu, A. Boucherle, H. Cousse and G. Mouzin, Tetrahedron Lett., 1986, 27, 4095. 13 T. Yamauchi, K. Hattori, K. Nakao and K. Tamaki, Synthesis, 1986, 1044. 14 Dictionary of Organic Compounds, ed. J. Buckingham, Chapman and Hall, New York, 1982. 15 C. Giordano, G. Gastaldi, F. Uggeri and F. Guzzoni, Synthesis, 1985, 436. 16 M. Wechwsberg, P. A. Bulliner, F. O. Sladky, R. Mews and N. Bartlett, Inorg. Chem., 1972, 11, 3063. Received: 2nd February 1999; Com. 99/1435

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC