二[氧合-二(3-二茂铁基丙烯酸二正丁基锡(Ⅳ))]配合物的合成及谱学表征

由FcCH=CHCO2H和(n Bu)2SnO反应合成了{[(FcCH=CHCO2)Sn(n Bu)2]2O}2(A)新配合物[其中Fc=(η5 C5H5)Fe(η5 C5H4)].经红外光谱和核磁共振(1H、13C、119Sn)谱学研究, 确定其组成和结构.提出 [(RCOOSnR′2)2O]2类化合物中一一指认与内环锡、外环锡键连的两类烷基R′中各个碳峰的原则.     

硼氢及客体二十面体簇合物的结构和稳定性

在(n=0、－1、－2、－3、－4)簇合物几何构型及稳定性研究的基础上,进一步对它的各种内含式和外 接式二十面体簇合物(X@B12H122－和XB12H122－,X=H0/＋、Li0/＋、He、Ne、Be0/2＋、Na＋、Mg2＋)进行了优化和 计 算.发现在内含式结构X@ B12H122－中,当X=Li＋、Be2＋、Mg2＋时,构型较稳定;在外接式结构中, XB12H122－(C3v)结构比XB12H122－(C2v)的结构稳定.通过IRC计算,确定XB12H122－(C2v)是X与B12H122－作用生成产物XB12H122－(C3v)的一种过渡态.     

Selective cyclopalladation of R3P=NCH2Aryl iminophosphoranes. Experimental and computational study

The orientation of the orthopalladation of iminophosphoranes R3P=NCH2Aryl (R=Ph, Aryl=Ph (1a), C6H(4)-2-Br (1b), C6H4-Me-2 (1e), C6H3-(Me)(2)-2,5 (1f); R=p-tolyl, Aryl=Ph (1c); R=m-tolyl, Aryl=Ph (1d); R3P=MePh2P, and Aryl=Ph (1g)) has been studied. 1a reacts with Pd(OAc)2 (OAc=acetate) giving endo-[Pd(micro-Cl){C,N-C6H4(PPh2=NCH2Ph)-2}]2 (3a), while exo-[Pd(micro-Br){C,N-C6H4(CH2N=PPh3)-2}]2 (3b) could only be obtained by the oxidative addition of 1b to Pd2(dba)3. The endo form of the metalated ligand is favored kinetically and thermodynamically, as shown by the conversion of exo-[Pd(micro-OAc){C,N-C6H4(CH2N=PPh3)-2}]2 (2b) into endo-[Pd(micro-OAc){C,N-C6H4(PPh2=NCH2Ph)-2}]2 (2a) in refluxing toluene. The orientation of the reaction is not affected by the introduction of electron-releasing substituents at the Ph rings of the PR3 (1c and 1d) or the benzyl units (1e and 1f), and endo complexes (3c-3f) were obtained in all cases. The palladation of MePh2P=NCH2Ph (1g) can be regioselectively oriented as a function of the solvent. The exo isomer [Pd(micro-Cl){C6H4(CH2N=PPh2Me)-2}]2 (exo-3g) is obtained in refluxing CH2Cl2, while endo-[Pd(micro-Cl){C,N-C6H4(PPh(Me)=NCH2Ph)-2}]2 (endo-3g) can be isolated as a single isomer in refluxing toluene. In this case, the exo metalation is kinetically favored while an endo process occurs under thermodynamic control, as shown through the rearrangement of [Pd(micro-OAc){C6H4(CH2N=PPh2Me)-2}]2 (exo-2g) into [Pd(micro-OAc){C,N-C6H4(P(Ph)Me=NCH2Ph)-2}]2 (endo-2g) in refluxing toluene. The preference for the endo palladation of 1a and the kinetic versus thermodynamic control in 1g has been explained through DFT studies of the reaction mechanism.     

A computational study of the Diels-Alder reaction of ethyl-S-lactyl acrylate and cyclopentadiene. Origins of stereoselectivity

The eight diastereoisomeric transition structures of the Diels-Alder addition of ethyl-S-lactyl acrylate and cyclopentadiene have been investigated in the gas phase and in solution by HF, MP2, and density functional theory (B3LYP and B3PW91) methods with the 6-31G(d,p) basis set. At all levels of theory used, the s-cis transition structures are more stable than the s-trans ones. The contribution of the s-trans transition structures increases in solution and, although still small, has to be taken in consideration for correct prediction of stereoselectivity. Diastereofacial selectivity is interpreted in terms of electrostatic (weak hydrogen bonding) C=O...H(C) interactions between the carbonyl group(s) of the dienophile and cyclopentadiene in the energetically favored transition structures. Endo/exo reaction selectivity is attributed to positive orbital interactions between the diene and the acrylate carbonyl oxygen in the endo s-cis transition structures. Ab initio methods reproduce well the experimentally observed trends in both endo/exo and diastereofacial selectivity. Density functional calculations in the gas phase correctly reproduce the observed trends in diastereofacial selectivity but single-point MP2 calculations are necessary to reproduce the experimental trend in endo/exo selectivity.     

C-甲基硝酮与丙烯腈1,3-偶极环加成反应从头算研究

用从头算方法在MP2 / 6 31G(d)水平上研究了C 甲基硝酮与丙烯腈 1,3 偶极环加成反应 ,该反应可生成endo 4,exo 4,endo 5 ,exo 5四种不同的产物 ,反应势垒分别为 8.35、17.2 3、-0 .18和 4.88kJ/mol。在C 甲基硝酮与丙烯腈接近的过程中 ,首先生成 3个不同的氢键复合物 ,相对能量为 -4 7.8、-4 6 .6和 -33 .7kJ/mol。由这 3个不同的氢键复合物导致了 4个不同的过渡态而形成 4个不同的产物     

Origins of stereoselectivity in the Diels-Alder addition of chiral hydroxyalkyl vinyl ketones to cyclopentadiene: a quantitative computational study

Modest basis set level MP2/6-31G(d,p) calculations on the Diels-Alder addition of S-1-alkyl-1-hydroxy-but-3-en-2-ones (1-hydroxy-1-alkyl methyl vinyl ketones) to cyclopentadiene correctly reproduce the trends in known experimental endo/exo and diastereoface selectivity. B3LYP theoretical results at the same or significantly higher basis set level, on the other hand, do not satisfactorily model observed endo/exo selectivities and are thus unsuitable for quantitative studies. The same is valid also with regard to subtle effects originating from, for example, conformational distributions of reactants. The latter shortcomings are not alleviated by the fact that observed diastereoface selectivities are well-reproduced by DFT calculations. Quantitative computational studies of large cycloaddition systems would require higher basis sets and better account for electron correlation than MP2, such as, for example, CCSD. Presently, however, with 30 or more non-hydrogen atoms, these computations are hardly feasible. We present quantitatively correct stereochemical predictions using a hybrid layered ONIOM computational approach, including the chiral carbon atom and the intramolecular hydrogen bond into a higher level, MP2/6-311G(d,p) or CCSD/6-311G(d,p), layer. Significant computational economy is achieved by taking account of surrounding bulky (alkyl) residues at 6-31G(d) in a low HF theoretical level layer. We conclude that theoretical calculations based on explicit correlated MO treatment of the reaction site are sufficiently reliable for the prediction of both endo/exo and diastereoface selectivity of Diels-Alder addition reactions. This is in line with the understanding of endo/exo selectivity originating from dynamic electron correlation effects of interacting pi fragments and diastereofacial selectivity originating from steric interactions of fragments outside of the Diels-Alder reaction site.     

Regioselective functionalization of iminophosphoranes through Pd-mediated C-H bond activation: C-C and C-X bond formation

The orthopalladation of iminophosphoranes [R(3)P=N-C(10)H(7)-1] (R(3) = Ph(3) 1, p-Tol(3) 2, PhMe(2) 3, Ph(2)Me 4, N-C(10)H(7)-1 = 1-naphthyl) has been studied. It occurs regioselectively at the aryl ring bonded to the P atom in 1 and 2, giving endo-[Pd(μ-Cl)(C(6)H(4)-(PPh(2=N-1-C(10)H(7))-2)-κ-C,N](2) (5) or endo-[Pd(μ-Cl)(C(6)H(3)-(P(p-Tol)(2)=N-C(10)H(7)-1)-2-Me-5)-κ-C,N](2) (6), while in 3 the 1-naphthyl group is metallated instead, giving exo-[Pd(μ-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-κ-C,N](2) (7). In the case of 4, orthopalladation at room temperature affords the kinetic exo isomer [Pd(μ-Cl)(C(10)H(6)-(N=PPh(2)Me)-8)-κ-C,N](2) (11exo), while a mixture of 11exo and the thermodynamic endo isomer [Pd(μ-Cl)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-κ-C,N](2) (11endo) is obtained in refluxing toluene. The heating in toluene of the acetate bridge dimer [Pd(μ-OAc)(C(10)H(6)-(N=PPh(2)Me)-8)-κ-C,N](2) (13exo) promotes the facile transformation of the exo isomer into the endo isomer [Pd(μ-OAc)(C(6)H(4)-(PPhMe=N-C(10)H(7)-1)-2)-κ-C,N](2) (13endo), confirming that the exo isomers are formed under kinetic control. Reactions of the orthometallated complexes have led to functionalized molecules. The stoichiometric reactions of the orthometallated complexes [Pd(μ-Cl)(C(10)H(6)-(N=PPhMe(2))-8)-κ-C,N](2) (7), [Pd(μ-Cl)(C(6)H(4)-(PPh(2)[=NPh)-2)](2) (17) and [Pd(μ-Cl)(C(6)H(3)-(C(O)N=PPh(3))-2-OMe-4)](2) (18) with I(2) or with CO results in the synthesis of the ortho-halogenated compounds [PhMe(2)P=N-C(10)H(6)-I-8] (19), [I-C(6)H(4)-(PPh(2)=NPh)-2] (21) and [Ph(3)P=NC(O)C(6)H(3)-I-2-OMe-5] (23) or the heterocycles [C(10)H(6)-(N=PPhMe(2))-1-(C(O))-8]Cl (20), [C(6)H(5)-(N=PPh(2)-C(6)H(4)-C(O)-2]ClO(4) (22) and [C(6)H(3)-(C(O)-1,2-N-PPh(3))-OMe-4]Cl (24).     

Radical ring expansion reactions of methylenecyclopropane derivatives: a theoretical study

The evolution of the primary radicals from 1-(3-bromopropyl)-2-ethyl-3-methylenecyclopropane, 1-(3-bromopropyl)-1-trimethylsilyl-2-methylenecyclopropane, 1-(3-bromobutyl)-2-ethyl-3-methylenecyclopropane, and 1-(3-bromobutyl)-1-trimethylsilyl-2-methylenecyclopropane was theoretically studied at the ROMP2/6-311++G(d,p)//UB3LYP/6-31G(d,p) theory level taking into account the effect of solvent through a PCM-UAHF model. For the propyl-substituted radicals, the attack of the radical center on the double bond takes place most favorably in an exo fashion. The subsequent ring expansions yield the product corresponding to the rupture of the endo C-C bond as the most favorable one in accordance with the experimental results. In the case of 1-(3-bromobutyl)-2-ethyl-3-methylenecyclopropane, the Gibbs energy barriers for the endo and exo attacks are the same, and the subsequent reversible evolution yields the product corresponding to the rupture of the exo C-C bond as the most favorable one through thermodynamic control in agreement with experiment. Finally, for 1-(3-bromobutyl)-1-trimethylsilyl-2-methylenecyclopropane, our calculations predict that the endo attack is 0.8 kcal/mol more favorable than the exo one. In the subsequent reversible ring expansion, the product corresponding to the rupture of the endo C-C bond is kinetically the most favored one in reasonable agreement with the experimental observations.     

endo/exo isomerism in norcarane and 2-norcaranol hydrotrioxides (ROOOH)

Ozonation of norcarane (1) yielded endo and exo norcarane hydrotrioxides (2a, 2b), as characterized by (1)H and (13)C NMR spectroscopy. Further ozonation of the primary decomposition products of these hydrotrioxides, i.e., 2-norcaranols (3), produced the corresponding isomeric 2-norcaranol hydrotrioxides (4a, 4b), and hydrogen trioxide (HOOOH).     

exo-selective asymmetric Diels-Alder reaction catalyzed by diamine salts as organocatalysts

[reaction: see text] A novel binaphthyl-based diamine (R)-2 was designed and synthesized. A protonic acid-(R)-2 salt catalyst has the advantage of exhibiting unprecedented high exo selectivity in the asymmetric Diels-Alder reaction of alpha,beta-unsaturated aldehydes. For instance, the reaction between cinnamaldehyde and cyclopentadiene in the presence of 12 mol % of binaphthyl-based diamine (R)-2 and 10 mol % of p-TsOH.H(2)O in alpha,alpha,alpha-trifluorotoluene at -20 degrees C gave the corresponding exo cycloadduct with 92% ee as a major diastereomer (exo/endo = 13/1).     

Analysis of a cycloheptenone derivative: an experimental and theoretical approach

A detailed analysis with total assignment of (1)H and (13)C NMR spectral data for a cycloheptenone derivative, a key intermediate for the synthesis of perhydroazulene terpenoids, is related. These assignments are based on 1D (1)H and (13)C NMR and on 2D NMR techniques including gCOSY, gHSQC, gHMBC, J-resolved and NOEDIF experiments. The unequivocal assignments were supported by theoretical chemical shifts and scalar coupling constant calculations at GIAO B3LYP/cc-pVDZ level from optimized structures at the same level of theory.     

CpRu((R)-Binop-F)(H2O)][SbF6], a new fluxional chiral Lewis acid catalyst: synthesis, dynamic nmr, asymmetric catalysis, and theoretical studies

The C(2)-symmetric electron-poor ligand (R)-BINOP-F (4) was prepared by reaction of (R)-BINOL with bis(pentafluorophenyl)-phosphorus bromide in the presence of triethylamine. The iodo complex [CpRu((R)-BINOP-F)(I)] ((R)-6) was obtained by substitution of two carbonyl ligands by (R)-4 in the in situ-prepared [CpRu(CO)(2)H] complex followed by reaction with iodoform. Complex 6 was reacted with [Ag(SbF(6))] in acetone to yield [CpRu((R)-BINOP-F)(acetone)][SbF(6)] ((R)-7). X-ray structures were obtained for both (R)-6 and (R)-7. The chiral one-point binding Lewis acid [CpRu((R)-BINOP-F)][SbF(6)] derived from either (R)-7 or the corresponding aquo complex (R)-8 activates methacrolein and catalyzes the Diels-Alder reaction with cyclopentadiene to give the [4 + 2] cycloadduct with an exo/endo ratio of 99:1 and an ee of 92% of the exo product. Addition occurs predominantly to the methacrolein C(alpha)-Re face. In solution, water in (R)-8 exchanges readily. Moreover, a second exchange process renders the diastereotopic BINOP-F phosphorus atoms equivalent. These processes were studied by the application of variable-temperature (1)H, (31)P, and (17)O NMR spectroscopy, variable-pressure (31)P and(17)O NMR spectroscopy, and, using a simpler model complex, density functional theory (DFT) calculations. The results point to a dissociative mechanism of the aquo ligand and a pendular motion of the BINOP-F ligand. NMR experiments show an energy barrier of 50.7 kJ mol(-1) (12.2 kcal mol(-1)) for the inversion of the pseudo-chirality at the ruthenium center.     

A NMR and theoretical study of the aggregates between alkyllithium and chiral lithium amides: control of the topology through a single asymmetric center

The complexes between methyllithium and chiral 3-aminopyrrolidine (3-AP) lithium amides bearing a second asymmetric center on their lateral amino group were studied using multinuclear ((1)H, (6)Li, (13)C, (15)N) low-temperature NMR spectroscopies in tetrahydrofuran-d(8). The results indicate that lithium chelation forces the pyrrolidine ring of the 3-AP to adopt a norbornyl-like conformation and that robust 1:1 noncovalent complexes between methyllithium and 3-AP lithium amides form in the medium. A set of (1)H-(1)H and (1)H-(6)Li NMR cross-coupling correlations shows that the binding of methyllithium can take place along the "exo" or the "endo" face of this puckered structure, depending on the relative configuration of the lateral chiral group. This aggregation step renders the nitrogen of the 3-amino group chiral, the "exo" and "endo" topologies corresponding to the (S) and (R) configurations, respectively, of this atom. Density functional theory calculations show that the "exo" and "endo" arrangements are, for both diastereomers, almost isoenergetic even when solvent is taken into account. This result suggests that the formation of the mixed aggregates is under strict kinetic control. A relationship between the topology of these complexes and the sense of induction in the enantioselective alkylation of aromatic aldehydes by alkyllithiums is proposed.     

Azabrendanes. III. Synthesis of stereoisomeric exo‐ and endo‐5‐acylaminomethyl‐exo‐2,3‐epoxybicyclo[2.2.1]heptanes and their reduction by lithium aluminum hydride

A number of stereoisomeric N‐[aryl(alkyl, cycloalkyl)carbonyl]‐exo(endo)‐5‐aminomethylbicyclo[2.2.1]hept‐2‐enes have been synthesized from bicyclo[2.2.1]hept‐2‐en‐exo(endo)‐5‐carbonitrile via reduction of the latter by lithium aluminum hydride and subsequent reactions of the resulting amines with aryl(alkyl, cycloalkyl)carbonyl chlorides and anhydrides. The direction of reaction of amides with peroxy acids does not depend on orientation of substituents in the bicyclic fragment: that is, for both exo‐ and endo‐isomers the epoxidations are completed by the formation of N‐[aryl(alkyl, cycloalkyl)carbonyl]‐exo(endo)‐5‐aminomethyl‐exo‐2,3‐epoxybicyclo[2.2.1] heptanes. The reduction of stereoisomeric epoxides by lithium aluminium hydride proceeds in different directions; that is, isomers with an exo‐oriented amido group form the substituted exo‐5‐alkylaminomethyl‐exo‐2,3‐epoxybicyclo[2.2.1]heptanes and the reactions of epoxides of endo‐amides are accompanied by intramolecular cyclization and completed by the formation of N‐[aryl(alkyl, cycloalkyl)]‐exo‐2‐hydroxy‐4‐azatricyclo[4.2.1.0^3,7]nonanes. The structures and stereochemical homogenity of the products have been confirmed by the analysis of ¹H and ¹³C NMR spectra, correlation spectroscopy, and nuclear Overhauser enhancement spectroscopy experiments. We discuss the behavior of epoxides and provide an analysis of the coefficients of the atomic orbitals in the molecular orbital–linear combination of atomic orbitals equation (AM1 method). © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:119–130, 2001     

Group 14 Metal Terminal Phosphides: Correlating Structure with |J(MP)|

A series of heavier group 14 element, terminal phosphide complexes, M(BDI)(PR(2)) (M = Ge, Sn, Pb; BDI = CH{(CH(3))CN-2,6-iPr(2)C(6)H(3)}(2); R = Ph, Cy, SiMe(3)) have been synthesized. Two different conformations (endo and exo) are observed in the solid-state; the complexes with an endo conformation have a planar coordination geometry at phosphorus (M = Ge, Sn; R = SiMe(3)) whereas the complexes possessing an exo conformation have a pyramidal geometry at phosphorus. Solution-state NMR studies reveal through-space scalar coupling between the tin and the isopropyl groups on the N-aryl moiety of the BDI ligand, with endo and exo exhibiting different J(SnC) values. The magnitudes of the tin-phosphorus and lead-phosphorus coupling constants, |J(SnP)| and |J(PbP)|, differ significantly depending upon the hybridization of the phosphorus atom. For Sn(BDI)(P{SiMe(3)}(2)), |J(SnP)| is the largest reported in the literature, surpassing values attributed to compounds with tin-phosphorus multiple-bonds. Low temperature NMR studies of Pb(BDI)(P{SiMe(3)}(2)) show two species with vastly different |J(PbP)| values, interpreted as belonging to the endo and exo conformations, with sp(2)- and sp(3)-hybridized phosphorus, respectively.     

Toward direct determination of conformations of protein building units from multidimensional NMR experiments. V. NMR chemical shielding analysis of N-formyl-serinamide,a model for polar side-chain containing peptides

Knowledge of chemical shift-structure relationships could greatly facilitate the NMR chemical shift assignment and structure refinement processes that occur during peptide/protein structure determination via NMR spectroscopy. To determine whether such correlations exist for polar side chain containing amino acid residues the serine dipeptide model, For-L-Ser-NH(2), was studied. Using the GIAO-RHF/6-31+G(d) and GIAO-RHF/TZ2P levels of theory the NMR chemical shifts of all hydrogen ((1)H(N), (1)H(alpha), (1)H(beta1), (1)H(beta2)), carbon ((13)C(alpha), (13)C(beta), (13)C') and nitrogen ((15)N) atoms have been computed for all 44 stable conformers of For-L-Ser-NH(2). An attempt was made to establish correlation between chemical shift of each nucleus and the major conformational variables (omega(0), phi, psi, omega(1), chi,(1) and chi(2)). At both levels of theory a linear correlation can be observed between (1)H(alpha)/phi, (13)C(alpha)/phi, and (13)C(alpha)/psi. These results indicate that the backbone and side-chain structures of For-L-Ser-NH(2) have a strong influence on its chemical shifts.     

13C and1H NMR spectra and structure of 2-aryl-1,3-dibenzoyl-1,3-diazabicyclo[3.3.1]nonanes

Conclusion ¹³C and¹H NMR spectroscopy was used to determine the structures of 2-aryl-1,3-dibenzoyl-1, 3-diazabicyclo[3.3.1]nonanes and 2-aryl-1-benzyl-3-benzoyl-1,3-diazabicyclo[3.3.1]nonane. These compounds were found to exist predominantly in the boat-chair conformation (boat for the diaza ring), while the 2-aryl substituents occupy the exo or endo position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1023–1028, May, 1988.     

1,3‐Dipolar Cycloaddition Reactions Leading to the Synthesis of New 2,3,5‐Triaryl‐4H,2,3,3a,5,6,6a‐hexahydropyrrolo[3,4‐d]isoxazole‐4,6‐diones

Cycloaddition of C,N‐diphenylnitrones 1 to N‐aryl maleimides 2 afforded two diastereomeric isoxazolidines with high selectivity. The structure and steric configuration of the adducts have been assigned on the basis of ¹H NMR, ¹H NMR COSY, ¹³C NMR and IR spectroscopy. The π–π stacking interactions between maleimide's and nitrone's aromatic rings during the 1,3‐dipolar cycloaddition were assumed to control the exo–endo selectivity of the reaction. Thus, the exo–endo ratio depends upon the position of the substituent present on the C‐phenyl ring of the C,N‐diphenylnitrones.     

Stereoselectivity in Diels-Alder reactions of diene-substituted N-alkoxycarbonyl-1,2-dihydropyridines

Diene substituent effects on the regiochemical and stereochemical outcomes of uncatalyzed Diels-Alder reactions of N-alkoxycarbonyl-1,2-dihydropyridines with both styrene and methyl vinyl ketone (MVK) were studied. Alkyl substitution on the diene in all cases examined resulted in a kinetic preference for 7-endo isomers (7-phenyl 51-96% exo and 7-acetyl 54-96% exo). For both dienophiles, the highest stereoselectivities (>or=89% endo) were observed with 5-methyl or 6-methyl substituents in the dihydropyridine. Theoretical calculations of the energies of gas phase endo and exo transition states at the RHF/3-21G(*) predict that total entropy, DeltaStotal, considerations favor endo cycloadducts for both dienophiles with DHP, while total energy considerations, DeltaEo, favor endo cycloadducts for styrene and exo cycloadducts for MVK. At this level, favored endo-phenyl isomers are correctly predicted for styrene reactions, but the calculation of 7-acetyl exo or endo isomer dominance is diene-substituent-dependent for MVK reactions. The preference for endo addition of MVK to the parent, 5-methyl, and 6-methyl-DHPs was successfully predicted by calculations at the B3LYP/6-31G* theory level.     

13C and1H NMR spectra and stereoconfiguration of 1,4-adducts of the Diels-Alder reaction of furan with methyl acrylate and maleic anhydride

¹³C and¹H NMR spectra were taken for the 1,4-adducts of furan with methyl acrylate and maleic anhydride. The¹³C chemical shifts are characteristic: these values for C¹, C³, and C⁶ (adducts (I) and (II)) and C¹, C⁴ C², C³, C⁵, and C⁶ (adducts (III) and (IV)) depend on the orientation of the substituent at C² in the case of methyl acrylate and at C² and C³ in the case of maleic anhydride and may be used for the assignment of the adducts to the endo and exo isomers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1669–1671, July, 1990.