I. S. Ignat’ev

Quantum-chemical study of the stereoelectronic structure of 1-fluorosilatrane, 1,1-difluoroquasisilatrane, 1,1,1-trifluorohyposilatrane, and cations formed thereof

Quantum-chemical study of the electronic structure and the equilibrium geometry of the molecules X4−nM(OCH2CH2)nNH3−n and cations X3−n[M(OCH2CH2)nNH3−n]+ (M = Si, Ge; X = F, H; n = 1–3) is performed by the B3LYP method using the cc-PVDZ basis set. It is shown that for X = F the strength of the coordination bond N→M increases with the number of the cycles (n), while for X = H, on the contrary, decreases, that is, the strength of the N→M bond increases with the total electronegativity of the substituents surrounding atom M. Effect of the number of the coordination cycles on the strength of the N→M bond in the cations is negligible. The obtained results agree with the experimental data on the structure and spectral properties of the studied compounds.

Structures and mutual transformations of isomers of germylium ions (CH3)H2Ge+ and (CH3)2HGe+ and their silicon analogs

The potential energy surfaces of the (CH3)nH3−nM+ ions, where n = 1, 2; M = Si, Ge, were scanned using the B3LYP method with 6–31G* and aug-cc-pVDZ basis sets. The major attention was given to isomeric species having the form of complexes of the HM+ and CH3M+ ions with hydrogen, methane, and ethane molecules. These species were characterized previously neither by experimental nor by theoretical methods. It was found that these species become more stable in going from Si to Ge; the complex [CH3Ge+CH4] is the second isomer in the energy after (CH3)2HGe+. However, the heights of the activation barriers to formation of these complexes from the most stable isomer, though decreasing in going from Si to Ge, remain relatively high and, what is particularly important, somewhat exceed the activation barrier to formation of the complex [H3Ge+·C2H4].

Reactions of silylium ions with nucleophiles

Transformation of the diethylsilylium cation Et2Si+H into ethyl-and dimethylsilylium ions EtSi+H2 and Me2Si+H in reactions with nucleophiles is induced by electron-donor compounds. Their activity increases in the order Bu2O < BuOH < (Me3Si)2O < C6H6 and is determined by the structure of the intermediate adduct and electron density distribution in it. Qualitative estimation shows that the affinity of the tritiated diethylsilylium cation Et2Si+T for a nucleophile increases in the order C6H6 < BuOH < Bu2O < (Me3Si)2O. The higher affinity of the Et2Si+H cation for hexamethyldisiloxane compared to dibutyl ether, at similar basicity of the nucleophiles, is attributable to the higher charge of the oxygen atom in (Me2Si)2O.

Synthesis of phenylsilocane tritium-labeled at the benzene ring

A strategy for synthesis of the 2-phenyl-2-hydro-1,3-oxa-6-aza-2-silacyclooctane doubly tritium-labeled (2,4- or 2,6-) at the benzene ring has been elaborated. The products are sources of the silyl cations having the atrane structure.

Radiochemical study of gas-phase reactions of diethylstannilium cations Et2SnT+ with oxygen-containing compounds: I. Interaction of diethylstannilium cations with methyl tert-butyl ether

Radiochemical method was applied to study the gas-phase interaction between the nucleogenic diethylstannyl cations Et2SnT+ and methyl tert-butyl ether. The possible reaction mechanisms are considered. Diethylstannylium cations are found to isomerize during the reaction to tertiary cation Me2EtSn+, as well as undergo a rearrangement accompanied by elimination of ethane rater than ethylene, in contrast to the cases of silicon and germilium analogs.

Interconversion of stannylium ions in the C4H11Sn+ system

B3LYP method with the LANL2DZ basis for tin and aug-cc-pVDZ basis for carbon and hydrogen were used to obtain the equilibrium geometry of the main (with a positive charge on the tin) isomers in the C4H11Sn+ system and the transition states at their interconversion. As in the case of silicon and germanium, the cations of lighter elements of the 14th group, the most stable isomer is shown to be the tertiary ion, however, the energy of its complexes with ethane and propane is higher only by several kJ mol−1. Nevertheless, the formation of these complexes from the tertiary ion requires overcoming a rather high barrier (293 and 272 kJ mol−1, respectively). The barrier for isomerization of the secondary ion in the ethane complex is somewhat lower (222 kJ mol−1), but still is significantly greater than the energy gained at the appearance of the nucleogenic ion. The most probable transformation pathways of the nucleogenic stannylium ions are the formation of complexes with ethylene, which requires overcoming barriers of 130 and 117 kJ mol−1 for the tertiary and secondary ions, respectively.

Isomerization of silicenium and germenium ions in the systems C4H11M+ (M = Si, Ge)

Equilibrium structures of the isomers and transition states of their interconversion in the system C4H11M+ (M = Si, Ge) have been obtained at theB3LYP level of theory using the cc-pVTZ basis set. The structures of these stationary points are close for Si and Ge; the most stable isomer in both systems is the tertiary cation (C2H5)(CH3)2M+, the second in energy is complex with ethylene [(CH3)2HM·C2H4]+. The secondary cation (C2H5)2HM+ is third in energy isomer, the height of the barrier of interconversion for these three cations being practically independent on M. However, for M = Ge a substantial decrease in the energy of isomeric forms corresponding to complexes with alkanes is observed. As a result, in the system C4H11Ge+ the fourth in energy is isomer [(C2H5)Ge·C2H6]+ rather than [(C2H5)H2Ge·C2H4]+ as for M = Si. Nevertheless, the height of the barriers for transition into these structures, although decreasing from M = Si to Ge, remain rather high, and the most favorable route of decomposition in both systems is the elimination of ethylene.

Synthesis and Structure of Trichlorogermane Aminate

Trichlorogermane triethylaminate [HGeCl3·NEt3] has been synthesized and its structure investigated using the methods of NMR and IR spectroscopy and quantum chemistry. Possible structures of complexes of triethylamine with trichlorogermane are considered. The presence of two minima on the potential energy surface is shown; the global minimum corresponds to the structure with proton transfer to the nitrogen atom, [Et3NH]+[GeCl3]–, while the local minimum lying by 25.8 kcal/mol above is characterized by the presence of very weak van-der-Waals interaction N···Ge. The comparison of the experimental and calculated chemical shifts of the proton is indicative of the formation of complex with proton transfer to the nitrogen atom in the liquid phase.

Generation of the atrane cations by nuclear-chemical method: Quantum-chemical study

Comparative analysis of equilibrium structures of cations [RM(OCH2CH2)2NCH3]+ (M = Si, Ge; R = F, Me, Ph) and the corresponding neutral compounds HRM(OCH2CH2)2NCH3 was performed based on quantum-chemical calculations. The possibility was analyzed for expanding nuclear-chemical method to generation of cations having the atrane structure. Quantum-chemical method was applied to estimate the heights of barriers to hydrolysis by the М–О bond in ocanes acting as the sources of the corresponding cations with the atrane structure.

Radiochemical study of gas-phase reactions of diethylstannyl cations Et2SnT+ with oxygen-containing compounds: II. Reaction of diethylstannyl cations with butanol

Gas-phase reaction of nucleogenic diethylstannyl cations Et2SnT+ with butan-1-ol has been studied by the radiochemcal method, and probable reaction mechanisms have been proposed. During the process diethylstannyl cations undergo isomerization into tertiary Me2EtSn+ cations and rearrangement with elimination of ethane. Thermochemical parameters of reactions of diethyl-substituted cations derived from Group 14 elements (Et2TM+; M = C, Si, Ge, Sn) with alcohols have been analyzed by the M06L aug-cc-pVDZ quantum chemical method.