Vad. V. Negrebetskii

Scheme of hydrolysis of five-coordinate chlorosilanes by X-ray diffraction data

Hydrolysis of monochelate five-coordinate chlorosilanes MeC(O)N(Me)CH2SiMe2Cl (Ia), L7CH2SiMe2Cl (Ib), L8CH2SiMe2Cl (Ic), PhtImCH2SiMe2Cl (Id), MeC(O)N(Me)CH2SiMePhCl (IIa), and Im5CH2SiMePhCl (IIe), containing a monoanionic C,O-chelating ligand LCH2 [L is an amide, n-membered lactam (Ln), imide (Imn), or phthalimide (PhtIm) residue]. The structures of the starting chlorides and their hydrolysis products were established by means of X-ray diffraction analysis. Based on experimental and published data, a general scheme of hydrolysis of mono-C,O-chelate chlorosilanes was suggested, including initial formation of silyloxonium chlorides III and subsequent formation of disiloxane dihydrochlorides IV.

Intra- and intermolecular coordination reactions in solution involving pentacoordinated fluorosilanes based on proline

NMR spectroscopy was used to study a series of C,O-monochelate N′-(fluorodimethyl-silylmethyl)-N′-methyl-N-(organosulfonyl)proline amides in the solid state and in solutions in chloroform, pyridine, and acetone. The structure of one of the complexes was established by X-ray crystallography. Quantum chemical calculations were performed to interpret the spectral data obtained. The molecular conformation observed in crystal was found to be retained in solutions. The coordination bonds of silicon atom with acetone and pyridine are very weak and cannot stabilize the acyclic form (without the Si-O coordination bond). The 29Si chemical shift was found to be directly dependent on the Si-O bond distance. The mutual influence of organosulfonyl group and chelate ring was described in terms of polarization effects.

Silicon-nitrogen bond cleavage in N-(dimethylimidosilylmethyl)imides and dimethyl(lactamomethyl)aminosilanes with BF3 etherate as an alternative route to N-(dimethylfluorosilylmethyl)imides and related compounds

N-(Dimethylfluorosilylmethyl)succinimide (2a) and N-(dimethylfluorosilylmethyl)phthalimide (2b) were synthesized by the Si—N bond cleavage in readily accessible N-(dimethylimidosilylmethyl)imides with BF3 etherate. Analogously, (O→Si)-chelated 1-(dimethylfluorosilylmethyl)-2-pyrrolidone was prepared from 1-(dimethylmorpholinosilylmethyl)-2-pyrrolidone. X-ray diffraction study demonstrated that the silicon atom in the crystals of 2b is pentacoordinated.

Modern Trends of Organic Chemistry in Russian Universities

This review is devoted to the scientific achievements of the departments of organic chemistry in higher schools of Russia within the past decade.

Some problems of the teaching of organic chemistry in universities of Russia

Original Russian Text

Trichloro- and methyldichlorogermyl monochelates and dibromo- and dichlorogermyl bischelates derived from N,N-disubstituted amides of 2-hydroxycarboxylic acids

The reactions of GeCl4, GeBr4, and MeGeCl3 with O-trimethylsilyl derivatives of N,N-disubstituted amides of 2-hydroxycarboxylic acids afforded pentacoordinate and hexacoordinate neutral (O,O)-mono- and (O,O)-bischelates. The reactions of glycolic acid derivatives with GeX4 produced bischelates X2Ge[OCH2C(O)NR2R3]27a,c,d (X = Cl, R2 = R3 = Me (a), (CH2)5 (c), (CH2CH2)2O (d)) and 8a (X = Br). By contrast, the reactions of lactic and mandelic acid derivatives with GeCl4 and MeGeCl3 gave monochelates Cl3Ge[OCH(R1)C(O)NR2R3] (S)-9a–c (R1 = Me) and Cl2MeGe[OCH(R1)C(O)NR2R3] 10a (R1 = H), (S)-11a,b (R1 = Me), and (S)-12a (R1 = Ph) (R2R3 = (CH2)4 (b)), respectively. According to the X-ray diffraction data, the Ge atom in bischelates 7c,d and 8a has a coordination number 6, and its coordination polyhedron can be described as a slightly distorted octahedron. In monochelates (S)-9a-c, 10a, (S)-11a,b, and (S)-12a, the Ge atom has a coordination number 5, and its coordination polyhedron can be described as a trigonal bipyramid with two halogen atoms or one halogen atom and one ethereal oxygen atom in equatorial positions and the halogen atom and the amide oxygen atom in the axial positions. The bonds in the axial positions are somewhat longer than the corresponding bonds in tetracoordinate Ge compounds.

Unexpected formation of a dimeric cation-anionic complex of hypercoordinated tin in the reaction of bis[(2-oxopyrrolidino)methyl]tin dichloride with AgBF4

A new cation-anionic complex of hypercoordinated tin, {[L2Sn(OH)]+ BF4−}2 (L is a bidentate (2-oxopyrrolidino)methyl C,O-chelating ligand), was obtained by the reaction of L2SnCl2 with AgBF4 and structurally characterized by X-ray diffraction analysis. In crystalline form, the BF4− anions are bound to the dications through O−H...F hydrogen bonds (the H−F distance is 1.78 Å). The octahedral coordination of the Sn atoms is strongly distorted because of a weak additional interaction with solvate molecules of dioxane (the Sn−O distance is 3.16 Å).

Structure of the Adduct of N-(α-Phenylethyl)acetamide with HCl in the Liquid, Solid, and Gas Phases

The structure of the adduct of N-(α-phenylethyl)acetamide with HCl in the liquid and solid phases was examined by elemental analysis, 1H and 13C NMR spectroscopy, and X-ray diffraction to show that the positive charge is localized on the nitrogen atom. The electronic structure of the adduct in the gas phase was studied by means of ab initio calculations at the 6-31G** level of theory. In the latter case, the positive charge is delocalized over the acetamide fragment of the molecule.

The hindered inversion of the seven-membered ring inN-(chlorodimethylgermylmethyl)- andN-(chlorodimethylstannylmethyl)hexahydroazepin-2-ones

The stereochemical flexibility ofN-(chlorodimethylgermylmethyl)- andN-(chlorodimethylstannylmethyl)hexahydroazepin-2-ones was studied by dynamic NMR spectroscopy. Protons of the NCH2M and MMe2 groups (M=Ge, Sn) were shown to be anisochronic at low temperatures (<−70°C). The free activation energy of the process resulting in chemical equivalence of the protons indicated was determined. The anisochronicity of signals observed is due to the restricted inversion of the seven-membered cycle.