Yuri I. Baukov

Synthesis and crystal structure of enantiomeric N-(dimethylfluorosilylmethyl) and N-(dimethylchlorosilylmethyl)-[N-(S)-1-phenylethyl)] acetamides

Abstract Synthesis of the first optically active compounds containing asymmetric carbon and pentacoordinated silicon has been carried out. The enantiomeric (O-Si)-chelate N-(dimethylhalogenosilylmethyl) acetamides, MeC(O)N(CH(Ph)Me)CH2SiMe2 X (X = F, Cl), obtained are the model compounds in studies of the stereodynamic processes at the trigonal-bipyramidal silicon atom and asymmetric induction. An X-ray structural investigation confirmed a 3 + 2 pentacoordination of the Si atom in the title compounds and an axial arrangement of the oxygen and halogen atoms. The geometrical parameters of hypervalent moieties are in good agreement with relations established earlier.

Reactions of silamorpholinones and acylsilamorpholines with electrophilic reagents. X-ray structure of products including a pentacoordinated silicon compound

Reactions of 2-sila-5-morpholinones, 4-acyl-2-silamorpholines and 4-acyl-2,6-disilamorpholines with electrophilic reagents generally lead to the opening of the sila- or disilacycle by cleavage of the Si–O bond with subsequent rearrangement to form five-membered chelate derivatives where the amide oxygen atoms coordinate with the silicon to form pentacoordinate silicon species. Multinuclear NMR spectroscopy and X-ray diffraction studies were used for structural investigation of the products. 4-Acyl-2,6-disilamorpholines initially form adducts with strong acids where the amide oxygen is protonated by the acid as demonstrated by X-ray crystallography.

Modelling nucleophilic substitution at silicon using solution 19F-NMR chemical shift, 1JSiF and 2JCF coupling constant data of pentacoordinate silicon compounds. Correlation with other magnetic nuclei and X-ray structures

Abstract Solution 1 J SiF and 2 J CF NMR coupling constant and 19 F-NMR chemical shift data have been analysed in a series of pentacoordinate silyl monofluoride complexes used to model nucleophilic substitution at silicon. Patterns in the data reveal strong correlations between both coupling constants and 19 F-NMR chemical shifts and the degree of substitution displayed by each. Excellent correlation is obtained between the new data and our previous 13 C- and 29 Si-NMR studies to further confirm the validity of the NMR technique for structural correlation in solution. By pooling the X-ray crystal structures of a large number of compounds of this class from both our own results and the literature we are able to provide a possible explanation for some of the trends in the NMR data we observe in solution.

Cationic complexes of silicon and germanium with (O,S)-chelate ligands

Synthesis and X-ray diffraction study of cationic bischelates MeSi(SCH(2)CONMe(2))(2)(+)Cl(-) and MeGe(SCH(2)CONMe(2))(2)(+)Br(-) are reported. According to X-ray data, the Si and Ge atoms in these compounds have distorted TBP environments with two coordinating oxygen atoms in axial positions.

Stereochemical non-rigidity of N-(dimethylhalogenosilylmethyl)-N-(1-phenylethyl) acetamides in solutions

Abstract The structure and dynamic behavior of (O-Si)-chelate N -(dimethylhalogenosilyl)methyl acetamides of the type MeC(O)N(CH(Ph)Me)CH 2 SiMe 2 X, where X = F, Cl, Br with the OSiC 3 X coordination set, were studied by multinuclear ( 1 H, 13 C, 17 O, 29 Si) and dynamic 1 H NMR spectroscopy. Ligand permutation at silicon was detected. The observed influence of the solvent, nucleofugacity of the X substituent and the external nucleophile on the calculated values of the free energies of activation testify to the dissociative and/or associative mechanisms of the process, but including the stages in which the regular (pseudo-rotation or ‘turnstile’) mechanism takes place. At lower temperatures (up to −90°C) the 1 H, 13 C, 29 Si NMR spectra of N -(dimethylchlorosilyl)methyl acetamide contain the signals of two species of unequal intensity. This effect was explained by an equilibrium between monomers containing the intramolecular O → Si bond and dimers with a hexacoordinate silicon and the bridging chlorine atoms.

Intermolecular and intramolecular coordination interactions in solutions of N-(dimethylchlorosilylmethyl) acetamides

Abstract The coordinate structure of N-methyl- and N-phenyl-N-(dimethylchlorosilylmethyl) acetamide in solutions is investigated by multinuclear 1H, 13C, 17O, and 29Si NMR spectroscopy. At low temperatures (up to −90°C), two pentacoordinated silicon species are detected for the first time as an example of compounds including the coordinative OSiC3Cl unit. At higher temperatures their fast (on the NMR time scale) interconversions are observed. On the basis of concentration, solvent and temperature dependence we assume that one species contains the intramolecular coordination O → Si bond, while the other includes the intermolecular coordination O → Si bond.

Six- and seven-membered 1-oxa-4-aza-2-silacyclanes as possible correctors of adaptational mechanisms.

The biological activity of eight 1-oxa-4-aza-2-silacyclanes with the OSiCH2N fragment including 6-membered 2-sila-5-morpholinones (1–3) and 4-acyl-2-silamorpholines (4–6)and previously unknown 7-membered derivatives of salicylic acid (7, 8) was studied. Compounds 1 and 3–6 show the certain antihypoxic action. Compounds 2 (40 mg/kg), 4 (20 mg/kg), 6 (40 mg/kg), 7 (20 mg/kg) and 8 (40 mg/kg) reduce the physical serviceability of intact animals. Compound 1 (20 mg/kg) influences the physical serviceability in a moderate-positive way on the background of chlorophos-poisoning. Compounds 5–8 displayed protective properties against chlorophos-poisoning at the LD50 dose and compounds 2, 4, 5, 7 at the LD100 dose. Influence of compounds 1 and 2 on the emotional-research behavior of mice was studied.

Proton catalysis of nucleophilic substitution at pentacoordinate silicon

Addition of acid to the pentacoordinate fluorosilane 8, leads to enhanced exchange of fluorine and loss of diastereotopicity of the silicon methyl groups. A DNMR study of the H-1-NMR spectra suggests a dissociative mechanism involving protonation of the fluorine leaving group. Variable temperature studies suggest that at lower temperatures the tetracoordinate form is favoured

Stereochemical rearrangements of dibromides of hexacoordinated germanium containing amidomethyl and lactamomethyl chelate ligands

For the first time a slow (on the NMR time scale) dynamic exchange between two diastereomers of hexacoordinated dibromogermanes containing two amidomethyl and lactamomethyl C,O-chelate ligands has been observed at room temperature in solution. The influence of temperature and solvent on the ratio of diastereomers was studied. At higher temperatures only one set of signals of the products were detected in the NMR spectra. Based on the dynamic NMR and quantum-chemical calculations (ab initio FR 3-21G), as well as on the structures determined for these compounds in the solid state, a cis-configuration of monodentate ligands was proposed for one of the diastereomers and an all-trans-configuration for the other. At low temperatures interconversion of enantiomers in the cis-diastereomer was observed. In the case of bis[(N-methylacetamido)methyl]dibromogermane the activation and thermodynamic parameters of enantiomerization (DeltaG(298)(#) 12.0+/-0.1 kcal mol(-1), DeltaH(#) 10.7+/-0.3 kcal mol(-1), DeltaS(#) -4.6+/-2.5 cal mol(-1) K-1) and diastereomeric exchange OcCtBrcreversible arrowOtCtBrt (DeltaG(298)(#), 15.0+/-0.1 kcal mol(-1); DeltaH(#) 0.1+/-0.8 kcal mol(-1); DeltaS(#) -50.0+/-5.8 cal mol(-1) K-1; DeltaG(298)degrees -0.2+/-0.1 kcal mol(-1); DeltaHdegrees -0.8+/-0.8 kcal mol(-1); DeltaSdegrees -2.6+/-1.0 cal mol(-1) K-1) were determined

Chlorido­bis[(2-oxoazocan-1-yl)methyl]­germanium(IV) trifluoro­methane­sulfonate

In the title compound, [Ge(C(8)H(14)NO)(2)Cl]CF(3)SO(3), which is the first complex containing an eight-membered lactam (enantholactam) as ligand, the coordination polyhedron of the Ge(IV) atom is intermediate between trigonal-bipyramidal and square-pyramidal. Quantum chemical calculations of the crystal structure indicate the absence of additional coordination bonding between the Ge(IV) atom and the trifluoromethanesulfonate anion.