Svetlana V. Kirpichenko

1,3-Thiasilacyclopentane and 1,3- and 1,4-thiasilacyclohexane derivatives

Abstract The reaction of dimethyl(chloromethyl)alkenylsilanes, ClCH2Me2Si(CH2)n-CHCH2 (n = 0, 1) with alcoholic KSH solution or thiourea followed by hydrolysis in the latter case leads to the corresponding dimethyl(mercaptomethyl)alkenylsilanes which are unstable compounds readily undergoing polymerization or cyclization. Intramolecular ring closure of dimethyl(mercaptomethyl)allylsilane affords 3,3,5-trimethyl-1-thia-3-silacyclopentane or 3,3-dimethyl-1-thia-3-silacyclohexane, depending on the reaction conditions. Photochemical addition of gaseous H2S to the above dimethyl(chloromethyl)alkenylsilanes yields 3,3-dimethyl-1-thia-3-silacyclopentane and 3,3-dimethyl-1-thia-3-silacyclohexane, respectively. H2S adds to dimethyldivinylsilane upon UV-irradiation to give a mixture of isomeric 2,3,3-trimethyl-1-thia-3-silacyclopentane and 4,4-dimethyl-1-thia-4-silacyclohexane. Thiasilacyclopentane and thiasilacyclohexane derivatives are readily converted to the corresponding sulfonium salts by CH3I. In contrast, 3,3-dimethyl-1-thia-3-silacyclobutane undergoes ring opening to form sulphonium dimethyl(iodomethyl)silylmethiodide, [ICH2Me2SiCH2 S + (CH3)2]I−.

1,3-Dimethyl-3-silapiperidine: Synthesis, Molecular Structure, and Conformational Analysis by Gas-Phase Electron Diffraction, Low Temperature NMR, IR and Raman Spectroscopy, and Quantum Chemical Calculations

The first Si-H-containing azasilaheterocycle, 1,3-dimethyl-3-silapiperidine 1, was synthesized, and its molecular structure and conformational properties were studied by gas-phase electron diffraction (GED), low temperature NMR, IR and Raman spectroscopy and quantum chemical calculations. The compound exists as a mixture of two conformers possessing the chair conformation with the equatorial NMe group and differing by axial or equatorial position of the SiMe group. In the gas phase, the SiMe(ax) conformer predominates (GED: ax/eq = 65(7):35(7)%, ΔG = 0.36(18) kcal/mol; IR: ax/eq = 62(5):38(5)%, ΔG = 0.16(7) kcal/mol). In solution, at 143 K the SiMe(eq) conformer predominates in the frozen equilibrium (NMR: ax/eq = 31.5(1.5):68.5(1.5)%, ΔG = -0.22(2) kcal/mol). Thermodynamic parameters of the ring inversion are determined (ΔG(‡) = 8.9-9.0 kcal/mol, ΔH(‡) = 9.6 kcal/mol, ΔS(‡) = 2.1 eu). High-level quantum chemical calculations (MP2, G2, CCSD(T)) nicely reproduce the experimental geometry and the predominance of the axial conformer in the gas phase.

The synthesis and some properties of 1-thia-3-silacyclobutanes and 1-thia-3-silacyclopentane

3,3-Dimethyl-1-thia-3-silacyclobutane has been obtained by the reaction of Me2Si(CH2Cl)2 with potassium hydrosulfide in abs. ethanol. Intramolecular hydrosilylation of isomeric vinylthioethyldiethylsilanes, HEt2SiXSCHCH2 (X = CH(CH3) or CH2CH2) proceeds selectivity as α-addition to afford cyclic compounds, Et2SiCH(CH3)SCHCH3 and Et2SiCH2CH2SCHCH3, respectively. This ring closure reaction is catalyzed by (Ph3P)3RhCl. The endocyclic SiC bond of 3,3-dimethyl-1-thia-3-silacyclobutane undergoes cleavage upon treatment with ethanolic KOH leading to Me2(EtO)SiCH2SCH3 and O(SiMe2CH2SCH3)2. The reaction of 3,3-dimethyl-1-thia-3-silacyclobutane with ethanolic HgCl2 involves ring opening and formation of a complex, O[SiMe2CH2S(HgCl2)CH2HgCl]2.

Regioselectivity of inter- and intramolecular hydrosilylation of the vinyloxy group

Abstract The addition of dialkylethoxysilanes to divinyl ether in the presence of chloroplatinic acid occurs at the terminal carbon atom whereas the regioselect

Aminomercuration-demercuration of dimethyl(chloroalkyl)alkenylsilanes as a route to azasilacycloalkanes

Abstract 3,3-Dimethyl-1-phenyl-1-aza-3-silacyclopentane and 3,3,5-trimethyl-1-phenyl-1-aza-3-silacyclopentane were obtained by the reaction of dimethyl(chloromethyl)vinylsilane and dimethyl(chloromethyl)allylsilane with aniline in THF in the presence of mercury acetate followed by reduction with sodium borohydride. Aminomercuration-demercuration of dimethyl(3-chloropropyl)vinylsilane and dimethyl(3-chloropropyl)allylsilane results in the corresponding 3-chloropropylphenylaminoalkyl derivatives. Dimethyl(3-chloropropyl)(2-phenylaminopropyl)-silane undergoes cyclization under the same reaction conditions giving 2,4,4-trimethyl-1-phenyl-1-aza-4-silacycloheptane in low yield. Competitive nucleophilic substitution of the chloroalkyl group of initial silanes by aniline affords dimethyl(phenylaminoalkyl)alkenylsilanes.

Structure and conformational properties of 1,3,3-trimethyl-1,3-azasilinane: gas electron diffraction, dynamic NMR, and theoretical study.

Structure and the conformational properties of 1,3,3-trimethyl-1,3-azasilinane have been studied. According to gas electron diffraction (GED), the molecule exists in a slightly distorted chair conformation with the N-Me group in equatorial position. High-level quantum chemical calculations excellently reproduce the experimental geometry. Employing variable temperature (1)H and (13)C NMR spectroscopy down to 103 K, the conformational equilibrium could be frozen and the barrier to ring inversion determined.

Electrophilic Cyclization of Dimethyl(ω-phenylaminoalkyl)alkenylsilanes

Unsaturated organosilicon amines [CH2 = CH(CH2)n]Me2Si[(CH2)mNHPh] at the action of Hg(OAc)2 in THF solution transform to corresponding heterocycles. Regioselectivity of this intramolecular electrophilic heterocyclization is defined by the position of double bond relatively to the silicon atom. This is caused by β-effect of the silyl group.

Conformational behavior of 3,3-dimethyl-3-silathiane 1-oxide and its diastereomeric 2-methyl derivatives

The conformational behavior of 3,3-dimethyl-3-silathiane 1-oxide 3 and its trans-4 and cis-4 2-methyl derivatives has been studied by 1H and 13C NMR. The equatorial conformer 3-eq for 3 and the diequatorial isomer trans-4-eq for trans-4 predominate (>95%) in CDCl3 solution. In contrast, the cis-4-ax conformer is the more preferred form of cis-4. The conformational free energy (ΔG°) in the equilibrium cis-4-ax ↔ cis-4-eq was determined to be about +0.01 and +0.52 kcal mol−1 at 26 and −120°C, respectively. The Gibbs free energy of activation (ΔG ‡) for the inversion cis-4-ax → cis-4-eq was estimated to be 8.1 kcal mol−1 at −100°C.

The sila-Pummerer rearrangement of 3,3-dimethyl-3-silathiane S-oxide

Abstract The thermal conversion of sulfoxide 1 into the O-silylated cyclic O,S-acetal ( 2 ) is the first example of the sila-Pummerer rearrangement of cyclic organosilicon sulfoxides leading to ring expansion. The kinetics of the rearrangement are studied and thermodynamic parameters are determined. The results are in compliance with mechanism involving a pentacoordinated silicon atom.

A DFT Study of the Structure and Relative Stability of 1,3-Thiasilacycloalkanes and Their S-Functional Derivatives

A series of 1,3-thiasilacycloalkanes and their S-oxides, S,S-dioxides, and sulfonium salts were studied by the DFT (B3LYP/6-31G*) method. In six-membered sulfoxides, the oxygen atom preferentially occupies the axial position, whereas in the corresponding sulfonium salts the S-alkyl group occupies the equatorial position. The calculation results explain the lower hydrolytic stability of the five-membered rings compared to the six-membered analogs and the lower stability of sulfoxides compared to sulfones.