A. I. Chernyavskii

New cyclolinear permethyloligosilane-siloxanes

Abstract α , ω -Bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes have been synthesized by heterofunctional condensation of hydroxyheptamethylcyclotetrasiloxane with α , ω -dichloropermethyloligosilanes, Cl(Me 2 Si) n Cl ( n =1–4, or 6). The substances are characterized by mass spectrometry, 29 Si-NMR, IR and UV spectroscopy.

Synthesis of α,ω-dihalopermethyloligosilanes and silane-siloxane copolymers

Abstractα,ω-Dibromopermethyloligosilanes, Br(SiMe2)nBr (n=2–4, 6), were prepared by the reaction of dodecamethylcyclohexasilane with bromine. The reaction of (Me2Si)6 with MCl4 (M=Sn, Ti) proceeds with the cleavage of Si−Si- and Si−C-bonds with the formation of α,ω-dichloropermethyloligosilanes, Cl(SiMe2)nCl (n=2–4, 6), and chloro derivatives of cyclohexasilane, ClmSi6Me12−m (m=1, 2). Silane-siloxane copolymers of regular structure were obtained by heterofunctional copolycondensation of α,ω-dihalopermethyloligosilanes with 1,5-dihydroxyhexamethyltrisiloxane.

A new way of introducing metal oxide fragments into polysilane chains

When permethyl-α,ω-dichlorooligosilanes undergo heterofunctional condensation with metal acetates, the formation of a metallosiloxane fragment is the pretiominant process, whereas the formation of cyclosilane-siloxane resulting from the exchange of functional groups between the silicon and metal atoms is a side reaction. The scheme of these transformations is proposed.

Synthesis and mass spectrometric study of α,ω-bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes

Abstractα,ω-Bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes were synthesized by the reaction of dichlorodimethylsilane and 1,3-dichlorohexamethyltrisilane with hydroxyheptamethylcyclotetrasiloxane. The peculiarities of fragmentation of the compounds obtained by electron impact mass spectrometry are discussed.

The ESR study of the structure and reactivity of α-ketoradicals, derivatives of (CF3)3CC(O)C(O)CF3

The structure and reactivity of α-ketoradicals, derivatives of (CF3)3CC(O)C(O)CF3 (1), were studied by ESR spectroscopy. The photoreduction of α-diketone1 in a solution of cyclohexane in perfluorodipentyl ether results in the formation of radicals of two types, (CF3)3CC(2)(O(4))·C(3)(O(6)H)CF3 (1a) and (CF3)3C·C(OH)C(O)CF3 (1b) in a ∼40∶1 ratio. The degree of delocalization of the spin density in two conformers of radical1a was calculated by the MNDO/PM3 method in the UHF approximation. It was established that radicals1a and1b are capable of reversible dimerization. The rate constant of dimerization and the enthalpy of the radical—dimer equilibrium were measured for radical1a. A decrease in the rate of dimerization of radical1a upon addition of complexing solvents ((CF3)3COH andp-CF3C6H4CF3) was found. The influence of the solvents on the rate of dimerization was also detected for α-ketoradical (CF3)3CC(O)·C(OSiMe2Ph)CF3 (1c).

SYNTHESIS OF NEW CYCLOLINEAR PERMETHYLOLIGOSILANE-SILOXANES

Abstractα,ω-Bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes were synthesized for the first time by heterofunctional condensation of hydroxyheptamethylcyclotetrasiloxane with α,ω-dichloropermethyloligosilanes, Cl(Me2Si)nCl (n=2, 4, or 6). The compounds obtained were characterized by spectroscopic methods.

The reductive cocondensation of chlorotrimethylsilane and dichlorodimethylsilane

Linear and cyclic permethyloligosilanes were prepared by the Wurtz-type cocondensation of chlorotrimethylsilane and dichlorodimethylsilane in the presence of sodium metal or samarium iodide as reducing agents. The yields and composition of the reaction products depend on the cocondensation conditions.

Synthesis of α,ω-dichloropermethyloligosilanes by reactions of polydimethylsilane with metal chlorides

The reactions of high-molecular-weight polydimethylsilane with metal chlorides in variable oxidation states at high temperature in the absence of a solvent afford mixtures of α,ω-dichloropermethyloligosilanes Cl(Me2Si)mCl (m= 2—9). The influence of the reaction conditions (temperature, reaction time, and the reagent ratio) on the composition and yields of the reaction products was examined.

Unusual exchange of functional groups at the silicon and metal atoms

Reactions of α,ω-dichlorooligosilanes with metal hydroxides in the presence of pyridine results in the exchange of halogen and oxygen atoms and the formation of cyclic siloxyoligosilanes and pyridine complexes of metal halides. The metallosiloxane groups are not formed. A scheme for the transformations observed is proposed.

Some peculiarities of hydrosilylation of α,ω-divinyloligosilanes

The stability of Si-Si bonds in linear and cyclic permethyloligosilanes and in α,ω-divinyloligosilanes under conditions of hydrosilylation in the presence of the Speiers catalyst was studied. Polycarbosilanes containing silylene fragments in their backbone chains were prepared by the reaction of 1,4-bis(dimethylsilyl)benzene with α,ω-divinyloligosilanes. It was found that the structure of these polymers is disturbed due to the side reaction involving the cleavage of the Si-Si bond in vinyloligosilanes under the action of H2PtCl6.