Dialkyl dichlorosilanes

Silicon reacts with alkyl halides at high temperature to yield dialkyl dichlorosilanes. 

The polymerizations of hexyl- and propylmethyldichlorosilane were performed as before (11c) in the presence and absence 15-crown-5. The cyclic tetrasilane was polymerized by heating under vacuum. The tetracyclosilanes used were isolated from the products of the reaction of the dialkyl-dichlorosilanes with sodium in the presence of 15-crown-5. This was near 35% of the final product, and contained up to 10% of the pentacyclosilane. 

Sonochemical homopolymerization of dichlorosilanes in the presence of sodium is successful at ambient temperatures in nonpolar aromatic solvents (toluene or xylenes) only for monomers with a-aryl substituents. Dialky 1-dichlorosilanes do not react with dispersed sodium under these conditions, but they can be copolymerized with phenylmethyldichlorosilane. Copolymers with a 30-45% content of dialkylsilanes were formed from equimolar mixtures of the corresponding comonomers. Copolymerization might indicate anionic intermediates. A chloroterminated chain end in the polymerization of phenylmethyldichlorosilane can participate in a two-electron-transfer process with sodium (or rather two subsequent steps separated by a low-energy barrier). The resulting silyl anion can react with both dichlorosilanes. The presence of a phenyl group in either a or P position in chloroterminated polysilane allows reductive coupling, in contrast to peralkyl species, which do not allow the reaction. Therefore, dialkyl monomers can copolymerize, but they cannot homopolymerize under sonochemical conditions. 

Pentavalent silicon adducts (78,79) can be isolated from the reaction of dialkyl- or diaryl-dichlorosilanes with (1) (R = Et, i-Pr R = Me), whereas when Me3SiI is reacted with (1), ionic imidazolium salts are formed (77). Unfortunately, no information regarding the structure of these compounds is available. A crystalline carbene-silylene adduct 1,2-C6H4[N(R)]2C-Si[N(R)]2C6H4-l,2 (80, R = CH2-t-Bu) has... 

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