Reactions of Photochemically Generated Silylenes

Photochemically generated silylene species may react either with themselves to form poly silane polymers, or with a trapping agent added to intercept the species. The fate of the silylene and the structure of reaction products depend on the relative rates of these two processes, which may proceed simultaneously. 

As already described, hydrosilanes are one of the most suitable silylene trapping agents and are often used in photolysis. Thus, the photolysis of dodecamethylcyclohexasilane in diethylmethylsilane affords the insertion product in 46% yield, on the basis of the following stoichiometric equation (31). 

The photolysis of tetradecamethylhexasilane in dimethyldichlorosi-lane gives rise to unexpected results hexamethyldisilane, dichlorotetra-methyldisilane, dichlorohexamethyltrisilane, chloropentamethyldisilane, and 1-chloroheptamethyltrisilane are formed in the ratio of 1.0 1.6 2.6 2.0 1.3, respectively. 

This unusual feature of the photolysis in dimethyldichlorosilane indicates that a direct reaction of photochemically excited polysilanes with the chlorosilane to give monochloropolysilanes occurs in competition with the generation of dimethylsilylene (31). 

Internal olefins and cyclic olefins also react with methylphenylsilylene to give silyl-substituted olefins. Irradiation of 10 with a high-pressure mercury lamp in the presence of cis-2-butene in hexene yields 3-methylphenylsilyl-l-butene in 29% yield. Small amounts of the photoisomer 1-methyl- 

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