Photolysis of organopolysilanes. Photochemical formation and reactions of 1-trimethylsilyl-1-phenyl-1-silacyclopropene derivatives

The photolysis of tris(trimethylsilyl)phenylsilane (I) in the presence of 1-hexyne, 3,3-dimethyl-1-butyne, trimethylsilylacetylene, 3-hexyne, 1-trimethylsilylpropyne, 1,2-bis(trimethylsilyl)acetylene and 2,2,5,5-tetramethyl-3-hexyne afforded the respective silacyclopropenes. The silacyclopropenes produced from monosubstituted acetylenes underwent photochemical isomerization to give disilanylacetylene derivatives, via a 1,2-hydrogen shift in the silacyclopropene ring. Irradiation of I in the presence of 3-hexyne, 1-trimethylsilylpropyne or 2,2,5,5-tetramethyl-3-hexyne, gave the corresponding silacyclopropenes which could be isolated by preparative GLC. The silacyclopropene from 1,2-bis(trimethylsilyl)acetylene, however, readily underwent thermal rearrangement to give bis(trimethylsilyl)phenylsily] trimethylsilylacetylene via a 1,2-trimethylsilyl shift. This type of rearrangement was also found in the photochemical process.