PHOTOLYSIS OF 1,3-DIMESITYLHEXAMETHYLTRISILANE AND 1,2-DIMESITYLTETRAMETHYLDISILANE

Irradiation at 254 nm of solutions containing 1,3-dimesitylhexamethyltrisilane, (MesMe2Si)2SiMe2, leads to the formation of 1-mesityl-1-methylsilene, MesMeSi=CH2, in addition to the anticipated dimethylsilylene, Me2Si:. The coproduct of dimethylsilylene extrusion, 1,2-dimesityltetramethyldisilane, (MesMe2Si)2, is itself photolabile, producing high yields of mesityldimethylsilane, MesMe2SiH, and 1-mesityl-1-methylsilene. Trapping experiments indicate that both molecular elimination and silicon-silicon bond homolysis followed by disproportionation lead to the silene, whose dimerization yields cis- and trans-1,3-dimesityl-1,3-dimethyl-1,3-disilacyclobutanes. Both the cis- and trans-1,3-disilacyclobutanes were structurally characterized by X-ray crystallography. The silene can be trapped by a variety of reagents in high yield.