Photoinduced ionic and free-radical reactions of some organosilicon iodides

Abstract

U.v. irradiation (medium-pressure Hg lamp) induces reaction of TsiSiPh₂l (1a)[Tsi =(Me₃Si)₃C] with methanol to give both the unrearranged and rearranged methoxides TsiSiPh₂OMe and (Me₃Si)₂C(SiPh₂Me)(SiMe₂OMe); in the presence of LiNO₃some (Me₃Si)₂C(SiPh₂Me)(SiMe₂ONO₂) is also formed. The analogous solvolysis in PhNH₂gives the rearranged anilide (Me₃Si)₂C(SiPh₂Me)(SiMe₂NHPh). These reactions are thought to involve the intermediate formation of a silico-cation. On the other hand the exclusive formation of the unrearranged chloride TsiSiPh₂Cl upon irradiation in CCl₄appears to involve a free-radical process. The photoinduced rearrangement of (1a) to (Me₃Si)₂C(SiPh₂Me)(SiMe₂l) in n-C₅H₁₂, n-C₆H₁₄, Et₂O, and PhOMe may involve a cationic intermediate, but a free radical rearrangement cannot be ruled out; the subsequent formation of a disilaindane derivative (6) in PhOMe probably involves cyclization of a free radical. The iodide TsiSiPhMel also undergoes rearrangement to (Me₃Si)₂C(SiPhMe₂)(SiMe₂l) upon irradiation in n-C₅H₁₂. The methanolysis of TsiSiMe₂l is also photo-catalysed, though less effectively than that of (1a).