PHOTOINDUCED ELECTRON-TRANSFER OXYGENATION OF 1,2-DISILETENE

Photo-induced electron transfer oxygenation of 3-phenyl-1,1,2,2-tetramesityl-1,2-disilet-3-ene (1) in acetonitrile-methylene chloride afforded the corresponding 1,2-dioxa-3,6-disilin (2) in moderate yield as a dioxygen insertion product into a silicon-silicon sigma-bond together with 1-oxa-2,5-disilolene (3). The results are reasonably accounted for by an electron transfer from disiletene 1 to the excited singlet state of the sensitizer to form a radical ion pair followed by addition of oxygen. Interestingly, a remarkable solvent effect was observed in the product ratio of dioxadisilin 2 and oxadisilolene 3 as a monooxygenated product. The solvent acetonitrile, acting as a nucleophile, participates for predominant formation of 2. Meanwhile, in the absence of acetonitrile, 3 was afforded as a major product. The conceivable mechanism is proposed.