Reprinted from Organometallics, 15, 2554-2561 (1996).
© American Chemical Society, 1996.
Nicholas P. Toltl and William J. Leigh*
Contribution from the Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1
Abstract: Direct irradiation of 1,1,1-trialkyl-2,2,2-triphenyldisilanes (R3Si-SiPh3; SiR3 = SiMe3, SiEt3, SiMe2Bu) in hydrocarbon solution in the presence of acetone leads to the formation of 1,2-siloxetanes and silyl ethers, from reaction of the ketone with the 1,3,5-(1-sila)hexatriene resulting from photochemical [1,3]-trialkylsilyl migration into one of the aromatic rings of the disilane. The two products have been identified on the basis of spectroscopic data. The siloxetane is the major product in each case, and its yield relative to silyl ether increases with increasing steric bulk of the -SiR3 group. Photolysis of the three disilanes in the presence of di-tert-butyl ketone affords the corresponding silyl ether in nearly quantitative yield, to the exclusion of siloxetane. 1,1,1-Triisopropyl-2,2,2-triphenyldisilane yields an intractable mixture upon photolysis in the presence of acetone under the above conditions but shows clear evidence for the formation of the corresponding siloxetane and silyl ether (in addition to chlorotriphenyl- and chlorotriisopropylsilane) when photolyzed in the presence of acetone and chloroform. Nanosecond laser flash photolysis techniques have been employed to determine absolute rate constants for the reaction of acetone, pinacolone, and di-tert-butyl ketone with the silatriene intermediates. These experiments also show that the triisopropyl derivative undergoes Si-Si bond homolysis to yield silyl radicals in competition with rearrangement to silatriene. The yield of silyl radicals is substantially higher in acetonitrile solution than in cyclohexane solution.