The mercury-sensitized photolysis of pentamethyldisilane

Two primary processes were observed in the Hg-sensitized photolysis of Me(5)Si(2)H: (I) hydrogen abstraction from the Si-H bond with a quantum yield of phi (I) = 0.85, (V) Si-Si bond breaking with phi (V) = 0.04. The hydrogen atoms formed in (I) undergo an H atom abstraction reaction (k (3)), as well as substitution reactions at the Si centers resulting in the formation of dimethylsilane and trimethylsilyl radical (k(4)) or trimethylsilane and dimethylsilyl radical (k(5)). The following branching ratios have been determined: k(3)/k(3) + k(4) + k(5) = 0.87, k(4)/k(3) + k(4) + k(5) = 0.096, k(5)/k(3) + k(4) + k(5) = 0.034. The ratio of disproportionation (k (2)) to combination (k(1)) for the pentamethyldisilyl radical has been determined with MeOH as the scavenger for 1-methyl-1-trimethylsilylsilene, 0.046 less than or equal to k(2)/k(1) less than or equal to 0.071. A mechanism with pertinent rate constants has been proposed which accounts for the results.