Mechanism and Unusual Fragmentation Selectivities of Aryltrialkylstannane Cation Radicals

Aryltrialkylstannane cation radicals were generated and characterized by nanosecond transient absorption spectroscopy. Kinetics show the fragmentations of the stannane cation radicals occur by a bimolecular, nucleophile-assisted mechanism (S(N)2). Consistent with this hypothesis, steric effects on both the nucleophile and the stannane cation radicals were observed. Steady-state, preparative photooxidation experiments show that aryltrimethylstannane cation radicals have an unusual preference for loss of aryl radicals over methyl radicals and that the selectivity for aryl vs methyl radical loss is dependent on the identity of the nucleophile. The preference for loss of aryl radicals is rationalized by a hypothesis based on Bent's rules.