Cumene Oxidation bycis-[RuIV(bpy)2(py)(O)]2+, Revisited

Abstract

cis-[Ru^IV(bpy)₂(py)(O)]²⁺ oxidizes cumene (2-phenylpropane) in acetonitrile solution primarily to cumyl alcohol (2-phenyl-2-propanol), α-methylstyrene, and acetophenone. Contrary to a prior report, the rate of the reaction is not accelerated by added nucleophiles. There is thus no evidence for the hydride transfer mechanism originally proposed. Instead, the results are consistent with a mechanism of initial hydrogen atom transfer from cumene to the ruthenium oxo group. This is indicated by the correlation of rate with C−H bond strength and by the various products observed. The formation of acetophenone, with one carbon less than cumene, is suggested to occur via a multistep pathway involving decarbonylation of the acyl radical from 2-phenylpropanal. An alternative mechanism involving β-scission of cumyloxyl radical is deemed unlikely because of the difficulty of generating alkoxyl radicals under anaerobic conditions and the lack of rearranged products in the oxidation of triphenylmethane by cis-[Ru^IV(bpy)₂(py)(O)]²⁺.