Phosphadioxirane: A peroxide from an ortho-substituted arylphosphine and singlet dioxygen

We prepared the primary adduct for the reaction of singlet dioxygen (O-1(2)) with an arylphosphine by using the sterically hindered arylphosphine tris(omethoxyphenyl) phosphine. The resulting phosphadioxirane has a dioxygen molecule triangularly bound to the phosphorus atom. Olefin trapping experiments show that the phosphadioxirane can undergo nonradical oxygen atom-transfer reactions. Under protic conditions, two different intermediates are formed during the reaction of singlet dioxygen with tris(o-methoxyphenyl) phosphine, namely, the corresponding hydroperoxy arylphosphine and a hydroxy phosphorane. Experiments with other arylphosphines possessing different electronic and steric properties demonstrate that the relative stability of the tris(o-methoxyphenyl) phosphadioxirane is due to both steric and electronic effects.