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Phosphadioxirane: A Peroxide from an Ortho-Substituted Arylphosphine and Singlet Dioxygen

We prepared the primary adduct for the reaction of singlet dioxygen (1O2) with an arylphosphine by using the sterically hindered arylphosphine tris(o-methoxyphenyl)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.