Theoretical consideration on phosphorus–oxygen bond formation of sterically crowded triarylphosphines and their radical cations

The phosphorus–oxygen bond formation reactions often observed for the sterically crowded triarylphosphines and their radical cations were studied by DFT calculation. The oxidations of the trimethyl-, triphenyl-, and trimesityl-phosphines to the corresponding phosphine oxides with peroxides are shown to proceed through the S_N2 like transition states and the overall influence of the steric hindrance on the activation energy is limited. The reaction of the radical cation of tris(2,4,6-triisopropylphenyl)phosphine with oxygen to give the heterocyclic phosphonium cation is modeled by employing (2,6-diisopropylphenyl)diphenylphosphine and the comparison of the intermediates suggests highly exergonic nature of the reaction.