Oxidations of ER3 (E = P, As, or Sb) by hydrogen peroxide. Methylrhenium trioxide as catalyst

Article abstract of DOI:10.1021/ja00106a030

Catalytic and noncatalytic conversions of tertiary phosphines to their oxides by hydrogen peroxide have been investigated. The catalyst is methylrhenium trioxide, CH₃ReO₃. The kinetics were investigated in acetonitrile-water (1:1 by volume) at 25°C. Stepwise interactions between CH₃ReO₃ and H₂O₂ form CH₃Re(η²-O₂)(O)₂(OI₂). A, and CH₃Re(η²-O₂)₂(O)(OH₂), B. In CH₃CN-H₂O (1:1 v/v) the equilibrium constants are K₁ = 13 ± 2 L mol^-1 and K₂ = 136 ± 28 L mol^-1 at pH 1.0 and 25°C. The forward and reverse rate constants for the formation of A in this medium are k₁ = 32.5 ± 0.3 L mol^-1 s^-1 and k_-1 - 3.0 ± 0.2 s^-1. Systematic changes in the substituents on phosphorus were made to vary the nucleophilicity of the phosphine and its cone angles; the kinetic effects are discernible, although they lie in a narrow range. Triphenylarsine and triphenylstibine were also studied, and their rates are within a factor of 2 of that for PPh₃. The rhenium peroxides A and B show a small difference in reactivity. The bimolecular reactions between A and most of the phosphines have rate constants of the order 10⁵ L mol^-1 s^-1. The kinetic data support a mechanism that allows nucleophilic attack of the substrate at the rhenium peroxides.