Oxidation of tertiary phosphines by molecular oxygen catalysed by RuIII-EDTA complex. Electronic effect of phosphine substituent on the oxygen atom transfer reaction; X-ray crystal structure of the complex [RuIII(EDTA-H)PPh3]

Abstract The catalytic oxidation of tertiary phosphines, PR 3 (R = p -fluorophenyl, phenyl and cyclohexyl), by molecular oxygen to the corresponding phosphine oxide, (PR 3 O), catalysed by Ru III (EDTA-H)(H 2 O) is reported as a function of catalyst, substrate (PR 3 ) and molecular oxygen concentration at a constant pH 3.0 in water-dioxan (50% v/v) medium. The reactivity of PR 3 towards catalytic oxidation by molecular oxygen decreases in the order tris( p -fluorophenyl)phosphine triphenylphosphine tris-(cyclohexyl)-phosphine. A reverse reactivity order was observed in the case of stoichiometric oxidation of PR 3 by [ORu V (EDTA)] − . The proposed mixed-ligand complex Ru III -EDTA-PR 3 intermediate in the catalytic oxidation of PR 3 with molecular oxygen has been isolated and its structure solved by single-crystal X-ray diffraction. The experimental results are discussed in terms of the σ-basic and π-acidic character of the phosphine substrates in the homolytic bond cleavage of OO bonds of the μ-peroxo intermediate and oxygen atom transfer to the substrate. The bond dissociation energy for OO bond cleavage is computed by the kinetic data obtained for oxygen atom transfer from the oxo complex [ORu V (EDTA)] − .