OXIDATION OF TERTIARY PHOSPHINES BY MOLECULAR-OXYGEN CATALYZED BY RU(III)-EDTA COMPLEX - ELECTRONIC EFFECT OF PHOSPHINE SUBSTITUENT ON THE OXYGEN-ATOM TRANSFER-REACTION - X-RAY CRYSTAL-STRUCTURE OF THE COMPLEX[RU(III)(EDTA-H)PPH3]

The catalytic oxidation of tertiary phosphines, PR3 (R = p-fluoropheny l, phenyl and cyclohexyl), by molecular oxygen to the corresponding ph osphine oxide, (PR3O), catalysed by Ru(III)(EDTA-H)(H2O) is reported a s a function of catalyst, substrate (PR3) and molecular oxygen concent ration at a constant pH 3.0 in water-dioxan (50% v/v) medium. The reac tivity of PR3 towards catalytic oxidation by molecular oxygen decrease s in the order tris(p-fluorophenyl)phosphine > triphenylphosphine > tr is-(cyclohexyl)-phosphine. A reverse reactivity order was observed in the case of stoichiometric oxidation of PR3 by [O=Ru(V)(EDTA)]-. The p roposed mixed-ligand complex Ru(III)-EDTA-PR3 intermediate in the cata lytic oxidation of PR3 with molecular oxygen has been isolated and its structure solved by single-crystal X-ray diffraction. The experimenta l results are discussed in terms of the sigma-basic and pi-acidic char acter of the phosphine substrates in the homolytic bond cleavage of O- O bonds of the mu-peroxo intermediate and oxygen atom transfer to the substrate. The bond dissociation energy for O-O bond cleavage is compu ted by the kinetic data obtained for oxygen atom transfer from the oxo complex [O=Ru(V)(EDTA)]-.