OXYGEN-TRANSFER FROM ORGANOELEMENT OXIDES TO CARBON-MONOXIDE CATALYZED BY TRANSITION-METAL CARBONYLS

Solutions of Rh(PR3)(2)(CO)Cl (R = Me, Ph) are found to catalyze the r apid transfer of oxygen from amine oxides or organoselenium oxides to carbon monoxide; however, the rhodium complexes undergo no reaction wi th the oxides in the absence of added CO. Kinetic studies indicate tha t the catalytically active species is the CO-substituted complex Rh(PR 3)(CO)(2)Cl, although it is not present in any observable concentratio n under the conditions of the reaction. Ir(PPh3)(2)(CO)(2)Cl also acts as an efficient catalyst precursor for the same oxygen transfer react ions, although like the rhodium complex it undergoes little or no dire ct reaction with the oxides. The catalytically active species is again found to be the product of substitution of a ligand (in this case, ch loride) by CO: [Ir(PPh3)(2)(CO)(3)](+) in either ion-paired or unpaire d states. Among substrates with weak E-O bonds (E = N, Se), reactivity correlates with substrate basicity in accord with a transition state having the character of a nucleophilic attack (at carbonyl carbon). Ox ides with much stronger E-O bonds, even the highly basic triphenylarsi ne oxide, are much less reactive; the transition state in this case ap parently involves significant E-O bond breaking and is presumably not well modeled as a simple nucleophilic attack. Pt(Ph3As)(CO)Cl-2 was fo und to act asa good catalyst precursor for deoxygenation of arsine oxi de, but this system is apparently very complex and the nature of the-c atalytically active species has not been elucidated.