Synthetic, electrochemical and kinetic studies of phosphinites and their rhodium(I) complexes

[摘要] English: Organophosphorus ligands of the type, C6H5XPPh2, where X = O, S and NH, meta- and para-Ph2POC6H4OPPh2, were synthesised by the reaction between chlorophenylphosphine and the desired phenyl substituent in the presence of a base. The rhodium(I) complexess, [Rh(acac)CO(C6H4XPPh2)] where X = O, S and NH, as well as [(Rh(acac)CO(Ph2POC6H4-m-OPPh2)] and [(Rh(acac)CO(Ph2POC6H4-p-OPPh2)], were obtained by treating [Rh(acac)(CO)2] with the appropriate organophosphorus ligands.Kinetic results for the oxidative addition of methyl iodide to the rhodium(I) complexes of the type, [Rh(acac)CO(C6H4XPPh2)] where X = O, S and NH, revealed that the reaction exhibited only the oxidative addition. The reaction was found to be first order dependent on the concentration of the methyl iodide. The large negative activation entropy vales that were obtained, suggested an associative mechanism and no observable solvent pathway was found. It was found that as the Pauling electronegativity of O, S and N, increased, the first order rate constant of the oxidative addition decreased.The cyclic voltammetry of the organophosphorus ligands, C6H5XPPh2 where X = S and NH, meta- and para-Ph2POC6H4OPPh2, was found to be chemically and electrochemically irreversible. Only one oxidation and one reduction peak was observed and the oxidation peak was assigned to the one-electron oxidation of the free electron-pair on the phosphorous moiety, while the reduction peak was assigned to the reduction of the radical cation back to the neutral form.The rhodium complexes to which the phosphorus ligand was bound, showed two oxidation peaks of which the first one, O1, was assigned to the rhodium metal center and the second, O2, to the phosphorus moiety. Similar to the ligands system, the rhodium complex system is both chemically and electrochemically irreversible. The reduction peaks (R1) and (R2) assigned reduction of the Rh(III) back to Rh(I) in a two electron process and the second reduction peak (R2), which is the reduction of the radical cation of the organophosphorus ligand back to the neutral form (with the free electron-pair on the phosphorous moiety), respectively.

[发布机构] University of the Free State