KINETIC-STUDIES OF THE OXYGEN-ATOM TRANSFER-REACTIONS BETWEEN BIS(DIETHYLDITHIOCARBAMATO)DIOXOMOLYBDENUM AND TRIPHENYLPHOSPHINE

The kinetics of the oxygen-atom transfer reactions from bis(diethyldit hiocarbamato)dioxomolybdenum [MoO2(S2CNEt2)(2)] to triphenylphosphine (PPh3) in several nonaqueous organic solvents were studied in detail b y means of the stopped-flow technique at temperatures between 25 and 4 0 degrees C. The kinetic and activation parameter data for the oxygen- atom transfer reactions in several nonaqueous solutions were obtained. It was found that the rate constants and the activation energies foll ow, linear relationships vs the function of the refractive index (n(2) - 1)/(2n(2) - 1). In addition, it was also observed that the pre-expo nential factor increases slightly with a decrease of (n(2) - 1)/(2n(2) + 1). Furthermore, two linear equations between the rate constant and the activation energy vs (n(2) - 1)/(2n(2) + 1) with good correlation coefficients were obtained. A one-step mechanism which supposes that the electrons of the lone pair on the P atom of triphenylphosphine ent ers directly into the pi antibonding orbital, which makes the Mo=O bo nd break, was proposed. (C) 1997 Elsevier Science Ltd.