Kinetic studies of the oxygen-atom transfer reactions between bis(diethyldithiocarbamato)dioxomolybdenum and triphenylphosphine

The kinetics of the oxygen-atom transfer reactions from bis(diethyldithiocarbamato)dioxomolybdenum [MoO₂(S₂CNEt₂)2] to triphenylphosphine (PPh₃) in several nonaqueous organic solvents were studied in detail by means of the stopped-flow technique at temperatures between 25 and 40°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 follow linear relationships vs the function of the refractive index (n² - 1)/(2n² + 1). In addition, it was also observed that the pre-exponential factor increases slightly with a decrease of (n² - 1)/(2n² + 1). Furthermore, two linear equations between the rate constant and the activation energy vs (n² - 1)/(2n² + 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 enters directly into the π* antibonding orbital, which makes the Mo=O bond break, was proposed.