C. Lorber et al., KINETICS OF OXYGEN-ATOM TRANSFER-REACTIONS INVOLVING MOLYBDENUM DITHIOLENE COMPLEXES, Journal of the Chemical Society. Dalton transactions, (21), 1997, pp. 3997-4003
Oxo transfer reactions from [MoO2(mnt)(2)](2-) [mnt(2-) = 2,3-disulfan
ylmaleonitrile dianion (1,2-dicyanoethylene-dithiolate)] to the abiolo
gical oxygen acceptors PPh3-xEtx (x = 0-3) have been studied spectroph
otometrically in acetonitrile. The pseudo-first-order rate constants d
epend linearly on the concentration of the oxo accepters. The sequence
of reactivity is PEt3 > PEt2Ph > PEtPh2 > PPh3, reflecting the basici
ties of the phosphines, while the steric influence of the substituents
on the phosphorus atom appears to be of minor importance. The activat
ion entropies for the reaction with PEt3 and PPh3 are negative. These
observations are in agreement with the proposal that in the intermedia
te the entering phosphine binds to the molybdenum complex through the
oxygen ligand. Oxidation of HSO3- by [MoO2(mnt)(2)](2-) has also been
studied in acetonitrile and in acetonitrile-water mixtures. The reacti
on exhibits Michaelis-Menten behaviour, In CH3CN-H2O, the rate of the
reaction increases as the water concentration decreases; the reacting
species appears to be a product from the reaction of the molybdenum st
arting complex with water.