Model reactions of molybdo-oxidase. Importance of water on the air oxidation of PPh3 by catalysis of [MoVIO2(Cys-OR)2](Cys-OR = S-deprotonated cysteine ester; R = Me, Et, Pri, or CH2Ph) in NN-dimethylformamide
Catalytic air oxidation of PPh3 using [MoVIO2(Cys-OR)2](Cys-OR = S-deprotonated cysteine ester; R = Me, Et, Pri, or CH2Ph) in NN-dimethylformamide was found to require the presence of water. 18-Oxygen of H218O has been shown to be involved in the oxidation of PPh3 both stoicheiometrically and catalytically. However, a large excess of water prevents the catalytic redox cycle. The results of e.s.r. and 1H n.m.r. spectra of the reduced species from [MoVIO2(Cys-OR)2] indicate that a mononuclear Mov complex [MoO(OH)(Cys-OR)2] is probably involved in the catalytic cycle, while [Mov2O3(Cys-OR)4] is not. An increase in the bulkiness of R increases the turnover numbers of the oxidation.