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

Abstract

Catalytic air oxidation of PPh₃ using [Mo^VIO₂(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 [Mo^VIO₂(Cys-OR)₂] indicate that a mononuclear Mo^v complex [MoO(OH)(Cys-OR)₂] is probably involved in the catalytic cycle, while [Mo^v₂O₃(Cys-OR)₄] is not. An increase in the bulkiness of R increases the turnover numbers of the oxidation.