Electron transfer-oxygen transfer oxygenation of sulfides catalyzed by the H5PV2Mo10O40 polyoxometalate. 
The oxygenation of sulfides to the corresponding sulfoxides catalyzed by H(5)PV(2)Mo(10)O(40) and other acidic vanadomolybdates has been shown to proceed by a low-temperature electron transfer-oxygen transfer (ET-OT) mechanism.  First, a sulfide reacts with H(5)PV(2)Mo(10)O(40) to yield a cation radical-reduced polyoxometalate ion pair, R(2)(+*),H(5)PV(IV)V(V)Mo(10)O(40), that was identified by UV-vis spectroscopy (absorptions at 650 and 887 nm for PhSMe(+*) and H(5)PV(IV)V(V)Mo(10)O(40)) and EPR spectroscopy (quintet at g = 2.0079, A = 1.34 G for the thianthrene cation radical and the typical eight-line spectrum for V(IV)).  Next, a precipitate is formed that shows by IR the incipient formation of the sulfoxide and by EPR a VO(2+) moiety supported on the polyoxometalate.  Dissolution of this precipitate releases the sulfoxide product.  ET-OT oxidation of diethylsulfide yielded crystals containing [V(O)(OSEt(2))(x)(solv)(5-x)](2+) cations and polyoxometalate anions.  Under aerobic conditions, catalytic cycles can be realized with formation of mostly sulfoxide (90%) but also some disulfide (10%) via carbon-sulfide bond cleavage.