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The selective oxidation of sulfides to sulfoxides is an important reaction because of the synthetic versatility of sulfoxides.1 A variety of transition-metal complexes have been used to carry out this oxidation including the catalytic system based on Fe(TPP)Cl (TPP is 5,10,15,20-tetraphenylporphyrinato) with iodosylbenzene as cooxidant.2•3 With metal-oxo reagents such as chromic acid,4 permanganate,5 or Os045,6 however, selectivity is not observed because the sulfoxides are often more reactive than the corresponding sulfides. Riley and co-workers have investigated the oxidation of sulfides to sulfoxides by 02 catalyzed with dihaloruthenium(II) complexes,7•8 which give sulfoxide/sulfone ratios parallel to those observed in the H202 oxidation of sulfides,9 and have proposed a Ru(IV) intermediate.Here we report the results of a kinetic study on the oxidation of dimethyl sulfide to dimethyl sulfoxide and of dimethyl sulfoxide to dimethyl sulfone by the Ru(IV)-oxo complex [(bpy)2(py)-Ru(0)]2+. Our goals were to establish the mechanisms of oxidation in order to make comparisons with mechanistic results obtained for other substrates,10-15 to attempt to provide some insight into how sulfide oxidations based on RuC1316 and RuCl2(PPh3)317 occur, and to assess the possibility of developing an electrocatalytic procedure for the selective oxidation of sulfides to sulfoxides.18 Experimental SectionMaterials. Acetonitrile (Baker) was distilled immediately before use from P2Os under an argon atmosphere or used directly. Dimethyl sulfide (Aldrich) was distilled before use. Dimethyl sulfoxide (Burdick and Jackson) was distilled under vacuum before use.Preparations. The salts [(trpy)(bpy)Ru(0H2)](C104)2, [(trpy)-(bpy)Ru(O)] (C104)2, and [(bpy)2(py)Ru(0)](C104)2 were prepared by previously reported procedures.19,20