Monooxomolybdenum(VI) Complexes Possessing Olefinic Dithiolene Ligands: Probing Mo−S Covalency Contributions to Electron Transfer in Dimethyl Sulfoxide Reductase Family Molybdoenzymes

A monooxomolybdenum(VI) model complex for the oxidized active site in the DMSOR family of molybdoenzymes has been synthesized and structurally characterized. The compound was obtained from the desoxomolybdenum(IV) derivative by clean oxygen-atom transfer from an amine N-oxide in a manner similar to that observed in the enzyme. A combination of electronic absorption and resonance Raman spectroscopies, coupled with the results of bonding and excited-state calculations, has been used to provide strong support for a highly covalent Mo(dxy)−S(dithiolene) π*-bonding interaction in the molybdenum(VI) complex. It is proposed that the resulting Mo−S covalency facilitates electron-transfer regeneration of the catalytically competent DMSOR MoIV active site.