One-Pot Intermolecular C–S Self-Coupling of Dimethyl Sulfoxide Promoted by Molybdenum Pentachloride

The reactions between MoCl5 and 1–2 equiv. of a selection of sulfoxides at room temperature in dichloromethane as solvent were studied. The 1:1 molar reaction between MoCl5and dimethyl sulfoxide (DMSO) afforded the C–S coupling product [Me2SCH2SMe][MoOCl4] (1), which was isolated in 46 % yield and characterized by analytical and spectroscopic methods and by X-ray diffraction. MoOCl3, SMe2and HCl were identified as side products. The reactions between MoCl5and tetrahydrothiophene 1-oxide, nBu2SO, MePhSO or (PhCH2)2SO yielded the corresponding sulfides and, in the cases of (PhCH2)2SO and MePhSO, also C–S activation compounds. According to DFT calculations, the unusual formation of 1 is the consequence of thermodynamically feasible Cl/O interchange between MoCl5and DMSO, this being a prerequisite for successive C–H bond activation.