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 MoCl₅ and 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, SMe₂ and HCl were identified as side products. The reactions between MoCl₅ and 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 MoCl₅ and DMSO, this being a prerequisite for successive C-H bond activation. [ABSTRACT FROM AUTHOR]