Chromium-Thiolate Complex Undergoing C-S Bond Cleavage

The cleavage of C-S bonds represents a crucial step in fossil fuel refinement to remove organosulfur impurities. Efforts are required to identify alternatives that can replace the energy-intensive hydrodesulfurization process currently in use. In this context, we have developed a series of bis-thiolato-ligated Cr-III complexes supported by the L2- ligand (L2- = 2,2 '-bipyridine-6,6 '-diyl(bis(1,1-diphenylethanethiolate), one of them displaying desulfurization of one thiolate of the ligand under reducing and acidic conditions at ambient temperature and atmospheric pressure. While only 5-coordinated complexes were previously isolated by reaction of L2- with 3d metal M-III ions, both 5- and 6-coordinated mononuclear complexes have been obtained in the case of Cr-III, viz., [(CrLCl)-L-III], [(CrLCl2)-L-III](-), and [(CrLCl)-L-III(CH3CN)]. The investigation of the reactivity of [(CrLCl)-L-III(CH3CN)] under reducing conditions led to a dinuclear [(Cr2L2)-L-III(mu-Cl)(mu-OH)] compound and, in the presence of protons, to the mononuclear Cr-III complex [Cr-III(L-N2S)(2)](+), where LN2S- is the partially desulfurized form of L2-. A desulfurization mechanism has been proposed involving the release of H2S, as evidenced experimentally.