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 L^2- ligand (L^2- = 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 L^2- with 3d metal M^III ions, both 5- and 6-coordinated mononuclear complexes have been obtained in the case of Cr^III, viz., [Cr^IIILCl], [Cr^IIILCl₂]^-, and [Cr^IIILCl(CH₃CN)]. The investigation of the reactivity of [Cr^IIILCl(CH₃CN)] under reducing conditions led to a dinuclear [Cr^III₂L₂(μ-Cl)(μ-OH)] compound and, in the presence of protons, to the mononuclear Cr^III complex [Cr^III(L^N2S)₂]⁺, where L^N2S- is the partially desulfurized form of L^2-. A desulfurization mechanism has been proposed involving the release of H₂S, as evidenced experimentally.