Two synthetic routes to bis(1-methyl-imidazole-2-thione)methane and bis(1-benzyl-imidazole-2-thione)methane complexes including sulfur atom insertion into copper−NHC bonds

The synthesis of novel bis-thione ligand, bis(1-benzyl-imidazole-2-thione)methane, SS^Bn is reported for the first time. This ligand along with the previously reported bis(1-methyl-imidazole-2-thione)methane, SS^Me has been utilised in the synthesis of a series of copper(I) halide complexes. The syntheses have been achieved by two methodologies. The first method involves the direct addition of the ligands to the copper halide salts, CuCl, CuBr and CuI. The second methodology involves an insertion of a sulfur atom into the copper‒NHC bond of the preformed organometallic complexes, [CuBr(CS^Me)]₂ and [CuI(CS^Me)]₂ {where CS^Me = 1-(3-methyl-2H-imidazol-1-yl-2-thione)methyl-3-methyl-2H-imidazol-2-ylidene} and [CuBr(CS^Bn)]₂ and [CuI(CS^Bn)]₂ {where CS^Bn = 1-(3-benzyl-2H-imidazol-1-yl-2-thione)methyl-3-benzyl-2H-imidazol-2-ylidene}. These sulfur atom insertion reactions provide an indirect route to the first copper−halide complexes containing the SS^Me and SS^Bn ligands. All six complexes prepared have been fully characterised by spectroscopic and analytical methods as well as X-ray crystallography. Dinuclear structures were obtained for the complexes containing SS^Me, mononuclear complexes were obtained for the copper‒chloride and copper‒bromide complexes containing SS^Bn and an extended network containing [Cu₄I₄] clusters bridged by the SS^Bn were formed for the corresponding copper‒iodide complex for the latter ligand. The coordination and structural features of the two bis-thione ligands are discussed.