A new family of thiolate-bridged bimetallic complexes featuring a benzimidazole moiety: synthesis, structure and redox reactivity

Thiolate-bridged bimetallic complexes have attracted considerable attention owing to their extensive applications in bioinspired catalysis as biological metalloenzymes. Compared with bimetallic complexes supported by common thiolate ligands, those featuring functional groups that may adopt different patterns to coordinate to the metal centers are usually difficult to access, limiting their exploration. The benzimidazole moiety is a multi-faceted functional group; for example, it can act as a biomolecule-responsive ligand for the development of transition metal complexes with anticancer and antitumor properties. However, so far, there has been no report on thiolate-bridged bimetallic complexes featuring a benzimidazole moiety as the functional group. In this work, we use half-sandwich type monometallic (iron, cobalt or ruthenium) complexes as precursors to synthesize a series of thiolate-bridged bimetallic complexes via reactions with benzimidazolylmethyl disulfide (bzmds) and benzimidazol-2-ylmethanethiol (bzmt). X-ray crystallographic analyses show that diiron and dicobalt complexes feature two bzmt ligands in a syn configuration, which are bridged to the two M III centers through the sulfur and nitrogen atoms. In contrast, the diruthenium complex possesses syn - and anti -configuration isomers in both solution- and solid-state, and the corresponding ratio of the two isomers varies upon employing different solvents. Electrochemical studies reveal that these complexes possess two or more redox couples. In particular, an Fe III Fe III complex can undergo one-electron reduction to give an isolable Fe II Fe III species. In addition, we investigated their electronic structures by UV/vis spectroscopy and density functional theory (DFT). A novel family of thiolate-bridged bimetallic complexes featuring a benzimidazole moiety was constructed and fully characterized by spectroscopy and X-ray crystallography.