Structural characterization and proton reduction electrocatalysis of thiolate-bridged bimetallic (CoCo and CoFe) complexes.

Using an assembly method, dinuclear CoCo and CoFe complexes supported by a bdt ligand, [Cp*Co(μ-η2:η2-bdt)(μ-I)CoCp*][PF6] (1[PF6], Cp* = η5-C5Me5, bdt = benzene-1,2-dithiolate), and [Cp*Co(μ-η2:η4-bdt)FeCp'][PF6] (3[PF6], Cp' = η5-C5Me4H) were synthesized in high yields. Upon chemical reduction with CoCp2, complexes 1[PF6] and 3[PF6] were converted to [Cp*Co(μ-η2:η2-bdt)CoCp*] (2) and [Cp*Co(μ-η2:η4-bdt)FeCp'][PF6] (3), respectively. Treatment of 2 with HBF4 resulted in the protonation of two cobalt centers to generate a hydride bridged complex, [Cp*Co(μ-η2:η2-bdt)(μ-H)CoCp*][BF4] (4[BF4]), which was identified by spectroscopy and X-ray crystallography. When treating 3 with HBF4, a one-electron oxidation occurred to afford complex 3[BF4] along with the formation of H2. Importantly, heterodinuclear complex 3[PF6] and hydride bridged complex 4[BF4] can serve as effective catalysts to promote proton reduction for hydrogen evolution, as evidenced by cyclic voltammetry.