Synthesis,characterization, and electrochemical properties of diiron azadithiolate complexes related to the active site of [FeFe]-hydrogenases

Treatment of [(μ-SCH₂)₂NPh]Fe₂(CO)₆ (A) with PPh₃ or PPh₂H in the presence of the decarbonylating agent Me₃NO·2H₂O afforded complexes [(μ-SCH₂)₂NPh]Fe₂(CO)₅(PPh₃) (1) and [(μ-SCH₂)₂NPh]Fe₂(CO)₅(PPh₂H) (2) in 87% and 74% yields, respectively. Complexes 1 and 2 were characterized by elemental analysis and various spectroscopic techniques. The molecular structures of 1 and 2 were further determined by X-ray crystallography. In both cases, the monophosphine ligand resides in an axial position of the square-pyramidal Fe atom and trans to the benzene ring of the azadithiolate ligand, in order to minimize steric repulsion. On the basis of electrochemical studies, all these complexes were found to catalyze proton reduction to H₂ in the presence of acetic acid.