Synthesis and Characterization of [FeFe] Hydrogenase Mimics

Abstract

The hydrogenase enzyme catalytically converts protons to hydrogen. The hydrogenase enzyme contains a number of [Fe₄S₄] clusters that act as an electron transport chain, shuttling electrons to the active site. To replicate this, [FeFe]hydrogenase mimics featuring redox active quinone moieties annealed onto an Fe₂S₂(CO)₆ core were synthesized. EPR of these compounds revealed significant communication between the quinone ligand and the Fe₂S₂(CO)₆ core upon one electron reduction. Mimics featuring the redox active 2-phenylazopyridine ligand annealed onto [μ-1,3-propanedithiolato]bis(tricarbonyliron) and [μ-1,2-benzenedithiolato]bis (tricarbonyliron) were also synthesized. UV-Visible spectroscopy showed that metal to ligand charge transfer was occurring in these complexes The hydrogenase enzyme also contains a proton transport chain. [μ-1,2-Benzenedithiolato]bis(tricarbonyliron) complexes substituted with hydrogen donating phosphines were synthesized to mimic this. Attempts to synthesize the thiol substituted phosphine complex were unsuccessful, so protection group chemistry was employed. Electrochemistry of the resulting complexes showed an increase in catalytic current as well as a decrease in overpotential, when compared to the triphenylphosphine substituted complex. Finally, an effort to combine a redox active and hydrogen donating moiety into a single complex using substituted 2-phenylazopyradine moieties was attempted without success.