Synthesis Of Functionalized [Fe₂S₂] Complexes And Their Electrochemistry And Hydrogen-generating Mechanism

The iron-only hydrogenases can catalyze the reduction of proton to hydrogen at extraordinarily high rates.The active site,wherein the catalytic chemistry takes place,adopts a bi-octahedral butterfly geometry,highly resembling the well-known organometalic complex [Fe₂(μ-SR)₂(CO)_6-xL_x].Because of the simple structure and high efficiency,biomimetic models related to the active site of the Fe-only hydrogenase are of particular interest to bioinorganic chemists.The major challenge is now to understand the enzymatic catalytic mechanism and search the synthetic competitive catalysts that function as hydrogenase-like capability.Herein,a series of diiron dithiolate complexes were synthesized as the structural and functional models of the Fe-only hydrogenase active site.In order to investigate the function of the bridged-N in the active site of Fe-only hydrogenase,azadithiolate diiron model complex 1,2,4 and 5 with active functional group were synthesized.Complex[(μ-SCH₂CH₂OH)₂Fe₂(CO)₆](3)with two SCH₂CH₂OH thiolate ligands was also prepared.All structures of these complexes were characterized by IR,NMR, MS spectroscopy.The molecular structures of 1,3,4 and 5 were determined by single crystal X-ray diffration.An S…O intermolecular interaction was found in the crystals of 5,which is scarcely found for organometallic complexes.The redox properties of 1,3,4 and 5 as well as the property of 1 for the electrocatalytic proton reduction in the presence of HOAc were investiged.In order to create bio-inspired photochemical catalysts based on the diiron dithiolate complex for proton reduction to molecular hydrogen,an NH₂-functionlized model complex(2) of the iron-only hydrogenase active site was covalently linked to the tris(bipyridine)ruthenium photosensitizer.The[RuFeFe]trinuclear complex 10 was characterized by HRMS,IR, UV-vis,¹H & ¹³C NMR spectra.The photophysical properties of complex 10 were investigated by absorption and emission spectra as well as flash photolysis.The results show that neither the intramolecular energy transfer nor the intramolecular electron transfer occurs with phenothiazine as electron donor in the present of trifluoroacetic acid.The structures of complexes 13 and 14 were optimized by density functional theory (DFT).In comparison of the molecular electrostatic potential of complexes 13 and 14,the absorb proton capability of complex 14 is more than complex 13.We implemented the intrinsic reaction coordinate(IRC)method into DFT framework and applied the combined DFT and IRC method to study the catalytic mechanism of complex 14.