| Fe-Fe hydrogenases are enzymes which can reversibly catalyze the proton reduction to hydrogen in microorganisms.Crystallographic and IR spectroscopy studies reveal that the active site of Fe-Fe hydrogenases adopts a square-pyramidal butterfly coordination geometry,which highly resemble the well-known organometallic complexes formulated as [Fe2(μ-SR)2(CO)6-nLn].Owing to the simple structure and the high efficiency,biomimetic models related to the active site of the Fe-Fe hydrogenases are of particular interest to bioinorganic chemists.They try to further understand the catalytic mechanism for proton reduction and eventually find the synthetic competitive catalysts that function with hydrogenase-like capability.In this thesis,a series of diiron complexes were synthesized as the structural and functional models for the Fe-Fe hydrogenases active site.Three N-substituted aza diselenide diiron complexes[{(μ-SeCH2)2NC6H4R}Fe2(CO)6] (R=4-NO2,7;R=H,8;R=4-CH3,9) were firstly synthesized to investigate the effects of changing the S atoms of the bridging dithiolate ligands on the biomimetic models.X-ray single crystal diffraction reveals the overall molecular structures of 7-9 are analogous to those of their dithiolate analogues[{(μ-SCH2)2NC6H4R}Fe2(CO)6](R=4-NO2,7s;R=H, 8s;R=4-CH3,9s).IR spectra and electrochemical studies indicate that changing the S atoms of the bridging ligands to Se atoms enhance the average electron density of the iron cores.As a typical object we chose,complex 9 shows a slightly higher electrocatalytic activity for proton reduction from HOTs than its dithiolate analogue 9s.On the basis of the concept of light-induced electron transfer(ET) to drive proton reduction to hydrogen,three novel benzothiazole photosensitizer-[2Fe2S]complexes 16-18 were successfully synthesized and well characterized.In addition,three reference compounds 16r-18r were prepared to further investigate the electronic interaction between the photosensitizer and the[2Fe2S]subunit.The photophysical properties of 16-18 and 16r-18r have been investigated by absorption & emission spectra and flash photolysis.As compared to 16r and the equimolar mixture of 16r and[(μ-S)2Fe2(CO)6],the fluorescent spectra of 16 is quenched.Meanwhile,the emission lifetime is shorter than that of 16r. These results show that the intramolecular energy transfer from the photosensitizer to the [2Fe2S]subunit occurs in complex 16. Mono-and disubstituted complexes,[(μ-pdt)Fe2(CO)5(TMP)](20) and[(μ-pdt) Fe2(CO)4(TMP)2](21),were synthesized to introduce a water soluble phosphine ligand, tris(morpholino)phosphine(TMP),to the[2Fe2S]model complex.IR spectra indicate that the TMP ligand has better electron-donating ability than that of other phosphine ligands, such as PMe3,PTA(1,3,5-triaza-7-phosphaadamantane),PPh3.Electrochemical CVs reveal that both complexes 20 and 21 could electrocatalyze the protons reduction from HOAc in higher activity in CH3CN/H2O mixed solutions than in pure CH3CN solution.And in CH3CN/H2O(10:1,v/v),the catalytic activity is highest.In order to tune the reduction potential of the[2Fe2S]model,complex [μ-SC4N2H2S-μ]Fe2(CO)6(24) with the rigid and conjugated bridge was prepared by the reaction of Fe3(CO)12 and pyrazine-2,3-dithiol in THF at refluxing temperature.The monotrimethylphosphine substituted complex[μ-SC4N2H2S-μ]Fe2(CO)5(PMe3)(26) and an unexpected monometallic complex[μ-SC4N2H2S-μ]Fe(CO)2(PMe3)2(25) were obtained in the PMe3 ligand replacements.Protonated species of complexes 24 and 25,those 24H+,25H+ and 25H22+ were isolated and characterized by X-ray crystal diffraction.The protonation processes are traced by UV/Vis,IR and NMR spectra in the presence of HOTf. The results of electrochemistry indicate that the rigid and conjugated bridge indeed results in the positive shift of the reduction potential.The first reduction peak of complex 24 appears at -1.19V(vs.Fc/Fc+).All synthesized complexes were characterized by IR,NMR and HR-MS.Structures of complexes 7-9,16-18,20,21,24-26,24H+,25H+ and 25H22+ were determined by X-ray single crystal diffraction.
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