| Hydrogenase enzymes can efficiently catalyze the reduction of proton or the oxidation ofhydrogen. Since the crystal structure of hydrogenases was published, more and more effortshave been put on the bio-inspired structural/functional models of hydrogenases. Through thestructural and electrochemical studies of diiron dithiolate complexes, people can make thecatalytic mechanism for hydrogenases clear. It is thought that the active sites in both iron-onlyand nickel-iron hydrogenases possess an internal base near the metallic catalytic centerswhich can assist the heterolytic cleavage of hydrogen and the H-H bond formation between aproton and a hydride. In this thesis, a series of diiron dithiolate complexes with the internalbasic site as a proton relay were synthesized aiming at preparing structural/functional modelsfor hydrogenases.Two asymmetrically disubstituted diiron complexes (μ-pdt)[Fe(CO)3][Fe(CO)(η2-L)] (L=1-methyl-3-(2-pyridyl)imidazol-2-ylidene (NHCMePy), 2;1,3-bis(2-picolyl)imidazol-2-ylidene (NHCdiPic), 4) and a mono-substituted diiron complex(μ-pdt)[Fe(CO)3][Fe(CO)2(NHCdiPic)] (3) were prepared as biomimetic models of the Fe-onlyhydrogenase active site. The large ranges of the highest and the lowest v(CO) frequencies of 2and 4 reflect that the relatively uneven electron density on the two iron atoms of the 2Fe2Smodel complexes 2 and 4 is as that observed for mono-substituted diiron complexes of gooddonor ligands. The cyclic voltammograms and the electrochemical proton reduction by 2 and3 were studied in the presence of HOAc to evaluate the effect of asymmetrical substitution ofstrong donor ligands on the redox properties of the iron atoms and on the electrocatalyticactivity for proton reduction. Complex 2 can readily react with the HOTf to afford theprotonated species [2H][OTf]. The 1H NMR study shows that the chemical shift of thehydride is at -10.54 ppm, which is between the chemical shift of the terminal hydride and thebridgedμ-hydride of (μ-pdt)(μ-H)[Fe(CO)2(PMe3)]2+.As biomimetic models for the active sites of iron-only and nickel-iron hydrogenases, twonew trinuclear [NiFe2] complexes [Fe2(CO)6(μ3-S)2 {Ni(Ph2PCH2)2NR}] (R=nBu, 9; Ph, 10)containing an internal nitrogen base were prepared. The electron density on the iron centers ofcomplexes 9 and 10 is much richer than that of the parent complex (μ-S)2Fe2(CO)6. The redoxevents observed for these two [NiFe2] complexes are assigned to the redox processes of ironion within the acetonitrile solution window (from+1.00 to-2.50 V vs. Ag/Ag+). Treatment of complex 9 with HOTf gave complex [Fe2(CO)6(μ3-S)2{Ni(Ph2PCH2)2NHnBu}][OTf]([9H][OTf]), and the first reductive event is shifted to anodic direction by ca. 330 mV incomparison with complex 9.Complexes 2, [2H][OTf], 3, 4, 9, [9H][OTf] and 10 have not been reported by othergroups. These complexes were characterized by EA, 1H NMR and IR spectra (complexes[1H][OTf]and [9H][OTf] were not detected by EA), and the molecular structures of allcomolexes were determined by X-ray crystal diffraction.
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