| Fe-Fe hydrogenases can reversibly catalyze the redox reactions of dihydrogen oxidationand proton reduction. Since the crystal structure of the Fe-Fe hydrogenases was publishedfirst in 1998, intensive attention has been paid to the structural and functional biomimic of theFe-Fe hydrogenase active site because of its high efficiency in catalyzing the reduction ofprotons to hydrogen. At present, many scientific key problems for mimicking the Fe-Fehydrogenase active site are still unsolved, such as how to isolate and identify terminalhydrides after protonation of model complexes of the Fe-Fe hydrogenases, how to design andprepare model complexes with mixed-valence (Feâ…¡Feâ… or Feâ… Fe0), and how to link a [4Fe4S]cluster to the [2Fe2S] subunit by the sulfur atom of cysteine. On the basis of this context, aseries of diiron azadithiolate model complexes were synthesized by introduction ofhalo-benzyl substitutents to bridging-N and by the displacement of the CO ligand on the ironatom of the [2Fe2S] unit. The structural characters and protonation properties of the modelcomplexes were studied. In addition, model complexes [2Fe2S]-Scys-[Fe] were designed andsynthesized by coordination of the sulfur atom of the (η5-C5H5)Fe(CO)2(SR) (R=4-NH2C6H4-or(t-Bu)OCONHCH(COOCH3)CH2-) moiety to the iron center of the [2Fe2S]unit, to explore the synthetic route for a [2Fe2S]-Scys-[4Fe4S] supermolecular model.In this dissertation, three halogen-functionalized diiron azadithiolate model complexes[{(μ-SCH2)2N(CH2C6H4X)}{Fe(CO)3}2] (X=2-Br,1; 2-F, 2; 3-Br, 3) were synthesized.Complexes 1-3, [1(NH)]+ClO4- and [2(NH)]+ClO4-were characterized by FTIR, NMR, MSspectroscopy and elemental analysis. The molecular structures of complexes 1 and[1(NH)]+ClO4-were determined by X-ray single crystal diffraction analysis. The resultsshowed that the protonation of complexes 1, 2 and 3 occurred on the bridging-N, and noevidence for the formation of theμ-H species between two iron atoms was observed. Theprotonation species of complexes 1 and 2 were successfully isolated, and spectroscopicallyidentified. But the protonation species of complex 3 was only detected in situ as previouslyreported [2Fe2S] species. It indicates that the intramolecular N-H…X interaction of theortho-halogen and the bridging-N atom exists in the N-protonated species, which can promotethe stability of the N-protonated species.Considering that production of a molecular hydrogen requires the reduction of twoprotons, the second protonation site was built by displacing the CO ligand(s) of the iron atom of [2Fe2S] model complexes. Phosphine ligand symmetrically substituted complex[{(μ-SCH2)2N(CH2C6H4-2-Br)} {Fe(CO)2(PMe3)}2] (4) was synthesized. In the presence ofstrong acid, the protonation of complex 4 occurred first on the bridging-N atom, and then onthe position between the two iron atoms. The double protonation process of complex 4 wasmonitored by in situ NMR and FTIR. Because the high stability of theμ-H species does notfavor hydrogen production, phosphine ligand asymmetrically substituted complex[{(μ-SCH2)2N(CH2C6H4-2-Br)}{Fe(CO)2}2(dppe)] (5) was designed and synthesized. Theprotonation of complex 5 occurred on the terminal position of the iron atom at 218K in thepresence of acid, with increase of temperature, terminal hydride converted to more stableμ-hydride species. Complexes 4, [4(FeHFe)]+(PF6)-and 5 were characterized by FTIR, NMR,MS spectroscopy and elemental analysis. Their molecular structures were determined byX-ray single crystal diffraction analysis.In addition, according to structural characters of the Fe-Fe hydrogenase active site, themetallo-thioether substituted [3Fe3S] complexes [{(μ-SCH2)2N(C6H4-4-COOCH3)}Fe2(CO)5{CpFe(CO)2SR}] (R=4-NH2C6H4-,7; (t-Bu)OCONHCH(COOCH3)CH2-, 8) weresynthesized with complex [{(μ-SCH2)2N(C6H4-4-COOCH3)} {Fe(CO)3}2] (6) as a precursor,and cyano-substituted complexes [{(μ-SCH2)2N(C6H4-4-COOCH3)} {Fe(CO)2}2(CN)]-(NEt4)+ (9), [{(μ-SCH2)2N(C6H4-4-COOCH3)}{Fe(CO)2(CN)}2]2-(NEt4)2+ (10) and[{(μ-SCH2)2N(C6H4-4-COOCH3)}Fe2(CO)4(CN) {CpFe(CO)2SR}]-(NEt4)+(R=(t-Bu)OCONHCH(COOCH3)CH2-,11) were synthesized. Complexes 6-11 werecharacterized by FTIR, NMR and MS spectroscopy. The molecular structure of complex 6was determined by X-ray single crystal diffraction analysis. Cyano-disubstituted intermediate[{(μ-SCH2)2N(C6H4-4-COOCH3)}(μ-CO)Fe2(CO)2(CN)2{CpFe(CO)2SR}]2-(NEt4)2+(R=(t-Bu)OCONHCH(COOCH3)CH2-,12) with bridging-carbonyl group was identified byin-situ FTIR in the reaction solution of Et4NCN and complex 8 containing a cysteine ligand at263K. With an [Fe]-Scys unit and a bridging-CO ligand, the structure of the intermediate 12 ismore resemble to the structure of the Fe-Fe hydrogenase active site.
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