Chemical Mimic Of The Fe-Only Hydrogenase Active Site

Hydrogenases are a series of important enzymes in many microorganisms, which can catalyze the redox reaction of hydrogen. They are classified into three categories according to their active site metal ion, that is, Fe-only, [Ni-Fe] and metal free hydrogenases. The activity of H2 production of Fe-only hydrogenase is 10-100 times as high as that of [Ni-Fe] hydrogenase. Chemical mimic of the Fe-only hydrogenase active site is mainly discussed in this thesis.Based on the structure of [2Fe2S] in the active site of Fe-only hydrogenase, two cysteines were introduced and the complex [CysFe(CO)3]2 (1) was synthesized. In polar solvent, an intramolecular cyclization reaction of 1 occurred and a chiral two-carbon-bridged [2Fe2S] complex 2 was obtained and a Boc protected alanine methyl ester was eliminated. The structure of 2 was characterized by single crystal X-ray diffraction, NMR and high resolution MS. Two reaction mechanisms were proposed.One or two CO ligands of (μ-PDT)Fe2(CO)6 (4) (PDT = propanedithiolate) were replaced by different phosphine ligands (PMe3, PMe2Ph, PPh3 and P(OEt)3) to afford eight phosphine substituted complexes. The conditions of the reactions were optimized. The effect of different phosphine ligands on the structure and redox properties was investigated by X-ray diffraction and cyclic voltammetry (CV).Two complexes with structure of [3Fe2S] were obtained by the reaction of [Fe2S2(CO)6] and PMe2Ph. The average valence of each Fe atom is 4/3 and the bond lengths of Fe-Fe are about 2.60 A. It was found that the S atoms of the bridged heads have strong nucleophilicity and can coordinate to metal ions, which provides a new evidence for possible protonation on S-bridge in the active site of hydrogenase.To explore the role of the bridged N atom for a possible proton transfer in the active site of hydrogenase, we tried to introduce a hydrogen bond into a couple of designed molecules. Using 2-aminobenzoic acid as starting material, it was failed to obtain the expected complex of 2-[N,N-bis(chloromethyl)]aminobenzoic acid. The bromination of [(μ-SCH2)2N(4-NO2C6H4)]Fe2(CO)6 (16) was unsuccessful either. When N(CH2Cl)3 was reacted with [Fe2S2(CO)6]2- an azadithiolate bridged complex (μ-ADT)Fe2(CO)6 (17) was obtained.All complexes were characterized by NMR, IR and MS.. The structures of most complexes were determined by single crystal X-ray diffraction. Redox properties ofsome complexes were investigated by CV.