Investigations On Chemistry Of The New Types Of [FeFe] Hydrogenase Models With Single, Double And Triple-Butterfly [2Fe2S] Skeleton

The [FeFe] hydrogenases are highly efficient enzymes that catalyze the reduction of proton to hydrogen and the oxidation of hydrogen in microorganisms. In recent years, the biomimetic studies on chemistry of [FeFe] hydrogenases have received special attention. This is because such studies are not only of theoretical interest but also of practical importance for solving the problems of the increasingly environmental pollution and energy crisis. In order to develop the biomimetic chemistry of [FeFe] hydrogenases, we carried out studies on synthesis, structures, properties and functions of new models for [FeFe] hydrogenase active site. The main results in this thesis are described as follows:1. Six functionalized model compounds:[(μ-SCH₂)₂NCH₂CH₂O₂CC₄H₃X-2]Fe₂(CO)₆ (1, X = O; 2, X = S), [(μ-SCH₂)₂NC(O)CC₄H₃X-2]Fe₂(CO)₆(3, X=O; 4, X = S) and [(μ-SCH₂)₂CHO₂CC₄H₃X-2]Fe₂(CO)₆(8, X = O; 9, X =S) were synthesized by reactions of [μ-SCH₂)₂NCH₂CH₂OH]Fe₂(CO)₆, [(μ-SCH₂)₂NH]Fe₂(CO)₆ and [(μ-SCH₂)₂CH(OH)]Fe₂(CO)₆ with 2-C₄H₃OC(X)Cl(X = O, S), respectively. All of these compounds were fully characterized by elemental analysis, IR and ¹H NMR spectroscopies. Five molecular structures of these compounds were confirmed by X-ray diffraction techniques. Their electrochemical properties were studied by cyclic voltammetry experiments. The electrochemical properties of 2 indicated that it can electrocatalyze reduction of the acetic acid protons to H₂ under electrochemical conditions. The mechanism for this electrocatalytic process is proposed.2.Three N-heterocyclic carbene-substituted type model complexes:(6) and [(μ-SCH₂)₂NCH₂CH₂O₂CC₄H₃S-2]Fe₂(CO)₅L(7) (L = l-methyl-3-(2, 4, 6-tri methylphenyl)imidazol-2-ylidene) were prepared by CO substitution reactions with N-heterocyclic carbene ligand, respectively. All of these compounds were fully characterized by elemental analysis and IR and ¹H NMR spectroscopies and their molecular structures were confirmed by X-ray diffraction techniques. Their IR spectra indicated that the N-heterocyclic carbene ligand has strong electron-donating ability.3.Two model compounds: [Fe₄S₄(TriS){Fe₂N(CH₂S-μ)₂(CH₂CH₂S)(CO)₅}][PPh₄]₂ (17) and [Fe₄S₄(TriS){Fe₂N(CH₂S-μ)₂(CH₂CH₂S)(CO)₅}][Bu₄N]₂ (18), which contain the {[2Fe2S](μ-S)[4Fe4S]} structure like [FeFe] hydrogenases were synthesized through ester exchange and decarbonylation reactions of [(μ-SCH₂)₂NCH₂CH₂SC(O)CH₃]Fe₂(CO)₆ with cubane clusters [PPh₄]₂[Fe₄S₄(TriS)(SEt)] and [NBu₄]₂[Fe₄S₄(TriS)(SEt)], respectively. The two new compounds were characterized by elemental analysis, IR, ¹H NMR and MS.4.Three new double butterfly model complexes: C₅H₃N{[(μ-SCH₂)₂NCH₂CH₂O₂C]Fe₂(CO)₆} (1), C₅H₃N{[(μ-SCH₂)₂NC(O)]Fe₂(CO)₆}₂ (2) and C₅H₃N{[(μ-SCH₂)₂CHO₂C]Fe₂(CO)₆}₂(3) were prepared through functional transformation of [(μ-SCH₂)₂NCH₂CH₂OH]Fe₂(CO)₆,[(μ-SCH₂)₂NH]Fe₂(CO)₆ and [(μ-SCH₂)₂CH(OH)]Fe₂(CO)₆, respectively. All of these compounds were fully characterized by elemental analysis, IR and ¹H NMR spectroscopies and the molecular structure of 2 was confirmed by X-ray diffraction techniques. The electrochemical properties of 2 was also studied by cyclic voltammetry experiments and its electrochemical properties indicated that it can electrocatalyze reduction of the acetic acid protons to H₂ under electrochemical conditions. 5.Four triple butterfly model complexes:C₆H₃{[(μ-SCH₂)₂NCH₂CH₂O₂C]Fe₂(CO)₆}₃(4), C₆H₃{[(μ-SCH₂)₂NCH₂CH₂O₂C]Fe₂(CO)₅PPh₃}₃(5),C₆H₃{[(μ-SCH₂)₂CHCH₂O₂C]Fe₂(CO)₆}₃(6) and NN{[(μ-SCH₂)₂NCH₂CH₂O₂CCH₂]Fe₂(CO)₆}₃(7) were prepared through functional transformation. All of these compounds were fully characterized by elemental analysis, IR and ¹H NMR spectroscopies and the molecular structure of 4 was confirmed by X-ray diffraction techniques.6.Four new double butterfly N-functionalized model complexes: {[(μ-SCH₂)₂NCH₂CH₂O₂CCH₃]Fe₂(CO)₅Ph₂PCH₂}₂(8),{[μ-SCH₂)₂NCH₂CH₂O₂CCH₃] Fe₂(CO)₅Ph₂PCH}₂(9),{[μ-SCH₂)₂NCH₂CH₂O₂CC₄H₃O-2]Fe₂(CO)₅Ph₂PCH₂}₂ (10) and {[(μ-SCH₂)₂NCH₂CH₂O₂CC₄H₃O-2]Fe₂(CO)₅Ph₂PCH}₂(11) were prepared by CO displacement of [(μ-SCH₂)₂NCH₂CH₂O₂CCH₃]Fe₂(CO)₆ and [(μ-SCH₂)₂NCH₂CH₂O₂CC₄H₃O-2]Fe₂(CO)₆ with PPh₂CH₂CH₂PPh₂ and trans-PPh₂CH=CHPPh₂,respectively.All of these compounds were fully characterized by elemental analysis , IR, ¹H NMR and ³¹P NMR spectroscopies and their molecular structures were confirmed by X-ray diffraction techniques.