Synthesis, Structures And Properties Of New Butterfly Fe/E(E=S,Se) Cluster Compounds Related To[FeFe]-hydrogenase Active Site

Butterfly Fe/E(E=S,Se) cluster complexes have attracted growing interest during recent years, presumably owing to their important theoretical significances and practical applications and particularly their close relationships with the active site of [FeFe]-hydrogenases. To find cheap and efficient catalysts for hydrogen production and to develop the butterfly Fe/E(E=S,Se) cluster chemistry and biomimetic chemistry of [FeFe]-hydrogenases, we have lauched a study on the synthesis, structures, and properties of a series of new Fe/E(E=S,Se) cluster complexes, some of them could be used as [FeFe]-hydrogenase active site models. The main results described in this thesis are as follows:1. A total of18novel compounds were successfully synthesized. The structures were characterized by elemental analysis,1H NMR,13C NMR,31P NMR,77Se NMR and IR spectroscopy. In addition some of them were studied by electrochemistry and photochemistry, and the structures of8compounds were determined by single crystal X-ray diffraction analysis.2. In chapter two, three novel [FeFe]-hydrogenase models,[1,2-(CH2S2CH2)-4,5-(μ-SCH2)2C6H2][Fe2(CO)6](A),[1,2,4,5-(μ-SCH2)4C6H2][Fe2(CO)6]2(B),[1,2-Cu-SCH2)2-4,5-(CH3)2C6H2](1) were synthesized by reactions of tetrathiol1,2,4,5-(HSCH2)4C6H2with Fe3(CO)12under different conditions. Treatment of complex A with PPh3or PMe3in the presence of Me3NO or with the in situ generated N-heterocyclic carbene IMes (IMes=1,3-bis(mesityl)imidazol-2-ylidene) afforded the complexes[1,2-(CH2S2CH2)-4,5-Cu-SCH2)2C6H2][Fe2(CO)5L](2, L=PPh3;3, L=PMe3;4, L=IMes)-Except that the possible pathways for production of complexes A, B and1are proposed, the suggested intermediate [1,2-(HSCH2)2-4,5-(μ-SCH2)2C6H2][Fe2(CO)6](M6) for formation of complex A has been successfully isolated under anaerobic conditions and the structures of complexes1-3have been confirmed by X-ray crystallography. In addition,the redox properties of A and2-4as well as the properties for the electrocatalytic proton reduction in the presence of HOAc were investigated by cyclic voltammetry. Compared to parent model A, complexes2-4have much better electrocatalytic activities, but they have greater overpotential.3. In chapter two, tetrathiol1,2,4,5-(HSCH2)4C6H2reacted with Fe3(CO)12and Et3N in a1:4:4molar ratio in THF at room temperature followed by treatment of the intermediate μ-CO-containing tetraanion{[(μ-CO)Fe2(CO)6]4[1,2,4,5-(μ-SCH2)4C6H2]}4-(A) with CS2/RCH2Br to give quadruple-butterfly complexes [(RSC=S-μ)Fe2(CO)6]4[1,2,4,5-(μ-SCH2)4C6H2](5, R=2,5-Me2PhCH2;6, R=4-MePhCH2;7, R=2-C10H7CH2S;8, R=PhCH2), while μ4-S-containing quintuple-butterfly complexes [Fe2(CO)6][1,2,4,5-(μ-SCH2)4C6H2][Fe2(CO)6(μ4-S)Fe2(CO)6(μ-SR)]2(9, R=PhCH2;10, R=CH3) could be produced by reactions of [(μ-S)2Fe2(CO)6]/RCH2Br with the μ-CO-containing dianion {[(μ-CO)Fe2(CO)6]2[Fe2(CO)6][1,2,4,5-(μ-SCH2)4C6H2]}2-(B) generated in suit from the initially formed tetraanion A. The structure of complex8has been confirmed by X-ray crystallography. The electrocatalytic proton reduction of HOAc or HOTs was investigated by cyclic voltammetry. Furthermore, the photoinduced H2production of a system which consist of a proton source, Ru(bpy)32+as a photosensitizer and complex8as a photocatalyst was stuied. More than42equivalents of H2were achieved in a3:2ratio of CH3CN/H2O. A possible mechanism of photoinduced catalytic cycle of hydrogen production for this kind of models was proposed.4. In chapter three, by using direct separation or exchange with cation, the intermediate μ-CO-containing cluster salts [(μ-CO)(μ2,4-(CH3)2C6H3S)Fe2(C O)6][Et3NH](1),[(μ-CO)(μ-4-NH2C6H4S)Fe2(CO)6][Et3NH](2),[(μ-CO)2(μ-Se CH2CH2CH2Se-μ)[Fe2(CO)6]2[PPh4]2(3),[(μCO)(μ-4-PhC6H4S)Fe2(CO)6][N(C H3)4](4) and [(μ-CO)(μ-PhC6H4Se)Fe2(CO)6][N(CH3)4](5) were successfully isolated. The structures of complexes1,2and4have been confirmed by X-ray crystallography.5. In chapter four, to reduce the reduction potential of the [FeFe]-hydrogenase models, the rigid and conjugated naphthalene bridge complexes2-CHO-1,8-(μ-SC10H5S-μ)Fe2(CO)6(1),2-CH2OH-1,8-(μ-SCioH5S-μ)Fe2(CO)6(2),4-CHO- 1,8-(μ-SC10H5S-μ)Fe2(CO)6(3) were prepared. The complexes land3were characterized by X-ray crystallography. The electrocatalytic proton reduction of HOAc or CF3CO2H was investigated by cyclic voltammetry.The first reduction potential of2at-1.52V(vs Fc/Fc+) is140mV more positive than that(-1.66V) found for complex [(u-PDT)Fe2(CO)6].