Electrochemistry And Related Studies On New Types Of [FeFe] Hydrogenase Models And Organotransition Metal Complexes

The biomimetic chemistry of[FeFe]hydrogenases is one of the most important branches of bioorganometallic chemistry.The electrochemical study of the[FeFe] hydrogenase model complexes is of great importance,since it is the main method to find out whether these complexes can catalyze the reduction of protons to hydrogen. This paper involves the electrochemical study on a series of[FeFe]hydrogenase model complexes synthesized by our group.In addition the photoinduced catalytic hydrogen production catalyzed by the light-driven model compounds each containing a H₂TPP photosensitizer,as well as electrochemical properties of some transition metal fullerene complexes,self-assembly organometallic complexes and metallocrown ethers each containing a butterfly Fe₂S₂ core were also discussed in this paper.The main results described in this thesis are as follows: 1.Seven[FeFe]hydrogenase active site models synthesized by our group were studied by cyclic voltammetry,differential pulse voltammetry and controlled potential electrolysis.The electrochemical processes were described and the catalytic behavior of these models with different acids were investigated. Hydrogen evolved during the electrolysis was gathered and detected,which further proved the catalytic properties of these complexes.The mechanisms for this electrocatalytic process were proposed.The IR and EPR techniques were used to track the intermediate formed during the electrolysis of models Fe₂[(μ-SCH₂)₂NC₆H₄CO₂Me-p](CO)₅(PPh₃) and Fe₂[(μ-SeCH₂)₂CHOH)](CO)₆.These spectroelectrochemical measurements further confirmed these mechanisms.2.The novel light-driven model compound with a H₂TPP photosensitizer and a strong donor ligand carbene 5-{p-[Fe₂(CO)₅L_1Mes(μ-SCH₂)₂CHO₂C]phenyl}-10,15,20-Ph₃PorphH₂ (L_1Mes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene) was synthesized. The structure of this complex was fully characterized by ¹H NMR,IR and elemental analysis.The electrochemical study of this model complex and its precursor compound 5-{p-[Fe₂(CO)₆(μ-SCH₂)₂CHO₂C]phenyl}-10,15,20-Ph₃PorphH₂ indicated that these two complexes have the electrochemical catalytic ability for evolution of hydrogen.Further study indicated that these two complexes have the catalytic ability for reducing protons to hydrogen under the action of visible light.3.The electrochemical study of a novel hydrogenase model containing a[4Fe4S] cluster synthesized by our group was carried out while the electrochemical process was analyzed,the electrocatalytic H₂ evolution was observed.4.The electrochemistry of three transition metal fullerene complexes synthesized by our group were investigated while their electrochemical processes were analyzed,the influence of the number ofη² metal fragments coordinated to C₆₀ upon the negative shift of the reduction potentials of C₆₀ was discussed.5.The cyclic voltammetry of the self-assembled organometallic complexes containing the cluster C₂Co₂(CO)₆ was studied.The electrochemical reduction and decomposition processes of these complexes at the surface of the electrode under different temperatures were analyzed.The electrochemical study of the assembled complex containing two dicyclopentadienyl iron groups was carried out in order to find out whether the intramolecular electron transfer effect exists.6.The electrochemical behavior of the metallocrown ethers each containing a butterfly Fe₂S₂ core Fe₂[μ-SCH₂(CH₂OCH₂)nCH₂S-μ](CO)₆(n=1-4) was studied.The electrochemical investigations of these complexes with metal cations and without metal cations indicated that metal cations such as Li⁺ and K⁺ can not only decrease the reduction potentials of their Fe atoms,but also decrease the electrochemical catalytic potentials catalyzed by each metallocrown ethers.