[Re-fe] Supramolecular Complexes As The Molecular Devices For H2Photo-evolution

With the growth of the population and the development of the society, the contradiction between the decreasing of the fossil fuels and the human demand for the energy comes out, so looking for new renewable energy instead of traditional energy sources receives widespread attention. Hydrogen with its high heating value and a product with no pollution is considered to be the best energy. Since the Fe-Fe hydrogenase was found in vivo, its high efficiency of catalyzing protons reduction caused scientists'great interest, and a lot of research groups began to study the Fe-Fe hydrogenase model complexes, including the structural mimic and the functional mimic. The active center of hydrogenase includes two sulfur atoms and two iron atoms, forming a butterfly-shaped structure, a [4Fe4S] cluster in the cysteine connects to the active center of hydrogenase.In this thesis we carried out the work about the Fe-Fe hydrogenase model complexes in two parts:1. The structural mimic for the Fe-Fe hydrogenase by synthesizing several heterocyclic-substituted Fe-Fe hydrogenase model complexes;2. Designed and synthesized [Re-Fe] supramolecular complexes as the molecular devices for H2photo-evolution and applied the Fe-Fe hydrogenase model complexes into the photo-induced hydrogen evolution system.We have designed and synthesized the Fe-Fe hydrogenase model complexes with neutral imidazole ligand [(μ-SCH2)2CH2[Fe2(CO)5(P(Ph)2(C4H5N2))](1), with tetrahydrofuran ligand [(μ-SCH2)2N(C5H9O)[Fe2(CO)6](2) and with pyridine group [(μ-SCH2)2N(C8H8O2N)[Fe2(CO)6](4) and [(μ-SCH2)2N(C6H6N)[Fe2(CO)6](5). Electrochemical tests show that the complexes1,4,5can catalyze the proton reduction. We explored a new synthetic route for complex2, which can reach the principle of the optimal use of the atoms, and this method improved the yield greatly. Using the good coordination ability of the pyridine groups, we synthesized several [Re-Fe] supramolecular complexes9,12-15, connected by the ester group and methylene group. We studied their UV-vis absorption spectra, fluorescence emission spectra, electrochemical properties and photo-induced hydrogen evolution properties. The studies confirmed that the rhenium photosensitizers have higher reduction potential, the longer excited state lifetime, and good light stability. They can transfer the electrons to the active center of the Fe-Fe hydrogenase model complexes and achieve the photo-induced hydrogen evolution.The photo-induced hydrogen evolution properties have shown that under the same condition, the efficiency of the hydrogen evolution by the [Re-Fe] supramolecular complexes was significantly higher than the multi-component intermolecular systems. When TEA was used as the electron donor, the turnover number can reach1.5from complex9after5hours irradiation. In contrast, for the intermolecular multi-component systems, no hydrogen has been detected from complexes4and8. Though turnover number is still relatively low, it proved that the [Re-Fe] supramolecular complexes as molecular devices for photo-induced hydrogen evolution was feasible, and it provides the foundation for the subsequent studies. Under the same conditions, the turnover numbers can reach11.8for complex14,8.75for15after5.5hours irradiation, which are the best results compared with other hydrogen evolution systems with Re photosensitizers linked to [2Fe2S] complexes. In contrast, much lower TON are obtained for the intermolecular multi-component systems, which is5.23for complex12and5,3.8for complex13and5. We can conclude that the efficiency of photo-induced hydrogen evolution by the [Re-Fe] supramolecular complexes connected by chemical bonds is higher than that of the multi-component systems. Even so, the intermolecular multicomponent system from either (12and5) or (13and5) performs more efficiently for the catalytic activity than the current (best) intramolecular Re-based complexes, this may be related to the different complexes structure and different mechanism of photo-induced hydrogen evolution in our system. Further investigations are in progress.