Ruthenium-based Complexes As Catalysts For Water Oxidation

It has been a worldwide research hotspot that solar energy is converted to chemical fuels or electrical energy. Plants oxidize water and reduce carbon dioxide to organic substance through photosynthesis which is known as the most important reaction in the world because it converts solar energy to chemical energy. Artificial photosynthesis system is a good way to harness sun energy which is induced by photosynthesis. Photosystem II (PSII) absorbs sun light, oxidizes water, and provides protons and electrons to photosynthesis, for these reasons that it becomes the most important parts of the photosynthesis. In order to make water be splitted into hydrogen and oxygen driven by sun light, structure and function simulations of PSII were reported frequently. The main works of function simulation are design and synthesis catalysts of water oxidation in homogeneous and heterogeneous system, which catalyze this reaction driven by the suitable photosencitizer under sunlight. Ruthenium complexes are the best catalyst for water oxidation in homogeneous system.A series of ruthenium complexes were designed and synthesized for catalyzing water oxidation, all of them got pretty good catalytic efficiency. First, four imidazole derivatives were prepared upon the introduction of different groups such as-CH3,-Br,-NO2 as axial ligands. Ru-containing catalysts 1-5 were prepared from imidazole,four ligands and 2,2'-bipyridine-6,6'-dicarboxylic acid as axial and equator ligands respectively, their quality were investigated immediately. Catalyst 6 was prepared from different Ru substrate while the same axial ligands with 4, and its catalytic efficiency were compared with catalyst 4.Next, another axial ligand was prepared from L-histidine in which the amino-group was protected by carboxyl. Catalyst 7 was synthesized from this ligand and the same equator ligand, and it was absorb on the titanium dioxide film to form a device for water oxidation.Five derivatives of imidazole and seven ruthenium complexes were synthesized in this work, all of them have been characterized by NMR and HRMS, and among them the structure of catalyst 4 was further confirmed by X-ray crystallography. All of the catalysts are new complexes that never reported before.