The photocatalytic reduction of CO2 with heterodinuclear catalysts based on earth abundant metals

我们的目标是开发和详细研究用于光驱动二氧化碳还原的催化系统。主要目的是比较基于相同光敏剂和催化剂组合的分子间和分子内体系。光敏剂单元以及催化单元将基于非贵金属化合物，例如第一种情况下的铬和钼配合物以及在后一种情况下的铁、钴和镍配合物。它们的催化性能取决于所使用的溶剂、牺牲电子供体和其他相关参数。具有不同连接单元的光敏剂-催化剂二元体被合成为分子内体系。分子内体系中两个金属单元的紧密邻近应该有利于电子向催化单元的转移，并且整个化合物结构应该减缓有害的反向电子转移。将探索将二氧化碳选择性还原为一氧化碳、甲酸甚至甲烷。通过正确选择反应条件、催化活性金属中心类型和配体结构来实现产物的选择性。第二个主要目标是更深入地了解光催化系统（分子间和分子内）的能量和电子转移过程。因此，将进行扩展光谱研究，以确定从基态和还原态开始的化合物的光物理性质，例如电荷分离态的寿命。中间体的分离和表征应该为理解反应过程增加另一块拼图，这将导致提出一个精细的反应机制-特别是对于异双核化合物。

Our goal is the development and in detail investigation of catalytic systems for the light-driven reduction of carbon dioxide. A major aim is to compare inter- and intramolecular systems that are based on the same combination of photosensitizer and catalyst. The photosensitizer units as well as the catalytic units will be based on non-noble metal compounds, such as chromium and molybdenum complexes in first case and iron, cobalt and nickel complexes in later case. Their catalytic performance will be determined in dependence of the used solvent, sacrificial electron donor and other relevant parameters. Photosensitizer-catalyst dyads with varying linker units are synthesized as intramolecular systems. The close vicinity of the two metal units in the intramolecular system should favor an electron transfer event towards the catalytic unit and the overall compound architecture should slow down a detrimental back electron transfer. The selective reduction of carbon dioxide to carbon monoxide, formic acid or even methane will be explored. Product selectivity should be achieved with the right choice of reaction conditions, type of catalytically active metal center and ligand architecture. The second major goal is obtaining more insight into the energy and electron transfer processes within the photocatalytic systems (inter- as well as intramolecular). Thus, extended spectroscopic studies will be performed to determine the photophysical properties, e.g. lifetime of charge-separated states, of the compounds starting from the ground state as well as from reduced species. The isolation and characterization of intermediates should add another piece to the puzzle of understanding the proceeding processes, which should lead to the proposal of a refined reaction mechanism – especially for the heterodinuclear compounds.