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

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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.