CO2Chem - Redox-Neutral Photocatalytic CH Carboxylation of Hydrocarbons with CO2

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Recent years have seen large efforts in mimicking biological photosynthesis by technical processes with the goal of converting solar energy into chemically stored energy. The energy-rich molecules produced in such processes are typically dihydrogen, methane or methanol from the reduction of carbon dioxide or syngas (H2/CO) as feed for the Fischer-Tropsch process. In contrast, the solar-driven synthesis of valuable chemicals using carbon dioxide is still at a very early stage of development. So far, carbon dioxide is only used to a small extent as a raw material in chemical synthesis, but industrial projects in polymer production have shown the feasibility and sustainability of the approach. This project aims to develop the synthetic and mechanistic basis for the photochemical, redox-neutral C-H carboxylation of saturated hydrocarbons with carbon dioxide. Our preliminary data clearly show that carbon dioxide is a valuable reagent in functionalizations of C-H bonds in which carbon dioxide is formally inserted into the carbon hydrogen bond. The redox neutral carboxylation of arenes, styrenes as well as benzylic or α-carbonyl C-H bonds was already realized. The developed methods are highly valuable and proved useful in the synthesis of drug molecules, such as ibuprofen, from simple arene precursors and carbon dioxide. It should be clearly stated, however, that both existing methods preclude the use of the most abundant, non-activated C(sp3)-H bonds. In order to address this challenge, we propose new synthetic strategies based on photocatalytically generated alkyl radicals and earth-abundant metal complexes to provide C-H carboxylation in an overall redox-neutral process. The combined experience of the applicants in cobalt-catalysis and photocatalysis will be used to establish methodologies for the conversion of non-activated aliphatic hydrocarbons into functionalized chemicals with carbon dioxide as a C1 synthon.