Photoinduced electron transfer (PET) is the process by which a redox reaction is energetically driven by the absorption of light. The mechanism is found in a diverse set of chemical environments ranging from photosynthetic systems to materials. More recent years have seen an emergence of photoredox catalysts for synthetic organic transformations, such as carbon-heteroatom bond breaking/forming reactions. The standard paradigm by which these photocatalysts operate is often limited by their relatively mild redox potentials. Herein, we leverage a Lewis acid-transition metal interaction (E-Rh, where E=Ga, In) in order to address these limitations. This interaction allows for the isolation of subvalent Rh-I compounds, that when subjected to 395 nm light, are photoexcited to create highly reducing photocatalysts. These photocatalysts, in the presence of H2 gas and base, demonstrate both aryl-F and aryl-CF3 hydrodefluorination. Substrate scope, emission spectrum, and mechanistic investigations point toward a novel catalytic paradigm, allowing for the generation of extremely reducing potentials generated under relatively mild conditions.

Anionic Rh→(Group 13) complexes as extremely reducing photoredox catalysts

ACS Fall 2021

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