Synthetic Application of Bismuth LMCT Photocatalysis in Radical Coupling Reactions

Ligand-to-metal charge transfer (LMCT) photo-catalysis allows the activation and synthetic utilization of halides and other heteroatoms in metal complexes. Many metals are known to undergo LMCT but so far remain underutilized in the field of catalysis. A screening assay identifying LMCT activity helped us to expand this catalysis concept to the application of bismuth LMCT in organic radical coupling reactions. We demonstrate its application for the generation of two different radicals (chlorine and carboxyl) in net-oxidative as well as redox-neutral photochemical reactions. Detailed investigation of the model Giese-type coupling revealed BiCl4- and BiCl52- as catalytically active bismuth species under 385 nm irradiation. Combined cyclic voltammetry and UV-vis studies gave insight into the reactivity of the highly reactive bismuth(II) catalyst fragment.