Transforming Inert CeCl3 into a Recyclable Heterogeneous Visible Light Photocatalyst

Abstract Synthetic chemists encounter increasing financial and environmental challenges in their quest for innovative catalysis. We have discovered a method to harness visible light using inert CeCl3, transforming it into a recyclable heterogeneous photocatalyst. CeCl3 is a well-known Lewis acid, is insoluble in acetonitrile, and does not absorb light. However, when combined with NXS (NBS or NCS) in acetonitrile, a transient charge-transfer complex forms, enabling visible light absorption. The formed complex facilitated the photoexcitation of Ce(III) ions, transforming them into powerful reductants that donate electrons to NXS. This led to the generation of halide radicals from NXS radical anions, enabling the solar synthesis of gem-dihaloketones from terminal alkynes through C-X cross-coupling reactions. Remarkably, the catalyst could be recovered after the reactions and reused without significant decomposition.