En Route to Recyclable Semi-Heterogeneous Photocatalysis with Photoinert CeCl₃

Our study proposes an approach to semiheterogeneous photocatalysis, focusing on recyclability challenges. We developed a method employing visible light with photoinert anhydrous CeCl3, rendering it into a reusable semiheterogeneous photocatalyst. Despite being photoinert and insoluble in organic solvents, anhydrous CeCl3 formed a transient charge transfer complex in acetonitrile, denoted as CeCl3 - NXS (NBS or NCS), due to the strong oxophilicity of trivalent cerium toward oxygen. This complex facilitated visible-light absorption, leading to the photoexcitation of the Ce(III) complexes and conversion of Ce(III) centers into potent reductants, donating electrons to NXS. As a proof of concept, we demonstrated organic reactions where NXS, upon accepting electrons, generated halide radicals, allowing the synthesis of gem-dihaloketones under sunlight from terminal aromatic alkynes via C–X cross-coupling reactions. Significantly, CeCl3 exhibited recyclability without notable decomposition, demonstrated by its regeneration and isolation through simple filtration postreaction, underscoring its potential for prolonged use.