Metal–Organic Framework-Derived p‑Type Cu₃P/Hexagonal Boron Nitride Nanostructures for Photocatalytic Oxidative Coupling of Aryl Halides to Biphenyl Derivatives

The C–C coupling is an efficient route toward the synthesis of symmetric biphenyls from aryl halides. Herein, a cost-effective visible nanophotocatalyst system (Cu₃P/hBN), consisting of heterogeneous, nanoporous, and nanosized Cu₃P (derived from HKUST MOF) and hexagonal boron nitride (hBN), is employed for the photocatalytic coupling of aryl halides. The catalyst efficiently executes the aryl halide coupling to biphenyls under visible light and in the presence of air at room temperature. The electron/hole pairs can be readily generated upon visible light excitation of the Cu₃P nanophotocatalyst, but the low band gap of Cu₃P promotes the fast recombination of generated electrons/holes, thereby rendering Cu₃P inefficient for photocatalysis. However, the association of a small amount of hBN, which is a structural analogue of graphene and carbon nitride, with Cu₃P to form the Cu₃P/hBN composite promotes the separation of electrons as hBN can provide its surface to the excited electrons of Cu₃P, making them active to act on surface-adsorbed active reactant molecules, whereas the holes remain confined to the valence band of Cu₃P. Cu₃P is a P-type semiconductor that provides Cu (+1) active sites that change to Cu (+2) during the photocatalytic cycle. The oxidized active sites consisting of Cu (+2) promote further enhancement of electrostatic interactions between the catalyst and the attached aromatic halide molecules. The excited electrons generated in the catalyst upon light exposure act on oxygen molecules to further lead to superoxide radical anion (O₂^–•) radical formation. The formed O₂^–• radicals then act on activated halide molecules and convert them to biphenyls.