Metal‐free Semiconductor Photocatalysis for sp2 C−H Functionalization with Molecular Oxygen

Designing metal-free catalysts for solar energy conversion is a long-standing challenge in semiconductor photoredox catalysis (SPC). With visible-light-responsive hexagonal boron carbon nitride (h-BCN) as a non-metal photocatalyst, this system affords C−H/N−H coupling products with broad substitution tolerance and high efficiency with molecular oxygen as the terminal oxidant. The catalyst exhibits remarkable performance for the selective C−H functionalization of electron-rich arenes to C−N products (yields up to 95 %) and good stability (6 recycles). Both nitrogen heteroarenes and amine salts are competent coupling nucleophiles. Mechanically, the reactive oxygen species are superoxide anion radical (O2−.) and H2O2, which are proved by electron spin resonance (ESR) data, KI-starch, and control experiments. In addition, kinetic isotope effect (KIE) experiments indicate that C−H bond cleavage is not involved in the rate limiting step. This semiconductor-based photoredox system allows for C−H amination free of any metals, ligands, strong oxidants, and additives. It provides a complementary avenue to C−H functionalizations and enables synthetic applications efficiently in a sustainable manner.