Chlorine-Mediated Metal-Free Photocatalysis for Highly Selective Oxidation of C–H Bonds

Abstract Selective activation of C–H bonds remains a fundamental challenge under mild and metal-free conditions. Here, we present a Cl-mediated metal-free photocatalytic approach for C–H bond oxidation using mesoporous graphitic carbon nitride (mpg-C3N4) as the photocatalyst and NaCl as a redox mediator. Under light irradiation, chlorine radicals (Cl·), generated from a NaCl additive, facilitate selective oxidation of the C–H bond in methyl- and alkylarenes, yielding aldehydes, nitriles, ketones, and oximes. In situ spectroscopic analysis and density functional theory (DFT) calculations elucidate mechanistic insights into the reaction pathway, identifying the Cl-mediated hydrogen atom transfer (HAT) as the rate-determining step (RDS) under mild and metal-/cyanide-free conditions. Furthermore, correlation heatmap analysis reveals that high local electron density and nucleophilicity at the reaction center are key descriptors for efficiency, rationalizing the observed broad substrate scope and high selectivity. This report provides mechanistic insight into heterogeneous semiconductor halide-induced radical chemistry and demonstrates the integration of Cl-mediated HAT with recyclable semiconductor photocatalysis, offering a low-carbon and efficient strategy for metal-free CH functionalization and contributing to the general advancement of sustainable synthetic methodologies.