Interfacial Mn-Carbon Nitride Synergy Enables Selective Photocatalytic C─H Chlorination via Single-Atom Catalysis.

Single-atom photocatalysts offer a structurally defined platform for merging homogeneous and heterogeneous catalysis, yet their application in selective C─H functionalisation remains limited. In this study, we report a manganese-based single-atom photocatalyst (Mn@f-g-C3N4) comprising atomically dispersed Mn─Nx sites anchored on an arylamino-functionalised graphitic carbon nitride support. Band-gap engineering was used to enhance visible-light absorption to afford a robust and recyclable photocatalyst for selective visible-light-driven C(sp2)─H chlorination of arenes and heteroarenes under mild conditions. Mechanistic investigations support a dual-site pathway initiated at the carbon nitride support and continued at the Mn centre. Photoexcitation of the carbon nitride support triggers single-electron transfer to the N-chlorosuccinimide chlorination reagent, generating reactive Cl species, leading to the formation of well-defined Mn─Cl intermediates. Chlorine transfer to the arene substrate is mediated via a cyclohexadienyl radical intermediate, followed by oxidation and deprotonation, affording the chlorinated product. Cooperation between the Mn atom and support suppresses unselective free-radical chlorination pathways and enforces surface-confined selectivity.