Unraveling Mechanistic Pathways and Selectivity Patterns in Visible-Light-Driven Aliphatic C–H Functionalization with a Carbon Nitride Photocatalyst

Abstract

Visible-light-driven heterogeneous photocatalysis based on carbon nitride materials has recently emerged as a sustainable platform for aliphatic C–H functionalization, although key mechanistic aspects and selectivity factors remain poorly understood. Herein, we report a combined experimental and computational investigation wherein mesoporous graphitic carbon nitride (mpg-CN) has been exploited in Giese-type C–H functionalization reactions of diverse aliphatic substrates. Under mild and additive-free conditions, mpg-CN enabled the redox-neutral formation of C–C bonds with electron-poor olefins, displaying a reactivity profile strongly dependent on substrate structure. Mechanistic studies, supported by density functional theory calculations, reveal that C–H bond cleavage proceeds via a proton-coupled electron transfer (PCET) pathway. A correlation between bond dissociation free energies and functionalization yield has been identified, establishing a thermodynamic threshold for reactivity. Furthermore, adsorption of substrates within the catalyst surface grooves emerges as a key factor dictating both reactivity and site selectivity, when applicable. In particular, steric constraints and substrate–surface interactions govern accessibility to reactive sites, leading to distinctive selectivity patterns compared to homogeneous photocatalysts, notably the decatungstate anion. These findings highlight the unique role of heterogeneous catalysts in guiding the outcome of photocatalytic processes and provide fundamental insights for the rational design of selective carbon nitride-based synthetic transformations.