Single-Atom Iron-Catalyzed Oxidative Esterification: From Methylarenes to the Upcycling of Polystyrene and Lignin-Derived Feedstocks

The catalytic oxidation of C─H bonds represents a transformative strategy for converting abundant hydrocarbons into high-value functional molecules. We report a sustainable heterogeneous methodology for the oxidative esterification of methyl (hetero)arenes and the oxidative C─C bond cleavage of alkyl arenes to synthesize aromatic methyl esters using molecular oxygen in water. This process is driven by an atomically dispersed iron catalyst supported on N-doped porous carbon (Fe-SAC), featuring well-defined Fe-N₄ active sites. The catalyst exhibits exceptional activity and selectivity, effectively overcoming the intrinsic inertness of C(sp³)─H and C─C bonds without the need for noble metals or hazardous additives. Mechanistic investigations, combining kinetic studies, in situ DRIFTS, and DFT simulations, identify superoxide radicals (O₂^●−) as key reactive species and pinpoint benzylic C─H bond cleavage as the rate-determining step. Beyond small molecules, the Fe-SAC system demonstrates high efficiency in the valorization of lignin derivatives and the chemical upcycling of polystyrene waste into value-added esters. Its remarkable stability, ease of recycling, and use of an eco-friendly solvent/oxidant system make this iron-catalyzed process a cost-effective and green alternative to traditional esterification methods.