Cooperative Fe-LMCT and Ni-S_H2 Catalysis for Native Carboxylic Acid Methyl Editing

Native functional-group conversion represents a powerful complement to C-H methylation, yet the selective installation of methyl groups directly from free carboxylic acids remains an outstanding challenge. Herein, we report a reaction design that addresses these challenges through the integration of Fe-mediated ligand-to-metal charge transfer (LMCT) photocatalysis and Ni-mediated S_H2 radical-sorting. Native carboxylic acids are directly converted into alkyl radicals through catalytic Fe-LMCT activation, whereas selective C(sp³)─C(sp³) bond formation is achieved by Ni-mediated S_H2 catalysis. Central to this design is a multifunctional cumyl hydroperoxide reagent that simultaneously promotes Fe-LMCT catalyst turnover, generates methyl radicals through a Fenton-type process, and facilitates in situ iron carboxylate formation, thereby merging both catalytic manifolds within a single cooperative reaction network. This platform enables the direct peripheral methyl editing of a broad range of primary, secondary, and tertiary carboxylic acids, including structurally complex and bioactive molecules. Extension to trideuteromethylation further illustrates the modularity of the catalytic platform. Mechanistic studies support the proposed reaction design and the multifunctional role of the peroxide reagent. This work establishes a blueprint for integrating LMCT radical generation with catalytic radical sorting, opening new opportunities for C(sp³)─C(sp³) bond formation through coupled radical processes.