Ligand Coordination Directing High-Valent Iron-Oxo Reactivity for Pathway-Selective Pollutant Degradation

The application of high-valent iron-oxo species for the degradation of organic contaminants is a promising strategy. However, the role of the catalyst’s coordination sphere in regulating the reaction mechanism remains ambiguous. Here, we elucidate this structure–reactivity relationship by deploying three iron porphyrins with strategically varied ligand substitutions to activate H 2 O 2 for bisphenol A (BPA) degradation. We demonstrate that the ligand coordination of the catalyst directs the nature of the generated Fe IV -oxo species, the identity of the cogenerated radicals, and the pollutant degradation pathways. Specifically, the β-substituted catalyst exclusively generates the Fe IV ═O unit with a ligand π-cation radical, transforming BPA to hydroxylation products via an oxygen adduct formation pathway with strong matrix tolerance. Conversely, meso-substituted catalysts generate protonated Fe IV –OH species and coexisting oxygen-centered radicals. Meso-carboxyl substitution yields (por)Fe IV –OH and HO •, which synergistically induce ring cleavage of BPA through a single-electron-transfer (SET)-initiated attack. Meso-sulfoxyl substitution produces [(por)Fe IV –OH] + and HO 2 •, which drive quinonization of BPA via a coupled SET and hydrogen-atom-abstraction mechanism. These findings reveal that the coordination environment of the catalyst critically modulates the protonation state and reactivity of the generated high-valent iron-oxo species, thereby steering pollutant degradation toward pathway-selective transformations. This work provides fundamental mechanistic insights into the targeted detoxification of organic compounds.