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 H₂O₂ 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 HO₂^•, 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.