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

Area of Science:

• Environmental Chemistry
• Catalysis
• Organic Chemistry

Background:

• High-valent iron-oxo species show promise for degrading organic contaminants.
• The influence of catalyst coordination sphere on reaction mechanisms is not fully understood.

Purpose of the Study:

• To elucidate the structure-reactivity relationship in iron porphyrin catalysts for bisphenol A (BPA) degradation.
• To investigate how ligand substitution affects high-valent iron-oxo species and degradation pathways.

Main Methods:

• Utilized three iron porphyrins with varied ligand substitutions to activate hydrogen peroxide (H2O2).
• Analyzed the generated high-valent iron-oxo species, cogenerated radicals, and BPA degradation products.
• Investigated BPA degradation pathways including hydroxylation, ring cleavage, and quinonization.

Main Results:

• Catalyst ligand coordination dictates the type of Fe(IV)-oxo species and radicals formed.
• A β-substituted catalyst yielded Fe(IV)=O and a ligand π-cation radical, leading to BPA hydroxylation.
• Meso-substituted catalysts generated protonated Fe(IV)-OH species and oxygen-centered radicals, inducing ring cleavage or quinonization.

Conclusions:

• The catalyst's coordination environment critically influences the reactivity of high-valent iron-oxo species.
• Ligand design enables pathway-selective transformations for targeted organic pollutant detoxification.
• Provides fundamental insights into the mechanisms of targeted detoxification of organic compounds.