Proton-Coupled Electron Transfer and Rebound Studies of (bTAML)Iron(IV)-Hydroxo Complex

High-valent iron-oxo intermediates are well established as key oxidants in biological and synthetic oxidation chemistry, whereas their protonated counterparts, iron(IV)-hydroxo (FeIVOH) species, remain comparatively underexplored despite their central role in Cytochrome P450 catalysis. Herein, we report the synthesis, spectroscopic characterization, and reactivity of a room-temperature-stable FeIVOH complex supported by a biuret-modified tetraamido macrocyclic ligand (bTAML). One-electron oxidation of the crystallographically characterized precursor [Et4N]2[(Ph,Me-bTAML)FeIIIOH] using tris(4-bromophenyl)ammoniumyl hexachloroantimonate (Magic Blue) affords the one-electron-oxidized species [(Ph,Me-bTAML)Fe(OH)]- under ambient conditions. Comprehensive characterization by UV-vis, HRMS, EPR, Mössbauer spectroscopy, and X-ray absorption spectroscopy (XANES/EXAFS) conclusively identifies this species as a mononuclear FeIVOH complex. This species represents the first TAML-supported Compound II analogue and a rare non-heme model of the biologically relevant FeIVOH intermediate. Reactivity studies reveal efficient hydroxyl radical rebound chemistry, achieving hydroxylation of the trityl radical derived from Gomberg's dimer in 60% yield. Thermodynamic analysis revealed an O-H bond dissociation free energy of 76.3 kcal mol-1, which is reflected in its selective reactivity toward O-H bond oxidation of substituted 2,6-di-tert-butylphenols. Kinetic and mechanistic studies support a concerted proton-electron transfer (CPET) pathway, providing new insights into the structure, thermodynamics, and reactivity of FeIVOH intermediates.