Reactivity of an Fe^IV-Oxo Complex with Protons and Oxidants

High-valent Fe-OH species are often invoked as key intermediates but have only been observed in Compound II of cytochrome P450s. To further address the properties of non-heme Fe^IV-OH complexes, we demonstrate the reversible protonation of a synthetic Fe^IV-oxo species containing a tris-urea tripodal ligand. The same protonated Fe^IV-oxo species can be prepared via oxidation, suggesting that a putative Fe^V-oxo species was initially generated. Computational, Mössbauer, XAS, and NRVS studies indicate that protonation of the Fe^IV-oxo complex most likely occurs on the tripodal ligand, which undergoes a structural change that results in the formation of a new intramolecular H-bond with the oxido ligand that aids in stabilizing the protonated adduct. We suggest that similar protonated high-valent Fe-oxo species may occur in the active sites of proteins. This finding further argues for caution when assigning unverified high-valent Fe-OH species to mechanisms.