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

Abstract

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 FeIV–OH complexes we demonstrate the reversible protonation of a synthetic FeIV–oxo species containing a tris-urea tripodal ligand. The same protonated FeIV–oxo species can be prepared via oxidation, suggesting a putative FeV–oxo species was initially generated. Computational, Mössbauer, XAS, and NRVS studies indicate that protonation of the FeIV–oxo complex most likely occur on the tripodal ligand, which undergoes a structural change that results in the formation of a new intramolecular hydrogen bond with the oxido ligand that aids in stabilizing the protonated adduct. We suggest that similar species for 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.

Probing Hydrogen Bonding Interactions to Iron‐Oxido/Hydroxido Units by 57Fe Nuclear Resonance Vibrational Spectroscopy

“…v [Fe=O] was reported to be 794 cm −1 for this complex from the NRVS data recorded on a frozen solution, [38,42] which is also consistent with the v [Fe IV =O] of 799 cm −1 reported from FTIR measurements. [43] Here, both 16 O and 18 O isotopomers were further recorded on solid powders (Figure 3e) to confirm its origin as v [Fe IV =O] vibration with Δ v ( 16 O/ 18 O) = 30 cm −1 (Δ v = 35 cm −1 based on Hook’s law).…”

Manganese–Hydroxido Complexes Supported by a Urea/Phosphinic Amide Tripodal Ligand

“…A similar reorientation of a urea arm has been proposed for the protonated form of [Fe IV H 3 buea(O)] – . 46 The computed equatorial Mn-N bond lengths were more similar for species A relative to those found for species B which suggests A corresponds to the species with E/D values of 0.17 and 0.33, respectively. DFT calculations of the spin-dipolar A-tensors for the two species gave (29, −2, −27) MHz (A) and (30, 6, −36) MHz (B), which were in approximate agreement with the experimental values of (17, 3, −20) MHz for A and (26, −5, −21) MHz for B .…”

A new look at the role of thiolate ligation in cytochrome P450

“…Even today, a definitive characterization of a synthetic iron(IV)hydroxide complex remains elusive. 49,50 Ferryl species are typically electrophilic in nature, and the report of a nucleophilic/basic iron(IV)oxo in CPO-II was somewhat unexpected. There were some suggestions that the CPO-II sample may have been photoreduced in the synchrotron x-ray beam, and that the long 1.82 Å Fe-O bond obtained from XAS measurements was representative of ferric enzyme in an unusual coordination environment.…”