Dataset Information

O-O Bond Formation and Liberation of Dioxygen Mediated by N5 -Coordinate Non-Heme Iron(IV) Complexes.

ABSTRACT: Formation of the O-O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High-valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O-O bond in solution, from non-heme, N5 -coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta-chloroperbenzoic acid is administered in excess. Oxygen-isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)-initiated free-radical pathways of the peroxides, which are typical of catalase-like reactivity, and iron-borne O-O coupling, which is unprecedented for non-heme/peroxide systems. Interpretation in terms of [FeIV (O)] and [FeV (O)] being the resting and active principles of the O-O coupling, respectively, concurs with fundamental mechanistic ideas of (electro-) chemical O-O coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting.

SUBMITTER: Kroll N

PROVIDER: S-EPMC6772150 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Publications

O-O Bond Formation and Liberation of Dioxygen Mediated by N<sub>5</sub> -Coordinate Non-Heme Iron(IV) Complexes.

Kroll Nicole N Speckmann Ina I Schoknecht Marc M Gülzow Jana J Diekmann Marek M Pfrommer Johannes J Stritt Anika A Schlangen Maria M Grohmann Andreas A Hörner Gerald G

Angewandte Chemie (International ed. in English) 20190813 38

Formation of the O-O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High-valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O-O bond in solution, from non-heme, N<sub>5</sub> -coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta-chloroperbenzoic acid is administered in ...[more]

PMID: 31271694

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Project description:Oxoiron(IV) species have been found to act as the oxidants in the catalytic cycles of several mononuclear nonheme iron enzymes that activate dioxygen. To gain insight into the factors that govern the oxidative reactivity of such complexes, a series of five synthetic S = 1 [Fe(IV)(O)(L(N5))](2+) complexes has been characterized with respect to their spectroscopic and electrochemical properties as well as their relative abilities to carry out oxo transfer and hydrogen atom abstraction. The Fe=O units in these five complexes are supported by neutral pentadentate ligands having a combination of pyridine and tertiary amine donors but with different ligand frameworks. Characterization of the five complexes by X-ray absorption spectroscopy reveals Fe=O bonds of ca. 1.65 Å in length that give rise to the intense 1s?3d pre-edge features indicative of iron centers with substantial deviation from centrosymmetry. Resonance Raman studies show that the five complexes exhibit ?(Fe=O) modes at 825-841 cm(-1). Spectropotentiometric experiments in acetonitrile with 0.1 M water reveal that the supporting pentadentate ligands modulate the E(1/2)(IV/III) redox potentials with values ranging from 0.83 to 1.23 V vs. Fc, providing the first electrochemical determination of the E(1/2)(IV/III) redox potentials for a series of oxoiron(IV) complexes. The 0.4-V difference in potential may arise from differences in the relative number of pyridine and tertiary amine donors on the L(N5) ligand and in the orientations of the pyridine donors relative to the Fe=O bond that are enforced by the ligand architecture. The rates of oxo-atom transfer (OAT) to thioanisole correlate linearly with the increase in the redox potentials, reflecting the relative electrophilicities of the oxoiron(IV) units. However this linear relationship does not extend to the rates of hydrogen-atom transfer (HAT) from 1,3-cyclohexadiene (CHD), 9,10-dihydroanthracene (DHA), and benzyl alcohol, suggesting that the HAT reactions are not governed by thermodynamics alone. This study represents the first investigation to compare the electrochemical and oxidative properties of a series of S = 1 Fe(IV)=O complexes with different ligand frameworks and sheds some light on the complexities of the reactivity of the oxoiron(IV) unit.

Dataset Information

O-O Bond Formation and Liberation of Dioxygen Mediated by N5 -Coordinate Non-Heme Iron(IV) Complexes.

Publications

O-O Bond Formation and Liberation of Dioxygen Mediated by N<sub>5</sub> -Coordinate Non-Heme Iron(IV) Complexes.

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