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.
Highlights
Formation of the OÀO bond is considered the critical step in oxidative water cleavage to produce dioxygen
Oxygen-isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT-initiated free-radical pathways of the peroxides, which are typical of catalase-like reactivity, and iron-borne OÀO 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 OÀO coupling, respectively, concurs with fundamental mechanistic ideas of chemical OÀO coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting
Summary
Formation of the OÀO bond is considered the critical step in oxidative water cleavage to produce dioxygen. In neat MeCN the measured ratio of dioxygen isotopomer inactive solutions of [FeIV(L)(O)]2+ can be activated in a second step and immediately produce significant amounts of O2 upon addition of mCPBA (Figure 1 c; green curve).
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