O−O Bond Formation and Liberation of Dioxygen Mediated by N5‐Coordinate Non‐Heme Iron(IV) Complexes. Issue 38 (13th August 2019)

• Record Type: Journal Article
• Authors: Kroll, Nicole; Speckmann, Ina; Schoknecht, Marc; Gülzow, Jana; Diekmann, Marek; Pfrommer, Johannes; Stritt, Anika; Schlangen, Maria; Grohmann, Andreas; Hörner, Gerald
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 38(2019)
• Page Start: 13472
• Page End: 13478
• Publication Date: 2019-08-13
• Subjects: bioinorganic chemistry -- iron -- nitrogen ligands -- O−O activation -- oxo ligands; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201903902
• Languages: English
• ISSNs: 1433-7851

Abstract

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 [Fe IV (O)] and [Fe V (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. Abstract : The O−O bond is efficiently formed and dioxygen stoichiometrically released in the reaction of non‐heme oxoiron(IV) complexes with meta ‐chloroperbenzoic acid. High‐valent iron(IV) is identified as a resting state. It is suggested to be activated towards O–O coupling through concerted inner‐sphere transfer of an electron and a hydroxyl anion.