The Role of the Redox Non‐Innocent Hydroxyl Ligand in the Activation of O2 Performed by [Ni(H)(OH)]

• Published in: Chemistry : a European journal 2023-03, Vol.29 (14), p.e202203128-n/a
• Main Authors: Kim, Jun‐Hyeong, Buyuktemiz, Muhammed, Alıcı, Gökçe, Baik, Mu‐Hyun, Dede, Yavuz
• Format: Article
• Language: English
• Subjects: Chemical reactions; Chemistry; Density functional theory; dioxygen activation mechanism; electron transfer; Electronic structure; Free radicals; Hydroxyl radicals; Internal energy; Ligands; multiconfigurational calculation; Nickel; non-innocent ligand; Oxidation; Substrates; Valence; Vapor phases; Wave functions
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202203128

The cationic complex [Ni(H)(OH)]+ was previously found to activate dioxygen and methane in gas phase under single collision conditions. These remarkable reactivities were thought to originate from a non‐classical electronic structure, where the Ni‐center adopts a Ni(II), instead of the classically expected Ni(III) oxidation state by formally accepting an electron from the hydroxo ligand, which formally becomes a hydroxyl radical in the process. Such radicaloid oxygen moieties are envisioned to easily react with otherwise inert substrates, mimicking familiar reactivities of free radicals. In this study, the reductive activation of dioxygen by [Ni(H)(OH)]+ to afford the hydroperoxo species was investigated using coupled cluster, multireference ab initio and density functional theory calculations. Orbital and wave function analyses indicate that O2 binding tranforms the aforementioned non‐classical electronic structure to a classical Ni(III)‐hydroxyl system, before O2 reduction takes place. Remarkably, we found no evidence for a direct involvement of the radicaloid hydroxyl in the reaction with O2, as is often assumed. The function of the redox non‐innocent character of the activator complex is to protect the reactive electronic structure until the complex engages O2, upon which a dramatic electronic reorganization releases internal energy and drives the chemical reaction to completion. Mechanism of dioxygen activation by [Ni(H)(OH)]+ was studied by a state‐of‐art multiconfigurational calculations. The role of redox‐non‐innocent hydroxyl in [Ni(H)(OH)]+ was elucidated, that is an energy reservoir instead of being the reaction center as what most of bioinorganic complexes show.