Dioxygenase-like reactivity of an isolable superoxo-nickel(II) complex

Although O(2) activation by metals such as iron and copper has been a matter of intensive research in the last decades, this type of chemistry for nickel systems is still in its infancy. Moreover, studies regarding the oxidizing ability of the resulting "Ni(n)-O(2)" species towards exogenous substrates are scarce. In this work, we report on the reactivity of an isolable and thermally stable mononuclear superoxo-nickel compound [Ni(II)(beta-diketiminato)(O(2))] (1) towards different types of organic substrates. In addition, we have been able to prove that the beta-diketiminato ligand can undergo partial intramolecular oxidation due to close proximity between the isopropyl groups of the beta-diketiminato-aryl and the superoxo subunits. Compound 1 performs hydrogen-atom abstraction from O-H and N-H groups and most importantly it shows an unprecedented dioxygenase-like reactivity in the oxidation of 2,4,6-tri-tert-butylphenol. The latter reaction most likely occurs through the mediation of a putative [Ni(III)-oxo] intermediate, affording an unprecedented oxidation product of the phenol that incorporates two oxygen atoms from a single O(2) subunit. Results presented herein provide evidence of the striking oxidizing ability of dioxygen-nickel species and further support the viability to use such systems as oxidation catalysts analogous to its heavy metal congener, palladium.