Nucleophilic versus Electrophilic Reactivity of Bioinspired Superoxido Nickel(II) Complexes

Abstract

AbstractThe formation and detailed spectroscopic characterization of the first biuret‐containing monoanionic superoxido‐NiII intermediate [LNiO2]− as the Li salt [2; L=MeN[C(=O)NAr)2; Ar=2,6‐iPr2C6H3)] is reported. It results from oxidation of the corresponding [Li(thf)3]2[LNiIIBr2] complex M with excess H2O2 in the presence of Et3N. The [LNiO2]− core of 2 shows an unprecedented nucleophilic reactivity in the oxidative deformylation of aldehydes, in stark contrast to the electrophilic character of the previously reported neutral Nacnac‐containing superoxido‐NiII complex 1, [L′NiO2] (L′=CH(CMeNAr)2). According to density‐functional theory (DFT) calculations, the remarkably different behaviour of 1 versus 2 can be attributed to their different charges and a two‐state reactivity, in which a doublet ground state and a nearby spin‐polarized doublet excited‐state both contribute in 1 but not in 2. The unexpected nucleophilicity of the superoxido‐NiII core of 2 suggests that such a reactivity may also play a role in catalytic cycles of Ni‐containing oxygenases and oxidases.