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

Abstract

Abstract The formation and detailed spectroscopic characterization of the first biuret‐containing monoanionic superoxido‐Ni II intermediate [LNiO 2 ] − as the Li salt [ 2 ; L=MeN[C(=O)NAr) 2 ; Ar=2,6‐iPr 2 C 6 H 3 )] is reported. It results from oxidation of the corresponding [Li(thf) 3 ] 2 [LNi II Br 2 ] complex M with excess H 2 O 2 in the presence of Et 3 N. The [LNiO 2 ] − 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‐Ni II complex 1 , [L′NiO 2 ] (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‐Ni II core of 2 suggests that such a reactivity may also play a role in catalytic cycles of Ni‐containing oxygenases and oxidases.