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

Angew Chem Int Ed Engl. 2018 Nov 5;57(45):14883-14887. doi: 10.1002/anie.201808085. Epub 2018 Oct 17.

Abstract

The 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-iPr2 C6 H3 )] is reported. It results from oxidation of the corresponding [Li(thf)3 ]2 [LNiII Br2 ] complex M with excess H2 O2 in the presence of Et3 N. 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.

Keywords: dioxygen ligands; nickel; structure elucidation; structure-activity relationships; two-state reactivity.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Coordination Complexes / chemistry*
  • Lithium / chemistry*
  • Models, Molecular
  • Nickel / chemistry*
  • Oxidation-Reduction
  • Oxidoreductases / chemistry
  • Oxygen / chemistry
  • Oxygenases / chemistry
  • Quantum Theory
  • Salts / chemistry
  • Superoxides / chemistry*

Substances

  • Coordination Complexes
  • Salts
  • Superoxides
  • Nickel
  • Lithium
  • Oxidoreductases
  • Oxygenases
  • Oxygen