Five Nitrogen Oxidation States from Nitro to Amine: Stabilization and Reactivity of a Metastable Arylhydroxylamine Complex

J Am Chem Soc. 2020 Nov 11;142(45):19023-19028. doi: 10.1021/jacs.0c09300. Epub 2020 Oct 30.

Abstract

Redox noninnocent ligands enhance the reactivity of the metal they complex, a strategy used by metalloenzymes and in catalysis. Herein, we report a series of copper complexes with the same ligand framework, but with a pendant nitrogen group that spans five different redox states between nitro and amine. Of particular interest is the synthesis of a unprecedented copper(I)-arylhydroxylamine complex. While hydroxylamines typically disproportionate or decompose in the presence of transition metal ions, the reactivity of this metastable species is arrested by the presence of an intramolecular hydrogen bond. Two-electron oxidation yields a copper(II)-(arylnitrosyl radical) complex that can dissociate to a copper(I) species with uncoordinated arylnitroso. This combination of ligand redox noninnocence and hemilability provides opportunities in catalysis for two-electron chemistry via a one-electron copper(I/II) shuttle, as exemplified with an aerobic alcohol oxidation.

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

  • Alcohols / chemistry
  • Amines / chemistry*
  • Coordination Complexes / chemistry*
  • Copper / chemistry
  • Density Functional Theory
  • Hydroxylamines / chemistry
  • Ligands
  • Molecular Conformation
  • Nitrogen / chemistry*
  • Oxidation-Reduction

Substances

  • Alcohols
  • Amines
  • Coordination Complexes
  • Hydroxylamines
  • Ligands
  • Copper
  • Nitrogen