Intramolecularly hydrogen-bonded versus copper(II) coordinated mono- and bis-phenoxyl radicals

Dalton Trans. 2004 Sep 7:(17):2662-9. doi: 10.1039/b406009a. Epub 2004 Aug 5.

Abstract

Ligands bearing two salicylidene imine moieties substituted in ortho and para positions by tert-butyl groups have been electrochemically oxidized into mono- and bis-phenoxyl radicals. The process involves an intramolecular proton coupled to electron transfer and affords a radical in which the oxygen atom is hydrogen-bonded to a protonated ammonium or iminium group. A weak intramolecular dipolar interaction exists between the two phenoxyl moieties in the bis-radical species. The copper(II) complexes of these ligands have been characterized and electrochemically oxidized. The mono-phenoxyl radical species are X-band EPR silent. The bis-phenoxyl radical species exhibits a (S= 3/2) ground state: it arises from a ferromagnetic exchange coupling between the two spins of the radicals and that of the copper(II) when the spacer is rigid enough; a flexible spacer such as ethylidene induces decomplexation of at least one phenoxyl group. Metal coordination is more efficient than hydrogen-bonding to enhance the chemical stability of the mono-phenoxyl radicals.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biomimetic Materials / chemistry
  • Cations, Divalent
  • Copper / chemistry*
  • Electrochemistry
  • Free Radicals / chemistry
  • Hydrogen Bonding
  • Imines / chemistry
  • Ligands
  • Organometallic Compounds / chemistry
  • Oxidation-Reduction
  • Phenols / chemistry*
  • Salicylates / chemistry

Substances

  • Cations, Divalent
  • Free Radicals
  • Imines
  • Ligands
  • Organometallic Compounds
  • Phenols
  • Salicylates
  • phenoxy radical
  • Copper