Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 269

Recent progress in bimetallic dioxygen complexes containing compart-
mental ligands has been reviewed. 17

3. OXIDATIONS CATALYZED BY Co(salen)
COMPLEXES

The cobalt(II) complexes of salen type ligands have long been used as
catalysts for the oxidation of substituted phenols. The subject has been
extensively reviewed 22,23 . In this chapter emphasis is placed on recent
advances.

3.1 Oxidation of substituted phenols

3.1.1 2,6-di- tert -butylphenol

The properties of oxygen adducts of complexes
(Figure 3) have been studied by cyclic
voltammetry, IR, electronic and ESR spectroscopy. The complexes exhibit
oxygen-binding ability in the presence of an axial ligand (py), and end-on
superoxocobalt type dioxygen adducts are formed 18 . Electron-donating
substituents gave higher concentrations of the superoxo complex. The Me-
and derivatives give superior catalytic activity in the
oxygenation of 2,6-di- tert -butylphenol to the corresponding quinone.

The oxidation of 2,3,6-tri-tert-butylphenol and 2,4,6-tri- tert -butylaniline