Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 284

in methanol 66 and benzene. 67 The overall stoichiometry
is given by the equation:
An intermediate catecholatocobaloxime (III) has been isolated from the
reacting mixture. Its molecular structure determined by x-ray diffraction 66
revealed an axially bonded unidentate catecholato ligand, which is formed
via free-radical coupling between the cobaloxime(II) and the semiquinone
anion radical The latter has been detected by EPR spectroscopy
during the reaction together with its cobaloxime(III)-bonded derivative
which indicates a free-radical mechanism for catechol
oxidation. The mechanism proposed for the catalytic oxidation on the basis
of the detectable intermediates is shown in Figure 26. In this scheme
stands for also referred to as cobaloxime(II). The
double catalytic cycle is joined together by and -activation takes
place via formation of superoxocobaloxime(III), followed by H-
atom abstraction from affording During the catalytic
reaction, and catechol oxidation are taking place according to the
lower cycle, while the cobaloxime species in the upper cycle are present at
steady state or equilibrium concentrations.