Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 312

When cyclohexane is used as the substrate, cyclohexanol, cyclohexanone
and cyclohexyl chloride are the products. In single turnover oxidation of
cyclohexane at the optimum temperature of 80°C, a maximum yield of 59%
of the oxidized products is obtained.
The mechanism of cyclohexane oxidation involves homolytic scission
of the 0-0 bond exclusively. The radicals generated abstract an H-
atom from cyclohexane to afford cyclohexyl radicals, which in turn react
with dioxygen and produce cyclohexanol (CyOH) and cyclohexanone (CyO)
presumably via the Russell-type termination reaction 171 :

The oxidation of cyclohexane can be either stoichiometric or catalytic. In
the presence of excess TBHP, higher yields of oxidized products are
obtained, indicating multiple turnovers.
Twelve additional Co(III)-alkylperoxo complexes have been synthe-
sized, including those of the ligand N,N -bis[2-( 1 -pyrazolyl)-ethyl]-pyridine-

2,6-dicarboxamide (Figure 60), with various primary, secondary,

groups 172 .
When the various complexes are warmed (60-80°C) in
dichloromethane in the presence of cyclohexane(CyH ), the formation of
cyclohexanol (CyOH ) and cyclohexanone (CyO ) is observed in good yields.
Homolysis of the

and tertiary R

O - O bond in the complexes generating

radicals is responsible for the alkane oxidation.
Since species are converted into complexes at
the end of a single turnover in stoichiometric oxidations, catalytic systems
can be generated by the addition of excess ROOH to the reaction mixtures.
Catalytic oxidations proceed at considerable rates at moderate temperatures