Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 110

under air at 20 °C for 20 hours, yielding the corresponding aldehydes with
approximate 55 % yield. The proposed mechanism for this catalytic oxidation
reaction is shown in Scheme 12. The catalytic cycle starts with complex
binding an alcohol to form an alkoxide compound and then in
the rate-determining step ligand is reduced to through
hydrogen-atom transfer from the atom of the alkoxide. The resulting
coordinated ketyl radical anion transfers one electron to ion rapidly to
form the and the aldehyde which dissociates. The regeneration
of the catalyst occurs by oxidizing the complex with through a
superoxide species ] and release of The
superoxide species can be generated on the benchtop and characterized
spectroscopically ( and 650 nm).
A copper-based aerobic catalytic system that transforms a wide range
of alcohols to the corresponding aldehydes or ketones under mild condition
was reported by Marko et al. 120 Upon treatment with a mixture of 5 % CuCl,
5 % phenanthroline, 5% (di- t ert -butyl hydrazodiformate) o r
(1,2-dicarbethoxyhydrazine) and 2 equiv in toluene under
or air at 70 ° to 90 °C, a wide range of primary, secondary, allylic and
benzylic alcohols can be oxidized to the corresponding aldehydes and ketones
with very good yields. The proposed reaction mechanism (Scheme 13)