Mechanistics Studies on the Cobalt(II) Schiff Base Catalyzed Oxidation of Olefins by O2

Article abstract of DOI:10.1021/ja00236a014

The cobalt complex cobalt(II), CoSMDPT, has been shown to catalystically oxidize olefins in the presence of dioxygen or hydrogen peroxide.When terminal olefins are oxidized, the methyl ketone and corresponding secondary alcohol are produced selectively.Internal as well as terminal olefins are oxidized.The most common pathway for the oxidation of olefins catalyzed by first-row transition metals - autoxidation - has been ruled out in this system.A Wacker-type mechanism, oxidation by peracids, and mechanisms involving the formation of peroxymetallocycles have also been ruled out.A new mechanism for O2 oxidations is proposed which involves oxidation of the primary alcohol solvent by CoSMDPT to produce the corresponding aldehyde and hydrogen peroxide.Reaction of hydrogen peroxide with CoSMDPT occurs to form a cobalt hydroperoxide, which can be viewed as a stabilized hydroperoxy radical which has spin paired with the d_z2 electron of CoSMDPT.The cobalt hydroperoxide then adds to the olefin double bond, leading to formation of an alkyl hydroperoxide.Haber-Weiss decomposition of this alkyl hydroperoxide by CoSMDPT produces the observed ketone and alcohol products.Deactivation of the catalysts is due to oxidation of the ligand system of the cobalt complex as well as formation op a μ-peroxo-dicobalt complex.