Intermediates of the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCatH2) by O2 in the presence of (triphenylphosphine)bis(dimethylglyoximato)cobalt(II) as catalyst have been studied. The complex [Co(Hdmg)2-(Ph3P)(3,5-DTBCatH)] has been isolated from the reaction mixture and characterized by X-ray diffraction (monoclinic, P21/c, a = 16.498(1) Å, b = 9.254(1) Å, c = 26.038(2) Å, β = 103.59(1)°, V = 3864.0(4) Å3, Dc = 1.33 g cm−3, Z = 4, µ(Cu Ka) = 44.4 cm−1, R = 0.0480). It contains a unidentate 3,5-di-tert-butylcatecholato-(1−) ligand. Upon dissolution and warming in benzene under N2, homolytic Co-O bond cleavage produces cobaloxime(II) and the free 3,5-di-tert-butylsemiquinonato(1−) anion radical, as demonstrated by ESR spectroscopy. In O2-containing solution, the complex restarts the catalytic reaction, during which the [CoIII(Hdmg)2(Ph3P)(3,5-DTBSQ*)] species can also be detected by ESR. The observed behavior is rationalized by a mechanism incorporating the intermediates identified.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry