OXYGENATION OF SUBSTITUTED PHENOLS USING MOLECULAR-OXYGEN AND COBALT(II) CYCLIDENE COMPLEXES

The superstructured cobalt(II) cyclidene complexes function as both oxidase and oxygenase models in oxygenation of substituted phenols. The catalytic cycle for oxygenation of 2,6-di-tert-butylphenol is considered, including the reaction pathways to the two oxygenation products, benzoquinone and diphenoquinone. The product selectivity of the oxygenation reaction varies with the structures and dioxygen binding behavior, providing insight into the reaction mechanism. This, the kinetics of the oxygenation reaction, and modeling studies lead to a minor modification of the previously proposed mechanism, in which electron transfer is suggested for the formation of the intermediate phenoxy radical. The stabilities of the complexes under a dioxygen atmosphere control their catalytic abilities because autoxidation destroys the catalysts.