Selective oxidation of ethylbenzene by dioxygen. The effect of chelate center on catalysis by bicyclic nickel complexes

The effect of the nature of the chelate center in Ni-II complexes on their catalytic activity in the selective oxidation of ethylbenzene by dioxygen to alpha-phenylethyl hydroperoxide in the presence of nickel bis(acetylacetonate) (chelate center Ni(O,O)(2)) and nickel bis(enamino-acetonate) (chelate center NI(O,NH)(2)) was studied. The efficiency of selective oxidation of ethylbenzene increases substantially in the presence of the chelate with the NI(O,NH)(2) active center as a catalyst, which is mainly due to the transformation of the catalyst into more active species during the oxidation process. The mechanism of transformation of nickel bis(enaminoacetonate) under the action of dioxygen was suggested. The sequence of formation of the reaction products at different stages of the catalytic process was determined. The activity of the nickel complex with the Ni(O,NH)(2) chelate center and the products of its transformation in the elementary stages of chain oxidation of ethylbenzene is discussed.