Conveniently Constructing Cu+ Sites and Oxygen Vacancies in Layered Double Hydroxides for the Efficient Aerobic Oxidation of Alkylarenes Via Hydrogen Atom Transfer Process

Abstract

A convenient protocol has been developed for constructing active Cu+ sites and oxygen vacancies based on layered double hydroxides (LDHs) simply by introducing ethanol during the coprecipitation. The prepared CuZnAl-LDH(H) has been systematically characterized, and the results demonstrated that the catalyst was rich in Cu+ sites and oxygen vacancies. The studies on the structure-activity relationship indicated that the surface oxygen vacancies could effectively activate molecular oxygen and promote the formation of active singlet oxygen 1O2, and Cu+ sites could react with oxygen to generate active intermediate Cu2+ superoxides (Cu2+OO•). On the mechanism, Cu2+OO• species abstracted hydrogen atom from the O‒H bond of NHPI (N-hydroxyphthalimide) to generate active PINO (phthalimide N-oxyl) intermediates, which subsequently activated the C‒H bond in alkylarenes via HAT (hydrogen atom transfer) process. Then the formed radicals reacted with the activated 1O2 species to finish the transformation. The CuZnAl-LDH(H) also displayed the advantages of catalytical and structural stability, recyclability, and tolerance of wide substrate scope.

Keywords: Cu+ species, Oxygen vacancy, Ethanol, Alkylarenes oxidation, Hydrogen atom transfer