Additive-free aerobic oxidative dehydrogenation of N-heterocycles under catalysis by NiMn layered hydroxide compounds

NiMn layered hydroxide compounds have been found to be efficient catalysts for the oxidative dehydrogenation of N-heterocycles by molecular oxygen under mild conditions. Various tetrahydroquinoline derivatives and some other N-heterocycles have been found to be tolerated by the catalytic system. A synergistic effect between Ni and Mn has been observed in the reaction. A kinetic study concluded that the dehydrogenation of 1,2,3,4-tetrahydroquinoline is a first-order reaction, and an apparent activation energy of 113 kJ/mol has been obtained. A probable reaction mechanism comprising an imine intermediate has been proposed according to the obtained results and XPS analysis. The key catalytic site for the dehydrogenation is thought to be Mn 3+ , which could be stabilized by Ni 2+ in the hydrotalcite structure.