Copper metal–organic framework: Structure and activity in the allylic oxidation of cyclohexene with molecular oxygen

Abstract

Cu-MOF [Cu(bpy)(H 2O) 2(BF 4) 2(bpy)] (bpy: 4,4′-bipyridine) shows promising catalytic activity and high selectivity in allylic oxidation of cyclohexene with molecular oxygen as the only oxidant. Under close to ambient conditions and in the absence of solvent the selectivity in cyclohexene hydroperoxide reached 90%. The combined catalytic, spectroscopic, thermogravimetric, and electron microscopic study indicates that the reaction occurs at the surface of the latent porous framework and both bpy and water are involved in the active complex. Removal of the structural water at 100 °C in vacuum induces a crystal-to-crystal restructuring and opens the pores but eliminates the oxidation activity. Rehydration under ambient conditions in air regenerates Cu-MOF with small structural changes and each dehydration–rehydration cycle increases the oxidation activity. Not only dehydration–rehydration but also stirring the slurry during oxidation induces remarkable changes in the shape and size of the crystallites.