Microwave-Assisted Synthesis as an Efficient Method to Enhance the Catalytic Activity of Zr-Based Metal Organic Framework UiO-66 in a Heterocyclization Reaction

Zr-based metal-organic frameworks have been considered promising heterogeneous catalysts in various reactions. It has been proven that the defect sites in these frameworks, which result from deficiency of linkers, could act as the reaction active sites. In this work, microwave irradiation was used for rapid synthesis and increasing defects on Zr-6 clusters of metal-organic framework UiO-66. Powder X-ray diffraction, thermal gravimetric analysis, and N-2 sorption isotherms were performed to characterize and calculate the defect number in the framework. UiO-66 prepared by microwave method for a few minutes could reach 1.8 missing linkers per cluster. The material with acetic acid as a co-catalyst showed highly heterogeneous catalytic activity in the solvent-free heterocyclization of 2,2-disubstituted 2,3-dihydroquinazolin-4(1H)-ones from anthranilamide and ketones/aldehydes. The synthetic scheme consisted of zirconium cluster catalysed carbonyl group of anthranilamide to achieve the C-N propitious combination and succeeding ring closure process.