Catalytic performance of metal azolate frameworks in the solventless synthesis of cyclic carbonates from CO2 and epoxides

Abstract

Two types of metal azolate frameworks (MAFs) with uncoordinated and coordinated nitrogen atoms composed of zinc coordinated with 3-amino-1,2,4-triazole and 3,5-dimethyl-1,2,4-triazole linkers denoted as MAF-66 and MAF-X5, respectively have been synthesized and characterized using various physicochemical techniques. The uncoordinated N donors present in the MAFs show high adsorption affinity for carbon dioxide. The synthesized MAFs showed promising catalytic activity towards the cycloaddition of carbon dioxide and epoxides under solvent-free conditions with excellent selectivity towards the desired five-membered cyclic carbonates. The importance of uncoordinated N donors and amine groups in the effective catalysis of the cycloaddition of CO2 and epoxides was investigated. Both catalysts were separable by simple filtration and reusable without any considerable loss in the initial activity. Various reaction parameters including temperature, reaction time, and CO2 pressure were studied. A possible reaction mechanism explaining the role of amine groups in the cycloaddition reaction was proposed based on literature and experimental inferences.