Ionic liquid tethered post functionalized ZIF-90 framework for the cycloaddition of propylene oxide and CO2

Abstract

A novel heterogeneous one-component catalyst was developed by the covalent post functionalization of zeolitic imidazolate framework-90 (ZIF-90) with a pyridinium based ionic liquid (IL) to generate IL supported ZIF-90 (IL-ZIF-90). The synthesized catalyst has been characterized using a range of analytical, spectroscopic, and electron microscopy techniques followed by successful employment for the solventless cycloaddition of epoxides and CO₂ to yield cyclic carbonates under mild reaction conditions. The effects of reaction parameters like catalyst amount, reaction time, reaction temperature, and CO₂ pressure have been investigated. A reaction mechanism for the IL-ZIF-90 catalyzed PO–CO₂ cycloaddition has been proposed on the basis of density functional theory (DFT) calculations. The catalyst system was separable by centrifugation and reused four consecutive times successfully. In general, it can be suggested that IL supported porous metal organic frameworks (MOFs) may introduce a new class of highly porous catalyst species showing excellent CO₂ transforming capability.