Metal–organic framework functionalized with deep eutectic solvent as the efficient, green, reusable, and heterogeneous catalyst for one-pot three-component synthesis of pyrimido[1,2-a]benzimidazoles

Abstract

Deep eutectic solvents (DESs) depict a class of solvents including some features of their ionic liquid cousins – relatively wide liquid range, low vapor pressure, and non-flammability. Nonetheless, since DESs are liquid and their transportation and separation are inconvenient, a new method is suggested that the immobilization of DESs on appropriate support could be a feasible solution. Herein, a DES-supported catalyst was prepared. Initially, metal–organic framework (MOF), NH₂- MIL-101(Cr), was modified with D-( +)-ribonic γ-lactone (RL), as a class of carbohydrates (CHs), which prepares plenty of hydroxyl groups on the surface for stabilizing choline chloride (ChCl) via hydrogen bonding, based on DESs. NH₂-MIL-101-RL@ChCl with appealing qualities like thermal and chemical stability and reusable catalyst is utilized for the one-pot synthesis of pyrimido[1,2-a] benzimidazoles. Its great catalytic performance was related to a synergistic effect between active sites of NH₂-MIL-101-RL and ChCl. The hot filtration test of the catalyst confirmed the heterogeneous nature and structural stability of the hybrid system. The porous NH₂-MIL-101-RL@ChCl was characterized using FTIR, powder XRD, SEM, EDX elemental mapping, TGA, and BET techniques.