Using sulfate-functionalized Hf-based metal–organic frameworks as a heterogeneous catalyst for solvent-free synthesis of pyrimido[1,2-a]benzimidazoles via one-pot three-component reaction

Abstract Functionalized metal–organic frameworks have recently received significant attention in heterogeneous catalysis applications due to their high catalytic activity. In this work, a sulfate-functionalized Hf-cluster-based metal–organic framework was prepared via sulfation of a Hf-MOF, named Hf-BTC, constructed by Hf6 clusters and 1,3,5-tricarboxylate linkers. The Hf-BTC-SO4 material was consequently demonstrated to be an efficiently reusable superacid catalyst for a one-pot three-component reaction of pyrimido[1,2-a]benzimidazoles synthesis. The reaction catalyzed by the sulfated Hf-BTC could be carried out under mild and solvent-free conditions and give superior performance in a wide range of substrates. According to detailed investigation, the good catalytic performance of the sulfated-functionalized MOF likely originates from the high-porosity framework and the high active sites of the functionalized clusters. Importantly, the catalyst could be easy to recover and reuse the functionalized framework several times with minor changes in catalytic efficiency.