Comparison of Catalytic Behaviors of Brønsted Versus Lewis Acidic MOFs in Synthesis of 2,4,5-Trisubstituted Imidazoles

Abstract

The catalytic efficacy of the Lewis acidic site in Cu₃(BTC)₂ MOF was compared with the Brønsted acidic site in MIL-101-SO₃H MOF. Both Lewis and Brønsted acidic MOFs demonstrate strong conversion rates in the synthesis of 2,4,5-triaryl imidazoles through a one-pot multicomponent reaction under a microwave condition. This outcome underscores the stability and reusability of both MOFs. The catalytic activity of the MOFs relies on the facile accessibility of catalytically active centers/sites to the reactants. Superior results were achieved with MIL-101-SO₃H MOF's Brønsted acidic sites compared with Cu₃(BTC)₂ MOF's Lewis acidic sites due to the latter's shortcomings in reusability and stability as a catalyst in the synthesis of 2,4,5-TSIs (2,4,5-trisubstituted imidazoles). MIL-101-SO₃H MOF can be reused multiple times without any loss in its catalytic activity, as demonstrated by hot filtration tests and various analytical techniques such as FTIR, powder XRD, SEM, and EDAX conducted on both fresh and reused MOF catalysts.