The role of carboxylic acid contents in calcium-based metal-organic frameworks for the enhancement of Biginelli reaction

Abstract

Metal-organic frameworks (MOFs) can carry different functional groups such as COOH, NH2, and SO3H. The most commonly used functional group was COOH due to its Brønsted acidity, polarity, and ability to bond with organic compounds and metals through various interactions. Here, calcium-based MOFs (Ca-MOFs) with different carboxylic arms were successfully prepared and used in heterogeneous Biginelli catalytic reactions. The prepared materials (Ca-BDC-H, Ca-BDC-COOH, and Ca-BDC-(COOH)2) were characterized using different spectroscopic techniques and the morphological structures were determined using microscopic analysis. Besides elucidating the fine form of MOFs, the role of the carboxylic content was tested in multicomponent reaction catalysis in different kinetics and thermodynamic studies, the formation of catalytic products was determined using NMR analysis, and the proposed mechanism was investigated. The results obtained showed that as the carboxylic content in the network increases, the catalytic reaction yield increases which can support the possibility of using the COOH group present in the network with acidic properties in heterogeneous catalysts giving high product yield.