Brønsted-Lewis dual acid sites in a chromium-based metal-organic framework for cooperative catalysis: Highly efficient synthesis of quinazolin-(4H)-1-one derivatives.

A novel MIL-101(Cr) (MIL, Matérial Institut Lavoisier) supported propyl carboxylic acid, denoted here as MIL-101(Cr)-NH-CO-Pr-COOH, has been fabricated by post-synthetic modifications of nitro-functionalized MIL-101(Cr), MIL-101(Cr)-NO. The resulting MOF was successfully characterized by using FT-IR, XRD, N adsorption-desorption, H NMR, SEM, ICP-OES, elemental analysis and TGA. Then, the prepared solid was used as an extremely highly effective multifunctional catalyst for the one-pot three-component synthesis of quinazolin-4(1H)-one derivatives as biologically active nitrogen heterocyclic compounds under solvent-free conditions. The important features of this methodology are good to excellent yields of products, the use of very small amounts of catalyst, short reaction time, non-requirement of organic solvents, and environmental benign and mild reaction conditions. Furthermore, turnover frequency was found to be in the range 3.5-50 h under neat conditions, which is comparable to the reported previously for this reaction. Significantly, compared with the pristine MOF and the related homogenous catalysts, the MIL-10 1(Cr)-NHCO-Pr-COOH exhibited superior catalytic activity which can be attributed to the synergistic effect between isolated Lewis acidic Cr(III) nodes and Brønsted acidic free COOH groups in addition to the cooperative interplay of the Brønsted acid and the amine sites within the framework. More remarkably, MOF was stable and reusable up to three times without any changes in its activity and structure.