Choline chloride-coated UiO-66-Urea MOF: A novel multifunctional heterogeneous catalyst for efficient one-pot three-component synthesis of 2-amino-4H-chromenes

A new Zr-based MOF, namely, UiO-66-Urea, was prepared through polymerization between the 2-aminoterephthalate linkers of UiO-66-NH2 MOF and 1,4-phenylene diisocyanate under mild reaction conditions. Post-synthetic coating of UiO-66-Urea with choline chloride (ChCl), as easily available, inexpensive, and nontoxic reagent, under thermal and solvent-free conditions resulted in in-situ formation of a deep-eutectic solvent-like on the UiO-66-Urea's surface, called here ChCI@UiO-66-Urea. The presence of Zr6O4(OH)(4) nodes and urea groups may capable of strong hydrogen bond formation with ChCl. The porous and bioinspired ChCl@UiO-66-Urea was characterized using FT-IR, powder XRD, SEM, EDX elemental mapping, TGA, and BET surface area measurements. Choline chloride-coated UiO-66-Urea was successfully promoted one-pot three-component synthesis of 2-amino-4H-chromenes, as biologically active heterocycles, through reactions of aldehydes, malononitrile, and alpha-naphthol or 4-hydroxycoumarin under solvent-free conditions. The catalytic activity of the respective solid was superior than UiO-66, UiO-66-NH2, UiO-66-Urea, and even ChCl-2Urea due to synergistic effect between actives sites of UiO-66-Urea and ChCl. The reaction includes a consecutive three-step Knoevenagel condensation/Michael addition/cydization mechanism. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

A new Zr-based MOF, UiO-66-Urea, was synthesized through polymerization and post-synthetic coating with choline chloride to form ChCl@UiO-66-Urea, which exhibited superior catalytic activity in the synthesis of biologically active compounds under solvent-free conditions. The interaction between UiO-66-Urea and ChCl led to a synergistic effect, enhancing the overall catalytic performance of the solid material.