Engineering of Porous Polyamide-Supported Deep Eutectic Solvent as a Metal-Free Heterogeneous Catalyst for the Synthesis of 3,4-Dihydropyrimidinones and 5-Substituted-1H-Tetrazoles

Abstract

Deep eutectic solvents (DESs) have emerged as environmentally friendly and tunable green alternatives to traditional ionic liquids and organic solvents, offering advantages such as low toxicity, thermal stability, and negligible vapor pressure. However, challenges related to their separation and reuse limit their practical application in catalysis. Immobilizing DESs on solid substrates, particularly porous organic polymers (POPs), addresses these limitations by enhancing catalyst recovery, stability, and reusability. POPs, especially those based on triazine-containing polyamides, provide a robust, chemically stable, and highly porous framework that facilitates effective mass transfer and substrate activation through Lewis basic sites. In this study, the synthesis of a novel metal-free catalyst, ChCl@TPA, was achieved by in situ formation of a DES via hydrogen bonding between choline chloride (ChCl) and amide groups on the POP surface. This immobilized DES catalyst exhibits bifunctional catalytic activity arising from the synergistic effect between the hydrogen bond network and triazine moieties (as basic sites), enabling efficient synthesis of Biginelli and tetrazole derivatives under mild and green conditions. The catalyst demonstrates excellent recyclability and structural integrity over multiple cycles, highlighting the potential of DES immobilization on POP supports for sustainable and multifunctional catalysis aligned with green chemistry principles.

Graphical Abstract