Copper immobilized MIL-125-NH₂ as an efficient nanocatalyst for click reaction and synthesis of benzo[b]pyrans

Multicomponent reactions (MCRs) offer a significant opportunity for simplicity, efficiency, and sustainability in the development of catalytic protocols for synthesizing medicinally important heterocycles. By minimizing environmental impact through the use of green solvents and recyclable heterogeneous catalysts, researches contribute directly to the principles of green chemistry and sustainable industrial practices. In this article, we present the development of a new multifunctional heterogeneous nanocatalyst, Cu@MIL-125-NH-Ac-Met, which was created by sequentially modifying MIL-125-NH₂ with bromoacetyl bromide and metformin ligands to enable the efficient immobilization of copper nanoparticles. A variety of characterization techniques, including XRD, FESEM, FT-IR, EDS, ICP-OES, BET, TGA, and TEM, were employed to analyze the structural properties of the nanocomposite. The results confirmed the successful formation of uniformly distributed Cu nanoparticles (9-23 nm) with a 3.92% Cu loading. The Cu@MIL-125-NH-Ac-Met nanocomposite exhibited outstanding catalytic performance in the synthesis of tetrahydrobenzo[b]pyrans and in Cu-catalyzed click reactions. These reactions were conducted in a water/ethanol (1:1) medium at 50 °C, achieving high product yields (85-99%) under mild conditions. The catalyst retained excellent stability and activity over at least five consecutive cycles, with Cu leaching below 1%. This work demonstrates an efficient, recyclable, and environmentally sustainable catalytic system with significant potential for diverse organic transformations and green synthetic applications.