Copper-Carboxamide Complex Immobilized on Magnetic Carbon Quantum Dots: A Green Approach to Spirooxindole Synthesis

Abstract

This research details the development of an innovative, eco-friendly magnetic nanocatalyst, referred to as Cu-MCQD-Ugi, produced via a simple one-pot Ugi-4CR approach. The catalyst is formed by immobilizing copper ions onto Ugi-ligands that are affixed to the surface of magnetic carbon quantum dots (MCQD). A thorough characterization of the synthesized catalyst was conducted employing a range of analytical methods, such as X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and Barret–Joyner–Halenda (BJH), elemental analysis, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and EDS mapping. The integration of Ugi ligands significantly enhanced the homogeneity, reactivity, and coordination ability of the catalyst with Cu ions. The performance of the resulting Cu-carboxamide complex was evaluated in the synthesis of Spirooxindoles, achieving impressive product yields ranging from 80% to 98%. This reaction was conducted in a solvent mixture of water and ethanol (1:1) at ambient temperature within a 30-min timeframe. Significant benefits of this catalytic system encompass minimal work-up demands, ease of recovery, high stability, swift reaction times, a straightforward setup process, excellent product yields, and impressive reusability across 11 successive times. This study underscores a promising catalytic strategy for the synthesis of advantageous heterocyclic compounds under mild environmental conditions.