ZnFe2O4-SiO2@PC-Ni nanoparticles for one-pot, solvent-free synthesis of imidazo[1,2-a]pyridines by A3 coupling reactions under ultrasound conditions

This study reports the development of ZnFe2O4-SiO2@PC-Ni magnetic nanoparticles as a novel by immobilizing phycocyanin onto magnetized silica and then immobilizing Ni (II) ions using nickel (II) chloride, the recyclable heterogeneous catalyst for the efficient one-pot synthesis of imidazo[1,2-a]pyridines via A3 coupling reactions under solvent-free ultrasound irradiation. Utilizing 2-aminopyridine, various aldehydes, and alkynes, the reactions were conducted solvent-free under ultrasound conditions, enhancing reaction rates and sustainability. The core-shell nanocomposite, comprising a ZnFe2O4 magnetic core, silica interlayer, and porous carbon-supported nickel shell, was characterized by XRD, TEM, BET, and VSM analyses. The synergistic effects of Ni active sites, high surface area, and magnetic retrievability enabled rapid catalytic activation of the three-component reaction between aldehydes, amines, and alkynes. Ultrasound irradiation significantly enhanced mass transfer and reaction kinetics, achieving 90-95 % yields within 10-20 min under mild conditions. The catalyst demonstrated exceptional stability, retaining >88 % activity over six cycles, and facile magnetic separation minimized metal leaching. This eco-friendly protocol eliminates toxic solvents, reduces energy consumption, and offers broad substrate scope, including aromatic, heteroaromatic, and aliphatic substrates. This work not only contributes a novel catalyst to the field of organic synthesis but also aligns with environmental directives by minimizing hazardous solvent use and employing energy-efficient reaction conditions.