Fe ₃ O ₄ @SiO ₂ –NH ₂ –ECH–HMTA-Supported Trifluoroacetic Acid: A Magnetically Recyclable Catalyst for One-Pot Synthesis of Imidazole–Indole Derivatives

A novel series of magnetic nanocatalysts based on Fe₃O₄@SiO₂-NH₂ frameworks were synthesized and functionalized with epichlorohydrin (ECH), hexamethylenetetramine (HMTA), and trifluoroacetic acid (TFA) to afford highly active, magnetically recoverable catalytic systems. Comprehensive physicochemical characterization confirmed the successful stepwise functionalization, morphological stability, and controlled porosity of the materials. The catalytic performance was evaluated in the synthesis of indole derivatives and diketone compounds, where Fe₃O₄@SiO₂-NH₂-ECH-HMTA-TFA exhibited superior activity compared with its non-ECH-functionalized analog, attributable to enhanced surface acidity and improved active-site accessibility. Reaction optimization demonstrated excellent yields under mild and green conditions, highlighting the synergistic effect of organic functional groups and the magnetic nanoplatform. The catalysts showed remarkable reusability, maintaining high activity over several cycles without significant structural degradation. This study demonstrates a sustainable route for designing multifunctional magnetic catalysts with broad applicability in C-C bond-forming reactions.