Iron-Based Heterogenous Nanocatalyst from <i>Taraxacum officinale</i> for Hantzsch, Knoevenagel, and Biginelli Reactions

<i>Taraxacum officinale</i> leaves (TOL) extract has been used for the synthesis of biogenic iron oxide nanoparticles (TOL-Fe₃O₄ NPs) using a green coprecipitation method, and its catalytic potential has been explored for multicomponent reactions (MCRs). Phytoconstituents such as phenolic compounds help in nanocatalyst formation and its stabilization. Comprehensive characterization using EDX, FE-SEM, XPS, FTIR, TGA, <i>P</i>-XRD, and TEM, confirmed the successful synthesis of TOL-Fe₃O₄ NPs. TEM and <i>P</i>-XRD analysis confirmed the size of biogenic NPs as 6.9 nm with a crystalline nature. Further, the catalytic activity of the synthesized TOL-Fe₃O₄ NPs was investigated for MCRs to access various 1,4-dihydropyridines (1,4-DHPs), benzylidene malononitriles, and 3,4-dihydropyrimidin-2(1H)-one (3,4-DHPMs) derivatives with yields of 80-90, 77-85, and 74-85%, respectively. The developed protocols displayed broad substrate scope with several functional group tolerances and high catalytic performance under green chemistry metrics like turnover number (TON), turnover frequency (TOF), reaction mass efficiency (RME), atom economy (AE), atom efficiency (AEf), optimum efficiency (OE), and E-factor which support the efficiency and sustainability of the process. Developed methods showed high efficiencies for Hantzsch (maximum up to 168.21 TON; 84.10 h^-1 TOF), Knoevenagel (maximum up to 264.77 TON; 264.77 h^-1 TOF), and Biginelli reactions (maximum up to 158.86 TON; 52.95 h^-1 TOF). Eco Scale scores above 75% for each protocol highlight the green nature. In addition to this, excellent recyclability, maintaining activity for up to five cycles without significant deactivation, further confirm the sustainable nature of the catalyst. Developed plant-based catalysts showed better performance over the bare iron nanocatalyst and iron salts. The reaction pathways have been proven via ESI-MS studies. Various control experiments in the absence of catalyst and using bare catalyst have demonstrated the crucial role of the synthesized nanocatalyst. A comparative analysis on the basis of literature reports of other iron-based catalysts with our biogenic NPs demonstrated the superior performance of TOL-Fe₃O₄ NPs.