A recyclable dendrimeric Ni nanocatalyst anchored on magnetic nanoparticles for the green reduction of nitroarene pollutants and one-pot synthesis of imines.

Nitroarenes compounds are important intermediates in the chemical industry but are also recognized as persistent environmental pollutants due to their toxicity and stability. Therefore, their catalytic reduction to the corresponding amines has emerged as an efficient and eco-friendly route for detoxification and for producing valuable building blocks in pharmaceuticals, agrochemicals, and dyes. In this study, a facile and efficient approach was developed for the construction of dendrimeric architectures on the surface of magnetic nanoparticles through a thiol–ene click reaction. The successful grafting of dendrimer moieties onto the magnetic support provided a robust and versatile platform for the immobilization of Ni nanoparticles, leading to the preparation of the Ni-PAMAM@SMNPs nanocomposite. The synthesized Ni-PAMAM@SMNPs nanocomposite was thoroughly characterized by FT-IR, CHN, TGA, EDX-EDS, TEM, FESEM, ICP, XRD, VSM, and BET analyses to confirm its structural, morphological, and magnetic features. The resulting material was subsequently employed as a highly active heterogeneous catalyst for the reduction of hazardous nitroarenes compounds into their corresponding amino derivatives using sodium borohydride under mild, aqueous, and room-temperature conditions. A broad spectrum of nitroarenes containing various functional groups including nitriles, halogens, carbonyls, hydroxyls, and carboxylic acids was smoothly transformed into the corresponding anilines with high to excellent yields. The remarkable catalytic performance can be attributed to the uniform dispersion of Ni nanoparticles within the dendrimer framework, which promotes rapid reaction kinetics and excellent product selectivity. Furthermore, building on the promising results achieved in the reduction of nitro compounds, the developed catalytic system was further extended to a one-pot tandem process integrating the reduction of nitroarenes and subsequent condensation with aldehydes to afford the corresponding imines. This transformation confirms the high efficiency and versatility of the catalyst in promoting sequential reduction–Schiff base formation reactions under heterogeneous conditions. Finally, owing to the intrinsic magnetic properties of the support, the catalyst could be readily separated from the reaction medium using an external magnet and reused for at least six consecutive cycles with negligible loss of activity, underscoring its potential for sustainable and practical applications.