Synthesis and characterization of Ni(II) complex supported on magnetite‑silica nanoparticles and investigation of its catalytic activity in Biginelli reaction under solvent‑free conditions

Abstract

In this work a new core–shell nanocatalyst, Fe3O4@ SiO2/Schiff base of Ni(II), ( Fe3O4@SiO2/SB(Ni)), was synthesized and characterized. The Schiff base immobilized on magnetite nanoparticles introduced in this study, is a simple and aliphatic Schiff base. The synthesis steps were meticulously followed. First, magnetite-silica nanoparticles were prepared and functionalized by –NH2 groups using 3-amino propyl triethoxysilane (APTES). Subsequently, the aliphatic Schiff base ligand was immobilized through a condensation reaction between the –NH2 groups on the magnetite-silica and the –C=O groups of acetylacetone. The supported Schiff base complex of Ni(II) on magnetite-silica was synthesized by a reaction between immobilized Schiff base and Ni(II) acetate tetrahydrate salt. Finally, the immobilized Ni(II) Schiff base complex was fully characterized using several techniques including, FT-IR, VSM, XRD, FE-SEM, EDX, TEM, BET, TGA-DTA, and AAS. The magnetically recoverable core–shell nanocatalyst, demonstrated remarkable catalytic activity in the synthesis of 3,4-dihydropyrimidine-2-(1H)-one. This reaction involved three components: an aldehyde, β-keto ester, and urea, and was carried out via the solvent-free Biginelli reaction. The results indicate that the products are synthesized in good to excellent yields (82–91%) within 13–22 min. At the end of the reaction, the nanocatalyst can be easily removed from the reaction mixture using an external magnet and reused several times. The synthesized products were purified and characterized by FT-IR and 1H NMR techniques.