Picolylamine–Ni(ii) complex attached on 1,3,5-triazine-immobilized silica-coated Fe3O4 core/shell magnetic nanoparticles as an environmentally friendly and recyclable catalyst for the one-pot synthesis of substituted pyridine derivatives

Abstract

In the current study, an environmentally friendly and facile method was proposed for designing and constructing a catalyst with Ni(II) attached to a picolylamine complex on 1,3,5-triazine-immobilized Fe₃O₄ core–shell magnetic nanoparticles (Ni^II-picolylamine/TCT/APTES@SiO₂@Fe₃O₄) via a stepwise procedure. The as-synthesized nanocatalyst was identified and characterized via Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating-sample magnetometry (VSM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field-emission scanning electron microscopy (FE-SEM), inductively coupled plasma (ICP), and energy-dispersive X-ray spectrometry (EDX). The obtained results from the BET analysis indicated that the synthesized nanocatalyst had high specific area (53.61 m² g⁻¹) and mesoporous structure. TEM observations confirmed the particle size distribution was in the range 23–33 nm. Moreover, the binding energy peaks observed at 855.8 and 864.9 eV in the XPS analysis confirmed the successful and stable attachment of Ni(II) on the surface of the picolylamine/TCT/APTES@SiO₂@Fe₃O₄. The as-fabricated catalyst was used to produce pyridine derivatives by the one-pot pseudo-four component reaction of malononitrile, thiophenol, and a variety of aldehyde derivatives under solvent-free conditions or EG at 80 °C. The highest yield achieved was 97% for compound 4d in EG at 80 °C with a TOF of 823 h⁻¹ and TON of 107. It was found that the used catalyst was recyclable for eight consecutive cycles. On the basis of ICP analysis, the results indicated that the Ni leaching was approximately 1%.