Synthesis and characterization of the immobilized Ni–Zn–Fe layered double hydroxide (LDH) on silica-coated magnetite as a mesoporous and magnetically reusable catalyst for the preparation of benzylidenemalononitriles and bisdimedones (tetraketones) under green conditions

Abstract

Herein, novel magnetic Fe₃O₄@SiO₂@Ni–Zn–Fe layered double hydroxide (LDH) intercalated with water molecules and carbonate anions as interlayer contents was prepared as a new heterogeneous and separable nanocatalyst. The mesoporous catalyst was characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET) technique, vibration sample magnetometry (VSM), thermogravimetric analysis (TGA), differential thermal gravity (DTG), and transmission electron microscopy (TEM). The Knoevenagel and tandem Knoevenagel–Michael reactions were carried out between aromatic aldehydes, malononitrile, and dimedone using the magnetically reusable nanocatalyst in water as a green and eco-friendly solvent to afford benzylidenemalononitrile and bisdimedone derivatives (tetraketones), respectively. The reusability and recoverability of the core–shell hydrotalcite was examined six times without any significant loss of its catalytic activity. This magnetic LDH catalyst provides high yields, mild reaction conditions, satisfactory reaction times, and high purity of the obtained products without utilizing any hazardous organic solvents during the titled transformations.