Ni-0 NPs anchored on acid-activated montmorillonite (Ni-0-Mont) as a highly efficient and reusable nanocatalyst for synthesis of biscoumarins and bisdimedones

摘要

Ni-0 nanoparticles were immobilized on acid-activated montmorillonite (Ni-0-Mont) by anchoring Ni(OAc)(2)4H(2)O on modified micro/mesoporous montmorillonite followed by reduction with ethylene glycol. The prepared clay composite system was then characterized using Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) analysis, and Brunauer-Emmett-Teller (BET) analysis. SEM analysis revealed perfect dispersion of metallic nickel nanoparticles with size distribution of 641nm on the clay matrix. Micro/mesoporous montmorillonite was prepared by activation of Na+-montmorillonite with HCl (4M) under controlled conditions. The catalytic activity of the prepared Ni-0-Mont clay was studied in one-pot microwave-assisted synthesis of biscoumarins and bisdimedones via Knoevenagel reaction of aromatic aldehydes with 4-hydroxycoumarin or dimedone in solvent-free conditions. All reactions were carried out at room temperature within 515min (for biscoumarins) and 5-20min (for bisdimedones) to afford the products in high to excellent yield. The reusability of the Ni-0-Mont catalyst was also investigated in seven consecutive cycles, without significant loss of catalytic activity.