Preparation of Ag-doped Nano Magnetic γ-Fe2O3@SiO2 Core–Shell Hollow Spheres: Investigation of the Catalytic activity for ligand-free N-arylation Coupling Reaction

A novel heterogeneous nano-catalyst, (h-Fe2O3@SiO2/Ag), was fabricated via biosynthesis approach. The design of the catalyst was based on the synthesis of core-shell h-Fe2O3@SiO2 followed by amine functionalization and subsequent Ag(0) doping using Achillea millefolium flower as reducing and stabilizing agent. The novel catalyst was fully characterized by using SEM, TGA, ICP-AES, FTIR, VSM and XRD techniques. The hybrid catalyst was successfully applied for promoting N-arylation of azoles and aliphatic amines with aryl halide (Scheme 1). The hybrid catalyst is found to be applicable to a variety of nitrogen-containing heterocycles, such as imidazole and indole as well as aliphatic amines in high yields and practical simplicity under cost-effective “ligand-free” condition. However, the catalyst was still super-magnetic and could be simply separated from the reaction mixture by using an external magnet. The heterogeneous nature of the catalysis was also confirmed by studying the reusability and stability of the catalyst and silver leaching. Upon reusing for the seven run, however, slight leaching of Ag(0) and consequently loss of catalytic activity was observed