A green approach to the synthesis of Ag doped nano magnetic γ-Fe2O3@SiO2-CD core-shell hollow spheres as an efficient and heterogeneous catalyst for ultrasonic-assisted A3 and KA2 coupling reactions

Using a green approach and ultrasonic-assisted template-free five-step process, a novel heterogeneous catalyst, gamma-Fe2O3@SiO2-CD/Ag hollow spheres (h-Fe2O3@SiO2-CD/Ag), was fabricated. The design of the catalyst was based on the synthesis of core-shell h-Fe2O3@SiO2 followed by amine functionalization, reaction with tosylated cyclodextrin and subsequent Ag(0) doping using hollyhock flowers collected from the Banaruiyeh District, in Larestan, Iran as extract-based reducing agent. The novel catalyst was fully characterized using SEM/EDX, BET, TGA, ICP-AES, FTIR, VSM and XRD techniques. The hybrid catalyst was successfully applied for promoting A(3) and KA(2) coupling reactions under mild and green conditions, i.e. ultrasonic irradiation at room temperature in aqueous media. Studying the reusability of the catalyst and Ag(0) nanoparticle leaching established that the catalyst can be recovered and reused with preserving its catalytic activity and negligible Ag(0) leaching for five reaction runs. Upon reusing for the sixth run, however, slight leaching of Ag(0) and consequently loss of catalytic activity was observed.