Bis-salophen palladium complex immobilized on Fe3O4@SiO2 nanoparticles as a highly active and durable phosphine-free catalyst for Heck and copper-free Sonogashira coupling reactions.

Abstract

New Fe3O4@SiO2 core-shell superparamagnetic nanoparticles functionalized by a bis-salophen Schiff base Pd complex were synthesized and employed as an efficient magnetic nanocatalyst in the Heck and Sonogashira cross coupling reactions. The synthesized nanostructures were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic light scattering (DLS), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), elemental analysis (CHN), cyclic voltammetry (CV), Brunauer-Emmett-Teller analysis (BET), and UV-vis spectroscopy. The morphology and size of the nanoparticles were investigated by FE-SEM and TEM analyses. Furthermore, the magnetic properties of the catalyst were investigated by VSM analysis. The loading content and leaching amounts of palladium on the catalyst were measured by inductively coupled plasma (ICP) analysis. Also, the thermal behavior of this magnetic heterogeneous catalyst was studied using a TGA instrument. This heterogeneous catalytic system showed a good performance in the coupling of aryl halides with alkynes (Sonogashira reaction) as well as aryl halides with alkene derivatives (Heck reaction). High to excellent yields were achieved for these C-C coupling reactions. The catalyst can be simply separated from the reaction media by an external magnet and reused for eight consecutive runs without any significant loss of activity. Finally, the kinetics of the reactions were studied in this work.