M(II) Schiff base complexes (M = zinc, manganese, cadmium, cobalt, copper, nickel, iron, and palladium) supported on superparamagnetic Fe3O4@SiO2 nanoparticles: synthesis, characterization and catalytic activity for Sonogashira–Hagihara coupling reactions

A series of magnetically separable catalysts consisting of Schiff base complexes of metal ions (Zn, Mn, Cd, Co, Cu, Ni, Fe and Pd) supported on superparamagnetic Fe3O4@SiO2 nanoparticles has been prepared. The structural features of the catalysts were characterized by XRD, FTIR, TEM, FE-SEM, DLS, VSM, UV–Vis, TGA, AFM and N2 adsorption–desorption. Some of the Fe3O4@SiO2/Schiff base complexes were found to be efficient catalysts for the Cu-free and the phosphine free Sonogashira–Hagihara coupling reaction of aryl halides and phenylacetylene. The catalysts are superparamagnetic, and thus could be easily separated by the utilization of an external magnetic field, and could be reused for six cycles without significant loss of activity.