Magnetic Mesoporous SBA-15 Functionalized with a NHC Pd(II) Complex: An Efficient and Recoverable Nanocatalyst for Hiyama Reaction

In this study, magnetic nanoparticles (MNPs) were prepared by co-precipitation method under ultrasound and then successively covered by a silica shell and a mesoporous silica (SBA-15) with a high surface area. Magnetic mesoporous nanoparticles of Fe3O4@SiO2@SBA-15 were then reacted with 3-chloropropyltriethoxysilane (CPTS), sodium salt of imidazole and 2-bromopyridine to give Fe3O4@SiO2@SBA-15 functionalized with 3-(pyridin-2-yl)-1H-imidazol-3-ium-propyl (PIP) [1] as a supported pincer ligand for Pd(II). The functionalized mesoporous MNPs were then treated with t-BuOK at -80°C in THF and then reacted with [PdCl2(SMe2)2] to give supported Pd(II)-carbene complex containing C,N-bidentate ligand. The chloride ions were then exchanged by bromide ions using a NaBr solution of diethylether/acetone mixture, Scheme 1. The prepared magnetic nanoparticles were effectively used in the coupling reaction of triethoxyphenylsilane with aryl halides (Hiyama reaction) in the presence of a base [2]. The reaction parameters such as solvents, amount of catalyst, base and temperature were optimized. The catalyst was then magnetically decanted, washed, and reused several times.