Supported Metal Complexes on Fe3O4@Silica@SBA-15: Magnetically Retrievable Catalysts for Cross Coupling Reactions

Highly ordered mesoporous silica materials have attracted a considerable deal of attention in development of different applications, such as diagnosis, drug delivery, extraction and hyperthermia. Their non-toxic nature, high surface area (700 to 1200 m2 g-1), abundant Si–OH bonds, tunable volume and pore diameter (2 to 50 nm) and potency of surface modification have represented them as an attractive candidate for coating and catalyst support purposes. For these reasons, SBA-15 has been considered for simple internal surface functionalization and release of large molecules [1]. Magnetite nanoparticles (MNPs) take advantage from nontoxicity, high dispersibility, biocompatibility, a noticeably high surface-to-volume ratio, high coercivity, superparamagnetic properties, great extraction efficiency and convenient separation [2]. In addition, MNP-supported catalysts can easily and rapidly be collected from various reaction mixtures by the means of an external magnet. Anchoring catalysts on MNPs is very exciting and it has been the topic of many research activities in recent years [3]. Combination of MNPs and mesoporous silica, e.g. SBA-15 and various kinds of MCMs, as core-shell structures provides the advantages of both high surface area and magnetic properties. These nanoparticles can be employed as magnetically retrievable catalyst supports [4]. Our current research activity has been directed toward developing of new Pd(II) complexes, e.g. NHC Pd(II), pyridine-type and other nitrogen-based ligand, supported on magnetic mesoporous core-shells of Fe3O4@Silica@SBA-15. The capabilities of these supported catalysts for C-C and C-N bonds formation, e.g. the reactions of halogenated hydrocarbons with, organoboron (Suzuki reactions), organosilicon (Hiyama reactions), alkenes (Heck reactions), alkynes (Sonogashira reactions), N-arylation and O-arylation are also under investigation, Scheme 1. Though magnetic silica mesoporous core-shells have been widely applied to coupling reactions, limited studies have been reported about anchoring homogeneous catalysts on magnetic silica mesoporous core-shells for coupling reactions.