Fabrication of a Fe3O4@SiO2@mSiO2-HPG-COOH-Pd(0) supported catalyst and its performance in catalyzing the Suzuki cross-coupling reaction

Abstract

In this paper, magnetic Fe₃O₄@SiO₂@mSiO₂ microspheres with core–shell structure were chosen as a catalyst support, then hyperbranched polyglycerol (HPG) was successfully grafted onto the exterior surface and mesopore wall of this material under the catalysis of isopropanol aluminum. Subsequently, the terminal hydroxyl groups of HPG were successfully transformed into carboxyl groups after modification with succinic anhydride. Ultimately, palladium nanoparticles (Pd NPs) were successfully anchored onto the surface of the aforementioned magnetic Fe₃O₄@SiO₂@mSiO₂ microspheres with high density carboxylic HPG, nanocrystallization by the complexation between Pd²⁺ ions and carboxyl groups and the subsequent reduction, a novel Fe₃O₄@SiO₂@mSiO₂-HPG-COOH-Pd(0) supported catalyst was successfully obtained. This novel supported Pd NP catalyst is very conducive to the transference and exchange of each component in the reaction system for the orderly mesoporous opening structure. Furthermore, the introduction of a magnetism nucleus can provide convenient magnetic separation. More importantly, the numerous terminal carboxyl groups on the surface of the magnetic Fe₃O₄@SiO₂@mSiO₂ microspheres can provide plenty of sufficient binding sites for Pd NPs, and the unique hyperbranched structure is very conducive to capture uniformly dispersed nanosized palladium and can effectively enhance the catalytic activity and stability. Research indicates that this novel supported Pd NP catalyst not only possesses extremely high Pd NPs loading capacity but also shows remarkable catalytic activity to the Suzuki cross-coupling reaction between aryl halides and phenylboronic acid. Simultaneously, the catalytic activity of this supported catalyst did not show evident loss after being used at least eight times.