Magnetic Core-Shell to Yolk-Shell Structures in Palladium-Catalyzed Suzuki-Miyaura Reactions: Heterogeneous versus Homogeneous Nature

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• 作者：Dr. Yinle Li ; Zhuqing Zhang ; Tao Fan ; Xiaoguang Li ; Jin Ji ; Pei Dong ; Robert Baines ; Prof. Jianfeng Shen and Prof. Mingxin Ye
• 刊名：ChemPlusChem
• 出版年：2016
• 出版时间：June 2016
• 年：2016
• 卷：81
• 期：6
• 页码：564-573
• 全文大小：2251K
• ISSN：2192-6506

文摘

This study describes a comparative investigation on the heterogeneous versus homogeneous nature of the Pd-catalyzed Suzuki–Miyaura cross-coupling reaction mechanism with specific magnetic hierarchical core–shell and yolk–shell structures. The hierarchical core–shell Fe₃O₄@SiO₂-Pd@mCeO₂ (m=mesoporous) catalyst contains a core of nonporous silica-sheltered magnetite (Fe₃O₄) nanoparticles (NPs), a transition layer of active palladium (Pd) NPs, and an outer shell of porous ceria (CeO₂). The magnetic yolk–shell Fe₃O₄@h-Pd@mCeO₂ (h=hollow) catalyst was prepared by selectively etching the nonporous silica interlayers. Notably, the results of the hot-filtration heterogeneity test, the effect of Pd concentration, and solid-phase poisoning, indicate that the two kinds of catalysts function in Pd-catalyzed Suzuki–Miyaura cross-coupling reactions through different catalytic mechanisms. Moreover, both catalysts demonstrated better catalytic activity than the Fe₃O₄@SiO₂-Pd catalyst. This finding can be ascribed to the outermost CeO₂ shell having a high concentration of trivalent cerium and oxygen vacancies, which gives rise to the increased electron density of Pd NPs, and a faster rate-determining step in the oxidative addition reaction for the Suzuki reaction. In addition, we propose a feasible mechanism elucidating the synergistic effect between the supporting CeO₂ and active species.