Distinctive ligand effects of functionalized magnetic microparticles immobilizing palladium acetate as heterogeneous coordination catalysts for selective oxidation of styrene to acetophenone

作者：Long, Yu^*; Zhao, Ziming; Wu, Li; Luo, Sha; Wen, He; Wu, Wei; Zhang, Hongbo; Ma, Jiantai^*

来源：Molecular Catalysis, 2017, 433: 291-300.

DOI：10.1016/j.mcat.2017.02.028

• Ligand effect
• Heterogeneous coordination catalysts
• Selective oxidation
• Styrene
• Acetophenone

A series of functionalized magnetic nanoparticles immobilizing palladium acetate with different ligands, including beta-diketimine, Schiff base and (3-aminopropyl) triethoxysilane (APTES), were prepared by a facile surface modification method. These prepared heterogeneous coordination catalysts were characterized by TEM, XRD, FT-IR, VSM, XPS and ICP. Fe3O4@ SiO2-beta-diketimine was found to be an excellent scaffold for the immobilization of palladium acetate through the complexation between palladium acetate and nitrogen atoms (and oxygen atoms). Among the three catalysts, Fe3O4@SiO2-beta-diketiminePd(OAc)(2) with the highest steric hindrance exhibited extraordinary catalytic property to undergo Wacker type reaction with a high selectivity of 94% toward the formation of acetophenone in liquid phase using H2O2 as oxidant. Meanwhile, Fe3O4@SiO2-Schiff base-Pd(OAc)(2) and Fe3O4@SiO2-APTES-Pd(OAc)(2) afforded 49% and 32% selectivities of acetophenone, which were just a little higher than homogeneous Pd( OAc)(2) (15%). Importantly, the proposed reaction mechanism of the styrene selective oxidation reactions by ligand immobilized Pd(OAc)(2) catalyst was also inferred according to the distinctive catalytic activities of the three heterogeneous coordination catalysts and reported literatures. It could be concluded that the steric hindrance of the ligand probably played an important role in the selective oxidation of styrene, and big steric hindrance of the ligand probably was beneficial to form acetophenone. Furthermore, Fe3O4@SiO2-beta-diketimine-Pd(OAc)(2) revealed high efficiency and stability during recycling stages.

• 出版日期2017-5
• 单位兰州大学