Palladium complex catalysts immobilized on silica via a tripodal linker unit with amino groups: Preparation, characterization, and application to the Suzuki–Miyaura coupling

Abstract

To clarify the effectiveness of a tripodal linker unit (3-bromopropyltris[3-(dimethylisopropoxysilyl)propyl]silane), which can be bound to a silica surface via three independent Si–O–Si bonds, silica-immobilized palladium amine complex catalysts employing the tripodal linker unit were prepared and applied toward the Suzuki–Miyaura coupling reaction. N-Functionalized ( N = 3-methylaminopropyl, 3-dimethylaminopropyl, or N, N-dimethylethylenediaminopropyl) silica materials were prepared by grafting the tripodal linker unit onto mesoporous silica followed by treatment with the corresponding amine. A series of silica-immobilized amino-palladium complex catalysts were prepared by reacting N-functionalized silica materials with palladium acetate. A catalyst that included a methylamino ligand and a ligand-to-Pd molar ratio of 6:1 gave the best performance for the reaction between aryl bromides and phenylboronic acid in toluene. Moreover, catalysts containing the tripodal linker showed lower levels of palladium leaching after the reaction and better recyclability compared to catalysts having conventional trialkoxy-type linkers.