Anchoring palladium acetate onto imine-functionalized silica gel through coordinative attachment: An effective recyclable catalyst for the Suzuki–Miyaura reaction in aqueous-isopropanol

Silica supported palladium catalyst, Pd@imine–SiO2, was prepared by immobilizing Pd(OAc)2 onto silica gel through coordination of imine, generated via Schiff-base condensation between 3-aminopropyltriethoxysilane (APTES) functionalized silica gel and acetamide. The catalyst was characterized by FTIR, BET surface area measurements, XRD, SEM-EDX and ICP-AES. The imine-based catalyst, exhibited excellent activity for the Suzuki–Miyaura cross-coupling reactions of aryl halides with arylboronic acids in iPrOH/H2O (1:1) under mild conditions (T = 60 °C, air, 0.08 mol% of palladium). Interestingly, under the same experimental conditions, for the reaction between p-bromoanisole and phenylboronic acid the imine-based catalyst, Pd@imine–SiO2, exhibited comparable result with that of homogeneous Pd(OAc)2 and much higher activity than amine-based catalyst, Pd@APTES–SiO2. Furthermore, the imine-based catalyst could be recovered by simple filtration and reused several times without significant loss of activity.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (90 K)Download as PowerPoint slideHighlights► Silica-supported Pd-catalyst developed for the Suzuki–Miyaura reaction. ► Aqueous-isopropanol could be used as solvent. ► The catalyst could be recycled up to six times without loss in activity. ► Imine-based catalyst is more effective than amine-based catalyst. ► Comparable activity has been obtained with that of homogeneous palladium acetate.