Novel chitosan-based/montmorillonite/palladium hybrid microspheres as heterogeneous catalyst for Sonogashira reactions

Abstract

The objective of this study was to develop novel chitosan-based/montmorillonite/palladium (CS/MMT/Pd) hybrid microsphere catalysts with improved properties for use in Sonogashira reactions. Interactions between a chitosan matrix and a montmorillonite nanofiller were revealed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric (TG) analysis. The results confirmed the formation of the intercalation structure between CS macromolecules and MMT layers. X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM) analysis results showed that the Pd species of different valencies were dispersed at the nano-level in both the CS matrix and the interlayers of MMT. CS/MMT/Pd hybrid microspheres were highly active for the Sonogashira reactions of aryl iodides and alkynes at a palladium catalyst loading of 0.3 mol%. They can be recycled 10 times without a significant decrease in coupling yields. It was concluded that introducing MMT into the CS matrix will effectively improve the thermal stability and Pd leaching-resistance of the hybrid microsphere catalysts. The results in this study demonstrated the great potential of such heterogeneous catalysts applied in Sonogashira reactions.