Chitosan as a support for heterogeneous Pd catalysts in liquid phase catalysis

Four different chitosan-supported palladium catalysts were prepared. The activity of these catalysts was tested in thermal and microwave-assisted Suzuki reactions in aqueous media, and resulted without phase-transfer catalyst in good yields and selectivities. The study was extended to microwave-assisted Heck and Sonogashira reactions with NaOAc as base in organic solvents. Four different chitosan-supported palladium catalysts were prepared, whereby two of them were modified as Schiff base by reaction with salicylaldehyde and 2-pyridinecarboxaldehyde before complexation with palladium. The remaining differ in their preparation method: co-precipitation or adsorption. The properties of the catalysts were characterized by FTIR, XPS, ICP-MS, and TGA. Comparison of the catalysts activity was assessed in microwave-assisted Suzuki reactions in aqueous media, resulting in good yields and excellent selectivities concerning cross-coupling product. Additionally, the catalysts prove their activity under conductive heating conditions. The study was extended to microwave-assisted Heck and Sonogashira reactions in DMF, confirming the efficiency of chitosan-supported palladium derivatives as catalysts for C–C couplings. Experiments revealed that catalysts prepared by co-precipitation furnished inferior yields concerning the employed C–C coupling reactions. Modification of chitosan with 2-pyridinecarboxaldehyde and subsequent palladium deposition resulted in highly active catalysts affording high product selectivities and yields.