A Highly Efficient and Stable Palladium Catalyst Entrapped within the Cross-Linked Chitosan Membrane for Heck Reactions

In this study, chitosan directly cross-linked by PdII cation membranes (Pd-cr-CSM) with good mechanical strength and thermal stabilities have been prepared. Although the prepared Pd-cr-CSM has neither open porous structure nor high specific surface areas, it has similar good catalytic activity and much higher stability as compared with typical prepared chitosan-stabilized palladium heterogeneous catalysts for Heck reactions. It is highly active for the Heck reactions of aryl iodides and bromides with a strong electron-withdrawing group at a palladium catalyst loading of 0.15 mol %. It can be recycled 12 times in dimethyl sulfoxide (DMSO) solution or 7 times in aqueous solution. The high activity and extreme stability of the Pd-cr-CSM catalyst are mainly attributed to the well-entrapped palladium nanoparticles inside the chitosan matrix, which might catalyze the coupling reactions in the free volume holes (open spaces) of the swollen cross-linked chitosan gel networks.