Palladium Catalyst For Coupling Reactions Research Articles

Microstructure-stability relations studies of porous chitosan microspheres supported palladium catalysts

In this study, polyethylene glycol (PEG) with different molecular weight, polyvinyl pyrrolidone (PVP), and polyvinyl alcohol (PVA), are chosen as porogens for preparing chitosan base porous microsphere supported palladium catalyst for coupling reactions. The pore structure of the microspheres was controlled by the compatibility of chitosan and counterpart polymers. The prepared porous chitosan microspheres supported palladium heterogeneous catalysts have been evaluated using the well-established Ullmann reductive homocoupling and the Heck cross-coupling reactions. The activities, stabilities and recyclability of the porous chitosan microspheres supported palladium catalysts are not only highly dependent upon the surface areas of the solid supports, but also upon the chemical properties of the water-soluble polymers. The degradation of the prepared heterogeneous palladium catalysts is mainly caused by a combination of the palladium leaching and the morphological transformation of the palladium species from the amorphous into the crystals.

Highly porous chitosan microspheres supported palladium catalyst for coupling reactions in organic and aqueous solutions

Porous chitosan microspheres (PCMS) were prepared from crosslinking chitosan/polyethylene glycol (PEG) interpenetrating microspheres through selective dissolution of the water-soluble PEG component for the immobilization of palladium catalyst. The resultant Pd/PCMS supported palladium has been demonstrated as a highly active and easily recyclable heterogeneous catalyst for the Ullmann-type reductive homocoupling of aromatic halides and the Heck cross-coupling of aromatic halides with acrylates. Most interestingly, the prepared Pd/PCMS heterogeneous palladium catalyst can also be employed in the environmentally-benign aqueous solution due to the highly hydrophilic hydroxyl and amino functional groups of chitosan. The large size of the microsphere structure can greatly facilitate separation and recycling of the expensive and toxic palladium catalysts from the reaction mixture and the recovered Pd/PCMS catalyst can preserve the catalytic activity and selectivity for the Heck reaction without any observable degradation over ten recycling times. The high activity and stability of the Pd/PCMS catalyst have been attributed to a combination of the high specific surface area of the porous structure as well as the strong chelation of palladium species with the abundant chitosan surface hydroxyl, amino and carbonyl functional groups.

Mercaptopropyl‐Modified Mesoporous Silica: A Remarkable Support for the Preparation of a Reusable, Heterogeneous Palladium Catalyst for Coupling Reactions.

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