Study On The Suzuki Coupling Reaction Catalyzed By Microcapsule-supported Palladium Catalyst

The palladium-catalyzed Suzuki cross coupling reaction provides a powerful and general methodology for the formation of carbon-carbon bonds. Nevertheless, the development in the industrial processes is often hindered due to difficulties in recovering costly noble metals and ligands as well as in removing trace amount of metal species from the resulting products and solvent waste. As a result, immobilizations of the homogeneous catalysts have been pursued, proven effective in overcoming these problems and do meet both economical and green chemistry requirements. The work in supported metal complexes would always be focused on developing and screening various heterogeneous catalysts with minimization of metal leaching and higher activity and selectivity.A novel heterogeneous catalyst of microcapsulated palladium catalyst has been synthesized for Suzuki cross coupling reaction in this paper.1. The microcapsule with triphenylphosphine moiety containing inside is synthesized by suspending polymerization method, using p-styryldiphenylphospine as monomer, divinylbenzene as crosslinker, and azobisiobutyronitrile as initiator. The amount of crosslinker, the type and amount of the initiator, and the reaction time are important facts to the morphology and size distribution of the microcapsules. An ideal recipe has been gotten and applied to get the regular shaped microcapsule with average size distribution and slippy surfaces.2. The microcapsule was treated with Pd₂(dba)₃ in dichloromethane to get the microcapsulated palladium catalyst through ligand-exchange reaction. The Pd and P loadings of the catalyst were determined to be 0.197 and 0.252 mmol/g respectively by inductively coupled plasma-atomic emission spectrometry (ICP-AES), and the structures of microcapsule and microcapsulated palladium catalyst were characterized by Infrared spectroscopy (FT-IR), transmission electron microscope(TEM), and scanning electron microscope(SEM).3. The Suzuki coupling reaction of aryl boronic acids with aryl bromides are found to proceed smoothly in the presence of the microcapsulated palladium catalyst, to afford the corresponding products in high yields in isopropanol/toluene(1/1) at 80°C. And the catalyst could be reused for 4 times. The advantages of this supported catalyst are:â‘ The average size distribution of the material makes the catalyst highly disperse in the reaction medium just like a homogeneous catalyst and can be separated by simple filtration after the reaction and reused like a heterogeneous one;â‘¡The phosphine ligands inside the microcapsule effectively prevent the leaching of the palladium species;â‘¢The microcapsule offers microcircumstance for the cross reaction.