Studies On Nanopalladium-catalyzed Suzuki Coupling Reaction

The palladium-catalyzed Suzuki coupling reaction has been recognized as one of the most important and attractive methods for the formation of carbon-carbon bonds,such as natural products,pharmaceuticals and polymers,etc.Most applications of the reaction involve expensive homogeneous palladium catalysts along with phosphine and bulky imine ligands,which exhibit better activity and selectivity,however it is difficult to recover them from the reaction system and phosphine ligands are difficult to synthesize,also they are toxic,and sensitive to air and moisture.These problems have to be overcome in the application of homogeneous Pd-catalyzed coupling reactions in industry.Therefore the development of using copper or nickel replace palladium catalysts and ligand-free recoverable heterogeneous palladium catalysts have received much more attention.Here,ligand-free heterogeneous palladium catalysts were fixed to a solid support,such as activated carbon,zeolites,molecular sieves and metal oxides,in addition,the recovery and reuse of catalysts by traditional centrifugation and filtration.To meet the green,efficient and rapid separation challenge,ligand-free magnetic-supported nanopalladium catalysts have been studied.The main contents are as follows:A kind of easy separation and recoverable magnetic-supported nanopalladium catalyst Pd/Si02/Fe304 was synthesdized.Characterization of the catalyst was realized by TEM,XRD and ICP-AES.The results of the test have shown that palladium particles are dispersed on the silica-coated magnetic nanoparticles.The particle size of the synthesized materials Pd/SiO2/Fe3O4 were uniformly distributed in the range 50-100 nm,and the palladium content of catalyst was 25.4%wt.The optimal reaction conditions were screened using the coupling of iodobenzene with phenylboronic acid as the model reaction in ordinary heating stirring(100 ?,Pd/SiO2/Fe304-K2CO3-CH3CN/H2O).For the couplings of various arylboronic with aryl iodides,60%-90%yields were achieved.However,the catalyst was magnetically recovered and reused with obvious decrease of catalytic activity.In order to address these problems,an efficient Pd/Si02/Fe3O4 catalytic system for the aryl halides Suzuki coupling reaction by using hydrothermal(solvothermal)conditions has been development.It indicated that hydrothermal(solvothermal)conditions was better promoting the reaction than that of ordinary heating stirring by the couplings of aryl iodides with aryl boronic.The reusability of Pd/Si02/Fe3O4 nanoparticles was evaluated.To address this issue,recycling experiments were carried out for the cross-coupling of 1-chloro-4-iodobenzene and(4-(tert-butyl)phenyl)boronic acid.The coupling product was obtained with a yield of 90%in the first cycle.However,the isolated yield decreased to 34%in the 4th recycling reaction by ordinary heating stirring.The catalyst exhibited good activities by using heating oscillation and hydrothermal(solvothermal)conditions and could be recycled 10 times without losing catalytic activity.From the standpoint of experimental conditions,operations and peoduction rate hydrothermal(solvothermal)conditions is better than heating oscillation.This catalyst can be a kind of recoverable,easy separation magnetic-supported nanopalladium catalyst for efficient catalytic coupling reaction has been development in hydrothermal(solvothermal)conditions.Therefore,the catalyst will have good application and research value.