Molecular Sieve-supported Palladium Materials Are Used To Selectively Catalyze CC Bond Cross-coupling Reactions

Metal heterogeneous catalysts are widely used to catalyze C-C bond cross-coupling reactions due to their recyclable and reusable properties.Zeolites have grown as a kind of ideal support because of their large surface area,high stability,adjustable acidity.Since zeolite have unique regular pore structure,extensive attentions have been paid on their application in selectively catalysis,which has shown great application prospects in industry in recent years.In this thesis,Pd@ZSM-5 catalyst was prepared by traditional ion exchange method.Pd@ZSM-5 achieved selectively catalysis of the C-C bond crosscoupling reaction in an aqueous solution,which may be attributed to the channel confinement of ZSM-5 and the high activity of Pd species.Moreover,several possible factors affecting the selective catalysis were also discussed.The main contents of this thesis are as follows:(1)A heterogeneous catalyst,Pd@ZSM-5,was prepared by simple ion exchange method at room temperature to selectively catalyze the cross-coupling reaction between Suzuki-Miyaura and Sonogashira in water.The experimental results show that Pd@ZSM5 exhibits obvious selectivity on catalyzing 4-nitro-aryl halides and halogenated benzene.For Sonogashira reaction,the coupling yield of iodobenzene and phenylacetylene reached 98%after reacting for 3 h,while that of 4-nitroiodobenzene and phenylacetylene was 24%at 6 h.For Suzuki-Miyaura reaction,the coupling yield of bromobenzene and phenylboronic acid reached 99%at 3.5 h,while that of 4-nitrobromobenzene and phenylboronic acid was 0 even after reacting for 10 h.However,both of the substrates can be catalyzed without significant differences by using traditional catalysts,such as Pd/.C,in Suzuki-Miyaura or Sonogashira reactions,and even the coupling rate of 4-nitroaryl halides is faster than that of the corresponding aryl halides.Therefore,Pd@ZSM-5 realized the selective conversion of 4-nitro-aryl halides and other aryl halides.(2)The factors affecting the selective catalysis were investigated by introducing small cations or other substrates in a catalytic system catalyzed by Pd@ZSM-5 for 4nitro-aryl halide coupling reaction.The results show that the key factor of selective catalysis in aqueous phase is to ensure that palladium cannot flee into the liquid phase in any form.When a small cation(e.g.Na+,K+,TMA+)existed in the system,the Pd@ZSM5 catalyst would lose its selective catalytic effect on the coupling reaction,presumably due to the ion exchange between palladium and small cation.And the leaching of palladium to the solution caused it catalyzed the reactions without any selection.The introduction of other substrate(e.g.iodobenzene,bromobenzene)could also promote the coupling reaction for 4-nitro-aryl halide.This may be due to some Pd species escaping into the solution during the coupling reaction of the additional substrate,which opened the coupling reaction of 4-nitro-aryl halides.Besides,the coupling reaction rate of 4-nitroaryl halides was faster than that of the corresponding aryl halides,which further confirmed the escape of Pd species.Therefore,we have studied the selectivity of substrates in Pd@ZSM-5 catalyzed CC cross-coupling reaction in this thesis,which provides a basis for the development of metal heterogeneous catalysts to achieve selective catalysis in aqueous solutions.