Preparation And Application Of Polymer Supported Palladium Catalysts Based On Triarylimidazole-Containing Polymers

The polymer supported palladium catalysts have advantages of high catalytic activity,simple separation and reusability,which have attracted much attention in recent years.Among them,polymer-palladium catalysts based on the homopolymer or copolymer of N-vinyl imidazole were widely studied because of their outstanding catalytic properties.In this dissertation,two kinds of polymer supported palladium catalysts based on triarylimidazole-containing polymers were synthesized and used to catalyze Suzuki coupling reaction and cyanation reaction,respectively.The main research contents were shown as follows:(1)Preparation of PDD-Pd catalysts and their catalytic performance for Suzuki coupling reaction.A series of poly((1-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-4-vinyl-1,2,3-triazole)-co-N,N-dimethylacrylamide)((poly(DVT-co-DMA),referred to as simply PDD)with different copolymer compositions were first prepared by RAFT polymerization.And then Pd was supported on these copolymers to prepare the corresponding polymer-palladium catalysts.Followed by the catalytic action of model Suzuki coupling reaction,the PDD prepared by comonomer DVT/DMA molar ratio of3/7 was selected for the next study.It was found that the Pd particle in the as-prepared PDD-Pd catalyst was mainly present at the 0 valence with Pd particle size of around 7nm and Pd content of about 64.1 wt%.Such PDD-Pd catalyst showed excellent catalytic activity for catalyzing Suzuki coupling reaction.For example,the yields for the PDD-Pd catalyzed Suzuki coupling reactions of aryl bromides and chlorides with phenylboronic acid in water solvent were above 95%.The PDD-Pd catalyst can be recovered and reused for five times with product yield up to 95%,implying promising reusability.(2)Preparation of poly(TMI)-Pd catalyst and its catalytic performance for cyanation reaction.Firstly,organic porous polymer poly(TMI)was prepared by Yamamoto coupling reaction using 2,4,5-tris(4-bromophenyl)-1-methyl imidazole)(TMI)as the monomer and bis(1,5-cyclooctadiene)nickel(0)as the catalyst.N2 gas isotherm analysis showed the poly(TMI)to have a BET surface area of 514.83 m2 g–1and total pore volume of 0.35 cm3g–1.The as-prepared poly(TMI)was used to support Pd,yielding poly(TMI)-Pd catalyst.Upon loading Pd,the BET surface area of the catalyst was decreased to 299.41 m2 g–1 and the total pore volume decreased to0.18 cm3g–1due to the fact that part of the cavity of the poly(TMI)was occupied byPd nanoparticles.The Pd particles in the poly(TMI)-Pd catalyst were mainly present in the 0 valence with particle size of about 2.7 nm and Pd content of 1.4 wt%.The yield of such poly(TMI)-Pd catalyzed cyanation reaction of aryl iodides using K4[Fe(CN)6] as a green cyanating agent was about 90%.The poly(TMI)-Pd catalyst can be recovered and reused for five times without significant loss of catalytic activity.