The Application Of Nitrogen-containing Polymer Supported Metal Catalysts In Suzuki Coupling Reaction And 4-nitrophenol Reduction

Heterogeneous catalysts have been extensively studied in Suzuki-Miyaura coupling reaction and 4-nitrophenol reduction.However,the preparation method and application of heterogeneous catalysts still face some challenges,such as preparation of catalysts with harsh reaction conditions,long synthesis route,toxic and harmful solvents,and catalyst with low recyclability,high metal leaching,low catalytic activity,inert gas protection in reaction process and so on.From the perspective of practical application,economy and environmental protection,it is extremely necessary to develop heterogeneous catalysts with low cost,simple synthetic method,super catalytic activity and strong stability.In particular,the design and synthesis of supports are crucial.In addition,there are a few reports about comparative investigation among catalysts with different structure,among catalysts with different metal and among catalyst with different degrees of conjugation.In this dissertation,nitrogen-containing polymers with different structures and different degrees of conjugation were prepared by different synthetic methods,and a series of catalysts were obtained after loading metals.The structure composition,morphology and metal valence of polymer supports and catalysts were characterized,and the catalytic activity of these catalysts was also studied in Suzuki coupling reaction and 4-nitrophenol reduction.The main contents are as follows:(1)Three hyper-crosslinked polymers were synthesized by Friedel-Crafts reaction under control of monomers ratio.Three catalysts with high specific surface area up to 512m²·g^-1 were obtained after loading Pd.Efficient contact between substrates and active centers was due to high specific surface area,and Poly-salen-a-Pd(II)catalyst exhibited excellent performance in Suzuki coupling reaction for a series of substrates with higher than90%yield within 7 h at 60?.Meanwhile,three catalysts also showed good performance in coupling reaction of gram-grade bromobenzene.In addition,it is also identified that difference of three catalyst recyclability may related to the specific surface area of catalysts,monomer structure,metal leaching in the reaction and so on.(2)Salen monomer and benzene were linked directly by Scholl reaction for the formation of conjugated nitrogen-containing polymer Ph-Sa-1,and five Pd_xCu_y/Ph-Sa-1catalysts were obtained after loading different quantity of Pd and Cu.The catalytic performance of Pd_xCu_y/Ph-Sa-1 catalysts with different metal ratios were studied in 4-nitrophenol reduction in water at room temperature.Results indicated that conjugated Pd/Ph-Sa-1 catalyst could be recycled five consecutive times,and higher than 80%conversion is still achieved in 4-nitrophenol reduction at the fifth recycle.Pd/Ph-Sa-1catalyst also exhibited excellent catalytic activity in Suzuki-Miyaura coupling reaction of many substrates besides 4-nitrophenol reduction.(3)Based on the previous work,two nitrogen-containing polymers of Poly-Sa were prepared via cross-linking salen monomers with different structure and benzene in Scholl reaction,respectively.Two economic and efficient Poly-Sa-Pd catalysts were obtained after coordinating Pd.It has been demonstrated that Poly-Sa-Pd catalysts were excellent in 4-nitrophenol reduction with the apparent rate constants of 0.398 min^-1 and 0.170 min^-1,respectively,and catalysts also could be recycled 5 times.In addition,Poly-Sa-1-Pd was efficient for various substrates in Suzuki-Miyaura coupling reaction,and higher than 90%yields were achieved within 5 h in green Et OH/H₂O solution.(4)Nitrogen-containing polymer(Phen-bip)with high thermal stability was prepared through Scholl reaction with 2,2'-bipyridine and 1,3,5-triphenylbenzene,and Phen-bip-Pd catalyst was obtained after loading Pd.The results showed that 4-nitrophenol could be rapidly converted in reduction reaction catalyzed by Phen-bip-Pd,and 95.7%conversion was achieved after 15 min in water.In addition,Phen-bip-Pd(0.075 mol%Pd)was efficient in Suzuki coupling reaction for bromobenzene derivatives and phenylboric acid derivatives in Et OH/H₂O solution at 60?.