Synthesis And Applications Of Fiber-supported N-heterocyclic Carbene Metal Complexes And Thiourea Functionalized Fibers

Recently,polyacrylonitrile fiber（PANF）has become a new support for heterogeneous catalysis because of its unique structure and proporties.Since PANF is abundant with cyano groups,it can immobilize many active functions by amination.Based on these,a series of polyacrylonitrile fiber supported N-heterocyclic carbene metal catalysts were originally prepared.And three-component coupling reactions of aldehydes,amines and alkynes were used to investigate their catalytic performances.More over a series of thiourea modified polyacrylonitrile fibers were synthesized to scavenge Pd（II）efficiently.A series of N-heterocyclic carbine（NHC）silver complexes supported on polyacrylonitrile fiber were prepared.Their catalytic performances in three-component coupling reactions of aldehydes,secondary amines and alkynes were evaluated.The reactions proceeded smoothly even with only 1 mol%catalyst loading and 11 different types of propargylamines were synthesized successfully（yield:71-92%）.After 10 consecutive cycles,the activity remained virtually unchanged.The catalysts were also used to prepare fused triazoles in one-pot reactions with excellent yields and diastereoselectivities.In these reactions the substrates underwent three-component coupling followed by 1,3-dipolar cycloaddition.The above reactions were also successfully performed in a continuous-flow process.And rapid,modular and efficient syntheses of propargylamines and fused triazoles were achieved.Well defined NHC Au（III）and Cu（I）complexes were prepared using NHC Ag（I）complex as starting material.They were grafted on aminated polyacrylonitrile fiber to prepare fiber supported NHC IB group metals catalysts.Their catalytic activities were evaluated by three-component coupling reactions.Fiber supported NHC Au（III）and NHC Cu（I）showed higher catalytic activity than fiber supported NHC Ag（I）in the three-component reaction of 2-butanone,phenylacetylene and pyrrolidine.And more challenged secondary propargylamines were prepared using fiber supported NHC Au（III）as catalyst（yield:87%）.The reaction activity is enhanced by a microenvironment which is consisted with NHC,–NH₂ and–CN groups in the surface layer of fiber catalysts.The yield of immobilized NHC Au（III）catalyst is twice higher than its small molecule counterpart.Besides,the activity kept the same as the first use of the catalyst after the 8th run,which displays outstanding recyclability and reusability.A series of thiourea modified fibers were prepared and characterized.They were used as effective and reusable Pd ion scavengers.The absorption process follows a pseudo-second-order model and the equilibrium data fit well to the Langmuir isotherm model.It shows that the process is chemisorption in a one-on-one manner.The maximum absorption capacity according to the Langmuir model was 169 mg/g with an absorption limit of 0.03 ppm.The functionalized fibers exhibited excellent absorption properties both in organic solutions and in aqueous solutions.After five recycles,the adsorption efficiency of the absorbent remained at 96%of its original efficiency.The modified fibers were also used to remove palladium from reaction solutions containing active pharmaceutical ingredients as sustainable and efficient absorbents.