Design,Preparation And Catalytic Performance Of Biguanide Covalent Organic Frameworks Materials

With the development of emerging crystalline organic porous structural materials,Covalent Organic Frameworks(COFs)materials have attracted widespread attention due to their structural design,synthesis controllable and functionally customizable characteristics.The pores are relatively regular and easy to modify,and the specific surface area is relatively high.Since the report,COFs have become one of the research hotspots of porous materials.COFs have developed related applications in the fields of medicine,pesticides,dyes,conductive polymers and optoelectronic materials.In the structural design of COFs,combining different functionalized structural units will produce COFs with specific frame structures and apertures.Among them,guanidine is a type of functional group that has a certain basicity and can chelate metals.In this paper,the construction of nitrogen-rich COF with biguanide group(DG-COF-JNU series)is studied and applied to heterogeneous catalysis.The main contents of this paper are as follows:(1)DG-COF-JNU1 was synthesized by solvothermal method from melamine and N,N’-bis(4-bromophenyl)biguanide.The biguanide group was introduced into COF to directly act as a heterogeneous catalyst.It could be recovered and recycled after washing.DG-COF-JNU1 has lamella stacking,and finally forms a spherical aggregate structure,with a high specific surface area and good thermal stability.DG-COF-JNU1 exhibits high catalytic activity in Knoevenagel condensation reaction,Knoevenagel-Michael-cyclocondensation reaction and Biginelli reaction.After 8 reaction cycles,the catalytic activity of DG-COF-JNU1 did not decrease significantly.In addition,DG-COF-JNU3 and DG-COF-JNU4 were synthesized by acid-catalyzed solvothermal method,and the structure of biguanide COF was expanded in order to have more practical applications.(2)DG-COF-JNU2 was synthesized from 1,3,5-tris(4-bromophenyl)benzene and1,4-benzenedibiguanide by solvothermal method.It has a high surface area and a clear porous sheet morphology.Pd(II)nanoparticles were immobilized in DG-COF-JNU2 to obtain Pd/DG-COF-JNU2,and applied to the catalysis of Suzuki-Miyaura reaction,Heck reaction and Sonogashira reaction.Pd/DG-COF-JNU2 combines the advantages of COF,biguanide and palladium nanocatalysts,and shows enhanced activity in the coupling reaction.The catalyst exhibits a higher reaction yield and a wide substrate universality.Due to the unique porous structure and electronic structure of the COF framework,DG-COF-JNU2 has significant stability before and after coordination with palladium.After 8 catalytic cycles,the catalytic activity did not decrease significantly.