Construction Of Supported Catalysts Based On Nitrogen-containing Ligands And Their Application In Hydrogen Borrowing Reactions

As a large class of chelating ligands,nitrogen-containing ligands are widely used in the preparation of metal complexes by combining transition metal ions.The nitrogen atom can supply a lone pair of electrons to coordinate with the metal active center,and has high coordination capacity.Although the homogeneous catalyst prepared in this way has high activity,it has the fatal disadvantage that it cannot be recycled in industrial production.As the concept of green chemistry becomes more and more popular,the preparation of highly active and recyclable heterogeneous catalyst has attracted more and more attention.And then,it is possible to graft different inorganic supports on the basis of nitrogen-containing ligand with strong coordination ability to prepare supported catalysts with high catalytic activity and recyclability simultaneously.Moreover,the catalyst is used in the hydrogen borrowing reaction which is very friendly to the environment（because the water is the unique by-product）,and the recycling is realized at the same time.Details are as follows:（1）A symmetric N,P-ligand was designed and synthesized.Next,the palladium complex DPA-Pd was prepared by coordinating with 1,5-cyclooctadiene palladium dichloride（Pd Cl₂（COD））.The carrier C₃N₄ was prepared by a traditional thermal polymerization method using melamine as raw material,and then DPA-Pd and C₃N₄ were calcined in a tube furnace to prepare the heterogeneous catalyst DPA-Pd@g-C₃N₄.Moreover,SEM,TEM,TGA,XPS,XRD,EDX and others have characterized the catalyst.After confirming the morphological characteristics of the catalyst and the presence of metal particle,the catalyst was used in the hydrogen borrowing reaction of 2-aminopyridine and benzyl alcohols to verify its catalytic activity.At the same time,due to the existence of the inorganic carrier,the catalyst can be recycled by simple centrifugation after use,and the recyclability is pretty good.（2）A N,S-ligand was designed and synthesized,which was linked to pyrene containing a highly conjugated structure,and then iridium complex PTB-Ir was prepared by coordinated with dichloro（pentamethylcyclopentadienyl）iridium（III）dimer.Reduced graphene oxide（r GO）and PTB-Ir were combined to prepare the heterogeneous catalyst PTB-Ir@r GO viaπ-πstacking and metal ion adsorption.The catalyst was also characterized and analyzed by SEM,TEM,EDX,XPS,etc.,and its catalytic activity was detected in the hydrogen borrowing reaction between 8-aminoquinoline and benzyl alcohols.The catalyst also has a certain recyclability.（3）Based on the strong stabilizing effect of the N,S-ligand of the second part,the ligand 2-（5-（4-vinylphenyl）thiophen-2-yl）benzo[d]thiazole（VTB）with a double bond was prepared by coupling with 4-vinylbenzeneboronic acid,and ligand-functional porous organic polymer（POP）was synthesized by radical initiation between VTB and divinylbenzene（DVB）in the presence of2,2’-Azobis（2-methylpropionitrile）（AIBN）.The supported catalyst POP-Ru was prepared by POP and metal ruthenium,which is commonly used in hydrogen borrowing reaction.Firstly,the porous structure was verified by SEM and TEM,and then the specific surface area and pore size distribution of POP-Ru were explored by BET,as well as EDX and TGA,which all proved the successful synthesis of the heterogeneous catalyst.When the POP-Ru was used for the hydrogen borrowing reaction of anilines and benzyl alcohols,we found that a good yield was also obtained in water,which is a kind of green solvent.And the POP-Ru still maintained a certain activity after at least 5 times of recovery.