Synthesis And Catalytic Properties Of N-Heterocyclic-Carbene-Metal Loaded Covalent Organic Frameworks And Covalent Organic Gels

As two kinds of emerging porous organic materials,covalent organic frameworks(COFs)and covalent organic gels(COGs)show great potential in catalytic applications due to their high porosity,functional versatility and outstanding stability.However,since COFs and COGs are metal-free,they cannot meet the requirement of catalytic applications that require the presence of metal catalyst.Due to the unique structure and properties,N-heterocyclic carbene(NHC)can bind various metal ions into NHC-metal complex(NHC-M)which has been recognized as an important class of organometallic catalysts.For expanding the catalytic application scope of COFs and COGs,NHC-M-loaded metalated COF-and COG-catalysts are first synthesized by the direct polymerization of NHC-M-containing monomers with their counterparts.The obtained metalated COF-and COG-catalysts possess one or two catalytic active sites,which can promote either single reaction or tandem reaction.Ⅰ.By direct polymerization of NHC-AuCl-decorated 4,4"-p-terphenyldicarboxaldehyde monomer with 1,3,5-tris(4-aminophenyl)triazine(TAPT)under solvothermal conditions,a new NHC-AuCl-loaded NHC-AuCl-COF was generated.The obtained NHC-AuCl-COF can be a highly active reusable catalyst to promote the carboxylation of the terminal alkyne with CO2 under mild conditions.Ⅱ.NHC-AuSbF6-COF is synthesized from NHC-AuCl-COF by ion exchange.The ion-exchange yield of Cl-by SbF6-is up to 97%.Powder X-ray diffraction analysis shows that the COF structure and crystallinity are intact after ion-exchange.Compared with NHC-AuCl-COF,NHC-AuSbF6-COF displays higher catalytic activity in the alkyne hydration reaction.Ⅲ.By direct polymerization of NHC-Au monomer with its chiral secondary amine-counterpart under solvothermal conditions,an new imine-linked and NHC-Au-loaded chiral covalent organic framework(CCOF)is achieved.The obtained(S)-NHC-Au-SA-COF can be a reusable dual catalyst to highly promote the asymmetric aryl methanol oxidation-aldol relay reaction in a heterogeneous way.In addition,a CCOF@chitosan aerogel-based cup-like reactor is designed and fabricated via a facile templating freeze-drying approach,by which the gram-scale asymmetric aerobic alcohol oxidation-aldol relay reaction was successfully realized.Ⅳ.In the presence of aminocatalyst,both NHC-M(M=Pd,Au)and chiral secondary amine decorated COG catalysts of(S)-NHC-Au-SA-COG and(S)-NHC-Pd-SA-COG are prepared.Due to possessing two active catalytic sites,the obtained COGs can be the bifunctional catalysts to catalyze asymmetric alcohol oxidation-aldol tandem reaction in heterogeneous manner.Compared with(S)-NHC-Au-SA-COG,(S)-NHC-Pd-SA-COG exhibits higher catalytic activity.