Metal-loaded Covalent Organic Frameworks:Synthesis,Characterization,and Application For Selective Catalysis

Covalent organic frameworks（COFs）,connected by covalent bonds,are a new type of organic porous polymer.Benefiting from large surface area,ordered channel,tunable pore size and available active sites,COFs have shown superior potential in storage,separation,catalysis,sensing and drug delivery.In this thesis,the construction of functional COFs and its application in heterogeneous catalysis are regarded as the research objectives.Two COFs with different pore structures and functional groups were synthesized by condensation reaction,and applied in regulating the regioselectivity of oxidation Heck reaction and olefin diarylation reaction.This thesis can be divided into four parts.（1）A brief overview of the research ideas,contents and COFsFirstly,the background and meanings of this thesis are described.Secondly,the design principle,synthesis method,characterization method and the application of COFs in catalysis are introduced,and then the challenges of COFs in regulating regioselective reactions are pointed out.Finally,the research content,method and innovation are summarized.（2）Synthesis,characterization and functionalization of imine COFsThe imine COFs（COF-BTDH）was constructed by condensation reaction with1,3,5-tricarbaldehyde and 3,3’-dihydroxybenzidine as organic monomers.The structure of COF-BTDH was confirmed by Fourier transform infrared spectrum,solid-state ¹³C NMR spectroscopy,powder X-ray diffraction,and Materials Studio software.Then,via a simple adsorption method,Pd（OAc）₂ was loaded on COF-BTDH to prepare functional COFs（Pd/COF-BTDH）.Scanning electron microscopy,transmission electron microscopy,thermogravimetric analysis,nitrogen adsorption and desorption experiments,and X-ray photoelectron spectroscopy were used to investigate the morphology,stability,pore size,surface area of COF-BTDH and the loading,existing form and coordination mode of Pd（OAc）₂ in COF-BTDH.The results show that Pd²⁺can form a stable pentavalent chelate with N and O atoms in the pore,which is different from Pd（OAc）₂ coordination between layer and layer reported in the literature.This study provides a useful design idea for the rational selection of organic monomers to realize selective loading of active species（Pd,Pt,Cu,Ag,etc.）in COFs.（3）Application of COFs in regioselective control of oxidative Heck reactionOxidative Heck reaction provides a common strategy for C-C bonds construction and has been widely used to synthesize various drugs intermediates.For electronically biased alkenes,high regioselectivity can be achieved.Electron-poor alkenes tend to form linear products,and electron-rich alkenes tend to form branched products.However,electronically unbiased alkenes can cause complex and inseparable mixtures.In this chapter,COF-BTDH was used as heterogeneous ligand to regioselectively regulate oxidative Heck reaction of electronically unbiased alkenes.1-octene and phenylboronic ester were used as model substrates,and the linear product was obtained with the selectivity of 50:1.Then,we used model substrates to investigate the reaction conditions,and carried out 21 substrate applicability studies under the optimal conditions.The results show that the catalytic system has good compatibility and selectivity for various olefins and arylborates.In addition,COF-BTDH can be reused 9 times.Finally,COF-LZU1 and COP-BTDH were synthesized to compare the experimental results with COF-BTDH.The results show that the regular pore structure of COF-BTDH and the coordination mode of N,O with Pd²⁺play a key role for high regioselectivity regulation of oxidative Heck reaction.Density functional theory calculation shows that the catalytic system tends to produce linear products in thermodynamics and kinetics.In this study,COFs was innovatively used in the oxidation Heck reaction,which achieved high regioselective regulation of oxidation Heck reaction,and laid a foundation for COFs in regioselective regulation of organic reactions.（4）Application of COFs in regioselectively control of olefins diarylationDiarylation structure is the core skeleton of urokinase receptor,vitellin receptor antagonist and flumurin.Transition metal catalyzed olefins diarylation is one of the most effective methods for synthesize diarylation compounds.However,due to the nature of transition metals,the reaction faces two challenges:（1）easy conductβ-H eliminate to obtain Heck reaction products;（2）regioselective competition between1,1-diarylation and 1,2-diarylation.Base on the regulation ability in oxidative Heck reaction,COF-BTDH was used to regulate olefin diarylation.（allyloxy）benzene and phenylboronic ester were used as model substrates,the 1,1-diarylation structure was obtained by analyse single crystal data.Then,we optimized the reaction conditions and investigated the substrate applicability.The results show that the 1,1-diarylation products of（allyloxy）benzene and 1-octene could be obtained in good yield,but other olefins were not suitable.We used carbene ligand to expand 9 substrates and made a comparison between COF-BTDH and carbene ligand.The results show that the reaction yield and reusability of COF-BTDH as the ligand were better than carbene as ligand,although the substrate applicability of COF-BTDH as heterogeneous ligand was limited.In this study,COFs was innovatively used in olefin diarylation,proved the advantages and feasibility of COFs in regioselectively control olefin diarylation,and provided ideas for the application of COFs in regioselective regulation.