Preparation And Catalytic Properties Of Quaternary-ammonium Functional Metal-organic Frameworks

The transformation and utilization of carbon dioxide has been a research hotspot in green chemistry,and a large variety of conversion reactions have been developed.The cycloaddition of carbon dioxide and epoxides is the most widely investigated conversion reactions due to its advantages such as mild conditions,high atom-economy and environment friendliness.Lots of porous functional catalysts have been used to catalyze this kind of reactions.As a newly-emerged porous material,metal-organic frameworks?MOFs?have been applied in the field of catalysis due to their high specific surface area,highly ordered channels and adjustable pore size.Furthermore,MOFs can be modified by pre-functionalization or post-synthetic modification to obtain various catalytic sites for designated organic catalytic reactions.A number of MOFs have been used as catalysts for the cycloaddition of carbon dioxide to epoxides.However,most MOFs exhibit neutral frameworks.To achieve good catalytic performance for the above-mentioned reaction,it is often necessary to add homogeneous ionic compounds?such as tetrabutylammonium bromide?to provide the nucleophilic anion that attack the epoxide during the catalytic cycle.So the catalytic systems with homogeneous co-catalysts are only partially heterogeneous and thus less eco-friendly.A promising strategy is to create cationic MOFs which encapsulate counter-anions within the pore and thus eliminate the use of co-catalysts.In this thesis,we demonstrated that aldehyde-tagged dicarboxylate ligands undergo an in-situ Leuckart-Wallach reductive amination reaction under solvothermal conditions,which allowed us to successfully obtain different types of MOFs with tertiary amine functionalities.Through post-synthetic N-methylation modification of the tertiary amine groups and subsequent anionic exchange,we were able to prepare a series of quaternary ammonium functionalized MOFs catalysts with different halide ions as counter-anions.Catalytic studies suggest that the MOFs can catalyze the cycloaddition of carbon dioxide and epoxides in the absence of any co-catslysts.This thesis includes three chapters:1.Synthesis and characterization of tertiary amine functional UiO-66In this part,we introduced the synthetic procedures of UiO-66-CH₂-N?CH₃?₂.We have prepared a series of tertiary amino functional products UiO-66-CH₂-N?CH₃?₂ via in situ conversion by 2-formyl-1,4-terephthalic acid,and obtained products with different ligand ratio through adjusting the ratio of terephthalic acid and 2-formyl-1,4-terephthalic acid.We characterized these MOFs through a variety of methods such as XRD,TG,NMR,etc.It turned out that the MOF maintained integrity after post-synthetic modification and there was no significantly change in crystallinity,cage construction and thermal stability.The modification proportion was calculated by 1H NMR and EDS.2.Quaternization post-synthetic modification of tertiary amine functional UiO-66 and its catalytic properties for the cycloaddition of carbon dioxide and epoxidesIn this part,we prepared the quaternization post-synthetic modification products via methylation between tertiary amino and methyl iodide,and obtained catalyst within different halide anion by anion exchange.In addition,we studied the catalytic properties of MOFs for the cycloaddition of carbon dioxide and epoxides,including the effects of ligand ratio,temperature,pressure and time.We found that the optimal temperature,pressure and time is 100?,1 MPa and 4 h,respectively.And UiO-66-CH₂-N⁺?CH₃?₃Br-ML0.72 has the best catalytic property due to its medium pore size and modification proportion.Besides,we also extend to other reactants,such as styrene oxide,epichlorohydrin,1,2-epoxybutane and cyclohexene oxide.These reactants all can take the cycloaddition with carbon dioxide by our catalyst,however the catalytic property is depended on the size and substituents of the reactants.3.Halomethylated with methyl MOFsIn this part,we have tried two ways to synthesize the bromomethylated MIL-101-CH₂Br.On the one hand,we successfully synthesized MIL-101-CH₃,then the bromination reaction can't occur;on the other,we successfully synthesized 2-bromomethyl terephthalate firstly;however during the hydrolysis of 2-bromomethylterephthalic acid methyl ester with hydrochloric acid,4-carboxyphthalide was produced instead of the desired 2-bromomethylterephthalic acid ligand.