Syntheses, Post-Synthetic Modification And Catalytic Properties Of Zr-Metal-organic Frameworks

Metal-organic frameworks ?MOFs? are a class of hybrid materialscomposed of organic modules joined with inorganic modules ?metal ions or metal clusters?. As a subset of coordination compounds, some intrinsic characteristics make MOFs distinctly different fromthe traditional coordination compounds, such asporosity, high specific surface area, tailorability, high thermal stability and chemical stability. These affords MOFs with potential applications for gas adsorption and separation, fluorescence sensing, chemical recognition, drug delivery and heterogeneous catalysis.The internal surfaces of MOFs can be chemically modified by various methods, and in particular various functional sites can be introduced through the rich library of organic transformation reactions.This thesis explored the modification and functionalization of the UiO-series Zr-MOFs, which have been well known for high thermal and chemical stabilities:constructing Zr-MOFs with modifiable sites by judicious design of rigid dicarboxylate ligands bearing different reactive groups; postsynthetically functionalizing the MOFs through different organic transformation reactions; screening appropriate MOFs for catalytic reactions. The focushas been the modification of MOFs based on formyl-containing ligands:UiO-66-and UiO-67-type MOFs bearing formyl tags have been synthesized and various postsynthetic functionalization achieved through organic reactions of the formyl group; furthermore, the in-situ Leuckart-Wallach reaction of aldehydes under solvothermal conditions has led to MOFs with tertiary alkylamine groups, which show excellent catalytic activity for the Knoevenagel condensation reaction. The result illustrates a new strategy of functionalizing MOFs:modification via in-situ transformation reactions of ligands.Besides the introduction chapter, this thesis contains the following two chapters.1). Synthesis, modification and catalytic properties of functionalize dUiO-67 MOFs. ?i? 2-formyl-biphenyl-4,4'-dicarboxylic acid ?H₂BPDC-CHO? was synthesized by an improved procedure. With this ligand, were prepared by three methods:fully modified UiO-67-CHOby direct solvothermal synthesis; partially modified UiO-67-CHO-MLand UiO-67-CHO-ML-PSEby direct solvothermal synthesis and postsynthetic ligand exchange, respectively, ??? Postsynthetic and tandem postsynthetic modifications of the aldehyde-tagged Zr-MOFs were performed via the reactions involving the aldehyde group including imine condensation reaction, NaBH₂ reduction, Knoevenagel condensation, silylcyanation and metallation. Imine condensation using ethylenediamine can convert aldehyde to imine quantitativelyto give material UiO-67-en. The modification conversions using 2-picolylamine,2-aminophenol, and thiosemicarbazide are above 80%. Modification of mix-ligand material UiO-67-CHO-ML-PSE with 2-picolylamine and 2-aminophenol can also lead to complete conversions. Modification via C-C coupling Knoevenagel condensation and cyanosilylation proceeded readily with about 98%and 83% conversion.,For tandem modification, the UiO-67-en was reduced by NaBH₂. giving rise to a diaminefunctionlizedUiO-67-diamine, which can efficiently catalyze the Knoevenagel condensation between benzaldehyde and malononitrile. ??? During the synthesis of UiO-67-CHO, we found that the aldehyde group underwent in-situ transformation at higher temperature. Further investigations revealed that the well-known Leuckart-Wallach reductive animation reaction occurs under the solvothermal conditions. Thus, we proposed a new strategy of functionalizing MOFs, which make use of the in-situ ligand transform under the solvothermal synthetic conditions. With this strategy, we have successfully prepared the ?dimethylamino?methyl functionalized MOF, UiO-67-CH₂-N?CH3?2 directly from H₂BPDC-CHO.the result. The strategy has also been successfully applied to the synthesis of a Zn??? MOF, IRMOF-9-CH₂-N?CH3?2, for which the formyl to tertiary amine transformation was confirmed by single-crystal X-ray crystallography. 2) The synthesis, modification and catalytic properties of functionalized UiO-66 MOFs: ??? The in-situ ligand transformation strategy was used to synthesize the ?dimethylamino?methyl functionalized UiO-66. By changing the initial ratio of H₂BDC-CHO and H₂BDC we synthesized partly functionalized materials UiO-66-CH₂-N?CH3?2-14/24/60/100. The UiO-66-CH₂-N?CH3?2-14 can efficiently catalyze the Knoevenagel condensation between benzaldehyde and malononitrile with excellent activity, thanks to the strong basicity of the alkylamine group. Cycling and filtration experiments testified that the material is a good heterogeneous catalyst, ?ii? The aldehyde-tagged UiO-66 was also synthesized and can be postsynthetically modified through NaBH₂ reduction and Knoevenagel condensation, ?iii? Synthesis of UiO-66-type MOFs with pyridine-2,5-dicarboxylic acid ?H₂PYDC? as linkers has been attempted in order to introduce the pyridine group into the UiO-66 structure. While H₂PYDC alone cannot generate the desired MOF, mixed-ligand MOFs with the desired structure have been synthesized through a direct solvothermal method using mixed H₂PYDC and H₂BDC or through the postsynthetic ligand exchange strategy.