Studies On The Synthesis Of Metal-Organic Frameworks And Their Applications In Catalysis

Catalysis is a key to the modern chemical industry,more than 90%of chemicals such as dyes,polymers,fibers,fine chemicals,and pharmaceuticals are prepared involving at least one catalytic step.Therefore,the development of highly-efficient,highly-selective,environmentally friendly and low-cost catalysts is a permanent goal.Conventional catalysts mainly include homogeneous and heterogeneous catalysts,but these two types of catalysts have been developed parallelly without much overlap between each other.Metal-organic Frameworks(MOFs)are novel organic-inorganic hybrid materials composed of inorganic metal nodes and organic bridging ligands.MOFs are porous materials with large specific surface area,adjustable pore size and are easy to be functionalized.MOFs materials have gradually bridging the gap between heterogeneous catalysts and homogeneous catalysts because they possess ordered and specific catalytic active sites.The inorganic metal nodes,functionalized organic ligands and supported metal nanoparticles,etc.of MOFs can work as catalytic active centers,and the synergistic interactions between adjacent sites can be employed to catalyze multi-step sequential reactions with a single catalyst,which helps realizing process integration.Inspired by the achievements of homogeneous catalysis,several types of functionalized MOFs materials were successfully constructed by means of postsynthetic-modification and metal loading.The coordinatively unsaturated metal sites(CUMSs),functionalized organic ligands and the supported components can provide MOFs with abundant of catalytic centers,which enables the efficient preparation of various drugs and pharmaceutical intermediates by heterogeneous catalysis.The main research points of this thesis are as follows:1.Preparation of MOFs with catalytically active metal centers and its applications in catalyzing the cyanosilylation of aldehydes and olefin oxidation reactions.Catalytic addition of trimethylsilyl cyanide to aldehydes is one of the important organic reactions for the formation of carbon-carbon bonds.The product cyanohydrin trimethylsilyl ether can be conveniently converted into a-hydroxy acid and β-amino alcohol,which are building blocks for the synthesis of biologically active products,etc.In the first part of the work,MOFs materials with different structures were prepared by hydrothermal/solvothermal reactions.The abundant CUMSs within MOFs were used as Lewis acids to catalyze the cyanosilylation reaction.The Lewis acidity and the interaction between MOFs and substrates were systematically studied by infrared spectroscopy(IR),and the effect of the pore structure on the reaction was evaluated by N2 sorption experiments.Experimental results revealed that MIL-101(Cr)with good stability,large pore size and strong Lewis acidity has the best catalytic activity toward the cyanosilylation reaction,with a selectivity of 99%for the cyanohydrin product.Allylic oxidation products are widely used in organic synthesis for the preparation of perfumes,pharmaceutics,dyes and agrochemicals.In this work,a Mn-based MOFs material CPF-5 is prepared for the selective allylic oxidation of olefin.CPF-5 is capable of oxidizing cyclohexene in the presence of a catalytic amount of tert-butyl hydroperoxide(tBHP)using molecular oxygen as oxidant,α,β-unsaturated ketone was obtained with 87%selectivity.Furthermore,X-ray photoelectron spectroscopy was used to investigate the catalytic reaction mechanism2.Preparation of Lewis acid and Br(?)nsted acid bifunctional MOFs and their applications in biomimetic catalytic transfer hydrogenation and oxidative dehydrogenation coupling.Lewis acid and Br(?)nsted acid dual functionalized MOFs material MIL-101(Cr)-SO3H was prepared by introducing sulfonic acid functional groups on MOFs bridging organic ligands.Coenzyme I(NADH)analogues was used as hydrogen donors,and a biomimetic catalytic transfer hydrogenation reaction system is constructed to prepare amine compounds.The system is widely applicable to diverse substrates,and the catalyst is stable and can be reused.Furthermore,MIL-101(Cr)-SO3H is used to activate the inert C(sp3)-H bond,and oxygen is used as the only oxidant to catalyze the cross-dehydrogenative coupling reaction to realize the green preparation of the xanthene derivatives.The system is capable of catalyzing the coupling of xanthene with different nucleophiles.NMR was used to monitor the evolution of different species and the reaction process.Experimental results revealed that the Cr site in MIL-101(Cr)-SO3H accelerates the autoxidation of xanthene,and the formed peroxide intermediate is then coupled with the nucleophile under the catalysis of adjacent sulfonic acid sites.The two catalytic sites of MIL-101(Cr)-SO3H work synergistically,which makes it superior to conventional solid acids.3.Construction of chiral MOFs and its application in asymmetric transfer hydrogenation of imines.Chiral molecule was introduced into the pores of MOF by postsynthetic modification via coordination bond.The catalytically active components are stabilized by the confinement effect of MOFs,the asymmetric reduction of imine is realized by chiral MOF catalysis with inexpensive and easily available trichlorosilane as the reductant.In-situ infrared spectroscopy was used to investigate the interaction between the catalyst and substrate.Experimental results revealed that MOFs material can effectively activate the imine substrate and trichlorosilane,and the porous structure of the MOFs material allows the free diffusion of substrates,making it efficient in catalyzing the hydrosilylation of imine.4.Preparation of functionalized MOFs-metal nanoparticle composites and their applications in catalyzing the synthesis of quinoline derivatives by multi-step tandem reaction.MOFs materials were used as host to disperse metal nanoparticles(MNPs),stabilize MNPs and improve the utilization of active sites.MOFs in combination with MNPs with different types of catalytic sites were able to catalyze multi-step tandem reaction for the synthesis of quinoline derivatives from simple starting materials.Furthermore,the in-situ magic angle spinning(MAS)solid-state nuclear magnetic resonance technique combined with mass spectrometry,were used to study the reaction kinetics and monitor the changes of the reaction intermediates in situ to reveal the mechanism for the formation of tetrahydroquinoline derivatives.