Design And Synthesis Of Metal Organic Frameworks And Their Application In Cross-Coupling Reaction

Palladium-catalyzed cross-coupling reactions,one of the most powerful tools for the formation of the C-C bonds,such as Suzuki and Heck reactions,are nowadays of great interest from both academic and industrial points of view.Because of the limited availability and high price of palladium,the environmental concerns and economic considerations make it essential to develop the palladium catalysts with full utilization of each palladium active site,as well as excellent recyclability and negligible metal leaching in order to reduce the cost of catalysts and pollution to the environment.Owing to their high surface area,porosity,and chemical tenability,Metal-organic frameworks(MOFs)have emerged as an important class of functional porous materials with distinct structural properties constructed by metal ions or clusters and bridging organic ligands.The advantages of MOFs have led to the intensive examination of their properties for potential applications in several areas,including gas storage,sensors,thin films,optics,drug carriers,catalysis,and so on.Heterogeneous catalysis is superior to homogeneous catalysis for easier separation,reusability,minimized waste and cleaner products.MOFs have been also pursued as heterogeneous catalysts by virtue of inherent catalytically active sites within the frameworks or as supporting materials for various catalysts.The research content is divided into the following two parts:(?)Two series of amine-functionalized Zr-based mixed-linker metal-organic frameworks(UiO-66-Mix and UiO-67-Mix)have been synthesized with the different ratios of 1,4-benzenedicarboxylate(H2BDC)/2-amino-1,4-benzenedicarboxylate(H2ABDC)and 4,4'-biphenyldicarboxylic acid(H2BPDC)/2-amino-biphenyl-4,4'-dicarboxylic acid(H2ABPDC)incorporated into their structures.The pendant amino groups were post-modified by the condensation reaction with pyridine-2-carboxaldehyde and then palladium metal centers were anchored onto MOFs via the coordination to pyridylimine moieties.The two series of heterogeneous palladium catalysts(UiO-66-Mix-PI-Pd and UiO-67-Mix-PI-Pd)have been utilized for the Suzuki and Heck cross-coupling reactions in ethanol-water under mild reaction conditions,showing remarkably high catalytic activity.The porosity of MOFs and the density of metal binding sites of palladium catalysts had great influence on the Suzuki and Heck cross-coupling reactions.The best results were achieved with very low Pd loading(0.054 mol%)of UiO-67-3-PI-Pd catalyst could yield the complete conversion of reaction substrates.Moreover,the catalysts could be readily recovered and recycled for at least 10 cycles without significant leaching and loss of catalytic activity.The catalysts were also generally applicable for different reaction substrates with various substituents in both Suzuki and Heck reactions.(?)Under the optimized conclusion of the previous chapter,a series of amine-functionalized Zr-based mixed-linker metal-organic frameworks(UiO-67-MixDiimine)have been synthesized with the different ratios of 4,4'-biphenyldicarboxylic acid(H2BPDC)/4,4'-(((2E,3E)-butane-2,3-diylidene)bis(azanylylidene))dibenzoic acid(?-Dumine Ligand)incorporated into their structures.The structure and chemical properties of?-diimine have been further reduced.The structural integrity and porosity of the metal-organic frameworks during the post-modification process are maximally protected and the properties are improved.A series of UiO-67-MixDiimine-Pd catalysts with different palladium content densities were obtained by adjusting the feed ratio of ligands containing functional groups in the mixed ligands during the synthesis of mixed ligands.By comparison,UiO-67-33%MixDiimine-Pd catalyst achieves the optimal coordination of surface area and palladium density.Furthermore,the UiO-67-33%MixDiimine-Pd catalyst was applied to various Suzuki and Heck reactions to obtain more excellent catalytic performance than UiO-67-3-PI-Pd catalyst.