Design And Catalytic Performance Of Ionic Organic Molecular Cages For The Preparation Of Small Size Palladium Nanoparticles

Metal nanoparticles（MNPs）are widely used in modern industry due to their unique physical and chemical properties.MNPs as catalysts usually show better catalytic activity than conventional bulk metals,but their high surface energy and low surface atom coor-dination lead to agglomeration during usage,which greatly limits their practical applica-tion.At present,the widely used method to solve this problem is to load palladium nano-particles（PdNPs）on various organic and inorganic porous materials.Organic molecular cage（OMC）as one special kind of organic porous materials,has good solubility in most organic solvents and keeps a high dispersion state.The special elements or functional groups can be introduced into the porous structure of OMC during the synthesis stage or via post-modification to expand its application scope,being a very ideal MNPs porous carrier.In this thesis,we have synthesized four OMCs and used them as the carrier materials for the preparation of small-size PdNPs.Two OMCs（i.e.Py-OMC and Ph-OMC）with different numbers of nitrogen atoms were efficiently synthesized by using three common organic small molecules as building units via dynamic imine chemistry.Their chemical structures were confirmed by NMR and HRMS analysis.The yield of Py-OMC with 11nitrogen atoms is 74.47%,and the yield of Ph-OMC containing 8 nitrogen atoms is 85.3%.Most of the organic molecular cages are water-insoluble,which greatly limits their appli-cation in water phase.Therefore,we have tried to protonate these two obtained OMCs to give water-soluble molecular cages I-Py-OMC-Cl and Ph-OMC-Cl,the chemical struc-tures of which were confirmed by NMR and HRMS analysis as well.The nitrogen atoms with lone pair electrons in Py-OMC,Ph-OMC,I-Py-OMC-Cl and I-Ph-OMC-Cl provide a good opportunity for the coordination of metal ions and the growth of nanoparticles.The four obtained OMCs were then used as carrier materials to prepare the composite PdNPs@Py-OMC,PdNPs@Ph-OMC,PdNPs@I-Py-OMC-Cl,PdNPs@I-Ph-OMC-Cl.The size and dispersion of the four Pd nanoparticles were char-acterized by TEM.The analysis results showed that the three more nitrogen atoms of Py-OMC compared with Ph-OMC did not play a significant role in enhancing the anchoring point of Pd nanoparticles,but played a great role in improving the solubility of Pd nano-particles composites in organic solvents.At the same time,the protonation of the molec-ular cage played a decisive role in expanding the space size of molecular cage in the solvent.In order to explore the application potential of PdNPs in catalysis,we employed PdNPs@I-Py-OMC-Cl,commercial K₂Pd Cl₄ and PdNPs@I-Ph-OMC-Cl as a catalyst,respectively,to catalyze various organic reactions for the comparison of their stability and catalytic performance.The experimental results showed that PdNPs@I-Py-OMC-Cl was more stable than PdNPs@I-Ph-OMC-Cl,and PdNPs@I-Ph-OMC-Cl was more stable than K₂Pd Cl₄.Meanwhile,PdNPs@I-Py-OMC-Cl showed the best catalytic activity in Suzuki coupling reaction assisted by microwave.These phenomena fully demonstrates the advantages of water-soluble ionic organic cage supported palladium nanoparticles in the field of green homogeneous catalysis.The knowledge gained here can open new pos-sibilities for the catalyst development.