Synthesis And Properties Of Supramolecular Cages Based On Metal N-Heterocyclic Carbene Moieties And Their Precursors

Metal-organic cages are discrete supramolecular entities composed of organic linkers and metal knots（metal ions or metal clusters）by coordination-driven self-assembly.Metal-organic cages have received extensive attention due to their unique characters,such as persistent porosity,good solubility,high chemical/thermal stability in specific environments,and potential applications in recognition,catalysis,host-guest chemistry,and drug delivery.The incorporation of functional groups into the cavity of discrete supramolecular cages will bring unique functions and applications.The imidazolium salt derivatives are used as the precursor of N-heterocyclic carbene（NHC）.Due to their inherent cationic nature,imidazolium derivatives can form strong interactions with anions through（C-H）⁺···X^-ionic hydrogen bonds and electrostatic attraction,and have the potential to recognize anions.Metal N-heterocyclic carbene（NHC-M）complexes have now developed into an important class of complexes in organometallic chemistry,and have been widely applied in the fields of catalysis,materials science,and pharmaceuticals.Therefore,the introduction of NHC-M complexes and their precursors into metal-organic cages is a promising research direction.In this dissertation,pyridyl or carboxyl functionalized imidazolium salts and NHC-M ligands were designed and synthesized,which were successfully introduced into the metal-organic cages through coordination self-assembly.The compounds were characterized by ¹H NMR spectroscopy,electrospray-ionization mass spectrometry,and single crystal X-ray diffraction.The main contents are as follows:1.Imidazolium functionalized Pd₃L₆-type tri-prisms frameworks,[Pd₃L₆¹]（PF₆）₁₂,[Pd₃L₆¹]（OTf）₁₂ and[Pd₃L₆²]（PF₆）₁₂,were synthesized.Interestingly,two different solid-state packing modes could be selectively obtained by adjusting the solution concentration of[Pd₃L₆¹]（PF₆）₁₂ during crystal growth.When the concentration was high,α-[Pd₃L₆¹]（PF₆）₁₂type packing pattern was obtained,in which a cavity with a diameter of about 24?surrounded by eight Pd₃L₆ units was found.However,when the concentration was low,β-[Pd₃L₆¹]（PF₆）₁₂ type packing pattern was obtained,which displayed an A/B/A/B stacking mode,and one-dimensional channel with a diameter of 22?was observed.2.Imidazolium functionalized Pd₂L₄-type compounds,[Pd₂L₄³]（BF₄）₈,[Pd₂L₄⁴]（PF₆）₈and[Pd₂L₄⁶]（PF₆）₈,were synthesized.The cage-frame-type cavity contains four imidazole groups,which may have potential applications in the recognition and encapsulation of anionic.In addition,two NHC-Au functionalized compounds,[Pd₂(L^3Au)₄]（BF₄）₄ and[Pd₂(L^4Au)₄]（BF₄）₈,have been successfully synthesized.Four NHC-Au-Cl groups are all located in the cage cavity,which may have potential applications in the field of confined-space catalysis.3.Three carboxyl-functionalized imidazolium ligands featuring different lengths,H₂L⁷Cl,H₂L⁸Cl,and H₂L⁹Cl,were synthesized,and then self-assembled with the in-situ Cp₃Zr₃ clusters to form imidazolium-functionalized zirconium base supramolecular organometallic cages（SOC）SOC 1-3 containing different cavity sizes.The framework consists of two Cp₃Zr₃ clusters and three ligands.With increasing the length of the ligand,the cavity of the cage becomes larger.Due to the cationic nature of imidazolium salts,they also have a cationic cavity,giving them the ability to recognize and encapsulate anionic guests.On this account,we explored the host-guest chemistry between the organic sulfonate anionic guests G¹-G⁹ and SOC-2,characterized by ¹H NMR spectroscopy and electrospray-ionization mass spectrometry and isothermal titration calorimetry.The results showed 1:1 binding stoichiometry,and SOC-2 has the strongest binding ability with p-methylbenzene acid anion（G³）.In addition,the single crystal structures of four host-guest complexes were obtained.4.Three carboxyl functionalized NHC-Au ligands with different lengths,H₂L^7Au,H₂L^8Au and H₂L^9Au were synthesized,and then self-assembled with the in-situ Cp₃Zr₃clusters,and two geometrical configurations were obtained.For H₂L^7Au and H₂L^8Au,tetrahedral（Cp₃Zr₃）₄L₆ cages SOC-4 and SOC-5 were obtained.While for longer H₂L^9Au,a rugby-shaped（Cp₃Zr₃）₂L₃ cage SOC-6 was obtained.This phenomenon can be attributed to steric hindrance.When the rugby-shaped cage can accommodate three NHC-Au-Cl groups at the same time,the resulting geometrical configuration remains unchanged,otherwise,the tetrahedral coordination cage is obtained.Furthermore,we have researched the transformation from homogeneous cages to heteroleptic cages through ligand exchange,and the processes were detected and monitored by ¹H NMR spectroscopy and electrospray-ionization mass spectrometry.In the process,the transformation from tetrahedral cage to rugby-shaped cage was also observed.This is the first research of cage-to-cage transformation in Zr-SOC.