Synthesis,Structure,Anion Recognition,and Self-Assembly Of Functional Oxacalix[4]arenes

The development of classic supramolecular chemistry has evolved four generations of macrocyclic host molecules,including crown ethers,cyclodextrins,calixarenes,and cucurbiturils.Design and synthesis of new type of macrocycles is always a driving force for supramolecular chemistry.Recently,heteroatom bridged calixarenes,by replacing the methylene bridges in classic calixarenes with other atoms,has become a hot research topic of this field.Based on the previous work on the synthesis of oxacalix[4]arene,the current thesis was focused on a series of derivation reactions to introduce functional groups into this skeleton.Based on the study of their structures,we wish to realize anion recognition and formation of supramolecular polymer via hydrogen bonding mediated self-assembly.In the first part,we adjusted the solubility of oxacalix[4]arenes by introduction of different ester groups into the precursors to facilitate successive derivation.Based on the one-step,high efficient,and large scale synthesis of oxacalix[4]arene skeletons,we converted the nitro groups to amino groups under catalytic hydrogenation conditions.Subsequently through three type of amino derivation reactions,including amidation,condensation with isocyanate,and condensation with aldehyde,different functional groups were successfully introduced.Furthermore,through the hydrolysis of ester groups into carboxyl groups,and then coupling with acetohydrazide,we got tetraacetohydrazide derived oxacalix[4]arene.Starting from an unsymmetrically substituted precursor,we selectively synthesized a symmetrical oxacalix[4]arene via multi-step fragment coupling strategy.X-ray single crystal analysis revealed chair conformation for tetraamido oxacalix[4]arene in the solid state,which is the first chair conformation for oxacalix[4]arene family.In the second part,we found that tetraamido oxacalix[4]arene cannot recognize common anions,which might result from its unique chair conformation.Tetraureido oxacalix[4]arenes could really complex with anions such as F^-,Cl^-,Br^-,I^-,Ac^-and HSO₄^-,which was confirmed via NMR and UV-vis spectroscopy.Job-plot via UV-vis measurements revealed 1:1 stoichiometry of the complexation between macrocyclic host and anion guests.The association constants were determined to be of 10⁴-10⁵order of magnitude via titration studies.Finally ¹H NMR investigation confirmed preliminarily that the tetraacetohydrazide oxacalix[4]arene could form a stable supramolecular polymer in chloroform solution.