Synthesis And Property Of Nitrogen-Bridged Tetrazine-Containing Corona[6]Arenes

A novel class of macrocyclic molecules constructed by different p-?het?arylene such as tetrazine,pyridazine and pyrazine,and heteroatoms such as oxygen and sulfur,in a cyclic fashion,have been synthesized recently.The macrocyclic molecules were named as“coronarenes”according to the unique coronary conformational structures.This dissertation mainly focuses on the synthesis,structure,property,molecular recogniton and assembly of novel corona[6]arenes containing tetrazine rings and nitrogen atom as linking units.The process of molecualr recognition of S₆-corona[3]arene[3]pyridazine toward various organic ammonium cations was also systematically studied.We initially synthesized a linear tetramer from the nucleophilic aromatic substitution reaction of N,N-bis?4-hydroxyphenyl?acetamide and 3,6-dichlorotetrazine.Subsequently,the nitrogen-bridged tetrazine-containing corona[4]arene[2]tetrazines were synthesized from the reaction of the tetramer and aromatic diols and dithiols.The resulting corona[4]arene[2]tetrazines have cylindroid cavities.The conformational structures,physicochemical properties of corona[4]arene[2]tetrazines could be finely regulated by the combination of varied bridging heteroatoms.These tetrazine-containing corona[4]arene[2]tetrazineswereelectrondeficient,and N₂,O₄-corona[4]arene[2]tetrazine was able to form complexes and supramolecular assemblies with anions of different shapes and geometries driven by anion-?interactions.An intermediate containing nitrogen-bridged tetrazine rings was obtained from the reaction of benzylamine and 3,6-dichlorotetrazine.Nitrogen-bridged tetrazine-containing corona[2]arene[4]tetrazines were then synthesized by using a fragment coupling strategy from the nucleophilic aromatic substitution reaction of the reaction intermediate and 1,4-aromatic dithiols or 1,4-aromatic diols.The resulting macrocyclic molecules contain cylinder cavities.Because of the conjugation between tetrazine rings and the bridging nitrogen atoms,corona[2]arene[4]tetrazines exhibit unique spectral and redox properties.The corona[2]arene[4]tetrazine was found to form host-guest complexes with different anions in the gas phase.Thebindingbehaviorsandthermodynamicoriginof S₆-corona[3]arene[3]pyridazine toward 21 N-alkyl ammonium cations were systematically investigated.S₆-corona[3]arene[3]pyridazine was able to form 1:1complexes with most guests.The magnitude of binding constants increases with the size and the charge number of the cation guest,up to?1.48±0.11?×10⁵ M^-1.The enthalpy changes of the binding behaviors were mainly due to multiple noncovalent interactions such as C-H…N hydrogen bond,?/?and lpe/?interactions between host and guest.While the entropy changes were attributable to the desolvation effect.In summary,we have developed the fragment coupling strategy,and obtained two novel classes of tetrazine-bearing coronarenes containing nitrogen atoms as linking units.The conformational structures,the spectral and electrochemical properties of the resulting macrocycles could be finely regulated owing to the interplay between heteroatoms and aromatic rings.The electron deficient corona[6]arenes are capable of forming complexes and diverse supramolecular assemblies with various anions in the gas phase and in the solid phase mainly driven by anion-?interactions.We have also elucidated the binding behaviors and thermodynamic origin of S₆-corona[3]arene[3]pyridazine toward organic ammonium cations.With the in-depth understanding of the synthesis,structure and property of coronarenes,the application prospects of coronarenes will be even broader,thus promoting the development of macrocyclic chemisty and supramolecular chemistry.