Synthesis,Structure And Property Of O₆-Corona[3]arene[3]pyridazines

Synthetic macrocycles play a paramount role in the establishment and development of supramolecular chemistry.Corona[n]arenas is a new class of macrocycles consisting of para-?het?arylenes and heteroatoms in an alternative fashion.Notably,the combination of heteroatoms and?het?arenes would advantageously engender numerous diverse macrocycles of tunable cylinder cavities and electronic features.As a continuation of previous work on corona[n]arenas,this thesis mainly concentrates on the synthesis,structure and host-guest property of O₆-corona[3]arene[3]pyridazines.We have shown a very convenient one-pot synthesis of O₆-corona[3]arene[3]tetrazines from the nucleophilic aromatic substitution reaction of 3,6-dichlorotetrazine and aromatic diols of different sizes and geometries.Inverse electron demand Diels-Alder reactions of the tetrazine with an enamine followed by denitrogenative aromatization led to effective macrocyclic transformation from O₆-corona[3]arene[3]tetrazines to O₆-corona[3]arene[3]pyridazines.The established method ensured the engineering of O₆-corona[6]arenes of varied cavity sizes and electronic features.The synthesized O₆-corona[3]arene[3]pyridazines are useful macrocyclic hosts to interactbothorganicneutralandchargedguestspecies.O₆-corona[3]arene[3]pyridazines were found to form 1:1 host-guest complexes in toluene with both fullerenes C₆₀0 and C₇₀0 with the association constants(K_1:1)spanning from 10⁴M^-1to 10⁵M^-1.Interesting,O₆-corona[3]arene[3]tetrazine exhibited remarkable selectivity in fullerene recognition.They acted as powerful hosts to complex strongly with C₇₀0 giving association constants K_1:1:1 up to 10⁴ M^-11 whereas interaction with C₆₀0 was not observed.The drastic difference in selectivity might be ascribed to an electronic effect of the hosts.Being a slightly stronger electron receptor than C₆₀,C₇₀0 is able to interact with both the tetrazine and the pyridazine in macrocycles.C₆₀,however,interacts only with the pyridazine which is a stronger electron donor than tetrazine.Additionally,O₆-corona[3]arene[3]pyridazines were able to form 1:1 complexes with dinitriles.Toward a number of dinitrile guests,the strongest binding was found with succinonitrile which gave an association constant(K_1:1)up to 10³ M^-1.Moreover,the ester-bearing O₆-corona[3]arene[3]pyridazines were able to form 1:1 complexes with a series of dicationic guests selectively in organic media with association constants ranging from 10² M^-11 to 10⁵ M^-1.Water soluble O₆-corona[3]arene[3]pyridazines were able to recognize dicationic guests in NaH₂PO₄-Na₂HPO₄ neutral buffer solution albeit with decreased association constants.We conclude that oxygen-bridged coronarenes are attractive and useful macrocyclic hosts in the study of supramolecular chemistry due to the ease of their synthesis and unique cavity structure.