Initial Study On The Synthesis And Host-guest Properties Of Pillar[6] Arenes

The preparation of novel macrocyclic hosts is very important since it is one of the majordriving forces to accelerate the development of supramolecular chemistry. Calixarenes haveemerged as the third generation of host-guest supramolecular compounds with unique holestructure. Because of their flexible structure and the characteristics, such as easy modification,calixarenes and their derivatives have highly autonomous selectivity. Therefore, calixareneand their derivatives can bind a variety of guest molecules, showing special recognition ability,are widely used in separation and extraction, chromatographic separation, chemical sensors,pollution control, life sciences, host-guest chemistry and so on, playing an increasinglysignificant role in social development and economic construction.A new type of supramolecular hosts called pillararenes were reported by Ogoshi et al in2008for the first time, which opened a novel direction in supramolecular chemistry.Compared with classic calixarene, pillararenes have much higher symmetry structure. Untilnow, a major progress has been made in the research on the synthesis and host-guest propertyof pillar[5]arenes. However, the literature about pillar[6]arenes are very seldom. The firstmember of pillar[6]arene was reported in2009. However, the yield of pillar[6]arenes werelow. Thus, how to improve the yield of pillar[6]arenes and synthesize a series of novelstructure with particular property pillar[6]arene derivatives become our subject. At the sametime, to reseach and develop their host-guest property also become an important researchwork.In this paper we developed a new and efficient preparation of pillar[6]arenes. Thismethod was easy to operate, and spent short reaction time. In contrast to the first reportedmethod, the reaction steps were shorten and the yields were increased. In order to know thedetails of the reaction, we studied the influence of solvent, catalyst, reaction temperature onthe reaction. Throuth the efforts we found the best reaction conditions: pillar[6]arenes wereprepared at room temperature in one pot by chloroform as solvent and ferric chloride ascatalyst. A series of pillar[6]arene derivatives were prepared by choosing differentalkoxy-substituent reagents, expanding the pillar[6]arene family members. Their structureswere characterized with NMR and MS.In order to understand the property of pillar[6]arene, their host-guest property was discussedfirstly. After choosing a variety of guest molecules to be combined with pillar[6]arenes, wefound that the quaternary ammonium salt could be a very good guest molecule. Their combinephenomenon was characterized with1H NMR and MS. In addition, we studied the chemical reaction stoichiometry by Job plot, the assoiaction constant was determined by Scatchardmethod. The conclusions are as follows: Mole ratio plot data indicated1:1stoichiometry;Scatchard plots data showed that the association constant is Ka=(0.449±0.006)×102M-1) forHexadecyl trimethyl ammonium bromide, correlation coefficient: R=0.998.We infered that pillar[6]arenes show higher selectivity in the host-guest relationshipbecause pillar[6]arenes have larger molecule cavity than pillar[5]arenes. Therefore, we choosea variety of quaternary ammonium salt respectively to be combined with pillar[6]arene andpillar[5]arene to study their host-guest properties respectively. Moreover, to examine theinfluence of the substituted groups of pillar[6]arenes on the binding interaction, similarinvestigations were carried out. The results indicate that the substituted groups ofpillar[6]arenes have little influence on the binding ability with quaternary ammonium salts.