Synthesis, Self-assembly And Selective Molecular Recognition Of Monofunctionalized Pillar[n]arenes

Macrocyclic chemistry is an important part in supramolecular chemistry. The studies onsynthesis of new macrocyclic host and their host-guest chemistry have been at the core of thisfield. As a new generation of macrocyclic hosts after crown ether, cyclodextrin, calixareneand cucurbit as four generations of traditional macrocyclic hosts, pillar[5]arene was firstreported in2008. Pillar[n]arenes are a novel kind of host molecules, which are connectedhydroquinone by methylene bridges at the para-position. Owing to their uniquecharacteristecs, such as highly symmetric, rigid and rich electronic structure, pillararenesshow excellent host-guest properties and have been applied in the field of molecular sensors,single-molecular artificial transmembrane Channels, thermoresponsive materials, et al.Similar with traditional macrocyclic hosts, monofunctional modification of pillar[n]arene canobtain a variety of new host derivatives，which show excellent molecular recognition andself-assembly properties. Research works of this dissertation mainly include synthesis,self-assembly and selective molecular recognition of monofunctionalized pillararenes. Themain contents are as follows:(1) Since the cyclization reaction for constructing pillararene skeleton is suitable only forsome simple hydroquinone monomers, it is difficult to synthesize some mono-substitutedcopillar[n]arenes with specific functional properties via the simple copolymer cyclizationreaction. Therefore, in this dissertation, we employed and optimized the ring postmodification method to synthesize monofunctionalized pillar[5]arenes. Dimethoxypillar[5]arene was synthesized via using1,4-methoxybenzene and formaldehyde as rawmaterial in the presence of the catalyst BF3·O(Et)2. The cyclization reaction completelyfinished in just2min and fifty seconds. Then boron tribromide as demethylation reagent wasused to selectively remove one methyl to obtain important intermediate monohydroxypillar[5]arene in60%yield. Some groups can be introducted into the rim of pillar[5]arenecavity via Williamson reaction, hydrolysis or esterification. This work enriches the syntheticmethods of monofunctionalized pillar[5]arenes, and lays the foundation of the wideapplication for the method.(2) In view of the importance of selective molecular recognition in host-guest chemistry,we designed and synthesized a sieries of monofunctional copillar[5]arenes (1and2) bearingester side chains and studied their self-assembly behavior and host-guest properties. Owing tointroduction of a rigid acetate group as linkage between pillar[5]arene and alkyl chain group,alkyl moieties are deeply included in the pillar[5]arene cavity. Compound1forms the self-inclusion complexs (SICs).1H NMR， NOESY�'�X-ray diffraction experimentsconfirmed that compound1forms stable SICs at low and high concentrations in solution, andeven in the solid state. Furthermore, the formation of the host–guest complex depends on thecompetition complexation between guest and the alkyl ester side chain, realizing the selectivemolecular recognition and being used to investigate its stability. Additionally， acopillar[5]arene2bearing a butyrate chain can not form a self-inclusion complex and exhibitslow guest selectivity。(3) In view of the importance of noncovalent intermolecular interactions in molecularrecognition process，we designed and synthesized a monophosphoryl copillar[5]arene8.Compared with the unmodified1,4-dimethoxypillar[5]arene4, the introduction of thephosphoryl group remarkably promoted the binding affinity of8with alkanols andalkanediols. Furthormore,8can form a stable1:1host-guest complex with alkanols in CDCl3.(4) Because pillar[6]arenes have a relatively large cavity, they may complex with largeguests. We designed and synthesized a monofunctional copillar[6]arenes13bearing pyridinesalt side chain and successfully explored a synthetic route of monofunctionalcopillar[6]arenes. In addition, we studied it’s self-assembly behavior via1H NMRexperiments. The results indicate that the “supramolecular structure” of13isconcentration-dependent.(5) In order to enrich family members of pillararenes, we chose the FeCl3-catalyzedcondensation reaction of1,4-dimethoxybenzene with paraformaldehyde in CHCl3to givedimethoxypillar[7]arene14. Per-hydroxylated pillar[7]arene15was obtained viademethylation of dimethoxypillar[7]arene with BBr3and its host-gues properities wasinvestigated preliminarily. The pillar[7]arene cavity is large enough to let adamantanemolecule through. But adamantane can not be steadily included in pillar[7]arene cavity.Additionaly, Per-hydroxylated pillar[7]arene shows weak binding ability towords bipyridinesalt. Thus pillar[7]arene host will have special molecular recognition ability.