Amino-Functionalized Pillar[5]arene

The recently introduced pillar[n]arenes have provided chemists with receptors that, when incorporated into materials, confer unique properties upon them. The symmetrical rims and cylindrical shape of pillar[5]arene begs the question-can these pillar-like receptors be linked covalently end-to-end in order to create tubular structures by a growth-from-template approach? In our efforts to produce these one-dimensional extended structures, we have developed a new method of functionalizing pillar[5]arene in which one of the five hydroquinone units is converted into a diaminobenzoquinone analogue. The resulting diamino-pillar[5]arene derivative, which undergoes a stereochemical inversion process that is slow on the H-1 NMR timescale, can be chemically modified yet further in a direction that is orthogonal to the plane of its methylene bridging carbons through the formation of oxazole heterocycles. This strategy has been employed to create rigid oligomers that resemble one-dimensional tubular arrays. As a proof-of-principle, a rigid pillar[5]arene dimer has been isolated and characterized in the solution state as a 1:1 complex with an extended viologen for which it acts as a receptor.