Resorcinarenes with 2-benzimidazolone bridges: Self-aggregation, self-assembled dimeric capsules, and guest encapsulation

摘要

The synthesis and spectroscopic characterization of self-assembleddimeric resorcinarenes 1a–d containing four2-benzimidazolone (cyclic urea) bridges are reported. Thenanometer-size capsules are held together by a cyclic array ofcomplementary hydrogen bonds. Unlike the related imide-bridgedresorcinarenes reported by Rebek and coworkers [Heinz, T., Rudkevich,D. M. & Rebek, J., Jr. (1998) Nature (London) 394,764–766], these strongly bound dimers aggregate in chloroformsolutions yielding different self-organized structures, depending onthe nature and length of the four carbon chains attached at the bottomof each resorcinarene platform, as revealed by transmission electronmicroscopy. Thus, phenethyl groups (dimer 1c⋅1c)produce long fibers, probably arising from tail to tail contacts andsubsequent threading of the resulting linear self-assembled polymers,whereas long alkyl chains (dimers 1a⋅1a and1b⋅1b) induce formation of large reverse vesicles of0.8–2.2 μm diameter through side to side extensive stacking.Presumably, the rigidity of the dimer precludes folding of theaggregate into smaller vesicles. On the contrary, dimer1d⋅1d, containing four nine-carbon chains and acis-double bond, does not substantially aggregate and gives rise toreasonably resolved 1H NMR spectra. The compound was shownto be dimeric either by matrix-assisted laser desorptionionization–time-of-flight and vapor pressure osmometry. Encapsulationstudies were followed by NMR. Propionic or pivalic acid was included inthe capsules, probably as head to head hydrogen-bonded dimers inmesitylene-d12, a solvent too big to be aguest by its own. Longer dimeric carboxylic acids or larger substrates,like 2-adamantyl azide or cyclohexylcarbodiimide, do not encapsulate,but mixtures of a long and a short carboxylic acid (i.e.,propionic-adamantyl or propionic-cyclohexyl) yield pairwise complexes.