Synthesis of benzo[6]urils and their selective interactions with bipyridines

Abstract

Members of a new class of macrocyclic compounds, benzo[6]urils bearing hydroxymethyl or methyl groups, have been synthesized under mild conditions in high yields. These macrocycles have been employed as hosts to encapsulate bipyridine guests. Fluorescence spectrometric titrations confirmed the formation of interaction complexes in a 1 : 1 ratio and curve-fitting of the decreases in fluorescence intensity of the benzo[6]urils in the presence of the guests provided moderate association constants of about 1.5 × 10³–1.3 × 10⁶ L mol⁻¹. The stabilities of the supramolecular complexes proved to be dependent on both the structures of the guests and the substituents present on the host. The host–guest interactions have also been probed by means of ¹H NMR spectrometry, whereby small shifts in the resonances of the benzo[6]uril upon the addition of the guest were observed. The results of DFT calculations suggested that the encapsulation capabilities of benzo[6]urils should rest with the electronic structures of the guests.