Molecular Complexation of Arenediazonium Ions by a Calix[4]arene Possessing Two Ester Groups: Molecular Tweezers

Abstract

The spectroscopic behaviors of arenediazonium ions in the absence and the presence of a novel calix[4]arene 1,3-alternate conformer possessing two (ethoxycarbonyl) methoxy groups 4 were studied by UV-visible, ¹H NMR, and IR spectra for the first time. 1,3-alternate conformer 4 exhibits the large hyposochromic shifts of 85 nm and the binding constants (K_a) values are greater than 10⁴ M^-1, indicating the fact that 4 strongly associates with the diazo group, the interaction being comparable with that with 18-crown-6. However, 4 can not inhibit the dediazoniation of the diazo group indicating the mechanism (A), the macrocyclic effect which sterically inhibits dediazoniation proceeding from the linear Ar-N⁺ ≡ N inserted in the crown ring to the bulky π-intermediate II, is responsible for the stabilization of the diazo group.