Tetraaza[14]- and Octaaza[18]paracyclophane: Synthesis and Characterization of Their Neutral and Cationic States.

Abstract

Two kinds of aza[1n]paracyclophanes, tetraaza[14]paracyclophane (P4) and octaaza[18]paracyclophane (P8), were synthesized as the smallest and the largest monodisperse macrocyclic oligomers of polyaniline ever made. Herein we report the electronic nature of the cationic species of these two macrocycles with different ring size. By combining ESR spectroscopy and DFT calculations it was suggested that P4·+ was classified as delocalized class III or poised on the class II/III borderline while P8·+ was regarded as a localized class II mixed-valence system. We successfully isolated the dication of P4 as a stable dicationic salt P42+·2[SbF6]-, and the structure of P42+ was determined by X-ray crystal analysis. Variable-temperature NMR measurements for P42+·2[SbF6]- unequivocally showed that P42+ was a 22π electron system with a singlet ground state. The supercharged hexacation of P8 was also isolated as P86+·6[SbCl6]-, and X-ray crystal analysis revealed that P86+ includes one SbCl6- anion in its macrocyclic cavity.