Phenylboron(III) complexes of tripyrrins: A new class of macrocycles closed by hydrogen-bonding

Dianilinotripyrrin was condensed with phenylboronic acid at high temperature to give its phenylboron(III) complex in which the conjugation system changed to serve as a divalent ligand. As a result, two aniline moieties form an intramolecular hydrogen bond between the NH and iminic N sites, fixing the conformation to stand as a closed macrocycle. The structure of this macrocycle contains both cone-shaped boron center and helical terminal moieties. The twisted helical moieties can be perturbed by the substituents at the aniline moiety, while the optical properties are not drastically altered thereby. p-Phenylene-bridged face-to-face dimer was also synthesized by the same approach, which exhibited negligible electronic communication between the chromophores.