Heliphyrin: a ring open porphyrinoid with helical chirality

Abstract

Heliphyrin, a new porphyrinoid with a helicene-type structure, can be produced in two steps from commercially available reagents. Three macrocycle–like structures were produced via a template reaction involving a benzimidazolylylidene modified iminoisoindoline and divalent metal (Co, Ni, and Cu) salts. The heliphyrins are tetradentate, dianionic ligands that coordinate the central metal in a square planar configuration, while forming a helical structure around the metal due to the steric bulk of the benzimidazole units. These compounds are panchromatic chromophores, and we interrogated their electronic structures using DFT and TDDFT methods. We could also separate racemic heliphyrins into enantiomers using chiral chromatography, and axial ligation by tartaric acid induces formation of chiral species as detected by circular dichroism spectroscopy. Due to their chiral nature, these complexes may have uses in biological and sensor applications.