Stable thiophene-embedded N-confused homoporphyrins: Partial conjugation, fusion and fluoride binding

Abstract

In the past decades, porphyrin analogues have attracted increasing attention in light of their unique properties and potential applications in various areas. In this work, novel nonconjugated thiophene-embedded N-confused homoporphyrins 1 and 2 as well as a fully-conjugated N-fused homoporphyrin 3 have been prepared through acid-catalyzed condensation reactions followed by oxidation. Both 1 and 2 comprise two meso-sp3-carbon atoms. However, they are insensitive to the air or common oxidants. Single crystal X-ray diffraction analysis reveals that 2 adopts a highly distorted boat-like conformation, with the NH moieties of two pyrrolic units pointing outwards and an O atom attached to the α position of the N-confused pyrrole unit. As a result, hydrogen-bonded dimers are formed through the intermolecular hydrogen bonds between the lactam-like moieties. In contrast to the highly distorted structure of 2, N-fused homoporphyrin 3 contains a unique 5,5,5–tricyclic fused ring, and thus demonstrates a relatively coplanar conformation except one inverted pyrrole unit. Because of the different structural characters, 3 exhibits F− binding behavior distinct from that of 1 and 2.