Aromatic and Antiaromatic Cyclophane-type Hexaphyrin Dimers

A peripherally strapped [28]hexaphyrin takes a rectangular conformation and exhibits antiaromatic character. A cyclophane-type dimer consisting of such [28]hexaphyrins was synthesized from hexakis(pentafluorophenyl) [26]hexaphyrin via SNAr reaction with allyl alcohol, one-pot intra- and intermolecular olefin metathesis under improved Hoveyda-Grubbs catalysis, and final reduction with NaBH4. The cyclophane-type structures of [26]- and [28]hexaphyrin dimers have been revealed by X-ray analysis. Studies on the structural, optical, and electronic properties have led to a conclusion that there is no favorable electronic interaction between the two [28]hexaphyrin segments and thus no indication of 3D aromaticity.