Conformation and Aromaticity Switching in a Curved Non-Alternant sp2 Carbon Scaffold.

Abstract

A curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd‐catalyzed [5+2] annulation from a 3,9‐diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly‐like motion. Stepwise oxidation produced radical cation 1 .+ and dication 1 2+. In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π‐overlap between the enantiomers. For the radical cation 1 .+, a less curved cisoid conformation is observed with a π‐dimer‐type arrangement. 1 2+ adopts a more planar structure with transoid conformation and slip‐stacked π‐overlap with closest neighbors. We also observed an intermolecular mixed‐valence complex of 1⋅(1 .+)3 that has a huge trigonal unit cell [(1)72(SbF6)54⋅(hexane)101] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.