Conformation and Aromaticity Switching in a Curved Non‐Alternant sp<sup>2</sup> Carbon Scaffold
Chongwei Zhu, Kazutaka Shoyama, Frank Würthner
Abstract
Abstract A curved sp 2 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 (SbF 6 ) 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.