Conformation and Aromaticity Switching in a Curved Non-Alternant sp2Carbon Scaffold

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 cation1(.+)and dication1(2+). In the crystal structure,1exhibits a chiralcisoidconformation and partial pi-overlap between the enantiomers. For the radical cation1(.+), a less curvedcisoidconformation is observed with a pi-dimer-type arrangement.1(2+)adopts a more planar structure withtransoidconformation and slip-stacked pi-overlap with closest neighbors. We also observed an intermolecular mixed-valence complex of1.(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 of1changes from localized to delocalized, as demonstrated by AICD and NICS(1)(zz)calculations.