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

Abstract

A curved sp 2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pdcatalyzed [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 1C + and dication 1 2+. In the crystal structure, 1 exhibits a chiral cisoid conformation and partial p-overlap between the enantiomers. For the radical cation 1C + , a less curved cisoid conformation is observed with a p-dimer-type arrangement. 1 2+ adopts a more planar structure with transoid conformation and slip-stacked p-overlap with closest neighbors. We also observed an intermolecular mixed-valence complex of 1•(1C +) 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.

Stereoselective Chiral Molecular Carbon Imides Featuring 12‐Fold [5]helicenes Around Four Cores**

“…In early times, long branched alkyl chains, large bulky groups, and strong electron‐withdrawing atoms or groups are selected to introduce to the margins of graphene nanoribbon and nanographene which have excellent planar structures to improve their solubility and stability [4d–f] . Recently, nonhexagons such as five‐, seven‐, and eight‐membered rings are embedded into the backbone of nanographene, which convert the planar carbons into curved ones [5b–g] . Meanwhile, introducing helicene units into the planar backbone of nanographene is another effective strategy to not only improve their solubility and stability in air but also enrich the geometry of molecular carbons.…”

Stereoselective Chiral Molecular Carbon Imides Featuring 12‐Fold [5]helicenes Around Four Cores**

“…In early times, long branched alkyl chains, large bulky groups, and strong electron‐withdrawing atoms or groups are selected to introduce to the margins of graphene nanoribbon and nanographene which have excellent planar structures to improve their solubility and stability [4d–f] . Recently, nonhexagons such as five‐, seven‐, and eight‐membered rings are embedded into the backbone of nanographene, which convert the planar carbons into curved ones [5b–g] . Meanwhile, introducing helicene units into the planar backbone of nanographene is another effective strategy to not only improve their solubility and stability in air but also enrich the geometry of molecular carbons.…”

Rupturing Aromaticity by Periphery Overcrowding

“…Since Doering and Knox's seminal work 11 on its isolation and structural elucidation, its electronic properties have been exploited in organocatalysis, 12 stimuliresponsive dyes, 13 and redox-active polycyclic aromatic hydrocarbons (PAHs). [14][15][16] Relative to benzene, its larger ring size, increased conformational flexibility, and the smaller angles subtended by its substituents (51.4° c.f. 60° for benzene) allow tropylium to undergo more facile strain-induced deformations.…”