PAHs Containing both Heptagon and Pentagon: Corannulene Extension by [5+2] Annulation

Utilizing Pd-catalyzed [5+2] annulation a series of heptagon-extended corannulenes could be synthesized from a borinic acid precursor furnished by C-H borylation strategy. Single-crystal X-ray analysis revealed the presence of two conformational enantiomers crystallizing in a racemic mixture. Through their embedded five- and seven-membered rings these polycyclic aromatic hydrocarbons (PAHs) exhibit both negative and positive curvature and UV/Vis/NIR absorption spectroscopy as well as cyclic voltammetry experiments provided insights into the influence of larger flanking aromatic systems and electron-donating substituents encompassing the heptagonal ring. Through [5+2] annulation of acenaphthylene an azulene-containing PAH with intriguing optoelectronical properties including a very small bandgap and absorption over the whole visible spectrum could be obtained. Theoretical calculations were employed to elucidate the long-wavelength absorption and aromaticity.

Automated summary

In this study, a series of heptagon-extended corannulenes were synthesized using Pd-catalyzed [5+2] annulation from a borinic acid precursor obtained by C-H borylation strategy. Single-crystal X-ray analysis revealed the presence of two conformational enantiomers crystallizing in a racemic mixture. Theoretical calculations were employed to elucidate their optoelectronic properties and aromaticity.