Electron Delocalization in Reduced Forms of 2‑(BMes2)pyrene and 2,7-Bis(BMes2)pyrene

Reduction of 2-(BMes2)­pyrene (B1) and 2,7-bis­(BMes2)­pyrene (B2) gives rise to anions with extensive delocalization over the pyrenylene bridge and between the boron centers at the 2- and 2,7-positions, the typically unconjugated sites in the pyrene framework. One-electron reduction of B2 gives a radical anion with a centrosymmetric semiquinoidal structure, while two-electron reduction produces a quinoidal singlet dianion with biradicaloid character and a relatively large S0–T1 gap. These results have been confirmed by cyclic voltammetry, X-ray crystallography, DFT/CASSCF calculations, NMR, EPR, and UV–vis–NIR spectroscopy.