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

Lei Ji ^†, Robert M. Edkins ^†, Andreas Lorbach ^†, Ivo Krummenacher ^†, Charlotte Brückner ^‡, Antonius Eichhorn ^†, Holger Braunschweig ^†, Bernd Engels ^‡, Paul J. Low ^§, and Todd B. Marder ^*†

^† Institut für Anorganische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

^‡ Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Emil-Fischer-Straße 42, 97074 Würzburg, Germany

^§ School of Chemistry and Biochemistry, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/jacs.5b03805

Publication Date (Web): May 7, 2015

Copyright © 2015 American Chemical Society

Abstract

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.