Reshaping rubrene by controlled reduction with alkali metals

Mono-, di- and tetraanions of rubrene, (C₄₂H₂₈, Rub⁰), were generated by the controlled reduction of neutral polyarene with various alkali metals in the appropriate solvent. The X-ray diffraction studies of the resulting adducts of Rub^1-, Rub ^2- and Rub^4- with alkali-metal ions revealed the distortion of the rubrene core upon the stepwise acquisition of electrons. Coordination of the Cs⁺ ion and a noticeable deformation of Rub ^1- are observed at the first reduction step. Two types of rubrene dianions showing an essentially different conformation and coordination environment for the central tetracene core have been seen in the cesium adduct of Rub^2-. Various types of supramolecular assembly between the tetrareduced rubrene anion, Rub^4-, and lithium or rubidium cations have been found in the corresponding products in the solid state. The structures of rubrene anions and their aggregation with alkali-metal ions in solution have been studied by ESR and multinuclear NMR (¹H, ¹³C, ⁷Li and ¹³³Cs) spectroscopy.