Reduction of π‐Expanded Cyclooctatetraene with Lithium: Stabilization of the Tetra‐Anion through Internal Li<sup>+</sup> Coordination
Zheng Zhou, Yikun Zhu, Zheng Wei, John Bergner, Christian Neiß, Susanne Doloczki, Andreas Görling, Milan Kivala, Marina A. Petrukhina
Abstract
Abstract The chemical reduction of a π‐expanded polycyclic framework comprising a cyclooctatetraene moiety, octaphenyltetrabenzocyclooctatetraene, with lithium metal readily affords the corresponding tetra‐anion instead of the expected aromatic dianion. As revealed by X‐ray crystallography, the highly contorted tetra‐anion is stabilized by coordination of two internally bound Li + , while two external cations remain solvent separated. The variable‐temperature 7 Li NMR spectra in THF confirm the presence of three types of Li + ions and clearly differentiate internal binding, consistent with the crystal structure. Density‐functional theory calculations suggest that the formation of the highly charged tetra‐reduced carbanion is stabilized through Li + coordination under the applied experimental conditions.