Reduction of π-Expanded Cyclooctatetraene with Lithium: Stabilization of the Tetra-Anion through Internal Li+ Coordination

The chemical reduction of a pi-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 Li-7 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.

Automated summary

The study found that the chemical reduction of octaphenyltetrabenzocyclooctatetraene framework can readily produce the corresponding tetra-anion instead of the expected aromatic dianion. X-ray crystallography shows that the highly contorted tetra-anion is stabilized by the coordination of two internally bound Li+ ions, while two external cations are solvent separated. 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.