Reduction of π‐Expanded Cyclooctatetraene with Lithium: Stabilization of the Tetra‐Anion through Internal Li+ Coordination. (14th December 2020)

• Record Type: Journal Article
• Authors: Zhou, Zheng; Zhu, Yikun; Wei, Zheng; Bergner, John; Neiß, Christian; Doloczki, Susanne; Görling, Andreas; Kivala, Milan; Petrukhina, Marina A.
• Is Part Of: Angewandte Chemie. Volume 133:Number 7(2021)
• Page Start: 3552
• Page End: 3556
• Publication Date: 2020-12-14
• Subjects: polycycles -- density-functional calculations -- reduction -- structure elucidation -- X-ray diffraction; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202013353
• Languages: English
• ISSNs: 0044-8249

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. Abstract : A highly contorted π‐expanded polycyclic tetra‐anion comprising a cyclooctatetraene moiety is readily formed upon reduction of the neutral precursor with lithium metal. The highly charged carbanion crystallizes with four lithium counterions, two of which stabilize the contorted structure through internal coordination. Density‐functional theory calculations rationalize the unexpected formation of the tetra‐anion and provide insights into its electronic properties.