Cyclooctatetraene (COT), an 8-membered representative of the family of [n]annulenes, possesses a tub-shaped conformation with 8 π-electrons. According to Hückel's rule, the COT core upon two-fold reduction is expected to be aromatic and planar, which has been confirmed for the COT dianion and its derivatives by X-ray diffraction analysis. Incorporation of the COT core into an expanded carbon framework can be a viable synthetic strategy that enables discoveries of novel carbon-rich polycyclic aromatic hydrocarbons (PAHs) with positive and negative curvatures. Charging such non-planar nanocarbons with multiple electrons reveals unusual structural perturbations, diverse metal binding preferences, and unique molecular self-assembly, which stimulates broad exploration of the redox chemistry of PAHs with different topological frameworks. However, the related efforts on π-expanded COT-based PAHs remain comparably scarce, let alone the studies of their multi-electron accepting abilities. Therefore, in this work, several COT-based scaffolds have been selected, and their stepwise chemical reduction with alkali metals has been investigated. The resulting products have been isolated as bulk crystalline materials and fully characterized using X-ray crystallographic and spectroscopic tools, revealing significant geometry changes and core transformation upon chemical reduction. The modulation of alkali metal binding as well as solid state packing patterns will be also discussed and compared.

π-Expanded cyclooctatetraenes in stepwise reduction reactions: Structural rearrangement and alkali metal coordination

ACS Fall 2021

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