Incorporation of the cyclooctatetraene (COT) core into a large carbon framework has been used as an effective synthetic strategy for symmetry modification and π-surface extension. A variety of novel carbon-rich polycyclic aromatic hydrocarbons (PAHs) with positive and negative curvatures have been recently reported as potential multi-electron acceptors in energy storage applications. Charging non-planar PAHs with multiple electrons reveals their unusual reactivity, diverse metal binding, and remarkable self-assembly patterns, promoting a broad exploration of redox chemistry of PAHs with different topological frameworks. However, the redox properties of π-expanded COT-based PAHs have not been systematically studied. In this work, the chemical reduction of sym-dibenzo[a,e]cyclooctatetraene (DBCOT) with Group 1 metals has been investigated. DBCOT was found to readily undergo a two-fold reduction to afford the doubly-reduced DBCOT2- anion. A set of complexes with all Group 1 metals has been crystallized and fully characterized, revealing the ligand core planarization upon two-fold reduction as well as the versatile alkali-metal coordination. A broad range of solid-state structural arrangements of the resulting products stems from different metal binding patterns and secondary interactions involving coordinating agents used for crystallization. This family of alkali metal salts of DBCOT2– provides new useful reagents for ligand metathesis reactions that can be used in preparation of various transition metal or lanthanide-based organometallic complexes.

Alkali metal complexes of dibenzo[a,e]cyclooctatetraene: New ligand transfer reagents

ACS Spring Meeting 2021

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