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Stabilizing Contorted Doubly-Reduced Tetraphenylene with Heavy Alkali Metal Complexation: Crystallographic and
Yikun Zhu1, Zheng Zhou1,2, Zheng Wei1
1Department of Chemistry, University at Albany, State University of New York, Albany, NY, 12222, USA.
Chemistry, an Asian Journal
|January 16, 2025
Summary
The reduction of tetrabenzo[a,c,e,g]cyclooctatetraene (TBCOT) with alkali metals creates a novel butterfly-shaped core structure. This transformation is reversible and offers unique coordination sites for metal ions.
Area of Science:
- Organic Chemistry
- Inorganic Chemistry
- Materials Science
Background:
- Tetrabenzo[a,c,e,g]cyclooctatetraene (TBCOT) is a polycyclic aromatic hydrocarbon with a unique structure.
- Alkali metal reduction is a common method for modifying organic molecules.
- Understanding the structural and electronic changes upon reduction is crucial for designing new materials.
Purpose of the Study:
- To investigate the core transformation pathway of TBCOT upon two-fold reduction with potassium, rubidium, and cesium.
- To characterize the resulting dianions and their coordination complexes with alkali metals.
- To explore the reversibility of the reduction and bond rearrangement process.
Main Methods:
- Two-fold reduction of TBCOT using K, Rb, and Cs metals in THF.
- Isolation and characterization of the resulting dianions and their metal complexes using X-ray crystallography.
- NMR spectroscopy to demonstrate the reversibility of the reduction and rearrangement.
- Computational analysis to understand charge transfer and aromaticity.
Main Results:
- A new C-C bond is formed, converting the central eight-membered ring into a twisted core with two fused five-membered rings.
- The resulting 1TR 2- dianions exhibit a butterfly shape with perpendicular π-surfaces.
- Polymeric and discrete metal complexes were formed, with varying coordination modes (internal and external) depending on the alkali metal and presence of ligands like 18-crown-6.
- The reduction and rearrangement process was found to be reversible.
Conclusions:
- The two-fold reduction of TBCOT induces a significant core transformation, leading to a unique butterfly-shaped ligand.
- The resulting dianions can form diverse coordination complexes with alkali metals, influenced by metal size and auxiliary ligands.
- The observed structural changes and charge transfer are reversible, highlighting the dynamic nature of the TBCOT system.
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