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Open AccessFeature PaperArticle

Synthesis and Characterization of Ion Pairs between Alkaline Metal Ions and Anionic Anti-Aromatic and Aromatic Hydrocarbons with π-Conjugated Central Seven- and Eight-Membered Rings

1
Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland
2
Department of Chemistry & Biochemistry, 1306 E. University Blvd., Tucson, AZ 85719, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Yves Canac
Molecules 2020, 25(20), 4742; https://doi.org/10.3390/molecules25204742
Received: 21 September 2020 / Revised: 2 October 2020 / Accepted: 4 October 2020 / Published: 15 October 2020
(This article belongs to the Special Issue Carbon Ligands: From Fundamental Aspects to Applications)
The synthesis, isolation and full characterization of ion pairs between alkaline metal ions (Li+, Na+, K+) and mono-anions and dianions obtained from 5H-dibenzo[a,d]cycloheptenyl (C15H11 = trop) is reported. According to Nuclear Magnetic Resonance (NMR) spectroscopy, single crystal X-ray analysis and Density Functional Theory (DFT) calculations, the trop and trop2−• anions show anti-aromatic properties which are dependent on the counter cation M+ and solvent molecules serving as co-ligands. For comparison, the disodium and dipotassium salt of the dianion of dibenzo[a,e]cyclooctatetraene (C16H12 = dbcot) were prepared, which show classical aromatic character. A d8-Rh(I) complex of trop was prepared and the structure shows a distortion of the C15H11 ligand into a conjugated 10π -benzo pentadienide unit—to which the Rh(I) center is coordinated—and an aromatic 6π electron benzo group which is non-coordinated. Electron transfer reactions between neutral and anionic trop and dbcot species show that the anti-aromatic compounds obtained from trop are significantly stronger reductants. View Full-Text
Keywords: aromaticity; ion pairs; alkali metals; tropylidenyl ions; cyclooctatetraene ions; rhodium; electron paramagnetic resonance (EPR) spectroscopy; density functional theory (DFT); electrochemistry aromaticity; ion pairs; alkali metals; tropylidenyl ions; cyclooctatetraene ions; rhodium; electron paramagnetic resonance (EPR) spectroscopy; density functional theory (DFT); electrochemistry
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MDPI and ACS Style

Bloch, J.; Kradolfer, S.; L. Gianetti, T.; Ostendorf, D.; Dey, S.; Mougel, V.; Grützmacher, H. Synthesis and Characterization of Ion Pairs between Alkaline Metal Ions and Anionic Anti-Aromatic and Aromatic Hydrocarbons with π-Conjugated Central Seven- and Eight-Membered Rings. Molecules 2020, 25, 4742.

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