Redox Chemistry of the Cyclononatetraenyl Ligand: A Tale of Radical Coupling, Homo – and Möbius Aromaticity, and Comproportionation

@misc{mahieu2026redox,
  title = {{Redox Chemistry of the Cyclononatetraenyl Ligand: A Tale of Radical Coupling, Homo – and Möbius Aromaticity, and Comproportionation}},
  author = {Nolwenn Mahieu and Mohamed Mounir and Hugh Sanderson and Luca Demonti and Camille Chartier and Ysée Laplanche and Mathieu Xémard and Nicolas Casaretto and Grégoire David and Thayalan Rajeshkumar and Boris Le Guennic and Laurent Maron and Olivier Cador and Thomas Simler and Grégory Danoun and Grégory Nocton},
  howpublished = {ChemRxiv},
  year = {2026},
  month = aug,
  doi = {10.26434/chemrxiv.15008058/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008058/v1},
  note = {CC BY},
}

TY  - UNPB
TI  - Redox Chemistry of the Cyclononatetraenyl Ligand: A Tale of Radical Coupling, Homo – and Möbius Aromaticity, and Comproportionation
AU  - Nolwenn Mahieu
AU  - Mohamed Mounir
AU  - Hugh Sanderson
AU  - Luca Demonti
AU  - Camille Chartier
AU  - Ysée Laplanche
AU  - Mathieu Xémard
AU  - Nicolas Casaretto
AU  - Grégoire David
AU  - Thayalan Rajeshkumar
AU  - Boris Le Guennic
AU  - Laurent Maron
AU  - Olivier Cador
AU  - Thomas Simler
AU  - Grégory Danoun
AU  - Grégory Nocton
PY  - 2026
DA  - 2026/08/31
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15008058/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008058/v1
AB  - The cyclononatetraenyl ligand represents a remarkably versatile hydrocarbon scaffold capable of accessing distinct topological and aromatic states dictated by its oxidation state.The 10 -electron monoanion exists as a dynamic between planar Hückel aromatic all-cis and puckered cis-cis-cis-trans isomers.The formally antiaromatic 8 -electron cation Cnt + straddles the boundary between Hückel and Möbius topologies.Despite this rich electronic landscape, exploiting the Cnt framework in coordination chemistry has been bottlenecked by the high lability and pronounced susceptibility of the monoanion to decomposition or rearrangement.Herein, the redox chemistry of the cyclononatetraenyl anionic ligand is reported using the soluble [Ln(Cp ttt )I2], 1-Ln (Y, Gd-Tm) as metallic platform to confer stability.Hence, the [Ln(Cp ttt )(Cnt)I], 2-Ln (Y, Gd-Tm) have been synthesized in good yields with the cis-cis-cis-trans isomer of the Cnt ligand, which can be partially isomerized to the all-cis isomer.The reduction of 2-Ln does not occur when the Cnt ligand is all-cis, while it does lead to an intermolecular radical-radical coupling through the Cnt ligands to form [{Ln(Cp ttt )}2(Cnt2)], 3-Ln (Y, Gd-Tm).The analyses of the XRD, 1 H, and 13 C NMR data as well as DFT computations, indicate the formation of an overall Cnt2 4-ligand, in which the identical pair of Cnt 2-(C9H9 2-) are 10 -electron homo-aromatic with a persistent diatropic ring current.A short Ln-Cnt(ctr) distance (1.5897(17) Å, 3-Tm, to 1.6933(9) Å, 3-Gd) results from this peculiar electronic structure.Along the series, 3-Er is the only complex that present a Single Molecule Magnet (SMM) behavior under zero field.While kinetics of the reactions were monitored an intermediate was observed and was independently synthesized from the reduction of 1-Ln in presence of the Cnt ligand in its cis-cis-cis-trans, leading to a different dimeric structure, [Ln2(Cp ttt )2I(Cnt)], 4-Ln, in which the XRD, 1 H and 13 C NMR data, and DFT computations indicate a doubly reduced Cnt 3-(C9H9 3-) 12 -electron scaffold, which has not been reported to date.Specifically, the variable temperature 1 H NMR data show a highly fluxional behavior and integrate Möbius aromaticity with significant continuous electron current.The (C9H9 2-)2 and (C9H9 3-) fragments in 3-Ln and 4-Ln, which have different degree of reduction are shown to interconvert through comproportionation with the anionic Cnt ligand (C9H9 -) to close the loop on the rich redox chemistry of the cyclononatetraenyl ligand.
ER  -