Spin-Delocalization in a Helical Open-Shell Hydrocarbon

Ravat, Prince and Ribar, Peter and Rickhaus, Michel and Häussinger, Daniel and Neuburger, Markus and Juríček, Michal. (2016) Spin-Delocalization in a Helical Open-Shell Hydrocarbon. Journal of Organic Chemistry, 81 (24). pp. 12303-12317.

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Official URL: http://edoc.unibas.ch/52027/

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Neutral open-shell molecules, in which spin density is delocalized through a helical conjugated backbone, hold promise as models for investigating phenomena arising from the interplay of magnetism and chirality. Apart from a handful of examples, however, the chemistry of these compounds remains largely unexplored. Here, we examine the prospect of extending spin-delocalization over a helical backbone in a model compound naphtho[3,2,1- no ]tetraphene, the first helically chiral open-shell hydrocarbon, in which one benzene ring is fused to [5]helicene, forming a phenalenyl subunit. The unpaired electron in this molecule is delocalized over the entire helical core composed of six rings, albeit in a nonuniform fashion, unlike in phenalenyl. In the case of a monosubstituted derivative, the uneven spin-distribution results in a selective σ-dimer formation in solution, as confirmed by 2D NMR spectroscopy. In contrast, the dimerization process is suppressed entirely when four substituents are installed to sterically hinder all reactive positions. The persistent nature of the tetrasubstituted derivative allowed its characterization by EPR, UV–vis, and CD spectroscopies, validating spin-delocalization through a chiral backbone, in accord with DFT calculations. The nonuniform spin-distribution, which dictates the selectivity of the σ-dimer formation, is rationalized by evaluating the aromaticity of the resonance structures that contribute to spin-delocalization.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Molecular Devices and Materials (Mayor)
05 Faculty of Science > Departement Chemie > Chemie > Nuclear Magnetic Resonance (Häussinger)
UniBasel Contributors:Juricek, Michal and Ravat, Princekumar and Ribar, Peter and Rickhaus, Michel and Neuburger, Markus and Häussinger, Daniel
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:11 Jan 2017 15:48
Deposited On:11 Jan 2017 15:48

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