Aromaticity and sterics control whether a cationic olefin radical is resistant to disproportionation

Messelberger J, Grünwald A, Goodner SJ, Zeilinger F, Pinter P, Miehlich M, Heinemann FW, Hansmann MM, Munz D (2020)

Publication Type: Journal article

Publication year: 2020

Journal

Chemical Science Royal Society of Chemistry

Book Volume: 11

Pages Range: 4138-4149

Journal Issue: 16

DOI: 10.1039/d0sc00699h

Abstract

We elucidate why some electron rich-olefins such as tetrathiafulvalene (TTF) or paraquat (1,1 '-dimethyl-4,4 '-bipyridinylidene) form persistent radical cations, whereas others such as the dimer of N,N '-dimethyl benzimidazolin-2-ylidene (benzNHC) do not. Specifically, three heterodimers derived from cyclic (alkyl) (amino) carbenes (CAAC) with N,N '-dimethyl imidazolin-2-ylidene (NHC), N,N '-dimethyl imidazolidin-2-ylidene (saNHC) and N-methyl benzothiazolin-2-ylidene (btNHC) are reported. Whereas the olefin radical cations with the NHC and btNHC are isolable, the NHC compound with a saturated backbone (saNHC) disproportionates instead to the biscation and olefin. Furthermore, the electrochemical properties of the electron-rich olefins derived from the dimerization of the saNHC and btNHC were assessed. Based on the experiments, we propose a general computational method to model the electrochemical potentials and disproportionation equilibrium. This method, which achieves an accuracy of 0.07 V (0.06 V with calibration) in reference to the experimental values, allows for the first time to rationalize and predict the (in)stability of olefin radical cations towards disproportionation. The combined results reveal that the stability of heterodimeric olefin radical cations towards disproportionation is mostly due to aromaticity. In contrast, homodimeric radical cations are in principle isolable, if lacking steric bulk in the 2,2 ' positions of the heterocyclic monomers. Rigid tethers increase accordingly the stability of homodimeric radical cations, whereas the electronic effects of substituents seem much less important for the disproportionation equilibrium.

Authors with CRIS profile

Julian Messelberger Lehrstuhl für Anorganische und Allgemeine Chemie Annette Grünwald Lehrstuhl für Anorganische und Allgemeine Chemie Piermaria Pinter Lehrstuhl für Anorganische und Allgemeine Chemie Matthias Miehlich Lehrstuhl für Anorganische und Allgemeine Chemie Frank Wilhelm Heinemann Lehrstuhl für Anorganische und Allgemeine Chemie Dominik Munz Lehrstuhl für Anorganische und Allgemeine Chemie

Involved external institutions

Georg-August-Universität Göttingen DE Germany (DE)

How to cite

APA:

Messelberger, J., Grünwald, A., Goodner, S.J., Zeilinger, F., Pinter, P., Miehlich, M.,... Munz, D. (2020). Aromaticity and sterics control whether a cationic olefin radical is resistant to disproportionation. Chemical Science, 11(16), 4138-4149. https://dx.doi.org/10.1039/d0sc00699h

MLA:

Messelberger, Julian, et al. "Aromaticity and sterics control whether a cationic olefin radical is resistant to disproportionation." Chemical Science 11.16 (2020): 4138-4149.

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