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Series of Fluorinated Benzimidazole-Substituted Nitronyl Nitroxides: Synthesis, Structure, Acidity, Redox Properties, and Magnetostructural Correlations.
- Source :
-
The Journal of organic chemistry [J Org Chem] 2023 Aug 04; Vol. 88 (15), pp. 10355-10370. Date of Electronic Publication: 2022 Oct 05. - Publication Year :
- 2023
-
Abstract
- A special series of nitronyl nitroxides was synthesized: 2-(benzimidazol-2'-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyls mono-, di-, tri-, or tetrafluorinated on the benzene ring. The structure of all paramagnets was unambiguously confirmed by single-crystal X-ray diffraction. It was found that in crystals, the radicals are assembled into chains due to intermolecular H-bonds between the benzimidazole moiety (H-bond donor) and the nitronyl nitroxide group or benzimidazole ring (H-bond acceptor). The magnetic properties of nitronyl nitroxides depend on the type of binding of radicals by H-bonds. The magnetic motif of 4-fluoro-, 5-fluoro-, 4,6-difluoro-, 4,5,6-trifluoro-, 4,5,7-trifluoro-, and 4,5,6,7-tetrafluoro-derivatives, as well as the nonfluorinated compound, consists of ferromagnetic chains ( J / k <subscript>B</subscript> ≈ 20-40 K) formed by the McConnell type I mechanism. In the 5,6-difluoro- and 4,5-difluoro-derivatives, the distances between the paramagnetic centers are large, as a result of which the exchange interactions are weak. According to cyclic voltammetry, paramagnets are oxidized reversibly, while their reduction is a quasi-reversible electron transfer (EC mechanism); experimental redox potentials of radicals correlate well with the calculated values. Quantum chemical assessment of the acidity of benzimidazolyl-substituted nitronyl nitroxides revealed that the introduction of fluorine atoms into the benzene ring enhances the acidity of the paramagnets by more than 5 orders of magnitude.
Details
- Language :
- English
- ISSN :
- 1520-6904
- Volume :
- 88
- Issue :
- 15
- Database :
- MEDLINE
- Journal :
- The Journal of organic chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 36198196
- Full Text :
- https://doi.org/10.1021/acs.joc.2c01793