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Stable radical versus reversible σ-bond formation of (porphyrinyl)dicyanomethyl radicals

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Abstract

(Porphyrinyl)dicyanomethyl radicals were produced by oxidation of dicyanomethyl-substituted porphyrins with PbO2. These radicals constitute a rare example displaying stable radical versus dynamic covalent chemistry (DCC) depending upon the substitution position of the dicyanomethyl radical. meso-Dicyanomethyl-substituted radicals exist as stable monomeric species and do not undergo any dimerization processes either in the solid state or in solution. In contrast, β-dicyanomethyl-substituted radicals are isolated as σ-dimers that are stable in the solid-state but display reversible σ-dimerization behavior in solution; monomeric radical species exist predominantly at high temperatures, while σ-dimerization is favoured at low temperatures. This dynamic behaviour has been confirmed by variable-temperature 1H NMR, UV-vis and EPR measurements. The structures of the stable radical and σ-dimer have been revealed by single-crystal X-ray diffraction analysis. The observed different reactivities of the two (porphyrinyl)dicyanomethyl radicals have been rationalized in terms of their spin delocalization behaviours.

Graphical abstract: Stable radical versus reversible σ-bond formation of (porphyrinyl)dicyanomethyl radicals

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Publication details

The article was received on 03 Apr 2019, accepted on 13 May 2019 and first published on 13 May 2019


Article type: Edge Article
DOI: 10.1039/C9SC01631G
Chem. Sci., 2019, Advance Article
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    Stable radical versus reversible σ-bond formation of (porphyrinyl)dicyanomethyl radicals

    B. Adinarayana, D. Shimizu, K. Furukawa and A. Osuka, Chem. Sci., 2019, Advance Article , DOI: 10.1039/C9SC01631G

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