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

Chemical Science
B AdinarayanaAtsuhiro Osuka

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.

References

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Citations

Aug 17, 2019·Chemistry, an Asian Journal·Takayuki YamamotoAtsuhiro Osuka
Jan 22, 2021·Chemistry : a European Journal·Irene Badía-DomínguezM Carmen Ruiz Delgado
Jul 24, 2020·The Journal of Organic Chemistry·Gary W Breton, Kenneth L Martin
Jan 31, 2020·Journal of the American Chemical Society·Liliia MoshniahaMarcin Stępień

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Methods Mentioned

BETA
X-ray
column chromatography
NMR
silica
gel column chromatography

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