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

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, ?-dicyanomethyl-substituted radicals are isolated as ?-dimers that are stable in the solid-state but display reversible ?-dimerization behavior in solution; monomeric radical species exist predominantly at high temperatures, while ?-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 ?-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.

SUBMITTER: Adinarayana B 

PROVIDER: S-EPMC6566382 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature