Spin-Localized Cyclopentadienyl Radical Annelated with Homoadamantene Frameworks:  Isolation, X-ray Crystal Structure, and ESR Characterization

A cyclopentadienyl radical annelated with two homoadamantene frameworks 1 was synthesized and isolated in stable, crystalline form by the single-electron oxidation of the corresponding cyclopentadienyl anion. The X-ray structure clearly demonstrated distinct bond alternation in the cyclopentadienyl ring, suggesting that radical 1 has the characteristics of a spin-localized 2,4-cyclopentadien-1-yl radical. The two homoadamantene frameworks are nonequivalent in crystals at 100 K, while ESR spectra indicated that they are equivalent in toluene at room temperature due to rapid changes in conformation.