Radical Ions in the Pentalene Series. Part III. Three Paramagnetic Redox Stages of a Dicyclopenta[a,e]pentalene

Five redox stages have been observed for the recently synthesized 1,3,5,7-tetra(tert-butyl) derivative 1 of the dicyclopenta[a,e]pentalene, a novel non-alternant hydrocarbon: the radical cation 1 , the neutral compound 1, the radical anion Is, the dianion 1²-, and the radical trianion 1³. Information about the electronic structure of the three paramagnetic stages, 1, 1⁻, and 1³⁻ is provided by the use of ESR, ENDOR, and TRIPLE resonance spectroscopy. The unpaired electron in the trianion resides mainly on the ‘inner’ butadiene-π-system, whereas in the cation and the anion, it is largely localized on the two ‘outer’ five-membered rings.