5,10-Dimesityldiindeno[1,2-a:2',1'-i]phenanthrene: A Stable Biradicaloid Derived from Chichibabin’s Hydrocarbon

Majewski, M. A.; Chmielewski, P. J.; Chien, A.; Hong, Y.; Lis, T.; Witwicki, M.; Kim, D.; Zimmerman, P.; Stępień, M.
Chem. Sci. 2019,10, 3413-3420 | view at publisher's site

A diindenophenanthrene biradicaloid, formally derived from Chichibabin’s hydrocarbon, is obtained in a short, scalable synthesis. The present system is electron-rich and devoid of conjugated substituents, and still exhibits very good stability under ambient conditions. The introduction of the diindeno[1,2-a:2',1'-i] phenanthrene ring framework results in a singlet biradicaloid system with an easily accessible triplet state (ΔES−T = −1.30 kcal/mol) and a small electronic bandgap (1.39 V). The stability limits of the title hydrocarbon were explored systematically in the solid state, to reveal an unusual thermally initiated hydrogen-scrambling oligomerization process.