Dicyclopenta[4,3,2,1- ghi:4',3',2',1'- pqr]perylene: A Bowl-Shaped Fragment of Fullerene C70 with Global Antiaromaticity.

Solution-phase synthesis of buckybowls remains a big challenge, and there are limited reports on the fragments of C70. Herein, we report a new basic subunit of C70 with C2v symmetry, the dicyclopenta[4,3,2,1- ghi:4',3',2',1'- pqr]perylene (2CP-Per). Its aryl-substituted derivative 2CP-Per-Ar was synthesized and shows a bowl-shaped geometry according to X-ray crystallographic analysis. A fast bowl-to-bowl inversion process was observed above 183 K by variable temperature nuclear magnetic resonance (NMR), with a small inversion energy barrier. 2CP-Per-Ar displays amphoteric redox behavior with a small electrochemical energy gap (1.29 eV). Different from many other aromatic buckybowls, 2CP-Per exhibits global antiaromaticity with a strong paratropic ring current associated with the 16π-electrons rim, as revealed by NMR measurements and theoretic calculations. Its dianion is aromatic, similar to its isoelectronic structure coronene. Its dication is predicted to be aromatic, with a [6]annulene-within-[14]annulene structure.