Synthesis and Crystal Structure of Li+@Fluoreno[60]fullerene: Effect of Encapsulated Lithium Ion on Electrochemistry of Spiroannelated Fullerene.

The reaction of [Li+@C60]TFSI- (TFSI = bis(trifluoromethanesulfonyl)imide) with 9-diazofluorene directly produced a [6,6]-adduct of lithium-ion-containing fluoreno[60]fullerene, [6,6]-[Li+@C60(fluoreno)]TFSI-, which was crystallographically characterized. Cyclic voltammetry of the compound showed a reversible one-electron reduction wave at -0.51 V (vs Fc/Fc+) and an irreversible reduction wave for the second electron. The latter was attributed to opening of the three-membered ring due to strong stabilization of the resulting sp3-carbanion by the encapsulated Li+ and formation of a 14π-electron aromatic fluorenyl anion.