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

Enhanced reactivity of Li+@C60 toward thermal [2 + 2] cycloaddition by encapsulated Li+ Lewis acid

Lithium ion-endohedral fullerene (Li+@C60), a member of the burgeoning family of ion-endohedral fullerenes, holds substantial promise for diverse applications owing to its distinctive ionic properties. Despite the high demand for precise property tuning through chemical modification, there have been only a few reports detailing synthetic protocols for the derivatization of this novel material. In this study, we report the synthesis of Li+@C60 derivatives via the thermal [2 + 2] cycloaddition reaction of styrene derivatives, achieving significantly higher yields of monofunctionalized Li+@C60 compared to previously reported reactions. Furthermore, by combining experimental and theoretical approaches, we clarified the range of applicable substrates for the thermal [2 + 2] cycloaddition of Li+@C60, highlighting the expanded scope of this straightforward and selective functionalization method.

Synthesis and Characterization of Ionic Li+ @C70 Endohedral Fullerene

Ion-endohedral-fullerene has attracted growing interest due to the unique electronic and structural characteristics arising from its distinctive ionic nature. Although there has been only one reported ion-encapsulated fullerene, Li+ @C60 , a significant number of fundamental and applied studies have been conducted, making a substantial impact not only in chemistry and physics but also across various interdisciplinary research fields. Nevertheless, studies on ion-endohedral fullerenes are still in their infancy due to the limitations in variety, and hence, it remains an open question how the size and symmetry of fullerene, as well as the motion and position of the encapsulated ion, affect their physical/chemical properties. Herein, we report the synthesis of lithium-ion-endohedral [70]fullerene (Li+ @C70 X- , X=PF6 - and TFSI- ), a novel ionic endohedral fullerene. X-ray crystallography confirmed the encapsulation of Li+ by C70 cage as well as its ion-pair structure stabilized by external TFSI- counter anion. The encapsulated Li+ drastically lowered the orbital energy of the C70 cage by Coulomb interactions but did not affect the orbital energy gap and degeneracy. DFT studies were also performed, which supported the experimentally observed electronic effects caused by the encapsulated Li+ .

Solvation-Free Li+ Lewis Acid Enhancing Reaction: Kinetic Study of [5,6]-Li+@PCBM to [6,6]-Li+@PCBM

Kinetic parameters for the [5,6]- to [6,6]-[Li⁺@PCBM]TFSI^- transformation were determined experimentally, revealing a ca. 700-fold faster reaction rate at 423 K than empty PCBM and a 57.4 kJ mol^-1 lower activation energy. The encapsulated Li⁺ can be considered as solvation-free Li⁺, forming a 1:1 complex with the substrate.