Unprecedented Chemical Reactivities and Potential Utilities of Paramagnetic Endohedral Metallofullerenes

The inside metals of endohedral metallofullerenes (EMFs) lead remarkable features, such as unique molecular structures, and magnetic and electronic properties.^[1] Among EMFs, paramagnetic EMFs are of particular interest because interplay between π-electron spins on the fullerene cage and inside metal atoms is expected to produce unconventional magnetic features.

   Unique properties of paramagnetic EMFs may lead to unique chemical reactivities. In this regard, despite the former efforts, much work is still needed for a better control on the chemical reactivity of the increasing variety of EMFs. For an easier accessibility to EMFs based materials, a wider availability of chemical functionalization methods on EMFs is required.

   Meanwhile, La@C₈₂ has extensively been investigated as a prototype paramagnetic fullerene because it is the first EMF which was reported the successful isolation for the first time.^[2] Moreover, it was demonstrated that a family of lanthanum containing fullerenes were produced and that extraction with toluene yielded abundantly La@C₈₂. La@C₈₂ has an electronic structure which is best described as [La]³⁺[C₈₂]^3- with an open-shell electronic character that is a consequence of transferring three electrons from lanthanum to C₈₂(Scheme). The resulting electron spin imposes unique chemical reactivity, radical character, and magnetic properties.

   In this talk, I will present remarkable chemical reactivities and molecular properties of paramagnetic EMFs; La@C_2v-C₈₂,^[3] La@C_s-C₈₂^[4] and Ce@C_2v-C₈₂.^[5] Their unique characteristics cannot be expected in ordinary chemical compounds and empty fullerenes, and are promising for creating novel electronic and magnetic materials with utilizing their unprecedented electronic properties.

References:

[1] (For reviews of EMFs) (a) Chemistry of Nanocarbons; Akasaka, T., Wudl, F., Nagase, S., Eds.; Wiley: Chichester, 2010. (b) Popov, A. A. et al. Chem. Rev. 2013, 113, 5989.

[2] Chai, Y. et al. J. Phys. Chem. 1991, 95, 75648.

[3] (a) Takano, Y. et al. J. Am. Chem. Soc. 2008, 130, 16224. (b) Takano, Y. et al. Chem. Commun. 2010, 46, 8035.

[4] Takano, Y. et al. J. Am. Chem. Soc. in press. DOI: 10.1021/ja509407j

[5] Takano, Y.et al. J. Am. Chem. Soc. 2009, 131, 9340.