Endohedral Fullerenes

Among carbon nanostructures, endohedral metallofullerenes, which are carbon cages that encapsulate metal atoms or cluster in their inner space, have attracted increasing attention, largely due to their potential relevance in the fields of biomedicine and nanomaterials sciences. Because of the scarce availability of this class of fullerenes in the past, their chemical, electrochemical, and photophysical properties are almost unknown. In collaboration with the groups of Prof. Akasaka (University of Tsukuba, Japan), Prof. Richard J. Whitby (University of Southampton, UK) and Prof. Echegoyen (University of Texas at El Paso, USA), able to produce metallofullerene species, we have recently initiated a program to explore and control the reactivity of endohedral fullerenes.
Endohedral metallofullerenes possess larger absorptive coefficients than C₆₀ in the visible region of the electromagnetic spectrum and a low HOMO-LUMO energy gap, while preserving a remarkable electron accepting ability, similar to that of C₆₀. Considering these electronic features, Sc₃N@C₈₀, Y₃N@C₈₀, La₂@C₈₀ and Ce₂@C₈₀ have shown to be applicable as part of electron-donor/acceptor systems in combination with powerful donors such as ferrocene,¹ metalloporphyrins² or p-extended tetrathiafulvalene derivatives (exTTFs).³ Interestingly, Lu₃N@C₈₀-perylenebisimides(PDI)⁴ and La₂@C₈₀-TCAQ⁵ demonstrated an unprecedented electron-transfer behaviour, in which the endohedral metallofullerene consistently acts as an electron donor (see Figure below).

 

 

Chemical modification of endohedral fullerenes with electron-donor (exTTF) and electron-acceptor (TCAQ) molecules.

Other interesting aspects being investigated in our group are the chemical derivatization of open-shell species⁶ or the chiral selective synthesis of endohedral metallofullerenes. In 2011, chiral 1,3-dipolar cycloaddition of N-metalated azomethine ylides was extended to the enantio- and regioselective synthesis of endofullerene derivatives. This process catalyzed by a copper chiral complex on a racemic mixture of non-IPR La@C₇₂C₆H₃Cl₂) produced only eight enantiopure bisadducts with high enantiomeric excesses (90− 98%).⁷ The scope of the enantioselective cycloaddition was explored in the symmetric endohedral fullerene H₂@C₆₀ and H₂O@C₆₀.⁸The reaction afforded both enantiomers of each cis and trans diastereomer with high enantiomeric excesses.

Synthesis of Enantiopure Derivatives of La@C₇₂ (C₆H₃Cl₂) (^f,sC and ^f,sA).

 

A deeper study in the molecule revealed the stereochemical of cis−trans isomerization of optically pure [60], [70], and endohedral H2O@C60fulleropyrrolidines, and surprisingly the incarcerated water molecule plays a crucial role in this rearrangement process.

Isomerization Reaction of (2R,5R )-cis-fulleropyrrolidine to (2R,5S )-trans fulleropyrrolidine of H₂O@C₆₀.

 

Referencias

J.R. Pinzón, M.E. Plonska-Brzezinska, C.M. Cardona, A.J. Athans, S.S. Gayathri, D. M. Guldi, M.A. Herranz, N.Martín, T.Torres, L. Echegoyen, Angew. Chem. Int. Ed. 2008, 47, 4173-4176; b) J.R. Pinzón, C.M. Cardona, M.A. Herranz, M.E. Plonska-Brzezinska, A. Palkar, A.J. Athans, N. Martín, A. Rodríguez-Fortea, J.M. Poblet, G. Bottari, T. Torres, S.S. Gayathri, D.M. Guldi, L. Echegoyen, Chem. Eur. J. 2009, 15, 864-877.

D.M. Guldi, L. Feng, S.G. Radhakrishnan, H. Nikawa, M. Yamada, N. Mizorogi, T. Tsuchiya, T. Akasaka, S. Nagase, M.A. Herranz, Nazario Martín, J. Am. Chem. Soc. 2010, 132, 9078-9086; b) L. Feng, S.G. Radhakrishnan, N. Mizorogi, Z. Slanina, H. Nikawa, T. Tsuchiya, T. Akasaka, S. Nagase, N. Martín, D.M. Guldi, , J. Am. Chem. Soc. 2011, 133, 7608-7618.

Y. Takano, M.A. Herranz, N. Martín, S.G. Radhakrishnan, D.M. Guldi, T. Tsuchiya, S. Nagase, T. Akasaka, J. Am. Chem. Soc. 2010, 132, 8048-8055.

L. Feng, M. Rudolf, S. Wolfrum, A.Troeger, Z. Slanina, T. Akasaka, S. Nagase, N. Martín, T. Ameri, C.J. Brabec, D.M. Guldi, J. Am. Chem. Soc. 2012, 134, 12190-12197.

Y. Takano, S. Obuchi, N. Mizorogi, R. García, M.A. Herranz, M. Rudolf, D.M. Guldi, N. Martín, S. Nagase, T. Akasaka, J. Am. Chem. Soc. 2012, 134, 19401-19408.

L. Feng, Z. Slanina, S. Sato, K. Yoza, T. Tsuchiya, N. Mizorogi, T. Akasaka, S. Nagase, N. Martín, D.M. Guldi, Angew. Chem. Int. Ed. 2011, 50, 5909-5912; b) Y. Takano, S. Obuchi, N. Mizorogi, R. García, M. A. Herranz, M. Rudolf, S. Wolfrum, D. M. Guldi, N. Martín, S. Nagase, T. Akasaka, J. Am. Chem. Soc. 2012, 134, 16103-16106; c) C. Schubert, M. Rudolf, D.M. Guldi, Y. Takano, N. Mizorogi, M. A. Herranz, N. Martín, S. Nagase, T. Akasaka, Phil. Trans. R. Soc. A, 2013, 371, 20120490.

K. Sawai, Y. Takano, M. Izquierdo, S. Filippone, N. Martin, Z. Slanina, N. Mizorogi, M. Waelchli, T. Tsuchiya, T. Akasaka, S. Nagase, J. Am. Chem. Soc. 2011, 133, 17746-17752.

E. E. Maroto, M. Izquierdo, M. Murata, S. Filippone, K. Komatsu, Y. Murata, N. Martín, Chem. Commun. 2014, 50, 740−742. b) E.E. Maroto, M. Izquierdo, S. Reboredo, J. Marco-Martínez, S. Filippone, N. Martín, Acc. Chem. Res. 2014, 47, 2660−2670 c) E.E. Maroto, J. Mateos, M. García-Borrás, S. Osuna, S. Filippone, M.Á. Herranz, Y. Murata, M. Solá, N. Martín, J. Am. Chem. Soc. 2015, 137, 1190−1197.