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).

1

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.

2
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.

3
Isomerization Reaction of (2R,5R )-cis-fulleropyrrolidine to (2R,5S )-trans fulleropyrrolidine of H2O@C60.

  1. 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.
  2. 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.
  3. 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.
  4.   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.
  5.  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.
  6. 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.
  7.    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.
  8.  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.

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