Prato reaction

The Prato reaction in fullerene chemistry describes the functionalization of fullerenes and nanotubes with azomethine ylides in a 1,3-dipolar cycloaddition.[1] The amino acid sarcosine reacts with paraformaldehyde when heated at reflux in toluene to an ylide which reacts with a double in a 6,6 ring position in a fullerene in a 1,3-dipolar cycloaddition to yield a N-methylpyrrolidine derivative or pyrrolidinofullerene or pyrrolidino[[3,4:1,2]] [60]fullerene in 82% yield.

Contents

Applications

In one application a liquid fullerene is obtained when the pyrrolidone substituent is a 2,4,6-tris(alkyloxy)phenyl group [2] although a small amount of solvent is still required.

Nanotubes

This method is also used in the functionalization of single wall nanotubes [3]. When the amino acid is modified with a glycine chain the resulting nanotubes are soluble in common solvents such chloroform and acetone. Another characteristic of the treated nanotubes is their larger aggregate dimensions compared to untreated nanotubes.

In an alternative method a nanotube addition is performed with the N-oxide of trimethylamine and LDA [4] at reflux in tetrahydrofuran with an efficiency of 1 functional group in 16 nanotube carbon atoms. When the amine also carries an aromatic group such as pyrene the reaction takes place even at room temperature because this group preorganizes itself to the nanotube surface prior to reaction by pi stacking.

Retro-Prato reaction

Just as in other fullerene reactions like the Bingel reaction or Diels-Alder reactions this reaction can be reversed. A thermal retro-cycloaddition of a pyrrolidinofullerene with a strong dipolarophile such as maleic acid and a catalyst such as Wilkinson's catalyst or copper triflate in 1,2-dichlorobenzene at reflux 8 to 18 hours regenerates the pristine C60 fullerene [5]. The dipolarophile is required in a 30 fold excess and traps the ylide driving the reaction to completion. The N-methylpyrrolidine derivative reacts poorly (5% yield) and for a successful reaction the nitrogen ring also requires substitution in the α-position with methyl, phenyl or carboxylic ester groups.

Other methods have been investigated: by applying heat [6] or via a combination of ionic liquid and microwave chemistry [7] [8].

References

  1. ^ M. Maggini, G. Scorrano and M. Prato (1993). "Addition of azomethine ylides to C60: synthesis, characterization, and functionalization of fullerene pyrrolidines". J. Am. Chem. Soc. 115 (21): 9798–9799. doi:10.1021/ja00074a056. 
  2. ^ T. Michinobu, T. Nakanishi, J. P. Hill, M. Funahashi and K. Ariga (2006). "Room Temperature Liquid Fullerenes: An Uncommon Morphology of C60 Derivatives". J. Am. Chem. Soc. 128 (32): 10384–10385. doi:10.1021/ja063866z. PMID 16895401. 
  3. ^ V. Georgakilas, K. Kordatos, M. Prato, D. M. Guldi, M. Holzinger and A. Hirsch (2002). "Organic Functionalization of Carbon Nanotubes". J. Am. Chem. Soc. 124 (5): 760–761. doi:10.1021/ja016954m. PMID 11817945. 
  4. ^ C. Menard-Moyon, N. Izard, E. Doris and C. Mioskowski (2006). "Separation of Semiconducting from Metallic Carbon Nanotubes by Selective Functionalization with Azomethine Ylides". J. Am. Chem. Soc. 128 (20): 6552–6553. doi:10.1021/ja060802f. PMID 16704243. 
  5. ^ N. Martín, M. Altable, S. Filippone, A. Martín-Domenech, L. Echegoyen and C. M. Cardona (2006). "Retro-Cycloaddition Reaction of Pyrrolidinofullerenes". Angewandte Chemie International Edition 45 (1): 110–114. doi:10.1002/anie.200502556. PMID 16240308. 
  6. ^ Filippone, Salvatore; Barroso, Marta Izquierdo; Martín-Domenech, ÁNgel; Osuna, SíLvia; Solà, Miquel; Martín, Nazario (2008). "On the Mechanism of the Thermal Retrocycloaddition of Pyrrolidinofullerenes (Retro-Prato Reaction)". Chemistry - A European Journal 14 (17): 5198. doi:10.1002/chem.200800096. PMID 18438770. 
  7. ^ Guryanov, Ivan; Montellano López, Alejandro; Carraro, Mauro; Da Ros, Tatiana; Scorrano, Gianfranco; Maggini, Michele; Prato, Maurizio; Bonchio, Marcella (2009). "Metal-free, retro-cycloaddition of fulleropyrrolidines in ionic liquids under microwave irradiation". Chemical Communications (26): 3940. doi:10.1039/b906813a. PMID 19662259. 
  8. ^ Guryanov, Ivan; Toma, Francesca Maria; Montellano lópez, Alejandro; Carraro, Mauro; Da ros, Tatiana; Angelini, Guido; D'aurizio, Eleonora; Fontana, Antonella et al. (2009). "Microwave-Assisted Functionalization of Carbon Nanostructures in Ionic Liquids". Chemistry - A European Journal 15 (46): 12837. doi:10.1002/chem.200901408. PMID 19847823. 

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