It was shown for the first time that reactions of C60 halides with aliphatic amines provide a facile route for the synthesis of aminofullerenes, valuable precursors for water-soluble cationic fullerene derivatives. Particularly, chlorofullerene C60Cl6 and N-substituted piperazines were investigated in this work. It was shown that substitution of chlorine atoms in C60Cl6 by amine groups is accompanied by partial elimination of addends from the fullerene cage that yields mixtures of di-, tetra- and, hexaaminofullerenes as the final products. Separation of these mixtures by column chromatography resulted in isolation of pure 1,4-diaminofullerenes; this procedure gives much higher and more reproducible yields of these compounds than direct oxidative photoaddition of secondary amines to C60. ESI mass spectrometry and NMR spectroscopy data showed that hexaaminofullerene isomers are major components in inseparable mixtures of polyaddition products. Polyaminofullerenes were found to be readily soluble in aqueous acids; these solutions are unstable because of a facile substitution of protonated amine groups with hydroxyls. Nevertheless, the use of other amine substrates in the investigated reaction can potentially allow the preparation of more stable water-soluble cationic fullerene derivatives for biological studies.
- Nucleophilic substitution