Reactions of chlorofullerene C 60Cl 6 with N-substituted piperazines

Abstract

It was shown for the first time that reactions of C 60 halides with aliphatic amines provide a facile route for the synthesis of aminofullerenes, valuable precursors for water-soluble cationic fullerene derivatives. Particularly, chlorofullerene C 60Cl 6 and N-substituted piperazines were investigated in this work. It was shown that substitution of chlorine atoms in C 60Cl 6 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 C 60. 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.