Stepwise Regioselective Hydrogenation of cis-2-C60 (CF2 )2 Homofullerene with [6,6]-Open/Closed Valence Tautomerism.

The homofullerene compound cis-2-C60 (CF2 )2 , which has an unusual kind of open/closed valence tautomerism undergoes consecutive regioselective hydrogenation at bridgehead carbon atoms upon reduction with Zn/Cu couple in H2 O-toluene mixture. The tautomerism barrier in cis-2-C60 (CF2 )2 is negligible in the neutral state, whereas negative charging both impedes tautomeric transformation and promotes regioselective addition of electrophilic species at the bridgehead carbon atoms. In light of this observation, two novel homofullerene derivatives, mixed [6,6]-open/closed C60 (CF2 )2 H2 and [6,6]-open cis-2-C60 (CF2 )2 H4 , were synthesized and their structures were unambiguously determined by means of single crystal X-ray crystallography and NMR spectroscopy.