Electrosynthesis of a Sc3N@Ih-C80 Methano Derivative from Trianionic Sc3N@Ih-C80
journal contributionposted on 02.05.2012, 00:00 by Fang-Fang Li, Antonio Rodríguez-Fortea, Ping Peng, Guillermo A. Campos Chavez, Josep M. Poblet, Luis Echegoyen
The electrosynthetic method has been used for the selective synthesis of fullerene derivatives that are otherwise not accessible by other procedures. Recent attempts to electrosynthesize Sc3N@Ih-C80 derivatives using the Sc3N@Ih-C80 dianion were unsuccessful because of its low nucleophilicity. Those results prompted us to prepare the Sc3N@C80 trianion, which should be more nucleophilic and reactive with electrophilic reagents. The reaction between Sc3N@C80 trianions and benzal bromide (PhCHBr2) was successful and yielded a methano derivative, Sc3N@Ih-C80(CHPh) (1), in which the >CHPh addend is selectively attached to a [6,6] ring junction, as characterized by MALDI–TOF mass spectrometry and NMR and UV–vis–NIR spectroscopy. The electrochemistry of 1 was studied using cyclic voltammetry, which showed that 1 exhibits the typical irreversible cathodic behavior of pristine Sc3N@Ih-C80, resembling the behavior of other methano adducts of Sc3N@Ih-C80. The successful synthesis of endohedral metallofullerene derivatives using trianionic Sc3N@Ih-C80 and dianionic Lu3N@Ih-C80, but not dianionic Sc3N@Ih-C80, prompted us to probe the causes using theoretical calculations. The Sc3N@Ih-C80 trianion has a singly occupied molecular orbital with high spin density localized on the fullerene cage, in contrast to the highest occupied molecular orbital of the Sc3N@Ih-C80 dianion, which is mainly localized on the inside cluster. The calculations provide a clear explanation for the different reactivities observed for the dianions and trianions of these endohedral fullerenes.