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@I-h-C-80 derivatives using the Sc3N@I-h-C-80 dianion were unsuccessful because of its low nucleophilicity. Those results prompted us to prepare the Sc3N@C-80 trianion, which should be more nucleophilic and reactive with electrophilic reagents. The reaction between Sc3N@C-80 trianions and benzal bromide (PhCHBr2) was successful and yielded a methano derivative, Sc3N@I-h-C-80(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@I-h-C-80, resembling the behavior of other methano adducts of Sc3N@I-h-C-80. The successful synthesis of endohedral metallofullerene derivatives using trianionic Sc3N@I-h-C-80 and dianionic Lu3N@I-h-C-80, but not dianionic Sc3N@I-h-C-80, prompted us to probe the causes using theoretical calculations. The Sc3N@I-h-C-80 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@I-h-C-80 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.