Electrosynthesis of a\nSc₃N@<i>I</i>_<i>h</i>-C₈₀ Methano Derivative from\nTrianionic Sc₃N@<i>I</i>_<i>h</i>-C₈₀

Abstract

The electrosynthetic method has been used for the selective\nsynthesis\nof fullerene derivatives that are otherwise not accessible by other\nprocedures. Recent attempts to electrosynthesize Sc₃N@<i>I</i>_<i>h</i>-C₈₀ derivatives\nusing the Sc₃N@<i>I</i>_<i>h</i>-C₈₀ dianion were unsuccessful because of its low\nnucleophilicity. Those results prompted us to prepare the Sc₃N@C₈₀ trianion, which should be more nucleophilic and\nreactive with electrophilic reagents. The reaction between Sc₃N@C₈₀ trianions and benzal bromide (PhCHBr₂) was successful and yielded a methano derivative, Sc₃N@<i>I</i>_<i>h</i>-C₈₀(CHPh) (<b>1</b>), in which the >CHPh addend is selectively\nattached to a [6,6] ring junction, as characterized by MALDI–TOF\nmass spectrometry and NMR and UV–vis–NIR spectroscopy.\nThe electrochemistry of <b>1</b> was studied using cyclic voltammetry,\nwhich showed that <b>1</b> exhibits the typical irreversible\ncathodic behavior of pristine Sc₃N@<i>I</i>_<i>h</i>-C₈₀, resembling the behavior\nof other methano adducts of Sc₃N@<i>I</i>_<i>h</i>-C₈₀. The successful synthesis\nof endohedral metallofullerene derivatives using trianionic Sc₃N@<i>I</i>_<i>h</i>-C₈₀ and dianionic Lu₃N@<i>I</i>_<i>h</i>-C₈₀, but not dianionic Sc₃N@<i>I</i>_<i>h</i>-C₈₀, prompted\nus to probe the causes using theoretical calculations. The Sc₃N@<i>I</i>_<i>h</i>-C₈₀ trianion has a singly occupied molecular orbital with high spin\ndensity localized on the fullerene cage, in contrast to the highest\noccupied molecular orbital of the Sc₃N@<i>I</i>_<i>h</i>-C₈₀ dianion, which is mainly\nlocalized on the inside cluster. The calculations provide a clear\nexplanation for the different reactivities observed for the dianions\nand trianions of these endohedral fullerenes.