Preparation, Structural Determination, and Characterization of Electronic Properties of Bis-silylated and Bis-germylated Lu3N@Ih-C80

Bis-silylated and bis-germylated derivatives of Lu3N@I-h-C-80 (3, 4, 5) were successfully synthesized by the photochemical addition of disiliranes 1a, 1b or digermirane 2, and fully characterized by spectroscopic, electrochemical, and theoretical studies. Interestingly, digermirane 2 reacts more efficiently than disiliranes 1a and 1b because of its good electron-donor properties and lower steric hindrance around the GeGe bond. The 1,4-adduct structures of 3, 4, 5 were unequivocally established by single-crystal X-ray crystallographic analyses. The electrochemical and theoretical studies reveal that the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the 1,4-adducts are remarkably smaller than those of Lu3N@I-h-C-80, because the electron-donating groups effectively raise the HOMO levels. It is also observed that germyl groups are slightly more electron-donating than the silyl groups on the basis of the redox properties and the HOMO-LUMO energies of 4 and 5. Bis-silylation and bis-germylation are effective and versatile methods for tuning the electronic characteristics of endohedral metallofullerenes.