Unexpected Formation of 1,2- and 1,4-Bismethoxyl Sc3N@Ih-C80 Derivatives via Regioselective Anion Addition: Unambiguous Structural Identification and Mechanism Study
An attempt to achieve heterocyclic cycloadducts of Sc3N@Ih-C80 via the reaction with Ph2C=O, PhC≡CPh or PhC≡N in the presence of tetrabutylammonium hydroxide (TBAOH) stored in CH3OH led to the formation of the unexpected bismethoxyl adducts of Sc3N@Ih-C80 (1 and 2). Further studies reveal that TBAOH in CH3OH can boost the CH3O addition efficiently, regardless of the presence of the other reagents. Single-crystal X-ray diffraction results firmly assign the molecular structures of 1 and 2 as respective 1,4- and 1,2-bismethoxyl adducts, and reveal unusual relationships between the internal Sc3N cluster and the addition modes, in addition to the unusual packing mode in view of the orientation of the methoxyl groups. Electrochemical results demonstrate smaller electrochemical gaps for 1 and 2, relative to that of Sc3N@Ih-C80, confirming their better electron-active properties. Finally, a plausible reaction mechanism involving anion addition and radical reaction was proposed, presenting new insights into the highly selective reactions between methoxyl anion and metallofullerenes. 1 and 2 represent as the first examples of methoxyl derivatives of metallofullerenes. This work not only presents a novel and facile strategy for the controllable synthesis of alkoxylated metallofullerene derivatives, but also provides new non-cycloadducts for the potential applications of EMFs.