Trapping a C₂ Radical in Endohedral Metallofullerenes: Synthesis and Structures of (Y₂C₂)@C₈₂ (Isomers I, II, and III)

Abstract

Three isomers of yttrium carbide (Y2C2) endohedral metallofullerenes, i.e., (Y2C2)@C82(I, II, III), have been synthesized and chromatographically isolated for the first time. The structures of (Y2C2)@C82(I, II, III) metallofullerenes have been characterized by 13C NMR measurements, whose molecular symmetries have been determined to be Cs, C2v, and C3v, respectively. In addition, a pure diyttrium metallofullerene, Y2@C82(III), has also been synthesized and structurally characterized. The 13C NMR structural analyses indicate that (Y2C2)@C82(III) has exactly the same fullerene cage as that of Y2@C82(III). On the basis of the results, we propose a C2-trapping and loss of growth mechanism of dimetallofullerenes of (M2C2)@C82 and M2@C82 from M2@C84, respectively.