Capturing the Unconventional Metallofullerene M@C₆₆ by Trifluoromethylation: A Theoretical Study

The endohedral metallofullerenes M@C₆₆ (M=rare-earth metal) have a unique structure that violates the well-known "isolated pentagon rule" of fullerene science. Although the synthesis of M@C₆₆ has been achieved by using the arc discharge method, the solvent extraction and purification of M@C₆₆ remain challenges because of their radical character and extremely high reactivity. In this paper, the possibility of capturing these missing metallofullerenes by exohedral functionalization of the C₆₆ cage is demonstrated theoretically. Stable trifluoromethylated derivatives of Y@C₆₆ are revealed by density functional theory calculations. Mono- or poly-trifluoromethylation of Y@C₆₆ results in a closed-shell electronic configuration and a large band gap. Thus Y@C₆₆ can be greatly stabilized through trifluoromethylation. The trifluoromethyl group prefers to be attached to the fused pentagon region to relieve local steric strain. The mechanism of isomerization of Y@C₆₆ (CF₃ )₃ is also investigated and it is found that the attached trifluoromethyl group can migrate from a carbon atom to another via a transition state.