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

Abstract

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.