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

Abstract

The endohedral metallofullerenes M@C (M=rare-earth metal) have a unique structure that violates the well-known "isolated pentagon rule" of fullerene science. Although the synthesis of M@C has been achieved by using the arc discharge method, the solvent extraction and purification of M@C 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 C cage is demonstrated theoretically. Stable trifluoromethylated derivatives of Y@C are revealed by density functional theory calculations. Mono- or poly-trifluoromethylation of Y@C results in a closed-shell electronic configuration and a large band gap. Thus Y@C 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@C (CF ) is also investigated and it is found that the attached trifluoromethyl group can migrate from a carbon atom to another via a transition state.

Isolation and structure determination of missing fullerenes Gd@C 74 (CF 3 ) n through in situ trifluoromethylation

“…The preferential detection of Gd@C 74 in the positive-ion spectra results from the elimination of the electron-withdrawing CF 3 group. After the dissociation of the CF 3 moieties, the remaining Gd@C 74 tends to lose electrons and be detected as a cation [16][17][18][19]. Figure 2a shows the molecular arrangement of the monoclinic crystal consisting of Gd@C 74 (CF 3 ) (I) and Ni(OEP) in a ratio of 1 : 1.…”

“…The present trifluoromethylation method provides only mono- and tri-substituted derivatives [ 16 – 18 ]. One of the possible reasons for the selectivity is that it has an open-shell structure.…”

“…Recently, we developed an in situ trifluoromethylation method for the extraction and purification of these missing metallofullerenes [16][17][18][19]. CF 3 groups [20][21][22][23], furnished by the thermal pyrolysis of polytetrafluoroethylene (PTFE), were introduced to the outer cages of fullerenes and stabilized reactive missing metallofullerenes during the production simultaneously.…”

The smallest endohedral borafullerene: structural isomerization, electronic properties, aromaticity and reactivity of U@C27B

“…Because of the easy dimerization of U@T d -C 27 B, we infer that the radical additions among the various EMF functionalization reactions, 103 e.g., trifluoromethylation, [104][105][106][107][108] can help obtain its monomer in the experiments. To demonstrate such a possibility, we selected several carbon sites with large spin densities and pyramidalization angles of U@T d -C 27 B to undergo the CF 3 addition (Fig.…”