Xu Dan, Wang Zhiyong, Shinohara Hisanori
Department of Chemistry, Renmin University of China, Beijing, 100872, China.
Department of Chemistry and Institute for Advanced Research, Nagoya University, Nagoya, 464-8602, Japan.
Chemphyschem. 2017 Nov 3;18(21):3007-3011. doi: 10.1002/cphc.201700830. Epub 2017 Sep 21.
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.
内嵌金属富勒烯M@C（M = 稀土金属）具有独特的结构，违反了富勒烯科学中著名的“孤立五边形规则”。尽管通过电弧放电法已实现M@C的合成，但由于其自由基特性和极高的反应活性，M@C的溶剂萃取和纯化仍然具有挑战性。本文从理论上证明了通过C笼的外表面功能化捕获这些缺失的金属富勒烯的可能性。密度泛函理论计算揭示了Y@C的稳定三氟甲基化衍生物。Y@C的单三氟甲基化或多三氟甲基化导致闭壳电子构型和大的带隙。因此，Y@C可以通过三氟甲基化得到极大的稳定。三氟甲基基团倾向于连接到稠合五边形区域以缓解局部空间应变。还研究了Y@C(CF₃)的异构化机理，发现连接的三氟甲基基团可以通过过渡态从一个碳原子迁移到另一个碳原子。
