Poly(perfluoroalkylation) of Metallic Nitride Fullerenes Reveals Addition-Pattern Guidelines: Synthesis and Characterization of a Family of Sc3N@C80(CF3)n (n = 2−16) and Their Radical Anions

A family of highly stable (poly)perfluoroalky-lated metallic nitride cluster fullerenes was prepared in high-temperature reactions and characterized by spectroscopic (MS, 19F NMR, UV−vis/NIR, ESR), structural and electrochemical methods. For two new compounds, Sc3N@C80(CF3)10 and Sc3N@C80(CF3)12, single crystal X-ray structures are determined. Addition pattern guidelines for endohedral fullerene derivatives with bulky functional groups are formulated as a result of experimental (19F NMR spectroscopy and single crystal X-ray diffraction) studies and exhaustive quantum chemical calculations of the structures of Sc3N@C80(CF3)n (n = 2-16). Electrochemical studies revealed that Sc3N@C80(CF3)n derivatives are easier to reduce than Sc3N@C80, the shift of E1/2 potentials ranging from +0.11 V (n = 2) to +0.42 V (n = 10). Stable radical anions of Sc3N@C80(CF3)n were generated in solution and characterized by ESR spectroscopy, revealing their 45Sc hyperfine structure. Facile further functionalizations via cycloadditions or radical additions were achieved for trifluoromethylated Sc3N@C80 making them attractive versatile platforms for the design of molecular and supramolecular materials of fundamental and practical importance.

本研究通过高温反应合成了一系列高稳定性的（多）全氟烷基化金属氮化物团簇富勒烯，并借助光谱学（质谱（MS）、氟-19核磁共振波谱（19F NMR）、紫外-可见/近红外光谱（UV−vis/NIR）、电子顺磁共振（ESR））、结构表征与电化学方法完成了对该类化合物的表征。针对两种新型化合物Sc₃N@C₈₀(CF₃)₁₀与Sc₃N@C₈₀(CF₃)₁₂，我们解析得到了其单晶X射线结构。通过实验（氟-19核磁共振波谱与单晶X射线衍射）研究，以及对Sc₃N@C₈₀(CF₃)ₙ（n=2~16）结构的全面量子化学计算，我们提出了带有大体积官能团的内嵌富勒烯（endohedral fullerene）衍生物的加成模式规则。电化学研究结果显示，Sc₃N@C₈₀(CF₃)ₙ衍生物相较于原始的Sc₃N@C₈₀更易被还原，其半波电位（E1/2）的偏移区间为+0.11 V（n=2）至+0.42 V（n=10）。我们在溶液中制备得到Sc₃N@C₈₀(CF₃)ₙ的稳定自由基阴离子，并通过电子顺磁共振（ESR）波谱对其进行表征，观测到了其45Sc的超精细结构（hyperfine structure）。经三氟甲基化修饰后的Sc₃N@C₈₀可通过环加成反应（cycloaddition）或自由基加成反应（radical addition）实现简便的后续官能化修饰，使其成为用于构建兼具基础研究与应用价值的分子及超分子材料（supramolecular materials）的极具潜力的多功能平台。