Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes.
The [4 + 2] cycloaddition of o-quinodimethanes, generated in situ from the sultine 4,5-benzo-3,6-dihydro-1,2-oxathiin 2-oxide and its derivative, to La metal-encapsulated fullerenes, La2@C80 or La@C82, afforded the novel derivatives of endohedral metallofullerenes (3a,b, 4a,b and 5b). Molecular structures of the resulting compounds were elucidated using spectroscopic methods such as MALDI-TOF mass, optical absorption, and NMR spectroscopy. The [4 + 2] adducts of La2@C80 (3a,b, and 4a,b) and La@C82 (5b), respectively, retain diamagnetic and paramagnetic properties, as confirmed by EPR spectroscopy. Dynamic NMR measurements of 4a at various temperatures demonstrated the boat-to-boat inversions of the addend. In addition, 5b revealed remarkable thermal stability in comparison with the reported [4 + 2] cycloadduct of pentamethylcyclopentadiene and La@C82 (6). These findings demonstrate the utility of sultines to afford thermodynamically stable endohedral metallofullerene derivatives for the use in material science.
Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Yuta
Y
Takano
Life Science Center of Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan.
Yuki
Y
Nagashima
Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense, E-28040 Madrid, Spain.
M Ángeles
MÁ
Herranz
Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense, E-28040 Madrid, Spain ; IMDEA-Nanoscience, Campus de Cantoblanco, Madrid E-28049, Spain.
Nazario
N
Martín
Life Science Center of Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan ; Foundation for Advancement of International Science, Tsukuba, Ibaraki 305-0821, Japan ; State Key Laboratory of Materials Processing and Die & Mould Technology, School of Materials Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China and Department of Chemistry, Tokyo Gakugei University, Tokyo 184-8501, Japan.
Takeshi
T
Akasaka
La2@C80; La@C82; carbon nanomaterials; dynamic NMR; endofullerenes; sultine