Chemical understanding of a non-IPR metallofullerene:: Stabilization of encaged metals on fused-pentagon bonds in La2@C72
Chemical understanding of a non-IPR metallofullerene:: Stabilization of encaged metals on fused-pentagon bonds in La2@C72
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DOI：
10.1021/ja8019577
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发表时间：
2008-07-16
影响因子：
15
通讯作者：
Nagase, Shigeru
中科院分区：
文献类型：
--
作者：
Lu, Xing;Nikawa, Hidefumi;Nagase, Shigeru
违反孤立五边形规则（IPR）的富勒烯只能以其衍生物的形式获得。由于[5，5]-键碳是高度反应性的，它们很容易被试剂攻击以释放键应变。然而，非IPR内嵌金属富勒烯在[5，5]键结处仍然具有不饱和sp（2）碳，这允许探测它们的化学性质。在这项工作中，选择La-2@C-72作为代表性的非IPR金属富勒烯，因为已经实验性地提出其具有#10611或#10958非IPR笼状结构（J. Am. Soc.2003，125，7782），而理论计算表明#10611笼更稳定（J. Phys. Chem. A 2006，110，2231）。用2-金刚烷-2，3-[3 H]-二氮杂环丙烷（diazirine）光解La-2@C-72，对La-2@C-72进行了光化学修饰。六个异构体的金刚烷单加合物的分离和使用各种测量，包括高效液相色谱，基质辅助激光解吸电离质谱，紫外可见-近红外光谱，循环伏安法，差分脉冲伏安法，C-13 NMR光谱，和单晶X-射线衍射的特点。电子光谱和电化学研究表明，六种异构体均保留了La-2@C-72的基本电子结构，且金刚烷亚基对La-2@C-72起弱供电子作用. X射线结构结果明确地阐明了La-2@C-72具有#10611手性笼（即，D-2对称性），在笼的每个极处具有两对稠合五边形，并且两个La原子靠近两个稠合五边形对。基于这些结果和理论计算，可以得出结论，稠合五边形位点对卡宾具有很强的反应性，但是形成[5，5]结的碳比相邻的碳反应性低;这证实了这些碳与笼状金属强烈相互作用，因此被它们稳定。
Fullerenes violating the isolated pentagon rule (IPR) are only obtained in the form of their derivatives. Since the [5,5]-bond carbons are highly reactive, they are easily attacked by reagents to release the bond strains. Non-IPR endohedral metallofullerenes, however, still have unsaturated sp(2) carbons at the [5,5] bond junctions, which allow their chemical properties to be probed. In this work, La-2@C-72 was chosen as a representative non-IPR metallofullerene, since it has been experimentally proposed to have either the #10611 or #10958 non-IPR cage structure (J. Am. Chem. Soc. 2003, 125, 7782), while theoretical calculations have suggested that the #10611 cage is more stable (J. Phys. Chem. A 2006, 110, 2231). La-2@C-72 was modified by photolytic reaction with the carbene reagent 2-adamantane-2,3-[3H]-diazirine. Six isomers of adamantylidene monoadducts were isolated and characterized using various kinds of measurements, including high-performance liquid chromatography, matrix-assisted laser desorption ionization mass spectrometry, UV-vis-near-infrared spectroscopy, cyclic voltammetry, differential-pulse voltammetry, C-13 NMR spectroscopy, and single-crystal X-ray diffraction. Electronic spectra and electro-chemical studies revealed that the essential electronic structures of La-2@C-72 are retained in the six isomers and the adamantylidene group acts as a weak electron-donating group toward La-2@C-72. X-ray structural results unambiguously elucidated that La-2@C-72 has the #10611 chiral cage (i.e., D-2 symmetry) with two pairs of fused pentagons at each pole of the cage and that the two La atoms reside close to the two fused-pentagon pairs. On the basis of these results and theoretical calculations, it is concluded that the fused-pentagon sites are very reactive toward carbene but that the carbons forming the [5,5] junctions are less reactive than the adjacent ones; this confirms that these carbons interact strongly with the encaged metals and thus are stabilized by them.