Li Fang-Fang, Gao Xiang, Zheng Min
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate School of Chinese Academy of Sciences, 5625 Renmin Street, Changchun, Jilin 130022, China.
J Org Chem. 2009 Jan 2;74(1):82-7. doi: 10.1021/jo801769q.
The electrochemical properties of a series of structurally related fullerooxazoles, [6,6] cyclic phenylimidate C(60) (1), 1,2-benzal-3-N-4-O-cyclic phenylimidate C(60) (2), and 1,4-dibenzyl-2,3-cyclic phenylimidate C(60) (3), are described, and the spectroscopic characterizations of their anionic species are reported. The results show that compounds 1 and 2 undergo retro-cycloaddition reactions that lead to the formation of C(60) and C(61)HPh, respectively, upon two-electron-transfer reduction. However, compound 3 demonstrates much more electrochemical stability as no retro-cycloaddition reaction occurs under similar conditions. Natural bond orbital (NBO) calculations on charge distribution show there is no significant difference among the dianions of 1, 2, and 3, indicating that the electrochemical stability of 3 is unlikely to be caused by the charge distribution difference of the dianions of three compounds. Examination on the crystal structure of compound 3 reveals close contacts of the C-H group with the heteroatoms (N and O) of cyclic phenylimidate, suggesting the existence of C-H...X (X = N, O) intramolecular hydrogen bonding among the addends, which is further confirmed by NBO analysis. The results thus suggest that intramolecular hydrogen bonding is responsible for the electrochemical stability of 3.
描述了一系列结构相关的富勒烯恶唑的电化学性质，即[6,6]环苯基亚氨酸酯C(60)（1）、1,2-亚苄基-3-N-4-O-环苯基亚氨酸酯C(60)（2）和1,4-二苄基-2,3-环苯基亚氨酸酯C(60)（3），并报道了它们阴离子物种的光谱表征。结果表明，化合物1和2在双电子转移还原时会发生逆环加成反应，分别生成C(60)和C(61)HPh。然而，化合物3表现出更高的电化学稳定性，因为在相似条件下没有发生逆环加成反应。基于电荷分布的自然键轨道（NBO）计算表明，1、2和3的二价阴离子之间没有显著差异，这表明3的电化学稳定性不太可能是由三种化合物二价阴离子的电荷分布差异引起的。对化合物3晶体结构的研究揭示了C-H基团与环苯基亚氨酸酯的杂原子（N和O）之间的紧密接触，表明加成物之间存在C-H...X（X = N，O）分子内氢键，NBO分析进一步证实了这一点。因此，结果表明分子内氢键是3电化学稳定性的原因。
