Why [6,6]- and 1,2-benzal-3-N-4-O-cyclic phenylimidate C60 undergo electrochemically induced retro-addition reactions while 1,4-dibenzyl-2,3-cyclic phenylimidate C60 does not? C-H...X (X = N, O) intramolecular interactions in organofullerenes.
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.
Li
Fang-Fang
FF
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.
Gao
Xiang
X
Zheng
Min
M
D018360:Crystallography, X-Ray; D003500:Cyclization; D004563:Electrochemistry; D037741:Fullerenes / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D010080:Oxazoles / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
C535005:(6,6)cyclic phenylimidate C60; C535004:1,2-benzal-3-N-4-O-cyclic phenylimidate C60; C535003:1,4-dibenzyl-2,3-cyclic phenylimidate C60; D037741:Fullerenes; D010080:Oxazoles; C069837:fullerene C60