Synthesis of 18pi annulenic fluorofullerenes from tertiary carbanions: size matters!
Synthesis of 18pi annulenic fluorofullerenes from tertiary carbanions: size matters!
复制标题
从叔碳负离子合成 18pi 环烯氟富勒烯：尺寸很重要！
DOI：
10.1039/b301820m
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发表时间：
2003
影响因子：
3.2
通讯作者：
R. Taylor
中科院分区：
文献类型：
--
作者：
G. Burley;A. G. Avent;O. Boltalina;T. Drewello;I. V. Goldt;M. Marcaccio;F. Paolucci;Demis Paolucci;J. M. Street;R. Taylor
一系列不同尺寸的叔碳负离子XCH（CO2 Et）2已与C60 F18反应，以评估X对亲核取代位置的空间效应。对于X = CO_2Et，NO_2，P（O）（OMe）_2，SO_2CH_2Ph，全反式轮烯（transnulenes）是由S（N）_2 ′（S（N）_2 ″）取代得到的;对于磷化合物，在碱（DBU）用量减少的情况下，一个或多个P（O）（OMe）_2基团被氢去膦酰化。对于X = F，CN，由于亲核试剂的尺寸较小，没有发生反铀烯的形成，并且在后一种情况下，取代被证明是通过S（N）2'机制发生的，导致加数与氟加数相邻。Trannulenes（X = CO2 Et，Br，Cl）在电位（-0.02至-0.09 V）下表现出可逆的单电子还原，比[60]富勒烯明显更正。反铀烯（X = NO2）表现出不可逆的单电子还原（0.08 V），不可逆性可能与氟的损失。构象异构在低于298 K的温度下观察到所有transnulene衍生物作为一个结果的重叠addend-addend相互作用。当用分子力学计算这些相互作用时，观察到具有12-15 kcal mol（-1）的旋转能垒的最小能量构象。
A range of tertiary carbanions XCH(CO2Et)2 of differing sizes have been reacted with C60F18 to assess the steric effect of X on the position of nucleophilic substitution. For X = CO2Et, NO2, P(O)(OMe)2, SO2CH2Ph, the all trans annulenes (trannulenes) were obtained as a result of extended S(N)2' (i.e. S(N)2'') substitution; in the case of the phosphorus compound, with reduced amounts of base (DBU) dephosphonylation of one or more P(O)(OMe)2 groups by hydrogen occurred. Trannulene formation did not occur for X = F, CN due to the smaller size of the nucleophile, and in the latter case substitution was shown to take place by an S(N)2' mechanism, resulting in the addend being adjacent to a fluorine addend. Trannulenes (X = CO2Et, Br, Cl) exhibited reversible one-electron reductions at potentials (-0.02 to -0.09 V) significantly more positive than for [60]fullerene. Trannulene (X = NO2) exhibited an irreversible one-electron reduction (0.08 V); the irreversibility may be associated with fluorine loss. Conformational isomerism at temperatures below 298 K was observed for all trannulene derivatives as a result of eclipsing addend-addend interactions. Minimum energy conformations with a rotational energy barrier of 12-15 kcal mol(-1) were observed when these interactions are calculated using molecular mechanics.