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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Specific Effects of Room Temperature Ionic Liquids on Cleavage Reactivity: Example of the Carbon-Halogen Bond Breaking in Aromatic Radical Anions
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Specific Effects of Room Temperature Ionic Liquids on Cleavage Reactivity: Example of the Carbon-Halogen Bond Breaking in Aromatic Radical Anions

机译：室温离子液体对裂解反应性的特定影响：芳族自由基阴离子中碳-卤素键断裂的例子

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Specific solvation effects of ionic liquids have been evidenced on the chemical reactivity of radical anions with three different ionic liquids(l-butyl-3-methylimidazolium,trimethylbutylammonium,and triethylbutyl-ammonium cations associated with the same anion(bis(trifluoromethylsulfonyl)imide).Large modifications depending on the localization of the negative charge in the radical anions and,to a less extent,on the nature of the ionic liquids cations are reported.When the charge is spread out over the entire molecule as in the 9-chloroanthracene radical anion,an acceleration of the carbon-halogen bond cleavage when passing from acetonitrile to the ionic liquid is observed.On the contrary,in the case of 4-chlorobenzophenone radical anion where the negative charge is more localized on the oxygen atom of the carbonyl group,a large decrease of the C-Cl cleavage rate occurs in relation with a positive shift of the reduction standard potentials.These effects can be explained by specific ion-pair associations between the radical anion and the cation of the ionic liquid that stabilizes the unpaired electron in the pi_* orbital of the aromatic system and thus decreases its presence in the a* bond breaking.The experimental results can be rationalized using Marcus-type formalism(Saveant's model describing the dynamics of electron transfers and bond cleavage)and agree well with the calculated ion-pair stabilization energies estimated with density functional theory(B3LYP).Besides the decrease of the cleavage rate,the ion pairing favors the dimerization between two radical anions that prevails over the cleavage reaction,leading to a different mechanism.
机译：离子液体对自由基阴离子与三种不同离子液体（1-丁基-3-甲基咪唑鎓，三甲基丁基铵和与相同阴离子缔合的三乙基丁基铵阳离子（双（三氟甲基磺酰基）酰亚胺）结合）的化学反应性已得到证明。据报道，根据负电荷在自由基阴离子中的位置以及在较小程度上取决于离子液体阳离子的性质，进行了较大的修饰。当电荷像9-氯蒽自由基阴离子那样分布在整个分子上时当从乙腈传递到离子液体时，观察到碳-卤素键裂解加速。相反，在4-氯二苯甲酮自由基阴离子中，负电荷更多地位于羰基的氧原子上，与还原标准电势的正偏移有关，C-Cl裂解速率会大大降低。这些影响可以通过特定的离子-自由基阴离子和离子液体的阳离子之间的成对缔合，可稳定芳香体系pi_ *轨道中未成对的电子，从而减少其在a *键断裂中的存在。使用Marcus型形式主义可以使实验结果合理化（Saveant模型描述了电子转移和键断裂的动力学），与密度泛函理论（B3LYP）估算的离子对稳定能非常吻合。除裂解率降低外，离子对还有利于两个自由基之间的二聚化阴离子在裂解反应中占主导地位，从而导致了不同的机理。

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