Proton transfer reactions of a bridged bis -propyl bis -imidazolium salt
Proton transfer reactions of a bridged bis -propyl bis -imidazolium salt
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桥联双丙基双咪唑鎓盐的质子转移反应
DOI：
10.1002/poc.3567
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发表时间：
2016
影响因子：
1.8
通讯作者：
Massey R
中科院分区：
文献类型：
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作者：
Massey R
四氮杂富瓦烯1在还原和其他相关转化中具有广泛的应用，并且可以方便地由双丙基双咪唑盐4与强碱在非质子溶剂中生成。1的形成机制包括在C（2）处的初始去质子化，得到单卡宾9，然后在第二个唑鎓中心发生分子内反应。在本文中，我们报告了二丙基双咪唑鎓二碘化物盐4和相关单体二丙基咪唑鎓碘化物10在水溶液中氘氧化物催化的C（2）-氢交换的二级速率常数kDO分别为1.37 × 104和1.79 × 102 M − 1 s −1，并使用这些数据计算出pKa值为21.2和23.1。双桥双丙基双咪唑鎓盐4相对于10的更大的C（2）-H酸性可能归因于共轭酸双阳离子唑鎓离子4相对于单阳离子卡宾9的诱导或静电不稳定性，这通过双栓系而增强。在所采用的水性条件下未观察到四氮杂富瓦烯1的形成，这突出表明在这些条件下卡宾再聚化显著胜过二聚化。版权所有© 2016约翰威利父子有限公司.
Tetraazafulvalene1has found broad application in reduction and other related transformations and is conveniently generated frombis‐propylbis‐imidazolium salt4with a strong base in a non‐protic solvent. The proposed mechanism for the formation of1involves initial deprotonation at C(2) to give a mono‐carbene9followed by intramolecular reaction at the second azolium centre. Herein, we report the second‐order rate constants for deuteroxide‐catalysed exchange in aqueous solution of the C(2)‐hydrogens ofbis‐propylbis‐imidazolium di‐iodide salt4and related monomeric dipropyl imidazolium iodide10ofkDO= 1.37 × 104and 1.79 × 102M−1s−1, respectively, and used these data to calculate pKavalues of 21.2 and 23.1. The greater C(2)‐H acidity of the doubly bridgedbis‐propylbis‐imidazolium salt4relative to10may be attributed to the inductive or electrostatic destabilization of the conjugate acid dicationic azolium ion4relative to the monocationic carbene9, which is enhanced bybis‐tethering. Formation of tetraazafulvalene1was not observed under the aqueous conditions employed highlighting that carbene reprotonation significantly outcompetes dimerization under these conditions. Copyright © 2016 John Wiley & Sons, Ltd.