Structure of Silver-N-Heterocyclic Carbenes in Solution: Evidence of Equilibration in DMSO at Very Different Time Scales by 1H NMR Experiments
Structure of Silver-N-Heterocyclic Carbenes in Solution: Evidence of Equilibration in DMSO at Very Different Time Scales by 1H NMR Experiments
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DOI：
10.1021/om401124y
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发表时间：
2014-04-28
期刊：
影响因子：
2.8
通讯作者：
Roland, Sylvain
中科院分区：
文献类型：
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作者：
Caytan, Elsa;Roland, Sylvain
银-N-杂环卡宾(NHC)络合物在溶液中可以以中性[(NHC)AgX]和/或离子[(NHC)(2)Ag][AgX2]形式存在。在此，我们研究了四个含有普通大体积N，N‘-二芳基NHC的配合物在DMSO中的行为。在CDCl3和DMSO-d(6)中系统地进行了H-1核磁共振实验，在非常不同的时间尺度上检测了DMSO或氯离子诱导的中性和离子形式之间的平衡。我们观察到，在300K下，IMesAgCl和SIMesAgCl在DMSO中的增溶作用在不到几分钟内就达到了完全平衡。在这里，磁化交换速率常数是由EXSY实验确定的。相比之下，在300K时，具有较大体积的NHCs的lPrAgCl和SIPrAgCl的交换率(或无交换)要低得多。在DMSO中，IPrAgCl在达到平衡之前的几个小时内缓慢地生成数量不断增加的同质阳离子络合物。在这种情况下，阳离子络合物的初始形成速度被确定。
Ag-N-heterocyclic carbene (NHC) complexes can occur as neutral [(NHC)AgX] and/or ionic [(NHC)(2)Ag][AgX2] species in solution. Herein, the behavior of four complexes bearing common bulky N,N'-diaryl NHCs was examined in DMSO. H-1 NMR experiments performed systematically in CDCl3 and in DMSO-d(6) were used to detect DMSO or chloride ion induced equilibration between the neutral and ionic forms at very different time scales. We observed that solubilization of IMesAgCl and SIMesAgCl in DMSO at 300 K led in less than a few minutes to a complete equilibration. Here, magnetization exchange rate constants were determined from EXSY experiments. In contrast, lPrAgCl and SIPrAgCl, which possess more bulky NHCs, were found to exhibit much lower exchange rates (or no exchange) at 300 K. IPrAgCl was shown to slowly generate an increasing amount of homoleptic cationic complex in DMSO for several hours before reaching equilibrium. In this case, the initial rate of formation of the cationic complex was determined.