Revisiting the Reaction of IPr with Tritylium: An Alternative Mechanistic Pathway.
Revisiting the Reaction of IPr with Tritylium: An Alternative Mechanistic Pathway.
复制标题
重新审视 IPr 与氚的反应：另一种机制途径。
作者：
Hayoung Song;Eunsung Lee
尽管最近有人基于瞬态IPr自由基阳离子中间体（[IPr]●+）形成的证据提出了tritylium和2,6-bis（二异丙基苯基）咪唑-2-ylidene （IPr）之间的单电子转移（SET）过程机制，但由于n -杂环碳烯的高氧化电位，这种氧化仍然存在争议。我们的实验分析表明，深紫色的出现，以前被认为是来自瞬态[IPr]●+，源于两性离子中间体（3a），而不是自由基阳离子。在这里，我们提出了涉及氚和IPr的反应的另一种机制。这一机制值得注意，它解释了[NHC- h]+是如何在不形成瞬态[NHC]●+的情况下生成的，而瞬态[NHC]●+经常被认为是NHC与氧化剂之间反应的中间产物。这些结果还表明，NHCs与氧化剂的替代机制可以产生瞬态强单电子给体（3a），这是NHCs与氧化剂反应性的更可行的解释。
Despite a recent proposal on the mechanism of a single-electron transfer (SET) process between tritylium and 2,6-bis(diisopropylphenyl)imidazol-2-ylidene (IPr) based on evidence of transient IPr radical cation intermediate ([IPr]●+) formation, such oxidation is still contentious because of the high oxidation potential of N-heterocyclic carbenes. Our experimental analysis indicates that the appearance of deep purple color, previously considered to be from transient [IPr]●+, originates from a zwitterionic intermediate (3a), not a radical cation. Here, we propose an alternative mechanism for the reaction involving tritylium and IPr. This mechanism is noteworthy for explaining how [NHC-H]+ can be generated without the formation of transient [NHC]●+, which has been frequently proposed as an intermediate for the reaction between NHC and oxidants. These results also show that a transient strong single-electron donor (3a) could be generated by the alternative mechanism for oxidants using NHCs, which is a more feasible explanation for the reactivity of NHCs with oxidants.