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首页> 外文期刊>Chemistry: A European journal >Mechanistic insight into the Staudinger reaction catalyzed by N-heterocyclic carbenes
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Mechanistic insight into the Staudinger reaction catalyzed by N-heterocyclic carbenes

机译：N杂环卡宾催化Staudinger反应的机理

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摘要

Four zwitterions were prepared by treating 1,3-dimesitylimidazolin-2- ylidene (SIMes) or 1,3-dimesitylimidazol-2-ylidene (IMes) with either N-tosyl benzaldimine or diphenylketene. They were isolated in high yields and characterized by IR and NMR spectroscopy. The molecular structures of three of them were determined by using X-ray crystallography and their thermal stability was monitored by using thermogravimetric analysis. The imidazol(in)ium-2-amides were rather labile white solids that did not show any tendency to tautomerize into the corresponding 1,2,2-triaminoethene derivatives. They displayed a mediocre catalytic activity in the Staudinger reaction of N-tosyl benzaldimine with diphenylketene. In contrast, the imidazol(in)ium-2-enolates were orange-red crystalline materials that remained stable over extended periods of time. Despite their greater stability, these zwitterions turned out to be efficient promoters for the model cycloaddition under scrutiny. As a matter of fact, their catalytic activity matched those recorded with the free carbenes. Altogether, these results provide strong experimental insight into the mechanism of the Staudinger reaction catalyzed by N-heterocyclic carbenes. They also highlight the superior catalytic activity of the imidazole-based carbene IMes compared with its saturated analogue SIMes in the reaction under consideration. Catalysts caught in the act: The N-heterocyclic carbenes 1,3-dimesitylimidazolin-2- ylidene (SIMes) and 1,3-dimesitylimidazol-2-ylidene (IMes) react with N-tosyl benzaldimine or diphenylketene to afford the corresponding zwitterions in high yields (see scheme). The molecular structures of three of them were determined by X-ray crystallography and their thermal stability was monitored by thermogravimetric analysis. The NHC×ketene betaines were found to be key intermediates for the Staudinger reaction catalyzed by NHCs.
机译：通过用N-甲苯磺酰基苯甲二胺或二苯乙烯酮处理1,3-二甲并咪唑啉-2-亚基（SIMes）或1,3-二甲并咪唑-2-亚胺（IMes）来制备四个两性离子。它们以高收率分离并通过IR和NMR光谱表征。通过X射线晶体学确定其中三个的分子结构，并通过热重分析监测其热稳定性。咪唑（2-）鎓的酰胺是相当不稳定的白色固体，没有显示出互变异构成相应的1,2,2-三氨基乙烯衍生物的趋势。他们在N-甲苯磺酰基苯甲二胺与二苯乙烯酮的施陶丁格反应中表现出中等的催化活性。相比之下，咪唑（2-）-2-烯醇盐是橙红色的结晶材料，可以长时间保持稳定。尽管它们具有更高的稳定性，但这些两性离子在仔细研究下仍然是模型环加成反应的有效启动子。事实上，它们的催化活性与游离碳烯记录的催化活性相匹配。总而言之，这些结果为N杂环卡宾催化Staudinger反应的机理提供了强大的实验见解。他们还强调了在考虑的反应中，基于咪唑的卡宾IMes与其饱和的类似物SIMes相比，具有更高的催化活性。陷入困境的催化剂：N-杂环卡宾1,3-dimesitylimidazolin-2-yylne（SIMes）和1,3-dimesitylimidazol-2-yylne（IMes）与N-甲苯磺酰基苯甲二胺或二苯乙烯酮反应，得到相应的两性离子高产量（请参阅计划）。通过X射线晶体学确定其中三个的分子结构，并通过热重分析监测其热稳定性。发现NHC x烯酮甜菜碱是NHC催化的Staudinger反应的关键中间体。

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