Catalytic metal-free ketone hydrogenation: a computational experiment.
Catalytic metal-free ketone hydrogenation: a computational experiment.
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DOI：
10.1039/c001399d
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发表时间：
2010-06
影响因子：
4
通讯作者：
Haixia Li;Lili Zhao;G. Lu;Fangcheng Huang;Zhi‐Xiang Wang
中科院分区：
文献类型：
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作者：
Haixia Li;Lili Zhao;G. Lu;Fangcheng Huang;Zhi‐Xiang Wang
使用环己酮（3）及其衍生物（4-6）作为酮模型，进行了计算研究以检查设计用于亚胺氢化的无金属催化剂（1）是否能够使酮氢化。催化循环包括两个主要步骤：氢活化和氢转移。氢转移步骤中的协同途径优于逐步途径。用于氢活化和氢转移的两个分开的步骤可有利于将氢添加到基底（例如，酮），其不具有强的刘易斯碱中心，因为底物不需要参与氢活化。通常，底物的空间效应越大，副反应变得越不严重，并且所需反应越难以发生。能量分析结果表明，3-5的加氢反应在动力学和热力学上都是可行的，但6的加氢反应在能量上不太有利。因此，重要的是在促进期望的反应和同时避免不期望的反应之间建立适当的平衡。静止状态的问题，所造成的形成稳定的醇盐配合物，如在酮加氢催化的金属配体双功能催化剂，也进行了讨论。
A computational study has been carried out to examine if the metal-free catalyst (1) designed for imine hydrogenation is able to hydrogenate ketones, using the cyclohexanone (3) and its derivatives (4-6) as ketone models. The catalytic cycle includes two major steps: hydrogen activation and hydrogen transfer. The concerted pathway in the hydrogen transfer step is preferred over the stepwise pathway. The two separated steps for hydrogen activation and hydrogen transfer can benefit the hydrogen addition to the substrates (e.g., ketones) which do not have strong Lewis base centres, because the substrates need not to be involved in the hydrogen activation. In general, the larger the steric effect of the substrate is, the less severe the side reactions become, and the more difficultly the desired reaction occurs. The energetic results show that the hydrogenations of 3-5 are kinetically and thermodynamically feasible under ambient conditions, but the hydrogenation of 6 is less energetically favourable. Therefore, it is important to establish a proper balance between promoting the desired reaction and meanwhile avoiding the undesired reactions. The issue of the resting state, caused by forming stable alkoxide complexes like in the ketone hydrogenation catalyzed by the metal-ligand bifunctional catalysts, is also discussed.