Alkali Metal Dihydropyridines in Transfer Hydrogenation Catalysis of Imines: Amide Basicity versus Hydride Surrogacy
Alkali Metal Dihydropyridines in Transfer Hydrogenation Catalysis of Imines: Amide Basicity versus Hydride Surrogacy
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碱金属二氢吡啶在亚胺转移氢化催化中的作用：酰胺碱度与氢化物替代
DOI：
10.1002/ange.202304966
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发表时间：
2023
影响因子：
--
通讯作者：
Macdonald P
中科院分区：
文献类型：
--
作者：
Macdonald P
已经使用从1，4-二环己二烯的转移氢化研究了具有代表性的一组亚胺（醛亚胺和酮亚胺）催化还原为胺。不寻常的是，这已经使用s-嵌段预催化剂实现，即1-金属-2-叔丁基-1，2-二氢吡啶，2-tBuC 5 H5 NM，M（tBuDHP），其中M=Li-Cs。在C6 D 6和四氢呋喃-d8（THF-d8）中监测反应。一个明确的趋势是观察催化剂的效率与较重的碱金属BuDHP优于较轻的同系物。一般来说，Cs（tBuDHP）是最佳的预催化剂，在最好的情况下，在室温下使用5摩尔%的催化剂，反应在几分钟内产生定量的胺产率。 支持的实验研究，密度泛函理论（DFT）的计算也进行了揭示，Cs具有一个显着较低的速率决定步骤比锂同系物的途径。在假定的引发途径中，DHP可以作为碱或替代氢化物。
Catalytic reduction of a representative set of imines, both aldimines and ketimines, to amines has been studied using transfer hydrogenation from 1,4‐dicyclohexadiene. Unusually, this has been achieved using s‐block pre‐catalysts, namely 1‐metallo‐2‐tert‐butyl‐1,2‐dihydropyridines, 2‐tBuC5H5NM, M(tBuDHP), where M=Li–Cs. Reactions have been monitored in C6D6and tetrahydrofuran‐d8(THF‐d8). A definite trend is observed in catalyst efficiency with the heavier alkali metaltBuDHPs outperforming the lighter congeners. In general, Cs(tBuDHP) is the optimal pre‐catalyst with, in the best cases, reactions producing quantitative yields of amines in minutes at room temperature using 5 mol % catalyst. Supporting the experimental study, Density Functional Theory (DFT) calculations have also been carried out which reveal that Cs has a pathway with a significantly lower rate determining step than the Li congener. In the postulated initiation pathways DHP can act as either a base or as a surrogate hydride.