Magnesium Catalysis for the Hydroboration of Carbodiimides
Magnesium Catalysis for the Hydroboration of Carbodiimides
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DOI：
10.1002/chem.201600681
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发表时间：
2016-05-17
影响因子：
4.3
通讯作者：
Mahon, Mary F.
中科院分区：
文献类型：
--
作者：
Weetman, Catherine;Hill, Michael S.;Mahon, Mary F.
[CH{C(Me)NDipp}(2)}MgnBu] (Dipp=2,6- ipr (2)C（6)H(3)）是首次报道的烷基取代和芳基取代碳二亚胺与蒎醇硼烷（HBpin）催化硼氢化反应的有效预催化剂。催化反应在温和条件下进行，产率高，得到相应的n -硼化甲脒化合物。观察到这些反应是通过偕胺酸镁和甲脒酸甲酯中间体进行的，其中一种后一种的例子已经通过x射线衍射分析进行了结构表征。关键是，在没有碳二亚胺和HBpin底物的情况下，没有观察到n -硼基甲脒产物的形成。这一观察结果得到了双环己基碳二亚胺硼化氢的s形动力学曲线的支持，并被合理地解释为甲脒酸镁中间体对吡纳柯硼烷和碳二亚胺的变构效应的结果。
A beta-diketiminato magnesium alkyl complex, [CH{C(Me)NDipp}(2)}MgnBu] (Dipp=2,6-iPr(2)C(6)H(3)), was shown to be an effective pre-catalyst for the first reported catalytic hydroboration of alkyl-and aryl-substituted carbodiimides with pinacol borane (HBpin). The catalytic reactions proceed under mild conditions to afford the corresponding N-borylated formamidine compounds in good yields. The reactions were observed to proceed through the intermediacy of magnesium amidinate and formamidinatoborate intermediates and an example of one of these latter species has been structurally characterised by an X-ray diffraction analysis. Crucially, no formation of the N-boryl formamidine products was observed in the absence of additional equivalents of the carbodiimide and HBpin substrates. This observation, supported by the evolution of a sigmoidal kinetic profile for the hydroboration of dicyclohexylcarbodiimide, has been rationalised as the consequence of an allosteric effect of the pinacol borane and carbodiimide on the magnesium formamidinatoborate intermediates.