Imine hydrogenation with simple alkaline earth metal catalysts
Imine hydrogenation with simple alkaline earth metal catalysts
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DOI：
10.1038/s41929-017-0006-0
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发表时间：
2018-01-01
期刊：
影响因子：
37.8
通讯作者：
Harder, Sjoerd
中科院分区：
文献类型：
--
作者：
Bauer, Heiko;Alonso, Mercedes;Harder, Sjoerd
不饱和键的氢化主要由过渡金属催化。与过渡金属相比，其他金属的使用较少被探索，尤其是对于 s 区元素，尽管它们易于获得且成本低廉。在这里，我们发现第 2 族金属酰胺 (M[N(SiMe3)(2)](2)，M = Mg、Ca、Sr、Ba）在 80 摄氏度和 1-6 bar 的极低 H-2 压力下意外地催化醛亚胺与 H-2 的氢化。转化率随着金属尺寸的增加而增加：Mg < Ca < Sr < Ba（对于 Ba，在 15 分钟内达到定量转化）。这种催化的关键是通过弱碱 M[N(SiMe3)(2)](2) (HN(SiMe3)(2)：pK(a) 近似于 25.8) 使 H-2 (pK(a) 近似于 49) 去质子化，意外地形成金属氢化物物质。密度泛函理论计算表明，最有利的途径确实涉及金属氢化物中间体。在非常低的压力下，碱土金属催化的亚胺与分子氢的有效氢化提供了过渡金属催化的有吸引力的替代方案。
Hydrogenation of unsaturated bonds is dominated by transition metal catalysis. Compared with transition metals, the use of other metals is less explored, especially so for the s-block elements despite their ready availability and low cost. Here, we show that group 2 metal amides (M[N(SiMe3)(2)](2), M = Mg, Ca, Sr, Ba) unexpectedly catalyse the hydrogenation of aldimines with H-2 at 80 degrees C and a remarkably low H-2 pressure of 1-6 bar. Conversion rates increase with metal size: Mg < Ca < Sr < Ba (for Ba, quantitative conversion is reached within 15 min). The key to this catalysis is the unanticipated formation of metal hydride species by deprotonation of H-2 (pK(a) approximate to 49) with a weak base M[N(SiMe3)(2)](2) (HN(SiMe3)(2): pK(a) approximate to 25.8). Density functional theory calculations suggest that the most favourable pathway indeed involves metal hydride intermediates. The efficient alkaline earth metal-catalysed hydrogenation of imines with molecular hydrogen at remarkably low pressure provides an attractive alternative to transition metal catalysis.