研究室工作進展 Jun. 11th, 2019

Scandium-Promoted Direct Conversion of Dinitrogen into 

Hydrazine Derivatives via N−C Bond Formation

Ze-Jie Lv, Zhe Huang, Wen-Xiong Zhang,* and Zhenfeng Xi*

J. Am. Chem. Soc. 2019 , 141, 8773−8777.

Most N-containing organic compounds are currently synthesized through ammonia (NH3), the product of the Haber−Bosch process that converts N2 and H2 to NH3 using metal catalysts under high temperature and pressure. Direct conversion of N2 into high-value N-containing organic compounds, not through NH3, is of great significance and challenging both fundamentally and practically. Although some progress in making C−N bonds through N2 –metal complexes and carbon-based reagents have been reported in the literature, such an approach is still in its infancy. In this work we report a highly efficient scandium-mediated synthetic cycle affording hydrazine derivatives (RMeN−NMeR’) directly from N2 and carbon-based electrophiles. The cycle includes three main steps: (i) reduction of a halogen-bridged discandium complex under N2 leading to a (N2)3− -bridged discandium complex via a (N2)2− intermediate; (ii) treatment of the (N2)3− complex with methyl triflate (MeOTf), affording a (N2Me2)2− -bridged discandium complex; and (iii) further reaction of the (N2Me2)2− complex with the carbon-based electrophile, producing the hydrazine derivative and regenerating the halide precursor. Furthermore, insertion of a CO molecule into one Sc−N bond in the (N2Me2)2− −scandium complex was observed. Most notably, this is the first example of rare-earth metal-promoted direct conversion of N2 to organic compounds; the formation of C−N bonds by the reaction of these (N2)3− and (N2Me2)2− complexes with electrophiles represents the first case among all N2−metal complexes reported.

目前幾乎所有人工合成的含氮有機化合物都是基于合成氨。而傳統的工業合成氨（NH3）過程 (Haber-Bosch Process)條件極其苛刻，據推算年耗能占全球能耗的2%左右，消耗約25%的化石資源，産生大量溫室氣體。因此，将氮氣直接轉化為含氮有機化合物，而不經過NH3, 是解決以上問題的重要途徑之一（見中文綜述：從氮氣直接合成含氮有機化合物，李嘉鵬 殷劍昊 俞超 張文雄 席振峰，化學學報2017, 75, 733-743）。但相關文獻報道很少, 催化反應體系還沒有實現。

本工作報道了稀土金屬钪促進的直接由氮氣、MeOTf和親電試劑等有機底物反應高效合成肼衍生物的過程，分離和表征了(N2)2−-, (N2)3−-和(N2Me2)2−-Sc中間體，并發現CO能有效插入(N2Me2)2−-Sc中間體的Sc−N鍵中，實現了N2與CO的高效偶聯。

本工作首次實現了稀土金屬促進的從氮氣直接合成含氮有機化合物，并為四取代和15N标記的肼衍生物的制備提供了新方法。将該計量反應轉化為催化過程是我們的下一個重要研究目标。