On the Origin of Magnesium-Enchanced Synthesis of N,N-Diisopropylethylamine As Catalyzed By ZnCl2: A Combination of Theoretical and Experimental Study

Aminolysis of haloalkanes continues to be an attractive approach to make C-N bonds. In the past decades, various catalysts involving metal center such as Pd and Cu have been used for making C-N bonds, while the preparation of hindered non-nucleophilic amine is still challenging. In this work, we developed a strategy concerning magnesium-enchanced, ZnCl₂-catalyzed preparation of diisopropylamine (DIPEA) from ethyl chloride and diisopropylamine. To investigate the enhancing effect of magnesium, the catalyst combination such as Mg/ZnCl₂, Zn/MgCl₂, Zn/ZnCl₂ were characterized by XPS. According to XPS results, it can be speculated that the charge transfer from magnesium to the reactive center matters for its promotion effect. Further mechanism was studied using DFT. According to the calculations, the C-N coupling process in all selected systems proceeds in an ethylium-transfer mode, and the electronic origins for the enhancing effect of magnesium was discussed. Generally, this enhancement effect can be attributed to the magnesium-induced lowing of the reaction barriers for the processes taking place at the Lewis acid centers. Our results highlight a promising new class of low-cost, abundant metal catalysts for building C-N bonds.