LiAlH 4 ‐catalyzed Imine Hydrogenation with Dihydrogen: New DFT Mechanistic Insights

Recently, it was found that the widely used stoichiometric reducing reagent LiAlH 4 can also be used as a useful catalyst for imine hydrogenation with H 2 under relatively mild conditions. In this work, extensive state‐of‐the‐art DFT calculations are conducted to explore the detailed catalytic mechanism. In sharp contrast to the recent proposal involving heterolytic H 2 ‐activation over Al−N amide bonds after multiple imine insertion, our new mechanism highlights the dual role of the Lewis‐acidic lithium cation in frustrated‐Lewis‐pair‐like activation of both imine substrate and H 2 when combined with the aluminum‐bound hydride and amide ligands, respectively. Ionic Li−N amide bonds are about 13 kcal/mol more reactive than Al−N amide bonds for H 2 activation, thus providing a useful structural feature for rational design of active hydrogenation catalysts.