LiAlH4 : From Stoichiometric Reduction to Imine Hydrogenation Catalysis.

Imine-to-amine conversion with catalytic instead of stoichiometric quantities of LiAlH4 is demonstrated (85 °C, catalyst loading≥2.5 mol %, pressure≥1 bar). The effects of temperature, pressure, solvent, and catalyst modifications, as well as the substrate scope are discussed. Experimental investigations and preliminary DFT calculations suggest that the catalytically active species is generated in situ: LiAlH4 +Ph(H)C=NtBu→LiAlH2 [N(tBu)CH2 Ph]2 . A cooperative mechanism in which Li and Al both play a prominent role is proposed.