Selective Hydrogenation of Nitriles to Secondary Imines Using a Pincer Manganese Complex

An earth‐abundant manganese‐based pincer phosphine complex (Ph‐PNP)Mn(Br)(CO) 2 , (Ph‐PN P = bis(2‐(diphenylphosphaneyl)ethyl)amine) Mn‐1 catalyzed selective hydrogenation of nitriles to secondary imines is reported. The reaction proceeds in the presence of catalytic base under H 2 pressure generating NH 3 as a byproduct. An optimized loading of 2 mol% Mn‐1, 20 mol% KO t Bu revealed hydrogenation of benzonitrile to corresponding N ‐benzylidenenbenzylamine in 92% yield after 24 h at 140°C in toluene under 40 bar H 2 . A wide range of substituted benzonitriles could be hydrogenated to corresponding secondary imines in good to excellent yields under the reaction conditions. The substrate scope displayed promising outcome for heteroaromatic nitriles but poor yields for aliphatic nitrile hydrogenation. Notably, the reaction does not lead to further hydrogenation of intermediate imines to form secondary amines. Stoichiometric evidences and computational studies indicate possible mechanism involving metal–ligand cooperative H 2 activation and subsequent transfer of H 2 to unsaturated nitrile moiety.