Reduction of Nitriles to Amines with H2 Catalyzed by Nonclassical Ruthenium Hydrides - Water-Promoted Selectivity for Primary Amines and Mechanistic Investigations

Catalytic hydrogenation of nitriles to amines by nonclassical ruthenium hydride complexes derived from PNP pincer ligands is described. Aromatic as well as aliphatic nitriles are reduced to the corresponding primary amines. Hydrogen pressure influences the selectivity for the primary amines. The mechanism of nitrile reduction with nonclassical ruthenium hydride pincer complexes is investigated by DFT calculations. A catalytic cycle involving the coordination of nitrile trans to the pincer backbone after an initial hydride rearrangement at the ruthenium center, and the subsequent first transfer of the hydride ligand to the carbon center of the nitrile ligand is suggested as a possible reaction mechanism. Interestingly, the use of water as additive increases the selectivity for the primary amines and the rate of the reactions.