Hydrogenation of carbon–nitrogen double bonds

Despite these challenges, methods have been developed that address particular substrate classes, such as N-aryl, N-alkyl, and endocyclic imines.

Relevant to the inner sphere mechanism are the two modes by which imines can coordinate, as a π or as a σ-donor ligand.

Examples:[6][7][8][9][10] [11] Ruthenium(II) complexes of amine ligands are known for engaging in the outer-sphere mechanism, during which the imine/iminium substrate does not bind to the metal center directly.

However, catalyst systems have been developed that catalyze hydrogenation of particular classes of imines with high enantioselectivity and yield.

A key step in its industrial production involves the enantioselective reduction of an N-aryl imine.

This reduction is achieved with extremely high turnover number (albeit moderate enantioselectivity) through the use of a specialized catalyst system consisting of [Ir(COD)Cl]2, modified Josiphos ligand 3, and acid and iodide additives.