text: Relevant to the inner sphere mechanism are the two modes by which imines can coordinate, as a π or as a σ-donor ligand.  The pi-imines are also susceptible to conversion to iminium ligands upon N-protonation. The binding mode for the imine is unclear, both η (σ-type) and η (π-type). The final step in the mechanism is release of the amine. In some iridium-catalyzed hydrogenations, the mechanism is believed to proceed via a monohydride species.  The oxidation state of iridium is always +3.
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