Impact of Protic Ligands in the Ir-Catalyzed Dehydrogenation of Formic Acid in Water

New Ir-IPr complexes featuring a variety of chelate ligands, some of them featuring NH moieties, were synthesized. These complexes proved to be efficient catalysts for the dehydrogenation of formic acid in DMF and H2O. The dehydrogenation rates were dependent on the nature of the ligands that accompany IPr in the coordination sphere of the metal. In fact, complexes that contain protic ligands, namely, [Ir(8aminoquinoline)(H)(2)(IPr)(PPhMe2)]BF4 and [Ir(CH3CN)(2-phenylimidazole)(H)(IPr)(PPhMe2)]BF4, showed the best activities in H2O. The former, which presents an NH2 group bound to the Ir center, is the most active (in H2O) of the catalysts presented in this work and can be recycled up to 10 times without an apparent loss of activity. This behavior may be attributed to the robust ligand system and, likely, to its ability to establish outer-sphere interactions. This postulation is supported by the fact that complex [Ir(8-dimethylaminoquinoline)(H)(2)(IPr)(PPhMe2)]BF4, which features an -NMe2 instead of an -NH2 donor group, gives rise to a strikingly lower catalytic activity.