Synthesis of Ru(II) complexes containing N-heterocyclic carbenes functionalized with secondary donor groups: Catalytic activity toward enantioselective transfer hydrogenation

• Hydroxy-amide-functionalized NHC–Ru(II) complexes have been synthesized.
• A potential application of the Ru complexes was explored in the asymmetric reduction.
• The effect of varying the η6-arene ligands on the Ru complex was investigated.
• The hydroxy functionality on the NHC ligand was found to be of critical importance.

A series of new N-heterocyclic carbene (NHC)–Ru(II) complexes functionalized with additional hemilabile donor groups, such as a hydroxy-amide group, were successfully synthesized and structurally characterized. Preliminary studies indicated that the complexes acted as precatalysts with moderate activity in the asymmetric transfer hydrogenation at room temperature without temperature control. The investigation of the effect of varying the η6-arene ligands showed that these ligands appeared to significantly alter the activity of the complexes as precatalysts. Furthermore, it was revealed that the hydroxy functional group on the NHC ligand side-arm not only induced the stereoselectivity of the reaction but also enhanced the reaction rate.

A series of new N-heterocyclic carbene–Ru(II) complexes functionalized with a hydroxy-amide group were successfully synthesized. The Ru(II) complexes catalyzed asymmetric transfer hydrogenation reaction at room temperature.Figure optionsDownload as PowerPoint slide