Inhibiting deactivation of iridium catalysts with bulky substituents on coordination atoms

Introducing bulky groups on the coordination phosphorus atoms can effectively block the formation of inactive dimer species and improve the activity of the iridium catalysts. Results of ESI-MS analysis gave strong evidence. This strategy was successfully applied to the asymmetric hydrogenation of quinolines with up to 93% ee on S/C ratio of 25,000.