Kinetic Studies of the Asymmetric Transfer Hydrogenation of Imines with Formic Acid Catalyzed by Rh−Diamine Catalysts

Kinetic studies of the asymmetric transfer hydrogenation of imines with HCOOH using Rh−chiral diamine catalysts reveal anomalous concentration dependences attributed to the participation of both reactant and product in the formation of formate salts. The resting state of the catalyst is suggested to be the Rh hydride species 5. The role of bases such as Et3N in metering HCOOH into the catalytic cycle is discussed. A practical reaction protocol for achieving high productivity based on slow addition of HCOOH is presented. These studies highlight the value of in situ reaction monitoring techniques in developing a detailed mechanistic picture of a complex reaction system.