Chiral phosphino- and (phosphinooxy)-substituted N-heterocyclic carbene ligands and their application in iridium-catalyzed asymmetric hydrogenation

摘要

Enantiomerically pure iridium complexes with phosphino- and (phosphinooxy)-substituted N-heterocyclic carbene (NHC) ligands were synthesized. Investigation of their electronic properties showed a similar trans influence of the phosphino (or phosphinooxy) and the NHC units. The complexes were tested in iridium-catalyzed hydrogenation. While low conversions were observed with unfunctionalized olefins, the catalysts proved to be suitable for hydrogenation of the alpha,beta-unsaturated ester 20, allylic alcohol 21, and imine 22. The enantioselectivities were, however, moderate.