Enantioselectivity in the Iridium-Catalyzed Hydrogenation of Unfunctionalized Olefins

The iridium-catalyzed asymmetric hydrogenation of largely unfunctionalized olefins has been studied by DFT calculations using a full, experimentally tested combination of ligand and substrate. All possible diastereomeric pathways were considered within four different hydrogenation mechanisms. The effect of a solvent continuum was also considered, and both the gas-phase and solvent-continuum calculations favored the same mechanism. This mechanism passed through Ir III and Ir V intermediates and was consistent with the sense of stereoselection observed experimentally. Comparing the calculations to those performed on a model system permitted an evaluation of the model system’s utility in representing the full one. A simple, general method for predicting the sense of stereoselection in iridium-catalyzed olefin hydrogenation was developed and tested against published data.