Mechanism of the asymmetric hydrogenation of exocyclic α,β- unsaturated carbonyl compounds with an iridium/BiphPhox catalyst: NMR and DFT studies

The mechanism of the asymmetric hydrogenation of exocyclic α,β-unsaturated carbonyl compounds with the (aS)-Ir/iPr-BiphPhox catalyst was studied by NMR experiments and DFT computational analyses. Computed optical yields of the asymmetric hydrogenation proceeding by an iridium(I)/iridium(III) mechanism involving a transition state stabilized through two intramolecular hydrogen bonds are in good accordance with the experimental ee values. H in a fix: The title studies show an equilibrium of dinuclear iridium hydrides at low temperature after hydrogenation of the precatalyst. Computations of the conceivable R and S pathways allowed elucidation of the mechanism for enantioselection, thus affording computed optical yields which are consistent with the experimental values. The structure S1 features hydrogen bonding between the catalyst and the carbonyl group of the substrate.