Asymmetric Transfer Hydrogenation of Imines and Ketones Using Chiral RuIICl(η6-p-cymene)[(S,S)-N-TsDPEN] as a Catalyst: A Computational Study

Abstract

Density functional theory (DFT) computational methods were used to investigate the increasingly popular ionic mechanistic concept for the asymmetric transfer hydrogenation of imines on the chiral catalyst RuIICl(η6-p-cymene)[(S,S)-N-p-tosyl-1,2-diphenylethylenediamine]. On application of the ionic mechanism, the reaction preferentially affords the (R)-amine product, which is in agreement with the experimental observations. Calculated transition state structures for the hydrogenation of protonated 1-methyl-3,4-dihydroisoquinoline are discussed together with their preceding and following energy minima. Stabilization of the favorable transition state by a CH/π interaction between the η6-p-cymene ligand and the substrate molecule is explored in depth to show that both C(sp2)H/π is more probable than C(sp3)H/π in this molecular system. Finally, transition state geometries for the asymmetric transfer hydrogenation of acetophenone are proposed, which take the “standard” six-membered cyclic form.