RuII-SDP-Complex-Catalyzed Asymmetric Hydrogenation of Ketones. Effect of the Alkali Metal Cation in the Reaction

Abstract
The RuII complexes of SDP and DPEN combined with t-BuOK in 2-propanol formed a very effective catalyst for the hydrogenation of simple aromatic ketones with high activity and enantioselectivity. The racemic α-arylcycloalkanones can also be hydrogenated by this system, providing α-arylcycloalkanols in excellent cis/trans stereoselectivity (>99:1) and enantioselectivity (up to 99.9%) for the cis isomer. In the study of the effect of the alkali metal cation in the hydrogenation of acetophenone using RuCl2(Tol-SDP)(DPEN) and RuCl2(Xyl-SDP)(DPEN) catalysts, we found that t-BuONa provided a faster reaction than t-BuOK, which indicated that the sterically hindered diphosphine ligands preferred the base with the smaller metal cation.

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