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The state of the art for the enantio-differentiating hydrogenation over an asymmetrically modified nickel catalyst is reviewed along with the background development of the catalyst. An enantioselectivity up to 98% was obtained for the hydrogenation of β-functionalized ketones. The durability of the enantioselectivity was significantly improved using an in-situ-modified nickel powder catalyst (80-90% enantioselectivity for over 20 runs). Recent mechanistic investigations based on surface science are also summarized for the discussion of the enantio-differentiating model.

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The role of acetic acid added to the reaction media for the enantio-differentiating hydrogenation of methyl acetoacetate over a (R,R)-tartaric acid-in-situ-modified nickel catalyst was studied from the viewpoint of the hydrogenation rate during repeated runs. The hydrogenation of methyl acetoacetate on the ''enantio-differentiating sites'' of a tartaric acid-modified nickel catalyst was specifically accelerated by the acetic acid added to the reaction media to increase the enantio-differentiating ability of the catalyst. In order to increase the enantio-differentiating ability, the addition of acetic acid to the reaction media was required in each run during the repeated use of the catalyst.