Simplified preparation of chirally modified nickel catalyst for enantioselective hydrogenation: A step forward to industrial use

摘要

A chirally modified nickel catalyst for the enantio-differentiating hydrogenation of β-ketoesters is conventionally prepared by immersing the pre-activated metallic nickel into an aqueous solution of enantiopure tartaric acid (so called "modification step"). During the pre-activation step, nickel precursor is commonly treated with hydrogen gas at elevated temperatures of up to 473 K. The X-ray photoelectron spectral examinations of chirally modified nickel catalysts obtained under the different modification conditions revealed that the chiral modification process itself plays a major role in activating the nickel surface whilst the pre-activation procedure is a less important factor. The corresponding enantio-differentiating hydrogenations of methyl acetoacetate in the liquid phase using the prepared chiral catalysts unambiguously confirmed this conclusion, providing quantitative conversions and high enantioselectivities of up to 90%.