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

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%.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (215 K)Download as PowerPoint slideHighlights► Metallic 3-μm nickel powder catalyst modified with (R,R)-tartaric acid and NaBr. ► Modified catalyst afforded up to 90% ee in the hydrogenation of methyl acetoacetate. ► Chiral modification process activates nickel surface prior to the modification. ► Potentially hazardous pre-activation by hydrogen gas can be avoided.