Asymmetric Hydrogenation with Modified Raney Nickel. I. Studies on Modified Hydrogenation Catalyst. II

Abstract

1. Raney nickel catalyst treated with optically active glutamic acid has the property of catalyzing the hydrogenation of carbonyl compounds asymmetrically with high reproducibility and efficiency. 2. Excellent results were obtained in the hydrogenation of methyl acetoacetate to optically active methyl 2-hydroxybutyrate in the presence of Raney nickel catalyst treated with l- or d-glutamic acid. 3. The capacity for asymmetric hydrogenation was strongly dependent upon the pH of the modifying solution. The highest capacity was obtained when modifying solutions were adjusted to pH 4.8∼5.5. 4. With elevation of the temperature of the modifying process, the asymmetric capacity of the catalyst decreased markedly, nearly disappearing at 60°C, and yielding products with reverse optical rotation above 80°C. 5. The asymmetric capacity was independent of the concentration of the modifying solution within the range of 6 to 0.0625%. 6. Hydrogenation in the presence of catalyst modified with d-glutamic acid yielded a product with reverse optical rotation to that obtained when l-glutamic acid was used. 7. Asymmetric yield of the reducing product of methyl acetoacetate by the catalyst treated with Glu was varied with the relative amount of the substrate and the catalyst.

Enantioselective Heterogeneous Catalysis

“…As adsorbate-induced restructuring of metal surfaces by chiral molecules is well known to redistribute surface metal atoms into a chiral arrangement (e.g., (S)-lysine on Cu{1 0 0} [96]), the corrosion of Ni by acidic modifiers is highly likely to yield a chiral distribution of surface atoms in the metallic component. Under conditions that optimize the enantioselectivity of aspartate-modified Ni catalysts for β-ketoester hydrogenation [97], the aspartate coverage has been found to be vanishingly small [66,98], implying that chiral Ni sites are responsible for enantioselectivity in this system. However, there is no evidence that the chiral kink sites influence the behavior of neighboring terrace sites via amplification effects [98].…”

Enantioselective Hydrogenation of α,β-Unsaturated Carboxylic Acids：Effects of Palladium Particle Size and Support Acidic Property

“…[5] The highly efficient enantioselective hydrogenation of ketones to optical alcohols over chirally modified metal catalysts has been well established in industry. [6][7][8][9][10][11] However, the equally important enantioselective hydrogenation of α,β-unsaturated carboxylic acids was less studied. [12,13] Chirally modified palladium catalysts, which were used in various enantioselective reactions, [14][15][16][17] were shown to be effective for enantioselective hydrogenation of aryl-substituted α,β-unsaturated carboxylic acids with the ee values of more than 90%.…”

Asymmetric heterogeneous catalytic hydrogenation; is it a useful tool for the synthetic organic chemist?

“…9 The most significant stages of these processes are the following: The unequal competition is still going on, the number of publications characterises the situation, papers about asymmetric homogeneous catalysed hydrogenations are at least ten times as much as those about heterogeneous asymmetric hydrogenations. The latter papers however indicate a firm development, not only in numbers but in the scope and efficiency of this research.…”