Selectivity in Metal-Catalysed Hydrogenation

摘要: The many factors that influence selectivity in metal-catalysed reaction are reviewed. Alka-1,3-diene hydrogenation occurs by 1:2- and 1:4-addition; the extent of 1:2-addition is determined electronegativity metal but electronegative additives promote I:4-adition at expense 1:2-addition. In α,β-unsaturated aldehyde saturation carbon-carbon double bond normally favoured over carbon-oxygen bond, cause formation Mδ+ carbonyl to (desired) unsaturated alcohol. Detailed evidence presented show influenced molecular congestion ad-layer, surface, hydrogen occlusion bulk metallic crystallites as a result their defective structure. Selectivity always degraded side reactions such reactant polymerisation isomerisation alkyne hydrogenations. Adsorption chiral modifiers, particularly naturally occurring alkaloids, onto achiral surfaces supported metals, induces enantioselectivity; mechanism pyruvate ester cinchona-modified Pt discussed detail. Platinum crystals cut so expose adsorb L- D-sugars differently, this recognition leading differences oxidation. thus total environment catalytically active sites.