Anionic metal hydride catalysts. 2. Application to the hydrogenation of ketones, aldehydes, carboxylic acid esters, and nitriles

Article abstract of DOI:10.1021/ja00415a022

The application of the potassium hydrido(phosphine)ruthenate complexes K⁺[(Ph₃P)₂Ph₂-PC₆H ₄RuH₂]^-·C₁₀H ₈·(C₂H₅)₂O (1) and K₂⁺[(Ph₃P)₃(Ph₂P)Ru ₂H₄]^2-·2C₆H ₁₄O₃ (2) as catalysts for the homogeneous phase hydrogenation of a variety of unsaturated organic compounds is described. Ketones and aldehydes are catalytically hydrogenated with 1 and 2 typically at 85°C and under 620 kPa of hydrogen, to yield the corresponding alcohols as well as minor aldol condensation byproducts. The hydrogenation of acrolein, depending on conditions, can give either propionaldehyde or mixtures of propionaldehyde and allyl alcohol. Carboxylic acid esters, which are activated by adjacent electron-withdrawing groups, e.g., CF₃CO₂CH₃, CF₃CO₂CH₂CF₃, (-CO₂CH₃)₂, can be hydrogenated, with 1 and 2, to yield, respectively, CF₃CH₂OH and CH₃OH, CF₃CH₂OH, and HOCH₂CO₂CH₃. Methyl acetate diluted with toluene (1:10 (v/v)) in the presence of 2 is hydrogenated (at 90°C, under 620 kPa of H₂) giving methanol, ethanol, and ethyl acetate (formed by trans-esterification with the ethanol product). This represents the first instance of a homogeneous catalytic hydrogenation of a simple aliphatic ester. Nitriles are hydrogenated with 1 and 2 (at 90°C, 620 kPa of H₂) to give, selectively, primary amines. The rates and achievable conversions for these reactions are dependent upon the solvent medium used and on the nature of the cation associated with the hydridometalate catalysts.