Reductions of carboxylic acid derivatives by silanes in the presence of rhodium complexes were studied. Carboxylic esters were reduced to alcohols by diphenylsilane catalyzed by [RhCl(cod)]2/4PPh3 or [RhCl(PPh3)3] at room temperature in up to 99% yields. For example, ethyl decanoate and ethyl phenylacetate were converted to decanol and 2-phenylethanol in 98 and 92% yields, respectively. Carboxylic acids were also reduced by this reducing system to the corresponding alcohols in high yields. Furthermore, N-monosubstituted amides were reduced to secondary amines in moderate to good yields. For sterically hindered amides, the yields were moderate, and imines were produced in competitive yields.

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Ruthenium complexes, prepared by mixing the potassium salt of a-amino acids and [RuCl 2 (arene)] 2 , acted as catalysts for the asymmetric transfer hydrogenation of ketones from 2-propanol in the presence of KOH. For example, the transfer hydrogenation of acetophenone from 2-propanol was catalyzed effectively by the ruthenium complex prepared from potassium L-prolinate and [RuCl 2 (p-cymene)] 2 to give (R)-1-phenylethanol in 72% yield with 81% ee. The yields and enantioselectivities of the product were influenced strongly by the structure of the a-amino acidate ligand, arene ligand, and substrate, by the amount of additional base, and by the concentration of the substrates. The best enantiomeric excesses of the products was 92%, when 1-tetralone was subjected to this reaction using a prolinated ruthenium complex bearing p-cymene. Furthermore, the potassium salts of dipeptides were tested as a ligand for this transfer hydrogenation.