A cationic rhodium(l) catalyst bearing the air-stable and crystalline diphosphine 1 ,l'-bis-(diisopropylphosphino)ferrocene (1, DiiFc) allows the hydrogenation of aldehydes and ketones under mild conditions. The preparation of alcohols through reduction of the carbon-oxygen double bond of aldehydes and ketones is one of the most fundamental and useful transformations in organic chemistry. In contrast to the multitude of effective stoichiometric reagents available for the reduction of aldehydes and ketones, very few general and efficient catalytic methods are known.1 In terms of ease, efficency, and commercial viability, catalytic hydrogenation represents one of the most attractive procedures for reduction. Although several homogeneous hydrogenation catalysts have been reported for carbonyl reduction, these generally require high pressures, high temperatures, or the use of air-sensitive trtalkylphosphine ligands that are not readily available.2-5 While the advantages of hydrogenation over stoichiometric hydride reducing agents are apparent, no aldehyde or ketone hydrogenation catalyst has yet been developed into a useful synthetic tool for the practicing organic chemist. We now report that the cationic rhodium complex [(COD)Rh(DiPFc)]+OTf-bearing the airstable and crystalline diphosphine l,l'-bis(diisopropylphosphino)ferrocenes (1, DiPFc) behaves as a very efficient catalyst precursor for aldehyde and ketone hydrogenations. For example, benzaldehyde was smoothly converted to benzyl alcohol under mild conditions (25oC. 30 psi HP, S/C 500, 3h) and in essentially quantitative yield. The hydrogenation of acetophenone occurred under similarly mild conditions (25cC, 60 psi HP, S/C 450, 4 h), and again in essentialfy quantitative yield. In contrast, the analogous catalyst derived from 1,i '-bis(diphenylphosphino)ferrocene afforded less than 5% acetophenone reduction product under otherwise identical conditions. While 1 ,l'-bis(dialkylphosphino)ferrocene ligands previously have been used in olefin hydrogenations,7 no report of their use in ketone hydrogenations has appeared. Studies aimed at optimizing the efficiency of ketone hydrogenations revealed the influence of solvent, concentration, and pressure on the rate of acetophenone reduction. Protic solvents (i.e., MeOH, EtOH) appear to be required as incomplete conversion and catalyst inactivation were observed in solvents such as CH&l2, EtOAc, and THF. Complete conversion was observed only