Transfer Hydrogenation of Ketones Catalyzed by Surface-Active Ruthenium and Rhodium Complexes in Water

An improved, high-yield, one-pot synthetic procedure for water-soluble ligands functionalized with trialkyl ammonium side groups H2N(CH2)(2)NHSO2-p-C6H4CH2[NMe2(CnH2n+1)](+) ([HLn](+); n=8, 16) was developed. The corresponding new surface-active complexes [(p-cymene)RuCl(L-n)] and [Cp*RhCl(L-n)] (Cp*=(5)-C5Me5) were prepared and characterized. For n=16 micelles are formed in water at concentrations as low as 0.6mM, as demonstrated by surface-tension measurements. The complexes were used for catalytic transfer hydrogenation of ketones with formate in water. Highly active catalyst systems were obtained in the case of complexes bearing C-16 tails due to their ability to be adsorbed at the water/substrate interface. The scope of these catalyst systems in aqueous solutions was extended from partially water soluble aryl alkyl ketones (acetophenone, butyrophenone) to hydrophobic dialkyl ketones (2-dodecanone).