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 Ts-EN ligands functionalized with trialkylammonium side groups H2N(CH2)2NHSO2-p-C6H4CH2[NMe2(CnH2n+1)]+ ([HLn]+, n = 8, 16) was obtained. The corresponding new surface active complexes [(p-cymene)RuCl(Ln)] and [Cp*RhCl(Ln)] were prepared and characterized. For n = 16 micelles are formed in water at concentrations as low as 0.6 mM, as demonstrated by surface tension measurements. The complexes were used for catalytic transfer hydrogenation of ketones using formate in water. Highly active catalytic systems were obtained in the case of complexes bearing C16 tails due to their ability to adsorb at the water/substrate interface. The scope of these catalytic systems in aqueous solutions was extended from partially water-soluble aryl-alkyl ketones (acetophenone, butyrophenone) to hydrophobic dialkyl ketones (dodecanone-2).