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 H 2 N(CH 2 ) 2 NHSO 2 ‐ p ‐C 6 H 4 CH 2 [NMe 2 (C n H 2 n +1 )] + ( [HL n ] + ; n =8, 16) was developed. The corresponding new surface‐active complexes [( p ‐cymene)RuCl( L n )] and [Cp*RhCl( L n )] (Cp*=η 5 ‐C 5 Me 5 ) were prepared and characterized. For n =16 micelles are formed in water at concentrations as low as 0.6 m M , 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).