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

• Published in: Chemistry : a European journal 2014-01, Vol.20 (3), p.846-854
• Main Authors: Kalsin , Alexander M., Peganova, Tat'yana A., Novikov, Valentin V., Zhamoytina, Alexandra I., Gonsalvi, Luca, Peruzzini, Maurizio
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Bearing; Catalysts; Chemistry; Emissions; Formates; Hydrogenation; Ketones; Ligands; micellar catalysis; Rhodium; Ruthenium; water-soluble ligands
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201301679

An improved, high‐yield, one‐pot synthetic procedure for water‐soluble ligands functionalized with trialkyl ammonium side groups H2N(CH2)2NHSO2‐p‐C6H4CH2[NMe2(CnH2n+1)]+ ([HLn]+; n=8, 16) was developed. The corresponding new surface‐active complexes [(p‐cymene)RuCl(Ln)] and [Cp*RhCl(Ln)] (Cp*=η5‐C5Me5) 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 with formate in water. Highly active catalyst systems were obtained in the case of complexes bearing C16 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). Micellar catalysts for the transfer hydrogenation of ketones were developed by using tosylethylenediamine‐type ligands functionalized with ammonium side groups bearing alkyl chains (Cn), which were synthesized in high yields by an improved one‐pot procedure, to prepare surface‐active complexes [(p‐cymene)RuCl(Ln)] (RuLn) and [(η5‐C5Me5)RhCl(Ln)]. The complexes catalyze the transfer hydrogenation of water‐soluble and insoluble ketones with formate in water, owing to their ability to be adsorbed at the water/substrate interface (see figure).