Surfactant-accelerated asymmetric transfer hydrogenation with recyclable water-soluble catalyst in aqueous media

Water-soluble ligands (R,R)-2 were successfully prepared, in which the bis-meta-sulphonated ligand was definitely detected as the major product. The corresponding transition-metal complexes containing the ligands displayed excellent catalytic performance in asymmetric transfer hydrogenation (ATH) of aromatic ketones. Especially, the aromatic ketones with a bromine group in the α position could be smoothly reduced to the expected alcohol, keeping the bromine group intact with excellent enantioselectivities (up to 96% ee). The catalyst could be reused at least 21 times without erosion of the enantioselectivity in high conversion. Moreover, it was found that cationic surfactant and proper pH values were necessary for the maintenance of high reactivity.