Polymer‐covered SiO ₂ Composite: A New Strategy to Facilitate the Aqueous Asymmetric Transfer Hydrogenation

Abstract Asymmetric transfer hydrogenation (ATH) is an efficient and mild way to obtain chiral compounds. However, the toxic metal ions and the low turnover number (TON) in aqueous ATH limited the further application. We reported a polystyrene‐covered mesoporous SiO 2 supported Noyori's Ru‐TsDPEN named Ru‐PCMS, consisting of an inner mesoporous silica core and an outer organic polystyrene layer, which could promote the aqueous ATH of β ‐keto esters to afford various chiral β ‐hydroxy ester with excellent yields (up to 99%) and ee values (up to 99%). It showed excellent water stability that successfully recycled 8 times without the enantioselectivity reduction and the metal loss.