Asymmetric transfer hydrogenation (ATH) of prochiral aromatic ketones was carried out with a water-soluble complex of Rh(III)Cp* and mononitrobenzenesulfonamide bidentate ligand (1R,2R)-N-(2-aminocyclohexyl)-4-nitrobenzenesulfonamide 1 derived from chiral cyclohexane-1,2-diamine. Aqueous sodium formate was used as the hydride source. The reaction afforded the chiral alcohols in good enantioselectivities (79-93%) and yields (>99%). The modified monosulfonamide ligand was also covalently immobilized on solid phase such as silica, resin, and mesoporous SBA-15 silica and then explored as a catalyst with Rh(III)Cp* in the ATH of acetophenone.
Ligands L1 and L2 were synthesized from commercially available (R)-(+)-1,1’-binaphthyl-2,2’-diamine and tested with RhIIICp* as catalysts in the asymmetric transfer hydrogenation of aromatic ketones in aqueous sodium formate. The results were compared with ligands derived from 1,2-, 1,4-, and 1,6-diamines, and correlated to the metal chelate ring size and the N-N torsion angles determined by theoretical calculations.
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