Asymmetric transfer hydrogenation of carbonyl compounds catalyzed by rhodium nanoparticles
Abstract Transfer hydrogenation of acetophenone and methyl benzoylformate with 2-propanol has been studied on rhodium nanoparticles obtained by the reduction of rhodium(I) complexes in the presence of optically active compounds, including chiral diamine S , S -DIODMA, (4 S ,5 S )- N 4 , N 4 , N 5 , N 5 ,2,2-hexamethyl-4,5-bis-(aminomethylene)-1,3-dioxolane, quaternary diammonium salt (4 S ,5 S )-(-)- N 1 , N 4 -dibenzyl-2,3-dihydroxy- N 1 , N 1 , N 4 , N 4 -tetramethylbutane-1,4-diammonium dichloride, and (8 S ,9 R )-(-)-cinchonidine. Increasing the modifier to Rh ratio leads to an increase in the enantiomeric excess ( ee ) of the reaction products. The greatest ee values (43.8% for ( R )-1-phenylethanol and 58.2% for the methyl ester of ( R )-mandelic acid) were achieved at (8 S ,9 R )-(-)-cinchonidine/Rh ratios of 9:1 and 3:1, respectively.