Dithiourea ligands in the rhodium-catalyzed hydride-transfer reduction of ketones - A theoretical and experimental approach

Various dithioureas bearing an aromatic ring on their terminal nitrogen ato ms have been synthesized. These have been tested in the asymmetric reductio n of ketones as catalyzed by a rhodium complex. The influence of electron-w ithdrawing and electron-donating substituents on the aromatic rings on the reactivity and the enantiomeric excess (ee) has been assessed. The coordina tion modes of a model thiourea have been studied by Density Functional Theo ry (DFT) calculations. The electronic effects have also been analyzed and a n interpretation of the variation in the enantiomeric excess, based on a su pposed change in the coordination mode, is given.