New ruthenium catalysts containing chiral Schiff bases for the asymmetric hydrogenation of acetophenone
摘要:
A series of new chiral N-4-Schiff bases, containing amine or sulfonamide functionalities has been synthesized. Coupled with ruthenium catalysts, these Schiff bases induce interesting results in the hydrogenation of acetophenone: complete conversion and 76% ee were obtained with the catalytic system Ru(PPh3)(3)Cl-2/(1R,2R)-N,N'-bis-(2-p-tosylaminobenzylidene)-1,2-diphenyl-ethylenediamine. A very important phosphine co-ligand effect was observed on both activity and enantioselectivity of the catalysts. However, without the co-ligand, we obtained an enantioselectivity for the (R)-enantiomer, whereas with nonchiral co-ligand an enantioselectivity for the (S)-enantiomer was observed. (C) 2004 Elsevier Ltd. All rights reserved.