A highly effective water-soluble polymer-supported catalyst for the two-phase asymmetric hydrogenation: preparation and use of a PEG-bound BINAP ligand

A new type of amphiphilic PEG-bound BINAP ligand was synthesized through polycondensation of 5,5'-diamino BINAP (1), polyethylene glycol and terephthalyol chloride in the presence of pyridine. It was proven that ruthenium complex based on the new polymeric ligand was an effective catalyst for the asymmetric hydrogenation of prochiral alpha,beta-unsaturated carboxylic acids in both ethyl acetate/water two-phase and in methanolic solvent systems. The activity and/or enantioselectivity in two-phase systems were observed to be higher than that in ethyl acetate or methanol-water homogeneous systems. The replacement of water with ethylene glycol increased the activity and enantioselectivity. The activity of the new catalyst was shown to be about 30 times higher in the two-phase hydrogenation of 2-(6'-methoxy-2'-naphthyl)-acrylic acid than the Ru(BINAP-4SO(3)Na) catalyst without the long hydrophilic polymer chain, which illustrated the importance of the amphiphilic structure of the polymeric ligand. (C) 2000 Elsevier Science B.V. All rights reserved.