Preparation of the enantiopure 1,2-diamine monomer and its polymerization: The efficient polymeric chiral ligand of an asymmetric hydrogenation catalyst

An enantiopure 1,2-diamine monomer possessing a p-vinylbenzyl group as a polymerizable group was synthesized from chiral 1,2-bis(p-hydroxyphenyl)-N,N'-bis(tert-butoxycarbonyl)-1,2-diaminoethane. The chiral monomer was copolymerized with styrene, and this was followed by the deprotection of the tert-butoxycarbonyl group, which yielded the polymer-supported chiral 1,2-diamine. The polymeric catalyst system was established with the polymeric chiral 1,2-diamine complexed with 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl/RuCl2. In the presence of potassium tert-butoxide (t-BuOK), the polymeric catalyst system worked well in the asymmetric hydrogenation of aromatic ketones. The corresponding chiral secondary alcohols were obtained in quantitative yields with a high level of enantioselectivity. The insolubility of the catalyst, caused by the crosslinked structure of the polymer, made it recyclable. The polymeric catalyst was reused several times without a loss of catalytic activity. (C) 2004 Wiley Periodicals, Inc.