Asymmetrische katalysen L. Heterogene enantioselektive hydrierungen mit immobilisierten rhodium(I)-komplexen

Abstract

The supports BaSO 4, cellulose, silica gel, aluminum oxide, AgCl, and charcoal are impregnated with the complexes [Rh(COD)(−)-Diop]PF 6, [Rh(COD)(−)-Norphos]PF 6 and [Rh(COD)(+)-Norphos]PF 6, so that they are insoluble under the reaction conditions. These catalysts hydrogenate the substrate ( Z)-α- N-acetamidocinnamic acid (AAZ), dissolved in aqueous NaOH, with up to 79% ee to N-acetylphenylalanine (AcPhe). On repeated use of the [Rh(COD)(−)-Diop]PF 6 systems optical induction decreases, whereas it increases with the [Rh(COD)(−)-Norphous]PF 6 and [Rh(COD)(+)-Norphos]PF 6 systems in the first re-uses. The hydrogenation activity of all the catalysts declines on repeated use. The cations of the complexes [Rh(COD)(−)-Diop]PF 6, [Rh(COD)(−)-Norphos]PF 6, and [Rh(COD)(+)-Norphos]PF 6 are bound to the strongly acidic ion exchangers v DOWEX HCR-S and DOWEX MSC-1 and to the weakly acidic ion exchangers SERDOLIT CW-18 and SERVACEL CM-32. These catalysts hydrogenate the substrate ( Z)-α- N-acetamidocinnamic acid in aqueous or alcoholic solutions in optical yields of up to 87% ee. The results regarding the repeated use of the catalysts fixed on the ion exchange resins are similar to those obtained with the catalysts fixed on the other supports. N-Acetamidoacrylic acid (AAA) and methyl ( Z)-α- N-acetamidocinnamate (AAZM) are also hydrogenated enantioselectively by the heterogeneous catalysts.