ausblenden:
Schlagwörter:
asymmetric catalysis;
hydrogenation;
ionic liquids;
phosphane ligands;
rhodium
Zusammenfassung:
The continuous-flow Rh-catalyzed asymmetric hydrogenation of the enol ester 1-(trifluoromethyl)vinyl acetate was investigated by using supercritical carbon dioxide (scCO2) as the mobile phase and either ionic liquids (IL) or supported ionic liquids (SILP) as the catalyst matrix. Three molecular catalysts based on chiral ligands were evaluated. The catalyst based on the phosphine-phosphoramidite ligand (Sa,Rc)-Xyl-QUINAPHOS in combination with the SILP/scCO2 immobilization strategy provided the most effective system under continuous-flow conditions and gave a remarkably stable performance. During 233 h on stream, high single-pass conversions (90–70 %), slightly increased enantioselectivity (80–84 % ee), and a turnover number of 70 400 were observed; this turnover number shows a six-fold increase over that achieved in the IL/scCO2 system with the same catalyst.
