Substituent effects in enantioselective hydrogenations catalyzed by immobilized Rh complexes

Differently substituted [Rh(S,S)BDPP]PF6 complexes were immobilized on Al2O3 support, via a modified Augustine method. The heterogenized catalysts were successfully applied in the hydrogenation of (Z)-α-acetamidocinnamic acid and its methyl ester. The ligand basicity was varied with the different substituents and the electronic tuning could improve the activity and the selectivity of the studied reaction. Additionally the immobilized catalysts can be reused in several subsequent experiments without any significant loss of catalytic properties.