Chiral NHC-Complexes with Dioxolane Backbone Heterogenized on MCM-41. Catalytic Activity

Rhodium, palladium, and gold complexes of chiral (NHC)-dioxolane-amino ligands were prepared. Herein, new methods for the heterogenization of NHC-chiral complexes on porous silica supports are demonstrated for the facile recovery and recycling of these expensive catalysts. Activity, selectivity, and recyclability were investigated and compared to that of the analogous homogeneous catalysts for asymmetric hydrogenation reactions. The compounds were characterized by using a variety of methods, including solid state cross-polarization magicangle spinning (CP MAS) C-13 NMR, FT-IR spectroscopy, and elemental analysis. Heterogenized rhodium(I) and palladium(II) catalysts could be used at least four times without loss of activity or enantioselectivity. (NHC)-gold(I) complexes were easily immobilized and recycled by a treatment with benzonitrile during the washing steps between cycles. This washing maintained the activity and enantioselectivity.