Heterogeneous asymmetric hydroformylation of olefins on chirally modified Rh/SiO2 catalysts

Heterogeneous chiral catalysts were prepared by modifying silica-supported rhodium (Rh/SiO2) with chiral phosphorus ligands. The chirally modified Rh/SiO2 catalysts exhibited high activity, regioselectivity, and enantioselectivity for the asymmetric hydroformylation of styrene and vinyl acetate. Up to 72% ee and 100% selectivity of branched aldehyde for the hydroformylation of vinyl acetate were obtained for (R)-BINAP-Rh/SiO2 catalysts. It is noteworthy that the modification of Rh/SiO2 with (S,S)-DIOP resulted in increased activity for the hydroformylation of vinyl acetate and gave a TOF of 128 h-1, even higher than that of the unmodified Rh/SiO2 catalyst (90 h-1). It is found that chiral modifiers with bidentate phosphines and an optimized modifier/rhodium molar ratio close to 1.0 were prerequisites for chiral induction on the chirally modified catalysts. Click to view the MathML source MAS NMR results and IR spectra of adsorbed CO indicated that the chiral modification via the coordination of phosphines to rhodium produces chirally active sites on the Rh/SiO2 catalysts. [PUBLICATION ABSTRACT]