Abstract
Heterogeneous chiral catalysts were prepared by modifying silica-supported rhodium (Rh/SiO 2) with chiral phosphorus ligands. The chirally modified Rh/SiO 2 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/SiO 2 catalysts. It is noteworthy that the modification of Rh/SiO 2 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/SiO 2 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. P 31 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/SiO 2 catalysts.
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