Asymmetric hydroformylation of olefins catalyzed by rhodium nanoparticles chirally stabilized with (R)-BINAP ligand

Rhodium nanoparticles have been conveniently synthesized by one-pot chemical reduction of aqueous rhodium chloride (RhCl₃·3H₂O) dispersed in toluene solution in the presence of amphiphilic tetraoctylammonium bromide (TOAB) and chiral (R)-BINAP at ambient conditions. The resulting highly dispersed rhodium nanoparticles show small and narrowly distributed core sizes (1.5-2.0 nm). The chirally stabilized rhodium nanoparticles were also immobilized on silica by impregnation to give the corresponding supported catalysts. ³¹P MAS NMR results and IR spectra of adsorbed CO confirm that chiral (R)-BINAP ligands stabilize the nanoparticles by coordinative interaction between phosphine and rhodium, and produce chirally catalytic active sites on the rhodium nanocatalysts. Chirally stabilized catalysts exhibit high regioselectivity and chiral induction ability for the asymmetric hydroformylation of olefins. The supported rhodium nanocatalysts show the increased activities compared to the unsupported catalysts (e.g. from 12 to 22 h^-1 for the hydroformylation of styrene). One hundred percentage regioselectivity of branched aldehyde and up to 59% ee were obtained for the hydroformylation of vinyl acetate.