Analysis of the enantioselectivities and initial rates of the hydrosilylation of acetophenone catalyzed by [Rh(cod)Cl]2/(chiral diphosphine). The quantitative analysis of ligand effects

Abstract Through the application of the quantitative analysis of ligand effects (QALE) method to the study of the hydrosilylation of acetophenone, we have shown, for the first time, that the initial rate and enantioselectivity of a complicated catalytic system responds in a rational manner to the variations in the stereoelectronic properties of the silane. The reactions (in benzene- d 6 at 63 °C) were catalyzed by [Rh(cod)Cl] 2 /(chiral diphosphine) (chiral diphosphine=( R )-BINAP [( R )-(+)-2,2′-bis(diphenylphosphino)-1,1′binaphthyl], ( R , R )-tolyl-BINAP [( R )-(+)-2,2′-bis(di- p -tolylphosphino)-1,1′-binaphthyl], ( R , R )-Me-DUPHOS [( R , R )-(–)-1,2-Bis-2,5-dimethylphospholano)benzene], ( R , R )-DIOP [( R , R )-(−)-2,3- O -isopropylidine-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane], and ( R )-QUINAP [( R )-(+)-1-(2-diphenylphosphino-1-naphthyl)isoquinoline]. The ee's ( R ) of the hydrosilylation products (CH 3 CH(OSiR 3 )Ph) range between −9 and 53% with the ( R )-QUINAP giving the poorest enantioselectivity. The QALE analyses of log( R / S ) for ( R )-BINAP, ( R )-tolyl-BINAP, ( R , R )-Me-DUPHOS, and ( R , R )-DIOP reveal that the steric effects associated with the silanes are not monotonic.