The Influence of Substituents in Diphosphine Ligands on the Hydrogenation Activity and Selectivity of the Corresponding Rhodium Complexes as Exemplified by ButiPhane

The influence of substituents in ButiPhane ligands (with R=Me, Et, iPr) on the hydrogenation activity and selectivity of the corresponding rhodium complexes has been quantitatively assessed. Increasingly demanding substituents negatively affect the reduction rate of 1,5-cyclooctadiene in catalyst precursors en route to catalytically active MeOH–solvent complexes. The same trend as to activity is observed in the hydrogenation of prochiral olefins [methyl-(Z)-α-acetamidocinnamate, methyl (Z)-3-N-acetylamino-3-methylacrylate, and methyl (Z)-3-N-acetylamino-3-phenylacrylate], which however is counterbalanced by an increase in the stereorecognition ability of the bulkier catalysts.