Fine-tuning monophosphine ligands for enhanced enantioselectivity. Influence of chiral hemilabile pendant groups.

[reaction: see text] C(2)-Symmetric P-(2-X-aryl)-2,5-dialkylphospholanes (X = dioxolan-2-yl or dioxan-2-yl), designed on the basis of a working model for asymmetric induction, are effective ligands for the Ni(II)-catalyzed asymmetric hydrovinylation of styrenes. Excellent yields (>99%), selectivities for the desired 3-arylbutenes (>99%), high S/C ratios (>1200), and ee's (up to 91%) have been realized for a number of prototypical vinylarenes. In the dioxolane series, the selectivity depends on the configuration of the C(4) and C(5)() carbons.