First-principles investigation of enantioselective catalysis: Asymmetric allylic amination with Pd complexes bearing P,N-ligands

Site selectivity for nucleophilic attack of a pi-allyl-Pd(II) complex with a bidentate phosphine-pyrazole ligand by an amine has been investigated with first-principles density functional calculations using the projector augmented wave method. The interplay between steric and electronic effects, namely the trans influence, is elucidated. While the trans influence favors nucleophilic attack at the carbon in a pseudo-trans position to the phosphine, site selectivity is dominated by steric effects between the allyl group and a groove in the catalyst surface, which prescribe an orientation of the allyl out-of the P-Pd-N plane. The direction of this out-of-plane orientation determines the site of nucleophilic attack for a given isomer of the allyl complex, irrespective of whether this site is cis or trans to the phosphine. Our results provide insight into the observed relation between isomeric distributions of the allyl complexes and the resulting selectivities.