Density Functional Study on the Regioselectivity of Nucleophilic Attack in 1,3-Disubstituted (Diphosphino)(η³-allyl)palladium Cations

A density functional study has been performed to analyze the influence of electronic effects on the regioselectivity of the Tsuji-Trost reaction. Optimized geometries of model (diphosphino)(η3-allyl)palladium cations 6 and 7 show that for unsymmetrical allyl ligands the shortest Pd-C(terminal) bond is the one closest to the most electron-withdrawing group. The calculated energy barriers for the attack of an ammonia molecule at each one of the terminal allyl carbon atoms of 7b-d predict that nucleophilic attack would take place preferentially on the carbon atom remote from the most electron-withdrawing group, in excellent agreement with experimental observations on allylic precursors of cations 4.