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.

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13C NMR chemical shifts of the terminal allyl carbon atoms C-1 and C-3 of (1,2-bis(diphenylphosphino)ethane)(η3-1,3-diarylallyl)palladium tetrafluoroborates correlate with σ Hammett substituent constants. For each complex the chemical shift at lower field indicates the site of preferred attack by soft nucleophiles in the Tsuji−Trost reaction.

Complete 1H and 13C NMR assignments of several aryl‐substituted π‐allyl–Pd(II) complexes were achieved using modern gradient‐based 1D and 2D experiments. In addition, unambiguous 31P assignments were readily made using an improved gradient‐enhanced 1H–31P HMBC experiment from which the regiochemistry of cationic complexes containing asymmetric bidentate ligands could also be elucidated. The effect of the nature of the substituent on allylic proton and carbon chemical shifts is briefly evaluated. Finally, a partial π–σ–π isomerization mechanism is proposed taking into account some observed dynamic NMR processes which are largely dependent on the ligand nature of these complexes. © 1997 by John Wiley & Sons, Ltd.

Preparation of 1,3-Diarylpropenes by Phosphine-Free Palladium(0)-Catalyzed Suzuki-Type Coupling of Allyl Bromides with ArylboronicAcids.--(MORENO-MANAS, M.; PAJUELO, F.; PLEIXATS, R.; J.