(η3-Phenylallyl)(phosphanyloxazoline)palladium Complexes: X-Ray Crystallographic Studies, NMR Investigations, and Ab Initio/DFT Calculations

All possible (η3‐allyl)palladium complexes (1–4) of the ligand (4S)‐[2‐(2′‐diphenylphosphanyl)phenyl]‐4,5‐dihydro‐4‐(2‐propyl)‐oxazole (L 1) and η3‐allyl ligands with one to three phenyl substituents at the terminal allylic centers were synthesized and characterized by X‐ray crystal structure analysis and, with respect to allylic isomers, by NMR investigations. Equilibrium geometries, electronic structures, and relative energies of isomeric complexes were computed by restricted Hartree–Fock (RHF) and density functional theory (DFT) calculations; experimentally determined isomer ratios could be reproduced. The results allowed important conclusions to be drawn regarding the mechanism of Pd‐catalyzed asymmetric allylic substitutions. The nonobserved (η3‐allyl)palladium complex 1 xc was found to be more reactive in allylic substitutions by a factor >10 000 than the observed isomeric complex 1 xt. This is one of the results obtained in a study of (η3‐allyl)palladium complexes of the ligand (4S)‐[2‐(2′‐diphenylphosphanyl)phenyl]‐4,5‐dihydro‐4‐(2‐propyl)oxazole with one to three phenyl substituents at the terminal allylic centers. The complexes were characterized by X‐ray crystal structure analysis and, with respect to allylic isomers in solution, by NMR investigations. Equilibrium geometries, electronic structures and relative energies of isomeric complexes were assessed by quantum‐chemical calculations.