Nuclear magnetic resonance studies in coordination chemistry. I: Structure and conformational rearrangements of π‐allyl complexes containing group‐V donor ligands

Nuclear magnetic resonance has been employed to investigate the structure of the complexes (π‐allyl) PdCl(L) (L = phosphine, Ph3As, Ph3Sb) and the conformational rearrangements of the allyl group in these compounds as affected by the ligand, the ligand‐to‐metal ration and the temperature (in CDCl3). Several types of rearrangement were observed, depending on the choice of the variables mentioned above. At low temperatures a short‐lived σ‐allyl intermediate was found in the case of the phosphines only, whereas at higher temperatures rotation of the π‐allyl group was inferred for all the ligands. At very high temperatures and high ligand‐to‐metal ratios a σ‐allyl group had to be postulated to explain the NMR spectra, which are analogous to those of σ‐allyl‐magnesium halide compounds. A molecular orbital description has been used to rationalize some of the experimental results.