The naphthylamine palladium(II) template induced E–Z isomerism of exocyclic vinyl group in five-membered P–N chelates: detailed spectroscopic studies

The exocyclic CC bond E–Z isomerism of chelating Ph2PC(CHPh)–CHNAr in organopalladium complexes containing orthometallated [(S)-1-(dimethylamino)ethyl]naphthalene is reported. In dilute solutions of non-coordinating CH2Cl2 or CHCl3, all the original E-isomers, in which the CHPh phenyl rings are located trans to PPh2 moieties were partly converted to their Z-isomers. The isomerism was found to be dependent on temperature, concentration and solvent. At higher temperature, the Z-isomers were transformed completely back to their original E-isomers. Removal of the chiral auxiliaries of the E–Z mixtures by concentrated HCl, gave only the dichloro complexes of the E-isomers. The E–Z isomerization processes were well established by detailed spectroscopic studies, including 31P NMR, 1H NMR and 2D 1H–1H ROESY NMR studies. It is noteworthy that the dichloro complexes and free P–N ligands did not show such isomerization processes, indicating that the isomerization processes were triggered by the orthopalladated naphthylamine moiety.