Optically active cyclopalladated compounds containing P-chiral ligands. Restricted rotation around the PdP bond

The synthesis of the optically active complexes [PdCl(C10H6CHMeNMe2)L] (L=PPh3, PBn2Ph, PHBnPh and PBnCyPh) and the resolution of the secondary phosphine PHBnPh is reported. The study of the NMR data of these mononuclear compounds shows that in some of these complexes the rotation around the PdP bond is restricted. A relationship between the δ values of the aromatic proton adjacent to the PdC bond and the conformation of the Pd–phosphine fragment can be found and NMR data permit the assignment of the absolute configuration of the phosphine in [PdCl(C10H6CHMeNMe2)(PBnCyPh)]. Several molecular mechanics geometry optimizations were performed using the MMFF94 force field to estimate the height of the energy barrier corresponding to the rotation of the phosphine ligands around the PdP bond. These calculations show the rotation around the PdP bond to be restricted, if the phosphine contains at least one benzylic group, and agree with the results obtained in solution by means of mono- and bi-dimensional NMR.