Chiral bis(oxazoline) ligands.: Synthesis of mono- and bi-metallic complexes of nickel and palladium

The co-ordination behaviour of the chiral bis(oxazoline) ligands ortho-, meta-, and para-bis[(4R)-4-ethy1-3,4-dihydrooxazol-2-yl]benzene (A, B, C, respectively) has been studied. Palladium and nickel complexes were synthesized and characterized in solution and in the solid state. With regard to N,N' co-ordination, A gave bidentate monometallic species, while B and C gave bimetallic compounds, with one or two bridging chiral molecules between two palladium atoms. Complexes with the C-2-symmetrical ligand A showed a loss of symmetry both in solution and in the solid state, due to the phenyl spacer group between the two oxazoline moieties in the seven-membered ring. The crystal structure of a monometallic complex has been determined. Palladation with these ligands was also tested. Ligand A did not give metallated species, but B and C gave mono- and bis-cyclopalladated compounds, respectively.