Stereoelectronic and catalytic properties of chiral cyclometalated phospha-palladium and -platinum complexes

The stereoelectronic properties of palladium(II) and platinum(II) complexes containing ortho-metalated (1-(diphenylphosphino)ethyl)naphthalene were examined by X-ray crystallography in the solid state and by NMR spectroscopy in solution. The studies revealed that the aromatic carbon induced a significantly stronger electronic trans-influence than the phosphorus donor within the same five-membered chelate. Both the organopalladium and organoplatinum chelate complexes were formed with classical hard oxygen and soft phosphorus donor atoms. Computational studies further confirmed the observations in the solid state and solution that the C-metal bond in the trans C-Pt-O moiety has a stronger π-character than that in the trans C-Pt-P moiety. Both organometallic units are efficient catalysts for the asymmetric P-H addition reaction. They showed almost identical efficiency in dichloromethane, but their reactivity in THF is markedly different.