Development of a synthetic route to unsymmetrical triphosphine ligands and an investigation of their coordination chemistry with nickel and palladium

Chiral tridentate phosphines, R(2)P(CH2)(3)PPh(CH2)(2)PPh(2) where E = C6H5, p-ClC6H4, and p-FC6H4, can be prepared from simple starting materials, (R(3)P, I(CH2)(3)I, and Ph(2)P(CH2)(2)PPh(2)), in a few stages involving phosphonium salts and phosphine oxides as intermediates. Crystalline diamagnetic complexes of nickel(II) and palladium(II) have been isolated. In solution these show first-order 12 line P-31 NMR spectra consistent with three nonequivalent phosphorus nuclei coupled to one another in a square planar geometry. A single X-ray crystallographic study of NiI2{P(CH2)(3)PPh(CH2)(2)PPh(2)} showed that this was square pyramidal in the solid state with a weakly held apical iodo ligand.