Transition metal complexes of the pyridylphosphine ligand o-C6H4(CH2PPy2)2

The synthesis and coordination behaviour of the pyridylphosphine ligand o-C6H4(CH2PPy2)(2) (Py = 2-pyridyl) are reported. The phosphine selenide was synthesised and the (1)J(PSe) value of 738 Hz indicates the phosphorus atoms have a similar basicity to PPh3. The ligand reacts with platinum(II) and palladium(II) complexes to give simple diphosphine complexes of the type [MX2(PP)] (M = Pt, X = Cl, I, Me, Et; M = Pd, X = Cl, Me). When the ligand is reacted with chloromethyl(hexa-1,5-diene) platinum the [PtClMe(PP)] complex results, from which a series of unsymmetrical platinum complexes of the type [PtMeL(PP)](+) (L = PPh3, PTA, SEt2 and pyridine) can be made. This enabled the comparison of the cis and trans influences of a range of ligands. The following cis influence series was compiled based on P-31 NMR data of these complexes: Py approximate to Cl > SEt2 > PTA > PPh3. Reaction of [PtClMe(PP)] with NaCH(SO2CF3)(2) and carbon monoxide slowly formed an acyl complex, where the CO had inserted in the Pt-Me bond. Attempts to achieve P, P, N chelation, through abstracting the chloride ligand in [PtClMe(PP)], were unsuccessful. When the ligand reacted with platinum(0), palladium(0) and silver(I) complexes the bis-chelated complexes [M(PP)(2)] (M = Pt, Pd) and [Ag(PP)(2)](+) were formed respectively. Reaction of the ligand with [Ir(COD)(mu-Cl)](2) formed [IrCl (PP)(COD)]. When the chloride ligand was abstracted, the pyridyl nitrogens were able to interact with the iridium centre facilitating the isomerisation of the 1,2,5,6-eta(4)-COD ligand to a 1-kappa-4,5,6-eta(3)-C8H12 ligand. The X-ray crystal structure of [Ir(1-kappa-4,5,6-eta(3)-C8H12)(PPN)] BPh4 confirmed the P, P, N chelation mode of the ligand. In solution, this complex displayed hemilabile behaviour, with the pyridyl nitrogens exchanging at a rate faster than the NMR time scale at room temperature.