Reactions of an azine diphosphine with platinum(II) and palladium(II) and the formation of a novel heterocyclic diphosphine ligand. Crystal structure of [Pdl2{PPh2CHC(But)N–NC(But)CH2PPh}]

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Abstract
The azine diphosphine Z,ZPPh2CH2C(But)N–NC(But)CH2PPh2I was treated with [Pt-Me2(cod)](cod = cycloocta-1,5-diene) to give the dimethylplatinum(II) complex [[graphic omitted]Ph2}]1a containing a nine-membered chelate ring with an E,Z configuration for the bidentate azine diphosphine ligand. This complex undergoes oxidative addition with Mel to give the fac-trimethylplatinum(IV) complex [[graphic omitted]PPh2}]2. The corresponding platinum(II) complexes [[graphic omitted]PPh2}](X CCC6H4Me-p1b or Cl 1c) were also prepared. Treatment of trans-[PtCl2(NCR)2](R = Me or Ph) with I gave a hexanuclear species trans-[{PtCl2[PPh2CH2C(But)N–NC(But)CH2PPh2]}6]3a in which the azine diphosphine is acting as a bridging group and is still symmetrical, i.e. the configuration is still Z,Z. The palladium analogue 3b was made by treating [PdCl2(NCPh)2] or Na2[PdCl4] with 1 but might only be binuclear. This complex was unstable in hot chloroform and at 60 °C (30 min) was completely converted into the salt [[graphic omitted]PPh2}]Cl 4a in which the azine diphosphine is tridentate with E,Z configuration and mutually trans-co-ordinated phosphorus donors and one of the azine nitrogens is co-ordinated. Treatment of [PtCl2(cod)] with I and addition of NH4PF6 gave the platinum salt [[graphic omitted]PPh2}]PF64c; [[graphic omitted]PPh2}]I 4d was also prepared. On prolonged (8 d) heating in chloroform solution the bridged complex 3b was quantitatively converted into the novel and very stable heterocyclic complex [[graphic omitted]PPh}]5a with loss of a molecule of benzene. Treatment of 5a with LiBr or Nal gave the corresponding dibromide 5b or diiodide 5c complexes. The crystal structure of 5c has been determined. The corresponding platinum complexes [[graphic omitted]PPh}]5d-5f(X = Cl, Br or I) were also prepared and treatment of the dichloro complex with MgMel gave the dimethyl complex 5g. Treatment of this dimethyl complex with an excess of Mel gave [[graphic omitted]PPh}]6. Proton, 13C-{1H} and 31P-{1H} NMR and infrared data are given.

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