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Palladium complexes of diphosphazane and related ligands.

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The synthesis, characterisation and X-ray structure detenninations of homonuclear nickel, palladium and platinum complexes with bis(phosphino)amine ligands is reviewed in Chapter 1. Particular attention is given to the mode of coordination that these ligands may adopt when coordinating to a transition metal i.e., as a monodentate (n'-), chelating (n2-) or bridging (u-) ligand. The Chapter is concluded with a brief summary of (i) The dependence of the 31P chemical shift for the bonded phosphorus atom(s) on the mode of coordination and (ii) The dependence of key, ligand-based, structural parameters on the mode of coordination. The synthesis and characterisation of the bis(diphenylphosphino )-ethylamine, Ph2PN(Et)PPh2, ligand and its subsequent reactions with various palladium precursors is described in Chapter 2. Reaction with the Pd(II) precursor, [PdCI2(PhCN)2], afforded the mononuclear complex cis-[PdCI2{ n2-Ph2PN(Et)PPh2}]1; when the same reaction was carried-out in the presence of the Pd(0) species [Pd2(dba)3] (dba = dibenzylideneacetone) the dinuclear ligand-bridged complex [Pd2C12 {u-Ph2PN(Et)PPh2}2] was formed. Reaction of 2 with I2 afforded 1, as well as the mononuclear di-iodo species cis-[PdI2 {n2-Ph2PN(Et)PPh2}] 3, and the mixed-halogeno complex [PdClI{n2-Ph2PN(Et)PPh2}] 4. Direct reaction of the ligand with [Pd2(dba)3] afforded, in the first instance, [Pd2{u-Ph2PN(Et)PPh2}3] 5, an extremely air-sensitive red compound, that readily reacted with oxygen in the solution to afford palladium metal and a yellow clathrate species that contained the oxidised ligand i.e., Ph2P(O)N(Et)P(O)PPh2. dba. H2O. Apart from 4, all compounds were characterised by means of elemental analysis, 1H and 3IP{1H} NMR spectroscopy and, in the case of 1, 2, 3 and Ph2P(O)N(Et)P(O)PPh2. dba. H2O, by means of single crystal X-ray structure determinations. The structures of the palladium complexes are, as expected, dominated by the requirement that the coordination geometry at the Pd atom is square-planar. In the case of the dinuclear ligand-bridged complex 2, this is achieved through formation of a Pd-Pd bond of length 2.600(1)A. Of particular interest is the crystal structure of the clathrate, which has the oxidised ligand and dba molecules stacked in alternating lines approximately parallel to the [c ]-axis of the unit cell. The synthesis and characterisation of the bis(2-pyridyl)phenylphosphine, PhP(py)2 ligand and its subsequent reaction with [PdCI2(PhCN)2] to afford the mononuclear complex cis-[PdCI2{n1-PhP(py)2}2] 6 is decribed in Chapter 3. The latter reacted with [Pd2(dba)3] to afford the dinuclear ligand-bridged species [Pd2CI2{u-PhP(py)2}2] 7. The 1H and 31P{1H} NMR spectral data, as well the results of single crystal X-ray structure determinations are reported for 6 and 7. The square-planar coordination at each palladium atom in 7 is achieved through the formation of a Pd-Pd bond of length 2.586(1)A. The synthesis and characterisation of the 2,5-(diphenylphosphino)thiophene, Ph2P(C4H2S)PPh2 ligand is described in Chapter 4. Reaction of the ligand with [PdCI2(PhCN)2] afforded the dinuclear ligand-bridged species [Pd2C14 {u-Ph2P(C4H2S)PPh2}2] 8. Characterisation of 8 was by means of elemental analysis, 1H and 31P{1H} NMR spectroscopy. Reaction of 8 with Ag+ in acetonitrile afforded a compound isolated as a yellow solid and formulated as [Pd2CI3(MeCN){u-Ph2P(C4H2S)PPh2}2] 9. Evidence for this formulation is based on the 31P{1H} NMR spectrum which shows two closely-spaced singlets, consistent with two sets of phosphorus atoms in different chemical environments, and too far separated (by 4 bonds) for magnetic coupling. Unfortunately, single crystals of these thienylphosphine ligand-bridged compounds could not be grown.


Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.


Ligands., Palladium compounds., Theses--Chemistry.