Showing papers by "William Levason published in 2008"

Complexes of germanium(IV) fluoride with phosphane ligands: structural and spectroscopic authentication of germanium(IV) phosphane complexes.

Abstract: The first phosphane complexes of germanium(IV) fluoride, trans-[GeF4(PR3)2] (R = Me or Ph) and cis-[GeF4(diphosphane)] (diphosphane = R2P(CH2)2PR2, R = Me, Et, Ph or Cy; o-C6H4(PR2)2, R = Me or Ph) have been prepared from [GeF4(MeCN)2] and the ligands in dry CH2Cl2 and characterised by microanalysis, IR, Raman, 1H, 19F{1H} and 31P{1H} NMR spectroscopy. The crystal structures of [GeF4(diphosphane)] (diphosphane = Ph2P(CH2)2PPh2 and o-C6H4(PMe2)2) have been determined and show the expected cis octahedral geometries. In anhydrous CH2Cl2 solution the complexes are slowly converted into the corresponding phosphane oxide adducts by dry O2. The apparently contradictory literature on the reaction of GeCl4 with phosphanes is clarified. The complexes trans-[GeCl4(AsR3)2] (R = Me or Et) are obtained from GeCl4 and AsR3 either without solvent or in CH2Cl2, and the structures of trans-[GeCl4(AsEt3)2] and Et3AsCl2 determined. Unexpectedly, the complexes of GeF4 with arsane ligands are very unstable and have not been isolated in a pure state. The behaviour of the germanium(IV) halides towards phosphane and arsane ligands are compared with the corresponding silicon(IV) and tin(IV) systems.

The first examples of germanium tetrafluoride and tin tetrafluoride complexes with soft thioether coordination--synthesis, properties and crystal structures.

Abstract: The first thioether complexes of the hard Lewis acidic GeF4 and SnF4 have been prepared by reaction of [GeF4(MeCN)2] or [SnF4(MeCN)2] respectively with the thioether ligand in rigorously anhydrous CH2Cl2 solution. The isolated compounds were characterised spectroscopically (IR, 1H and 19F{1H} NMR) and by microanalyses. Crystal structures of four representative examples, [GeF4{MeS(CH2)2SMe}], [GeF4{EtS(CH2)2SEt}], [SnF4{EtS(CH2)2SEt}] and [SnF4{iPrS(CH2)2SiPr}], reveal distorted octahedral adducts with chelating thioethers, and weak, secondary Ge–S and Sn–S bonds. These compounds are the first reported examples of thioether complexes with any main group metal/metalloid fluoride acceptor.

Synthesis, characterisation and structures of thio-, seleno- and telluro-ether complexes of gallium(III)

Abstract: The reactions of GaX3 (X = Cl, Br or I) with SMe2, SeMe2 and TeMe2 (L) in non-coordinating solvents produces only the pseudo-tetrahedral [GaX3L], which have been characterised by IR, Raman and multinuclear NMR (1H, 71Ga, 77Se or 125Te) spectroscopy, and by the crystal structure of [GaCl3(SeMe2)]. The 71Ga NMR resonances show small low frequency shifts for fixed halides as the neutral donors change from S → Se → Te. Bidentate ligands including MeS(CH2)2SMe, PhS(CH2)2SPh, MeSe(CH2)2SeMe, nBuSe(CH2)2SenBu and MeTe(CH2)3TeMe (L–L) also produce complexes with 4-coordinate gallium centres, [(GaX3)2(μ-L–L)], confirmed by the crystal structures of [(GaI3)2{μ-MeS(CH2)2SMe}], [(GaCl3)2{μ-PhS(CH2)2SPh}] and [(GaCl3)2{μ-nBuSe(CH2)2SenBu}]. The structural data are consistent with the weaker Lewis acidity of the gallium as the halide co-ligands become heavier. Multinuclear NMR studies suggest that in chlorocarbon solutions partial dissociation of the ligands occur, which increases with the halide co-ligand Cl < Br < I. The o-xylyl dithioether, o-C6H4(CH2SMe)2, despite being pre-organised for chelation, also forms [(GaCl3)2(μ-L–L)]. The corresponding diselenoether complex decomposes in solution with C–Se bond cleavage to form the selenonium salt [o-C6H4CH2Se(Me)CH2][GaCl4], which was structurally characterised. The ditelluroethero-C6H4(CH2TeMe)2 undergoes rapid C–Te bond fission and rearrangement upon reaction with GaCl3, and the telluronium species [o-C6H4CH2Te(Me)CH2]+ and [MeTe{CH2(o-C6H4)CH2TeMe}2]+ have been identified by ES+ mass spectrometry from their characteristic isotope patterns.

Complexes of Vanadium(V) oxide trifluoride with nitrogen and oxygen donor ligands: Coordination chemistry and some fluorination reactions

Abstract: [VOF3(MeCN)], obtained by dissolving VOF3 in dry acetonitrile, is a useful synthon for the preparation of complexes of the oxide-fluoride, and the reaction with 2,2-bipyridyl, 1,10-phenanthroline, Me2N(CH2)2NMe2 and Ph2P(O)CH2P(O)Ph2 (L-L), or Ph3PO, Me3PO, Ph3AsO, pyridine and pyridine N-oxide (L), produces the complexes [VOF3(L-L)] or [VOF3(L)2] respectively. These were characterised by microanalysis, IR, UV/Vis and multinuclear NMR [51V, 19F{1H}, 31P{1H}, 1H] spectroscopy, the data showing them to besix-coordinate with trans F-V-F units and the neutralligands trans to O and F, respectively. X-ray crystal structures of [VOF3(1,10-phenanthroline)], [VOF3(Ph3PO)2] and [VOF3(pyNO)2] confirm the geometry, although the first two exhibit O/F disorder trans to the neutral ligand. Unstable complexes with ether and thioether ligands including [VOF3{MeO(CH2)2OMe}], [VOF3{MeS(CH2)2SMe}] and [VOF3(15-crown-5)] are also described; these decompose rapidly even in the solid state, with fluorination of the ligands. The [VOF3(Ph3AsO)2] also decomposes in solutionto a mixture of products including Ph3AsF2 and [V6O12F4(Ph3AsO)2(Ph2AsO2)2] identified crystallographically. Comparisons with complexes of VOCl3 are also described.

Synthesis, chemistry and structures of complexes of the dioxovanadium(V) halides VO2F and VO2Cl

Abstract: [VO2F(L–L)] (L–L = 2,2′-bipyridyl, 1,10-phenanthroline, Me2N(CH2)2NMe2) and [VO2F(py)2] (py = pyridine) have been prepared from the corresponding [VOF3(L–L)] or [VOF3(py)2] and O(SiMe3)2 in MeCN solution. VO2F (itself made from VOF3 and O(SiMe3)2 in MeCN) forms [Me4N][VO2F2] with [Me4N]F, but does not react with neutral N- or O-donor ligands. VO2Cl, prepared from VOCl3 and ozone, reacts with 2,2′-bipyridyl or 1,10-phenanthroline to form [VO2Cl(L–L)], with pyridine or pyridine-N-oxide (L) to produce [VO2Cl(L)2], and with OPPh3 or OAsPh3 (L′) gives [VO2Cl(L′)]. A second product from the OPPh3 system is the ionic [VO2(OPPh3)3][VO2Cl2] containing a trigonal bipyramidal cation. Neither VO2F nor VO2Cl form isolable complexes with MeCN, thf or MeO(CH2)2OMe, and both are reduced by P-, As-, S- or Se-donor ligands. [Ph4As][VO2X2] (X = F or Cl) react with 2,2′-bipyridyl to form [VO2X(2,2′-bipyridyl)], but similar reactions with weaker O-donor ligands fail. The complexes have been characterised by IR, multinuclear NMR (1H, 19F, 51V or 31P) and UV-visible spectroscopy. X-ray crystal structures are reported for [VO2F(py)2], [VO2Cl(L)2] (L = py or pyNO) and [VO2(OPPh3)3][VO2Cl2].

Evaluation of Group 4 Metal Bis-cyclopentadienyl Complexes with Selenolate and Tellurolate Ligands for CVD of ME2 Films (E = Se or Te)

Abstract: The selenolate and tellurolate complexes [Cp2M(SeR)2] (M = Ti, Zr, or Hf; R = Me or But) and [Cp2M(TeBut)2] (M = Zr or Hf) have been prepared and characterized by 1H, 13C{1H}, 77Se{1H} and 125Te{1H} NMR spectroscopy and microanalysis Crystal structures of representative examples are reported, together with the structure of the oxo-bridged species [{Cp2Zr(SeMe)}2(?-O)] formed by partial hydrolysis Trends in the NMR parameters are discussed These molecular [Cp2M(SeBut)2] complexes are shown to be suitable as precursors for the single source LPCVD of intensely colored MSe2 thin films for each of the Group 4 elements, confirmed by SEM/EDX and PXD These are the first examples of single source CVD of ZrSe2 and HfSe2 thin films The corresponding [Cp2M(TeBut)2] species (M = Zr or Hf) deposit elemental Te under similar LPCVD conditions

Synthesis, Structures and DFT Calculations on Alkaline‐Earth Metal Azide‐Crown Ether Complexes

Abstract: The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown-6)(N3)2(MeOH)], [Sr([15]crown-5)(N3)2(H2O)], [Ca([15]crown-5)(N3)2(H2O)] and [Sr([15]crown-5)(N3)(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including 1-, -1,3- and linkages via H-bonded water molecules, in addition to azide ions. The [Ba([18]crown-6)(N3)2(MeOH)]1/3 MeOH contains dinuclear cations with three -1,3-NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density functional theory (DFT). This has allowed the effects of the crystal lattice to be investigated. A study of the MNterminal metal-azide bond length and charge densities on the metal (M) and terminal nitrogen centre (Nterminal) in these complexes has allowed the nature of the metal-azide bond to be investigated in each case. As in our earlier work on alkali metal azide-crown ether complexes, the bonding in the alkaline-earth complexes is believed to be predominantly ionic or ion-dipole in character, with the differences in geometries reflecting the balance between maximising the coordination number of the metal centre, and minimising ligand-ligand repulsions.

Preparation and properties of sterically demanding and chiral distibine ligands.

Abstract: A series of new rigid distibines, 1,8-bis(R2Sb)naphthalene (R = Me: (1); R = Ph: (2)), and chiral distibines, 2,2′-bis(R2Sb)-1,1′-binaphthyl (R = Me: (3); R = Ph: (4) obtained as racemic mixtures) and the discrete enantiomers of 4,5-bis((R2Sb)methyl)-2,2-dimethyl-1,3-D/L-dioxolane (R = Me: (5) (L), (7) (D); R = Ph: (6) (L), (8) (D)) have been obtained in high yields, using either electrophilic halostibine reagents with di-lithium reagents ((1)–(4)) or nucleophilic stibide reagents with dibromo-derivatives ((5)–(8)). The distorted octahedral complexes [Mo(CO)4(L)], L = (1)–(8), planar [PtCl2(L)], L = (1), (2), (3), (5), and neutral, five-coordinate [RhCl(cod)(L)], L = (2), (4), (6), are reported and trends in the spectroscopic data are discussed in terms of the ligand donor properties. Crystal structures of (3) and [Mo(CO)4(3)] reveal significant structural changes occur upon coordination, and these are also reflected in the solution NMR spectroscopic parameters. Changes in the C–Sb–C angles and C–Sb bond distances upon coordination of (3) are discussed in term of increased s/p orbital mixing. Air oxidation of (1) forms a very unusual stibine oxide, the structure of which shows a distorted Sb4O4 cubane core (bridging O atoms) with two orthogonal naphthalene units.

Selenoether macrocyclic chemistry—syntheses and properties of new potentially tridentate and hexadentate Se/O-donor macrocycles

Abstract: Treatment of O(CH2CH2SeCN)2 with Na in NH3(l), followed by dropwise addition of a thf solution of o-C6H4(CH2Br)2 at −40 °C leads to formation of three mixed Se/O-donor macrocycles which are separable by column chromatography, the [1 + 1] species L1, the [2 + 2] ring L2 and the [3 + 3] ring L3, of which L2 is by far the major species. Using the same starting materials, but in a high dilution cyclisation at room temperature with NaBH4 in thf/EtOH gives exclusively the [1 + 1] ring, L1. The saturated ring Se/O-donor macrocycles, L4 and L5 are obtained by simultaneous dropwise addition of solutions of O(CH2CH2SeCN)2 and Br(CH2)3Br to NaBH4 suspended in thf/EtOH. The small tridentate Se2O-donor ring, L4, is again the dominant product under these conditions (71%), although the more flexible precursors in this reaction also give rise to the larger Se4O2-donor ring, L5, as a by-product in 8% yield. These compounds are readily separated and purified by column chromatography (ethyl acetate:hexane, 1:19). The new macrocycles have been characterised by 1H, 13C{1H} and 77Se{1H} NMR spectroscopy and mass spectrometry, together with crystal structures of L1 and L2. Complexes of L1 and L2 with late transition metals (Pd(II), Pt(II), Cu(I) and Ag(I)) are also described.

Bis(η5-cyclo­penta­dien­yl)bis­(2,4,6-tri­methyl­phenyl­tellurolato)zirconium(IV)

Abstract: The structure of the title compound, [Zr(C5H5)2(C9H11Te)2], consists of a zirconium(IV) centre bonded to two η5-coord­inated cyclo­penta­dienyl groups and two mesityltellurolate ligands; the discrete mol­ecule has crystallographic twofold rotation symmetry. The structural parameters compared with those in [(η5-Me5Cp)2Zr(TePh)2] [Howard, Trnka & Parkin (1995). Inorg. Chem. 34, 5900–5909] show that the greater steric demands of the bulky mesityl substituents are accommodated by widening Te—Zr—Te (∼8°) and by more acute Zr—Te—C (∼5°) angles, although the Zr—Te distances are essentially the same. The crystal studied exhibited some inversion twinning.

Synthesis, Structures and DFT Calculations on Alkaline-Earth Metal Azide-Crown Ether Complexes.

Abstract: The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown-6)(N3)2(MeOH)], [Sr([15]crown-5)(N3)2(H2O)], [Ca([15]crown-5)(N3)2(H2O)] and [Sr([15]crown-5)(N3)(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including 1-, -1,3- and linkages via H-bonded water molecules, in addition to azide ions. The [Ba([18]crown-6)(N3)2(MeOH)]1/3 MeOH contains dinuclear cations with three -1,3-NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density functional theory (DFT). This has allowed the effects of the crystal lattice to be investigated. A study of the MNterminal metal-azide bond length and charge densities on the metal (M) and terminal nitrogen centre (Nterminal) in these complexes has allowed the nature of the metal-azide bond to be investigated in each case. As in our earlier work on alkali metal azide-crown ether complexes, the bonding in the alkaline-earth complexes is believed to be predominantly ionic or ion-dipole in character, with the differences in geometries reflecting the balance between maximising the coordination number of the metal centre, and minimising ligand-ligand repulsions.

[{Cp2(tBuSe)Nb}2E] (E = O and Se) with bridging oxide or selenide ligands.

Abstract: The title compounds, μ-oxido-bis­[(tert-butyl­seleno­lato)bis­(η5-cyclo­penta­dien­yl)niobium(IV)] toluene solvate, [Nb2(C5H5)4(C4H9Se)2O]·C7H8, and μ-selenido-bis­[(tert-butyl­selenol­ato)bis­(η5-cyclo­penta­dien­yl)niobium(IV)], [Nb2(C5H5)4(C4H9Se)2Se], consist of niobium(IV) centres each bonded to two η5-coordinated cyclo­penta­dienyl groups and one tert-butyl­seleno­late ligand and are the first organometallic niobium seleno­lates to be structurally characterized. A bridging oxide or selenide completes the niobium coordination spheres of the discrete dinuclear mol­ecules. In the oxide, the O atom lies on an inversion centre, resulting in a linear Nb—O—Nb linkage, whereas the selenide has a bent bridging group [Nb—Se—Nb = 139.76 (2)°]. The difference is attributable to strong π bonding in the oxide case, although the effects on the Nb—C and Nb—SetBu bond lengths are small.