Showing papers by "Malcolm L. H. Green published in 1992"
TL;DR: In this article, the partial oxidation of methane by oxygen giving synthesis gas can be catalysed to thermodynamic equilibrium using the transition metals Ni, Ru, Rh, Pd, Pt and Ir supported on inert oxides.
229 citations
TL;DR: In this article, a simplified method for obtaining rate constants from dynamic NMR experiments in which the exchange processes are defined by more than a single rate-limiting step is described, which can be used in the construction of kinetic (Kubo-Sack) matrices.
102 citations
66 citations
TL;DR: In this article, a series of new donor-acceptor compounds of the form (η-C 5 H 5 )Fe( η-c 5 H 4 ) CHCHR, where R is a π- acceptor group and the ferrocenyl moiety is a donor has been synthesized.
59 citations
TL;DR: The second-order nonlinear optical properties of a series of diironalkenylidyne complexes have been examined by the Kurtz powder technique as discussed by the authors, and one compound exhibited a powder efficiency for second harmonic generation 3.6 times that of a urea reference standard (ω = 1907 nm, 2ω = 953.5 nm).
40 citations
TL;DR: In this article, the new compounds [Ta({eta}-C{sub 7}H{sub 6}H-sub 7] (Ta, C{sub 5}H {sub 4}Me) and [NB(C{ sub 7} H{sub 4]Me] (NB, Nb) have been obtained and the X-ray crystal structures of 4a and 7 have been determined.
34 citations
TL;DR: The pseudo-trigonal bis(η-cyclopentadienyl)-molybdenum and -tungsten imido complexes were reported in this article.
Abstract: The pseudo-trigonal bis(η-cyclopentadienyl)-molybdenum and -tungsten imido complexes [M(η-C5H4R)(η-C5H4R′)(NBut)](M = Mo or W; R = R′= Me or H, R′= Pri R = H) are reported together with the ring-slipped indenyl analogue [Mo(η-C5H4Pri)(η3-C9H7)(NBut)] and the metal-methylated salts [Mo(η-C5H4Me)2(NBut)Me]X (X = I or BF4); the X-ray structures of [Mo(η-C5H5)2(NBut)] and [Mo(η-C5H4Me)2(NBut)Me]BF4 suggest that the NBut ligand acts as a strong π-donor to the metal centre; photoelectron studies identify an unusually low ionization-energy band largely localized on the ligands.
31 citations
TL;DR: The new imido compounds [M(η-C5H4R)Cl2(NR′)] and [Mo(NBut)Cl(PMe3)3] are synthesized; * indicates that the crystal structure has been determined.
Abstract: The new imido compounds [M(η-C5H4R)Cl2(NR′)]*(M = Mo, R = H, R′= But, Prn or Ph; M = Mo, R = Me, R′= But or Ph; M = W, R = H, R′= But), [Mo (η-C5H4R)Cl(L)(NR′)](R = H, R′= But, L =η-C2H4, or η-C2Me2; R = Me, R′= But, L = C2H4*; R = H, R′= Ph, L =η-C2Me2), [{Mo(η-C5H4R)(η-C2H4)(NBut)}2Hg]*(R = H, Me), [Mo (NBut)Cl2(PMe3)3], [Mo(η-C5H5)Cl3(NBut)] and the π-allyl complex [Mo(η-C5H4Me)(η-C3H5)(NBut)] are synthesised; *indicates that the crystal structure has been determined.
29 citations
TL;DR: This study found that repetitive supramaximal stimulation of an affected peripheral nerve is commonly performed to detect abnormal transmission at the neuromuscular junction may be a useful and non-invasive method for identifying patients with myasthenia gravis in whom weakness of the diaphragm is suspected.
Abstract: BACKGROUND: In the investigation of patients with myasthenia gravis, repetitive supramaximal stimulation of an affected peripheral nerve is commonly performed to detect abnormal transmission at the neuromuscular junction. A study was undertaken to determine whether abnormal transmission could similarly be detected during stimulation of the phrenic nerves. METHODS: The phrenic nerves were stimulated supramaximally with surface electrodes in 13 patients with myasthenia gravis and in 16 control subjects (six control patients with diaphragmatic weakness but not with myasthenia and ten normal subjects). The amplitude of diaphragm muscle action potentials was measured with surface electrodes during phrenic nerve stimulation at frequencies of 1-5 Hz for 3-4 seconds. RESULTS: In five patients with myasthenia gravis, a significant decrement (15-43% decrease) occurred in the amplitude of diaphragm muscle action potential during stimulation at 3 Hz. When stimulation frequency was reduced to 1 Hz, diaphragm muscle action potentials returned to their original amplitude within 4-5 seconds. The decrement in the amplitude of the diaphragm muscle action potential was reduced temporarily in three of four patients after the administration of intravenous edrophonium chloride (Tensilon). There was no significant change (< 10% decrease) in the amplitude of diaphragm muscle action potentials during stimulation at increased frequencies either in the 16 control subjects or in eight of the patients with myasthenia gravis. CONCLUSION: A significant reduction in the amplitude of diaphragm muscle action potential occurred in five of 13 patients with myasthenia gravis during phrenic nerve stimulation at 3 Hz but in none of the control subjects. This may be a useful and non-invasive method for identifying patients with myasthenia gravis in whom weakness of the diaphragm is suspected.
28 citations
TL;DR: In this paper, the authors investigated the effect of temperature, pressure and residence time on the reactions of methane and oxygen over an empty silica tube and found that at elevated pressure and temperature a considerable amount of aromatics (benzene and toluene) is formed.
Abstract: The temperature, pressure and residence time effects on the reactions of methane and oxygen over an empty silica tube have been studied. It has been found that at elevated pressure and temperature a considerable amount of aromatics (benzene and toluene) is formed. The yield of aromatic products is comparable to that for the gas-phase production of methanol, and is higher than that reported for form-aldehyde. Metal oxide catalysts enhance the selectivity and the yield of aromatics. Thus, chlorine-promoted manganese oxide gives a consistently higher yield of aromatics than the empty tube reactions. However, we are unable to reproduce recent reports of high benzene selectivity over supported nickel catalysts. The mechanisms for the formation of aromatics have been investigated and the possible path-ways are discussed.
26 citations
TL;DR: In this paper, Li(CH2D) is described and the isotope shift for all these complexes are essentially temperature independent, indicating the presence of a monoagostic methyl group.
Abstract: Nuclear magnetic resonance studies on [W(η-C5Me4Et)(CH2D)4][PF6] show a strong temperature dependence of the isotope shift [δ(CH3)–δ(CH2D)] indicating the presence of a monoagostic methyl group. The magnitude and sign of the geminal coupling constant 2J(H–D)[and 2J(H–H)] and the isotope shift, together with the temperature dependence of this shift, have been recorded for [Ti(CH2D)Cl3], [Ti(CH2D)Cl3(dmpe)](dmpe = Me2PCH2CH2PMe2), [Ta(CH2D)nCl5–n](n= 1–3), [M(η-C5H5)2(CH2D)2](M = Ti, Zr or Hf), [M(η-C5H5)2(CH2D)(thf)][BPh4](M = Ti or Zr, thf = tetrahydrofuran), [Ti(η-C5H5)2(CH2D)F], [Zr(η-C5H5)2(CH2D)(MeCN)2][BPh4], [Ti(η-C5H5)(CH2D)3], [M(η-C5Me4Et)(CH2D)3](M = Ti, Zr or Hf) and [Y(η-C5Me5)2(CH2D)(thf)]. The isotope shifts for all these complexes are essentially temperature independent. A convenient synthesis of Li(CH2D) is described.
TL;DR: In this paper, the fluxional processes in the compounds exo-[M({eta}-C{sub 5}H{sub 4]{sub 3}CH=CH{sub 2})H] (M = Nb, Ta) have been investigated by magnetization and spin-saturation transfer and two-dimensional exchange NMR techniques.
TL;DR: In this article, the structure of diene compounds was determined by low-temperature neutron diffraction (15 K) and the σ2, π nature of the bonding mode of the 2,3-dimethylbutadiene ligand demonstrated from the methylene hydrogen positions.
Abstract: The diene compounds [Hf(η4-CH2CMeCMeCH2)(PMe3)2Cl2]1, [M(η4-C6H8)(PMe3)2Cl2](M = Zr 2 or Hf 3) and the divalent [Zr(η6-C6H5Me)(PMe3)2Cl2]5 have been prepared. The structure of compound 1 has been determined by low-temperature neutron diffraction (15 K) and the σ2, π nature of the bonding mode of the 2,3-dimethylbutadiene ligand demonstrated from the methylene hydrogen positions. Treatment of 1 with lithium indenide gave [Hf(η5-C9H7)2(η4-CH2CMeCMeCH2)]4. The crystal structure of 5 has been determined by X-ray diffraction.
TL;DR: The crystal structure of the compound [Nb(η:σ-C 5 H 4 (CH 2 ) 3 N) (PMe 3 )Cl 2 ] has been determined as discussed by the authors.
TL;DR: In this paper, the X-ray crystal structures of [W(η-C6H5Me)(PMe3)3H2][PF6] have been determined by multinuclear two-dimensional NMR spectroscopy.
Abstract: The compounds [W(η-C6H5Me)(PMe3)3] and [W(η-C6H5Me){SiMe(CH2PMe2)3}] have been prepared from [W(η-C6H5Me)2] and tertiary phosphines. They are protonated by NH4BF4 to give [W(η-C6H5Me)(PMe3)3H]BF4 and [W(η-C6H5Me){SiMe(CH2PMe2)3}H]BF4, respectively. Reaction of [W(η-C6H5Me)(PMe3)3] with HCl gas gives the diprotonated cation [W(η-C6H5Me)(PMe3)3H2]2+. Treatment of [W(η-C6H5Me)(η-C3H5)(dmpe)]PF6[dmpe = 1,2-bis(dimethylphosphino)ethane] with LiAlH4 gives the η-methylcyclohexadienyl complex [W(η5-C6H6Me)(η-C3H5)(dmpe)], as a mixture of inseparable isomers. These have been characterised by multinuclear two-dimensional NMR spectroscopy. The fluorohydride [W(η-C6H5Me)(dmpe)H(F)] has also been prepared. The X-ray crystal structures of [W(η-C6H5Me)(PMe3)3H2][PF6]2 and [W(η-C6H5Me)(dmpe)H(F)] have been determined.
TL;DR: In this article, one-pot reactions have been used to obtain the exo-trimethylsilylcycloheptatriene compound [Zr{exo-η6-C7H7(SiMe3)}(PMe3)2I2]
Abstract: Treatment of [Zr(η6-C7H8)2]1 in tetrahydrofuran with iodine gives [Zr(η-C7H7)(thf)2I]2 which reacts with PMe3 forming [Zr(η-C7H7)(PMe3)2I]3. The latter reacts with iodotrimethylsilane to give the exo-trimethylsilylcycloheptatriene compound [Zr{exo-η6-C7H7(SiMe3)}(PMe3)2I2]4. Thermolysis of 4 gives [Zr(η6-C7H8)(PMe3)2I2]5. The compounds [M(η-C7H7)L2Cl][M = Ti, L2=(PMe3)26, Me2NCH2CH2NMe27 or Me2PCH2CH2PMe28; M = Zr, L2= Me2NCH2CH2NMe29] have been prepared in one-pot reactions.
TL;DR: In this paper, the new compounds [M(η-C7H8)L2Cl2] have been synthesised by reduction of MCl4 using sodium amalgam in the presence of the tertiary phosphine and cycloheptatriene.
Abstract: The new compounds [M(η-C7H8)L2Cl2](M = Zr, L = PMe31; M = Hf, L = PMe32; M = Zr, L = PMe2Ph 3; M = Hf, L = PMe2Ph 4; M = Zr, L = PMePh25) have been synthesised by reduction of MCl4 using sodium amalgam in the presence of the tertiary phosphine and cycloheptatriene. Lithium indenide reacts with the triene compounds to give [M(η-C7H7)(η5-C9H7)](M = Zr 6 or Hf 8) which react with trimethylphosphine or 1,2-bis(dimethylphosphino)ethane (dmpe) to form [M(η-C7H7)(η5-C9H7)(PMe3)](M = Zr 7 or Hf 9) and [{Hf(η-C7H7)(η5-C9H7)}2(µ-dmpe)]10 respectively. Treatment of 1 or 2 with sodium cyclopentadienide gives [M(η-C5H5)2{η2-1,2-(or -3,4-) C7H8}(PMe3)][M = Zr 11 or Hf 12). The X-ray crystal structures of 1, 10 and [Zr(η-C5H5)2(η2-3,4-C7H8)(PMe3)]11a have been determined.
TL;DR: The WW triply bonded dimers readily undergo addition reactions with various Lewis bases to give the complexes [W2(η-C5H4Me)2Cl2(µ-Cl)2(DMpe)][DMpe = 1,2-bis(dimethylphosphino)ethane] as discussed by the authors.
Abstract: The WW triply bonded dimers [W2(η-C5H4R)2X4](X = Cl, R = Pri1a or Me 1b; X = Br, R = Pri2) readily undergo addition reactions with various Lewis bases to give the complexes [W2(η-C5H4Me)2Cl2(µ-Cl)2(dmpe)][dmpe = 1,2-bis(dimethylphosphino)ethane],*[W2(η-C5H4R)2Cl2(µ-Cl)2(CO)2],*fac-[W(η-C5H4Pri)Br3(CO)2],*[W2(η-C5H4R)2Cl3(µ-Cl)(µ-σ:η2-ButNC)(ButNC)], [N(PPh3)2][W2(η-C5H4R)2Cl4(µ-Cl)] and [W2(η-C5H4R)2Cl3(µ-Cl)(µ-σ:η2-R′CN)](R′= Me, Et* or Ph; R = Pri or Me). Treatment of the last compounds with HCl affords the µ-iminoacyl derivatives trans- and cis-[W2(η-C5H4R)2Cl4(µ-Cl)(µ-R′CNH)].* The compounds labelled* have been crystallographically characterised.
TL;DR: In this paper, the activation barrier to olefin hydride exchange has been determined by coalescene methods to be ΔG‡= 70.0 ± 2 kJ mol−1 at 50 °C, which is significantly lower than that for the analogous η-C5H5 and ηC5Me5 complexes.
Abstract: The reaction between [NbCl4(thf)2](thf = tetrahydrofuran) and Li[C9H7] or Na[C9H7]·thf gives [Nb(η-C9H7)2Cl2]1, which reacts with NaBH4 to give [Nb(η-C9H7)2(µ-H2BH2)]2. The bridging and terminal tetrahydroborate protons in 2 exchange on the NMR time-scale (ΔG‡= 55.2 ± 1.6 kJ mol–1). Compound 2 reacts with PMe2Ph or pyridine via BH3 extraction to give [NbH(η-C9H7)2(PMe2Ph)]3 and [NbH(η-C9H7)2(NC5H5)]4 respectively. The pyridine ligand in 4 undergoes restricted rotation about the Nb–N bond (ΔG‡= 52 ± 1 kJ mol–1). The reaction of 2 with NMe3 in the presence of CO, H2CCCH2, trans,trans-hexa-2,4-diene or styrene gives the new complexes [Nb(η-C9H7)(CO)4]5, [Nb(η-C9H7)2(η-CH2CHCH2)]6, [Nb(η-C9H7)2(η-MeCHCHCHCH2Me)]7 and endo-[NbH(η-C9H7)2(η-H2CCHPh)]9 respectively. The styrene hydride (complex 9) is fluxional and this process has been studied using both one- and two-dimensional NMR techniques. The activation barrier to olefin hydride exchange has been determined by coalescene methods to be ΔG‡= 70.0 ± 2 kJ mol–1 at 50 °C, this is significantly lower than that for the analogous η-C5H5 and η-C5Me5 complexes. A mechanism that involves a ring slipped intermediate is proposed.
TL;DR: In this article, three catalytic processes are combined to give 13% yield of propanal based on total methane input, which is substantially higher than that of ethene from the oxidative coupling reaction.
Abstract: High yield synthesis of propanal from methane and air can be obtained in a single pass at atmospheric pressure. Three catalytic processes are combined to give 13% yield of propanal based on total methane input. Ethene is made from the oxidative coupling reaction and carbon monoxide and hydrogen is generated from partial oxygenation of methane. These gases are combined and passed to a hydroformylation catalyst to give liquid propanal. The unreacted methane is inert in the hydroformylation stage, while oxygen deactivates the catalyst readily. The results imply that propanal can be obtained, in good yield, from methane and air provided that total oxygen conversion is achieved. The yield of propanal from the three combined processes can be substantially higher than that of ethene from the oxidative coupling reaction. Thus, higher yields of a condensible and oxygenated product are obtained.
TL;DR: The planar bridging C4Me4 moiety in the crystallographically characterised trans-[W2(η-C5H4Me)2Cl4(µ-C4Me 4] is found to be perpendicular to the W-W bond and bound to each metal atom in a tetrahapto fashion as mentioned in this paper.
Abstract: The WW triply bonded dimers [W2(η-C5H4Pri)2X4](X = Cl or Br) react with alkynes C2R2 to afford the dimetallatetrahedrane complexes [W2(η-C5H4Pri)2X4(µ-C2R2)](X = Cl, R = Et or SiMe3; X = Br, R = Me, Et or Ph†) or poorly defined polynuclear complexes [{W(η-C5H4Pri)Br2(CR)}3x](R = Me or Et) depending upon the reaction conditions. Treatment of [W2(η-C5H4R)2X4](X = Cl, R = Pri or Me; X = Br, R = Pri) with an excess of but-2-yne affords the corresponding flyover bridge complexes [W2(η-C5H4R)2X4(µ-C4Me4)]; treatment of [W2(η-C5H4Pri)2Cl4] with pent-2-yne gives a mixture of the isomers [W2(η-C5H4Pri)2Cl4{µ-(2,3)-C4Et2Me2}] and [W2(η-C5H4Pri)2Cl4{µ-(1,4)-C4Et2Me2}]. The planar bridging C4Me4 moiety in the crystallographically characterised trans-[W2(η-C5H4Me)2Cl4(µ-C4Me4)] is found to be perpendicular to the W–W bond and bound to each metal atom in a tetrahapto fashion. Treatment of [W2(η-C5H4Pri)2Cl4(µ-C2Et2)] or [{W(η-C5H4Pri)Br2(CEt)}3x] with an excess of but-2-yne affords the mixed-alkyne flyover bridge complexes [W2(η-C5H4Pri)2X4{µ-(1,2)-C4Et2Me2}](X = Cl or Br). The complexes [W2(η-C5H4R)2Cl4(µ-C4Me4)](R = Me or Pri) are readily hydrolysed in wet acetone to form the corresponding monooxo complexes [W2(η-C5H4R)2Cl2O(µ-C4Me4)]†. Complexes labelled † have been crystallographically characterised.
TL;DR: The synthesis of [Mo(η-C7H7)LX2] from MoCl5 provides a convenient route to η-cycloheptatrienylmolybdenum compounds such as [Mo[C 7H7]L2X], where L = tertiary phosphines or acetonitrile and X = halogen, and R = H, Me.
Abstract: The synthesis of [Mo(η-C7H7)(η-C7H9)] from MoCl5 provides a convenient route to η-cycloheptatrienylmolybdenum compounds such as [Mo(η-C7H7)LX2] and [Mo(η-C7H7)L2X], where L = tertiary phosphines or acetonitrile and X = halogen, and [Mo(η-C7H7)(η-C5H4R)], R = H, Me.
Journal Article•
TL;DR: Reduction of WCl6 with sodium amalgam in the presence of cycloheptatriene gives [W(η-C7H7)LX2], where L = tertiary phosphines or acetonitrile and X = halogen as mentioned in this paper.
Abstract: Reduction of WCl6 with sodium amalgam in the presence of cycloheptatriene gives [W(η-C7H7)(η-C7H9)], which is a precursor to the compounds [W(η-C7H7)LX2], [W(η-C7H7)L2X], where L = tertiary phosphines or acetonitrile and X = halogen, [W(η-C7H7)(η-C5H4R)], R = H, Me, and [W(η-C7H7)(η-C9H7)].
TL;DR: The 17-electron compound [Nb(η6-C7H8)(PMe3)2Cl2] as mentioned in this paper contains mutually trans tertiary phosphine and chloro ligands, and the first crystallographically characterised η4-cycloheptatriene ligand, which is discussed in relation to its 13C NMR spectrum and the use of inverse-mode (1H-observed)13C-1H shift correlation NMR spectroscopy.
Abstract: The new compounds [Nb(η6-C7H8)(PMe3)2Cl2]1, [Nb(η-C7H7)(η4-C7H8)(PMe3)]2 and [Nb(η-C7H7)(CO)3]4 have been prepared. The 17-electron compound 1 has been crystallographically characterised and contains mutually trans tertiary phosphine and chloro ligands. Compound 2 contains the first crystallographically characterised η4-cycloheptatriene ligand, the structure of which is discussed in relation to its 13C NMR spectrum and the use of inverse-mode (1H-observed)13C–1H shift correlation NMR spectroscopy. Treatment of 1 with magnesium butadiene reagent gives [Nb(η-C7H7)(η4-C4H6)(PMe3)]3 and photolysis of 4 in the presence of cycloheptatriene gives [Nb(η-C7H7)(η-4-C7H8)(CO)]5. Compound 2 is protonated readily to yield [Nb(η-C7H7)(η5-C7H9)(PMe3)][PF6]6, and reacts with iodomethane to yield paramagnetic [Nb(η-C7H7)(PMe3)2I]7 which is isomorphous with the analogous 16-electron compound [Zr(η-C7H7)(PMe3)2I], but has an unusually long Nb–I bond. Compound 4 reacts with Me2PCH2CH2PMe2(dmpe) to give the monomeric [Nb(η-C7H7)(dmpe)(CO)]9. The analogous compound [Nb(η-C7H7)(PMe3)2(CO)]10 is prepared by reaction of 4 with PMe3. The paramagnetic sandwich complexes [Nb(η-C5H5)(η-C7H7)]11 and [Nb(η-C5H4Me)(η-C7H7)]12 react with 1 equivalent of allyl bromide to yield the diamagnetic bent-sandwich species [Nb(η-C5H5)(η-C7H7)Br]13 and [Nb(η-C5H4Me)(η-C7H7)Br]14 respectively.
TL;DR: The 17-electron compounds Nb(η-C7H7)(η -C5H4R) undergo reversible oneelectron oxidation and reduction, giving the structurally characterised compounds [Nb(nb(c7h7),c5h4Me)(thf)]PF6 and [K(18crown-6)], respectively; the latter has an unusual distorted chain structure as discussed by the authors.
Abstract: The 17-electron compounds Nb(η-C7H7)(η-C5H4R) undergo reversible one-electron oxidation and reduction giving the structurally characterised compounds [Nb(η-C7H7)(η-C5H4Me)(thf)]PF6 and [K(18-crown-6)][Nb(η-C7H7)(η-C5H5)] respectively; the latter has an unusual distorted chain structure.