- Synthesis and structures of vanadium(II) alkynide complexes: [(LiTMEDA)2V(μ-C≡CPh)4(TMEDA)] and V(C≡CR)2(TMEDA)2 (R = Ph, tBu; TMEDA = N,N,N′,N′-tetramethylethylenediamine)
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The V(II) tetrakis- and bis(alkynide) complexes, [(LiTMEDA)2V(μ-C≡CPh)4 (TMEDA)] (1) and V(C≡CPh)2(TMEDA)2 (2) have been synthesized from the reaction between VCl3(THF)3 and LiC≡CPh in THF in the presence of TMEDA (=N,N,N′,N′-tetramethylethylenediamine). In the case of the analogous VCl3(THF)3/LiC≡CtBu/TMEDA reaction system, only the bis(alkynide) complex V(C≡CtBu)2 (TMEDA)2 (3) was isolable. Reduction of vanadium occurred during these reactions, and use of a divalent vanadium chloride, VCl2(TMEDA)2, instead of VCl3(THF)3 was found to give 1-3 in higher yields. Complex 1 crystallizes in the monoclinic space group P21/c with Z = 4 in a unit cell of dimensions a = 15.761(4) A?, b = 14.325(4) A?, c = 22.614(9) A?, and β = 98.38(4)°. Crystals of 2 are orthorhombic, space group Cmcm, with a = 10.045(5) A?, b = 22.379(7) A?, c = 12.306(4) A?, and Z = 4. Crystals of 3 are triclinic, space group P1, with a = 9.402(2) A?, b = 9.833(2) A?, c = 8.907(2) A?, and Z = 1. Reactions of these alkynide complexes with electrophiles such as Me3SiCl, MeI, PhNCO, CO2, and CO were examined.
- Kawaguchi, Hiroyuki,Tatsumi, Kazuyuki
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p. 4294 - 4299
(2008/10/09)
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- Dinitrogenvanadates(-1): Synthesis, Reactions and Conditions for their Stability
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Reduction of by Na or Li (M) in the presence of phosphines (Lm) and N2 yielded the complexes Na (n = 1 or 2), M2(4-n)> 2 = Me2PCH2CH2PMe2 (dmpe) or Ph2PCH2CH2PPh2>, Na3> 3 = PhP2, MeP2 (bdmpm) or MeP2> and Na4> 4 = P3, P3 or P3>.Generally, the complexes are labile, with a maximum stability for cis- and trans-M.In the presence of CO or CN-t-Bu, N2 is replaced by these ligands.The compounds have been characterized by their ν(NN) pattern and by 51V; 23Na and 7Li NMR spectroscopy.The 51 V NMR spectra exhibit well resolved multiplets.All spectroscopic data, in particular 7Li NMR of cis- and trans- in tetrahydrofuran, are indicative of close contact ion-pair interaction of the kind V-NN...M(1+).The potassium ion and large cations such as (1+) do not provide stable complexes, and complexation of Li(1+) and Na(1+) by crown ethers leads to immediate decomposition of the N2 complexes.The reductive protonation of part of the co-ordinated N2 to NH4(1+) (plus small amounts of N2H5(1+)) is discussed in term of similar reactivity features to the analogous complexes, and in the context of these N2 complexes as functional models for nitrogenases.The compound , isolated as an intermediate product of the reduction of VCl3, reacted with LiNHNH2 to yield ammonia.
- Gailus, Hartmut,Woitha, Claus,Rehder, Dieter
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p. 3471 - 3478
(2007/10/02)
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- Steric effects in the oxidative-addition reactions of gaseous V(CO)5-
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Some gas-phase reactions of the 16-electron complex V(CO)5- are reported. The reactions of V(CO)5-, generated by dissociative electron capture from V(CO)6, were performed in a Fourier transform ion cyclotron resonance mass spectrometer. V(CO)5- reacts with V(CO)6 to generate V(CO)6- and V2(CO)9-. V(CO)4-, also generated by dissociative electron capture from V(CO)6, reacts with V(CO)6 to generate V2(CO)7- and V2(CO)8-. These results contrast with condensed-phase photolysis studies of V(CO)6-. The reaction of V(CO)5- with CH3OH generates V(CO)4CH2O-. Labeling studies indicate a 1,2-dehydrogenation with retention of the incoming C-O group. V(CO)5- is unreactive with larger alcohols (C2-C4). this difference in reactivity is ascribed to a steric effect in the reaction intermediate. A positive second derivative in a plot of the decay kinetics for V(CO)5- consumed in the V(CO)5-/CH3OH reaction indicates the process is endothermic or there is an energy barrier along the reaction coordinate. These results also indicate internal excitation drives the dehydrogenation reaction.
- Buckner, Steven W.,VanOrden, Steven L.
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p. 1093 - 1097
(2008/10/08)
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- Synthesis of hexacarbonyl derivatives of group 5 metals and electron-transfer processes. Crystal and molecular structure of tetracarbonyl(1,2-bis(diphenylphosphino)ethane)iodotantalum
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Vanadium, niobium, and tantalum hexacarbonylmetalate(-I) derivatives of several heterocyclic nitrogen bases, RnB[M(CO)6]n (R = H, Me; n = 1, 2), have been synthesized. In some cases an electron transfer from the hexacarbonylmetalate to the protonated or methylated BRnn+ cation has been observed. Pyridinium halides react with Na[M(CO)6] (M = Nb, Ta) in the presence of 1 equiv of 1,2-bis(diphenylphosphino)ethane (diphos) to give high yields of the halo tetracarbonyl derivatives MX(CO)4(diphos). The red-orange TaI(CO)4(diphos) complex has been studied by X-ray diffraction methods. Crystal data: space group P21/n; Mr 818.3; a = 14.864 (10) ?, b = 9.875 (7) ?, c = 19.335 (13) ?; β = 105.61 (2)°; U = 2733 (3) ?3; Z = 4; Dcalcd = 1.988 g cm-3; F(000) = 1568; μ(Mo Kα) = 52.4 cm-1. The geometry of the seven-coordinate tantalum atom is best described as a capped trigonal prism with the iodide ligand in the capping position. By reaction of Na[Ta(CO)6] with 1 equiv of hydrogen chloride and diphos in toluene, the hydride TaH(CO)4(diphos) has been isolated in good yield.
- Calderazzo, Fausto,Pampaloni, Guido,Pelizzi, Giancarlo,Vitali, Francesca
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p. 1083 - 1092
(2008/10/08)
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- PROTON- AND CARBONYL-MEDIATED ELECTRON TRANSFER PROCESSES FROM THE HEXACARBONYLVANADATE(-I) ANION
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Hexacarbonylvanadate(-I) derivatives of several heterocyclic nitrogen bases, BH+-, have been synthesized.The deep red volatile pyridinium derivative +-, was studied by X-ray diffraction methods and found to be tetragonal, space group I41/amd, with a 10.384(3), c 12.373(3) Angstroem and Z=4.Solution of the structure by the heavy-atom method followed by full-matrix least-squares refinement gave the final residuals (R=0.0450 and Rw=0.0442) for 180 unique observed reflections.Coordination about the vanadium atom, which lies at a site of local 42m symmetry, is octahedral due to two independent carbonyl groups.The pyridine moiety is disordered.The major feature of the molecular structure is the interaction of the nitrogen proton with the carbonyl oxigens of - inb the equatorial plane of the octahedron.The structural features are regarded as evidence in favour of the carbyne-type of structure for the C6HO6V precursor of V(CO)6 (C6HO6V -> 1/2 H2 + V(CO)6).Several substitution and redox processes involving the protonated nitrogen base derivatives have been observed, namely: (a) nitrogen base exchange; (b) dihydrogen evolution upon treatment with sodium metal; (c) electron-transfer from - to the nitrogen-bonded proton, with dihydrogen evolution; (d) electron-transfer from - to the cation with carbon-carbon coupling in the case of acridinium derivative.All the compounds reported are deeply coloured (the quinolinium derivative is black), suggesting the existence of a multicentre CO-mediated charge transfer from vanadium to the nitrogen base.
- Calderazzo, Fausto,Pampaloni, Guido,Lanfranchi, Maurizio,Pelizzi, Giancarlo
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- Redox Reactions of Metal Carbonyls of Group 5A
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Redox reactions of V(CO)6 with -, -, 2-, or 5-C5H5)(CO)3>- (M = Cr, Mo, W), or Co(η5-C5H5)2 occur rapidly at 25 degC and lower in hydrocarbons; on the other hand, V(CO)6 is oxidized to V(η5-C5H5)(CO)4 by Mn(η5-C5H5)2 or Ni(η5-C5H5)2 and the two-electron oxidation of - to the - anion (X = Cl, Br, I, acetylacetonato), can be carried out using a number of oxidizing agents (HgII, CuII, CuI, AgI, or FeIII).
- Calderazzo, Fausto,Pampaloni, Guido
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p. 1249 - 1250
(2007/10/02)
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- Studies on carbonyl derivatives of early transition elements. A convenient method for the preparation of the [Nb(CO)6]- anion at atmospheric pressure and room temperature. Crystal and molecular structure of [M(CO)6]- (M = Nb, Ta) as their bis(triphenylphosphine)nitrogen(1+) derivatives
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A new method is reported for the preparation of [Nb(CO)6]- and [Ta(CO)6]- by reductive carbonylation of M2Cl10 (M = Nb, Ta) with the magnesium-zinc-pyridine-CO system. In the case of niobium, the reductive carbonylation occurs at atmospheric pressure and room temperature with yields as high as 48%. The tetrahydrofuran-stabilized sodium derivatives [Na(THF)][M(CO)6] and the bis(triphenylphosphine)nitrogen(1+) derivatives, PPN[M(CO)6] (M = Nb, Ta), are reported. The crystal and molecular structures of both niobium and tantalum PPN[M(CO)6] complexes are described. Both compounds are isostructural with the corresponding vanadium derivative: rhombohedral, space group R3, one molecule per cell; M = Nb, a = 9.832 (4) ?, α = 91.98 (5)°, V = 948.7 (7) ?3, ρcalcd = 1.399 g cm-3, R = 0.0391; M = Ta, a = 9.814 (4) ?, α = 92.02 (8)°, V = 943.4 (7) ?3, ρcalcd = 1.562 g cm-3, R = 0.0294 (Mo Kα, λ = 0.710 69 ?). The geometry of the two hexacarbonylmetalates is that of an almost perfect octahedron. Chemical and spectroscopic comparisons of the three [M(CO)6]- (M = V, Nb, Ta) anions are made.
- Calderazzo, Fausto,Englert, Ullrich,Pampaloni, Guido,Pelizzi, Giancarlo,Zamboni, Roberto
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p. 1865 - 1870
(2008/10/08)
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