- Synthesis and Reactivity of Bis(η-cyclopentadienyl) Trimethyltin derivatives of Niobium: Crystal and Molecular Structure of 2(μ-O)>
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The reaction between and LiBu followed by SnMe3Cl gives 2, also produced from and SnMe3H.Heating 2 with styrene, PMe3, isoprene or but-2-yne gives (L=η-H2C=CH-C6H5, 3; PMe3, 4; η-H2C=CHCMe=CH2, 5; or η-C2Me2, 6).Photolysis of complex 3 in the presence of CO, 2,6-Me2C6H3NC, MeCN, or PMe3 gives (L=CO, 7; 2,6-Me2C6H3NC, 8; η2-MeCN, 9a and 9b; or PMe3, 4).Heating 3 with H2 regenerates 2 and releases styrene.Compound 3, 5 or 6 reacts with SnMe3H to give the bis(stannyl) derivative 10, which is also formed by prolonged heating of with SnMe3H.Photolysis of 3 under CO2 gives a mixture of 7 and 2(μ-O)> 11 by cleavage of the CO2 molecule.Compound 11 crystallises in the orthorhombic space group Pbca with a=8.409(3), b=21.109(4) and c=15.582(3) Angstroem.The bridging oxygen atom sits on a crystallographic inversion centre giving a linear Nb-O-Nb group with Nb-O 1.9434(4) and Nb-Sn 2.8619(5) Angstroem.
- Green, Malcolm L. H.,Hughes, Andrew K.,Mountford, Philip
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- BIS(η-ISOPROPYLCYCLOPENTADIENYL)TANTALUM CHEMISTRY: SOME HYDRIDE, CARBONYL, ALKYL, ALKYNE AND TERTIARYPHOSPHINE DERIVATIVES, AND AN IMPROVED SYNTHESIS OF DICHLOROBISCYCLOPENTADIENYLNIOBIUM
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The new compounds Cl2, H3, H(CO), Cl(CO), Cl(PMe3); Me(PMe3) and Cl(Me2C2), where = Ta(η-i-PrC5H4)2, are described.Nb(η-C5H5)Cl2 is synthesised in high yield from Nb(η-C5H5)Cl4 and C5H5Sn(n-Bu)3.
- Green, Malcolm L.H.,Jousseaume, Bernard
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- Phosphinomethyl complexes of niobocene
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Reaction of LiCH2P(C6H5)2 with Cp2NbCl2 gives paramagnetic Cp2Nb[CH2P(C6H5)2] 2 (1); Cp2Nb(Cl)CH2P(C6H5)2 (4) is observed only as an unstable intermediate. Oxidation of 1 by AgBF4 gives Cp2Nb[CH2P(C6H4)2] 2+BF4- (6); reduction by Na/C10H8 gives Na+{Cp2Nb[CH2P(C6H4) 2]2}- (5), both isolable in analytically pure form as stable, diamagnetic solids. The anion of the latter crystallizes as its Na(18-crown-6)(THF)2+ salt in the monoclinic space group C2/c with cell parameters a = 27.088 (15) ?, b = 9.560 (5) ?, c = 25.903 (14), β = 126.19 (3)°, and Z = 4. The structure was refined to R = 0.044 and Rw = 0.046 using 3493 uniquely observed reflections. Reaction of 1 with (C7H8)Mo(CO)4 gives Cp2Nb[μ-CH2P-(C6H5) 2]2Mo(CO)4 (7), which crystallizes in the monoclinic space group P21/n with cell parameters a = 13.401 (5) ?, b = 17.188 (5) ?, c = 19.768 (6), β = 99.25 (3)°, and Z = 4. The structure was refined to R = 0.081 and Rw = 0.085 using 1851 uniquely observed reflections. Both 5 and 7 possess pseudotetrahedral Nb atoms, the latter octahedral Mo. Both Nb and Na in 5 lie on crystallographic 2-fold axes; no interaction between Nb and P is evident. The C-Nb-C angles to the phosphinomethyl groups are found to be 74.2 (2)° in 5- (d2 Nb), ca. 80-85° in 1 (d1 Nb, estimated from ESR data), and 90.4° in 7 (d1 Nb).
- Tueting, David R.,Olmstead, Marilyn M.,Schore, Neil E.
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- Synthesis, characterization and reactivity of tetracyclopentadienylniobium(IV), a precursor to organometallic derivatives of niobium(IV)
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In toluene as medium, tetra(cyclopentadienyl)niobium(IV), NbCp4, has been prepared in satisfactory yields from the reaction of NaCp with: (a) Nb2C110, (b) NbCl4(THF)2, or (c) NbCp2Cl2. Tetracyclopentadienylniobium(IV) has been characterized by X-ray diffraction. Crystal data: C20H20Nb, M=353.29 g mol-1, hexagonal, space group P65 (no. 170), a=b=9.396(2), c=31.23(3) ?, V=2388(2) ?3, Z=6, dcalc=1.48 g cm-3, λ(Cu-Kα)=1.54184 ?, T=291 K, μ=62.04 cm-1, F(000)=1686. Two of the four cyclopentadienyl ligands are bonded to niobium in a pentahapto fashion, the other two being monohapto. NbCp4 undergoes cyclopentadiene elimination in the presence of species containing active protons such as Ph3SiOH or strong acids, the products being tris- or biscyclopentadienyl compounds depending on the molar ratio of the reagents.
- Calderazzo, Fausto,Giardi, Cecilia,Englert, Ulli,Pampaloni, Guido
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p. 275 - 280
(2007/10/03)
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- The carbenoid nature of halophosphines. Carbene-like insertion mechanism in the reaction of chlorophosphines with Cp2NbH3
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We have studied the reactivity of Cp2NbH3 (1) with different chlorophosphines and showed that all the reactions occur at the niobium-hydride bond and proceed by two competitive routes, via the direct insertion of a chlorophosphine into the Nb-H bond and electron or/and hydride transfer mechanism. Reaction of 1 with the unhindered dialkyl-and diaryl-chlorophosphines C1PR2 (R = Et, Bu, Pri, Ph) gave the insertion product - the ionic complexes [Cp2NbH2(PHR2)]C1 (2) - in high yields. In contrast, reaction of 1 with the bulkier C1PBu12 proceeded much slower and resulted in the steady formation of Cp2NbC12 and HPBu12. Cp2NbC12 was also the product of the reactions of 1 with excess of C1P(OEt)2 and catecholechlorophosphite 7. The reaction of 1 with one equivalent of cyclic chlorodiaminophosphine C1P(N(CH3)2CH2-)2 (5) resulted in two competitive routes that led to the ionic complex [Cp2NbH2(HP(NR2)2)]C1 (2f) and molecular complex Cp2NbC1(HP(NR2)2) (6j). The reaction of 1 with two equivalents of cyclic 1-chloro-5,5-dimethyl-1-phospha-2,6-dioxahexane gave cationic diphosphite complex [Cp2Nb(PHR2)2]C1 (8) in high yield. This reactivity was explained in terms of the carbenoid nature of halophosphines due to the proposed relationship in the electronic structures of halophosphines and singlet methylene. Thus, reaction of 1 with the unhindered dialkyl-and diaryl-chlorophosphines proceeded by the direct insertion of a chlorophosphine C1PR2 into the Nb-H bond whereas with the more electron withdrawing substituents R at phosphorus the electron or/and hydride transfer mechanisms, leading to 6 and eventually to Cp2NbC12, could be operative. This concept also allowed us to explain the reactivity of chlorophosphines toward different unsaturated organic products. The facile syntheses of complexes Cp2Nb(PHR2)C1 (6) and Cp2Nb(PHR2)H (11) by the thermolysis and deprotonation of 2, respectively, was performed and the comparison with other methods was undertaken. Crystallographic studies of complexes 8 and Cp2Nb(PHPri2)Br are reported.
- Nikonov, Georgii I.,Grishin, Yuri K.,Lemenovskii, Dmitry A.,Kazennova, Nadezhda B.,Kuzmina, Lyudmila G.,Howard, Judith A. K.
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p. 183 - 198
(2007/10/03)
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- Preparation and reaction chemistry of trimethylsilyl derivatives of niobium. Redox chemistry of (η5-C5H5)2Nb(SiMe3)Cl and x-ray structures of (η5-C5H5)2Nb(SiMe 3)(η2-C2H4) and [(η5-C ...
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Full title: Preparation and reaction chemistry of trimethylsilyl derivatives of niobium. Redox chemistry of (η5-C5H5)2Nb(SiMe3)Cl and x-ray structures of (η5-C5H5)2Nb(SiMe 3)(η2-C2H4) and [(η5-C5H5)2Nb(CH 2SiMe3)Cl]PF6. The purple niobium(IV) silyl complex (η5-C5H5)2Nb(SiMe3)Cl (1) is prepared from reaction of (η5-C5H5)2NbCl2 with Hg(SiMe3)2. Reduction of 1 in the presence of ligands (L) affords niobium(III) silyl complexes (η5-C5H5)2Nb(SiMe 3)(L), where L = CO, PMe3, and C2H4. (η5-C5H5)2Nb(SiMe 3)(η2-C2H4) (4) crystallizes in the orthorhombic space group Pnma with a = 13.756 (3) A?, b = 12.819 (3) A?, c = 8.541 (2) A?, Z = 4, and RF = 2.26%. A crystallographic mirror plane in 4 contains the niobium atom, the ethylene ligand, Si, and C(9). The Nb-Si distance is 2.669 (1) A?. Oxidation of 1 in dichloromethane with ferrocenium hexafluorophosphate results in a complex reaction that produces Me3SiCl, Me3SiF, [(η5-C5H5)2Nb-(CH 2SiMe3)Cl]PF6 (5), and [(η5-C5H5)2NbCl 2]PF6 (6). The methylene group in 5 originates from the dichloromethane solvent. The mechanism of this reaction is discussed. Crystals of 5 are orthorhombic, space group P212121, with a = 10.542 (2) A?, b = 12.546 (2) A?, c = 14.712 (2) A?, Z = 4, and RF = 4.11%. The Nb-C σ bond distance in 5 is 2.208 (8) A?.
- Arnold, John,Don Tilley,Rheingold, Arnold L.,Geib, Steven J.
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p. 473 - 479
(2008/10/08)
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- MIXED HALODICYCLOPENTADIENYL-NIOBIUM(V) AND -TANTALUM(V)
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Oxidation of (η5-C5H5)2MCl (M = Nb, Ta) with 1 mol of Cl2, Br2 or I2 gives (η5-C5H5)2MClX2, whereas the reaction with an excess of the halogen gives the cationic complexes 5-C5H5)2MClX>+X3- (X = Br
- Antinolo, A.,Fajardo, M.,Otero, A.,Royo, P.
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- NIOBIUM ORGANOMETALLIC CHEMISTRY. X. SYNTHESIS OF NEW (η2-DISULFIDO) COMPLEXES; COMPARISON OF THEIR REACTIVITY WITH THAT (η2-DIOXO) DERIVATIVES
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The new compounds 5-C5H5)2(X-X)R> ( with M = Nb : X = S, R = Me, Bu, η1-C5H5; X = Se, R = Me; with M = Ta : X = S, R = Me) are described.The reactions of 5-C5H5)2(S-S)Me> (A) with some nucleophiles and electrophiles have been studied.A reacts with triphenylphosphine to give the corresponding monosulfido complex.Loss of the S2 ligand and formation of a μ-oxoderivative 5-C5H5)2Me>2O> X2 * 2OH2 (X = I or BF4) occurs upon treatment of A with CH3I or Ph3CBF4. 5-C5H5)2Me I>I, MeSSMe, have also been identified as product from the reactionwith CH3I.Reaction of A with hexafluorobutyne gives an unexpected new compound, the nature of which is discussed.
- Migot, Jean-Louis,Sala-Pala,Jean,Guerchais, Jacques-E.
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p. 427 - 436
(2007/10/02)
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- DICYCLOPENTADIENYL-NIOBIUM(III) AND -NIOBIUM(IV) COMPLEXES
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The reduction of (η-C5H5)2NbCl2 (I) under various conditions gives the dimer (η-C5H5)4Nb2Cl3 (II) containing niobium(III) and niobium(IV).Reaction of II with AgClO4 gives + ClO4- (III).FeCl3 and (C6F5)2TlBr displace
- Antinolo, A.,Fajardo, M.,Otero, A.,Royo, P.
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p. 309 - 314
(2007/10/02)
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- SYNTHESE ET ETUDE DE CHLOROTRICYCLOPENTADIENYLNIOBIUM(IV)
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The action of cyclopentadienide anions on (Cp)2-n(RCp)nNbCl2 complexes (n=2, 1 or 0; R=C(CH3)3) is reported.In all cases, the formation of tricyclopentadienyl complexes, identified by ESR spectroscopy, is observed.Some tricyclopentadienyl species are able to be transformed by η1-η5 fluctuation.An example of a tricyclopentadienyl complex involving a stereochemical blocking is presented.By use of this intermediate a dicyclopentadienyl derivative of niobium(IV) containing two different rings is selectively synthetized.
- Broussier, R.,Olivier, J. D.,Gautheron, B.
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