Synthesis of neutral and cationic monocyclopentadienyl alkyl niobium and tantalum complexes

Sánchez‐Nieves, Javier; Tabernero, Vanessa; Camejo, Claudimar; Royo, Pascual

doi:10.1016/j.jorganchem.2010.06.030

Cited by 5 publications

(3 citation statements)

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“…The [MeB(C 6 F 5 ) 3 ] − counteranion is generally noncoordinating, but there are examples of [MeB(C 6 F 5 ) 3 ] − acting as a ligand . However, the [MeB(C 6 F 5 ) 3 ] − counteranion does not act as a ligand in 3a – c : the 1 H, 11 B, 13 C{ 1 H}, and 19 F NMR spectra of the counteranions in 3a – c match the reported values for free [MeB(C 6 F 5 ) 3 ] − . Additionally, the NMR spectra of the counteranions in 3a – c are identical with those of the counteranion in [ n -Bu 4 N] + [MeB(C 6 F 5 ) 3 ] − and the coordinatively saturated complex [Cp*Ir(I Me )Me(CO)] + [MeB(C 6 F 5 ) 3 ] − ( 5b ).…”

Section: Resultsmentioning

confidence: 54%

C–H Bond Activation by Cationic Iridium(III) NHC Complexes: A Combined Experimental and Computational Study

et al. 2012

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The cationic complexes [Cp*Ir(NHC)Me(solv)] + [MeB-(C 6 F 5 ) 3 ] − were prepared and studied as models for methane oxyfunctionalization catalysts (Cp* = η 5 -C 5 Me 5 ; NHC = 1,3,4,5-tetramethylimidazol-2-ylidene (MeI Me , 3a), 1,3-dimethylimidazol-2-ylidene (I Me , 3b), 1,3-dimethylbenzimidazol-2-ylidene (BI Me , 3c); solv = solvent or open site). These complexes were targeted on the basis of the C−H bond activation reactions of the previously reported complexes [Cp*Ir(PMe 3 )R] + (R = Me, H) and the general robustness of Ir−NHC complexes under oxidizing conditions. The syntheses of the new iridium(III) complexes Cp*Ir(NHC)Me 2 are described (NHC = MeI Me (4a), I Me (4b), BI Me (4c)). When 4a−c were allowed to react with B(C 6 F 5 ) 3 in CH 2 Cl 2 , the methyl abstraction products [Cp*Ir(NHC)Me(solv)] + [MeB(C 6 F 5 ) 3 ]  (3a−c) were produced. Complexes 3a−c reacted with arenes to form the aryl complexes [Cp*Ir(NHC)Ar(solv)] + [MeB(C 6 F 5 ) 3 ]  and methane (Ar = C 6 H 5 (7), C 6 H 4 F (8)). Complexes 3a−c reacted very slowly with alkanes; the slow reaction rate is attributed to steric congestion due to the NHC ligand. DFT calculations support this hypothesis: the barriers to C−H activation are in qualitative agreement with the empirical reaction rates, and the C−H activation transition state structures show significant steric crowding. Several of these complexes have been analyzed by X-ray diffraction.

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Section: Resultsmentioning

confidence: 54%

C–H Bond Activation by Cationic Iridium(III) NHC Complexes: A Combined Experimental and Computational Study

et al. 2012

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“…Elemental analyses were performed on a Perkin-Elmer 240C. The compounds [TaCp*Cl 4 ], [NbCp′Cl 4 ], [NbCp′Me 4 ], [TaCp*Me 4 ], [TaCp*(CHPh)(CH 2 Ph) 2 ], [TaCp*R 2 {O·B(C 6 F 5 ) 3 }] (R = Cl 1a , CH 2 Ph 1b , Me 1c ), H 2 O·B(C 6 F 5 ) 3 , (0.5 toluene)·Al(C 6 F 5 ) 3 and H 2 O·Al(C 6 F 5 ) 3 were prepared by literature methods.…”

Section: Methodsmentioning

confidence: 99%

Trapping Unstable Terminal M−O Multiple Bonds of Monocyclopentadienyl Niobium and Tantalum Complexes with Lewis Acids

Sánchez‐Nieves

Frutos²,

Royo³

et al. 2010

Inorg. Chem.

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Hydrolysis of [NbCp'Cl(4)] (Cp' = η(5)-C(5)H(4)SiMe(3)) with the water adduct H(2)O·B(C(6)F(5))(3) afforded the oxo-borane compound [NbCp'Cl(2){O·B(C(6)F(5))(3)}] (2a). This compound reacted with [MgBz(2)(THF)(2)] giving [NbCp'Bz(2){O·B(C(6)F(5))(3)}] (2b), whereas [NbCp'Me(2){O·B(C(6)F(5))(3)}] (2c) was obtained from the reaction of [NbCp'Me(4)] with H(2)O·B(C(6)F(5))(3). Addition of Al(C(6)F(5))(3) to solutions containing the oxo-borane compounds [MCp(R)X(2){O·B(C(6)F(5))(3)}] (M = Ta, Cp(R) = η(5)-C(5)Me(5) (Cp*), X = Cl 1a, Bz 1b, Me 1c; M = Nb, Cp(R) = Cp', X = Cl 2a) afforded the oxo-alane complexes [MCp(R)X(2){O·Al(C(6)F(5))(3)}] (M = Ta, Cp(R) = Cp*, X = Cl 3a, Bz 3b, Me 3c; M = Nb, Cp(R) = Cp', X = Cl 4a), releasing B(C(6)F(5))(3). Compound 3a was also obtained by addition of Al(C(6)F(5))(3) to the dinuclear μ-oxo compound [TaCp*Cl(2)(μ-O)](2), meanwhile addition of the water adduct H(2)O·Al(C(6)F(5))(3) to [TaCp*Me(4)] gave complex 3c. The structure of 2a and 3a was obtained by X-ray diffraction studies. Density functional theory (DFT) calculations were carried out to further understand these types of oxo compounds.

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“…On the other hand, niobium compounds appear interesting due to their modest toxicity, low sensitivity to deactivation by polar species, and large availability of stable oxidation states (from +5 to +2), which make them potential precursors for polymerization reactions.…”

Section: Introductionmentioning

confidence: 99%

Ethylene Polymerization by Niobium(V) N,N-Dialkylcarbamates Activated with Aluminum Co-catalysts

et al. 2011

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The niobium N,N-dialkylcarbamates Nb(O2CNR2) n [n = 5, R = Me, 1, Et, 2; n = 4, R = Et, 3; n = 3, R = Et, 4], in combination with organoaluminum cocatalysts, were found to be active in the polymerization of ethylene. The effects of the main reaction parameters (solvent, ethylene pressure, time, temperature, cocatalyst, reactivator) on the polymerization reaction were investigated in detail. When 2 was used as precursor in combination with trimethylaluminum (TMA)-depleted MAO and 1,2-dichloroethane as reactivator, activity up to 110 kgpolyethylene molNb −1 h−1 bar−1 was ascertained and linear, high molecular weight polyethylene was produced. The catalytic activities related to the different precursors increase along the series 2 > 1 > 3 > 4. The 1:1 reaction of 2 with Al2Et3Cl3 proceeds via ligand exchange, giving the X-ray characterized mixed alkyl-carbamato derivative [Al3(μ-O2CNEt2)6Et2]Cl (6), in admixture with presumable species containing niobium in lower oxidation state. The latter and not the former seem to be responsible for directing the polymerization process, according to the evidence that 6, produced by ligand exchange between Al(O2CNEt2)3 and AlEt2Cl, is not active under analogous experimental conditions.

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Synthesis of neutral and cationic monocyclopentadienyl alkyl niobium and tantalum complexes

Cited by 5 publications

References 56 publications

C–H Bond Activation by Cationic Iridium(III) NHC Complexes: A Combined Experimental and Computational Study

C–H Bond Activation by Cationic Iridium(III) NHC Complexes: A Combined Experimental and Computational Study

Trapping Unstable Terminal M−O Multiple Bonds of Monocyclopentadienyl Niobium and Tantalum Complexes with Lewis Acids

Ethylene Polymerization by Niobium(V) N,N-Dialkylcarbamates Activated with Aluminum Co-catalysts

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