- Paramagnetic Organometallics: Preparation, Stuctural, and Redox Chemistry of Tantalum(II) η6-Arene Complexes
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The reduction of (η6-C6R6)Ta(OR')2Cl with excess Na/Hg provides the first well characterised TaII organometallics, viz. the monomeric compounds (η6-C6R6)Ta(OR')2 (3)R=Et; (4
- Wexler, Pamela A.,Wigley, David E.
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p. 664 - 665
(2007/10/02)
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- Evidence for Intramolecular C-H Bond Activation and the Formation of a "Tucked-In" Complex of Hexamethylbenzene at a Tantalum(III) Center
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The reactions of the d2 tantalum complex (η6-C6Me6)Ta(OR)2Cl (1, OR=2,6-diisopropylphenoxide) with 3,3-dimethyl-1-butyne and 3-chloropropene provide the η1-pentamethylbenzyl compounds (E)-(η1-C6Me5CH2)Ta(CH=CH-(CMe3))(OR)2Cl (3) and (η1-C6Me5CH2)Ta(CH2CH2CH2Cl)(OR)2Cl (5), respectively.Both complexes are proposed to have arisen through the intermediacy of an unprecedented d0 "tucked-in" hexamethylbenzene compound, viz. (η6,η1-C6Me5CH2)Ta(H)(OR)2Cl (4).The intramolecular metalation of a methyl C-H bond in 1 and the existence of a hydride intermediate are also inferred from various deuterium labeling and kinetics studies.The metalated hexamethylbenzene can be functionalized selectively as demonstrated in the iodination of 3 to form C6(CH3)5CH2I and (E)-CHI=CH(CMe3).
- Ballard, Kurt R.,Gardiner, Ian M.,Wigley, David, E.
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p. 2159 - 2162
(2007/10/02)
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- Reactive alkyne complexes of tantalum and their metallacyclization chemistry: Models for alkyne cyclotrimerization by the early transition metals
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The reduction of Ta(DIPP)3Cl2 (DIPP = 2,6-diisopropylphenoxide) in the presence of bulky alkynes RC≡CR′ (R = R′ = Ph; R = Me3Si, R′ = Me) provides the alkyne adducts (DIPP)3Ta(RC≡CR′) in high yield. Unlike all previously known tantalum alkyne complexes, (DIPP)3Ta(PhC≡CPh) readily undergoes metallacyclization reactions with smaller alkynes RC≡CR′ (R = R′ = Me or Et) and terminal alkynes RC≡CR′ (R = CMe3, SiMe3, or Ph; R′ = H) to form the tantalacyclopentadienes (DIPP)3Ta(CPh=CPhCR′=CR). The molecular structure of the related metallacyclic complex (DIPP)3Ta(CEt=CEtCEt=CEt) has been determined. This compound crystallizes in the monoclinic space group P21/n [No. 14] with a = 14.340 (15) ?, b = 16.322 (22) ?, c = 19.929 (11) ?, β = 94.05 (7)°, V = 4655.9 ?3, and ρ(calcd) = 1.25 g cm-3 for mol wt 877.05 and Z = 4. Structure solution and refinement included 3191 reflections with Fo2 > 3.0σ(Fo2) of 9088 total (8245 unique) reflections measured for final discrepancy indices of RF = 4.6% and RwF = 4.5%. The molecular structure reveals a severely crowded coordination sphere, which is consistent with the fact that alkyne cyclotrimerization does not proceed beyond this point. By using the less crowded precursor Ta(DIPP)2Cl3 and decreasing the alkyne size from Me3SiC≡CSiMe3 to PhC≡CPh to MeC≡ CMe, successively higher coordinated alkyne cyclooligomers (C2, C4, and C6 compounds, respectively) can be isolated.
- Strickler, Jamie R.,Wexler, Pamela A.,Wigley, David E.
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p. 2067 - 2069
(2008/10/08)
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