Intramolecular hydrogenation of aryloxide ligands at niobium metal centers: Stereochemical consequences of reaction regiochemistry

Lockwood, Mark A.; Potyen, Mark C.; Steffey, Bryan D.; Fanwick, Phillip E.; Rothwell, Ian P.

doi:10.1016/0277-5387(95)85012-0

Cited by 29 publications

(34 citation statements)

References 42 publications

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“…Photolysis experiments were carried out using an Ace Hanovia 450 W Hg lamp cooled by a water condenser. The 1 H and 13 C NMR spectra were recorded on a Varian Associates Gemini-200 spectrometer and referenced to protio impurities of commercial C 6 D 6 or C 6 D 5 CD 3 . Variable-temperature 1 H NMR spectra were recorded on a broad band Gemini XL 200A spectrometer and referenced to the protio impurities in C 6 D 5 CD 3 .…”

Section: Methodsmentioning

confidence: 99%

“…1 H NMR (C 6 D 6 , 30 ЊC): δ 6.82-7.50 (m, 26 H, aromatics), 0.42 (s, 4 H, CH 2 SiMe 3 ), Ϫ0.04 (s, 18 H, SiMe 3 ). 13 C NMR (C 6 D 6 , 30 ЊC): δ 157.4 (TaOC), 123.5-140.6 (aromatics), 83.9 (TaCH 2 SiMe 3 ), 2.61 (SiMe 3 ).…”

Section: Methods (B)mentioning

confidence: 99%

“…1 H NMR (C 6 D 6 , 30 ЊC): δ 6.89-7.41 (m, 42 H, aromatics), 0.15 (s, 27 H, CH 2 SiMe 3 ), Ϫ0.24 (br s, 6 H, CH 2 SiMe 3 ). 13 A benzene solution (50 cm 3 ) containing [Ta(OC 6 HMe 2 -3,5-Ph 2 -2,6) 2 Cl 3 ] 1c (1.0 g, 1.2 mmol) was treated with LiCH 2 SiMe 3 (0.4 g, 4.2 mmol) and the resulting mixture was stirred at room temperature for 2 h during which time a fine white precipitate of LiCl formed. The solution was filtered and the solvent removed in vacuo.…”

Section: [Ta(oc 6 H 3 Ph 2 -26) 2 (Ch 2 Sime 3 ) 3 ] 4amentioning

confidence: 99%

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Intramolecular activation of aromatic C–H bonds at tantalum(V) metal centers: evaluating cyclometallation ‘resistant’ and ‘immune’ aryloxide ligation

Vilardo¹,

Lockwood²,

Hanson³

et al. 1997

J. Chem. Soc., Dalton Trans.

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The trichloride compounds [Ta(OC 6 HPh 2 -2,6-R 2 -3,5)Cl 3 ] (1: R = H a, Ph b, Me c, Pr i d or Bu t e) have been obtained by treating [Ta 2 Cl 10 ] with the corresponding 3,5-disubstituted-2,6-diphenylphenols Ia-Ie. The solid-state structures of 1c and 1d show a square-pyramidal structure with an axial aryloxide ligand. The reaction of 1 with LiCH 2 SiMe 3 (3 equivalents) led to the isolation of the tris(alkyls) [Ta(OC 6 HPh 2 -2,6-R 2 -3,5) 2 (CH 2 SiMe 3 ) 3 ] (4a-4d) except in the case of the 3,5-di-tert-butyl derivative 1e which generated the alkylidene compound [Ta(OC 6 H 3 Ph 2 -2,6-Bu t -3,5) 2 (᎐ ᎐ CHSiMe 3 )(CH 2 SiMe 3 )] 6e. The alkylidenes 6a-6d can be produced by photolysis of the corresponding tris(alkyls) 4a-4d. The alkylidenes 6a-6d undergo intramolecular cyclometallation of the aryloxide ligand (addition of an aromatic C᎐H bond to the tantalum alkylidene) at a rate which is extremely dependent on the meta substituents on the phenoxide nucleus. Kinetic studies show that conversion of 6a-6d into monometallated 7a-7d is first order with the phenyl, methyl and isopropyl substituents slowing the ring closure down by factors of 20, 90 and 360 respectively. The tert-butyl substituent completely shuts down cyclometallation of the adjacent phenyl ring. It is argued that bulky substituents inhibit rotation of the ortho-phenyl ring into a conformation necessary for C᎐H bond activation. Structural analysis of the torsion angles between ortho-phenyl and phenoxy rings has been carried out. The use of 1 H NMR chemical shifts has been demonstrated to be a valuable tool to probe the average conformations adopted in solution.

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Section: Methodsmentioning

confidence: 99%

Section: Methods (B)mentioning

confidence: 99%

Section: [Ta(oc 6 H 3 Ph 2 -26) 2 (Ch 2 Sime 3 ) 3 ] 4amentioning

confidence: 99%

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Intramolecular activation of aromatic C–H bonds at tantalum(V) metal centers: evaluating cyclometallation ‘resistant’ and ‘immune’ aryloxide ligation

Vilardo¹,

Lockwood²,

Hanson³

et al. 1997

J. Chem. Soc., Dalton Trans.

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“…H 2 was directly observed when the reaction was followed by 1 H NMR spectroscopy. Previously, Rothwell and co‐workers reported a similar abstraction in a niobium–aryloxide complex 16. Complex 5 is likely formed through σ‐bond metathesis (Scheme ).…”

Section: Resultsmentioning

confidence: 84%

CH Bond Activation during and after the Reactions of a Metallacyclic Amide with Silanes: Formation of a μ‐Alkylidene Hydride Complex, Its H–D Exchange, and β‐H Abstraction by a Hydride Ligand

Wang

Hunter

Song

et al. 2014

Chemistry A European J

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Metallacyclic complex [(Me2N)3Ta(η(2)-CH2SiMe2NSiMe3)] (3) undergoes C-H activation in its reaction with H3SiPh to afford a Ta/μ-alkylidene/hydride complex, [(Me2N)2{(Me3Si)2N}Ta(μ-H)2(μ-C-η(2)-CHSiMe2NSiMe3)Ta(NMe2)2] (4). Deuterium-labeling studies with [D3]SiPh show H-D exchange between the Ta-D-Ta unit and all methyl groups in [(Me2N)2{(Me3Si)2N}Ta(μ-D)2(μ-C-η(2)-CHSiMe2NSiMe3)Ta(NMe2)2] ([D2]-4) to give the partially deuterated complex [Dn]-4. In addition, 4 undergoes β-H abstraction between a hydride and an NMe2 ligand and forms a new complex [(Me2N){(Me3 Si)2N}Ta(μ-H)(μ-N-η(2)-C,N-CH2NMe)(μ-C-η(2)-C,N-CHSiMe2NSiMe3)Ta(NMe2)2] (5) with a cyclometalated, η(2)-imine ligand. These results indicate that there are two simultaneous processes in [Dn]-4:1) H-D exchange through σ-bond metathesis, and 2) H-D elimination through β-H abstraction (to give [Dn]-5). Both 4 and 5 have been characterized by single-crystal X-ray diffraction studies.

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“…1 In this context we are presently examining the chemistry of 3,5-disubstituted-2,6-diphenylphenoxidest in the expectation that the rneta-substituents will sterically hinder cyclometallation of the ortho-phenyl rings. 2 This communication details a study aimed at quantifying the metallation resistance of these new ligands.…”

mentioning

confidence: 99%

Intramolecular activation of aromatic C–H bonds by tantalum alkylidene groups: evaluating ‘cyclometallation resistant’ aryloxide ligation

Lockwood¹,

Clark²,

Parkin³

et al. 1996

Chem. Commun.

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Intramolecular hydrogenation of aryloxide ligands at niobium metal centers: Stereochemical consequences of reaction regiochemistry

Cited by 29 publications

References 42 publications

Intramolecular activation of aromatic C–H bonds at tantalum(V) metal centers: evaluating cyclometallation ‘resistant’ and ‘immune’ aryloxide ligation

Intramolecular activation of aromatic C–H bonds at tantalum(V) metal centers: evaluating cyclometallation ‘resistant’ and ‘immune’ aryloxide ligation

CH Bond Activation during and after the Reactions of a Metallacyclic Amide with Silanes: Formation of a μ‐Alkylidene Hydride Complex, Its H–D Exchange, and β‐H Abstraction by a Hydride Ligand

Intramolecular activation of aromatic C–H bonds by tantalum alkylidene groups: evaluating ‘cyclometallation resistant’ aryloxide ligation

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