Carbonylation Chemistry of the Tantalum Silyl Hydride Cp*(2,6-iPr2C6H3N)Ta[Si(SiMe3)3]H:  The Unexpected Formation of a Ta(V) Carbonyl Complex and the Complete Reduction of CO

Burckhardt, Urs; Tilley, T. Don

doi:10.1021/ja9905849

Cited by 41 publications

(27 citation statements)

References 21 publications

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“…Such highly downfield shifts for Ta(V) hydride species have precedent in the literature. [28][29][30] The 1 H NMR spectrum of 2a also displays a characteristic doublet of doublet of quartets at 3.1 ppm, corresponding to the methine proton of the cyclometallated isopropyl group; this feature results from coupling to each of the diastereotopic protons of the Ta bound methylene, as well as the unactivated methyl group. Compound 2b shows an analogous signal at 4.5 ppm.…”

Section: Synthesis and Characterization Of Cyclometallated Tantalum H...mentioning

confidence: 99%

Generation of low-valent tantalum species by reversible C–H activation in a cyclometallated tantalum hydride complex

2014

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The cyclometallated tantalum(v) hydride complex {ArNC(Me)CHC(Me)N[2-(CHMeCH2)-6-(i)Pr-C6H3]}Ta(N(t)Bu)H (2) was prepared from hydrogenolysis of (BDI)TaN(t)BuMe2 (BDI = N,N'-diaryl-β-diketiminate, aryl = 2,6-(i)Pr2-C6H3). Based on mechanistic studies, formation of 2 likely proceeds through a dihydride intermediate generated from successive σ-bond metathesis steps. Compound 2 was found to undergo reductive elimination under certain conditions to form trivalent tantalum species. Coordination of DMAP to 2, followed by gentle heating under H2, gives (MAD)Ta(N(t)Bu)(NAr)(DMAP), which is produced through reductive C-N bond cleavage of the BDI ligand in a Ta(iii) intermediate. Ta(iii) dicarbonyl derivatives have been accessed by either introducing CO atmosphere to the DMAP adduct of 2 at room temperature, or by directly adding CO to 2 at low temperature.

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Section: Synthesis and Characterization Of Cyclometallated Tantalum H...mentioning

confidence: 99%

Generation of low-valent tantalum species by reversible C–H activation in a cyclometallated tantalum hydride complex

2014

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“…While 1 reacts with HSiMe 2 Cl to give the agostic complexes 2 b and 2 b' as the only observed thermodynamic products (Scheme 1), the analogous reactions of silanes HSiClR 2 (R 2 = ClMe, Cl 2 , Ph 2 ) with more electron-withdrawing R groups at Si lead exclusively to silyl hydride derivatives 3 d-f (Scheme 2). [23] These compounds were characterized by spectroscopic methods and X-ray structure analyses of 2 b, [18] 3 e, 3 f [22] and 3 g. In particular, agostic species give rise to high-field hydride resonances in the 1 H NMR spectra in the range À2 to À7 ppm and to low frequency Si À H À Nb bands in the range 1620-1670 cm…”

Section: H T U N G T R E N N U N G (=Nar)a C H T U N G T R E N N U mentioning

confidence: 99%

Non‐Innocent Behaviour of Imido Ligands in the Reactions of Silanes with Half‐Sandwich Imido Complexes of Nb and V: A Silane/Imido Coupling Route to Compounds with Nonclassical SiH Interactions

Ignatov¹,

Rees

Merkoulov

et al. 2007

Chemistry A European J

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Reactions of imido complexes [M(Cp)(=NR')(PR''3)2] (M=V, Nb) with silanes afford a plethora of products, depending on the nature of the metal, substitution at silicon and nitrogen and the steric properties of the phosphine. The main products are [M(Cp)(=NR')(PR3)(H)(SiRnCl3-n)] (M=V, Nb; R'=2,6-diisopropylphenyl (Ar), 2,6-dimethylphenyl (Ar')), [Nb(Cp)(=NR')(PR''3)(H)(SiPhR2)] (R2=MeH, H2), [Nb(Cp)(==NR')(PR''3)(Cl)(SiHRnCl2-n)] and [Nb(Cp)(eta 3-N(R)SiR2--H...)(PR''3)(Cl)]. Complexes with the smaller Ar' substituent at nitrogen react faster, as do more acidic silanes. Bulkier groups at silicon and phosphorus slow down the reaction substantially. Kinetic NMR experiments supported by DFT calculations reveal an associative mechanism going via an intermediate N-silane adduct [Nb(Cp){=N(-->SiHClR2)R'}(PR''3)2] bearing a penta-coordinate silicon centre, which then rearranges into the final products through a Si--H or Si--Cl bond activation process. DFT calculations show that this imido-silane adduct is additionally stabilized by a Si--HM agostic interaction. Si--H activation is kinetically preferred even when Si--Cl activation affords thermodynamically more stable products. The niobium complexes [NbCp(=NAr)(PMe3)(H)(SiR2Cl)] (R=Ph, Cl) are classical according to X-ray studies, but DFT calculations suggest the presence of interligand hypervalent interactions (IHI) in the model complex [Nb(Cp) (==NMe)(PMe3)(H)(SiMe2Cl)]. The extent of Si--H activation in the beta-Si--HM agostic complexes [Cp{eta 3-N(R')SiR2--H}M(PR''3)(Cl)] (R''=PMe3, PMe2Ph) primarily depends on the identity of the ligand trans to the Si--H bond. A trans phosphine leads to a stronger Si--H bond, manifested by a larger J(Si--H) coupling constant. The Si--H activation diminishes slightly when a less basic phosphine is employed, consistent with decreased back-donation from the metal.

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“…Hence, complex 3 shows significantly more interaction based on these metrics. For further comparison, nearly all carbonyl complexes with d 0 metals fall into the range of 1980–2200 cm −1 for their observed CO stretching frequencies [34–39] . For example, (C 5 Me 5 ) 2 Zr( η 2 ‐E 2 )(CO) show stretching frequencies of 2057 (E=S), 2037 (E=Se), and 2006 (E=Te) cm −1 [33] .…”

Section: Methodsmentioning

confidence: 99%

“…For further comparison, nearly all carbonyl complexes with d 0 metals fall into the range of 1980-2200 cm À 1 for their observed CO stretching frequencies. [34][35][36][37][38][39] For example, (C 5 Me 5 ) 2 Zr(η 2 -E 2 )(CO) show stretching frequencies of 2057 (E = S), 2037 (E = Se), and 2006 (E = Te) cm À 1 . [33] One notable exception is (C 5 H 5 ) 2 Zr(η 2 -Me 2 Si=NtBu)(CO) with ν CO of 1797 cm À 1 , [40][41] which showed an unusual interaction between the silicon and carbonyl.…”

mentioning

confidence: 99%

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

Tarlton

Ward

et al. 2021

Chemistry A European J

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The coordination of tBuNC and CO with the diarsenido complexes (C 5 Me 5 ) 2 An(η 2 -As 2 Mes 2 ), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of Th IV and U IV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the Th IV and U IV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon An IV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(CÀ O) orbitals relative to the AnÀ As bond.

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Carbonylation Chemistry of the Tantalum Silyl Hydride Cp*(2,6-ⁱPr₂C₆H₃N)Ta[Si(SiMe₃)₃]H: The Unexpected Formation of a Ta(V) Carbonyl Complex and the Complete Reduction of CO

Cited by 41 publications

References 21 publications

Generation of low-valent tantalum species by reversible C–H activation in a cyclometallated tantalum hydride complex

Generation of low-valent tantalum species by reversible C–H activation in a cyclometallated tantalum hydride complex

Non‐Innocent Behaviour of Imido Ligands in the Reactions of Silanes with Half‐Sandwich Imido Complexes of Nb and V: A Silane/Imido Coupling Route to Compounds with Nonclassical SiH Interactions

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

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