Site selectivity and reversibility in the reactions of titanium hydrazides with Si–H, Si–X, C–X and H+ reagents: TiNα 1,2-silane addition, Nβ alkylation, Nα protonation and σ-bond metathesis

Tiong, Pei Jen; Nova, Ainara; Schwarz, Andrew D.; Selby, Jonathan D.; Clot, Eric; Mountford, Philip

doi:10.1039/c2dt12359b

Cited by 32 publications

(31 citation statements)

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“…Therefore, the reaction is a hydride-based reduction. [11] As for 3, the 1 H-29 Si HSQC experiment with J = 7 Hz shows coupling of Si with H1M-H3M, whereas that with J = 200 Hz only shows the coupling of Si with H2M and H3M. The molecular structure of 4 is shown in Figure 2.…”

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confidence: 87%

An Yttrium Hydride–Silane Complex as a Structural Model for a σ‐Bond Metathesis Transition State

et al. 2013

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The transition-metal-promoted Si À H bond cleavage is a pivotal step in several important catalytic processes, such as hydrosilylation, hydrosilane dehydropolymerization, and dehydrogenative silylation. [1][2][3][4] There are two different mechanisms for the metal-mediated SiÀH bond cleavage: a) oxidative addition of Si À H bond toward a low-valent electronrich metal, in which a s-complex is believed to be the key intermediate; and b) s-bond metathesis of Si À H and M À E bonds (E = C, N, H, etc.) via a four-center transition state (Scheme 1). [5] As evidence for the oxidative addition mechanism, s-silane transition-metal complexes have been well documented. [5] For d 0 -transition-metal complexes, the oxidative addition is impossible, and the Si À H bond cleavage proceeds through the s-bond metathesis mechanism. However, to the best of our knowledge, there has been no report of such a d 0 -transition-metal complex, which can be considered as a model for the s-bond metathesis transition state. On the other hand, b-agostic interactions between metal ions and SiÀ H bonds are commonly observed in the coordinative unsaturated d 0 -transition-metal complexes. [6] Rare-earth-metal hydrides attract intense interest because of their fascinating structural features and high reactivity. [7] Recently, we have developed a b-diketiminato-

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confidence: 87%

An Yttrium Hydride–Silane Complex as a Structural Model for a σ‐Bond Metathesis Transition State

et al. 2013

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“…As part of our ongoing interest in titanium imido and hydrazido chemistry we have reported previously in detail on the synthesis, bonding and reactivity of a series of cyclopentadienyl‐amidinate complexes [Cp*Ti{MeC(N i Pr) 2 }(N t Bu)] ( 5 a ), [Cp*Ti{MeC(N i Pr) 2 }(NAr)] ( 5 b , Ar=Tol or Xyl) and [Cp*Ti{MeC(N i Pr) 2 }(NNRR′)] (R=R′=Ph ( 6 a ) or Me ( 7 ); R=Ph, R′=Me ( 6 b )) 3n. p, 8 The reactions of these compounds with CO 2 , CS 2 , isocyanates, many other polar and non‐polar substrates and silanes are well understood, and provide a good basis for further studies of titanium–nitrogen multiple bond chemistry. In this contribution we report the synthesis and bonding of a new titanium alkylidene hydrazido(2−) complex and its reactivity with a range of substrates, a number of which are studied for the first time with the TiNNCR 2 functional group…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Bonding and Reactivity of a Terminal Titanium Alkylidene Hydrazido Compound

Tiong

Groom

Clot

et al. 2013

Chemistry A European J

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We report a detailed study of the reactions of the Ti=NNCPh2 alkylidene hydrazide functional group in [Cp*Ti{MeC(NiPr)2}(NNCPh2)] (8) with a variety of unsaturated and saturated substrates. Compound 8 was prepared from [Cp*Ti{MeC(NiPr)2}(NtBu)] and Ph2CNNH2. DFT calculations were used to determine the nature of the bonding for the Ti=NNCPh2 moiety in 8 and in the previously reported [Cp2Ti(NNCPh2)(PMe3)]. Reaction of 8 with CO2 gave dimeric [(Cp*Ti{MeC(NiPr)2}{μ-OC(NNCPh2)O})2] and the "double-insertion" dicarboxylate species [Cp*Ti-{MeC(NiPr)2}{OC(O)N(NCPh2)C(O)O}] through an initial [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(O)O}], the congener of which could be isolated in the corresponding reaction with CS2. The reaction with isocyanates or isothiocyanates tBuNCO or ArNCE (Ar = Tol or 2,6-C6 H3 iPr2 ; E = O, S) gave either complete NNCPh2 transfer, [2+2] cycloaddition to Ti=Nα or single- or double-substrate insertion into the Ti=Nα bond. The treatment of 8 with isonitriles RNC (R = tBu or Xyl) formed σ-adducts [Cp*Ti{MeC(NiPr)2}(NNCPh2)(CNR)]. With Ar(F5)CCH (Ar(F5)=C6F5) the [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(Ar(F5))C(H)}] was formed, whereas with benzonitriles ArCN (Ar = Ph or Ar(F5)) two equivalents of substrate were coupled in a head-to-tail manner across the Ti=Nα bond to form [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(Ar)NC(Ar)N}]. Treatment of 8 with RSiH3 (R = aryl or Bu) or Ph2SiH2 gave [Cp*Ti{MeC(NiPr)2}{N(SiHRR')N(CHPh2)}] (R' = H or Ph) through net 1,3-addition of Si-H to the N-N=CPh2 linkage of 8, whereas reaction with PhSiH2X (X = Cl, Br) led to the Ti=Nα 1,2-addition products [Cp*Ti{MeC(NiPr)2}(X){N(NCPh2)SiH2Ph}].

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“…Fryzuk and co‐workers reported that the dinitrogen complexes [{(P 2 N 2 )Zr} 2 (μ‐η 2 ‐N 2 )] [P 2 N 2 =PhP(CH 2 SiMe 2 NSiMe 2 CH 2 ) 2 PPh)]3e and [{(NPN)Ta} 2 (μ‐η 1 :η 2 ‐N 2 )(μ‐H) 2 ] ( 2 ; NPN=(PhNSiMe 2 CH 2 ) 2 PPh)3f undergo hydrosilylation to yield new NSi bonds and new terminal metal–hydride complexes derived from one SiH unit, respectively. Clot, Mountford, and co‐workers found that the Ti dimethylhydrazido compound [Cp*Ti{MeC(N i Pr) 2 }(NNMe 2 )] undergoes reversible SiH 1,2‐ addition to TiN α with, for example, PhSiH 3 , forming the Ti–hydride–hydrazide complex [Cp*Ti{MeC(N i Pr) 2 }H{N(NMe 2 )SiH 2 Ph}] 3g …”

Section: Introductionmentioning

confidence: 99%

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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Site selectivity and reversibility in the reactions of titanium hydrazides with Si–H, Si–X, C–X and H+ reagents: TiNα 1,2-silane addition, Nβ alkylation, Nα protonation and σ-bond metathesis

Cited by 32 publications

References 103 publications

An Yttrium Hydride–Silane Complex as a Structural Model for a σ‐Bond Metathesis Transition State

An Yttrium Hydride–Silane Complex as a Structural Model for a σ‐Bond Metathesis Transition State

Synthesis, Bonding and Reactivity of a Terminal Titanium Alkylidene Hydrazido Compound

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

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