Reactions of titanium imido complexes with α-diimines: complexation versus TiN/CN bond metathesis

McInnes, Jacqueline M.; Blake, Alexander J.; Mountford, Philip

doi:10.1039/a806393a

Cited by 29 publications

(23 citation statements)

References 29 publications

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“…3,4 In contrast, analogous metalcatalyzed methods for selectively metathesizing double bonds to nitrogen (e.g., imines, diazenes) have been virtually unexplored until recently. [5][6][7][8] Scheme 1 illustrates a potential mechanism for imine metathesis catalyzed by zirconium imido complexes that is analogous to the pathway established for olefin metathesis catalyzed by metal alkylidene complexes. A Zr=NR species can react with an organic imine in an overall [2 + 2] cycloaddition reaction to generate a diazametallacyclobutane intermediate.…”

Section: Introductionmentioning

confidence: 99%

Zirconium-Mediated Metathesis of Imines: A Study of the Scope, Longevity, and Mechanism of a Complicated Catalytic System

2000

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By kinetically stabilizing imidozirconocene complexes through the use of a sterically demanding ligand, or by generating a more thermodynamically stable resting state with addition of diphenylacetylene, we have developed transition metal-catalyzed imine metathesis reactions that are mechanistically analogous to olefin metathesis reactions catalyzed by metal carbene complexes. When 5 mol % of Cp*Cp(THF)Zr=N t Bu is used as the catalyst precursor in the metathesis reaction between PhCH=NPh and p-TolCH=N-p-Tol, a 1:1:1:1 equilibrium mixture with the two mixed imines p-TolCH=NPh and PhCH=N-p-Tol is generated in C 6 D 6 at 105 °C. The catalyst was still active after 20 days with an estimated 847 turnovers (t 1/2 170 m; TON = 1.77 h −1 ). When the azametallacyclobutene Cp 2 Zr(N(Tol)C(Ph)=C(Ph)) is used as the catalyst precursor under similar reaction conditions, a total of 410 turnovers are obtained after 4 days (t 1/2 170 m; TON = 4.3 h −1 ). An extensive kinetic and equilibrium analysis of the metallacyclobutene-catalyzed metathesis of PhCH=N-p-Tol and p-F-C 6 H 4 CH=N-p-F-C 6 H 4 was carried out by monitoring the concentrations of imines and observable metal-containing intermediates over time. Numerical integration methods were used to fit these data to a detailed mechanism involving coordinatively unsaturated (16-electron) imido complexes as critical intermediates. Examination of the scope of reaction between different organic imines revealed characteristic selectivity that appears to be unique to the zirconium-mediated system. Several zirconocene complexes that could generate the catalytically active "CpCp′ Zr=NAr" (Cp′ = Cp or Cp*) species in situ were found to be effective agents in the metathetical exchange between different N-aryl imines. N-Alkyl aldimines were found to be completely unreactive toward metathesis with N-aryl aldimines, and metathesis reactions involving the two N-alkyl imines TolCH=NPr and PhCH=NMe gave slow or erratic results, depending on the catalyst used. Metathesis was observed between N-aryl ketimines and N-aryl aldimines, but for N-aryl ketimine substrates, the catalyst resting state consists of zirconocene enamido complexes, generated by the formal C-H activation of the α position of the ketimine substrates.

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Section: Introductionmentioning

confidence: 99%

Zirconium-Mediated Metathesis of Imines: A Study of the Scope, Longevity, and Mechanism of a Complicated Catalytic System

2000

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“…Table 2 [24] POCKAT [25] POCKUN [25] ML 2 X 2 [TiCl 2 (DAD)(thf) 2 ] PEBQOC [22] [ZrCl 2 (DAD)(tmeda)], bent GUHYEN [23] [Zr(guanidinate) 2 (DAD)] PUXTEH [26] M(NR)X 2 L [TiCl 2 (DAD)(NAr)(py)] VEBYIK [27] MX 4 [ZrCl 4 (DAD)] YOBXUI [19] First of all, we satisfactorily optimized models of complexes 2 and 3 with the unsubstituted DAD ligand (see Figure 3). The Ti-N distances and Cl-Ti-Cl angle are underestimated and overestimated with respect to the experimental structure of PEBCOQ [22] by about 0.04 Å and 13°, respectively, in 3.…”

Section: Pseudo-octahedral Complexes With ML 4 Fragmentsmentioning

confidence: 99%

A Critical Review of Electronic Effects in Enediamido and α‐Diimino Complexes of the Group 4 Metals

et al. 2007

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. The M-DAD metallacycle is generally either planar or folded at the N···N vector, the latter arrangement being observed when the number of co-ligands is reduced and hence there is insufficient saturation at the metal. The conformation also depends on the relative electron population of DAD, which is a noninnocent ligand and exists as a continuum between the neutral and dianionic resonance forms. Herein some theoretical concepts, that have

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“…Lastly, aldimines26 and imines,56 can undergo metathesis with titanium imides to generate new imide ligands via a ureate intermediate 4. Likewise, carbodiimides can also undergo exchange with the titanium imide group 31.…”

Section: Wittig‐like Reactionsmentioning

confidence: 99%

“…In general, terminal and early-transition-metal imides are expected to be reactive, given the polarized nature of the M À N multiple bond, especially for complexes with low-coordination environments. For these reasons, it is not surprising that titanium imides are often required for several catalytic reactions such as the intermolecular and intramolecular hydroamination of alkynes and allenes, [4,24,33,[53][54][55] hydrohydrazination of alkynes, [6] multi-coupling reactions to generate a,b-unsaturated b-aminoimines, [6,28] guanylations, [32] imine metathesis, [56] carbodiimide metathesis, [31] carboamination of alkynes with aldimines, [57,58] transamidations, [35] and cyclization reactions to produce multisubstituted quinolines [58] among other important processes. [4][5][6][7] Given the tremendous amount of literature recounting transition-metal-nitrogen multiple bonds, we will cover only descriptive chemistry surrounding the assembly of the terminal imide motif onto titanium.…”

Section: Introductionmentioning

confidence: 99%

The Progression of Synthetic Strategies to Assemble Titanium Complexes Bearing the Terminal Imide Group

Fout¹,

Kilgore²,

Mindiola³

2007

Chemistry A European J

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The synthesis of terminal titanium imides is described in this account. The incorporation of this functional group has evolved from more simplistic approaches to more complex or unusual methods. Past and current synthetic strategies to incorporate the terminal imide functionality are explained with particular emphasis on low-coordinate titanium environments bearing this ubiquitous but vital type of motif. More recently, the imide functionality has demonstrated to be a key intermediate for modeling important industrial processes such as the hydrodenitrogenation of crude oil.

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Reactions of titanium imido complexes with α-diimines: complexation versus TiN/CN bond metathesis

Cited by 29 publications

References 29 publications

Zirconium-Mediated Metathesis of Imines: A Study of the Scope, Longevity, and Mechanism of a Complicated Catalytic System

Zirconium-Mediated Metathesis of Imines: A Study of the Scope, Longevity, and Mechanism of a Complicated Catalytic System

A Critical Review of Electronic Effects in Enediamido and α‐Diimino Complexes of the Group 4 Metals

The Progression of Synthetic Strategies to Assemble Titanium Complexes Bearing the Terminal Imide Group

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