C−H Bond Activation of Hydrocarbons by an Imidozirconocene Complex

Hoyt, Helen M.; Michael, Forrest E.; Bergman, Robert G.

doi:10.1021/ja0385944

Cited by 134 publications

(94 citation statements)

References 14 publications

(11 reference statements)

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“…[1][2][3][4] Such transformations are potentially useful since subsequent N-C reductive elimination (RE) would produce a free amine; however, RE is often a high-energy reaction for early transition metals. In contrast, REs of N-C and O-C bonds form the foundation of routes to aryl amines and ethers using late transition metal catalysts.…”

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confidence: 99%

Evidence for the Net Addition of Arene C−H Bonds across a Ru(II)−Hydroxide Bond

et al. 2005

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The activation of C-H bonds by transition metal complexes can proceed by multiple pathways, including the 1,2-addition of C-H bonds across early transition metal imido bonds. [1][2][3][4] Such transformations are potentially useful since subsequent N-C reductive elimination (RE) would produce a free amine; however, RE is often a high-energy reaction for early transition metals. In contrast, REs of N-C and O-C bonds form the foundation of routes to aryl amines and ethers using late transition metal catalysts. 5,6 Thus, it is anticipated that accessing the net addition of C-H bonds (regardless of the specific mechanism) across late transition metal M-X bonds (X ) anionic N or O-based ligand) could ultimately lead to the development of routes for hydrocarbon functionalization. Late transition metal oxo and related systems are known to initiate hydrogen atom abstraction; 7 however, these transformations do not involve direct interaction of the metal center with the external C-H substrate. In addition, Ru-amido complexes have been demonstrated to deprotonate "acidic" C-H bonds. 8 The previously reported complex TpRu(PMe 3 ) 2 (OTf) (OTf ) trifluoromethanesulfonate) reacts with CsOH‚H 2 O in refluxing toluene to produce TpRu(PMe 3 ) 2 (OH) (1). A solid-state X-ray diffraction study of 1 has confirmed its structure as a monomeric Ru ( Kinetic studies reveal that H/D exchange at the hydroxide ligand of 1 in C 6 D 6 is first-order with k obs ) 8.0(2) × 10 -5 s -1 (80°C, t 1/2 ≈ 2.4 h). This rate of H/D exchange suggests a more active catalyst for H/D scrambling between H 2 O and C 6 D 6 than has been observed; however, the poor solubility of H 2 O in benzene likely slows the rate of catalysis. The addition of 10 mol % of TpRu(PMe 3 ) 2 (OTf) (precursor to 1) to a solution of 1 and C 6 D 6 does not increase the rate of H/D exchange at the hydroxide ligand of 1. The presence of coordinating ligands suppresses the rate of H/D exchange at the hydroxide ligand as well as the rate of catalysis, which is consistent with a metal-mediated process. For example, heating a solution of complex 1 in C 6 D 6 in the presence of 0.1 equiv (based on 1) of PMe 3 results in no observable H/D exchange at the hydroxide ligand after 168 h at 80°C. The addition of the "non-coordinating" base 2,6-lutidine does not increase the rate of H/D exchange at the hydroxide ligand.In order for the proposed pathway to be viable, complex 1 must access a five-coordinate species on a time scale that is consistent with the observed H/D exchange at the hydroxide ligand. Monitoring the rate of exchange of PMe 3 upon combination of complex 1 with PMe 3 -d 9 at 80°C reveals that k obs ) 1.7(1) × 10 -4 s -1 (t 1/2 ≈ 68 min). Thus, the rate of PMe 3 exchange is greater than the rate of H/D exchange and indicates that external substrates (e.g., C 6 D 6 ) † North Carolina State University. ‡ University of North Texas. § West Virginia University.

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confidence: 99%

Evidence for the Net Addition of Arene C−H Bonds across a Ru(II)−Hydroxide Bond

et al. 2005

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“…4 If binding followed by cycloaddition of the N-heterocycle were the steps preceding the C-F bond activation reaction, then a β-fluoride elimination process should be culminating this type of reaction. Experimentally it was found that treatment of (PNP)-TivCH the exact coordination geometry about the titanium center, we resorted to single crystal X-ray structural analysis.…”

Section: Resultsmentioning

confidence: 99%

“…4 C-F bond breaking was proposed to be driven by a combination of the inherent reactivity of the pyridine C-F motif as well as formation of a very strong Zr-F bond. 4 Given the similarity of our reaction to that of the Bergman system, we may speculate that both processes follow similar pathways. However, the coordinating abilities of perfluoropyridine versus perfluoroarene should render these two reactions intuitively different especially if a binding event precedes C-F bond activation.…”

Section: Introductionmentioning

confidence: 99%

“…This pathway contrasts the more commonly proposed 1,2-CX (X = H, F, etc.) bond addition pathway across early-transition metal imides, 4,5 alkylidenes, 6 and more recently, alkylidynes. 2,7,8 Based on this observation we convincingly demonstrate that [2 + 2]-cycloaddition is a viable pathway along the C-F bond activation of the ortho fluoropyridine while 3-fluoropyridine undergoes ring-opening metathesis of the N-heterocycle to form a three-sevenmetallaazabicyclic.…”

Section: Introductionmentioning

confidence: 99%

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Understanding intermolecular C–F bond activation by a transient titanium neopentylidyne: experimental and theoretical studies on the competition between 1,2-CF bond addition and [2 + 2]-cycloaddition/β-fluoride elimination

et al. 2013

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“…ond activation in methane and other saturated hydrocarbons has been the subject of numerous studies to date [1][2][3][4][5][6][7]. Methane activation by bare transition-metal atoms and ions has also been studied extensively [8][9][10][11][12]; however, thermalized ground-state monoatomic 3d-and 4d-transition-metal cations generally do not react with methane because of repulsive interactions with substituent s orbitals [9,[12][13][14][15].…”

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confidence: 99%

Activation of Methane by the Pyridine Radical Cation and its Substituted Forms in the Gas Phase

Stewart

Liu

et al. 2015

J. Am. Soc. Mass Spectrom.

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Abstract. We present an experimental study of methane activation by pyridine cation and its substituents in the gas phase. Mass spectrometric experiments in an ion trap demonstrate that pyridine cation and some of its substituent cations are able to react with methane. The deuterated methane experiment has confirmed that the hydrogen atom in the ionic product of reaction does come from methane. The collected information about kinetic isotope effects has been used to distinguish the nature of the bond activation as a hydrogen abstraction. Furthermore, experimental results demonstrated that the substituent groups on the pyridine ring can crucially influence their reactivity in methane bond activation processes. Density functional calculation (DFT) was employed to study the electronic structures of the complex and reaction mechanism of CH 4 +C 5 H 5 N + . The calculations confirmed the hypothesis from the experimental observation, namely, the reaction is rapid with no energy barrier.

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C−H Bond Activation of Hydrocarbons by an Imidozirconocene Complex

Cited by 134 publications

References 14 publications

Evidence for the Net Addition of Arene C−H Bonds across a Ru(II)−Hydroxide Bond

Evidence for the Net Addition of Arene C−H Bonds across a Ru(II)−Hydroxide Bond

Understanding intermolecular C–F bond activation by a transient titanium neopentylidyne: experimental and theoretical studies on the competition between 1,2-CF bond addition and [2 + 2]-cycloaddition/β-fluoride elimination

Activation of Methane by the Pyridine Radical Cation and its Substituted Forms in the Gas Phase

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