Spectroscopic capture and reactivity of S = 1/2 nickel(iii)–oxygen intermediates in the reaction of a NiII-salt with mCPBA

Pfaff, Florian Felix; Heims, Florian; Kundu, Subrata; Mebs, Stefan; Ray, Kallol

doi:10.1039/c2cc30716b

Cited by 87 publications

(98 citation statements)

References 33 publications

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“…8 Ray observed the formation of multiple metastable putative Ni III –OX species, from the reaction of a Ni II complex and 3-chloroperoxybenzoic acid ( m -CPBA), and the resulting mixture was capable of oxidizing hydrocarbons with weak C–H bonds (1,4-cyclohexadiene). 9 To date, the most powerful high-valent nickel oxidant, reported by Company, was a putative formally Ni IV species, obtained from the reaction of a macrocyclic Ni II complex with m -CPBA. 10 Overall, the Ray/Company species lacked sufficient stability to allow exhaustive characterization.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

et al. 2016

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Two metastable NiIII complexes, [NiIII(OAc)(L)] and [NiIII(ONO2)(L)] (L = N,N’-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate, OAc = acetate), were prepared, adding to the previously prepared [NiIII(OCO2H)(L)], with the purpose of probing the properties of terminal late-transition metal oxidants. These high-valent oxidants were prepared by the one-electron oxidation of their NiII precursors ([NiII(OAc)(L)]h− and [NiII(ONO2)(L)]−) with tris(4-bromophenyl)ammoniumyl hexachloroantimonate. Fascinatingly, the reaction between any [NiII(X)(L)]− and NaOCl/acetic acid (AcOH) or cerium ammonium nitrate ((NH4)2[CeIV(NO3)6], CAN), yielded [NiIII(OAc)(L)] and [NiIII(ONO2)(L)], respectively. An array of spectroscopic characterizations (electronic absorption, electron paramagnetic resonance, X-ray absorption spectroscopies), electrochemical methods, and computational predictions (density functional theory) have been used to determine the structural, electronic, and magnetic properties of these highly reactive metastable oxidants. The NiIII-oxidants proved competent in the oxidation of phenols (weak O–H bonds) and a series of hydrocarbon substrates (some with strong C–H bonds). Kinetic investigation of the reactions with di-tert-butylphenols showed a 15-fold enhanced reaction rate for [NiIII(ONO2)(L)] compared to [NiIII(OCO2H)(L)] and [NiIII(OAc)(L)], demonstrating the effect of electron-deficiency of the O-ligand on oxidizing power. The oxidation of a series of hydrocarbons by [NiIII(OAc)(L)] was further examined. A linear correlation between the rate constant and the BDE of the C–H bonds in the substrates was indicative of a hydrogen atom transfer mechanism. The reaction rate with DHA (k2 = 8.1 M−1s−1) compared favorably with the most reactive high-valent metal-oxidants, and showcases the exceptional reactivity of late transition metal-oxygen adducts.

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Section: Introductionmentioning

confidence: 99%

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

et al. 2016

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“…[10] However, the low yield (15%) of Ni III and identification of at least two Ni III species in the reaction mixture hampered their characterization. Latos-Grażyński reacted a Ni III –Br complex with hydroxide to yield a new species that was claimed to be a Ni III –OH complex.…”

Section: Introductionmentioning

confidence: 99%

Characterization and Reactivity of a Terminal Nickel(III)–Oxygen Adduct

Pirovano

Farquhar

Swart

et al. 2015

Chemistry A European J

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High-valent terminal metal-oxygen adducts are hypothesized to be the potent oxidising reactants in late transition metal oxidation catalysis. In particular, examples of high-valent terminal nickel-oxygen adducts are sparse, meaning there is a dearth in the understanding of such oxidants. In this study, a monoanionic NiII-bicarbonate complex was found to react in a 1:1 ratio with the one-electron oxidant tris(4-bromophenyl)ammoniumyl hexachloroantimonate, yielding a thermally unstable intermediate in high yield (~95%). Electronic absorption, electronic paramagnetic resonance and X-ray absorption spectroscopies and density functional theory calculations confirm its description as a low-spin (S = ½), square planar NiIII-oxygen adduct. This rare example of a high-valent terminal nickel-oxygen complex performs oxidations of organic substrates, including 2,6-ditertbutylphenol and triphenylphosphine, which are indicative of hydrogen atom abstraction and oxygen atom transfer reactivity, respectively.

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“…8,9 Elucidating the mechanisms by which reactions catalyzed by late transition metal complexes proceed is essential for the rational development of selective catalytic reagents based on these metals, and requires a comprehensive understanding of the structure and properties of the key reactive species. It is only in recent years that the structural, spectroscopic and reactivity of well-defined oxido-cobalt(IV), hydroxido-cobalt(III), 12 hydroxido-copper(III), 13 oxido/hydroxido-nickel(III) 14 and bicarbonatenickel(III) 15 have been reported. Indeed, we reported earlier the formation of a metastable oxylnickel(III) species.…”

Section: Introductionmentioning

confidence: 99%

Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel–Oxygen Species

et al. 2016

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Abstract.Terminal high-valent metal-oxygen species are key reaction intermediates in the catalytic cycle of both enzymes (e.g., oxygenases) and synthetic oxidation catalysts. While tremendous efforts have been directed towards the characterization of the biologically relevant terminal manganese-oxygen and iron-oxygen species, the corresponding analogues based on late-transition metals such as cobalt, nickel or copper are relatively scarce. This is in part related to the "Oxo Wall" concept, which predicts that late transition elements cannot support a terminal oxido ligand in a tetragonal environment. Here, the nickel(II) complex (1) of the tetradentate macrocyclic ligand bearing a 2,6-pyridinedicarboxamidate unit is shown to be an effective catalyst in the chlorination and oxidation of C-H bonds with sodium hypochlorite as terminal oxidant in the presence of acetic acid (AcOH). Insight into the active species responsible for the observed reactivity was gained through the study of the reaction of 1 with ClO -at low temperature by UV/Vis absorption, resonance Raman, EPR, ESI-MS, and XAS analyses. DFT calculations aided the assignment of the trapped chromophoric species (3) as a nickel-hypochlorite species. Despite the fact that the formal oxidation state of the nickel in 3 is +4, experimental and computational analysis indicate that 3 is best formulated as a Ni III complex with one unpaired electron delocalized in the ligands surrounding the metal center. Most remarkably, 3 reacts rapidly with a range of substrates including those with strong aliphatic C-H bonds, indicating the direct involvement of 3 in the oxidation/chlorination reactions observed in the 1/ClO -

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Spectroscopic capture and reactivity of S = 1/2 nickel(iii)–oxygen intermediates in the reaction of a NiII-salt with mCPBA

Cited by 87 publications

References 33 publications

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

Characterization and Reactivity of a Terminal Nickel(III)–Oxygen Adduct

Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel–Oxygen Species

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