Aerobic oxidation of 2,4,6-tri-tert-butylphenol to quinones catalyzed by copper(II) complexes of an N-octylated bis-benzimidazolyl ligand

Yadav, Anjana; Mathur, Pavan

doi:10.1016/j.ica.2015.06.026

Cited by 5 publications

(5 citation statements)

References 30 publications

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“…These spectroscopic changes indicate the occurrence of a two-electron oxidation process of Ru II (OH 2 ) in conjunction with deprotonation, giving rise to the formation of Ru IV O in an organic medium similarly to in an aqueous medium. Furthermore, with the incremental addition of MG, a new absorption band emerged at 634 nm, similar to that of the 2,3,6-tri- tert -butylphenoxyl radical, 65 supporting the assignment that the second oxidation wave observed in the CVs originates from the oxidation of the phenolic moiety of [ 1 ] 2+ . Subsequent introduction of 3,5-di- tert -butylcatechol as a reductant served to regenerate the MLCT band of Ru II (bpy) at 507 nm (Fig.…”

Section: Resultssupporting

confidence: 67%

“…Although the inherent paramagnetism of the hexacoordinated Ru IV ]O species (S = 1), X-band EPR of Ru IV ]O generally exhibit no EPR signal because of a large spin coupling exhibited in a zero magnetic eld. [65][66][67][68][69][70][71][72][73][74][75][76] Mukai reported that a powder sample of 2,6di-tert-butyl-4-phenyl phenoxyl radical displayed a sharp EPR signal at g = 2.0047. 77 In solution, both the 2,6-di-tert-butyl-4phenyl phenoxyl radical and the 2,4,6-di-tert-butyl phenoxyl radical demonstrated EPR signals at g = 2.0044 and 2.0046, Scheme 1 Redox behavior of [1] 2+ at pH < 9.8 (upper) and pH > 9.8 (lower).…”

Section: Assignment Of the Oxidized Form Of [1] 2+mentioning

confidence: 99%

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Water oxidation utilizing a ruthenium complex featuring a phenolic moiety inspired by the oxygen-evolving centre (OEC) of photosystem II

Kumagai,

Takabe,

Nakazono

et al. 2024

Sustainable Energy Fuels

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Section: Resultssupporting

confidence: 67%

Section: Assignment Of the Oxidized Form Of [1] 2+mentioning

confidence: 99%

Water oxidation utilizing a ruthenium complex featuring a phenolic moiety inspired by the oxygen-evolving centre (OEC) of photosystem II

Kumagai,

Takabe,

Nakazono

et al. 2024

Sustainable Energy Fuels

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“…Addition of an excess of 2,4,6‐TTBP results in similar spectral changes as the reaction with TEMPO−H (Figure S24) indicating the formation of the same hydroperoxo Co species. Gas chromatography‐mass spectrometry (GC‐MS) of the reaction mixture proves the presence of a small amount 2,6‐di‐ tert ‐butyl‐1,4‐benzoquinone known to be formed after oxidation of 2,4,6‐TTBP to the phenoxy radical (Figure S25) [77] . Due to the low substrate conversion, the substrate amount was reduced using only one equivalent 2,4,6‐TTBP.…”

Section: Resultsmentioning

confidence: 99%

“…Gas chromatography-mass spectrometry (GC-MS) of the reaction mixture proves the presence of a small amount 2,6-di-tert-butyl-1,4-benzoquinone known to be formed after oxidation of 2,4,6-TTBP to the phenoxy radical (Figure S25). [77] Due to the low substrate conversion, the substrate amount was reduced using only one equivalent 2,4,6-TTBP. After 24 h the corresponding UV/vis spectrum indicated complete conversion since spectral changes were no longer observed.…”

Section: Substrate Oxidation Reactivitymentioning

confidence: 99%

How Ligand Geometry Affects the Reactivity of Co(II) Cyclam Complexes

Iffland‐Mühlhaus,

Battistella,

Siegmund

et al. 2023

Eur J Inorg Chem

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Cobalt complexes are extensively studied as bioinspired models for non‐heme oxygenases as they facilitate both the stabilization and characterization of metal‐oxygen intermediates. As an analog to the well‐known Co(cyclam) complex Co{N4} (cyclam = 1,4,8,11‐tetraazacyclotetradecane), the CoII complex Co{i‑N4} with the isomeric isocyclam ligand (isocyclam = 1,4,7,11‐tetraazacyclotetradecane) was synthesized and characterized. Despite the identical N4 donor set of both complexes, Co{i‐N4} enables the 2e‾/2H+ reduction of O2 with a lower overpotential (ηeff of 385 mV vs. 540 mV for Co{N4}), albeit with a diminished turnover frequency. Characterization of the intermediates formed upon O2 activation of Co{i‐N4} reveals a structurally identified stable µ‐peroxo CoIII dimer as the main product. A superoxo CoIII species is also formed as a minor product, as indicated by EPR spectroscopy. In further reactivity studies, the electrophilicity of these in situ generated Co‐O2 species was demonstrated by the oxidation of the O‐H bond of TEMPO‐H (2,2,6,6‐tetramethylpiperidin‐1‐ol) via a H atom abstraction process. Unlike the known Co(cyclam), Co{i‐N4} can be employed in oxygen atom transfer reactions oxidizing triphenylphosphine to the corresponding phosphine oxide highlighting the impact of geometrical modifications of the ligand while preserving the ring size and donor atom set on the reactivity of biomimetic oxygen activating complexes.

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“…The transient species above 600 nm may be ascribed to a phenoxyl radical generated during chemical oxidation . Phenoxyl radicals also have an absorption band at 400 nm. , Reportedly, the yield of phenoxyl radical was much higher in the presence of water in organic solvent due to deprotonation of phenol radical cation to give a phenoxyl radical. Hence, under chemical oxidation conditions, compounds 1 – 5 undergo a mechanism which involves formation of phenoxyl radicals, as detected spectrophotometrically.…”

Section: Resultsmentioning

confidence: 99%

Selective Electrochemical versus Chemical Oxidation of Bulky Phenol

et al. 2016

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The electrochemical oxidation of selected tert-butylated phenols 2,6-di-tert-butyl-4-methylphenol (1), 2,6-di-tert-butylphenol (2), 2,4,6-tri-tert-butylphenol (3), 2-tert-butylphenol (4), and 4-tert-butylphenol (5) was studied in an aprotic environment using cyclic voltammetry, square-wave voltammetry, and UV-vis spectroscopy. All compounds exhibited irreversible oxidation of the corresponding phenol or phenolate ion. Compound 2 was selectively electrochemically oxidized, while other phenol analogues underwent mostly chemical oxidation. The electrochemical oxidation of 2 produced a highly absorbing product, 3,5,3',5'-tetra-tert-butyl-4,4'-diphenoquinone, which was characterized by X-ray crystal diffraction. The electrochemical oxidation was monitored as a function of electrochemical parameters and concentration. Experimental and theoretical data indicated that the steric hindrance, phenoxyl radical stability, and hydrogen bonding influenced the outcome of the electrochemical oxidation. The absence of the substituent at the para position and the presence of the bulky substituents at ortho positions were structural and electrostatic requirements for the selective electrochemical oxidation.

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Aerobic oxidation of 2,4,6-tri-tert-butylphenol to quinones catalyzed by copper(II) complexes of an N-octylated bis-benzimidazolyl ligand

Cited by 5 publications

References 30 publications

Water oxidation utilizing a ruthenium complex featuring a phenolic moiety inspired by the oxygen-evolving centre (OEC) of photosystem II

Water oxidation utilizing a ruthenium complex featuring a phenolic moiety inspired by the oxygen-evolving centre (OEC) of photosystem II

How Ligand Geometry Affects the Reactivity of Co(II) Cyclam Complexes

Selective Electrochemical versus Chemical Oxidation of Bulky Phenol

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