O2 Activation and Selective Phenolate ortho Hydroxylation by an Unsymmetric Dicopper μ‐η1:η1‐Peroxido Complex

“…The role of the Cu 2 O 2 complex as the hydroxylating species in the monophenolase reaction was demonstrated in 2003 [12]. Monooxygenation of external substrates was also studied in many other systems [13][14][15][16]. Detailed mechanistic insight into the monooxygenation of external substrates was achieved by the Cu(I)DBED system (DBED = 1,2-bis(di-tert-butyl)ethylene-diamine) [17].…”

Section: Introductionmentioning

confidence: 97%

Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations

2016

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Four new imidazole-based ligands, 4-((1H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (L OL 1), 4-((1H-imidazol-4-yl)methyl)-2-(tert-butyl)-4,5-dihydrooxyzole (L OL 2), 4-((1H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (L OL 3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1H-imidazol-4-yl-)ethyl amine (L imz 1), have been synthesized. The corresponding copper(I) complexes [Cu(I)(L OL 1)(CH3CN)]PF6 (CuL OL 1), [Cu(I)(L OL 2)(CH3CN)]PF6 (CuL OL 2), [Cu(I)(L OL 3)(CH3CN)]PF6 (CuL OL 3), [Cu(I)(L imz 1)(CH3CN)2]PF6 (CuL imz 1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)(BIMZ)(CH3CN)]PF6 (CuBIMZ), are screened as catalysts for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC-H2) to 3,5-di-tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di-tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order CuL OL 3 ≈ CuL OL 1 > CuBIMZ > CuL OL 2 > CuL imz 1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di-tert-butylphenol (2,4-DTBP-H), 3-tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl-L-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (CuL imz 1 and CuBIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed.

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“…Thus, we were intrigued by a recent report of phenolate ortho -hydroxylation by an end-on peroxo adduct, [5] a reaction otherwise believed to proceed via electrophilic aromatic substitution. [3a, 3d] This led us to consider the possible involvement of an unobserved bis-μ-oxo species that possesses the electrophilic character needed to affect a phenol-to-catechol conversion.…”

mentioning

confidence: 99%

Observation of a Cu^II₂(μ‐1,2‐peroxo)/Cu^III₂(μ‐oxo)₂ Equilibrium and its Implications for Copper–Dioxygen Reactivity

et al. 2014

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Synthesis of small molecule Cu2O2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the CuII2(μ-η2:η2-peroxo) and CuIII2(μ-oxo)2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)CuI]+ initially yields an “end-on peroxo” species, that subsequently converts to the thermodynamically more stable “bis-μ-oxo” isomer (Keq = 3.2 at −90 °C). Calibration of density functional theory calculations to these experimental data suggest that the electrophilic reactivity previously ascribed to end-on peroxo species is in fact a result of an accessible bis-μ-oxo isomer, an electrophilic Cu2O2 isomer in contrast to the nucleophilic reactivity of binuclear CuII end-on peroxo species. This study is the first report of the interconversion of an end-on peroxo to bis-μ-oxo species in transition metal-dioxygen chemistry.

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O₂ Activation and Selective Phenolate ortho Hydroxylation by an Unsymmetric Dicopper μ‐η¹:η¹‐Peroxido Complex

Cited by 104 publications

References 27 publications

Recent advances in transition-metal-catalyzed selective oxidation of substituted phenols and methoxyarenes with environmentally benign oxidants

Recent advances in transition-metal-catalyzed selective oxidation of substituted phenols and methoxyarenes with environmentally benign oxidants

Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations

Observation of a Cu^II₂(μ‐1,2‐peroxo)/Cu^III₂(μ‐oxo)₂ Equilibrium and its Implications for Copper–Dioxygen Reactivity

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O2 Activation and Selective Phenolate ortho Hydroxylation by an Unsymmetric Dicopper μ‐η1:η1‐Peroxido Complex

Cited by 104 publications

References 27 publications

Recent advances in transition-metal-catalyzed selective oxidation of substituted phenols and methoxyarenes with environmentally benign oxidants

Recent advances in transition-metal-catalyzed selective oxidation of substituted phenols and methoxyarenes with environmentally benign oxidants

Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations

Observation of a CuII2(μ‐1,2‐peroxo)/CuIII2(μ‐oxo)2 Equilibrium and its Implications for Copper–Dioxygen Reactivity

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O₂ Activation and Selective Phenolate ortho Hydroxylation by an Unsymmetric Dicopper μ‐η¹:η¹‐Peroxido Complex

Observation of a Cu^II₂(μ‐1,2‐peroxo)/Cu^III₂(μ‐oxo)₂ Equilibrium and its Implications for Copper–Dioxygen Reactivity