A N3S(thioether)-Ligated CuII-Superoxo with Enhanced Reactivity

Kim, Sunghee; Lee, Jung Yoon; Cowley, Ryan E.; Ginsbach, Jake W.; Siegler, Maxime A.; Solomon, Edward I.; Karlin, Kenneth D.

doi:10.1021/ja511504n

Cited by 69 publications

(80 citation statements)

References 34 publications

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“…Karlin and coworkers synthesized [Cu I ( DMA TMPA)] + , a [Cu I (TMPA)] + derivative bearing a dimethylamino group at the para position of each pyridyl ligand arm. Cyclic voltammetry of the compound revealed a Cu II/I reduction potential of −700 mV vs. Fc + /Fc in MeCN, [55] 380 mV lower than the parent TMPA complex, measured to be −420 mV under the same conditions (Table 2). [77] Oxygenation of the carbonyl derivative [Cu I ( DMA TMPA)(CO)] + in THF, at −85°C, yielded a brilliant green solution that was EPR silent.…”

Section: Cupric-superoxide Model Complexesmentioning

confidence: 99%

“…The Cu II/I reduction potential of this complex was found to be in between [Cu II ( DMA TMPA)] 2+ and [Cu II (TMPA)] 2+ at −570 mV vs. Fc + /Fc in MeCN (Table 2). [55] It was expected that the less electronically stabilized Cu II center in [Cu II ( DMM TMPA)] + , relative to [Cu II ( DMA TMPA)] + , imparts the corresponding superoxide species with greater electrophilic character, capable of reacting with substrates possessing a larger range of bond dissociation energies (BDEs).…”

Section: Cupric-superoxide Model Complexesmentioning

confidence: 99%

“…[55] Oxygenation of [Cu I ( DMA N 3 S)] + at −135°C in MeTHF led to formation of [Cu II ( DMA N 3 S)(O 2 •− )] + , which rapidly converted to [{Cu II ( DMA N 3 S)} (O 2 2− )] 2+ over 50s Fortunately, [Cu II ( DMA N 3 S)(O 2 •− )] + was found to be selectively stabilized by oxygenating [Cu I ( DMA N 3 S)] + in MeTHF solutions containing the polar, and potentially hydrogen-bonding solvent trifluoroethanol (TFE) in a 4 :1 mixture. This new superoxide complex was confirmed via UV-Vis and resonance Raman spectroscopies, containing features similar to previously characterized tetradentate end-on cupric superoxides.…”

Section: Cupric-superoxide Model Complexesmentioning

confidence: 99%

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Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Liu

Díaz

Quist

et al. 2016

Israel Journal of Chemistry

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Primary copper(I)-dioxygen (O2) adducts, cupric-superoxide complexes, have been proposed intermediates in copper-containing dioxygen-activating monooxygenase and oxidase enzymes. Here, mechanisms of C–H activation by reactive copper-(di)oxygen intermediates are discussed, with an emphasis on cupric-superoxide species. Over the past 25 years, many synthetically derived cupric-superoxide model complexes have been reported. Due to the thermal instability of these intermediates, early studies focused on increasing their stability and obtaining physical characterization. More recently, in an effort to gain insight into the possible substrate oxidation step in some copper monooxygenases, several cupric-superoxide complexes have been used as surrogates to probe substrate scope and reaction mechanisms. These cupric superoxides are capable of oxidizing substrates containing weak O–H and C–H bonds. Mechanistic studies for some enzymes and model systems have supported an initial hydrogen-atom abstraction via the cupric-superoxide complex as the first step of substrate oxidation.

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Section: Cupric-superoxide Model Complexesmentioning

confidence: 99%

Section: Cupric-superoxide Model Complexesmentioning

confidence: 99%

Section: Cupric-superoxide Model Complexesmentioning

confidence: 99%

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Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Liu

Díaz

Quist

et al. 2016

Israel Journal of Chemistry

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“…In this respect, Karlin and co-workers recently reported a mononuclear copper(II)−(end-on)-superoxide complex 2 supported by a N 2 S-tridentate ligand, which exhibits higher reactivity compared with the one supported by a similar N 3 -tridentate ligand 1 (Chart 2). 32 Apparently, a subtle change of the coordination sphere greatly influences the reactivity of CuS E species.…”

Section: Accounts Of Chemical Researchmentioning

confidence: 99%

Developing Mononuclear Copper–Active-Oxygen Complexes Relevant to Reactive Intermediates of Biological Oxidation Reactions

2015

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Active-oxygen species generated on a copper complex play vital roles in several biological and chemical oxidation reactions. Recent attention has been focused on the reactive intermediates generated at the mononuclear copper active sites of copper monooxygenases such as dopamine β-monooxygenase (DβM), tyramine β-monooxygenase (TβM), peptidylglycine-α-hydroxylating monooxygenase (PHM), and polysaccharide monooxygenases (PMO). In a simple model system, reaction of O2 and a reduced copper(I) complex affords a mononuclear copper(II)-superoxide complex or a copper(III)-peroxide complex, and subsequent H(•) or e(-)/H(+) transfer, which gives a copper(II)-hydroperoxide complex. A more reactive species such as a copper(II)-oxyl radical type species could be generated via O-O bond cleavage of the peroxide complex. However, little had been explored about the chemical properties and reactivity of the mononuclear copper-active-oxygen complexes due to the lack of appropriate model compounds. Thus, a great deal of effort has recently been made to develop efficient ligands that can stabilize such reactive active-oxygen complexes in synthetic modeling studies. In this Account, I describe our recent achievements of the development of a mononuclear copper(II)-(end-on)superoxide complex using a simple tridentate ligand consisting of an eight-membered cyclic diamine with a pyridylethyl donor group. The superoxide complex exhibits a similar structure (four-coordinate tetrahedral geometry) and reactivity (aliphatic hydroxylation) to those of a proposed reactive intermediate of copper monooxygenases. Systematic studies based on the crystal structures of copper(I) and copper(II) complexes of the related tridentate supporting ligands have indicated that the rigid eight-membered cyclic diamine framework is crucial for controlling the geometry and the redox potential, which are prerequisites for the generation of such a unique mononuclear copper(II)-(end-on)superoxide complex. Reactivity of a mononuclear copper(II)-alkylperoxide complex has also been examined to get insights into the intrinsic reactivity of copper(II)-peroxide species, which is usually considered as a sluggish oxidant or just a precursor of copper-oxyl radical type reactive species. However, our studies have unambiguously demonstrated that copper(II)-alkylperoxide complex can be a direct oxidant for C-H bond activation of organic substrates, when the C-H bond activation is coupled with O-O bond cleavage (concerted mechanism). The reactivity studies of these mononuclear copper(II) active-oxygen species (superoxide and alkylperoxide) will provide significantly important insights into the catalytic mechanism of copper monooxygenases as well as copper-catalyzed oxidation reactions in synthetic organic chemistry.

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“…Kim and co-workers recently employed a new thioether sulfur ligated (N 3 S) complex (Figure 4c) [54]. It exhibits enhanced reactivity compared to N 4 ligated E S analogs.…”

Section: Primary Cui/o2 Adducts and Reactivitymentioning

confidence: 99%

Elaboration of copper–oxygen mediated C–H activation chemistry in consideration of future fuel and feedstock generation

Lee

Karlin

2015

Current Opinion in Chemical Biology

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108

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To contribute solutions for current energy concerns, improvements in the efficiency of C-H bond cleavage chemistry, e.g., selective oxidation of methane to methanol, could minimize losses in natural gas usage or produce feedstocks for fuels. Oxidative C-H activation is also a component of polysaccharide degradation, affording alternative biofuels from abundant biomass. Thus, an understanding of active-site chemistry in copper monooxygenases, those activating strong C-H bonds is briefly reviewed. Then, recent advances in the synthesis-generation and study of various copper-oxygen intermediates are highlighted. Of special interest are cupric-superoxide, Cu-hydroperoxo and Cu-oxy complexes. Such investigations can contribute to an enhanced future application of C-H oxidation or oxygenation processes using air, as concerning societal energy goals.

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A N₃S_(thioether)-Ligated Cu^II-Superoxo with Enhanced Reactivity

Cited by 69 publications

References 34 publications

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

Developing Mononuclear Copper–Active-Oxygen Complexes Relevant to Reactive Intermediates of Biological Oxidation Reactions

Elaboration of copper–oxygen mediated C–H activation chemistry in consideration of future fuel and feedstock generation

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