Chemical Reactivity of Copper Active‐Oxygen Complexes

Itoh, Shinobu

doi:10.1002/9781118094365.ch8

Cited by 23 publications

(23 citation statements)

References 262 publications

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“…We know from many years of study of dioxygen reduction chemistry employing copper ion complexes, that ligand denticity, along with other factors such as the exact nature of the donor (e.g., alkylamine vs. pyridyl) and the chelate ring sizes (e.g., five- vs. six-membered), govern the structures obtained, the redox properties of derived Cu II /Cu I complexes and thus overall reactivity [50–55]. When [(AN)Cu II (NO 2 )] + with tridentate N-chelate is reacted with two equiv (F 8 )Fe II , the same overall reaction occurs, Scheme 2.…”

Section: Resultsmentioning

confidence: 99%

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity

2014

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Nitric oxide (NO) as a cellular signaling molecule and vasodilator regulates a range of physiological and pathological processes. Nitrite (NO2−) is recycled in vivo to generate nitric oxide, particularly in physiologic hypoxia and ischemia. The cytochrome c oxidase (CcO) binuclear hemea3/CuB active site is one entity known to be responsible for cellular nitrite conversion to nitric oxide. We recently reported that a partially reduced heme/Cu assembly reduces nitrite ion, producing NO; the heme serves as the reductant and cupric ion provides a Lewis Acid interaction with nitrite, facilitating nitrite (N−O) bond cleavage (Hematian et al., J Am Chem Soc 134:18912–18915, 2012). To further investigate this nitrite reductase (NIR) chemistry, copper(II)-nitrito complexes with tri-and tetra-dentate ligands were used in this study, where either O,O'-bidentate or O-unidentate modes of nitrite binding to the cupric center are present. To study the role of the reducing ability of the ferrous heme center, two different tetraarylporphyrinate-iron(II) complexes, one with electron donating para-methoxy peripheral substituents, (TMPP)FeII, and the other with electron withdrawing 2,6-difluorophenyl substituents, (F8)FeII, were employed. The results show that differing nitrite coordination modes to copper(II) ion leads to varying kinetic behavior. Here, also, the ferrous heme is in all cases the source of the reducing equivalent required to take nitrite to nitric oxide, but the reduction ability of the heme center does not play a key role in the observed overall reaction rate. Based on our observations, reaction mechanisms are proposed and discussed in terms of heme/Cu heterobinuclear structures.

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Section: Resultsmentioning

confidence: 99%

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity

2014

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“…(B) Cu/O 2 -derived species proposed to carry out the hydroxylation of C−H bonds in natural systems 5 and model complexes. 32 …”

Section: Figurementioning

confidence: 99%

Decoding the Mechanism of Intramolecular Cu-Directed Hydroxylation of sp³ C–H Bonds

et al. 2017

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The use of copper in directed C−H oxidation has been relatively underexplored. In a seminal example, Schönecker showed that copper and O2 promoted the hydroxylation of steroid-containing ligands. Recently, Baran (J. Am. Chem. Soc. 2015, 137, 13776) improved the reaction conditions to oxidize similar substrates with excellent yields. In both reports, the involvement of Cu2O2 intermediates was suggested. In this collaborative article, we studied the hydroxylation mechanism in great detail, resulting in the overhaul of the previously accepted mechanism and the development of improved reaction conditions. Extensive experimental evidence (spectroscopic characterization, kinetic analysis, intermolecular reactivity, and radical trap experiments) is provided to support each of the elementary steps proposed and the hypothesis that a key mononuclear LCuII(OOR) intermediate undergoes homolytic O−O cleavage to generate reactive RO• species, which are responsible for key C−H hydroxylation within the solvent cage. These key findings allowed the oxidation protocol to be reformulated, leading to improvements of the reaction cost, practicability, and isolated yield.

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“…[6] In response to this, the synthesis and reactivity of multiple copper model complexes featuring hydroperoxide coordination were described and they have been reviewed. [38,39] In 1998, Masuda and coworkers isolated a cupric hydroperoxide containing H-bonding moieties in the secondary coordination sphere and analyzed the complex using X-ray diffraction. [40] Karlin and coworkers have reported the reactivity of several cupric hydroperoxides.…”

Section: Cu Hydroperoxide or Oxyl Complexesmentioning

confidence: 99%

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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Chemical Reactivity of Copper Active‐Oxygen Complexes

Cited by 23 publications

References 262 publications

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity

Decoding the Mechanism of Intramolecular Cu-Directed Hydroxylation of sp³ C–H Bonds

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

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Chemical Reactivity of Copper Active‐Oxygen Complexes

Cited by 23 publications

References 262 publications

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity

Decoding the Mechanism of Intramolecular Cu-Directed Hydroxylation of sp3 C–H Bonds

Copper(I)‐Dioxygen Adducts and Copper Enzyme Mechanisms

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Decoding the Mechanism of Intramolecular Cu-Directed Hydroxylation of sp³ C–H Bonds