Involvement of a Formally Copper(III) Nitrite Complex in Proton-Coupled Electron Transfer and Nitration of Phenols

Bouchey, Caitlin J.; Tolman, William B.

doi:10.1021/acs.inorgchem.1c03790

Cited by 15 publications

(19 citation statements)

References 76 publications

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“…[39] A recent report demonstrates reactivity of a formal copper(III)-nitrite species towards phenol through proton-coupled-electron-transfer (PCET) pathway. [40] Influenced by the presence of a H-bonding network in the second-coordination-sphere of the T2 site in CuNiR, the design principles of a number of recent NiR models employ a protonresponsive functionalities such as 2-hydroxypyridine, pyridine-2carboxylic acid, and/or 3°amine. [24,41,42] Employing a {[Cu II ](k 2 -O 2 N)} + core supported by a tripodal heteroditopic cryptand (mC), our recent report depicted that {[mC]Cu II (k 2 -O 2 N)}(ClO 4 ) (1-NO 2 ) yields NO through a proton-coupled-electron-transfer (PCET) from substituted phenols (Figure 2).…”

Section: Introductionmentioning

confidence: 99%

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A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

et al. 2022

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Nitrous acid (HONO) plays pivotal roles in various metal‐free as well as metal‐mediated routes relevant to biogeochemistry, atmospheric chemistry, and mammalian physiology. While the metastable nature of HONO hinders the detailed investigations into its reactivity at a transition metal site, this report herein utilizes a heteroditopic copper(II) cryptate [oC]CuII featuring a proton‐responsive second‐coordination‐sphere located at a suitable distance from a [CuII](ONO) core, thereby enabling isolation of a [CuII](κ1‐ONO⋅⋅⋅H+) complex (2H‐NO2). A set of complementary analytical studies (UV‐vis, 14N/15N FTIR, 15N NMR, HRMS, EPR, and CHN) on 2H‐NO2 and its 15N‐isotopomer (2H‐15NO2) reveals the formulation of 2H‐NO2 as {[oCH]CuII(κ1‐ONO)}(ClO4)2. Non‐covalent interaction index (NCI) based on reduced density gradient (RDG) analysis on {[oCH]CuII(κ1‐ONO)}2+ discloses a H‐bonding interaction between the apical 3° ammonium site and the nitrite anion bound to the copper(II) site. The FTIR spectra of [CuII](κ1‐ONO⋅⋅⋅H+) species (2H‐NO2) shows a shift of ammonium NH vibrational feature to a lower wavenumber due to the H‐bonding interaction with nitrite. The reactivity profile of [CuII](κ1‐ONO⋅⋅⋅H+) species (2H‐NO2) towards anaerobic nitration of substituted phenol (2,4‐DTBP) is distinctly different relative to that of the closely related tripodal [CuII]‐nitrite complexes (1‐NO2/3‐NO2/4‐NO2).

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Section: Introductionmentioning

confidence: 99%

“…Tricopper(II) nitrite complexes also catalyze nitrite reduction by thiol to afford NO and disulfide [39] . A recent report demonstrates reactivity of a formal copper(III)‐nitrite species towards phenol through proton‐coupled‐electron‐transfer (PCET) pathway [40] …”

Section: Introductionmentioning

confidence: 99%

A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

et al. 2022

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“…Two pathways exist in the CuO/PMS system. One way is high-valent copper-initiated carbon-hydrogen bond oxidation with the generation of small molecules eventually mineralized to CO 2 , which is similar to the intermediates in radical and Fe(V)-dominated systems. ,, Another pathway for 4-CP degradation is to form phenolic polymers via single-electron transfer (SET) since Cu(III) is a one-electron oxidant, which may be further mineralized in the CuO/PMS system. ,, …”

Section: Resultsmentioning

confidence: 99%

“…19,56,57 Another pathway for 4-CP degradation is to form phenolic polymers via single-electron transfer (SET) since Cu(III) is a one-electron oxidant, which may be further mineralized in the CuO/PMS system. 49,51,58 The structure−activity relationship for organic degradation in the Cu(III)-mediated CuO/PMS system was also investigated. In the SET mechanism dominated nonradical reaction of PMS activation, the degradation rates of organics depend greatly on the electron-donating ability of organics, 28 which can be described by ionization potential (IP, eV).…”

Section: Cu(iii) Enhances Pms Utilization By Minimizing Its Decomposi...mentioning

confidence: 99%

Ultrahigh Peroxymonosulfate Utilization Efficiency over CuO Nanosheets via Heterogeneous Cu(III) Formation and Preferential Electron Transfer during Degradation of Phenols

Wei

Miao

et al. 2022

Environ. Sci. Technol.

175

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In persulfate activation by copper-based catalysts, high-valent copper (Cu(III)) is an overlooked reactive intermediate that contributes to efficient persulfate utilization and organic pollutant removal. However, the mechanisms underlying heterogeneous activation and enhanced persulfate utilization are not fully understood. Here, copper oxide (CuO) nanosheets (synthesized with a facile precipitation method) exhibited high catalytic activity for peroxymonosulfate (PMS) activation with 100% 4-chlorophenol (4-CP) degradation within 3 min. Evidence for the critical role of surface-associated Cu(III) on PMS activation and 4-CP degradation over a wide pH range (pH 3–10) was obtained using in situ Raman spectroscopy, electron paramagnetic resonance, and quenching tests. Cu(III) directly oxidized 4-CP and other phenolic pollutants, with rate constants inversely proportional to their ionization potentials. Cu(III) preferentially oxidizes 4-CP rather than react with two PMS molecules to generate one molecule of 1O2, thus minimizing this less efficient PMS utilization pathway. Accordingly, a much higher PMS utilization efficiency (77% of electrons accepted by PMS ascribed to 4-CP mineralization) was obtained with CuO/PMS than with a radical pathway-dominated Co3O4/PMS system (27%) or with the 1O2 pathway-dominated α-MnO2/PMS system (26%). Overall, these results highlight the potential benefits of PMS activation via heterogeneous high-valent copper oxidation and offer mechanistic insight into ultrahigh PMS utilization efficiency for organic pollutant removal.

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“…It has been demonstrated recently that metal complexes without bearing activated oxygen atom(s), such as metal-hydroxo and -aqua complexes, are active oxidants in both HAT and OAT reactions, affording oxygenated products. ,,− Similarly, McDonald and co-workers have demonstrated that high-valent metal-halide species are highly effective oxidants in activating hydrocarbon C–H bonds to yield hydroxylated or halogenated products . However, different from the metal–oxygen intermediates, such as metal-oxo, -peroxo, and -superoxo complexes, acid effects on the chemical properties of the metal-hydroxo, -aqua, and -halide complexes have been rarely explored previously. , Herein, we report for the first time a large decelerating effect of triflic acid (HOTf) on HAT reactions of [Ni III (PaPy 3 *)] 2+ ( 1 , PaPy 3 * = N , N -bis(4-methoxy-3,5-dimethyl-2-pyridylmethyl)-amine- N -ethyl-2-pyridine-2-carboxamidate) but a large accelerating effect of HOTf on ET and OAT reactions.…”

Section: Introductionmentioning

confidence: 99%

A Contrasting Effect of Acid in Electron Transfer, Oxygen Atom Transfer, and Hydrogen Atom Transfer Reactions of a Nickel(III) Complex

et al. 2022

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There have been many examples of the accelerating effects of acids in electron transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. Herein, we report a contrasting effect of acids in the ET, OAT, and HAT reactions of a nickel(III) complex, [Ni III (PaPy 3 *)] 2+ (1) in acetone/CH 3 CN (v/v 19:1). 1 was synthesized by reacting [Ni II (PaPy 3 *)] + (2) with magic blue or iodosylbenzene in the absence or presence of triflic acid (HOTf), respectively. Sulfoxidation of thioanisole by 1 and H 2 O occurred in the presence of HOTf, and the reaction rate increased proportionally with increasing concentration of HOTf ([HOTf]). The rate of ET from diacetylferrocene to 1 also increased linearly with increasing [HOTf]. In contrast, HAT from 9,10-dihydroanthracene (DHA) to 1 slowed down with increasing [HOTf], exhibiting an inversely proportional relation to [HOTf]. The accelerating effect of HOTf in the ET and OAT reactions was ascribed to the binding of H + to the PaPy 3 * ligand of 2; the one-electron reduction potential (E red ) of 1 was positively shifted with increasing [HOTf]. Such a positive shift in the E red value resulted in accelerating the ET and OAT reactions that proceeded via the rate-determining ET step. On the other hand, the decelerating effect of HOTf on HAT from DHA to 1 resulted from the inhibition of proton transfer from DHA •+ to 2 due to the binding of H + to the PaPy 3 * ligand of 2. The ET reactions of 1 in the absence and presence of HOTf were well analyzed in light of the Marcus theory of ET in comparison with the HAT reactions.

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Involvement of a Formally Copper(III) Nitrite Complex in Proton-Coupled Electron Transfer and Nitration of Phenols

Cited by 15 publications

References 76 publications

A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

A Copper(II)‐Nitrite Complex Hydrogen‐Bonded to a Protonated Amine in the Second‐Coordination‐Sphere

Ultrahigh Peroxymonosulfate Utilization Efficiency over CuO Nanosheets via Heterogeneous Cu(III) Formation and Preferential Electron Transfer during Degradation of Phenols

A Contrasting Effect of Acid in Electron Transfer, Oxygen Atom Transfer, and Hydrogen Atom Transfer Reactions of a Nickel(III) Complex

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