Electrode-adsorption activates trans-[Cr(cyclam)Cl2]+ for electrocatalytic nitrate reduction

Braley, Sarah E; Ashley, Daniel C.; Jakubı́ková, Elena; Smith, Jeremy M.

doi:10.1039/c9cc08550e

Cited by 16 publications

(20 citation statements)

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“…Furthermore, an oxygen‐deficient polyoxovanadate–alkoxide has been shown to reduce NO 3 − to NO via the intermediacy of NO 2 − [13] . Similarly, [Cr(cyclam)Cl 2 ] + has been described as an efficient electrocatalyst for NO 3 − reduction [14] . While most of the previously reported NO 3 − reduction routes lead to the selective generation of NO, electrocatalytic reduction of NO 3 − by [Co(DIM)Br 2 ] + supported by a redox‐noninnocent ligand (DIM=2,3‐dimethyl‐1,4,8,11‐tetraazacyclotetradeca‐1,3‐diene) yields NH 3 as the sole reduction product [15] .…”

Section: Figurementioning

confidence: 99%

“…[13] Similarly, [Cr(cyclam)Cl 2 ] + has been described as an efficient electrocatalyst for NO 3 À reduction. [14] While most of the previously reported NO 3 À reduction routes lead to the selective generation of NO, electrocatalytic reduction of NO 3…”

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confidence: 99%

“…Thus, this study sheds light on the oxidative reactivity of diaryl oxoammonium species.Illustrating the water sensitivity of the diaryl oxoammonium cations, [(TMB) 2 N + = O] (in 2 a) reacts with water and results in 2,6-dimethoxybenzoquinone (4 a) in quantitative yield (FigureS36). Intriguingly, the 1 H NMR spectrum of a crude reaction mixture consisting of 2 a (or 2 a-15 N) and water in d 6 -dimethylsulfoxide exhibits a triplet (for 2 a) and a doublet (for 2 a-15 N) centered at d % 7.2 ppm ( 1 J NH = 50.3 Hz for14 N and 1 J NH = 71.8 Hz for 15 N), which can be assigned to14 NH 4 + and 15 NH 4 +…”

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confidence: 99%

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Metal‐free Transformations of Nitrogen‐Oxyanions to Ammonia via Oxoammonium Salt

Sahana

Mondal

et al. 2021

Angewandte Chemie

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Transformations of nitrogen‐oxyanions (NOx−) to ammonia impart pivotal roles in sustainable biogeochemical processes. While metal‐mediated reductions of NOx− are relatively well known, this report illustrates proton‐assisted transformations of NOx− anions in the presence of electron‐rich aromatics such as 1,3,5‐trimethoxybenzene (TMB−H, 1 a) leading to the formation of diaryl oxoammonium salt [(TMB)2N+=O][NO3−] (2 a) via the intermediacy of nitrosonium cation (NO+). Detailed characterizations including UV/Vis, multinuclear NMR, FT‐IR, HRMS, X‐ray analyses on a set of closely related metastable diaryl oxoammonium [Ar2N+=O] species disclose unambiguous structural and spectroscopic signatures. Oxoammonium salt 2 a exhibits 2 e− oxidative reactivity in the presence of oxidizable substrates such as benzylamine, thiol, and ferrocene. Intriguingly, reaction of 2 a with water affords ammonia. Perhaps of broader significance, this work reveals a new metal‐free route germane to the conversion of NOx to NH3.

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Section: Figurementioning

confidence: 99%

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Metal‐free Transformations of Nitrogen‐Oxyanions to Ammonia via Oxoammonium Salt

Sahana

Mondal

et al. 2021

Angewandte Chemie

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“…30−32 Although IR, NMR, and X-ray photoelectron spectroscopy (XPS) can all be useful in distinguishing between complexes of different metals and oxidation states of the coordinated nitrogen oxides, mass spectrometry of these compounds often favors loss of an oxyanion ligand, which precludes identification of the molecular species. Loss of an Xtype ligand must be avoided when other characterization techniques are insensitive to those: for example, 15 N NMRsilent paramagnetic complexes. The ability to see an intact molecular ion with a complex that has nitrogen oxyanion ligands is increasingly important for characterizing subsequent reactivity and was a hindrance in a previous study with a nickel nitrogen oxyanion complex (see the Supporting Information).…”

Section: ■ Introductionmentioning

confidence: 99%

“…The increase in anthropogenically derived nitrogen oxyanions has led to a variety of economic and environmental problems, including large algal blooms in eutrophic bodies of water, inducing hypoxia and often leading to dead zones. − Mitigation of this eutrophication has been approached through photochemical, − electrochemical, − and chemical reduction of nitrogen oxyanions. − One approach involves reductive borylation (Scheme ) where equimolar bis(boryl)pyrazine reagent removes oxygen, as (Bpin) 2 O, because of the affinity of boron for oxygen. Our group has recently shown several examples of reductive deoxygenation using reduced N-heterocycles, − including deoxygenation of a nickel complex to induce N–N bond formation …”

Section: Introductionmentioning

confidence: 99%

An Integrated View of Nitrogen Oxyanion Deoxygenation in Solution Chemistry and Electrospray Ion Production

et al. 2021

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There has been an increasing interest in chemistry involving nitrogen oxyanions, largely due to the environmental hazards associated with increased concentrations of these anions leading to eutrophication and aquatic “dead zones”. Herein, we report the synthesis and characterization of a suite of MNO x complexes (M = Co, Zn: x = 2, 3). Reductive deoxygenation of cobalt bis(nitrite) complexes with bis(boryl)pyrazine is faster for cobalt than previously reported nickel, and pendant O-bound nitrito ligand is still readily deoxygenated, despite potential implication of an isonitrosyl primary product. Deoxygenation of zinc oxyanion complexes is also facile, despite zinc being unable to stabilize a nitrosyl ligand, with liberation of nitric oxide and nitrous oxide, indicating N–N bond formation. X-ray photoelectron spectroscopy is effective for discriminating the types of nitrogen in these molecules. ESI mass spectrometry of a suite of M(NO x ) y (x = 2, 3 and y = 1, 2) shows that the primary form of ionization is loss of an oxyanion ligand, which can be alleviated via the addition of tetrabutylammonium (TBA) as a nonintuitive cation pair for the neutral oxyanion complexes. We have shown these complexes to be subject to deoxygenation, and there is evidence for nitrogen oxyanion reduction in several cases in the ESI plume. The attractive force between cation and neutral is explored experimentally and computationally and attributed to hydrogen bonding of the nitrogen oxyanion ligands with ammonium α-CH2 protons. One example of ESI-induced reductive dimerization is mimicked by bulk solution synthesis, and that product is characterized by X-ray diffraction to contain two Co(NO)2 + groups linked by a highly conjugated diazapolyene.

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Supramolecular Enhancement of Electrochemical Nitrate Reduction Catalyzed by Cobalt Porphyrin Organic Cages for Ammonia Electrosynthesis in Water**

Narouz

Smith

et al. 2023

Angewandte Chemie

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The electrochemical nitrate (NO3−) reduction reaction (NO3RR) to ammonia (NH3) represents a sustainable approach for denitrification to balance global nitrogen cycles and an alternative to traditional thermal Haber‐Bosch processes. Here, we present a supramolecular strategy for promoting NH3 production in water from NO3RR by integrating two‐dimensional (2D) molecular cobalt porphyrin (CoTPP) units into a three‐dimensional (3D) porous organic cage architecture. The porphyrin box CoPB‐C8 enhances electrochemical active site exposure, facilitates substrate–catalyst interactions, and improves catalyst stability, leading to turnover numbers and frequencies for NH3 production exceeding 200,000 and 56 s−1, respectively. These values represent a 15‐fold increase in NO3RR activity and 200‐mV improvement in overpotential for the 3D CoPB‐C8 box structure compared to its 2D CoTPP counterpart. Synthetic tuning of peripheral alkyl substituents highlights the importance of supramolecular porosity and cavity size on electrochemical NO3RR activity. These findings establish the incorporation of 2D molecular units into 3D confined space microenvironments as an effective supramolecular design strategy for enhancing electrocatalysis.

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Electrode-adsorption activates trans-[Cr(cyclam)Cl₂]⁺ for electrocatalytic nitrate reduction

Abstract: The mercury working electrode promotes electrocatalytic nitrate reduction by trans-Cr(cyclam)Cl2+.

Cited by 16 publications

References 37 publications

Metal‐free Transformations of Nitrogen‐Oxyanions to Ammonia via Oxoammonium Salt

Metal‐free Transformations of Nitrogen‐Oxyanions to Ammonia via Oxoammonium Salt

An Integrated View of Nitrogen Oxyanion Deoxygenation in Solution Chemistry and Electrospray Ion Production

Supramolecular Enhancement of Electrochemical Nitrate Reduction Catalyzed by Cobalt Porphyrin Organic Cages for Ammonia Electrosynthesis in Water**

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