Chemical and Electrocatalytic Ammonia Oxidation by Ferrocene

Boroujeni, Mahdi Raghibi; Greene, Christine; Bertke, Jeffery A.; Warren, Timothy H.

doi:10.26434/chemrxiv.9729635.v1

Cited by 10 publications

(4 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…With interest growing in the study of molecular (electro)catalysts for AO, a fascinating multielectron redox reaction that represents the microscopic reverse of N 2 -to-NH 3 conversion, electrochemically well-defined model systems are needed. In this context we described in detail the capacity of a polypyridyl iron catalyst, [(TPA)Fe(MeCN) 2 ]OTf 2 , to perform AO at extremely fast rates (∼10 7 M –1 ·s –1 via FOWA) under the application of a 1.1 V applied bias. We also used CPC to confirm that N 2 is selectively formed via this AO reaction, confirming as many as 16 equiv of N 2 (32 equiv of NH 3 being consumed) per Fe.…”

Section: Concluding Remarksmentioning

confidence: 99%

Electrocatalytic Ammonia Oxidation Mediated by a Polypyridyl Iron Catalyst

2019

View full text Add to dashboard Cite

S1. General ProceduresGeneral Considerations: All manipulations were carried out using standard Schlenk or glovebox techniques under an N2 or Ar atmosphere. Unless otherwise noted, solvents were deoxygenated and dried by thoroughly sparging with N2 gas followed by passage through an activated alumina column in the solvent purification system by SG Water, USA LLC. For electrochemical measurements under an Ar atmosphere, solvents were further degassed and then left under Ar. All solvents were stored over activated 4 Å molecular sieves prior to use. Anhydrous ammonia gas was dried by passage through a calcium oxide drying tube. All reagents were purchased from commercial vendors and used without further purification unless otherwise stated. Tris(2pyridylmethyl)amine (TPA) 1 and tris(2-pyridylmethylamine) iron(II) triflate bis acetonitrile 2 were synthesized according to literature procedures. 15 NH4OTf was prepared from 15 NH4Cl (Cambridge Isotope Laboratories) by anion exchange with silver triflate followed by repeated recrystallization from acetonitrile. 1 H NMR chemical shifts are reported in ppm relative to tetramethylsilane, using residual solvent resonances as internal standards.Electrochemistry: Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), Differential Pulse Voltammetry (DPV) and Controlled Potential Coulometry (CPC) experiments were carried out with a Biologic VSP-300 potentiostat using a one-compartment three-electrode cell. For CV, LSV and DPV, a Boron Doped Diamond (BDD) disk electrode (3 mm diameter) was used as the working electrode, Pt wire as the counter electrode, and a Ag/AgOTf reference electrode was employed using an acetonitrile solution containing 5 mM AgOTf and 0.1 M TBAPF6. For CPE, the same reference electrode was used, but a BDD plate (geometric area: 1 cm 2 ) and a Pt mesh were used respectively as working and counter electrode. All redox potentials in the present work are reported versus the Fc/Fc + couple, measured before each experiment to be +0.115 V versus our Ag/AgOTf reference electrode.CVs and LSVs were collected at 100 mV•s -1 unless specified otherwise. DPVs were obtained with the following parameters: amplitude = 50 mV, step height = 4 mV, pulse width = 0.05 s, pulse period = 0.5 s and sampling width = 0.0167 s. E1/2 values for the reversible waves were obtained from the half potential between the oxidative and reductive peaks. All measurements were performed applying IR compensation, compensating 85% of the resistance measured at one high frequency value (100 kHz).Gas Chromatography: Gas chromatography was performed in the Environmental Analysis Center using HP 5890 Series II instruments. Gas quantification was performed using a molecular sieve column attached to a thermal conductivity detector. Argon was the carrier gas. Standard curves were generated by direct injection of hydrogen or nitrogen gas. Quantification of background nitrogen was determined using the background oxygen signal. Isotopic measurements were performed with a separate HP 5890 Series II equipped ...

show abstract

Section: Concluding Remarksmentioning

confidence: 99%

Electrocatalytic Ammonia Oxidation Mediated by a Polypyridyl Iron Catalyst

2019

View full text Add to dashboard Cite

show abstract

“…Additionally, the centralization of industrial NH 3 synthesis around H 2 feedstocks contributes to geopolitical disparities in affordable fertilizer access . Nascent efforts to utilize NH 3 as a carbon-free energy vector similarly reckon with the unsustainability of NH 3 mass production. , Yet, NH 3 oxidation methods such as H 2 cracking or electrocatalytic oxidation − may be key in availing strategies to tackle the microscopic reverse: sustainable N 2 reduction to NH 3 . The nearly thermoneutral N 2 reduction and NH 3 oxidation suggests proton-coupled electron transfer (PCET) as an attractive approach to minimize kinetic barriers between intermediates.…”

Section: Introductionmentioning

confidence: 99%

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes

et al. 2021

Self Cite

View full text Add to dashboard Cite

The life-sustaining reduction of N2 to NH3 is thermoneutral yet kinetically challenged by high-energy intermediates such as N2H2. Exploring intramolecular H-bonding as a potential strategy to stabilize diazene intermediates, we employ a series of [ xHetTpCu]2(μ-N2H2) complexes that exhibit H-bonding between pendant aromatic N-heterocycles (xHet) such as pyridine and a bridging trans-N2H2 ligand at copper(I) centers. X-ray crystallography and IR spectroscopy clearly reveal H-bonding in [pyMeTpCu]2(μ-N2H2) while low-temperature 1H NMR studies coupled with DFT analysis reveals a dynamic equilibrium between two closely related, symmetric H-bonded structural motifs. Importantly, the xHet pendant negligibly influences the electronic structure of xHetTpCuI centers in xHetTpCu(CNAr2,6‑Me2 ) complexes that lack H-bonding as judged by nearly indistinguishable ν(CN) frequencies (2113–2117 cm–1). Nonetheless, H-bonding in the corresponding [ xHetTpCu]2(μ-N2H2) complexes results in marked changes in ν(NN) (1398–1419 cm–1) revealed through resonance Raman studies. Due to the closely matched N–H BDEs of N2H2 and the pyH0 cation radical, the aromatic N-heterocyclic pendants may encourage partial H-atom transfer (HAT) from N2H2 to xHet through redox-non-innocent H-bonding in [ xHetTpCu]2(μ-N2H2). DFT studies reveal modest thermodynamic barriers for concerted transfer of both H-atoms of coordinated N2H2 to the xHet pendants to generate tautomeric [ xHetHTpCu]2(μ-N2) complexes, identifying metal-assisted concerted dual HAT as a thermodynamically favorable pathway for N2/N2H2 interconversion.

show abstract

“…Ammonia oxidation is also a critical step in global nitrogen cycling, and research on ammonia oxidation has attracted great interest in clean energy and environmental pollution control. 15–18 NH 3 can be readily liquified and its oxidation (chemical or electrochemical) may yield dinitrogen plus H 2 (g), thus NH 3 can be thought of as a hydrogen carrying fuel (f). Again illustrating the extremely broad based subject matter of bioinorganic chemistry, none of the lectures/papers in this Faraday Discussion in any way pertained to nitrogenase or N 2 -reduction.…”

Section: Small Molecule Activation and Key Reactions In (Bioinorganic...mentioning

confidence: 99%