Computational analysis of metal–metal bonded dimetal tetrabenzoate redox potentials in the context of ammonia oxidation electrocatalysis

Pavelic, Alex; Trenerry, Michael; Berry, John F.

doi:10.1039/d3dt00552f

Cited by 2 publications

(4 citation statements)

References 126 publications

(152 reference statements)

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“…Overlap between the d xy orbitals of the bimetallic core and the conjugated π-system of equatorial hydroxypyridinate ligands allows for tuning of the relative energy of the δ* molecular orbital by changing the equatorial ligand identity. These effects are well documented for metal–metal bonded complexes bearing bridging π-donor ligands, and our lab has previously reported the significance of the δ* orbital in bimetallic paddlewheel complexes for modulating the thermodynamic potential of M 2 4+/5+ redox couples. , …”

Section: Resultsmentioning

confidence: 81%

“…Varying the metal identity enables further control over [M 2 ] 4+/5+ redox potentials. In literature reports of redox potentials of analogous Ru and Os compounds, the latter are typically more cathodic by ∼500 mV, including in examples of metal–metal bonded compounds. − Relative to the calculated [Ru 2 ] 4+/5+ redox couples in 1–3NH 3 , the predicted potentials for the corresponding [Os 2 ] 4+/5+ redox couples of 4–6NH 3 lie substantially lower and approach or go beyond E NRR ° in acetonitrile of −0.94 V (Figure ). This drop in redox potential may effectively minimize η AOR if the Os 2 compounds display analogous chemical reactivity with ammonia to the catalytically active Ru 2 systems.…”

Section: Resultsmentioning

confidence: 90%

“…These effects are well documented for metal−metal bonded complexes bearing bridging π-donor ligands, 63 and our lab has previously reported the significance of the δ* orbital in bimetallic paddlewheel complexes for modulating the thermodynamic potential of M 2 4+/5+ redox couples. 13,64 Computationally predicted thermodynamic potentials, calibrated to experimental values (see the Supporting Information), for the [M 2 ] 4+/5+ redox couple are shown in Figure 3. These [M 2 ] 4+/5+ redox potentials follow a trend across compounds 1NH 3 − 3NH 3 that is consistent with the calculated energy of the δ* orbital in each species (see Figure S1 in the Supporting Information).…”

Section: T H Imentioning

confidence: 99%

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Computational Analysis of Low Overpotential Ammonia Oxidation by Metal–Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts

Trenerry,

Acosta,

Berry

2024

J. Phys. Chem. A

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The catalyzed electrochemical oxidation of ammonia to nitrogen (AOR) is an important fuel-cell half-reaction that underpins a future nitrogen-based energy economy. Our laboratory has reported spontaneous chemical and electrochemical oxidation of ammonia to dinitrogen via reaction of ammonia with the metal–metal bonded diruthenium complex Ru2(chp)4OTf (chp– = 2-chloro-6-hydroxypyridinate, TfO– = trifluoromethanesulfonate). This complex facilitates electrocatalytic ammonia oxidation at mild applied potentials of −255 mV vs ferrocene, which is the [Ru2(chp)4(NH3)]0/+ redox potential. We now report a comprehensive computational investigation of possible mechanisms for this reaction and electronic structure analysis of key intermediates therein. We extend this analysis to proposed second-generation electrocatalysts bearing structurally similar fhp and hmp (2-fluoro-6-hydroxypyridinate and 2-hydroxy-6-methylpyridinate, respectively) equatorial ligands, and we further expand this study from Ru2 to analogous Os2 cores. Predicted M2 4+/5+ redox potentials, which we expect to correlate with experimental AOR overpotential, depend strongly on the identity of the metal center, and to a lesser degree on the nature of the equatorial supporting ligand. Os2 complexes are easier to oxidize than analogous Ru2 complexes by ∼640 mV, on average. In contrast to mono-Ru catalysts, which oxidize ammonia via a rate-limiting activation of the strong N–H bond, we find lowest-energy reaction pathways for Ru2 and Os2 complexes that involve direct N–N bond formation onto electrophilic intermediates having terminal amido, imido, or nitrido groups. While transition state energies for Os2 complexes are high, those for Ru2 complexes are moderate and notably lower than those for mono-Ru complexes. We attribute these lower barriers to enhanced electrophilicity of the Ru2 intermediates, which is a consequence of their metal–metal bonded structure. Os2 intermediates are found to be, surprisingly, less electrophilic, and we suggest that Os2 complexes may require access to oxidation states higher than Os2 5+ in order to perform AOR at reasonable reaction rates.

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Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 90%

Section: T H Imentioning

confidence: 99%

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Computational Analysis of Low Overpotential Ammonia Oxidation by Metal–Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts

Trenerry,

Acosta,

Berry

2024

J. Phys. Chem. A

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“…This result has important implications regarding ability of the diruthenium system to carry out both half-reactions in a direct NH 3 fuel cell and was investigated further by DFT calculations in a subsequent report. [84] A plausible mechanism for the spontaneous Rumediated reaction of NH 3 to generate N 2 was constructed using stoichiometric experiments and DFT calculations. Starting from in situ formation of [Ru 2 (chp) 4 (NH 3 )] + , the addition of 20 equiv.…”

Section: Molecular Electrocatalysts For Nh 3 Oxidation To Nmentioning

confidence: 99%

Molecular Complexes for Catalytic Ammonia Oxidation to Dinitrogen and the Cleavage of N−H Bonds

Stephens,

Mock

2024

Eur J Inorg Chem

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The molecular complexes described herein use main‐group elements or transition metals to control the stoichiometric cleavage of N−H bonds of ammonia (NH3) and/or catalyze chemical and electrochemical NH3 oxidation to dinitrogen (N2). We highlight the phenomenon of coordination‐induced bond weakening and a variety of N−H bond cleavage mechanisms of NH3 including H atom abstraction, inter‐ and intra‐molecular deprotonation reactions, oxidative addition, and 𝝈‐bond metathesis that have been demonstrated with molecular systems. We provide an overview of the molecular complexes reported for the rapidly developing field of NH3 oxidation catalysis to form N2. These systems exhibit several diverse structure types and innovative ligands to support transition metals capable of activating NH3 and mediating a challenging chemical transformation that requires breaking strong N−H bonds and forming an N−N bond en route to N2 formation.

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Computational analysis of metal–metal bonded dimetal tetrabenzoate redox potentials in the context of ammonia oxidation electrocatalysis

Abstract: Metal-metal bonded complexes are promising candidates for catalyzing redox transformations. Of particular interest is the oxidation of ammonia to dinitrogen, an important half reaction for the potential utilization of ammonia...

Cited by 2 publications

References 126 publications

Computational Analysis of Low Overpotential Ammonia Oxidation by Metal–Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts

Computational Analysis of Low Overpotential Ammonia Oxidation by Metal–Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts

Molecular Complexes for Catalytic Ammonia Oxidation to Dinitrogen and the Cleavage of N−H Bonds

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