(Electro)chemical N<sub>2</sub> Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

Ostermann, Nils; Rotthowe, Nils; Stückl, A. Claudia; Siewert, Inke

doi:10.1021/acsorginorgau.3c00056

Cited by 3 publications

(1 citation statement)

References 61 publications

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“…Other Mo-pincer complexes have also been found to effectively catalyze ammonia formation or, in some cases, to effect the key N2 cleavage step though not as part of an catalytic cycle for ammonia formation. 12,16,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] Figure 1. (a) Schrock's (triamidoamine)Mo catalyst.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

Malakar,

Mandal,

Zhou

et al. 2024

Preprint

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The thioether-diphosphine pincer-ligated molybdenum complex, (PSP)MoCl3 (1-Cl3, PSP = 4,5-bis(diisopropylphosphino)-2,7-di-tert-butyl-9,9-dimethyl-9H-thioxanthene) has been synthesized as a catalyst-precursor for N2 reduction catalysis, with a focus on an integrated experimental/computational mechanistic investigation. The (PSP)Mo unit is isoelectronic with the (PNP)Mo (PNP = 2,6-bis(di-t-butylphosphinomethyl)pyridine) fragment found in the family of catalysts for the reduction of N2 to NH3 first reported in 2011 by Nishibayashi and co-workers. Under an atmosphere of N2 the reaction of 1-Cl3 with three reducing equivalents yields the dinuclear penta-dinitrogen Mo complex [(PSP)Mo(N2)2](-N2), 2. Electrochemical studies reveal that 1-Cl3 is significantly more easily reduced than (PNP)MoCl3 (with a potential ca. 0.4 eV less negative). The bridging-nitrogen complex 2 shows no indication of undergoing N2 cleavage to Mo nitride complexes. The reaction of 1-Cl3 with only two reducing equivalents, however, under N2 atmosphere and in the presence of iodide, affords the product of N2 cleavage, the nitride complex (PSP)Mo(N)(I). DFT calculations implicate another N2-bridged complex, [(PSP)Mo(I)]2(N2), as a viable intermediate in facile N2 cleavage to yield (PSP)Mo(N)(I). Conversion of the nitride ligand to NH3 has been studied. If considering sequential addition of H atoms to the nitride, formation of the first N-H bond is by far the thermodynamically least favorable of the three N-H bond formation steps. The first N-H bond was formed by reaction of (PSP)Mo(N)(I) with [LutH]Cl, where coordination of Cl– to Mo plays an essential role. Computations suggest that a second protonation, followed by a rapid and very favorable one-electron reduction, and then a third protonation, furnishes ammonia. In agreement with calculations, ammonia can be generated using either mild H-atom transfer reagents or mild reductants/acids. This comprehensive analysis of the elementary steps of ammonia synthesis and the role of the central pincer donor and halide association provides guidance for future catalyst designs.

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Section: Introductionmentioning

confidence: 99%

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

Malakar,

Mandal,

Zhou

et al. 2024

Preprint

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Isocyanide Ligation Enables Electrochemical Ammonia Formation in a Synthetic Cycle for N₂ Fixation

Weber,

McMillion,

Hegg

et al. 2024

J. Am. Chem. Soc.

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Transition-metal-mediated splitting of N 2 to form metal nitride complexes could constitute a key step in electrocatalytic nitrogen fixation, if these nitrides can be electrochemically reduced to ammonia under mild conditions. The envisioned nitrogen fixation cycle involves several steps: N 2 binding to form a dinuclear end-on bridging complex with appropriate electronic structure to cleave the N 2 bridge followed by proton/electron transfer to release ammonia and bind another molecule of N 2 . The nitride reduction and N 2 splitting steps in this cycle have differing electronic demands that a catalyst must satisfy. Rhenium systems have had limited success in meeting these demands, and studying them offers an opportunity to learn strategies for modulating reactivity. Here, we report a rhenium system in which the pincer supporting ligand is supplemented by an isocyanide ligand that can accept electron density, facilitating reduction and enabling the protonation/reduction of the nitride to ammonia under mild electrochemical conditions. The incorporation of isocyanide raises the N−H bond dissociation free energy of the first N−H bond by 10 kcal/mol, breaking the usual compensation between pK a and redox potential; this is attributed to the separation of the protonation site (nitride) and the reduction site (delocalized between Re and isocyanide). Ammonia evolution is accompanied by formation of a terminal N 2 complex, which can be oxidized to yield bridging N 2 complexes including a rare mixed-valent complex. These rhenium species define the steps in a synthetic cycle that converts N 2 to NH 3 through an electrochemical N 2 splitting pathway, and show the utility of a second, tunable supporting ligand for enhancing nitride reactivity.

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Electro-Chemical Energy Conversion and Storage Systems - Analytical Review

Nagpal,

Reddy,

Aswini

et al. 2024

E3S Web of Conf.

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This study emphasises how crucial it is to implement clean energy technology, especially electro-chemical systems, in order to reduce the emission of green-house and fulfil the world's growing energy needs. The study highlights the significance of sustainable resources such as wind and solar electricity. It also examines the difficulties associated with their intermittent nature and proposes changes to consumer behaviour and power producing practices. It talks about current research on candidate materials at the fundamental level and emphasises the crucial role customised materials play in electro-chemical systems. The paper explores the several uses of electro-chemical energy technology, explaining the classifications and operation of fuel cells, batteries, and capacitors, among other devices. The paper concludes by arguing that further advancements in materials and technology are essential to securing a reliable and efficient energy supply in the future.

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(Electro)chemical N₂ Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

Cited by 3 publications

References 61 publications

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

Isocyanide Ligation Enables Electrochemical Ammonia Formation in a Synthetic Cycle for N₂ Fixation

Electro-Chemical Energy Conversion and Storage Systems - Analytical Review

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(Electro)chemical N2 Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

Cited by 3 publications

References 61 publications

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

Isocyanide Ligation Enables Electrochemical Ammonia Formation in a Synthetic Cycle for N2 Fixation

Electro-Chemical Energy Conversion and Storage Systems - Analytical Review

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Product

Resources

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(Electro)chemical N₂ Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

Isocyanide Ligation Enables Electrochemical Ammonia Formation in a Synthetic Cycle for N₂ Fixation