Design and reactivity of pentapyridyl metal complexes for ammonia oxidation

Johnson, Samantha I.; Heins, Spencer P.; Klug, Christina M.; Wiedner, Eric S.; Bullock, R. Morris; Raugei, Simone

doi:10.1039/c9cc01249d

Cited by 38 publications

(68 citation statements)

References 36 publications

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“…[29][30][31][32][33] Bullock and coworkers recently reported a detailed theoretical investigation using the PY5 ligand platform 34,35 for AO with M = Cr, Mo, W, Mn, Fe, Ru, Os. 36 They observed that the [PY5]Fe(II) complex behaved quite differently to the rest of the metals Please do not adjust margins Please do not adjust margins investigated, notably due to the significant radical character of the Fe-amido and Fe-imido intermediates computed. We therefore thought of using our tetrapodal dianionic pentadentate B 2 Pz 4 Py ligand platform, which has been successful at accessing a variety of first-row metal complexes.…”

Section: Introductionmentioning

confidence: 99%

Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

et al. 2021

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Section: Introductionmentioning

confidence: 99%

Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

et al. 2021

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“…[29][30][31][32][33] Bullock and coworkers recently reported a detailed theoretical investigation using the PY5 ligand platform [34][35] for AO with M = Cr, Mo, W, Mn, Fe, Ru, Os. 36 They observed that the [PY5]Fe(II) complex behaved quite differently to the rest of the metals investigated, notably due to the significant radical character of the Fe-amido and Fe-imido intermediates computed. We therefore thought of using our tetrapodal dianionic pentadentate B2Pz4Py ligand platform, which has been successful at accessing a variety of first-row metal complexes.…”

Section: Introductionmentioning

confidence: 99%

Activation of Ammonia and Hydrazine by Electron Rich Fe(II) Complexes Supported by a Dianionic Pentadentate Ligand Platform Through a Common Terminal Fe(III) Amido Intermediate

Nurdin¹,

Yan²,

Neate³

et al. 2020

Preprint

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We report the use of electron rich iron complexes supported by a dianionic diborate pentadentate ligand system, B2Pz4Py, for the coordination and activation of ammonia (NH3) and hydrazine (NH2NH2). For ammonia, coordination to neutral (B2Pz4Py)Fe(II) or cationic [(B2Pz4Py)Fe(III)]+ platforms leads to well characterized ammine complexes from which hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (B2Pz4Py)Fe(III)- NH2 complex (3Ar-NH2). DFT computations suggest a high degree of spin density on the amido ligand, giving it significant aminyl radical character. It rapidly traps the H atom abstracting agent 2,4,6-tri-tert-butylphenoxy radical (ArO•) to form a C-N bond in a fully characterized product (2Ar), or scavenges hydrogen atoms to return to the ammonia complex (B2Pz4Py)Fe(II)-NH3 (1ArNH3). Interestingly, when (B2Pz4Py)Fe(II) is reacted with NH2NH2, a fully characterized bridging diazene complex, 4Ar, is formed along with ammonia adduct 1Ar-NH3 as the spectroscopically observed (-78˚C) (B2Pz4Py)Fe(II)-NH2NH2-Fe(II)( B2Pz4Py) dimer (1Ar)2-NH2NH2 is allowed to warm to room temperature. Experimental and computational evidence is presented to suggest that (B2Pz4Py)Fe(II) induces reductive cleavage of the N-N bond in hydrazine to produce the Fe(III)-NH2 complex 3Ar-NH2, which abstracts H• atoms from (1Ar)2-NH2NH2 to generate the observed products. All of these transformations are relevant to proposed steps in the ammonia oxidation reaction, an important process for the use of nitrogen-based fuels enabled by abundant first row transition metals.

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“…2 Welldefined molecular model systems are amenable to detailed mechanistic interrogation, and their study in this context is expanding rapidly. Stoichiometric ammonia oxidation (AO) to N2 has been demonstrated for transition metal complexes of Mo, 3 Mn, 4 Os, 5 and Ru. 6,7 More recently, AO catalysis has been reported using Ru 8 and Fe 9 complexes under chemical and electrochemical conditions.…”

Section: Introductionmentioning

confidence: 99%

Hydrazine Formation via NiIII-NH2 Radical Coupling in Ni-Mediated Ammonia Oxidation

Gu¹,

Oyala²,

Peters

2020

Preprint

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Given the diverse mechanistic possibilities for the overall 6e-/6H+ transformation of ammonia to dinitrogen, identification of M(NHx) intermediates involved in N–N bond formation is a central mechanistic challenge. In analogy to water oxidation mechanisms, which widely invoke metal oxo intermediates, metal imide and nitride intermediates have commonly been proposed for ammonia oxidation, and stoichiometric demonstration of N–N bond formation from these metal-ligand multiply bonded species is well-precedented. In contrast, while the homocoupling of M–NH2 species to form hydrazine has been hypothesized as the key N–N bond forming step in certain molecular ammonia oxidation systems, well-defined examples of this transformation from M–NH2 complexes are essentially without precedent. This work reports the first example of net ammonia oxidation mediated by a molecular Ni species, a transformation carried out via formal NiII/NiIII oxidation states. The available data are consistent with a NiIII–NH2 intermediate featuring substantial spin at N undergoing N–N bond formation to generate a NiII2(N2H4) complex. Additional and structurally unusual Nix(NyHz) species – including a Ni2(trans-N2H2) complex – are characterized and studied as intermediates in the Ni-mediated ammonia oxidation cycle described herein.

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Design and reactivity of pentapyridyl metal complexes for ammonia oxidation

Abstract: Computational and experimental work shows that Mo pentapyridal complexes can oxidize ammonia in the presence of a chemical mediator and evolve N2.

Cited by 38 publications

References 36 publications

Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

Activation of Ammonia and Hydrazine by Electron Rich Fe(II) Complexes Supported by a Dianionic Pentadentate Ligand Platform Through a Common Terminal Fe(III) Amido Intermediate

Hydrazine Formation via NiIII-NH2 Radical Coupling in Ni-Mediated Ammonia Oxidation

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