Nitrogenase Model Complexes [Cp*Fe(μ-SR1)2(μ-η2-R2N═NH)FeCp*] (R1 = Me, Et; R2 = Me, Ph; Cp* = η5-C5Me5): Synthesis, Structure, and Catalytic N−N Bond Cleavage of Hydrazines on Diiron Centers

Chen, Yanhui; Zhou, Yuhan; Chen, Pingping; Tao, Yinsong; Li, Yang; Qü, Jingping

doi:10.1021/ja805025w

Cited by 108 publications

(71 citation statements)

References 41 publications

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“…43 In several cases, bridging cis -diazene ligands were observed, which can be protonated to give hydrazido complexes with formal oxidation of the metal center. Crystallography and DFT calculations showed a μ-η 1 :η 2 -N 2 H 2 R intermediate in the N-N cleaving process.…”

Section: Resultsmentioning

confidence: 99%

The Mechanism of N–N Double Bond Cleavage by an Iron(II) Hydride Complex

et al. 2016

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The use of hydride species for substrate reductions avoids strong reductants, and may enable nitrogenase to reduce multiple bonds without unreasonably low redox potentials. In this work, we explore the N=N bond cleaving ability of a high-spin iron(II) hydride dimer with concomitant release of H2. Specifically, this diiron(II) reacts with azobenzene (PhN=NPh) to perform the four-electron reduction to two imido groups, where two electrons come from H2 reductive elimination and the other two come from iron oxidation. The rate law of the H2 releasing reaction indicates that diazene binding occurs prior to H2 elimination, and the negative entropy of activation and inverse kinetic isotope effect indicate that H-H bond formation is the rate-limiting step. Thus, substrate binding causes reductive elimination of H2 that formally reduces the metals, and the metals use the additional two electrons to cleave the N-N multiple bond.

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Section: Resultsmentioning

confidence: 99%

The Mechanism of N–N Double Bond Cleavage by an Iron(II) Hydride Complex

et al. 2016

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“…Furthermore, complex 1 also facilitates the 4 e − reduction of azobenzene to yield triiron bis-imido cluster ( tbs L)Fe 3 (µ 3 -NPh)(µ 2 -NPh). While iron compounds have been shown to reduce hydrazines, 37,38,39,40,41,42,43 there are fewer examples in which iron facilitates the N=N bond cleavage. 44,45 For example, low-valent trinuclear Fe(0) carbonyl clusters facilitates thermolytic N=N bond cleavage of azoalkanes.…”

Section: Discussionmentioning

confidence: 99%

Testing the Polynuclear Hypothesis: Multielectron Reduction of Small Molecules by Triiron Reaction Sites

Powers

Betley

2013

J. Am. Chem. Soc.

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High-spin trinuclear iron complex (tbsL)Fe3(thf) ([tbsL]6− = [1,3,5- C6H9(NPh-o-NSitBuMe2)3]6−) (S = 6) facilitates 2 and 4e− reduction of NxHy type substrates to yield imido and nitrido products. Reaction of hydrazine or phenylhydrazine with (tbsL)Fe3(thf) yields triiron µ3-imido cluster (tbsL)Fe3(µ3-NH) and ammonia or aniline, respectively. (tbsL)Fe3(µ3-NH) has a similar zero-field 57Fe Mössbauer spectrum compared to previously reported [(tbsL)Fe3(µ3-N)]NBu4, and can be directly synthesized by protonation of the anionic triiron nitrido with lutidinium tetraphenylborate. Deprotonation of the triiron parent imido (tbsL)Fe3(µ3-NH) with lithium bis(trimethylsilyl)amide results in regeneration of the triiron nitrido complex capped with a thf-solvated Li cation [(tbsL)Fe3(µ3-N)]Li(thf)3. The lithium capped nitrido, structurally similar to the pseudo C3-symmetric triiron nitride with a tetrabutylammonium counter cation, is rigorously C3-symmetric featuring intracore distances of Fe–Fe 2.4802(5) Å, Fe–N(nitride) 1.877(2) Å, and N(nitride)–Li 1.990(6) Å. A similar 2e− reduction of 1,2-diphenylhydrazine by (tbsL)Fe3(thf) affords (tbsL)Fe3(µ3-NPh) and aniline. The solid state structure of (tbsL)Fe3(µ3-NPh) is similar to the series of µ3-nitrido and -imido triiron complexes synthesized in this work with average Fe–Nimido and Fe–Fe bond lengths of 1.941(6) Å and 2.530(1) Å, respectively. Reductive N=N bond cleavage of azobenzene is also achieved in the presence of (tbsL)Fe3(thf) to yield triiron bisimido complex (tbsL)Fe3(µ3-NPh)(µ2-NPh), which has been structurally characterized. Ligand redox participation has been ruled out and, therefore, charge balance indicates that the bisimido cluster has undergone a 4e− metal based oxidation resulting in an (FeIV)(FeIII)2 formulation. Cyclic voltammograms of the series of triiron clusters presented herein demonstrate that oxidation states up to (FeIV)(FeIII)2 (in the case of [(tbsL)Fe3(µ3-N)]NBu4) are electrochemically accessible. These results highlight the efficacy of high-spin, polynuclear reaction sites to cooperatively mediate small molecule activation.

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“…Additionally, none of these S-based systems has been reported to perform N 2 reduction, though some are capable of catalytic reduction of hydrazine. 200,201 …”

Section: Fe-nxhy Complexes With Sulfur Ligandsmentioning

confidence: 99%

Insight into the Iron–Molybdenum Cofactor of Nitrogenase from Synthetic Iron Complexes with Sulfur, Carbon, and Hydride Ligands

2016

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Nitrogenase enzymes are used by microorganisms for converting atmospheric N2 to ammonia, which provides an essential source of N atoms for higher organisms. The active site of the molybdenum-dependent nitrogenase is the unique carbide-containing iron-sulfur cluster called the iron-molybdenum cofactor (FeMoco). On the FeMoco, N2 binding is suggested to occur at one or more iron atoms, but the structures of the catalytic intermediates are not clear. In order to establish the feasibility of different potential mechanistic steps during biological N2 reduction, chemists have prepared iron complexes that mimic various structural aspects of the iron sites in FeMoco. This reductionist approach gives mechanistic insight, and also uncovers fundamental principles that could be used more broadly for small molecule activation. Here, we review recent results and highlight directions for future research. In one direction, synthetic iron complexes have now been shown to bind N2, break the N-N triple bond, and produce ammonia catalytically. Carbon and sulfur based donors have been incorporated into the ligand spheres of Fe-N2 complexes to show how these atoms may influence the structure and reactivity of the FeMoco. Hydrides have been incorporated into synthetic systems, which can bind N2, reduce some nitrogenase substrates, and/or reductively eliminate H2 to generate reduced iron centers. Though some carbide-containing iron clusters are known, none yet have sulfide bridges or high-spin iron atoms like the FeMoco.

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Nitrogenase Model Complexes [CpFe(μ-SR¹)₂(μ-η²-R²N═NH)FeCp] (R¹ = Me, Et; R² = Me, Ph; Cp* = η⁵-C₅Me₅): Synthesis, Structure, and Catalytic N−N Bond Cleavage of Hydrazines on Diiron Centers

Cited by 108 publications

References 41 publications

The Mechanism of N–N Double Bond Cleavage by an Iron(II) Hydride Complex

The Mechanism of N–N Double Bond Cleavage by an Iron(II) Hydride Complex

Testing the Polynuclear Hypothesis: Multielectron Reduction of Small Molecules by Triiron Reaction Sites

Insight into the Iron–Molybdenum Cofactor of Nitrogenase from Synthetic Iron Complexes with Sulfur, Carbon, and Hydride Ligands

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