Light Enhanced Fe-Mediated Nitrogen Fixation: Mechanistic Insights Regarding H<sub>2</sub> Elimination, HER, and NH<sub>3</sub> Generation

Schild, Dirk J.; Peters, Jonas C.

doi:10.1021/acscatal.9b00523

Cited by 45 publications

(64 citation statements)

References 70 publications

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“…Their analysis indicated substantial spin delocalization onto the CAAC ligand. More recently, Schild and Peters reported a phosphine-supported system where reduction gave formally iron(−I) or iron(−II) species that were more reactive at the N 2 ligands . The structure of 7 -K 3 is not clear based on the limited spectroscopic characterization we were able to obtain.…”

Section: Discussionmentioning

confidence: 84%

Nitrogenase-Relevant Reactivity of a Synthetic Iron–Sulfur–Carbon Site

et al. 2019

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Simple synthetic compounds with only S and C donors offer a ligation environment similar to the active site of nitrogenase (FeMoco) and thus demonstrate reasonable mechanisms and geometries for N 2 binding and reduction in nature. We recently reported the first example of N 2 binding at a mononuclear iron site supported by only S and C donors. In this work, we report experiments that examine the mechanism of N 2 binding in this system. The reduction of an iron(II) tris(thiolate) complex with 1 equiv of KC 8 leads to a thermally unstable intermediate, and a combination of Mossbauer, EPR, and X-ray absorption spectroscopies identifies it as a high-spin (S = 3/2) iron(I) species that maintains coordination of all three sulfur atoms. DFT calculations suggest that this iron(I) intermediate has a pseudotetrahedral geometry that resembles the S 3 C iron coordination environment of the belt iron sites in the resting state of the FeMoco. Further reduction to the iron(0) oxidation level under argon causes the dissociation of one of the thiolate donors and gives an η 6 -arene species which reacts with N 2 . Thus, in this system the loss of thiolate and binding of N 2 require reduction beyond the iron(I) level to the iron(0) level. Further reduction of the iron(0)−N 2 complex gives a reactive, formally iron(−I) species. Treatment of the putative iron(−I) complex with weak acids gives low yields of ammonia and hydrazine, demonstrating that these nitrogenase products can be generated from N 2 at a synthetic Fe−S−C site. Catalytic N 2 reduction is not observed, which is attributed to protonation of the supporting ligand and degradation of the complex via ligand dissociation. Identification of the challenges in this system gives insight into the design features needed for functional biomimetic complexes.

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Section: Discussionmentioning

confidence: 84%

Nitrogenase-Relevant Reactivity of a Synthetic Iron–Sulfur–Carbon Site

et al. 2019

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“…The most noteworthy feature of the solid state structure of 7 is the ligand distortion (C1–C2–C3–P1 torsion angle: 29.8(5)°, Table S7) necessary to accommodate the Fe–N 2 –Fe linkage. Otherwise, it resembles a previously reported, untethered congener, which also reacts with H 2 to generate an Fe(H) 2 (N 2 ) complex following exposure to N 2 . , The singlet ground state of 7 likely arises from antiferromagnetic coupling of two low spin Fe(I) centers through the linear N 2 bridge . Generation of the intermediate 7 requires the addition of 2 equiv of H 2 to 5 , with the central carbyne ligand being fully protonated.…”

Section: Resultsmentioning

confidence: 99%

Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen

Arnett

Agapie

2020

J. Am. Chem. Soc.

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Experimental and Synthetic Details General Considerations All reactions were performed at room temperature in a nitrogen filled M. Braun glovebox or using standard Schlenk techniques unless otherwise specified. Glassware was oven dried at 140 o C for at least two hours prior to use, and allowed to cool under vacuum. Bis(odiisopropylphosphinophenyl)-chlorophosphine (P2P Cl) was prepared as described elsewhere. 1 All other reagents were obtained commercially unless otherwise noted and typically stored over activated 4 Å molecular sieves. Tetrahydrofuran, toluene-d8 and benzene-d6 were dried using sodium/benzophenone ketyl, degassed with three freeze-pump-thaw cycles, vacuum transferred, and stored over 3 Å molecular sieves prior to use. Diethyl ether, benzene, toluene, acetonitrile, hexanes, and pentane were dried by sparging with nitrogen for at least 15 minutes, then passing through a column of activated A2 alumina under positive nitrogen pressure. 1 H and 31 P NMR spectra were recorded on a Varian 300 or 400 MHz spectrometer. All chemical shifts (δ) are reported in ppm, and coupling constants (J) are in hertz. The 1 H-NMR spectra were referenced using residual H impurity in the deuterated solvent. UV-Vis spectra were recorded on a Varian Cary Bio 50 spectrophotometer. Infrared (ATR-IR) spectra were recorded on a Bruker ALPHA ATR-IR spectrometer. Elemental analyses were performed at Caltech. Physical Methods Mössbauer Measurements. Zero field 57 Fe Mössbauer spectra were recorded in constant acceleration on a spectrometer from See Co (Edina, MN) equipped with an SVT-400 cryostat (Janis, Wilmington, WA). The quoted isomer shifts are relative to the centroid of the spectrum of α-Fe foil at room temperature. Unless otherwise noted, samples were prepared by grinding polycrystalline (20-50 mg) into a fine powder and pressed into a homogenous pellet with boron nitride in a cup fitted with a screw cap. The data were fitted to Lorentzian lineshapes using the program WMOSS (www.wmoss.org). Magnetic Measurements. Magnetic measurements for 5 were conducted with a Quantum Design MPMS3 SQUID Magnetometer at the University of California, Los Angeles. A polycrystalline sample of 5 was wrapped in plastic film and placed in a gelatin capsule. The capsule was then inserted into a plastic straw. Magnetization data at 100 K from 0 to 4 T were collected to confirm the absence of ferromagnetic impurities. Direct current variable temperature magnetic susceptibility measurements were collected between 1.8 and 300 K with a 0.1 T field. Magnetic susceptibility data was corrected for diamagnetism of the sample, estimated using Pascal's constants. Magnetic susceptibility data was simulated with PHI. 2 X-ray Crystallography. For compounds 4-8, low-temperature (100 K) diffraction data (φand ω-scans) were collected on a Bruker AXS D8 VENTURE KAPPA diffractometer coupled to a PHOTON 100 CMOS detector with Mo Kα radiation (λ = 0.71073 Å) or with Cu Kα (λ = 1.54178 Å). All diffractometer manipulations, including data collection, integration, and ...

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“…For example, tris(phosphine)borane ligated Fe(I), ([Fe(N2)(PNP)], where PNP = 2,5-bis(di-tertbutylphosphinomethyl) pyrrolide etc., have been also explored as electrocatalysts for NRR. [158][159][160][161]…”

Section: Fe Compoundsmentioning

confidence: 99%

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

Patil

Wang

2020

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Light Enhanced Fe-Mediated Nitrogen Fixation: Mechanistic Insights Regarding H₂ Elimination, HER, and NH₃ Generation

Cited by 45 publications

References 70 publications

Nitrogenase-Relevant Reactivity of a Synthetic Iron–Sulfur–Carbon Site

Nitrogenase-Relevant Reactivity of a Synthetic Iron–Sulfur–Carbon Site

Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

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Light Enhanced Fe-Mediated Nitrogen Fixation: Mechanistic Insights Regarding H2 Elimination, HER, and NH3 Generation

Cited by 45 publications

References 70 publications

Nitrogenase-Relevant Reactivity of a Synthetic Iron–Sulfur–Carbon Site

Nitrogenase-Relevant Reactivity of a Synthetic Iron–Sulfur–Carbon Site

Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

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Light Enhanced Fe-Mediated Nitrogen Fixation: Mechanistic Insights Regarding H₂ Elimination, HER, and NH₃ Generation