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1. The N ‐Methylpyrrolidone (NMP) Effect in Iron‐Catalyzed Cross‐Coupling with Simple Ferric Salts and MeMgBr

   https://doi.org/10.1002/anie.201802087  

   Muñoz, III, Salvador B. ; Daifuku, Stephanie L. ; Sears, Jeffrey D. ; Baker, Tessa M. ; Carpenter, Stephanie H. ; Brennessel, William W. ; Neidig, Michael L. ( May 2018 , Angewandte Chemie International Edition)

   The use ofN‐methylpyrrolidone (NMP) as a co‐solvent in ferric salt catalyzed cross‐coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross‐coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP)₆][FeMe₃]₂(1), which forms as the major iron species in situ in reactions of Fe(acac)₃and MeMgBr under catalytically relevant conditions where NMP is employed as a co‐solvent. Importantly, combined GC analysis and⁵⁷Fe Mössbauer spectroscopic studies identified1as a highly reactive iron species for the selective formation generating cross‐coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of1over [Fe₈Me₁₂]⁻cluster generation, which occurs in the absence of NMP.

    

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2. The Effect of β‐Hydrogen Atoms on Iron Speciation in Cross‐Couplings with Simple Iron Salts and Alkyl Grignard Reagents

   https://doi.org/10.1002/ange.201813578  

   Sears, Jeffrey D. ; Muñoz, III, Salvador B. ; Daifuku, Stephanie L. ; Shaps, Ari A. ; Carpenter, Stephanie H. ; Brennessel, William W. ; Neidig, Michael L. ( January 2019 , Angewandte Chemie)

   The effects of β‐hydrogen‐containing alkyl Grignard reagents in simple ferric salt cross‐couplings have been elucidated. The reaction of FeCl₃with EtMgBr in THF leads to the formation of the cluster species [Fe₈Et₁₂]²⁻, a rare example of a structurally characterized metal complex with bridging ethyl ligands. Analogous reactions in the presence of NMP, a key additive for effective cross‐coupling with simple ferric salts and β‐hydrogen‐containing alkyl nucleophiles, result in the formation of [FeEt₃]⁻. Reactivity studies demonstrate the effectiveness of [FeEt₃]⁻in rapidly and selectively forming the cross‐coupled product upon reaction with electrophiles. The identification of iron‐ate species with EtMgBr analogous to those previously observed with MeMgBr is a critical insight, indicating that analogous iron species can be operative in catalysis for these two classes of alkyl nucleophiles.

    

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3. The Effect of β‐Hydrogen Atoms on Iron Speciation in Cross‐Couplings with Simple Iron Salts and Alkyl Grignard Reagents

   https://doi.org/10.1002/anie.201813578  

   Sears, Jeffrey D. ; Muñoz, III, Salvador B. ; Daifuku, Stephanie L. ; Shaps, Ari A. ; Carpenter, Stephanie H. ; Brennessel, William W. ; Neidig, Michael L. ( January 2019 , Angewandte Chemie International Edition)

   The effects of β‐hydrogen‐containing alkyl Grignard reagents in simple ferric salt cross‐couplings have been elucidated. The reaction of FeCl₃with EtMgBr in THF leads to the formation of the cluster species [Fe₈Et₁₂]²⁻, a rare example of a structurally characterized metal complex with bridging ethyl ligands. Analogous reactions in the presence of NMP, a key additive for effective cross‐coupling with simple ferric salts and β‐hydrogen‐containing alkyl nucleophiles, result in the formation of [FeEt₃]⁻. Reactivity studies demonstrate the effectiveness of [FeEt₃]⁻in rapidly and selectively forming the cross‐coupled product upon reaction with electrophiles. The identification of iron‐ate species with EtMgBr analogous to those previously observed with MeMgBr is a critical insight, indicating that analogous iron species can be operative in catalysis for these two classes of alkyl nucleophiles.

    

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4. A Nonheme Mononuclear {FeNO} 7 Complex that Produces N 2 O in the Absence of an Exogenous Reductant

   https://doi.org/10.1002/ange.202109062  

   Dey, Aniruddha ; Gordon, Jesse B. ; Albert, Therese ; Sabuncu, Sinan ; Siegler, Maxime A. ; MacMillan, Samantha N. ; Lancaster, Kyle M. ; Moënne‐Loccoz, Pierre ; Goldberg, David P. ( August 2021 , Angewandte Chemie)

   A new nonheme iron(II) complex, Fe^II(Me₃TACN)((OSi^Ph2)₂O) (1), is reported. Reaction of1with NO_(g)gives a stable mononitrosyl complex Fe(NO)(Me₃TACN)((OSi^Ph2)₂O) (2), which was characterized by Mössbauer (δ=0.52 mm s⁻¹, |ΔE_Q|=0.80 mm s⁻¹), EPR (S=3/2), resonance Raman (RR) and Fe K‐edge X‐ray absorption spectroscopies. The data show that2is an {FeNO}⁷complex with anS=3/2 spin ground state. The RR spectrum (λ_exc=458 nm) of2combined with isotopic labeling (¹⁵N,¹⁸O) reveals ν(N‐O)=1680 cm⁻¹, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm⁻¹). Complex2reacts rapidly with H₂O in THF to produce the N‐N coupled product N₂O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N₂O in the absence of an exogenous reductant.

    

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5. A Nonheme Mononuclear {FeNO} 7 Complex that Produces N 2 O in the Absence of an Exogenous Reductant

   https://doi.org/10.1002/anie.202109062  

   Dey, Aniruddha ; Gordon, Jesse B. ; Albert, Therese ; Sabuncu, Sinan ; Siegler, Maxime A. ; MacMillan, Samantha N. ; Lancaster, Kyle M. ; Moënne‐Loccoz, Pierre ; Goldberg, David P. ( August 2021 , Angewandte Chemie International Edition)

   A new nonheme iron(II) complex, Fe^II(Me₃TACN)((OSi^Ph2)₂O) (1), is reported. Reaction of1with NO_(g)gives a stable mononitrosyl complex Fe(NO)(Me₃TACN)((OSi^Ph2)₂O) (2), which was characterized by Mössbauer (δ=0.52 mm s⁻¹, |ΔE_Q|=0.80 mm s⁻¹), EPR (S=3/2), resonance Raman (RR) and Fe K‐edge X‐ray absorption spectroscopies. The data show that2is an {FeNO}⁷complex with anS=3/2 spin ground state. The RR spectrum (λ_exc=458 nm) of2combined with isotopic labeling (¹⁵N,¹⁸O) reveals ν(N‐O)=1680 cm⁻¹, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm⁻¹). Complex2reacts rapidly with H₂O in THF to produce the N‐N coupled product N₂O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N₂O in the absence of an exogenous reductant.

    

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