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1. Synergizing Fe ₂ O ₃ Nanoparticles on Single Atom Fe‐N‐C for Nitrate Reduction to Ammonia at Industrial Current Densities

   https://doi.org/10.1002/adma.202401133  

   Murphy, Eamonn; Sun, Baiyu; Rüscher, Martina; Liu, Yuanchao; Zang, Wenjie; Guo, Shengyuan; Chen, Yu‐Han; Hejral, Uta; Huang, Ying; Ly, Alvin; et al (July 2024, Advanced Materials)

   Abstract The electrochemical reduction of nitrates (NO₃⁻) enables a pathway for the carbon neutral synthesis of ammonia (NH₃), via the nitrate reduction reaction (NO₃RR), which has been demonstrated at high selectivity. However, to make NH₃synthesis cost‐competitive with current technologies, high NH₃partial current densities (j_NH3) must be achieved to reduce the levelized cost of NH₃. Here, the high NO₃RR activity of Fe‐based materials is leveraged to synthesize a novel active particle‐active support system with Fe₂O₃nanoparticles supported on atomically dispersed Fe–N–C. The optimized 3×Fe₂O₃/Fe–N–C catalyst demonstrates an ultrahigh NO₃RR activity, reaching a maximum j_NH3of 1.95 A cm⁻²at a Faradaic efficiency (FE) for NH₃of 100% and an NH₃yield rate over 9 mmol hr⁻¹cm⁻². Operando XANES and post‐mortem XPS reveal the importance of a pre‐reduction activation step, reducing the surface Fe₂O₃(Fe³⁺) to highly active Fe⁰sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe₂O₃particles and Fe–N_xsites at highly cathodic potentials, maintaining a current of −1.3 A cm⁻²over 24 hours. This work exhibits an effective and durable active particle‐active support system enhancing the performance of the NO₃RR, enabling industrially relevant current densities and near 100% selectivity. 

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2. Dianionic Mononuclear Cyclo ‐P ₄ Complexes of Zero‐Valent Molybdenum: Coordination of the Cyclo ‐P ₄ Dianion in the Absence of Intramolecular Charge Transfer

   https://doi.org/10.1002/anie.201908885  

   Mandla, Kyle A.; Neville, Michael L.; Moore, Curtis E.; Rheingold, Arnold L.; Figueroa, Joshua S. (September 2019, Angewandte Chemie International Edition)

   Abstract Relative to other cyclic poly‐phosphorus species (that is,cyclo‐P_n), the planarcyclo‐P₄group is unique in its requirement of two additional electrons to achieve aromaticity. These electrons are supplied from one or more metal centers. However, the degree of charge transfer is dependent on the nature of the metal fragment. Unique examples of dianionic mononuclear η⁴‐P₄complexes are presented that can be viewed as the simple coordination of the [cyclo‐P₄]²⁻dianion to a neutral metal fragment. Treatment of the neutral, molybdenumcyclo‐P₄complexes Mo(η⁴‐P₄)I₂(CO)(CNAr^Dipp2)₂and Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)₂with KC₈produces the dianionic, three‐legged piano stool complexes, [Mo(η⁴‐P₄)(CO)(CNAr^Dipp2)₂]²⁻and [Mo(η⁴‐P₄)(CO)₂(CNAr^Dipp2)]²⁻, respectively. Structural, spectroscopic, and computational studies reveal a similarity to the classic η⁶‐benzene complex (η⁶‐C₆H₆)Mo(CO)₃regarding the metal‐center valence state and electronic population of the planar‐cyclic ligand π system. 

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3. Catalytic Ammonia Oxidation to Dinitrogen by a Nickel Complex

   https://doi.org/10.1002/anie.202213462  

   Stephens, David N.; Szilagyi, Robert K.; Roehling, Paige N.; Arulsamy, Navamoney; Mock, Michael T. (November 2022, Angewandte Chemie International Edition)

   Abstract We report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6‐tri‐tert‐butylphenoxyl (^tBu₃ArO⋅) as a H atom acceptor to cleave the N−H bond of a coordinated NH₃ligand up to 56 equiv of N₂per Ni center can be generated. Employing theN‐oxyl radical 2,2,6,6‐(tetramethylpiperidin‐1‐yl)oxyl (TEMPO⋅) as the H‐atom acceptor, up to 15 equiv of N₂per Ni center are formed. A bridging Ni‐hydrazine product identified by isotopic nitrogen (¹⁵N) studies and supported by computational models indicates the N−N bond forming step occurs by bimetallic homocoupling of two paramagnetic [Ni]−NH₂fragments. Ni‐mediated hydrazine disproportionation to N₂and NH₃completes the catalytic cycle. 

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4. Nuclear Spin Hyperpolarization of NH ₂ ‐ and CH ₃ ‐Substituted Pyridine and Pyrimidine Moieties by SABRE

   https://doi.org/10.1002/cphc.202000483  

   Mandal, Ratnamala; Pham, Pierce; Hilty, Christian (September 2020, ChemPhysChem)

   Abstract Hyperpolarization of N‐heterocycles with signal amplification by reversible exchange (SABRE) induces NMR sensitivity gains for biological molecules. Substitutions with functional groups, in particular in theortho‐position of the heterocycle, however, result in low polarization using a typical Ir catalyst with a bis‐mesityl N‐heterocyclic carbene ligand for SABRE, presumably due to steric hindrance. With the addition of allylamine or acetonitrile as coligands to the precatalyst chloro(1,5‐cyclooctadiene)[4,5‐dimethyl‐1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene] iridium, the¹H signal enhancement increased in several substrates withorthoNH₂substitutions. For example, for a proton in 2,4‐diaminopyrimidine, the enhancement factors increased from −7±1 to −210±20 with allylamine or to −160±10 with acetonitrile. CH₃substituted molecules yielded maximum signal enhancements of −25±7 with acetonitrile addition, which is considerably less than the corresponding NH₂substituted molecules, despite exhibiting similar steric size. With the more electron‐donating NH₂substitution resulting in greater enhancement, it is concluded that steric hindrance is not the only dominant factor in determining the polarizability of the CH₃substituted compounds. The addition of allylamine increased the signal enhancement for the 290 Da trimethoprim, a molecule with a 2,4‐diaminopyrimidine moiety serving as an antibacterial agent, to −70. 

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5. Inorganic and organic carbon and nitrogen uptake strategies of picoplankton groups in the northwestern Atlantic Ocean

   https://doi.org/10.1002/lno.11909  

   Berthelot, Hugo; Duhamel, Solange; L'Helguen, Stéphane; Maguer, Jean‐François; Cassar, Nicolas (August 2021, Limnology and Oceanography)

   Abstract Picoplankton populations dominate the planktonic community in the surface oligotrophic ocean. Yet, their strategies in the acquisition and the partitioning of organic and inorganic sources of nitrogen (N) and carbon (C) are poorly described. Here, we measured at the single‐cell level the uptake of dissolved inorganic C (C‐fixation), C‐leucine, N‐leucine, nitrate (NO₃⁻), ammonium (NH₄⁺), and N‐urea in pigmented and nonpigmented picoplankton groups at six low‐N stations in the northwestern Atlantic Ocean. Our study highlights important differences in trophic strategies betweenProchlorococcus,Synechococcus, photosynthetic pico‐eukaryotes, and nonpigmented prokaryotes. Nonpigmented prokaryotes were characterized by high leucine uptake rates, nonsignificant C‐fixation and relatively low NH₄⁺, N‐urea, and NO₃⁻uptake rates. Nonpigmented prokaryotes contributed to 7% ± 3%, 2% ± 2%, and 9% ± 5% of the NH₄⁺, NO₃⁻, and N‐urea community uptake, respectively. In contrast, pigmented groups displayed relatively high C‐fixation rates, NH₄⁺and N‐urea uptake rates, but lower leucine uptake rates than nonpigmented prokaryotes.Synechococcusand photosynthetic pico‐eukaryotes NO₃⁻uptake rates were higher thanProchlorococcusones. Pico‐sized pigmented groups accounted for a significant fraction of the community C‐fixation (63% ± 27%), NH₄⁺uptake (47% ± 27%), NO₃⁻uptake (62% ± 49%), and N‐urea uptake (81% ± 35%). Interestingly,Prochlorococcusand photosynthetic pico‐eukaryotes showed a greater reliance on C‐ and N‐leucine thanSynechococcuson average, suggesting a greater reliance on organic C and N sources. Taken together, our single‐cell results decipher the wide diversity of C and N trophic strategies between and within marine picoplankton groups, but a clear partitioning between pigmented and nonpigmented groups still remains. 

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