Catalytic Reduction Of Dinitrogen Research Articles

Catalytic Dinitrogen Reduction to Silylamines by Molybdenum Nitride Complexes Bearing a Diphenolate N-Heterocyclic Carbene Ligand

Catalytic Dinitrogen Reduction to Silylamines by Molybdenum Nitride Complexes Bearing a Diphenolate N-Heterocyclic Carbene Ligand

Catalytic reduction of dinitrogen to silylamines by earth-abundant lanthanide and group 4 complexes

Catalytic reduction of dinitrogen to silylamines by earth-abundant lanthanide and group 4 complexes

Iron promoted end-on dinitrogen-bridging in heterobimetallic complexes of uranium and lanthanides.

End-on binding of dinitrogen to low valent metal centres is common in transition metal chemistry but remains extremely rare in f-elements chemistry. In particular, heterobimetallic end-on N2 bridged complexes of lanthanides are unprecedented despite their potential relevance in catalytic reduction of dinitrogen. Here we report the synthesis and characterization of a series of N2 bridged heterobimetallic complexes of U(iii), Ln(iii) and Ln(ii) which were prepared by reacting the Fe dinitrogen complex [Fe(depe)2(N2)] (depe = 1,2-bis(diethylphosphino)-ethane), complex A with [MIII{N(SiMe3)2}3] (M = U, Ce, Sm, Dy, Tm) and [LnII{N(SiMe3)2}2], (Ln = Sm, Yb). Despite the lack of reactivity of the U(iii), Ln(iii) and Ln(ii) amide complexes with dinitrogen, the end-on dinitrogen bridged heterobimetallic complexes [{Fe(depe)2}(μ-η1:η1-N2)(M{N(SiMe3)2}3)], 1-M (M = U(iii), Ce(iii), Sm(iii), Dy(iii) and Tm(iii)), [{Fe(depe)2}(μ-η1:η1-N2)(Ln{N(SiMe3)2}2)], 1*-Ln (Ln = Sm(ii), Yb(ii)) and [{Fe(depe)2(μ-η1:η1-N2)}2{SmII{N(SiMe3)2}2}], 3 could be prepared. The synthetic method used here allowed to isolate unprecedented end-on bridging N2 complexes of divalent lanthanides which provide relevant structural models for the species involved in the catalytic reduction of dinitrogen by Fe/Sm(ii) systems. Computational studies showed an essentially electrostatic interaction of the end-on bridging N2 with both Ln(iii) and Ln(ii) complexes with the degree of N2 activation correlating with their Lewis acidity. In contrast, a back-bonding covalent contribution to the U(iii)-N2Fe bond was identified by computational studies. Computational studies also suggest that end-on binding of N2 to U(iii) and Ln(ii) complexes is favoured for the iron-bound N2 compared to free N2 due to the higher N2 polarization.

Catalytic dinitrogen reduction to hydrazine and ammonia using Cr(N2)2(diphosphine)2 complexes.

The synthesis, characterization of trans-[Cr(N2)2(depe)2] (1) is described. 1 and trans-[Cr(N2)2(dmpe)2] (2) catalyze the reduction of N2 to N2H4 and NH3 in THF using SmI2 and H2O or ethylene glycol as proton sources. 2 produces the highest total fixed N for a molecular Cr catalyst to date.

Catalytic reduction of dinitrogen to ammonia using molybdenum porphyrin complexes.

Porphyrin complexes are well-known in O2 and CO2 reduction, but their application to N2 reduction is less developed. Here, we show that oxo and nitrido complexes of molybdenum supported by tetramesitylporphyrin (TMP) are effective precatalysts for catalytic N2 reduction to ammonia, verified by 15N2 labeling studies and other control experiments. Spectroscopic and electrochemical studies illuminate some relevant thermodynamic parameters, including the N-H bond dissociation free energy of (TMP)MoNH (43 ± 2 kcal mol-1). We place these results in the context of other work on homogeneous N2 reduction catalysis.

Catalytic Reduction of Dinitrogen to Ammonia and Hydrazine Using Iron–Dinitrogen Complexes Bearing Anionic Benzene-Based PCP-Type Pincer Ligands

Abstract Among synthetic models of nitrogenases, iron–dinitrogen complexes with an Fe–C bond have attracted increasing attention in recent years. Here we report the synthesis of square-planar iron(I)–dinitrogen complexes supported by anionic benzene-based PCP- and POCOP-type pincer ligands as carbon donors. These complexes catalyze the formation of ammonia and hydrazine from the reaction of dinitrogen (1 atm) with a reductant and a proton source at −78 °C, producing up to 252 equiv of ammonia and 68 equiv of hydrazine (388 equiv of fixed N atom) based on the iron atom of the catalyst. Anionic iron(0)–dinitrogen complexes, considered an essential reactive species in the catalytic reaction, are newly isolated from the reduction of the corresponding iron(I)–dinitrogen complexes. This study examines their reactivity using experiments and DFT calculations.

Cover Feature: Catalytic Reduction of Dinitrogen into Ammonia and Hydrazine by Using Chromium Complexes Bearing PCP‐Type Pincer Ligands (Chem. Eur. J. 25/2022)

A series of chromium complexes bearing a carbene- and phosphine-based PCP-type pincer ligand has been newly prepared, and some of them are found to work as effective catalysts to reduce dinitrogen into ammonia and hydrazine under atmospheric pressure. This reaction can be expressed as nitrogen molecules (raindrops) being converted into ammonia and hydrazine on the chromium complex (umbrella). More information can be found in the Research Article by K. Yoshizawa, Y. Nishibayashi et al. (DOI: 10.1002/chem.202200557).

Catalytic Reduction of Dinitrogen into Ammonia and Hydrazine by Using Chromium Complexes Bearing PCP-Type Pincer Ligands.

A series of chromium-halide, -nitride, and -dinitrogen complexes bearing carbene- and phosphine-based PCP-type pincer ligands has been newly prepared, and some of them are found to work as effective catalysts to reduce dinitrogen under atmospheric pressure, whereby up to 11.60 equiv. of ammonia and 2.52 equiv. of hydrazine (16.6 equiv. of fixed N atom) are produced based on the chromium atom. To the best of our knowledge, this is the first successful example of chromium-catalyzed conversion of dinitrogen to ammonia and hydrazine under mild reaction conditions.

Mechanisms of Electrochemical N2 Splitting by a Molybdenum Pincer Complex.

Molybdenum complexes supported by tridentate pincer ligands are exceptional catalysts for dinitrogen fixation using chemical reductants, but little is known about their prospects for electrochemical reduction of dinitrogen. The viability of electrochemical N2 binding and splitting by a molybdenum(III) pincer complex, (pyPNP)MoBr3 (pyPNP = 2,6-bis(tBu2PCH2)-C5H3N)), is established in this work, providing a foundation for a detailed mechanistic study of electrode-driven formation of the nitride complex (pyPNP)Mo(N)Br. Electrochemical kinetic analysis, optical and vibrational spectroelectrochemical monitoring, and computational studies point to two concurrent reaction pathways: In the reaction-diffusion layer near the electrode surface, the molybdenum(III) precursor is reduced by 2e- and generates a bimetallic molybdenum(I) Mo2(μ-N2) species capable of N-N bond scission; and in the bulk solution away from the electrode surface, over-reduced molybdenum(0) species undergo chemical redox reactions via comproportionation to generate the same bimetallic molybdenum(I) species capable of N2 cleavage. The comproportionation reactions reveal the surprising intermediacy of dimolybdenum(0) complex trans,trans-[(pyPNP)Mo(N2)2](μ-N2) in N2 splitting pathways. The same "over-reduced" molybdenum(0) species was also found to cleave N2 upon addition of lutidinium, an acid frequently used in catalytic reduction of dinitrogen.

Computational Design of Single Mo Atom Anchored Defective Boron Phosphide Monolayer as a High‐performance Electrocatalyst for the Nitrogen Reduction Reaction

Catalytic reduction of molecular dinitrogen (N2) to ammonia (NH3) is one of the most important and challenging industrial reactions. Electrochemical reduction is considered as an energy‐saving technology for artificial ambient nitrogen fixation, which is emerging as an optimal potential sustainable strategy to substitute for the Haber–Bosch process. However, this process demands efficient catalysts for the N2 reduction reaction (NRR). Here, by means of first‐principles calculations, we systematically explored the potential electrocatalytic performance of single transition metal atoms (Pd, Ag, Rh, Cu, Ti, Mo, Mn, Zn, Fe, Co, Ru, and Pt) embedded in monolayer defective boron phosphide (TMs/BP) monolayer with a phosphorus monovacancy for ambient NH3 production. Among them, the Mo/BP exhibits the best catalytic performance for ambient reduction of N2 through the typical enzymatic and consecutive reaction pathways with an activation barrier of 0.68 eV, indicating that Mo/BP is an efficient catalyst for N2 fixation. We believe that this work could provide a new avenue of ambient NH3 synthesis by using the designed single‐atom electrocatalysts.

Catalytic reduction of dinitrogen to tris(trimethylsilyl)amine using rhodium complexes with a pyrrole-based PNP-type pincer ligand.

Rhodium complexes bearing an anionic pyrrole-based PNP-type pincer ligand are synthesised and found to work as effective catalysts for the transformation of molecular dinitrogen into tris(trimethylsilyl)amine under mild reaction conditions. This is the first successful example of rhodium-catalysed dinitrogen reduction under mild reaction conditions.

Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine-Titanium Complex.

Catalytic reduction of N2 to NH3 by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH3 by N2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of [TiIV(TrenTMS)X] (X=Cl, 1A; I, 1B; TrenTMS=N(CH2CH2NSiMe3)3) with KC8 affords [TiIII(TrenTMS)] (2). Addition of N2 affords [{(TrenTMS)TiIII}2(μ‐η1:η1‐N2)] (3); further reduction with KC8 gives [{(TrenTMS)TiIV}2(μ‐η1:η1:η2:η2‐N2K2)] (4). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2)][K(B15C5)2]2 (5). Complexes 3–5 treated under N2 with KC8 and [R3PH][I], (the weakest H+ source yet used in N2 reduction) produce up to 18 equiv of NH3 with only trace N2H4. When only acid is present, N2H4 is the dominant product, suggesting successive protonation produces [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2H4)][I]2, and that extruded N2H4 reacts further with [R3PH][I]/KC8 to form NH3.

Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine–Titanium Complex

AbstractCatalytic reduction of N2 to NH3 by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH3 by N2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of [TiIV(TrenTMS)X] (X=Cl, 1A; I, 1B; TrenTMS=N(CH2CH2NSiMe3)3) with KC8 affords [TiIII(TrenTMS)] (2). Addition of N2 affords [{(TrenTMS)TiIII}2(μ‐η1:η1‐N2)] (3); further reduction with KC8 gives [{(TrenTMS)TiIV}2(μ‐η1:η1:η2:η2‐N2K2)] (4). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2)][K(B15C5)2]2 (5). Complexes 3–5 treated under N2 with KC8 and [R3PH][I], (the weakest H+ source yet used in N2 reduction) produce up to 18 equiv of NH3 with only trace N2H4. When only acid is present, N2H4 is the dominant product, suggesting successive protonation produces [{(TrenTMS)TiIV}2(μ‐η1:η1‐N2H4)][I]2, and that extruded N2H4 reacts further with [R3PH][I]/KC8 to form NH3.

Catalytic Reduction of Molecular Dinitrogen to Ammonia and Hydrazine Using Vanadium Complexes

AbstractNewly designed and prepared vanadium complexes bearing anionic pyrrole‐based PNP‐type pincer and aryloxy ligands were found to work as effective catalysts for the direct conversion of molecular dinitrogen into ammonia and hydrazine under mild reaction conditions. This is the first successful example of vanadium‐catalyzed dinitrogen reduction under mild reaction conditions.

Catalytic Reduction of Molecular Dinitrogen to Ammonia and Hydrazine Using Vanadium Complexes.

Newly designed and prepared vanadium complexes bearing anionic pyrrole-based PNP-type pincer and aryloxy ligands were found to work as effective catalysts for the direct conversion of molecular dinitrogen into ammonia and hydrazine under mild reaction conditions. This is the first successful example of vanadium-catalyzed dinitrogen reduction under mild reaction conditions.

Molecular Catalysts for N2 Reduction: State of the Art, Mechanism, and Challenges

Fixation of atmospheric nitrogen is central for the production of ammonia, which is the source of nitrogen fertilizers and is also emerging as a promising renewable fuel. While the development of efficient molecular-based artificial nitrogen fixation systems working under mild conditions is probably a Holy Grail, the catalytic reduction of N2 by transition-metal complexes is-above all-the main instrument to progress in the mechanistic understanding of N2 splitting. In this Minireview we first give an overview of molecular-based catalytic systems, including recent breakthroughs, and then we illustrate the alternative pathways for N2 reduction. We mainly focus on multistep hydrogenation of N2 by separated proton and electron sources, with a particular attention for the possibility of proton-coupled electron transfer events. Finally, we try to identify the key factors to achieve catalytic reduction of dinitrogen by metal complexes and to enhance their efficiency.

N2‐to‐NH3 Conversion by a triphos–Iron Catalyst and Enhanced Turnover under Photolysis

AbstractBridging iron hydrides are proposed to form at the active site of MoFe‐nitrogenase during catalytic dinitrogen reduction to ammonia and may be key in the binding and activation of N2 via reductive elimination of H2. This possibility inspires the investigation of well‐defined molecular iron hydrides as precursors for catalytic N2‐to‐NH3 conversion. Herein, we describe the synthesis and characterization of new P2P′PhFe(N2)(H)x systems that are active for catalytic N2‐to‐NH3 conversion. Most interestingly, we show that the yields of ammonia can be significantly increased if the catalysis is performed in the presence of mercury lamp irradiation. Evidence is provided to suggest that photo‐elimination of H2 is one means by which the enhanced activity may arise.

N2 -to-NH3 Conversion by a triphos-Iron Catalyst and Enhanced Turnover under Photolysis.

Bridging iron hydrides are proposed to form at the active site of MoFe-nitrogenase during catalytic dinitrogen reduction to ammonia and may be key in the binding and activation of N2 via reductive elimination of H2 . This possibility inspires the investigation of well-defined molecular iron hydrides as precursors for catalytic N2 -to-NH3 conversion. Herein, we describe the synthesis and characterization of new P2P'Ph Fe(N2 )(H)x systems that are active for catalytic N2 -to-NH3 conversion. Most interestingly, we show that the yields of ammonia can be significantly increased if the catalysis is performed in the presence of mercury lamp irradiation. Evidence is provided to suggest that photo-elimination of H2 is one means by which the enhanced activity may arise.

Nitrogenase Assembly: Strategies and Procedures.

Nitrogenase is a metalloenzyme system that plays a critical role in biological nitrogen fixation, and the study of how its metallocenters are assembled into functional entities to facilitate the catalytic reduction of dinitrogen to ammonia is an active area of interest. The diazotroph Azotobacter vinelandii is especially amenable to culturing and genetic manipulation, and this organism has provided the basis for many insights into the assembly of nitrogenase proteins and their respective metallocofactors. This chapter will cover the basic procedures necessary for growing A. vinelandii cultures and subsequent recombinant transformation and protein expression techniques. Furthermore, protocols for nitrogenase protein purification and substrate reduction activity assays are described. These methods provide a solid framework for the assessment of nitrogenase assembly and catalysis.

Catalytic reduction of dinitrogen to ammonia by use of molybdenum-nitride complexes bearing a tridentate triphosphine as catalysts.

Newly designed and prepared molybdenum-nitride complexes bearing a mer-tridentate triphosphine as a ligand have been found to work as the most effective catalysts toward the catalytic reduction of dinitrogen to ammonia under ambient conditions, where up to 63 equiv of ammonia based on the Mo atom of the catalyst were produced.