Catalytic nitrogen fixation using visible light energy.

The synthesis of ammonia from atmospheric dinitrogen, nitrogen fixation, is one of the essential reactions for human beings. Because the current industrial nitrogen fixation depends on dihydrogen produced from fossil fuels as raw material, the development of a nitrogen fixation reaction that relies on the energy provided by renewable energy, such as visible light, is an important research goal from the viewpoint of sustainable chemistry. Herein, we establish an iridium- and molybdenum-catalysed process for synthesizing ammonia from dinitrogen under ambient reaction conditions and visible light irradiation.

Reactivity of molybdenum-nitride complex bearing pyridine-based PNP-type pincer ligand toward carbon-centered electrophiles.

A molybdenum-nitride complex bearing a pyridine-based PNP-type pincer ligand derived from dinitrogen is reacted with various kinds of carbon-centered electrophiles to functionalize the nitride ligand in the molybdenum complex. Methylation with MeOTf and acylation with diphenylacetyl chloride of the nitride complex afford the corresponding imide complexes a carbon-nitrogen bond formation. In the case of reactions with phenylisocyanate and diphenylketene, the PNP ligand works as a non-innocent ligand to form the corresponding ureate and acylimide complexes, respectively.

Cycling between Molybdenum-Dinitrogen and -Nitride Complexes to Support the Reaction Pathway for Catalytic Formation of Ammonia from Dinitrogen.

Invited for the featured front cover of Kazuya Arashiba, Hiromasa Tanaka, Kazunari Yoshizawa, and Yoshiaki Nishibayashi at The University of Tokyo, Daido University, and Kyushu University. The image depicts a roulette wheel to represent the cycling reaction used in this work. Read the full text of the article at 10.

Cycling between Molybdenum-Dinitrogen and -Nitride Complexes to Support the Reaction Pathway for Catalytic Formation of Ammonia from Dinitrogen.

Cycling between molybdenum(I)-dinitrogen and molybdenum(IV)-nitride complexes was investigated under ambient reaction conditions. A kinetic study of the second-order reaction rate for the conversion of the molybdenum-dinitrogen complex into the molybdenum-nitride complex indicates that the formation of the dinitrogen-bridged dimolybdenum complex is involved in the rate-determining step. DFT calculations indicate that the molybdenum-dinitrogen complex transforms into the molybdenum-nitride complex via direct cleavage of the nitrogen-nitrogen triple bond of the bridging dinitrogen ligand of the dinitrogen-bridged dimolybdenum complex.

Structural characterization of molybdenum-dinitrogen complex as key species toward ammonia formation by dispersive XAFS spectroscopy.

The structural characterization of a hardly-isolatable molybdenum-dinitrogen complex bearing a PNP-type pincer ligand, which is assumed to be a key reactive complex in the stoichiometric transformation of a molybdenum triiodide complex [MoI(PNP)] into the corresponding molybdenum nitride complex under an atmospheric pressure of dinitrogen, was carried out by using dispersive XAFS.

Molybdenum-Catalyzed Ammonia Formation Using Simple Monodentate and Bidentate Phosphines as Auxiliary Ligands.

We have found molybdenum-catalyzed ammonia formation using simple and commercially available monodentate and bidentate phosphines as auxiliary ligands with a simple and convenient procedure. Molybdenum complexes generated in situ from [MoI(THF)] and the corresponding phosphines such as PMePh and 1,5-bis(diphenylphosphino)pentane worked effectively toward ammonia formation.

Molybdenum-catalysed ammonia production with samarium diiodide and alcohols or water.

The production of ammonia from nitrogen gas is one of the most important industrial processes, owing to the use of ammonia as a raw material for nitrogen fertilizers. Currently, the main method of ammonia production is the Haber-Bosch process, which operates under very high temperatures and pressures and is therefore very energy-intensive. The transition-metal-catalysed reduction of nitrogen gas is an alternative method for the formation of ammonia.

Catalytic Reactivity of Molybdenum-Trihalide Complexes Bearing PCP-Type Pincer Ligands.

Molybdenum-iodide complexes bearing a PCP[1] ligand have been found to work as excellent catalysts toward ammonia formation under ambient reaction conditions among dinitrogen-bridged dimolybdenum complexes and other molybdenum complexes bearing PNP and PCP[2] ligands.

Effect of substituents on molybdenum triiodide complexes bearing PNP-type pincer ligands toward catalytic nitrogen fixation.

Molybdenum triiodide complexes bearing various substituted pyridine-based PNP-type pincer ligands are prepared and characterized by X-ray analysis. Their catalytic activity is investigated toward the reduction of nitrogen gas into ammonia under ambient reaction conditions.

Synthesis and reactivity of titanium- and zirconium-dinitrogen complexes bearing anionic pyrrole-based PNP-type pincer ligands.

Dinitrogen-bridged dititanium and dizirconium complexes bearing anionic pyrrole-based PNP-type pincer ligands are prepared and characterized by X-ray analysis. Their catalytic activity is investigated toward reduction of nitrogen gas into ammonia and hydrazine 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.

Preparation and reactivity of iron complexes bearing anionic carbazole-based PNP-type pincer ligands toward catalytic nitrogen fixation.

Iron-chloride, -dinitrogen, and -methyl complexes bearing anionic carbazole-based PNP-type pincer ligands are designed, prepared and characterized by X-ray analysis. Some iron complexes are found to work as catalysts toward nitrogen fixation under mild reaction conditions.

Synthesis and reactivity of iron-dinitrogen complexes bearing anionic methyl- and phenyl-substituted pyrrole-based PNP-type pincer ligands toward catalytic nitrogen fixation.

Iron-dinitrogen complexes bearing methyl- and phenyl-substituted pyrrole-based anionic PNP-type pincer ligands are prepared and characterized by X-ray analysis. The former complex is found to work as a more effective catalyst than that bearing a non-substituted PNP-type pincer ligand toward the transformation of nitrogen gas into ammonia and hydrazine under mild reaction conditions.

Catalytic Conversion of Dinitrogen into Ammonia under Ambient Reaction Conditions by Using Proton Source from Water.

Molybdenum-catalyzed conversion of molecular dinitrogen into ammonia under ambient reaction conditions has been achieved by using a proton source generated in situ from the ruthenium-catalyzed oxidation of water in combination with visible light and a photosensitizer. The preset reaction system is considered as a new model for the nitrogen fixation by photosynthetic bacteria.

Remarkable catalytic activity of dinitrogen-bridged dimolybdenum complexes bearing NHC-based PCP-pincer ligands toward nitrogen fixation.

Intensive efforts for the transformation of dinitrogen using transition metal-dinitrogen complexes as catalysts under mild reaction conditions have been made. However, limited systems have succeeded in the catalytic formation of ammonia. Here we show that newly designed and prepared dinitrogen-bridged dimolybdenum complexes bearing N-heterocyclic carbene- and phosphine-based PCP-pincer ligands [{Mo(N)(PCP)}(μ-N)] (1) work as so far the most effective catalysts towards the formation of ammonia from dinitrogen under ambient reaction conditions, where up to 230 equiv.

Direct Transformation of Molecular Dinitrogen into Ammonia Catalyzed by Cobalt Dinitrogen Complexes Bearing Anionic PNP Pincer Ligands.

The direct formation of ammonia from molecular dinitrogen under mild reaction conditions was achieved by using new cobalt dinitrogen complexes bearing an anionic PNP-type pincer ligand. Up to 15.9 equivalents of ammonia were produced based on the amount of catalyst together with 1.

Catalytic transformation of dinitrogen into ammonia and hydrazine by iron-dinitrogen complexes bearing pincer ligand.

Synthesis and reactivity of iron-dinitrogen complexes have been extensively studied, because the iron atom plays an important role in the industrial and biological nitrogen fixation. As a result, iron-catalyzed reduction of molecular dinitrogen into ammonia has recently been achieved. Here we show that an iron-dinitrogen complex bearing an anionic PNP-pincer ligand works as an effective catalyst towards the catalytic nitrogen fixation, where a mixture of ammonia and hydrazine is produced.

Nitrogen fixation catalyzed by ferrocene-substituted dinitrogen-bridged dimolybdenum-dinitrogen complexes: unique behavior of ferrocene moiety as redox active site.

A series of dinitrogen-bridged dimolybdenum-dinitrogen complexes bearing metallocene-substituted PNP-pincer ligands is synthesized by the reduction of the corresponding monomeric molybdenum-trichloride complexes under 1 atm of molecular dinitrogen. Introduction of ferrocene as a redox-active moiety to the pyridine ring of the PNP-pincer ligand increases the catalytic activity for the formation of ammonia from molecular dinitrogen, up to 45 equiv. of ammonia being formed based on the catalyst (22 equiv.

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.