Teaching old compounds new tricks: efficient N2 fixation by simple Fe(N2)(diphosphine)2 complexes

The Fe(0) species Fe(N2)(dmpe)2 exists in equilibrium with the previously unreported dimer, [Fe(dmpe2)2(μ-N2)]. For the first time these complexes, alongside Fe(N2)(depe)2, are shown unambiguously to produce N2H4 and/or NH3 upon addition of triflic acid; for Fe(N2)(depe)2 this represents one of the highest electron conversion efficiencies for Fe complexes to date

Oxygen vacancy engineering in spinel-structured nanosheet wrapped hollow polyhedra for electrochemical nitrogen fixation under ambient conditions

Electrochemical nitrogen-to-ammonia conversion by the nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to tackle the energy-intensive Haber–Bosch process with excessive CO2 emission. However, the NRR is still restricted by low faradaic efficiency and NH3 yield, which is due to the chemical inertness of N-related groups for efficient adsorption/activation on the electrocatalysts. Here, a series of spinel-structured nanosheet wrapped hollow nitrogen-doped carbon polyhedra with abundant oxygen vacancies are constructed successfully. From theoretical aspects, these materials show increased charge density on their surface for enhanced capture and activation of N2 molecules. As a result, oxygen vacancy-rich NiCo2O4 on hollow N-carbon polyhedra (Vo-rich NiCo2O4@HNCP) shows outstanding electrocatalytic NRR performance with high production yield (NH3: 4.1 μg h−1 cm−2/17.8 μg h−1 mg−1; faradaic efficiency: 5.3%) and high stability under ambient conditions and is superior to the counterpart oxygen vacancy-poor electrocatalysts. Oxygen vacancy engineering introduces a new concept for rational design of advanced NRR catalysts for energy conversion systems

Small Molecule Activation by Uranium Tris(aryloxides): Experimental and Computational Studies of Binding of N-2, Coupling of CO, and Deoxygenation Insertion of CO2 under Ambient Conditions

Previously unanticipated dinitrogen activation is exhibited by the well-known uranium tris(aryloxide) U(ODtbp)(3), U(OC6H3-Bu-2(t)-2,6)(3), and the tri-tert-butyl analogue U(OTtbp)(3), U(OC6H2-Bu-3(t)-2,4,6)(3), in the form of bridging, side-on dinitrogen complexes [U(OAr)(3)](2)(mu-eta(2):eta(2)-N-2), for which the tri-tert-butyl N-2 complex is the most robust U-2(N-2) complex isolated to date. Attempted reduction of the tris(aryloxide) complex under N-2 gave only the potassium salt of the uranium(III) tetra(aryloxide) anion, K[U(OAr)(4)], as a result of ligand redistribution. The solid-state structure is a polymeric chain formed by each potassium cation bridging two arenes of adjacent anions in an eta(6) fashion. The same uranium tris(aryloxides) were also found to couple carbon monoxide under ambient conditions to give exclusively the ynediolate [OCCO](2-) dianion in [U(OAr)(3)](2)(mu-eta(1):eta(1)-C2O2), in direct analogy with the reductive coupling recently shown to afford [U{N(SiMe3)(2)}(3)](2)(mu-eta(1):eta(1)-C2O2). The related U-III complexes U{N(SiPhMe2)(2)}(3) and U{CH(SiMe3)(2)}(3) however do not show CO coupling chemistry in our hands. Of the aryloxide complexes, only the U(OC6H2-Bu-3(t)-2,4,6)(3) reacts with CO2 to give an insertion product containing bridging oxo and aryl carbonate moieties, U-2(OTtbp)(4)(mu-O)(mu-eta(1):eta(1)-O2COC6H2-Bu-3(t)-2,4,6)(2), which has been structurally characterized. The presence of coordinated N-2 in [U(OTtbp)(3)](2)(N-2) prevents the occurrence of any reaction with CO2, underscoring the remarkable stability of the N-2 complex. The di-tert-butyl aryloxide does not insert CO2, and only U(ODtbp)(4) was isolated. The silylamide also reacts with carbon dioxide to afford U(OSiMe3)(4) as the only uranium-containing material. GGA and hybrid DFT calculations, in conjunction with topological analysis of the electron density, suggest that the U-N-2 bond is strongly polar, and that the only covalent U -> N-2 interaction is pi backbonding, leading to a formal (U-IV)(2)(N-2)(2-) description of the electronic structure. The N-N stretching wavenumber is preferred as a metric of N-2 reduction to the N-N bond length, as there is excellent agreement between theory and experiment for the former but poorer agreement for the latter due to X-ray crystallographic underestimation of r(N-N). Possible intermediates on the CO coupling pathway to [U(OAr)(3)](2)(mu-C2O2) are identified, and potential energy surface scans indicate that the ynediolate fragment is more weakly bound than the ancillary ligands, which may have implications in the development of low-temperature and pressure catalytic CO chemistry

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. of ammonia based on each molybdenum atom of the catalyst). The time profile for the catalytic reaction reveals that the presence of the ferrocene unit in the catalyst increases the rate of ammonia formation. Electrochemical measurement and theoretical studies indicate that an interaction between the Fe atom of the ferrocene moiety and the Mo atom in the catalyst may play an important role to achieve a high catalytic activity