Dinitrogen Activation Upon Reduction of a Triiron(II) Complex

Reaction of a trinuclear iron(II) complex, Fe₃Br₃ L ( 1 ), with KC₈ under N₂ leads to dinitrogen activation products ( 2 ) from which Fe₃(NH)₃ L ( 2‐1 ; L is a cyclophane bridged by three β‐diketiminate arms) was characterized by X‐ray crystallography. ¹H NMR spectra of the protonolysis product of 2 synthesized under ¹⁴N₂ and ¹⁵N₂ confirm atmospheric N₂ reduction, and ammonia is detected by the indophenol assay (yield ～30 %). IR and Mössbauer spectroscopy, and elemental analysis on 2 and 2‐1 as well as the tri(amido)triiron(II) 3 and tri(methoxo)triiron 4 congeners support our assignment of the reduction product as containing protonated N‐atom bridges.     

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 [Ti^IV(Tren^TMS)X] (X=Cl, 1A ; I, 1B ; Tren^TMS=N(CH₂CH₂NSiMe₃)₃) with KC₈ affords [Ti^III(Tren^TMS)] ( 2 ). Addition of N₂ affords [{(Tren^TMS)Ti^III}₂(μ‐η¹:η¹‐N₂)] ( 3 ); further reduction with KC₈ gives [{(Tren^TMS)Ti^IV}₂(μ‐η¹:η¹:η²:η²‐N₂K₂)] ( 4 ). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(Tren^TMS)Ti^IV}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 [{(Tren^TMS)Ti^IV}₂(μ‐η¹:η¹‐N₂H₄)][I]₂, and that extruded N₂H₄ reacts further with [R₃PH][I]/KC₈ to form NH₃.     

分子氮的电催化还原

对温和条件下分子氮的络合活化已有研究,但用修饰电极法电催化固氮成氨(或肼)尚未见报道,Shilov等曾发现在V(OH)_2-Mg(OH)_2的悬浮液中,V(Ⅱ)可起络合及还原作用,钒固氮酶在缺钼条件下也可活化分子氮,其活性中心可能与钼酶相似,也是通过有机硫配体而定位在蛋白质的肽链上,能否用含有机硫配体的钒表面配合物模拟钒酶,用电催化方法进行电子与能量的偶联从而固氮成氨?本文对此进行了研究。     

Photochemical Reduction of Water to Hydrogen Catalyzed by Mixed-Valent Tetranuclear Platinum Complex

Abstract

Mixed-valent tetranuclear platinum complex, [Pt₄(NH₃)₈(C₄H₆NO)₄] ⁿ⁺ (n = 4, 5, 6, 8; C₄H₆NO = deprotonated α-pyrrolidone), is used as a homogeneous hydrogen-producing catalyst in a photochemical model system containing EDTA as an electron donor, Ru(bpy)₃ ²⁺ as a sensitizer and methylviologen (MV²⁺) as an electron relay.     

硝酸钐丙氨酸配合物生成焓的量热法测定

配位反应;量热分析;硝酸钐丙氨酸配合物生成焓的量热法测定     

Crystal Structure and Photoluminescence of a Tetranuclear Cadmium Complex

A novel tetranuclear cadmium complex ([{Cd(C₁₅H₈O₇S)(H₂O)(DMSO)}₃{Cd(C₁₅H₈O₇S)(H₂O)₂}]·3DMSO·H₂O) was obtained by the self‐assembly of Cd(II) with 5,7‐dihydroxyflavone‐6‐sulfonate. The complex was characterized by ¹H NMR, IR, elemental analysis and X‐ray single‐crystal diffraction studies. It crystallizes in triclinic, space group $ P {\bar 1} $ . In the complex, the chelate atoms of Cd(II) are all from oxygen. Four Cd(II) are connected via the carbonyl and 5‐hydroxyanion of four ligands and form an approximate square. Four ligands locate at two sides of the square, and two of them at the same side are almost parallel and exist aromatic π‐π stacking. Ligands on the opposite side of the square are nearly perpendicular. The result of the luminescent studies indicated that the solid of the complex shwed photoluminescent properties because of a combination of coordination, hydrogen bonding and π‐π stacking interaction in the molecule structure. The complex emits green fluorescence (λ_em=496 nm) when it is excited at the wavelength of 440 nm.     

Bimetallic Ruthenium PNP Pincer Complex As a Platform to Model Proposed Intermediates in Dinitrogen Reduction to Ammonia

A series of ruthenium complexes was isolated and characterized in the course of reactions aimed at studying the reduction of hydrazine to ammonia in bimetallic systems. The diruthenium complex {[HPNPRu(N(2))](2)(μ-Cl)(2)}(BF(4))(2) (2) (HPNP = HN(CH(2)CH(2)P(i)Pr(2))(2)) reacted with 1 equiv of hydrazine to generate [(HPNPRu)(2)(μ(2)-H(2)NNH(2))(μ-Cl)(2)](BF(4))(2) (3) and with an excess of the reagent to form [HPNPRu(NH(3))(κ(2)-N(2)H(4))](BF(4))Cl (5). When phenylhydrazine was added to 2, the diazene species [(HPNPRu)(2)(μ(2)-HNNPh)(μ-Cl)(2)](BF(4))(2) (4) was obtained. Treatment of 2 with H(2) or CO yielded {[HPNPRu(H(2))](2)(μ-Cl)(2)}(BF(4))(2) (7) and [HPNPRuCl(CO)(2)]BF(4) (8), respectively. Abstraction of chloride using AgOSO(2)CF(3) or AgBPh(4) afforded the species [(HPNPRu)(2)(μ(2)-OSO(2)CF(3))(μ-Cl)(2)]OSO(2)CF(3) (9) and [(HPNPRu)(2)(μ-Cl)(3)]BPh(4) (10), respectively. Complex 3 reacted with HCl/H(2)O or HCl/Et(2)O to produce ammonia stoichiometrically; the complex catalytically disproportionates hydrazine to generate ammonia.     

Formal Three-Electron Reduction by an f-Element Complex: Formation of

Steric crowding can be coupled with a U(III) reduction to make the complex [(C(5)Me(5))(3)U] a formal three-electron reductant in its reaction with C(8)H(8), which generates a product, 1, containing a bridging nonplanar C(8)H(8)(2-) ligand [Eq. (1)].     

Catalytic Ammonia Oxidation to Dinitrogen by a Nickel Complex

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 NH₃ ligand up to 56 equiv of N₂ per Ni center can be generated. Employing the N-oxyl radical 2,2,6,6-(tetramethylpiperidin-1-yl)oxyl (TEMPO⋅) as the H-atom acceptor, up to 15 equiv of N₂ per 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]−NH₂ fragments. Ni-mediated hydrazine disproportionation to N₂ and NH₃ completes the catalytic cycle.     

Tetrametallic Copper Complex to Nanoscale Copper: Selective and Switchable Dehydrogenation-Hydrogenation under Light

A discrete, photoactive, ultrafine copper nanocluster of fewer than hundreds of atoms with stimuli-responsive switchable redox-active states is highly desired to control two different antagonistic reactions. Herein, a mixed-valent tetrametallic copper complex ( C-1 ) of N−O-N Schiff base ligand is disclosed, in which the five different Cu−Cu interactions were used to generate photoactive nanoscale copper [LCu⁰_n, S-1 ] through the reduction of coordinated imine to the amine of C-1 . The presence of a ligand provides stability and helps to homogenize the material ( S-1 ) in the organic solvent. The cluster showed stimuli (O₂/light)-responsive switching between its reduced ( S-1 ) and oxidized [LCu⁰_n−mCuO_m, S-2 ] states that allows it to serve as a highly and poorly active (bistate, relative rate >5–12 fold) catalyst for the dehydrogenation of alcohols to aldehydes and hydrogenation of nitroaromatics to amino aromatics under the light.     

A Dinuclear Nickel(I) Dinitrogen Complex and its Reduction in Single‐Electron Steps

Electron by electron : β‐Diketiminato nickel(I) complex fragments are capable of activating N₂ through coordination. The resulting complex can be reduced in two single‐electron steps, which further activates the N? N bond. The picture shows the structure of the singly reduced complex with μ‐η¹:η¹‐bound N₂.

     

Rate Study of Haloadamantane Reduction by Samarium Diiodide

Rate constants directly measured by GC/MS‐analyzed method for reduction of haloadamantanes by SmI₂ in presence of HMPA and H₂O were obtained. HMPA exhibits stronger catalytic effect than H₂O does. The result of faster reaction rate of 1‐bromoadamantane than that of 2‐bromoadamantane can be used to confirm the formation of alkyl radical as the rate limiting step of this reduction.     

Asymmetric Ring Opening in a Tetrazine-Based Ligand Affords a Tetranuclear Opto-Magnetic Ytterbium Complex

We report the formation of a tetranuclear lanthanide cluster, [Yb₄(bpzch)₂(fod)₁₀] ( 1 ), which occurs from a serendipitous ring opening of the functionalised tetrazine bridging ligand, bpztz (3,6-dipyrazin-2-yl-1,2,4,5-tetrazine) upon reacting with Yb(fod)₃ (fod⁻=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octandionate). Compound 1 was structurally elucidated via single-crystal X-ray crystallography and subsequently magnetically and spectroscopically characterised to analyse its magnetisation dynamics and its luminescence behaviour. Computational studies validate the observed M_J energy levels attained by spectroscopy and provides a clearer picture of the slow relaxation of the magnetisation dynamics and relaxation pathways. These studies demonstrate that 1 acts as a single-molecule magnet (SMM) under an applied magnetic field in which the relaxation occurs via a combination of Raman, direct, and quantum tunnelling processes, a behaviour further rationalised analysing the luminescent properties. This marks the first lanthanide-containing molecule that forms by means of an asymmetric tetrazine decomposition.     

邻香兰素甲硫氨酸席夫碱四核铜配合物的合成及结构表征

邻香兰素甲硫氨酸席夫碱四核铜配合物的合成及结构表征     

Predicting Dinitrogen Coupling with a Series of Small Molecules Catalyzed by a Pincer Complex

Due to consumption of more than 2% of the world‘s annual energy supply by Haber–Bosch process and the strongest triple bond (N≡N) in nature, directly coupling N₂ with small molecules is particularly important and challenging, let alone in a catalytic fashion. Here we first demonstrate that a NNN-type pincer phosphorus complex could act as a catalyst to couple dinitrogen with a series of small molecules including carbon dioxide, formaldehyde, N-ethylidenemethylamine, and acetonitrile in the presence of diborane(4) under a mild condition by theoretical calculations. N₂ fixation proceeds via a stepwise mechanism involving initial N₂ activation by diborane(4), followed by intramolecular isomerization to a key intermediate (zwitterion). Such a zwitterion can be used to couple a series of small molecules with activation barriers of 23.5–25.2 kcal mol⁻¹. All these findings could be particularly useful for main group chemistry aimed at N₂ activation.