Cobalt Cyclopentadienyl-Phosphine Dinitrogen Complexes

By applying the potassium salts of cyclopentadienyl-phosphine ligands LK to CoCl₂, the corresponding cobalt chlorides ( 1 , L Co^IICl) were prepared. By reducing complexes 1 with KHBEt₃ under a N₂ atmosphere, bridging end-on complexes, L Co^I−N₂−Co^I L ( 2 a and 2 b ), were successfully obtained. ¹⁵N₂-labeled [¹⁵N₂]- 2 a was prepared under ¹⁵N₂/¹⁴N₂ exchange in THF solution. L Co^I−N₂−Co^I L complex 2 a could react with P₄ molecules to release N₂ and generate a Co−P₄−Co moiety 4 . Further reduction of complex 2 b led to cleavage of a P−C bond in the cyclopentadienyl-phosphine ligand to provide novel μ-PCy₂-bridged Co⁰−N₂ complex 5 . DFT calculations confirmed the experimental observations.     

Tetrametallic Reduction of Dinitrogen: Formation of a Tetranuclear Samarium Dinitrogen Complex

The cooperative attack of four (dipyrromethanyl)Sm(II) units on dinitrogen resulted in a novel tetranuclear samarium dinitrogen complex (shown schematically). The presence of halogen atoms inhibited reactivity with dinitrogen through the assembly of divalent samarium clusters. dipyrr=diphenylmethyldipyrrolide dianion.     

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。     

Side-On Bonded Beryllium Dinitrogen Complexes

The preparation and spectroscopic identification of the complexes NNBe(η²-N₂) and (NN)₂Be(η²-N₂) and the energetically higher lying isomers Be(NN)₂ and Be(NN)₃ are reported. NNBe(η²-N₂) and (NN)₂Be(η²-N₂) are the first examples of covalently side-on bonded N₂ adducts of a main-group element. The analysis of the electronic structure using modern methods of quantum chemistry suggests that NNBe(η²-N₂) and (NN)₂Be(η²-N₂) should be classified as π complexes rather than metalladiazirines.     

铀催化的氮气活化

氮气约占空气总体积的78%,是大自然赋予人类的宝贵资源。如何实现氮气转化为动植物可利用的含氮化合物,关系着人类的未来和社会的可持续发展。氮气活化,作为一个非常重要的研究领域,一直以来都是科学家面临的重大挑战。目前,低价铀金属有机化合物展现出良好的小分子活化能力。本综述主要介绍了含铀化合物对氮气活化的研究进展,并对其未来进行了展望。     

Dinitrogen Splitting Coupled to Protonation

The coupling of electron- and proton-transfer steps provides a general concept to control the driving force of redox reactions. N₂ splitting of a molybdenum dinitrogen complex into nitrides coupled to a reaction with Brønsted acid is reported. Remarkably, our spectroscopic, kinetic, and computational mechanistic analysis attributes N−N bond cleavage to protonation in the periphery of an amide pincer ligands rather than the {Mo−N₂−Mo} core. The strong effect on electronic structure and ultimately the thermochemistry and kinetic barrier of N−N bond cleavage is an unusual case of a proton-coupled metal-to-ligand charge transfer process, highlighting the use of proton-responsive ligands for nitrogen fixation.     

Dinitrogen complexes of sulfur-ligated iron

We report a unique class of dinitrogen complexes of iron featuring sulfur donors in the ancillary ligand. The ligands utilized are related to the recently studied tris(phosphino)silyl ligands (2-R(2)PC(6)H(4))(3)Si (R = Ph, iPr) but have one or two phosphine arms replaced with thioether donors. Depending on the number of phosphine arms replaced, both mononuclear and dinuclear iron complexes with dinitrogen are accessible. These complexes contribute to a desirable class of model complexes that possess both dinitrogen and sulfur ligands in the immediate iron coordination sphere.     

Nitrosation of Dimethylamine with Dinitrogen Trioxide

A two-step procedure for preparing N-nitrosodimethylamine by direct nitrosation of aqueous solutions of dialkylamines with dinitrogen dioxide was suggested. The first step involves preparation of dialkylammonium nitrite, and in the second step, on heating to 70–90°С in a weakly acidic solution, it transforms into N-nitrosodialkylamine. The yield of N-nitrosodialkylamines is 95–98% based on the converted dialkylamine. A low-waste process for N-nitrosodimethylamine production was developed.     

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 1.0 equivalent of hydrazine (17.9 equiv of fixed nitrogen atoms).     

Dinitrogen activation by titanium sandwich complexes

The activation of dinitrogen by titanium sandwich complexes of the general form (eta5-C5Me4R)2Ti (R = CHMe2, CMe3, SiMe3) has been systematically investigated. Low-temperature, in situ, solution infrared spectroscopy has allowed detection of monomeric bis-dinitrogen complexes of titanium that are isostructural with more familiar dicarbonyl derivatives. One example, (eta5-C5Me4CHMe2)2Ti(N2)2, has also been characterized by X-ray diffraction and reveals weakly activated dinitrogen ligands. From the solution IR data, the relative azophilicity of the titanium sandwich complexes has been established and increases with smaller cyclopentadienyl substituents.     

Catalytic Dinitrogen Fixation to Form Ammonia at Ambient Reaction Conditions Using Transition Metal‐Dinitrogen Complexes

This paper presents recent progress in catalytic transformation of molecular dinitrogen into ammonia or its equivalents, such as silylamine, especially using transition metal‐dinitrogen complexes under ambient reaction conditions. Several catalytic systems have been recently established using molybdenum‐, iron‐, and cobalt‐dinitrogen complexes or their precursors as catalysts, providing new approaches to the development of novel nitrogen fixation under ambient reaction conditions.     

Dinitrogen and acetylide complexes of low-valent chromium

Reaction of trans-(dmpe) 2CrCl2 (dmpe=1,2-bis(dimethylphosphino)ethane) with one equivalent of LiCCSiMe3 and one equivalent of nBuLi in THF under a dinitrogen atmosphere affords dark orange trans,trans-[(Me 3SiCC)(dmpe)2Cr]2(micro-N2).hexane (1). Under similar conditions but in the absence of acteylide ligand, the reaction of trans-(dmpe)2CrCl2 with 2 equivalents of nBuLi yields the previously characterized complex trans-(dmpe)2Cr(N2)2 (2), while the reaction of trans-(dmpe)2CrCl2 with 2 equivalents of LiCCSiMe3 in THF yields trans-(dmpe)2Cr(CCSiMe3)2 (3). Compound 3 can also be synthesized by irradiating a mixture of trans-(dmpe)2CrMe2 and HCCSiMe3 or by reduction of HCCSiMe3 with compound 2. The magnetic properties, electrochemistry, and crystal structure of trans,trans-[(Me3SiCC)(dmpe)2Cr]2(micro-N2) are consistent with the complex containing two CrI ions bridged by a neutral N2 moiety, with a 1.178(10) A N[TRIPLE BOND]N bond distance. For complex 1 redox processes centered at E1/2=-1.69 V (DeltaEp=185 mV) and -1.43 V (DeltaEp=182 mV) versus Fe(Cp)2/Fe(Cp)2+ are assigned to the CrICrI/CrICrII and CrICrII/CrIICrII couples, respectively. For trans-(dmpe)2Cr(CCSiMe3)2 a reversible couple assigned as the CrII/III couple was observed at -1.59 V (DeltaEp=242 mV) versus Fe(Cp)2/Fe(Cp)2+. The dinuclear CrI-dinitrogen complex 1 has a room temperature magnetic moment of 2.77 microB while compound 3 displays a moment of 2.55 microB. Density-functional theory calculations performed on a model compound of 1, namely, trans,trans-[(HCC)(dpe)2Cr]2(micro-N2) (dpe=diphospinoethane), indicate that oxidation of the molecule should result in weakening of the dinitrogen triple bond.     

Dinitrogen activation by low-coordinate transition metal complexes

In this article, several avenues in the ongoing computational study of first row transition metal β-diketiminate dinitrogen complexes are discussed. Analysis of monometallic N–N bond length changes reveals that upon complexation of free N₂, side-bound N₂ is 0.018–0.054?Å longer than analogous end-bound N₂. Although the same isomeric preferences across the 3-D series were calculated for bimetallic β-diketiminate N₂ complexes, the N–N bond lengths and hence N₂ activation was found to be greater compared to the monometallic species. This present research demonstrates that a useful starting point for activated dinitrogen complexes is the choice of bimetallic supporting ligands, which unlike monometallic ligands allow both metals to activate N₂ in a concerted fashion.     

Dinitrogen extrusion from diazene in organic synthesis

Radical-mediated reactions have many advantages in the construction of complex molecular scaffolds by forging chemical bonds of high challenge. Diazenes, including 1,1-diazenes and 1,2-diazenes, can generate biradical species via nitrogen extrusion under thermal or photochemical conditions. The superior reactivity of the generated biradical enables various types of synthetic transformations with excellent chemoselectivity and has been applied to the complex natural products synthesis. In this mini-review, the modes of reaction are summarized and discussed, namely ring contraction via nitrogen deletion, homo or hetero-dimerization, trimethylenemethane (TMM)-diyl cycloaddition. Applications of these classes of reactions in complex natural product synthesis are illustrated. Last but not least, the current state, future directions, and opportunities for dinitrogen extrusion reaction from diazenes are highlighted and discussed.     

Trichloro(Dinitrogen)Platinate(II)

Zeise's salt, [PtCl₃(H₂C=CH₂)]⁻_, is the oldest known organometallic complex, featuring ethylene strongly bound to a platinum salt. Many derivatives are known, but none involving dinitrogen, and indeed dinitrogen complexes are unknown for both platinum and palladium. Electrospray ionization mass spectrometry of K₂[PtCl₄] solutions generate strong ions corresponding to [PtCl₃(N₂)]⁻, the identity of which was confirmed through ion-mobility spectrometry and MS/MS experiments that proved it to be distinct from its isobaric counterparts [PtCl₃(C₂H₄)]⁻ and [PtCl₃(CO)]⁻. Computational analysis established a gas-phase platinum–dinitrogen bond strength of 116 kJ mol⁻¹, substantially weaker than the ethylene and carbon monoxide analogues but stronger than for polar solvents such as water, methanol and dimethylformamide, and strong enough that the calculated N−N bond length of 1.119 Å represents weakening to a degree typical of isolated dinitrogen complexes.