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1.
Qian Wang Sudip Pan Yan‐Bo Wu Guohai Deng Jian‐Hong Bian Guanjun Wang Lili Zhao Mingfei Zhou Gernot Frenking 《Angewandte Chemie (International ed. in English)》2019,58(48):17365-17374
We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)3 (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D3 symmetric structure involving three equivalent η6‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n?1)d AOs of M and strong backdonation from the occupied (n?1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals. 相似文献
2.
Heiko Bauer Katharina Thum Mercedes Alonso Christian Fischer Sjoerd Harder 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4292-4297
The alkene transfer hydrogenation (TH) of a variety of alkenes has been achieved with simple AeN′′2 catalysts [Ae=Ca, Sr, Ba; N′′=N(SiMe3)2] using 1,4‐cyclohexadiene (1,4‐CHD) as a H source. Reaction of 1,4‐CHD with AeN′′2 gave benzene, N′′H, and the metal hydride species N′′AeH (or aggregates thereof), which is a catalyst for alkene hydrogenation. BaN′′2 is by far the most active catalyst. Hydrogenation of activated C=C bonds (e.g. styrene) proceeded at room temperature without polymer formation. Unactivated (isolated) C=C bonds (e.g. 1‐hexene) needed a higher temperature (120 °C) but proceeded without double‐bond isomerization. The ligands fully control the course of the catalytic reaction, which can be: 1) alkene TH, 2) 1,4‐CHD dehydrogenation, or 3) alkene polymerization. DFT calculations support formation of a metal hydride species by deprotonation of 1,4‐CHD followed by H transfer. Convenient access to larger quantities of BaN′′2, its high activity and selectivity, and the many advantages of TH make this a simple but attractive procedure for alkene hydrogenation. 相似文献
3.
Chaoxian Chi Sudip Pan Luyan Meng Mingbiao Luo Lili Zhao Mingfei Zhou Gernot Frenking 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(6):1746-1752
The alkali metal‐nickel carbonyl anions ENi(CO)3? with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3? fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. 相似文献
4.
Xianghui Shi Guorui Qin Yang Wang Lanxiao Zhao Zhizhou Liu Jianhua Cheng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4400-4404
Hydrogenolysis of the half‐sandwich penta‐arylcyclopentadienyl‐supported heavy alkaline‐earth‐metal alkyl complexes (CpAr)Ae[CH(SiMe3)2](S) (CpAr=C5Ar5, Ar=3,5‐iPr2‐C6H3; S=THF or DABCO) in hexane afforded the calcium, strontium, and barium metal–hydride complexes as the same dimers [(CpAr)Ae(μ‐H)(S)]2 (Ae=Ca, S=THF, 2‐Ca ; Ae=Sr, Ba, S=DABCO, 4‐Ae ), which were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. 2‐Ca , 4‐Sr , and 4‐Ba catalyzed alkene hydrogenation under mild conditions (30 °C, 6 atm, 5 mol % cat.), with the activity increasing with the metal size. A variety of activated alkenes including tri‐ and tetra‐substituted olefins, semi‐activated alkene (Me3SiCH=CH2), and unactivated terminal alkene (1‐hexene) were evaluated. 相似文献
5.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2018,130(21):6344-6349
We report the gas‐phase synthesis of stable 20‐electron carbonyl anion complexes of group 3 transition metals, TM(CO)8− (TM=Sc, Y, La), which are studied by mass‐selected infrared (IR) photodissociation spectroscopy. The experimentally observed species, which are the first octacarbonyl anionic complexes of a TM, are identified by comparison of the measured and calculated IR spectra. Quantum chemical calculations show that the molecules have a cubic (Oh) equilibrium geometry and a singlet (1A1g) electronic ground state. The 20‐electron systems TM(CO)8− are energetically stable toward loss of one CO ligand, yielding the 18‐electron complexes TM(CO)7− in the 1A1 electronic ground state; these exhibit a capped octahedral structure with C3v symmetry. Analysis of the electronic structure of TM(CO)8− reveals that there is one occupied valence molecular orbital with a2u symmetry, which is formed only by ligand orbitals without a contribution from the metal atomic orbitals. The adducts of TM(CO)8− fulfill the 18‐electron rule when only those valence electrons that occupy metal–ligand bonding orbitals are considered. 相似文献
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Junnian Wei Liang Liu Ming Zhan Ling Xu Wen‐Xiong Zhang Zhenfeng Xi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(22):5740-5744
Metallacyclopentadienes have attracted much attention as building blocks for synthetic chemistry as well as key intermediates in many metal‐mediated or metal‐catalyzed reactions. However, metallacyclopentadienes of the alkaline‐earth metals have not been reported, to say nothing of their structures, reaction chemistry, and synthetic applications. In this work, the first series of magnesiacyclopentadienes, spiro‐dilithio magnesiacyclopentadienes, and dimagnesiabutadiene were synthesized from 1,4‐dilithio 1,3‐butadienes. Single‐crystal X‐ray structural analysis of these magnesiacycles revealed unique structural characteristics and bonding modes. Their reaction chemistry and synthetic application were preliminarily studied and efficient access to amino cyclopentadienes was established through their reaction with thioformamides. Experimental and DFT calculations demonstrated that these magnesiacyclopentadienes could be regarded as bis(Grignard) reagents wherein the two Mg C(sp2) bonds have a synergetic effect when reacting with substrates. 相似文献
8.
Formation and Unimolecular Dehydrogenation of Gaseous Alkaline‐earth Metal Amidoboranes M(NH2BH3)2 (M = Be – Ba): Comparative Computational Study
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Formation of alkaline‐earth metal amidoboranes M(NH2BH3)2 (M = Be, Mg, Ca, Sr, Ba) and unimolecular dehydrogenation reactions were computationally studied at the B3LYP/def2‐TZVPPD level of theory. Formation of M(NH2BH3)2 from ammonia borane and MH2 is exergonic, but subsequent unimolecular dehydrogenation reactions are endergonic at room temperature. In contrast to alkali metal amidoboranes, for M(NH2BH3)2 the nature of M significantly affects their reactivity. Activation energies for the dehydrogenation of first and second hydrogen molecules decrease from Be to Ba. In case of Be compounds, intramolecular M ··· H–B contacts play an important role, whereas for heavier analogs such contacts are much less pronounced. 相似文献
9.
Novel Transition‐Metal (M=Cr,Mo, W,Fe) Carbonyl Complexes with Bis(guanidinato)silicon(II) Ligands
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Felix M. Mück Dorit Kloß Johannes A. Baus Dr. Christian Burschka Prof. Dr. Reinhold Tacke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9620-9626
The donor‐stabilized silylene 2 (the first bis(guanidinato)silicon(II ) complex) reacts with the transition‐metal carbonyl complexes [M(CO)6] (M=Cr, Mo, W) to form the respective silylene complexes 7 – 10 . In the reactions with [M(CO)6] (M=Cr, Mo, W), the bis(guanidinato)silicon(II ) complex 2 behaves totally different compared with the analogous bis(amidinato)silicon(II ) complex 1 , which reacts with [M(CO)6] as a nucleophile to replace only one of the six carbonyl groups. In contrast, the reaction of 2 leads to the novel spirocyclic compounds 7 – 9 that contain a four‐membered SiN2C ring and a five‐membered MSiN2C ring with a M?Si and M?N bond (nucleophilic substitution of two carbonyl groups). Compounds 7 – 10 were characterized by elemental analyses (C, H, N), crystal structure analyses, and NMR spectroscopic studies in the solid state and in solution. 相似文献
10.
Frank Kubel Nicole Wandl Mariana Pantazi Vincenza D'Anna Hans Hagemann 《无机化学与普通化学杂志》2013,639(6):892-898
The crystal structures of the M2NaIO6 series (M = Ca, Sr, Ba), prepared at 650 °C by ceramic methods, were determined from conventional laboratory X‐ray powder diffraction data. Synthesis and crystal growth were made by oxidizing I– with O2(air) to I7+ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali‐metal periodate with the alkaline‐earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) Å, whereas the strontium and calcium compounds crystallize in the monoclinic space group P21/c (no. 14) with a = 5.7600(1) Å, b = 5.7759(1) Å, c = 9.9742(1) Å, β = 125.362(1)° and a = 5.5376(1) Å, b = 5.7911(1) Å, c = 9.6055(1) Å, β = 124.300(1)°, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba2NaIO6 contains the first perfectly octahedral [IO6]5– unit reported. The compounds of the ortho‐periodates are stable up to 800 °C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR‐ and Raman‐active vibrations. 相似文献
11.
A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds. 相似文献
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Influence of Precursor Chemistry on the Formation of MTiO3 (M = Ba,Sr) Ceramic Thin Films 总被引:1,自引:0,他引:1
Thin films of BaTiO3 and SrTiO3 were prepared by a chemical solution deposition method. The impact of the precursor on the processing, on the microstructure, and on the dielectric properties has been studied by systematically varying the alkyl chain length of the used Ba- and Sr-carboxylates. In addition, the effect of stabilizing the Ti-alkoxide precursor by acetylacetone has been investigated. The decomposition process, the crystallization behavior, and the film morphology were analyzed by glancing incidence XRD, reflectance FT-IR and field emission SEM. Distinct precursor effects on the thin film morphology and properties were revealed. Part of this influence can be attributed to an intermediate complex carbonate phase which forms for selected carboxylates with short alkyl chains. The high transformation temperature of this intermediate phase to the perovskite obviously has a marked influence on the crystallization and densification process of the alkaline earth titanate thin films. We correlate the morphological differences of the films to their dielectric properties. 相似文献
14.
The mechanochemical synthesis offers an easy access to obtain alkaline earth metal terephthalates M(C8H4O4) · nH2O (M = Ca, Sr, Ba). In the presented study we describe for the first time the mechanochemical synthesis of powders of Ca(C8H4O4) · 3H2O, Ca(C8H4O4), Sr(C8H4O4) · H2O, and Ba(C8H4O4), which so far were only synthesized as single crystals from aqueous solutions or by reactions in an autoclave. Furthermore, a new hydrate Ba(C8H4O4) · 2(1.5)H2O, not described so far in the literature, was prepared. All compounds were characterized by X‐ray powder diffraction, thermal analysis, elemental analysis, FT‐IR, and MAS NMR spectroscopic measurements. 相似文献
15.
Dr. Bo Liu Dr. Thierry Roisnel Prof. Dr. Jean‐François Carpentier Dr. Yann Sarazin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(8):2784-2802
The behavior of the first aminophenolate catalysts of the large alkaline earth metals (Ae) [(LOi)AeN(SiMe2R)2(thf)x] (i=1–4; Ae=Ca, Sr, Ba; R=H, Me; x=0–2) for the cyclohydroamination of terminal aminoalkenes is discussed. The complexes [(BDI)AeN(SiMe2H)2(thf)x] (Ae=Ca, Sr, Ba, x=1–2; (BDI)H=H2C[C(Me)N‐2,6‐(iPr)2C6H3]2)) and [(BDI)CaN(SiMe3)2(thf)] supported by the β‐diketiminate (BDI)? ligand have also been employed for comparative and mechanistic considerations. The catalytic performances decrease in the order Ca>Sr?Ba, which is the opposite trend to that previously observed during the intermolecular hydroamination of activated alkenes catalyzed by the same alkaline‐earth metal complexes. Catalyst efficacy increases when the chelating and donating ability of the aminophenolate ligands decreases. For given metals and ancillary scaffolds, disilazide catalysts that incorporate the N(SiMe3)2? amido group outclass their congeners containing the N(SiMe2H)2? amide owing to the lower basicity of the N(SiMe2H)2? with respect to the N(SiMe3)2? group, and also because Ae–N(SiMe2H)2 catalysts suffer from irreversible deactivation through the dehydrogenative coupling of amine and hydrosilane moieties. This deactivation process takes place at 25 °C in the case of [(LOi)AeN(SiMe2H)2(thf)x] phenolate complexes and occurs even with the related [(BDI)AeN(SiMe2H)2(thf)x] complex, albeit under conditions harsher than those required for effective cyclohydroamination catalysis. A mechanistic scenario for cyclohydroamination catalyzed by [(LX)AeN(SiMe2H)2(thf)x] complexes ((LX)?=(LOi)? or (BDI)?) is proposed. Although beneficial for the synthesis of Ae heteroleptic complexes able to resist deleterious Schlenk‐type equilibria, the use of the N(SiMe2H)2? is prejudicial to catalytic activity in the case of catalyzed transformations that involve reactive amine (and potentially other) substrates. Mechanistic and kinetic investigations further illustrate the interplay between the catalytic activity, operative mechanism, and identity of the metal, ancillary ligand, and amido group. These studies suggest that the widely accepted mechanism for cyclohydroamination reactions cannot be extended systematically to all alkaline‐earth catalysts. The [(BDI)CaN(SiMe2H)2{H2NCH2C(CH3)2CH2CH?CH2}2] complex, the first Ca–aminoalkene adduct structurally characterized, was prepared quantitatively and essentially behaves like [(BDI)CaN(SiMe2H)(thf)], thus serving as a model compound for mechanistic studies, as illustrated during stoichiometric reactions monitored by 1H NMR spectroscopy. 相似文献
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Jason M. Lynam Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(28):8238-8247
Transition‐metal vinylidene complexes are intermediates in a number of synthetically important transformations of alkynes. Underpinning these applications is the ability of various electron‐rich transition‐metal complexes to effectively facilitate the conversion of alkynes into their vinylidene tautomers. Recent experimental and theoretical studies have provided considerable insight into the mechanisms by which this process occurs and they are detailed herein. In particular, it has been demonstrated that different substituents on both the metal and the alkyne may have profound effects on both the kinetic and thermodynamic profiles of the alkyne/vinylidene tautomerisation. An important finding is that internal alkynes may be employed to prepare disubstituted vinylidene complexes under easily accessible conditions. This discovery brings to light a new facet of the potential synthetic applications of transition metal vinylidene complexes. 相似文献
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Prof. Dr. Wolfgang Scherer M. Sc. Petra Meixner Dipl.‐Phys. Kilian Batke Dr. José E. Barquera‐Lozada Prof. Dr. Klaus Ruhland M. Sc. Andreas Fischer Dr. Georg Eickerling Dr. Klaus Eichele 《Angewandte Chemie (International ed. in English)》2016,55(38):11673-11677
We will outline that the sign and magnitude of J(Si,H) coupling constants provide a highly sensitive tool to measure the extent of Si?H bond activation in nonclassical silane complexes. Up to now, this structure–property relationship was obscured by erroneous J(Si,H) sign determinations in the literature. These new findings also help to identify the salient control parameters of the Si?H bond activation process in nonclassical silane complexes. 相似文献
20.
Ce~(3+)在钙钛矿型KMF_3(M=Mg、Ca、Sr、Ba)基质中的发光特性 总被引:2,自引:0,他引:2
采用高温固相反应法,在Ar气氛中合成了KMF3(M=Mg、Ca、Sr、Ba)基质化合物和掺杂Ce3+的磷光体。经X射线衍射分析确定,KMgF3和KCaF3属于立方晶系、钙钛矿型结构,KSrF3和KBaF3具有类似的结构。测定了KMF3∶Ce3+的发光光谱,观察到与其结构对应的分为二种不同的光谱结构,讨论了Ce3+的取代格位 相似文献