共查询到20条相似文献,搜索用时 15 毫秒
1.
Dr. Andreas Stasch 《Angewandte Chemie (International ed. in English)》2014,53(5):1338-1341
The assembly of well‐defined large cluster compounds of ionic light metal hydrides is a synthetic challenge and of importance for synthesis, catalysis, and hydrogen storage. The synthesis and characterization of a series of neutral and anionic pyrazolate‐stabilized lithium hydride clusters with inorganic cores in the nanometer region is now reported. These complexes were prepared in a bottom‐up approach using alkyl lithium and lithium pyrazolate mixtures with silanes in hydrocarbon solutions. Structural characterization using synchrotron radiation revealed isolated cubic clusters that contain up to 37 Li+ cations and 26 H? ions. Substituted pyrazolate ligands were found to occupy all corners and some edges for the anionic positions. 相似文献
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Discrete Magnesium Hydride Aggregates: A Cationic Mg13H18 Cluster Stabilized by NNNN‐Type Macrocycles 下载免费PDF全文
Daniel Martin Dr. Klaus Beckerle Silvia Schnitzler Dr. Thomas P. Spaniol Prof. Dr. Laurent Maron Prof. Dr. Jun Okuda 《Angewandte Chemie (International ed. in English)》2015,54(13):4115-4118
Large magnesium hydride aggregates [Mg13(Me3TACD)6(μ2‐H12)(μ3‐H6)][A]2 ((Me3TACD)H=1,4,7‐trimethyl‐1,4,7,10‐tetraazacyclododecane; A=AlEt4, AlnBu4, B{3,5‐(CF3)2C6H3}4) were synthesized stepwise from alkyl complexes [Mg2(Me3TACD)R3] (R=Et, nBu) and phenylsilane in the presence of additional MgII ions. The central magnesium atom is octahedrally coordinated by six hydrides as in solid α‐MgH2 of the rutile type. Further coordination to six magnesium atoms leads to a substructure of seven edge‐sharing octahedra as found in the hexagonal layer of brucite (Mg(OH)2). Upon protonolysis in the presence of 1,2‐dimethoxyethane (DME), this cluster was degraded into a tetranuclear dication [Mg2(Me3TACD)(μ‐H)2(DME)]2[A]2. 相似文献
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Dr. Debabrata Mukherjee Prof. Dr. Jun Okuda 《Angewandte Chemie (International ed. in English)》2018,57(6):1458-1473
Solid magnesium hydride [MgH2]∞ has been pursued as a potential hydrogen‐storage material. Organic chemists were rather interested in soluble magnesium hydride reagents from mid‐20th century. It was only in the last two decades that molecular magnesium hydride chemistry received a major boost from organometallic chemists with a series of structurally well‐characterized examples that continues to build a whole new class of compounds. More than 40 such species have been isolated, ranging from mononuclear terminal hydrides to large hydride clusters with more than 10 magnesium atoms. They provide not only insights into the structure and bonding of Mg?H motifs, but also serve as models for hydrogen‐storage materials. Some of them are also recognized to participate in catalytic transformations, such as hydroelementation. Herein, an overview of these molecular magnesium hydrides is given, focusing on their synthesis and structural characterization. 相似文献
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Merle Arrowsmith Michael S. Hill Dr. Dugald J. MacDougall Dr. Mary F. Mahon Dr. 《Angewandte Chemie (International ed. in English)》2009,48(22):4013-4016
High‐de‐hydride! A straightforward reaction between a magnesium silylamido/N‐heterocyclic carbene adduct and phenylsilane provides a {Mg4H6} cluster molecule that may be regarded as a combination of two magnesium dihydride and two magnesium monohydride moieties.
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Silvia Schnitzler Dr. Thomas P. Spaniol Prof. Dr. Laurent Maron Prof. Dr. Jun Okuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11330-11334
A complex featuring a terminal magnesium hydride bond supported by an NNNN macrocyclic ligand, [Mg{Me3TACD ? Al(iBu)3}H] ( 3 ), was formed from its labile Al(iBu)3 adduct. Use of Al(iBu)3 to block the amido nitrogen of the NNNN macrocyclic ligand was essential to prevent aggregation. The structurally characterized compound 3 reacted with BH3 to give the BH4 derivative, whereas Me3SiC?CH and PhSiH3 led to the corresponding acetylide and silyl derivative under H2 elimination. Pyridine is inserted into the Mg?H bond to give selectively the 1,4‐dihydropyridinate. 相似文献
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The effect on the hydrogen storage attributes of magnesium hydride (MgH2) of the substitution of Mg by varying fractions of Al and Si is investigated by an ab initio plane‐wave pseuodopotential method based on density functional theory. Three supercells, namely, 2×2×2, 3×1×1 and 5×1×1 are used for generating configurations with varying amounts (fractions x=0.0625, 0.1, and 0.167) of impurities. The analyses of band structure and density of states (DOS) show that, when a Mg atom is replaced by Al, the band gap vanishes as the extra electron occupies the conduction band minimum. In the case of Si‐substitution, additional states are generated within the band gap of pure MgH2—significantly reducing the gap in the process. The reduced band gaps cause the Mg? H bond to become more susceptible to dissociation. For all the fractions, the calculated reaction energies for the stepwise removal of H2 molecules from Al‐ and Si‐substituted MgH2 are much lower than for H2 removal from pure MgH2. The reduced stability is also reflected in the comparatively smaller heats of formation (ΔHf) of the substituted MgH2 systems. Si causes greater destabilization of MgH2 than Al for each x. For fractions x=0.167 of Al, x=0.1, 0.167 of Si (FCC) and x=0.0625, 0.1 of Si (diamond), ΔHf is much less than that of MgH2 substituted by a fraction x=0.2 of Ti (Y. Song, Z. X. Guo, R. Yang, Mat. Sc. & Eng. A 2004 , 365, 73). Hence, we suggest the use of Al or Si instead of Ti as an agent for decreasing the dehydrogenation reaction and energy, consequently, the dehydrogenation temperature of MgH2, thereby improving its potential as a hydrogen storage material. 相似文献
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Dong Young Kim N. Jiten Singh Dr. Han Myoung Lee Dr. Kwang S. Kim Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(22):5598-5604
Hydrogen storage : In lithium amidoboranes an initial molecule of H2 is released by the formation of LiH, followed by a redox reaction of the dihydrogen bond formed between LiHδ? and NHδ+. In this dehydrogenation process, an intermolecular N? B bond forms through the catalytic effect of a Li cation. After releasing the first molecule of H2, a Li cation binds to a nitrogen atom, lowering the energy barrier for the second H2 loss per lithium amidoborane dimer (see figure).
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Hai Zhang Chaoran Luan Dong Gao Meng Zhang Nelson Rowell Maureen Willis Meng Chen Jianrong Zeng Hongsong Fan Wen Huang Xiaoqin Chen Kui Yu 《Angewandte Chemie (International ed. in English)》2020,59(39):16943-16952
Little is known about the pathway of room‐temperature formation of ternary CdTeSe magic‐size clusters (MSCs) obtained by mixing binary CdTe and CdSe induction period samples containing binary precursor compounds (PCs) of MSCs, monomers (Ms), and fragments (Fs). Also, unestablished are dispersion effects that occur when as‐mixed samples (without incubation) are placed in toluene (Tol) and octylamine (OTA) mixtures. The resulting ternary MSCs, exhibiting a sharp optical absorption peak at 399 nm, are labelled CdTeSe MSC‐399, and their PCs are referred to as CdTeSe PC‐399. When the amount of OTA is relatively small, single‐ensemble MSC‐399 evolved without either binary CdTe or CdSe MSCs. When the OTA amount is relatively large, CdTe MSC‐371 appeared initially and then disappeared, while single‐ensemble MSC‐399 developed more deliberately. The larger the OTA amount, the more slowly these changes proceeded. The substitution reaction of CdTe PC + CdSe M/F?CdTeSe PC‐399 + CdTe M/F is proposed to be rate‐determining for the MSC‐399 formation in a Tol and OTA mixture. This study provides further understanding of the transformation pathway between MSCs. 相似文献
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Metal‐Borohydride‐Modified Zr(BH4)4⋅8 NH3: Low‐Temperature Dehydrogenation Yielding Highly Pure Hydrogen 下载免费PDF全文
Dr. Jianmei Huang Prof. Dr. Liuzhang Ouyang Dr. Qinfen Gu Prof. Dr. Xuebin Yu Prof. Dr. Min Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(42):14931-14936
Due to its high hydrogen density (14.8 wt %) and low dehydrogenation peak temperature (130 °C), Zr(BH4)4 ? 8 NH3 is considered to be one of the most promising hydrogen‐storage materials. To further decrease its dehydrogenation temperature and suppress its ammonia release, a strategy of introducing LiBH4 and Mg(BH4)2 was applied to this system. Zr(BH4)4 ? 8 NH3–4 LiBH4 and Zr(BH4)4 ? 8 NH3–2 Mg(BH4)2 composites showed main dehydrogenation peaks centered at 81 and 106 °C as well as high hydrogen purities of 99.3 and 99.8 mol % H2, respectively. Isothermal measurements showed that 6.6 wt % (within 60 min) and 5.5 wt % (within 360 min) of hydrogen were released at 100 °C from Zr(BH4)4 ? 8 NH3–4 LiBH4 and Zr(BH4)4 ? 8 NH3–2 Mg(BH4)2, respectively. The lower dehydrogenation temperatures and improved hydrogen purities could be attributed to the formation of the diammoniate of diborane for Zr(BH4)4 ? 8 NH3–4 LiBH4, and the partial transfer of NH3 groups from Zr(BH4)4 ? 8 NH3 to Mg(BH4)2 for Zr(BH4)4 ? 8 NH3–2 Mg(BH4)2, which result in balanced numbers of BH4 and NH3 groups and a more active Hδ+ ??? ?δH interaction. These advanced dehydrogenation properties make these two composites promising candidates as hydrogen‐storage materials. 相似文献
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Dr. Lea Fohlmeister Dr. Andreas Stasch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10235-10246
A series of magnesium(II) complexes bearing the sterically demanding phosphinoamide ligand, L?=Ph2PNDip?, Dip=2,6‐diisopropylphenyl, including heteroleptic magnesium alkyl and hydride complexes are described. The ligand geometry enforces various novel ring and cluster geometries for the heteroleptic compounds. We have studied the stoichiometric reactivity of [(LMgH)4] towards unsaturated substrates, and investigated catalytic hydroborations and hydrosilylations of ketones and pyridines. We found that hydroborations of two ketones with pinacolborane using various Mg precatalysts is very rapid at room temperature with very low catalyst loadings, and ketone hydrosilylation using phenylsilane is rapid at 70 °C. Our studies point to an insertion/σ‐bond metathesis catalytic cycle of an in situ formed “MgH2” active species. 相似文献
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Molecular Calcium Hydride: Dicalcium Trihydride Cation Stabilized by a Neutral NNNN‐Type Macrocyclic Ligand 下载免费PDF全文
Valeri Leich Dr. Thomas P. Spaniol Prof. Dr. Laurent Maron Prof. Dr. Jun Okuda 《Angewandte Chemie (International ed. in English)》2016,55(15):4794-4797
Hydrogenolysis of bis(triphenylsilyl)calcium containing the neutral NNNN‐type macrocyclic amine ligand Me4TACD [Ca(Me4TACD)(SiPh3)2] ( 2 ), gave the cationic dinuclear calcium hydride [Ca2H3(Me4TACD)2](SiPh3) ( 3 ), characterized by NMR spectroscopy, single‐crystal X‐ray analysis, and DFT calculations. Compound 3 reacted with deuterium to give the deuteride [D3]‐ 3 . 相似文献
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Simon J. Bonyhady Cameron Jones Prof. Sharanappa Nembenna Dr. Andreas Stasch Dr. Alison J. Edwards Dr. Garry J. McIntyre Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(3):938-955
The preparation and characterization of a series of magnesium(II) iodide complexes incorporating β‐diketiminate ligands of varying steric bulk and denticity, namely, [(ArNCMe)2CH]? (Ar=phenyl, (PhNacnac), mesityl (MesNacnac), or 2,6‐diisopropylphenyl (Dipp, DippNacnac)), [(DippNCtBu)2CH]? (tBuNacnac), and [(DippNCMe)(Me2NCH2CH2NCMe)CH]? (DmedaNacnac) are reported. The complexes [(PhNacnac)MgI(OEt2)], [(MesNacnac)MgI(OEt2)], [(DmedaNacnac)MgI(OEt2)], [(MesNacnac)MgI(thf)], [(DippNacnac)MgI(thf)], [(tBuNacnac)MgI], and [(tBuNacnac)MgI(DMAP)] (DMAP=4‐dimethylaminopyridine) were shown to be monomeric by X‐ray crystallography. In addition, the related β‐diketiminato beryllium and calcium iodide complexes, [(MesNacnac)BeI] and [{(DippNacnac)CaI(OEt2)}2] were prepared and crystallographically characterized. The reductions of all metal(II) iodide complexes by using various reagents were attempted. In two cases these reactions led to the magnesium(I) dimers, [(MesNacnac)MgMg(MesNacnac)] and [(tBuNacnac)MgMg(tBuNacnac)]. The reduction of a 1:1 mixture of [(DippNacnac)MgI(OEt2)] and [(MesNacnac)MgI(OEt2)] with potassium gave a low yield of the crystallographically characterized complex [(DippNacnac)Mg(μ‐H)(μ‐I)Mg(MesNacnac)]. All attempts to form beryllium(I) or calcium(I) dimers by reductions of [(MesNacnac)BeI], [{(DippNacnac)CaI(OEt2)}2], or [{(tBuNacnac)CaI(thf)}2] have so far been unsuccessful. The further reactivity of the magnesium(I) complexes [(MesNacnac)MgMg(MesNacnac)] and [(tBuNacnac)MgMg(tBuNacnac)] towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes [(MesNacnac)Mg(L)Mg(L)(MesNacnac)] (L=THF or DMAP), [(MesNacnac)Mg(μ‐AdN6Ad)Mg(MesNacnac)] (Ad=1‐adamantyl), [(tBuNacnac)Mg(μ‐AdN6Ad)Mg(tBuNacnac)], and [(MesNacnac)Mg(μ‐tBu2N2C2O2)Mg(MesNacnac)] and revealed that, in general, the reactivity of the magnesium(I) dimers is inversely proportional to their steric bulk. The preparation and characterization of [(tBuNacnac)Mg(μ‐H)2Mg(tBuNacnac)] has shown the compound to have different structural and physical properties to [(tBuNacnac)MgMg(tBuNacnac)]. Treatment of the former with DMAP has given [(tBuNacnac)Mg(H)(DMAP)], the X‐ray crystal structure of which disclosed it to be the first structurally authenticated terminal magnesium hydride complex. Although attempts to prepare [(MesNacnac)Mg(μ‐H)2Mg(MesNacnac)] were not successful, a neutron diffraction study of the corresponding magnesium(I) complex, [(MesNacnac)MgMg(MesNacnac)] confirmed that the compound is devoid of hydride ligands. 相似文献
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Koushik Acharyya Prof. Dr. Partha Sarathi Mukherjee 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1646-1657
A supramolecular approach that uses hydrogen‐bonding interaction as a driving force to accomplish exceptional self‐sorting in the formation of imine‐based covalent organic cages is discussed. Utilizing the dynamic covalent chemistry approach from three geometrically similar dialdehydes ( A , B , and D ) and the flexible triamine tris(2‐aminoethyl)amine ( X ), three new [3+2] self‐assembled nanoscopic organic cages have been synthesized and fully characterized by various techniques. When a complex mixture of the dialdehydes and triamine X was subjected to reaction, it was found that only dialdehyde B (which has OH groups for H‐bonding) reacted to form the corresponding cage B3X2 selectively. Surprisingly, the same reaction in the absence of aldehyde B yielded a mixture of products. Theoretical and experimental investigations are in complete agreement that the presence of the hydroxyl moiety adjacent to the aldehyde functionality in B is responsible for the selective formation of cage B3X2 from a complex reaction mixture. This spectacular selection was further analyzed by transforming a nonpreferred (non‐hydroxy) cage into a preferred (hydroxy) cage B3X2 by treating the former with aldehyde B . The role of the H‐bond in partner selection in a mixture of two dialdehydes and two amines has also been established. Moreover, an example of unconventional imine bond metathesis in organic cage‐to‐cage transformation is reported. 相似文献
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Bimetallic NiCo Functional Graphene: An Efficient Catalyst for Hydrogen‐Storage Properties of MgH2 下载免费PDF全文
Ying Wang Guang Liu Cuihua An Li Li Fangyuan Qiu Prof. Yijing Wang Lifang Jiao Prof. Huatang Yuan 《化学:亚洲杂志》2014,9(9):2576-2583
Bimetallic NiCo functional graphene (NiCo/rGO) was synthesized by a facile one‐pot method. During the coreduction process, the as‐synthesized ultrafine NiCo nanoparticles (NPs), with a typical size of 4–6 nm, were uniformly anchored onto the surface of reduced graphene oxide (rGO). The NiCo bimetal‐supported graphene was found to be more efficient than their single metals. Synergetic catalysis of NiCo NPs and rGO was confirmed, which can significantly improve the hydrogen‐storage properties of MgH2. The apparent activation energy (Ea) of the MgH2? NiCo/rGO sample decreases to 105 kJ mol?1, which is 40.7 % lower than that of pure MgH2. More importantly, the as‐prepared MgH2? NiCo/rGO sample can absorb 5.5 and 6.1 wt % hydrogen within 100 and 350 s, respectively, at 300 °C under 0.9 MPa H2 pressure. Further cyclic kinetics investigation indicates that MgH2? NiCo/rGO nanocomposites have excellent cycle stability. 相似文献
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Desolvation and Dehydrogenation of Solvated Magnesium Salts of Dodecahydrododecaborate: Relationship between Structure and Thermal Decomposition 下载免费PDF全文
Prof. Dr. Xuenian Chen Prof. Dr. Yi‐Hsin Liu Dr. Anne‐Marie Alexander Dr. Judith C. Gallucci Dr. Son‐Jong Hwang Dr. Hima Kumar Lingam Dr. Zhenguo Huang Cong Wang Dr. Huizhen Li Dr. Qianyi Zhao Prof. Dr. Umit S. Ozkan Prof. Dr. Sheldon G. Shore Prof. Dr. Ji‐Cheng Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7325-7333
Attempts to synthesize solvent‐free MgB12H12 by heating various solvated forms (H2O, NH3, and CH3OH) of the salt failed because of the competition between desolvation and dehydrogenation. This competition has been studied by thermogravimetric analysis (TGA) and temperature‐programmed desorption (TPD). Products were characterized by IR, solution‐ and solid‐state NMR spectroscopy, elemental analysis, and single‐crystal or powder X‐ray diffraction analysis. For hydrated salts, thermal decomposition proceeded in three stages, loss of water to form first hexahydrated then trihydrated, and finally loss of water and hydrogen to form polyhydroxylated complexes. For partially ammoniated salts, two stages of thermal decomposition were observed as ammonia and hydrogen were released with weight loss first of 14 % and then 5.5 %. Thermal decomposition of methanolated salts proceeded through a single step with a total weight loss of 32 % with the release of methanol, methane, and hydrogen. All the gaseous products of thermal decomposition were characterized by using mass spectrometry. Residual solid materials were characterized by solid‐state 11B magic ‐ angle spinning (MAS) NMR spectroscopy and X‐ray powder diffraction analysis by which the molecular structures of hexahydrated and trihydrated complexes were solved. Both hydrogen and dihydrogen bonds were observed in structures of [Mg(H2O)6B12H12] ? 6 H2O and [Mg(CH3OH)6B12H12] ? 6 CH3OH, which were determined by single‐crystal X‐ray diffraction analysis. The structural factors influencing thermal decomposition behavior are identified and discussed. The dependence of dehydrogenation on the formation of dihydrogen bonds may be an important consideration in the design of solid‐state hydrogen storage materials. 相似文献