Solving restricted open-shell equations in excited state molecular dynamics simulations

Different approaches to the solution of restricted open-shell equations are summarized and a general implementation for the first excited singlet state in the Car–Parrinello molecular dynamics code (CPMD) is presented. For molecular dynamics simulations where energy conservation is an important criterion, different choices of parameters are necessary depending on the particular chemical situation.     

Iron and Cobalt Complexes of a Series of Tridentate P,N, P Ligands — Synthesis,Characterization, and Application in Ethene Polymerization Reactions

A series of tridentate P, N, P ligands comprising a central pyridine unit and two pendent diarylphosphane moieties (2, 6‐bis(CH₂PAr₂)pyridine; Ar = phenyl ( 1 ), 2‐methylphenyl ( 2 ), 2, 4, 6‐trimethylphenyl ( 3 )) as well as the corresponding iron ( 1‐FeCl₂ , 2‐FeCl₂ , 3‐FeCl₂ ) and cobalt ( 1‐CoCl₂ , 2‐CoCl₂ , 3‐CoCl₂ ) complexes were synthesized and characterized. An X‐ray structure analysis of 2‐CoCl₂ and 3‐CoCl₂ exhibited a trigonal‐bipyramidal coordination geometry at the metal center, the two chlorine atoms and the nitrogen occupying the equatorial and the phosphane units the apical positions. IR analysis indicated, that in all complexes the pyridine unit is coordinated to the metal center. The cobalt compounds were applied as catalyst precursors for the polymerization of ethene after activation with MAO.     

An Efficient Synthesis of Chromeno[2,3‐d]pyrimidine‐2,4‐diones with a Nitroketene‐Aminal Moiety at C(5) by a One‐Pot Four‐Component Reaction

An efficient and novel synthesis of chromeno[2,3‐d]pyrimidine‐2,4‐dione derivatives with a nitroketene‐aminal moiety at C(5) via four‐component reaction of salicylaldehydes, barbituric acid, diamines, and 1,1‐bis(methylsulfanyl)‐2‐nitroethene in EtOH and in the presence of AcOH is reported. Easy performance, good yields, and easy purification are the main advantages of this method. All structures were confirmed by IR, MS, and ¹H‐ and ¹³C‐NMR, and by X‐ray crystal‐structure analyses. A plausible mechanism for this type of reaction is proposed (Scheme).     

乙烷与CO2制乙烯反应的热力学和动力学研究

乙烷与ＣＯ２的主要反应及其热力学研究表明，乙烷与ＣＯ２反应很复杂，提高ＣＯ２氧化乙烷脱氢生成乙烯的选择，关键在一催化剂的开发；ＣＯ２不但可提高乙灶脱氢制乙烯的热力学平衡转化率，而且可与催化剂表面的积碳发生反应，延长催化剂的使用寿命。研究了催化剂上乙烷与ＣＯ２制乙烯反应的动力学，确定了ＣＯ２氧化乙烷脱氢反应的动力学方程及参数，表明乙烷与ＣＯ２制乙烯的反应速度比乙烷热裂解制乙烯的反应速度要大得多。     

介孔二氧化硅负载高分散钒催化剂的制备及乙烷选择氧化性能

以高比表面积的介孔二氧化硅为载体, 采用等体积浸渍法制备了一系列介孔二氧化硅负载钒催化剂, 并探究了其乙烷选择氧化反应性能. 利用X射线衍射(XRD)、 紫外-可见漫反射光谱(UV-Vis DRS)和氢气程序升温还原(H₂-TPR)等方法对催化剂的物化性质进行了表征, 研究了钒负载量对催化剂结构特征的影响. 结果表明,随着钒负载量的增加, 钒物种在催化剂表面的存在形式由高分散低聚的VO _x 转变为高聚的VO _x, 其中高分散钒物种有利于提高目标产物乙烯和乙醛的选择性.     

Adsorption of ethene on Pt(1 1 1) and ordered PtxSn/Pt(1 1 1) surface alloys: A comparative HREELS and DFT investigation

The adsorption of ethene (C₂H₄) on Pt(1 1 1) and the Pt₃Sn/Pt(1 1 1) and Pt₂Sn/Pt(1 1 1) surface alloys has been investigated experimentally by high-resolution electron energy loss spectroscopy and temperature programmed desorption. The experimental results have been compared with density functional theory (DFT) calculations allowing us to perform a complete assignment of all vibration modes and loss features to the species present on the surfaces. On Pt(1 1 1) as well as on the Pt-Sn surface alloys an η² di-σ-bonded conformation of ethene has been found to be the most stable adsorbed form. In addition to this majority species a minor amount of π-bonded ethene has been identified, which is more abundant on the Pt₂Sn surface alloy than on the other surfaces. Additionally the HREELS spectra of ethene on Pt(1 1 1) and the Pt-Sn surface alloys differ only slightly in terms of the energetic positions of the loss peaks.     

Titanium and zirconium complexes containing the new 2,3-dimethyl-1,4-diphenylcyclopentadienyl ligand. Synthesis, characterization and polymerization behavior

An easy and inexpensive three-step synthesis of new 2,3-dimethyl-1,4-diphenylcyclopentadiene (3) ligand and the titanium and zirconium homometallocene dichlorides [TiCl₂(η⁵-C₅H-2,3-Me₂-1,4-Ph₂)₂] (4), [ZrCl₂(η⁵-C₅H-2,3-Me₂-1,4-Ph₂)₂] (5), and the mixed ligand zirconium complex [ZrCl₂(η⁵-C₅H-2,3-Me₂-1,4-Ph₂)(η⁵-C₅H₅)] (6) prepared thereof are described. The polymerization of ethene using 4-6/MAO catalysts revealed that zirconocene complexes 5 and 6 displayed moderate and high activity, respectively, whereas the titanium catalyst 4/MAO was inactive. The crystal structures of 4 and 5 were determined by X-ray crystallography.     

1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile: Enol Ethers and Ketene Acetals as Cycloaddition Partners

(E)‐ and (Z)‐1,2‐bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile ((E)‐ and (Z)‐BTE, resp., =(E)‐ and (Z)‐2,3‐bis(trifluoromethyl)but‐2‐enedinitrile) were used as a stereochemical probe in studying (2+2) cycloadditions of acceptor with donor alkenes. The additions to methyl (E)‐ and (Z)‐propenyl ether gave rise to the eight conceivable cyclobutanes 8 , although in different ratios in reactions of (E)‐ and (Z)‐BTE. The ¹⁹F‐NMR data served the structural assignment and the quantitative analysis. The mechanistic discussion is based on rotations and ring closures of the assumed 1,4‐zwitterionic intermediates. Dimethylketene dimethyl acetal, methylketene dimethyl acetal, and ketene diethyl acetal show an increasing rate in their reactions with BTE as well as in the equilibration of the cycloadducts.     

NiP非晶态合金的负载方法及催化剂的结构与催化性能

采用ＮｉＢ作为引导剂,使ＮｉＰ完全定向沉积到载体上,用ＩＣＰ,ＸＲＤ,ＤＳＣ,ＢＥＴ,ＴＥＭ对制备的负载型ＮｉＰ（Ｂ）催化剂进行表征,研究了这类催化剂对乙烯中微量乙炔的选择加氢性能,结果表明,ＮｉＰ（Ｂ）以超细颗粒分散到载体上,由于少量Ｂ的存在,使其比相应的ＮｉＰ或ＮｉＢ具有更高的热稳定性。非晶态ＮｉＰ（Ｂ）合金催化剂具有比相应的晶态合金更好的催化性能。低温氢气处理可以除去表面镍的氧化物,从而提高     

Conversion of ethene and propene adsorbed on Pt foil

The conversion of ethene and propene has been studied in the process of adsorption on Pt foil and in adsorbed state. Mainly C−C bond cleavage and limited C−C bond formation was observed in 323–523 K temperature interval.