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131.
Dawei Guo Lingqin Han Tianzhu Zhang Wen‐Hua Sun Ting Li Xiaozhen Yang 《Macromolecular theory and simulations》2002,11(9):1006-1012
A combination of molecular mechanics and the charge equilibration method was applied and further developed to predicting the catalyst activity of a metal complex. A late transition metal catalyst, {di‐μ‐bromotetra [N,N′‐bis(3,5‐dimethylanil)‐4‐methyl‐2,6‐bis(imino)phenoxy]nickel} bromide (MOL) was dealt with. A modified molecular force field from universal force field was set and validated for this system. Simulations predict that the activity of MOL varies little with temperature. Simulation results were in good agreement with experimental results for ethylene oligomerization with MOL.
132.
Federica Benvenuti Carlo Carlini Anna Maria Raspolli Galletti Glauco Sbrana Mario Marchionna Paolo Ferrarini 《先进技术聚合物》1998,9(2):113-120
Styrene–divinylbenzene resins were used for the synthesis of different polymer-bound β-diketones, obtained by anchoring the chelating group through either the central or the lateral position. The heterogenized diketone ligand was subsequently reacted with Ni(COD)2 analogously to the corresponding homogeneous catalysts active in α-olefin oligomerization. The heterogenized catalysts showed a good activity only when the central position of the chelate moiety was free. Heterogenization caused a significant change of selectivity: olefin oligomerization was accompanied by the formation of a large amount of polymeric products. This behavior is discussed in terms of steric effects caused by the bulky polymeric ligand. © 1998 John Wiley & Sons, Ltd. 相似文献
133.
134.
以2-(2-吡啶基)咪唑(pIM)、Co2+和NaVO3为原料,在水热条件下,制备了新的钒氧簇化合物[Co (pIM) V2O6](1)。采用X射线单晶衍射、粉末X射线衍射、傅里叶变换红外光谱和元素分析等方法对化合物进行了表征。单晶解析表明,该化合物由VO4四面体和CoO3N2四方锥通过氧原子共边、共角连接成二维结构。基于钒氧簇在催化氧化体系中的高效活性,1作为非均相反应的催化剂,在以H2O2为氧化剂的催化烯烃环氧化反应中表现出优秀的催化性能,催化剂能够多次重复使用且活性基本保持不变。此外,磁化率研究表明1中存在反铁磁相互作用。 相似文献
135.
理论研究F2BN3多聚体的结构特色和热力学稳定性 总被引:1,自引:0,他引:1
在密度泛函理论(DFT)B3LYP/6-311+G*水平上计算研究了叠氮二氟硼多聚体(F2BN3)n (n=1-4),获得了它们的结构和热力学性质,讨论了几何参数随聚合度的变化趋势。多聚体(F2BN3)2-4的优化构型均为由不同子体系的叠氮基α−N和B原子相连形成的环状结构。三聚体的船扭式构象比椅式构象的结合能低10.54 kJ•mol-1;四个新获得的四聚体的结合能差异较大,大小为3.1~45.65 kJ•mol-1。由焓变可知,单体形成二聚体在热力学上是不利的,而形成三聚体和四聚体在高达1200 K的温度下是有利的,同时分析比较了后续反应的热力学参数。 相似文献
136.
A series of chromium(III) complexes bearing 2-benzoxazolyl-6-aryliminopyridines was synthesized and characterized by IR spectroscopic and CHN analysis. The X-ray crystallographic analysis of complex Cr3 revealed a distorted octahedral geometry. When activated by Et2AlCl, MAO or MMAO, these chromium complexes exhibited activities towards ethylene reactivity. High activities of ethylene oligomerization (up to 9.19 × 106 g mol−1 (Cr) h−1) were observed in the catalytic system using MMAO as a cocatalyst, meanwhile good activities of ethylene polymerization were achieved (up to 5.20 × 105 g mol−1 (Cr) h−1) by using MAO as a cocatalyst. Various reaction parameters were investigated in detail, and the steric and electronic effects of ligands were discussed. 相似文献
137.
Kuhn P Sémeril D Jeunesse C Matt D Neuburger M Mota A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5210-5219
Three SHOP-type catalysts, in which the C=C(O) double bond was substituted by electron-withdrawing substituents, [Ni{Ph2PC(R1)=C(R2)O}Ph(PPh3)] (2: R1,R2 = -C(Me)=NN(Ph)-; 3: R1 = CO2Et, R2 = Ph; 4: R1 = CO2Et, R2 = CF3), were assessed as ethylene-oligomerisation and -polymerisation catalysts and compared to Keim's complex, [Ni{Ph2PCH=C(Ph)O}Ph(PPh3)] (1). A rationale for the influence of the double-bond substituents of the P,O-chelate unit on the catalytic properties is proposed, on the basis of X-ray diffraction studies, spectroscopic data and DFT-B3 LYP calculations. Whatever their relative electron-withdrawing strength, the R1 and R2 substituents induce an increase in activity with respect to catalyst 1. For those systems in which the basicity of the oxygen atom is decreased relative to that of the phosphorus atom, the chain-propagation rate increases with respect to that for catalyst 1. Reduction of the basicity of the P relative to that of the O, however, induces higher chain-termination rates. 相似文献
138.
Two novel dendritic poly(amido-amine) (PAMAM) bridged salicylaldimine ligands were synthesized by Schiff base reaction using 1.0 generation dendritic PAMAM as bridged groups. The cobalt complex with 1,4-butanediamine as core (C1) and the cobalt complex with 1,6-hexanediamine as core (C2) based on dendritic PAMAM bridged salicylaldimine ligands were prepared by metallic coordination reaction, respectively. The structures of the ligands and the dendritic cobalt complexes were characterized by fourier transform infrared (FTIR), ultraviolet spectra (UV), hydrogen nuclear magnetic resonance (1H NMR) and electrospray ionization mass spectra (ESI-MS). The complexes C1 and C2 were evaluated as catalyst precursors for ethylene oligomerization after being activated with methylaluminoxane (MAO), diethylaluminum chloride (Et2AlCl), ethylaluminium dichloride (EtAlCl2) and ethylaluminum sesquichloride (EASC). The dendritic cobalt complexes exhibited the highest activity and selectivity for high carbon oligomers with EASC as activator. Under the conditions of 1.0 MPa, 25°C and Al/Co molar ratio 1500, the catalytic activity and selectivity for C10–C20 using C1 were 3.44×106 g·(mol Co·h)?1 and 76.53% after activation with EASC, and the catalytic activity and selectivity for C10–C20 using C2 were 3.42×106 g·(mol Co·h)?1 and 84.50%, respectively. 相似文献
139.
Exocyclic Olefinic Maleimides: Synthesis and Application for Stable and Thiol‐Selective Bioconjugation 下载免费PDF全文
Dr. Dimpy Kalia Pushpa V. Malekar Manikandan Parthasarathy 《Angewandte Chemie (International ed. in English)》2016,55(4):1432-1435
Michael addition reactions between biological thiols and endocyclic olefinic maleimides are extensively used for site‐specific bioconjugation. The resulting thio‐succinimidyl linkages, however, lack stability because of their susceptibility to thiol exchange. Reported herein is that in contrast to their endocyclic counterparts, exocyclic olefinic maleimides form highly stable thio‐Michael adducts which resist thiol exchange at physiological conditions. A high‐yielding approach for synthesizing a variety of exocyclic olefinic maleimides, by 4‐nitrophenol‐catalyzed solvent‐free Wittig reactions, is reported. Mechanistic studies reveal that the catalyst facilitates the formation of the Wittig ylide intermediate through sequential proton donation and abstraction. Overall, this report details an improved thiol bioconjugation approach, a facile method for synthesizing exocyclic olefinic maleimides, and demonstrates that phenolic compounds can catalyze ylide formation. 相似文献
140.
As a representative folding system that features a conjugated backbone, a series of monodispersed (o‐phenyleneethynylene)‐alt‐(p‐phenyleneethynylene) (PE) oligomers of varied chain length and different side chains were studied. Molecules with the same backbone but different side‐chain structures were shown to exhibit similar helical conformations in respectively suitable solvents. Specifically, oligomers with dodecyloxy side chains folded into the helical structure in apolar aliphatic solvents, whereas an analogous oligomer with tri(ethylene glycol) (Tg) side chains adopted the same conformation in polar solvents. The fact that the oligomers with the same backbone manifested a similar folded conformation independent of side chains and the nature of the solvent confirmed the concept that the driving force for folding was the intramolecular aromatic stacking and solvophobic interactions. Although all were capable of inducing folding, different solvents were shown to bestow slightly varied folding stability. The chain‐length dependence study revealed a nonlinear correlation between the folding stability with backbone chain length. A critical size of approximately 10 PE units was identified for the system, beyond which folding occurred. This observation corroborated the helical nature of the folded structure. Remarkably, based on the absorption and emission spectra, the effective conjugation length of the system extended more effectively under the folded state than under random conformations. Moreover, as evidenced by the optical spectra and dynamic light‐scattering studies, intermolecular association took place among the helical oligomers with Tg side chains in aqueous solution. The demonstrated ability of such a conjugated foldamer in self‐assembling into hierarchical supramolecular structures promises application potential for the system. 相似文献