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1.
The directed oligomerization of propene and 1-hexene was carried out with a series of Cp′(C 5H 5)ZrCl 2 and Cp 2′ZrCl 2 pre-catalysts (Cp′=C 5HMe 4, C 4Me 4P, C 5Me 5, C 5H 4tBu, C 5H 3-1,3- tBu 2, C 5H 2-1,2,4- tBu 3) together with (C 5H 5) 2ZrCl 2. Oligomers in the molar mass range 300–1500 g/mol for propene and 200–3000 g/mol for 1-hexene were synthesized at 50 °C. The majority of oligomer molecules contain a double-bond end group. Oligomer characterization was carried out by gel permeation chromatography (GPC), 1H and 13C NMR. Vinylidene double bonds (from β-hydrogen elimination) are solely found for the tert-butyl-substituted zirconocenes and for most of the unsymmetrical methyl-substituted Cp′(C 5H 5)ZrCl 2 systems (except Cp′=phospholyl). With (C 4Me 4P)(C 5H 5)ZrCl 2 and with the symmetrical methyl-containing Cp 2′ZrCl 2 pre-catalysts, also vinyl end groups (from β-methyl elimination) are observed in the case of oligopropenes. The vinylidene/vinyl ratio depends on the ligand and the vinyl content increases from C 5HMe 4 (65/35) over C 4Me 4P (61/39) to C 5Me 5 (9/91). The phospholyl zirconocenes and (C 5HMe 4) 2ZrCl 2 also exhibit chain-transfer to aluminum thereby giving saturated oligomers. 相似文献
2.
以Ni +与C 3H 8反应作为过渡金属离子与烷烃反应的范例体系,用B 3LYP密度泛函方法计算了[Ni,C 3,H 8] +基态势能面上各驻点的构型、频率和能量,结果表明,该反应的H 2分子消除需经历两个基元步骤,即Ni +首先插入一级或二级C-H键,然后经H转移过渡态异构化为较稳定的中间体,继而解离产生H 2分子.计算的反应热为142.28kJ/mol,与相应的实验值(127.85kJ/mol)符合较好. 相似文献
3.
采用密度泛函理论UB3LYP/6-31G(d)方法,对模型化合物纤维二糖热解反应机理进行了量子化学理论计算研究。设计了三种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了不同温度下热解反应的标准热力学和动力学参数。计算结果表明,糖苷键均裂而形成两个自由基中间体IM 1a和IM 1b,吸收热量为321.26kJ/mol,中间体IM 1a经过渡态TS 1a进一步形成左旋葡聚糖P 1,反应势垒为202.72kJ/mol;与分步反应相比,纤维二糖经过渡态TS 2协同反应直接形成左旋葡聚糖P 1和吡喃葡萄糖P 2的反应势垒低于分步反应的总势垒,其反应势垒为377.54kJ/mol;H +的加入有利于糖苷键的断裂,断裂形成的中间体IM 3很难进一步反应形成左旋葡聚糖。 相似文献
4.
The complex triplet potential energy surface of the C 2H 3N system is investigated at the UB3LYP and CCSD(T) (single-point) levels in order to explore the possible reaction mechanism of C 2H 3 radical with N( 4S). Eleven minimum isomers and 18 transition states are located. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained. Starting from the energy-rich reactant C 2H 3+N( 4S), the first step is the attack of the N atom on the C atom having one H atom attached in C 2H 3 radical and form the intermediate C 2H 3N(1). The associated intermediate 1 can lead to product P 1 CH 2CN+H and P 2 3CH 2+ 3HCN by the cleavage of C–H bond and C–C bond, respectively. The most favorable pathway for the C 2H 3+N( 4S) reaction is the channel leading to P 1, which is preferred to that of P 2 due to the comparative lower energy barrier. The formation of P 3 3C 2H 2+ 3NH through hydrogen-abstraction mechanism is also feasible, especially at high temperature. The other pathways are less competitive comparatively. 相似文献
5.
Two new half-sandwich zirconium(IV) complexes bearing salicylaldimine ligands of the type Cp*Zr[2-tBu-4-R-6-(CH=NiPr)C6H2O]C12[R=H(1), tBu(2)] were prepared by the reaction of Cp*ZrC13 with the corresponding lithium of salicylaldimine ligands 2-tBu-4-R-6-(CH=NiPr)C6H2OLi[R=H(LiLa), tBu(LiLb)]. Com- plexes 1 and 2 were characterized by 1H NMR, BC NMR spectroscopy and elemental analysis. When activated with AliBu3 and Ph3CB(C6F5)4, both complexes 1 and 2 exhibited reasonable catalytic activities for ethylene polymeriza- tion, producing polyethylenes with moderate molecular weight. Complexes 1 and 2 also exhibited reasonable catalyt- ic activities for ethylene copolymerization with 1-hexene, producing poly(ethylene-co-l-hexene)s with moderate molecular weight and reasonable 1-hexene content. 相似文献
6.
The coordinatively unsaturated uranium(IV) complex U[N(C 6H 5) 2] 4 has been prepared via the stoichiometric reaction of diphenylamine with [(Me 3Si) 2N] 2
H 2. U[N(C 6H 5) 2] 4 coordinates Lewis bases such as Et 2O, THF, pyridine or (EtO) 3PO, based on electronic absorption spectroscopy and 1H NMR studies. Exchange between U[N(C 6H 5) 2] 4 and U[N(C 6H 5) 2] 4(L), where L is THF or pyridine, is rapid on the NMR time-scale between 307 and 323 K. Measurement of equilibrium constants for L = THF provides Δ H and Δ S values of −60 kJ mol −1 and −1.8 × 10 2 J K −1 mol −1, respectively. U[N(C 6H 5) 2] 4 coordinates and binds (EtO) 3PO much more tightly ( Keq = & > 10 4 M −1) than THF or pyridine with the exchange rate between U[N(C 6H 5) 2] 4 and U[N(C 6H 5) 2] 4[OP(OEt) 3] being close to the NMR time-scale. 相似文献
7.
In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A 2A″ state (C 2H 3 (A 2A″)) and examined possible pathways for nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+). In the calculations we used the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the cc-pVDZ and cc-pVTZ basis sets. Mechanisms for the following three dissociation channels of C 2H 3 in the A 2A″ state were explored: (1) C 2H 3 (A 2A″) → C 2H 2 ( trans, 3A u) + H, (2) C 2H 3 (A 2A″) → C 2H 2 ( cis, 3A 2) + H, and (3) C 2H 3 (A 2A″) → H 2CC ( 3A 2) + H. The CASSCF and CASPT2 potential energy curve calculations for the C 2H 3 (A 2A″) dissociation channels (1)–(3) indicate that there is neither transition state nor intermediate for each of the channels. At the CASPT2//CASSCF/cc-pVTZ level, the dissociation energies for channels (1)–(3) are predicted to be 84.3, 91.1, and 86.9 kcal/mol, respectively. For a recently observed nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+) + H [J. Chem. Phys. 111 (1999) 3783], two previously suggested internal conversion (IC) pathways were examined based on our CASSCF and CASPT2 calculations. Our preliminary CASSCF and CASPT2 calculations indicate that the assumed IC pathway via the twisted C 2H 3 (A 2A ′) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C 2v bridge structures in the 2B 2, 2A 2, 2B 1, and 2A 1 states along the pathways of the 1 2A ′ (X 2A ′), 1 2A″ (A 2A″), 2 2A″, and 2 2A ′ states of C 2H 3, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C 2v ( 2A 2) structure and then 2A 2/ 2A 1 surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C 2v ( 2A 2) structure could not be accessed. 相似文献
8.
运用密度泛函(DFT)理论,采用Materials Studio 8.0,用GGA/BP方法研究了C_6H_2(OH)_3CH_3氧化成羟基苯甲酸的反应路径。结果表明,甲基上的氢原子被氧化成羟基以及羟基被氧化为醛基及醛基被氧化成羧基均为放热过程。分子C_6H_2(OH)_3CH_3中甲基氧化成羧基的主路径为三个氢原子氧化反应路径,其路径为C_6H_2(OH)_3CH_3+3O→C6H2(OH)3C(OH)3→C6H2(OH)3COOH+H2O,该路径受限于羟基直接被氧化成羧基过程,需克服130 k J/mol的反应势垒,反应速率常数对数ln(k)为-22.96 s-1;醛基、羟基优先被氧化成羧基的顺序为:-CHO-C(OH)3-HC(OH)2-H2C(OH);提高反应温度、氧气浓度均有利于羟基苯甲酸的生成,适当的催化剂有利于促进整个反应的进行。 相似文献
9.
CpIr(η 4-C 6H 6) (2) has been obtained in high yield by a four-step synthesis. Thermal reaction of 2 with CpCO(C 2H 4) 2 and photochemical reaction of 2 with CpRh(C 2H 4) 2 or CpRh(C 2H 4) 2 give the compounds μ-(η 3: η 3-C 6H 6)CoIrCp 2 (3), μ-(η 3: η 3-C 6H 6)RhIrCp 2 (4), and μ-(η 3: η 3-C 6H 6)(RhCp)(IrCp) (5), respectively. The X-ray crystallography data of 3 and 4 reveal a boat-shaped conformation of the synfacially bridging benzene ligand with a rather long Co---Ir bond distance in 3 and a relatively short Rh---Ir bond length in 4 which are caused by almost constant folding angles of the benzene unit. The dynamic behaviour of the benzene bridge was investigated by NMR spectrometry. 相似文献
10.
A Co-based two-dimensional (2D) microporous metal-organic frameworks (UPC-32) with narrow distance between layers and layers (3.8 Å) exhibits high selectivity of C 3H 6/CH 4 (31.46) and C 3H 8/CH 4 (28.04) at 298 K and 1 bar. It is the first 2D Co-MOF that showed selective separation of C3 hydrocarbon from CH 4. 相似文献
11.
The oxidative dehydrogenation of ethane over NiO-loaded MgO with high surface area was carried out using a fixed-bed flow reactor at 600 °C under atmospheric pressure. At 600 °C, the oxidative dehydrogenation of ethane (C2H6/O2 = 1) without dilution with an inert gas resulted in C2H6 conversion of 68.8% and a high C2H4 selectivity of 52.8%, which corresponds to a C2H4 yield of 36.3%. In addition, the catalytic activity did not decrease for at least 10 h. X-ray photoelectron spectra of the catalysts after the reaction exhibited that the initial valence state of Ni2+ (NiO) was maintained during the oxidative dehydrogenation of ethane. However, when NiO-loaded MgO was reduced with H2 prior to the reaction, C2H4 selectivity decreased to nearly zero and high CO and H2 selectivities were observed with the C2H6 conversion of 50 %, indicating that partial oxidation of C2H6 proceeded. Therefore, it seems important to keep Ni species as an oxide phase on the support, and for this purpose, use of the high surface area of MgO is essential. 相似文献
12.
Reaction of R---N=C=N---R (R= p-Me-C 6H 4) and R---P==C=P---R (R=2,4,6- tBu 3C 6H 2) with the di-iron aminocarbene complex [Fe 2(CO) 7{1μ-C(Ph)C(NEt 2)}] (1c) gave corresponding complexes [Fe 2(CO) 6{C(Ph)C(NEt 2)C(NC 6H 4Me)N (C 6H 4Me)}] (2) and [Fe 2(CO) 6{C(Ph)C(NEt 2)C(PC 6H 2tBu 3)P(C 6H 2tBu 3)}] (4), resulting from a coupling reaction with carbon-carbon bond formation. [Fe 2(CO) 5(CNC 6H 4Me){C(Ph)C(NEt 2)N(C 6H 4Me)}], complex 3, obtained in the reaction with R---N=C=N---R, resulted from C=N bond rupture insertion of a nitrene fragment into the Fe=C bond. Complexes 2–4 were characterized by X-ray diffraction. The different geornetries of complexes 2 and 4 are discussed. The formation of these complexes may be explained by cycloaddition on the Fe =C metal-carbene bond. 相似文献
13.
硫代嘧啶碱基是光动力疗法潜在的重要光敏剂,其最低单重激发态的光物理研究已有广泛报道。然而,其较高激发态的跃迁性质和反应动力学研究较为稀少。因此,本文采用共振拉曼光谱和密度泛函理论计算方法研究2,4-二硫代尿嘧啶的紫外光谱和几个较高单重激发态的短时结构动力学。首先,基于共振拉曼光谱强度与电子吸收带振子强度f的关系,将紫外光谱去卷积成四个吸收带,分别为358 nm(f=0.0336)中等强度吸收带(A带),338 nm(f=0.1491)、301 nm(f=0.1795)和278 nm(f=0.3532)强而宽的吸收带(B、C和D带)。这一结果既吻合密度泛函理论计算结果,又符合共振拉曼光谱强度模式对紫外光谱带的预期。据此,去卷积得到的四个吸收带被分别指认为S0→S2跃迁、S0→S6跃迁、S0→S7跃迁和S_0→S_8跃迁。同时,分别对B,C和D带共振拉曼光谱进行了详细的指认,获得了短时动力学信息。结果表明,S_8态短时动力学的显著特征是在Franck-Condon区域或附近发生了S8(ππ~*)/S(nπ~*)势能面交叉引发的、伴随超快结构扭转的非绝热过程。S7和S6态短时动力学的主要特征是反应坐标的多维性,它们分别沿C_5C_6/C_2S_8/C_4S_(10)/N_2C_3+C_4N_3H_9/N_1C_2N_3/C_2N_1C_6/C_6N_1H_7/C_5C_6H_(12)和C_5C_6/N_3C_2/C_4S_(10)/C_2S_8+C_6N_1H_7/C_5C_6H_(12)/C_5C_6N_1/C_5C_6H_(12)/C_2N_1C_6/N_1C_2N_3/C_4N_3H_9/N_1C_2N_3等内坐标演化。 相似文献
14.
The complexes [Zn 2(S 2CTR) 4] (T = 2,5-disubstituted thiophene, R = C 4H 9 (1), C 6H 13 (2), C 8H 17 (3), C 12H 25 (4) and C 16H 33 (5)) have been synthesized and their structural features investigated. Compared to the analogous dithiobenzoate complexes, the crystal structure determination of 2 revealed that the thiophene induces a “step-rod” chain pattern instead of the linear, rodlike structure found for the corresponding dithiobenzoates. Complexes 1–5 did not display mesophases under thermal conditions, but an irregular melting pattern was observed for 3 and 4. 相似文献
15.
The molecular structures and electron affinities of the C 6HCl 5 and C 6Cl 6 molecules have been determined using seven pure Density Functional Theory (DFT) or hybrid Hartree–Fock/DFT methods. The EAs of ten kinds of monochlorobenzene, dichlorobenzene, trichlorobenzene and tetrachlorobenzene are also predicted. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem. Rev. 2002, 102, 231). The geometries are fully optimized with each DFT method independently. The equilibrium configuration of hexachlorobenzene is found to be planar with D6h symmetry. The pentachlorobenzene is planar with C2υ symmetry. Three different types of the neutral-anion energy separations reported in this work are the adiabatic Electron Affinity (EA ad), the vertical Electron Affinity (EA vert), and the Vertical Detachment Energy (VDE). The most reliable adiabatic electron affinities of the chlorinated benzenes obtained at the BHLYP level of theory are −0.18 eV (C 6H 5Cl), 0.07 eV (1,2-C 6H 4Cl 2), 0.07 eV (1,3-C 6H 4Cl 2), 0.04 eV (1,4-C 6H 4Cl 2), 0.29 eV (1,2,3-C 6H 3Cl 3), 0.31 eV (1,2, 4-C 6H 3Cl 3), 0.31 eV (1,3,5-C 6H 3Cl 3), 0.51 eV (1,2,3,4-C 6H 2Cl 4), 0.48 eV (1,2,4,5-C 6H 2Cl 4), 0.50 eV (1,2,3,5-C 6H 2Cl 4), 0.74 eV (C 6HCl 5) and 0.79 eV (C 6Cl 6), respectively. 相似文献
16.
Spatial structure of six β-substituted enones, with common structure R 1O–CR 2CH–COCF 3, were R 1 = C 2H 5, R 2 = H (ETBO); R 1 = R 2 = CH 3 (TMPO); R 1 = C 2H 5, R 2 = C 6H 5 (ETPO); R 1 = C 2H 5, R 2 = 4- O 2NC 6H 4 (ETNO); R 1 = C 2H 5, R 2 = C(CH 3) 3 (ETDO) were investigated by 1H and 19F NMR, infrared spectroscopy and AM1 calculations. NMR spectra revealed that enones (MBO), (ETBO) and (TMPO) are exclusively (3 E) isomers, whereas in (ETPO), (ETNO) and especially in (ETDO) the percentage of (3 Z) isomers is significant and depends on the nature of solvents. Conformational behaviour of studied enones are determined by the rotation around of CC double bond, C–C and C–O single bonds (correspondingly trifluoroacetyl and alkoxy groups), and ( EZZ) conformer being the most stable in all cases. IR spectra revealed that with the exception of (ETDO) ( EZZ) conformer is most populated in all cases. Bulky substituents like phenyl or tert-butyl group at β-position of enone result in the equilibrium mainly between ( EZZ) and ( ZZZ) forms, whereas β-hydrogen and β-methyl substituents determine the equilibrium between ( EZZ) and ( EEZ) or ( EZE) conformers. 相似文献
17.
The title compound 2,3-dicyclopentadiene-2,3-dimethylbutane (C 5H 5CMe 2CMe 2C 5H 5) 1 shows the typical staggered conformation of a highly substituted ethane derivative with the two largest substituents (C 5H 5) adopting a trans position. The molecule shows C 2 symmetry about the central C–C bond. Due to the high substitution, the central bond of the ethane is elongated to 160.0 pm (X-ray structure analysis) while the DFT calculation finds a value of 159.2 pm. 相似文献
18.
对2~6个环的多环芳烃的氢提取反应类进行了系统研究, 提取氢原子的不饱和自由基包括丙炔基自由基(C 3H 3)、 烯丙基自由基(C 3H 5)、 丁二烯基自由基(nC 4H 5, iC 4H 5)、 环戊二烯基自由基(C 5H 5)以及苯基自由基(C 6H 5). 采用M06-2X/cc-pVTZ方法得到了多环芳烃的电子结构信息, 利用过渡态理论并结合Eckart隧道校正, 计算了所有反应在500~2500 K范围内的反应速率常数.考察了多环芳烃的大小、 结构对反应速率常数的影响, 对比了不同氢提取自由基及不同氢提取反应类型的速率常数. 结果表明, 多环芳烃的大小对反应速率常数影响不大, 但是多环芳烃的环结构对反应速率常数影响较大. 将不同的氢提取反应类简化为发生在五元环上的C 5类和发生在六元环上的C 6类两类, 结果表明, C 6类的反应活性高于C 5类. 研究了nC 4H 5, iC 4H 5以及C 6H 5自由基与多环芳烃的氢提取反应, 它们的氢提取反应活性大小顺序为C 6H 5>nC 4H 5>iC 4H 5. 通过对每类典型反应的速率常数取平均值, 总结出相应类型的速率规则, 可用于构建多环芳烃和碳烟机理. 相似文献
19.
Using velocity map ion imaging technique, the photodissociation of n-C 4H 9Br in the wavelength range 231–267 nm was studied. The results and our ab initio calculations indicated that the absorption of n-C 4H 9Br in the investigated region originated from the excitations to the lowest three repulsive states, as assigned as 1A″, 2A′ and 3A′ in C s symmetry. Dissociations occurred on the PES surfaces of the three states, terminating in C 4H 9+Br ( 2P 3/2) or C 4H 9 + Br * ( 2P 1/2) as two channels, and being impacted by an avoided crossing between the PES surfaces of the 2A′ and 3A′ states. The transition dipole to the 1A″ state was perpendicular to the symmetry plane, so perpendicular to the C–Br bond. The transitions to the 3A′ state was polarized parallel to the symmetry plane, and also parallel to the C–Br bond. While the transition dipole to the 2A′ state was in the symmetry plane, but formed an angle of about 53.1° with the C–Br bond. We have also determined the avoided crossing probabilities, which affected the relative fractions of the individual pathways, for the photolysis of n-C 4H 9Br near 234 nm and 267 nm. 相似文献
20.
The thermolysis of C 60H 2 to yield C 60 and H 2 was studied by hybrid density functional theory (B3LYP/6-311G**//B3LYP/3-21G). The concerted loss of dihydrogen requires an activation energy of 92 kcalmol −1 at T=452 K. An alternative radical mechanism, which is first order in the C 60H 2 concentration, has an activation energy at 452 K of only 61 kcalmol −1. Monitoring of the C 60H 2 decomposition in 1,2-dichloro-[D 4]-benzene solution by NMR spectroscopy indicates a pseudo first-order reaction with an activation energy of 61.38±2.35 kcalmol −1. 相似文献
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