Iron and cobalt complexes are a new family of catalysts for ethylene oligomerization and polymerization. The extensive researches on bis(imino)pyridyl metal complexes have been carried out with the aim of synthesizing their derivatives and finding suitable reaction parameters for the optimum activity. Beyond the modification works of bis(imino)pyridyl metal complexes, several alternative models with similar coordination sphere have been developed in our group. This review article describes our experiences in innovating new models of iron and cobalt complexes as catalysts for ethylene oligomerization and polymerization. 相似文献
<正>The discovery of highly active 2,6-bis(imino)pyridyl iron and cobalt complexes provided a milestone of latetransition metal catalysts for ethylene oligomerization and polymerization with being currently investigated for the scale-up process.The crucial problems are remaining in the catalytic systems:the catalytic systems targeting ethylene polymerization produce more oligomers at elevated reaction temperatures,however,there is a recognizable amount of high-molecular-weight polyethylene remained in the modified catalytic system for the oligomerization process.Beyond the modification of bis(imino)pyridyl metal complexes,several alternative procatalysts' models have been developed in our group.This review highlighted the achievements in exploring new iron and cobalt complexes with tridentate NNN ligands as procatalysts for ethylene oligomerization and polymerization. 相似文献
To reduce the simultaneous production of insoluble polymers during the bis(imino)pyridyl iron‐catalyzed ethylene oligomerization, in this study, p‐BrPhOH (4‐bromophenol) has been chosen as the most optimal modifier for the production of linear α‐olefins. It is found that the polymer share in the total products is largely reduced with the use of p‐BrPhOH as the modifier. The catalytic system also possesses a high activity with the liquid production maintained high level of linearity. Moreover, the introduction of p‐BrPhOH promoted the high‐temperature stability of the catalytic system, leading to the enhanced oligomerization activity as the catalytic system can catalyze ethylene oligomerization at higher temperatures. A characterization of the catalytic system with electron paramagnetic resonance shows that introduction of p‐BrPhOH significantly inhibits the formation of ferric ions, which can be the main active centers responsible for generating undesired insoluble polymers, thus this can largely retard the production of insoluble polymers during ethylene oligomerization. 相似文献
Ethylene polymerizations carried out with various bis(imino)pyridyl iron, chromium and vanadium complexes immobilized on a MgCl2/AlRn(OEt)3−n support gave relatively broad polyethylene molecular weight distributions in the case of iron, but high molecular weight and a very narrow molecular weight distribution with vanadium, indicative of a single active species. The narrow MWD was confirmed by melt rheometry. Similar results were obtained after reaction of the bis(imino)pyridyl complex LVCl3 (6) with MeLi or AlEt3, where alkylation of the pyridine ring gives a complex L′VCl2 (7). In the case of chromium, a bimodal distribution was obtained, with evidence of incomplete catalyst immobilization. The polyethylene molecular weights obtained with the iron complexes were strongly dependent on the substituents in the bis(imino)pyridyl ligand, and were somewhat higher than have been obtained in homogeneous polymerization. In contrast, the molecular weights obtained with the bis(imino)pyridyl chromium and vanadium complexes were much higher that those previously obtained under homogeneous conditions. In all cases, the activities of the immobilized catalysts were higher than those found in homogeneous polymerization. 相似文献
Bis(imino)pyridyl Fe(II) complexes are important catalysts in ethylene oligomerization for preparing α-olefins. The metal net charge-activity relationship of bis(imino)pyridyl Fe(II) complexes was investigated by molecular mechanics (MM) and net charge equilibration (QEq) method with modified Dreiding force field. It was found that metal net charge was in reverse ratio to ethylene oligomerization activity. Electron-donor substituents with less steric hindrance to the central metal were favorable to Fe complex activity. Metal net charge-activity relationship could be used to assist the design of new Fe oligomerization catalysts with higher activity. 相似文献
A surface science model for a silica supported bis(imino)pyridyl iron complexes is applied to reveal the surface chemistry of these heterogeneous polymerization catalysts. The polymerization activity of these models and the molecular weight distribution of the resulting polymer are comparable to similar catalysts supported on amorphous silica. The catalyst deactivates partially during the first hour of ethylene polymerization. Based on photoelectron spectroscopy (XPS) we attribute this deactivation to iron extrusion by the aluminium alkyl activator. 相似文献
Summary: The bis(imino)pyridyl vanadium(III ) complex [VCl3{2,6‐bis[(2,6‐iPr2C6H3)NC(Me)]2(C5H3N)}] activated with different aluminium cocatalysts (AlEt2Cl, Al2Et3Cl3, MAO) promotes chemoselective 1,4‐polymerization of butadiene with activity values higher than classical vanadium‐chloride‐based catalysts. The polymer structure depends on the nature of the cocatalyst employed. The MAO‐activated complex was also found to be active in ethylene‐butadiene copolymerization, producing copolymers with up to 45 mol‐% of trans‐1,4‐butadiene. Crystalline polyethylene and trans‐1,4‐poly(butadiene) segments were detected in these copolymers by DSC and 13C NMR spectroscopy.
Summary: A well‐defined flat model of a supported homogeneous polyolefin catalyst is prepared on the basis of an immobilized bis(imino)pyridyl iron complex on a super flat silica surface. The amount of supported catalyst precursor is quantified using XPS. This model catalyst remains active over extended periods, i.e., an average activity of 0.25 × 103 kg PE · (molCat · h · bar)−1 is obtained for 24 h of ethylene polymerization. The morphology of the nascent polyethylene film is investigated by SEM.
A side‐view SEM image of the PE produced from the supported bis(imino)pyridyl Fe catalyst. 相似文献
Data on ethylene polymerization on homogeneous and supported catalysts based on 2,6-bis(imino)pyridyl Fe(II) complexes activated by trialkylaluminums are considered (activity, the molecular-weight characteristics of polymers, the number of active sites, and the propagation rate constants). Unlike homogeneous systems, the supported catalysts prepared with the use of various carriers (SiO2, Al2O3, and MgCl2) exhibited high stability and activity at 70–80°C and produced high-molecular-weight polyethylene with a broad molecular-weight distribution (MWD). The molecular weights and MWDs of polymers and the propagation rate constant depended on the nature of the carrier only slightly. The reasons for an unusual effect of an increase in the activity of the supported catalysts in ethylene polymerization in the presence of hydrogen are discussed. 相似文献
Unique features of earth‐abundant transition‐metal catalysts are reviewed in the context of catalytic carbon–carbon bond‐forming reactions. Aryl‐substituted bis(imino)pyridine iron and cobalt dihalide compounds, when activated with alkyl aluminum reagents, form highly active catalysts for the polymerization of ethylene. Open‐shell iron and cobalt alkyl complexes have been synthesized that serve as single‐component olefin polymerization catalysts. Reduced bis(imino)pyridine iron and cobalt dinitrogen compounds have also been discovered that promote the unique [2+2] cycloaddition of unactivated terminal alkenes. Studies of the electronic structure support open‐shell intermediates, a deviation from traditional strong‐field organometallic compounds that promote catalytic C−C bond formation. 相似文献