Novel functionalized bis(imino)pyridine cobalt(II) catalysts for ethylene polymerization

This report describes synthesis and ethylene polymerization in the various conditions by two novel 2,6-bis(imino)pyridine (BIMP) catalysts B and C based on cobalt activated by methylaluminoxane (MAO) in a slurry semi-batch reactor. The catalyst activities as well as polymer properties were affected dramatically by electronic effects of the attached substitutions on the para-position of the pyridine ring. Theoretical study exhibited more positive charge on the central metal of the catalyst B resulted in higher activity at the expense of lower thermal stability and lifetime. The polymer obtained using the catalysts exhibited high molecular weight and almost narrow molecular weight distribution (MWD) ranging from 2.35 to 4.10 at the employed polymerization conditions. The highest and lowest molecular weight of the obtained polymers were produced by the catalyst A and C respectively. Hydrogen could slightly increase the catalyst activities with the exception of the catalyst B. The catalyst C bearing electron-donor OMe substitution at the para-position of the pyridine ring, produced PE with narrower PDI relative to the polymer resulted by catalysts A and B.     

Homogeneous catalysts for ethylene polymerization based on bis(imino)pyridine complexes of iron, cobalt, vanadium and chromium

Results of a comparative study of ethylene polymerization activity and the structure of polyethylene (PE) produced over homogeneous catalysts based on bis(imino)pyridine complexes with close ligand frameworks and different transition metal centers (Fe(II), Co(II), Cr(III) and V(III)) are reported. The effects of the activator nature and polymerization conditions on the activity of these complexes and the resulting PE structure (molecular weight, molecular weight distribution, content of methyl and vinyl groups) have been studied. The experimental data obtained under comparable conditions demonstrate a pronounced effect of transition metal center on the catalytic properties of bis(imino)pyridine complexes (polymerization activity, copolymerization reactivity, thermal stability, PE structure, composition of optimal activator, formation of single-site or multiple-site catalytic system).     

铁(钴)系吡啶二亚胺类催化剂研究发展

综述了Fe(Co)系吡啶二亚胺类催化剂的研究情况，介绍了催化剂的合成及其结构特征、催化乙烯聚合的反应机理、聚合反应特点以及影响因素等，详细列举了各个因素对催化活性和聚合物分子量的影响情况。对该类催化剂的应用进行概括，并展望了其今后的发展方向。     

QSAR model for ethylene polymerisation catalysed by supported bis(imino)pyridine iron complexes

We present a quantitative structure–activity relationship study performed over a set of bis(imino)pyridine iron catalyst used for olefin polymerisation. The experimental results were previously obtained by our research group. The structural variability of this catalyst set is mainly focused on the substituents of the aryl rings. We managed to find a statistically robust model which correlates the experimentally determined polymer's molecular weight with the steric and electrostatic fields. As a result the main contribution comes from the steric contribution which amounts up to 75% of the model. The predictive capability of the model was successfully probed with a test set of catalyst reported in the literature by other research group.     

Ethylene polymerization with homogeneous and heterogeneous catalysts based on bis(4‐fluorophenyl)methyl‐substituted bis(imino)pyridyliron complexes

A series of bis(4‐fluorophenyl)methyl‐substituted bis(imino)pyridyliron chloride complexes were immobilized on oxide supports. The kinetics of ethylene polymerization by both homogeneous and heterogeneous systems was followed, the catalysts mostly demonstrating high activities. The effect of the ligands nature and reaction conditions on the catalytic activities and molecular weights of the resultant polyethylenes was examined. In contrast to homogeneous systems, the supported iron complexes were found to exhibit high and stable activity upon activation with triisobutyl aluminium, producing high‐molecular‐weight polyethylene with good morphology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42674.     

Fe(acac)3‐bis(imino)pyridine/MAO: A new catalytic system for ethylene polymerization

Formulations of chemically crosslinked and radiation-crosslinked low-density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with poly(ethylene vinyl acetate) (EVA) as well as the effects of a coadditive such as talc on flammability was investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron-beam accelerator were both used and compared. An increase in the limiting oxygen index (LOI) was found by the partial replacement of LDPE with EVA. The effect of talc on the flammability depended on the amount of talc in the formulations. The addition of a small amount of talc increased LOI and reduced smoke during cone calorimeter measurements. A higher amount of talc led to a decrease in the LOI values. Formulations crosslinked by ionizing radiation yielded lower LOI values than chemically crosslinked formulations. This could be attributed to the use of trimethylolpropane triacrylate as a crosslinking coagent in formulations crosslinked by ionizing radiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of compositional heterogeneity in the polyethylene prepared with bis(imino)pyridyl iron(II) precatalyst and triethylaluminum

Analytical tools including solvent gradient elution fractionation (SGEF), GPC, ¹³C NMR, and differential scanning calorimetry (DSC) are integrated for the characterization of compositional heterogeneity in the polyethylene (PE) prepared with the LFeCl₂/AlEt₃ catalytic system. The results indicate that at least two different kinds of catalytic species are present in ethylene polymerization. One active species generating branched PE gives low molecular weight; another kind of active species gives high molecular weight PE with high linear structure. The amount of branch decreases with increasing the molecular weights, and the small proportion of the branched PE shows low molecular weight with vinyl‐terminated end group, indicating that the branched PE is generated from the catalytic species giving low activity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polymerization of 1,3-butadiene by bis(salicylaldiminate)cobalt(II) catalysts combined with organoaluminium cocatalysts

The one-pot reactions of salicylaldehyde or its derivatives with 2,6-dialkyl substituted anilines in the presence of metallating agent, Co(OAc)₂.4H₂O, yield a series of cobalt(II) complex precatalysts (Ar¹-NC-Ar²-O)₂Co (1, Ar¹ = 2,6-dimethylaryl, Ar² = aryl; 2, Ar¹ = 2,6-diethylaryl, Ar² = aryl; 3, Ar¹ = 2,6-diisopropylaryl, Ar² = aryl; 4, Ar¹ = 2,6-dimethylaryl, Ar² = 3-t-butylaryl; 5, Ar¹ = 2,6-diethylaryl, Ar² = 3-t-butylaryl; 6, Ar¹ = 2,6-diisopropylaryl, Ar² = 3-t-butylaryl) in high yields. The treatment of these cobalt(II) salicylaldimine complexes with ethylaluminum sesquichloride (EAS) forms highly active 1,3-butadiene (BD) polymerization catalysts, yielding polybutadienes of moderate molecular weights (MW = 33,900–44,500) with narrow molecular weight distributions (MWD = 1.29–2.36). All Co(II) complexes yield highly cis-1,4-polybutadienes (>94%) with negligible amounts of 1,4-trans (<2.32%) and 1,2-added (<3.37%) products in polymerizations at 30 °C combined with EAS. As the steric bulk at the cobalt center increases by changing the alkyl substituents on the ligand environment, 1,4-cis content decreases. The cis content and MW decrease as polymerization temperature increases. The polymerization yield and the cis content increase as BD concentration increases. The nonlinearity of [BD] to yield and [BD] to MW relationships demonstrates that the narrow MWD comes from uniform active species present in the polymerization system. The activation procedures of the Co(II) complexes in conjunction with EAS are studied by using UV-visible spectroscopy. Suitable correlations are found between polymerization activities and the changes in UV-visible absorption spectra of the complex.     

Fe(acac)n and Co(acac)n bearing different bis(imino)pyridine ligands for ethylene polymerization and oligomerization

A series of iron and cobalt complexes ligated with different bis(imino)pyridyl ligands were synthesized and used in ethylene polymerization. The reaction temperature and Al/Fe ratio had a great influence on the activities and properties of the polymer in the iron system when methylaluminoxane was used as the cocatalyst. Bimodal polyethylene, unimodal polyethylene, and oligomers were achieved with ethylene polymerization according to the structures of the ligands and polymerization conditions. The cobalt systems showed low activities when bis(imino)pyridyl was used as the ligand in comparison with the iron system catalysts. Ethylene oligomerization was conducted, and the main products were 1‐butylene and 1‐hexene. A fast deactivation process was observed from the curve of the polymerization kinetics. The polymerization mechanism was examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Quantum-chemical calculations of the effect of cycloaliphatic groups in α-diimine and bis(imino)pyridine ethylene polymerization precatalysts on their stabilities with respect to deactivation reactions

For the first time, it is attempted to interpret an experimentally found enhancing effect of cycloaliphatic substituents in aromatic rings of Ni^II- and Pd^II-α-diimine and Fe^II-bis(imino)pyridine ethylene polymerization precatalysts on their catalytic activities at elevated temperatures (60-80 °C), using quantum chemical density functional theory calculations of relative stabilities of the complexes with respect to different deactivation processes, including thermal decomposition and one-electron reduction. It was shown that the effect correlates with the calculated higher thermal stabilities of cycloalkyl-substituted Fe^II-, Ni^II- and Pd^II-complexes as compared to the corresponding alkyl-substituted ones. Ni^II- and Pd^II-α-diimine complexes with cycloalkyl substituents are shown to be more stable than their alkyl-substituted analogues with respect to both thermal decomposition and one-electron reduction. The averaged difference of the thermal decomposition energies between the complexes with cycloaliphatic substituents on one side and aliphatic ones on the other side is ∼2.3 kcal/mol, corresponding to ∼30 times lower equilibrium constant of the thermal decomposition reaction for the cycloalkyl-containing complexes. For the Fe^II- and Pd^II-complexes, the thermal stability correlates with the calculated overlap population of the metal-nitrogen bonds. It was shown that the structure of o-substituents (cycloalkyls vs. alkyls) in the phenyl rings of the ligands does not affect the reaction energies for the transformation reactions of the precatalysts into their corresponding active catalytic cationic forms.     

Highly active and selective ethylene oligomerization catalysts: Asymmetric 2,6-bis(imino)pyridyl iron (II) complexes with alkyl and halogen substitutients

A series of asymmetric 2,6-bis(arylimino)pyridines with alkyl and halogen substitutients on different iminoaryl rings and corresponding iron (II) complexes ([2-(Ar₁N = CCH₃)-6-(Ar₂N = CCH₃)C₅H₃N]FeCl₂, 3a–3j) are synthesized and characterized. These Fe(II) complexes are highly active for ethylene oligomerization with high selectivity for linear α-olefins. The oligomer distributions can be tuned by the synergism of alkyl-steric effect and halogen electronic effect, and the production of C₆–C₁₆ can reach more than 80% with the highest selectivity being 87.5% for 3 g (Ar₁ = 2-ethylphenyl, Ar₂ = 2-fluorophenyl), which is 15–30% higher than that catalyzed by their methyl or fluoro-substituted symmetric counterparts.     

Polymerization and characterization of various di(pyridine)bis(trihalophenolato)cobalt(II) complexes in solid and melt states

The syntheses of distorted tetrahedral bis(pyridine)bis(trihalophenolato)cobalt(II) complexes from an aqueus solution were achieved and their characterization by FT‐IR, X‐ray, DSC, UV‐visible and elemental analysis in solid state or in melt form is reported. Polymerizations of these complexes were accomplished either at constant temperature, employing different time intervals or constant decomposition times while varying the temperature range. The slow decomposition at constant temperature leads to long chain products, whereas long chains formed at higher temperatures were during a constant time. The resulting poly(dihalophenylene oxide)s were characterized by FT‐IR, ¹H NMR, ¹³C NMR spectral analysis, differential scanning calorimetry and molecular weight determinations by viscometric method. © 2001 Society of Chemical Industry     

Vinyl polymerization of norbornene with bis(imino)pyridyl nickel(II) complexes

A series of different steric hindrance nickel(II) complexes 1 – 6 bearing 2,6‐bis(imino)pyridine ligands have been synthesized and characterized. The molecular structures of the complexes 3 – 5 were determined by X‐ray diffraction analysis. The coordination geometry around the nickel center of the complexes is either square pyramid for complexes 3 and 4 or trigonal bipyramid for complex 5 . All of the nickel complexes exhibit high catalytic activity for norbornene polymerization in the presence of MAO, although low activity for ethylene oligomerization and polymerization. The effects of the Al/Ni ratio, halogen, monomer concentration, temperature, and reaction time on activity of catalyst for norbornene polymerization and polymer microstructure were investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Silica‐supported bis(imino)pyridyl iron(II) catalyst: nature of the support–catalyst interactions

Ethylene polymerizations were performed using silica‐supported 2,6‐bis[1‐(2,6‐diisopropylphenylimino) ethyl] pyridine iron(II) dichloride with methylaluminoxane (MAO) as co‐catalyst. Silica was calcined at 600, 400 and 200 °C under vacuum for 8 h. The effect of calcination temperature of silica on the polymerization activity and the properties of the polymers obtained were examined. Catalyst–support interactions were examined by both a chemical method and XPS. It was observed that upon supporting the catalyst on the surface of silica, there is an increase in the binding energy of the metal center. However, no change in the metal binding energy was observed on supporting the catalyst to silica calcined at different temperatures. Ethylene polymerizations were performed using MAO as co‐catalyst. Catalysts were also prepared by first pretreating silica with MAO, followed by addition of the Fe(II) catalyst and contacting a complex of Fe(II) catalyst–MAO with silica previously calcined at 400 °C for 8 h. The results indicate that there is no chemical bonding between the support and the catalyst. Copyright © 2006 Society of Chemical Industry     

Homogeneous hydroformylation of cyclohexene with bis(acetylacetonato)diaquo cobalt (II)

Hydroformylation of cyclohexane by bis(acetylacetonato)diaquo cobalt(II) [Co(acac)₂ (H₂O)₂] in benzene solution produced the corresponding aldehyde, alcohol and saturated hydrocarbon. The influence of various experimental conditions on the product distribution has been investigated and the optimum conditions for the maximum yield of aldehyde (45%) and alcohol (55%) have been established. A tentative mechanism for hydroformylation has been suggested on the basis of the isolated green complex [Co(acac)₂]₂(C₆H₁₀) having catalytic activity comparable with Co (acac)₂(H₂O)₂ which has been isolated from the product mixture and also synthesised separately.     

Cobalt(II) and nickel(II) complexes bearing mono(imino)pyridyl and bis(imino)pyridyl ligands: preparation,structure and ethylene polymerization/oligomerization behaviors

BACKGROUND: Ethylene oligomerization is the major industrial process to produce linear α‐olefins. Recently much work has been devoted to late transition metal catalysts used in this process, especially those with 2,6‐bis(imino)pyridyl dihalide ligands. Considering that most work has focused on simple modification to the substituents in imino‐aryl rings based on the symmetric bis(imino)pyridyl framework, here we expand this work to the asymmetric mono(imino)pyridyl ligands. RESULTS: The preparation, structure and ethylene polymerization/oligomerization behavior of series of mono(imino) pyridyl–MCl₂ and bis(imino)pyridyl–MX_n complexes are presented. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for ethylene polymerization/oligomerization and reaction conditions, ligand structures, metal centers and counter‐anions. The influence of the coordination environment on catalyst behavior is also discussed. CONCLUSION: For mono(imino)pyridyl–Co(II) and ? Ni(II) catalysts bearing the Cl^? counter‐anion, good activities ranging from 0.513 × 10⁵ to 1.58 × 10⁵ g polyethylene (mol metal)^?1 h^?1 atm^?1 are afforded, and the most active catalysts are those with methyl in both ortho‐ and para‐positions of the imine N‐aryl ring. For bis(imino)pyridyl–Co(II) and ? Ni(II) catalysts bearing the SO₄^2? and NO₃^? counter‐anions, the low activities for ethylene oligomerization are in sharp contrast to those of their chloride analogues. Copyright © 2009 Society of Chemical Industry     

楔形树枝状二亚胺吡啶的合成及其在丙烯聚合催化剂中的应用

设计并合成了一种具有楔形树枝状结构的2,6-二［1-(4-(3,4,5-三(苄氧基)苄氧基)苯亚胺)乙基］吡啶化合物。用该化合物作为铁系丙烯聚合催化剂配体,制备出新型后过渡金属丙烯聚合催化剂,并对催化剂进行初步聚合评价。研究表明,相比传统的铁系丙烯聚合催化剂,制备的催化剂具有更高的活性,得到的聚丙烯数均分子量有较大的提高。     

Polymerization and characterization of bis(trichlorophenolato)di(pyridine) nickel(II) and bis(tribromophenolato)di(pyridine) nickel(II) dihydrate complexes in solution in the presence of iodine

The syntheses of bis(trihalophenolato)di(pyridine) nickel(II) complexes were achieved in aqueous solution, and their characterizations were performed by Fourier transform infrared (FTIR) spectroscopy, ultraviolet‐visible analysis, differential scanning calorimetry, and elemental analysis. The thermal polymerization of these complexes was studied in toluene solution in the presence of iodine. The effect of time, temperature, and amount of iodine added on the percentage conversion, structure of polymers, and intrinsic viscosity ([η]) were investigated. Polymers were characterized by FTIR, ¹H‐NMR, and ¹³C‐NMR spectroscopic analyses, glass‐transition temperatures determined by differential thermal analysis, and [η] values determined by the viscometric method. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2232–2239, 2002     

Chiral bis(oxazoline) copper(II) complexes: versatile catalysts for enantioselective cycloaddition, Aldol, Michael, and carbonyl ene reactions

A bis(oxazoline) (box) copper(II) complex and its hydrated counterpart (1 and 2) function as enantioselective Lewis acid catalysts for carbocyclic and hetero Diels-Alder, aldol, Michael, ene, and amination reactions with substrates capable of chelation through six- and five-membered rings. X-ray crystallography of the chiral complexes reveals a propensity for the formation of distorted square planar or square pyramidal geometries. The sense of asymmetric induction is identical for all the processes catalyzed by [Cu((S,S)-t-Bu-box)](X)(2) complexes 1 and 2 (X = OTf and SbF) resulting from the intervention of a distorted square planar catalyst-substrate binary complex. These catalyzed processes exhibit excellent temperature-selectivity profiles. Reactions catalyzed by [Cu(S,S-Ph-pybox)](SbF(6))(2) and their derived chelation complexes are also discussed.