The number of active centers and propagation rate constant in ethylene polymerization with a homogeneous catalyst based on cobalt 2,6-bis[imino]pyridyl complex with methylaluminoxane activator

The number of active centers C _p and propagation rate constant k _p upon ethylene polymerization with a homogeneous catalyst based on a cobalt complex with bis[imino]pyridyl ligands (LCoCl₂, where L is 2,6-(2,6-(Me)₂C₆H₃N=CMe)₂C₅H₃N) using methylaluminoxane as an activator was determined by quenching by radioactive carbon monoxide (¹⁴CO). It was found that the drop in activity during polymerization on the above catalyst is due to the decreasing number of active centers (from 0.23 to 0.14 mol/mol Co within 15 min of polymerization); the propagation rate constant remained unchanged, 3.5 × 10³ l/(mol s) at 35°C, which is substantially lower than for a catalyst based on an iron complex with analogous bis[imino]pyridyl ligands. It follows from the data on molecular mass characteristics of the produced polymer that the homogeneous catalyst LCoCl₂/methylaluminoxane is of monocenter type, and the obtained value of the propagation rate constant reflects the true reactivity of its active centers.     

α-二亚胺钴配合物催化1,3-丁二烯高活性与高顺式-1,4选择性聚合

合成了一系列α-二亚胺钴配合物[ArN=C(Me)-(Me)C=NAr]CoCl₂(Ar=C₆H₅, 3a; 4-MeC₆H₄, 3b; 4-MeOC₆H₄, 3c; 4-FC₆H₄, 3d; 4-ClC₆H₄, 3e; 2-MeC₆H₄, 3f; 2-EtC₆H₄, 3g; 2-ⁱPrC₆H₄, 3h; 2,4,6-Me₃C₆H₂, 3i; 2,6-Et₂C₆H₃, 3j; 2,6-ⁱPrC₆H₃, 3k)和作为对比的吡啶双亚胺二氯化钴配合物(4a), 并用X射线单晶衍射方法研究了配合物3i, 3k和4a的分子结构. α-二亚胺钴配合物在倍半乙基氯化铝的作用下对丁二烯聚合有较高的催化活性,得到的顺式-1,4结构含量达98%,且有较高分子量(M_n≈1×10⁴-1×10⁵)的聚丁二烯. 配体的电子效应影响催化剂的活性及顺式-1,4选择性, 而配体的空间位阻对丁二烯聚合几乎没有影响. 详细研究了聚合时间、聚合温度、烷基铝助催化剂及铝比等条件对丁二烯聚合行为的影响.     

o-Trityl phenoxy-imino vanadium (III) complexes: synthesis,characterization, and catalysis on ethylene (co)polymerization

Several phenoxy-imine ligands bearing o-trityl group in phenoxy moiety RN=CHArOH (Ar = C₆H₂(CPh₃)^tBu, R = 2,6-Me₂C₆H₃ ( L ₁ H ); 2,6-ⁱPr₂C₆H₃ ( L ₂ H ); 3,5-(CF₃)₂C₆H₃ ( L ₃ H ); 3,5-(OMe)₂C₆H₃ ( L ₄ H ); CHPh₂ ( L ₅ H ); CPh₃ ( L ₆ H )) were synthesized and characterized by¹H NMR and ¹³C NMR spectroscopy. The vanadium complexes based on these ligands LVCl₂(THF)₂ ( 1–6 ) were synthesized via conventional transmetalation reaction in moderate to high yields. Complexes 1–6 were fully characterized by FT-IR, elemental analyses and the molecular structures of 1 , 2 ·H₂O, (2 ·H₂O ) ₂ (μ-Cl) ₂ , 4 , and 5 were confirmed by X-ray crystallographic analysis in which the six-coordinated vanadium centers are in a typical octahedral geometry. Upon activation with Et₂AlCl in toluene, complexes 1–6 showed high activities in ethylene polymerization affording polymers with moderate molecular weight (5.9–11.8 × 10⁴ Da). Moreover, in hexane or CH₂Cl₂, 1–6 /Et₂AlCl exhibited enhanced activities. When activated with MAO or MMAO in toluene, these complexes showed relatively low activities but afforded polymers with ultra-high molecular weight (up to 3.30 × 10⁶ Da). 1–6 /Et₂AlCl also showed high activities in ethylene/1-hexene copolymerization at room temperature giving moderate molecular-weight polymers (6.5–11.4 × 10⁴ Da) with co-monomer incorporation being of 6.0 ~ 7.8%.     

Polymerization initiated by an electron donor–acceptor complex. VI. Polymerization of methyl methacrylate initiated by a liquid SO2–nicotine complex and carbon tetrachloride

A kinetic study has been made of polymerization of methyl methacrylate initiated by an electron donor–acceptor complex of liquid SO₂ (electron acceptor) and nicotine (donor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates similar to the cases of liquid SO₂–pyridine and liquid SO₂–poly(2-vinylpyridine) complexes. The overall rate of polymerization is proportional to the square root of both liquid SO₂ and nicotine concentrations, and the values of k_p/k_t^½ under various polymerization conditions are in satisfactory agreement with the literature values. For the activation energy of initiation, 13.6 kcal/mole is estimated from the k_p/k_t^½ values obtained at temperatures ranging from 0 to 80°C.     

Investigating the Effects of Para-methoxy Substitution in Sterically Enhanced Unsymmetrical Bis(arylimino)pyridine-cobalt Ethylene Polymerization Catalysts

A group of five bis(arylimino)pyridine-cobalt(Ⅱ)chloride complexes,[2-{(2,6-(Ph₂CH)₂-4-MeOC₆H₂)N=CMe}-6-(ArN=CMe)C_5 H₃N]CoCl₂(Ar=2,6-Me₂C₆H₃Co1,2,6-Et₂C₆H₃Co2,2,6-iPr₂C₆H₃Co3,2,4,6-Me₃C₆H₂Co4,2,6-Et₂-4-MeC₆H₂Co5),each containing one N-4-methoxy-2,6-dibenzhydrylphenyl group and one smaller sterically/electronically variable N-aryl group,have been synthesized in good yield(>71%)from the corresponding neutral terdentate nitrogen-donor precursor,L1-L5.All complexes have been characterized by¹H-NMR and FTIR spectroscopy with the former highlighting the paramagnetic nature of these cobaltous species and the unsymmetrical nature of the chelating ligand.The molecular structures of Co3 and Co4 emphasize the steric differences of the two inequivalent N-aryl groups and the distorted square pyramidal geometry about the metal centers.In the presence of MAO or MMAO,Co1-Co5 collectively displayed high activities for ethylene polymerization producing high molecular weight polyethylenes that,in general,exhibited narrow dispersities(M_w/M_n values:2.12-4.07).Notably,the least sterically hindered Co1 when activated with MAO was the most productive(6.92×10⁶g_PE·mol^-1_(Co)·h^-1)at an operating temperature of60℃.Conversely,the most sterically hindered Co3/MMAO produced the highest molecular weight polyethylene(M_w=6.29×10⁵g·mol^-1).All the polymers displayed high linearity as demonstrated by their melting temperatures(>130℃)and their~1 H-and¹³C-NMR spectra.By comparison of Co1 with its para-methyl,-chloro and-nitro counterparts,the presence of the para-methoxy substituent showed the most noticeable effect of enhancing the thermal stability of the catalyst.     

Synthesis and spectral characterization of diorganodiaminosilanes [(ArNH)2SiPhMe] (Ar = 2,6-Pr2C6H3; 2,4,6-Me3C6H2) and lithium silylamide [(2,6-Et2C6H3NLi)(2,6-Et2C6H3NH)SiPh2]

Aminosilanes bearing bulky substituents on nitrogen centers, [(ArNH)₂SiPhMe] (Ar = 2,6-ⁱPr₂C₆H₃ (1), 2,4,6-Me₃C₆H₂ (2)) and half-sandwich lithium silylamide [(2,6-Et₂C₆H₃NLi)(2,6-Et₂C₆H₃NH)SiPh₂] (3) have been prepared and characterized by elemental analysis, IR, EI mass and NMR (¹H and ²⁹Si) spectroscopic studies. The solid state structures of 2 and 3 have been determined by single crystal X-ray diffraction studies. The molecule 2 has a C₁ symmetry due to the steric crowding, and the two N-H protons are approximately trans to each other. The amido nitrogen atoms in 2 show significant deviation from trigonal-planar geometry, and as a result, the observed Si-N bonds are marginally longer than those observed in aminosilanes with planar nitrogen atoms. The molecule 3 exists as discrete dimer with an inversion center. The Li ion in 3 forms intramolecular π-complex with the neighboring aryl (2,6-Et₂C₆H₃) group, to form a half-sandwich lithium silylamide.     

Prediction of ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous acetonitrile

The second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C₆H₄CO₂C₆H₅, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σ_m,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σ_I, resonance, σ^○ _R, and steric, E _s ^B, and Charton υ substituent constants. For ortho derivatives the predicted (log k _X)_calc values were calculated with equation (log k _ortho)_calc = (log k ^H _AN)_exp + 0.059 + 2.19σ_I + 0.304σ^○ _R + 2.79E _s ^B ? 0.0164ΔEσ_I — 0.0854ΔEσ^○ _R, where DE is the solvent electrophilicity, ΔE = E _AN — E _H20 = ?5.84 for aqueous 50.9% acetonitrile. The predicted (log k _X)_calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work. The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C₆H₄CO₂C₆H₅, in various media with the corresponding log k values for substituted phenyl benzoates, C₆H₅CO₂C₆H₄-X.     

Guanylation of aromatic amines catalyzed by vanadium imido complexes

The reaction of formation of guanidines by coupling of carbodiimides and aromatic amines using imido vanadium complexes as catalyst have been investigated. Results demonstrate that the complex V(N-2,6-ⁱPr₂C₆H₃)Cl₃ is an effective catalyst for this process.     

Synthesis and characterization of a series of 2‐aminopyridine nickel(II) complexes and their catalytic properties toward ethylene polymerization

A series of 2‐aminopyridine Ni(II) complexes bearing different substituent groups {(2‐PyCH₂NAr)NiBr, Ar = 2,4,6‐trimethylphenyl ( 3a) , 2,6‐dichlorophenyl ( 3b ), 2,6‐dimethylphenyl ( 3c) , 2,6‐diisopropylphenyl ( 3d ), 2,6‐difluorophenyl ( 3e ); (2‐PyCH₂NHAr)₂NiBr₂, Ar = 2,6‐diisopropylphenyl ( 4a )} have been synthesized and investigated as precatalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight branched polymers as well as short‐chain oligomers were simultaneously produced with these complexes. Enhancing the steric bulk of the ortho‐aryl‐substituents of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. With ortho‐haloid‐substitution, the catalysts afforded a product with low polymer/oligomer ratio ( 3b ) and even only oligomers ( 3e ) in which C₁₄H₂₈ had the maximum content. Compared with complex 3d containing ionic ligand, complex 4a containing neutral ligand exhibited obviously low catalytic activity for ethylene polymerization. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and ¹³C NMR spectrogram. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1618–1628, 2008     

(Imido)vanadium Complexes as Efficient Catalyst Precursors for Olefin Polymerization/Oligomerization

(Arylimido)vanadium(V) complexes containing anionic ancillary donor ligands of type, V(NAr)Cl₂(L) (Ar = 2,6-Me₂C₆H₃, L = aryloxo, ketimide phenoxyimine, etc.) exhibited high catalytic activities for ethylene polymerization in the presence of Al cocatalyst; V(NAr)Cl₂(O-2,6-Me₂C₆H₃) showed the exceptionally high activities in the presence of halogenated Al alkyls such as Et₂AlCl, EtAlCl₂, etc. (Arylimido)vanadium(V)-alkylidene complexes, V(CHSiMe₃)(NAr)(L′) (L′ = N=C ^t Bu₂, O-2,6- ⁱ Pr₂C₆H₃) exhibited the remarkable catalytic activities for ring-opening metathesis polymerization of norbornene. (Imido)vanadium(V) complexes containing the (2-anilidomethyl)pyridine ligand, V(NR)Cl₂[2-Ar′NCH₂(C₅H₄N)] (R = 1-adamantyl, cyclohexyl, phenyl, Ar′ = 2,6-Me₂C₆H₃, 2,6- ⁱ Pr₂C₆H₃), exhibit the remarkable activities for ethylene dimerization in the presence of MAO, affording 1-butene exclusively (selectivity 90.4 to >99%). The steric bulk of the imido ligand plays an important role in the selectivity, and the electronic nature directly affects the activity.     

Organoaluminum Compounds as Catalysts for Monohydroboration of Carbodiimides

The effective catalytic activity of organoaluminum compounds for the monohydroboration of carbodiimides has been demonstrated. Two aluminum complexes, 2 and 3 , were synthesized and characterized. The efficient catalytic performances of four aluminum hydride complexes L¹AlH₂ (L¹=HC(CMeNAr)₂, Ar=2,6-Et₂C₆H₃; 1 ), L²AlH₂(NMe₃) (L²=o-C₆H₄F(CH=N-Ar), Ar=2,6-Et₂C₆H₃; 2 ), L³AlH (L³=2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine; 3 ), and L⁴AlH(NMe₃) (L⁴=o-C₆H₄(N-Dipp)(CH=N-Dipp), Dipp=2,6-iPr₂C₆H₃; 4 ), and an aluminum alkyl complex L¹AlMe₂ ( 5 ) were used for the monohydroboration of carbodiimides investigated under solvent-free and mild conditions. Compounds 1 – 3 and 5 can produce monohydroborated N-borylformamidine, whereas 4 can afford the C-borylformamidine product. A suggested mechanism of this reaction was explored, and the aluminum formamidinate compound 6 was characterized by single-crystal X-ray, also a stoichiometric reaction was investigated.     

Effect of temperature on the number of active sites and propagation rate constant at ethylene polymerization over supported bis(imino)pyridine iron catalysts

The inhibition of ethylene polymerization with radioactive carbon monoxide (¹⁴CO) was used to obtain data on the number of active sites (C_P) and propagation rate constant (k_P) at ethylene polymerization in the temperature range of 35–70 °C over supported catalysts LFeCl₂/Al₂O₃, LFeCl₂/SiO₂, and LFeCl₂/MgCl₂ (L: 2,6‐(2,6‐(Me)₂C₆H₃N = CMe)₂C₅H₃N) with activator Al(i‐Bu)₃. The values of effective activation energy (E_eff), activation energy of propagation reaction (E_P), and temperature coefficients of variation of the number of active sites (E_Cp = E_eff ? E_P) were determined. The activation energies of propagation reaction for catalysts LFeCl₂/Al₂O₃, LFeCl₂/SiO₂, and LFeCl₂/MgCl₂ were found to be quite similar (5.2–5.7 kcal/mol). The number of active sites diminished considerably as the polymerization temperature decreased, the E_Cp value being 5.2–6.2 kcal/mol for these catalysts at polymerization in the presence of hydrogen. The reactions of reversible transformations of active centers to the surface hydride species at polymerization in the presence and absence of hydrogen are proposed as the derivation of E_Cp. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6621–6629, 2008     

An investigation of the catalytic systems Co(acac)2or3, C3H4, (iBu)3Al for the polymerization of propadiene

In the catalytic systems Co(acac)₂ or Co(acac)₃, C₃H₄, (iBu)₃Al, the active catalyst is formed via exchange of acac for iBu groups. From kinetic measurements it follows that Co(acac)₂ and Co(acac)₃ give the same catalyst with a polymerization rate constant k _p = 29 ± 3 min⁻¹ at relatively high Al/Co ratios (≥30). At low Al/Co ratios (≤0.05) a less active catalyst is formed with a polymerization rate constant k_p = 3.6 ± 0.4 min⁻¹, possibly due to the acac groups remaining in the catalytically active complex. The kinetic results show that the highly active cobalt catalyst is formed via an equilibrium with (iBu)₃Al which indicates that the active catalyst complex is bimetallic.     

STUDIES ON THE KINETICS OF PROPYLENE POLYMERIZATION WITH THE COMPLEXTYPE TiCl_3 CATALYST

The active center concentration C_p, the rate constant k_p, and the activation energy of chain propagation E_p in the polymerization of propylene with complex-type TiCl_3-(C_2H_5)_2AlCl catalyst system were studied. The Mn was corrected by (?) value determined by GPC. The values thus obtained for C_p, k_p, and E_p at 50℃were 3.01 mol/mol Ti, 6.27 1/mol·sec, and 5.10 Kcal/mol respectively.The kinetic parameters were compared with those obtained from conventional TiCl_3·AlCl_2 catalyst, showing that the higher activity of the complex-type catalyst over the conventional catalyst is not only due to the higher C_p of the former, but to a greater extent due to the increase of the k_p value.     

Kinetic studies on the reactions of some tetrakis(arylisocyanide)cobalt(II) complexes with pyridine in 2,2,2-trifluoroethanol

The interaction of pyridine with four tetrakis(arylisocyanide)cobalt(II) complexes, [Co(CNR)₄(ClO₄)₂] R = 2,6-Me₂C₆H₃ (A), 2,4,6-Me₃C₆H₂ (B), 2,6-Et₂C₆H₃ (C) and 2,6-iPr₂C₆H₃ (D), have been studied in 2,2,2-trifluoroethanol medium. The kinetics of the reactions were investigated over the 293–318 K temperature range. The reaction profile exhibited two distinct processes, proposed to be an initial fast substitution followed by a slow reduction, for each of the reactions. The pseudo first-order rate constants for both processes increased with increasing concentration of pyridine with the reduction processes exhibiting saturation kinetics at high pyridine concentrations. Steric hindrance plays a significant role in the rates of the reactions, as the rates decrease in the order k(A) > k(B) > k(C) > k(D). The activation enthalpies, ΔH^‡, increase from A to D while the activation entropies, ΔS^‡, are relatively similar for the four reactions, indicating similar transition states and hence similar mechanisms. Complex B was first synthesized and characterized in this study.     

The chloro-substituent enhances performance of 2,4-bis (imino)pyridylchromium catalysts yielding highly linear polyethylene

The five unsymmetrical 2-[1-(2,4-dibenzhydryl-6-chlorophenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridine compounds (aryl: 2,6-Me₂Ph L1 , 2,6-Et₂Ph L2 , 2,6-ⁱPr₂Ph L3 , 2,4,6-Me₃Ph L4 and 2,6-Et₂–4-MePh L5 ) were prepared and characterized with FT-IR and ¹H/¹³C NMR spectroscopy as well as elemental analysis. The treatment of L1 – L5 with CrCl₃·3THF affords the corresponding chromium chloride complexes ( Cr1 – Cr5 ) in excellent yields. The molecular structures of Cr2 and Cr3 characterized by X-ray diffraction show a distorted octahedral geometry with three nitrogen atoms and three chlorine atoms around the metal center. On activation with either MAO or MMAO, Cr1 – Cr5 collectively display high activity (up to 14.96 × 10⁶ g (PE) mol⁻¹ (Cr) h⁻¹ at 60 °C) affording highly linear polyethylene with low molecular weight distribution (M_w/M_n) ranging from 1.06 to 2.81. An in-depth catalytic evaluation of Cr1 was conducted in order to investigate how the cocatalyst type and its amount, reaction temperature and polymerization time affect the catalytic activities and polymer properties.     

Olefin polymerization and copolymerization with soluble transition‐metal complex catalysts

Olefin polymerizations catalyzed by Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 1 – 5 ; Cp′ = cyclopentadienyl group), RuCl₂(ethylene)(pybox) { 7 ; pybox = 2,6‐bis[(4S)‐4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine}, and FeCl₂(pybox) ( 8 ) were investigated in the presence of a cocatalyst. The Cp*TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 5 )–methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and 1‐hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1‐hexene incorporation and a lower r_E · r_H value with 5 than with [Me₂Si(C₅Me₄)(N^tBu)]TiCl₂ ( 6 ) were obtained, despite the rather wide bond angle of Cp Ti O (120.5°) of 5 compared with the bond angle of Cp Ti N of 6 (107.6°). The 7 –MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1‐hexene copolymerization, and the resultant copolymer incorporated 1‐hexene. The 8 –MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1‐hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring‐opened poly(norbornene) substituent was accomplished by ringopening metathesis polymerization with the well‐defined Mo(CHCMe₂Ph)(N‐2,6‐ⁱPr₂C₆H₃)[OCMe(CF₃)₂]₂ ( 10 ). The key step for the macromonomer synthesis was the exclusive end‐capping of the ring‐opened poly(norbornene) with p‐Me₃SiOC₆H₄CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4613–4626, 2000     

Synthesis of (adamantylimido)vanadium(V)-alkyl complexes containing aryloxo ligands and their use as the catalyst precursors for ring-opening metathesis polymerization of norbornene, and ring-opening polymerization of tetrahydrofuran

Various (adamantylimido)vanadium(V) dialkyl complexes containing aryloxo ligands, V(NAd)(CH₂SiMe₃)₂(OAr) [Ad = 1-adamantyl (1); Ar = Ph (a), 4-FC₆H₄ (b), 2,6-F₂C₆H₃ (c), 2,6-Me₂C₆H₃ (d), C₆F₅ (e)], have been prepared and identified. These complexes were employed as the catalyst precursors for ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of PMe₃ at 80 °C. The activity was strongly affected by the aryloxo substituent and increased in the order: C₆H₅ < 4-FC₆H₄ < 2,6-Me₂C₆H₃ << 2,6-F₂C₆H₃, C₆F₅. The same trend was observed in the ROMPs by the arylimido-aryloxo analogues, V(NAr′)(CH₂SiMe₃)₂(OAr) (2a-e; Ar′ = 2,6-Me₂C₆H₃), under the same conditions, and the activities by the arylimido analogues were generally higher than the adamantylimido analogues in most case. The (imido)vanadium(V) complexes containing O-2,6-F₂C₆H₃ (1,2c) or OC₆F₅ (1,2e) exhibited high catalytic activities, and these results strongly suggest that electronic as well as steric factors play a role. Living ring-opening polymerization of THF proceeded in the presence of V(NAd) (CH₂SiMe₃)(OAr)₂ (Ar = 2,6-Me₂C₆H₃, C₆F₅) and [Ph₃C][B(C₆F₅)₄], affording high molecular weight polymers with narrow molecular weight distributions (ex. M_n = 2.11 × 10⁵, M_w/M_n = 1.18).     

Unifying Molecular Weights of Highly Linear Polyethylene Waxes through Unsymmetrical 2,4-Bis(imino)pyridylchromium Chlorides

By dealing CrCl₃∙3THF with the corresponding ligands (L1–L5), an array of fluoro-substituted chromium (III) chlorides (Cr1–Cr5) bearing 2-[1-(2,4-dibenzhydryl-6-fluoro- phenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridine (aryl = 2,6-Me₂Ph Cr1, 2,6-Et₂Ph Cr2, 2,6-iPr₂Ph Cr3, 2,4,6-Me₃Ph Cr4, 2,6-Et₂-4-MePh Cr5) was synthesized in good yield and validated via Fourier Transform Infrared (FT-IR) spectroscopy and elemental analysis. Besides the routine characterizations, the single-crystal X-ray diffraction study revealed the solid-state structures of complexes Cr2 and Cr4 as the distorted-octahedral geometry around the chromium center. Activated by either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the chromium catalysts exhibited high activities toward ethylene polymerization with the MMAO-promoted polymerizations far more productive than with MAO (20.14 × 10⁶ g (PE) mol⁻¹ (Cr) h⁻¹ vs. 10.03 × 10⁶ g (PE) mol⁻¹ (Cr) h⁻¹). In both cases, the resultant polyethylenes were found as highly linear polyethylene waxes with low molecular weights around 1–2 kg mol⁻¹ and narrow molecular weight distribution (MWD range: 1.68–2.25). In general, both the catalytic performance of the ortho-fluorinated chromium complexes and polymer properties have been the subject of a detailed investigation and proved to be highly dependent on the polymerization reaction parameters (including cocatalyst type and amount, reaction temperature, ethylene pressure and run time).     

Copolymerization of Ethylene with lO-Undecen-l-ol Using Highly Active Vanadium（III） Precatalysts Bearing Bis（imino）pyrrolyl Ligands

The copolymerizations of ethylene with 10-undecen-1-ol have been investigated using vanadium precatalysts, bis（imino）pyrrolyl vanadium（Ⅲ） complexes 1-3, 2,5-C4H2N（CH=NR）2VCl2（THF）2 [R = C6H5 （1）, 2,6-iPr2C6H3 （2）, C6F5 （3）], and the iminopyrrolyl and b-diketiminate ones for comparison. The polar monomer was pretreated by diethylaluminium chloride （present also as the cocatalyst） before the copolymerization. The monomer reactivity ratios were evaluated using the Fineman-Ross method. The ligand structure considerably influenced the catalytic activity and tolerance towards the polar monomer, the polar monomer incorporation and the molecular weights of the resultant copolymers. The bis（imino）pyrrolyl vanadium complexes exhibited promising catalytic performance for the copolymerization, and a high catalytic activity up to 3.84 kg/mmolv·h with a high comonomer incorporation of 14.0 mol% was achieved by complex 3 under mild conditions.