High Activity For Ethylene Polymerization Research Articles

The synthesis of asymmetrical anilinotropone nickel and palladium complexes for olefin polymerization

For the Coordination-insertion olefin polymerization, the development of high-performance transition-metal catalysts is always the key issue and extensive efforts have been made in this field. In this contribution, we designed several asymmetrical anilinotropone nickel and palladium catalysts. Compared to palladium complex, the nickel catalysts exhibited high activity in ethylene polymerization. The topology microstructure of polyethylene could be modulated by different polymerization temperature. The anilinotropone nickel catalysts Ni2 and Ni3 in this work demonstrated higher thermolability, generating polyethylene with higher molecular weight (up to 285.9 kg mol−1). Moreover, these nickel systems also promoted the copolymerization of ethylene with norbornene-type polar monomers (NB–COOMe, NB-OAc), which demonstrated great polar group tolerance in this system. The generated copolymer exhibited high molecular weight (up to 93.1 kg mol−1) and high polar monomer incorporation ratio (up to 6.9 mol%). The design of asymmetrical anilinotropone catalysts in this work presented a unique form in olefin polymerization and may attract wide application interests in metal catalysis areas.

Non-Symmetrically Fused Bis(arylimino)pyridines with para-Phenyl Substitution: Exploring Their Use as N′,N,N″-Supports in Iron Ethylene Polymerization Catalysis

Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me2Ph Fe1, 2,6-Et2Ph Fe2, 2,6-i-Pr2Ph Fe3, 2,4,6-Me3Ph Fe4, and 2,6-Et2-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 106 g (PE) mol−1 (Fe) h−1 seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (Mw/Mn = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol−1 and MAO: 4.9 kg mol−1), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol−1 and MAO: 72.4–95.5 kg mol−1). Moreover, analysis of these polyethylenes by 1H and 13C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system.

Impact of o-aryl halogen effects on ethylene polymerization: steric vs. electronic effects.

Ligand steric hindrance and electronic effects play a crucial role in late-transition metal-catalyzed olefin polymerization. In this research, a series of o-aryl halogenated α-diimine ligands bearing bulky dibenzhydryl substituents, along with their corresponding nickel catalysts, have been synthesized and thoroughly characterized. The nickel catalysts demonstrated very high activity in ethylene polymerization, achieving a high rate of up to 107 g mol-1 h-1. The produced polyethylenes displayed a broad spectrum of molecular weights (12.2-871.7 kg mol-1) but maintained consistent branching densities (50-82/1000 C) when polymerized at a fixed temperature with different nickel catalysts. Notably, the polymerization temperature has a significant influence on both the molecular weight and branching density of the resulting polyethylene. Higher temperatures led to the formation of polyethylenes with lower molecular weights and increased branching densities. Interestingly, the o-aryl halogens significantly impact the molecular weight of the polyethylene. The size of the halogen substituents primarily determines the molecular weight of the polyethylene. However, in terms of branching density, the steric and electronic effects of these substituents appear to counteract each other. In addition, the branched high molecular weight polyethylenes from the bromine and chlorine substituted nickel catalysts are excellent polyethylene thermoplastic elastomers with high strain at break values (688-2478%) and high strain recovery values (42-62%).

Nickel catalysts with asymmetric steric hindrance for ethylene polymerization

α-Diimide catalysts have attracted widespread attention due to their unique chain walking characteristics. A series of α-diimide nickel/palladium catalysts with different electronic effects and steric hindrances were designed and synthesized for olefin polymerization. In this work, we synthesized a series of asymmetric α-diimide nickel complexes with different steric hindrances and used them for ethylene polymerization. These nickel catalysts have high ethylene polymerization activity, up to 6.51×10<sup>6</sup> g·mol<sup>−1</sup>·h<sup>−1</sup>, and the prepared polyethylene has a moderate melting point and high molecular weight (up to 38.2 × 10<sup>4</sup> g·mol<sup>−1</sup>), with a branching density distribution between 7 and 94 branches per 1000 carbons. More importantly, the polyethylene prepared by these catalysts exhibits excellent tensile properties, with strain and stress reaching 800% and 30 MPa, respectively.

Exploring Long Range para-Phenyl Effects in Unsymmetrically Fused bis(imino)pyridine-Cobalt Ethylene Polymerization Catalysts

Unsymmetrical 11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, incorporating a para-phenyl substituted pyridine unit fused by both 6- and 7-membered carbocyclic rings, has been prepared on the gram-scale via a multi-step procedure involving cyclization, hydrogenation and oxidation. Templating this diketone, in the presence of cobalt(II) chloride hexahydrate, with the corresponding aniline afforded in good yield five examples of doubly fused bis(arylimino)pyridine-cobalt(II) chlorides, Co1 (aryl = 2,6-dimethylphenyl), Co2 (2,6-diethylphenyl), Co3 (2,6-diisopropylphenyl), Co4 (2,4,6-trimethylphenyl) and Co5 (2,6-diethyl-4-methylphenyl). Structural characterization of Co1, Co2 and Co3 highlights the flexible nature of the inequivalent fused rings on the NNN’-ligand and the skewed disposition of the para-phenyl group. On activation with MAO, Co1–Co5 exhibited high activity for ethylene polymerization at 30 °C (up to 5.66 × 106 g (PE) mol−1 (Co) h−1) with the relative order being as follows: Co4 > Co1 > Co5 > Co3 > Co2. All polyethylenes were strictly linear, while their molecular weights and dispersities showed some notable variations. For Co1, Co2, Co4 and Co5, all polymerizations were well controlled as evidenced by the narrow dispersities of their polymers (Mw/Mn range: 1.8–2.7), while their molecular weights (Mw range: 2.9–10.9 kg mol−1) steadily increased in line with the greater steric properties of the N-aryl ortho-substituents. By contrast, the most hindered 2,6-diisopropyl counterpart Co3 displayed a broad distribution with bimodal characteristics (Mw/Mn = 10.3) and gave noticeably higher molecular weight polymer (Mw = 75.5 kg mol−1). By comparison, the MMAO-activated catalysts were generally less active, but showed similar trends in molecular weight and polymer dispersity. End group analysis of selected polymers via 13C and 1H NMR spectroscopy revealed the presence of both saturated and unsaturated polyethylenes in accordance with competing chain transfer pathways. Notably, when comparing Co3/MAO with its non-phenyl substituted analogue (E2,6-iPr2Ph)CoCl2/MAO, the former, though less controlled, displayed higher activity and molecular weight, a finding that points towards a role played by the remote para-phenyl group.

Nitro and 4,4′-flourobenzhydryl functionalized bis(imino)pyridine-cobalt complexes for high molecular weight linear polyethylenes

A series of nitro and 4,4′-fluorobenzhydryl functionalized bis(imino)pyridine-cobalt complexes, [2-{(2,6-iPr2-3-NO2-4-((4-F-Ph)2CH)Ph)N=CMe}-6-{(Ar)N=CMe}C5H5N]CoCl2 (where Ar is 2,6-Me2Ph for Co1; 2,6-Et2Ph for Co2; 2,6-iPr2Ph for Co3; 2,4,6-Me3Ph for Co4; 2,6-Et2-4-Me-Ph for Co5; 2,6-iPr2-3-NO2-4-((4-F-Ph)2CH)Ph for Co6) were prepared and investigated for ethylene polymerization. The resultant compounds were characterized by elemental analysis, 1H/13C NMR and FT-IR spectra. The molecular structure determination revealed a distorted square pyramidal geometry for Co3. All prepared complexes demonstrated high catalytic activity for ethylene polymerization (up to 10.7 × 106 g PE (mol of Co)−1 h−1) and produced high-molecular-weight polyethylenes in the level of 105 g mol−1. Structural variations in the catalyst design revealed that the unsymmetrical complexes with sterically less hindrand substituents exhibited comparatively higher polymerization activity, while sterically encumbered symmetrical complexes proved more efficient in enhancing the molecular weight of resultant polyethylenes. Additionally, high-temperature 1H/13C NMR spectra of the produced polyethylenes confirmed their strictly linear microstructure, which is also evident from their high melting temperature (Tm ∼135 °C).

Investigations of aryl substituents electronic effects in the catalytic behavior of thermostable α‐diimine nickel (II) catalyst on ethylene polymerization

AbstractIn α‐diimine‐based catalytic systems, it is highly challenging to increase the thermal stability of the α‐diimine Ni(II) catalyst. In this work, we are focused on examining the polymerization of ethylene by a number of α‐diimine Ni(II) complexes with camphyl backbone and various electron‐donating and withdrawing substituents as catalysts. The synthesized camphyl‐based ligands were characterized by 1H nuclear magnetic resonance (NMR), 13C NMR, HH correlation spectroscopy, Fourier‐transform infrared (FT‐IR), and elemental analysis. The formation of the Ni(II) complexes was approved by the far infrared (Far‐IR) and energy dispersive x‐ray spectroscopy (EDS). The Box–Behnken method was used to select the optimal polymerization conditions. The ligand electronic effect on the catalytic activity of Ni(II) complexes in ethylene polymerization was systematically investigated. All of the synthesized complexes were active in ethylene polymerization with activities at 105 g of polyethylenes (PE) (mol of Ni h)−1. The electron‐withdrawing substituent catalyst exhibited high activity in ethylene polymerization.

Nickel complexes bearing substituted 2-(naphthylen-1-yl)iminopyridines as catalysts for the formation of highly branched unsaturated PE waxes

A set of six 2-iminopyridine-nickel(II) complexes, [2-{C(Me)=NAr}C5H4N]NiCl2 (Ar = 1-C10H7Ni1, 2-Me-1-C10H6Ni2, 2-(CHMePh)-1-C10H6Ni3, 4-(NNC6H5)-1-C10H6Ni4, 4-(NNC6H4-4-Me)-1-C10H6Ni5, 4-(NNC6H4-4-F)-1-C10H6Ni6), all N-functionalized with naphthalen-1-yl or its substituted alkyl or aryldiazenyl derivatives, have been readily synthesized from their corresponding free N,N-ligand, L1 – L6. On crystallization of Ni3, the chloride-bridged trimetallic species, [(L3)3Ni3Cl6(OH2)], was identified as an aqua adduct by single crystal X-ray diffraction. When activated with either MAO or MMAO, high catalytic activity for ethylene polymerization was achieved using Ni1–Ni6 (up to 10.1 × 106 g (PE) mol−1 h−1 for Ni3/MAO), affording low molecular weight polyethylene (Mw range: 0.81–3.50 kg mol−1) with low melting temperature and narrow dispersity. 13C NMR spectroscopic analyses of these polyethylenic waxes revealed the formation of branched macromolecules with branching densities up to 69 per 1000 carbons. Further analysis revealed these polymers to contain predominantly methyl branches (%Me range: 7.8–9.0), with lower levels of longer chain branching and some branch-on branch structure (%sec-Bu range: 0.07–0.12%). Moreover, their 1H and 13C NMR spectra showed various levels of unsaturated functionality in the form of terminal and internal olefins.

Amine-Imine Nickel Catalysts with Pendant O-Donor Groups for Ethylene (Co)Polymerization.

The introduction of a secondary interaction is an efficient strategy to modulate transition-metal-catalyzed ethylene (co)polymerization. In this contribution, O-donor groups were suspended on amine-imine ligands to synthesize a series of nickel complexes. By adjusting the interaction between the nickel metal center and the O-donor group on the ligands, these nickel complexes exhibited high activities for ethylene polymerization (up to 3.48 × 106 gPE·molNi-1·h-1) with high molecular weight up to 5.59 × 105 g·mol-1 and produced good polyethylene elastomers (strain recovery (SR) = 69-81%). In addition, these nickel complexes can catalyze the copolymerization of ethylene with vinyl acetic acid, 6-chloro-1-hexene, 10-undecylenic, 10-undecenoic acid, and 10-undecylenic alcohol to prepare the functionalized polyolefins.

Exploring fluoride effects in sterically enhanced cobalt ethylene polymerisation catalysts; a combined experimental and DFT study.

The fluoro-substituted 2,6-bis(arylimino)pyridine dichlorocobalt complexes, [2-{CMeN(2,6-(Ph2CH)2-3,4-F2C6H)}-6-(CMeNAr)C5H3N]CoCl2 (Ar = 2,6-Me2C6H3 Co1, 2,6-Et2C6H3Co2, 2,6-iPr2C6H3Co3, 2,4,6-Me3C6H2Co4, 2,6-Et-4-MeC6H2Co5), were synthesized in good yield from the corresponding unsymmetrical N,N,N'-ligands, L1-L5. Besides characterization of Co1-Co5 by FT-IR spectroscopy, 19F NMR spectroscopy and elemental analysis, the molecular structures of Co2 and Co5 were also determined highlighting the unsymmetrical nature of the terdentate ligand and the pseudo-square pyramidal geometry about the metal center. When either MAO or MMAO were employed as activators, Co1-Co5 were able to achieve a wide range of catalytic activities for ethylene polymerisation. Co5/MAO exhibited the highest activity of the study at 60 °C (7.6 × 106 g PE mol-1 (Co) h-1) which decreased to 3.3 × 106 g PE mol-1 (Co) h-1 at 80 °C. In addition, it was found that the polymerisation activity increased as the steric hindrance imparted by the ortho groups was enhanced (for MMAO: Co3 > Co5 > Co2 > Co1 > Co4), a finding that was supported by DFT calculations. Furthermore, it was shown that particularly high molecular weight polyethylene could be generated (up to 483.8 kg mol-1) when using Co5/MMAO at 30 °C, while narrow dispersities (M w/M n range: 1.8-4.7) and high linearity (T m > 131.4 °C) were a feature of all polymers produced. By comparison of Co3 with its non-fluorinated analogue using experimental data and DFT calculations, the substitution of fluorides at the meta- and para-positions was demonstrated to boost catalytic activity and improve thermal stability.

Thermally Stable and Highly Efficient N,N,N-Cobalt Olefin Polymerization Catalysts Affixed with N-2,4-Bis(Dibenzosuberyl)-6-Fluorophenyl Groups

The cobalt(II) chloride N,N,N-pincer complexes, [2-{(2,4-(C15H13)2-6-FC6H2)N=CMe}-6-(ArN=CMe)C5H3N]CoCl2 (Ar = 2,6-Me2C6H3) (Co1), 2,6-Et2C6H3 (Co2), 2,6-i-Pr2C6H3 (Co3), 2,4,6-Me3C6H2 (Co4), 2,6-Et2-4-MeC6H2 (Co5), and [2,6-{(2,4-(C15H13)2-6-FC6H2)N=CMe}2C5H3N]CoCl2 (Co6), each containing at least one N-2,4-bis(dibenzosuberyl)-6-fluorophenyl group, were synthesized in good yield from their corresponding unsymmetrical (L1–L5) and symmetrical bis(imino)pyridines (L6). The molecular structures of Co1 and Co2 spotlighted their distorted square pyramidal geometries (τ5 value range: 0.23–0.29) and variations in steric hindrance offered by the dissimilar N-aryl groups. On activation with either MAO or MMAO, Co1–Co6 all displayed high activities for ethylene polymerization, with levels falling in the order: Co1 > Co4 > Co5 > Co2 > Co3 > Co6. Indeed, the least sterically hindered 2,6-dimethyl Co1 in combination with MAO exhibited a very high activity of 1.15 × 107 g PE mol−1 (Co) h−1 at the operating temperature of 70 °C, which dropped by only 15% at 80 °C and 43% at 90 °C. Vinyl-terminated polyethylenes of high linearity and narrow dispersity were generated by all catalysts, with the most sterically hindered, Co3 and Co6, producing the highest molecular weight polymers [Mw range: 30.26–33.90 kg mol−1 (Co3) and 42.90–43.92 kg mol−1 (Co6)]. In comparison with structurally related cobalt catalysts, it was evident that the presence of the N-2,4-bis(dibenzosuberyl)-6-fluorophenyl groups had a limited effect on catalytic activity but a marked effect on thermal stability.

2-(Arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline Cobalt(II) Dichloride Polymerization Catalysts for Polyethylenes with Narrow Polydispersity

A series of 2-(arylimino)benzylidene-8-arylimino-5,6,7-trihydroquinoline cobalt(II) chlorides (Co1–Co6) containing a fused ring and a more inert phenyl group as the substituent at the imino-C atom has been synthesized using a one-pot synthesis method and fully characterized by FT-IR and elemental analysis. The molecular structures of Co2 and Co5 have been confirmed by X-ray diffraction as having a distorted square pyramidal geometry around a cobalt core with a tridentate N,N,N-chelating ligand and two chlorides. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1–Co6 exhibited high activities for ethylene polymerization. The least sterically hindered Co2 showed a maximum activity of 16.51 × 106 g (PE) mol−1 (Co) h−1 at a moderate temperature 50 °C. Additionally, ortho-fluoride Co6 was able to maintain a high activity not only at 70 °C but also after 60 min at 50 °C, highlighting its excellent thermal-stability and long catalytic lifetime. The resultant polyethylene showed clearly narrower molecular weight distribution (PDI: 1.3–3.1) than those produced by structurally related cobalt counterparts, indicating the positive influence of benzhydryl substitution on the catalysis. Moreover, the molecular weight (1.7–386.6 kg mol−1) of vinyl- or n-propyl-terminated polyethylene can be finely regulated by controlling polymerization parameters.

Ethylene homo and copolymerization by phosphorus‐benzoquinone based homogeneous and heterogeneous nickel catalysts

AbstractThe low cost and high abundancy of nickel makes it highly attractive for both industrial and academic researchers in the field of polyolefin. However, the development of high performance nickel catalysts for ethylene homo and copolymerization is highly challenging. In this contribution, two novel cationic nickel catalysts with quinone backbone and sterically hindered aryl substituents on phosphine have been synthesized and supported on solid supports to prepare heterogeneous catalysts. The homogeneous catalysts showed high activity and high thermal stability in ethylene polymerization. After heterogenization of these catalysts, all the polymerization parameters (polymerization activity, thermal stability, and polymer molecular weight) were significantly improved. The heterogeneous catalyst can achieve activity of up to 3.26 × 106 g mol−1 h−1, along with polyethylene molecular weight of up to 81.8 × 104 g mol−1. More importantly, these homogeneous and heterogeneous catalysts can realize copolymerization of ethylene with a series of polar comonomers such as methyl 10‐undecenoate, 10‐undecenol, and 6‐chloro‐1‐hexene.

Modulating Thermostability and Productivity of Benzhydryl‐Substituted Bis(imino)pyridine‐Iron C2H4 Polymerization Catalysts through ortho‐CnH2n−1 (n=5, 6, 8, 12) Ring Size Adjustment

AbstractFour types of benzhydryl‐containing bis(arylimino)pyridine‐iron(II) chloride complex, [2‐{CMeN(2,4,6‐Me3C6H2)}‐6‐{CMeN(Ar)}C5H3N]FeCl2 (Ar=2,4‐(CHPh2)2‐6‐(C5H9)C6H2 Fe1, 2,4‐(CHPh2)2‐6‐(C6H11)C6H2 Fe2, 2,4‐(CHPh2)2‐6‐(C8H15)C6H2 Fe3 and 2,4‐(CHPh2)2‐6‐(C12H23)C6H2 Fe4), discriminable by the ring size of the ortho‐CnH2n−1 (n=5, 6, 8, 12) group, have been prepared in good yield (>85 %) via the reaction of the corresponding N,N,N′‐ligand, L1–L4, with ferrous chloride tetrahydrate. All new complexes were characterized by FT‐IR spectroscopy and elemental analysis. The molecular structure of Fe3 emphasizes the distorted pseudo‐square pyramidal geometry bestowed to the metal center and the steric unevenness provided by the inequivalent N‐mesityl and N‐2,4‐dibenzyhydryl‐6‐cyclooctylphenyl groups. Extremely high activities for ethylene polymerization were achieved at temperatures between 60 °C and 70 °C following pre‐treatment of the iron(II) precatalyst with either MMAO or MAO, with the relative performance being: Fe2>Fe1>Fe3>Fe4. Notably, ortho‐cyclohexyl Fe2, under activation with MMAO, afforded the highest level of performance of this study reaching 2.82×107 g PE per mol (Fe) per h at 70 °C forming strictly linear and narrowly dispersed polyethylene (Mw/Mn=2.0) with moderate molecular weight (11.3 kg per mol). Furthermore, runs performed using Fe1/MMAO at 90 °C saw the catalytic activity drop by around only 40 % highlighting the remarkable thermostability of these catalysts. By comparison, polymerizations performed using MAO as co‐catalyst were less controlled with broader dispersities (Mw/Mn range: 4.8–10.1), while the molecular weights were generally higher (55.7–150.9 kg per mol).

Polyethylene Waxes with Short Chain Branching via Steric and Electronic Tuning of an 8-(Arylimino)-5,6,7-trihydroquinoline-nickel Catalyst

Ten examples of nickel(II) halide complexes [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiBr2 [R = Me (Ni1), Et (Ni2), iPr (Ni3), Cl (Ni4), or F (Ni5)] and [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiCl2 [R = Me (Ni6), Et (Ni7), iPr (Ni8), Cl (Ni9), or F (Ni10)], each incorporating a sterically encumbered N,N-chelating 8-[2,4-bis(dibenzocycloheptyl)-6-R-phenylimino]-5,6,7-trihydroquinoline ligand, are disclosed. Full details for the preparation of these complexes as well as the zinc-mediated synthesis of precursor ligands L1–L5 are given. Structural characterization of Ni3(H2O), Ni6, Ni7(H2O), and Ni8(H2O) reveals halide-bridged dinuclear structures of the type (N,N)NiX(μ-X)2NiX(N,N) with the ortho-substituted dibenzocycloheptyl groups providing steric protection to each metal center. In the presence of ethylaluminum dichloride (EtAlCl2) or methylaluminoxane (MAO), Ni1–Ni10 displayed high activities for ethylene polymerization [≤6.17 × 106 g of PE (mol of Ni)−1 h–1 for Ni6/EtAlCl2 at 20 °C], generating low-molecular weight polyethylene waxes. Notably, catalysts incorporating a 6-alkyl group (Me, Et, or iPr) as the N-aryl substituent proved to be more active than their 6-halide (Cl or F) counterparts and formed relatively higher-molecular weight polymers (Mw range of 9.1–22.9 kg mol–1) with a narrow dispersity. Moreover, analysis of these waxes by 13C nuclear magnetic resonance spectroscopy showed that they typically possessed short chain branching (>83% methyl) with branching densities of 79–90 branches per 1000 Cs. In addition, chain end analysis revealed the presence of both vinyl (−CH═CH2) and internal vinylene (−CH═CH−) functional groups, highlighting the role of both β-H elimination and isomerization.

Zirconium Complexes with Bulkier Amine Bis(phenolate) Ligands and Their Catalytic Properties for Ethylene (Co)polymerization.

A series of new zirconium complexes bearing bulkier amine bis(phenolate) tetradentate ligands, Me2NCH2CH2N{CH2(2-O-3-R-5-tBu-C6H2)}2ZrCl2 [R = CPhMe2 (1); CMePh2 (2); CPh3 (3); Ph (4); 3,5-Me2C6H3 (5); 3,5-tBu2C6H3 (6); 4-tBuC6H4 (7)], were synthesized and characterized by 1H nuclear magnetic resonance (NMR), 13C NMR, and elemental analyses. The molecular structures of complexes 1 and 3 were determined by single-crystal X-ray diffraction analysis. The X-ray crystallography analysis reveals that these complexes display a slightly distorted octahedral geometry around their metal centers. Upon activation with methylaluminoxane (MAO), dry-MAO, MAO/butylated hydroxytoluene (BHT), or AliBu3/CPh3B(C6F5)4, these zirconium complexes exhibit high catalytic activity for ethylene polymerization [up to 1.07 × 107 g PE (mol Zr)-1 h-1] and ethylene/1-hexene copolymerization [up to 2.78 × 107 g polymer (mol Zr)-1 h-1], affording (co)polymers with moderate to high molecular weights and good comonomer incorporations. The zirconium complexes with bulkier R groups show higher catalytic activities and longer lifetimes and produce polymers with higher molecular weights, while the zirconium complexes with aryls as R groups demonstrate relatively good comonomer incorporation ability for the copolymerization reactions. These catalytic systems also show moderate catalytic activities for the polymerization reactions of propylene, 1-hexene, and 1-decene. Upon activation with MAO, the zirconium complexes also show moderate catalytic activities for the copolymerization reaction of ethylene with 3-buten-1-ol (treated with 1 equiv of AliBu3), affording copolymers with the incorporation of 3-buten-1-ol up to 1.05%.

Highly active and thermostable camphyl α‐diimine–nickel(II) catalysts for ethylene polymerization: Effects of N‐aryl substituting groups on catalytic properties and branching structures of polyethylene

A group of nickel bromide complexes containing the rigid bidentate bis(arylimino)camphane ligands (Ar‐BIC) with different N‐aryl substituents, [ArN═C(camphyl)C(camphyl)═NAr]NiBr2 (Aryl = 2,6‐Me2C6H3 [Ni1], 2,4‐Me2C6H3 [Ni2], 2,4,6‐Me3C6H2 [Ni3], 2,6‐Me2‐4‐{(C6H4F)2CH}‐C6H2 [Ni4], 2,4‐Me2‐6‐{(C6H4F)2CH}‐C6H2 [Ni5, with the corresponding ligand as L5], and 2‐Me‐4,6‐{(C6H4F)2CH}2‐C6H2 [Ni6]), has been synthesized and characterized. The molecular structures of L5, Ni1, Ni3, Ni4, and Ni6 were elucidated with single‐crystal X‐ray diffraction. The nickel centers displayed a four‐coordinate geometry that can be best described as a distorted tetrahedral geometry. Upon treatment with either MMAO or Me2AlCl, Ni1–Ni6 showed moderate to high activities for ethylene polymerization, producing polyethylenes (PEs) with low to high molecular weights (0.02–23.7 × 105 g mol−1) and low polydispersity indices (PDI: 1.6–2.6). In comparison with reference nickel precatalysts ligated by bis(arylimino)acenaphthene (Ar‐BIAN) and bis(arylimino)butane (Ar‐BIB), the title complexes displayed much better thermal stability and higher catalytic activities (up to 11.2 × 106 g PE (mol Ni)−1 h−1 at 70°C), delivering polyethylenes with higher molecular weights. All the resultant polyethylenes are moderately to highly branched with the branching content and type of branching strongly affected by the type of N‐aryl substituting groups. Notably, the polymers produced with ortho‐hydrogen Ni2/Me2AlCl possessed the highest branching density and unique terminal vinyl (CH═CH2) and internal vinylene (CH═CH) structure. On the other hand, ortho‐di(p‐fluorophenyl)methyl‐containing Ni5 and Ni6 just gave 30 and 19 branches per 1000 Cs due to the reduced chain walking capability as a result of the bulkier substituting groups.

High molecular weight PE elastomers through 4,4-difluorobenzhydryl substitution in symmetrical α-diimino-nickel ethylene polymerization catalysts.

The following family of N,N-diaryl-2,3-dimethyl-1,4-diazabutadienes, ArN Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C(Me)C(Me)NAr (Ar = 2,6-Me2-4-{CH(4-FC6H4)2}C6H2L1, 2-Me-6-Et-4-{CH(4-FC6H4)2}C6H2L2, 2,4-{CH(4-FC6H4)2}2-6-MeC6H2L3, 2,4-{CH(4-FC6H4)2}2-6-EtC6H2L4, 2,4-{CH(4-FC6H4)2}2-6-iPrC6H2L5), each incorporating para-substituted 4,4-difluorobenzhydryl groups but differing in the ortho-pairing, have been synthesized and used as precursors to their respective nickel(ii) bromide complexes, Ni1–Ni5. Compound characterization has been achieved through a combination of FT-IR, multinuclear NMR spectroscopy (1H, 13C, 19F) and elemental analysis. In addition, L1, Ni1 and Ni5 have been structurally characterized with Ni1 and Ni5 revealing similarly distorted tetrahedral geometries about nickel but with distinct differences in the steric protection offered by the ortho-substituents. All nickel complexes, under suitable activation, showed high activity for ethylene polymerization with a predilection towards forming branched high molecular weight polyethylene with narrow dispersity. Notably the most sterically bulky Ni5, under activation with either EtAlCl2, Et2AlCl or EASC, was exceptionally active (0.9–1.0 × 107 g of PE per (mol of Ni) per h) at an operating temperature of 40 °C. Furthermore, the polyethylene generated displayed molecular weights close to one million g mol−1 (Mw range: 829–922 kg mol−1) with high branching densities (86–102/1000 carbons) and a selectivity for short chain branches (% Me = 94.3% (EtAlCl2), 87.2% (Et2AlCl), 87.7% (EASC)). Further analysis of the mechanical properties of the polymers produced at 40 °C and 50 °C using Ni5 highlighted the key role played by crystallinity (Xc) and molecular weight (Mw) on tensile strength (σb) and elongation at break (εb). In addition, stress–strain recovery tests reveal these high molecular weight polymers to exhibit characteristics of thermoplastic elastomers (TPEs).

Fluorinated 2,6-bis(arylimino)pyridyl iron complexes targeting bimodal dispersive polyethylenes: probing chain termination pathways via a combined experimental and DFT study.

In this work, fluorinated 2,6-bis(arylimino)pyridyl iron(II) complexes, [2-[CMeN{2,4-{(4-FC6H4)2CH}2-6-F}]-6-(CMeNAr)C5H3N]FeCl2 (Ar = 2,6-Me2C6H3Fe1, 2,6-Et2C6H3Fe2, 2,6-iPr2C6H3Fe3, 2,4,6-Me3C6H2Fe4, and 2,6-Et2-4-MeC6H2Fe5) and [2-[CMeN{2-{(4-FC6H4)2CH}-4-{(C6H5)CHAr'}-6-F}]-6-(CMeN(2,6-iPr2C6H3))C5H3N]FeCl2 (Ar' = 3-{(4-FC6H4)2CH}2-4-NH2-5-FC6H2Fe6), verified with different steric substituents, were synthesized and characterized. The molecular structures of Fe2 and Fe3 were determined by X-ray diffraction, revealing a pseudo-square-pyramidal geometry. High activities were achieved toward ethylene polymerization in each iron complex case. The sterically least demanding ligand enhanced the activity of its complex Fe1 with the highest activity up to 16.8 × 106 g of PE (mol of Fe)-1 h-1at 70 °C, while the bulkiest ligand led to the formation of the highest molecular weight of the resulting polyethylene using Fe6. Generally, the resulting polyethylenes are highly linear and most of them have a tendency to display bimodal distributions by virtue of the presence of multiple sites or competing chain transfer reactions. End-group analysis of polyethylenes confirms that the end groups include both unsaturated vinyl-end groups and saturated n-propyl or i-butyl, revealing the co-existence of two chain termination pathways including primary chain transfer to aluminium and secondary β-H transfer. The chain termination processes were interpreted with the 1D sequence inverse-gated decoupled 13C NMR measurement of the resulting polyethylenes and DFT calculations along with the relevant polymerization mechanism.

Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups

Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (η5-C5Me5)TiCl2(O-2,6-iPr2C6H3) (1), (η5-C5Me5)TiCl2(N=CtBu2) (2) and [Me2Si(η5-C5Me4)(NtBu)]TiCl2 (3), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex 1, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes 1 and 2, while both side insertion orientations are comparable for complex 3. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from 3. At the chain termination stage, β-H transfer was calculated to be a dominant chain termination route over β-H elimination, presumably owing to the thermodynamic perspective.