Catalytic Activity For Ethylene Polymerization Research Articles

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.

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).

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.

A strategy for high ethylene polymerization performance using titanium single-site catalysts.

The synthesis of heterogeneous Ti(IV)-based catalysts for ethylene polymerization following surface organometallic chemistry concepts is described. The unique feature of this catalyst arises from the silica support, KCC-1700. It has (i) a 3D fibrous morphology that is essential to improve the diffusion of the reactants, and (ii) an aluminum-bound hydroxyl group, [(Si-O-Si)(Si-O-)2Al-OH] 2, used as an anchoring site. The [(Si-O-Si)(Si-O-)(Al-O-)TiNp3] 3 catalyst was obtained by reacting 2 with a tetrakis-(neopentyl) titanium TiNp4. The structure of 3 was fully characterized by FT-IR, advanced solid-state NMR spectroscopy [1H, 13C], elemental and gas-phase analysis (ICP-OES and CHNS analysis), and XPS. The benefits of combining these morphological (3D structure) and electronic properties of the support (aluminum plus titanium) were evidenced in ethylene polymerization. The results show a remarkable enhancement in the catalytic performance with the formation of HDPE. Notably, the resulting HDPE displays a molecular weight of 3 200 000 g mol-1 associated with a polydispersity index (PD) of 2.3. Moreover, the effect of the mesostructure (2D vs. 3D) was demonstrated in the catalytic activity for ethylene polymerization.

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%.

Synthesis and characterization of the titanium catalysts supported by pyrrolide-benzoxazole ligands and their application in ethylene polymerization

The novel pyrrolide-benzoxazole [NN] titanium complexes TiL2Cl2 [L = 2-(5-R-benzo-[d]xazol-2-yl)-pyrrole, R = H (2a), R = CH3 (2b), R = tBu (2c), R = Cl (2d)] were synthesized. All the complexes were fully characterized by 1H, 13C NMR spectra and elemental analyses and the molecular structures of 2b and 2d were determined by single crystal X-ray diffraction. In the presence of methylaluminoxane (MAO), the titanium complexes showed moderate catalytic activities for ethylene polymerization to afford high-molecular-weight polymers.

A Ni0 σ‐Borane Complex Bearing a Rigid Bidentate Borane/Phosphine Ligand: Boryl Complex Formation by Oxidative Dehydrochloroborylation and Catalytic Activity for Ethylene Polymerization

AbstractWhile of interest, synthetically feasible access to boryl ligands and complexes remains limited, meaning such complexes remain underexploited in catalysis. For bidentate boryl ligands, oxidative addition of boranes to low‐valent IrI or Pt0 are the only examples yet reported. As part of our interest in developing improved group 10 ethylene polymerization catalysts, we present here an optimized synthesis of a novel, rigid borane/phosphine ligand and its Ni0 σ‐borane complex. From the latter, an unprecedented oxidative dehydrochloroborylation, to give a NiII boryl complex, was achieved. Furthermore, this new B/P ligand allowed the nickel‐catalyzed polymerization of ethylene, which suggests that Ni0 σ‐hydroborane complexes act as masked NiII boryl hydride reagents.

Naphthalenyl‐Substituted α,α′‐Bisimino‐2,3 : 5,6‐Bis(pentamethylene)pyridines as Thermally Robust Supports for Iron Ethylene Polymerization Catalysts

AbstractSix examples of N,N,N‐chelated iron(II) chloride complex, [2,3 : 5,6‐{C4H8C(NAr)}2C5H3N]FeCl2 (Ar=1‐C10H7 Fe1, 2‐Me‐1‐C10H6 Fe2, 2‐(CHMePh)‐1‐C10H6 Fe3, 2‐Cl‐1‐C10H6 Fe4, 4‐Br‐1‐C10H6 Fe5, 4‐NO2‐1‐C10H6 Fe6), differing in the steric/electronic properties of the substituents appended to the N‐naphthalen‐1‐yl groups, have been synthesized in reasonable yield via a facile one‐pot route. The molecular structure of five‐coordinate Fe3 emphasizes the steric hindrance imposed on the iron center by the CHMePh‐substituted bicyclic aromatic groups. With either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) as activator, the complexes displayed a wide range in catalytic activities for ethylene polymerization with the order for MMAO being: Fe3>Fe2≫Fe1>Fe4≫Fe5 while Fe6 was almost inactive. In particular, Fe3/MMAO exhibited exceptionally high activity at 70 °C (up to 15.7×106 g (PE) mol−1 (Fe) h−1) affording low molecular weight (2.97 kg mol−1) polyethylene of high linearity and narrow dispersity (Mw/Mn=1.38). Moreover, the same catalyst displayed excellent thermostability by maintaining high activity at 90 °C (up to 9.26×106 g (PE) mol−1 (Fe) h−1). Similar activity trends were observed with MAO though the catalysts were in general less active but formed distinctly higher molecular weight polyethylene.

Half-sandwich chromium(III) complexes containing salicylbenzoxazole and salicylbenzothiazole ligands for ethylene polymerization

Half-sandwich chromium(III) complexes bearing salicylbenzoxazole ligands 2a-2f [L = R-2-(benzo[d]xazol-2-yl)-phenol (R = H (2a), R = 6-CH3 (2b), R = 6-tBu (2c), R = 4-OCH3 (2d), R = 4-Cl (2e), R = 4-NO2 (2f)] and salicylbenzothiazole ligands 3a-3f [L = R-2-(benzo[d]xazol-2-yl)-phenol (R = H (3a), R = 6-CH3 (3b), R = 6-tBu (3c), R = 4-OCH3 (3d), R = 4-Cl (3e), R = 4-NO2 (3f)] were synthesized by the salt-elimination reaction of CpCrCl2(THF) and the sodium salt of the corresponding ligands in THF at −78 °C. The molecular structures of complexes 3a and 3e are confirmed by single-crystal X-ray crystallographic analysis. Upon the activation of a small amount of AlEt3, all the half-sandwich chromium(III) complexes showed moderate to high catalytic activities for ethylene polymerization and afforded high molecular weight polyethylene (PE).

Binuclear Ti(IV) complex with new compartmental ligand 2,6‐(bis‐CF3‐carbinol)‐4‐tert‐butylphenol as precatalysts for ethylene polymerization and its copolymerization with propylene and 5‐ethylidene‐norbornene

AbstractThe coordination chemistry of a new compartmental ligand 2,6‐(bis‐CF3‐carbinol)‐4‐tert‐butylphenol with Ti(IV) and Zr(IV) has been studied. The structures of Al, Ti, and Zr complexes with the participation of this ligand were established by X‐ray diffraction. Upon activation with Et2AlCl or Et3Al2Cl3 and Bu2Mg, Ti(IV) complex exhibited moderate catalytic activity for ethylene polymerization. The obtained UHMWPE samples were processed into high‐strength (up to 2.7 GPa) and high‐modulus (up to 162 GPa) films through solid‐phase molding and orientation drawing. The mononuclear and binuclear Ti(IV) complexes catalyzed the ternary copolymerization of ethylene, propylene, and 5‐ethylidene‐norbornene. Tercopolymers with a content of propylene units up to 36 mol% and 5‐EBN up to 8.6 mol% were synthesized with a high activity (2.8–6.3 tons of copolymer/mol Ti h); the mechanical characteristics of elastomeric materials have been studied.

The Stronger the Better: Donor Substituents Push Catalytic Activity of Molecular Chromium Olefin Polymerization Catalysts.

The donor strength of bifunctional pyridine‐cyclopentadienyl ligands was altered systematically by the introduction of donating groups in the para‐position of the pyridine. In the resulting chromium complexes an almost linear correlation between donor strength and the nitrogen‐chromium distance as well as the electronic absorption maximum is experimentally observed. The connection of electron‐donating groups in the ligand backbone leads to an efficient transfer of the electronic influences to the catalytically active metal centre without restricting it through steric effects. Therefore, catalytic olefin polymerization activity, which is already very high for the previously studied catalysts, increase considerably by attaching para‐amino groups to the chelating pyridine or quinoline, respectively. Combining electron‐rich indenyl ligands with para‐amino substituted pyridines lead to the highest catalytic activities observed so far for this class of organo chromium olefin polymerisation catalysts. The resulting polymers are of ultra‐high molecular weight and the ability of the catalysts to incorporate co‐monomers is also very high.

Exploring ortho‐(4,4′‐dimethoxybenzhydryl) substitution in iron ethylene polymerization catalysts: Co‐catalyst effects, thermal stability, and polymer molecular weight variations

Six different types of 4,4′‐dimethoxybenzhydryl‐substituted bis(arylimino)pyridine‐iron(II) chloride complex—[2‐{{2,6‐((p‐MeOPh)2CH)2‐4‐MeC6H2}N=CMe}‐6‐(ArN=CMe)C5H3N]FeCl2 (Ar = 2,6‐Me2C6H3 (Fe1), 2,6‐Et2C6H3 (Fe2), 2,6‐iPr2C6H3 (Fe3), 2,4,6‐Me3C6H2 (Fe4), 2,6‐Et2‐4‐MeC6H2 (Fe5), 2,6‐((p‐MeOPh)2CH)2‐4‐MeC6H2 (Fe6)—are reported. The molecular structures of Fe2 and Fe3 emphasize the unsymmetrical nature of the N,N,N‐chelating ligand and the steric protection exerted by the ortho‐(4,4′‐dimethyoxybenzhydryl) groups. A range in catalytic activities for ethylene polymerization was observed when Fe1–Fe6 were treated with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO). In particular, Fe1/MAO bearing the least bulky N‐2,6‐dimethylphenyl group exhibited a very high activity of 1.11 × 107 g (PE) mol−1 (Fe) h−1 at 70°C/10 atm over a 30‐min run time that remained high even after 60 min, an observation highlighting its appreciable catalyst lifetime and thermal stability. In addition, the polyethylene formed by this catalyst class displayed desirable characteristics such as high linearity and high molecular weight (Mw range: 5.17–7.62 × 105 g mol−1). Indeed, the molecular weight of the polymer produced using Fe1 (with MAO or MMAO) exceeds that obtained using related benzhydryl‐containing bis(imino)pyridine‐iron catalysts. As a general feature, activation of Fe1–Fe6 with MMAO led to lower activity and lower molecular weight polyethylene, especially for runs performed at 1 atm ethylene pressure.

Metallocene encapsulated within a hybrid silica-polystyrene support

A series of heterogeneous metallocene catalysts were prepared by encapsulating Cp2ZrCl2 within silica-polystyrene hybrid support. Immobilization was performed through a non-hydrolytic sol–gel process in which polystyrene (PS) dissolved in toluene and metallocene (1% by wt) were combined. The effect of PS (0 to 5% by wt) and silicon tetrachloride (0.5 to 1.6 [TEOS]/[SiCl4]) was evaluated in terms of catalyst activity in ethylene polymerization with methylaluminoxane as the cocatalyst. According to FTIR measurements, an increase in PS content promoted a decrease in (SiO)6 content, which indicated the formation of more compact structures. Furthermore, homogeneous distributions of polymer and silica phases were observed both in bulk and on the support surface. The results showed very small surface areas (< 20 m2 g−1), probably because PS would fill the silica pores. The catalytic activity for ethylene polymerization was shown to decrease with increasing polystyrene content within the catalyst support of low surface area. A positive correlation was found between the (SiO)6 content and catalyst activity. The increase in the PS content was followed by an increase in the degree of polyethylene crystallization, which ranged from 77 to 84%.

Rational Design of Cycloheptyl‐Fused Bis(arylimino)pyridyl‐cobalt(II) Precatalysts Adorned with Sterically and Electronically Modified N‐Aryls for Enhancing Ethylene Polymerization

AbstractThe sterically and electronically modified cycloheptyl‐fused bis(arylimino)pyridine‐cobalt(II) chloride precatalysts [2,3 : 5,6‐{C4H8C(N‐2,4‐(C15H13)‐6‐R‐C6H2}2C5HN]CoCl2 (R=Me (Co1), Et (Co2), i‐Pr (Co3), Cl (Co4), and F (Co5)) have been prepared via one‐pot synthesis approach. All the precatalysts were characterized by elemental analysis, FT‐IR spectroscopy and the single‐crystal X‐ray diffraction for Co2 confirmed distorted‐square‐pyramidal geometry around the cobalt center. On activation with either MAO (methylaluminoxane) or MMAO (modified methylaluminoxane), all the cobalt precatalysts displayed high catalytic activities for ethylene polymerization with peak performance of 3.47×106 g (PE) mol−1 (Co) h−1 at 50 °C using MAO and 4.53×106 g (PE) mol−1 (Co) h−1 at 30 °C with MMAO. The steric and electronic influence of the ortho‐substitutions (R) displayed significant effect on the catalytic activity and molecular weight of the resultant polyethylene. Notably, the precatalyst Co5 (R=F) exhibited high activity, delivering high‐molecular‐weight (558.17 kg mol−1) polyethylene; highlights the beneficial effect of ortho‐substituents (R) alongside with dibenzocycloheptyl groups. In addition, analysis of the obtained polyethylene showed strictly linear structure with saturated and unsaturated (vinyl) end groups.

Adjusting Ortho-Cycloalkyl Ring Size in a Cycloheptyl-Fused N,N,N-Iron Catalyst as Means to Control Catalytic Activity and Polyethylene Properties

Five examples of bis(arylimino)tetrahydrocyclohepta[b]pyridine dichloroiron(II) complex, [2-{(Ar)N=CMe}-9-{N(Ar)}C10H10N]FeCl2 (Ar = 2-(C5H9)-4,6-(CHPh2)2C6H2Fe1, 2-(C6H11)-4,6-(CHPh2)2C6H2Fe2, 2-(C8H15)-4,6-(CHPh2)2C6H2Fe3, 2-(C12H23)-4,6-(CHPh2)2C6H2Fe4, and 2,6-(C5H9)2-4-(CHPh2)C6H2Fe5), incorporating ortho-pairings based on either benzhydryl/cycloalkyl (ring sizes ranging from 5 to 12) or cyclopentyl/cyclopentyl groups, have been prepared in reasonable yield by employing a simple one-pot template strategy. Each complex was characterized by FT-IR spectroscopy, elemental analysis, and for Fe3 and Fe5 by single crystal X-ray diffraction; pseudo-square pyramidal geometries are a feature of their coordination spheres. On treatment of Fe1–Fe5 with modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), a range in catalytic activities for ethylene polymerization were observed with benzhydryl/cyclopentyl-containing Fe1/MMAO achieving the maximum level of 15.3 × 106 g PE mol−1 (Fe) h−1 at an operating temperature of 70 °C. As a key trend, the activity was found to drop as the ortho-cycloalkyl ring size increased: Fe1C5H9/CHPh2~Fe5C5H9/C5H9 &gt; Fe2C6H11/CHPh2 &gt; Fe3C8H15/CHPh2 &gt; Fe4C12H23/CHPh2. Furthermore, strictly linear polyethylenes (Tm &gt; 126 °C) were formed with molecular weights again dependent on the ortho-cycloalkyl ring size (up to 55.6 kg mol−1 for Fe1/MAO); narrow dispersities were a characteristic of all the polymers (Mw/Mn range: 2.3–4.7), highlighting the well-controlled nature of these polymerizations.

A Titanium(IV) Complex with an OSO-Type Ligand as a Catalyst for the Synthesis of Ultrahigh-Molecular-Weight Polyethylene

Coordination compounds of titanium(IV) with OSO-type ligands have been prepared and characterized, and their catalytic activity in ethylene polymerization has been studied. It has been shown that in the presence of an {Et2AlCl + Bu2Mg} binary cocatalyst, the activity of the titanium-containing catalyst system reaches 1629 kgPE mol(Ti)−1 h−1 and leads to the preparation of ultrahigh-molecular-weight polyethylene (UHMWPE). The UHMWPE reactor powder has been processed by a solvent-free method to high-strength and high-modulus films (σ = 2.32 GPa, E = 125 GPa).

α-Diimine nickel complexes bearing axially bulky terphenyl and equatorially bulky dibenzobarrelene groups: synthesis, characterization and olefin polymerization studies

A new family of asymmetric α-diimine nickel complexes bearing axially and equatorially bulky groups were synthesized successfully. They exhibited high catalytic activities for ethylene polymerization and afforded ultra-high-molecular-weight elastomeric polyethylenes.

A screening DFT study of the para-substituent effect on local hyper-softness in bis(phenoxy-imine) titanium complexes to get insights about their catalytic activity in ethylene polymerization

Quantum chemical calculations of substituted α-Cumyl and tBu bis(phenoxy-imine) titanium catalysts were performed at the RBP86/SVP level. The impact of para-substitution in the phenoxy-imine ligands on the electronic structure of the titanium complexes was studied within the framework of the Conceptual density functional theory. We found that such a reactivity descriptor as local hyper-softness on titanium correlates well with the Hammett constant for a series of substituents. The effect of the substitution in three para-positions of the phenoxy-imine ligand for the Cumyl catalysts weakens while passing from the α-Cumyl through the salicylic and further to the aniline moiety. By contrast, in the tBu complexes the presence of a substituent in the salicylic part has similar influence on the local hyper-softness on titanium as compared with the aniline moiety. Moreover, placement of the groups with opposite electronic effects at the termini of the phenoxy-imine framework was shown to provide electronic flexibility in both the α -Cumyl and the tBu complexes. Within the framework of the "ligand-oriented" concept, such flexibility increases the activity of a bis(phenoxy-imine) catalyst. In addition, we demonstrated that the hyper-conjugation between the π-system of the phenoxy-imine ligand and the α-Cumyl group raises the energy of the highest occupied molecular orbital keeping the lowest unoccupied orbital almost unchanged. This makes the α-Cumyl complexes chemically softer than their tBu analogs and thereby more active in ethylene polymerization.

Vanadium chlorides supported by BIAN (BIAN = bis(arylimo)-acenaphthene) ligands: Synthesis, characterization, and catalysis on ethylene polymerization

Several vanadium chlorides bearing bis(arylimino)-acenaphthene (BIAN) ligands, (2,6-Me2C6H3-BIAN)V(THF)Cl3 (1), (2,6-Et2C6H3-BIAN)V(THF)Cl3 (2), (2,6-iPr2C6H3-BIAN)V(THF)Cl3 (3), [3,5-(CF3)2C6H3-BIAN]V(THF)Cl3 (4), [4-OMe-C6H4-BIAN]V(THF)Cl3 (5), and [2,6-(Ph2CH)2-4-OMeC6H2-BIAN]V.(THF)Cl3 (6) were synthesized by direct reaction of VCl3(THF)3 with corresponding BIAN ligands. All these complexes were characterized by elemental analyses, and FT-IR spectroscopy. The molecular structures of 1, 2, and 4 were identified by X-ray crystallography, in which the six-coordinated vanadium metal centers were in distorted octahedral geometry with the oxygen atom of the coordinated THF, two nitrogen atoms of the diimine ligand and one chlorine atom in the same plane. When activated with AlEt2Cl these vanadium complexes showed high catalytic activities for ethylene polymerization affording linear polyethylene with high molecular weight. However, when MAO was used as co-catalyst, ultra high molecular-weight polymers were obtained albeit with decreased activity.

Synthesis and characterization of chromium complexes 2-Me4CpC6H4CH2(R)NHCrCl2 and their catalytic properties in ethylene homo- and co-polymerization.

A series of new half-sandwich secondary amine-coordinated dichlorochromium complexes chelated by 2-(tetramethylcyclopentadienyl)benzylamine ligands, 2-Me4CpC6H4CH2(R)NHCrCl2 [R = iPr (1), Cy (2), Ph (3), 4-MePh (4), 2,6-Me2Ph (5), 2,6-Et2Ph (6)], have been synthesized from the reactions of CrCl3(THF)3 with the dilithium salts of the corresponding ligands in THF, followed by the addition of 1/2 eq. of H2O to the reaction mixtures. The isolated yields of the chromium complexes were found to increase with the increase in the amount of H2O introduced and reach the highest values (66-76%) when 1/2 eq. of H2O is added. Attempts to isolate the 2-(tetramethylcyclopentadienyl)benzylamidochromium complexes, 2-Me4CpC6H4CH2(R)NCrCl, were not successful. The new dichlorochromium complexes were characterized by IR, 1H NMR, EPR, and UV/Vis spectroscopy and elemental analyses, and the molecular structures of complexes 1, 5 and 6 were determined by X-ray crystallography. The X-ray crystallographic analysis reveals that these chromium complexes possess a three-legged piano-stool geometry with the amine N atom in a mitered six-membered chelating ring and the two chloride atoms as the legs. Upon activation with AlR3 and Ph3CB(C6F5)4, complexes 1-6 exhibit reasonable catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing polyethylenes with moderate to high molecular weights and poly(ethylene-co-1-hexene)s with moderate comonomer incorporation which are typical linear low-density polyethylenes (LLDPE). Complex 4 was found to show higher catalytic activity for ethylene homo- and co-polymerization than other complexes under similar conditions, while complex 3 produced poly(ethylene-co-1-hexene)s with the highest comonomer incorporation.