Activities For Ethylene Oligomerization Research Articles

Synthesis and characterization of monomeric and polymeric pyridinylimine-based Ni(II) complexes and their catalytic activities in ethylene oligomerization

A new polymeric ligand was synthesized through the reaction of 4-(pyridinylimine)phenol and formaldehyde in a basic medium, and its corresponding polymer–nickel complexes were formed in a 1:1 molar ratio. The synthesized compounds were characterized using elemental and spectral analyses. The monomeric and polymeric Ni(II) complexes (C1 and C2, respectively) were evaluated as catalyst precursors for ethylene oligomerization, using methylaluminoxane as an activator at two different ethylene pressures. C2 was found to be a more effective pre-catalyst than C1, with the co-catalyst having a similar effect in both cases. C2 exhibited an activity of 1.282 × 106 g (mol Ni)−1 h−1 bar−1, with an Al:Ni ratio of 2000:1 at room temperature and 1 atm ethylene pressure. Meanwhile C1 exhibited an activity of 1.126 × 106 g (mol Ni)−1 h−1 bar−1 under similar experimental conditions. At 5 atm ethylene pressure, C1 favoured the formation of high-density polyethylene, whereas C2 favoured the formation of branched low-density polyethylene. Copyright © 2012 Society of Chemical Industry

Nickel halide complexes bearing 2-benzimidazolyl-N-arylquinoline-8-carboxamide derived ligands: Synthesis, characterization and catalytic behavior towards ethylene oligomerization and the vinyl polymerization of norbornene

Nickel halide complexes of the type L2NiX2 (Ni1–Ni6, X = Cl; Ni7–Ni12, X = Br) bearing 2-benzimidazolyl-N-arylquinoline-8-carboxamide derived ligands have been synthesized and characterized by IR spectroscopy and elemental analysis. The molecular structures of the representative nickel complexes Ni8 and Ni11 revealed a distorted octahedral geometry at the nickel center. Upon activation with Et2AlCl, all such nickel pre-catalysts exhibited high activities for ethylene oligomerization. Furthermore, in the presence of MAO, they were shown to perform with good activities for the vinyl polymerization of norbornene.

2-Substituted 8-(2-benzhydrylarylimino)-5,6,7-trihydroquinoline-N,N′ nickel dichlorides: Synthesis, characterization and catalytic behavior towards ethylene

A series of 2-substituted 8-(2-benzhydrylarylimino)-5,6,7-trihydroquinolines (L) was synthesized and fully characterized, and their nickel chloride complexes, namely 2-substituted 8-(2-benzhydrylarylimino)-5,6,7-trihydroquinoline-N,N′ nickel dichlorides (LNiCl2), were prepared and characterized by FT-IR and elemental analysis. The structures of representative complexes were confirmed by single crystal X-ray crystallography, which revealed a distorted trigonal bipyramidal geometry at the metal for complexes Ni3 and Ni5 containing an additional solvent molecule, and a distorted tetrahedral geometry for the complex Ni8. Upon activation with methylaluminoxane (MAO), all nickel pre-catalysts showed good activity for ethylene polymerization and considerable activity for ethylene oligomerization.

Nickel and Palladium Complexes with New Phosphinito-Imine Ligands and Their Application as Ethylene Oligomerization Catalysts

Phosphinito-imines, a new class of P,N donors, are readily generated by reaction of bulky arylamide anions [R2CONAr]− (R2 = Me or t-Bu; Ar = 2,6-i-Pr2C6H4) with chlorophosphines ClP(R1)2. In solution, free phosphinito-imines exist in equilibrium with the corresponding amidophosphine tautomers, containing a nitrogen-bound P(R1)2 group. However, reacting the tautomer mixtures with metal precursor complexes, such as NiBr2(dme) or PdCl2(cod), selectively affords stable phosphinito-imine complexes MX2(P-N) (M = Ni, Pd) in excellent yields. These complexes are diamagnetic and exhibit square-planar structures in the solid state, but in solution, the Ni derivatives exchange with a small amount of the corresponding high-spin tetrahedral isomers. On treatment with MMAO or DEAC, NiX2(P-N) complexes become active ethylene oligomerization catalysts, affording mainly butenes along with smaller amounts of hexenes and octenes. The activity and the selectivity of these catalysts depend on the structure of the phosphinito-imine ligand and the cocatalyst used. When activated with DEAC, complexes containing the P(i-Pr)2 moiety are extremely active, achieving TOFs over 106 mol C2H4/mol Ni·h and high selectivity for butenes.

2-(1-Arylimino)quinolylnickel halides: Synthesis, characterization and catalytic behavior towards ethylene

A series of 2-(1-arylimino)quinolylnickel halides were synthesized and characterized by IR and elemental analyses. Distorted trigonal bipyramidal geometries are adopted for the nickel complexes C1, C4, C7 and C11 as crystallized from either DMF or methanol solution. When activated by Et2AlCl, the nickel pre-catalysts exhibited good to high catalytic activities in ethylene oligomerization.

Oligomerization of ethylene using tridentate nickel catalysts bearing ether-pyrazol ligands with pendant O- and S-donor groups

Abstract A series of tridentate pyrazol ligands with pendant O- and S-donor groups (L1-L5) and their corresponding nickel(II) chloride complexes (1–5) were synthesized and fully characterized. All nickel precatalysts, activated with methylaluminoxane (MAO), exhibited high activities for ethylene oligomerization [TOF = 17.1–75.8 × 10 3 mol(ethylene)(mol(Ni)) − 1 h − 1 )] with good selectivities for 1-butene produced (62.9 – 81.3%). The catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-donor groups, and the substituents on the phenol group. Activation of nickel precatalyst 1 with ethylaluminum sesquichloride (Et 3 Al 2 Cl 3 , EASC) instead of MAO produced a significantly better catalyst system than 1/MAO (TOF = 227,000 vs. 30,900 (mol C 2 H 4 )⋅(mol Ni − 1 h − 1 ); however, the 1-butene selectivity was drastically reduced, attaining only 28% with a concomitant production of larger amounts of internal butenes (51.4%) and hexenes (28.2%). Under optimized conditions ([Ni] = 10μmol, 30°C, oligomerization time = 20 min, 40 bar ethylene, [Al]/[Ni] = 250), precatalyst 1 led to TOF = 75,800 (mol C 2 H 4 )⋅(mol Ni − 1 h − 1 ) and 76.1% selectivity for 1-butene.

Highly Active Ethylene Oligomerization Catalysts

Reaction of RN(H)PBr(Ph)2N(H)R [R = t-Bu, i-Pr, Ph] with two equivalents of n-BuLi followed by reaction with CrCl2(THF)2 afforded the divalent chromium complexes [(t-Bu)NP(Ph)2N(t-Bu)]Cr(μ2-Cl)2Li(THF)2 (1), [(i-Pr)NP(Ph)2N(i-Pr)]Cr(μ2-Cl)2Li(THF)2 (2), and [{[(Ph)NP(Ph)2N(Ph)]Cr}2(μ2-Cl)3][Li(DME)3] (3). The trivalent analogue of 1, {[(t-Bu)NP(Ph)2N(t-Bu)]Cr(μ2-Cl)3(μ3-Cl)2}{Li (THF)2} (4), was obtained in a similar manner via treatment of the double deprotonated ligand with CrCl3(THF)3. Both reactions of the divalent1 or trivalent4 with AlMe3 yielded the trivalent and cationic complex {[(t-Bu)NP(Ph)2N(t-Bu)]2Cr}{(Me3Al)2Cl}·toluene (5). Upon activation with MAO, 1–3 produced unprecedented and potentially useful catalytic systems for nonselective ethylene oligomerization devoid of polymer. Divalent chromium is clearly the species responsible for the catalytic behavior, ruling out that nonselective oligomerization proceeds via a redox metallacycle mechanism. The absence of polymer in combination with the record activity makes 1 competitive with the best performing industrially used systems.

Reactions between an Ethylene Oligomerization Chromium(III) Precatalyst and Aluminum-Based Activators: Alkyl and Cationic Complexes with a Tridentate NPN Ligand

To gain a deeper knowledge of the nature of the species formed in situ by reaction of a catalyst precursor complex and typical cocatalysts used for ethylene oligomerization or polymerization, the Cr(III) complex fac-[Cr(NPN)Cl3] (1; NPN = bis(2-picolyl)phenylphosphine) was reacted with MAO and partial methylation to give the mononuclear complex fac-[Cr(NPN)Cl2.23Me0.77] (2) was observed, whereas reaction with AlMe3 in toluene led to partial halide abstraction and produced the dinuclear, chloride-bridged dicationic complex [{fac-Cr(NPN)Me(μ-Cl)}2][AlMexCl4–x]2 (3·[AlMexCl4–x]2), in which the metal centers are bridged by two chloride ligands. The complex fac-[Cr(NPN)Cl2Et] (4) was isolated in high yield from the reaction of 1 with AlEt3 and contains a rare example of CrIII–Et function. Upon treatment of 1 with EtAlCl2, the dinuclear Cr(III) complex [{fac-Cr(NPN)}2(μ-Cl)3][AlCl4]3 (5·[AlCl4]3) was obtained, which contains three bridging chlorides. Thus, under the conditions investigated, MAO and AlEt3 behaved as alkylation agents, whereas AlMe3 and EtAlCl2 reacted as cationization agents. On activation with MAO and under comparable conditions, 1–5 exhibited similar catalytic properties, with activities between 2700 and 2800 g of C2H4/((g of Cr) h), but the major oligomer produced using the 4/MAO system was 1-decene. The neutral alkyl complexes 2 and 4 and the cationic complexes 3 and 5 did not exhibit catalytic activity for ethylene oligomerization in the absence of MAO. The structures of the complexes 2, 3·[AlMexCl4–x]2, 4, and 5·[AlCl4]3 have been determined by single-crystal X-ray diffraction.

2-Benzimidazolyl-N-phenylquinoline-8-carboxamide Chromium(III) Trichlorides: Synthesis and Application for Ethylene Oligomerization and Polymerization

A series of chromium(III) complexes, LCrCl3 (C1–C6: L = 2-(1H-benzo[d]imidazol-2-yl)-N-(2,6-R1-4-R2-phenyl)quinoline-8-carboxamide; C1: R1 = iPr, R2 = H; C2: R1 = Et, R2 = H; C3: R1 = Me, R2 = H; C4: R1 = Me, R2 = Me; C5: R1 = H, R2 = H; C6: R1 = F, R2 = H), was synthesized and characterized by IR spectroscopy, elemental analysis, mass spectra, and magnetic moments. The X-ray crystallographic analysis of complexes C2 and C3 reveals distorted octahedral geometries around the chromium atoms. Upon activation with MAO, these complexes exhibit high activities for ethylene oligomerization (up to 1.28 × 107 g·mol–1(Cr)·h–1) and ethylene polymerization (up to 6.30 × 106 g·mol–1(Cr)·h–1). The oligomers were produced with high selectivity for α-olefins (>99%), and the distribution closely resembled the Schultz–Flory rule. Various reaction parameters were investigated in detail, and the results revealed that both the steric and electronic effects of the ligands effect the catalytic activities of these chromium complexes as well as the distribution of the products formed.

Ethylene Oligomerizations by Diazene Bridged Ni(II) Catalysts Derived from Pyrazole-Scaffold-Based Binucleating Ligands with Alkyl and Aryl Pendant Arms

The coordination and organometallic chemistry of a series of diazene (N2)-bridged Ni(II) catalysts derived from pyrazole-scaffold-based ligands bearing alkyl and aryl pendent arms was investigated. Binucleating ligands were obtained as products of the condensation reaction between 3,5-dichloroformyl-1H-pyrazole and aliphatic/ aromatic primary/secondary amines under anhydrous con- ditions. The Ni(II) catalysts were activated with ethyl aluminum sesquichloride (EASC) to oligomerize the eth- ylene mainly into C4, C6, C8, and C10 fractions with activities up to 1.2 and 0.5 9 10 6 g (mol-Ni) -1 bar -1 h -1 at 30 and 50 C, respectively. All catalysts were found to be electrochemically active in the working potential range of - 2t o?2 V. A change in the potential of Ni(II) was provoked by the N4 donor bridging ligands, increasing the ethylene oligomerization activity.

Synthesis, characterization and ethylene oligomerization behavior of 2-(chloro-substituted-1 H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridylnickel dihalides

A series of 2-(chloro-substituted-1 H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridines ( L1– L6) was synthesized and fully characterized. They reacted with NiCl 2 or (DME)NiBr 2 to form the corresponding N^N^N tridentate nickel dichlorides ( C1– C6) or dibromides ( C7– C12). All nickel complexes were characterized by elemental analysis and infrared spectroscopy, while the X-ray diffraction study reveals the distorted octahedral geometry of representative nickel dichloride complex C3 and nickel dibromide complex C7. All nickel complexes, activated with either Et 3Al 2Cl 3 or Et 2AlCl, showed good activities in ethylene oligomerization, and notably remarkably high selectivity of α-olefins was achieved in the presence of Et 3Al 2Cl 3. The chloro-substituted ligands enhanced the activities of complexes in ethylene polymerization.

Synthesis, characterization and ethylene oligomerization behaviour of 8-(1-aryliminoethylidene)quinaldinylnickel dihalides

A series of 8-(1-aryliminoethylidene)quinaldines and the nickel halides thereof were synthesized and characterized, and the molecular structures of two representative nickel complexes were confirmed by single-crystal X-ray diffraction studies. Upon treatment with diethylaluminium chloride (Et2AlCl), the nickel pro-catalysts exhibited high activity for ethylene oligomerization (1.24–1.83 × 106 g mol−1(Ni) h−1) with good thermal stability at 60 °C under 10 atm of ethylene. The influence of the reaction parameters on the catalytic behaviour was investigated for these nickel-based systems, including variation of Al/Ni molar ratio and reaction temperature. Furthermore, the effect of the ancillary ligand Ph3P was also probed.

Pyrazolyl iron, cobalt, nickel, and palladium complexes: synthesis, molecular structures, and evaluation as ethylene oligomerization catalysts

Reactions of [2-(3,5-dimethyl-pyrazol-1-yl)-ethanol] ( L1) and [1-(2-chloro-ethyl)-3,5-dimethyl-1H-pyrazole] ( L2) with Fe(II), Co(II), Ni(II), and Pd(II) salts gave the complexes [( L1) 2FeCl 2] ( 1), [( L1) 2CoCl 2] ( 2), [( L1) 2NiBr 2] ( 3), [( L1) 2Pd(Me)Cl] ( 5), [( L2) 2CoCl 2] ( 6), and [( L2) 2NiBr 2] ( 7). Whereas L2 behaves as a monodentate ligand, L1 can behave as either a monodentate or bidentate ligand depending on the nature of the metal centre. For palladium, L1 is monodentate in the solid state structure of 5 but bidentate in the structure of 4, obtained during attempts to crystallize 3. While the activation of iron, cobalt and palladium complexes with EtAlCl 2 did not produce active ethylene oligomerization catalysts, the nickel complexes 3 and 7 produced active ethylene oligomerization catalysts. Activities as high as 4329 kg/mol Ni h were obtained. Catalyst 3 produced mainly butenes (57%) and hexenes (43%); of which a combined 20% were converted to Friedel-Crafts alkylated-toluene. Catalyst 7, on other hand, produced mainly butenes (90%) and small amounts of hexenes (10%) which were then completely converted to the corresponding Friedel-Crafts alkylated-toluene products. This difference in product distribution in catalysis performed by complexes 3 and 7 is indicative of the role of the OH functionality in L1 on the EtAlCl 2 co-catalysts.

Synthesis, characterization and ethylene oligomerization studies of nickel(II) based new formazane derivatives

A series of nickel(II) complexes based novel mono- and bis-formazan ligands has been synthesized and characterized with IR, UV, NMR spectroscopies, CHN analysis, mass spectrometry, and single crystal X-ray diffraction analysis. The prepared complexes have been tested for catalytic activity in ethylene oligomerization.

Synthesis Characterization of Polyamide Metallodendrimers and their Catalytic Activities in Ethylene Oligomerization

Nickel complexes with aromatic amine terminated first generation (G1) and second generation (G2) polyamide dendrimers {POA-(NH2)n (n = 6 or 12, POM = Polyamide)} were synthesized. All the synthesized dendrimers and metallodendrimers were characterized by elemental and spectral analysis. These novel dendritic complexes were evaluated as catalyst precursors in the oligomerization of ethylene, using methylaluminoxane (MAO) as an activator at two different pressure and different Al/M (M = Zn) ratio. In the case of 1 atm pressure of ethylene, and 500:1 and 1,000:1 Al/Ni molar ratio, for C 1 and C 2 respectively display higher catalytic activity towards ethylene polymerization. Oligomerization using the generation 1 dendrimer complex, C 1 yields short chain oligomers whereas those obtained from the generation 2 dendrimer catalyst, C 2 resulted in longer chain products with molecular weights up to 9.54 × 104 and 9.86 × 104 g/mol at 1 and 5 atm respectively. Two new Nickel metallodendrimers C 1 and C 2 were evaluated as catalysts precursor in the polymerization of ethylene using methylaluminooxane (MOA) as co-catalyst at two different pressure and different Al/M (M = Zn) ratio. Both catalysts evaluated were found to be active for ethylene oligomerization giving polymers and higher molecular weight products.

Chemical composition optimization and characterization of the NiO/B2O3-Al2O3 system as a catalyst for ethylene oligomerization

The samples of the NiO/B2O3-Al2O3 system with NiO contents from 0.48 to 38.30 wt % were synthesized by the impregnation of borate-containing alumina (20 wt % B2O3). It was found that nickel oxide occurred in an X-ray amorphous state in the samples containing to 23.20 wt % NiO. At a NiO content of 4.86 wt % or higher, the support was blocked by the modifier to cause a decrease in the specific surface area from 234 to 176 m2/g and in the amount of acid sites from 409–424 to 333 μmol/g. An extremal character of the dependence of catalyst activity in ethylene oligomerization on NiO content was found with a maximum in the range of 4.86–9.31 wt %. Based on spectroscopic data, it was found that ethylene activation on the NiO/B2O3-Al2O3 catalyst can be associated with the presence of Ni2+ cations, which chemically interact with the support. The catalyst containing 4.86 wt % NiO at 200°C, a pressure of 4 MPa, and an ethylene supply rate of 1.1 h−1 provided almost complete ethylene conversion at the yield of liquid oligomerization products to 90.0 wt %; the total concentration of C8+ alkenes in these products was 89.0 wt %.

2-Ethyl-ketimino-1,10-phenanthroline iron(II) complexes as highly active catalysts for ethylene oligomerization

A series of 2-(1-aryliminopropyl)-1,10-phenanthrolines ( L1– L7) and their corresponding iron(II) chlorides ( Fe1– Fe7) are synthesized and characterized by elemental and spectroscopic analyses. The molecular structures of 2-[1-(2,6-diisopropy1phenylimino)propyl]-1,10-phenanthroline ( L3) and {2-[1-(2,6-diethylphenylimino)propyl]-1,10-phenanthroline}·FeCl 2 ( Fe2) are determined by the single crystal X-ray diffraction. All iron complexes, activated with methylaluminoxane (MAO), exhibit high activities in ethylene oligomerization with high selectivity for α-olefins produced. Compared with other 2-imino-phenanthrolines, the title complexes show better thermal stability, and their oligomerization products are potentially more useful due to lower contents of butenes and waxes observed.

Ethylene Oligomerization Using First-Row Transition Metal Complexes Featuring Heterocyclic Variants of Bis(imino)pyridine Ligands

This report examines the replacement of the imine and pyridine functionalities of the ubiquitous bis(imino)pyridine ligand with various heterocycles. The synthesis of a new class of ligand based around thiazole is described; 2,4-bis[1-(arylimino)ethyl]thiazole (aryl = Ph, 1a; Dipp, 1b) and 2,5-bis[1-(arylimino)ethyl]thiazole (aryl = Ph, 1c; Dipp, 1d) have been prepared in good yield and fully characterized. The coordination chemistry of these ligands with chromium, iron, and cobalt is explored, and the potential of these complexes as ethylene oligomerization initiators is assessed. The chromium complex 2a shows an extremely unusual alternating distribution of higher α-olefin products, which has been previously observed on only one occasion. Both series of products, C4n and C4n+2, show Schulz−Flory behavior but with distinctly different k values. The new ligand 2,5-bis[1-(phenylimino)ethyl]-1-methylpyrrole (1e) is reported along with the attempted synthesis of some corresponding iron complexes. The complexation of chromium by 2,5-bis(phenyliminomethyl)thiophene (1f) is also described, and this material was screened for ethylene oligomerization activity, detailed studies indicating that the ligand may be labile under catalytic conditions. A number of other known heterocyclic ligands incorporating pyrazolyl and benzimidazole functionalities have also been explored with iron, and for the first time their potential to facilitate ethylene oligomerization was assessed. All complexes have been tested via activation with MMAO-3A and AlEt3/[Ph3C][Al(OtBuF)4].

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

AbstractBACKGROUND: 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–MXn 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 SO42− 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

Synthesis, characterization and ethylene oligomerization and polymerization of 2-( 1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylchromium chlorides

A series of N^N^N tridentate chromium complexes ( C1– C6) bearing 2-( 1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine derivatives was synthesized and characterized by elemental and spectroscopic analysis along with single-crystal X-ray crystallography. X-ray crystallographic analyses reveal chromium complex C1 as a distorted six-coordinated octahedral geometry. On treatment with modified methylaluminoxane (MMAO), the chromium complexes exhibited high activities for ethylene oligomerization (up to 1.50 × 10 6 g mol −1 (Cr) h −1) and polymerization (up to 2.06 × 10 6 g mol −1 (Cr) h −1) at 10 atm ethylene pressure. Various reaction parameters were investigated in detail, and less steric hindrance and electron-withdrawing substituents of ligands enhance the catalytic activities of their chromium complexes.