Nickel(II) complexes bearing phosphinooxazoline ligands: Synthesis, structures and their ethylene oligomerization behaviors

A series of Ni(II) complexes 4a-f ligated by the unsymmetrical phosphino-oxazolines (PHOX) were synthesized and characterized by elemental analysis and IR spectroscopy, and the structures of complexes 4c-4e were confirmed by the X-ray crystallographic analysis. All derivatives showed distorted tetrahedron geometry by the nickel center and coordinative atoms. Upon activation with methylaluminoxane (MAO) or Et₂AlCl, these complexes exhibited considerable to high activity of ethylene oligomerization. The ligands environments and reaction conditions significantly affect their catalytic activities, while the highest oligomerization activity (up to 1.18 × 10⁶ g · mol⁻¹(Ni) · h⁻¹) was observed for 4d at 20 atm of ethylene. Incorporation of 2-4 equivalents of PPh₃ as auxiliary ligands in the 4a-f/MAO catalytic systems led to higher activity and longer catalytic lifetime.     

2-(7-methyl-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridinylnickel complexes: Synthesis, characterization and their ethylene oligomerization

A series of 2-(methyl-substituted-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridines (L1–L6) were synthesized and used as N^N^N tridentate ligands for their nickel complexes (C1–C12). All ligands were fully characterized by elemental, NMR and IR spectroscopic analyses, while their nickel complexes were characterized by elemental and IR spectroscopic analyses. The single-crystal X-ray diffraction reveals that the complexes C1, C3 and C9 have distorted octahedral geometry around the Ni center. All nickel complexes, activated with Et₂AlCl, exhibit good catalytic activities toward ethylene oligomerization with major dimerization.     

Iron(III) complexes bearing 2-(benzimidazole)-6-(1-aryliminoethyl)pyridines: Synthesis, characterization and their catalytic behaviors towards ethylene oligomerization and polymerization

A series of iron(III) complexes ligated by 2-(benzimidazole)-6-(1-aryliminoethyl)pyridines was synthesized and examined by ¹H NMR, ESI-MS, IR spectroscopic, elemental analysis and X-ray photoelectron spectroscopy (XPS). Activated with methylaluminoxane (MAO), all ferric complexes exhibited good activities (up to 5.38 × 10⁶ g mol⁻¹(Fe) h⁻¹) of ethylene oligomerization and polymerization, and resultant oligomers and polyethylene waxes showed high α-olefin feature, meanwhile the distribution of oligomers mostly resembled Schulz-Flory rules. The various reaction parameters were investigated in detail, and the less bulky and electron-withdrawing substituents of ligands could enhance the catalytic activities of their ferric complexes. The observations explain the cause for unstable activities performed by stored iron(II) complexes.     

N-(Pyridin-2-yl)picolinamide tetranickel clusters: Synthesis,structure and ethylene oligomerization

A series of N-(pyridin-2-yl)picolinamide derivatives was synthesized and characterized. Tetranickel complexes were obtained by stoichiometric reaction of NiBr₂ and corresponding ligands, and characterized by elemental and spectroscopic analysis. Moreover, the coordination pattern of complex 3a was confirmed by single-crystal X-ray diffraction. In the structure, two ligands linked two nickel atoms to form a unit, and two units were bridged via μ₃-OMe and μ₂-Br to form a tetranickel cluster. These Ni(II) complexes were investigated in ethylene oligomerization and found to exhibit remarkable catalytic activities upon activation with MAO. Reaction conditions as well as ligand environment significantly affected the catalytic performance of the nickel complexes; the highest activity could be achieved to be 2.7 × 10⁶ g mol⁻¹ Ni h⁻¹.     

Iron(II) and cobalt(II) complexes bearing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives: Synthesis and application to ethylene oligomerization

A series of tridentate NˆNˆN iron(II) and cobalt(II) complexes containing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives were synthesized and characterized by elemental and spectroscopic analyses. The molecular structure of 1a was confirmed by X-ray diffraction analyses. On treatment with modified methylaluminoxane, these metal complexes exhibited good catalytic activities up to 2.8 × 10⁶ g mol⁻¹(Fe) h⁻¹ for ethylene oligomerization, and butenes were the major products with nice selectivity for 1-C₄. The steric and electronic effects on catalytic activities of metal complexes were carefully investigated as well as the influence of various reaction parameters. In the catalytic system, Fe(II) complexes performed better catalytic activities than their Co(II) analogues. With ligands having bulky substituents, the better catalytic activity was observed in catalytic system of Fe(II) complex, however, the lower catalytic activity was obtained in catalytic system of Co(II) complexes.     

2-(Benzimidazol-2-yl)-1,10-phenanthrolyl metal (Fe and Co) complexes and their catalytic behaviors toward ethylene oligomerization

The N^∧N^∧N-tridentate metal complexes, LMCl₂ (M = Fe or Co; L represents a ligand of 2-(benzimidazol-2-yl)-1,10-phenanthrolines), were synthesized and fully characterized with spectroscopic and elemental analysis. The single-crystal X-ray crystallographic analyses revealed complex 1a with a distorted octahedron geometry due to incorporating one methanol molecule, and complexes 5a and 9b with a distorted trigonal-bipyramidal geometry. Upon activation with modified methylaluminoxane (MMAO), these complexes showed good to high catalytic activities toward ethylene oligomerization. The detailed investigations were carried out to disclose the influences of various reaction conditions and nature of ligands on their performing activities of metal complexes.     

Synthesis, characterization and ethylene oligomerization studies of nickel complexes bearing 2-imino-1,10-phenanthrolines

A series of nickel (II) complexes ligated by 2-imino-1,10-phenanthrolines were synthesized and characterized by elemental and spectroscopic analysis as well as by single-crystal X-ray crystallography. X-ray crystallographic analysis reveals complexes 3, 5, 7 and 11 as the five-coordinated distorted trigonal-bipyramidal geometry. Upon activation with Et₂AlCl, these complexes exhibited considerably high activity for ethylene oligomerization (up to 3.76 × 10⁷ g mol⁻¹(Ni) h⁻¹ for 12 with 10 equiv. of PPh₃). The ligand environment and reaction conditions significantly affect the catalytic activity of their nickel complexes.     

Nickel(II) complexes chelated by 2-quinoxalinyl-6-iminopyridines: Synthesis, crystal structures and ethylene oligomerization

A series of nickel(II) complexes ligated by tridentate ligands of 2-quinoxalinyl-6-iminopyridines was synthesized and characterized by elemental and spectroscopic analysis as well X-ray diffraction analysis. X-ray crystallographic analysis revealed the nickel complexes as five-coordinated distorted trigonal bipyramidal geometry. In the presence of Et₂AlCl, these complexes displayed high catalytic activity for ethylene oligomerization and the dimmers were produced as main products. The nickel dibromide complexes exhibited relative higher activity than their dichloride analogues. Both elevation of the ethylene pressure and addition of auxiliary ligand have catalytic enhancement effects on all the complexes.     

Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12-16/MAO systems is up to 3.3 × 10⁴ g mol⁻¹ h⁻¹ whereas for 17-24/MAO systems it is up to 4.94 × 10⁵ g mol⁻¹ atm⁻¹ h⁻¹. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh₃/Ni molar ratio on catalytic activity was investigated.     

Chromium(III) complexes ligated by 2-(1-isopropyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines: Synthesis, characterization and their ethylene oligomerization and polymerization

A series of chromium(III) complexes bearing 2-(1-isopropyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines were synthesized and characterized by IR spectroscopic and elemental analysis. The X-ray crystallographic analysis revealed a distorted octahedral geometry of the chromium complexes. When activated by Et₂AlCl, MAO or MMAO, these chromium complexes exhibited catalytic activities for ethylene oligomerization and polymerization; while the good to high activities (up to 3.95 × 10⁶ g mol⁻¹ (Cr) h⁻¹) were observed in the catalytic systems with MMAO. Therefore, various reaction parameters of the catalytic system with MMAO were investigated in detail. The steric and electronic effects of ligands affected the catalytic activities and the distribution of the products predominantly. Interestingly, sometimes their distributions of oligomers did not resemble the rules of Schulz-Flory or Poisson due to the hexenes produced in low yield.     

Nickel (II) complexes bearing 2-ethylcarboxylate-6-iminopyridyl ligands: synthesis, structures and their catalytic behavior for ethylene oligomerization and polymerization

A series of nickel (II) complexes (L)NiCl₂ (7-9) and (L)NiBr₂ (10-12) were prepared by the reactions of the corresponding 2-carboxylate-6-iminopyridine ligands 1-6 with NiCl₂ · 6H₂O or (DME)NiBr₂ (DME = 1,2-dimethoxyethane), respectively. All the complexes were characterized by IR spectroscopy and elemental analysis. Solid-state structures of 7, 8, 10, 11 and 12 were determined by X-ray diffraction. In the cases of 7, 8 and 10, the ligands chelate with the nickel centers in tridentate fashion in which the carbonyl oxygen atoms coordinate with the metal centers, while the carbonyl oxygen atoms are free from coordinating with the nickel centers in 11 and 12. Upon activation with methylaluminoxane (MAO), these complexes are active for ethylene oligomerization (up to 7.97 × 10⁵ g mol⁻¹ (Ni) h⁻¹ for 11 with 2 equivalents of PPh₃ as auxiliary ligand) and/or polymerization (1.37 × 10⁴ g mol⁻¹ (Ni) h⁻¹ for 9). The ethylene oligomerization activities of 7-12 were significantly improved in the presence of PPh₃ as auxiliary ligands. The effects of the coordination environment and reaction conditions on the ethylene catalytic behaviors have been discussed.     

Unsymmetric bimetal(II) complexes: Synthesis, structures and catalytic behaviors toward ethylene

A series of unsymmetric bimetal(II) (Fe, Co and Ni) complexes ligated by 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines were synthesized and characterized by IR spectra and elemental analysis, while a representative nickel(II) complex (5a) was determined by single-crystal X-ray crystallography. These iron(II) complexes were found to exhibit good activities for ethylene oligomerization and polymerization in the presence of MMAO and afforded α-olefins in high selectivity, and the composition of oligomers followed the Schluz-Flory distribution. The nickel(II) complexes mainly dimerize ethylene with considerable activity. The influences of coordinative ligands and reaction parameters were fully investigated on the catalytic activity and properties of these complexes.     

Bridged bis-pyridinylimino dinickel(II) complexes: Syntheses, characterization, ethylene oligomerization and polymerization

A series of bridged bis(pyridinylimino) ligands were efficiently synthesized through the condensation reaction of 4,4′-methylene-bis(2,6-disubstituted aniline) with 2-pyridinecarboxaldehyde or 2-benzoylpyridine. They reacted with (DME)NiBr₂ to form dinuclear Ni(II) complexes. All resultant compounds were characterized by elemental analysis, IR spectra as well as the single-crystal X-ray diffraction to confirm the structures of ligands and complexes. Activated with methylaluminoxane (MAO), these nickel complexes showed considerably good activities for ethylene oligomerization and polymerization. Their catalytic activities and the properties of PEs obtained were depended on the arched environment of ligand and reaction conditions.     

Cobalt(II) complexes bearing 2-imino-1,10-phenanthroline ligands: synthesis, characterization and ethylene oligomerization

A series of cobalt(II) complexes containing 2-imino-1,10-phenanthrolines have been synthesized and characterized by elemental and spectroscopic analysis. The molecular structures of complexes 2, 3, 8 and 14 were confirmed by X-ray diffraction analysis. On treatment with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), these cobalt(II) complexes show moderate to high catalytic activities for ethylene oligomerization and butene predominates among the oligomers produced. The parameters of the reaction conditions and the effects of the ligands environment were investigated. To cite this article: S. Jie et al. C. R. Chimie 9 (2006).     

Chromium(III) complexes bearing 2-benzoxazolyl-6-arylimino-pyridines: Synthesis and their ethylene reactivity

A series of chromium(III) complexes bearing 2-benzoxazolyl-6-aryliminopyridines was synthesized and characterized by IR spectroscopic and CHN analysis. The X-ray crystallographic analysis of complex Cr3 revealed a distorted octahedral geometry. When activated by Et₂AlCl, MAO or MMAO, these chromium complexes exhibited activities towards ethylene reactivity. High activities of ethylene oligomerization (up to 9.19 × 10⁶ g mol⁻¹ (Cr) h⁻¹) were observed in the catalytic system using MMAO as a cocatalyst, meanwhile good activities of ethylene polymerization were achieved (up to 5.20 × 10⁵ g mol⁻¹ (Cr) h⁻¹) by using MAO as a cocatalyst. Various reaction parameters were investigated in detail, and the steric and electronic effects of ligands were discussed.     

2-(1-Aryliminoethylidene)quinolylnickel(II) dibromides: Synthesis, characterization and ethylene dimerization capability

A series of 2-(1-aryliminoethylidene)quinoline derivatives (L1-L9) and the nickel(II) dibromides (C1-C9) thereof, were synthesized and characterized. The molecular structures of C2 (R¹ = Et, R² = H, R = Me) and C9 (R¹ = ⁱPr, R² = H, R = ⁱPr) were confirmed as being distorted tetrahedral at nickel by single crystal X-ray diffraction. On treatment with diethylaluminium chloride (Et₂AlCl) or ethylaluminum sesquichloride (EASC), these nickel pre-catalysts exhibited high activity for selective ethylene dimerization (0.89-3.29 × 10⁶ g mol⁻¹(Ni) h⁻¹) at 20 °C under 10 atm of ethylene. The influence of the reaction parameters on the catalytic behaviour was investigated for these nickel systems, including variation of Al/Ni molar ratio and reaction temperature.     

Half-Titanocene chlorides 2-(benzimidazol-2-yl)quinolin-8-olates: Synthesis, characterization and ethylene (co-)polymerization behavior

 A series of half-titanocene chloride 2-(benzimidazol-2-yl)quinolin-8-olates C1-C6 were synthesized by treating the lithium salts of the ligand with CpTiCl₃. All the complexes were characterized by ¹H-NMR, ¹³C-NMR and elemental analyses, and the crystal structure of C3 and C6 was measured by X-ray. These half-titanocene complexes showed moderate catalytic activities toward ethylene polymerization (up to 1840 kg·mol^-1(Ti)·h^-1) when activated with MMAO, affording the high molecular weight polymers. And they also exhibited good activity for copolymerization of ethylene and α-olefin with low content of co-monomer.     

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 × 10⁶ g mol⁻¹ (Cr) h⁻¹) and polymerization (up to 2.06 × 10⁶ 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.     

Nickel(II) complexes bearing pyrazolylpyridines: synthesis,structures and ethylene oligomerization reactions

Reactions of 2‐bromo‐6‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine ( L1 ) and 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine ( L2 ) with NiCl₂ and NiBr₂ led to the formation of their respective metal complexes [NiCl₂(L1)] ( 1 ), [NiBr₂(L1)] ( 2 ) and [NiBr₂(L2)] ( 3 ) in moderate to high yields. The complexes were characterized using elemental analyses, mass spectrometry and single‐crystal X‐ray diffraction for 2 . The solid‐state structure of 2 confirmed the bidentate coordination mode of L1 and formation of a monometallic compound. Activation of the nickel(II) pre‐catalysts with methylaluminoxane afforded active catalysts in the ethylene oligomerization reaction to produce mainly butenes (84–86%). In contrast, activation of nickel(II) pre‐catalyst 2 with ethylaluminium dichloride resulted in partial Friedel–Crafts alkylation of the toluene solvent by the preformed oligomers. Complex structure, nature of co‐catalyst employed, type of solvent and reaction conditions influenced the catalytic behaviour of these pre‐catalysts. Copyright © 2015 John Wiley & Sons, Ltd.