Selectivity Effects on N,N,N′-Cobalt Catalyzed Ethylene Dimerization/Trimerization Dictated through Choice of Aluminoxane Cocatalyst

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.

4,4'-Dimethoxybenzhydryl substituent augments performance of bis(imino)pyridine cobalt-based catalysts in ethylene polymerization

A series of cobalt complexes with bis(imino)pyridine derivatives featuring unsymmetrical substitution with bulky groups has been synthesized and characterized. The molecular structures of two representatives have been determined by the single-crystal X-ray diffraction study, revealing distorted tetrahedral geometry with different degrees of steric hindrance imparted by the two inequivalent aryl groups attached to the imine nitrogen atoms. On activation with either MAO or MMAO, these complexes display high activity toward ethylene polymerization, reaching 8.71 × 10⁶ g of PE (mol of Co)⁻¹ h⁻¹ at 60 °C and produce polyethylene of high molecular weight (M_w = 5.27 × 10⁵ g mol⁻¹) and low dispersity. The presence of the methoxy-substituent noticeably enhances the activity of the cobalt catalyst and increases the molecular weight of the resultant polyethylene.

Employing ligands with 4,4′-dimethoxybenzhydryl groups, the cobalt precatalysts display high activities toward ethylene polymerization and produce highly linear polyethylenes, the high density polyethylene (HDPE).

Achieving polydispersive HDPE by N,N,N-Co precatalysts appended with N-2,4-bis(di(4-methoxyphenyl)methyl)-6-methylphenyl

A family of unsymmetrical 2-(2,4-bis(di(4-methoxyphenyl)methyl)-6-MeC₆H₂N)-6-(1-(arylimino)ethyl)pyridine-cobalt dichloride complexes has been synthesized and characterized by NMR spectroscopy, FT-IR spectroscopy and elemental analysis as well as single crystal X-ray diffraction for Co2 and Co4. Activated with either MAO or MMAO, all the cobalt precatalysts displayed high activities toward ethylene polymerization and produced highly linear polyethylenes with high molecular weights as well as wide polydispersities; for example, the performance using Co1/MAO at 50 °C reached 9.17 × 10⁶ g PE (mol of Co)⁻¹ h⁻¹ with the production polyethylene of molecular weight as high as M_w = 3.14 × 10⁵ g mol⁻¹, T_m = 134.3 °C besides its wide polydispersity of M_w/M_n of 54.6. Besides the terminal vinyl group of the resultant polyethylenes, it is rare for a late-transition metal catalyst to achieve highly linear polyethylenes with not only wide polydispersity but also high molecular weights, being similar to high-density polyethylenes produced using Phillips catalyst.

Introducing a practical application of N,N,N-Co precatalysts for highly linear polyethylenes with wide polydispersity and high molecular weights, targeting HDPE using Phillips catalyst.

Fusing Carbocycles of Inequivalent Ring Size to a Bis(imino)pyridine-Iron Ethylene Polymerization Catalyst: Distinctive Effects on Activity, PE Molecular Weight, and Dispersity

The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II) chlorides (aryl = 2,6-Me₂C₆H₃Fe1; 2,6-Et₂C₆H₃Fe2; 2,6-i-Pr₂C₆H₃Fe3; 2,4,6-Me₃C₆H₂Fe4; and 2,6-Et₂-4-Me₂C₆H₂Fe5) have been prepared in good yield by a straightforward one-pot reaction of 2,3,7,8,9,10-hexahydro-1H-cyclohepta[b]quinoline-4,6-dione, FeCl₂·4H₂O, and the appropriate aniline in acetic acid. All ferrous complexes have been characterized by elemental analysis and FT-IR spectroscopy. In addition, the structure of Fe3 has been determined by single crystal X-ray diffraction, which showed the iron center to adopt a distorted square pyramidal geometry with the saturated sections of the fused six- and seven-membered carbocycles to be cis-configured. In combination with either MAO or MMAO, Fe1–Fe5 exhibited exceptionally high activities for ethylene polymerization (up to 15.86 × 10⁶ g(PE) mol⁻¹ (Fe) h⁻¹ at 40°C (MMAO) and 9.60 × 10⁶ g(PE) mol⁻¹ (Fe) h⁻¹ at 60°C (MAO)) and produced highly linear polyethylene (HLPE, T_m ≥ 128°C) with a wide range in molecular weights; in general, the MMAO-promoted polymerizations were more active. Irrespective of the cocatalyst employed, the 2,6-Me₂-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr₂Fe3 the least but afforded the highest molecular weight polyethylene (M_w: 65.6–72.6 kg mol⁻¹). Multinuclear NMR spectroscopic analysis of the polymer formed using Fe4/MMAO at 40°C showed a preference for fully saturated chain ends with a broad bimodal distribution a feature of the GPC trace (M_w/M_n = 13.4). By contrast, using Fe4/MAO at 60°C a vinyl-terminated polymer of lower molecular weight (M_w = 14.2 kg mol⁻¹) was identified that exhibited a unimodal distribution (M_w/M_n = 3.8). Moreover, the amount of aluminoxane cocatalyst employed, temperature, and run time were also found to be influential on the modality of the polymer.

2-(N,N-Diethylaminomethyl)-6,7-trihydroquinolinyl-8-ylideneamine-Ni(ii) chlorides: application in ethylene dimerization and trimerization

The unusual influence of co-catalysts on the oligomerization of ethylene is observed with the title nickel complexes, indicating major dimerization and major trimerization with the co-catalysts MAO and MMAO, respectively.

Enhancing thermostability of iron ethylene polymerization catalysts through N,N,N-chelation of doubly fused α,α′-bis(arylimino)-2,3:5,6-bis(hexamethylene)pyridines

At temperatures up to 80 °C, high catalytic activity and high molecular weight PE was achievable using the Fe-catalyst depicted.

gem-Dimethyl-substituted bis(imino)dihydroquinolines as thermally stable supports for highly active cobalt catalysts that produce linear PE waxes

Linear polyethylene waxes with vinyl content can be generated using the depicted N,N,N′-Co catalyst at an industrially relevant operating temperature of 70 °C.

Steric and electronic modulation of iron catalysts as a route to remarkably high molecular weight linear polyethylenes

The depicted N,N,N-iron(ii) chloride precatalysts, upon activation with either MAO or MMAO, not only display excellent thermal stability but are also capable of generating exceptionally high molecular weight linear polyethylenes.

1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects

The title dinuclear Co complexes showed high activity for ethylene oligo-/polymerization with the run temperature having an unexpected effect on the PE to oligomer ratio.