Ultrahigh activity and broad temperature resistance of amine-imine cobalt precatalysts for butadiene polymerization

A series of amine-imine cobalt complexes (Co1-Co7) has been prepared and characterized. The complexes Co3, Co4, and Co6 have a distorted tetrahedral geometry, as determined by single crystal X-ray diffraction. In the presence of ethylaluminum sesquichloride (EASC), Co3 exhibited ultra-high activity toward butadiene (Bd) polymerization (up to 7813 kgpolymer mol-1 h-1). The activity is higher than any yet recorded for which yield high cis-1,4 polybutadiene by the well-defined late-transition metal catalytic system. The catalyst also exhibited excellent tolerance towards the ratio of Co/Bd and broad temperature stability. At a ratio of Bd/Co3 = 50 000, the complexes Co1-3 can afford polybutadiene with yields higher than 96% within 2 hours. At -20 °C to 100 °C, the complex Co3 afforded relatively high polymer yields at low catalyst concentrations (Bd/Co3 = 25 000). In addition, all polymers showed a relatively high molecular weight (up to 1.06 × 106 g mol-1).

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 g_PE·mol_Ni^-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.

Structural evolution of iminopyridine support for nickel/palladium catalysts in ethylene (oligo)polymerization

The interest in the late transition metal catalyst based design of new architectures of polyethylene (PE) has continuously been increasing over the last few years. The structure of these catalysts is predominantly important in controlling the morphological and architectural properties of the resulting polyethylene. Particularly, iminopyridine is a versatile bidentate support for Ni and Pd catalysts in ethylene (oligo)polymerization providing a wide variety of products ranging from volatile oligomers to ultra-high molecular weight polyethylene. Extensive structural modifications have been induced in the iminopyridine ligand through steric and electronic substitution, tuning the catalyst behavior in terms of activity and properties of the resulting polymer. Carbocyclic-fused iminopyridine and N-oxide iminopyridine are the new state of the art iminopyridine ligand designs. In this review, we aim to summarize all the developments in mononuclear iminopyridine-nickel and -palladium catalysts for ethylene (oligo)polymerization since the first report published in 1999 to present, focusing on the correlation among the pre-catalyst, co-catalyst type, thermal stability and polymer/oligomer structure. For comparison, the structural variations in the binuclear iminopyridine-nickel catalysts are also described. The detailed comparison of the structural variations in these catalysts with respect to their polymerization performance will give deep understanding in the development of new efficient catalyst designs.

Direct Synthesis of Chain-End Toluene Functionalized Hyperbranched Ethylene Oligomers

Chain-end functionalized polymers play an important role in the field of building complex macromolecular structures. In this study, we have synthesized and characterized four dibenzhydryl iminopyridine Ni(II) complexes bearing remote flexible substituents (Et and n-Bu) to provide hyperbranched ethylene oligomers in ethylene oligomerization with moderate to good activities. Most notably, toluene-end-functionalized hyperbranched ethylene oligomers were obtained under elevated temperature conditions and validated by NMR. The tandem catalysis of ethylene oligomerization and the subsequent Friedel–Crafts addition of the resulting unsaturated products to toluene molecules was proposed as the cause of the observed phenomenon.

Synthesis of High-Molecular-Weight Branched Polyethylene Using a Hybrid “Sandwich” Pyridine-Imine Ni(II) Catalyst

Most pyridine-imine Ni(II) and Pd(II) catalysts tend to yield low-molecular-weight polyethylene and ethylene-based copolymers in olefin insertion polymerization, as the unilateral axial steric structure of such complexes often cannot provide effective shielding of the metal center. In this study, we synthesized a series of hybrid “semi-sandwich” and “sandwich” type pyridine-imine Ni(II) complexes by incorporating diarylmethyl or dibenzosuberyl groups onto 8-aryl-naphthyl motif. The as-prepared Ni(II) complexes afforded highly branched polyethylene with high molecular weights (level of 10⁵ g/mol), and moderate activities (level of 10⁵ g/(molh)) in ethylene polymerization. Most interestingly, compared to “semi-sandwich” Ni(II) complexes bearing (2-diarylmethyl-8-aryl)naphthyl units, the “full-sandwich” counterpart containing (2-dibenzosuberyl-8-aryl)naphthyl motif was able to produce higher-molecular-weight polyethylene with higher branching density. In addition, the effect of remote non-conjugated electronic substituents in diarylmethyl groups of the Ni(II) system was also observed in ethylene polymerization.

A rigid-flexible double-layer steric strategy for ethylene (co)oligomerization with pyridine-imine Ni(ii) and Pd(ii) complexes

A rigid-flexible double-layer steric strategy enhances the molecular weight of the resulting ethylene oligomers and promotes the co-oligomerization of ethylene and methyl acrylate.

Facile Synthesis of Hyperbranched Ethylene Oligomers and Ethylene/Methyl Acrylate Co-oligomers with Different Microscopic Chain Architectures

Low-molecular-weight (MW) ethylene oligomers with hyperbranched microstructures are often difficult to be synthesized by traditional catalytic processes. In this study, a series of N-terphenyl iminopyridyl ligands and the corresponding Pd(II) and Ni(II) complexes bearing remote conjugated substituents with different electronic effects (H, Me, F, Cl, and tBu) were synthesized in a simple and efficient way. These Pd(II) and Ni(II) complexes were highly effective in the ethylene oligomerization and co-oligomerization with methyl acrylate (MA). Low-MW ethylene oligomers with hyperbranched microstructures were generated using the iminopyridyl Pd(II) and Ni(II) complexes in ethylene oligomerization. More importantly, polar functionalized ethylene-MA co-oligomers with low MWs and varying incorporation ratios were generated via ethylene and MA co-oligomerization using the Pd(II) complexes. Most notably, these ethylene oligomers obtained by different metal species showed a significant difference in microscopic chain architectures. The remote conjugated electron effect showed little effect on the polymerization parameters of the iminopyridyl system, which is very different from those of the salicylaldiminato system.

Influence of intramolecular π–π and H-bonding interactions on pyrazolylimine nickel-catalyzed ethylene polymerization and co-polymerization

Pyrazolylimine-based nickel catalysts bearing intramolecular π–π and H-bonding interactions show high activity, thermal stability, and Mn of polyethylene.

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.

Comprehensive studies of the ligand electronic effect on unsymmetrical α-diimine nickel(ii) promoted ethylene (co)polymerizations

The ligand electronic effects on the horizontal axis and vertical axis are systematically disclosed in unsymmetrical α-diimine Ni(ii)-promoted ethylene polymerization and copolymerization reactions.