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.

Ethylene Polymerization through Neutral Nickel Complexes Bearing Cyclic Imides

The catalyst synthesis of salicylaldimine Ni(II) complexes with bulky imide moieties, ethylene polymerization, and characterization of synthesized polyethylenes are described in this paper. These Ni(II) complexes are designed to bear 2-aminobiphenyl and 4-tritylaniline. Results confirmed relatively high activity (up to $4\times {10}^4$  g PE mol Ni-1 h-1) of these catalysts in ethylene polymerization. Moreover, Ni(II) complexes demonstrated enhanced thermal stability, maintaining activity level up to 80°C. The generated polyethylenes possess moderate branching density and high melting temperatures. Less bulky 2-aminobiphenyl group resulted in higher branch content, while in Ni(II) complexes bearing 4-tritylaniline, more linear structure was observed. These semicrystalline polyethylenes showed mechanical properties similar to thermoplastics.

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.

Thermally stable vanadium complexes supported by the iminophenyl oxazolinylphenylamine ligands: synthesis, characterization and application for ethylene (co-)polymerization

In this work, a series of oxovanadium complexes bearing the ligands (S,E)-(+)-2, 6-dialkyl-N-(2-((2-(4-isopropyl-4,5-dihydrooxazole-2-yl)phenyl)amino)benzylidene)aniline (dialkyl = dimethyl (V1), diethyl (V2), and isopropyl (V3)) have been synthesized and characterized by FTIR spectroscopy and elemental analysis. Moreover, the molecular structures of complexes V2 and V3 were defined by X-ray diffraction. On activation with ethylaluminium sesquichloride (Al₂Et₃Cl₃), these complexes exhibited high activity towards ethylene polymerization (up to 1.39 × 10⁷ g mol_v^-1 h^-1) and showed excellent thermal stability (up to 60 °C). The obtained polyethylene had a moderate molecular weight (21.9 × 10⁴ to 66.4 × 10⁴ g mol^-1) and exhibited narrow distribution (1.91 to 2.86) and unimodal features. The effect of the substituents on the ligands was also investigated in detail. The compound bearing the diisopropyl group showed the highest activity toward ethylene polymerization as the bimolecular deactivation of the catalyst can be effectively inhibited by the steric hindrance of the ortho-substituent on aniline. The complex V2 with moderate steric hindrance was also evaluated as a catalyst for the copolymerization of ethylene with norbornene and showed moderate to high activity.

Influences of Ligand Backbone Substituents on Phosphinecarbonylpalladium and -nickel Catalysts for Ethylene Polymerization and Copolymerization with Polar Monomers

A series of phosphinecarbonylpalladium and -nickel catalysts bearing various substituents on the ligand backbone were prepared, characterized, and used in ethylene polymerization and copolymerization with polar monomers. The Pd and Ni catalysts can achieve high activities as well as high polymer molecular weights in both ethylene polymerization and copolymerization with polar monomers. The electron-donating group from the carbonyl side can effectively increase the polymer molecular weights. Utilization of a cyclic backbone structure can increase the catalytic activities at the expense of the polymer molecular weights. Moreover, installation of a pyridyl moiety in the ligand backbone can enable Lewis acid responsiveness and can enhance the polymerization activities. These results suggest the importance of the ligand backbone for the properties of catalysts in ethylene polymerization and copolymerization reactions.