Sterically and Electronically Modified Aryliminopyridyl-Nickel Bromide Precatalysts for an Access to Branched Polyethylene with Vinyl/Vinylene End Groups

Abstract

A series of 2-((arylimino)ethyl)pyridine derivatives (L1−L5), each containing N-2,4-bis(dibenzocycloheptyl) groups with variations in the steric/electronic properties of the orthosubstituent in the aryl ring, and the corresponding nickel bromide precatalysts [2-N{2,4-(C 15 H 13 )-6-R-C 6 H 2 }C 7 H 7 N]NiBr 2 (R = Me (Ni1), Et (Ni2), i− Pr (Ni3), Cl (Ni4), or F (Ni5)), have been prepared in high yield. All the precatalysts are air-stable and characterized by Fourier transform infrared spectroscopy and elemental analysis. The molecular structures of Ni2 and Ni5 were proved through single-crystal X-ray diffraction analysis. The steric/ electronic impact of the catalysts on ethylene polymerization and the resulting polymer properties were studied. Upon activation with either MAO or EASC, all the complexes displayed higher activities (up to 7.93 × 10 6 g of PE (mol of Ni) −1 h −1 with MAO) in ethylene polymerization and produced moderate to highly branched unsaturated polyethylene with a molecular weight of up to 16.55 kg/mol with narrow dispersities (1.6−2.4). Significantly, the generated polyethylenes are branched and unsaturated with a major class of internal double bond (−CHCH−) as compared to the terminal double bond (−CHCH 2 ) (vinylene/vinyl = 9.8:1 to 1.8:1). Notably, their catalytic activities, types of unsaturation, and branches are highly affected by the nature of the orthosubstituent and reaction temperature. Moreover, the precatalysts Ni4 and Ni5 (with N-ortho = Cl and F) exhibited lower catalytic activities, produced low-molecular-weight polyethylene with a high melt temperature and the least number of branches with an increased level of terminal double bonds.

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

“…9). 41 The molecular structures of these catalysts were found to be in three different forms, i.e. , mono-ligated, bis-ligated and mono-ligated dimers.…”

Iminopyridine Ni(II) Catalysts Affording Oily Hyperbranched Ethylene Oligomers and/or Crystalline Polyethylenes Depending on the Reaction Conditions: Possible Role of In Situ Catalyst Structure Modifications

“…A related ligand modification introducing a 2,6-dialkylphenyl substituent in the 6-position of pyridine resulted in prevailing ethylene dimerization to 1-butene with minor amounts of C6, C8, and higher oligomers [11]. A large number of complexes with increasing steric bulk Macromol 2021, 1 122 on the arylimino moiety of the ligand, e.g., o-benzhydryl, dibenzhydryl or dibenzocycloheptyl substituents but no substituents on the pyridine moiety, have been synthesized and tested by the group of Sun [12][13][14][15][16][17][18], resulting in thermally stable and highly active catalysts yielding low molecular weight moderately branched polyethylenes (Scheme 1B). Incorporation of very bulky 8-arylnaphtyl substituents on the imino moiety [19], blocking only one of the two coordination sites at the metal center, resulted in catalysts producing moderately branched polyethylenes with increased molecular weight (∼10 4 g mol −1 ) (Scheme 1C).…”

Synthesis and Characterization of Phosphinobenzenamine Palladium Complexes and Their Application in Ethylene Polymerization and Copolymerization with Polar Monomers

“…The microstructures of the obtained polyethylenes were studied using 1 H and 13 C NMR spectroscopies. In the 1 H NMR spectra (Figure ) of Pd2 at different temperatures, the characteristic signals of the vinyl group (−CHCH 2 ) appeared at 5.82 and 4.97 ppm, whereas the signal at 5.43 ppm was assigned to the vinylene group (−CHCH−). − The ratio of vinylene to the vinyl group increased from 0.75:1 to 2.0:1, based on the increasing in the temperature from 60 to 100 °C. Moreover, the ratio could be influenced by changing the structure of the utilized catalyst, where Pd3 gave polyethylene with a high vinyl content (Figure S23).…”