Cobalt(II) and nickel(II) complexes bearing mono(imino)pyridyl and bis(imino)pyridyl ligands: preparation, structure and ethylene polymerization/oligomerization behaviors

Abstract

BACKGROUND: Ethylene oligomerization is the major industrial process to produce linear α‐olefins. Recently much work has been devoted to late transition metal catalysts used in this process, especially those with 2,6‐bis(imino)pyridyl dihalide ligands. Considering that most work has focused on simple modification to the substituents in imino‐aryl rings based on the symmetric bis(imino)pyridyl framework, here we expand this work to the asymmetric mono(imino)pyridyl ligands. RESULTS: The preparation, structure and ethylene polymerization/oligomerization behavior of series of mono(imino) pyridyl–MCl2 and bis(imino)pyridyl–MXn complexes are presented. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for ethylene polymerization/oligomerization and reaction conditions, ligand structures, metal centers and counter‐anions. The influence of the coordination environment on catalyst behavior is also discussed. CONCLUSION: For mono(imino)pyridyl–Co(II) and Ni(II) catalysts bearing the Cl− counter‐anion, good activities ranging from 0.513 × 105 to 1.58 × 105 g polyethylene (mol metal)−1 h−1 atm−1 are afforded, and the most active catalysts are those with methyl in both ortho‐ and para‐positions of the imine N‐aryl ring. For bis(imino)pyridyl–Co(II) and Ni(II) catalysts bearing the SO42− and NO3− counter‐anions, the low activities for ethylene oligomerization are in sharp contrast to those of their chloride analogues. Copyright © 2009 Society of Chemical Industry

Vinyl Polymerization of Norbornene on Nickel Complexes with Bis(imino)pyridine Ligands Containing Electron-Withdrawing Groups

“…Butene-1 was the only detectable product of this reaction, and no traces of solid polymer were found. Such reaction behavior is similar to that reported for bis(imino)pyridine-based and structurally related nickel(II) complexes with N,N,N-donor ligands. − …”

Syntheses and Preferred Structure Elucidation of N‐heterocyclic Imine Nickel and Cobalt Catalysts for MMA Polymerization

“…The activity increases sharply when the temperature rises from 80 °C (1.177×10 4 g mol −1 ⋅ h −1 ) to 110 °C (1.604×10 4 g mol −1 ⋅ h −1 ), and then decreases as the temperature continues to rise to 120 °C (1.334×10 4 g mol −1 ⋅ h −1 ). A low temperature is unfavorable probably because it hinders the formation of active species, but too high a temperature may cause a decrease of MMA solubility and deactivation of catalyst [26–28] . All the resulting PMMA had high molecular weights of around 10 5 g mol −1 with narrow molecular weight distributions (dispersity indices [PDI]: 1.72∼2.73) in all cases.…”

Nickel(II) complexes with mono(imino)pyrrole ligands: preparation, structure and ethylene polymerization behavior

“…Although a number of mono(imino)pyrrole ligands were developed, nearly all of the reported ligands bore H side arms [10][11][12][13][14][15][16]. We have expanded this work to mono(imino) pyrrole ligands with a -CH 3 side arm in order to have greater electronic and steric effects.…”

“…Bis(imino)pyridyl-metal catalysts have been an attractive research field because of their flexible structural modifications and complexation between ligand and metal, as well as outstanding catalytic performance. Studies have mainly concentrated on adjusting the structure of the ligand, usually using the following ways [5][6][7][8]: (1) introducing heteroatoms to the pyridine ring to get an N-based sixmembered heterocyclic imino ligand, such as pyrimidine, pyrazine, and triazine ligands; (2) replacing the six-membered heterocycle with a five-membered heterocycle such as a pyrrole, thiophene, or furan ring; (3) modifying the imino substituent to get ligands with different side arms, such as carbazole or Pybox ligands [9]; or (4) changing the symmetric bis (imino) structure to an asymmetric structure [10][11][12][13]. For example, zirconium and titanium complexes bearing mono(imino)pyrrole ligands, reported by Fujita [14,15] and Bochmann et al [7], were demonstrated to be good catalysts for ethylene polymerization.…”