Transition-metal complexes of phenoxy-imine ligands modified with pendant imidazolium salts: Synthesis, characterisation and testing as ethylene polymerisation catalysts

Reaction between 3-((1R,2R)-2-{[1-(3,5-di-tert-butyl-2-hydroxy-phenyl)-meth-(E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3H-imidazol-1-ium bromide (1a) or the derivative 3-((1R,2R)-2-{[1-(2-hydroxy-5-nitro-phenyl)-meth-(E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3H-imidazol-1-ium bromide (1b) and metal halides MClx.yTHF (M = Zr, x = 4, y = 2; M = V, x = y = 3; M = Cr, x = y = 3), in THF, at −78 °C gives the metal complexes of general formula [MClx(κ2-N,O-OC6H2R1R2C(H)N–C6H10–Im)2][Br]2 (where M = Zr, x = 2, R1 = R2 = tBu, 2; M = Zr, x = 2, R1 = H, R2 = NO2, 3; M = V, x = 1, R1 = R2 = tBu, 4; M = Cr, x = 1, R1 = R2 = tBu, 5; M = Fe, x = 0, R1 = R2 = tBu, 6; Im = 1-isopropyl-4-phenyl-3H-imidazol-1-ium-3-yl). 1H and 13C NMR spectroscopy of 2 and 3 indicate κ2-N,O-ligand coordination via the phenoxy-imine moiety with pendant imidazolium salt that is corroborated by a single crystal structure of 6. Compounds 2, 3, 4 and 5 were tested as precatalysts for ethylene polymerisation in the presence of methylaluminoxane (MAO) cocatalyst, showing low activity. Selected polymer samples were characterised by GPC showing multimodal molecular weight distributions.

Graphical abstractA series of zirconium, vanadium, chromium and iron complexes with modified phenoxy-imine chiral ligands containing pendant imidazolium bromide salts, have been synthesised and characterised. The zirconium, vanadium and chromium complexes are active as precatalysts for ethylene polymerisation using methylaluminoxane (MAO) cocatalyst.Figure optionsDownload full-size imageDownload as PowerPoint slide