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)double bond; length as m-dashN–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.