Tandem ethylene oligomerisation and Friedel–Crafts alkylation of toluene catalysed by bis-(3,5-dimethylpyrazol-1-ylmethyl)benzene nickel(ii) complexes and ethylaluminium dichloride

Abstract

Three ligands, 1,2-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene (L1), 1,3-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene (L2) and 1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene (L3), were reacted with either nickel(II) chloride or nickel(II) bromide to produce four nickel complexes, Ni(L1)Br₂ (1), Ni(L1)Cl₂ (2), Ni(L2)Br₂ (3), and Ni(L1)Br₂ (4). The complexes were either mononuclear, 1 and 2, or polymeric, 3 and 4, depending on the positions of the pyrazolyl units on the benzene linker in the ligand. This was established from the crystal structures of 1, 2 and 3. All four complexes upon activation with ethylaluminium dichloride produced a tandem catalyst system that oligomerised ethylene to mainly 1-butene and 1-hexene and subsequently used the olefins present in the reaction medium to alkylate toluene that was used as solvent in the reactions. This led to mono-, di- and tri-alkyltoluenes with ethylene, butene and hexene.