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

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)Br sub(2) (1), Ni(L1)Cl sub(2) (2), Ni(L2)Br sub(2) (3), and Ni(L1)Br sub(2) (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.