Symmetrically and unsymmetrically substituted bis(pyrazole)-palladium(II) and nickel(II) halides as pre-catalysts for ethylene dimerization and Friedel-Crafts alkylation of toluene and benzene

Bis(pyrazole)-palladium(II) and nickel(II) halide complexes, [(pz)₂PdCl₂] (1), [(3,5-Me₂pz)₂PdCl₂] (2), [(3,5-^tBu₂pz)₂PdCl₂] (3), [(3,5-Ph₂pz)₂PdCl₂] (4), [(3-CF₃,5-Phpz)₂PdCl₂] (5),[(pz)₄NiBr₂] (6), [(3,5-Me₂pz)₂NiBr₂] (7), [(3,5-^tBu₂pz)₂NiBr₂] (8), [(3,5-Ph₂pz)₂NiBr₂] (9) and [(3-CF₃,5-Phpz)₂NiBr₂] (10), were investigated as catalysts for ethylene oligomerization using four alkylaluminium compounds as co-catalysts in toluene, benzene and chlorobenzene. The palladium complexes with ethylaluminium dichloride (EtAlCl₂) in toluene selectively produced ethyl- and butyl- toluenes via a Friedel-Crafts alkylation of toluene from the ethylene and butenes formed from the dimerization of ethylene. On the other hand, the nickel complexes produced a mixture of butenes and their Friedel-Crafts toluene alkylation products, but very little ethyltoluene. Changing the solvent to benzene produced similar alkyl-aromatics but in chlorobenzene the reaction produced butenes and a yellow oil, with a molecular weight between 501 to 509 g mol^-1; representing C₁₈-C₂₀ carbon-containing compounds. Similarly changing the co-catalyst to methylaluminoxane (MAO), modified methylaluminoxane (MMAO), diethylaluminium chloride (Et₂AlCl) and ethylaluminiumsesquichloride (Et₃Al₂Cl₃) also selectively produced butenes and little or no alkylaromatics.