(Ferrocenylpyrazolyl)nickel(II)-catalysed ethylene oligomerisation

Compounds L1-L6 (3-ferrocenylpyrazole (L1), 3-ferrocenyl-5-methylpyrazole (L2), 3-ferrocenylpyrazolyl-methylenepyridine (L3), 3-ferrocenyl-5-pyrazolyl-methylenepyridine (L4), 3-ferrocenylpyrazolyl-ethylamine (L5) and 3-ferrocenyl-5-pyrazolyl-ethylamine (L6)) reacted with [NiBr₂(DME)] or [NiCl₂·6H₂O] to give the mononuclear nickel complexes [NiBr₂(κ¹-L1)₂] (1), [NiBr₂(κ¹-L2)₂] (2), [NiBr₂(κ²-L3)] (3), [NiBr₂(κ²-L4)] (4), [NiBr₂(κ²-L5)] (5), [NiBr₂(κ²-L6)] (6), [NiCl₂(κ²-L3)] (7) and [NiCl₂(κ²-L4)] (8). Because these nickel complexes are paramagnetic, they were characterised by a combination of IR spectroscopy, mass spectrometry, elemental analysis and, in selected cases, single crystal X-ray crystallography. Activation of complexes 1-8 with EtAlCl₂ in chlorobenzene produced active species that catalysed ethylene oligomerization to butenes and C₁₆-C₆₄ olefins, showing a non-Schulz-Flory distribution of products. Complexes 2 and 3 were the most active (1989 kg of ethylene oligomer per mol of Ni per h and 1776 kg of ethylene oligomer per mol of Ni per h, respectively) and, in toluene, produced isomers of butene and small amounts of butyltoluenes via Friedel-Crafts alkylation of toluene by the butenes.