(Ferrocenylpyrazolyl)nickel(ii)-catalysed ethylene oligomerisation

Abstract

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.