(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