Novel alpha-nitroketonate nickel(II) complexes as homogeneous catalysts for ethylene oligomerization

The oxidative addition of alpha -nitroacetophenone (naph) to bis(cyclooctad ienyl)nickel(0) [Ni(cod)(2)], in the presence or not of tricyclohexylphosph ine (PCy3) was proven to give the eta (1),eta (2)-cyclooctenyl)(naph)nickel (II) complex (III). When this reaction was carried out in the presence of P Cy3, further addition of methylalumoxane (MAO) or trialkylaluminium compoun ds afforded the corresponding alkyl(PCy3)(naph)nickel(II) complex. This was also obtained by an alternative synthetic procedure involving the addition of a trialkylaluminium to the equimolar adduct of Ni(naph)(2) with PCy3. W hen the above complexes, independently of the synthetic procedure adopted, were generated in situ by using MAO as a co-catalyst (Al/Ni=100), they resu lted in being active in ethylene oligomerization. Whereas in the absence of PCy3, they gave mainly linear C-4-C-6 oligomers with turnover frequencies (TOFs) in the 4000-8000 h(-1) range, the presence of the phosphine ancillar y Ligand not only produced a remarkable increase in activity (TOF=26,00012 1,000 h(-1)) but also afforded a completely different distribution of oligo mers, mainly branched C-6-C-13 products being obtained. (C) 2001 Elsevier S cience B.V. All rights reserved.