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

The oxidative addition of α-nitroacetophenone (naph) to bis(cyclooctadienyl)nickel(0) [Ni(cod) 2 ], in the presence or not of tricyclohexylphosphine (PCy 3 ) was proven to give the η 1 ,η 2 -cyclooctenyl)(naph)nickel(II) complex ( III ). When this reaction was carried out in the presence of PCy 3 , further addition of methylalumoxane (MAO) or trialkylaluminium compounds afforded the corresponding alkyl(PCy 3 )(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 PCy 3 . When the above complexes, independently of the synthetic procedure adopted, were generated in situ by using MAO as a co-catalyst (Al/Ni=100), they resulted in being active in ethylene oligomerization. Whereas in the absence of PCy 3 , 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 ancillary ligand not only produced a remarkable increase in activity (TOF=26,000–41,000 h −1 ) but also afforded a completely different distribution of oligomers, mainly branched C 6 –C 13 products being obtained.