NNNO‐Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins

The unprecedented observation of odd carbon number olefins is reported during nickel- catalyzed ethylene oligomerization. Two complexes based on Co (II) and Ni (II) with novel tetradentate heteroscorpionate ligand have been synthesized and fully characterized. These complexes showed the ability to oligomerize ethylene upon activation with various organoaluminum compounds (Et2AlCl, Et3Al2Cl3, EtAlCl2, MMAO). Ni (II) based catalytic systems were sufficiently more active (up to 1900 kg center dot mol (Ni)(-1)center dot h(-1)center dot atm(-1)) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh(3)as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg center dot mol (Ni)(-1)center dot h(-1)center dot atm(-1)and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl(2)produce up to 5 mol. % of odd carbon number olefins; two probable mechanisms for their formation are suggested - metathesis and beta-alkyl elimination.