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

• Published in: Applied organometallic chemistry 2020-10, Vol.34 (10), p.n/a
• Main Authors: Zubkevich, Sergey V., Tuskaev, Vladislav A., Gagieva, Svetlana Ch, Kayda, Anatoliy S., Khrustalev, Victor N., Pavlov, Alexander A., Zarubin, Dmitry N., Bulychev, Boris M.
• Format: Article
• Language: English
• Subjects: Activated carbon; Alkenes; Carbon; Chemistry; cobalt; Ethylene; ethylene oligomerization; heteroscorpionate; Metathesis; Nickel; odd carbon number olefins; Oligomerization; Selectivity
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.5873

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·mol (Ni)−1·h−1·atm−1) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh3 as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg·mol (Ni)−1·h−1·atm−1 and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl2 produce up to 5 mol. % of odd carbon number olefins; two probable mechanisms for their formation are suggested – metathesis and β‐alkyl elimination. The first example of formation of odd carbon number olefins during ethylene oligomerization using nickel complexes is reported. Two neutral monoligated complexes (Ni, Co) with novel NNNO‐heteroscorpionate ligand have been synthesized and characterized. The nickel compound exhibited the highest catalytic activity (up to 4,173 kg·mol (Ni)−1·h−1·atm−1 in the presence of PPh3) in ethylene oligomeriztion, high hexene selectivity, ability to catalyze the Friedel‐Crafts alkylation of toluene with ethylene oligomers.