Unsymmetrical pyrazole-based PCN pincer NiII halides: Reactivity and catalytic activity in ethylene oligomerization

• Published in: Journal of organometallic chemistry Vol. 912; p. 121163
• Main Authors: Gafurov, Zufar N., Bekmukhamedov, Giyjaz E., Kagilev, Alexey A., Kantyukov, Artyom O., Sakhapov, Il’yas F., Mikhailov, Ilya K., Khayarov, Khasan R., Zaripov, Ruslan B., Islamov, Daut R., Usachev, Konstantin S., Luconi, Lapo, Rossin, Andrea, Giambastiani, Giuliano, Yakhvarov, Dmitry G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2020
• Subjects: Ethylene oligomerization; Nickel borohydrides; Nickel complexes; PCN pincer ligands; Unsymmetrical ligands; PCN pincer ligands; Nickel complexes; Unsymmetrical ligands; Ethylene oligomerization; Nickel borohydrides
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2020.121163

The reactivity of unsymmetrical pyrazole-based PCN pincer Ni(II) halides has been tested in the presence of copper(II) halides as an oxidizing agent as well as with NaBH4 and LiAlH4 as a hydride source. While the reaction with CuX2 resulted into the generation of metastable PCN pincer Ni(III) species, the treatment of (tBuPCN)NiCl with NaBH4 led to the preparation and isolation of the borohydride complex (tBuPCN)Ni(BH4). Attempts to isolate nickel-hydride species upon treatment of (tBuPCN)NiCl with either NaBH4 or LiAlH4 invariably led to the formation of free PCN(H) ligand and metallic Ni(0) nanoparticles after an in situ reductive elimination from the (metastable) hydride derivative (tBuPCN)NiH. Finally, the halide complexes (pre-activated by MMAO) have been tested as homogeneous catalysts in ethylene oligomerization showing moderate activity (∼ 14 × 103 molC2H4⋅molNi−1⋅h−1) with the formation of even-numbered olefins (mainly C4–C10 fractions) as products. [Display omitted] •Treatment of (tBuPCN)NiCl with NaBH4 leads to formation of stable borohydride organonickel pincer complex (tBuPCN)Ni(BH4).•Nickel-hydride species form free PCN(H) ligand and metallic Ni(0) nanoparticles.•(tBuPCN)NiX pincer complexes (pre-activated by MMAO) form active catalysts for ethylene oligomerization.•Homogeneous ethylene oligomerization leads to even-numbered olefins (mainly C4–C10 fractions) as products.