The dinuclear complexes [Ni(µ-Cl){(4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol}]2Cl214 and [Ni(µ-Cl){(pyridin-2-yl)methanol}]2Cl216 have been synthesized in high yields by reaction of NiCl2 with 2 mol. equiv. of the ligands 4,5-dihydro-4,4-dimethyloxazol-2-yl)methanol 13 or (pyridin-2-yl)methanol 15, respectively. The reaction of NiCl2 with 3 mol. equiv. of 15 afforded in high yield the mononuclear, octahedral mer-[Ni{(pyridin-2-yl)methanol}3Cl2] complex 18. The reaction of 16 with NaH led to the deprotonation of one of the pyridine alcohol ligands to form [Ni{(pyridin-2-yl)methanol}{(pyridin-2-yl)methanolate}Cl] 21 in which the metal is coordinated by one pyridine alcohol and one pyridine alcoholate ligand. The crystal structures of the dinuclear, chloride-bridged octahedral complexes in 14·C6H12 and in 16·3CH2Cl2 and of the mononuclear, octahedral complex 18 in 18·CH2Cl2 have been determined by X-ray diffraction. In the latter case, intermolecular OH⋯Cl bonding interactions generate a centrosymmetric pseudo-dimer. Complexes 14, 16 and 21 have been tested in ethylene oligomerization with AlEtCl2 (Al/Ni ratios of 2, 4 or 6) or MAO (50, 100 or 200 equiv.) as co-catalysts under 10 bar of ethylene and yielded mostly dimers and trimers. Complex 16 in the presence of 6 equiv. of AlEtCl2 proved to be the most active system with a turnover frequency (TOF) up to 187 500 C2H4 (mol Ni h)−1. Complex 16 with 200 equiv. of MAO was also the most active, with TOF up to 104 300 C2H4 (mol Ni h)−1 under 30 bar of ethylene.
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