2-(N,N-Diethylaminomethyl)-6,7-trihydroquinolinyl-8-ylideneamine-Ni(ii) chlorides: application in ethylene dimerization and trimerization

Abstract

A series of Ni(II) complexes with the general formula [2-((NEt₂)Me)-8-{N(Ar)}C₉H₈N]NiCl₂, where Ar = 2,6-Me₂C₆H₃ in Ni1, 2,6-Et₂C₆H₃ in Ni2, 2,6-i-Pr₂C₆H₃ in Ni3, 2,4,6-Me₃C₆H₂ in Ni4, 2,6-Et₂-4-MeC₆H₂ in Ni5, and 2,4,6-t-Bu₃C₆H₂ in Ni6, has been prepared using a one-pot reaction of 2-(N,N-diethylaminomethyl)-6,7-dihydroquinolin-8(5H)-one with the corresponding aniline and nickel dichloride hexahydrate. The resultant complexes were characterized using elemental analysis and FT-IR spectroscopy, while the mononuclear Ni1 and Ni3 were also the subject of single-crystal X-ray diffraction study. On activation with MMAO, the complexes Ni1–Ni6 displayed good activity in ethylene oligomerization, forming hexenes (ca. 48% 1-hexene) as the major products and exhibiting thermal stability up to 50 °C under 10 atm C₂H₄. When MAO was applied as the cocatalyst, lower activity was observed, but the catalyst showed higher selectivity toward ethylene dimerization. It is also worth noticing that an induction period was observed as the Ni/MAO catalysts reached their peak activity after 30 min.