Chromium(III) Complexes of Sterically Crowded Bidentante {ON^R} and Tridentate {ONN^R} Naphthoxy-Imine Ligands: Syntheses, Structures, and Use in Ethylene Oligomerization

Abstract

New bidentate {ONR}H (R = C6F5, 2c) and tridentate {ONNR}H (R = quinolyl, 2a; 2-pyridylmethyl, 2b} naphthol-imine and phenol-imine (R = quinolyl, 2d) pro-ligands sterically encumbered by an ortho-triphenylsilyl moiety have been prepared and converted to the corresponding naphthoxy-imino (3a−c) and phenoxy-imino (3d) CrBr2{ON(N)R}(CH3CN) complexes, respectively, via reaction with (p-tolyl)CrBr2(THF)3 and subsequent recrystallization from acetonitrile. The molecular structures of 2a, 2d, 3a, and 3b have been established by single-crystal X-ray diffraction studies. Upon activation with MAO, complexes 3a, 3b, and 3d, despite the presence of coordinated acetonitrile in those precursors, lead to highly active catalysts for the oligomerization of ethylene (activities up to 23 730 kg mol−1 h−1 at 25−100 °C, 6 bar), yielding selectively linear α-olefins (89−96% vinyl-end; Mn = 600−1450 g mol−1, Mw/Mn = 1.9−2.3).