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

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).本研究制备了两类带有邻位三苯基硅基空间位阻取代基的前配体：分别为双齿{ONR}H（R = C₆F₅, 2c）以及三齿{ONNR}H（R = 喹啉基, 2a；2-吡啶甲基, 2b）型萘酚亚胺与苯酚亚胺（R = 喹啉基, 2d）前配体。随后，这些前配体分别与(对甲苯基)三(四氢呋喃（THF）)合溴化铬(II)反应，并经乙腈重结晶，得到对应的萘氧基亚胺基（3a−3c）与苯氧基亚胺基（3d）CrBr₂{ON(N)R}(乙腈)配合物。通过单晶X射线衍射分析，确定了配体2a、2d以及配合物3a、3b的分子晶体结构。经甲基铝氧烷（MAO）活化后，尽管前驱体中存在配位乙腈，配合物3a、3b与3d仍可作为高活性乙烯齐聚催化剂：在25−100 ℃、6 bar压力下，催化活性最高可达23730 kg·mol⁻¹·h⁻¹，且可高选择性地生成直链α-烯烃（乙烯基端基占比89−96%；数均分子量Mₙ = 600−1450 g·mol⁻¹，分子量分布M_w/M_n = 1.9−2.3）