Raising the N-aryl fluoride content in unsymmetrical diaryliminoacenaphthylenes as a route to highly active nickel(ii) catalysts in ethylene polymerization

Abstract

Five examples of selectively fluorinated unsymmetrical diiminoacenaphthylenes, 1-[2,6-{(4-FC₆H₄)₂CH}₂-4-FC₆H₄N]-2-(ArN) C₂C₁₀H₆ (Ar = 2,6-Me₂C₆H₃L1, 2,6-Et₂C₆H₃L2, 2,6-iPr₂C₆H₃L3, 2,4,6-Me₃C₆H₂L4, 2,6-Et₂-4-MeC₆H₂L5), have been synthesized and used to prepare their corresponding nickel(II) halide complexes, LNiBr₂ (Ni1–Ni5) and LNiCl₂ (Ni6–Ni10). Both ¹H and ¹⁹F NMR spectroscopy techniques have been employed to characterize paramagnetic Ni1–Ni10; an inequivalent fluorine environment is a feature of the tetrahedral complexes in solution. Upon activation with relatively low ratios (ca. 600 equiv.) of ethylaluminum sesquichloride (Et₃Al₂Cl₂, EASC), all the nickel complexes displayed high activities toward ethylene polymerization at 30 °C with precatalyst Ni4 the standout performer at 2.20 × 10⁷ g of PE per mol of Ni per h, producing highly branched polyethylenes. In comparison with related diiminoacenaphthylene-nickel catalysts, these current systems, incorporating a high fluorine content on one N-aryl group, display superior productivity. In addition, the molecular structures of Ni2 and Ni4 are reported and the active catalyst is probed using ¹⁹F NMR spectroscopy.