2-Benzimidazolyl-N-phenylquinoline-8-carboxamide Chromium(III) Trichlorides: Synthesis and Application for Ethylene Oligomerization and Polymerization

A series of chromium(III) complexes, LCrCl₃ (C1–C6: L = 2-(1H-benzo[d]imidazol-2-yl)-N-(2,6-R¹-4-R²-phenyl)quinoline-8-carboxamide; C1: R¹ = ⁱPr, R² = H; C2: R¹ = Et, R² = H; C3: R¹ = Me, R² = H; C4: R¹ = Me, R² = Me; C5: R¹ = H, R² = H; C6: R¹ = F, R² = H), was synthesized and characterized by IR spectroscopy, elemental analysis, mass spectra, and magnetic moments. The X-ray crystallographic analysis of complexes C2 and C3 reveals distorted octahedral geometries around the chromium atoms. Upon activation with MAO, these complexes exhibit high activities for ethylene oligomerization (up to 1.28 × 10⁷ g·mol^–1(Cr)·h^–1) and ethylene polymerization (up to 6.30 × 10⁶ g·mol^–1(Cr)·h^–1). The oligomers were produced with high selectivity for α-olefins (>99%), and the distribution closely resembled the Schultz–Flory rule. Various reaction parameters were investigated in detail, and the results revealed that both the steric and electronic effects of the ligands effect the catalytic activities of these chromium complexes as well as the distribution of the products formed.