2-Benzimidazol-6-pyrazol-pyridine Chromium(III) Trichlorides: Synthesis, Characterization, and Application for Ethylene Oligomerization and Polymerization

A series of chromium(III) complexes, LCrCl3 (Cr1-Cr4: L = 2-(N-R-2-benzimidazol-2=yl)-6-(3,5-R-1-pyrazol-1-yl)pyridine; Cr1: R-1 = H, R-2 = H; Cr-2: = Me, R-2 = H; Cr-3: = R-1, R-2 = Me; Cr4: R-1 = Me, R-2 = Bn), were syntheized and-characterized by IR spectroscopy and elemental analysis. The, studies of the solid state of Cr2 and :Cr3 revealed distorted octahedral geometries around the chromium centers by X-ray diffractions. In the presence of MAO, Cr1 Cr4 exhibited:high activities toward ethylene oligomerization (up to 2.17 X 10(6) g.Mol(-1)(Cr).h(-1)) and ethylene polymerization (up to 6.78 X los g.mol(-1)(Cr).h(-1)). The oligomers Were produced with high selectivity for alpha-olefins (>99%), confirmed by FT-IR and C-13 NMR, and the distributions followed the Schulz-Flory equation. Various reaction parameters including the amount,of cocatalyst, reaction temperature, and time were evaluated in detail, and it-was evident that the title complexes had good thermal stability and the substituents on imidazole-N of the ligands dramatically impacted the catalytic activities as well as the distribution of the products.