The five unsymmetrical 2‐[1‐(2,4‐dibenzhydryl‐6‐chlorophenylimino)ethyl]‐6‐[1‐(arylimino)ethyl]pyridine compounds (aryl: 2,6‐Me2Ph L1, 2,6‐Et2Ph L2, 2,6‐iPr2Ph L3, 2,4,6‐Me3Ph L4 and 2,6‐Et2–4‐MePh L5) were prepared and characterized with FT‐IR and 1H/13C NMR spectroscopy as well as elemental analysis. The treatment of L1 – L5 with CrCl3·3THF affords the corresponding chromium chloride complexes (Cr1 – Cr5) in excellent yields. The molecular structures of Cr2 and Cr3 characterized by X‐ray diffraction show a distorted octahedral geometry with three nitrogen atoms and three chlorine atoms around the metal center. On activation with either MAO or MMAO, Cr1 – Cr5 collectively display high activity (up to 14.96 × 106 g (PE) mol−1 (Cr) h−1 at 60 °C) affording highly linear polyethylene with low molecular weight distribution (Mw/Mn) ranging from 1.06 to 2.81. An in‐depth catalytic evaluation of Cr1 was conducted in order to investigate how the cocatalyst type and its amount, reaction temperature and polymerization time affect the catalytic activities and polymer properties.

Polyolefin materials are the most synthesized polymer used nowadays and symbolize the development level of the national petrochemical industry, in which polyethylenes are major along with alternative product α-olefins for co-monomer and substrates for fine chemicals. Likely operating catalysts such as Ziegler-Natta and metallocene meet all demanding of various polyethylene materials, what is any business in developing late-transition metal catalysts for ethylene reactivity? In the past two decades, we realized the advantages of late-transition metal catalysts, such as easy variousness and easy preparation, good stability and high catalytic activity. Besides these, the characteristic different polyethylenes have been achieved as either highly linear polyethylene or highly branched polyethylenes. Therefore, there are some spaces in developing new catalytic system on the base of late-transition metal catalysts to compromise the demanding for new polyethylenes from sole ethylene polymerization.

By dealing CrCl3∙3THF with the corresponding ligands (L1–L5), an array of fluoro-substituted chromium (III) chlorides (Cr1–Cr5) bearing 2-[1-(2,4-dibenzhydryl-6-fluoro- phenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridine (aryl = 2,6-Me2Ph Cr1, 2,6-Et2Ph Cr2, 2,6-iPr2Ph Cr3, 2,4,6-Me3Ph Cr4, 2,6-Et2-4-MePh Cr5) was synthesized in good yield and validated via Fourier Transform Infrared (FT-IR) spectroscopy and elemental analysis. Besides the routine characterizations, the single-crystal X-ray diffraction study revealed the solid-state structures of complexes Cr2 and Cr4 as the distorted-octahedral geometry around the chromium center. Activated by either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the chromium catalysts exhibited high activities toward ethylene polymerization with the MMAO-promoted polymerizations far more productive than with MAO (20.14 × 106 g (PE) mol−1 (Cr) h−1 vs. 10.03 × 106 g (PE) mol−1 (Cr) h−1). In both cases, the resultant polyethylenes were found as highly linear polyethylene waxes with low molecular weights around 1–2 kg mol−1 and narrow molecular weight distribution (MWD range: 1.68–2.25). In general, both the catalytic performance of the ortho-fluorinated chromium complexes and polymer properties have been the subject of a detailed investigation and proved to be highly dependent on the polymerization reaction parameters (including cocatalyst type and amount, reaction temperature, ethylene pressure and run time).