The chloro-substituent enhances performance of 2,4-bis (imino)pyridylchromium catalysts yielding highly linear polyethylene

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 (M_w/M_n) 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.