Nitro and 4,4′-flourobenzhydryl functionalized bis(imino)pyridine-cobalt complexes for high molecular weight linear polyethylenes

Abstract

A series of nitro and 4,4′-fluorobenzhydryl functionalized bis(imino)pyridine-cobalt complexes, [2-{(2,6-iPr2-3-NO2-4-((4-F-Ph)2CH)Ph)N=CMe}-6-{(Ar)N=CMe}C5H5N]CoCl2 (where Ar is 2,6-Me2Ph for Co1; 2,6-Et2Ph for Co2; 2,6-iPr2Ph for Co3; 2,4,6-Me3Ph for Co4; 2,6-Et2-4-Me-Ph for Co5; 2,6-iPr2-3-NO2-4-((4-F-Ph)2CH)Ph for Co6) were prepared and investigated for ethylene polymerization. The resultant compounds were characterized by elemental analysis, 1H/13C NMR and FT-IR spectra. The molecular structure determination revealed a distorted square pyramidal geometry for Co3. All prepared complexes demonstrated high catalytic activity for ethylene polymerization (up to 10.7 × 106 g PE (mol of Co)−1 h−1) and produced high-molecular-weight polyethylenes in the level of 105 g mol−1. Structural variations in the catalyst design revealed that the unsymmetrical complexes with sterically less hindrand substituents exhibited comparatively higher polymerization activity, while sterically encumbered symmetrical complexes proved more efficient in enhancing the molecular weight of resultant polyethylenes. Additionally, high-temperature 1H/13C NMR spectra of the produced polyethylenes confirmed their strictly linear microstructure, which is also evident from their high melting temperature (Tm ∼135 °C).