Unimodal polyethylenes of high linearity and narrow dispersity by using ortho-4,4′-dichlorobenzhydryl-modified bis(imino)pyridyl-iron catalysts

Abstract

Six different examples of 4,4′-dichlorobenzhydryl-substituted 2,6-bis(arylimino)pyridyl-iron(II) chloride complex, [2-{{2,6-((p-ClPh)₂CH)₂-4-MeC₆H₂}NCMe}-6-(ArNCMe)C₅H₃N]FeCl₂ (Ar = 2,6-Me₂C₆H₃Fe1, 2,6-Et₂C₆H₃Fe2, 2,6-ⁱPr₂C₆H₃Fe3, 2,4,6-Me₃C₆H₂Fe4, 2,6-Et₂-4-MeC₆H₂Fe5, 2,6-((p-ClPh)₂CH)₂-4-MeC₆H₂Fe6), have been synthesized in good yield and characterized by various spectroscopic and analytical techniques. The molecular structures of Fe2 and Fe5 emphasize the uneven steric protection of the ferrous center imposed by the unsymmetrical N,N,N′-chelate. When treated with either MAO or MMAO (modified-MAO) as activators, Fe1–Fe5 exhibited very high productivities at elevated temperature with peak performance of 21.59 × 10⁶ g PE mol⁻¹(Fe) h⁻¹ for Fe5/MMAO at 50 °C and 15.65 × 10⁶ g PE mol⁻¹(Fe) h⁻¹ for Fe1/MAO at 60 °C. By contrast, the most sterically hindered Fe6 was either inactive (using MAO) or displayed very low activity (using MMAO). As a further feature, this class of iron catalyst was capable of displaying long lifetimes with catalytic activities up to 10.77 × 10⁶ g PE mol⁻¹(Fe) h⁻¹ observed after 1 h. In all cases, strictly linear and unimodal polyethylene was formed with narrow dispersity, while the polymer molecular weight was strongly influenced by the aluminoxane co-catalyst (M_w using MAO > MMAO) and also by the steric properties of the second N-aryl group (up to 32.9 kg mol⁻¹ for Fe3/MAO).