Novel vanadium(iii) complexes with bidentate N,N-chelating iminopyrrolide ligands: synthesis, characterization and catalytic behaviour of ethylenepolymerization and copolymerization with 10-undecen-1-ol

Abstract

A series of novel vanadium(III) complexes bearing iminopyrrolide chelating ligands [2-(RNCH)C₄H₃N]V(THF)₂Cl₂ (2a: R = cyclohexyl; 2b: R = Ph; 2c: R = 2,6-iPr₂C₆H₃; 2d: R = p-CF₃C₆H₄; 2e: R = C₆F₅) have been synthesized and characterized. Single-crystal X-ray diffraction revealed that complexes 2a, 2c and 2e adopt an octahedral geometry around the vanadium center. In the presence of Et₂AlCl as a co-catalyst, these complexes displayed high catalytic activities up to 48.6 kg PE mmol_V⁻¹ h⁻¹ bar⁻¹ for ethylene polymerization, and produced high molecular weight polymers. 2a–e/Et₂AlCl catalytic systems were tolerant to elevated temperature (70 °C) and yielded unimodal polyethylenes, indicating the single site behaviour of these catalysts. By pre-treating with equimolar amounts of alkylaluminums, functional α-olefin 10-undecen-1-ol can be efficiently incorporated into polyethylene chains. 10-Undecen-1-ol incorporation can easily reach 15.8 mol% under the mild conditions. When compared with VCl₃(THF)₃ or rac-Et[Ind]₂ZrCl₂, these vanadium(III) complexes exhibited higher activities towards the copolymerization, and can incorporate more 10-undecen-1-ol into polymer chains under the similar conditions.