Iron-based ethylene polymerization catalysts supported by bis(imino)pyridine ligands: Derivatization via deprotonation/alkylation at the ketimine methyl position

Bis(imino)pyridine ligands, L [where L = 2,6-(ArNCR1)2C5H3N R1 = Et, iPr, CH2CH2Ph or CH(CH2Ph)2 and Ar = 2,4,6-(Me)3C6H2 (MES) or 2,6-(iPr)2C6H3 (DIPP)] have been prepared by deprotonation of the parent ketimine ligand (R1 = Me) using lithium diisopropylamide (LDA), followed by alkylation with the appropriate alkylhalide. The corresponding iron dichloride complexes LFeCl2 are highly active ethylene polymerisation catalysts upon treatment with methylaluminoxane (MAO), with activities in the range of 3000–18,000 g/mmol bar h. The molecular weights (Mn) of the resultant polyethylenes lie in the range of 6500–24,000 with broad molecular weight distributions (16.5–38.0). The nature of the imine carbon substituent has a marked effect on the polymer molecular weight whereas the catalyst activity is largely unaffected by changes to this substituent.

Graphical abstractA family of bis(imino)pyridine pre-ligands bearing bulky substituents at the imine carbon position has been prepared using a deprotonation/alkylation procedure. Their iron complexes are highly active ethylene polymerisation catalysts when treated with MAO; increasing the size of the ketimine substituent leads to an increase in the molecular weight of the resultant polyethylene and high catalyst productivities are maintained. Figure optionsDownload full-size imageDownload as PowerPoint slide