Dibenzosuberyl substituents suppressing chain transfer in Bis(imino)pyridyl Iron(II) catalyzed ethylene polymerization

Abstract

It is an efficient way to introduce ortho-aryl dibenzosuberyl substituents into late-transition metal catalysts for retarding chain transfer in olefin polymerization. Here, we further found that dibenzosuberyl substituents could also suppress chain transfer and thus increase the molecular weight in ethylene polymerization with bis(imino)pyridyl Fe(II) catalysts. A series of bis(imino)pyridyl ligands with unilateral diarylmethyl or dibenzosuberyl moiety on the ortho-positions of N-aryl rings and their corresponding Fe(II) catalysts were synthesized and characterized. All these bis(imino)pyridyl Fe(II) catalysts exhibited high polymerization activity and could generate high weight-average molecular weight polyethylenes with very broad molecular weight distributions in most cases. Among them, the dibenzosuberyl Fe(II) catalysts could generate ultra-high weight-average molecular weight (Mw = 2038–2137 kg/mol) polyethylenes at low temperatures, significantly higher than the diarylmethyl catalysts. The obtained polyethylenes are all highly linear with almost no branching distribution.