Biaryl Group 4 Metal Complexes as Non‐Metallocene Catalysts for Polyethylene with Long Chain Branching

Maria M Gragert,Andrew J P White,Gaëlle Pannier,Serge Bettonville,George J P Britovsek,Atanas K Tomov

doi:10.1002/ejic.202000734

Abstract

A series of biaryl Group 4 complexes with a bidentate and a tridentate pincer ligand have been synthesized and characterized. The complexes have been applied as metallocene analogues for the controlled polymerization of ethylene and the copolymerization of ethylene and 1‐hexene, with a particular focus on the control of the degree of long chain branching in these polymers.

Highlights

Polyethylene (PE) is currently the most widely used and least expensive synthetic polymer on the market, accounting for ca. 32 % of global plastics demand in 2015, which translates to approximately 86 million tonnes
The success of metallocenes in olefin polymerisation is in part due to the catalyst stability offered by the cyclopentadienyl (Cp) ligand scaffold and the tuneability in terms of polymer properties such as molecular weight and chain branching
In search of alternative non-metallocene catalysts that enable control over branching levels, we have investigated whether bi-aryl complexes of type II and pincer-type complexes

Summary

Introduction

Polyethylene (PE) is currently the most widely used and least expensive synthetic polymer on the market, accounting for ca. 32 % of global plastics demand in 2015, which translates to approximately 86 million tonnes. An early example by van Koten used the 2,6-bis[(dimethylamino)methyl]phenyl pincer ligand in combination with TiCl4,[5] which were active in both ethylene homo-polymerisation and co-polymerisation with 1-hexene.[6]. Another important class of aryl Group IV catalysts for olefin polymerization, identified by high throughput screening methods, are the tridentate aryl pyridine amide pincer complexes reported in 2003.[7,8] These complexes received considerable attention and have shown activity in both ethylene homo-polymerisation and co-polymerisation with alkenes, as well as 1-hexene polymerisation.[9–12]. We report here the first mono(biaryl) complexes of type II and tridentate pincer complexes of type III with ancillary X ligands that can be activated with co-catalysts for ethylene polymerisation catalysis. M–C(aryl) bonds are generally stronger than aliphatic M–C bonds which should ensure that ethylene insertion occurs preferentially in M–C(alkyl) bonds, rather than the M–C (phenyl) bonds.[25,26] it has been shown that alkene insertion into the M–C(aryl) bond can be an essential catalyst activation process.[9,12]

Results and Discussion

Ethylene Polymerisation Results

Conflict of Interest