Tandem catalysis using group 5 and 6 imido complexes and group 4 permethylindenyl catalysts

Lead Research Organisation: University of Oxford
Department Name: Oxford Chemistry

Abstract

Complexes known as constrained geometry catalysts (CGC) of the form R2Si(C5R'4)(R''N)MX2 are of great interest for the synthesis of polyethylene; both industrially and scientifically. Furthermore, in recent years, the O'Hare group have synthesised a number of novel metallocenes based on group 4 permethylindenyl (I*) complexes for use as ethylene polymerisation catalysts.
Ethylene oligomerisation, generating higher alpha-olefins from ethylene, is as the forefront of industrial research. This includes the Dimersol, Alphabutol and Phillips trimerisation processes. Work within the O'Hare group has shown that tungsten imido complexes to be extremely active and selective towards the ethylene dimerisation to 1-butene in both the solution and slurry phase. Recently niobium imido complexes of the form Nb(CHSiMe3)(NAr)(OC(CF3)3)(PMe3)2 (Figure 2(b)) were found to be active towards the ring opening metathesis polymerisation of norbornene.
Tandem catalysis involves the cooperative action of two or more catalysts to afford a product that is not accessible by the individual catalyst alone. There have been a number of reported tandem catalytic systems reported in the literature, both in solution, and more recently in the heterogeneous phase. Karbach and co-workers developed a silica-supported system that allowed incorporation of 1-hexene into at polymer chain.
Ethylene polymerisation catalysts - the aim of this part of the project is to synthesise new group 4 constrained geometry I* complexes of the general formula R12SB(R2N,I*)MX2 with intention of developing them into commercial viable ethylene polymerisation catalysts.
Ethylene oligomerisation catalysts - the aims of this project include the synthesis of niobium and tantalum imido complexes of the form M(NAr)Cl3.THF, M(NAr)Me2Cl and the solid supported equivalents. These complexes will then be developed into commercially viable ethylene oligomerisation catalysts for higher alpha-olefins, in particular 1-octene or 1-butene with high selectivity.
Tandem catalysis - the final aim is to simultaneously support both an ethylene polymerisation and an oligomerisation catalyst on a solid support, such as polymethylaluminoxane, in order to form LLDPE from a single ethylene feed source.

This project falls within the EPSRC Physical Sciences research area. In particular this project focuses on catalysis with the aim to develop new catalysts for ethylene polymerisation and oligomerisation.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1811574 Studentship EP/N509711/1 01/10/2016 31/03/2020 Thomas James Williams
 
Description We have developed a library of constrained geometry catalysts with variation of a number of fragments to investigate how these effect the ethylene polymerisation activities. Firstly, by variation of the amido fragment, we have been able to establish that complexes with more electron donating amido fragments show much higher polymerisation activities. This work has been published at https://pubs.rsc.org/en/Content/ArticleLanding/2018/CY/C8CY01374H#!divAbstract
After this, we looked at variation of the leaving group, and how these effected polymerisation activity. We found alkylation of the complex resulted in increases in polymerisation activity, and that it was also possible to greatly change the polymer molecular weight produced.
We investigated variation of the support and how this could be used to increase the polymer molecular weight, without overly decreasing the activity. Whilst we were able to increase the molecular weight up to ultra high molecular weight polyethylene, but the results couldn't be maintained on scale up
Finally these complexes have been found to be good incorporators of comonomers into the polyethylene chains during copolymerisation studies
When tested for solution ethylene/octene and ethylene/hexene copolymerisation studies, these complexes were shown to have comparable levels of olefin incorporation to the previously developed industrial catalyst, but at three times higher activities
Exploitation Route Further work can be undertaken to investigate the copolymerisation potential of these complexes
It would also be of interest to look at variation of the heteroatom, away from amido complexes
Sectors Chemicals

URL https://pubs.rsc.org/en/Content/ArticleLanding/2018/CY/C8CY01374H
 
Description These catalysts are being tested for scale up in ethylene/1-hexene copolymerisations, with the aim of producing controlled short chain branched polymer, to enhance and tailor the properties of the polymer as desired
First Year Of Impact 2019
Sector Chemicals
Impact Types Economic