This document describes research into using titanium fluoride complexes as pre-catalysts for ethylene polymerization. Ligand libraries were designed and synthesized to modify the electronic and steric properties of the titanium centers. Titanium fluoride and chloride complexes were characterized, and the fluoride complexes showed higher stability. Polymerization testing found the fluoride complexes had significantly higher activities than chloride analogues. The "fluoride effect" was observed to produce higher molecular weight polyethylene with broader distributions. Future work aims to further optimize ligand sterics and electronic effects to control polymer properties.
4. Why Ti(IV) Fluoride Complexes?
• Underexplored as ethylene
polymerisation pre-catalysts
• Ti-F bond has a bond
enthalpy of 570 kJmol-1
• Ti-Cl bond has a bond
enthalpy of 494 kJmol-1
• Is Ti-F bond more stable
than Ti-Cl to hydrolysis?
• Can we handle pre-catalysts
on the bench?
• Al-F bond has a bond
enthalpy of 663 kJmol-1
• Al-Cl bond has a bond
enthalpy of 511 kJmol-1
• Thermodynamic driving force
to abstract F- (-94 kJmol-1)
is higher than abstraction of
Cl- (-17 kJmol-1).
• Is activation with MAO more
facile from Ti-F?
J. A. Kerr, CRC Handbook of Chemistry and Physics 1999-2000: A Ready-Reference Book of Chemical and
Physical Data, D. R. Lide (ed), CRC Press, Boca Raton, Florida, USA 81st Edn., 2000
5. Existing use of Ti(IV) Fluoride Complex as
Ethylene Polymerisation Pre-catalyst
• Only one other example of non-metallocene Ti-F complex as ethylene
polymerisation pre-catalyst
• 60 mL toluene
• [MAO:Ti] 500:1
• 1 bar ethylene
• Low activity: 6 g(PE) mmol-1 h-1 bar-1
G. B. Nikiforov, H. W. Roesky and P. G. Jones, J. Fluor. Chem., 2008, 129, 376
6. Ligand Design and Synthesis
• Cheap readily available starting materials
• Common intermediates – effective pipeline
• Can selectively add/remove steric bulk/ electron density
• Fast, reproducible chemistry
• High yielding
7. Ligand Synthesis – an example
• 2 pot, 3 step procedure to non-trivial ligand systems
• Suzuki reaction to form C-C bond
• Imine Condensation to form C=N bond from ketone
• Can generate large quantities of the ketone in 2 days
• Easy to diversify at various stages – change phenol
– change aniline – change pyridine core
8. Pro-Ligand Library
a) L. A. Wright, E. G. Hope, G. A. Solan, W. B. Cross and K. Singh, Dalton Trans., 2015, 44, 6040 (b) L. A. Wright, E. G. Hope, G. A. Solan, W. B. Cross and K. Singh,
Dalton Trans., 2015, 44, 7230 (c) O. Adeyi, W. B. Cross, G. Forrest, L. Godfrey, E. G. Hope, A. McLeod, A. Singh, K. Singh, G. A. Solan, Y. Wang and L. A. Wright, Datlton
Trans., 2013, 42, 7710 (d) W. B. Cross, E. G. Hope, G. Forrest, K. Singh and G. A. Solan, Polyhedron, 2013, 59, 124 (e) W. Alkarekshi, A. P Armitage, O. Boyron, C. J.
Davies, M. Govere, A. Gregory, K. Singh and G. A. Solan, Organometallics, 2013, 32, 249
9. Preparation of Precatalysts
Synthesis of [(THF)2TiF4]: M. Jura, W. Levason, E. Petts, G. Reid, M. Webster and W. Zhang, Dalton Trans., 2010,
39, 10264
i) CH2Cl2, 3 h, RT
- 2THF, - HF
ii) Precipitation
10. Library of Ti(IV) Fluoride Complexes
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
11. Characterisation and Stability -Ti(IV) Fluoride
Complexes
1H and 19F NMR spectra recorded at 300 K for 1a in CDCl3.
(400 MHz, 375 MHz)
N.B. No effort to exclude moisture
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
12. Characterisation and Stability – Ti(IV)
Fluoride Complexes
Entry Complex Axial F (δ ppm) Equatorial F (δ
ppm)
2JFF (Hz)
1 1a +131 +202 28
2 2a +125 +199 n/da
3 3a +132 +201 32
4 4a +130 +193 29
5 5a +134 +205 32
6 6a +100 +141 n/da
Comparison of 19F NMR data for Ti-F complexes:
a poorly resolved signals therefore coupling constants were not determined.
Complex 6a displays different chemical shift from other complexes – attributed to
subtle changes in the ligand design – crystallography reveals no unique structural
motif
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
13. Molecular Structure of 3a
3a
3a
Bond Lengths (Å)
Ti(1)-F(1) (ax-F) 1.835(3)
Ti(1)-F(2) (eq-F) 1.793(3)
Ti(1)-F(3) (ax-F) 1.832(3)
Bond Angles (o)
trans-F-Ti(1)-F 167.34(15)
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
14. Characterisation and Stability – Ti(IV)
Fluoride Complexes
• Titanium(IV) fluoride complexes amenable to
synthesis without rigorous exclusion of moisture
• Titanium(IV) fluoride complexes amenable to full
characterisation (incl. crystal growth) with no
exclusion of moisture
• 19F NMR allows a powerful probe of pre-catalyst
structure
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
15. Titanium(IV) Chloride Complexes
i) CH2Cl2, RT, 1.5 - 3 h
ii) Evaporation
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
16. Polymerisation Testing
Conditions
• 0.01 mmol titanium
complex
• 1 bar ethylene
• 300:1 [MAO:Ti]
• 30 min
• 40 mL dry toluene
• Schlenk techniques
Investigating
1. Investigate difference in
Ti-X (X = F, Cl) towards
ethylene polymerisation
2. Investigate ligand effects
on the titanium towards
polymerisation of ethylene
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
17. Polymerisation Testing
Entry Complex Temperature
(oC)
Mass PE
(g)
Activity
(g mmol-h-bar-)
1 [(THF)2TiF4]a RT 0 0
2 1aa RT 0.209 42
3 2aa RT 0.432 86
4 3aa RT 1.699 340
5 3aa 50 1.182 236
6 4aa RT 0.774 155
7 5aa RT 0.449 90
8 6aa RT 0.014 2.8
9 TiCl4
a RT 0.01 2
10 1ba RT 1.791 358
11 2ba RT 2.950 590
12 3ba RT 4.950 990
13 4ba RT 2.228 446
14 n/aa RT 0.00 0
15 3ab RT 0.00 0
a 1 mmol “Ti”, 300:1 [Al:Ti], 30 min, 1 bar ethylene. b No MAO, 1 mmol “Ti”, 30 min, 1 bar ethylene. Reactions quenched with 2M HCl.
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
18. Polymerisation Testing – ‘Fluoride Effect ’
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
19. Polymerisation Testing – ‘Fluoride Effect ’
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
20. Polymerisation Testing – ‘Fluoride Effect ’
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
/MAO
SEC/GPC traces and detector modes. DRI, LS and DP
/MAO
21. Conclusions
• The most active Ti(IV) non-metallocene fluoride pre-catalyst known
• It is possible to modulate the activity of pre-catalysts by altering the
steric bulk of the ligand framework
• Modulate molecular weight of PE by increasing the steric bulk the
of supporting pincer ligand manifold
• Titanium chloride pre-catalysts give higher activities to ethylene
polymerisation for given ligand framework – exceptionally high
activities
L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation
22. Conclusions – ‘The Fluoride Effect’
• Fluoride-containing systems always give higher molecular weight
polyethylene – UHMWPE
• Effect of fluoride is to ‘smear’ molecular weight distribution of PE
• Would imply multiple modes of activation
23. Future Work
• Make ligand systems more sterically bulky
• Investigate amine-containing ligands on Ti(IV) fluoride complexes
as ethylene polymerisation pre-catalysts
• Make dianionic ligand systems to generate bisfluoride species
• What is(are) the active catalyst(s)?
• Probe the origin of ‘Fluoride Effect’
24. Acknowledgments
Joy and George Fraser (Funding)
University of Leicester (Funding)
Dr. G. Solan
Prof. E. Hope
Mr. K. Singh (X-ray)
Mr. M. Lee (Mass spec)
Dr. G. Griffith (NMR)
Dr. T. Boller (ExxonMobil, GPC analysis)
