luka wright fluorine meeting 2015

Bench Stable Ethylene Polymerisation Pre-Catalysts:

A Step Change using Titanium Fluorides

Luka A. Wright

n

LnTi(F)m MAO, RT

Highly Active Non-Metallocene Pyridine-Based Pincer Pre-Catalysts – State of the Art

NMe

ON

Zr

XX

R2

NN

Zr

XX

N

NN

Hf

XX

Ar NN

M

XX

N

McConville et al., 2000 Solan and Giesbrecht, 2009

Busico et al., 2005M = Co, Fe

Gibson/Brookhart, 1998

NN N

Fe

XX

Me

Gibson et al., 2000

NN N

Fe

XX

Ar

Sun et al., 2008

X = Cl, Br, alkyl

Cossee-Arlmann MechanismCo-ordination/Insertion MechanismAl

O

Me

n

MAO structure

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

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

nMAO, RT

TiN

N FTi

F

N

N

Ar Ar

ArAr

F

F

F

F

Ligand Design and Synthesis

NN

Ar HO

R1

R2

NO

Br

R3 R3

R4

NH2R1

HO

Br

R2

• Cheap readily available starting materials• Common intermediates – effective pipeline• Can selectively add/remove steric bulk/ electron density• Fast, reproducible chemistry• High yielding

Ligand Synthesis – an example

HO

Br

HO

(HO)2B NO

Br

NO

HO

1: BuLi2: B(OiPr)33: H3O+

Cat. Pd(OAc)2, PPh3, Toluene, EtOH2M K2CO3100 C12 h

NH2

i-Pri-Pr

NN

HO

i-Pr

i-Pr

MgSO4, MeOH, Reflux 12 h

84%90%

78%

• 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

Pro-Ligand Library

NN OH

NNH

HO

i-Pr

i-Pr

NNH

HO

i-Pr

i-Pr

NNH

HO

i-Pr

52%

88%92%

96%

61% 72%

NN

HO

i-Pr

i-Pr

NN

HO

i-Pr

i-Pr

58%

NN

HO

i-Pr

i-Pr

NN

HO

i-Pr

i-Pr

NN

HO

i-Pr

i-Pri-Pr

FN

NHO

NN

HO

i-Pr

NN

HO

i-Pr

i-Pr

NN OH

1H78%

5H80%

4H69%

2H60%

3H70%

6H60%

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

Preparation of Precatalysts

1H-6H [(THF)2TiF4]

Synthesis of [(THF)2TiF4]: M. Jura, W. Levason, E. Petts, G. Reid, M. Webster and W. Zhang, Dalton Trans., 2010, 39, 10264

TiN F

N O

F

F

i) CH2Cl2, 3 h, RT

- 2THF, - HF

ii) Precipitation

Library of Ti(IV) Fluoride Complexes

NN

ON

N

O

F

TiF

F F

TiF

F F

NN

OTiF

F F

NN

OTiF

F FN

N

OTiF

F F

1a38%

2a48%

3a63%

4a96%

5a49%

NON Ti

F FF

6a26%

L. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation

Characterisation and Stability -Ti(IV) Fluoride Complexes

NN

OTiF

F F

1a

1H and 19F NMR spectra recorded at 300 K for 1a in CDCl3. (400 MHz, 375 MHz)N.B. No effort to exclude moisture

TiN Fequatorial

N O

Faxial

Faxial


Characterisation and Stability – Ti(IV) Fluoride Complexes

Entry Complex Axial F (δ ppm) Equatorial F (δ ppm)

2JFF (Hz)

1 1a +131 +202 282 2a +125 +199 n/da

3 3a +132 +201 324 4a +130 +193 295 5a +134 +205 326 6a +100 +141 n/da

Comparison of 19F NMR data for Ti-F complexes:

TiN Fequatorial

N O

Faxial

Faxial

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

NN

OTiF F

F

1a - 5a

NON Ti

F F

F

6a

R1

Ar R2


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)


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


Titanium(IV) Chloride Complexes

i) CH2Cl2, RT, 1.5 - 3 hii) Evaporation

1H-5H TiCl4

NN

ON

N

O

F

TiCl

Cl Cl

TiCl

Cl Cl

NN

OTiCl

Cl Cl

NN

OTiCl

Cl ClN

N

OTiCl

Cl Cl

1b>99%

2b>99%

3b>99%

4b>99%

5b>99%


Polymerisation Testing

Conditions• 0.01 mmol

titanium complex• 1 bar ethylene• 300:1 [MAO:Ti]• 30 min• 40 mL dry toluene• Schlenk techniques

Investigating1. Investigate

difference in Ti-X (X = F, Cl) towards ethylene polymerisation

2. Investigate ligand effects on the titanium towards polymerisation of ethyleneL. A. Wright, G. A. Solan, E. G. Hope and K. Singh, Manuscript in Preparation

n

LnTi(X)m MAO, RT

Polymerisation TestingEntry Complex Temperature

(oC)Mass PE

(g)Activity

(g mmol-h-bar-)1 [(THF)2TiF4]a RT 0 0

2 1aa RT 0.209 423 2aa RT 0.432 864 3aa RT 1.699 3405 3aa 50 1.182 2366 4aa RT 0.774 1557 5aa RT 0.449 908 6aa RT 0.014 2.89 TiCl4

a RT 0.01 2

10 1ba RT 1.791 35811 2ba RT 2.950 59012 3ba RT 4.950 99013 4ba RT 2.228 44614 n/aa RT 0.00 015 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.


Polymerisation Testing – ‘Fluoride Effect ’

n

/MAO

Toluene, RT

N

N

OTiF

F F

1a

1 bar 42 g mmol-1 h-1 bar-1

Mw 149,379Mn 3,682PDI 41

n

/MAO

Toluene, RT

N

N

OTiCl

Cl Cl

1b


Mw 22,784Mn 2,600PDI 9



n

/MAO

Toluene, RT

N

N

OTiF

F F

3a


Mw 1,089,817Mn 22,683PDI 48

n

/MAO

Toluene, RT

N

N

OTiCl

Cl Cl

3b


Mw 209,689Mn 28,918PDI 7



N

N

OTiF

F F

3a

N

N

OTiCl

Cl Cl

3b


/MAO

SEC/GPC traces and detector modes. DRI, LS and DP

/MAO

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


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

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’

AcknowledgmentsJoy and George Fraser (Funding)University of Leicester (Funding)Dr. G. SolanProf. E. HopeMr. K. Singh (X-ray)Mr. M. Lee (Mass spec)Dr. G. Griffith (NMR)Dr. T. Boller (ExxonMobil, GPC analysis)

Thank You for Listening• Any Questions?

luka wright fluorine meeting 2015

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