Highly active ethylene polymerization catalysts based on titanium complexes having two phenoxy-imine chelate ligands

Article abstract of DOI:10.1016/S1381-1169(01)00303-X

Five titanium complexes having F(s) or CF₃(s) containing phenoxy-imine chelate ligands were prepared and investigated for their potential as ethylene polymerization catalysts using methylalumoxane (MAO) as a co-catalyst at 25°C under atmospheric pressure. Polymerization results showed that the electrophilicity of the titanium center plays a dominant role in determining activity. These results clearly demonstrate, for the first time, the electron-withdrawing substituent effects on polymerization activity. The complexes possessing plural F(s) or CF₃(s) in the phenoxy-imine ligand displayed very high activities exceeding those for Cp₂TiCl₂ and Cp₂ZrCl₂. The activity, 43,300 kg polyethylene (PE) mol-cat^-1 h^-1, exhibited by the complex having three fluorines in the ligand, represents the highest value reported to date for ethylene polymerization catalysts based on titanium complexes under atmospheric pressure at ambient temperatures.

Full text of DOI:10.1016/S1381-1169(01)00303-X

Journal of Molecular Catalysis A: Chemical 179 (2002) 11–16
Highly active ethylene polymerization catalysts based on titanium
complexes having two phenoxy-imine chelate ligands
Sei-ichi Ishii∗, Junji Saito, Makoto Mitani, Jun-ichi Mohri, Naoto Matsukawa,
Yasushi Tohi, Shigekazu Matsui, Norio Kashiwa, Terunori Fujita∗
Research and Development Center, Mitsui Chemicals Inc., 580-32 Nagaura, Sodegaura-City, Chiba 299-0265, Japan
Received 18 June 2001; received in revised form 10 August 2001; accepted 13 August 2001
Abstract
Five titanium complexes having F(s) or CF3(s) containing phenoxy-imine chelate ligands were prepared and investigated for
their potential as ethylene polymerization catalysts using methylalumoxane (MAO) as a co-catalyst at 25 ◦C under atmospheric
pressure. Polymerization results showed that the electrophilicity of the titanium center plays a dominant role in determining
activity. These results clearly demonstrate, for the first time, the electron-withdrawing substituent effects on polymerization
activity. The complexes possessing plural F(s) or CF3(s) in the phenoxy-imine ligand displayed very high activities exceeding
those for Cp2TiCl2 and Cp2ZrCl2. The activity, 43,300 kg polyethylene (PE) mol-cat−1 h−1, exhibited by the complex having
three fluorines in the ligand, represents the highest value reported to date for ethylene polymerization catalysts based on
titanium complexes under atmospheric pressure at ambient temperatures. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Olefin polymerization catalyst; Post-metallocene; Phenoxy-imine ligand; Titanium; FI catalysts
1. Introduction
active catalysts based on both early and late tran-
sition metal complexes have been developed [7,8].
There are, however, only a few examples of titanium
complexes displaying high ethylene polymerization
activities [9–11] though titanium metal is the major
player in highly active heterogeneous Ziegler–Natta
catalysts. As a result of ligand-oriented catalyst design
research in our laboratories, we have developed a new
family of group 4 transition metal complexes bearing
two phenoxy-imine chelate ligands, named FI Cata-
lysts, exhibiting high catalytic performance for olefin
polymerization including living olefin polymerization
[12–26]. Although we successfully obtained very ac-
tive zirconium FI catalysts, we did not obtain highly
active titanium FI catalysts [14]. Accordingly, we have
conducted further research on titanium FI Catalysts
with the intention of developing the highly active ti-
tanium catalysts and applying them to new polymers.
Historically, the development of highly active
olefin polymerization catalysts has been a trigger for
creating new polymers which impact on our daily
lives in countless beneficial ways [1–5]. A recent
instance is the development of group 4 metallocene
catalysts which exhibit very high ethylene polymer-
ization activities [4,5]. Based on the highly active
group 4 metallocene catalysts, high performance
linear low-density polyethylene (LLDPE), isotactic
polypropylene (iPP), and syndiotactic polystyrene
(sPS), etc. have been developed [6]. Therefore, much
effort has been directed towards the development of
highly active catalysts, following the group 4 metal-
locene catalysts. In consequence, quite a few highly
∗ Corresponding author.
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(01)00303-X

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S.-i. Ishii et al. / Journal of Molecular Catalysis A: Chemical 179 (2002) 11–16
In this paper, we would like to describe the catalytic
performance of new titanium complexes having F(s)
or CF3(s) containing phenoxy-imine chelate ligands
for ethylene polymerization in order to introduce
a new method for acquiring highly active titanium
complexes with phenoxy-imine chelate ligands.
25 mg/decalin 25 ml). Viscosity average molecular
weight (Mv) values of polyethylenes were calculated
from the following equation: (η) = 6.2 × 10−4 Mv0.7
[27].
2.2. General complex syntheses procedure
2.2.1. Ligand syntheses
2. Experimental
Ligand syntheses were carried out under an at-
mosphere of nitrogen using oven-dried glassware.
3-t-Butylsalicylaldehyde reacted with a primary amine
compound via Schiff base condensation in dried
toluene to afford the corresponding phenoxy-imine
ligand in approximately 70–98% yield [14].
2.1. General
2.1.1. Solvents and reagents
Dried solvents (diethyl ether, toluene, dichloro-
methane, and hexane) used for ligand and complex
syntheses were purchased from Wako Pure Chem-
ical Industries, Ltd., and used as received. Toluene
used as a polymerization solvent (Wako Pure
Chemical Industries, Ltd.) was dried over Al2O3.
3-t-Butylsalicylaldehyde was obtained from Aldrich
Chemical Company Inc. 4-Fluoroaniline, 3,5-di-
fluoroaniline, 3,4,5-trifluoroaniline, 4-trifluoromethyl-
aniline, and 3,5-bis(trifluoromethyl)aniline were
purchased from Tokyo Kasei Kogyo Co., Ltd. An
n-butyllithium hexane solution (Kanto Chemical Co.,
Inc.) were also used as received. TiCl4 and ethy-
lene were obtained from Aldrich Chemical Company
Inc. and Sumitomo Seika Co., Ltd., respectively.
Methylalumoxane (MAO) was purchased from Albe-
mare as a 1.2 M toluene solution, and the remaining
trimethylaluminum was evaporated in vacuo prior
to use.
2.2.2. Complex synthesis
All manipulations were performed with the ex-
clusion of oxygen and moisture under argon using
standard Schlenk techniques. A typical procedure
for a complexation is as follows: to a stirred solu-
tion of a phenoxy-imine ligand (3.0 mmol) in dried
diethyl ether (20 ml) at −78 ◦C, an n-butyllithium
hexane solution (3.0 mmol) was added dropwise over
a 5 min-period. The solution was allowed to warm
to room temperature and stirred for 2 h, the resulting
solution was added dropwise over a 30 min-period to
a stirred solution of TiCl4 (1.5 mmol) in dried diethyl
ether (20 ml) at −78 ◦C. The mixture was allowed to
warm to room temperature and stirred for 15 h. The
resulting mixture was concentrated in vacuo to give
a solid, to which dried dichloromethane (20 ml) was
added, and the mixture was stirred for 5 min. The re-
sulting mixture was filtered, and then the residue was
washed with dried dichloromethane. The combined
organic filtrates were concentrated in vacuo to af-
ford the crude complex. To the crude complex, dried
diethyl ether (3 ml) and dried hexane (10 ml) were
added and stirred for 15 min. A titanium complex was
collected by filtration, washed with dried hexane and
dried in vacuo.
2.1.2. Ligand and complex analyses
NMR spectra were recorded on a JEOL270 spec-
trometer at ambient temperatures. Chemical shifts for
1
the H NMR were referenced to an internal solvent
resonance and reported relative to tetramethylsilane
(TMS). Elemental analysis for CHN was carried out
by the CHNO type from the Helaus Co. The elemental
analysis for Ti was carried out using the ICP method
by a SHIMADZU ICPS-8000 after dry ashing and di-
lute nitric acid dissolution. The FD-MS spectra were
recorded on a SX-102A from Japan Electron Optics
Laboratory Co., Ltd.
2.3. Bis(N-(3-t-butylsalicylidene)-
4ꢀ-fluoroanilinato)titanium(IV)dichloride (2)
Reddish brown powder (22% yield). 1H NMR
2.1.3. Polymer characterization
(CDCl3); δ. 1.33–1.50 (m, 18H, t-Bu), 6.71–7.67
=
Intrinsic viscosity (η) was measured in decalin at
(m, 14H), 7.96–8.06 (m, 2H, CH N). Anal. found:
135 ◦C using an Ubbelohde viscometer (polyethylene
C, 62.04; H, 5.30; N, 3.77; Ti, 6.93%. Calcd.:

S.-i. Ishii et al. / Journal of Molecular Catalysis A: Chemical 179 (2002) 11–16
13
TiC34H34N2O2F2Cl2; C, 61.93; H, 5.20; N, 4.25; Ti,
reactor equipped with a mechanical stirrer and a tem-
perature probe. Toluene (250 ml) was introduced into
the nitrogen-purged reactor and stirred vigorously
(600 rpm). The toluene was kept at 25 ◦C, and then the
ethylene gas feed (100 l/h) was started. After 15 min,
polymerization was initiated by the addition of a
toluene solution of MAO and then a toluene solution
of a complex into the reactor with vigorous stirring
(600 rpm). After 5 min, isobutyl alcohol (10 ml) was
added to terminate the polymerization, and the ethy-
lene gas feed was stopped. The resulting mixture was
added to the acidic methanol (1000 ml including 2 ml
of conc. HCl). The polyethylene was isolated by fil-
tration, washed with methanol (200 ml × 2), and then
dried in vacuo to constant weight (80 ◦C, vacuum
oven).
7.26%. FD-MS, 658 (M+).
2.4. Bis(N-(3-t-butylsalicylidene)-3ꢀ,
5ꢀ-difluoroanilinato)titanium(IV)dichloride (3)
Reddish brown powder (69% yield). 1H NMR
(CDCl3); δ. 1.32–1.62 (m, 18H, t-Bu), 6.33–7.33 (m,
=
10H), 7.52–7.70 (m, 2H), 8.03–8.10 (m, 2H, CH N).
Anal. found: C, 58.83; H, 4.91; N, 3.78; Ti, 6.86%.
Calcd.:TiC34H32N2O2F4Cl2; C, 58.72; H, 4.64; N,
4.03; Ti, 6.89%. FD-MS, 694 (M+).
2.5. Bis(N-(3-t-butylsalicylidene)-3ꢀ,4ꢀ,
5ꢀ-trifluoroanilinato)titanium(IV)dichloride (4)
Reddish brown powder (33% yield). 1H NMR
(CDCl3); δ. 1.17–1.62 (m, 18H, t-Bu), 6.41–7.69 (m,
2.9. HOMO energy level calculation
=
10H), 8.03–8.09 (m, 2H, CH N). Anal. found: C,
55.96; H, 4.00; N, 3.56; Ti, 6.48%. Calcd.:TiC34H30
N2O2F6Cl2; C, 55.83; H, 4.13; N, 3.83; Ti, 6.55%.
FD-MS, 730 (M+).
Highest Occupied Molecular Orbital (HOMO) en-
ergy level calculations for anionic phenoxy-imine
chelate ligands were performed using MNDO-PM3
method (HyperChem Ver. 5.1).
2.6. Bis(N-(3-t-butylsalicylidene)-4ꢀ-
trifluoromethylanilinato)titanium(IV)dichloride (5)
Reddish brown powder (27% yield). 1H-NMR
(CDCl3); δ. 1.18–1.59 (m, 18H, t-Bu), 6.78–6.93 (m,
4H), 7.05–7.17 (m, 4H), 7.31–7.69(m, 6H), 8.09 (s,
3. Results and discussion
A general synthetic route for titanium complexes
used in this study is depicted in Scheme 1. The
synthesis of complex 1 has already been reported
[14]. The phenoxy-imine ligands, A–E, are pre-
pared in high yields (A: 98%, B: 89%, C: 98%, D:
70%, E: 72%) from an aniline having F(s) or CF3(s)
and 3-t-butylsalicylaldehyde in dried toluene. The
titanium complexes are obtained in moderate to
good yields (2: 22%, 3: 69%, 4: 33%, 5: 27%, 6:
51%) by the reaction of TiCl4 with two equivalents of
the lithium salt of the phenoxy-imine ligand in dried
diethyl ether, followed by the purification using dried
diethyl ether and dried hexane.
=
2H, CH N). Anal. found: C, 56.47; H, 4.85; N, 3.50;
Ti, 6.45%. Calcd.:TiC36H34N2O2F6Cl2; C, 56.94; H,
4.51; N, 3.69; Ti, 6.30%. FD-MS, 758 (M+).
2.7. Bis(N-(3-t-butylsalicylidene)-3ꢀ,
5ꢀ-bis(trifluoromethyl)anilinato)titanium(IV)
dichloride (6)
Reddish brown powder (51% yield). 1H NMR
(CDCl3); δ. 1.06–1.47 (m, 18H, t-Bu), 6.99–7.11 (m,
4H), 7.33–7.39 (m, 4H), 7.53–7.70 (m, 4H), 8.28 (s,
=
2H, CH N). Anal. found: C, 50.86; H, 3.55; N, 2.93;
Ti, 5.12%. Calcd.:TiC38H32N2O2F12Cl2; C, 50.97;
Ethylene polymerization behavior of complexes
1–6 was investigated at 25 ◦C in toluene with MAO as
a co-catalyst under ethylene at atmospheric pressure.
Polymerization results are compiled in Table 1. All
complexes are active toward ethylene polymerization
and in all cases, high molecular weight polyethylenes
were obtained (viscosity average molecular weight
H, 3.60; N, 3.13; Ti, 5.35%. FD-MS, 894 (M+).
2.8. Ethylene polymerization
Ethylene polymerization was carried out under at-
mospheric pressure in toluene using a 500 ml glass

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S.-i. Ishii et al. / Journal of Molecular Catalysis A: Chemical 179 (2002) 11–16
Scheme 1. Synthetic route for titanium complexes.
Table 1
Ethylene polymerization resultsa
Entry
Complex
Catalyst (␮mol)
Yield (g)
Activity (kg-PE mol-cat−1 h−1
)
Mvb × 10−4
1
2
3
4
5
6
7
8
1
2
3
4
5
6
0.2
0.2
0.2
0.2
0.2
0.2
1.0
0.5
0.06
0.07
0.58
0.72
0.06
0.67
1.39
1.16
3,580
3,960
34,800
43,300
3,600
40,320
16,700
27,900
32.6
41.9
62.3
37.8
54.2
136.5
125.4
104.0
Cp2TiCl2
Cp2ZrCl2
a Polymerization conditions: solvent; toluene, 250 ml, MAO,1.25 mmol; ethylene, atmospheric pressure 100 l/h; Polymerization
time,5 min; Polymerization temperature, 25 ◦C.
b (η) = 6.2 × 10−4 Mv0.7
.
(Mv) 326,000–1,3700,00). 1 A comparison of cat-
alytic performance in Table 1 shows that the intro-
duction of F(s) or CF3(s) in the ligand had profound
effects on activities whereas it had relatively small
effects on molecular weight (Mv) values. Considering
that a molecular weight value is determined by the
relative rate of chain growth and chain termination,
the introduction of F(s) or CF3(s) in the ligand had
similar effects on chain growth and on chain termina-
tion. Although the introduction of one F(s) or CF3(s)
in the ligand (complexes 2 and 5) gave rise to no sig-
nificant increase in activity, the introduction of plural
F(s) or CF3(s) in the ligand (complexes 3, 4, and 6)
resulted in a great increase in catalytic activity, unlike
the group 4 metallocene catalysts whose activity is
decreased by the introduction of electron-withdrawing
substituent(s) in cyclopentadienyl (Cp) ligand [28,29].
Complexes 3 and 4, having two or three fluorines,
showed 34,800 (complex 3) and 43,300 (complex 4)
kg-PE mol-cat−1 h−1 of activities, on the order of one
digit larger than that exhibited by the non-fluorinated
parent complex 1. Likewise, complex 6, possessing
two CF3(s), displayed 40,320 kg-PE mol-cat−1 h−1 of
activity.
1 The molecular weight distribution (Mw/Mn) values exhibited
by complexes 1–6 are ca. 2.0 under the conditioned employed
in Table 1, confirming that complexes 1–6 work as single-site
catalysts.
For the purposes of having a quantitative discus-
sion on the effects of introducing F(s) or CF3(s)
in the ligand, the HOMO energy level of anionic

S.-i. Ishii et al. / Journal of Molecular Catalysis A: Chemical 179 (2002) 11–16
15
Fig. 1. Relationship between activity and HOMO energy level of anionic phenoxy-imine chelate ligand.
phenoxy-imine chelate ligand (an indication of elec-
tron donation ability of the ligands) was calculated
using MNDO-PM3 method. As shown in Fig. 1, the
basic trend observed is that decreases in HOMO en-
ergy level of anionic phenoxy-imine chelate ligand
resulted in increased activity. These results provide
the first clear demonstration that the electrophilic-
ity of the titanium center in active species plays a
dominant role in determining the catalytic activity.
A different trend vis-à-vis activity—HOMO energy
level relationship observed for F(s) containing com-
plexes (complexes 2, 3, and 4) and CF3(s) containing
complexes (complexes 5 and 6) may result from the
difference in steric factors between F(s) and CF3(s),
which probably causes the structural difference of the
active species.
A possible explanation for the activity increase
as a result of introducing electron-withdrawing
F(s) or CF3(s) is that a more electrophilic titanium
center, generated by a more electron-withdrawing
ligand, results in an increase in metal-carbon
reactivity, leading to reduced activation energy
for ethylene insertion. The activities obtained
with complexes 3 (34,800 kg-PE mol-cat−1 h−1), 4
(43,300 kg-PE mol-cat−1 h−1), and 6 (40,320 kg-PE
mol-cat−1 h−1) are much larger than those for
Cp2TiCl2 (16,700 kg-PE mol-cat−1 h−1) and Cp2ZrCl2
(27,900 kg-PE mol-cat−1 h−1 ) under the same poly-
merization conditions. Therefore, highly active new
titanium catalysts have been developed. To the best
of our knowledge, the activity displayed by complex
4 (43,300 kg-PE mol-cat−1 h−1) represents the high-
est value reported to date for titanium-based ethylene
polymerization catalysts including titanocenes under
atmospheric pressure at ambient temperatures. Highly
active titanium FI catalysts for the polymerization
of ␣-olefins and co-polymerization of ethylene and
␣-olefins are currently being applied with the purpose
of producing polymers possessing novel properties
and uses.
4. Conclusions
In conclusion, titanium complexes having electron-
withdrawing F(s) or CF3(s) containing phenoxy-imine
chelate ligands have been developed, which represent
the first titanium catalysts displaying ethylene poly-
merization activities exceeding those for the group
4 metallocene catalysts under mild conditions. The
results described herein together with our previous re-
sults [30] may provide a catalyst design guideline for
developing highly active non-metallocene titanium
complexes.
Acknowledgements
We acknowledge stimulating discussions with
Dr. M. Mullins.
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