Fluorine- and trimethylsilyl-containing phenoxy-imine Ti complex for highly syndiotactic living polypropylenes with extremely high melting temperatures

Article abstract of DOI:10.1021/ja026229r

A fluorine- and trimethylsilyl-containing phenoxy-imine titanium complex was synthesized and the structure was determined by an X-ray analysis. The complex on activation with MAO initiates highly controlled syndiospecific living propylene polymerization to form extremely high T_m syndiotactic polypropylenes (M_w/M_n = 1.05-1.08, T_m = 156-152 °C) at 0 or 25 °C. Moreover, at 50 °C, the complex afforded monodisperse syndiotactic polypropylene with very high T_m's of 149, 150 °C. In contrast, complexes having a t-Bu group instead of the silyl group provided lower tacticity polymers with much lower T_m's. In addition, we revealed the substituent effect that plays a key role for the highly controlled syndiospecific polymerization displayed by the catalyst. Copyright

Full text of DOI:10.1021/ja026229r

Published on Web 06/18/2002
Fluorine- and Trimethylsilyl-Containing Phenoxy-Imine Ti Complex for Highly
Syndiotactic Living Polypropylenes with Extremely High Melting
Temperatures
Makoto Mitani, Rieko Furuyama, Jun-ichi Mohri, Junji Saito, Seiichi Ishii, Hiroshi Terao,
Norio Kashiwa, and Terunori Fujita*
R & D Center, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura, Chiba, 299-0265, Japan
Received March 19, 2002
The developmental activities of catalysts capable of promoting
stereospecific living propylene polymerization have been very
intense. This is because these catalysts may provide potentially high-
performance polymers such as monodisperse polypropylenes (PPs)
with high melting temperatures (Tm’s) and block copolymers
containing the high Tm segments. Recent progress in the rational
Figure 1. Fluorine-containing phenoxy-imine Ti complexes 1-4.
design of well-defined transition metal complexes for olefin
polymerization1 has spurred the development of high performance
catalysts which initiate stereospecific living polymerization of
R-olefins.2 However, despite the fact that nearly perfect stereo-
specific propylene polymerization can be performed using group 4
metallocene catalysts, highly stereospecific living propylene
polymerization has not yet been achieved.3
Previously, we found that a new series of titanium complexes
bearing fluorine-containing phenoxy-imine chelate ligands (which
are members of our FI Catalyst family) are capable of promoting
living polymerization of ethylene or R-olefins or both to produce
various block copolymers4 and have described the details of their
catalytic behavior5 including unprecedented propylene polymeri-
zation mechanism.5d Recently, living propylene polymerization with
Figure 2. Molecular structure of complex 1 with thermal ellipsoids at 30%
fluorinated titanium FI Catalysts have been studied by Coates6 and
Zambelli.7 Further efforts aimed at developing higher-performance
FI Catalysts led us to the discovery of a new living propylene
polymerization catalyst. In this communication, we introduce a Ti-
FI Catalyst having fluorine- and trimethylsilyl-containing ligands,
which polymerizes propylene above room temperature to form
highly syndiotactic monodisperse PPs with extremely high Tm’s.
The titanium complex employed in this study is bis[N-(3-
trimethylsilylsalicylidene)-2,3,4,5,6-pentafluoroanilinato]Ti(IV) di-
chloride (complex 1, Figure 1). X-ray analysis indicates that
complex 1 adopts a distorted octahedral structure with a trans-O,
cis-N, and cis-Cl arrangement. Although the molecular structure is
similar to that of complex 2 described in our previous paper,5a the
bond distances of Ti-N and Ti-O are slightly elongated as a result
of introducing a trimethylsilyl group into the ligand (Figure 2).
Polymerization of propylene with complex 1 using methyl-
alumoxane (MAO) cocatalyst under atmospheric pressure at 25 °C
for 5 h yielded crystalline polypropylene having an extremely
narrow polydispersity (Mn ) 47 000, Mw/Mn ) 1.08, Table 1, entry
3). The linear dependence of the Mn value upon the polymerization
time (entries 2, 3) together with the narrow MWD values indicates
that the polymerization proceeds in a living fashion under the given
conditions.
probability level. Selected bond distances (Å) and angles (deg): Ti-O(1)
) 1.860(2), Ti-O(2) ) 1.854(2), Ti-N(1) ) 2.268(3), Ti-N(2) )
2.253(3), Ti-Cl(1) ) 2.245(1), Ti-Cl(2) ) 2.284(1), Si(1)-C(2) )
1.893(4), Si(2)-C(18) ) 1.890(4), O(1)-Ti-O(2) ) 165.6(1), N(1)-
Ti-N(2) ) 85.30(10) Cl(1)-Ti-Cl(2) ) 99.19(4).
Table 1. Results of Propylene Polymerization with Complexes
1-4/MAOa
b
d
T
(°C)
time
(h)
yield
(g)
TOF
(h-1
M c
Tm
n
entry
complex
)
(×103)
M /M c
(°C)
w
n
1
2
3
4
5
6
7
8
9
1
1
1
1
1
2
2
2
3
3
3
4
0
25
25
50
50
0
25
50
0
5
3
5
3
5
5
5
5
5
5
5
5
0.151
0.205
0.293
0.157
0.237
0.144
0.183
0.151
0.109
0.219
0.263
1.534
72
162
139
124
112
68
87
72
52
24.7
34.2
47.0
25.5
35.1
23.6
28.5
18.6
19.2
29.8
31.3
189.0
1.08
1.05
1.08
1.18
1.23
1.05
1.11
1.59
1.05
1.15
3.19
1.51
156
153
152
150
149
136
137
117
141
135
127
n.d.e
10
11
12
25
50
25
104
125
729
a Conditions: complex (10 µmol), cocat. MAO (2.5 mmol), 1 atm,
toluene 250 mL. b Turnover frequency. c Determined by GPC using polyprop-
ylene calibration. d Melting temperature of produced PP determined by DSC.
e Not detected.
Microstructural analysis using 13C NMR spectroscopy reveals
that the monodisperse polymer is highly syndiotactic PP (syn-PP)
containing 93% rr triad. The isolated m-dyad errors suggest that
the polymer is probably produced via a chain-end control mech-
anism.8 Interestingly, the syn-PP produced by 1 displays an
extremely high Tm (152 °C). Moreover, polymerization at 0 °C
* To whom correspondence should be addressed. E-mail: Terunori.Fujita@
mitsui-chem.co.jp.
9
7888
J. AM. CHEM. SOC. 2002, 124, 7888-7889
10.1021/ja026229r CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
previous reports11 suggest that FI Catalysts are capable of producing
novel polymers that are unobtainable from conventional Ziegler-
Natta catalysis.
Acknowledgment. We would like to thank Dr. M. Mullins for
his fruitful discussions and suggestions.
Supporting Information Available: Synthesis and characterization
of the complexes, polymer synthesis, and analysis data (GPC, DSC,
NMR) (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
References
Figure 3. Plots of Tm vs polymerization temperature with 1-3/MAO.
(1) (a) Kaminsky, W. Catal. Today 1994, 20, 257-271. (b) Brintzinger, H.
H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1143-1170. (c) Britovsek, G. J. P.; Gibson,
V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428-447.
(2) (a) Scollard, J. D.; McConville, D. H. J. Am. Chem. Soc. 1996, 118,
10008-10009. (b) Killian, C. M.; Tempel, D. J.; Johnson, L. K.;
Brookhart, M. J. Am. Chem. Soc. 1996, 118, 11664-11665. (c) Liang, L.
C.; Schrock, R. R.; Davis, W. M.; McConville, D. H. J. Am. Chem. Soc.
1999, 121, 5797-5798. (d) Tshuva, E. Y.; Goldberg, I.; Kol, M. J. Am.
Chem. Soc. 2000, 122, 10706-10707. (e) Jayaratne, K. C.; Sita, L. R. J.
Am. Chem. Soc. 2000, 122, 958-959.
(3) (a) Doi, Y.; Suzuki, S.; Soga, K. Macromolecules 1986, 19, 2896-2900.
(b) Hasan, T.; Ioku, A.; Nishii, K.; Shiono, T.; Ikeda, T. Macromolecules
2001, 34, 3142-3145.
(4) Mitani, M.; Yoshida, Y.; Mohri, J.; Tsuru, K.; Ishii, S.; Kojoh, S.; Matsugi,
T.; Saito, J.; Matsukawa, N.; Matsui, S.; Nakano, T.; Tanaka, H.; Kashiwa,
N.; Fujita, T. WO Pat. 01/55231 A1, 2001; Chem. Abstr. 2001, 135,
137852.
(5) (a) Saito, J.; Mitani, M.; Mohri, J.; Yoshida, Y.; Matsui, S.; Ishii, S.;
Kojoh, S.; Kashiwa, N.; Fujita, T. Angew. Chem., Int. Ed. 2001, 40, 2918-
2920. (b) Saito, J.; Mitani, M.; Mohri, J.; Ishii, S.; Yoshida, Y.; Matsugi,
T.; Kojoh, S.; Kashiwa, N.; Fujita, T. Chem. Lett. 2001, 576-577. (c)
Kojoh, S.; Matsugi, T.; Saito, J.; Mitani, M.; Fujita, T.; Kashiwa, N. Chem.
Lett. 2001, 822-823. (d) Saito, J.; Mitani, M.; Onda, M.; Mohri, J.; Ishii,
S.; Yoshida, Y.; Nakano, T.; Tanaka, H.; Matsugi, T.; Kojoh, S.; Kashiwa,
N.; Fujita, T. Macromol. Rapid Commun. 2001, 22, 1072-1075. (e)
Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui,
S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.; Matsugi, T.;
Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 3327-3336.
(6) (a) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123,
5134-5135. (b) Hustad, P. D.; Tian, J.; Coates, G. W. J. Am. Chem. Soc.
2002, 124, 3614-3621.
afforded syn-PP with an exceptionally high Tm of 156 °C ([rr] 94%),
which probably represents the highest value reported to date for
not only monodisperse syn-PPs but also highly syn-PPs obtained
with exquisitely designed group 4 metallocene catalysts.9,10 On the
other hand, complexes 24,5 and 36 previously introduced as catalysts
for highly syndiospecific living propylene polymerization, provided
lower tacticity polymers with much lower Tm’s (135-141 °C, Table
1, entries 6, 7, 9, 10). These results show that complex 1 possesses
a great potential for syndiospecific living propylene polymerization.
Surprisingly, at 50 °C, complex 1 initiated living propylene
polymerization and furnished narrow polydispersity syn-PPs with
very high Tm’s (150, 149 °C, Table 1, entries 4 and 5 and Figure
3), which is of great significance because generally chain-end
control rapidly loses stereoregulating ability at elevated tempera-
tures.
In contrast, at 50 °C, complexes 2 and 3 produced syn-PPs having
Tm’s below 130 °C (Table 1, entries 8 and11 and Figure 3), with
broadened polydispersities (Mw/Mn; 2, 1.59; 3, 3.19). These results
indicate that the R1 substituent has an effect on syndiospecificity
of fluorinated Ti-FI Catalysts.
To gain further information on the effect of R1 substituent, we
synthesized complex 4 having a hydrogen atom at R1 position and
investigated its potential as a propylene polymerization catalyst.
Complex 4 showed considerably higher activity than 2 and 3,
probably due to the structurally open nature of the complex (entry
12), and much lower syndiospecificity (rr 43%, no Tm). These results
suggest that the steric bulk of the R1 substituent plays a key role in
determining the syndiospecificity of the polymerization. Although,
at present, mechanistic details for propylene polymerization with
fluorinated FI Catalysts are not clear, it is obvious that the ligand
structure of the catalyst has a dramatic effect on polymerization
behavior and that sterically bulky substituents at the R1 position
result in a highly controlled syndiospecific polymerization though
chain-end control. Therefore, we have given the name “ligand-
directed chain-end control” to our newly discovered highly
controlled syndiospecific propylene polymerization that enables us
to have highly syn-PPs with extremely high Tm’s. In summary, a
new titanium complex with fluorine- and trimethylsilyl-containing
phenoxy-imine chelate ligands has been introduced, which forms
highly syndiotactic monodisperse PPs with high Tm’s even at
elevated temperatures. The results described herein along with our
(7) Lamberti, M.; Pappalardo, D.; Zambelli, A.; Pellecchia, C. Macromolecules
2002, 35, 658-663.
(8) This mechanism is also operative in propylene polymerization with
complexes 2 and 3. See refs 5b and d, 6, and 7.
(9) (a) Veghini, D.; Henling, L. M.; Burkhardt, T. J.; Bercaw, J. E. J. Am.
Chem. Soc. 1999, 121, 564-573. (b) Grisi, F.; Longo, P.; Zambelli, A.;
Ewen, J. A. J. Mol. Catal. A: Chem. 1999, 140, 225-233.
(10) Obviously, the Tm’s of monodisperse syn-PPs arising from fluorinated FI
Catalysts are higher than the values expected from the syndiotacticity of
the polymers. (For example; syn-PP formed with Ph2C(Cp, 2,7-di-t-Bu-
Flu)ZrCl2, [rr] 95%, Tm 148 °C; under the same DSC measurement
conditions. Shiomura, T.; Kohno, M.; Inoue, N.; Yokote, Y.; Akiyama,
M.; Asanuma, T.; Sugimoto, R.; Kimura, S.; Abe, M. Catalyst Design
for Tailor-Made Polyolefins; Kodansha and Elsevier: Tokyo and Am-
sterdam, 1994; pp 327-338). The difference probably originates from
the microstructures or unimodality of the polymers. Detailed investigations
are underway.
(11) (a) Fujita, T.; Tohi, Y.; Mitani, M.; Matsui, S.; Saito, J.; Nitabaru, M.;
Sugi, K.; Makio, H.; Tsutsui, T. Eur. Patent, EP-0874005, 1998; Chem.
Abstr. 1998, 129, 331166. (b) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.;
Makio, H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano,
T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2001, 123,
6847-6856. (c) Saito, J.; Mitani, M.; Matsui, S.; Kashiwa, N.; Fujita, T.
Macromol. Rapid Commun. 2000, 21, 1333-1336. (d) Ishii, S.; Saito, J.;
Mitani, M.; Mohri, J.; Matsukawa, N.; Tohi, Y.; Matsui, S.; Kashiwa,
N.; Fujita, T. J. Mol. Catal. A 2002, 179, 11-16.
JA026229R
9
J. AM. CHEM. SOC. VOL. 124, NO. 27, 2002 7889