Novel synthetic strategy for developing an isospecific unbridged metallocene system for propylene polymerization

Article abstract of DOI:10.1002/chem.200700512

New unbridged zirconocenes functionalized with a Lewis base, [{1-(E-C ₆H₄)-3,4-Me₂C₅H₂} ₂ZrCl₂] (E = p-NMe₂ (3); p-OMe (4); p-SMe (5)) were prepared and their propylen

Full text of DOI:10.1002/chem.200700512

FULL PAPER
DOI: 10.1002/chem.200700512
Novel Synthetic Strategy for Developing an Isospecific Unbridged
Metallocene System for Propylene Polymerization
Seong Kyun Kim, Hwa Kyu Kim, Min Hyung Lee, Seung Woong Yoon, and
Youngkyu Do*[a]
Abstract: New unbridged zirconocenes
functionalized with a Lewis base, [{1-
(E-C6H4)-3,4-Me2C5H2}2ZrCl2](E = p-
NMe2 (3); p-OMe (4); p-SMe (5))
were prepared and their propylene
polymerization behavior was examined.
Under methylaluminoxane (MAO) ac-
tivation at atmospheric monomer pres-
sure, these complexes afford mixtures
of polymers exhibiting multimelting
transition temperatures and broad mo-
lecular weight distribution, whereas
they produce completely atactic poly-
the polymer mixtures reveals that the
polymers consist of amorphous, moder-
ately isotactic, as well as, highly isotac-
tic portions and the weight ratio of
each portion is dependent upon reac-
tion temperature. The generation of
rigid rac-like cationic active species in
situ by the interaction between basic
sites of catalysts and acidic sites of the
[Me-MAO]À counter anion is consid-
ered to be the origin of the observed
isospecificity. Further investigation of
bulk polymerization in liquid propyl-
ene shows not only a considerable in-
crease of the isotactic portion of the
obtained polypropylenes but also ap-
parent isospecificity of 4 and 5/MAO
systems even at high temperature. Var-
iation of the Lewis basic center leads
to a dramatic change in stereoselectiv-
ity of the catalyst in the decreasing
order of 3>4@5, in spite of their
structural similarity.
Keywords: isotactic polypropylene ·
Lewis bases
·
metallocenes
·
propylenes under [Ph3C][B(C6F5)4]ac-
N
polymerization · zirconium
tivation. Stepwise solvent extraction of
Introduction
geometry of the catalyst precursors and the stereo- and re-
giocontrol conforming to an enantiomorphic site-control
mechanism in propylene polymerization has been intensive-
ly investigated by using chiral ansa-metallocene catalysts
having a fixed geometry around the metal center.[3,4,9,10] In
this manner, highly isotactic[11] and syndiotactic polypropy-
lene[12,13] can be provided by C2- and Cs-symmetric ansa-met-
allocenes, respectively.
On the other hand, non ansa-metallocenes that are easily
accessible synthetically had attracted relatively little atten-
tion due to their generally aspecific nature until the first
report by Erker and co-workers[14–16] that unbridged metallo-
cene systems having bulky substituents can produce isotactic
([mmmm]=0.5–0.7) polypropylenes. Although the isospeci-
ficity could be achieved at a relatively low reaction tempera-
ture, this result showed that an unbridged metallocene
system is capable of inducing isotactic chain propagation by
restricting the rapid ligand rotation. After this significant
finding, the “oscillating” [(2-phenylindenyl)2ZrCl2]that pro-
duces isotactic–atactic, block polypropylene was also report-
ed by Waymouth and co-workers.[17] The key concept of
these papers was to impart isospecific stereocontrol to un-
bridged metallocene catalysts by introducing hindered
Single-site catalytic systems based on organometallic com-
plexes have been extensively developed in the field of olefin
polymerization during the last two decades to optimize poly-
mer properties, leading to the establishment of the relation-
ship between the nature of catalytic systems and the proper-
ties of the resulting polymers, and thereby providing various
opportunities to tailor the polymer properties.[1–10] Among
various classes of catalysts, Group 4 metal complex systems
have a unique ability to control molecular weight and the
distribution, comonomer incorporation, and stereoregularity
of the polymer with high activity in a wide range of olefin
polymerizations. The correlation between the coordination
[a]Dr. S. K. Kim, H. K. Kim, Dr. M. H. Lee, S. W. Yoon, Prof. Dr. Y. Do
Department of Chemistry, School of Molecular Science BK-21
Center for Molecular Design and Synthesis
Polyolefin Materials Research Center, College of Natural Science
Korea Advanced Institute of Science and Technology
Daejeon, 305–701 (Korea)
Fax : (+82)42-869-2810
homepage: http://xray.kaist.ac.kr/
E-mail: ykdo@kaist.ac.kr
Chem. Eur. J. 2007, 13, 9107 – 9114
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9107

ligand rotation.[15–26] Although several reports showed that
the microstructure of the produced polypropylene strongly
depends on the steric and electronic effects of the substitu-
ents, as well as on the ion-pair structure of a cationic active
center and a counter anion,[16,20,23,25] in most cases, the un-
bridged metallocenes afforded atactic polypropylene due to
rapid ligand rotation.[19,27]
actions and the resultant isospecificity in propylene polymer-
ization, including the investigation of the effect of monomer
concentration on isospecificity. Herein, the synthesis and the
complete set of comparative propylene polymerization stud-
ies by using novel Lewis base functionalized zirconocenes,
[{1-(E-C6H4)-3,4-Me2C5H2}2ZrCl2](E = p-NMe2 (3); p-OMe
(4); p-SMe (5)) are described.
When we consider the relative ease of synthesis of un-
bridged metallocenes compared to that of ansa-metallo-
cenes, it is still of great interest to develop unbridged metal-
locene catalytic systems capable of inducing stereospecific
polymerization of propylene. To achieve this goal, we have
been pursuing the development of isospecific unbridged
metallocene catalytic systems that can be generated in situ
during the activation step and have designed a new “class I”
of unbridged zirconocenes having Lewis basic substituents.
Results and Discussion
Synthesis and characterization: The overall synthetic route
of class I unbridged zirconocenes is outlined in Scheme 2.
Treatment of para-E-bromobenzene (E = NMe2 and SMe)
Whereas zirconocenes having H, Me, or Ph substituents at
the para-position of the phenylene group (class II) produce
completely atactic polypropylene due to the rapid ligand ro-
tation,[19,27] the Lewis basic sites E in “class I” could interact
with [Me-MAO]À and thereby generate rigid rac-like cation-
ic active species, endowing aspecific unbridged metallocene
precatalysts with isospecificity. In this regard, we recently
communicated the first example of a dimethylamine-substi-
tuted “class I” unbridged zirconocene that exhibits high iso-
selectivity in propylene polymerization under MAO activa-
tion, and also showed that the simultaneous cation–anion
pairing and the interactions of Lewis acidic sites in the [Me-
MAO]À with nitrogen atoms of amine-functionalized un-
bridged zirconocene cations prevents rapid ligand rotation
and favors racemic C2-symmetric-like conformers as active
species that lead to isospecificity.[28] (IS in Scheme 1)
Scheme 2. Synthetic route of class I unbridged zirconocenes 3–5.
with one equivalent of nBuLi in diethyl ether gave white
lithium salts that were further purified and isolated by wash-
ing with n-hexane. Subsequent reaction of the resulting lithi-
um salts or Grignard reagent (p-MeO-C6H4-MgBr) with
one equivalent of 3,4-dimethylcyclopent-2-enone in THF
followed by dehydration with p-TsOH in CH2Cl2 afforded
the desired final ligands, 1-(p-E-C6H4)-3,4-Me2C5H3 (E =
NMe2; OMe (1); SMe (2)) in good yield. The zirconium
complex 3 was synthesized as reported previously,[28] and the
complexes [{1-(p-MeOC6H4)-3,4-Me2C5H2}2ZrCl2] (4) and
[{1-(p-MeSC6H4)-3,4-Me2C5H2}2ZrCl2] (5) were also pre-
pared straightforwardly by the direct transmetalation of lith-
ium salts of the ligands 1 and 2 with 0.5 equivalents of
We expanded our research directions to other Lewis basic
heteroatoms such as oxygen and sulfur to address the rela-
tionship between the strength of the Lewis acid–base inter-
[ZrCl4(thf)2]in toluene. Dimethylated complexes 3-Me, 4-
G
Me, and 5-Me were prepared by the reaction of 3, 4, and 5
with two equivalents of MeLi, respectively. All these com-
plexes are quite soluble in common organic solvents such as
toluene and CH2Cl2. According to the molecular structure
determination of complex 4, the C2-symmetric, rac-like
isomer is only seen in the asymmetric unit as similarly ob-
Scheme 1. Isospecific active species (IS) and thermal equilibrium with
the related species.
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Chem. Eur. J. 2007, 13, 9107 – 9114

An Isospecific Unbridged Metallocene System
FULL PAPER
higher-molecular-weight poly-
propylene. Most of the crude
polypropylenes
from
this
system show multimelting tran-
sitions (Tm) and a broad molec-
ular-weight
distribution
(MWD) of Mw/Mn =2–10 by
differential scanning calorime-
try (DSC) and gel-permeation
Figure 1. Crystal structure of complex 4 (front and top views).
chromatography
(GPC)
(Figure 2) diagrams, respective-
ly, indicating the involvement
served in the structure of 3[28] (Figure 1). In case of [(2-phe-
nylindenyl)2ZrCl2], both rac- and meso-like isomers are
present in the unit cell.[17] The bonding geometry around the
zirconium center, such as bond angles of Cl1-Zr-Cl2 and
of multicatalytic active species.[30] Whereas the polymer
from 3/MAO shows a relatively narrow MWD at 08C
(Table 1, entry 1), the multimodality is clearly seen at higher
reaction temperatures (Table 1, entries 2–4). In contrast, the
broad MWD from 4/MAO at 0, 25, and 508C (Table 1, en-
tries 5–7) becomes much narrower at 708C (Table 1,
entry 8). Unlike the 3/MAO and 4/MAO systems, 5/MAO
gave polymers with a narrow MWD at all reaction tempera-
tures (Table 1, entries 9–12). These results indicate that 3/
MAO maintains a multicatalytic active nature even at high
temperature, whereas single active species are dominant at
high temperature in 4/MAO and at all temperatures for 5/
MAO. Consistent with the GPC results, DSC diagrams of
the polymers from 3/MAO (Table 1, entries 1–4) and 4/
MAO (Table 1, entries 5–8) also show multimelting transi-
tions with high Tm (132–1568C). In the case of borate activa-
À
ring-centroid–Zr–ring-centroid, and bond lengths of Zr Cl
and Zr–ring-centroid are in the range similar to those for
other nonbridged zirconocene complexes[19,29] and very simi-
lar to those of 3[28] and [{1-(p-C6H5C6H4)-3,4-
[27]
Me2C5H2}2ZrCl2](BPZr).
Propylene polymerization: The polymerization of propylene
with zirconocenes 3, 4, and 5 was achieved at various tem-
peratures of Tp =0, 25, 50, and 708C under MAO and
[Ph3C][B(C6F5)4]/TIBA activation at atmospheric monomer
G
pressure and the polymerization results are summarized in
Table 1. To compare their polymerization properties, the
polymerizations with unfunctionalized “class II”, [{1-(p-
C6H5C6H4)-3,4-Me2C5H2}2ZrCl2](BPZr) and the well known
tion, however, 3-Me/
U
A
4-Me/[Ph3C][B(C6F5)4](Table 1, entry 14) give completely
A
ACHTREUNG
isospecific catalyst, rac-[Et
A
amorphous polypropylene with low molecular weight and a
carried out. When compared with EBIZr/MAO (Table 1,
entry 17) under identical polymerization conditions, this
“class I” system shows lower catalytic activity but produces
narrow MWD. Interestingly, 5/MAO (Table 1, entry 10) and
5-Me/
G
G
polymerization results under otherwise identical conditions,
Table 1. Propylene polymerization data.[a]
Entry Catalyst Cocatalyst
Tp
[8C]
tp
Yield
Productivity[b] Mw
(”10À3
Mw/Mn Tm
[8C]
EE-sol EE-insol/C7-sol EE-insol/C7-insol
[min] [g]
G
)
wt%[c]
wt%[c]
wt%[c]
1
2
3
4
5
6
7
8
3
3
3
3
4
4
4
4
5
5
5
5
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
borate/TIBA 25
borate/TIBA 25
borate/TIBA 25
MAO
MAO
0
25
50
70
0
25
50
70
0
120
120
120
120
60
60
60
60
120
60
60
60
120
60
60
1.02
6.24
7.25
3.41
0.588
3.91
6.20
2.31
3.71
3.88
5.54
3.14
6.95
2.69
3.05
2.83
12.36
72.9
931
2270
1710
227
166
4.6
10.7
9.5
5.3
4.7
7.3
5.1
2.1
2.4
2.3
2.2
2.2
2.1
2.8
2.7
1.9
2.1
156.2
156.6
153.0
141.0
151.8
154.0
132.7
n/o[g]
n/o
n/o
n/o
n/o
n/o
13
20
50
64
8
19
65
90
87
21
21
32
22
33
33
30
10
11
3
0
0
0
0
0
0
97
66
59
18
14
59
48
5
0
2
0
0
0
0
0
0
0
0
32.0
10.1
259
144
18.8
1.98
35.9
16.7
5.37
0.90
15.2
84.0
1170
3880
2310
265
1160
3460
3140
1040
803
9
10[b]
11
12
13[d]
14[d]
15[d]
16[e]
17[f]
25
50
70
97
100
100
100
100
100
100
3
3-Me
4-Me
5-Me
BPZr
EBIZr
17.4
14.9
58.9
19.1
n/o
n/o
n/o
128.7
910
404
8855
0
25
60
25
[a]Polymerization conditions: P(propylene) =1 bar; [Zr]=5.0 mmol; [Al]/[Zr]=1000; solvent=50 mL of toluene. [b]In units of (Kg of PP)(mol of
Zr)À1 hÀ1 [propylene]À1. Propylene solubility has been taken from ref. [31]. [c] EE = diethyl ether; C7 = n-heptane. [d]Borate = [Ph3C][B
(C6F5)4]; [B]/
(Ind)2ZrCl2. [g]Not ob-
AHCTREUNG
[Zr]=1; TIBA = triisobutylaluminum, [Al]/[Zr]=200. [e]BPZr = [1-(p-C6H5C6H4)-3,4-Me2C5H2]2ZrCl2. [f]EBIZr = rac-Et
ACHTREUNG
served.
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9109

Y. Do et al.
Figure 2. GPC diagram of polypropylenes from entries 1–4 in Table 1 (3/MAO at 0, 25, 50, and 708C; left) and from entries 5–8 in Table 1 (4/MAO at 0,
25, 50, and 708C; right).
giving amorphous, low-molecu-
lar-weight polypropylene. Thus,
it can be seen that the NMe2-
and OMe-substituted zircono-
cenes 3 and 4 display complete-
ly different polymerization be-
havior upon MAO and [Ph3C]
Table 2. Detailed analysis of each extracted portion of the polymer samples (EE = diethyl ether, C7 = n-
heptane).
Entry[a]
No.
Extract Portion
wt%
Tm
Mw
Mw/Mn
mmmm[b]
[8C]
A
)
[%]
1
1–1
1–2
1–3
2–1
2–2
2–3
3–1
3–2
3–3
4–1
4–2
4–3
5–1
5–2
5–3
6–1
6–2
6–3
7–1
7–2
7–3
8–1
8–2
9–1
9–2
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
C7-insol
EE-sol
C7-sol
13
21
66
20
21
59
50
32
18
64
22
14
8
33
59
19
33
48
65
30
5
n/o[c]
151.1
155.7
n/o
131.8
151.3
n/o
146.4
148.3
n/o
127.3
140.6
n/o
155.3
155.7
n/o
153.2
155.3
n/o
143.4
n/d
n/o
n/d[d]
85.8
337
27.2
68.4
273
10.7
39.4
113
n/d
2.5
4.2
5.2
4.2
4.3
4.7
3.8
2.6
3.4
2.6
2.2
n/d
2.4
3.2
n/d
4.8
5.1
2.9
3.0
3.7
2.1
2.9
2.1
2.4
2.1
2.1
14
55
85
19
53
86
17
67
86
14
63
82
n/d
n/d
n/d
26
58
85
n/d
n/d
n/d
n/d
n/d
n/d
n/d
5.4
76
2
3
4
5
6
7
[B(C6F5)4]activation, whereas
N
the polymerization behavior of
zirconocene 5 is almost unaf-
fected by the kind of activator
at atmospheric monomer pres-
sure.
5.3
17.8
18.1
To obtain more detailed in-
formation on the properties of
the obtained polypropylenes,
the crude polymers were frac-
tionated by a stepwise solvent
extraction method into three
portions for further analysis: di-
ethyl ether soluble, diethyl
ether insoluble and n-heptane-
soluble, and diethyl ether in-
soluble and n-heptane-insoluble
n/d
102.6
419
n/d
158
160
7.34
27.0
49.2
2.04
9.57
36.2
43.6
15.2
19.1
8
9
90
10
87
11
100
97
n/d
n/o
155.8
n/o
128.7
EE-sol
C7-sol
EE-sol
C7-sol
portions.[32]
The
[mmmm]
13
17
methyl pentad values and Tm of
each extracted portion in
Table 2 indicate that the forego-
ing portions correspond to atac-
tic-like, moderately isotactic,
and highly isotactic polypropy-
[a]Entry numbers correspond to those in Table 1. [b]Determined by 13C NMR spectroscopy. [c]Not observed.
[d]Not determined.
lene, respectively. In the case of the polypropylenes ob-
tained particularly from 3/MAO (Table 2, entries 1–4) and 4/
MAO (Table 2, entries 5–8), the amount of each portion
varies upon polymerization temperature in a way that the n-
heptane-insoluble portion decreases with increasing temper-
ature, whereas that of the diethyl ether soluble portion in-
creases (Figures 3 and 4). This explains that thermal equili-
bria between active species exist that are responsible for
each extracted portion as described in Scheme 1 and the
equilibria are largely affected by temperature. Moreover, it
can also be seen that the isospecific active species give
higher molecular weight products than the aspecific active
species at all temperatures.
In contrast, the polypropylenes from 3-Me, 4-Me, and 5-
Me/
G
G
diethyl ether soluble and atactic with the low [mmmm]
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Chem. Eur. J. 2007, 13, 9107 – 9114

An Isospecific Unbridged Metallocene System
FULL PAPER
an interaction may play a crucial role in governing isospeci-
ficity. When the heteroatom was changed from nitrogen (3)
to oxygen (4), and to sulfur (5), the amount of the n-hep-
tane-insoluble portion decreased in the order of 3>4@5 at
all temperatures. The n-heptane-insoluble portion of poly-
mer from 3/MAO varies from 66 to 59, 18, and 14% as the
temperature changes from 0 to 25, 50, and 708C, whereas 4/
MAO gives the n-heptane-insoluble portion of 59, 48, 5, and
0% as the temperature increases, and 5/MAO produces
almost 0% of the n-heptane-insoluble portion at all temper-
atures. These results clearly show that the OMe group, as
well as the NMe2 group, interacts strongly enough with the
Lewis acidic sites of the [Me-MAO]À ion to attain isospecific
propagation of the propylene monomer, whereas the sulfur
atom fails to achieve such an interaction in spite of the
structural similarity of 5 with 3 and 4. Although 4/MAO
readily produces an isotactic portion at low temperature (0
and 258C), the smaller amount than that from 3/MAO and
the sharp decrease with increasing temperature (50 and
708C) reflect that the Lewis acid–base interaction in 4/
MAO is weaker than that in 3/MAO. Furthermore, this find-
ing is well correlated with the strength of the interaction of
the Lewis acidic metals with N, O, and S atoms.[33] There-
fore, the foregoing demonstration that the Lewis basicity of
a functional group affects the isoselectivity of the unbridged
class I zirconocene system is supportive of our proposition[28]
with regards to the origin of the isospecificity of heteroa-
tom-functionalized unbridged zirconocenes.
Figure 3. Weight percentage of each extracted fraction from entries 1–4
in Table 1 (3/MAO at 0–708C).
To investigate the effect of monomer concentration on
the isospecific polymerization behavior of the above-men-
tioned catalytic systems, we conducted propylene polymeri-
zation experiments under liquid propylene conditions. Since
the isospecificity results from an in situ generated, C2-sym-
metric-like cation–anion ion pair, the monomer concentra-
tion may control the amount of the resulting isotactic por-
tion by changing the rate of monomer insertion in the equi-
librium between such an ion pair and the separated aspecific
species. Moreover, it was previously revealed that the rate
of ligand rotation in 3/MAO is extremely slow.[28] It is thus
expected that the overall isotactic polypropylene content of
the system could be increased as the monomer concentra-
tion increases. The polymerization results presented in
Table 3 are in good agreement with this hypothesis, and 3
and 4/MAO indeed afford much increased amounts of
highly isotactic polypropylene even at high temperature
(Table 3, entries 18–23). Most remarkably, the SMe-substi-
tuted 5 that produces negligible amounts of isotactic poly-
propylene under atmospheric monomer pressure also gives
appreciable amounts of a highly isotactic portion (Table 3,
entries 24–26). Consistent with this result is the high Tm
value of all the polypropylenes, and the Tm values are still
greater than that from EBIZr, indicating higher isotacticity,
as similarly observed under atmospheric conditions. In addi-
tion, the relative catalytic activity with respect to EBIZr is
dramatically increased when compared to that at atmospher-
ic monomer pressure. The increase of an isotactic portion
further leads to the increase of overall molecular weight of
Figure 4. Weight percentage of each extracted fraction from entries 5–8
in Table 1 (4/MAO at 0–708C).
value similar to the result from the aspecific BPZr/MAO
system (Table 1, entry 16), indicating essentially no stereo-
control under [Ph3C][B(C6F5)4]activation. The extracted
A
portions of polypropylene from the well-known isospecific
catalytic system EBIZr/MAO (Table 1, entry 17), on the
other hand, comprise an almost diethyl ether insoluble, but
n-heptane-soluble portion that corresponds to the [mmmm]
value of 76%. The fact that 3/MAO (Table 2, entry 2) and 4/
MAO (Table 2, entry 6) afforded moderate amounts of n-
heptane-insoluble portions having the [mmmm]value of 86
and 85%, respectively, under the same condition indicates
that the foregoing 3/MAO and 4/MAO systems are highly
isospecific.
The proposition that the origin of isospecificity is the con-
current working of the cation–anion pairing and the Lewis
acid–base interaction between the [Me-MAO]À ion and the
heteroatom-functionalized unbridged cationic zirconocene
species[28] leads to the expectation that the strength of such
Chem. Eur. J. 2007, 13, 9107 – 9114
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9111

Y. Do et al.
Table 3. Propylene polymerization data under liquid propylene condition.[a]
Entry
Catalyst
Tp
[8C]
Pressure
[bar]
Yield
[g]
Productivity[b]
Mw
(”10À3
Mw/Mn
Tm
[8C]
EE-sol
wt%[c]
EE-insol/C7-sol
wt%[c]
EE-insol/C7-insol
wt%[c]
G
A
)
18
19
20
21
22
23
24
25
26
27[d]
3
3
3
4
4
4
5
5
42
60
70
30
60
70
30
60
70
70
16
24
30
13
24
30
13
24
30
30
45
78
102
8.0
54
54
15
65
82
710
1260
1610
130
850
850
240
100
130
2120
222
170
128
389
233
180
349
144
95
7.6
8.4
12.2
5.9
6.7
9.4
5.0
5.3
6.0
2.6
153.4
152.8
157.1
149.7
151.0
153.9
156.1
157.0
156.0
130.6
20
16
17
17
10
17
13
48
30
23
23
4
28
25
45
39
31
n/d
50
61
60
79
62
58
42
13
12
n/d
5
57
EBIZr
80
30.3
n/d[e]
[a]Polymerization conditions: propylene monomer =500 g; [Zr]=5.0 mmol; [Al]/[Zr]=2000. [b]In units of (Kg of PP)(mol of Zr) À1 hÀ1 [propylene]À1
.
[c]EE = diethyl ether; C7 = n-heptane. [d][Zr] =3.0 mmol. [e]Not determined.
the crude polypropylene. The broad MWD of the obtained
polypropylenes at all reaction temperatures indicates the in-
volvement of multiactive species in the bulk polymerization.
Since the structurally similar but unfunctionalized catalyst
[{1-(C6H5)-3,4-Me2C5H2}2ZrCl2]was reported to afford atac-
tic polypropylene with an almost identical level of [mmmm]
content regardless of the monomer concentration,[19] it can
be assumed that the aspecific active species in the form of a
completely separated ion pair does not contribute to the in-
creased amount of the isotactic portion; thus, the observed
isospecificity is attributed to the in situ generated, C2-sym-
metric-like cation–anion ion pair. The increased rate of mo-
nomer insertion upon increasing the monomer concentra-
tion, which is evident from a sharp increase of the catalytic
activity, most likely results in the increase of the isotactic
portion even in a weakly interacting 5/MAO system and at
high temperature.[34] In addition to the polymerization re-
These results indicate that the simple Lewis base functional-
ization of a “class II” unbridged metallocene system into a
“class I” system produces an isospecific catalytic system
through the in situ generation of rigid rac-like cationic
active species, the Lewis acid–base interaction of which is
dependent upon functionality.
Experimental Section
General considerations: All operations were performed under inert nitro-
gen gas by using standard Schlenk and glovebox techniques. Anhydrous
grade toluene, CH2Cl2, and n-hexane (Aldrich) were purified by passing
through an activated alumina (Acros, 50–200 mm) column. Anhydrous
grade THF (Aldrich) and Et2O (J.T. Baker) were distilled from Na-ben-
zophenone ketyl. All solvents were stored over activated molecular
sieves (5 Š, Yakuri Pure Chemicals Co). Chemicals were used without
further purification after purchase from Aldrich (4-bromo-N,N-dimethyl-
sults from the atmospheric monomer conditions, the present
results of bulk polymerizations suggest that the given class
of heteroatom-functionalized, unbridged zirconocenes pro-
vides a novel strategy for isospecific propylene polymeri-
zation.
aniline, 4-methoxyphenylmagnesium bromide, 4-bromothioanisole, poly-
phosphoric acid, nBuLi (2.5m solution in n-hexane), p-toluenesulfonic
acid (p-TsOH), MeLi (1.6m solution in diethyl ether), triisobutylalumi-
num (TIBA, 1.0m in hexanes)), and Strem ([ZrCl4
ACHTREUNG
cyclopent-2-enone,[35] [{1-(p-Me2NC6H4)-3,4-Me2C5H2}2ZrX2](X
=
(3); Me (3-Me)),[28] and [{1-(p-C6H5C6H4)-3,4-Me2C5H2}2ZrCl2](BPZr)
were prepared according to the literature procedures. CDCl3 was dried
over activated molecular sieves (5 Š) and used after vacuum transfer to a
Schlenk tube equipped with
(MAO) was used as solid MAO obtained by evaporation of the solvent
from a solution of PMAO (Witco, 30T) in toluene. The [Ph3C][B(C6F5)4]
a J. Young valve. Methylaluminoxane
Conclusion
ACHTREUNG
We have synthesized a set of various Lewis base functional-
ized unbridged zirconocene complexes 3, 4, and 5 and exam-
ined their catalytic properties in propylene polymerization
was used as received (Asahi Glass Co.). Polymerization-grade propylene
monomer from the Honam Petrochemical Corporation was used after
purification by passing through Labclear and Oxiclear filters. 1H and
13C NMR spectra of compounds were recorded on a Bruker Spectro-
spin 400 spectrometer at ambient temperature. All chemical shifts are re-
ported in d units with reference to the residual peaks of CDCl3 for
proton (d=7.24 ppm) and carbon (d=77.0 ppm) chemical shifts. Elemen-
tal analyses were carried out on an EA 1110-FISONS (CE Instruments)
at KAIST.
under MAO, as well as, [Ph3C][B(C6F5)4]activation. The
A
complexes 3 and 4 that contain nitrogen and oxygen atoms,
respectively, showed isospecific propylene polymerization
behavior under MAO activation, whereas they gave com-
pletely amorphous polypropylene under [Ph3C][B(C6F5)4]at
N
Synthesis of 1-(p-MeOC6H4)-3,4-Me2C5H3 (1): A solution of 3,4-dime-
thylcyclopent-2-enone (2.20 g, 20 mmol) in THF (20 mL) was slowly
added through a cannula at À788C to a solution of 4-methoxyphenylmag-
nesium bromide (0.5m) in THF (40 mL). The reaction mixture was
slowly allowed to warm to room temperature and was stirred overnight.
The resulting orange solution was treated with saturated aqueous solu-
tion of NH4Cl (50 mL) to quench the reaction. Next, the organic portion
was separated and the aqueous layer was further extracted with diethyl
ether (50 mL). The combined organic portions were dried over MgSO4,
filtered, and evaporated to dryness, affording a light orange oily product.
atmospheric monomer pressure. In contrast, the unfunction-
alized zirconocene of a similar structure and the SMe-substi-
tuted 5 gave only atactic polypropylene under both activa-
tion conditions. Interestingly, further investigation of the
bulk polymerization under liquid propylene showed not
only a large increase in an isotactic portion of the obtained
polypropylenes, but also the apparent isospecific nature of
4/MAO and 5/MAO systems even at high temperature.
9112
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Chem. Eur. J. 2007, 13, 9107 – 9114

An Isospecific Unbridged Metallocene System
FULL PAPER
The crude product was redissolved in CH2Cl2 (30 mL), and then a catalyt-
ic amount of p-TsOH (ca. 0.1 g) was added as a solid into the solution at
room temperature followed by stirring for about 60 min. After reduction
of the volume of the resulting reaction mixture, recrystallization in etha-
nol at À208C afforded 1 (2.20 g) in 47% yield. 1H NMR (400.13 MHz,
CDCl3): d=7.36 (d, 2H), 6.81 (d, 2H), 6.50 (s, 1H), 3.79 (s, 3H), 3.22 (s,
2H), 1.95 (s, 3H), 1.87 ppm (s, 3H); 13C{1H} NMR (100.62 MHz, CDCl3):
d=158.1, 142.2, 135.4, 134.7, 129.8, 129.6, 125.7, 113.9, 55.3, 45.3, 13.4,
12.6 ppm.
132.0, 127.0, 124.7, 122.5, 119.8, 108.9, 31.1, 16.1, 12.9; elemental analysis
calcd (%) for C30H36S2Zr: C 65.28, H 6.57, S 11.62; found: C 64.25, H
6.47, S 12.63.
X-ray structure determination of 4: The crystallographic measurement
was performed by using a Bruker Apex II-CCD area detector diffractom-
eter, with graphite-monochromated MoKa radiation (l=0.71073 Š). A
specimen of suitable size and quality was selected and mounted onto a
glass capillary. The structure was solved by direct methods and all non-
hydrogen atoms were subjected to anisotropic refinement by full-matrix
least-squares on F2 by using the SHELXTL/PC package. Hydrogen
atoms were placed at their geometrically calculated positions and refined
riding on the corresponding carbon atoms with isotropic thermal parame-
ters. Final refinement converged at R1=0.0367 (I>2.0s(I)) and wR2=
0.0974 (all data). The detailed crystallographic data and selected bond
lengths and angles are given in the Supporting Information.
Synthesis of 1-(p-MeSC6H4)-3,4-Me2C5H3 (2): A solution of 4-bromo-
thioanisole (4.33 g, 20 mmol) in diethyl ether (50 mL) was treated with
one equivalent of nBuLi (8.0 mL) at 08C. After the mixture had been
stirred for 2 h at room temperature, the solvent was evaporated in vacuo,
and the obtained white lithium salt was washed with n-hexane (2”
20 mL). After the addition of THF (40 mL), one equivalent of 3,4-dime-
thylcyclopent-2-enone (2.20 g, 20 mmol) in THF (20 mL) was slowly
added through a cannula at À788C. The reaction mixture was slowly al-
lowed to warm to room temperature and was stirred overnight. Further
work-up and dehydration were carried out in a manner analogous to the
procedure for 1. Recrystallization in ethanol at À208C afforded 2 (1.69 g)
in 39% yield. 1H NMR (400.13 MHz, CDCl3): d=7.34 (d, 2H), 7.17 (d,
2H), 6.61 (s, 1H), 3.22 (s, 2H), 2.46 (s, 3H), 1.96 (s, 3H), 1.87 ppm (s,
3H); 13C{1H} NMR (100.62 MHz, CDCl3): d=141.9, 135.7, 135.55, 135.50,
133.6, 131.4, 127.1, 124.9, 45.2, 16.2, 13.4, 12.6 ppm.
CCDC-642347 (4) contains the supplementary crystallographic data for
this paper. This data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Propylene polymerization under atmospheric conditions: Freshly distilled
toluene (48 mL) was transferred into a well-degassed 250-mL glass reac-
tor charged with a pre-weighed amount of s-MAO ([Al]/[Zr]=1000), and
the temperature was adjusted by using an external bath. After saturation
of the propylene monomer at 1 bar with vigorous stirring for 30 min,
polymerization was started by the injection of a solution of catalyst
Synthesis of [{1-(p-MeOC6H4)-3,4-Me2C5H2}2ZrCl2] (4): A slurry of 1
(1.202 g, 6.0 mmol) in diethyl ether (30 mL) was treated with one equiva-
lent of nBuLi (2.4 mL) at À788C. The reaction mixture was allowed to
warm to room temperature and was stirred for 4 h. The resulting reaction
mixture was evaporated to dryness, and the lithium salt of 1 was com-
(2.0 mL, 5.0 mmol of Zr) in toluene. When [Ph3C][B(C6F5)4]was used as a
cocatalyst instead of MAO, the activated catalyst solution (2.0 mL,
5.0 mmol of Zr) was first prepared by treating a dimethyl precursor with
G
an equimolar amount of [Ph3C][B(C6F5)4]in the presence of a measured
E
amount of TIBA (Al/Zr=200). Next, the polymerization was started by
the injection of the solution into the reactor. After 120 min, all the reac-
tions were quenched by the injection of acidified ethanol (5 mL, 10%
HCl in EtOH). The resulting polypropylenes were further precipitated
by the addition of EtOH (200 mL). After the mixtures had been stirred
for 1–2 h, the polypropylenes were collected by filtration or decanting
the solution (in the case of a sticky polymer) and were washed with
bined with 0.5 equivalents of [ZrCl4(thf)2](3.0 mmol, 1.132 g). Toluene
A
(50 mL) was then introduced into the solid mixture at À788C. After al-
lowing to warm to room temperture, the reaction mixture was heated to
508C and stirred at this temperature overnight. The orange suspension
formed was filtered through a Celite pad and the filtrate was evaporated
to dryness. Washing with n-hexane followed by drying in vacuo afforded
4 (0.891 g) in 53% yield. Light yellow single crystals suitable for X-ray
structural determination could be obtained by cooling of a solution of 4
in diethyl ether/n-hexane at À208C. 1H NMR (400.13 MHz, CDCl3): d=
7.38 (d, 4H), 6.96 (d, 4H), 6.16 (s, 4H), 3.85 (s, 6H), 1.78 ppm (s, 12H);
13C{1H} NMR (100.62 MHz, CDCl3): d=159.0, 127.7, 126.5, 126.1, 122.7,
115.4, 114.5, 55.4, 13.2 ppm; elemental analysis calcd (%) for
C28H30Cl2O2Zr: C 59.98, H 5.39; found: C 59.63, H 5.64.
EtOH several times. The resulting polypropylenes were dried in
a
vacuum oven at 808C to a constant weight.
Propylene polymerization under liquid propylene conditions: A solution
of pre-weighed catalyst (5.0 mmol of Zr) and s-MAO ([Al]/[Zr]=2000) in
toluene (20 mL) was transferred into a well-degassed 2-L stainless-steel
reactor charged with nitrogen, and the temperature was adjusted by
using a circulator. Polymerization was started by the addition of liquid
propylene monomer (500 g). After 60 min, all the reactions were finished
by exhausting the remaining propylene monomer. The resulting polypro-
pylenes were precipitated by addition of EtOH (1 L). After the mixtures
had been stirred for 1–2 h, the polypropylenes were collected by filtration
and were washed with EtOH several times. The resulting polypropylenes
were dried in a vacuum oven at 808C to a constant weight.
Synthesis of [{1-(p-MeSC6H4)-3,4-Me2C5H2}2ZrCl2] (5): An analogous
procedure for 4 was employed by using the ligand 2 (1.298 g, 6.0 mmol)
which afforded 5 (0.907 g) as a yellow solid in 51% yield. 1H NMR
(400.13 MHz, CDCl3): d=7.35 (d, 4H), 7.30 (d, 4H), 6.20 (s, 4H), 2.51 (s,
6H), 1.79 ppm (s, 12H); 13C{1H} NMR (100.62 MHz, CDCl3): d=137.8,
130.1, 128.2, 126.9, 125.6, 122.0, 115.7, 15.8, 13.2 ppm; elemental analysis
calcd (%) for C28H30Cl2S2Zr: C 56.73, H 5.10; found: C 56.21, H 5.36.
Polymer extraction: Solvent extraction of all the polypropylenes was car-
ried out by using a Soxhlet extractor. A pre-weighed polypropylene
(1.00 g) was successively extracted with boiling diethyl ether (100 mL)
for 12 h. Then, the residue was further extracted with boiling n-heptane
(100 mL) for another 12 h. Evaporation of the resulting solutions by
using a rotary evaporator afforded diethyl ether soluble and diethyl ether
insoluble/n-heptane-soluble portions of polypropylene, respectively. The
obtained portions and the remaining residue (n-heptane-insoluble por-
tion) were finally dried under vacuum at 808C to a constant weight.
Polymer analysis: 13C NMR spectra of polypropylenes were recorded on
a Bruker Spectrospin 400 (13C; 100.62 MHz) for the diethyl ether soluble
and diethyl ether insoluble/n-heptane-soluble portions at 1008C, and on a
Bruker AMAX 500 (13C; 125.77 MHz) spectrometer for the n-heptane-in-
soluble portions at 1208C with a 908 pulse angle, an acquisition time of
2 s, and a relaxation delay of 8 s. The samples were dissolved in 1,1,2,2-
[D2]tetrachloroethane to form a 10 wt% solution (about 90 mg/0.5 mL)
in 5 mm tubes. All the measurements were performed after complete dis-
solution by warming (for the diethyl ether soluble and diethyl ether in-
soluble/n-heptane-soluble portions) or pre-heating (for the n-heptane-in-
soluble portions) to about 1108C in an oil bath. The chemical shift value
Synthesis of [{1-(p-MeOC6H4)-3,4-Me2C5H2}2ZrMe2] (4-Me): A slurry of
4 (1.121 g, 2.0 mmol) in diethyl ether (30 mL) was treated with two
equivalents of MeLi (2.5 mL) at À788C. The reaction mixture was al-
lowed to warm to room temperature and was stirred for 4 h. The result-
ing reaction mixture was evaporated to dryness and extracted with
CH2Cl2 (30 mL). Filtration followed by evaporation of the solvent gave a
yellow residue. Recrystallization from the concentrated CH2Cl2 solution
layered by n-hexane at À208C afforded 4-Me (0.613 g) in 59% yield.
1H NMR (400.13 MHz, CDCl3): d=7.11 (d, 4H), 6.86 (d, 4H), 5.57 (s,
4H), 3.82 (s, 6H), 1.81 (s, 12H), À0.49 ppm (s, 6H); 13C{1H} NMR
(100.62 MHz, CDCl3): d=158.1, 127.8, 125.4, 122.0, 120.5, 114.1, 108.5,
55.3, 30.5, 12.9 ppm. MS (HR EI): m/z calcd for C30H36O2Zr: 518.1762;
found: 518.1758; elemental analysis calcd (%) for C30H36O2Zr: C 69.32,
H 6.98; found: C 67.27, H 6.57.
Synthesis of [{1-(p-MeSC6H4)-3,4-Me2C5H2}2ZrMe2] (5-Me): An analo-
gous procedure to that which gave 4-Me was employed with 5 (1.186 g,
2.0 mmol) to afford 5-Me (0.440 g) in 40% yield. 1H NMR (400.13 MHz,
CDCl3): d=7.20 (d, 4H), 7.07 (d, 4H), 5.62 (s, 4H), 2.49 (s, 6H), 1.82 (s,
12H), À0.49 ppm (s, 6H); 13C{1H} NMR (100.62 MHz, CDCl3): d=135.9,
Chem. Eur. J. 2007, 13, 9107 – 9114
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9113

Y. Do et al.
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pentad sequence distributions were made according to the reported liter-
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Mn) of polypropylenes were determined by gel-permeation chromatogra-
phy (GPC, Polymer Laboratories PL-GPC 220, 1408C) in 1,2,4-trichloro-
benzene by using standard polystyrenes as a reference. Melting tempera-
tures (Tm) of polypropylenes were measured by differential scanning cal-
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The authors gratefully acknowledge financial support from CMDS-
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9114
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Chem. Eur. J. 2007, 13, 9107 – 9114