From unstable to stable: Half-metallocene catalysts for olefin polymerization

Article abstract of DOI:10.1021/ic800198e

The reaction of LAlMeOH [L = CH(N(Ar)(CMe))₂, Ar = 2,6-i-Pr ₂C₆H₃] with CpTiMe₃, Cp*TiMe₃, and Cp*ZrMe₃ was investigated to yield LAlMe(μ-O)TiMe₂Cp (2), LAlMe(μ-O)TiMe ₂Cp* (3), and LAlMe(μ-O)ZrMe₂Cp* (4), respectively. The resulting compounds 2-4 are stable at elevated temperatures, in contrast to their precursors such as CpTiMe₃ and Cp*ZrMe₃, which already decompose below room temperature. Compounds 2-4 were characterized by single-crystal X-ray structural analysis. Compounds 2 and 3 were tested for ethylene polymerization in the presence of methylaluminoxane. The half-metallocene complex 3 has higher activity compared to 2. The polydispersities are in the range from 2.8 to 4.2. A copolymerization with styrene was not observed.

Full text of DOI:10.1021/ic800198e

Inorg. Chem. 2008, 47, 5324-5331
From Unstable to Stable: Half-Metallocene Catalysts for Olefin
Polymerization†
Prabhuodeyara M. Gurubasavaraj, Herbert W. Roesky,* Bijan Nekoueishahraki, Aritra Pal,
and Regine Herbst-Irmer
Institute of Inorganic Chemistry, UniVersity of Go¨ttingen, Tammannstrasse 4,
37077 Go¨ttingen, Germany
Received January 31, 2008
The reaction of LAlMeOH [L ) CH(N(Ar)(CMe))2, Ar ) 2,6-i-Pr2C6H3] with CpTiMe3, Cp*TiMe3, and Cp*ZrMe3 was
investigated to yield LAlMe(µ-O)TiMe2Cp (2), LAlMe(µ-O)TiMe2Cp* (3), and LAlMe(µ-O)ZrMe2Cp* (4), respectively.
The resulting compounds 2-4 are stable at elevated temperatures, in contrast to their precursors such as CpTiMe3
and Cp*ZrMe3, which already decompose below room temperature. Compounds 2-4 were characterized by single-
crystal X-ray structural analysis. Compounds 2 and 3 were tested for ethylene polymerization in the presence of
methylaluminoxane. The half-metallocene complex 3 has higher activity compared to 2. The polydispersities are in
the range from 2.8 to 4.2. A copolymerization with styrene was not observed.
Introduction
These catalysts need a large amount of MAO or expensive
fluorinated borate activators to obtain adequate polymeriza-
tion activity, which causes concern over the high cost of
metallocene catalysts and the high ash content (Al2O3) of
the product polymers. Consequently, there is a great need
to develop new catalyst systems that can provide high
catalytic activity with no need for a large amount of
expensive cocatalysts. The design and synthesis of new
transition-metal catalyst precursors and main-group organo-
metallic cocatalysts is a very important subject that can
provide high catalytic activity with low cocatalyst-to-catalyst
precursor ratios and allows unprecedented control over the
polymer microstructure, producing new polymers with
improved polymer properties. The growing demand for high-
performance polymer products has inspired extensive aca-
demic and industrial research interest in developing new
efficient catalysts that can produce polymers of significant
rheological and mechanical properties.
Well-defined “single-site” metallocene catalysts have been
attracting immense research interest over conventional
Ziegler-Natta heterogeneous catalysts.1 This is mainly due
to the fact that metallocene catalysts in combination with
methylaluminoxane (MAO) exhibit higher stereoselectivity,
narrower molecular weight distribution, and high catalytic
activity in ethylene, propylene, and styrene polymerization.1,2
Other advantages are that these systems produce structurally
well-defined “single-site” active catalytic species.3 This leads
to a variety of high-performance polyolefin products includ-
ing isotactic,2 syndiotactic,4 and atactic polypropylenes,5
high-density polyethylene (PE),6 linear low-density PE,7
syndiotactic polystyrene (PS),8 and cycloolefin copolymers9
with a uniform and tuneable microstructure.
In spite of the success of metallocene catalysts in polym-
erization reactions, they also exhibit some disadvantages.
The development of these metallocene catalysts was
closely related to the discovery of MAO as a cocatalyst,
which is thought to generate a cationic metal alkyl active
†
Dedicated to Professor George M. Sheldrick on the occasion of his
65th birthday.
* To whom correspondence should be addressed. E-mail: hroesky@
gwdg.de.
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5324 Inorganic Chemistry, Vol. 47, No. 12, 2008
10.1021/ic800198e CCC: $40.75  2008 American Chemical Society
Published on Web 05/21/2008

Half-Metallocene Catalysts for Olefin Polymerization
site by alkylation of the catalyst precursor and abstraction
of anionic substituents.3 Recently, we isolated the unprec-
edented LAlMeOH [1; L ) CH(N(Ar)(CMe))2, Ar ) 2,6-
i-Pr2C6H3], which has only one -[AlMeO]- unit, and its
reaction with group 4 metallocene compounds for the design
of well-defined highly active homogeneous catalysts that
exhibit high catalytic activity in olefin polymerization.10 The
oxophilicity of group 4 metals and Bro¨nsted acidic character
of the Al(O-H) moiety resulted in the isolation of complexes
containing the Al(µ-O)M (M ) Ti, Zr, Hf) fragment, which
is known to exhibit high activity in olefin polymerization.10,11
The formation and stability of the cation is one of the key
steps in the polymerization reaction. It depends on the
electronic and steric bulk of the ligand that surrounds the
metal center. The stability of the cation leads to the “living
catalyst” character, which increases the catalytic activity in
the polymerization reaction and produces narrowly distrib-
uted high molecular weight polymers.12
Recently, we studied the role of oxygen in homogeneous
heterobimetallic complexes of zirconium and titanium.
Theoretical studies on the complexes reveal that the oxygen
enhances the intrinsic Lewis acidity at the metal centers,
which, as a consequence, requires a lower amount of MAO
to produce “cation-like” highly electrophilic active species,
which catalyze the polymerization reaction.13
Although considerable attention has been devoted to the
synthesis, characterization, and catalytic studies of sandwich
metallocene complexes,14,15 homogeneous half-metallocene
complexes of group 4 metals bearing terminal methyl groups
(except for Cp*TiMe3) have received little attention because
of the instability of these complexes at ambient tempera-
ture.16 However, in recent decades, there is growing inter-
est17,18 in monocyclopentadienyl group 4 metal complexes
because of the fact that the most active catalysts are those
containing the lowest number of valence electrons.19 The
recent developments of monocyclopentadienyl-based met-
allocene catalysts are heterogeneous oxide-supported com-
plexes of the type Cp*MMe3 (M ) Ti, Zr) for olefin
polymerization. These systems exhibit moderate-to-good
catalytic activity and were characterized by some advanced
techniques (such as 13C CPMAS and EXAFS).20 There are
some reports on zirconium and titanium compounds bearing
bulky Cp* ligands and terminal methyl groups.21 However,
preparation of the complexes bearing one Cp and methyl
groups on the metal centers still remains a synthetic
challenge. Overall, well-characterized and catalytically well-
studied compounds with one Cp and methyl substituents are
still elusive.
In this contribution, we report a facile route for the
preparation and catalytic property of Al(µ-O)M (M ) Ti,
Zr) containing half-metallocene (Cp′ ) C5H5 or C5Me5)
complexes by a tailor-made precursor such as 1. The
monocyclopentadienyl metallocene complexes attached to the
LMeAlO fragment were structurally characterized and used
for the olefin polymerization and copolymerization of styrene
and ethylene. These complexes exhibit high activity toward
olefin polymerization and produce linear PE.
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Gurubasavaraj et al.
Scheme 1
Scheme 3
Scheme 2
molecular ion. The base peak at m/z 588 corresponds to [M
- 2Me]+. The next most intense peak for compound 2 is
observed at m/z 202, which can be assigned to [Dipp-
NCMe]+.24 The 1H NMR spectrum of 2 exhibits two
resonances (δ -0.84 and -0.32 ppm) of 1:2 relative
intensities, which can be attributed to the methyl protons of
the AlMe and TiMe2 groups, respectively. The characteristic
Cp protons for 2 resonate as singlet (δ 5.5 ppm). In addition,
a set of resonances assignable to the isopropyl and methyl
protons associated with the ꢀ-diketiminate ligand is found
in the range between δ 1.76 and 1.01 ppm, and the absence
of the OH proton resonance features complex 2. The 27Al
NMR is silent because of the quadruple moment of alumi-
num.
Synthesis of Compounds 3 and 4. The higher stability
of Cp*MMe3 (M ) Ti, Zr) compared to that of CpTiMe3
allowed its reaction with 1 at room temperature to form the
oxygen-bridged heterobimetallic compound LMeAl(µ-
O)MMe2Cp* [M ) Ti (3), Zr (4)]. The solution of Cp*MMe3
(M ) Ti, Zr) in ether was added drop by drop to the stirred
etheral solution of 1 at -30 °C using a cannula. The solution
was allowed to stir for 10 min and warmed to room
temperature. After stirring for 4 h, the precipitate was filtered
off and washed with n-hexane before drying under vacuum
(Scheme 3).
Results and Discussion
In the course of the synthesis of 1, we followed the
improved route by using a strong nucleophilic reagent,
N-heterocyclic carbene, as an HCl acceptor for the reaction
of LAlMeCl with 1 equiv of water.22
Synthesis of LAlMe(µ-O)TiMe2Cp [2; L ) CH(N(Ar)-
(CMe))2, Ar ) 2,6-i-Pr2C6H3]. The high oxophilicity of
titanium and also the Bro¨nsted acidic character of the proton
of the O-H moiety on the aluminum center allowed us to
isolate compound 2 under methane elimination at low
temperature in high yield. CpTiMe3 was added slowly to
the solution of 1 in hexane at -78 °C under vigorous stirring.
The mixture was allowed to stir for 10 min before the
temperature was slowly raised to 30 °C. It was observed that
the transparent solution becomes turbid, indicating the
formation of compound 2. The temperature of the reaction
was raised to 0 °C, and stirring was continued for an
additional 2 h. Then the temperature was raised to 20 °C
under stirring before filtration (Scheme 1).
Efforts were made to isolate the corresponding chloro
analogues. However, the reaction of CpTiMeCl2 with 1
yielded the eight-membered Ti4O4 ring (by X-ray structural
analysis), indicating that the aluminum and titanium centers
exchange the chlorine and oxygen atoms (Scheme 2).23
Compound 2 is insoluble in hexane, toluene, and pentane
but sparingly soluble in tetrahydrofuran (THF) and ether,
whereas it is freely soluble in hot toluene. Complex 2 was
characterized by 1H NMR spectroscopy, electron impact (EI)
mass spectrometry, elemental analysis, and X-ray structural
determination. Compound 2 is a yellow solid that melts at
135 °C. Decomposition was observed at the melting point.
Unlike CpTiMe3, compound 2 is thermally stable and not
photosensitive. Compound 2 is stable and can be stored for
a period of time at room temperature in the absence of air
and moisture. The mass spectral data for 2 is in accordance
with the assigned structure. Complex 2 does not exhibit a
Compounds 3 and 4 are insoluble in hexane, toluene, and
pentane but sparingly soluble in THF and ether, whereas they
are freely soluble in hot toluene. Complex 3 was character-
ized by 1H NMR spectroscopy, EI mass spectrometry,
elemental analysis, and X-ray structural analysis, while
1
compound 4 was characterized by H NMR spectroscopy,
elemental analysis, and X-ray structural analysis. Compound
3 is a yellow crystalline solid that melts at 235 °C, while 4
is a colorless crystalline solid that melts at 181 °C.
Decomposition was observed at the melting points of 3 and
4. Unlike Cp*MMe3 (M ) Ti, Zr), complexes 3 and 4 are
thermally stable for a long period of time at room temperature
in the absence of air and moisture. The mass spectral data
for 3 is in accordance with the assigned structure. Compound
3 does not exhibit a molecular ion but shows the base peak
at m/z 658 corresponding to [M - 2Me]+. The next most
intense peak was observed at m/z 202, which can be assigned
(22) Jancik, V.; Pineda, L. W.; Pinkas, J.; Roesky, H. W.; Neculai, D.;
Neculai, A. M.; Herbst-Irmer, R. Angew. Chem. 2004, 116, 2194–
2197; Angew. Chem., Int. Ed. 2004, 43, 2142-2145.
(24) Prust, J.; Most, K.; Mu¨ller, I.; Alexopoulos, E.; Stasch, A.; Uso´n, I.;
(23) Saunders, L; Spirer, L. Polymer 1965, 6, 635–644.
Roesky, H. W. Z. Anorg. Allg. Chem. 2001, 627, 2032–2037.
5326 Inorganic Chemistry, Vol. 47, No. 12, 2008

Half-Metallocene Catalysts for Olefin Polymerization
Figure 1. Molecular structure of 2. Thermal ellipsoids are set at the 50%
probability level. H atoms are omitted for clarity.
Figure 2. Molecular structure of 3. Thermal ellipsoids are set at 50%
24
to [DippNCMe]+. The H NMR spectrum of 3 exhibits
two resonances (δ -0.22 and -0.11 ppm) of 1:2 intensities,
which can be attributed to the methyl protons of AlMe and
TiMe2, respectively, whereas the respective protons of AlMe
and ZrMe2 in compound 4 resonate in 1:2 relative intensities
(δ -0.23 and -0.32 ppm). The characteristic Cp* protons
for 3 and 4 appear as singlets (δ 1.67 and 1.85 ppm). In
addition, a set of resonances assignable to the isopropyl and
methyl protons associated with the ꢀ-diketiminate ligand are
found in the range between δ 1.9 and 1.0 ppm, and the
absence of the OH proton resonance features both 3 and 4.
The 27Al NMR is silent because of the quadruple moment
of aluminum.
1
probability level. H atoms are omitted for clarity.
The Al(µ-O) bond lengths in 2 [1.743(1) Å], 3 [1.736(2)
Å], and 4 [1.732(2) Å] are similar to each other but slightly
longer than those for the bis(cyclopentadienyl) analogues
LMeAl(µ-O)MMeCp2 (M ) Ti,11 Zr,10 Hf11) (average 1.71
Å) and significantly longer than those found in compounds
[{(Me3Si)2HC}2Al]2(µ-O)[1.69(4)Å]and[HC{(CMe)(NMe)}2-
AlCl]2(µ-O) [1.68(6) Å]. The Al(µ-O)Ti angle [142.2(1)°]
in 2 is significantly narrower than the corresponding Al(µ-
O)M (M ) Ti, Zr) bond angles in 3 [154.0(1)°], 4
[155.37(10)°], and LMeAl(µ-O)MMeCp2 (M ) Ti,11 Zr,10
Hf11) (average 158.3°) complexes. Furthermore, the Al(µ-
O)M (M ) Ti, Zr) angles in 2-4 are considerably less
opened than those of homobimetallic M(µ-O)M (M ) Zr,
Hf) in (Cp2ZrMe)2(µ-O) [174.1(3)°] and (Cp2HfMe)2(µ-O)
[173.9(3)°]. The Al-Me bond lengths in compounds 2
[1.957(2) Å], 3 [1.956(3) Å], and 4 [1.958(2) Å] are
comparable to each other and are similar to those of 1 and
LMeAl(µ-O)MMeCp2 [L ) CH((CMe)(NAr))2, Ar ) 2,6-
i-Pr2C6H3, M ) Ti,11 Zr,10 Hf11] (average 1.96 Å). Selected
bond parameters are listed in Table 2.
The Ti(1)-O(1) bond distance in compound 2 [1.764(1)
Å] is slightly shorter than the Ti-O bond lengths in
compound 3 [1.778(2) Å] and LMeAl(µ-O)TiMeCp2 [1.808(3)
Å]11 but significantly shorter when compared to those in
[Cp2Ti(CF3CdC(H)CF3)]2O [average Ti-O 1.86(6)Å] and
the alkoxide-bridged clusters (Ti4Zr2O4(OBu)n(OMc)10 [OMc
) methacrylate, n ) 2, 4, 6; average Ti-O 2.04(5) Å] and
Ti2(O-i-Pr)2[(O-2,4-Me2C6H2-6-CH2)2(µ-OCH2CH2)N]2 (av-
erage Ti-O 1.90 Å). The Ti–Me bond lengths in 2 [2.104(2)
and 2.112(2) Å] and 3 [2.111(3) and 2.116(3) Å] are
comparable to each other and are slightly shorter when
compared to those (average 2.18) in Cp2TiMe2. The Ti-XB1A
(XB1A ) centroid of the Cp ring) distances in 2 (2.084 Å)
and 3 (2.082 Å) are identical and are similar to those in
dimethyltitanocene (average Ti-XB1A 2.08 Å).
Molecular Structure Description of Complexes 2-4.
The yellow single crystals of 2 and 3 and the colorless single
crystals of 4 were obtained from cooling of their hot toluene
solutions and were unambiguously analyzed by X-ray
diffraction studies (Figures 1–3). The important bond pa-
rameters for compounds 2-4 are listed in Table 1.
Compounds 3 and 4 crystallize in the monoclinic space
group P21/n, while complex 2 crystallizes in the triclinic
space group P1. All of the three compounds show the
aluminum atom bonded through an oxygen atom to titanium
(2 and 3) and zirconium (4), respectively, and contain a bent
Al(µ-O)M (M ) Ti, Zr) core. The aluminum atom exhibits
a highly distorted tetrahedral geometry with two nitrogen
atoms of the ꢀ-diketiminato ligand, a methyl group, and one
µ-O unit. The titanium (in 2 and 3) and zirconium (in 4)
exhibit tetrahedral geometry, and their coordination spheres
are completed by one Cp′ (Cp′ ) Cp in the case of 2 and
Cp* in the case of 3 and 4) ligand, two methyl groups around
each metal atom, and one µ-O unit. The methyl groups on
aluminum and titanium in 2 and 3 and aluminum and
zirconium in 4 are bent out of the Al(µ-O)M (M ) Ti, Zr)
plane in a trans configuration.
j
Inorganic Chemistry, Vol. 47, No. 12, 2008 5327

Gurubasavaraj et al.
Table 1. Crystal Data and Structure Refinement for Compounds 2-4
2
3
4
empirical formula
fw
C37H55AlN2OTi
618.72
C42H65AlN2OTi
688.84
C42H65AlN2OZr
732.16
color
yellow
yellow
colorless
cryst syst
space group
a, Å
triclinic
P1
9.240(1)
monoclinic
P21/n
12.033(1)
monoclinic
P21/n
12.232(2)
j
b, Å
10.499(1)
19.076(2)
19.009(2)
c, Å
19.982(1)
17.519(1)
17.498(2)
R, deg
ꢀ, deg
γ, deg
V, Å3
91.54(1)
90.02(1)
115.26(1)
1752.3(3)
90
96.79(1)
90
3993.1(6)
90
97.36(1)
90
4035.1(9)
Z
F
2
4
4
calcd, Mg m-3
1.173
2.526
668
1.146
2.263
1496
1.205
2.675
1568
σ, mm-1
F(000)
θ range for data collection, deg
4.43-59.06
3.44-59.00
3.45-59.39
index ranges
-10 e h e 10
-11 e k e 11
-22 e l e 22
18 109
-13 e h e 13
-20 e k e 21
-19 e l e 19
30 327
-13 e h e 13
-21 e k e 21
-19 e l e 19
35 043
no. of reflns collcd
no. of indep reflns (Rint
refinement method
GOF
)
4920 (Rint ) 0.0313)
full-matrix least squares on F2
1.080
5577 (Rint ) 0.0711)
full-matrix least squares on F2
1.046
5798 (Rint ) 0.0532)
full-matrix least squares on F2
1.034
final R indices [I > 2σ(I)]
R1 ) 0.0288, wR2 ) 0.0783
R1 ) 0.0298, wR2 ) 0.0789
-0.255/+0.281
R1 ) 0.0508, wR2 ) 0.1298
R1 ) 0.0730, wR2 ) 0.1442
-0.517/+0.326
R1 ) 0.0291, wR2 ) 0.736
R1 ) 0.0339, wR2 ) 0.0771
-0.408/+0.383
R indices (all data)a, b
largest diff peak/hole (e Å-3
a R1 ) ∑|Fo| - |Fc|/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]0.5
)
2
2
2
.
The Zr(1)-O(1) bond distance in 4 [1.920(2) Å] is shorter
compared to the corresponding bond length in the oxygen-
bridged (µ-O) compounds (Cp2ZrL)2(µ-O) [L ) Me, SC6H5;
1.95(1) and 1.97(5) Å] and Cp*2MeZr(µ-O)TiMe2Cp* [Zr-O
2.02(4) Å].13 The Zr-C bond lengths [2.271(3) and 2.249(2)
Å] in 4 are comparable to that in the heterobimetallic
compound Cp*2MeZr(µ-O)TiMe2Cp* (2.30 Å).13 The
Zr-XB1A distance (2.231 Å) in 4 is comparable to that in
dimethylzirconocene (average Zr-XB1A 2.3 Å).25
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compounds 2-4a
Compound 2
Ti(1)-O(1)
Ti(1)-C(19)
Ti(1)-C(20)
Ti(1)-X1A
1.764(1) Al(1)-O(1)
2.104(2) Al(1)-N(1)
2.112(2) Al(1)-N(2)
1.743(1)
1.913(1)
1.894(1)
1.957(2)
2.084
Al(1)-C(18)
Al(1)-O(1)-Ti(1)
O(1)-Ti(1)-C(19)
O(1)-Ti(1)-C(20)
N(1)-Al(1)-C(18)
C(19)-Ti(1)-C(20)
X1A-Ti(1)-O(1)
X1A-Ti(1)-C(20)
142.2(1)
105.19(6)
102.50(7)
111.83(7)
97.85(8)
121.9
O(1)-Al(1)-C(18) 113.27(7)
O(1)-Al(1)-N(1)
O(1)-Al(1)-N(2)
N(2)-Al(1)-C(18) 113.95(7)
N(1)-Al(1)-N(2) 96.65(6)
X1A-Ti(1)-C(19) 114.3
110.51(6)
109.46(6)
Accounting for the Thermal Stability of Compounds
2-4. The thermal stability of the metallocene catalysts is
one of the most important factors for their application in
industry.26 For efficient catalytic processes, the ideal situation
is that the catalyst has to be both highly active and thermally
stable. The instability of the Cp′MMe3 (Cp′ ) Cp or Cp*;
M ) Ti or Zr)16 complexes does not allow to use them in
the polymerization reactions. The heterobimetallic complexes
2-4 exhibit good thermal stability and can be stored for a
long period of time in the absence of air or moisture, unlike
their precursors, which should be stored only at very low
temperature. The heterobimetallic complexes are stable to
air and moisture for a short period of time, while their
precursors are very sensitive to air and moisture. For
111.9
Compound 3
Ti(1)-O(1)
Ti(1)-C(19)
Ti(1)-C(20)
Ti(1)-X1A
1.778(2) Al(1)-O(1)
2.111(3) Al(1)-N(1)
2.116(3) Al(1)-N(2)
1.736(2)
1.916(2)
1.921(2)
1.956(3)
2.082
Al(1)-C(18)
Al(1)-O(1)-Ti(1)
O(1)-Ti(1)-C(19)
O(1)-Ti(1)-C(20)
N(1)-Al(1)-C(18)
C(19)-Ti(1)-C(20)
X1A-Ti(1)-O(1)
X1A-Ti(1)-C(20)
154.0(1)
101.1(11)
106.4(1)
111.9(1)
97.0(2)
124.5
O(1)-Al(1)-C(18) 114.4(1)
O(1)-Al(1)-N(1)
O(1)-Al(1)-N(2)
N(2)-Al(1)-C(18) 108.9(1)
N(1)-Al(1)-N(2) 96.3(1)
X1A-Ti(1)-C(19) 112.5
112.6(10)
111.3(1)
111.15
16
Compound 4
example, CpTiMe3 is only stable below -30 °C, while
Zr(1)-O(1)
Zr(1)-C(19)
Zr(1)-C(20)
Zr(1)-X1A
1.920(2) Al(1)-O(1)
2.271(3) Al(1)-N(1)
2.249(2) Al(1)-N(2)
1.732(2)
1.910(2)
1.921(2)
1.958(2)
compound 2 decomposes at 135 °C.
Ethylene Polymerization Studies of Compounds 2
and 3. In the presence of MAO, compounds 2 and 3 act as
catalysts and exhibit high catalytic activity for the polym-
erization of ethylene. All polymeric materials were isolated
as white powders. Table 3 summarizes the polymerization
2.231
Al(1)-C(18)
O(1)-Zr(1)-C(19)
O(1)-Zr(1)-C(20)
109.08(9)
102.32(8)
O(1)-Al(1)-N(1)
O(1)-Al(1)-N(2)
111.19(7)
111.23(7)
96.36(7)
C(19)-Zr(1)-C(20) 100.07(11) N(1)-Al(1)-N(2)
N(1)-Al(1)-C(18)
Al(1)-O(1)-Zr(1)
X1A-Zr(1)-O(1)
X1A-Zr(1)-C(20)
112.73(8)
N(2)-Al(1)-C(18) 109.31(9)
155.37(10) O(1)-Al(1)-C(18) 114.57(10)
122.2
111.0
(25) Hunter, W. E.; Hrncir, D. C.; Bynum, R. V.; Penttila, R. A.; Atwood,
J. L. Organometallics 1983, 2, 750–755.
X1A-Zr(1)-C(19) 109.7
(26) Jia, L.; Yang, X.; Stern, C. L.; Marks, T. J. Organometallics 1997,
16, 842–875.
a XB1A ) centroid of the Cp ring.
5328 Inorganic Chemistry, Vol. 47, No. 12, 2008

Half-Metallocene Catalysts for Olefin Polymerization
Table 3. Ethylene Polymerization Data for Compounds 2 and 3a
Table 4. Styrene Polymerization Data for Compounds 2 and 3a
MAO/
catalyst
MAO/catalyst
t (min)
PS (g)
A × 104
Tg (°C)
catalyst catalyst t (min) PE (g) A × 105
Mw
Mw/Mn Tm (°C)
2
2
2
2
3
3
3
3
400
800
1200
1600
400
800
1200
1600
60
60
60
60
60
60
60
60
0.3
0.8
1.1
1.7
0.4
1.0
1.4
2.5
1.4
3.8
5.2
8.1
1.9
4.8
6.7
12.0
87
93
87
81
91
89
97
88
2
2
2
2
3
3
3
3
100
200
300
400
100
200
300
400
30
30
30
30
30
30
30
30
0.3
0.9
1.7
3.1
0.8
1.7
3.6
5.0
0.3
0.9
1.6
3.0
0.8
1.6
3.4
4.8
121
103 263 2.84
225 027 4.23
127
124
129
119
127
130
129
124 265 4.02
470 431 3.14
a Polymerization conditions: 2 and 3 ) 21 µmol, 100 mL of toluene at
25 °C, 10 mL of styrene under argon. Activity (A) ) g of PS/mol of
catalyst·h.
a Polymerization conditions: 2 and 3 ) 21 µmol, 100 mL of toluene at
25 °C, 1 atm of ethylene pressure. Activity (A) ) g of PE/mol of catalyst ·h.
ing a gradual increase in the activity with the MAO/catalyst
ratios. In general, the activities of the bisCp complexes were
found to be the highest, about 10 orders of magnitude more
than those of the monoCp′ (Cp′ ) Cp or Cp*) analogues.
The same trend was previously reported in the literature.20
The data presented in Table 3 clearly demonstrate that both
compounds 2 and 3 act as active catalysts even at low MAO/
catalyst ratios; a similar result was previously observed for
the corresponding LAlMe(µ-O)M(Me)Cp2 (M ) Ti,11 Zr10)
complexes. The plot of activities for compounds 2 and 3
indicates that compound 3 is more active than compound 2
under comparable conditions. This may be due to the
formation of a more stable cation in 3, which has a bulky
and more electron-donating Cp* ligand in its coordination
sphere compared to 2, which has a less steric and less
electron-donating Cp ligand. Unfortunately, compound 4
could not be isolated in a pure form; it always crystallizes
with impurities.
PE Properties. Melting points (Tm) for the polymers are
in the range of 119-130 °C, and 13C NMR spectra exhibit
a single resonance at around 30 ppm, which can be attributed
to the backbone carbon of linear PE. The gel permeation
chromatography (GPC) for measured PE samples exhibits
monomodal property for measured PE samples. The poly-
dispersities show narrow distribution ranging from 2.8 to 4.2,
which corresponds to single-site catalysts (Table 3).1
Figure 3. Molecular structure of 4. Thermal ellipsoids are set at the 50%
probability level. H atoms are omitted for clarity.
Styrene Polymerization Studies for Compounds 2
and 3. The catalytic properties of complexes 2 and 3 for the
polymerization of styrene were preliminarily investigated.
These complexes show living catalyst activity at ambient
temperature in toluene when activated with MAO. All
polymeric materials were isolated as white powders, and
Table 4 summarizes the activity values of catalysts 2 and 3.
Figure 5 exhibits a plot for activity versus MAO/catalyst
ratio.
Properties of PS Produced by 2 and 3. The differential
scanning calorimetry (DSC) measurements of the polymers
show that the characteristic glass transition temperatures (Tg)
are in the range from 81 to 97 °C, which is within the typical
Tg range for the atactic polymers. As expected, compound 3
shows more activity compared to that of compound 2 because
of the formation of a more stable cation intermediate in 3
when compared to 2.
Figure 4. Comparative plot of the activity toward the MAO/catalyst ratio
for compounds 2 and 3 in ethylene polymerization.
results of compounds 2 and 3. Under comparable polymer-
ization conditions, both MAO/2 and MAO/3 catalyst systems
show lower activity compared to that of MAO/LAlMe(µ-
O)M(Me)Cp2 (M ) Ti,11 Zr10). Figure 4 exhibits a plot of
activities for different ratios of MAO/2 and MAO/3, reveal-
Ethylene and Styrene Copolymerization Studies for
Compounds 2 and 3. Preliminary investigations of ethylene
and styrene copolymerization reactions were carried out. The
Inorganic Chemistry, Vol. 47, No. 12, 2008 5329

Gurubasavaraj et al.
Synthesis of LAlMe(µ-O)TiMe2Cp (2). A solution of freshly
prepared CpTiMe3 (0.21 g, 1.01 mmol) in toluene (20 mL) was
added via a cannula to a solution of 1 (0.48 g, 1.01 mmol) in toluene
(20 mL) at -30 °C. The mixture was stirred at -30 °C for 1 h,
then the temperature was slowly raised to 0 °C, and the stirring
was continued. After 3 h, the solution was allowed to attain room
temperature and stirred for 12 h. (Caution! Care must be taken
because methyl deriVatiVes of titanium are photosensitiVe.) The
yellow precipitate formed was filtered off, washed with n-hexane,
1
and dried in vacuum. Yield: 0.41 g (61%). Mp: 135 °C (dec). H
NMR (500.13 MHz, C6D6, 25 °C, TMS): δ 7.1-7.2 (m, 6H, m-
and p-ArH), 5.50 (s, 5H, C5H5), 5.14 (s, 1H, γ-CH), 3.38 (sept,
3
3
2H, JH-H ) 6.8 Hz, CH(CH3)2), 3.11 (sept, 2H, JH-H ) 6.8 Hz,
3
CH(CH3)2), 1.73 (s, 6H, CH3), 1.25 (d, 12H, JH-H ) 6.8 Hz,
CH(CH3)2), 1.15 (d, 12H, 3JH-H ) 6.80 Hz, CH(CH3)2), -0.32 (s,
3H, TiCH3)), -0.84 (s, 3H, AlCH3)) ppm. MS (EI) m/z (%): 588
(100) [M+ - 2Me], 202 (26) [DippNCMe]+. Anal. Calcd for
C37H55AlN2OTi (618.69): C, 71.83; H, 8.96; N, 4.53. Found: C,
70.01; H, 8.93; N, 5.37.
Figure 5. Comparative plot of the activity toward the MAO/catalyst ratio
for compounds 2 and 3 in styrene polymerization.
Table 5. Ethylene and Styrene Copolymerization Data for Compounds
2 and 3a
Synthesis of LAlMe(µ-O)TiMe2Cp* (3). Freshly sublimed
Cp*TiMe3 (0.34 g, 1 mmol) dissolved in ether (20 mL) was
transferred using a cannula to a flask charged with 1 (0.48 g, 1
mmol) in diethyl ether (30 mL) at -30 °C. The reaction mixture
was slowly warmed to ambient temperature and stirred for 12 h.
The yellow precipitate was filtered, washed with n-hexane, and dried
MAO/
catalyst catalyst t (min) PE (g) A × 105
Mw
Mw/Mn Tm (°C)
2
2
3
3
200
400
200
400
60
60
60
60
0.82
1.70
1.31
2.00
0.39
0.81
0.62
0.95
117
116
119
1
422018 7.17
120
in vacuum. Yield: 0.54 g (67.4%). Mp: 235 °C (dec). H NMR
a Polymerization conditions: 2 and 3 ) 21 µmol, 100 mL of toluene at
25 °C, at 1 atm of ethylene pressure, 10 mL of styrene. Activity (A) ) g
of PE/mol of catalyst ·h.
(500.13 MHz, C6D6, 25 °C, TMS) δ 7.13-7.24 (m, 6H, m- and
3
p-ArH), 4.90 (s, 1H, γ-CH), 3.69 (sept, 4H, JH-H ) 6.8 Hz,
3
CH(CH3)2), 3.34 (sept, 4H, JH-H ) 6.8 Hz, CH(CH3)2), 1.67 (s,
3
MAO-activated complexes 2 and 3 exhibit moderate catalytic
activity and produce polymer products. These polymer
products were characterized in order to observe the incor-
poration of styrene into ethylene, which can produce
polymers of interesting microstructure. The DSC measure-
ments of the polymers show that the melting point temper-
atures (Tm) are in the range from 116 to 119 °C. The 13C
NMR spectra exhibits only one peak (∼30.0 ppm) corre-
sponding to the backbone carbon. These data indicate that
the polymer produced by 2 and 3 is PE. The styrene
incorporation is negligible (even we can say there is no
styrene incorporation) because we did not observe any other
resonances in the 13C NMR spectra. The copolymerization
results in homopolymerization of ethylene (Table 5).
15H, C5(CH3)5), 1.64 (s, 6H, CH3), 1.50 (d, 6H, JH-H ) 6.8 Hz,
CH(CH3)2), 1.44 (d, 6H, 3JH-H ) 6.8 Hz, CH(CH3)2), 1.23 (d, 6H,
3
3JH-H ) 6.8 Hz, CH(CH3)2), 1.22 (d, 6H, JH-H ) 6.8 Hz,
CH(CH3)2), -0.11 (s, 6H, TiCH3)2), -0.22 (s, 6H, AlCH3) ppm.
MS (EI) m/z (%): 658 (100) [M+ - 2Me], 770 (8) [M+ - 2Me],
202 (26) [DippNCMe]+. Anal. Calcd for C42H65AlN2OTi (688.83):
C, 73.23; H, 9.51; N, 4.07. Found: C, 72.88; H, 9.43; N, 3.98.
Synthesis of LAlMe(µ-O)ZrMe2Cp* (4). A solution of freshly
prepared Cp*ZrMe3 (0.21 g, 1.01mmol) in toluene (20 mL) was
added via a cannula to a solution of 1 (0.48 g, 1.01 mmol) in toluene
(20 mL) at -30 °C. The mixture was stirred at -30 °C for 3 h and
then slowly raised to 0 °C, and the stirring was continued for 12 h.
The white precipitate formed was filtered off, washed with n-hexane,
1
and dried in vacuum. Yield: 0.57 g (73%). Mp: 181 °C (dec). H
NMR (500.13 MHz, C6D6, 25 °C, TMS): δ 7.13-7.24 (m, 6H, m-
3
and p-ArH), 4.92 (s, 1H, γ-CH), 3.65 (sept, 4H, JH-H ) 6.8 Hz,
3
Experimental Section
CH(CH3)2), 3.36 (sept, 4H, JH-H ) 6.8 Hz, CH(CH3)2), 1.85 (s,
3
15H, C5(CH3)5), 1.78 (s, 6H, CH3), 1.63 (d, 6H, JH-H ) 6.8 Hz,
General Comments. All experimental manipulations were
carried out under an atmosphere of dry argon using standard Schlenk
techniques. The samples for spectral measurements were prepared
in a glovebox. The solvents were purified according to conventional
procedures and were freshly distilled prior to use. CpMCl3 and
Cp*MCl3 (M ) Ti, Zr) were purchased from Aldrich, and methyl
derivatives were prepared by procedures that were published
elsewhere.16 NMR spectra were recorded on a Bruker Avance 300
instrument, and the chemical shifts are reported with reference to
tetramethylsilane (TMS). 13C NMR assays of the polymer micro-
structure were conducted in 1,1,2,2-tetrachloroethane-d2 at 90 °C.
Resonances were assigned according to the literature for PE.3 Mass
spectra were obtained on a Finnigan MAT 8230 spectrometer by
the EI technique. Melting points were measured in sealed capillaries
on a Bu¨chi B 540 instrument. Elemental analyses were performed
at the Analytical Laboratory of the Institute of Inorganic Chemistry
at Go¨ttingen, Germany.
CH(CH3)2), 1.60 (d, 6H, 3JH-H ) 6.8 Hz, CH(CH3)2), 1.30 (d, 6H,
3
3JH-H ) 6.8 Hz, CH(CH3)2), 1.22 (d, 6H, JH-H ) 6.8 Hz,
CH(CH3)2), -0.23 (s, 3H, AlCH3), -0.32 (s, 6H, ZrCH3)2) ppm.
Anal. Calcd for C42H65AlN2OZr (732.18): C, 68.90; H, 8.95; N,
3.83. Found: C, 68.28; H, 8.93; N, 3.58.
X-ray Structure Determination of 2-4. Data for the structures
2-4 were collected on a Bruker three-circle diffractometer equipped
with a SMART 6000 CCD detector. Intensity measurements were
performed on a rapidly cooled crystal. The structures were solved
by direct methods (SHELXS-97)27 and refined with all data by full-
matrix least squares on F2.28 The hydrogen atoms on C-H bonds
were placed in idealized positions and refined isotropically with a
(27) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467–473.
(28) Sheldrick, G. M. SHELXS-97 and SHELXL-97. Program for Crystal
Structure Refinement; Go¨ttingen University: Go¨ttingen, Germany,
1997.
5330 Inorganic Chemistry, Vol. 47, No. 12, 2008

Half-Metallocene Catalysts for Olefin Polymerization
riding model, whereas the non-hydrogen atoms were refined
anisotropically. They were refined with distance restraints and
restraints for the anisotropic displacement parameters. Crystal data
and selected bond lengths and angles are shown in Tables 1 and 2.
Ethylene Polymerization Experiments. Ethylene polymeriza-
tions were carried out on a vacuum line (10-5 Torr) in an autoclave
(Bu¨chi). In a typical experiment, the catalyst (see Table 3) was
taken and an appropriate amount of MAO (1.6 M, Aldrich) was
added and stirred for 20 min for the activation. After stirring, the
resulting mixture was placed into the autoclave by using a gastight
syringe, which was previously saturated with 100 mL of toluene
under an ethylene atmosphere (1 atm). After stirring for an
appropriate time, the reaction was quenched using methanol and
the white PE formed was collected by filtration and dried.
Styrene Polymerization Experiments. Styrene polymerizations
were carried out on a vacuum line (10-5 Torr) in an autoclave
(Buchi). In a typical experiment, the catalyst (see Table 4) was
taken and an appropriate amount of MAO (1.6 M, Aldrich) was
added and stirred for 20 min for the activation. After stirring, the
resulting mixture was placed into the autoclave by using a gastight
syringe, which was previously saturated with argon, 100 mL of
toluene, and 10 mL of styrene. After stirring for an appropriate
time, the reaction was quenched using methanol and the white PS
formed was collected by filtration and dried.
MAO (1.6 M, Aldrich) was added and stirred for 20 min for the
activation. After stirring, the resulting mixture was placed into the
autoclave by using a gastight syringe. The autoclave was previously
saturated with purified ethylene (1 atm), 100 mL of toluene, and
10 mL of styrene. After stirring for an appropriate time, the reaction
was quenched using methanol and the white PE formed was
collected by filtration and dried.
DSC. The polymer melting range was measured on a TA
Instrument 2920 (modulated differential scanning calorimeter),
which was calibrated against indium metal (ca. 4 mg samples were
used at 10 °C/min).
GPC. GPC was carried out at Basell R&D Polymer Physics and
Characterization, Industriepark, Hoechst, Frankfurt, Germany. 1,2,4-
Trichlorobenzene was used as the solvent. The columns were
calibrated with narrow molar mass distribution standards of PS.
Acknowledgment. This work was supported by the
Go¨ttinger Akademie der Wissenschaften, Deutsche For-
schungsgemeinschaft, and the Fonds der Chemischen Indus-
trie. The authors thank Dr. Volker Dolle for his kind help in
analyzing polymer samples by GPC.
Supporting Information Available: X-ray crystallographic data
of 2-4 in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
Ethylene and Styrene Copolymerization Experiments. Co-
polymerization of ethylene and styrene was carried out on a vacuum
line (10-5 Torr) in an autoclave (Bu¨chi). In a typical experiment,
the catalyst (see Table 5) was taken and an appropriate amount of
IC800198E
Inorganic Chemistry, Vol. 47, No. 12, 2008 5331