Zirconocene complexes with a biphenyl substituted cyclopentadienyl ligand: Synthesis, characterization, and olefin polymerization behavior

Article abstract of DOI:10.1016/j.jorganchem.2004.11.031

Novel zirconocene complexes (1-Biph-3,4-Me₂Cp) ₂ZrCl₂ (3), (C₅Me₅)(1-Biph-3,4- Me₂Cp)ZrCl₂ (4), and (C₅H₅)(1-Biph- 3,4-Me₂Cp)ZrCl₂ (5) containing a 1-biphenyl-3,4- dimethylcyclopentadienyl ligand (2) have been prepared and their solid state structures were characterized by X-ray diffraction method. The crystal structure of 3 revealed a racemic, C₂-symmetric nature in the solid state. In ethylene polymerization, they all afforded high-density polyethylene with very high activity. Especially, the catalytic properties of 3 were most marked in terms of both polymerization activity and molecular weight of polyethylene among them. They also showed good activity on the polymerization of propylene, but afforded nearly atactic, amorphous polypropylenes with a little higher [mmmm] methyl pentad values by 3 and 4 than that by the most active 5 under the given reaction conditions.

Full text of DOI:10.1016/j.jorganchem.2004.11.031

Journal of Organometallic Chemistry 690 (2005) 1240–1248
www.elsevier.com/locate/jorganchem
Zirconocene complexes with a biphenyl substituted
cyclopentadienyl ligand: synthesis, characterization, and
olefin polymerization behavior
*
Min Hyung Lee, Youngkyu Do
Department of Chemistry, School of Molecular Science BK-21 and Center for Molecular Design and Synthesis,
Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
Received 6 October 2004; accepted 17 November 2004
Abstract
Novel zirconocene complexes (1-Biph-3,4-Me2Cp)2ZrCl2 (3), (C5Me5)(1-Biph-3,4-Me2Cp)ZrCl2 (4), and (C5H5)(1-Biph-3,4-
Me2Cp)ZrCl2 (5) containing a 1-biphenyl-3,4-dimethylcyclopentadienyl ligand (2) have been prepared and their solid state structures
were characterized by X-ray diffraction method. The crystal structure of 3 revealed a racemic, C2-symmetric nature in the solid state.
In ethylene polymerization, they all afforded high-density polyethylene with very high activity. Especially, the catalytic properties of
3 were most marked in terms of both polymerization activity and molecular weight of polyethylene among them. They also showed
good activity on the polymerization of propylene, but afforded nearly atactic, amorphous polypropylenes with a little higher
[mmmm] methyl pentad values by 3 and 4 than that by the most active 5 under the given reaction conditions.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Metallocene; Biphenyl; Ethylene; Propylene; Polymerization
1. Introduction
the polymer had a stereoblock microstructure in which
amorphous and crystalline segments were parts of the
same polypropylene chain [5]. After this finding, Collette
et al. [6] reported that elastomeric polypropylene could
be also produced by supported tetraalkyl group 4 cata-
lysts. The first homogeneous catalyst for the production
of elastomeric polypropylene was introduced by Chien
et al. [7] using a chiral ansa-titanocene, [MeHC(C5-
Me4)(Ind)]TiCl2, in which the monomer insertion oc-
curred sequentially at aspecific and isospecific
coordination sites. The recent discovery by Waymouth
et al. that the nonbridged metallocene, (2-PhInd)2ZrCl2
(1) can also produce elastomeric polypropylene when
activated by methylaluminoxane (MAO) provided a
new concept on the control of microstructure of poly-
propylene [8]. This zirconocene catalyst was designed
to switch between chiral rac-like symmetric and achiral
meso-like symmetric geometries generated alternately
Homogeneous group 4 metallocene catalysts have
provided various opportunities to tailor the microstruc-
ture and physical properties of polyolefins by manipula-
tions of the catalyst ligand structure [1]. For propylene
polymerization, especially, C2- and Cs-symmetric ansa-
metallocene catalysts can now afford high-melting
stereoregular isotactic [2,4] and syndiotactic [3,4] poly-
propylenes, respectively, while stereorandom, amor-
phous atactic polypropylene [4] can be prepared using
C2v-symmetric metallocene catalysts.
Polypropylene consisting of isotactic and atactic
blocks is a thermoplastic elastomer. Natta first discov-
ered an elastomeric polypropylene and concluded that
*
Corresponding author. Tel.: +82428692829; fax: +82428692810.
E-mail address: ykdo@kaist.ac.kr (Y. Do).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.031

M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
1241
by hindered rotation of the indenyl ligands in order to
give isotactic and atactic stereoblocks in the same poly-
mer chain (Fig. 1). Followed by this important finding,
they extensively investigated the effects of the 2-aryl
groups on the indenyl ligand [9] and the nature of the
metal [10] and cyclopentadienyl ring fragment [11],
including mixed-ring complex systems [12] on the pro-
duction of elastomeric polypropylene.
In this regard, it is of value to examine the catalytic
properties of the Waymouth-type catalyst that contains
a sterically demanding substituent, especially, on the 4-
position of phenyl group attached to the cyclopentadie-
nyl ligand in order to control the rate of mutual rotation
of the ligands, by which the stereoblock length in the
polymer chain can be varied. We present here the syn-
thesis, characterization of nonbridged zirconocene com-
where Cp = C5H5, Cp* = C5Me5). ZrCl4(thf)2 [13] and
3,4-dimethylcyclopent-2-enone [14] were prepared
according to the literature procedures. CDCl3 was dried
over activated molecular sieves (4A), and used after vac-
uum transfer to a Schlenk tube equipped with a
J. Young valve. 1H and 13C NMR spectra were recorded
on Bruker Avance 400 spectrometer at ambient temper-
ature. All chemical shifts are reported in d units with
reference to the residual peaks of CDCl3 for proton
(7.24 ppm) and carbon (77.0 ppm) chemical shifts.
Elemental analyses were carried out on an EA 1110-FI-
SONS (CE Instruments) at KAIST.
2.2. X-ray structural determination
2.2.1. Crystal structures of 3 and 4
plexes containing
cyclopentadienyl ring fragment and their catalytic
behavior in olefin polymerization.
a
biphenyl group on the
An air stable, single crystal suitable for X-ray struc-
ture determination was mounted on glass capillary.
The measurements of diffraction intensity were carried
out on an Enraf-Nonius CAD4TSB diffractometer using
graphite-monochromated Mo Ka radiation (k = 0.71073
˚
2. Experimental
A) at 293 K. Accurate unit cell parameters and orienta-
tion matrices were determined from the least-square fit
of 25 accurately centered reflections in the range of
19.36ꢁ < 2h < 31.79ꢁ for 3 and 19.19ꢁ < 2h < 26.72ꢁ for
4. Intensity data were collected by using x and x ꢀ 2h
scan mode with a range of 1.32ꢁ < h < 24.97ꢁ for 3 and
1.34ꢁ < h < 24.99ꢁ for 4, respectively. All the intensity
data were corrected for Lorentz and polarization effects.
The structures were solved by semi-invariant direct
method (SIR 92 in MoleN) [15] and refined by full ma-
trix least-squares refinement (SHELXL 93) [16] with
anisotropic thermal parameters for all non-hydrogen
atoms. Hydrogen atoms were placed at their geometrically
2.1. General procedures
All operations were performed under an inert dinitro-
gen atmosphere using standard Schlenk and glove box
techniques. THF, toluene, and n-hexane were distilled
from Na–K alloy, Et2O from Na-benzophenone ketyl,
and CH2Cl2 from CaH2. Chemicals were used without
any further purification after purchasing from Aldrich
(4-Bromobiphenyl, n-butyllithium (2.5 M solution in n-
hexane), para-toluenesulfonic acid monohydrate (p-
TsOH Æ H2O)), and Strem (CpZrCl3 and Cp*ZrCl3
k1
k-1
Zr
Zr
P
P
1
1
rac-like
meso-like
y
x
n
atactic
isotactic
Fig. 1. Elastomeric polypropylene from (2-PhInd)2ZrCl2 (1).

1242
M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
calculated positions and refined riding on the corre-
sponding carbon atoms with isotropic thermal parame-
ters. Final refinement based on the reflections
(I > 2.0r(I)) converged at R1 = 0.0768, wR2 = 0.1411
Hydrogen atoms were placed at their geometrically cal-
culated positions and refined riding on the correspond-
ing carbon atoms with isotropic thermal parameters.
Final refinement based on the reflections (I > 2.0r(I))
and GOF = 1.112 for
3
and at R1 = 0.0451,
converged
at
R1 = 0.0298,
wR2 = 0.0771
and
wR2 = 0.1018 and GOF = 1.050 for 4. All calculations
were performed on a Silicon Graphics Indigo2XZ
workstation. The detailed data for 3 and 4 are listed in
Table 1.
GOF = 1.076 for 5. All calculations were performed
on a Pentium computer. The detailed data for 5 are
listed in Table 1.
2.3. Ethylene polymerization
2.2.2. Crystal structure of 5
X-ray diffraction measurements were performed on a
Bruker AXS diffractometer with a CCD area detector,
using graphite-monochromated Mo Ka radiation
Into a well-degassed 250-mL glass reactor was
charged with freshly distilled toluene (49 mL) and
MMAO (0.5 mL, Al/Zr = 1000, Akzo), and the temper-
ature was adjusted to a constant (25 and 50 ꢁC) using an
external bath. Ethylene monomer was then saturated at
1 bar with vigorous stirring after degassing with it sev-
eral times. Polymerization was started by the injection
of a toluene solution of catalyst (1.0 mL, 1.0 lmol). A
formation of a white slurry and a rapid consumption
of ethylene were observed. All the reactions were
quenched by pouring the reaction mixture into the 50
mL of 10% HCl solution of MeOH, and the resulting
polyethylene was further precipitated by the addition
of 200 mL of MeOH after the given reaction time in Ta-
ble 3. After stirring for 1 h, polyethylene was filtered off
˚
(k = 0.71073 A) at 293 K. Cell parameters and orienta-
tion matrices were obtained from a set of 20 data
frames, followed by a least-squares refinement. A hemi-
sphere of data was collected using x scans. The frame
data sets were processed using the SAINT and XPREP
processing package. An empirical absorption correction
was applied to each data set with the program SADABS
.
All the intensity data were corrected for Lorentz and
polarization effects. The structure was solved by direct
methods and refined by full matrix least-squares meth-
ods using the SHELXTL program package with aniso-
tropic thermal parameters for all non-hydrogen atoms.
Table 1
Crystallographic data and parameters for 3, 4, and 5
Compound
3
4
5
Formula
Fw
C
652.81
38H34Cl2Zr
C29H32Cl2Zr
542.69
C24H22Cl2Zr
472.56
Triclinic
Crystal system
Space group
Unit cell dimensions
Triclinic
ꢀ
Monoclinic
P21/c
ꢀ
P1
P1
˚
a (A)
13.172(3)
15.586(5)
15.644(5)
90.10(3)
99.65(3)
100.29(2)
3113.7(2)
4
16.454(3)
8.773(1)
18.989(4)
90
12.539(1)
16.030(1)
17.750(1)
71.02(0)
86.91(0)
69.19(0)
3145.9(3)
6
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
112.98(1)
90
3
˚
V (A )
2523.6(8)
4
1.428
Z
Dcalc (g/cm3)
F(0 0 0)
T (K)
l(Mo Ka) (mmꢀ1
Scan mode
1.393
1344
1.497
1440
1120
293
293
0.550
293
0.785
)
0.662
x/2h
1.34; 24.99
x
1.32; 24.97
x
h Range (ꢁ)
Number of unique reflections
1.55; 28.06
14,137
11,133
736
8452
4765
3957
3222
Number of observed reflections (I > 2r(I))
Number of parameters refined
747
296
a
R1
0.0768
0.1411
1.112
0.0451
0.1018
1.050
0.0298
0.0771
1.076
b
wR2
GOF
Minimum and maximum deflections (e A
ꢀ3
˚
)
.
ꢀ0.647; 0.637
ꢀ0.451; 0.796
ꢀ0.623; 0.458
P
P
a
R1 = |Fo| ꢀ |Fc|/ |Fo|.
P
P
2
2 1=2
b
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁꢁ

M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
1243
and washed with MeOH several times, and then dried
under vacuum overnight at 60 ꢁC.
tion mixture was allowed to warm to room temperature
and stirred overnight. The reaction was stopped by the
addition of 30 mL of saturated aqueous solution of
NH4Cl, and the organic portion was separated. The
aqueous layer was further extracted with diethyl ether
(30 mL), and the combined organic portions were dried
over MgSO4, filtered and evaporated to dryness, afford-
ing a colorless oily product. The crude product was
redissolved in CH2Cl2 (30 mL), and then a catalytic
amount of p-TsOH (ca. 0.1 g) was added into the solu-
tion at room temperature. Immediate white precipita-
tion was observed, and the stirring was further
continued for about 30 min. A volume of the resulting
reaction mixture was reduced to 10 mL, and 30 mL of
n-hexane was poured in to the flask in order to precipi-
tate the product. A large amount of a white shimmering
solid formed was filtered on a glass frit and successively
washed with ethanol (20 mL), diethyl ether (20 mL) and
n-pentane (30 mL). Drying in vacuo gave 3.27 g of a
2.4. Propylene polymerization
Into a well-degassed 250-mL glass reactor, freshly
distilled toluene (45 mL) was transferred via cannula.
Subsequently, 2.5 mL of a toluene solution of MMAO
(Al/Zr = 1000, Akzo) was syringed into the reactor.
The temperature was then adjusted to a constant (0
and 20 ꢁC) using an external bath, and propylene was
saturated at 1 bar with vigorous stirring after degassing
with it several times. After pre-saturation of propylene
for 30 min at 0 ꢁC and 15 min at 20 ꢁC, respectively,
polymerization was started by the injection of a toluene
solution of catalyst (2.5 mL, 5.0 lmol). Initial color
change of the reaction mixture was observed. For the
entry 1 in Table 4, the reaction was quenched by the
addition of 5 mL of 10% HCl solution of MeOH after
1 h. The resulting solution was then washed with 50
mL of aqueous solution of 6 N HCl. The organic layer
was separated, and the toluene was evaporated. The vis-
cous polymer residue was finally dried under vacuum
overnight at 60 ꢁC. For the entries 2, 3, and 4 in Table
4, the reactions were stopped by the addition of 10 mL
of MeOH after 30 min. The polymer products were pre-
cipitated by adding 10% HCl solution of MeOH (50 mL)
followed by 200 mL of MeOH. After stirring for 1 h,
polypropylene was filtered off and washed with MeOH
several times, and then dried under vacuum overnight
at 60 ꢁC.
1
white solid of 2 in 66% yield. H NMR (400.13 MHz,
CDCl3): d 7.60 (d, 2H), 7.52 (dd, 4H), 7.42 (t, 2H),
7.33 (t, 1H), 6.71 (s, 1H), 3.30 (s, 2H), 2.00 (s, 3H),
1.92 (s, 3H). 13C{1H} NMR (100.62 MHz, CDCl3): d
142.0, 140.9, 138.6, 136.1, 135.6, 135.4, 131.9, 128.7,
127.1, 127.0, 126.7, 124.9, 45.2, 13.5, 12.6. Anal. Calc.
for C19H18: C, 92.64; H, 7.36. Found: C, 92.25; H,
7.28%.
2.6.2. Synthesis of Bis(1-biphenyl-3,4-
dimethylcyclopentadienyl)zirconium dichloride (3)
The slurry of 0.739 g (3.0 mmol) of 2 in 20 mL of
diethyl ether was treated with one equiv of n-BuLi (1.2
mL) at 0 ꢁC. The reaction mixture was allowed to warm
to room temperature and stirred for an additional 6 h.
The resulting reaction mixture was evaporated to dry-
ness, and the gray lithium salt of 2 was combined with
0.5 equiv of ZrCl4(thf)2 (1.5 mmol, 0.566 g). Toluene
(30 mL) was then introduced into the solid mixture at
ꢀ78 ꢁC. After allowing to room temperature, the reac-
tion mixture was heated to 50 ꢁC and stirred at this tem-
perature overnight. The yellow suspension formed was
filtered through a Celite pad, and the bright yellow fil-
trate was evaporated to dryness to give a yellow solid.
The crude product was washed twice with 10 mL of a
mixed solvent of n-hexane/diethyl ether (v/v = 9:1). Dry-
ing in vacuo afforded 0.711 g of a bright yellow solid of 3
in 73% yield. Single crystals suitable for X-ray diffrac-
tion study were grown up from the concentrated CH2Cl2
solution of 3 layered by n-hexane at room temperature.
1H NMR (400.13 MHz, CDCl3): d 7.69 (d, 4H), 7.64 (d,
4H), 7.55 (d, 4H), 7.46 (t, 4H), 7.37 (t, 2H), 6.32 (s, 4H),
1.81 (s, 12H). 13C{1H} NMR (100.62 MHz, CDCl3): d
140.2, 139.9, 132.2, 128.9, 128.4, 127.7, 127.6, 126.8,
125.6, 121.9, 116.0, 13.2. Anal. Calc. for C38H34Cl2Zr:
C, 69.91; H, 5.25. Found: C, 70.46; H, 6.00%.
2.5. Polymer analysis
13C NMR spectra of polypropylenes were recorded
on a Bruker Avance 400 spectrometer in C2D2Cl4 with
reference to the residual peak of C2D2Cl4 (d 74.14
ppm) at 80 ꢁC. Molecular weight and molecular weight
distribution of polypropylenes and polyethylenes were
determined by GPC (Waters 150C, 135 ꢁC) in 1,2,4-tri-
chlorobenzene using polystyrene columns as a standard.
Melting temperatures (Tm) of polyethylenes were mea-
sured by differential scanning calorimetry (DSC, TA
Instrument).
2.6. Synthesis
2.6.1. Synthesis of 1-Biphenyl-3,4-
dimethylcyclopentadiene (2)
A solution of 4.66 g (20 mmol) of 4-bromobiphenyl in
30 mL of diethyl ether was treated with one equiv of n-
BuLi (8 mL) at ꢀ30 ꢁC. The reaction mixture was slowly
allowed to warm to room temperature and stirred for an
additional 2 h. To the resulting lithium solution was
added 2.20 g (20 mmol) of 3,4-dimethylcyclopent-2-en-
one in 30 mL of THF via cannula at ꢀ78 ꢁC. The reac-

1244
M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
1. n-BuLi
2.6.3. Synthesis of (Cp*)(1-biphenyl-3,4-
Br
O
2.
dimethylcyclopentadienyl)zirconium dichloride (4)
0.505 g (2 mmol) of a lithium salt of 2 prepared by the
same method described above was combined with the
same equiv of Cp*ZrCl3 (0.666 g), and the mixture
was then treated with 30 mL of toluene at ꢀ78 ꢁC.
The resulting reaction mixture was allowed to warm to
room temperature and further heated at 50 ꢁC for 24 h.
After work-up similar to that for 3 except for washing
with n-hexane only, 0.875 g of a shimmering light yellow
solid of 4 was obtained in 81% yield. Recrystallization of
4 in the concentrated CH2Cl2 solution layered by n-hex-
ane at room temperature afforded single crystals suitable
for X-ray diffraction study. 1H NMR (400.13 MHz,
CDCl3): d 7.63 (dd, 4H), 7.53 (d, 2H), 7.44 (t, 2H),
7.34 (t, 1H), 6.39 (s, 2H), 2.10 (s, 6H), 1.80 (s, 15H).
13C{1H} NMR (100.62 MHz, CDCl3): d 140.3, 139.7,
132.1, 128.8, 127.9, 127.7, 127.4, 126.9, 126.8, 124.4,
121.7, 116.6, 13.6, 12.1. Anal. Calc. for C29H32Cl2Zr:
C, 64.18; H, 5.94. Found: C, 64.64; H, 5.86%.
3. p-TsOH
2, 66%
2. 1/2 ZrCl4(thf)2
ZrCl2
Toluene
50 oC/12 h
3, 73%
2. Cp*ZrCl3
1. n-BuLi
2
ZrCl2
Toluene
50 oC/24 h
4, 81%
2. CpZrCl3
ZrCl2
Toluene
r.t./36 h
5, 59%
Scheme 1.
2.6.4. Synthesis of (Cp)(1-biphenyl-3,4-
dimethylcyclopentadienyl)zirconium dichloride (5)
The mixture of 0.505 g (2 mmol) of a lithium salt of 2
and the same equiv of CpZrCl3 (0.525 g) was treated
with 30 mL of toluene at ꢀ78 ꢁC. The reaction mixture
was allowed to warm to room temperature and stirred
for an additional 36 h at this temperature. Filtration
and evaporation of the resulting yellow solution gave a
yellow solid, which was further washed with n-hexane/
diethyl ether (v/v = 1:1). Drying in vacuo afforded
0.562 g of 5 in 59% yield. Single crystals were obtained
obtained from 4-bromobiphenyl and n-BuLi with 3,4-
dimethylcyclopent-2-enone and subsequent dehydration
by p-TsOH. The resulting white solid 2 is insoluble in
hydrocarbon solvents, poorly soluble in diethyl ether,
and moderately in chlorinated solvents such as CH2Cl2
and CHCl3. The synthesis of bis-Cp0 zirconium complex
3 was achieved by the direct metallation of lithium salt
of 2 with ZrCl4(thf)2 in toluene. Mixed-ring complexes
4 and 5 were also prepared by the similar method for
3 using appropriate starting zirconium compounds in
order to investigate the ligand effects on olefin
polymerization.
1
by the similar method for 3 and 4. H NMR (400.13
MHz, CDCl3): d 7.69 (d, 2H), 7.67 (d, 2H), 7.60 (d,
2H), 7.48 (t, 2H), 7.39 (t, 1H), 6.64 (s, 2H), 6.20 (s,
5H), 2.21 (s, 6H). 13C{1H} NMR (100.62 MHz, CDCl3):
d 140.2, 140.0, 132.5, 128.9 (2C), 127.7, 127.6, 126.8,
125.6, 122.0, 116.5, 114.3, 13.8. Anal. Calc. for
C24H22Cl2Zr: C, 61.00; H, 4.69. Found: C, 60.86; H,
5.21%.
In contrast to the poor solubility of the ligand 2, all of
the complexes are well dissolved in organic solvents such
as toluene, CH2Cl2, and CHCl3, indicating that conjuga-
tion between the cyclopentadienyl ring and the biphenyl
group in 2 is partially broken after complexation. The
1
complexes were fully characterized by H, 13C NMR
spectroscopy, elemental analysis, and finally X-ray dif-
fraction method.
3. Results and discussion
3.1. Synthesis
3.2. X-ray structures
The 3,4-dimethylcyclopentadienyl (Cp0) fragment in
the ligand 2 was chosen as a steric equivalent to the inde-
nyl ring in 1. This moiety has often been used before in
the studies for the preparation of the Waymouth-type
catalysts [11a,17], while our main effort was focused
on modification of 1-position of the Cp0 ring by intro-
ducing a biphenyl group.
The molecular structures of 3, 4, and 5 are shown in
Figs. 2, 3 and 4, respectively and the listed in Tables 1
and 2 are the summaries of the detailed crystallographic
data and the selected interatomic distances and angles.
ꢀ
The complex 3 crystallizes, in space group P1, as two
independent molecules in the asymmetric unit, and both
are rac-like isomers different from the catalyst 1 that
contains both a rac-like and a meso-like isomer in the
unit cell [8]. Fig. 2 shows only one of two molecules.
The huge biphenyl groups are equally oriented away
All synthetic routes to the ligand 2 and the zirconium
complexes 3, 4, and 5 are depicted in Scheme 1. The li-
gand 2 was prepared by the reaction of biphenyllithium

M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
1245
C6
C2
C1
C3
C13
C12
C11
C7
C8
C15
C14
C16
C19
C4
Zr1
C17
C18
C5
Cl2
C9
C10
C26
Cl1
C24
C23
C22
C25
C20
C21
Fig. 2. Molecular structure of (1-Biph-3,4-Me2C5H2)2ZrCl2 (3) (front and top views). Thermal ellipsoids are drawn at the 50% probability level.
Table 2
Selected interatomic distances (A) and angles (ꢁ) for 3, 4, and 5
C6
˚
C1
C2
C18
C19
C13
C12
C11
Compound
3
4
5
C8
C14
C3
C7
Angles
C5
C4
C9
Cl1
Cl(1)–Zr(1)–Cl(2)
Cn(1)–Zr(1)–Cn(2)a
Cp0(1)–Ph(1)b
Ph(1)–Ph(2)b
98.5(1)
131.5
6.4(5)
95.1(1)
132.6
98.1(0)
131.0
3.0(1)
C10
C17
Zr1
Cl2
C15
C16
24.3(2)
29.1(2)
33.2(5)
25.1(1)
C22
C23
C20
C28
C27
Distances
Zr(1)–Cl(1)
Zr(1)–Cl(2)
Zr(1)–Cn(1)
Zr(1)–Cn(2)
a
C29
C24
C26
2.420(3)
2.430(3)
2.216(4)
2.224(5)
2.454(1)
2.437(1)
2.420(1)
2.216(1)
2.207(2)
C21
C25
2.436(1)
2.240(2)
2.229(2)
Fig. 3. Molecular structure of (Cp*)(1-Biph-3,4-Me2C5H2)ZrCl2 (4).
Thermal ellipsoids are drawn at the 50% probability level.
Cn(1) and Cn(2) are the centroids of the Cp rings of C(1–5) and
C(20–24), respectively.
b
Cp0(1); the plane of C(1–5), Ph(1); the plane of C(8–13), Ph(2); the
plane of C(14–19).
C6
C2
C1
C3
C13
C10
from the chlorine atoms, by which the molecule ideally
adopts C2-symmetry in the solid state. Interestingly,
the methyl groups of the Cp0 ring are eclipsed over the
chlorine atoms contrary to that observed in the similar
para-tolyl substituted zirconocene complex [11a].
C12
C7
C8
C4
C5
C14
C15
C19
C16
Zr1
Cl2
C18
C9
C11
Cl1
C23
Unlike the catalyst 3, the mixed-ring complexes 4 and
5 shown in Figs. 3 and 4, respectively, have no symmetry
group, exhibiting overall C1-symmetry. Especially, the
C17
C22
C21
C24
C20
ꢀ
complex 5 which also crystallizes in space group P1
abnormally contains three independent molecules in
the asymmetric unit, and two of them are the same
Fig. 4. Molecular structure of (Cp)(1-Biph-3,4-Me2C5H2)ZrCl2 (5).
Thermal ellipsoids are drawn at the 35% probability level.

1246
M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
conformers but the other one is inverted through an
inversion center in the unit. Both complexes also show
a similar orientation of the biphenyl group and the
eclipsed conformation between one methyl group of
the Cp0 ring and the chlorine atom as observed in 3.
The detailed relevant structural analysis indicates that
some important bond distances and angles for 3, 4,
and 5 (Table 2) are nearly identical or similar to those
reported for 1 and related nonbridged zirconocenes [8–
12,17,18]. When comparing the structural parameters
between three complexes, the complexes 3 and 5 show
a close resemblance in the values such as angles of
Cl(1)–Zr(1)–Cl(2) and Cn(1)–Zr(1)–Cn(2) and distances
of Zr(1)–Cl and Zr(1)–Cn(1) except for the slightly long-
3.3. Olefin polymerization
Ethylene and propylene polymerizations of the zirco-
nium complexes 3, 4, and 5 were carried out in the pres-
ence of MMAO cocatalyst in toluene solution.
According to the results of ethylene polymerization data
given in Table 3, it can be known that all the complexes
act as highly active catalysts for ethylene polymerization
at both 25 and 50 ꢁC, and furthermore these activities
are several times higher than that of the known catalyst
Cp2ZrCl2 under the same conditions. Polyethylenes pro-
duced show high melting temperature (Tm), indicating
that they are high-density polyethylene generally ob-
served in usual metallocene catalyst systems. Narrow
molecular weight distribution (Mw/Mn) also indicates
that these complexes consist of single active site
catalysts.
Among three catalysts, 4 is most active and followed
by 3 and 5 at both temperatures. However, molecular
weight of polyethylene is decreasing in the order of 3,
5, and 4. In particular, molecular weight of polyethylene
from 4 at 50 ꢁC is considerably low about 80,900 similar
to that from Cp2ZrCl2. These observations suggest that
catalytic activity correlates with the increase of an elec-
tron density at the metal center, while molecular weight
of polyethylene depends more on the steric crowding
around the metal center rather than the electronic effect
of the ligands. In this regards, the catalyst 3 meets prop-
erly for the requirement of both steric and electronic ef-
fects, affording high molecular weight polyethylenes
with high activity.
˚
er distance of Zr(1)–Cn(2) in 3 (2.224(5) A) than that in
˚
5 (2.207(2) A). Therefore, it can be seen that the intro-
duction of the ligand 2 instead of Cp ring does not influ-
ence significantly on the geometrical parameters around
the metal center. However, the values for 4 are some-
what different from those for 3 and 5; the reduced angle
of Cl(1)–Zr(1)–Cl(2), the increased angle of Cn(1)–
Zr(1)–Cn(2), and the slightly increased distances of
Zr(1)–Cl and Zr(1)–Cn. These observations are well
consistent with the consequence of an increased steric
hindrance around the metal center exerted by the bulky
Cp* group.
The small dihedral angles between the plane defined
by the biphenyl substituted Cp0 ring and the phenyl ring
adjacent to the Cp0 ring in both 3 (6.4(5)ꢁ) and 5
(3.0(1)ꢁ) are in a similar range of those found in 1 and
its derivatives [8–12,18], while the angle exceptionally in-
creased to 24.3(2)ꢁ in 4 similar to those for monophenyl
and para-tolyl substituted analogues of 3 [11a,17]. How-
ever, the dihedral angles between two phenyl rings in the
biphenyl group are not following the trend observed
above, showing relatively large values in all complexes
(Table 2). This different trend in dihedral angles can
be explained by the different steric requirements around
the metal center;
Propylene polymerization data in Table 4 show an-
other polymerization behavior of the complexes 3, 4,
and 5. The activity of 3 at 20 ꢁC is high enough to be
comparable with those of similar nonbridged zirconoc-
enes [11a,17], while the methyl pentad value [mmmm]
of the polypropylene is low, indicating that atactic poly-
propylene was produced.
In order to partly enhance the stereospecificity of
the resulting polypropylene, polymerization reactions
The nonbonded interaction between the methyl
group, especially C(28) (Fig. 3), of the Cp* ring and
the hydrogen atoms on the ortho-carbon atoms of the
phenyl ring (Ph(1)) in 4 appears to push the phenyl ring
out of the plane defined by the Cp0 ring, resulting in a
large dihedral angle. In contrast, it can be expected that
such interactions are little or weak in the sterically less
demanding 3 and 5, showing a small discrepancy of
the angle and thus being capable of the retention of an
electronic interaction between two ring planes. Because
the dihedral angle between two phenyl rings is not
directly related to the steric crowding around the metal
center, the second phenyl rings (Ph(2)) in all the com-
plexes can be distorted to the extent enough to minimize
possible nonbonded interactions between the hydrogen
atoms on the ortho-carbon atoms adjacent to the single
bond (C11–C14) linking two phenyl rings.
Table 3
Ethylene polymerization data with catalysts 3–5/MMAOa
Entry Catalyst
Tp (ꢁC) Activityb Mw
(·10ꢀ3
Mw/Mn Tm (ꢁC)
)
1
2
3
4
5
6
7
3
4
5
3
4
5
25
25
25
50
50
50
6570
10,710
4670
–
–
–
–
–
–
–
280
–
–
11,210
12,960
10,180
2430
1.77
1.78
2.33
2.42
136.0
133.5
138.0
132.4
80.9
215
73.8
Cp2ZrCl2 50
a
Conditions: P(ethylene), 1 bar; [Zr], 1.0 lmol; Solvent, 50 mL of
toluene; [Al]/[Zr], 1000.
b
Activity, kg PE/(mol of Zr) h bar.

M.H. Lee, Y. Do / Journal of Organometallic Chemistry 690 (2005) 1240–1248
1247
Table 4
Propylene polymerization data with catalysts 3–5/MMAOa
Entry
Catalyst
Tp (ꢁC)
Activityb
Mw (·10ꢀ3
)
Mw/Mn
mmmm (%)c
m (%)c
1
2
3
4
a
3
3
4
5
20
0
819
394
489
874
13.7
36.0
12.6
25.0
2.24
1.91
2.13
1.90
7.9
12.5
13.4
8.4
54.6
59.9
64.0
56.4
0
0
Conditions: P(propylene), 1 bar; [Zr], 5.0 lmol; Solvent, 50 mL of toluene; [Al]/[Zr], 1000.
Activity, kg PP/(mol of Zr)h bar.
Determined by 13C NMR spectroscopy.
b
c
were performed under low temperature, e.g., 0 ꢁC, at
4. Supplementary material
which the concentration of propylene in solution also
increases. The catalytic activities are in the range of
400–900 kg PP/(mol of Zr) h bar, and the catalyst 5 is
most active in contrast to the result in ethylene poly-
merization. The other complexes 3 and 4 show similar
activity with a slightly higher value for 4. This fact
indicates that the activity of propylene polymerization
in the given catalyst systems depends largely on the ste-
ric hindrance around the metal center as similarly ob-
served in other Waymouth-type metallocene catalyst
systems [12a]. Thus the less hindered 5 is more produc-
tive than the electron-rich 3 and 4. The molecular
weights of polypropylenes are in the order of
3 > 5 > 4. This trend is the same as is in ethylene poly-
merization, suggesting that chain transfer processes are
also much governed by the steric factor around the me-
tal center. The [mmmm] methyl pentad values indica-
tive of isotactic block length of polypropylene for 3
and 4 (Entries 2 and 3) are similar and slightly in-
creased compared with that of the polypropylene ob-
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 248935–248937 for complexes
3, 4, and 5, respectively. Copies of this information may
be obtained free of charge from the Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or Inter-
net: http://www.ccdc.cam.ac.uk).
Acknowledgement
Financial support from the Korea Science and
Engineering Foundation (R02-2002-000-00057-0) is
gratefully acknowledged.
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