1,2-Bis(dimethylsilyl)phenylidene bridged zirconocene and hafnocene dichloride complexes as precatalysts for ethylene polymerization

Article abstract of DOI:10.1016/j.jorganchem.2017.11.010

The synthesis and characterization of a new class of ansa bis(indenyl) complexes of zirconium and hafnium is described. Two indenyl moieties are linked at the 1-,1′-positions via a 1,2-bis(dimethylsilyl)benzene unit. The ligand precursor was prepared via

Full text of DOI:10.1016/j.jorganchem.2017.11.010

Accepted Manuscript
1,2-bis(dimethylsilyl)phenylidene bridged zirconocene and hafnocene dichloride
complexes as precatalysts for ethylene polymerization
Mohamed E.M. Abdelbagi, Wolfgang Milius, Swastik Mondal, Sander van Smaalen,
Helmut G. Alt
PII:
S0022-328X(17)30651-4
10.1016/j.jorganchem.2017.11.010
JOM 20175
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 2 July 2017
Revised Date: 11 October 2017
Accepted Date: 9 November 2017
Please cite this article as: M.E.M. Abdelbagi, W. Milius, S. Mondal, S. van Smaalen, H.G. Alt,
1,2-bis(dimethylsilyl)phenylidene bridged zirconocene and hafnocene dichloride complexes as
precatalysts for ethylene polymerization, Journal of Organometallic Chemistry (2017), doi: 10.1016/
j.jorganchem.2017.11.010.
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ACCEPTED MANUSCRIPT
1,2-Bis(dimethylsilyl)phenylidene bridged zirconocene and hafnocene dichloride
complexes as precatalysts for ethylene polymerization
Mohamed E. M. Abdelbagi, Wolfgang Milius, Swastik Mondal, Sander van
*
Smaalen, Helmut G. Alt
Laboratorium für Anorganische Chemie, Universität Bayreuth
Postfach 101251, D-95440 Bayreuth, Germany
Keywords:
-
-
-
-
-
ansa Bis(indenyl) complexes
Bis(dimethylsilyl)phenylidene bridge
Zirconium and hafnium complexes
X-ray structures
Catalytic ethylene polymerization
*
Corresponding author: Tel.: +49 921 43864.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt)

ACCEPTED MANUSCRIPT
Abstract
The synthesis and characterization of a new class of ansa bis(indenyl) complexes of
zirconium and hafnium is described. Two indenyl moieties are linked at the 1-,1’-
positions via a 1,2-bis(dimethylsilyl)benzene unit. The ligand precursor was prepared
via three reaction steps including Grignard coupling of chlorodimethylsilane and 1,2-
dibromobenzene, PdCl -catalyzed chlorination, and the reaction with indenyllithium. The
2
zirconium and hafnium complexes were obtained by deprotonation of the corresponding
4
bis-(indenyl) compound with n-BuLi followed by metalation reactions of MCl (M = Zr,
Hf) in tetrahydrofuran. The solid state molecular structures of both complexes were
established by single crystal X-ray diffraction analyses. In ethylene polymerization
reactions, both complexes exhibited high activities. The zirconocene catalyst 4 showed
a higher activity (7610 kg PE/mol cat. h) compared to the hafnium catalyst 5 (3590 kg
PE/mol cat. h).
1. Introduction
A wide range of bridged bis(indenyl) metallocene complexes has been synthesized and
tested as catalyst precursors for olefin polymerization [1-7]. These complexes include
different bridging-type moieties. However, the most commonly used bridges are the
dimethylsilylene, ethylidene, isopropylidene, and methylene units [8, 9, 10-14]. The
structure of the bridging unit in ansa metallocene complexes has a strong influence on
the catalyst activity and the molecular weight of the generated polymers [15]. The
activity can be improved by enlarging the reaction space around the metal center,
mainly by increasing the metal-centroid distance and the dihedral angle between the
two indenyl based π-ligands. In contrast to silylene and alkylidene bridged metallocene
complexes, few examples of ansa-metallocene complexes are known containing bulky
aromatic groups as bridges. For instance, o-xylidene- and naphthylidene-bridged
catalysts have recently been synthesized and evaluated as catalysts for ethylene and
propylene polymerization after activation with MAO [16, 17]. In this context ansa

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bis(indenyl) complexes of Ti, Zr and Hf with dimethylsilylene bridges and sterically
demanding 4-aryl substituents proved as highly isoselective catalyst precursors for the
polymerization of propylene [18-20]. Herein, a synthesis of new ansa-complexes of
zirconium and hafnium is described, with two indenyl ligands linked through a 1,2-
bis(dimethylsilyl)phenylidene bridge. The catalytic behavior for ethylene polymerization
after activation with methylaluminoxane (MAO) in homogeneous solution is described.
Si
Si
M
Cl
Cl
M = Zr, Hf
Scheme 1: General structural formula of the prepared metallocene complexes.
2. Results and discussion
2.1. Synthesis of the ligand precursor
1,2-Bis(inden-1-yldimethylsilyl)benzene 3 was prepared via a three step reaction that
comprises Grignard coupling of 1,2-dibromobenzene with chlorodimethylsilane to give
,2-bis(dimethylsilyl)benzene (1), followed by chlorination with carbon tetrachloride in
1
the presence of a catalytic amount of palladium dichloride to obtain 1,2-
bis(chlorodimethylsilyl)benzene (2) [21]. The desired compound was readily prepared
by the reaction of compound 2 with two equivalents of indenyllithium (prepared
separately via reaction of indene and n-butyllithium in ether) (Scheme 2). This reaction
was necessarily conducted in ether at room temperature. If another solvent such as
tetrahydrofurane (THF) is used, the undesired monoindenyl spiro compound is formed
as a side product. This proceeds by deprotonation at the C1-position in the already silyl
bonded indene followed by an intramolecular reaction with the chlorine atom of the
same molecule leading to the formation of the cyclic mono substituted indenyl derivative
3
with a sp - hybridized carbon atom. Compound 3 was initially obtained with trace

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amounts of the monoindenyl substituted derivative as side product. Thus, the purity was
improved via prolonged evacuation at elevated temperatures.
Scheme 2: Three-step synthesis of compound 3.
2.2. Characterization of compound 3
1
13
Compound 3 was characterized by H NMR, C NMR and GC/MS (Experimental, Table
1
4
). The H NMR spectrum of compound 3 (Scheme 3) shows multiplet signals at δ =
7.76-7.73 (m, 2H), 7.50-7.46 (m, 2H), 7.29-7.26 (m, 4H) and 7.14-7.09 ppm (m, 4H) for
the aromatic protons of both the bridge and the indenyl moiety (H10, H11, H4, H5, H6
3
and H7). The two signals appearing at δ = 6.96 (d, J(H,H) = 5.2 Hz, 2H) and 6.57 ppm
(
dd, 2H) can be assigned to the protons at the 3- and 2-positions of the indenyl moiety
H3 and H2). The protons at the 1-positions of the indenyl moieties (H1) produce the
(
signal at δ = 4.00 ppm (s, 2H) while the silyl protons H8 and H9 appear as singlets at δ
0.19 (s, 6H) and 0.21 ppm (s, 6H) indicating slightly different magnetic environment.
=

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1
Scheme 3: H NMR spectrum of 3 in C D .
6
6
13
The C NMR spectrum of compound 3 (Scheme 4) shows three resonance signals at δ
145.0, 144.4 and 144.0 ppm attributed to the quaternary carbon atoms C8, C9, and
=
C12. The two signals at δ =136.2 and 135.7 ppm correspond to C2 and C3 of the
indene five membered ring, while the CH–type carbon atoms in the indenyl moiety (C4,
C5, C6 and C7) give signals at δ =129.7, 125, 123.6, and 123.0 ppm. The two signals at
δ =128.3 and 121.0 ppm can be assigned to the carbon atoms of the phenyl ring (C13
and C14). The carbon atom at the 1-position of the indenyl ligand (C1) shows a signal at
δ = 45.8 ppm while the silyl methyl groups (C10 and C11) show signals at δ = -1.3 and -
1.9 ppm indicating slightly different magnetic environment.

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13
6 6
Scheme 4: C NMR spectrum of 3 in C D
The mass spectrum of 3 (Scheme 5) shows the molecular ion peak at m/z = 422 with
+
8
8% intensity. The ion formed by the loss of one indenyl unit [M -indenyl] generates the
peak at m/z = 306 (intensity 45%) while the loss of two indenyl units from the molecule
gives rise to the base peak at m/z = 191.

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Scheme 5: Mass spectrum of compound 3.
2.5. Synthesis of 1,2-phenylene-bis(inden-1-yldimethylsilyl) complexes of zirconium (4)
and hafnium (5)
The 1,2-phenylidenedisilyl bridged bis(indenyl) complexes of zirconium and hafnium
were synthesized by a method that comprises the deprotonation of the bridged
bis(indenyl) compound 3 with two equivalents of n-butyllithium (n-BuLi) in ether at -
78°C. A subsequent reaction of the resulting dilithium salt with one equivalent of
zirconium (IV) chloride or hafnium (IV) chloride in THF at -78°C afforded the
mononuclear zirconocene dichloride complex 4 and the hafnocene dichloride complex
4 4
5. The general synthetic method is illustrated in Scheme 6. Reactions of ZrCl and HfCl
with the ligand precursor 3 proceeded successfully to afford the corresponding ansa
metallocene complexes. However, the reaction of TiCl with compound 3 under various
4
reaction conditions was not successful.

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Scheme 6: Synthesis of complexes 4 and 5.
.6. Characterization of the complexes 4 and 5
2
1
13
The synthesized metallocene dichloride complexes were characterized by H NMR, C
NMR, mass spectroscopy (Experimental, Table 5), and elemental analysis. The
molecular structures of both complexes were determined with single crystal X-ray
diffraction (Schemes 10 and 11).
1
13
1
The H and C NMR spectra of complex 4 are discussed as examples. The H NMR
spectrum of complex 4 (Scheme 7) shows a multiplet at δ = 7.99-7.97 ppm (2H) which
is assigned to the aromatic protons H13. The overlapping signal appearing at δ = 7.59-
7.53 ppm (m, 6H) can be assigned to the protons H14, H4 and H7 while the multiplet
signal appearing at δ = 7.23-7.20 ppm (m, 4H) is attributed to the protons H5 and H6 at
the six-membered ring of the indenyl ligands. The protons at the 3- and 2-positions of
the indenyl moieties (H3 and H2) are characterized by the signals at δ = 6.56 ppm (br,
2H) and δ = 5.72 ppm (br, 2H) The methyl groups (H10 and H11) produce two singlets
at δ = 0.70 (6H) and δ = 0.61 ppm (6H) indicating different magnetic environments.

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1
Scheme 7: H NMR spectrum of the complex 4 in CDCl
3
13
The C NMR spectrum for complex 4 (Scheme 8) shows a signal at δ = 143.5 ppm
corresponding to the quaternary carbon atom C12. The aromatic carbon atoms C13 and
C14 give the two signals at δ =136.7 and 129.4 ppm. The two signals appearing at δ
=
132.4 and 131.9 ppm are generated by the quaternary carbon atoms of the indenyl
moiety (C8 and C9). The signal at δ =131.7 ppm is assigned to C3 while the four
resonances at 127.1, 126.9, 125.8 and 125.7 ppm are attributed to the CH-type carbon
atoms of indene C7, C4, C5, and C6. The signal which appears at δ =110.8 ppm is
assigned to C2 while the signal at δ = 107.0 ppm is characteristic for the quaternary
carbon atom C1 at the 1-position of the indenyl moiety. The two signals appearing at δ =
3.4 and 1.2 ppm are attributed to the silyl methyl groups C10 and C11 indicating a
slightly distorted molecule.

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13
Scheme 8: C NMR spectrum of complex 4 in CDCl
3
The mass spectrum of the zirconium complex 4 (Scheme 9) shows the molecular ion
peak at m/z = 582 with 62% intensity. Due to the presence of isotopes (Zr, Cl), a
.+
characteristic distribution of M peaks are observed. The ion formed by the loss of one
chloro ligand or one HCl molecule produces the peaks around m/z = 544 with 58%
intensity. The ionized ligand molecule gives a 10% intensity peak at m/z = 422, while
the loss of one indenyl unit from the ligand [ligand-Ind] produces the peak at m/z = 306
with 45% intensity. The base peak at m/z = 172 results from a fragment containing an
indenyldimethylsilyl unit.

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Scheme 9: Mass spectrum of complex 4
2.7. Crystal structures of complexes 4 and 5
Single crystals suitable for the X-ray diffraction analyses of complexes 4 and 5 were
obtained by slow solvent evaporation from concentrated solutions of pentane/toluene
mixtures in an approximately 9:1 ratio. The molecular structures of the complexes have
been established by single crystal X-ray diffraction analyses. The ORTEP diagrams of 4
and 5 are displayed in Schemes 10 and 11 Selected bond lengths and angles for
complexes 4 and 5 are presented in Tables 1 and 2, crystal data and structural
refinements in Tables 6 and 7 (Experimental).

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Scheme 10: ORTEP diagram of complex 4, ellipsoids are drawn in 30% probability
level. Hydrogen atoms have been omitted for clarity.

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Scheme 11: ORTEP diagram of complex 5, along with atom numbering scheme,
ellipsoids are drawn in 30% probability level. Hydrogen atoms are drawn as spheres
with fixed small radius. Hydrogen atom names are omitted for clarity.
Table 1: Selected Bond lengths and angles of 4
Selected bond lengths [Å]
Si(1)-C(1)
Si(2)-C(20)
Cen1-Zr
1.867(4)
1.872(4)
2.2513
2.2114
4.0520
Zr-Cl(1)
Zr-Cl(2)
Zr-C(1)
2.4230(14)
2.4398(11)
2.499(3)
Cen2-Zr
Zr-C(2)
Zr-C(7)
2.634(3)
2.654(3
Cen1-Cen2
Selected bonds angles[°]
Cl(1)-Zr-Cl(2) 96.81(5)
Zr-C(8)
2.506(4)

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Zr-C(9)
2.490(3)
2.491(3)
2.465(3)
2.479(3)
2.565(4)
2.617(4)
C(1)-Si(1)-C(12)
C(20)-Si(2)-C(17)
111.68(18)
114.49(16)
126.2(3)
Zr-C(20)
Zr-C(21)
Zr-C(22)
Zr-C(23)
Zr-C(28)
C(2)-C(1)-Si(1)
C(28)-C(20)-Si(2) 129.1(3)
Dihedral angle
Cen1-Zr-Cen2
51.36(8)
130.453
Table 2: Selected Bond lengths and angles of 5
Selected bond lengths [Å]
Si(1)-C(1)
1.868(4)
1.855(4)
2.194(4)
2.231(5)
4.024(8)
Hf-Cl(1)
Hf-Cl(2)
Hf-C(1)
Hf-C(2)
Hf-C(3)
Hf-C(4)
Hf-C(9)
Hf-C(10)
Hf-C(11)
Hf-C(12)
2.4095(14)
2.3921(14)
2.469(4)
2.449(4)
2.464(4)
2.549(4)
2.596(4)
2.473(4)
2.452(4)
2.485(4)
Si(2)-C(10)
Cen1-Hf
Cen2-Hf
Cen1-Cen2
Selected bonds angles[°]
Cl(1)-Hf-Cl(2)
95.91(4)
C(1)-Si(1)-C(23)
113.77(15)
C(10)-Si(2)-C(24) 111.32(19)
C(9)-C(1)-Si(1) 129.7(3)
C(18)-C(10)-Si(2) 125.8(3)
Hf-C(13)
Hf-C(18)
2.644(4)
2.625(4)
Dihedral angle
Cen1-Hf-Cen2
51.478(150)
130.813(10)

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The solid state crystal structure analysis shows that the metallocene dichloride
complexes 4 and 5 are isostructural and adopt a pseudotetrahedral coordination
5
geometry around the metal atom formed by two chlorine atoms and two η -coordinated
indenyl ligands. As both complexes have closely equivalent bond lengths and angles,
the following description of complex 4 is also valid for 5. One of the important features is
that the indenyl ligand planes in the molecule are twisted from being perfectly C
symmetric thus leading to a distorted rac orientation. In 4, the angle Cl(1)-Zr-Cl(2) is
6.81° which is comparable to that of the unbridged zirconocene complex Ind ZrCl
2
-
9
2
2
(
94.71°) [22] and the Me
The angle that comprises the zirconium atom and the two five membered ring planes,
Cen-Zr-Cen, is 130.45° which is larger than that of Ind ZrCl (128.3°) and the bridged
Me Si(Ind) ZrCl (127.8°). The Zr-C bond distances are different; the quaternary carbon
2 2 2 2
Si bridged metallocene complex Me Si(Ind) ZrCl (98.76°) [23].
2
2
2
2
2
atoms between the five- and six-membered rings, C(2), C(7), C(23), and C(28), are
apparently further away from the zirconium atom compared to the three remaining
carbon atoms. These two common carbon atoms are covalently bonded to three other
carbon atoms, which reduces their bonding ability to zirconium [24]. The value of the
dihedral angle between the two planes of the five ring centroids is 51.37° which is
smaller than that of Me Si(Ind) ZrCl with a difference of ∆ = 10.57°. For metallocene
2
2
2
complexes prepared for catalytic functions, the greater dihedral angle allows better
access of the monomer molecules to the cationic metal center. Therefore, catalysts with
wider dihedral angles should show comparatively higher activities. The distance
between the zirconium and the Cen1 plane is 2.2513 Å being slightly longer than the Zr-
Cen2 distance (2.2114 Å), the distance between the two centroids is 4.05 Å and the
zirconium atom is located 0.935 Å out of this Cen1-Cen2 vector.
2.9. Ethylene polymerization experiments with complexes 4 and 5
Complexes 4 and 5 are ansa bis(1-indenyl) metallocene dichloride complexes, the two
indenyl ligands are tethered via a 1,2-bis(dimethylsilyl) phenylene bridge.

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Si
Si
M
Cl
Cl
4
5
(M= Zr)
(M= Hf)
The catalytic activities of complexes 4 and 5 in the homogeneous polymerization of
ethylene along with the results of the polymer analyses are summarized in Table 3.
Methylaluminoxane (MAO) was used as a cocatalyst (M:Al = 1:2000), the experiments
were conducted at a polymerization temperature of 60°C, 10 bar ethylene pressure, and
in 250 ml of pentane for one hour. The produced polyethylene samples were analyzed
by GPC, DSC and viscosimetry.
Table 3: Ethylene polymerization activities and analyses of the polymers produced with
complexes 4/MAO and 5/MAO.
Complex
No.
DSC
a
η
M [g/mol]
M
Activity
∆Hm
J/g]
Tm
[°C]
[α]
[
4
5
Zr
Hf
7610
124.5 135.5
0.43
0.43
366000
375000
3590
124.6 135.5
a
(
kg PE/mol cat. h)
Both MAO-activated zirconium and hafnium catalysts were active in ethylene
polymerization. The zirconium catalyst 4/MAO gave a higher activity compared to the
hafnium complex derived from the same ligand while the hafnium catalyst 5/MAO
produced polyethylene with apparently higher molecular weight. This result is consistent
with the experience that zirconocene catalysts provide higher activities while the

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hafnocene analogues produce polyolefins with greater molecular weights [25]. The
difference in the polymerization behavior between Zr- and Hf-based catalysts could be
attributed to thermodynamically stronger σ-bonds between hafnium and the polymer
chain (Hf-C), slowing down not only the chain propagation but also the release of the
chain, giving rise to less activities and higher molecular weight polyethylenes [26]. In
line with this assumption, a recent study of hafnocene catalysts demonstrated that the
activation energies for chain propagation and termination are significantly higher
compared with zirconium catalysts [27]. The catalytic activity of 4/MAO in
homogeneous polymerization of ethylene is, as expected, lower, than the activities
observed for the unbridged bis-indenyl metallocene complex [28] and that of the single
atom bridged metallocene complexes such as -CH - [29,30], -Me C- [31,32], and -
2
2
2
Me Si-[33,34] bridged species. Similar results are observed when comparing the activity
of 4/MAO with the widely known ethylidene bridged catalyst precursor, [35,36] rac-
[
Et(Ind) )]ZrCl ("Brintzinger catalyst"). However, in terms of molecular weight, catalyst
2 2
4/MAO produces a polyethylene with the highest molecular weight compared with the
above mentioned catalysts (except the Me Si-bridged one). The comparatively lower
2
activity of 4/MAO can be rationalized by the existence of the 4 atoms-bridge, 1,2-
bis(dimethylsilyl)phenylene, incorporating 2 C and 2 Si atoms. This rigid and long bridge
resulted in a smaller dihedral angle and thus the zirconium center becomes more
shielded. From the crystal structure data of complex 4 (Table 1), the value of the
dihedral angle was determined to 51.4°, whereas the dihedral angles reported for CH2-,
2 2 2 4
Me C-, Me Si-, and C H -bridged metallocene complexes are 72.4°, 70.9°, 61.6° and
62.1°. A greater value of the dihedral angle between the ligand planes enhances the
activity in olefin polymerization by increasing the reaction space of the metal center [34].
Catalyst 4 exhibited a far better catalytic performance in terms of both activity and
molecular weight compared with the known metallocene catalysts comprising 4-atom-
2 2 2 2
bridges such as o-xylidene-bridge [24] and (-Me Si-CH -CH -Me Si-)-bridged [37]
catalysts. This distinction could be explained by the favourable replacement of the two
methylene groups with two dimethylsilyl groups in 4. In this context it also must be
considered that the silicon atoms in the bridge can behave as Lewis acids and interact
with the Lewis basic oxygen atoms of the MAO counter anion of the activated catalyst in

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an advantageous manner. Changing the metal centre in this catalyst system seems to
have no influence on the melting points and crystallinity values of the polyethylenes.
The polyethylene produced with the zirconium catalyst 4/MAO was analyzed by high
temperature gel permeable chromatography, GPC. The values of polymer molecular
weights and PD are as follows; M = 90116, M = 265361 (g/mole); PD = 2.94
n
w
The molecular weight distribution of the polymer sample produced with 4/MAO is shown
in Scheme 12
Scheme 12: Molecular weight distribution curve of the polyethylene produced with
4/MAO
3. Experimental
3.1 General
All reactions were carried out under an inert gas atmosphere of pure oxygen-free argon
using standard Schlenk techniques. n-Pentane, n-hexane, diethyl ether, toluene, and
tetrahydrofuran were purified by distillation over Na/K alloy. Diethyl ether was
additionally distilled over lithium aluminum hydride. Toluene was additionally distilled
over phosphorus pentoxide. Methylene chloride and carbon tetrachloride were dried
over phosphorus pentoxide. Deuterated organic solvents (CDCl , CD Cl , and C D ) for
3
2
2
6
6
NMR spectroscopy were purchased from Euriso-Top and stored over molecular sieves
3 Å). Argon (5.0) and ethylene (3.5) were purchased from Rieβner Company.
(

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Methylaluminoxane (10% in toluene) was purchased from Chemtura Europe Limited
(Bergkamen). All other starting materials were commercially available and used without
further purification.
3.2 NMR spectroscopy
NMR spectra were recorded with Bruker ARX (250 MHz), Varian Inova (300 MHz) or
1
Varian Inova (400 MHz) spectrometers. All spectra were recorded at 298 K. In the H-
NMR spectra, the chemical shift of the residual proton signal of the solvent was used as
a reference (δ = 7.24 ppm for chloroform, δ = 5.32 ppm for methylene chloride, δ = 7.16
13
ppm for benzene). In the C-NMR spectra, the chemical shift of the solvent was used
as a reference (δ = 77.0 ppm for chloroform-d
δ = 128.0 ppm for benzene-d6).
1 2
, δ = 54.0 ppm for methylene chloride-d ,
3.3 GC/MS
GC/MS spectra were recorded with a Thermo FOCUS gas chromatograph combined
with a DSQ mass detector. A 30 m HP-5 fused silica column (internal diameter 0.32
mm, film 0.25 µm and flow 1 ml/min) was used and helium (4.6) was applied as carrier
gas. The measurements were recorded using the following temperature program:
Starting temperature: 50 °C, duration: 2 minutes;
Heating rate: 20 °K/minute, duration: 12 minutes;
Final temperature: 290 °C, duration: 27 minutes.
3
.4 Mass spectrometry
Mass spectra were recorded with a VARIAN MAT CH-7 instrument (direct inlet, EI, E =
0 EV) and a VARIAN MAT 8500 spectrometer at the Zentrale Analytik of the University
of Bayreuth.
7
3.5 Elemental analysis
Elemental analyses were performed with a Vario EL ІІІ CHN instrument. Therefore, 4-6
mg of the complex were weighed into a standard tin pan. The tin pan was carefully

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closed and introduced into the auto sampler of the instrument. The values of C, H and N
were calibrated using acetamide as a standard.
3.6 High temperature gel permeable chromatography GPC
The molecular weights (Mw/Mn) of the ethylene polymers were determined by gel
permeation chromatography, HT-GPC PL-220 chromatograph at 150°C using 1,2,4-
trichlorobenzene as the mobile phase. The sample was prepared by dissolving the
polymer (0.2 mg/l) in the mobile phase solvent in an external oven and was run without
filtration. The molecular weight was referenced to polystyrene (Mw = 510 – 3100000
g/mol) standards. The reported values are the average of at least two independent
determinations.
3
.7 DSC analysis
Differential scanning calorimetry experiments were conducted at a heating rate of
0°C/min under N atmosphere with a Mettler Toledo DSC/SDTA 821e instrument.
1
2
Melting enthalpies and melting points were taken from the second heating phase. The
values were calibrated using indium as a standard (m.p. 429.78 K, H = 28.45 J/g).
m
3
.8 Viscosimetry analysis
Viscosimetry analyses for the determination of the viscosity average molecular weights
] of the polyethylene samples were performed on an Ubbelohde precision capillary
[M
η
viscometer in cis/trans-decalin at 135 ± 0.1 °C. For the preparation of the sample
solutions, an amount of 50 mg of the polymer was dissolved in decalin (45 ml) by
η
heating for 3 hours at 135 °C. M values were determined by comparing the obtained
values with calibration curves available for different polymer concentrations.
3.9 Single crystal X-rays diffraction
The crystal structure analysis of complex 4 was performed with a STOE-IPDS II
diffractometer equipped with an Oxford Cryostream low-temperature unit. The crystal
structure analysis of complex 5 was performed with a MarIP MAR345DTB devise (Mo-
Kα radiation, λ = 0.71073 Å).

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Crystal data:
Complex 4: Yellow cubic crystals, crystal system is triclinic; space group is P-1; a =
9.1925 (18) Å, b = 10.110(2) Å, c = 15.726(3) Å; α = 91.36(3)°, β = 100.26(3)°, γ =
3
3
1
11.24(3)°; volume is 1333.6(5) Å ; d (calc) = 1.451 g/cm ; wavelength = 0.71073 Å;
-1 ;
absorption coefficient = 0.718 mm
F(000) = 596; reflections collected 6271;
independent reflections 4372 [R(int) = 0.0396]; Goodness-of-fit = 0.938; R indices (R1 =
.0547, wR2 = 0.1022).
0
Complex 5: Yellow cubic crystals, crystal system is triclinic; space group is P-1;, a =
9.1624 (16) Å, b = 10.0503(18) Å, c = 15.643(3) Å; α = 91.567(19)°, β =100.285(18)°, γ
3 3
111.167(8)°; volume is 1315.0(4) Å ; d = 1.6918 g/cm ; wavelength = 0.71069 Å;
=
-1 ;
absorption coefficient = 4.276 mm
F(000) = 660; no. of all reflections 11018; no. of
observed reflections 8001 [R(int) = 0.056]; GOF (obs/all) = 1.01/-0.87; R(F) = 0.0422
wR(F) = 0.0395).
(
Crystallographic data on (4) and (5) have been deposited at the Cambridge
Crystallographic Data Centre. The data can be retrieved free of charge under numbers
CCDC 1557277 for (4) and CCDC 1557278 for (5).
3.10 Polymerization of ethylene
Few milligrams of the complexes were dissolved or suspended in toluene (5-10 ml) and
mixed with the appropriate amount of methylaluminoxane (MAO). The activated
complexes were suspended in pentane (250 ml) in a 1l Schlenk flask and then
transferred under argon to a 1l Büchi autoclave. The temperature of the thermostat was
adjusted to the desired value and an ethylene pressure of 10 bar was applied for one
hour. After releasing the pressure, the obtained polymer was filtered over a frit, washed
with dilute hydrochloric acid, water, and finally with acetone and dried under vacuum.

ACCEPTED MANUSCRIPT
3
.11. Synthesis procedures
.11.1 Preparation of 1,2-bis(chlorodimethylsilyl)benzene (2)
3
A solution of 1,2-dibromobenzene (16.5 g, 70 mmol) in 70 ml of THF was added slowly
to a stirred mixture of magnesium powder (3.7 g, 147 mmol) and chlorodimethylsilane
(14.0 g, 147 mmol) in 15 ml of THF. The mixture was refluxed for 3 hours. After cooling,
the solution was decanted from solid magnesium salts and the solvent was removed
under vacuum. The residual oil was extracted and washed with a large amount of n-
hexane. After removal of the solvent, the residue was purified by distillation under
reduced pressure to afford 1,2-bis(dimethylsilyl)benzene (1) in 60% yield. Compound 1
(20 mmol) was mixed with 40 ml of dry carbon tetrachloride and 0.2 g of palladium
dichloride in a 100 ml two necked flask equipped with a reflux condenser. The mixture
was refluxed for 3 hours and excess carbon tetrachloride and chloroform were removed
by evacuation. The residual oil was distilled at 85 °C (1 mbar) to obtain compound 2 in
90% yield.
3.11.2. General synthesis of the ligand precursor 3
An amount of 16 mmol of indene was dissolved in 70 ml of diethyl ether and cooled to -
°C. Subsequently, n-butyllithium (16 mmol) was added dropwise over 30 minutes
followed by stirring at room temperature for 2 hours. To this mixture, another solution of
,2-bis(chlorodimethylsilyl)benzene (8 mmol) in 50 ml of diethyl ether was added
5
1
dropwise from a dropping funnel equipped with a pressure equalizer. After the addition
was completed, the solution was stirred for one hour and filtered from the solid lithium
chloride. The solution was evaporated and methylene chloride (200ml) was added. After
filtration, the solvent was removed under high vacuum. Compounds 3 was obtained as
heavy brownish waxy material in 80-90% yields.
3.11.3. General synthesis of the transition metal complexes 4 and 5

ACCEPTED MANUSCRIPT
A quantity of 2 mmol of 1,2-bis(1-indenyldimethylsilyl)benzene (3) was dissolved in 50
ml of THF and cooled to -78 °C. To this solution, n-butyllithium (4 mmol, 1.6 M in
hexanes) was slowly syringed. This solution was allowed to warm to room temperature
and stirred for further 3 hours till no more gas evolution was observed. The resulting
solution was transferred via cannula to a solution of zirconium tetrachloride (2 mmol) or
hafnium tetrachloride (2 mmol) in 20 ml of THF at -78 °C. After warming to room
temperature, the mixture was subsequently stirred for 48 hours at 60-65 °C. The solvent
was removed in vacuo and toluene (100) ml was added. The toluene suspension was
filtered, the clear solution was concentrated to approximately 5 ml and the complexes
were precipitated by the addition of n-pentane. After filtration, the precipitate was
washed several times with n-pentane and dried in vacuo to obtain the desired
complexes as yellow powders in 70-75% yields. Both complexes were crystallized from
concentrated pentane/toluene mixtures to obtain yellow cubic crystals suitable for X-ray
crystallography analysis. Elemental analysis:
No.
4
C
exp
%
C
theor
%
H
exp
%
theor
H %
57.65
49.75
57.70
50.19
4.79
4.25
4.84
4.21
5
1
13
Table 4: H, C NMR and GC/MS data for compounds 1-3
1
13
No.
H NMR
C NMR
MS [m/z] (%)
+
7
7
.64-7.60 m (2H)
.44-7.38 m (2H)
144.3 (C
134.3, 128.4 (CH)
q
)
194 [M ] (10)
+
179 M -Me (46)
a
1
4.78-4.72 m (2H)
-2.6 (Si(CH
)
3
)
2
134 (100)
0.43 s (6H, Si-CH3)
3
0.41 s (6H, Si-CH )
+
7
7
0
.90-7.88 m (2H)
.47-7.45 m (2H)
.80 s (12H, Si(CH ) )
141.7 (Cq)
135.5, 129.3 (CH)
5.2 (Si(CH3)2)
247.0 M -Me (100)
+
a
211 M -HCl (38)
119 (23)
2
3
2

ACCEPTED MANUSCRIPT
+
1
45.0, 144.4, 144.0 (Cq)
422 M (88)
7
7
7
7
.76-7.73 m (2H)
.50-7.46 m (4H)
.29-7.26 m (2H)
+
136.2 (CH, C
2
3
-Ind)
-Ind)
306 M -Ind (45)
135.7 (CH, C
135 (85)
+
1
1
4
29.7, 128.3, 125.0,
23.6 123.0, 121.0 (CH)
5.8 (CH, C -Ind)
191 M -2Ind (100)
.14-7.09 m (4H)
3
b
6.96 d ( J =5.2 Hz,
3
2
6
4
0
0
H, C -Ind)
.57 dd (2H, C -Ind)
.00 s (2H, C -Ind)
.22 s (6H, Si-CH
.20 s (6H, Si-CH
1
3
-
1.3, -1.9 (Si(CH3)2)
2
1
3
)
)
3
a
b
1
13
δ
(ppm) rel. CDCl (7.24 ppm, H NMR and 77.0 ppm, C NMR) at 298 K.
3
1
13
δ
(ppm) rel. C D (7.16 ppm, H NMR and 128.0 ppm, C NMR) at 298 K.
6 6
1
13
Table 5: H, C NMR and MS data for complexes 4 and 5.
1
13
Complex
H-NMR
C-NMR
MS [m/z] (%)
+
7
7
7
6
.99-7.97 m (2H)
.59-7.53 m (6H)
.23-7.20 m (4H)
143.5 (C
136.7 (CH)
132.4, 131.9 (Cq)
131.7 (CH, C -Ind)
q
)
582 M (62)
+
544 M -HCl (58)
+
422 M -ZrCl (10)
2
.56 br (2H, C -Ind)
307 (46)
3
3
a
5.72 br (2H, C -Ind)
129.4, 127.1, 126.9,
125.8, 125.7 (CH)
172 (100)
2
4
0.70 s (6H, Si-CH
.61 s (6H, Si-CH
3
)
)
0
3
110.8 (CH, C
2
-Ind)
1
3
07.0 (C , C -Ind)
q
1
.4, 1.2 (Si(CH ) )
3
2
+
7
7
7
6
5
0
0
.98-7.95 q (2H)
.57-7.48 m (6H)
.20-7.17 q (4H)
143.7 (Cq)
136.6 (CH)
131.9 (Cq)
131.5 CH (C -Ind)
q
131.1 (C )
670 M (85)
+
634 M -HCl (10)
+
421 M -HfCl -H (30)
2
.54 br (2H, C -Ind)
172 (100)
3
3
.58 br (2H, C
2
-Ind)
a
5
.68 s (6H, Si-CH
.59 s (6H, Si-CH3)
3
)
129.4, 127.0, 126.9,
125.7, 125.5 (CH)
1
1
3
08.0 (CH, C -Ind)
2
03.8 (C , C -Ind)
q
1
3 2
.5, 1.0 (Si(CH ) )
a
)
1
13
δ
(ppm) rel. CDCl (7.24 ppm, H NMR and 77.0 ppm, C NMR) at 298 K.
3

ACCEPTED MANUSCRIPT
Table 6: Crystal data and structure refinement for 4.
Chemical formula
C H Cl Si Zr
28 28 2 2
Mr
582.80
293(2)
Temperature (K)
Space group, crystal system
P-1, Triclinic
9.1925(18)
10.110(2)
15.726(3)
91.63(3)
100.26(3)
111.24(3)
1333.6(5)
2
a (Å)
b (Å)
c (Å)
α
β
γ
(°)
(°)
(°)
3
Volume (Å )
Z
3
Density (calculated) (g/cm )
1.451
Wavelength (Å)
0.71073
0.718
-
1
Absorption coefficient (mm )
3
Crystal size (mm )
0.28 x 0.18 x 0.16
0.6170
-
1
[
sin(θ)/λ]max (Å )
Absorption correction
Unique reflections, all
observed [I > 2σ(I)]
Rint
None
4372
3350
0.0396
Completeness up to θ = 26.01°
GoF (obs/all)
83.0 %
0.938
wR2 (obs/all)
0.0956 / 0.1022
0.0398 / 0.0547
298
R1 (obs/all)
No. of parameters
-
3
∆
ρmax/ ∆ρmin (eÅ )
0.534 / -0.314

ACCEPTED MANUSCRIPT
Table 7: Crystal data for the hafnium complex 5.
Chemical formula
C H Cl Si Hf
28 28 2 2
Mr
670.10
293
Temperature (K)
Space group, crystal system
P-1, Triclinic
9.1624(16)
10.0503(18)
15.643(3)
91.567(19)
100.285(18)
111.167(8)
1315.0(4)
2
a (Å)
b (Å)
c (Å)
α
β
(°)
(°)
γ (°)
3
Volume (Å )
Z
-
3
Density (g cm )
Wavelength (Å)
1.692
0.71069
-
1
Absorption coefficient (mm )
4.276
3
Crystal size (mm )
0.3 × 0.2 × 0.2
0.8709
-
1
[
sin(θ)/λ]max (Å )
Absorption correction
Unique reflections, all
Empirical, multiscan
11018
observed [I > 3σ(I)]
8001
Rint
0.056
Completeness up to θ = 38.24°
75.8 %
GoF (obs/all)
1.61/1.79
0.0395 / 0.0663
0.0422 / 0.0446
299
wR (obs/all)
F
R (obs/all)
F
No. of parameters
-
3
∆
ρmax/ ∆ρmin (eÅ )
1.01/-0.87
Conclusions
This contribution confirms the statement for ansa metallocene catalysts: the bridge
makes the difference. On the first look, this is hard to understand because the bridge
of ansa metallocene complexes is far away from the active center. However, the
bridge has an influence on the dihedral angle the aromatic ligands are forming and
hence on the kinetics of the incoming monomer and the produced polymer chain. In

ACCEPTED MANUSCRIPT
addition, the bridge seems to interact with the bulky MAO counteranion that is formed
in the activation process of the catalyst precursor. Since the bridge of the catalyst
precursors contains the Lewis acidic heteroatom silicon, an advantageous electronic
effect of the bridge must also be considered.
Acknowledgements
The authors thank the Deutsche Akademischer Austauschdienst, DAAD, for financial
support and Dr. W.P. Kretschmer for the GPC measurements.
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