2,2′-Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride complexes of Ti, Zr and Hf as catalyst precursors for ethylene polymerization

Article abstract of DOI:10.1016/j.poly.2018.01.015

ansa metallocene complexes of Ti, Zr and Hf were synthesized, characterized and tested as catalysts for homogeneous ethylene polymerization. The ligand system comprises two indenyl moieties tethered at the 1,1′-positions via a 2,2′-dimethyl biphenylene bridge. The ligand precursor was obtained by the reduction of diphenic acid using lithium aluminum hydride (LiAlH₄), followed by the reaction with phosphorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by reactions of the corresponding metal tetrachloride. After activation with methylaluminoxane (MAO), the zirconium and hafnium complexes proved as highly active catalysts for ethylene polymerization. The zirconium complex 6 showed the best performance with 12,460 kg PE/mol cat. h. The titanium complex 5 showed no catalytic activity obviously because of decomposition reactions.

Full text of DOI:10.1016/j.poly.2018.01.015

Polyhedron 144 (2018) 176–186
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
0
2
,2 -Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride
complexes of Ti, Zr and Hf as catalyst precursors for ethylene
polymerization
a
b
b
a,
⇑
Mohamed E.M. Abdelbagi , Swastik Mondal , Sander van Smaalen , Helmut G. Alt
a
Laboratorium für Anorganische Chemie, Universität Bayreuth, Postfach 101251, D-95440 Bayreuth, Germany
Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany
b
a r t i c l e i n f o
a b s t r a c t
Article history:
ansa metallocene complexes of Ti, Zr and Hf were synthesized, characterized and tested as catalysts for
homogeneous ethylene polymerization. The ligand system comprises two indenyl moieties tethered at
Received 15 November 2017
Accepted 17 January 2018
Available online 31 January 2018
0
0
the 1,1 -positions via a 2,2 -dimethyl biphenylene bridge. The ligand precursor was obtained by the
reduction of diphenic acid using lithium aluminum hydride (LiAlH ), followed by the reaction with phos-
4
phorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal
complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by
reactions of the corresponding metal tetrachloride. After activation with methylaluminoxane (MAO),
the zirconium and hafnium complexes proved as highly active catalysts for ethylene polymerization.
The zirconium complex 6 showed the best performance with 12,460 kg PE/mol cat. h. The titanium com-
plex 5 showed no catalytic activity obviously because of decomposition reactions.
Keywords:
ansa bis(indenyl) complexes
0
2
,2 -Bis(methylene)biphenylidene bridge
Titanium, zirconium and hafnium
complexes
X-ray structure
Catalytic ethylene polymerization
Ó 2018 Elsevier Ltd. All rights reserved.
1
. Introduction
The activity and stereoselectivity of a metallocene-based cata-
2. Results and discussion
2.1. Preparation of the ligand precursors 3 and 4
lyst in olefin polymerization can be significantly influenced by
slight structural variations in the bridging unit (structure property
relationship) [1–8]. In this context ansa bis(indenyl) complexes of
Ti, Zr and Hf with dimethylsilylene bridges and sterically demand-
ing 4-aryl substituents proved as highly isoselective catalyst pre-
cursors for the polymerization of propylene [9–11] and ethylene
Diphenic acid was converted to the corresponding 2,2-bis
(hydroxymethyl) biphenyl (1) according to a reported method
[14]. Reduction of diphenic acid with lithium aluminum hydride
in THF and purification by crystallization from a chilled methanol
solution gave 1 in good yield. Treatment of the diol compound 1
0
[
12,13]. In this study, the synthesis of new ansa titanocene, zir-
with phosphorus tribromide in methyl-ene chloride afforded 2,2 -
conocene, and hafnocene dichloride complexes is reported. The
title complexes comprise two indenyl or 3-methylindenyl ligands,
bis(bromomethyl) biphenyl 2 [15]. Compounds 3 and 4 were then
obtained via reactions of 2,2 -bis(bromomethyl) biphenyl 2 with
two equivalents of indenyllithium or 2-methylindenyllithium.
Both reactions were carried out in THF at ꢀ78 °C Thus the indenyl
moieties were coupled through the 3-position (Scheme 1).
0
0
0
tethered at the 1-positions, via
a
2,2 -bis(methylene)-1,1 -
biphenylidene bridge. Moreover, the catalytic behavior of the pre-
pared ansa metallocene catalysts in the homopolymerization of
ethylene was investigated after activation with methylaluminox-
ane (MAO).
2.2. Characterization of compounds 3 and 4
Compounds 3 and 4 and the intermediates were characterized
by NMR spectroscopy. The complete data are given in Table 3.
1
13
The H and C NMR spectra of compound 3 are discussed as exam-
1
ples. In the H NMR spectrum of compound 3 (Scheme 2), the four
⇑
Corresponding author.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt).
multiplet resonance signals appearing at d = 7.48–7.08 ppm
represent the 16 aromatic protons belonging to the indenyl and
https://doi.org/10.1016/j.poly.2018.01.015
277-5387/Ó 2018 Elsevier Ltd. All rights reserved.
0

M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
177
0
Scheme 1. Preparation of compounds 3 and 4 from 2,2 -bis(bromomethyl)-biphenyl.
C14, C15, C12, and C2) produce the signals at d = 130.2, 129.9,
29.7, 127.3, 125.9, 125.8, 124.4, 123.6 and 119.2 ppm. The two
signals appearing at d = 37.6 and 31.8 ppm are assigned to the
indenyl CH group carbon atoms (C1) and the benzylic carbon
Table 1
1
Selected bond lengths and bond angles of 6.
Atoms
Distance [Å]
2.4245(1)
2.4279(1)
2.6147(2)
2.5122(1)
2.4627(1)
2.4989(1)
2.5434(1)
2.5775(2)
2.6504(1)
2.6049(2)
2.4291(1)
2.4723(1)
1.5092(1)
C(23)–C(24)
Zr–Cen1
Zr–Cen2
Cen1-Cen2
1.5075(1)
2.2230(5)
2.2486(5)
4.0317(2)
Angle [°]
97.233(2)
124.566(4)
115.183(4)
123.387(4)
113.375(4)
128.734(3)
53.723(4)
79.829(5)
2
Zr–Cl(1)
Zr–Cl(2)
Zr–C(1)
Zr–C(6)
Zr–C(7)
Zr–C(8)
Zr–C(9)
Zr–C(24)
Zr–C(25)
Zr–C(30)
Zr–C(31)
Zr–C(32)
C(9)–C(10)
atoms of the bridging unit (C10).
Compounds 3 and 4 were also characterized by GC/MS (Table 3).
The mass spectrum of compound 3 is discussed as an example. The
mass spectrum of compound 3 (Scheme 4) shows the molecular
ion peak at m/z = 410 with 25% intensity. The ion with the mass
m/z = 293 and 30% intensity can be explained by the loss of one
Atoms
Cl(1)–Zr–Cl(2)
C(1)–C(9)–C(10)
C(9)–C(10)–C(11)
C(23)–C(24)–C(25)
C(22)–C(23)–C(24)
Cen1–Zr–Cen2
Cen (1) ^ Cen(2)
Ph(1) ^ Ph(2)
+
indenyl fragment [M ꢀInd] and 2H atoms. The indenyl fragments
(
+2hydrogen atoms, probably as indanyl moieties) separated from
the molecule give rise to the base peak at m/z = 117.
2.3. Synthesis of the titanium, zirconium and hafnium complexes 5–9
biphenylene bridged six-membered rings (H4–H7 and H8–H11).
The protons at the 2-position of the indenyl moieties (H2) display
the broad signal at d = 5.96 ppm (2H) while the protons at the 1-
position of the indenyl rings produce the broad signal at d = 3.68
ppm (4H). The methylene group protons of the bridging element
The bridged bis(indenyl) compound 3 was deprotonated with
two equivalents of n-butyllithium (n-BuLi) at ꢀ78 °C in diethyl
ether. Subsequently, reactions of the resulting dilithium salt of
the ligand with one equivalent of either titanium tetrachloride,
zirconium tetrachloride or hafnium tetrachloride yielded the
desired metallocene dichloride complexes 5–7. The general syn-
thesis method is illustrated in Scheme 5.
(
H3) produce the signal at d = 3.22 ppm (dd, 4H).
1
3
The C NMR spectrum for compound 3 (Scheme 3) shows three
sets of resonances: the five signals at d = 145.1, 144.4, 143.2, 141.1
and 137.2 ppm are assigned to the five quaternary carbon atoms in
the bridging biphenyl and indenyl moieties (C8, C9, C11, C16, and
C3). The CH-type carbon atoms in the molecule (C4, C5, C6, C7, C13,
For the synthesis of complexes 8 and 9, compound 3 was
deprotonated with two equivalents of n-butyllithium. A subse-
quent reaction of the resulting dilithium salt with two equiva-
0
lents of methyl iodide furnished the 1,1 -dimethyl substituted

1
78
M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
Table 2
Activities and polymer analysis results of catalysts 5–9.
Complex
No.
Activity [kg PE/mol cat. h]
Inactive
DSC
M
g
[g/mol]
D
H
m
[J/g]
T
[
m
[°C]
a]
5
6
7
8
9
–
–
Ti
Zr
Hf
Zr
Hf
Cl
Cl
Cl
Cl
Cl
Cl
12,460
3810
3010
1020
148.1
355,000
310,000
485,000
n.d.
1
0
35.0
.51
Cl
Cl
Cl
Cl
144.9
1
0
35.2
.5
145.1
1
0
35.4
.5
n.d.
ligand precursor which was transformed simultaneously to its
corresponding dilithium salt via reaction with two equivalents
of n-BuLi in diethyl ether. The desired complexes 8 and 9 were
obtained by the reactions of equimolar quantities of the
dilithium salt and zirconium tetrachloride or hafnium tetra-
chloride (Scheme 5). Attempts to synthesize the titanium com-
plex did not succeed. Attempts to synthesize the titanium,
zirconium or hafnium complexes of compound 4 did not suc-
ceed either.
spectra of complex 6 are discussed as examples. In the 1H NMR
spectrum of compound 6 (Scheme 6) the 16 aromatic protons
(H3–H6 and H9–H12) display four signals at d = 7.50 (d, 2H),
7.35–7.31 (m, 6H) 7.27–7.24 (t, 2H) and 7.22–7.17 (m, 6H) ppm.
The protons located at the 2-positions of the indenyl rings (H2)
3
generate the doublet at d = 6.08 (d, J = 3.3 Hz, 2H) ppm while
the protons at the 1-positions of the indenyl rings (H1) produce
3
the doublet at d = 5.11 (d, J = 3.3 Hz, 2H) ppm. The protons of
the methylene group (H7, H8) give the two signals at d = 4.23 (d,
J = 15.9 Hz, 2H) and 4.00 (d, J = 16.2 Hz, 2H) ppm.
1
3
2.4. Characterization of complexes 5–9
The C NMR spectrum of complex 6 (Scheme 7) shows two res-
onances at d = 141.4 and 136.2 ppm attributed to the quaternary
carbon atoms in the biphenyl bridging unit (C11 and C16). The
two signals appearing at d = 131.1 and 130.7 ppm are assigned to
C5 and C6 of the indenyl rings. The remaining quaternary carbon
atoms C8, C9 and C3 are identified with the signals appearing at
The metallocene complexes 5–9 were characterized by NMR
and mass spectroscopy (Table 4), and elemental analysis (Table 6,
see Section 3). Additionally, complex 6 was structurally character-
ized with single crystal X-ray diffraction. The 1H and C NMR
13

M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
179
Table 3
1
H, 13C NMR and MS data for compounds 1–4.
No.
1H NMR
13C NMR
MS [m/z] (%)
3
+
1
7.48 d ( J = 7.5 Hz, 2H)
140.1, 138.6 (C
129.6, 129.5, 128.1, 127.6 (CH)
62.9 (CH
q
)
196 (100) M ꢀH
165 (70)
152 (35)
2
O
7
7
4
3
.43–7.32 m (4H)
3
.15 d ( J = 7.5 Hz, 2H)
2
)
.37–4.28 t (4H)
.20 br (2H)
3
340 (2) M+
2
3
7.57 d ( J = 7.2 Hz, 2H)
139.4, 135.8 (C
130.6, 130.1, 128.6, 128.3 (CH)
32.0 (CH
q
)
+
7
7
4
4
.47–7.37 m (4H)
259 M ꢀBr (12)
3
.29 d ( J = 7.2 Hz, 2H)
2
)
179 (100)
3
.38 d ( J = 10 Hz, 2H)
3
.22 d ( J = 10 Hz, 2H)
7.48–7.45 m (2H)
145.1, 144.4, 143.2, 141.1, 137.2 (C
130.2, 129.9, 129.7, 127.3, 125.9, 125.8,124.4, 123.6, 119.2 (CH)
37.6 (Ind-CH
31.8 (CH
q
)
410 (25) M+
293 (30)
117 (100)
7
7
7
5
3
3
.34–7.27 m (8H)
.22–7.19 m (4H)
.11–7.08 m (2H)
.96 br (2H, C
.68 br (4H, C
2
)
2
)
2
-Ind)
-Ind)
1
2
.24 dd (4H, CH )
3
438 (22) M+
179 (79)
128 (100)
4
7.37 d ( J = 6.9 Hz, 2H)
146.6, 142.4, 141.2, 140.6, 137.3, 134.8 (C
129.5, 128.3, 127.5, 126.0, 125.9, 123.5, 123.0, 118.9 (CH)
42.7, 29.1 (CH
14.1 (CH
q
)
7
7
6
3
3
1
.29–7.25 m (4H)
.22–7.06 (8H)
2
)
3
.97 d ( J = 6.9 Hz, 2H)
3
)
1
.69 s (4H, C -Ind)
.34 s (4H, CH
.97 s (6H, CH
2
)
)
3
d (ppm) rel. CDCl
3
(7.24 ppm, 1H NMR and 77.0 ppm, 13C NMR) at 298 K.
Scheme 2. 1H NMR spectrum of compound 3 in CDCl
.
3
d = 127.9, 126.0, and 118.4 ppm. The signal at d = 127.8 ppm can be
assigned to the CH carbon atom C7 while the carbon atom C4 cor-
responds to the chemical shift at d = 122.8 ppm. The aromatic CH-
type carbon atoms in the biphenyl moiety (C12, C13, C14, and C15)
are associated with the signals at d = 126.6, 126.2, 125.9, and 124.9
ppm. The signal at d = 122.1 ppm is assigned to the carbon atom at
the 2-positions of the indenyl groups (C2) while the signal at d =
the ligand gives rise to the peak at m/z = 293 with 47% intensity
relative to the base peak. The base peak at m/z = 117 is generated
by indanyl fragments.
2.5. Crystal structure of complex 6
The solid state molecular structure of the zirconocene complex
6 was determined by single crystal X-ray diffraction analysis. Crys-
tals suitable for X-ray measurements were grown from a concen-
trated solution of a pentane/toluene mixture. The ORTEP view of
the molecular structure of complex 6 is displayed in Scheme 9.
Selected bond lengths and angles are collected in Table 1. A sum-
mary of crystallographic data is given in Table 5. Complete crystal-
lographic data have been deposited with the Cambridge
Crystallographic Data Centre and are available under No. CCDC
1571280. The arrangement of the two five-membered ring cen-
troids and the two chlorine atoms around the zirconium can be
1
04.7 ppm is characteristic for the carbon atom at the 1-position
of the indenyl moieties (C1). The benzylic CH carbon atoms
C10) appear at d = 30.8 ppm.
The mass spectrum of complex 7 is also discussed as an exam-
2
(
ple. In the mass spectrum of complex 7 (Scheme 8), the molecular
ion peak appears at m/z = 658 with 14% intensity. The ion with m/z
=
530 and 14% intensity can be explained by the loss of one methy-
lene-indenyl fragment from the molecule, while the peak appear-
ing at m/z = 410 with 78% relative intensity arises from the free
bis(indenyl) ligand. Further loss of one indenyl fragment from

1
80
M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
Scheme 3. 13C NMR spectrum of compound 3.
Scheme 4. Mass spectrum of compound 3.
0
0
described as a pseudo tetrahedral geometry. The two indenyl
ligands are aligned in a staggered conformation leading to an
asymmetric rac orientation. In consistence with this, the values
of the angles Cl1–Zr–Cl2 and Cen–Zr–Cen are 97.23° and 128.73°.
These values correspond to those of previously characterized
bridged metallocene complexes [9]. The bond lengths of the zirco-
nium atom with the carbon atoms vary between 2.46–2.61 and
tethered through the 3-positions via a 2,2 -bis(methylene)-1,1 -
biphenylidene bridge.
2
.43–2.65 Å for the two five-membered rings. The two phenyl rings
of the biphenyl bridge are aligned in different planes with a dihe-
dral angle of 79.8°. The value of the dihedral angle between the
two planes of the five rings centroids is 53.72° which is smaller
M
R
R
Cl
Cl
2 2 2
compared to the value known for Me Si(Ind) ZrCl (61.9°) [15].
2
.6. Ethylene polymerization studies of complexes 5–9
The catalytic activities of complexes 5–9 in the homogeneous
polymerization of ethylene were investigated after activation with
MAO (M:Al = 1:2000). The experiments were conducted at a poly-
merization temperature of 60 °C, 10 bar ethylene pressure, and in
Complexes 5–9 are ansa-metallocene dichloride complexes
of group IV metals (Ti, Zr, and Hf). The two indenyl ligands are

M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
181
Scheme 5. Synthesis of the metallocene complexes 5–9.
Table 4
1
H, 13C NMR and MS data for complexes 5–9.
No.
1H NMR
13C NMR
MS [m/z] (%)
5a
7.64–7.61 m (2H)
142.4, 141.3, 132.8 (C
131.5, 131.0, 129.6 (CH)
129.4 (C
128.8, 128.4, 128.3, 127.1, 125.8, 123.3 (CH)
120.9 (C
108.1 (CH)
32.6 (CH
)
526 M (12)
+
q
+
7
7
7
5
5
4
4
.40–7.36 m (2H)
.26–7.19 m (8H)
.18–7.12 m (4H)
.99 br (2H)
491 M ꢀCl (52)
+
q
)
455 M ꢀClꢀHCl (15)
409 ligand-H (100)
293 (90)
q
)
.12 br (2H)
.30 d (J = 15.4 Hz, 2H)
.14 d (J = 15.4 Hz, 2H)
3
2
)
6b
7.50 d ( J = 8.6 Hz, 2H)
141.4, 136.2 (C
131.1,130.7 (CH)
127.9 (C
127.8, 126.6, 126.5, 126.2 (CH)
126.0 (C
125.9, 122.8, 122.1 (CH)
118.4 (C
104.7 (CH)
30.8 (CH
)
570 M+ (45)
410 ligand (100)
293 (67)
q
7
7
7
6
C
5
C
4
4
.35–7.31 m (6H)
.27–7.24 t (2H)
.22–7.17 m (6H)
q
)
117 (96)
3
.08 d ( J = 3.3 Hz, 2H,
q
)
2
-Ind)
3
.11 d ( J = 3.3 Hz, 2H,
-Ind)
q
)
1
.23 d (J = 15.9 Hz, 2H)
.00 d (J = 16.2 Hz, 2H)
2
)
7a
7.52–7.49 m (2H)
142.1, 137.0 (C
131.7, 131.2, 128.3, 127.0, 126.9, 126.5, 126.3 (CH)
126.2 (C
123.3, 122.2 (CH)
)
658 M+ (14)
529 (14)
410 ligand (78)
293 (47)
q
7
7
7
6
5
4
4
.40–7.38 m (2H)
.28–7.21 m (8H)
.17–7.12 m (4H)
.10 d ( J = 3.4 Hz, 2H)
.02 br (2H)
q
)
3
118.6, 116.5 (C
101.8 (CH)
q
)
117 (100)
.29 d (J = 16 Hz, 2H)
.15 d (J = 16 Hz, 2H)
2
31.1 (CH )
8a,c
7.85–6.76 m (16H, Ar-H)
141.5, 138.3, 136.7 (C
133.0, 131.1, 129.5 (CH)
129.1 (C
127.7, 126.1, 125.8, 124.3, 123.0, 119.8 (CH)
117.0, 114.5 (C
4.3 (CH
)
599 M (5)
+
q
+
6
4
4
2
.35 s (2H)
.54 d (J = 15.8 Hz, 2H, CH
.03 d (J = 15.8 Hz, 2H, CH
527 M ꢀ2Cl (13)
+
2
)
)
q
)
437 M ꢀZrCl
307 (33)
2
ꢀH (22)
2
.21 br (6H, CH
3
)
q
)
131 (100)
3
2
)
(
continued on next page)

1
82
M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
Table 4 (continued)
No.
1H NMR
13C NMR
MS [m/z] (%)
2
1.8 (CH
144.0, 140.1, 137.7 (C
134.8, 132.1, 130.1 (CH)
129.0 (C
128.8, 126.9, 126.4, 124.9, 123.5, 121.0 (CH)
117.3, 115.9 (C
3
)
9a,c
7.95–7.08 m (8H, Ar-H)
n.d.
q
)
6
4
4
2
.85 s (1H)
.58 d (J = 16.3 Hz, 1H, CH
.07 d,(J = 16.3 Hz, 1H, CH
.32 br (3H, CH
2
)
2
)
q
)
3
)
q
)
3
2
4.7 (CH
2.0 (CH
2
)
)
3
a
2 2
d (ppm) rel. CD Cl
(5.30 ppm, 1H NMR and 54.0 ppm, 13C NMR) at 298 K.
b
d (ppm) rel. CDCl
3
(7.24 ppm, 1H NMR and 77.0 ppm, C NMR) at 298 K.
13
Table 5
Crystal data for complex 6.
relevant ansa-metallocene catalysts, there is a good correlation
between the catalytic activity of the ansa-catalysts and their dihe-
dral angles. The dihedral angle of complex 6 is 53.7° (Table 1)
Formula
32 24
C H Cl2Zr
570.70
293
M
r
which is smaller than that of the CH
Me C-bridged metallocene complexes (70.9°). However, catalyst
/MAO exhibited higher catalytic activity (12,460 kg PE/mol cat.
h) than the CH -bridged catalyst (6900 kg PE/mol cat. H) [18]
and the Me C-bridged catalyst (10,000 kg PE/mol cat. h) [18]. This
2
-bridged (72.4°) and the
T (K)
Space group
a (Å)
2
1
I4 /a, tetragonal
6
26.045(2)
14.9997(10)
10175.1(13)
16
1.490
0.71069
0.662
c (Å)
2
3
V (Å )
2
Z
D
could be originated to the thermal instability of the single carbon
atom bridged metallocene complex. Moreover, catalyst 6/MAO
produces a polyethylene with higher molecular weight compared
with the above mentioned single carbon atom bridged metallocene
complexes. Additionally, catalyst 6/MAO showed a better catalytic
performance in terms of both activity and molecular weight of the
produced polymers compared with the o-xylylene [19] and the 1,2-
bis(dimethylsilyl)ethylene-bridged [20] metallocene catalysts. The
catalytic activity performed by 6/MAO is significantly lower than
the activity reported for the unbridged catalyst (29,300 kg PE/mol
calc (g/cm3)
k (Å)
Absorption coefficient (mmꢀ1)
Crystal dimensions (mm)
0.30 ꢁ 0.28 ꢁ 0.20
ꢀ
1
[
sin(h)/k]max (Å
)
0.600
Absorption correction
Unique reflections, all
Observed [I > 3s(I)]
multiscan
4589
2054
R
int
0.125
Goodness-of-fit (GOF) (obs/all)
wR (obs/all)
(obs/all)
No. of parameters
1.59/2.00
0.0435/0.0544
0.0522/0.1801
316
2
R
1
2
cat. h) [21], the Me Si-bridged catalyst (19,870 kg PE/mol cat. H)
minimum (e Åꢀ3
[17], and the ethylidene-bridged catalyst [22] (16,500 kg PE/mol
cat. h) due to the remarkable difference in the dihedral angle val-
ues and thus the accessibility of the metal center and the space
for the growing polymer chain.
D
q
maximum
/
D
q
)
1.22/ꢀ1.46
2
50 ml of pentane for one hour. The produced polyethylene sam-
ples were analyzed by DSC and viscosimetry. The results are illus-
trated in Table 2.
3
. Experimental
The polyethylene produced with the zirconium catalyst 6/MAO
was analyzed by high temperature gel permeable chromatography,
GPC. The values of polymer molecular weights and PD are as fol-
lows; Mn = 53,944, Mw = 260,624 (g/mol); PD = 4.83.
The molecular weight distribution of the polymer sample pro-
duced with 6/MAO is shown in Scheme 10.
In the series of complexes 5–9, the zirconium catalyst 6MAO
was the most active catalyst [12,460 kg PE/mol cat. h] whereas
the hafnium catalyst 7/MAO bearing the same ligand showed
lower activity [3810 kg PE/mol cat. h]. The titanium complex 5
was inactive in ethylene polymerization under the prescribed con-
ditions. This inactivity can be attributed to the instability of Ti(IV)
complexes and their tendency to reduction to give inactive Ti(III)
species at conventional polymerization temperatures [16]. On
going from 6/MAO to the 3-methyl substituted zirconium catalyst
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
3 2 2 6 6
pentoxide. Deuterated organic solvents (CDCl , CD Cl , and C D )
for NMR spectroscopy were purchased from Euriso-Top and stored
over molecular sieves (3 Å). Argon (5.0) and ethylene (3.5) were
purchased from Riebner Company. Methylaluminoxane (10% in
toluene) was purchased from Chemtura Europe Limited
(
Bergkamen). All other starting materials were commercially
8/MAO, a marked decrease in activity is observed (from 12,460 to
available and used without further purification.
3
010 kg PE/mol cat. h). A similar decrease in activity has been
Table 6
observed when using the 3-alkyl substituted Me
2
Si-bridged cata-
Composition from elemental analysis.
lysts [Me Si(3-R-Ind) ]ZrCl [17]. In this regard. The drop in activ-
2
2
2
ity can be attributed to the increase of steric congestion around the
metal center caused by the two methyl groups at the indenyl
ligands. Across the series, changing the metal and introduction of
methyl groups proved to have no influence on the thermal proper-
ties and the crystallinities of the produced polymers. By comparing
the catalytic performance of 6/MAO with the previously reported
No.
C
exp
%
C
theor
%
H
exp
%
theor
H %
5
6
7
8
9
72.02
67.14
57.50
67.23
58.66
72.89
67.35
58.42
68.21
59.53
4.73
4.35
3.91
4.44
3.86
4.59
4.24
3.68
4.71
4.11

M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
183
Scheme 6. 1H NMR spectrum of complex 6 in CDCl
.
3
Scheme 7. 13C NMR spectrum of complex 6 in CDCl
.
3
3
.2. NMR spectroscopy
reference (d = 7.24 ppm for chloroform, d = 5.32 ppm for methy-
lene chloride, d = 7.16 ppm for benzene). In the C NMR spectra,
the chemical shift of the solvent was used as a reference (d =
1
3
NMR spectra were recorded with Bruker ARX (250 MHz), Varian
Inova (300 MHz) or Varian Inova (400 MHz) spectrometers. All
spectra were recorded at 298 K. In the H NMR spectra, the chem-
ical shift of the residual proton signal of the solvent was used as a
77.0 ppm for chloroform-d
, d = 128.0 ppm for benzene-d
given in Tables 3 and 4.
1
, d = 54.0 ppm for methylene chloride-
1
d
2
6
). A summary of the results is

1
84
M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
Scheme 8. Mass spectrum of complex 7.
3.3. GC/MS
GC/MS spectra were recorded with a Thermo FOCUS gas chro-
matograph combined with a DSQ mass detector. A 30 m HP-5 fused
silica column (internal diameter 0.32 mm, film 0.25 mm 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 min;
Heating rate: 20 °C/minute, duration: 12 min;
Final temperature: 290 °C, duration: 27 min.
3.4. Mass spectrometry
Mass spectra were recorded with a VARIAN MAT CH-7 instru-
ment (direct inlet, EI, E = 70 EV) and a VARIAN MAT 8500 spec-
trometer at the Zentrale Analytik of the University of Bayreuth.
3.5. Elemental analysis
Elemental analyses were performed with a Vario EL III CHN
instrument. Therefore, 4–6 mg of the complex were weighed into
a standard tin pan. The tin pan was carefully closed and introduced
into the auto sampler of the instrument. The values of C, H and N
were calibrated using acetamide as a standard. The results for
compounds 5–9 is compiled in Table 6.
Scheme 9. The ORTEP diagram of the complex 6, ellipsoids are drawn in a 30%
probability level. Hydrogen atoms are omitted for clarity.
Scheme 10. Molecular weight distribution curve of polyethylene produced with 6/MAO.

M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
185
3
.6. High temperature gel permeable chromatography GPC
15% sodium hydroxide solution (75 ml). Diethyl ether (100 ml)
was added and the organic phase was separated, dried over sodium
sulfate, and evaporated to dryness. The residue was purified by
The molecular weights (Mw/Mn) of the ethylene polymers were
0
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
crystallization from methanol at ꢀ20 °C to afford 2,2 -bis(hydrox-
ymethyl) biphenyl 1 as yellow crystals in 60% yield. A solution of
compound 1 (10 mmol) in methylene chloride (70 ml) was cooled
to 0 °C and phosphorus tribromide (30 mmol) was added dropwise
via a syringe. The reaction mixture was stirred at room tempera-
ture for 12 h and washed with distilled water (3 ꢁ 100 ml). After
drying of the methylene chloride phase over sodium sulfate, the
(
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 = 510–3,100,000 g/mol) standards. The reported
values are the average of at least two independent determinations.
0
solvent was removed by evacuation to afford 2,2 -bis(bro-
3.7. DSC analysis
momethyl) biphenyl as a yellow powder in 80% yield.
Differential scanning calorimetry experiments were conducted at
0
3
2
.10.2. Preparation of 2,2 -bis(inden-3-ylmethyl) biphenyl (3), and
a heating rate of 10 °C/min under N
2
atmosphere with a Mettler
0
,2 -bis(2-methylinden-3-ylmethyl) biphenyl (4)
An amount of 24 mmol of n-butyllithium (1.6 M in hexanes)
was added dropwise to a solution of indene or 2-methylindene
24 mmol) in 100 ml of THF at 0 °C. The resulting mixture was stir-
Toledo DSC/SDTA 821e instrument. 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
Liquid nitrogen was used as a cooling medium. Melting enthal-
pies and melting points were taken from the second heating phase.
The values were calibrated using indium as a standard (m.p.
(
red at room temperature for 3 h and cooled to ꢀ40 °C. To this mix-
0
ture was added a solution of 2,2 -bis(bromomethyl)biphenyl (2)
(
12 mmol) in 40 ml of THF and the mixture was stirred over night
4
m
29.78 K, H = 28.45 J/g).
at room temperature. After removal of the solvent under vacuum,
distilled water was added and an extractive workup was per-
formed by adding methylene chloride (3 ꢁ 100 ml). Drying of the
organic phase over sodium sulfate and removal of the solvent
under vacuum gave the crude product as yellow powder. The pure
product was obtained as shining yellow crystals upon crystalliza-
tion from a methylene chloride/pentane mixture in 75% yield.
3
.8. Viscosimetry analysis
Viscosimetry analyses for the determination of the viscosity
average molecular weights [M ] of the polyethylene samples were
g
performed on an Ubbelohde precision capillary 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 dec-
3
.10.3. General synthesis of the transition metal complexes 5–7
An amount of 2 mmol of 2,2 -bis(inden-1-ylmethyl) biphenyl
3) was dissolved in 50 ml of diethyl ether. To this solution, n-
butyllithium (4 mmol, 1.6 M in hexanes) was added dropwise at
78 °C. The solution was allowed to come to room temperature
g
alin (45 ml) by heating for 3 h at 135 °C. M values were deter-
0
mined by comparing the obtained values with calibration curves
available for different polymer concentrations.
(
ꢀ
3
.9. Single crystal X-rays diffraction
and stirred for 3 h. This solution was then added to titanium tetra-
chloride (2 mmol), zirconium tetrachloride (2 mmol), or hafnium
tetrachloride (2 mmol), respectively, suspended in 50 ml of diethyl
ether at ꢀ78 °C. The corresponding mixture was slowly allowed to
come to room temperature and stirred for 24 h. The solvent was
evaporated to dryness and an amount of 100 ml of toluene was
added. The toluene suspension was filtered, the volume of the fil-
trate was reduced and the complexes were precipitated by the
addition of n-pentane. After filtration, the precipitate was washed
several times with n-pentane and dried by evacuation to obtain the
desired complexes 5–7 as yellow powders in 60–65% yields. Com-
plex 6 afforded shining cubic crystals suitable for X-ray diffraction
analysis upon crystallization from a toluene/pentane mixture.
The crystal structure of the complex 6 has been determined by
single-crystal X-ray diffraction of the yellow crystals on a MARIP
MAR345DTB diffractometer equipped with Mo K radiation. Data
a
processing has been performed with the software EVAL15 and
SADABS. Structure solution and refinement has been done with
SUPERFLIP and JANA2006. Complete crystallographic data have been
deposited with the Cambridge Crystallographic Data Centre and
are available under No. CCDC 1571280. A summary of the crystal
data is given in Table 5.
3
.10. Polymerization of ethylene
Few milligrams of the complexes were dissolved or suspended
3.10.4. General synthesis of the transition metal complexes 8 and 9
An amount of 4 mmol of n-butyllithium (1.6 M in hexanes) was
added to 2 mmol of 2,2 -bis(inden-1-ylmethyl) biphenyl (3) dis-
in toluene (5–10 ml) and mixed with the appropriate amount of
methylaluminoxane (MAO). The activated complexes were sus-
pended in pentane (250 ml) in a 1 l Schlenk flask and then trans-
ferred under argon to a 1 l 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.
0
solved in 50 ml of diethyl ether at ꢀ78 °C. After stirring for further
3 h at room temperature, the solution was cooled to ꢀ78 °C and an
amount of 4 mmol of methyl iodide was carefully added. The solu-
tion was allowed to come to room temperature and stirred for one
hour. Then it was cooled again to ꢀ78 °C and an amount of 4 mmol
of n-butyllithium was added. After stirring at room temperature
overnight, the solution was transferred to a suspension of zirco-
nium tetrachloride (2 mmol) or hafnium tetrachloride (2 mmol)
in 50 ml of diethyl ether at ꢀ78 °C. The mixture was allowed to
come to room temperature slowly and it was stirred for further
24 h. Diethyl ether was evaporated and toluene (100 ml) was
added. The toluene suspension was filtered, the volume of the fil-
trate was reduced and the complexes were precipitated by addi-
tion of n-pentane. After filtration, the precipitate was washed
0
3
.10.1. Preparation of 2,2 -bis(bromomethyl) biphenyl (2)
A solution of diphenic acid (7.74 g, 32 mmol) in 40 ml of THF
was added over 40 min to a suspension of lithium aluminum
hydride (2.508 g, 66.0 mmol) and 50 ml THF at 0 °C. After the addi-
tion, the flask contents were heated under reflux over night. Then,
the reaction was carefully hydrolyzed with water (75 ml) and a

1
86
M.E.M. Abdelbagi et al. / Polyhedron 144 (2018) 176–186
several times with n-pentane and dried by evacuation to obtain the
desired complexes 8 and 9 as yellow powders in 40–55% yields.
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4
. Conclusions
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[
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merization of ethylene after the activation of the catalyst
precursor with MAO confirms that zirconium as a metal gives the
best performance in terms of catalyst activity and molecular
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temperatures.
[
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