ω-Phenoxyalkyl substituted bis(indenyl)zirconium dichloride complexes as catalysts for homogeneous ethylene polymerization

Article abstract of DOI:10.1016/j.ica.2015.04.035

Nine bis(indenyl)zirconium dichloride complexes of the type [C₉H₆-(CH₂)_n-O-Ar]₂ZrCl₂ (n = 3-5; Ar = Ph, t-Bu-Ph) were synthesized, characterized, activated with methylalumoxane (MAO) and tested for ethylene polymerization. Structure-property-relationship studies showed that the activities of the catalysts depend on the length of the bridging chain between the indenyl and the phenoxy group as well as on the bulk at the phenoxy substituent. A t-Bu substituent at the ortho position of the phenoxy group (5a/MAO) gives a much higher catalyst activity (27,500 kg PE/mol cat h) than the isomer 8a/MAO with a t-Bu substituent at the para position of the phenoxy group (16,700 kg PE/mol cat h). Obviously substituents in the ortho position of the phenyl ring generate a bulkier catalyst cation and this can keep the MAO anion at a further distance to allow easier ethylene coordination and chain growth in the polymerization steps. The mono substituted bis(indenyl) complex (C₉H₇)[C₉H₆-(CH₂)₄-O-4-t-Bu]ZrCl₂ shows lower activity (11,700 kg PE/mol cat h) than 8a indicating that the electronic effect is dominating in this type of catalysts.

Full text of DOI:10.1016/j.ica.2015.04.035

Inorganica Chimica Acta 433 (2015) 63–71
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x
-Phenoxyalkyl substituted bis(indenyl)zirconium dichloride complexes
as catalysts for homogeneous ethylene polymerization
⇑
Khalil Ahmad, Helmut G. Alt
Laboratorium für Anorganische Chemie, Universität Bayreuth, Postfach 101251, D-95440 Bayreuth, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Nine bis(indenyl)zirconium dichloride complexes of the type [C9H6-(CH2)n-O-Ar]2ZrCl2 (n = 3–5; Ar = Ph,
t-Bu-Ph) were synthesized, characterized, activated with methylalumoxane (MAO) and tested for ethy-
lene polymerization. Structure–property-relationship studies showed that the activities of the catalysts
depend on the length of the bridging chain between the indenyl and the phenoxy group as well as on
the bulk at the phenoxy substituent. A t-Bu substituent at the ortho position of the phenoxy group
(5a/MAO) gives a much higher catalyst activity (27,500 kg PE/mol cat h) than the isomer 8a/MAO with
a t-Bu substituent at the para position of the phenoxy group (16,700 kg PE/mol cat h). Obviously
substituents in the ortho position of the phenyl ring generate a bulkier catalyst cation and this can keep
the MAO anion at a further distance to allow easier ethylene coordination and chain growth in the poly-
merization steps. The mono substituted bis(indenyl) complex (C9H7)[C9H6-(CH2)4-O-4-t-Bu]ZrCl2 shows
lower activity (11,700 kg PE/mol cat h) than 8a indicating that the electronic effect is dominating in this
type of catalysts.
Received 18 March 2015
Received in revised form 20 April 2015
Accepted 30 April 2015
Available online 9 May 2015
Keywords:
x
-Phenoxyalkyl substituted
bis(indenyl)zirconium dichloride complexes
Homogeneous ethylene polymerization
Polyethylene
Ó 2015 Published by Elsevier B.V.
1. Introduction
[17]. Alkoxy- and siloxy substituents are applied to immobilize
metallocene catalysts on dehydroxylated silica [35] and oxygen
During the past 30 years an enormous amount of group (IV)
metallocene complexes has been synthesized and tested for cat-
alytic ethylene polymerization reactions. The scope of this research
is mainly justified by the fact that slight modifications in the ligand
structure of such complexes can result in drastic consequences in
the catalyst performance and the properties of the produced poly-
mers [1–10]. In many cases, structure–property-relationship stud-
ies allowed the production of tailored polymers. The size and
nature of the substituents linked to cyclopentadienyl or indenyl
ligands play an important role on the catalytic activity as well as
on the molecular weight and molecular weight distributions of
the produced polyolefins. Several metallocene complexes contain-
ing functional groups linked to cyclopentadienyl or indenyl ligands
have been reported [11–34]. Donor atoms can alter the activity of a
catalyst by coordinating reversibly or irreversibly to the metal cen-
ter and block the vacant coordination site. Electron donating alkyl
groups on bis(indenyl)zirconium dichloride complexes have a
favourable effect on the ethylene polymerization activity of the
catalyst while electron withdrawing groups decrease the catalyst
activity and the molecular weight of the polyethylene produced
containing bridges are used for the synthesis of symmetric and dis-
symmetric dinuclear metallocene complexes [36–39].
We are reporting herein the synthesis and catalytic ethylene
polymerization properties of nine zirconocene dichloride com-
plexes bearing
x-phenoxyaryl substituents on the indenyl ligands.
2. Results and discussion
2.1. Synthesis and characterization of the
x-phenoxyalkyl substituted
indenes 1–9
The substituted indene compounds 1–9 were synthesized
according to Scheme 1 via a two step reaction. In the first step
the reaction of a phenol with an excess of an
a,x-dibromoalkane
in the presence of potassium carbonate and catalytic amounts of
a
x
x
crown ether (18-crown-6) under reflux conditions gave
-bromo-1-phenoxyalkanes in good yields. The reaction of
-bromo-1-phenoxyalkanes with indenyl lithium provided
x-
phenoxyalkyl substituted indene compounds in almost quantita-
tive yields.
The synthesized compounds were characterized by GC/MS and
NMR spectroscopy (Table 2). In the 1H NMR spectrum of compound
4 (Fig. 1), the signals at d = 7.56–7.53 (m, 1H), 7.50–7.47 (m, 1H),
⇑
Corresponding author. Tel.: +49 921 43864.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt).
http://dx.doi.org/10.1016/j.ica.2015.04.035
0020-1693/Ó 2015 Published by Elsevier B.V.

64
K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
R
18-crown-6
R
+
HO
K2CO3
Br
O
Br
Br
+
acetone
reflux
n
n
+
Br
O
n
R
-LiBr
O
n
Li
1 (n = 3; R = H)
2 (n = 4; R = H)
3 (n = 5; R = H)
4 (n = 3; R = 2-t-Bu)
5 (n = 4; R = 2-t-Bu)
6 (n = 5; R = 2-t-Bu)
7 (n = 3; R = 4-t-Bu)
8 (n = 4; R = 4-t-Bu)
9 (n = 5; R = 4-t-Bu)
Scheme 1. Synthesis of the indene compounds 1–9.
Table 1
2.2. Synthesis and characterization of the zirconocene dichloride
complexes
Ethylene polymerization activities and thermal analysis data for complexes 1a–9a.
Complex No.
n
R
Activitya
D
Hm [J/g] Tm [°C] Crystallinity
(kg PE/mol cat h)
(a)
The zirconocene dichloride complexes 1a–9a were synthesized
according to Scheme 2 by deprotonating the indene compounds 1–
9 with n-butyllithium followed by the reaction with zirconium
tetrachloride in an appropriate solvent.
1a
2a
3a
4a
5a
6a
7a
8a
9a
3
4
5
3
4
5
3
4
5
H
H
H
3860
9450
3380
–
–
–
–
–
–
–
–
–
0.42
0.46
0.45
0.46
0.45
0.39
2-t-Bu 16,300
2-t-Bu 27,500
2-t-Bu 7670
4-t-Bu 6670
4-t-Bu 16,700
121.9
134.3
131.2
135.1
130.7
112.9
126.3
127.7
127.2
133.2
126.3
126.0
Complexes 1a–9a were characterized by 1H and 13C NMR spec-
troscopy (Table 3) and elemental analysis (Table 4). They exist as a
mixture of rac and meso isomers, each rotamer with its own
spectrum.
4-t-
BU
9430
The 1H NMR spectrum of complex 4a (Fig. 3) shows signals at
d = 7.55–7.51 (m, 4H), 7.35–7.30 (m, 6H), 7.20–7.07 (m, 6H),
7.02–6.88 (m, 12H) and 6.62–6.55 (m, 4H) ppm for 32 protons
(rac and meso H7, H6, H5, H4, H16, H15, H14 and H13). Four sig-
nals appear at d = 6.14 (d, 3JH,H = 3.2 Hz, 2H), 5.92 (d,
D
Hm = heat of fusion, Tm = melting temperature,
a = degree of crystallinity
(1,0 = 100%).
a
Polymerization conditions: M: Al = 1: 2000; 250 mL n-pentane; 65 °C; 10 bar
ethylene pressure; 1 h.
3
3
3JH,H = 3.2 Hz), 5.50 (d, JH,H = 3.2 Hz) and 5.47 (d, JH,H = 3.2 Hz)
ppm for the indenyl protons H2 and H3 (rac and meso). The methy-
lene protons attached to the oxygen atom (H10) can be observed as
two sets of triplets at d = 3.60–3.50 (8H) ppm. Two multiplet sig-
nals at d = 3.25–3.13 (4H) and 3.05–2.93 (4H) ppm can be assigned
to rac and meso H8. The signal at d = 2.00–1.76 (m, 8H) ppm
belongs to H9. The signals for the tertiary butyl groups (H18)
appear at d = 1.56 (s, 18H) and 1.52 (s, 18H) ppm.
7.41–7.37 (m, 2H), 7.32–7.22 (m, 2H) and 7.00–6.92 (m, 2H) ppm
derive from the aryl protons H7, H6, H5, H4, H16, H15, H14 and
H13. The signal at d = 6.34 (br, 1H) ppm is assigned to H2, while
the signal at d = 4.14 (t, 3JH,H = 6.2 Hz, 2H) ppm is due to the methy-
lene group attached to the oxygen atom (H10). The protons of the
indenyl CH2 group appear at d = 3.42 (br, 2H) ppm. The signals at
d = 2.93–2.87 (m, 2H) and 2.36–2.28 (m, 2H) ppm can be assigned
to the methylene protons H8 and H9. The methyl protons of the
tertiary butyl group can be observed at d = 1.57 (s, 9H) ppm.
The J-modulated 13C NMR spectrum of compound 4 (Fig. 2)
shows positive signals for CH and CH3 groups and negative signals
for CH2 groups and Cquart. Comparisons with similar bis(indenyl)
complexes proved the following signal assignments: The signal
for the quaternary carbon atom C11 arises at d = 157.8 ppm, while
the signals at d = 145.2, 144.5 and 143.6 ppm can be assigned to
the indenyl quaternary carbon atoms C7a, C3a and C3. The signal
at d = 137.9 ppm belongs to the quaternary carbon atom C12. The
signals at d = 128.2, 127.0, 126.6, 126.0, 124.6, 123.8, 120.1 and
118.9 ppm can be assigned to the CH groups C15, C14, C13, C7,
C6, C5, C4 and C2. At d = 111.7 ppm, the signal for the aryl CH car-
bon atom C16 can be observed. The signal for the CH2 carbon atom
C10 arises at d = 67.1 ppm, while the signals at d = 37.7, 34.8 and
29.9 ppm derive from C1, C17 and C18. The signals at d = 28.0
and 24.8 ppm can be assigned to the alkyl chain carbon atoms C8
and C9.
The J-modulated 13C NMR spectrum of complex 4a (Fig. 4)
shows two sets of signals for both rac and meso isomers. Only
one set of signals will be described here. The signal for the qua-
ternary carbon atom C11 appears at d = 158.0 ppm. At
d = 138.0 ppm the signal for the quaternary carbon atom C12
shows up. The signals for the indenyl quaternary carbon atoms
C7a, C3a and C1 appear at d = 127.4, 126.4 and 122.4 ppm. The
signals at d = 127.3, 127.0 and 120.8 ppm can be assigned to the
CH carbon atoms C13, C14 and C15. At d = 112.2 ppm, the signal
for the CH group ortho to the phenolic oxygen atom can be
observed. The signals at d = 126.5, 125.8, 125.7, 124.2 and
122.4 ppm can be assigned to the indenyl carbon atoms C7, C6,
C5, C4 and C3, while the signal for C2 appears at d = 99.2 ppm.
The signals at d = 66.8, 35.1 and 30.3 ppm can be assigned to
the methylene group attached to the oxygen atom (C10) and
the tertiary-butyl group (C17 and C18), while the signals at
d = 30.1 and 25.5 ppm can be assigned to the alkyl chain carbon
atoms C8 and C9.

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
65
Table 2
NMRa and MS data for compounds 1–9.
No. Compound
1H NMR
13C NMR
MS
m/z (%)
1
O
3
7.53–7.50 m (1H), 7.46–7.43 m (1H), 7.38–7.31 m (3H), 159.0, 145.2, 144.4, 143.6 (Cq), 29.4, 128.2, 126.0, 124.6, 250 [M+] (4) 155
7.29–7.24 m (1H), 7.01–6.95 m (3H), 6.29 m (br, 1H, Ind- 123.7, 120.5, 118.9, 114.5 (CH), 67.2 (OCH2), 37.7 (CH2- (12) 141 (22)
H2), 4.09 t (2H, OCH2), 3.87 br (2H, Ind-H1), 2.84–2.78 m Ind), 27.6, 24.1 (CH2)
(2H, CH2), 2.27–2.20 m (2H, CH2)
130 (100) 115
(49)
2
O
4
7.47–7.43 m (1H), 7.38–7.35 m (1H), 7.32–7.25 m (3H), 159.0, 145.4, 144.5, 144.1 (Cq), 29.4, 128.0, 126.0, 124.5, 264 [M+] (3)
7.22–7.17 m (1H), 6.95–6.88 m (3H), 6.23 m (br, 1H, Ind- 123.7, 120.5, 118.9, 114.5 (CH), 67.6 (OCH2), 37.7 (CH2- 171 (90)
H2), 4.00 t (2H, OCH2), 3.32 br (2H, Ind-H1), 2.66–2.59 m Ind), 29.2, 27.4, 24.5 (CH2)
(2H, CH2), 1.93–1.85 m (4H, CH2)
129 (100)
3
O
5
7.48–7.44 m (1H), 7.39–7.35 m (1H), 7.32–7.25 m (3H), 159.0, 145.4, 144.5, 144.3 (Cq), 129.4, 127.8, 126.0, 124.4, 278 [M+] (1)
7.23–7.17 m (1H), 6.96–6.88 m (3H), 6.20 m (br, 1H, Ind- 123.7, 120.5, 118.9, 114.5 (CH), 67.7 (OCH2), 37.7 (CH2- 185 (49)
H2), 3.96 t (2H, OCH2), 3.32 br (2H, Ind-H1), 2.63–2.55 m Ind), 29.2, 27.8, 27.6, 26.1 (CH2)
(2H, CH2), 1.88–1.72 m (4H, CH2), 1.63–1.54 m (2H, CH2)
129 (100)
115 (27)
4
7.56–7.53 m (1H), 7.50–7.47 m (1H), 7.41–7.37 m (2H), 157.8, 145.2, 144.5, 143.6, 137.9 (Cq), 128.2, 127.0, 126.6, 306 [M+] (3)
7.32–7.22 m (2H), 7.00–6.92 m (2H), 6.34 br (1H, Ind-H2), 126.0, 124.6, 123.8, 120.0, 118.9, 111.7 (CH), 67.1 (OCH2), 157 (44)
4.14 t (2H, OCH2), 3.42 br (2H, Ind-H1), 2.93–2.87 m (2H, 37.7 (CH2-Ind), 34.8 (Cq), 29.9 (CH3), 28.0, 24.8 (CH2)
CH2), 2.36–2.28 m (2H, CH2), 1.57 s (9H, CH3)
129 (100)
115 (64)
O
3
5
7.46–7.43 m (1H), 7.38–7.35 m (1H), 7.30–7.25 m (2H), 157.8, 145.4, 144.6, 144.1, 138.0 (Cq), 127.9, 127.0, 126.6, 320 [M+] (2)
7.21–7.12 m (2H), 6.88–6.83 m (2H), 6.22 br (1H, Ind-H2), 126.0, 124.5, 124.8, 120.0, 119.0, 111.7 (CH), 67.5 (OCH2), 171 (100)
4.01 t (2H-OCH2), 3.32 br (2H, Ind-H1), 2.66–2.61 m (2H, 37.7 (CH2-Ind), 34.9 (Cq), 29.8 (CH3), 29.5, 27.5, 24.9 (CH2) 129 (68)
O
4
CH2), 1.97–1.91 m (4H, CH2), 1.38 s (9H, CH3)
115 (18)
6
7.46–7.43 m (1H), 7.39–7.35 m (1H), 7.31–7.26 m (2H), 157.7, 145.2, 144.4, 144.2, 137.8 (Cq), 127.6, 126.8, 126.4, 334 [M+] (1)
7.21–7.12 m (2H), 6.90–6.82 m (2H), 6.20 br (1H, Ind-H2), 125.8, 124.4, 123.6, 119.9, 118.8, 111.6 (CH), 67.4 (OCH2), 185 (100)
3.97 t (2H, OCH2), 3.31 br (2H, Ind-H1), 2.63–2.57 m (2H, 37.6 (CH2-Ind), 34.7 (Cq), 29.7 (CH3), 29.4, 27.6, 27.5, 26.3 129 (60)
O
5
CH2), 1.94–1.86 m (2H, CH2), 1.83–1.75 m (2H, CH2),
1.68–1.61m (2H, CH2), 1.41 s (9H, CH3)
(CH2)
115 (22)
7
O
3
7.47–7.43 m (1H), 7.39–7.35 m (1H), 7.32–7.25 m (3H), 156.8, 145.3, 144.5, 143.7, 143.2 (Cq), 128.2, 128.1, 126.2, 306 [M+] (8)
7.22–7.16 m (1H), 6.87–6.82 m (2H), 6.23 br (1H, Ind-H2), 126.0, 124.6, 123.8, 119.0, 114.0 (CH), 67.3 (OCH2), 37.8 176 (78)
4.02 t (2H, OCH2), 3.31 br (2H, Ind-H1), 2.77–2.69 m (2H, (CH2-Ind), 34.0 (Cq), 31.5 (CH3), 27.7, 24.2 (CH2)
CH2), 2.21–2.11 m (2H, CH2), 1.29 s (9H, CH3)
161 (81)
129 (100)
115 (56)
8
O
4
7.45–7.42 m (1H), 7.36–7.33 m (1H), 7.29–7.24 m (3H), 156.8, 145.5, 144.6, 144.2, 143.1 (Cq), 128.0, 126.2, 126.0, 320 [M+] (6)
7.20–7.15 m (1H), 6.83–6.79 m (2H), 6.20 br (1H, Ind-H2), 124.5, 123.8, 119.0, 114.0 (CH), 67.7 (OCH2), 37.7 (CH2- 171 (100)
3.96 t (2H, OCH2), 3.30 br (2H, Ind-H1), 2.63–2.57 m (2H, Ind), 34.0 (Cq), 31.5 (CH3), 29.2, 27.4, 24.5 (CH2)
CH2), 1.88–1.83 m (4H, CH2), 1.27 s (9H, CH3)
129 (78)
115 (22)
9
O
5
7.46–7.43 m (1H), 7.37–7.34 m (1H), 7.30–7.26 m (3H), 156.8, 145.5, 144.5, 144.4, 143.1 (Cq), 127.8, 126.1, 125.9, 334 [M+] (3)
7.21–7.16 m (1H), 6.84–6.81 m (2H), 6.19 br (1H, Ind-H2), 124.4, 123.7, 118.9, 113.9 (CH), 67.8 (OCH2), 37.7 (CH2- 204 (6)
3.94 t (2H, OCH2), 3.31 br (2H, Ind-H1), 2.60–2.54 m (2H, Ind), 34.0 (Cq), 31.5 (CH3), 29.2, 27.8, 27.7, 26.1 (CH2)
CH2), 1.86–1.71 m (4H, CH2), 1.61–1.52 m (2H, CH2), 1.29
s (9H, CH3)
185 (100)
135 (74)
117 (65)
115 (23)
a
d (ppm) rel. CHCl3 (7.24 ppm, 1H NMR) and rel. CDCl3 (77.0 ppm, 13C NMR) at 298 K.
Fig. 1. 1H NMR spectrum of compound 4 in CDCl3.

66
K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
Fig. 2. J-modulated 13C NMR spectrum of compound 4 in CDCl3.
R
O
n
ZrCl4
2 n-BuLi
-2 n-BuH
Cl
Cl
Zr
-2 LiCl
O
n
O
n
Li
O
n
R
1a (n = 3; R = H)
2a (n = 4; R = H)
3a (n = 5; R = H)
4a (n = 3; R = 2-t-Bu)
5a (n = 4; R = 2-t-Bu)
6a (n = 5; R = 2-t-Bu)
7a (n = 3; R = 4-tBu)
8a (n = 4; R = 4-t-Bu)
9a (n = 5; R = 4-tBu)
Scheme 2. Synthesis of complexes 1a–9a.
2.3. Ethylene polymerization
active than catalyst 1a without a substituent. This can be attribu-
ted to the fact that the bulky t-butyl group protects the cationic
metal centre of the activated catalyst from the approaching oxygen
atom of the phenoxy group. Catalyst 4a shows higher activity than
catalyst 7a because the tertiary butyl group at the ortho position to
the donor oxygen atom of the phenoxy group provides more pro-
tection than a tertiary butyl group at the para position. The same
trend is obvious for catalysts 2a, 5a and 8a as well as for 3a, 6a
and 9a.
The metallocene complexes 1a–9a were activated with an
excess of MAO (Al: Zr = 2000: 1). The activated complexes were
applied for homogeneous ethylene polymerization in 250 ml of
n-pentane, at 10 bar ethylene pressure and the desired tempera-
ture. The polymerization activities of the activated complexes,
the thermal analysis data of the representative polymer samples
and their crystallinities [41] are listed in Table 1.
2.4. Influence of the bulk on the polymerization activities of the
zirconocene dichloride complexes 1a–9a
2.5. Influence of the spacer length on the polymerization performance
In the series of complexes 1a–9a bearing
x
-phenoxyalkyl sub-
A comparison of the activities of catalysts 4a, 5a and 6a differ-
ing in the chain length between the indenyl and the phenoxy
groups showed that catalyst 5a with four methylene bridging units
was more active (27,500 kg PE/mol cat h) than catalyst 4a with
three methylene bridging units (16,300 kg PE/mol cat h) and cata-
lyst 6a with five methylene bridging units (7670 kg PE/mol cat h).
The same trend could be observed for catalysts 1a–3a and 7a–9a.
This can be explained by the fact that the 1-substituted
stituents on the indenyl groups, catalyst 5a with a 2-Bu substituent
showed the highest activity for ethylene polymerization while cat-
alyst 3a without a substituent at the phenyl ring showed the low-
est activity (Fig. 5). A comparison of the activities of catalysts 1a, 4a
and 7a with equal distances (three CH2 groups) between the inde-
nyl and the phenoxy group showed that catalysts 4a and 7a bear-
ing a tertiary butyl group on the phenoxy substituent were more

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
67
Table 3
1H and 13C NMR data of complexes 1a–9a.
No. Complex
1H NMR [d (ppm)]
13C NMR [d (ppm)]
1aa
7.63–7.60 m (2H), 7.58–7.53 m (4H), 7.43–7.40 m (2H), 7.30–7.16 m 158.8, 127.3, 126.2, 122.2 (Cq), 129.4, 126.4, 125.6, 124.6, 123.8,
(16H), 6.94–6.81 m (12H), 6.29 d (J = 3.2 Hz, 2H, Ind-H), 6.04 d
(J = 3.2 Hz, 2H, Ind-H), 5.81 d (J = 3.2 Hz, 2H, Ind-H), 5.66 d
(J = 3.2 Hz, 2H, Ind-H), 3.97–3.83 m (8H), 3.20–3.07 m (4H), 2.98–
2.81 m (4H), 2.19–1.92 m (8H)
122.2, 120.6, 114.5, 99.3 (CH), 66.7 (OCH2), 29.4, 24.2 (CH2)
O
3
Cl
Zr
Cl
O
3
2aa
7.57–7.54 m (2H), 7.52–7.47 m (4H), 7.38–7.35 m (2H), 7.24–7.09 m 158.9, 127.3, 125.9, 123.0 (Cq), 129.4, 126.3, 125.6, 125.5, 123.8,
(16H), 6.86–6.75 m (12H), 6.25 d (J = 3.2 Hz, 2H, Ind-H), 5.97 d
(J = 3.2 Hz, 2H, Ind-H), 5.77 d (J = 3.2 Hz, 2H, Ind-H), 5.57 d
(J = 3.2 Hz, 2H, Ind-H), 3.90–3.80 m (8H), 3.00–2.60 m (8H), 1.82–
1.56 m (16H)
122.0, 120.5, 114.4, 99.1 (CH), 67.4 (OCH2), 29.1, 27.9, 26.6 (CH2)
O
4
Cl
Zr
Cl
O
4
3aa
7.58–7.55 m (2H), 7.52–7.47 m (4H), 7.39–7.35 m (2H), 7.26–7.12 m 159.0, 127.3, 125.9, 123.2 (Cq), 129.4, 126.2, 125.7, 125.4, 123.8,
(16H), 6.87–6.77 m (12H), 6.23 d (J = 3.2 Hz, 2H, Ind-H), 5.97 d
(J = 3.2 Hz, 2H, Ind-H), 5.74 d (J = 3.2 Hz, 2H, Ind-H), 5.57 d
(J = 3.2 Hz, 2H, Ind-H), 3.87–3.81 m (8H), 2.95–2.82 m (4H), 2.74–
2.56 m (4H), 1.79–1.37 m (24H)
122.1, 120.5, 114.5, 99.2 (CH), 67.6 (OCH2), 29.8, 29.0, 28.1, 26.0
(CH2)
O
5
Cl
Zr
Cl
O
5
4aa
7.55–7.51 m (4H), 7.35–7.30 m (6H), 7.20–7.07 m (6H), 7.02–6.88 m 158.0, 138.0, 127.4, 126.4, 122.4 (Cq), 127.3, 127.0, 126.5, 125.8,
(12H), 6.62–6.55 (m, 4H), 6.14 d (J = 3.2 Hz, 2H, Ind-H), 5.92 d
(J = 3.2 Hz, 2H, Ind-H), 5.50 d (J = 3.2 Hz, 2H, Ind-H), 5.47 d
(J = 3.2 Hz, 2H, Ind-H), 3.60–3.50 m (8H, CH2), 3.25–3.13 m (4H,
CH2), 3.05–2.93 m (4H, CH2), 2.00–1.76 m (8H, CH2), 1.56 s (18H),
1.52 s (18H)
125.7, 124.2, 122.1, 120.8, 112.2, 99.2 (CH), 66.8 (OCH2)
35.1 (Cq), 30.3 (CH3), 30.1, 25.5 (CH2)
O
3
Cl
Zr
Cl
O
3
5aa
7.60–7-56 m (2H), 7.53–7.47 m (4H), 7.39–7.35 m (2H), 7.24–7.02 m 157.7, 137.8, 127.3, 125.8, 123.0 (Cq), 126.9, 126.5, 126.3, 125.6,
(16H), 6.81–6.69 m (8H), 6.26 d (J = 3.2 Hz, 2H, Ind-H), 5.98 d
(J = 3.2 Hz, 2H, Ind-H), 5.76 d (J = 3.2 Hz, 2H, Ind-H), 5.56 d
(J = 3.2 Hz, 2H, Ind-H), 3.93–3.82 m (8H, CH2), 3.02–2.89 m (4H,
CH2), 2.81–2.61 m (4H, CH2), 1.86–1.68 m (16H, CH2), 1.28 s (18H),
1.26 s (18H)
125.5, 123.8, 122.2, 120.0, 111.7, 99.1 (CH), 67.2 (OCH2), 34.8 (Cq),
29.8 (CH3), 29.4, 28.0, 26.9 (CH2)
O
4
Cl
Zr
Cl
O
4
6aa
7.66–7.53 m (4H), 7.45–7.10 m (20H), 6.90–6.77 m (8H), 6.31 d
(J = 3.2 Hz, 2H, Ind-H), 6.04 d (J = 3.2 Hz, 2H, Ind-H), 5.82 d
(J = 3.2 Hz, 2H, Ind-H), 5.04 d (J = 3.2 Hz, 2H, Ind-H), 4.04–3.83 m
(8H, CH2), 3.04–2.87 m (4H, CH2), 2.81–2.56 m (4H, CH2), 1.88–1.44
m (24H, CH2), 1.34 s (18H)
157.7, 137.9, 127.3, 125.9, 123.2 (Cq), 126.9, 126.5, 126.2, 125.7,
125.4, 123.8, 122.1, 120.0, 111.7, 99.1 (CH), 67.4 (OCH2), 34.8 (Cq),
29.8 (CH3), 29.2, 28.1, 27.7, 26.3 (CH2)
O
5
Cl
Zr
Cl
O
5
(continued on next page)

68
K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
Table 3 (continued)
No. Complex
1H NMR [d (ppm)]
13C NMR [d (ppm)]
7aa
7.63–7.53 m (6H), 7.44–7.40 m (2H), 7.30–7.18 m (16H), 6.83–6.75 156.6, 143.4, 127.3, 126.0, 122.2 (Cq), 126.4, 126.2, 125.7, 125.6,
m (8H), 6.29 d (J = 3.2 Hz, 2H, Ind-H), 6.07 d (J = 3.2 Hz, 2H, Ind-H), 123.8, 122.1, 114.0, 99.4 (CH), 66.8 (OCH2), 34.1 (Cq), 31.5 (CH3),
5.82 d (J = 3.2 Hz, 2H, Ind-H), 5.67 d (J = 3.2 Hz, 2H, Ind-H), 3.98–3.82 29.4, 24.6 (CH2)
m (8H, CH2), 3.19–3.06 m (4H, CH2), 2.98–2.80 m (4H, CH2), 2.18–
O
O
3
1.90 m (8H, CH2), 1.30 s (18H), 1.28 s (18H)
Cl
Cl
Zr
Zr
Zr
3
8aa
7.58–7.36 m (8H), 7.25–7.13 m (16H), 6.76–6.70 m (8H), 6.25 (d,
J = 3.2 Hz, 2H, Ind-H), 5.98 (d, J = 3.2 Hz, 2H, Ind-H), 5.76 (d,
156.7, 143.2, 127.3, 125.9, 123.0 (Cq), 126.2, 126.1, 125.7, 125.5,
123.8, 122.1, 113.9, 99.2 (CH), 67.5 (OCH2), 34.0 (Cq), 31.5 (CH3),
J = 3.2 Hz, 2H, Ind-H), 5.57 (d, J = 3.2 Hz, 2H, Ind-H), 3.88–3.81 (m, 129.2, 127.9, 126.6 (CH2)
8H), 3.00–2.60 (m, 8H), 1.80–1.55 (m, 16H), 1.21 (s, 36H)
O
4
Cl
Cl
O
4
9aa
7.67–7.57 m (6H), 7.49–7.45 m (2H), 7.34–7.22 m (16H), 6.86–6.79 156.7, 143.1, 127.3, 126.0, 123.2 (Cq), 126.2, 126.1, 125.7, 125.4,
m (8H), 6.33 d (J = 3.2 Hz, 2H, Ind-H), 6.07 d (J = 3.2 Hz, 2H, Ind-H), 123.8, 122.0, 113.9, 99.2 (CH), 67.6 (OCH2), 34.0 (Cq), 31.5 (CH3),
5.85 d (J = 3.2 Hz, 2H, Ind-H), 5.67 d (J = 3.2 Hz, 2H, Ind-H), 3.96–3.88 29.8, 29.1, 28.1, 26.0 (CH2)
m (8H, CH2), 3.06–2.92 m (4H, CH2), 2.84–2.66 m (4H, CH2), 1.83–
O
5
1.46 m (24H, CH2), 1.33 s (18H), 1.32 s (18H)
Cl
Cl
O
5
a
d (ppm) rel. CHCl3 (7.24 ppm, 1H NMR) and rel. CDCl3 (77.0 ppm, 13C NMR) at 298 K.
2.6. Influence of the temperature on the polymerization behaviour
Table 4
Elemental analysis data for complexes 1a–9a.
To study the effect of the temperature, the ethylene polymeriza-
tion activity of catalyst 5a was investigated at different tempera-
tures (Fig. 6). By increasing the polymerization temperature from
55 to 65 °C the activity increased. A further increase of the temper-
ature resulted in a sharp decrease of activity. The reason could be
decomposition reactions of the active species at higher
temperatures.
DSC measurements (see Table 1) showed that the catalyst sys-
tems 1a–9a/MAO produced polyethylenes with comparatively
low melting points, low degrees of crystallinity and low heats of
fusion.
No.
Cexp (%)
Ctheor (%)
Hexp (%)
Htheor (%)
1a
2a
3a
4a
5a
6a
7a
8a
9a
65.75
65.37
67.03
68.34
68.79
69.94
68.46
68.71
69.75
65.44
66.26
67.02
68.37
68.97
69.53
68.37
68.97
69.53
5.95
5.50
6.20
6.82
6.94
6.80
6.79
7.04
7.18
5.19
5.56
5.91
6.52
6.79
7.05
6.52
6.79
7.05
metallocene complexes are able to exist in different conformations
[40]. The reason for the higher activities of catalysts 2a, 5a and 8a
could be that the conformation obtained with four methylene
bridging units minimizes the intramolecular deactivation of the
active species via interaction of the oxygen atom and the oxophilic
metal more efficiently than a conformation with three or five
methylene groups. The deactivation can also happen via inter-
molecular interactions. A comparison with dissymmetric mono
substituted bis(indenyl) complexes with this type of ligands
showed that the disubstituted species have a somewhat better per-
formance [42].
3. Experimental
3.1. General
Schlenk technique was used to carry out the experimental
work. Argon was purified before its use as an inert gas.
Methylene chloride was distilled over phosphorus pentoxide.
Toluene, tetrahydrofuran, diethyl ether and n-pentane were puri-
fied by distillation over Na/K alloy. Diethyl ether was additionally
distilled over lithium aluminum hydride, while toluene was

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
69
Fig. 3. 1H NMR spectrum of complex 4a (rac and meso isomers) in CDCl3.
Fig. 4. J-modulated 13C NMR spectrum of complex 4a in CDCl3.

70
K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
Fig. 5. Ethylene polymerization activities of complexes 1a–9a/MAO.
Fig. 6. Effect of the temperature on the ethylene polymerization activity of 5a/MAO.
additionally distilled over phosphorus pentoxide. Deuterated sol-
vents (CDCl3 and C6D6) were purchased from Eurisotop and stored
over molecular sieves (3 Å). Argon (5.0) and ethylene (3.5) were
purchased from Riebner Company. Methylalumoxane (10% in
toluene) was purchased from Chemtura Europe Limited. All other
starting materials were commercially available and used as
received.
3.4. Elemental analysis
Elemental analyses were performed with a Vario EL III CHN
instrument. The values of C, H and N were calibrated using aceta-
mide as a standard.
3.5. DSC analysis
3.2. NMR spectroscopy
DSC analyses were performed on a Mettler Toledo DSC/SDTA
821e instrument. The polymer samples were prepared by
enclosing 4–6 mg of the polymer in standard aluminum pans.
The samples were introduced into the auto sampler of the instru-
ment and the measurements were recorded using the following
temperature program:
First heating phase: from 50 °C to 160 °C (10 °C/min);
Cooling phase: 160 °C to 50 °C (10 °C/min);
Second heating phase: from 50 °C to 160 °C (10 °C/min).
Nitrogen was used as a cooling medium. Melting enthalpies and
melting points were taken from the second heating phase. The val-
ues were calibrated using indium as a standard (m.p. 429.78 K,
Hm = 28.45 J/g).
NMR spectra were recorded with a Varian Inova (400 MHz)
spectrometer. All spectra were recorded at 298 K. In the 1H NMR
spectra the chemical shift of the residual proton signal of the sol-
vent was used as a reference (d = 7.24 ppm for chloroform and
d = 7.16 ppm for benzene), while in the 13C NMR spectra the chem-
ical shift of the solvent was used as a reference (d = 77.0 ppm for
chloroform-d1 and d = 128.0 ppm for benzene-d6).
3.3. GC/MS
GC/MS spectra were recorded with a FOCUS Thermo 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
lm and flow
3.6. General synthesis procedure for the x-phenoxyalkyl-substituted
1 mL/min) was used and helium (4.6) was applied as carrier gas.
The measurements were recorded using the following temperature
program:
indene compounds 1–9
An amount of 10 mmol of an appropriate phenol, 10 mmol of
potassium carbonate, 30 mmol of the desired -dibromoalkane
and catalytic amounts of 18-crown-6 were refluxed in acetone
Starting temperature: 50 °C, duration: 2 min;
Heating rate: 20 °C/min, duration: 12 min;
Final temperature: 290 °C, duration: 27 min.
a,x
for 24–72 h. The reaction mixture was cooled, the solvent was

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71
71
removed followed by the addition of distilled water and extraction
with diethyl ether (2 Â 100 mL). After passing over sodium sulfate
and removing the solvent, the residue was distilled to obtain the
results. It is expected that catalysts with such spacious sub-
stituents are suitable oscillating catalysts for propylene polymer-
ization and olefin copolymerization [43].
x
-bromo-1-phenoxyalkane compound. An amount of 5 mmol of
n-butyllithium (1.6 M in n-hexane) was added to 5 mmol of indene
dissolved in 100 ml of diethyl ether at À78 °C. After warming up to
room temperature and stirring for further 3 h, the solution was
Acknowledgements
We thank to Higher Education Commission of Pakistan (HEC
Pakistan) and Deutscher Akademischer Austauschdienst (DAAD)
for the financial support.
cooled to À78 °C and an amount of 5 mmol of the
x-bromo-1-phe-
noxyalkane was added. The solution was allowed to warm up to
room temperature and stirred for further 12 h. The solution was
washed with distilled water and dried over sodium sulfate.
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Removal of the solvent provided the desired
stituted indene in 80% yield.
x-phenoxyalkyl-sub-
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Bis(indenyl)zirconium dichloride complexes of the type [C9H6-
(CH2)n-O-Ar]2ZrCl2 (n = 3–5; Ar = Ph, t-Bu-Ph) can be activated
with MAO and then be applied as efficient ethylene polymerization
catalysts in solution They have higher activities as the unsubsti-
tuted or mono phenoxyalkyl substituted indenyl derivatives.
Because of the high oxophilicity of zirconium, the crucial presence
of oxygen in the phenoxy substituent must be compensated with
steric shielding of bulky substituents like t-Bu in order to achieve
high activities. In this context also the length of the alkylphenoxy
substituent plays an important role. Four CH2-groups gave the best