Influence of the para-substitution in bis(arylimino)pyridine iron complexes on the catalytic oligomerization and polymerization of ethylene

Article abstract of DOI:10.1016/j.jorganchem.2007.05.036

A series of nine bis(arylimino)pyridine iron complexes containing halogen or alkynyl substituents in their ligand frameworks was synthesized and characterized. After activation with methylalumoxane (MAO), these catalysts oligomerize or polymerize ethylene to give highly linear products. The introduction of halogen or alkynyl substituents in the para-position of the iminophenyl rings has a great influence on the polymerization activities of the corresponding iron complexes.

Full text of DOI:10.1016/j.jorganchem.2007.05.036

Journal of Organometallic Chemistry 692 (2007) 4580–4592
www.elsevier.com/locate/jorganchem
Influence of the para-substitution in bis(arylimino)pyridine
iron complexes on the catalytic oligomerization
and polymerization of ethylene
*
Christian Gorl, Helmut G. Alt
¨
Laboratorium fu¨r Anorganische Chemie, Universita¨t Bayreuth, Postfach 10 12 51, Bayreuth D-95440, Germany
Received 21 March 2007; received in revised form 22 May 2007; accepted 22 May 2007
Available online 2 June 2007
Dedicated to Professor Gerhard Erker on the occasion of his 60th birthday.
Abstract
A series of nine bis(arylimino)pyridine iron complexes containing halogen or alkynyl substituents in their ligand frameworks was syn-
thesized and characterized. After activation with methylalumoxane (MAO), these catalysts oligomerize or polymerize ethylene to give
highly linear products. The introduction of halogen or alkynyl substituents in the para-position of the iminophenyl rings has a great influ-
ence on the polymerization activities of the corresponding iron complexes.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Bis(arylimino)pyridine iron complexes; Ethylene polymerization; Oligomerization; Polyethylene
1. Introduction
reactions [18,19] proved to be widely applicable for the
introduction of aliphatic or aromatic substituents employ-
ing terminal alkyne derivatives [20–25]. As demonstrated
by Ionkin et al. [14], halogen substituents at the iminophe-
nyl rings of bis(arylimino)pyridine compounds can be eas-
ily exchanged with aryl groups applying Suzuki coupling
reactions. As a more general method, Sonogashira cou-
pling reactions were chosen to combine para-bromo and
para-iodo substituted bis(arylimino)pyridine compounds
with x-alkynyl substituted indene or fluorene derivatives.
The corresponding iron complexes were synthesized and
used for the catalytic oligomerization and polymerization
of ethylene. For Sonogashira reactions, para-substitution
at the iminophenyl moieties is preferred against ortho-
and meta-substitution due to less steric bulk around the
catalytically active iron center and higher symmetry for
the finally resulting complexes. The influence of different
para-substituents on the polymerization behavior was
investigated. Attempts to prepare multinuclear iron–zirco-
nium complexes are presented.
Gibson [1–4] and Brookhart [5–7] independently reported
the application of 2,6-bis(arylimino)pyridine iron com-
plexes as effective catalysts for the polymerization and olig-
omerization of ethylene leading to highly linear products.
Especially the substitution pattern of the iminophenyl rings
has a great influence on the polymerization activities and
the product compositions [1–17]. In the past five years,
bis(arylimino)pyridine iron complexes with halogen substi-
tuted iminophenyl rings were published by Qian et al. [8,9].
While fluoro, chloro, and bromo substituted bis(aryli-
mino)pyridine compounds and their complexes are known,
the analogous iodo substituted compounds were not
described in the literature so far. Bromo or iodo substituted
compounds are also useful as reactants in palladium cata-
lyzed coupling reactions. Especially Sonogashira coupling
*
Corresponding author. Tel.: +49 921 552555; fax: +49 921 552044.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.05.036

C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
4581
2. Results and discussion
ethylammonium dichloroiodate as an iodinating agent
which is available from the addition reaction of benzyltrim-
ethylammonium chloride and iodine monochloride [26].
Starting from 2,6-dimethylaniline, 4-iodo-2,6-dimethy-
laniline (1) [26] and 4-ethynyl-2,6-dimethylaniline (3) [28]
were prepared (see Scheme 1).
The palladium catalyzed reaction of 1 with trimethylsi-
lylacetylene furnished 4-ethynyl-2,6-dimethylaniline (3)
after removal of the trimethylsilyl protecting group.
2.1. General remarks
To introduce more complex structures into the bis(aryli-
mino)pyridine ligand framework, Suzuki coupling reac-
tions [14] are in some cases disadvantageous due to the
necessity of appropriate arylboronic acids. Other types of cou-
pling reactions, especially Sonogashira reactions, proved to
be more useful in this context. As starting materials, bromo
or iodo substituted anilines are required. On this way, it is
also possible to introduce terminal alkynyl functions into
bis(arylimino)pyridine compounds. The combination of
halogen substituted bis(arylimino)pyridine compounds
and alkynyl substituted fluorenyl or indenyl compounds
leads to ligand precursors which should be subsequently
reacted with iron(II)chloride and n-butyllithium/zirconium
tetrachloride to give trinuclear iron–zirconium complexes.
2.3. Preparation of halogen substituted 2,6-bis(arylimino)
pyridine compounds
Condensation reactions of 2,6-diacetylpyridine with
para-bromo or para-iodo substituted anilines yielded the
2,6-bis(arylimino)pyridine compounds 4–8 (see Scheme 2)
[29,30]. For comparison purposes, 2-methylaniline and 2,6-
dimethylaniline were also reacted with 2,6-diacetylpyridine
to give the well-known corresponding bis(arylimino)pyri-
dine compounds 9 [5] and 10 [6]. The 1H NMR, 13C NMR,
and MS data for compounds 1–10 are given in Table 1.
Condensation reactions using 3-ethynylaniline, 4-ethy-
nylaniline, or 4-ethynyl-2,6-dimethylaniline (3) as aniline
compounds did not lead to imino compounds but yielded
2.2. Synthesis of iodo and alkynyl substituted anilines
The introduction of iodo substituents into the ortho- and
para-positions of aniline [26] or phenol [27] derivatives can
be easily performed at room temperature using benzyltrim-
NH
2
NH
2
NH
NH
-
BzNMe3+ ICl2
2
2
CH2Cl2
MeOH
Me Si
CH2Cl2, MeOH
3
- HCl
(PPh3)2PdCl2
CuI, NEt3
K2CO3
- BzNMe3+Cl-
I
1 [26]
SiMe
3
3 [28]
2
Scheme 1. Synthesis of 4-iodo-2,6-dimethylaniline (1) and 4-ethynyl-2,6-dimethylaniline (3).
R2
N
R2
N
X
X
O
O
R2
X
toluene
p-TosOH
N
NH2
reflux
- 2 H2O
R1
R1
N
R1
R1, R2 = H, Alkyl
= Br, I
X
compound
R1
Me
Me
H
R2
H
X
Br
Br
I
yield [%]
4 [29]
5 [30]
6
28
78
53
54
75
60
68
Me
H
7
Me
Me
Me
Me
H
I
8
Me
H
I
9 [5]
10 [6]
H
H
Me
Scheme 2. Synthesis of 2,6-bis(arylimino)pyridine compounds with para-halogen substituted iminophenyl rings.

4582
C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
Table 1
NMR and MS data of compounds 1–10 and 19–29
Compound
1H NMR
13C NMR
MS [m/z]
1
7.23 s (2H, Ar-H), 3.61 s (br, 2H, NH2), 2.11 s (6H,
CH3)
142.5, 124.2, 79.2 (Cq), 136.4 (Ar-CH), 17.3 (CH3) 247 Mꢀ+ (100), 120 M ꢁ I
(28)
2
3
4
7.09 s (2H, Ar-H), 3.70 s (br, 2H, NH2), 2.08 s (6H,
CH3), 0.25 s (9H, SiMe3)
143.6, 121.1, 111.5 (Cq), 132.0 (Ar-CH), 106.6,
90.8 (Cq, C„C), 17.3 (CH3), 0.2 (SiMe3)
217 Mꢀ+ (50), 202
M ꢁ Me (100)
7.09 s (2H, Ar-H), 3.73 s (br, 2H, NH2), 2.91 s (1H,
„CH), 2.12 s (6H, CH3)
143.7, 121.3, 110.5 (Cq), 132.1 (Ar-CH), 109.1 (Cq, 145 Mꢀ+ (100), 130
C„C), 74.4 („CH), 17.4 (CH3)
M ꢁ Me (31)
8.38 d (2H, PyH3), 7.87 t (1H, PyH4), 7.28–7.36 m (4H, 167.4, 155.1, 148.9, 129.6, 116.3 (Cq), 136.9, 133.1, 499 Mꢀ+ (60), 484
Ar-H), 6.56 d (2H, Ar-H), 2.33 s (6H, CH3), 2.09 s (6H, 129.3, 122.5, 119.8 (Ar-CH), 17.6, 16.4 (CH3)
CH3)
M ꢁ Me (100)
5
6
8.47 d (2H, PyH3), 7.93 t (1H, PyH4), 7.22 s (4H, Ar-H), 167.8, 154.8, 147.7, 127.7, 115.6 (Cq), 137.0, 130.5, 527 Mꢀ+ (58), 512
2.25 s (6H, CH3), 2.02 s (12H, CH3) 122.5 (Ar-CH), 17.8, 16.6 (CH3)
M ꢁ Me (100)
8.30 d (2H, PyH3), 7.85 t (1H, PyH4), 7.64–7.68 m (4H, 167.8, 155.1, 150.8, 87.2 (Cq), 137.9, 136.9, 122.5, 565 Mꢀ+ (22), 550
Ar-H), 6.58–6.62 m (4H, Ar-H), 2.38 s (6H, CH3)
121.5 (Ar-CH), 16.3 (CH3)
M ꢁ Me (3), 438 M ꢁ I
(3)
7
8
9
8.36 d (2H, PyH3), 7.87 t (1H, PyH4), 7.23–7.55 m (4H, 167.3, 155.1, 149.6, 129.9, 87.1 (Cq), 139.0, 136.9, 593 Mꢀ+ (22), 578
Ar-H), 6.43 d (2 H, Ar-H), 2.31 s (6 H, CH3), 2.06 s
(6H, CH3)
135.3, 122.5, 120.2 (Ar-CH), 17.5, 16.4 (CH3)
M ꢁ Me (18), 466 M ꢁ I
(6)
8.45 d (2H, PyH3), 7.92 t (1H, PyH4), 7.39 s (4H, Ar-H), 167.8, 154.8, 148.5, 128.0, 86.6 (Cq), 137.4, 136.5, 621 Mꢀ+ (74), 605
2.28 s (6H, CH3), 1.97 s (12H, CH3)
122.5 (Ar-CH), 17.6, 16.6 (CH3)
M ꢁ Me (79), 494 M ꢁ I
(7)
8.46 d (2H, PyH3), 7.89 t (1H, PyH4), 7.21–7.28 m (4H, 166.8, 155.4, 149.9, 127.1 (Cq), 136.8, 130.4, 126.4, 341 Mꢀ+ (47), 326
Ar-H), 7.04–7.09 m (2H, Ar-H), 6.72–6.75 m (2H,
Ar-H), 2.39 s (6H, CH3), 2.17 s (6H, CH3)
123.6, 122.3, 118.1 (Ar-CH), 17.8, 16.3 (CH3)
M ꢁ Me (100)
10
19
8.56 d (2H, PyH3), 7.94 t (1H, PyH4), 6.97–7.15 m (6H, 167.2 155.1, 148.8, 125.4 (Cq), 136.9, 128.0, 123.1, 369 Mꢀ+ (37), 354
Ar-H), 2.25 s (6H, CH3), 2.12 s (12H, CH3) 122.3 (Ar-CH), 18.0, 16.5 (CH3)
M ꢁ Me (100)
7.60–7.63 m (2H), 7.34–7.41 m (2H), 7.07–7.10 m (1H), 145.5, 144.2 (Cq), 135.8, 129.0, 124.9, 123.8, 122.8, 188 Mꢀ+ (9), 173 M ꢁ Me
6.79–6.82 m (1H), 3.67 s (1H), 0.13 s (9H, SiMe3)
121.1 (Ar-CH), 46.6 (CH), ꢁ2.4 (SiMe3)
(3), 115 M ꢁ SiMe3 (6), 73
SiMe3 (100)
20
(1H NMR data for the vinylic isomer) 7.70–7.79 m (1H,
Ar-H), 7.43–7.48 m (3H, Ar-H), 7.04–7.06 m (1H,
Ind-H2), 3.82–3.88 dt (1H, Ind-H1), 2.79–2.83 m (1H,
(
13C NMR data for the vinylic isomer) 147.7,
226 Mꢀ+ (23), 211
147.3, 144.9 (Cq), 148.1, 127.3, 124.9, 123.4, 122.4 M ꢁ Me (14), 152 M ꢁ H
(Ar-CH), 83.0 (Cq, C„C), 69.6 („CH), 50.4 (CH, – SiMe3 (33)
CH2), 2.51–2.60 m (1H, CH2), 2.28 t (1H, „CH), 0.60 Ind-C1), 21.3 (CH2), 0.8 (SiMe3)
s (9H, SiMe3)
21
22
7.30–7.72 m (7H, Ar-H), 3.82 s (2H, CH2), 2.43 s (br,
1H, OH), 1.67 s (6H, CH3)
143.5, 143.1, 141.8, 141.0, 120.7, 65.7 (Cq), 130.5, 248 Mꢀ+ (72), 233
128.2, 127.1, 126.9, 125.1, 120.2, 119.7 (Ar-CH),
M ꢁ Me (100)
93.8, 82.8 (Cq, C„C), 36.7 (CH2), 31.6 (CH3)
7.35–7.78 m (7H, Ar-H), 3.87 s (2H, CH2), 3.11 s (1H, 143.6, 143.1, 142.3, 140.9, 120.0 (Cq), 131.0, 128.7, 190 Mꢀ+ (100), 189
„CH)
127.3, 126.9, 125.1, 120.2, 119.7 (Ar-CH), 84.4
(Cq, C„C), 76.9 („CH), 36.7 (CH2)
M ꢁ H (98)
23
2.65 t (2H, CH2), 2.36–2.43 m (2H, CH2), 2.13 s (3H,
CH3), 1.91 t (1H, „CH)
206.3 (Cq), 82.8 (Cq, C„C), 68.7 („CH), 42.1,
12.9 (CH2), 29.8 (CH3)
96 Mꢀ+ (7), 95 M ꢁ H
(60), 81 M ꢁ H ꢁ Me (67)
24/240
6.53–6.56 m (4H, Cp), 2.79 t (2H, CH2), 2.43–2.50 m
(2H, CH2), 2.26 s (3H, CH3), 2.04 t (1H, „CH)
150.2, 143.6 (Cq), 131.5, 131.2, 120.8, 120.4
(Cp–CH), 83.1 (Cq, C„C), 69.7 („CH), 35.5,
18.5 (CH2), 20.9 (CH3)
144 Mꢀ+ (83), 129
M ꢁ Me (100)
25/250
7.63–7.84 m (3H, Ar-H), 7.36–7.50 m (3H, Ar-H),
7.17–7.20 m (1H, Ar-H), 6.83–7.00 m (1H, Ar-H),
6.57–6.73 m (2H, Cp), 6.22–5.99 m (1H, Cp), 4.19/4.13 127.4, 127.3, 127.3, 127.2, 126.9, 126.4, 126.3,
153.8/151.6, 144.9/144.6, 144.5, 142.5/142.4, 141.9 310 Mꢀ+ (100), 295
(Cq), 135.1, 132.8, 132.3, 131.6, 129.8, 128.1,
M ꢁ Me (21), 165
Fluorenyl (42)
s (1H), 3.14 m (2H, Cp), 2.30–2.39 m (2H, CH2),
2.07–2.10 m (3H, CH2/„CH), 0.68 s (3H, CH3)
126.2, 126.1, 126.1, 125.7, 119.8, 119.4, 119.3
(Ar-CH), 85.3/85.1 (Cq, C„C), 68.6/68.5 („CH),
58.2/56.0 (CH), 43.0, 41.1, 41.0, 40.3, 38.7, 14.5/
14.4 (CH2/Cq/bridge), 17.8/17.3 (CH3)
26
8.43 d (1H, PyH4), 7.90 t (2H, PyH3/5), 7.29–7.53 m (4H, 165.9 (Cq, C@N), 156.1, 150.4, 147.3, 146.9, 140.1, 589 Mꢀ+ (1), 516
Ar-H), 6.92–7.19 m (8H, Ar-H), 6.70–6.75 m (2H,
Ar-H), 6.07–6.15 m (2H, Ar-H), 3.80 s (4H, CH2),
2.93–2.98 m (2H, CH), 2.35 s (6H, CH3), 2.10 s
(6H, CH3), 0.20 (SiMe3)
130.7, 117.6 (Cq), 136.9, 132.8, 130.2, 126.5, 126.2, M ꢁ SiMe3 (8), 412
125.2, 124.5, 123.5, 121.6, 119.2 (Ar-CH), 88.9,
86.3 (Cq, C„C), 47.9 (CH), 29.3 (CH2), 18.6, 16.4
(CH3), ꢁ1.8 (SiMe3)
M ꢁ IndSiMe3 (14)

C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
4583
Table 1 (continued)
Compound
1H NMR
13C NMR
MS [m/z]
27
8.41 d (1H, PyH4), 7.88 t (2H, PyH3/5), 7.63–7.75 m
166.5 (Cq, C@N), 155.8, 145.1, 143.4, 141.1, 134.9,
717 Mꢀ+ (2), 702
(4H, Ar-H), 7.49–7.54 m (2H, Ar-H), 7.19–7.34 m
(12H, Ar-H), 6.60–6.63 m (2H, Ar-H), 3.86 s (4H,
CH2), 2.36 s (6H, CH3), 2.10 s (6H, CH3)
131.1, 130.6, 122.0, 112.4 (Cq), 136.3, 133.7, 130.5,
M ꢁ Me (3), 552
130.1, 128.0, 126.9, 126.8, 125.0, 124.4, 120.0, 119.7, M ꢁ Flu (8), 165 Flu
114.6 (Ar-CH), 90.4, 87.8 (Cq, C„C), 36.7 (CH2),
(100)
17.2, 16.4 (CH3)
28
29
8.40 d (1H, PyH4), 7.90 t (2H, PyH3/5), 7.63–7.76 m
(6H, Ar-H), 6.50–7.39 m (22H, Ar-H), 4.19 s (2H,
Flu-H9), 3.13–3.19 m (4H, Cp–CH2), 2.35 s (6H,
CH3), 2.17–2.26 m (8H, CH2), 2.11 s (6H. CH3), 0.64 126.0, 122.4, 119.6, 119.2, 118.2 (Ar-CH), 89.5, 80.5
s (6H. CH3)
167.1 (Cq, C@N), 155.2, 151.6, 149.5, 144.9, 144.6,
142.4, 141.9, 127.3, 119.0 (Cq), 136.9, 134.9, 133.7,
132.8, 129.8, 128.0, 127.2, 127.0, 126.8, 126.2, 126.1, Flu (5), 165 Flu (100)
957 Mꢀ+ (3), 792
M ꢁ Flu (6), 627 M ꢁ 2
(Cq, C„C), 58.3, 56.0 (CH), 44.2 (Cq), 43.0, 41.0,
15.2 (CH2), 17.6, 17.3, 16.4 (CH3)
8.46 d (1H, PyH4), 7.92 t (2H, PyH3/5), 7.59–7.75 m
(6H, Ar H), 6.48–7.39 m (20H, Ar-H), 4.18 s (2H,
FluH9), 3.11–3.18 m (4H, Cp–CH2), 2.23 s (6H.
167.4 (Cq, C@N), 154.9, 152.5, 151.6, 144.9, 144.6,
142.4, 141.8, 125.5, 118.4 (Cq), 137.4, 134.9, 132.8,
131.5, 131.1, 128.0, 127.2, 126.8, 126.2, 126.1, 125.9, M ꢁ (C32H29) (15), 165
985 Mꢀ+ (5), 820
M ꢁ Flu (6), 574
CH3), 2.01 s (6H. CH3), 2.00–2.35 m (8H, CH2) 0.62 124.5, 122.7, 119.6, 119.1 (Ar-CH) 89.1, 80.5 (Cq,
Flu (100)
s (6H. CH3)
C„C), 58.3, 56.0 (CH), 44.2 (Cq), 43.0, 40.9, 15.3
(CH2), 17.8, 17.3, 16.6 (CH3)
condensation products of the corresponding anilines.
While some fluoro, chloro, and bromo substituted
bis(arylimino)pyridines are known in the literature [8–
10,31,32], compounds 6–8 are the first examples containing
iodo substituents.
the corresponding bis(arylimino)pyridine iron complexes
11–18 (Scheme 3). Spectral data for complexes 11–18 are
given in Table 2.
The complexes were characterized by mass spectrometry
and elemental analyses. Due to their paramagnetism and
their poor solubility, 1H NMR investigations could not
be performed for all complexes. Scheme 4 shows the mass
spectrum of complex 14.
2.4. Synthesis of iron complexes containing halogen
substituted 2,6-bis(arylimino)pyridine ligands
The molecular ion appears at m/z = 719 with an inten-
sity of 2% relative to the base peak. The loss of one chloro
ligand leads to the peak at m/z = 684, while the base peak
The bis(arylimino)pyridine compounds 4–10 were
reacted with iron(II) chloride or iron(III) chloride to give
R2
N
R2
N
Cln
Fe
R2
N
R2
N
X
X
X
X
FeCl
n
R1
R1
R1
N
N
R1
n-BuOH,
r.t., 3h
R1, R2 = H, Alkyl
X
n
= Br, I
= 2, 3
compound
R1
R2
X
Br
Br
I
n
2
2
2
2
2
3
2
2
yield [%]
11 [29]
12 [30]
13
Me
Me
H
H
96
92
37
57
78
71
77
81
Me
H
14
Me
Me
Me
Me
Me
H
I
15
Me
Me
H
I
16
I
17 [5]
18 [6]
H
H
Me
Scheme 3. Synthesis of the iron complexes 11–18.

Table 2
MS, elemental analysis, and 1H NMR data of the iron complexes 11–18 and 30–32
Complex
MS (m/z)
1H NMR d (ppm)
Cexp
(%)
Ctheor
(%)
Hexp
(%)
Htheor
(%)
Nexp
(%)
Ntheor
(%)
11
12
13
14
15
16
17
625 Mꢀ+ (1), 589 M ꢁ H ꢁ Cl (4), 499 M ꢁ FeCl2
(16), 484 M ꢁ FeCl2 ꢁ Me (21)
–
44.1
44.1
45.9
36.5
38.4
40.1
38.3
59.0
3.43
3.97
2.61
3.01
3.46
3.30
5.02
3.38
3.85
2.48
2.94
3.37
3.22
4.95
6.69
6.41
6.03
5.80
5.49
5.43
8.78
6.71
6.42
6.07
5.84
5.62
5.36
8.97
653 Mꢀ+ (2), 618 M ꢁ Cl (3), 527 M ꢁ FeCl2 (13),
512 M ꢁ FeCl2 ꢁ Me (19)
84.62 (2H, PyH3/5), 34.17 (1H, PyH4), 16.50 (4H, Ar-H), 12.88 45.8
(12H, Ar-CH3), ꢁ20.18 (6H, N@C–CH3)
691 Mꢀ+ (1), 565 M ꢁ FeCl2 (4), 438 M ꢁ FeCl2 ꢁ I
(3)
–
–
36.1
38.9
719 Mꢀ+ (2), 684 M ꢁ Cl (7), 649 M ꢁ 2Cl (5) 593
M ꢁ FeCl2 (100), 578 M ꢁ FeCl2 ꢁ Me (98)
747 Mꢀ+ (4), 712 M ꢁ Cl (9), 621 M ꢁ FeCl2 (61),
606 M ꢁ FeCl2 ꢁ Me (62)
88.52 (2H, PyH3/5), 34.97 (1H, PyH4), 17.00 (4H, Ar-H), 13.43 40.7
(12H, Ar-CH3) ꢁ15.44 (6H, N@C–CH3)
783 Mꢀ+ (1), 768 M ꢁ Me (4), 621 M ꢁ FeCl2 (5),
606 M ꢁ FeCl2 ꢁ Me (6)
–
39.0
58.1
467 Mꢀ+ (17), 341 M ꢁ FeCl2 (46), 326
M ꢁ FeCl2 ꢁ Me (100)
83.90 (1H, PyH4), 82.58 (2H, PyH3/5), 20.15, 7.13, ꢁ14.65,
ꢁ19.04 (each 2H, Ar-H), 17.34 (6H, Ar-CH3), ꢁ23.96 (6H,
N@C–CH3)
18
495 Mꢀ+ (24), 460 M ꢁ Cl (15), 444 M ꢁ Cl ꢁ HMe 86.19 (2H, PyH3/5), 39.60 (1H, PyH4), 16.28 (4H, ArylH3/5),
60.1
60.5
5.33
5.44
8.42
8.47
(26), 369 M ꢁ FeCl2 (37), 354 M ꢁ FeCl2 ꢁ Me
ꢁ11.31 (2H, ArylH4), 13.40 (12H, Ar-CH3), ꢁ17.02 (6H,
(100)
N@C–CH3)
30
31
32
843 Mꢀ+ (1), 678 M ꢁ Flu (4), 316 Me–
C@N(C22H15) (21), 165 Flu (100)
1083 Mꢀ+ (1), 1048 M ꢁ Cl (2), 957 M ꢁ FeCl2 (2),
165 Flu (100)
–
74.6
77.9
77.9
75.4
78.6
78.8
4.79
5.76
6.01
4.65
5.85
6.07
4.92
3.81
3.66
4.98
3.87
3.78
–
–
1111 Mꢀ+ (1), 1076 M ꢁ Cl (1), 671
M ꢁ Me ꢁ C@N(C23H17) (5), 165 Flu (100)

C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
4585
at m/z = 593 can be explained with the loss of both chloro
ligands and the iron center resulting in the molecular ion of
the bis(arylimino)pyridine ligand. Further cleavage of a
methyl group from the ligand framework gives the ion with
m/z = 578.
(24) (see Scheme 7). The reaction of fluorenyllithium and
fulvene 24 and subsequent hydrolysis gave the C1 bridged
1
ligand precursor 25 [35]. The H NMR, 13C NMR, and
MS data for compounds 18–25 are given in Table 1.
2.5. Synthesis of alkynyl substituted indene and fluorene
compounds
HO
Starting from indene, 1-(trimethylsilyl)indene (19) and
1-(2-propynyl)-1-(trimethyl-silyl)indene (20) were prepared
in high yields (Scheme 5).
I
2-Iodofluorene was reacted with 2-methylbut-3-yn-2-ol
under Sonogashira conditions. Deprotection of the alkynyl
function using potassium hydroxide furnished 2-ethynylflu-
orene (22) (Scheme 6) [33].
For the synthesis of alkynyl substituted bridged metallo-
cene type ligand precursors, 5-hexyn-2-one (23) was pre-
pared according to the literature [34]. Reaction with
freshly distilled cyclopentadiene in a mixture of pyrrolidine
and methanol yielded 6-(but-3-yn-1-yl)-6-methyl fulvene
OH
KOH
toluene
110 ˚C, 2h
(PPh3)2PdCl2
CuI, NEt3
[33]
22
21
Scheme 6. Synthesis of 2-ethynyl fluorene (22).
Scheme 4. Mass spectrum of complex 14.
1. n-BuLi, pentane
- n-BuH
1. n-BuLi, pentane
- n-BuH
2. 3-bromopropyne
toluene
2. Me3SiCl, toluene
- LiCl
Me3Si
- LiBr
SiMe3
19
Scheme 5. Preparation of compounds 19 and 20.
20

4586
C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
2.6. Sonogashira coupling reactions of halogenated 2,6-
bis(arylimino)pyridines with alkynyl substituted indene or
fluorene derivatives
temperature, 24 h, see Schemes 8 and 9), and the coupling
products were isolated in good yields.
While the fluorenyl substituted compounds 27–29 are
air stable, the indenyl derivative 26 decomposed on air
within a few hours. The bromo substituted bis(aryli-
mino)pyridines 4 and 5 did not react under Sonogashira
conditions. Instead of coupling reactions, the loss of the
bromo substituents could be observed at prolonged reac-
The iodo substituted 2,6-bis(arylimino)pyridine com-
pounds 7 and 8 were reacted with bridged or unbridged
alkynyl substituted indene or fluorene derivatives using
palladium catalyzed Sonogashira coupling. The reactions
proceeded smoothly at mild reaction conditions (room
1
tion times and elevated temperatures. The H NMR, 13C
O
O
O
K2CO3
EtOH
1. FluLi
+
pyrrol-
idine,
MeOH
2. H2O
Cl
23
[34]
25
+ isomer
24
[35]
[35]
Scheme 7. Synthesis of the C1 bridged ligand precursor 25.
I
N
N
(Ph3P)2PdCl2
CuI, NEt3
r.t., 20h
(Ph3P)2PdCl2
CuI, NEt3
r.t., 20h
N
- HNEt3I
- HNEt3I
Me3Si
22
I
20
7
Me3Si
N
N
N
N
N
N
SiMe3
26
27
Scheme 8. Sonogashira reactions of compound 7 with unbridged alkynyl substituted indene and fluorene derivatives.

C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
4587
I
R
N
I
R
N
N
+
R = H:
R = Me: 8
7
25
(Ph3P)2PdCl2
CuI, NEt3
- HNEt3I
r.t., 20h
R
R
N
N
N
R = H: 28
R = Me: 29
Scheme 9. Synthesis of the alkynyl substituted bis(arylimino)pyridine compounds 28 and 29.
NMR, and MS data for the ligand precursors 26–29 are
given in Table 1.
A possible explanation for these results could be the
nucleophilic attack of n-butyllithium on the (imino)pyri-
dine moiety. A couple of reactions of different nucleophiles
with bis(arylimino)pyridine compounds have been
described in the literature. Deprotonation of the iminom-
ethyl groups [37–39], reduction of the metal centers [40–
42], addition of nucleophiles to the imino carbon atoms
to give amido complexes [38,43], reductive dimerization
at the iminomethyl groups [44,45], alkylation at the pyri-
dine C-2 or C-4 carbon atoms [43,46] and even at the pyr-
idine nitrogen atom [47–49] were observed depending on
the applied nucleophilic reagent and the reaction condi-
tions. Since the acidities of the iminomethyl protons and
the fluorenyl protons (for free fluorene pKa = 22.9) [50]
seem to be similar, both positions may be deprotonated
in complexes 30–32. Probably, the competition of these
two groups is the reason, why no clean complexation
reactions were observed after addition of zirconium tetra-
chloride or the half-sandwich complex cyclopentadienylzir-
conium trichloride. Therefore, another synthetic strategy
has to be developed on the way to the desired trinuclear
iron–zirconium complexes.
2.7. Preparation of bis(arylimino)pyridine iron complexes
from the Sonogashira coupling products 27–29
The fluorenyl substituted 2,6-bis(arylimino)pyridine
compounds 27–29 were reacted with anhydrous iron(II)
chloride affording the corresponding iron complexes 30–
32 (Schemes 10 and 11) in yields of 55–70%.
In contrast to other bis(arylimino)pyridine iron com-
plexes [17,36], the compounds 30–32 are only slightly blue.
The spectral data for the complexes 30–32 are given in
Table 2.
2.8. Attempts to prepare multinuclear complexes from the
iron complexes 30–32
The deprotonation of the cyclopentadienyl and fluorenyl
moieties of the iron complexes 30–32 using n-butyllithium
and the subsequent reaction with the half-sandwich com-
plex cyclopentadienylzirconium trichloride (in case of com-
plex 30) or zirconium tetrachloride (for complexes 31 and
32) did not lead to the desired multinuclear iron–zirconium
complexes. However, black solids were isolated which did
not show any polymerization activities. The reaction of
the bis(arylimino)pyridine ligand precursors 27–29 with
n-butyllithium and cyclopentadienylzirconium trichloride
or zirconium tetrachloride also did not yield defined dinu-
clear zirconium complexes.
2.9. Results of the catalytic oligomerization and
polymerization of ethylene
The iron complexes 11–18 and 30–32 were used as cata-
lyst precursors for the homogeneous polymerization and
oligomerization of ethylene. The complexes were activated
with methylalumoxane (MAO) applying a ratio Fe:Al =

4588
C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
N
N
N
N
Cl
1-BuOH
r.t., 3h
N
+
FeCl2
N
Fe
Cl
26
30
Scheme 10. Synthesis of complex 30.
1:2500. The polymerization runs were routinely performed
at a temperature of 60 °C over one hour employing an eth-
ylene pressure of 10 bar. As a solvent n-pentane was used.
The polymerization results are given in Table 3. The liquid
fractions (noted as ‘‘oligomer share’’ in Table 3) contained
a-olefins (chain length C6–C40) with purities higher than
95%. These oligomer mixtures were characterized by gas
chromatography while the polymers were characterized
using GPC.
The complexes 11, 14, 17, and 30 produced exclusively
oligomers. Surprisingly, also complex 13 which does not
contain substituents at the ortho-positions to the imino
nitrogen atoms was an active ethylene oligomerization cat-
alyst albeit its activity was distinctly lower compared with
complexes 11, 14, 17, and 30. The activity of complex 13
could be explained with the size of the iodo substituents
at the para-positions of the iminophenyl rings, since analo-
gous bis(arylimino)pyridine compounds with smaller sub-
stituents (H, Me, F) at the same positions usually afford
inactive ionic complexes of the type [ML2]2+[MCl4]2ꢁ when
reacted with iron(II) chloride [51].
of the influence of different para-substituents on both the
polymerization activity and the resulting product composi-
tions, the well-known para-unsubstituted bis(arylimino)-
pyridine iron complexes 17 and 18 were chosen as
references. While complex 17 produces a-olefins with high
activity [5], complex 18 polymerizes ethylene to high molec-
ular weight polyethylenes [6]. With 2,4-dialkyl substituted
bis(arylimino)pyridine iron complexes [36,52], lower oligo-
merization activities were achieved compared with complex
17. Also, some iron(II) complexes with 2-methyl-4-halogen
substituted ligand frameworks were described in the litera-
ture [9,53] which, in contrast, exhibited higher oligomeriza-
tion activities compared with the reference complex 17. As
therefore expected, the iron complexes 11 and 14 showed
higher oligomerization activities compared with the
4-unsubstituted complex 17 (Scheme 12).
The extremely high polymerization activities of 4-halo-
gen-2-methyl substituted complexes can be explained with
the electronic influence of the electronegative halogen
substituents in the para-positions of the iminophenyl
rings, since the electron donating ortho-methyl groups
remained unvaried. The complex containing fluorine sub-
stituents [9] showed the highest activity among the 4-hal-
ogen-2-methyl substituted complexes. Due to the high
electronegativity of fluoro substituents, the electron den-
sity at the cationic iron center is significantly reduced.
Due to steric reasons, 2,6-bis(arylimino)pyridine com-
pounds containing halogen substituents at the para-posi-
tions of the iminophenyl rings seemed to be most suitable
for Sonogashira coupling reactions with alkynyl substi-
tuted indenyl or fluorenyl derivatives. For investigation

C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
4589
R
N
R
R
N
R
N
N
N
N
Cl
Cl
1-BuOH
r.t., 3h
Fe
+
FeCl2
R = H:
R = Me: 29
28
R = H: 31
R = Me: 32
Scheme 11. Synthesis of the iron complexes 31 and 32.
Table 3
Ethylene polymerization results for the iron complexes 11–18 and 30–32 (solvent: 250 ml n-pentane, activator: MAO, Fe:Al = 1:2500, 10 bar ethylene,
60 °C, 1h)
Complex
Activity (kg/mol Fe h)
Mn (g/mol)
Mw (g/mol)
PD
Oligomer share (wt.%)
11
12
13
14
15
16
17
18
30
31
32
95660
41100
2490
–
–
–
4.80
–
100
–
94.4
100
–
–
100
–
19400
–
–
22700
27160
–
6670
–
92940
–
–
102400
122500
–
90950
–
117100
146650
224170
90800
27900
24590
74275
89820
–
4.51
4.51
–
13.6
–
100
–
–
14050
16200
198900
158000
14.2
9.70
Therefore, its Lewis acidic character increases and the
coordination of an ethylene molecule is facilitated. Com-
plexes with chloro or bromo substituents at the para-posi-
tions gave lower activities, while the introduction of iodo
substituents again increased the activity. Possibly due to
the sterically more demanding iodo substituents, complex
14 showed a higher polymerization activity than the cor-
responding bromo substituted complex 11. The same
effect could be observed comparing the polymerization
catalysts 12, 15, and 18 (see Table 3). Again, the para-
unsubstituted reference complex 18 showed the lowest
polymerization activity among these three complexes,
while the activity increases from bromo (complex 12) to
iodo substitution (complex 15). The iron(III) complex
16 with a tremendous polymerization activity of 224170
[kg PE/mol Fe h] was found to be even more active than
its analogous iron(II) complex 15. This result can be
explained with a stronger Lewis acidic character of the
iron(III) center compared with an iron(II) center and,
therefore, an increased affinity to coordinate an electron
rich ethylene molecule. The combination of substituents
with contrary electronic properties at the iminophenyl
rings seems to favor high polymerization activities, since
iron complexes with 2,4-dialkyl, 2,4-dihalogen, 2,6-dial-
kyl, or 2,6-dihalogen substituted ligand frameworks are
reported to exhibit lower activities than catalysts with
2-alkyl-4-halogen or 2,6-dialkyl-4-halogen substituted
iminophenyl rings [8,9,36,52,53].

4590
C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
Cl
Cl
iminophenyl rings is decisive for high polymerization activ-
R
R
ities, but also their bulkiness. Bulky groups at the para-
positions also exert influence on the molecular weights of
the polymerization products. Although only one of the
ortho-positions of the bis(arylimino)pyridine ligand in com-
plex 31 is substituted, the steric bulk caused by the cyclo-
pentadienyl and fluorenyl units seems to be high enough
to decrease the rate of b-H elimination significantly. The
average molecular weights Mn and Mw produced with 31/
MAO are 14050 and 198900 g/mol. These values are very
similar to those obtained for the polyethylene produced
with 32/MAO (Mn = 16200 g/mol, Mw = 158000 g/mol).
Therefore, substitution at both ortho-positions to the imino
groups is not obligatory for polymer producing bis(aryli-
mino)pyridine iron catalysts, if the para-positions are
substituted with sterically demanding groups.
Fe
N
N
N
200000
150000
100000
50000
0
159250
117100
112150
90800
95660
56730
R = H
17
R = Me
[8]
R = F
[8]
R = Cl
[8]
R = Br
11
R = I
14
3. Conclusion
Seven new bis(arylimino)pyridine iron complexes con-
taining halogen or alkynyl substituents in their ligand
frameworks were synthesized and characterized. After acti-
vation with methylalumoxane (MAO), these catalysts oli-
gomerize or polymerize ethylene to give highly linear
products. The influence of substituents in the para-posi-
tions of the iminophenyl groups on the ethylene polymeri-
zation activities and the product compositions was
investigated. Both the size and the electronegativity of the
substituents play an important role. In case of rather small
halogen substituents (F, Cl, Br), the electronegativity is the
decisive factor leading to the highest activity for the fluoro
substituted complex and decreased activities for the corre-
sponding chloro and bromo substituted complexes. If iodo
substituents were introduced in the para-positions, again a
higher polymerization activity was observed along with an
increased content of higher molecular weight olefins in the
resulting product compositions. When sterically demand-
ing alkynyl substituted cyclopentadienyl-fluorenyl-moieties
were introduced applying Sonogashira coupling reactions,
the resulting complexes produced exclusively polymers.
Attempts to prepare multinuclear iron–zirconium com-
plexes from the fluorenyl or cyclopentadienyl-fluorenyl
substituted mononuclear iron complexes failed, possibly
due to side reactions at the imino groups.
Scheme 12. Activities of 4-halogen-2-methyl substituted 2,6-bis(aryli-
mino)pyridine iron complexes. All complexes produce 100% oligomers.
Table 4
Influence of the size of para-substituents in iron complexes with 2-methyl-
4-halogen or 2-methyl-4-alkynyl substituted bis(arylimino)pyridine
ligands on the product character
Complex
para-Substituent
Oligomer share [wt.%]
17
11
14
30
31
H
Br
I
100
100
100
100
0
2-Fluorenylethynyl
5-(9-Flu)-5-(1-Cp)-hex-1-yn-yl
The 2-methyl-4-alkynyl substituted complex 30 contain-
ing an ethynylfluorenyl group produced exclusively oligo-
mers yielding
a very similar product composition
compared to the ‘‘iodo precursor’’ 14. If the two-dimen-
sional ethynylfluorenyl groups were replaced by three-
dimensional substituents, the resulting complex 31 pro-
duced exclusively polymer (see Table 4). Complex 30 exhib-
its a dramatically lower oligomerization activity compared
with complexes 11 and 14 containing 2-methyl-4-halogen
substituted bis(arylimino)pyridine ligands. The expanded
conjugated p-electron system of the ligand framework
including both ethynylfluorenyl moieties possibly stabilizes
the cationic iron center by transferring some electron den-
sity to the cationic metal center.
4. Experimental
In contrast to complex 30, the conjugated p-electron sys-
tems in complexes 31 and 32 only include the internal alky-
nyl groups but not the cyclopentadienyl and fluorenyl
groups so the transfer of p-electron density from these
groups to the metal center is prevented. The polymeriza-
tion activities of complexes 31 and 32 are distinctly higher
compared with the activities of complex 30 and reference
complex 18 (see Table 3). As indicated for the complexes
with iodo substituted bis(arylimino)pyridine ligands, not
only the electronegativity of the para-substituents at the
4.1. General considerations
All experimental work was routinely carried out using
Schlenk technique. Dried and purified argon was used as
inert gas. Solvents were purified by distillation from appro-
priate drying agents. Methylalumoxane (30% in toluene)
was purchased from Crompton (Bergkamen) and Albe-
marle (Baton Rouge, USA/Louvain–La Neuve, Belgium).
Ethylene (3.0) and argon (4.8/5.0) were supplied by Rieß-
ner Company (Lichtenfels). All other starting materials

C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
4591
were commercially available and were used without further
purification.
(83 mg, 0,12 mmol), copper(I) iodide (45 mg, 0,24 mmol),
and 2-methylbut-3-yne-2-ol (1 ml, 7 mmol) were added,
and the reaction mixture was stirred for 20 h at room tem-
perature. After removal of the solvent, water (50 ml) and n-
pentane (50 ml) were added. The organic phase was sepa-
rated, and the aqueous phase was extracted with n-pentane.
The combined organic phases were dried over sodium sul-
fate. Removal of the solvent in vacuo and recrystallization
from n-pentane furnished 4-(2-fluorenyl)-2-methylbut-3-
yn-2-ol (21) as colorless crystals in 85% yield.
4-(2-Fluorenyl)-2-methylbut-3-yn-2-ol (5 mmol) (21)
was dissolved in 100 ml of a mixture of methanol and
methylene chloride (4:1). Anhydrous potassium carbonate
(7.5 mmol) was added. After 2 h of stirring at room tem-
perature, the mixture was filtered over sodium sulfate,
and the solvent was removed in vacuo. The raw product
was purified by column chromatography (ethyl acetate/n-
pentane = 3:7). Yield: 80%.
NMR spectra were recorded at 25 °C on a Bruker ARX
250 spectrometer. The chemical shifts in the 1H NMR spec-
tra are referred to the residual proton signal of the solvent
(d = 7.24 ppm for CDCl3, d = 5.32 ppm for CDCl2) and in
13C NMR spectra to the solvent signal (d = 77.0 ppm for
CDCl3, d = 53.5 ppm for CDCl2). Mass spectra were rou-
tinely recorded at the Zentrale Analytik of the University
of Bayreuth with a VARIAN MAT CH-7 instrument
(direct inlet, EI, E = 70 eV) and a VARIAN MAT 8500
spectrometer. GC/MS spectra were recorded with a HP
5890 gas chromatograph in combination with a HP
5971A mass detector. At the Zentrale Analytik of the Uni-
versity of Bayreuth, GC/MS spectra were routinely
recorded with a HP5890 gas chromatograph in combina-
tion with a MAT 95 mass detector. For the analysis of
organic compounds, especially oligomer mixtures, a PER-
KIN ELMER Auto System gas chromatograph was used.
GPC measurements were routinely performed by SABIC
Company (Riyadh, Saudi Arabia). Some of the elemental
analyses were performed by the Mikroanalytisches Labor
Pascher at Remagen. The residual analyses were performed
with a VarioEl III CHN instrument.
4.5. General procedure for the Sonogashira coupling
reactions of halogenated bis(aryl-imino)pyridines with the
x-alkynyl functionalized indene and fluorene derivatives
26–29
Compounds 1–3 and 23–25 were prepared according to
the mentioned literature.
In 15 ml of triethylamine, an amount of 0.35 mmol of
the iodo substituted 2,6-bis(arylimino)pyridine compound
7 or 8, 0.70 mmol of an alkynyl substituted indene or fluo-
rene derivative, bis(triphenylphosphino)palladium dichlo-
ride (7 lmol) and copper(I) iodide (14 lmol) were
dissolved. The mixture was stirred for 20 h at room temper-
ature. After removal of the solvent, water (50 ml) and
n-pentane (50 ml) were added. The organic phase was sep-
arated, and the aqueous phase was extracted several times
with n-pentane. The combined organic phases were dried
over sodium sulfate. Removal of the solvent in vacuo, puri-
fication by column chromatography, and recrystallization
from n-pentane furnished the coupling products as yellow-
ish or brownish powders (yields: 55–60%).
4.2. Synthesis of the 2,6-bis(arylimino)pyridine compounds
4–10
To a solution of 0.82 g (5 mmol) 2,6-diacetylpyridine in
150 ml of toluene were added 12.5 mmol (2.5 equiv) of a
substituted aniline and a few milligrams of para-toluene-
sulfonic acid. The reaction mixture was heated under reflux
for 8–24 h applying a Dean–Stark-trap. After cooling to
room temperature, an amount of 200 ml of a saturated
sodium hydrogencarbonate solution was added, the
organic phase was separated, filtered over sodium sulfate
and silica. The solvent was removed and 10 ml ethanol
were added. The imino compounds precipitated when
stored at ꢁ20 °C for some days (yields: 50–80%).
4.6. General synthesis of the 2,6-bis(arylimino)pyridine
iron(II) and iron(III) complexes 11–18 and 30–32
4.3. Synthesis of 1-trimethylsilylindene (19) and 1-(2-
propinyl)-1-trimethylsilylindene (20)
An amount of 1.0 mmol of the 2,6-bis(arylimino)pyri-
dine compound was dissolved in 20 ml 1-butanol and
reacted with 1.0 mmol of anhydrous iron(II) chloride or
iron(III) chloride resulting in an immediate color change.
The mixture was stirred for 3 h at room temperature,
whereby the complexes precipitated. n-Pentane (10 ml)
was added for complete precipitation. The iron complexes
were filtered over a glass frit, washed three times with 15 ml
n-pentane and were dried in vacuo. Yields: 37–96%.
Indenyllithium (50 mmol) or 1-(trimethylsilyl)indenylli-
thium (50 mmol) were suspended in 200 ml of toluene.
The alkylation reagent (50 mmol) was added, and the reac-
tion mixture was stirred at room temperature over night.
Filtration over sodium sulfate and removal of the solvent
in vacuo yielded the substituted indene derivatives 19 and
20 as bright yellow viscous oils (90–95%).
4.7. Polymerization of ethylene in the 1 l Bu¨chi autoclave
4.4. Synthesis of 2-ethynylfluorene (22)
An amount of 0.2–2 mg of the desired iron complex was
suspended in 5 ml of toluene. Methylalumoxane (30% in
toluene, Fe:Al = 1:2500) was added resulting in an immedi-
2-Iodofluorene (6 mmol) was dissolved in 30 ml of tri-
ethylamine. Bis(triphenylphosphino)palladium dichloride

4592
C. Go¨rl, H.G. Alt / Journal of Organometallic Chemistry 692 (2007) 4580–4592
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ate color change. The mixture was added to a 1 l Schlenk
flask filled with 250 ml n-pentane. This mixture was trans-
ferred to a 1 l Buchi laboratory autoclave under inert atmo-
¨
sphere and thermostated at 60 °C. An ethylene pressure of
10 bar was applied for 1 h. The polymer was filtered off
using a glass frit, washed with diluted hydrochloric acid,
water, and acetone, and finally dried in vacuo.
To the oligomer solutions diluted hydrochloric acid was
added. The organic phase was separated and dried over
sodium sulfate. n-Pentane was distilled using a Vigreux col-
umn. The resulting oligomer mixtures were characterized
using gas chromatography.
[25] K. Onitsuka, M. Fujimoto, N. Ohshiro, S. Takahashi, Angew.
Chem., Int. Ed. 38 (1999) 689.
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Acknowledgement
We thank Saudi Basic Industries Corporation (SABIC),
Saudi Arabia, for the financial support.
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