Ferrous and cobaltous chloride complexes bearing 2-(1-(arylimino)methyl)-8- (1H-benzimidazol-2-yl)quinolines: Synthesis, characterization and catalytic behavior in ethylene polymerization

Article abstract of DOI:10.1016/j.polymer.2011.10.037

The series of ligands 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl) quinolines was synthesized and used to prepare new iron(II) and cobalt(II) dichloride complexes. X-ray diffraction studies revealed that the coordination geometry around the metal cent

Full text of DOI:10.1016/j.polymer.2011.10.037

Polymer 52 (2011) 5803e5810
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Polymer
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Ferrous and cobaltous chloride complexes bearing 2-(1-(arylimino)methyl)-
8-(1H-benzimidazol-2-yl)quinolines: Synthesis, characterization and catalytic
behavior in ethylene polymerization
,
Tianpengfei Xiao a, Shu Zhang a, Baixiang Li b, Xiang Hao a, Carl Redshawc
**
,
,b,
Yue-Sheng Li b, Wen-Hua Sun a
*
a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, China
b State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun 130022, China
c School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The series of ligands 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinolines was synthesized and
used to prepare new iron(II) and cobalt(II) dichloride complexes. X-ray diffraction studies revealed that
the coordination geometry around the metal center can best be described as distorted square-based
pyramidal. Upon activation with methylaluminoxane (MAO), both families (Fe and Co) of complexes
showed good activities in ethylene polymerization, affording highly linear polyethylenes. Enhanced
activities were observed on increasing the reaction temperature to 100 ꢀC. The optimization of the
reaction parameters and the influence of the substituents on the imino-bound aryl group of the chelate
ligands were investigated.
Received 28 August 2011
Received in revised form
11 October 2011
Accepted 20 October 2011
Available online 25 October 2011
Keywords:
2-Imino-8-benzimidazolylquinolines
Late-transition metal complex
Ethylene polymerization
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
2-imino-1,10-phenanthrolines [15e19], 2-(benzimidazol-2-yl)-1,10-
phenanthrolines [20], 2-benzimidazolyl-6-iminopyridines [21e24],
The discovery of bis(imino)pyridine complexes of iron(II) and
cobalt(II) as highly active pro-catalysts in ethylene polymerization
[1,2] provided a landmark from the view of both polyolefins and
catalysis [3e8]. In particular, not withstanding their high activity,
ferrous pro-catalysts have been explored for ethylene oligomeriza-
2-benzoxazolyl-6- iminopyridines [25,26], 2-quinoxalinyl-6-
iminopyridines [27], 2-methyl-2,4-bis-(6-iminopyridin-2-yl)-1H-
1,5-benzodiazepines [28,29], iminoquinolines [30], 2,8-bis(imino)
quinoline [31], and 8-(2-benzimidazolyl)-quinolines [32,33].
Despite these advances, the critical problem of the poor thermal
stability of such iron and cobalt systems remained, and the resul-
tant dramatic decreases in both catalyst activities and polymer
molecular weight at increased reaction temperatures were clearly
a hurdle to potential industrial application [3e14]. Given this,
catalytic development is targeted the thermally stable systems
[34e37], and variation of the substituents at the ortho-position of
the iminoaryl groups was mostly probed [38e42]. Moreover, new
ligand frameworks have been created [43e49], and indeed the
metal pro-catalysts bearing the 2,8-bis(imino)quinoline ligands
exhibited optimized performance at high temperature (100 ꢀC) for
ethylene polymerization [31]. Encouraged by the results obtained
by pro-catalysts bearing the 2,8-bis(imino)quinoline ligand system
[31], as well as for those bearing 2-benzimidazolyl-6-
iminopyridines [21e24], a series of 2-(1-(arylimino)methyl)-8-
(1H-benzimidazol-2-yl)quinoline ligands were synthesized and
the iron and cobalt complexes thereof prepared. When activated
with methylaluminoxane (MAO), these complexes exhibit good
tion due to their high selectivity for linear a-olefins [3]. Numerous
modifications of the bis(imino)pyridine framework have been made
in order to improve the catalytic performance of the complexes
[3e8]. Such modifications illustrate the influence of the steric and
electronic properties of the substituents on the catalytic behaviourof
the metal complexes [9e14], which can lead to the formation of
either high molecular weight polyethylene and/or oligomeric prod-
ucts [3e14]. Alternative models of the pro-catalysts have relied
on designing new tridentate ligands, and indeed, we have
reported highly active metal pro-catalysts bearing ligands such as
* Corresponding author. Key Laboratory of Engineering Plastics and Beijing
National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese
Academy of Science, Beijing 100190, China. Tel.: þ86 1062557955; fax: þ86
1062618239.
** Corresponding author. Fax: þ44 (0) 1603 592003.
E-mail addresses: carl.redshaw@uea.ac.uk (C. Redshaw), whsun@iccas.ac.cn
(W.-H. Sun).
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.10.037

5804
T. Xiao et al. / Polymer 52 (2011) 5803e5810
activities for ethylene polymerization, especially at higher reaction
temperatures. Herein, we report the synthesis and characterization
of the 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinoline
ligands, together with their ferrous and cobaltous complexes, and
investigate their catalytic performance in ethylene polymerization.
CDCl3, 25 ꢀC, TMS):
d
¼ 162.8, 154.3, 151.6, 150.1, 145.5, 143.7, 139.1,
134.6, 133.3, 131.6, 130.3, 130.2, 128.8, 127.0, 125.4, 123.7, 123.0,
120.1, 119.2, 111.9, 25.3, 15.1 ppm; Elemental analysis: calcd. (%) for
C27H24N4 (404.5): C 80.17, H 5.98, N 13.85; Found: C 80.21, H 6.18, N
13.56.
2. Experimental
2.2.3. 2-(1-(2,6-Diisopropylphenylimino)methyl)-8-(1H-benzimi-
dazol-2-yl)quinoline (L3)
2.1. General considerations
As for the synthesis of L1, L3 was obtained in the similar manner
in 70.0% yield as the yellow solid. m.p 121e123 ꢀC; FT-IR (KBr Disc):
v ¼ 3280, 3065, 1637, 1589, 1570, 1431, 1316, 1276, 1178, 848, 767,
All manipulations of air- and moisture-sensitive compounds
were performed under a nitrogen atmosphere using standard
Schlenk techniques. Toluene was refluxed over sodium-
benzophenone and distilled under argon prior to use. Methyl-
aluminoxane (MAO, a 1.46 M solution in toluene) was purchased
from Akzo Nobel Corp. 1H and 13C NMR spectra were recorded on
a Bruker DMX 400 MHz instrument at ambient temperature using
TMS as an internal standard. IR spectra were recorded on a Per-
kineElmer System 2000 FT-IR spectrometer. Elemental analysis
was carried out by using a Flash EA 1112 microanalyzer. DSC trace
and melting points of polyethylene were obtained from the second
scanning run on PerkineElmer DSC-7 at a heating rate of 10 ꢀC/min.
Molecular weights and molecular weight distribution of poly-
ethylenes were determined by a PL-GPC220 at 135 ꢀC with 1,2,4-
trichlorobenzene as the solvent.
739 cmꢁ1; 1H NMR (400 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 13.36 (br, 1H,
NH), 9.21 (d, 3J(H,H) ¼ 7.3 Hz, 1H, quin), 8.66 (s, 1H, ArN]CH), 8.47
(d, 3J(H,H) ¼ 8.5 Hz, 1H, quin), 8.44 (d, 3J(H,H) ¼ 8.5 Hz, 1H, quin),
7.99 (d, 3J(H,H) ¼ 7.9 Hz, 1H, quin), 7.90-7.84 (m, 1H, aryl), 7.80 (t,
3J(H,H) ¼ 7.7 Hz, 1H, quin), 7.55-7.49 (m, 1H, aryl), 7.32-7.27 (m, 2H,
aryl), 7.24 (d, 3J(H,H) ¼ 7.5 Hz, 2H, aryl), 7.22 (t, 3J(H,H) ¼ 7.4 Hz, 1H,
aryl), 3.08 (sept, 3J(H,H) ¼ 7.5 Hz, 2H, CH(CH3)2), 1.26 ppm (d,
3J(H,H) ¼ 6.8 Hz, 12H, CH(CH3)2); 13C{1H} NMR (100 MHz, CDCl3,
25 ꢀC, TMS):
d
¼ 162.3, 153.7, 151.1, 148.5, 145.0, 143.2, 138.6, 137.3,
134.1,131.1, 129.8, 129.7, 128.3, 126.5, 125.1, 123.4, 123.2, 122.5, 119.6,
118.8, 111.3, 28.2, 23.5 ppm; Elemental analysis: calcd. (%) for
C29H28N4 (432.6): C 80.52, H 6.52, N 12.95; Found: C 80.61. H 6.58, N
12.56.
2.2.4. 2-(1-(2,4,6-Trimethylphenylimino)methyl)-8-(1H-benzimi-
dazol-2-yl)quinoline (L4)
2.2. Preparation of the ligands
As for the synthesis of L1, L4 was obtained in the similar manner
in 53.9% yield as the yellow solid. m.p 118e120 ꢀC; FT-IR (KBr Disc):
v ¼ 3236, 3065, 1640, 1591, 1569, 1433, 1319, 1277, 1205, 1141, 845,
2.2.1. 2-(1-(2,6-Dimethylphenylimino)methyl)-8-(1H-
benzimidazol-2-yl)quinoline (L1)
Both 2,6-dimethylaniline (0.456 g, 3.77 mmol) and p-toluene-
sulfonic acid (0.010 g) were added to a solution of 2-formyl-8-(1H-
benzimidazol-2-yl)quinoline [50] (0.686 g, 2.51 mmol) in toluene,
using 4 Å molecular sieves as the water absorption agent. The
reaction mixture was refluxed for 12 h under an N2 atmosphere.
After the reaction was stopped, the solvent was removed and the
residue was eluted on an alumina column (petrol ether/ethyl
acetate (v/v) 10:1). L1 (0.5043 g, 1.36 mmol) was obtained in 54.3%
yield as a yellow solid. m.p. 114e116 ꢀC; FT-IR (KBr Disc;): v ¼ 3286,
766, 740 cmꢁ1; 1H NMR (400 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 13.34 (br,
1H), 9.21 (d, 3J(H,H) ¼ 7.4 Hz, 1H, quin), 8.68 (s, 1H, ArN]CH), 8.49
(d, 3J(H,H) ¼ 8.5 Hz, 1H, quin), 8.44 (d, 3J(H,H) ¼ 8.3 Hz, 1H, quin),
8.00 (d, 3J(H,H) ¼ 8.0 Hz, 1H, quin), 7.92-7.85 (m, 1H, aryl), 7.81 (t,
3J(H,H) ¼ 7.7 Hz, 1H, quin), 7.60-7.53 (m, 1H, aryl), 7.35-7.27 (m, 2H,
aryl), 7.00 (s, 2H, aryl), 2.35 (s, 3H, CH3), 2.23 ppm (s, 6H, CH3). 13
C
{1H} NMR (100 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 162.7, 153.8, 151.0,
147.9, 144.9,143.2, 138.3, 134.1, 131.0, 129.7,129.6, 129.0, 128.1, 126.7,
126.4, 123.1, 122.4, 119.5, 118.6, 111.4, 108.8, 20.8, 18.3 ppm;
Elemental analysis: calcd. (%) for C26H22N4 (390.5): C 79.97, H 5.68,
N 14.35; Found: C 80.11, H 5.58, N 14.56.
3051, 1644, 1593, 1567, 1401, 1315, 1194, 856, 742, 655 cmꢁ1
;
1H
NMR (400 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 13.32 (br, 1H, NH), 9.22 (d,
3J(H,H) ¼ 7.4 Hz, 1H, quin), 8.69 (s, 1H, ArN]CH), 8.50 (d,
3J(H,H) ¼ 8.6 Hz, 1H, quin), 8.45 (d, 3J(H,H) ¼ 8.6 Hz, 1H, quin), 8.01
(d, 3J(H,H) ¼ 8.1 Hz, 1H, quin), 7.91-7.85 (m, 1H, aryl), 7.81 (t,
3J(H,H) ¼ 7.8 Hz, 1H, quin), 7.64-7.56 (m, 1H, aryl), 7.35-7.25 (m, 2H,
aryl), 7.18 (d, 3J (H,H) ¼ 7.5 Hz, 2H, aryl), 7.07 (t, 3J(H,H) ¼ 7.3 Hz, 1H,
aryl), 2.26 ppm (s, 6H, CH3); 13C{1H} NMR (100 MHz, CDCl3, 25 ꢀC,
2.2.5. 2-(1-(2,6-Difluorophenylimino)methyl)-8-(1H-benzimidazol-
2-yl)quinoline (L5)
2-formyl-8-(1H-benzimidazol-2-yl)quinoline
(0.7253
g,
2.66 mmol), 2,6-difluoroaniline (0.5147 g, 3.99 mmol), and p-tol-
uenesulfonic acid (0.030 g) were combined with tetraethyl silicate
(5 mL) in a flask. The flask was equipped with a condenser along
with a water knockout trap, and the mixture was refluxed under
nitrogen for 28 h. Tetraethyl silicate was removed at reduced
pressure, and the resulting solid was eluted with petroleum ether/
ethyl acetate (v/v) 10:1) on an alumina column. The second eluting
part was collected and concentrated to give a yellow solid in 24.5%
yield. m.p. 125e127 ꢀC; FT-IR (KBr Disc): v ¼ 3258, 3060, 1635,1575,
1433, 1327, 1278, 1147, 850, 809, 769, 741 cmꢁ1 1H NMR (400 MHz,
TMS):
d
¼ 162.9, 153.8, 151.0, 150.3, 144.9, 143.2, 138.4, 134.2, 131.0,
129.8, 129.7, 128.3, 128.1, 126.8, 126.4, 124.6, 123.2, 122.5, 119.5,
118.6, 111.5, 18.4 ppm; Elemental analysis: calcd. (%) for C25H20N4
(376.5): C 79.76, H 5.35, N 14.88; Found: C 79.75, H 5.44, N 14.76.
2.2.2. 2-(1-(2,6-Diethylphenylimino)methyl)-8-(1H-benzimidazol-
2-yl)quinoline (L2)
As for the synthesis of L1, L2 was obtained in the similar manner
in 49.3% yield as the yellow solid. m.p. 117-119 ꢀC; FT-IR (KBr Disc):
v ¼ 3291, 3056, 1632, 1589, 1569, 1432, 1315, 1276, 1120, 845, 771,
CDCl3, 25 ꢀC, TMS):
d
¼ 13.26 (br, 1H, NH), 9.23 (d, 3J(H,H) ¼ 7.3 Hz,
1H, quin), 8.84 (s, 1H, ArN]CH), 8.51-8.41 (m, 2H, quin), 8.00 (d,
3J(H,H) ¼ 8.0 Hz, 1H, quin), 7.94-7.84 (m, 1H, aryl), 7.82 (t,
3J(H,H) ¼ 7.7 Hz, 1H, quin), 7.67-7.56 (m, 1H, aryl), 7.46 (d,
3J(H,H) ¼ 8.0 Hz, 2H, aryl), 7.36-7.27 (m, 2H, aryl), 7.12 ppm (t,
3J(H,H) ¼ 8.0 Hz, 1H, aryl); 13C{1H} NMR (100 MHz, CDCl3, 25 ꢀC,
740, 658 cmꢁ1; 1H NMR (400 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 13.34 (br,
1H, NH), 9.22 (d, 3J(H,H) ¼ 7.3 Hz, 1H, quin), 8.69 (s, 1H, ArN]CH),
8.49 (d, 3J(H,H) ¼ 8.5 Hz, 1H, quin), 8.45 (d, 3J(H,H) ¼ 8.5 Hz, 1H,
quin), 8.01 (d, 3J(H,H) ¼ 7.8 Hz, 1H, quin), 7.90-7.86 (m, 1H, aryl),
7.81 (t, 3J(H,H) ¼ 7.8 Hz, 1H, quin), 7.57-7.53 (m, 1H, aryl), 7.33-7.27
(m, 2H, aryl), 7.20 (d, 3J(H,H) ¼ 7.5 Hz, 2H, aryl), 7.15 (t,
3J(H,H) ¼ 7.4 Hz, 1H, aryl), 2.61 (q, 3J(H,H) ¼ 7.5 Hz, 4H, CH2CH3),
1.22 ppm (t, 3J(H,H) ¼ 7.5 Hz, 6H, CH2CH3); 13C {1H} NMR (100 MHz,
TMS):
d
¼ 165.6, 156.9, 154.4, 153.7, 151.1, 145.1, 143.3, 138.5, 134.4,
131.2, 129.8, 128.5, 126.8, 123.2, 122.6, 119.6, 119.4, 112.4, 112.2,
111.6 ppm; Elemental analysis: calcd. (%) for C23H14F2N4 (384.4): C
71.87, H 3.67, N 14.58; Found: C 71.49, H 3.75, N 14.23.

T. Xiao et al. / Polymer 52 (2011) 5803e5810
5805
2.2.6. 2-(1-(2,6-Dichlorophenylimino)methyl)-8-(1H-benzimidazol-
2-yl)quinoline (L6)
Complex Co2 was obtained as a yellow powder in 91.8% yield.
FT-IR (KBr Disc): v ¼ 3107, 1620, 1589, 1507, 1434, 1327, 1222, 988,
870, 750 cmꢁ1. Elemental analysis: calcd. (%) for C27H24Cl2CoN4
(534.4): C 60.69, H 4.53, N 10.49; Found: C 60.96, H 4.67, N 10.14.
Complex Co3 was obtained as a yellow powder in 90.3% yield.
FT-IR (KBr Disc): v ¼ 3166, 1624, 1590, 1523, 1435, 1327, 1221, 990,
856, 762 cmꢁ1; Elemental analysis: calcd. (%) for C29H28Cl2CoN4
(562.4): C 61.93, H 5.02, N 9.96; Found: C 61.72, H 5.24, N 9.63.
Complex Co4 was obtained as a yellow powder in 87.4% yield.
FT-IR (KBr Disc): v ¼ 3121, 1627, 1594, 1526, 1439, 1330, 1221, 993,
850, 768 cmꢁ1; Elemental analysis: calcd. (%) for C26H22Cl2CoN4
(520.3): C 60.02, H 4.26, N 10.77; Found: C 59.98, H 4.28, N 10.66.
Complex Co5 was obtained as a yellow powder in 86.1% yield.
FT-IR (KBr Disc): v ¼ 3062, 1635, 1590, 1514, 1433, 1322, 1212, 987,
861, 762 cmꢁ1; Elemental analysis: calcd. (%) for C23H14Cl2F2CoN4
(514.2): C 53.72, H 2.74, N 10.90; Found: C 53.76, H 2.95, N 10.67.
Complex Co6 was obtained as a yellow powder in 79.4% yield.
FT-IR (KBr Disc): v ¼ 3059, 1635, 1593, 1516, 1436, 1326, 1214, 988,
857, 763 cmꢁ1; Elemental analysis: calcd. (%) for C23H14Cl4CoN4
(547.1): C 50.49, H 2.58, N 10.24; Found: C 50.69, H 2.92, N 10.35.
As for the synthesis of L5, L6 was obtained in the similar manner
in 23.7% yield as the yellow solid. m.p. 130e132 ꢀC; FT-IR (KBr Disc):
v ¼ 3319, 3059, 1637, 1563, 1425, 1327, 1260, 1143, 1019, 843, 764,
738 cmꢁ1; 1H NMR (400 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 13.36 (br, 1H,
NH), 9.21 (d, 3J(H,H) ¼ 7.2 Hz, 1H, quin), 9.12 (s, 1H, ArN]CH), 8.42
(s, 2H, quin), 7.98 (d, 3J(H,H) ¼ 7.9 Hz, 1H, quin), 7.93-7.84 (m, 1H,
aryl), 7.80 (t, 3J(H,H) ¼ 7.5 Hz,1H, quin), 7.68-7.58 (m,1H, aryl), 7.39-
7.27 (m, 2H, aryl), 7.23-7.16 (m, 1H, aryl), 7.14-7.02 ppm (m, 2H,
aryl); 13C{1H} NMR (100 MHz, CDCl3, 25 ꢀC, TMS):
d
¼ 166.4, 153.1,
151.0,146.5,145.1,143.3,138.7,134.3,131.4,130.0,129.8,128.7,126.8,
126.0, 125.8, 123.3, 122.6, 119.7, 119.3, 111.7 ppm; Elemental anal-
ysis: calcd. (%) for C23H14Cl2N4 (417.3): C 66.20, H 3.38, N 13.43;
Found: C 66.15, H 3.75, N 13.23.
2.3. Synthesis of the iron complexes Fe1 e Fe6
The stoichiometric reaction of ligand and FeCl2$4H2O was
carried out in a Schlenk tube, which was purged three times with
N2 and then charged with freshly distilled THF. The reaction
mixture was stirred at room temperature for 10 h. The resulting
precipitate was filtered, washed with diethyl ether three times, and
dried in a vacuum at 60 ꢀC. All the iron(II) complexes (Fe1 e Fe6)
were prepared in high yields in this manner. Data for iron
complexes are as follows:
Complex Fe1 was obtained as a green powder in 72.4% yield. FT-
IR (KBr Disc): v ¼ 3116, 1621, 1589, 1519, 1434, 1406, 1326, 1176, 986,
865, 743 cmꢁ1; Elemental analysis: calcd. (%) for C25H20Cl2FeN4
(503.2): C 59.67, H 4.01, N 11.13; Found: C 59.49, H 4.12, N 10.77.
Complex Fe2 was obtained as a green powder in 84.4% yield. FT-
IR (KBr Disc): v ¼ 3103, 1625, 1592, 1517, 1432, 1324, 987, 848,
749 cmꢁ1; Elemental analysis: calcd. (%) for C27H24Cl2FeN4 (531.3):
C 61.04, H 4.55, N 10.55; Found: C 61.24, H 4.75, N 10.36.
2.5. Procedure for ethylene polymerization
Ethylene polymerization were performed in a stainless steel
autoclave (0.25 L capacity) equipped with a mechanical stirrer and
a temperature controller. A 100 mL amount of toluene containing
the catalyst precursor was transferred to the fully dried reactor
under nitrogen atmosphere. The required amount of co-catalyst
was then injected into the reactor via a syringe. At the required
reaction temperature, the reactor was immediately pressurized to
high ethylene pressure, and the ethylene pressure was kept
constant with feeding of ethylene. After the reaction mixture was
stirred for the desired period, the pressure was released and the
mixture was cooled to room temperature. Following this, the
residual reaction solution was quenched with 30% hydrochloride
acid ethanol, and then the precipitated polymer was collected by
filtration, and was adequately washed with ethanol and water, and
was dried in a vacuum until of constant weight.
Complex Fe3 was obtained as a green powder in 87.4% yield. FT-
IR (KBr Disc): v ¼ 3168, 1629, 1592, 1518, 1434, 1323, 985, 861,
745 cmꢁ1; Elemental analysis: calcd. (%) for C29H28Cl2FeN4 (559.3):
C 62.27, H 5.05, N 10.02; Found: C 62.25, H 5.01, N 9.79.
Complex Fe4 was obtained as a green powder in 88.1% yield. FT-
IR (KBr Disc): v ¼ 3168, 1619, 1592, 1437, 1325, 1214, 1143, 990, 848,
734 cmꢁ1; Elemental analysis: calcd. (%) for C26H22Cl2FeN4 (517.2):
C 60.38, H 4.29, N 10.83; Found: C 60.33, H 4.33, N 10.96.
Complex Fe5 was obtained as a green powder in 85.8% yield. FT-
2.6. X-ray crystallographic Study
Data were collected with an MM007-HF CCD (Saturn 724þ)
diffractometer with graphite monochromated Mo-K
a radiation
IR (KBr Disc): v ¼ 3143, 1613, 1590, 1528, 1146, 842, 685 cmꢁ1
;
(l
¼ 0.71073 Å) at 173(2) K. Cell parameters were obtained by global
Elemental analysis: calcd. (%) for C23H14Cl2F2FeN4 (511.1): C 54.05, H
2.76, N 10.96; Found: C 54.33. H 2.85, N 10.73.
Complex Fe6 was obtained as a green powder in 80.7% yield. FT-
IR (KBr Disc): v ¼ 3059, 1613, 1531, 1569, 1514, 1454, 1404, 850, 773,
749 cmꢁ1; Elemental analysis: calcd. (%) for C23H14Cl4FeN4 (544.0):
C 50.78, H 2.59, N 10.30; Found: C 50.68, H 2.83, N 10.31.
refinement of the positions of all collected reflections. Intensities
were corrected for Lorentz and polarization effects and empirical
absorption. The structures were solved by direct methods and
refined by full-matrix least-squares on F2. All hydrogen atoms were
placed in calculated positions. Structure solution and refinement
were performed by using the SHELXL-97 package [51]. Crystal data
and processing parameters for of Fe1, Fe4, Co2, Co3 and Co4 are
summarized in Table 1.
2.4. Synthesis of the cobalt complexes Co1 e Co6
The solution of CoCl2 in ethanol was added to a solution of
ligand L1 at room temperature, and the solution turned blue
immediately. After the reaction mixture was stirred for 10 h, diethyl
ether was added into the mixture. The resultant precipitate was
filtered, washed with diethyl ether and dried in a vacuum to obtain
the pure product. All the cobalt (II) complexes (Co1 e Co6) were
prepared in high yields in this manner. Data for cobalt complexes
are as follows:
Complex Co1 was obtained as a yellow powder in 88.2% yield.
FT-IR (KBr Disc): v ¼ 3112, 1625, 1593, 1512, 1436, 1327, 1147, 992,
850, 749 cmꢁ1; Elemental analysis: calcd. (%) for C25H20Cl2CoN4
(506.3): C 59.31, H 3.98, N 11.07; Found: C 59.04, H 4.38, N 11.36.
3. Results and discussion
3.1. Synthesis and characterization of ligands and complexes
The 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quino-
line ligands (L1eL6) were synthesized in satisfactory yields
through the condensation reaction of 2-formyl-8-(1H-benzimida-
zol-2-yl)quinoline with the corresponding anilines, in the presence
of a catalytic amount of p-toluenesulfonic acid. However, adapta-
tions were necessary using different solvents and water absorbing
reagents in order to improve the yields. All ligands (L1eL6) were
consistent with their elemental analyses and were characterized by

5806
T. Xiao et al. / Polymer 52 (2011) 5803e5810
Table 1
Crystal data and structure refinement for Fe1, Fe4, Co2, Co3 and Co4.
Fe1
Fe4
Co2
Co3
Co4
CCDC No.
Empirical formula
Fw
829448
C25H20Cl2FeN4
503.20
829449
C26H22Cl2FeN4
517.23
829450
C27H24Cl2CoN4
534.33
829451
C29H28Cl2CoN4
562.38
829452
C26H22Cl2CoN4
520.31
Crystal color
Crystal system
space group
a (Å)
green
Monoclinic
P2(1)/n
12.955(3)
10.611(2)
16.057(3)
98.51(3)
2182.9(8)
4
green
Monoclinic
P2(1)/c
18.312(4)
7.4549(15)
16.962(3)
90.53(3)
2315.5(8)
4
black
Monoclinic
P2(1)/c
7.3558(15)
19.744(4)
16.566(3)
94.37(3)
2399.0(8)
4
brown
Monoclinic
P2(1)/n
13.000(3)
14.352(3)
14.380(3)
93.00(3)
2679.3(9)
4
brown
Monoclinic
P2(1)/c
18.486(4)
7.3998(15)
16.828(3)
90.90(3)
2301.7(8)
4
b (Å)
c (Å)
b
(ꢀ)
Volume (Å3)
Z
Dcalc(Mg mꢁ3
)
1.531
0.957
1.484
0.905
1.479
0.962
1.394
0.865
1.501
1.000
m
(mmꢁ1
)
F(000)
Crystal size (mm)
range (ꢀ)
1032
1064
1100
1164
1068
0.22 ꢂ 0.21 ꢂ 0.06
1.89e27.48
ꢁ16 ꢃ h ꢃ 16,
ꢁ13 ꢃ k ꢃ 13,
ꢁ13 ꢃ l ꢃ 20
0.12 ꢂ 0.07 ꢂ 0.01
2.22e27.47
ꢁ23 ꢃ h ꢃ 23,
ꢁ8 ꢃ k ꢃ 9,
ꢁ19 ꢃ l ꢃ 22
0.13 ꢂ 0.12 ꢂ 0.12
1.61e27.46
ꢁ9ꢃh ꢃ 7,
ꢁ25 ꢃ k ꢃ 25,
ꢁ15 ꢃ l ꢃ 21
0.28 ꢂ 0.21 ꢂ 0.21
2.01e27.45
ꢁ16 ꢃ h ꢃ 16,
ꢁ16 ꢃ k ꢃ 18,
ꢁ18 ꢃ l ꢃ 18
0.11 ꢂ 0.11 ꢂ 0.02
2.20e27.50
ꢁ24 ꢃ h ꢃ 16,
ꢁ9ꢃk ꢃ 9,
ꢁ21 ꢃ l ꢃ 18
q
Limiting indices
Completeness to
q
(%)
99.7 (
Empirical
4997/0/289
q
¼ 27.48)
99.8 (
Empirical
5298/0/298
q
¼ 27.47)
97.3 (
Empirical
5348/0/307
q
¼ 27.46)
99.2 (
Empirical
6083/0/325
q
¼ 27.45)
97.7 (
Empirical
5168/0/298
q
¼ 27.05)
Absorption correction
Data/restraints
/parameters
Goodness-of-fit on F2
Final R indices
[I > 2s (I)]
1.088
1.179
1.097
1.112
1.165
R1 ¼ 0.0469,
wR2 ¼ 0.1139
R1 ¼ 0.0510,
wR2 ¼ 0.1172
0.454 and ꢁ0.597
R1 ¼ 0.0989,
wR2 ¼ 0.1675
R1 ¼ 0.1365,
wR2 ¼ 0.1839
0.443 and ꢁ0.641
R1 ¼ 0.0487,
wR2 ¼ 0.0981
R1 ¼ 0.0550,
wR2 ¼ 0.1018
0.317 and ꢁ0.513
R1 ¼ 0.0416,
wR2 ¼ 0.0978
R1 ¼ 0.0446,
wR2 ¼ 0.0999
0.401 and ꢁ0.621
R1 ¼ 0. 0817,
wR2 ¼ 0.1753
R1 ¼ 0.0953,
wR2 ¼ 0.1843
0.521 and ꢁ0.790
R indices (all data)
Largest diff peak and
hole (e Åꢁ3
)
1H and 13C NMR spectroscopy as well as by FT-IR, in which the C]N
stretching frequencies appeared in the range of 1632e1644 cmꢁ1
As shown in Fig. 1, the iron atom in Fe1 is coordinated with five
atoms comprising three nitrogen atoms and two chlorides within
a pseudo square-pyramid. The square-basal atoms of N1, N2, N3
and Cl2 are almost co-planar with a deviation of less than 0.2 Å,
.
The metal complexes were synthesized by mixing the corre-
sponding ligands with one equivalent of MCl2 in suitable solvents
(Scheme 1), and the resultant products were precipitated from the
solution and collected via filtration. All iron complexes Fe1eFe6
were formed as green solids, and were stable in the solid state.
However, solutions slowly changed from green to yellow, due to the
oxidation of FeII to FeIII. The cobalt analogs Co1eCo6 were yellow
powders and stable in both solution and the solid state.
All metal complexes were obtained in good yields, and were of
sufficient purity (elemental analyses) for further use. Compared
with the corresponding ligands, the stretching vibration bands of
C]N of these metal complexes in the IR spectra shifted to lower
frequencies in the range 1613e1629 cmꢁ1, and with the greatly
reduced intensities, indicating the effective coordination between
the imino-nitrogen and the metal. Moreover, the molecular struc-
tures of complexes Fe1, Fe4 and Co2e4 were confirmed by the
single crystal X-ray diffraction.
whilst the iron lies 0.438
Å
out of the basal plane
(Cl2eN1eN2eN3). The plane of three nitrogen atoms (N1, N2, and
N3) is almost co-planar with the quinolinyl plane with the dihedral
angle of ca. 7.86ꢀ. Considering the FeeCl bond lengths, the longer
bond is to the apical chloride (2.3705(8) Å), compared to that to the
basal counterpart (2.2973(10) Å). The coordination of the benz-
imidazole group with iron centre is via an sp2 nitrogen (N3) instead
R1
H2N
R2
N
N
N
R1
O
N
NH
R1
R1
N
NH
R2
3.2. X-ray crystallographic studies
L1 − L6
R1
R2
THF or
Me Et
iPr Me
Me
F
H
Cl
H
MCl2
Single crystals of Fe1, Fe4 and Co2-4 suitable for the X-ray
diffraction analysis were obtained by slow diffusion of diethyl ether
into the methanol solutions. In the case of iron, it was necessary for
the complexes to be crystallized under a nitrogen atmosphere. The
X-ray crystallographic studies revealed that all metal complexes
can be described as adopting a pseudo square-based pyramidal
geometry at the metal, in which the square base is comprised of the
three coordinating nitrogen atoms of the chelate ligand and one
chloride, whilst the other chloride atom is at the apical position. For
comparison, selected bond lengths and angles are tabulated in
Table 2.
ethanol
H
H
H
L1 L2 L3 L4 L5 L6
R1
N
Fe1 Fe2 Fe3 Fe4 Fe5 Fe6
N
M
Cl Cl
Co1 Co2 Co3 Co4 Co5 Co6
N
NH
R2
R1
Fe1 − Fe6; Co1 − Co6
Scheme 1. Synthetic procedure for 2-(1-(arylimino)methyl)-8-(benzimidazolyl)-2-
lines and their metal complexes.

T. Xiao et al. / Polymer 52 (2011) 5803e5810
5807
Table 2
Selected bond lengths (Å) and angles (ꢀ) for Fe1, Fe4, Co2, Co3, and Co4.
Fe1
Fe4
Co2
Co3
Co4
Bond lengths (Å)
MeN1
MeN2
MeN3
2.202(2)
2.201(4)
2.153(5)
2.079(4)
2.165(2)
2.112(2)
2.066(2)
2.1873(17)
2.1279(16)
2.0726(17)
2.3540(7)
2.175(4)
2.179(2)
2.119(2)
2.3705(8)
2.122(4)
2.055(4)
2.3358(14)
2.3149(14)
1.322(5)
1.360(6)
1.281(6)
1.444(6)
1.342(6)
1.403(6)
MeCl1
MeCl2
N1eC1
N1eC9
N2eC10
N2eC11
N3eC17
N3eC18
2.3461(17) 2.3323(8)
2.2973(10) 2.3356(17) 2.3021(10) 2.2979(9)
1.338(3)
1.366(3)
1.274(3)
1.447(3)
1.342(3)
1.410(3)
1.335(6)
1.365(6)
1.284(7)
1.444(6)
1.334(6)
1.415(7)
1.333(3)
1.355(3)
1.279(3)
1.450(3)
1.333(3)
1.405(3)
1.336(2)
1.357(2)
1.283(2)
1.449(2)
1.343(2)
1.407(2)
Bond angles (ꢀ)
N1eMeN2
N1eMeN3
N2eMeN3 142.00(8)
N1eMeCl1 91.32(6)
N1eMeCl2 163.05(6)
N2eMeCl1 102.21(6)
N2eMeCl2
N3eMeCl1 109.39(6)
N3eMeCl2 102.81(6)
Cl1eMeCl2 101.35(3)
75.38(8)
83.18(8)
74.70(17)
81.47(17)
133.22(17) 132.17(8)
89.44(13) 88.77(6)
169.49(13) 171.62(6)
105.25(14) 109.50(6)
95.61(14)
114.27(13) 111.43(7)
103.00(13)
97.19(6)
75.11(8)
82.05(8)
75.52(6)
82.25(6)
131.86(6)
83.82(4)
175.25(4)
104.45(5)
99.77(5)
115.02(5)
101.60(4)
96.92(2)
75.59(14)
82.38(15)
133.08(15)
86.66(11)
173.12(11)
105.19(12)
97.72(11)
114.38(11)
101.47(12)
96.79(5)
90.82(6)
98.10(6)
Fig. 2. Molecular structure of complex Co2 with thermal ellipsoids at the 30% prob-
ability. Hydrogen atoms have been omitted for clarity.
99.48(6)
98.24(3)
of the sp3 nitrogen (N4). The dihedral angle between the aryl plane
linked to the imino group and the basal coordination plane
N1eN2eN3 is 76.58ꢀ, indicating a twist away from the quinolinyl
plane, ie approaching perpendicular.
Similar structural features were observed for the iron complex
Fe4, however, the iron atom has a larger deviation (0.829 Å) from
3.3. Ethylene polymerization
Various alkylaluminum reagents were employed as co-catalysts
with both the iron and cobalt pro-catalysts. Catalytic systems with
methylaluminoxane (MAO) were found to exhibit the best catalytic
activity in ethylene polymerization. As a consequence, activation
employing MAO as co-catalyst was investigated in detail.
the basal coordination plane (Q N1eN2eN3). Its molecular struc-
ture is available in the Supporting Information.
A similar pseudo square-pyramid geometry was also exhibited
by the cobalt complexes Co2, Co3 and Co4; the molecular structure
of Co2 is shown in Fig. 2 whilst the molecular structures of Co3 and
Co4 are available in the Supporting Information. The three coor-
dinated nitrogen atoms and one chloride which comprise the basal
square are almost co-planar with deviations in the range
0.37e0.44 Å, and the cobalt atoms deviate from the basal plane at
a distance of 0.447 Å (Co2), 0.385 Å (Co3) and 0.405 Å (Co4). The
dihedral angles between the planes of the phenyl and the quinolyl
rings are different (Co2: 87.75ꢀ; Co3: 70.50ꢀ; Co4: 54.55ꢀ), while
the dihedral angles between the benzoimidazolyl and the quinolyl
rings are 39.13ꢀ (C2b), 17.11ꢀ (C3b) and 20.00ꢀ (C4b), respectively.
3.3.1. Ethylene polymerization by iron complexes
The pro-catalyst Fe3 was typically investigated by varying
various reaction parameters such as the reaction temperature,
molar ratio of Al/Fe and the ethylene pressure. There was no
activity observed at ambient temperature, and the catalytic system
produced only trace polyethylene at 40 ꢀC. When the reaction
temperature was elevated to 60 ꢀC or higher (runs 1e3, Table 3),
ethylene polymerization occurred with good activity. The activities
steadily increased with increased reaction temperature (runs 1e3,
Table 3), whilst the molecular weights of the resultant poly-
ethylenes gradually decreased and with narrower molecular
weight distribution (Fig. 3). It was believed that the formation of
Table 3
Ethylene polymerization using iron Complexes.a
Run Pro-cat. Al/Fe T/ꢀC P/MPa Activityb PE yield/g Tm /ꢀC Mw
Mw/Mn
c
d
d
( ꢂ 10ꢁ4
)
1
2
3
4
5
6
7
8
9
Fe3
Fe3
Fe3
Fe3
Fe3
Fe3
Fe3
Fe3
Fe3
3000 60
3000 80
3000 100
1000 100
2000 100
2500 100
3500 100
3000 100
3000 100
3000 100
3000 100
3000 100
3000 100
3000 100
3
3
3
3
3
3
3
2
1
3
3
3
3
3
1.53
3.21
6.53
2.32
3.86
5.66
6.19
3.63
1.23
2.83
4.64
3.31
0.941
1.46
0.383
0.803
1.63
0.581
0.965
1.42
135.6 159.0
19.0
11.5
4.1
nd
135.1 91.3
134.6 26.7
134.9 nd
134.5 42.0
134.5 29.4
133.0 16.5
134.6 33.2
134.2 36.0
133.0 20.1
134.4 24.5
133.5 23.5
132.6 17.7
133.3 28.4
7.3
5.9
4.0
5.0
6.6
5.4
4.8
5.8
5.4
6.8
1.55
0.908
0.253
0.708
1.16
0.828
0.235
0.366
10 Fe1
11 Fe2
12 Fe4
13 Fe5
14 Fe6
a
Conditions: 5 mmol Fe; polymerization time: 30 min; 100 mL toluene.
b
105 g molꢁ1(Fe)$hꢁ1
Determined by DSC.
Determined by GPC.
.
c
Fig. 1. Molecular structure of complex Fe1 with thermal ellipsoids at the 30% proba-
bility. Hydrogen atoms have been omitted for clarity.
d

5808
T. Xiao et al. / Polymer 52 (2011) 5803e5810
Fig. 5. The GPC curves of PEs produced by iron complexes at different ethylene
pressure.
Fig. 3. The GPC curves of PEs produced by iron complexes at different reaction
temperature.
of a methyl group at the para position of the imino phenyl ring
group increased the catalytic activities probably due to enhanced
solubility properties. On changing the substituents at the ortho
position of the imino phenyl ring from an alkyl group to a halogen
group, the activities greatly decreased. In general, the molecular
weight distributions of resultant polyethylenes were relatively
broad, indicating multimodal features of the polymers formed, and
also more than one active species [55e70]. Checking the influences
of the ligand environment on the properties of polyethylenes (runs
3, 10e14, Table 3), the molecular weights of the resultant poly-
ethylenes gradually increased in the order of L1 < L2 < L3 due to
the bulky effect of substituents on arylimino ring, and the Mw ob-
tained by C6 (R1 ¼ Cl) was higher than that obtained by C5 (R1 ¼ F).
At the same time, the introduction of a methyl group at the para
position of the imino phenyl ring group also slightly increased the
molecular weights. Similar trends also could be found for the cobalt
complexes.
the thermally stable active species required relatively high
temperatures. Within bis(imino)pyridylmetal pro-catalysts, there
are few examples of systems providing good activities at high
temperature [32,41,52e54]; the current pro-catalysts provide an
alternative model of tridentate iron pro-catalysts in ethylene
polymerization.
The Al/Fe molar ratio was varied from 1000 to 3500 (runs 4e7,
Table 3), the highest activity was observed with an Al/Fe of 3000.
Though similar activities were observed over the Al/Fe range of
2500e3500, the molecular weights and distributions both
decreased on employing a higher Al/Fe molar ratio (Fig. 4), indic-
ative of chain transfer and termination from the iron-species to
aluminum. According to the narrower molecular distribution of
polyethylene obtained with higher Al/Fe molar ratios, common
active species were present displaying similar catalytic processes.
Upon increasing the ethylene pressure (runs 3, 8 and 9, Table 3),
the activities were increased, whilst lower molecular weights and
narrower distributions of the resultant polyethylenes were
observed with higher ethylene pressure (Fig. 5), indicating probable
migration of the active species from the polymeric chain to the
monomer.
In the following, the iron pro-catalysts with differing substitu-
ents were investigated for their catalytic performance (runs 3,
10e14, Table 3). The activities gradually increased on tuning the
sterics of the group on the ortho position of imino phenyl ring, e.g.
on going from a methyl group to an isopropyl group. The bulkier
substituent could retard the effect of unwanted impurities and
impart protection at the active species [1,2,9e14]. The introduction
3.3.2. Ethylene polymerization by cobalt pro-catalysts
When using the Co3/MAO system (runs 1e9, Table 4), similar to
the catalytic system Fe3/MAO, the higher the reaction temperature
used (runs 1e3, Table 4), the higher the catalytic activities
observed, but the lower the molecular weight and the narrower
molecular weight distribution of the polyethylene obtained. The
higher the Al/Fe molar ratio employed, the lower the molecular
weight and the narrower the molecular weight distribution of
polyethylene formed. The best activity was observed at the Al/Fe of
3000. The higher the ethylene pressure used (runs 3, 8 and 9,
Table 4), the higher the catalytic activity observed, but the lower
the molecular weight of the polyethylene obtained.
All the other cobalt pro-catalysts were investigated using these
optimum polymerization conditions (runs 3, 10e14, Table 4). The
catalytic activities were observed to be in the order
Co3 > Co2 > Co4 > Co1 and Co6 > Co5, consistent with the
performance of their iron analogs, and again, pro-catalysts bearing
halo-substituents at the ortho position of the imino phenyl ring
exhibited lower activities than did their analogs bearing alkyl-
substituents. Compared with the iron complexes, the cobalt
complexes exhibited slightly lower catalytic activities; the Mw ob-
tained by the cobalt complexes were equal to those of the iron
complexes. In general, the Fe catalysts are more active than the
corresponding Co analogues in bis(imino)pyridine system [1e6].
The nature of the metal center has a large influence on catalyst
performance. However, catalyst performance is also strongly
dependent on the nature of the donor atoms, the electronic and
steric effects of the substituents, and the nature of the chelate
ligand.
Fig. 4. The GPC curves of PEs obtained at different molar ratios of Al/Fe.

T. Xiao et al. / Polymer 52 (2011) 5803e5810
5809
d
Table 4
Ethylene polymerization using the cobalt Pro-catalysts.a
Activityb
PE/g
c
Tm /ꢀC
Run
Complex
Al/Co
T/ꢀC
P/MPa
Mwd( ꢂ 10ꢁ4
)
Mw/Mn
1
2
3
4
5
6
7
8
Co3
Co3
Co3
Co3
Co3
Co3
Co3
Co3
Co3
Co1
Co2
Co4
Co5
Co6
3000
3000
3000
1000
2000
2500
3500
3000
3000
3000
3000
3000
3000
3000
60
80
3
3
3
3
3
3
3
2
1
3
3
3
3
3
1.08
2.11
4.05
0.963
2.83
3.39
3.88
2.67
1.01
2.33
3.67
3.03
0.663
0.936
0.269
0.529
1.01
135.6
135.3
134.1
135.1
134.6
134.3
132.5
134.5
134.8
133.3
133.6
133.6
133.3
134.1
nd
nd
122.7
29.0
nd
14.7
6.2
nd
100
100
100
100
100
100
100
100
100
100
100
100
0.241
0.708
0.848
0.969
0.668
0.253
0.583
0.918
0.758
0.189
0.234
34.2
29.2
24.4
29.5
39.2
21.3
25.4
22.1
18.2
25.9
5.2
6.2
6.4
6.3
6.4
4.8
4.7
4.7
4.0
5.5
9
10
11
12
13
14
a
Conditions: 5 mmol Co; polymerization time: 30 min; 100 mL toluene.
b
c
105 g molꢁ1(Co)$hꢁ1
Determined by DSC.
Determined by GPC.
.
d
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4. Conclusion
The series of iron(II) and cobalt(II) complexes bearing 2-(1-
(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinoline ligands
were synthesized and fully characterized. X-ray diffraction studies
confirmed the structural geometry at the metal as a distorted
square-based pyramidal. Upon activation with MAO, the iron and
the cobalt pro-catalysts all exhibited good activities in ethylene
polymerization at 100 ꢀC, indicating the thermal stability of the
active species. Although the bulk of the ligands could enhance the
catalytic activities of the metal pro-catalysts, lower molecular
weights and narrower distributions of resultant polyethylenes were
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Acknowledgment
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Appendix. Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.polymer.2011.10.037.
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