Dichlorocobalt(II) complexes ligated by bidentate 8-(benzoimidazol-2-yl) quinolines: Synthesis, characterization, and catalytic behavior toward ethylene

Article abstract of DOI:10.1021/om2003392

A series of (8-(benzoimidazol-2-yl)quinoline)dichlorocobalt(II) complexes was prepared and characterized, and single-crystal X-ray diffraction revealed the distorted-tetrahedral geometry around the cobalt atom. Activated with methylaluminoxane (MAO), thes

Full text of DOI:10.1021/om2003392

ARTICLE
pubs.acs.org/Organometallics
Dichlorocobalt(II) Complexes Ligated by Bidentate
8-(Benzoimidazol-2-yl)quinolines: Synthesis, Characterization,
and Catalytic Behavior toward Ethylene
Tianpengfei Xiao,† Peng Hao,† Gerald Kehr,‡ Xiang Hao,† Gerhard Erker,‡ and Wen-Hua Sun*,†,§
†Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Science, Beijing 100190, People's Republic of China
‡Organisch-Chemisches Institut der Universit€at M€unster, Corrensstraße 40, 48149 M€unster, Germany
§State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Science,
Lanzhou 730000, People's Republic of China
S Supporting Information
b
ABSTRACT: A series of (8-(benzoimidazol-2-yl)quinoline)dichlorocobalt(II) complexes was prepared and
characterized, and single-crystal X-ray diffraction revealed the distorted-tetrahedral geometry around the cobalt
atom. Activated with methylaluminoxane (MAO), these cobaltous complexes showed special properties of
ethylene reactivity: ethylene oligomerization with an observed activity up to 3 Â 104 g (mol of Co)À1 hÀ1 atmÀ1
with reaction temperature lower than 60 °C at ambient or 10 atm ethylene pressure and ethylene poly-
merization with an observed activity up to 1 Â 105 g (mol of Co)À1 hÀ1 atmÀ1 with reaction temperature higher
than 60 °C at 30 atm ethylene pressure, indicating two potentially active species formed at different reaction parameters. The
obtained polyethylenes with high molecular weights and narrow molecular weight distributions, to the best of our knowledge, give
the first proof of dichlorocobalt complex precatalysts bearing bidentate ligands acting as single-site catalysts in ethylene polymerization.
Scheme 1. Cobalt Precatalysts for Ethylene Polymerization
at Elevated Temperature
1. INTRODUCTION
The utilization of bis(imino)pyridine complexes of iron(II) or
cobalt(II) for ethylene oligomerization and polymerization has
attracted much interest in both academic and industrial fields
over the past dozen years.1 The extensive investigations have
favored the iron derivatives because of better catalytic perfor-
mances by iron precatalysts than by cobalt precatalysts,2 and their
active species and reaction mechanisms have also been illustrated.3
The catalytic features rely on the electronic and/or steric influence of
the ligands used,4 and the variations of bis(imino)pyridines and their
metal precatalysts have been studied.5 Meanwhile, some effort has
been made to exploit new tridentate N-donating ligands for new
model precatalysts,6 and series of successful precatalysts included
novel ligands from our group in Beijing such as 2-benzoimidazolyl-6-
iminopyridines,7 2-quinoxalinyl-6-iminopyridines,8 2-benzoxazolyl-6-
iminopyridines,9 2-imino-1,10-phenanthrolines,10 2-(benzoimidazol-
2-yl)-1,10-phenanthrolines,11 iminoquinoline derivatives,12 and
2-methyl-2,4-bis-(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines.13
Elevated reaction temperatures commonly resulted in deactivation
of the catalytic systems of late-transition-metal procatalysts,1,5a,14
which has been a critical deficiency because of the highly exother-
mic reaction of the ethylene polymerization or oligomerization re-
actions. Therefore, enhancing the stabilities of precatalysts has been
targeted through modifying ligands for certain potential precatalysts.15
Regarding cobalt precatalysts operating at elevated reaction tempera-
tures, two model complexes bearing either 2-(2-benzoxazolyl)-6-
iminopyridines (Scheme 1, A)9a or 2,8-bis(imino)quinolines
(Scheme 1, B)16 maintained good activities of ethylene polymeriza-
tion and produced polyethylenes with narrow molecular distributions.
The molecular structures of cobalt(II) complexes bearing
2,8-bis(imino)quinoline ligands showed a distorted-pyramidal
geometry; therefore, it is worth considering the metal precatalysts
bearing bidentate ligands. There were some trials of bidentate
cobalt precatalysts showing either ethylene oligomerization4a,b,17,18
or low polymerization activity at low temperature.19 The cobalt
complexes ligated by N-(1-(quinolin-2-yl)propylidene)benzenamines
(Scheme 1, C) showed temperature-switch features in ethylene
reactivity and favored ethylene polymerization at elevated
Received: April 21, 2011
Published: August 25, 2011
r
2011 American Chemical Society
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Scheme 2. Synthesis of Cobalt Complexes
temperatures,20 and such a phenomenon was similar to the
observation for the 2-(2-benzoxazolyl)-6-iminopyridylcobalt
precatalysts.9a The achievement by model C,20 maintaining only
an 2-imino group on the quinoline rings from the model B,
inspired us to explore the extensive 8-(benzoimidazol-2-yl)-
quinolines for cobalt complexes (this work) herein. Iron com-
plexes bearing 8-(benzoimidazol-2-yl)quinolines showed high
activities toward ethylene polymerization;21a meanwhile, dialky-
laluminum compounds ligated by 8-(benzimidazol-2-yl)-
quinaldine exhibited high activities in the ring-opening poly-
merization of ε-caprolactone.21b Their cobalt complexes were
prepared and characterized, and their catalytic behaviors were
investigated under various reaction parameters. Herein the
syntheses and characterizations of (8-(benzoimidazol-2-yl)-
quinolyl)cobalt dichlorides are reported along with a detailed
investigation of their catalytic performance in ethylene reactivity.
Figure 1. Molecular structure of C1. Thermal ellipsoids are shown at
the 30% probability level; hydrogen atoms and solvent (one molecule of
DMF) have been omitted for clarity.
2. RESULTS AND DISCUSSION
2.1. Preparation and Characterization of the Cobalt Com-
plexes. The stoichiometric reaction of CoCl2 with one of the
ligands L1ÀL1421 in ethanol at room temperature produced a
blue powder with the general formula LCoCl2 (C1ÀC14) in high
yields (Scheme 2). Similar to the case for their iron analogues,21a
all cobalt complexes were characterized by elemental analyses and
FT-IR spectra. In comparison with the FT-IR spectra of the free
organic compounds L1ÀL14,21a the characteristic absorptions of
the cobalt complexes shifted to lower frequencies due to coordina-
tion effects. These cobalt complexes were stable in the solid state.
Their molecular structures were confirmed by single-crystal X-ray
diffraction analysis.
2.2. X-ray Crystallographic Studies. Blue crystals were
obtained by slow diffusion of diethyl ether into a DMF solution
of the complex C1, whereas single crystals of complexes C2, C3,
and C8 suitable for X-ray diffraction analysis were obtained by
slow diffusion of diethyl ether into their methanol solutions. All
cobalt complexes C1ÀC3 and C8 could be described as featuring
a distorted-tetrahedral geometry around the cobalt atom; there-
fore, complex C1, shown in Figure 1, is discussed as an example.
The cobalt atom is bound by two N atoms and two chlorines,
assuming a distorted-tetrahedral coordination geometry. The
CoÀN1 distance of 1.954(3) Å is slightly shorter than that of
CoÀN2 (2.061(4) Å), and both are within the normal range for
this class of four-coordinate cobalt complexes.22 The CoÀCl1 distance
of 2.2476(2) Å is longer than that of CoÀCl2 (2.2354(2) Å).
The complex C1 has a six-membered cobaltacyclic ring with
the sum of the internal angles of the ring (712.12°) deviating
from the theoretical value of 720°. Unlike other six-membered
Figure 2. Molecular structure of C2. Thermal ellipsoids are shown at
the 30% probability level; hydrogen atoms have been omitted for clarity.
metallacyclic rings with a boat conformation,18a the atoms in the
current ring CoÀN2ÀC9ÀC8ÀC10ÀN1 lie nearly in the same
plane (mean deviation of 0.0377 Å), with deviations of 0.074 Å at
C10 and 0.0542 Å at Co. The dihedral angle between quino-
line and benzoimidazole is 17.2°. The other complexes C2, C3,
and C8 have similar molecular structures and are shown in
Figures 2À 4, and selected bond lengths and angles of complexes
C1ÀC3 and C8 are given in Table 1.
2.2. Ethylene Oligomerization and Polymerization. At
ambient pressure of ethylene, the catalytic behavior of precatalyst
C1 with various cocatalysts of methylaluminoxane (MAO),
modified methylaluminoxane (MMAO), and triisobutylalumi-
nium (iBu3Al) were evaluated (runs 1À3, Table 2), but a full-
range ethylene oligomerization remained elusive. The obtained
oligomers ranged from C4 to C18 with high selectivity for
α-olefins (>95%). The distributions of oligomers resembled
SchulzÀFlory rules, and the chain propagations were repre-
sented with the constant K, where K = (rate of propagation)/
((rate of propagation) + (rate of chain transfer)) = (moles of Cn+2)/
(moles of Cn); the K values were determined by the molar ratio of
C12 and C14 fractions.23 Within the C1/MAO catalytic system at
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20 °C, more oligomers were obtained through increasing the
ethylene pressure (run 3 vs run 4, Table 2), though the activities
likely decreased due to being divided by ethylene pressures. At
10 atm of ethylene pressure, the optimum condition of the Al/Co
molar ratio was observed at 1500 (runs 4À7, Table 2), indicating
the activity as 1.19 Â 104 g molÀ1 hÀ1 atmÀ1. When the reaction
temperature was varied from 20 to 60 °C (runs 6, 8, and 9), the
catalytic activities gradually decreased with production of more
low-molecular-weight oligomers. However, there was no ethy-
lene oligomerization at 80 °C; instead, a trace amount of poly-
ethylene was obtained. Therefore, all cobalt precatalysts were
investigated with a Al/Co molar ratio of 1500 at 10 atm of
ethylene and 20 °C, and the results are given in Table 2 (runs
10À22). Considering the influences of two substituents (R1 and R2)
on the catalytic performance of cobalt complexes, when the R2
substituent was fixed, the oligomerization activities were gradually
enhanced with bulky R1 substituents in the order iPr > Et > Ph > Me;
for example, when R2 = H, the catalytic activities were observed in the
order C7 > C3 > C11 > C1. On the other hand, when the R1
substituents were fixed, for example R1 = Et, the catalytic perfor-
mancewasintheorderC3 (R2 =H) >C4 (R2 =Me) >C5 (R2 =Et)
> C6 (R2 = iPr). The influence of R2 substituents on the catalytic
activities agreed with results reported in the literature.5,7
Figure 3. Molecular structure of C3. Thermal ellipsoids are shown at
the 30% probability level; hydrogen atoms have been omitted for clarity.
Regarding the influence of ethylene solubility in toluene at
different temperatures and various ethylene pressures, the ad-
justed activities (Table 2) were obtained by calculations on the
basis of ethylene concentration (Cethylene, mol LÀ1 atmÀ1).24
Beyond the same tendency of catalytic behavior performed the
cobalt precatalysts, the better adjusted activity was observed in
the catalytic system C1/MAO at 40 °C (run 8, Table 2),
indicating favorable activation at a slightly elevated temperature.
2.2.2. Ethylene Polymerization. Encouraged with observing
trace amounts of polyethylene obtained at 80 °C and 10 atm
ethylene using C1 and with regard to the ethylene polymerization
by their iron analogues,21a we explored in detail the catalytic system
of C1/MAO under 30 atm of ethylene with varying reaction
temperature and Al/Co molar ratios. According to the results
(runs 1À4, Table 3), higher activities were achieved at higher
temperature. The adjusted activities, on the basis of ethylene
concentration at different reaction temperatures, showed a higher
value at elevated temperature, giving higher stable active species at
100 °C. The optimum Al/Co molar ratio was found to be 3000 at
100 °C, which was observed through varying the Al/Co ratios
(runs 4À8, Table 3). Under the optimum catalytic conditions, the
other precatalysts C2ÀC14 were investigated and also showed
high activities in ethylene polymerization (runs 9À21, Table 3).
With regard to the influences of R1 substituents on the catalytic
performances of their cobalt complexes, shown with the series of
cobalt complexes with R2 = H, the catalytic activities gave the order
R1 = Me (C1) > Ph (C11) > Pr (C7) > Et (C3); meanwhile, the
catalytic activities of cobalt precatalysts with R1 = Et showed the
order with R2 substituent as Me (C4) > Et (C5) > iPr (C6). This is
the similar to the trend obtained for their iron analogues.21a
Moreover, the precatalyst C3 (R2 = H) also showed higher catalytic
activity, indicating the possible formation of the anionic amide or
NÀAl species when adding aluminum cocatalyst.7
Figure 4. Molecular structure of C8. Thermal ellipsoids are shown at
the 30% probability level; hydrogen atoms have been omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
C1ÀC3 and C8
C1
C2
C3
C8
Bond Lengths
1.979(3)
CoÀN1
CoÀN2
CoÀCl1
CoÀCl2
N1ÀC10
N3ÀC10
1.954(3)
2.061(4)
2.2476(2)
2.2354(2)
1.330(6)
1.350(6)
1.9714(18)
2.0427(18)
2.2640(7)
2.2232(10)
1.328(3)
1.990(2)
2.092(2)
2.2304(9)
2.2464(11)
1.334(3)
1.358(3)
2.063(3)
2.2482(1)
2.2566(1)
1.331(5)
1.373(4)
1.366(3)
Bond Angles
93.44(1)
N1ÀCoÀN2
N1ÀCoÀCl1
N1ÀCoÀCl2
N2ÀCoÀCl1
N2ÀCoÀCl2
Cl1ÀCoÀCl2
93.34(2)
93.94(7)
94.09(9)
The GPC measurements of the resulting polyethylenes
showed high molecular weights ranging from 97 kg/mol to 891
kg/mol and relative narrow molecular distributions from 2.6 to
5.4. Employing a higher reaction temperature (runs 1À4,
Table 3) or higher Al/Co molar ratio (runs 4À8, Table 3) gave
polyethylenes with lower molecular weights. Such phenomena
109.38(1)
114.38(1)
122.91(1)
105.30(1)
110.74(7)
114.23(9)
109.73(9)
109.22(9)
119.01(9)
110.42(4)
107.74(6)
107.63(6)
114.14(5)
114.93(5)
115.67(3)
119.61(7)
107.81(7)
103.78(6)
121.45(7)
110.10(3)
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Table 2. Ethylene Oligomerization by Cobalt Precatalysts C1ÀC14a
oligomer distribn/%b
P/
Al/
Co
T/°
C
product
adjusted
activityc
C4/
C6/
C8/
C10
/
Cg12/
run
compd
cocat.
atm
yield/mg
K
activityb
∑C
∑C
∑C
∑C
∑C
1
C1
C1
C1
C1
C1
C1
C1
C1
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
MMAO
iBu3Al
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
1
1
1000
500
20
20
20
20
20
20
20
40
60
20
20
20
20
20
20
20
20
20
20
20
20
20
57.3
78.2
72.2
121
242
297
49.4
244
156
218
597
485
199
50.3
747
537
372
82.5
425
362
327
26.3
22.8
31.3
28.9
4.84
9.68
11.9
1.96
9.77
6.25
8.71
23.9
19.4
7.95
2.01
29.9
21.5
14.9
3.30
17.0
14.5
13.1
1.04
16.10
22.10
20.41
3.42
83.2
95.3
39.2
42.1
36.8
35.8
37.1
66.1
68.2
36.0
41.7
42.3
39.1
38.3
37.3
32.3
37.3
30.3
37.7
38.2
59.6
46.9
16.8
4.7
2
3
1
1000
1000
1250
1500
2000
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
1500
0.62
0.59
0.44
0.53
0.54
0.48
0.55
0.58
0.56
0.58
0.51
0.48
0.46
0.48
0.53
0.55
0.51
0.54
0.51
0.52
15.3
22.0
29.3
28.3
24.5
16.6
18.7
29.3
23.6
24.8
22.8
22.4
25.8
21.2
29.1
25.5
27.4
22.4
21.3
26.1
12.1
12.7
17.0
15.3
15.2
8.8
10.1
9.2
23.3
14.0
7.8
4
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
5
6.84
9.1
6
8.40
7.6
13.0
14.4
3.5
7
1.38
8.8
8
8.88
5.0
9
7.42
6.5
4.0
2.6
10
11
12
13
14
15
16
17
18
19
20
21
22
6.15
17.1
13.0
12.7
10.3
11.9
14.2
14.7
16.9
18.0
18.8
16.7
9.1
10.9
8.1
6.7
16.88
13.70
5.61
13.6
13.2
19.2
17.2
13.6
21.9
8.6
7.0
8.6
1.42
9.1
21.12
15.18
10.52
2.33
8.9
9.9
8.1
12.4
11.1
10.9
3.9
13.8
5.0
12.01
10.24
9.25
11.8
6.1
0.73
11.8
6.1
9.1
a General conditions: 5 μmol of Co; 30 min; toluene (30 mL at 1 atm; 100 mL at 10 atm). b Activity in units of 103 g (mol of Co)À1 hÀ1 atmÀ1
,
determined by GC; ∑C signifies the total amount of oligomers. c Adjusted activity: 104 g (mol of Co)À1 hÀ1 CÀ1
.
ethylene
Table 3. Ethylene Polymerization by Cobalt Precatalysts C1ÀC14/MAOa
activityb
adjusted activityc
10À4Mw
Mw/Mn
d
d
run
complex
Al/Co
T/°C
PE yield/g
1
C1
3000
3000
3000
3000
2000
2500
3500
4000
3000
3000
3000
3000
3000
3000
3000
3000
3000
3000
3000
3000
3000
40
60
0.533
1.78
2.33
3.04
1.72
2.48
3.07
3.08
3.30
1.38
2.30
1.37
1.01
1.49
2.32
1.39
1.12
1.54
3.09
1.62
1.16
1.78
5.93
7.77
10.1
5.73
8.27
10.2
10.3
11.0
4.60
7.66
4.57
3.37
4.97
7.73
4.63
3.73
5.13
10.3
5.40
3.87
1.61
7.05
11.5
18.3
10.3
14.9
18.5
18.5
19.9
8.30
1.38
8.24
6.08
8.97
14.0
8.36
6.74
9.27
18.6
9.75
6.98
89.1
59.7
37.5
14.3
35.8
20.6
14.2
9.7
5.1
2.7
3.2
3.0
3.8
3.3
3.6
2.6
3.0
2.9
2.9
3.1
3.0
3.0
3.2
4.4
2.7
5.3
5.4
4.8
4.6
2
C1
3
C1
80
4
C1
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
5
C1
6
C1
7
C1
8
C1
9
C2
15.2
16.5
18.6
19.2
20.3
20.7
24.0
24.9
26.6
24.5
25.5
25.8
28.1
10
11
12
13
14
15
16
17
18
19
20
21
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
a Conditions: 2 μmol of Co; MAO; 30 atm of ethylene; 30 min; toluene (40 mL). b Observed activity: 104 g (mol of Co)À1 hÀ1 atmÀ1. c Adjusted activity:
105 g (mol of Co)À1 hÀ1 CÀ1ethylene. d Determined by GPC.
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were consistent with the suggestion of the extreme sensitivity for
chain transfer to aluminum species occurring for the chain
termination.25 In general, the more bulky the substituent used
at the 2-position of the quinoline rings, the higher the molecular
weight obtained. The precatalysts containing more electron-
donating alkyl (R2) groups produced polyethylenes with higher
molecular weights, which is similar to the results reported in the
literature.26 In comparison with polyethylenes obtained by their
iron analogues,21a the polyethylenes produced by the cobalt
precatalysts have narrower molecular distributions. The poly-
ethylenes obtained by complexes C3, C8, and C14 (runs 10, 15,
4.2. Synthesis of Cobalt Complexes C1ÀC14. The cobalt
complexes C1ÀC14 were synthesized by the reaction of CoCl2 with the
corresponding ligand in ethanol. A typical synthetic procedure for C1
can be described as follows. To a mixture of ligand L1 (78 mg, 0.3 mmol)
and CoCl2 (39 mg, 0.3 mmol) was added ethanol (4 mL) at room
temperature. The solution turned blue immediately. The reaction
mixture was stirred for 6 h, and absolute diethyl ether was added. The
resulting precipitate was filtered, washed with diethyl ether, and dried
under vacuum to furnish the pure product as a blue powder (107.1 mg,
0.275 mmol) in 92.1% yield. IR (KBr; cmÀ1): 3210, 3056, 1604, 1570,
1514, 1432, 1411, 844, 772, 762, 743. Anal. Calcd for C17H13Cl2CoN3
(389.14): C, 52.47; H, 3.37; N, 10.80. Found: C, 52.57; H, 3.25; N, 10.63.
Complex C2 was obtained as a blue powder in 90.2% yield. IR
(KBr; cmÀ1): 3055, 1607, 1567, 1512, 1474, 1463, 1432, 1391, 851, 774,
760, 750. Anal. Calcd for C18H15Cl2CoN3 (403.17): C, 53.62; H, 3.75;
N, 10.42. Found: C, 53.24; H, 3.80; N, 10.24.
Complex C3 was obtained as a blue powder in 92.3% yield. IR
(KBr; cmÀ1): 3180, 2976, 1606, 1515, 1416, 1296, 1151, 1043, 852, 748,
677. Anal. Calcd for C18H15Cl2CoN3 (403.17): C, 53.62; H, 3.75; N,
10.42. Found: C, 53.66; H, 4.08; N, 10.12.
Complex C4 was obtained as a blue powder in 90.5% yield. IR
(KBr; cmÀ1): 2986, 1611, 1506, 1466, 1296, 1203, 1051, 856, 786, 746,
678. Anal. Calcd for C19H17Cl2CoN3 (417.20): C, 54.70; H, 4.11; N,
10.07. Found: C, 54.61; H, 4.09; N, 9.98.
1
and 21, Table 3) were characterized by H and 13C NMR at
90 °C in bromobenzene-d5, and each showed a single peak in the
1H NMR and 13C NMR spectra, indicating the feature of highly
linear polyethylene with high molecular weight. Though there is
no direct evidence for their active species, two individual species
are supposed for ethylene reactivity of either oligomerization or
polymerization. Further investigations are still ongoing for the
determination of active species and mechanism by experimental
and simulation research.
3. CONCLUSIONS
Cobalt(II) complexes bearing 8-(benzoimidazol-2-yl)quinolines,
activated with MAO, showed unique properties: ethylene oligo-
merization at relatively low ethylene pressure and low reaction
temperature but high ethylene polymerization at 30 atm and high
reaction temperature. The resultant polymers possessed high
molecular weights with narrow molecular weight distributions.
The current bidentate cobalt precatalysts show good thermal
stability in ethylene polymerization. The nature of the ligands
finely adapted the catalytic behaviors of their cobalt complexes.
Two active species could be formed for ethylene oligomerization
and polymerization. Further investigations are still ongoing to
determine the active species and mechanism by experimental and
simulation research.
Complex C5 was obtained as a blue powder in 91.2% yield. IR
(KBr; cmÀ1): 3057, 1606, 1564, 1513, 1432, 967, 845, 759, 721. Anal.
Calcd for C20H19Cl2CoN3 (431.22): C, 55.71; H, 4.44; N, 9.74. Found:
C, 55.44; H, 4.07; N, 9.76.
Complex C6 was obtained as a blue powder in 89.1% yield. IR
(KBr; cmÀ1): 2986, 1602, 1507, 1465, 1206, 1066, 854, 784, 751, 678.
Anal. Calcd for C21H21Cl2CoN3 (445.25): C, 56.65; H, 4.75; N, 9.44.
Found: C, 56.46; H, 4.55; N, 9.79.
Complex C7 was obtained as a blue powder in 92.5% yield. IR
(KBr; cmÀ1): 3214, 2960, 1603, 1511, 1412, 1330, 1146, 839, 750, 677.
Anal. Calcd for C19H17Cl2CoN3 (417.20): C, 54.70; H, 4.11; N, 10.07.
Found: C, 54.51; H, 4.14; N, 9.91.
Complex C8 was obtained as a blue powder in 92.5% yield. IR
(KBr; cmÀ1): 2970, 1607, 1462, 1394, 1127, 1084, 853, 759, 677. Anal.
Calcd for C20H19Cl2CoN3 (431.22): C, 55.71; H, 4.44; N, 9.74. Found:
C, 55.58; H, 4.55; N, 9.40.
4. EXPERIMENTAL SECTION
Complex C9 was obtained as a blue powder in 90.1% yield. IR
(KBr; cmÀ1): 2964, 1608, 1572, 1457, 1431, 1335, 1088, 855, 784, 748,
678. Anal. Calcd for C21H21Cl2CoN3 (445.25): C, 56.65; H, 4.75; N,
9.44. Found: C, 56.37; H, 4.75; N, 9.21.
Complex C10 was obtained as a blue powder in 93.2% yield. IR
(KBr; cmÀ1): 2974, 1609, 1462, 1395, 1296, 1096, 849, 785, 741, 677.
Anal. Calcd for C22H23Cl2CoN3 (459.28): C, 57.53; H, 5.05; N, 9.15.
Found: C, 57.88; H, 5.29; N, 9.11.
Complex C11 was obtained as a blue powder in 75.8% yield. IR
(KBr; cmÀ1): 3054, 1607, 1566, 1511, 1444, 1408, 1328, 1148, 848, 760,
746, 707, 681. Anal. Calcd for C22H15Cl2CoN3 (451.21): C, 58.56; H,
3.35; N, 9.31. Found: C, 58.34; H, 3.45; N, 9.26.
Complex C12 was obtained as a blue powder in 71.6% yield. IR
(KBr; cmÀ1): 3057, 2940, 1598, 1571, 1487, 1474, 1454, 1423, 1288,
845, 770, 750, 696. Anal. Calcd for C23H17Cl2CoN3 (465.24): C, 59.38;
H, 3.68; N, 9.03. Found: C, 59.68; H, 3.99; N, 9.18.
Complex C13 was obtained as a blue powder in 72.4% yield. IR
(KBr; cmÀ1): 3058, 2875, 1599, 1571, 1487, 1452, 1418, 1279, 1016,
845, 769, 749, 697. Anal. Calcd for C24H19Cl2CoN3 (479.27): C, 60.15;
H, 4.00; N, 8.77. Found: C, 60.46; H, 4.25; N, 8.95.
Complex C14 was obtained as a blue powder in 69.9% yield. IR
(KBr; cmÀ1): 3053, 2984, 1600, 1571, 1488, 1454, 1429, 1413, 1289,
1158, 1092, 849, 758, 697. Anal. Calcd for C25H21Cl2CoN3 (493.29): C,
60.87; H, 4.29; N, 8.52. Found: C, 61.14; H, 4.05; N, 8.74.
4.1. General Considerations. All manipulations of air- and
moisture-sensitive compounds were performed under a nitrogen atmo-
sphere using standard Schlenk techniques. Toluene was refluxed over
sodium benzophenone and distilled under argon prior to use. Methy-
laluminoxane (MAO, a 1.46 M solution in toluene) was purchased from
Akzo Nobel Corp. Other reagents were purchased from Aldrich or Acros
Chemicals. 1H and 13C NMR spectra were recorded on a Bruker DMX
300 MHz or a Bruker DMX 400 MHz instrument at ambient temperature
using TMS as an internal standard. IR spectra were recorded on a Perkin-
Elmer System 2000 FT-IR spectrometer. Elemental analysis was carried
out using an HPMOD 1106 microanalyzer. GC analysis was performed
with a Varian CP-3800 gas chromatograph equipped with a flame
ionization detector and a 30 m (0.2 mm i.d., 0.25 μm film thickness)
CP-Sil 5 CB column. The yield of oligomers was calculatedbyreference to
the mass of the solvent on the basis of the prerequisite that the mass of
each fraction was approximately proportional to its integrated area in the
GC trace. Selectivity for the linear α-olefin was defined as (amount of
linear α-olefin of all fractions)/(total amount of oligomer products) in
percent. The activities of ethylene polymerization were calculated on the
basis of isolated polyethylenes. A microwave oven, the Midea PJ21B-A
(800 W, 21 L), was used for microwave-assisted condensation reactions.
1H and 13C NMR spectra of the PE samples were recorded on a Bruker
DMX 200 MHz instrument at 90 °C in bromobenzene-d5 using TMS as
the internal standard.
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Organometallics
ARTICLE
4.3. Procedure for Ethylene Oligomerization and Polym-
erization. Ethylene oligomerization at 1 atm of ethylene pressure was
carried out as follows: the catalyst precursor was dissolved in toluene in a
Schlenk tube, and the reaction solution was stirred with a magnetic stir bar
under an ethylene atmosphere (1 atm), with the reaction temperature
beingcontrolledbya waterbath. Cocatalyst wasadded byasyringe. After a
limited time, the reaction was terminated by acidified water, and the
products were analyzed by GC.
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’ ASSOCIATED CONTENT
S
Supporting Information. A table giving crystal data and
b
processing parameters for complexes C1ÀC3 and C8 and CIF files
giving X-ray crystal structure data for these complexes. This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: +86-10-62557955. Fax: +86-10-62618239. E-mail: whsun@
iccas.ac.cn.
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