Iron(II) and cobalt(II) complexes bearing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives: Synthesis and application to ethylene oligomerization

Article abstract of DOI:10.1016/j.jorganchem.2007.12.030

A series of tridentate N?N?N iron(II) and cobalt(II) complexes containing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives were synthesized and characterized by elemental and spectroscopic analyses. The molecular structure of 1a was confirmed by X-ray diffraction analyses. On treatment with modified methylaluminoxane, these metal complexes exhibited good catalytic activities up to 2.8 × 10⁶ g mol^-1(Fe) h^-1 for ethylene oligomerization, and butenes were the major products with nice selectivity for 1-C₄. The steric and electronic effects on catalytic activities of metal complexes were carefully investigated as well as the influence of various reaction parameters. In the catalytic system, Fe(II) complexes performed better catalytic activities than their Co(II) analogues. With ligands having bulky substituents, the better catalytic activity was observed in catalytic system of Fe(II) complex, however, the lower catalytic activity was obtained in catalytic system of Co(II) complexes.

Full text of DOI:10.1016/j.jorganchem.2007.12.030

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1073–1080
www.elsevier.com/locate/jorganchem
Iron(II) and cobalt(II) complexes bearing
N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives: Synthesis
and application to ethylene oligomerization
Kefeng Wang, Katrin Wedeking, Weiwei Zuo, Dongheng Zhang, Wen-Hua Sun *
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
Received 20 October 2007; received in revised form 23 December 2007; accepted 28 December 2007
Available online 8 January 2008
Abstract
A series of tridentate N^N^N iron(II) and cobalt(II) complexes containing N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives
were synthesized and characterized by elemental and spectroscopic analyses. The molecular structure of 1a was confirmed by X-ray dif-
fraction analyses. On treatment with modified methylaluminoxane, these metal complexes exhibited good catalytic activities up to
2.8 Â 106 g molÀ1(Fe) hÀ1 for ethylene oligomerization, and butenes were the major products with nice selectivity for 1-C4. The steric
and electronic effects on catalytic activities of metal complexes were carefully investigated as well as the influence of various reaction
parameters. In the catalytic system, Fe(II) complexes performed better catalytic activities than their Co(II) analogues. With ligands hav-
ing bulky substituents, the better catalytic activity was observed in catalytic system of Fe(II) complex, however, the lower catalytic activ-
ity was obtained in catalytic system of Co(II) complexes.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Fe(II) and Co(II) complex; N-((Pyridin-2-yl)methylene)-quinolin-8-amine; Ethylene oligomerization
1. Introduction
and Co(II) catalysts [4], which were reviewed by the recent
articles [5].
The oligomerization of ethylene is currently the primary
resource of linear a-olefins, which are important substances
extensively used in the preparation of detergents, lubri-
cants, plasticizers, oil chemicals and monomers for
copolymerization. In recent years, substantive progress
has been made in Fe(II) and Co(II) complexes bearing
2,6-bis(imino)pyridines as highly active catalysts by the
groups of Brookhart [1] and Gibson [2]. Encouraged by
that, many studies have been conducted for the effects of
ligand environment on activity, selectivity and the property
of the products [3]. Moreover, there have many efforts of
chemists devoting to the development of tridentate Fe(II)
In devising late-transition metal complexes as catalysts
for ethylene polymerization and oligomerization, our
group recently reported series of tridentate N^N^N com-
plexes (Scheme 1) with good to high activities for ethylene
polymerization and oligomerization, in which the com-
plexes contained ligands such as 2-imino-1,10-phenanthro-
lines (A) [6], 2-(benzoimidazolyl)-6-iminopyridines (B) [7],
2-quinoxalinyl-6-iminopyridines (C) [8], 2-(benzimidazol-
2-yl)-1,10-phenanthrolines (D) [9], and 2-methyl-2,4-
bis-(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines (E) [10].
Indeed, those Fe(II) and Co(II) catalysts conducted ethyl-
ene oligomerization in high activities and high selectivity
of 1-olefins, which could be promising catalysts in indus-
trial consideration. Therefore, their derivatives have been
synthesized and further investigations for better catalytic
performances have been conducted through controlling
*
Corresponding author. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.12.030

1074
K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
B
D
A
C
N
R2
N
N
X
N
N
R1
N
N
N
N
N
N
R
R'
N
N
R
Ar
M
M
N
M
Ar
M
N
X
X
X
X
X
X
Ar
X
E
F
R
N
N
N
N
R2
N
N
M
N
NH
M
M
X
N
X
X
X
X
X
R
R
R1
Scheme 1. Tridentate N^N^N catalysts.
steric and electronic effects of their ligands by modifying
their substituents. Basically those existing catalytic models
of Fe(II) and Co(II) complexes have been coordinated with
various ligands centered of N-heteroaromatic ring. Instead,
we are searching for an alternative model with ligands con-
taining Schiff-base in center along with N-heteroaromatic
rings. Therefore, this work deals with Fe(II) and Co(II)
complexes ligated by N-((pyridin-2-yl)methylene)-quino-
lin-8-amine derivatives.
Actually the nickel complexes bearing N-((pyridin-2-
yl)methylene)-quinolin-8-amine derivatives were synthe-
sized and performed high catalytic activity in ethylene
oligomerization [11]. Extensively, their Fe(II) and Co(II)
analogues were synthesized in similar procedure. Their cat-
alytic behaviors were carefully investigated with various
reaction parameters along with the effects of substituents
of the ligands. Herein we report the synthesis and charac-
terization of the title complexes and their catalytic proper-
ties for ethylene oligomerization.
FeCl2·4H2O or
CoCl2
+
+
R1
N
R2
N
NH2
O
N
N
CH3COOH
reflux
R2
M
N
Cl
Cl
R1
1a 2a 3a 4a 5a 6a 7a
R1 Me H Me iPr iPr Cy Cy
R2
1b 2b 3b 4b 5b 6b 7b
R1 Me H Me iPr iPr Cy Cy
R2
Me H Me
H
Me Me
H
Me
H
Me
H
Me Me
H
M
M
Fe Fe Fe Fe Fe Fe Fe
Co Co Co Co Co Co Co
Scheme 2. Synthesis of tridentate iron(II) and cobalt(II) complexes.
indicating their oxidation in solution. All complexes were
characterized with elemental analysis and IR spectroscopy;
In the IR spectra, strong and sharp band in the ranges of
1613–1624 cmÀ1 could be ascribed to the stretching vibra-
tion of C@N. Due to the paramagnetic nature of iron(II)
and cobalt(II) complexes, the NMR data could not be
obtained. To confirm their unambiguous structures, the
single-crystal X-ray crystallography was employed to
determine the molecular structure of 1a.
2. Results and discussions
2.1. Synthesis and characterization of the complexes
The substituted 8-aminoquinolines were synthesized
according to literature procedures [12]. However, those
compounds were not stable well for purification [11,13],
one-pot template synthesis was employed in the synthesis
of the Fe(II) and Co(II) complexes [14]. Closer to this
work, their nickel analogues were synthesized using nickel
template reaction [11]. Similarly, the template synthetic
reaction of the 8-aminoquinoline derivative, pyridine-
2-aldehyde derivative and FeCl2 Á 4H2O or CoCl2 were
carried out in presence of acetic acid to afford the corre-
sponding complexes (Scheme 2). The resulting products
were precipitated from the reaction solution and collected
by filter, washed with diethyl ether to remove acetic acid
and dried in vacuum. The complexes were separated as
air-stable powders in moderate to high yields, however,
they will turn to purple in solution when exposed to air,
2.2. Crystal structures
Previous research revealed that nickel complexes of the
same framework could form either dimeric or monomeric
structures in the solid state, depending on the bulk of the
substitutes [11]. Herein the Fe(II) complex (1a) was con-
firmed to be monomeric one, though 1a (R1 = Me,
R2 = H) was the least bulky one of the series of complexes.
Crystals of 1a suitable for X-ray structural determina-
tion were grown from a methanol solution through slowly
evaporation of the solvent at room temperature. The
molecular structure is shown in Fig. 1, whereas selected
bond lengths and angles are listed in Table 1. The

K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
1075
Figure 1. Molecular structure of 1a, with thermal ellipsoids at the 30% probability level. Hydrogen atoms have been omitted for clarity.
Table 1
much difference in the bond lengths and bond angles. How-
ever, not only Me group, but also Cy is smaller than 2,6-
substituted aryl group, maybe it is why only short chain
oligomers could be obtained (see Section 2.3) while other
system [1,3e,6b,7a,10] could provide polymer along with
long-chain oligomers. Similarly, other catalysts ligated by
less bulky ligands also gave short chain oligomers [9b],
indicating the importance of bulky substituent. The Fe–
˚
Selected bond lengths (A) and angles (°) for 1a
Bond length
Fe(1)–N(1)
Fe(1)–N(2)
Fe(1)–N(3)
2.217(3)
2.122(3)
2.199(4)
Fe(1)–Cl(1)
Fe(1)–Cl(2)
N(2)-C(11)
2.3069(2)
2.2972(2)
1.284(5)
Bond angle
N(2)–Fe(1)–N(1)
N(2)–Fe(1)–N(3)
N(1)–Fe(1)–N(3)
N(1)–Fe(1)–Cl(1)
N(2)–Fe(1)–Cl(1)
75.46(1)
74.32(1)
149.53(1)
101.41(1)
124.45(1)
N(3)–Fe(1)–Cl(1)
N(1)–Fe(1)–Cl(2)
N(2)–Fe(1)–Cl(2)
N(3)–Fe(1)–Cl(2)
Cl(1)–Fe(1)–Cl(2)
92.51(1)
99.76(1)
118.96(1)
98.06(1)
116.22(6)
˚
center deviates by 0.0788 A out of the equatorial plane.
The axial plane is almost vertical to the equatorial plane,
with the dihedral angle of 87.7°. The ligand backbone of
1a is not planar, having the dihedral angle of 4.9° between
quinoline and pyridine ring.
coordination of the Fe-center can be described as distorted
trigonal bipyramid geometry in which an equatorial plane
is formed by the imine nitrogen (N(2)) and the two chlo-
rides, while the nitrogen (N(1)) of the quinolyl group and
the nitrogen (N(3)) of the pyridyl group are located in axial
positions. As expected, the iron center coordinated with
N1, N2 and N3 of the ligand, forming two fused five-
membered rings with acute N–Fe–N angles: 75.46(1)° of
N1–Fe1–N2 and 74.32(1)° of N2–Fe1–N3. The N(2)–
2.3. Ethylene oligomerization
The Fe(II) and Co(II) complexes 1a–7a and 1b–7b were
systematically investigated for ethylene oligomerization.
Among the various aluminium activators, modified meth-
ylaluminoxane (MMAO) is the best one which exhibited
catalytic activities in the order of 105–106 g molÀ1(M) hÀ1
.
Therefore, MMAO was used as activator for further
investigations. During ethylene oligomerization, ethylene
consumption was smoothly kept on about 20 min. How-
ever, ethylene consumption decreased sharply after
20 min, suggesting partly deactivations of the active spe-
cies. Butenes predominate among the produced oligomers,
with moderate to good selectivity for 1-C4. Since the low
content of C6 and several isomers of C6 detected, it is dif-
ficult to quantify the individual isomer accurately. How-
ever, the selectivity for 1-C6 is low. Compared with the
nickel analogues [11], the Fe(II) and Co(II) complexes
containing N-((pyridin-2-yl)methylene)-quinolin-8-amine
derivatives showed comparable activities and selectivities,
indicating that the late-transition metal complexes (Fe(II),
˚
C(11) bond distance is 1.284(5) A, displaying typical
C@N double bond character. The Fe–N bonds are different
˚
from each other. The shortest bond with 2.122(3) A is
found for the imine–N (Fe(1)–N(2)), followed by the pyri-
˚
dine–N with Fe(1)–N(3) of 2.199(4) A and the quinoline–N
˚
with Fe(1)–N(1) of 2.217(3) A. This trend is different from
the monomeric structures of the nickel analogues [11], in
which N(2)–Ni < N(1)–Ni < N(3)–Ni is observed. More-
over, the length of Fe–N bond is a little longer than the
corresponding Ni–N bond [11]. The angle of Cl(1)–Fe(1)–
Cl(2) is 116.22(6)°, which is obviously smaller than the
nickel analogues [11]. Compared with other tridentate
N^N^N iron(II) complexes [1,3e,6b,7a,9b,10], there is no

1076
K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
Co(II) and Ni(II)) bearing these series of ligand could
exhibit good catalytic performance in ethylene oligomeri-
zation. Moreover, if compared with other bidentate Fe(II)
and Co(II) catalysts [15], the series of complexes exhibit
much better catalytic performance, not only in activity,
but also in selectivity.
solubility at higher temperature. Moreover, the selectivity
for 1-C4 decreased sharply at elevated temperatures,
(entries 6 and 7 in Table 2) indicating that isomerization
is favored in higher temperatures.
Ethylene oligomerization of complex 5a was also carried
out at different pressures (entries 8 and 9 in Table 2). As
expected, the higher pressure, the higher catalytic activity.
In 10 atm, the activity decreased to about 1/7 of the value
in 30 atm. The catalytic activities predominantly decreased
at lower ethylene pressure, due to lower monomer concen-
tration at lower pressure. With higher temperatures or
lower pressure, the content of C6 became higher; such phe-
nomenon was reported in some complexes [3h,6h,11].
2.3.1. Effects of reaction parameters on catalytic behavior of
iron complexes
Complex 5a was typically investigated in detail under a
range of reaction conditions, such as molar ratio of cocata-
lyst to catalyst, reaction temperature and pressure. The olig-
omerization results are summarized in Table 2. As revealed
in Table 2, the reaction parameters significantly affect the
catalytic activity and selectivity; however, no obvious influ-
ence on the product distribution could be observed.
With complex 5a, the amount of MMAO played an
important role on the catalytic performance. Increasing
the Al/Fe molar ratio from 500 to 2000 (entries 1–4 in
Table 2), the catalytic activity of 5a increased obviously
and the highest activity (27.7 Â 105 g molÀ1(Fe) hÀ1, entry
4 in Table 2) was observed at Al/Fe ratio of 2000, which
may be attributed to the fact that MMAO scavenged
adventitious water and impurities in the solvent at low
Al/Fe ratio and the iron complex required more cocatalyst
to be activated. However, when Al/Fe molar ratio was fur-
ther increased (entry 5 in Table 2), the activity decreased.
The decrease in oligomerization activity might be caused
by the impurities in commercial MMAO such as alkyl alu-
minium, which led to the deactivation of active catalytic
sites [3b]. Though the activity was sensitive to the Al/Fe
ratio, the selectivity for 1-C4 kept stable in different ratios,
and higher activity could not result in oligomers longer
than C6.
2.3.2. Effect of the ligand environment on the catalytic
behavior of Fe(II) complexes
To compare the effect of ligand environment, complexes
1a–7a were examined for oligomerization of ethylene under
the same condition (20 °C; Al/Fe = 2000; 30 atm) and the
results are summarized in Table 3. The substitution pattern
of the ligand plays a major role on the performance of the
catalysts.
The substituents R1 and R2 have considerable effects on
the catalytic behaviors. For complexes 1a–3a, the best
activity and selectivity for 1-C4 was obtained with 3a
(18.2 Â 105 g molÀ1(Fe) hÀ1, entry 3, Table 3), indicating
that, higher activity and selectivity could be realized by
introducing bulkier substituent to the ligand framework.
Furthermore, changing the R1 substituent from Me to
i-Pr or Cy while keeping the R2 = Me, higher activities
were observed and the highest activity of 28.3 Â 105
g molÀ1(Fe) hÀ1 (entry 7 in Table 3) was obtained with
the most bulky complexes 7a. And for complex 5a, the
activity of 27.7 Â 105 g molÀ1(Fe) hÀ1 (entry 5 in Table 3)
was observed. A possible explanation is that the active site
of the catalyst is protected by bulky substituents, leading to
increase in activities. However, when the R2 substituent is
less bulky, the activity of its complex became apparently
lower. For example, complex 5a gave much higher activity
(27.7 Â 105À1(Fe) hÀ1, entry 5 in Table 3) than complex 4a
(6.9 Â 105 g molÀ1(Fe) hÀ1, entry 4 in Table 3). Such
When Al/Fe molar ratio of 2000 was fixed, the reaction
temperature significantly affects the catalytic activity. Ele-
vation of the temperature from 20 °C to 60 °C (entries 6
and 7 in Table 2) led to a significant decline in activity;
indicating that the catalyst is not stable in higher tempera-
ture, another reason could be attributed to lower ethylene
Table 2
Oligomerization of ethylene with 5a/MMAOa
Table 3
Ethylene oligomerization with 1a–7a/MMAOa
Entry Al/
Fe
T
P
Oligomer
Activity
105 g molÀ1(Fe) hÀ1
(°C) (atm) distribution (%)b
Entry Catalyst Oligomer distribution Activity 105 g molÀ1(Fe) hÀ1
(%)b
C4 1-C4 C6
C4
1-C4
C6
1
2
3
4
5
6
7
8
9
500
20
30
30
30
30
30
30
30
20
10
95.7 95.7
96.9 92.1
99.5 93.3
97.9 97.6
98.3 89.9
83.2 73.2 16.8
82.7 72.3 17.3
89.1 50.7 10.9
85.4 82.6 14.6
4.3
3.1
0.5 17.3
2.1 27.7
1.7 10.4
3.8
8.2
1000 20
1500 20
2000 20
2500 20
2000 40
2000 60
2000 20
2000 20
1
2
3
4
5
6
7
1a
2a
3a
4a
5a
6a
7a
99.1
99.0
98.5
88.1
97.9
98.4
98.9
93.6
87.6
96.6
79.8
97.6
50.5
98.2
0.9
1.0
1.5
11.9
2.1
1.6
12.1
17.2
18.2
6.9
27.7
6.4
3.4
2.2
6.1
3.7
1.1
28.3
a
General conditions: 5 lmol of complex; 100 ml of toluene; 20 min;
20 °C; MMAO, Al/Fe = 2000; 30 atm.
a
General conditions: 5 lmol of complex; 100 ml of toluene; 20 min.
Weight percentage determined by GC.
b
b
Weight percentage determined by GC.

K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
1077
phenomenon was also reported in other complexes [9b].
Nevertheless, for complex 4a, the content of C6 is higher.
As to the selectivity for 1-C4, the complexes with bulky
substituents both on R1 and R2 showed good result, higher
than 90%. Comparison of complexes 4a and 5a (entries 4
and 5 in Table 3), it could be observed that 5a exhibited
not only better activity, but also better selectivity, suggest-
ing that protection from R1 and R2 position is necessary
for high activity and selectivity. Comparison of complexes
6a and 7a (entries 6 and 7 in Table 3) could give the same
conclusion.
22.8 Â 105 g molÀ1(Co) hÀ1, was obtained by the least
bulky complex 1b (entry 1 in Table 4). With bulkier com-
plexes 5b, lower activity was obtained (13.9 Â 105 g molÀ1
(Co) hÀ1, entry 5, Table 4). Similar performance was also
observed for another bulky complex 7b, which showed
activity as low as 18.5 Â 105 g molÀ1(Co) hÀ1 (entry 7,
Table 4). A possible explanation is that the active site of
the catalyst is blocked by bulky substituents, leading to
decrease in activities. Similar tendency had been observed
for the nickel analogues [11] and other reported iron(II)
complexes [6h].
Compared with the analogue nickel complexes [11], the
catalytic performances of the Fe(II) complexes in activity,
selectivity and product distributions were observed to be
similar. However, the influence of substituents on activity
and selectivity is different from the nickel analogues.
Furthermore, the effects of catalyst concentration and
ethylene pressure were also investigated by employing com-
plex 1b. At lower ethylene pressure, its activity obviously
decreased (entry 8 to entry 1, Table 4), which was in line
with its Fe(II) analogue. The higher catalyst concentration,
the lower catalytic activity (entry 9 to entry 1, Table 4).
That was caused by having less chance for active species
to coordinate ethylene for further reaction.
2.3.3. Catalytic behavior of Co(II) complexes
Although in most cases, the cobalt(II) complexes
showed much lower activities than their iron(II) analogues
under similar reaction conditions, there are some reports in
which comparable performance was observed with cobalt(II)
complexes in comparison with its iron(II) analogues
[3d,6h].
In our system, complexes 1b–7b were examined under
optimized conditions for oligomerization of ethylene with
MMAO as the cocatalyst and the results are summarized
in Table 4. It could be observed that the cobalt(II) com-
plexes showed comparable activities with their iron(II) ana-
logues for ethylene oligomerization. Complexes 4b and 6b
even showed better activities than complexes 4a and 6a,
respectively (entries 4 and 6 in Table 4). However, detailed
comparison revealed that there are some differences in the
catalytic properties from the iron(II) complexes. One is
that all of the cobalt(II) complexes exhibit good selectivity
for 1-C4, regardless of the substituents bulkiness, which is
quite different with the iron(II) analogues but in line with
the nickel analogues [11]. Secondly, the highest activity,
3. Conclusions
A series of tridentate (N^N^N) Fe(II) and Co(II) com-
plexes of N-((pyridin-2-yl)methylene)-quinolin-8-amine
derivatives have been synthesized and fully characterized.
These complexes were synthesized by metal template reac-
tion. X-ray crystallographic analysis revealed that the
Fe(II) complex forms monomeric structure with distorted
trigonal bipyramid geometry. Activated with MMAO, all
the Fe(II) complexes exhibited high catalytic activities up
to 106 g molÀ1(M) hÀ1 for ethylene oligomerization with
dimers and trimers as products. The selectivity for 1-C4 is
moderate to high. Bulky substituents resulted in both good
activity and selectivity for 1-C4. Catalytic reaction param-
eters significantly affect the catalytic activity and higher
temperature or lower pressure brought lower activities.
The Co(II) complexes also showed good catalytic activity
and selectivity comparable with Fe(II) analogues. How-
ever, the influence of substituents is different from the
Fe(II) analogues and less bulky substituents resulted in bet-
ter activity. This research confirmed that late-transition
metal complexes (Ni, Fe and Co) ligated by N-((pyridin-
2-yl)methylene)-quinolin-8-amine derivatives exhibit good
catalytic performance in ethylene oligomerization. There-
fore, the Schiff-base centered tridentate ligands could pro-
vide alternative catalytic models and are worthy of
further investigation for highly active performance.
Table 4
Ethylene oligomerization with 1b–7b/MMAOa
Entry Catalyst Oligomer distribution Activity 105 g molÀ1(Co) hÀ1
(%)b
C4
1-C4
C6
1
2
3
4
5
6
7
1b
2b
3b
4b
5b
6b
7b
1b
1b
96.9
97.2
96.4
96.2
99.2
96.7
98.2
97.4
96.8
95.9
96.3
94.9
95.2
84.2
95.2
97.5
93.7
96.1
3.1
2.8
3.6
3.8
0.8
3.3
1.8
2.6
3.2
22.8
17.8
22.2
15.1
13.9
8.5
18.5
10.9
15.5
4. Experimental
4.1. General considerations
8c
9d
All manipulations of air and/or moisture-sensitive com-
pounds were carried out under an atmosphere of nitrogen
using standard Schlenk techniques. Solvents were refluxed
over an appropriate drying agent, distilled and degassed
before using. Methylaluminoxane (MAO, 1.46 M in
a
General conditions: 5 lmol of complex; 100 ml of toluene; 20 min;
20 °C; MMAO, Al/Co = 1500; 30 atm.
b
Weight percentage determined by GC.
20 atm.
10 lmol of complex 1b.
c
d

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K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
toluene) and modified methylaluminoxane (MMAO,
1.93 M in heptane) were purchased from Akzo Corp
(USA). Substituted 8-nitro-quinolines and 8-aminoquino-
lines were prepared according to literature procedures
[12]. High purity ethylene was purchased from Beijing Yan-
shan Petrochemical Co. and used as received. Other
reagents were purchased from Aldrich, Acros or local sup-
plier. Elemental analyses were performed on a Flash EA
1112 microanalyzer. IR spectra were recorded on a Per-
kin–Elmer System 2000 FT-IR spectrometer using KBr
Complex 6a was obtained as a deep green powder in
92.9% yield. M.p: >300 °C. Anal. Calc. for C21H21Cl2-
N3Fe Á 0.5H2O: C, 55.90; H, 4.91; N, 9.31 Found: C,
55.48; H, 4.64; N, 9.18%. IR (KBr; cmÀ1): 2925, 2853,
1614, 1593, 1568, 1541, 1506, 1472, 1445, 1382, 1319,
1296, 1145, 998, 840, 767.
Complex 7a was obtained as a deep green powder in
72.3% yield. M.p: >300 °C. Anal. Calc. for C22H23Cl2-
N3Fe Á 0.5H2O: C, 56.80; H, 5.20; N, 9.03. Found: C,
56.39; H, 5.05; N, 8.62%. IR (KBr; cmÀ1): 1621, 1592,
1570, 1504, 1460, 1446, 1387, 1319, 994, 840, 766.
General procedure. Complexes 1b–7b were prepared in a
similar procedure [11] by using CoCl2 (Scheme 2). A sus-
pension of pyridine-2-aldehyde derivative (1.00 mmol),
8-aminoquinoline derivative (1.00 mmol), and CoCl2
(1.00 mmol) in glacial acetic acid (20 ml) was refluxed for
4 h. The precipitate was collected by filtration, washed with
diethyl ether (3 Â 5 ml). The resulting solid was dried in
vacuum.
1
disc in the range of 4000–400 cmÀ1. The H NMR spectra
were recorded on a Bruker DMX-300 instrument with
TMS as the internal standard. GC analysis was performed
with a VARIAN CP-3800 gas chromatograph equipped
with a flame ionization detector and a 30 m (0.25 mm
i.d., 0.25 lm film thickness) CP-Sil 5 CB column.
4.2. Synthesis of complexes
General procedure. Complexes 1a–7a were prepared by
using our previous procedure [11] (Scheme 2). A suspen-
sion of pyridine-2-aldehyde derivative (1.00 mmol), 8-ami-
noquinoline derivative (1.00 mmol), and FeCl2 Á 4H2O
(1.00 mmol) in glacial acetic acid (10 ml) was refluxed for
4 h. The precipitate was collected by filtration and washed
with diethyl ether (3 Â 5 ml). After washing, the collected
solid was dried in vacuum.
Complex 1a was obtained as a deep green powder in
87.2% yield. M.p: 258 °C (dec.). Anal. Calc. for
C16H13Cl2N3Fe Á 0.5H2O: C, 50.17; H, 3.68; N, 10.97.
Found: C, 50.56; H, 3.50; N, 11.18%. IR (KBr; cmÀ1):
3340, 3192, 1619, 1594, 1570, 1504, 1471, 1440, 1376,
1321, 1295, 1223, 1149, 1033, 847, 761.
Complex 2a was obtained as a deep green powder in
81.7% yield. M.p: 244 °C (dec.). Anal. Calc. for C16H13-
Cl2N3Fe Á 0.5H2O: C, 50.17; H, 3.68; N, 10.97. Found: C,
49.84; H, 3.51; N, 10.89%. IR (KBr; cmÀ1): 3397, 3261,
1623, 1592, 1503, 1464, 1381, 1318, 1254, 1168, 1131,
1074, 1032, 832, 784.
Complex 3a was obtained as a deep green powder in
80.7% yield. M.p: 254 °C (dec.). Anal. Calc. for C17H15-
Cl2N3Fe Á 0.5H2O: C, 51.42; H, 4.06; N, 10.58. Found: C,
51.00; H, 3.88; N, 10.08%. IR (KBr; cmÀ1): 3332, 3188,
1618, 1592, 1502, 1464, 1434, 1381, 1321, 1254, 1218,
1145, 1039, 841, 763.
Complex 4a was obtained as a deep green powder in
52.3% yield. M.p: >300 °C. Anal. Calc. for C18H17-
Cl2N3Fe Á H2O: C, 51.46; H, 4.56; N, 10.00. Found: C,
51.71; H, 4.19; N, 10.07%. IR (KBr; cmÀ1): 3057, 2968,
2867, 1613, 1593, 1567, 1505, 1457, 1373, 1297, 1227,
1150, 1044, 848, 766.
Complex 5a was obtained as a deep green powder in
51.6% yield. M.p: >300 °C. Anal. Calc. for C19H19-
Cl2N3Fe Á 1.5H2O: C, 51.50; H, 5.00; N, 9.48. Found: C,
51.72; H, 4.28; N, 9.60%. IR (KBr; cmÀ1): 3063, 2967,
2864, 1618, 1588, 1504, 1460, 1382, 1252, 1217, 1038,
844, 775.
Complex 1b was obtained as a yellow powder in 89.1%
yield. M.p: >300 °C. Anal. Calc. for C16H13Cl2N3Co: C,
50.96; H,3.47; N, 11.14. Found: C, 50.71; H, 3.56; N,
11.15%. IR (KBr; cmÀ1): 3446, 3058, 3020, 1618, 1593,
1571, 1506, 1474, 1443, 1370, 1294, 1222, 1152, 1013,
854, 772, 760.
Complex 2b was obtained as a yellow powder in 79.2%
yield. M.p: >300 °C. Anal. Calc. for C16H13Cl2N3Co: C,
50.96; H,3.47; N, 11.14. Found: C, 50.62; H, 3.29; N,
11.10%. IR (KBr; cmÀ1): 3419, 3039, 1621, 1595, 1503,
1463, 1398, 1382, 1254, 1004, 965, 835, 785, 762.
Complex 3b was obtained as a brown powder in 80.5%
yield. M.p: >300 °C. Anal. Calc. for C17H15Cl2Co Á
0.5H2O: C, 51.02; H, 4.03; N, 10.50. Found: C, 50.97; H,
3.69; N, 10.19%. IR (KBr; cmÀ1): 3445, 3063, 1618, 1590,
1505, 1462, 1382, 1254, 1216, 1168, 1003, 842, 791, 764,
736.
Complex 4b was obtained as a brown powder in 72.3%
yield. M.p: >300 °C. Anal. Calc. for C18H17Cl2N3Co Á
H2O: C, 51.08; H, 4.53; N, 9.93. Found: C,51.43; H,
4.22; N, 9.87%. IR (KBr; cmÀ1): 3444, 1617, 1595, 1571,
1506, 1471, 1373, 1043, 1012, 844, 770.
Complex 5b was obtained as a brown powder in 79.7%
yield. M.p: >300 °C. Anal. Calc. for C19H19Cl2N3Co: C,
54.44; H, 4.57; N, 10.02. Found: C, 54.73; H, 4.22; N,
9.99%. IR (KBr; cmÀ1): 3367, 3051, 2962, 1619, 1597,
1571, 1505, 1374, 1223, 1040, 841, 769.
Complex 6b was obtained as a brown powder in 83.2%
yield. M.p: >300 °C. Anal. Calc. for C21H21Cl2N3Co: C,
56.65; H, 4.75; N, 9.44. Found: C, 56.19; H, 4.78; N,
9.36%. IR (KBr; cmÀ1): 3058, 1617, 1593, 1569, 1504,
1473, 1445, 1376, 1300, 1245, 1221, 1150, 842, 767.
Complex 7b was obtained as a brown powder in 83.2%
yield. M.p: >300 °C. Anal. Calc. for C22H23Cl2N3Co:
C, 57.53; H, 5.05; N, 9.15. Found: C, 57.33; H, 5.04;
N, 8.67%. IR (KBr; cmÀ1): 1624, 1594, 1568, 1503, 1471,
1427, 1398, 1319, 1252, 1213, 1136, 1110, 1076, 1006,
828.

K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
1079
Table 5
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Summary of crystallographic data for 1a
Formula
Fw
C16H13Cl2FeN3
374.04
Monoclinic
P21/c
11.673(2)
10.094(2)
13.628(3)
93.50(3)
1602.6(5)
4
Acknowledgements
Crystal system
Space group
This work was supported by NSFC No. 20674089 and
MOST No. 2006AA03Z553.
˚
a (A)
˚
b (A)
˚
c (A)
b (°)
3
˚
References
V (A )
Z
Dcalc (g cmÀ3
)
1.550
1.272
[1] B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc. 120
(1998) 4049–4050.
Absorption coefficient, l (mmÀ1
)
[2] G.J.P. Britovsek, V.C. Gibson, S.J. McTavish, G.A. Solan, A.J.P.
White, D.J. Williams, B.S. Kimberley, P.J. Maddox, Chem. Com-
mun. (1998) 849–850.
F(000)
h Range (°)
760
2.51–27.48
6823
Number of data collected
[3] (a) B.L. Small, M. Brookhart, J. Am. Chem. Soc. 120 (1998) 7143–
7144;
Number of unique data
Goodness-of-fit
3664
1.069
(b) G.J.P. Britovsek, M. Bruce, V.C. Gibson, B.S. Kimberley, P.J.
Maddox, S. Mastroianni, S.J. McTavish, C. Redshaw, G.A. Solan,
S. Stromberg, A.J.P. White, D.J. Williams, J. Am. Chem. Soc. 121
(1999) 8728–8740;
(c) G.J.P. Britovsek, S. Mastroianni, G.A. Solan, S.P.D. Baugh, C.
Redshaw, V.C. Gibson, A.J.P. White, D.J. Williams, M.R.J. Else-
good, Chem. Eur. J. 6 (2000) 2221–2231;
R
Rw
0.0661
0.1432
4.3. Procedure for oligomerization of ethylene
High-pressure ethylene oligomerization was performed
in a stainless steel autoclave (0.5 L capacity) equipped with
gas ballast through a solenoid clave for continuous feeding
of ethylene at constant pressure. A 100 mL amount of tol-
uene containing the catalyst precursor was transferred to
the fully dried reactor under a nitrogen atmosphere. The
required amount of cocatalyst was then injected into the
reactor using a syringe. As the prescribed temperature
was reached, the reactor was pressurized to the desired
pressure. After the reaction mixture was stirred for the
desired period of time, the reaction was stopped and about
1 mL of the reaction solution was collected, quenched by
the addition of 10% aqueous hydrogen chloride and then
analyzed by gas chromatography (GC).
(d) W.-H. Sun, X. Tang, T. Gao, B. Wu, W. Zhang, H. Ma,
Organometallics 23 (2004) 5037–5047;
(e) Y. Chen, R. Chen, C. Qian, X. Dong, J. Sun, Organometallics 22
(2003) 1231–1236;
(f) F.A.R. Kaul, G.T. Puchta, G.D. Frey, E. Herdtweck, W.A.
Herrmann, Organometallics 26 (2007) 988–999;
(g) S. Mctavish, G.J.P. Britovsek, T.M. Smit, V.C. Gibson, A.J.P.
White, D.J. Williams, J. Mol. Catal. A 261 (2007) 293–300;
(h) N. Ajellal, M.C.A. Kuhn, A.D.G. Boff, M. Ho¨rner, C. M
Thomas, J.-F. Carpentier, O.L. Casagrande, Organometallics 25
(2006) 1213–1216;
(i) C. Zhang, W.-H. Sun, Z.-X. Wang, Eur. J. Inorg. Chem. (2006)
4895–4902;
(j) Y.-M. Zhang, Q. Lin, T.-B. Wei, D.-H. Zhang, S.-Y. Jie, Inorg.
Chim. Acta 358 (2005) 4423–4430;
(k) X. Tang, W.-H. Sun, T. Gao, J. Hou, J. Chen, W. Chen, J.
Organomet. Chem. 690 (2005) 1570–1580.
4.4. X-ray crystallographic studies
[4] (a) M. Qian, M. Wang, R. He, J. Mol. Catal. A 160 (2000) 243–247;
(b) M. Qian, M. Wang, B. Zhou, R. He, Appl. Catal. A 209 (2001)
11–15;
Single-crystal X-ray study for complex 1a was carried
out on a Rigaku R-AXIS Rapid IP diffractometer with
graphite-monochromated Mo Ka radiation (k = 0.71073
(c) L. LePichon, D.W. Stephan, X. Gao, Q. Wang, Organometallics
21 (2002) 1362–1366;
(d) C. Bianchini, G. Mantovani, A. Meli, F. Migliacci, F. Laschi,
Organometallics 22 (2003) 2545–2547;
˚
A) at 296(2) K. Cell parameters were obtained by global
(e) M.-S. Zhou, S.-P. Huang, L.-H. Weng, W.-H. Sun, D.-S. Liu, J.
Organomet. Chem. 665 (2003) 237–245;
(f) G.J.P. Britovsek, V.C. Gibson, O.D. Hoarau, S.K. Spitzmesser,
A.J.P. White, D.J. Williams, Inorg. Chem. 42 (2003) 3454–3465;
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 non-hydrogen atoms were refined aniso-
tropically. All hydrogen atoms were placed in calculated
positions. Structure solution and refinement were per-
formed by using the SHELXL-97 package [16]. Crystal data
and processing parameters for complex 1a are summarized
in Table 5.
´
(g) R. Cowdell, C.J. Davies, S.J. Hilton, J.-D. Marechal, G.A. Solan,
O. Thomas, J. Fawcett, Dalton Trans. (2004) 3231–3240;
(h) C. Bianchini, D. Gatteschi, G. Giambastiani, I.G. Rios, A. Ienco,
F. Laschi, C. Mealli, A. Meli, L. Sorace, A. Toti, F. Vizza,
Organometallics 26 (2007) 726–739;
(i) B.L. Samll, R. Rios, E.R. Fernandez, M.J. Carney, Organome-
tallics 26 (2007) 1744–1749;
(j) C. Go¨rl, H.G. Alt, J. Mol. Catal. A 273 (2007) 118–132.
[5] (a) S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000)
1169–1203;
Supplementary material
(b) S. Mecking, Angew. Chem. Int. Ed. 40 (2001) 534–540;
(c) V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283–315;
(d) W. Zhang, W. Zhang, W.-H. Sun, Prog. Chem. 17 (2005) 310–
319;
CCDC 661233 contains the supplementary crystallo-
graphic data for compound 1a. These data can be obtained

1080
K. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 1073–1080
(e) S. Jie, S. Zhang, W.-H. Sun, Petrochem. Tech. (Shiyou Huagong)
35 (2006) 295–300;
(c) Y. Chen, W. Zuo, P. Hao, S. Zhang, K. Gao, W.-H. Sun, J.
Organomet. Chem., in press, doi:10.1016/j.jorganchem.2007.11.049.
[8] (a) W.-H. Sun, P. Hao, G. Li, S. Zhang, W. Wang, J. Yi, M. Asma,
N. Tang, J. Organomet. Chem. 692 (2007) 4506–4518;
(b) S. Adewuyi, G. Li, S. Zhang, W. Wang, P. Hao, W.-H. Sun, N.
Tang, J. Yi, J. Organomet. Chem. 692 (2007) 3532–3541.
[9] (a) M. Zhang, S. Zhang, P. Hao, S. Jie, W.-H. Sun, P. Li, X. Lu,
Eur. J. Inorg. Chem. (2007) 3816–3826;
(f) W.-H. Sun, D. Zhang, S. Zhang, S. Jie, J. Hou, Kinet. Catal. 47
(2006) 278–283;
(g) C. Bianchini, G. Giambastiani, I.G. Rios, G. Mantovani, A.
Meli, A.M. Segarra, Coord. Chem. Rev. 250 (2006) 1391–1418;
(h) V.C. Gibson, C. Redshaw, G.A. Solan, Chem. Rev. 107 (2007)
1745–1776.
[6] (a) L. Wang, W.-H. Sun, L. Han, H. Yang, Y. Hu, X. Jin, J.
Organomet. Chem. 658 (2002) 62–70;
(b) M. Zhang, P. Hao, W. Zuo, S. Jie, W.-H. Sun, J. Organomet.
Chem. 693 (2008) 483–491.
(b) W.-H. Sun, S. Jie, S. Zhang, W. Zhang, Y. Song, H. Ma, J. Chen,
K. Wedeking, R. Fro¨hlich, Organometallics 25 (2006) 666–677;
(c) W.-H. Sun, S. Zhang, S. Jie, W. Zhang, Y. Li, H. Ma, J. Chen, K.
Wedeking, R. Fro¨hlich, J. Organomet. Chem. 691 (2006) 4196–4203;
(d) S. Jie, S. Zhang, K. Wedeking, W. Zhang, H. Ma, X. Lu, Y.
Deng, W.-H. Sun, C.R. Chim. 9 (2006) 1500–1509;
[10] (a) S. Zhang, I. Vystorop, Z. Tang, W.-H. Sun, Organometallics 26
(2007) 2456–2460;
(b) S. Zhang, W.-H. Sun, X. Kuang, I. Vystorop, J. Yi, J. Organomet.
Chem. 692 (2007) 5307–5316.
[11] W.-H. Sun, K. Wang, K. Wedeking, D. Zhang, S. Zhang, J. Cai, Y.
Li, Organometallics 26 (2007) 4781–4790.
(e) S. Jie, S. Zhang, W.-H. Sun, X. Kuang, T. Liu, J. Guo, J. Mol.
Catal. A: Chem. 269 (2007) 85–96;
[12] (a) S. Vangapandu, M. Jain, R. Jain, S. Kaur, P.P. Singh, Bioorg.
Med. Chem. 12 (2004) 2501–2508;
(f) S. Zhang, S. Jie, Q. Shi, W.-H. Sun, J. Mol. Catal. A: Chem. 276
(2007) 174–183;
(b) U. Jordis, F. Sauter, M. Rudolf, G. Cai, Monatsh. Chem. 119
(1988) 761–780;
(g) J.D.A. Pelletier, Y.D.M. Champouret, J. Cadarso, L. Clowes, M.
Ganete, K. Singh, V. Thanarajasingham, G.A. Solan, J. Organomet.
˜
(c) E.C. Riesgo, X. Jin, R.P. Thummel, J. Org. Chem. 62 (1996)
3017–3022.
Chem. 691 (2006) 4114–4123;
(h) S. Jie, S. Zhang, W.-H. Sun, Eur. J. Inorg. Chem. (2007) 5584–
5598.
[13] F. Lions, K.V. Martin, J. Am. Chem. Soc. 79 (1957) 2733–2738.
[14] A.M. Archer, M.W. Bouwkamp, M.-P. Cortez, E. Lobkovsky, P.J.
Chirik, Organometallics 25 (2006) 4269–4278.
[7] (a) W.-H. Sun, P. Hao, S. Zhang, Q. Shi, W. Zuo, X. Tang, X. Lu,
Organometallics 26 (2007) 2720–2734;
[15] L.P. Spencer, R. Altwer, P. Wei, L. Gelmini, J. Gauld, D.W.
Stephen, Organometallics 22 (2003) 3841–3854.
(b) P. Hao, S. Zhang, W.-H. Sun, Q. Shi, S. Adewuyi, X. Lu, P. Li,
Organometallics 26 (2007) 2439–2446;
[16] G.M. Sheldrick, SHELXTL-97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.