Synthesis, characterization and catalytic behavior toward ethylene of cobalt(II) and iron(II) complexes bearing 2-(1-aryliminoethylidene)quinolines

Article abstract of DOI:10.1016/j.jorganchem.2011.06.003

A series of 2-(1-aryliminoethylidene)quinolines (L) were synthesized and used as bidentate N^N ligands in coordinating with metal (cobalt and iron) chlorides to form complexes of the type LMCl₂, cobalt(II) (Co1-Co5) and iron(II) (Fe1-Fe5). All

Full text of DOI:10.1016/j.jorganchem.2011.06.003

Journal of Organometallic Chemistry 696 (2011) 3029e3035
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Journal of Organometallic Chemistry
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Synthesis, characterization and catalytic behavior toward ethylene of cobalt(II)
and iron(II) complexes bearing 2-(1-aryliminoethylidene)quinolines
,
a
a,c,
Shengju Song a, Weizhen Zhao a, Lin Wang a, Carl Redshaw b , Fosong Wang , Wen-Hua Sun
*
**
a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK
c State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 2-(1-aryliminoethylidene)quinolines (L) were synthesized and used as bidentate N^N ligands
in coordinating with metal (cobalt and iron) chlorides to form complexes of the type LMCl2, cobalt(II)
(Co1eCo5) and iron(II) (Fe1eFe5). All organic compounds and metal complexes were fully characterized,
and the molecular structures of the representative complexes Co3$DMF and Fe4$DMF were confirmed as
distorted bipyramidal geometry at the metal by single-crystal X-ray diffraction. Upon activation with
either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) under 10 atm ethylene,
all complexes showed high activities in ethylene dimerization with activities of up to 1.82 ꢀ 106 g molꢁ1
(Co) hꢁ1 and 5.89 ꢀ 105 g molꢁ1 (Fe) hꢁ1, respectively.
Received 19 April 2011
Received in revised form
28 May 2011
Accepted 4 June 2011
Keywords:
Ethylene dimerization
2-(1-Aryliminoethylidene)quinoline
Cobalt
Iron
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
lene)-quinolin-8-amine derivatives [42], and 2,8-bis(imino)quino-
lines [43], as well as 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-
The discovery of bis(imino)pyridylmetal (Fe or Co) chlorides as
pre-catalysts provided a milestone in ethylene oligomerization and
polymerization [1e5], and this in turn has led to extensive inves-
tigations into modifying the substituents of the aryl groups within
the bis(arylimino)pyridines [6e12]. Recent reviews have high-
lighted how less bulky substituents favor oligomerization processes
[2,5,8e22]. Inspired by the success of the bis(arylimino)pyridine
ligand set, much effort has been devoted to developing new
Fe(II) and Co(II) pre-catalysts through the design of new suitable
tridentate ligands [23e28]. Our laboratory has successfully
designed ligands such as 2-benzimidazole-6-iminopyridines
[29e31], 6-(quinoxalin-2-yl)-2-iminopyridines [32], 2-benzo-
xazolyl-6-iminopyridines [33,34], 2-imino-1,10-phenanthrolines
[35e39], 2-benzimidazole-1,10-phenanthrolines [40], 2-oxazoline/
benzoxazole-1,10-phenanthrolines [41], N-((pyridin-2-yl)methy-
1,5-benzodiazepines for bimetallic complexes [44,45]. Upon real-
izing the difference of distorted square-based pyramidal geometry
around cobalt complexes bearing 2,8-bis(imino)quinolines [43],
further attention was paid to developing bidentate ligands for
complex pre-catalysts of the 2-(1-aryliminopropylidene) quino-
lylcobalt dichlorides [46] and the 8-(1-aryliminoethylidene)qui-
naldylmetal (Fe or Co) dichlorides [47]. The latter 8-(1-
aryliminoethylidene)quinaldylmetal (Fe or Co) dichlorides [47]
showed high activities in ethylene dimerization, however, the 2-
(1-aryliminopropylidene)quinolylcobalt pre-catalysts exhibited
interesting catalytic behavior such that they were ethylene
dimerization pre-catalysts at room temperature, but ethylene
polymerization pre-catalysts at high temperature. The scope of N-
bidentate metal (Fe or Co) complexes and their catalytic behavior
has not been well explored, and as a consequence 2-acetylquinoline
instead of the previous 2-propionylquinoline [46] has been
employed herein to prepare 2-(1-aryliminoethylidene)quinolines
(L) and their cobalt (Co1eCo5) and iron (Fe1eFe5) complexes. In
the presence of methylaluminoxane (MAO) or modified methyl-
aluminoxane (MMAO), all metal complexes showed high activities
toward ethylene dimerization, and surprisingly the cobalt pre-
catalysts exhibited higher activities than did their iron analogs.
* Corresponding author. Tel.: þ44 (0) 1603 593137; fax: þ44 (0) 1603 592003.
** Corresponding author. Key Laboratory of Engineering Plastics and Beijing
National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy
of Sciences, Beijing 100190, China. Tel.: þ86 10 62557955; fax: þ86 10 62618239.
E-mail addresses: carl.redshaw@uea.ac.uk (C. Redshaw), whsun@iccas.ac.cn
(W.-H. Sun).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.06.003

3030
S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3029e3035
Ar NH2
N
N
N
p-TsOH
Toluene
O
R1
Ar
L1 - L5
R2
MCl2
C2H5OH
Ar =
R1
Me Et iPr Me Et
Me Me
L5
R1
R2
N
M
H
H
H
N
L1 L2 L3 L4
Cl
Ar
Cl
M = Co Co1Co2Co3 Co4 Co5
M = Fe Fe1 Fe2 Fe3 Fe4 Fe5
Co1 - Co5
Fe1 - Fe5
Scheme 1. Synthetic procedure.
Fig. 2. Molecular structure of Fe4$DMF. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
2. Results and discussion
2.1. Synthesis and characterization of 2-(1-aryliminoethylidene)
quinolines and their metal (Co or Fe) complexes
diffusion of diethyl ether into their DMF solutions. The coordination
geometry around the metal center observed in both complexes can
be described as a distorted trigonal-bipyramid, in which the metal
center is surrounded by two nitrogen atoms of the bidentate ligand,
two chlorides and one oxygen atom of coordinated DMF molecule.
The molecular structures are shown of Co3$DMF in Fig. 1 and
Fe4$DMF in Fig. 2, respectively. Selected bond lengths and angles
are collected in Table 1. The quinolyl and aryl planes are approxi-
mately perpendicular such as the dihedral angle with 82.37ꢂ in
Co3$DMF (Fig. 1).
The stoichiometric reaction of 2-acetylquinoline with 2,4,6-
substituted anilines afforded the 2-(1-aryliminoethylidene)quino-
lines in good isolated yields (Scheme 1). All the ligands were char-
acterized by FT-IR, 1H and 13C NMR measurements as well as by
elementalanalysis. Further reaction of the2-(1-aryliminoethylidene)
quinolines with an equivalent of CoCl2 or FeCl2$4H2O in ethanol
afforded the title cobalt (Co1eCo5) and iron complexes (Fe1eFe5)
(Scheme 1) in high yields. The resultant complexes were precipitated
from the reaction solution and separated as yellow or green air-stable
powders. All complexes were characterized by FT-IR spectroscopic
and elemental analyses, and were found to be highly stable either in
the solid-state or in solution. In the IR spectra, the stretching vibra-
tion band of C]N within these cobalt(II) and iron(II) complexes was
found in the range 1611e1622 cmꢁ1 and with the greatly reduced
2.3. Ethylene dimerization
2.3.1. Ethylene dimerization of cobalt complexes
Various alkylaluminium reagents such as methylaluminoxane
(MAO), modified methylaluminoxane (MMAO) and dieth-
ylaluminium chloride (Et2AlCl) were evaluated with Co3 as co-
catalysts for ethylene activation, and the results are tabulated in
Table 2. Good activities were achieved with either MAO or MMAO,
and MAO was chosen for further studies on the basis of economics
and activity considerations.
intensity
compared
to
their
corresponding
ligands
(1633e1641 cmꢁ1), indicating the effective coordination between
the N-imino with the cationic metal center. The molecular structures
of representative cobalt and iron complexes were confirmed by
single-crystal X-ray diffraction analysis.
Reaction parameters such as the molar ratio of Al/Co and
reaction temperature were also optimized. The best activity was
observed for the Al/Co molar ratio of 1000 (entries 3e8, Table 2).
Elevating the reaction temperature resulted in deactivation
(entries 3 and 9e13 in Table 2), resulting in only trace oligomers
2.2. Crystal structures
Single crystals of complexes Co3$DMF and Fe4$DMF suitable for
X-ray diffraction analysis were individually obtained by slow
Table 1
Selected bond lengths (Å) and angles (ꢂ) for Co3$DMF and Fe4$DMF.
Co3$DMF
Fe4$DMF
Bond lengths (Å)
M(1)eO(1)
M(1)eN(2)
2.062 (3)
2.072 (3)
2.117 (2)
2.152 (2)
M(1)eN(1)
2.175 (3)
2.219 (2)
M(1)eCl(2)
M(1)eCl(1)
2.2924 (11)
2.3160 (11)
2.3599 (9)
2.2865 (11)
Bond angles (ꢂ)
O(1)eM(1)eN(2)
O(1)eM(1)eN(1)
N(2)eM(1)eN(1)
O(1)eM(1)eCl(2)
N(2)eM(1)eCl(2)
N(1)eM(1)eCl(2)
O(1)eM(1)eCl(1)
N(2)eM(1)eCl(1)
N(1)eM(1)eCl(1)
Cl(2)eM(1)eCl(1)
94.35 (12)
169.92 (12)
76.09 (12)
92.02 (9)
114.66 (10)
89.16 (9)
94.48 (9)
112.85 (10)
92.24 (9)
88.55 (9)
163.44 (9)
74.92 (9)
93.48 (7)
114.41 (7)
92.59 (7)
93.96 (7)
121.87 (7)
95.53 (7)
123.33 (4)
Fig. 1. Molecular structure of Co3$DMF. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
131.31 (4)

S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3029e3035
3031
Table 2
Table 3
Ethylene dimerization by the Co3.a
Ethylene dimerization by Co1eCo5.a
Entry T/ꢂC t/min Co-catalyst Al/Co Activity/
Oligomer
Entry
Catalyst
Activity/
Oligomer distributionb (%)
106 g molꢁ1 hꢁ1 distributionb (%)
106 g molꢁ1 hꢁ1
P
P
a
-C4
C4/
C
C6/
C
P
P
a
-C4 C4/
C
C6/
C
1
2
3
4
5
Co1
Co2
Co3
Co4
Co5
1.22
1.30
1.65
1.71
1.82
67.2
65.3
67.1
67.9
65.5
99.4
99.6
99.8
99.7
99.8
0.6
0.4
0.2
0.3
0.2
1
2
3
4
5
6
7
8
20
20
20
20
20
20
20
20
30
40
60
80
90
100
20
20
20
20
30
30
30
30
30
30
30
30
30
30
30
30
30
30
15
45
60
90
Et2AlCl
MMAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
200
e
e
e
e
1000 1.51
1000 1.65
500 0.57
65.3 99.9
67.1 99.8
69.0 99.8
66.3 99.9
66.5 99.8
64.2 99.8
63.4 99.8
65.1 99.7
62.1 99.6
65.3 99.3
66.7 98.6
0.1
0.2
0.2
0.1
0.2
0.2
0.2
0.3
0.4
0.7
1.4
e
750 1.38
a
Conditions: 5
m
mol Co, 1000 equiv., 10 atm C2H4, 30 min, 100 mL of toluene.
P
1250 1.43
1500 1.39
2000 1.31
1000 1.27
1000 1.12
1000 1.06
1000 0.80
1000 Trace
b
Determined by GC. C denotes the total amount of oligomers.
9
Regarding the lifetime of the active species in the Co3/MAO
10
11
12
13
14
15
16
17
18
19
system, ethylene dimerization runs were conducted over different
time periods (entries 3 and 15e19 in Table 2). The activities slightly
decreased on prolonged reaction time, with no significant deacti-
vation observed over 60 min (entry 18 in Table 3), indicating
a significant amount of the active species were not deactivated. In
general, the catalytic system was well maintained for ꢃ60 min.
According to the data in Table 3, for the complexes Co1eCo3
containing 2,6-dialkyl substituents (entries 1e3 in Table 3), the
bulkier the R1 group used, the higher the activity achieved.
Presumably, the bulkiness of these ligands is helpful in protecting
the active species formed [6]. In addition, the bulkier substituents
might also enhance the solubility of such a complex [1,3]; and such
phenomena would be consistent with better activity by complexes
bearing ligands with an additional methyl group, thus the activity
order Co4 > Co1 and Co5 > Co2. Similar to the performance by the
2-propionylquinoline counterpart pre-catalysts [46], the ethylene
dimerization was also achieved by the title cobalt pre-catalysts but
e
e
1000
e
e
e
e
1000 1.90
1000 1.45
1000 1.20
1000 1.00
1000 0.83
62.3 99.8
64.3 99.7
63.2 99.5
64.1 99.6
63.6 99.7
0.2
0.3
0.5
0.4
0.3
20 120
a
Conditions: 5
m
mol Co, 10 atm C2H4, 100 mL of toluene.
P
b
Determined by GC. C denotes the total amount of oligomers.
at 90 ꢂC and no oligomers at 100 ꢂC. On comparison with the
observations for the analogous pre-catalysts bearing 2-(1-
aryliminopropylidene)quinoline [46], it is observed that the
current cobalt pre-catalysts showed a higher activity, a better
selectivity for
a-C4 and enhanced thermo-stability for ethylene
with a better selectivity for a-C4. In general, the systems herein and
other literature imino-quinolyl bidentate cobalt pre-catalysts
[46,47] perform ethylene dimerization without high selectivity
dimerization, but no polyethylene was obtained at the elevated
reaction temperature. Given that slightly fine-tuning of these
ligands had significantly changed the catalytic performance over
that of the analog complexes, this encouraged us to further
exploration this series of ligands and their metal complexes
under the optimum catalytic condition as the Al/Co molar ratio
of 1000:1 and 20 ꢂC under 10 atm of ethylene pressure; results
are collected in Table 3.
for a-C4.
2.3.2. Ethylene dimerization by iron complexes
Using a similar procedure, complex Fe5 was used in exploring
suitable co-catalysts (entries 1e3 in Table 4) for optimum
Table 4
Dimerization of ethylene with Fe1eFe5.a
Entry
Catalyst
T/ꢂC
t/min
Co-catalyst
Al/Fe
Activity/
Oligomer distributionb (%)
105 g molꢁ1 hꢁ1
P
a
-C4
C4/
C
1
2
3
4
5
6
7
8
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe5
Fe1
Fe2
Fe3
Fe4
20
20
20
20
20
20
20
20
20
20
20
30
40
50
20
20
20
20
20
20
20
20
30
30
30
30
30
30
30
30
30
30
30
30
30
30
15
45
60
90
30
30
30
30
MAO
1000
200
0.03
e
65.1
e
100
e
Et2AlCl
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
1000
1500
2000
2250
2500
2750
3000
3500
4000
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
1.11
2.01
2.23
3.99
5.89
3.56
2.42
1.51
1.32
1.91
1.72
1.55
6.57
4.12
3.21
1.72
3.61
3.91
3.99
4.49
67.5
69.2
67.6
67.4
66.3
66.6
66.2
65.1
65.0
66.5
62.8
63.0
63.2
64.2
63.6
63.9
61.5
62.2
64.1
65.5
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
9
10
11
12
13
14
15
16
17
18
19
20
21
22
a
Conditions: 5
m
mol Fe, 10 atm C2H4, 100 mL of toluene.
P
b
Determined by GC. C denotes the total amount of oligomers.

3032
S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3029e3035
Table 5
with the title cobalt pro-catalysts. The catalytic nature of cobalt and
iron, and thereby the observed activity, can be controlled through
the ancillary ligand set. According to the observations for Co3/
MMAO (Table 2), the catalytic species were well maintained within
a suitable reaction temperature range of up to 60 ꢂC for ethylene
dimerization, which indicated better thermo-stability of the cobalt
species over their iron counterparts.
Crystal data and structure refinement details for Fe4 and Co3.
Co3$DMF
Fe4$DMF
Cryst color
Empirical formula
fw
Green
C26H33N3OCl2Co
533.38
173 (2)
0.71073
Monoclinic
P2(1)/n
8.1586 (16)
19.572 (4)
17.345 (4)
90
101.83 (3)
90
2710.8 (9)
4
1.307
0.852
1116
0.20 ꢀ 0.15 ꢀ 0.10
1.59e27.48
ꢁ10 ꢃ h ꢃ 10
ꢁ23 ꢃ k ꢃ 25
ꢁ22 ꢃ l ꢃ 22
21934
Green
C23H27N3OCl2Fe
488.23
173 (2)
0.71073
Monoclinic
P2(1)/c
8.0952 (16)
9.2307 (18)
17.763 (4)
90
95.89 (3)
90
2336.0 (8)
4
1.388
0.894
1016
0.50 ꢀ 0.45 ꢀ 0.15
1.43e27.48
ꢁ18 ꢃ h ꢃ 18
ꢁ9ꢃ k ꢃ 11
ꢁ18 ꢃ l ꢃ 23
18418
T (K)
Wavelength (Å)
Cryst syst
Space group
a (Å)
b (Å)
c (Å)
3. Conclusion
A series of 2-(1-aryliminoethylidene)quinolines and the cobalt
and iron complexes thereof have been synthesized and fully char-
acterized. The pre-catalysts ligated by bulky substituents resulted
in better catalytic activities with high selectivity for ethylene
dimerization, whilst the ligands with an additional methyl group
enhanced the activities of their pre-catalysts. Compared to the 2-
(1-aryliminopropylidene)quinolylcobalt(II) pre-catalysts, the cur-
rent 2-(1-aryliminoethylidene)quinolylcobalt(II) analogs showed
better thermo-stability for ethylene dimerization, however, no
polymer was observed at the elevated temperature. As observed
herein, the fine-tuning of these ligands can adapt the catalytic
behavior of the metal complexes, and thus the exploration of new
derivatives as pre-catalysts in ethylene reactivity remains a fruitful
and fertile area.
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
V (Å3)
Z
Dcalcd (mgmꢁ3
)
m
(mmꢁ1
)
F (000)
Cryst size (mm)
range (ꢂ)
q
Limiting indices
No. of rflns collected
No. unique rflns [R(int)]
Completeness to
21934 (0.0568)
99.9%
5333 (0.0447)
99.8%
q (%)
Data/restraints/params
6213/0/298
1.350
5333/0/271
1.166
Goodness of fit on F2
4. Experimental section
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 ¼ 0.0727
wR2 ¼ 0.1770
R1 ¼ 0.0843
wR2 ¼ 0.1864
0.502 and ꢁ0.720
R1 ¼ 0.0572
wR2 ¼ 0.1467
R1 ¼ 0.0625
wR2 ¼ 0.1543
0.607 and ꢁ0.559
4.1. General considerations
All manipulations of air- and moisture-sensitive compounds
were performed under a nitrogen atmosphere using standard
Schlenk techniques. Methylaluminoxane (MAO, 1.46 M solution in
toluene) and modified methylaluminoxane (MMAO, 1.93 M in
heptane, 3A) were purchased from Akzo Nobel Corp. Dieth-
ylaluminium chloride (Et2AlCl, 1.7 M in toluene) was purchased
from Acros Chemicals. The 2-acetylquinoline was available free of
charge from Astatech Inc. (www.astatechinc.com). 1H and 13C NMR
spectra were recorded on a Bruker DMX 400 MHz instrument at
ambient temperature using TMS as an internal standard. FT-IR
spectra were recorded on a PerkineElmer System 2000 FT-IR
spectrometer. Elemental analyses were carried out using a Flash
EA 1112 microanalyzer. GC analyses were performed with a Varian
CP-3800 gas chromatograph equipped with a flame ionization
Largest diff peak and hole (e Åꢁ3
)
conditions. The catalytic system employing as co-catalyst MMAO
revealed higher activities than when using either MAO or Et2AlCl. In
light of these results, MMAO was chosen as the co-catalyst for
further investigation. Changing the Al/Fe molar ratio or reaction
temperature, the optimum condition was obtained as the Al/Fe
molar ratio as 2500 at 20 ꢂC (entry 7 in Table 4). All the iron (II) pre-
catalysts displayed good activities in the ethylene dimerization
with considerable selectivity for
a-butene (>60%) at 10 atm
ethylene (Table 4). In addition, ethylene dimerization was steadily
maintained over 45 min (entries 7, 15 and 16 in Table 4), however,
there was a sharp decrease in activities on further prolonging the
reaction time to 90 min (entries 17 and 18 in Table 4). As shown in
Table 4 (entries 7, 19e22), the ethylene oligomerization activity
varied in the order Fe5 > Fe4 > Fe3 > Fe2 > Fe1, which is consistent
with the activity tendency for the dimerization observed for the
cobalt analogs. Such phenomenon was also observed by the iron
pre-catalysts ligated by 2-quinoxalinyl-6-iminopyridines [32] and
2-(1-isopropyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines
[30]. The current title bidentate iron pre-catalysts formed butenes
detector and a 30 m (0.2 mm i.d., 0.25 mm film thickness) CP-Sil 5 CB
column. The yields of oligomers were calculated by referencing
with the mass of the solvent, on the basis of the prerequisite that
the mass of each fraction was approximately proportional to its
integrated areas in the GC trace.
4.2. Syntheses and characterization
4.2.1. 2-(1-(2,6-Dimethylphenylimino)ethylidene)quinoline (L1)
A reaction mixture of 2-acetylquinoline (1.71 g, 10.0 mmol), 2,6-
dimethylaniline (1.21 g, 10.0 mmol), p-toluenesulfonic acid (0.20 g),
and toluene (60 mL) was refluxed for 12 h. The solvent was rotary
evaporated and the resulting solid was eluted with petroleum ether
on an alumina column. The second eluting part was collected,
concentrated to give a yellow solid and L1 was obtained in 72%
yield. Mp: 145e146 ꢂC. dH (400 MHz; CDCl3; Me4Si) 8.54 (1H, d,
J ¼ 8.6 Hz, quinoline3), 8.25 (1H, d, J ¼ 8.6 Hz, quinoline4), 8.19 (1H,
d, J ¼ 8.4, quinoline8), 7.89 (1H, d, J ¼ 8.0, quinoline5), 7.76 (1H, t,
J ¼ 8.4 Hz, quinoline7,), 7.60 (1H, t, J ¼ 8.0 Hz, quinoline6), 7.11 (2H,
d, J ¼ 7.4 Hz, m-Ar), 6.97 (1H, t, J ¼ 7.4 Hz, p-Ar), 2.34 (3H, s, eCH3),
2.07 (6H, s, eCH3). dC (100 MHz; CDCl3; Me4Si) 167.8 (C]N), 156.3
(quinoline2), 149.0 (quinoline10), 147.5 (CeN), 136.2 (quinoline4),
with
a lower selectivity for a-butene than did the 8-(1-
aryliminoethylidene)quinaldyliron dichloride pre-catalysts [47],
and this is thought to be due to the different ligand coordination at
the iron center.
Comparing the catalytic activities by the cobalt and iron pre-
catalysts, it was surprising that the cobalt systems showed higher
activity than did their iron analogs, for example, the cobalt pre-
catalyst Co5 with 1.82 ꢀ 106 g molꢁ1 (Co) hꢁ1 vs its iron pre-
catalyst Fe5 with 5.89 ꢀ 105 g molꢁ1 (Fe) hꢁ1; note different
aluminum co-catalysts were employed. On comparison with
observations for analogous systems [47], where iron pro-catalysts
tend to have higher activities than their cobalt analogs, by
contrast, herein the favorable catalytic performance was obtained

S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3029e3035
3033
130.2 (quinoline8), 129.6 (quinoline7), 128.8 (quinoline9), 128.0 (m-
Ar), 127.7 (quinoline5), 127.5 (quinoline6), 125.4 (p-Ar), 123.2 (m-
Ar), 118.8 (quinoline3), 18.09 (eCH3), 16.59 (CH3eC]N). Anal. Calcd
for C19H18N2 (274.36) requires C, 83.18; H, 6.61; N, 10.21%. Found: C,
83.10; H, 6.64; N, 10.13%. FT-IR (Diamond disk, cmꢁ1): 2915, 1641,
1593, 1558, 1465, 1431, 1362, 1203, 1126, 1085, 833, 751, 687.
J ¼ 8.4 Hz, quinoline4), 8.17 (1H, d, J ¼ 8.4 Hz, quinoline8), 7.88
(1H, d, J ¼ 8.0 Hz, quinoline5), 7.75 (1H, t, J ¼ 7.4 Hz, quino-
line7), 7.61 (1H, t, J ¼ 7.6 Hz, quinoline6), 6.94 (2H, s, m-Ar), 2.43
(4H, m, 2ꢀ eCH2e), 2.34 (6H, s, 2ꢀ eCH3), 1.13 (6H, s, 2ꢀ eCH3).
dC (100 MHz; CDCl3; Me4Si) 167.8 (C]N), 156.5 (quinoline2),
147.5(quinoline10), 145.6 (CeN), 136.2 (quinoline4), 132.6 (p-Ar),
131.1 (o-Ar), 130.2 (quinoline8), 129.6 (quinoline7), 128.9 (quin-
oline9), 127.7 (quinoline5), 127.4 (quinoline6), 126.9 (m-Ar), 118.9
(quinoline3), 24.78 (eCH2e), 21.18 (eCH3), 16.89 (CH3eC]N),
14.01 (eCH3). Anal. Calcd for C22H24N2 (316.41) requires C,
83.50; H, 7.64; N, 8.85%. Found: C, 83.32; H, 7.78; N, 8.48%. FT-IR
(Diamond disk, cmꢁ1): 2966, 2361, 1638, 1595, 1457, 1360, 1207,
1128, 1081, 841, 758, 687.
4.2.2. 2-(1-(2,6-Diethylphenylimino)ethylidene)quinoline (L2)
In a manner similar to that described for L1, L2 was prepared as
a yellow solid in 68% yield. Mp: 147e148 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.55 (1H, d, J ¼ 8.6 Hz, quinoline3), 8.25 (1H, d, J ¼ 8.4 Hz,
quinoline4), 8.20 (1H, d, J ¼ 8.6 Hz, quinoline8), 7.89 (1H, d,
J ¼ 8.4 Hz, quinoline5), 7.76 (1H, t, J ¼ 8.2 Hz, quinoline7), 7.62 (1H, t,
J ¼ 8.6 Hz, quinoline6), 7.14 (2H, d, J ¼ 8.4 Hz, m-Ar), 7.02 (1H, t,
J ¼ 7.4 Hz, p-Ar), 2.50 (4H, m, 2ꢀ eCH2e), 2.39 (3H, s, eCH3), 1.18
(3H, s, eCH3), 1.14 (3H, s, eCH3). dC (100 MHz; CDCl3; Me4Si) 167.6
(C]N), 156.4 (quinoline2), 148.1 (quinoline10), 147.6 (CeN), 136.3
(quinoline4), 131.2 (o-Ar), 130.3 (quinoline8), 129.7 (quinoline7),
128.9 (quinoline9), 127.8 (quinoline5), 127.5 (quinoline6), 126.2 (m-
Ar), 123.6 (p-Ar), 118.9 (quinoline3), 24.87 (eCH2e), 17.03 (CH3eC]
N), 13.97 (eCH3). Anal. Calcd for C21H22N2 (302.41) requires C,
83.40; H, 7.33; N, 9.26%. Found: C, 83.22; H, 7.39; N, 9.12%. FT-IR
(Diamond disk, cmꢁ1): 2963, 1635, 1590, 1558, 1450, 1364, 1198,
1128, 846, 752, 690.
4.2.6. 2-(1-(2,6-Dimethylphenylimino)ethylidene)quinolylcobalt
dichloride (Co1)
To a solution of the ligand (E)-2,6-dimethyl-N-(1-(quinolin-2-
yl)ethylidene)benzenamine (0.288 g, 1.0 mmol) in ethanol
(10 mL), CoCl2 (0.130 g, 1.0 mmol) was added. The reaction
mixture was stirred at room temperature for 12 h to afford
a green precipitate from the reaction mixture. Co1 was obtained
as a blue powder in 91% yield. C19H18Cl2N2Co (403.02) requires C,
56.46; H, 4.49; N, 6.93%; Found: C, 56.20; H, 4.53; N, 6.77%. IR
(Diamond; cmꢁ1): 2916, 1617, 1587, 1506, 1467, 1369, 1307, 1218,
1144, 827, 785, 756.
4.2.3. 2-(1-(2,6-Diisopropylphenylimino)ethylidene)quinoline (L3)
In a manner similar to that described for L1, L3 was prepared as
a yellow solid in 84% yield. Mp: 150e151 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.50 (1H, d, J ¼ 8.6 Hz, quinoline3), 8.23 (1H, d, J ¼ 8.4 Hz,
quinoline4), 8.16 (1H, d, J ¼ 8.4 Hz, quinoline8), 7.87 (d, 1H,
J ¼ 8.6 Hz, quinoline5), 7.73 (1H, t, J ¼ 7.1 Hz, quinoline7), 7.60 (1H, t,
J ¼ 7.3 Hz, quinoline6), 7.17 (1H, t, J ¼ 7.4 Hz, p-Ar), 7.13e7.11 (2H, d,
J ¼ 8.4 Hz, m-Ar), 2.72 (2H, m, 2ꢀ eCHe), 2.35 (3H, s, eCH3), 1.00
(12H, s, 4ꢀ eCH3). dC (100 MHz; CDCl3; Me4Si) 167.6 (C]N), 156.3
(quinoline2), 147.5 (quinoline10), 146.7 (CeN), 136.3 (quinoline4),
135.8 (o-Ar), 130.2 (quinoline8), 129.6 (quinoline7), 128.9 (quino-
line9), 127.7 (quinoline5), 127.5 (quinoline6), 123.7 (p-Ar), 123.1 (m-
Ar), 118.9 (quinoline3), 28.45 (eCHe), 23.39 (eCH3), 23.03 (eCH3),
17.27 (CH3eC]N). Anal. Calcd for C23H26N2 (330.47) requires C,
83.59; H, 7.93; N, 8.48%. Found: C, 83.55; H, 7.96; N, 8.27%. FT-IR
(Diamond disk, cmꢁ1): 2963, 1637, 1594, 1559, 1428, 1364, 1319,
1192, 1128, 1087, 841, 750, 691.
4.2.7. 2-(1-(2,6-Diethylphenylimino)ethylidene)quinolylcobalt
dichloride (Co2)
Co2 was obtained as a blue powder in 90% yield. C21H22Cl2N2Co
(431.05) requires C, 58.35; H, 5.13; N, 6.48%; Found: C, 58.30; H,
5.33; N, 6.38%. IR (Diamond; cmꢁ1): 2965, 1611, 1586, 1508, 1453,
1372, 1346, 1306, 1219, 1197, 833, 784, 754.
4.2.8. 2-(1-(2,6-Diisopropylphenylimino)ethylidene)quinolylcobalt
dichloride (Co3)
Co3 was obtained as a blue powder in 93% yield. C23H26Cl2N2Co
(459.08) requires C, 60.01; H, 5.69; N, 6.09%; Found: C, 59.84; H,
5.79; N, 6.01%. IR (Diamond; cmꢁ1): 2966, 1615, 1586, 1558, 1506,
1463, 1435, 1367, 1303, 1253, 1218, 1190, 1057, 833, 811, 755.
4.2.9. 2-(1-(2,4,6-Trimethylphenylimino)ethylidene)quinolylcobalt
dichloride (Co4)
Co4 was obtained as a blue powder in 89% yield. C20H20Cl2N2Co
(417.03) requires C, 57.44; H, 4.82; N, 6.70%; Found: C, 57.30; H,
4.89; N, 6.42%. IR (Diamond; cmꢁ1): 2916, 1613, 1595, 1561, 1511,
1470, 1366, 1224, 1160, 834, 787, 757.
4.2.4. 2-(1-(2,4,6-Trimethylphenylimino)ethylidene)quinoline (L4)
In a manner similar to that described for L1, L4 was prepared as
a yellow solid in 62% yield. Mp: 143e144 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.53 (1H, d, J ¼ 8.5 Hz, quinoline3), 8.24 (1H, d, J ¼ 8.4 Hz,
quinoline4), 8.18 (1H, d, J ¼ 8.4 Hz, quinoline8), 7.88 (1H, d,
J ¼ 8.6 Hz, quinoline5), 7.75 (1H, t, J ¼ 8.1 Hz, quinoline7), 7.61 (1H, t,
J ¼ 7.8 Hz, quinoline6), 6.91 (2H, s, m-Ar), 2.33 (3H, s, eCH3), 2.31
(3H, s, eCH3), 2.03 (6H, s, 2ꢀ eCH3). dC (100 MHz; CDCl3; Me4Si)
168.1 (C]N), 156.5 (quinoline2), 147.5 (quinoline10), 146.5 (CeN),
136.2 (quinoline4), 132.4 (p-Ar), 130.2 (quinoline8), 129.6 (quino-
line7), 128.8 (quinoline9), 128.7 (m-Ar), 127.7(quinoline5), 127.4
(quinoline6), 125.2 (o-Ar), 118.9 (quinoline3), 20.91 (eCH3), 18.04
(eCH3), 16.55 (CH3eC]N). Anal. Calcd for C20H20N2 (288.39)
requires C, 83.30; H, 6.99; N, 9.71%. Found: C, 83.10; H, 7.06; N,
9.51%. FT-IR (Diamond disk, cmꢁ1): 2934, 2361, 1633, 1595, 1475,
1365, 1216, 1205, 1125, 1084, 851, 757, 685.
4.2.10. 2-(1-(2,6-Diethyl-4-methylphenylimino)ethylidene)
quinolylcobalt dichloride (Co5)
Co5 was obtained as a blue powder in 91% yield. C22H24Cl2N2Co
(445.06) requires C, 59.21; H, 5.42; N, 6.28%; Found: C, 58.99; H,
5.61; N, 6.08%. IR (Diamond; cmꢁ1): 2917, 1614, 1589, 1507, 1465,
1370, 1306, 1217, 1195, 831, 785, 755.
4.2.11. 2-(1-(2,6-Dimethylphenylimino)ethylidene)quinolyliron
dichloride (Fe1)
A Schlenk tube was charged with the 2,6-dimethyl-N-(1-(qui-
nolin-2-yl)ethylidene)benzenamine (0.086 g, 0.3 mmol) and
FeCl2$4H2O (0.06 g, 0.3 mmol) and purged three times with
nitrogen, followed by the addition of 10 mL ethanol. The reaction
mixture was stirred at room temperature for 6 h. The resulting
precipitate was filtered off, washed twice with diethyl ether and
dried in vacuum to furnish the pure product. Fe1 was obtained as
a gray powder in 80% yield. C19H18Cl2N2Fe (401.11) requires C,
56.89; H, 4.52; N, 6.98%; Found: C, 56.71; H, 4.63; N, 6.76%. IR
4.2.5. 2-(1-(2,6-Diethyl-4-methylphenylimino)ethylidene)quinoline
(L5)
In a manner similar to that described for L1, L5 was prepared
as a yellow solid in 68% yield. Mp: 147e148 ꢂC. dH (400 MHz;
CDCl3; Me4Si) 8.52 (1H, d, J ¼ 8.6 Hz, quinoline3), 8.24 (1H, d,

3034
S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3029e3035
(Diamond; cmꢁ1): 2919, 1619, 1588, 1506, 1465, 1428, 1370, 1306,
1217, 1203, 1143, 1120, 828, 784, 755.
Acknowledgments
This work is supported by MOST 863 program No.
2009AA033601. The EPSRC are thanked for the award of a travel
grant (to CR).
4.2.12. 2-(1-(2,6-Diethylphenylimino)ethylidene)quinolyliron
dichloride (Fe2)
Fe2 was obtained as a gray powder in 89% yield. C21H22Cl2N2Fe
(429.16) requires C, 58.77; H, 5.17; N, 6.53%; Found: C, 58.66; H,
5.26; N, 6.43%. IR (Diamond; cmꢁ1): 2966, 1615, 1589, 1556, 1506,
1452, 1406, 1371, 1344, 1306, 1218, 1198, 1141, 832, 782, 756.
Appendix A. Supplementary material
CCDC 822277 and 822278 contain the supplementary crystal-
lographic data for the complexes Co3 and Fe4. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre,12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk.
4.2.13. 2-(1-(2,6-Diisopropylphenylimino)ethylidene)quinolyliron
dichloride (Fe3)
Fe3 was obtained as a gray powder in 91% yield. C23H26Cl2N2Fe
(457.22) requires C, 60.42; H, 5.73; N, 6.13%; Found: C, 60.19; H,
5.79; N, 6.01%. IR (Diamond; cmꢁ1): 2964, 1620, 1590, 1505, 1407,
1367, 1191, 1125, 833, 810, 755.
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