2-(1-Arylimino)quinolylnickel halides: Synthesis, characterization and catalytic behavior towards ethylene

Article abstract of DOI:10.1016/j.jorganchem.2011.11.001

A series of 2-(1-arylimino)quinolylnickel halides were synthesized and characterized by IR and elemental analyses. Distorted trigonal bipyramidal geometries are adopted for the nickel complexes C1, C4, C7 and C11 as crystallized from either DMF or methanol solution. When activated by Et ₂AlCl, the nickel pre-catalysts exhibited good to high catalytic activities in ethylene oligomerization.

Full text of DOI:10.1016/j.jorganchem.2011.11.001

Journal of Organometallic Chemistry 699 (2012) 18e25
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Journal of Organometallic Chemistry
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2-(1-Arylimino)quinolylnickel halides: Synthesis, characterization and catalytic
behavior towards ethylene
,
a
a,c,
Shengju Song a, Tianpengfei Xiao 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-arylimino)quinolylnickel halides were synthesized and characterized by IR and elemental
analyses. Distorted trigonal bipyramidal geometries are adopted for the nickel complexes C1, C4, C7 and
C11 as crystallized from either DMF or methanol solution. When activated by Et2AlCl, the nickel pre-
catalysts exhibited good to high catalytic activities in ethylene oligomerization.
Ó 2011 Elsevier B.V. All rights reserved.
Received 20 September 2011
Received in revised form
31 October 2011
Accepted 1 November 2011
Keywords:
Ethylene oligomerization
Nickel pre-catalyst
X-ray diffraction
2-(1-Arylimino)quinoline
1. Introduction
complexes toward polar substrates in comparison to that of the
cationic complexes, there has been a renewed effort in the devel-
Late transition metals catalysts for olefin polymerization/oligo-
merization have received increasing attention of late. In part, this is
because they have a higher tolerance towards polar reagents due to
reduced oxophilicity when compared to early transition metal
catalysts, and thus offer the potential to yield polymers with
different microstructures and properties. One of the more prom-
inent catalytic systems investigated was the nickel-ylide complex
containing PeO chelate ancillary ligation developed by Keim et al.,
and which was employed in the Shell higher olefin process (SHOP)
for the synthesis of linear oligomers (C4eC20 range) [1e3]. In the
middle of the 1990s, the discovery by Brookhart et al. of the unique
catalytic properties of cationic diimino nickel and palladium cata-
lysts in olefin polymerization brought about renewed interest in
the field [4e6]. Indeed, single-site catalysts of nickel are one of the
most studied types, and two main kinds of nickel complexes,
namely neutral and cationic complexes have been utilized. Due to
the difficult syntheses and the high sensitivity of the neutral Ni
opment of cationic nickel-based polymerization catalysts. A wide
variety of cationic nickel catalysts bearing different ligands were
reported, most commonly four coordinate nickel halides bearing
bidentate ligands such as P^O [7,8], P^P [9,10], and N^N [11e18],
and also a number of the five-coordinated nickel halides incorpo-
rating tridentate ligands such as N^N^O [19,20], N^P^N [21], P^N^P
[22], P^N^N [22,23], N^N^N [24e31] and N^S^N [26,31]. This,
together with further successes with other late transition metal
systems, has stimulated extensive research activity in the area,
much of which has been the focus of a number of recent reviews
[32e39].
A series of nickel halide complexes containing bidentate N^N
ligands have been developed by our group [40e50]. The systems
catalyzed ethylene oligomerization and/or polymerization with
good to high observed activities. These achievements has stimu-
lated further explorations through the design and synthesis of
alternative bidentate N^N complexes. Recently
a series of
8-substituted (methyl, ethyl, isopropyl) 2-(1-aryliminoethylidene)
quinoline derivatives and the nickel(II) dibromide complexes
thereof were synthesized and characterized. The catalytic proper-
ties of these nickel bromide pre-catalysts were explored, and a high
affinity for ethylene dimerization was observed [51]. Differences in
the catalytic performances of such nickel pre-catalysts bearing
2-(1-aryliminomethylidene)quinolines were found to rely on the
different substituents positioned at the 8-position of the quinoline
* 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.2011.11.001

S. Song et al. / Journal of Organometallic Chemistry 699 (2012) 18e25
19
[52]. In particular, nickel pre-catalysts bearing 8-isopropyl-2-(1-
aryliminomethylidene)quinoline ligands exhibited ethylene poly-
merization, whereas no activity was observed for nickel complexes
bearing 2-(1-aryliminomethylidene)quinoline or 8-methyl-2-(1-
aryliminomethylidene) quinoline ligands. To get the whole
picture, it is necessary to explore 2-(1-arylimino)quinoline deriv-
atives without any 8-substituent present. Thus, nickel halide
complexes bearing 2-(1-arylimino)quinoline derivatives are now
synthesized and characterized, and interestingly it was found that
they exhibit good to high activities in ethylene oligomerization.
Herein, the synthesis and characterization of nickel halide
complexes bearing 2-(1-arylimino)quinolines are reported and
their catalytic performance during ethylene oligomerization has
been investigated under various reaction conditions.
Fig. 1. Molecular structure of C1$DMF with thermal ellipsoids at the 30 % probability
2. Results and discussion
level. Hydrogen atoms have been omitted for clarity.
2.1. Synthesis and characterization of ligands and complexes
2.2. Molecular structures
A series of 2-(1-arylimino)quinoline derivatives (L1eL10) were
prepared using our previously reported procedures [53,54].
A general synthetic route for these complexes is shown in Scheme
1. It is noteworthy that the steric bulkiness of the ligands could be
controlled easily by changing the bulky arylamine employed. All of
these complexes have been characterized by IR spectroscopy and
elemental analyses.
After the quinolineeimine ligands were obtained,1 equiv of (1,2-
dimethoxyethane) nickel(II) bromide ((DME)NiBr2) or NiCl2$6H2O
was added to an ethanol solution of the ligand and stirred for 12 h at
room temperature. The nickel complexes C1eC20 were obtained as
dark yellow solids, and were characterized by IR spectroscopy and
elemental analyses. In the IR spectra, the vC]N stretching
frequencies shifted to lower values (1597e1631 cmꢀ1) with weaker
intensity compared with those of the corresponding free ligand
[53,54]. Such changes are in line with the coordination existing
between the imino nitrogen atom and the nickel center. The struc-
tures of nickel complexes C1, C4, C7 and C11 were confirmed by
single crystal X-ray diffraction studies.
Single crystals of the complexes C1, C4, C7 and C11 suitable for
X-ray diffraction were individually obtained by slow diffusion of
diethyl ether into their methanol or DMF solutions. The molecular
structures are shown in Figs. 1e4, respectively, along with selected
bond lengths and angles in Table 1.
In the structure of C1, the geometry around the nickel center can
be described as a distorted trigonal bipyramidal, in which the nickel
atom is surrounded by one bidentate ligand, two bromines and one
DMF molecule coordinated via oxygen. The axial positions are
occupied by N1 of the chelate and O1 from the DMF molecule
(O(1)eNi(1)eN(1) 171.36(17)ꢁ), while the equatorial plane is
formed by the nitrogen (N2) atom and two bromides, with the
deviation of the nickel center from the equatorial plane of 0.060 Å.
The axial plane and the equatorial plane make a dihedral angle of
87.72ꢁ. The Ni1eN2 bond (2.031(4) Å) is significantly shorter than
the Ni1eN1 bond (2.079(4) Å), which can be attributed to the
coordination of the DMF molecule. It is noteworthy that the quin-
oline ring and aryl ring are not coplanar, having a dihedral angle of
84.85ꢁ.
Complexes C4 (Fig. 2.), C7 (Fig. 3.) and C11 (Fig. 4.) have a similar
structure to that of complex C1. However, the Ni1eN2 bond
(2.021(2) Å), the Ni1eN1 bond (2.077(2) Å) and the O(1)eNi(1)e
N(1) 174.27(9)ꢁ of C11 are different from C1’s, which can be
attributed to the coordination of the CH3OH molecule and two
chlorides. The dihedral angle of quinoline and phenyl plane is of
85.67ꢁ in C4, 83.93ꢁ in C7, 83.39ꢁ in C11.
R2
R2
(DME)NiBr2
R1
R
R1
or
R1
R
R1
X
.
NiCl2 6H2O
N
N
N
N
Ni
C2H5OH
X
L1 - L10
C1 - C20
R1
R2
Me
H
R = Me L1
R = Et L6
Et
H
i-Pr
H
Me
Me
Et
Me
L5
L2
L3
L4
L7
L8
L9 L10
C4 C5
C9 C10
X = Br
C1
C2
C7
C3
C8
C6
X = Cl C11 C12 C13 C14 C15
C16 C17 C18 C19 C20
Fig. 2. Molecular structure of C4$2DMF. Thermal ellipsoids are shown at the 30%
Scheme 1. Synthetic procedure.
probability level. Hydrogen atoms and a DMF have been omitted for clarity.

20
S. Song et al. / Journal of Organometallic Chemistry 699 (2012) 18e25
Table 1
Selected bond lengths (Å) and angles (ꢁ) for nickel complex C1$DMF, C4$2DMF,
C7$DMF and C11$CH3OH.
C1$DMF
C4$2DMF
C7$DMF
C11$CH3OH
Bond lengths (Å)
Ni(1)eO(1)
Ni(1)eN(1)
Ni(1)eN(2)
Ni(1)eBr(1)
Ni(1)eCl(1)
Ni(1)eBr(2)
Ni(1)eCl(2)
N(1)eC(8)
2.046(4)
2.079(4)
2.031(4)
2.4480(11)
e
2.046(3)
2.095(3)
2.023(3)
2.4583(9)
e
2.040(5)
2.110(6)
2.043(6)
2.4581(14)
e
2.069(2)
2.077(2)
2.021(2)
e
2.2855(11)
e
2.4549(11)
e
2.4678(9)
e
2.4509(13)
e
2.3003(12)
1.329(3)
1.362(4)
1.286(4)
1.444(4)
1.326(7)
1.372(7)
1.276(7)
1.456(7)
1.338(5)
1.369(5)
1.294(5)
1.443(5)
1.348(9)
1.375(9)
1.277(9)
1.459(8)
N(1)eC(9)
N(2)eC(10)
N(2)eC(12)
Bond angles (ꢁ)
N(2)eNi(1)eO(1)
N(2)eNi(1)eN(1)
O(1)eNi(1)eN(1)
N(2)eNi(1)eBr(1)
N(2)eNi(1)eCl(1)
O(1)eNi(1)eBr(1)
O(1)eNi(1)eCl(1)
N(1)eNi(1)eBr(1)
N(1)eNi(1)eCl(1)
N(2)eNi(1)eBr(2)
N(2)eNi(1)eCl(2)
O(1)eNi(1)eBr(2)
O(1)eNi(1)eCl(2)
N(1)eNi(1)eBr(2)
N(1)eNi(1)eCl(2)
Br(1)eNi(1)eBr(2)
Br(1)eNi(1)eCl(2)
93.45(16)
78.98(17)
171.36(17)
108.81(13)
e
91.70(13)
79.34(13)
170.37(12)
116.72(10)
e
94.2(2)
79.1(2)
173.0(2)
111.19(16)
e
96.54(9)
79.31(9)
174.27(9)
e
Fig. 3. Molecular structure of C7$DMF. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
110.19(7)
e
92.38(12)
e
89.39(9)
e
91.99(15)
e
91.48(7)
e
2.3. Ethylene oligomerization
94.01(13)
e
91.48(10)
e
92.40(16)
e
93.67(7)
e
Ethylene Oligomerization catalyzed by these nickel complexes
with various co-catalysts has been systematically investigated.
Various reaction factors such as categories of co-catalysts, the molar
ratio of co-catalysts to nickel complex, the reaction temperature and
the nature of the complexes have an influence on the activity
towards ethylene oligomerization as well as the structures of the
products.
114.06(13)
e
109.83(10)
e
110.20(16)
e
111.78(7)
e
89.19(11)
e
92.39(9)
e
88.99(15)
e
86.81(7)
e
90.12(12)
e
93.98(10)
e
91.36(16)
e
91.05(7)
e
136.92(4)
e
133.34(3)
e
138.41(5)
e
137.92(4)
For the catalytic discussion below, the nickel pre-catalysts can
be divided into two groups, namely bromide compounds [LNiBr2
(C1eC10)] and chloride compounds [LNiCl2 (C10eC20)].
less selectivity for a-C4 and with less C6 olefins formed. The use of
Et3Al resulted in systems with the least activity. For Et3Al2Cl3,
systems exhibited less activity, but more selectivity for -C4 and
more C4 olefins than did the Et2AlCl system. The best co-catalyst for
the system was deemed to be Et2AlCl, and thus further studies of
the nickel complexes for ethylene oligomerization were carried out
with Et2AlCl as co-catalyst (Table 2).
The reaction parameters greatly affected the catalytic activity
(entries 5e16, Table 2). When the ethylene pressure was 1 bar, the
system exhibited quite low activity, but on the ethylene pressure
increasing from 1 to 10 bar, the catalytic activity increased. Herein,
2.3.1. Ethylene oligomerization by nickel bromide complexes
In order to evaluate the nickel bromine complexes described
above for their ability to catalyze ethylene oligomerization or
polymerization reactions, pre-catalyst C3 was selected for further
optimization. Screening for the influence of the co-catalyst, the
ethylene pressure, the reaction temperature and [Al]/[Ni] molar
ratio was conducted; results are given in Table 2.
a
Initial studies were carried out at 20 ꢁC under 10 bar of ethylene
with five co-catalysts (MAO, MMAO, Et2AlCl, Et3Al and Et3Al2Cl3),
which revealed that these catalyst systems behave quite differently
in terms of activity. The nature of the co-catalyst has an impact on
the catalytic results: the use of MAO formed more C6, but with low
activity. The use of MMAO induced the highest activity, but with
Table 2
Oligomerization of ethylene with pre-catalyst C3.a
Entry T/ꢁC Co-catalyst Al/Ni Activityb Oligomer distributionc (%)
P
P
P
P
a
-C4 C4/ C C6/ C C8/ C ꢂC10
/
C
1
2
3
4
5
6
7
8
20 MAO
20 MMAO
20 Et3Al
1000 0.78
1000 1.54
200 0.16
200 0.65
200 1.37
200 5.21
200 8.08
200 10.0
200 12.7
200 10.3
200 1.00
100 11.2
150 12.0
79.3 25.2
57.6 28.8
57.8 21.2
93.5 27.1
70.4 20.1
72.1 21.2
74.3 12.0
73.8 20.7
73.7 19.6
70.5 13.2
74.2 33.3
77.5 33.5
73.3 19.4
75.2 14.5
74.1 17.6
73.2 22.3
24.8
11.2
19.8
12.9
12.1
13.7
10.9
13.0
10.0
8.7
9.2
10.1
11.3
9.0
40.8
49.9
48.7
51.0
57.7
55.2
65.2
57.8
59.4
68.7
48.7
48.5
59.5
64.3
59.4
53.8
20 Et3Al2Cl3
20 Et2AlCl
40 Et2AlCl
60 Et2AlCl
70 Et2AlCl
80 Et2AlCl
90 Et2AlCl
100 Et2AlCl
80 Et2AlCl
80 Et2AlCl
80 Et2AlCl
80 Et2AlCl
80 Et2AlCl
10.1
9.9
11.9
8.5
11.2
9.4
3.7
9
10
11
12
13
14
15
16
10.7
11.4
10.2
8.1
12.0
12.5
6.6
11.1
13.3
11.2
11.4
250 10.9
300 9.00
450 6.54
a
Conditions: 5 mmol Ni, 10 bar C2H4, 30 min, 100 mL of toluene.
b
c
Fig. 4. Molecular structure of C11$CH3OH. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
In units of 105 g molꢀ1(Ni) hꢀ1
.
P
Determined by GC. C denotes the total amount of oligomers.

S. Song et al. / Journal of Organometallic Chemistry 699 (2012) 18e25
21
C3 was typically investigated for ethylene oligomerization at 10 bar
ethylene pressure. The activity for ethylene oligomerization was
substantially affected by the reaction temperature. To estimate the
influence of the temperature, the catalytic system of C3 with
200 equiv of Et2AlCl at 10 bar of ethylene was investigated at
various reaction temperatures (entries 5e11 in Table 2). On
increasing the temperature from 20 to 100 ꢁC, the optimum cata-
lytic activity of 1.27 ꢃ 106 g molꢀ1(Ni) hꢀ1 was observed at 80 ꢁC.
The catalytic activity at 80 ꢁC was almost 10 times that at 20 ꢁC,
reflecting the high thermal stability of the nickel active species.
Indeed, the enhanced thermal stability is an issue of great impor-
tance in relation to catalytic practices, and the systems herein
behave favorably when compared to our bidentate nickel complex
pre-catalysts [46,53]. The contents of the oligomeric proportions
were randomly changed, implying that the reaction temperature
did the related ortho methyl bearing complex C1. Compared with the
analogous complex C2 bearing a 2,6-diethylphenyl group, complex
C5 containing the 2,6-diethyl-4-methylphenyl group exhibited
slightly higher activity. Such observations were thought to be due to
the electronic effects of the methyl group, as reported in other cata-
lytic systems [55]. On comparison with the nickel analogs bearing 8-
substituted 2-(1-arylimino)quinolines [51], the current series of
nickel pre-catalysts showed relatively higher activity for ethylene
oligomerization. In other words, less bulk at the 8-position of the
quinoline framework aids ethylene insertion, or alternatively, less
bulk results in better chain propagation [3]. On changing R from the
methyl (R ¼ Me) to ethyl (R ¼ Et) derivative (for a given aryl group) of
C1and C6, C2 and C7, C3 and C8, C4and C9, C5 and C10, a similar trend
for the catalytic activities was observed in regard to the nature of the
ligands present. For the literature concerning 2-(1-aryliminomethy-
lidene)quinolylnickel analogs [52], the conclusion that they were
inactive for ethylene polymerization may well have been concluded
without also checking for the presence of oligomers in the solution.
did not rationally control the rate of chain propagation to
b-
hydrogen elimination. A similar influence of temperature on the
oligomer distribution using nickel-based systems has previously
been reported by our group [45,55]. The effects of the Al/Ni molar
ratio on the activities for ethylene oligomerization were further
investigated using C3. Increasing the Al/Ni molar ratio in the range
100e450 resulted in an initial increase and then a gradual decrease,
with the highest activity of 1.27 ꢃ 106 g molꢀ1(Ni) hꢀ1 observed at
an Al/Ni molar ratio of 200 at 80 ꢁC. Beyond the highest activity
observed at the Al/Ni ratio of 200, the distribution of oligomers and
2.3.2. Ethylene oligomerization by nickel chloride complexes
In a similar procedure, complex C13 was used in exploring suit-
able co-catalysts (entries 1e5 in Table 4) for optimum oligomeriza-
tion conditions. The nickel chloride complex C13 was investigated
for ethylene oligomerization at 80 ꢁC in the presence of different
co-catalysts at 10 bar of ethylene. The results showed that the
catalytic systems using Et2AlCl as co-catalyst exhibited higher
activities than when employing any other co-catalyst, whilst
observing oligomers in similar distributions and a similar selectivity
the selectivity of a-olefins are similar.
The structure of the ligand had an obvious effect on the catalytic
behavior of the nickel complexes. Under the optimum conditions
observed for the catalytic system employing C3, all complexes
C1eC10 were investigated for ethylene oligomerization in order to
elucidate the effects of the substituents R1 and R2. The results are
summarized in Table 3. The substituents on the ligands clearly
affected the catalytic activities of their nickel complexes, however,
random data were observed for the distribution of the oligomers
produced by the different nickel pre-catalysts. The nickel bromide
complexes LNiBr2 (Table 3) showed comparable catalytic activities in
the region of 106 g molꢀ1(Ni) hꢀ1 or so under similar reaction
conditions, and also a similar distribution of oligomers. The greater
the bulkiness of R1 (entries 1e3 inTable 3), the higher the activity was
for the a-olefins. Therefore, further catalytic studies were performed
via activation with Et2AlCl. Elevating the reaction temperature from
40 to 80 ꢁC resulted in enhanced activity (entries 5e8 in Table 4). On
elevating the reaction temperature further from 80 to 100 ꢁC resul-
ted in a reduction in the activity (entries 5, 9 and 10 in Table 4). Over
the Al/Ni molar ratio range 100e450 for the C8/Et2AlCl system, the
highest oligomerization activity was observed at the Al/Ni molar
ratio of 200 (entries 2 and 11e15 in Table 4). Given this, all nickel
chloride complexes were investigated with the Al/Ni molar ratio of
200 at 80 ꢁC (Table 5).
Similarly, by replacing bromide with chloride, a similar trend for
catalytic activities was displayed in regard to the nature of the ligands
observed, for example C3 (R1 ¼ i-Pr) at 1.27 ꢃ 106 g molꢀ1(Ni) hꢀ1
,
followed by C2 (R1 ¼ Et) and C1 (R1 ¼ Me). It is possible that the
greater bulkiness of the isopropyl groups at the ortho position of the
imino-N aryl ring of complex C3 may protect the active sites from
deactivation. Furthermore, the substituents at the 4-position of the
aryl ring also had an obvious influence on the catalytic activity. For
example, the complex C4, which bears an electron-donating methyl
group at the4-positionof the aryl ring, exhibited highercatalyticthan
present,
such
that
the
order
C13 > C12 > C11
and
C14 > C15 > C12 > C11 was observed. The nickel bromide complexes
showed lower catalytic performance compared to the nickel chloride
catalysts. These results are consistent with the results of
Table 4
Oligomerization of ethylene with pre-catalyst C13.a
Entry T/ꢁC Co-catalyst Al/Ni Activityb Oligomer distributionc (%)
P
P
P
P
Table 3
a
-C4 C4/ C C6/ C C8/ C ꢂC10
/
C
Ethylene oligomerization by nickel pre-catalysts C1eC10.a
1
2
3
4
5
6
7
8
80 MAO
80 MMAO
80 Et3Al
1000 4.91
1000 1.31
200 2.15
200 3.78
200 15.7
200 5.55
200 8.09
200 9.90
200 12.3
200 1.08
100 12.2
150 15.3
250 9.54
300 8.14
450 7.54
73.2 32.3
74.2 32.6
72.2 31.5
73.1 29.6
70.1 30.2
72.5 25.3
74.3 24.0
73.2 20.7
70.5 33.2
69.7 22.3
71.2 22.6
76.1 20.2
71.5 21.6
70.2 18.8
73.4 30.2
10.7
10.4
11.3
12.4
10.8
12.7
11.9
12.0
11.7
11.7
11.4
10.8
12.4
13.4
11.4
11.1
12.4
9.7
45.9
44.6
47.7
47.6
48.7
50.9
53.2
56.8
45.7
55.9
54.6
58.7
55.6
56.4
48.3
Entry Pre-catalyst Activityb Oligomer distributionc (%)
P
P
P
P
a
-C4 C4/
C
C6/
C
C8/
C
ꢂC10
/
C
80 Et3Al2Cl3
80 Et2AlCl
40 Et2AlCl
60 Et2AlCl
70 Et2AlCl
90 Et2AlCl
100 Et2AlCl
80 Et2AlCl
80 Et2AlCl
80 Et2AlCl
80 Et2AlCl
80 Et2AlCl
10.4
10.3
11.1
10.9
10.5
9.4
10.1
11.4
10.3
10.4
11.4
10.1
1
2
3
4
5
6
7
8
9
10
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
8.94
9.75
12.7
12.8
11.0
7.89
9.65
11.9
10.8
9.90
75.3 34.2
71.1 51.8
73.7 19.6
73.2 23.5
71.4 40.4
65.3 33.2
67.1 41.8
71.7 29.6
72.2 28.5
71.5 43.4
12.1
7.3
10.5
6.1
43.2
34.8
59.4
37.0
34.8
45.2
37.8
50.2
36.8
31.7
10.0
24.7
13.7
10.1
12.3
10.0
20.7
13.7
11.2
14.8
11.1
11.5
8.1
10.2
14.0
11.2
9
10
11
12
13
14
15
a
Conditions: 5 m
mol Ni, 200 equiv. Et2AlCl, 80 ꢁC, 10 bar C2H4, 30 min, 100 mL of
a
toluene.
Conditions: 5 mmol Ni, 10 bar C2H4, 30 min, 100 mL of toluene.
b
c
b
c
In units of 105 g molꢀ1(Ni) hꢀ1
Determined by GC. C denotes the total amount of oligomers.
.
In units of 105 g molꢀ1(Ni) hꢀ1
.
P
P
Determined by GC. C denotes the total amount of oligomers.

22
S. Song et al. / Journal of Organometallic Chemistry 699 (2012) 18e25
Table 5
4.2.2. Preparation of C1
Ethylene oligomerization by nickel pre-catalysts C11eC20.a
To a solution of the ligand 2,6-dimethyl-N-(1-(quinolin-2-yl)
ethylidene)benzenamine (L1, 0.274 g, 1.0 mmol) in 10 mL ethanol,
(DME)NiBr2 (0.308 g, 1.0 mmol) was added. The reaction mixture
was stirred at room temperature for 12 h to afford a yellow
precipitate from the reaction mixture (C1, 0.434 g, 88% yield). Anal.
Calcd for C19H18Br2N2Ni (489.92) requires C, 46.30; H, 3.68; N, 5.68;
Found: C, 46.53; H, 3.73; N, 5.39. FT-IR (Diamond disk, cmꢀ1): 2898,
1624, 1590, 1510, 1465, 1430, 1369, 1219, 1144, 832, 790,751.
Entry Pre-catalyst Activityb Oligomer distributionc(%)
P
P
P
9.5
10.3
13.5
8.5
11.8
11.5
10.5
8.7
P
a
-C4 C4/
C
C6/
C
C8/
C
ꢂC10/
C
1
2
3
4
5
4
5
6
7
8
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
8.90
9.10
15.7
18.0
11.3
8.58
9.05
10.9
76.3 32.1
72.1 38.8
70.1 30.2
73.2 44.6
74.4 22.5
70.2 29.5
70.4 34.4
67.3 32.2
68.1 38.8
72.7 32.6
10.3
11.8
10.8
7.4
8.7
48.9
39.9
48.7
34.5
57.3
43.0
40.4
44.2
39.9
46.2
11.7
15.7
13.7
13.1
12.6
11.0
4.2.3. Preparation of C2
11.0
11.9
Using the same procedure as for the synthesis of complex C1, the
stoichiometric reaction of 2,6-diethyl-N-(1-(quinolin-2-yl)ethyl-
idene)benzenamine (L2, 0.302 g, 1.0 mmol) and 1.0 mmol (DME)
NiBr2 in 10 mL ethanol gave complex C2 as a yellow powder
(0.475 g, 91% yield). Anal. Calcd for C21H22Br2N2Ni (517.95) requires
C, 48.42; H, 4.26; N, 5.38; Found: C, 48.32; H, 4.36; N, 5.29. IR
(Diamond; cmꢀ1): 2967, 1617, 1587, 1506, 1451, 1371, 1345, 1312,
1216, 829, 779, 755.
10.2
a
Conditions: 5 m
mol Ni, 200 equiv. Et2AlCl, 80 ꢁC, 10 bar C2H4, 30 min, 100 mL of
toluene.
b
In units of 105 g molꢀ1(Ni) hꢀ1
Determined by GC. C denotes the total amount of oligomers.
.
P
c
computational studies [56e58], suggesting that the higher net charge
of the late transition metal complexes, the higher the catalytic activity
of the complex pre-catalysts. The highest activity of C14 reached
1.80 ꢃ 106 g molꢀ1(Ni) hꢀ1 at a Al/Ni molar ratio of 200 at 80 ꢁC, with
little change in the distribution of oligomers. For complexes C16eC20,
similar results to C11eC15 were observed, the highest activity of C20
reached 1.19 ꢃ 106 g molꢀ1(Ni) hꢀ1 under the optimized conditions.
4.2.4. Preparation of C3
Using the same procedure as for the synthesis of complex C1, to
a solution of the compound 2,6-diisopropyl-N-(1-(quinolin-2-yl)
ethylidene) benzenamine (L3, 0.330 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C3 was obtained as a yellow
powder, 0.500 g, 92% yield. Anal. Calcd for C23H26Br2N2Ni (545.98)
requires C, 50.32; H, 4.77; N, 5.10; Found: C, 50.26; H, 4.79; N, 4.93.
IR (Diamond; cmꢀ1): 2965, 1613, 1585, 1463, 1369, 1308, 1190, 1056,
831, 810, 753.
3. Conclusion
A series of 2-(1-arylimino)quinolyl nickel complexes have been
synthesized and characterized. It was found that the LNiCl2 and
LNiBr2 complexes displayed good activities for ethylene oligomer-
ization, and both the variation of the substituents and the reaction
parameters affected the catalytic behavior. Activities as high as
1.80 ꢃ 106 g molꢀ1(Ni) hꢀ1 were attained using a Al/Ni molar ratio
of 200 at 80 ꢁC under 10 bar ethylene.
4.2.5. Preparation of C4
Using the same procedure as for the synthesis of complex C1, to
a solution of the compound 2,4,6-trimethyl-N-(1-(quinolin-2-yl)
ethylidene) benzenamine (L4, 0.288 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C4 was obtained as a yellow
powder, 0.457 g, 90% yield. Anal. Calcd for C20H20Br2N2Ni (503.93)
requires C, 47.39; H, 3.98; N, 5.53; Found: C, 47.08; H, 4.05; N, 5.29.
IR (Diamond; cmꢀ1): 2913, 1619, 1512, 1471, 1430, 1371, 1222, 834,
786, 750.
4. Experimental section
4.1. General considerations
4.2.6. Preparation of C5
Using the same procedure as for the synthesis of complex C1, to
a solution of the ligand 2,6-diethyl-4-methyl-N-(1-(quinolin-2-yl)
ethylidene) benzenamine (L5, 0.316 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C5 was obtained as a yellow
powder, 0.487 g, 91% yield. Anal. Calcd for C22H24Br2N2Ni (531.97)
requires C, 49.40; H, 4.52; N, 5.24; Found: C, 49.36; H, 4.59; N, 4.98.
IR (Diamond; cmꢀ1): 2915, 1617, 1513, 1474, 1431, 1370, 1223, 832,
785, 751.
All manipulations involving air and moisture-sensitive comp-
ounds were carried out under an atmosphere of dried and purified
nitrogen using standard Schlenk and vacuum-line techniques.
Toluene was dried over sodium metal and distilled under nitrogen.
Methylaluminoxane (MAO, 1.46 M solution in toluene) and modified
methylaluminoxane (MMAO, 1.93 M in heptane) were purchased
from Akzo Nobel Corp. Diethylaluminium chloride (Et2AlCl, 1.70 M in
toluene), triethylaluminium (AlEt3, 2.00 M in heptane), ethyl-
aluminium sesquichloride (Et3Al2Cl3, 0.87 M in toluene) and other
reagents were purchased from Acros Chemicals. (DME)NiBr2 was
synthesized by the reaction of 1,2-dimethoxyethane with anhydrous
nickel(II) bromide. FT-IR spectra were recorded on a PerkineElmer
System 2000 FTeIR spectrometer. Elemental analysis was carried out
using a Flash EA 1112 microanalyzer. GC analyses were performed
with a Varian CPe3800 gas chromatograph equipped with a flame
4.2.7. Preparation of C6
Using the same procedure as for the synthesis of complex C1, to
a solution of the ligand 2,6-dimethyl-N-(1-(quinolin-2-yl)propyli-
dene) benzenamine (L6, 0.288 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C6 was obtained as a yellow
powder, 0.457 g, 90% yield. Anal. Calcd for C20H20Br2N2Ni (503.93)
requires C, 47.39; H, 3.98; N, 5.53; Found: C, 47.26; H, 4.02; N, 5.45. IR
(Diamond; cmꢀ1): 3346, 2905, 1611, 1589, 1556, 1508, 1462, 1431,
1383,1346,1319,1303,1217,1200,1164,1140,1039, 983, 953, 867, 788.
ionization detector and a 30 m (0.2 mm i.d., 0.25 mm film thickness)
CPeSil 5 CB column.
4.2. Syntheses and characterization
4.2.8. Preparation of C7
Using the same procedure as for the synthesis of complex C1, to
a solution of the ligand 2,6-diethyl-N-(1-(quinolin-2-yl)propyli-
dene)benzenamine (L7, 0.316 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C7 was obtained as a yellow
4.2.1. Preparation of L1eL10
A series of 2-(1-arylimino)quinoline ligands (L1eL10) were
prepared using our previously reported procedures [53,54].

S. Song et al. / Journal of Organometallic Chemistry 699 (2012) 18e25
23
powder, 0.504 g, 94% yield. Anal. Calcd for C22H24Br2N2Ni (531.97)
requires C, 49.40; H, 4.52; N, 5.24; Found: C, 49.20; H, 4.65; N, 5.04.
IR (Diamond; cmꢀ1): 3337, 2966, 1610, 1554, 1511, 1445, 1379, 1344,
1319, 1302, 1218, 1191, 1036, 952, 869, 805, 760.
H, 4.82; N, 6.70; Found: C, 57.18; H, 4.81; N, 6.59. IR (Diamond;
cmꢀ1): 2965, 1623, 1592, 1512, 1465, 1432, 1373, 1384, 1220, 1145,
834, 785, 750.
4.2.16. Preparation of C15
4.2.8. Preparation of C8
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L5 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C15 was obtained (yellow powder, 0.396 g,
89% yield). Anal. Calcd for C22H24Cl2N2Ni (444.07) requires C, 59.24;
H, 5.42; N, 6.28; Found: C, 58.99; H, 5.51; N, 6.14. IR (Diamond;
cmꢀ1): 2966, 1618, 1594, 1509, 1458, 1432, 1372, 1346, 1309, 1214,
1156, 873, 825, 786, 749.
Using the same procedure as for the synthesis of complex C1, to
a solution of the ligand 2,6-diisopropyl-N-(1-(quinolin-2-yl)pro-
pylidene) benzenamine (L8, 0.344 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C8 was obtained as a yellow
powder, 0.524 g, 93% yield. Anal. Calcd for C24H28Br2N2Ni (560.00)
requires C, 51.20; H, 5.01; N, 4.98; Found: C, 51.00; H, 5.02; N, 4.78.
IR (Diamond; cmꢀ1): 3337, 2990, 1613, 1558, 1509, 1467, 1436, 1384,
1349, 1321, 1228, 1143, 1034, 952, 835, 802, 761.
4.2.17. Preparation of C16
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L6 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C16 was obtained (yellow powder, 0.363 g,
87% yield). Anal. Calcd for C20H20Cl2N2Ni (416.04) requires C, 57.47;
H, 4.82; N, 6.70; Found: C, 57.37; H, 5.00; N, 6.54. IR (Diamond;
cmꢀ1): 3056, 2906, 1613, 1590, 1557, 1509, 1463, 1432, 1385, 1347,
1307, 1218, 1202, 1142, 1041, 868, 837, 798, 757.
4.2.10. Preparation of C9
Using the same procedure as for the synthesis of complex C1, to
a solution of the ligand 2,4,6-trimethyl-N-(1-(quinolin-2-yl)pro-
pylidene) benzenamine (L9, 0.302 g, 1.0 mmol) in 10 mL ethanol,
1.0 mmol (DME)NiBr2 was added. C9 was obtained as a yellow
powder, 0.480 g, 92% yield. Anal. Calcd for C21H22Br2N2Ni (517.95)
requires C, 48.42; H, 4.26; N, 5.38; Found: C, 48.26; H, 4.36; N, 5.20.
IR (Diamond; cmꢀ1): 3341, 2978, 1613, 1558, 1509, 1462, 1432, 1379,
1347, 1304, 1217, 1145, 1038, 980, 953, 869, 827, 768.
4.2.18. Preparation of C17
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L7 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C17 was obtained (yellow powder, 89%
yield). Anal. Calcd for C22H24Cl2N2Ni (444.07) requires C, 59.24; H,
5.42; N, 6.28; Found: C, 58.99; H, 5.51; N, 6.14. IR (Diamond; cmꢀ1):
3070, 2971,1611,1590,1557,1512,1447,1434,1347,1320,1305,1220,
1192, 1146, 1039, 954, 873, 809, 755.
4.2.11. Preparation of C10
Using the same procedure as for the synthesis of complex C1, to
a solution of the ligand 2,6-diethyl-4-methyl-N-(1-(quinolin-2-yl)
propylidene) benzenamine L10 (0.330 g, 1.0 mmol) in 10 mL
ethanol, 1.0 mmol (DME)NiBr2 was added. C10 was obtained as
a yellow powder, 0.505 g, 91% yield. Anal. Calcd for C23H26Br2N2Ni
(545.98) requires C, 50.32; H, 4.77; N, 5.10; Found: C, 50.26; H, 4.90;
N, 5.00. IR (Diamond; cmꢀ1): 3333, 2968, 1608, 1510, 1458, 1434,
1381, 1349, 1218, 1211, 1042, 953, 870, 827, 783, 753.
4.2.19. Preparation of C18
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L8 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C18 was obtained (yellow powder, 0.417 g,
88% yield). Anal. Calcd for C24H28Cl2N2Ni (472.1) requires C, 60.80;
H, 5.95; N, 5.91; Found: C, 60.70; H, 5.99; N, 5.80. IR (Diamond;
cmꢀ1): 2968, 1597, 1553, 1507, 1458, 1433, 1384, 1308, 1217, 1190,
1059, 956, 832, 803, 763, 753.
4.2.12. Preparation of C11
To a solution of 1.0 mmol ligand L1 in 10 mL ethanol, NiCl2$6H2O
(0.238 g, 1.0 mmol) was added. The reaction mixture was stirred at
room temperature for 12 h to afford a yellow precipitate from the
reaction mixture (C11, 0.331 g, 82% yield). Anal. Calcd for
C19H18Cl2N2Ni (402.02) requires C, 56.49; H, 4.49; N, 6.93; Found: C,
56.29; H, 4.45; N, 6.85. IR (Diamond; cmꢀ1): 2898, 1631, 1592, 1465,
1370, 1220, 1205, 1143, 834, 790, 750.
4.2.20. Preparation of C19
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L9 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C19 was obtained (yellow powder, 0.371 g,
86% yield). Anal. Calcd for C21H22Cl2N2Ni (430.05) requires C, 58.38;
H, 5.13; N, 6.48; Found: C, 58.15; H, 5.33; N, 6.29. IR (Diamond;
cmꢀ1): 2981, 1613, 1558, 1509, 1463, 1433, 1358, 1348, 1312, 1219,
1147, 1039, 879, 832, 758.
4.2.13. Preparation of C12
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L2 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C12 was obtained (yellow powder, 0.388 g,
90% yield). Anal. Calcd for C21H22Cl2N2Ni (430.05) requires C, 58.38;
H, 5.31; N, 6.48; Found: C, 58.36; H, 5.10; N, 6.38. IR (Diamond;
cmꢀ1): 2965, 1618, 1589, 1352, 1370, 1310, 1217, 831, 780, 755.
4.2.21. Preparation of C20
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L10 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C20 was obtained (yellow powder, 0.414 g,
90% yield). Anal. Calcd for C23H26Cl2N2Ni (458.08) requires C, 60.04;
H, 5.70; N, 6.09; Found: C, 59.90; H, 5.81; N, 6.04. IR (Diamond;
cmꢀ1): 2977, 1610, 1558, 1511, 1460, 1434, 1350, 1313, 1220, 1209,
1156, 1043, 955, 876, 834, 786, 756.
4.2.14. Preparation of C13
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L3 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C13 was obtained (yellow powder, 0.418 g,
91% yield). Anal. Calcd for C23H26Cl2N2Ni (458.08) requires C, 60.04;
H, 5.70; N, 6.09; Found: C, 59.84; H, 5.51; N, 6.01. IR (Diamond; cmꢀ1):
2965,1615,1587,1463,1453,1369,1309,1192,1145, 831, 812, 781, 753.
4.3. General procedure for ethylene oligomerization
4.2.15. Preparation of C14
Ethylene oligomerization at 10 bar ethylene pressure was per-
formed in a stainless steel autoclave (0.25 L capacity) equipped with
a mechanical stirrer, a temperature controller and gas ballast
through a solenoid clave for continuous feeding of ethylene at
constant pressure. The catalyst precursor was dissolved in 50 ml
Using the same procedure as for the synthesis of complex C11, to
a solution of 1.0 mmol ligand L4 in 10 mL ethanol, 1.0 mmol
NiCl2$6H2O was added. C14 was obtained (yellow powder, 0.367 g,
88% yield). Anal. Calcd for C20H20Cl2N2Ni (416.04) requires C, 57.47;

24
S. Song et al. / Journal of Organometallic Chemistry 699 (2012) 18e25
Table 6
Crystal data and structure refinement for complexes C1$DMF, C4$2DMF, C7$DMF and C11$CH3OH.
C1$DMF
C4$2DMF
C7$DMF
C11$CH3OH
Cryst color
Empirical formula
fw
Yellow
C22H25Br2N3NiO
565.98
Brown
C26H34Br2N4NiO2
653.10
Brown
C25H31Br2N3NiO
608.06
Yellow
C20H22Cl2N2NiO
436.01
T (K)
173(2)
293(2)
173(2)
173(2)
Wavelength (Å)
Cryst syst
Space group
a (Å)
b (Å)
c (Å)
0.71073
Triclinic
Pe1
8.0952(16)
9.899(2)
15.662(3)
102.18(3)
99.11(3)
107.28(3)
1138.1(4)
2
0.71073
Triclinic
Pe1
8.0265(16)
13.492(3)
13.714(3)
76.76(3)
86.89(3)
74.32(3)
0.71073
Monoclinic
P2(1)/n
16.519(3)
10.599(2)
18.875(4)
90
115.19(3)
90
0.71073
Triclinic
Pe1
8.2411(16)
11.787(2)
12.117(2)
72.28(3)
82.27(3)
88.79(3)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
V (Å3)
1391.9(5)
2
1.558
2990.3(10)
4
1.351
1110.7(4)
2
1.304
Z
Dcalcd. (mg mꢀ3
)
1.652
4.381
m
(mmꢀ1
)
3.597
3.340
1.124
F (000)
Cryst size (mm)
range (ꢁ)
Limiting indices
568
664
1232
452
0.09 ꢃ 0.08 ꢃ 0.07
1.37e27.43
e10 ꢄ h ꢄ 10
e12 ꢄ k ꢄ 12
e20 ꢄ l ꢄ 20
14,242
0.65 ꢃ 0.42 ꢃ 0.21
1.53e27.50
e10 ꢄ h ꢄ 10
e17 ꢄ k ꢄ 17
e17 ꢄ l ꢄ 17
18,661
0.30 ꢃ 0.20 ꢃ 0.02
1.38e25.98
e20 ꢄ h ꢄ 20
e13 ꢄ k ꢄ 11
e23 ꢄ l ꢄ 21
21,322
0.25 ꢃ 0.20 ꢃ 0.08
1.78e27.46
e10 ꢄ h ꢄ 10
e15 ꢄ k ꢄ 15
e15 ꢄ l ꢄ 15
13,667
q
No. of rflns collected
No. unique rflns [R(int)]
5174(0.0584)
99.7
None
6388(0.0504)
99.8
None
5792(0.0916)
98.9
None
5057(0.0324)
99.4
None
Completeness to
Abs corr
q (%)
Data/restraints/params
5174/0/262
1.179
6388/0/291
1.227
5792/19/300
1.133
5057/0/240
1.135
Goodness of fit on F2
Final R indices [I > 2
s
(I)]
R1 ¼ 0.0565
wR2 ¼ 0.1370
R1 ¼ 0.0709
wR2 ¼ 0.1652
0.906 and e0.793
R1 ¼ 0.0523
wR2 ¼ 0.1264
R1 ¼ 0.0616
wR2 ¼ 0.1410
0.868 and e0.569
R1 ¼ 0.0761
wR2 ¼ 0.960
R1 ¼ 0.0960, wR2 ¼ 0.1840
R1 ¼ 0.0459
wR2 ¼ 0.1367
R1 ¼ 0.0498
wR2 ¼ 0.1399
0.585 and e0.477
R indices (all data)
Largest diff peak and hole (e Åꢀ3
)
0.581 and e0.611
toluene in a Schlenk tube stirred with a magnetic stirrerand injected
into the reactor under an ethylene flux. The co-catalyst EtAlCl2 and
50 mL toluene were added. When the required reaction tempera-
ture had been reached, ethylene at the desired pressure was intro-
duced to start the reaction. After the reaction mixture had been
stirred for the desired period of time, the reaction was stopped and
about 1 ml of the reaction solution was collected, terminated by the
addition of 10 % aqueous hydrogen chloride. The organic layer was
analyzed by gas chromatography (GC) for determining the compo-
sition and mass distribution of the oligomers obtained.
C4$2DMF, C7$DMF and C11$CH3OH, respectively. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
This work is supported by MOST 863 program No. 2009AA033601.
The EPSRC are thanked for the award of a travel grant (to CR).
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