2-(1-Aryliminoethylidene)quinolylnickel(II) dibromides: Synthesis, characterization and ethylene dimerization capability

Article abstract of DOI:10.1016/j.jorganchem.2011.08.037

A series of 2-(1-aryliminoethylidene)quinoline derivatives (L1-L9) and the nickel(II) dibromides (C1-C9) thereof, were synthesized and characterized. The molecular structures of C2 (R¹ = Et, R² = H, R = Me) and C9 (R¹ =

Full text of DOI:10.1016/j.jorganchem.2011.08.037

Journal of Organometallic Chemistry 696 (2011) 3772e3778
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
2-(1-Aryliminoethylidene)quinolylnickel(II) dibromides: Synthesis,
characterization and ethylene dimerization capability
,
a
a,c,
Shengju Songa, Yan Lia, Carl Redshawb , 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)quinoline derivatives (L1eL9) and the nickel(II) dibromides (C1
eC9) thereof, were synthesized and characterized. The molecular structures of C2 (R1 ¼ Et, R2 ¼ H,
R ¼ Me) and C9 (R1 ¼ iPr, R2 ¼ H, R ¼ iPr) were confirmed as being distorted tetrahedral at nickel by
single crystal X-ray diffraction. On treatment with diethylaluminium chloride (Et2AlCl) or ethylaluminum
sesquichloride (EASC), these nickel pre-catalysts exhibited high activity for selective ethylene dimer-
ization (0.89e3.29 ꢀ 106 g molꢁ1(Ni) hꢁ1) at 20 ꢂC under 10 atm of ethylene. The influence of the reaction
parameters on the catalytic behaviour was investigated for these nickel systems, including variation of
Al/Ni molar ratio and reaction temperature.
Received 25 June 2011
Received in revised form
18 August 2011
Accepted 25 August 2011
Keywords:
Ethylene dimerization
Nickel pre-catalyst
Ó 2011 Elsevier B.V. All rights reserved.
X-ray diffraction
2-(1-Aryliminoethylidene)quinoline
1. Introduction
N^N ligands were attractive targets to explore and more fully
understand the scope for improving purification during the
The emergence of diimine-type nickel dichloride complexes
[1e3] as highly active pre-catalysts together with the commer-
cializing of the Shell Higher Olefin Process (SHOP) [4e6] resur-
rected research into nickel systems for ethylene reactivity. 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
[6e13]. In the case of nickel-based pre-catalysts, much of the
research has related to the variation of different ligand sets at the
metal center, with bidentate chelate ligands of the type P^O [14,15],
P^P [16], N^O [17e22], P^N [23e29], and N^N [30e47], and some
tridentate ligands of N^N^O [48], N^P^N [49], P^N^N [44,50], and
N^N^N [51e57], etc, proving to be popular. However, oligomers and
polymers, both produced as a mixture in a catalytic system, can be
considered as by-products of one another; such a catalytic system
would be less important. With this in mind, pre-catalysts bearing
production process. Therefore a series of 2-(1-aryliminoethylidene)
quinoline derivatives (L1eL9) were designed and used to form the
nickel(II) dibromides complexes (C1eC9). Interestingly, the current
nickel pre-catalysts were capable of selective dimerization with an
optimum reaction temperature of 20 ꢂC, more importantly,
showing high activity and high selectivity for
a-olefins. As
a consequence, herein a series of 2-(1-aryliminoethylidene)quino-
line derivatives have been synthesized, reacted with nickel dibro-
mides, and the resultant pre-catalysts were investigated. Upon
activation with Et2AlCl or EASC, all the nickel pre-catalysts reported
herein showed high activity towards ethylene dimerization, and
the affects of reaction parameters on their catalytic performance
has been investigated.
2. Results and discussion
2.1. Synthesis and characterization of complexes
A
series of 2-(1-aryliminoethylidene)quinoline derivatives
* 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.
(L1eL9) were prepared by Scheme 1. All the ligands were charac-
terized by FTeIR, 1H and 13C NMR spectroscopic measurements as
well as by elemental analysis. Further reaction of the 2-(1-
aryliminoethylidene)quinoline derivatives with an equivalent of
1,2-dimethoxyethane nickel(II) bromide [(DME)NiBr2] in THF
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.2011.08.037

S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3772e3778
3773
Ar NH2
N
N
p-TsOH
Toluene
R
O
R
N
Ar
L1 -L9
2 THF
R1
(DME)NiBr
R2
Ar =
R1
N
R
Ni
N
Br
Ar
Br
Fig. 2. ORTEP structure of C9 with thermal ellipsoids at the 30% probability level.
Hydrogen atoms omitted for clarity.
C1-C9
R
Me M e Me Me Me Me
Me Et i-Pr
In the complex C9 (Fig. 2), the geometry is slightly distorted
tetrahedral geometry around each nickel, for example bond angles
of N1eNi1eN2 [81.62(15)ꢂ]. The distances of the Ni1eN1
[2.041(4) Å] and Ni1eN2 [1.987(4) Å] more closely resemble those
of C2. Comparison of the corresponding bond lengths in complexes
C2, reveals that the bond distances associated with the nickel atoms
in complex C9 are somewhat shorter, for example Ni1eBr1
[2.3797(8) Å] and Ni1eBr2 [2.3410(9) Å].
R1
R2
CH(Ph)2
Me Et i-Pr Me Et
i-Pr i-Pr i-Pr
NO2
H
H
H
Me Me Me
L1 L2 L 3 L 4 L 5 L6
C1 C2 C3 C4 C5 C6
H
H
L7 L8 L9
C7 C8 C9
Scheme 1. Synthetic procedure of ligands (L1eL9) and their nickel bromide complexes
(C1eC9).
afforded the title nickel complexes (Scheme 1: C1eC9) in high
yields. All nickel complexes were characterized by FTeIR spectro-
scopic and elemental analyses, and were found to be highly stable
both in the solid-state and in solution.
In the FTeIR spectra, the C]N stretching frequencies of the
nickel complexes shifted to lower values with weaker intensity
compared with those of the corresponding free ligand
(1631e1646 cmꢁ1). Such changes are in line with the coordination
between the imino-nitrogen and nickel. The molecular structures
of the nickel complexes C2 and C9 were confirmed by single crystal
X-ray diffraction studies.
2.3. Ethylene dimerization
The catalytic behaviour of nickel (II) complexes towards
ethylene was evaluated in the presence of various alkylaluminum
reagents (Et2AlCl, EASC, MAO and MMAO). The results are
summarized in Table 2. Higher activities were obtained with Et2AlCl
and the selectivity for
a-C4 was more than 90%. The nickel (II)
complex C3 showed activities of up to 2.76 ꢀ 106 g molꢁ1 (Ni) hꢁ1
upon activation with EASC. Based on catalytic activity, economic
considerations (less co-catalyst) and the selectivity for a-C4, both
Et2AlCl and EASC were selected for further investigation, and the
catalytic system under 10 atm of ethylene was typically investi-
gated, with variation of various reaction parameters (Table 3).
Ethylene activation in the presence of Et2AlCl: According to
Table 3, the reaction parameters have an influence on the ethylene
dimerization activity. For example, upon changing the Al/Ni molar
ratio or elevating the reaction temperature, the catalytic activity
was greatly influenced. Such phenomena have been commonly
observed in catalytic system of late-transition metal pre-catalysts
[35,45,57]. Upon changing the Al/Ni molar ratio, the catalytic
activities of C3 initially increased and then decreased and the
2.2. Crystal structures
Single crystals of the nickel complexes C2 and C9 suitable for X-
ray diffraction studies were obtained by slow diffusion of diethyl
ether into THF solutions. The molecular structures are shown in
Figs. 1 and 2, respectively, with selected bond lengths and angles
given in Table 1.
As shown in the Fig. 1, the geometry around the nickel center
can be described as distorted tetrahedral, comprising one bidentate
N^N ligand and two bromides. The Ni1eN1 bond length is
2.024(5) Å, which is longer than that of Ni1eN2 bond. The Ni1 atom
deviates by 0.304 Å from the plane of the Br1eN1eBr2 atoms. The
dihedral angle between the quinoline plane and the aryl ring is
86.83ꢂ.
selectivity for a-olefins varied from 90.1% to 96.2%. Increasing the
reaction temperature resulted in a considerable reduction in
activity (entries 4 and 7e9 in Table 3), which might be caused by
the instability of the active species or possibly a lower concentra-
tion of ethylene in the reaction solution at the elevated reaction
temperature [40,55,57]. On increasing the temperature up to 50 ꢂC,
much lower activity resulted, indicating decomposition of the
nickel active species, but with higher selectivity for the a-olefins.
To compare the influence of the ligand environment on the
catalytic behaviour of the nickel pre-catalysts, the bromide pre-
catalysts C1eC9 were investigated under optimum reaction
condition of molar ratio Et2AlCl/Ni at 200:1, 20 ꢂC at 10 atm
ethylene, and the data is tabulated in Table 4. Different substituents
on the quinoline (R) and on the phenyl group of the ligand (R1, R2)
affected the catalytic behaviour of these nickel complexes. For
complexes C1eC3 containing 2,6-dialkyl substituents (entries 1e3
in Table 4), the bulkier the R1 group used, the higher activity of
dimerization observed, giving the activity order: C1 (R1 ¼ Me) < C2
(R1 ¼ Et) < C3 (R1 ¼ iPr). The greater bulkiness of the isopropyl
Fig. 1. ORTEP structure of C2 with thermal ellipsoids at the 30% probability level.
Hydrogen atoms omitted for clarity.

3774
S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3772e3778
Table 1
Selected bond lengths (Å) and bond angles (ꢂ) for C2 and C9.
C2
C9
2.041(4)
1.987(4)
2.3797(8)
2.3410(9)
C2
1.282(7)
1.447(7)
1.333(7)
1.383(7)
C9
1.283(6)
1.445(5)
1.338(6)
1.375(6)
Bond lengths (Å)
Ni(1)eN(1)
Ni(1)eN(2)
Ni(1)eBr(1)
2.024(5)
2.006(5)
2.3875(11)
2.3455(11)
N(2)eC(10)
N(2)eC(12)
N(1)eC(8)
N(1)eC(9)
Ni(1)eBr(2)
Bond angles (ꢂ)
N(2)eNi(1)eN(1)
N(2)eNi(1)eBr(1)
N(2)eNi(1)eBr(2)
82.0(2)
109.01(14)
103.99(14)
81.62(15)
107.91(11)
107.07(11)
N(1)eNi(1)eBr(1)
N(1)eNi(1)eBr(2)
Br(2)eNi(1)eBr(1)
96.43(14)
139.24(15)
118.27(4)
93.66(10)
144.62(11)
114.79(3)
groups at the ortho-position of the imino-N aryl ring of complex C3
may protect the active site from deactivation; moreover, bulkier
alkyl substituents help to solubilize the nickel pre-catalysts thereby
enhancing activity [58]. Regarding results observed by C2 versus C5
and C1 versus C4, these pre-catalysts containing ligands with an
additional methyl group showed better activity and gave the
activity order C4 > C1 and C5 > C2, presumably because they have
a better solubility in solution, which can be helpful for activating
the complex [39,40,56]. However, the catalytic activities slightly
decreased in the presence of larger electron-donating groups
[R1 ¼ CH(Ph)2] on the phenyl ring. When the more electron-
withdrawing nitro group (R2 ¼ NO2) was present on the aryl, the
activity order was C3 > C7, which suggested that electron-
withdrawing substituents in the R2 position were not favourable
for enhanced catalytic activities. Considering the groups at the 8-
of complex C3 was observed at 20 ꢂC (entry 4 in Table 5), with
activities as high as 3.29 ꢀ 106 g molꢁ1 (Ni) hꢁ1. A similar trend for
catalytic activities was displayed in regard to the nature of the
ligands present. The dimerization activity, similar to that for the
C1eC9/Et2AlCl
system,
decreased
in
the
order
of
C3 > C5 > C2 > C5 > C4 > C1, C3 > C9 > C8, C3 > C6, C3 > C7.
However, on comparison with the catalytic systems using the co-
catalyst Et2AlCl, the obtained dimerization with co-catalyst EASC
afforded lower selectivity for a-olefins.
3. Conclusions
A
series of nickel bromide complexes bearing 2-(1-
aryliminopropylidene)quinoline ligands (L1eL9) were synthe-
sized and characterized. Single crystal X-ray crystallographic
studies for representative complexes were performed. The catalytic
activities exhibited by these nickel pre-catalysts revealed clear
activity trends. These nickel complexes exhibited high activities in
position of the quinoline (R1
¼
iPr and R2 ¼ H), the catalytic
activity of C3 was the highest, giving the order C8 (R ¼ Et) < C9
(R ¼ iPr) < C3 (R ¼ Me) (entries 3, 8 and 9 in Table 4). Analogues of
the 2-(1-aryliminomethylidene)quinolylnickel halide pre-catalysts,
employing the same coordination environment, performed
ethylene polymerization [59]; the current 2-(1-aryliminoethy-
lidene)quinolylnickel(II) bromide pre-catalysts showed good
activities in ethylene dimerization, but without the production of
any observable polyethylene. Thus, substituents distant from the
active metal center together with electronic effects changed the
behaviour of the system, and in particular the nature of the
ethylene reactivity; the influence of fine-tuning the ligands will be
the focus of future studies. Moreover, nickel catalytic systems in
ethylene oligomerization (including dimerization) commonly
ethylene dimerization, with a-C4 as the main product. The catalytic
activities decreased on elevating the reaction temperature. Further
research efforts indicated that the ligand substituents present had
a remarkable influence on the observed activities. However, the
influence on selectivity for a-olefins was not obvious. The highest
activity was obtained with the complexes having R as methyl, R1 as
isopropyl and R2 as hydrogen. This implied that the less bulky R
group was favourable for enhanced activity. It could also be
observed that electron-withdrawing substituents at the R2 position
led to lower activities. Under optimum conditions, the activity was
as high as 3.29 ꢀ 106 g molꢁ1 (Ni) hꢁ1 with EASC.
produced low portions of
a-olefins due to b-H transfer processes
[6,11]. It is noteworthy that the title nickel pre-catalysts showed
higher activities in ethylene dimerization with high selectivity of a-
4. Experimental section
olefin.
4.1. General considerations
Ethylene activation in the presence of EACS: After variation of
the ratio of EACS to nickel catalyst, high catalytic activity was
observed with an Al/Ni molar ratio of 250 at 20 ꢂC. Therefore, the
catalytic behaviours of all the nickel complexes were investigated
with a fixed Al/Ni molar ratio of 250, and the results are summa-
rized in Table 5. On comparison with systems employing Et2AlCl, all
the complexes displayed higher catalytic activities for ethylene
dimerization at 10 atm of ethylene pressure. The best performance
All manipulations involving air and moisture-sensitive
compounds were carried out under an atmosphere of dried and
Table 3
Dimerization of ethylene with C3/Et2AlCl.a
Activityb
a-C4
c
Entry
T/ꢂC
Al/Ni
1
2
3
4
5
6
7
8
9
20
20
20
20
20
20
30
40
50
50
100
150
200
250
300
200
200
200
4.95
10.5
10.6
24.0
13.0
5.72
5.03
3.91
2.81
94.1
93.5
92.9
92.5
90.7
96.2
90.1
92.2
93.1
Table 2
Dimerization of ethylene with pre-catalyst C3.a
Activityb
a-C4
c
Entry
Co-catalyst
Al/Ni
1
2
3
4
MAO
1000
1000
200
4.78
5.04
24.0
27.6
91.5
90.5
92.5
82.4
MMAO
Et2AlCl
EASC
200
a
Conditions: 5 mmol Ni, Et2AlCl as Co-catalyst, 10 atm C2H4, 20 min, 100 mL
a
Conditions: 5
m
mol Ni, 10 atm C2H4, 20 min, 20 ꢂC, 100 mL toluene.
toluene.
b
c
b
Activity, 105 g molꢁ1 (Ni) hꢁ1
.
Activity, 105 g molꢁ1 (Ni) hꢁ1
Determined by GC, C denotes the total amount of oligomers, C4/ C ¼ 100%.
.
P
P
P
P
c
Determined by GC, C denotes the total amount of oligomers, C4/ C ¼ 100%.

S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3772e3778
3775
Table 4
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 57% yield. Mp: 93e94 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.51 (1H, d, J ¼ 8.6 Hz, quinoline), 8.20 (1H, d, J ¼ 8.6 Hz,
quinoline), 7.71 (1H, d, J ¼ 8.1 Hz, quinoline), 7.60 (1H, d, J ¼ 6.9 Hz,
quinoline), 7.46 (1H, t, J ¼ 10.0 Hz, quinoline), 7.09 (2H, d, J ¼ 7.5 Hz,
m-Ar), 6.96 (1H, t, J ¼ 10.0 Hz, p-Ar), 2.87 (3H, s, eCH3), 2.34 (3H, s,
eCH3), 2.07(6H, s, 2ꢀ eCH3). dC (100 MHz; CDCl3; Me4Si) 168.1,
154.9, 149.4, 146.5, 138.2, 136.5, 130.1, 129.8, 128.9, 127.4, 125.8,
125.5, 123.4, 118.2, 18.32, 18.09, 16.55. Anal. Calcd for C20H20N2
(288.16) C, 83.30; H, 6.99; N, 9.71. Found: C, 83.11; H, 7.02; N, 9.51.
FTeIR (Diamond disk, cmꢁ1): 2962, 1639, 1599, 1567, 1494, 1449,
1361, 1310, 1193, 1138, 1101, 865, 762.
Dimerization of ethylene by nickel bromide pre-catalyst C1eC9.a
Activityb
a-C4
c
Entry
Pre-catalyst
1
2
3
4
5
6
7
8
9
C1
C2
C3
C4
C5
C6
C7
C8
C9
8.90
14.1
24.0
9.10
17.3
16.3
10.2
21.9
23.7
91.4
92.6
92.5
93.6
94.5
93.3
95.4
91.7
92.4
a
Conditions: 5 m
mol Ni, 200 equiv. Et2AlCl, 20 ꢂC, 10 atm C2H4, 20 min, 100 mL of
toluene.
b
Activity, 105 g molꢁ1 (Ni) hꢁ1
Determined by GC, C denotes the total amount of oligomers, C4/ C ¼ 100%.
.
P
P
c
4.2.2. 2-(1-(2,6-Diethylphenylimino)ethylidene)-8-methylquinoline
(L2)
In a manner similar to that described for L1, L2 was prepared as
a yellow solid in 74% yield. Mp: 102e104 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.51 (1H, d, J ¼ 8.5 Hz, quinoline), 8.20 (1H, d, J ¼ 8.6 Hz,
quinoline), 7.71 (1H, d, J ¼ 8.0 Hz, quinoline), 7.60 (1H, d, J ¼ 6.7 Hz,
quinoline), 7.49 (1H, t, J ¼ 10.0 Hz, quinoline), 7.14 (2H, d, J ¼ 7.6 Hz,
m-Ar), 7.04 (1H, t, J ¼ 10.0 Hz, p-Ar), 2.87 (3H, s, eCH3), 2.52e2.36
(7H, m, 2ꢀ eCH2e, eCH3), 1.16 (6H, s, 2ꢀ eCH3). dC (100 MHz;
CDCl3; Me4Si) 167.8, 154.8, 148.2, 146.3, 138.2, 136.4, 131.2, 129.7,
128.8, 127.3, 126.0, 125.6, 123.3, 118.3, 24.75, 17.88, 16.75, 13.83.
Anal. Calcd for C22H24N2 (316.19) C, 83.50; H, 7.64; N, 8.85. Found: C,
83.56; H, 7.69; N, 8.75. FTeIR (Diamond disk, cmꢁ1): 2964, 1637,
1589, 1569, 1496, 1445, 1363, 1322, 1196, 1138, 1101, 855, 763, 690.
purified nitrogen using standard Schlenk and vacuum-line tech-
niques. 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), ethylaluminum sesquichloride (EASC,
0.87 M in toluene) and other reagents were purchased from Aldrich
or Acros Chemicals. (DME)NiBr2 was synthesized by the reaction of
1,2-dimethoxyethane with anhydrous nickel(II) bromide. The 1H
and 13C NMR spectra were recorded on Bruker DMX 400 MHz
instruments at ambient temperature using TMS as an internal
standard. FTeIR 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
4.2.3. 2-(1-(2,6-Diisopropylphenylimino)ethylidene)-8-
methylquinoline (L3)
In a manner similar to that described for L1, L3 was prepared as
a yellow solid in 78% yield. Mp: 182e184 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.52 (1H, d, J ¼ 8.5 Hz, quinoline), 8.21 (1H, d, J ¼ 8.5 Hz,
quinoline), 7.71 (1H, d, J ¼ 8.0 Hz, quinoline), 7.60 (1H, d, J ¼ 8.6 Hz,
quinoline), 7.49 (1H, t, J ¼ 9.8 Hz, quinoline), 7.20(2H, s, m-Ar), 7.11
(1H, t, J ¼ 10.0 Hz, p-Ar), 2.88 (3H, s, eCH3), 2.80 (2H, m, 2ꢀ eCHe),
2.39 (3H, s, eCH3), 1.19 (12H, s, 4ꢀ eCH3). dC (100 MHz; CDCl3;
Me4Si) 167.8, 154.9, 146.9, 146.4, 138.2, 136.4, 135.8, 129.7, 128.8,
127.3, 125.6, 123.6, 123.1, 118.4, 28.45, 23.35, 23.00, 17.87, 17.08.
Anal. Calcd for C24H28N2 (344.23) C, 83.68; H, 8.19; N, 8.13. Found: C,
83.58; H, 8.33; N, 8.09. FTeIR (Diamond disk, cmꢁ1): 2958, 1643,
1591, 1567, 1456, 1430, 1361, 1321, 1193, 1135, 1098, 852, 756, 689.
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
4.2.1. 2-(1-(2,6-Dimethylphenylimino)ethylidene)-8-
methylquinoline (L1)
A
reaction mixture of 1-(8-methylquinolin-2-yl)ethanone
(1.85 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
Table 5
4.2.4. 2-(1-(2,4,6-Trimethylphenylimino)ethylidene)-8-
methylquinoline (L4)
Dimerization of ethylene with C1eC9/EASC.a
Entry
Pre-catalyst
T/ꢂC
Al/Ni
Oligomer
In a manner similar to that described for L1, L4 was prepared as
a yellow solid in 58% yield. Mp: 95e96 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.51 (1H, d, J ¼ 8.6 Hz, quinoline), 8.20 (1H, d, J ¼ 8.9 Hz,
quinoline), 7.71 (1H, d, J ¼ 8.1 Hz, quinoline), 7.60 (1H, d, J ¼ 6.9 Hz,
quinoline), 7.48 (1H, t, J ¼ 10.0 Hz, quinoline), 6.92 (2H, s, m-Ar),
2.88 (3H, s, eCH3), 2.34e2.31 (6H, 2ꢀ eCH3), 2.03 (6H, s, 2ꢀ eCH3).
dC (100 MHz; CDCl3; Me4Si) 168.3, 154.9, 146.7, 146.4, 138.2, 136.4,
132.3, 129.7, 128.8, 128.7, 127.3, 125.6, 125.3, 118.4, 20.93, 18.08,
17.93, 16.40. Anal. Calcd for C21H22N2 (302.18) C, 83.40; H, 7.33; N,
9.26 Found: C, 83.30; H, 8.48; N, 7.21. FTeIR (Diamond disk, cmꢁ1):
2908, 1638, 1567, 1494, 1470, 1361, 1318, 1284, 1209, 1096, 1037, 856,
842, 764, 681.
distributionc (%)
Activityb
a-C4
1
2
3
4
5
6
7
8
C3
C3
C3
C3
C3
C3
C3
C3
C1
C2
C4
C5
C6
C7
C8
C9
20
20
20
20
20
20
30
40
20
20
20
20
20
20
20
20
100
150
200
250
300
400
250
250
250
250
250
250
250
250
250
250
1.48
1.76
2.76
3.29
3.27
2.44
0.56
0.32
0.90
2.19
0.95
2.40
1.78
1.45
1.79
2.23
85.8
83.5
82.4
74.6
78.8
81.4
83.2
80.9
80.7
76.4
79.2
84.7
81.3
78.9
80.1
82.1
9
10
11
12
13
14
15
16
4.2.5. 2-(1-(2,6-Diethyl-4-methylphenylimino)ethylidene)-8-
methylquinoline (L5)
In a manner similar to that described for L1, L5 was prepared as
a yellow solid in 73% yield. Mp: 105e106 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.50 (1H, d, J ¼ 8.6 Hz, quinoline), 8.19 (1H, d, J ¼ 8.6 Hz,
quinoline), 7.70 (1H, d, J ¼ 8.0 Hz, quinoline), 7.59 (1H, d, J ¼ 6.9 Hz,
a
Conditions: 5 mmol Ni, Co-catalyst EASC, 10 atm C2H4, 20 min, 100 mL of toluene.
b
c
Activity, 106 g molꢁ1 (Ni) hꢁ1
.
P
Determined by GC, C denotes the total amount of oligomers.

3776
S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3772e3778
quinoline), 7.48 (1H, t, J ¼ 10.1 Hz, quinoline), 6.95 (2H, s, m-Ar),
2.87 (3H, s, eCH3), 2.45e2.29 (10H, m, 2ꢀ eCH2e, 2ꢀ eCH3), 1.15
(6H, s, 2ꢀ eCH3). dC (100 MHz; CDCl3; Me4Si) 168.0, 155.0, 146.4,
145.7,138.2,136.4,132.5,131.1,129.7,128.8,127.3,126.8, 125.6, 118.4,
24.80, 21.18, 17.91, 16.73, 14.01. Anal. Calcd for C23H26N2 (330.21) C,
83.59; H, 7.93; N, 8.48. Found: C, 83.39; H, 8.10; N, 8.34. FTeIR
(Diamond disk, cmꢁ1): 2967, 1646, 1570, 1456, 1362, 1253, 1099,
868, 842, 803, 760, 689.
4ꢀ eCH3). dC (100 MHz; CDCl3; Me4Si) 167.9, 154.7, 148.1, 146.9,
145.2, 136.7, 135.9, 128.9, 127.6, 125.5, 125.4, 123.7, 123.1, 118.3,
28.48, 28.07, 23.56, 23.38, 23.07, 17.23. Anal. Calcd for C26H32N2
(372.26) C, 83.82; H, 8.66; N, 7.52. Found: C, 83.72; H, 8.70; N, 7.42.
FTeIR (Diamond disk, cmꢁ1): 2962, 1631, 1594, 1566, 1461, 1434,
1364, 1191, 1104, 847, 791, 764, 695.
Preparation of C1. To a solution of the ligand 2,6-dimethyl-N-(1-
(quinolin-2-yl)ethylidene)benzenamine (L1, 0.288, 1.0 mmol) in
THF (10 mL), (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, 0.491 g, 88%
yield). Anal. Calcd for C20H20Br2N2Ni (503.93) C, 47.39; H, 3.98; N,
5.53. Found: C, 47.28; H, 4.03; N, 5.41. FTeIR (Diamond disk, cmꢁ1):
2965, 1624, 1513, 1447, 1366, 1311, 1231, 854, 764.
Preparation of C2. Using the same procedure as for the
synthesis of C1, L2 was used in the reaction with (DME)NiBr2 to
form C2 (yellow powder, 91% yield). Anal. Calcd for C22H24Br2N2Ni
(531.97) C, 49.40; H, 4.52; N, 5.24. Found: C, 49.20; H, 4.56; N, 5.14.
FTeIR (Diamond; cmꢁ1): 2968, 1625, 1510, 1448, 1369, 1311, 1221,
854, 774.
Preparation of C3. Using the same procedure as for the synthesis
of C1, L3 was used in the reaction with (DME)NiBr2 to form C3
(yellow powder, 92% yield). Anal. Calcd for C24H28Br2N2Ni (560.00)
C, 51.20; H, 5.01; N, 4.98. Found: C, 51.00; H, 5.13; N, 4.73. FTeIR
(Diamond; cmꢁ1): 2967, 1625, 1589, 1513, 1446, 1370, 1307, 1257,
1216, 1059, 836, 805, 763.
Preparation of C4. Using the same procedure as for the synthesis
of C1, L4 was used in the reaction with (DME)NiBr2 to form C4
(yellow powder, 90% yield). Anal. Calcd for C21H22Br2N2Ni (517.95)
C, 48.42; H, 4.26; N, 5.38. Found: C, 48.16; H, 4.43; N, 5.19. FTeIR
(Diamond; cmꢁ1): 2966, 1625, 1509, 1462, 1441, 1370, 1301, 1219,
1153, 1031, 844, 776.
Preparation of C5. Using the same procedure as for the synthesis
of C1, L5 was used in the reaction with (DME)NiBr2 to form C5
(yellow powder, 91% yield). Anal. Calcd for C23H26Br2N2Ni (545.98)
C, 50.32; H, 4.77; N, 5.10. Found: C, 50.14; H, 4.89; N, 4.88. FTeIR
(Diamond; cmꢁ1): 2967, 1619, 1510, 1447, 1367, 1313, 1220, 854, 775.
Preparation of C6. Using the same procedure as for the synthesis
of C1, L6 was used in the reaction with (DME)NiBr2 to form C6
(yellow powder, 89% yield). Anal. Calcd for C45H38Br2N2Ni (822.08)
C, 65.49; H, 4.64; N, 3.39. Found: C, 65.29; H, 4.89; N, 3.25. FTeIR
(Diamond; cmꢁ1): 2917, 1601, 1494, 1446, 1370, 1304, 1255, 1214,
1073, 1031, 840, 751, 680.
Preparation of C7. Using the same procedure as for the synthesis
of C1, L7 was used in the reaction with (DME)NiBr2 to form C7
(yellow powder, 90% yield). Anal. Calcd for C24H27Br2N3NiO2
(604.98) C, 47.41; H, 4.48; N, 6.91. Found: C, 47.21; H, 4.59; N, 4.26.
FTeIR (Diamond; cmꢁ1): 3339, 2965, 1640, 1585, 1510, 1305, 1253,
1096, 1070, 905, 842.
Preparation of C8. Using the same procedure as for the synthesis
of C1, L8 was used in the reaction with (DME)NiBr2 to form C8
(yellow powder, 91% yield). Anal. Calcd for C25H30Br2N2Ni (574.01)
C, 52.04; H, 5.24; N, 4.85. Found: C, 51.99; H, 5.44; N, 4.65. FTeIR
(Diamond; cmꢁ1): 2963, 1618, 1515, 1463, 1441, 1372, 1310, 1193,
1060, 856, 762.
4.2.6. 2-(1-(2,6-Dibenzhydryl-4-methylphenylimino)ethylidene)-8-
methylquinoline (L6)
In a manner similar to that described for L1, L6 was prepared as
a yellow solid in 71% yield. Mp: 189e190 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.12 (2H, d, J ¼ 8.3 Hz), 7.70 (1H, d, J ¼ 8.0 Hz, quinoline),
7.59 (1H, d, J ¼ 6.9 Hz, quinoline), 7.47 (1H, t, J ¼ 10.1 Hz, quinoline),
7.23e7.00 (20H, m), 6.70 (2H, s, m-Ar), 5.31 (2H, s, 2ꢀ eCHe), 2.75
(3H, s, eCH3), 2.19 (3H, s, eCH3), 1.21 (3H, s, eCH3). dC (100 MHz;
CDCl3; Me4Si) 170.9, 154.8, 146.5, 146.3, 143.9, 142.8, 138.3, 136.1,
132.3, 131.6, 130.0, 129.6, 129.4, 128.8, 128.6, 128.4, 128.1, 127.1,
126.2, 126.1, 125.5, 118.6, 52.24, 31.74, 22.97, 22.81, 21.49, 17.86,
16.83, 14.28. Anal. Calcd for C45H38N2 (606.3) C, 89.07; H, 6.31; N,
4.62. Found: C, 89.00; H, 6.42; N, 4.46. FTeIR (Diamond disk, cmꢁ1):
2955, 1645, 1597, 1569, 1493, 1447, 1363, 1321, 1240, 1103, 1030, 851,
765, 682.
4.2.7. 2-(1-(2,6-Isopropyl-4-nitrolphenylimino)ethylidene)-8-
methylquinoline (L7)
In a manner similar to that described for L1, L7 was prepared as
a yellow solid in 65% yield. Mp: 206e207 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.45 (1H, d, J ¼ 8.6 Hz, quinoline), 8.24 (1H, d, J ¼ 8.6 Hz,
quinoline), 8.04 (2H, s, m-Ar), 7.74 (1H, d, J ¼ 8.1 Hz, quinoline), 7.63
(1H, d, J ¼ 6.9 Hz, quinoline), 7.50 (1H, t, J ¼ 10.1 Hz, quinoline), 3.03
(3H, s, eCH3), 2.87e2.80 (2H, m, 2ꢀ eCHe), 2.40 (3H, s, eCH3),
1.24e1.19 (12H, s, 4ꢀ eCH3). dC (100 MHz; CDCl3; Me4Si) 168.2,
153.6, 153.0, 146.4, 144.6, 138.2, 137.3, 136.8, 130.0, 128.9, 127.8,
125.6, 119.4, 118.1, 28.74, 22.90, 22.52, 17.85, 17.62. Anal. Calcd for
C24H27N3O2 (389.21) C, 74.01; H, 6.99; N, 10.79. Found: C, 73.92; H,
7.14; N, 10.69. FTeIR (Diamond disk, cmꢁ1): 2962, 1645, 1576, 1509,
1459, 1363, 1312, 1245, 1096, 900, 846, 766, 680.
4.2.8. 2-(1-(2,6-Diisopropylphenylimino)ethylidene)-8-
ethylquinoline (L8)
In a manner similar to that described for L1, L8 was prepared as
a yellow solid in 73% yield. Mp: 126e127 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.50 (1H, d, J ¼ 8.5 Hz, quinoline), 8.20 (1H, d, J ¼ 8.5 Hz,
quinoline), 7.71 (1H, d, J ¼ 8.0 Hz, quinoline), 7.60 (1H, d, J ¼ 8.6 Hz,
quinoline), 7.51 (1H, t, J ¼ 9.9 Hz, quinoline), 7.18(2H, d, m-Ar), 7.10
(1H, t, J ¼ 10.0 Hz, p-Ar), 3.38 (2H, m, eCH2e), 2.81 (2H, m, 2ꢀ
eCHe), 2.34 (3H, s, eCH3),1.47 (3H, s, eCH3),1.17 (12H, s, 4ꢀ eCH3).
dC (100 MHz; CDCl3; Me4Si) 167.8, 154.9, 146.9, 145.8, 144.0, 136.5,
135.8, 128.9, 128.2, 127.5, 125.6, 123.7, 123.2, 118.4, 28.47, 24.91,
23.37, 23.02, 17.12, 15.31. Anal. Calcd for C25H30N2 (358.24) C, 83.75;
H, 8.43; N, 7.81. Found: C, 83.59; H, 8.56; N, 7.21. FTeIR (Diamond
disk, cmꢁ1): 2959, 1642, 1591, 1569, 1458, 1432, 1361, 1312, 1191,
1135, 1099, 851, 765, 692.
Preparation of C9. Using the same procedure as for the synthesis
of C1, L9 was used in the reaction with (DME)NiBr2 to form C9
(yellow powder, 92% yield). Anal. Calcd for C26H32Br2N2Ni (588.03)
C, 52.83; H, 5.46; N, 4.74. Found: C, 52.67; H, 5.71; N, 4.51. FTeIR
(Diamond; cmꢁ1): 2961, 1627, 1510, 1456, 1374, 1310, 1194, 841, 765.
4.2.9. 2-(1-(2,6-Diisopropylphenylimino)ethylidene)-8-
isopropylquinoline (L9)
In a manner similar to that described for L1, L9 was prepared as
a yellow solid in 73% yield. Mp: 100e102 ꢂC. dH (400 MHz; CDCl3;
Me4Si) 8.49 (1H, d, J ¼ 8.6 Hz, quinoline), 8.21 (1H, d, J ¼ 8.6 Hz,
quinoline), 7.70 (1H, d, J ¼ 7.9 Hz, quinoline), 7.63 (1H, d, J ¼ 6.8 Hz,
quinoline), 7.55 (1H, t, J ¼ 10.1 Hz, quinoline), 7.19 (2H, d, m-Ar), 7.12
(1H, t, J ¼ 10.1 Hz, p-Ar), 4.42e4.36 (1H, m, eCHe), 2.82e2.76 (2H,
m, 2ꢀ eCHe), 2.35 (3H, s, eCH3), 1.44 (6H, s, 2ꢀ eCH3), 1.17 (12H, s,
4.3. General procedure for ethylene dimerization
Ethylene dimerization at 10 atm ethylene pressure was per-
formed in a stainless steel autoclave (0.25 L capacity) equipped

S. Song et al. / Journal of Organometallic Chemistry 696 (2011) 3772e3778
3777
Table 6
Crystal data and structure refinement for complexes C2 and C9.
Acknowledgements
This work is supported by MOST 863 program No.
2009AA033601. The EPSRC are thanked for the award of a travel
grant (to CR).
C2
C9
Cryst colour
Empirical formula
fw
Yellow
C22H24Br2N2Ni
534.96
Brown
C26H32Br2N2Ni
591.07
T (K)
446(2)
293(2)
Wavelength (Å)
Cryst syst
Space group
a (Å)
b (Å)
c (Å)
0.71073
Monoclinic
P2(1)/c
8.0242(16)
19.652(4)
13.681(3)
90
102.08(3)
90
2109.6(7)
4
1.684
4.717
1072
0.20 ꢀ 0.15 ꢀ 0.10
1.84e27.49
ꢁ10 ꢃ h ꢃ 10
ꢁ25 ꢃ k ꢃ 20
ꢁ17 ꢃ l ꢃ 17
17,033
4770 (0.0626)
98.4%
None
0.71073
Orthorhombic
Pbca
15.609(3)
16.917(3)
19.492(4)
90
Appendix A. Supplementary material
CCDC 831463 and 831464 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
90
90
V (Å3)
5146.9(18)
8
1.526
3.875
2400
0.24 ꢀ 0.22 ꢀ 0.05
2.06e27.48
ꢁ20 ꢃ h ꢃ 20
ꢁ21 ꢃ k ꢃ 20
ꢁ21 ꢃ l ꢃ 25
44,073
5889(0.0950)
99.8%
None
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Z
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)
(mmꢁ1
)
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Single crystals of C2 and C9 suitable for X-ray diffraction studies
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a
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