2-(7-methyl-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridinylnickel complexes: Synthesis, characterization and their ethylene oligomerization

Article abstract of DOI:10.1016/j.crci.2010.05.026

A series of 2-(methyl-substituted-1H-benzoimidazol-2-yl)-6-(1- aryliminoethyl)pyridines (L1-L6) were synthesized and used as N^N^N tridentate ligands for their nickel complexes (C1-C12). All ligands were fully characterized by elemental, NMR and IR spectr

Full text of DOI:10.1016/j.crci.2010.05.026

C. R. Chimie 13 (2010) 1450–1459
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´
Full paper/Memoire
2-(7-methyl-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)
pyridinylnickel complexes: Synthesis, characterization and their
ethylene oligomerization
Xia Chen a, , Liping Zhang a,b, Tongling Liang b, Xiang Hao b, Wen-Hua Sun b,
*
*
a School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China
b Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, 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-(methyl-substituted-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridines
(L1–L6) were synthesized and used as N^N^N tridentate ligands for their nickel complexes
(C1–C12). All ligands were fully characterized by elemental, NMR and IR spectroscopic
analyses, while their nickel complexes were characterized by elemental and IR
spectroscopic analyses. The single-crystal X-ray diffraction reveals that the complexes
C1, C3 and C9 have distorted octahedral geometry around the Ni center. All nickel
complexes, activated with Et2AlCl, exhibit good catalytic activities toward ethylene
oligomerization with major dimerization.
Received 26 January 2010
Accepted after revision 21 May 2010
Available online 7 July 2010
Keywords:
Benzimidazole
Nickel complex
Ethylene oligomerization
Substituent effects
´
ß 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
tridentate N^N^N ligands have been prepared. Interesting-
ly, some N^N^N tridentate nickel complexes show nice
a
-olefins are important substances used extensively for
activities for either ethylene oligomerization or polymeri-
zation [21–25]. Various tridentate nickel complexes have
been focused in our group, and most of them showed good
to high catalytic activity towards ethylene reactivity [26–
30].
the detergents, synthetic lubricants, plasticizers, alcohols
and comonomers used for branched polyolefins. The linear
-olefins were first manufactured by the Ziegler (Alfen)
a
process in the presence of triethylaluminum (TEA). The
large scale process developed as the SHOP process using
nickel complex catalyst in the end of 1970s [1], and was
successfully industrialized in the 1980s [2–4]. From the
middle of 1990s, the late-transition metal complex
catalysts have attracted great attention in olefin reactivity
[5]; therefore the nickel complexes in ethylene oligomeri-
zation [6,7] have been resurrected. As far as efficient
catalytic systems are expected, nickel complexes bearing
bidentate ligands such as N^N [8–10], N^O [11,12] and P^N
[13,14] have been extensively studied. Within ferrous and
cobaltous complexes acting as catalysts [15–20], various
In order to improve catalytic activities of metal com-
plexes and finely tune their products, the useful way is to
modify ligands through different substituents on the frame
of ligands. Regarding catalysts employing iminopyridines, it
is common to prepare derivatives of ligands through the
condensation reaction using anilines bearing different
substituents. It is a challenge and more promising to have
the frame of ligands substituted. Recently, we explored
metal complexes ligated by 2-(benzimidazole)-6-(1-aryli-
mino-ethyl)pyridines (Scheme 1), all of their metal (iron,
cobalt or nickel) complexes showed high activities up to
107 g.molÀ1 (M)ÁhÀ1 for ethylene oligomerization [20,31–
36]. ConsideringtheinfluenceofsubstituentslinkedontoN-
atom of benzimidazole, the nickel complexes containing N–
H in the benzimidazole ring [34] showed better catalytic
activitiesthantheiranalogues containingalkyl-substituents
* Corresponding author.
E-mail addresses: chenxia@sxu.edu.cn (X. Chen), whsun@iccas.ac.cn
(W.-H. Sun).
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.05.026

[(Scheme_1)TD$FIG]
X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
1451
prepared and used to synthesize the nickel complexes of
the title (Scheme 1). The nickel complexes showed good
catalytic activities toward ethylene oligomerization using
Et2AlCl as cocatalyst. The effects of substituents on the
ligands, the Al/Ni molar ratio, and reaction temperature on
their catalytic activities and resultant oligomers have been
investigated in detail. Herein the syntheses and character-
izations these title nickel complexes are reported, along
with the study of their catalytic activities towards ethylene
oligomerization.
Scheme 1. Variation of Catalyst Models.
[32,33]. Such phenomena also appeared in their analogue
iron complexes [20,31,33] and chromium complexes
[35,36].
2. Results and discussion
It is very difficult to further modify the imidazole ring of
benzimidazole; therefore the functionalization of benz-
imidazole will be fused with the benzene ring. Keeping this
idea in mind, the 6-(7-methyl-1H-benzoimidazol-2-yl)-2-
acetylpyridine and its isomer 6-(4-methyl-1H-benzoimi-
dazol-2-yl)-2-acetylpyridine were newly synthesized
according to our developed procedure [31]. A series of
2-(benzimidazol-2-yl)-6-(1-aryliminoethyl)pyridines was
2.1. Synthesis and characterization of ligands and complexes
The starting compound 6-(methyl-substituted-1H-
benzo-imidazol-2-yl)-2-acetylpyridine was synthesized
according to our previous procedure (Scheme 2) [31].
There are two isomers of the product obtained, the 6-(7-
methyl-1H-benzoimidazol-2-yl)-2-acetylpyridine
and
6-(4-methyl-1H-benzoimidazol-2-yl)-2-acetylpyridine
[(Scheme_2)TD$FIG]
Scheme 2. Synthesis of nickel complexes.

1452
X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
approximately in the ratio of 3:2 based on the 1H NMR
spectrum. However, they were not separated by column
chromatography. The ligands L1–L6 were prepared by
treating the starting substance with corresponding aniline
in toluene (Scheme 2) according to our previous procedure
[37]. All of them were similarly isomerized in two
configurations in the ratios about of 3:2. On the base of
the 1H NMR measurement in the CDCl3 solution, ligand L5
within the range of 25 8C to 55 8C, there is no significant
difference to indicate different ratios of isomes. All these
compounds are stable in solid state, and fully characterized
by elemental analysis, FT-IR, 1H and 13C NMR.
Table 1
Selected bond lengths and Angles for C1ÁCH3OH and C3ÁCH3OH.
C1ÁCH3OH C3ÁCH3OH
˚
Bond lengths (A)
2.097(5)
Ni–N2
Ni–N3
Ni–N4
Ni–Cl1
Ni–Cl2
N1–C8
N2–C8
N4–C14
Ni–O
2.117(3)
2.023(3)
2.214(3)
2.3187(10)
2.4112(11)
1.357(4)
1.332(4)
1.284(4)
2.174(3)
2.013(5)
2.197(5)
2.2924(17)
2.5237(18)
1.356(7)
1.324(7)
1.287(8)
2.160(4)
The dichloronickel(II) complexes (C1–C6) were pre-
pared by the stoichiometric reactions of the appropriate
ligands with NiCl2Á6H2O in ethanol for 12 h. The equimolar
interactions of L1–L6 with (DME)ÁNiBr2 in tetrahydrofuran
(THF) for 12 h gave dibromonickel(II) complexes (C7–C12)
(Scheme 2). All the nickel(II) complexes of the title
obtained are air-stable, yellow in color and in good yields
(65–95%). Their IR spectra showed absorption bands
between 1590 and 1560 cmÀ1, which correspond to the
Bond angles (8)
78.74(19)
155.23(18)
76.50(18)
101.02(14)
176.65(15)
103.66(13)
96.45(7)
N2–Ni–N3
N2–Ni–N4
N3–Ni–N4
N2–Ni–Cl1
N3–Ni–Cl1
N4–Ni–Cl1
Cl1–Ni–Cl2
N2–Ni–Cl2
N3–Ni–Cl2
N4–Ni–Cl2
O1–Ni–Cl1
O1–Ni–Cl2
78.30(11)
153.78(11)
75.98(11)
102.88(8)
170.83(9)
101.72(8)
96.51(4)
89.15(14)
86.89(14)
90.26(13)
92.23(13)
169.86(12)
88.90(9)
92.60(9)
97.19(8)
n
(C = N) stretching frequencies about 50 cmÀ1 shifted to
81.82(8)
176.08(7)
lower wavenumber in comparison with their free ligands.
The single crystals of nickel complexes C1, C3 and C9
suitable for X-ray diffraction analysis were obtained by
laying diethyl ether on their methanol solutions. Their
complexes’ analogues reported [30–36], the dibromonickel
complexes coordinate with ligands in the N^N^N triden-
tate manner, in which the sp2–hybridized nitrogen of
benzoimidazole coordinated with nickel atom. The other
isomer could not be figured out; both complexes were
surprisingly observed as one isomer with methyl-substit-
uent far away to nickel center by the X-ray diffraction
analysis (Scheme 2). The favorable structures of nickel
complexes were formed due to the steric hindrance of the
methyl-substituent on the benzoimidazole along with its
proton immigrated within the benzoimidazole.
˚
C1ÁCH3OH, the nickel atom deviates by 0.0182 A from the
plane formed by N(2), N(3) and N(4). The chlorine atom
Cl(1) is almost in coplanar manner with deviation of
˚
˚
0.0947 A, and the other chlorine atom Cl(2) deviates by
2.5367 A from this plane in the opposite direction. The
dihedral angle between the iminoaryl ring and the
benzimidazole ring is 105.78, the basal plane which formed
by N(2), N(3), N(4) is nearly coplanar to the pyridine ring
with the dihedral angle of 2.98, and the dihedral angle
between iminoaryl ring and the pyridine ring is 102.88. The
˚
N(2)–C(8) (1.324(7) A) is shorter than the N(1)–C(8)
(1.356(7) A), suggesting typical SP –N character of the
2
˚
The coordination geometry of complexes C1 and C3
could be described as distorted octahedral including one
coordinated methanol, individually. In addition, there are
independent methanol molecules in the crystal cell of the
complex C1. The molecular structure of C1ÁCH3OH is
shown in Fig. 1, and the selected bond lengths and angles
are tabulated in Table 1. In the molecular structure of
coordinated nitrogen of the benzoimidazole. The three Ni–
˚
N bond lengths are Ni(1)–N(2) 2.097(5) A, Ni(1)–N(3)
˚
˚
2.013(5) A and Ni(1)–N(4) 2.197(5) A, respectively. Beyond
˚
the coordinated methanol with Ni(1)–O(1) (2.160(4) A),
˚
there are slight differences of Ni(1)–Cl(1) (2.2924(17) A)
˚
and Ni(1)–Cl(2) (2.5237(18) A). The differences of the O–
Ni–Cl angles are 92.23(13)8 and 169.86(12)8.
[(Fig._1)TD$FIG]
Like complex C1, the molecular structure of C3ÁCH3OH
(Fig. 2) also shows the six-coordinated geometry with
coordination of solvent methanol molecule and two Cl
atoms. The selected bond lengths and angles are tabulated
˚
in Table 1. The central nickel atom deviates by 0.1235 A
from the plane containing N(2), N(3), N(4), while the Cl(1)
˚
˚
deviates by 0.0993 A and Cl(2) deviates by 2.5276 A in the
opposite direction. The plane composed by N(2), N(3) and
N(4) is almost coplanar to the pyridyl ring with dihedral
angle of 2.38, the pyridyl ring and the benzimidazole ring
are also nearly coplanar with dihedral angle of 2.88. The
dihedral angles between the phenyl plane and the
benzimidazole ring, and the phenyl plane with the
pyridine ring are 95.58 and 96.98, respectively. Due to
the isopropyl group in complex C3ÁCH3OH instead of
methyl in complex C1ÁCH3OH (Table 1), there are slightly
longer Ni–N bond lengths observed for complex C3 such as
Fig. 1. ORTEP Molecular structure of C1ÁCH3OH. Thermal ellipsoids are
shown at 30% probability level. Hydrogen atoms have been omitted for
clarity.

[(Fig._2)TD$FIG]
X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
1453
chloroanalogue ligated by 2-(1H-2-benzimidazolyl)-6-(1-
(arylimino)ethyl)pyridines [34]. Compared with the chlor-
oanalogue of [L1NiCl(CH3OH)2]Cl [34], the N–Ni bond
˚
lengths of [L3NiBr2CH3OH]Br, Ni(1)–N(2) = 2.140(3) A,
˚
˚
Ni(1)–N(3) = 2.016(3) A and Ni(1)–N(4) = 2.204(3) A, are
within the typical values of coordination bonds [27,32,34].
In general, all the three complexes show the six-
coordinated geometry around nickel atom with coordina-
tion of additional methanol molecules. The catalytic
behaviors of all complexes are investigated with the prior
dried precatalysts in order to avoid any solvent incorpa-
rated. The elemental analyses of their complexes are past
after being dried under vacuum more than 4 h.
Fig. 2. ORTEP Molecular structure of C3ÁCH3OH. Thermal ellipsoids are
shown at 30% probability level. Hydrogen atoms have been omitted for
clarity.
2.2. Ethylene oligomerization
The nickel (II) complexes C1–C12 are systematically
investigated for the oligomerization of ethylene with the
Et2AlCl as a cocatalyst. Because of low catalytic activity at
ambient pressure of ethylene, the screening for catalysis is
carried out at 10 atm of ethylene. Complex C4 is typically
investigated under a range of reaction conditions, such as
molar ratios of cocatalyst to nickel and various tempera-
ture. The oligomers are only obtained and measured by GC.
When the Al/Ni molar ratios of Et2AlCl to C4 are changed
from 400 to 800 (Entries 1–4, Table 2), the catalytic
activities first increase and then decrease. The optimum
activity is observed at the Al/Ni molar ratio of 700. The
influence of reaction temperatures on their catalytic
activities are checked by the catalytic systems of C4
(Entries 3 and 5–7, Table 2) and C10 (Entries 21–24,
Table 2). The highest activity is obtained at 30 8C (Entries 3
and 22, Table 2), and higher temperatures led to an obvious
decrease of the catalytic activity. At room temperature, it is
observed a little lower catalytic activity (Entries 5 and 21,
Table 2) than that at 30 8C. It is assumed that the lower
temperature do not activate active sites or relative lower
movements of reactive substances. Meanwhile, decompo-
sition of some active centers or unfavorable intermediates
formed might happen along with a lower solubility of
ethylene in toluene at higher temperature. Such phenom-
ena have also observed in their analogue complexes [31–
36]. Regarding lifetime of active species, the catalytic
reactions are terminated within different reaction periods
of the catalytic system of complex C4 (Entries 8–12,
Table 2). The higher activities are observed in shorter
reaction times; the highest in 10 mins, on the other hand,
activities are decreased along with time prolongation and
almost terminated after 40 mins. These results indicate
that active species are immediately formed when cocata-
lyst is added, the catalytic activity will be slowly decreased
along with prolonged reaction time and the deactivation of
partial active sites due to the cumulation of impurities.
Therefore, further investigations of other nickel complexes
are carried out with the optimum condition at Al/Ni ratio
700 at 30 8C within 30 mins.
˚
˚
Ni(1)–N(2) 2.117(3) A, Ni(1)–N(3) 2.023(3) A and Ni(1)–
˚
N(4) 2.214(3) A. The Ni–Cl bond lengths are closer: Ni(1)–
˚
˚
Cl(1) (2.3187(10) A) and Ni(1)–Cl(2) (2.4112(11) A).
As shown in the Fig. 3, with the coordination of two
methanol molecules, the coordination geometry of
[L3NiBr2CH3OH]Br can be described as
a distorted
octahedron. In the single crystals of [L3NiBr2CH3OH]Br,
one bromine atom of C9 was replaced by one methanol
molecule and acted as a counterion which was relatively
far from the nickel center. The axial plane (O(1)–Ni(1)–
O(2)) is nearly perpendicular to the equatorial plane which
formed by N(2), N(3) and N(4) with a dihedral angle of
91.88. The benzimidazole ring is nearly coplanar with the
pyridine ring with a dihedral angle of 2.4o. Two O-atoms
(O(1) and O(2)) of coordinated methanols located in
mutually trans-positions form an angle of 176.39(13)8 with
the nickel core and the bond lengths of the O–Ni(1) are
˚
slightly different as O(1)–Ni(1) 12.068(3) A and O(2)–Ni(1)
2.086(3) A. The coordination geometry was observed in its
˚
[(Fig._3)TD$FIG]
Fig. 3. ORTEP Molecular structure of [L3NiBr2CH3OH]Br. Thermal
ellipsoids are shown at 30% probability level. Hydrogen atoms have been
˚
omitted for clarity. Selected bond lengths (A) and angles (deg): Ni(1)–
N(2) = 2.140(3), Ni(1)–N(3) = 2.016(3), Ni(1)–N(4) = 2.204(3), Ni(1)–Br(1) =
2.4742(9), Ni(1)–O(1) = 2.068(3), Ni(1)–O(2) = 2.086(3), N(2)–C(8) =
1.327(5), N(1)–C(8) = 1.348(5); N(3)–Ni(1)–N(2) = 78.46(13), N(3)–Ni(1)–
N(4) = 76.14(13), N(2)–Ni(1)–N(4) = 154.57(12), O(1)–Ni(1)–O(2) = 176.39
(13), N(3)–Ni(1)–O(1) = 90.82(14), N(3)–Ni(1)–O(2) = 86.99(13), O(1)–
Ni(1)–N(2) = 88.73(13), O(2)–Ni(1)–N(2) = 88.03(13), O(1)–Ni(1)–N(4) =
90.38(12), O(2)–Ni(1)–N(4) = 91.87(12).
All nickel complexes displayed high activities and good
selectivity of
a-olefin with a dimer as predominated
product, as summarized in Table 2. To compare the
environmental influence of the ligands on their catalytic
activities, the title complexes were classified into two

1454
X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
Table 2
Ethylene catalytic activity with nickel complexes using Et2AlCla.
Entry
Precatalyst
Al/Ni
T (8C)
t (min)
Activityc
Oligomer distributionb
C4/SC
C6/
SC
a-Olefin (%)
1
2
C4
400
600
700
800
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
700
30
30
30
30
20
40
50
30
30
30
30
30
30
30
30
30
30
30
30
30
20
30
40
50
30
30
30
30
30
30
30
30
30
10
20
40
50
60
30
30
30
30
30
30
30
30
30
30
30
30
30
30
5.4
6.6
38
6.6
26
23
11
52
42
30
25
21
28
25
17
35
8.1
35
14
8.3
31
52
43
8.4
36
5.6
96.5
99.1
99.7
96.0
90.2
91.6
95.0
99.8
99.7
99.7
99.7
99.7
3.5
0.9
0.3
4.0
9.8
8.4
5.0
0.2
0.3
0.3
0.3
0.3
–
91.8
94.3
> 99
96.0
92.1
50.7
83.1
> 99
> 99
> 99
> 99
> 99
91.3
98.1
77.1
21.0
93.3
60.1
34.6
12.7
> 99
97.0
62.5
27.4
> 99
71.0
C4
3
Ci4
C4
4
5
C4
6
C4
7
C4
8
C4
9
C4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
C4
C4
C4
C1
> 99.9
99.4
94.0
94.7
96.3
99.3
98.9
97.4
97.9
98.8
98.5
98.9
99.7
96.6
C2
0.6
6.0
5.3
3.7
0.7
1.1
2.6
2.1
1.2
1.5
1.1
0.3
3.4
C3
C5
C6
C7
C8
C9
C10
C10
C10
C10
C11
C12
a
Reaction condition: 5
mmol Ni; 30 min, Et2AlCl; 10 atm ethylene; 100 mL toluene.
b
c
Determined by GC.
105 g molÀ1(Ni) hÀ1
.
groups based upon the anionic halides, dichlorides C1–C6
and dibromides C7–C12. The complexes C4 and C10
bearing 2,4,6-trimethyl-substituted showed the highest
additional methyl group generally enhance the solubilities
of all complexes, therefore, the leaving groups of anionic
halides synergically affect their catalytic activities with
substituents of their ligands. With ortho-methyl groups of
the imino-N aryl rings (Entry 13 vs. Entry 18, and Entry 3 vs.
Entry 22, Table 2), the bromonickel catalysts perform
better activities than these of chloronickel complexes due
to the solubility of complexes. Ethyl or iso-propyl groups at
ortho-positions of the imino-N aryl rings (Entry 14 vs. Entry
19, and Entry 15 vs. Entry 20, Table 2), better activities
showed for chloronickel catalyst than bromonickel cata-
lyst, which is caused by the net charge influence on
catalytic acivity [39].
As previously observed [32,33], most complexes con-
taining N–H group on the benzimidazole showed higher
activities. It is imaged that some active species of anionic
amides or aluminum amides formed in situ with adding
organoaluminum, based on the evidences of metallocene
[40,41] and complex catalysts [13]. Due to better solubility,
the title complexes performed higher activities than their
analogues without methyl on the phenyl ring of the
benzimidazoles [34]. This is an alternative way to modify
ligands with changing its solubility for improving the
catalytic activities.
catalytic activity in each group (Entries
3 and 22
respectively, Table 2). Variation of the R1 groups at the
ortho-positions of the imino-N aryl rings affects their
catalytic performances, the increasing steric hindrance
leads to decrease the catalytic activities in order of
C1 > C2 > C3 (Entries 13–15, Table 2) and C7 > C8 > C9
(Entries 18–20, Table 2). With the same steric influence,
the activity of complex C4 (Entry 3, Table 2) is higher than
that of complex C5 (Entry 16, Table 2), and so is the activity
of C10 (Entry 22, Table 2) better than that of C11 (Entry 25,
Table 2). Meanwhile, complexes C6 (Entry 17, Table 2) and
C12 (Entry 26, Table 2) containing ligands with chloro-
substituents show lower catalytic activities. These phe-
nomenon are caused by the solubility factors of nickel
complexes, complexes with ligands containing additional
methyl-substituents enhance their solubility, but com-
plexes with ligands containing halides have lower
solubility. The similar phenomena were also observed
within complexes ligated by their analogues of the ligands
[33,34].
Regarding the effects of anionic halides (chloride for
C1–C6 and bromides for C7–C12), the synergic influences
of halides and the ligands were observed for their catalytic
activities. It is common for bromide precursors showing
better activity than the corresponding chlorides [26,27,38],
which is attributed to better solubility of the bromo
complexes. In current system, ligands containing an
3. Conclusions
A series of nickel complexes was synthesized and fully
characterized. The X-ray crystallographic studies on the
nickel complexes C1 and C3 displayed the distorted

X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
1455
octahedral geometry around nickel atom with incorpo-
ration of solvent molecule. All nickel complexes, activated
by Et2AlCl, exhibited high activities for ethylene oligomer-
ization. Their activities were generally higher than their
analogues [34] because the title complexes, containing
ligands with an additional methyl group of the benzoimi-
dazoles, have better solubility. Within present system of
ligands, the bulkier substituents decrease catalytic activi-
ties. The synergic influences of ligands and anionic halides
have the considerable effects on their catalytic activities.
1H-benzoimidazol-2-yl)-2-acetylpyridine and 6-(4-meth-
yl-1H-benzoimidazol-2-yl)-2-acetylpyridine. For com-
bined isomers solids: Mp: 165–166 C. IR (KBr; cmÀ1):
˚
3414.4 (s), 3055.7 (w), 1694.3 (s), 1591 (s), 1567 (w),
1505.6 (w), 1459.6 (m), 828.2 (s), 747.1 (s). Anal. Calcd for
C
15H13N3O: C, 71.70; H, 5.21; N, 16.72. Found: C, 71.42; H,
5.49; N, 16.73. 6-(7-methyl-1H-benzoimidazol-2-yl)-2-
acetylpyridine: 1H NMR (400 MHz, CDCl3, TMS):
10.31
d
(s, 1H, NH), 8.65 (d, J = 3.9 Hz, 1H, Py), 8.03–8.11 (m, 1H,
Py), 7.98–8.02 (m, 1H, Py), 7.40 (d, J = 8.1 Hz, 1H, Ph), 7.15–
7.24 (m, 1H, Ph), 7.13 (t, J = 8.6 Hz, 1H, Ph), 2.86 (s, 3H, CH3),
2.75 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, TMS):
d 199.3,
4. Experimental
153.1, 149.6, 148.1, 144.1, 138.2, 133.7, 125.0, 123.3, 122.3,
4.1. General considerations
117.9, 108.9, 25.9, 17.0. 6-(4-methyl-1H-benzoimidazol-2-
yl)-2-acetylpyridine: 1H NMR (400 MHz, CDCl3, TMS):
d
All manipulations of air- and moisture-sensitive
compounds were carried out in nitrogen atmosphere
using standard Schlenk techniques. Toluene was refluxed
over sodium-benzophenone and distilled under nitrogen
prior to use. Diethylaluminum chloride (Et2AlCl, 1.7 M in
toluene) was purchased from Acros Chemicals. Other
reagents were purchased from Aldrich or Acros Chemicals.
1H and 13C NMR spectra were recorded on a Bruker DMX
400 MHz instrument at ambient temperature using TMS as
an internal standard. IR spectra were recorded on a Perkin-
Elmer System 2000 FT-IR spectrometer. Elemental analysis
was carried out using a Flash EA 1112 micro-analyzer. GC
10.19 (s, 1H, NH), 8.61 (d, J = 3.9 Hz, 1H, Py), 8.03–8.11 (m,
1H, Py), 7.98–8.02 (m, 1H, Py), 7.70 (d, J = 8.1 Hz, 1H, Ph),
7.15–7.26 (m, 1H, Ph), 7.13 (t, J = 8.6 Hz, 1H, Ph), 2.86 (s, 3H,
CH3), 2.64 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, TMS):
d
199.3, 153.1, 149.3, 148.1, 144.1, 138.2, 130.6, 125.0, 124.3,
122.5, 121.3, 108.9, 25.9, 17.2.
4.2.2. Synthesis of 2-(methyl-substituted-1H-benzoimidazol-
2-yl)-6-(1-aryliminoethyl)pyridines (L1–L6)
6-[1-(2,6-dimethylphenylimio)ethyl]-2-(7-methyl-1H-
benzoimidazol-2-yl)pyridine and 6-[1-(2,6-dimethylphe-
nylimio)ethyl]-2-(4-methyl-1H-benzoimidazol-2-yl)pyri-
dine (L1). A solution of precursor compounds (0.75 g,
3.0 mmol), 2,6-dimethylaniline (0.54 g, 4.50 mmol), and a
catalytic amount of p-toluenesulfonic acid dissolved in
toluene (25 mL) was refluxed for 24 h. After solvent
evaporation, the crude product was purified by column
chromatography on basic Al2O3 with petroleum ether/
ethyl acetate (v/v, 8:1) as eluent to afford the product as a
light yellow powder in 62.3% yield, with the roughly molar
ratio of 3:2 for 6-[1-(2,6-dimethylphenylimio)ethyl]-2-(7-
methyl-1H-benzo imidazol-2-yl)pyridine and 6-[1-(2,6-
dimethylphenylimio)ethyl]-2-(4-methyl-1H-benzoimida-
zol-2-yl)pyridine. For combined isomers solids: Mp: 217–
analysis was performed with
chromatograph equipped with a flame ionization detector
and a 30-m (0.2 mm i.d., 0.25 m film thickness) CP-Sil 5
a Varian CP-3800 gas
m
CB column. The yield of oligomers was calculated by
referencing with the mass of the solvent on the basis of the
prerequisite that the mass of each fraction was approxi-
mately proportional to its integrated areas in the GC trace.
Selectivity for the linear
a-olefin was defined as (amount
of linear -olefin of all fractions)/(total amount of oligomer
a
products) in percent.
4.2. Preparation of the organic compounds and nickel
complexes
219 C. IR (KBr; cmÀ1): 3641.4 (w), 3079.0 (w), 1658.3 (vs),
˚
1595.1 (w), 1570.6 (m), 1464.1 (w), 1428.1 (m), 1313.1 (s),
822.7 (m), 755.4 (s). Anal. Calcd for C23H22N4: C, 77.94; H,
6.26; N, 15.81. Found: C, 77.58; H, 6.49; N, 15.61. 6-[1-(2,6-
dimethylphenylimio)ethyl]-2-(7-methyl-1H-benzoimida-
4.2.1. Preparation of 6-(methyl-substituted-1H-
benzoimidazol-2-yl)-2-acetylpyridine
According to the synthetic procedure of 6-(1H-benzoi-
midazol-2-yl)-2-acetylpyridine [31], a mixture of diethyl
zol-2-yl)pyridine: 1H NMR (400 MHz, CDCl3, TMS):
d 10.45
2,6-bis(
b
-keto-carboxylate)pyridine
[37]
(9.27 g,
(s, 1H, NH), 8.57 (d, J = 5.2 Hz, 1H, Py), 8.43 (d, J = 8.0 Hz, 1H,
Py), 7.97–7.99 (m, 1H, Py), 7.71 (d, J = 8.0 Hz, 1H, Py), 7.19–
7.23 (m, 1H, Ph), 7.08–7.11 (m, 3H, Ph), 6.93–6.96 (m, 1H,
0.030 mol), 1.5 equivalent molar 3-methylbenzene-1,2-
diamine (5.49 g, 0.045 mol), and a catalytic amount of p-
toluenesulfonic acid in the 80 mL solution of toluene and
isopropyl alcohol (3:1, v/v) was refluxed for 14 h. A
mixture of 20 mL of acetic acid and 5 mL of concentrated
HCl was added and continued to reflux for additional 6 h.
The resultant solution was cooled to room temperature, a
20% KOH solution was added to neutralize the solution to
the pH value between 9 and 10. The aqueous phase was
extracted with ethyl acetate (20 mL Â 3), all organic
extracts were combined and dried over anhydrous Na2SO4.
After drying and purification by column chromatography
(alumina column 3/1 petroleum ether/ethyl acetate), the
product obtained as white solids (3.77 g, 50.7% isolated
yield) with the roughly molar ratio of 3:2 for 6-(7-methyl-
Ph), 2.62 (s, 3H, CH3), 2.30 (s, 3H, CH3), 2.06 (s, 6H, CH3). 13
C
NMR (100 MHz, CDCl3, TMS):
d 166.5, 154.3, 150.7, 148.1,
138.4, 128.3, 128.2, 125.8, 123.9, 123.2, 109.0, 50.3, 18.1,
17.9, 15.2. 6-[1-(2,6-dimethylphenylimio)ethyl]-2-(4-
methyl-1H-benzoimidazol-2-yl)pyridine:
1H
NMR
(400 MHz, CDCl3, TMS): 10.25 (s, 1H, NH), 8.53 (d,
d
J = 5.5 Hz, 1H, Py), 8.43 (d, J = 8.0 Hz, 1H, Py), 7.97–7.99 (m,
1H, Py), 7.39 (d, J = 12 Hz, 1H, Ph), 7.19–7.23 (m, 1H, Ph),
7.08–7.11 (m, 3H, Ph), 6.93–6.96 (m, 1H, Ph), 2.76 (s, 3H,
CH3), 2.30 (s, 3H, CH3), 2.06 (s, 6H, CH3). 13C NMR
(100 MHz, CDCl3, TMS): d 166.5, 150.7, 148.8, 148.1, 138.4,
138.1, 134.5, 128.3, 128.2, 125.8, 123.9, 123.2, 117.0, 50.1,
18.1, 17.6, 15.2.

1456
X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
6-[1-(2,6-diethylphenylimio)ethyl]-2-(7-methyl-1H-
Ph), 2.77 (s, 3H, CH3), 2.74–2.80 (m, 2H, CH), 2.33 (s, 3H,
benzoimidazol-2-yl)pyridine and 6-[1-(2,6-diethylpheny-
limio)ethyl]-2-(4-methyl-1H-benzoimidazol-2-yl)pyri-
dine (L2). Using the same procedure as for L1, L2 was
obtained as a light yellow powder in 78.8% yield, with the
roughly molar ratio of 3:2 for 6-[1-(2,6-diethylphenyli-
mio)ethyl]-2-(7-methyl-1H-benzoimidazol-2-yl)pyridine
and 6-[1-(2,6-diethylphenylimio)ethyl]-2-(4-methyl-1H-
benzoimidazol-2-yl)pyridine. For combined isomers
solids: Mp: 188–189 oC. IR (KBr; cmÀ1): 3641.4 (w),
3079.0 (w), 1658.3 (vs), 1595.1 (w), 1570.6 (m), 1464.1
(w), 1428.1 (m), 1313.1 (s), 822.7 (m), 755.4 (s). Anal. Calcd
for C25H26N4: C, 78.50; H, 6.85; N, 14.65. Found: C, 78.23;
H, 7.04; N, 14.62. 6-[1-(2,6-Diethylphenylimio)ethyl]-2-
(7-methyl-1H-benzoimidazol-2-yl)pyridine: 1H NMR
CH3), 1.17 (d, J = 3.9 Hz, 12H, CH3). 13C NMR (100 MHz,
CDCl3, TMS):
d 166.4, 155.9, 150.1, 147.6, 144.2, 137.8,
133.6, 131.3, 126.1, 124.0, 123.6, 123.1, 122.8, 122.1, 121.3,
117.8, 108.8, 24.7, 17.2, 17.0, 13.0.
6-[1-(2,4,6-trimethylphenylimio)ethyl]-2-(7-methyl-
1H-benzoimidazol-2-yl)pyridine
and
6-[1-(2,4,6-tri-
methylphenylimio)ethyl]-2-(4-methyl-1H-benzoimida-
zol-2-yl)pyridine (L4). Using the same procedure as for L1,
L4 was obtained as a light yellow powder in 68.7% yield,
with the roughly molar ratio of 3:2 for 6-[1-(2,4,6-
trimethylphenylimio)ethyl]-2-(7-methyl-1H-benzoimida-
zol-2-yl)pyridine
and
6-[1-(2,4,6-trimethylphenyli-
mio)ethyl]-2-(4-methyl-1H-benzoimidazol-2-yl)pyridine.
For combined isomers solids: Mp: 170 oC. IR (KBr; cmÀ1):
3459.6 (w), 2918.5 (m), 1646.8 (vs), 1592.0 (m), 1568.5 (s),
1465.3 (m), 1428.5 (m), 1323.8 (s), 1125.0 (m), 853.6 (s),
823.5 (m), 753.2 (s). Anal. Calcd for C24H24N4: C, 78.23; H,
6.57; N, 15.21. Found: C, 78.22; H, 6.94; N, 14.95. 6-[1-
(2,4,6-trimethylphenylimio)ethyl]-2-(7-methyl-1H-ben-
zoimidazol-2-yl)pyridine: 1H NMR (400 MHz, CDCl3, TMS):
(400 MHz, CDCl3, TMS):
d 10. 36 (s, 1H, NH), 8.57 (d,
J = 3.9 Hz, 1H, Py), 8.43 (d, J = 7.8 Hz, 1H, Py), 7.95–8.01 (m,
1H, Py), 7.71 (d, J = 8.1 Hz, 1H, Ph), 7.20–7.24 (m, 1H, Ph),
7.13–7.15 (m, 3H, Ph), 7.04–7.08 (m, 1H, Ph), 2.77 (s, 3H,
CH3), 2.35–2.48 (m, 4H, CH2), 2.32 (s, 3H, CH3), 1.16 (t,
J = 7.5 Hz, 6H, CH3). 13C NMR (100 MHz, CDCl3, TMS):
d
166.2, 156.0, 147.7, 144.3, 137.9, 133.6, 133.3, 130.5, 126.1,
124.0, 123.1, 122.8, 122.3, 122.1, 117.8, 108.8, 24.4, 17.1,
13.9, 13.2. 6-[1-(2,6-diethylphenylimio)ethyl]-2-(4-meth-
yl-1H-benzoimidazol-2-yl)pyridine: 1H NMR (400 MHz,
d 10.43 (s, 1H, NH), 8.56 (d, J = 3.9 Hz, 1H, Py), 8.40 (t,
J = 8.1 Hz, 1H, Py), 7.96–7.98 (m, 1H, Py), 7.71 (d, J = 8.3 Hz,
1H, Ph), 7.20–7.23 (m, 1H, Ph), 7.12 (t, J = 5.9 Hz, 1H, Ph),
6.92 (s, 2H, Ph), 2.62 (s, 3H, CH3), 2.31 (s, 3H, CH3), 2.30 (s,
3H, CH3), 2.03 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3,
CDCl3, TMS): d 10.27 (s, 1H, NH), 8.53 (d, J = 3.9 Hz, 1H, Py),
8.43 (d, J = 7.8 Hz, 1H, Py), 7.95–8.01 (m, 1H, Py), 7.38 (d,
J = 8.1 Hz, 1H, Ph), 7.20–7.24 (m, 1H, Ph), 7.13–7.15 (m, 3H,
Ph), 7.04–7.08 (m, 1H, Ph), 2.63 (s, 3H, CH3), 2.35–2.48 (m,
TMS): d 166.7, 156.1, 150.5, 147.6, 146.1, 144.1, 137.8,
133.8, 132.6, 130.4, 128.8, 125.3, 124.0, 123.1, 122.8, 121.3,
117.7, 108.9, 22.8, 20.9, 18.0, 17.7, 16.8. 6-[1-(2,4,6-
trimethylphenylimio)ethyl]-2-(4-methyl-1H-benzoimida-
zol-2-yl)pyridine: 1H NMR (400 MHz, CDCl3, TMS):
d 10.38
4H, CH2), 2.32 (s, 3H, CH3), 1.16 (t, J = 7.5 Hz, 6H, CH3). 13
C
NMR (100 MHz, CDCl3, TMS):
d
166.2, 156.0, 150.0, 147.6,
144.2, 137.8, 133.6, 131.3, 130.5, 126.1, 124.0, 123.6, 123.1,
122.3, 122.2, 117.8, 108.8, 24.4, 17.1, 13.9, 13.2.
(s, 1H, NH), 8.52 (d, J = 4.0 Hz, 1H, Py), 8.40 (t, J = 8.1 Hz, 1H,
Py), 7.96–7.98 (m, 1H, Py), 7.39 (d, J = 8.3 Hz, 1H, Ph), 7.20–
7.23 (m, 1H, Ph), 7.12 (t, J = 5.9 Hz, 1H, Ph), 6.92 (s, 2H, Ph),
2.76 (s, 3H, CH3), 2.31 (s, 3H, CH3), 2.30 (s, 3H, CH3), 2.03 (s,
6-[1-(2,6-diisopropylphenylimio)ethyl]-2-(7-methyl-
1H-benzoimidazol-2-yl)pyridine and 6-[1-(2,6-diisopro-
pylphenylimio)ethyl]-2-(4-methyl-1H-benzoimidazol-2-
yl)pyridine (L3). Using the same procedureas for the L1, L3
was obtained as a light yellow powder in 81.3% yield, with
the roughly molar ratio of 3:2 for 6-[1-(2,6-diisopropyl-
phenylimio)ethyl]-2-(7-methyl-1H-benzoimidazol-2-
yl)pyridine and 6-[1-(2,6-diisopropylphenylimio)ethyl]-2-
(4-methyl-1H-benzoimidazol-2-yl)pyridine. For combined
isomers solids: Mp: 201–202 oC. IR (KBr; cmÀ1): 3457.8
(m), 3058.1 (w), 2962.9 (m), 1645.0 (vs), 1591.4 (s), 1567.8
(s), 1461.3 (m), 1431.1 (m), 1316.1 (s), 905.7 (s), 755.8 (s).
Anal. Calcd for C27H30N4: C, 78.99; H, 7.37; N, 13.65. Found:
C, 78.61; H, 7.37; N, 13.36. 6-[1-(2,6-diisopropylphenyli-
mio)ethyl]-2-(7-methyl-1H-benzoimidazol-2-yl)pyridine:
6H, CH3). 13C NMR (100 MHz, CDCl3, TMS):
d 166.7, 156.1,
150.2, 147.6, 146.2, 144.1, 137.7, 133.8, 132.6, 130.4, 128.8,
125.3, 124.0, 123.1, 122.8, 121.3, 117.7, 108.9, 22.8, 20.9,
18.0, 17.1, 16.7.
6-[1-(2,6-diethyl-4-methylphenylimio)ethyl]-2-(7-
methyl-1H-benzoimidazol-2-yl)pyridine and 6-[1-(2,6-
diethyl-4-methylphenylimio)ethyl]-2-(4-methyl-1H-ben-
zoimidazol-2-yl)pyridine (L5). Using the same procedure
as for L1, L5 was obtained as a light yellow powder in 65.3%
yield, with the roughly molar ratio of 3:2 for 6-[1-(2,6-
diethyl-4-methylphenylimio)ethyl]-2-(7-methyl-1H-
benzo imidazol-2-yl)pyridine and 6-[1-(2,6-diethyl-4-
methylphenylimio)ethyl]-2-(4-methyl-1H-benzoimida-
zol-2-yl)pyridine. For combined isomers solids: Mp: 200–
202 oC. IR (KBr; cmÀ1): 3458.0 (m), 2981.4 (m), 1645.2 (vs),
1568.2 (s), 1473.2 (m), 1443.8 (m), 1316.6 (s), 1210.2 (s),
990.0 (m), 858.8 (m), 752.0 (s). Anal. Calcd for C26H28N4: C,
78.75; H, 7.12; N, 14.13. Found: C, 78.85; H, 7.18; N, 13.97.
6-[1-(2,6-diethyl-4-methylphenylimio)ethyl]-2-(7-meth-
yl-1H-benzoimidazol-2-yl)pyridine: 1H NMR (400 MHz,
1H NMR (400 MHz, CDCl3, TMS):
d 10.45 (s, 1H, NH), 8.57
(d, J = 3.9 Hz, 1H, Py), 8.41–8.45 (m, 1H, Py), 7.98 (d,
J = 3.7 Hz, 1H, Py), 7.25 (d, J = 4.5 Hz, 1H, Ph), 7.18–7.20 (m,
3H, Ph), 7.10–7.15 (m, 2H, Ph), 2.74–2.80 (m, 2H, CH), 2.62
(s, 3H, CH3), 2.33 (s, 3H, CH3), 1.17 (d, J = 3.9 Hz, 12H, CH3).
13C NMR (100 MHz, CDCl3, TMS):
d 166.4, 155.9, 150.3,
147.7, 144.3, 138.0, 133.6, 131.3, 126.1, 124.7, 123.6, 123.1,
122.8, 122.3, 122.2, 117.8, 108.8, 24.7, 17.1, 17.0, 13.8. 6-
[1-(2,6-Diisopropylphenylimio)ethyl]-2-(4-methyl-1H-
benzoimidazol-2-yl)pyridine: 1H NMR (400 MHz, CDCl3,
CDCl3, TMS): d 10.35 (s, 1H, NH), 8.56 (d, J = 3.9 Hz, 1H, Py),
8.41 (d, J = 7.7 Hz, 1H, Py), 7.96–7.98 (m, 1H, Py), 7.71 (d,
J = 8.1 Hz, 1H, Ph), 7.20–7.24 (m, 1H, Ph), 7.12 (t, J = 6.4 Hz,
1H, Ph), 6.95 (s, 2H, Ph), 2.62 (s, 3H, CH3), 2.39–2.43 (m, 4H,
CH2), 2.35 (s, 3H, CH3), 2.32 (s, 3H, CH3), 1.15 (t, J = 7.5 Hz,
TMS):
d 10.32 (s, 1H, NH), 8.54(d, J = 3.9 Hz, 1H, Py), 8.41–
8.45 (m, 1H, Py), 7.98 (d, J = 3.7 Hz, 1H, Py), 7.38 (d,
J = 4.0 Hz, 1H, Ph), 7.18–7.20 (m, 3H, Ph), 7.10–7.15 (m, 2H,
6H, CH3). 13C NMR (100 MHz, CDCl3, TMS):
d 166.5, 156.1,

X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
1457
150.4, 147.5, 145.1, 144.1, 137.7, 133.6, 132.7, 131.0, 130.3,
126.8, 124.6, 122.9, 122.6, 122.2, 117.7, 108.8, 24.6, 21.0,
17.1, 17.0, 13.9. 6-[1-(2,6-diethyl-4-methylphenyli-
mio)ethyl]-2-(4-methyl-1H-benzoimidazol-2-yl)pyridine:
Data for C2 Yield: 84.1%. IR (KBr; cmÀ1): 3420.1 (w),
3046.6 (w), 2971.7 (w), 1598.8 (vs), 1449.1 (m), 1377.6 (s),
1317.7 (s), 1158.1 (m), 794.6 (s), 752.4 (s). Anal. Calcd for
C25H26Cl2NiN4: C, 58.63; H, 5.12; N, 10.94. Found: C, 58.77;
1H NMR (400 MHz, CDCl3, TMS):
d
10.21 (s, 1H, NH), 8.52
H, 5.17; N, 10.72.
(d, J = 3.9 Hz, 1H, Py), 8.41 (d, J = 7.7 Hz, 1H, Py), 7.96–7.98
(m, 1H, Py), 7.38 (d, J = 7.9 Hz, 1H, Ph), 7.20–7.24 (m, 1H,
Ph), 7.12 (t, J = 6.4 Hz, 1H, Ph), 6.95 (s, 2H, Ph), 2.77 (s, 3H,
CH3), 2.39–2.43 (m, 4H, CH2), 2.35 (s, 3H, CH3), 2.32 (s, 3H,
CH3), 1.15 (t, J = 7.5 Hz, 6H, CH3). 13C NMR (100 MHz, CDCl3,
Data for C3 Yield: 90.1%. IR (KBr; cmÀ1): 3390.0 (m),
3058.4 (m), 2966.0 (m), 1591.0 (vs), 1472.0 (w), 1444.9
(w), 1319.5 (s), 1202.7 (s), 816.9 (m), 766.7 (s), 746.1 (s).
Anal. Calcd for C27H30Cl2NiN4: C, 60.04; H, 5.60; N, 10.37.
Found: C, 60.11; H, 5.61; N, 10.22.
Data for C4 Yield: 88.7%. IR (KBr; cmÀ1): 3467.8 (w),
3017.4 (w), 1597.9 (vs), 1445.9 (m), 1319.1 (s), 1197.2 (s),
823.4 (m), 792.4 (s), 760.7 (m). Anal. Calcd for
TMS):
d
166.5, 156.1, 150.1, 147.5, 145.1, 144.0, 137.6,
133.6, 132.6, 131.0, 130.3, 126.7.
6-[1-(2,6-dichlorophenylimio)ethyl]-2-(7-methyl-1H-
benzoimidazol-2-yl)pyridine and 6-[1-(2,6-dichlorophe-
nylimio)ethyl]-2-(4-methyl-1H-benzoimidazol-2-yl)pyri-
dine (L6). Using a similar procedure as for L1, but using
silicic acid tetraethyl ester as a solvent instead of toluene,
L6 was obtained as a white powder in 38.3% yield, with the
ougly molar ratio of 3:2 for 6-[1-(2,6-dichlorophenyli-
mio)ethyl]-2-(7-methyl-1H-benzoimidazol-2-yl)pyridine
and 6-[1-(2,6-dichlorophenylimio)ethyl]-2-(4-methyl-1H-
benzoimidazol-2-yl)pyridine. For combined isomers
solids: Mp: 235 oC. IR (KBr; cmÀ1): 3464.3 (m), 3082.9
(w), 1663.0 (vs), 1593.1 (m), 1568.9 (m), 1461.8 (m),
1224.3 (m), 822.0 (m). Anal. Calcd for C21H16N4Cl2: C,
63.81; H, 4.08; N, 14.17. Found: C, 63.84; H, 4.10; N, 13.83.
6-[1-(2,6-dichlorophenylimio)ethyl]-2-(7-methyl-1H-
benzo imidazol-2-yl)pyridine: 1H NMR (400 MHz, CDCl3,
C24H24Cl2NiN4: C, 57.87; H, 4.86; N, 11.25. Found: C,
57.53; H, 5.10; N, 11.06.
Data for C5 Yield: 85.3%. IR (KBr; cmÀ1): 3282.5 (m),
3114.0 (m), 2968.5 (m), 1598.6 (vs), 1479.4 (m), 1457.0
(m), 1422.5 (m), 1316.6 (s), 1087.4 (m), 1042.4 (s), 814.6
(s), 750.5 (s). Anal. Calcd for C26H28Cl2NiN4: C, 59.35; H,
5.36; N, 10.65. Found: C, 59.00; H, 5.28; N, 10.35.
Data for C6 Yield: 67.5%. IR (KBr; cmÀ1): 3362.3 (m),
3084.3 (w), 1599.9 (vs), 1478.2 (w), 1409.8 (vs), 1316.6 (s),
1277.5 (s), 819.2 (m), 789.8 (s). Anal. Calcd for
C21H16Cl4NiN4: C, 48.05; H, 3.07; N, 10.67. Found: C,
47.86; H, 3.43; N, 10.46.
Data for C7 Yield: 94.9%. IR (KBr; cmÀ1): 3268.9 (s),
1599.8 (vs), 1475.9 (m), 1420.9 (m), 1316.6 (s), 1209.6 (s),
816.4 (m), 788.5 (w). Anal. Calcd for C23H22Br2NiN4: C,
48.21; H, 3.87; N, 9.78. Found: C, 48.51; H, 3.99; N, 9.53.
Data for C8 Yield: 91.7%. IR (KBr; cmÀ1): 3278.9 (s),
1599.5 (vs), 1475.0 (m), 1419.2 (m), 1316.4 (s), 1271.5 (s),
868.4 (w), 793.4 (m), 747.8 (m). Anal. Calcd for
TMS): d 10.36 (s, 1H, NH), 8.59 (d, 1H, J = 3.9 Hz, Py), 8.43 (d,
1H, J = 7.8 Hz, Py), 7.99–8.02 (m, 1H, Py), 7.71(d, 1H,
J = 8.1 Hz, Ph), 7.39 (d, 3H, J = 8.0 Hz, Ph), 7.18–7.24 (m, 1H,
Ph), 7.10–7.14 (t, 1H, J = 6.7 Hz, Ph), 7.00–7.04 (m, 1H, Ph),
2.62 (s, 3H, CH3), 2.42 (s, 3H, CH3). 13C NMR (100 MHz,
C25H26Br2NiN4: C, 49.96; H, 4.36; N, 9.32. Found: C,
CDCl3, TMS):
d
170.8, 155.2, 150.0, 147.7, 145.5, 144.1,
49.65; H, 4.17; N, 9.68.
137.9, 130.5, 128.3, 124.6, 124.1, 123.1, 122.7, 108.8, 17.9,
17.0. 6-[1-(2,6-dichlorophenylimio)ethyl]-2-(4-methyl-
1H-benzoimidazol-2-yl)pyridine: 1H NMR (400 MHz,
Data for C9 Yield: 89.4%. IR (KBr; cmÀ1): 3381.5(m),
3054.9(w), 1597.0(vs), 1461.3(m), 1422.6(m), 1316.8(s),
1205.4(m), 816.6(m), 766.3(s). Anal. Calcd for
CDCl3, TMS):
d
10.26 (s, 1H, NH), 8.56 (d, 1H, J = 3.9 Hz,
C27H30Br2NiN4: C, 51.55; H, 4.81; N, 8.91. Found: C,
Py), 8.43(d, 1H, J = 7.8 Hz, Py), 7.99–8.02 (m, 1H, Py), 7.39
(d, 2H, J = 8.0 Hz, Ph), 7.18–7.24 (m, 1H, Ph), 7.10–7.14 (t,
1H, J = 6.7 Hz, Ph), 7.00–7.04 (m, 1H, Ph), 2.76 (s, 3H, CH3),
2.42 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, TMS):
d 170.8,
51.81; H, 5.01; N, 8.65.
Data for C10 Yield: 93.7%. IR (KBr; cmÀ1): 3245.7 (s),
1600.7 (vs), 1477.7 (s), 1419.8 (w), 1316.5 (s), 1238.0 (m),
1216.5 (s), 856.0 (m), 788.4 (s), 749.0 (m). Anal. Calcd for
155.2, 159.9, 147.7, 145.5, 144.1, 137.9, 133.7, 128.3, 124.6,
123.5, 122.8, 108.8, 17.9, 17.0.
C24H24Br2NiN4: C, 49.11; H, 4.12; N, 9.54. Found: C, 49.37;
H, 4.38; N, 9.25.
Data for C11 Yield: 86.8%. IR (KBr; cmÀ1): 3308.7 (s),
1600.4 (vs), 1476.6 (w), 1417.4 (m), 1315.5 (s), 1273.4 (m),
1212.5 (m), 814.5 (m), 788.9 (s), 749.7 (s). Anal. Calcd for
4.2.3. Synthesis of tridentate nickel complexes C1–C12
Nickel complexes C1–C12 were prepared by the same
synthetic procedures and obtained as a yellow powder.
The synthetic procedure for C1 can be described as
follows: to a mixture of ligand L1 (0.124 g, 0.35 mmol) and
NiCl2. 4H2O (0.083 g, 0.35 mmol) was added freshly
prepared distilled ethanol (5 mL) at room temperature.
The solution turned yellow immediately. The reaction
mixture was stirred for 10 h, and the precipitate was
collected by filtration and washed with diethyl ether,
followed by drying in vacuum. The target complex was
obtained as a yellow powder in 87.6% yield. IR (KBr;
cmÀ1): 3496.3 (w), 2975.3 (w), 1599.6 (vs), 1476.7 (m),
1424.1 (m), 1317.6 (m), 817.0 (s), 750.4 (s). Anal. Calcd for
C26H28Br2NiN4: C, 50.77; H, 4.59; N, 9.11. Found: C, 50.38;
H, 4.63; N, 9.41.
Data for C12 Yield: 72.4%. IR (KBr; cmÀ1): 3278.3 (s),
3067.2 (w), 1599.8 (vs), 1466.0 (m), 1413.2 (s), 1315.1 (s),
1210.2 (m), 933.0 (s), 806.2 (s), 740.3 (m). Anal. Calcd for
C21H16Br2Cl2NiN4: C, 41.09; H, 2.63; N, 9.13. Found: C,
41.28; H, 2.67; N, 8.85.
4.3. Procedure for ethylene oligomerization
Ethylene oligomerization was performed in a stainless
steel autoclave (0.5 L capacity) equipped with a gas ballast
through a solenoid clave for continuous feeding of ethylene
C
23H22Cl2N4Ni: C, 57.07; H, 4.58; N, 11.57. Found: C,
56.77; H, 4.72; N, 11.90.
at constant pressure.
A 100 mL amount of toluene

1458
X. Chen et al. / C. R. Chimie 13 (2010) 1450–1459
Table 3
Crystal data and structure refinement for [C1ÁCH3OH]ÁCH3OH, C3ÁCH3OH and [L3NiBr2CH3OH]Br.
[C1ÁCH3OH]ÁCH3OH
C3ÁCH3OH
[L3NiBr2CH3OH]Br
Empirical formula
Formula weight
Temperature [K]
C25H30Cl2N4NiO2
548.14
C28H34Cl2N4NiO
572.0
C29H38Br2N4NiO2
693.16
173(2) K
173 (2) K
0.71073
173 (2) K
0.71073
˚
Wavelength [A]
0.71073
Crystal system
Space group
Monoclinic
P2(1)/n
Monoclinic
P2(1)/c
Triclinic
P-1
˚
a [A]
6.8170(14)
20.386(4)
18.047(4)
90
14.330(3)
11.022(2)
18.306(4)
90
9.3652(19)
10.904(2)
17.576(4)
91.64(3)
˚
b [A]
˚
c [A]
a
b
g
[8]
[8]
[8]
93.30
112.33(3)
90
94.54(3)
90
97.71(3)
3
˚
V [A ]
2503.8(9)
4, 1.454
2674.5(9)
4, 1.421
1771.7(6)
2, 1.299
Z, Dcalcd. [gcmÀ3
]
m
[mmÀ1
]
1.019
0.954
2.830
F(000)
Crystal size [mm]
range [8]
1144
1200
708
0.19 Â 0.07 Â 0.04
1.51–25.50
À8 ꢀ h ꢀ 8
À24 ꢀ k ꢀ 24
0 ꢀ l ꢀ 21
17274
0.20 Â 0.20 Â 0.20
1.54–27.48
À18 ꢀ h ꢀ 18
À14 ꢀ k ꢀ 14
À22 ꢀ l ꢀ 23
21196
0.20 Â 0.20 Â 0.20
1.16–27.49
À11 ꢀ h ꢀ 12
À14 ꢀ k ꢀ 14
À22 ꢀ l ꢀ 22
21779
u
Limiting indices
Reflections collected
Independent reflections
No. of parameters
4643 [R(int) = 0.0760]
316
6075 [R(int) = 0.0374]
327
8084 [R(int) = 0.0368]
355
Completeness to
u
[%]
99.8%
99.2%
99.4%
Goodness of fit on F2
1.258
1.253
1.113
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 = 0.0796
wR2 = 0.1923
R1 = 0.0905
wR2 = 0.2005
0.965 and À0.557
R1 = 0.0522
wR2 = 0.1530
R1 = 0.0580
wR2 = 0.1660
0.494 and À0.611
R1 = 0.0562
wR2 = 0.1680
R1 = 0.0664
wR2 = 0.1763
1.185 and À0.863
À3
˚
Max./min. Dr[a] [eA
]
containing the complex and the required amount of
cocatalyst was transferred into the fully dried reactor
via a syringe under a nitrogen atmosphere. At the reaction
temperature, the reactor was sealed and pressurized to
high ethylene pressure, and the ethylene pressure was
maintained during feeding of ethylene. After the reaction
mixture was stirred for the desired period, the pressure
was released and a small amount of the reaction solution
was collected, which was then analyzed by gas chroma-
tography (GC) to determine the composition and mass
distribution of the oligomers obtained. To keep the
reaction temperature constant, the autoclave is equipped
with inert heat exchange tube of water.
Table 3. Crystallographic data have been deposited with
the Cambridge Crystallographic Data Centre, CCDC 749265
([C1CH3OH]ÁCH3OH), 749266 (C3CH3OH) and 755621
([L3NiBr2CH3OH]Br), which could be obtained free of
charge from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (e-mail: deposit@ccdc.cam.ac.uk; web: http://
www.ccdc.cam.ac.uk).
Acknowledgments
This work was supported by the National Natural
Science Foundation of China (grant Nos. 20942009 and
20674089) and the Foundation for Returned Overseas
Chinese Scholars of Shanxi Province (2009, X. Chen).
4.4. X-ray crystallographic studies
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were obtained by laying diethyl ether on a methanol
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