2-(1-Isopropyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyridyl transition metal (Fe, Co, and Ni) dichlorides: Syntheses, characterizations and their catalytic behaviors toward ethylene reactivity

Article abstract of DOI:10.1016/j.jorganchem.2008.02.007

A series of 2-(1-isopropyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyridyl metal complexes [iron (II) (1a-6a), cobalt (II) (1b-6b) and nickel (II) (1c-6c)] were synthesized and fully characterized by elemental and spectroscopic analyses. Single-crystal X-ray diffraction analyses of five coordinated complexes 5a, 3b, 5b, 1c and 2c reveal 5a and 5b as distorted trigonal-bipyramidal geometry, and 3b, 1c and 2c as distorted square pyramidal geometry. All complexes performed ethylene reactivity with the assistance of various organoaluminums. The iron complexes displayed good activities in the presence of MAO and MMAO. Upon activated by Et₂AlCl, the cobalt analogues showed moderate ethylene reactivity, while the nickel analogues exhibited relatively higher activities.

Full text of DOI:10.1016/j.jorganchem.2008.02.007

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1829–1840
www.elsevier.com/locate/jorganchem
2-(1-Isopropyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyridyl
transition metal (Fe, Co, and Ni) dichlorides:
Syntheses, characterizations and their catalytic behaviors
toward ethylene reactivity
b
b
a,
a,b,
*
Yanjun Chen a,b, Peng Hao , Weiwei Zuo , Kun Gao , Wen-Hua Sun
*
a State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
b Key Laboratory of Engineering Plastics, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
Received 13 December 2007; received in revised form 2 February 2008; accepted 8 February 2008
Available online 15 February 2008
Abstract
A series of 2-(1-isopropyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyridyl metal complexes [iron (II) (1a–6a), cobalt (II) (1b–6b) and
nickel (II) (1c–6c)] were synthesized and fully characterized by elemental and spectroscopic analyses. Single-crystal X-ray diffraction
analyses of five coordinated complexes 5a, 3b, 5b, 1c and 2c reveal 5a and 5b as distorted trigonal-bipyramidal geometry, and 3b, 1c
and 2c as distorted square pyramidal geometry. All complexes performed ethylene reactivity with the assistance of various organoalu-
minums. The iron complexes displayed good activities in the presence of MAO and MMAO. Upon activated by Et2AlCl, the cobalt ana-
logues showed moderate ethylene reactivity, while the nickel analogues exhibited relatively higher activities.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Transition metal complex; Iron; Cobalt; Nickel; 2-(Benzimidazolyl)-6-iminopyridine; Ethylene reactivity
1. Introduction
developed as famous SHOP process [4]. Along with explor-
ing new transition metal complexes as catalysts for ethylene
polymerization [5], the great progress has been made for
ethylene oligomerization due to the same reaction concept
of ethylene oligomerization and polymerization. The past
decade witnessed the discovery of numerous models of
transition metal complexes as catalysts, in which the most
famous model has been focused on metal complexes bear-
ing 2,6-bis(imino)pyridines initially developed by the
groups of Brookhart [6] and Gibson [7]. Beyond following
works regarding to this model [8], the alternative models of
heterocyclic compounds providing three-nitrogen in coor-
dination have been developed in our group [5h]. Those
interesting complexes with good to high activities in ethyl-
ene reactivity contain newly developed ligands such as 2-
imino-1,10-phenanthroline derivatives (A, Scheme 1) [9],
N-((pyridin-2-yl)methylene)-quinolin-8-amine derivatives
Ethylene oligomerization presents one of the major
industrial processes for the production of linear a-olefins
in the range of C6–C20 with annual millions of tons produc-
tivities [1–3]. a-Olefins are fundamental substances
amongst manufactures of detergents, synthetic lubricants
and plasticizer alcohol and some co-polymers. Originally
linear a-olefins were manufactured by the Ziegler (Alfen)
process in the presence of TEA (triethylaluminum). Later
on, the catalytic system employing nickel complex was
*
Corresponding authors. Address: Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100080, China. Tel.: +86 10 62557955; fax:
+86 10 62618239.
E-mail addresses: npchem@lzu.edu.cn (K. Gao), whsun@iccas.ac.cn
(W.-H. Sun).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.02.007

1830
Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
Me
R
N
N
MCl2
N
R1
N
R1
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
C2H5OH
M
M
M
M
Ar
Ar
Ar
R2
Cl Cl
X
X
X
X
X
R2
R1
R2
R1
X
A
B
C
1
2
3
4
5
6
1a-6a: M=Fe;
1b-6b: M=Co;
1c-6c: M=Ni.
R1
Et
H
Me
H
iPr Cl Me Me
Br
Scheme 1. Highly effective catalysts of newly N3-tridentate metal
complexes.
R2
H
H
Me
Scheme 2. Synthesis of metal complexes.
[10], 2-quinoxalinyl-6-iminopyridines (B, Scheme 1) [11],
and recently 2-(1-methyl-2-benzimidazolyl)-6-(1-aryl imi-
noethyl)pyridines (C, Scheme 1) [12]. With those model
complexes, the further modifications have been progressing
along with finding optimum catalytic conditions.
ders, separated by filtration, washed with diethyl ether and
dried in vacuum as air-stable compounds with good purity
in yields (80–99%). The complexes were characterized by
FT-IR spectra and elemental analyses. In the IR spectra
of these iron (II) complexes, the stretching vibration bands
of the C@N groups apparently shifted to lower wave num-
ber (1591–1599 cmÀ1) with greatly reduced intensity, com-
In our extensive research of model catalyst C containing
2-(1-methyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyri-
dines [12], 2-(1-isopropyl-2-benzimidazolyl)-6-(1-arylimi-
noethyl) pyridines have been synthesized and used to
form chromium complexes as catalysts for ethylene reac-
tions [13]. The substantive and systematic research includes
transition metals such as iron, cobalt, nickel, etc. In
comparison of their analogues ligated by 2-(1-methyl-
2-benzimidazolyl)-6-(1-aryliminoethyl)pyridines, the titled
complexes with isopropyl instead of methyl group are
expected to be more soluble and more active. The titled
complexes were synthesized and characterized in detail;
moreover, their molecular structures of complexes 5a, 3b,
5b, 1c and 2c were confirmed by single-crystal X-ray dif-
fraction. In the presence of suitable organoaluminums,
these complexes showed moderate to good catalytic activi-
ties toward ethylene oligomerization and polymerization
for oligomers and polyethylene wax. The effects of substit-
uents on the ligands, cocatalysts, the Al/metal molar ratio,
and reaction temperature on their catalytic activities and
selectivities have been investigated in detail. Herein, the
syntheses and characterizations of the titled complexes
are reported along with their catalytic performances
towards ethylene oligomerization and polymerization.
pared with the corresponding ligands (1643–1658 cmÀ1
)
[13], indicating the coordination interaction between the
imine nitrogen atom and the metal cation. In addition,
the molecular structure of 5a was confirmed by the sin-
gle-crystal X-ray diffraction analysis.
Using the same synthetic method (Scheme 2), the cobalt
analogues (1b–6b) were successfully prepared and charac-
terized by FT-IR spectra and elemental analyses. The lower
frequencies of C@N bonds (1591–1593 cmÀ1) in complexes
indicated effective coordination of the imine nitrogen atom
to the cobalt one. The molecular structures of 3b and 5b
were determined by single crystal X-ray diffraction analy-
ses. Similarly, their nickel analogues (1c–6c) were prepared
(Scheme 2) and carefully characterized. Moreover, the
molecular structures of 1c and 2c were further determined
by single crystal X-ray diffraction analyses.
2.2. Molecular structures
Single crystals of complex 5a suitable for X-ray diffrac-
tion analysis were obtained by slow diffusion of diethyl
ether into its methanol solution under nitrogen. The asym-
metric unit of complex 5a contains the halves of two inde-
pendent molecules, as shown in Fig. 1; and the poor
structural quality might be the cause for R1 = 0.0998.
The coordination geometry around the iron center can be
described as a distorted trigonal-bipyramidal in which
one nitrogen atom N(2) of pyridyl ring and two chlorine
atoms (Cl(1), Cl(2)) form the equatorial plane, which is
similar to their iron analogue complexes ligated by 2-(1-
methyl-2-benzimidazole)-6-(1-aryliminoethyl)pyridines [12a].
The two independent molecules have slightly different bond
lengths and bond angles, as shown in Table 1. In molecule
2. Results and discussion
2.1. Synthesis and characterization
The syntheses and characterizations of organic
compounds used as ligands were reported in our previous
paper [13], in addition, the new 4-bromo-N-(1-(6-(1-isopro-
pyl-1H- benzo[d]imidazol-2-yl)pyridin-2-yl)ethylidene)-2,6-
dimethylbenzenamine was prepared in the same manner
through the condensation reaction of 2-(1-isopropyl-2-
benzimidazolyl)-6-acetylpyridine
dimethylaniline.
and
4-bromo-2,6-
˚
(5a-1), the iron center slightly deviates by 0.0295 A from
According to the literature method, all titled complexes
were formed in good to high yields. The iron (II) complexes
1a–6a were easily prepared by mixing the corresponding
ligands and 1 equiv. of FeCl2 Á 4H2O in ethanol at room
temperature under nitrogen (Scheme 2). The complexes
were precipitated from the reaction solutions as blue pow-
the triangular plane formed by N(2), Cl(1) and Cl(2), while
this deviation is 0.0058 A in molecule (5a-2). Furthermore,
differences are observed for the dihedral angles between the
equatorial plane and the pyridyl one, the imino-aryl ring
and the pyridyl ring (91.4° and 84.7° in (5a-1) vs. 80.3°
and 75.9° in (5a-2)). In (5a-1), the plane of the chelating
˚

Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
1831
85.4(3)°). In both molecules, the bond angles subtended
by the axial Fe–N bonds are 145.5(3)° (N(1)–Fe(1)–N(3))
and 144.4(3)° (N(1A)–Fe(1A)–N(3A)), respectively. The
Fe–N bond in the equatorial plane in each molecule is
clearly shorter than the two axial Fe–N bonds, and the
axial Fe–N (N from the imidazole ring) bond is shorter
than the Fe–Nimino one. The two Fe–Cl bond lengths are
similar in each molecular structure. Although the two
˚
imino C@N bonds are slightly different (1.294(1) A in
˚
(5a-1) and 1.269(1) A in (5a-2)), they are both typical imino
C@N double bonds.
Single crystals of cobalt complexes 3b and 5b were
grown by laying diethyl ether on their methanol solutions.
The coordination geometry of complex 3b could be
described as a distorted square pyramidal, while the coor-
dination geometry of complex 5b is a distorted trigonal-
bipyramidal.
The molecular structure of 3b is shown in Fig. 2, while
selected bond lengths and angles are collected in Table 2.
In the molecular structure of 3b, the cobalt atom deviates
˚
by 0.4529 A from the plane formed by N(1), N(2) and
N(3), meanwhile the chlorine atom Cl(1) is almost in copla-
˚
nar manner with deviation of 0.1729 A, and the other chlo-
˚
rine atom Cl(2) deviates 2.1936 A from this plane in the
opposite direction. Based on this structural character, the
coordination geometry of complex 3b can be best described
as a distorted square pyramidal with the basal plane com-
posed by N(1), N(2), N(3) and Cl(1). This phenomenon is
different from those of their analogue cobalt complexes,
whose geometries around the cobalt center are trigonal-
bipyramidal [12a].
Fig. 1. Crystal structure of complex 5a showing the two independent
molecules of the asymmetric unit. Thermal ellipsoids are shown at 30%
probability; hydrogen atoms and solvent have been omitted for clarity.
Table 1
˚
Selected bond lengths (A) and angles (°) for complex 5a
The dihedral angle between the basal plane and the pyr-
idine ring is 17.0°, while that between the basal plane and
the benzimidazole ring is 12.5°. The imino-aryl ring is
nearly perpendicular to the pyridine ring with the dihedral
angle of 88.9°, so is the dihedral angle between the imino-
aryl ring and the benzimidazole ring as 85.4°. The molecule
˚
Bond lengths (A)
Fe(1)–N(1)
Fe(1)–N(2)
Fe(1)–N(3)
Fe(1)–Cl(1)
Fe(1)–Cl(2)
N(1)–C(16)
N(1)–C(18)
N(2)–C(1)
N(2)–C(5)
N(3)–C(6)
N(3)–C(7)
2.309(9)
2.154(7)
2.160(8)
2.305(3)
2.287(3)
1.294(1)
1.422(1)
1.354(1)
1.347(1)
1.327(1)
1.413(1)
Fe(1A)–N(1A)
Fe(1A)–N(2A)
Fe(1A)–N(3A)
Fe(1A)–Cl(1A)
Fe(1A)–Cl(2A)
N(1A)–C(16A)
N(1A)–C(18A)
N(2A)–C(1A)
N(2A)–C(5A)
N(3A)–C(6A)
N(3A)–C(7A)
2.307(8)
2.115(7)
2.209(7)
2.281(3)
2.294(3)
1.269(1)
1.444(1)
1.344(1)
1.324(1)
1.313(1)
1.379(1)
Bond angles (°)
N(2)–Fe(1)–N(3)
N(2)–Fe(1)–N(1)
N(3)–Fe(1)–N(1)
N(2)–Fe(1)–Cl(1)
N(3)–Fe(1)–Cl(1)
N(1)–Fe(1)–Cl(1)
N(2)–Fe(1)–Cl(2)
N(3)–Fe(1)–Cl(2)
N(1)–Fe(1)–Cl(2)
Cl(1)–Fe(1)–Cl(2)
73.1(3)
72.9(3)
145.5(3)
124.9(2)
96.3(2)
98.4(2)
120.1(2)
99.6(2)
N(2A)–Fe(1A)–N(3A)
N(2A)–Fe(1A)–N(1A)
N(3A)–Fe(1A)–N(1A)
N(2A)–Fe(1A)–Cl(1A)
N(3A)–Fe(1A)–Cl(1A)
N(1A)–Fe(1A)–Cl(1A)
N(2A)–Fe(1A)–Cl(2A)
N(3A)–Fe(1A)–Cl(2A)
N(1A)–Fe(1A)–Cl(2A)
Cl(1A)–Fe(1A)–Cl(2A)
73.8(3)
72.7(3)
144.4(3)
131.2(2)
93.5(2)
99.50(2)
109.9(2)
104.9(2)
97.57(2)
118.88(2)
102.1(2)
114.97(1)
ring Fe(1)–N(3)–C(6)–C(5)–N(2)–C(1)–C(16)–N(1) is nearly
perpendicular to both equatorial plane (89.3°) and the
imino-aryl ring (91.9°), while the corresponding two
dihedral angles deviated from 90° in (5a-2) (83.2(2)°,
Fig. 2. Molecular structure of complex 3b. Thermal ellipsoids are shown
at 30% probability; hydrogen atoms and solvent have been omitted for
clarity.

1832
Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
Table 2
Table 3
˚
˚
Selected bond lengths (A) and angles (°) for complexes 3b
Selected bond lengths (A) and angles (°) for complex 5b
˚
Bond lengths (A)
˚
Bond lengths (A)
Co–N(1)
Co–N(3)
Co–Cl(2)
N1–C(18)
N2–C(5)
N3–C(7)
2.180(3)
2.150(3)
2.2856(1)
1.442(5)
1.344(5)
1.367(5)
Co–N(2)
Co–Cl(1)
N1–C(16)
N2–C(1)
N3–C(6)
2.079(3)
2.2750(1)
1.284(5)
1.334(5)
1.332(5)
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
Co(1)–Cl(1)
Co(1)–Cl(2)
N(1)–C(16)
N(1)–C(18)
N(2)–C(1)
N(2)–C(5)
N(3)–C(6)
N(3)–C(7)
2.295(5)
2.072(4)
2.150(5)
2.2718(2)
2.2724(2)
1.285(7)
1.457(7)
1.342(7)
1.345(7)
1.319(7)
1.372(7)
Co(2)–N(5)
Co(2)–N(6)
Co(2)–N(7)
Co(2)–Cl(4)
Co(2)–Cl(3)
N(5)–C(42)
N(5)–C(44)
N(6)–C(27)
N(6)–C(31)
N(7)–C(32)
N(7)–C(33)
2.320(5)
2.070(4)
2.152(4)
2.2566(2)
2.274(2)
1.282(7)
1.437(7)
1.349(7)
1.350(6)
1.324(7)
1.412(7)
Bond angles (°)
N(2)–Co–N(3)
N(3)–Co–N(1)
N(3)–Co–Cl(1)
N(2)–Co–Cl(2)
N(1)–Co–Cl(2)
74.88(1)
144.56(1)
99.55(1)
93.72(9)
102.85(1)
N(2)–Co–N(1)
N(2)–Co–Cl(1)
N(1)–Co–Cl(1)
N(3)–Co–Cl(2)
Cl(1)–Co–Cl(2)
74.83(1)
151.44(1)
98.27(9)
97.04(1)
114.83(5)
Bond angles (°)
N(2)–Co(1)–N(3)
N(2)–Co(1)–N(1)
N(3)–Co(1)–N(1)
N(2)–Co(1)–Cl(1)
N(3)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(2)
N(3)–Co(1)–Cl(2)
N(1)–Co(1)–Cl(2)
Cl(1)–Co(1)–Cl(2)
75.98(2)
74.14(2)
149.73(2)
118.12(1)
97.63(2)
100.60(1)
126.22(1)
95.51(1)
98.10(1)
115.63(7)
N(6)–Co(2)–N(7)
N(6)–Co(2)–N(5)
N(7)–Co(2)–N(5)
N(6)–Co(2)–Cl(3)
N(7)–Co(2)–Cl(3)
N(5)–Co(2)–Cl(3)
N(6)–Co(2)–Cl(4)
N(7)–Co(2)–Cl(4)
N(5)–Co(2)–Cl(4)
Cl(3)–Co(2)–Cl(4)
75.94(2)
73.33(2)
147.25(2)
108.26(2)
104.11(1)
96.05(1)
132.26(1)
94.72(1)
97.55(1)
119.37(9)
is asymmetric with slight difference of Co(1)–Cl(1)
(2.2750(1) A) and Co(1)–Cl(2) (2.2856(1) A), and So three
Co–N bond lengths as Co(1)–N(1) 2.180(3) A, Co(1)–
˚
˚
˚
˚
˚
N(2) 2.079(3) A and Co(1)–N(3) 2.150(3) A, respectively.
Those phenomena are similar to those in its chromium
(III) analogue [13]. In addition, the N–Co–N angles are
74.83(1)°, 77.88(1)° and 144.56(1)°, which are smaller than
those angles found in its chromium (III) analogues [13].
Unlike complex 3b, however, the asymmetric unit of
complex 5b contains the halves of two independent mole-
cules (Fig. 3). In the structure of complex 5b, the two inde-
pendent molecules give slightly different bond lengths and
bond angles (Table 3). Both the coordination geometries
around the cobalt centers in these two molecules are dis-
torted trigonal-bipyramidal due to the significant devia-
tions of the chlorine atoms from the plane N(1)–N(2)–
˚
˚
˚
N(3) (1.6183 A and 2.1936 A in (5b-1), 1.1361 A and
˚
2.5314 A in (5b-2), respectively). In molecule (5b-1), the
˚
cobalt center slightly deviates by 0.0233 A from the trian-
gular plane formed by N(2), Cl(1) and Cl(2), while this
˚
deviation is 0.0421 A in molecule (5b-2). The dihedral
angles are 89.3° and 95.0° in molecule (5b-1) between the
equatorial plane and the pyridyl plane, and the imino-aryl
ring and the benzimidazole ring, which are obviously differ-
ent from the dihedral angles 80.5° and 82.1° in molecule
(5b-2), respectively. In addition, the dihedral angles
between the phenyl ring and the pyridyl ring are largely dif-
ferent as 94.2° in (5b-1) and 75.5° in (5b-2), respectively. In
both molecules, the bond angles subtended by the axial
Co–N bonds (149.73(2)° in (5b-1), and 147.25(2)° in (5b-
2), respectively) are much wider than those of the iron
analogue 5a and cobalt analogue 3b. In each molecule,
the Co–N bond in the equatorial plane is shorter than that
of the two axial Co–N bonds, which is agreeable with those
of complexes 3b and 5a. In addition, the Co–N (imino)
bond length of 5b is obviously longer than that of complex
3b. This effect is due to the introduction of the substituent
at the para-position of the phenyl ring in 5b.
Single crystals of nickel complexes 1c and 2c were
obtained by slow diffusion diethyl ether into their corre-
sponding methanol solutions. Similar to the structure of
cobalt complex 3b, the coordination geometries of 1c and
2c can be described as distorted square pyramidal with
the basal plane composed by three coordination nitrogen
atoms and one chlorine atom. In terms of reconsidering
molecular structures of their analogues ligated by
Fig. 3. Crystal structure of complex 5b showing the two independent
molecules of the asymmetric unit. Thermal ellipsoids are shown at 30%
probability; hydrogen atoms and solvent have been omitted for clarity.

Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
1833
Table 4
2-(1-methyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyri-
˚
Selected bond lengths (A) and angles (°) for complexes 1c and 2c
1c 2c
dines [12b], those nickel complexes are also close to dis-
torted square pyramidal geometry instead of distorted
trigonal-bipyramidal (but it does not mean the previous
express wrong to some extent with considering coordina-
tion geometry around nickel atom). Their molecular struc-
tures are shown in Figs. 4 and 5, respectively, and selected
bond lengths and angles are collected in Table 4.
˚
Bond lengths (A)
Ni–N(1)
Ni–N(2)
Ni–N(3)
Ni–Cl(1)
Ni–Cl(2)
N1–C(16)
N1–C(18)
N2–C(1)
N2–C(5)
N3–C(6)
N3–C(7)
2.156(5)
2.006(5)
2.089(5)
2.2643(2)
2.3129(2)
1.282(7)
1.445(7)
1.348(7)
1.331(7)
1.335(7)
1.385(7)
2.166(3)
2.010(3)
2.089(2)
2.2611(9)
2.3147(1)
1.280(4)
1.445(4)
1.338(4)
1.345(4)
1.333(4)
1.384(4)
The central nickel atom in complex 1c deviates by
˚
0.2359 A from the plane containing N(1), N(2), N(3), while
˚
the Cl(1) deviates by 0.5264 A in the opposite direction.
The basal plane composed by N(1), N(2), N(3) and Cl(1)
is almost coplanar to the pyridyl ring with dihedral angle
of 8.4°, and the pyridyl ring and the benzimidazole ring
are also nearly coplanar with dihedral angle of 8.2°. The
dihedral angles between the phenyl plane and the benz-
imidazole ring, and the phenyl plane with the pyridine ring
are 78.0° and 84.7°, respectively. With the ligands contain-
ing the isopropyl group on benzimidazole ring instead of
methyl one, slightly longer Ni–N bond (Ni–N(3)
Bond angles (°)
N(2)–Ni–N(3)
N(2)–Ni–N(1)
N(3)–Ni–N(1)
N(2)–Ni–Cl(1)
N(3)–Ni–Cl(1)
N(1)–Ni–Cl(1)
N(2)–Ni–Cl(2)
N(3)–Ni–Cl(2)
N(1)–Ni–Cl(2)
Cl(1)–Ni–Cl(2)
76.68(2)
77.40(2)
152.23(2)
153.46(1)
101.95(1)
96.78(1)
94.25(1)
94.99(1)
96.69(1)
112.21(7)
76.89(1)
76.81(1)
149.97(1)
157.81(8)
101.34(8)
97.56(8)
92.13(8)
96.97(8)
98.22(8)
109.99(4)
˚
2.089(5) A) is observed compared with the datum of its
˚
analogue with 2.0701(2) A [12b], meanwhile slightly smal-
ler angle N(1)–Ni–N(3) (152.23(2)°) and wider angle
Cl(1)–Ni–Cl(2) (112.21(7)°) are observed than those angles
in its analogue complex as 152.60(6)° and 110.17(2)°,
respectively [12b]. In addition, the imino C@N bond still
keeps distinctive double-bond character, and two Ni–Cl
linkages show slightly differences, the Ni–Cl(1) being about
˚
0.0486 A shorter than that of Ni–Cl(2).
With ethyl instead of methyl of phenyl ring on imino
group in complex 1c, the molecular structure of complex
2c (Fig. 5) is similar to that of complex 1c, and its selected
bond lengths and angles are listed in Table 4. In the molec-
Fig. 4. Molecular structure of complex 1c. Thermal ellipsoids are shown
at 30% probability; hydrogen atoms and solvent have been omitted for
clarity.
˚
ular structure of 2c, the nickel deviation (0.3417 A) and the
˚
chlorine (Cl(1)) deviation (0.1403 A) from the plane N(1)–
N(2)–N(3) are slightly different to those in complex 1c. The
dihedral angle between the pyridine ring and the benzimid-
azole ring is 19.6° of complex 2c, which is bigger than that
of complex 1c (8.2°). The difference of two Ni–Cl bond dis-
˚
tances shows 0.0536 A in complex 2c, while the corre-
˚
sponding difference is 0.0486 A in complex 1c.
2.3. Catalytic behavior toward ethylene reactivity
2.3.1. Catalytic behavior of iron complexes
Various aluminum-based cocatalysts were used for
exploring the catalytic activity of the iron complexes. Mod-
erate to good activities were obtained with MAO and mod-
ified methylaluminoxane (MMAO) as cocatalysts.
Complex 1a was typically investigated under a range of
reaction conditions, such as different cocatalysts, molar
ratio of cocatalyst to iron and reaction temperature at
Fig. 5. Molecular structure of complex 2c. Thermal ellipsoids are shown
at 30% probability; hydrogen atoms and solvent have been omitted for
clarity.

1834
Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
Table 5
Ethylene oligomerization and polymerization with 1a–6a/MAOa
Entry Compound Al/Fe P (atm) T (°C)
K
Wax (g) Activityb
Oligomer distributionc
P
P
P
P
Oligomer Wax
C4/
C
C6/
C
C8/
C
PC10
/
C
a-Olefin (%)
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
2a
3a
4a
5a
6a
5a
200
500
10
10
10
10
10
10
10
10
10
10
10
30
20
20
20
20
40
60
20
20
20
20
20
20
0.02
1.52
2.34
1.31
1.28
0.02
1.62
0.48
0.02
8.67
3.01
32.0
100
>99
>98
>98
>98
>98
>99
>98
>98
>99
>98
>98
>98
0.52 Trace
0.60 0.27
0.55 0.13
0.54 0.08.
0.52 0.03
0.43 0.10
0.43 0.07
Trace
Trace 29.2
23.2
20.7
22.6
22.9
34.4
26.0
18.4
14.7
20.2
14.7
17.6
32.9
32.5
31.4
30.8
1000
1500
1000
1000
1000
1000
1000
1000
1000
1000
1.08
0.52
0.32
0.12
0.40
0.28
26.6
31.3
28.7
65.6
49.4
59.7
11.1
13.5
13.5
8.4
9
Trace 100
10
11
12
a
0.60 1.12
0.61 0.04
0.58 2.50
4.48
0.16
10.0
30.3
26.0
38.7
20.6
20.5
24.5
19.6
18.8
19.8
29.5
34.7
17.0
Reaction conditions: 5 lmol of catalyst; 10 atm of ethylene; 30 min; 100 mL of toluene.
In units of 105 g (mol of Fe)À1 hÀ1
.
b
P
c
Determined by GC; C signifies the total amounts of oligomers.
10 atm of ethylene. Oligomers were predominant products.
The detailed results are summarized in Table 5. The distri-
bution of oligomers obtained in all cases resembles Schulz–
Flory rules, which is characterized by the constant K,
where K represents the probability of chain propagation
(K = rate of propagation/((rate of propagation) + (rate of
chain transfer) = (moles of Cn+2)/(moles of Cn)) [14] and
the K values are determined by the molar ratio of C14
and C12 fractions.
systems of their analogues with MAO as cocatalyst [12a].
In addition, under the same conditions, the activity of its
analogue 2-(1-methyl-2-benzimidazolyl)-6-(1-aryliminoeth-
yl) pyridyliron complex [12a] was four times higher than
that of complex 1a. In fact, the titled complexes containing
isopropyl substituted benzimidazole are commonly more
soluble than their analogues containing methyl substituted
benzimidazole [12a]. The negative influence might be
caused by other factors. Previously it was concluded that
the increase in net charge of metal center lowers the inser-
tion barrier of ethylene to result in better catalytic activity
in ethylene reaction with nickel systems [15]. The results in
this work are consistent with this conclusion. The less cat-
alytic activity than its analogue with methyl substituted
benzimidazole was caused by the ligand with more elec-
tron-donating isopropyl substituent. The steric nature of
the aromatic substituents may also make an influence on
the activity. However, the substitution of two alkyl groups
(complexes 1a–3a) by two chloro groups (complex 4a) in
the ortho-positions leads to an almost inactive species
(Entries 3 and 7–9, Table 5), which is in line with the results
observed in their catalytic analogues [12a]. This looks
totally different to the correlation between net charge of
metal center and catalytic activity, however, un-monoto-
nous relation of net charge and catalytic activity of iron
(II) catalysts was obtained [16]. Therefore, further experi-
mental and simulation researches are necessary for predict-
ing catalytic activities of designing metal complexes as
catalysts.
2.3.1.1. Ethylene activation in the presence of MAO. When
MAO was employed as the cocatalyst and the Al/Fe molar
ratio was changed from 200 to 1500, the catalytic activity
of 1a firstly increased and then decreased and displayed
the maximum value at the Al/Fe molar ratio of 1000. With
a fixed Al/Fe molar ratio of 1000 using MAO, the reaction
temperature strongly affected the catalytic activity. The
highest activity was obtained at 20 °C (Entry 3, Table 5).
Higher reaction temperatures led to an obvious decrease
in the catalytic activity (Entries 5 and 6, Table 5), most
likely due to the decomposition of some active centers
and the lower solubility of ethylene in toluene. It is well
known that elevated ethylene pressure promotes higher
activities; this phenomenon was also observed with the iron
catalytic system. For 5a/MAO system, its reactivity for
oligomers and polymers were both enhanced sharply at
30 atm of ethylene pressure (Entry 12, Table 5).
To compare the effect of the ligand environments on the
catalytic behaviors, all iron complexes 1a–6a were investi-
gated under the same conditions (Al/Fe molar ratio of
1000 and 20 °C). The 2,4,6-trimethyl-substituted complex
5a performed the highest catalytic activity (Entry 10, Table
5). The variation of the R substituent on the phenyl ring of
ligands resulted in changes of the catalytic performance.
For complexes bearing alkyl substituents on the phenyl
ring, it was observed that a decrease in steric hindrance
of the R1 group led to an enhanced activity with the order
as 1a > 2a > 3a. This observation was reversed in catalytic
In addition, it seems that the substituent in the para-
position of the imino-aryl group has a beneficial influence
on the activity. The complexes 5a and 6a, which respec-
tively bear an electron-donating methyl group and an elec-
tron-withdrawing bromo group in the para-position of the
aryl ring, exhibited much higher activities than the corre-
sponding complex 1a. This is in agreement with the results
observed for the chromium catalysts [13] and 2-quinoxali-
nyl-6-iminopyridyl iron catalysts [11b]. Furthermore,

Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
1835
catalyst 5a with a less bulky and electron-donating substi-
tuent exhibited higher catalytic activity than catalyst 6a
with bromo group, which could be the combined results
of the electronic and steric effects.
This phenomenon is different from what observed using
MAO as the cocatalyst.
2.3.2. Ethylene oligomerization by cobalt and nickel
complexes
2.3.1.2. Ethylene activation in the presence of MMAO.
After routine selection of the ratio of MMAO to iron cat-
alyst, good catalytic activity was observed at an Al/Fe
molar ratio of 1000. Therefore, the catalytic behaviors of
all tridentate iron complexes were investigated with a fixed
Al/Fe molar ratio of 1000, and their results are summa-
rized in Table 6. All the complexes displayed moderate
catalytic activities for ethylene oligomerization with high
a-olefin selectivity (>98%) at 10 atm of ethylene pressure.
A noticeable effect of the alkyl substituents on the aryl ring
can be observed. For catalysts bearing alkyl groups in the
ortho-aryl positions, a reduction of steric bulk resulted in
increased activity of the complexes. Hence, complex
1a with methyl groups showed better activities of
5.96 Â 105 g (mol of Fe)À1 hÀ1 than complexes 2a (with
ethyl) and 3a (with isopropyl) at 10 atm of ethylene. This
followed the same tendency as the iron complexes with
MAO as the cocatalyst discussed above, and such observa-
tions were also found in literature [17]. Similar to the result
of system 1a/MAO, under the same conditions, in the pres-
ence of MMAO, the activity of its analogue 2-(1-methyl-2-
benzimidazolyl)-6-(1-aryliminoethyl) pyridyliron complex
[12a] was two times higher than that of complex 1a. In
the presence of MMAO, the electronic effect on catalytic
activity also followed the same tendency as the iron/
MAO system. Complex 4a with dichloro-phenyl group
showed much lower activity than other catalysts. The intro-
duction of electron-donating substituent in the para-posi-
tion of the phenyl group resulted in increased activity
(Entry 5, Table 6). Complex 5a, which bears 2,4,6-trimeth-
ylphenyl group showed better catalytic activity than its
analogues bearing 2,6-dialkylphenyl group (Entry 5 vs.
Entries 1–3, Table 6). Additionally, complex 6a, showed
relatively lower activity than 5a and comparable activity
to its analogue complex 3a, which demonstrated that the
electron-withdrawing substituent in the para-position of
the aryl ring had no obvious influence on the reactivity.
The cobalt (II) complexes 1b–6b were systematically
investigated for the oligomerization of ethylene. When
Et2AlCl was used as cocatalyst, complex 1b showed higher
ethylene activity with high selectivity of a-olefins than
those with MAO or MMAO as cocatalyst. The further
detailed investigations were carried out with cocatalyst of
Et2AlCl, mainly producing butanes. It is notable that
cobalt systems are less active than their iron analogues,
and this is apparent for complexes ligated by
bis(imino)pyridines [18] as well as other systems [19,20].
The influences of the Al/Co molar ratio and the reaction
temperature on ethylene oligomerization were investigated
in detail with complex 1b. Variation of the Al/Co molar
ratio from 400 to 900 significantly affected the oligomeriza-
tion activity, and the optimum oligomerization activity was
observed at the Al/Co molar ratio of 700. The catalytic per-
formance of cobalt complex 1b was greatly affected by the
reaction temperature and the highest activity was observed
at 30 °C (Entry 6, Table 7). In addition, increasing the tem-
perature leads to a rapid decrease in the selectivity for a-
olefins such as 97.5% at 20 °C and 86.6% at 60 °C (Entries
9–11, Table 7).
As shown in Table 7, the substituents of the ligands in
the cobalt complexes significantly affect the catalytic
activity of ethylene oligomerization. Among complexes
1b–3b, 1b with the methyl groups in the ortho-positions
of the phenyl ring, showed the highest activity, and the
activity decreased in the order 1b (with substituent of
dimethyl) > 2b (with diethyl) > 3b (with diisopropyl)
under identical reaction conditions, but a little influence
was observed on the selectivity of a-olefins. Complex
4b bearing 2,6-dichlorophenyl group showed lower
activity than its analogue 2b, but better activity than
3b. The same tendency was observed in the correspond-
ing 2-(1-methyl-2-benzimidazolyl)-6-(1-aryliminoethyl)pyri-
dylcobalt systems [12a]. The functional groups on the
para-position of the phenyl ring in complexes 5b and
Table 6
Ethylene oligomerization and polymerization with 1a–6a/MMAOa
Entry
Compound
P (atm)
K
Wax (g)
Activityb
Oligomer distributionc
P
P
P
P
Oligomer
Wax
C4/
C
C6/
C
C8/
C
PC10
/
C
a-Olefin (%)
1
2
3
4
5
6
7
a
1a
2a
3a
4a
5a
6a
5a
10
10
10
10
10
10
30
0.58
0.45
0.07
0.02
0.03
Trace
1.40
0.05
2.70
5.96
3.57
1.41
0.03
8.24
1.52
32.0
0.28
0.08
0.12
Trace
5.60
0.20
10.8
28.5
46.6
69.8
83.7
35.2
31.6
45.2
20.2
22.2
19.6
16.3
22.2
19.6
24.3
21.5
15.8
7.3
29.8
15.4
3.3
>98
>98
>98
>99
>98
>98
>98
0.49
0.59
0.45
20.1
14.4
20.0
22.5
34.4
10.5
Reaction conditions: 5 lmol of catalyst; 10 atm of ethylene; 30 min; 20 °C; Al/Fe = 1000; 100 mL of toluene.
b
c
In units of 105 g (mol of Fe)À1 hÀ1
.
P
Determined by GC; C signifies the total amounts of oligomers.

1836
Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
Table 7
Ethylene oligomerization with 1b–6ba
Entry
Compound
Cocatalyst
Al/Co
T (°C)
Activityb
Oligomer distribution
P
P
C4/
C
C6/
C
a-Olefin (%)
1
2
3
4
5
6
7
8
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
2b
3b
4b
5b
MAO
1000
1000
200
400
600
700
800
900
700
700
700
700
700
700
700
700
20
20
20
30
30
30
30
30
20
40
60
30
30
30
30
30
0.14
0.22
3.97
12.1
14.1
16.2
6.40
5.79
4.77
7.78
6.92
11.0
5.59
6.81
17.8
9.03
100
100
100
99.0
99.0
97.5
96.9
98.5
96.9
99.0
98.5
98.6
93.0
86.6
90.3
93.5
92.3
92.5
91.3
MMAO
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
99.2
97.9
94.9
100
0.8
2.1
5.1
100
100
9
10
11
12
13
14
15
16
93.3
90.6
89.7
92.8
91.8
91.9
95.2
6.7
9.4
10.3
7.2
8.2
8.1
6b
4.8
P
Determined by GC; C signifies the total amounts of oligomers.
a
Reaction conditions: 5 lmol of catalyst; 30 min; 100 mL of toluene.
b
In units of 104 g (mol of Co)À1 hÀ1
.
Table 8
Ethylene oligomerization with 1c–6ca
Entry
Complex
Cocatalyst
Al/Ni
T (°C)
Activityb
Oligomer distributionc
P
P
C4/
C
C6/
C
a-Olefin (%)
1
2
3
4
5
6
7
8
5c
5c
5c
5c
5c
5c
5c
5c
5c
5c
1c
2c
3c
4c
6c
5c
MAO
1000
1000
200
100
300
400
500
400
400
400
400
400
400
400
400
400
20
20
20
20
20
20
20
30
40
60
30
30
30
30
30
30
0.36
0.59
2.40
0.39
3.09
4.49
3.42
17.4
12.8
2.15
12.0
8.95
6.29
3.08
7.31
52.0
100
100
98.5
94.5
93.3
93.7
95.1
91.2
91.4
48.6
67.7
78.9
75.3
82.6
87.2
91.2
86.5
21.4
MMAO
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
97.8
97.4
99.0
97.5
97.4
89.7
97.5
96.2
93.1
94.8
95.6
96.9
95.7
95.3
2.2
2.6
1.0
2.5
2.6
10.3
2.5
3.8
6.9
5.2
4.4
3.1
4.3
3.5
9
10
11
12
13
14
15
16d
a
Reaction conditions: 5 lmol of catalyst; 10 atm of ethylene; 30 min; 100 mL of toluene.
b
c
In units of 105 g (mol of Ni)À1 hÀ1
.
P
Determined by GC; C signifies the total amounts of oligomers.
20 equiv. of PPh3.
d
6b slightly affected the catalytic activities, in which 5b
exhibited better activity than 6b.
decreasing activity, but higher selectivity of a-olefins
(Entries 11–13, Table 8). Furthermore, the complex con-
tained electron-withdrawing substituents on aniline
showed lower activity than that with alkyl substituents.
For example, complex 4c showed lower catalytic activity
than complexes 1c, 2c and 3c. The similar result was also
obtained by complex 6c comparing with 5c. In terms of
electronic effect, it can be concluded that the introduc-
tion of electron-withdrawing groups led to lower
In similar manner, ethylene oligomerization with
nickel analogues 1c–6c/Et2AlCl systems was investigated
under the optimum conditions (Al/Ni molar ratio of
400 and 30 °C). Variation of the R1 group at the
ortho-positions of the imino-N aryl ring resulted in
strong influence on the catalytic performance. The
increase of steric hindrance of the R1 group led to

Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
1837
catalytic activity in the nickel-based catalytic system.
This is consistent to the simulation results [15] and late
transition metal complexes [21]. As observed in the iron
catalysts, the nickel complexes containing isopropyl
group (in current work) instead of methyl group [12b]
perform lower catalytic activities.
Previous studies on nickel-based catalysts have demon-
strated that incorporating PPh3 into catalytic systems led
to higher activity and longer catalyst lifetime
[9b,12b,22,23]. Therefore, the oligomerization of 5c/
Et2AlCl was investigated with addition of PPh3. The addi-
tion of 20 equiv. PPh3 lead to three times higher catalytic
activity of 52.0 Â 105 g (mol of Ni)À1 hÀ1 than that without
PPh3. Moreover, larger amounts of C6 and C8 were
observed (Entry 17, Table 8). This phenomenon may be
attributed to the fact that the active nickel species are coor-
dinated with auxiliary PPh3, then protected from the impu-
rities in the catalytic reactants.
(Et2AlCl, 1.70 M in hexane) was purchased from Acros
Chemicals. All other reagents were purchased from Aldrich
or Acros Chemicals; the boiling range of light petroleum is
60–90 °C and the type of silica gel used is 200–300 mesh.
1H NMR spectra were recorded on a Bruker DMX 300
MHz instrument at ambient temperature using TMS as
an internal standard, while 13C NMR spectra were
recorded on a Bruker DMX 75 MHz. IR spectra were
recorded on a Perkin–Elmer System 2000 FT-IR spectrom-
eter. Elemental analysis was carried out using an HPMOD
1106 microanalyzer. GC analysis was performed with a
Carlo Erba Strumentazione gas chromatograph equipped
with a flame ionization detector and a 30 m (0.25 mm
i.d., 0.25 lm film thickness) DM-1 silica capillary column.
The yield of oligomers was calculated by referencing to the
mass of the solvent on the basis of the prerequisite that the
mass of each fraction was approximately proportional to
its integrated area in the GC trace. Selectivity for the linear
a-olefin was defined as (amount of linear a-olefin of all
fractions)/(total amount of oligomer products) in percent.
3. Conclusion
A series of iron (II), cobalt (II) and nickel (II) com-
plexes bearing 2-(1-isopropyl- 2-benzimidazolyl)-6-(1-
aryliminoethyl)pyridine ligands have been synthesized,
characterized and evaluated as catalyst precursors in eth-
ylene activation. Their results confirm that the increase in
net charge of metal center lowers the insertion barrier of
ethylene to result in better catalytic activity in ethylene
reaction. For all titled complexes, the nature of ligand
environments and the reaction parameters, such as differ-
ent cocatalysts, molar ratio of cocatalyst to metal and
reaction temperature, play important roles in influencing
the catalytic activity. Upon treatment with MAO or
MMAO, the iron (II) complexes showed good catalytic
activities for ethylene oligomerization with very high a-
olefin selectivity and polymerization for polyethylene
wax. Regarding to the catalytic systems of cobalt and
nickel complexes, the best suitable cocatalyst is Et2AlCl.
The cobalt catalysts showed considerable to moderate
catalytic activities. The nickel catalytic systems enable
oligomerization of ethylene to mainly dimmerize for
butenes with high activity and moderate to high selectiv-
ity of a-olefins. The addition of PPh3 into the nickel cat-
alytic system can lead to higher catalytic activity.
4.2. Preparation of the (E)-4-bromo-N-(1-(6-(1-isopropyl-
1H-benzo[d]imidazol-2-yl)pyridin-2-yl)ethylidene)-2,6-
dimethylbenzenamine (6)
In a manner similar to that described for 1–5 [13], the
ligand 6 was synthesized as a white solid in 15% yield.
1
M.p.: 170–171 °C. H NMR (300 MHz, CDCl3, TMS): d
8.44 (d, 1H, J = 7.9 Hz, Py), 8.39 (d, 1H, J = 7.7 Hz, Py),
7.99 (t, 1H, J = 7.9, 7.7 Hz, Py), 7.86 (m, 1H, Ph), 7.69 (m,
1H, Ph), 7.32 (m, 2H, Ph), 7.23 (s, 2H, Ph), 6.04 (m, 1H,
CH), 2.03 (s, 6H, CH3), 1.76 (d, 6H, J = 6.9 Hz, CH3). 13
C
NMR (75 MHz, CDCl3, TMS): d 167.4, 155.0, 150.1,
147.7, 143.6, 137.7, 134.6, 130.6, 127.8, 127.0, 123.0, 122.4,
121.3, 120.7, 115.8, 113.0, 49.1, 21.5, 17.9, 16.7. IR (KBr disc,
cmÀ1): 2972, 1656, 1570, 1454, 1399, 1204, 853, 823, 771, 749.
Anal. Calc. for C25H25BrN4 (461.4): C, 65.08; H, 5.46; N,
12.14. Found: C, 65.28; H, 5.57; N, 11.94%.
4.3. Synthesis of iron complexes 1a–6a
General procedure: The complexes 1a–6a were synthe-
sized by the reaction of FeCl2 Á 4H2O with the correspond-
ing ligands in ethanol. A typical synthetic procedure for
complex 1a can be described as follows. The ligand 1
(382.5 mg, 1.0 mmol) and FeCl2 Á 4H2O (198.8 mg,
1.0 mmol) were added to a Schlenk tube that was purged
three times with nitrogen and then charged with freshly dis-
tilled ethanol. The solution turned blue immediately. After
the reaction mixture being stirred at room temperature for
12 h, diethyl ether was added to precipitate the complex.
The precipitate was filtered, washed with diethyl ether
and finally was dried under vacuum to give the pure prod-
uct as a blue powder in 90% yield. FT-IR (KBr disc, cmÀ1):
2970, 1593 (mC@N), 1466, 1383, 1212, 1159, 796, 749. Anal.
Calc. for C25H26Cl2FeN4 (509.3): C, 58.96; H, 5.15; N,
11.00. Found: C, 58.86; H, 5.47; N, 10.80%.
4. Experimental
4.1. General considerations
All manipulations of air- and moisture-sensitive com-
pounds were carried out under a nitrogen atmosphere
using standard Schlenk techniques. Toluene was refluxed
over sodium-benzophenone and distilled under nitrogen
prior to use. Methylaluminoxane (MAO) was purchased
from Albemarle as a 1.46 M solution in toluene. Modified
methylaluminoxane (MMAO-3A, 1.93 M in heptane) was
purchased from Akzo Corp. Diethylaluminum chloride

1838
Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
Compound 2a was obtained as a blue powder in 99%
1434, 1402, 1379, 1276, 1163, 1133, 1097, 1022, 771, 754.
Anal. Calc. for C23H20Cl4CoN4 (553.2): C,49.94; H, 3.64;
N, 10.13. Found: C, 50.09; H, 3.56; N, 10.18%.
yield. FT-IR (KBr disc, cmÀ1): 2972, 1593 (mC@N), 1463,
1380, 1212, 1160, 1108, 1014, 814, 792, 754. Anal. Calc.
for C27H30Cl2FeN4 (537.3): C, 60.35; H, 5.63; N, 10.43.
Found: C, 59.95; H, 5.73; N, 10.09%.
Compound 5b was isolated as a green powder in 74%
yield. FT-IR (KBr disc, cmÀ1): 2974, 1592 (mC@N), 1464,
1434, 1406, 1380, 1282, 1159, 1132, 1099, 1019, 815, 752.
Anal. Calc. for C26H28Cl2CoN4 (526.4): C, 59.33; H,
5.36; N, 10.64. Found: C, 59.48; H, 5.46; N, 10.76%.
Compound 6b was isolated as a green powder in 93%
yield. FT-IR (KBr disc, cmÀ1): 2985, 1591 (mC@N), 1467,
1432, 1405, 1380, 1215, 1161, 1133, 1099, 1019, 814, 749.
Anal. Calc. for C25H25BrCl2CoN4 (591.2): C, 50.79; H,
4.26; N, 9.48. Found: C, 50.65; H, 4.58; N, 9.78%.
Compound 3a was obtained as a blue powder in 95%
yield. FT-IR (KBr disc, cmÀ1): 2965, 1592 (mC@N), 1462,
1381, 1334, 1161, 1132, 814, 792, 752. Anal. Calc. for
C29H34Cl2FeN4 (565.4): C, 61.61; H, 6.06; N, 9.91. Found:
C, 61.59; H, 6.36; N, 9.98%.
Compound 4a was obtained as a blue powder in 92%
yield. FT-IR (KBr disc, cmÀ1): 2979, 1599 (mC@N), 1463,
1380, 1336, 1203, 1162, 1132, 844, 787, 750. Anal. Calc.
for C23H20Cl4FeN4 (550.1): C, 50.22; H, 3.66; N, 10.19.
Found: C, 50.02; H, 3.36; N, 9.98%.
4.5. Synthesis of nickel complexes 1c–6c
Compound 5a was obtained as a blue powder in 99%
yield. FT-IR (KBr disc, cmÀ1): 2974, 1591 (mC@N), 1462,
1380, 1334, 1217, 1158, 1132, 1014, 814, 751. Anal. Calc.
for C26H28Cl2FeN4 (523.3): C, 59.68; H, 5.39; N, 10.71.
Found: C, 59.80; H, 5.44; N, 10.51%.
Compound 6a was obtained as a blue powder in 80%
yield. FT-IR (KBr disc, cmÀ1): 2970, 1591 (mC@N), 1465,
1379, 1334, 1214, 1160, 1132, 1016, 812, 748. Anal. Calc.
for C25H25BrCl2FeN4 (588.2): C, 51.05; H, 4.28; N, 9.53.
Found: C, 51.00; H, 4.48; N, 9.72%.
General procedure: The nickel complexes 1c–6c were
also prepared by the same procedure as for 1a–6a and
1b–6b.
described as follows.
A
typical synthetic procedure of 1ccan be
solution of NiCl2 Á 6H2O
A
(237.7 mg, 1.0 mmol) in ethanol was added dropwise to
a solution of ligand 1 (382.5 mg, 1.0 mmol) in ethanol
at room temperature. The color of the solution changed
immediately. The reaction mixture was stirred at room
temperature for 10 h then precipitated with diethyl ether.
The resulting precipitate was collected, washed with
diethyl ether and dried in vacuum. Finally, the objected
product was obtained as a yellow powder in 82% yield.
FT-IR (KBr disc, cmÀ1): 2978, 1593 (mC@N), 1468,
1407, 1335, 1189, 1130, 796, 750. Anal. Calc. for
C25H26Cl2N4Ni (512.1): C, 58.63; H, 5.12; N, 10.94.
Found: C, 58.68; H, 5.37; N, 10.76%.
4.4. Synthesis of cobalt complexes 1b–6b
General procedure: The cobalt complexes 1b–6b were
prepared by the same procedure as for 1a–6a and were
obtained as green powder. The synthetic procedure of
1b can be described as follows. A solution of anhydrous
CoCl2 (129.8 mg, 1.0 mmol) in absolute ethanol was
Compound 2c was isolated as a yellow powder in 98%
yield. FT-IR (KBr disc, cmÀ1): 2973, 1594 (mC@N), 1467,
1407, 1378, 1279, 1217, 1163, 1133, 1108, 1021, 790, 749.
Anal. Calc. for C27H30Cl2N4Ni (540.2): C, 60.04; H, 5.60;
N, 10.37. Found: C, 60.08; H, 5.56; N, 10.21%.
Compound 3c was isolated as a yellow powder in 93%
yield. FT-IR (KBr disc, cmÀ1): 2966, 1595 (mC@N), 1467,
1407, 1378, 1156, 1122, 790, 749. Anal. Calc. for
C29H34Cl2N4Ni (568.2): C, 61.30; H, 6.03; N, 9.86. Found:
C, 61.18; H, 5.98; N, 9.79%.
Compound 4c was isolated as a yellow powder in 79%
yield. FT-IR (KBr disc, cmÀ1): 2966, 1593 (mC@N), 1467,
1406, 1377, 1335, 1228, 1161, 1132, 787, 751. Anal. Calc.
for C23H20Cl4N4Ni (552.9): C, 49.96; H, 3.65; N, 10.13.
Found: C, 50.01; H, 3.50; N, 10.05%.
Compound 5c was isolated as a yellow powder in 94%
yield. FT-IR (KBr disc, cmÀ1): 2977, 1591 (mC@N), 1466,
1407, 1380, 1335, 1221, 1159, 1134, 813, 751. Anal. Calc.
for C26H28Cl2N4Ni (526.1): C, 59.35; H, 5.36; N, 10.65.
Found: C, 59.45; H, 5.40; N, 10.55%.
added dropwise to the solution of the ligand
1
(382.5 mg, 1.0 mmol) in absolute ethanol. Immediately
the color of the solution changed and some green precip-
itate formed. Then the reaction mixture was stirred at
room temperature for 9 h then diluted with diethyl ether.
The resulting precipitate was filtered, washed with diethyl
ether three times and dried in vacuum. The desired com-
plex was obtained as a green powder in 76% yield. FT-
IR (KBr disc, cmÀ1): 2977, 1593 (mC@N), 1470, 1407,
1385, 1280, 1214, 1160, 1101, 809, 749. Anal. Calc. for
C25H26Cl2CoN4 (512.3): C, 58.61; H, 5.12; N, 10.94.
Found: C, 58.86; H, 5.15; N, 10.84%.
Compound 2b was isolated as a green powder in 78%
yield. FT-IR (KBr disc, cmÀ1): 2971, 1592 (mC@N), 1465,
1404, 1378, 1278, 1215, 1163, 1132, 1108, 1021, 789, 749.
Anal. Calc. for C27H30Cl2CoN4 (540.4): C, 60.01; H,
5.60; N, 10.37. Found: C, 59.96; H, 5.56; N, 10.08%.
Compound 3b was isolated as a green powder in 82%
yield. FT-IR (KBr disc, cmÀ1): 2965, 1591 (mC@N), 1464,
1405, 1380, 1281, 1163, 1132, 1100, 1018, 793, 752. Anal.
Calc. for C29H34Cl2CoN4 (568.5): C, 61.27; H, 6.03; N,
9.86. Found: C, 59.99; H, 6.07; N, 9.83%.
Compound 6c was isolated as a yellow powder in 80%
yield. FT-IR (KBr disc, cmÀ1): 2979, 1592 (mC@N), 1468,
1409, 1382, 1335, 1279, 1217, 1159, 1135, 806, 749. Anal.
Calc. for C25H25BrCl2N4Ni (591.0): C, 50.81; H, 4.26; N,
9.48. Found: C, 50.76; H, 4.50; N, 9.76%.
Compound 4b was isolated as a green powder in 64%
yield. FT-IR (KBr disc, cmÀ1): 2983, 1591 (mC@N), 1466,

Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
1839
4.6. Procedure for ethylene oligomerization and
polymerization
tration, washed with ethanol and water, and dried under
vacuum to constant weight.
Ethylene oligomerization and polymerization were per-
formed in a stainless steel autoclave (0.5 L capacity)
equipped with a gas ballast through a solenoid clave for
continuous feeding of ethylene at constant pressure. A
100 mL amount of toluene containing the catalyst precur-
sor was transferred to the fully dried reactor under a nitro-
gen atmosphere. The required amount of cocatalyst
(MAO, MMAO, or Et2AlCl) was then injected into the
reactor via a syringe. At the reaction temperature, the reac-
tor was sealed and pressurized to high ethylene pressure,
and the ethylene pressure was maintained with 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 chromatography (GC) for determin-
ing the composition and mass distribution of oligomers
obtained. Then the residual reaction solution was
quenched with 5% hydrochloric acid in ethanol. The pre-
cipitated low-molecular-weight waxes were collected by fil-
4.7. X-ray crystallographic studies
All of the crystals of 5a, 3b, 5b, 1c and 2c suitable for
X-ray diffraction analysis were obtained by laying diethyl
ether on a methanol solution at room temperature.
With graphite-monochromated Mo Ka radiation (k =
˚
0.71073 A), single-crystal X-ray diffraction studies for 3b,
1c and 2c were carried out on a Bruker SMART 1000
CCD diffractometer, while the intensity data for crystals
5a and 5b were collected on a Rigaku RAXIS Rapid IP dif-
fractometer. Cell parameters were obtained by global
refinement of the positions of all collected reflections.
Intensities were corrected for Lorentz and polarization
effects and empirical absorption. The structures of 5a, 3b,
5b, 1c and 2cwere solved by direct methods and refined
by full-matrix least squares on F2. All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were
placed in calculated positions. Structure solution and
refinement were performed by using the SHELXL-97 package
Table 9
Crystal data and refinement details for 5a, 3b, 5b, 1c, and 2c
5a
3b
5b
1c
2c
Empirical formula
Formula weight
Crystal color
C
523.27
Blue
26H28Cl2FeN4
C30H38Cl2CoN4O
600.47
Green
C26H28Cl2Co N4
526.35
Green
C25H26Cl2N4Ni
512.11
Green
C27H30Cl2N4Ni
540.16
Green
Temperature(K)
293(2)
0.71073
Orthorhombic
Pca21
17.698(4)
11.800(2)
24.482(5)
90
90
90
5113.1(2)
8
1.360
293(2)
293(2)
293(2)
293(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21
9.6001(2)
13.2098(2)
12.5413(2)
90
99.6100(1)
90
1568.11(5)
2
0.71073
Orthorhombic
Pca21
17.595(4)
11.824(2)
24.446(5)
90
90
90
5085.6(2)
8
1.375
0.71073
Monoclinic
P21/n
11.0385(6)
15.8136(1)
14.3146(8)
90
107.212(3)
90
2386.8(2)
4
0.71073
Triclinic
P
Crystal system
Space group
˚
a (A)
8.0041(4)
10.9729(6)
15.4537(9)
82.114(2)
86.097(2)
73.549(2)
1288.79(1)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
Volume (A )
Z
Dcalc (Mg mÀ3
)
1.272
0.746
630
1.425
1.057
1064
1.392
0.983
564
l (mmÀ1
F(000)
)
0.820
2176
0.906
2184
Crystal size (mm)
Limiting indices
0.27 Â 0.16 Â 0.06 0.26 Â 0.24 Â 0.20 0.20 Â 0.18 Â 0.16 0.40 Â 0.33 Â 0.30 0.33 Â 0.25 Â 0.20
À21 6 h 6 21,
À14 6 k 6 14,
À29 6 l 6 28
27168
À12 6 h 6 12,
À17 6 k 6 14,
À16 6 l 6 16
17452
À22 6 h 6 22,
À15 6 k 6 15,
À31 6 l 6 31
36543
À14 6 h 6 14,
À19 6 k 6 21,
À14 6 l 6 19
23104
À6 6 h 6 10,
À14 6 k 6 14,
À20 6 l 6 20
16572
Number of reflections collected
Number of unique reflections
Rint
8852
6475
11102
5893
6339
0.1121
0.0375
0.0722
0.1664
0.0252
Completeness (%) to (h)
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r (I)]
99.9 (2.07–25.00)
Empirical
8852/1/596
1.253
R1 = 0.0998
wR2 = 0.2006
R1 = 0.1190
wR2 = 0.2087
0.760 and À0.434
98.7 (1.65–28.30)
Empirical
6475/1/345
1.071
R1 = 0.0493
wR2 = 0.1196
R1 = 0.0669
wR2 = 0.1292
0.378 and À0.202
99.9 (1.67–27.43)
Empirical
11102/1/595
0.847
R1 = 0.0491
wR2 = 0.0993
R1 = 0.1083
wR2 = 0.1119
0.353 and 0.266
98.9 (1.97–28.33)
Empirical
5893/0/290
0.986
R1 = 0.0846
wR2 = 0.1406
R1 = 0.2065
wR2 = 0.1823
0.373 and À0.464
98.3 (1.33–28.35)
Empirical
6339/0/301
1.049
R1 = 0.0539
wR2 = 0.1450
R1 = 0.0724
wR2 = 0.1661
1.556 and À1.151
R indices (all data)
À3
˚
Largest difference in peak and hole (e A
)

1840
Y. Chen et al. / Journal of Organometallic Chemistry 693 (2008) 1829–1840
(c) S. Jie, S. Zhang, K. Wedeking, W. Zhang, H. Ma, X. Lu, Y. Deng,
W.-H. Sun, C.R. Chim. 9 (2006) 1500–1509;
(d) S. Jie, S. Zhang, W.-H. Sun, X. Kuang, T. Liu, J. Guo, J. Mol.
Catal. A: Chem. 269 (2007) 85–96;
(e) L. Wang, W.-H. Sun, L. Han, H. Yang, Y. Hu, X. Jin, J. Organomet.
Chem. 658 (2002) 62–70;
[24]. Crystal data and processing parameters for 5a, 3b, 5b,
1c and 2c are summarized in Table 9.
Acknowledgements
This work was supported by NSFC No. 20674089 and
MOST No. 2006AA03Z553.
(f) M. Zhang, S. Zhang, P. Hao, S. Jie, W.-H. Sun, P. Li, X. Lu, Eur. J.
Inorg. Chem. (2007) 3816–3826;
(g) M. Zhang, P. Hao, W. Zuo, S. Jie, W.-H. Sun, J. Organomet.
Chem. 693 (2008) 483–491.
Appendix A. Supplementary material
[10] W.-H. Sun, K. Wang, K. Wedeking, D. Zhang, S. Zhang, J. Cai, Y.
Li, Organometallics 26 (2007) 4781–4790.
CCDC 670656, 670657, 670658, 670659 and 670660 con-
tain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.02.007.
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