Synthesis and characterization of iron and cobalt dichloride bearing 2-quinoxalinyl-6-iminopyridines and their catalytic behavior toward ethylene reactivity

Article abstract of DOI:10.1016/j.jorganchem.2007.04.027

The 1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethanone was synthesized in order to prepare a series of N-(1-(6-(quinoxalin-2-yl)pyridine-2-yl)ethylidene)benzenamines (L1-L7), which provided new alternative N^∧N^∧N tridentate ligands coordinating with iron(II) and cobalt(II) dichloride to form complexes of general formula LFeCl₂ (1-7) and LCoCl₂ (8-14). All organic compounds were fully characterized by NMR, IR spectroscopic and elemental analysis along with and magnetic susceptibilities and metal complexes were examined by IR spectroscopic and elemental analysis, while their molecular structures (L1, L4, 1, 4, 10, 13) were confirmed by single crystal X-ray diffraction analysis. Upon activation with methylaluminoxane (MAO), all iron complexes gave good catalytic activities for ethylene reactivity (oligomerization and polymerization), while their cobalt analogues showed moderate activities toward ethylene oligomerization with modified methylaluminoxane (MMAO). Various reaction parameters were investigated for better catalytic activities, the higher activities were observed at elevated ethylene pressure. The iron and cobalt complexes with para-methyl substituents of aryl group linked on imino group showed highest activity.

Full text of DOI:10.1016/j.jorganchem.2007.04.027

Journal of Organometallic Chemistry 692 (2007) 4506–4518
www.elsevier.com/locate/jorganchem
Synthesis and characterization of iron and cobalt dichloride
bearing 2-quinoxalinyl-6-iminopyridines and their catalytic
behavior toward ethylene reactivity
a,
a
a
a
Wen-Hua Sun *, Peng Hao , Gang Li a,b, Shu Zhang , Wenqing Wang ,
c
a
b,
*
Jianjun Yi , Maliha Asma , Ning Tang
a
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
b
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
Petrochemical Research Institute, PetroChina Company Limited, No. 20 Xueyuan Road, Beijing 100083, China
c
Received 14 February 2007; received in revised form 16 April 2007; accepted 20 April 2007
Available online 25 April 2007
Dedicated to Prof. Dr. Gerhard Erker on the occasion of his 60th birthday.
Abstract
The 1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethanone was synthesized in order to prepare a series of N-(1-(6-(quinoxalin-2-yl)pyridine-2-
yl)ethylidene)benzenamines (L1–L7), which provided new alternative NꢀNꢀN tridentate ligands coordinating with iron(II) and cobalt(II)
dichloride to form complexes of general formula LFeCl2 (1–7) and LCoCl2 (8–14). All organic compounds were fully characterized by
NMR, IR spectroscopic and elemental analysis along with and magnetic susceptibilities and metal complexes were examined by IR spec-
troscopic and elemental analysis, while their molecular structures (L1, L4, 1, 4, 10, 13) were confirmed by single crystal X-ray diffraction
analysis. Upon activation with methylaluminoxane (MAO), all iron complexes gave good catalytic activities for ethylene reactivity (olig-
omerization and polymerization), while their cobalt analogues showed moderate activities toward ethylene oligomerization with modified
methylaluminoxane (MMAO). Various reaction parameters were investigated for better catalytic activities, the higher activities were
observed at elevated ethylene pressure. The iron and cobalt complexes with para-methyl substituents of aryl group linked on imino group
showed highest activity.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: 2-Quinoxalinyl-6-iminopyridines; Iron and cobalt complex; Ethylene oligomerization; Ethylene polymerization
1. Introduction
merization. Driven by academic and industrial consider-
ations, new catalysts and catalytic systems are pursued
for high catalytic activity and high linear a-olefins selectiv-
ity. Inspired by the SHOP process using nickel complex
bearing PꢀO ligands as catalyst [1b,1c,4], nickel complexes
as catalysts have drawn much attentions and their progress
has been well documented in recent several review articles
[5]. Breakthroughs in organometallic chemistry and new
metal complexes as catalysts for ethylene catalytic reac-
tions were recorded with the pioneering works by Gibson
group and Brookhart group employing bis(imino)pyridyl
iron and cobalt complexes as highly active catalysts for
The importance of a-olefins as substances with various
applications has generally been recognized, and they are
mainly produced by three full range processes of ethylene
oligomerization by BP, Chevron Phillips and Shell compa-
nies [1] in addition to on-purpose range process of Phillips
[2] and Sasol process [3] for ethylene trimerization or tetra-
*
Corresponding authors. Tel.: +86 10 62557955; fax: +86 10 62618239
(W.-H. Sun).
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.04.027

W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
4507
ethylene polymerization [6] and oligomerization [7]. Exten-
sive research on bis(imino)pyridyl iron complexes has been
focused upon the understanding of the active species or
intermediates [8], controlling the products of polymers
and oligomers and improving the catalytic activities
through varying the steric and electronic characteristics
of complexes [5a,5c,5e,9]. Especially, iron and cobalt cat-
alysts for ethylene reactivities showed not only highly cat-
alytic activities but also the unique properties of resultant
polyethylene or oligomers with highly linear and vinyl-
type features, which rooted to the absence of ‘‘chain walk-
ing’’ during ethylene insertion and is characteristically dif-
ferent from nickel catalytic system. Currently, there is only
1-butene annually separated with 87 kilotons in Chinese
refinery factories while all other a-olefins are imported.
With the advantage of high selectivity of linear a-olefins
by catalytic system of bis(imino)pyridyl iron complexes,
a full range process of ethylene oligomerization has been
scaling-up with the joint-investment by PetroChina and
DuPont in order to have first commercial process of eth-
ylene oligomerization catalyzed by iron complexes in
China. Searching alternative models of iron and cobalt
catalysts, however, had not awarded reasonable credits
to scientists due to the lower catalytic activities [7f,10].
On the base of 1,10-phenanthroline, fortunately, the
frameworks showed promising results of their metal com-
plexes as catalysts for ethylene reactivities. Though the
iron and cobalt complexes bearing 2,9-diimino-1,10-phen-
anthrolines showed low activity for ethylene reactivity
[11], it was assumed that the additional imino group
would coordinate with active sites to prevent the coordi-
nation of ethylene. The direct evidence was provided by
our recent results, the iron complexes ligated by 2-
imino-1,10-phenanthrolines indeed showed very high
activities for ethylene oligomerization and polymerization
[12], while the contributing works by the Solan group [13]
and ours [14] revealed their cobalt analogues as catalysts
with good activity along with the highly active nickel cat-
alysts [15].
Comparing the models of highly active catalysts of iron
and cobalt complexes with the backbones of 2,6-bis(imino)-
pyridines (A) [6,7] and 2-imino-1,10-phenanthrolines (B)
[12–14], the heteroatomic compounds as flexible ligands
would be interesting on the basis of pyridine derivatives.
Extensively, the iron and cobalt complexes bearing 2-
(2-benzimidazole)-6-(1-aryliminoethyl)pyridines (C) also
showed highly ethylene catalytic activities [16]. In addition,
the 2-ethylcarboxylate-6-iminopyridyl iron and cobalt
complexes equally exhibited considerable catalytic activity
for ethylene oligomerization and polymerization [17].
Recently bimetallic complexes based on 2-methyl-2,4-
bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines showed
good activity for ethylene oligomerization and polymeriza-
tion with high selectivity for a-olefins and vinyl-type poly-
ethylene waxes [18]. Inspired by these good results, we
embarked on the preparation of (6-(quinoxalin-2-yl)pyri-
dine-2-yl)ethylidene)benzenamines [2-quinoxalinyl-6-imi-
nopyridines] and their metal complexes. The desired
ligand substance, 1-(6-(quinoxalin-2-yl)pyridin-2-yl)etha-
none, however, could not be available neither commercially
nor by standing synthetic methodology. Therefore the suit-
able synthetic procedure for this compound was developed,
subsequently the condensation reaction with substituted
anilines gave N-(1-(6-(quinoxalin-2-yl)pyridine-2-yl)ethyli-
dene)benzenamines [2-quinoxalinyl-6-iminopyridines] for
their iron and cobalt complexes. The organic compounds
and their iron and cobalt complexes were fully character-
ized, and their structural features were discussed in detail.
Activated with methylaluminoxane (MAO), the iron com-
plexes exhibited good activities for ethylene oligomeriza-
tion and polymerization; meanwhile their cobalt
analogues showed moderate catalytic activity with modi-
fied methylaluminoxane (MMAO). Herein, the synthesis
and characterization of N-(1-(6-(quinoxalin-2-yl)pyridine-
2-yl)ethylidene)benzenamines and their iron and cobalt
complexes are reported and discussed along with their cat-
alytic behaviors toward ethylene oligomerization and
polymerization.
2. Results and discussion
R
R
R
N
2.1. Synthesis and characterization
N
N
N
Ar
N
N
M
M
In order to design new iron and cobalt catalysts model,
the synthesis of organic compounds as the hybrid of func-
tional groups will be mainly challenged. With the purpose
of synthesizing N-(1-(6-(quinoxalin-2-yl)pyridine-2-yl)eth-
ylidene)benzenamines, the basic substance 1-(6-(quinoxa-
lin-3-yl)pyridine-2-yl)ethanone, however, is not available
with synthetic protocol in the literature. Though the reac-
tion of arylethanone with o-phenylenediamine to produce
the aryl-quinoxaline derivatives was investigated in our
group [19], such reaction pathway cannot be extended to
the reaction of 6-acetylpyridine-2-carboxylate [17,20] with
Ar
Ar
Cl
N
Cl
Cl
Cl
A
B
N
N
N
N
N
N
N
M
Ar
Ar
M
Cl
Cl
Cl
Cl
C
This work
M = Fe or Co

4508
W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
o-phenylenediamine for ethyl 6-(quinoxalin-2-yl)picolinate.
Instead, it produced a domain 7-membered cyclic com-
pound as in the reported case of 1,5-benzodiazepine
derivatives [19a,22]. The general synthetic method of
quinoxalines consists of the condensation reactions of
ethane-1,2-diol with o-phenylenediamine [21], the obstacle
is that no suitable starting material which bears appropri-
ate functional groups is available. Therefore, the need to
explore new synthetic methodology for the target com-
pound of 1-(6-(quinoxalin-3-yl)pyridine-2-yl)ethanone, on
the base of new compound 6-acetylpyridine-2-carboxylate,
is inevitable [17,20].
R1
N
O
N
N
N
Anilines
Toluene
N
R1
R2
N
N
L1 L2 L3 L4 L5 L6 L7
R1
R2
Me Et i-Pr Me F Cl Br
H
H
H
Me H
H
H
MCl2 THF
According to the plausible mechanism in forming
6-membered or 7-membered cyclic compounds by the reac-
tions of arylethanones with o-phenylenediamines [19a], the
competition of the intra- or inter-molecular coupling reac-
tions after amine-ketone condensation is a key issue to be
addressed. The intramolecular coupling reaction obviously
favored must be to form 6-membered cyclic compounds,
the quinoxalinyl group. In order to achieve this, the acetyl
group was selectively activated through the bromination of
its methyl end. For the bromination [23], with one equiva-
lent of bromine which is often used, the ethyl 6-(2-bromo-
acetyl)pyridine-2-carboxylate was obtained in 60% yield,
however, in 89% yield with two equivalent moles of bro-
mine. In the following, the solvent mixture of methanol
and pyridine was used in the reaction of ethyl 6-(2-bromo-
acetyl)pyridine-2-carboxylate with o-phenylenediamine,
based on the consideration of the common solvent metha-
nol and pyridine used to neutralize the formed acidic
hydrogen bromide. The ethyl 6-(quinoxalin-3-yl)pyridine-
2-carboxylate was obtained as white solid in 52% isolated
yield . Furthermore, the conversion of carbethoxy group
into acetyl group affords the white solid 1-(6-(quinoxalin-
3-yl)pyridine-2-yl)ethanone in 65% isolated yield. With
6-acetylpyridine-2-carboxylate as a starting material, the
synthesis of 1-(6-(quinoxalin-3-yl)pyridine-2-yl)ethanone
was finally achieved and the synthetic procedure is illus-
trated in Scheme 1.
N
N
R1
N
N
M
Cl
Cl
R1
R2
1
2
3
4
5
6
7
8
9
10 11 12 13 14
M
R1
R2
Fe Fe Fe Fe Fe Fe Fe Co Co Co Co Co Co Co
Me Et i-Pr Me F Cl Br Me Et i-Pr Me F Cl Br
H
H
H
Me H
H
H
H
H
H
Me H
H
H
Scheme 2. Synthesis of 2-quinoxalinyl-6-iminopyridines and their iron
and cobalt complexes.
(Scheme 2). For the synthesis of 2-quinoxalinyl-6-imino-
pyridines, compounds L1–L5 were easily synthesized
in acceptable yields in the presence of catalytic amount of
p-toluenesulfonic acid. However, it is necessary to use
excessive amount of the corresponding anilines (1.2 equiv.)
and tetraethyl silicate as the water absorbent in synthesiz-
ing compounds L6 and L7 with relatively lower yields.
All the synthesized 2-quinoxalinyl-6-iminopyridines were
obtained as yellow powders and confirmed by IR, 1H
NMR, 13C NMR and elemental analysis. Moreover, the
single crystals of L1 and L4 suitable for X-ray diffraction
analysis were grown by slow evaporation of their hex-
ane–EtOAc (8:1) solution.
Their iron complexes (1–7) were obtained in good yields
as blue solid by the reaction of FeCl2 Æ 4H2O and one
equivalent 2-quinoxalinyl-6-iminopyridines in freshly dis-
tilled tetrahydrofuran (THF) at room temperature; while
their cobalt complexes (8–14) were obtained in good yields
(69–78%) as green solids by the same procedure (Scheme
2). All the complexes are stable in solid states, but iron
complexes are unstable in their solution due to the oxida-
tion of Fe(II) into Fe(III) which is indicated by the color
change of the solution from blue to yellow when exposed
to air. These complexes were characterized by elemental
analysis and IR spectroscopy. For the iron complexes,
compared with the IR absorptions of C@N group of free
ligands in the range of 1637–1651 cmÀ1 with strong inten-
sities, the C@N stretching frequencies of complexes were
shown between 1611 and 1634 cmÀ1 with weak intensities
confirming the coordination interaction between ligands
and iron center. Similar to the iron complexes, all cobalt
complexes also showed lower C@N stretching frequencies
along with decreased peak intensity in contrast to their
corresponding free ligands. These iron(II) and cobalt(II)
The routine synthetic method for 2-quinoxalinyl-6-imi-
nopyridines (L1–L7) is the condensation of 1-(6-(quinoxa-
lin-3-yl)pyridine-2-yl)ethanone with corresponding anilines
Br
Br2
OEt
OEt
N
N
CH3CO2H
O
O
O
O
NH2
CH3OH
+ C5H5N
NH2
OEt
N
N
N
N
EtONa
+ EtOAc
H3O+
N
O
N
O
Scheme 1. Synthesis of 1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethanone.

W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
4509
complexes are paramagnetic, and magnetic susceptibilities
were determined by Evans’ NMR method [24]. The mag-
netic moments for these complexes suggest the presence
of high spin (S = 5/2) configurations and lower field
strength of the title ligands. However, magnetic susceptibil-
ities of complexes 2 and 9 were not obtained due to their
lower solubility. In addition, the single crystals of 1, 4, 10
and 13 suitable for X-ray diffraction analysis were obtained
and their unambiguous molecular structures were
determined.
The crystal structures of L1 and L4 were shown in Figs.
1 and 2. According to the molecular structure, the quinox-
alinyl group and substituted phenyl group were stretched
far away for releasing the steric constraints and the imine
group is in the E formation with typical C@N double bond
˚
˚
in L1 (1.267(3) A) and L4 (1.2652(2) A). The N-aryl ring
forms a dihedral angle of 68.5ꢂ in L1 and 106.0ꢂ in L4 with
the pyridyl ring, while the quinoxalinyl group is approxi-
mately coplanar with pyridyl ring, and forms a dihedral
angle of 11.3ꢂ and 5.0ꢂ, respectively. The quinoxalinyl
group is located as the anti-form to pyridyl ring in its solid,
and the single bond nature of C(8)–C(9) indicates that qui-
noxalinyl group may rotate around the C(8)–C(9) bond to
interconvert syn- and anti-forms. Their selected bond
lengths and angles are listed in Table 1.
Fig. 1. Molecular structure of L1. Thermal ellipsoids are shown at 30%
probability. Hydrogen atoms have been omitted for clarity.
To confirm the molecular structures of these metal com-
plexes, the conclusive results could be obtained by single
crystal X-ray diffraction analysis. Single crystals of com-
plexes 1, 4, 10, 13 suitable for X-ray diffraction analysis
Fig. 2. Molecular structure of L4. Thermal ellipsoids are shown at 30%
probability. Hydrogen atoms have been omitted for clarity.
Table 1
˚
Selected bond lengths (A) and angles (ꢂ) for L1, L4, 1, 4, 10 and 13
L1
L4
1
4
10
13
˚
Bond lengths (A)
M–N(1)
M–N(2)
M–N(3)
M–Cl(1)
–
–
–
–
–
–
–
–
2.276(4)
2.122(4)
2.234(4)
2.2827(2)
2.2925(2)
1.332(6)
1.329(6)
1.342(6)
1.273(6)
1.448(6)
1.465(7)
1.487(6)
1.502(7)
2.286(5)
2.125(5)
2.227(5)
2.2863(2)
2.3059(2)
1.327(7)
1.332(7)
1.345(7)
1.280(7)
1.444(7)
1.469(8)
1.492(8)
1.490(8)
2.287(3)
2.063(3)
2.221(3)
2.2694(1)
2.2581(1)
1.318(4)
1.350(4)
1.339(4)
1.280(4)
1.451(4)
1.475(5)
1.493(5)
1.501(5)
2.191(2)
2.021(2)
2.220(2)
2.2249(9)
2.2773(8)
1.326(3)
1.345(3)
1.341(3)
1.284(3)
1.432(3)
1.482(3)
1.497(4)
1.493(4)
M–Cl(2)
–
–
N(1)–C(8)
N(2)–C(9)
N(2)–C(13)
N(3)–C(14)
N(3)–C(16)
C(8)–C(9)
C(13)–C(14)
C(14)–C(15)
1.320(3)
1.348(3)
1.338(3)
1.267(3)
1.425(3)
1.474(3)
1.498(3)
1.507(3)
1.3182(2)
1.3444(2)
1.3397(2)
1.2652(2)
1.4230(2)
1.4818(2)
1.4959(2)
1.498(2)
Bond angles (ꢂ)
N(1)–C(8)–C(9)
N(2)–C(9)–C(8)
N(2)–C(13)–C(14)
N(3)–C(14)–C(13)
C(14)–N(3)–C(16)
N(1)–M–N(2)
N(1)–M–N(3)
N(2)–M–N(3)
N(1)–M–Cl(1)
N(1)–M–Cl(2)
N(2)–M–Cl(1)
N(2)–M–Cl(2)
N(3)–M–Cl(1)
N(3)–M–Cl(2)
Cl(1)–M–Cl(2)
117.47(2)
116.95(2)
116.80(2)
117.21(2)
117.77(1)
116.48(1)
117.18(1)
116.96(1)
116.2(4)
114.6(4)
114.5(4)
116.2(4)
118.2(4)
72.65(1)
146.10(1)
73.45(1)
96.46(1)
98.05(1)
124.13(1)
127.34(1)
102.42(1)
102.33(1)
108.24(6)
116.0(5)
115.5(5)
115.3(5)
114.8(5)
120.2(5)
72.97(2)
145.84(2)
73.45(2)
94.78(1)
98.80(1)
117.47(1)
132.52(1)
106.06(1)
99.18(1)
109.70(6)
117.0(3)
114.1(3)
114.5(3)
116.2(3)
118.9(3)
74.06(1)
147.95(1)
75.12(1)
93.04(8)
100.72(8)
109.54(8)
140.31(9)
105.35(8)
97.34(8)
110.03(5)
116.2(2)
113.6(2)
113.9(2)
115.7(2)
121.2(2)
76.67(8)
151.70(8)
75.51(8)
93.99(6)
91.33(6)
127.91(7)
107.06(6)
98.96(6)
101.64(6)
124.50(4)
122.28(2)
122.46(1)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–

4510
W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
bis(imino)pyridyl iron(II) complexes [6,7] and 2-imino-
1,10-phenanthrolinyl iron(II) complexes [12]. Furthermore,
the imino N3–C14 bond in 1 displays clear double-bond
˚
˚
character (1.273(6) A) and is slightly (0.0063 A) longer
than that in the free ligand L1.
The molecular structure of complex 4 is shown in Fig. 4
with its selected bond lengths and angles in Table 1. It has a
similar coordinate geometry with 1. The observed similari-
ties include the identical bond lengths and angles and the
˚
shortest Fe–N2(pyridine) bond (2.125(5) A) among the
three Fe–N bonds. Also the equatorial plane and phenyl
plane is nearly perpendicular to the quinoxalinyl ring.
However, there are some slight differences between the
˚
two structures. The iron atom deviates by 0.1715 A from
Fig. 3. Molecular structure of complex 1. Thermal ellipsoids are shown at
30% probability. Hydrogen atoms and one diethyl ether molecule have
been omitted for clarity.
the coordinated plane, which is much larger than that in
complex 1.
Complex 10 with 2,6-diisopropylphenyl and complex 13
with 2,6-dichlorophenyl almost have similar structural
characters, as shown in Figs. 5 and 6 (their bond lengths
and angles are listed in Table 1). The nitrogen atom of
pyridine and two chlorides form the equatorial plane.
were obtained by slow diffusion of diethyl ether into their
methanol solutions. The crystal structure of iron complex
1 revealed the coordinated geometry around the metal cen-
ter as a distorted trigonal-bipyramidal with the pyridyl
nitrogen atom and the two chlorine atoms forming an
equatorial plane (Fig. 3). The deviation of the iron center
˚
The cobalt atom deviates this plane by 0.0439 A in 10
˚
and 0.0904 A in 13. The equatorial planes of these two
˚
from the equatorial plane is 0.0701 A. The two nitrogen
atoms (N1 and N3) occupy the axial coordination sites
with the bond angle of 146.10(1)ꢂ for N1–Fe–N3 and the
dihedral angle between the equatorial plane and the axial
plane is 89.4ꢂ. The phenyl ring lies almost perpendicular
to the plane formed by the coordinated nitrogen atoms
(90.1ꢂ), which is similar to the 2,6-bis(imino)pyridyl iro-
n(II) complexes [6,7] 2-imino-1,10-phenanthrolinyl iron(II)
complexes [12] and 2-(2-benzimidazole)-6-(1-arylimino-
ethyl)pyridyl iron(II) complexes [16]. Furthermore, the
two Fe–Cl bond lengths show a slight difference between
˚
˚
the Fe–Cl1 (2.2827(2) A) and Fe–Cl2 (2.2925(2) A). The
difference usually appears in the tridentate NꢀNꢀN iron(II)
complexes because of apical elongation in the square-pyra-
˚
midal complex [25]. The Fe–N2(pyridyl) (2.122(4) A) bond
is shorter than the Fe–N3(imino) (2.234(4) A) bond and the
Fe–N1(quinoxalinyl) (2.276(4) A) bond, similar to the 2,6-
˚
Fig. 5. Molecular structure of complex 10. Thermal ellipsoids are shown
at 30% probability. Hydrogen atoms have been omitted for clarity.
˚
Fig. 4. Molecular structure of complex 4. Thermal ellipsoids are shown at
30% probability. Hydrogen atoms and diethyl ether molecule have been
omitted for clarity.
Fig. 6. Molecular structure of complex 13. Thermal ellipsoids are shown
at 30% probability. Hydrogen atoms have been omitted for clarity.

W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
4511
complexes are nearly perpendicular to the quinoxalinyl
ring, with dihedral angles of 86.5ꢂ in 10 and 91.1ꢂ in 13.
The equatorial Co–N bonds are relatively shorter than
their axial Co–N bonds. All these characters are similar
with the reported NꢀNꢀN tridentate cobalt complexes
[6,7,13,16]. Furthermore, the imino N3–C14 bond reveals
ene oligomerization were investigated with complex 4 in
order to find the suitable molar ratio for better activity.
With the Al/Fe ratio enhanced from 200 to 1500, the
activity of 4 was initially increased and then decreased with
optimum catalytic activity at Al/Fe molar ratio of 1000.
These observed phenomena are often explained by the fact
that enough amount of MAO is necessary in activating pre-
cursors in order to obtain more active species, however, the
plausible remaining trimethylaluminium in MAO may
deactivate the active species [8d]. The reaction temperature
should also be considered because the ethylene reactivity is
a highly exothermic reaction and the catalytic activity will
therefore be varied at different temperatures. To understand
such influence, the catalytic system of 4 with 1000 equiv.
MAO at 1 atm was investigated with changing reaction
temperature (entries 3, 5–7 in Table 3). Elevating the reac-
tion temperature from 0 to 60 ꢂC, the catalytic system
showed highest activity at 20 ꢂC; and solubility of ethylene
and stability of active species would be both considered
[7b,7d]. Moreover, the oligomers distribution became
narrower along with the decreased catalytic reactivity.
The proportion of C4 and other short-chain oligomers were
greatly increased at higher temperature because of the faster
b-hydrogen elimination than ethylene propagation.
˚
clear double-bond character (1.280(4) A in 10 and
˚
1.284(3) A in 13). Due to the different substituent on the
phenyl ring, these two complexes show different equatorial
angles especially for the Cl1–Co–Cl2 bond angles
(110.03(5)ꢂ in 10 and 124.50(4)ꢂ in 13). A slight difference
˚
(0.011 A) between the Fe–Cl1 and Fe–Cl2 bonds is
˚
observed, however, the difference(0.052 A) is much larger
in 13. In complex 10, the pyridine plane and quinoxalinyl
ring are almost coplanar, with a dihedral angle of 1.7ꢂ.
In complex 13, the quinoxalinyl ring deviates the pyridine
plane with a dihedral angle of 15.2ꢂ.
2.2. Ethylene oligomerization and polymerization
The catalytic reactivity of the title NꢀNꢀN tridentate
metal complexes were generally investigated in the presence
of various cocatalysts such as MAO, MMAO or Et2AlCl.
Considering significant differences of catalytic behaviors
between iron and cobalt complexes, the results and discus-
sions are separated into two individual parts for the iron
and cobalt systems.
Different substituents on the imino-N aryl ring could
have some influences on their catalytic performance. For
complexes 1–3, their activities are in same order with
comparable values (entries 1–3 and 8–10 in Table 4). In
the catalytic systems of complexes 5–7 containing 2,6-
dihalosubstituted ligands, the bulkier substituents at the
ortho-positions of the imino-N aryl ring resulted in lower
catalytic activities (6, 5 > 7, entries 11–13 in Table 4). This
phenomenon could be rooted back to the combination of
bulky and electronic effects of ligands, the covalent radius
2.2.1. Ethylene reactivity of iron complexes
2.2.1.1. The selection of cocatalyst. Various cocatalysts
such as Et2AlCl, MMAO and MAO were used to activate
complex 4 for ethylene reactivity at room temperature and
ambient pressure (Table 2). The iron catalytic system con-
taining MAO showed the highest activities for ethylene
oligomerization, and the butenes were observed as the
major products. Beyond that, only butenes were formed
in the catalytic system with Et2AlCl. Though, the system
with MMAO showed considerable catalytic activities, the
analyses of oligomers produced were somehow affected
due to the isobutyl group in MMAO. Therefore, further
catalytic studies were performed by the activation with
MAO, and the analyses of the obtained oligomers were car-
ried out by GC and GC–MS.
˚
are F, 0.72, Cl, 0.99 and Br, 1.14 A, while the electronega-
tivties of fluorine, chlorine and bromine atom are 4.0, 3.0
and 2.8, respectively. The complexes with electron-with-
drawing groups showed similar catalytic reactivity as their
analogues with electron-donating groups, but the narrower
distribution of oligomers with shorter chains was observed
because of the faster b-hydrogen elimination than ethylene
propagation. Interestingly, the substituent at the para-
position of the aryl ring had an obvious influence on the
reactivity and distribution of oligomers. In contrast to
2.2.1.2. Ethylene reactivity in the presence of MAO. The
effects of Al/Fe molar ratio on catalytic activities of ethyl-
Table 3
Oligomerization of ethylene with 4/MAO
Entry Al/
Fe
T/
ꢂC
Oligomer
activitya
Oligomer distribution
Table 2
P
C4
C6
4.7
4.2
C8 C10
CP12
Selection of the suitable cocatalyst based on 4
1
2
3
4
5
6
7
200 20
500 20
1000 20
1500 20
1000
1000 40
1000 60
0.52
0.63
7.13
2.69
0.77
1.04
0.13
95.3
95.8
–
–
–
–
–
–
Entry Cocatalyst Al/
Fe
Oligomer Oligomer distribution
activitya
P
C4
C6
C8 C10
CP12
71.0 10.9 2.0 1.9 14.2
1
2
3
Et2AlCl
MMAO
MAO
200 0.01
1000 5.07
1000 7.13
100
80.7
–
–
–
–
84.7
90.1
80.0
92.4
6.3 3.3 1.0
5.0 3.7 0.3
6.5 6.0 1.8
4.7
0.9
5.7
8.3 3.5 1.7
5.8
0
71.0 10.9 2.0 1.9 14.2
7.6
–
–
–
Reaction condition: 5 lmol Fe; 30 mL toluene. 1 atm of ethylene; 20 ꢂC;
30 min.
Reaction condition: 5 lmol Fe; 30 mL toluene; 1 atm of ethylene; 30 min.
a
105 g mol FeÀ1 hÀ1
.
a
105 g mol FeÀ1 hÀ1
.

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W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
Table 4
Table 5
Oligomerization of ethylene with 1–7/MAO
Entry Complex T/ Oligomer
Oligomer distributionb
min activitya
Ethylene reactivity with 1–7/MAO at 10 atm
Entry Complex Activitya
Oligomer distribution
Polymer Oligomer C4
P
0.1
–
P
0.9
1.0
C4
C6
C8 C10
CP12
C6 C8 C10
CP12
1
2
1
2
3
4
5
6
7
1
2
3
4
5
6
7
7
7
7
7
7
10
10
10
10
10
10
10
30
30
30
30
30
30
30
5
4.50
5.32
4.12
91.4
96.1
98.6
84.8
6.7 0.6 0.2
3.4 0.3 0.1
1.1
1
2
3
4
5
6
7
1
2
3
4
5
6
7
3.86
–
4.27
8.56
–
7.94
3.71
0.78
87.7 5.9 2.6 0.5
91.6 4.0 3.2 0.3
94.9 1.9 1.9 0.3
3.3
3
1.4
–
–
4
12.0
9.2 1.5 1.1
3.4
22.4
74.5 7.3 2.9 2.0 13.3
95.4 3.2 1.4
5
6
7
8
4.62
5.07
1.72
1.53
2.66
1.69
7.13
2.20
2.55
1.39
1.65
1.72
1.78
1.62
1.51
87.4 12.2 0.4
–
–
–
2.40
3.91
4.65
–
–
0.6
0.6
96.4
94.6
90.7
95.6
98.8
3.6
5.4
–
–
–
–
1.1
0.1
–
–
94.5 3.9 0.7 0.3
92.2 3.9 3.0 0.3
7.4 0.6 0.2
4.0 0.2 0.1
1.2
Reaction condition: 5 lmol Fe; cocat.: MAO; Al/Fe = 1000; 10 atm
9
ethylene; 20 ꢂC; 30 min; 100 mL toluene.
10
11
12
13
14
15
16
17
18
19
–
–
–
a
105 g mol FeÀ1 hÀ1
.
71.0 10.9 2.0 1.9 14.2
86.2 13.6 0.2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
95.6
94.4
94.0
94.6
94.8
94.3
94.5
4.4
5.6
6.0
5.4
5.2
5.7
5.5
–
–
–
–
–
–
–
ring also showed an important influence on the activity
and 4/MAO system displayed the highest reactivity. From
the IR spectra, the obtained PE samples demonstrated the
PE’s linear characteristics and the presence of the vinyl end
groups. Moreover, the NMR spectra confirm their vinyl-
type olefin waxes.
10
15
20
25
Reaction condition: 5 lmol Fe; cocat.: MAO; Al/Fe = 1000; 1 atm eth-
ylene; 20 ꢂC; 30 mL toluene.
2.2.2. Ethylene reactivity by cobalt complexes
a
105 g mol FeÀ1 hÀ1
.
Similar to the above iron complexes, all cobalt(II) ana-
logues displayed considerable catalytic activities for ethyl-
ene oligomerization. Though catalytic systems with MAO
or Et2AlCl also demonstrated catalytic activities (entries
1 and 3 in Table 6), the catalytic system with MMAO
showed better result; therefore further investigation of
cobalt catalysts was carried out with MMAO as cocatalyst.
Various results of ethylene oligomerization by cobalt
complexes at ambient pressure were collected in Table 6.
The catalytic activity of the cobalt complexes was also
remarkably influenced by different substituents on the aryl
rings. Similar to the iron complexes, cobalt complex 9 per-
formed better reactivity than 8 and 10. In the catalytic sys-
tems of complexes 12–14 containing 2,6-dihalosubstituents
(entries 5–7 in Table 7), their activities remained in the
order of bromo- > chloro- > fluoro-, in which the bulkier
substituents at the ortho-positions of the imino-N aryl ring
resulted in higher catalytic activities. Additionally the sub-
stituent at the para-position of the aryl ring had no obvious
influence on the reactivity which is different with the iron
analogues. Another notable difference between the cobalt
and iron complexes is that cobalt analogues produced
more oligomers with shorter-chains because of the faster
b-hydrogen elimination.
b
Determined by GC.
1/MAO system, 4/MAO with 2,4,6-trimethylphenyl group
showed four times higher catalytic activity with greatly
increased long-chain oligomers (entries 1, 4 and 8, 11 in
Table 4).
Ethylene reactivity with different reaction times was also
investigated and the results were summarized in Table 4.
Accordingly the catalytic activity within 10 min was higher
than that obtained within 30 min, in which sharp decrease
was clearly observed. It could be imagined that the active
species were not stable and rendered the activity remark-
ably reduced within 30 min (entries 1–7 in Table 4). To
understand such influence, the catalytic system of 7 was
investigated in detail with changing reaction time (entries
14–19 in Table 4). When the reaction time was increased
from 5 to 15 min, the activity was slowly enhanced, and
then decreased with longer time which indicated that the
active species performed best within 15 min and then deac-
tivated because of their instability.
It is well known that elevated ethylene pressure pro-
motes higher activities, this phenomenon was also observed
with the iron catalytic system. The results of ethylene reac-
tivity at 10 atm were summarized in Table 5.
Comparing Table 5 with Table 4, both activity and con-
tents of longer-chain oligomers increased at 10 atm. In the
cases of 1, 3 and 4 catalytic systems, the polyethylene waxes
were collected to prove good polymerization activity; espe-
cially for 4/MAO system, its reactivity for oligomers and
polymers were both enhanced sharply at 10 atm pressure.
According to Table 5 (entries 1–3), the oligomerization
activity was decreased sharply with large bulkier substitu-
ents on the N-aryl ring. Besides, similar to the catalytic sys-
tem at 1 atm, the substituent at the 4-position of the aryl
Table 6
Influences of cocatalyst on activity of complex 8
Entry
Co-cat.
Al/Co
Activitya
Oligomer distribution
P
Oligomer
C4
C6
CP8
1
2
3
Et2AlCl
MMAO
MAO
200
1000
1000
0.1
10.5
4.1
100
–
–
96.5
88.1
1.6
2.9
1.9
9.0
Reaction condition: 5 lmol Co; 30 mL toluene. 1 atm ethylene; 20 ꢂC;
30 min.
a
104 g mol CoÀ1 hÀ1
.

W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
4513
Table 7
Oligomerization of ethylene with 8–14/MMAO
2.3. Conclusions
The new NꢀNꢀN ligand 2-imino-6-(quinoxalin-3-
yl)pyridines were prepared and reacted with iron and
cobalt chlorides to form the title complexes. Sharing the
similar framework with complexes containing 2,6-
bis(imino)pyridines [6,7] or 2-imino-1,10-phenanthrolines
[12–14], and 2-(2-benzoimidazole)-6-(1-aryliminoethyl)-
pyridines [16], the iron complexes exhibited good activities
for ethylene oligomerization and polymerization in the
presence of MAO, and a large amount of a-linear poly-
ethylene waxes were produced at 10 atm ethylene pres-
sure. The higher activities were obtained at lower
reaction temperature because of the thermal instability
for active species. The cobalt complexes exhibited moder-
ate to good activities for ethylene reactivity in the pres-
ence of MMAO.
Entry
Complex
Al/Co T/ꢂC Activitya Oligomer distributionb
P
Oligomer C4
C6
CP8
1
2
3
4
5
6
7
8
8
9
1000
1000
1000
1000
1000
1000
1000
200
20
20
20
20
20
20
20
20
20
20
20
20
0
10.5
14.3
10.6
10.8
7.7
16.1
16.7
2.2
96.5 1.6 1.9
98.5 1.5
98.9 1.1
–
–
10
11
12
13
14
11
11
11
11
11
11
11
11
96.6 1.4 2.0
96.7 3.3
97.8 2.2
96.4 3.6
98.4 1.6
–
–
–
–
9
500
7.8
94.1 1.3 4.6
96.1 1.1 2.8
97.4 1.0 1.6
97.4 0.9 1.7
97.0 1.6 1.4
96.9 0.8 2.3
10
11
12
13
14
15
1500
2000
2500
1000
1000
1000
13.0
16.1
15.4
13.2
3.4
40
60
6.3
100
–
–
Reaction condition: 5 lmol Co; cocat.: MMAO; 1 atm ethylene; 0.5 h;
20 ꢂC; 30 mL toluene.
3. Experimental
a
104 g mol CoÀ1 hÀ1
.
b
Determined by GC.
All synthetic manipulations were carried out under
nitrogen atmosphere using standard Schlenk and cannula
techniques. NMR were recorded on Bruker DMX-300
spectrometer, with TMS as the internal standard. Elemen-
tal analyses were performed on a Flash EA 1112 microan-
alyzer. IR spectra were obtained as KBr pellets on a
Perkin–Elmer FTIR 2000 spectrometer. Melting points
(Mp) were determined with a digital electrothermal appa-
ratus without further correction. Magnetic susceptibilities
were determined by Evans’ NMR method [24] in metha-
nol-d4/cyclohexane (97:3 v/v) solution at room tempera-
ture. GC analyses were performed with a VARIAN CP-
3800 Strumentazione gas chromatograph equipped with a
flame ionization detector and a 30 m (0.2 mm i.d.,
0.25 lm film thickness) CP-Sil 5 CB column. GC–MS anal-
yses were performed with HP 5890 SERIES II and HP
5971 SERIES mass detectors. THF and toluene were
refluxed over as sodium benzophenone and distilled under
nitrogen, while other solvents were refluxed over an appro-
priate drying agent and distilled under nitrogen prior to
use. Methylaluminoxane (MAO, 1.46 M solution in tolu-
ene) and modified methylaluminoxane (MMAO, 1.93 M
in heptane, 3A) were purchased from Akzo Nobel Corp.
Diethylaluminum chloride (Et2AlCl, 1.7 M in toluene)
was purchased from Acros Chemicals. All other chemicals
were purchased and used without further purification,
except for ethyl 6-acetylpyridine-2-carboxylate prepared
with an established procedure [17,20]. The boiling range
of petroleum ether is 30–60 and brand of silica gel is
200–300 mesh.
The catalytic activity of cobalt complexes was also
affected by varying the reaction parameters, and complex
11 was used as an example. When the Al/Co molar ratio
was enhanced from 200 to 2500, the catalytic activities ini-
tially increased and then decreased with optimum activity
at the Al/Co molar ratio of 2000 (entries 4, 8–12 in Table
7). Notably, the catalytic activity increased sharply with
broader oligomers distribution when the Al/Co molar
ratio was increased from 200 to 500, which may be attrib-
uted to MMAO scavenged adventitious water and impu-
rities in the solvent at the Al/Fe ratio of 200 a such,
the cobalt complex required more cocatalyst to be active.
When the Al/Co molar ratio was increased to 2000, the
activity was slowly enhanced, and then decreased at Al/
Co molar ratio of 2500 which could be traced to the
increasing amount of isobutyl group, and the generated
species hinder the insertion of ethylene due to steric bulk-
iness [26]. Elevating the reaction temperature from 0 to
60 ꢂC resulted in decreasing catalytic activity (entries 4,
13–15 in Table 7), which might be caused by instability
of the active species or lower concentration of ethylene
at high temperature. Only butenes were produced with
the reaction temperature of 60 ꢂC.
Ethylene reactivity by cobalt complexes 8–14 was stud-
ied at 10 atm of ethylene with MMAO at Al/Co ratio of
1000. However, their catalytic activities were not signifi-
cantly enhanced except for 11. In 11/MMAO system at
10 atm, a large amount of polyethylene waxes was pro-
duced with the activity of 4.04 · 105 g molÀ1 (Co) hÀ1
and the contents of longer-chain oligomers were also
increased. The polyethylene waxes were confirmed possess-
ing linear characteristics with the presence of the vinyl end
groups. The effect of substituents on ethylene reactivity at
10 atm of ethylene followed the same trend with those
obtained at 1 atm.
3.1. Synthesis of 1-(6-(quinoxalin-2-yl)pyridine-2-
yl)ethanone
3.1.1. Ethyl 6-(2-bromoacetyl)pyridine-2-carboxylate
The solution of bromine (1.06 mL, 0.02 mol) in acetic
acid (10 mL) was added dropwise to a solution of ethyl

4514
W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
6-acetylpyridine-2-carboxylate (1.93 g, 0.01 mol) and sev-
eral drops of hydrobromic acid in acetic acid (20 mL),
the mixture was then stirred at room temperature for
3–4 h. The solvents were evaporated and the residue
was eluted on column chromatography [silica gel; eluting
reagent light petroleum–EtOAc (6:1)]. The desired prod-
uct was obtained as white solid with 89% isolated yield
(2.42 g). Mp: 98–99 ꢂC. IR (KBr, cmÀ1): 1722 (s, mC@O),
1586, 1320, 1256, 1154 (s, mC–O–C), 1007, 993, 762, 665,
632. 1H NMR (300 MHz, CDCl3, d): 8.35 (d, 1H,
J = 7.9 Hz, Py–H), 8.26 (d, 1H, J = 7.70 Hz, Py–H),
8.05 (t, J = 7.56 Hz, 1H, Py–H), 4.99 (s, 2H, CH2Br),
4.51 (m, 2H, –OCH2–), 1.47 (t, 3H, J = 7.70 Hz, CH3).
13C NMR (75.45 MHz, CDCl3, d): 191.8, 164.1, 151.2,
147.9, 138.3, 128.7, 125.2, 62.0, 32.6, 14.2. Anal. Calc.
for C10H10BrNO3: N, 5.15; C, 44.14; H, 3.70. Found:
N, 4.96; C, 44.10; H, 3.84%.
gel; eluting reagent: light petroleum–EtOAc (8:1)]. The
1-(6-(quinoxalin-2-yl)pyridine-2-yl)ethanone was obtained
as white solid (0.74 g) in 65% isolated yield. Mp: 115–
116 ꢂC. IR (KBr, cmÀ1): 1694 (s, mC@O), 1582, 1411,
1
1354, 1262, 1105, 764, 411. H NMR (300 MHz, CDCl3,
d): 10.10 (s, 1H, o-quinoxalin-H), 8.84 (d, 1H,
J = 7.77 Hz, Py–H), 8.21 (d, 1H, J = 7.86 Hz, Py–H),
8.18 (m, 2H, quinoxalin-H), 8.08 (t, 1H, J = 7.65 Hz,
Py–H), 7.85 (m, 2H, quinoxalin-H), 2.92 (s, 3H,
CH3C@O). 13C NMR (75.45 MHz, CDCl3, d): 199.8,
153.8, 153.1, 149.3, 143.9, 142.7, 141.7, 138.1, 130.4,
130.3, 129.7, 129.4, 125.2, 122.3, 25.8. Anal. Calc. for
C15H11N3O: N, 16.86; C, 72.28; H, 4.45. Found: N,
16.80; C, 72.21; H, 4.45%.
3.2. Synthesis of 2-quinoxalinyl-6-iminopyridines
3.2.1. (E)-2,6-Dimethyl-N-(1-(6-(quinoxalin-2-yl)pyridin-
2-yl)ethylidene)benzenamine (L1)
3.1.2. Ethyl 6-(quinoxalin-2-yl)pyridine-2-carboxylate
Ethyl 6-(2-bromoacetyl)pyridine-2-carboxylate (1.87 g,
0.006 mol) was added to the solution of 1,2-phenylene
diamine (0.65 g, 0.006 mol) in methanol (20 mL) and pyr-
idine (5 mL). The mixture was stirred and refluxed for
3 h. The solvents were evaporated and the residue was
eluted on column chromatography [silica gel, eluting
reagent: light petroleum–EtOAc (5:1)] to obtain the
product as white solid in 52% isolated yield (0.87 g).
Mp: 137–138 ꢂC. IR (KBr, cmÀ1): 1714 (s, mC@O), 1588,
1568, 1554, 1310, 1247, 1148 (s, mC–O–C), 771, 405. 1H
NMR (300 MHz, CDCl3, d): 10.11 (s, 1H, o-quinoxa-
lin-H), 8.81 (d, 1H, J = 7.7 Hz, Py–H ), 8.25 (d, 1H,
J = 7.95 Hz, Py–H), 8.20 (m, 2H, quinoxalin-H), 8.07
(t, 1H, J = 7.50 Hz, Py–H), 7.83 (m, 2H, quinoxalin-
H), 4.55 (m, 2H, OCH2), 1.52 (t, 3H, J = 5.34 Hz,
CH3). 13C NMR (75.45 MHz, CDCl3, d): 165.1, 154.7,
149.3, 148.1, 144.3, 142.8, 141.6, 138.1, 130.3, 130.2,
129.7, 129.4, 125.7, 125.0, 62.0, 14.3. Anal. Calc. for
C16H13N3O2: N, 15.05; C, 68.81; H, 4.69. Found: N,
14.65; C, 68.36; H, 4.78%.
2,6-Dimethylaniline (0.39 mL, 3 mmol) was added to a
solution of 1-(6-(quinoxalin-3-yl)pyridine-2-yl)ethanone
(0.75 g, 3 mmol) with a catalytic amount of p-toluenesulf-
onic acid in toluene (50 mL). The mixture was refluxed
for 12 h under nitrogen atmosphere. During this reaction,
the water formed was eliminated by using a dean-Stark
apparatus. After the solvent was evaporated under reduced
pressure, the residue was separated by column chromatog-
raphy with silica gel with an eluting reagent of light petro-
leum/EtOAc (8/1). The expected compound L1 was
obtained as yellow solid in 63% isolated yield (0.66 g).
Mp: 142–143 ꢂC. IR (KBr, cmÀ1): 1642 (s, mC@N), 1568,
1552, 1464, 1360, 1203, 765, 405. 1H NMR (300 MHz,
CDCl3, d): 10.11 (s, 1H, o-quinoxalin-H), 8.74 (d, 1H,
J = 7.45 Hz, Py–H), 8.53 (d, 1H, J = 7.83 Hz, Py–H),
8.19 (m, 2H, quinoxalin-H), 8.04 (t, 1H, J = 7.92 Hz, Py–
H), 7.82 (m, 2H, quinoxalin-H), 7.11 (d, 2H, J = 7.47 Hz,
Ph–H), 6.98 (t, 1H, J = 7.17 Hz, Ph–H), 2.38 (s, 3H,
N@C–CH3), 2.09 (s, 6H, –CH3 ). 13C NMR (75.45 MHz,
CDCl3, d): 168.6, 157.4, 154.8, 151.5, 150.2, 145.7, 144.2,
143.3, 139.2, 131.7, 131.6, 131.2, 130.9, 129.4, 126.9,
124.6, 124.5, 123.6, 19.5, 18.1. Anal. Calc. for C23H20N4:
N, 15.90; C, 78.38; H, 5.72. Found: N, 15.60; C, 78.16;
H, 5.75%.
3.1.3. 1-(6-(Quinoxalin-2-yl)pyridine-2-yl)ethanone
Sodium (0.54 g, 23.2 mmol) was dissolved in 20 mL of
freshly dried ethanol, then the excess ethanol was fully
removed via vacuum. A solution of ethyl 6-(quinoxalin-
2-yl)pyridine-2-carboxylate (1.30 g, 4.64 mmol) in freshly
distilled ethyl acetate (30 mL) was added dropwise to
the dry EtONa. The yellow mixture was refluxed for
8 h to become a brown solution. Concentrated HCl
(20 mL) acid was added dropwise to the solution and
resultant mixture was further refluxed for 10 h. After
cooling to room temperature, 50 mL water was added
and the aqueous phase was extracted with CH2Cl2
(5 · 20 mL). The mixture of combined organic phases
was washed with a solution (30 mL) of 5% aqueous
Na2CO3, and dried over anhydrous Na2SO4. The solvents
were evaporated under reduced pressure, the residue was
subsequently purified by column chromatography [silica
3.2.2. (E)-2,6-Diethyl-N-(1-(6-(quinoxalin-2-yl)pyridin-2-
yl)ethylidene)benzenamine (L2)
Using the same procedure as for the synthesis of L1, L2
was obtained as yellow powder in 39% yield. Mp: 155–
156 ꢂC. IR (KBr, cmÀ1): 1645 (s, mC@N), 1567, 1546,
1451, 1363, 1244, 1197, 1111, 1060, 828, 757, 406. 1H
NMR (300 MHz, CDCl3, d): 10.13 (s, 1H, o-quinoxalin-
H), 8.77 (d, 1H, J = 7.65 Hz, Py–H), 8.55 (d, 1H,
J = 7.83 Hz, Py–H), 8.22 (m, 2H, quinoxalin-H), 8.07 (t,
1H, J = 7.80 Hz, Py–H), 7.86 (m, 2H, quinoxalin-H),
7.18 (d, 2H, J = 7.86 Hz, Ph–H), 7.09 (t, 1H,
J = 6.54 Hz, Ph–H), 2.48 (m, 4H, –CH2–), 2.39 (s, 3H,
N@C–CH3), 1.20 (t, 6H, J = 7.47 Hz, CH3). 13C NMR

W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
4515
(75.45 MHz, CDCl3, d): 166.8, 155.9, 153.4, 150.0, 147.7,
3.2.6. (E)-2,6-Dichloro-N-(1-(6-(quinoxalin-2-yl)pyridin-
2-yl)ethylidene)benzenamine (L6)
144.3, 142.7, 141.8, 137.7, 131.2, 130.2, 130.1, 129.7,
129.4, 129.0, 128.2, 126.0, 125.3, 123.4, 122.9, 122.1, 24.6,
21.5, 16.9, 13.7. Anal. Calc. for C25H24N4: N, 14.73; C,
78.92; H, 6.36. Found: N, 14.50; C, 79.30; H, 6.49%.
In the condensation reaction of 2.4 mmol 2,6-dichloro-
aniline (0.39 g) with 2 mmol 1-(6-(quinoxalin-2-yl)pyri-
dine-2-yl)ethanone (0.50 g) in 30 mL of toluene along
with 3 mL of tetraethyl silicate as the water absorbent,
compound L6 was obtained as yellow powder in 31% yield
(0.24 g). Mp: 194–195 ꢂC. IR (KBr, cmÀ1): 1651 (s, mC@N),
1565, 1555, 1433, 1362, 1224, 1115, 1063, 819, 765, 408. 1H
NMR (300 MHz, CDCl3, d): 10.13 (s, 1H, o-quinoxalin-H),
8.80 (d, 1H, J = 7.74 Hz, Py–H ), 8.57 (d, 1H, J = 7.68 Hz,
Py–H), 8.21 (m, 2H, quinoxalin-H), 8.15 (m, 1H, Py–H),
7.85 (m, 2H, quinoxalin-H), 7.33 (d, 2H, J = 8.01 Hz,
Ph–H ), 7.02 (t, 1H, J = 7.74 Hz, Ph–H), 2.51 (s, 3H,
N@C–CH3). 13C NMR (75.45 MHz, CDCl3, d): 171.2,
155.0, 153.4, 149.7, 145.6, 144.1, 142.6, 141.8, 137.8,
130.2, 130.1, 129.7, 129.3, 128.2, 124.5, 124.4, 123.5,
122.8, 17.7. Anal. Calc. for C21H 14Cl2N4: N, 14.25; C,
64.14; H, 3.59. Found: N, 13.81; C, 64.04; H, 3.65%.
3.2.3. (E)-2,6-Diisopropyl-N-(1-(6-(quinoxalin-2-yl)-
pyridin-2-yl)ethylidene)benzenamine (L3)
Using the same procedure as for the synthesis of L1, L3
was obtained as yellow powder in 74% yield. Mp: 215–
216 ꢂC. IR (KBr, cmÀ1): 1637 (s, mC@N), 1568, 1458,
1361, 1241, 1112, 1059, 829, 758, 406. 1H NMR
(300 MHz, CDCl3, d):10.11 (s, 1H, o-quinoxalin-H), 8.74
(d, 1H, J = 7.68 Hz, Py–H), 8.51 (d, 1H, J = 7.89 Hz,
Py–H), 8.20 (m, 2H, quinoxalin-H), 8.04 (t, 1H,
J = 7.80 Hz, Py–H), 7.82 (m, 2H, quinoxalin-H), 7.17 (m,
3H, Ph–H), 2.80 (m, 2H, CH(CH3)2), 2.38 (s, 3H, N@C–
CH3), 1.20 (s, 12H, CH3). 13C NMR (75.45 MHz, CDCl3,
d): 166.8, 155.9, 153.4, 150.0, 146.4, 144.3, 142.7, 141.8,
137.7, 135.8, 130.2, 130.1, 129.7, 129.4, 123.7, 123.0,
122.9, 122.1, 28.3, 23.2, 22.9, 17.3. Anal. Calc. for
C27H28N4: N, 13.71; C, 79.38; H, 6.91. Found: N, 13.69;
C, 78.99; H, 6.84%.
3.2.7. (E)-2,6-Dibromo-N-(1-(6-(quinoxalin-2-yl)pyridin-
2-yl)ethylidene)benzenamine (L7)
Using the same procedure as for the synthesis of L6,
L7 was obtained as yellow powder in 26% yield. Mp:
206–207 ꢂC. IR (KBr, cmÀ1): 1650 (s, mC@N), 1565, 1547,
1426, 1363, 1224, 1114, 1063, 821, 763, 727, 408.
1H NMR (300 MHz, CDCl3, d): 10.10 (s, 1H, o-quinoxa-
lin-H ), 8.77 (d, 1H, J = 7.84 Hz, Py–H), 8.54 (d,
1H, J = 7.8 Hz, Py–H ), 8.19 (m, 2H, quinoxalin-H), 8.05
(t, 1H, Py–H), 7.82 (m, 2H, quinoxalin-H), 7.60 (d, 2H,
J = 8.04 Hz, Ph–H), 6.88 (t, 1H, J = 7.96 Hz, Ph–H),
2.46 (s, 3H, N@C–CH3). 13C NMR (75.45 MHz, CDCl3,
d): 170.9, 155.1, 153.6, 149.9, 148.1, 144.2, 142.7, 141.9,
137.9, 132.0, 130.2, 130.1, 129.8, 129.4, 125.3, 123.6,
122.9, 113.6, 17.7. Anal. Calc. for C21H14Br2N4: N,
11.62; C, 52.31; H, 2.93. Found: N, 11.64; C, 52.46; H,
2.95%.
3.2.4. (E)-2,4,6-Trimethyl-N-(1-(6-(quinoxalin-2-yl)-
pyridin-2-yl)ethylidene)benzenamine (L4)
Using the same procedure as for the synthesis of L1, L4
was obtained as yellow powder in 28% yield. Mp: 132–
133 ꢂC. IR (KBr, cmÀ1): 1645 (s, mC@N), 1568, 1546,
1476, 1361, 1217, 1112, 824, 763, 409. 1H NMR
(300 MHz, CDCl3, d): 10.12 (s, 1H, o-quinoxalin-H), 8.74
(d, 1H, J = 7.89 Hz, Py–H), 8.52 (d, 1H, J = 7.92 Hz,
Py–H), 8.21 (m, 2H, quinoxalin-H), 8.04 (t, 1H,
J = 7.95 Hz, Py–H), 7.84 (m, 2H, quinoxalin-H), 6.94 (s,
2H, Ph–H), 2.36 (s, 3H, N@C–CH3), 2.33 (s, 3H, p-CH3),
2.06 (s, 6H, o-CH3). 13C NMR (75.45 MHz, CDCl3, d):
166.9, 155.7, 152.9, 149.7, 145.8, 143.9, 142.3, 141.5,
137.3, 131.9, 129.8, 129.7, 129.4, 129.0, 128.2, 124.9,
122.6, 121.7, 20.4, 17.5, 16.2. Anal. Calc. for C24H22N4:
N, 15.29; C, 78.66; H, 6.05. Found: N, 14.99; C, 78.38;
H, 6.11%.
3.3. Synthesis of metal complexes
3.3.1. Synthesis of (L)FeCl2 (1–7)
Iron complexes 1–7 were synthesized by the reaction of
FeCl2 Æ 4H2O with the corresponding ligands in THF. A
typical synthetic procedure for complex 1 is described as
follows. A mixture of FeCl2 Æ 4H2O (0.040 g, 0.20 mmol)
with compound L1 (0.071 g, 0.20 mmol) in freshly distilled
THF (5 mL) was stirred at room temperature for 12 h
under nitrogen atmosphere. The precipitate was formed,
collected through a filter, and washed with freshly distilled
diethyl ether. After drying in vacuum, iron(II) complex 1
was obtained as the blue powder in 95% yield (0.092 g).
IR (KBr, cmÀ1): 1623 (m, mC@N), 1592, 1371, 1213, 778,
763, 411. Anal. Calc. for C23H20Cl2FeN4 Æ 3H2O: N,
10.51; C, 51.81; H, 4.91. Found: N, 11.11; C, 51.41; H,
5.08%. leff = 6.2 lB. Data for complex 2 are as follows.
Yield: 42%. IR (KBr, cmÀ1): 1609 (w, mC@N), 1589, 1501,
1482, 1374, 1273, 1198, 1129, 1094, 910, 817, 770, 413.
3.2.5. (E)-2,6-Difluoro-N-(1-(6-(quinoxalin-2-yl)pyridin-2-
yl)ethylidene)benzenamine (L5)
Using the same procedure as for the synthesis of L1,
L5 was obtained as yellow powder in 40% yield. Mp:
163–164 ꢂC. IR (KBr, cmÀ1): 1639 (s, mC@N), 1567, 1469,
1365, 998, 829, 766, 741, 406. 1H NMR (300 MHz, CDCl3,
d): 10.09 (s, 1H, o-quinoxalin-H), 8.74 (d, 1H, J = 7.8 Hz,
Py–H), 8.49 (d, 1H, J = 7.83 Hz, Py–H), 8.19 (m, 2H, qui-
noxalin-H), 8.03 (t, 1H, J = 7.83 Hz, Py–H), 7.82 (m, 2H,
quinoxalin-H), 7.01 (m, 3H, Ph–H ), 2.57 (s, 3H, N@C–
CH3). 13C NMR (75.45 MHz, CDCl3, d): 172.5, 155.3,
154.2, 153.4, 151.8, 149.8, 144.2, 142.6, 141.8, 137.7,
130.2, 130.2, 129.7, 129.4, 124.2, 123.4, 122.8, 111.8,
111.5, 17.7. Anal. Calc. for C21H14F2N4: N, 15.55; C,
69.99; H, 3.92. Found: N, 15.48; C, 69.52; H, 3.92%.

4516
W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
Anal. Calc. for C25H24Cl2FeN4: N, 11.05; C, 59.20; H,
4.77. Found: N, 10.73; C, 58.74; H, 4.78%. Data for com-
plex 3 are as follows. Yield: 65%. IR (KBr, cmÀ1): 1613 (w,
11.43; C, 51.45; H, 2.88. Found: N, 11.23; C, 51.68; H,
2.86%. leff = 6.3 lB. Data for complex 13 are as follows.
Yield: 75%. IR (KBr, cmÀ1): 1631 (w, mC@N), 1592, 1436,
1369, 1272, 1229, 1092, 819, 792, 769, 731, 416. Anal. Calc.
for C21H14Cl4CoN4: N, 10.71; C, 48.22; H, 2.70. Found: N,
10.50; C, 47.76; H, 2.77%. leff = 6.2 lB. Data for complex
14 are as follows. Yield: 69%. IR (KBr, cmÀ1): 1627 (w,
m
C@N), 1589, 1498, 1444, 1371, 1273, 1196, 1092, 820, 798,
774, 411. Anal. Calc. for C27H28Cl2FeN4: N, 10.47; C,
60.58; H, 5.27. Found: N, 10.01; C, 59.93; H, 5.24%.
l
eff = 6.6 lB. Data for complex 4 are as follows. Yield:
96%. IR (KBr, cmÀ1): 1609 (w, mC@N), 1591, 1503, 1371,
1274, 1218, 1093, 825, 762, 440. Anal. Calc. for
C24H22Cl2FeN4: N, 11.36; C, 58.45; H, 4.50. Found: N,
11.30; C, 58.63; H, 5.04%. leff = 5.6 lB. Data for complex
5 are as follows. Yield: 56%. IR (KBr, cmÀ1): 1614 (w,
mC@N), 1591, 1501, 1481, 1426, 1370, 1273, 1224, 1141,
1094, 819, 768, 728, 418. Anal. Calc. for
C21H14Br2Cl2CoN4: N, 9.15; C, 41.21; H, 2.31. Found:
N, 8.96; C, 40.83; H, 2.41%. leff = 5.6 lB.
m
C@N), 1591, 1498, 1471, 1371, 1279, 1225, 1143, 1094,
3.4. X-ray crystallographic studies
1006, 816, 773, 413. Anal. Calc. for C21H14Cl2F2FeN4:
N, 11.50; C, 51.78; H, 2.90. Found: N, 11.19; C, 51.41;
H, 2.94%. leff = 5.7 lB. Data for complex 6 are as follows.
Yield: 71%. IR (KBr, cmÀ1): 1629 (w, mC@N), 1592, 1501,
1435, 1370, 1275, 1228, 1142, 1093, 819, 792, 769, 740,
415. Anal. Calc. for C21H14Cl4FeN4: N, 10.77; C, 48.50;
H, 2.71. Found: N, 11.00; C, 48.15; H, 2.71%. leff = 6.6
lB. Data for complex 7 are as follows. Yield: 74%. IR
(KBr, cmÀ1): 1624 (w, mC@N), 1590, 1550, 1502, 1427,
1370, 1276, 1223, 1140, 1096, 818, 791, 768, 729, 416. Anal.
Calc. for C21H14Br2Cl2FeN4: N, 9.20; C, 41.42; H, 2.32.
Found: N, 9.21; C, 40.99; H, 2.53%. leff = 5.8 lB.
The crystals of compound L1 and L4 suitable for single-
crystal X-ray diffraction analysis were grown by slow evap-
oration of its hexane–EtOAc (8:1) solution in NMR tube,
while crystals of complexes 1, 4, 10 and 13 suitable for
X-ray diffraction analysis were obtained by slow diffusion
of Et2O into their methanol solutions at room temperature
under nitrogen atmosphere. With graphite-monochro-
˚
mated Mo Ka radiation (k = 0.71073 A) at 293(2) K, the
intensity data for crystals of L1, L4 and 10 were carried
out on a Bruker SMART 1000 CCD diffractometer, and
the data for crystals of 1 and 13 were collected on a Rigaku
RAXIS Rapid IP diffractometer while the data for crystal
of 4 was collected on Siemens Smart. Cell parameters were
obtained by global refinement of the positions of all col-
lected reflections. Intensities were corrected for Lorentz
and polarization effects and empirical absorption. The
structures were 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
[27]. The crystal data collection and refinement data for
ligand L1, L4 and complexes 1, 4, 10, 13 are summarized
in Table 8.
3.3.2. Synthesis of (L) CoCl2 (8–14)
Cobalt complexes 8–14 were prepared by the same syn-
thetic procedures for iron complexes 1–7 and obtained as
green powder. The synthetic procedure of 8 can be
described as follows: to a mixture of ligand L1 (0.071 g,
0.20 mmol) and CoCl2 (0.026 g, 0.20 mmol) was added
freshly distilled THF (5 mL) at room temperature. The
solution turned green immediately. The reaction mixture
was stirred for 6 h, and the precipitate was collected by fil-
tration and washed with diethyl ether, followed by drying
in vacuum. The desired complex was obtained as green
powder in 78% yield. IR (KBr, cmÀ1): 1624 (w, mC@N),
1592, 1502, 1481, 1372, 1273, 1213, 1093, 819, 774, 414.
Anal. Calc. For C23H20Cl2CoN4: N, 11.62; C, 57.28; H,
4.18. Found: N, 11.79; C, 56.95; H, 4.32%. leff = 6.4 lB.
Data for complex 9 are as follows. Yield: 73%. IR (KBr,
cmÀ1): 1611 (w, mC@N), 1589, 1480, 1442, 1371, 1270,
1213, 1198, 1092, 816, 771, 415. Anal. Calc. for:
C25H24Cl2CoN4: N, 10.98; C, 58.84; H, 4.74. Found: N,
10.75; C, 58.51; 4.70%. Data for complex 10 are as follows.
Yield: 74%. IR (KBr, cmÀ1): 1618 (w, mC@N), 1592, 1370,
1272, 1212, 1200, 1091, 817, 769, 415. Anal. Calc. for
C27H28Cl2CoN4: N, 10.41; C, 60.23; H, 5.24. Found: N,
10.32; C, 60.38; H, 5.05%. leff = 5.8 lB. Data for complex
11 are as follows. Yield: 72%. IR (KBr, cmÀ1): 1616 (w,
3.5. Procedure for ethylene oligomerization
3.5.1. Ethylene oligomerization at ambient pressure
The pre-catalyst (5 lmol) was added to a Schlenk-type
flask under nitrogen atmosphere. After the flask was evac-
uated-filled three times with nitrogen and final one with
ethylene, then charged with 30 mL of fleshly distilled tolu-
ene. The mixture was intensively stirred for 5 min at setting
temperature. The required amount of activator was subse-
quently added, and the reaction solution was intensively
stirred for desired period of time under 1 atm of ethylene
during the entire experiment. The reaction was terminated
with 50 mL acidified ethanol. The organic layer was ana-
lyzed by using gas chromatography.
m
C@N), 1591, 1482, 1368, 1219, 1092, 1022, 826, 763, 742,
411. Anal. Calc. for C24H22Cl2CoN4: N, 11.29; C, 58.08;
H, 4.47. Found: N, 11.27; C, 58.52; H, 4.21%. leff = 5.7 lB.
Data for complex 12 are as follows. Yield: 72%. IR (KBr,
cmÀ1): 1634 (w, mC@N), 1591, 1471, 1371, 1278, 1225, 1094,
1006, 781, 415. Anal. Calc. for C21H14F2Cl2CoN4: N,
3.5.2. Ethylene oligomerization at elevated pressure
The ethylene oligomerization at elevated-pressure
was performed in a stainless autoclave (500 mL) through

W.-H. Sun et al. / Journal of Organometallic Chemistry 692 (2007) 4506–4518
4517
Table 8
Crystal data and structure refinement for compound L1, L4, 1, 4, 10, 13
Data
L1
L4
1 Æ Et2O
4 Æ 0.5Et2O
10
13
Formula
Formula weight
Color
C
23H20N4
C24H21N4
365.45
Yellow
293(2)
C27H30Cl2FeN4O C26H27Cl2FeN4O0.5 C27H28CoCl2N4
C21H14Cl4CoN4
523.09
Black
293(2)
Orthorhombic
Fdd2
31.2837(7)
31.9642(7)
8.7312(2)
90
90
90
352.43
Yellow
294(2)
Triclinic
553.30
Black
530.27
Black
538.36
Black
Temperature (K)
Crystal system
Space group
293(2)
Monoclinic
P21/c
293(2)
Monoclinic
C2/c
293(2)
Monoclinic
P2(1)/c
Triclinic
ꢀ
ꢀ
P1
P1
˚
a (A)
7.621(2)
8.1766(2)
9.3682(2)
9.3848(2)
16.517(3)
16.998(3)
90
26.068(5)
11.744(2)
18.709(3)
90
9.6406(1)
15.413(2)
17.516(3)
90
˚
b (A)
11.455(3)
11.567(3)
99.315(5)
96.938(5)
99.134(5)
972.6(5)
˚
c (A)
13.7087(3)
86.4580(1)
78.1780(1)
82.0770(1)
1017.39(4)
2
a (ꢂ)
b (ꢂ)
c (ꢂ)
104.75(3)
90
119.291(2)
90
93.868(3)
90
3
˚
V (A )
2548.0(8)
4
4995.4(2)
8
2596.7(7)
4
8730.8(3)
16
0.71073
Z
2
˚
Wavelength (A)
Dcalc (mg mÀ3
0.71073
1.203
0.71073
1.193
0.71073
1.442
0.71073
1.410
0.71073
1.377
)
1.592
Crystal size (mm)
h Range (ꢂ)
0.60 · 0.50 · 0.40
1.80–26.44
À7 6 h 6 9,
À12 6k 6 14,
À14 6 l 6 10
5438/3898
0.56 · 0.43 · 0.19
2.20–28.32
À10 6 h 6 9,
À12 6 k 6 12,
À12 6 l 6 18
9953/4976
0.25 · 0.21 · 0.07 0.51 · 0.23 · 0.10
0.20 · 0.08 · 0.08
1.76–26.33
À11 6 h 6 12,
À19 6 k 6 18,
À17 6 l 6 21
14,375/5255
0.30 · 0.30 · 0.10
1.82–28.30
À41 6 h 6 37,
À40 6 k 6 41,
À11 6 l 6 11
11,687/4526
2.24–27.48
0 6 h 6 12,
0 6 k 6 21,
À22 6 l 6 21
22,435/6042
1.79–25.01
Limiting indices
À30 6 h 6 30,
À10 6 k 6 13,
À15 6 l 6 22
11,912/4393
Reflections
collected/unique
Rint
0.0246
0.0232
0.0640
0.0578
0.0598
0.0290
Data/restraints/
parameters
Absorption
coefficient
3898/0/244
4976/0/253
5822/7/316
4393/0/303
5255/0/307
4526/1/271
0.073
0.072
0.830
0.842
0.889
1.292
(mmÀ1
F000
)
372
386
1152
2200
1116
4208
Final R indices
[(I) > 2r(I)]
R indices (all data)
R1 = 0.0525,
wR2 = 0.1325
R1 = 0.1106,
wR2 = 0.1669
1.011
R1 = 0.0493,
wR2 = 0.1638
R1 = 0.0754,
wR2 = 0.1807
1.131
R1 = 0.0665,
wR2 = 0.1554
R1 = 0.1348,
wR2 = 0.1802
0.952
R1 = 0.0833,
wR2 = 0.1765
R1 = 0.1065,
wR2 = 0.1896
1.030
R1 = 0.0445,
wR2 = 0.0882
R1 = 0.1155,
wR2 = 0.1117
0.993
R1 = 0.0304,
wR2 = 0.0641
R1 = 0.0439,
wR2 = 0.0667
0.985
Goodness-of-fit
Largest difference in 0.227 and À0.194
0.227 and À0.190
0.680 and À0.360 0.625 and À0.603
0.379 and À0.284
0.329 and À0.248
peak and hole
À3
˚
(e A
)
a solenoid clave by continuous feeding of ethylene at
desired pressures. The complex (5 lmol) was dissolved in
100 mL of freshly distilled toluene under nitrogen atmo-
sphere, and the solution was subsequently transferred to
the fully dried reactor via a syringe. The required amount
of activator was then injected into the reactor, and the
reaction mixture was intensively stirred for the desired time
under corresponding pressure of ethylene during the entire
experiment. The reaction was terminated and analyzed by
using the same method as described above for the reaction
with 1 atm ethylene.
Appendix A. Supplementary material
CCDC 639003, 639004, 639005, 639006, 639007 and
639008 contain the supplementary crystallographic data
for L1, L4, 1, 4, 10 and 13. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2007.04.027.
Acknowledgements
References
This work was supported by NSFC No. 20674089 and
MOST 2006AA03Z553. M.A. is grateful to the Chinese
Academy of Science (CAS) and The Academy of Science
for The Developing World (TWAS) for the Postgraduate
Fellowships.
[1] (a) D. Vogt, in: B. Cornils, W.A. Herrmann (Eds.), Applied
Homogeneous Catalysis with Organometallic Compounds, vol. 1,
VCH, Weinheim, 2002, p. 240;
(b) W. Keim, F.H. Kowaldt, R. Goddard, C. Kruger, Angew. Chem.
¨
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