2-(Benzimidazol-2-yl)-1,10-phenanthrolyl metal (Fe and Co) complexes and their catalytic behaviors toward ethylene oligomerization

Article abstract of DOI:10.1016/j.jorganchem.2007.11.020

The N^∧N^∧N-tridentate metal complexes, LMCl₂ (M = Fe or Co; L represents a ligand of 2-(benzimidazol-2-yl)-1,10-phenanthrolines), were synthesized and fully characterized with spectroscopic and elemental analysis. The single-crystal X-ray crystallographic analyses revealed complex 1a with a distorted octahedron geometry due to incorporating one methanol molecule, and complexes 5a and 9b with a distorted trigonal-bipyramidal geometry. Upon activation with modified methylaluminoxane (MMAO), these complexes showed good to high catalytic activities toward ethylene oligomerization. The detailed investigations were carried out to disclose the influences of various reaction conditions and nature of ligands on their performing activities of metal complexes.

Full text of DOI:10.1016/j.jorganchem.2007.11.020

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 483–491
www.elsevier.com/locate/jorganchem
2-(Benzimidazol-2-yl)-1,10-phenanthrolyl metal (Fe and Co)
complexes and their catalytic behaviors toward ethylene oligomerization
Min Zhang, Peng Hao, Weiwei Zuo, Suyun Jie, Wen-Hua Sun *
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
Received 3 October 2007; received in revised form 8 November 2007; accepted 13 November 2007
Available online 21 November 2007
Abstract
The N^N^N-tridentate metal complexes, LMCl2 (M = Fe or Co; L represents a ligand of 2-(benzimidazol-2-yl)-1,10-phenanthrolines),
were synthesized and fully characterized with spectroscopic and elemental analysis. The single-crystal X-ray crystallographic analyses
revealed complex 1a with a distorted octahedron geometry due to incorporating one methanol molecule, and complexes 5a and 9b with
a distorted trigonal-bipyramidal geometry. Upon activation with modified methylaluminoxane (MMAO), these complexes showed good
to high catalytic activities toward ethylene oligomerization. The detailed investigations were carried out to disclose the influences of var-
ious reaction conditions and nature of ligands on their performing activities of metal complexes.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Iron and cobalt tridentate complexes; 2-(Benzimidazol-2-yl)-1,10-phenanthrolines; Ethylene oligomerization
1. Introduction
catalysts toward ethylene reactivity. However, a few mod-
els of iron catalysts showed only limited activities [5,6].
Regarding to the coordination environmental require-
ments of bis(imino)pyridyl iron and cobalt complexes, the
N^N^N-tridentate ligands would be focused as the core in
devising new complexes with potential catalytic activities.
During the course of our study, some late-transition metal
catalysts have been explored [7]; fortunately, several models
of iron and cobalt complexes, ligated by such as derivative
ligands of 2-imino-1,10-phenanthrolines (A) [8], 2-(2-benz-
imidazole)-6-iminopyridines (B) [9], and 6-(quinoxalin-2-
yl)-2-iminopyridines (C) [10], showed highly catalytic
activities toward ethylene oligomerization and polymeriza-
tion. 2-(Benzimidazol-2-yl)-1,10-phenanthrolines (D) [11],
resulted from the incorporation of a benzimidazole group
in place of an imino unit of ligands A, were designed as
ligands in nickel complexes performing high activity toward
ethylene dimerization. In parallel, the iron and cobalt com-
plexes containing 2-(benzimidazol-2-yl)-1,10-phenanthro-
lines have also been synthesized and fully investigated for
their catalyticbehaviors in ethylenereactivity (see Scheme 1).
The major chemical industry of more than 5 million tons
of a-olefins provides basic feedstocks for the preparation of
detergents, plasticizers and also the comonomers in the
copolymerization with ethylene for the linear low-density
polyethylene (LLDPE) [1]. The iron and cobalt catalysts
showed unique properties for the high selectivity of vinyl-
type oligomers and polyolefins (polyolefin waxes) pro-
duced, which was initially found by research groups of
Brookhart [2] and Gibson [3] using bis(imino)pyridyl iron
and cobalt complexes. In the catalytic systems of
bis(imino)pyridyl iron and cobalt complexes, more ten-
dency toward ethylene oligomerization was obtained with
less steric hindrance of ligands derivatives [4]. In the recent
decade, therefore, the intensive researches have explored
numerous model complexes of late-transition metals as
*
Corresponding author. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.11.020

484
M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
R2
N
N
N
N
R
N
N
N
N
N
N
N
N
N
Ar
N
N
Ar
Ar
R1
B
A
C
D
Scheme 1.
The titled iron and cobalt complexes, as a new model of
catalysts, showed good catalytic activities toward ethylene
oligomerization in the presence of modified methylalumi-
noxane (MMAO). The influences of catalytic reaction
parameters and the steric and electronic effects of ligands
were investigated in detail on their catalytic activities and
their oligomers obtained. Herein the syntheses and charac-
teristics of those complexes and their catalytic behaviors
are reported along with some discussion.
2. Results and discussion
2.1. Synthetic aspects
The tridentate 2-(benzimidazol-2-yl)-1,10-phenanthroli-
nyl ligands used in this study were prepared via the litera-
ture procedures [11]. The iron dichloride complexes 1a–10a
were formed by the reaction of an ethanol solution of the
corresponding ligand with one equivalent of FeCl2 ꢀ 4H2O
at ambient temperature under nitrogen for 6 h. Following
the filtration and washing with cold diethyl ether, the com-
plexes were isolated to give purple powders in good yields
(66–82%) with high purity. These complexes are air-stable
in the solid state but turned from purple to brown in solu-
tion when exposed to air for a few minutes, indicating their
oxidation in solution.
Fig. 1. ORTEP drawing of complex 1a with thermal ellipsoids at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
The cobalt dichloride complexes 1b–10b could be syn-
thesized in a fashion similar to the corresponding iron com-
plexes. Reactions of these ligands with anhydrous CoCl2 in
ethanol at room temperature for 4 h afforded the corre-
sponding complexes 1b–10b, which were isolated in good
yields (71–83%). The cobalt complexes are stable in both
solution and solid state.
The identity of these iron and cobalt complexes was
established by elemental analysis and IR spectrometry. In
comparison with the IR spectrometry of free organic com-
pounds [11], the absorption bands of complexes were
shifted to lower frequencies, indicating the coordination
effects. To understand their real structures, the single crys-
tals of complexes 1a, 5a and 9b were determined by single-
crystal X-ray diffraction.
Fig. 2. ORTEP drawing of complex 5a with thermal ellipsoids at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
2.2. Molecular structures
Crystals of complexes 1a and 5a suitable for X-ray struc-
tural determination were obtained by crystallization
through the slow layering of diethyl ether onto their meth-
anol solutions. However, single crystals of 9b were isolated
by diffusing the dichloromethane solution with light diethyl
ether. Their molecular structures are shown in Figs. 1–3,
Fig. 3. ORTEP drawing of complex 9b with thermal ellipsoids at the 30%
probability level. Hydrogen atoms and one molecular of CH2Cl2 have
been omitted for clarity.

M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
485
Table 1
Selected bond lengths (A) and angles (°) for complexes 1a, 5a and 9b
rial plane is nearly perpendicular to the phenanthrolinyl
plane with a dihedral angle of 93.3°. The dihedral angle
between bulky benzyl group (R2) and the phenanthrolinyl
plane is nearly perpendicular as 78.0°. It is notable that dif-
ferent R2 substituents in the ligands have some influence on
the Fe1–N3 bond length. The Fe1–N3 bond length of com-
˚
1a (M = Fe)
5a (M = Fe)
9b (M = Co)
M–N1
M–N2
M–N3
M–Cl1
M–Cl2
N3–C13
N3–C14
N4–C13
2.148(3)
2.353(3)
2.232(3)
2.3161(1)
2.5889(1)
1.326(4)
1.396(5)
1.359(5)
1.375(5)
73.33(1)
146.81(1)
73.57(1)
113.85(8)
171.73(9)
99.01(9)
88.46(8)
86.26(8)
95.18(9)
95.97(5)
2.117(4)
2.258(4)
2.182(4)
2.2972(2)
2.3204(2)
1.329(5)
1.382(6)
1.366(5)
1.402(6)
74.69(2)
146.84(2)
72.90(2)
100.55(1)
129.30(1)
94.53(1)
107.38(1)
95.99(1)
100.13(1)
123.26(6)
2.087(4)
2.167(4)
2.144(4)
2.2634(2)
2.3236(2)
1.334(6)
1.379(7)
1.359(6)
1.395(7)
75.97(2)
144.27(2)
73.77(2)
98.26(1)
157.83(1)
102.61(1)
92.90(1)
98.31(1)
101.72(1)
109.19(6)
2
˚
plex 5a (2.182(4) A, R = Bn) is shorter than that of com-
2
˚
plex 1a (2.232(3) A, R = H). Similar to complex 1a, the
Fe1–N1(phenanthroline) bond is shorter by about
˚
˚
0.065 A than Fe1–N3 (benzimidazole) (2.1824 A) bond
N4–C19
˚
˚
and 0.141 A than Fe1–N2 (phenanthroline) (2.2584 A)
bond, respectively. The two Fe–Cl bond lengths just show
a slight difference between the Fe1–Cl2 (2.3204(2) A) and
N2–M–N1
N2–M–N3
N1–M–N3
N2–M–Cl1
N1–M–Cl1
N3–M–Cl1
N1–M–Cl2
N2–M–Cl2
N3–M–Cl2
Cl1–M–Cl2
˚
˚
Fe1–Cl1 (2.2972(2) A).
As shown in Fig. 3, with the structural features similar
to complex 5a, the cobalt complex 9b exhibits a distorted
trigonal-bipyramidal geometry, with one nitrogen atom
(N1) of the phenanthroline and two chlorides composing
the equatorial plane. The cobalt atom is almost coplanar
with the equatorial plane with the slight deviation of
˚
0.0307 A. The three equatorial angles N1–Co1–Cl1,
individually, and selected bond lengths and angles are
listed in Table 1.
N1–Co1–Cl2 and Cl1–Co1–Cl2 are, respectively,
157.83(1)°, 92.90(1)°, and 109.19(6)° whereas the axial
Co–N bonds form an angle of 144.27(2)°. The equatorial
plane is nearly perpendicular to the phenanthroline plane
with a dihedral angle of 93.9°. The two axial Co–N bond
In the structure of 1a (Fig. 1), the coordination geome-
try around the iron center can be described as a distorted
octahedron because of the coordination of the solvent,
which is essentially similar to its nickel analogue [11]. As
expected, the iron center is coordinated to N1, N2 in the
phenanthroline ring and sp2 hybridized N3 instead of sp3
N4 in the benzimidazole ring, forming two fused 5-mem-
bered rings with acute N–Fe–N angles: 73.33(1)°
(N1–Fe1–N2) and 73.57(1)° (N1–Fe1–N3), in which the
˚
˚
lengths, 2.167(4) A and 2.144(4) A, are longer than that
˚
of Co1–N1 in the equatorial plane, 2.087(4) A. Further-
more, the two Co–Cl bond distances show a difference of
˚
about 0.0602 A.
2.3. Ethylene oligomerization
˚
iron atom lies ca. 0.0666 A out of the coordinated plane.
The benzimidazole plane is nearly oriented coplanar to
the phenanthroline plane with a dihedral angle of 4.8°.
The bond lengths of Fe–N are significantly different: the
The catalytic activity of the novel iron and cobalt pre-
catalysts 1a–10a and 1b–10b presented in Scheme 2 for
the oligomerization of ethylene has been evaluated employ-
ing modified methylaluminoxane (MMAO) as cocatalyst.
The catalysts displayed similar activation characteristics
to their analogous nickel systems [11], in which an immedi-
ate exotherm was observed without induction period. Dur-
ing the oligomerization reaction (20 min), a decrease in
activity was noticed; the final activity was only 5–15% of
the initial activity.
˚
Fe1–N1 bond length (2.148(3) A) is shorter than that of
˚
˚
Fe1–N2 (2.353(3) A) and Fe1–N3 (2.232(3) A), in which
the differences were virtually identical to those seen in the
2,6-bis(imino)pyridyl iron(II) complexes [3] and 2-imino-
1,10-phenanthrolinyl iron(II) complexes [8a]. However,
there is an unexceptional asymmetry in the two Fe–Cl link-
˚
ages, with Fe1–Cl(2) being about 0.2728 A longer than
Fe1–Cl(1) in two terminal Cl in trans-location, which is
much larger than that of its nickel analogue (0.0637 A) [11].
Many efforts were devoted to optimizing the catalytic
performance. Complexes 6a and 6b, the most active precat-
alysts, were typically scrutinized under a range of reaction
conditions (see Tables 2 and 3). The noteworthy results in
Tables 2 and 3 disclose some important trends relating
reaction parameters to both activity and selectivity for
1-butene. Under optimized conditions, it was observed that
ligand environment and metal center have predominant
effects on the catalytic properties of the complexes.
˚
In the solid state of 5a, the iron atom is surrounded by a
2-(1-benzyl-benzimidazol-2-yl)-9-methyl-1,10-phenanthro-
line ligand, and two terminal chlorides. The geometry of
the five-coordinate complex can be described as distorted
trigonal bipyramidal, with the phenanthroline nitrogen
atom (N1) and the two chlorides (Cl1 and Cl2) forming
the equatorial plane (Fig. 2). The iron atom slightly devi-
˚
ates by 0.0316 A from the plane with the equatorial angles
between 107.38(1)° and 129.30(1)°, deviating from 120°.
The two axial Fe–N bonds subtend an angle of
146.84(2)°, a distortion is a consequence of satisfying the
tridentate chelating constraints of the ligand. This equato-
2.3.1. Effects of cocatalyst
The precatalysts 6a and 6b have been tested in the olig-
omerization of ethylene with Et2AlCl, MAO or MMAO as
cocatalyst and showed high activities for the dimerization

486
M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
R2
N
R2
N
FeCl2·4H2O or CoCl2
EtOH
N
N
N
N
N
N
M
R1
R1
Cl
Cl
1a 2a 3a 4a 5a 6a 7a 8a 9a 10a 1b 2b 3b 4b 5b 6b 7b 8b 9b 10b
R1 Me Me Me Me Me H
Me Me Me Me Me H
Me Et i-Pr Bn
H
H
H
H
H
H
H
H
R2
M
H
Me Et i-Pr Bn
H
Me Et i-Pr Bn
H
H
Me Et i-Pr Bn
Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Co Co Co Co Co Co Co Co Co Co
Scheme 2. Synthesis of tridentate iron and cobalt complexes.
Table 2
Ethylene oligomerization with different cocatalysta
and trimerization of ethylene (Table 2). The use of different
cocatalyst greatly influenced the catalytic results: for both
of the complexes 6a and 6b, MMAO led to more active
and higher selective systems for a-C4 than Et2AlCl or
MAO (Entries 5 and 10, Table 2). Therefore, further cata-
lytic studies were performed by the activation of MMAO.
Entry Complex Cocatalyst Al/ Activityb Oligomer
a-C4
(%)
M
distributionc (%)
P
P
C4=
C
C6=
C
1
2
3
4
5
6
7
8
9
6a
6a
6a
6a
6a
6b
6b
6b
6b
6b
Et2AlCl
MAO
MAO
1000 7.27
500 10.2
800 14.3
1000 11.4
1000 35.1
1000 5.13
800 4.22
1000 8.03
1200 6.20
1000 10.7
100
92.7
70.3
91.5
87.3
85.1
92.0
75.1
83.8
80.1
72.5
87.0
7.3
6.7
3.7
5.0
1.2
8.8
9.6
10.7
11.1
93.3
96.3
95.0
98.8
91.2
90.4
89.3
88.9
MAO
2.3.2. Effects of reaction parameters in the presence of
MMAO
MMAO
Et2AlCl
MAO
MAO
MAO
On the basis of the above preliminary results above,
complexes 6a and 6b were selected for further optimization,
investigating the influence of the [Al]/[M] (M = Fe or Co)
molar ratio, reaction temperature and ethylene pressure.
The detailed results are shown in Table 3.
10
a
MMAO
General conditions: 5 lmol complex; 100 mL toluene; 20 °C, 30 atm of
C2H4, 20 min.
The amount of cocatalyst MMAO significantly affected
the catalytic results. For iron complex 6a, the enhancement
of Al/Fe molar ratio from 500 to 1000 resulted in an
increase of catalytic activity (Entries 1–3, Table 3), which
may be attributed to the fact that MMAO scavenged
adventitious water and impurities in the solvent at low
Al/Fe ratio and the iron complex required more cocatalyst
to be activated. With an Al/Fe molar ratio of 1000, the cat-
alytic activity of 6a peaked at 3.51 ꢁ 106 g molꢂ1(Fe) hꢂ1
(Entry 3, Table 3). A further increase of the Al/Fe molar
ratio resulted in decreased oligomerization activity (Entries
3–5, Table 3). This observation could be traced to the
increasing amount of isobutyl groups which come from
MMAO and the generated species hindered the insertion
reaction of ethylene due to steric bulkiness [9b,12]. Mean-
while, it is noteworthy that the a-C4 selectivity of 6a
decreased gradually with the increase of the Al/Fe molar
ratio. Therefore, a Al/Fe ratio of 1000 appeared as a good
tradeoff between activity and selectivity. For cobalt com-
b
105 g molꢂ1 (M) hꢂ1
.
c
Determined by GC.
Table 3
Ethylene oligomerization with 6a/MMAO and 6b/MMAO systema
Entry Complex Al/
M
T
P
Activityb Oligomer
distributionc (%)
a-C4
(%)
(°C) (atm)
P
96.4
95.0
94.1
95.6
98.2
99.1
P
C4=
C
C6=
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
6b
500 20 30
10.1
21.7
35.1
25.3
18.1
10.6
97.1
2.9
3.6
5.0
5.9
4.4
1.8
0.9
94.8
93.5
92.0
87.2
80.1
71.8
44.0
20.1
73.8
82.6
88.2
87.0
84.4
83.0
78.0
75.2
60.5
33.2
23.6
68.6
77.5
800 20 30
1000 20 30
1200 20 30
1500 20 30
1000 40 30
1000 60 30
1000 80 30
1000 20 10
1000 20 20
500 20 30
1000 20 30
1200 20 30
1500 20 30
1800 20 30
2000 20 30
1500 40 30
1500 60 30
1500 80 30
1500 20 10
1500 20 20
3.10
1.43
5.72
10.2
4.54
10.7
15.4
23.2
13.2
10.1
100
94.1
93.7
90.5
88.9
87.4
88.2
90.1
92.0
95.1
97.7
98.5
90.4
91.3
5.9
6.3
9.5
11.1
12.6
11.8
9.9
8.0
4.9
2.3
1.5
plex 6b, the highest activity (2.32 ꢁ 106 g molꢂ1(Co) hꢂ1
)
was observed at the Al/Co ratio of 1500 (Entry 14, Table
3), and higher or lower amounts of MMAO led to lower
activities (Entries 14–16, Table 3). Notably, for both of
complexes 6a and 6b, the varied amounts of cocatalyst
showed no clear impact on the proportion of C4 compo-
nent in the products.
As the ethylene oligomerization is a highly exothermic
reaction, the reaction temperature significantly affects
the catalytic activity. To understand this influence, the
two catalytic systems, 6a/MMAO(Al/Fe = 1000) and
9.52
4.90
1.62
3.25
9.83
9.6
8.7
General conditions: 5 lmol complex; 100 mL toluene; 20 min.
b
105 g molꢂ1 (M) hꢂ1
Determined by GC.
.
c

M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
487
Table 4
6b/MMAO(Al/Co = 1500) were investigated at 30 atm of
Ethylene oligomerization with 1a–10a and 1b–10b/MMAO systemsa
ethylene. For the two systems, the elevation of the reaction
temperature from 20 °C to 80 °C resulted in a sharp
decrease of activity, which may be attributed to the decom-
position of the active catalytic sites and lower ethylene sol-
ubility at higher temperature (Entries 3, 6–8 and Entries 14,
17–19). Moreover, higher reaction temperature resulted in
an increase of the proportion of C4, but a sharp decrease
of selectivity for 1-butene. A similar influence of tempera-
ture on the oligomer distribution produced by iron- and
cobalt-based systems has been reported [9b].
The studies of pressure variation on ethylene oligomeri-
zation by catalysts (6a and 6b) have shown in both cases
the ethylene concentration significantly affects the catalytic
behavior of the complexes. The increase of ethylene pres-
sure resulted in much higher activities, probably owning
to an effect of increased ethylene concentration in solution
(Entries 3, 9, 10 and Entries 14, 20, 21). It is also worth
mentioning that better selectivity for 1-butene were
observed at higher pressure, which can be ascribed to the
fact that the increased dimerization activity in turn attenu-
ated the effect of parallel isomerization of 1-butene into 2-
butene [13].
Entry Complex Al/M Activityb Oligomer distributionc a-C4 (%)
(%)
P
P
C4=
C
C6=
C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
a
1a
2a
3a
4a
5a
6a
7a
8a
9a
10a
1 b
2 b
3b
4b
5b
6b
7b
8b
9b
10b
1000 10.2
95.6
92.1
93.6
94.6
94.2
95.0
93.2
95.3
93.2
92.9
92.1
90.3
90.0
89.2
90.2
88.2
87.5
90.1
91.2
90.7
4.4
7.9
6.4
5.4
5.8
5.0
6.8
4.7
6.8
7.1
7.9
9.7
10.0
10.8
9.8
11.8
12.5
9.9
8.8
9.3
95.0
84.4
86.0
85.1
81.6
92.0
82.2
80.7
78.4
75.3
91.0
83.4
80.5
81.7
77.3
83.0
75.0
74.2
75.7
71.2
1000
1000
1000
1000
7.55
6.23
6.06
8.37
1000 35.1
1000 10.7
1000
1000
1000
9.17
9.22
7.15
1500 10.9
1500
1500
1500
1500
7.21
5.02
5.52
7.57
1500 23.2
1500 10.4
1500
1500
1500
8.49
8.61
7.02
General conditions: 5 lmol complex; 100 mL toluene; MMAO as
cocatalyst; 20 °C, 30 atm of C2H4, 20 min.
b
105 g molꢂ1 (M) hꢂ1
Determined by GC.
.
2.3.3. Effects of ligand environment and metal center
c
The results of ethylene oligomerization with all the iron
and cobalt complexes as precatalysts are listed in Table 4.
It can be observed that the variation of the R1 and R2 sub-
stituents in the ligands resulted in great changes of the cat-
alytic behaviors, such as activity and a-C4 selectivity.
Similar to the nickel analogues [11], the introduction of a
methyl group on the 9-position of the phenanthroline ring
led to a decrease in oligomerization activity and a slight
increase in a-C4 selectivity. This could be demonstrated
by comparing complexes 1a–4a (R1 = Me) with 6a–9a
(R1 = H). As shown in Table 4, complexes 6a–9a (Entries
6–9, Table 4) displayed higher activities and lower a-C4
selectivity than their analogues 1a–4a (Entries 1–4, Table
4). The same trend was also observed for the cobalt dichlo-
ride complexes 1b–4b, 6b–9b (compare Entries 16–19 with
Entries 11–14, Table 4).
Replacing the active proton on the nitrogen atom of the
benzimidazole group in the complex with an alkyl group
led to a decrease in oligomerization activity and a-C4 selec-
tivity. Complexes 1a, 6a and 1b, 6b containing the N–H
group showed much higher activities than their N-alkylated
analogues (compare Entry 1 with Entries 2–5, Entry 6 with
Entries 7–10; Entry 11 with Entries 12–15, Entry 16 with
Entries 17–20, Table 4). These results, which concurred
with the literature reports [9,14], can be attributed to the
deprotonation of the N–H group to give anionic amide
ligands when activated by the organoaluminum cocatalyst,
and form N–Al species to enhance their catalytic activity.
Different alkyl groups, such as methyl, ethyl, isopropyl
and benzyl group, showed no obvious influence on a-C4
selectivity. Meanwhile, the steric bulk effects of these
groups on oligomerization activities are not very regular,
which may be attributed to the longer distance between
the alkyl group and the metal center.
The nature of the metal center has a large influence on
catalyst performance. Except for 1a and 1b, the activities
of the cobalt complexes are substantially lower than for
their iron analogues, which keep the trend paralleling the
behavior of iron versus cobalt ethylene reactivity catalysts
[2,3,8,9b]. Meanwhile, comparison of the oligomerization
properties between iron and cobalt catalysts indicated that
the cobalt complexes gave a slightly smaller amount of
butene and higher amount of hexenes than their corre-
sponding iron complexes. Similar results were also dis-
closed in 2-arylimino-9-phenyl-1,10-phenanthrolinyl-iron
and cobalt complexes [8g]. Compared with the nickel ana-
logues [11], the iron(II) and cobalt(II) complexes contain-
ing 2-(benzimidazol-2-yl)-1,10-phenanthroline derivatives
showed comparable activities, and as expected, higher
selectivity for 1-butene.
3. Conclusions
The synthesis and characterization of a new class of
iron- and cobalt-based ethylene oligomerization catalysts
ligated by 2-(benzimidazol-2-yl)-1,10-phenanthroline deriv-
atives have been described. On treatment with MMAO,
these complexes oligomerize ethylene to dimers and trimers
with high activities and good selectivity of a-olefins. This
result confirm the hypothesis of N^N^N-tridentate iron
dihalides potentially having high catalytic activity toward
ethylene reactivity. Further experimental results illustrate

488
M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
their sensitivity toward different ligand environment, Al/M
molar ratio, reaction temperature and ethylene pressure.
Complexes 1a–4a and 1b–4b with methyl group on the
9-position of the phenanthrolinyl ring (R1 = Me) gave
lower activities but higher selectivities for 1-butene than
those of complexes 6a–9a and 6b–9b (R1 = H). The incor-
poration of an alkyl group (R2) on the N atom of the benz-
imidazole led to the decrease in oligomerization activity
and selectivity for 1-butene (complexes 1a, 1b, 6a and
6b). In general, higher activities and better selectivity of
a-olefin could be obtained under higher ethylene pressure
and ambient temperature.
IR (KBr disk, cmꢂ1): 3052, 2961, 1621, 1583, 1519, 1479,
1448, 1429, 1335, 858, 751. Anal. Calc. for C27H20N4FeCl2
(526.04): C, 61.51; H, 3.82; N, 10.63. Found: C, 61.22; H,
3.51; N, 10.32%. Complex 6a: purple powder in 77% yield.
IR (KBr disk, cmꢂ1): 3281, 3057, 1622, 1579, 1515, 1453,
1323, 862, 747, 703. Anal. Calc. for C19H12N4FeCl2
(421.98): C, 53.94; H, 2.86; N, 13.24. Found: C, 53.66; H,
2.49; N, 13.61%. Complex 7a: purple powder in 82% yield.
IR (KBr disk, cmꢂ1): 3054, 2942, 1620, 1580, 1528, 1504,
1462, 1415, 1330, 855, 742, 704. Anal. Calc. for
C20H14N4FeCl2 (435.99): C, 54.96; H, 3.23; N, 12.82.
Found: C, 54.63; H, 3.01; N, 12.47%. Complex 8a: purple
powder in 79% yield. IR (KBr disk, cmꢂ1): 3058, 2948,
1620, 1606, 1576, 1526, 1483, 1442, 1334, 861, 746. Anal.
Calc. for C21H16N4FeCl2 (450.01): C, 55.91; H, 3.57; N,
12.42. Found: C, 55.52; H, 3.19; N, 12.04%. Complex 9a:
purple powder in 73% yield. IR (KBr disk, cmꢂ1): 3057,
2956, 1626, 1581, 1519, 1439, 1334, 1310, 848, 741. Anal.
Calc. for C22H18N4FeCl2 (464.03): C, 56.81; H, 3.90; N,
12.04. Found: C, 56.47; H, 3.51; N, 12.38%. Complex
10a: purple powder in 68% yield. IR (KBr disk, cmꢂ1):
3058, 2953, 1622, 1604, 1581, 1526, 1499, 1440, 1334,
851, 737. Anal. Calc. for C26H18N4FeCl2 (512.03): C,
60.85; H, 3.54; N, 10.92. Found: C, 61.20; H, 3.91; N,
10.66%.
4. Experimental
4.1. General
All air- or moisture-sensitive manipulations were carried
out under nitrogen using standard Schlenk techniques. The
IR spectra were obtained on a Perkin–Elmer FT-IR 2000
spectrophotometer by using KBr disks in the range of
4000–400 cmꢂ1. Elemental analyses were performed with
a Flash EA 1112 microanalyzer. GC was performed with
a VARIAN CP-3800 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.
Toluene was refluxed in the presence of sodium/benzo-
phenone and distilled under nitrogen prior to use. The
polymerization-grade ethylene was supplied by Beijing
Yansan Petrochemical Co. Et2AlCl (1.90 M) solution in
toluene was purchased from Acros Chemicals, while meth-
ylaluminoxane (MAO, 1.46 M in toluene) and modified
methylaluminoxane (MMAO, 1.93 M in heptane, 3A) were
purchased from Akzo Nobel Corp. All other commercial
chemicals were used without further purification.
4.2.2. Characterization of complexes 1b–10b
Characterization data of diclorocobalt complexes
(1b–10b). Complex 1b: Green powder in 79% yield. IR
(KBr disk, cmꢂ1): 3271, 3058, 2964, 1624, 1586, 1503,
1464, 1321, 1148, 863, 745. Anal. Calc. for C20H14N4CoCl2
(438.99): C, 54.57; H, 3.21; N, 12.73. Found: C, 54.66; H,
3.55; N, 12.38%. Complex 2b: Green powder in 77% yield.
IR (KBr disk, cmꢂ1): 3060, 2947, 1621, 1585, 1524, 1485,
1464, 1335, 1130, 857, 741. Anal. Calc. for C21H16N4CoCl2
(453.01): C, 55.53; H, 3.55; N, 12.33. Found: C, 55.87; H,
3.19; N, 12.69%. Complex 3b: Green powder in 80% yield.
IR (KBr disk, cmꢂ1): 3061, 2946, 1620, 1583, 1520, 1487,
1448, 1334, 1154, 859, 744. Anal. Calc. for C22H18N4CoCl2
(467.02): C, 56.43; H, 3.87; N, 11.97. Found: C, 56.81; H,
3.50; N, 12.31%. Complex 4b: Green powder in 82% yield.
IR (KBr disk, cmꢂ1): 3062, 2959, 1620, 1584, 1513, 1455,
1335, 1308, 1162, 867, 743. Anal. Calc. for C23H20N4CoCl2
(481.04): C, 57.28; H, 4.18; N, 11.62. Found: C, 57.59; H,
4.52; N, 11.27%. Complex 5b: Green powder in 75% yield.
IR (KBr disk, cmꢂ1): 3057, 2960, 1621, 1583, 1520, 1480,
1449, 1335, 1153, 859, 750. Anal. Calc. for C27H20N4CoCl2
(529.04): C, 61.15; H, 3.80; N, 10.56. Found: C, 61.52; H,
3.45; N, 10.18%. Complex 6b: Green powder in 71% yield.
IR (KBr disk, cmꢂ1): 3283, 3059, 1623, 1576, 1512, 1447,
1321, 1147, 982, 863, 743. Anal. Calc. for C19H12N4CoCl2
(424.98): C, 53.55; H, 2.84; N, 13.15. Found: C, 53.22; H,
2.51; N, 13.48%. Complex 7b: Green powder in 76% yield.
IR (KBr disk, cmꢂ1): 3057, 2948, 1620, 1574, 1529, 1508,
1459, 1418, 1333, 1131, 848, 741, 704. Anal. Calc. for
C20H14N4CoCl2 (438.99): C, 54.57; H, 3.21; N, 12.73.
Found: C, 54.96; H, 3.60; N, 12.37%. Complex 8b: Green
4.2. Characterization of complexes 1a–10a and 1b–10b
4.2.1. Characterization of complexes 1a–10a
Characterization data of dichloroiron complexes
(1a–10a). Complex 1a: purple powder in 80% yield. IR
(KBr disk, cmꢂ1): 3250, 3055, 2984, 1623, 1585, 1503,
1427, 1321, 861, 746. Anal. Calc. for C20H14N4FeCl2
(435.99): C, 54.96; H, 3.23; N, 12.82. Found: C, 54.59; H,
3.42; N, 12.60%. Complex 2a: purple powder in 72% yield.
IR (KBr disk, cmꢂ1): 3047, 2950, 1621, 1585, 1502, 1484,
1465, 857, 741. Anal. Calc. for C21H16N4FeCl2 (450.01):
C, 55.91; H, 3.57; N, 12.42. Found: C, 55.61; H, 3.44; N,
12.17%. Complex 3a: purple powder in 69% yield. IR
(KBr disk, cmꢂ1): 3056, 2954, 1621, 1585, 1489, 1450,
1334, 859, 744. Anal. Calc. for C22H18N4FeCl2 (464.03):
C, 56.81; H, 3.90; N, 12.04. Found: C, 56.55; H, 3.71; N,
12.41%. Complex 4a: purple powder in 70% yield. IR
(KBr disk, cmꢂ1): 3051, 2968, 1620, 1583, 1513, 1453,
1335, 1315, 1163, 867, 743. Anal. Calc. for C23H20N4FeCl2
(478.04): C, 57.65; H, 4.21; N, 11.69. Found: C, 57.29; H,
4.55; N, 11.29%. Complex 5a: purple powder in 66% yield.

M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
489
powder in 77% yield. IR (KBr disk, cmꢂ1): 3061, 2942,
1621, 1608, 1579, 1526, 1483, 1442, 1334, 860, 746. Anal.
Calc. for C21H16N4CoCl2 (453.01): C, 55.53; H, 3.55; N,
12.33. Found: C, 55.80; H, 3.91; N, 12.71%. Complex 9b:
Green powder in 83% yield. IR (KBr disk, cmꢂ1): 3064,
2950, 1622, 1578, 1520, 1439, 1335, 1307, 854, 744. Anal.
Calc. for C22H18N4CoCl2 (467.02): C, 56.43; H, 3.87; N,
11.97. Found: C, 56.74; H, 3.52; N, 11.57%. Complex
10b: Green powder in 74% yield. IR (KBr disk, cmꢂ1):
3065, 2951, 1621, 1605, 1576, 1524, 1435, 1333, 854, 742,
707. Anal. Calc. for C26H18N4CoCl2 (515.02): C, 60.49;
H, 3.51; N, 10.85. Found: C, 60.77; H, 3.89; N, 11.03%.
CCD diffractometer with graphite-monochromated Mo
Ka radiation (k = 0.71073 A). 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 of F2. All non-hydrogen atoms
were refined anisotropically. Structure solution and refine-
ment were performed using the SHELXL-97 Package [15].
Crystal date and processing parameters are summarized
in Table 5.
4.4. General procedure for ethylene oligomerization
4.3. X-ray crystal structure determination of 1a, 5a and 9b
A 250 mL stainless steel autoclave equipped with a
mechanical stirrer and a temperature controller was heated
in vacuo at 80 °C for 2 h. It was cooled to the required
reaction temperature under ethylene, and charged with tol-
uene, the desired amount of cocatalyst, and toluene solu-
tion of catalytic precursor; the total volume was 100 mL.
Single-crystal X-ray diffraction studies for complex 1a
and 9b were carried out on a Rigaku RAXIS Rapid IP dif-
fractometer with graphite-monochromated Mo Ka radia-
tion (k = 0.71073 A). Intensity data for crystals of
complex 5a was collected with a Bruker SMART 1000
˚
Table 5
Crystallographic data and refinement for 1a, 5a and 9b
1a ꢀ CH3OH
5a
9b
Empirical formula
fw
C
468.14
21H17Cl2FeN4O
C27H20Cl2FeN4
527.22
C23H20Cl4CoN4
553.16
Temperature (K)
Wavelength (A)
Crystal system
296(2)
0.71073
Triclinic
293(2)
293(2)
˚
0.71073
Monoclinic
P2(1)/c
12.8396(7)
12.8513(8)
15.4641(9)
90
72.080(2)
90
2427.9(2)
4
0.71073
Monoclinic
C2/c
23.124(5)
12.674(3)
17.258(4)
90
110.56(3)
90
4735.4(2)
8
ꢀ
Space group
P1
˚
a (A)
6.9675(1)
11.179(2)
13.640(3)
76.77(3)
80.16(3)
72.09(3)
978.3(3)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
Volume (A )
Z
Dcalc (g mꢂ3
)
1.589
1.065
478
1.442
0.865
1080
1.552
1.196
2248
l (mmꢂ1
F(000)
)
Crystal size (mm)
h Range (°)
0.31 ꢁ 0.25 ꢁ 0.08
0.20 ꢁ 0.15 ꢁ 0.11
0.32 ꢁ 0.15 ꢁ 0.13
2.70–27.48
2.10–28.31
1.86–27.42
Limiting indicates
ꢂ8 6 h 6 9,
ꢂ14 6 k 6 14,
ꢂ17 6 l 6 17
ꢂ17 6 h 6 17,
ꢂ17 6 k 6 13,
ꢂ20 6 l 6 20
ꢂ29 6 h 6 29,
ꢂ16 6 k 6 16,
ꢂ22 6 l 6 22
No. of reflections collected
No. of unique reflections
Rint
6954
4371
0.0414
24953
5962
0.1293
10288
5388
0.0490
Completeness to h (%)
Absorption coefficient
No. of parameters
Goodness-of-fit on F2
97.4 (h = 27.48°)
Empirical
271
98.7 (h = 28.31°)
Empirical
307
99.7 (h = 27.42°)
Empirical
294
1.145
0.939
1.071
Final R indices (I > 2r(I))
R1 = 0.0572
R1 = 0.0603
R1 = 0.0670
wR2 = 0.1113
wR2 = 0.1232
wR2 = 0.1637
R indices (all data)
R1 = 0.0852
R1 = 0.2212
R1 = 0.1225
wR2 = 0.1225
wR2 = 0.1746
wR2 = 0.1965
ꢂ3
˚
Largest diff peak, hole (e A
)
0.290, ꢂ0.332
0.338, ꢂ0.262
0.792, ꢂ0.477

490
M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
(c) C. Bianchini, G. Mantovani, A. Meli, F. Migliacci, F. Laschi,
Organometallics 22 (2003) 2545–2547;
(d) M.-S. Zhou, S.-P. Huang, L.-H. Weng, W.-H. Sun, D.-S. Liu,
J. Organomet. Chem. 665 (2003) 237–245;
(e) G.J.P. Britovsek, V.C. Gibson, O.D. Hoarau, S.K. Spitz-
messer, A.J.P. White, D.J. Williams, Inorg. Chem. 42 (2003)
3454–3465;
(f) R. Cowdell, C.J. Davies, S.J. Hilton, J.-D. Mare´chal, G.A.
Solan, O. Thomas, J. Fawcett, Dalton Trans. (2004) 3231–
3240;
The reactor was sealed and pressurized to the desired eth-
ylene pressure, and the ethylene pressure was maintained
with feeding of ethylene. After the reaction was carried
out for the required period, the pressure was released. A
small amount of the reaction solution was collected, and
the reaction in this small sample was terminated by the
addition of 5% aqueous hydrogen chloride. The organic
layer was analyzed by gas chromatography (GC) for deter-
mining the composition and mass distribution of oligomers
obtained.
(g) W.-H. Sun, X. Tang, T. Gao, B. Wu, W. Zhang, H. Ma,
Organometallics 23 (2004) 5037–5047.
[6] (a) C. Popeney, Z. Guan, Organometallics 24 (2005) 1145–1155;
(b) Q.-Z. Yang, A. Kermagoret, M. Agostinho, O. Siri, P. Braunstein,
Organometallics 25 (2006) 5518–5527;
5. Supplementary material
(c) V.C. Gibson, C. Redshaw, G.A. Solan, Chem. Rev. 107 (2007)
1745–1776;
(d) B.L. Small, R. Rios, E.R. Fernandez, M.J. Carney, Organome-
tallics 26 (2007) 1744–1749;
(e) P. Barbaro, C. Bianchini, G. Giambastiani, I.G. Rios, A. Meli,
W. Oberhauser, A.M. Segarra, L. Sorace, A. Toti, Organometallics
26 (2007) 4639–4651;
CCDC 662797 and 662798 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
(f) V.C. Gibson, C. Redshaw, G.A. Solan, A.J.P. White, D.J.
Williams, Organometallics 26 (2007) 5119–5123;
(g) L. Wang, C. Zhang, Z.-X. Wang, Eur. J. Inorg. Chem. (2007)
2477–2487;
Acknowledgements
This work was supported by NSFC No. 20674089 and
MOST No. 2006AA03Z553.
(h) C. Go¨rl, H.G. Alt, J. Organomet. Chem. 692 (2007) 4580–4592.
[7] (a) L. Wang, W.-H. Sun, L. Han, Z. Li, Y. Hu, C. He, C. Yan, J.
Organomet. Chem. 650 (2002) 59–64;
(b) W.-H. Sun, W. Zhang, T. Gao, X. Tang, L. Chen, Y. Li, X. Jin,
J. Organomet. Chem. 689 (2004) 917–929;
References
(c) W.-H. Sun, Z. Li, H. Hu, B. Wu, H. Yang, N. Zhu, X. Leng, H.
Wang, New J. Chem. 26 (2002) 1474–1478;
(d) C. Shao, W.-H. Sun, Z. Li, Y. Hu, L. Han, Catal. Commun. 3
(2002) 405–410;
[1] (a) D. Vogt, in: B. Cornils, W.A. Herrmann (Eds.), Applied
Homogeneous Catalysis with Organometallic Compounds, vol. 1,
VCH, Weinheim, Germany, 2002, pp. 240–253;
(b) G.W. Parshall, S.D. Ittel, in: Homogeneous Catalysis: The
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes, Wiley, New York, 1992, pp. 68–72;
(e) S. Jie, D. Zhang, T. Zhang, W.-H. Sun, J. Chen, Q. Ren, D. Liu,
G. Zheng, W. Chen, J. Organomet. Chem. 690 (2005)
1739–1749;
(c) J. Skupinska, Chem. Rev. 91 (1991) 613–648.
[2] (a) B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc.
120 (1998) 4049–4050;
(b) B.L. Small, M. Brookhart, Macromolecules 32 (1999) 2120–2130.
[3] (a) G.J.P. Britovsek, V.C. Gibson, S.J. McTavish, G.A. Solan,
A.J.P. White, D.J. Williams, B.S. Kimberley, P.J. Maddox, Chem.
Commun. (1998) 849–850;
(f) J. Hou, W.-H. Sun, S. Zhang, H. Ma, Y. Deng, X. Lu,
Organometallics 25 (2006) 236–244;
(g) L. Wang, W.-H. Sun, L. Han, H. Yang, Y. Hu, X. Jin, J.
Organomet. Chem. 658 (2002) 62–70;
(h) D. Zhang, S. Jie, T. Zhang, J. Hou, W. Li, D. Zhao, W.-H. Sun,
Acta Polym. Sinica. 5 (2004) 758–762;
(i) S. Zhang, I. Vystorop, Z. Tang, W.-H. Sun, Organometallics 26
(2007) 2456–2460;
(b) G.J.P. Britovsek, S. Mastroianni, G.A. Solan, S.P.D. Baugh, C.
Redshaw, V.C. Gibson, A.J.P. White, D.J. Williams, M.R.J. Else-
good, Chem. Eur. J. 6 (2000) 2221–2231.
(j) S. Zhang, W.-H. Sun, X. Kuang, I. Vystorop, J. Yi, J. Organomet.
Chem. 692 (2007) 5307–5316;
[4] (a) B.L. Small, M. Brookhart, J. Am. Chem. Soc. 120 (1998) 7143–
7144;
(k) W.-H. Sun, K. Wang, K. Wedeking, D. Zhang, S. Zhang, J. Cai,
Y. Li, Organometallics 26 (2007) 4781–4790.
(b) G.J.P. Britovsek, M. Bruce, V.C. Gibson, B.S. Kimberley, P.J.
Maddox, S. Mastroianni, S.J. McTavish, C. Redshaw, G.A. Solan,
S. Strolmberg, A.J.P. White, D.J. Williams, J. Am. Chem. Soc. 121
(1999) 8728–8740;
[8] (a) W.-H. Sun, S. Jie, S. Zhang, W. Zhang, Y. Song, H. Ma,
Organometallics 25 (2006) 666–677;
(b) W.-H. Sun, S. Zhang, S. Jie, W. Zhang, Y. Li, H. Ma, J. Chen,
K. Wedeking, R. Frohlich, J. Organomet. Chem. 691 (2006) 4196–
¨
(c) Z. Ma, W.-H. Sun, N. Zhu, Z. Li, C. Shao, Y. Hu, Polym. Int. 51
(2002) 349–352;
4203;
(c) J.D.A. Pelletier, Y.D.M. Champouret, J. Cadarso, L. Clowes, M.
(d) A.S. Abu-Surrah, K. Lappalainen, U. Piironen, P. Lehmus, T.
Repo, M. Leskela, J. Organomet. Chem. 648 (2002) 55–61;
(e) C. Bianchini, G. Mantovani, A. Meli, F. Migliacci, F. Zanobini,
F. Laschi, A. Sommazzi, Eur. J. Inorg. Chem. (2003) 1620–1631;
(f) M.E. Bluhm, C. Folli, M. Do¨ring, J. Mol. Catal. A: Chem. 212
(2004) 13–18;
Ganete, K. Singh, V. Thanarajasingham, G.A. Solan, J. Organomet.
˜
Chem. 691 (2006) 4114–4123;
(d) S. Jie, S. Zhang, K. Wedeking, W. Zhang, H. Ma, X. Lu, Y.
Deng, W.-H. Sun, C.R. Chim. 9 (2006) 1500–1509;
(e) S. Jie, S. Zhang, W.-H. Sun, X. Kuang, T. Liu, J. Guo, J. Mol.
Catal. A: Chem. 269 (2007) 85–96;
(g) I.S. Paulino, U. Schuchardt, J. Mol. Catal. A: Chem. 211 (2004)
55–58.
(f) S. Zhang, S. Jie, Q. Shi, W.-H. Sun, J. Guo, J. Mol. Catal. A:
Chem. 276 (2007) 174–183;
[5] (a) M. Qian, M. Wang, R. He, J. Mol. Catal. A: Chem. 160 (2000)
243–247;
(g) S. Jie, S. Zhang, W.-H. Sun, Eur. J. Inorg. Chem. (2007) 5584–
5598.
(b) L. LePichon, D.W. Stephan, X. Gao, Q. Wang, Organometallics
21 (2002) 1362–1366;
[9] (a) P. Hao, S. Zhang, W.-H. Sun, Q. Shi, S. Adewuyi, X. Lu, P. Li,
Organometallics 26 (2007) 2439–2446;

M. Zhang et al. / Journal of Organometallic Chemistry 693 (2008) 483–491
491
(b) W.-H. Sun, P. Hao, S. Zhang, Q. Shi, W. Zuo, X. Tang,
Organometallics 26 (2007) 2720–2734.
[13] (a) F. Speiser, P. Braunstein, L. Saussine, Organometallics 23 (2004)
2633–2640;
[10] (a) W.-H. Sun, P. Hao, G. Li, S. Zhang, W. Wang, J. Yi, M. Asma,
N. Tang, J. Organomet. Chem. 692 (2007) 4506–4518;
(b) S. Adewuyi, G. Li, S. Zhang, W. Wang, P. Hao, W.-H.
Sun, N. Tang, J. Yi, J. Organomet. Chem. 692 (2007) 3532–
3541.
(b) X. Tang, D. Zhang, S. Jie, W.-H. Sun, J. Chen, J. Organomet.
Chem. 690 (2005) 3918–3928;
(c) N. Ajellal, M.C.A. Kuhn, A.D.G. Boff, M. Ho¨rner, C.M.
Thomas, J.-F. Carpentier, O.L. Casagrande Jr., Organometallics 25
(2006) 1213–1216.
[11] M. Zhang, S. Zhang, P. Hao, S. Jie, W.-H. Sun, P. Li, X. Lu, Eur. J.
Inorg. Chem. (2007) 3816–3826.
[14] (a) D.S. McGuinness, P. Wasserscheid, D.H. Morgan, J.T. Dixon,
Organometallics 24 (2005) 552–556;
[12] (a) E.Y. Chen, T.J. Marks, Chem. Rev. 100 (2000) 1391–1434;
(b) W. Zhang, W.-H. Sun, S. Zhang, J. Hou, K. Wedeking, S.
Schultz, R. Fro¨hlich, H. Song, Organometallics 25 (2006)
1961–1969.
´
´
(b) A.R. Karam, E.L. Catarı, F. Lopez-Linares, G. Agrifoglio, C.L.
´
Albano, A. Dıaz-Barrios, T.E. Lehmann, S.V. Pekerar, L.A. Albor-
´
noz, R. Atencio, T. Gonzalez, H.B. Ortega, P. Joskowics, Appl.
[15] G.M. Sheldrick, SHELXTL-97 Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
Catal. A: Gen. 280 (2005) 165–173.