Unsymmetric bimetal(II) complexes: Synthesis, structures and catalytic behaviors toward ethylene

Article abstract of DOI:10.1016/j.jorganchem.2007.08.020

A series of unsymmetric bimetal(II) (Fe, Co and Ni) complexes ligated by 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines were synthesized and characterized by IR spectra and elemental analysis, while a representative nickel(II) complex (5a) w

Full text of DOI:10.1016/j.jorganchem.2007.08.020

Journal of Organometallic Chemistry 692 (2007) 5307–5316
www.elsevier.com/locate/jorganchem
Unsymmetric bimetal(II) complexes: Synthesis, structures
and catalytic behaviors toward ethylene
a
a,
a
a
b
Shu Zhang , Wen-Hua Sun *, Xiaofei Kuang , Igor Vystorop , Jianjun Yi
a
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
b
Petrochemical Research Institute, PetroChina Company Limited, No. 20 Xueyuan Road, Beijing 100083, China
Received 18 April 2007; received in revised form 16 August 2007; accepted 16 August 2007
Available online 23 August 2007
Abstract
A series of unsymmetric bimetal(II) (Fe, Co and Ni) complexes ligated by 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiaze-
pines were synthesized and characterized by IR spectra and elemental analysis, while a representative nickel(II) complex (5a) was
determined by single-crystal X-ray crystallography. These iron(II) complexes were found to exhibit good activities for ethylene oligomer-
ization and polymerization in the presence of MMAO and afforded a-olefins in high selectivity, and the composition of oligomers
followed the Schluz–Flory distribution. The nickel(II) complexes mainly dimerize ethylene with considerable activity. The influences
of coordinative ligands and reaction parameters were fully investigated on the catalytic activity and properties of these complexes.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: 2-Methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines; Bimetal complexes; Ethylene oligomerization; Ethylene polymerization
1. Introduction
models have been relied on designing new ligands [5] and
recently effective ones such as 2-imino-1,10-phenanthro-
lines [6], 2-benzimidazolylpyridines [7] and 2-quinoxali-
nyl-6-iminopyridines [8] in our group. At the same time,
the nickel complexes as homogeneous catalysts have also
drawn many attentions toward ethylene activation with
the complexes bearing bidentate [9] and tridentate ligands
[6b,7a,10].
The use of compartmental ligands with multi-binding
sites imposing close special confinement on two metal
centers has drawn much attention [11]. Within the alkene
polymerization/oilgomerization, there are several examples
of bimetallic compartmentalized LM2 catalytic systems
incorporating early transition metals [12], meanwhile there
is a few of reports on the late transition metal [13] and
heterobimetallic complexes [14]. Moreover, these ligands
usually provided same coordination pockets for bimetallic
catalytic systems. On the base of bis(imino)pyridyl metal
(iron or cobalt) complexes [3] and the extensive works of
monoiminopyridyl metal complexes [15], the bimetallic
iron(II) and cobalt(II) complexes bearing 2-methyl-2,
a-Olefins are major industrial reactants and extensively
used in the preparation of detergents, lubricants, plasticiz-
ers, oil field chemicals as well as monomers for copolymer-
ization. The increasing demand of a-olefin industry has
annually been growing around 5%. Therefore there is an
increasing interest of developing new catalyst and process
to produce a-olefins in both academic and industrial
consideration. Recently, the investigation for ethylene
polymerization and oligomerization with late transition
metals has mushroomed over the past decade [1], which
was initiated by the discovery of highly active catalysts of
diimino Ni(II) and Pd(II) [2] as well as 2,6-bis(imino)pyrid-
inyl Fe(II) and Co(II) precursors [3]. The products by the
iron(II) and cobalt(II) catalysts varied from polyethylene
to oligomers [4] through tuning the steric and electronic
properties of the ligands, thereafter alternative catalysts’
*
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 ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.08.020

5308
S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines
were
and the metal cation. According to the elemental analysis
data, nickel complexes were in accordant with the formula
LNi2Cl4 Æ 2H2O. The unambiguous molecular structures of
1, 4c and 5a were determined by X-ray diffraction analysis,
and the molecular structure of 4c was reported in our
previous work [16].
recently synthesized and provided two different coordina-
tion environments for two active sites [16]. The iron and
cobalt complexes showed good catalytic activity for ethyl-
ene oligomerization and polymerization with high a-olefin
selectivity. Extensively more analogues of iron and cobalt
complexes were prepared and investigated for the scope
of ethylene reactivity with comparing the influences of
the ligands’ environments. Moreover, the bimetallic nicke-
l(II) complexes were also prepared and could dimerize eth-
ylene to butenes in the presence of diethylaluminum
chloride (Et2AlCl). Herein their results are going reported
with discussions.
2.2. Crystal structures
In the solid state of 1 (Fig. 1), two pyridine rings are
linked by the seven-membered ring of the benzodinazepine.
˚
The N(3)–C(10) bond length is 1.2772(2) A with the typical
character of C@N double-bond. However, the N(2)–C(8)
˚
(1.4735(2) A) shows the character of C–N single bond.
2. Results and discussion
2.1. Synthesis and characterization of the ligands and
complexes
The ligands and their iron and cobalt complexes were
efficiently synthesized according to our reported procedure
[16]. The binickel complexes were easily formed in high
yield by the reaction of nickel dichloride with the ligands
(Scheme 1). All the organic compounds were characterized
by IR spectra, 1H NMR, 13C NMR and elemental analysis
while the complexes were characterized by elemental anal-
ysis and FT-IR spectra. In the IR spectra of bimetallic
complexes, the C@N stretching frequencies appeared in
the range of 1614–1623 cmÀ1. The wave number shifted
to lower and the peak intensity were greatly induced with
comparing the corresponding ligands, indicating the coor-
dination interaction between all the imino nitrogen atoms
Fig. 1. Molecular structure of 1 with thermal ellipsoids at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
NH2
R1
R1
NH2
R2
ethanol, p-TsOH,
silica-alumina catalyst,
molecular sieves
N
N
silica-alumina catalyst
2
+
O
O
N
NH
N
NH2
O
O
1
R1
R1
.
2FeCl2 4H2O
or 2CoCl2
R1
R1
N
N
N
N
N
N
N
NH
N
N
N
NH
R2
R2
M
M
R1
R2
R1
R2
R1
R1
Cl
Cl
Cl
Cl
2a-2d
M=Fe, 3a-3d
M=Co, 4a-4d
2NiCl2.6H2O
a: R1=Me, R2=H;
b: R1=Et, R2=H;
c: R1=i-Pr, R2=H;
d: R1=Me, R2=Me
EtOH
R1
R1
N
N
Cl-
R2
N
N
N
N
H
Ni
Ni
R2
Cl
Cl
R1
R1
OH2
H2O
Cl
5a-5d
Scheme 1. Synthesis of ligands and bimetallic complexes.

S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
5309
3
˚
A), which can be due to the sp N3. However, the difference
is not as obvious as that in its cobalt analogues. The same
trend as the cobalt complex 4c for the M2–N bond lengths
[16] is observed in 5a. The Ni2–N5 (pyridine) bond
˚
˚
(2.020(1) A) is shorter by about 0.21 A than the Ni2–N4
(benzodinazepine) bond (2.234(1) A) and 0.24 A than the
Ni2–N6 (imino) bond (2.265(1) A). The Ni1–Cl bond
lengths (2.534(5) A and 2.625(4) A) are much longer than
Ni2–Cl bond lengths (2.276(4) A and 2.479(4) A). As
would be expected, the Ni–Cl (bridging) distance is longer
than the Ni–Cl (terminal) distance for both Ni1 and Ni2.
˚
˚
˚
˚
˚
˚
˚
˚
The imino N6–C23 bond length is 1.280(2) A with the
typical character of a C@N double bond. However, the
˚
˚
N1–C2 (1.319(2) A) and N4–C15 (1.347(2) A) bond
become longer compared with the free ligand. This could
be explained as the distortion caused by the seven-mem-
bered ring and the bridging chloride. The phenyl rings link
to the imino groups are oriented nearly perpendicular to
the coordination plane with the dihedral angle of 76.5ꢁ
(Ni1) and 79.9ꢁ (Ni2). A shorter intermetallic distance
Fig. 2. Molecular structure of 5a with thermal ellipsoids at the 30%
probability. Hydrogen atoms and solvent have been omitted for clarity.
Single crystals of 5a, grown by laying diethyl ether on a
dichloromethane/methanol (v/v = 1:1) solution were used
to determine its structure by single-crystal X-ray diffraction
analysis (Fig. 2). Selected bond lengths and angles are
reported in Table 1. The structure of 5a consists of a
binuclear asymmetric unit in which the ligand behaves as
a bischelate and bridges two nickel(II) fragments. The
geometry at each nickel center can be best described as
distorted octahedral, in which each nickel atom is coordi-
nated to three nitrogen atoms as one bridging chlorine
atom connect the two metal centers. A chloride and an
oxygen atom of water complete two independent six-coor-
dinated geometries (Fig. 3). Some differences in the coordi-
nation sphere at each metal center are observed because of
the unsymmetric ligand. The Ni1–N3 (benzodinazepine)
˚
(4.717 A) for Ni1Á Á ÁNi2 is observed than the Co1Á Á ÁCo2
˚
˚
bond length (2.126(1) A) is longer about 0.09 A than the
˚
Ni1–N2 (pyridine) bond length (2.034(1) A) and about
0.14 A than the Ni1–N1 (imino) bond length (1.990(1)
˚
˚
Fig. 3. Skeleton of complex 5a. The Ni1Á Á ÁNi2 distance is 4.717 A.
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) for complex 5a
˚
Bond lengths (A)
Ni1–N1
Ni1–N2
Ni1–N3
Ni1–Cl1
Ni1–Cl2
Ni1–O1
1.990(1)
2.034(1)
2.126(1)
2.534(5)
2.625(4)
2.074(1)
Ni2–O2
Ni2–N4
Ni2–N5
Ni2–N6
Ni2–Cl3
2.026(1)
2.234(1)
2.020(1)
2.265(1)
2.276(4)
Ni2–Cl2
N1–C2
N3–C8
N4–C15
N6–C23
2.479(4)
1.319(2)
1.518(2)
1.347(2)
1.280(2)
Bond angles (ꢁ)
N1–Ni1–N2
N2–Ni1–N3
N1–Ni1–N3
N1–Ni1–Cl1
N2–Ni1–Cl1
N3–Ni1–Cl1
N1–Ni1–Cl2
N2–Ni1–Cl2
N3–Ni1–Cl2
Cl1–Ni1–Cl2
N1–Ni1–O(1)
75.7(5)
77.7(4)
152.1(5)
95.8(4)
89.3(4)
75.3(3)
88.6(3)
96.0(3)
102.7(3)
173.86(2)
106.9(5)
N2–Ni1–O1
N3–Ni1–O1
O1–Ni1–Cl1
O1–Ni1–Cl2
N4–Ni2–N5
N5–Ni2–N6
N4–Ni2–N6
N4–Ni2–Cl3
N5–Ni2–Cl3
N6–Ni2–Cl3
175.6(5)
N4–Ni2–Cl2
N5–Ni2–Cl2
N6–Ni2–Cl2
Cl3–Ni2–Cl2
N5–Ni2–O2
O2–Ni2–N4
O2–Ni2–N6
O2–Ni2–Cl3
O2–Ni2–Cl2
Ni1–Cl2-Ni2
71.3(3)
77.4(3)
100.2(4)
93.9(3)
80.7(3)
74.3(5)
80.5(5)
154.8(5)
97.2(3)
104.4(3)
88.0(3)
104.3(3)
167.70(2)
171.9(4)
106.9(5)
98.2(5)
83.5(3)
95.3(3)
135.08(2)

5310
S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
Fig. 4. (a) Hydrogen-bond interactions in complex 5a. (b) Hydrogen-bond containing sheets in 5a.
distance in 4c [16], which could be attributed to the
bridging chloride. However, it is longer than that in similar
complexes [13m], which caused by the tension of the seven-
membered ring.
2.3. Catalytic behavior for ethylene
2.3.1. Ethylene oligomerization and polymerization of Fe(II)
and Co(II) complexes
In addition, extensive hydrogen bonds are formed
between the chlorides and some hydrogen atoms of the
ligand. As shown in Fig. 4a and Table 2, three kinds of
hydrogen-bonding interaction exist in 5a. The result is
the creation of a polymeric hydrogen-bonded supermolec-
ular sheet by self-assembly of the complex (Fig. 4b).
The iron complexes were studied for their catalytic activ-
ities with various alkylaluminums as co-catalysts. The cat-
alytic system with modified methylaluminoxane (MMAO)
showed best catalytic activity for ethylene oligomerization
and polymerization with very high selectivity for a-olefin,
and the detailed results of precursors 3a and 3c were
reported [16]. Here, the effect of ligand environment on cat-
alytic behavior was investigated in detail.
The variation of the R substituent on the imino-N of
ligands resulted in great changes of the catalytic perfor-
mance. In the presence of MMAO as cocatalyst, the biiron
complexes 3a–d showed high activities for ethylene reactiv-
ity (Table 3, entries 3–6). Based on these data, the
oligomerization and the polymerization activities as well
Table 2
Hydrogen-bond interactions in complex 5a
D–HÁ Á ÁA
D–H
HÁ Á ÁA
DÁ Á ÁA
\DHA (ꢁ)
C6–H6AÁ Á ÁCl3
C16–H16AÁ Á ÁCl3
C24–H24BÁ Á ÁCl1
0.930
0.970
0.960
2.609
2.710
2.668
3.446
3.627
3.354
150.11
158.06
128.85

S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
5311
Table 3
Results of ethylene oligomerization and polymerization by complexes 3a–d, 4a–da
Entry
Cat.
Cocat.
Al/Fe
Tb (ꢁC)
Oligomers
Activityc
Polymer activitye
PEf (wt%)
71.4
K
%a-Od
1
2
3
4
5
6
7
8
9
3a
3a
3a
3b
3c
3d
4a
4b
4c
4d
4a
4a
4b
4c
4d
4d
MAO
Et3Al
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1500
1500
1500
1500
1500
1500
30
30
30
30
30
30
30
30
30
30
60
80
60
60
50
60
1.05
–
0.59
>99
2.62
–
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
6.17
1.36
0.46
2.98
1.83
0.81
0.73
2.02
7.38
1.58
1.06
2.13
1.81
1.16
0.71
0.61
0.59
0.62
0.64
0.57
0.53
0.57
0.80
0.74
0.68
0.40
0.56
0.60
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
4.15
1.19
0.30
3.46
1.36
0.74
0.45
1.35
22.1
1.92
1.21
0.86
7.76
2.04
40.2
46.7
39.5
53.7
42.6
47.7
38.1
40.1
75.0
54.9
53.3
28.8
81.1
63.8
10
11
12
13
14
15
16
a
General conditions: cat: 2.5 lmol; reaction time: 30 min; ethylene pressure: 30 atm; solvent: toluene (100 mL).
Reaction temperature.
Activity for oligomers: 106 g molÀ1(cat.) hÀ1
%a-olefin content determined by GC and GC–MS.
Activity for polyethylene wax: 106 g molÀ1(cat.) hÀ1
The percentage of polyethylene wax.
b
c
d
e
f
.
.
as the K value varied in the order of 3a (with substituent of
dimethyl) > 3b (with diethyl) > 3c (with diisopropyl). The
introduction of the methyl group on para-position (3d)
led to lower activity and higher percentage of polyethylene
wax. The oligomer distribution was also influenced by the
ligand environment which could be observed from Fig. 5.
For the sterically bulkier catalyst 3c, relatively smaller
amount of longer-chain oligomers were produced with
comparing its analogue 3a and 3b. In addition, the methyl
substituted at the 4-position of the aryl ring also led to
decreased productivity of longer-chain oligomers.
tion and polymerization with bimetallic cobalt analogues
4a–d/MMAO system were investigated under the same
conditions (Al/Co molar ratio of 1000 and 30 ꢁC). Varia-
tion of the R1 group at the ortho-positions of the
imino-N aryl ring resulted in changes of the catalytic
performance. It was observed that increase in steric hin-
drance of the R1 group led to decreased activity and lower
K value. Furthermore, the methyl group at 4-position of
the aryl ring had slight influence on the catalytic activity
with a decreased K value. The oligomer distribution
obtained by 4a–d/MMAO system was shown in Fig. 6.
The catalytic performance of cobalt complex 4a was greatly
affected by the reaction temperature. Very high activity was
In similar manner, to compare the effect of the ligand
environment on the catalytic activity, ethylene oligomeriza-
55
50
45
3d
40
3a
45
4d
3b
3c
35
30
25
20
15
10
5
40
35
30
25
20
15
10
5
4a
4b
4c
0
0
4
6
8
10
12
14
16
18
20
22
24
26
28
4
6
8
10
12
14
16
18
20
22
24
Carbon number
Fig. 5. Oligomers distribution obtained in entries 3–6 in Table 3.
Carbon number
Fig. 6. Oligomers distribution obtained in entries 7–10 in Table 3.

5312
S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
Table 4
Ethylene oligomerization by 5a–da
Entry
Complex
Cocat.
Al/Ni
T (ꢁC)
Activityb
Oligomer distribution
C4 (%)
C6 (%)
a-C4 (%)
1
2
3
4
5
6
7
8
9
10
11
12
a
5a
5a
5a
5a
5a
5a
5a
5a
5a
5b
5c
5d
Et3Al
MAO
1000
1000
100
200
300
400
500
300
300
300
300
300
25
25
25
25
25
25
25
40
60
25
25
25
1.86
0.25
0.69
3.56
7.55
6.65
5.73
6.91
3.77
9.12
3.37
5.62
95.5
64.9
100
4.5
35.1
0
93.2
99.2
95.3
97.1
97.5
97.2
95.2
97.7
96.5
94.1
92.7
92.5
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
95.2
95.9
97.0
96.5
96.7
96.4
96.8
94.7
95.8
4.8
4.1
3.0
3.5
3.3
3.6
3.2
5.3
4.2
General conditions: 5 lmol cat.; 30 atm ethylene pressure; 100 mL toluene as solvent; 30 min; 25 ꢁC.
b
Activity for oligomers: 105 g molÀ1(cat.) hÀ1
.
observed at 60 ꢁC. However, further enhancement of reac-
tion temperature to 80 ꢁC resulted in sharply decrease of
catalytic activity which can be attributed to the decompo-
sition of the active species. The catalytic performance of
complex 4b–d was also investigated at 60 ꢁC, and the cata-
lytic activity was not greatly increased. It was noteworthy
that complex 4d showed higher polymerization activity
and percentage of polyethylene wax at 50 ꢁC.
tion of the aryl ring led to lower catalytic activity and a-C4
selectivity. However, ligand environments had no obvious
influence on the distribution of oligomers.
3. Conclusion
A series of bimetallic iron(II), cobalt(II) and nickel(II)
complexes had been synthesized and characterized. Upon
treatment with MMAO, these iron(II) and cobalt(II) com-
plexes showed high catalytic activity for ethylene oligomer-
ization and polymerization with very high a-olefin
selectivity. As an extensive work, the effect of ligand envi-
ronment was investigated in detail, the increase in steric
hindrance of the R1 group led to decreased activity. The
iron(II) complexes showed relative higher activity than
their cobalt analogues. Furthermore, larger amount of
longer-chain olefins were obtained with the iron complexes
than those produced by cobalt analogues. In the presence
of Et2AlCl, the nickel(II) catalytic systems enable oligo-
merization of ethylene to dimerize mainly for butenes with
high activity and a-C4 selectivity. Complex 5b with ethyl
substituents in the ortho-positions of the aryl ring in the
ligand backbone displayed the highest activity of
2.3.2. Ethylene oligomerization of nickel(II) complexes
Various co-catalysts such as Et2AlCl, Et3Al and MAO
were used to activate complex 5a for ethylene reactivity
at room temperature (Table 4). The nickel catalytic system
containing Et2AlCl showed the highest activity for ethylene
oligomerization, and the butenes were observed as the
major products. Therefore, further catalytic studies were
performed using Et2AlCl as cocatalyst, and the analyses
of oligomers obtained were carried out by GC.
The effects of Al/Ni molar ratio on catalytic activities of
ethylene oligomerization were investigated with complex 5a
in order to find the suitable molar ratio for better activity.
When the Al/Ni ratio was enhanced from 100 to 500, the
activity of 5a was initially increased and then decreased
with optimum catalytic activity with Al/Ni molar ratio of
300. In addition, the distribution of oligomers was not
greatly affected by the Al/Ni molar ratio (Table 4, entries
3–7). The catalytic activity was also affected by the reaction
temperature. Similar to the diiron complexes, the nickel
complexes displayed lower activity at higher reaction
temperature because of lower ethylene solubility and the
possibility of less stability of nickel active species. Different
substituents on the imino-N aryl ring could have some
influences on their catalytic behavior. For the 2,6-dialkyl-
substituted complexes 5a–c, somewhat reduced catalytic
activity and a-C4 selectivity was observed for the sterically
bulkier catalyst systems. This could be demonstrated by
comparing the 2,6-diisopropyl-substituted 5c with the 2,
6-dimethyl-substituted 5a or 2,6-diethyl-substituted 5b
(Table 4, entries 5, 10 and 11). The methyl group at 4-posi-
9.12 · 105 g molÀ1(cat.) hÀ1
.
4. Experimental
4.1. General considerations
All manipulations of air and/or moisture sensitive com-
pounds were carried out under a nitrogen atmosphere
using standard Schlenk techniques. NMR spectra were
recorded on Bruker DMX-300 spectrometer, with TMS
as the internal standard. IR spectra were recorded on a
Perkin–Elmer FT-IR 2000 spectrometer using KBr disc in
the range of 4000–400 cmÀ1. Elemental analysis was
performed on a Flash EA 1112 microanalyzer. GC analysis
was performed with a VARIAN CP-3800 gas chromato-
graph equipped with a flame ionization detector and a

S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
5313
30 m (0.2 mm i.d., 0.25 lm film thickness) CP-Sil 5 CB col-
umn. The yields of oligomers were calculated by referenc-
ing with the mass of the solvent on the basis of the
prerequisite that the mass of each fraction was approxi-
mately proportional to its integrated areas in the GC trace.
GC–MS analysis was performed with HP 5890 SERIES II
(s, 3H); 2.03 (m, 12H, PhCH3); 1.97 (s, 3H). 13C NMR
(75 MHz, CDCl3): d 167.33, 167.24, 164.67, 155.61
155.18, 146.36, 139.43, 139.22, 137.34, 137.05, 132.37,
129.47, 128.74, 127.13, 125.42, 125.35, 122.47, 121.90,
121.62, 121.24, 120.75, 120.00, 119.37, 73.67, 38.08,
31.77, 20.92, 18.07, 16.67. Anal. Calc. for C42H44N6
(632.84): C, 79.71; H, 7.01; N, 13.28. Found: C, 79.42; H,
7.02; N, 13.13%.
1
and HP 5971 SERIES mass detectors. H NMR and 13C
NMR of the polymer samples were recorded on a Brucker
DMS-300 instrument at 110 ꢁC in 1,2-dichlorobenzene-d4
using TMS as an internal standard. Solvents were dried
by the appropriate drying reagents and distilled under
nitrogen prior to use. Modified methylaluminoxane
(MMAO, 1.93 M in heptane, 3A) was purchased from
Akzo Corp. Et2AlCl (1.90 M) solution in hexane was pur-
chased from Acros Chemicals. All other chemicals were
obtained commercially and used without further purifica-
tion unless otherwise stated.
4.2.2. Synthesis of iron and cobalt complexes
All the iron and cobalt complexes were efficiently syn-
thesized according to our reported procedure [16]. The data
for 3b are as follows. Yield: 96%. FT-IR (KBr disk, cmÀ1):
3247 (mN–H), 3067, 2967, 1622 (mC@N), 1586, 1456, 1371,
1258, 1202, 814, 773. Anal. Calc. for C44H48Cl4Fe2N6
(914.39): C, 57.79; H, 5.29; N, 9.19. Found: C, 57.93; H,
5.08; N, 8.85%.
Data for 3d are as follows. Yield: 97%. FT-IR (KBr
disk, cmÀ1): 3184 (mN–H), 3075, 2950, 1616 (mC@N), 1590,
1470, 1371, 1258, 1216, 853, 814, 749. Anal. Calc. for
C42H44Cl4Fe2N6 (886.34): C, 56.91; H, 5.00; N, 9.48.
Found: C, 56.95; H, 4.69; N, 9.28%.
Data for 4b are as follows. Yield: 83%. FT-IR (KBr
disk, cmÀ1): 3237 (mN–H), 3068, 2966, 1623 (mC@N), 1586,
1466, 1372, 1259, 1203, 813, 772. Anal. Calc. for
C46H54Cl4Co2N6O (966.64): C, 57.16; H, 5.63; N, 8.69.
Found: C, 56.82; H, 5.81; N, 8.80%.
Data for 4d are as follows. Yield: 85%. FT-IR (KBr
disk, cmÀ1): 3244 (mN–H), 3071, 2915, 1619 (mC@N), 1588,
1470, 1371, 1259, 1218, 1022, 855, 815, 749. Anal. Calc.
for C44H50Cl4Co2N6O (938.59): C, 56.31; H, 5.37; N,
8.95. Found: C, 56.17; H, 5.22; N, 8.69%.
4.2. Synthesis and characterization
4.2.1. Synthesis of ligands
4.2.1.1. 3,3-Dihydro-2-methyl-2,4-bis{[((2,6-diethylphe-
nyl)imino)ethyl]pyridin-2-yl}-1H-1,5-benzodiazepine
(2b). In a manner similar to that described for 2a [16],
the ligand 2b was synthesized as a yellow solid in 32% yield.
Mp: 144–146 ꢁC. FT-IR (KBr disk, cmÀ1): 3327 (mN–H),
3060, 2965, 1646 (mC@N), 1571, 1452, 1363, 1308, 1237,
1196, 1107, 818, 752. 1H NMR (300 MHz, CDCl3): d
8.49 (d, J = 7.7 Hz, 1H, Py Hm); 8.42 (d, J = 7.7 Hz, 1H,
Py Hm); 8.20 (d, J = 7.7 Hz, 1H, Py Hm); 7.89
(t, J = 7.8 Hz, 1H, Py Hp); 7.74 (t, J = 7.7 Hz, 1H, Py
Hp); 7.60 (d, J = 7.6 Hz, 1H, Py Hm); 7.39 (d,
J = 7.7 Hz, 1H, Ar H); 7.13–6.93 (m, 9H, Ar H); 5.27
(s, 1H); 4.11 (d, J = 12.4 Hz, 1H,); 3.36 (d, J = 12.7 Hz,
1H); 2.57–2.29 (m, 8H,CH2CH3); 2.24 (s, 3H); 2.18
(s, 3H); 1.75 (s, 3H); 1.18–1.08 (m, 12H, CH2CH3).
13C NMR (75 MHz, CDCl3): d 166.40, 166.22, 166.15,
164.06, 155.11, 154.48, 147.27, 138.63, 136.83, 136.48,
130.67, 129.00, 126.56, 125.49, 122.91, 121.87, 121.27,
120.93, 120.54, 120.16, 118.76, 72.67, 37.53, 31.16, 24.17,
16.45, 13.25. Anal. Calc. for C44H48N6 (660.89): C, 79.96;
H, 7.32; N, 12.72. Found: C, 79.83; H, 7.44; N, 12.33%.
4.2.3. Synthesis of L Æ 2NiCl2 (5a–d)
Complexes 5a–d were synthesized by the reaction of
NiCl2 Æ 6H2O with the corresponding ligands in ethanol.
A typical synthetic procedure for 5a could be described
as follows. The ligand 2a (0.0901 g, 0.15 mmol) and
2.1 equiv. of NiCl2 Æ 6H2O (0.0748 g, 0.31 mmol) were
added together in a Schlenk tube which was purged three
times with nitrogen and then charged with freshly distilled
ethanol (3 mL). The reaction mixture was stirred at room
temperature for 6 h and absolute diethyl ether was added
to precipitate the complex. The resulted precipitate was fil-
tered, washed with diethyl ether and dried in a vacuum to
furnish the pure product as a yellow powder (0.1250 g,
0.14 mmol) in 93% yield. FT-IR (KBr disk, cmÀ1): 3379,
3201 (mN–H), 3071, 2916, 1614 (mC@N), 1586, 1469, 1373,
1260, 1206, 815, 774. Anal. Calc. for C40H44Cl4N6Ni2O2
(900.02): C, 53.38; H, 4.93; N, 9.34. Found: C, 53.52; H,
4.78; N, 9.01%. Data for 5b are as follows. Yield: 97%.
FT-IR (KBr disk, cmÀ1): 3380, 3188 (mN–H), 3072, 2966,
1614 (mC@N), 1585, 1469, 1373, 1261, 1204, 814, 773. Anal.
Calc. for C44H52Cl4N6Ni2O2 (956.12): C, 55.27; H, 5.48; N,
8.79. Found: C, 55.62; H, 5.17; N, 8.56. Data for 5c are as
follows. Yield: 74%. FT-IR (KBr disk, cmÀ1): 3368, 3190
(mN–H), 3072, 2967, 1614 (mC@N), 1585, 1468, 1370, 1263,
4.2.1.2. 3,3-Dihydro-2-methyl-2,4-bis{[(2,4,6-trimethylphe-
nyl)imino]ethylpyridin-2-yl}-1H-1,5-benzodiazepine
(2d). In a manner similar to that described for 2a [16],
the ligand 2d was synthesized as a yellow solid in 26% yield.
Mp: 161–162 ꢁC. FT-IR (KBr disk, cmÀ1): 3327 (mN–H),
3058, 2920, 1642 (mC@N), 1572, 1475, 1452, 1362, 1311,
1
1216, 1129, 1036, 819, 752. H NMR (300 MHz, CDCl3):
d 8.51 (d, J = 7.9 Hz, 1H, Py Hm); 8.44 (d, J = 6.9 Hz,
1H, Py Hm); 8.24 (d, J = 6.9 Hz, 1H, Py Hm); 7.88
(t, J = 7.7 Hz, 1H, Py Hp); 7.73 (t, J = 7.7 Hz, 1H, Py
Hp); 7.63 (d, J = 7.6 Hz, 1H, Py Hm); 7.41 (d, J = 6.2
Hz, 1H, Ar H); 7.07 (m, 2H, Ar H); 6.92 (m, 5H, Ar H);
5.20 (s, 1H); 4.09 (d, 1H, J = 12.7 Hz,); 3.39 (d, 1H,
J = 12.0 Hz); 2.33 (d, 6H, PhCH3); 2.24 (s, 3H); 2.20

5314
S. Zhang et al. / Journal of Organometallic Chemistry 692 (2007) 5307–5316
1203, 817, 771. Anal. Calc. for C48H60Cl4N6Ni2O2
(1012.23): C, 56.95; H, 5.97; N, 8.30. Found: C, 57.31; H,
5.66; N, 8.23%. Data for 5d are as follows. Yield: 78%.
FT-IR (KBr disk, cmÀ1): 3379, 3188 (mN–H), 3063, 2957,
1614 (mC@N), 1587, 1473, 1372, 1263, 1218, 856, 817, 750.
Anal. Calc. for C42H48Cl4N6Ni2O2 (928.07): C, 54.35; H,
5.21; N, 9.06. Found: C, 54.16; H, 5.01; N, 8.77%.
quenched with 5% aqueous hydrogen chloride in ice-water
base in accordance with the oligomers of C4 and C6 pro-
duced and then analyzed by gas chromatography (GC)
for determining the distribution of oligomers obtained.
The remaining solution was quenched with HCl-acidified
ethanol (5%), and the precipitated polyethylene was fil-
trated, washed with ethanol, dried in a vacuum at 60 ꢁC
until constant weigh.
4.3. General procedure for ethylene oligomerization and
polymerization
4.4. Crystal structure determination
Ethylene oligomerization and polymerization was
carried out in a 500 mL autoclave stainless steel reactor
equipped with a mechanical stirrer and a temperature con-
troller. Briefly, toluene, the desired amount of cocatalyst
and toluene solution of catalytic precursor (the total vol-
ume was 100 mL) was added to the reactor in this order
under an ethylene atmosphere. Reaching the desired reac-
tion temperature, ethylene with 30 atm pressure was intro-
duced to start the reaction, and the ethylene pressure was
kept by constant feeding of ethylene. After 30 min, the
reaction was stopped. The catalytic reaction mixture was
Crystals of 1 suitable for X-ray diffraction analysis were
obtained by slow evaporation of their ethyl acetate solu-
tion. Crystals of 5a suitable for X-ray diffraction analysis
were obtained by laying diethyl ether on a dichlorometh-
ane/methanol (v/v = 1:1) solution at room temperature.
Single-crystal X-ray diffraction study for 1 were carried
out on a Bruker SMART 1000 CCD diffractometer with
graphite-monochromated Mo Ka radiation (k = 0.71073
˚
A). Intensity data for a crystal of 5a were collected on a
Rigaku RAXIS Rapid IP diffractometer with graphite-
˚
monochromated Mo Ka radiation (k = 0.71073 A). Cell
parameters were obtained by global refinement of the posi-
tions of all collected reflections. Intensities were corrected
for Lorentz and polarization effects and empirical absorp-
tion. The structures were solved by direct methods and
refined by full-matrix least squares on F2. All non-hydro-
gen atoms were refined anisotropically. Structure solution
and refinement were performed by using the SHELXL-97
package [17]. Crystal data and processing parameters were
summarized in Table 5.
Table 5
Crystal data and structure refinement for compound 1 and complex 5a
Data
1
5a Æ 3H2O
Formula
Formula weight
T (K)
Wavelength (A)
Crystal system
C
398.46
293(2)
0.71073
Triclinic
24H22N4O2
C40H39Cl4N6Ni2O2 Æ 3H2O
942.95
293(2)
0.71073
Monoclinic
P21/c
14.397(3)
16.584(3)
22.753(7)
90
123.81(2)
90
4513.8(2)
4
˚
ꢀ
Space group
P1
Acknowledgement
˚
a (A)
8.42990(1)
10.8619(2)
12.2771(2)
104.3390(1)
95.6480(1)
92.5980(1)
1081.01(3)
2
˚
b (A)
˚
c (A)
This work was supported by NSFC No. 20674089 and
MOST 2006AA03Z553.
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Appendix A. Supplementary material
Volume (A )
Z
Dcalc. (Mg mÀ3
)
1.224
0.080
420
1.388
1.118
1940
CCDC 657365 and 657366 contain the supplementary
crystallographic data for 1 and 5a. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.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.a-
c.uk. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.jorganchem.
2007.08.020.
l (mmÀ1
F(000)
)
Crystal size (mm)
h Range (ꢁ)
0.65 · 0.13 · 0.11 0.36 · 0.22 · 0.16
1.72–28.33
À11 6 h 6 11,
À14 6 k 6 14,
À16 6 l 6 16
21309
1.63–25.01
Limiting indices
À16 6 h 6 17,
À19 6 k 6 19,
À27 6 k 6 27
11365
No. of refections
collected
No. of unique reflections 5357
7239
Rint
0.0236
0.1046
Completeness to h (%)
Absorption correction
Goodness-of-fit on F2
Final R indices
[I > 2r(I)]
99.2
Empirical
1.102
R1 = 0.0552,
wR2 = 0.1692
R1 = 0.0757,
wR2 = 0.1841
91.0
Empirical
1.213
R1 = 0.1262,
wR2 = 0.2981
R1 = 0.2104,
wR2 = 0.3491
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