2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl] pyridylnickel(II) halides: Synthesis, characterization and ethylene oligomerization behavior

Article abstract of DOI:10.1016/j.jorganchem.2011.12.031

A series of nickel(II) halide complexes ligated by 2-[1-(2,6-dibenzhydryl- 4-methyl-phenylimino)ethyl]-6-[1-(arylimino)-ethyl]pyridines was synthesized and characterized by FT-IR spectroscopy and elemental analysis. Single-crystal X-ray crystallographic studies revealed that the nickel halide complexes possess pseudo square-pyramidal geometry at nickel. Following screening with the co-catalysts Et₂AlCl, MAO, MMAO and ethylaluminum sesquichloride (EASC, Et₃Al₂Cl₃), EASC was chosen as the co-catalyst of choice, and activities as high as 2.5 × 10⁶ g mol^-1 (Ni) h^-1 were observed for ethylene oligomerization. The influence of the ligands and of the reaction parameters on the catalytic behavior of the nickel pre-catalysts was investigated.

Full text of DOI:10.1016/j.jorganchem.2011.12.031

Journal of Organometallic Chemistry 702 (2012) 52e58
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]
pyridylnickel(II) halides: Synthesis, characterization and ethylene
oligomerization behavior
,
,
b,
Jingjuan Lai a b, Xiaohua Hou b, Yongwen Liu a, Carl Redshawc , Wen-Hua Sun
*
**
a Center of Analysis and Measurement, Shanxi Datong University, Datong 037009, China
b Key laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
c Energy Materials Laboratory, School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of nickel(II) halide complexes ligated by 2-[1-(2,6-dibenzhydryl-4-methyl-phenylimino)ethyl]-6-
[1-(arylimino)-ethyl]pyridines was synthesized and characterized by FTeIR spectroscopy and elemental
analysis. Single-crystal X-ray crystallographic studies revealed that the nickel halide complexes possess
pseudo square-pyramidal geometry at nickel. Following screening with the co-catalysts Et2AlCl, MAO,
MMAO and ethylaluminum sesquichloride (EASC, Et3Al2Cl3), EASC was chosen as the co-catalyst of
choice, and activities as high as 2.5 ꢀ 106 g molꢁ1 (Ni) hꢁ1 were observed for ethylene oligomerization.
The influence of the ligands and of the reaction parameters on the catalytic behavior of the nickel pre-
catalysts was investigated.
Received 8 November 2011
Received in revised form
20 December 2011
Accepted 22 December 2011
Keywords:
Ethylene oligmerization
Nickel pre-catalyst
Ó 2011 Elsevier B.V. All rights reserved.
X-ray diffraction
2-[1-(2,6-Dibenzhydryl-4-
methylphenylimino)ethyl]-6-[1-(arylimino)
ethyl]pyridine
1. Introduction
electronic properties [26e28]. In addition, much academic work
focuses on elucidating the reactive species [29e36] and on the
Late-transition metal pre-catalysts have attracted much atten-
tion with respect to ethylene polymerization and oligomerization
in last two decades, and notable achievements are reflected in
a number of review articles [1e6]. The resurrection of late-
transition metal complex pre-catalysts for ethylene reactivity was
initiated after pioneer work on nickel or palladium complexes
formation of self-activating catalysts [37,38]. This is particularly the
case for bis(imino)pyridyl derivatives, which have also made a huge
impact on the ethylene polymerization and oligomerizaion field.
We have been attracted by the use of N^N bi-dentate pre-catalysts
and have designed a number of new ligand sets, namely 2-(2-
pyridyl)quinoxaline [39], 2-ethylcarboxylate-6-iminopyridine
[40], and pyrazolyliminophosphorane [41]. In addition, we also
reported some new N^N^N tridentate ligands, such as 2-imino-
1,10-phenanthrolines [42,43], 2-benzimidazolyl-6-(1-(arylimino)
ethyl)pyridines [44e47], 2-quinoxalinyl-6-imino-pyridines [48], 2-
(benzimidazol-2-yl)-1,10-phenanthrolines [49], 2-(benzoxazolyl)-
1,10-phenanthrolines [50] and 8-(1-aryliminoethylidene) qui-
naldines [51]. By employing these ligands, numerous metal
complex pre-catalysts have been developed, and some of them
have performed with high catalytic activities in either the oligo-
merization or polymerization of ethylene.
bearing
a-diimine ligands [7e9], together with work on iron or
cobalt complexes containing bis(imino)pyridines [10,11], and
subsequently, the number of research papers has mushroomed, and
these employ a variety metals [12e16] such as iron, cobalt, nickel,
or palladium and various ligand sets. In general, it has proved
possible to control their catalytic behavior in ethylene oligomeri-
zation and/or polymerization through modifying the ligand back-
bones [17] or the N-bound aryl groups [18e25]. a-Diimine ligands
are well-known in the area of ethylene polymerization and oligo-
merization due to their important feature of easily varied steric and
Recently nickel complex pre-catalysts bearing bi-dentate
ligands have been highlighted due to their high activity and
enhanced thermo-stability, which has been achieved via the use of
unsymmetrical bulky diimines [52]. Interestingly, the alternative
* Corresponding author. Tel.: þ44 1603 593137; fax: þ44 1603 592003.
** Corresponding author. Tel.: þ86 10 62557955; fax: þ86 10 62618239.
E-mail addresses: carl.redshaw@uea.ac.uk (C. Redshaw), whsun@iccas.ac.cn
(W.-H. Sun).
bi-dentate
ligands
N-(5,6,7-trihydroquinolin-8-ylidene)aryl-
amines, when coordinated to nickel exhibited different ethylene
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.12.031

J. Lai et al. / Journal of Organometallic Chemistry 702 (2012) 52e58
53
Table 1
reactivity, and high polymerization was achieved by derivatives
Bond lengths (Å) and bond angles (ꢂ) for complexes Ni4, Ni5 and Ni6.
bearing ligands without substituents at their 2-positions [53,54]. By
contrast, high oligomerization activity was observed when
employing 2-substituted N-(5,6,7-trihydroquinolin-8-ylidene)
arylamines [55] or tridentate pyrazolyl [56e58]. On extending the
work with bulky unsymmetrical diimino nickel pre-catalysts [52],
Ni4 (X ¼ Br)
2Ni5 (X ¼ Br)
Ni6 (X ¼ Cl)
Ni5
Ni5A
Bond lengths (Å)
Ni(1)eN(1)
Ni(1)eN(2)
Ni(1)eN(3)
Ni(1)eX(1)
Ni(1)eX(2)
N(1)eC(6)
N(1)eC(10)
N(2)eC(1)
N(2)eC(5)
2.193(4)
1.955(4)
2.141(4)
2.3712(10)
2.4338(10)
1.294(6)
1.421(6)
1.341(6)
1.357(6)
1.271(6)
1.461(6)
2.166(6)
1.999(6)
2.147(6)
2.3747(14)
2.4468(15)
1.303(9)
1.470(10)
1.312(9)
1.332(9)
1.258(10)
1.456(9)
2.155(7)
1.957(7)
2.149(7)
2.155(3)
1.974(3)
2.139(3)
2.2185(13)
2.3118(13)
1.288(5)
1.454(5)
1.336(5)
1.340(5)
1.280(5)
1.447(5)
a
number of bulky unsymmetrical bis(imino)pyridines were
developed for iron and cobalt and were found to be highly active
and thermally-stable [59,60]. Given this, the synthesis of
bulky unsymmetrical bis(imino)pyridylnickel complexes became
an attractive target, with a view to examining their catalytic
behavior. Herein, the nickel complexes, 2-[1-(2,6-dibenzhydryl-4-
methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridyl nickel(II)
dibromide or dichloride, are synthesized and fully characterized.
When activated with ethylaluminum sesquichloride (EASC,
Et3Al2Cl3), all nickel complex pre-catalysts performed with high
activity and good selectivity in ethylene dimerization.
2.3585(14)
2.4748(13)
1.279(10)
1.435(11)
1.334(11)
1.378(11)
1.310(11)
1.424(11)
N(3)eC(8)
N(3)eC(43)
Bond angles (ꢂ)
N(2)eNi(1)eN(3)
N(2)eNi(1)eN(1)
N(3)eNi(1)eN(1)
N(2)eNi(1)eX(1)
N(3)eNi(1)eX(1)
N(1)eNi(1)eX(1)
N(2)eNi(1)eX(2)
N(3)eNi(1)eX(2)
N(1)eNi(1)eX(2)
Br(1)eNi(1)eX(2)
77.45(17)
76.42(17)
150.97(16)
156.60(13)
101.47(12)
97.51(11)
91.44(12)
94.88(11)
98.20(10)
111.88(3)
76.4(2)
76.3(2)
148.5(2)
77.5(3)
77.3(3)
149.7(3)
160.17(18)
99.16(18)
98.79(17)
90.42(18)
96.66(17)
100.07(16)
109.41(5)
77.60(13)
76.32(13)
149.14(13)
159.52(12)
100.57(10)
98.11(9)
160.5(2)
2. Results and discussion
101.54(18)
98.92(16)
90.89(19)
95.84(19)
99.99(16)
108.61(5)
2.1. Synthesis and characterization of the nickel(II) complexes
(Ni1eNi10)
88.99(11)
98.27(10)
97.49(9)
111.38(6)
The ligands 2-[1-(2,6-dibenzhydryl-4-methylphenylimino)
ethyl]-6-[1-(arylimino) ethyl]pyridines (L1eL5), were prepared by
the reported procedures [60,61], The stoichiometrical reaction of
the ligands (L1eL5) with (1,2-dimethoxyethane)nickel bromide or
chloride in ethanol led to the corresponding nickel(II) halides in
good yields (Scheme 1). The elemental analysis data of all the nickel
complexes are consistent with their formula. In the FTeIR spectra,
the C]N stretching vibration bands of the nickel(II) complexes
appear in the range of 1583e1588 cmꢁ1 instead of those observed
in the region 1635e1642 cmꢁ1 for the free ligands [59], indicating
the effective coordination to nickel.
N(1), N(2), N(3) and one bromine atom, Br(1), are located in
a square plane, and bond angles almost form a right angle such as
N(2)eNi(1)eBr(2), 91.44(12)ꢂ. In addition, the NieNimino bond
lengths are almost equal, with Ni(1)eN(1), 2.193(4) Å and Ni(1)e
N(3) 2.141(4) Å, which both are longer than the NieNpyridine bond,
Ni(1)eN(2), 1.955(4) Å. The bond lengths of N(1)eC(6) 1.294(6) Å
and N(3)eC(8) 1.271(6) Å are indicative of the double bonding
characteristic of the C]N moiety.
There are two independent molecules of complex Ni5 in the
solid state, and the molecular structures are shown in Fig. 2. The
N(2)eNi(1)eBr(2) bond angle is 90.89(19)ꢂ and the N(2A)eNi(1A)e
Br(2A) bond angle is 90.42(18)ꢂ, which in both cases more closely
approach a right angle than the angles observed in complex Ni4.
Moreover, the Ni(1)eN(2) and Ni(1A)eN(2A) bond lengths are
significantly shorter than the other two NieN bond lengths in
complex Ni5, indicating stronger coordination. Other structural
features of complex Ni5 are similar to those of Ni4, with the slight
differences caused by the diethyl substituents of Ni5 versus the
dimethyl of Ni4.
2.2. Crystal structures
To confirm the unambiguous molecular structures, single-crystals
of the complexes Ni4, Ni5 and Ni6 were grown from their dichloro-
methane solutions layered with diethylether at room temperature. A
pseudo square-pyramidal geometry at nickel was observed for all
three nickel complexes; their selected bond lengths and angles are
tabulated together in Table 1, and the molecular structures of three
nickel complexes are shown in Figs. 1e3, respectively.
The structure of the chloride complex Ni6 was also determined
and is shown in Fig. 3. A similar coordination geometry around the
In complex Ni4 as shown in Fig. 1, three coordinated nitrogen
atoms and two bromides are situated around the nickel center. The
Ph
Ph
Ph
Ph
R1
N
R1
N
(DME)NiX2
Ethanol
N
Ni
N
N
N
X
X
R1
R2
R1
R2
Ph
Ph
Ph
Ph
Ni1-Ni10
L1-L5
Ni1 Ni2 Ni3 Ni4 Ni5 Ni6 Ni7 Ni8 Ni9 Ni10
R1 Me Et i-Pr Me Et Me Et i-Pr Me Et
R2
X
H
H
H
Me Me
H
H
H
Me Me
Cl Cl
Br Br Br Br Br
Cl Cl Cl
Scheme 1. Synthesis of nickel(II) complexes.

54
J. Lai et al. / Journal of Organometallic Chemistry 702 (2012) 52e58
Fig. 1. ORTEP drawing of complex Ni4 with thermal ellipsoids at 30% probability level.
Hydrogen atoms have been omitted for clarity.
Fig. 3. ORTEP drawing of complex Ni6 with thermal ellipsoids at 30% probability level.
Hydrogen atoms have been omitted for clarity.
nickel center is observed, closely approaching that observed for
Ni5, with bonding of Ni(1)eN(2) being stronger than either Ni(1)e
N(1) and Ni(1)eN(3) in Ni6. The NieCl bond lengths are commonly
longer than the NieBr bonds of their analogs Ni4 and Ni5, indi-
cating the weaker bonding of the chloride to the nickel center.
2.3. Ethylene dimerization by nickel(II) pre-catalysts
When regarding the influence of the bromide and chloride
ligation, the two series of nickel complexes can be considered
separately. Given that the anionic influence probably does not
affect the nature of the alkylaluminium co-catalysts, one bromide
complex Ni4 was selected to screen for a suitable co-catalyst.
2.3.1. Co-catalysts selection
The influence of different alkylaluminium reagents was inves-
tigated by employing complex Ni4 pre-catalyst in order to find the
most suitable co-catalyst. However, as low activity was observed at
atmospheric pressure, further explorations were carried out at
10 atm ethylene pressure. The function of co-catalyst is not only the
alkylation of nickel halide complex, but also to allow for the
formation of the active species in the presence of ‘detrimental’
impurities such as moisture and oxygen. Given this, a minimum
amount of MAO/MMAO is required, and this is commonly higher
than the required minimum needed when using diethylaluminum
chloride (Et2AlCl) or ethylaluminum sesquichloride (Et3Al2Cl3,
EASC) as co-catalyst. The evaluation results are tabulated in Table 2
with co-catalysts such as Et2AlCl, MAO, MMAO and EASC. It is clear
to see that the most suitable co-catalyst is EASC, and when acti-
vated with EASC, the catalytic system employing Ni4 achieved the
highest productivity at 10 atm ethylene pressure. Thus, the co-
catalyst EASC was selected for all further investigations.
2.3.2. Effects of the molar ratio of Al/Ni and the reaction
temperature
Over the range 200e700 molar ratio of EASC/Ni4 (Table 3, entries
1e7) under 10 atm ethylene at room temperature, the highest
activity was observed with an Al/Ni ratio of 500:1, indicating that the
active species required an optimum amount of alkylaluminium
reagent, but that either lower or higher ratios were detrimental to
these optimum conditions. On increasing the Al/Ni molar ratio, more
Fig. 2. ORTEP drawing of complex Ni5 with thermal ellipsoids at 30% probability level.
Hydrogen atoms have been omitted for clarity.

J. Lai et al. / Journal of Organometallic Chemistry 702 (2012) 52e58
55
Table 2
attributed to the isomerization or the faster chain transfer at higher
temperature.
Selection of suitable co-catalyst based on Ni4a
Entry
Co-cat.
Al/Ni
T(ꢂC)
Activityb
Oligomerization
distribution (%)c
2.3.3. Lifetime of the active species
P
P
For any catalyst, one of the most important factors is to maintain
activity over a prolonged period in order to be feasible for industrial
applications. Therefore, using EASC as co-catalyst, the nickel
complex Ni4 and an Al/Ni molar ratio of 500 at 40 ꢂC, the effect of
the reaction time on the catalytic activity was investigated over
60 min. On extending the reaction time from 15 min to 60 min, the
oligomerization activity decreased (entries12 and 13, Table 3).
Similar phenomena were also observed for ethylene oligomeriza-
tion using nickel(II) catalysts bearing N-((pyridin-2-yl)methyl-ene)
quinolin-8-amine [65] and (pyrazol-1-ylmethyl)pyridine [66].
C4/
C
C6/
C
a
-C4
100
97.5
1
2
3
4
5
6
Et2AlCl
Et2AlCl
MAO
MMAO
MMAO
EASC
200
300
1000
1000
1500
200
25
25
25
25
25
25
0.99
2.28
0.36
4.29
5.33
6.72
57.5
79
42.5
21
100
0
92.7
98.5
99.1
98.0
98.5
99.1
98.6
1.5
0.9
1.4
a
Conditions: 5
mmol Ni4, 100 mL toluene, 10 atm ethylene, 30 min.
b
c
104 g molꢁ1 (Ni) hꢁ1
.
P
Determined by GC and C signifies the total amounts of oligomers.
hexenes are produced (entries 1e6, Table 3); it is possible to have
active nickel species with a bi-dentate manner of ligands due to the
possible coordination of the excessive amount of aluminum with
one of the imino-nitrogen [61]. In addition, it was found that the
activity for ethylene oligomerization initially increased with the
optimum ratio of Al/Ni 500 (entries 1e6, Table 3), and good selec-
tivity for 1-butene was observed (87.1e98.6%; the exceptionwas run
11 at 45.9%, see Table 3). The activity observed for ethylene oligo-
merization decreased greatly when the ratio was 700, but with
higher selectivity for hexenes. Given this, further experiments were
performed at the molar ratio of Al/Ni 500:1.
2.3.4. Effect of the ligand environment
In order to investigate the catalytic behavior of these tridentate
nickel(II) dibromide complexes on variation of the substituents on
the ligands, the activity and distribution of ethylene oligomeriza-
tion were investigated using Ni1eNi5. Using the optimized reac-
tion conditions (entry 8, Table 3), all the title nickel(II) dibromide
pre-catalysts(Ni1eNi5) exhibited catalytic activity toward ethylene
oligomerization (Table 3). According to the data in Table 3, the
variation of the ligand environment, caused by changing the
substituents on the aryl ring linked to the imino-nitrogen atom, had
a great influence on the catalytic behavior of the (Ni1eNi5)/EASC
system for ethylene reactivity. The order decreased through Ni1
[2,6-di(Me)] > Ni2[2,6-di(Et)] > Ni3[2,6-di(i-Pr)] and Ni4[2,4,6-
tri(Me)] > Ni5[2,6-di(Et)-4-Me], which is the same order as
observed for nickel(II) catalysts ligated by 2-(benzoimidazol-2-yl)-
6-(1-aryliminoethyl)pyridines [67].
On increasing the reaction temperature from 25 to 100 ꢂC, the
trend for oligomerisation activity is the same as that for the
influence of the molar ratio of Al/Ni (entries 3 and 7e11, Table 3).
This could be due to the deactivation of the active species and lower
ethylene solubility [62] at higher temperature. In light of the
observations, the best activity was observed at 40 ꢂC (entry 8,
Table 3). This phenomenon is different from that usually observed
for nickel(II) complexes bearing 2-benzimidazolylpyridine [63]
and N-(2-(1H-benzoimidazol-2-yl)quinolin-8-yl)benzamide [64],
which perform best (highest activity) at 20 ꢂC. Interestingly, the
2.4. Ethylene activation behavior of the N^N^N coordinated
nickel(II) dichloride complexes
Similar to the nickel(II) dibromide complexes, the Al/Ni molar
ratio, the reaction temperature, time and the nature of the
complexes have been shown to have an influence on the activities,
distribution of oligomers and
a-olefin selectivity were far less
affected by the Al/Ni molar ratio; however, when the reaction
temperature was increased to 100 ꢂC, the amount of butenes was
distribution of oligomers and the
a-olefin selectivity. Using the
drastically reduced to 45.9% with the lower selectivity of
a-C4
optimized oligomerization reaction temperature for the nickel(II)
dibromide complexes, viz 40 ꢂC, the ethylene activation behavior of
the chloride Ni6/EASC system was investigated (entries 1e6 in
Table 4). The optimum Al/Ni ratio, 300, was found by increasing the
molar ratio of Al/Ni from 100 to 500, and with this molar ratio fixed,
the influence of the reaction temperature was investigated (entries
7e11 in Table 4). It was found that the highest activity was observed
at 40 ꢂC, which is the same as the observation by its bromide
analog. Thus, using EASC as co-catalyst, the best performance for
ethylene oligomerization activity was obtained with Ni6/EASC at
40 ꢂC and with the Al/Ni molar ratio of 300 (entry 3 in Table 4)
under 10 atm. In addition, the catalytic activity of Ni6 was increased
greatly to 2.5 ꢀ 106 g molꢁ1 (Ni) hꢁ1, when 20 equiv. of PPh3 was
(54.2%) and higher hexenes (54.1%). This elevation in temperature
had an influence on the oligomerization activity, which could be
Table 3
Ethylene catalytic activity with Ni1eNi5/EASC system.a
Entry Cat. Al/Ni t (min) T (ꢂC) Activityb Oligomerization
distribution (%)c
P
P
C4/
C
C6/
C
a-C4
1
2
3
4
5
6
7
8
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni4
Ni1
Ni2
Ni3
Ni5
200
400
500
550
600
700
500
500
500
500
500
500
500
500
500
500
500
30
30
30
30
30
30
30
30
30
30
30
15
60
30
30
30
30
25
25
25
25
25
25
30
40
50
80
100
40
40
40
40
40
40
6.72
7.65
8.24
3.99
2.45
0.49
8.74
13.3
12.6
11.7
9.15
23.7
7.5
17.0
14.6
7.4
98.6
97.1
96.1
95.2
94.8
87.1
95.6
95.4
95.0
95.0
45.9
95.5
95.2
95.5
97.8
95.1
93.4
1.4
98.0
96.5
99.1
98.4
97.3
95.9
96.9
95.8
95.6
90.0
54.2
95.7
94.9
97.2
94.2
94.5
97.2
2.9
3.9
4.8
5.2
12.9
4.4
4.6
5.0
5.0
54.1
4.5
4.8
4.5
2.2
4.9
6.6
added into the catalytic system, while the selectivity for a-C4 was
dramatically decreased (entry 4 in Table 4). This may be attributed
to the protecting of the auxiliary PPh3 for the active species during
the catalytic reaction, and inducing isomerization along with
9
10
11
12
13
14
15
16
17
b-hydrogen elimination; this phenomena was consistent with
previous results [68e74].
Finally, the oligomerization behavior of the nickel(II) dichloride
complexes were investigated using EASC at 40 ꢂC and an Al/Ni
molar ratio of 300 under 10 atm ethylene (entries 3 and 12e15,
Table 4). Compared with the behavior for the nickel(II) dibromide
complexes Ni1eNi5, the dichloride complexes exhibited much
higher catalytic activities with a similar order as their bromide
analogs, Ni9 > Ni10 and Ni6 > Ni7 > Ni8. Presumably the higher
2.8
a
Conditions: 5
mmol Ni, 100 mL toluene, 10 atm ethylene.
b
c
104 g molꢁ1 (Ni) hꢁ1
.
P
Determined by GC and C signifies the total amounts of oligomers.

56
J. Lai et al. / Journal of Organometallic Chemistry 702 (2012) 52e58
Table 4
For the dichloride catalysts, the reaction time played the same
Ethylene catalytic activity with Ni6eNi10/EASC system.a
important role on the influence of the catalytic activity as for the
nickel(II) dibromide complexes (entries 16 and 17, Table 4). For
example, when the reaction time was extended from 15 min to
60 min, the oligomerization activity decreased.
Entry Complex Al/Ni t (min) T (ꢂC) Activityb Oligomer distributionc
(%)
P
P
C4/
C
C6/
C
a-C4
1
2
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni6
Ni7
Ni8
Ni9
Ni10
Ni6
Ni6
100
200
300
300
400
500
300
300
300
300
300
300
300
300
300
300
300
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
15
60
40
40
40
40
40
40
25
30
50
60
80
40
40
40
40
40
40
0.718
4.12
4.2
95.9
95.7
95.8
93.7
95.8
97.3
97.1
96.4
95.4
93.0
90.2
95.4
95.0
95.9
95.8
94.6
95.2
4.1
4.3
4.2
6.3
4.2
2.7
2.9
3.6
4.6
7.0
9.8
4.6
5.0
4.1
4.2
5.4
4.8
92.2
90.1
89.7
36.1
92.8
93.4
96.5
93.2
88.1
83.5
92.3
95.8
87.1
93.9
92.5
91.7
93.1
3. Conclusion
3
4d
5
24.8
A series of nickel(II) dibromide and dichloride catalysts bearing
2-[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(aryli-
mino)ethyl]pyridyl were synthesized and fully characterized. With
EASC as co-catalyst, these complexes could be easily activated and
showed high activities for ethylene oligomerization with moderate
to good selectivities for 1-butene (54.2e99.1%) at 10 atm ethylene
pressure. However, the Ni4/EASC system exhibited different olig-
omerization behavior, and selectivity for hexenes, which substan-
tially increased from 3.9% to 54.1%, when the reaction temperature
was elevated from 25 ꢂC to 100 ꢂC. The catalytic activity for ethylene
oligomerization and selectivity for butenes and hexenes could be
easily controlled by altering the reaction conditions such as
temperature and the molar ratio of Al/Ni.
3.24
2.78
1.56
2.3
4.18
4.11
2.01
2.67
1.01
2.03
1.58
7.9
6
7
8
9
10
11
12
13
14
15
16
17
2.3
a
Conditions: 5
mmol Ni, 100 mL toluene, 10 atm ethylene, 30 min.
b
c
105 g molꢁ1 (Ni) hꢁ1
.
P
Determined by GC and C signifies the total amounts of oligomers.
20 equiv. of PPh3.
d
4. Experiment
chloride activity is associated with higher net charge of the metal
center [75e77]. We note however that the reverse trend was
observed for the family of 8-(1-aryliminoethylene)quinalinyl nickel
dihalide complexes due to the better solubility of the bromide
complexes [51].
4.1. General considerations
All manipulations of air- and moisture-sensitive compounds
were performed under a nitrogen atmosphere using standard
Schlenk techniques. Before use, toluene was refluxed over sodium-
benzophenone and distilled under nitrogen. Methylaluminoxane
(MAO, 1.46 M solution in toluene) and modified methylaluminox-
ane(MMAO, 1.93 M in heptane, 3A) were purchased from Akzo
Nobel Corp. Ethylaluminum sesquichloride (EASC, 0.87 M in
toluene) and diethylaluminum chloride (Et2AlCl, 0.5 M in toluene)
were purchased from Acros Chemicals. High-purity ethylene was
purchased from Beijing Yansan Petrochemical Company and used
as received. Other reagents were purchased from Aldrich, Acros, or
local suppliers. FTeIR spectra were recorded on a Perkin-Elmer
System 2000 FTeIR spectrometer. Elemental analysis was carried
out using a Flash EA 1112 microanalyzer. GC analyses were per-
formed with a Varian CP-3800 gas chromatograph equipped with
Table 5
Crystal data and structure refinement details for Ni4, Ni5 and Ni6.
Ni4
2Ni5
Ni6
Empirical formula C51H47Br2N3Ni
C106H101Br4N6Ni2 C50H45Cl2N3Ni
Fw
T (K)
Wavelength (Å)
Cryst system
Space group
a (Å)
920.45
173(2)
0.71073
Monoclinic
P2(1)/c
17.446(4)
15.401(3)
18.774(4)
90
105.01(3)
90
4872.6(17)
4
1895.99
293(2)
0.71073
Triclinic
Pꢁ1
817.50
173(2)
0.71073 A
Monoclinic
P2(1)/n
9.6228(19)
34.330(7)
13.403(3)
90
106.87(3)
90
4237.1(15)
4
13.329(3)
16.784(3)
24.933(5)
81.55(3)
80.58(3)
87.66(3)
5441.8(19)
2
b (Å)
c (Å)
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
a flame ionization detector and a 30 m (0.2 mm i.d., 0.25 mm film
thickness) CP-Sil 5 CB column.
V (Å3)
Z
Dcalcd. (g cmꢁ3
)
1.255
2.072
1.157
1.857
1.282
0.622
4.2. Synthesis of title nickel complexes
m
(mmꢁ1
)
F(000)
Cryst size (mm)
range (ꢂ)
1888
1950
1712
0.24 ꢀ 0.21 ꢀ 0.18 0.35 ꢀ 0.28 ꢀ 0.22 0.20 ꢀ 0.17 ꢀ 0.10
4.2.1. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-dimethylphenylimino)ethyl]pyridine NiBr2 (Ni1)
The complexes Ni1eNi5 were synthesized in the same manner
by the reaction of (DME)NiBr2 with the corresponding 2-[1-(2,6-
dibenzhydryl-4-methylphenylimino) ethyl]-6-[1-(arylimino)ethyl]
pyridine ligands in dichloromethane.
A typical synthesis of complex Ni1 is described as follows: the
ligand L1 (0.1374 g, 0.20 mmol) and (DME)NiBr2 (0.0617 g,
0.20 mmol) were added to a Schlenk tube together with 5 mL of
dichloromethane and then the reaction mixture was stirred for 8 h
at room temperature. Diethylether (10 mL) was added in order to
precipitate the complex when the reaction was finished, and then
the precipitate was washed with diethylether (3 ꢀ 5 mL) and dried
under vacuum to obtain a brown powder of Ni1 in 75.06% (0.14 g)
yield. Anal. Calcd for C50H45Br2N3Ni (906.41): C, 66.25; H, 5.00; N,
4.64. Found: C, 66.14; H, 5.22; N, 4.35. FTeIR (Diamond disk, cmꢁ1):
q
1.73e7.47
0.84e27.47
ꢁ17 ꢃ h ꢃ 17
ꢁ21 ꢃ k ꢃ 1
ꢁ21 ꢃ l ꢃ 32
46,060
2.39e27.46
ꢁ12 ꢃ h ꢃ 7
ꢁ44 ꢃ k ꢃ 26
ꢁ17 ꢃ l ꢃ 16
18,586
Limiting indices
ꢁ22 ꢃ h ꢃ 16
ꢁ19 ꢃ k ꢃ 13
ꢁ24 ꢃ l ꢃ 24
21,375
No. of rflns
collected
No. unique rflns
[R(int)]
11,019 (0.0663)
98.8%
24,281 (0.0797)
97.4%
9574 (0.0542)
98.6%
Completeness
to
q (%)
Data/restraints/
params
11,019/0/514
1.038
24,281/0/1063
1.030
9574/0/505
1.104
Goodness of
fit on F2
Final R indices
R1 ¼ 0.0737
R1 ¼ 0.1019
wR2 ¼ 0.2774
R1 ¼ 0.1523
wR2 ¼ 0.3145
R1 ¼ 0.0863
wR2 ¼ 0.2044
R1 ¼ 0.1112
wR2 ¼ 0.2240
[I > 2
s(I)]
wR2 ¼ 0.1883
R indices (all data) R1 ¼ 0.1037
wR2 ¼ 0.2092
Largest diff peak
and hole (e Åꢁ3
0.477 and ꢁ0.721 0.849 and ꢁ1.183 0.481 and ꢁ0.472
3024, 1976, 1588 (nC]N), 1494, 1445, 1371, 1262, 1217, 1078, 1030,
)
862, 803, 748, 702.

J. Lai et al. / Journal of Organometallic Chemistry 702 (2012) 52e58
57
4.2.2. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
4.2.9. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-diethylphenylimino)ethyl]pyridine NiBr2 (Ni2)
(2,4,6-trimethylphenylimino)ethyl]pyridine NiCl2 (Ni9)
Obtained as brown powder in 59.8% (0.11 g) yield. Anal. Calcd. for
C52H49Br2N3Ni (931.47): C, 66.84; H, 5.29; N, 4.50. Found: C, 66.54; H,
Obtained as reddish brown powder in 93.86% (0.16 g) yield.
Anal. Calcd. for C51H47Cl2N3Ni (831.54): C, 73.66; H, 5.70; N, 5.05.
Found: C, 73.34; H, 5.85; N, 4.96. FTeIR (Diamond disk, cmꢁ1):
5.31; N, 4.33. FTeIR (Diamond disk, cmꢁ1): 2967, 1975, 1584 (
nC]N),
1494, 1447, 1371, 1260, 1215, 1077, 1031, 918, 864, 805, 769, 746, 702.
3022, 2166, 1977, 1587 (
nC]N), 1494, 1447, 1371, 1262, 1223, 1079,
1032, 856, 813, 748, 701.
4.2.3. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-diisopropylphenylimino)ethyl]pyridine NiBr2 (Ni3)
Obtained as brown powder in 81.29% (0.16 g) yield. Anal. Calcd.
for C54H53Br2N3Ni (962.52): C, 67.38; H, 5.55; N, 4.37. Found: C,
67.28; H, 5.64; N, 4.25. FTeIR (Diamond disk, cmꢁ1): 3058, 2961,
4.2.10. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-diethyl-4-methylphenylimino)ethyl]pyridine NiCl2 (Ni10)
Obtained as reddish brown powder in 89.58% (0.15 g) yield.
Anal. Calcd. for C53H51Cl2N3Ni (948.49): C, 67.11; H, 5.42; N, 4.43.
Found: C, 66.98; H, 5.31; N, 4.57. FTeIR (Diamond disk, cmꢁ1): 3372,
2165, 2024, 1584 (nC]N), 1494, 1447, 1371, 1320, 1263, 1210, 1099,
1031, 795, 769, 746, 700.
3023, 2964, 2165, 2027, 1584 (nC]N), 1494, 1449, 1371, 1261, 1219,
1079, 1031, 858, 818, 768, 746, 700.
4.2.4. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,4,6-trimethylphenylimino)ethyl]pyridine NiBr2 (Ni4)
Obtained as brown powder in 83.7% (0.23 g) yield. Anal. Calcd.
for C51H47Br2N3Ni (920.44): C, 66.55; H, 5.15; N, 4.57. Found: C,
66.35; H, 5.03; N, 4.62. FT-IR (Diamond disk, cmꢁ1): 3024, 2166,
4.3. X-ray crystallographic studies
X-ray diffraction studies of single-crystal of Ni4, Ni5 and Ni6
were obtained respectively by slow laying of diethylether on its
dichloromethane solution at room temperature. With graphite-
2030, 1978, 1586 (nC]N), 1494, 1445, 1371, 1264, 1222, 1184, 1077,
1032, 859, 808, 747, 700.
monochromated Mo K
a
radiation (k ¼ 0.71073 Ǻ) at 173(2) K, cell
parameters were obtained by global refinement of the positions of
all collected reflections. Intensities were corrected for Lorentz and
polarization effects and empirical absorption. The structures were
solved by direct methods and refined by full-matrix least squares
on F2. All hydrogen atoms were placed in calculated positions.
Using the SHELXL-97 package [78], structure solution and refine-
ment were performed. Details of the X-ray structure determina-
tions and refinements are provided in Table 5.
4.2.5. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-diethyl-4-methylphenylimino)ethyl]pyridine NiBr2 (Ni5)
Obtained as brown powder in 63.6% (0.12 g) yield. Anal. Calcd.
for C53H51Br2N3Ni (948.49): C, 67.11; H, 5.42; N, 4.43. Found: C,
67.02; H, 5.54; N, 4.23. FTeIR (Diamond disk, cmꢁ1): 3023, 2964,
2030, 1978, 1584 (nC]N), 1494, 1446, 1371, 1263, 1219, 1078, 1031,
859, 813, 768, 747, 700.
4.2.6. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-dimethylphenylimino)ethyl]pyridine NiCl2 (Ni6)
4.4. General procedure for ethylene activation
The complexes Ni6eNi10 were synthesized in the same manner
by the reaction of (DME)NiCl2 with the corresponding 2-[1-(2,6-
dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]
pyridine ligands in dichloromethane.
A 250 mL stainless steel autoclave, equipped with a mechanical
stirrer and a temperature controller, was used to perform the
reaction of ethylene oligomerization at 10 atm ethylene pressure.
Firstly, when the requisite temperature was attained, the complex
A typical synthesis of complex Ni6 is described as follows: the
ligand L1 (0.1374 g, 0.20 mmol) and (DME)NiCl2 (0.0617 g,
0.20 mmol) were added to a Schlenk tube together with 5 mL of
dichloromethane and then the reaction mixture was stirred for 8 h
at room temperature. Diethylether (10 mL) was added in order to
precipitate the complex when the reaction was finished, and then
the precipitate was washed with diethylether (3 ꢀ 5 mL) and dried
under vacuum to obtain a reddish brown powder of Ni1 in 96.88%
(0.16 g) yield. Anal. Calcd. for C50H45Cl2N3Ni (817.51): C, 73.46; H,
5.55; N, 5.14. Found: C, 73.21; H, 5.65; N, 5.03. FTeIR (Diamond disk,
(5 mmol) was dissolved in 50 mL toluene in a Schlenk tube then
injected into the autoclave, which was full of ethylene. Secondly,
the require amount of co-catalyst (MAO, MMAO, EASC and Et2AlCl)
and the residual toluene were added continuously by syringe under
an ethylene atmosphere (the total volume of toluene was 100 mL).
The system was then stirred strongly for the desired time under
corresponding pressure of ethylene. On completion, nearly 1 mL of
the reaction solution was collected to be analyzed by gas chroma-
tography (GC) to determine the distribution of oligomers obtained
after terminating the reaction. The leftover solution was quenched
with HCl-acidified ethanol (5%), and the precipitated polyethylene
was filtered, washed with ethanol, dried under vacuum at 60 ꢂC and
weighed.
cmꢁ1): 3352, 2166, 1586 (
nC]N), 1494, 1447, 1371, 1261, 1215, 1078,
1031, 860, 809, 768, 746, 699.
4.2.7. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-diethylphenylimino)ethyl]pyridine NiCl2 (Ni7)
Obtained as reddish brown powder in 64.65% (0.16 g) yield.
Anal. Calcd. for C52H49Cl2N3Ni (845.56): C, 73.86; H, 5.84; N, 4.97.
Found: C, 73.65; H, 5.54; N, 5.07. FTeIR (Diamond disk, cmꢁ1): 2914,
2164, 2030, 1978, 1583 (nC]N), 1495, 1446, 1373, 1318, 1256, 1216,
1080, 1032, 866, 809, 772, 747, 704.
Acknowledgments
This work was supported by the Youth Projects Fund of Shanxi
Datong University No. 2011Q3 and MOST 863 program No.
2009AA033601.
4.2.8. 2-[1-(2,6-Dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-
(2,6-diisopropylphenyl imino)ethyl]pyridine NiCl2 (Ni8)
Appendix A. Supplementary material
Obtained as reddish brown powder in 94.36% (0.16 g) yield.
Anal. Calcd. for C54H53Cl2N3Ni (873.62): C, 74.24; H, 6.11; N, 8.12.
Found: C, 74.03; H, 6.22; N, 8.09. FTeIR (Diamond disk, cmꢁ1):
CCDC 852859, 852860, and 852861 contain the supplementary
crystallographic data for the complexes Ni4, Ni5 and Ni6. These
data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
3355, 2961, 2166, 2028, 1621, 1586 (
nC]N), 1494, 1447, 1371, 1321,
1263, 1211, 1100, 1032, 861, 795, 769, 746, 700.

58
J. Lai et al. / Journal of Organometallic Chemistry 702 (2012) 52e58
[40] X. Tang, W.-H. Sun, T. Gao, J. Hou, J. Chen, W. Chen, J. Organomet. Chem. 690
References
(2005) 1570e1580.
[41] C. Zhang, W.-H. Sun, Z.-X. Wang, Eur. J. Inorg. Chem. 23 (2006) 4895e4902.
[42] W.-H. Sun, S. Jie, S. Zhang, W. Zhang, Y. Song, H. Ma, J. Chen, K. Wedeking,
R. Frohlich, Organometallics 25 (2006) 666e667.
[43] S. Jie, S. Zhang, W.-H. Sun, Eur. J. Inorg. Chem. 35 (2007) 5584e5598.
[44] W.-H. Sun, P. Hao, S. Zhang, Q. Shi, W. Zuo, X. Tang, X. Lu, Organometallics 26
(2007) 2720e2734.
[45] Y. Chen, P. Hao, W. Zuo, K. Gao, W.-H. Sun, J. Organomet. Chem. 693 (2008)
1829e1840.
[46] L. Xiao, R. Gao, M. Zhang, Y. Li, X. Cao, W.-H. Sun, Organometallics 28 (2009)
2225e2233.
[47] R. Gao, Y. Li, F. Wang, W.-H. Sun, M. Bochmann, Eur. J. Inorg. Chem. 27 (2009)
4149e4156.
[48] W.-H. Sun, P. Hao, G. Li, S. Zhang, W. Wang, J. Yi, M. Asma, N. Tang, J. Orga-
nomet. Chem. 692 (2007) 4506e4518.
[49] M. Zhang, P. Hao, W. Zuo, S. Jie, W.-H. Sun, J. Organomet. Chem. 693 (2008)
483e491.
[50] M. Zhang, R. Gao, X. Hao, W.-H. Sun, J. Organomet. Chem. 693 (2008)
3867e3877.
[51] S. Song, T. Xiao, T. Liang, F. Wang, C. Redshaw, W.-H. Sun, Catal. Sci. Technol. 1
(2011) 69e75.
[52] H. Liu, W. Zhao, X. Hao, C. Redshaw, W.-H. Sun, Organometallics 30 (2011)
2418e2424.
[53] J. Yu, Y. Zeng, W. Huang, X. Hao, W.-H. Sun, Dalton Trans. 40 (2011)
8436e8443.
[54] L. Zhang, X. Hao, W.-H. Sun, C. Redshaw, ACS Catal. 1 (2011) 1213e1220.
[55] J. Yu, X. Hu, Y. Zeng, L. Zhang, C. Ni, X. Hao, W.-H. Sun, New J. Chem. 35 (2011)
178e183.
[56] L. Oliveira, R. Campedelli, M. Kuhn, J.-F. Carpentier, O.L. Casagrande Jr., J. Mol.
Catal. A: Chem. 288 (2008) 58e62.
[57] L.L. de Oliveira, R.R. Campedelli, A.L. Bergamo, A.H.D.P. dos Santos,
O.L. Casagrande Jr., J. Braz. Chem. Soc. 21 (2010) 1318e1328.
[58] A. Ulbrich, A. Bergamo, O. Casagrande Jr., Catal. Commun. (2011). doi:10.1016/
j.catcom.2011.09.006.
[59] J. Yu, H. Liu, W. Zhang, X. Hao, W.-H. Sun, Chem. Commun. 47 (2011)
3257e3259.
[60] J. Yu, W. Huang, L. Wang, C. Redshaw, W.-H. Sun, Dalton Trans. 40 (2011)
10209e10214.
[61] M. Shen, W. Huang, W. Zhang, C. Redshaw, X. Hao, W.-H. Sun, Dalton Trans. 39
(2010) 9912e9922.
[62] M. Shen, P. Hao, W.-H. Sun, J. Organomet. Chem. 693 (2008) 1683e1695.
[63] P. Hao, S. Zhang, W.-H. Sun, Q. S.Shi, S. Adewuyi, X. Lu, P. Li, Organometallics
26 (2007) 2439e2446.
[64] K. Wang, M. Shen, W.-H. Sun, Dalton Trans. (2009) 4085e4095.
[65] W.-H. Sun, K. Wang, K. Wedeking, D. Zhang, S. Zhang, J. Cai, Y. Li, Organo-
metallics 26 (2007) 4781e4790.
[66] S. Ojwach, I. Guzei, L. Benade, S. Mapolie, J. Darkwa, Organometallics 28
(2009) 2127e2133.
[67] X. Chen, L. Zhang, J. Yu, X. Hao, H. Liu, W.-H. Sun, Inorg. Chim. Acta 370 (2011)
156e163.
[68] X. Tang, Y. Cui, W.-H. Sun, Z. Miao, S. Yan, Polym. Int. 53 (2004) 2155e2161.
[69] W.-H. Sun, W. Zhang, T. Gao, X. Tang, L. Chen, Y. Li, X. Jin, J. Organomet. Chem.
689 (2004) 917e929.
[1] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169e1204.
[2] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283e316.
[3] C. Bianchini, G. Giambastiani, I.G. Rios, G. Mantovani, A. Meli, A.M. Segarra,
Coord. Chem. Rev. 250 (2006) 1391e1418.
[4] V.C. Gibson, C. Redshaw, G.A. Solan, Chem. Rev. 107 (2007) 1745e1776.
[5] C. Bianchini, G. Giambastiani, L. Luconi, A. Meli, Coord. Chem. Rev. 254 (2010)
431e455.
[6] F. Speiser, P. Braunstein, L. Saussine, Acc. Chem. Res. 38 (2005) 784e793.
[7] L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem. Soc. 117 (1995)
6414e6415.
[8] A.C. Gottfried, M. Brookhart, Macromolecules 34 (2001) 1140e1142.
[9] C.M. Killian, D.J. Tempel, L.K. Johnson, M. Brookhart, J. Am. Chem. Soc. 118
(1996) 11664e11665.
[10] G.J.P. Britovsek, V.C. Gibson, B.S. Kimberley, P.J. Maddox, S.J. McTavish,
G.A. Solan, A.J.P. White, D.J. Williams, Chem. Commun. (1998) 849e850.
[11] B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc. 120 (1998)
4049e4050.
[12] Z. Li, W.-H. Sun, Z. Ma, Y. Hu, C. Shao, Chin. Chem. Lett. 12 (2001)
691e692.
[13] W. Keim, S. Killat, C.F. Nobile, G.P. Suranna, U. Englert, R. Wang, S. Mecking,
D.L. Schroder, J. Organomet. Chem. 662 (2002) 150e171.
[14] F. Liu, H. Gao, K. Song, Y. Zhao, J. Long, L. Zhang, F. Zhu, Q. Wu, Polyhedron 28
(2009) 673e678.
[15] T. Xiao, J. Lai, S. Zhang, X. Hao, W.-H. Sun, Catal. Sci. Technol. 1 (2011)
462e469.
[16] T. Xiao, W. Zhang, J. Lai, W.-H. Sun, C. R. Chimie 14 (2011) 851e855.
[17] F.-S. Liu, H.-B. Hu, Y. Xu, L.-H. Guo, S.-B. Zai, K.-M. Song, H.-Y. Gao, L. Zhang, F.-
M. Zhu, Q. Wu, Macromolecules 42 (2009) 7789e7796.
[18] D.P. Gates, S.A. Svejda, E. Onate, C.M. Killian, L.K. Johnson, P.S. White,
M. Brookhart, Macromolecules 33 (2000) 2320e2334.
[19] R.J. Maldanis, J.S. Wood, A. Chandrasekaran, M.D. Rausch, J.C.W. Chien,
J. Organomet. Chem. 645 (2002) 158e167.
[20] H. Zou, F.M. Zhu, Q. Wu, J.Y. Ai, S.A. Lin, J. Polym. Sci., Part A: Polym. Chem. 43
(2005) 1325e1330.
[21] B.K. Bahuleyan, G.W. Son, D.-W. Park, C.-S. Ha, I. Kim, J. Polym. Sci., Part A:
Polym. Chem. 46 (2008) 1066e1082.
[22] M.M. Wegner, A.K. Ott, B. Rieger, Macromolecules 43 (2010) 3624e3633.
[23] C.-L. Song, L.-M. Tang, Y.-G. Li, X.-F. Li, J. Chen, Y.-S. Li, J. Polym. Sci., Part A:
Polym. Chem. 44 (2006) 1964e1974.
[24] H.-R. Liu, P.T. Gomes, S.I. Costa, M.T. Duarte, R. Branquinho, A.C. Fernandes,
J.C.W. Chien, R.P. Singh, M.M. Marques, J. Organomet. Chem. 690 (2005)
1314e1323.
[25] C.S. Popeney, Z. Guan, Macromolecules 43 (2010) 4091e4097.
[26] H. Tom Dieck, M. Svoboda, T.Z. Grieser, Naturforsh 36b (1981) 823e832.
[27] R. Van Asselt, C.J. Elsevier, W.J.J. Smeets, A.L. Spek, R. Benedix, Recl. Trav. Chim.
Pays-Bas 113 (1994) 88e98.
[28] G. Van Koten, K. Vrieze, Adv. Organomet. Chem. 21 (1982) 151e239.
[29] G.J.P. Britovsek, G.K.B. Clentsmith, V.C. Gibson, D.M.L. Goodgame,
S.J. McTavish, Q.A. Pankhurst, Catal. Commun. 3 (2002) 207e211.
[30] K.P. Bryliakov, N.V. Semikolenova, V.A. Zakharov, E.P. Talsi, Organometallics
23 (2004) 5375e5378.
[31] K.P. Bryliakov, N.V. Semikolenova, V.N. Zudin, V.A. Zakharov, E.P. Talsi, Catal.
Commun. 5 (2004) 45e48.
[32] V.L. Cruz, J. Ramos, J. Martınez-Salazar, S. Gutierrez-Oliva, A. Toro-Labbe,
Organometallics 28 (2009) 5889e5895.
[33] R. Raucoules, T. de Bruin, P. Raybaud, C. Adamo, Organometallics 28 (2009)
5358e5367.
[34] K.P. Bryliakov, E.P. Talsi, N.V. Semikolenova, V.A. Zakharov, Organometallics
28 (2009) 3225e3232.
[35] A.M. Tondreau, C. Milsmann, A.D. Patrick, H.M. Hoyt, E. Lobkovsky,
K. Wieghardt, P.J. Chirik, J. Am. Chem. Soc. 132 (2010) 15046e15059.
[36] C. Wallenhorst, G. Kehr, H. Luftmann, R. Frohlich, G. Erker, Organometallics 27
(2008) 6547e6556.
[37] M.W. Bouwkamp, E. Lobkovsky, P.J. Chirik, J. Am. Chem. Soc. 127 (2005)
9660e9661.
[70] X. Tang, D. Zhang, S. Jie, W.-H. Sun, J. Chen, J. Organomet. Chem. 690 (2005)
3918e3928.
[71] S. Al-Benna, M.J. Sarsfield, M. Thornton-Pett, D.L. Ormsby, P. J.Maddox, P. Bre`s,
M. Bochmann, J. Chem. Soc. Dalton Trans. (2000) 4247e4257.
[72] W.-H. Sun, S. Zhang, S. Jie, W. Zhang, Y. Li, H. Ma, J. Chen, K. Wedeking,
R. Fröhlich, J. Organomet. Chem. 691 (2006) 4196e4203.
[73] J.C. Jenkins, M. Brookhart, Organometallics 22 (2003) 250e256.
[74] W. Keim, Angew. Chem. Int. Ed. Engl. 29 (1990) 235e244.
[75] D. Guo, L. Han, T. Zhang, W.-H. Sun, T. Li, X. Yang, Macromol. Theory Simul. 11
(2002) 1006e1012.
[76] T. Zhang, D. Guo, S. Jie, W.-H. Sun, T. Li, X. Yang, J. Polym. Sci., Part A: Polym.
Chem. 42 (2004) 4765e4774.
[77] X. Zhang, B. Duan, W.-H. Sun, S. Hsu, X. Yang, Sci. China Ser. B. Chem. 52
(2009) 48e55.
[38] J. Campora, M. Naz, P. Palma, E. Alvarez, M.L. Reyes, Organometallics 24 (2005)
4878e4881.
[39] C. Shao, W.-H. Sun, Z. Li, Y. Hu, L. Han, Catal. Commun. 3 (2002) 405e410.
[78] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures,
University of Göttingen, Germany, 1997.