N-(5,6,7-Trihydroquinolin-8-ylidene)-2-benzhydrylbenzenaminonickel halide complexes: Synthesis, characterization and catalytic behavior towards ethylene polymerization

Article abstract of DOI:10.1039/c1dt11766a

A series of N-(5,6,7-trihydroquinolinylidene)-2-benzhydrylbenzenamine ligands was synthesized and characterized by ¹H/¹³C NMR and IR spectroscopy, and by elemental analysis. These ligands reacted with NiCl₂ or NiBr₂(DME) to form the title halide complexes, which were also characterized by IR spectroscopy and elemental analysis. Single crystal X-ray diffraction revealed that the representative nickel complexes crystallized as centro-symmetric dimers with chloro-bridges linking distorted octahedral nickel centers. On activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et₂AlCl), all nickel pre-catalysts showed high activities for ethylene polymerization, producing polyethylene with narrow molecular weight distribution, consistent with single-site catalysis. The nature of the ligands and reaction parameters were investigated and discussed in terms of their influence on the catalytic behavior of these nickel pre-catalysts.

Full text of DOI:10.1039/c1dt11766a

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 1617
www.rsc.org/dalton
PAPER
N-(5,6,7-Trihydroquinolin-8-ylidene)-2-benzhydrylbenzenaminonickel halide
complexes: synthesis, characterization and catalytic behavior towards ethylene
polymerization†
Xiaohua Hou,a,b Zhengguo Cai,c Xia Chen,*a Lin Wang,b Carl Redshaw*d and Wen-Hua Sun*b,c
Received 18th September 2011, Accepted 31st October 2011
DOI: 10.1039/c1dt11766a
A series of N-(5,6,7-trihydroquinolinylidene)-2-benzhydrylbenzenamine ligands was synthesized and
characterized by 1H/13C NMR and IR spectroscopy, and by elemental analysis. These ligands reacted
with NiCl2 or NiBr2(DME) to form the title halide complexes, which were also characterized by IR
spectroscopy and elemental analysis. Single crystal X-ray diffraction revealed that the representative
nickel complexes crystallized as centro-symmetric dimers with chloro-bridges linking distorted
octahedral nickel centers. On activation with either methylaluminoxane (MAO) or diethylaluminium
chloride (Et2AlCl), all nickel pre-catalysts showed high activities for ethylene polymerization,
producing polyethylene with narrow molecular weight distribution, consistent with single-site catalysis.
The nature of the ligands and reaction parameters were investigated and discussed in terms of their
influence on the catalytic behavior of these nickel pre-catalysts.
for ethylene polymerization, as illustrated by the bis(imino)nickel
halides,4 because mostly these newly developed systems induced
1. Introduction
ethylene oligomerization.5 However, inspired by the successful
shift from bis(imino)nickel4,5 to pyridyliminonickel pre-catalysts,13
the N-(5,6,7-trihydro-quinolin-8-ylidene)arylaminonickel pre-
catalysts have recently been explored, and interesting prop-
erties were observed for ethylene oligomerization when em-
ploying N-(2-Cl/Ph-5,6,7-trihydroquinolin-8-ylidene)arylamine14
and for ethylene polymerization with N-(5,6,7-trihydroquinolin-
8-ylidene)-arylamines.15 Encouraged by these new findings,
whereby the use of bulky substituents have stabilized the
active species,16 the scope for using other 2-dibenzhy-
drylbenzenamines instead of the more common anilines was
investigated. The resulting N-(5,6,7-trihydroquinolin-8-ylidene)-
2-benzhydrylbenzenamines were then complexed with nickel
halides, and the resulting N-(5,6,7-trihydroquinolin-8-ylidene)-
2-benzhydrylbenzenaminonickel dichlorides were evaluated for
ethylene polymerization catalysis. The nature of the ligands, as
well as the reaction conditions employed, have been studied for
their effects on the catalytic performance of the systems herein.
Both ethylene oligomerization and polymerization play pivotal
roles in today’s petrochemical industry, and the products are
tremendously important in our everyday life.1 Amongst the cata-
lysts deployed, nickel-based complexes have enjoyed much success,
acting as pre-catalysts in ethylene oligomerization (including
ethylene dimerization).2 By overcoming the problems associated
with b-hydrogen elimination,3 the use of bis(imino)nickel halides
proved to be a notable milestone in late-transition metal ethylene
polymerization catalysis, achieving high activities and producing
polyethylene with high molecular weight.4 Subsequently, varia-
tions of the bis(imino)nickel pre-catalyst model have been the
focus of much attention. New systems were developed either by
fine-tuning the substituents present on the parent ligand set,5 or
by employing newly designed ligands such as bidentate NŸN,6
NŸP,7 NŸO,8 PŸO,9 or tridentate NŸNŸN,10 NŸNŸO,11 NŸPŸN ligand
sets.12 In general, these nickel pre-catalysts are not as attractive
aSchool of Chemistry and Chemical Engineering, Shanxi University, Taiyuan,
030006, China. E-mail: chenxia@sxu.edu.cn
bKey Laboratory of Engineering Plastics and Beijing National Laboratory
for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
2. Results and discussion
2.1 Synthesis and characterization
cCollege of Material Science and Engineering & State Key Laboratory
for Modification of Chemical Fibers and Polymer Materials, Donghua
University, Shanghai, 201620, China
N-(5,6,7-Trihydroquinolinylidene)-2-benzhydrylbenzenamine lig-
ands can be easily prepared by the condensation of 5,6,7-
trihydroquinolin-8-one with bulky anilines in moderate yields
(Scheme 1). All the compounds were characterized by FT-IR,
1H and 13C NMR spectroscopy as well as by elemental analysis.
Further reaction of the ligands with NiCl2·6H2O or NiBr2·DME
dSchool of Chemistry, University of East Anglia, Norwich, UK, NR4 7TJ.
E-mail: Carl.Redshaw@uea.ac.uk
† CCDC reference numbers 843822 and 843823 for crystallographic data
of complexes Ni2 and Ni3 respectively. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c1dt11766a
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1617–1623 | 1617
©

View Article Online
Scheme 1 Synthetic procedure.
Fig. 1 ORTEP drawing of complex Ni2·CH3OH.
afforded the title complexes, which were characterized by FT-IR
and elemental analysis. In addition, the molecular structures of
the complexes Ni2 and Ni3 were confirmed by single-crystal X-ray
diffraction studies.
2.2 Molecular structures
Single crystals of Ni2·CH3OH and Ni3·C2H5OH suitable for X-
ray diffraction analysis were obtained by laying diethyl ether onto
dichloromethane/methanol or ethanol (v/v = 1 : 1) solutions of
the respective complex at room temperature. Both complexes
Ni2·CH3OH and Ni3·C2H5OH crystallized as centro-symmetric
dimers and their molecular structures show a distorted octahedral
geometry at the nickel center, which is completed by the coordina-
tion of a solvent molecule. The molecular structures of complexes
Ni2·CH3OH and Ni3·C2H5OH are shown in Fig. 1 and 2, and the
selected bond lengths and angles are tabulated in Table 1.
Fig. 2 ORTEP drawing of complex Ni3·C2H5OH. Thermal ellipsoids are
In both structures, the nickel centers are symmetrically bridged
by two chloride atoms (Cl2 and Cl2i), and each is further
coordinated by two nitrogen atoms (N1 and N2) from the ligand
shown at 30% probability. Hydrogen atoms have been omitted for clarity.
as well as the oxygen from the solvent molecule. As shown in
Fig. 1, there is a five-membered heteronickel-cycle constructed
from Ni, N1, C5, C9 and N2, in which the C9 atom deviates
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for Ni2·CH3OH and
Ni3·C2H5OH
˚
by 0.0396 A from the plane of the atoms N1, N2, and Ni1,
˚
whilst the C5 atom deviates by 0.0096 A, i.e. the five atoms are
Ni2·CH3OH
Ni3·C2H5OH
almost in the same plane. The two Ni–N bond lengths are Ni–N1
˚
˚
(2.056 A) and Ni–N2 (2.134 A). The pyridyl and imino-phenyl
planes are nearly perpendicular with a dihedral angle of 98.4◦.
There is no direct bonding between the two nickel atoms with an
˚
Bond lengths (A)
Ni . . . Ni
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–Cl(2)
Ni(1)–Cl(1)
Ni(1)–O(1)
N(1)–C(1)
N(1)–C(5)
3.449
3.425
2.056(3)
2.134(3)
2.4696(12)
2.4268(12)
2.137(3)
1.327(5)
1.366(5)
1.300(5)
1.436(5)
2.057(6)
2.153(5)
2.3854(18)
2.398(2)
2.153(5)
1.324(10)
1.348(9)
1.282(8)
1.428(8)
˚
intramolecular distance of 3.4491 A, which is similar to 3.4810
˚
A found in the [2,6-diethyl-N-(2-chloro-5,6,7-trihydroquinolin-8-
ylidene)phenylamino]nickel(II) dichloride.14 The axial chloride Cl1
˚
forms stronger bonding with the nickel centre (Ni–Cl1, 2.4268 A)
˚
than does the equatorial bridging chloride Cl2 [Ni–Cl2 (2.4696 A)].
N(2)–C(9)
N(2)–C(10)
˚
The Ni ◊ ◊ ◊ Ni length is 3.425 A for Ni3·C2H5OH which is slightly
˚
Bond angles (◦)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–O(1)
N(2)–Ni(1)–O(1)
N(1)–Ni(1)–Cl(1)
O(1)–Ni(1)–Cl(1)
N(2)–Ni(1)–Cl(1)
N(1)–Ni(1)–Cl(2)
O(1)–Ni(1)–Cl(2)
N(2)–Ni(1)–Cl(2)
Cl(1)–Ni(1)–Cl(2)
shorter than that of Ni2·CH3OH (3.449 A) and the dihedral
angle of pyridyl and imino-phenyl planes is 91.5◦. The small
differences between the molecular structures of Ni2·CH3OH and
Ni3·C2H5OH are probably caused by the introduction of bulky
substituents at the ortho-position of the N-aryl ring.
78.66(13)
95.66(13)
88.33(12)
89.14(10)
170.97(9)
100.14(9)
174.69(10)
83.74(9)
78.6(2)
91.3(2)
90.6(2)
90.52(18)
171.07(14)
98.36(16)
172.18(17)
84.72(14)
94.69(15)
94.48(7)
2.3 Ethylene polymerization
96.05(9)
92.17(4)
The ethylene polymerization behavior of these nickel complexes
was investigated. Trace quantities of oligomers were found during
1618 | Dalton Trans., 2012, 41, 1617–1623
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Table 2 Polymerization of ethylene in the presence of MAOa
T/ ◦
C
Al/Ni
t/ min
Polymer/ g
Activityb
Mwc/ kg mol-1
Mw/Mn
Tm /
◦C
Branches/1000Ce
c
d
Entry
Pre-cat.
1
2
3
4
5
6
7
8
Ni1
Ni1
Ni1
Ni1
Ni1
Ni1
Ni1
Ni1
Ni1
Ni1
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
Ni7
Ni8
20
20
20
20
20
30
40
50
20
20
20
20
20
20
20
20
20
20
500
600
750
1000
1500
750
750
750
750
750
750
750
750
750
750
750
750
750
30
30
30
30
30
30
30
30
10
20
40
30
30
30
30
30
30
30
3.20
8.15
14.15
11.84
11.63
9.61
6.86
3.27
4.61
9.03
16.67
10.48
2.31
1.62
7.52
5.46
1.94
1.42
1.28
3.26
5.66
4.74
4.65
3.84
2.74
1.31
5.17
5.42
4.00
4.19
0.92
0.65
3.01
2.18
0.78
0.57
12.0
7.7
5.7
5.2
5.4
10.6
4.1
2.5
7.9
7.0
6.8
4.8
6.7
7.4
6.3
7.0
7.3
6.8
2.6
1.8
2.2
2.0
2.0
2.0
2.3
2.3
2.4
2.7
2.5
2.3
2.1
1.9
1.9
2.6
2.5
1.8
114.6
102.9
95.6
93.6
80.8
103.5
88.8
77.9
92.3
98.7
90.9
58.9
61.2
64.9
95.2
90.5
60.8
64.1
176
132
113
141
150
113
150
186
115
121
136
127
181
226
123
136
209
246
9
10
11
12
13
14
15
16
17
18
a Reaction conditions: 5 mmol of Ni; 10 atm of ethylene; 100 mL toluene. b 106 g(PE)·mol(Ni)-1·h-1. c Determined by GPC. d Determined by DSC.
e Determined by FT-IR.
the polymerization process through GC detection. Different co-
catalysts were employed to activate the pre-catalyst. Both MAO
and EtAlCl2 showed higher activity than did other alkylaluminium
reagents and thus were selected for further study. All the catalysts
exhibited very low activity when the ethylene pressure was 1 bar,
thus subsequent entries were performed with 10 bar ethylene as
the routine condition. Herein, the effect of ligand environment
on catalytic behavior was investigated in further detail. Also the
molar ratio of Al/Ni, the temperature, and the reaction time have
been considered. The pre-catalysts showed high catalytic activity
(up to 106) for ethylene polymerization.
2.3.1 Ethylene polymerization in the presence of MAO. The
influence of the reaction parameters, including the molar ratio
of Al/Ni, the reaction time and the reaction temperature, were
Fig. 3 GPC traces of polyethylene produced by Ni1/MAO catalytic
investigated using the Ni1/MAO system. On variation of the
system (a: T = 30 ◦C, entry 6; b: T = 20 ◦C, entry 3; c: T = 40 ◦C,
entry 7; d: T = 50 ◦C, entry 8 in Table 2).
Al/Ni from 500 to 1500 (entries 1–5 in Table 2), the catalyst
showed the highest activity at an optimum ratio of 750, namely
£5.66 ¥ 106 g(PE)·mol(Ni)-1·h-1 (entry 3 in Table 2). The molecular
weight distributions were relatively narrow, with values in the
region of about 2.00, suggesting fairly well controlled behavior.
It was found that when the ratio of Al/Ni was raised to 750,
the molecular weights remained almost unaffected. This indicated
that the amount of MAO is enough to activate the pre-catalyst
at the ratio of 750. Also the influence of the reaction temperature
was investigated (entries 6 and 7, 8 in Table 2) at the constant
molar ratio of Al/Ni = 750. The activity decreased with increasing
reaction temperature. It was found that the polymer of highest
molecular weight was attainable at 30 ◦C (Fig. 3). When the
temperature was raised to 50 ◦C, only a small amount of wax was
obtained possessing a very low molecular weight of about 2500.
Thus, the activity decreased sharply and the resultant polymer
possessed lower molecular weight than runs conducted at room
temperature, which is similar to results for other late-transition
iminopyridyl-based pre-catalysts.17 The present system is much
more sensitive to temperature than the N-(5,6,7-trihydroquinolin-
8-ylidene)arylamine nickel complexes previously reported by our
group,15 thus revealing that the active centre formed by this kind of
pre-catalyst possessing bulky substituents at the ortho-position is
more unstable at higher temperatures. The 13C NMR spectrum for
Ni1/MAO (entry 3 in Table 2) showed 100 branches/1000 carbons
(Fig. 4).18 The formation of the highly branched PEs obtained
was due to b-hydrogen migration, which occurred at the active
nickel species.19 Furthermore, the influence of the reaction time
was studied, and in general, the catalytic activities slowly decreased
on prolonging the reaction time, indicating a relative long lifetime
of the active species. The other complexes herein were also screened
under these optimized conditions (entries 12, 13 and 14 in Table
2). The activity decreased sharply when the ortho-position of the
phenyl ring was occupied by the bulky dibenzhydryl [-CH(Ph)2]
group. Contrastingly, the substituent at the para-position played
a relatively minor role in influencing the catalytic activity of the
ethylene polymerization (Ni1>Ni2>Ni3>Ni4). When the halogen
at nickel is bromide, the activities showed much lower values than
did the corresponding nickel chloride complexes; similar trends
with the other ligand variations were noted (Ni5>Ni6>Ni7>Ni8).
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1617–1623 | 1619
©

View Article Online
Fig. 5 GPC traces of polyethylene produced by Ni1/Et2AlCl catalytic
system (a: T = 30 ◦C, entry 22; b: T = 20 ◦C, entry 20; c: T = 40 ◦C, entry
23 in Table 3).
Fig. 4 13C NMR spectrum of polyethylene (entry 3 in Table 2).
2.3.2 Ethylene polymerization in the presence of Et2AlCl.
Using Et2AlCl as co-catalyst rather than MAO, the complexes
performed with a relatively lower activity toward ethylene poly-
merization. The influence of the reaction parameters on the
catalytic activities, including the molar ratio of Et2AlCl and the
reaction temperature, were investigated with complex Ni1. The
detailed results are summarized in Table 3. The results showed a
similar tendency as for those observed when using MAO, but the
PDI of the waxes were somewhat narrower. The molecular weights
were higher than using MAO (entries 20 and 24–30 in Table 3).
Also both the ratio of Al/Ni and the temperature played important
roles in the polymerization behavior. The optimum ratio of Al/Ni
was found to be 150, whilst increasing the reaction temperature
from 20 ◦C to 40 ◦C (entries 21, 22 and 23 in Table 3) led to
an obvious decrease in the activity and the isolation of lower
molecular weight polymers (Fig. 5). It is interesting that the Tm
values were lower than the entries using MAO though the wax
possessed higher molecular weight. This can be attributed to the
higher degree of branching, which can be detected and calculated
via IR spectroscopic analysis.20
catalyst family to study their influence on the catalytic behavior
during ethylene polymerization. The results showed that all
these nickel complexes exhibited high activity (up to 5.66 ¥
106 g mol(Ni)-1·h-1) for ethylene polymerization, producing highly
branched wax-like products with narrow molecular weight dis-
tribution. The molecular weight can be easily controlled through
ligand modification, i.e. substituent variation. Complexes bearing
one bulky substituent [-CH(Ph)2] at an ortho-position of the N-
aryl ring (Ni1 and Ni2) exhibited higher activities than did the
complexes with two bulky substituents [-CH(Ph)2] at both ortho-
positions of the N-aryl ring (Ni3 and Ni4), which illustrates the
fine balance steric bulk plays on the catalytic performance of these
nickel-based ethylene polymerization systems.
4. Experimental section
4.1 General considerations and materials
All work involving air or moisture-sensitive compounds was
carried out under nitrogen atmosphere using standard Schlenk
techniques. Toluene was dried by refluxing with sodium and
distilled under nitrogen. Methylaluminoxane (MAO, 1.46 M in
toluene) was purchased from Albemarle and diethylaluminium
chloride (Et2AlCl, 0.50 M in toluene) was purchased from Acros
3. Conclusions
A number of bulky substituents were introduced to the N-(5,6,7-
trihydroquinolinylidene)-2-benzhydrylbenzenamines-Ni(II) pre-
Table 3 Polymerization of ethylene in the presence of Et2AlCla
T/ ◦
C
Al/Ni
t/ min
Polymer/ g
Activityb
Mwc/ kg mol-1
Mw/Mn
Tm /
◦C
Branches/1000Ce
c
d
Entry
Pre-cat.
19
20
21
22
23
24
25
26
27
28
29
30
Ni1
Ni1
Ni1
Ni1
Ni1
Ni2
Ni3
Ni4
Ni5
Ni6
Ni7
Ni8
20
20
20
30
40
20
20
20
20
20
20
20
100
150
250
150
150
150
150
150
150
150
150
150
30
30
30
30
30
30
30
30
30
30
30
30
5.75
10.28
9.49
6.79
1.93
10.08
3.15
2.80
5.75
5.49
2.74
1.97
2.30
4.11
3.80
2.72
0.77
4.03
1.26
1.12
2.30
2.20
1.10
0.79
5.8
3.7
3.8
4.2
3.4
4.0
9.1
6.8
7.2
7.0
7.0
7.7
1.8
2.2
1.8
1.9
1.8
2.0
1.9
1.7
1.9
1.9
1.7
1.8
82.0
69.3
64.9
72.7
56.4
60.8
61.2
63.8
89.9
84.2
60.8
64.8
175
210
240
227
260
184
229
193
154
144
219
189
a Reaction conditions: 5 mmol of Ni; 10 atm of ethylene; 100 mL toluene. b 106 g(PE)·mol(Ni)-1·h-1. c Determined by GPC. d Determined by DSC.
e Determined by FT-IR.
1620 | Dalton Trans., 2012, 41, 1617–1623
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Chemicals. High-purity ethylene was purchased from Beijing
Yansan Petrochemical Co. and used as received. Other reagents
1H, Py Hm), 7.41 (t, J = 6.0 Hz, 1H, Py Hp), 7.05–7.37 (m, 20H,
Ph-H), 6.69 (s, 2H, Ph-H), 5.51 (s, 2H, -CH(Ph)2), 2.28 (t, J = 5.9
Hz, 2H, -C N-CH2-), 2.16 (s, 3H, Ph-CH3), 0.86 (t, J = 6.1 Hz,
2H, Py-CH2-), 0.54 (m, 2H, -CH2-) ppm. 13C NMR (100 MHz,
CDCl3 TMS): d 168.4, 148.5, 144.8, 142.8, 137.0, 132.4, 130.1,
129.7, 129.1, 128.4, 128.0, 126.1, 125.9, 124.7, 51.7, 31.1, 29.1,
21.4, 20.5 ppm. FT-IR (KBr, cm-1): 3345 (w), 2929 (m), 2029 (m),
1734 (s), 1637 (s, C N), 1598 (m), 1562 (m), 1493 (vs), 1238 (s),
1033 (vs), 746 (vs). Anal. Calcd for C42H36N2 (568): C, 88.69; H,
6.38; N, 4.93%. Found: C, 88.57; H, 6.33; N, 4.86%.
were purchased from Aldrich, Acros, or local suppliers. 1H and 13
C
NMR spectra were recorded on a Bruker DMX 400 MHz instru-
ment at ambient temperature, using TMS as an internal standard.
IR spectra were recorded on a Perkin-Elmer System 2000 FT-IR
spectrometer. Elemental analysis was carried out using a Flash
EA 1112 microanalyzer. Molecular weights (Mw) and molecular
weight distribution (Mw/Mn) of polyethylenes were determined
by a PL-GPC220 at 120 ◦C, with 1,2,4-trichlorobenzene as the
solvent. Melting points of polyethylenes were obtained from the
sec◦ond scanning run on Perkin-Elmer DSC-7 at a heating rate of
10 C min-1.
2,6-Dibenzhydryl-4-(1-methylethyl)-N-(5,6,7-trihydro-quino-
lin-8-ylidene)phenylamine (L4). This compound was prepared
according to the method described for 1. The pr◦oduct was collected
1
in 45% yield as a yellow powder. Mp 96–98 C. H NMR (400
4.2 Syntheses and characterization
MHz, CDCl3 TMS): d 8.74 (d, J = 4.0 Hz, 1H, Py Hm), 7.41 (d,
J = 7.6 Hz, 1H, Py Hm), 7.27 (t, J = 6.1 Hz, 1H, Py Hp), 7.03–7.24
(m, 20H, Ph-H), 6.72 (s, 2H, Ph-H), 5.51 (s, 1H, -CH(Ph)2), 2.69
(m, 1H, -CH2(CH3)2), 2.27 (t, J = 5.9 Hz, 2H, -N CCH2-), 1.05
(d, J = 6.8 Hz, 6H, -CH3), 0.88 (t, J = 6.0 Hz, 3H, Py-CH2-),
0.55 (m, 2H, -CH2-) ppm. 13C NMR (100 MHz, CDCl3 TMS): d
167.3, 144.0, 143.3, 142.8, 139.3, 132.5, 129.8, 129.6, 129.1, 128.5,
128.0, 126.7, 126.4, 126.0, 51.9, 33.6, 33.2, 24.1, 21.3, 19.8 ppm.
FT-IR (KBr, cm-1): 3338 (w), 2957 (m), 1976 (m), 1735 (s), 1639
(s, C N), 1598 (s), 1570 (m), 1446 (vs), 1030 (s), 742 (vs). Anal.
Calcd for C44H40N2 (596): C, 88.55; H, 6.76; N, 4.69%. Found: C,
88.34; H, 6.78; N, 4.80%.
4.2.1 Synthesis of ligands.
2-Methyl-4,6-dibenzhydryl-N-(5,6,7-trihydroquinolin-8-ylide-
ne)phenylamine (L1). A 15 mL toluene solution of 5,6,7-
trihydroquinolin-8-one (2 mmol, 0.294 g) and 2-methyl-4,6-
dibenzhydrylaniline (2.2 mmol, 0.966 g) together with a catalytic
amount of p-toluenesulfonic acid was refluxed for 3 h. The toluene
was then evaporated at reduced pressure, and the residue was
purified by alumina column chromatography [V (petroleum ether):
V (dichloromethane) = 5 : 1]. The product wa◦s a yellow powder,
1
which was collected in 38% yield. Mp 84–86 C. H NMR (400
MHz, CDCl3 TMS): d 8.73 (d, J = 4.3 Hz, 1H, Py Hm), 8.33 (d,
J = 7.5 Hz, 1H, Py Hm), 7.46 (t, J = 5.8 Hz, 1H, Py Hp), 6.88–
7.29 (m, 20H, Ph-H), 6.78 (s, 1H, Ph-H), 6.56 (s, 1H, Ph-H), 5.62
(s, 1H, p-CH(Ph)2), 5.40 (s, 1H, o-CH(Ph)2), 2.69, 2.52 (m, 2H,
-N CCH2-), 1.95 (s, 3H, Ph-CH3), 2.06, 1.25 (m, 2H, py-CH2-),
1.60, 1.05 (m, 2H, -CH2-) ppm.13C NMR (100 MHz, CDCl3 TMS):
d 165.8, 148.4, 146.9, 144.5, 144.3, 144.0, 142.8, 137.2, 136.8, 136.7,
133.3, 129.9, 129.2, 128.8, 128.6, 127.8, 127.5, 125.8, 125.7, 125.4,
56.1, 51.6, 30.3, 28.9, 21.0, 17.8 ppm. FT-IR (KBr, cm-1): 3344
(w), 2925 (m), 2027 (w), 1640 (s, C N), 1598 (m), 1564 (m), 1492
(vs), 1032 (s), 738 (vs). Anal. Calcd for C42H36N2 (568): C, 88.69;
H, 6.38; N, 4.93%. Found: C, 88.54; H, 6.41; N, 5.10%.
4.2.2 Synthesis of nickel complexes.
General procedure. NiCl2·6H2O or (DME)NiBr2 (0.5 mmol)
was dissolved in 10 mL ethanol and added to the solution of
the ligand (0.5 mmol) in 5 mL CH2Cl2 (but not ethanol because of
inferior solubility). The mixture was stirred overnight, and then
ether was poured into the mixture to precipitate the complex. The
precipitant was collected by filtration, washed with diethyl ether
(3 ¥ 5 mL), and dried under vacuum at 60 ◦C.
2-Methyl-4,6-dibenzhydryl-N -(5,6,7-trihydroquinolin-8-ylide-
ne)phenylaminonickel(II) dichloride (Ni1) (yellow, 0.31 g, 91%
yield): FT-IR (KBr, disk, cm-1): 3026 (m), 2028 (w),1976 (w), 1623
(s, C N), 1584 (s), 1494 (vs), 1029 (s), 730(vs). Anal. Calcd for
C42H36Cl2N2Ni (698): C, 72.23; H, 5.20; N, 4.01%. Found: C, 72.43;
H, 5.09; N, 4.04%.
2,4-Dimethyl-6-benzhydryl-N -(5,6,7-trihydroquinolin-8-ylide-
ne)phenylaminonickel(II) dichloride (Ni2)(yellow, 0.25 g, 93%
yield): FT-IR (KBr, disk, cm-1): 3190 (w), 2920 (m), 2030 (m),
1622 (s, C N), 1583 (s), 1451 (vs), 1212 (s), 1033 (s), 746 (vs).
Anal. Calcd for C30H28Cl2N2Ni (546): C, 65.97; H, 5.17; N, 5.13%.
Found: C, 65.89; H, 5.16; N, 5.10%.
2,6-Dibenzhydryl-4-methyl-N -(5,6,7-trihydroquinolin-8-ylide-
ne)phenylamineonickel(II) dichloride (Ni3) (yellow, 0.33 g, 94%
yield): FT-IR (KBr, disk, cm-1): 2919 (m), 2030 (m), 1624 (s,
N), 1584 (s), 1494 (vs), 1208 (s), 1029 (vs), 753 (vs). Anal. Calcd
for C42H36Cl2N2Ni (698): C, 72.23; H, 5.20; N, 4.01%. Found: C,
71.88; H, 5.17; N, 4.24%.
2,6-Dibenzhydryl-4-(1-methylethyl)-N-(5,6,7-trihydro-quinolin-
8-ylidene)phenylaminonickel(II) dichloride (Ni4) (yellow, 0.35 g,
96% yield): FT-IR (KBr, disk, cm-1): 2957 (m), 1975 (m), 1620
(s, C N), 1581 (s), 1449 (vs), 1129 (s), 747 (vs). Anal. Calcd for
C44H40Cl2N2Ni (698): C, 72.75; H, 5.55; N, 3.86%. Found: C, 72.34;
H, 5.21; N, 3.62%.
2,4-Dimethyl-6-benzhydryl-N-(5,6,7-trihydroquinolin-8-ylide-
ne)phenylamine (L2). This compound was prepared according
to the method described for 1. The product was a yellow powder
and the yield was 48%. Mp 80–82 ◦C. 1H NMR (400 MHz, CDCl3
TMS): d 8.73 (d, J = 4.1 Hz, 1H, Py Hm), 7.46 (d, J = 7.5 Hz, 1H,
Py Hm), 7.25 (t, J = 6.1 Hz, 1H, Py Hp), 7.04–7.22 (m, 10H, Ph-
H), 6.88 (s, 1H, Ph-H), 6.59 (s, 1H, Ph-H), 5.65 (s, 1H, -CH(Ph)2),
2.66, 2.47 (m, 2H, -N CCH2-), 2.21 (s, 3H, o-Ph-CH3), 1.99 (s,
3H, p-Ph-CH3), 1.91, 1.14 (m, 2H, Py-CH2-), 1.42, 0.89 (m, 2H,
-CH2-) ppm. 13C NMR (100 MHz, CDCl3 TMS): d 166.1, 150.0,
148.7, 146.5, 143.2, 137.1, 131.6, 130.1, 129.7, 129.1, 128.3, 128.0,
126.0, 124.8, 51.9, 30.5, 29.3, 21.3, 21.0, 18.1 ppm. FT-IR (KBr,
cm-1): 3342 (w), 2921 (m), 2017 (w), 1638 (s, C N),1599 (m),
1564 (m), 1444 (vs), 1189 (s), 1031 (s), 744 (vs). Anal. Calcd for
C30H28N2 (416): C, 86.50; H, 6.78; N, 6.72%. Found: C, 86.62; H,
6.83; N, 6.88%.
C
2,6-Dibenzhydryl-4-methyl-N-(5,6,7-trihydroquinolin-8-ylide-
ne)phenylamine (L3). This compound was prepared according
to the method described for 1. Th◦e product was a yellow powder
isolated in 42% yield. Mp 103–104 C. 1H NMR (400 MHz, CDCl3
TMS): d 8.74 (d, J = 4.1 Hz, 1H, Py Hm), 7.41 (d, J = 7.6 Hz,
This journal is The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1617–1623 | 1621
©

View Article Online
Table 4 Crystal data and structure refinement for Ni2·CH3OH and
Ni3·C2H5OH
2-Methyl-4,6-dibenzhydryl-N -(5,6,7-trihydroquinolin-8-ylide-
ne)phenylaminonickel(II) dibromide (Ni5) (yellow,0.33g 86% yield):
FT-IR (KBr, disk, cm-1): 3024 (m), 2032(w), 1978 (w), 1623 (s,
Ni2·CH3OH
Ni3·C2H5OH
C
N), 1581(s), 1493 (vs), 1030 (vs), 750 (vs). Anal. Calcd for
C42H36Br2N2Ni (787): C, 64.08; H, 4.61; N, 3.56%. Found: C, 64.26;
H, 4.65; N, 3.57%.
2,4-Dimethyl-6-benzhydryl-N -(5,6,7-trihydroquinolin-8-ylide-
ne)phenylaminonickel(II) dibromide (Ni6) (yellow, 0.27 g, 84%
yield): FT-IR (KBr, disk, cm-1): 2965 (m), 2036 (m), 1622 (s,
Empirical formula
Fw
C62H64Cl4N4Ni2O2
1156.39
173(2)
0.71073
Monoclinic
P21/n
14.895(3)
15.229(3)
15.550(3)
90
103.64(3)
90
3427.6(12)
2
1.120
C88H82Cl4N4Ni2O2
1486.8
173(2)
0.71073
Monoclinic
P21/c
16.059(2)
17.764(3)
15.868(3)
90
108.03(4)
90
4304.0(6)
2
1.147
T/K
˚
l/A
Cryst system
Space group
˚
a/A
C
N), 1580 (s), 1451 (vs), 1213 (vs), 1033 (vs), 740 (vs). Anal.
˚
b/A
Calcd for C30H28Br2N2Ni (635): C, 56.74; H, 5.09; N, 4.41%.
Found: C, 56.94; H, 5.06; N, 4.38%.
2,6-Dibenzhydryl-4-methyl-N -(5,6,7-trihydroquinolin-8-ylide-
ne)phenylaminonickel(II) dibromide (Ni7) (yellow, 0.31 g, 80%
yield): FT-IR (KBr, disk, cm-1): 2911 (m), 2029 (m), 1620 (s,
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
C
N), 1582 (s), 1494 (vs), 1208 (s), 1132 (vs), 742 (vs). Anal. Calcd
Dcalcd, (g cm-3)
m/mm-1
0.744
1208
0.607
1556
for C42H36Br2N2Ni (787): C, 64.08; H, 4.61; N, 3.56%. Found: C,
63.87; H, 4.55; N, 3.46%.
F(000)
Cryst size/mm
0.30 ¥ 0.26 ¥ 0.19
1.70–25.35
-16 £ h £ 17
-18 £ k £ 18
-18 £ l £ 16
25 336
6266 (0.0526)
99.8%
None
0.21 ¥ 0.18 ¥ 0.06
1.33–25.34
-17 £ h £ 19
-21 £ k £ 19
-17 £ l £ 19
17 249
7802 (0.0826)
99.2%
None
q range (◦)
2,6-Dibenzhydryl-4-(1-methylethyl)-N-(5,6,7-trihydro-quinolin-
8-ylidene)phenylaminonickel(II) dibromide (Ni8) (yellow, 0.33 g,
80% yield): FT-IR (KBr, disk, cm-1): 2955 (m), 1978 (m), 1605
(s, C N), 1578 (s), 1448 (vs), 1129 (s), 748 (vs). Anal. Calcd
for C44H40Br2N2Ni (815): C, 64.82; H, 4.95; N, 3.44%. Found: C,
65.03; H, 5.12; N, 3.76%.
Limiting indices
No. of rflns collected
No. unique rflns [R(int)]
Completeness to q (%)
Abs corr
Data/restranints/params
Goodness of fit on F2
Final R indices [I > 2s(I)]
6266/0/335
1.147
7802/0/451
1.049
4.3 X-ray crystallographic studies
R1 = 0.0641
wR2 = 0.1859
R1 = 0.0723
wR2 = 0.1924
0.571 and -0.543
R1 = 0.1030
wR2 = 0.2662
R1 = 0.1398
wR2 = 0.2920
0.700 and -0.999
Single crystals of Ni2·CH3OH and Ni3·C2H5OH suitable for X-
ray diffraction analyses were obtained by laying diethyl ether on
dichloromethane/methanol (v/v = 1 : 1) solution at room tempera-
ture. X-ray studies were carried out on a Rigaku Saturn724+ CCD
R indices (all data)
Largest diff peak and
-3
˚
hole/e A
˚
with graphite-monochromatic Mo-Ka radiation (k = 0.71073 A)
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. Structure solution and refinement were performed by
using the SHELXL-97 package.21 Details of the X-ray structure
determinations and refinements are provided in Table 4.
Acknowledgements
This work is supported by MOST 863 program No.
2009AA034601 and NSFC No. 21072120. CR thanks the EPSRC
for an Overseas Travel Grant.
Notes and references
1 D. B. Malpass, Introduction to Industrial Polyethylene, John Wiley &
Sons, Inc., Hoboken, New Jersey, 2010.
2 (a) W. Keim, F. H. Kowaldt, R. Goddard and C. Kru¨ger, Angew. Chem.,
Int. Ed. Engl., 1978, 17, 466; (b) W. Keim, A. Behr, B. Limba¨cker and
C. Kru¨ger, Angew. Chem., Int. Ed. Engl., 1983, 22, 503.
4.4 General procedure for ethylene polymerization
A 250 mL stainless steel autoclave, equipped with a mechanical
stirrer and a temperature controller, was evacuated by a vacuum
pump and back-filled three times with N2 and twice with ethylene.
50 mL toluene was added under ethylene atmosphere, and the
nickel pre-catalyst in 30 mL toluene was injected. When the desired
reaction temperature was reached, the required amount of co-
catalyst (MAO or Et2AlCl) and additional toluene (maintaining
total volume as 100 mL in reactor) were added by syringe.
A pressure of 10 atm ethylene was then rapidly reached and
maintained through a solenoid clave, the mixture was vigorously
stirred during the ethylene polymerization. After the desired
reaction time, the reaction solution was quenched by the addition
of acidic ethanol, and the precipitated polymer was washed with
ethanol and water several times, and then dried in vacuum until
of constant weight.
3 (a) A. L. Monteiro, M. B. de Souza and R. F. de Souza, Polym. Bull.,
1996, 26, 331; (b) S. A. Svejda and M. Brookhart, Organometallics,
1999, 18, 2734; (c) Z. L. Li, W.-H. Sun, Z. Ma, Y. L. Hu and C. X.
Shao, Chin. Chem. Lett., 2001, 12, 691; (d) W.-H. Sun, Z. Li, H. Hu,
B. Wu, H. Yang, N. Zhu, X. Leng and H. Wang, New J. Chem., 2002,
26, 1474; (e) F. Speiser, P. Braunstein and L. Saussine, Organometallics,
2004, 23, 2628; (f) J. Hou, W.-H. Sun, D. Zhang, L. Chen, W. Li, D.
Zhao and H. Song, J. Mol. Catal. A: Chem., 2005, 231, 221; (g) J. Hou,
W.-H. Sun, S. Zhang, H. Ma, Y. Deng and X. Lu, Organometallics,
2006, 25, 236; (h) P. Chavez, I. G. Rios, A. Kermagoret, R. Pattacini,
A. Meli, C. Bianchini and P. Braunstein, Organometallics, 2009, 28,
1776.
4 (a) L. Johnson, K. C. M. Killian and M. Brookhart, J. Am. Chem. Soc.,
1995, 117, 6414.
5 (a) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000,
100, 1169; (b) W.-H. Sun, D. Zhang, S. Zhang, S. Hou and J. Jie, Kinet.
Catal., 2006, 47, 278; (c) M. Delferro and T. J. Marks, Chem. Rev.,
2011, 111, 2450.
1622 | Dalton Trans., 2012, 41, 1617–1623
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
6 (a) M. Schmid, R. Eberhardt, M. Klinga, M. Leskela¨ and B. Rieger,
Organometallics, 2001, 20, 2321; (b) H. Gao, W. Guo, F. Bao, G. Gui,
J. Zhang, F. Zhu and Q. Wu, Organometallics, 2004, 23, 6273; (c) D.
H. Camacho and Z. Guan, Macromolecules, 2005, 38, 2544; (d) D.
Meinhard, P. Reuter and B. Pieger, Organometallics, 2007, 26, 751;
(e) C. S. Popeney, A. Rheingold and L. Z. Guan, Organometallics,
2009, 28, 4452; (f) F.-Z. Yang, Y.-C. Chen, Y.-F. Lin, K.-H. Yu, Y.
Wang, S.-T. Liu and J.-T. Chen, Dalton Trans., 2009, 1243; (g) S. Zai, F.
Liu, H. Gao, C. Li, G. Zhou, S. Cheng, L. Guo, L. Zhang, F. Zhu and Q.
Wu, Chem. Commun., 2010, 46, 4321; (h) J. M. Benito, E. de Jesu´s, F. J.
de la Mata, J. C. Flores, R. Go´mez and P. Go´mez-Sal, Organometallics,
2006, 25, 3876; (i) S.-J. Song, T. Xiao, T. Liang, F. Wang, C. Redshaw
and W.-H. Sun, Catal. Sci. Technol., 2011, 1, 69; (j) G. J. P. Britovsek,
S. P. D. Baugh, O. Hoarau, V. C. Gibson, D. F. Wass, A. J. P. White and
D. J. Williams, Inorg. Chim. Acta, 2003, 345, 279.
7 (a) Z. Guan and W. J. Marshall, Organometallics, 2002, 21, 3580; (b) F.
Speiser, P. Braunstein, L. Saussine and R. Welter, Organometallics,
2004, 23, 2613; (c) Z. Weng, S. Teo and T. S. A. Hor, Organometallics,
2006, 25, 4878.
8 (a) T. R. Younkin, E. F. Connor, J. I. Henderson, S. K. Friedrich, R.
H. Grubbs and D. A. Bansleben, Science, 2000, 287, 460; (b) D.-P.
Song, W.-P. Ye, Y.-X. Wang, J.-Y. Liu and Y.-S. Li, Organometallics,
2009, 28, 5697; (c) B. A. Rodriguez, M. Delferro and T. J. Marks,
Organometallics, 2008, 27, 2166; (d) D. Zhang and G.-X. Jin,
Organometallics, 2003, 22, 2851.
9 (a) C. Wang, S. Friedrich, T. R. Younkin, R. R. Li, R. H. Grubbs, D.
A. Bansleben and M. W. Day, Organometallics, 1998, 17, 3149; (b) J.
Heinicke, N. Peulecke, M. Kohler, M. He and W. Keim, J. Organomet.
Chem., 2005, 690, 2449; (c) T. Hu, L.-M. Tang, X.-F. Li, Y.-S. Li and
N.-H. Hu, Organometallics, 2005, 24, 2628; (d) A. Kermagoret and P.
Braunstein, Dalton Trans., 2008, 1564; (e) D.-P. Song, J.-Q. Wu, W.-P.
Ye, H.-L. Mu and Y.-S Li, Organometallics, 2010, 29, 2306.
10 (a) N. Ajellal, M. C. A. Kuhn, A. D. G. Boff, M. Ho¨rner, C. M. Thomas,
J.-F. Carpentier and O. L. Jr. Casagrande, Organometallics, 2006, 25,
1213; (b) Y. Yang, P. Yang, C. Zhang, G. Li, X. J. Yang, B. Wu and C.
Janiak, J. Mol. Catal. A: Chem., 2008, 296, 9; (c) S. O. Ojwach, I. A.
Guzei, L. L. Benade, S. F. Mapolie and J. Darkwa, Organometallics,
2009, 28, 2127; (d) L. Xiao, M. Zhang, R. Gao and W.-H. Sun, Aust. J.
Chem., 2010, 63, 109; (e) J. Yu, H Liu and W.-H. Sun, Chem. Commun.,
2011, 47, 3257.
11 (a) X. Tang, W.-H. Sun, T. Gao, J. Hou, J. Chen and W. Chen,
J. Organomet. Chem., 2005, 690, 1570; (b) W.-H. Sun, X. Tang,
T. Gao, B. Wu, W. Zhang and H. Ma, Organometallics, 2004, 23,
5037.
12 (a) J. Hou, W.-H. Sun, S. Zhang, H Ma, Y. Deng and X. Lu,
Organometallics, 2006, 25, 236; (b) R. L. Stapleton, J. Chai, N. J. Taylor
and S. Collins, Organometallics, 2006, 25, 2514.
13 (a) T. V. Laine, M. Klinga and M. Leskela¨, Eur. J. Inorg. Chem., 1999,
959; (b) T. V. Laine, K. Lappalainen, J. Liimatta, E. Aitola, B. Lo¨fgren
and M. Leskela¨, Macromol. Rapid Commun., 1999, 20, 487; (c) T. V.
Laine, U. Piironen, K. Lappalainen, M. Klinga, E. Aitola and M.
Leskela¨, J. Organomet. Chem., 2000, 606, 112; (d) S. Jie, D. Zhang, T.
Zhang, W.-H. Sun, J. Chen, Q. Ren, D. Liu, G. Zheng and W. Chen, J.
Organomet. Chem., 2005, 690, 1739.
14 J. Yu, X. Hu, Y. Zeng, L. Zhang, C. Ni, X. Hao and W.-H. Sun, New J.
Chem., 2011, 35, 178.
15 (a) X. Hu, Y. Zeng and W.-H. Sun, Dalton Trans., 2011, 40, 8436; (b) L.
Zhang, X. Hao, W.-H. Sun and C. Redshaw, ACS Catal., 2011, 1, 1213.
16 (a) H. Liu, W. Zhao, X. Hao, C. Redshaw and W.-H. Sun,
Organometallics, 2011, 30, 2418; (b) J. Yu, H. Liu, W. Zhang, X. Hao
and W.-H. Sun, Chem. Commun., 2011, 47, 3257.
17 (a) P. Hao, S. Zhang, W.-H. Sun, Q. Shi, S. Adewuyi, X. Lu and P. Li,
Organometallics, 2007, 26, 2439; (b) F. A. Kunrath, R. F. de Souza, O.
L. Casagrande, N. R. Jr. Brooks and V. G. Jr. Young, Organometallics,
2003, 22, 4739; (c) R. Gao, M. Zhang, T. Liang, F. Wang and W.-H.
Sun, Organometallics, 2008, 27, 5641; (d) D. P. Gates, S. A. Svejda and
M. Brookhart, Macromolecules, 2000, 33, 2320.
18 G. B. Galland, R. F. de Souza, R. S. Mauler and F. F. Nunes,
Macromolecules, 1999, 32, 1620.
19 (a) R. Chen and S. F. Mapolie, J. Mol. Catal. A: Chem., 2003, 193, 33;
(b) B. K. Bahuleyan, B. R. Jermy, I. Y. Ahn, H. Suh, D.-W. Park, C. S.
Ha and I. Kim, Catal. Commun., 2009, 11, 252; (c) M. W. Wegner, A.
K. Ott and B. Rieger, Macromolecules, 2010, 43, 3624.
20 T. Usami and S. Takayama, Polym. J., 1984, 16, 731.
21 G. M. Sheldrick, SHELXTL-97, Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1617–1623 | 1623
©