N-(5,6,7-Trihydroquinolin-8-ylidene)arylaminonickel dichlorides as highly active single-site pro-catalysts in ethylene polymerization

Article abstract of DOI:10.1039/c1dt10541h

A series of N-(5,6,7-trihydroquinolin-8-ylidene)arylamine ligands was synthesized and fully characterized by NMR, IR spectroscopy and elemental analysis. Dimeric N-(5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides were prepared and examined by IR spectroscopy and elemental analysis, and the molecular structures of the representative nickel complexes were determined by the single crystal X-ray diffraction. On treatment with various alkylaluminiums, all the title complexes exhibited highly active, single-site active behavior for ethylene polymerization producing polyethylene (PE) waxes. The catalytic systems using the co-catalysts diethylaluminium chloride (Et₂AlCl) or methylaluminoxane (MAO) were investigated in detail, and the molecular weights and distributions of the PEs obtained were found to significantly rely on the nature of the different ligands present and reaction parameters such as the molar ratios of Al/Ni, reaction temperature and reaction time. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10541h

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PAPER
N-(5,6,7-Trihydroquinolin-8-ylidene)arylaminonickel dichlorides as highly
active single-site pro-catalysts in ethylene polymerization†
Jiangang Yu,a Yanning Zeng,a Wei Huang,a Xiang Haoa and Wen-Hua Sun*a,b
Received 31st March 2011, Accepted 8th June 2011
DOI: 10.1039/c1dt10541h
A series of N-(5,6,7-trihydroquinolin-8-ylidene)arylamine ligands was synthesized and fully
characterized by NMR, IR spectroscopy and elemental analysis. Dimeric N-(5,6,7-
trihydroquinolin-8-ylidene)arylaminonickel dichlorides were prepared and examined by IR
spectroscopy and elemental analysis, and the molecular structures of the representative nickel
complexes were determined by the single crystal X-ray diffraction. On treatment with various
alkylaluminiums, all the title complexes exhibited highly active, single-site active behavior for ethylene
polymerization producing polyethylene (PE) waxes. The catalytic systems using the co-catalysts
diethylaluminium chloride (Et2AlCl) or methylaluminoxane (MAO) were investigated in detail, and the
molecular weights and distributions of the PEs obtained were found to significantly rely on the nature
of the different ligands present and reaction parameters such as the molar ratios of Al/Ni, reaction
temperature and reaction time.
nickel pro-catalysts3d,5 bearing N,N-bidentate ligands including 2-
1. Introduction
iminopyridines have drawn more attention.13 However, it would
The discovery of diiminonickel dichlorides as highly active pro-
be critical that nickel pro-catalysts should have single-site active
catalysts in ethylene polymerization resurrected nickel research
species in order to produce polymers with a narrow molecular
weight dispersion. In exploring new ligands from the fused-
dous surge in publications of nickel pro-catalysts, which have
cycloalkanonylpyridines instead of 2-acetylpyridine, we have
reported the nickel pro-catalysts bearing N-(2-substituted-5,6,7-
olefins, which can be produced by ethylene oligomerization, and
trihydroquinolin-8-ylidene) arylamines, which showed good ac-
in ethylene reactivity.1 Subsequently, there has been a tremen-
recently been reviewed.2 There is industrial demand for both
tivities towards ethylene oligomerization.14 Using 5,6,7-trihydro-
quinolin-8-one as the starting material, a series of N-(5,6,7-
trihydroquinolin-8-ylidene)arylamines and their nickel complexes
were prepared. Surprisingly the newly synthesized nickel pro-
catalysts showed high activities for ethylene polymerization with-
out the observation of any oligomers. Moreover, the polyethylenes
obtained were confirmed as waxes with narrow molecular weight
distribution. Herein, the synthesis and characterization of N-
(5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides are
reported in detail, as well as their catalytic behavior in the
polymerization of ethylene.
polyethylenes, which can be produced by ethylene polymerization.
However the catalytic systems used to produce both olefins and
polyethylenes would be useless in this context due to the fact
that polyethylenes are produced as the by-product of ethylene
oligomerization and olefins are produced as the by-product of
ethylene polymerization. In fact, some amount of oligomers
have been commonly observed during ethylene polymerization
using nickel pro-catalysts,3 and ethylene oligomerization is often
reported due to b-hydrogen elimination in nickel-induced ethylene
reactivity.4 Driven by academic and commercial considerations,
different models of nickel pro-catalysts have been verified us-
ing ligands such as bidentate NŸN,3d,5 NŸP,6 NŸO,7 PŸO,4f,8
and tridentate NŸNŸN,9 NŸNŸO,3e,10 NŸPŸN.4g,11 Inspired by
cationic olefin polymerization employing active 14e-species,12 the
2. Results and discussion
2.1 Synthesis and characterization
aKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
The condensation reaction of 5,6,7-trihydroquinolin-8-one with
various anilines15 in toluene produces the corresponding N-(5,6,7-
trihydroquinolin-8-ylidene)arylamine derivatives in good yields
(Scheme 1). All organic compounds were characterized by FT-IR,
1H NMR and 13C NMR spectra as well as by elemental analyses.
bState Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou,
730000, China
† CCDC reference numbers 798841 and 798842 for crystallographic data
of complexes Ni1 and Ni3 respectively. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c1dt10541h
1
However, the H-NMR and FT-IR spectra for those products
revealed the presence of two isomers due to the enolization of the
8436 | Dalton Trans., 2011, 40, 8436–8443
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Table 1 Selected bond lengths and angles for Ni1·CH3OH and
Ni3·CH3OH
Ni1·CH3OH
Ni3·CH3OH
˚
Bond lengths (A)
Ni ◊ ◊ ◊ Ni
Ni–N1
Ni–N2
Ni–O
Ni–Cl1
Ni–Cl2
N1–C1
N1–C5
N2–C9
N2–C10
3.409
3.369
2.078(3)
2.108(3)
2.133(3)
2.3911(10)
2.4368(10)
1.328(4)
1.349(4)
1.284(4)
1.441(4)
2.062(3)
2.115(2)
2.128(2)
2.3940 (9)
2.4221(10)
1.327(4)
1.355(4)
1.278(4)
1.441(4)
Scheme 1 Synthetic procedure.
Bond angles (◦)
N1–Ni–N2
N1–Ni–O1
N2–Ni–O1
N1–Ni–Cl1
N2–Ni–Cl1
O1–Ni–Cl1
N1–Ni–Cl2
N2–Ni–Cl2
O1–Ni–Cl2
Cl1–Ni–Cl2
imine16 (Scheme 1). It was noteworthy that only the sp2-N (imine
isomer) can easily coordinate with nickel dichloride. Therefore
the stoichiometric reaction of the corresponding ligands with
NiCl2·6H2O was performed in ethanol, the FT-IR showed that
only N-(5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlo-
ride was obtained (Scheme 1). According to their IR spectra,
the C N stretching frequencies of nickel complexes appeared
at lower values (1580–1590 cm-1) with weaker intensity than those
of their free ligands, indicating the effective coordination between
the imino-nitrogen and the nickel atom. Meanwhile, there is no
signal around 3360 or 1570 cm-1 (nN–H) in the complexes indicating
the isomerization of L1¢–L5¢ into L1–L5 happened during the
coordination reaction with NiCl2. In addition, the unambiguous
structures of the complexes Ni1 and Ni3 in the solid state were
further confirmed by single-crystal X-ray diffraction studies.
78.54(9)
97.66(10)
91.46(9)
86.60(7)
96.12(8)
171.93(8)
96.25(7)
173.00(7)
84.57(7)
88.16(3)
78.60(10)
94.42(10)
90.06(10)
88.53(8)
98.08(7)
171.75(7)
96.57(7)
172.26(7)
84.26(7)
87.76(4)
˚
deviates by 0.418 A from the co-plane of the four atoms N1,
C8, C9 and N2 with two Ni–N bond lengths of Ni–N1 [2.079(3)
˚
˚
A] and Ni–N2 [2.109(3) A]. The pyridyl and iminophenyl planes
are nearly perpendicular with a dihedral angle of 88.83◦. The
˚
intra-molecular Ni ◊ ◊ ◊ Ni distance (3.409 A) is slightly shorter
than that (3.475 A) within their iminopyridylnickel dimer. The
17
˚
axial chloride Cl1 forms stronger bonding with the nickel center
2.2 Molecular structures
˚
[Ni–Cl1, 2.3910(10) A] than does the horizontal bridging chloride
Crystals of complexes Ni1·CH3OH and Ni3·CH3OH suitable for
single crystal X-ray analysis were grown by layering diethyl ether
on methanol solutions at room temperature. Both complexes
Ni1·CH3OH and Ni3·CH3OH crystallized as centrosymmetric
dimers and their molecular structures show distorted octahedral
geometry around each nickel center with the coordinative assis-
tance of a methanol solvent molecule. The molecular structures
of complexes Ni1·CH3OH and Ni3·CH3OH are shown in Fig. 1
and 2, and the selected bond lengths and angles are tabulated in
Table 1.
˚
Cl2 {Ni–Cl2 [2.4368(10) A]}. The phenomenon is similar to that
observed in the analogous iminopyridylnickel dimer, in which the
Ni–Cl bond lengths were 2.3366(8) A with the related terminal
chloride and 2.2729(9) A with the bridging chloride.
Compared with the intra-molecular Ni ◊ ◊ ◊ Ni (3.409 A) in Ni1,
the interaction observed in Ni3, with Ni ◊ ◊ ◊ Ni length 3.369 A, is
a little shorter (Fig. 2). The nickel atom is more planar with the
co-plane of N1, C8, C9 and N2 atoms with a deviated distance
of 0.156 A in Ni3, and a similar structural feature is observed
˚
17
˚
˚
˚
˚
˚
with Ni–N bond distances of Ni–N1 [2.062(3) A] and Ni–N2
˚
˚
[2.116(2) A], and Ni–Cl bond lengths of Ni–Cl1 [2.3934(9) A] and
˚
Ni–Cl2 [2.4221(10) A]. The differences are caused by the various
substituents on the iminophenyl group.
Fig. 1 ORTEP drawing of complex Ni1·CH3OH. Thermal ellipsoids are
shown at 30% probability. Hydrogen atoms have been omitted for clarity.
As shown in Fig. 1, there is a five-membered heteronickel-cycle
constructed by Ni, N1, C8, C9 and N2, in which the nickel atom
Fig. 2 ORTEP drawing of complex Ni3·CH3OH. Thermal ellipsoids are
shown at 30% probability. Hydrogen atoms have been omitted for clarity.
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Table 2 Selection of the suitable alkylaluminiums based on Ni3a
Tm ◦C
Branches/1000Ce
c
c
d
Entry
Cocat.
Al/Ni
Polymer g
Activityb
Mw kg mol-1
Mw/Mn
1
2
3
4
5
Et2AlCl
Et3Al2Cl3
AlEt3
MAO
MMAO
200
200
200
1000
1000
3.90
4.32
3.81
4.42
3.92
5.20
5.76
5.08
5.89
5.23
3.2
3.3
3.2
4.5
4.2
1.7
1.8
1.8
1.9
1.8
92.7
93.0
92.0
100.1
97.9
12.52
16.6
8.52
5. 54
11.8
a Reaction conditions: 1.5 mmol of Ni; 20 ◦C; 30 min; 10 atm of ethylene; 100 mL total volume of toluene. b 106 g(PE) mol(Ni)-1 h-1. c Determined by
GPC. d Determined by DSC. e Determined by FT-IR18
Table 3 Polymerization of ethylene in the presence of MAOa
T/◦C
Al/Ni
t/min
Polymer/g
Activityb
Mw kg mol-1
Mw/Mn
Tmd/◦C
Branches/1000Ce
c
c
Entry
Procat.
1
2
3
4
5
6
7
8
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni1
Ni2
Ni4
Ni5
20
20
20
20
20
20
40
60
80
20
20
20
20
20
20
20
20
20
20
1000
1500
2000
2250
2500
3000
2250
2250
2250
2250
2250
2250
2250
2250
2250
2250
2250
2250
2250
30
30
30
30
30
30
30
30
30
10
20
40
60
90
120
30
30
30
30
4.42
4.64
5.33
5.59
5.30
4.45
3.83
1.98
1.03
1.90
3.76
6.26
8.92
13.2
17.5
5.51
5.53
6.34
6.43
5.89
6.19
7.11
7.45
7.07
5.93
5.11
2.64
1.37
7.60
7.52
6.26
5.95
5.87
5.83
7.35
7.37
8.45
8.57
4.5
4.2
4.3
4.3
4.5
4.5
4.4
5.4
6.9
2.3
4.2
4.8
5.0
5.1
5.0
9.2
6.0
5.5
3.3
1.9
1.9
1.9
1.9
1.9
2.0
2.1
2.1
3.5
1.6
2.0
2.1
2.0
1.9
2.1
2.2
2.2
2.2
2.4
100.1
100.6
99.1
89.0
89.5
89.6
89.3
89.1
111.9
98.6
101.2
101.0
103.9
102.3
103.1
112.5
108.0
107.7
106.9
5. 54
4.18
5.87
6.70
6.13
5.79
2.11
8.45
11.2
2.50
4.47
12.0
10.7
12.7
12.3
9.82
5.12
1.36
0.81
9
10
11
12
13
14
15
16
17
18
19
a Reaction conditions: 1.5 mmol of Ni; 10 atm of ethylene; 100 mL total volume of toluene. b 106 g(PE)·mol(Ni)-1·h-1. c Determined by GPC. d Determined
by DSC. e Determined by FT-IR.18
2.3 Ethylene oligomerization
(2250) fixed, the influence of reaction temperature was investigated
(entries 4 and 7–9 in Table 3). Similar to the observations by other
iminopyridyl late-transition pro-catalysts,13 the catalytic activities
of Ni3/MAO sharply decreased as the temperature was elevated
from 20 ◦C to 80 ◦C. Therefore the active species are partly unstable
at higher temperature. Regarding the GPC curves of resultant PEs,
wider molecular distributions were observed at elevated reaction
temperature, and a clear bimodal feature of the GPC curves were
obtained for polyethylenes produced at 80 ◦C (shown in Fig. 3).
To understand the lifetime of the active species, trials of
Ni3/MAO were carried out over different reaction times (entries 4,
10–15 in Table 3) at 20 ◦C. In general, the catalytic activities slowly
decreased with prolonged reaction time, indicating a relatively long
lifetime of the active species. In addition, the Mw (2.3–5.1 kg mol-1)
and Mw/Mn (1.6–2.1) values of obtained for the PEs were slightly
increased on extending the reaction time, however, the narrow
molecular distributions indicated the single-site active species in
the catalytic system.
Ethylene polymerization catalyzed by these nickel complexes with
various co-catalysts has been systematically investigated. The type
of co-catalyst, the molar ratio of Al/Ni, temperature, reaction
time and the nature of the complexes have been shown to have a
large influence on the activities as well as the Mw and Mw/Mn of
the polyethylenes produced.
2.3.1 Selection of suitable co-catalysts. Several alkylalumini-
ums (Et2AlCl, Et3Al2Cl3, AlEt3, MAO, MMAO) were initially
used to activate complex Ni3 for ethylene reactivity at room
temperature (Table 2). Ni3/alkylaluminoxane (MAO) (entry 4 in
Table 2) exhibited higher activity and produced polyethylene with
higher molecular weight than did the Ni3 catalytic systems con-
taining other alkylaluminiums; the catalytic system using a smaller
molar ratio of common diethylaluminium chloride (Et2AlCl) also
showed good activity (entry 1 in Table 2). Therefore the co-
catalysts MAO or Et2AlCl were used in further investigations.
On the basis of the above results, all other pro-catalysts Ni1,
Ni2 and Ni4–Ni5 were examined for ethylene polymerization by
employing the optimum conditions found for Ni3 (entries 4, 16–
19 in Table 3). Accordingly the nickel pro-catalysts with bulky
substituent (R¢) showed higher catalytic activity (entries 4, 16
and 17 in Table 3). Such a phenomenon probably illustrates
the protection afforded to the active site by the sterically bulky
2.3.2 Ethylene polymerization in the presence of MAO. The
influence of the reaction parameters, including the molar ratio
of Al/Ni and reaction temperature, were investigated using
Ni3/MAO. Increasing the Al/Ni from 1000 to 3000 (entries 1–
6 in Table 3), the activities showed the best value with an optimum
ratio of 2250 (entry 4 in Table 3). With the molar ratio of Al/Ni
8438 | Dalton Trans., 2011, 40, 8436–8443
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indicating higher numbers of branches. Examining the data and
trends shown with Et2AlCl, the active species are rather stable and
retain single-site features on changing the reaction parameters of
temperature and time. The molecular weights of the resultant PEs
were slightly increased on elevating the reaction temperature and
prolonging the reaction time. Due to the slightly lower activity
observed at 10 min, the catalytic systems were assumed to exhibit
an initial time for starting the polymerization catalysis. Similarly,
the molecular weight distributions of the obtained PEs became
wider and bimodal feature for the PEs formed above 60 ◦C (Fig. 4).
Fig. 3 GPC traces of polyethylene produced by Ni3/MAO catalytic
system (entry 4, 7–9 in Table 3).
substituent (R¢).19 In addition, the para-methyl on the aryl groups
within Ni4 and Ni5 positively affected the catalytic activities
(entries 18 and 19 in Table 3), which was assumed to be due to the
better solubility of the methylated metal complexes.20
2.3.3 Ethylene polymerization in the presence of Et2AlCl.
Using the co-catalyst Et2AlCl instead of MAO, the pro-catalyst
Ni3 showed similar trends with regard to the reaction temperature,
time and Al/Ni molar ratio (entries 1–14 in Table 4). In general,
the molar ratio of Al/Ni could be reduced by using Et2AlCl. The
molecular weights of resultant PEs were reduced in the range of
Kg mol-1; however, the feature of narrow molecular distributions
remained. The best catalytic performance was observed with the
optimum condition of Al/Ni 500 at 20 ◦C (entry 3 in Table 4).
Notably, the increase of the Al/Ni molar ratio led to lower
molecular weight polymers (entries 1–5 in Table 4). Higher molar
ratios of Al/Ni enhanced chain transfer from nickel species to
aluminium and resulted in short-chain polymers,21 meanwhile the
melting points (Tm) of the polyethylene significantly decreased,
Fig. 4 GPC traces of polyethylene produced by Ni3/AlEt2Cl catalytic
system (entries 3, 6–8 in Table 4).
The nature of the ligands affected the catalytic activities of the
pro-catalysts (Nin)/Et2AlCl (n = 1–5) (entries 3, 15–18 in Table 4),
and showed the same tendency as for Nin/MAO. Again, the
nickel pro-catalysts (Ni4 and Ni5) bearing an additional para-
methyl substituent provided better catalytic activities, such as
Ni5/Et2AlCl reaching up to 1.24 ¥ 107 g(PE) mol(Ni)-1 h-1 (entry
18 in Table 4). The representative PE by Ni5/Et2AlCl (entry
18 in Table 4) was characterized by 13C NMR measurements,
Table 4 Ethylene polymerization in the presence of Et2AlCla
T/◦C
Al/Ni
t/min
Polymer/g
Activityb
Mwc/kg mol-1
Mw/Mn
Tmd/◦C
Branches/1000Ce
c
Entry
Procat.
1
2
3
4
5
6
7
8
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni3
Ni1
Ni2
Ni4
Ni5
20
20
20
20
20
40
60
80
20
20
20
20
20
20
20
20
20
20
200
400
500
600
800
500
500
500
500
500
500
500
500
500
500
500
500
500
30
30
30
30
30
30
30
30
10
20
40
60
90
120
20
20
20
20
3.90
3.91
4.12
4.01
3.80
3.88
2.85
2.53
1.30
2.70
5.90
8.12
11.9
14.2
2.73
3.90
8.70
9.30
5.20
5.21
5.49
5.35
5.07
5.17
3.80
3.37
5.20
5.40
5.90
5.41
5.29
4.73
3.64
5.20
11.6
12.4
3.2
3.2
3.0
2.8
1.8
2.8
3.4
8.4
2.9
3.1
3.2
3.2
4.7
5.4
2.3
3.9
3.2
3.4
1.7
1.9
2.0
1.8
1.9
1.8
2.4
4.3
1.7
1.7
1.9
1.9
2.0
1.9
1.8
2.1
1.9
2.0
92.7
74.1
71.4
71.6
71.6
71.4
82.1
96.2
71.4
73.4
74.6
74.6
84.7
91.2
80.1
87.5
82.1
84.2
12.52
25.8
36.8
32.7
28.0
31.7
31.9
31.1
35.1
35.4
31.9
30.5
9.82
10.6
18.4
9.81
13.1
22.1
9
10
11
12
13
14
15
16
17
18
a Reaction conditions: 1.5 mmol of Ni; 10 atm of ethylene; 100 mL total volume of toluene. b 106 g(PE)·mol(Ni)-1·h-1. c Determined by GPC. d Determined
by DSC. e Determined by FT-IR18
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and showed 39 branches/1000 carbons (Fig. 5) according to the
interpretation reported by Galland et al.22 The highly branched
PEs were obtained due to b- hydrogen migration, which happened
on the active nickel species.2b,23
The extensive research of further ligands derivatives is still on-
going in our group.
3. Conclusion
N-(5,6,7-Trihydroquinolin-8-ylidene)arylaminonickel(II)
com-
plexes were synthesized and fully characterized. Upon treatment
with either MAO or Et2AlCl, the nickel pro-catalysts worked
as single-site catalysts for ethylene polymerization, forming
polyethylene waxes with an activity of up to 107 g(PE)
mol(Ni)-1 h-1. The molecular weights and distributions of the
polyethylene waxes could be controlled by modifying the nature
of the different ligands and reaction conditions. The resultant
polyethylenes were shown to be highly branched polymers;
the b-hydrogen migration happened on the active species and,
moreover, chain transfers from nickel species to aluminium could
also take place.
4. Experimental
4.1 General considerations
Fig. 5 13C-NMR spectrum of polyethylene (entry 18 in Table 4).
All manipulations of air and/or moisture sensitive compounds
were carried out under a nitrogen atmosphere using stan-
dard Schlenk techniques. Toluene was refluxed over sodium–
benzophenone and distilled under nitrogen prior to use. Methy-
laluminoxane (MAO, 1.46 M solution in toluene) and modified
Compared with our previous work on N-(2-Cl (or Ph)-
5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides for
ethylene oligomerization,14 the title N-(5,6,7-trihydroquinolin-
8-ylidene)arylaminonickel pro-catalysts herein—for which there
is one substituent less in the ligands—showed higher activ-
ity in ethylene polymerization.24 Both chloro- and phenyl-
substituents generally have a significant difference due to their
size and electronic influence.14 The electronic and steric na-
tures of the substituents of the ligands changed the cat-
alytic behaviors of their metal pro-catalysts, either affecting
the microstructures of the polymers or producing oligomers
instead of polymers.4b,4g,20a,25 It has been reported that pro-
catalysts containing the electron-withdrawing substituents near
to metal centers led to ethylene oligomerization, e.g. nickel pro-
catalysts bearing the electron-withdrawing substituents on the
para-position of N-aryl groups produced polymers with higher
molecular weight and better activities, but pro-catalysts having
the electron-withdrawing substituents on the ortho-positions of
N-aryl groups resulted ethylene oligomerization.26 That may
be helpful in explaining why N-(2-Cl-5,6,7-trihydroquinolin-8-
ylidene)arylaminonickel pro-catalysts gave oligomers.14 In general,
the steric bulkiness of the ligands were commonly considered
a necessary feature for their nickel pro-catalysts to maintain
high activity and form highly-ordered polyethylene.1a,27 However,
there were examples of pro-catalysts containing bulky substituents
inducing ethylene oligomerization,18a,28 and our observations also
showed cases inconsistent with the effects associated with bulky
ligands,18a,28b,28d viz enhanced polymerization for the late-transition
metal pro-catalysts.6a Herein the current system not only gives an
additional example but also indicates that the significant feature of
fine-tuning the complex pro-catalyst fits the catalytic requirement
for sole polymerization of ethylene. In addition, the resultant
PEs are confirmed by their molecular weights, their formation
as waxes and their narrow molecular weight distributions; narrow
polydispersity waxes are material additives which are in demand.
˚
methylaluminoxane (MMAO, 1.93 M in heptane, 3A) were
purchased from Akzo Nobel Corp. Diethylaluminium chloride
(Et2AlCl, 0.79 M in toluene), triethylaluminium (AlEt3, 0.74 M in
toluene) and ethylaluminium sesquinochroride (Et3Al2Cl3, EASC,
0.87 M in toluene) was purchased from Acros Chemicals. High-
purity ethylene was purchased from Beijing Yansan Petrochemical
Co. and used as received. Other reagents were purchased from
Aldrich, Acros, or local suppliers. NMR spectra were recorded
on Bruker DMX 400 MHz instrument 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 microana-
lyzer. Molecular weights and molecular (Mw) weight distribution
(Mw/Mn) of polyethylenes were determined by a PL-GPC220 at
120 ◦C, with 1,2,4-trichlorobenzene as the solvent. DSC trace
and melting points of polyethylenes were obtained from the
second scanning run on Perkin–Elmer DSC-7 at a heating rate
of 10 ◦C min-1.
4.2 Syntheses and characterization
2,6-Dimethyl-N-(5,6,7-trihydroquinolin-8-ylidene)phenylamine
(L1) and N-(2,6-dimethylphenyl)-5,6-dihydroquinolin-8-amine
(L1¢).
A solution of 5,6,7-trihydroquinolin-8-one (0.59 g,
4 mmol), 2,6-dimethylaniline (0.50 g, 4.1 mmol), and a catalytic
amount of p-toluenesulfonic acid in toluene (50 mL) was refluxed
for 3.5 h. The solvent was evaporated at reduced pressure, then
the mixture was purified by column chromatography [alumina,
petroleum ether–ethyl acetate = 7 : 1 v/v] to get the desired
1
compound (yellow oil, L1 : L1¢ = 87 : 13, 0.66 g, 66% yield). H
NMR (400 MHz, CDCl3, TMS): d 8.72 (d, J = 4.0 Hz, 1H, L1-Py
H); 8.41 (d, J = 4.6 Hz, L1¢-Py H); 7.56 (d, J = 7.6 Hz, 1H, L1-Py
H); 7.43 (d, J = 7.4 Hz, L1¢-Py H), 7.29 (m, 1H, L1-Py H); 7.11
8440 | Dalton Trans., 2011, 40, 8436–8443
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The Royal Society of Chemistry 2011
©

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(m, L1¢-Py H); 7.02 (d, J = 7.5 Hz, 2H, L1-Ar H); 6.94 (m, L1¢-Ar
H); 6.90 (t, J = 7.5 Hz, 1H, L1-Ar H); 6.58 (s, L1¢-NH); 4.51
(t, L1¢-CH) 2.94 (t, J = 6.0 Hz, 2H, L1-CH2); 2.83 (t, L1¢-CH2);
2.35 (t, J = 6.2 Hz, 2H, L1-CH2); 2.27 (s, L1¢-2 ¥ CH3); 2.23 (t,
L1¢-CH2); 2.04 (s, 6H, L1-2 ¥ CH3); 1.93 (m, 2H, L1-CH2). 13C
NMR (100 MHz, CDCl3, TMS): d 164.6, 150.1, 149.0, 137.3,
137.1, 128.3, 125.3, 122.7, 122.1, 30.6, 29.6, 22.4, 18.4, 18.3.
FT-IR (KBr, cm-1): 3357 (nN–H), 3038, 2928, 2828, 1925, 1641
(nC N), 1569 (nN–H), 1476, 1435, 1279, 1195, 1099, 1041, 794, 796,
673. Anal. calcd for C17H18N2 (250): C, 81.56; H, 7.25; N, 11.19.
Found: C, 81.87; H, 7.30; N, 10.81
2.82 (t, L4¢-CH2); 2.36 (t, J = 6.1 Hz, 2H, L4-CH2); 2.29 (s, L4¢-
CH3); 2.27 (s, 3H, L4-CH3); 2.23 (s, 6H, L4¢-2 ¥ CH3); 2.20 (m,
L4¢-CH2); 2.01 (s, 6H, L4-2 ¥ CH3); 1.93 (m, 2H, L4-CH2). 13C
NMR (100 MHz, CDCl3): d 164.7, 150.1, 149.0, 146.8, 137.2,
137.0, 131.7, 128.9, 128.4, 125.1, 124.8, 30.5, 29.5, 22.4, 20.8, 18.3,
18.1. FT-IR (KBr, cm-1): 3368 (nN–H), 3001, 2916, 2841, 2728, 1942,
1902, 1861, 1636 (nC N), 1566 (nN–H), 1566, 1480, 1410, 1268, 1098,
1021, 846, 793, 668. Anal. calcd for C18H20N2 (264): C, 81.78; H,
7.63; N, 10.60. Found: C, 82.03; H, 7.42; N, 10.32.
2,6-Diethyl-4-ethyl-N -(5,6,7-trihydroquinolin-8-ylidene)phe-
nylamine (L5) and N-(2,6-diethyl-4-methylphenyl)-5,6-dihydro-
quinolin-8-amine (L5¢). Using the same procedure as for the
synthesis of L1, we got L5 and L5¢ (yellow oil, L5 : L5¢ = 89 : 11,
0.86 g, 74.1% yield). 1H NMR (400 MHz, CDCl3): d 8.72 (d, J =
4.4 Hz, 1H, L5-Py H); 8.41 (d, J = 4.3 Hz, L5¢-Py H); 7.56 (d, J =
7.4 Hz, 1H, L5-Py H); 7.43 (d, J = 7.2 Hz, L5¢-Py H); 7.30 (m, 1H,
L5-Py H); 7.10 (m, L5¢-Py H); 6.89 (s, 2H, L5-Ar H); 6.95 (s, L5¢-
Ar H); 6.52 (s, L5¢-NH); 4.49 (t, L5¢-CH2); 2.93 (t, J = 6.0 Hz, 2H,
L5-CH2); 2.81 (t, L5¢-CH2); 2.58 (m, L5¢-2 ¥ CH2); 2.40 (m, 4H,
L5-2 ¥ CH2); 2.33 (m, L5¢-CH3); 2.32(s, 3H, L5-CH3); 2.25 (m,
L5¢- CH2); 1.91 (m, 2H, L5-CH2); 1.13 (t, J = 7.5 Hz, 6H, L5-2 ¥
CH3). 13C NMR (100 MHz, CDCl3): d 164.7, 150.2, 149.0, 145.7,
137.3, 137.2, 137.0, 132.0, 131.0, 127.1, 126.3, 124.8, 30.7, 29.6,
24.7, 24.4, 22.3, 21.2, 14.0. FT-IR (KBr, cm-1): 3362 (nN–H), 2964,
2930, 2873, 2828, 1743, 1640 (nC N), 1571 (nN–H), 1531, 1426, 1326,
1293, 1270, 1195, 1098, 859, 193, 677. Anal. calcd for C20H24N2
(292): C, 82.15; H, 8.27; N, 9.58. Found: C, 82.32; H, 8.14; N, 9.46.
2,6-Diethyl-N -(5,6,7-trihydroquinolin-8-ylidene)phenylamine
(L2) and N-(2,6-diethylphenyl)-5,6-dihydroquinolin-8-amine (L2¢).
Using the same procedure as for the synthesis of L1, we got L2
and L2¢ (yellow oil, L2 : L2¢ = 86 : 14, 0.69 g, 62% yield). 1H NMR
(400 MHz, CDCl3): d 8.72 (d, J = 4.4 Hz, 1H, L2-Py H); 8.41 (d,
J = 4.5 Hz, L2¢-Py H); 7.56 (d, J = 7.4 Hz, 1H, L2-Py H); 7.43 (d,
J = 7.6 Hz, L2¢-Py H); 7.28 (m, 1H, L2-Py H); 7.14 (d, L2¢-Py H);
7.08 (d, J = 7.6 Hz, 2H, L2-Ar H); 7.00 (m, 1H, L2-Ar H and L2¢-
Ar H); 6.62 (s, L2¢-NH); 4.49 (t, L2¢-CH); 2.93 (t, J = 6.1 Hz, 2H,
L2-CH2); 2.81 (t, L2¢-CH2); 2.45 (t, J = 7.4 Hz, 2H, L2-CH2); 2.43
(m, L2¢-2 ¥ CH2); 2.35 (m, 4H, L2-2 ¥ CH2); 2.25 (m, L2¢-CH2);
1.91 (m, 2H, L2-CH2); 1.20 (t, L2¢-2 ¥ CH3); 1.14 (t, J = 7.5 Hz,
6H, L2-2 ¥ CH3). 13C NMR (100 MHz, CDCl3): d 164.4, 150.5,
149.9, 148.9, 137.0, 134.7, 131.0, 125.5, 124.9, 122.9.6, 30.8, 29.5,
24.4, 22.3, 13.9. FT-IR (KBr, cm-1): 3363 (nN–H),3034, 2963, 2932,
2870, 2831, 1940, 1639 (nC N), 1563 (nN–H), 1462, 1422, 1277, 1191,
1101, 819, 675. Anal. calcd for C17H18N2 (278): C, 81.97; H, 7.97;
N, 10.06. Found: C, 82.11; H, 7.60; N, 9.76.
Synthesis of nickel complexes
General procedure: A solution of NiCl2·6H2O (2 mmol) in ethanol
was added dropwise to the corresponding ligand (2 mmol) in
ethanol. The mixture was stirred at room temperature overnight,
then the precipitate was collected by filtration and washed with
diethyl ether (3 ¥ 5 mL), then dried under vacuum. All of the
complexes were prepared in high yield in this manner.
2,6-Bis(1-methylethyl)-N -(5,6,7-trihydroquinolin-8-ylidene)-
phenylamine (L3) and N-(2,6-diisopropylphenyl)-5,6-dihydro-
quinolin-8-amine (L3¢). Using the same procedure as for the
synthesis of L1, we got L3 and L3¢ (yellow oil, L3 : L3¢ = 85 : 15,
1
0.81 g, 66% yield). H NMR (400 MHz, CDCl3): d 8.73 (d, J =
4.1 Hz, 1H, L3-Py H); 8.39 (d, J = 4.3 Hz, L3¢-Py H); 7.57 (d, J =
7.7 Hz, 1H, L3-Py H); 7.41 (d, J = 7.8 Hz, L3¢-Py H); 7.30 (t, J =
4.5 Hz, 1H, L3-Py H); 7.20 (m, L3¢-Py H); 7.14 (d, J = 7.5 Hz, 2H,
L3-Ar H); 7.07 (t, J = 6.7 Hz, 1H, L3-Ar H); 7.00 (m, L3¢-Ar H);
6.55 (s, L3¢-NH); 4.48 (t, L3¢-CH); 3.23 (m, L3¢-CH2); 2.95 (t, J =
6.0 Hz, 2H, L3-CH2); 2.85 (m, 2H, L3-2 ¥ CH); 2.85 (m, L3¢-2 ¥
CH); 2.43 (t, J = 6.1 Hz, 2H, L3-CH2); 2.25 (m, L3¢-CH2); 1.93
(m, 2H, L3-CH2); 1.18 (m, L3¢-4 ¥ CH3); 1.15 (m, 12H, L3-4 ¥
CH3). 13C NMR (100 MHz, CDCl3): d 164.7, 148.9, 146.7, 137.5,
137.1, 136.2, 125.0, 123.5, 123.0, 122.9, 31.0, 21.6, 28.1, 23.6, 22.3.
FT-IR (KBr, cm-1): 3376 (nN–H),3047, 2960, 2866, 2829, 1929.3,
1864, 1640 (nC N), 1571 (nN–H),1571, 1476, 1426, 1329, 1254, 1194,
1104, 1050, 1016, 796, 771, 674. Anal. calcd for C21H26N2 (306):
C, 82.31; H, 8.55; N, 9.14. Found: C, 82.57; H, 8.23; N, 9.06.
2,6-Dimethyl-N -(5,6,7-trihydroquinolin-8-ylidene)phenylami-
nonickel(II) dichloride (Ni1). (Blue, 0.58 g, 76% yield): FT-IR
(KBr, disk, cm-1): 3067, 2949, 1624, 1583 (nC N), 1461, 1336, 1217,
1197, 1131, 1107, 789, 656. Anal. calcd for C17H18Cl2N2Ni (380):
C, 53.74; H, 4.78; N, 7.37. Found: C, 53.42; H, 4.42; N, 7.03.
2,6-Diethyl-N-(5,6,7-trihydroquinolin-8-ylidene)phenylamino-
nickel(II) dichloride (Ni2). (Blue, 0.64 g, 78% yield): FT-IR (KBr,
disk, cm-1): 3068, 2963, 2932, 2873, 1623, 1585 (nC N), 1487, 1334,
1287, 1217, 1192, 1131, 1046, 927, 859, 779, 661. Anal. calcd for
C19H22Cl2N2Ni (408): C, 55.93; H, 5.44; N, 6.87. Found: C, 55.61;
H, 5.15; N, 6.53.
2,6-Bis(1-methylethyl)-N -(5,6,7-trihydroquinolin-8-ylidene)-
phenylaminonickel(II) dichloride (Ni3). (Yellow, 0.71 g, 82%
yield): FT-IR (KBr, disk, cm-1): 3064, 2946, 2865, 2363, 1626,
1586 (nC N), 1459, 1330, 1217, 1136, 1050, 807, 779, 735, 661.
Anal. calcd for C21H26Cl2N2Ni (436): C, 57.84, H, 6.01; N, 6.42.
Found: C, 57.57; H, 5.64; N, 6.09.
2,4,6-Trimethyl-N -(5,6,7-trihydroquinolin-8-ylidene)phenyl-
amine (L4) and N-mesityl-5,6-dihydroquinolin-8-amine (L4¢). Us-
ing the same procedure as for the synthesis of L1, we got L4 and
1
L4¢ (yellow oil, L4 : L4¢ = 91 : 9, 0.86 g, 81.3% yield). H NMR
(400 MHz, CDCl3): d 8.72 (d, J = 4.1 Hz, 1H, L4-Py H); 8.41
(d, J = 4.6 Hz, L4¢-Py H); 7.56 (d, J = 7.7 Hz, 1H, L4-Py H);
7.43 (d, J = 7.4 Hz, L4¢-Py H); 7.10 (m, L4¢-Py H); 7.29 (m,
1H, L4-Py H); 6.92 (s, L4¢-Ar H); 6.85 (s, 2H, L4-Ar H); 6.48
(s, L4¢-NH); 4.50 (t, L4¢-CH2) 2.93 (t, J = 6.0 Hz, 2H, L4-CH2);
2,4,6-Trimethyl-N-(5,6,7-trihydroquinolin-8-ylidene)phenylami-
nonickel(II) dichloride (Ni4). (Yellow, 0.57 g, 72% yield): FT-IR
(KBr, disk, cm-1): 3055, 2920, 1626, 1585 (nC N), 1456, 1332, 1285,
1213, 1131, 924, 854, 789, 661. Anal. calcd for C18H20Cl2N2Ni
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Dalton Trans., 2011, 40, 8436–8443 | 8441
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(394): C, 54.88, H, 5.12; N, 7.11. Found: C, 55.09; H, 5.51; N,
7.27.
4.4 General procedure for ethylene polymerization
A 300 mL stainless steel autoclave, equipped with a mechanical
stirrer and a temperature controller, was employed for the reaction.
Firstly, 50 mL toluene (freshly distilled) was injected to the
autoclave which was filled with ethylene in advance. When the
temperature was stabilized at the required temperature, another
30 mL toluene (with the catalyst pre-dissolved in it), the required
amount of cocatalyst (MAO, MMAO, EASC, AlEt3, Et2AlCl)
and the residual toluene were successively added by syringe.
The reaction mixture was intensively stirred for the desired time
under the corresponding pressure of ethylene throughout the
entire experiment. The reaction was quenched by addition of
acidic ethanol. The precipitated polymer was washed with ethanol
several times and dried in vacuo.
2,6-Diethyl-4-methyl-N-(5,6,7-trihydroquinolin-8-ylidene)phe-
nylaminonickel(II) dichloride (Ni5). (Yellow, 0.63 g, 75% yield):
FT-IR (KBr, disk, cm-1): 3051, 2930, 2872, 1623, 1583 (nC N),
1460, 1336, 1287, 1212, 1130, 1045, 923, 859, 796, 663. Anal. calcd
for C20H24Cl2N2Ni (422): C, 56.92, H, 5.73; N, 6.64. Found: C,
56.53; H, 5.45; N, 6.25.
4.3 X-Ray crystallographic studies
Single crystals of Ni1·CH3OH, Ni3·CH3OH suitable for X-ray
diffraction analysis were obtained by layering diethyl ether on their
methanol solution at room temperature, and the single-crystal
X-ray diffraction studies for them were carried out on a Rigaku
Saturn724+ CCD diffractometer with graphite-monochromated
Acknowledgements
˚
Mo-Ka radiation (l = 0.71073 A) at 173(2) K. Cell parameters
This work is supported by MOST 863 program No.
2009AA033601.
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 SHELXTL-
97 package.29 Details of the X-ray structure determinations and
refinements are provided in Table 5.
Notes and references
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1995, 117, 6414; (b) M. D. Leatherman, S. A. Svejda, L. K. Johnson
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2009, 42, 1597.
Table 5 Crystal data and structure refinement for Ni1·CH3OH, and
Ni3·CH3OH
Ni1·CH3OH
Ni3·CH3OH
Empirical formula
Fw
C36H44Cl4N4Ni2O2
823.97
C44H60Cl4N4Ni2O2
936.18
´
3 (a) I. Albers, E. Alvarez, J. Ca´mpora, C. M. Maya, P. Palma, L. J.
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Bianchini and P. Braunstein, Organometallics, 2009, 28, 1776.
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Organometallics, 2001, 20, 2321; (b) H. Gao, W. Guo, F. Bao, G.
Gui, J. Zhang, F. Zhu and Q. Wu, Organometallics, 2004, 23, 6273;
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2009, 28, 4452; (f) H. Liu, W. Zhao, X. Hao, C. Redshaw, W. Huang
and W.-H. Sun, Organometallics, 2011, 30, 2418–2424; (g) F.-Z. Yang,
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46, 4321.
T/K
173(2)
173(2)
0.71073
˚
l/A
0.71073
Monoclinic
P21/n
11.372(2)
9.794(2)
16.445(3)
90
94.82(3)
90
1825.1(6)
2
1.496
1.363
856
0.21 ¥ 0.17 ¥ 0.13
2.75–27.48
-14 £ h £ 14
-12 £ k £ 12
-21 £ l £ 21
21761
Cryst. syst.
Monoclinic
P21/n
14.658(3)
10.414(2)
14.753(3)
90
95.14(3)
90
2243.0(8)
2
1.386
Space group
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V (A )
Z
Dcalcd (g cm-3)
m/mm-1
1.118
984
F(000)
Cryst. size/mm
q range (◦)
Limiting indices
0.28 ¥ 0.20 ¥ 0.10
2.79–27.50
-14 £ h £ 19
-12 £ k £ 13
-19 £ l £ 19
19512
5145 (0.0459)
99.7%
Numerical
5145/1/265
1.135
R1 = 0.0552
wR2 = 0.1121
R1 = 0.0615
wR2 = 0.1153
0.548 and -0.375
No. of rflns collected
No. unique rflns [R(int)] 4179 (0.0517)
Completeness to q (%)
Abs corr.
99.8%
Numerical
Data/restraints/params 4181/0/221
Goodness of fit on F2
1.166
Final R indices [I > 2s(I)] R1 = 0.0497
wR2 = 0.1091
R indices (all data)
R1 = 0.0521
wR2 = 0.1109
0.615 and -0.609
6 (a) W.-H. Sun, Z. Li, H. Hu, B. Wu, H. Yang, N. Zhu, X. Leng
and H. Wang, New J. Chem., 2002, 26, 1474; (b) Z. Guan and W. J.
Marshall, Organometallics, 2002, 21, 3580; (c) F. Speiser, P. Braunstein,
L. Saussine and R. Welter, Organometallics, 2004, 23, 2613; (d) F.
Largest diff peak and
hole/e A
-3
˚
8442 | Dalton Trans., 2011, 40, 8436–8443
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Speiser, P. Braunstein and L. Saussine, Organometallics, 2004, 23, 2625;
(e) Z. Weng, S. Teo and T. S. A. Hor, Organometallics, 2006, 25, 4878.
7 (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) T. Hu,
L.-M. Tang, X.-F. Li, Y.-S. Li and N.-H. Hu, Organometallics, 2005,
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