{Bis[N,N′-(2-alkyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane} dibromonickel complexes bearing chiral sec-phenethyl groups: Synthesis, characterization and their application in catalytic polymerization for ethylene and styrene

Article abstract of DOI:10.1016/j.jorganchem.2014.03.006

A series of new chiral and achiral nickel (II) complexes, {bis[N,N′-(2-methyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane} dibromonickel rac-(RR/SS)-3a, {bis[N,N′-(4-isopropyl-2-sec- phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RSRS)-3b, {bis[N,N′-(2-methyl-4,6-di(sec-phenethyl)phenyl)imino]-1,2-dimethylethane} dibromonickel rac-(RSRS)-3c, and {bis[N,N′-(2,6-diisopropyl-4-(p- methylphenyl)phenyl)imino]-1,2-dimethylethane}dibromonickel 3d, were synthesized and characterized. The molecular structures of the representative ligand rac-(RSRS)-2c, complex rac-(RR/SS)-3a, complex rac-(RSRS)-3b, and complex 3d were determined by X-ray crystallography. Complex 3e {bis[N,N′-(2,6- dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel was also synthesized for comparison. These complexes, activated by diethylaluminum chloride (DEAC) were tested in the polymerization of ethylene and styrene under mild conditions. Complex rac-(RSRS)-3c bearing one ortho-methyl group and two chiral bulky sec-phenethyl groups in the ortho- and para-aryl position of the ligand, activated by diethylaluminum chloride (DEAC) shows highly catalytic activity for the polymerization of ethylene [5.56 × 10⁶ g PE/(mol Ni h bar)] and produced branched polyethylene (75 methyl, 9 ethyl, 5 propyl and 19 butyl or longer branches/1000 C at 40 °C). Interestingly, complex rac-(RSRS)-3c also displays highly catalytic activity (3.62 × 10 ⁵ g polystyrene/(mol Ni h)) for styrene polymerization, and could produce syndiotactic-rich polystyrene (stereo-triad distributions: rr, 66.2%; mr, 18.8%; mm, 15.0%; stereo-diad distributions: r, 75.6%; m, 24.4% at 70 °C). The achiral catalyst 3d gave nearly atactic polystyrene (stereo-triad distributions: rr, 37.0%; mr, 32.7%; mm, 30.3%; stereo-diad distributions: r, 53.4%; m, 46.6% at 70 °C).

Full text of DOI:10.1016/j.jorganchem.2014.03.006

Accepted Manuscript
{Bis[N,N’-(2-alkyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel
complexes bearing chiral sec-phenethyl groups: synthesis, characterization and their
application in catalytic polymerization for ethylene and styrene
Jianchao Yuan, Yanqiong Mu, Jie Zhao, Weibing Xu, Jingjing Chen, Zhenghua Zhang
PII:
S0022-328X(14)00118-1
10.1016/j.jorganchem.2014.03.006
JOM 18509
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 4 January 2014
Revised Date: 2 March 2014
Accepted Date: 4 March 2014
Please cite this article as: J. Yuan, Y. Mu, J. Zhao, W. Xu, J. Chen, Z. Zhang, {Bis[N,N’-(2-alkyl-6-sec-
phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel complexes bearing chiral sec-phenethyl
groups: synthesis, characterization and their application in catalytic polymerization for ethylene and
styrene, Journal of Organometallic Chemistry (2014), doi: 10.1016/j.jorganchem.2014.03.006.
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ACCEPTED MANUSCRIPT
Graphical abstract: synopsis
A series of chiral and achiral nickel (II) complexes were synthesized. The molecular
structures of ligand 2c, complexes 3a, 3b, and 3d were determined by X-ray
crystallography. Chiral bulky complex 3c shows highly catalytic activity for the
polymerization of ethylene and styrene, and produced branched polyethylene and
syndiotactic-rich polystyrene.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
{Bis[N,N’-(2-alkyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel
complexes bearing chiral sec-phenethyl groups: synthesis, characterization and their application
in catalytic polymerization for ethylene and styrene
Jianchao Yuan*, Yanqiong Mu, Jie Zhao, Weibing Xu, Jingjing Chen, and Zhenghua Zhang
Key Laboratory of Eco-Environment-Related Polymer Materials of Ministry of Education; Key Laboratory of Polymer Materials
of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, China
ABSTRACT
A
series
of
new
chiral
and
achiral
nickel
(II)
complexes,
{bis[N,N’-(2-methyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel rac-(RR/SS)-3a,
{bis[N,N’-(4-isopropyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel
rac-(RSRS)-3b,
{bis[N,N’-(2-methyl-4,6-di(sec-phenethyl)phenyl)imino]-1,2-dimethylethane}dibromonickel
rac-(RSRS)-3c,
and
{bis[N,N’-(2,6-diisopropyl-4-(p-methylphenyl)phenyl)imino]-1,2-dimethylethane}dibromonickel 3d,
were synthesized and characterized. The molecular structures of the representative ligand
rac-(RSRS)-2c, complex rac-(RR/SS)-3a, complex rac-( RSRS)-3b, and complex 3d were determined
by
X-ray
crystallography.
Complex
3e
{bis[N,N’-(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel was also synthesized for
comparison. These complexes, activated by diethylaluminum chloride (DEAC) were tested in the
polymerization of ethylene and styrene under mild conditions. Complex rac-(RSRS)-3c bearing one
ortho-methyl group and two chiral bulky sec-phenethyl groups in the ortho- and para-aryl position of
the ligand, activated by diethylaluminum chloride (DEAC) shows highly catalytic activity for the
*
Corresponding author. Tel.: +86-931-7971539; fax: +86-931-7971261.
E-mail address: jianchaoyuan@nwnu.edu.cn (J. Yuan).
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polymerization of ethylene [5.56 × 106 g PE/(mol Ni.h.bar)] and produced branched polyethylene (75
methyl, 9 ethyl, 5 propyl and 19 butyl or longer branches/1000 C at 40°C). Interestingly, complex
rac-(RSRS)-3c also displays highly catalytic activity (3.62 × 105 g polystyrene/(mol Ni·h)) for styrene
polymerization, and could produce syndiotactic-rich polystyrene (stereo-triad distributions: rr, 66.2%;
mr, 18.8%; mm, 15.0%; stereo-diad distributions: r, 75.6%; m, 24.4% at 70 °C). The achiral catalyst 3d
gave nearly atactic polystyrene (stereo-triad distributions: rr, 37.0%; mr, 32.7%; mm, 30.3%;
stereo-diad distributions: r, 53.4%; m, 46.6% at 70 °C).
Key words: Chiral α-diimine ligand; nickel (II) complex; crystal structure; branched polyethylene;
syndiotactic polystyrene
1. Introduction
The development of well-defined Ni(II)/Pd(II) catalysts containing a bulky α-diimine ligand for the
polymerization of ethylene and α-olefins has been the subject of intense recent study [1–13]. In contrast
to metallocene catalysts based on early transition metals [14–17], Ni(II) and Pd(II) catalysts discovered
by Brookhart and coworkers could produce branched polyethylene with different concentration and
individual length of branches, exclusively from the ethylene monomer and accommodated even polar
monomers [1–13]. However, they generally produce amorphous, atactic polymers [11]. Recently,
Geoffrey W. Coates and co-workers proposed a new Brookhart type catalyst for olefin polymerization,
which bears a new class of chiral anilines and their incorporation in α-diimine Ni(II) catalysts that
exhibit stereoselectivity in α-olefins polymerization [18,19]. However, the effects of ortho and para
chiral substituents of the ligand on the catalytic behavior of α-diimine-Ni(II) complexes and the
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properties of the resulting polymers, especially on the stereoselectivity of the resulting polystyrenes has
never been studied.
Recently, we have reported the “Chain Walking Polymerization” of ethylene using chiral [10–22] or
achiral [23–25] α-diimine Ni(II) complexes. In this work, we first report the synthesis and
characterization of a series of new chiral nickel complexes of the type [NiBr2(Ar-DAB)] (Ar-DAB =
N,N’-diaryl-1,4-diaza-1,3-butadiene) bearing bulky chiral sec-phenethyl groups in different aryl
position of the ligand, in order to study the influence of chiral groups, steric effects and polymerization
temperature on the catalyst activity, microstructure of polyethylene and, in particular, on the
stereoregular structure of polystyrene.
2. Results and discussion
2.1. Synthesis and characterization of ligands 2a-e and complexes 3a-e
Scheme 1
The general synthetic route to four nickel (II) complexes 3a-e is shown in Scheme 1. Reaction of the
anilines with styrene at elevated temperature (160 ºC) in the presence of CF3SO3H catalyst resulted in
the corresponding sec-phenethylanilines rac-1a-1c (Scheme 1). Reaction of the aniline with iodine at
room temperature in the presence of NaHCO3 in H2O resulted in 4-iodo-2,6-diisopropylaniline. The
Suzuki coupling reaction of 4-iodo-2,6-diisopropylaniline and p-methylphenyboronic acid catalyzed by
Pd(OAc)2 in PEG-400 led to the desired amine 2,6-diisopropyl-4-(p-methyl)aniline 1d (Scheme 1). The
α-diimine ligands (2a-e) were finally obtained by acid catalyzed condensation of the amines and
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1
2,3-butanedione. The ligands (2a-c) were characterized by H-NMR and 13C-NMR and were found
elementally pure.
The reaction of equimolar amounts of NiBr2(DME) and the α-diimine ligand 2a-e in CH2Cl2 led to
the displacement of 1,2-dimethoxyethane and afforded the catalyst precursor 3a-e as a moderately
air-stable deep red microcrystalline solid in almost quantitative yields. Elemental analysis of ligand 2b,
complex 3a, complex 3c, and complex 3d fits the molecular structure obtained by the X-ray structural
studies (see below).
Figure 1
Figure 2
Figure 3
Figure 4
2.2. X-ray crystallographic studies
Single crystals of ligand rac-(RSRS)-2c, complex rac-(RR/SS)-3a, complex rac-(RSRS)-3b, and
complex 3d for X-ray diffraction were obtained at -30 ºC by double layering a CH2Cl2 solution of the
ligand and complexes with n-hexane.
The molecular structures of ligand rac-(RSRS)-2c, complex rac-(RR/SS)-3a, complex rac-(RSRS)-3b,
and complex 3d were determined, their corresponding diagrams are shown in Figures 1-4, and selected
bond distances and angles are summarized in Figures 1-4. The X-ray structure of representative chiral
ligand rac-(RSRS)-2c exhibits trans-conformation about the central C-C bond of the ligand backbone.
Bond lengths and angles are within the expected range for α-diimines; for example, the bond distances
for the C24=N1 double bond and the central C24–C24a single bond are 1.262 (5) and 1.478 (8), which
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are very close to the values for other structurally characterized free α-diimines [26]. Both C24 and
C11 possess essentially rather planar geometry (sp2 character), as shown by the C24–N1–C11 angles
122.1 (4)º, which is very close to 120º.
The structures of complexes rac-(RR/SS)-3a and 3d have pseudo-tetrahedral geometry about the
nickel center, showing a pseudo-C2 molecular symmetry for rac-(RR/SS)-3a, and a pseudo-C2v
molecular symmetry for 3d. The X-ray structures of ligands rac-(RR/SS)-2a and 2d (similar as
representative ligand rac-(RSRS)-2c) and their complexes rac-(RR/SS)-3a and 3d exhibit trans- and
cis-conformation about the central C–C bond of the backbone, respectively. In the solid state, the most
interesting feature of ligands rac-(RR/SS)-2a and 2d are the conformation of the substituents attached
to N1 and N1a (or N2). These groups are rotated about 180º from the position they must occupy to
chelate metal Ni. The rotation has been confirmed by the crystal structure of their complexes
rac-(RR/SS)-3a and 3d. Their imino C=N bonds have typical double bond character with C=N bond
lengths of 1.279 (3) and 1.279 (12) Å for rac-(RR/SS)-3a and 3d, respectively. Both aryl rings bonded
to the iminic nitrogens of the α-diimine lie nearly perpendicular to the plane formed by the nickel and
coordinated nitrogen atoms (torsion angles for rac-(RR/SS)-3a: C2–C1–N1–Ni1, 93.9 (3)º;
C6–C1–N1–Ni1, −84.1 (3)º; torsion angles for 3d: C2–C1–N1–Ni1, −76.9 (13)º; C6–C1–N1–Ni1, 99.5
(11)º). The chiral phenethyl, methyl or isopropyl groups in the 2,6-position of the aniline fragments in
rac-(RR/SS)-3a and 3d point toward each other above and below the plane, thus shielding the apical
positions of the Ni(II) center. The axial sites for the metal center are almost blocked by the
ortho-sec-phenethyl methyl or isopropyl substituents, which will play a critical role in maintaining high
activity and obtaining high-molecular-weight polymers at elevated temperatures. Their structures are
similar to those reported in the literature for other similar [NiBr2(α-diimine)] compounds characterized
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by X-ray diffraction, {bis[N,N’-4-bromo-2,6-dimethylphenyl]imino]acenaphthene}dibromonickel [27]
and {bis[N,N′-(2,4,6-trimethylphenyl)imino]acenaphthene}dibromonickel [28]. In fact, the Ni-N bond
distances in complexes rac-(RR/SS)-3a and 3d (Ni1–N1, 2.0090 Å for rac-(RR/SS)-3a; Ni1–N1, 2.012
Å for 3d) are similar to those determined for these compounds (2.026 and 2.021 Å, respectively), as
well as the Ni-Br bond distances (2.3569 Å for complex rac-(RR/SS)-3a, 2.329 Å for complex 3d vs.
2.3229 and 2.323 Å, respectively) and the N–Ni–Br angles (116.13º for complex rac-(RR/SS)-3a,
113.2º for complex 3d vs. 113.32 and 114.4°, respectively).
Interestingly, the structure of complex rac-(RSRS)-3b has pseudo-hexahedral geometry about each
nickel center, showing pseudo-C2v molecular symmetry. Complex rac-(RSRS)-3b contains two normal
α-diimine nickel complexes, its two nickel atoms are connected via two bromine bridges, and each
nickel atom is surrounded by a N,N’-(4-isopropyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane
ligand and three bromides, showing pseudo-hexahedral geometry about each nickel center. The
geometry of the five-coordinate complex can be described as two distorted hexahedron, with the plane
composed by the three atoms N1, N2 and Br1a (or N1a, N2a and Br1) as the basal plane and the Br1,
Br2 (or Br1a, Br2a) atoms occupying the apical positions.
2.3. Polymerization of ethylene with nickel complexes 3a-e
The five α-diimine nickel (II) complexes 3a-e, activated by DEAC, were tested as catalyst precursors
for the polymerization of ethylene, under the same reaction conditions. The results of the
polymerization experiments are shown in Table 1. Noteworthy is the fact that blank experiments
carried out with DEAC alone, under similar conditions, showed its inability to polymerize ethylene on
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its own.
Table 1
At 20 °C, the activity of complex rac-(RR/SS)-3a increases slightly with the increase of [Al]/[Ni]
ratio (runs 1-3), the maximum around [Al]/[Ni] ratio 600 (run 3), and then the activity decreases
slightly with the increase of [Al]/[Ni] ratio (runs 3-5). For a ratio [Al]/[Ni] 600, an increase in the
polymerization temperature in the range 0-60 °C decreases slightly the activity of the precatalyst
rac-(RR/SS)-3a (runs 6, 7, 3, 8 and 9). The performances of the nickel precatalysts are significantly
affected by the ortho- and para-position substituents on the aryl rings of the α-diimine Ni(II)
complexes (Table 1). Complex rac-(RSRS)-3c, bearing one ortho-methyl group and two bulky chiral
sec-phenethyl groups in the ortho- and para-aryl positions of the ligand, displays the highest catalytic
activity, 5.56 × 106 g PE/(mol Ni·h·bar), and produces one of higher molecular weights (run 15, Mw =
22.1 × 104 g/mol, 0 °C, [Al]/[Ni] = 600) among our five complexes. Complex 3d, bearing two
ortho-isopropyl groups and one bulky methylphenyl group in the para-aryl positions of the ligand, also
displays high catalytic activity (the highest activity: run 21, 3.53 × 106 g PE/(mol Ni·h·bar), Mw = 19.7
× 104 g/mol).
Complex rac-(RR/SS)-3a (bearing a ortho-position methyl group and one bulky chiral sec-phenethyl
group in the ortho-aryl positions of the ligand), exhibits slightly lower catalytic activity [the highest
activity: run 3, 2.91 × 106 g PE/(mol Ni·h·bar)] due to the absence of para-position bulky group.
Complex 3e (bearing two ortho-position methyl groups), shows the lowest catalytic activity [the
highest activity: run 26, 1.36 × 106 g PE/(mol Ni·h·bar)] among our five complexes due to the absence
of both ortho-position and para-position bulky groups.
Interesting, new chiral hexahedral bis[α-diimine Ni(II)] complex rac-(RSRS)-3b also exhibits high
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activity toward ethylene polymerization [run 10, the highest activity: 1.89 × 106 g PE/(mol Ni·h·bar);
Mw: 12.4 × 104 g/mol] under low ethylene pressure, which is comparable to that of catalyst precursor
3e under the same experimental conditions. These high activities may indicate that the active species
operating in the case of our precatalyst rac-(RSRS)-3b ([NiBr2(Ar-DAB)]2) is the same as that admitted
for the corresponding species [NiBr2(Ar-DAB)] [10]. The bis[α-diimine nickel(II)] used in the present
work may be involved in an equilibrium where two bromine bridges of [NiBr2(Ar-DAB)]2 dissociate,
giving rise to two complexes [NiBr2(Ar-DAB)] (Scheme 2). The [NiBr2(Ar-DAB)] precatalyst can then
follow the classical polymerization mechanism put forward by Brookhart and co-workers [10].
Scheme 2
These results indicate that the rate of chain propagation is greatly promoted by the bulky
ortho-sec-phenethyl groups of the ligand’s aryl rings and significantly affected by the bulky
para-sec-phenethyl groups of the ligand’s aryl rings [rac-(RR/SS)-3a]. As a result, the following
activity trend can be summarized for our substituted precatalysts under low ethylene pressure (0.2 bar),
in the range 0-60 °C: 3c>3d>3a>3b~3e.
Figure 5
Figure 6
The type and amount of branches formed in the polymerization of ethylene promoted by typical
α-diimine nickel precatalysts depend on reaction parameters such as the reaction temperature, ethylene
pressure and ligand structure [10]. Generally, low ethylene pressure and high polymerization
temperature favor the Chain-Walking, and afford high branched polyethylenes [10]. However, the
effect of ligand structure on polyethylene branching is much more complicated.
As shown in Table 1 and Figure 5, complex rac-(RSRS)-3c bearing one ortho-methyl group and two
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bulky chiral sec-phenethyl groups in the ortho- and para-aryl positions of the ligand, generated
polyethylene with the highest degrees of branching. The total branching degrees of the polymer
samples prepared with rac-(RSRS)-3c/DEAC (runs 16, 18 and 19, branching degree: 90.6, 110.0 and
126.7 branches/1000 C at 20, 40 and 60 °C, respectively) are significantly higher than those observed
for rac-(RR/SS)-3a/DEAC (runs 3, 8 and 9, branching degree: 83.5, 97.6 and 108.2 branches/1000 C at
20, 40 and 60 °C, respectively), rac-(RSRS)-3b/DEAC (runs 11, 13 and 14, branching degree: 71.8,
81.3 and 95.4 branches/1000 C at 20, 40 and 60 °C, respectively), 3d/DEAC (runs 21, 23 and 24,
branching degree: 82.3, 94.5 and 103.5 branches/1000 C at 20, 40 and 60 °C, respectively), and
3e/DEAC systems (runs 26, 28 and 29, branching degree: 69.7, 80.6 and 91.2 branches/1000 C at 20,
40 and 60 °C, respectively). Also the total branching degrees of the polymer samples prepared with
rac-(RSRS)-3c/DEAC are higher than those observed for similar precatalyst/DEAC systems such as
{bis[N,N’-(4-tert-butyl-diphenylsilyl-2,6-diisopropylphenyl)imino]acenaphthene}dibromonickel
(45
as
branches/1000
C,
at
20
°C)
[10]
or
precatalyst/MAO
systems
such
{bis[N,N’-(2,6-diisopropylphenyl)imino]-1,2-dimethylethane}dibromonickel (30, 67, 80 and 90
branches/1000
C,
at
25,
50,
65
and
80
°C,
respectively)
[10],
and
{bis[N,N’-(2,6-diisopropylphenyl)imino]acenaphthene}dibromonickel (65 branches/1000 C, at 25 °C)
[10], although the reaction conditions are not exactly the same as in the present work. The total
branching degree of the polymer sample obtained with 3e bearing two ortho-methyl groups is the
lowest among our five nickel complexes.
The 13C NMR spectrum of the polyethylene prepared with the catalyst rac-(RSRS)-3c/DEAC at
40 °C is shown in Figure 6. The number of branches was calculated according to the literature [30], and
it was found that the polyethylene with 107 branches/1000 carbons (73 methyl, 9 ethyl, 4 propyl and 21
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butyl or longer branches/1000 C) was obtained at 40 ºC (run 16 in Table 1). This result was consistent
with that calculated from 1H NMR.
2.4. Polymerization of styrene with nickel complexes 3a-d
Table 2
Polymerizations of styrene with complexes rac-(RR/SS)-3a, rac-(RSRS)-3b rac-(RSRS)-3c and 3d in
combination with DEAC were carried out at 30-90 °C, and the results are summarized in Table 2. For a
ratio [Al]/[Ni] 600, the activity of the complexes increases slightly with the increase of temperature
(30-70), the maximum around 70 °C, and then the activity decreases slightly with the increase of
temperature (70-90). The molecular weight decreases significantly with the increase of polymerization
temperature (70-90). The rate of chain propagation is significantly promoted by the bulky ortho and
para-sec-phenethyl of the ligand’s aryl rings (the highest activity: rac-(RR/SS)-3a run 3: 2.14 ×105 g
PSt/(mol Ni·h); rac-(RSRS)-3b run 7: 0.96 ×105 g PSt/(mol Ni·h); rac-(RSRS)-3c run 11: 3.62 ×105 g
PSt/(mol Ni·h); 3d run 16: 3.04 ×105 g PSt/(mol Ni·h)).
The aromatic ipso carbon spectra of the polystyrenes obtained with catalysts rac-(RSRS)-3c and
3d/DEAC were analyzed in term of triads (Table 2 and Figure 7). The three main peaks, at 144.7-145.4,
145.5-145.9 and 146.0-146.4 ppm, are assigned to syndiotactic (rr), heterotactic (mr) and isotactic
triads (mm), respectively [31–34]. As in Table 2, and Figure 7, chiral catalyst rac-(RSRS)-3c bearing
one ortho-methyl group and two bulky chiral sec-phenethyl groups in the ortho- and para-aryl
positions of the ligand, generated polystyrene with the highest degrees of stereoregularity. The
stereoregularity degrees of the polymer sample prepared with rac-(RSRS)-3c/DEAC (stereo-triad
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distributions run 11: rr, 66.2%; mr, 18.8%; mm, 15.0%; stereo-diad distributions: r, 75.6%; m, 24.4% at
70 °C) are significantly higher than those observed for rac-(RR/SS)-3a/DEAC (stereo-triad
distributions run 3: rr, 49.9%; mr, 25.3%; mm, 24.8%; stereo-diad distributions: r, 62.6%; m, 37.4% at
70 °C), rac-(RSRS)-3b/DEAC (stereo-triad distributions run 7: rr, 46.2%; mr, 26.8%; mm, 27.0%;
stereo-diad distributions: r, 59.6%; m, 40.4% at 70 °C), and 3d/DEAC (stereo-triad distributions run 15:
rr, 37.0%; mr, 32.7%; mm, 30.3%; stereo-diad distributions: r, 53.4%; m, 46.6% at 70 °C). The achiral
catalyst 3d gave nearly atactic polystyrene at 70 °C. An aryl ligand bearing chiral bulky sec-phenethyl
groups in the ortho and/or para-aryl position may better control the stereoselective of monomer
insertion, which should afford a highly syndiotactic polystyrene.
An decrease of the reaction temperature has a minor influence on the sequence distribution (Table 2:
runs 1 and 3, performed with rac-(RR/SS)-3a/DEAC at 30 and 70 °C, respectively) as a slight increase
of the syndiotactic content is observed (at 30 °C run 1, stereo-triad distributions: rr, 51.2%; mr, 24.6%;
mm, 24.2%; stereo-diad distributions: r, 63.5%; m, 36.5%).
Figure 7
3. Conclusions
A series of new α-diimine ligands containing sec-phenethyl or naphthyl groups and their Ni(II)
complexes have been prepared and characterized. Ligands 2a-e were modified in an attempt to change
chiral environment, steric effects and the electronic density of the metal center, eventually to improve
the activity in the polymerization of ethylene/styrene and control the microstructure of polyethylene, in
particular, the stereoregularity structure of polystyrene. The results obtained show that the chiral
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complex rac-(RSRS)-3c produces highly active catalyst system for the polymerization of ethylene and
highly branched polyethylene due to its bulky ortho and para-sec-phenethyl groups of the ligand’s aryl
rings. Interestingly, rac-(RSRS)-3c/DEAC catalyst system could produce high stereoregularity of
syndiotactic polystyrene at 70 °C due to its chiral bulky sec-phenethyl groups in the ortho- and
para-aryl position.
4. Experimental
4.1. General Considerations
All operations were carried out under N2 atmosphere using standard Schlenk techniques unless
otherwise noted. Methylene chloride and o-dichlorobenzene were predried with 4 Å molecular sieves
and distilled from CaH2 under dry nitrogen. Toluene, diethyl ether, and 1,2-dimethoxyethane (DME)
were distilled from sodium/benzophenone under N2 atmosphere. Anhydrous NiBr2 (99%),
4-methylphenylboronic acid (97%), trifluoromethanesulfonic acid (99 %), Pd(OAc)2 and
diethylaluminum chloride (DEAC, 0.9 M solution in toluene) were obtained from Acros.
2,3-Butanedione (98%), 2-methylaniline (98%), 4-isopropylaniline (98%), 2,6-diisopropylaniline (98%)
and styrene (98%) were purchased from Alfa Aesar, used without further purification. NiBr2(DME)
was synthesized according to the literature [35].
NMR spectra were recorded at 400 (1H) and 100 (13C) MHz, respectively, on a Varian Mercury
plus-400 instrument TMS as internal standard. FT-IR spectra were recorded on a Digilab Merlin FTS
3000 FTIR Spectrophotometer in KBr pellets. The molecular weights and molecular weight
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distributions (Mw/Mn)
of the polymers
were
determined by Gel
Permeation
Chromatography/Size-Exclusion Chromatography (GPC/SEC) via a Waters Alliance GPCV2000
chromatograph, using 1,2,4-trichlorobenzene as eluent, at a flow rate of 1.0 ml/min and operated at 140
°C. The elemental content of samples was determined by elemental analyzer (Vaiio-EL106, Germany).
The single-crystal structure was determined on a Bruker APEX-II CCD diffractometer with MoKα
radiation (λ = 0.71073 Å) a ω scan mode.
4.2. Synthesis of 2-methyl-6-sec-phenethylphenylaniline 1a
CF3SO3H (0.06 g, 0.40 mmol), 2-methylaniline (0.21 g, 2.00 mmol), styrene (0.31 g, 3.00 mmol) and
xylene (1 ml) were placed in a 10 ml Schlenk flask and allowed to stir at 160 °C for 5 h. Volatile
materials were removed and the residue was purified by chromatography on silica gel with petroleum
1
ether/ethyl acetate (v/v = 50:1) to give 2-methyl-6-sec-phenethylaniline (0.30 g, 71% yield). H NMR
(400 MHz, CDCl3): δ 7.21-7.39 (m, 6H, C6H5CHCH3 and aniline ring), 7.07 (d, J = 7.0 Hz, 1H, aniline
ring), 6.86 (d, J = 7.5 Hz, 1H, aniline ring), 4.18 (q, J = 7.0 Hz, 1H, C6H5CHCH3), 3.71 (br, s, 2H,
–NH2), 2.20 (s, 3H, –CH3 of aniline), 1.68 (d, J = 7.1 Hz, 3H, C6H5CHCH3). 13C NMR (100 MHz,
CDCl3): δ 145.56 (aniline carbon connected with NH2), 141.71 (phenethyl ring carbon connected with
ethyl), 129.40 (aniline carbon connected with methyl), 128.67 (phenyl carbon), 128.60 (aniline carbon),
127.41 (phenyl carbon), 126.29 (phenyl carbon), 125.14 (aniline carbon), 122.80 (aniline carbon),
118.30 (aniline carbon connected with phenethyl), 40.06 (C6H5CHCH3), 21.97 (C6H5CHCH3), 17.38
(–CH3 of aniline).
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4.3. Synthesis of 4-isopropyl-2-sec-phenethylaniline 1b
Using the same procedure as for the synthesis of 1a, 1b was obtained as light yellow oil (0.38 g, 79%
yield). 1H NMR (400 MHz, CDCl3): δ 7.17-7.32 (m, 6H, C6H5CHCH3 and aniline ring), 6.98 (d, J = 7.2
Hz, 1H, aniline ring), 6.60 (d, J = 7.4 Hz, 1H, aniline ring), 4.10 (q, J = 7.2 Hz, 1H, C6H5CHCH3), 3.23
(br, s, 2H, –NH2), 2.89 (m, 1H, –CH(CH3)2), 1.65 (d, J = 7.2 Hz, 3H, C6H5CHCH3), 1.28 (d, J = 6.9 Hz,
6H, –CH(CH3)2). 13C NMR (100 MHz, CDCl3): δ 146.08 (aniline carbon connected with NH2), 142.34
(phenethyl ring carbon connected with ethyl), 139.44 (aniline carbon connected with isopropyl), 130.04
(aniline carbon), 128.99 (phenyl carbon), 127.65 (phenyl carbon), 126.46 (phenyl carbon), 125.60
(aniline carbon), 124.93 (aniline carbon connected with phenethyl), 116.60 (aniline carbon), 40.69
(C6H5CHCH3), 33.72 (–CH(CH3)2 of aniline), 24.57 (–CH(CH3)2 of aniline), 22.09 (C6H5CHCH3).
4.4. Synthesis of 2-methyl-4,6-di-sec-phenethylphenylaniline 1c
CF3SO3H (0.06 g, 0.40 mmol), 2-methylaniline (0.21 g, 2.00 mmol), styrene (0.62 g, 6.00 mmol) and
xylene (1 ml) were placed in a 10 ml Schlenk flask and allowed to stir at 160 °C for 12 h. Volatile
materials were removed and the residue was purified by chromatography on silica gel with petroleum
1
ether/ethyl acetate (v/v = 50:1) to give 2-methyl-4,6-di-sec-phenethylaniline (0.46 g, 73% yield). H
NMR (400 MHz, CDCl3): δ 7.29-7.57 (m, 11H, C6H5CHCH3 and aniline ring), 7.11 (s, 1H, aniline
ring), 4.25-4.41 (m, 2H, C6H5CHCH3), 3.65 (br, s, 2H, –NH2), 2.29 (s, 3H, –CH3 of aniline), 1.78-1.96
(m, 6H, C6H5CHCH3). 13C NMR (100 MHz, CDCl3): δ 147.18 (para-phenethyl ring carbon connected
with ethyl), 145.61(ortho-phenethyl ring carbon connected with ethyl), 140.17 (aniline carbon
14

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connected with NH2), 135.63 (aniline para-carbon connected with methyl), 130.35 (aniline carbon
connected with methyl), 128.56 (para-phenethyl ring carbon), 128.12 (ortho-phenethyl ring carbon),
127.64 (aniline carbon), 127.39 (para-phenethyl ring carbon), 127.28 (ortho-phenethyl ring carbon),
126.15 (para-phenethyl ring carbon), 125.60 (ortho-phenethyl ring carbon), 124.29 (aniline carbon),
122.44 (aniline ortho-carbon connected with methyl), 44.13 (C6H5CHCH3), 40.38 (C6H5CHCH3),
22.20 (C6H5CHCH3), 21.95 (C6H5CHCH3), 17.74 (–CH3 of aniline).
4.5. Synthesis of 4-iodo-2,6-diisopropylaniline
NaHCO3 (0.43 g, 4.30 mmol), 2,6-diisopropylaniline (0.50 g, 2.82 mmol) and I2 (0.72 g, 2.84 mmol)
were placed in a 10 ml flask and allowed to stir for 24 h, in the presence of 2.56 g H2O. The mixture
was extracted three times with 15 ml diethyl ether. The combined organic phase was dried over MgSO4,
filtered, and the solvent was removed. The residue was purified by chromatography on silica gel with
1
petroleum ether/ethyl acetate (v/v = 10:1) to give 4-iodo-2,6-diisopropylaniline (0.51g, 60% yield). H
NMR (400 MHz, CDCl3): δ 7.15 (s, 2H, aniline ring), 3.57 (br, s, 2H, -NH2), 2.87-3.09 (m, 2H,
–CH(CH3)2), 1.24 (d, J = 7.1 Hz, 12H, –CH(CH3)2). 13C NMR (100 MHz, CDCl3): δ 138.45 (aniline
carbon connected with NH2), 135.21 (aniline carbon connected with isopropyl), 132.79 (aniline carbon
near I), 112.17 (aniline carbon connected with I), 28.25 (–CH(CH3)2), 21.91 (–CH(CH3)2).
4.6. Synthesis of 2,6-diisopropyl-4-(4-methyl)phenylaniline 1d
Pd(OAc)2 (0.01 g, 0.04 mmol), 2,6-diisopropylamine (0.91 g, 3.00 mmol), K2CO3 (0.55 g, 4.00
15

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mmol) and 4-methylphenyboronic acid (0.45 g, 3.31 mmol) were placed in a 50 ml flask and allowed to
stir at 25 °C for 24 h, in the presence of 10 ml PEG-400. The mixture was extracted three times with 15
ml diethyl ether. The combined organic phase was dried over MgSO4, filtered, and the solvent was
removed. The residue was purified by chromatography on silica gel with petroleum ether/ethyl acetate
(v/v = 20:1) to give 2,6-diisopropyl-4-(4-methyl)phenyaniline (0.42 g, 52% yield). 1H NMR (400 MHz,
CDCl3): δ 7.44 (d, J = 7.5 Hz, 2H, –C6H2H2CH3), 7.24 (s, 2H, aniline ring), 7.20 (d, J = 8.4 Hz, 2H,
–C6H2H2CH3), 3.70 (br, s, 1H, –NH2), 2.91-3.01 (m, 2H, –CH(CH3)2), 2.36 (s, 3H, –C6H4CH3), 1.31 (d,
J = 6.8 Hz, 12H, –CH(CH3)2). 13C NMR (100 MHz, CDCl3): δ 139.65 (aniline ring carbon connected
with NH2), 139.59 (methylphenyl ring carbon connected with CH3), 135.76 (methylphenyl ring carbon
connected with aniline), 132.83 (aniline ring carbon connected with isopropyl), 131.58 (aniline ring
carbon connected with methylphenyl), 129.37 (methylphenyl ring carbon), 126.67 (methylphenyl ring
carbon), 121.76 (aniline ring carbon), 28.20 (–CH(CH3)2), 22.61 (–CH(CH3)2), 21.13 (–C6H4CH3).
4.7. Synthesis of bis[N,N’-(2-methyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane 2a
4-Methylbenzenesulfonic acid (17 mg, 0.10 mmol) was added to a stirred solution of
2,3-butanedione (0.09 g, 1.00 mmol) and 2-methyl-6-sec-phenethylphenylaniline (0.44g, 2.10 mmol)
in toluene (20 ml). The mixture was refluxed for 16 h, and then the solvent was removed. The residue
was purified by chromatography on silica gel with petroleum ether/ethyl ester (v/v = 20:1) to give a
1
light yellow powder. Yield: 0.35 g (74 %). H NMR (400 MHz, CDCl3): δ 7.18-7.35 (m, 12H,
C6H5CHCH3 and aniline ring), 7.04 (d, J = 7.5 Hz, 2H, aniline ring), 6.67 (d, J = 7.0 Hz, 2H, aniline
ring), 4.11 (q, J = 7.0 Hz, 2H, C6H5CHCH3), 2.21 (s, 6H, –CH3 of aniline), 1.53 (d, J = 7.1 Hz, 6H,
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C6H5CHCH3), 1.19 (s, 6H, –N=C(CH3)C(CH3)=N–). 13C NMR (100 MHz, CDCl3): δ 168.65 (C=N),
148.02 (aniline carbon connected with N), 146.99 (phenylethyl ring carbon connected with ethyl),
133.05 (aniline carbon connected with phenylethyl), 128.97 (aniline carbon connected with methyl),
128.52 (phenylethyl ring carbon), 127.54 (phenylethyl ring carbon), 126.74 (aniline carbon), 125.67
(aniline carbon), 124.28 (aniline carbon), 123.26 (phenylethyl ring carbon), 40.93 (C6H5CHCH3), 22.87
(C6H5CHCH3), 17.98 (–CH3 of aniline), 15.55 (–N=C(CH3)C(CH3)=N–). Anal. Calc. for C34H36N2: C,
86.40; H, 7.68; N, 5.93. Found: C, 86.52; H, 7.54; N, 5.72.
4.8. Synthesis of bis[N,N'-(2-sec-phenethylphenyl-4-isopropyl)imino]-1,2-dimethylethane 2b
Using the same procedure as for the synthesis of 2a, 2b was obtained as light yellow powder (0.44 g,
83% yield). 1H NMR (400 MHz, CDCl3) δ 7.16-7.34 (m, 12H, C6H5CHCH3 and aniline ring), 7.04 (d, J
= 6.1 Hz, 2H, aniline ring), 6.92 (d, J = 7.1 Hz, 2H, aniline ring), 4.20 (q, J = 7.1 Hz, 2H, C6H5CHCH3),
3.89 (m, 2H, –CH(CH3)2), 1.70 (d, J = 7.2 Hz, 6H, C6H5CHCH3), 1.47 (d, J = 7.2 Hz, 12H,
–CH(CH3)2), 1.15 (s, 6H, –N=C(CH3)C(CH3)=N–). 13C NMR (100 MHz, CDCl3): δ 169.25 (C=N),
146.00 (aniline carbon connected with NH2), 144.82 (phenethyl ring carbon connected with ethyl),
143.41 (aniline carbon connected with isopropyl), 132.43 (aniline carbon connected with phenethyl),
128.38 (aniline carbon), 128.31 (phenyl carbon), 127.79 (phenyl carbon), 127.38 (phenyl carbon),
125.82 (aniline carbon), 123.25 (aniline carbon), 40.06 (C6H5CHCH3), 33.73 (–CH(CH3)2 of aniline),
24.23 (–CH(CH3)2 of aniline), 22.22 (C6H5CHCH3), 16.65 (–N=C(CH3)C(CH3)=N–). Anal. Calc. for
C38H44N2: C, 86.31; H, 8.39; N, 5.30. Found: C, 86.40; H, 8.21; N, 5.12.
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4.9. Synthesis of bis[N,N’-(2-(2-methyl-4,6-di-sec-phenethylphenyl)imino]-1,2-dimethylethane 2c
Using the same procedure as for the synthesis of 2a, 2c was obtained as yellow powder (0.52 g, 76%
yield). 1H NMR (400 MHz, CDCl3): δ 7.09-7.34 (m, 20H, C6H5CHCH3), 6.98 (s, 2H, aniline ring), 6.92
(s, 2H, aniline ring), 4.20 (q, J = 7.1 Hz, 2H, C6H5CHCH3), 3.87 (q, J = 7.1 Hz, 2H, C6H5CHCH3), 1.96
(s, 6H, –CH3 of aniline), 1.70 (d, J = 7.2 Hz, 6H, C6H5CHCH3), 1.47 (d, J = 7.2 Hz, 6H, C6H5CHCH3),
1.15 (s, 6H, –N=C(CH3)C(CH3)=N–). 13C NMR (100 MHz, CDCl3) δ 168.64 (C=N), 147.04
(phenylethyl ring carbon connected with ethyl), 146.88 (phenylethyl ring carbon connected with ethyl),
145.86 (aniline carbon connected with N), 140.77 (aniline carbon connected with phenylethyl), 132.64
(aniline carbon connected with phenylethyl), 128.34 (phenylethyl ring carbon), 128.24 (phenylethyl
ring carbon), 127.58 (phenylethyl ring carbon), 127.54 (phenylethyl ring carbon), 127.41 (aniline
carbon connected with methyl), 125.83 (aniline carbon near methyl), 125.60 (aniline carbon near
phenethyl), 123.94 (phenylethyl ring carbon), 123.70 (phenylethyl ring carbon), 44.42 (C6H5CHCH3),
40.85 (C6H5CHCH3), 22.65 (C6H5CHCH3), 22.00 (C6H5CHCH3), 18.01 (–CH3 of aniline), 15.57
(–N=C(CH3)C(CH3)=N–). Anal. Calc. for C50H52N2: C,88.19; H, 7.70; N, 4.11. Found: C, 88.23; H,
7.61; N, 4.35. Single crystals of ligand 2c suitable for X-ray analysis were obtained at -30 °C by
dissolving the ligand in CH2Cl2, following by slow layering of the resulting solution with n-hexane.
4.10. Synthesis of bis[N,N’-(2,6-diisopropyl-4-(4-methyl)phenylphenyl)imino]-1,2-dimethylethane 2d
Using the same procedure as for the synthesis of 2a, 2d was obtained as orange powder (0.49 g, 84%
1
yield). H NMR (400 MHz, CDCl3): δ 7.51 (m, 4H, –C6H2H2CH3), 7.36 (s, 4H, aniline ring), 7.25 (m,
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4H, –C6H2H2CH3), 2.74-2.76 (m, 4H, –CH(CH3)2), 2.40 (s, 6H, –C6H4CH3), 2.12 (s, 6H,
–N=C(CH3)C(CH3)=N–), 1.23 (m, 24H, –CH(CH3)2). 13C NMR (100 MHz, CDCl3): δ 168.51 (C=N),
145.52 (aniline ring carbon connected with NH2), 139.21 (methylphenyl ring carbon connected with
CH3), 136.67 (methylphenyl ring carbon connected with aniline), 136.48 (aniline ring carbon connected
with methylphenyl), 135.55 (aniline ring carbon connected with isopropyl), 129.50 (methylphenyl ring
carbon), 126.91 (methylphenyl ring carbon), 121.97 (aniline ring carbon), 28.81 (–CH(CH3)2), 23.19
(–CH(CH3)2), 22.86 (–CH(CH3)2), 21.21 (–C6H4CH3), 16.86 (–N=C(CH3)C(CH3)=N–). Anal. Calc. for
C42H52N2: C, 86.25; H, 8.96; N, 4.79. Found: C, 86.37; H, 8.76; N, 4.61.
4.11. Synthesis of bis[N,N’-(2,6-dimethylphenyl)imino]-1,2-dimethylethane 2e
Bis[N,N’-(2,6-dimethylphenyl)imino]-1,2-dimethylethane 2e was synthesized according to the
literature [36].
4.12.
Synthesis
of
{bis[N,N’-(2-methyl-6-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel 3a
[NiBr2(DME)] (0.31 g, 1.00 mmol), the ligand 2a (0.47 g, 1.00 mmol) and dichloromethane (30 ml)
were mixed in a Schlenk flask and stirred at room temperature for 16 h. The resulting suspension was
filtered. The solvent was removed under vacuum and the residue was washed with diethyl ether (3 × 16
ml), and then dried under vacuum at room temperature to give catalyst 3a as light brown micro-crystals.
Yield: 0.63 g (91%). Anal. Calc. for C34H36Br2NiN2: C, 59.08; H, 5.25; N, 4.05. Found: C, 58.86; H,
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5.37; N, 28. FT-IR (KBr): 1628 cm-1 (vC=N). Single crystals of complex 3a suitable for X-ray analysis
were obtained at -30 °C by dissolving the complex in CH2Cl2, following by slow layering of the
resulting solution with n-hexane.
4.13.
Synthesis
of
{bis[N,N’-(4-isopropyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel 3b
Using the same procedure as for the synthesis of 3a, 3b was obtained as brown micro-crystals. Yield:
0.69 g ( 92%). Anal. Calc. for C38H44Br2NiN2: C, 61.08; H, 5.93; N, 3.75. Found: C, 61.14; H, 5.76; N,
3.62. FT-IR (KBr): 1624 cm-1 (vC=N). Single crystals of complex 3b suitable for X-ray analysis were
obtained at -30 °C by dissolving the complex in CH2Cl2, following by slow layering of the resulting
solution with n-hexane.
4.14.
Synthesis
of
{bis[N,N’-(2-methyl-4,6-di-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel 3c
Using the same procedure as for the synthesis of 3a, 3c was obtained as brown micro-crystals. Yield:
0.79 g (88%). Anal. Calc. for C50H52Br2NiN2: C, 66.77; H, 5.83; N, 3.11. Found: C, 66.91; H, 5.69; N,
2.97. FT-IR (KBr): 1625 cm-1 (vC=N).
4.15.
Synthesis
of
{bis[N,N'-(2,6-diisopropyl-4-(4-methyl)phenylphenyl)imino]-1,2-dimethylethane}dibromonickel 3d
20

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Using the same procedure as for the synthesis of 3a, 3d was obtained as dark brown micro-crystals.
Yield: 0.69 g (86%). Anal. Calc. for C42H52Br2NiN2: C, 62.79; H, 6.52; N, 3.49. Found: C, 62.97; H,
6.38; N, 3.66. FT-IR (KBr): 1629 cm-1 (vC=N). Single crystals of complex 3d suitable for X-ray analysis
were obtained at -30 °C by dissolving the complex in CH2Cl2, following by slow layering of the
resulting solution with n-hexane.
4.16. Synthesis of {bis[N,N’-(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel 3e
{Bis[N,N’-(2,6-dimethylphenyl)imino]-1,2-dimethylethane}dibromonickel 3e was synthesized
according to the literature [36].
4.17. X-ray Structure Determinations
Single crystals of ligand 2c, complex 3a, complex 3b and complex 3d suitable for X-ray analysis
were obtained at -30 ºC by dissolving the ligand and nickel complexes in CH2Cl2, following by slow
layering of the resulting solution with n-hexane. Data collections were performed at 296(2) K on a
Bruker SMART APEX diffractometer with a CCD area detector, using graphite monochromated MoKα
radiation (λ= 0.71073 Å). The determination of crystal class and unit cell parameters was carried out by
the SMART program package. The raw frame data were processed using SAINT and SADABS to yield
the reflection data file. The structures were solved by using the SHELXTL program. Refinement was
performed on F2 anisotropically for all non-hydrogen atoms by the full-matrix least-squares method.
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The hydrogen atoms were placed at the calculated positions and were included in the structure
calculation without further refinement of the parameters. Crystal data, data collection, and refinement
parameters are listed in Table 3.
Table 3
4.18. Ethylene polymerization
The polymerization of ethylene was carried out in a flame dried 250 ml crown capped pressure bottle
sealed with neoprene septa. After drying the polymerization bottle under N2 atmosphere, 50 ml of dry
toluene was added to the polymerization bottle. The resulting solvent was then saturated with a
prescribed ethylene pressure. The co-catalyst (DEAC) was then added in Al/Ni or Al/Pd molar ratios in
the range of 200-1000 to the polymerization bottle via a syringe. At this time, the solutions were
thermostated to the desired temperature and allowed to equilibrate for 15 min. Subsequently, an
o-dichlorobenzene solution of Ni or Pd catalyst was added to the polymerization reactor. The
polymerization, conducted under a dynamic pressure of ethylene (0.2 bar), was terminated by
quenching the reaction mixtures with 100 ml of a 2% HCl-MeOH solution. The precipitated polymer
was filtered, washed with methanol and dried under vacuum at 60 ºC to a constant weight.
4.19. Polymerization of styrene
The homopolymerization of styrene was carried out in a flame dried 250 ml Schlenk flask under dry
nitrogen in toluene at 30-90 ºC. Dry toluene (25 ml) and dry styrene (5 ml) were added to the
22

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polymerization reactor, the co-catalyst (DEAC) was then added in Al/Ni molar ratios 600 to the
polymerization bottle via a syringe. Subsequently, an o-dichlorobenzene solution of Ni catalyst was
added to the polymerization reactor. After a given reaction time, the polymerization mixture was
terminated by quenching the reaction mixtures with 100 ml of a 2% HCl-MeOH solution. The
precipitated polymer was filtered, washed with methanol and dried under vacuum at 50 ºC to a constant
weight.
Acknowledgements
We thank the National Natural Science Foundation of China (NSFC 21364011 and 20964003), the
Scientific Research Foundation for the Returned Overseas Chinese Scholars of State Education
Ministry (2009-1341) and the Science and Technology Activities Merit-based Foundation for the
Returned Overseas Chinese Scholars of State Human Resources and Social Security Ministry
(2009-416) for funding. We also thank Key Laboratory of Eco-Environment-Related Polymer
Materials of State Education Ministry, Key Laboratory of Polymer Materials of Gansu Province
(Northwest Normal University), for financial support.
Appendix A. Supplementary material
CCDC 979396, 979404, 979419 and 979406 contain the supplementary crystallographic data for
ligand 2c and complexes 3a, 3b, 3d. The data can be obtained free of charge via
http://www.ccdc.cam.ac.uk, or from the Cambridge Crystallographic Data Centre, 12 Union Road,
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Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Tables
Table 1 Ethylene polymerizations using nickel precatalysts 3a-e activated by DEAC.
Table 2 Polymerization results for styrene using 3a-d/DEACa catalytic systems.
Table 3 Crystal data and structure refinements of ligand 2c, complex 3a, complex 3b and complex 3d.