Methylene-bridged bimetallic α-diimino nickel(ii) complexes: Synthesis and high efficiency in ethylene polymerization

Article abstract of DOI:10.1039/c3dt00023k

A series of 1,2-bis(arylimino)acenaphthylidenes (L1-L5) and their corresponding 4,4′-methylenebis(1-(2,6-diisopropylphenylimino)-2- (arylimino)acenaphthylene) derivatives (L6-L10) were synthesized and used to form mono-nuclear nickel bromides LnNiBr₂ (n = 1-5, Ni1-Ni5) and bi-nuclear nickel halides LnNi₂X₄ (n = 6-10: X = Br, Ni2-1-Ni2-5; n = 4, X = Cl, Ni2-6). All the organic compounds were fully characterized by FT-IR spectra, NMR measurements and elemental analysis. The nickel complexes were characterized by FT-IR spectra and elemental analysis and the molecular structures of the representative complexes Ni1, Ni2-1 and Ni2-3 were confirmed by single-crystal X-ray diffraction. Upon activation with either Et₂AlCl or MAO, all the nickel complex pre-catalysts exhibited high activity toward ethylene polymerization over the temperature range from ambient to 50 °C. In general, the bi-nuclear complexes showed a positive synergetic effect with higher activity than their mono nuclear analogs. The resultant polyethylene possessed higher molecular weight and a high degree of branching.

Full text of DOI:10.1039/c3dt00023k

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Methylene-bridged bimetallic α-diimino nickel(II)
complexes: synthesis and high efficiency in ethylene
Cite this: DOI: 10.1039/c3dt00023k
polymerization†
Shaoliang Kong,a,b Kuifeng Song,b Tongling Liang,b Cun-Yue Guo,*a Wen-Hua Sun*b
and Carl Redshaw*c
A series of 1,2-bis(arylimino)acenaphthylidenes (L1–L5) and their corresponding 4,4’-methylenebis-
(1-(2,6-diisopropylphenylimino)-2-(arylimino)acenaphthylene) derivatives (L6–L10) were synthesized and
used to form mono-nuclear nickel bromides LnNiBr2 (n = 1–5, Ni1–Ni5) and bi-nuclear nickel halides
LnNi2X4 (n = 6–10: X = Br, Ni2-1–Ni2-5; n = 4, X = Cl, Ni2-6). All the organic compounds were fully charac-
terized by FT-IR spectra, NMR measurements and elemental analysis. The nickel complexes were charac-
terized by FT-IR spectra and elemental analysis and the molecular structures of the representative
complexes Ni1, Ni2-1 and Ni2-3 were confirmed by single-crystal X-ray diffraction. Upon activation with
either Et2AlCl or MAO, all the nickel complex pre-catalysts exhibited high activity toward ethylene
polymerization over the temperature range from ambient to 50 °C. In general, the bi-nuclear complexes
showed a positive synergetic effect with higher activity than their mono nuclear analogs. The resultant
polyethylene possessed higher molecular weight and a high degree of branching.
Received 3rd January 2013,
Accepted 12th February 2013
DOI: 10.1039/c3dt00023k
www.rsc.org/dalton
methylene-bridged bis(iminopyridyl) di-nickel(II) complexes (A,
Introduction
Scheme 1) derived from 2-iminopyridylnickel complexes14 and
α-Diimino nickel type complex pre-catalysts have drawn much investigated their catalytic activity.10 Additionally, bi-nuclear
attention with respect to ethylene reactivity since their initial nickel complexes bearing 2-methyl-2,4-bis-(6-iminopyridin-2-yl)-
publication in 1995.1 With the intention of enhancing their cata- 1H-1,5-benzodiazepine ligands (B, Scheme 1) were designed and
lytic properties, different substituents have been used to modify used for ethylene oligomerization and polymerization.11 2,3,5,6-
such complex pre-catalysts.2 Moreover, various nickel complexes Tetramethylbenzene linked bis(iminopyridyl) bi-metallic nickel
bearing a variety of bi-dentate N^N3 and tri-dentate N^N^N4 complexes (C, Scheme 1) were also reported to be capable of
ligand sets have been designed with subsequent ethylene reac- ethylene polymerization and oligomerization.12 All these bi-met-
tivity studies in mind. The progress has been reviewed in a allic nickel pre-catalysts commonly produced both mixtures of
number of articles,5 which also indicate that there is ongoing oligomers and polyethylenes,10–13 however, they are also impor-
research into tandem or bi-metallic catalytic systems.6 In the tant sources of solely oligomeric products.
case of reported bi-nuclear nickel complex pre-catalysts,6–13
Recently, 1,2-bis(arylimino)acenaphthylidene nickel complex
ligands of bridged coordination models have been favorably pre-catalysts have been extensively explored and shown to solely
considered.7,13 In our previous work, we have synthesized polymerize ethylene.15 With this in mind, bridged bi-nuclear
nickel pre-catalysts based on such models would be worthy of
revisiting. In the literature, methylene-bridged α-diimino bi-met-
aSchool of Chemistry and Chemical Engineering, University of Chinese Academy of
allic nickel pre-catalysts (D, Scheme 1)13 were reported to be
Sciences, Beijing 100049, China. E-mail: cyguo@ucas.ac.cn; Fax: +86 10 88256092;
highly active in ethylene polymerization. In addition, the use of
Tel: +86 10 88256827
bKey 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: +8610 6261 8239;
Tel: +86 10 6255 7955
bulky anilines enhanced the catalytic performance, particularly
the use of i-Pr substituents. Given this, 4,4′-methylenebis(2,6-di-
isopropylaniline) was chosen to target methylene-bridged 1,2-bis
(arylimino)acenaphthylidenes and the nickel complexes
(E, Scheme 1) thereof. For comparison, the catalytic performance
of the 1-arylimino-2-(2,6-diisopropylphenylimino)acenaphthyle-
nylidene-nickel complexes (F, Scheme 1) is also reported.
cDepartment of Chemistry, University of Hull, Hull, HU6 7RX, UK.
E-mail: c.redshaw@hull.ac.uk; Fax: +44 (0) 1482 466410; Tel: +44 (0) 1482 465219
†CCDC 917315, 917316 and 917317 for Ni1, Ni2-1 and Ni2-3. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3dt00023k
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Scheme 1 Examples of bi-nuclear nickel complexes and model complexes in the current work.
Herein, the target bi-metallic and mono-nuclear nickel characterized by FT-IR spectroscopy and elemental analysis
complexes (E and F, Scheme 1) were synthesized and fully and the structures of the nickel complexes Ni1, Ni2-1 and Ni2-
characterized. All the nickel complex pre-catalysts revealed 3 were confirmed by single-crystal X-ray diffraction analysis.
high activity in ethylene polymerization in the presence of
either Et2AlCl or MAO. All the bi-metallic nickel pre-catalysts
exhibited a positive synergic activity compared to their corres-
ponding mono-nuclear analogs. The bi-metallic nickel catalytic
systems had higher activity for polyethylene and the obtained
polyethylene possessed higher molecular weight but with a
slightly broader molecular weight polydispersity.
X-Ray crystallographic studies
Single crystals of Ni1 were obtained by the slow diffusion of
diethyl ether into a saturated solution of dichloromethane,
whilst single crystals of Ni2-1 and Ni2-3 were obtained by the
slow diffusion of diethyl ether into a saturated mixture solu-
tion of dichloromethane and toluene at ambient temperature.
The solid-state structures of Ni1, Ni2-1 and Ni2-3 are shown in
Fig. 1–3 and selected bond lengths and bond angles are
provided in Table 1. The molecular structures indicate the
adoption of a distorted trigonal bipyramidal coordination at
Results and discussion
Synthesis and characterization of 1-arylimino-2-(2,6-
the nickel, consistent with the structures of the classical
diisopropylphenylimino)acenaphthylenylidene (L1–L5), the
α-diimine nickel pre-catalysts.15 There are also free toluene
methyl-bridged 1-arylimino-2-(2,6-diisopropylphenylimino)-
acenaphthylenylidene (L6–L10) and their corresponding nickel
complexes (Ni1–Ni5 and Ni2-1–Ni2-5)
molecules incorporated in the nickel complexes, however,
these toluene molecules are somewhat disordered in the
single crystals of Ni2-1 and Ni2-3. Therefore, the Platon
The 1-arylimino-2-(2,6-diisopropylphenylimino)acenaphthyl- Squeeze procedure was used to kill the free toluene molecules
enylidenes (L1, L2, L4, and L5) were synthesized by the reaction when refining Ni2-1 and Ni2-3.
of 1-(2,6-diisopropylphenylimino)acenaphthylen-2-one with
The crystal structure of the nickel complex Ni1 is shown in
various anilines (Scheme 2) according to the synthetic pro- Fig. 1. The atoms N1, N2 and Ni form a basal plane, with the
cedure for 1,2-bis(2,6-diisopropylphenylimino)acenaphthyl- apical positions occupied by the Br1 and Br2 atoms with the
enylidene (L3),1 following which the reaction of 1-arylimino-2- Br1 atom placed 1.963 Å above the basal plane. The N1–C1
(2,6-diisopropylphenylimino)acenaphthylenylidenes with nickel and N2–C12 CvN bonds are of equal length at 1.286(5) Å and
bromide formed the corresponding nickel complexes (Ni1–Ni5). the Ni–N bond lengths of 2.026(3) Å (Ni–N1) and 2.036(3) Å
The nickel complex Ni3 has been previously reported.1,16 The (Ni–N2) are similar. The planes of the two arenes linked to the
reaction of acenaphthylene-1,2-dione with 4,4′-methylenebis imine-N atoms are nearly perpendicular with respect to the
(2,6-diisopropylaniline) formed a methylene-bridged 1-(2,6-dii- plane of the acenaphthylene with an angle of 80.90° for the
sopropylphenylimino)acenaphthylen-2-one, which was further arene at N1 and 89.39° for the arene at N2. These geometrical
reacted with various anilines to form the methylene-bridged parameters reflect the different steric demands of the two aryl
bis(α-diimino)compounds (L6–L10) (Scheme 2). These methyl- groups linked to the coordinating N atom and reveal that the
ene-bridged bis(α-diimino)compounds (L6–L10) were reacted bulkier ortho substituent resulted in a larger dihedral angle, as
with nickel halide to form the corresponding bi-nuclear nickel reflected in previous work.15
complexes Ni2-1–Ni2-6, as shown in Scheme 2.
In the solid state of both of the bi-metallic nickel complexes
It was necessary to add a slight excess (2.2 equivalents) of Ni2-1 and Ni2-3, the nickel centres possess similar coordi-
nickel halide to the methylene-bridged bis(α-diimino)com- nation geometries to complex Ni1. Indeed, the corresponding
pounds (L6–L10) in order to achieve a higher yield of the bi- bond lengths and angles, as shown in Table 1, for each struc-
nuclear nickel complexes (Ni2-1–Ni2-6). All the complexes were ture are very similar. Fig. 2 depicts the bi-metallic nickel
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Scheme 2 Synthetic procedure for the organic compounds and nickel complexes.
Fig. 1 ORTEP drawing of Ni1. Thermal ellipsoids are shown at a 30% prob-
ability level. Hydrogen atoms have been omitted for clarity.
Fig. 2 ORTEP drawing of Ni2-1. Thermal ellipsoids are shown at a 30% prob-
ability level. Hydrogen atoms have been omitted for clarity and one toluene
molecule has been killed by the Platon Squeeze procedure.
complex Ni2-1 and it can be seen that both nickel centres
‘point’ in the same direction with respect to the ligand frame-
work and that the framework adopts a pinched structure with
an angle at C4–C13–C14 of 109.7(9)°.
In the molecular structure of the bi-metallic complex Ni2-3 planes linked to the imine-N with the corresponding ace-
(Fig. 3), the two nickel atoms are coordinated to the methyl- naphthylene plane are almost perpendicular at 87.37° for the
ene-bridged framework in more of a trans-like form with the arenes at N1 and 88.65° for the arenes at N2, respectively.
angle at C4–C13–C14 = 108.0(6)°, i.e. rotation about the However, these dihedral angles within Ni2-1 have different
methylene-bridge has occurred. Generally though, the coordi- angles of 86.03° and 89.86° due to the unsymmetrical substitu-
nation geometry at each nickel is similar and related to that ents, each derived from 2,6-dimethylaniline and 2,6-diisopro-
observed in Ni2-1 and the mono-nuclear nickel complex Ni1. pylaniline. The use of these frameworks results in significant
In the framework derived solely from the aniline bearing bis differences due to the folding of the two different ligands
(ortho-isopropyl)substituents, the dihedral angles of the arene within Ni2-1 and Ni2-3.
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Ethylene polymerization
pre-catalyst Ni2-4 under 10 atm of ethylene (Table 2) and in
general, good activities with co-catalysts such as methylalumi-
noxane (MAO), modified methylaluminoxane (MMAO), diethy-
This primary focus of this work was to investigate for the pres-
ence of synergetic effects during the catalysis conducted by the
bi-metallic complexes. Thus with this in mind, the catalytic be-
havior of complexes Ni2-1–Ni2-6 have been explored. To ascer-
tain the optimum catalytic conditions, various alkylaluminium
reagents have been screened in conjunction with the nickel
laluminium
chloride
(Et2AlCl)
and
ethylaluminium
sesquichloride (EASC) were observed, whereas low activity was
found when employing triethylaluminium (TEA). Further
investigations using either MAO or Et2AlCl (entries 1 and 3 in
Table 2) as a co-catalyst were conducted.
Ethylene polymerization employing the co-catalyst Et2AlCl
The catalytic system Ni2-4/Et2AlCl was investigated by varying
the Al : Ni ratio from 400 to 700 (entries 1–4 in Table 3) at
room temperature, which indicated that the optimum Al : Ni
ratio was 500 : 1, achieving an activity of 5.60 × 106 g PE
(mol Ni)−1 h−1 (entry 2 in Table 3). The resultant polyethylene
Table 2 Ethylene polymerization by pre-catalyst Ni2-4 with various co-catalysts
Mwc/105
Activitya
Tmb/°C
g mol−1
Mw/Mn
c
Entry
Co-cat.
PE/g
1
2
3
4
5
MAO
2.85
1.20
4.12
2.26
Trace
3.80
1.60
5.49
3.01
—
129.9
130.9
126.9
125.0
—
3.15
2.54
3.50
3.19
—
2.50
2.19
2.50
2.57
—
MMAO
Et2AlCl
EASC
TEA
Fig. 3 ORTEP drawing of Ni2-3. Thermal ellipsoids are shown at a 30% prob-
ability level. Hydrogen atoms have been omitted for clarity and two free toluene
molecules has been killed by the Platon Squeeze procedure.
Conditions: 1.5 μmol of [Ni]; Al/[Ni] = 600; 30 min; 20 °C; 10 atm of
ethylene; total volume 100 mL.a Activity:106 g PE (mol Ni)−1 h−1
b Determined by DSC. c Determined by GPC.
.
Table 1 Selected bond lengths (Å) and angles (°) for complexes Ni1, Ni2-1 and Ni2-3
Ni1
Ni2-1
Ni2-3
Bond lengths (Å)
Ni–N(1)
Ni–N(2)
Ni–Br(2)
Ni–Br(1)
N(1)–C(1)
N(1)–C(25)
N(2)–C(13)
N(2)–C(12)
2.026(4)
2.036(4)
2.316(10)
2.336(9)
1.286(5)
1.451(5)
1.445(5)
1.286(5)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–Br(2)
Ni(1)–Br(1)
N(1)–C(26)
N(1)–C(38)
N(2)–C(1)
N(2)–C(37)
Ni(2)–N(3)
Ni(2)–N(4)
Ni(2)–Br(3)
Ni(2)–Br(4)
N(3)–C(46)
N(3)–C(58)
N(4)–C(57)
N(4)–C(17)
Ni(1)⋯Ni(2)
2.035(7)
2.036(7)
2.327(19)
2.348(19)
1.306(10)
1.462(11)
1.478(11)
1.276(10)
2.025(8)
2.042(8)
2.343(19)
2.327(2)
1.283(10)
1.451(11)
1.303(11)
1.469(12)
13.204
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–Br(2)
Ni(1)–Br(1)
N(1)–C(26)
N(1)–C(38)
N(2)–C(1)
N(2)–C(37)
Ni(2)–N(3)
Ni(2)–N(4)
Ni(2)–Br(3)
Ni(2)–Br(4)
N(3)–C(50)
N(3)–C(62)
N(4)–C(61)
N(4)–C(17)
Ni(1)⋯Ni(2)
2.020(6)
2.031(6)
2.330(16)
2.327(17)
1.279(9)
1.477(9)
1.467(8)
1.292(9)
2.027(6)
2.035(6)
2.299(15)
2.331(15)
1.283(9)
1.420(4)
1.269(9)
1.468(9)
10.641
Bond angles (°)
N(2)–Ni–N(1)
N(1)–Ni–Br(2)
N(1)–Ni–Br(1)
N(2)–Ni–Br(1)
N(2)–Ni–Br(2)
Br(1)–Ni–Br(2)
83.33(14)
116.29(11)
104.82(11)
111.46(10)
108.25(11)
125.00(3)
N(2)–Ni(1)–N(1)
N(1)–Ni(1)–Br(2)
N(1)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(2)
Br(1)–Ni(1)–Br(2)
N(3)–Ni(2)–N(4)
N(3)–Ni(2)–Br(3)
N(3)–Ni(2)–Br(4)
N(4)–Ni(2)–Br(3)
N(4)–Ni(2)–Br(4)
Br(3)–Ni(2)–Br(4)
84.0(3)
N(2)–Ni(1)–N(1)
N(1)–Ni(1)–Br(2)
N(1)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(2)
Br(1)–Ni(1)–Br(2)
N(3)–Ni(2)–N(4)
N(3)–Ni(2)–Br(3)
N(3)–Ni(2)–Br(4)
N(4)–Ni(2)–Br(3)
N(4)–Ni(2)–Br(4)
Br(3)–Ni(2)–Br(4)
82.2(2)
113.1(2)
106.9(2)
103.7(2)
115.8(2)
125.38(7)
82.7(3)
107.3(2)
110.5(2)
108.7(2)
113.1(2)
125.9(7)
111.70(19)
110.84(18)
113.14(19)
110.04(19)
122.01(6)
82.1(2)
123.93(17)
103.32(17)
109.31(18)
115.35(18)
117.94(6)
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identical, thereby affording the narrower observed PDIs. The
optimum reaction temperature was shown to be 50 °C and
higher temperatures led to lower activities due to deactivation
of the activated species, consistent with other mono-α-diimino
nickel pre-catalysts.1,15a
Table 3 Ethylene polymerization by all the pre-catalysts activated with Et2AlCl
Mwc/105
Entry Pre-cat. Al/Ni T/°C Activitya Tmb/°C g mol−1 Mw/Mn
c
1
2
3
4
5
6
7
8
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-1
Ni2-2
Ni2-3
Ni2-5
Ni2-6
Ni1
400
500
600
700
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
20
20
20
20
30
40
50
60
70
50
50
50
50
50
50
50
50
50
50
3.03
5.60
5.49
4.70
5.89
7.30
7.86
7.67
5.92
6.73
5.62
5.42
5.69
7.29
3.85
3.84
2.05
5.43
4.68
128.2
125.3
126.9
126.7
120.9
111.3
106.7
125.2
65.9
83.7
76.3
72.9
90.6
97.5
96.5
78.3
86.1
81.2
83.2
3.87
3.58
3.50
3.38
3.48
2.79
2.05
1.01
0.93
1.41
2.08
2.93
2.11
1.51
1.01
1.58
1.40
1.02
1.32
2.80
2.48
2.50
3.24
2.84
2.89
2.83
2.61
2.33
2.18
2.24
2.31
2.36
2.35
2.09
2.04
2.14
1.95
1.95
Under such optimized conditions (10 atm of ethylene,
50 °C and Et2AlCl/Ni = 500), all the nickel complex pre-cata-
lysts were investigated and the results are tabulated in Table 3.
According to the data performed by pre-catalysts Ni2-1–Ni2-6
(entries 2, 10–14 in Table 3), the substituents present signifi-
cantly affected the catalytic activities and an order of Ni2-4
(with 2,4,6-tri(Me)) > Ni2-1 (with 2,6-di(Me)) > Ni2-5 (with 2,6-
di(Et)-4-Me) > Ni2-2 (with 2,6-di(Et)) > Ni2-3 (with 2,6-(i-Pr))
was observed. These results are consistent with previous obser-
vations in the literature15c,17 and confirmed that the catalytic
activities could be enhanced by either using less bulky ortho
substituents or having an additional para-methyl substituent
present. The chloride complex Ni2-6 exhibited a slightly lower
activity than its analog Ni2-4. For comparison, the mono-
nuclear nickel pre-catalysts (Ni1–Ni5) were investigated under
the same conditions (entries 15–19 in Table 3). The catalytic
influence exerted by the substituents on their mono-nuclear
nickel pre-catalysts followed a similar trend to the bi-metallic
nickel pre-catalysts. However, significantly better catalytic
activities were achieved by the bi-metallic nickel complex pre-
catalysts. Moreover, the resultant polyethylene obtained using
the bi-metallic pre-catalysts showed a higher molecular weight
and broader PDI. These results suggest a positive synergetic
effect for these systems (bi- versus mono-metallic) under such
conditions.
9
10
11
12
13
14
15
16
17
18
19
Ni2
Ni3
Ni4
Ni5
Conditions: 1.5 μmol of [Ni]; 10 atm of ethylene; 30 min; total volume
100 mL;a Activity: 106 g PE (mol Ni)−1 h−1
;
b Determined by DSC.
c Determined by GPC.
had a slightly decreased molecular weight on increasing the
ratio of Al : Ni, which was attributed to the faster chain transfer
at higher Al concentrations.15b The lowest molecular weight
polydispersity was observed for the polyethylene obtained at
the Al : Ni ratio of 500 : 1, suggesting a single active species
under such conditions.
Regarding the thermal stability of the catalytic system, the
reaction temperature was varied from 20 to 70 °C (entries 2,
5–9 in Table 3) using an Al : Ni ratio of 500 : 1 and revealed the
highest catalytic activity of 7.86 × 106 g PE (mol Ni)−1 h−1 at
50 °C (entry 7 in Table 3). In addition, very close activities have
been observed over the range of 40 to 60 °C (entries 6–8 in
Table 3). The classical mono-metallic α-diimino nickel pre-
catalysts displayed their highest activities between at 0 to
20 °C.1,2 At elevated temperatures, the resultant polyethylene
gradually revealed lower molecular weights due to higher
chain termination at elevated temperatures.15 According to the
data in entries 2, 5–9 in Table 3, a slight increase of the PDI
values was observed on going from 20 °C to 40 °C (entries 2, 5
and 6), whilst a decrease in the PDI values was observed over
40 °C to 70 °C (entries 6–9). In view of the structures of Ni2-1
and Ni2-3, the bi-metallic nickel complex Ni2-4 could yield two
nickel-based active species possessing slightly different coordi-
nation environments. Such differing coordination means that
the two active species could individually polymerize ethylene
(i.e. multi-active species) at elevated temperatures, thereby pro-
ducing polyethylene with a wider PDI. However, on further
increasing the reaction temperature, it is possible that the
different active centres exhibit different thermal stabilities and
on increasing the temperature beyond 40 °C, one of the active
centres no longer operates. Alternatively, an internal rearrange-
ment may occur at elevated temperatures, which results in
many of the coordination sites/active centres being nearly
Ethylene polymerization using MAO as a co-catalyst
In a similar manner, MAO was also explored with nickel pre-
catalyst Ni2-4 for the optimum condition (Table 4). Based on a
temperature of 50 °C for the catalytic system with Et2AlCl,
different ratios of MAO : Ni were explored at this temperature
(entries 1–5 in Table 4), which indicated an optimum ratio of
2000 : 1 (entry 3 in Table 4). The obtained polyethylene showed
gradually lower molecular weights on increasing the amount
of MAO. This suggested that there was increased chain transfer
to the aluminium in the MAO-activated catalytic process.
With the molar ratio of Al : Ni (2000) fixed, the influence of
the polymerization temperature was surveyed (entries 3, 6–9 in
Table 4). Different from the Ni2-4/Et2AlCl system, on elevating
the reaction temperature from 20 °C to 60 °C, the highest
activity was found at 20 °C (up to 1.41 × 107 g PE (mol Ni)−1 h−1).
On increasing the polymerization temperature, the molecular
weights of the obtained polymer decreased, which was attribu-
ted to a much faster β-hydride elimination/chain transfer rate
at elevated polymerization temperatures.5b Compared to the
above Ni2-4/Et2AlCl system, the Ni2-4/MAO system exhibited a
lower thermo-stability and required more co-catalyst. These
observations suggest that different active species were operat-
ing in the Ni2-4/MAO and Ni2-4/Et2AlCl systems.
Regarding the lifetime of the Ni2-4/MAO system (entries 6,
10 and 11 in Table 4), the polymerization activity was
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Table 4 Ethylene polymerization by the pre-catalyst activated with MAO
Activitya
Tmb/°C
Mwc/105 g mol−1
Mw/Mn
c
Entry
Pre-cat.
Al/Ni
T/°C
t/min
1
2
3
4
5
6
7
8
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-4
Ni2-1
Ni2-2
Ni2-3
Ni2-5
Ni2-6
Ni1
1500
1750
2000
2250
2500
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
50
50
50
50
50
20
30
40
60
20
20
20
20
20
20
20
20
20
20
20
20
20
20
30
30
30
30
30
30
30
30
30
15
45
30
30
30
30
30
30
30
30
30
30
30
30
6.36
7.40
9.35
8.71
7.29
14.05
10.45
9.52
101.6
102.7
105.1
107.2
118.6
124.5
119.3
108.5
100.4
126.9
124.7
110.9
126.9
123.6
118.8
116.8
126.6
121.6
120.1
118.6
107.7
123.5
123.6
1.63
—
2.57
—
1.57
1.11
1.08
3.03
2.67
1.90
0.89
2.62
3.09
3.59
2.57
2.96
4.24
3.79
4.84
3.15
2.35
2.88
2.72
2.82
3.49
2.32
2.15
2.37
3.06
2.80
2.86
2.37
2.86
2.94
2.20
2.15
2.54
2.71
2.60
2.28
2.66
2.53
2.25
2.34
2.40
2.19
9
8.95
10
11
12d
13e
14
15
16
17
18
19
20
21
22
23
15.86
10.41
0.92
2.00
12.71
10.94
9.07
12.50
15.99
7.13
5.35
3.84
7.15
5.67
Ni2
Ni3
Ni4
Ni5
Conditions: 1.5 μmol of [Ni]; 10 atm of ethylene; total volume 100 mL.a Activity: 106 g PE (mol Ni)−1 h−1 b Determined by DSC. c Determined by
.
GPC. d 1 atm of ethylene. e 5 atm of ethylene.
monitored at different time intervals. On prolonging the reac- higher activities than their analogous mono-metallic pre-cata-
tion time from 15 to 45 min, more polymer was obtained, lysts. Given that positive synergic effects can be achieved in
whilst the overall activity declined. The highest activity of such nickel model pre-catalysts, these bi-metallic complex pre-
1.59 × 107 g PE (mol Ni)−1 h−1 was observed within 15 min catalysts are promising candidates in ethylene polymerization.
(entry 10 in Table 4). Compared to many classical mono-met- At the same time, it is noted that the anion (bromide or chlo-
allic α-diimino pre-catalysts,15 the bi-metallic Ni2-4/MAO ride) did not markedly change the catalytic activity or the prop-
system achieved higher catalytic activities over a much longer erties of the resultant polyethylene (entries 6 and 18 in
polymerization period. This observation is tentatively ascribed Table 4). The observed Mw values for the polyethylene obtained
to the synergetic effect arising from the two metal sites. The via the bi-metallic complex pre-catalysts were higher than
Ni2-4/MAO system was also studied under increased ethylene those obtained using their mono-nuclear analogues. This
pressure (from 1 to 10 atm: entries 6, 12 and 13 in Table 4) observation is consistent with the ‘rule’ that bi-metallic
and it was found that the activity rapidly rose from 0.92 × 106 complex pre-catalysts enhance chain propagation and result in
to 14.1 × 106 g PE (mol Ni)−1 h−1 on increasing the ethylene polyethylene with a higher molecular weight.6a We note,
pressure.
On employing the optimum conditions (Al : Ni of 2000 : 1 at would result in polyethylene with a broader PDI.
20 °C over 30 min), all the nickel/MAO catalytic systems were To assess for any branching in the obtained PE samples,
however, that multi-active species of bi-metallic pre-catalysts
evaluated for ethylene polymerization (entries 6, 14–23 in representative polyethylene prepared with pre-catalyst Ni2-4/
Table 4). In contrast to the mono-metallic nickel/E2tAlCl MAO at 60 °C (entry 9 in Table 4) was measured by 13C NMR
systems (entries 19–23 in Table 3), the methylene-bridged bi- spectroscopy (Fig. 4). The signals were interpreted (Table 5)
metallic Ni2-1–Ni2-5 pre-catalysts (entries 2, 10–14 in Table 3) according to the literature,19 which indicated that the main
exhibited more than double the activity (most up to 1 × 107 g branches were methyl (41%) and ethyl (21%) as well as some
PE (mol Ni)−1 h−1), whilst the polyethylene produced pos- longer chains, which is consistent with previous
sessed a higher molecular weight and broader PDIs. In observations.15
general, the Ni/MAO systems (entries 6, 14–23 in Table 4) per-
formed with higher activities than the Ni/E2tAlCl systems
(entries 2, 10–14 in Table 3) but the optimum reaction temp-
erature was lower: 20 °C for the Ni/MAO systems versus 50 °C
for the Ni/E2tAlCl systems. This was attributed to a different
Experimental details
General procedures
degree of ion-pair formation between the cationic active nickel
center and the weakly coordinating aluminium-based anion.18
In both systems, all the bi-metallic nickel pre-catalysts showed
All operations were carried out under a nitrogen atmosphere
using standard Schlenk techniques. All solvents were distilled
from sodium wire prior to use and chemicals were obtained
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melting points of polyethylene were measured from the second
scanning run on a Perkin-Elmer TA-Q2000 differential scan-
ning calorimetry (DSC) analyzer under a nitrogen atmosphere.
In the procedure, a sample of about 2.0–4.0 mg was heated to
140 °C at a rate of 20 °C min−1 and kept for 5 min at 140 °C to
remove the thermal history and then cooled at a rate of 10 °C
min−1 to 0 °C. 13C NMR spectra of the polyethylene were
recorded on a Bruker DMX-300 MHz instrument at 115 °C in
deuterated 1,2-dichlorobenzene with TMS as an internal
standard.
Syntheses and characterization
Synthesis of 1-(2,6-diisopropylphenylimino)-2-aryliminoace-
naphthylenylidenes (L1–L5). The 1-(2,6-diisopropylphenyl-
imino)-2-aryliminoacenaphthylenylidene series (L1–L5) was
synthesized by the reaction of various anilines and 1-(2,6-di-
isopropylphenylimino)acenaphthylen-2-one according to the
literature procedure.1,16 The 1,2-bis(2,6-diisopropylphenyl-
imino)acenaphthylenylidene (L3) and its nickel bromide (Ni3)
were previously synthesized.1,16
Fig. 4 13C NMR spectrum of polyethylene by Ni2-4/MAO at 60 °C (entry 9 in
Table 4).
Table 5 Experimental integrals and percentage of branching over the total
branching of Fig. 4
1-(2,6-Diisopropylphenylimino)-2-(2,6-dimethylphenylimino)-
acenaphthylenylidene (L1). A catalytic amount of p-toluene-
sulfonic acid (0.03 g) was added to a stirred mixture of 0.20 g
(0.58 mmol) of 1-(2,6-diisopropylphenylimino)acenaphthylen-
2-one and 0.08 g (0.70 mmol) of 2,6-dimethylaniline in 30 mL
of toluene. The mixture was stirred at 110 °C for 9 h and the
solvent was evaporated to dryness. The resultant residue was
dissolved in dichloromethane, filtered and the resulting solu-
tion was reduced in volume to saturation point when 10 mL
ethyl acetate was added and the solution was cooled overnight.
Yield 0.13 g (51%) of orange solid L1. 1H NMR (400 Hz, CDCl3,
TMS): 7.88 (t, J = 8.0 Hz, 2H), 7.40 (t, J = 8.0 Hz, 2H), 7.35 (m,
3H), 7.29–7.23 (m, 3H), 6.98 (s, 1H), 6.78 (d, J = 7.2 Hz, 1H),
6.62 (d, J = 7.2 Hz, 1H), 2.84 (m, 2H), 2.21 (s, 6H), 1.17 (d, J =
6.8 Hz, 6H), 0.90 (d, J = 6.8 Hz, 6H). 13C NMR (100 Hz, CDCl3,
TMS): 161.13, 160.93, 148.78, 147.62, 140.91, 135.58, 131.25,
130.89, 129.75, 129.64, 129.07, 128.27, 128.05, 126.64, 124.49,
124.17, 123.64, 123.49, 123.12, 28.77, 24.93, 23.54, 23.32,
14.07. IR (KBr; cm−1): 2960(s), 2926(m), 2867(w), 1674(s),
1593(s), 1464(s), 1428(s), 1326(m), 1228(s), 1159(w), 1085(s),
925(s), 867(s), 786(vs), 747(s), 655(m). Anal. Calcd for C32H32N2
(444.61): C, 86.44; H, 7.25; N, 6.30%. Found: C, 86.35; H, 7.30;
N, 6.30%.
1-(2,6-Diisopropylphenylimino)-2-(2,6-diethylphenylimino)ace-
naphthylenylidene (L2). Using the same procedure as for the
synthesis of L1, except that 2,6-diethylaniline (0.10 g,
0.70 mmol) was used in place of 2,6-dimethylaniline, L2 was
obtained as a yellow powder in 65% (0.18 g). 1H NMR (400 Hz,
CDCl3, TMS): 7.88 (d, J = 8.4 Hz, 1H), 7.87 (d, J = 8.0 Hz, 1H),
7.39–7.34 (m, 2H), 7.25–7.29 (m, 3H), 7.23–7.44 (m, 3H), 6.69
(d, J = 7.2 Hz, 1H), 6.64 (d, J = 7.2 Hz, 1H), 3.02 (m, 2H), 2.58
(m, 2H), 2.46 (m, 2H), 1.23 (d, J = 6.8 Hz, 6H), 1.11 (t, J =
7.6 Hz, 6H), 0.97 (d, J = 6.8 Hz, 6H). 13C NMR (100 Hz, CDCl3,
TMS): 161.13, 160.93, 148.78, 147.62, 140.91, 135.58,
131.25, 130.89, 129.75, 129.07, 128.27, 128.05, 126.64, 124.49,
124.17, 123.64, 123.49, 123.12, 28.77, 24.93, 23.54, 14.07.
Percentage
over total
branching
Chem.
Entry shift/ppm exp.
Integral Peak Branch
no.
content
1
2
3
4
5
6
7
8
11.16
14.10
14.43
19.96
22.88
26.65
27.27
27.44
27.81
29.58
30.00
30.37
30.46
32.19
1.00
2.71
0.62
10.04
1.67
1
2
3
5
8
Nm
5.13
1.23
0.00
0.94
2.57
0.00
0.84
0.00
1.78
41.07%
9.85%
0.00%
7.53%
20.58%
0.00%
6.73%
0.00%
14.25%
0.00%
Nm(1,4)
Nm(1,5)
Nm(1,6)
Ne
0.95
7.41
14.59
1.87
1.78
141.92
16.18
11.26
1.66
10
11
12
13
15
16
17
18
20
Np
Nb
Na
Nl
Nl(1,4)
CH2
[E]
9
10
11
12
13
14
0.00
140.26
70.13
[R]
12.49 100.00%
Branching = 151 Branches/
1000C
15
16
17
18
19
20
21
33.20
33.57
33.99
34.48
34.81
37.52
38.11
6.50
2.51
2.77
6.43
2.42
15.73
2.42
22
23
24
26
27
29
31
from commercial suppliers. MAO (1.46 M solution in toluene)
and MMAO (1.93 M in heptane, 3A) were purchased from Akzo
Nobel Corp. Et2AlCl (0.79 M in toluene) and EASC (0.87 M in
toluene) were purchased from Acros Chemicals. High-purity
ethylene was purchased from Beijing Yanshan Petrochemical
Co. and used as received. Other reagents were purchased from
Aldrich, Acros or local suppliers. NMR spectra were recorded
on a Bruker DMX 400 MHz instrument at ambient temperature
using TMS as an internal standard. δ values are given in ppm
and J values in Hz. IR spectra were recorded on a Perkin-Elmer
System 2000 FT-IR spectrometer. Elemental analysis was
carried out using a Flash EA 1112 micro-analyzer. The mole-
cular weights of polyethylene were determined by PL-GPC220
at 150 °C with 1,2,4-trichlorobenzene as the solvent. The
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IR (KBr; cm−1): 2962(s), 2929(m), 2867(m), 1673(s), 1650(s), 41.7, 28.4, 23.6. IR (KBr; cm−1): 2959(s), 2928(m), 2868(m),
1592(s), 1456(s), 1430(s), 1362(w), 1326(m), 1255(s), 1088(m), 1728(vs), 1651(s), 1595(s), 1461(s), 1437(s), 1360(m), 1300(w),
1039(m), 925(s), 835(s), 810(vs), 747(vs), 656(w). Anal. Calcd for 1273(s), 1216(s), 1170(s), 1120(m), 1071(s), 1027(s), 957(m),
C34H36N2 (472.66): C, 86.40; H, 7.68; N, 5.93%. Found: C, 908(s), 827(s), 777(vs), 732(s), 701(s). Anal. Calcd for
86.25; H, 7.57; N, 5.80%.
1-(2,6-Diisopropylphenylimino)-2-(2,4,6-trimethylphenylimino)-
acenaphthylenylidene (L4). The synthetic procedure for L4 was
C49H46N2O2 (694.90): C, 84.69; H, 6.67; N, 4.03%. Found: C,
84.39; H, 6.75; N, 4.10%.
Synthesis of 4,4′-methylenebis(1-(2,6-diisopropylphenyl-
analogous to that for L1, except that 2,4,6-trimethylaniline imino)-2-(arylimino)acenaphthylene) derivatives (L6–L10)
4,4′-Methylenebis(1-(2,6-diisopropylphenylimino)-2-(2,6-dimethyl-
phenylimino)acenaphthylene) (L6). A solution of 4,4′-methylene-
bis(1-(2,6-diisopropylphenylimino)-acenaphthylen-2-one) (0.19 g,
0.27 mmol), 2,6-dimethylaniline (0.080 g, 0.66 mmol) and a cata-
lytic amount of p-toluenesulfonic acid in 70 mL of toluene at
110 °C were stirred for 9 h and then the solvent was removed
by vacuum evaporation. The residue was further purified by
silica column chromatography (40 : 1 petroleum ether : ethyl
acetate) to afford 0.15 g of L6 (yellow, 62% yield). 1H NMR
(400 MHz, CDCl3, TMS): δ 7.89 (d, J = 8.2 Hz, 2H), 7.84 (d, J =
8.4 Hz, 2H), 7.40 (d, J = 7.6 Hz, 1H), 7.38 (t, J = 7.6 Hz, 1H),
7.31 (t, J = 7.6 Hz, 2H), 7.19–7.16 (m, 8H), 7.09 (d, J = 7.2 Hz,
1H), 7.07 (d, J = 7.6 Hz, 1H), 6.76 (d, J = 7.2 Hz, 2H), 6.71 (d, J =
7.2 Hz, 2H), 4.20 (s, 2H), 3.02 (m, 4H), 2.15 (s, 12H), 1.25 (d,
J = 6.8 Hz, 12H), 0.98 (d, J = 6.8 Hz, 12H). 13C NMR (100 Hz,
CDCl3, TMS): 161.4, 160.9, 149.5, 145.4, 140.9, 137.6, 135.4,
131.3, 129.8, 129.7, 129.1, 128.9, 128.4, 128.0, 124.9, 124.4,
123.8, 123.3, 122.6, 41.9, 28.8, 23.6, 23.4, 17.9. IR (KBr; cm−1):
2958(s), 2867(m), 1665(s), 1635(s), 1592(s), 1462(s), 1434(s),
1379(m), 1361(m), 1272(m), 1228(s), 1203(s), 1171(s), 1086(s),
1029(s), 921(s), 827(s), 773(vs), 703(s). Anal. Calcd for C65H64N4
(901.23): C, 86.63; H, 7.16; N, 6.22%. Found: C, 86.45; H, 7.23;
N, 6.15%.
(0.09 g, 0.70 mmol) was used in place of 2,6-dimethylaniline.
A yellow solid of L4 was collected in a yield of 60% (0.16 g). 1H
NMR (400 Hz, CDCl3, TMS): 7.88 (t, J = 8.0 Hz, 2H), 7.40 (t, J =
8.0 Hz, 1H), 7.35 (t, J = 8.0 Hz, 1H), 7.29–7.23 (m, 3H), 6.98 (s,
1H), 6.78 (d, J = 7.2 Hz, 1H), 6.64 (d, J = 7.2 Hz, 1H), 3.00 (m,
2H), 2.39 (s, 3H), 2.10 (s, 6H), 1.23 (d, J = 7.2 Hz, 6H), 0.98 (d,
J = 7.2 Hz, 6H). 13C NMR (100 Hz, CDCl3, TMS): 161.1, 161.0,
147.5, 146.9, 140.8, 135.5, 132.9, 131.1, 129.7, 129.6, 129.1,
128.9, 128.3, 127.9, 124.6, 124.4, 124.1, 123.5, 123.3, 122.6,
28.7, 23.4, 23.2, 21.0, 17.8. IR (KBr; cm−1): 2961(s), 2925(m),
2864(w), 1675(s), 1655(s), 1594(m), 1471(s), 1429(s), 1361(w),
1326(w), 1237(s), 1153(m), 1037(m), 934(s), 836(vs), 786(vs),
657(w). Anal. Calcd for C33H34N2 (458.64): C, 86.42; H, 7.47; N,
6.11%. Found: C, 86.25; H, 7.50; N, 5.98%.
1-(2,6-Diisopropylphenylimino)-2-(2,6-diethyl-4-methylphenyl-
imino)acenaphthylenylidene (L5). Using the same procedure as
for the synthesis of L1, except that 2,6-diethyl-4-methylaniline
(0.11 g, 0.70 mmol) was used in place of 2,6-dimethylaniline,
L5 was obtained as a yellow powder in a 58% (0.17 g) yield.
1H NMR (400 Hz, CDCl3, TMS): 7.88 (d, J = 8.0 Hz, 1H), 7.86 (d,
J = 8.0 Hz, 1H), 7.40–7.33 (m, 2H), 7.23–7.28 (m, 3H), 7.01 (s,
2H), 6.75 (d, J = 7.2 Hz, 1H), 6.62 (d, J = 6.8 Hz, 1H), 3.02 (m,
2H), 2.47–2.38 (m, 5H), 1.22 (d, J = 6.8 Hz, 6H), 1.09 (t, J =
7.6 Hz, 6H), 0.96 (d, J = 6.8 Hz, 6H). 13C NMR (100 Hz, CDCl3,
TMS): 161.1, 147.6, 146.2, 140.8, 135.6, 133.3, 131.2, 130.7,
129.8, 129.7, 128.9, 128.8, 128.2, 128.0, 127.4, 124.4, 123.6,
123.4, 123.1, 28.7, 24.8, 23.5, 23.3, 21.3, 14.1. IR (KBr; cm−1):
2960(s), 2926(m), 2865(w), 1675(s), 1654(s), 1594(w), 1461(s),
1431(w), 1325(w), 1255(s), 1224(m), 1090(s), 1038(s), 924(s),
785(vs), 756(vs), 657(w). Anal. Calcd for C35H38N2 (486.69): C,
86.37; H, 7.87; N, 5.76%. Found: C, 86.31; H, 7.95; N, 5.65%.
Synthesis of 4,4′-methylenebis(1-(2,6-diisopropylphenyl-
imino)acenaphthylen-2-one). A solution of 4,4′-methylenebis
(2,6-diisopropylaniline) (1.83 g, 5.0 mmol), acenaphthylene-
1,2-dione (1.82 g, 10.0 mmol) and a catalytic amount of
p-toluenesulfonic acid in dichloromethane (150 mL) were
stirred for 24 h under atmospheric temperature. The solvent
was then removed by vacuum evaporation and the residue was
further purified by silica column chromatography (40 : 1 pet-
roleum ether : ethyl acetate) to afford 1.91 g of 4,4′-methylene-
bis(1-(2,6-diisopropylphenylimino)-acenaphthylen-2-one)
(yellow, 55% yield). 1H NMR (400 MHz, CDCl3, TMS): δ 8.20 (d,
J = 7.6 Hz, 2H), 8.18 (d, J = 8.8, 2H), 7.97 (d, J = 8.4 Hz, 2H),
4,4′-Methylenebis(1-(2,6-diisopropylphenylimino)-2-(2,6-diethyl-
phenylimino)acenaphthylene) (L7). The synthetic procedure of
L7 was similar to that for L6, except that 2,6-diethylaniline
(0.098 g, 0.66 mmol) was used in place of 2,6-dimethylaniline.
A yellow solid of L7 was collected in a yield of 60% (0.16 g).
1H NMR (400 MHz, CDC13, TMS): 7.87 (d, J = 8.4 Hz, 2H), 7.84
(d, J = 8.4 Hz, 2H), 7.35–7.39 (m, 2H), 7.29–7.33 (m, 2H),
7.21–7.19 (m, 10H), 6.76 (d, J = 7.2 Hz, 2H), 6.69 (d, J = 7.2 Hz,
2H), 4.20 (s, 2H), 3.04 (m, 4H), 2.63–2.57 (m, 4H), 2.45–2.50
(m, 4H), 1.25 (d, J = 6.8 Hz, 12H), 1.12 (t, J = 7.4 Hz, 12H), 0.98
(d, J = 6.4 Hz, 12H). 13C NMR (100 MHz, CDCl3, TMS): 161.4,
161.1, 146.3, 145.6, 140.9, 137.6, 135.4, 133.2, 131.2, 130.9,
130.7, 129.9, 128.9, 128.2, 127.9, 127.39, 126.6, 124.4, 124.1,
123.3, 123.1, 42.0, 28.8, 24.9, 23.7, 23.4, 21.3, 14.2, 14.1. IR
(KBr; cm−1): 2961(s), 2928(m), 2867(m), 1663(s), 1641(s), 1594
(s), 1459(s), 1437(s), 1362(m), 1334(w), 1271(m), 1228(m), 1205
(m), 1172(m), 1089(s), 1037(s), 955(w), 921(s), 857(m), 830(s),
780(vs), 702(m). Anal. Calcd for C69H72N4 (957.34): C, 86.57;
H, 7.58; N, 5.85%. Found: C, 86.35; H, 7.45; N, 5.72%.
4,4′-Methylenebis(1-(2,6-diisopropylphenylimino)-2-(2,6-diiso-
7.83 (t, J = 7.6 Hz, 2H), 7.35 (t, J = 7.6 Hz, 2H), 7.16 (s, 4H), propylphenylimino)acenaphthylene) (L8). Using the same pro-
6.73 (d, J = 7.2 Hz, 2H), 4.18 (s, 2H), 2.85 (m, 4H), 1.18 (d, J = cedure as for the synthesis of L6, except that 2,6-
6.8 Hz, 12H), 0.90 (d, J = 6.8 Hz, 12H). 13C NMR (100 Hz, diisopropylaniline (0.12 g, 0.66 mmol) was used in place of
CDCl3, TMS): 189.7, 160.8, 144.5, 143.1, 138.1, 135.3, 132.3, 2,6-dimethylaniline, L8 was obtained as a yellow powder in
131.1, 131.0, 129.5, 128.4, 128.1, 127.8, 124.3, 123.3, 122.3, 53% (0.15 g). 1H NMR (400 MHz, CDC13, TMS): 7.87 (d, J =
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8.4 Hz, 2H), 7.85 (d, J = 8.4 Hz, 2H), 7.36 (m, 2H), 7.33–7.26 1-(2,6-diisopropylphenylimino)-2-(2,6-dimethyl-phenylimino)-
(m, 8H), 7.19 (s, 4H), 6.75 (d, J = 6.8 Hz, 2H), 6.64 (d, J = acenaphthylenylidene (L1) (0.09 g, 0.20 mmol) and (DME)
7.2 Hz, 2H), 4.20 (s, 2H), 3.04 (m, 8H), 1.25 (d, J = 6.4 Hz, NiBr2 (0.06 g, 0.20 mmol) in dried dichloromethane (10 mL)
12H), 1.24 (d, J = 6.4 Hz, 12H), 0.97 (d, J = 6.8 Hz, 24H). was stirred for 24 h at room temperature in a Schlenk tube.
13C NMR (100 MHz, CDCl3, TMS): 161.3, 161.1, 147.7, 145.5, The majority of the solvent was then removed and cyclohexane
140.9, 137.6, 135.6, 135.4, 131.3, 129.7, 129.6, 129.0, 128.0, (10 mL) was added to precipitate the complex. The residue was
127.9, 124.4, 124.3, 123.6, 123.5, 123.4, 41.9, 28.8, 23.7, 23.5, washed with cyclohexane and dried under vacuum to obtain a
23.4, 23.3. IR (KBr; cm−1): 2960(s), 2928(m), 2868(m), 1978(w), red powder of Ni1 in an 80% yield (0.11 g). IR (KBr; cm−1):
1650(s), 1592(s), 1460(s), 1431(s), 1382(m), 1361(m), 1272(m), 2960(s), 2926(m), 2866(w), 1649(s), 1622(s), 1590(s), 1463(s),
1249(s), 1175(s), 1107(m), 1038(m), 945(w), 921(w), 834(s), 782 1419(s), 1382(w), 1290(m), 1085(s), 1043(s), 926(m), 770(vs).
(vs), 750(s), 702(w), 667(w). Anal. Calcd for C73H80N4 (1013.44): Anal. Calcd for C32H32Br2N2Ni (663.11): C, 57.96; H, 4.86;
C, 86.52; H, 7.96; N, 5.53%. Found: C, 86.45; H, 7.83; N, 4.22%. Found: C, 57.88; H, 4.88; N, 4.19%.
N, 5.44%.
Nickel dibromide bearing 1-(2,6-diisopropylphenylimino)-2-(2,6-
diethylphenylimino)acenaphthylenylidene (Ni2). Using the same
procedure as for the synthesis of Ni1, except that 1-(2,6-diiso-
propylphenylimino)-2-(2,6-diethylphenylimino)acenaphthyl-
enylidene (L2) (0.09 g, 0.20 mmol) was in place of L1, Ni2 was
obtained as a red powder in an 85% (0.12 g) yield. IR (KBr;
cm−1): 2961(s), 2929(m), 2867(m), 1644(s), 1593(s), 1456(s),
1430(s), 1363(w), 1326(w), 1254(m), 1189(s), 1089(s), 1038(s),
924(s), 874(m), 835(m), 845(s), 784(vs), 747(vs). Anal. Calcd for
C34H36Br2N2Ni (691.16): C, 59.08; H, 5.25; N, 4.05%. Found: C,
59.14; H, 5.23; N, 4.10%.
Nickel dibromide bearing 1-(2,6-diisopropylphenylimino)-
2-(2,4,6-trimethylphenylimino)acenaphthylenylidene (Ni4). The
synthetic procedure of Ni4 was similar to that for Ni1, except
that 1-(2,6-diisopropylphenylimino)-2-(2,4,6-trimethylphenyl-
imino)acenaphthylenylidene (L4) (0.09 g, 0.20 mmol) was used
in place of L1. Red powdered Ni4 was collected in a yield of
86% (0.12 g). IR (KBr; cm−1): 2960(s), 2925(m), 2865(w),
1622(s), 1646(s), 1581(s), 1461(m), 1431(s), 1324(w), 1255(m),
1039(m), 924(s), 886(w), 835(s), 784(vs), 756(vs). Anal. Calcd for
C33H34Br2N2Ni (677.14): C, 58.53; H, 5.06; N, 4.14%. Found: C,
58.34; H, 5.10; N, 4.20%.
Nickel dibromide bearing 1-(2,6-diisopropylphenylimino)-2-(2,6-
diethyl-4-methylphenylimino)acenaphthylenylidene (Ni5). Using
the same procedure as for the synthesis of Ni1, except that
1-(2,6-diisopropylphenylimino)-2-(2,6-diethyl-4-methylphenyl-
imino)acenaphthylenylidene (L5) (0.10 g, 0.20 mmol) was used
in place of L1, Ni5 was obtained as a red powder in a 90%
(0.13 g) yield. IR (KBr; cm−1): 2960(s), 2925(m), 2865(w),
1646(s), 1622(s), 1581(s), 1428(s), 1326(w), 1291(m), 1224(s),
1131(s), 1045(s), 929(m), 832(s), 773(vs), 737(vs). Anal. Calcd
for C35H38Br2N2Ni (705.19): C, 59.61; H, 5.43; N, 3.97%.
Found: C, 59.49; H, 5.40; N, 3.89%.
Bimetallic nickel tetrabromide bearing 4,4′-methylenebis(1-(2,6-
diisopropylphenylimino)-2-(2,6-dimethylphenylimino)-acenaphthy-
lene) (Ni2-1). A mixture of 4,4′-methylenebis(1-(2,6-diisopropyl-
phenylimino)-2-(2,6-dimethylphenylimino)acenaphthylene) (L6)
(0.09 g, 0.10 mmol) and (DME)NiBr2 (0.07 g, 0.22 mmol) in
dried dichloromethane (10 mL) was stirred for 24 h at room
temperature in a Schlenk tube and then the solvent was evapo-
rated to dryness. The resultant residue was dissolved in
dichloromethane and filtered and the dichloromethane was
evaporated. Then diethyl ether (10 mL) was added to
4,4′-Methylenebis(1-(2,6-diisopropylphenylimino)-2-(2,4,6-tri-
methylphenylimino)acenaphthylene)
(L9). The
synthetic
procedure for L9 was analogous to that for L6, except that
2,4,6-trimethylaniline (0.089 g, 0.66 mmol) was used in place
of 2,6-dimethylaniline. A yellow solid of L9 was collected in a
yield of 57% (0.14 g). 1H NMR (400 MHz, CDCl3, TMS): 7.88 (d,
J = 8.4 Hz, 2H), 7.83 (d, J = 8.4 Hz, 2H), 7.38–7.42 (m, 2H),
7.32–7.26 (m, 4H), 7.19 (s, 3H), 6.98 (s, 3H), 6.78 (d, J = 7.2 Hz,
2H), 6.75 (d, J = 7.2 Hz, 2H), 4.20 (s, 2H), 3.02 (m, 4H), 2.39 (s,
6H), 2.11 (s, 12H), 1.24 (d, J = 6.4 Hz, 12H), 0.98 (d, J = 6.8 Hz,
12H). 13C NMR (100 MHz, CDCl3, TMS): 161.3, 160.9, 149.5,
145.4, 140.9, 137.6, 131.2, 129.7, 129.7, 129.1, 128.9, 128.4,
127.5, 124.9, 124.3, 123.8, 123.3, 122.6, 41.9, 28.7, 23.5, 23.4,
17.9. IR (KBr; cm−1): 2960(s), 2926(m), 2867(w), 1664(s),
1636(s), 1592(s), 1462(s), 1435(s), 1380(w), 1361(m), 1228(s),
1203(s), 1085(s), 1032(s), 905(s), 831(s), 774(vs), 726(vs). Anal.
Calcd for C67H68N4 (929.28): C, 86.60; H, 7.38; N, 6.03%.
Found: C, 86.53; H, 7.42; N, 5.98%.
4,4′-Methylenebis(1-(2,6-diisopropylphenylimino)-2-(2,6-diethyl-
4-methylphenylimino)acenaphthylene) (L10). Using the same
procedure as for the synthesis of L6, except that 2,6-diethyl-
4-methylaniline (0.11 g, 0.66 mmol) was used in place of 2,6-
dimethylaniline, L10 was obtained as a yellow powder in a
1
64% yield (0.17 g). H NMR (400 MHz, CDC13, TMS): 7.87 (d,
J = 8.4 Hz, 2H), 7.83 (d, J = 8.0 Hz, 2H), 7.39 (m, 2H), 7.31–7.26
(m, 2H), 7.19 (s, 4H), 7.01 (s, 4H), 6.76–6.73 (m, 4H), 4.19 (s,
2H), 3.03 (m, 4H), 2.56 (m, 4H), 2.48–2.38 (m, 10H), 1.24 (d, J =
6.8 Hz, 12H), 1.09 (t, J = 7.6 Hz, 12H), 0.98 (d, J = 6.4 Hz, 12H),
13C NMR (100 MHz, CDCl3, TMS): 161.4, 161.1, 146.3, 145.6,
140.9, 137.6, 135.4, 133.2, 131.2, 130.7, 129.9, 129.8, 128.9,
128.2, 127.9, 127.4, 124.3, 123.3, 123.1, 41.9, 28.7, 24.9, 23.7,
23.4, 21.3, 14.1 IR (KBr; cm−1): 2959(s), 2927(m), 2866(m),
1663(s), 1641(s), 1595(m), 1460(s), 1438(s), 1362(w), 1273(m),
1228(s), 1088(s), 1038(s), 921(s), 834(vs), 782(vs), 702(w). Anal.
Calcd for C71H76N4 (985.39): C, 86.54; H, 7.77; N, 5.69%.
Found: C, 86.45; H, 7.78; N, 5.55%.
Preparation of nickel halides bearing 1-(2,6-diisopropylphe-
nylimino)-2-aryliminoacenaphthylenylidene (Ni1–Ni5) and the
bimetallic nickel halides bearing 4,4′-methylenebis(1-(2,6-di-
isopropylphenylimino)-2-(arylimino)-acenaphthylene) deriva-
tives (Ni2-1–Ni2-6)
Nickel dibromide bearing 1-(2,6-diisopropylphenylimino)-2-(2,6-
dimethylphenylimino)acenaphthylenylidene (Ni1). A mixture of precipitate the complex. The deposit was washed with diethyl
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ether and dried under vacuum to obtain a crimson powder of Ni2-4, except that (DME)NiCl2 (0.05 g, 0.22 mmol) was used in
Ni2-1 in 69% yield (0.08 g). IR (KBr; cm−1): 2960(m), 2924(m), place of (DME)NiBr2 (0.07 g, 0.22 mmol), Ni2-6 was obtained
2867(w), 1622(s), 1581(s), 1462(s), 1435(s), 1382(m), 1291(s), as a red powder in a yield of 60% (0.07 g). IR (KBr; cm−1):
1189(s), 1129(m), 1045(s), 953(s), 832(s), 773(vs), 656(s). Anal. 2961(s), 2925(s), 2868(m), 1625(s), 1584(s), 1463(m), 1438(m),
Calcd for C65H64Br4N4Ni2 (1338.23): C, 58.34; H, 4.82; N, 1291(m), 1224(w), 1194(w), 1081(w), 1041(w), 732(w), 775(vs),
4.19%. Found: C, 58.22; H, 4.80; N, 4.10%.
656(w). Anal. Calcd for C67H68Cl4N4Ni2 (1188.48): C, 67.71;
H, 5.77; N, 4.71%. Found: C, 67.58; H, 5.69; N, 4.57%.
Bimetallic nickel tetrabromide bearing 4,4′-methylenebis(1-(2,6-
diisopropylphenylimino)-2-(2,6-diethylphenylimino)-acenaphthy-
lene) (Ni2-2). Using the same procedure as for the synthesis of
Ni2-1, except that 4,4′-methylenebis(1-(2,6-diisopropylphenyli-
mino)-2-(2,6-diethylphenylimino)acenaphthylene) (L7) (0.09 g,
X-Ray crystallographic studies
0.10 mmol) was used in place of L6, Ni2-2 was obtained as a Single-crystal X-ray diffraction studies for Ni1, Ni2-1 and Ni2-3
crimson powder in a 76% (0.11 g) yield. IR (KBr; cm−1): were carried out on a Rigaku RAXIS Rapid IP diffractometer
2962(s), 2928(s), 2868(m), 1621((s), 1580(s), 1458(s), 1437(s), with graphite-monochromatic Mo–Kα radiation (λ
=
1381(w), 1291(s), 1225(m), 1128(m), 1046(m), 931(s), 776(vs), 0.71073 Å). Cell parameters were obtained by a global refine-
659(w). Anal. Calcd for C69H72Br4N4Ni2 (1394.34): C, 59.44; ment of the positions of all the collected reflections. The
H, 5.20; N, 4.02%. Found: C, 59.35; H, 5.15; N, 4.08%.
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
Bimetallic nickel tetrabromide bearing 4,4′-methylenebis(1-(2,6-
diisopropylphenylimino)-2-(2,6-diisopropylphenylimino)acenaphthy-
lene) (Ni2-3). The synthetic procedure for Ni2-3 was analogous non-hydrogen atoms were refined anisotropically. The hydro-
to that for Ni2-1, except that 4,4′-methylenebis(1-(2,6-diisopro- gen atoms were placed in calculated positions. The structure
pylphenylimino)-2-(2,6-diisopropylphenylimino)acenaphthylene) solution and refinement were performed using the SHELXL-97
(L8) (0.10 g, 0.10 mmol) was used in place of L6. A crimson package.20 Crystal data and processing parameters for Ni1,
solid of Ni2-3 was collected in a yield of 74% (0.11 g). IR (KBr; Ni2-1 and Ni2-3 are summarized in Table 6. Using the Platon
cm−1): 2961(s), 2928(s), 2867(m), 1648(m), 1622(s), 1585(s), Squeeze procedure,21 the free solvent was killed off (one
1462(m), 1436(s), 1383(w), 1290(w), 1182(w), 1047(w), 954(w), toluene molecule for Ni2-1 and two toluene molecules for
832(m), 776(vs), 706(m). Anal. Calcd for C73H80Br4N4Ni2 Ni2-3).
(1450.45): C, 60.45; H, 5.56; N, 3.86%. Found: C, 60.36; H,
5.59; N, 3.78%.
Bimetallic nickel tetrabromide bearing 4,4′-methylenebis(1-(2,6-
diisopropylphenylimino)-2-(2,4,6-trimethylphenylimino)ace-
General procedure for ethylene polymerization
naphthylene) (Ni2-4). The synthetic procedure for Ni2-4 was
Ethylene polymerization under 10/5 atm of ethylene.
analogous to that for Ni2-1, except that 4,4′-methylenebis Equipped with a mechanical stirrer and temperature control-
(1-(2,6-diisopropylphenylimino)-2-(2,4,6-trimethylphenylimino)- ler, a 300 mL stainless steel autoclave was employed for the
acenaphthylene) (L9) (0.09 g, 0.10 mmol) was used in place of polymerization reaction. First of all, 20 mL of freshly distilled
L6. Crimson powdered Ni2-4 was collected in a yield of 70% toluene was injected into the autoclave which was full of ethyl-
(0.10 g). IR (KBr; cm−1): 2959(s), 2923(s), 2865(m), 1622(s), ene. When the temperature was stabilized, another 40 mL of
1581(vs), 1460(s), 1435(s), 1359(m), 1291(s), 1240(m), 1129(m), toluene which dissolved the complex (1.5 μmol [Ni]), the
1043(s), 831(vs), 777(vs), 658(w). Anal. Calcd for required amount of the co-catalyst (MAO, MMAO, EASC,
C67H68Br4N4Ni2 (1366.29): C, 58.90; H, 5.02; N, 4.10%. Found: Et2AlCl) and the residual toluene were added by syringe suc-
C, 58.77; H, 5.00; N, 4.01%.
cessively. The reaction mixture was intensively stirred for the
desired time under the corresponding pressure of ethylene
(10/5 atm) throughout the entire experiment. The reaction was
Bimetallic nickel tetrabromide bearing 4,4′-methylenebis(1-(2,6-
diisopropylphenylimino)-2-(2,6-diethyl-4-methylphenylimino)ace-
naphthylene) (Ni2-5). Using the same procedure as for the syn- quenched with acidic ethanol containing 30% hydrochloric
thesis of Ni2-1, except that 4,4′-methylenebis(1-(2,6- acid and then the precipitated polymer was collected by fil-
diisopropylphenylimino)-2-(2,6-diethyl-4-methylphenylimino) tration, adequately washed with ethanol and water and dried
acenaphthylene) (L10) (0.10 g, 0.10 mmol) was used in place of in a vacuum until of constant weight.
L6 (0.09 g, 0.10 mmol), Ni2-5 was obtained as a crimson
Ethylene polymerization under 1 atm of ethylene. The pre-
powder in a yield of 77% (0.11 g). IR (KBr; cm−1): 2962(s), catalyst Ni2-4 was dissolved in toluene using standard Schlenk
2929(s), 2868(m), 1622(s), 1581(s), 1458(s), 1437(s), 1382(w), techniques and the reaction solution was stirred with a mag-
1291(s), 1128(m), 1045(m), 953(w), 831(s), 776(vs), 658(w). netic stirrer under an ambient ethylene atmosphere. The
Anal. Calcd for C71H76Br4N4Ni2 (1422.39): C, 59.95; H, 5.39; required amount of the co-catalyst (MAO) was added by a
N, 3.94%. Found: C, 60.14; H, 5.45; N, 4.01%.
syringe. After the reaction was carried out for the required
period, the reaction was terminated and analyzed using the
same procedure shown above for ethylene polymerization at
Bimetallic nickel tetrachloride bearing 4,4′-methylenebis(1-(2,6-
diisopropylphenylimino)-2-(2,4,6-trimethylphenylimino)acenaphthy-
lene) (Ni2-6). Using the same procedure as for the synthesis of an elevated pressure.
Dalton Trans.
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Table 6 Crystal data and structure refinement for Ni1, Ni2-1 and Ni2-3
Identification code
Ni1
Ni2-1
Ni2-3
CCDC
Empirical formula
Fw
917315
917316
C65H64Br4N4Ni2
1338.26
917317
C73H80Br4N4Ni2
1450.47
C
32H32Br2N2Ni
663.13
T (K)
Wavelength (Å)
173(2)
0.71073
173(2)
0.71073
173(2)
0.71073
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
Monoclinic
P2(1)/n
10.642(2)
20.891(4)
13.085(3)
90
97.26(3)
90
2885.9(10)
4
1.526
Triclinic
P1
Monoclinic
P2(1)/n
20.688(4)
19.271(4)
21.750(4)
90
112.01(3)
90
8039(3)
ˉ
10.690(6)
15.864(8)
21.146(9)
73.54(19)
80.11(2)
86.03(17)
3387(3)
γ (°)
V (Å3)
Z
2
4
Dcalcd (mg m−3
)
1.312
2.953
1356
1.198
2.493
2968
μ (mm−1
F(000)
)
3.465
1344
Cryst size (mm)
θ range (°)
Limiting indices
0.56 × 0.38 × 0.10
2.16–27.46
−13 ≤ h ≤ 8
−25 ≤ k ≤ 26
−16 ≤ l ≤ 16
19 252
6546 (0.0743)
99.3(θ = 27.46)
1.113
R1 = 0.0666
wR2 = 0.1456
R1 = 0.0811
wR2 = 0.1553
0.673 and −0.678
0.28 × 0.26 × 0.22
1.02–27.32
−12 ≤ h ≤ 12
−18 ≤ k ≤ 18
−19 ≤ l ≤ 25
24 233
12 812 (0.0635)
99.0 (θ = 25.00)
1.042
R1 = 0.0995
wR2 = 0.2458
R1 = 0.1455
wR2 = 0.2782
0.948 and −0.785
0.28 × 0.26 × 0.22
1.16–25.00
−24 ≤ h ≤ 24
−22 ≤ k ≤ 13
−24 ≤ l ≤ 25
34 573
14 119 (0.0769)
99.7(θ = 25.00)
1.073
R1 = 0.0915
wR2 = 0.2304
R1 = 0.1376
wR2 = 0.2579
0.617 and −0.688
No. of rflns collected
No. unique rflns [R(int)]
Completeness to θ (%)
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R induces (all data)
Largest diff. peak and hole (Å−3
)
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