Nickel(ii) complexes bearing 4,5-bis(arylimino)pyrenylidenes: Synthesis, characterization, and ethylene polymerization behaviour

Article abstract of DOI:10.1039/c2dt32343e

A series of nickel(ii) dihalides complexes bearing 4,5-bis(arylimino) pyrenylidenes, NiX₂(2,6-R¹-4-R²C ₆H₂N)₂C₁₆H₈, was synthesized and characterized by FT-IR spectroscopy, elemental analysis, and single crystal X-ray diffraction for the organic compounds (L2 and L3) and the nickel complexes (C1 and C2). The molecular structures of C1 (R¹ = Me, R² = H, X = Br) and C2 (R¹ = R² = Me, X = Br) revealed a distorted tetrahedral geometry around the nickel centre. Upon treatment with the co-catalysts MAO, EASC and MMAO, all the nickel pre-catalysts exhibited high activities (of up to 4.42 × 10⁶ g(PE) mol(Ni)^-1 h^-1) for ethylene polymerization, and produced polyethylene products with a high degree of branching (up to 130 branched per 1000 carbons) and narrow molecular weight distribution. The influence of the reaction parameters and the nature of the ligands on the catalytic behavior of the title nickel complexes have been investigated.

Full text of DOI:10.1039/c2dt32343e

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Nickel(II) complexes bearing 4,5-bis(arylimino)-
pyrenylidenes: synthesis, characterization, and
Cite this: Dalton Trans., 2013, 42, 9166
ethylene polymerization behaviour†
Kuifeng Song,a,b Wenhong Yang,b Baixiang Li,c Qingbin Liu,*a Carl Redshaw,*d
Yuesheng Lic and Wen-Hua Sun*b
A
series of nickel(II) dihalides complexes bearing 4,5-bis(arylimino)pyrenylidenes, NiX2(2,6-R1-4-
R2C6H2N)2C16H8, was synthesized and characterized by FT-IR spectroscopy, elemental analysis, and single
crystal X-ray diffraction for the organic compounds (L2 and L3) and the nickel complexes (C1 and C2).
The molecular structures of C1 (R1 = Me, R2 = H, X = Br) and C2 (R1 = R2 = Me, X = Br) revealed a distorted
tetrahedral geometry around the nickel centre. Upon treatment with the co-catalysts MAO, EASC and
MMAO, all the nickel pre-catalysts exhibited high activities (of up to 4.42 × 106 g(PE) mol(Ni)−1 h−1) for
ethylene polymerization, and produced polyethylene products with a high degree of branching (up to
130 branched per 1000 carbons) and narrow molecular weight distribution. The influence of the reaction
parameters and the nature of the ligands on the catalytic behavior of the title nickel complexes have
been investigated.
Received 4th October 2012,
Accepted 23rd November 2012
DOI: 10.1039/c2dt32343e
www.rsc.org/dalton
feature of the resultant polyethylenes obtained by these nickel
catalytic systems is the highly branched nature of the poly-
Introduction
Late transition metal pre-catalysts bearing α-diimines have mers, which are formed via the ‘chain-walking’ mechan-
attracted great attention over the past two decades for the ism.2a,12 To date, observed catalytic activities and the
polymerization/oligomerization of ethylene and α-olefins.1 properties of the polyethylene products have been tuned/con-
This stems from the pioneering work on nickel(II) and trolled to some degree by changing the substituents at the aryl
palladium(II) complexes by Brookhart and co-workers.2 Due to the groups1b,13 or by modifying the ligand backbone,13,14 includ-
significant influence exerted by the nature of ancillary ligands ing more recent studies on 9,10-phenanthrenequinone-based
present on the catalytic activities of such complexes, a variety diimine ligands.15 In order to target new diimine-based
of nickel pre-catalysts have been explored via the development ligands, pyrene-4,5-dione has successfully been prepared and
of new bidentate ligand sets of the types N^N,3 N^P,4 N^O,5 used in preparing 4,5-bis(arylimino)pyrenylidenes and the
and tridentate ligand sets comprising N^P^N,6 O^N^N,7 nickel complexes thereof. These nickel(II) complexes exhibit
P^N^N,8 N^N^N,9 and P^N^P.10 Driven by the demand for high activities towards ethylene polymerization and produce
advanced polyolefins and new metal pre-catalyst systems highly branched polyethylene, with narrow molecular disper-
(i.e., new IP), alternative ligand sets and the complexes thereof sity, indicative of a single-site catalytic system. Herein, the syn-
have been explored and extensively reviewed.1m,11 A unique thesis and characterization of 4,5-bis(arylimino)pyrenylidenes
and their nickel complexes is reported. Furthermore, the
impact of the polymerization parameters and the nature of
the ligands present on the observed catalytic activity as well as the
aInstitute of Chemistry and Chemical Engineering, Hebei Normal University,
Shijiazhuang 050091, China. E-mail: liuqingb@heinfo.net;
properties of the polyethylene produced, has been investigated.
Fax: +86 (10) 80787432; Tel: +86 (10) 80787432
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: +86 (10) 62618239;
Tel: +86 (10) 62557955
Results and discussion
Synthesis and characterization of 4,5-bis(arylimino)
cState Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China
dDepartment 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 903462–903465. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt32343e
pyrenylidenes (L1–L4)
The condensation reactions of the pyrene-4,5-dione with
various aniline derivatives were conducted in the presence of
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Fig. 1 ORTEP drawing of L2. Thermal ellipsoids are shown at the 30% prob-
ability level. Hydrogen atoms have been omitted for clarity.
Scheme 1 Synthesis of ligands (L1–L4) and nickel complexes (C1–C5).
TiCl4 and Et3N in toluene, and the corresponding 4,5-bis-
(arylimino) pyrenylidenes (L1–L4) were formed in acceptable
yields (Scheme 1). The reaction of pyrene-4,5-dione with
2,6-diisopropyl benzamine did not occur, despite various
conditions and differing reagents being explored. Organic
compounds L1–L4 were characterized by elemental analysis,
NMR and IR spectroscopy.
Synthesis and characterization of nickel complexes
Further reactions of 4,5-bis(arylimino)pyrenylidenes L1 and L2
with (DME)nickel(II) dihalide (bromide or chloride) smoothly
afforded the corresponding diiminonickel halides (Scheme 1),
in varying yields: 66–74% for bromides C1–C2 and <38% for
chlorides C4 and C5. However, the 4,5-bis(2,6-diethylphenyl-
imino)pyrenylidene L3 could react with (DME)nickel(II)
bromide to form the corresponding nickel complex C3, the
nickel bromide complex was not accessible. Even worse, the
reaction trials of 4,5-bis(2,6-diethyl-4-methylphenylimino)-
pyrenylidene L4 with (DME)nickel(II) dihalide in various solvents
have not been successful in obtaining its nickel complexes. All
isolated nickel complexes were characterized by elemental
analysis and IR spectroscopy. To confirm the structures of the
nickel complexes, single crystals of complexes C1 and C2 were
obtained and the molecular structures were determined by
single crystal X-ray diffraction.
Fig. 2 ORTEP drawing of L3. Thermal ellipsoids are shown at the 30% prob-
ability level. Hydrogen atoms have been omitted for clarity.
Fig. 3 ORTEP drawing of C1. Thermal ellipsoids are shown at the 30% prob-
X-Ray crystallography
ability level. Hydrogen atoms have been omitted for clarity.
Single crystals of L2, L3, C1 and C2 suitable for X-ray crystallo-
graphic analysis were grown by slow diffusion of diethyl ether
into the respective dichloromethane solutions. The molecular
structures of each are shown in Fig. 1–4, respectively, with
selected bond lengths and angles tabulated in Table 1. In the
solid-state structures of compounds L2 and L3, the double
bonding features are illustrated by N1–C1 1.279(3) and
N2–C14 1.282(3) Å in L2 and 1.295(6) and 1.288(6) Å in L3,
whilst the single bonds for N1–C17 and N2–C23 are 1.424(3)
and 1.427(3) Å in L2 and 1.421(6) and 1.451(7) Å in L3. The
dihedral angle formed by the two imino-phenyl rings con-
nected to the nitrogen atoms is 72.67° in L2 and is 70.7° in
L3. Similar characteristics were observed in analogues bearing
9,10-bis(2,6-dimethylphenylimino)phenanthrenylidene with
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imino-phenyl rings connected to the nitrogen atoms are 148.2°
in C1 and 140.61° in C2, respectively.
There are obvious changes of the dihedral angles involv-
ing the two imino-phenyl rings at 72.67° in L2 and 140.61° in
C2, the difference being attributed to the efficient coordination
to the nickel center in C2.
Ethylene polymerization
To ascertain
a suitable co-catalyst, pre-catalyst C2 was
employed with different activators such as methylaluminoxane
(MAO), modified methylaluminoxane (MMAO), diethylalumi-
nium chloride (Et2AlCl) or ethylaluminium sesquichloride
(Et3Al2Cl3, EASC) at a temperature of 40 °C and under 10 atm
ethylene. The results are summarized in Table 2, from which it
can be seen that EASC, MAO and Et2AlCl are all effective as
activators. Different co-catalysts also affect the property of the
obtained polyethylenes; the polyethylene via C2/MAO exhibited
lower molecular weight but higher branching than that from
C2/MMAO (entries 1 and 2 in Table 2). According to Table 2,
all polyethylenes exhibited narrow molecular polydispersity
and significant branching (from 21 to 53 per 1000 carbons) as
well as potentially useful molecular weights (2.0 to 6.4 ×
105 g mol−1). Each of these co-catalysts, in combination with
C2, was then investigated in more detail.
Fig. 4 ORTEP drawing of C2. Thermal ellipsoids are shown at the 30% prob-
ability level. Hydrogen atoms have been omitted for clarity.
Table 1 Selected bond lengths (Å) and angles (°) for compounds L2, L3, C1
and C2
L2
L3
C1
C2
Bond lengths (Å)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–Br(1)
Ni(1)–Br(2)
N(1)–C(1)
N(1)–C(17)
N(2)–C(14)
N(2)–C(23)
—
—
—
—
1.279(3)
1.424(2)
1.282(3)
1.427(3)
—
—
—
—
1.295(6)
1.421(6)
1.288(6)
1.451(7)
1.994(6)
1.998(5)
2.3541(14)
2.3648(13)
1.303(8)
1.444(8)
1.291(8)
1.426(8)
1.987(6)
2.003(6)
2.3488(18)
2.3615(16)
1.313(9)
1.456(9)
1.309(9)
1.430(9)
Ethylene polymerization using the C1–C5/EASC systems
Using EASC as co-catalyst, the polymerization reaction para-
meters, including Al : Ni molar ratio, reaction time and tem-
perature, were varied, and the results are collected in Table 3. In
the case of the Al : Ni molar ratio (entries 1–4 in Table 3), on
increasing the ratio from 250 to 500, the catalytic activity first
increased and then decreased, whilst the increase of the Al/Ni
molar ratio led to polyethylene of lower molecular weight (GPC
curves shown in Fig. 5).
Such observations are consistent with the previous con-
clusion that high molar ratios of Al/Ni enhance chain transfer
from nickel species to aluminium, which results in lower mole-
cular weight polymers.16 The optimum Al/Ni molar ratio was
found to be 300 : 1 with activities of up to 3.53 × 106 g(PE) mol
Bond angles (°)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–Br(1)
N(1)–Ni(1)–Br(2)
N(2)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(2)
Br(1)–Ni(1)–Br(2)
C(17)–N(1)–Ni(1)
C(1)–N(1)–Ni(1)
C(23)–N(2)–Ni(1)
C(14)–N(2)–Ni(1)
C(1)–N(1)–C(17)
C(14)–N(2)–C(23)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
126.7(4)
127.0(4)
79.9(2)
80.0(3)
116.38(18)
113.16(19)
111.35(17)
111.89(16)
118.02(5)
118.4(4)
115.6(4)
116.1(4)
116.5(4)
126.0(6)
127.4(5)
112.57(18)
112.32(18)
120.85(18)
109.32(19)
116.38(6)
115.6(4)
117.3(5)
116.4(5)
115.1(5)
127.1(6)
115.1(5)
—
—
123.63(17)
123.74(18)
double-bonding for CvN at 1.2839(19) and 1.271(2) Å and (Ni)−1 h−1 observed. According to the entries 2 and 5–6 in
single bonding for C–N at 1.4099(19) and 1.417(2) Å.15
Table 3, the optimum reaction temperature in the present
As shown in Fig. 3 and 4, the complexes C1 and C2 possess study was found to be 40 °C; higher or lower temperatures led
similar structures, that is, the distorted tetrahedral geometry to a slight decrease of the catalytic activity, similar to the pre-
at the nickel centre is comprised of two nitrogen atoms (of the viously observed situation for reported α-diimine catalyst sys-
chelate) and two bromine atoms. On comparison of analogous tems.13a–e In addition, when elevating the temperature from
bond lengths and angles, there is evidence of some substituent 30 to 50 °C, a marked decrease in the polymer molecular weight
effects, such as the bond lengths of Ni1–N1, Ni1–N2, Ni1– was observed. Lifetime studies indicated that higher activities
Br1 and Ni1–Br2 in C1 [1.994(6), 1.998(5), 2.3541(14) and were observed over shorter reaction times (entry 7 in Table 3),
2.3648(13) Å] versus those of C2 [1.987(6), 2.003(6), 2.3488(18) i.e. the activities decreased on prolonging the period of
and 2.3615(16) Å]. The distances from the nickel atom to the polymerization. This suggested that there was no induction
plane formed by N1, N2 and Br1 and to the plane formed by period, and that the active species was rather short-lived. More-
N1, N2 and Br2 are 0.894 and 0.834 Å in C1, respectively, over, both the Mw and Mw/Mn values of the obtained PEs
whilst these values are 0.834 and 0.834 Å for C2, respectively. increased slightly on extending the reaction time; the Mw
The dihedral angle between the plane formed by N1, N2 and changes are shown by GPC (Fig. 6). Given that the optimum
Ni1 and the plane formed by N1, N2 and Br2 is 35.75° in C1 conditions for the C2/EASC system were found to be an Al/Ni
and 33.08° in C2. The dihedral angles formed by the two ratio of 300 at 40 °C over 30 min, further investigations using
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Table 2 Ethylene polymerization by pre-catalyst C2 with various co-catalystsa
Activityb
Tm/°C c
Mw/105 g mol−1 d
Mw/Mn
Branches/1000C e
d
Entry
Co-cat.
Al/Ni
T/°C
1
2
3
4
MAO
1000
1000
300
40
40
40
40
3.23
1.11
2.47
3.53
113.7
121.6
97.1
3.85
6.38
1.98
3.56
2.4
2.2
2.1
2.4
29
21
53
46
MMAO
Et2AlCl
EASC
300
103.1
a Conditions: 3 μmol of C2; 30 min; 10 atm of ethylene; 100 ml toluene. b 106 g(PE) mol(Ni)−1 h−1
.
c Determined by DSC. d Determined by GPC.
e Determined by FT-IR.
Table 3 Ethylene polymerization by pre-catalysts C1–C5 with EASCa
Activityb
Tm/°C c
Mw/105 g mol−1 d
Mw/Mn
Branches/1000 C e
d
Entry
Pre-cat.
Al/Ni
T/°C
t/min
1
2
3
4
5
6
7
8
C2
C2
C2
C2
C2
C2
C2
C2
C1
C3
C5
C5
C5
C5
C5
C5
C4
250
300
400
500
300
300
300
300
300
300
250
300
400
500
400
400
400
40
40
40
40
30
50
40
40
40
40
40
40
40
40
30
50
40
30
30
30
30
30
30
15
45
30
30
30
30
30
30
30
30
30
2.67
3.53
2.56
2.25
3.23
3.07
4.42
1.96
3.03
3.63
1.26
2.81
4.41
2.16
2.45
2.29
0.18
102.4
103.1
117.3
107.5
102.5
56.5
103.9
99.7
106.6
107.5
115.5
107.5
99.9
4.04
3.56
3.13
2.95
3.73
1.52
2.30
3.91
4.68
7.29
3.87
3.18
2.01
1.89
4.13
2.05
3.20
2.5
2.4
2.4
3.2
2.5
2.3
2.2
2.5
2.4
2.1
2.1
2.3
2.1
2.1
2.4
2.2
2.0
42
46
18
26
40
130f
49
79
26
44
33
34
32
58
5
9
10
11
12
13
14
15
16
17
103.3
110.7
87.4
49
12
117.4
a Conditions: 3 μmol of complex; 10 atm of ethylene; 100 ml toluene. b 106 g(PE) mol(Ni)−1 h−1 c Determined by DSC. d Determined by GPC.
.
e Determined by FT-IR. f Determined by 13C NMR spectroscopy.
Fig. 5 GPC curves of polyethylene obtained at different molar ratios of Al to Ni
(entries 1–4 in Table 3).
Fig. 6 GPC curves of polyethylene obtained at different times (entries 2, 7 and
8 in Table 3).
the other pre-catalysts (C1 and C3) were conducted under such of Table 3, the degree of branching for the obtained PE pro-
conditions. Shown in entries 2, 9 and 10 of Table 3, results ducts increased on increasing the temperature.
reveal the activity order of C3 > C2 > C1, in line with the
A representative chain of PE formed by the C2/EASC cata-
decreasing bulk of the aniline-derived aryl groups. As illus- lytic system (entry 6 in Table 3) was characterized by 13C NMR
trated by the above structural features for C1 with C2, efficient spectroscopic measurements, which revealed 130 branches per
coordination to the nickel center in C2 can stabilize the active 1000 carbons (Fig. 7) according to the interpretation reported
species and thereby result in better activity, which is consistent by Galland et al.18 These highly branched PEs were obtained
with previous observations.2a,17 As shown in entries 2, 5 and 6 due to β-hydrogen migration at the active nickel species.1k,m,19
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In a similar way, the chloride complex C5 was used to deter- molar ratio of Al : Ni at 400 (entry 13 in Table 3). There is no
mine the optimum reaction conditions for the ethylene general approach for adapting complex pre-catalysts for better
polymerization and the data are tabulated in Table 3. Accord- catalytic property, and this emphasizes the importance of
ingly, the highest activities were observed when the Al/Ni finely tuning ligands with different substituents and using
molar ratio was increased to 400 (entries 11–14 in Table 3), different anionic ions.
and the optimum temperature remained at 40 °C (entries 13,
15 and 16 in Table 3).
Ethylene polymerization with the C1–C5/MAO systems
These optimum conditions were also employed on the C4
system to study the ethylene polymerization behaviour (entry
17 in Table 3); the activity order C5 > C4 was observed. The
influence of the substituents on the catalytic activities of these
nickel chlorides followed the same trend as observed for the
bromide systems, i.e. the bulkier the substituent, the higher
the activity. Ligated by the same ligand, 4,5-bis(2,6-dimethyl-
phenylimino)pyrenylidene (L1), the bromonickel complex C1
shows much higher activity than did the chloronickel complex
C4 (entries 9 and 17 in Table 3);9d this is thought to be due to
the low solubility of the chloro-complex. Under the same con-
ditions, for complexes bearing the ligand L2, the same ten-
dency was observed for the bromo-complex C2 and the chloro-
complex C5 (entries 2 and 12 in Table 3); a better activity was
achieved for the chloro-complex C5 by further increasing the
Using MAO as the co-catalyst, all the nickel complexes also
exhibited good catalytic activities for ethylene polymerization.
The results using different Al/Ni molar ratios, temperatures,
and pressures are presented in Table 4. Under ambient
pressure of ethylene at 40 °C, good activities were observed for
ethylene polymerization in the presence of MAO (entry 8 in
Table 4).
As seen from the entries 2, 8 and 9 in Table 4, the Tm value
of the polyethylene increased on increasing the ethylene
pressure, and the trend of decreased branching with increas-
ing ethylene pressure here reinforced earlier observations.13a
The current nickel pre-catalysts based on the pyrene unit pro-
duced polyethylene of higher molecular weight than did their
nickel analogues derived from α-diimino13a and phen-
anthrene;15 all nickel pre-catalysts produced highly branched
polyethylene as a characteristic property. Moreover, the mole-
cular weight of the polyethylene increased on increasing the
pressure of ethylene (shown in Fig. 8).
The catalytic activity was enhanced on increasing the Al/Ni
molar ratios from 750 to 1000 (entries 1 and 2 in Table 4) for
the C2/MAO catalytic system and from 1250 to 1500 (entries 10
and 11 in Table 4) for the C5/MAO catalytic system. For the C2/
MAO catalytic system (entries 2 and 3 in Table 4) and the C5/
MAO catalytic system (entries 11 and 12 in Table 4), a clear
decrease of activity was observed on further increasing the
Al/Ni molar ratios. Thus, the optimum Al/Ni molar ratio was
found to be 1000 : 1 for the C2/MAO catalytic system and
1500 : 1 for the C5/MAO catalytic system, which afforded
the highest activities of 3.23 × 106 g(PE) mol(Ni)−1 h−1 and
3.43 × 106 g(PE) mol(Ni)−1 h−1, respectively over 30 min. Along
with increasing the Al/Ni molar ratio, the molecular weight poly-
dispersity became wider with slightly differing molecular weights
Fig. 7 13C-NMR spectrum of polyethylene (entry 6 in Table 3).
Table 4 Ethylene polymerization by pre-catalysts C1–C5 with MAOa
Activityb
Tmc/°C
Mwd/105 g mol−1
Mw/Mn
Branches/1000C e
d
Entry
Pre-cat.
Al/Ni
T/°C
1
2
3
4
5
6
7
C2
C2
C2
C2
C2
C1
C3
C2
C2
C5
C5
C5
C4
750
1000
1250
1000
1000
1000
1000
1000
1000
1250
1500
1750
1500
40
40
40
30
50
40
40
40
40
40
40
40
40
1.89
3.23
2.57
2.83
1.58
2.07
3.53
0.22
1.26
2.27
3.43
1.23
0.36
106.9
113.7
115.6
117.6
104.4
114.4
115.8
95.2
101.4
112.3
116.2
117.6
120.3
5.21
3.85
3.63
3.50
2.86
4.57
7.33
1.80
2.70
3.56
3.49
4.69
2.94
2.3
2.4
2.1
2.2
2.0
2.5
2.2
2.3
1.9
2.2
2.3
2.4
2.1
31
29
28
27
42
8
29
47
35
29
35
38
23
8f
9g
10
11
12
13
a Conditions: 3 μmol of complex; 30 min; 10 atm of ethylene; total volume 100 ml. b 106 g(PE) mol(Ni)−1 h−1 c Determined by DSC. d Determined
.
by GPC. e Determined by FT-IR. f 1 atm of ethylene. g 5 atm of ethylene.
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(entries 10, 11 and 12 in Table 4), indicating that the higher 2 and 3 in Table 5). In the C5/Et2AlCl system, the optimum Al/
the Al/Ni ratio, the more chain transfer and termination Ni molar ratio at 40 °C was found to be 400 : 1 (entries 8, 9 and
occurs. The best performance was observed at 40 °C (entries 2, 10 in Table 5). Moreover, the Mw and Mw/Mn values for poly-
4 and 5 in Table 4), and the other pre-catalysts were employed ethylene decreased on increasing the Al/Ni molar ratio (entries
under such conditions. When MAO was used as co-catalyst, 8, 9 and 10 in Table 5). All the products obtained possessed a
the order of the catalytic activity performance decreases in the relatively high degree of branching, which increased on
order C3 > C2 > C1 for the bromides, and C5 > C4 for the increasing the temperature. At the optimum reaction con-
chlorides.
ditions, the catalytic activity of the C5 system is higher than
that of C4. Also, from the data in Table 5, the catalytic activity
was found to decrease in the order C3 > C2 > C1 (Table 5).
Ethylene polymerization with C1–C5/Et2AlCl system
Similarly using Et2AlCl as co-catalyst, catalytic screening
results were also obtained at different Al/Ni molar ratios and
reaction temperatures. For the C2/Et2AlCl system, elevating the
reaction temperature from 30 to 40 °C resulted in enhanced
activity (entries 4 and 2 in Table 5).
Elevating the reaction temperature further from 40 to 50 °C
resulted in a reduction in the activity (entries 2 and 5 in
Table 5). Meanwhile, the Mw/Mn values of the obtained poly-
ethylene decreased when the temperature was increased. Over
the Al/Ni molar ratio range 100 to 300 for the C2/Et2AlCl
system, the highest polymerization activity and molecular
weight were observed at the Al/Ni molar ratio of 200 (entries 1,
Conclusions
The newly designed 4,5-bis(arylimino)pyrenylidenes were suc-
cessfully synthesized and used to form nickel halide com-
plexes. The resulting nickel complex pre-catalysts showed high
activities for ethylene polymerization with various co-catalysts
such as EASC, Et2AlCl and MAO. Reaction parameters such as
the Al/Ni molar ratio, the reaction temperature and time have
a significant influence on the catalytic activity and properties
of the obtained polyethylene. The polyethylene products were
confirmed to be highly branched.
Experimental
General procedure
All manipulations of air and/or moisture sensitive compounds
were carried out under a nitrogen atmosphere using standard
Schlenk techniques. The solvents were purified and dried
under nitrogen by conventional methods prior to use unless
otherwise stated. Methylaluminoxane (MAO, 1.46 M solution
in toluene) and modified methylaluminoxane (MMAO, 1.93 M
in heptane, 3A) were purchased from Akzo Nobel Corp. Diethyl-
aluminium chloride (Et2AlCl, 0.79 M in toluene) and ethyl-
aluminium sesquichloride (EASC, 0.87 M in toluene) were
purchased from Acros Chemicals. High-purity ethylene was
purchased from Beijing Yansan Petrochemical Co. and used as
received. Other reagents were purchased from Aldrich, Arcos,
or local suppliers. 1H and 13C NMR spectra were recorded on a
Fig. 8 GPC curves of polyethylene obtained at different the pressure of
ethylene.
Table 5 Ethylene polymerization by pre-catalysts C1–C5 with Et2AlCla
Activityb
Tmc/°C
Mwd/105 g mol−1
Mw/Mn
Branches/1000C e
d
Entry
Pre-cat.
Al/Ni
T/°C
1
2
3
4
5
6
7
8
C2
C2
C2
C2
C2
C1
C3
C5
C5
C5
C4
100
200
300
200
200
200
200
300
400
500
400
40
40
40
30
50
40
40
40
40
40
40
0.79
2.81
2.47
2.24
0.20
1.29
3.22
2.31
2.65
2.39
0.068
120.3
105.7
97.1
2.68
3.32
1.98
2.97
1.98
3.90
6.70
3.28
3.02
2.86
6.08
2.3
2.5
2.1
2.9
2.1
2.2
2.2
2.3
2.2
1.9
2.6
29
39
53
31
37
27
52
47
33
38
19
109.0
107.1
119.5
107.6
103.6
110.3
106.7
115.3
9
10
11
a Conditions: 3 μmol of complex; 30 min; 10 atm of ethylene; total volume 100 ml. b 106 g(PE) mol(Ni)−1 h−1 c Determined by DSC. d Determined
.
by GPC. e Determined by FT-IR.
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Table 6 Crystal data and structure refinements for L2, L3, C1 and C2
L2
L3
C1
C2
Empirical formula
Cryst. color
Fw
C
Red
34H30N2
C38H38N2
Red
522.70
173(2)
0.71073
Triclinic
ˉ
P1
8.0890(16)
18.545(4)
19.786(4)
79.56(3)
C32H27Br2N2Ni
Brown
658.05
C34H30Br2N2Ni
Red
685.13
466.60
446(2)
0.71073
Triclinic
T (K)
173(2)
173(2)
Wavelength (Å)
Cryst. syst.
Space group
a (Å)
b (Å)
c (Å)
0.71073
Triclinic
ˉ
P1
11.613(2)
15.244(3)
18.470(4)
106.33(3)
0.71073
Triclinic
ˉ
P1
14.873(3)
16.510(3)
16.616(3)
99.21(3)
ˉ
P1
8.8655(18)
11.826(2)
13.450(3)
88.28(3)
α (°)
β (°)
75.63(3)
70.27(3)
1283.6(4)
2
1.207
0.070
496
86.95(3)
88.80(3)
2914.6(10)
4
1.191
0.069
1120
98.48(3)
96.40(3)
3063.0(10)
4
1.368
3.262
1216
101.46(3)
113.54(3)
3533.6(12)
4
1.288
2.832
1384
γ (°)
V (Å3)
Z
Dcalcd (mg m−3
)
μ (mm−1
F (000)
)
Cryst size (mm)
θ range (°)
Limiting indices
0.20 × 0.13 × 0.09
1.83–27.42
−11 ≤ h ≤ 11
−15 ≤ h ≤ 15
−17 ≤ h ≤ 12
12 718
5801 (0.0541)
99.0 (θ = 27.42)
1.022
R1 = 0.0820
wR2 = 0.2297
R1 = 0.0951
wR2 = 0.2475
0.388 and −0.331
0.25 × 0.20 × 0.10
1.05–25.00
−9 ≤ h ≤ 9
−22 ≤ h ≤ 22
−23 ≤ h ≤ 22
22 029
10 223 (0.1117)
99.6 (θ = 25.00)
1.098
R1 = 0.1339
wR2 = 0.3404
R1 = 0.1793
wR2 = 0.3873
0.552 and −0.461
0.25 × 0.23 × 0.21
1.17–27.46
−15 ≤ h ≤ 14
−19 ≤ h ≤ 19
−18 ≤ h ≤ 23
29 319
13 734 (0.0787)
98.0 (θ = 27.46)
1.075
R1 = 0.0831
wR2 = 0.1903
R1 = 0.1115
wR2 = 0.2112
0.760 and −1.022
0.26 × 0.24 × 0.10
1.30–27.41
−19 ≤ h ≤ 19
−21 ≤ h ≤ 21
−21 ≤ h ≤ 21
45 507
15 927 (0.1035)
98.9 (θ = 27.41)
1.049
R1 = 0.0995
wR2 = 0.2617
R1 = 0.1506
wR2 = 0.2991
0.985 and −0.959
No. of rflns collected
No. unique rflns [R(int)]
Completeness to θ (%)
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Largest diff. peak and hole (e Å−3
)
Bruker DMX 400 MHz instrument at ambient temperature 827 (s), 758 (vs), 716 (vs). 1H NMR (400 MHz, CDCl3, TMS):
using TMS as an internal standard; δ values were given in ppm δ 8.66 (d, J = 7.2 Hz, 1H, Pyrene H), 8.09 (d, J = 7.6 Hz, 1H,
and J values in Hz. FT-IR spectra were recorded on a Perkin- Pyrene H), 7.78–7.76 (m, 4H, Pyrene H), 7.72 (t, J = 7.6 Hz, 1H,
Elmer System 2000 FT-IR spectrometer. Elemental analyses Ph H), 7.04–7.01 (m, 3H, Pyrene H, Ph H), 6.91–6.81 (m, 4H,
were carried out using a Flash EA 1112 microanalyzer. Mole- Pyrene H, Ph H), 2.11 (s, 6H, Ph–CH3), 1.33 (s, 6H, Ph–CH3).
cular weights and molecular weight distribution (MWD) of 13C NMR (100 MHz, CDCl3, TMS): δ 159.27, 157.50, 149.53,
polyethylene were determined by a PL-GPC220 at 150 °C, with 148.15, 133.06, 131.87, 131.61, 130.97, 130.73, 128.06, 127.83,
1,2,4-trichlorobenzene as the solvent. DSC trace and melt- 127.63, 127.39, 127.22, 126.77, 126.28, 125.34, 125.05, 124.33,
ing points of polyethylene were obtained from the second 123.03, 122.45, 18.62, 17.35. Anal. Calcd for C32H26N2:
scanning run on Perkin-Elmer DSC-7 at a heating rate of C, 87.64; H, 5.98; N, 6.39. Found: 87.46; H, 5.78; N, 6.76.
10 °C min−1
.
4,5-Bis(mesitylimino)pyrenylidene (L2). Using the same pro-
cedure as for the synthesis of L1, L2 (0.57 g) was obtained as a
deep red crystalline solid. Yield: 24.26%. Mp: 180–181 °C.
FT-IR (KBr, cm−1): 3053 (w), 2902 (m), 1634 (s, CvN), 1601 (s),
Syntheses and characterization
4,5-Bis(2,6-dimethylphenylimino)pyrenylidene (L1). To
a
mixture of 2,6-dimethylaniline (15.00 mmol, 1.81 g) and tri- 1471 (m), 1272 (m), 1216 (m), 828 (vs), 713 (vs). 1H NMR
(400 MHz, CDCl3, TMS): δ 8.36 (d, J = 7.6 Hz, 1H, Pyrene H),
ethylamine (45.00 mmol, 4.54 g) in toluene (50 ml) was added
dropwise 1.6 ml of the 9.0 M solution of TiCl4 in toluene over 8.07 (d, J = 7.6 Hz, 1H, Pyrene H), 7.86–7.75 (m, 4H, Pyrene H),
10 min at 90 °C, followed by addition of a suspension of 7.22 (d, J = 7.6 Hz, 1H, Pyrene H), 7.06 (d, J = 7.6 Hz, 1H,
Pyrene H), 6.82 (s, 2H, Ph H), 6.65 (s, 2H, Ph H), 2.28 (s, 3H,
pyrene-4,5-dione (5.00 mmol, 1.18 g) in 15 ml of toluene. The
reaction mixture was heated to reflux for 30 min, and the pre- Ph–CH3), 2.21 (s, 3H, Ph–CH3), 2.06 (s, 6H, Ph–CH3), 1.28
cipitate was removed by hot filtration. The filtrate was evapor- (s, 6H, Ph–CH3). 13C NMR (100 MHz, CDCl3, TMS): δ 159.71,
157.66, 147.11, 145.72, 133.31, 132.27, 131.86, 131.60, 131.46,
ated in vacuo. Finally, 0.47 g of deep red crystalline solid was
isolated by silica gel column chromatography (petroleum 130.83, 128.77, 128.29, 128.07, 127.81, 127.67, 127.42, 127.21,
ether–dichloromethane = 5 : 1, v/v) and re-crystallization in petro- 126.76, 126.31, 125.26, 124.94, 124.20, 20.85, 20.79, 18.56,
leum ether. Yield: 21%. Mp: 181–182 °C. FT-IR (KBr, cm−1):
17.21. Anal. Calcd for C34H30N2: C, 87.52; H, 6.48; N, 6.00.
3056 (m), 2940 (m), 1637 (s, CvN), 1593 (s), 1461 (s), 1236 (m), Found: C, 87.24; H, 6.92; N, 5.64.
9172 | Dalton Trans., 2013, 42, 9166–9175
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4,5-Bis(2,6-diethylphenylimino)pyrenylidene (L3). Using the 1464 (m), 1416 (m), 1353 (m), 1299 (s), 1096 (m), 834 (s),
same procedure as for the synthesis of L1, L3 (0.33 g) was 761 (s), 704 (vs). Anal. Calcd for C32H30Br2N2Ni: C, 58.14;
obtained as a deep red crystalline solid. Yield: 12.55%. Mp: H, 4.57 N, 4.24. Found: C, 58.26; H, 4.55; N, 4.23.
178–180 °C. FT-IR (KBr, cm−1): 2964 (s), 2929 (s), 2866 (m),
Data for C3 (brown powder, 74.18% yield) are as follows.
1639 (s, CvN), 1604 (s), 1454 (vs), 1203 (s), 855 (s), 627 (vs), FT-IR (KBr, cm−1): 2962 (m), 2929 (m), 2873 (m), 1621
712 (vs). 1H NMR (400 MHz, CDCl3, TMS): δ 8.64 (d, J = 7.6 Hz, (s, CvN), 1601 (m), 1513 (m), 1452 (s), 1350 (s), 1305 (vs),
1H, Pyrene H), 8.08 (d, J = 7.6 Hz, 1H, Pyrene H), 7.78–7.75 1203 (m), 852 (vs), 837 (vs), 711 (vs). Anal. Calcd for
(m, 4H, Pyrene H), 7.21 (t, J = 7.6 Hz, 1H, Pyrene H), 7.04 (d, J = C38H42Br2N2Ni: C, 61.24; H, 5.68; N, 3.76. Found: C, 61.08;
7.6 Hz, 1H, Pyrene H), 6.89 (s, 2H, Ph H), 6.72 (s, 2H, Ph H), H, 5.28; N, 3.76.
2.54–2.47 (m, 2H, Ph–CH2–), 2.41–2.32 (m, 5H, Ph–CH2–, Ph–
Data for C4 (brown powder, 38.82% yield) are as follows.
CH3), 2.26 (s, 3H, Ph–CH3), 1.60–1.46 (m, 4H, Ph–CH2–), 1.13 FT-IR (KBr, cm−1): 2955 (w), 2931 (m), 2866 (m), 1619
(t, J = 7.2 Hz, 6H, Ph–CH3), 0.743 (t, J = 7.6 Hz, 6H, Ph–CH3). (s, CvN), 1600 (m), 1463 (m), 1421 (m), 1278 (s), 1198 (m), 829
13C NMR (100 MHz, CDCl3, TMS): δ 159.05, 157.70, 146.08, (s), 761 (vs), 713 (vs). Anal. Calcd for C32H26Cl2N2Ni: C, 67.65;
144.77, 133.35, 132.45, 131.55, 130.70, 130.45, 130.39, 129.69, H, 4.61; N, 4.93. Found: C, 67.46; H, 4.69; N, 4.81.
128.13, 127.77, 127.59, 127.17, 127.12, 126.76, 126.37, 126.16,
Data for C5 (brown powder, 25.53% yield) are as follows.
125.93, 125.42, 24.97, 23.36, 21.21, 13.41, 13.35. Anal. Calcd FT-IR (KBr, cm−1): 2966 (w), 2929 (m), 2870 (m), 1623
for C38H38N2: C, 87.21; H, 7.33; N, 5.36. Found: C, 86.92; (s, CvN), 1604 (m), 1472 (m), 1274 (m), 1206 (m), 824 (s), 811
H, 7.41; N, 5.42.
(vs), 712 (s). Anal. Calcd for C34H30Cl2N2Ni: C, 68.49; H, 5.07;
4,5-Bis(2,6-diethyl-4-methylphenylimino)pyrenylidene N, 4.70. Found: C, 68.52; H, 5.02; N, 4.76.
(L4). Using the same procedure as for the synthesis of L1, L4
(0.23 g) was obtained as a deep red crystalline solid. Yield:
9.24%. Mp: 172–174 °C. FT-IR (KBr, cm−1): 3055 (w), 2965 (m),
1641 (s, CvN), 1507 (m), 1439 (m), 1339 (m), 1190 (m),
Procedure for ethylene polymerization
1056 (m), 900 (m), 831 (vs), 752 (vs), 7159 (vs). 1H NMR Ethylene polymerization was conducted in a stainless steel
(400 MHz, CDCl3, TMS): δ 8.63 (d, J = 6.8 Hz, 1H, Pyrene H), autoclave (0.25 L capacity) equipped with a mechanical stirrer
8.09 (d, J = 8 Hz, 1H, Pyrene H), 7.87–7.76 (m, 4H, Pyrene H), and a temperature controller. Then, 100 ml of toluene contain-
7.18 (t, J = 7.6 Hz, 1H, Pyrene H), 7.08–6.98 (m, 4H, Pyrene H, ing the catalyst precursor was transferred to the fully dried
Ph H), 6.90 (m, 3H, Ph H), 2.56–2.50 (m, 2H, Ph–CH2–), reactor under nitrogen atmosphere. The required amount of
2.41–2.36 (m, 2H, Ph–CH2–), 1.61–1.45 (m, 4H, Ph–CH2–), 1.13 co-catalyst was then injected into the reactor via a syringe. At
(t, J = 7.2 Hz, 6H, Ph–CH3), 0.84 (t, J = 6.3 Hz, 6H, Ph–CH3). the required reaction temperature, the reactor was immediately
13C NMR (100 MHz, CDCl3, TMS): δ 158.63, 157.60, 148.51, pressurized to high ethylene pressure, and the ethylene
147.23, 133.16, 131.85, 131.62, 130.88, 130.63, 130.48, 129.86, pressure was kept constant with feeding of ethylene. After the
127.96, 127.85, 127.61, 127.27, 127.20, 126.84, 126.19, 125.66, reaction mixture was stirred for the desired period, the
125.17, 123.34, 122.69, 24.99, 23.39, 13.33, 13.27. Anal. Calcd pressure was released and the mixture was cooled to room
for C36H34N2: C, 87.41; H, 6.93; N, 5.66. Found: C, 87.44; temperature. Following this, the residual reaction solution was
H, 6.92; N, 5.64.
quenched with 30% hydrochloride acid ethanol, and then the
precipitated polymer was collected by filtration, and was ade-
quately washed with ethanol, and was dried in a vacuum until
Synthesis of nickel complexes (C1–C5)
The complexes (C1–C5) were prepared by the reaction of of constant weight.
(DME)NiBr2 and (DME)NiCl2 with the corresponding ligands
(L1–L3) in dichloromethane (L1/L2 afforded the bromides C1/
C2 or the chlorides C4/C5; L3 afforded the bromide C3).
X-Ray crystallographic studies
A typical synthetic procedure for C2 can be described as
follows: the ligand L2 (0.40 mmol, 0.20 g) and (DME)NiBr2 Single crystals of L2, L3, C1 and C2 suitable for X-ray diffrac-
(0.40 mmol, 0.12 g) were added to a flame-dried Schlenk flask tion analysis were obtained by layering diethyl ether on their
tube, then 20 ml dichloromethane was subsequently added dichloromethane solutions at room temperature. With graph-
with rapid stirring at room temperature for 24 h. The solvent ite-monochromatic Mo-Kα radiation (λ = 0.71073 Å) at 173(2)
was removed in vacuo and the residual solid was washed with K, the cell parameters were obtained by global refinement of
Et2O several times. Finally, C2 was isolated as a brown powder the positions of all collected reflections. Intensities were cor-
(0.20 g, 66.78%). FT-IR (KBr, cm−1): 2910 (w), 2853 (w), 1622 rected for Lorentz and polarization effects and empirical
(s, CvN), 1605 (m), 1498 (m), 1466 (m), 1351 (m), 1297 (s), absorption. The structures were solved by direct methods and
1205 (m), 1026 (m), 831 (vs), 707 (vs). Anal. Calcd for refined by full-matrix least-squares on F2. All hydrogen atoms
C34H34Br2N2Ni: C, 59.17; H, 4.97; N, 4.06. Found: C, 59.29; were placed in calculated positions. Structure solution and
H, 4.86; N, 4.15.
refinement were performed by using the SHELXL-97
Data for C1 (brown powder, 71.16% yield) are as follows. package.20 Details of the X-ray structure determinations and
FT-IR (KBr, cm−1): 2969 (w), 2858 (w), 1623 (s, CvN), 1602 (m), refinements are provided in Table 6.
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Acknowledgements
This work is supported by NSFC no. 20904059 as well as the
MOST 863 program no. 2009AA034601. The RSC and EPSRC
are thanked for the awarded of travel grant (to CR).
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