Synthesis, characterization and ethylene polymerization behaviour of binuclear nickel halides bearing 4,5,9,10-tetra(arylimino)pyrenylidenes

Article abstract of DOI:10.1039/c4dt00503a

Pyrene-4,5,9,10-tetraone was prepared via the oxidation of pyrene, and reacted with various anilines to afford a series of 4,5,9,10-tetra(arylimino) pyrenylidene derivatives (L1-L4). The tetraimino-pyrene compounds L1 and L2 were reacted with two equivalents of (DME)NiBr₂ in CH₂Cl ₂ to afford the corresponding dinickel bromide complexes (Ni1 and Ni2). The organic compounds were fully characterized, whilst the bi-metallic complexes were characterized by FT-IR spectra and elemental analysis. The molecular structures of representative organic and nickel compounds were confirmed by single-crystal X-ray diffraction studies. These nickel complexes exhibited high activities towards ethylene polymerization in the presence of either MAO or Me₂AlCl, maintaining a high activity over a prolonged period (longer than previously reported dinickel complex pre-catalysts). The polyethylene obtained was characterized by GPC, DSC and FT-IR spectroscopy and was found to possess branched features. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt00503a

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PAPER
Synthesis, characterization and ethylene
polymerization behaviour of binuclear nickel
halides bearing 4,5,9,10-tetra(arylimino)-
pyrenylidenes†
Cite this: Dalton Trans., 2014, 43,
7830
Qifeng Xing,a Kuifeng Song,a,b Tongling Liang,a Qingbin Liu,b Wen-Hua Sun*a and
Carl Redshaw*c
Pyrene-4,5,9,10-tetraone was prepared via the oxidation of pyrene, and reacted with various anilines to
afford a series of 4,5,9,10-tetra(arylimino)pyrenylidene derivatives (L1–L4). The tetraimino-pyrene com-
pounds L1 and L2 were reacted with two equivalents of (DME)NiBr2 in CH2Cl2 to afford the corresponding
dinickel bromide complexes (Ni1 and Ni2). The organic compounds were fully characterized, whilst the
bi-metallic complexes were characterized by FT-IR spectra and elemental analysis. The molecular struc-
tures of representative organic and nickel compounds were confirmed by single-crystal X-ray diffraction
studies. These nickel complexes exhibited high activities towards ethylene polymerization in the presence
of either MAO or Me2AlCl, maintaining a high activity over a prolonged period (longer than previously
reported dinickel complex pre-catalysts). The polyethylene obtained was characterized by GPC, DSC and
FT-IR spectroscopy and was found to possess branched features.
Received 17th February 2014,
Accepted 28th March 2014
DOI: 10.1039/c4dt00503a
www.rsc.org/dalton
A,8a B8b and C8c (Scheme 1) provided two active sites and per-
formed with different catalytic behaviour to their mono-ana-
Introduction
Inspired by the bulky α-diimino nickel/palladium complex pre- logs.1a,8d In comparison to the good ethylene polymerization
catalysts reported by the Brookhart group,1 the use of nickel achieved by mono-nickel pre-catalysts,8d the methyl-bridged
complex pre-catalysts in ethylene poly-/oligo-merization has
been extensively investigated through the modification of the
ligands used2 and alternative models of the nickel complexes
have been reported.3 High activity and enhanced thermo-stabi-
lity for nickel pre-catalysts has been pursued and a number of
successful examples such as the ortho-difurylaryl4 and bulky
unsymmetrical α-diiminonickel complexes have been
isolated.5
Binuclear metal complexes have been explored in catalysis
with the potential of synergistic effects,6 and have also been
considered in ethylene poly-/oligo-merization.7 A number of
dinickel complex pre-catalysts have been employed in olefin
polymerization,8,9 for example, the bridged dinickel complexes
aKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing
100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
bInstitute of Chemistry and Chemical Engineering, Hebei Normal University,
Shijiazhuang 050091, China
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 986062 and 986063 for L1 and Ni2. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c4dt00503a
Scheme 1 Representative nickel complex pre-catalysts.
7830 | Dalton Trans., 2014, 43, 7830–7837
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dinickel complexes A appeared to act with two active sites pro-
ducing both polyethylenes and oligomers,8a meanwhile
phenyl-bridged B polymerized ethylene with relative lower acti-
vities.8b The dinickel complexes C8c exhibited higher activities
than their ‘mono’ analogs,1a whilst D, containing a rigid back-
bone,9 revealed twice the activities of their ‘mono’ analogs.1a
On the basis of the oxidation of pyrene, we achieve the prepa-
ration of pyrene-4,5-dione10 and pyrene-4,5,9,10-tetraone. The
mono-nickel complexes ligated by 4,5-diiminopyrenylidenes
were found to be highly active pre-catalysts in ethylene
polymerization and produced highly branched polyethylenes.10
Subsequently, herein the 4,5,9,10-tetra(arylimino)pyrenylidene
derivatives (L1–L4) are prepared and were reacted with (DME)
NiBr2 in CH2Cl2. In two cases, dinickel complexes (Ni1 and
Ni2) were successfully isolated. The obtained nickel complexes
exhibited high activity for ethylene polymerization, and more
importantly were capable of maintaining the activities over a
prolonged reaction period. The synthesis and characterization
of the tetraiminopyrenylidenes and their nickel complexes are
reported in detail, as well as the ethylene polymerization be-
haviour of these nickel complex pre-catalysts.
Scheme 2 Synthesis procedures.
Results and discussion
Synthesis and characterization of 4,5,9,10-tetra(arylimino)-
pyrenylidenes and their nickel complexes
The precursor pyrene was oxidized to pyrene-4,5,9,10-tetraone
using a mixture of ruthenium(III) chloride, sodium periodate,
dichloromethane, acetonitrile and water using a modification
of the literature procedure.11 It was found that subsequent
condensation of pyrene-4,5,9,10-tetraone with anilines had
limited synthetic use, and only the four 4,5,9,10-tetra(aryli-
mino)pyrenylidene derivatives (L1–L4)10 were successfully iso-
lated, i.e. less bulky substituents were necessary. For example,
prolonged reaction with excessive molar ratios of 2,6-diisopro-
pylaniline was unsuccessful. The reaction of all compounds
L1–L4 using (DME)NiBr2 was, in our hands, limited to the
compounds L1 and L2, which afforded the nickel complexes
Ni1 and Ni2 (Scheme 2). All of the organic compounds and the
complexes were fully characterized by elemental analysis and
FT-IR spectroscopy as well as by 1H and 13C NMR measure-
ments for the organic compounds. Moreover, the structures of
the representative compounds L1 and Ni2 were confirmed by
single-crystal X-ray diffraction.
Fig. 1 ORTEP drawing of L1. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
X-ray crystallography
Single crystals of L1 and Ni2 suitable for single-crystal X-ray
crystallographic analysis were individually obtained by layering
diethyl ether onto their dichloromethane solutions at room
temperature. The molecular structures of L1 and Ni2 are
shown in Fig. 1 and 2 and selected bond lengths and bond
angles are tabulated in Table 1. There is a free dichloromethane
molecule in the single crystal of Ni2, when drawing in ORTEP,
it is neglected. Considering the double bonds within the
4,5,9,10-tetra(arylimino)pyrenylidene derivatives, though the
Fig. 2 ORTEP drawing of Ni2. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
conjugated phenyl rings have been linked through imino-
double bonds, the total 2n double-bonds result in non-conju-
gation and non-planarity of the 4,5,9,10-tetraylidenylpyrenes.
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Table 1 The selected bond lengths (Å) and angles (°) for L1 and Ni2
Table 2 Ethylene polymerization with MAOa
L1
Ni2
Temp
(°C)
Brs.e/
1000C
Act.b
Mw
Mw c/Mn
Tmd/°C
c
Entry
Al/Ni
Bond lengths (Å)
N(1)–C(1)
N(2)–C(2)
1.300(5)
1.269(5)
1.244(5)
1.283(5)
1.435(5)
1.429(5)
1.418(5)
1.412(5)
1.312(15)
1.300(14)
1.284(16)
1.257(15)
1.433(14)
1.451(17)
1.472(16)
1.449(16)
1.970(9)
1
2
3
4
5
6
7
8
9f
200
300
400
500
600
500
500
500
500
500
500
500
500
30
30
30
30
30
20
40
50
30
30
30
30
30
0.55
0.85
1.16
1.50
0.42
0.62
1.01
0.07
1.20
1.30
1.30
0.65
1.26
2.6
2.4
2.3
2.3
4.4
2.3
2.2
1.5
2.1
2.3
2.4
2.2
4.9
3.8
3.7
2.9
2.2
2.9
4.0
3.2
3.1
2.0
2.4
4.2
4.7
3.0
131.6
131.9
132.4
131.4
130.3
133.9
125.0
126.5
134.5
129.7
129.4
130.2
129.4
11
8
8
9
10
8
11
12
7
8
10
9
N(3)–C(12)
N(4)–C(11)
N(1)–C(17)
N(2)–C(23)
N(3)–C(29)
N(4)–C(35)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–Br(1)
Ni(1)–Br(2)
Ni(2)–N(3)
Ni(2)–N(4)
Ni(2)–Br(4)
Ni(2)–Br(3)
2.003(11) 10g
2.323(2)
2.355(2)
11h
12
1.999(11) 13i
1.981(10)
14
a General conditions: 2 μmol Ni1; 100 mL toluene with 10 atm ethylene
for entries 1–11 and 13 and 5 atm for entry 12; 30 min. b 106 g (PE)
2.342(2)
2.355(3)
mol−1 (Ni) h−1 c Determined by GPC, 105 g mol−1 d Determined by
. .
DSC. e Determined by FT-IR. f 15 min. g 45 min. h 60 min. i Ni2.
Bond angles (°)
C(1)–N(1)–C(17)
C(2)–N(2)–C(23)
C(12)–N(3)–C(29)
C(11)–N(4)–C(35)
Br(1)–Ni(1)–Br(2)
Br(4)–Ni(2)–Br(3)
N(4)–Ni(2)–Br(4)
C(29)–N(3)–Ni(2)
C(11)–N(4)–Ni(2)
120.3(3)
126.3(3)
123.0(3)
122.9(3)
122.9(9)
124.4(11)
125.5(11)
123.6(10)
118.64(9)
122.52(9)
114.9(3)
119.9(9)
116.2(8)
ture barely has any effect on the activity, presumably because
the ‘steric clash’ is the same regardless of the addition of the
other metal center. On changing the Al/Ni molar ratio, the best
activity, namely 1.5 × 106 g (PE) mol−1 (Ni) h−1 was observed
for Al/Ni at 500, i.e. less co-catalyst was required than for the
mono-nuclear catalysts.10 Regarding the stability of the
complex pre-catalysts, the lifetime studies indicated that the
Such a feature is consistent with the observed classical single activity increased slightly on prolonging the time from 15 to
and double C–N bonds to every nitrogen atoms in Table 1. In 30 min (entries 4, 9, Table 2), which indicated a period of
addition, both molecular structures (L1 and Ni2) do not show induction. After this time, the activity does not decrease, but
any symmetry, and their corresponding bond lengths and was maintained for over 60 min (entries 10–11, Table 2). The
angles are comparably similar. The CvN bond lengths of long lifetime of the pre-catalyst may be attributed to the pres-
organic compound L1 are slightly shorter than those within ence of two metal centers in the complex, indicating that at
the nickel complex Ni2, indicating the effective coordination least one of them is active in the catalytic system. The mole-
of the nickel ions with all nitrogen atoms; the electronic cular weight and the polydispersity of the polymers decreased
donation from nitrogen to nickel ions causes weaker CvN slightly as the temperature increased, and similarly as the
bonds as well as corresponding C–N bonds.
Al/Ni ratio increased (shown in Fig. 3 and 4), which are consist-
The 4,5,9,10-tetra(arylimino) pyrenylidene derivatives ent with the previous conclusion12 that high temperature and
provide tetradentate ligands to coordinate with two nickel high molar ratios of Al/Ni enhance chain transfer from the
ions, resembling two classical α-diiminonickel species. In com- nickel species to aluminium, thereby resulting in lower mole-
parison to its mono-analogs10 and also rigid backbone dinickel cular weight polymers.
complexes D,9 the current organic compound L1 and nickel
Using Me2AlCl as co-catalyst, the polymerization reaction
complex Ni2 exhibit similar geometrical data at the nitrogen parameters, including Al/Ni molar ratio, reaction time and
and nickel atoms.
Ethylene polymerization
According to our previous work,10 co-catalysts such as methyl-
aluminoxane (MAO) or dimethylaluminium chloride (Me2AlCl)
are commonly employed with nickel complex pre-catalysts;
therefore, Ni1 was used to optimize the catalytic parameters
with methylaluminoxane (MAO) or dimethyl(or diethyl)-
aluminium chloride (Me2AlCl/Et2AlCl) as co-catalyst.
When the nickel pre-catalysts were activated with MAO, the
activity reached a maximum at 30 °C, and then fell as the
temperature increased to 40 and 50 °C. Comparison with the
analogous mono-nuclear complex,10 reveals that the tempera- different temperatures (entries 4, 6–8, Table 2).
Fig. 3 The GPC curves of polyethylenes obtained by Ni1 with MAO at
7832 | Dalton Trans., 2014, 43, 7830–7837
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active nickel species were probably stabilized with more co-cat-
alysts. So chain propagations generally surpassed both chain
migrations and hydrogen-elimination, therefore, the obtained
polyethylenes showed higher molecular weights as well as low
branches. According to the entries 3 and 5–7 in Table 3, the
optimum reaction temperature in the present study was found
to be 30 °C; higher or lower temperatures led to a slight
decrease of the catalytic activity, similar to the previously
observed situation for reported α-diimine catalyst systems.13
The temperature effect on the activity is more sensitive here
than for the mono-nuclear catalyst,10 which may relate to the
quick responses of the two metal centers. In addition, when
elevating the temperature from 20 to 50 °C, a remarkable
decrease in the polymer molecular weight was observed
(Fig. 6).
Fig. 4 The GPC curves of polyethylenes obtained by Ni1 with MAO at
different Al/Ni ratio (entries 1–5, Table 2).
temperature, 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 200 to 600, the catalytic
activity first increased and then decreased; the best activity
was observed with the Al/Ni molar ratio at 400/1. The increase
of the Al/Ni molar ratio led to polyethylene of higher molecular
weight (Fig. 5), which was not consistent of polyethylenes
obtained with lower molecular weights at higher molar ratio of
Al/Ni caused by the chain transfer from nickel species to
aluminium.12 This may be due to the large steric clash, the
From the high temperature 13C NMR spectrum of the poly-
ethylene (entry 1 in Table 3) in Fig. 7, there are some branches
of polyethylenes, also indicated by the results of the FT-IR
spectra. In general, these obtained polyethylenes revealed less
branches than those by the mono-analogs10 and other dinickel
pre-catalysts;8,9 it is thought that the current ligands possibly
protect the active sites thereby reducing hydrogen elimination.
Lifetime studies indicated that higher activities were observed
over shorter reaction time, the activities decreased on prolong-
ing the period of polymerization (entries 8–10 in Table 3). This
suggested that there was a rather short induction period, and
Table 3 Ethylene polymerization with Me2AlCla
Temp
(°C)
Brs.e/
1000C
Act.b
Mw
Mw c/Mn
Tmd/°C
c
Entry
Al/Ni
1
2
3
4
5
6
7
300
400
500
600
400
400
400
400
400
400
400
400
30
30
30
30
20
40
50
30
30
30
30
30
2.00
2.25
1.45
0.65
1.65
1.35
0.25
4.20
1.60
1.25
2.05
0.50
1.32
1.41
1.47
1.59
1.55
0.79
0.60
1.21
1.44
1.75
1.62
1.17
2.84
3.24
3.53
4.58
4.30
3.10
3.00
2.91
3.70
4.47
3.00
3.46
123.9
122.3
124.5
126.7
122.3
121.1
108.6
119.7
121.2
123.3
122.2
120.6
13
12
10
11
8
12
13
7
8f
9g
10h
11
12i
8
10
12
10
a General conditions: 2 μmol Ni1; 100 mL toluene with 10 atm ethylene Fig. 6 The GPC curves of polyethylenes obtained at different tempera-
for entries 1–10 and 12 and 5 atm for entry 11. b 106 g (PE) mol−1 (Ni)
tures (entries 2, 5–7, Table 3).
h−1
. g .
c Determined by GPC, 105 mol−1 d Determined by DSC.
e Determined by FT-IR. f 15 min. g 45 min. h 60 min. i Ni2.
Fig. 5 The GPC curves of polyethylenes obtained at different Al/Ni ratio
(entries 1–4, Table 3).
Fig. 7 The 13C NMR spectra of the polyethylene (entry 1 in Table 3).
Dalton Trans., 2014, 43, 7830–7837 | 7833
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this is beneficial to the chain transfer cf. 10 atm; contrastingly,
the use of 10 atm is beneficial to chain growth.
Conclusion
The newly synthesized 4,5,9,10-tetra(arylimino)pyrenylidenes
were successfully complexed with nickel halide. The resulting
nickel complex pre-catalysts showed high activities for ethylene
polymerization with various co-catalysts, such as Me2AlCl 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 polyethy-
lene. Comparison with the analogous mono-nuclear complexes
revealed that although there was no significant improvement
in activity for the binuclear nickel complexes, there was a sig-
nificant increase in the lifetime when activated with MAO. The
polyethylene products were found to be moderately branched
when the activators MAO, Me2AlCl or Et2AlCl were employed
herein.
Fig. 8 The GPC curves of polyethylenes obtained over different times
(entry 2, 8–10, Table 3).
that the active species did not live as long as that formed on
activation with MAO. Moreover, both the Mw and Mw/Mn values
of the obtained PEs increased slightly on extending the reac-
tion time; the Mw changes are shown by GPC (Fig. 8). Given
that the optimum conditions for the Ni1/Me2AlCl system were
found to be an Al/Ni ratio of 400 at 30 °C over 30 min (entry 2,
Table 3), further investigations using the other pre-catalyst Ni2
was conducted under such conditions (entry 12, Table 3). As
shown in entries 2 and 12 of Table 3, results reveal the activity
order Ni1 > Ni2, which may result from electron donation or
increased solubility. As illustrated by the above structural fea-
tures for Ni1, efficient coordination to the nickel center in Ni1
can stabilize the active species and thereby result in better
activity, which is consistent with previous observations.14
Ni1 was also screened for ethylene polymerization under
1 atm pressure. The co-catalysts MAO and Et2AlCl were chosen,
and it was found that Et2AlCl performed better than MAO
(entries 1 and 2, Table 4). Parameters such as temperature and
the Al/Ni ratio were varied. The activity decreased as the molar
ratio of Al/Ni increased, and as the temperature increased, the
activity decreased dramatically indicating here that the activity
is much more sensitive to the temperature. The molecular
weight of the polymers obtained at 1 atm also decreased as the
temperature increased, as observed for the polymers at 10 atm.
The degree of branching was greater at 1 atm, suggesting that
Experimental
General considerations
All manipulations of air and/or moisture sensitive compounds
were carried out under a nitrogen atmosphere using standard
Schlenk techniques. Toluene was refluxed over sodium-benzo-
phenone and distilled under nitrogen prior to use. Methyl-
aluminoxane (MAO, 1.46
M
solution in toluene),
dimethylaluminium chloride (Me2AlCl, 1.0 M solution in
toluene) and diethylaluminium chloride (Et2AlCl, 1.0 M in
heptane) were purchased from Akzo Nobel Corp. High-purity
ethylene was purchased from Beijing Yansan Petrochemical
Co. and used as received. Other reagents were purchased from
Aldrich, Acros, or local suppliers. NMR spectra were recorded
on Bruker DMX 400 MHz instrument at ambient temperature
using TMS as an internal standard. FT-IR spectra were
recorded on a Perkin-Elmer System 2000 FT-IR spectrometer.
Elemental analysis was carried out using an HPMOD
1106 microanalyzer. MALDI-TOF spectra were detected on
autoflex III Bruker, using CCA as the substrate. Molecular
weights (Mw) and molecular weight distribution (Mw/Mn) of
polyethylenes were determined by a PL-GPC220 at 150 °C with
three PLgel 10 µm MIXED-B columns, with 1,2,4-trichloro-
benzene as the solvent. Melting points of polyethylenes were
obtained from the second scanning run on Q2000 DSC-7 at a
heating rate of 10 °C per minute to 150 °C; branches of the
polymers were tested and calculated by FT-IR spectra.
Table 4 Ethylene polymerization by Ni1 under 1 atma
Temp
Entry Al/Ni (°C)
Brs./
Activityb Mw
Mw c/Mn Tmd/°C 1000Ce
c
1
2
3
4
5
6
7
8
1000 20
2.5
15
12
9.0
7.5
12.5
4.0
10.7 3.6
7.7 4.9
3.0 2.8
3.3 2.9
5.2 3.5
5.9 4.4
2.1 2.5
1.7 2.3
121.5
117.7
114.3
113.9
113.4
79.5
22
27
24
41
52
30
45
53
200 20
400 20
600 20
800 20
200 30
200 40
200 50
Pyrene-4,5,9,10-tetraone
55.1
54.9
Pyrene was used as the starting material for synthesizing the
pyrene-4,5,9,10-tetraone. To a solution of 20.2 g pyrene
(0.1 mol) in CH2Cl2 (400 mL) and CH3CN (400 mL) were added
water (1000 mL), 175 g (0.8 mol) sodium periodate and 2.5 g
(12 mmol) RuCl3. The dark brown suspension was heated at
1.0
a General conditions: 2 μmol Ni1; Et2AlCl as co-catalyst for entries 2–8,
MAO as co-catalyst for entry 1; 30 mL toluene; 30 min. b 104 g (PE)
mol−1 (Ni) h−1 c Determined by GPC, 104 g mol−1 d Determined by
. .
DSC. e Determined by FT-IR.
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30–40 °C overnight. The next day, 3.5 L water was added to the was added to the mixture, and the solution darkened. The
mixture with intensive mixing and the aqueous phase was reaction was stirred for 30 min, then the mixture was separated
extracted by 2 L CH2Cl2 for 5 times, then the organic phase by column chromatography and 1.62 g red solid was collected,
1
was combined together and washed by saturated NaCl solu- yield 41.5%. H NMR (400 MHz, CDCl3, ppm): 8.36 (d, J = 8.0
tion, the CH2Cl2 solution was condensed, which resulted in Hz, 2H, Ph-H), 7.11–7.04 (m, 10H, Ph-H), 6.96–6.83 (m, 6H, Ph-
1
4.45 g of a dark yellow solid, yield 17.0%. H NMR (400 MHz, H), 2.52–2.46 (m, 4H, 2 × CH2), 2.39–2.34 (m, 4H, 2 × CH2),
CDCl3, ppm): 8.52 (d, J = 7.6 Hz, 2H, Ph-H), 7.72 (t, J = 7.6, 1H, 1.69–1.62 (m, 8H, 4 × CH2), 0.87 (t, J = 7.6 Hz, 12H, 4 × CH3),
Ph-H). 13C NMR (100 MHz, CDCl3, ppm): 180.5, 138.9, 136.5, 0.73 (t, J = 7.6 Hz, 12H, 4 × CH3). 13C NMR (100 MHz, CDCl3,
131.2, 128.3. FT-IR (KBr, cm−1): 3066 (m), 2164 (m), 1668 ppm): 157.2, 156.6, 147.7, 146.3, 133.2, 131.2, 130.8, 130.7,
(νCvO, s), 1553 (m), 1416 (m), 1332 (w), 1271 (m), 1168 (m), 130.5, 130.2, 130.1, 129.4, 128.5, 125.9, 125.4, 125.2, 124.0,
1050 (m), 903 (s), 803 (m), 706 (s).
123.2, 24.8, 23.5, 13.5, 13.4. FT-IR (cm−1): 2908 (m), 1686 (w),
1641 (νCvN, m), 1614 (s), 1440 (s), 1371 (w), 1320 (m),
1288 (m), 1194 (m), 1080 (m), 848 (s), 801 (m), 709 (s). Anal.
4,5,9,10-Tetra(2,6-dimethylphenylimino)pyrenylidene (L1)
3.60 g (30 mmol) 2,6-dimethylaniline and 9.08 g (90 mmol) Calcd for C56H58N4 (787): C, 85.45; H, 7.43; N, 7.12. Found: C,
Et3N was dissolved in 100 mL toluene and heated to 90 °C, 85.66; H, 7.21; N, 7.32.
then 3.2 mL TiCl4 was added into the solution, some white fog
4,5,9,10-Tetra(2,6-diethyl-4-methyl-phenylimino)pyrenylidene
(L4)
appeared and then 1.33 g (5 mmol) pyrene-4,5,9,10-tetraone
was added to the mixture, and the solution darkened. The
reaction was stirred for 30 min, then the mixture was separated 4.89 g (30 mmol) 2,6-diethyl-4-methylaniline and 9.08 g
by column chromatography and 1.94 g red solid was collected, (90 mmol) Et3N was dissolved in 100 mL toluene and heated
yield 57%. 1H NMR (400 MHz, CDCl3, ppm): 8.37 (d, J = 8.0 to 90 °C, then 3.2 mL TiCl4 was added into the solution, some
Hz, 2H, Ph-H), 7.13 (t, J = 7.6, 2H, Ph-H), 7.02 (d, J = 7.6 Hz, white fog appeared and then 1.33 g (5 mmol) pyrene-4,5,9,10-
4H, Ph-H), 6.92 (t, J = 7.6, 2H, Ph-H), 6.82–6.86 (m, 8H, Ph-H), tetraone was added into the mixture, and the solution
2.09 (s, 12H,4 × CH3), 1.44 (s, 12H, 4 × CH3). 13C NMR darkened. The reaction was carried for 30 min, then the
(100 MHz, CDCl3, ppm): 130.4, 129.1, 128.5, 128.0, 127.7, mixture was separated by column chromatography and 1.73 g
123.6, 122.9, 18.5, 17.1. FT-IR (cm−1): 2938 (w), 1645 (νCvN
,
red solid was collected, yield 41.1%. 1H NMR (400 MHz,
m), 1619 (s), 1589 (m), 1464 (s), 1373 (w), 1320 (w), 1261 (m), CDCl3, ppm): 8.33 (d, J = 8.0 Hz, 2H, Ph-H), 7.10 (t, J = 8.0 Hz,
1199 (s), 1090 (m), 935.5 (m), 765 (s), 722 (s). Anal. Calcd for 2H, Ph-H), 6.89–6.84 (m, 8H, Ph-H), 6.74 (s, 6H, Ph-H),
C48H42N4 (673): C, 85.43; H, 6.27; N, 8.30. Found: C, 85.35; H, 2.48–2.42 (m, 4H, 2 × CH2), 2.36–2.25 (m, 10H, 5 × CH2), 2.34
6.50; N, 8.11. Ms (MALDI-TOF, m/z): 674.34. Found: 674.4.
(s, 6H, 2 × CH3), 2.23 (s, 6H, 2 × CH3), 1.13 (t, J = 7.6 Hz, 12H, 4
× CH3), 0.84 (t, J = 7.6 Hz, 12H, 4 × CH3). 13C NMR (100 MHz,
CDCl3, ppm): 157.7, 156.7, 145.2, 143.9, 133.2, 132.1, 130.8,
4,5,9,10-Tetra(mesitylimino)pyrenylidene (L2)
4.00 g (30 mmol) mesitylamine and 9.08 g (90 mmol) Et3N was 130.5, 130.1, 130.0, 129.8, 129.2, 128.7, 128.4, 126.8, 126.6,
dissolved in 100 mL toluene and heated to 90 °C, then 3.2 mL 126.2, 126.0, 24.8, 23.5, 23.2, 21.2, 21.1, 13.4. FT-IR (cm−1):
TiCl4 was added into the solution, and some white fog 2966 (s), 1745 (w), 1615 (νCvN, s), 1453 (s), 1373 (w), 1321 (m),
appeared and then 1.33 g (5 mmol) pyrene-4,5,9,10-tetraone 1264 (m), 1207 (m), 1087 (m), 859 (s), 799 (m), 722 (s). Anal.
was added into the mixture, and the solution darkened. The Calcd for C60H66N4 (843): C, 85.47; H, 7.89; N, 6.64. Found: C,
reaction was stirred for 30 min, then the mixture was separated 85.57; H, 8.04; N, 6.46.
by column chromatography and 1.69 g red solid was collected,
Synthesis and characterization of binuclear nickel complexes
yield 45.6%. 1H NMR (400 MHz, CDCl3, ppm): 8.29 (d, J =
7.6 Hz, 2H, Ph-H), 7.12 (t, J = 7.6 Hz, 2H, Ph-H), 6.88 (t, J =
Ni1. A mixture of 0.67 g (1 mmol) 4,5,9,10-tetra(2,6-
7.6 Hz, 2H, Ph-H), 6.84 (s, 4H, Ph-H), 6.63 (s, 4H, Ph-H), 2.34 dimethylphenylimino)pyrenylidene (L1) and 0.60 g (2 mmol)
(s, 6H, 2 × CH3), 2.27 (s, 6H, 2 × CH3), 2.18 (s, 12H, 4 × CH3), (DME)NiBr2 in CH2Cl2 (5 mL) was stirred for 12 h at room
1.31 (s, 12H, 4 × CH3). 13C NMR (100 MHz, CDCl3, ppm): temperature. The precipitate was collected by filtration and
158.6, 157.3, 146.2, 144.8, 133.3, 133.0, 132.1, 131.2, 130.4, washed with diethyl ether (3 × 5 mL), then dried under
129.0, 128.7, 128.8, 128.5, 128.4, 125.1, 124.7, 20.8, 18.5, 17.0. vacuum to afford Ni1 as a brown solid (1.06 g, yield 96.3%).
FT-IR (cm−1): 2911 (m), 1738 (w), 1632 (νCvN, m), 1606 (s), FT-IR (cm−1): 3314 (s), 1608 (νCvN, m), 1463 (m), 1381 (w),
1472 (s), 1374 (w), 1319 (m), 1265 (m), 1211 (s), 1089 (m), 1338 (s), 1284 (s), 1164 (w), 1091 (w), 1033 (w), 764 (s), 703 (s).
937 (m), 788 (s), 721 (s). Anal. Calcd for C52H50N4 (730): C, Anal. Calcd for C48H42Br4N4Ni2 (1111): C, 51.85; H, 3.81; N,
85.44; H, 6.89; N, 7.66. Found: C, 85.42; H, 7.26; N, 7.42.
5.04. Found: C, 51.54; H, 3.67; N, 4.93.
Ni2. A mixture of 0.73 g (1 mmol) 4,5,9,10-tetra(mesityl-
imino)pyrenylidene (L2) and 0.60 g (2 mmol) (DME)NiBr2 in
4,5,9,10-Tetra(2,6-diethylphenylimino)pyrenylidene (L3)
4.47 g (30 mmol) 2,6-diethylaniline and 9.08 g (90 mmol) Et3N CH2Cl2 (5 mL) was stirred for 12 h at room temperature. The
was dissolved in 100 mL toluene and heated to 90 °C, then precipitate was collected by filtration and washed with diethyl
3.2 mL TiCl4 was added into the solution, some white fog ether (3 × 5 mL), then dried under vacuum to afford Ni2 as a
appeared and then 1.33 g (5 mmol) pyrene-4,5,9,10-tetraone brown solid (0.98 g, yield 83.9%). FT-IR (cm−1): 3328 (s),
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1608 (νCvN, m), 1456 (m), 1380 (w), 1337 (s), 1286 (s), 1194 (w), amount of co-catalyst (MAO, Me2AlCl or Et2AlCl) was added by
1111 (w), 1032 (w), 753 (m), 703 (s). Anal. Calcd for a syringe. After the reaction was carried out for the required
C52H50Br4N4Ni2 (1167): C, 53.47; H, 4.31; N, 4.80. Found: C, period, a small amount of the reaction solution was collected
53.42; H, 4.26; N, 4.42.
and terminated by the addition of 10% aqueous hydrogen
chloride immediately. The organic layer was analyzed by gas
chromatography (GC) for monitoring the oligomers formed;
the precipitated polymer was collected, washed with water and
ethanol, and finally dried.
X-ray crystallographic studies
Single crystals of ligand L1 and complex Ni2 suitable for X-ray
diffraction analysis were obtained by laying ethyl ether on
their respective dichloromethane solutions at room tempera-
ture. With graphite-monochromated Mo-Kα radiation (k =
0.71073 Å), single-crystal X-ray diffraction for ligand L1 and
complex Ni2 was performed on a Rigaku Saturn724+ CCD at
100(2) K. Intensities were corrected for Lorentz and polariz-
ation effects and empirical absorption. The structures were
solved by direct methods and refined by full-matrix least
squares on F2. All hydrogen atoms were placed in calculated
positions. Structure solution and refinement were performed
by using the SHELXTL-97 package.15 Crystal data is given in
Table 5 and refinement details are given in the ESI.†
Ethylene polymerization at elevated pressure (10 atm). A
300 mL stainless steel autoclave, equipped with a mechanical
stirrer and a temperature controller, was employed for the reac-
tion. Firstly, 50 mL toluene (freshly distilled) was injected to
the clave which is full of ethylene. When the temperature
required was reached, another 30 mL toluene which dissolved
the complex (2.0 mol of metal) before, the required amount of
co-catalyst (MAO or Me2AlCl), the residual toluene were added
by syringe successively. The reaction mixture was intensively
stirred for the desired time under corresponding pressure of
ethylene through the entire experiment. The reaction was ter-
minated and analyzed using the same procedure as above for
ethylene polymerization.
General procedure for ethylene polymerization
Ethylene polymerization at ambient pressure. The pre-cata-
lyst was dissolved in toluene using standard Schlenk tech-
niques, and the reaction solution was stirred with a magnetic
stir bar under ethylene atmosphere (1 atm) with a steam bath
for controlling the desired temperature. Finally, the required
Acknowledgements
This work is supported by NSFC no. 21374123 and U1362204.
The EPSRC is thanked for the awarded of a travel grant (to
CR).
Table 5 Crystal data and structure refinement details for L1 and Ni2
L1
Ni2
Notes and references
Crystal color
Red
Black
Empirical formula
FW
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C48H46N4
678.89
100(2)
0.71073
Monoclinic
C53H52N4Br4Ni2Cl2
1252.95
100(2)
1 (a) L. K. Johnson, C. M. Killian and M. Brookhart, J. Am.
Chem. Soc., 1995, 117, 6414; (b) C. M. Killian, D. J. Tempel,
L. K. Johnson and M. Brookhart, J. Am. Chem. Soc., 1996,
118, 11664.
0.71073
Orthorhombic
P2(1)2(1)2(1)
13.286(3)
14.439(3)
29.687(6)
90.00
90.00
90.00
5695(2)
4
1.461
3.597
2512
0.28 × 0.17 × 0.05
1.37–27.47
−17 ≤ h ≤ 17
−18 ≤ k ≤ 18
−37 ≤ l ≤ 38
12 792
7195
99.9%
1.416
R1 = 0.1172
wR2 = 0.3006
R1 = 0.1399
wR2 = 0.3230
3.96 and −1.17
Cc
2 (a) C. Popeney and Z.-B. Guan, Organometallics, 2005, 24,
1145; (b) D. H. Leung, J. W. Ziller and Z.-B. Guan, J. Am.
Chem. Soc., 2008, 130, 7538; (c) C. Popeney and Z.-B. Guan,
J. Am. Chem. Soc., 2009, 131, 12384; (d) W.-H. Sun,
S. Zhang, S. Jie, W. Zhang, Y. Li, H. Ma, J. Chen,
K. Wedeking and R. Fröhlich, J. Organomet. Chem., 2006,
691, 4196; (e) W.-H. Sun, K. Wang, K. Wedeking, D. Zhang
and S. Zhang, Organometallics, 2007, 26, 4781; (f) S. Zhang,
W.-H. Sun, X. Kuang, I. Vystorop, J. Yi, J. Cai and Y. J. Li,
J. Organomet. Chem., 2007, 692, 5307.
3 (a) Z. Guan and C. S. Popeney, J. Am. Chem. Soc., 2009, 131,
12384; (b) R. Gao, W.-H. Sun and C. Redshaw, Catal. Sci.
Technol., 2013, 3, 1172; (c) S. Wang, W.-H. Sun and
C. Redshaw, J. Organomet. Chem., 2014, 751, 717–741.
4 A. S. Ionkin and W. J. Marshall, Organometallics, 2004, 23,
3276.
28.504(6)
10.357(2)
12.460(3)
90.00
90.05(3)
90.00
3678.3(13)
4
1.226
α (°)
β (°)
γ (°)
V (Å3)
Z
Dcalcd (mg m−3
)
μ (mm−1
F(000)
)
0.072
1448
Cryst size (mm)
θ range (°)
Limiting indices
0.33 × 0.16 × 0.13
1.43–27.47
−36 ≤ h ≤ 36
−13 ≤ k ≤ 13
−16 ≤ l ≤ 16
12 077
7140 (0.0315)
99.0%
1.071
R1 = 0.066
wR2 = 0.1802
R1 = 0.0695
wR2 = 0.1855
0.35 and −0.74
No. of rflns collected
No. unique rflns [R(int)]
Completeness to θ (%)
Goodness of fit on F2
Final R indices [I > 2σ(I)]
5 (a) H. Liu, W. Zhao, X. Hao, C. Redshaw, W. Huang and
W.-H. Sun, Organometallics, 2011, 30, 2418; (b) H. Liu,
W. Zhao, J. Yu, W. Yang, X. Hao, C. Redshaw, L. Chen and
W.-H. Sun, Catal. Sci. Technol., 2012, 2, 415; (c) S. Kong,
R induces (all data)
Largest diff. peak and
hole (Å−3
)
7836 | Dalton Trans., 2014, 43, 7830–7837
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
C. Guo, W. Yang, L. Wang and W.-H. Sun, J. Organomet.
Chem., 2013, 725, 37; (d) D. Jia, W. Zhang, W. Liu, L. Wang,
C. Redshaw and W.-H. Sun, Catal. Sci. Technol., 2013, 3,
2737; (e) Q. Liu, W. Zhang, D. Jia, X. Hao, C. Redshaw and
W.-H. Sun, Appl. Catal., A, 2014, 475, 195.
B. Lofgren and M. Leskela, Macromol. Rapid Commun.,
1999, 20, 487.
9 L. Zhu, Z.-S. Fu, H.-J. Pan, W. Feng, C. Chen and Z.-Q. Fan,
Dalton Trans., 2014, 43, 2900–2906.
10 K. Song, W. Yang, B. Li, Q. Liu, C. Redshaw, Y. Li and
W.-H. Sun, Dalton Trans., 2013, 42, 9166.
6 (a) N. Guo, C. L. Stern and T. J. Marks, J. Am. Chem. Soc.,
2008, 130, 2246; (b) L. R. Gahan, S. J. Smith, A. Neves and 11 J. Hu, D. Zhang and F. W. Harris, J. Organomet. Chem.,
G. Schenk, Eur. J. Inorg. Chem., 2009, 2745; (c) Y. Guo, P. Ai, 2005, 70, 707.
L. Han, L. Chen, B. Li and S. Jie, J. Organomet. Chem., 2012, 12 (a) G. J. P. Britovsek, M. Bruce, V. C. Gibson,
716, 222.
B. S. Kimberley, P. J. Maddox, S. Mastroianni,
S. J. McTavish, C. Redshaw, G. A. Solan, S. Strolmberg,
A. J. P. White and D. J. Williams, J. Am. Chem. Soc., 1999,
121, 8728; (b) G. J. P. Britovsek, S. A. Cohen, V. C. Gibson
and M. V. Meurs, J. Am. Chem. Soc., 2004, 126, 10701;
(c) M. V. Meurs, G. J. P. Britovsek, V. C. Gibson and
S. A. Cohen, J. Am. Chem. Soc., 2005, 127, 9913.
7 (a) A. L. Gavrilova and B. Bosnich, Chem. Rev., 2004, 104,
349; (b) E. Szuromi, H. Shen, B. L. Goodall and
R. F. Jordan, Organometallics, 2008, 27, 402;
(c) P. M. Gurubasavaraj and K. Nomura, Organometallics,
2010, 29, 3500; (d) M. R. Salata and T. J. Marks, Macro-
molecules, 2009, 42, 1920; (e) Y. Cui, S. Zhang and
W.-H. Sun, Chin. J. Polym. Sci., 2008, 26, 539; 13 (a) R. J. Maldanis, J. S. Wood, A. Chandrasekaran,
(f) W.-H. Sun, Q. Xing, J. Yu, E. Novikova, W. Zhao,
X. Tang, T. Liang and C. Redshaw, Organometallics, 2013,
32, 2309; (g) M. Delferro and T. Marks, Chem. Rev., 2011,
111, 2450.
M. D. Rausch and J. C. W. Chien, J. Organomet. Chem.,
2002, 645, 158; (b) D. P. Gates, S. A. Svejda, E. Onate,
C. M. Killian, L. K. Johnson, P. S. White and M. Brookhart,
Macromolecules, 2000, 33, 2320; (c) M. M. Wegner, A. K. Ott
and B. Rieger, Macromolecules, 2010, 43, 3624.
8 (a) S. Jie, D. Zhang, T. Zhang, W.-H. Sun, J. Chen, Q. Ren,
D. Liu, G. Zheng and W. Chen, J. Organomet. Chem., 2005, 14 (a) L. Xiao, R. Gao, M. Zhang, Y. Li, X. Cao and W.-H. Sun,
690, 1739; (b) J. D. A. Pelletier, J. Fawcett, K. Singh and
G. A. Solan, J. Organomet. Chem., 2008, 693, 2723;
Organometallics, 2009, 28, 2225; (b) M. Zhang, K. Wang and
W.-H. Sun, Dalton Trans., 2009, 6354.
(c) S. Kong, K. Song, T. Liang, C.-Y. Guo, W.-H. Sun and 15 G. M. Sheldrick, SHELXTL-97, Program for the Refinement of
C. Redshaw, J. Chem. Soc., Dalton Trans., 2013, 9176;
(d) T. V. Laine, K. Lappalainen, J. Liimatta, E. Aitola,
Crystal Structures, University of Göttingen, Göttingen,
Germany, 1997.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 7830–7837 | 7837