Synthesis, characterization and ethylene polymerisation of 9,10-phenanthrenequinone-based nickel(II)-α-diimine complexes

Article abstract of DOI:10.1016/j.molcata.2009.01.007

Two 9,10-phenanthrenequinone-based α-diimine ligands (N,N′Z, N,N′E)-N,N′-(phenanthrene-9,10- diylidene)bis(2,6-dimethylaniline) (1) and (Z)-2,6-dimethyl-N-((E)-10-methylbenzo[f]phenanthro[10,1- bc]azepin-8(14H)-ylidene)aniline (2), were prepared by conden

Full text of DOI:10.1016/j.molcata.2009.01.007

Journal of Molecular Catalysis A: Chemical 303 (2009) 110–116
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Synthesis, characterization and ethylene polymerisation of
9,10-phenanthrenequinone-based nickel(II)-␣-diimine
complexes
Lidong Li∗, Manseong Jeon, Sang Youl Kim
Polyolefin Materials Research Center, Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute
of Science and Technology (KAIST), 373-1, Guseong-dong, Yuseong-Gu, Daejeon 305-701, South Korea
a r t i c l e i n f o
a b s t r a c t
Two 9,10-phenanthrenequinone-based ␣-diimine ligands (N,NꢀZ, N,NꢀE)-N,Nꢀ-(phenanthrene-9,10-
diylidene)bis(2,6-dimethylaniline) (1) and (Z)-2,6-dimethyl-N-((E)-10-methylbenzo[f]phenanthro[10,1-
bc]azepin-8(14H)-ylidene)aniline (2), were prepared by condensation of 2,6-dimethylaniline and
9,10-phenanthrenequinone in the presence of the TiCl4/1,4-diazabicyclo[2.2.2]octane catalytic system
in a one-pot reaction. It was experimentally demonstrated that a reaction temperature increase favors
the formation of ligand 2. Nickel dibromide complexes 3 and 4 were synthesized from ligands 1 and
2, respectively, and both showed high productivities as catalysts for polymerisation of ethylene. Com-
plex 3 yielded ultrahigh molecular weight polyethylenes at low temperature (e.g., 1.26 × 106 g/mol at
−15 ◦C), which are significantly higher than those produced by the corresponding 2,3-butanedione- or
acenaphthenequinone-based ␣-diimine nickel complexes. Complex 4 produced polyethylenes with rel-
atively lower molecular weights, when compared to 3. It was shown that the catalyst structure and
reaction conditions, like the reaction temperature and concentration of activator (MAO), have substantial
influence on the polymerisation activities and molecular weights and microstructures of the resulting
polymers.
Article history:
Received 25 August 2008
Received in revised form 5 January 2009
Accepted 6 January 2009
Available online 14 January 2009
Keywords:
Nickel complex
9,10-Phenanthrenequinone
Polyethylene (PE)
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
The design of ligands is very important to determine the perfor-
mance of late transition metal complexes, and much research has
In the last decade, late transition metal complexes have attracted
increased interests in the field of olefin addition polymerisation [1].
Compared to the early Ziegler-Natta catalysts and metallocenes, late
transition metal complexes show better tolerance to the functional
groups, which make them have an ability to form copolymers with
a variety of polar-functionalized comonomers, e.g., methyl acry-
late (MA) [2a], methyl methacrylate (MMA) [2b] and ␻-unsaturated
fatty acid methyl esters [2c]. In addition, due to their less oxophilic-
ities, these complexes can run the polymerisation in polar media,
and even in emulsion or water [3]. Marked chain isomerisation
mechanism (“chain walking”) of nickel and palladium complexes
allows them to produce polymers with a broad spectrum of branch-
ing topologies, ranging from relatively linear to hyperbranched or
dendritic [4].
been dedicated to this subject [1a,1b]. It has been suggested that,
in the case of NiII- and PdII-␣-diimine complexes, the increase of
the steric demands of the aryl ring substituents can dramatically
retard bimolecular deactivation and lead to increased activities of
catalysts and molecular weights of the resulting polymers. Guan
and coworkers [5] reported cyclophane-based nickel and palladium
complexes, in which the rigid frameworks of the ligands completely
block the axial faces of the metals and prohibit free rotation of the
aryl-nitrogen bonds so that these complexes can polymerise olefin
at elevated temperature with high activities. Ionkin and Marshall
[6] introduced sterically large 5-methylfuran and benzofuran sub-
stituents on the aryl rings of ␣-diimine ligands, which lead to highly
active nickel complexes producing polyethylenes with ultrahigh
molecular weights. Müller et al. [7] demonstrated that the introduc-
tion of dendritic substituents on the bidentate P,O ligands of SHOP
nickel complexes can efficiently hamper bimolecular deactivation,
andsubstantially improvetheactivities ofthe finalcomplexes. More
recently, Grubbs and coworkers [8] reported the salicylaldimine-
based neutral nickel complexes. It has been shown that the steri-
cally demanding substituents have similar influences on the neutral
nickel complexes to those on the ␣-diimine nickel complexes.
∗
Corresponding author at: Centro de Química Estrutural, Departamento de
Engenharia Química e Biológica, Instituto Superior Técnico, Av. Rovisco Pais, 1049-
001 Lisboa, Portugal. Tel.: +351 21 841 7713; fax: +351 21 841 9612.
E-mail address: dick lld@hotmail.com (L. Li).
1381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.01.007

L. Li et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 110–116
111
dimethyl ethylene glycol ether) were purchased from Aldrich and
used as received.
2.3. Syntheses of ligands and complexes
2.3.1. Synthesis of ligand 1
To a solution of 2,6-dimethylaniline (14.4 mmol, 1.77 ml) and
Dabco (43.2 mmol, 4.85 g) in toluene (30 ml) was added dropwise
14.4 ml of the 1.0 M solution of TiCl4 in toluene over 30 min at 90 ◦C,
followed by addition of a suspension of 9,10-phenanthrenequinone
(4.80 mmol, 1.0 g) in 10 ml of toluene. The reaction mixture was
heated to reflux (ca. 140 ◦C) for 24 h. The precipitate was removed
by hot filtration. The filtrate was evaporated in vacuo. Finally, 1.0 g
of deep red crystalline solid was isolated by silica gel column
chromatography (hexane/ethyl acetate, 8:1) and recrystallisation
in hexane. Yield: 50%. 1H NMR (400 MHz, CDCl3, ppm): 8.34 (d,
1H), 7.92 (m, 2H), 7.60 (t, 1H), 7.51 (t, 1H), 7.39 (t, 1H), 6.99 (br,
2H), 6.92 (t, 1H), 6.87 (t, 1H), 6.83 (br, 3H), 6.73 (d, 1H), 2.06 (s,
6H), 1.39 (s, 6H). 13C NMR (100 MHz, CDCl3, ppm): 159.9, 158.2,
148.8, 147.4, 134.5, 134.0, 133.3, 131.8, 131.3, 129.0, 128.9, 127.8,
127.6, 127.5, 127.3, 126.9, 125.2, 124.8, 124.5, 123.4, 123.0, 122.5,
18.3, 17.1. IR (KBr, cm−1): 1646 (C N), 1622 (C N). EI-MS (m/z):
calcd for C30H26N2, 414.54; found, 414 [M]+ (14%), 399 [M−CH3]+
(100%).
In the present work, we reported two new 9,10-
phenanthrenequinone-based ␣-diimine ligands (1 and 2), and
tested the catalytic performance of two nickel complexes (3 and 4),
which were formed from ligands 1 and 2, respectively, on ethylene
polymerisation.
2. Experimental
2.1. General considerations
All manipulations of air and/or water sensitive compounds
were conducted under argon atmosphere using the standard
Schlenk techniques. Infrared (IR) spectra were recorded on a
Bruker Equinox55 FT-IR spectrometer. Mass spectra (MS) were
recorded on a VG Autospec Ultima MS spectrometer. 1H NMR
2.3.2. Synthesis of ligand 2
The synthetic procedure was similar to that described for ligand
1, but chlorobenzene was used in place of toluene as solvent and
the reflux temperature was raised over 160 ◦C. An orange crystalline
solid was isolated. Yield: 35%. 1H NMR (400 MHz, CDCl3, ppm): 8.42
(d, 1H), 7.92 (d, 1H), 7.81 (d, 1H), 7.55 (m, 3H), 7.21 (d, 1H), 7.04
(t, 1H), 6.97 (br, 3H), 6.86 (d, 1H), 6.77 (t, 1H), 3.58 (d, 1H), 3.20
(d, 1H), 2.40 (s, 3H), 2.19 (s, 3H), 1.84 (s, 3H). 13C NMR (100 MHz,
CDCl3, ppm): 161.3, 157.0, 149.2, 143.2, 142.0, 135.2, 134.3, 133.8,
133.6, 132.5, 131.4, 130.9, 129.2, 128.9, 128.7, 128.0, 127.3, 127.0,
126.9, 126.4, 126.1, 124.8, 123.5, 122.4, 122.3, 121.0, 38.7, 18.8, 18.7,
18.4. IR (KBr, cm−1): 1645 (C N). EI-MS (m/z): calcd for C30H24N2,
412.52; found, 412 [M]+ (62%), 397 [M−CH3]+ (100%).
spectra were recorded on
a Bruker Avance-400 NMR spec-
trometer. Chemical shifts are reported relative to the residual
solvent (CDCl3, ı(1H) = 7.24, ı(13C) = 77.0; tetrachloroethane-d2,
ı(1H) = 6.0). The branching of polymer was measured by 1H NMR
spectroscopy in tetrachloroethane-d2 at 120 ◦C. The degrees of
branching of polymers were calculated from the integrals of
the methyl, methylene and methine groups as the following
equations:
Branches/1000 C
SA(methyl)/3
=
× 1000
2.3.3. Synthesis of complex 3
SA(methyl)/3 + SA(methylene)/2 + SA(methine)
Ligand 1 (0.50 g, 1.21 mmol) and (DME)NiBr2 (0.37 g, 1.21 mmol)
where SA(methyl), SA(methylene) and SA(methine) are the integrals
of the methyl, methylene and methine groups of polymers, respec-
tively. Weight-average (Mw) and number-average (Mn) molecular
weight and molecular weight distribution (MWD) were measured
by gel permeation chromatography (GPC) on a SSC-7100 apparatus,
at 145 ◦C, using the o-dichlorobenzene as the eluent. The calibration
curve was determined with polystyrene standards. Glass transition
temperature (Tg) and melting temperature (Tm) of polymer samples
were determined using a TA-Q100 differential scanning calorimeter
at a scanning rate of 10 ◦C/min.
were combined as solids in
a flame-dried Schlenk flask.
Dichloromethane (50 ml) was added to the solid mixture and the
reaction was stirred at room temperature (ca. 20 ◦C) for 24 h. The
solvent was removed in vacuo and the residual solid was washed
with Et2O several times. Finally, complex 3 was isolated as a brown
powder (0.66 g, 86%). Anal. calcd for C30H26Br2N2Ni: C, 56.92; H,
4.14; N, 4.43. Found: C, 56.55; H, 4.13; N, 4.35.
2.3.4. Synthesis of complex 4
The synthetic procedure was similar to that described for com-
plex 3. A brown powder was obtained. Yield: 96%. Anal. calcd for
2.2. Materials
C30H24Br2N2Ni: C, 57.10; H, 3.83; N, 4.44. Found: C, 57.53; H, 3.52;
N, 4.21.
All the solvents were purified prior to use. Toluene (J.T. Baker,
USA) and ethyl ether (Junsei Chemical Co., Ltd., Japan) were
purified over sodium/benzophenone ketyl, and distilled prior
to use. Chlorobenzene (Junsei Chemical Co., Ltd., Japan) and
dichloromethane (Junsei Chemical Co., Ltd., Japan) was purified
over calcium hydride powder, and distilled prior to use. Polymeri-
sation grade ethylene gases were purified by passing 4 Å molecular
sieves column and Ridox® oxygen scavenger (R31-500) column,
respectively. 1,4-Diazabicyclo[2.2.2]octane (Dabco) (95%) was pur-
chased from Aldrich and purified by sublimation. MAO (10 wt%
in toluene), 9,10-phenanthrenequinone (95%), titanium tetrachlo-
ride (99.9%), 2,6-dimethylaniline (99%), and (DME)NiBr2 (DME,
2.4. X-ray crystallography
Single crystals of ligand 2 suitable for X-ray diffraction charac-
terization were grown from a dilute hexane solution at 0 ◦C. Crystal
data was collected in a Bruker AXS-KAPPA APEX II diffractometer
equipped with an Oxford Cryosystems open-flow nitrogen cryo-
stat, at 150 K, using graphite monochromated Mo K␣ radiation
(ꢀ = 0.71069 Å). Cell parameters were retrieved using Bruker SMART
software and refined using Bruker SAINT on all observed reflections.
Absorption corrections were applied using SADABS [9]. Structure
solution and refinement were performed using direct methods with

112
L. Li et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 110–116
Table 1
The flask was flamed in vacuo and back-filled with ethylene. The
Crystal data and structure refinement for ligand 2.
appropriate amount of toluene and the MAO were injected into
the reactor, and the ethylene inlet was opened to make the sys-
tem saturated by ethylene at a certain reaction temperature. The
polymerisation was initiated by addition of the catalyst solution in
dichloromethane. After 60 min, the polymerisation was terminated
by addition of the acidified methanol. The resulting polyethylene
was filtered, washed with a large amount of methanol and dried in
vacuo at 60 ◦C.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
C30H24N2
412.51
150(2)
0.71073
Triclinic, P-1
Unit cell dimensions
a = 8.252 Å, ˛ = 76.32◦
b = 11.119 Å, ˇ = 89.20◦
c = 12.233 Å, ꢁ = 86.08◦
Volume (Å3)
1084.0
2, 1.259
0.073
436
3. Results and discussion
Z, calculated density (Mg m−3
)
)
Absorption coefficient (mm−1
3.1. Preparation of ligands and complexes
F(0 0 0)
Theta range for data collection (◦)
Index ranges
2.23–30.97
−11 ≤h ≤11, −16 ≤k ≤15, −17 ≤l ≤17
38697/6867 [Rint = 0.0471]
99.3%
Semi-empirical from equivalents
Full-matrix least-squares on F2
0.9869 and 0.9783
Full-matrix least-squares on F2
6867/0/289
Ligand
1 was prepared by dehydrating condensation of
Reflections collected/unique
Completeness to theta = 30.97
Absorption correction
Refinement method
Max. and min. transmission
Refinement method
2,6-dimethylaniline and 9,10-phenanthrenequinone, using the
TiCl4/Dabco system in toluene (Scheme 1). Based on NMR results
and comparison with the analogue (Z,Z)-9,10-bis(phenylimino)-
9,10-dihydrophenanthrene already published [14], it can be
concluded that ligand 1 adopts a (Z,E) configuration. The two strik-
ingly different methyl peaks (2.05 and 1.39 ppm), obtained by 1H
NMR spectra, correspond to methyl groups on aromatic rings with
different configurations, respectively. At the same time, two pairs of
different –C N–C peaks (159.9 and 158.2 ppm) and –C N–C peaks
(148.8 and 147.4), obtained by 13C NMR spectra, further indicate that
the aromatic rings should be assigned to different configurations
with respect to C N bonds. In the case of ligand 1, the energeti-
cally favored ␲-stacking in (Z,Z) configuration might be retarded
by introduction of methyl groups on the ortho positions of the
aromatic rings.
Ligand 2 was simultaneously produced along with ligand 1 in
a one-pot reaction. Reaction temperature has a significant impact
on the selectivity for ligands 1 and 2. As reaction temperature was
controlled at 140–150 ◦C, using toluene as solvent, the major prod-
uct was ligand 1 (50%) and a small amount of ligand 2 was isolated
as a byproduct (ca. 5%). As the toluene was replaced by chloroben-
zene and the reaction temperature was increased to 160–170 ◦C,
ligand 2 became the major product (35%) and the amount of ligand
1 formed decreased to ∼10%. This indicates that ligand 1 is prefer-
entially formed at a relatively lower reaction temperature, and that
a reaction temperature increase favors the formation of ligand 2.
Crystals of ligand 2, suitable for single crystal X-ray diffraction, were
grown from a dilute solution in hexane at 0 ◦C (Fig. 1). As shown in
Fig. 1, the two aromatic rings of ligand 2 adopt (Z,E) configurations
Data/restraints/parameters
Goodness-of-fit on F2
0.993
Final R indices [I > 2ꢂ(I)]
R indices (all data)
Largest diff. peak and hole (e. Å−3
R1 = 0.0626, wR2 = 0.1902
R1 = 0.0857, wR2 = 0.2034
0.645 and −0.578
)
the programs SIR92 [10] and SHELXL [11] both included in the pack-
age of programs WINGX-Version 1.70.01 [12]. Non-hydrogen atoms
were refined with anisotropic thermal parameters. All hydrogen
atoms were inserted in idealized positions and allowed to refine rid-
ing in the parent C atoms. All remaining crystal data and refinement
parameters are presented in Table 1. The figures were generated
using ORTEP-III [13].
CCDC 673942 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via www.
ccdc.cam.ac.uk/data request/cif, or by emailing data request@ccdc.
cam.ac.uk, or by contacting The Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336033.
2.5. Ethylene polymerisation
Ethylene polymerisation was conducted in a 50-ml Schlenk flask
equipped with vacuum line, ethylene inlet and magnetic stirrer.
Scheme 1. Syntheses of the ligands and the complexes.

L. Li et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 110–116
113
the value of 2.28 × 106 g of PE mol−1 of Ni h−1 (entry 7 in Table 2).
Polyethylenes formed using complex 3 as a catalyst contain similar
extent of branching to those obtained using the typical ␣-dimine
nickel complexes, e.g., 29–35 branches/1000 C (entries 16–19 in
Table 2) versus 29 branches/1000 C ([ArN C(H)–C(H) NAr]NiBr2,
Ar = 2,6-dimethylphenyl, 1 atm ethylene pressure, 25 ◦C [1c]). Com-
plex 4 produces polyethylenes with higher extent of branching
compared to complex 3 (Table 3).
As shown in Tables 2 and 3, under the same polymerisation
conditions, complex 3 displays higher polymerisation activities
than complex 4, and polyethylenes formed using complex 3 con-
tain molecular weights approximately 5 times larger than those
obtained using complex 4. In addition, as the polymerisation tem-
perature increases, the activities of complex 3 decrease slower than
those of complex 4, indicating that the former is more thermally
stable than the latter. All of these results may be attributed to
the fact that complex 3 has more steric protection on the axial
faces of the coordination plane than complex 4. Compared to 3,
the methylene linkage of complex 4 makes the N-aryl group devi-
ate the perpendicular orientation to the coordination plane, and
renders the substituents of the N-aryl group away from the axial
faces, which lead to a substantial decrease of the steric protection
on the axial faces of the coordination plane. On the basis of the
proposed mechanism [1], the steric bulk on the axial faces of the
coordination plane may inhibit bimolecular deactivation of cata-
lysts and suppress associative chain transfer or chain transfer to
ethylene monomer. Therefore, complex 3 is more active for ethy-
lene polymerisation and more stable against reaction temperature
than complex 4, and the resulting polymers formed by complex 3
have higher molecular weights than those obtained by complex 4.
It is worth to note that complex 3 produces polyethylenes
with ultrahigh molecular weights at lower polymerisation tem-
perature, e.g., 1.26–2.14 × 106 g/mol at −15 ◦C (entries 4–7 in
Table 2), and 1.27 and 1.01 × 106 g/mol at 0 ◦C (entries 11 and
14 in Table 2). Additionally, molecular weights of polyethylenes
formed by complex 3 are much higher than those obtained by
the structurally similar Brookhart’s ␣-diimine nickel complexes,
e.g., (2.6–12.7) × 105 g/mol at 0 ◦C (entries 8–14 in Table 2) ver-
sus 4.3 and 17 × 104 g/mol at 0 ◦C for [ArN C(R)–C(R) NAr]NiBr2
(Ar = 2,6-dimethylphenyl, R = H or Me) (entries 13 and 15 in Table 1
Fig. 1. ORTEP view of crystal structure of ligand 2 with 50% probability displacement
ellipsoids. H-atoms are omitted for clarity.
with respect to the C N bonds, which is in agreement with the NMR
result. The mechanism for the formation of ligand 2 is still unclear,
and the subject is being investigated in our laboratory.
Reaction of ligands 1 and 2 with (DME)NiBr2 in dichloro-
methane, at room temperature, resulted in the formation of the
nickel complexes 3 and 4, in considerably good yields (86% and
96%, respectively).
3.2. Ethylene polymerisation
3.2.1. Effects of the catalysts
Complexes 3 and 4 are both catalytically active towards ethylene
polymerisation, in the presence of MAO as activator. The polymeri-
sation data are summarized in Tables 2 and 3. These two nickel
complexes exhibit high activities for ethylene polymerisation,
which are comparable to the typical ␣-dimine nickel complexes
[1c]. For example, the catalytic activity of complex 3 can reach
Table 2
Ethylene polymerisation catalyzed by the 3/MAO systema.
Entry
Catalyst
(␮mol)
MAO
(mmol/equiv.)
Temp. (◦C)
Yield (g)
Activity
Mnb (105 g/mol)
Mw/Mnb
Branches/1000 Cc
Thermal
(105 g/mol Ni h)
anal.d (◦C)
1
2
3
4
5
6
7
8
4.0
4.0
2.0
1.0
1.0
0.5
0.5
2.0
2.0
2.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0
1.0
1.0
0.2/50
−15
−15
−15
−15
−15
−15
−15
0
0
0
0
0
0.46
0.86
1.11
1.27
1.05
0.64
1.14
0.97
1.58
1.71
1.28
1.19
1.58
1.52
0.20
0.84
1.28
1.26
1.47
1.15
2.15
5.55
12.70
10.50
12.80
22.80
4.85
5.0
4.9
1.1
16.9
12.6
14.2
21.4
2.6
6.4
9.1
12.7
5.9
3.3
3.7
3.6
8.5
2.0
2.1
2.0
1.8
6.4
3.6
2.6
2.4
3.9
5.9
2.2
2.4
2.7
2.8
2.5
2.5
3.0
3.0
2.0
3.0
132.9 (Tm
131.7 (Tm
132.5 (Tm
130.0 (Tm
132.4 (Tm
131.7 (Tm
130.6 (Tm
124.6 (Tm
123.4 (Tm
122.9 (Tm
125.9 (Tm
124.5 (Tm
124.9 (Tm
121.7 (Tm
103.6 (Tm
91.4 (Tm
)
0.4/100
0.5/250
0.5/500
1.0/1000
1.0/2000
1.5/3000
0.1/50
0.2/100
0.5/250
0.5/500
1.0/1000
2.0/2000
3.0/3000
0.5/250
1.0/500
2.0/1000
2.0/2000
3.0/3000
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
e
–
–
e
2.0
7.0
10.0
7.0
4.0
7.0
9
7.90
8.55
10
11
12
13
14
15
16
17
18
19
12.80
11.90
15.80
15.20
1.00
4.20
6.40
12.60
14.70
0
0
4.0
8.0
10.1
3.2
2.2
2.2
2.6
30
30
30
30
30
21.0
35.0
35.0
30.0
29.0
82.6 (Tm
94.9 (Tm
93.7 (Tm
3.4
a
General polymerisation conditions: toluene as solvent, total volume (40 ml), ethylene pressure (1.20 atm), reaction time (1.0 h).
b
c
Determined by GPC.
Determined by 1H NMR.
Determined by DSC.
Not detectable.
d
e

114
L. Li et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 110–116
Table 3
Ethylene polymerisation catalyzed by the 4/MAO systema.
Entry
Catalyst
MAO
Temp. (◦C)
Yield (g)
Activity (105 g/mol Ni h)
Mnb (105 g/mol)
Mw/Mnb
Branches/1000Cc
Thermal anal.d (◦C)
(␮mol)
(mmol/equiv)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
4.0
4.0
2.0
2.0
2.0
1.0
0.5
4.0
4.0
2.0
2.0
2.0
1.0
1.0
2.0
2.0
2.0
0.2/50
−15
−15
−15
−15
−15
−15
−15
0
0
0
0
0
0
0
30
30
30
0.64
0.92
0.59
0.76
0.87
0.49
0.25
0.99
1.44
0.84
0.97
1.06
0.66
0.69
0.31
0.35
0.36
1.60
2.30
2.95
3.80
4.35
4.90
5.00
2.48
3.60
4.20
4.85
5.30
6.60
6.90
1.55
1.75
1.80
1.2
1.4
1.8
1.0
1.7
1.2
2.4
0.9
1.3
1.4
1.5
1.3
2.0
2.0
0.4
0.4
0.4
2.4
2.8
2.3
3.1
2.4
3.0
2.2
3.9
3.2
3.9
2.9
3.9
3.0
3.1
2.0
2.1
2.0
5.0
4.0
4.0
4.0
5.0
128.2 (Tm
127.3 (Tm
129.0 (Tm
128.7 (Tm
128.7 (Tm
128.6 (Tm
129.7 (Tm
119.3 (Tm
119.0 (Tm
120.6 (Tm
121.0 (Tm
119.7 (Tm
120.0 (Tm
119.3 (Tm
)
)
)
)
)
)
)
)
)
)
)
)
)
)
0.4/100
0.5/250
1.0/500
2.0/1000
2.0/2000
1.5/3000
0.2/50
0.4/100
0.5/250
1.0/500
2.0/1000
2.0/2000
3.0/3000
2.0/1000
4.0/2000
6.0/3000
4.0
4.0
15.0
15.0
13.0
11.0
12.0
11.0
13.0
69.0
67.0
69.0
−44.1 (Tg), 41.4 (Tm
)
)
)
−49.0 (Tg), 44.3 (Tm
−47.6 (Tg), 45.4 (Tm
a
General polymerisation conditions: toluene as solvent, total volume (40 ml), ethylene pressure (1.20 atm), reaction time (1.0 h).
b
c
Determined by GPC.
Determined by 1H NMR.
Determined by DSC.
d
[1c]), and (2.2–3.4) × 105 g/mol at 30 ◦C (entries 15–19 in Table 2)
versus 1.43 × 104 g/mol at 35 ◦C for [ArN C(An)–C(An) NAr]NiBr2
(Ar = 2,6-dimethylphenyl) (entry 6 in Table 1 [1f]). This sug-
gests that the ␣-diimine nickel complexes based on 9,10-
phenanthrenequinone (3) can introduce more steric demands on
the axial faces than those based on 2,3-butanedione and acenaph-
thenequinone.
mercially expensive. Fig. 2 shows that the Al/Ni molar ratio of 500
is an optimum value, which allows to maintain the high activities
and simultaneously to reduce the amount of MAO used. In fact, the
activities dramatically reduce as the Al/Ni molar ratio goes below
500, whereas they slightly increase as the ratio is above 500. Several
factors may play roles over determining the effect of temperature
on the polymerisation activity, which involve stabilities of com-
plexes and the formed active species in the reaction, solubility of
the monomer in media, and the influence of the reaction tempera-
ture on the propagation rate. In the case of complexes 3 and 4, these
factors render the complexes more active at 0 ◦C than at −15 ◦C or
30 ◦C, and the activities at 0 ◦C and −15 ◦C are noticeably higher
than those at 30 ◦C (Fig. 2).
Both the Al/Ni molar ratio and the reaction temperature have
influences on the molecular weights of the resulting polymers, as
shown in Fig. 3. The molecular weights decrease as the polymeri-
sation temperature increases, for both 3 and 4, since the higher
temperature more favors the chain transfer than the chain propa-
gation. The Al/Ni molar ratio hardly influence the molecular weights
of polymers obtained by complex 4, at various temperatures, and
complex 3 at 30 ◦C. However, at −15 ◦C and 0 ◦C, the molecular
Another striking feature that can be observed from Tables 2 and 3
is that the extents of branching of polyethylenes obtained by com-
plex 4 are approximately two times higher than those obtained by
complex 3, which exhibits a substantially different trend from the
Brookhart’s ␣-dimine nickel complexes [1c,1f]. In the case of the
latter, the extent of branching increases with the bulk of the aryl
subsituents, that is to say, an increase of the steric demands on
the axial faces of the coordination plane will yield a polymer with
higher branching. Brookhart and his coworkers [1f] suggested that,
since the propagation rate is suppressed by bulky substituents more
than the rate of chain running, more chain running and branching
can occur in the catalysts that bear bulky substituents, in compar-
ison with those that possess less bulky substituents. However, in
the case of complexes 3 and 4, polyethylenes formed by complex 4,
with less steric demands on the axial faces, have more branching
than those obtained by complex 3, with more steric demands. This
is possibly due to the asymmetric geometry of complex 4, which
not only enhances the propagation rate but also favors the chain
running.
3.2.2. Effects of the polymerisation conditions
The effects of the Al/Ni molar ratio and the reaction temper-
ature on polymerisation activities are summarized in Fig. 2. As
displayed in Fig. 2, the catalytic activities of complex 3 are much
higher than those of complex 4. Since increasing the concentration
of MAO may improve the number of the active species in the reac-
tion and contribute to the stabilization of the formed active species
[15], the polymerisation activities progressively increase with the
Al/Ni molar ratio (Fig. 2). In addition, it is worth to note that, due
to enhanced tolerance of nickel complexes to moisture and polar
functionalities, complexes 3 and 4 can be activated by a quite small
amount of MAO to promote ethylene polymerisation, e.g., Al/Ni = 50
(entries 1 and 8 in Tables 2 and 3). This gains a marked advan-
tage over the early transition metal catalysts (e.g., metallocene)
since it avoids the use of a large amount of MAO which is com-
Fig. 2. Effects of the Al/Ni molar ratio and the reaction temperature on the polymeri-
sation activities promoted by complexes 3 and 4. Solid, 3; open, 4; square, −15 ◦C;
circle, 0 ◦C; up triangle, 30 ◦C.

L. Li et al. / Journal of Molecular Catalysis A: Chemical 303 (2009) 110–116
115
Fig. 3. Effects of the Al/Ni molar ratio and the reaction temperature on the molecular
weights of polyethylenes prepared by complexes 3 and 4. Solid, 3; open, 4; square,
Fig. 5. 1H NMR spectra of polyethylenes prepared by complex 3 at different temper-
atures. a, b and c correspond to entries 5, 12 and 17 in Table 2, respectively.
−15 ◦C; circle, 0 ◦C; up triangle, 30 ◦C.
weights of polymers obtained by complex 3 pronouncedly vary
with the Al/Ni molar ratio. The reason for this effect is still unclear.
It might be related to the fact that, for the more catalytically
active complex 3, the lower reaction temperatures result in the
precipitation of the formed polymers with relatively higher molec-
ular weights from the reaction solution, which heterogenizes the
reaction system (although a lower concentration of complex was
used, as the Al/Ni molar ratio was increased, in order to avoid this
effect).
The effects of the Al/Ni molar ratio and the temperature on the
extents of branching of the resulting polymers are shown in Fig. 4.
It can be seen that the branching markedly increases as the reaction
temperature increases. This trend can also be clearly observed by
analysis of the 1H NMR spectra in Fig. 5. The small doublet observed
at ı = 0.95 ppm, which is assigned to the methyl branches, becomes
more intense with the temperature increase, when compared with
the methylene resonances at ı = 1.37 ppm. At the same time, the
methine resonances, which are observed as broad resonances at
ı = 1.22 ppm, increase with the reaction temperature. Furthermore,
the fact that the methyl resonances are split into doublets indi-
cates that these polyethylenes mainly have CH3 branches. The Al/Ni
molar ratio has an insignificant influence on the branching degree,
just like it was found for the Brookhart ␣-dimine nickel complexes
[1c,1f].
4. Conclusions
Two novel 9,10-phenanthrenequinone-based ␣-diimine ligands
1 and 2, prepared by condensation of 9,10-phenanthrenequinone
with 2,6-dimethylaniline in the presence of the TiCl4/Dabco system
in a one-pot reaction, are reported. A higher reaction temperature
favors the formation of ligand 2. Nickel complexes 3 and 4 are
prepared from ligands 1 and 2, respectively, and both show good
activities for ethylene polymerisation, in the presence of MAO. The
final polyethylenes obtained by complexes 3 and 4 have comparable
structures of branching to the Brookhart’s ␣-diimine nickel com-
plexes. Complex 3 exhibits a higher polymerisation activity than
complex 4, and yields polyethylenes with higher molecular weights
and less extents of branching. Additionally, complex 3 produces
polyethylenes with ultrahigh molecular weights, at a relatively
lower polymerisation temperature, e.g., (1.26–2.14) × 106 g/mol at
−15 ◦C (entries 4–7 in Table 1). It was demonstrated that the
reaction conditions, e.g., the reaction temperature and the con-
centration of activator (MAO), have significant influences on the
polymerisation activities and the degrees of branching of the result-
ing polymers.
Acknowledgments
We thank the Brain Korea 21 (BK21) program for financial sup-
ports of this work. We are grateful to Dr. Sónia A. Carabineiro for
polishing this paper.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2009.01.007.
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