Synthesis of palladium complexes containing 2-methoxycarbonyl-6-iminopyridine ligand and their catalytic behaviors in reaction of ethylene and norbornene

Article abstract of DOI:10.1016/j.jorganchem.2006.07.026

A series of palladium complexes (C1-C7) have been prepared by the reaction of PdCl₂(CH₃CN)₂ with 2-methoxycarbonyl-6-iminopyridines, L1-L7. The 2-methoxycarbonyl-6-iminopyridines and their complexes were fully characterized by FT-IR, NMR spectra and elemental analysis. Structures of C1, C2, C4, C5 and C6, C7 were determined by X-ray crystallography, and these complexes fold slightly distorted square planar structures around palladium coordinated with two nitrogen atoms and two chlorides. These palladium complexes exhibited moderate catalytic activities for ethylene dimerization and/or polymerization in the presence of methylaluminoxane, and showed remarkable catalytic activity for norbornene polymerization. The catalytic behaviors of these complexes were highly affected by both the ligand employed and reaction conditions.

Full text of DOI:10.1016/j.jorganchem.2006.07.026

Journal of Organometallic Chemistry 691 (2006) 4759–4767
www.elsevier.com/locate/jorganchem
Synthesis of palladium complexes containing
2-methoxycarbonyl-6-iminopyridine ligand and their catalytic
behaviors in reaction of ethylene and norbornene
a
a,
b
a
a
Wenjuan Zhang , Wen-Hua Sun *, Biao Wu , Shu Zhang , Hongwei Ma ,
a
c
a
Yan Li , Jiutong Chen , Peng Hao
a
Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
b
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, China
c
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
Chinese Academy of Sciences, Fuzhou 350002, China
Received 8 March 2006; received in revised form 15 July 2006; accepted 20 July 2006
Available online 1 August 2006
Abstract
A series of palladium complexes (C1–C7) have been prepared by the reaction of PdCl2(CH3CN)2 with 2-methoxycarbonyl-6-imino-
pyridines, L1–L7. The 2-methoxycarbonyl-6-iminopyridines and their complexes were fully characterized by FT-IR, NMR spectra and
elemental analysis. Structures of C1, C2, C4, C5 and C6, C7 were determined by X-ray crystallography, and these complexes fold slightly
distorted square planar structures around palladium coordinated with two nitrogen atoms and two chlorides. These palladium complexes
exhibited moderate catalytic activities for ethylene dimerization and/or polymerization in the presence of methylaluminoxane, and
showed remarkable catalytic activity for norbornene polymerization. The catalytic behaviors of these complexes were highly affected
by both the ligand employed and reaction conditions.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Iminopyridine; Palladium complexes; Ethylene; Norbornene; Polymerization
1. Introduction
to prevention of certain chain-transfer process (b-hydrogen
elimination and subsequent dissociation of olefins) [1a,2].
Following this pioneer work, many reports for syntheses
and ethylene polymerization/oligomerization using various
nickel and palladium complexes containing bidentate nitro-
gen ligands, such as bipyridine [3] and imino-pyridine
ligands [4] were reported as the modified forms. However,
in most cases, the nickel complexes showed higher catalytic
activities for ethylene polymerization/oligomerization,
and their palladium analogues usually showed low catalytic
activities [5].
Olefin polymerization using late transition metal com-
plex catalysts has received great attraction over the past
decade especially since the Brookhart’s discovery of palla-
dium(II) and nickel(II) complexes containing a-diimine
ligands, which exhibited notable catalytic activities for poly-
merization of ethylene and a-olefins affording high molecu-
lar weight polymers with uniform composition [1]. The
origin of this success for using these complexes with a-di-
imine ligand has been postulated that bulky substituents
on the ligand hinder the apical coordination sites, leading
The polymerization of strained cycloalkanes like nor-
bornene using transition metal complex catalysts produced
polymers with promising possibilities as high-performance
polymeric materials [6] with unique properties such as good
*
Corresponding author. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.07.026

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W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
NH2
mechanical strength, optical transparency and low birefrin-
gence [7]. Simple palladium(II) salts and their nitrile or
phosphine adducts were used as the conventional catalyst
precursors for norbornene polymerization [8], but recent
rapid progress introduced more efficient palladium com-
plex catalysts [9,10] by modification of ligands, the pro-
posed cationic catalytically-active species [8,11]. MAO
was often used as cocatalyst to activate various palla-
dium-based precursors [10,12].
R1
R1
R1
R1
R2
toluene, p-TsOH
R2
CO2Me
N
N
N
CO2Me
O
L
PdCl2(MeCN)2
R1
CH2Cl2
r.t
1.R1 = Me, R2 = H 5.R1 = F, R2 = H
2.R1 = Et, R2 = H 6.R1 = Cl, R2 = H
3.R1 = i-Pr, R2 = H 7.R1 = Br, R2 = Me
4.R1 = Me, R2 = Me
There were numerous reports dealing with late-transi-
tion catalytic systems for polynorbornenes, seldom with
measuring the molecular weights of polynorbornenes.
The polymers without information of molecular weights
and distributions would be difficult to explore their proper-
ties and find their application. Fortunately, the nickel com-
plexes as catalysts for norbornene polymerization not only
showed high catalytic activities but also produced the solv-
able polynorbornenes with successively measuring their
molecular weights and distributions [13], which were earli-
est documented with molecular weights of polymers
produced by homopolymerization of norbornene [14].
Meanwhile, Novak and Li groups [15] reported that neu-
tral palladium complexes are efficient catalytic precursors
for olefin and vinyl monomer polymerization although
both molecular weights and the distributions for resultant
polynorbornenes were not described. The palladium com-
plexes containing pyrazolylpyridines were known to be
active for ethylene polymerization [16], and most palladium
complexes show only moderate activity for either oligomer-
ization or polymerization of ethylene [17]. The nickel,
cobalt and iron complexes containing 2-ethoxycarbonyl-
6-iminopyridines showed unique characteristics in ethylene
oligomerization and/or polymerization [18]. It is worthy to
try the synthesis and catalytic measurement of their palla-
dium analogues. The titled complexes had been synthesized
and tested for olefin reactivity. The palladium complexes
containing 2-methoxycarbonyl-6-iminopyridines showed
moderate activity for ethylene oligomerization as well as
polymerization, it is unusual to observe the combined
products of oligomer and polymer in palladium catalytic
systems. Moreover, their behavior for norbornene poly-
merization was investigated to show their high catalytic
activity. Herein we describe the synthesis and characteriza-
tion of the titled complexes as well as their catalytic behav-
iors in ethylene and norbornene reactivity.
R2
N
N
Pd
CO2Me
Cl
Cl
R1
C
Scheme 1.
methane at room temperature (Scheme 1). Complexes C1,
C2 and C5 tended to precipitate from the reaction solution,
and optimized yields were obtained when the reaction was
continued for a desired period of time. Complexes C3, C4,
C6 and C7 were precipitated by adding excessive amount of
Et2O. All methyl 2-carboxylate-6-iminopyridines are yel-
low solids, while their palladium complexes are orange
solids.
All newly synthesized compounds were fully character-
ized and confirmed by IR, NMR and elemental analysis.
Comparing their IR spectra, we noted that the palladium
complexes did not show the suitable absorptions in the
C@N range. This observation is attributed to the infrared
inactive C@N vibration in the palladium complexes [19],
which confirms the coordination of palladium with imino
groups. Moreover, the shifts of the NMR peaks of the pal-
ladium complexes provide additional evidences for the exis-
tence of strong coordination of the pyridine nitrogen and
the imine nitrogen to the palladium center [4].
2.2. Structural features
The single crystals of complexes C1, C2, C4, C5, C6, C7
suitable for X-ray crystallography were grown by diffusing
Et2O into the CH2Cl2 solution. Crystallographic data and
refinement residuals are summarized in Table 1. The coor-
dination geometry around the palladium atom in all title
complexes can be described as a distorted square planar.
Therefore, the complexes C1, C5, C6 were discussed here,
while their analogues C2, C4 and C7 were only collected
in the supporting information. The molecular structures
of complexes C1, C5, C6 are depicted in Figs. 1–3, respec-
tively, and their selected bond lengths and bond angles are
summarized in Table 2. As shown in Table 2, their corre-
sponding bond lengths and angles in the coordination pal-
ladium frame are similar. Hence, the crystal structures of
complexes C1 and C5 are selected to be described in detail.
The molecular structure of complex C1 is shown in
Fig. 1. The palladium center is coordinated by two nitrogen
and two chlorine atoms, which is different from its nickel
2. Results and discussion
2.1. Synthesis and spectroscopic characterization
2-Methoxycarbonyl-6-iminopyridines L1–L7 shown in
Scheme 1 were prepared according to the previous proce-
dure [18], by the condensation of methyl 6-acetylpyridine-
2-carboxylate with appropriate aniline in the presence of
catalytic amount of p-TsOH. The palladium (II) dichloride
complexes C1–C7 were thus obtained by the reaction of the
corresponding ligands with PdCl2(CH3CN)2 in dichloro-

W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
4761
Table 1
Crystallographic data and refinement for complexes C1, C2, C4, C5, C6 and C7
C1 C2 C4
C5
C6
C7
Empirical formula
C17H18Cl2N2O2Pd C19H22Cl2N2O2Pd C18H20Cl2 N2O2Pd C15H12Cl2 F2N2O2Pd C15H12Cl4-
N2O2Pd
C16H14Br2Cl2-
N2O2Pd
Formula weight
Crystal system
Space group
459.63
Orthorhombic
Pna2(1)
487.69
Monoclinic
P2(1)/c
473.66
Orthorhombic
Pna2(1)
467.57
Monoclinic
P2(1)/n
500.47
Monoclinic Monoclinic
P2(1)/n
603.41
P2(1)/n
Unit cell dimensions
˚
a (A)
16.558(3)
7.9864(16)
13.439(3)
90.00
90.00
90.00
1777.1(6)
4
1.718
13.445(3)
9.4185(19)
17.195(3)
90.00
105.36(3)
90.00
2099.7(7)
4
1.543
17.212(5)
7.995(2)
13.392 (4)
90.00
90.00
90.00
1842.8(10)
4
1.707
7.585(3)
11.738(5)
18.494(8)
90.00
99.623(7)
90.00
1623.4(12)
4
1.913
7.560(3)
12.349(5)
19.201(9)
90.00
99.662(6)
90.00
1767.0(13)
4
1.881
8.866(4)
8.916(4)
24.463(11)
90.00
99.684(4)
90.00
1906.2(14)
4
2.103
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
dcalc (g cmÀ3
)
h Range (°)
Number of data collected
2.83–27.47
2129
1.57– 27.48
4709
2.37–27.48
4184
3.23–27.46
3691
2.15–25.02
3110
3.10–27.48
4370
Number of parameters refined 217
223
226
217
217
226
Number of unique data
1637
3229
4085
3504
2775
4047
R
Rw
0.0365
0.0748
0.908
0.0427
0.1111
0.990
0.0249
0.0571
1.062
0.0204
0.0488
1.069
0.0496
0.0797
1.195
0.0260
0.0590
1.082
Goodness-of-fit
Fig. 3. Molecular structure of C6. Hydrogen atoms are omitted for
clarity.
Fig. 1. Molecular structure of complex C1. Hydrogen atoms are omitted
for clarity.
analogue coordinated by two nitrogen and oxygen atoms
along with two chlorides [18a]. There is no direct bonding
between palladium and oxygen atoms such as O1Á Á ÁPd1
˚
˚
(3.397 A) and O2Á Á ÁPd1 (4.354 A). The average deviation
˚
from the plane of Pd1–N2–C7–C9–N1 is 0.1142 A, which
indicates that the coordination is nearly the plane. Accord-
ing to the literature [20], the Pd–Cl distances in C1 (2.314
˚
˚
(2) A) and (2.2783 (19) A) are within the normal range of
Pd–Cl bonds, and the Pd–N bonds were measured as Pd–
˚
˚
N(py) (2.023(6) A) and Pd–N(imino) (2.014(5) A).
The bond angle of N1–Pd–N2 (79.4(2)°) results from the
relatively longer Pd–N bonds than other C–N and C–C
bonds in the coordination plane. Therefore, the palladium
complexes display the distorted planar structure. The struc-
tural feature of the distorted square was often observed in
other palladium complexes ligated by pyridylimine or
bipyridine [21]. The plane of the phenyl ring is oriented
Fig. 2. Molecular structure of complex C5. Hydrogen atoms are omitted
for clarity.

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W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
Table 2
Selected bond lengths and bond angles for complexes C1, C5, and C6
˚
Bond length (A)
Bond angle(°)
C1
C5
C6
Pd(1)–N(1)
Pd(1)–N(2)
N(2)–C(7)
N(1)–C(9)
2.014(5)
2.023(6)
1.353(9)
1.289(9)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
N(2)–C(3)
N(1)–C(10)
2.2784(19)
2.314(2)
1.362(9)
1.480(8)
N(1)–Pd(1)–N(2)
Cl(1)–Pd(1)–Cl(2)
N(2)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(1)
79.4(2)
87.39(8)
98.52(18)
95.30(18)
Pd(1)–N(1)
Pd(1)–N(2)
N(2)–C(7)
N(1)–C(9)
2.0217(15)
2.0607(16)
1.373(2)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
N(1)–C(10)
N(2)–C(3)
2.2723(8)
2.2863(8)
1.430(2)
1.332(2)
N(1)–Pd(1)–N(2)
Cl(1)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(2)
79.17(6)
93.27(5)
93.27(5)
99.00(5)
1.293(2)
Pd(1)–N(1)
Pd(1)–N(2)
N(2)–C(7)
N(1)–C(9)
2.019(4)
2.069(4)
1.387(6)
1.283(7)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
N(1)–C(10)
N(2)–C(3)
2.2752(15)
2.2857(15)
1.432(7)
N(1)–Pd(1)–N(2)
Cl(1)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(2)
79.47(17)
88.96(5)
93.10(13)
98.30(12)
1.336(6)
approximately orthogonal to the coordination plane with
the angle of 92.6°.
presence of methylaluminoxane (MAO) as cocatalyst. At
ambient pressure, these complexes were inactive for ethyl-
ene reaction. By increasing the ethylene pressure to
8 atm, polyethylene was obtained along with butene with-
out other oligomers, which is the first example of simulta-
neous dimerization and polymerization of ethylene by
catalytic system of palladium complexes. The results of eth-
ylene dimerization and polymerization are listed in Table 3.
The results show that the ligand environment had signif-
icant influence on ethylene reactivity. There are two types
of substituents on the aryl group of imine, the alkyl and
halide. As shown in the entries 1–3 of Table 3, the dimer-
ization activity decrease in the order C1 > C2 > C3. For
ethylene polymerization, the activity decrease in the order
C3 > C2 > C1, which is consistent with the fact that cata-
lytic activity increases along with their bulky effects. For
the complexes that incorporated halides, the activity
decreases in the order C5 > C6 > C7. Those observations
reveal that the less bulky substituents will ease ethylene
coordination on active centers and lead higher ethylene
reactivity [22].
For C5, the average deviation from the plane of Pd1,
˚
N1, C9, C7, N2 is 0.0991 A, and the dihedral angle between
the coordination plane and phenyl ring is 74.5°. There is no
direct interaction between palladium and oxygen atom
˚
(O2) with the distance of 3.574 A, but the distance is much
˚
shorter than that (4.354 A) of C1. The plausible explana-
tion for this observation is the influence of ligand contain-
ing electron-withdrawing fluoro-group that decreased the
electron density on N atom of the imine, which in turn
decreased electron density on metal atom resulting in a
weak interaction between electron donating oxygen and
palladium atom.
For C6, the average deviation from the coordination
˚
plane of Pd1, N1, C9, C7, N2 is 0.0896 A, and the dihedral
angle between the coordination plane and phenyl ring is
76.0°. The bond lengths of Pd–N1 and Pd–N2 are nearly
the same with that of C5, the distance of Pd–O2
˚
(3.615 A) indicates the weak interaction between palladium
and oxygen atom (O2).
Two individual active sites are possibly formed as the
catalytic centers in the catalytic systems, one which cata-
lyzes the dimerization of ethylene for butene, and the other
which polymerizes ethylene to polymer. Due to the equip-
ments limits, those active sites could not be determined yet.
2.3. Ethylene reaction
The catalytic activities of precursors C1–C7 for ethylene
dimerization and polymerization were determined in the
Table 3
Ethylene reaction catalyzed by palladium complexes with MAO
Entry number
Precursor
Al/Pd
Production activityc
Dimerization (g)
Polyethylene (g)
Tm (°C)
1
2
3
4
5
6
7
8
C1
C2
C3
C4
C5
C6
C7
C4
C4
C4
1000
1000
1000
1000
1000
1000
1000
500
8.84
6.14
6.80
12.3
8.86
7.86
3.44
3.60
5.64
15.0
0.418
0.272
0.300
0.570
0.402
0.361
0.151
0.170
0.267
0.750
0.024
0.035
0.040
0.045
0.041
0.032
0.021
0.010
0.015
Trace
130.7
133.5
134.0
134.1
133.5
132.8
nd
nd
133.2
nd
9a
10b
1000
1000
Reaction conditions: 5 lmol complex, 150 mL toluene, 8 atm ethylene, 1 h, 20 °C.
a
Adding Ph3P with ratio of Pd/Ph3P = 1:2.
Solvent: CH2Cl2.
104 g PE/molPd h.
b
c

W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
4763
However, some additional experiments of precursor C4
were performed to confirm the formation of different cata-
lytic centers. Changing the ratio of MAO to palladium
(entry 8) does not change the ratio of active centers except
for lowering the activities. Adding auxiliary ligand of Ph3P
(entry 9) to the reactor, the catalytic activities of both eth-
ylene dimerization and polymerization decreased because
of the potential coordination of auxiliary ligands with
active sites [23]. Changing the solvent by using dichloro-
methane (entry 10), higher activity of ethylene dimerization
was obtained. Therefore, one major active site was possibly
formed to perform ethylene dimerization. In this case, the
catalytic sites might be selectively formed because of sol-
vent environment. Due to the low catalytic activity of eth-
ylene polymerization, the Tm of polyethylene obtained
were measured and ranged from 130.7 to 134 °C, which
are in line with the characteristics of HDPE.
ture and the reaction time, were probed for their effects
on catalytic activities and polymer yields. Like in nickel
systems studied previously [13], a significant improvement
of catalytic activity was observed when either molar
ratio of MAO to the palladium precursor or the concentra-
tion of norbornene was increased. It has been noted that
longer reaction time rendered higher yield of polymers,
and the activity of the catalyst decreased rapidly due to
the presence of less number of monomers in the system.
The optimal temperature is between 15 and 25 °C for indi-
vidual palladium precursors in the norbornene polymeriza-
tion. Unlike the poly(norbornene) obtained in nickel
catalytic systems [13], the poly(norbornene) generated from
palladium catalytic systems could not be measured for their
molecular weights and distributions, partly because it was
not fully soluble in diclorobenzene. This may be the reason
that molecular weight information of poly(norbornene)
was often not reported until our report on nickel catalytic
system [13]. The poly(norbornene) obtained in palladium
systems produce some polymers with high molecular
weight which is beyond the measurement scale of GPC.
Moreover, the absence of the peaks corresponding to
C@C double bond in IR spectra indicates the occurrence
of vinyl-type polymerization rather than ring-opening
metathesis polymerization (ROMP) [25,13].
2.4. Polymerization of norbornene
The palladium complexes were further investigated for
catalyzing the vinyl-polymerization of norbornene. Preli-
minary experiments demonstrated that the single-compo-
nent palladium complex does not polymerize norbornene.
However, when MAO was used as the co-catalyst, the title
palladium complexes displayed high activities for norborn-
ene polymerization. The results of vinyl-polymerization of
norbornene are summarized in Table 4. In general, the com-
plexes containing the ligand with electron- withdrawing
halides exhibit higher catalytic activities than those of other
complexes, and the order is C5 > C6 > C7 > C1 > C2 >
C3 > C4. The C5 and C1 showed better activity for com-
plexes incorporating the halides or alky groups individually.
It is worth noting that both the size of the difluro and
methyl substituents are smaller than that of other halides
and other alkyl groups, which can explain for it. In addition
to the electronic effect, less bulky substituents provide the
favorable environmental insertion of norbornene, and
therefore, result in higher catalytic activity. This result is
in contrast with what has been observed for some nickel cat-
alytic systems [24], for which no clear effect of stereo-bulky
of substitutes on the catalytic activities was observed.
As usual, various reaction parameters, including mono-
mer concentration, the ratio of Al/Pd, reaction tempera-
3. Conclusions
A series of palladium complexes containing 2-methoxy-
carbonyl-6-iminopyridine ligands have been synthesized
and characterized along with their single-crystal X-ray
analysis. Activated with MAO, they showed moderate
activity for ethylene dimerization and polymerization
simultaneously. There are two different catalytically active
sites for ethylene dimerization and polymerization, individ-
ually. The productivity increased with the decrease of
bulky substituents, because the less bulky substituents will
ease ethylene coordination on the active center and give
higher ethylene reactivity. Though good catalytic activities
were obtained for vinyl-polymerization of norbornene, the
PNB is less interesting because of their partly insolubility.
These new palladium catalysts exhibit interesting proper-
ties for ethylene and norbornene reactivity, and the reac-
tion conditions greatly affect the products.
4. Experimental section
Table 4
Norbornene polymerization
4.1. General procedures
Entry
Precursor
Activity (105 gPNB molÀ1Pd hÀ1
)
Yield (%)
1
2
3
4
5
6
7
C1
C2
C3
C4
C5
C6
C7
8.23
8.05
8.00
7.92
10.5
10.0
8.57
58.4
57.1
56.7
56.2
74.5
71.1
61.4
All manipulations of the moisture-sensitive compounds
were carried out under an atmosphere of nitrogen using
standard Schlenk techniques. Melting points were deter-
mined with a digital electrothermal apparatus without cal-
ibration. The IR spectra were obtained on a Perkin–Elmer
FT-IR 2000 spectrophotometer by using the KBr disc in
the range of 4000–400 cmÀ1. The NMR spectra were
recorded on a Bruker DMX-300 instrument with TMS as
Reaction conditions: 5 lmol complex, total volume 30 mL with toluene as
solvent [norbornene]/[Pd] = 5000, MAO/Pd = 1000, 20 °C, 30 min.

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W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
the internal standard. Elemental analyses were performed
on a Flash EA 1112 microanalyzer.
for C17H18N2O2: C, 72.32; N, 9.92; H, 6.43. Found: C,
72.10; N, 9.64; H, 6.49%.
Melting points of the polymers were obtained on a Per-
kin–Elmer DSC-7 in the standard DSC run mode. The
instrument was initially calibrated for melting point of an
indium standard at a heating rate of 10 °C/min. The poly-
mer sample was first equilibrated at 0 °C and then heated
to 160 °C at a rate of 10 °C/min to remove thermal history.
The sample was then cooled to 0 °C at a rate of 10 °C/min.
A second heating cycle was used for collecting DSC thermo
gram data at a ramping rate of 10 °C/min. Toluene was
refluxed over sodium–benzophenone until the purple color
appeared and distilled under nitrogen prior to use. Dichlo-
ride methane was distilled under nitrogen from CaH2. All
other chemicals were obtained commercially and used
without further purification unless stated otherwise.
To ligand L1 (0.2821 g, 1 mmol) and PdCl2(CH3CN)2-
(0.259 g, 1 mmol) was added 10 mL fresh distilled dichloro-
methane at the room temperature .The reaction mixture was
stirred 24 h, and 10 mL diethyl ether was added to precipi-
tate the complex. The desired complex, 2-methoxycarbo-
nyl-6-(1-(2,6-dimethylphenylimino)ethyl)pyridyl palladium
dichloride (C1), was obtained as orange powder (0.413 g)
1
in 89.7% yield. IR (Nujol, cmÀ1): 1743; 1589. H NMR
(CD3OCD3): d 8.58 (t, 1H, J = 9.00 Hz, Py–H), 8.49 (d,
1H, J = 6.00 Hz, Py–H), 8.04 (d, 1H, J = 6.00 Hz, Py–H),
7.12 (m, 3H, Ar–H), 3.89 (s, 3H, OCH3), 2.41 (s, 3H,
CH3C@N), 2.27 (s, 6H, CH3). 13C NMR(d6-DMSO): d
167.1, 165.4, 156.2, 148.8, 147.2, 138.9, 128.9, 128.3, 126.9,
125.2, 124.9, 123.5, 53.1, 18.6, 18.0. Anal. Calc. for
C17H18Cl2N2O2Pd: C, 44.42; H, 3.95; N, 6.09. Found: C,
44.28; H, 4.16; N, 6.09%.
4.2. Synthesis of palladium complexes
4.2.1. Synthesis of 2-methoxycarbonyl-6-iminopyridine
The compound was prepared according to the literature
method [18], except that ethyl acetate and ethanol were
used, instead of methyl acetate and methanol. The
desired compound 2-methoxycarbonyl-6-acetylpyridine, was
obtained as white solid in 30.0% yield after purified by col-
umn chromatography (silica-gel, petroleum ether:ethyl ace-
tate = 8:1); m.p.: 64 °C. IR (Nujol, cmÀ1): 1721 (COOCH3);
1700 (C@O).1H NMR (CDCl3): d 8.27 (d, 1H, J = 6.51 Hz,
Py–H); 8.21 (d, 1H, J = 6.51 Hz, Py–H); 8.01 (t, 1H,
J = 7.89 Hz, Py–H); 4.04 (s, 3H, –OCH3); 2.81 (s, 3H,
C(O)CH3). 13C NMR (CDCl3): d 199.8, 165.4, 153.8,
147.8, 138.2, 128.4, 124.8, 53.2, 25.9. Anal. Calc. for
C9H9NO3: C, 60.33; H, 5.06; N, 7.82. Found: C, 60.10; H,
4.95; N, 7.81%.
4.2.3. Synthesis of 2-methoxycarbonyl-6-(1-
(2,6-diethylphenylimino)ethyl)pyridyl palladium
dichloride (C2)
Using the same procedure for L1, by 2-methoxycar-
bonyl-6-acetylpyridine (0.500 g, 3.3 mmol) and 2, 6-diethy-
laniline (0.520 g, 3.50 mmol), the 2-methoxycarbonyl-6-(1-
(2,6-diethylphenylimino)ethyl)pyridine (L2) was obtained
as yellow powder (0.705 g, 2.27 mmol) in yield 68.8%;
m.p.: 98 °C; IR (Nujol, cmÀ1): 1728 (COOCH3), 1637
1
(C@N). H NMR (CDCl3): d 8.57 (d, 1H, J = 7.23 Hz,
Py–H), 8.21(d, 1H, J = 7.56 Hz, Py–H), 7.94 (t, 1H,
J = 7.92 Hz, Py–H), 7.12 (d, 2H, J = 6.51 Hz, Ar–H),
7.03 (t, 1H, J = 6.74 Hz, Ar–H), 4.02 (s, 3H, –OCH3),
2.36 (m, 4H, J = 9.27 Hz, CH2-), 2.27(s, 3H, CH3C@N),
1.12(t, 6H, J = 7.20 Hz, –CH3). 13C NMR (CDCl3): d
166.7, 165.8, 156.5, 147.6, 147.2, 137.5, 131.1, 126.3,
126.0, 124.5, 123.6, 52.9, 24.7, 16.9, 13.8. Anal. Calc. for
C19H22N2O2: C, 73.52; H, 7.14; N, 9.03. Found: C, 73.60;
H, 7.14; N, 9.03%. Using ligand L2 (0.310 g, 1 mmol)
and PdCl2(CH3CN)2 (0.259 g, 1 mmol), the 2-methoxy-
carbonyl-6-(1-(2,6-diethylphenylimino)ethyl)pyridyl palla-
dium dichloride (C2)(0.442 g, 0.91 mmol) was obtained in
91.0% yield. IR (Nujol, cmÀ1): 1738(COOCH3),
4.2.2. Synthesis of 2-methoxycarbonyl-6-(1-
(2,6-dimethylphenylimino)ethyl)pyridyl palladium
dichloride (C1)
All synthesis of L1–L7 and C1–C7 were prepared by sim-
ilar procedures, thus only the synthesis of L1 and C1 is
described in detail. A solution of 2-methoxycarbonyl-6-
acetylpyridine (0.500 g, 3.3 mmol) and 2,6-dimethylaniline
(0.500 g, 4.26 mmol), and p-toluenesulfonic acid (0.05 g)
1589(C@N). 1H NMR (CDCl3):
d
8.37 (t, 1H,
ꢀ
˚
with 4 A molecular sieves in toluene (50 mL) was refluxed
J = 7.89 Hz, Py–H), 8.10 (d, 1H, J = 6.54 Hz, Py–H),
8.01 (d, 1H, J = 6.54 Hz, Py–H), 7.31 (t, 1H, J =
6.87 Hz, Ar–H), 7.18 (d, 2H, J = 7.56 Hz, Ar–H), 4.02 (s,
3H, –OCH3), 2.84 (m, 2H, –CH2-), 2.48 (d, 2H,
J = 7.56 Hz, –CH2-), 2.25 (s, 3H, CH3C@N), 1.31 (t, 6H,
J = 7.56 Hz, –CH3). Anal. Calc. for C19H22Cl2N2O2Pd:
C, 46.79; H, 4.55; N, 5.74. Found: C, 46.62; H, 4.55; N,
5.73. 13C NMR(CDCl3): d 167.0, 165.4, 156.0, 147.8,
139.1, 126.9, 126.2, 124.8, 123.9, 53.1, 24.7, 17.2, 14.4%.
for 12 h. The mixture was cooled to room temperature,
filtered, and separated by column chromatography (silica-
gel, petroleum ether: EtOAc = 15:1). The product, 2-meth-
oxycarbonyl-6-(1-(2,6-dimethylphenylimino)ethyl)pyridine
(L1), was obtained as yellow crystals (0.726 g, 2.6 mmol) in
yield 92.2%; m.p.: 100 °C; IR (Nujol, cmÀ1): 1718
(COOCH3), 1646 (C@N). 1H NMR(CDCl3): d 8.60 (d,
1H, J = 7.26 Hz, Py–H), 8.22 (d, 1H, J = 7.56 Hz, Py–H),
7.93 (t, 1H, J = 7.28 Hz, Py–H), 7.06 (d, 2H, J = 7.60 Hz,
Ar–H), 6.95 (t, 1H, J = 6.78 Hz, Ar–H), 4.05 (s, 3H, –
OCH3), 2.25 (s, 3H, C(CH3)=N), 2.02 (s, 6H, –CH3). 13C
NMR (CDCl3): d 167.0, 165.8, 156.5, 148.6, 147.2, 137.5,
128.0, 126.4, 125.4, 124.6, 123.3, 53.0, 18.0, 16.6. Anal. Calc.
4.2.4. Synthesis of 2-methoxycarbonyl-6-(1-(2,6-di-i-
propylphenylimino)ethyl)pyridyl palladium dichloride (C3)
Using the same procedure for L1, by 2-methoxycar-
bonyl-6-acetylpyridine (0.500 g, 3.3 mmol) and 2,6-dipro-

W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
4765
pylaniline (1.20 g, 3.55 mmol), the 2-methoxycarbonyl-6-
(1-(2,6-di-i-propylphenylimino)ethyl)pyridine (L3) was
obtained as yellow crystals (0.507 g, 1.50 mmol) in
45.4% yield; m.p.: 148–150 °C. IR (Nujol, cmÀ1):
20.9, 19.9, 18.6, 18.0. Anal. Calc. for C21H26Cl2N2O2P-
d Æ CH2Cl2: C, 40.85; H, 3.97; N, 5.01. Found: C, 40.66;
H, 3.97; N, 5.08%.
1
1725(COOCH3), 1648(C@N). H NMR (CDCl3): d 8.59
4.2.6. Synthesis of 2-methoxycarbonyl-6-(1-(2,6-
difluorophenylimino)ethyl)pyridyl palladium
dichloride (C5)
(d, 1H, J = 6.87 Hz, Py–H); 8.21 (d, 1H, J = 7.05 Hz,
Py–H), 7.95 (t, 1H, J = 7.89 Hz, Py–H), 7.16(d, 2H,
J = 6.18 Hz, Ar–H), 7.12 (t, 1H, Ar–H), 4.02 (s, 3H,
OCH3), 2.71 (m, 2H, –CH (CH3)2), 2.28 (s, 3H, CH3C@N),
1.13 (d, 12H, -CH3). 13C NMR (CDCl3): d 166.6, 165.8,
156.5, 147.2, 146.3, 137.5, 135.7, 126.3, 124.6, 123.8,
123.1, 53.0, 28.3, 23.3, 22.9, 17.2. Anal. Calc. for
C21H26N2O2: C, 74.52; H, 7.74; N, 5.43. Found: C, 74.08;
H, 7.74; N, 5.43%. Using ligand L3 (0.338 g, 1 mmol)
and PdCl2(CH3CN)2 (0.259 g, 1 mmol), the 2-methoxycar-
bonyl-6-(1-(2,6-di-i-propylphenylimino) ethyl)pyridyl pal-
ladium dichloride (C3) (0.289 g, 0.56 mmol) was also
obtained in 55.7% yield. IR (Nujol, cmÀ1): 1733
(COOCH3); 1584.1H NMR (CDCl3): d 8.34 (t, 1H, J =
7.86 Hz, Py–H), 8.01 (t, 2H, J = 7.20 Hz, Py–H), 7.35 (t,
1H, J = 7.85 Hz, Ar–H), 7.22 (d, 2H, J = 7.56 Hz, Ar–H),
4.03 (s, 3H, –OCH3), 3.10 (m, 2H, –CH(CH3)2), 2.28 (s,
3H, CH3C@N), 1.45 (d, 6H, J = 6.51 Hz, –CH3), 1.14 (d,
6H, J = 6.87 Hz, –CH3). 13C NMR(d6-DMSO): d 167.1,
165.5, 157.3, 156.0, 147.4, 146.2, 140.3, 139.1, 135.5, 127,
124.7, 124.3, 123.5, 53.1, 28.3, 24.3, 24.2, 23.6, 23.1, 17.5.
Anal. Calc. for C21H26Cl2N2O2Pd: C, 48.90; H, 5.08; N,
5.43. Found: C, 48.57; H, 5.08; N, 5.32%.
Using the same procedure for L1, 2-methoxycarbonyl-6-
acetylpyridine (0.500 g, 3.3 mmol) and 2,6-difuluroaniline
(0.500 g, 3.87 mmol), the 2-methoxycarbonyl-6-(1-(2,6-
difluorophenylimino)ethyl)pyridine (L5) (0.612 g, 2.11
mmol) was obtained as pale yellow solid in yield 64.0%;
m.p.: 52 °C. IR (Nujol, cmÀ1): 1724 (COOCH3); 1649
(C@N).1H NMR (CDCl3): d 8.52 (d, 1H, J = 9.2 Hz, Py–
H), 8.21(d, 1H, J = 9.2 Hz, Py–H), 7.94 (t, 1H,
J = 7.84 Hz, Py–H ), 7.03 (m, 1H, Ar–H), 6.97 (m, 2H,
Ar–H), 4.02 (s, 3H, OCH3), 2.45 (s, 3H, N@CCH3). 13C
NMR (CDCl3): d 172.4, 165.6, 156.0, 154.6, 154.5, 151.3,
151.2, 147.1, 137.6, 126.7, 125.2, 124.3, 124.2, 111.9,
111.7, 111.5, 52.9, 17.7. Anal. Calc. for C15H12F2N2O2:
C, 62.07; H, 4.17; N, 9.65. Found: C, 62.09; H, 4.29;
N, 9.51%. Using ligand L5 (0.290 g, 1 mmol) and
PdCl2(CH3CN)2 (0.259 g, 1 mmol), the 2-methoxy-
carbonyl-6-(1-(2,6-difluorophenylimino)ethyl)pyridyl pal-
ladium dichloride (C5)(0.312 g, 0.67 mmol) was obtained
in yield 67.0%. IR (Nujol, cmÀ1): 1732 (COOCH3), 1693
(C@N), 1591. 1H NMR (DMSO): d 8.26 (t, 1H,
J = 7.24 Hz, Py–H), 8.20 (m, 2H, Py–H), 6.85 (t, 2H,
J = 6.96 Hz, Ar–H), 6.50 (m, 1H, Ar–H), 3.90 (s, 3H,
OCH3), 2.63 (s, 3H, N@C–CH3). 13C NMR(d6-DMSO):
d 172.6, 165.3, 155.3, 154.2, 150.9, 147.5, 139.2, 128.8,
127.5, 125.2, 124.9, 112.7, 112.4, 111.1, 53.1, 17.98. Anal.
Calc. for C15H12F2N2O2Pd: C, 38.53; H, 2.59; N, 5.99.
Found: C, 37.99; H, 2.53; N, 5.72%.
4.2.5. Synthesis of 2-methoxycarbonyl-6-(1-(2,4,6-
trimethylphenylimino)ethyl)pyridyl palladium
dichloride (C4)
Using the same procedure for L1, 2-methoxycarbonyl-6-
acetylpyridine (0.500 g, 3.3 mmol) and 2,4,6-trimethylani-
line (0.490 g, 3.63 mmol), the 2-methoxycarbonyl-6-(1-
(2,4,6-trimethylphenylimino) ethyl)pyridine (L4) ( 0.612 g,
2.07 mmol) was obtained as pale yellow solid in yield
62.8%; m.p.: 127 °C. IR (Nujol, cmÀ1): 1717 (COOCH3),
1634 (C@N). 1H NMR (CDCl3): d 8.56 (d, 1H, J =
6.00 Hz, Py–H), 8.19 (d, 1H, J = 9.00 Hz, Py–H), 7.94 (t,
1H, J = 9.00 Hz, Py–H), 6.89 (s, 2H, Ar–H), 4.02 (s, 3H,
OCH3), 2.29 (s, 3H, CH3C@N), 2.25 (s, 3H, p-Ar-CH3),
1.98 (s, 6H, o-Ar-CH3). 13C NMR (CDCl3): d 166.8,
165.6, 156.4, 153.3, 147.2, 146.6, 137.2, 135.6, 129.8,
127.9, 126.9, 126.1, 124.5, 52.9, 21.0, 19.1, 18.7, 17.5. Anal.
Calc. for C18H20N2O2: C, 72.95; H, 6.80; N, 9.45. Found:
C, 73.30; H, 6.90; N, 9.45%. Using ligand L4 (0.296 g,
1 mmol) and PdCl2(CH3CN)2 (0.259 g, 1 mmol), the 2-
methoxycarbonyl-6-(1-(2,4,6-trimethylphenylimino)ethyl)-
pyridyl palladium dichloride (C4) (0.428 g, 0.88 mmol) was
also obtained in yield 88.4%. IR (Nujol: cmÀ1): 1740
(COOCH3), 1587. 1H NMR(CDCl3): d 8.31 (t, 1H,
J = 6.00 Hz, Py–H); 8.00 (t, 2H, J = 6.00 Hz, Py–H);
6.93 (s, 2H, Ar–H), 4.03 (s, 3H, OCH3), 2.29 (s, 3H,
N@C–CH3), 2.26 (s, 6H, o-Ar–H), 2.24 (s, 3H, p-Ar–H).
13C NMR(d6-DMSO): d 167.4, 165.3, 156.3, 153.3, 147.3,
146.4, 139.7, 138.9, 132.1, 130.1, 128.9, 126.9, 125.0, 53.1,
4.2.7. Synthesis of 2-methoxycarbonyl-6-(1-(2,6-
dichlorophenylimino)ethyl)pyridyl palladium
dichloride (C6)
Using the same procedure for L1, 2-methoxycarbonyl-6-
acetylpyridine (0.500 g, 3.3 mmol) and 2,6-dichloroaniline
(5.60 g, 3.47 mmol), the 2-methoxycarbonyl-6-(1-(2,6-
dichlorophenylimino) ethyl)pyridine (L6) (0.274 g, 0.85
mmol) was obtained as pale yellow solid in yield 25.8%.
IR: 2954, 1728 (C@O), 1654 (C@N), 1438, 1138, 788, 766.
1H NMR (CDCl3): d 8.58 (d, 1H, J = 7.89 Hz, Py–H),
8.22 (d, 1H, J = 7.89 Hz, Py–H), 7.97 (m, 1H, Py–H), 7.36
(m, 2H, J1 = 7.89 Hz, J2 = 2.40 Hz, Ar–H), 7.00 (m, 1H,
Ar–H), 4.03(s, 3H, OCH3), 2.38(s, 3H, CH3C@N).13C
NMR (CDCl3): d 172.1, 165.3, 155.5, 147.3, 146.3, 145.5,
137.6, 128.5, 126.7, 125.8, 124.5, 124.4, 52.9, 17.60. Anal.
Calc. for C15H12Cl2N2O2: C, 55.75; H, 3.74; N, 8.67. Found:
C, 55.80; H, 3.82; N, 8.20%. Using ligand L6 (0.323 g,
1 mmol) and PdCl2(CH3CN)2 (0.2590 g, 1 mmol), the 2-
methoxycarbonyl-6-(1-(2,6-dichlorophenylimino)ethyl)pyr-
idyl palladium dichloride (C6) (0.434 g, 0.87 mmol) was also
obtained in yield 87.0%. IR (Nujol, cmÀ1): 1731
(COOCH3), 1590. 1H NMR (DMSO): d 8.25 (t, 1H,

4766
W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
J = 6.00 Hz, Py–H), 8.20 (m, 2H, Py–H), 7.21 (d, 2H,
J = 6.00 Hz, Ar–H), 6.58 (t, 1H, J = 6.52 Hz, Ar–H), 3.94
(s, 3H, OCH3), 2.29 (s, 3H, N@C–CH3). 13C NMR(d6-
DMSO): d 172.1, 165.1, 153.4, 147.5, 141.4, 139.6, 129.1,
128.8, 128.5, 124.8, 120.0, 118.6, 117.4, 53.2, 17.9. Anal.
Calc. for C21H26Cl2N2O2Pd: C, 36.00; H, 2.42; N, 5.60.
Found: C, 35.64; H, 2.40; N, 5.39%.
ene solution of palladium complex and 120 ml of toluene
were added to the reactor in this order under ethylene
atmosphere. When being to the reaction temperature, eth-
ylene with the desired pressure (8 atm) was introduced to
start the reaction. After 1 h, the reaction was stopped.
And then a small amount of the reaction solution was col-
lected, terminated by the addition of 5% aqueous hydro-
gen chloride and then analyzed by gas chromatography
(GC) for determining the distribution of oligomers
obtained. Then the residual solution was quenched with
HCl–acidified ethanol (5%). The precipitated polymer
was collected by filtration, washed with ethanol, dried in
vacuum at 60 °C until constant weight, weighed and finally
characterized.
4.2.8. Synthesis of 2-methoxycarbonyl-6-(1-
(2,6-dibromo-4-methylphenylimino)ethyl)
pyridyl palladium dichloride (C7)
Using the same procedure for L1, by 2-methoxycarbonyl-
6-acetylpyridine (0.500 g, 3.3 mmol) and 2,6-dibromo-3-
methylaniline (0.920 g, 3.50 mmol), the 2-methoxycarbonyl-
6-(1-(2,6-dibromo-4-methylphenylimino)ethyl)pyridine (L7)
(0.351 g, 0.83 mmol) was obtained as pale yellow solid in
yield 25.1%; m.p.:124–126 °C. IR (Nujol, cmÀ1): 1718
(COOCH3); 1635(C@N) .1H NMR (CDCl3): d 8.58 (d, 1H,
J = 9.00 Hz, Py–H), 8.22 (d, 1H, J = 9.00 Hz, Py–H), 7.96
(t, 1H, J = 9.00 Hz, Py–H), 4.03 (s, 3H, OCH3), 2.35 (s,
3H, CH3C@N), 2.32 (s, 3H, o-Ar–CH3). 13C NMR (CDCl3):
d 171.1, 165.6, 155.8, 147.2, 145.3, 137.7, 135.6, 132.6, 126.8,
125.2, 113.0, 52.9, 20.3, 17.6. Anal. Calc. for
C16H14Br2N2O2: C, 45.10; H, 3.31; N, 6.57. Found: C,
45.89; H, 3.31; N, 6.18%. Using ligand L7 (0.424 g, 1 mmol)
and PdCl2(CH3CN)2 (0.259 g, 1.0 mmol), the 2-methoxy-
carbonyl-6-(1-(2,6-dibromo-4-methylphenylimino)ethyl)-
pyridylpalladium dichloride (C7) (0.540 g, 0.9 mmol) was
obtained in yield 90%. IR (Nujol, cmÀ1): 1728.35
(COOCH3); 1589, 1613 (C@N).1 NMR (DMSO): 8.47 (d,
1H, J = 6.00 Hz, Py–H), 8.24(m, 2H, Py–H), 7.58 (s, 2H,
J = 6.05 Hz, Ar–H), 3.93 (s, 3H, OCH3), 2.31 (s, 3H,
N@C–CH3), 2.15 (s, 3H, –CH3). 13C NMR (d6-DMSO): d
171.0, 165.3, 155.2, 147.5, 145.1, 139.3, 136.7, 133.0, 127.6,
125.2, 112.9, 53.2, 20.1, 17.8. Anal. Calc. for
C16H14Br2Cl2N2O2Pd: C, 31.85; H, 2.34; N, 4.64. Found:
C, 31.49; H, 2.45; N, 4.63%.
4.5. General procedure for polymerization of norbornene
In a typical procedure, the catalyst (5 lmol) was dis-
solved in a Schlenk tube in 23 ml degassed toluene under
nitrogen and a 3.47 ml toluene solution of norbornene
(7.20 M, 25 mmol of norbornene) was added via a syringe.
The polymerization was initiated by adding 3.57 ml toluene
solution of 1.4 mol/L MAO (5.0 mmol). After 30 min, the
polymerization was terminated by injecting 200 ml acidic
methanol (methanol:HCl(conc.) = 95:5) into the reactor.
The polynorbornene was isolated by filtration, washed with
methanol, and dried in vacuum at 100 °C for 100 h. The
total reaction volume of norbornene polymerization was
30 ml unless otherwise stated, that was achieved by adding
solvent when necessary. Similarly, the polymerization of
norbornene was also carried out by using toluene as
solvent.
4.6. X-ray crystallography measurement
The single-crystal X-ray diffraction for complexes C1
and C2 were carried out on a Rigaku RAXIS Rapid IP dif-
fractometer with graphite monochromated Mo Ka radia-
˚
4.3. General procedure for ethylene polymerization at 1 atm
ethylene pressure
tion (k = 0.71073 A) at 120 k and 173 k, respectively.
Intensity data of complexes C4, C5, C6, C7 were collected
on a Bruker Smart 1000 CCD diffractometer at 130(2) K
with graphite monochromated Mo Ka radiation
A flame dried three-neck round flask was loaded with
the complexes C1–C7 and vacuum-filled three times by
nitrogen. Then ethylene was charged together with freshly
distilled toluene and stirred for 10 min. MAO was added by
a syringe. The reaction mixture was stirred under 1 atmo-
spheric ethylene pressure for a limited time, and the cata-
lytic reaction was terminated with acidified water. An
aliquot of the reaction mixture was analyzed by GC and
GC–MS.
˚
(k = 0.71073 A). Cell parameters were obtained by global
refinement of the positions of all collected reflections.
Intensities were corrected. The structures were solved by
direct methods and re- fined by full-matrix least-squares
on F2. Each H atom was placed in a calculated position
and refined anisotropically. Structure solution and refine-
ment were performed using the SHELXL-97 Package. Crystal
data and processing parameters are summarized in Table 1.
4.4. General procedure for ethylene polymerization at 8 atm
ethylene pressure
Acknowledgements
The project supported by NSFC No. 20473099 and
Polymer Chemistry Laboratory, Chinese Academy of Sci-
ences and China-Petro-Chemical Corporation. We thank
Dr. Jinkui Niu for polishing English usage.
It was carried out in a 250 ml autoclave stainless steel
reactor equipped with a mechanical stirrer and a tempera-
ture controller. The desired amount of MAO, 30 ml tolu-

W. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4759–4767
4767
(b) J. Melia, E. Connor, S. Rush, S. Breunig, C. Mehler, W. Risse,
Macromol. Symp. 89 (1995) 433;
Appendix A. Supporting information available
(c) C. Mehler, W. Risse, Macromolecules 25 (1992) 4226.
[12] (a) A.S. Abu-Surrah, B. Rieger, J. Mol. Catal. A: Chem. 128 (1998)
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(b) M. Arndt, M. Gosmann, Polym. Bull. 41 (1998) 433.
[13] (a) W.-H. Sun, H. Yang, Z. Li, Y. Li, Organometallics 22 (2003)
3678;
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data Cen-
ter, CCDC Nos. 291547, 291548, 291549, 291550, 291551
and 291552 for complexes C1, C2, C4, C5, C6 and C7,
respectively. Copies of this information may be obtained free
of charge from CCDC, 12 Union Road, Cambridge, CB2 1
EZ, UK; fax: +44 1223 336033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccd.cam.ac.uk. Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.jorganchem.2006.07.026.
(b) H. Yang, Z. Li, W.-H. Sun, J. Mol. Cat. A: Chem. 206 (2003) 23;
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261;
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