Synthesis, structure and norbornene polymerization behavior of neutral palladium complexes

Article abstract of DOI:10.1016/j.poly.2004.03.017

A series of neutral palladium(II) complexes bearing non-symmetric bidentate pyrrole-iminato or salicylaldiminato chelate ligands have been synthesized, and the structure of representative complexes (3a, 4a, and 5a) have been confirmed by X-ray crystallographic analysis. These palladium complexes have been investigated as catalysts for the polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display high activities and produce vinyl-addition polynorborenes. Catalytic activity of up to 8.52×10³ kg/mol_Pd h has been observed. Wide-angle X-ray diffraction (WAXD) has been used to investigate the polymer microstructure and it has been found that they are non-crystalline.

Full text of DOI:10.1016/j.poly.2004.03.017

Polyhedron 23 (2004) 1619–1627
www.elsevier.com/locate/poly
Synthesis, structure and norbornene polymerization behavior
of neutral palladium complexes q
*
Hua Liang, Jingyu Liu, Xiaofang Li, Yuesheng Li
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
5625 Renmin Street, Changchun 130022, China
Received 18 September 2003; accepted 28 March 2004
Available online 27 April 2004
Abstract
A series of neutral palladium(II) complexes bearing non-symmetric bidentate pyrrole-iminato or salicylaldiminato chelate ligands
have been synthesized, and the structure of representative complexes (3a, 4a, and 5a) have been confirmed by X-ray crystallographic
analysis. These palladium complexes have been investigated as catalysts for the polymerization of norbornene. Using modified
methylaluminoxane (MMAO) as a cocatalyst, these complexes display high activities and produce vinyl-addition polynorborenes.
Catalytic activity of up to 8.52 ꢀ 103 kg/molPd h has been observed. Wide-angle X-ray diffraction (WAXD) has been used to in-
vestigate the polymer microstructure and it has been found that they are non-crystalline.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Neutral palladium(II) complex; X-ray crystallography; Catalyst; Methylaluminoxane; Norbornene; Vinylic polymerizaition
1. Introduction
bond is opened. As the vinyl-poly(norbornene) has many
unique physical characteristics such as good mechanical
strength, heat resistivity, optical transparency and low
birefringence [8,9], many interests are focused on this
kind of polymerization. The selection of catalysts is the
key. Catalysts containing the metals nickel [8–16], chro-
mium [17], titanium [18], zirconium [19–22], cobalt
[23,24] and palladium [25–35] are reported in various
literatures for the vinyl-type polymerization of norn-
ornene. Nickel and palladium complexes display ex-
tremely high catalytic activity and produce high
molecular weight polymers with excellent performance.
Hence, our interest is keen on the well-defined complexes
of nickel and palladium (see Scheme 1).
We found that neutral nickel complexes activated
with methylaluminoxane display extremely high activity
for the vinylic polymerization of norbornene [14,15],
and Novak and co-workers [36] reported that neutral
palladium complexes as catalysts for olefin and vinyl
monomer polymerizations display excellent activity.
This urges us to investigate if neutral palladium(II)
complexes have high catalytic activity. Here, we would
like to report on the synthesis of novel neutral
palladium(II) complexes bearing pyrrole-iminato or
With the boom in transition metal catalysis, there is a
rapid development of a wide range of polyolefinic mate-
rials. A polymer with a certain microstructure can be
easily obtained by employing a certain catalyst. Nor-
bornene is a representative cycloolefin monomer which
can be polymerized through ring-opening metathesis
polymerization (ROMP), cationic (or radical) and vinylic
addition polymerization mechanisms. ROMP yields
poly(1,3-cyclopentylenevinylene) which retains one
double bond in each polymeric repeat unit [1–3]. Cationic
polymerization involves the rearrangement of the nor-
bornene framework and generally produces moderate
yields of poly (2,7-bicyclo [2,2,1] hept-2-ene) oligomers
[4–7]. Free-radical processes also produce low molecular
weight products [3]. In vinylic polymerization, the bicy-
clic structural unit remains intact and only the double
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.poly.2004.03.017.
* Corresponding author. Tel.: +86-431-5262124; fax: +86-431-
5685653.
E-mail address: ysli@ciac.jl.cn (Y. Li).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.03.017

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H. Liang et al. / Polyhedron 23 (2004) 1619–1627
2.2. Synthesis of neutral Pd(II) complexes 3a–d, 4a, 5a
and 8a–c
ROMP
n
A solution of ligand 1a (0.45 g, 1.76 mmol) in THF
Cationic Polym.
(20ml) was added to NaH (0.12 g, 2.5 mmol). The re-
sulting mixture was stirred at room temperature for 3 h,
then filtered and the filtrate was evaporated. The solid
residue was dried in vacuum. The sodium salt and
(COD)PdMeCl (0.32 g, 1.2 mmol) with PPh3 (0.32 g, 1.2
mmol) were dissolved in benzene (20 ml) in a 100 ml
Schlenk flask and stirred at room temperature for 18 h.
The resulting mixture was filtered by cannula filtration.
The filtrate should be concentrated in a vacuum to ca. 5
ml, and then pentane (ca. 20 ml) was added. After 24 h,
some yellow crystals were obtained from the solution
and isolated by cannula filtration to yield 0.55 g (71.9%)
of 3a. The other complexes were prepared by the same
procedure with similar yields.
n
n
Vinylic Polym.
n
Scheme 1.
salicylaldiminato ligands and the catalysis properties for
the vinylic polymerization of norbornene.
1
2. Experimental
3a: H NMR (CDCl3): d 7.74–7.44 (m, 15 H, PPh–
H), 7.42 (s,1 H, N@C–H), 7.07–6.98 (m, 6 H, Pyrrole-
H + Ph–H), 3.42–3.37 (m, 2 H, C–H),1.28–1.19 (m,15 H,
i-Pr–CH3 + Pd–CH3). 13C NMR (CDCl3): d 4.8, 23.0,
25.0, 28.9, 111.6, 118.0, 123.3, 128.6, 128.7, 130.8, 135.1,
135.5, 142.8, 145.0, 161.6.
2.1. General procedures and materials
All work involving air and moisture sensitive com-
pounds was carried out using standard Schlenk tech-
niques. NMR data of the ligands and the complexes
were obtained on a Varian Unity 300 MHz spectrometer
at ambient temperature, with CDCl3 (ligands) or C6D6
(complexes) as solvent. IR spectra were recorded on a
Bio-Rad FTS-135 spectrophotometer. Single-crystal X-
ray diffraction data were received by P4 X-ray crystal-
lography. The wide-angle X-ray diffraction (WAXD)
spectrum was measured on a Rigaku D/Max 2500V PC
3b (73.2%): 1H NMR (CDCl3): d 7.69 (m, 15 H, PPh–
H), 7.64 (s, 1 H, N@C–H), 7.03–7.01 (s, 3 H, Ph–H),
6.65–6.45 (s, 3H, Pyrrole-H), 2.77 (s, 6 H, Ph–CH3), 1.07
(s, 3 H, Pd–CH3). 13C NMR (CDCl3): d 15.0, 25.2, 25.5,
111.0, 111.6, 118.2, 126.7, 128.8, 131.6, 132.4, 137.9,
161.5, 161.9.
1
3c (69.4%): H NMR (CDCl3): d 7.75 (s, 1 H, N@C–
H), 7.71 (m, 15 H, PPh–H), 7.13 (s, 5 H, Ph–H), 6.75–
ꢀ
with Cu Ka radiation and a wavelength of 1.54 A.
R1
Tetrahydrofuran (THF), benzene and diethyl ether
were dried over sodium with dibenzophenone as indi-
cator. Chlorobenzene and dichloromethane were ref-
luxed over calcium hydride for two weeks before use.
Aniline derivatives were obtained from Acros and pu-
rified by distillation before use. Triphenyphosphine,
pyrrole-2-carboxaldehyde, sodium tetrachlopalladate-
(II) and tetramethyltin were obtained from Aldrich and
used without further purification. Pyridine was dried
over sodium hydroxide and obtained by reduced distil-
lation. Norbornene from Aldrich was refluxed with so-
dium, purified by reduced distillation and used as a
solution in toluene. Modified methylaluminoxane
(MMAO, 7% aluminum in heptane solution) was pur-
chased from Akzo Nobel Chemical Inc. (COD)PdMeCl
was prepared by the reaction of (COD)PdCl2 and
SnMe4 according to a procedure given by Richard and
co-workers [37,38]. Salicylaldehyde derivatives were
prepared according to the method of Casiraghi et al.
[39], and the salicylaldimines 6a–c were prepared ac-
cording to the procedure described by Grubbs and co-
workers [40]. The pyrrole-imines 1a–d were prepared
according to the procedure described previously [15].
R2
H
N
H
H2N
+
N
CHO
N
H
MeOH
R2
R1
1a-d
NaH
R2
N
PdMeCl (COD)
PPh3 or Py
N
Pd
Me
R2
L
N
R1
N
3a-d, 4a
R1
2a-d
PdMeCl (COD)
MeCN
R1
R2
N
N
Pd
N
N
a: R1= R2 = i-Pr
b: R1= R2 = Me
c: R1= H, R2 = t-Bu
d: R1= R2 = H
3a-d: L= PPh3
4a: L= Py
R2
R1
5a
Scheme 2.

H. Liang et al. / Polyhedron 23 (2004) 1619–1627
1621
NMR (CDCl3): d 158.7, 151.9, 145.2, 141.4, 125.0,
124.4, 123.3, 117.4, 110.7, 27.9, 24.9, 22.2.
R
4
R
R
OH
3
4
5a (66.3%): 1H NMR (CDCl3): d 7.38 (s, 2 H, N@C–
H), 7.17–6.80 (s, 10 H, Ph–H + Pyrrole-H), 6.36 (s, 2H,
Pyrrole-H), 3.33 (m, 4H, i-Pr–CH), 0.95 (t, 24 H, 8CH3).
13C NMR (CDCl3): d 164.6, 161.1, 146.9, 143.5, 142.7,
139.6, 137.4, 136.3, 127.5, 126.9, 118.5, 118.0, 28.1, 28.0,
25.7, 24.4, 22.7, 22.3.
OH
N
H
MeOH
R
CHO
1
R
R
3
H N
1
+
2
6a-c
R
2
R
2
NaH
R
Me
4
Ph P
8a (71.5%): 1H NMR (CDCl3): d 7.96 (s, 1 H, N@C–
H), 7.75 (m, 15 H, PPh–H), 7.39 (m, 5 H, Ph–H), 2.50 (s,
6H, Ph–CH3), 1.35–1.25 (s, 21 H, t-Bu–CH3 + Pd–CH3).
13C NMR (CDCl3): d 172.9, 172.7, 156.7, 140.8, 140.6,
137.4, 136.6, 133.6, 133.5, 130.6, 130.0, 124.6, 36.9, 35.2,
24.8, 24.3, 7.57, 7.43.
3
R
4
Pd
N
O
PdMeCl(COD)
OH
N
R
R
3
1
PPh /Benzene
3
R
R
3
1
8a-c
7a-c
R
2
R
2
8b (74.0%): 1H NMR (CDCl3): d 8.22 (s, 1 H, N@C–
H), 7.98 (m, 15 H, PPh–H), 7.2–6.95 (m, 5 H, Ph–H),
3.51–3.47 (m, 2 H, C–H), 1.27 (s, 12 H, i-Pr–CH3), 1.14
(s, 18 H, t-Bu–CH3), 1.1 (s, 3 H, Pd–CH3). 13C NMR
(CDCl3): d 167.3, 148.9, 141.8, 135.1, 132.0, 130.9,
130.6, 127.1, 126.3, 125.6, 123.3, 118.4, 35.3, 34.1, 31.9,
29.9, 29.0, 28.2, 25.4, 23.9, 23.3, 3.9.
a: R1 = R2 = t-Bu, R3 = R4 = Me
b: R1 = R2 = t-Bu, R3 = R4 = i-Pr
c: R1 = R2 = NO2, R3 = R4 = i-Pr
Scheme 3.
6.70 (s, 3H, pyrrole-H), 0.80 (s, 3 H, Pd–CH3). 13C
NMR (CDCl3): d 5.9, 6.0, 118.7, 118.9, 124.6, 128.6,
130.9, 135.6, 135.3, 137.9, 138.5, 160.8, 161.1.
1
8c (77.2%): H NMR (CDCl3): d 8.31–8.12 (s, 2 H,
Ph–H), 7.44 (s, 15 H, PPh3–H), 7.16 (s, 3 H, Ph–H), 3.36
(m, 2 H, C–H), 1.41–1.01 (m, 15 H, C–CH3 + Pd–CH3).
13C NMR (CDCl3): d 165.2, 162.4, 146.3, 140.5, 140.1,
135.9, 134.9, 134.0, 131.4, 128.1, 124.4, 122.6, 122.4,
29.0, 28.9, 28.2, 24.7, 24.3, 23.0.
3d (67.8%): 1H NMR (CDCl3): d 7.70–7.65 (m, 15 H,
PPh–H), 7.65 (s, 1 H, N@C–H), 7.29–7.18 (s, 4 H, Ph–
H), 6.76 (s, 3 H, Pyrrole-H), 1.34–1.26 (m, 12 H, t-Bu–
CH3 + Pd–CH3). 13C NMR (CDCl3): d 161.6, 149.9,
143.3, 140.5, 138.3, 135.5, 131.6, 130.2, 127.7, 127.4,
126.5, 125.7, 118.0, 111.5, 36.6, 33.1, 32.3, 31.0, 6.3.
2.3. Typical polymerization procedure
1
4a (73.0%): H NMR (CDCl3): d 8.16 (d, 2 H, Py-
1.0 ml of a fresh catalyst solution (chlorobenzene, 0.5
lmol catalyst), 3.0 ml of a solution of norbornene
(26.0 mmol, 2.45 g) in chlorobenzene, and 6.5 ml of
dine-H), 7.60 (s, 1 H, Pydine-H), 7.50 (s, 1 H, CH@N),
7.18–6.90 (m, 4 H, Ph–H + Pydine-H), 6.74 (d, 2 H), 6.25
(s, 1 H), 3.34 (m, 2 H), 0.99 (m, 12 H), 0.85 (s, 1 H). 13
C
Table 1
Crystal data and structure refinements of 3a, 4a and 5a
3a
4a
5a
Empirical formula
Formula weight
Crystal system
Space group
C
36H39N2PPd
C23H29N3Pd
453.89
monoclinic
C34H42N4Pd
613.12
monoclinic
637.06
orthorhombic
Pna21
19.017(8)
12.375(5)
13.986(5)
90
P21=n
P21=n
ꢀ
a (A)
8.7190(18)
20.457(3)
12.4825(12)
90
17.392(3)
10.5998(18)
17.800(4)
90
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
90
90
94.977(13)
90
108.351(15)
90
3
ꢀ
Volume (A )
3291(2)
1.286
2218.1(6)
1.359
0.71073
3114.5(9)
1.308
0.71703
qcalc (Mg mꢁ3
)
ꢀ
Wavelength (A)
0.71073
1320
1.96–26.01
F ð000Þ
936
1280
h Range (°)
1.92–25.99
4363 (Rint ¼ 0:0229)
w-scan
0.4895 and 0.4186
249
1.98–26.00
6113 (Rint ¼ 0:0242)
w-scan
0.5681 and 0.5130
360
Independent reflections
Absorption correction
Maximum and minimum transmission
Parameters
3648 (Rint ¼ 0:0192)
w-scan
0.4728 and 0.4239
366
Final R indices [I > 2rðIÞ]
R1 ¼ 0:0288, wR2 ¼ 0:0561
1.026
R1 ¼ 0:0286, wR2 ¼ 0:0669
1.045
R1 ¼ 0:0392, wR2 ¼ 0:0519
0.860
Goodness-of-fit on F 2
Largest differential peak and hole (e A
ꢁ3
ꢀ
)
0.354 and )0.375
0.209 and )0.629
0.353 and )0.408

1622
H. Liang et al. / Polyhedron 23 (2004) 1619–1627
chlorobenzene were added under inert gas atmosphere
into a Schlenk flask with a mechanical stirrer. The re-
action was started by the addition of 0.5 ml of a MMAO
solution (1.0 mmol in heptane) at 30 °C. After 10 min,
the reaction mixture was poured into 200 ml of acidic
ethanol (ethanol/HClconc: ¼ 50/1). The polymer was iso-
lated by filtration, washed with methanol, and dried
under vacuum at 80 °C for 24 h. Total reaction volume
was 11 ml, unless otherwise stated. This was achieved by
variation of the amount of chlorobenzene if necessary.
procedure described previously [15], they were deprot-
onated using sodium hydride and the anions allowed to
react with (COD)PdMeCl in the presence of neutral,
two-electron donor ligands to give palladium complexes
3a–d, and 4a. The neutral donors ligands are necessary
to stabilize the complexes. Different ligands have been
used to study their effects on metal catalytic activity.
Interestingly, attempts to prepare palladium complex
with the acetonitrile ligand have failed and complex 5a
was obtained instead. This shows that the binding
strength of the CH3CN ligand with palladium atom is
poorer than that of triphenylphosphine or pyridine,
which is in accordance with the results of Novak and co-
workers [36]. The general synthetic route for the kind of
neutral palladium complex in this study is shown in
Scheme 2. Meanwhile we have synthesized neutral
palladium complexes 8a–c bearing salicylaldiminato
ligands with a similar method, which is shown in
Scheme 3.
3. Results and discussion
3.1. Synthesis and characterization of neutral palladium
complexes
Ligands 1a–d were prepared by the condensation of
the corresponding aniline derivatives according to the
Table 2
ꢀ
Selected bond lenths (A) and angles (°) of 3a, 4a and 5a
3a
Bond lengths
Pd–C(1)
Pd–N(1)
Pd–N(2)
Pd–P
2.022(7)
2.123(6)
2.121(3)
2.2279(14)
N(1)–C(2)
N(1)–C(5)
N(2)–C(6)
N(2)–C(7)
1.336(8)
1.354(7)
1.304(6)
1.430(5)
P–C(25)
P–C(19)
P–C(31)
1.819(4)
1.818(5)
1.834(5)
Bond angles
C(1)–Pd–N(1)
C(1)–Pd–N(2)
N(1)–Pd–N(2)
C(25)–P–Pd
171.8(2)
93.8(2)
C(1)–Pd–P
N(1)–Pd–P
N(2)–Pd–P
C(19)–P–Pd
90.5(2)
C(25)–P–C(19)
C(25)–P–C(31)
C(19)–P–C(31)
C(31)–P–Pd
106.3(2)
96.80(15)
175.23(11)
108.00(15)
102.3(2)
104.8(2)
122.10(16)
79.12(17)
112.16(15)
4a
Bond lengths
Pd–C(1)
N(1)–C(6)
N(3)–C(12)
2.018(3)
1.325(4)
1.436(3)
Pd–N(2)
N(2)–C(10)
2.004(2)
1.369(3)
Pd–N(3)
N(3)–C(11)
2.168(2)
1.288(3)
Bond angles
N(2)–Pd–C(1)
N(2)–Pd–N(3)
C(6)–N(1)–C(2)
C(10)–N(2)–Pd
C(11)–N(3)–C(12)
94.05(11)
79.39(8)
116.9(2)
118.7(2)
121.0(2)
N(2)–Pd–N(1)
C(1)–Pd–N(3)
C(6)–N(1)–Pd
C(7)–N(2)–C(10)
C(11)–N(3)–Pd
174.50(9)
172.86(10)
118.7(2)
C(1)–Pd–N(1)
N(1)–Pd–N(3)
C(2)–N(1)–Pd
C(7)–N(2)–Pd
C(12)–N(3)–Pd
90.08(11)
96.65(8)
124.4(2)
105.9(2)
110.32(16)
140.0(2)
128.62(15)
5a
Bond lengths
Pd–N(1)
Pd–N(4)
N(2)–C(5)
N(3)–C(21)
2.026(3)
2.052(3)
1.298(4)
1.384(4)
Pd–N(2)
2.052(3)
1.337(4)
1.437(4)
1.305(4)
Pd–N(3)
2.030(3)
1.383(4)
1.342(4)
1.442(4)
N(1)–C(1)
N(2)–C(6)
N(4)–C(22)
N(1)–C(4)
N(3)–C(18)
N(4)–C(23)
Bond angles
N(1)–Pd–N(3)
N(1)–Pd–N(4)
C(1)–N(1)–C(4)
C(5)–N(2)–C(6)
C(18)–N(3)–C(21)
C(22)–N(4)–C(23)
179.75(13)
99.84(11)
105.8(3)
120.9(3)
106.5(3)
120.7(3)
N(1)–Pd–N(2)
N(3)–Pd–N(4)
C(1)–N(1)–Pd
C(5)–N(2)–Pd
C(18)–N(3)–Pd
C(22)–N(4)–Pd
80.37(11)
80.29(12)
142.0(2)
112.4(2)
141.0(2)
112.3(2)
N(2)–Pd–N(3)
N(2)–Pd–N(4)
C(4)–N(1)–Pd
C(46)–N(2)–Pd
C(21)–N(3)–Pd
C(23)–N(4)–Pd
99.50(11)
179.16(13)
112.3(2)
126.6(2)
112.5(2)
126.9(2)

H. Liang et al. / Polyhedron 23 (2004) 1619–1627
1623
3.2. Crystal structures of complexes 3a, 4a and 5a
marized in Table 2, and the molecule structures of 3a, 4a
and 5a are shown in Figs. 1–3, respectively.
Crystals of 3a, 4a and 5a suitable for X-ray structure
determination were grown from a benzene–pentane
(volume ratio ¼ 1:2) solution. The data collection and
refinement data of the analysis are summarized in Table
1, the selected bond lengths and bond angles are sum-
The Pd atom is at the center of an approximately
square-planar arrangement, which is applied to all these
three complexes. For 3a, the bulky 2,6-diisopropyl-
benzimine filled the position trans to the triphenyl-
phosphine ligand with a P–Pd–N2 angle of 175.23(11)°;
Fig. 1. ORTEP plot of the molecular structure of complex 3a. Displacement ellipsoids are drawn at the 50% probability level.
Fig. 2. ORTEP plot of the molecular structure of complex 4a. Displacement ellipsoids are drawn at the 50% probability level.

1624
H. Liang et al. / Polyhedron 23 (2004) 1619–1627
Fig. 3. ORTEP plot of the molecular structure of complex 5a. Displacement ellipsoids are drawn at the 50% probability level.
the pyrrole group attached to Pd is in the position trans
to the methyl ligand with a N1–Pd–C1 angle of
171.8(2)°, as shown in Fig. 1. While for 4a, the 2,6-dii-
sopropylbenzimine is at the position opposite to the
methyl ligand with a N3–Pd–C1 angle of 172.86(10)°.
The pyridine ligand lies trans to the pyrrole ligand
through Pd with a N1–Pd–N2 angle of 174.50(9)°, as
shown in Fig. 2. For 5a, the two 2,6-diisopropylbenzi-
mine ligands are trans to each other through Pd with a
N4–Pd–N2 angle of 179.16(13)°, so are the two pyrrole
ligands with a N1–Pd–N3 angle of 179.75(13)°, as
shown in Fig. 3. From X-ray structural data by com-
parison of 3a and 4a, the Pd–C1 is sensitive to the nature
catalyst. Yet these catalysts do not work for
polymerization of norbornene derivatives, which was
not listed in this article.
Catalyst activities and polymer yields depended sig-
nificantly on the reaction parameters applied to the
polymerization of norbornene, as shown in Figs. 4–7.
The concentration of norbornene should meet some
requirements for good polymerization. In this system
when the catalyst concentration reached 0.025 lmol/ml
it did well, as shown in Fig. 4. Variation of molar ratio
of MMAO to the catalyst 3c, which is expressed here as
the Al/Pd molar ratio, showed considerable effect on the
polymerization reaction. When the mole ratio of Al/Pd
ꢀ
of the trans ligand. The Pd–C1 length of 3a is 2.022(7) A
and the Pd–C1 length of 4a is shorter than that of 3a,
ꢀ
being 2.018(3) A. This shows the ligand 2,6-dii-
sopropylbenzimine has a stronger influence than the
pyrrole ligand, according to Abu-Surrah et al. [31].
7
6
5
4
24
22
20
18
16
14
12
10
3.3. Polymerization of norbornene
Our main interest in the study of these complexes is
their possible application as catalysts for the polymeri-
zation of norbornene and its derivatives. Preliminary
experiments indicated that the single-component palla-
dium complexes in the study, like single-component
nickel complexes [14,15], are not able to catalyze nor-
bornene polymerization, and MMAO alone is not able
to catalyze norbornene polymerization too. From ex-
periments, however, we found that these new neutral
palladium complexes display high activities for nor-
bornene polymerization when MMAO is used as a co-
3
0.00
0.02
0.04
0.06
0.08
0.10
Concentration of catalyst (µmol/ml)
Fig. 4. Plot of polymer yield and catalytic activity versus catalyst
concentration. 3a as catalyst. Vtotal ¼ 20 ml, polymerization reaction at
30 °C for 10 min.

H. Liang et al. / Polyhedron 23 (2004) 1619–1627
1625
10
12
10
8
50
8
40
30
20
10
0
6
4
2
0
6
4
2
500
1000
1500
2000
2500
Al/Pd (mole ratio)
10
20
30
40
50
Fig. 5. Plot of polymer yield and catalytic activity versus Al/Pd molar
ratio. Vtotal ¼ 20 ml, polynorbornene/Pd ¼ 50 000, catalyst (3a) ¼ 0.5
lmol, polymerization reaction at 30 °C for 10 min.
Reaction Temperature (oC)
Fig. 7. Plot of polymer yield and catalytic activity versus reaction
temperature (°C). Vtotal ¼ 11 ml, catalyst (8a) ¼ 0.5 lmol, Al/
Pd ¼ 2000, norbornene/Pd ¼ 51 900, polymerization reaction at 30 °C
for 10 min.
70
10
60
Table 3
Norbornene polymerizations catalysted with different neutral palla-
dium complexesa
50
8
Entry
Catalyst Al/Pd
(molar ratio)
Yield (g)
Activity
(106 g/molPd h)
40
6
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
4a
5a
8a
8b
8c
2000
0.14
0.23
0.22
0.25
0.32
0.13
0.71
0.47
0.26
1.68
2.76
3.00
2.64
3.84
1.56
8.52
5.64
3.12
2000
2000
2000
2000
2000
2000
2000
2000
30
4
20
0
20000
40000
60000
80000
NBE/Pd (molar ratio)
Fig. 6. Plot of polymer yield and catalytic activity versus norbornene/
Pd molar ratio. Vtotal ¼ 20 ml, catalyst (3a) ¼ 0.5 lmol, Al/Pd ¼ 1500,
polymerization reaction at 30 °C for 10 min.
a 0.5 lmol catalyst, 2.443 g norbornene, Vtotal ¼ 11 ml, polymeriza-
tion reaction for 10 min at 30 °C.
was 1500/1, the catalyst activity reached 1.01 ꢀ 107
g
displayed higher catalytic activities than those bearing
pyrrole-imine chelate ligands. According to entries 1–4,
with increasing the bulk in the ortho position of nitrogen
atom of aniline, the polymerization activities decline,
which means the bulkier the volumes of the substituents,
the harder the insertion of norbornene. This is similar to
some neutral nickel complexes [15].
polym/molPd h, as shown in Fig. 5. On increasing the
mole ratio of norbornene/Pd, while other conditions
were kept constant, the catalyst activity of the catalyst
3c grew, reaching 1.0 ꢀ 107 g polym/molPd h when the
mole ratio of norbornene/Pd equalled 70 000, as shown
in Fig. 6.
Meanwhile, the catalyst activity of the catalyst 8a has
been examined by varying the polymerization tempera-
ture, which is shown in Fig. 7. The catalyst activity first
reached a peak and then gradually decreased with the
increase of temperature, which means that to get high
catalytic activity, polymerization reaction should be at
the proper temperature.
The polymerization results using complexes 3a–d, 4a,
5a and 8a–c activated with MMAO are summarized in
Table 3. From the results, we can see that the neutral
palladium complexes bearing salicylaldiminato ligands
The poly(norbornene)s obtained are insoluble in
choloform, benzene, chlorobenzene, 1,2-dichloroben-
zene, N; N-dimethylformamide and N; N-dimethylace-
tamide, which is different from polymers got with
neutral nickel catalysts [14,15]. The molecular weights of
the polymers obtained could not be determined because
of their insolubility, which is similar to the result
reported by Hu and co-workers [16]. FTIR analyses of
the poly(norbornene)s were performed. In the range
of 1600–1670 cmꢁ1 no absorption is observed which
means the catalytic polymerization is via vinyl addition

1626
80
H. Liang et al. / Polyhedron 23 (2004) 1619–1627
polymerization of norbornene. The complexes bearing
salicylaldiminato ligands have more excellent activity
than those bearing pyrrole-imine ligands for norbornene
polymerization. IR analysis of the polymers identifies
the polymerization is via vinyl addition mechanism.
WAXD measurement implies the polymers are
non-crystalline.
70
60
50
40
30
5. Supplementary material
20
Crystallographic data for the structures reported in
this paper have been deposited at the Cambridge Crys-
tallographic Data Center as supplementary publication
numbers CCDC-219639, CCDC-219640 and CCDC-
219641. Copies of the data can be obtained on appli-
cation to: The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://www.
ccdc.cam.ac.uk).
10
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Wavenumber (cm-1)
Fig. 8. FTIR spectrum of polynorbornene catalyzed by complex 3d.
7000
6000
5000
4000
3000
2000
1000
0
Acknowledgements
The authors are grateful for the financial support by
Special Funds for Major State Basis Research Projects
(No. G1999064801) from Ministry of Science and
Technology of China.
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10
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