Synthesis of (N-O)-ligated palladium(II) complexes and their use in ethene homopolymerization and norbornene copolymerizations

Article abstract of DOI:10.1021/om1003013

Cyclic olefin copolymers are an important class of polymeric materials. Here, we report the synthesis and characterization of several (N-O)-ligated palladium(II) complexes and their use in ethene homopolymerization, as well as ethene/norbornene and carbon monoxide/norbornene copolymerizations. Most notably, these catalysts show relatively high activity toward ethene/functional norbornene copolymerizations, and a high level of incorporation of the norbornene derivative was observed. The molecular weight of the copolymers can be controlled by adjusting the ethene/norbornene feed ratio. The ethene/nonpolar functional norbornene copolymerizations have the characteristics of a living polymerization at low ethene/norbornene feed ratios. Finally, the successive stepwise insertions of carbon monoxide and norbornene into a preformed palladiumcarbon bond were observed by NMR spectroscopy.

Full text of DOI:10.1021/om1003013

3160 Organometallics 2010, 29, 3160–3168
DOI: 10.1021/om1003013
Synthesis of (N-O)-Ligated Palladium(II) Complexes and Their Use in
Ethene Homopolymerization and Norbornene Copolymerizations
Ying Chen, Sukhendu Mandal, and Ayusman Sen*
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802
Received April 14, 2010
Cyclic olefin copolymers are an important class of polymeric materials. Here, we report the
synthesis and characterization of several (N-O)-ligated palladium(II) complexes and their use in
ethene homopolymerization, as well as ethene/norbornene and carbon monoxide/norbornene
copolymerizations. Most notably, these catalysts show relatively high activity toward ethene/
functional norbornene copolymerizations, and a high level of incorporation of the norbornene
derivative was observed. The molecular weight of the copolymers can be controlled by adjusting the
ethene/norbornene feed ratio. The ethene/nonpolar functional norbornene copolymerizations have
the characteristics of a “living” polymerization at low ethene/norbornene feed ratios. Finally, the
successive stepwise insertions of carbon monoxide and norbornene into a preformed palladium-
carbon bond were observed by NMR spectroscopy.
Introduction
conversion;12 only late transition metal catalysts have the
tolerance toward polar functionalities.3,5-7,13-16 Herein, we
report the synthesis and characterization of several (N-O)-
ligated palladium(II) complexes and their use in ethene
homopolymerization, as well as ethene/norbornene and car-
bon monoxide/norbornene copolymerizations. Most notably,
these catalysts show good activity for ethene/nonpolar func-
tional norbornene copolymerizations, resulting in nearly alter-
nating copolymers with “living” characteristics at low ethene/
norbornene feed ratios. They are also active for ethene/polar
functional norbornene copolymerizations. In addition, the
stepwise carbon monoxide/norbornene copolymerization was
monitored by 13C NMR spectroscopy.
Cyclic olefin copolymers are an important class of amor-
phous, transparent materials. Among them, the ethene/nor-
bornene (E/NB) copolymer is of great commercial importance.
Due to its unique characteristics, such as high transparency,
excellent barrier property, and high mechanical strength, the
E/NB copolymer is used in pharmaceutical packaging, dispo-
sable diagnostics, moldings for optical lenses, etc.1 Generally
group 4 metallocene/MAO2 and late transition metal3-7 (Ni
and Pd) catalysts are used to synthesize E/NB copolymers.
More recently, cationic rare-earth metal catalysts8 have also
been reported. However, to copolymerize ethene with polar
functional norbornenes, group 4 catalysts require a pretreat-
ment of the polar norbornene monomers9-11 or a post-reaction
Results and Discussion
1. Synthesis and Characterization of Unsymmetric Palla-
dium Catalysts. The synthetic routes to three palladium
complexes are shown in Scheme 1. The complexes were
characterized by NMR spectroscopy and X-ray crystallo-
graphy. Figures 1-4 show the crystal structures of the ligand
1 (R = iPr) and the Pd(II) compounds A, B, and C of the
general type [(N-O)Pd(CH3)(L)]. According to the X-ray
crystal structures, both complexes A and B adopt a near
square-planar coordination geometry, and the alkyl group is
trans to the coordinated phenoxide. Under an N2 atmo-
sphere, complexes A and C are stable at room temperature
*To whom correspondence should be addressed. E-mail: asen@psu.
edu.
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pubs.acs.org/Organometallics
Published on Web 06/22/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 14, 2010 3161
Figure 3. ORTEP diagram of complex B (thermal ellipsoids are
given at 50% probability).
Figure 1. ORTEP diagram of ligand 1 (thermal ellipsoids are
given at 50% probability). One of the two molecules in the
asymmetric unit is shown for clarity.
Figure 4. ORTEP diagram of complex C with a CH3OH mole-
cule (thermal ellipsoids are given at 50% probability).
Table 1. Ethene Homopolymerization Experiments with Pd
Complexes A and Ba
Figure 2. ORTEP diagram of complex A (thermal ellipsoids are
given at 50% probability). One of the two molecules in the
asymmetric unit is shown for clarity.
temp yield
activity
entry catalyst co-catalyst (°C) (g) (kg/mol[Pd] h) Mnb PDIb
3
Scheme 1. Synthesis of (N-O)-Ligated Palladium Complexes
A, B, and C
1
2
3
4
A
A
A
B
60 0.15
90 0.95
90 0.29
2.6
15.8
5.0
630 1.3
340 1.6
170 1.7
BPh3
30
0
a Conditions: Pdcomplex, 0.03 mmol; toluene, 5 mL; BPh3, 0.06 mmol;
ethene, 300 psi; 2 h. b Determined by GPC using polystyrene standards.
strongly coordinating TMEDA ligand. However, the more
weakly ligated Pd(II) center in compounds A and B exhibited
good polymerization activity, as discussed below.
2. Ethene Homopolymerization. Due to the poor stability
of complex B, the reactions involving B as catalyst were
conducted at 30 °C. Table 1 summarizes the experimental
results of ethene polymerization with complexes A and B. The
activity of complex A increased with increasing reaction tem-
perature. However, complex A produced only ethene oligo-
mers with molecular weight (Mn) less than 700, and the addi-
tion of cocatalyst BPh3 did not increase catalyst activity. The
oligomers synthesized in entries 1-3 (Table 1) were highly
branched, as shown by their 13C NMR spectra (Figure 5). The
assignmentof thebranches follows thatinthe literaure.17-19 It
suggests that “chain walking” and β-H elimination occur
for weeks, but complex B decomposes in a few days. Complex
C exhibits no polymerization activity due to the presence of the
(17) Subramanyam, U.; Rajamohanan, P. R.; Sivaram, S. Polymer
2004, 45, 4063–4076.

3162 Organometallics, Vol. 29, No. 14, 2010
Chen et al.
Figure 5. (a) 1H NMR and (b) 13C NMR spectra (CDCl3, 25 °C) of ethene oligomers synthesized by complex A (sample from entry 2,
Table 1).
readily in this system.18,20 The presence of ethene accelerated
the decomposition of complex B, and product formation was
not observed.
13C NMR spectra using sufficient delay between pulses.
Figure 6 shows a typical 13C NMR spectrum of ethene/
norbornene copolymer. The chemical shift assignments are
based on literature reports.3,21 The resonances between 47.3
and 48.0 ppm are due to the norbornene CH carbons in the
polymer backbone, and the resonances between 41.5 and
42.1 ppm are due to the bridgehead CH carbons. The reso-
nance at 33.4 ppm can be assigned to the CH2 carbon on the
short bridge of norbornene. The rest of the CH2 carbons
from norbornene and the CH2 carbons from ethene appear
between 29.7 and 31.6 ppm. Both catalysts A and B exhibited
low activity toward norbornene homopolymerization (entries
1 and 9, Table 2). The norbornene homopolymerizaton was
not significantly affected by the addition of the radical trap,
galvinoxyl (entry 1 versus 2, Table 2). We surmise that the low
activity for norbornene homopolymerization was due to the
relative bulkiness of the monomer, which made sequential
insertions difficult. This is also evident from entries 3 and 4,
where a 4-fold increase in norbornene feed did not significantly
3. Ethene/Norbornene Copolymerization. Complexes A
and B demonstrated much higher activity for ethene/nor-
bornene copolymerization than for ethene or norbornene
homopolymerizations. Table 2 presents selected copolymer-
ization data. The amount of the norbornene derivative
incorporated was measured by NMR spectroscopy. Depend-
ing on the solubility of the copolymers, their NMR spectra
were obtained in either CDCl3 or toluene-d8 at 25 °C or in
tetrachloroethene-d2 at elevated temperature. The composi-
tion of the ethene/5-norbornene-2-methanol copolymer was
1
obtained from the H NMR spectrum by integrating the
-CH2-OH proton versus the rest. The compositions of the
other copolymers were determined by the integration of their
(18) Ittel, S. D; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169–1203.
(19) Galland, G. B.; de Souza, R. F.; Mauler, R. S.; Nunes, F. F.
Macromolecules 1999, 32, 1620–1625.
(20) Mohring, V. M.; Fink, G. Angew. Chem., Int. Ed. Engl. 1985, 24,
1001–1003.
€
(21) Tritto, I.; Boggioni, L.; Zampa, C.; Ferro, D. R. Macromolecules
2005, 38, 9910–9919.

Article
Organometallics, Vol. 29, No. 14, 2010 3163
Table 2. Ethene/Norbornene (NB) Copolymerizationsa
ethene
(psi)
NB derivative
(g)
temp
(°C)
yield
(g)
NB incorp
(mol %)b
activity
(kg/mol[Pd] h)
entry
catalyst
3
1
A
A
A
A
A
A
A
A
B
B
B
B
B
0
0
Nb, 2
Nb, 2
Nb, 0.5
Nb, 2
Nb, 2
5-Nb-2-nC4H9, 2
5-Nb-2-tBu ester, 2
5-Nb-2-CH2OH, 2
Nb, 2
30
30
30
30
90
90
90
90
30
30
30
30
30
0.07
0.06
0.63
2.67
2.34
2.29
1.20
1.00
0.16
2.53
2.35
0.30
0.45
1.2
1.0
2c
3
300
300
300
300
300
300
0
300
300
300
300
42.3
43.5
42.0
42.4
32.6
34.7
10.5
44.5
39.0
38.2
20.0
16.7
2.7
42.2
39.2
5.0
4
5
6
7
8
9
10
11
12
13
Nb, 2
48.5
42.2
32.1
34.8
5-Nb-2-nC4H9, 2
5-Nb-2-tBu ester, 2
5-Nb-2-CH2OH, 2
7.5
a Conditions: Pd complex, 0.03 mmol; toluene 5 mL; 2 h. b Entries 8 and 13 determined by 1H NMR in C2D2Cl4 at 115 °C; entries 3 and 10 determined
by 13C NMR in C2D2Cl4 at 115 °C; entries 6, 7, 11, and 12 determined by 13C NMR in CDCl3 at 25 °C; entries 4 and 5 determined by 13C NMR in toluene-
d8 at 25 °C. c In the presence of 1.5 equiv of galvinoxyl relative to Pd. d Molecular weight (Mn) and PDI determined by GPC using polystyrene standards,
entry 6, Mn = 17 Â 103, PDI = 2.3; entry 7, Mn = 28 Â 103, PDI = 1.5; entry 11, Mn = 65 Â 103, PDI = 1.3; entry 12, Mn = 18 Â 103, PDI = 1.6.
Figure 6. 13C NMR spectrum (toluene-d8 at 25 °C) of ethene/norbornene copolymer (sample from entry 4, Table 2; norbornene,
43.5 mol %).
Scheme 2. Reactivity Pattern for the Palladium Catalyst
boost its incorporation in the copolymer. The addition of
ethene resulted in more than a 20-fold increase of activity
over norbornene homopolymerization, suggesting that
ethene insertion following a norbornene insertion was
much more facile. Given the observed high norbornene
incorporation (close to alternating) in the copolymers, it
appears that, following ethene incorporation, the next
monomer incorporated preferentially is norbornene. On
the other hand, chain termination through β-H elimina-
tion occurs more readily following ethene insertion, as
suggested by the formation of oligomers in ethene homo-
polymerization experiments. The overall reactivity pat-
tern is shown in Scheme 2.
Ethene/functional norbornene copolymerizations were also
investigated. For nonpolar norbornene derivatives and nor-
bornene, both catalyst A and B have similar activities. The
level of incorporation was significantly lower for norbornene
derivatives with potentially coordinating oxygen functional-
ities, as is the activity for these copolymerizations. Presum-
ably, following the insertion of one of these polar norbornene
derivatives, the oxygen functionality coordinates to the metal
center, thereby preventing ready coordination andinsertion of
a new incoming monomer.22 Consistent with this hypothesis,
2-n-butyl-5-norbornene, which lacks a coordinating function-
ality, exhibitssimilaractivity andlevel of incorporationto that
of the parent norbornene.
4. Effect of Ethene/Norbornene Feed Ratio on Copolymer
Molecular Weight. The copolymerization of ethene with 2-n-
butyl-5-norbornene was examined because of the relatively
high solubility of the copolymer. The experimental results
using complex B are summarized in Table 3. It is clear that
the copolymer molecular weight (and yield) increases with an
increase in norbornene to ethene ratio in the feed. This is
consistent with our hypothesis (Scheme 2) that chain termi-
nation through β-H elimination occurs more readily follow-
ing ethene insertion (see Section 3 above). On the other hand,
the incorporation of norbornene in the copolymer plateaus
at ∼45 mol %, again consistent with the hypothesis that
successive incorporations of norbornene do not occur be-
cause of steric crowding around the metal.
(22) Funk., J.; Andes, C. E.; Sen, A. Organometallics 2004, 23, 1680–
1683.

3164 Organometallics, Vol. 29, No. 14, 2010
Chen et al.
Table 3. Influence of Norbornene Feed and Ethene Pressure on
Copolymer Molecular Weight (Mn) Using Catalyst Ba
c
ethene
entry (psi)
norbornene
(g)
yield Nb incorpb
(g)
Mn
(mol %) (Â10-3
)
PDIc
1
2
3
4
300 5-Nb-2-nC4H9, 0.5 0.57
30.6
41.2
42.2
43.5
22
47
64
89
1.2
1.1
1.3
1.2
300 5-Nb-2-nC4H9, 1
300 5-Nb-2-nC4H9, 2
100 5-Nb-2-nC4H9, 2
1.13
2.35
2.57
a Conditions: Complex B, 0.03 mmol; toluene, 5 mL; 30 °C; 2 h.
b Determined by 13C NMR spectroscopy in CDCl3 at 25 °C. c Deter-
mined by GPC using polystyrene standards.
Table 4. Copolymerization of Ethene with 2-n-Butylnorbornene
Using Complex Ba
NB convb
(mol %)
PDIc
(Mw/Mn)
Figure 7. Plot of Mn and PDI vs 2-n-butyl-5-norbornene con-
version for 2-n-butyl-5-norbornene/ethene copolymerization
using complex B.
entry
time (min)
Mnc (Â10-3
)
1
2
3
4
5
6
7
8
10
20
35
50
3.9
5.9
6.8
10
17
24
30
35
38
40
42
43
52
55
1.1
1.3
1.3
1.2
1.2
1.3
1.4
1.4
1.4
1.5
1.8
1.8
12.2
14.0
22.9
30.6
35.1
38.2
41.2
43.1
58.9
64.7
whether a similar trend persists in the present system, the
relative uptake of endo/exo isomers of several norbornene
derivatives was investigated by gas chromatography (Table5).
At relatively low conversions, complexes A and B both show
only a slight preference for the uptake of the exo isomer.
7. Copolymerization of Polar Monomers with Ethene and
Norbornene. Both catalysts A and B are active for the alter-
nating ethene/carbon monoxide and norbornene/carbon mon-
oxide copolymerizations, and the experimental results using
catalyst A are summarized in Table 6. Norbornene/methyl
acrylate (MA) copolymerization and MA homopolymerization
were also examined using complex A (Table 6). The NB/CO
polymer synthesized by catalyst A (entry 1, Table 6) was
insoluble in common organic solvents; therefore CH elemental
analysis was used to determine the product composition. It is
possible that the product is contaminated with a small amount
of the norbornene homopolymer. Unlike the NB/CO copoly-
mer, it appears that the NB/MA copolymer and MA homo-
polymer are formed via a radical mechanism,3,23 since the addi-
tion of the radical trap galvinoxyl shuts down these reactions
(entries 2 versus 5 and 7, Table 6). The NB/MA copolymer
structure was examined by 13C NMR spectroscopy. As we pre-
viously reported,24,25 CH2 carbons from consecutive MA-
MA units appear around 35.5 ppm. In an alternating MA/1-
hexene structure, the CH2 carbon from MA and the CH2
carbon from 1-hexene have similar chemical shifts, ∼36.8-
37.0 ppm. In the 13C NMR spectrum of a MA/norbornene
copolymer (entry 4, Table 6), a peak at 37.0 ppm was observed,
which likely belongs to the MA CH2 carbon from a MA/
norbornene alternating structure. The existence of the non-
sequential MA units suggests the presence of MA-norbornene
linkages. Also, this copolymer shows a single GPC trace,
suggesting that it is one copolymer, rather than a mixture of
polymers.
80
120
160
200
260
320
815
1470
9
10
11
12
a Conditions: Complex B, 0.045 mmol; toluene, 60 mL; 30 °C; 2-n-
butylnorbornene, 3 g; ethene, 1 atm; tetrachloroethane, 1 g (as internal
standard for GC). b Determined by GC analysis. c Determined by GPC
using polystyrene standards.
5. Living Copolymerization of Ethene/Nonpolar Functional
Norbornene Using Complex B. As shown in Table 3, catalyst B
was found to produce ethene/2-n-butyl-5-norbornene copoly-
mers with relatively narrow polydispersities. Thus, the living
nature of this copolymerization was investigated. Ethene/
2-n-butyl-5-norbornene copolymerization was carried out at
30 °C using complex B. Inordertoreduce β-Helimination, the
ethenepressure was kept at1 atm. Sampleswere takenatinter-
vals to determine the 2-n-butyl-5-norbornene conversion and
the copolymer molecularweight data. Results aresummarized
in Table 4, and plots of Mn and PDI (Mw/Mn) versus nor-
bornene conversion are shown in Figure 7. As expected for
living polymerization, the Mn of the copolymer increases
linearly with norbornene conversion. However, the PDI
values are higher than expected especially at high norbor-
nene conversions. Since the ethene pressure is maintained
constant at 1 atm, the ethene/norbornene ratio in the feed
increases with increasing norbornene conversion; this leads
to a higher probability for successive ethene insertions and
resultant chain termination by β-elimination (see Scheme 2).
Figure 8 illustrates the GPC traces for the growing copoly-
mer chain. The GPC traces shift to higher molecular weights
as norbornene conversion increases. Taken together, the
results shown in Table 4 and Figures 7 and 8 suggest that
the copolymerization exhibits “living” characteristics but
only at low ethene/norbornene feed ratios. To our knowledge,
this is the first example of a late transition metal-catalyzed
living ethene/norbornene copolymerization.
8. Stepwise Chain Growth of Norbornene/Carbon Monoxide
Copolymer. The stepwise growth of the NB/CO copolymer
chain at the metal center in complex A was monitored by
NMR spectroscopy through sequential addition of the re-
spective monomers. When 12CO (40 psi) was added to an
acetone-d6 solution of A in a high-pressure NMR tube, the
6. Study of the Catalyst Preference of Endo/Exo Isomers.
In samples of substituted norbornenes, the endo isomer do-
minates. On the other hand, because of steric reasons, the
insertion of norbornene into metal-carbon bonds preferen-
tially proceeds from the exo face.3,22 In order to ascertain
(23) Lopez-Fernandez, R.; Carrera, N.; Albeniz, A. C.; Espinet, P.
Organometallics 2009, 28, 4996–5001.
(24) Chen, Y.; Sen, A. Macromolecules 2009, 42, 3951–3957.
(25) Elyashiv-Barad, S.; Greinert, N.; Sen, A. Macromolecules 2002,
35, 7521–7526.

Article
Organometallics, Vol. 29, No. 14, 2010 3165
Figure 8. GPC traces for 2-n-butyl-5-norbornene/ethene copolymerization (samples from entries 2, 3, and 10, Table 4).
Table 5. Endo/Exo Ratio in Norbornene Derivatives before and
after Ethene/Norbornene Copolymerizationa
NMR spectrum, suggesting that the carbonyl group was
coordinated to the metal center. After this step, 13CO (40 psi)
was added again to the solution (step c). In 13C NMR spectrum,
new resonances appeared at 231.7 ppm (C3) and 206.7 ppm
(C4) due to Pd-CO-NB-COCH3. This insertion step is rever-
sible since the release of free 13CO (step d) resulted in the re-
formation of C2 (235.0 ppm). In the last step (step e), excess
norbornene (2 equiv relative to Pd) was added to the solution.
This resulted in two new resonances at 239.5 ppm (C5) and
207.3 ppm (C6) due to Pd-NB-CO-NB-COCH3. Note that the
successive insertions of neither two norbornene units nor two
CO units were observed. This is consistent with the observation
that complex A is not effective for the homopolymerization of
norbornene. Following one norbornene insertion, a smaller
monomer (ethene or CO) has to insert before the insertion of a
second norbornene unit (see Section 3 above). The successive
insertion of CO is disfavored on thermodynamic grounds.26,27
endo/exo endo/exo
before
norbornene
derivative
temp Nb conv
after
entry catalyst
(°C) (mol %)b reactionb reactionb
1
2
3
4
5
A
A
A
B
B
5-Nb-2-tBu ester
5-Nb-2-CH2OH
5-Nb-2-nC4H9
5-Nb-2-tBu ester
5-Nb-2-CH2OH
90
90
90
30
30
44
35
92
15
16
63/37
60/40
67/33
63/37
60/40
66/34
69/31
100/0
65/35
68/32
a Conditions: Pd complex, 0.03 mmol; ethene, 300 psi; norbornene
derivative, 2 g; toluene, 5 mL; chlorobenzene (GC internal standard),
0.15 g; 2 h. b Determined by GC.
Table 6. Copolymerization of Polar Monomers with Ethene and
Norbornenea
polar
monomer
olefin
temp yield incorpb
olefin
activity
entry catalyst (psi or g) (psi or g) (°C) (g) (mol %) (kg/mol[Pd] h)
3
Conclusion
1
A
A
A
A
A
A
A
CO, 50 Nb, 2
CO, 50 Nb, 2
CO, 50 C2H4, 300 90 0.40
90 0.77
90 0.64
53.8
12.9
6.7
2c
3
In conclusion, the synthesis, characterization, and poly-
merization activity of novel unsymmetric palladium com-
plexes have been described. Catalysts A and B show rela-
tively high activity toward ethene/functional norbornene
copolymerizations, and a high level of incorporation of the
norbornene derivative was observed. The molecular weight
of the copolymers can be controlled by adjusting the ethene/
norbornene feed ratio. The ethene/nonpolar functional nor-
bornene copolymerizations have the characteristics of a
“living” polymerization at low ethene/norbornene feed ra-
tios. Finally, the successive stepwise insertion of carbon
monoxide and norbornene into a preformed palladium-
carbon bond was observed by NMR spectroscopy.
50.0
21.5
96.5
4
MA, 2 Nb, 2
MA, 2 Nb, 2
50 0.20
50 0.02
50 0.84
5c
6
MA, 3
MA, 3
0
0
7c
50
0
a Conditions: Pd complex, 0.03 mmol; toluene, 5 mL; 2 h (entries
1-3), 15 h (entries 4-7). b Entry 1 was determined by CH analysis
(Galbraith Laboratories); entry 3 determined by 1H NMR in CDCl3/
1,1,1,3,3,3-hexafluoro-2-propanol at 25 °C; entries 4 and 5 determined
by 1H NMR in C6D6 at 25 °C. c In the presence of 1.5 equiv of galvinoxyl
relative to Pd.
1
Pd-CH3 resonance at 0.06 ppm in the H NMR spectrum
was replaced by a new resonance at 1.7 ppm due to the Pd-
COCH3 group (Figure 9). Subsequent studies were carried
out using 13CO and monitoring the reactions by 13C NMR
spectroscopy (Figure 10 and Scheme 3). In the first step (step a),
13CO (40 psi) was added to a high-pressure NMR tube con-
taining a solution of complex A in C6D6. This resulted in a
resonance at 230.5 ppm (C1) due to Pd-COCH3, and excess
unreacted 13CO was observed at 184.4 ppm. In the second
step (step b), the unreacted 13CO was released and approxi-
mately 0.5 equiv of norbornene relative to Pd was added to
the solution. Insertion of norbornene into the Pd-COCH3
occurred, and a new resonance at 235.1 ppm (C2) corres-
ponding to Pd-NB-COCH3 was observed. At the same time,
Experimental Section
Materials. All chemicals and reagents were obtained from
Aldrich unless otherwise stated. Methyl acrylate (99%) was
passed through a basic alumina column to remove the inhibitor
and impurities, then degassed and dried with CaH2. 5-Norbor-
nene-2-carboxylic tert-butyl ester (BF Goodrich, 98%), 5-nor-
bornene-2-methanol (98%), and 5-norbornene-2-n-butyl (BF
Goodrich) were degassed and dried with molecular sieves.
Norbornene was degassed. Palladium chloride (PdCl2, 99.9%),
(26) Margl, P.; Ziegler, T. J. Am. Chem. Soc. 1996, 118, 7337–7344.
(27) Sen, A. Acc. Chem. Res. 1993, 26, 303–310.
1
a resonance due to free pyridine was observed in the H

3166 Organometallics, Vol. 29, No. 14, 2010
Chen et al.
Figure 9. 1H NMR spectra (acetone-d6, 25 °C) of complex A: (a) before CO insertion, (b) following CO insertion.
Scheme 3. Schematic of the Observed Stepwise Insertions of 13CO and Norbornene into the Pd-C Bond in Complex A
pyridine (anhydrous, 99.8%), triphenylphosphine (PPh3, 99%),
2,6-diisopropylaniline (97%), and sodium hydride (NaH, dry,
95%) wereusedas received. (COD)PdMeCl, (TMEDA)PdMe2,28
and 2-formyl-1,8-naphthalenediol29,30 were synthesized by litera-
ture methods. All manipulations of air-sensitive materials were
performed in a N2-filled drybox.
Instrumentation. 1HNMR(300MHz) and13CNMR(75MHz)
spectra were recorded using a Bruker 300-DPX spectrometer.
Gas chromatography analysis was performed on an Agilent
5890 Series II GC using a RTX-5 split capillary column
(Restek) connected to an FID detector. Molecular weights
and molecular weight distributions were determined on a
(28) de Graaf, W. Organometallics 1989, 8, 2907–2917.
(29) Glaser, T.; Liratzis, I.; Frohlich, R. Dalton Trans. 2005, 2892–
2898.
(30) Rodriguez, B. A.; Delferro, M.; Marks, T. J. J. Am. Chem. Soc.
2009, 131, 5902–5919.

Article
Organometallics, Vol. 29, No. 14, 2010 3167
Figure 10. 13C NMR spectra (C6D6 at 25 °C) corresponding to stepwise insertions of 13CO and norbornene into complex A.
Shimadzu gel permeation chromatography (GPC) chromato-
graph containing a three-column bed (Styragel HR 7.8 Â
300 mm columns with 5 μm bead size; 100-5000, 500-30 000,
and 2000-4 Â 106 Da), a Shimadzu RDI-10A differential
refractometer, and a Shimadzu SPD-10A tunable absorbance
detector (254 nm). GPC samples were run in tetrahydrofuran
at a flow rate of 1 mL/min at 35 °C and calibrated against
polystyrene standards. Analysis was done using EZSTART
7.2 software.
formic acid and 2,6-diisopropylaniline (340 mg, 1.92 mmol) were
added into the solution. After that the solution was refluxed for
5 h. Ligand 1 precipitated out upon cooling and was collected by
filtration and washed with cold ethanol. Yield: 90%. 1H NMR
(acetone-d6, 25 °C, ppm): 14.0 (s, 1H, O-H), 13.4 (s, 1H, O-H), 8.1
(d, 1H, NdCH), 7.5-6.7(m,8H, aromatic), 3.2(m, 2H, CHMe2),
1.3 (d, 12H, CHMe2).
Synthesis of 2-(Phenyl)imino-1,8-dihydroxynaphthalene (Ligand 2).
Ligand 2 was synthesized similarly to that above from 2-formyl-
1,8-naphthalenediol and aniline. Yield: 93%. 1H NMR (acetone-d6,
25 °C, ppm): 13.9 (s, 1H, O-H), 13.8 (s, 1H, O-H), 8.8 (d, 1H,
NdCH), 7.5-6.7 (m, 10H, aromatic).
Synthesis of 2-(2,6-Diisopropylphenyl)imino-1,8-dihydroxy-
naphthalene (Ligand 1). 2-Formyl-1,8-naphthalenediol (361 mg,
1.92 mmol) was dissolved in ethanol (70 mL). Then one drop of

3168 Organometallics, Vol. 29, No. 14, 2010
Chen et al.
Synthesis of 2-[(2,6-Diisopropylphenyl)imino]-1,8-dihydroxy-
naphthalenediolate Sodium Salt (1-Na). To a solution of 1 (347 mg,
1 mmol) in dry THF (10 mL) was added NaH (240 mg, 10 mmol).
The resulting mixture was stirred at room temperature for 2 h, then
filtered by a syringe membrane. The solvent was removed, leaving
a yellow residue. This salt was immediately used. Yield: 80%. 1H
NMR (acetone-d6, 25 °C, ppm): 7.4 (s, 1H, NdCH), 7.5-6.7 (m,
8H, aromatic), 3.6 (broad, 2H, CHMe2), 1.3 (broad, 6H, CHMe),
1.0 (broad, 6H, CHMe).
Determination of the Relative Uptake of Endo versus Exo
Isomers of Functionalized Norbornene Copolymerizations. In a
typical experiment, in a N2-filled glovebox, a glass-lined stainless
steel autoclave was charged with palladium complex A (16.2 mg,
0.03 mmol), tert-butyl ester norbornene (2 g), chlorobenzene
(100 mg, internal reference), and toluene (5 mL). The autoclave
was sealed, removed from the glovebox, heated in an oil bath
to 90 °C, and charged with ethene (300 psi constant). The
amounts of unreacted exo and endo isomers before and after
the reaction were determined by GC analysis.
Synthesis of Palladium Complex, A. To a solution of 1-Na
(295 mg, 0.8 mmol) in toluene (10 mL) was added pyridine
(127 mg, 1.6 mmol), then (COD)PdMeCl (424 mg, 1.6 mmol).
The mixture was stirred at room temperature for 15 h and
filtered by a syringe membrane. The solvent was removed by
vacuum, and complex A was obtained as an orange powder.
X-ray Crystallography. Crystals suitable for X-ray analysis were
obtained by slowly evaporating toluene solutions. For complex C
we have used a mixture of toluene and methanol for good qua-
lity single crystals. A single crystal for each compound was selected
under a polarizing microscope and mounted on a loop using para-
tone oil. The crystal was cooled to 120 K by a Rigaku X-stream
2000 cryo-system. The single-crystal diffraction data were collected
on a Bruker-AXS diffractometer with a SMART APEX CCD area
detector. The X-ray generator was operated at 50 kV and 32 mA
1
Yield: 85%. H NMR (acetone-d6, 25 °C, ppm): 13.2 (s, 1H,
O-H), 8.9 (d, 2H, pyridine), 8.1 (m, 1H, pyridine), 7.9 (s, 1H,
NdCH), 7.7 (m, 2H, pyridine), 7.4-6.5 (m, 8H, aromatic), 3.6
(m, 2H, CHMe), 1.4 (d, 6H, CHMe2), 1.2 (d, 6H, CHMe2), 0.06
(s, 3H, Pd-Me).
˚
using Mo KR(λ= 0.71073 A) radiation. Data were collected with a
Synthesis of Palladium Complex, B. To a solution of 1-Na
(147 mg, 0.4 mmol) in toluene (5 mL) was added DMSO (34 mg,
0.44 mmol), then (COD)PdMeCl (212 mg, 0.8 mmol). The mix-
ture was stirred at room temperature for 15 h and filtered by a
syringe membrane. The solvent was removed by vacuum, and
ω scan width of 0.3°. A total of 600, 430, 235, and 50 frames were
collected in four different settings of j (0°, 90°, 180°, 270°), keeping
the sample-to-detector distance fixed at 5.8 cm and the detector
position (2θ) fixed at -25°. The data were reduced using SAINT-
PLUS,31 and an empirical absorption correction was applied using
the SADABS32 program. The crystal structure was solved by direct
methods using SHELXS97 and refined using SHELXL97 present
in the SHELXTL V6.1433 package. The atoms of the solvent mole-
cules in complex C were found to be scattered, and only fragments
were observed in the difference Fourier map. Because of disorder,
the hydrogen atoms on the methanol molecule in complex C could
not be located. All non-hydrogen atoms were easily found from the
differential Fourier maps and were refined anisotropically. For the
final refinement, the hydrogen atoms were placed in geometrically
ideal positions and refined using the riding mode. The last cycles of
the refinement included atomic positions, anisotropic thermal
parameters for all the non-hydrogen atoms, and isotropic thermal
parameters for all the hydrogen atoms. Full-matrix least-squares
structure refinement against F2 was carried out using the SHEL-
XTL V6.14 package of programs.
1
complex B was obtained as a yellow powder. Yield: 80%. H
NMR (acetone-d6, 25 °C, ppm): 12.8 (s, 1H, O-H), 8.1 (s, 1H,
NdCH), 7.5-6.6 (m, 8H, aromatic), 3.4 (m, 2H, CHMe), 3.3 (s,
6H, DMSO), 1.3 (d, 6H, CHMe2), 1.1 (d, 6H, CHMe2), 0.07 (s,
3H, Pd-Me).
Synthesisof Palladium Complex, C. (TMEDA)PdMe2 (253 mg,
1 mmol) and ligand 2 (263 mg, 1 mmol) were stirred in toluene
(10 mL) overnight at 40 °C. After that the solvent was removed by
vacuum, and the solid was washed by hexanes. Complex C was
obtained as an amber powder. Yield: 88%. 1H NMR (acetone-d6,
25 °C, ppm): 10.3 (d, 1H, NdCH), 8.9 (s, 1H, O-H), 7.8-6.4 (m,
10H, aromatic), 2.3-2.9 (m, 16H, TMEDA), 0.5 (s, 3H, Pd-Me).
General Procedure for Ethene Homopolymerization by Palla-
dium Catalysts. In a typical experiment, in a N2-filled glovebox,
a glass-lined stainless steel autoclave was charged with palla-
dium complex A (16.2 mg, 0.03 mmol) and toluene (5 mL). The
autoclave was sealed, removed from the glovebox, heated in an
oil bath to the desired temperature, and then charged with
ethene (300 psi constant). The resulting polymer was precipi-
tated out in methanol/HCl, collected, and dried under vacuum
oven overnight.
Crystal data for ligand 1 and complexes A, B, and C are given in
Table S1. CCDC 750324-750327 contain the supplementary crys-
tallographic data for ligand 1 and complexes A-C. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre (CCDC) via www.ccdc.cam.ac.uk/data_request/cif.
General Procedure for Ethene/Norbornene Copolymerization
by Palladium Catalysts. In a typical experiment, in a N2-filled
glovebox, a glass-lined stainless steel autoclave was charged
with palladium complex A (16.2 mg, 0.03 mmol), norbornene
(2 g, 21.2 mmol), and toluene (5 mL). The autoclave was sealed,
removed from the glovebox, heated in an oil bath to the desired
temperature, and then charged with ethene (300 psi constant).
The resulting polymer was precipitated out in methanol/HCl,
collected, and dried under vacuum oven overnight.
Living Copolymerization of Nonpolar Functional Norbornene/
Ethene Using Complex B. In a N2-filled glovebox, a two-neck
round-bottom flask (250 mL) was charged with palladium
complex B (24 mg, 0.045 mmol), 2-n-butyl-5-norbornene (3 g,
20 mmol), tetrachloroethane (1 g, as GC internal standard), and
toluene (60 mL). The flask was sealed, taken out of the glovebox,
and heated in an oil bath at 30 °C with stirring. Ethene (1 atm)
was purged into the flask and then kept at a constant 1 atm
pressure. Samples were taken at intervals to carry out GC and
GPC analysis.
Acknowledgment. This research was supported by the
U.S. Department of Energy, Office of Basic Energy
Sciences. We also thank Dr. Hemant Yennawar for help
in X-ray structure determinations.
Supporting Information Available: (a) Tables of crystal data,
positional parameters for atoms, bond distances and angles, and
anisotropic thermal parameters, and CIF files for the crystal
structures. (b) Annotated NMR spectra of the ligands and the
palladium complexes. This material is available free of charge
via the Internet at http://pubs.acs.org.
(31) SMART (V 5.628), SAINT (V 6.45a), XPREP, SHELXTL;
Bruker AXS Inc.: Madison, WI, 2004.
(32) Sheldrick, G. M. Siemens Area Correction Absorption Correction
€
€
Program; University of Gottingen: Gottingen, Germany, 1994.
(33) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
€
€
Solution and Refinement; University of Gottingen: Gottingen, Germany,
1997.