Palladium catalysts for norbornene polymerization. A study by NMR and calorimetric methods

Article abstract of DOI:10.1021/om800264a

Neutral trans-[Pd(C₆F₅)XL₂] (X = Cl, Br) and cationic trans-[Pd(C₆F₅)L₂(NCMe)]BF ₄ (L = SbPh₃, AsPh₃, As(C₆Cl ₂F₃)Ph₂, AsCyPh₂, AsMePh ₂, PPh₃) complexes have been studied and tested for norbornene (NB) polymerization and copolymerization with 5-norbornene-2- carboxaldehyde (NB-CHO). The neutral complexes are almost inactive and produce only small amounts of oligomers, but the cationic complexes with arsines and stibines are very good for palladium-catalyzed norbornene polymerization. External coordinating molecules (e.g., ligands or monomers with O-donor groups) compete with the olefin function for the coordination sites on Pd and inhibit the reaction. In spite of this, copolymerization of norbornene and 5-norbornene-2-carboxaldehyde could be achieved, with lower yields and higher incorporations of the functionalized norbornene as the NB:NB-CHO ratio decreases. The complex with the fluorinated arsine AsPh₂(C ₆Cl₂F₃) is the most active catalyst and allows for easy spectroscopic study of the reacting systems by ¹⁹F NMR. Calorimetry provides straightforward monitoring and detection of activation and deactivation processes in polymerization reactions that give insoluble products and cannot be followed by NMR spectroscopy.

Full text of DOI:10.1021/om800264a

Organometallics 2008, 27, 3761–3769
3761
Palladium Catalysts for Norbornene Polymerization. A Study by
NMR and Calorimetric Methods
Juan A. Casares,* Pablo Espinet,* and Gorka Salas
IU CINQUIMA/Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Valladolid,
E-47071 Valladolid, Spain
ReceiVed March 23, 2008
Neutral trans-[Pd(C6F5)XL2] (X ) Cl, Br) and cationic trans-[Pd(C6F5)L2(NCMe)]BF4 (L ) SbPh3,
AsPh3, As(C6Cl2F3)Ph2, AsCyPh2, AsMePh2, PPh3) complexes have been studied and tested for norbornene
(NB) polymerization and copolymerization with 5-norbornene-2-carboxaldehyde (NB-CHO). The neutral
complexes are almost inactive and produce only small amounts of oligomers, but the cationic complexes
with arsines and stibines are very good for palladium-catalyzed norbornene polymerization. External
coordinating molecules (e.g., ligands or monomers with O-donor groups) compete with the olefin function
for the coordination sites on Pd and inhibit the reaction. In spite of this, copolymerization of norbornene
and 5-norbornene-2-carboxaldehyde could be achieved, with lower yields and higher incorporations of
the functionalized norbornene as the NB:NB-CHO ratio decreases. The complex with the fluorinated
arsine AsPh2(C6Cl2F3) is the most active catalyst and allows for easy spectroscopic study of the reacting
systems by 19F NMR. Calorimetry provides straightforward monitoring and detection of activation and
deactivation processes in polymerization reactions that give insoluble products and cannot be followed
by NMR spectroscopy.
copolymerization of norbornene with ethylene and with other
functionalized norbornenes.1,3–17 Usually the polymerization
requires a nickel(II) catalyst and an organometallic cocatalyst
(typically methylaluminoxane or B(C6F5)3),1,3,4,9,10 but some
nickel10,11 and palladium organometallics are very efficient
without cocatalyst. Many of these catalysts are based on
chelating ligands, while phosphines are the most often used
Introduction
The increasing interest in the polymerization of cyclic olefins
is due to the attractive properties of these polymers, which show
high glass transition temperatures, high optical transparency,
low dielectric constant, and low birefringence. With norbornene
(bicyclo[2.2.1]hept-2-ene) and norbornene derivatives as the
starting materials, different classes of polymers can be obtained
by selecting polymerization catalysts that drive the reaction via
cationic or radical pathways, ring-opening metathesis, or inser-
tion routes (Scheme 1).1
Cationic polymerization of norbornene (NB) results in the
formation of low-molecular-weight polymers with rearranged
norbornanediyl units in the backbone (A). Metal catalyzed ring-
opening metathesis polymerization (ROMP) of norbornene
derivatives yields polymers containing unsaturations in the
backbone (B). Metal-catalyzed insertion polymerization of
norbornene, either with early-transition-metal metallocenes or
with late-transition-metal organometallics, can lead to two
different structures, one strictly linear containing norbornanediyl
units (C) and another in which norbornanediyl and rearranged
norbornanediyl with appended norbornanediyl units alternate
(D).1,2
(3) (a) Peruch, F.; Cramail, H.; Deffieux, A. Macromol. Chem. Phys.
1998, 199, 2221–2227. (b) Arndt, M.; Gosmann, M. Polym. Bull. 1998,
41, 433–440. (c) Mast, C.; Krieger, M.; Dehnicke, K.; Greiner, A. Macromol.
Rapid Commun. 1999, 20, 232–235. (d) Zhao, C-T.; Ribeiro, M. R.; Portela,
M. F. J. Mol. Catal. A Chem. 2002, 185, 81–85. (e) Li, Y.-S.; Li, Y.-R.;
Li, S.-F. J. Organomet. Chem. 2003, 667, 185–191. (f) Zhang, D.; Jin, G.-
X.; Weng, L.-H.; Wang, F. Organometallics 2004, 23, 3270–3275. (g)
Nelkenbaum, E.; Kapon, M.; Eisen, M. S. J. Organomet. Chem. 2005, 690,
3154–3164.
(4) (a) Lassahn, P. G.; Janiak, C.; Oh, J.-S. Macromol. Rapid Commun.
2002, 23, 16–20. (b) Janiak, C.; Lassahn, P. G. Polym. Bull. 2002, 47, 539–
546. (c) Lassahn, P. G.; Lozan, V.; Wu, B.; Weller, A. S.; Janiak, C. Dalton
Trans. 2003, 4437–4450. (d) Jang, Y.; Sung, H. K.; Lee, S.; Bae, C. Polymer
2005, 46, 11301–11310.
(5) Goodall, B. L. In Late Transition Metal Polymerization Catalysis;
Rieger, B., Saunders Baugh, L., Katcker, S., Striegler, S., Eds.;Wiley-VCH:
Weinheim, Germany, 2003; Chapter 4.
(6) (a) Sacchi, M. C.; Sonzogni, M.; Losio, S.; Forlini, F.; Locatelli, P.;
Tritto, I.; Licchelli, M. Macromol. Chem. Phys. 2001, 202, 2052–2058. (b)
Zhao, C.; Ribeiro, R.; Subrahmayam, V. S.; Gil, C. L.; de Lima, A. P.
Polymer 2001, 42, 2455–2462. (c) Janiak, C.; Lasshahn, P.-G. Polym. Bull.
2002, 47, 539–546.
Nickel and palladium complexes are very efficient catalysts
for the vinyl polymerization of norbornene, for the copolym-
erization of functionalized norbornenes, and also for the
(7) Diamanti, S. J.; Ghosh, P.; Shimizu, F.; Bazan, G. C. Macromolecules
2003, 36, 9731–9735.
(8) Lee, B. Y.; Kim, Y. H.; Shin, H. J.; Lee, C. H. Organometallics
2002, 21, 3481–3484.
(9) Sun, W.-H.; Yang, H.; Li, Z.; Li, Y. Organometallics 2003, 22, 3678–
3683.
(10) Benedikt, G. M.; Elce, E.; Goodall, B. L.; Kalamarides, H. A.;
McIntosh, L. H., III; Rhodes, L. F.; Selvy, K. T.; Andes, C.; Oyler, K.;
Sen, A. Macromolecules 2002, 35, 8978–8988.
(11) Barnes, D. A.; Benedikt, G. M.; Goodall, B. L.; Huang, S. S.;
Kalamarides, H. A.; Lenhard, S.; McIntosh, L. H. III.; Selvy, K. T.; Shick,
R. A.; Rhodes, L. F. Macromolecules 2003, 36, 2623–2632.
(12) Huang, C.-F.; Wang, S.-K.; Kuo, S.-W.; Huang, W.-J.; Chang, F.-
C. J. Appl. Polym. Sci. 2004, 92, 1824–1833.
* To whom correspondence should be addressed. E-mail: espinet@
qi.uva.es.
(1) (a) Janiak, C.; Lassahn, P. G. J. Mol. Catal. A: Chem. 2001, 166,
193–209. (b) Janiak, C.; Lassahn, P. G. Macromol. Rapid Commun. 2001,
22, 479–492.
(2) (a) Karafilidis, C.; Hermann, H.; Rufinska, A.; Gabor, B.; Mynott,
R. J.; Breitenbruch, G.; Weidenthaler, C.; Rust, J.; Joppek, W.; Brookhart,
M. S.; Thiel, W.; Fink, G. Angew. Chem., Int. Ed. 2004, 43, 2444–2446.
(b) Karafilidis, C.; Angermund, K.; Gabor, B.; Rufinska, A.; Mynott, R. J.;
Breitenbruch, G.; Thiel, W.; Fink, G. Angew. Chem., Int. Ed. 2007, 46,
3745–3749.
10.1021/om800264a CCC: $40.75
2008 American Chemical Society
Publication on Web 07/02/2008

3762 Organometallics, Vol. 27, No. 15, 2008
Casares et al.
bornene,4,11 that imposes serious limitations to GPC character-
ization and to spectroscopic studies. The latter problem has been
mitigated here by using microcalorimetry to monitor the
reactions.
Scheme 1
Results and Discussion
Synthesis of the Complexes. The cationic complexes trans-
[Pd(C6F5)L2(NCMe)]BF4 (L ) PPh3, AsPh3, AsMePh2, As-
CyPh2, AsRfPh2, SbPh3; Rf ) C6Cl2F3), were obtained by
abstracting the halogen from trans-[Pd(C6F5)XL2] with AgBF4
in acetonitrile (eq 1).
monodentate ligands.18,19 The use of very bulky monodentate
phosphines has proved to be advantageous for controlling the
polymerization of functionalized NB.14
The ligands used in Ni and Pd catalysis have to fulfill two
requirements: they have to stabilize the complex to keep it in
solution as an active metal center, but they also have to be weak
enough to allow for coordination of the norbornene. Often
phosphine ligands are too strongly donating. The weaker As
and Sb donor ligands are still able to sufficiently stabilize late-
transition-metal organometallic complexes, as we have shown
in a recent paper where stable nickel catalysts with As or Sb
donor ligands show very high activity in norbornene polymer-
ization.19 In an independent study it was proven that the As
and Sb donor ligands in these complexes are very easily
displaced and the complexes are isomerized in acetone solution
through a complex system of consecutive substitutions in
solution.20 Taken together, the results of these two studies
suggest that the less coordinating ligands (as far as they are
sufficiently stabilizing) give rise to the most efficient catalysts.
The coordinating ability of the ligands can be tuned through
the donor atom (SbPh3 vs AsPh3), by electronic means (AsPh3
vs AsMePh2), and also by steric means (AsMePh2 vs AsCyPh2).
In this paper we report the synthesis of complexes trans-
[Pd(C6F5)L2(NCMe)]BF4 (L ) PPh3, AsPh3, AsMePh2, As-
CyPh2, As(C6Cl2F3)Ph2, SbPh3) and their catalytic activity in
the insertion polymerization of norbornene. The polynorbornene
produced is highly insoluble. This is a frequent result, particu-
larly common in palladium-catalyzed polymerization of nor-
Complexes 1b-6b are stable in the solid state and can be
stored for long periods. The complexes have been characterized
1
in solution by H, 19F, and 13C NMR and IR spectroscopy.
Complexes 3b and 5b were also characterized by X-ray
diffraction (Figure 1). Table 1 collects relevant bond distances
and angles, and Figure 1 shows ORTEP representations of the
cations. Both compounds show a square-planar coordination,
with angles between adjacent donor atoms fairly close to 90°
and the two arsine ligands mutually trans. The Pd-C bond
lengths are similar to those found in the Cambridge Structural
Database (CSD) for other complexes with the (pentafluorophe-
nyl)palladium moiety. The Pd-As bond lengths are also similar
to those found in other trans-bis(arsine)palladium complexes,
and the Pd-N bond length is within the range found in the
CSD for Pd-NCMe bonds. In both complexes the pentafluo-
rophenyl ring is tilted, making angles of 84° (3b) and 77° (5b)
with the coordination plane, lying almost parallel to one phenyl
ring of one arsine in 3b, and being sandwiched by one Ph and
one Rf ring (each of one arsine) in 5b. The Pd-C bonds are
equal within experimental error for both complexes, whereas
the difference in bond lengths for Pd-AsRfPh2 in 5b (average
2.414 Å) and Pd-AsMePh2 in 3b (average 2.401 Å) is
significant and probably associated with the poorer donor ability
of AsRfPh2 and the different bulks of both ligands. The cone
angles, calculated from the X-ray structures as described in the
literature,21,22 are 143° for AsMePh2 and 167° for AsRfPh2.
Polymerization of Norbornene. The polymerization experi-
ments were carried out in CH2Cl2 at 25 °C. Under the mild
conditions used, the neutral compounds (1a-6a) and the cationic
compound with PPh3 (1b) do not afford a polymer, while the
cationic complexes (2b-6b) are efficient catalysts that produce
polynorbornene, which precipitates from the reaction as a white
solid. The amount of unreacted norbornene was measured, by
GC, on the supernatant liquids after pouring the suspension onto
methanol. Attempts to dissolve the polymers in organic solvents
(including ethers, chloroform, dichloromethane, 1,2-dichloro-
ethane, chlorobenzene, hot 1,2-dichlorobenzene, and hot 1,2,4-
trichlorobenzene) were unsuccessful, which precluded their
characterization by GPC.
(13) For the polymerization of functionalized norbornenes, see: (a)
Breunig, S.; Risse, W. Makromol. Chem. 1992, 193, 2915–2927. (b)
Reinmuth, A.; Mathew, J. P.; Melia, J.; Risse, W. Macromol. Rapid
Commun. 1996, 17, 173–180. (c) Mathew, J. P.; Reinmuth, A.; Melia, J.;
Swords, N.; Risse, W. Macromolecules 1996, 29, 2755–2763. (d) Heinz,
B. S.; Alt, F. P.; Heitz, W. Macromol. Rapid Commun. 1998, 19, 251–256.
(e) Shin, B.; Jang, M.; Yoon, D. Y.; Heitz, W. Macromol. Rapid Commun.
2004, 25, 728–732.
(14) Yamashita, M.; Takamiya, I.; Jin, K.; Nozaki, K. Organometallics
2006, 25, 4588–4595.
(15) Lipian, J.; Mimna, R. A.; Fondran, J. C.; Yandulov, D.; Shick, R. A.;
Goodall, B. L.; Rhodes, L. F.; Huffman, J. C. Macromolecules 2002, 35,
8969–8977.
(16) Kang, M.; Sen, A. Organometallics 2004, 23, 5396–5398.
(17) (a) Hennis, A. D.; Polley, J. D.; Long, G. S.; Sen, A.; Yandulov,
D.; Lipian, J.; Benedikt, G. M.; Rhodes, L. F. Organometallics 2001, 20,
2802–2812. (b) Funk, J. K.; Andes, C. E.; Sen, A. Organometallics 2004,
23, 1680–1683.
(18) (a) Sen, A.; Lai, T. W. Organometallics 1982, 1, 415–417. (b) Sen,
A.; Lai, T. W.; Thomas, R. R. J. Organomet. Chem. 1988, 358, 567–568.
(c) Goodall, B. L.; Jayaraman, S.; Shick, R. A.; Rhodes, L. F.; Allen, R. D.;
DiPietro, R. A.; Wallow, T. U.S. Patent 6,723,486, 2004. (d) Chemtob, A.;
Gilbert, R. G. Macromolecules 2005, 38, 6796–6805. (e) Myagmarsuren,
G.; Jeong, O. Y.; Ihm, S. K. Appl. Catal., A 2005, 296, 21–29. (f)
Myagmarsuren, G.; Lee, K. S.; Jeong, O. Y.; Ihm, S. K. Catal. Commun.
2005, 6, 337–342. (g) Myagmarsuren, G.; Lee, K. S.; Jeong, O. Y.; Ihm,
S. K. Polymer 2005, 46, 3685–3692.
(19) Casares, J. A.; Espinet, P.; Martin-Alvarez, J. M.; Martinez-Ilarduya,
J. M.; Salas, G. Eur. J. Inorg. Chem. 2005, 3825–3831.
(20) Casares, J. A.; Espinet, P.; Martinez-Ilarduya, J. M.; Mucientes,
J. J.; Salas, G. Inorg. Chem. 2007, 46 (3);), 1027–1032.
(21) Tolman, C. A. Chem. ReV. 1977, 77, 313–348.
(22) (a) Mingos, D. M. P.; Mu¨ller, T. E. J. Organomet. Chem. 1995,
500, 251–259. (b) Mu¨ller, T. E.; Mingos, D. M. P. Transition Met. Chem.
1995, 20, 533–539.

Pd Catalysts for Norbornene Polymerization
Organometallics, Vol. 27, No. 15, 2008 3763
Figure 1. ORTEP diagram of the cations trans-[Pd(C6F5)(AsMePh2)2(NCMe)]+ (3b, left) and trans-[Pd(C6F5)(AsRfPh2)2(NCMe)]+ (5b,
right).
Table 1. Selected Bond Lengths (Å) and Angles (deg)
trans-[Pd(C6F5)(AsMePh2)2(NCMe)]BF4 (3b)
trans[Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (5b)
Pd(1)-C(11)
1.998(5)
2.056(5)
Pd(1)-C(11)
2.001(4)
2.063(4)
2.4129(6)
2.4167(6)
89.58(10)
94.03(9)
88.72(10)
87.35(9)
Pd(1)-N(1)
Pd(1)-N(1)
Pd(1)-As(1)
Pd(1)-As(2)
C(11)-Pd(1)-As(1)
N(1)-Pd(1)-As(1)
C(11)-Pd(1)-As(2)
N(1)-Pd(1)-As(2)
2.4007(18)
2.4031(18)
87.22(14)
91.76(12)
88.50(14)
92.51(12)
Pd(1)-As(1)
Pd(1)-As(2)
C(11)-Pd(1)-As(1)
N(1)-Pd(1)-As(1)
C(11)-Pd(1)-As(2)
N(1)-Pd(1)-As(2)
a
Table 2. Polymerization of Norbornene with Catalysts [Pd(C6F5)L2(NCMe)]BF4
max cat. efficiency (105 g of
polymer/((mol of Pd) h))
cat. (L)
yield (%)b
induction time (min)c
max rate (10-4 M s-1
)
ligand cone angle ΘT(L) (deg)d
1b (PPh3)
2b (AsPh3)
3b (AsMePh2)
4b (AsCyPh2)
5b (AsRfPh2)
6b (SbPh3)
<2.0
62.8
21.7
83.8
100.0
96.6
145
141
143
3.2
2.8
12
1.1
0.8
2.4
2.2
1.1
9.2
1.2
2.9
2.6
1.3
11
167
142
1.4
a The reactions of 2.3 mmol of norbornene with 1.15 µmol of catalyst in dichloromethane (total solution volume taken to 4 mL; [NB] ) 0.575 M,
[complex] ) 2.8 × 10-4 M) were performed under isothermal conditions at 25 °C. b Calculated with respect to the consumed NB, which was measured
by GC. c The value given is the time elapsed to reach the maximun rate. For its calculation the curves have been corrected using the dynamic correction
provided by the instrument software. d Calculated for 3b and 5b from the X-ray structures. For structures of 1b, 2b, and 6b see ref 19. The calculated
cone angle for PPh3 is as reported by Tolman.21
Table 2 shows the polymerization results. The yields obtained
are strongly dependent on the L ligand, being noticeably higher
for AsRfPh2, SbPh3, AsCyPh2, and AsPh3 than for AsMePh2
and PPh3. Apparently the highest yields are obtained with more
weakly donating or bulkier ligands, which undergo easier
substitution (see below for support of this interpretation).
Complex 5b, bearing a bulky and relatively poorly donating
ligand (because of the electron-withdrawing effect of the
fluorinated ring), is the most efficient (in terms of yield) and
the fastest catalyst. Its activity was tested in separate experi-
ments: In a reaction with the ratio NB:5b ) 20 000:1, 91%
polymerization was produced in 24 h;23 a reaction using 1.65 g
of NB (17.5 mmol) and 1.0 µmol of 5b in 3 mL of dichlo-
romethane afforded 1.05 g of polymer in 30 min (63.6% yield,
conversion 2.1 × 106 g of polymer/((mol of Pd catalyst) h)).
NMR Monitoring of Polymerization Experiments.
Neutral Complexes. The reactions of NB with neutral com-
plexes [Pd(C6F5)XL2] do not lead to high-Mw polynorbornene
under the reaction conditions used (NB:Pd ) 2000:1 in CH2Cl2
as solvent, at 25 °C). Since this lack of reactivity could be due
to the inability of the NB to coordinate to the palladium center,
an experiment with a complex containing a ligand that was
easier to substitute (AsRfPh2) was carried out. The reaction of
trans-[Pd(C6F5)Br(AsRfPh2)2] (5a) with NB was followed by
19F NMR on the C6F5 group for the possible insertion reaction,
as well as on the fluorinated arsine AsRfPh2 (Rf ) 3,5-dichloro-
2,4,6-trifluorophenyl) for the possible substitution reaction by
NB at the palladium center. The complex was dissolved in
CDCl3, and a large excess of NB was added (NB:Pd ) 98:1).
After 24 h at room temperature the 19F NMR showed only 3%
of AsRfPh2 in the form of unreacted starting complex, with 73%
of AsRfPh2 appearing as uncoordinated ligand (Figure 2). Hence,
it must have been substituted by NB in the coordination sphere
of Pd; the remaining 24% of AsRfPh2 appeared coordinated to
palladium in one or more unidentified complexes, giving a broad
signal. Therefore, the mixture contains complexes with only one
or no coordinated arsine ligand. On the other hand, the C6F5
signals show that only 3% of the pentafluorophenyl groups
remain attached to palladium,24 while 97% of the groups have
added to norbornene (C-C6F5 groups). Integration of aliphatic
versus olefinic signals in 1H NMR shows that 65% of the starting
(23) A 1.732 g portion of norbornene (18.4 mmol) was dissolved in 6
mL of CH2Cl2. To this solution was added 1.16 mg of [PdC6F5-
(AsC6Cl2F3Ph2)2(CH3CN)]BF4. The formation of polynorbornene as a white
precipitate started immediately. The solution was stirred for 24 h, and the
solid was filtered and washed with EtOH.

3764 Organometallics, Vol. 27, No. 15, 2008
Casares et al.
Figure 2. 19F NMR spectrum of a mixture of trans-[Pd(C6F5)-
Br(AsRfPh2)2] (5a) and NB after 24 h of reaction.
norbornene remains unreacted.25 This NMR experiment shows
that, even when NB has doubtlessly coordinated to Pd (NB is
the only ligand in the reaction system able to replace the arsine
at the palladium center), the reaction on the neutral intermediates
formed is slow and is fruitless in terms of high-Mw polymer,
leading only to soluble oligomers. In other words, the slow
insertion is not due to difficult coordination of the norbornene
but to the insertion step itself. The slowness of the insertion
reaction observed is in line with reports which suggest that the
insertion of olefins into Pd-C bonds is faster for more
electrophilic palladium centers.18b,26
The same NMR experiment was performed with trans-
[Pd(C6F5)Br(AsPh3)2] (2a) and norbornene. The reaction was
noticeably slower, and after 24 h no significant consumption
of norbornene was observed in the 1H NMR spectrum, although
the 19F NMR spectrum indicated that 19% of C6F5 groups had
added to norbornene (they were detected as C-C6F5 groups;
this amount is negligible in terms of NB consumption). This
noticeable retardation is to be expected, considering that AsPh3
is a better ligand for neutral Pd centers compared to the bulkier
and poorer donor AsRfPh2.
Figure 3. 19F NMR spectra of a CDCl3 solution prepared from
NB and trans-[Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (5b) (NB:Pd ) 10:
1): (a) at 298 K; (b) at 217 K; (c) expansion of the spectrum at
217 K in the C6Cl2F3 range. Legend to symbols: (/) C6F5 in 5b;
(.) AsRfPh2 in 5b; ([) coordinated AsRfPh2 (other than 5b); (1)
C6F5 attached to a growing polymer chain (all fluorine nuclei; note
the narrower range of chemical shifts for C-C6F5 compared to
Pd-C6F5). The AsRfPh2 coordinated to 5b does not participate in
the ligand exchange equilibrium that leads to the coalescence of
other AsRfPh2 signals at 298 K.
librium is very much shifted toward 2b.28 When the same
experiment is performed on trans-[Pd(C6F5)(AsRfPh2)2(NCMe)]-
BF4 (5b) (NB:5b ) 34:1), a shift of the acetonitrile bands to
2314 and 2285 cm-1 is observed, with the complete disappear-
ance of the two bands due to coordinated acetonitrile in 5b.
This shows that a new complex, where the acetonitrile remains
coordinated, has been formed; hence, AsRfPh2 is more easily
replaced by NB, in cationic complexes, than the harder NCMe
or the stronger donor AsPh3. Consistently, the catalyzed
polymerization of NB in CDCl3 at 298 K (NB:Pd ) 10:1) is
faster with trans-[Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (5b) than
with trans-[Pd(C6F5)(AsPh3)2(NCMe)]BF4 (2b).
Cationic Complexes. The complexes trans-[Pd(C6F5)L2-
(NCMe)]BF4 are efficient in the production of high-Mw polymer
(except for L ) PPh3). In order to know which ligands are
displaced by NB under the reaction conditions, complexes 2b
and 5b were studied by IR spectroscopy to assess whether the
acetonitrile remains coordinated or not. Uncoordinated aceto-
nitrile dissolved in CHCl3 gives two bands at 2293 and 2266
1
The H NMR spectrum of a freshly prepared sample (298
cm ,
-1 27 whereas both absorptions appear at higher wavenumbers
K) of trans-[Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (NB:Pd ) 10:1)
does not show olefin signals of noncoordinated NB (6.01 ppm),
since it has already coordinated to Pd (a very broad signal at
6.5-6.9 ppm is assigned to coordinated norbornene) or is
incorporated into the polymer during the manipulation time. The
19F NMR spectra in the C6F5 region shows signals of the starting
complex and very broad signals of C-C6F5 (Figure 3a). In the
C6Cl2F3 region very broad signals of AsRfPh2 are observed.
Since the signals of the remaining unreacted 5b are sharp, the
broadness is suggestive of an exchange process between
AsRfPh2 groups noncoordinated and coordinated to palladium
centers that are participating in the polymerization reaction. The
19F NMR spectrum registered at 217 K in the C6F5 region
(Figure 3b) is similar to that at 298 K and does not show signals
when the acetonitrile is coordinated to palladium (2323 and 2293
cm-1 for complex 2b and 2324 and 2296 cm-1 for complex
5b). The IR spectrum of a solution of trans-[Pd(C6F5)(AsPh3)2-
(NCMe)]BF4 (2b) and norbornene (NB:2b ) 23:1) showed no
changes with respect to that of pure 2b, showing that, at this
NB concentration, the ligand-for-norbornene substitution equi-
(24) The chemical shifts for C-bonded and Pd-bonded C6F5 groups are
very different and are clearly identified; see for instance: (a) Albe´niz, A. C.;
Espinet, P.; Foces-Foces, C.; Cano, F. H. Organometallics 1990, 9, 1079–
1085. (b) Albe´niz, A. C.; Espinet, P.; Jeannin, Y.; Philoche-Levisalles, M.;
Mann, B. E. J. Am. Chem. Soc. 1990, 112, 6594–6600. (c) Albe´niz, A. C.;
Espinet, P. Organometallics 1991, 10, 2987–2988.
(25) Formation of soluble low-molecular-weight oligomers can explain
why no polymer is observed to precipitate in methanol in attempts at
polymerization with neutral complexes as catalysts.
(26) Sen, A. Acc. Chem. Res. 1988, 21, 421–428.
(27) One of the bands is assigned to ν(CN) stretching and the other to
a combination band: Storhoff, B. N.; Lewis, H. C. Coord. Chem. ReV. 1977,
23, 1–29.
(28) The high concentration of palladium complex required to record a
IR spectrum precluded the use of an excess of norbornene comparable to
the ratio used in the catalytic experiments.

Pd Catalysts for Norbornene Polymerization
Organometallics, Vol. 27, No. 15, 2008 3765
Scheme 2
Figure 4. Plot of the polymerization reaction rate (mmol L-1 s-1
vs time (s), using 2b-6b as catalyst.
)
assignable to complexes of the type [Pd(C6F5)(AsRfPh2)-
(NB)(NCMe)]BF4 or [Pd(C6F5)(NB)2(NCMe)]BF4. Three groups
of signals appear in the C6Cl2F3 region: (i) free AsRfPh2, (ii)
signals from the starting compound 5b, and (iii) signals from
other palladium-containing AsRfPh2 complex different from 5b.
The last signals are broader than the others at the same
temperature, suggesting that they might correspond to palladium
complexes containing growing oligomeric polynorbornene
chains.
These spectroscopic observations are consistent with the basic
sequence of reaction summarized in Scheme 2. The reaction
starts with the substitution of an L ligand cis to C6F5 by NB,
followed by insertion. Then a chain-growing process follows,
on intermediates with one or two coordinated NB monomers
that have displaced the arsine or stibine ligands. The ligand
exchange on complexes that participate in the chain growing is
faster than the exchange of free arsine with 5b, as shown by
the NMR spectra at 298 K; this is probably due to the very
high trans effect of coordinated NB as compared with the trans
effect of arsine (or stibine).
Calorimetric Monitoring of Polymerization. The formation
of large amounts of solid or of very viscous solutions precludes
spectroscopic monitoring of the polymerization under catalytic
conditions. However, the reactions can be properly monitored
by calorimetry.29,30 The calorimeter measures dq/dt (the instan-
taneous heat flow per time unit, in mJ ss1) at chosen times. At
constant pressure, the reaction rate at any instant is proportional
to the instantaneous heat flow.31 The conversion at any instant
can be calculated as a quotient between the total heat evolved
up to that instant and the total heat evolved when the reaction
is complete. As a result, instantaneous concentrations of
reactants and products can also be calculated.
The polymerization reactions were monitored in a micro-
calorimeter. In a standard experiment 2 mL of a dichloromethane
solution containing 2.3 mmol of NB was injected in a
calorimetric cell containing 2 mL of a solution containing 1.15
µmol of the palladium catalyst in CH2Cl2 under nitrogen. When
the reaction apparently ceased, 10 mL of methanol was added
to fully quench the system, and the content in unreacted NB of
the supernatant liquids was measured by GC. Figure 4 shows
the reaction rate/time plot for the polymerization experiments.
Because it takes time for the heat to flow through the reactor
vessel to the sensors in the isothermal block, this raw data curve
must be mathematically corrected (see the Experimental Sec-
tion). In all cases an activation or induction time is observed,
during which time the initial complexes form an intermediate,
a Pd complex with coordinated norbornene that will undergo
insertion. The activation time values given in Table 2 have been
taken from the corrected experimental curves, as the time
elapsed to reach the maximun rate.
The data collection was maintained until the release of heat
ceased, indicating that the reaction had finished. Reaction times
between 3 h (for the fastest) and 16 h (for the slowest) were
found. For complexes 2b-6b the reaction rate vs norbornene
conversion plots give curves, rather than the straight lines
expected for a pseudo-first-order rate law,29e revealing that a
more complex behavior is interfering with the simple first-order
behavior. In these plots the reaction rate (the slope of the curves)
increases during the activation time and then decreases as
catalyst deactivation progresses during the second part of the
experiment. As discussed below, this interference corresponds
to deactivation of the catalyst. In spite of this complication,
which precludes attaining exact kinetic parameters, very valuable
information can be obtained from the curves of Figure 4. Large
differences in activation time were observed (Table 1). For
complex 5b the maximum rate was reached after 1.1 min, but
complex 4b requires 12 min to reach the maximum. Apparently
there is no correlation between activation time and yield of the
reaction: complex 3b has a shorter activation time but a lower
yield than 2b or 4b. The activation time is short for the
complexes with the poorer donor ligands (AsRfPh2, SbPh3),
since they are more easily substituted by NB. For stronger
ligands (AsPh3, AsMePh2, AsCyPh2; the last ligand might
additionally impose severe steric hindrance to associative
substitution), the activation energy for L-for-NB substitution is
expected to be larger, and the induction time is consistently
longer.32,33
(29) For the use of calorimetry on catalysis kinetics see for instance: (a)
LeBlond, C.; Wang, J.; Larsen, R. D.; Orella, C. J.; Forman, A. L.; Landau,
R. N.; Laquidara, J., Jr.; Blackmond, D. G.; Sun, Y.-K. Thermochim. Acta
1996, 289, 189–207. (b) Singh, U. K.; Strieter, E. R.; Blackmond, D. G.;
Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 14104–14114. (c) Nielsen,
L. P. C.; Stevenson, C. P.; Blackmond, D. G.; Jacobsen, E. N. J. Am. Chem.
Soc. 2004, 126, 1360–1362. (d) Zogg, A.; Stoessel, F.; Fischer, U.;
Hungerbu¨hler, K. Thermochim. Acta 2004, 419, 1–17. (e) Blackmond, D. G.
Angew. Chem., Int. Ed. 2005, 44, 4302–4320.
Because of the activation period and the deactivation process
(see below), it is difficult to speak of initial rates, but the curves
in Figure 4 allow us to estimate maximum rates for the catalysts,
as well as the corresponding maximum catalyst efficiencies.
(30) For the use of calorimetry on kinetics of polymerization reactions
see: (a) Bechthold, N.; Landfester, K. Macromolecules 2000, 33, 4682–
4689. (b) Karlsson, O. J.; Hassander, H.; Wessle´n, B. J. Appl. Polym. Sci.
2000, 77, 297–311. (c) Saethre, B. Polym. Int. 1998, 45, 222–228.
(31) For a discussion of the relationship between heat flow and reaction
rates see refs 34d,e and the Supporting Information of ref 34c.
(32) Cross, R. J. AdV. Inorg. Chem. 1989, 34, 219–291.
(33) For associative and dissociative substitution processes in sterically
hindered complexes see (a) Bartolome´, C.; Espinet, P.; Martin-Alvarez,
J. M.; Villafan˜e, F. Eur. J. Inorg. Chem. 2003, 3127–3138. (b) Bartolome´,
C.; Espinet, P.; Martin-Alvarez, J. M.; Villafan˜e, F. Eur. J. Inorg. Chem.
2004, 2326–2337.

3766 Organometallics, Vol. 27, No. 15, 2008
Casares et al.
Figure 6. Effect of [AsPh3] on the polymerization rate. The lines
correspond to calorimetric runs of polymerization reactions of NB
([NB] ) 0.575 M) catalyzed by 2b ([2b] ) 2.88 × 10-4 M), for
several concentrations of added AsPh3.
Figure 5. Heat flow vs time plot from the calorimetry experiment
in which a second injection of NB is added (catalyst used 5b; see
text for a comprehensive description).
free ligand effect was tested on the polymerization reaction
catalyzed with [PdRf(AsPh3)2(CH3CN)]BF4 (2b). Increasing
concentrations of free AsPh3 produce increasing reduction of
the reaction rate (Figure 6). For AsPh3:catalyst ) 20:1, the
reaction is totally inhibited and no polynorbornene is detected
in 24 h.
These values are collected in Table 2 and are in the order
AsRfPh2 > AsPh3 > AsMePh2 > SbPh3 > AsCyPh2 . PPh3.
The catalyst with the ligand AsRfPh2 is about 4 times faster
than the next one.
That a kinetically relevant deactivation process exists, as
proposed above, is supported by the effect of adding extra
injections of NB to a running reaction mixture. In the experiment
shown in Figure 5, an extra amount of NB (2 mL of a CH2Cl2
solution containing 2.3 mmol of NB) was injected into a running
polymerization of NB (4 mL of a CH2Cl2 solution containing
2.3 mmol of NB) using 5b as catalyst, when the reaction rate
had dropped to one-tenth of its maximum value. If deactivation
were negligible, a second identical injection of NB should cause
the reaction rate to recover to a theoretical value of 260 mW
(calculated by correcting for the volume variation with the
injection and the remaining unreacted NB). The rate increase
was far lower than the expected value.34 Due to the continuing
deactivation the addition of more norbornene to the solution
after 150 min did not produce any measurable heat release (that
is, any further reaction), showing that the catalyst deactivation
at that moment was complete. The deactivation process was
further verified by running two polymerizations with the same
concentration of catalyst but different concentrations of NB.
When the experiment starting with the most concentrated
solution in NB reached a concentration in NB identical with
that used initially in the diluted experiment, its reaction rate
was noticeably lower, supporting that the active catalyst
concentration at that moment is noticeably lower than the initial
concentration, and a large percentage of the catalyst has been
deactivated.29
The evidence suggests that the origin of the observed
deactivation is 2-fold: (i) a decrease in active catalyst concentra-
tion, mostly by precipitation or coprecipitation of PolyNBs
+
Pd(MeCN)(L)(NB)+ or PolyNBsPd(MeCN)(NB)2 species,
and (ii) an increase in concentration of free L in solution, since
L is released in these catalyst sequestering reactions. In practice,
this means that the positive effect on the polymerization rate
of more poorly coordinating ligands has two origins: (i) the more
poorly coordinating ligands are more easily substituted by NB
and (ii) the rate retardation produced by the release of free L
via catalyst decomposition is less for more poorly coordinating
ligands.35 Thus, both effects cooperate in favor of the efficiency
of catalysts with more poorly coordinating ligands, which
should, however, be weighed against the survival time of the
catalytic species.
Norbornene Polymerization in the Presence of O-Donor
Groups. Complexes 1b-6b do not catalyze the polymerization
of 5-norbornene-2-carboxaldehyde. This is common for func-
tionalized norbornenes, because coordination of the monomer
to the metal through the oxygen atom inhibits the reaction.37–39
In this sense the functionalized monomer acts as an additional
ligand (as just discussed for added AsPh3), competing with the
double bond for the coordination positions. This could impede
(36) See also (a) Albe´niz, A. C.; Casado, A. L.; Espinet, P. Inorg. Chem.
1999, 38, 2510–2515. (b) Casado, A. L.; Espinet, P. Organometallics 1998,
17, 954–959.
(37) No specific experiments have been performed to differentiate
whether the retardation effect is due to the functionalized norbornene, to
norbornene units after one or several intramolecular insertions, or to
polymers containing O-functionalized norbornene units. Note, however, that
simple O-donor solvents also produce a retardation effect; thus, the excess
of functionalized norbornene monomer should be able to produce this
retardation.19
On the other hand, L ligands can compete with NB for the
coordination sites at palladium. Consequently, an excess of L
(which can be produced if the deactivation of the catalyst occurs
with decomposition of the Pd complex) is expected to have a
detrimental effect on the catalysis. It has been well studied that,
in processes where L substitution precedes the irreversible step,
the retarding effect of free L varies from very sharp to negligible
and is strongly dependent on the L coordinating ability.35,36 This
(38) Funk, J. K.; Andes, C. E.; Sen, A. Organometallics 2004, 23, 1680–
1683.
(39) (a) Sen, A. Acc. Chem. Res. 1993, 26, 303–310. (b) Markies, B.;
Kruis, D.; Rietveld, M. H. P.; Verkerk, K. A. N.; Boersma, J.; Kooijman,
H.; Lakin, M. T.; Speck, A. L.; van Koten, G. J. Am. Chem. Soc. 1995,
117, 5263–5274. (c) Delis, J. G. P.; Aubel, P. B.; Vrieze, D.; van Leeuwen,
P. W. N. M.; Veldman, N.; Spek, A. L. Organometallics 1997, 16, 4150–
4160.
(34) The NB consumed before the second injection is known from the
integrated area of the curve.
(35) For instance, to obtain the retarding effect of 2 × 10-4 M of PPh3,
5 × 10-2 M of AsPh3 is necessary: Casado, A. L.; Espinet, P. Organo-
metallics 2003, 22, 1305–1309.

Pd Catalysts for Norbornene Polymerization
Organometallics, Vol. 27, No. 15, 2008 3767
Table 3. Norbornene and 5-Norbornene-2-carboxaldehyde Copolymerization, Catalyzed with 5b (4.6 µmol), in CH2Cl2 (0.6 mL)
NB:NB-CHOa
amt of NB (mmol)
amt of NB-CHO (mmol)
yield (%)b
10-5Mw
Mw/Mn
CdO:C-Hc
1:1
2:1
3:1
6:1
9:1
4.6
6.1
6.9
7.9
8.3
4.6
3.1
2.3
1.3
0.9
4.6
10.6
16.6
31.5
43.8
0.30
0.24
0.21
0.16
0.14
0.38
0.46
1.12
2.18
1.7
2.1
2.4
2.8
a The total amount of monomer is 9.2 mmol. b The reactions were quenched with MeOH after 24 h. c Ratio of the IR signal integrals in the ranges
1750-1700 cm-1 (ν(CdO)) versus 3200-2675 cm-1 (ν(Caliphatic-H)). This column gives only a rough relative estimation of the incorporation of
5-norbornene-2-carboxaldehyde in the different copolymers.40
Table 4. IR Data for the Polymerization of Norbornene with 2b
and 5b
Finally, microcalorimetry is a useful method for monitoring
polymerization reactions that give insoluble products and cannot
be followed by NMR, providing straightforward detection of
activation and deactivation processes.
complex (mol/L) concn of norbornene (mol/L) νCN (cm-1 a
)
tb
2b
2323, 2293
2b (0.049)
1.13
0.92
2320, 2290
1 h
5b
2324, 2296
2314, 2285
Experimental Section
5b (0.027)
2 min
General Methods. All reactions were carried out under N2,
except when otherwise stated. Solvents were dried and distilled
under nitrogen using standard methods.41 The complexes
[Pd(C6F5)Br(NCMe)2],24a [Pd2(C6F5)2(µ-Cl)2(tht)2] (tht ) tetrahy-
drothiophene),42 [Pd(C6F5)Br(PPh3)2] (1a), [Pd(C6F5)Br(AsPh3)2]
(2a), and [Pd(C6F5)Br(SbPh3)2] (6a),43 AsBrPh2,19 the ligands
free MeCN
2293, 2266
a Significant absorption bands. b Reaction time.
double-bond coordination for high concentration of the func-
tionalized norbornene, whereas a more dilute concentration of
the polar monomer might permit the reaction to occur. In fact,
2b-6b copolymerized 5-norbornene-2-carboxaldehyde (NB-
CHO) with NB, giving moderate yields in 24 h. Table 3 shows
the results for 5b. As expected, the yields increased when the
NB-CHO:NB ratio was decreased (Table 3).
The GPC chromatograms of the polymerization product show
only one peak, suggesting a copolymerization reaction. The IR
spectra of the copolymer show an absorption at 1723 cm-1 due
to the carbonyl group, which allows the evaluation of polar
monomer incorporation in the copolymer chain (Table 3). The
incorporation of polar monomer decreases when the NB:NB-
CHO ratio increases. The results also show a trend to form
longer polymeric chains when the yields are higher. This
behavior was reported before for neutral nickel catalysts.19
44
AsMePh2 and AsCyPh2,19 and solutions of LiC6Cl2F3 were
prepared by published methods.45 Instrumental methods were as
in ref 19.
Synthesis of As(3,5-C6Cl2F3)Ph2. To a solution of LiC6Cl2F3
in Et2O (35 mL), prepared from C6Cl3F3 (2.97 g, 12.6 mmol) and
BuLi (1.6 M, 12.6 mmol), at -80 °C, was added a solution of
AsBrPh2 (3.90 g, 12.6 mmol) in Et2O (40 mL). After it was stirred
for 30 min at -80 °C, the reaction mixture was warmed to room
temperature. The flask was open to the air, and a solution of dilute
HCl (30 mL) was added. The organic layer was separated, and the
aqueous layer was extracted with diethyl ether (3 × 15 mL). The
collected organic layers were washed with water (20 mL), dried
over anhydrous MgSO4, and filtered. The solvent was removed,
affording an oil. After hexanes was added (10 mL), the solution
was cooled to -18 °C until crystallization of the product, which
was finally filtered and vacuum-dried. Yield: 3.02 g (56%). Anal.
Calcd for C18H10AsCl2F3: C, 50.38; H, 2.33. Found: C, 50.13; H,
2.34. 1H NMR (CDCl3, 293 K): δ 7.47-7.44 (m, 4H, Hortho),
7.40-7.36 (m, 6H, Hpara and Hmeta). 13C{1H} NMR (CDCl3, 293
K): δ 160.27 (Rf), 157.90 (Rf), 157.15 (Rf), 154.55 (Rf), 136.34
(Cipso of Ph), 133.27 (CH of Ph), 129.22 (CH of Ph), 128.98 (CH
of Ph). 19F NMR (CDCl3, 293 K): δ -98.5 (s, 2F, Fortho), -108.7
(s, 1F, Fpara).
Synthesis of [Pd(C6F5)Cl(AsMePh2)2] (3a). To a solution of
[Pd2(µ-Cl)2(C6F5)2(tht)2] (0.3771 g, 0.475 mmol) in CH2Cl2 (20 mL)
was added AsMePh2 (0.4996 g, 2.046 mmol). The solution was
stirred for 30 min, filtered, and vacuum-concentrated to 10 mL.
Then hexane (10 mL) was added, and the solution was again
concentrated until precipitation of the product. The mixture was
cooled to -18 °C to complete crystallization of the desired
compound, which was finally filtered and vacuum-dried. Yield:
0.4204 g (56%). Anal. Calcd for C32H26As2PdF5Cl: C, 48.21; H,
3.29. Found: C, 48.11; H, 3.48. 1H NMR (CDCl3, 293 K): δ
7.5-7.3 (m, 20H, Ph), 1.98 (s, 6H, CH3). 19F NMR (CDCl3, 293
Conclusions
The cationic palladium complexes with arsines and stibines
are good catalysts for norbornene polymerization. Among them,
the complex with the bulk and more poorly donating fluorinated
arsine As(C6Cl2F3)Ph2 is by far the most active catalyst and
affords interesting rates of polymerization. Moreover, it allows
for easy spectroscopic study of the reacting systems by 19F
NMR. The positive effect of more poorly coordinating ligands
on the polymerization rate has two origins: (i) the more poorly
coordinating ligands are more easily substituted by NB, allowing
for faster substitution, and (ii) the rate retardation produced by
the release of free L via catalyst decomposition is lower for
more poorly coordinating ligands.
External coordinating molecules (e.g., ligands or monomers
with O-donor groups) inhibit the reaction because they compete
with the olefin function for the coordination sites on Pd. In spite
of this, it is possible to achieve the copolymerization of
norbornene and 5-norbornene-2-carboxaldehyde, with lower
yields and higher incorporations of the functionalized nor-
bornene as the NB:NB-CHO ratio decreases.
(41) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, U.K., 1988.
(42) Uso´n, R.; Fornie´s, J.; Mart´ınez, F.; Toma´s, M. J. Chem. Soc., Dalton
Trans. 1980, 888–893.
(43) Uso´n, R.; Fornie´s, J.; Nalda, J. A.; Lozano, M. J.; Espinet, P.;
Albe´niz, A. C. Inorg. Chim. Acta 1989, 156, 251–256.
(44) Bayse, C. A.; Luck, R. L.; Schelter, E. J. Inorg. Chem. 2001, 40,
3463–3467.
(45) Espinet, P.; Mart´ınez-Ilarduya, J. M.; Pe´rez-Briso, C.; Casado, A. L.;
Alonso, M. A. J. Organomet. Chem. 1998, 551, 9–20.
(40) Integration of IR signals gives only a rough estimation of the
composition. It was used because NMR integration should be based on
integration the aliphatic signals versus the aldehydic proton. The latter gives
an extremely broad signal. This, along with the large difference in intensity,
makes compared integration impossible.

3768 Organometallics, Vol. 27, No. 15, 2008
Casares et al.
K): δ -116.40 (m, 2F, Fortho), -161.17 (t, J ) 20 Hz, 1F, Fpara),
-162.91 (m, 2F, Fmeta).
of Ph), 129.73 (Ph), 9.99 (CH3 of AsMePh2), 2.91 (CH3 of MeCN).
19F NMR (CDCl3, 293 K): δ -116.44 (m, 2F, Fortho), -152.81
3
(BF4), -152.86 (BF4), -157.86 (t, JF-F ) 19.9 Hz, 1F, Fpara),
Synthesis of [Pd(C6F5)Br(AsCyPh2)2] (4a). To a solution of
AsCyPh2 (0.2101 g, 0.673 mmol) in Et2O (20 mL) was added
[Pd(C6F5)Br(NCMe)2] (0.1465 g, 0.336 mmol). After the mixture
was stirred for 45 min, solvent was removed to 5 mL, and hexane
(5 mL) was added to precipitate the product. The mixture was
cooled to -18 °C to complete crystallization of 4a, which was
finally filtered and vacuum-dried. Yield: 0.2144 g (65%). Anal.
Calcd for C42H42As2PdF5Br: C, 51.58; H, 4.33. Found: C, 51.29;
-160.95 (m, 2F, Fmeta).
Synthesis of [Pd(C6F5)(AsCyPh2)2(NCMe)]BF4 (4b). To a
solution of AgBF4 (0.0366 g, 0.188 mmol) in acetonitrile (15 mL)
was added [Pd(C6F5)Br(AsCyPh2)2] (0.1839 g, 0.188 mmol). The
solution was stirred for 2 h, filtered through Celite, and evaporated
to dryness. The residue was stirred vigorously with diethyl ether
(4 mL), giving a colorless solid that was filtered and vacuum-dried.
Yield: 0.1309 g (68%). Anal. Calcd for C44H45As2BF9NPd: C,
51.51; H, 4.42; N, 1.37. Found: C, 51.90; H, 4.54; N, 1.38. IR
(ν(CN) region, Nujol-polyethylene, cm-1): 2321, 2291. 1H NMR
(CDCl3, 293 K): δ 7.5-7.3 (m, 20H, Ph), 2.76 (m, 2H, Hgem of
Cy), 2.12 (s, 3H, H of MeCN), 2.02 (m, 4H of Cy), 1.8-1.6 (m,
4H of Cy), 1.5-1.3 (m, 4H of Cy). 13C NMR DEPT (CDCl3, 293
K): δ 133.04 (CH of Ph), 131.49 (CHpara of Ph), 129.52 (CH of
Ph), 41.64 (CHgem of Cy), 30.82 (CH2 of Cy), 27.99 (CH2 of Cy),
26.15 (CH2 of Cy), 3.07 (CH3 of MeCN). 19F NMR (CDCl3, 293
K): δ -115.66 (m, 2F, Fortho), -152.87 (BF4), -152.92 (BF4),
1
H, 4.23. H NMR (CDCl3, 293 K): δ 7.42 (m, 8H, Hortho of Ph),
7.37-7.28 (m, 12H, Hpara and Hmeta of Ph), 2.98 (m, 2H, Hgem of
Cy), 2.26 (m, 4H of Cy), 1.84-1.71 (m, 8H of Cy), 1.43-1.26
(m, 8H of Cy). 19F NMR (CDCl3, 293 K): δ -115.95 (m, 2F, Fortho),
-162.07 (t, J ) 20 Hz, 1F, Fpara), -163.22 (m, 2F, Fmeta).
Synthesis of [Pd(C6F5)Br(AsRfPh2)2] (5a). This compound was
prepared as described for 4a, but using AsRfPh2 (1.2056 g, 2.810
mmol) and [Pd(C6F5)Br(NCMe)2] (0.5268 g, 1.210 mmol). Yield:
1.3922 g (95%). Anal. Calcd for C42H20As2PdF11Cl4Br: C, 41.64;
1
H, 1.66. Found: C, 41.46; H, 1.86. H NMR (CDCl3, 293 K): δ
3
7.67 (m, 8H, Hortho), 7.5-7.3 (m, 12H, Hpara and Hmeta). 19F NMR
(CDCl3, 293 K): δ -96.08 (s, 4F, Fortho C6Cl2F3), -105.57 (s, 2F,
Fpara C6Cl2F3), -116.57 (m, 2F, Fortho C6F5), -159.43 (t, J ) 20
Hz, 1F, Fpara C6F5), -161.98 (m, 2F, Fmeta C6F5). 13C DEPT NMR
(DEPT ) distortionless enhancement by polarization transfer;
CDCl3, 293 K): δ 133.40, 131.08, 128.90.
-158.71 (t, JF-F ) 20.1 Hz, 1F, Fpara), -161.27 (m, 2F, Fmeta).
Synthesis of [Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (5b). To a
solution of AgBF4 (0.2124 g, 1.091 mmol) in acetonitrile (50 mL)
was added [Pd(C6F5)Br(AsRfPh2)2] (1.3216 g, 1.091 mmol). The
solution was stirred for 1 h, filtered through Celite, and evaporated
to dryness. The residue was stirred vigorously with diethyl ether
(10 mL), giving a colorless solid that was filtered and vacuum-
dried. Yield: 0.9852 g (72%). Anal. Calcd for C44H23As2BCl4-
F15NPd: C, 41.96; H, 1.84; N, 1.11. Found: C, 41.64; H, 2.07; N,
1.09. IR (ν(CN) region, Nujol-polyethylene, cm-1): 2324, 2296.
1H NMR (CDCl3, 293 K): δ 7.6-7.4 (m, 20H, Ph), 1.82 (s, 3H,
CH3CN). 13C{1H} NMR (CDCl3, 293 K): δ 131.93 (Ph), 131.79
(Ph), 129.94 (Ph), 127.95 (Ph), 2.30 (CH3 of MeCN). 19F NMR
(CDCl3, 293 K): δ -96.56 (s, 4F, Fortho of C6Cl2F3), -101.44 (s,
2F, Fpara of C6Cl2F3), -117.90 (d, JF-F ) 22.9 Hz, 2F, Fortho of
C6F5), -153.44 (s, 4F, BF4), -153.49 (s, 4F, BF4), -157.04 (t,
3JF-F ) 20.3 Hz, 1F, Fpara of C6F5), -160.07 (t, 3JF-F ) 20.3 Hz,
2F, Fmeta of C6F5).
Synthesis of [Pd(C6F5)(PPh3)2(NCMe)]BF4 (1b). To a solution
of AgBF4 (0.1631 g, 0.838 mmol) in acetonitrile (15 mL) was added
[Pd(C6F5)Br(PPh3)2] (0.7356 g, 0.838 mmol). The solution was
stirred for 45 min, filtered through celite, and the solution evaporated
to 2 mL. Diethyl ether (15 mL) was added and the colorless solid
obtained was filtered and vaccuum-dried. Yield: 0.6923 g (89%).
Anal. Calcd for C44H33BF9NP2Pd: C, 57.08; H, 3.59; N, 1.51.
Found:C,56.94;H,3.56;N,1.75.IR(ν(CN)region,Nujol-polyethylene,
cm-1): 2327, 2298. 1H NMR (CDCl3, 293 K): δ 7.6-7.4 (m, 30H,
Ph), 2.02 (s, 3H, CH3CN). 13C{1H} NMR (CDCl3, 293 K): δ 133.58
(Ph), 131.95 (Ph), 129.18 (Ph), 127.28 (Cipso of Ph), 1.72 (Me of
MeCN). 19F NMR (CDCl3, 293 K): δ -118.09, (m, 2F, Fortho),
3
Synthesis of [Pd(C6F5)(SbPh3)2(NCMe)]BF4 · 0.5CH2Cl2 (6b).
To a solution of AgBF4 (0.2845 g, 1.461 mmol) in acetonitrile (15
mL) was added [Pd(C6F5)Br(SbPh3)2] (1.5484 g, 1.461 mmol). The
solution was stirred for 1 h, filtered through Celite, and evaporated
to 5 mL. Diethyl ether (15 mL) was added, and the colorless solid
obtained was filtered and vacuum-dried. Yield: 1.2129 g (75%).
Anal. Calcd for C44.5H34Sb2BClF9NPd: C, 46.76; H, 2.96; N, 1.21.
Found:C,46.71;H,3.14;N,1.15.IR(ν(CN)region,Nujol-polyethyl-
ene, cm-1): 2326, 2296. 1H NMR (CDCl3, 293 K): δ 7.6-7.3 (m,
30H, Ph), 2.11 (s, 3H, CH3CN). 13C{1H} NMR (CDCl3, 293 K):
δ 135.36 (Ph), 131.43 (Cpara, Ph), 130.10 (Ph), 127.65 (Cipso, Ph),
3.09 (CH3 of MeCN). 19F NMR (CDCl3, 293 K): δ -112.66 (m,
2F, Fortho), -153.07 (BF4), -153.12 (BF4), -157.54 (t, J ) 19 Hz,
1F, Fp), -160.51 (m, 2F, Fmeta).
-153.45 (BF4), -153.50 (BF4), -159.97 (t, JF-F ) 20 Hz, 1F,
F
para), -161.25 (m, 2F, Fmeta). 31P NMR (CDCl3, 293 K): δ 24.02
(s, PPh3).
Synthesis of [Pd(C6F5)(AsPh3)2(NCMe)]BF4 (2b). To a solution
of AgBF4 (0.0558 g, 0.287 mmol) in acetonitrile (20 mL) was added
[Pd(C6F5)Br(AsPh3)2] (0.2768 g, 0.287 mmol). The solution was
stirred for 1 h, filtered through Celite, and evaporated to 4 mL.
Isopropyl alcohol (10 mL) was added, and the solvent was again
removed to half volume, yielding the product as a colorless solid
that was filtered and vacuum-dried. Yield: 0.2076 g (71%). Anal.
Calcd for C44H33As2BF9NPd: C, 52.13; H, 3.28; N, 1.38. Found:
C, 51.79; H, 3.34; N, 1.72. IR (ν(CN) region, Nujol-polyethylene,
cm-1): 2323, 2293. 1H NMR (CDCl3, 293 K): δ 7.6-7.3 (m, 30H,
Ph), 1.79 (s, 3H, MeCN). 13C NMR DEPT (CDCl3, 293 K): δ
132.95 (Ph), 131.47 (Ph), 129.75 (Ph). 19F NMR (CDCl3, 293 K):
δ -116.98, (m, 2F, Fortho), -153.25 (BF4), -153.30 (BF4), -158.86
Polymerization Experiments. Experiments in NMR Tubes.
(a) Reaction of Norbornene with [Pd(C6F5)Br(AsPh3)2]. To a
solution of norbornene (64.0 mg, 0.68 mmol) in CDCl3 (0.5 mL)
3
(t, JF-F ) 20.1 Hz, 1F, Fpara), -161.04 (m, 2F, Fmeta).
1
was added [Pd(C6F5)Br(AsPh3)2] (2a; 6.6 mg, 6.8 µmol). H and
Synthesis of [Pd(C6F5)(AsMePh2)2(NCMe)]BF4 (3b). To a
solution of AgBF4 (0.0768 g, 0.394 mmol) in acetonitrile (20 mL)
was added [Pd(C6F5)Cl(AsMePh2)2] (0.3145 g, 0.394 mmol). The
solution was stirred for 30 min, filtered through Celite, and
evaporated to dryness. The residue was stirred vigorously with
diethyl ether (8 mL), yielding a colorless solid that was filtered
and vaccuum-dried. Yield: 0.2616 g (75%). Anal. Calcd for
C34H29As2BF9NPd: C, 45.90; H, 3.29; N, 1.57. Found: C, 45.89;
H, 3.37; N, 1.93. IR (ν(CN) region, Nujol-polyethylene, cm-1):
19F NMR spectra were recorded after 1 day at room temperature.
(b) Reaction of Norbornene with [Pd(C6F5)Br(AsRfPh2)2]. To
a solution of norbornene (154.0 mg, 1.64 mmol) in CDCl3 (0.5
mL) was added [Pd(C6F5)Br(AsRfPh2)2] (5a; 20.3 mg, 16.8 µmol).
1H and 19F NMR spectra were recorded after 1 day at room
temperature.
(c) Reaction of Norbornene with trans-[Pd(C6F5)(AsRfPh2)2-
(NCMe)]BF4 (5b). To a solution of norbornene (20.3 mg, 0.216
mmol) in CDCl3 (0.5 mL) was added trans-[Pd(C6F5)(AsRfPh2)2-
1
2323, 2295. H NMR (CDCl3, 293 K): δ 7.44 (m, 20H, Ph), 1.99
(s, 9H, methyl groups of AsMePh2 and MeCN). 13C{1H} NMR
(NCMe)]BF4 (5b) (27.3 mg, 21.7 µmol). The H and 19F NMR
1
(CDCl3, 293 K): δ 131.95 (Ph), 131.55 (Cipso of Ph), 131.31 (Cpara
spectra at room temperature were then recorded, followed by the

Pd Catalysts for Norbornene Polymerization
Organometallics, Vol. 27, No. 15, 2008 3769
217 K spectra.46 1H NMR (CDCl3, 293 K): δ 7.7-7.3 (m, Ph),
6.9-6.5 (b), 3.4-3.1 (b), 3.1-2.8 (b), 2.8-0.7 (a, poly-NB). 19F
NMR (CDCl3, 293 K): δ -96.56 (s, Fortho of Rf, 5b), -97.81 (a,
Fortho of Rf in 5b′ and free AsRfPh2), -101.54 (s, Fpara of Rf in
5b), -102 to -110 (a, Fpara of Rf in 5b′ and free AsRfPh2), -117.89
(d, J ) 24 Hz, Fortho of C6F5 in 5b), -133 to -135 (a, Fortho of
inserted C6F5), -136 to -141 (a, Fortho of inserted C6F5), -153.72
(s, BF4), -153.77 (s, BF4), -157.06 (t, J ) 20 Hz, Fpara of C6F5 in
5b), -157.73 (a, Fpara of inserted C6F5), -160.08 (t, J ) 21 Hz,
measured in the supernatant liquids by GC. The same procedure
was applied to the reactions with the rest of the cationic complexes
[Pd(C6F5)L2(NCMe)]BF4 (L ) PPh3, AsPh3, AsMePh2, AsCyPh2,
SbPh3).
The reaction was monitored by measuring the heat flow from
the sample vessel every 3 s to produce the data curve.
IR Analysis of the Polymerization Reaction of Norbornene
with trans-[Pd(C6F5)(AsPh3)2(NCMe)]BF4 (2b) and trans-
[Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (5b). Experiments were carried
out at room temperature in CHCl3 solution. Data are given in Ta-
ble 4.
F
meta of C6F5), -163.65 (a, Fmeta of inserted C6F5). 1H NMR (CDCl3,
217 K): δ 7.7-7.3 (m, Ph), 6.9-6.5 (b), 3.3-3.1 (b), 3.1-2.8 (b),
2.8-0.6 (a, poly-NB). 19F NMR (CDCl3, 217 K): δ -96.64 (s,
F
ortho of Rf in 5b), -97.33 (a, Fortho of Rf in 5b′), -98.61 (s, Fortho
of Rf in free AsRfPh2), -101.11 (s, Fpara of Rf in 5b), -102.74 (a,
para of Rf in 5b′), -108.29 (s, Fpara of Rf in free AsRfPh2), -118.20
Copolymerization Experiments of Norbornene with 5-Nor-
bornene-2-carboxaldehyde. In a typical experiment, trans-
[Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (5b; 5.8 mg, 4.6 µmol) was added
to a solution in CH2Cl2 (0.6 mL) of norbornene (4.6 mmol) and
5-norbornene-2-carboxaldehyde (4.6 mmol). The mixture was
stirred for 24 h. The mixture was then poured over methanol (50
mL). The copolymer was obtained as a colorless solid that was
filtered and vacuum-dried at 25 °C for several hours. The same
reaction was carried out with different ratios of the monomers, as
indicated in Table 3.
F
(d, J ) 24 Hz, Fortho of C6F5 in 5b), -133to -136 (a, Fortho of
inserted C6F5), -136 to -138 (a, Fortho of inserted C6F5), -138 to
-141 (a, Fortho of inserted C6F5), -153.35 (s, BF4), -153.40 (s,
BF4), -156.70 (t, J ) 20 Hz, Fpara of C6F5 in 5b), -157.84 (a,
Fpara of inserted C6F5), -159.58 (t, J ) 21 Hz, Fmeta of C6F5),
-163.15 (a, Fmeta of inserted C6F5).
Calorimetric Experiments: Polymerization of Norbornene
with [Pd(C6F5)L2(NCMe)]BF4. In a typical calorimetry experiment,
a solution of [Pd(C6F5)(AsRfPh2)2(NCMe)]BF4 (1.453 mg, 1.15
µmol) in CH2Cl2 (2 mL) was placed in the reaction cell, while
CH2Cl2 (2 mL) alone was placed in the reference cell. After the
system reached thermal equilibrium, a norbornene solution (1.15
M in CH2Cl2, 2 mL, 2.3 mmol) was added to each cell.47 When
the reaction had apparently finished, 10 mL of methanol was added
to quench the reaction, and the concentration of unreacted NB was
Acknowledgment. Financial support by the Ministerio de
Educacio´n y Ciencia (Project No. CTQ2007-67411/BQU),
Project INTECAT Consolider Ingenio 2010 (No. CSD2006-
0003), and the Junta de Castilla y Leo´n (No. VA044A07) is
gratefully acknowledged.
Supporting Information Available: Text and tables giving the
experimental procedure for X-ray crystallography and crystal data
and structure refinement details for for 3b and 5b and CIF files
giving crystallographic data for 3b and 5b. This material is available
free of charge via the Internet at http://pubs.acs.org.
(46) Signals assigned to 25′ arise from complexes in which the C6F5
group has undergone insertion. C6Cl2F3 (Rf) signals assigned to 25′ arise
from a cationic complex of the type [Pd{(poli-NB)-C6F5}(NB)(AsRfPh2)-
(NCMe)]+. The C6F5 signals arise from [Pd{(poly-NB)-C6F5}(NB)-
(AsRfPh2)(NCMe)]+ and [Pd{(poly-NB)-C6F5}(NB)2(NCMe)]+.
(47) Dilution heat of complexes was found to be negligible in our case.
OM800264A