Dual behavior of cationic palladium pentafluorophenyl complexes as catalysts for the homopolymerization of acrylates and of nonpolar olefins

Article abstract of DOI:10.1021/om900401p

[Pd(Pf)(NCMe)(N-N)]BF₄, (Pf = C₆F₅; N-N = ethylenediamine (en, 1), 2,2'-bipyridine (2), (2,6-ⁱPrC ₆H₃)N=C(Me)C(Me)=N(2,6-ⁱPrC₆H ₃) (diimine, 3)) are very ef

Full text of DOI:10.1021/om900401p

4996 Organometallics 2009, 28, 4996–5001
DOI: 10.1021/om900401p
Dual Behavior of Cationic Palladium Pentafluorophenyl Complexes as
Catalysts for the Homopolymerization of Acrylates and of Nonpolar
Olefins
ꢀ
Raquel Lopez-Fernandez, Nora Carrera, Ana C. Albeniz,* and Pablo Espinet*
ꢀ
ꢀ
´
ꢀ
IU CINQUIMA/Quımica Inorganica, Universidad de Valladolid, 47071 Valladolid, Spain
Received May 15, 2009
[Pd(Pf)(NCMe)(N-N)]BF4, (Pf = C6F5; N-N = ethylenediamine (en, 1), 2,20-bipyridine (2),
(2,6-iPrC6H3)NdC(Me)C(Me)dN(2,6-iPrC6H3) (diimine, 3)) are very efficient initiators of the
radical polymerization of alkyl acrylates. Mechanistic studies reveal that the polymerization of
methyl acrylate with 1 starts by the insertion of the monomer into the Pd-aryl bond of the catalyst to
give [Pd{CH(CO2Me)CH2Pf}(N-N)(NCMe)]BF4, (N-N = en (5), diimine (7)). In contrast to the
case for other cationic palladium complexes, the presence of a Pf group does not allow the formation
of C,O-palladacycles with a suitable ring size. This allows complex 5 (or 7) to decompose not only by
β-H elimination but also by homolytic cleavage of the Pd-C bond in the light. The radical species
generated in this process start the polymerization. Complex 1 is also a very efficient catalyst in the
vinyl addition polymerization of norbornene by an insertion mechanism. Complex 3 polymerizes
ethylene. Although complexes 1 and 3 are versatile polymerization initiators by two different
mechanisms, neither copolymerization of methyl acrylate and norbornene with 1 nor that of methyl
acrylate and ethylene with 3 were successful, leading to either very low yields or mixtures of
homopolymers.
Introduction
this type of complex becomes a resting state in the catalytic
cycle. Its formation severely slows down chain growth.6
Recently, the use of bulky cyclophane substituents on the
nitrogen of the diimine ligand has been shown to increase the
acrylate incorporation in the copolymerization of ethylene
and methyl acrylate in comparison with other diimines with
similar backbones, but the overall yield remains low.7
The homopolymerization of acrylates can be efficiently
carried out using neutral palladium complexes as catalysts,
as shown by several groups, including our own.8-10 Neutral
and anionic palladium pentafluorophenyl systems are active
in the insertion-triggered radical polymerization (ITRP) of
acrylates and in the copolymerization reactions with non-
polar monomers such as 1-hexene, with moderate yields and
low 1-hexene incorporation (ca. 11%).11 The chain growth in
these systems is a radical process initiated by insertion of the
acrylate into a Pd-C bond and subsequent homolytic clea-
vage. Palladium species are also involved in chain transfer.10
There are only two exceptions to this behavior where a
type of Pd complex is highly active for just one type of alkene:
The results reported in the literature indicate that a specific
palladium complex rarely shows high activity in the homo-
polymerization of both polar and nonpolar olefins. Most
of the efficient palladium catalysts in the polymerization
of nonpolar olefins are cationic and follow an insertion
mechanism. Brookhart’s diimine catalysts are the paradigm
of this type of derivative.1-3 However, these systems do not
homopolymerize acrylates, and the copolymerization of
acrylates with ethylene usually leads to low yields and low
incorporation of the polar monomer.4,5 Detailed studies for
the ethylene/methyl acrylate system have explained this lack
of activity. Insertion of acrylate into the Pd-C bond and
subsequent palladium migration leads eventually to stable
six-membered C,O-palladacycles (Scheme 1). O-coordina-
tion to the electrophilic Pd center to give the palladacycle is
favored over olefin coordination at room temperature, and
*To whom correspondence should be addressed. E-mail: albeniz@qi.
uva.es (A.C.A.); espinet@qi.uva.es (P.E.).
(1) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
(6) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.
Chem. Soc. 1998, 120, 888–899.
(7) Popeney, C. S.; Camacho, D. H.; Guan, Z. J. Am. Chem. Soc.
1995, 117, 6414–6415.
(2) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169–1203.
2007, 129, 10062–10063.
(3) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.;
Brookhart, M. J. Am. Chem. Soc. 2000, 122, 6686–6700.
(4) (a) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc.
1996, 118, 267–268. (b) Liu, W.; Malinoski, J. M.; Brookhart, M. Organo-
metallics 2002, 21, 2836–2838. (c) Gottfried, A. C.; Brookhart, M. Macro-
molecules 2003, 36, 3085–3100.
(8) Tian, G.; Boone, H. W.; Novak, B. M. Macromolecules 2001, 34,
7656–7663.
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Albeniz, A. C.; Espinet, P. Organometallics 2002, 21, 4249–4256.
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(11) Albeniz, A. C.; Espinet, P.; Lopez-Fernandez, R. J. Polym. Sci.,
(5) Heinemann, J.; Mulhaupt, R.; Brinkmann, P.; Luinstra, G.
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r
pubs.acs.org/Organometallics
Published on Web 08/17/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 17, 2009 4997
Scheme 1. Intermediates Formed by Reaction of Methyl Acry-
late with Brookhart’s Catalysts
Figure 1. Palladium complexes used in the polymerization
experiments (Pf = C6F5).
monomer. The reactions were carried out at room tempera-
ture, under a N2 atmosphere and in the light (Table 1). For
comparison, polymerization reactions of MA using the neu-
tral complex [Pd2Pf2(μ-Cl)2(tht)2] (4; Table 1, entry 7),10
AIBN as a radical initiator (Table 1, entry 8) or Brookhart’s
analogue to 3 ([PdMe(NCMe)(N-N)]BF4, 3-Me; Table 1,
entry 6), were also carried out. It must be noted that, as the
polymerizations proceeded, the reaction mixtures became
extremely viscous and stirring was completely halted. Conse-
quently, mass transfer problems may be limiting monomer
conversion and increasing the polydispersity.
Jordan et al. reported a dimeric cationic palladium complex
capable of homopolymerizing norbornene and also methyl
acrylate, although the latter occurred with moderate conver-
sions (up to 42%);12 Mecking et al. recently achieved the
copolymerization of methyl acrylate and ethylene with
incorporations up to 50% of acrylate by a neutral palladium
complex with a phosphinosulfonate type ligand.13 This type
of complex also polymerizes ethylene with high activities14
and other combinations of monomers.15
We report in this paper cationic palladium pentafluoro-
phenyl complexes with chelating nitrogen donors
[PdR(NCMe)(N-N)]BF4 (R=Pf, 1-3; Figure 1) which are
active catalysts in the polymerization of alkyl acrylates by
ITRP. This result is remarkable compared to the lack of
activity of Brookhart’s cationic palladium catalysts (R=Me;
N-N = diimine) toward these monomers. Studies on the
nature of intermediate species in the polymerization explain
the different behavior of similar [PdR(NCMe)(N-N)]þ
complexes differing only in the R group (R=Me, Pf).
Nonpolar alkenes are also polymerized by these complexes.
Complex 1 is active in the vinyl addition polymerization of
norbornene (which is not uncommon for other cationic
palladium derivatives),16-18 and 3 polymerizes ethylene as
Brookhart’s complexes do.
Atactic high-molecular-weight polymers were obtained in
good yields, except for 3-Me, which was inactive (Table 1,
entry 6). The presence of light is necessary for the success of
the polymerization. The addition of galvinoxyl inhibits the
reactions. These results point to a radical polymerization
analogous to that described before for the neutral palladium
complex 4.10
Mechanistic Studies. Considering the previous results in
the literature,4,6 it is somewhat surprising that cationic
complexes 1-3 are so active in the polymerization of alkyl
t
acrylates such as MA and BuA, considering that Broo-
khart’s are inactive. NMR studies of the polymerization
reaction of MA were carried out for 1 to determine the
nature of the intermediate species. A reaction of 1 with MA
(molar ratio 1:MA = 1:100) in CDCl3 was monitored by 19
F
1
and H NMR. Immediate insertion of MA into the Pd-Pf
bond of 1 takes place and gives the alkyl compound
[Pd{CH(CO2Me)CH2Pf}(en)(NCMe)]BF4 (5), which is
clearly seen in the 19F NMR spectrum, where typical signals
for a C-bound pentafluorophenyl appear (at about -140 ppm)
at the expense of the starting material (ca. -120 ppm).19 At
this point, no polymer is observed in the 1H NMR spectrum
(Scheme 2).
Complex 5 was isolated as a white solid from the reaction
of 1 with MA (molar ratio 1:MA = 1:75) in CH2Cl2 at room
temperature for 15 min. The CO frequency in the solid-state
IR spectrum (1680 cm-1) confirms that the ester group is not
coordinated to palladium.4a,6,20 The complex [Pd(CH-
(CO2Me)CH2Pf)(diimine)(NCMe)]BF4 (7) was also pre-
pared in the same way, starting from 3. Again, the alkyl
fragment is monodentate, and the ester group is not bound
to palladium (ν(CO), 1707 cm-1). In the absence of MA, both 5
and 7 decompose slowly at room temperature to give the β-H
elimination product 6, H-transfer product PfCH2CH2COOMe
(8), and the hydroxy and keto esters PfCH2CH(OH)CO2Me
(10), PfCH(OH)CH2CO2Me (11), and PfCH2C(O)CO2Me
(12) as a result of homolytic cleavage of the Pd-C bond and
Results and Discussion
Polymerization of Alkyl Acrylates. The compounds [Pd-
(Pf)(NCMe)(N-N)]BF4 (1-3) were prepared by reaction of
AgBF4 and the corresponding [PdBrPf(N-N)] complexes in
acetonitrile, followed by crystallization from Et2O. The com-
plexes were studied as initiators in the polymerization of
alkyl acrylates. The stoichiometry of the polymerization
reactions was Pd:monomer=1:2000, employing 1 mL of
(12) Szuromi, E.; Shen, H.; Goodall, B. L.; Jordan, R. F. Organome-
tallics 2008, 27, 402–409.
€
€
(13) Guironnet, D.; Roesle, P.; Runzi, T.; Gottker-Schenetmann, I.;
Mecking, S. J. Am. Chem. Soc. 2009, 131, 422–423.
(14) Drent, E.; Van Dijk, R.; Van Ginkel, R.; Van Oort, B.; Pugh, R.
I. Chem. Commun. 2002, 744–745.
(15) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem.
Soc. 2007, 129, 8948–8949.
(16) (a) Janiak, C.; Lassahn, P. G. J. Mol. Catal. A: Chem. 2001, 166,
193–209. (b) Goodall, B. L. In Late Transition Metal Polymerization
Catalysis; Riege, B., Saunders Baugh, L., Kacker, S., Striegler, S., Eds.;
Wiley-VCH: Weinheim, Germany, 2003; Chapter 4.
(17) (a) Sen, A.; Lai, T.-W. J. Am. Chem. Soc. 1981, 103, 4627–4629.
(b) Sen, A.; Lai, T.-W. Organometallics 1982, 1, 415–417.
(18) Some recent examples: (a) Thirupathi, N.; Amoroso, D.; Bell, A.;
Protasiewicz, J. D. J. Polym. Sci. A: Polym. Chem. 2009, 47, 103–110.
(b) Casares, J. A.; Espinet, P.; Salas, G. Organometallics 2008, 27, 3761–
3769. (c) Jung, I. G.; Seo, J.; Chung, Y. K.; Shin, D. M.; Chun, S.-H.; Son, S.
U. J. Polym. Sci. A: Polym. Chem. 2007, 45, 3042–3052. (d) Yamasita, M.;
Takamiya, I.; Jin, K.; Nozaki, K. Organometallics 2006, 25, 4588–4595.
ꢀ
(19) Albeniz, A. C.; Espinet, P.; Foces-Foces, C.; Cano, F. H.
Organometallics 1990, 9, 1079–1085.
(20) (a) Braunstein, P.; Frison, C.; Morise, X. Angew. Chem., Int. Ed.
2000, 39, 2867–2870. (b) Tian, G.; Boyle, P. D.; Novak, B. M. Organome-
tallics 2002, 21, 1462–1465.

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Lopez-Fernandez et al.
4998 Organometallics, Vol. 28, No. 17, 2009
Table 1. Polymerization of Alkyl Acrylates with Cationic Palladium Complexesa
b
entry
initiator
monomer (amt (mmol))
solvent
yield (%)
Mw (ꢀ10-6 b
)
Mw/Mn
1
2
3
4
5
6
7
8c
1
1
1
2
MA (11.1)
MA (11.1)
tBuA (6.48)
MA (11.1)
MA (11.1)
MA (11.1)
MA (11.1)
MA (11.1)
CH2Cl2
acetone
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
79
53
74
74
70
7.2
1.5
3.4
5.3
4.5
5.8
4.4
5.7
7.4
5.9
3
3-Me
4
AIBN
77
90
0.1
2.6
2.0
8.1
a Conditions: reactions carried out at room temperature, 24 h, N2 atmosphere, solvent (2 mL), [Pd]:[monomer] = 1:2000. b Molecular weight data
determined by SEC in CHCl3 vs polystyrene standards. c Conditions: AIBN (0.003 mmol) in CH2Cl2 (2 mL) at 70 °C.
Scheme 2. Different Behaviors of 1 (Left) and Brookhart’s
Complexes (Right) toward Homolytic Cleavage and Mechanisms
of Radical Polymerization and Catalyst Decomposition with 1
(also 2 or 3) as Initiator
has been elegantly demonstrated using deuterium-labeled
monomers,12 but the initiation mechanism in that system has
not been determined.
Polymerization Reactions of the Nonpolar Alkenes Norbor-
nene and Ethylene. The activity of 1-3 toward two different
nonpolar alkenes was tested. Several polymerization reac-
tions of norbornene (NB), using [PdPfen(NCMe)]BF4 (1:NB
= 1:2000), were carried out in CH2Cl2 at room temperature
(Table 2). The reactions were fast, and a white precipitate
of poly(NB) was observed immediately after mixing the
reagents. The final polymers have very low solubility, pre-
sumably due to a high molecular weight, and could not be
analyzed by size exclusion chromatography (SEC).
The polymerization reaction of NB with 1 (Pd:NB =
1:220) in CDCl3 was monitored by 19F and 1H NMR. After
15 min, broad Fortho signals (from C-Pf) in the range -135
to -140 ppm were clearly seen in the 19F NMR spectrum,
showing that the polymerization process starts with the
insertion of NB into the Pd-Pf bond of catalyst 1
(Scheme 3). The growth of the polymer chain is very rapid,
and the first insertion intermediate (A; Scheme 3) cannot be
detected. The broad signals observed in the 19F NMR spectra
correspond to the Pf fragment as a terminal group in
different poly(NB) chains, and their intensity decreases as
the polymerization proceeds. This effect is due to a drop in
polymer solubility as the molecular weight increases. The
signals of poly(NB) also appear in the 1H NMR spectra.
The addition of 2,6-di-tert-butylpyridine (TBPy), a com-
mon carbocation trap,22 had no influence on the polymeri-
zation (Table 1, entry 3). A radical mechanism was also ruled
out, because the absence of light or the presence of galvinoxyl
did not affect the yield of the polymerization (about 60%;
Table 1, entries 4 and 5). This suggests that the polymeriza-
tion of NB with 1 is taking place via consecutive insertions of
the monomer, as is known for other late-transition-metal
catalysts.16,23,24
subsequent reaction of the resulting radical with oxygen.21
These decomposition routes were reported for the neutral
complex 410 and support a radical chain growth for the
polymerization of MA with these catalysts.
In the reaction of methyl acrylate with Brookhart’s cata-
lysts (Scheme 1) MA insertion is followed by fast Pd migra-
tion until Pd is trapped at the former methyl carbon, by
forming a stable six-membered palladacycle by O-coordina-
tion of the ester to the electrophilic palladium center. From
this intermediate, the formation of a radical by homolytic
bond splitting is unlikely. This kind of palladacyclic complex
cannot be formed from complex 1, which has a Pf instead of
the Me group; in fact, the only intermediate observed is 5
(Scheme 2), from which the homolytic bond splitting gen-
Complexes 2 and 3 do not polymerize norbornene, prob-
ably because the bulkiness of the diimine, or the in-plane
hindrance introduced by bipy, hampers the process. Thus,
complex 3 remains unaltered in the presence of 5 equiv of NB
for 5 days at room temperature.
Complex 3 polymerizes ethylene as do Brookhart’s methyl
analogues, although with slightly lower activities, leading to
the same type of amorphous, highly branched polymers.1
Neither 1 nor 2 polymerizes ethylene, which corroborates the
•
erates the stable radical CH(CO2Me)Pf, which starts the
radical polymerization.
The Pd-Pf vs Pd-Me difference is more important in
cationic systems than in neutral initiator complexes, as the
formation of a C,O-palladacycle in the latter is less favorable
due to the lower electrophilicity of the metal. In fact, neutral
palladium methyl complexes have been used in the polym-
erization of acrylates.8 The Pd-allylic cationic dimers
described by Jordan et al. are also active in the polymeriza-
tion of methyl acrylate, and a radical chain growth occurs, as
(22) Gyor, M.; Wang, H. C.; Faust, M. J. Macromol. Sci., Pure Appl.
Chem. 1992, A29, 639–653.
(23) Casares, J. A.; Espinet, P.; Martı
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n-Alvarez, J. M.; Martı
´
´
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Ilarduya, J. M.; Salas, G. Eur. J. Inorg. Chem. 2005, 20, 3825–3831.
(24) 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.
(21) Boukouvalas, J., Haynes, R. K. In Radicals in Organic Synthesis;
Renaud, P., Sibi, M. P., Eds.; Wiley-VCH: Weinheim, Germany, 2001; Vol. 2,
Chapter 5.4.

Article
Organometallics, Vol. 28, No. 17, 2009 4999
Table 2. Polymerization of Norbornene with 1a
entry
amt of NB (mmol)
amt of CH2Cl2 (mL)
NB (mmol)/CH2Cl2 (mL)
additive
yield poly(NB) (%)
1
0.627
0.508
0.424
0.667
0.315
1.2
2
1.6
2.7
1.2
0.52
0.25
0.26
0.25
0.26
60
56
53
66
65
2
3b
4
TBPy
no light
galvinoxyl
5c
a Conditions: reactions carried out at room temperature, 24 h, N2 atmosphere, molar ratio 1:NB = 1:2000. b TBPy, 0.022 mmol. c Galvinoxyl, 0.002
mmol.
Scheme 3. Polymerization of Norbornene with 1
importance of the bulky diimine ligand in the success of the
process.3
Copolymerization Reactions. The activity shown by com-
pattern for acrylates and ethylene. Despite their activity, the
different mechanisms at play prevent the efficient copolym-
erization of both types of monomers.
plexes 1 and 3 in the homopolymerization of two very
different monomers encouraged us to test their copolymer-
ization activity for mixtures of MA and those nonpolar
monomers. Attempts at copolymerization reactions of MA
and NB using 1 afforded low yields (about 10%) of poly-
mers, but the SEC analysis did not show a unimodal dis-
tribution, suggesting that the polymer formed is a mixture of
homopolymers. Regardless of the good activity of 1 in the
homopolymerization of either monomer, the different me-
chanisms at play (radical or insertion, depending on the
monomer) efficiently discriminate between monomers and
make it very difficult to synthesize a copolymer.
The copolymerization of MA and ethylene (5 atm), at
room temperature, using 3 as catalyst afforded a viscous
material with 49% conversion of MA (see the Experimental
Section). The material is a mixture of polymers, as shown by
a bimodal SEC distribution (Mw=51.6ꢀ104 and 2.1ꢀ103).
The NMR spectrum of the polymer showed a superposition
of atactic polyMA and a polyethylene pattern similar to that
obtained in the homopolymerization experiments. We can-
not rule out that the latter polymer is a polyethylene/MA
copolymer with low MA incorporation, since the character-
istic signals of those copolymers overlap in the NMR spec-
trum with those of polyMA.
Experimental Section
General Considerations. 19F, 13C{1H} and H NMR spectra
1
were recorded on Bruker AC-300, ARX-300, and AV-400
instruments. Chemical shifts are reported in δ (ppm) and
referenced to Me4Si (1H and 13C) or CFCl3 (19F). All the
NMR spectra were recorded at 293 K, unless otherwise noted.
Size exclusion chromatography (SEC) was carried out on a
Waters SEC system using a three-column bed (Styragel 7.8 ꢀ
300 mm columns: 50-100 000, 5 000-500 000, and 2 000-
4 000 000 Da) and Waters 410 differential refractometer. SEC
samples were run in CDCl3 at 313 K and calibrated to poly-
styrene standards. All the reactions described were carried out
under an inert atmosphere.
Solvents were dried over CaH2, distilled, and deoxygenated
prior to use. Methyl acrylate, tert-butyl acrylate, and 1-hexene
(Aldrich) were distilled and deoxygenated prior to use; 99.95%
ethylene was used as received. NB, galvinoxyl, and 2,6-di-tert-
butylpyridine (TBPy) were purchased from Aldrich. 2,20-
Azobis(isobutyronitrile) (AIBN) was purchased from Fluka.
[PdBrPf(NCMe)2]19 and [PdBrPf(bipy)]25 were prepared ac-
cording to literature methods.
Synthesis of [PdBrPf(en)]. To a solution of [PdBrPf(NCMe)2]
(0.1110 g, 0.255 mmol) in acetone (30 mL) at 50 °C was added
ethylenediamine (0.0170 g, 0.280 mmol). The mixture was
stirred for 30 min at this temperature. After that time, it was
filtered and the resulting solution was evaporated to dryness.
The residue was triturated with Et2O (10 mL) to yield a white
solid, which was filtered, washed with Et2O, and air-dried.
Yield: 0.0620 g (60%). Anal. Calcd for C8H8BrF5N2Pd: C,
23.24; H, 1.95; N, 6.76. Found: C, 23.54; H, 1.88; N, 6.38. 19F
NMR (282 MHz, δ, (CD3)2CO): -166.0 (m, 2Fmeta), -163.6 (t,
1Fpara), -116.0 (m, 2Fortho). 1H NMR (300 MHz, δ, (CD3)2CO):
Conclusion
Cationic palladium complexes are suitable catalysts for the
homopolymerization of acrylate monomers by a radical
mechanism, provided that homolytic cleavage in a palladium
alkyl intermediate bearing an R-ester group occurs (as
happens for complexes 1-3). Since the generation of radicals
is hampered when a six-membered stable C,O-metallacycle
can be formed upon Pd migration the choice of the Pd-R
moiety is crucial. R groups not having hydrogen at the
bonding carbon atom should behave better than primary,
secondary, or tertiary alkyls, since they are not suited to the
formation of the six-membered C,O-metallacycle.
0
4.4 (br, 2H; NH2), 3.7 (br, 2H; NH2 ), 2.9 (br, 4H; CH2CH2).
Synthesis of [PdBrPf(diimine)]. To a solution of [NBu4]2-
[Pd2(μ-Br)2Br2Pf2] (1.1758 g, 0.870 mmol) in acetone (60 mL)
was added the diimine (0.7039 g, 1.740 mmol). The mixture was
stirred for 1 h at room temperature. After that time the resulting
solution was evaporated to dryness. The residue was treated
with EtOH (10 mL), and the resulting orange solid was filtered,
washed with EtOH, and air-dried. Yield 1.0757 g (82%). Anal.
Complex 1 is capable of homopolymerizing acrylates and
norbornene by radical and insertion chain growth mechan-
isms, respectively. Complex 3 shows this same dual activity
ꢀ
ꢀ
(25) Uson, R.; Fornies, J.; Nalda, J. A.; Lozano, M. J.; Espinet, P.;
ꢀ
Albeniz, A. C. Inorg. Chim. Acta 1989, 156, 251–256.

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Lopez-Fernandez et al.
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5000 Organometallics, Vol. 28, No. 17, 2009
Calcd for C34H40BrF5N2Pd: C, 53.87; H, 5.32; N, 3.70. Found:
C, 53.72; H, 5.10; N, 3.66. 19F NMR (282 MHz, δ, CDCl3):
-164.7 (m, 2Fmeta), -161.6 (t, 1Fpara), -117.9 (m, 2Fortho). 1H
NMR (300 MHz, δ, CDCl3): 7.30 (m, 3Haryl), 7.17 (m, 1Haryl),
7.05 (m, 2Haryl), 3.15 (septet, 2H, CHMe2), 3.08 (septet, 2H,
C0HMe2), 2.15 (s, 3H, NdC(Me)C0(Me)dN), 2.12 (s, 3H,
NdC(Me)C0(Me)dN), 1.50 (d, 6H, C0HMeMe0), 1.27 (d, 6H,
CHMeMe0), 1.22 (d, 6H, CHMeMe’), 1.10 (d, 6H, C0HMeMe0).
Synthesis of [PdPf(NCMe)(en)]BF4 (1). To a solution of
AgBF4 (0.1110 g, 0.571 mmol) in NCMe (30 mL) was added
[PdBrPf(en)] (0.2360 g, 0.571 mmol). The mixture was stirred,
protected from light, for 1 h at room temperature. The suspen-
sion was filtered, and the filtrate was concentrated to ca. 0.5 mL.
The oily residue was treated with Et2O (20 mL) and stirred to
yield a white solid, which was filtered, washed with Et2O, and
air-dried. Yield: 0.2330 g (88%). Anal. Calcd for C10H11-
BF9N3Pd: C, 26.03; H, 2.40; N, 9.11. Found: C, 26.22; H,
2.06; N, 8.83. 19F NMR (282 MHz, δ, CD3CN): -164.2 (m,
2Fmeta), -160.3 (t, 1Fpara), -151.0 (s, BF-4 ), -120.2 (m, 2Fortho).
1H NMR (300 MHz, δ, CD3CN): 3.9 (br, 2H; NH2), 3.6 (br, 2H;
Monitoring the Polymerization Reaction of Methyl Acrylate
with [PdPf(NCMe)(en)]BF4 (1). MA (0.1910 g, 2.221 mmol) was
added under N2 to a solution of 1 (0.0010 g, 0.022 mmol) in
CDCl3 (0.4 mL) in a 5 mm NMR tube. The reaction was
1
monitored by 19F and H NMR, and the formation of 5, 6,10
and Pf-containing polymer was observed as described in the
text. Data for 5 are as follows. 19F NMR (282 MHz, δ, CDCl3):
-163.9 (m, 2Fmeta), -159.0 (t, 1Fpara), -152.7 (s, BF-4 ), -144.3
(m, 2Fortho).
Synthesis of [Pd{CH(CO2Me)CH2Pf}(en)(NCMe)]BF4 (5).
MA (0.9560 g, 11.105 mmol) was added under N2 to a suspen-
sion of 1 (0.0680 g, 0.147 mmol) in CH2Cl2 (2 mL). The
suspension was stirred for 15 min and then evaporated to
dryness. The residue was treated with Et2O (4 mL) and stirred
to yield a white solid, which was filtered, washed with Et2O, and
air-dried. Yield: 0.0560 g (69%). Anal. Calcd for C14H17B1-
F9N3OPd2: C, 30.71; H, 3.13; N, 7.67. Found: C, 30.92; H, 2.92;
N, 7.29. 19F NMR (282 MHz, δ, CD3CN): -164.4 (m, 2Fmeta),
1
-159.7 (t, 1Fpara), -151.0 (s, BF-4 ), -143.7 (m, 2Fortho). H
NMR (300 MHz, δ, CD3CN): 3.6 (br, 2H; NH2), 3.53 (s, 3H;
OMe), 3.0 (br, 2H; NH02), 2.92 (m, 1H; CHCO2Me), 2.85 (m, 2H;
CH2Pf), 2.65 (m, 4H; CH2-CH2), 2.18 (s, 3H; NCMe). 13C{1H}
NMR (75.4 MHz, δ, CD3CN):0179.9 (C(O)O), 52.03 (OCH3),
0
NH2 ), 2.75 (m, 4H; CH2-CH2), 2.18 (s, 3H; NCMe).
Synthesis of [PdPf(NCMe)(bipy)]BF4 (2). To a solution of
AgBF4 (0.0920 g, 0.472 mmol) in NCMe (30 mL) was added
[PdBrPf(bipy)] (0.2400 g, 0.472 mmol). The mixture was stirred,
protected from light, for 6 h at room temperature. The suspen-
sion was filtered, and the filtrate was evaporated to dryness. The
residue was treated with Et2O (20 mL) and stirred to yield a
white solid, which was filtered, washed with Et2O, and air-dried.
Yield: 0.199 g (76%). Anal. Calcd for C18H11BF9N3Pd: C,
38.78; H, 1.99; N, 7.54. Found: C, 38.40; H, 2.01; N, 7.12. 19F
NMR (282 MHz, δ, CD3CN): -162.9 (m, 2Fmeta), -159.7
(t, 1Fpara), -151.1 (s, BF-4 ), -121.2 (m, 2Fortho). 01H NMR
0
48.64 (CH2NH2), 44.54 (CH2 NH2 ), 25.13 (CH2Pf), 24.07
(CHCO2Me). IR (cm-1): (MeO)CdO, 1682 (s); NCMe, 2359
(w), 2328 (w).
Synthesis of [Pd{CH(CO2Me)CH2Pf}(diimine)(NCMe)]BF4
(7). MA (0.3204 g, 3.722 mmol) was added under N2 to a sus-
pension of [PdPf(NCMe)(diimine)]BF4 (0.1000 g, 0.1241 mmol)
in CH2Cl2 (10 mL). The suspension was stirred for 16 h and
then evaporated to dryness. The residue was treated with hexane
(2 mL) and stirred to yield a yellow solid, which was filtered,
washed with hexane, and air-dried. Yield: 0.0981 g (84%). Anal.
Calcd for C40H49BF9N3O2Pd: C, 53.86; H, 5.54; N, 4.71. Found:
C, 53.77; H, 5.62; N, 4.34. 19F NMR (282 MHz, δ, CDCl3):
-163.6 (m, 2Fmeta), -158.2 (t, 1Fpara), -152.7 (s, BF-4 ), -143.4
(m, 2Fortho). 1H NMR (300 MHz, δ, CDCl3): 7.42 (m, 2Haryl),
7.30 (m, 4Haryl), 3.44 (s, 3H, OCH3), 3.27 (septet, 1H, CaHMe2),
3.17 (septet, 2H, CbHMe2, CcHMe2), 3.02 (septet, 1H,
CdHMe2), 2.72 (m, 1H, CHH0Pf), 2.53 (m, 1H, CHCO2Me),
2.46 (s, H, NdC(Me)C0(Me)dN), 2.41 (s, H, NdC(Me)-
C0(Me)dN), 2.22 (m, 1H, CHH0Pf), 1.85 (s, NCMe), 1.45 (d,
3H, CaHMeMe0), 1.40 (d, 3H, CbHMeMe0), 1.35 (d, 3H,
CcHMeMe0), 1.32 (d, 3H, CdHMeMe0), 1.27 (d, 3H, CaHMeMe0),
1.25 (d, 3H, CbHMeMe0), 1.23 (d, 3H, CcHMeMe0), 1.21 (d, 3H,
CdHMeMe0). 13C NMR (100.61 MHz, δ, CDCl3): 184.39 (s, 1C,
C(O)OMe), 177.57 (s, 1C, NdCC00N), 177.30 (s, 1C, NdCC00N),
(300 MHz, δ, 0CD3CN): 8.65 (d, J = 6.4 Hz, 1H; H6 bipy), 8.35
0
(m, 3H; H3,3 ,4 bipy), 8.22 (t, J = 6.4 Hz, 1H; H4bipy), 7.88 (d, J =
0
6.4 Hz, 1H; H6bipy), 7.80 (t, J = 6.4 Hz, 1H; H5 bipy), 7.45 (t, J =
6.4 Hz, 1H; H5bipy), 2.18, (s, 3H; NCMe).
Synthesis of [PdPf(NCMe)(diimine)]BF4 (3). To a solution of
AgBF4 (0.1592 g, 0.818 mmol) in NCMe (40 mL) was added
[PdBrPf(diimine)] (0.6199 g, 0.818 mmol). The mixture was
stirred, protected from light, for 1 h. The suspension was
filtered, and the filtrate was evaporated to ca. 2 mL. The residue
was treated with Et2O (20 mL) and stirred to yield a yellow solid,
which was filtered, washed with Et2O, and air-dried. Yield:
0.5377 g (82%). Anal. Calcd for C36H43BF9N3Pd: C, 53.65;
H, 5.38; N, 5.21. Found: C, 53.51; H, 4.94; N, 5.96. 19F NMR
(282 MHz, δ, CDCl3): -162.5 (m, 2Fmeta), -157.9 (t, 1Fpara),
1
-152.3 (s, BF4-), -121.1 (m, 2Fortho). H NMR (300 MHz, δ,
140.18, 140.15, 140.07, 138.46, 138.41, and 138.15 (s, 6 C, Cipso
,
CDCl3): 7.38 (m, 3Haryl), 7.20 (m, 1Haryl), 7.0 (m, 2Haryl), 3.20
(septet, 2H, CHMe2), 3.02 (septet, 2H, C0HMe2), 2.48 (s, 3H,
NdC(Me)C0(Me)dN), 2.46 (s, 3H, NdC(Me)C0(Me)dN), 1.77
(s, NCMe), 1.45 (d, 6H, C0HMeMe0), 1.33 (d, 6H, CHMeMe0),
1.21 (d, 6H, CHMeMe0), 1.13 (d, 6H, C0HMeMe0).
Cortho diimine), 129.39, 128.47, 125.10, 124.39, and 123.99 (s, 6C,
Cmeta, Cpara diimine), 120.40 (s, 1C, CNMe), 51.42 (s, 1C, OCH3),
33.64 (s, 1C, CHCO2Me), 28.98 (s, 1C, CdHMe2), 28.85 (s, 2C,
Cb,cHMe2), 28.62 (s, 1C, CaHMe2), 24.91 (s, 1C, CdHMeMe0),
24.26 (s, 1C, CcHMeMe0), 23.94 (s, 1C, CbHMeMe0), 23.67 (s, 1C,
CaHMeMe0), 23.63 (s, 1C, CdHMeMe0), 23.55 (s, 2C, Cc,
bHMeMe0), 23.49 (s, 1C, CaHMeMe0), 23.35 (s, 1C, CH2Pf),
22.87 and 20.33 (s, 1C each, NdC(Me)C0(Me)dN), 2.21 (s, 1C,
CNMe).
Decomposition of Complex 7. 7 (0.010 g, 0.0112 mmol) was
disolved in CDCl3 (0.5 mL) in a 5 mm NMR tube under N2. The
reaction was monitored by 19F and 1H NMR, and the formation
of 6 and 9-11 was observed (see text).10 After 1 month, 84% of
7 had decomposed to give the former products in the relative
ratio 6:9:10:11:12 = 1.08:4:2.16:1.36:1. The amount of products
was quantified by integration of their 19F NMR signals.
Polymerization Reactions of Norbornene. 1 (0.0010 g, 0.003
mmol) was added under N2 to a suspension of NB (0.5080 g,
5.395 mmol) in CH2Cl2 (2 mL). The reaction proceeded at room
temperature for 24 h. The polymer was precipitated by pouring
the mixture onto MeOH (30 mL). The MeOH was decanted off,
and the polymer was filtered, washed with MeOH, and dried
Polymerization Reactions of Alkyl Acrylates. MA (0.9560 g,
11.105 mmol) was added under N2 to a solution of 1 (0.0030 g,
0.006 mmol) in CH2Cl2 (2 mL). The reaction proceeded at room
temperature for 24 h. The polymer was precipitated by pouring
the mixture onto MeOH (30 mL). The MeOH was decanted off,
and the polymer was filtered, washed with MeOH, and dried
under vacuum. Data for poly(MA) are as follows. Yield: 0.7500 g
1
(79%); Mw =7.2ꢀ106, Mw/Mn=5.8. H NMR (300 MHz, δ,
CDCl3): 3.68 (s, 6H; OMe), 2.3 (br, 2H; CH(CO2Me)s, CH-
(CO2Me)i), 1.9 (br, 1H; CHHi), 1.68 (br, 2H; CHs2), 1.5 (br, 1H;
CHHi) (i=isotactic, s=syndiotactic).
The same procedure was used for other monomers, initiators,
and/or solvents (see Table 1).
Data for poly(tBuA) are as follows. Yield: 74%, atactic poly-
1
mer. Mw = 3.4 ꢀ 106, Mw/Mn = 5.7. H NMR (300 MHz, δ,
CDCl3): 2.23 (br, 2H; CH(COt2Bu)s, CH(CO2t Bu)i), 1.81 (br, 1H;
CHHi), 1.60 (br,1H;CHHi), 1.51 (br,2H; CHs2), 1.43(s,18H; tBu)
(i = isotactic, s = syndiotactic).

Article
Organometallics, Vol. 28, No. 17, 2009 5001
1
under vacuum to yield 0.2860 g (56%). H NMR (300 MHz, δ,
CDCl3):2.4-1.9 (br, 2H), 1.7-0.9 (br, 8H). 13CNMR(75.4MHz,
δ, CDCl3): 54-45 (br, CH), 45-38 (br, CH), 38-34 (br, CH2),
34-28 (br, CH2).
1H NMR (300.13 MHz, δ, CDCl3): 1.4-1.1 (br, -CH2), 0.84
(br, -CH3).
Polymerization Reactions of MA and Ethylene. A Fisher-
Porter flask containing 3 (0.010 g, 0.012 mmol) was cooled to
-78 °C, evacuated, and placed under an ethylene atmosphere.
CH2Cl2 (2.5 mL) and methyl acrylate (1.0681 g, 12.407 mmol)
were added, and the cold flask was back-filled with higher
ethylene pressure (5 atm). The reaction mixture was warmed to
room temperature and stirred for 24 h. The polymer was pre-
cipitated by pouring the mixture onto MeOH (50 mL). The
MeOH was decanted off, and the polymer was filtered, washed
withMeOH, anddriedundervacuum toyield1.0364g of polymer
(TONMA = 491; TONethylene = 1473). Data for poly(MA):
Mw =51.6 ꢀ 104, Mw/Mn =1.8. Data for poly(ethylene/MA):
Mw=2.1 ꢀ 103, Mw/Mn = 3.5. The 1H NMR spectrum of the
polymer is a superposition of the spectra of atactic polyMA and
polyethylene (or polyethylene/MA copolymer; see text).
The same procedure was used for other conditions or to test
the influence of additives (see Table 2).
Monitoring the Polymerization Reactions of Norbornene with
1. A solution of NB (0.2970 g, 3.154 mmol) in CDCl3 (0.6 mL)
was added under N2 to 1 (0.0070 g, 0.014 mmol) in an NMR
tube. The reaction was monitored by 19F and 1H NMR, and the
formation of Pf-containing polymer was observed as described
in the text. Precipitation of poly(NB) was also observed.
Polymerization Reaction of Ethylene. A Fisher-Porter flask
containing 3 (0.010 g, 0.012 mmol) was cooled to -78 °C,
evacuated, and placed under an ethylene atmosphere. CH2Cl2
(2.5 mL) was added, and the cold flask was back-filled with
higher ethylene pressure (5 atm). The reaction mixture was
warmed to room temperature and stirred for 24 h. The polymer
was precipitated by pouring the mixture onto MeOH (50 mL).
The MeOH was decanted off of the sticky polymer, which was
then dissolved in pentane (10 mL). After being treated with
activated charcoal and filtered through Kieselguhr, the solu-
tion appeared clear and yellow. The solvent was then removed,
and the viscous oil was dried under vacuum to yield 1.6265 g
of polymer (TON = 4675). Mw = 63.4 ꢀ 103, Mw/Mn = 1.9.
Acknowledgment. Financial support from the Spanish
MEC (DGI, Grant CTQ2007-67411/BQU; Consolider
Ingenio 2010, Grant INTECAT, CSD2006-0003; FPU
fellowships to R.L.-F. and N.C.) and the Junta de Castilla
ꢀ
y Leon (Grupos de Excelencia GR169) is gratefully
acknowledged.