Poly(2-oxazoline)s functionalized with palladium carbene complexes: Soluble, amphiphilic polymer supports for C-C coupling reactions in water

Article abstract of DOI:10.1021/ma048142r

This paper describes the synthesis and characterization of a new class of amphiphilic, watersoluble diblock copolymers based on 2-oxazoline derivatives with pendent N-heterocyclic carbene/palladium catalysts in the Hydrophobic block. The synthetic strategy involves a four-step synthesis of three functionalized monomers, each composed of a bis(imidazoline-2-ylidene)palladium(II) diiodide derivative that is covalently linked to a 2-oxazoline monomer via a flexible alkyl spacer (alkyl = butyl, hexyl, octyl). The structure of the monomers was analyzed by ¹H and ¹³C NMR spectroscopy, MALDI-TOF, and elemental analysis. Three diblock copolymers P1-P3 with the monomers being part of the hydrophobic block were prepared by living cationic ring-opening polymerization. The structure and composition of the polymers was characterized by ¹H and ¹³C NMR spectroscopy as well as GPC measurements and indicated rather low PDI of 1.3 and about 65% incorporation of the N-heterocyclic carbene/palladium-functionalized monomer into the polymer. Dynamic light scattering measurements of the polymers P1-P3 in water revealed aggregate formation with a hydrodynamic radius of 10-30 nm with high polydispersity as visualized by TEM micrographs. Subsequently, polymers P1-P3 were successfully utilized as a polymeric support for the Heck coupling of iodobenzene with styrene as a model reaction in water, showing high activities with turnover frequencies (TOF) up to 570 h^-1 at 90°C.

Full text of DOI:10.1021/ma048142r

254
Macromolecules 2005, 38, 254-262
Poly(2-oxazoline)s Functionalized with Palladium Carbene Complexes:
Soluble, Amphiphilic Polymer Supports for C-C Coupling Reactions in
Water
†
‡
‡
†
Daniel Sch o1 nfelder, Karl Fischer, Manfred Schmidt, Oskar Nuyken, and
Ralf Weberskirch*,†
TU M u¨ nchen, Department Chemie, Lehrstuhl f u¨ r Makromolekulare Stoffe, Lichtenbergstr. 4,
D-85747 Garching, Germany and Johannes-Gutenberg Universit a¨ t Mainz, Institut f u¨ r Physikalische
Chemie, D-55099 Mainz, Germany
Received September 10, 2004; Revised Manuscript Received November 2, 2004
ABSTRACT: This paper describes the synthesis and characterization of a new class of amphiphilic, water-
soluble diblock copolymers based on 2-oxazoline derivatives with pendent N-heterocyclic carbene/palladium
catalysts in the hydrophobic block. The synthetic strategy involves a four-step synthesis of three
functionalized monomers, each composed of a bis(imidazoline-2-ylidene)palladium(II) diiodide derivative
that is covalently linked to a 2-oxazoline monomer via a flexible alkyl spacer (alkyl ) butyl, hexyl, octyl).
1
13
The structure of the monomers was analyzed by H and C NMR spectroscopy, MALDI-TOF, and
elemental analysis. Three diblock copolymers P1-P3 with the monomers being part of the hydrophobic
block were prepared by living cationic ring-opening polymerization. The structure and composition of
1
13
the polymers was characterized by H and C NMR spectroscopy as well as GPC measurements and
indicated rather low PDI of 1.3 and about 65% incorporation of the N-heterocyclic carbene/palladium-
functionalized monomer into the polymer. Dynamic light scattering measurements of the polymers
P1-P3 in water revealed aggregate formation with a hydrodynamic radius of 10-30 nm with high
polydispersity as visualized by TEM micrographs. Subsequently, polymers P1-P3 were successfully
utilized as a polymeric support for the Heck coupling of iodobenzene with styrene as a model reaction in
-
1
water, showing high activities with turnover frequencies (TOF) up to 570 h at 90 °C.
Introduction
Recently, an increasing number of research groups
have focused on the development of new support ma-
terials for catalysis in water based on poly(ethylene
Soluble and insoluble polymer supports have received
much interest recently in combinatorial chemistry and
6
7
glyocle), poly(acrylic acid), or poly(N-isopropylacryl-
1
catalysis. This is not surprising considering the indus-
8
amide) copolymers. However, transformation of hydro-
trial need for highly efficient transformation of any
given substrate and the economic benefits of recyclable
catalyst systems for long-term usage. Whereas homo-
geneous catalysis often provides the best conditions to
achieve high activities, heterogeneous catalysis offers
the advantages of simplified product purification and
the potential for catalyst recycling. In addition, replace-
ment of expensive, toxic, and flammable organic sol-
vents by water is highly desirable for reducing costs and
phobic substrates in pure aqueous media without the
use of any organic cosolvent still remains a challenging
task due to their limited water solubility. The most
promising approach to increase the solubility of hydro-
phobic substrates in aqueous media is based on the use
of amphiphilic polymer supports.3 Of particular interest
is the work of Uozumi et al., who utilized commercially
available poly(ethylene glycole)-modified polystyrene
resins for catalyst immobilization in various transition-
e
2
development of environmentally benign processes. Due
9
metal-catalyzed reactions in pure aqueous media. More
to the rapid developments in aqueous two-phase cataly-
sis, the need for organometallic catalysts that are stable
and active in aqueous media has been a major driving
force for the intensive research activity in this field over
recently, Yamada et al. described the preparation of a
heterogeneous palladium catalyst by supramolecular
self-assembling of (NH4)2PdCl4 and poly[(N-isopropyl-
acrylamide)10-co-(4-diphenylstyrylphosphine)].10 How-
ever, typical limitations of cross-linked polymer materi-
als, such as lowered reactivity and extended reaction
times, remain unsolved. In addition, fine tuning of the
structure and composition of the polymer support to
allow a better correlation with catalyst activity is an
important feature of any support material and difficult
to achieve for heterogeneous catalyst supports.
3
the last 15 years. In the past decade metal complexes
of N-heterocyclic carbenes (NHC) have been reported
as a class of moisture- and air-stable catalysts with4
remarkable activity in various C-C coupling reactions.
The stronger metal-carbon bond of these ligands com-
pared to the conventional phosphine ligands reduces the
dissociation from the metal center even at elevated
temperatures, making the thermally and oxidatively
stable NHC complexes useful candidates for Heck and
Suzuki coupling reactions in both organic and aqueous
The scope of this contribution is the preparation of
three soluble, amphiphilic block copolymers with pal-
ladium N-heterocyclic carbene catalysts in the hydro-
phobic block by using appropriate functionalized mono-
mers. First, results of these polymer-bound catalysts in
a micellar catalytic variant of the Heck reaction of
iodobenzene with styrene in water revealed TOF num-
5
media as well.
*
To whom correspondence should be addressed. E-mail:
Ralf.Weberskirch@ch.tum.de.
†
‡
TU M u¨ nchen.
Johannes-Gutenberg Universit a¨ t Mainz.
-1
bers up to 570 h , which are the highest ever reported
1
0.1021/ma048142r CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/21/2004

Macromolecules, Vol. 38, No. 2, 2005
Poly(2-oxazoline)s Functionalized with Pd Complexes 255
for this reaction in neat water without addition of any
organic cosolvent.
Scheme 1. 2-Methyl-2-oxazoline,
Bis(1,3-dimethylimidazoline-2-ylidene)palladium(II)
Diiodide, and Methyltriflate or
2
,3-Dimethyl-2-oxazolinium Triflate Initiators for the
Test Polymerization of 2-Methyl-2-oxazoline in the
Presence of the NHC/Palladium Catalyst
Results and Discussion
1
. Monomer Synthesis. The cationic ring-opening
polymerization of 2-oxazolines provides a versatile
monomer system for the synthesis of amphiphilic poly-
mers with different architecture, composition, and func-
11
tionalization. Two different approaches can be utilized
to incorporate the catalytically active unit into the
polymer: either (i) directly via suitable functionalized
monomers or (ii) in a polymer analogous modification
step. As a result of the well-known drawbacks of the
second approach, such as low degree of polymer modi-
fication and separation of the polymer from unreacted
compounds, the first strategy seems to be the most
elegant and reliable methodology.
derivatization step provided a qualitative means of the
success of each reaction. The first step in the synthesis
involved the alkylation of N-methylimidazole with
Due to the fact that oxazolines are well known to be
12
excellent ligands for metal catalysts, our first objective
was to explore the influence of the NHC/palladium
catalyst on the polymerization behavior of 2-oxazoline,
whether the catalyst disturbs the living cationic polym-
erization or not. Two test experiments were conducted
using 2-methyl-2-oxazoline as monomer and bis(1,3-
dimethylimidazoline-2-ylidene)palladium(II) diiodide as
the NHC/palladium catalyst (Scheme 1).
1
,ω-dibromoalkane to give the imidazolium salts 1a-c
13
in yields of 68-73% as colorless oils. Low amounts of
disubstituted 1,ω-dibromoalkanes were removed by
column chromatography. The imidazolium salts 1a-c
were then subjected to the same synthetic protocol as
that previously described for the preparation of mixed
14
NHC/phosphine palladium complexes. Therefore, com-
pounds 1a-c were treated with palladium(II) acetate
t
Thus, a homopolymer of 2-methyl-2-oxazoline was
prepared with a monomer/initiator ratio ([monomer]:
in the presence of sodium iodide and KO Bu in THF and
resulted in orange-colored dimeric products 2a-c. In
dichloromethane and THF these complexes show a deep
red color, which is typical for such dinuclear complexes.
Additional, successful halogen exchange by the Finkel-
stein reaction due to an excess amount of sodium iodide
[
initiator]) ) 15. In the first experiment the polymeri-
zation was initiated with methyl triflate at 0 °C; after
2 h the reaction was terminated with piperidine. The
1
polymer was precipitated in diethyl ether, and the
catalyst was isolated after evaporation of diethyl ether.
1
was monitored by H NMR spectroscopy, showing a new
1
Polymer and catalyst were characterized by H NMR
signal at 3.25 ppm. According to NMR analysis, at least
80% of the bromide was replaced by iodide, which is of
advantage for coupling to the 2-methyl-2-oxazoline in
the last step of monomer synthesis due to the higher
reactivity of the iodide. Moreover, successful complex
formation was confirmed by shifting of the aromatic
signals for the protons from 7.78 and 7.71 ppm to 7.40
and 7.41 ppm, respectively. At room temperature the
mixed complexes 3a-c were prepared from THF solu-
tions of 2a-c by addition of 1 equiv of 1,3-dimethylimi-
dazoline-2-ylidene that was prepared according to a
spectroscopy. The degree of polymerization was calcu-
1
lated based on H NMR end-group analysis and gave a
value of 23 (theoretical 15), indicating clearly that the
palladium catalyst disturbs the cationic ring-opening
polymerization mechanism. 1H NMR of the catalyst
showed methylation of the N-heterocyclic carbene ligands
by methyl triflate. As a consequence, in the second
experiment we used 2,3-dimethyl-2-oxazolinium triflate
as initiator salt, which was obtained after reacting
2
-methyl-2-oxazoline with 1 equiv of methyl triflate
1
6
1
15
according to a literature procedure.
H NMR end-
literature procedure and were obtained as yellow
solids. 13C NMR spectroscopic analysis of 3a clearly
showed successful formation of the mixed complex by
the appearance of a second signal at 121.9 ppm, which
corresponds to the carbon atom close to the N-alkyl
group analysis revealed excellent agreement of the
theoretical and experimental degree of polymerization.
NMR analysis of the NHC/palladium catalyst after
polymerization did not show any changes in the struc-
ture of the catalyst.
me
alk
group, NCHCHN , in addition to the signal at 122.9
On the basis of these preliminary results, the mono-
mer route was chosen to introduce the catalytically
active NHC/palladium complex in the polymer. We
decided to attach the catalyst to the 2-oxazoline unit
via a flexible alkyl spacer, where we anticipated that
the linker would place the catalyst sufficiently away
from the polymer backbone to allow unimpeded access
of the substrate to the metal center. The synthetic
scheme depicted in Scheme 2 was chosen as the most
direct route to functionalized monomers with the NHC/
palladium catalyst attached to the 2-oxazoline monomer
unit via the alkyl spacer of four, six, or eight methylene
units.
ppm that can be assigned to the three other carbon
me
alk
me
me
1
atoms
NCHCHN
and
NCHCHN
.
H NMR
analysis shows two signals at 7.31 ppm which can be
me
alk
assigned to NCHCHN and a second signal at 7.28
me
me
me
alk
ppm corresponding to NCHCHN and NCHCHN
with an intensity ratio of 1:3.
Synthesis of the functional monomers was accom-
plished by treating a solution of 2-methyl-2-oxazoline
deprotonated with lithium diisopropylamide (LDA) in
THF at -60 °C with the intermediate compounds
3a-c for 2 h. The pure monomers 4a-c were obtained
after column chromatography as pale yellow compounds.
The structure and composition of 4a-c were confirmed
1
13
Purification of each step was achieved by column
by H and C NMR spectroscopy, MALDI-TOF, and
1
chromatography. The soluble intermediates were readily
elemental analysis. Figure 1 shows the H NMR spec-
1
13
characterized by H and C NMR spectroscopy. In
addition, the color change of the catalyst with each
trum of 4c. Characteristic are the two methylene groups
of the oxazoline ring at 3.66 (-N-CH2-) and 4.12 ppm

256 Sch o¨ nfelder et al.
Macromolecules, Vol. 38, No. 2, 2005
the functional monomers 4a-c into the polymer. Two
reasons might account for this result. Since it has
already been demonstrated that 2-oxazoline polymeri-
zation is not hindered by the NHC/palladium catalyst,
it can be speculated that the sterically more demanding
NHC/palladium catalyst in the monomer side chain is
the reason for the lowered reactivity of the monomers.
1
The H NMR spectrum of P3 is depicted in Figure 2.
The signal at 3.43 ppm can be clearly assigned to the
polymer main chain protons. In addition, the signals at
3
.90 and 6.85 ppm can be assigned to the three methyl
groups and the ring protons of the NHC/palladium
catalyst, respectively.
3
. Dynamic Light Scattering (DLS) and TEM
Analysis. The study of aggregate formation was guided
by two considerations. First, we wanted to make sure
that micellar aggregates were formed at the polymer
concentrations used in the catalytic experiments. In
addition, we were interested in finding out if there is
any correlation between aggregate size and catalytic
activity. Aggregate formation of P1-P3 in water was
analyzed by DLS measurements at a similar polymer
concentration used in the later catalysis reactions. The
results are summarized in Table 2. The hydrodynamic
radii of the particles were in the range of 10-30 nm,
which is typical for micellar aggregates based on poly-
Figure 1. 1H NMR spectrum of monomer 4c (d
MHz, T ) 20 °C).
6
-DMSO, 300.1
Scheme 2. Synthetic Scheme for the Functionalized
-Oxazoline Monomers 4a-c
2
(
2-oxazoline)s with a similar molar mass and block
17a
copolymer composition.
It is interesting to note,
however, that there is no direct correlation of spacer
length of the side chain and the hydrodynamic radii of
the aggregates formed.
TEM micrographs of the aggregates formed by P1
confirmed the high polydispersity of the aggregates
with an average hydrodynamic radius of about 15 nm
(
see Figure 3). This result has been found more recently
also for other poly(2-oxazoline) block copolymers. How-
ever, as reported by Papadakis and co-worker, under-
standing the aggregate formation of such amphiphilic
block copolymers with a comblike structure in the
hydrophobic block is very complex and still at an early
stage.1
7b
(
-O-CH2-). The singlets at 7.26 and 7.28 ppm can be
clearly assigned to the protons of the imidazoline ring.
. Synthesis of the Polymeric Macroligand. As
4
. Heck Reaction in Aqueous Media. Heck cou-
2
pling of sp -halides with alkenes promoted by palladium
catalysts is one of the most important methods for C-C
coupling in organic synthesis,18 the synthesis of impor-
2
already shown, the living chain end of the poly(2-
oxazoline)s does not interfere with the N-heterocyclic
carbene functionalities of monomers 4a-c. Thus, diblock
copolymers were prepared by sequential polymerization
of 2-methyl-2-oxazoline to form the hydrophilic block,
which provides water solubility, and subsequently a
mixture of monomer 4a-c with the corresponding
19
tant intermediates for pharmaceuticals, and conduct-
ing polymers.20 Although many efforts have been made
2
1
to prepare heterogeneous Heck catalysts, homoge-
neous catalysts still have many advantages on catalytic
activity.22 A major problem of the immobilized catalysts
is their reduced stability under Heck reaction condi-
tions. Moreover, salts accumulated during the reaction
lead to degradation of the catalytic system.23
2
2
-alkyl-2-oxazoline was used to form the second block.
-Alkyl-2-oxazolines with alkyl ) butyl, hexyl, octyl side
chains were hereby added to increase the hydrophobicity
of the second polymer block. The synthesis is depicted
in Scheme 3.
Few reports have been presented so far that deal with
Heck coupling in water without use of any organic
cosolvents. Jeffery intensively studied the reaction of
iodobenzene with methyl acrylate in the presence of
Pd(OAc)2/PPh3 in pure aqueous solution and the ben-
eficial effect of various tetrabutylammonium halides.24
Another typical test reaction is the coupling of styrene
as a more hydrophobic substrate with iodobenzene to
give trans-stilbene. The first approach to react iodoben-
zene derivatives and various olefinic substrates under
Heck conditions in water was presented by Y. Uozumi
et al. They used a PS-PEG resin-supported palladium
catalyst and obtained 92% yield after 14 h reaction time
of styrene with iodobenzene in pure aqueous solution
Piperidine was used as a highly effective termination
16
agent. After polymerization was finished, the polymers
were precipitated several times in diethyl ether and
obtained as citrus-colored solids. The results of the
polymer synthesis are summarized in Table 1. Size
exclusion chromatography gave monomodal curves with
polydispersity indices ranging from 1.32 to 1.39.
1
H NMR analysis indicated successful polymerization
of the NHC/palladium catalyst carrying monomers.
Quantitative analysis of polymer composition and pal-
ladium content as determined by H NMR spectroscopy
and ICP-OES revealed roughly 65% incorporation of
1

Macromolecules, Vol. 38, No. 2, 2005
Poly(2-oxazoline)s Functionalized with Pd Complexes 257
Scheme 3. Synthesis of the NHC/Palladium-Functionalized Block Copolymers (TCE ) tetrachloroethane)
Table 1. Analytical Data of the Amphphilic Polymer
Table 2. Hydrodynamic Radii of the Aggregates Formed
Supports P1-P3
by P1-P3 in Aqueous Solution
polymer
cP (mM)
Dapp (10- cm s-1)
7
2
rh (nm)
x
exp,(calcd)
,
y
exp,(calcd), zexp,(calcd)
,
Mh
n
,
polymer NMRa
NMR
a
NMR
a
NMR
PDIb,c
γ/%d
P1
P2
P3
0.24
0.23
0.20
1.50
2.19
0.69
14.2
9.8
30.7
P1
P2
P3
28.4 (30.7) 1.5 (2.4) 2.9 (3.0) 3920 (2584) 1.32 (1.35) 3.3
29.9 (32.2) 1.8 (2.7) 3.2 (3.2) 4400 (2661) 1.35 (1.33) 3.6
30.4 (30.6) 1.9 (2.9) 3.4 (3.1) 4730 (2668) 1.39 (1.32) 3.6
a
For meaning of x, y, and z, see Scheme 3. b As determined
We tested macroligands P1-P3 in a micellar catalytic
variant of the Heck reaction of iodobenzene with sty-
rene. Reactions were conducted at 90 °C with P3 and a
palladium content of 0.67 mol %. The course of the
reaction was monitored by periodically taking samples
and analyzing them by gas chromatography. Figure 4
shows the kinetics of substrate conversion and product
formation. As can be seen from Figure 4 there is an
induction period of 15 min to form the catalytically
active species by reducing palladium(II) to palladium-
by GPC with poly(styrene) standards. CI n brackets: Mh n and PDI
of the first block. d Palladium mass content as determined by
ICP-OES.
(0) with K2CO3 as the base. After 3 h reaction time 93%
of trans-stilbene as well as 4% of 1,1-diphenylethene and
less than 0.5% of cis-stilbene as side products were
detected. The reaction is very fast, and almost 90% of
all substrates are already converted after 40 min. The
1
Figure 2. H NMR of the soluble NHC/palladium-bound
3
polymer P3 (CDCl , 300.1 MHz, T ) 20 °C).
with 10 mol % palladium catalyst showing excellent
Figure 3. TEM micrograph of P1 (cP
-4
) 2.5 × 10
mol/L) with
recyclability but poor activities (TOF < 1 h-1).7a
the hydrodynamic radii r of the aggregates observed.
h

258 Sch o¨ nfelder et al.
Macromolecules, Vol. 38, No. 2, 2005
Table 4. Catalytic Results of the Heck Coupling of
Iodobenzene (PhI) with Styrene with the Polymer-Bound
Catalysts P3 (PhI:styrene:K2CO3 ) 1.0:1.25:1.5, cP ) 0.17
mM, nPd/nPhI ) 0.1 mol %, T ) 90 °C)
cycle
t (h)a
conversion (%)
trans-stilbene (%)b
1
2
3
5
5
5
89
82
76
80
75
68
a
Reaction time. b trans-Stilbene as determined by gas chroma-
tography.
the spacer length of four methylene units is too short
to separate the catalyst sufficiently from the polymer
backbone. According to our results a minimum spacer
length of six methylene groups is needed to achieve an
optimal combination of catalyst flexibility and the
possibility of being accessed by the substrates. Compar-
ing the catalytic results of P1 to P3 with the size of the
aggregates as determined by dynamic light scattering,
the results show clearly that there is no correlation of
aggregate size and catalytic activity; rather the spacer
length between the polymer backbone and the catalyti-
cally active unit are crucial parameters for optimal
catalyst activity. However, it should also be noted that
the results obtained by DLS at room temperature
cannot be transferred directly to the reaction conditions
at T ) 90 °C.
Figure 4. Kinetics of the Heck coupling of styrene and
2 3
iodobenzene (PhI) at 90 °C (PhI:styrene:K CO ) 1.0:1.25:1.5,
P3 ) 0.57 mM, nPd/nPhI ) 0.0067).
5
. Catalyst Recycling and Reuse. After the reac-
tion was complete, the product could be easily separated
by extraction with diethyl ether. The recovered aqueous
phase containing the catalyst was reused in another
reaction cycle. By doing so, two more cycles have been
performed to demonstrate separation and reuse of the
polymer-bound catalyst P3. The results summarized in
Table 4 show a slightly reduced activity in the second
cycle and reduced trans-stilbene formation of 6%. In the
third cycle product formation was again reduced by 9%
with respect to the second cycle. This is however due to
incomplete phase separation more than catalyst deac-
tivation, which is known to show thermal stability up
to 140 °C.4g Moreover, we assume that after extraction
with diethyl ether a considerable amount of solvent
stays solubilized in the micellar core that prevents
efficient solubilization of the substrate again and is in
addition responsible for the reduced activity in the
second cycle. In a more detailed study, however, leach-
ing experiments should be performed to rule out any
catalyst decomposition. New developments in catalyst
separation, such as nanofiltration, are particularly
interesting for such soluble support systems due to the
higher molecular weight of the polymer-bound ligand,
have already been proven to be very useful in catalyst
recycling without any loss of activity in a second or third
cycle, and will help to overcome this problem in future
Figure 5. Reaction kinetics of the Heck coupling of iodoben-
zene (PhI) and styrene as a function of amphiphile P1-P3 at
T ) 90 °C (PhI:styrene:K
Pd/nPhI ) 0.0067).
2 3 P
CO ) 1.0:1.25:1.5, c ) 0.67 mM,
n
Table 3. Catalytic Results of the Heck Coupling of
Iodobenzene (PhI) with Styrene with the Polymer-Bound
Catalysts P1-P3 (PhI:styrene:K2CO3 ) 1.0:1.25:1.5, cP )
0.57 mM, nPd/nPhI ) 0.0067)
polymer
t (h)a
trans-stilbene (%)b
TOF (h-1
)
P1
P2
P3
2
1.5
1.5
>93
>93
>93
150
570
530
a
Reaction time. b trans-Stilbene as determined by gas chroma-
tography.
TOF number as a measure of catalyst activity was
determined to be 530 h-1 from the point of inflection
25
experiments.
(
in comparison to the results of Uozumi et al. with a
In summary, we presented the first synthesis of
amphiphilic, water-soluble block copolymers based on
-
1
TOF value of 1 h
for the same substrates) and
indicates the high activity of the soluble, polymer-bound
NHC/palladium catalyst.
2
-oxazolines with pendent NHC/palladium catalysts.
The polymeric catalysts P1-P3 reveal aggregate forma-
tion in water with a hydrodynamic radius of 10-30 nm.
Using the polymer-bound catalysts P1-P3 in the Heck
coupling of iodobenzene and styrene as a model reaction
In the second set of experiments we studied P1-P3
under the same conditions and thus the effect of spacer
length on the catalytic performance. As can be visual-
ized from Figure 5 and Table 3, catalytic transformation
of iodobenzene in the presence of P1 with the butyl
spacer showed a very different kinetic behavior com-
pared to P2 and P3. Catalyst activity as determined
by TOF values is in the case of P1 by a factor of 3.5
lower compared to P2 and P3 (see Table 3). Most likely
-1
gave TOF values of up to 570 h , which are the highest
ever reported for this reaction in neat water without
use of any organic cosolvent. In view of the promising
results, it is expected that the synthetic approach
provides a versatile approach for the synthesis of other
NHC/palladium-functionalized polymers. More detailed

Macromolecules, Vol. 38, No. 2, 2005
Poly(2-oxazoline)s Functionalized with Pd Complexes 259
studies on the catalytic performance of the macroligands
P1-P3 in Heck and Suzuki coupling with various
substrates are currently under investigation.
1-(6-Bromohexyl)-3-methylimidazolium Bromide (1b). Yield
1
1
1.88 g (36.4 mmol, 73%), colorless viscous oil, r
f
) 0.52. H
3
NMR (d -DMSO, 300.13 MHz, 20 °C): δ ) 1.25 (tt, J ) 7.3
6
3
3 3
2
Hz, J ) 7.3 Hz, 2H; CH ), 1.40 (tt, J ) 7.3 Hz, J ) 7.3 Hz,
3
3
2
H; CH
CH CH
J ) 7.1 Hz, 2H; im-CH ), 7.70 (s, 1H; meNCHdCHNalk),
4.15 (t,
2
2
), 1.78 (tt, J ) 6.9 Hz, J ) 6.9 Hz, 4H; im-CH
2
CH
2
,
Experimental Section
3
2
2
Br), 3.52 (t, J ) 6.6 Hz, 2H; CH
2
Br), 3.84 (s, 3H; CH ),
3
Acronyms. alkyl (alk), broad (br), 2-butyl-2-oxazoline (bu-
3
tox), carbene (car), degree of polymerization (Ph
n
), 2-hexyl-2-
), melting
point (mp), methyl (me), 2-methyl-2-oxazoline (metox), 2-octyl-
-oxazoline (octox), oxazoline (ox), piperidine (pip), polydis-
persity index (PDI), refractive index (RI), retention factor (r ).
7.77 (s, 1H; meNCHdCHNalk), 9.14 (s, 1H; NCHN). 13C NMR
(d -DMSO, 75.47 MHz, 20 °C): δ ) 24.8 (CH ), 27.0 (CH ),
oxazoline (hexox), imidazolium (im), mass % (%
m
6
2
2
29.3 (im-CH CH ), 32.1 (CH Br), 35.2 (CH CH Br), 35.9 (CH ),
2
2
2
2
2
3
2
48.8 (im-CH ), 122.4 (meNCHdCHNalk), 123.8 (meNCHdCHNalk),
2
136.7 (NCHN). IR (ATR, substance): ν˜ (cm-1) ) 3056 m (ν
Csp2-H), 2940 s (ν C -H), 2857 m (ν C -H), 1634 w (ν C.C,
f
1
13
Measurements. H (300.13 MHz) and C NMR (75.47
MHz) spectra were recorded on a Bruker ARX 300 spectrom-
eter. FT-IR spectroscopy was carried out on a Bruker IFS 55
spectrometer. Elemental analyses were determined by the
Microanalytical Laboratory of the Inorganic Institute of the
TU M u¨ nchen. Size exclusion chromatography (SEC) was
carried out on a Waters GPC 510 equipped with UV and RI
detectors using poly(styrene) calibration for the poly(2-oxazo-
line) samples in chloroform as solvent. MALDI-TOF measure-
ments were performed on a Bruker Biflex III using chloroform
as solvent and 1,8,9-trihydroxyanthracene (dithranol) as ma-
trix substance. UV-vis spectra were recorded on a Varian
Cary 3 spectrometer. A Jobin Yvon JY 38 plus was used for
ICP-OES measurements, a MLS 1200 mega for microwave
experiments. Gas chromatographic analyses were performed
on a Varian CP-3380, capillary column CP-Sil 8 CB, length
sp3
sp3
ν C.N), 1570 s (ν C.C, ν C.N), 1459 m (δ CH , δ CH ),
2
as
3
1430 m (δ CH , δ CH ), 1378 w (δ CH ) 1248 m, 1165 vs (ν
2
as
3
s
3
C-N), 1092 w, 1020 w, 870 m, 824 m, 752 s, 725 m (γ CH ,
2
(CH ) ), 646 s, 620 vs.
2 ng4
1-(8-Bromooctyl)-3-methylimidazolium Bromide (1c). Yield
1
12.68 g (35.8 mmol, 72%), colorless viscous oil, r ) 0.54. H
f
NMR (d -DMSO, 300.13 MHz, 20 °C): δ ) 1.26 (m, 6H; CH ),
6
2
3
3
1.35 (m, 2H; CH ), 1.77 (tt, J ) 6.9 Hz, J ) 6.9 Hz, 4H; im-
2
3
CH CH , CH CH Br), 3.50 (t, J ) 6.7 Hz, 2H; CH Br), 3.85
2
2
2
2
2
3
(s, 3H; CH ), 4.15 (t, J ) 7.1 Hz, 2H; im-CH ), 7.71 (s, 1H;
3
2
alk
me
alk
me
NCHdCHN ), 7.78 (s, 1H; NCHdCHN ), 9.19 (s, 1H;
1
3
NCHN). C NMR (d -DMSO, 75.47 MHz, 20 °C): δ ) 25.5
6
(CH ), 27.6 (CH ), 28.0 (CH ), 28.3 (CH ), 29.5 (im-CH CH ),
2
2
2
2
2
2
32.3 (CH Br), 35.4 (CH CH Br), 36.0 (CH ), 48.9 (im-CH ),
2
2
2
3
alk
2
me
alk
me
122.4 ( NCHdCHN ), 123.8 ( NCHdCHN ), 136.7 (NCHN).
-
1
2
5 m, with helium in combination with a flame ionization
IR (ATR, substance): ν˜ (cm ) ) 3054 m (ν C -H), 2928 vs
sp2
detector, FID/1177. Melting points were measured using a
Mettler FP51 melting point apparatus. The TEM micrographs
were recorded at the Johannes-Gutenberg Universit a¨ t in
Mainz (Prof. M. Schmidt, Dr. K. Fischer) for this a FEI-Tecnai
F30 ST apparatus was used. The dynamic light scattering
(ν Csp3-H), 2854 s (ν C -H), 1630 w (ν C.C, ν C.N), 1568
sp3
s (ν C.C, ν C.N), 1460 s (δ CH , δ CH ), 1432 m (δ CH ,
2
as
3
2
δ
as
3 s 3
CH ), 1378 w (δ CH ), 1244 m, 1167 vs (ν C-N), 1091 w,
1024 w, 870 m, 828 m, 752 s, 725 s (γ CH , (CH ) ), 648 s,
2
2 ng4
621 vs.
(
DLS) measurements were carried out at the Johannes-
Synthesis of the Dinuclear Palladium Complexes
Gutenberg Universit a¨ t in Mainz (Prof. M. Schmidt, Dr. K.
Fischer) using a Uniphase He/Ne laser (λ ) 632.8 nm, 22 mW),
a ALV-SP 86 Goniometer, a ALV/High QE APD-Avalanche
photodiode with fiber optic detection, a ALV300 correlator, and
a Lauda RC-6 thermostatization unit.
Materials. All chemicals were purchased from Aldrich
Chemical Co., Fluka, and Deutero and used as received, unless
otherwise noted. Water-free solvents were purchased from
Fluka (benzene, DMF) or dried by standard procedures (THF
Na/benzophenone; diethyl ether, KOH molecular sieves 4 Å,
(2a-c). The imidazolium salt (1a-c, 22.3 mmol, 1 equiv),
t
palladium acetate (5.00 g, 22.3 mmol, 1 equiv), KO Bu (2.50
g, 22.3 mmol, 1 equiv), and sodium iodide (26.7 g, 178 mmol,
8 equiv) were stirred in 500 mL of THF at room temperature
overnight. After rotary evaporation of THF, the dark residue
was filtered through silica using ethyl acetate as solvent to
separate the polar byproducts. The resulting raw product was
purified by column chromatography (SiO , ethyl acetate:
2
hexane ) 1:1).
Di-µ-iodobis[1-(4′-iodobutyl)-3-methylimidazoline-2-ylidene]-
dipalladium(II) Diiodide (2a). Yield 8.98 g (7.2 mmol, 65%),
BTS catalyst; HMPT CaH
2
, P
2 5
O ; tetrachloroethane, metox,
1
piperidine CaH
2
) and stored under a dry nitrogen atmosphere
orange-colored solid, mp ) 164.5 °C (( 1.0 °C), r ) 0.56. H
f
3
and molecular sieves, 4 Å.
NMR (d -DMSO, 300.13 MHz, 20 °C): δ ) 1.80 (tt, J ) 7.0
6
3
3
3
Synthesis of the Asymmetric Substituted Imidazolium
Salts (1a-c). A portion of R,ω-dibromoalkane (200 mmol, 4
equiv) in 200 mL of DMF was placed in a 500 mL flask
equipped with a 100 mL addition funnel. To the stirred mix-
ture a solution of 4.11 g (50 mmol, 1 equiv) of N-methylimi-
dazole in 20 mL of DMF was added dropwise within 4 h at 80
Hz, J ) 7.0 Hz, 4H; im-CH
6.9 Hz, 4H; CH CH
(s, 6H; CH ), 4.19 (t, J ) 7.0 Hz, 4H; im-CH
NCHdCHN). C NMR (d
7.6 (CH I), 29.8 (CH CH I), 30.2 (im-CH
(im-CH
2 2
CH ), 2.04 (tt, J ) 6.9 Hz, J )
3
2
2
I), 3.28 (t, J ) 6.9 Hz, 4H; CH
2
I), 3.73
), 7.42 (s, 4H;
-DMSO, 75.47 MHz, 20 °C): δ )
CH ), 38.6 (CH ), 49.5
3
3
2
1
3
6
2
2
2
2
2
me
3
me
alk
alk
2
), 123.0 ( NCHdCHN ), 124.4 ( NCHdCHN ),
-
1
°
C. Stirring was continued for a further 12 h at this temper-
carbene signal not detected. IR (ATR, substance): ν˜ (cm ) )
3122 m (ν Csp2-H), 3031 vw (ν Csp2-H), 2937 s (ν Csp3-H),
2860 m (ν Csp3-H), 1653 m (ν C.C, ν C.N), 1569 m (ν C.C,
ature. The excess amount of R,ω-dibromoalkane can be re-
cycled by fine vacuum distillation. The residue was purified
by column chromatography (SiO
yield the desired imidazolium salt.
-(4-Bromobutyl)-3-methylimidazolium Bromide (1a). Yield
2
, acetone:methanol ) 3:1) to
ν C.N), 1467 s (δ CH
1368 w (δ CH
2 2
1084 m, 1014 w, 728 m (γ CH , (CH )ng4), 669 vs.
2
, δas CH
3 2 3
), 1418 m (δ CH , δas CH ),
), 1261 m, 1228 s, 1204 m, 1170 m, 1117 m,
s
3
1
1
1
0.10 g (33.9 mmol, 68%), colorless viscous oil, r
f
) 0.49. H
Di-µ-iodobis[1-(6′-iodohexyl)-3-methylimidazoline-2-ylidene]-
3
NMR (d -DMSO, 300.13 MHz, 20 °C): δ ) 1.77 (tt, J ) 6.9
6
dipalladium(II) Diiodide (2b). Yield 8.39 g (6.4 mmol, 58%),
3
3
3
1
Hz, J ) 6.7 Hz, 2H; im-CH
.5 Hz, 2H; CH CH Br), 3.55 (t, J ) 6.5 Hz, 2H; CH
s, 3H; CH ), 4.22 (t, J ) 6.9 Hz, 2H; im-CH
2
CH
2
), 1.91 (tt, J ) 6.7 Hz, J )
orange-colored solid, mp ) 144.2 °C (( 1.0 °C), r
f
) 0.64. H
3
6
2
2
2
Br), 3.85
), 7.73 (s, 1H;
NMR (d
6
-DMSO, 300.13 MHz, 20 °C): δ ) 1.36 (m, 8H; CH
2
),
3
3
3
(
3
2
alk
1.77 (tt, J ) 7.2 Hz, J ) 6.8 Hz, 4H; CH
2
CH
2
I), 1.99 (tt,
me
alk
me
3
3
3
NCHdCHN ), 7.80 (s, 1H; NCHdCHN ), 9.21 (s, 1H;
J ) 7.3 Hz, J ) 6.9 Hz, 4H; im-CH
7.2 Hz, 4H; CH I), 3.73 (s, 6H; CH
4H; im-CH ), 7.41 (s, 2H;
2
CH
2
), 3.26 (t, J )
), 4.15 (t, J ) 7.3 Hz,
1
3
3
NCHN). C NMR (d
6
-DMSO, 75.47 MHz, 20 °C): δ ) 28.4
), 28.9 (CH CH Br), 34.3 (CH Br), 36.0 (CH ), 48.0
), 122.4 ( NCHdCHN ), 123.8 ( NCHdCHN ),
2
3
me
alk
(
im-CH
im-CH
2
CH
2
2
2
2
2
3
2
NCHdCHN ), 7.42 (s, 2H;
6
-DMSO, 75.47 MHz, 20 °C): δ
me
alk
me
alk
me
alk 13
(
NCHdCHN ). C NMR (d
) 9.0 (CH I), 25.0 (CH
(CH CH I), 38.5 (CH ), 50.5 (im-CH
124.3 ( NCHdCHN ), carbene signal not detected. IR
-
1
1
C
36.8 (NCHN). IR (ATR, substance): ν˜ (cm ) ) 3057 m (ν
sp2-H), 2951 m (ν Csp3-H), 2860 w (ν Csp3-H), 1634 w (ν
2
2
), 28.6 (CH
2 2
), 29.5 (CH ), 32.9
me
alk
2
2
me
3
2
), 123.0 ( NCHdCHN ),
alk
C.C, ν C.N), 1569 s (ν C.C, ν C.N), 1456 m (δ CH
2
, δas
), 1259 m, 1237
-
1
CH
3
), 1425 m (δ CH
2
, δas CH
3
), 1362 w (δ
s
CH
3
(ATR, substance): ν˜ (cm ) ) 3124 w (ν Csp2-H), 3033 vw (ν
sp2-H), 2930 s (ν Csp3-H), 2855 m (ν Csp3-H), 1653 m (ν
C.C), 1569 m (ν C.N), 1471 s (δ CH , δas CH ), 1418 s (δ
w, 1165 vs (ν C-N), 1090 w, 1022 w, 872 m, 826 m, 764 s, 740
C
s, 644 s, 620 vs.
2
3

260 Sch o¨ nfelder et al.
Macromolecules, Vol. 38, No. 2, 2005
3
CH
w, 1124 w, 1083 m, 1016 m, 803 m, 730 vs (γ CH
70 vs.
Di-µ-iodobis[1-(8′-iodooctyl)-3-methylimidazoline-2-ylidene]-
dipalladium(II) Diiodide (2c). Yield 9.45 g (6.9 mmol, 62%),
2
, δas CH
3
), 1368 w (δ
s
CH
3
), 1262 m, 1222 m, 1193 m, 1166
(s, 3H; alk-car-CH
3
), 4.22 (t, J ) 7.4 Hz, 2H; im-CH
2
), 7.27
me
me
me
alk
2
, (CH
2
)
ng4),
(s, 3H;
NCHdCHN
,
NCHdCHN ), 7.29 (s, 1H;
-DMSO, 75.47 MHz, 20 °C): δ
), 27.9 (CH ), 28.6 (CH ), 29.7 (CH ),
CH I), 37.4 (CH ), 37.6 (CH ), 37.8 (CH ),
me
alk 13
6
NCHdCHN ). C NMR (d
) 9.2 (CH I), 26.1 (CH
29.9 (CH ), 33.0 (CH
6
2
2
2
2
2
2
2
2
3
alk
3
3
me
1
me
me
orange-colored solid, mp ) 121.6 °C (( 1.0 °C), r
f
) 0.69. H
2
50.2 (im-CH ), 121.9 ( NCHdCHN ), 122.9 ( NCHdCHN ,
meNCHdCHN ), 166.6, 166.8 (meNCN
alk
me
,
me
NCN ). IR
alk
NMR (d
6
-DMSO, 300.13 MHz, 20 °C): δ ) 1.31 (m, 16H; CH ),
2
3
3
3
-1
1
.76 (tt, J ) 6.9 Hz, J ) 6.9 Hz, 4H; CH
2
CH
2
I), 1.92 (tt, J
(ATR, substance): ν˜ (cm ) ) 3124 vw (ν Csp2-H), 3053 w (ν
3
3
)
7.3 Hz, J ) 7.0 Hz, 4H; im-CH
2
CH
2
), 3.25 (t, J ) 6.9
C
sp2-H), 2932 m (ν Csp3-H), 2856 w (ν Csp3-H), 1653 w (ν
C.C, ν C.N), 1576 m (ν C.C, ν C.N), 1471 s (δ CH , δas
CH ), 1419 m (δ CH , δas CH ), 1264 vs, 1225 s, 1078 m, 1014
w, 896 m, 731 vs (γ CH , (CH ng4), 694 vs.
3
Hz, 4H; CH
2
I), 3.72 (s, 6H; CH ), 4.14 (t, J ) 7.3 Hz, 4H;
3
2
me
alk
im-CH
2
), 7.40 (s, 2H;
NCHdCHN ), 7.41 (s, 2H;
NCHdCHNalk). C NMR (d
-DMSO, 75.47 MHz, 20 °C): δ
9.2 (CH I), 25.9 (CH ), 27.8 (CH ), 28.4 (CH ), 28.7 (CH ),
9.9 (CH ), 33.0 (CH CH I), 38.5 (CH ), 50.6 (im-CH ), 122.9
NCHdCHN ), 124.2 ( NCHdCHN ), carbene signal not
3
2
3
me
13
6
2
2
)
)
2
2
2
2
2
Synthesis of the Complex Functionalized 2-Oxazoline
Monomers (4a-c). A portion of 2.5 mL of LDA (2 m solution
in hexane, 5.0 mmol, 1.25 equiv) and 10 mL of THF were
placed in a 50 mL flask equipped with a 20 mL addition funnel.
2
2
2
2
me
3
2
me
alk
alk
(
-
1
detected. IR (ATR, substance): ν˜ (cm ) ) 3124 w (ν Csp2-H),
032 vw (ν Csp2-H), 2930 s (ν Csp3-H), 2852 s (ν Csp3-H), 1653
3
To the solution, which was cooled to -78 °C by a CO
2
w (ν C.C, ν C.N), 1569 m (ν C.C, ν C.N), 1470 s (δ CH
2
,
(s)/acetone bath, was added dropwise 0.51 g (6.0 mmol, 1.5
equiv) of 2-methyl-2-oxazoline in 6 mL of THF within 20 min.
The resulting reaction mixture was stirred for 2 h at -60 °C.
Then 4.0 mmol (1 equiv) of the precursor (3a-c) dissolved in
a mixture of 6 mL of THF and 6 mL of hexamethylphosphoric
acid triamide (HMPT) was added dropwise within 20 min at
-78 °C. The mixture was warmed to -50 °C and stirred for a
further 2 h. Afterward the solution was warmed to room
temperature overnight, and the solvent was separated by
rotary evaporation. The residue was purified by column
δ
as CH
3
), 1418 s (δ CH
2 3 s 3
, δas CH ), 1368 w (δ CH ), 1263 s,
1
221 s, 1204 m, 1182 m, 1117 w, 1082 m, 1015 m, 801 m, 731
vs (γ CH
2 2
, (CH )
ng4), 670 vs.
Synthesis of the Mononuclear Palladium Complexes
(3a-c). In a glovebox the dinuclear complex (2a-c, 5 mmol,
1
equiv) was dissolved in 250 mL of THF and stirred at room
temperature. Then 0.96 g (10 mmol, 2 equiv) of 1,3-dimeth-
ylimidazoline-2-ylidene in 50 mL of THF was added dropwise
within 1 h. Stirring was continued for a further 30 min. After
rotary evaporation of the solvent, the yellow residue was
purified by column chromatography (SiO , ethyl acetate:
2
hexane ) 1:1).
chromatography (SiO
dried using benzene.
2 3
, ethyl acetate:NEt ) 15:1) and freeze-
Monomer 4a. Yield 1.40 g (2.1 mmol, 52%), pale yellow-
1
[
1-(4′-Iodobutyl)-3-methylimidazoline-2-ylidene](1,3-dimeth-
colored solid, r
f
) 0.24. H NMR (d
6
-DMSO, 300.13 MHz, 20
), 1.60 (tt,
3
3
ylimidazoline-2-ylidene)palladium(II) Diiodide (3a). Yield 4.16
°C): δ ) 1.36 (tt, J ) 7.6 Hz, J ) 7.3 Hz, 2H; CH
2
3
3
3
g (5.8 mmol, 58%), citrus-colored solid, mp ) 208.0 °C (( 1.0
J ) 7.5 Hz, J ) 7.3 Hz, 2H; CH
2
CH
), 2.20 (t, J ) 7.3 Hz, 2H;
), 3.78 (s, 6H;
2
-ox), 2.01 (tt, J ) 7.5
1
3
3
°
C), r
f
) 0.52. H NMR (d
6
-DMSO, 300.13 MHz, 20 °C): δ )
Hz, J ) 7.3 Hz, 2H; im-CH
2
CH
2
3
3
3
1
.80 (tt, J ) 7.1 Hz, J ) 7.1 Hz, 2H; im-CH
2
CH
2
), 2.13 (tt,
CH
2
-ox), 3.67 (t, J ) 9.4 Hz, 2H; dNCH
-car-CH ), 3.81 (s, 3H; alk-car-CH ), 4.14 (t, J ) 9.4
), 4.22 (t, J ) 7.5 Hz, 2H; im-CH ), 7.27 (s,
NCHdCHN ), 7.29 (s, 1H;
NCHdCHN ). C NMR (d -DMSO, 75.47 MHz, 20 °C): δ
) 25.3 (CH ), 25.8 (CH ), 27.3 (im-CH CH ), 29.5 (CH -ox), 37.4
(CH ), 37.6 (CH ), 37.8 (CH ), 50.0 (im-CH ), 54.0 (dNCH ),
66.7 (OCH ), 122.0 ( NCHdCHN ), 122.9 ( NCHdCHN
2
3
3
3
3
J ) 7.2 Hz, J ) 7.2 Hz, 4H; CH
2
CH
3
2
I), 3.27 (t, J ) 7.2 Hz,
CH
3
3
3
3
2
4
7
H; CH
2
3
I), 3.79 (s, 6H; CH
3
-car-CH
), 3.82 (s, 3H; alk-car-CH
3
),
Hz, 2H; OCH
2
2
me
me
me
me
me
alk
.27 (t, J ) 7.1 Hz, 2H; im-CH
2
), 7.27 (s, 2H; NCHdCHN ),
3H;
NCHdCHN ,
me
alk
me
alk
me
alk 13
.29 (s, 1H; NCHdCHN ), 7.31 (s, 1H; NCHdCHN ).
6
13
C NMR (d
CH ), 30.5 (CH
im-CH ), 122.0 ( NCHdCHN ), 122.9 ( NCHdCHN
6
-DMSO, 75.47 MHz, 20 °C): δ ) 7.8 (CH
2
I), 30.3
2
2
2
2
2
(
(
2
2
), 37.5 (CH ), 37.6 (CH ), 37.9 (CH
3
3
3
), 49.0
3
3
3
2
2
me
alk
me
me
me
me
alk
me
me
2
,
2
,
me
alk
me me
alk
me
alk
me
me me
NCNalk,
NCHdCHN ), 166.6, 166.9 ( NCN
,
NCN ). IR (ATR,
substance): ν˜ (cm ) ) 3115 w (ν Csp2-H), 3032 vw (ν
sp2-H), 2935 m (ν Csp3-H), 2860 m (ν Csp3-H), 1653 w (ν
C.C, ν C.N), 1592 m (ν C.C, ν C.N), 1466 s (δ CH , δas
CH ), 1401 m (δ CH , δas CH ), 1376 w (δ CH ), 1264 s, 1223
s, 1175 m, 1110 m, 1077 m, 1011 w, 830 w, 734 s (γ CH
CH ng4), 696 vs.
1-(6′-Iodohexyl)-3-methylimidazolium-2-ylidene](1,3-di-
NCHdCHN ), 166.3, 166.8, 166.9 ( NCN
,
-
1
-1
OCN). IR (ATR, substance): ν˜ (cm ) ) 3115 w (ν Csp2-H),
3038 vw (ν Csp2-H), 2933 m (ν Csp3-H), 2868 w (ν Csp3-H),
1663 s (ν CdN, ν C.C, ν C.N), 1568 m (ν C.C, ν C.N),
C
2
3
2
3
s
3
1466 s (δ CH
2 3 2 3
, δas CH ), 1400 m (δ CH , δas CH ), 1265
2
,
m, 1223 s, 1077 m (νas C-O-C), 985 m (ν C-O-C), 958
s
(
2
)
m (ν
s
C-O-C), 730 vs (γ CH
2
, (CH
2
)ng4), 695 s. MALDI-TOF
+
[
(m/z): found 679.18, 550.59; calcd. 677.94 (M + H
)
+
-
+
methylimidazoline-2-ylidene)palladium(II) Diiodide (3b). Yield
17 28 2 5 27 1 5
C H I N OPd ), 550.03 (M - I ) C17H I N OPd ). Anal.
5
1
)
.02 g (6.7 mmol, 67%), citrus-colored solid, mp ) 193.8 °C ((
Calcd: C, 30.13; H, 4.02; I, 37.45; N, 10.33; Pd, 15.70. Found:
C, 30.57; H, 4.21; I, 36.98; N, 10.02; Pd, 15.88.
1
.0 °C), r
f
) 0.57. H NMR (d
6
-DMSO, 300.13 MHz, 20 °C): δ
3
3
1.37 (m, 4H; CH
2
), 1.76 (tt, J ) 7.2 Hz, J ) 6.7 Hz, 2H;
Monomer 4b. Yield 1.54 g (2.2 mmol, 55%), pale yellow-
3
3
1
CH
2
CH
2
I), 2.00 (tt, J ) 7.3 Hz, J ) 6.9 Hz, 2H; im-CH
2
CH
-car-CH
), 4.23 (t, J ) 7.3 Hz, 2H; im-CH
2
),
),
),
colored solid, r
f
) 0.31. H NMR (d
6
-DMSO, 300.13 MHz, 20
3
3
3
3
3
7
.26 (t, J ) 6.9 Hz, 2H; CH
.81 (s, 3H, alk-car-CH
2
I), 3.79 (s, 6H; CH
3
3
°C): δ ) 1.31 (m, 6H; CH ), 1.51 (tt, J ) 7.3 Hz, J ) 7.3 Hz,
2
3
3 3
3
2
2H; CH
CH CH
Hz, 2H; dNCH
car-CH ), 4.12 (t, J ) 9.3 Hz, 2H; OCH
2H; im-CH
2
CH
), 2.16 (t, J ) 7.3 Hz, 2H; CH
), 3.78 (s, 6H; CH -car-CH
), 4.22 (t, J ) 7.4 Hz,
2
-ox), 1.99 (tt, J ) 7.4 Hz, J ) 7.4 Hz, 2H; im-
me
me me
alk
3
3
.28 (s, 3H; NCHdCHN
,
NCHdCHN ), 7.31 (s, 1H;
-DMSO, 75.47 MHz, 20 °C): δ
), 29.6 (CH ), 29.6 (CH ), 32.9 (CH CH I),
), 37.6 (CH ), 37.8 (CH ), 50.2 (im-CH ), 121.9
2
2
2
-ox), 3.66 (t, J ) 9.3
), 3.81 (s, 3H; alk-
me
alk 13
NCHdCHN ). C NMR (d
6
2
3
3
3
3
)
9.1 (CH I), 25.2 (CH
2
2
2
2
2
2
3
2
me
me me
alk
3
7.5 (CH
3
3
3
2
2
me
), 7.27 (s, 3H; NCHdCHN
,
NCHdCHN ),
-DMSO, 75.47 MHz,
), 27.3 (CH CH -ox), 28.4
-ox), 37.4 (CH ), 37.6 (CH ), 37.9
), 54.0 (dNCH ), 66.7 (OCH ), 121.9
me
alk
me
me me
alk
7.29 (s, 1H; NCHdCHNalk). C NMR (d
13
(
NCHdCHN ), 122.9 ( NCHdCHN
,
NCHdCHN ),
6
me
me me
alk
1
66.6, 166.8 ( NCN
,
NCN ). IR (ATR, substance): ˜ν
20 °C): δ ) 25.7 (CH
2
), 26.1 (CH
), 29.7 (CH
), 50.2 (im-CH
2
2
2
-
1
(
in cm ) ) 3115 w (ν Csp2-H), 3052 w (ν Csp2-H), 2932 m (ν
sp3-H), 2855 w (ν Csp3-H), 1653 w (ν C.C, ν C.N), 1559 m
, δas CH ), 1419 m (δ CH
), 1264 s, 1225 m, 1170 w, 1112 w, 1078
, (CH ng4), 694 vs.
(CH
2
), 28.6 (CH
2
2
3
3
C
(CH
3
2
2
2
me
alk
me
me me
alk
(
ν C.C, ν C.N), 1466 s (δ CH
2
3
2
, δas
(
NCHdCHN ), 122.9 ( NCHdCHN
,
NCHdCHN ),
me
me me
alk
CH
3
), 1378 w (δ
s
CH
3
166.6, 166.8, 166.9 ( NCN ,
NCN , OCN). IR (ATR,
-
1
m, 1012 w, 895 w, 733 vs (γ CH
2
2
)
substance): ν˜ (cm ) ) 3054 w (ν Csp2-H), 2977 w (ν Csp3-H),
2943 m (ν Csp3-H), 2869 m (ν Csp3-H), 1660 s (ν CdN, ν C.C,
[
1-(8′-Iodooctyl)-3-methylimidazolium-2-ylidene](1,3-dimeth-
ylimidazoline-2-ylidene)palladium(II) Diiodide (3c). Yield 4.21
2 3
ν C.N), 1558 m (ν C.C, ν C.N), 1489 s (δ CH , δas CH ),
g (5.4 mmol, 54%), citrus-colored solid, mp ) 207.8 °C (( 1.0
C), r
1457 m (δ CH
(νas C-O-C), 990 m (ν
730 vs (γ CH , (CH ng4), 695 vs. MALDI-TOF (m/z): found
707.78, 578.59; calcd 705.98 (M + H ) C19
2
, δas CH
3
), 1264 vs, 1227 m, 1171 m, 1080 m
1
°
1
f
) 0.64. H NMR (d
6
-DMSO, 300.13 MHz, 20 °C): δ )
s
C-O-C), 956 m (ν C-O-C), 896 m,
s
3
3
.31 (m, 8H; CH
CH CH I), 1.99 (tt, J ) 7.4 Hz, J ) 6.9 Hz, 2H; im-CH
.25 (t, J ) 7.2 Hz, 2H; CH
2
), 1.73 (tt, J ) 7.2 Hz, J ) 7.2 Hz, 2H;
2
2
)
3
3
+
+
2
2
3
2
CH
2
),
H
32
I
2
N
5
OPd ),
-
+
3
2
I), 3.79 (s, 6H; CH
3
-car-CH
3
), 3.81
578.06 (M - I ) C19H I N OPd ). Anal. Calcd: C, 32.34; H,
31 1 5

Macromolecules, Vol. 38, No. 2, 2005
Poly(2-oxazoline)s Functionalized with Pd Complexes 261
3
4
3
.43; I, 35.96; N, 9.92; Pd, 15.08. Found: C, 32.62; H, 4.68; I,
5.04; N, 10.02; Pd, 15.44.
pip-C H
2
), 1.97 (sbr; car-CH
, COCH ), 2.32 (sbr; pip-C H
group, ZCH3,CdO), 3.02 (s; CH
2 2
CH ), 2.05, 2.08, 2.11 (s, s, s;
2
COCH
3
2
2 3
), 2.92 (s; CH -end
Monomer 4c. Yield 1.36 g (1.9 mmol, 46%), pale yellow-
3
-end group, ECH3,CdO), 3.43 (sbr
;
1
3
colored solid, r
f
) 0.40. H NMR (d
6
-DMSO, 300.13 MHz,
), 1.31 (sbr, 4H; CH ), 1.50
-ox), 1.99 (m, 2H; im-CH CH ), 2.16 (t, J )
-ox), 3.66 (t, J ) 9.4 Hz, 2H; dNCH
-car-CH ), 3.81 (s, 3H; alk-car-CH
), 4.22 (t, J ) 7.5 Hz, 2H; im-CH
CH
CH
2
-backbone), 3.91 (sbr; car-CH
3
), 4.29 (t, J ) 7.0 Hz; car-
1
3
2
0 °C): δ ) 1.25 (sbr, 6H; CH
m, 2H; CH CH
.4 Hz, 2H; CH
.78 (s, 6H; CH
2
2
2
), 6.85 (sbr; NCHdCHN). C NMR (CDCl
), 21.1 (metox-COCH
), 28.7-29.3 (CH ), 31.5-31.7
), 38.2-38.4 (car-CH ), 43.4-44.2 (CH -back-
bone), 44.9-45.5 (CH -backbone), 46.5-47.2 (CH -back-
bone), 47.4-48.1 (CH -backbone), 51.1 (car-CH ), 122.2-122.4
(NCHdCHN), 170.6-171.7 (CdO). UV-vis (H O, c ) 0.2 g‚L
3
, 75.47 MHz, 20
3
(
2
2
2
2
°C), signal groups: δ ) 14.1 (hexox-CH
22.5 (CH ), 24.9-25.6 (CH
(COCH , CH
3
3
),
3
7
2
2
),
),
2
2
2
3
3
3
3
), 4.12 (t,
2
2
3
2
3
3
J ) 9.4 Hz, 2H; OCH
2
2
2
2
me
me me
alk
7
.26 (s, 3H; NCHdCHN
,
NCHdCHN ), 7.28 (s, 1H;
-DMSO, 75.47 MHz, 20 °C): δ
), 27.3 (CH ), 28.7 (CH ), 28.8 (CH ),
), 29.8 (CH ), 37.4 (CH ), 37.6 (CH ), 37.8
), 54.0 (dNCH ), 66.7 (OCH ), 121.9
2
2
me
alk 13
-1
NCHdCHN ). C NMR (d
25.6 (CH ), 26.3 (CH
), 29.0 (CH
), 50.2 (im-CH
6
2
,
2
-1
)
2
2
2
2
2
d ) 1 cm): block copolymer λ (ꢀ in cm ‚mmol ) ) 200-244
(>20 000; polymer), 262 (15 900; car), 302 (18 600; PdI ), 330
(7300) to 410 (600), 460-900 (<300); hydrophilic block
λ (ꢀ) ) 200-226 (>20 000; polymer), 262 (1300), 300 (700),
380-900 (<300).
2
8.8 (CH
2
2
2
3
3
2
S
(
(
CH
3
2
2
2
S
me
alk
me
me me
alk
NCHdCHN ), 122.9 ( NCHdCHN
,
NCHdCHN ),
NCN , OCN). IR (ATR,
substance): ν˜ (cm ) ) 3053 w (ν Csp2-H), 2985 w (ν Csp3-H),
932 m (ν Csp3-H), 2855 w (ν Csp3-H), 1670 s (ν CdN, ν C.C,
ν C.N), 1559 s (ν C.C, ν C.N), 1489 s (δ CH , δas CH ),
), 1264 vs, 1227 m, 1163 m, 1078 m
C-O-C), 956 w (ν C-O-C), 896 m,
ng4), 702 vs MALDI-TOF (m/z): found
me
me me
alk
1
66.7, 166.8, 166.9 ( NCN ,
-1
P3. Yield 0.63 g (88%), citrus-colored solid. Ph (determined
n
1
2
by H NMR end-group analysis): (metox) [(4c)1.9(octox) ]
30.4 3.4 stat.
-
1
2
3
n 3
( Mh ) 4730 g‚mol ). SEC (CHCl , RI, poly(styrene) calibra-
1
-
-1
1
457 m (δ CH
as C-O-C), 990 m (ν
31 vs (γ CH , (CH
35.92, 606.65; calcd 734.01 (M + H ) C21
2
, δas CH
3
n w
tion): hydrophilic block Mh ) 1330 g‚mol , Mh ) 1760 g‚mol ,
1
-
(
ν
s
s
n w
PDI ) 1.32; block copolymer Mh ) 2970 g‚mol , Mh ) 4140
1 1
-
7
7
6
4
3
2
2
)
g‚mol , PDI ) 1.39. ICP-OES (Pd): 3.6% , Ph (4c) ) 1.6. H
m
n
+
+
3
H
36
I
2
N
5
OPd ),
NMR (CDCl , 300.13 MHz, 20 °C): δ ) 0.84 (t, J ) 6.1 Hz;
3
-
+
06.09 (M - I ) C21
H
35
I
1
N
5
OPd ). Anal. Calcd: C, 34.37; H,
octox-CH ), 1.25 (s ; CH ), 1.34 (s ; CH ), 1.56 (s ; COCH CH ,
3
br
2
br
2
br
2
2
3
.81; I, 34.59; N, 9.54; Pd, 14.50. Found: C, 34.82; H, 4.94; I,
4.04; N, 9.82; Pd, 14.38.
Synthesis of the Polymers (P1-P3). In a polymerization
2 br 2 2
pip-C H ), 2.00 (s ; car-CH CH ), 2.05, 2.08, 2.11 (s, s, s;
2
COCH , COCH ), 2.30 (s ; pip-C H ), 2.92 (s; CH -end
3
2
br
2
3
group, ZCH3,CdO), 3.02 (s; CH
3
-end group, ECH3,CdO), 3.43 (sbr
;
3
vessel 1 equiv of methyl triflate was dissolved in tetrachloro-
ethane so that the final concentration of methyl triflate is
about 30-40 mm. To this solution 30 equiv of 2-methyl-2-
oxazoline was added at room temperature. The reaction
mixture was stirred at 80 °C for 12 h. At room temperature
the metal-complex-functionalized monomer (4a-c, 2.5 equiv)
as well as the corresponding unfunctionalized 2-alkyl-2-
oxazoline (2.5 equiv) were added. The clear solution was stirred
at 60 °C for an additional 24 h. At room temperature 1.25 equiv
of piperidine was added as terminating reagent, and the
mixture was stirred for 3 h. Afterward 30 equiv of fine-ground
potassium carbonate was added, and the suspension was
stirred for 4 h. After filtration, the polymer was purified by
reprecipitation (diethyl ether) and dialysis using a membrane
CH
CH
2
-backbone), 3.90 (sbr; car-CH
3
), 4.29 (t, J ) 7.1 Hz; car-
1
3
2
), 6.85 (sbr; NCH)CHN). C NMR (CDCl
), 21.0-21.3 (metox-
), 26.8 (CH ), 29.1-29.5
), 38.2 - 38.5 (car-CH ), 43.4-43.9
-backbone), 44.8-45.7 (CH -backbone), 46.3-47.2
-backbone), 47.5-48.1 (CH -backbone), 51.1-51.3 (car-
3
, 75.47 MHz, 20
°C), signal groups: δ ) 14.1 (octox-CH
COCH ), 22.6 (CH ), 25.2-25.5 (CH
), 31.8 (COCH , CH
3
3
2
2
2
(CH
(CH
(CH
2
2
2
2
2
3
2
2
CH
2
), 122.2-122.5 (NCHdCHN), 170.6-171.5 (CdO).
-
1
UV-vis (H
2
O, c ) 0.2 g‚L , d ) 1 cm): block copolymer λ (ꢀ
2
-1
in cm ‚mmol ) ) 200-247 (>20 000; polymer), 262 (17 400;
S
car), 302 (16 300; PdI ), 330 (7100) to 410 (700), 570-900
2
S
(<300); hydrophilic block λ (ꢀ) ) 200-226 (>20 000; polymer),
262 (1300), 300 (700), 380-900 (<300).
ICP-OES Measurements. Aqua regia (3.0 mL) was added
to the supported catalyst (10.0 mg). The mixture was placed
inside high-pressure Teflon tubes, and leaching was carried
out under microwave conditions (50, 600, and 450 W pulses,
respectively, t ) 32 min). After cooling to room temperature,
the mixture was filtered and measured by ICP-OES for Pd
(λ ) 340.458 nm, atom line). The background was measured
at λ ) 340.4163 and 340.4997 nm.
-
1
(
molar mass cutoff at 1000 g‚mol ) and tetrachloroethane as
solvent to remove the low molecular weight byproducts, which
are insoluble in diethyl ether.
P1. Yield 0.59 g (83%), citrus-colored solid. Ph
n
(determined
1
by H NMR end-group analysis): (metox)28.4[(4a)1.5(butox)2.9
]
stat.
) 3920 g‚mol- ). SEC (CHCl
1
, RI, poly(styrene) calibra-
(
Mh
tion): hydrophilic block Mh
PDI ) 1.35; block copolymer Mh
n
3
-1
-1
n
) 1380 g‚mol , Mh
w
) 1870 g‚mol ,
-
1
n
) 2410 g‚mol , Mh
g‚mol , PDI ) 1.32. ICP-OES (Pd): 3.3% , Ph
, 300.13 MHz, 20 °C): δ ) 0.88 (tbr; butox-CH
), 1.40 (sbr; CH ), 1.54 (sbr; COCH CH ), 1.67 (sbr
CH ), 2.05, 2.08, 2.11 (s, s, s;
), 2.32 (sbr; pip-C H
group, ZCH3, CdO), 3.02 (s; CH -end group, ECH3,CdO), 3.43 (sbr
CH -backbone), 3.91 (sbr; car-CH ), 4.30 (tbr; car-CH ), 6.86 (sbr
NCHdCHN). C NMR (CDCl , 75.47 MHz, 20 °C), signal
groups: δ ) 13.9 (butox-CH ), 21.1-21.7 (COCH ), 22.5 (CH ),
7.2-27.5 (CH ), 29.6 (CH ), 32.2 (COCH ), 38.1-38.4 (car-
CH ), 43.4-44.2 (CH -backbone), 44.9-45.6 (CH -backbone),
6.5-47.2 (CH -backbone), 47.3-48.3 (CH -backbone), 52.4
car-CH ), 122.2-122.4 (NCHdCHN), 170.4-171.4 (CdO).
UV-vis (H
w
) 3190
Micellar Catalysis. Catalysis Experiments. All catalysis
experiments were carried out under argon in 50 mL reaction
tubes. In 10 mL of degassed water a portion of the polymer
-
1
1
m
n
(4a) ) 1.2. H
),
NMR (CDCl
3
3
1
.31 (sbr; CH
2
2
2
2
;
(
P1-P3) was dissolved so that the concentration of the
3
pip-C H
2
), 1.90 (sbr; car-CH
2
2
polymer is about 0.1-0.6 mm. Iodobenzene, potassium carbon-
2
COCH
3
, COCH
2
2 3
), 2.92 (s; CH -end
ate as base, and tetradecane as internal standard were added
3
;
(
2 3
iodobenzene:styrene:K CO ) 1:1.25:1.5). The mixture was
2
3
2
;
stirred and heated to the respective reaction temperature.
Then catalysis was started by adding styrene. The course of
the reaction was monitored by periodically taking samples and
analyzing them by means of gas-chromatographic analysis.
Recycling Experiments. After a reaction time of 5 h, the
reaction vessel was cooled to room temperature using an ice/
water cooling bath. Afterward a portion of 10 mL of degassed
diethyl ether was added. For extraction of the products and
potential residues of the starting compounds, the vessel was
agitated for 15 min. After a waiting period of at least 2 h,
nearly complete phase separation occurs. Then the organic
phase was removed using a syringe and analyzed by gas
chromatography. The remaining aqueous phase is still cata-
lytically active and was reused for the next runs in the same
manner as that described above.
1
3
3
3
3
2
2
2
2
2
3
2
2
4
(
2
2
2
-
1
2
O, c ) 0.2 g‚L , d ) 1 cm): block copolymer λ (ꢀ
2
-1
in cm mmol ) ) 200-243 (>20 000; polymer), 262 (13 000;
car), 300 (15 800; PdI ), shoulder: 330 (6000) to 410 (520),
40-900 (<300); hydrophilic block λ (ꢀ) ) 200-226 (>20 000;
polymer), 262 (1300), 300 (700), 380-900 (<300).
P2. Yield 0.56 g (84%), citrus-colored solid. Ph
2
4
n
(determined
1
by H NMR end-group analysis): (metox)29.9[(4b)1.8(hexox)3.2
]
stat.
) 4400 g‚mol- ). SEC (CHCl
1
, RI, poly(styrene) calibra-
(
Mh
tion): hydrophilic block Mh
PDI ) 1.33; block copolymer Mh
n
3
-1
-1
n
) 1260 g‚mol , Mh
w
) 1680 g‚mol ,
-
1
n
w
) 2790 g‚mol , Mh ) 3770
1
References and Notes
-
1
g‚mol , PDI ) 1.35. ICP-OES (Pd): 3.6%
NMR (CDCl , 300.13 MHz, 20 °C): δ ) 0.85 (t, J ) 6.1 Hz;
2
hexox-CH ), 1.26 (sbr; CH ), 1.36 (sbr; CH ), 1.56 (sbr; COCH CH ,
m n
, Ph (4b) ) 1.5. H
3
3
(1) For reviews, see: (a) Kollhofer, A.; Plenio, H. Chem Eur. J.
2003, 9 (6), 1416. (b) Osburn, P. L.; Bergbreiter, D. E. Prog.
3
2
2
2

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Macromolecules, Vol. 38, No. 2, 2005
Polym. Sci. 2001, 26 (10), 2015. (c) Toy, P. H.; Tanda, K. D.
Acc. Chem. Res. 2000, 33, 546. (d) Gravert, D. J.; Janda, K.
D. Chem. Rev. 1997, 97, 489. (e) Dickerson, T. J.; Reed, N.
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H.; Tanda, K. D. Acc. Chem. Res. 2000, 33 (3), 546. (g)
Leadbeater, N. E.; Marco, M. Chem. Rev. 2002, 102 (10), 3217.
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(
h) van Heerbeek, R.; Kamer, P. C. J.; Piet, W. N. M.; van
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Rev. 2002, 102 (10), 3717. (i) Fan, Q.-H.; Li, Y.-M.; Chan, A.
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(
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(
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2) For examples see: (a) Aqueous Phase Organometallic Ca-
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(
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(
(
1997, 116, 217. (b) Cornils, B.; Herrmann, W. A.; Eckl, R. W.
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