Palladium Nanoparticles Supported on Poly(N-vinyl- imidazole-co-N-vinylcaprolactam) as an Effective Recyclable Catalyst for the Suzuki Reaction

Article abstract of DOI:10.1002/cplu.201402111

A recyclable and effective polymer-immobilized ligandless palladium catalyst for the Suzuki reaction has been investigated. Palladium nanoparticles are formed in situ and stabilized by poly(N-vinylimidazole-co-N-vinylcaprolactam). A series of aryl bromides have been studied in the reaction with phenylboronic acid under mild conditions with water-alcohol systems as a solvent that complies with "Green Chemistry" demands. The catalyst can be recycled eight times without appreciable loss in activity and a low degree of palladium leaching. Kinetic studies reveal unusual behavior of the reaction; this can be explained on the basis of the observation of changes to the sizes of the particles during recycling, as determined by TEM results. The suggested mechanism of the reaction is in accordance with the concept of the role of leaching in the process. Fast or slow? Palladium nanoparticles immobilized on poly(N-vinylimidazole-co-N-vinylcaprolactam) reveal unusual kinetic behavior in the Suzuki reaction. This can be explained on the basis of the observation of changes to the sizes of the particles during recycling, and is in accordance with the concept of leaching during the process.

Full text of DOI:10.1002/cplu.201402111

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DOI: 10.1002/cplu.201402111
Palladium Nanoparticles Supported on Poly(N-vinyl-
imidazole-co-N-vinylcaprolactam) as an Effective
Recyclable Catalyst for the Suzuki Reaction
Alexandra V. Selivanova,[a] Vladimir S. Tyurin,[a] and Irina P. Beletskaya*[a, b]
A recyclable and effective polymer-immobilized ligandless pal-
ladium catalyst for the Suzuki reaction has been investigated.
Palladium nanoparticles are formed in situ and stabilized by
poly(N-vinylimidazole-co-N-vinylcaprolactam). A series of aryl
bromides have been studied in the reaction with phenylboron-
ic acid under mild conditions with water–alcohol systems as
a solvent that complies with “Green Chemistry” demands. The
catalyst can be recycled eight times without appreciable loss
in activity and a low degree of palladium leaching. Kinetic
studies reveal unusual behavior of the reaction; this can be ex-
plained on the basis of the observation of changes to the sizes
of the particles during recycling, as determined by TEM results.
The suggested mechanism of the reaction is in accordance
with the concept of the role of leaching in the process.
Introduction
The Suzuki reaction (Nobel Prize in Chemistry, 2010)[1] is the
mostly widely utilized cross-coupling technique for the synthe-
sis of biaryls and other compounds with Csp2ÀCsp2 bonds.[2] It is
also used as a model reaction (as the Heck reaction) to test
palladium catalysts for their activity with different ligands
under various conditions.[3] There have been attempts to re-
place relatively expensive palladium by cheaper alternatives,
such as nickel,[4] but the major trend is to increase the efficien-
cy of palladium catalysts and to decrease cost by multiple re-
cycling steps. Recently, the focus of investigations into cata-
lysts has shifted to the field of nanocatalysis, that is, catalysis
by palladium nanoparticles (PdNPs), obtained by various meth-
ods and differently stabilized[5] (on solid supports, polymers,
dendrimers, ionic liquids, etc.). The tremendous number of
studies have resulted in a great variety of protocols, and some
of them have achieved very interesting and useful results.[6]
PdNPs possess activity that is often comparable to that of ho-
mogeneous complexes, and even higher sometimes, especially
when using phosphine-functionalized polymers.[7] However,
the advantage of PdNPs over homogeneous complexes is the
ability to function without toxic phosphine ligands, even at
the expense of activity. Additionally, PdNPs are capable of
being recycled (allowing the catalyst to be separated from the
products used multiple times). This allows us to approach the
“ideal” catalyst in the context of Green Chemistry.
of catalysis, although there are many reports providing solid
arguments in its favor.[8] One of them was based on a very in-
teresting investigation into PdNPs on several supports by
using differences in their selectivity.[8j] Numerous other reports
attempted to prove the opposite, namely, that “leaching” was
responsible for catalysis and PdNPs provide molecular species,
which form the true catalyst, that are homogeneous in na-
ture.[5b, 9]
Surprisingly, different authors came to the opposite conclu-
sions regarding the mechanisms, even upon using the same
catalyst.[8e,10] The issues of the first stage of the reaction and
causes of possible “leaching ” are also disputed. In our opinion,
it proceeds through heterogeneous palladium oxidation by
ArHal on the surface of PdNPs.[11] Subsequent leaching could
lead to numerous kinds of species ranging from monoatomic
palladium complexes through a number of palladium clusters
to PdNPs of different sizes and shapes. Such a variety of states
that are intermediate between homogeneous and heterogene-
ous are called microheterogeneous; this hardly makes it possi-
ble to finalize a conclusion of the true mechanism, although
one could certainly exclude the extreme points, such as
atomic-level homogeneous and macro-level heterogeneous.
A clear understanding of the mechanism of PdNP-catalyzed
reactions is essential for the development of recyclable cata-
lysts. One of the major problems to solve is deactivation of the
catalyst associated with changes to the PdNPs during the reac-
tion.[11]
However, the use of a heterogeneous precursor, such as sta-
bilized PdNPs, is not evidence for a heterogeneous mechanism
Herein, we aimed to investigate conditions for recycling
PdNP-based catalysts in the Suzuki reaction. To achieve this,
we needed to clarify the catalyst state during the reaction and
during the process of recycling, and determine the causes of
deactivation of the catalyst.
[a] A. V. Selivanova, Dr. V. S. Tyurin, Prof. I. P. Beletskaya
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry
31-4, Leninskiy Prospect, 119071 Moscow (Russia)
[b] Prof. I. P. Beletskaya
Chemistry Department M. V. Lomonosov Moscow State University
1-3, Leninskie Gory, 119992 Moscow (Russia)
Fax: (+7)4959393618
E-mail: beletska@org.chem.msu.ru
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NaOH at 808C (Table 1, entries 11 and 12). The EtOH/K2CO3
system gave excellent results in both cycles. However, in the
EtOH/NaOH system, the yield sharply decreased (from 90 to
15%) in the second cycle (Table 1, entry 12). The catalyst was
clearly degraded and rather large palladium particles were ob-
served. “Green” aqueous medium was successfully used for the
Suzuki reaction with water-soluble reagents.[11] Unfortunately,
an attempt to perform the reaction under aqueous conditions
with aryl bromide, which is insoluble in water, did not give
positive results (Table 1, entries 15 and 16).
Results and Discussion
Previously, we developed a catalytic system of PdNPs support-
ed on a soluble statistical copolymer of N-vinylimidazole with
N-vinylcaprolacam (30%; PVI-PVCL), which revealed high activi-
ty and recyclability in the Heck reaction,[12] the cyanation of
aryl halides,[13] and the carbonylation of aryl iodides.[14] Polymer
PVI-PVCL successfully models natural enzymes on the basis of
peptide macromolecules.[15,16] The advantage of PVI-PVCL is its
solubility in aqueous solutions, wherein it forms aggregates.
Hydrophobic reagents are concentrated in such aggregates
and this leads to an increase in the rate of reactions by several
orders of magnitude. The interfacial nanolayer of aggregates
can be considered as a catalytic nanoreactor.
Aqueous organic solvents represent the optimal compro-
mise. Water participates in the reaction and stabilization of
PdNPs and the organic solvent allows dissolution of the sub-
strates. Aqueous DMF was reported to be more efficient than
pure DMF.[17] A more environmentally friendly 1:1 water/etha-
nol system was found to be optimal for the Suzuki reaction
catalyzed by PdNPs in numerous reports published recently,[18]
especially for aerobic conditions[18a] and catalyst recycling.[18b]
The use of a mixture of EtOH/H2O (1:1) as a solvent and K2CO3
as a base at 808C allowed the product to be obtained in close
to quantitative yields, with both PdNPs generated in situ and
those synthesized in advance (Table 1, entries 17 and 18).
We tested several typical bases for the Suzuki reaction.
Among them, KF gave the worst results (Table 1, entries 6 and
13). Moreover, the addition of KF to K2CO3 lowered the yields
(Table 1, entries 7, 14, and 16). This could be possible owing to
PVI-PVCL forms complexes with palladium dichloride owing
to the ligand donor ability of imidazole fragments. Palladium(II)
is easily reduced into a zero-valent palladium, which forms
PdNPs that are stabilized by the polymer. Notably, PdNPs are
obtained in situ both through the reduction of PdCl2 with phe-
nylboronic acid and through preliminary reduction by alcohol
in the presence of the polymer. (The PdNPs obtained by the
latter method are considerably larger.)
First, we tested different reaction conditions in the model re-
action of p-bromoacetophenone with phenylboronic acid cata-
lyzed by the PdCl2/PVI-PVCL (1:5) system through varying the
solvent, base, and temperature (Table 1). The aim was to find
conditions that provided not only high yields, but
stable catalysts.
It appears that all three factors, solvent, base, and
temperature, influence the reaction and also the pos-
sibility of recycling the catalyst. Some conditions
gave excellent yields in the first cycle, but failed in
the second. Undoubtedly, this confirmed a change in
the catalyst state at the end of the first cycle. Some-
times that change was visible by eye as palladium
black, so the degradation of the catalyst was clear.
A high yield of product was obtained in the
system DMF/K2CO3 at 1208C (Table 1, entry 1); how-
ever, such a reaction needed a high temperature and
long time (Table 1, entries 1 and 2). Upon decreasing
the temperature to 1008C, the yield of product fell
slightly (Table 1, entry 3). Surprisingly, Na2CO3 in DMF
gave a better result at 1008C than at 1208C (Table 1,
entries 4 and 5). PVP, which is similar in nature to PVI
and very popular in the Suzuki reaction, as a PdNP
support gave worse results (Table 1, entries 9 and 10).
A lower yield in the second cycle showed that the
stability of PdNPs on PVI/PVCL was better than that
on PVP. Recycling of the catalysts after the reactions
in DMF, in all cases, led to a noticeable decrease in
the yield. Thus, standard conditions for palladium-
catalyzed cross-coupling reactions (DMF at 100–
1208C) are not optimal for PdNPs immobilized on
PVI-PVCL and PVP.
Table 1. Screening of base, solvents, and temperature in the reaction of phenylboron-
ic acid with p-bromoacetophenone.[a]
Entry
Base
Solvent
T
[8C]
t
[h]
Yield [%]
Cycle 1
Cycle 2
1[b]
2[b]
3[b]
4
5
6
K2CO3
K2CO3
K2CO3
Na2CO3
Na2CO3
KF
K2CO3/KF
Bu3N
K2CO3
Bu3N
K2CO3
NaOH
KF
K2CO3/KF
K2CO3
K2CO3/KF
K2CO3
K2CO3
K2CO3
K2CO3
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
EtOH
EtOH
EtOH
EtOH
H2O
H2O
120
120
100
120
100
100
100
120
120
120
80
80
80
80
100
100
80
80
80
6
2
4
6
4
4
4
6
6
6
4
4
4
4
4
4
96
88
88
81
90
40
84
74
96
52
95
90
50
30
50
27
90
69
61
65
48
11
60
–
84
14
92
15
50
–
–
–
92
93
91
75
7
8
9[c]
10[c]
11
12
13
14
15
16
17
18[d]
19
20[e]
EtOH/H2O (1:1)
EtOH/H2O (1:1)
EtOH/H2O (1:1)
EtOH/H2O (1:1)
4
4
0.75
4
>99
>99
97
80
>99
[a] Reaction conditions: PdCl2 (1 mol%), PVI-PVCL (5 mol%, relative to the monomeric
unit), p-bromoacetophenone (0.2 mmol), PhB(OH)2 (0.22 mmol), base (0.4 mmol), sol-
vent (0.5 mL). [b] Determined by 1H NMR spectroscopy. [c] 20 mol% of poly(N-vinylpyr-
idine) (PVP) as a polymer component. [d] PdNPs synthesized in advance. [e] PdCl2
(0.1 mol%), p-bromoacetophenone (2.0 mmol), PhB(OH)2 (2.2 mmol), base (4.0 mmol),
solvent (5 mL).
A number of reports presented ethanol as a prom-
ising green solvent for the Suzuki reaction. High
yields were obtained in EtOH with both K2CO3 and
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the ability of FÀ to form inactive boron–fluoride anionic com-
plexes.[19] Bu3N was also inefficient (Table 1, entries 8 and 10),
as noted previously for amines.[19] NaOH was successfully used
before, but it promoted degradation of the catalyst for this
particular system of PdNPs on PVI/PVCL (Table 1, entry 12).
Mild and inexpensive K2CO3 was also shown to be efficient.
Thus, the optimal conditions for the Suzuki reaction were de-
termined as follows: 1:1 EtOH/H2O with K2CO3 at 808C. The
most important achievement was the highest stability of the
catalyst under these conditions. The activity of the catalyst
under the optimized conditions was higher; hence it allowed
the reaction time to be shortened from 4 h to 45 min (Table 1,
entry 19). A decrease in the palladium loading from 1 to
0.1 mol% did not lead to a decrease of the yield in the first
cycle (fresh), but the yield sharply dropped in the second cycle
(Table 1, entry 20).
Table 2. Suzuki reaction of aryl halides with phenylboronic acid.[a]
Entry
1[c]
Ar[Hetar]Br[b]
PhBr
t [h]
Product
Yield [%][c]
95
4
PhÀPh
2
3
6
6
79
89
4[d]
4
6
83
5
91[e]
6
7
4
8
90
73
Under the optimized conditions, the Suzuki reaction was
performed for a range of aryl bromides containing electron-
donor and -acceptor substituents (Table 2). Good yields of dia-
ryls were observed in all cases. A mixture of mono-, di-, and tri-
substituted products, of which the trisubstituted product was
the major product, were formed in the reaction of tribromo-
benzene. Chloro derivatives, even upon activation, did not
react under these conditions.
6
82[g]
8[f]
10
14
Recycling of the catalyst
Recycling of the catalyst was performed eight times for the
model reaction of p-bromoacetophenone with phenylboronic
acid; the yield in all eight cycles remained constant under the
optimized conditions (Table 3). However, in an attempt to cut
the reaction time (45 min instead of 4 h), the yield was not so
constantly high and noticeably dropped in the eighth cycle. To
shed some light on the catalyst state during the reaction,
more studies were performed.
62
9[d]
4
n.d.
[a] Reaction conditions: [Pd]=PdCl2/PVI-PVCL 1:5 (1 mol%; relative to the
monomeric unit), aryl bromide (0.2 mmol), PhB(OH)2 (0.22 mmol), K2CO3
(0.4 mmol), EtOH (0.25 mL), water (0.25 mL), 808C. [b] Hetar=heteroatom.
[c] Yield of product isolated. [d] EtOH (0.5 mL). [e] Determined by 1H NMR
spectroscopy. [f] PhB(OH)2 (0.62 mmol). [g] Overall yield.
Images recorded by TEM (Figure 1) after the first and subse-
quent cycles showed a significant change to the distribution of
the sizes of the particles, although the average size only slight-
ly increased. The noticeable decrease in the amount of smaller
particles with a simultaneous increase in the amount of larger
particles was observed from first to the third and from the
third to the eighth cycles (Figure 1c). After the eighth cycle,
the smallest particles (<1.7 nm) vanished completely and the
average size (2.1 nm) changed to 2.5 nm. The size of the nano-
particles synthesized before the reaction turned out to be
much larger, and consequently, the change in the particle size
during the reaction was also less, but the tendency to increase
the average size remained (Figure 1 f).
Table 3. Catalyst recycling in the reaction of phenylboronic acid with p-
bromoacetophenone.[a]
Run
Yield [%]
4 h
Run
Yield [%]
45 min
45 min
4 h
1
2
3
4
>99
91
96
>99 (>99)[b]
5
6
7
8
92
95
97
81
>99
>99
>99
98
92 (93)[b]
99 (98)[b]
99
92
Kinetic studies were performed at a lower temperature
(408C) than the optimized conditions (808C) because the initial
reaction rate was very high (Figure 2). It should be noted that
there was no induction period, which was always present for
other similar palladium(II)-catalyzed reactions (Heck, Sonoga-
shira); this can be explained by the instant reduction of PdII to
Pd0 with arylboronic acid. The kinetic behavior of the reaction
was totally unexpected. The reaction proceeded extremely
quickly at the beginning, so the conversion reached more than
[a] Reaction conditions: [Pd]=PdCl2/PVI-PVCL 1:5 (1 mol%; relative to the
monomeric unit), p-bromoacetophenone (0.2 mmol), PhB(OH)2
(0.22 mmol), K2CO3 0.4 mmol, EtOH (0.25 mL), water (0.25 mL), 808C.
[b] PdNPs synthesized in advance.
half after only 1 min, but then the rate sharply dropped and
more than one hour was needed for full conversion. To the
best of our knowledge, nobody has reported similar reaction
behavior. These results were completely reproducible. The ki-
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Figure 2. Quantity of p-bromoanisole as a function of the reaction time. Re-
action conditions: [Pd]=PdCl2/PVI-PVCL 1:5 (1 mol%; relative to the mono-
meric unit), p-bromoanisole (0.4 mmol), PhB(OH)2 (0.42 mmol), K2CO3
(0.8 mmol), EtOH (1 mL), water (1 mL), 408C, and veratrol (0.2 mmol) as an
internal standard.
temperature (808C instead of 408C) allowed consistently high
yields to be achieved in seven cycles, but completion of the re-
action in the eighth cycle required a longer reaction time (4 h
instead of 45 min; Table 3).
Such unusual behavior might be a consequence of the com-
plex nature of the reaction catalyzed by PdNPs. An attempt to
explain the kinetics is based on the observation of changes to
the sizes of the particles during recycling. The very fast reduc-
tion of PdII to Pd0 at the beginning of the first cycle produced
very active catalytic species, probably in the form of very small
palladium metal particles and clusters. Soon after that, the
active small particles took part in the reaction, and hence,
were dissolved. Subsequently, palladium atoms leaving the re-
action cycle precipitated to give only large, stable, and less
active nanoparticles. Those particles were responsible for the
lower reaction rate of the second part of the first cycle and all
subsequent cycles. The active smaller particles disappeared
from cycle to cycle accompanied by a gradual decrease in the
reaction rate. It should be noted that small PdNPs can arise in
the process of grinding large particles.[11] The ratio of the pro-
cesses of grinding and dissolution of PdNPs determines the
trend in their size distribution. Very active substrates, such as
aryl iodides, were shown to react fast enough with all types of
particles, including palladium black of micrometer particle
sizes,[20] causing their grinding.[11] In this study, we used less
active aryl bromides, the oxidation addition of which to palla-
dium proceeded very slowly; therefore, they reacted more se-
lectively and preferred smaller PdNPs, and consequently, the
rate of dissolution of small particles was considerably higher
than the rate of grinding of large particles, which resulted in
the disappearance of small particles and an increase in the
average size of the particles. PdNPs prepared in advance
through the process of the slow reduction of PdII by alcohol
had a three times larger initial average size and did not contain
smaller particles, and consequently, they were less active, but
their low activity remained constant.
Figure 1. TEM images of the catalytic system based on PdCl2/PVI-PVC=1:5
after the reaction of phenylboronic acid with p-bromoacetophenone for 4 h,
showing PdNPs after the first (a) and eighth (b) cycles; the particle size dis-
tribution of the PdNPs is also shown (c). TEM images of the PdNPs synthe-
sized in advance before the reaction (d) and after the third cycle (e); the par-
ticle size distribution of the PdNPs is also shown (f).
netic curve apparently consists of two parts: the first part re-
flects a high rate constant that lasts until 1 min and the
second part corresponds to a considerably lower rate of the re-
action. The rate in the second cycle repeated the slower part
of the first cycle. During the following consecutive cycles, the
activity of the catalyst gradually decreased. The use of a higher
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However, this is only a part of characteristics of the mecha-
nism. We performed a hot filtration test and found that only
a small amount of palladium was contained in the solution
(0.3%, much less than that expected for a homogeneous reac-
tion based on leaching). The reaction did not proceed in this
solution, although even homeopathic doses could catalyze the
reaction.[21] Maybe this is not so surprising if we examine our
kinetic curves, which show how fast the change in the activity
of PdNPs occurred, even during the course of the reaction. We
do not know if size and morphology are responsible. One can
see that even small changes to the conditions do not allow us
to recycle a successful reaction (see Table 1), and if we manage
to recycle the catalyst, the kinetic behavior is different in the
second cycle (see Figure 2). All of these observations clearly
show that the mechanism of this rather simple reaction is far
from being fully understood and needs to be studied further.
General procedure for the Suzuki–Miyaura cross-coupling
reaction
A 2ꢁ10À3 m solution (1 mL) of H2PdCl4 in EtOH, prepared by
a method reported previously,[11] was placed into the reactor and
evaporated in vacuum. Then polymer (1.0 mg; 5 mol% in relation
to aryl bromide), aryl bromide (0.2 mmol), base (2 equiv), phenyl-
boronic acid (0.22 mmol), and solvent (0.5 mL) were added. The
mixture was stirred at 80–1208C. The product was then extracted
with diethyl ether (3ꢁ2 mL; for reactions with EtOH/H2O as sol-
vent), or diethyl ether (4 mL) was added and the reaction mixture
was stirred for 5 min, the solution was separated, and the precipi-
tate was washed with diethyl ether (2ꢁ2 mL; for reactions with
DMF as the solvent). The combined ethereal extracts were passed
through a silica filter, which then was washed with dichlorome-
thane (5 mL), dried over Na2SO4, and evaporated in vacuum. The
products were isolated by flash chromatography by using petrole-
um ether (fraction 40–708C) as the eluent. The structure of the
products was determined by 1H NMR spectroscopy.
Conclusion
Recycling of the catalyst
The Suzuki reaction is one of the mostly investigated catalytic
processes: thousands of studies have been reported and the
huge flow of articles has not stopped. This could be explained
by the complex nature of the mechanism, the variety of re-
sults, difficulties in their interpretation, and problems with re-
cycling of the catalyst. The results obtained herein revealed
completely unexpected behavior for such a well-studied reac-
tion. Kinetic results and changes to the sizes of the particles
were in accordance with our view of the role of leaching in the
course of the reaction and supported the homogeneous
nature of the mechanism of the Suzuki reaction catalyzed by
palladium nanoparticles. The suggested protocol allows the re-
action of aryl bromides to be performed under mild conditions
with a high yield in a green solvent and undoubtedly complies
with Green Chemistry principles.
After completion of the reaction and cooling to room temperature,
the reaction mixture was filtered; the precipitate was washed with
water, EtOH, and diethyl ether; dried under air; and employed for
the next cycle. The organic layer was dried over Na2SO4 and evapo-
rated in vacuum. The product was isolated by flash column chro-
matography on silica gel by using petroleum ether (fraction 40–
708C) as the eluent. p-Acetodiphenyl yields were 97% after the
first cycle and 98% after the second cycle.
Acknowledgements
The study was supported by the Russian Academy of Sciences
(“Creation and investigation of macromolecules and macromo-
lecular structures of new generations” and “The bases of basic re-
searches of nanotechnology and nanomaterials” programs).
Experimental Section
Keywords: cross-coupling
·
kinetics
·
nanoparticles
·
palladium · supported catalysts
General
A copolymer of N-vinylimidazole and N-vinylcaprolactam (30%; Mr
20000) was prepared by a method reported in the literature.[12] All
reactions were performed under an argon atmosphere and were
monitored by TLC on silica-gel Alugram SilG/UV254 plates (Macher-
ey–Nagel). Column chromatography was performed on silica gel
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1
(60–200 nm) purchased from Alfa Aesar. H NMR spectra were ob-
tained by using a Bruker AMX-400 spectrometer at 400 MHz in
CDCl3 and a Bruker Avance III 600 spectrometer at 600 MHz. Quali-
tative 1H NMR spectroscopy analysis was performed by using di-
methyl terephthalate as an internal standard. TEM images were ob-
tained on an LEO912 AB OMEGA transmission electron microscope.
Preparation of the PdNP-supported copolymer
A solution of copolymer (21.5 mg, 0.2 mmol) of N-vinylimidazole
and N-vinylcaprolactam in EtOH (2 mL) was added to a stirred solu-
tion of Pd(OAc)2 (8.98 mg, 0.04 mmol) in ethanol (6 mL). The mix-
ture was stirred for 0.5 h at room temperature. The resulting solu-
tion of PdNPs was diluted with EtOH up to 10 mL; c(Pd)=4ꢁ
10À3 mmolmLÀ1
.
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Received: April 29, 2014
Published online on && &&, 0000
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FULL PAPERS
Fast or slow? Palladium nanoparticles
immobilized on poly(N-vinylimidazole-
co-N-vinylcaprolactam) reveal unusual
kinetic behavior in the Suzuki reaction.
This can be explained on the basis of
the observation of changes to the sizes
of the particles during recycling, and is
in accordance with the concept of
leaching during the process.
A. V. Selivanova, V. S. Tyurin,
I. P. Beletskaya*
&& – &&
Palladium Nanoparticles Supported on
Poly(N-vinyl-imidazole-co-N-
vinylcaprolactam) as an Effective
Recyclable Catalyst for the Suzuki
Reaction
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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7
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These are not the final page numbers!