Efficient and Recyclable Catalyst of Palladium Nanoparticles Stabilized by Polymer Micelles Soluble in Water for Suzuki-Miyaura Reaction, Ostwald Ripening Process with Palladium Nanoparticles

Article abstract of DOI:10.1055/s-2008-1078430

The Suzuki-Miyaura cross-coupling reaction of ArX (I, Br) with Ar'B(OH)₂, catalyzed by Pd-containing water-soluble micelle formed by PS-PEO copolymer and N-cetylpyridinium chloride as a surfactant, was studied in water and methanol. The reaction was performed under mild conditions (temperature up to 50 °C) and the catalyst can be recycled (5 runs) by ultrafiltration without any loss of its catalytic activity. The phenomenon was observed, consisting in growing Pd-nanoparticle size because the small nanoparticles dissolve to form larger nanoparticles in the course of reaction as well as in the presence of the only reagent, ArI. In the latter case, additionally, the formation of very small, not completely dissolved Pd nanoparticles, obviously having a high catalyst activity, is observed. This observation, together with the catalyst activity data might have an implication for a leaching mechanism for the studied catalytic system.

Full text of DOI:10.1055/s-2008-1078430

CLUSTER
1547
Efficient and Recyclable Catalyst of Palladium Nanoparticles Stabilized by
Polymer Micelles Soluble in Water for Suzuki–Miyaura Reaction, Ostwald
Ripening Process with Palladium Nanoparticles
a
a
b
c
P
I
d/polym
r
er Mice
i
lles
a
s
nC atalyst for aS uzuki–Miyaura
R
P
eaction . Beletskaya,* Alexander N. Kashin, Irina A. Khotina, Alexey R. Khokhlov
a
b
c
Department of Chemistry, Moscow State University, Leninskie Gory, 119992, Moscow, Russian Federation
Fax +7(495)9393618; E-mail: beletska@org.chem.msu.ru
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Science, Vavilova str. 28, 119991, Moscow,
Russian Federation
Department of Physics, Moscow State University, Leninskie Gory, 119992, Moscow, Russian Federation
Received 16 January 2008
The question of the actual active species in the catalytic
cycle for the reaction catalyzed by PdNP is still controver-
sial. The reaction is supposed to occur on the surface of
Abstract: The Suzuki–Miyaura cross-coupling reaction of ArX (I,
Br) with Ar¢B(OH) , catalyzed by Pd-containing water-soluble mi-
2
celle formed by PS-PEO copolymer and N-cetylpyridinium chlo-
1
0
ride as a surfactant, was studied in water and methanol. The reaction PdNP or via leaching of Pd as atoms/ions, especially in
1
1
was performed under mild conditions (temperature up to 50 °C) and the defect sites, into solution. The latter hypothesis has
been substantiated experimentally.12 At the same time,
the catalyst can be recycled (5 runs) by ultrafiltration without any
loss of its catalytic activity. The phenomenon was observed, con-
there are research groups, including the authors of the
sisting in growing Pd-nanoparticle size because the small nanopar-
present communication, who are inclined to believe that
ticles dissolve to form larger nanoparticles in the course of reaction
catalysis in such systems is mainly due to Pd atom leach-
as well as in the presence of the only reagent, ArI. In the latter case,
additionally, the formation of very small, not completely dissolved
ing from PdNP surface subsequent to the oxidative–addi-
Pd nanoparticles, obviously having a high catalyst activity, is ob- tion of organic halide.3
c,11c,13
Palladium(0) is subsequently
served. This observation, together with the catalyst activity data regenerated in the catalytic cycle and is deposited in the
might have an implication for a leaching mechanism for the studied
form of nanosized particles.
catalytic system.
Previously we used a micelle formed by styrene–ethylene
Key words: palladium nanoparticles, Suzuki–Miyaura cross-cou-
oxide block co-polymer containing PdNP prepared by the
pling, biaryls, block copolymer micelles, Ostwald ripening process
reduction of K PdCl with NaBH , as a palladium catalyt-
2
4
4
ic system. The micelle was further stabilized by the addi-
tive of N-cetyl pyridinium chloride, incorporated into the
polymer membrane. Such a micelle has a hydrophobic
polystyrene core and a hydrophilic polyethylene oxide
crown, containing the PdNP. This catalyst showed high
activity in Heck reaction with acrylates as well as cascade
The great importance of palladium-catalyzed reactions of
carbon–carbon bond formation, such as Suzuki–Miyaura
14
(
S–M), Sonogashira, Heck, and many other reactions, led
to an incessant pursuit of efficient catalysts for these pro-
cesses. The palladium complexes with phosphine ligands
had played a significant role in the development of this
field. However, in order to meet the challenges of catalyst
separation after the reaction and its possible recycling,
fundamentally new catalysts had to be developed – heter-
ogeneous palladium nanoparticles (PdNP) on solid sup-
reactions leading to substituted indoles and isocou-
marins.5
The elevated temperatures required for these reactions to
proceed, unfortunately, led to the micelle destruction.
Therefore the recycling of the catalyst with its separation
after the end of reaction was impossible, but a ‘fresh start’,
that is, the consecutive addition of a fresh batch of the re-
agents after the reaction completion, allowed to realize
several cycles without losing the catalyst activity. The re-
sult clearly indicated that under the set conditions the pal-
ladium ‘leaching’ leads to the formation of catalytically
active species.
1
port, for example, on activated carbon, bound to
2
3
polymer or dendrimer macromolecules. Catalytic sys-
tems have been developed based upon PdNP ‘homoge-
neously’ dispersed in the solution, stabilized in micelles
4
of block co-polymers of styrene with 4-vinylpyridine and
ethylene oxide or sodium acrylate, co-polymers of eth-
ylene oxide with 2-vinylpyridine or propylene oxide,
5
3
6
7
etc. Heterogeneous catalysts of this type meet the de- The solubility of this micellar catalyst in water allowed us
mands of Green Chemistry, since they are free from toxic to perform the usually facile S–M reaction with water-sol-
ligands, can be easily separated from the reaction products uble reagents in neat water, the ‘greenest’ of all solvents.15
and are capable of recycling. It emerged recently, that the For water-insoluble reagents we also used methanol to ex-
activity of such catalysts is dependent upon the state of tent the scope of reagents for the reaction with this cata-
8
,9
these nanosized particles.
lyst. The reaction temperature did not exceed 50 °C,
which allowed performing the recycling of the catalysts16
since low temperatures favor the micelle stability.
SYNLETT 2008, No. 10, pp 1547–1552
x
x
.x
x
.2
0
0
8
Advanced online publication: 19.05.2008
DOI: 10.1055/s-2008-1078430; Art ID: Y00508ST
©
Georg Thieme Verlag Stuttgart · New York

1
548
I. P. Beletskaya et al.
CLUSTER
The S–M reaction was performed in water and methanol The example of the reaction of m-iodobenzoic acid with
with KOH as a base (Equation 1). The use of other bases phenylboronic acid shows that under used conditions the
(
K CO , NaHCO , Bu NOH solution saturated with CO ) reaction proceeds at almost the same rate as the reaction
2 3 3 4 2
at required concentrations leads to the coagulation of the catalyzed by Pd(OAc) at 20 °C (Table 1, entries 5, 7),
2
1
7
catalyst or the precipitation of salts of arylboronic acid. though slower than the latter reaction at 75 °C.
The reactions were usually carried out under aerobic con-
The formation of biphenyl as byproduct can be observed
for some reactions with phenylboronic acid, which results
in decreasing the cross-coupling product yield. The yield
of biphenyl is minimal in case of the reaction with m-io-
dobenzoic acid (4%) and is maximal for the reaction with
p-iodophenol (more than 8%). This byproduct can be sep-
arated from the alkaline solution of reaction mixture by
filtration or centrifugation. As biphenyl is formed in the
absent of aryl iodide in trace quantity, its formation can be
supposed to be catalyzed by the active Pd(0) species
formed in the main S–M reaction.
ditions, since – as it has been shown for the model reaction
of m-iodobenzoic acid with phenylboronic acid – the
product yield is not dependant on the used type of atmo-
sphere (air, argon) or high vacuum.
Hal
Ar
[
Pd] (1 mol%)
R
+
ArB(OH)2
R
KOH, H2O or
MeOH, 20–50 °C
Hal = I, Br
Equation 1
In case of the reactions with aryl iodide and bromide in-
The analysis of estimated data has shown that the period
of ten hours is enough to complete the reaction, for exam-
ple, of m-iodobenzoic acid with phenylboronic acid at
room temperature and the set conditions (0.3 mmol of aryl
halide in the presence of 1.2 equiv of arylboronic acid, 5
equiv of KOH and, usually, not more than 1 mol% of Pd
catalyst). To complete the reaction and, especially, to get
high isolated product yield, reaction time varied from 4–
1
8
soluble in water, methanol was used as a solvent, and to
accelerate some reactions the temperature was increased
from 20 °C up to 50 °C (Table 2).
As in the case of the reaction in water, the reaction in
methanol proceeded without Pd-black formation, which is
evidence of the catalyst stability under these reaction con-
ditions. The example of the reaction of m-iodobenzoic
acid with phenylboronic acid at 20 °C shows that the re-
action in methanol proceeds slower than in water – a 52%
yield in methanol in seven hours (Table 2, entry 2) com-
pared to a 85% yield in water in four hours (Table 1, entry
2
0 hours. However, it was not possible to raise the product
yield for the reaction with p-iodophenol over 75% be-
cause of the byproduct formation (biphenyl). The corre-
sponding data on the conversion of the aryl halide and the
product yield for the reaction in water are summarized in
Table 1.
5
).
Table 1 Suzuki–Miyaura Cross-Coupling Reaction with Pd Nanoparticles as Catalyst in Watera
Entry
1
Aryl iodide
Arylboronic acid
Time (h)
Yield (%)b
Conversion (%)b
4
4
10
4
68
75
74
58
91
95
95
67
c
OH
2
3
4
d
I
B(OH)2
5
6
7
4
10
4
85
93
92
89
100
100
e
I
I
COOH
COOH
B(OH)2
B(OH)2
8f
20
97
100
S
COOH
9f
20
98
100
N
B(OH)2
I
a
Reaction conditions: ArI (0.075 mmol), Ar¢B(OH) (0.09 mmol), KOH (0.38 mmol), Pd (1 mol%), H O (0.25 mL), 20 °C.
2
2
b
Conversion – ArI conversion value – and product yield determined by GLC, using n-C H as an internal standard, biphenyl is formed as a
1
6
34
byproduct in a 4–8% yield.
c
Pd (2 mol%).
Pd (0.2 mol%).
Catalyst Pd(OAc) (1 mol%).
d
e
2
f
Isolated yield upon threefold increase of the reagents and water quantity, after acidation in EtOH, the purity of the products was confirmed by
H NMR.
1
Synlett 2008, No. 10, 1547–1552 © Thieme Stuttgart · New York

CLUSTER
Pd/Polymer Micelles as Catalyst for Suzuki-Miyaura Reaction
1549
Table 2 Suzuki–Miyaura Cross-Coupling Reaction of Functional-
ized Halobenzenes with Phenylboronic Acid in Methanol with Pd
Nanoparticles as Catalysta
the reaction with phenylboronic acid in six days, com-
pared to 45 minutes under normal reaction conditions with
the usual amount of the catalyst (1 mol%).
Entry R in
X in
Temp
Time Conversion of Yield
For the catalyst recycling in methanol one can use not
only an ultrafiltration but a centrifugation. The latter pro-
cedure allows appreciable time reduction at catalyst sepa-
ration. The example of the reaction of m-tolylboronic acid
with iodobenzene in methanol at 20 °C shows that the cat-
alyst can be reused in this way in no less than five runs
b
RC H X RC H X (°C)
(h)
RC H X (%) (%)
6
4
6
4
6 4
1c 3-COOH
2
3
4
I
20
20
40
50
7
7
7
7
69
67
52
77
94
54
79
98
(
Scheme 1).
5
3-CHO
4-MeO
I
I
50
20
20
20
4
83
78
88
15
99
18
75
86
10
87
6
7
[Pd] (1 mol%)
KOH/CH3OH
PhI + 3-MeC6H4B(OH)2
3-MeC12H9
5
5
0
2
0 °C, 20 h
8
9
2-NO2
4-NO2
I
20
4
Number of cycles
Yield (%)
1
2
3
4
82
85 83
84 84
5
0
4.5
Scheme 1 Recycling of catalyst by centrifugation for Suzuki–Miyau-
ra reaction of iodobenzene with m-tolylboronic acid in methanol
1
1
1
1
1
0
1
2
3
4
I
Br
20
20
50
20
50
4
4
4.5
4
4.5
99
19
72
0
92
12
65
0
Another situation arises if a centrifugation is used to sep-
arate the catalyst from the reaction mixture after, for ex-
ample, the reaction of m-iodobenzoic acid with
phenylboronic acid in water is completed. In this case, the
catalyst is not separated quantitatively – a part of it re-
mains in the solution. For this reason, a centrifugation
cannot be used for catalyst recycling. In addition, the ac-
tivity of the precipitated catalyst decreases sharply as the
run number increases [especially at Pd (1 mol%),
Table 4]. Using a centrifugation, however, we succeeded
in finding a certain important phenomenon. In the study of
the catalyst activity after the first run it was found that
Cl
Br
d
65
0
1
1
5
6
4-Ac
50
24
48
55
98
23
8
a
Reaction conditions: ArI (0.075 mmol), Ar¢B(OH) (0.09 mmol),
KOH (0.38 mmol), Pd (1 mol%), MeOH (0.25 mL), 20 °C.
Yield determined by GLC, using n-C H as an internal standard.
Pd (2 mol%).
2
b
1
6
34
c
d
Yield 63% of 4-O NC H OMe.
2
6
4
It is evident from Table 2 that the cross-coupling product
yield is high in many of the studied reactions not only with
aryl iodide but also with electron-deficient aryl bromides.
The reactions of phenylboronic acid with m-iodobenzal-
dehyde and with p-bromoacetophenone are exceptions, as
their product yield is low at the full conversion of reac-
tants. This is evidently determined by a side reaction, for
example, Cannizzaro reaction with the previously formed
cross-coupling product, since the product yield decreases
at a long reaction time (Table 2, entry 16).
7
5% of the loaded Pd amount (3 mol%) affords 35% yield
of the product in four hours. The smaller part of Pd (25%,
contained in the solution taken from the first run after cen-
trifugation of the reaction mixture) provides 86% yield in
the same conditions. In the following successive runs the
activity of the precipitated catalyst continues to decrease,
but the activity of the catalyst fraction in the solution, re-
mains practically unchanged (Scheme 2). It means that
only a quarter of the loaded Pd amount becomes catalyti-
cally active in the studied reaction.
The reaction of activated p-nitrochlorbenzene in methanol
proceeds with formation of p-nitroanisole (as product of
SNAr process) instead of the cross-coupling product. The
[Pd]0 (3 mol%)
attempt to carry out the reactions of phenylboronic acid
with the electron-rich aryl bromide of p-bromophenol and
even with activated m-bromobenzoic acid has failed al-
3-IC6H4COOH + PhB(OH)2
3-(COOH)C12H9
KOH, H2O
0 °C, 4 h
2
Number of cycles
Conversion of ArI (%)
Yield (%)
1
92
88
2 3
90 88
84 86
though these reactions are catalyzed by Pd(OAc) as effi-
2
1
7
ciently as the reactions of corresponding iodides.
The reuse of the catalyst was studied in water and metha-
Scheme 2 Recycling of the catalyst for Suzuki–Miyaura reaction of
nol. The example of the reaction of m-iodobenzoic acid m-iodobenzoic acid with phenylboronic acid under fresh starting con-
with phenylboronic acid in water at 20 °C shows that the ditions in aqueous solution taken from the first run after centrifugati-
on
catalyst can be separated from the reaction mixture by ul-
trafiltration and reused (no less than five runs) without
1
9
loss of its activity (Table 3). The membrane used for ul- The change of the catalyst morphology caused by differ-
trafiltration efficiently captures polymer micelles with the ent perturbations was assessed using transmission elec-
Pd nanoparticles. The filtrate contains an insignificant tron microscopy (TEM). It was found out that after the
quantity of the catalyst, since it exhibits a very low cata- first run of the reaction of m-iodobenzoic acid with phen-
lytic activity – 48% conversion of m-iodobenzoic acid in ylboronic acid the precipitated catalyst contains the ag-
Synlett 2008, No. 10, 1547–1552 © Thieme Stuttgart · New York

1
550
I. P. Beletskaya et al.
CLUSTER
Table 3 Recycling of Catalyst by Ultrafiltration for Suzuki–
Miyaura Reaction of m-Iodobenzoic Acid and Phenylboronic Acida
Number of cycles
1
2
3
4
5
b
Conversion of ArI (%) in H O
95
93
91
89
49
47
93
91
51
50
90
87
54
53
95
94
52
51
2
b
Yield of product (%) in H O
2
Conversion of ArI (%) in MeOHc 53
Yield of product (%) in MeOHc
52
a
Reaction conditions: ArI (0.31 mmol), PhB(OH) (0.36 mmol),
2
KOH (1.53 mmol), Pd (1 mol%), H O or MeOH (1 mL), 20 °C.
2
b
In 10 h.
In 7 h.
c
Table 4 Recycling of Catalyst by Centrifugation for Suzuki–
Miyaura Reaction of m-Iodobenzoic Acid and Phenylboronic Acid in
a
Water
Number of cycles
1
2
3
4
Figure 1 TEM images of the PdNP before (A) and after Suzuki–Mi-
yaura reaction (B for liquid phase, C for deposited phase) and after in-
teraction of the catalyst with m-iodobenzoic acid in the presence of
KOH (D)
Conversion of ArI (%) at Pd (1 mol%)b
Yield of product (%) at Pd (1 mol%)b
Conversion of ArI (%) at Pd (3 mol%)c
90
89
92
88
22 15 10
19 10
8
40 35 32
35 25 20
first run when both a new poor active catalyst fraction and
a soluble active catalyst fraction appear. The original cat-
alyst transformation in the first run of S–M reaction is also
supported by the fact that the centrifugation of the reac-
tion mixture results in partial precipitation of the catalyst,
while in the absence of the organic iodide the catalyst re-
mains in the solution, unchanged.
Yield of product (%) at Pd (3 mol%)c
a
Reaction conditions: ArI (0.075 mmol), PhB(OH) (0.09 mmol),
2
KOH (0.38 mmol), H O (0.25 mL), 20 °C.
2
b
In 8 h.
In 4 h.
c
To ascertain what factors influence the change of PdNP
size in a micelle and, accordingly, their activity in the
course of S–M reaction we have studied the individual ac-
tion of each reagent on the original catalyst. Using the re-
action of phenylboronic acid with m-iodobenzoic acid as
an example, we have shown that it is the organic iodide
and not phenylboronic acid that effects the changes in the
catalyst structure. The benzoic acid added instead of m-io-
dobenzoic acid does not influence the catalyst structure ei-
ther. The catalyst transformation in the presence of aryl
iodide is also supported by the fact mentioned above, that
the centrifugation of the alkaline solution of the catalyst
and ArI results in its partial precipitation, while in the ab-
sence of the organic iodide the catalyst remains in the so-
lution unchanged.
glomerates of micelles (up to 50 nm in size) with the
PdNP (2.4–3.1 nm in size, Figure 1, C). These PdNP are
larger than the ones contained in the original catalyst (1.7
nm in size, Figure1, A) and in the solution after centrifu-
gation (1.9 nm in size, Figure 1, B).
Thus, it becomes clear why the activity of the above-men-
tioned precipitated catalyst is substantially lower than the
activity of the catalyst remaining in the solution after a
centrifugation. It is due to significant growing the PdNP
size in the precipitated catalyst (from 1.7 nm to 2.4–3.1)
as well as to the formation of micelle agglomerates al-
ready after the first run of the reaction.20 As a rule, the
growing in size of metal nanoparticles results in the reduc-
tion of its catalytic activity which is usually attributed to
8
the increase of their surface area.
As in the S–M reaction, in the presence of m-iodobenzoic
acid the formation of new PdNP takes place. According to
TEM data, relatively small blackberry-like agglomerates
As regards the catalyst present in the solution of the first
run after centrifugation (with PdNP size being 1.9 nm), it
is a new catalyst but not the original catalyst remaining af-
ter the first run, otherwise its activity would be changeable
in the reaction under fresh start conditions (contrary to the
data of Scheme 2) because of the formation of the catalyst
precipitate.
(
0
(
2.6–7.2 nm) containing the very small Pd particles (0.6–
.8 nm) are present in the solution after centrifugation
Figure 1, D). The precipitate, in turn, consists of larger
loose agglomerates (about 20 nm in size), containing
small nanoparticles 1–3 nm in size, and solitary large Pd
These results, which could not be obtained using ultrafil- particles having the size of about 3 nm and a pronounced
tration, are in agreement with the fact that it is during the spherical form.
Synlett 2008, No. 10, 1547–1552 © Thieme Stuttgart · New York

CLUSTER
Pd/Polymer Micelles as Catalyst for Suzuki-Miyaura Reaction
1551
It can be supposed that leaching of the small PdNP takes tration, when all the micelles containing the PdNP are ef-
place by the action of m-iodobenzoic acid, further facili- ficiently captured. However, the analysis of the data
2
1
tated by the coordination of hydroxyl ion to palladium as obtained from the centrifugation and TEM experiments
well as by the stabilization of the [ArPdX(OH)2]2– inter- reveals that in the first run of the reaction the original cat-
mediate formed in this process by the hydroxyl ions as alyst converts to a new well recyclable catalyst along with
ligands. Since the oxidative addition process is reversible, the formation of low active clusters of PdNP. This process
the breakup of the intermediate should lead to the deposi- is accompanied by the change in size of the PdNP, which
tion of Pd(0) on the surface of larger PdNP, increasing is related to the Ostwald ripening process, when the small
their size. Such disproportionation in size of the PdNP PdNP dissolve to form the large ones. In addition, the very
(
the increase in size from 1.7 nm to 3 nm of some particles small, not completely dissolved PdNP, obviously having
and the decrease in size from 1.7 nm to 0.6–0.8 nm of oth- a high catalyst activity, are formed from the original cata-
ers) is much related to the Ostwald ripening process in lyst under the action of the organic iodide. It seems that
which small nanoparticles dissolve to form the large the significant size growing of the PdNP in the reaction
2
0,22
ones.
The disproportionation in size of the PdNP in the limits the run number in which the catalyst can be effi-
S–M reaction is related to the fast reductive elimination ciently recycled.
for ArPdR¢ intermediate giving Pd(0). The latter is depos-
ited on the larger PdNP further increasing their size.2
2b
Acknowledgment
The financial support from the Grant of the President of the Russian
Federation for the State Support of the Leading Research Schools
grant No HIII-6059.2006.3), Russian Academy of Science (pro-
gram N 4 ‘Creation and investigation of macromolecules and
macromolecular structures of new generations’) and CRDF (pro-
gram CGP-FASI, RUC1-2802-MO-06), is gratefully acknowled-
ged.
ArX + 2 OH–
Pd
Pd
Pd
(
ArPdX(OH)22–
Pd
Pd
ArX + Ar'B(OH)2
–
+
2 OH
ArPdAr'(OH)22–
References and Notes
PP dd
(
1) Seki, M. Synthesis 2006, 2975.
Pd
ArAr' + 2 OH–
(2) Bergbreiter, D. E.; Kippenberger, A.; Zhong, Z. Can. J.
Chem. 2006, 84, 1.
(
Scheme 3 Suggested mechanism for the Ostwald ripening process
with the PdNP in the presence of ArX (top) and in Suzuki–Miyaura
reaction (bottom)
3) (a) Li, Y.; El-Sayed, M. A. J. Phys. Chem. B 2001, 105,
938. (b) Rahim, E. H.; Kamounah, F. S.; Frederiksen, J.;
8
Christensen, J. D. Nano Lett. 2001, 1, 499. (c)Diallo, A. K.;
Ornelas, C.; Salmon, L.; Ruiz Aranzaes, J.; Astruc, D.
Angew. Chem. Int. Ed. 2007, 46, 8644.
Thus, the size of PdNP will be determined by the actual
ratio between the rates of all steps of S–M reaction, and,
in general, may differ from that observed in the presence
of the only reagent, m-iodobenzoic acid (Scheme 3, top).
The measurement of the size of Pd particles after the reac-
tion showed that if in the presence of m-iodobenzoic acid
the disproportionation in size of the PdNP leads to nano-
particles from 0.6–0.8 nm to 3 nm in size, in the S–M re-
action larger PdNP are formed, from 1.9 nm to 3.1 nm in
size. The fact, that 0.6–0.8 nm sized particles are not
found after the S–M reaction (Scheme 3, bottom) is in
agreement with the view on the participation of exactly
these obviously more active PdNP in the catalysis of the
reaction, resulting in the growth of other particles.
(
4) (a) Klingelhofer, S.; Heitz, W.; Greiner, A.; Oestreich, S.;
Forster, S.; Antonietti, M. J. Am. Chem. Soc. 1997, 119,
10116. (b) Seregina, M. V.; Bronstein, L. M.; Platonova, O.
A.; Chernyshov, D. M.; Valetsky, P. M.; Hartmann, J.;
Wenz, E.; Antonietti, M. Chem. Mater. 1997, 9, 923.
(5) Beletskaya, I. P.; Kashin, A. N.; Litvinov, A. E.; Tyurin, V.
S.; Valetsky, P. M.; van Koten, G. Organometallics 2006,
25, 154.
(
6) Semagina, N. V.; Bykov, A. V.; Sulman, E. M.; Matveeva,
V. G.; Sidorov, S. N.; Dubrovina, L. V.; Valetsky, P. M.;
Kiselyova, O. I.; Khokhlov, A. R.; Stein, B.; Bronstein, L.
M. J. Mol. Catal. A: Chem. 2004, 208, 273.
(7) Piao, Y.; Jang, Y.; Shokouhimehr, M.; Lee, I. S.; Hyeon, T.
Small 2007, 3, 255.
(
(
8) (a) Biffis, A.; Zecca, M.; Basato, M. Eur. J. Inorg. Chem.
001, 1131. (b) Biffis, A.; Zecca, M.; Basato, M. J. Mol.
2
To the best of our knowledge, the formation of PdNP –
with the size smaller than the size of PdNP in the original
catalyst – in S–M and related reactions has not been ob-
served. The discovered process of the PdNP ‘grinding’
with the formation of very small PdNP, obviously having
a high catalyst activity, points to a new role of the organic
halides in the activation of the Pd precatalyst in S–M and
related reactions.
Catal. A: Chem. 2001, 173, 249. (c) Bars, J.; Specht, U.;
Bradley, J.; Blackmond, D. Langmuir 1999, 15, 7621.
(d) Roucoux, A.; Schulz, J.; Patin, H. Chem. Rev. 2002, 102,
3757. (e) Raimondi, F.; Scherer, G. G.; Kotz, R.; Wokaun,
A. Angew. Chem. Int. Ed. 2005, 44, 2190.
9) This probably determines the catalytic activity of the ligand-
free palladium in water or the species forming from
palladacycles. See: Beletskaya, I. P.; Cheprakov, A. V.
J. Organomet. Chem. 2004, 689, 4055.
(
10) (a) Li, Y.; Hong, X. M.; Collard, D. M.; El-Sayed, M. A.
Org. Lett. 2000, 2, 2385. (b) Narayanan, R.; El-Sayed, M.
A. J. Am. Chem. Soc. 2003, 125, 8340.
In summary, the studied catalyst is efficient in S–M reac-
tions carried out in water or methanol at relatively low
temperatures. The catalyst can be recycled using ultrafil-
Synlett 2008, No. 10, 1547–1552 © Thieme Stuttgart · New York

1
552
I. P. Beletskaya et al.
CLUSTER
(16) (a) For Heck4a and S–M reactions,15b the catalyst of the
PdNP stabilized in micelles of co-polymers, of styrene with
4-vinylpyridine, was claimed to be reusable, but no details
were given about the catalyst separation procedure.
(b) Jiang, X.; Wei, G.; Zhang, W.; Zhang, X.; Zheng, P.;
Wen, F.; Shi, L. J. Mol. Catal. A: Chem. 2007, 277, 102.
(17) (a) Bumagin, N. A.; Bykov, V. V.; Beletskaya, I. P. Bull.
Acad. Sci. USSR, Div. Chem. Sci. 1989, 38, 2206.
(
11) (a) de Vries, A. H. M.; Mulders, J. M. C. A.; Mommers, J. H.
M.; Henderickx, H. J. W.; de Vries, J. G. Org. Lett. 2003, 5,
3
2
285. (b) Reetz, M. T.; de Vries, J. G. Chem. Commun.
004, 1559. (c) Thathagar, M. B.; Kooyman, P. J.;
Boerleider, R.; Jansen, E.; Elsevier, C. J.; Rothenberg, G.
Adv. Synth. Catal. 2005, 347, 1965.
(
12) (a) Thathagar, M. B.; ten Elshof, J. E.; Rothenberg, G.
Angew. Chem. Int. Ed. 2006, 45, 2886. (b) Gaikwad, A. V.;
Holuigue, A.; Thathagar, M. B.; ten Elshof, J. E.;
Rothenberg, G. Chem. Eur. J. 2007, 13, 6908.
(b) Korolev, D. N.; Bumagin, N. A. Tetrahedron Lett. 2006,
47, 4225.
(
(
13) (a) Shmidt, A. F.; Mametova, L. V. Kinet. Catal. 1996, 37,
(18) In water, these compounds precipitate the catalyst, making it
looking like black oil, probably because of the interaction
with the hydrophobic part of the micelle.
406. (b) Bhanage, B. M.; Shirai, M.; Arai, M. J. Mol. Catal.
A: Chem. 1999, 145, 69.
14) (a) Bronstein, L. M.; Chernyshov, D. M.; Timofeeva, G. I.;
Dubrovina, L. V.; Valetsky, P. M.; Obolonkova, E. S.;
Khokhlov, A. R. Langmuir 2000, 16, 3626. (b) Bronstein,
L. M.; Chernyshov, D. M.; Vorontsov, E.; Timofeeva, G. I.;
Dubrovina, L. V.; Valetsky, P. M.; Kazakov, S.; Khokhlov,
A. R. J. Phys. Chem. B. 2001, 105, 9077.
(19) The catalyst ultrafiltration was performed with equipment
XFUF 04701 Millipore Ultrafiltration Stirred Cell, 47 mm;
the membrane of regenerated cellulose with NMWL 3,000.
(20) (a) It was reported that the PdNP stabilized by poly(N-vinyl-
2-pyrrolidone) (PVP) had grown in size during S–M reaction
but this reaction had proceeded at 100 °C in 12 h with low
1
0b
(
15) For reviews, see: (a) Beletskaya, I. P.; Cheprakov, A. V. In
Organic Synthesis in Water; Grieco, P., Ed.; Blackie:
London, 1998, 141. (b) Beletskaya, I. P.; Cheprakov, A. V.
In Handbook of Organopalladium Chemistry, Vol. 2;
Negishi, E. I., Ed.; Wiley: New York, 2002, 2957. (c) Li,
C.-J. Chem. Rev. 2005, 105, 3095. (d) Organic Reactions in
Water; Lindström, U. M., Ed.; Blackwell Publishing:
Oxford, 2007.
yield of cross-coupling product. (b) Li, Y.; Boone, E.; El-
Sayed, M. Langmuir 2002, 18, 4921.
(21) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314.
(22) (a) Howard, A.; Mitchell, C.; Egdell, R. Surf. Sci. 2002, 515,
L504. (b) Hu, J.; Liu, Y. Langmuir 2005, 21, 2121.
Synlett 2008, No. 10, 1547–1552 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.