Palladium-dodecanethiolate nanoparticles as stable and recyclable catalysts for the Suzuki-Miyaura reaction of aryl halides under ambient conditions

Article abstract of DOI:10.1016/j.tetlet.2004.10.080

Palladium-dodecanethiolate nanoparticles (PdTNs) catalyze the quantitative Suzuki-Miyaura coupling of halogenoarenes under biphasic conditions in THF/water at room temperature and can be recovered by precipitation using ethanol and re-used.

Full text of DOI:10.1016/j.tetlet.2004.10.080

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 9443–9445
Palladium–dodecanethiolate nanoparticles as stable and
recyclable catalysts for the Suzuki–Miyaura reaction of aryl
halides under ambient conditions
Feng Lu, Jaime Ruiz and Didier Astruc*
´
Nanosciences and Catalysis Group, LCOO, UMR CNRS No 5802, Universite BordeauxI, 33405 Talence Cedex, France
Received 1 September 2004; revised 15 October 2004; accepted 15 October 2004
Available online 6 November 2004
Abstract—Palladium–dodecanethiolate nanoparticles (PdTNs) catalyze the quantitative Suzuki–Miyaura coupling of halogenoare-
nes under biphasic conditions in THF/water at room temperature and can be recovered by precipitation using ethanol and re-used.
Ó 2004 Elsevier Ltd. All rights reserved.
Palladium-catalyzed cross-coupling reactions of aryl
halides with aryl boronic acids, referred to as the
Suzuki–Miyaura reactions, are useful methods for the
synthesis of unsymmetrical biaryls. This reaction is
applied in the synthesis of natural products and it is
widely used in industry (equation 1).1
molecular components onto the Pd NP surface.2,3 More
recently CrooksÕ group has investigated the catalytic
properties of Pd NPs embedded in PAMAM dendrimers
and reported remarkable efficiencies and selectivities.5
Au-thiolate NPs are well known6 and Ullman and co-
workers have reported alkanethiol Pt NPs.7 Some thio-
late Pd NPs (PdTNPs) and their catalytic activity in the
hydrogenation of allylamine was published by KaiferÕs
group.8 These authors9 and NewmanÕs group10 have
reported the catalytic activity in the Suzuki–Miyaura
reactions of PdTNPs modified, respectively, with b-
cyclodextrin and polyoxometallates. Recently, Fox and
coworkers reported the catalytic behavior, including
for the Suzuki–Miyaura reaction, of Pd NP-cored dend-
rimers.11 In all these reports of the Pd NP-catalyzed
Suzuki–Miyaura reactions,8–10 catalysis was run at
relatively high temperatures (typically in refluxing water,
ethanol or a mixture of these solvents). Indeed, thiols
and thiolates are believed to be poisonous compounds
that should be avoided in catalysis by NPs.4,7,8
Whereas homogeneous catalysts exhibit a good reactiv-
ity and selectivity, heterogeneous catalysts avoid the use
of phosphines and are also advantageous for catalyst re-
moval from reaction mixtures and recycling. Nanoparti-
cles (NP),2 in particular Pd NPs whose general activity
in catalysis is well known,3 offer a compromise that
has been recently exploited and also avoid phosphines.
On the other hand, alkyl thiols and thiolate are well
known as poisons that inhibit the catalysis of reactions
by nanoparticles.4 It is thus necessary to gain insight
into the mode of reactivity of NPs even with thiolate lig-
ands. We report herein a surprising good reactivity of
well-defined dodecanethiolate Pd nanoparticles for the
Suzuki–Miyaura C–C coupling reaction, actually under
ambient conditions for the first time with such simple
nanoparticles. The formation of Pd NPs involves vari-
ous stabilizers that not only protect the metal core,
but also sterically inhibits its access. Pd NPs that are
used in catalysis are generally stabilized by incorpora-
tion into a polymer, since the lack of ligands in poly-
mer-embedded Pd NPs favors the access of the
Given the recent report that the Suzuki–Miyaura reac-
tion can be quantitatively achieved at 150°C in water
in the absence of catalyst,12 we have investigated the
synthesis and catalytic properties (including recyclabil-
ity) of simple dodecanethiolate Pd NPs (PdTNPs) for
the Suzuki–Miyaura reaction at room temperature; we
now report preliminary data showing a remarkable effi-
ciency and recyclability.
The PdTNPs tested in this study were prepared using a
procedure inspired by NishiharaÕs report13 using the
reduction of [PdCl2(CH3CN)2] by LiBEt3H in THF in
Keywords: Palladium; Thiolate; Nanoparticle; Catalysis; Coupling.
*
Corresponding author. Tel.: +33 05 40 00 62 71; fax: +33 05 40 00 66
46; e-mail: d.astruc@lcoo.u-bordeaux1.fr
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.10.080

9444
F. Lu et al. / Tetrahedron Letters 45 (2004) 9443–9445
Table 1. Suzuki–Miyaura cross-coupling reaction with 1 (Eq. 1)a
Entry R in 1 X in 1 Temperature (°C) Time Yieldc (%)
the presence of tetra-octylammonium bromide, followed
after 0.5h by the addition of 1-dodecanethiol in THF to
the black Pd NP suspension and precipitation using eth-
anol; purification was achieved by reprecipitation by
acetone of a toluene solution and washing with acetone.
The PdTNPs are relatively monodisperse, with a mean
diameter of 2.3 0.5nm as indicated by the TEM pic-
ture and histogram shown in Figure 1.
1
H
I
20
63
20
1d
1h
1d
100
100
100
2
CH3
CH3OI
I
3
20
17h
100
4b
5b
6
I
I
20
20
20
63
20
20
15h
15h
1d
87
70
I
Br
Br
H
100
2.5h 100
We find that good results for the catalysis of the Suzuki–
Miyaura reaction between iodo- or bromobenzene and
phenylboronic acid were obtained by using PdTNs
(1mol% Pd vs halogenoarene) in a 2:1 biphasic mixture
of THF–water with NaOH as a base14 under ambient
conditions (Table 1). For instance, on the mmol scale,
2.5mg of PdTNs was used leading to quantitative
heterocoupling of either iodo- or bromobenzene at
20°C after one day (1). Alternatively, the reaction could
also reach completion when the mixture was heated for
1h at 63°C, a temperature at which the PdTNPs are sta-
ble. The results are gathered in Table 1. Chlorobenzene,
for which bulky, electron-rich phosphines are most often
required also give some coupling at 20°C using homoge-
neous conditions (see Table 1) with PdTNPs, although
the yield is lower and the reaction times longer than with
the other halogenoarenes.
7d
8e
H
CH3
Cl
Cl
5d
3d
52
27
aReaction conditions: 2mmol of substrate, 3mmol phenylboronic acid,
5mg PdTN catalyst, 6mmol NaOH, THF/H2O(16mL/8mL).
b0.5mmol aryl halide, 1.5mmol PhB(OH)2, 2.5mg PdTN catalyst,
3mmol NaOH, THF/H2O(8mL/4mL), the product is terphenyl.
cIsolated yield.
d1mmol aryl halide, 1.2mmol PhB(OH)2, 6mL THF, 3mmol KF,
12mg PdTN catalyst.
e1mmol aryl halide, 1.2mmol PhB(OH)2, 6mL THF, 3mmol KF,
2.5mg PdTN catalyst.
We checked the recyclability and re-use of the PdTNP
catalyst in the case of the Suzuki–Miyaura reaction
with iodobenzene. The PdTNPs could be precipitated
after the reaction by addition of ethanol, filtered,
and re-used at least six times using this recycling
procedure for identical reactions. The reaction yield
remained quantitative or almost so upon these six recy-
cling reactions (resp. 100%, 100%, 98%, 94%, 92%, and
87%).
ð1Þ
In conclusion, we have shown that easily accessible,
well-defined PdTNPs can serve as efficient, recyclable
catalysts for the Suzuki–Miyaura C–C coupling reaction
of aromatic iodides and bromides under ambient condi-
tions for the first time. The PdTNPs are not as active as
the recently designed molecular palladium catalysts for
the Suzuki–Miyaura coupling of arylchlorides,15 but
they are phosphine-free and recyclable. The modest
yields obtained so far under ambient conditions with
the aryl chlorides open the route to more sophistications
of the PdTNP structure in order to improve these pre-
liminary results. The efficiency and usefulness of these
PdTNPs are already remarkable, however, and research
is in progress in our laboratory to improve their engi-
neering. This work also shows that, contrary to common
belief, extensive use of simple thiolate ligands is not
counter-productive in catalysis. It is especially notewor-
thy that Pd NP covered with ligands are so active, which
may imply that the edges and vertices of the polyhedral
nanoparticle cores play an important role for the reac-
tivity in nanoparticle catalysis as recently pointed out
by El-Sayed.2
Acknowledgements
Financial support from the Institut Universitaire de
France (IUF), the Centre National de la Recherche Sci-
entifique (CNRS) and the University Bordeaux I is
gratefully acknowledged.
Figure 1. TEM picture and histogram of the PdTNPs with diameter of
2.3 0.3nm.

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