Solid-supported palladium nano and microparticles: An efficient heterogeneous catalyst for ligand-free Suzuki-Miyaura cross coupling reaction

Article abstract of DOI:10.1016/j.tetlet.2011.01.009

Solid-supported nano and microparticles of Pd(0) (SS-Pd) were prepared and used as a heterogeneous catalysts for Suzuki-Miyaura cross coupling reactions of aryl halides (chloro, bromo and iodo) and phenyl boronic acid under mild and ligand-free conditions. Scanning electron microscope (SEM) and UV-vis based studies were performed to observe the distribution of nano and microparticles of palladium over solid surface and their oxidation states. In addition, the catalyst could be reused up to seven runs without significant loss of activity and stable enough under moist conditions.

Full text of DOI:10.1016/j.tetlet.2011.01.009

Tetrahedron Letters 52 (2011) 1176–1178
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Solid-supported palladium nano and microparticles: an efficient heterogeneous
catalyst for ligand-free Suzuki–Miyaura cross coupling reaction q
Pralay Das a, , Dharminder Sharma a, Arun K. Shil a, Avnesh Kumari b
⇑
a Natural Plant Products Division, Institute of Himalayan Bioresource Technology (Council of Scientific and Industrial Research), Palampur 176061, H.P., India
b Biotechnology Division, IHBT (CSIR), Palampur, H.P., India
a r t i c l e i n f o
a b s t r a c t
Article history:
Solid-supported nano and microparticles of Pd(0) (SS-Pd) were prepared and used as heterogeneous cat-
alysts for Suzuki–Miyaura cross coupling reactions of aryl halides (chloro, bromo and iodo) and phenyl
boronic acid under mild and ligand-free conditions. Scanning electron microscope (SEM) and UV–vis
based studies were performed to observe the distribution of nano and microparticles of palladium over
solid surface and their oxidation states. In addition, the catalyst could be reused up to seven runs without
significant loss of activity and stable enough under moist conditions.
Received 8 November 2010
Revised 20 December 2010
Accepted 6 January 2011
Available online 12 January 2011
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
Suzuki–Miyaura cross coupling
Solid-supported palladium
Heterogeneous catalyst
Nano and microparticles
Ligand free
Suzuki–Miyaura cross coupling reaction for aryl–aryl bond for-
mation using aryl halides and phenyl boronic acids is of enormous
interest through catalyst development.1 In reactions involving
homogeneous catalysis,2 metal contamination of the product is
the major problem to be solved. Several heterogeneous catalysts
have been developed to improve the reaction under mild basic
conditions.3,4 Immobilized heterogeneous transition metal cata-
lysts5 play an extensive role in environmentally benign chemical
processes by facile separation of products from the reaction mix-
ture with minimum contamination of metal residues.6,7 Most of
the heterogeneous catalysts were prepared by immobilizing palla-
dium(II) on supported ligands.8 In recent years, great interest has
been placed on the use of metal nanoparticles for catalysts devel-
opment.9 Control of surface properties and chemical activities of
metal nanoparticles are important aspects for catalyst develop-
ment.10 A few recent reports showed that ligand-free heteroge-
neous nanoparticles of palladium are capable of activating aryl
chlorides for Suzuki cross coupling reaction.11
nano and microparticles of Pd(0) (SS-Pd) were performed upto seven
runs without significant loss of activity under moist conditions.
In general, nanoparticles are chemically prepared by the reduc-
tion reactions of Pd(II) salts using different reducing agents.12
When amberlite IRA 900 resin as a solid surface was treated with
NaBH4 and Pd(OAc)2 in DMF at room temperature to 100 °C for
10 min, brown colour of the solution changed to black but the solid
surface remained unchanged. Consequently, SEM image of black
Herein, we report a facile process for in situ generation of Pd(0)
nano and microparticles from Pd(OAc)2 through a reduction reac-
tion and their stable deposition over solid matrix. Further, the het-
erogeneous catalyst has been applied for Suzuki–Miyaura cross
coupling reaction of aryl halides (chlorides, bromides and iodides)
and phenyl boronic acid. Recyclability experiments of solid-supported
q
IHBT communication no. 2074.
⇑
Corresponding author. Fax: +91 1894 230433.
E-mail address: pdas@ihbt.res.in (P. Das).
Figure 1. Scanning Electron Micrographs of aggregated Pd(0) in solution.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.01.009

P. Das et al. / Tetrahedron Letters 52 (2011) 1176–1178
1177
solution showed very fast aggregation of Pd(0) in solution phase
(Fig. 1). Thus nano and microparticles of Pd(0) in solution phase
were very unstable and showed very poor catalytic activity due
to decrease in surface area through aggregation. When amberlite
IRA 900 resin as solid surface was treated with the catalytic quan-
À
tity of NaBH4 to exchange partial chloride ions by BH4 ions and
then treated with Pd(OAc)2 in DMF for 1 h at room temperature
to 100 °C the brown colour of solution changed into blackish, to
colour less and simultaneously the white solid surface turned into
black (Fig. 2).13 In situ conversion of Pd(II) into Pd(0) was moni-
tored by UV–visible absorption spectroscopy. Gradual disappear-
ance of peak at kmax 390 nm indicated the complete conversion
of Pd(II) into Pd(0) (Fig. 2).
After the complete deposition of Pd(0), SS-Pd was washed prop-
erly with water and acetone, dried under reduced pressure. SEM
analysis of SS-Pd showed that nano and microparticles of Pd(0)
deposited over solid surface are separated by polymer units to in-
hibit aggregation and their spherical shapes provided an adequate
active surface area (Fig. 3).
Suzuki–Miyaura cross coupling reaction of 1,4-dibromobenzene
(1) with phenyl boronic acid (2) using different palladium salts un-
der same condition (as described for compound 16)14 were per-
formed with poor conversions of 3 (52–65%), whereas SS-Pd as a
heterogeneous catalyst under the same condition showed an excel-
lent yield of 3 (85%) (Table 1).
Figure 3. Scanning Electron Micrographs of SS-Pd nano and microparticles (10 mg
Pd(OAc)2/1 g solid surface).
Table 1
Suzuki–Miyaura cross coupling reaction under different catalytic conditions
Using SS-Pd(0) as a heterogeneous catalyst, the cross coupling
reaction of aryl iodides with phenyl boronic acid was tested with
satisfactory yields (Table 2, entries 1 and 2). Different electron-
donating and withdrawing groups of aryl bromides were tested
for the same reaction and found that electron withdrawing groups
gave comparatively better yields (Table 2, entries 3–6). Suzuki–
Miyaura cross coupling reaction of chloroarenes and phenyl boro-
nic acid under ligand-free, mild basic conditions is indeed a rare
entry and has immense industrial importance. Excellent result
was observed when 4-nitrochlorobenzene reacts with phenyl
boronic acid under the same catalytic condition (Table 2, entry
7). Electron withdrawing group with aryl chlorides showed high
reactivity than electron-donating groups (Table 2, entries 7–10).
4-Chloroacetophenone also gave moderate yield under the same
condition (Table 2, entry 8). In the case of inactive aryl chlorides
(Table 2, entries 9–10), the highest yields were observed as 25–
35%, which is considered good under mild reaction conditions.
Recyclability experiments of SS-Pd were tested on 4-bromotol-
uene (Table 3, entry 3) upto seven runs and no significant loss of
Br
+
B(OH)2
Catalyst, K2CO3
DMF, 6 h, 110 oC
Br
1
3
2
Entry
Catalyst
3 Yielda (%)
1.
2.
3.
4.
Pd(OAc)2
Pd(Cl)2
Pd2(CH2CHCH2)2Cl2
SS-Pd
65
53
52
85
a
Isolated yield.
Table 2
Suzuki–Miyaura cross coupling reaction of aryl halides and phenyl boronic acid
X
+
B(OH)2
SS-Pd, KCO3
DMF, 110 oC, 6-12 h
R
R
14-19
4-13
Entry
Substrate (R)
X
Time (h)
Product
Yielda (%)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
4 (p-CH3)
5 (p-Naphthyl)
6 (p-CH3)
7 (p-OCH3)
8 (p-NO2)
9 (p-COCH3)
10 (p-NO2)
11 (p-COCH3)
12 (p-CH3)
13 (H)
I
I
6
6
6
6
6
10
12
12
12
12
14
15
14
16
17
18
17
18
14
19
90
85
82
80
92
85
89
50
35
25
Br
Br
Br
Br
Cl
Cl
Cl
Cl
a
Isolated yield using both fresh and reused SS-Pd in different reactions.
activity was observed based on isolated yield of product 14
(82–78%).
In conclusion, a new, atom-economy and cost-effective process
for SS-Pd synthesis and their applications in Suzuki–Miyaura cross
coupling reaction have been developed. SEM and UV–vis spectro-
photometric studies were performed to characterize the nano
and microparticles deposition over solid surface and their oxida-
tion states. Different aryl iodides and bromides have been found
Figure 2. UV–vis absorption spectrophotometric study of in situ conversion of
Pd(II) salts to Pd(0). Reagents and conditions: (a) Pd(OAc)2, borohydride exchange
resins and DMF at initial stage; (b) after 1–2 min at rt (Pd(II)+ Pd(0)); (c) after
heated at 100 °C for 1 h (Pd(0)).

1178
P. Das et al. / Tetrahedron Letters 52 (2011) 1176–1178
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Recyclability experiments of SS-Pd catalyst
Run
1st
82
2nd
82
3rd
82
4th
81
5th
81
6th
80
7th
78
5. Ye, Z. W.; Yi, W. B. J. Fluorine Chem. 2008, 129, 1124.
14 Yielda(%)
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a
Isolated yield.
to be very reactive under SS-Pd catalytic conditions. Electron defi-
cient aryl chlorides are more reactive than electron rich com-
pounds under similar conditions. Due to the stability of SS-Pd
catalyst in moisture and air, it is very easy to handle under reaction
conditions and easy to separate from reaction mixture. No further
treatment is required to regenerate the catalyst for reuse. In the
near future, we feel that such moisture stable and recyclable so-
lid-supported palladium nano and microparticles as heterogeneous
catalysts will find industrial as well as academic interest in differ-
ent areas of organic transformations.
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Acknowledgements
12. (a) Chen, M.; Falkner, J.; Guo, W. H.; Zhang, J. Y.; Sayes, C.; Colvin, V. L. J. Colloid
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Authors are grateful to Dr. P.S. Ahuja, Director IHBT for provid-
ing necessary facilities during the course of the work. We gratefully
acknowledge the financial assistance from the Department of Sci-
ence & Technology (Nano Mission), New Delhi (Grant No. SR/NM/
NS-95/2009). D.S. and A.K.S. thank CSIR, New Delhi for awarding
junior research fellowships.
13. The solution of 100 mg of NaBH4 in 30 ml of water was added to 4 g of
amberliteÒ IRA 900 resin (chloride form) (Across, BE) in a 100 ml flask. The
mixture was stirred for 4 h at room temperature. Then the resin was washed
with water till pH became neutral and then with acetone to remove water from
the solid surface. The resin beads (borohydride exchanged) were dried under
reduced pressure. Borohydride exchanged resin beads (solid surface) (1 g)
were added into a solution of Palladium(II) acetate (10 mg) in DMF (2 ml) and
then the mixture was stirred at room temperature to 100 °C for 1 h or till the
brown colour of the solution was changed into colourless and simultaneously
white solid beads were turned into blackish. After cooling, the beads were
filtered through a cotton bed, washed with water and acetone, and dried under
reduced pressure.
14. 4-Methoxybiphenyl (16). A mixture of 7 (153 mg, 0.82 mmol), phenyl boronic
acid (100 mg, 0.82 mmol), potassium carbonate (452 mg, 3.28 mmol), SS-Pd
(370 mg, 2 mol% Pd) and DMF (1 ml) was stirred at 110 °C for 6 h under
nitrogen atmosphere. The reaction was monitored by TLC and after completion
the reaction mixture was cooled, diluted with 3 ml of water and filtered
through the cotton bed. The filtrate was extracted with ethyl acetate (3 Â 2 ml)
and dried over anhydrous Na2SO4. The solvent was evaporated under reduced
pressure and the crude residue was purified by silica gel (mesh 60–120)
column chromatography (hexane 100%) afforded 16 as a light white solid
(122 mg, 81%); mp 88–92 °C; 1H NMR (300 MHz, CDCl3) d 3.92 (s, 3H), 7.06–
7.08 (m, 2H) 7.37–7.42 (m, 1H), 7.48–7.53 (m, 2H), 7.61–7.67 (m, 4H); 13C NMR
(75 MHz, CDCl3) d 55.10, 114.18 (2C), 126.59, 126.65 (2C), 128.07 (2C), 128.66
(2C), 133.70, 140.77, 159.14.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.01.009.
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