Tetrahedron Letters
Enhanced heterogeneously catalyzed Suzuki–Miyaura reaction over
SiliaCat Pd(0)
Valerica Pandarus a, Delphine Desplantier-Giscard a, Genevieve Gingras a, Rosaria Ciriminna b,
Piera Demma Carà b, François Béland a, , Mario Pagliaro b,
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a SiliCycle Inc., 2500, Parc-Technologique Blvd, Quebec City, Quebec G1P 4S6, Canada
b Istituto per lo Studio dei Materiali Nanostrutturati, CNR, via U. La Malfa 153, 90146 Palermo, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The SiliaCat Pd(0) solid catalyst can be efficiently employed in the Suzuki–Miyaura cross-coupling of an
ample variety of haloarenes, including economically viable chloroarenes. The catalyst can be extensively
recycled without loss of activity and with low leaching of valued palladium, opening the route to wide-
spread utilization of the method to afford high yields of biaryls devoid of contaminating by-products.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 3 May 2013
Revised 19 June 2013
Accepted 21 June 2013
Available online 29 June 2013
Keywords:
Heterogeneous cross-coupling
Suzuki coupling
Catalyst immobilization
Palladium
SiliaCat Pd(0)
The palladium catalyzed Suzuki–Miyaura cross-coupling of
arylboronic acids with aryl halides is one of the most powerful
tools for carbon–carbon bond formation in modern organic synthe-
sis.1 The reaction tolerates a broad range of functional groups in
the coupling partners and is usually performed in solution, at room
temperature in many cases, and often using simple palladium salts
such as PdCl2, with low amounts of catalyst.2
Cat Pd(0)6 catalyst selectively affords high yields of coupled prod-
ucts.7 Now, we show how to broaden the scope of the method to
convert also readily available aryl chlorides and access high reac-
tion rates for both aryl chlorides and bromides using microwave
irradiation.
The two catalyst samples used throughout this work are those
now commercially available following optimization in light of
manufacturing requirements.8 The catalysts were first tested at
60 °C and at room temperature (22 °C) in the conversion of aryl io-
dides under optimized conditions in MeOH, EtOH, or n-PrOH/
MeOH (v/v, 1/1) mixture as protic solvents which are generally re-
quired for optimal reaction, while K2CO3 was the base normally
employed. No inert atmosphere was required.
Results in Table 1 show that using 0.5 mol % SiliaCat Pd(0) the
Suzuki–Miyaura can also be carried out at room temperature, with
complete conversion of the substrate after 6.5 h (entry 4 in Table 1).
The reaction time can be lowered to 2 h upon by simply doubling
the catalyst amount to 1 mol % (entry 5). The previous conditions,
using a slight excess (1.2 equiv) of boronic acid, were thus tested in
the cross-coupling of other aryl iodide substrates with different
boronic acid pinacol esters (Table 2).
Complete conversion was obtained for 2-iodothiophene after
1 h using phenylboronic acid pinacol ester (entry 1 in Table 2) or
4-chlorophenylboronic acid pinacol ester (entry 2). For 4-iodo-1-
methyl-1H-pyrazole more than 90% yield was obtained after 4 h
over 0.5 mol % catalyst (entry 3) or after 1 h when using 1 mol % Si-
liaCat Pd(0).
The original paper3 described cross-coupling of two functional-
ized alkenes, but subsequent work mostly addressed the synthesis
of biaryls, whose structure is found in various biologically active
compounds, in organic light emitting diodes, and in conducting
polymers. The two main problems adding cost to the products of
traditional Suzuki–Miyaura reaction, lie in the Pd impurities left
in the reaction product (for e.g., the EMEA approved upper limit
for Pd in final pharmaceuticals is in the 5–10 ppm range);4 and
to the fact that low cost chloroarenes cannot be employed due to
the stability of the C–Cl bond. A large body of research has there-
fore been devoted in the last decade to identify recyclable and truly
heterogeneous Pd catalysts of broad scope.5
In this context, we have recently reported that the heteroge-
neous Suzuki–Miyaura cross-coupling of iodo and bromoarenes
in environmentally benign alcohol over the sol–gel entrapped Silia-
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Corresponding authors. Fax: +1 418 874 0355 (F.B.); tel.: +39 091 680 93 70;
fax: +39 091 680 92 47 (M.P.).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.