A practical protocol for the hiyama cross-coupling reaction catalyzed by palladium on carbon

Article abstract of DOI:10.1055/s-0032-1316801

A method for the palladium on carbon (Pd/C) catalyzed cross-coupling reaction between aryl halides and trialkoxy(aryl)silanes in the presence of a small amount of water is established using tris(4-fluorophenyl)phosphine as the ligand. A range of biaryl compounds is prepared using this protocol. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0032-1316801

40▌
PRACTICAL SYNTHETIC PROCEDURES
pAracPticarlasycntthiecticaplroPcedruoretsocol for the Hiyama Cross-Coupling Reaction Catalyzed by
Palladium on Carbon
Hiyama Cross-Coupling Catalyzed by Palladium on Carbon
Yasunari Monguchi,* Takayoshi Yanase, Shigeki Mori, Hironao Sajiki*
Laboratory of Organic Chemistry, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi,
Gifu 501-1196, Japan
Fax +81(58)2308109; E-mail: monguchi@gifu-pu.ac.jp; E-mail: sajiki@gifu-pu.ac.jp
PSP
Received: 11.09.2012; Accepted after revision: 20.09.2012
No240
Abstract: A method for the palladium on carbon (Pd/C) catalyzed cross-coupling reaction between aryl halides and trialkoxy(aryl)silanes
in the presence of a small amount of water is established using tris(4-fluorophenyl)phosphine as the ligand. A range of biaryl compounds
is prepared using this protocol.
Key words: palladium, cross-coupling, heterogeneous, silicon, biaryls
10% Pd/C (0.5 mol%)
(4-FC6H4)3P (1 mol%)
TBAF·3H2O (2 equiv)
Si(OR3)3
R2
X
R1
X = I, Br, Cl
R2
+
R1
4.8% aq toluene
120 °C
1.5 equiv
R3 = Me, Et
up to 90% yield
Scheme 1 Pd/C-catalyzed cross-coupling between aryl halides and trialkoxy(aryl)silanes in the presence of (4-F-C6H4)3P, TBAF·3H2O and a
small amount of water in toluene
The palladium-catalyzed cross-coupling reaction between water as an additive on the reaction progress, the use of
organic halides and organosilanes, the Hiyama coupling, tris(4-fluorophenyl)phosphine [(4-FC6H4)3P] as the li-
is of practical use due to the low toxicity of organosilanes gand, and broad substrate applicability were demonstrat-
and the easy access it provides to biaryl skeletons, which ed.11 Furthermore, a ligand-free palladium on carbon
are partial structures of various functional molecules, in- catalyzed Hiyama reaction was achieved by the addition
cluding pharmaceuticals.1,2 The development of heteroge- of acetic acid.12 In this report, a detailed investigation
neous palladium-catalyzed cross-coupling reactions has leading to optimized conditions in the presence of tris(4-
attracted significant attention from both environmental fluorophenyl)phosphine as the ligand, and their applica-
and economic points of view, as the catalysts can be read- bility to a range of substrates is discussed (Scheme 1).
ily recovered from the reaction mixture.3 Although the ap-
While the cross-coupling reaction between 1-iodo-4-ni-
plication of palladium nanoparticles on surfactants,4
trobenzene and triethoxy(phenyl)silane (1.5 equiv) in the
polyethylene glycol,5 and a dendrimer6 have been report-
ed as heterogeneous catalysts for the Hiyama cross-cou-
pling, many of them require complicated procedures for
presence of 1,1′-bis(diphenylphosphino)ferrocene (dppf)
(10 mol%) and tetra-n-butylammonium fluoride trihy-
drate (TBAF·3H2O) (2 equiv) at 120 °C (bath tempera-
their preparation. We have been interested in the applica-
ture) proceeded disappointingly in alcoholic, ethereal, and
tion of palladium on carbon (Pd/C), a commercially avail-
polar aprotic solvents (Table 1, entries 1–9), toluene was
able conventional hydrogenation catalyst,7 for cross-
found to be a good solvent leading to the desired cross-
coupling reactions.8,9 Although a report on the palladium
coupled product, 4-nitrobiphenyl, in 64% yield (Table 1,
on carbon catalyzed Hiyama coupling was published10
entry 10). Although tetra-n-butylammonium fluoride tri-
hydrate and tetra-n-butylammonium fluoride in tetrahy-
during the course of our preparation of a previous commu-
nication,11 it focused on the variation in the catalyst activ-
drofuran
were
both
able
to
activate
ity of palladium on carbon supplied by different vendors
toward several types of cross-coupling reactions, includ-
ing the Hiyama reaction. However, the reaction condi-
tions and substrate scope were not investigated in detail.
In our above-mentioned communication, the effect of
triethoxy(phenyl)silane to promote the cross-coupling
(Table 1, entries 10 and 15), no reaction took place using
other inorganic fluoride salts, probably due to their poor
solubility in toluene (Table 1, entries 11–14). Therefore,
tetra-n-butylammonium fluoride trihydrate was chosen as
the activator of choice for silane derivatives because of its
better efficiency in the coupling reactions.
SYNTHESIS 2013, 45, 0040–0044
Advanced online publication: 09.10.2012
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DOI: 10.1055/s-0032-1316801; Art ID: SS-2012-Z0714-PSP
© Georg Thieme Verlag Stuttgart · New York

PRACTICAL SYNTHETIC PROCEDURES
Hiyama Cross-Coupling Catalyzed by Palladium on Carbon
41
Table 1 Evaluation of Solvents and Fluoride Sources on the 10%
Pd/C-Catalyzed Cross-Coupling between 1-Iodo-4-nitrobenzene and
Triethoxy(phenyl)silane
tylphosphino)biphenyl (JohnPhos), did not promote the
coupling as efficiently (Table 2, entries 15 and 16).
10% Pd/C (5 mol%)
DPPF (10 mol%)
Table 2 Evaluation of Ligands for the 10% Pd/C-Catalyzed Cross-
Coupling between 1-Iodo-4-nitrobenzene and Triethoxy(phenyl)si-
lane
I
Ph
F
– source (2 equiv)
PhSi(OEt)3
1.5 equiv
+
120 °C
O2N
O2N
10% Pd/C (5 mol%)
ligand
TBAF·3H2O (2 equiv)
I
Ph
Entry
Solvent
F– source
Time (h) Yield (%)a
+
PhSi(OEt)3
1.5 equiv
toluene
120 °C
O2N
O2N
1
MeOH
THF
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
TBAF·3H2O
NaF
24
8
0
mol%a
Time (h) Yield (%)b
2
7
Entry
Ligand
3
1,4-dioxane
MeCN
DMPU
NMP
5
7
1c
2
–
–
24
14
24
24
24
20
6
52
64
50
39
46
63
69
83
56
53
62
66
50
39
58
45
4
1
trace
0
dppf
dppe
dppp
dppb
PPh3
10
10
10
10
20
20
20
20
20
20
20
20
5
3
3
6
3
8b
16
17b
24b
64
0
4
7
DMF
1
5
8
DMAc
DMSO
toluene
toluene
toluene
toluene
toluene
toluene
3
6
9
3
7
(4-ClC6H4)3P
(4-FC6H4)3P
(C6F5)3P
10
11
12
13
14
15
14
9
8
6
9
6
KF
14
14
9
0
10
11
12
13
14
15
16
(2-MeC6H4)3P
(3-MeC6H4)3P
(4-MeC6H4)3P
(4-MeOC6H4)3P
24
20
20
24
20
12
24
CsF
0
CuF2
0
TBAF in THF
5
52
a Determined by 1H NMR spectroscopy with 1,4-dioxane as the inter-
nal standard.
[2,6-(MeO)2C6H3]3P 20
b Yield of isolated product.
Cy3P
20
20
c DMA = N,N-dimethylacetamide.
JohnPhos
a The total amount of phosphine atoms in each entry are equal.
b Determined by 1H NMR spectroscopy with 1,4-dioxane as the inter-
nal standard.
Interestingly, this cross-coupling was found to proceed
under ligand-free conditions to afford 4-nitrobiphenyl in
52% yield (Table 2, entry 1).12 No other bidentate ligands,
apart from 1,1′-bis(diphenylphosphino)ferrocene, in-
creased the efficiency of the reaction (Table 2, entries 2–
5). When triphenylphosphine derivatives were employed
as monodentate ligands, the reaction efficiency was af-
fected strongly by the electron density of the aromatic nu-
clei (Table 2, entries 7–14); triphenylphosphine
derivatives bearing electron-withdrawing chlorine or flu-
orine atoms on each aromatic ring were found to be good
ligands (Table 2, entries 7 and 8). However, no improve-
ment in the yield was observed when using perfluorinated
triphenylphosphine as the ligand (Table 2, entry 9). On the
other hand, ligands with one or two electron-donating
substituents on the aromatic rings proved to be less effec-
tive in this coupling reaction (Table 2, entries 10–14).
Furthermore, monodentate phosphine ligands with bulky
and non-aromatic substituents on the phosphine atom,
such as tricyclohexylphosphine (Cy3P) and 2-(di-tert-bu-
c PhSi(OEt)3 (2 equiv) were used.
When dried tetra-n-butylammonium fluoride13 was used
for the cross-coupling reactions, the efficiency decreased
significantly in comparison to those using tetra-n-butyl-
ammonium fluoride trihydrate (Table 3, entries 1 vs. 2 and
6 vs. 7), suggesting that the presence of water promotes
the coupling. The yield was improved significantly by
adding a small amount of water (4.8 v/v% aqueous tolu-
ene) (Table 3, entries 3 and 8). Increasing the amount of
added water (9.1, 17 or 31 v/v%) did not improve the re-
sults further (Table 3, entries 4, 5, 9 and 10). These results
indicate that addition of a small amount of water acceler-
ates the present cross-coupling reaction. Therefore, tris(4-
fluorophenyl)phosphine and 4.8 v/v% aqueous toluene
were chosen as the optimum ligand and solvent, respec-
tively.14–17
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 40–44

42
Y. Monguchi et al.
PRACTICAL SYNTHETIC PROCEDURES
Table 4 Optimization of the Amount of Catalyst and Ligand
Table 3 Effect of Water on the 10% Pd/C-Catalyzed Cross-Coupling
between 1-Iodo-4-nitrobenzene and Triethoxy(phenyl)silane
10% Pd/C
(4-FC6H4)3P
TBAF·3H2O (2 equiv)
10% Pd/C (5 mol%)
ligand (20 mol%)
TBAF·3H2O (2 equiv)
I
Ph
I
Ph
PhSi(OEt)3
1.5 equiv
+
PhSi(OEt)3
1.5 equiv
4.8% aq toluene
+
O2N
O2N
aq toluene
120 °C
O2N
O2N
Entry
Catalyst
(mol%)
Ligand
(mol%)
Temp
(°C)a
Time
(h)
Yield
(%)b
Entry
Ligand
H2O (v/v%)a Time (h) Yield (%)b
1c
2
(4-ClC6H4)3P
(4-ClC6H4)3P
(4-ClC6H4)3P
(4-ClC6H4)3P
(4-ClC6H4)3P
(4-FC6H4)3P
(4-FC6H4)3P
(4-FC6H4)3P
(4-FC6H4)3P
(4-FC6H4)3P
–
24
6
64
69
80
80
24
70
83
83
80
64
1
2
3
4
5
6
7
8
9
5
20
15
10
5
120
120
120
120
120
120
80
6
83
83
87
76
90
81
66
89
89
5
9
–
5
9
3
4.8
9.1
33
–
6
5
9
4
13
24
17
6
0.5
0.3
0.5
0.5
0.5
1
6
5
6c
7
0.6
1
6
24
24
6
–
1
100
140
8
4.8
9.1
17
4
1
9
4
a Bath temperature.
10
24
b Determined by 1H NMR spectroscopy with 1,4-dioxane as the inter-
nal standard.
a The percentage indicates the ratio of the volume of water to the
mixed solvent volume.
b Determined by 1H NMR spectroscopy with 1,4-dioxane as the inter-
nal standard.
c TBAF·3H2O was dried at 90 °C under reduced pressure for 30 min- substitution patterns (Table 5, entries 1–17). However, 1-
utes prior to use.13
bromonaphthalene was converted into the corresponding
biaryl in a low 31% yield (Table 5, entry 18). Heteroaryl-
phenyl moieties are found as important subunits in a vari-
ety of functional materials, such as pharmaceuticals, agro-
Next, the amount of the ligand [(4-F-C6H4)3P] required for
chemicals, liquid crystals and natural products. Although
a successful cross-coupling was investigated at 120 °C us-
heteroatoms sometimes cause a reduction in catalytic ac-
ing 10% palladium on carbon (5 mol%) as the catalyst. It
tivity, as catalyst poisons due to strong coordination with
was found that 10 mol% of the ligand (2 equiv with re-
the transition metal center of the catalyst,18 the phenyl-
spect to the amount of 10% Pd/C) was sufficient to cata-
ation of both 3-iodopyridine and 3-bromopyridine pro-
lyze the cross-coupling without any significant
ceeded smoothly under the present conditions to give the
suppression of the reaction efficiency (Table 4, entries 1–
desired phenylpyridines in very high yields (Table 5, en-
4). Furthermore, the amount of 10% palladium on carbon
tries 19 and 20). Furthermore, the desired phenylated
could be decreased (from 5 mol% to 0.5 mol%) in the
product was even obtained from the reaction of 1-chloro-
presence of tris(4-fluorophenyl)phosphine (1 mol%) to
4-nitrobenzene, in a moderate yield, despite the low reac-
give the corresponding biphenyl in 90% yield (Table 4,
tivity of chloroarenes based on their difficult oxidative ad-
entry 5); a further decrease in the amount of catalyst (to
dition to the metal in palladium-catalyzed cross-
0.3%) reduced the rate of the reaction (Table 4, entry 6).
couplings.
The reaction efficiency decreased at temperatures lower
than 120 °C (Table 4, entries 7 and 8) and was almost the We previously found that, during the course of a study on
same at 140 °C (Table 4, entry 9). Hence, subsequent in- the palladium on carbon catalyzed aromatic amination of
vestigations on the substrate scope of the Hiyama cross- aryl halides,9h a very small amount of palladium leached
coupling were carried out using the combination of 10% from the catalyst into the reaction medium when using
palladium on carbon (5 mol%) and tris(4-fluorophe- 1,1′-bis(diphenylphosphino)ferrocene as the phosphine li-
nyl)phosphine (1 mol%) at 120 °C (Table 5).
gand, which proved to be a very active catalyst species.
Since tris(4-fluorophenyl)phosphine was used as the
phosphine ligand in the present reaction, the extent of pal-
ladium leaching was also examined. Following the cross-
coupling reaction of 1-iodo-4-nitrobenzene with
triethoxy(phenyl)silane (1.5 equiv) under the optimized
conditions, the reaction mixture was filtered successively
through 0.45 and 0.20 μm membrane filters, and the con-
It was found that trimethoxy(phenyl)silanes also reacted
with aryl halides to afford the corresponding biphenyls in
good yields (Table 5, entries 2 and 9). Both iodobenzene
and bromobenzene derivatives, bearing either an electron-
withdrawing or electron-donating group on the aromatic
ring, readily underwent cross-coupling with trialkoxy(ar-
yl)silanes regardless of the nature of their substituents and
Synthesis 2013, 45, 40–44
© Georg Thieme Verlag Stuttgart · New York

PRACTICAL SYNTHETIC PROCEDURES
Hiyama Cross-Coupling Catalyzed by Palladium on Carbon
43
promoter. While a small amount of palladium metal
leaching from the catalyst into the reaction mixture was
observed, the leached palladium species could be re-
moved completely by silica gel column chromatography
to afford the uncontaminated cross-coupled product. It is
worth noting that only 0.5 mol% of the palladium catalyst
was required to promote the cross-coupling effectively.
The results of the present investigation complements our
previous report on the ligand-free palladium on carbon
(0.5 mol%) catalyzed Hiyama cross-coupling reaction in
the presence of acetic acid (1.5 equiv) and tetra-n-butyl-
ammonium fluoride trihydrate (2 equiv) in toluene.12
Table 5 Cross-Coupling of Various Aryl Halides with Triethoxy(ar-
yl)silanes
10% Pd/C (0.5 mol%)
(4-C6H4)3P (1 mol%)
TBAF·3H2O (2 equiv)
Si(OR2)3
R1
Ar
X
+
R1
4.8% aq toluene
120 °C
Ar
1.5 equiv
Entry
Ar–X
R1
R2
Time Yield
(h)
(%)a
1
4-O2NC6H4I
H
Et
Me
Et
Et
Et
Et
Et
Et
Me
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
6
88
83
75
80
85
83
79
81
80
85
86
86
49b
83
90
80
77
31b
85
81
47
2
4-O2NC6H4I
H
6
10% Pd/C (K-type, NX-type; dry) was supplied by the N.E. Chem-
cat Corporation (Tokyo, Japan). All reagents and solvents were pur-
chased from commercial sources and were used without further
purification. Flash column chromatography was performed using
silica gel 60 N (Kanto Chemical Co., Inc., 63–210 μm spherical,
neutral).
3
4-O2NC6H4I
4-Cl
4-Me
H
6
4
4-O2NC6H4I
12
6
5
4-MeOC6H4I
4-MeOC6H4I
4-MeOC6H4I
4-O2NC6H4Br
4-O2NC6H4Br
4-NCC6H4Br
4-OHCC6H4Br
4-AcC6H4Br
6
4-Cl
4-Me
H
9
Hiyama Cross-Coupling; General Procedure
7
12
6
A mixture of TBAF·3H2O (631 mg, 2.00 mmol), 10% Pd/C (5.4
mg, 5.00 μmol), tris(4-fluorophenyl)phosphine (3.2 mg, 10.0
μmol), aryl halide (1.00 mmol), and triethoxy(aryl)silane (1.50
mmol) in toluene–H2O (2 mL/100 μL) was stirred at 120 °C under
an Ar atmosphere (balloon) until the aryl halide was completely
consumed [monitored by GC-MS (JMS-Q1000GC Mk 2 from
JEOL, Tokyo) and TLC], and then passed through a Celite pad to
remove the catalyst. To the filtrate were added EtOAc (50 mL) and
sat. aq NH4Cl soln (50 mL), and the layers were separated. The aq
layer was extracted with EtOAc (10 mL) and the combined organic
layers dried over MgSO4, filtered, and concentrated in vacuo. The
residue was purified by flash column chromatography on silica gel
(hexane–EtOAc) to give the analytically pure biphenyl. The struc-
ture of the product was confirmed by comparison of NMR spectro-
scopic data with those reported in the literature (see the Supporting
Information).
8
9
H
4.5
12
12
12
24
24
12
17
24
24
12
18
18
10
11
12
13
14
15
16
17
18
19
20
21
H
H
H
3-AcC6H4Br
H
4-MeOC6H4Br
3-MeOC6H4Br
2-MeOC6H4Br
4-MeOC6H4Br
1-bromonaphthalene
3-iodopyridine
3-bromopyridine
4-O2NC6H4Cl
H
H
H
4-Me
H
Acknowledgment
We sincerely thank N.E. Chemcat Corporation for the gift of the ca-
talysts.
H
H
Supporting Information for this article is available online at
H
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
m
tgioSrantnugIifoop
r
itmnatr
a Yield of isolated product.
b Determined by 1H NMR spectroscopy with 1,4-dioxane as the inter-
nal standard.
References
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T.; Shirakawa, E. In Handbook of Organopalladium
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removed readily to a less than detectable level (<1 ppm).
In conclusion, we have demonstrated an efficient and
practical protocol for the synthesis of biaryls via the pal-
ladium on carbon catalyzed heterogeneous Hiyama cross-
coupling in the presence of a small amount of water as a
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 40–44

44
Y. Monguchi et al.
PRACTICAL SYNTHETIC PROCEDURES
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affected when 10% Pd/C obtained from different suppliers
was used (see Table 6).
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Molecules 2011, 16, 427.
Table 6
(7) Nishimura, S. Handbook of Heterogeneous Catalytic
Hydrogenation for Organic Synthesis; Wiley-Interscience:
New York, 2001.
Supplier
Time (h)
Yield (%)a
Aldrich
6
6
6
4
6
87
83
89
87
90
(8) For reviews on palladium on carbon catalyzed cross-
coupling reactions, see: (a) Nishida, M.; Tagata, T. J. Synth.
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(d) Felpin, F.-X.; Ayad, T.; Mitra, S. Eur. J. Org. Chem.
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Fouquet, E. ChemSusChem 2008, 1, 718. (g) Pal, M. Synlett
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C.; Fouquet, E.; Felpin, F.-X. Adv. Synth. Catal. 2010, 352,
33. (i) Molnár, A. Chem. Rev. 2011, 111, 2251.
Acros
Wako
N.E. Chemcat, NX-type
N.E. Chemcat, K-type
a Determined by 1H NMR spectroscopy with 1,4-dioxane as the inter-
nal standard.
(j) Djakovitch, L.; Batail, N.; Genelot, M. Molecules 2011,
16, 5241. (k) Djakovitch, L.; Koehler, K.; de Vries, J. G. In
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(16) When Pd(OAc)2 (5 mol%), as a homogeneous catalyst, and
(4-FC6H4)3P (20 mol%) were used for the cross-coupling of
1-iodo-4-nitrobenzene with triethoxy(phenyl)silane (1.5
equiv) in 4.8% aqueous toluene at 120 °C (bath temperature),
the desired 4-nitrobiphenyl was obtained in 72% yield,
together with the homo-coupled product derived from the
iodide, 4,4′-dinitrobiphenyl, in 5% yield. The use of 10%
Pd/C was more appropriate for the present conditions
compared to those applied in Table 3, entry 7; see also the
supporting information in our previous communication.11
(17) In the presence of a small amount of water, the alkoxy
groups of the triethoxy(aryl)silane would be hydrated into
the corresponding hydroxy groups, and the electrophilicity
of the silicon atom would increase. On the other hand,
addition of an excess amount of water resulted in the
formation of inactive caged siloxane derivatives, see
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(c) Sajiki, H.; Zhang, G.; Kitamura, Y.; Maegawa, T.;
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Synthesis 2013, 45, 40–44
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