1,2,3-Triazol-5-ylidene-palladium complex catalyzed Mizoroki-Heck and Sonogashira coupling reactions

Article abstract of DOI:10.1016/j.tet.2011.07.045

The bis-1,4-dimesityl-1,2,3-triazol-5-ylidene-palladium complex (1a) successfully catalyzes the Mizoroki-Heck and Sonogashira coupling reactions with aryl bromides to give the corresponding alkenes and alkynes, respectively, in good to excellent yields. In the Mizoroki-Heck reaction, electron-rich, electron-poor, and functionalized aryl bromides and alkenes are tolerated, while the substrates are limited to electron-poor aryl halides in the Sonogashira coupling reaction. The palladium complex also catalyzes cross-coupling reactions with aryl chlorides to give higher yields of products than does the bis-IMes-Pd complex analogue (2), under specific conditions.

Full text of DOI:10.1016/j.tet.2011.07.045

Tetrahedron 67 (2011) 7263e7267
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1,2,3-Triazol-5-ylideneepalladium complex catalyzed MizorokieHeck and
Sonogashira coupling reactions
*
Sayuri Inomata, Hidekatsu Hiroki, Takahiro Terashima, Kenichi Ogata, Shin-ichi Fukuzawa
Department of Applied Chemistry, Institute of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2011
Received in revised form 18 July 2011
Accepted 18 July 2011
Available online 22 July 2011
The bis-1,4-dimesityl-1,2,3-triazol-5-ylideneepalladium complex (1a) successfully catalyzes the Mizor-
okieHeck and Sonogashira coupling reactions with aryl bromides to give the corresponding alkenes and
alkynes, respectively, in good to excellent yields. In the MizorokieHeck reaction, electron-rich, electron-
poor, and functionalized aryl bromides and alkenes are tolerated, while the substrates are limited to
electron-poor aryl halides in the Sonogashira coupling reaction. The palladium complex also catalyzes
cross-coupling reactions with aryl chlorides to give higher yields of products than does the bis-IMesePd
complex analogue (2), under specific conditions.
Keywords:
1,2,3-Triazole
N-Heterocyclic carbene
Palladium
Ó 2011 Elsevier Ltd. All rights reserved.
Cross coupling
Catalysis
1. Introduction
Since its discovery 20 years ago, N-heterocyclic carbenes (NHCs)
have gained rapid popularity as versatile ligands for metal com-
plexes.1 In particular, numerous PdeNHC complexes have been
prepared and their catalytic activity in cross-coupling reactions,
such as SuzukieMiyaura and MizorokieHeck cross-coupling re-
actions2 have been investigated. The majority of NHC ligands is
based on an imidazole framework and imidazol-2-ylidenes (A) and
1,2,4-triazol-5-ylidenes (B) (Fig. 1),3 which are classified as normal
NHCs are frequently used. Crabtree first reported an abnormally
bonded NHC (aNHC, C) complex in which the imidazolium moiety
was coordinated at the C4 position.4 Nolan5 and Hong6 demon-
strated that PdeaNHC complex was more effective than the cor-
responding normal NHC complex in the SuzukieMiyaura and
MizorokieHeck reactions; and this enhanced catalytic activity may
Fig. 1. Traditional NHCs (A and B) and aNHCs (C and D) bound to transition metals.
catalytic activity in organic reactions.9 Sankararaman prepared
a pyrrolidinyl 1,2,3-triazol-5-ylideneepalladium complex and ex-
amined its catalytic effectiveness in the SuzukieMiyaura coupling
reaction,10 with aryl bromides as the substrate. Based on these
previous studies, we envision that the 1,4-dimesityl substituted
1,2,3-triazol-5-ylidene (TMes) ligand precursor should be an ef-
fective ligand as is its analogue, IMes [1,3-bis(mesityl)imidazol-2-
ylidene], which is an effective imidazole-carbene ligand owing to
its electronically rich and sterically hindered mesityl groups (Fig. 2).
be due to the stronger
of normal NHCs.
s-donor ability of aNHC compared with that
Albrecht first reported an aNHC ligand based on 1,2,3-triazol-5-
ylidene (D) and its metal complexes.7 Bertrand demonstrated that
the donor property of 1,2,3-triazol-5-ylidene was superior to those
of imidazol-2-ylidenes and 1,2,4-triazol-5-ylidenes in the vibra-
tional spectra study of its iridium carbonyl complexes.8 Abnormal
NHC ligands and their complexes show potential use for unique
* Corresponding author. E-mail address: orgsynth@kc.chuo-u.ac.jp (S.-i.
Fukuzawa).
Fig. 2. trans-Bis(1,2,3-triazol-5-ylidene)palladium (1) and trans-bis(imidazol-2-
ylidene)palladium (2).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.07.045

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S. Inomata et al. / Tetrahedron 67 (2011) 7263e7267
In our preliminary study, we reported the synthesis of trans-
(TMes)2PdCl2 (1a) and its catalytic behaviour in the Suzu-
kieMiyaura coupling reaction with aryl chlorides.11 The reaction
successfully yielded the coupling product in high amounts, and the
complex proved to be particularly effective for the reaction be-
tween the sterically hindered aryl chlorides and aryl boronic acids.
The palladium complex 1a was revealed to have a higher catalytic
activity than that of the corresponding imidazole NHCePd complex
[(IMes)2PdCl2] (2), under the same conditions.
We recently demonstrated that the 1,2,3-triazole NHCecopper
complex was superior to the imidazole NHCecopper analogue in
the CuAAC reaction.12 The triazole NHCecopper complex signifi-
cantly accelerated the reaction, and in the reaction between a ste-
(110 ꢀC, 15 h). The coupling reactions between a variety of aryl
bromides and tert-butyl acrylate were examined to explore the
scope of the 1a catalyzed MizorokieHeck coupling reaction. The
results are summarized in Table 1. The trans-isomers were obtained
as the sole products in excellent yields irrespective of the stereo-
electronic properties of the benzene substituents. Electronically
activated and deactivated aryl bromides tolerated the reaction, and
the corresponding cinnamate esters were obtained in excellent
yields (entries 1, 2 and 4e6). However, o-bromoanisole and o-
nitrobromobenzene produced low product yields of 51% and 0%,
respectively (entries 3 and 7). The coupling with other aromatic
rings, such as 1-bromonaphthalene (entry 10) gave the corre-
sponding a, b-unsaturated esters in quantitative yields. The heter-
rically hindered alkyne and
a
sterically hindered azide, it
oaromatic bromides, such as 3-bromopyridine and 2-
bromothiophene (entries 12e13) coupled with tert-butyl acrylate
to produce the corresponding products in low to moderate yields.
On the other hand, the reaction with 2-bromopyridine hardly gave
the coupling product (entry 11). Poor to low yields of the products
may be due to heteroatoms coordinating with the palladium,
therefore interfering with the catalysis role of the palladium
complex.
successfully yielded a highly sterically crowded triazole. To estab-
lish the advantages of the 1,2,3-triazole NHC ligand and its palla-
dium complexes in synthetic reactions, we extend the use of the
palladium catalyst to other cross-coupling reactions. Previously we
reported the MizorokieHeck coupling reaction between bromo-
benzene with tert-butyl acrylate using 1a as a catalyst.11 Herein, we
describe MizorokieHeck and Sonogashira coupling reactions using
1 as a catalyst.
Table 1
The scope of aryl bromides in the MizorokieHeck reaction with tert-butyl acrylatea
2. Results and discussion
To evaluate the activity of complex 1a,b, we carried out a kinetic
study of the MizorokieHeck coupling reaction of bromobenzene
with tert-butyl acrylate. The yield versus time graphs are shown in
Fig. 3 for 1a,b. The reaction was carried out in dimethylacetamide
(DMA) at 150 ꢀC with loading 1.0 mol % of the palladium complex
and was followed by gas chromatography (GC). The yield was de-
termined by GC by using biphenyl as an internal standard. As seen
in the graph, there was an initial 1-h induction period in the re-
action with 1a, and after this the reaction was accelerated and 80%
product yield was achieved after 3 h. As expected, the Pd complex
1b was less active catalyst giving 40% product yield after 8 h. The
lower activity of 1b was due to the poor electron-donor and low
sterically crowded TPh ligand. During the initial 30 min the active
TMesePd(0) complex was generated.13 An induction period was
also observed in the reaction with 1b, and it took more than 3 h to
generate the active catalyst, which was not as active as 1a.
Entry
Ar
Yieldb (%)
1
2
3
4
5
6
7
8
o-MeC6H4
p-MeC6H4
o-MeOC6H4
p-MeOC6H4
p-FC6H4
p-CH3COC6H4
o-NO2C6H4
p-NO2C6H4
m-NO2C6H4
1-C10H8
92
98
51
88
98
97
0
93
94
97
0
9
10
11
12
13
2-Pyridyl
3-Pyridyl
2-Thiophenyl
32
69
The reaction could be carried out with low catalyst loading or at
lower temperature, however, the yield decreased although the re-
action time was extended; 0.5 mol %, 85% (150 ꢀC, 15 h), 0.1 mol %,
62% (150 ꢀC, 15 h), 1 mol %, 56% (130 ꢀC, 15 h) and 1.0 mol %, 7%
a
Compound 1a (0.005 mmol), aryl bromide (0.5 mmol), tert-butyl acrylate
(0.75 mmol), NaOAc (1.0 mmol), DMA (1.5 mL); 150 ꢀC, 8 h.
b
Isolated yield: trans/cisy99.9/0.1.
We then examined the reactions p-bromotoluene with various
substituted styrenes under the same conditions as described above.
The results are summarized in Table 2. The trans-stilbene de-
rivatives were obtained from either electron-rich or electron-poor
styrenes in good yields. However, the reaction with o-methylstyr-
ene gave the corresponding coupling product in low yield probably
due to steric hindrance. The reaction with 2-vinylpyridine gave the
corresponding coupling product in low yield (entry 8); however,
the reaction of 2-bromopyridine with tert-butyl acrylate did not
give the coupling product at all (Table 1, entry 11).
As the above reactions with aryl and heteroaryl bromides and
alkenes were tolerated, we were encouraged to attempt the re-
action with aryl chlorides. Aryl chlorides have rarely been used for
MizorokieHeck reaction, and addition of ammonium halide is often
necessary to obtain a satisfactory yield product.2c,14 It is interesting
that moderate yields (64e69%) of products could be obtained in the
reaction with p-chloronitrobenzene and p-chlorobenzonitrile in
the absence of ammonium halide by using 1a as a catalyst (entries 2
and 4, Table 3). On the other hand, bis-imidazole carbene
[(IMes)2PdCl2] (2) gave low yields of the products (45% and 27%,
Fig. 3. Time versus yield (%) graph for the palladium catalyzed MizorokieHeck re-
action of bromobenzene with tert-butyl acrylate: A1a; :1b.

S. Inomata et al. / Tetrahedron 67 (2011) 7263e7267
7265
Table 2
potential of 1a is lower than that of 2. This result suggests that the
1,2,3-triazolylidene make the oxidation of Pd(II) more facile in
comparison with the 2-imidazolylidene. We confirmed that its Ag
complexes show no sign of significant oxidation, suggesting that
the ligand is not readily oxidized but palladium is oxidized.15
The complex 1a was evaluated in the Sonogashira coupling re-
actions of aryl halides with alkynes. The model reaction of p-bro-
monitrobenzene with phenylacetylene achieved maximum yields
when CsOAc was used as a base, DMA as a solvent, and the reaction
occurred at 100 ꢀC for 15 h under copper-free conditions. Under
these conditions, we examined the scope of the reaction of phe-
nylacetylene with various aryl halides and the results are shown in
Table 4. High yields of diaryl acetylenes were obtained in the re-
action with electron-poor aryl halides (entries 1e5), while poor
product yields were obtained in the reaction with electron-rich and
neutral aryl bromides (entries 6 and 7).16 When the reactions with
p-chloronitrobenzene was carried out in the absence of ammonium
halide at 130 ꢀC, 1a gave the coupling products in 63% (entry 2),
while the imidazoleecarbene complex (2) gave only 35% product
yield (entry 3), suggesting 1a again shows higher catalytic activity
than 2.
The scope of styrenes in the MizorokieHeck reaction with p-bromotoluenea
Entry
Ar
Yieldb (%)
1
2
3
4
5
6
7
8
C6H5
90
98
90
73
96
99
91
48
p-MeC6H4
m-MeC6H4
o-MeC6H4
p-MeOC6H4
p-NO2C6H4
p-FC6H4
2-Pyridyl
a
Compound 1a (0.005 mmol), p-bromotoluene (0.5 mmol), alkene (0.75 mmol),
NaOAc (1.0 mmol), DMA (1.5 mL); 150 ꢀC, 8 h.
b
Isolated yield: trans/cisy97/3 to 81/19.
Table 3
MizorokieHeck reaction with aryl chloridesa
Table 4
The Sonogashira coupling reactiona
Entry
Ar
Yieldb (%)
1
C6H5
p-NO2
p-NO2
p-CNC6H4
p-CNC6H4
0
64
45
69
27
Entry
X
Ar
R
Yieldb (%)
2
1
Br
Cl
Cl
p-NO2C6H4
p-NO2C6H4
p-NO2C6H4
p-CF3C6H4
p-AcC6H4
C6H5
p-MeOC6H4
p-AcC6H4
p-AcC6H4
p-AcC6H4
p-AcC6H4
p-AcC6H4
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
p-MeC6H4
o-MeC6H4
p-CF3C6H4
n-C6H13
i-Pr3Si
94
63d
35d
89
93
40
21
89
91
54
85
86
3c
4
2c
3c,e
4
5c
Br
Br
Br
Br
Br
Br
Br
Br
Br
a
Compound 1a (0.005 mmol), aryl chloride (0.5 mmol), n-butyl acrylate
5
6
7
8
(0.75 mmol), NaOAc (1.0 mmol), DMA (1.5 mL); 150 ꢀC, 8 h.
b
Isolated yield: trans/cisy99.9/0.1.
Compound 2 was used as a catalyst.
c
9
10
11
12
respectively; entries 3 and 5 in Table 3). Thus, the palladium
complex 1a was superior to 2. The reaction of chlorobenzene with
n-butyl acrylate gave no coupling product under the conditions.
We can consider that the efficiency of 1a is due to stronger
donor property of the 1,2,3-triazolylidene ligand than that of the 2-
imidazolylidene ligand. In order to estimate the donor property we
measured oxidation potential of palladium complexes 1a and 2 by
cyclic voltammetry (Fig. 4). This electrochemical studies show that
both complexes display irreversible oxidations, and oxidation
a
Compound 1a (0.005 mmol), aryl halide (0.5 mmol), phenylacetylene
(1.0 mmol), CsOAc (1.0 mmol), DMA (3.0 mL); 100 ꢀC, 15 h.
b
Isolated yield.
The reaction was carried out at 130 ꢀC.
GC conversion.
Compound 2 was used as a catalyst.
c
d
e
To evaluate the applicability of the 1a catalyst, we carried out
the reaction using various substituted phenylacetylenes and ter-
minal alkyl alkynes, by using p-bromoacetophenone as a counter-
part (Table 4). For electron-neutral and electron-rich
phenylacetylenes (o- and p-MeC6H4), the corresponding coupling
products were obtained in good yields (entries 8 and 9). For
electron-poor alkynes, such as p-trifluoromethylphenylacetylene,
a moderate yield of product was obtained (entry 10). Terminal al-
kyl- and silylalkynes (entries 11 and 12) couple with p-bromoace-
tophenone to give the corresponding internal alkynes in a good
yield. In summary, complex 1a was effective for Sonogashira cou-
pling between electron-poor aryl bromides and electron-rich
alkynes.
As 1a catalyzed both the MizorokieHeck and Sonogashira cou-
pling reactions under similar conditions, we expect that the con-
secutive coupling reactions can occur in one-pot. We first carried
out the reaction of p-bromoiodobenzene and tert-butyl acrylate
using CsOAc in DMA at 150 ꢀC for 8 h, and then phenylacetylene
was added to the same flask and the reaction was left to continue at
150 ꢀC for an additional 15 h (see Scheme 1). The tandem-coupling
Fig. 4. Cyclic voltammograms for 1a and 2 (dotted line).

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S. Inomata et al. / Tetrahedron 67 (2011) 7263e7267
4.2. General procedure for MizorokieHeck reaction
Under an atmosphere of argon, a 5 mL vial containing a stirring
bar was charged with 1 (0.005 mmol), NaOAc (82 mg,1.0 mmol) and
1.5 mL of degassed DMA (dimethylacetamide), and subsequently
were added aryl bromide (0.5 mmol) and alkene (0.75 mmol). The
vial was placed in a 150 ꢀC oil bath and the mixturewas magnetically
stirred for 8 h. The mixturewas quenched with water, extracted with
dichloromethane (20 mLꢁ3). The combined extracts were dried
(MgSO4) andfiltered. GC/MSanalysisof the organiclayershowedthe
presence of the corresponding coupling product (cinnamate or
stilbene derivative). The solvent was removed under reduced pres-
sure to give crude product. The product was isolated by PTLC and
identified by GC/MS and spectroscopy with reference to analytical
data of known compounds.
Scheme 1. One-pot consecutive MizorokieHeck and Sonogashira coupling reactions.
product, i.e., p-alkynylcinnamate ester was obtained with 69% yield
accompanied by small amounts of the double MizorokieHeck and
Sonogashira products.
3. Conclusion
Electron-rich, electron-poor and functionalized aryl bromides
and alkenes were tolerated in the MizorokieHeck reaction, while
substrates were limited to electron-poor aryl halides in the Sono-
gashira coupling reaction. The bis-TMesePd complex 1a was a more
active catalyst than the bis-IMesePd complex analogue 2, because it
catalyzed the cross-coupling reactions with aryl chlorides to give
relatively higher yields although the overall yields were low.
4.2.1. (E)-1-Methyl-2-(4-methylstyryl)benzene. White solid; 93.4 mg,
93% yield; mp: 44e47 ꢀC. FT-IR (KBr): 3022, 2916, 1906, 1597, 1512,
1483, 1458, 975, 809, 718 cmꢂ1. 1H NMR (300 MHz, CDCl3)
d 2.38 (s,
3H), 2.44 (s, 3H), 6.98 (d, 1H, J¼16.1 Hz), 7.17e7.23 (m, 5H), 7.30 (d,
1H, J¼16.1 Hz), 7,43 (d, 2H, J¼7.3 Hz), 7.59 (d, 1H, J¼7.4 Hz). 13C NMR
(75 MHz, CDCl3)
d 20.0, 21.3, 125.3, 125.6, 126.3, 126.5, 127.4, 129.4,
123.0, 130.4, 135.0, 135.8, 136.5, 137.6. MS (EI): m/z¼208 [Mþ].
4. Experimental section
4.1. General
4.2.2. (E)-1-Methyl-3-(4-methylstyryl)benzene. White solid; 76.2 mg,
73% yield; mp: 97e98 ꢀC. FT-IR (KBr): 3018, 2919, 1909, 1599, 1512,
1490, 1449, 976, 967, 810 cmꢂ1 1H NMR (400 MHz, CDCl3)
. d 2.37
The GC/MS analyses were carried out using a HewlettePackard
5975B/6890N instrument equipped with a capillary column (he-
lium as carrier gas). Preparative TLC was conducted using
a 20ꢁ20 cm glass sheet coated with a 1 mm thick layer of Wakogel
B-5F. All commercial compounds were used without further puri-
fication. The 1H and 13C NMR spectra were recorded using a Varian
300 MHz or 400 MHz NMR spectrometer as solutions in CDCl3. The
(s, 3H), 2.38 (s, 3H), 7.00e7.08 (m, 3H), 7.12e7.19 (m, 2H), 7.22e7.33
(m, 3H), 7.42 (d, 2H, J¼8.1 Hz). 13C NMR (100 MHz, CDCl3)
d 21.3, 21.5,
123.7, 126.5, 127.2, 127.9, 128.3, 128.5, 128.6, 129.5, 134.7, 137.5, 137.5,
138.2. MS (EI): m/z¼208 [Mþ].
4.2.3. (E)-2-(4-Methylstyryl)pyridine. Light yellow solid; 47.3 mg,
48% yield; mp: 76e78 ꢀC. FT-IR (KBr): 3027, 1909, 1883, 1855, 1632,
1606,1577,1193,1179,1146,1123, 975, 898 cmꢂ1. 1H NMR (300 MHz,
chemical shifts are reported in
d units downfield from the internal
reference, Me4Si. HRMS analyses were carried out using
MICROMASS-LCT Spectrometer.
CDCl3) d 2.37 (s, 3H), 7.11e7.20 (m, 4H), 7.38 (d, 1H), 7.49 (d, 2H,
J¼8.0 Hz), 7.61 (d, 1H, J¼16.0 Hz), 7.67 (d, 1H), 8.60 (d, 1H). 13C NMR
(75 MHz, CDCl3)
d 21.4, 121.8, 121.9, 127.0, 127.1, 129.5, 132.7, 133.9,
4.1.1. Preparation of the palladium complex. 1,4-Dimesityl-1,2,3-
triazole (400 mg, 1.3 mmol) and Me3OBF4 (252 mg, 1.7 mmol)
were stirred under a nitrogen atmosphere in dry dichloromethane
(30 mL) for 18 h. The reaction mixture was quenched by 2 mL of
MeOH and solvent was removed under reduced pressure to give the
crude product, which was washed with diethyl ether and dried to
give the triazolium salt quantitatively. Under an atmosphere of
nitrogen, a solution of the salt (490 mg, 1.2 mmol) in CH2Cl2/CH3CN
(15 mL/15 mL) was added Ag2O (142 mg, 0.6 mmol) and Me4NCl
(132 mg, 1.2 mmol) in a Schlenk tube. The mixture was stirred for
5 h in light shielding condition, then was added PdCl2(CH3CN)2
(157 mg, 0.6 mmol). The mixture was stirred for 5 h and filtered
through a pad of Celite. The solvent was removed under reduced
pressure and the crude product was subjected to column chroma-
tography on alumina (CH2Cl2, 100%) to give Pd complex 1a (419 mg,
0.51 mmol, 85% yield) as light yellow solid. Mp: 270e272 ꢀC. FT-IR
(KBr): 2918, 1712, 1612, 1460, 1378, 1322, 1272, 1184, 1110, 1063,
136.5, 138.4, 149.6, 155.8. HRMS: calcd for C14H13N [MþH]þ
196.1126; found 196.1143.
4.3. General procedures for Sonogashira coupling
Under an atmosphere of air, a 5 mL vial containing a stirring bar
was charged with 1a (0.005 mmol), CsOAc (192.0 mg, 1.0 mmol)
and DMA (3 mL), and subsequently were added aryl halide
(0.5 mmol) and terminal alkyne (1.0 mmol). The vial was heated at
100 ꢀC with magnetically stirring for 15 h. The mixture was
quenched with water, extracted with dichloromethane, dried
(MgSO4) and filtered. GC/MS analysis of the organic layer showed
the presence of the corresponding coupling product (diaryl alkyne
or aryl alkyl alkyne). The solvent was removed under reduced
pressure to give crude products. The product was isolated by PTLC
or its yield was determined by GC by using biphenyl as an internal
standard.
1023, 848 cmꢂ1. 1H NMR (300 MHz, CDCl3)
12H), 2.44 (m, 12H), 3.73 (s, 6H), 6.95 (m, 8H). 13C NMR (75 MHz,
CD2Cl2) 18.7, 21.0, 21.3, 21.4, 35.9, 124.6, 128.3, 128.8, 136.0, 136.5,
d 1.97 (s, 12H), 1.98 (s,
4.3.1. 1-(4-o-Tolylethynyl-phenyl)ethanone. Yellow solid; 106.3 mg,
91% yield; mp: 101e102 ꢀC. FT-IR (KBr): 3343, 2994, 2216, 1677,
d
139.0, 139.3, 139.7, 143.8, 163.0 (CePd). Anal. Calcd. C42H50Cl2N6Pd:
1595, 1456, 1403, 1358, 1263, 953, 839 cmꢂ1 1H NMR (400 MHz,
.
C, 61.80; H, 6.17; N, 10.30. Found: C. 61.89; H, 6.35; N, 10.11.
CDCl3) d 2.53 (s, 3H), 2.62 (s, 3H), 7.16e7.28 (m, 3H), 7.51 (d, 1H,
Compound 1b:17 1H NMR (400 MHz, CDCl3)
d
3.96 (s, 3H) 3.98 (s,
J¼7.5 Hz), 7.59e7.63 (m, 2H), 7.93e7.97 (m, 2H). 13C NMR (100 MHz,
3H), 7.16 (t, 2H, J¼8.0 Hz), 7.24 (d, 2H, J¼6.4 Hz), 7.38e7.44 (m, 6H),
CDCl3) d 20.7, 26.6, 91.7, 92.5, 122.3, 125.6, 128.2, 128.4, 128.8, 129.5,
7.47e7.57 (m, 2H), 7.85 (d, 4H, J¼7.6 Hz), 8.26 (d, 2H, J¼7.6 Hz), 8.31
131.5, 132.0, 136.0, 140.3, 197.2. MS (EI): m/z¼234 [Mþ].
(d, 2H, J¼8.0 Hz). 13C NMR (100 MHz, CDCl3)
d 37.1, 37.2,124.5,124.9,
125.3, 127.6, 127.9, 128.6, 128.9, 128.9, 129.0, 129.1, 129.2, 129.6,
4.3.2. 1-(4-Acetylphenyl)-2-triisopropylsilylacetylene. Yellow
oil;
130.5, 130.8, 131.5, 139.6, 139.8, 145.1, 158.2 (CePd), 158.4.
130.1 mg, 86% yield. FT-IR (neat): 3359, 2943, 2156, 1687, 1600,

S. Inomata et al. / Tetrahedron 67 (2011) 7263e7267
7267
1463, 1402, 1359, 1263, 1015, 996, 883 cmꢂ1
.
1H NMR (400 MHz,
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catalysis; Cazin, C. S. J., Ed.; Spronger: Dordrecht, 2011; (d) Hahn, F. E.; Jahke, M.
C. Angew. Chem., Int. Ed. 2008, 47, 3122; (e) Herrmann, W. A. Angew. Chem., Int.
Ed. 2002, 41, 1290.
CDCl3)
d
1.13e1.14 (m, 21H), 2.60 (s, 3H), 7.55 (d, 2H, J¼8.6 Hz), 7.89
(d, 2H, J¼8.6 Hz). 13C NMR (100 MHz, CDCl3)
d 11.2, 18.6, 26.6, 94.7,
106.0, 128.1, 128.3, 132.1, 136.2, 197.2. MS (EI): m/z¼300 [Mþ].
2. For reviews on NHCePd-catalyzed cross-coupling reactions, see: (a) Kantchev,
E. A. B.; O’Brien, C. J.; Organ, M. G. Angew. Chem., Int. Ed. 2007, 46, 2768; (b)
ꢀ
Díez-Gonzalez, S.; Nolan, S. P. Top. Organomet. Chem. 2007, 21, 47; (c) Whit-
4.4. Consecutive MizorokieHeck and Sonogashira coupling
reaction
combe, N. J.; Hii, K. K.; Gibson, S. E. Tetrahedron 2001, 57, 7449 For recent 4 years
research on SuzukieMiyaura cross-coupling reactions, see: (d) Godoy, F.;
Segarra, C.; Poyatos, M.; Peris, E. Organometallics 2011, 30, 684; (e) Antreas, S.;
Alireza, R. Chem. Commun. 2010, 2995; (f) Lee, D.-H.; Kim, J.-H.; Jun, B.-H.; Kang,
H.; Park, J.; Lee, Y.-S. Org. Lett. 2010, 10, 1609; (g) Jin, Z.; Guo, S.-X.; Gu, X.-P.; Qiu,
L.-L.; Song, H.-B.; Fang, J.-X. Adv. Synth. Catal. 2009, 351, 1575; (h) Organ, M. G.;
C¸ alimsiz, S.; Sayah, M.; Hoi, K. H.; Lough, A. J. Angew. Chem., Int. Ed. 2009, 48,
2383; (i) Diebolt, O.; Braunstein, P.; Nolan, S. P.; Cazin, C. S. J. Chem. Commun.
2008, 3190; (j) Marion, N.; Nolan, S. P. Acc. Chem. Res. 2008, 41, 1440. For recent
4 years research of MizorokieHeck reactions cross coupling reactions, see: (k)
Saito, S.; Saika, M.; Yamasaki, R.; Azumaya, I.; Masu, H. Organometallics 2011, 30,
1366; (l) Sie, M.-H.; Hsieh, Y.-H.; Tsai, Y.-H.; Wu, J.-R.; Chen, S.-J.; Kumar, P. V.;
Lii, J.-H.; Lee, H. M. Organometallics 2010, 29, 6473; (m) Lee, J.-Y.; Cheng, P.-Y.;
Tsai, Y.-H.; Lin, G.-R.; Liu, S.-P.; Sie, M.-H.; Lee, H. M. Organometallics 2010, 29,
3901; (n) Ren, G.; Cui, X.; Yang, F.; Wu, Y. Tetrahedron 2010, 66, 4022; (o) Peh,
G.-R.; Kantchev, E. A. B.; Zhang, C.; Ying, J. Y. Org. Biomol. Chem. 2009, 7, 2110;
(p) Meyer, D.; Taige, M. A.; Zeller, A.; Hohlfeld, K.; Ahrens, S.; Strassner, T.
Organometallics 2009, 28, 2142; (q) Liu, L-j.; Wang, F.; Shi, M. Eur. J. Inorg. Chem.
2009, 1723; (r) Kantchev, E. A. B.; Peh, G.-R.; Zhang, C.; Ying, J. Y. Org. Lett. 2008,
10, 3949; (s) Taige, M. A.; Zeller, A.; Ahrens, S.; Goutal, S.; Herdtweck, E.;
Strassner, T. J. Organomet. Chem. 2007, 692, 1519.
Under a nitrogen atmosphere, a 20 mL Schlenk tube containing
a stirring bar was charged with 1a (0.01 mmol), CsOAc (288 mg,
1.5 mmol) and DMA (3 mL), and subsequently were added p-
bromoiodobenzene (142 mg, 0.5 mmol) and tert-butyl acrylate
(73
magnetically stirring for 8 h. Then, phenylacetylene (82
m
L, 0.5 mmol). The Schlenk tube was heated at 150 ꢀC with
mL,
0.75 mmol) was added to the tube and the mixture was stirred at
the same temperature for additional 15 h. The mixture was
quenched with water, extracted with dichloromethane, dried
(MgSO4) and filtered. GC/MS analysis of the organic layer showed
the presence of the tandem-coupling product, (E)-tert-butyl 3-(4-
(phenylethynyl)phenyl)acrylate. The solvent was removed under
reduced pressure to give crude products, which was purified by
PTLC (hexane/ethyl acetate¼20/1). Yellow solid; 105.6 mg, 69%
yield; mp: 117e119 ꢀC. FT-IR (KBr): 3399, 2978, 2215, 1705, 1632,
ꢀ
3. Díez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612.
€
4. Grundemann, S.; Kovacevic, A.; Albrecht, M.; Faller, J. W.; Crabtree, R. H. Chem.
Commun. 2001, 2274.
1365, 1326, 139, 1160, 993, 831 cmꢂ1
1.54 (s, 9H), 6.39 (d, 1H, J¼16.0 Hz, C]CH), 7.36 (d, 3H, J¼5.4 Hz),
7.48e7.59 (m, 7H). 13C NMR (75 MHz, CDCl3)
28.2, 80.6, 89.0,
.
1H NMR (300 MHz, CDCl3)
5. Lebel, H.; Janes, M. K.; Charette, A. B.; Nolan, S. P. J. Am. Chem. Soc. 2004,126, 5046.
6. Xu, X.; Xu, B.; Li, Y.; Hong, S. H. Organometallics 2010, 29, 6343.
7. Mathew, P.; Neels, A.; Albrecht, M. J. Am. Chem. Soc. 2008, 130, 13534.
8. Guisad-Barrious, G.; Bouffard, J.; Donnadieu, B.; Bertrand, G. Angew. Chem., Int.
Ed. 2010, 49, 4759.
9. For reviews on abnormal NHCs see: (a) Schuster, O.; Yang, L.; Raubenheimer, H.
G.; Albrecht, M. Chem. Rev. 2009, 109, 3445; (b) Arnold, P. L.; Pearson, S. Coord.
Chem. Rev. 2007, 251, 596.
d
d
91.3, 120.8, 122.9, 124.8, 127.8, 128.4, 128.5, 131.6, 131.9, 134.4,
142.6, 166.1. MS (EI): m/z¼304 [Mþ].
Acknowledgements
10. Karthikeyan, T.; Sankararaman, S. Tetrahedron Lett. 2009, 50, 5834.
11. Nakamura, T.; Ogata, K.; Fukuzawa, S.-i. Chem. Lett. 2010, 39, 920.
12. Nakamura, T.; Terashima, T.; Ogata, K.; Fukuzawa, S.-i. Org. Lett. 2011, 13, 620.
13. (a) Scott, N. M.; Nolan, S. P. Eur. J. Inorg. Chem. 2005, 1815; (b) Herrmann, W. A.;
This study was financially supported by a Grant-in-Aid, No.
22550044, for Scientific Research from the Japan Society for the
Promotion of Science (JSPS) and a Chuo University Grant for Special
Research.
€
Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R. J. Angew. Chem., Int. Ed. Engl. 1995,
34, 2371.
€
14. Frey, G. D.; Schuts, J.; Herdweck, E.; Herrmann, W. A. Organometallics 2005, 24,
4416.
15. Blakemore, J. D.; Chalkley, M. J.; Farnaby, J. H.; Guard, L. M.; Hazari, N.; Incarvito,
C. D.; Luzik, E. D., Jr.; Suh, H. W. Organometallics 2011, 30, 1818.
16. The use of electron-rich aryl iodides instead of bromides gave the quantitative
yields of products.
17. Saravanakumar, R.; Ramkumar, V.; Sankararaman, S. Organometallics 2011, 30,
1789.
References and notes
1. For reviews on NHCs, see: (a) N-Heterocyclic Carbenes in Synthesis; Nolan, S. P.,
Ed.; Wiley-VCH: Weinheim, 2006; (b) N-Heterocyclic Carbenes, from Laboratory
Curiosities to Efficient Synthetic Tools; Díez-Gonzalez, S., Ed.; RSC: Cambridge,
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