Microwave-assisted Sonogashira cross-coupling reaction catalyzed by CN-ortho-palladated complex of tribenzylamine under copper-free conditions

Article abstract of DOI:10.1007/s13738-014-0577-5

Abstract The catalytic activity of [Pd{C₆H₄(CH₂N(CH₂Ph)₂)} (μ-Br)]₂ complex as an efficient, stable and non-sensitive to air and moisture catalyst was investigated in the Sonogashira cross-coupling reaction under microwave irradiation. In the presence of catalytic amount of this homogeneous catalytic system, various aryl halides were efficiently coupled with phenylacetylene under copper-free conditions. The substituted internal alkynes were produced in excellent yields in short reaction times in NMP at 100°. The combination of dimeric complex as homogenous catalyst and microwave irradiation and also NMP as microwave-active polar solvent gave higher yields in shorter reaction times.

Full text of DOI:10.1007/s13738-014-0577-5

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0577-5
ORIGINAL PAPER
Microwave‑assisted Sonogashira cross‑coupling reaction
catalyzed by CN‑ortho‑palladated complex of tribenzylamine
under copper‑free conditions
Abdol R. Hajipour · Fatemeh Rafiee
Received: 14 July 2014 / Accepted: 17 December 2014
©
Iranian Chemical Society 2014
Abstract The catalytic activity of [Pd{C H (CH N(CH
applied to a diverse wide range of pharmaceuticals, natural
products, biological active molecules, molecular electron-
ics, conducting polymers, non-linear optical and liquid
crystal materials [5–10].
6
4
2
Ph) )} (µ-Br)] complex as an efficient, stable and non-
2
2
2
sensitive to air and moisture catalyst was investigated in the
Sonogashira cross-coupling reaction under microwave irra-
diation. In the presence of catalytic amount of this homoge-
neous catalytic system, various aryl halides were efficiently
coupled with phenylacetylene under copper-free condi-
tions. The substituted internal alkynes were produced in
excellent yields in short reaction times in NMP at 100 °C.
The combination of dimeric complex as homogenous cata-
lyst and microwave irradiation and also NMP as micro-
wave-active polar solvent gave higher yields in shorter
reaction times.
The Sonogashira cross-coupling reactions are usually
performed using phosphane-based palladium complexes as
catalyst in the presence of a catalytic amount of a copper(I)
salt and an amine under homogeneous conditions [11–13].
The traditionally palladium–phosphane ligand complexes
include Pd(PPh ) , Pd(PPh ) Cl , Pd(PhCN) Cl /P(t-
3
4
3 2
2
2
2
Bu) , Pd (dba) /P(t-Bu) , Pd(dppe)Cl , Pd-(dppp)Cl , or
3
2
3
3
2
2
Pd(dppf)Cl have been employed for this cross-coupling
2
reaction in the presence of a catalytic amount of a copper(I)
salt as a co-catalyst and or under copper-free conditions
[14–18]. Phosphine ligands suffer some drawbacks such
as sensitivity to air or moisture and requirement for an
inert environment and large amounts of palladium source
for carrying out the reaction. Most research has developed
to obtain high catalytic activity with efficient catalytic
systems. Moreover, a number of important studies have
focused on the development of phosphine-free ligands such
as N-heterocyclic carbenes. Copper-free Sonogashira pro-
tocols have been developed using these types of carbene
complexes.
Keywords Cyclopalladated catalyst · Tribenzylamine ·
Sonogashira reaction · Internal alkynes
Introduction
Sonogashira coupling reaction of terminal alkynes with
aryl halides or triflates catalyzed by palladium and copper
is one of the most powerful tools in organic synthesis and
material science for the production of internal alkynes and
enynes [1–4]. This cross-coupling reaction has been widely
Although carbene ligands are more stable than alkyl
phosphines, they must be synthesized through multi-steps
[
19–22]. Therefore, designing efficient and phosphine-free
A. R. Hajipour (*)
ligands is still an important issue at present.
Pharmaceutical Research Laboratory, Department of Chemistry,
Isfahan University of Technology, Isfahan 84156,
Islamic Republic of Iran
Among the advanced catalysts the palladacycle catalysts
are the most important classes of catalysts that are used
for very efficient catalysis with very low concentration for
C–C bond formation in organic synthesis, material science,
biologically active compounds and macromolecular chem-
istry [23–26]. Oxime [27] and ferrocenylimine [28] pal-
ladacycles as effective catalysts were found to promote the
e-mail: haji@cc.iut.ac.ir
F. Rafiee
Department of Chemistry, Faculty of Science, Alzahra University,
Vanak, Tehran, Iran
e-mail: f.rafiee@alzahra.ac.ir
1
3

J IRAN CHEM SOC
Sonogashira reaction. The high productivity of the pallada-
cycle catalysts is due to the slow generation of low ligated
Pd(0) complexes from a stable palladium(II) pre-catalyst
complex (0.22 mmol) in acetone (25 ml). The suspension
was stirred for 24 h at room temperature; then acetone
was evaporated and 10 ml CH Cl was added and filtered
2
2
[29].
through a plug of MgSO . The filtrate was concentrated to
4
The other modifications to the Sonogashira coupling
2 ml under reduced pressure using a rotary evaporator and
20 ml n-hexane added. The produced suspension was fil-
tered off and air dried to afford the CN-dimeric complex as
the yellow solid.
procedure that have been reported contain reactions in ionic
liquids [30, 31], reactions in water [32, 33], polymer [20]
and silica-supported catalytic reaction systems [34], and
the use of microwave irradiation [35–39].
Anal. Calcd. For C H N Br Pd %: C, 58.90, H,
4
2
40
2
2
2
1
Transition metal-catalyzed cross-coupling reactions
typically need long reaction times and an inert atmosphere
to reach completion with traditional heating. Modern tech-
niques are focused on the design of novel methodologies
to modify these chemical transformations using simpler,
faster, and more efficient processes. The use of microwave
irradiation in homogeneous transition metal-catalyzed reac-
tions leads to the reduction of reaction times, production of
high yields and higher selectivity, the decrease of discarded
by-products from thermal side reactions, and increased life-
time of the catalyst [40].
4.70, N, 3.25. Found: C, 58.71, H, 4.73, N, 3.30, H-
NMR (500 MHz, ppm, CDCl , TMS) δ = 7.94 (d, 2H,
3
3
3
J = 7.5 Hz), 7.89 (d, 1H, J = 7.3 HZ), 7.43–7.34 (m,
3
3
6H), 7.21 (d, 1H, J = 7.8 Hz), 7.10 (d, 1H, J = 7.7 Hz),
3
3
6.91 (t, 1H, J = 7.2 Hz), 6.82 (d, 2H, J = 7.0 Hz), 4.66
(d, 1H, J = 13.0 Hz), 4.60 (d, 1H, J = 13.0 HZ), 4.08 (d,
2
2
2
2
1H, J = 13.0 Hz), 3.98 (d, 1H, J = 13.0 Hz), 3.89 (d, 2H,
2
−1
J = 13.0 HZ), FT-IR (KBr, cm ): ν 3,060, 1,590, 1,440,
1,100.
General procedure for the Sonogashira cross-coupling
reaction
Experimental
A mixture of the aryl halide (0.5 mmol), phenylacetylene
(0.5 mmol), piperidine (1 mmol), ortho-palladated catalyst
General
(0.2 mol %) was added to NMP (3 mL) in round-bottom
flask equipped with condenser and placed into the Mile-
stone microwave. Initially using a microwave power of
600 W the temperature was ramped from room tempera-
ture to 100 °C and then held at this temperature until the
reaction was completed. During this time, the power was
modulated automatically to keep the reaction mixture at
100 °C. The mixture was stirred continuously during the
reaction and monitored by both TLC and GC. After the
reaction was complete, the mixture was cooled to room
temperature and was diluted with n-hexane and water. The
All melting points were taken on a Gallenkamp melting
apparatus. H-NMR spectra were recorded using 400 MHz
in CDCl solutions at room temperature (TMS was used
as an internal standard) on a Bruker, Avance 500 instru-
ment (Rheinstetten, Germany) and Varian 400 NMR. FT-IR
spectra were recorded on a spectrophotometer (Jasco-680,
Japan). Spectra of solids were carried out using KBr pel-
lets. Vibrational transition frequencies were reported in a
1
3
−
1
wave number (cm ). We used the Milestone microwave
Microwave Labstation- MLS GmbH- ATC-FO 300) for
(
organic phase was dried over MgSO , filtered and concen-
4
synthesis. Furthermore, we used GC (BEIFIN 3420 Gas
Chromatograph equipped with a Varian CP SIL 5CB col-
umn—30 m, 0.32 mm, 0.25 μm) for examination of reac-
tion completion and yields. Palladium acetate, aryl halides
and all chemicals were purchased from Merck and Aldrich
and were used as received.
trated under reduced pressure using rotary evaporator. The
residue was purified by silica gel column chromatography.
The products were characterized by comparing their m.p.,
IR, H, C NMR spectra with those found in the literature
[28, 42–46].
1
13
4-Nitro-diphenylacetylene (Table 2, entries 2 and 16):
1
yellow solid, m.p. 117–119 °C. H NMR (400 MHz,
3
General procedure for the synthesis of CN-ortho-palladated
complex
CDCl ): δ = 8.15 (d, 2H, J = 8.8 Hz), 7.59 (d, 2H,
3
3
3
4
J = 8.8 Hz), 7.49 (dd, 2H, J = 7.2 Hz, J = 2 Hz), 7.34–
1
3
7
.30 (m, 3H). C NMR (100 MHz, CDCl ): δ = 147.0,
3
[
Pd{C H (CH N(CH Ph) )} (µ-OAc)] as a palladacycle
132.3, 131.9, 130.3, 129.3, 128.5, 123.7, 122.1, 94.7, 87.5.
6
4
2
2
2
2
complex was prepared according to the literature [41].
Cyclopalladation of tribenzylamine proceeds in ben-
zene at 80 °C when the amine is heated with an equimo-
lar amount of palladium(II) acetate. The halogen-bridged
ortho-palladate complex was prepared by the addition
of NaBr (2 mmol) to a solution of the acetate-bridged
3-Nitro-diphenylacetylene (Table 2, entry 3): pale yel-
1
low solid, m.p. 67–70 °C. H NMR (400 MHz, CDCl ):
3
4
4
δ = 8.31 (dd, 1H, J = 2 Hz, J = 2 Hz), 8.11 (ddd, 1H,
3
3
4
4
J = 8.4 Hz, J = 2.2 Hz, J = 1.2 Hz), 7.76 (ddd, 1H,
J = 7.6 Hz, J = 1.2 Hz, J = 1.2 Hz), 7.50–7.46 (m,
4
4
1
3
3H), 7.32–7.30 (m, 3H). C NMR (100 MHz, CDCl ):
3
1
3

J IRAN CHEM SOC
δ = 148.2, 137.2, 131.8, 129.4, 128.5, 126.4, 125.2, 122.9,
2-(Phenylethynyl)pyridine (Table 2, entry 17): pale yel-
1
1
22.2, 91.9, 86.9.
low oil, H NMR (400 MHz, CDCl ): δ = 8.60–8.58 (m,
3
4
-Methoxy-diphenylacetylene (Table 2, entries 4 and 6):
1H); 7.62–7.51 (m, 3H), 7.46 (d, 1H, J = 7.7 Hz), 7.33–
1
13
white solid, m.p. 58–60 °C. H NMR (400 MHz, CDCl ):
7.29 (m, 3H), 7.20–7.17 (m, 1H). C NMR (100 MHz,
3
δ = 7.53–7.47 (m, 4 H), 7.40–7.35 (m, 3 H), 6.90 (d, 2H,
CDCl ): δ = 149.5, 143.0, 135.9, 131.6, 128.7, 128.1,
3
3
13
J = 8.0 Hz), 3.85 (s, 3H). C NMR (100 MHz, CDCl ):
126.8, 122.4, 122.0, 89.1, 88.4.
3
δ = 159.6, 133.0, 131.4, 128.3, 127.9, 123.6, 115.4, 114.0,
8
9.3, 88.0, 55.3.
-Cyano-diphenylacetylene (Table 2, entry 7): pale yel-
4
Results and discussion
1
low solid, m.p. 108–110 °C. H NMR (400 MHz, CDCl ):
3
δ = 7.64–7.61 (m, 4H), 7.55–7.53 (m, 2H), 7.41–7.36 (m,
In continuation of our recent investigations on the synthe-
sis and application of the palladium catalysts [33, 34, 47,
48], we now wish to report the extension of CN-ortho-
palladated complex of tribenzylamine as an efficient and
highly active homogeneous catalyst for the cross-coupling
reaction of various aryl halides with phenylacetylene under
copper-free conditions (Scheme 1). A proper palladium-
catalyzed reaction requires high catalyst productivity and
activity. Also the availability and catalyst costs and the
price of the organic starting materials are of great impor-
tance. Tribenzylamine as an N-donor ligand is an available
and inexpensive amine. The ortho-palladation reaction of
this substrate is simple and leads to an efficient catalyst in
low loading for coupling reactions even aryl chlorides as
available and cheap substrates.
1
3
3
1
H). C NMR (100 MHz, CDCl ): δ 132.5, 132.4, 132.2,
3
29.5, 128.8, 128.5, 122.6, 119.0, 111.7, 93.4, 88.1.
4
-Acetyl-diphenylacetylene (Table 2, entry 10): white
1
solid, mp. 97–99 °C. H NMR (400 MHz, CDCl ):
3
3
3
δ = 7.96 (d, 2H, J = 8.8 Hz), 7.62 (d, 2H, J = 8.4 Hz),
3
3
7
7
.54 (d, 2H, J = 8.4 Hz), 7.42 (t, 2H, J = 8.8 Hz), 7.53-
1
3
.31 (m, 1H), 2.59 (s, 3H). C NMR (100 MHz, CDCl ):
3
δ = 196.5, 136.0, 131.7, 131.5, 128.9, 128.5, 128.3, 128.1,
22.2, 92.9, 88.7, 26.6.
-Chloro-diphenylacetylene (Table 2, entry 11): white
1
4
1
solid. m.p. 80–82 °C. H NMR (400 MHz, CDCl3):
δ = 7.55–7.53 (m, 2H), 7.48–7.46 (m, 2H), 7.38–7.33
1
3
(
1
m, 5H). C NMR (100 MHz, CDCl ): δ = 133.5, 132.1,
3
30.9, 128.0, 127.8, 127.7, 122.1, 121.1, 90.5, 88.1.
1
-(Phenylethynyl)naphthalene (Table 2, entry 14):
To optimize the reaction conditions, we first carried out
the cross-coupling reaction between 4-bromobenzonitrile
and phenylacetylene as a model reaction. We examined the
effect of various reaction parameters such as solvent, base
and temperature over the yields of the coupling products as
shown in Table 1.
1
colorless oil, H NMR (400 MHz, CDCl ): δ = 8.47 (d,
3
1
2
H, J = 8.0 Hz), 7.85 (d, 1H, J = 8.0 Hz), 7.89–7.86 (m,
13
H), 7.78–7.37 (m, 8H). C NMR (100 MHz, CDCl ):
3
δ = 138.2, 138.0.132.3, 132.1, 129.9, 128.3, 128.0, 127.4,
1
26.6, 126.4, 126.2, 125.7, 123.5, 93.9, 87.3.
Scheme 1 Sonogashira cross-coupling reaction using CN-ortho-palladated catalyst
1
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J IRAN CHEM SOC
Table 1 Optimization of reaction conditions for the Sonogashira cross-coupling reaction
Entry
Solvent
Base
Catalyst (mol %)
Temperature (°C)
Conversion
Product (%)a
By-product (%)a
1
2
3
4
5
6
7
8
9
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
DMF
DMAc
Cs CO
0.1
0.1
0.2
0.2
0.1
0.1
0.2
0.3
0.07
0.1
0.1
0.1
0.1
–
100
100
100
100
100
100
100
100
100
80
85
74
46
50
68
90
95
95
86
84
83
79
39
–
7
2
3
K CO
11
14
11
9
2
3
NEt3
NaOAc
Pyrrolidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
4
2
2
5
1
1
1
1
1
1
1
0
5
1
100
100
80
8
2
10
21
–
3
CH CN
3
4
NMP
100
100
100
5
6b
H O
0.2
0.3
40
90
15
8
2
NMP
Reaction conditions: 4-bromobenzonitrile (1 mmol), phenylacetylene (1 mmol), base (2 mmol), solvent (3 mL), ortho-palladated catalyst
(mol %), MW, 400 W, 5 min
a
GC yield was determined using n-dodecane as an internal standard
b
Sonogashira cross-coupling reaction under conventional heating in an oil bath, 120 min
Table 2 Sonogashira cross-
coupling reaction using
Yield (%)a
Entry
Ar–X
Product
Time (min)
References
CN-ortho-palladated catalyst
1
2
3
4
5
6
7
8
9
Ph–I
Ph–C≡C–Ph
3
1
95
95
92
86
91
64
95
92
77
81
88
84
69
67
78
44
65
[28]
[42]
[43]
[44]
[28]
[44]
[28]
[28]
[42]
[28]
[44]
[45]
[45]
[44]
[46]
[28]
[28]
p-O N–C H –I
p-O N–C H –C≡C–Ph
2
6
4
2
6
4
m-O N–C H –I
m-O N–C H –C≡C–Ph
2
2
6
4
2
6
4
p-MeO–C H –I
p-MeO–C H –C≡C–Ph
7
6
4
6
4
Ph–Br
p-MeO–C H –Br
Ph–C≡C–Ph
4
p-MeO–C H –C≡C–Ph
10
3
6
4
6
4
p-NC–C H –Br
p-NC–C H –C≡C–Ph
6
4
6
4
o-O N–C H –Br
o-O N–C H –C≡C–Ph
5
2
6
4
2
6
4
p-OHC–C H –Br
p-OHC–C H –C≡C–Ph
8
6
4
6
4
10
11
12
13
p-MeOC–C H –Br
p-MeOC–C H –C≡C–Ph
10
2
6
4
6
4
p-Cl–C H –Br
p-Cl–C H –C≡C–Ph
6
4
6
4
m-Cl–C H –Br
m-Cl–C H –C≡C–Ph
4
6
4
6
4
o-Cl–C H –Br
o-Cl–C H –C≡C–Ph
6
6
4
6
4
Reaction conditions: arylhalide
(1 mmol), phenylacetylene
14
1-Br–Naphthalene
9-Br–Phenanthrene
p-O N–C H –Cl
1-Ph–C≡C–Naphthalene
9-Ph–C≡C–Phenanthrene
p-O N–C H –C≡C–Ph
8
(1 mmol), piperidine (2 mmol),
15
16
17
8
NMP (3 ml), catalyst
15
15
2
6
4
2
6
4
(0.2 mol %), 100 °C, 400 W
2-Br–Pyridine
2-Ph–C≡C–Pyridine
a
Isolated yield
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J IRAN CHEM SOC
The data showed that the best results were obtained
using NMP as solvent, piperidine as a base and 0.2 mol %
of catalyst at 100 °C. Under these conditions 4-cyano-
diphenylacetylene was obtained as the desired product in
9
5 % yield and 1,4-diphenylbuta-1,3-diyne was formed as
a by-product in 2 % yield via the homo-coupling of pheny-
lacetylene. This coupling reaction performed in the absence
of Pd catalyst and no conversion of the substrate to prod-
uct was observed (Table 1, entry 14). The low palladium
concentration usually led to a low yield and long period of
reaction. The other bases such as Cs CO , Na CO , K CO
2
3
2
3
2
3
NaOAc, NEt and pyrrolidine were less effective. Several
3
different solvents such as NMP, DMF, DMAc, CH CN and
3
water were examined. Increasing the reaction tempera-
ture in this coupling reaction resulted to increase in yields.
The cross-coupling under conventional heating conditions
using an oil bath was carried out in lower yield and longer
reaction times with higher load of catalyst (0.3 mol %)
Scheme 2 Proposed mechanism for the Sonogashira cross-coupling
reaction
(Table 1, entry 16).
These optimized reaction conditions were applied in the
palladium complexes [50, 52]. When a drop of Hg(0) was
added to the reaction mixture of 4-bromobenzonitrile and
phenylacetylene under mentioned optimized conditions
and heated using an oil bath, no catalytic activity was
observed for the catalyst. The obtained data can confirm the
Pd(0):Pd(II) cycle.
Sonogashira cross-coupling reaction of various aryl halides
with phenylacetylene (Table 2). In some of these cross-
coupling reactions 1,4-diphenylbuta-1,3-diyne was formed
as a by-product (2–10 %). We examined the electronic and
steric effects on the resulted yields and conversion times of
the reactions. Aryl halides substituted with electron-with-
drawing groups transformed to the corresponding coupled
products rather than electron donating substituent with
better conversions and shorter reaction times. The chemo-
selectivity of the procedure was examined using 2-, 3- and
CN-ortho-palladated complex is a homogenous catalyst
and the load amount of palladacycle catalyst in this cross-
coupling reaction is low (0.2 mol %). It has been dem-
onstrated that palladacycles are precatalysts that behave
as a source of highly active Pd nanoparticles, therefore,
working as homogeneous ligand-free Pd catalyst by slow
decomposition [53]. To examine the reusability of catalyst,
after the cross-coupling reaction of iodobenzene with phe-
nylacetylene was complete, fresh reagents were added to
the reaction mixture and performed under typical reaction
conditions under microwave irradiation. Diphenylacetylene
was obtained in lower yield (60 %) at same time (3 min) in
first run. Subsequent catalytic runs performed for this cou-
pling reaction and also with activated aryl bromides such
as 4-bromobenzonitrile resulted in significantly lower yield
and longer reaction time even in the first run. As it was
indicated in the literature [54], although Pd nanoparticles
derived from palladacycle complex show some activity for
this coupling reaction either the complex or atomic Pd spe-
cies or Pd nanoparticles at early stages are more active cat-
alysts to promote the coupling reactions than aged Pd nano-
particles. Reusable homogeneous palladacycle catalysts
were developed using ionic liquid or polyethyleneglycol
(PEG) as media reaction to stabilize Pd nanoparticles [54].
To investigate the efficiency of ortho-palladated com-
plex, the cross-coupling of 4-nitro-iodobenzene with phe-
nylacetylene was considered and this catalytic system is
compared with other palladium-based catalytic systems. As
4
-chlorobromobenzene. In these reactions Br acted as bet-
ter leaving group. An increasing hindrance in the vicinity of
the leaving group in these substrates results in a decrease
in the conversion. Aryl chlorides converted to correspond-
ing products more slowly and with less yields in compari-
son to the similar aryl iodides and bromides. This catalytic
complex was compatible with a wide range of functional
groups such as nitro, cyano, methoxy, halogen, and car-
bonyl on aryl halides.
The Sonogashira reaction probably proceeds through
the oxidative addition of the aryl halide to the Pd(0) cata-
lytic species that generates homogenous Ar–Pd–X species.
The coordination of the alkyne to the metal center followed
base-assisted H–X elimination gave the Ar–Pd–C≡C–Ph
that by reductive elimination yields the coupling product
and Pd(0) (Scheme 2) [49].
A study on NC palladacycle catalyst cross-couplings
showed that palladacycles decompose to liberate catalytic
Pd(0) species and show a positive Hg(0) test [50, 51]. To
evaluate the proposed mechanism, the mercury drop test
was utilized, since mercury leads to the amalgamation of
the surface of a heterogeneous catalyst. In contrast, Hg(0)
is not expected to have a poisoning effect on homogeneous
1
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J IRAN CHEM SOC
Table 3 Comparison of various catalysts in cross-coupling reaction under conventional heating conditions
Entry Catalytic system Time (h) Yield (%) TON TOF References
1
2
3
4
5
6
7
PdCl (1 mol %), pyrroldine, H O, 25 °C
24
3
97
95
92
94
93
99
97
97
95
4
[55]
2
2
Pd(PPh ) Cl (2 mol %) CuI (1 mol %), TEA, DMF, 100 °C (N + H )
31.7 [42]
3.8 [56]
3
2
2
,
2
2
5 % PdO NPs/C (2 mol % Pd), K PO , i-PrOH/H O, 80 °C
12
46
3
4
2
Fe O @SiO /Shiffbase/Pd(II) nanocatalyst (0.7 mol %), DMF, NEt , 90 °C
0.75
134
31
178 [57]
2.5 [58]
3
4
2
3
[PdCl(SeCH CH CH NMe )] (3 mol %), dioxane, NEt , 100 °C
12
3
2
2
2
2
2
3
Polystyrene-supported triazine palladium complex (0.1 mol %), solvent free, NEt , rt
990
330 [59]
3
[Pd{C H (CH N(CH Ph) )} (µ-Br)] , (0.2 mol %), NMP, piperidine, 100 °C
0.4
485 1,212 This work
6
4
2
2
2
2
can be seen in Table 3, this CN-ortho-palladated complex
gave better yield in shorter time.
14. R. Chinchilla, C. Nájera, Chem. Rev. 107, 874 (2007)
15. D. Gelman, S.L. Buchwald, Angew. Chem. Int. Ed. 42, 5993 (2003)
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1
(2003)
1
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dron 62, 4829 (2006)
Conclusions
1
1
8. S.R. Dubbaka, P. Vogel, Adv. Synth. Catal. 346, 1793 (2004)
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In this investigation, a general protocol was applied for
the Sonogashira reaction of various aryl halides using CN-
ortho-palladated complex [Pd{C H (CH N(CH Ph) )}
6
94, 3477 (2009)
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7079 (2007)
6
4
2
2
2
2
2
2
1. C. Yang, S.P. Nolan, Organometallics 21, 1020 (2002)
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3. R.B. Bedford, L.T. Pilarski, Tetrahedron Lett. 49, 4216 (2008)
(
µ-Br)] as a highly efficient, stable, non-sensitive to air
2
and moisture catalyst. The catalytic amount of this catalyst
led to formation of substituted aromatic alkynes in good to
excellent yields under copper-free conditions.
24. J. Buey, P. Espinet, J. Organomet. Chem. 507, 137 (1996)
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2
2
2
6. C. Lopez, A. Caubet, S. Perez, X. Solans, M. Font-Bardía, J.
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7. D.A. Alonso, C. Nájera, M.C. Pacheco, Tetrahedron Lett. 43,
Acknowledgments We gratefully acknowledge the funding support
received for this project from the Isfahan University of Technology
(IUT), IR Iran and Isfahan Science & Technology Town (ISTT), IR,
9
365 (2002)
8. F. Yang, X. Cui, Y. Li, J. Zhang, G. Rena, Y. Wu, Tetrahedron 63,
963 (2007)
Iran. We also gratefully acknowledge the partial financial support
received from the research council of Alzahra University.
1
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