Palladacycle phosphine complexes as homogeneous catalysts for the Heck cross-coupling reaction at low catalyst loading under aerobic conditions

Article abstract of DOI:10.1016/j.ica.2013.04.048

A highly efficient Heck cross-coupling reaction between various aryl halides and olefins using mononuclear palladacycle complexes of the type [(Ph₂P CH2CH₂PPh₂)Pd(Ph₂PCH ₂PPh₂C(H)C(O)PhX)](OSO₂CF₃) ₂ (X= Br (1), No₂(2)) as catalyst precursors, under aerobic conditions has been developed. High yields of corresponding C-C products, low catalyst loadings and short reaction times are important features of these homogeneous reactions. Palladacycle 1 can be reduced to zerovalent palladium in DMF whilst dppe dioxide was formed.

Full text of DOI:10.1016/j.ica.2013.04.048

Inorganica Chimica Acta 405 (2013) 15–23
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Palladacycle phosphine complexes as homogeneous catalysts for the
Heck cross-coupling reaction at low catalyst loading under aerobic
conditions
⇑
Seyyed Javad Sabounchei , Mohsen Ahmadi
Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient Heck cross-coupling reaction between various aryl halides and olefins using mononu-
clear palladacycle complexes of the type [(Ph2P CH2CH2PPh2)Pd(Ph2PCH2PPh2C(H)C(O)PhX)](OSO2CF3)2
(X = Br (1), No2(2)) as catalyst precursors, under aerobic conditions has been developed. High yields of
corresponding C–C products, low catalyst loadings and short reaction times are important features of
these homogeneous reactions. Palladacycle 1 can be reduced to zerovalent palladium in DMF whilst dppe
dioxide was formed.
Received 7 November 2012
Received in revised form 28 April 2013
Accepted 30 April 2013
Available online 9 May 2013
Keywords:
Ó 2013 Elsevier B.V. All rights reserved.
Palladacycle phosphine complexes
Heck cross-coupling reaction
Homogeneous catalyst
Low catalyst loading
Aerobic conditions
1. Introduction
We have previously shown that the palladacycle complex 1 was
a highly efficient catalyst for the Suzuki cross coupling reactions in
Palladium-catalyzed coupling reactions such as Heck cross-
coupling reactions have became an extremely powerful method
for the formation of C–C bonds in organic synthesis, [1–4]
material science, [5] biologically active compounds [6] and as
building blocks in macromolecular chemistry [7–9]. A number
of Pd catalysts, usually simple palladium complexes associated
with appropriate ligands, can catalyze this reaction under various
reaction conditions. Among them, palladacycle complexes have
been extensively applied in coupling reactions as effective
catalysts, due to their ready preparation and modification, high
activity and relative stability [10–12]. The prevailing belief is that
chelating diphosphine Pd complexes are good catalysts for the
classical Heck reaction. In recent years, some of authors have
reported a variety of palladacycle complexes containing P-donor
phosphine ligands and found that these complexes were active
catalysts for the Heck reaction [13–15]. In view of these findings
and our continuing interest in the synthesis of palladacycle
complexes and the applications of these systems [16], we have
used palladacycle complexes 1 and 2 [17] as catalyst precursors
in Heck cross coupling reaction of various aryl halides under
relatively mild experimental conditions.
DMF as a solvent under air atmosphere [16]. Thus it was of interest
to investigate the catalytic properties, if any, of complexes 1 and 2
in the Heck C–C cross-coupling reactions. Synthetic route for prep-
aration of Pd (II) complexes is presented in Scheme 1.
2. Result and discussion
It is well established that palladium complexes containing
phosphine ligands, which combine both good donor strength and
p-accepting capacity, always have a high catalytic activity in Heck
cross-coupling reactions [10,18]. Therefore we have attempted to
use our palladium(II) complexes as catalysts in Heck reaction.
The ability to use small amounts of catalyst and still achieve high
yields is a great concern in cross coupling reactions due to the high
cost of metals and ligands.
The rate of coupling is depended on a variety of parameters
such as solvent, base and catalyst loading. Generally, the Heck
reactions conducted with phosphine complexes require high tem-
peratures and polar solvents. In order to optimize the reaction con-
ditions for the coupling reactions, different amounts of catalysts
(mol%) were taken and the yield of the products were measured.
The results are summarized in Table 1. A controlled experiment
indicated that the coupling reaction did not occur in the absence
of both of the catalysts. Good yields were obtained from catalysts
load down to a level of 0.01 mol%. A moderate yields were obtained
⇑
Corresponding author. Tel.: +98 8118272072; fax: +98 8118273231.
E-mail addresses: jsabounchei@yahoo.co.uk (S.J. Sabounchei), Ahmadi.chem@-
yahoo.com (M. Ahmadi).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.04.048

16
S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
Scheme 1. Synthetic route for preparation of palladacycle complexes.
Table 1
Optimization of catalyst concentration.
2, entry 2, 80%). While another polar aprotic solvent (DMF) gave
comparatively moderate yield (Table 2, entry 3, 69%). The highest
isolated yield was obtained with NMP in short reaction time (Table
2, entry 2, 80% Cat. 1 and 81% Cat. 2). After selecting NMP as the
optimal solvent, we investigated the influence of various bases
on the Heck reaction. In the presence of NaOAc and NaF bases,
yield of 54% and 45% were obtained, respectively (Table 2, entries
7 and 8). Among the similar bases of Cs2CO3, K2CO3 and Na2CO3
which were tested, the Cs2CO3 proved to be the most efficient
and gave the good isolated yield (Table 2, entry 2, 80%).
In another model to optimize the reaction conditions, we have
chosen the reaction between 4-bromobenzaldehyde with styrene
in the presence of various solvents and bases, as shown in
Table 3. Comparison of the results showed that the reaction in
the presence of dimethyl-formamide (DMF) as solvent proceeded
much better than other solvents with a good yield in short reaction
time (Table 3, entry 2, 83%). Among the studied bases; K2CO3 and
Cs2CO3 were found to be more efficient for this reaction. Therefore,
K2CO3 was chosen as the most suitable base under optimized
reaction conditions (Table 3, entry 2).
Under the determined reaction conditions, a wide range of aryl
halides bearing electron-donating and electron-withdrawing
groups coupled with olefins, affording the olefinic products in
moderate to good yields (Table 4). The palladacycle complexes as
homogenous catalyst precursors exhibited higher activity with
electron-withdrawing substituents relative to electron-donating
substituents on the aryl halides in Heck reaction [19]. It would
seem that the presence of strong electron-withdrawing groups
on the aryl halides make them more susceptible to further oxida-
tive-addition to the catalyst species [20]. In this work, the elec-
Entry Catalyst (mol%) Reaction conditiona,b (Time, h) Isolated yield (%)
1
2
3
4
5
6
7
8
None
a,b (8)
a (4)
b(4)
n.r.c
85
83
83
80
80
81
79
81
56
53
1 (0.01)
1 (0.01)
2 (0.01)
2 (0.01)
1 (0.001)
1 (0.001)
2 (0.001)
2 (0.001)
1 (0.0005)
1 (0.0005)
a (4)
b (4)
a (4)
b (4)
a (4)
b (4)
a (8)
b (8)
9
10
11
a
Reaction conditions: 4-bromobenzaldehyde (1 mmol), styrene (2.2 mmol),
K2CO3 (1.5 mmol), DMF (2 ml), 130 °C.
Reaction conditions: 4-bromobenzaldehyde (1 mmol), ethyl acrylate
(2.2 mmol), Cs2CO3 (1.5 mmol), NMP (2 ml), 130 °C.
b
c
No reaction.
even at catalysts loading as low as 0.0005 mol%. Various catalysts
concentrations were also tested, 0.001 mol% gave the best result
in both of the catalysts (Table 1, entries 6–9). As these catalysts
are not sensitive to oxygen, the reactions were carried out in the
air atmosphere.
Additional studies were carried out in order to optimize the
effect of different solvents and bases (Table 2). The vinylation of
4-bromobenzaldehyde with ethyl acrylate was studied as a model
reaction using catalysts 1 and 2. As can be seen in table 2, the
non-polar solvent gave moderate yield (Table 2, entry 1, 67%).
The polar protic solvent like methanol gave moderate yield (Table
2, entry 4, 55%), whereas polar aprotic solvent such as NMP is
found to be more efficient for the yield of biaryl compound (Table
Table 2
Optimization of base and solvent for Heck cross-coupling reaction of 4-bromobenzaldehyde with ethyl acrylate.a
O
O
Br
O
Cat. (0.001 mol%)
Solvent, Base
+
O
O
O
H
H
Entry
Base
Solvent
Temp. (°C)
Time (h)
Catalyst (yield%)b
1
2
3
4
5
6
7
8
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
Na2CO3
NaOAc
NaF
dioxane
NMP
DMF
methanol
NMP
NMP
110
130
130
65
130
130
130
130
8
4
10
10
8
10
12
12
1 (67), 2 (69)
1 (80), 2 (81)
1 (69), 2 (70)
1 (55), 2 (50)
1 (75), 2 (74)
1 (68), 2 (62)
1 (54), 2 (42)
1 (45), 2 (53)
NMP
NMP
a
Reaction conditions: 4-bromobenzaldehyde (1 mmol), ethyl acrylate (2.2 mmol), base (1.5 mmol), solvent (2 ml), 130 °C, under air.
Isolated yield.
b

S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
17
Table 3
Optimization of base and solvent for Heck cross-coupling reaction of 4-bromobenzaldehyde with styrene.a
Br
Cat. (0.001 mol%)
+
O
O
Solvent, Base
H
H
Entry
Base
Solvent
Temp. (°C)
Time (h)
Catalyst (yield %)b
1
2
3
4
5
6
7
8
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Cs2CO3
NaOAc
NaF
dioxane
DMF
methanol
NMP
DMF
DMF
110
130
65
130
100
130
130
130
8
4
10
8
10
8
12
12
1 (68), 2 (61)
1 (83), 2 (83)
1 (50), 2 (61)
1 (64), 2 (72)
1 (71), 2 (63)
1 (78), 2 (76)
1 (44), 2 (52)
1 (48), 2 (62)
DMF
DMF
a
Reaction conditions: 4-bromobenzaldehyde (1 mmol), styrene (2.2 mmol), base (1.5 mmol), solvent (2 ml), 130 °C, under air.
Isolated yield.
b
Table 4
Heck cross-coupling reaction of aryl halides with olefins catalyzed by Pd complexes.a,b
Time
(h)
Catalyst
Entryc
1
ArX
RCH=CH2
Product
(Yield %)d
O
O
O
O
O
I
1 (81)
2 (80)
3
OEt
OEt
O
O
Br
1 (80)
2 (73)
2
3
4
5
6
4
O
O
Cl
1 (76)
2 (75)
OEt
O
4
3.5
4
I
O
O
1 (76)
2 (76)
OEt
H3C
H3C
H3C
H3C
O
O
Br
O
O
1 (74)
2 (71)
OEt
Cl
O
O
1 (72)
2 (66)
OEt
OEt
6
H3C
H3C
O
O
Br
O
O
O
1 (83)
2 (81)
7
8
4
4
CH3
CH3
O
Cl
O
O
OEt
O
1 (78)
2 (75)
O
CH3
(continued on next page)
(continued on next page)
CH3

18
S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
Time
(h)
Catalyst
Entryc
ArX
RCH=CH2
Product
(Yield %)d
O
O
Br
Cl
O
O
OEt
OEt
O
O
1 (80)
2 (81)
9
4
O
O
H
H
H
H
O
O
1 (75)
2 (76)
10
4.5
O
Br
O
O
1 (83)
2 (85)
OEt
11
12
13
3
4
4
O2N
O2N
O
O
O
Br
1 (76)
2 (82)
OEt
S
S
Br
O
O
OEt
O
1 (79)
2 (80)
I
1 (82)
2 (83)
14
15
16
3.5
4
Br
Cl
1 (74)
2 (76)
1 (77)
2 (69)
4
I
1 (83)
2 (78)
17
18
19
3
H3C
H3C
H3C
H3C
H3C
Br
1 (71)
2 (70)
4.5
5.5
Cl
1 (67)
2 (71)
H3C
(continued on next page)

S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
19
Table 4 (continued)
Time
(h)
Catalyst
Entryc
ArX
RCH=CH2
Product
(Yield %)d
Br
Cl
O
O
1 (80)
2 (80)
20
4
5
O
O
CH3
CH3
1 (76)
2 (62)
21
22
CH3
CH3
Br
Cl
O
O
1 (83)
2 (82)
4
4
3
O
O
H
H
H
H
1 (78)
2 (77)
23
24
Br
1 (83)
2 (85)
O2N
O2N
Br
1 (77)
2 (82)
25
26
3.5
4
S
S
Br
1 (79)
2 (77)
I
I
27e
28e
29e
30e
4
4
4
4
65
64
45
46
H3C
H3C
H3C
H3C
H3C
O
O
O
OEt
H3C
H3C
Cl
Cl
O
O
O
OEt
H3C

20
S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
aReaction conditions for entries 1–13: aryl halide (1 mmol), ethyl acrylate (2.2 mmol), Cs2CO3 (1.5 mmol), NMP (2 ml), catalysts 1 and 2 (0.001 mol%), 130 °C.
bReaction conditions for entries 14–26: aryl halide (1 mmol), styrene (2.2 mmol), K2CO3 (1.5 mmol), DMF (2 ml), catalysts 1 and 2 (0.001 mol%), 130 °C.
cAll reactions carried out under aerobic conditions.
dIsolated yield.
eReaction conditions for entries 27–30: with precursor complex [Pd(dppe)(OTf)2] as catalyst (0.001 mol%). See Ref. [17].
tron-neutral and electron-rich aryl iodides react with olefins to
generate the corresponding cross-coupling products in high yields
(Table 4, entries 1, 4, 14 and 17). For instance, couplings of 4-meth-
yliodobenzene with the olefins proceeded in short times with good
yields in both of the catalysts (Table 4, entries 4 and 17). As shown
in Table 4, activated aryl bromides such as 4-nitrobromobenzene
underwent the Heck reaction with ethyl acrylate and styrene
under similar conditions to afford the corresponding products in
83–85% yields (Table 4, entries 11 and 24) whereas, inactivated
aryl bromides such as 4-methylbromobenzene gave 70–74% yields
(Table 4, entries 5 and 18). The electronically neutral bromoben-
zene (Table 4, entries 2 and 15) produced good amounts of desired
products. Trying to apply 2-bromothiophene and 1-bromonaph-
thalene as efficient substrate was successful (Table 4, entries
12–13 and 25–26). To extend the scope of our work, we next inves-
tigated the coupling of various aryl chlorides with ethyl acrylate
and styrene. A number of reported catalysts in literature need to
be used in high loadings, and showed little or no activity with aryl
chloride substrates [21]. As can be seen in Table 4, aryl chlorides
with electron-withdrawing groups reacted smoothly, and the cor-
responding products were obtained in good yields (Table 4, entries
8, 10, 21 and 23). But for chlorobenzene and 4-methylchloroben-
zene, lower yields were observed even after prolonged reaction
times (Table 4, entries 3, 6, 16 and 19). By using aryl chlorides a
good amounts of stilbene derivatives are yielded under the same
conditions employed for aryl iodides and aryl bromides (see Table
4). The higher C–Cl bond strength compared with C–Br and C–I
bonds disfavors oxidative addition step in catalytic coupling reac-
tions. The ideal substrates for coupling reactions are aryl chlorides,
since they tend to be cheaper and more widely available than their
bromide or iodide analogous. As can be seen in Table 4, we ob-
served that in all cross-coupling reactions, catalysts 1 and 2 had
approximately same catalytic activities and similar yields.
It seems that the precursor complex, [Pd(dppe)(OTf)2] can also
be used to behave as an active resource for producing Pd(0). We
used this complex as main catalyst under identical conditions.
The activity of precursor complex, [Pd(dppe)(OTf)2] with an ‘easy’
set of substrates (Table 4, entries 27 and 28) and a ‘difficult’ set
of substrates (Table 4, entries 29 and 30) was tested. Using this cat-
alyst in the reaction between 4-methyliodobenzene and 4-methyl-
chlorobenzene with styrene, gave 65% and 45% yield, respectively
(Table 4, entries 27 and 29). Therefore, the activities of the cata-
lysts 1 and 2 are found to be superior compared with the complex
[Pd(dppe)(OTf)2].
Likely mechanism for the Heck reaction of the aryl halides with
olefins using palladium complexes as catalysts has been proposed
(Scheme 2) by comparison with the literature reports [22].
In Heck cross-coupling reactions, where a reducing agent can-
not be clearly identified, a catalytic cycle involving Pd(II)/Pd(IV)
complexes [23] was first proposed rather than the traditional one
involving Pd(0)/Pd(II) complexes [24]. The first step of the catalytic
cycle would then be the classical oxidative addition of the aryl ha-
lide with a Pd(0) complex, as in a classical Pd(0)/Pd(II) catalytic cy-
cle [2,10a]. Even in the absence of any identified reducing agent, a
number of authors have nevertheless proposed the reduction of the
palladacycle to a low-ligated Pd(0) complex [22h,I,j,24b,25].
Some of the observations made us to think about a mechanism
being similar to that expressed in standard textbooks [26].
Unfortunately, very little is known about the actual structures
of catalytically active PdLn complexes generated from modern
and highly sophisticated Pd-precursors [27]. In addition, there
have been few attempts to elucidate the composition of the active
species present in the Heck cycle. Published studies have been
limited to the use of electrochemistry [28], anionic detection
(ESI-MS, EXAFS) [29] together with detailed kinetic studies, [30]
NMR detections [23a,24a,31] and catalyst poisoning experiments
[32].
Recently, numbers of cyclopalladated complexes have been re-
ported in which the palladium atom is at the zero oxidation state
[28,33]. Several reports on the existence of highly active soluble
palladium(0) colloids (nanoparticles) have established the function
of palladacycles as plain Pd(0) reservoirs in high temperature
applications like Heck and Suzuki couplings [34]. The reduction
of palladium occurs via insertion into the Pd–C bond followed by
a reductive elimination that provides the 2e to reduce Pd(II) into
Pd(0), but this is generally followed by the formation of Pd(0)
nanoparticles. The fact that metallic Hg does not kill the catalysis
is a good point that no metallic Pd is being produced. Electrochem-
istry is indeed one of the most convenient techniques to detect
Pd(0) complexes that are generated in situ from Pd(II) complexes
[35]. In the other way, we previously showed that Pd(II) in this pal-
ladacycle was reduced to Pd(0) by cyclic voltammetry [17]. In addi-
tion, the 31P NMR spectroscopy show that the activation of
palladacycle phosphine complex 1 produce some kind of active
Pd(0) spices [36]. Palladacycle 1 can be reduced to zerovalent pal-
ladium in DMF whilst dppe dioxide was formed. (See Supplemen-
tary data).
As with palladacycle 1 forms Pd(0) unsaturated 14 electron spe-
cies (Scheme 2) [2,16,17,22a,h–j,g], a highly reactive Pd(0) species
does undergo an oxidative addition with ArX. In the next, olefin in-
serts to catalytic cycle. The resulting complex enters the migratory
insertion step via the neutral route, which is revealed by a huge
acceleration by polar solvents, a common ion effect, and other typ-
ical criteria. The steric and bulky properties of bidentate phosphine
ligand (L) can be facilitating this process [22h,37]. A trans-effect of
a strong chelate phosphorus ligand makes the reductive elimina-
tion of alkene very fast, avoiding to the formation of Z-isomer.
The addition of K2CO3 to remove KHCO3 + KX gives catalytically ac-
tive Pd(0) complex (Scheme 2). In this work, with these aryl ha-
lides, several reactions were performed in the presence of olefins.
In the presence of styrene and ethyl acrylate, the regioselectivity
is generally in favor of the linear isomers (E-isomer) [22h]. Based
on the results, production of the E-isomers in all the cases with
good yields are the great advantages of the presented catalysts
(see Table 4).
Although several catalytic systems have been reported to sup-
port Heck C–C coupling reactions, a homogeneous catalyst of this
type is novel because of its P donor of dppe as ligand and P and
CH of phosphorus ylide environment. The homogeneous nature
of the catalysis was checked by the classical mercury test [38].
Addition of a drop of mercury to the reaction mixture did not affect
the yield of the reaction which suggests that the catalysis is homo-
geneous in nature, since heterogeneous catalysts would form an
amalgam, there by poisoning it.
The comparison data presented in Table 5 show the efficiency of
these new catalysts towards the coupling reactions. From an indus-

S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
21
3. Exprimental
3.1. General
The required chemicals were of analytical reagent grade and
were purchased from Merck and Aldrich. Melting points were
measured on a SMPI apparatus and are reported without correc-
tion. NMR Spectra were recorded on a 90 MHz Jeol spectrometer
(1H at 89.60 MHz) or 400 MHz Bruker spectrometer
(
13C at
100.62 MHz) in CDCl3 as solvent. The splitting of proton reso-
nances in the 1H and 13C NMR spectra is shown as, s = singlet,
d = doublet, t = triplet and m = multiplet.
3.2. Synthesis of palladacycle complexes
General procedure: To a [Pd(dppe)(OTf)2] (0.4 g, 0.5 mmol)
methanol solution (10 ml),
a solution of phosphorus ylides
(0.29 g, 0.5 mmol) (10 ml, CH3OH) was added dropwise. The result-
ing solution was stirred for 12 h at room temperature and then
concentrated to a 2 ml in volume and treated with diethylether
(2 Â 10 ml) to give a final product. The product was collected and
dried under vacuum.
Scheme 2. Proposed mechanism for Heck reaction.
trial view point, the low catalyst loading and short reaction time
and stable phosphine ligands provide an indisputable advantage
than the other catalytic systems. In all of the successful reactions,
the 1H and 13C NMR data of the products indicated no Heck cou-
pling byproducts and some of the NMR spectra of the C–C products
are given in Supplementary data.
3.3. Typical procedure for the Heck reaction
To a round-bottom flask equipped with a magnetic stirring bar
were added palladacycle complexes (0.001 mol%), aryl halide
(1 mmol), olefin (2.2 mmol) and base (1.5 mmol) in solvent
(2 ml). The mixture was heated using an oil bath and the progress
Table 5
Comparison with other catalytic system.
DMA: dimethylacetamide.

22
S.J. Sabounchei, M. Ahmadi / Inorganica Chimica Acta 405 (2013) 15–23
was monitored by thin-layer chromatography (n-hexane/EtOAc,
80:20). After completing the reaction, the mixture was diluted
with n-hexane (15 ml) and water (15 ml). The organic layer was
washed with brine (15 m1), dried over CaCl2, and concentrated un-
der reduced pressure. The liquid residues were purified by silica gel
column chromatography (n-hexane:EtOAc, 80:20) and The solid
residues were purified by re-crystallization from EtOH and H2O.
4. Conclusion
We used palladacycle complexes containing bidentate phos-
phine ligands as an efficient and well-defined catalyst for the
Heck olefination of various aryl halides. These complexes are
highly active and efficient catalyst for promoting the Heck
cross-coupling reaction of various aryl halides to produce the cor-
responding products in moderate to good yields. The ease of
preparation of the catalyst precursors, its high solubility in organ-
ic solvents, low catalyst loading, and stability toward air make
these complexes ideal starting materials for the above
transformations.
3.4. Characterization of cross-coupling products
3.4.1. (E)-Ethyl 3-phenylacrylate (Table 4, entries 1, 2, 3)
Light yellow liquid, 1H NMR (ppm): d = 7.56 (d, 1H,
J = 16.10 Hz), 7.24–7.65 (m, 5H), 6.30 (d, 1H, J = 16.03 Hz), 4.13
(q, 2H, J = 6.98 Hz), 1.20 (t, 3H, J = 6.98 Hz). 13C NMR (ppm):
d = 165.8 (s, CO), 143.4, 133.3, 129.1, 127.8, 126.9, 117.1, 59.3 (s,
CH2), and 13.2 (s, CH3). [41].
Acknowledgments
We gratefully acknowledge the funding support received for
this project from the Bu-Ali Sina University, I. R. Iran. Our gratitude
also goes to Dr. Abbas Abdoli and Mr. Zebarjadian for their
cooperation.
3.4.2. (E)-Ethyl 3-(4-methylphenyl)acrylate (Table 4, entries 4, 5, 6)
Light brown liquid, 1H NMR (ppm): d = 7.66 (d, 1H, J = 16.21 Hz),
7.13–7.47 (m, 4H), 6.38 (d, 1H, J = 16.03 Hz), 4.26 (q, 2H,
J = 7.07 Hz), 2.37 (s, 3H), 1.33 (t, 3H, J = 6.98 Hz). 13C NMR (ppm):
d = 167.2 (s, CO), 144.5, 140.6, 131.7, 129.6, 128.0, 117.1, 60.4 (s,
CH2), 21.4 (s, CH3), and 14.3 (s, CH3). [42].
Appendix A. Supplementary material
The supplementary data contain 1H and 13C NMR spectra of
Heck coupling products and 31P NMR spectrum of palladacycle 1
in DMF at 130 °C under air. Supplementary data associated with
this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2013.04.048.
3.4.3. (E)-Ethyl 3-(4-acetylphenyl)acrylate (Table 4, entries 7, 8)
M.P. 42–43 °C, 1H NMR (ppm): d = 7.77 (d, 1H, J = 15.68 Hz),
6.99–7.37 (m, 4H), 6.22 (d, 1H, J = 15.77 Hz), 4.23 (q, 2H,
J = 7.07 Hz), 2.56 (s, 3H), 1.31 (t, 3H, J = 7.16 Hz). 13C NMR (ppm):
d = 197.2 (s, CO), 166.7 (s, CO), 138.5, 137.0, 130.8, 128.3, 128.1,
117.0, 60.6 (s, CH2), and 14.2 (s, CH3). [43].
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