Heterogeneous photocatalysed Heck reaction over PdCl2/TiO 2

Article abstract of DOI:10.1039/c3nj40941d

The heterogeneous PdCl₂/TiO₂ efficiently catalyzes the C-C bond formation (Heck reaction) between aryliodides and olefins under photochemical and mild reaction conditions. This process gives good to excellent conversion under optimized reaction conditions. After completion of the reaction, Pd²⁺ is reduced to Pd⁰. Further, Pd⁰ can be easily converted into Pd²⁺ by heating with ammonium chloride at 400°C for 30 min and the regenerated catalyst could be reused up to the third recycle with good catalytic activity. The catalysts (before and after reaction, as well as regenerated) were systematically characterized using Transmission Electron Microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, temperature programmed reduction and DRUV-visible spectroscopy techniques.

Full text of DOI:10.1039/c3nj40941d

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Heterogeneous photocatalysed Heck reaction over
PdCl2/TiO2†
Suresh B. Waghmode,*a Sudhir S. Arbuja and Bina N. Wanib
Cite this: NewJ.Chem., 2013,
37, 2911
The heterogeneous PdCl2/TiO2 efficiently catalyzes the C–C bond formation (Heck reaction) between
aryliodides and olefins under photochemical and mild reaction conditions. This process gives good to
excellent conversion under optimized reaction conditions. After completion of the reaction, Pd2+ is
reduced to Pd0. Further, Pd0 can be easily converted into Pd2+ by heating with ammonium chloride at
400 1C for 30 min and the regenerated catalyst could be reused up to the third recycle with good catalytic
activity. The catalysts (before and after reaction, as well as regenerated) were systematically characterized
using Transmission Electron Microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, temperature
programmed reduction and DRUV-visible spectroscopy techniques.
Received (in Montpellier, France)
17th October 2012,
Accepted 24th June 2013
DOI: 10.1039/c3nj40941d
www.rsc.org/njc
and recyclability.15 In the last decade, simple palladium salts such
as PdCl2 or Pd(OAc)2 without any ligands are increasingly being
Introduction
The palladium-catalyzed Heck reaction1 for the carbon–carbon
(C–C) bond formation between aryl halides and olefins has
become a widely used tool in organic synthesis.2 It provides the
simplest and most efficient way to synthesize various compounds
useful in the pharmaceutical and agrochemical industries.3 The
Heck reaction is generally performed with 1–5 mol% palladium
along with phosphine ligands for stabilization of active palladium
intermediates in the presence of a suitable base under thermal
conditions. Most of the efforts have been directed to enhance the
catalytic activity of palladium by using homogeneous as well as
heterogeneous reaction conditions.4 Various phosphorous,5,6
nitrogen,7 sulfur8 and carbene9 based ligands have been tried
successfully. However, due to their drawbacks, viz. air and moist-
ure sensitive nature, toxicity, expense, non-recoverability and
severe reaction conditions, a ligand-free Heck reaction has been
developed. Also, the main problem associated with homogeneous
reaction media is the recovery of the precious palladium metal
and contamination of the product. To overcome this problem,
many researchers have studied the Heck reaction over hetero-
geneous catalysts such as palladium supported on various metal
oxides,10a silica,10b carbon,10c,d zeolite,2d graphene oxide,10e poly-
aniline,11 polyacrylamide,12 polyethylene glycol and non-cross-
linked polystyrene,13 Pd/TiO2,14 etc. Incorporation of palladium
in ordered mesoporous materials enhances the catalytic activity
used for the Heck reaction due to their low cost.16 In order to
increase the effectiveness of the catalyst, various methods such
as ultrasonication,17 microwaves18 and electrochemistry19 have
been used. Fredricks et al. reported the acceleration of the Heck
reaction using UV-visible irradiation over homogeneous Pd(OAc)2
and heterogeneous (Pd/Al2O3 and Pd/TiO2) catalysts.20 Generally,
the vast complexity of the Heck reaction at high temperatures
(480 1C) is well known and it is carried out between 80–160 1C.20
Even though Fredricks et al. reported the Heck reaction between
90–160 1C, there is a probability for domination of the thermal
reaction as compared to photochemical reactions (same conver-
sion observed with and without UV-visible light irradiation).20 The
recovery of precious Pd metal is important for a cost effective
process. The development of the Heck reaction at ambient
conditions and with catalyst recovery is also a challenging task
for researchers. Recently, Chaudhary and Bedekar reported
Mizoroki–Heck reaction over Pd(OAc)2 under sunlight with a
naphthalene derivative as a ligand.20c The time taken for this
reaction is very long (9 days).
As a part of our research program aimed towards the
development of new strategies for the C–C bond formation,
we were encouraged to design a convenient and effective route
to C–C bond formation under UV-visible light at mild reaction
conditions.21 In this context, herein a heterogeneous UV-visible
light irradiated Heck reaction of various aryl iodides with
olefins over PdCl2/TiO2 as a catalyst was carried out at ambient
reaction conditions. The reusability of eco-friendly hetero-
geneous catalyst and the systematic study of the influence of
different solvents, bases, catalyst concentrations and regenera-
tion of the catalyst are successfully investigated.
a Department of Chemistry, University of Pune, Ganeshkhind, Pune-411007, India.
E-mail: suresh@chem.unipune.ac.in; Fax: +91 020 25691728;
Tel: +91 020 25691354
b Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, India
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3nj40941d
c
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Results and discussion
Among the studied heterogeneous catalyst PdCl2/TiO2 showed
excellent catalytic activity under UV-visible light irradiation.
Among the various solvents studied, DMF and DMAc gave
excellent conversion and selectivity for the trans ethyl cinna-
mate (Table 2; entries 1 and 2). The NMP showed 74% conver-
sion (entry 3). The reaction in DMSO and ACN showed poor
conversion (entries 4 and 5). Non-polar solvents do not show
activity (entry 6). The order of activity is DMF B DMAc 4
NMP 4 DMSO 4 ACN 4 DPE 4 THF B diglyme 4 xylene.
The catalytic activity of different palladium concentrations
for the Heck coupling under photochemical conditions was
studied and the results are summarized in Fig. 1. It was
observed that percentage conversion increased with palladium
concentration. At lower Pd concentration (0.12 mol%), 97%
conversion was observed but it requires higher reaction time.
The effect of organic as well as inorganic bases was studied for
the reaction between iodobenzene and ethyl acrylate and
results are shown in Table 3. TEA and TBA showed higher
conversion compared to other inorganic bases. This was attrib-
uted to the solubility of bases in the solvent which directly
affects the conversion of the reaction. The study of different
bases shows that TEA was the best base among the bases in the
presence of 0.5 mol% PdCl2/TiO2 as a catalyst. Using the
At the outset of our study, iodobenzene and ethyl acrylate were
chosen as model substrates to optimize the reaction conditions
such as different palladium sources, various organic and inor-
ganic bases, solvents, and catalyst concentrations (Scheme 1).
Conversion of iodobenzene was obtained at 97% with B9 : 1
selectivity for trans and cis isomers (ethyl cinnamate) in 5 h
under UV-visible irradiation in the presence of PdCl2/TiO2
(0.5 mol% Pd) as catalyst (Table 1; entry 2). The observed cis
isomer may be due to the UV-visible light-induced isomeriza-
tion of alkenes (trans–cis).20c,22 In order to confirm whether the
reaction is photochemical or thermal, the reaction was carried
without UV-visible light irradiation at 45 1C by keeping all other
parameters constant. It gave only 2% conversion with 100%
selectivity for the trans ethyl cinnamate (Table 1; entry 3).
The reaction with TiO2 with or without UV-visible light did
not give conversion (entries 4 and 5). The reaction over PdCl2
without UV-visible light did not give conversion, however under
UV-visible light gave (homogeneous reaction conditions) 99%
conversion with 88% selectivity (entries 6 and 7). These results
show that the rate of reaction of C–C bond formation under
UV-visible light has been remarkably increased. The physical
mixture of PdCl2–TiO2 gave 75% conversion. The catalyst pre-
pared by weight impregnation method is much more superior
that the physical mixture. The screening of other sources of Pd
loaded on TiO2 gave conversion between 50–90% (entries 8–15).
Table 2 Reaction of iodobenzene with ethyl acrylate using different solventsa
Selectivity (% trans)
Entry
Solvent
Conversion (%)
1
DMF
DMF
DMAc
NMP
DMSO
ACN
97
2
97
74
33
10
9
89
100
86
84
63
100
85
1b
2
3
4
5
6
DPE
Scheme 1 Photochemical Heck reaction between iodobenzene and ethyl
7
8
Xylene
THF
1
4
100
47
acrylate.
9
10
Diglyme
1,4-Dioxane
4
NR
100
—
Table 1 Screening of the catalysts for Heck reactionc
a
Reaction conditions: iodobenzene (1 mmol), ethyl acrylate (3 mmol),
triethyl amine (3 mmol), 5 mL solvent, 0.5 mol% PdCl2/TiO2 were
stirred for 5 h under 400 W mercury vapour lamp at temperature
Selectivity
(% trans)
UV-Vis
light
Conversion
(%)
b
Entry Catalyst
45 ꢁ 3 1C. Reaction was carried out without UV-visible irradiation at
45 1C for 5 h; light intensity. NR – no reaction.
1
No
Yes
Yes
No
0
97
2
—
2
3
PdCl2/TiO2
PdCl2/TiO2
TiO2
89
100
—
4
No
0
5
6
7
8
TiO2
Yes
No
Yes
Yes
Yes
0
—
PdCl2a
12
99
75
90
51
80
64
2
40
90
51
0
100
88
95
92
91
88
91
100
89
92
91
—
PdCl2
b
PdCl2/TiO2
Pd(OAc)2/TiO2
9
10
11
12
13
14
15
16
17
Pd(NH3)4Cl2ꢀH2O/TiO2 Yes
Pd(NH3)4(OAc)2/TiO2
Na2PdCl6ꢀ4H2O/TiO2
10% Pd/C
Yes
Yes
Yes
Yes
Yes
[(C6H5)3P]4Pd/TiO2
Pd(OAc)2/TiO2
Pd(NH3)4Cl2ꢀH2O/TiO2 Yes
PdO–TiO2 Yes
a
b
c
Reaction time 3 h. Physical mixture. Reaction conditions: iodo-
benzene (1 mmol), ethyl acrylate (3 mmol), triethyl amine (3 mmol),
5 mL solvent, 0.5 mol% catalysts were stirred for 5 h under 400 W
mercury vapour lamp at temperature 45 ꢁ 3 1C.
Fig. 1 Graph of percentage conversion vs. time using different amounts of
catalyst concentration.
c
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Table 3 Reaction of iodobenzene with ethyl acrylate using different basesa
Table 4 Photocatalytic Heck coupling of aryl halides and olefins using PdCl2/
a
TiO2
Selectivity (% trans)
Entry
Base
Conversion (%)
Selectivity (% trans)
Entry R
X R0
Conversion (%)
1
2
3
4
5
6
TEA
TBA
NaOAc
K2CO3
Cs2CO3
Ca(OH)2
97
93
12
12
NR
NR
89
93
86
53
—
—
1
2
H
H
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
CO2Et
97
90
94
89
95
89
CO2Me
CO2nBu
Ph
COOH
CH2CO2nBu
CO2NH2
CN
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
3
4
H
H
11
90
5
6
H
H
29
100
100
—
—
100
93
80
—
—
—
—
100
82
93
95
7b
a
Reaction conditions: iodobenzene (1 mmol), ethyl acrylate (3 mmol),
base (3 mmol), 5 mL DMF, 0.5 mol% PdCl2/TiO2 were stirred for 5 h
under 400 W mercury vapour lamp. NR – no reaction.
7
8
H
H
NR
NR
49
40
85
NR
NR
NR
NR
48
72
55
89
94
100
100
99
9
2-OH
2-OMe
4-OMe
2-NO2
4-NO2
2-NH2
4-NH2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
optimized reaction conditions, the C–C coupling reactions were
studied with various substituted aryl iodides and olefins
(Scheme 2) and the results are summarized in Table 4. Reaction
of iodobenzene with ethyl, methyl and n-butyl acrylate gave
excellent conversion and selectivity (Table 4; entries 1–3).
Styrene, acryl acid and n-butyl methacrylate showed poor
reactivity towards iodobenzene (entries 4–6) and acryl amide,
while acrylonitrile did not react with iodobenzene under these
reaction conditions (entries 7 and 8). ortho-Iodophenol gave
49% conversion with 100% selectivity for the trans product
(entry 9). ortho- and para-iodoanisole gave 40% and 85%
conversion with 93% and 80% selectivity for the corresponding
trans products, respectively (entries 10 and 11). Under photo-
chemical reaction conditions it is very likely that UV-visible
light helps towards the formation of intermediate species
between PdCl2 and reaction mass, which accelerates the rate
of reaction. We tried to trap and characterize these species, but
it was not possible due to instrumental limitations.
2-NHCOMe I CO2Et
2-CO2Me
3-CO2Me
4-CO2Me
4-CH3
4-Cl
4-Br
3-I
I
I
I
I
I
I
I
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
86
94
94b
27
72c
a
Reaction conditions: substrate (1 mmol), olefin (3 mmol), triethyl-
amine (3 mmol), 5 mL DMF, 0.5 mol% PdCl2/TiO2 were stirred for 5 h
under 400 W (mercury vapor lamp) UV-visible irradiation at tempera-
ture 45 ꢁ 3 1C. Reaction time = 7 h. Di-substituted trans compound.
b
c
NR – no reaction.
Amino and nitro substituted substrates were not active under
optimized reaction conditions. These functional groups might
be retarding conversion of aryl iodides via competing efficiently
for optical absorption. Under these reaction conditions ortho-
and para-iodoaniline, and ortho- and para-iodonitrobenzene do
not show any reaction (entries 12–15). The ortho-iodo acetanilide
shows 48% conversion with 100% selectivity for the trans product.
The effect of substitution at various positions in an aromatic ring
on the activity of ortho-, meta- and para-iodomethylbenzoate was
studied and the activity was found to be in the order para > ortho >
meta (entries 17–19). The para-iodo toluene gave 94% conversion
with 86% selectivity for the trans product (entry 20). We found that
bromo and chloro substituted aryl iodides gave selectively the
iodo coupled product (entries 21 and 22). para-Bromo and para-
chloro iodobenzene gave 100% conversion with 94% selectivity
for the trans isomer. Di-substituted products were observed for
the reaction between 1,3 di-iodobenzene and ethyl acrylate with
Fig. 2 XPS spectra of PdCl2/TiO2 before and after the reaction and after
regeneration.
99% conversion showing 72% selectivity for the di-substituted
product (entry 23).
After completion of the reaction the spent catalyst was
recovered as Pd0 and does not show any conversion towards
Heck reaction under photochemical reaction condition for
Scheme 2 Photochemical Heck reaction between substituted aryl halides and
olefins.
c
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Table 5 Catalyst recycling study for Heck reactiona
that the Pd salts kept chemical integrity within the TiO2. The
XPS spectra of fresh and regenerated catalysts show similar
peaks for Pd 3d5/2 and Pd 3d3/2, which indicates that the Pd
states of fresh and regenerated catalyst are same (Fig. 2) and
Pd2+ (spent catalyst) is completely reduced to Pd0 after a
treatment of ammonium chloride. This catalyst is same as
fresh catalyst. The activity of regenerated catalyst supports the
Entry
Run
Conversion (%)
Selectivity (%)
1
2
3
First
Second
Third
96
90
87
90
95
93
a
Reaction conditions: iodobenzene (1 mmol), ethyl acrylate (3 mmol),
triethyl amine (3 mmol), 5 mL solvent, 0.5 mol% PdCl2/TiO2 were
stirred for 5 h under 400 W mercury vapour lamp at temperature integrity of the regenerated PdCl2/TiO2 catalyst also validates
45 ꢁ 3 1C.
the regeneration of catalyst (Table 5).
Conclusion
In conclusion, we have developed a facile reusable simple
PdCl2/TiO2 catalyzed under UV-visible light C–C coupling
reaction for various substituted aryl iodides and olefins which
affords good yield for the corresponding products at ambient
reaction conditions under UV-visible light with light intensity
(photon flux) of 2.1914 ꢂ 1012. The present heterogeneous
catalyst system is novel and provides many advantages over
the homogenous catalyst, such as being recyclable. The oxida-
tion of Pd0 to Pd2+ can be done by heating the palladium
with ammonium chloride at 400 1C, which gives smaller Pd
nano particles (3–5 nm) than fresh catalyst (5–10 nm). The
Scheme 3 Proposed reaction mechanism for photochemical Heck reaction.
regenerated PdCl2/TiO2 shows good activity up to the third
recycle. The TEM analysis confirms the formation of nano Pd
reuse (Fig. 2). To overcome this problem, Pd0 was oxidized to particles on the TiO2 surface.
Pd2+ by heating in presence of ammonium chloride at 400 1C
for 30 min. It gave PdCl2/TiO2 catalyst and this regenerated
catalyst was used for further study. The activity of the catalyst
remains the same up to the third recycle (shown in Table 5).
Experimental section
(a) General procedure for the photochemical Heck reaction
The overall photochemical Heck reaction mechanism is To a 25 mL round bottom flask 1 mmol of aryl iodide, 3 mmol
believed to involve the migratory insertion pathway shown in of olefin, 3 mmol of triethyl amine (TEA) in DMF (5 mL) were
Scheme 3. Palladium in PdCl2/TiO2 catalyst under UV-visible mixed, to this mixture 0.5 mol% PdCl2/TiO2 was added. The
irradiation is reduced to Pd(0). Oxidative addition of Pd(0) to resulting reaction mixture was irradiated under 400 W mercury
the aryl halide (C–X) bonds takes place. The olefin in the Heck vapor lamp with continuous stirring in a closed box. The
reaction coordinates to the palladium, and then undergoes an temperature of the reaction was controlled at 45 ꢁ 3 1C with
insertion into the C–C p bond with concurrent migration of the the help of fans. The mercury vapor lamp was kept vertically in
aryl group to the adjacent carbon. The newly coupled aryl-olefin a quartz tube provided with a water circulation arrangement in
compound is then eliminated via a reductive b-hydride elimina- order to minimize the heating effect due to IR radiation. The
tion (ethyl cinnamate) followed by a base deprotonation of the progress of the reaction was monitored by gas chromatography
Pd(II) species and loss of halogen to form a salt.23
The XRD patterns and UV-visible absorption of the fresh and 0.32 mm ꢂ 0.25 mm). After completion, the reaction mixture
spent and regenerated catalyst are shown in the ESI† (Fig. S1 was centrifuged at 4000 rpm for 20 min to separate the catalyst.
and S2). The structure of the support remains the same after The supernatant solution was diluted with water (10 mL) and
(HP-5890) equipped with capillary column (HP-5, 30 m ꢂ
regeneration of the catalyst.
the products were extracted using ethyl acetate (3 ꢂ 10 mL). The
The TEM technique was used to measure the size of the combined organic layer was dried over anhydrous sodium
supported Pd particles, which were in the size range of 2–10 nm sulphate and purified by using column chromatography over
uniformly distributed over TiO2 in fresh, spent and regenerated silica gel [hexane or hexane–ethyl acetate (9 : 1)]. The GC-MS
catalysts. The inter-planar d-spacing (inset of Fig. S3 in ESI†) is spectra were recorded on Shimadzu QP-5050 equipped with
0.22 nm support the (111) hkl plane of cubic palladium (Fig. S3 TCD and capillary column (DB-5). FTIR spectra were recorded
and S4 in ESI†).
in Nujol mull and are expressed in cmꢃ1. 1H (300 MHz) and 13
C
The XPS spectra of the spent catalyst showed two peaks at (75 MHz) NMR spectra were recorded in CDCl3.
340.6 and 335.5 eV for zero valent palladium (metallic). XPS of
(b) Preparation of 1 wt% PdCl2/TiO2 catalyst
fresh and regenerated catalyst showed two main peaks centered
at 343.6 and 338.3 eV and related to Pd 3d3/2 and Pd 3d5/2
.
In 30 mL of distilled water, 10 mg of PdCl2 and 1 g of TiO2 were
These signals were associated with PdCl2 species, suggesting added and stirred for 2 h at room temperature and then
c
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refluxed for 3 h with constant stirring. The excess water was (m, 2H), 6.52 (d, 1H, J = 16.2 Hz), 4.26 (q, 2H), 3.87 (s, 3H), 1.35
evaporated on a water bath and the solid powder was dried in (t, 3H). 13C NMR: d 167.2, 158.0, 139.8, 131.2, 128.7, 123.2,
an oven at 100 1C for 2 h. The dried PdCl2/TiO2 powder was 120.5, 118.6, 110.9, 60.2, 55.3, 14.4. FTIR (KBr, cmꢃ1): 1097,
mixed in a mortar and pestle for 30 min and used for further 1169, 1247, 1369, 1632, 1702, 2924. MS (EI): m/z 206.20 (M+).
reactions.
(E)-Ethyl 3-(4-methoxyphenyl)acrylate [entry 11]
Characterization data
NMR and IR data of the final products (entries from Table 4).
(E)-Ethyl cinnamate [entry 1]
1
Colourless solid, mp 48–49 1C, H NMR (CDCl3): d 7.58 (d, 1H,
J = 15.9 Hz), 7.42 (d, 2H, J = 8.8 Hz), 6.88 (d, 2H, J = 8.8 Hz), 6.25
(d, 1H, J = 15.9 Hz), 4.23 (q, 2H), 3.80 (s, 3H), 1.32 (t, 3H). 13C
NMR: d 167.0, 161.0, 144.0, 129.4, 126.9, 115.5, 114.1, 60.2, 55.2,
14.3. FTIR (KBr, cmꢃ1): 1033, 1170, 1250, 1365, 1632, 1714,
2942. MS (EI): m/z 206.19 (M+).
Colourless liquid, bp 271–272 1C, 1H NMR (CDCl3): d 7.66
(d, 1H, J = 15.9 Hz), 7.46 (m, 2H) 7.33 (t, 3H, J = 6.6 and
3.3 Hz), 6.38 (d, 1H, J = 15.9 Hz), 4.24 (q, 2H), 1.31 (t, 3H).
13C NMR: d 166.5, 144.2, 134.1, 129.9, 128.5, 127.7, 117.9, 60.2,
14.2. FTIR (KBr, cmꢃ1): 1040, 1164, 1260, 1310, 1648, 1734,
2983. MS (EI): m/z 176.17 (M+).
(E)-Ethyl 3-(2-acetamidophenyl)acrylate [entry 16]
(E)-Methyl cinnamate [entry 2]
Colourless solid, mp 140–142 1C, 1H NMR (CDCl3): d 7.74
(d, 1H, J = 15.6 Hz), 7.67 (d, 1H, J = 7.9 Hz), 7.46 (d, 1H, J =
7.7 Hz), 7.10–7.28 (m, 2H), 6.28 (d, 1H, J = 15.6 Hz), 4.16 (q, 2H),
2.16 (s, 3H), 1.26 (t, 3H). 13C NMR: d 168.6, 166.6, 139.0, 135.6,
130.6, 127.6, 126.9, 125.7, 125.0, 120.5, 60.7, 24.3, 14.3. FTIR
(KBr, cmꢃ1): 948, 1069, 1236, 1275, 1360, 1456, 1536, 1579,
1663, 1705, 2963, 3269. MS (EI): m/z 233.27 (M+).
Colourless liquid, bp 263–264 1C, 1H NMR (CDCl3): d 7.66
(d, 1H, J = 15.9 Hz), 7.49 (m, 2H) 7.36 (t, 3H, J = 6.6 and 3.3 Hz),
6.42 (d, 1H, J = 15.9 Hz), 3.79 (s, 1H). 13C NMR: d 167.2, 144.7,
134.2, 130.1, 128.7, 127.9, 117.6, 51.7. FTIR (KBr, cmꢃ1): 1170,
1275, 1315, 1642, 1741, 2989. MS (EI): m/z 162.15 (M+).
(E)-Butyl cinnamate [entry 3]
(E)-Ethyl 3-(2-methoxyphenyl)acrylate [entry 17]
Colourless liquid, bp 154–156 1C, 1H NMR (CDCl3): d 8.37
(d, 1H, J = 15.9 Hz), 7.91 (d, 1H, J = 7.7 Hz), 7.37–7.57
(m, 3H), 6.25 (d, 1H, J = 15.9 Hz), 4.23 (q, 2H), 3.91 (s, 3H),
1.35 (t, 3H). 13C NMR: d 166.9, 166.3, 143.4, 136.1, 132.1, 130.5,
129.5, 129.1, 127.7, 120.9, 60.5, 52.3, 14.3. FTIR (KBr, cmꢃ1):
765, 986, 1037, 1132, 1182, 1263, 1369, 1424, 1489, 1574, 1603,
1642, 1723, 2963. MS (EI): m/z 234.20 (M+).
Colourless liquid, bp 290–295 1C, 1H NMR (CDCl3): d 7.63
(d, 1H, J = 15.9 Hz), 7.46 (m, 2H) 7.32 (t, 3H, J = 6.6 and
3.3 Hz), 6.39 (d, 1H, J = 15.9 Hz), 4.17 (t, 2H), 1.68 (m, 2H), 1.45
(m, 2H), 0.94 (t, 3H). 13C NMR: d 166.8, 144.3, 134.2, 130.0,
128.6, 127.8, 118.0, 64.3, 30.7, 19.2, 13.7. FTIR (KBr, cmꢃ1):
1066, 1173, 1280, 1639, 1716, 2933. MS (EI): m/z 204.19 (M+).
(E)-Ethyl 3-(2-hydroxyphenyl)acrylate [entry 9]
(E)-Ethyl 3-(4-chlorophenyl)acrylate [entry 21]
1
Colourless solid, mp 49–51 1C, H NMR (CDCl3): d 7.56 (d, 1H,
1
J = 15.9 Hz), 7.38 (d, 2H, J = 8.2 Hz), 7.29 (d, 2H, J = 8.2 Hz), 6.34
(d, 1H, J = 15.9 Hz), 4.23 (q, 2H), 1.33 (t, 3H). 13C NMR: d 166.3,
142.6, 135.8, 132.6, 128.9, 128.8, 118.6, 60.5, 14.2. FTIR
(KBr, cmꢃ1): 2926, 1710, 1637, 1491, 1313, 1180. MS (EI): m/z
210.34 (M+).
Colourless solid, mp 83–84 1C, H NMR (CDCl3): d 8.02 (d, 1H,
J = 16.2 Hz), 7.42 (d, 1H, J = 6.8 Hz), 7.21 (m, 1H), 6.85 (m, 2H),
6.61 (d, 1H, J = 16.2 Hz), 4.26 (q, 3H), 1.32 (t, 3H). 13C NMR: d
168.7, 155.6, 140.9, 131.6, 129.0, 121.5, 120.3, 117.8, 116.3, 60.8,
14.3. FTIR (KBr, cmꢃ1): 1375, 1524, 1609, 1635, 1689, 3440. MS
(EI): m/z 192.12 (M+).
(E)-Ethyl 3-(4-bromophenyl)acrylate [entry 22]
(E)-Ethyl 3-(2-methoxyphenyl)acrylate [entry 10]
Colourless liquid, bp 198–199 1C, 1H NMR (CDCl3): d 7.65
Colourless solid, mp 38–41 1C, H NMR (CDCl3): d 7.96 (d, 1H, (d, 1H, J = 15.9 Hz), 7.44 (d, 2H, J = 8.5 Hz), 7.33 (d, 2H, J =
J = 16.2 Hz), 7.47 (d, 1H, J = 7.7 Hz), 7.30 (m, 1H), 6.87–6.96 8.5 Hz), 6.35 (d, 1H, J = 15.9 Hz), 4.12 (q, 2H), 1.32 (t, 3H).
1
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13C NMR: d 166.2, 142.7, 133.0, 131.7, 130.8, 129.1, 118.6, 60.4,
14.2. FTIR (neat, cmꢃ1): 1182, 1320, 1463, 1635, 1711, 2983. MS
(EI): m/z 254.04 (M+).
7 X. Gai, R. Grigg, M. I. Ramzan, V. Sridharan, S. Collard and
J. E. Muir, Chem. Commun., 2000, 2053–2054.
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2004, 6, 221–224.
Bis-ethyl (E)-3,30-(1,3-phenylene)-2-propenoate [entry 23]
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and H. M. Lee, Organometallics, 2010, 29, 3901–3911.
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V. Hagen and M. Muhler, Top. Catal., 2000, 13, 319–326;
(b) V. Polshettiwar and A. Molnar, Tetrahedron, 2007, 63,
6949–6976; (c) R. G. Heidenreich, J. G. E. Krauter, J. Pietsch
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1
Colourless solid, mp 50–52 1C, H NMR (CDCl3): d 7.62 (d, 3H,
J = 15.6 Hz), 7.43 (d, 2H, J = 7.4 Hz), 7.32 (t, 1H, J = 7.1 and
7.9 Hz), 6.41 (d, 2H, 16.2 Hz), 4.24 (q, 4H), 1.32 (t, 6H).
13C NMR: d 165.7, 142.8, 134.4, 128.7, 127.0, 118.5, 59.9, 13.8.
FTIR (KBr, cmꢃ1): 1197, 1496, 1643, 1719, 2746, 3056. MS (EI):
m/z 274.25 (M+).
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Acknowledgements
The authors SBW and SSA are thankful to the Department of
Science Technology, New Delhi, India and Bhabha Atomic
Research Centre, Mumbai for financial support and fellowship,
respectively. The authors are grateful to Drs D. P. Amalnerkar
and U. P. Mulik for fruitful discussion, and Dr K. R. Patil, NCL,
Pune for XPS analysis.
14 L. Zhaohao, C. Jing, S. Weiping and H. Maochun, J. Mol.
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