Solid supported palladium(0) nano/microparticle: A ligand-free efficient recyclable heterogeneous catalyst for mono- and β,β-double-Heck reaction

Article abstract of DOI:10.1016/j.tetlet.2012.10.062

Solid supported palladium nano/microparticles were found to be active catalysts to perform mono- and β,β-double-Heck reactions. Different β-unsubstituted and substituted alkenes including acrylate, methacrylate, crotonate, styrene, acrylonitrile, and acrylamide were investigated successfully for mono- and β,β-double-Heck reactions with aryl iodide under milder reaction condition. One-pot β,β-double-Heck reaction of aryl iodides with α,β-unsaturated ester, amide, nitrile, and styrene derivatives were also performed under standard reaction conditions. Wide functional group tolerance, easy catalyst recovery, and recyclability up to twelve times without significant loss of catalytic activity added extra importance to the present process.

Full text of DOI:10.1016/j.tetlet.2012.10.062

Tetrahedron Letters 53 (2012) 7044–7051
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Solid supported palladium(0) nano/microparticle: a ligand-free efficient
recyclable heterogeneous catalyst for mono- and b,b-double-Heck reaction q
⇑
Dharminder Sharma, Sandeep Kumar, Arun K. Shil, Nitul Ranjan Guha, Bandna, Pralay Das
Natural Plant Products Division, CSIR-Institute of Himalayan Bioresource Technology, Palampur 176061, H.P., India
a r t i c l e i n f o
a b s t r a c t
Article history:
Solid supported palladium nano/microparticles were found to be active catalysts to perform mono- and
b,b-double-Heck reactions. Different b-unsubstituted and substituted alkenes including acrylate, methac-
rylate, crotonate, styrene, acrylonitrile, and acrylamide were investigated successfully for mono- and b,
b-double-Heck reactions with aryl iodide under milder reaction condition. One-pot b,b-double-Heck
Received 12 July 2012
Revised 9 October 2012
Accepted 14 October 2012
Available online 23 October 2012
reaction of aryl iodides with
a,b-unsaturated ester, amide, nitrile, and styrene derivatives were also
performed under standard reaction conditions. Wide functional group tolerance, easy catalyst recovery,
and recyclability up to twelve times without significant loss of catalytic activity added extra importance
to the present process.
Keywords:
Heck
Heterogeneous catalyst
Solid supported palladium (SS-Pd)
Nano/microparticles
Mono- and b,b-double-Heck
Ó 2012 Elsevier Ltd. All rights reserved.
Palladium catalyzed Heck reaction of olefin and aryl halide is
one of the most fundamental reactions for carbon–carbon bond
formation in organic synthesis.1 Several reports have been pub-
lished for the Heck reaction of mono- and multi-substituted aryl
halides.2 b,b-Diarylalkenes synthesized via b,b-double-Heck reac-
tion, are valuable synthetic intermediates for natural products
and pharmaceuticals.3 Conventionally Heck reaction of olefin and
aryl halide is restricted to mono-Heck reaction due to less active
b-proton on the 1,2-disubstituted olefins.4 Therefore, b,b-double-
Heck has been scarcely reported in the literature with harsh
reaction conditions.5 The use of non-recyclable homogeneous
palladium catalyst,6 additives,7 moisture sensitive expensive
palladium complexes,8 longer reaction time, and tedious work-up
procedure draw a line of limitation over the previous methods.
Recently a greener approach has been developed for b,b-diarylation
of acrylate but applicable only in the case of higher alkyl acrylates
with longer reaction time (30 h) at 120 °C.9 Botella and Najera have
established b,b-diarylation of t-butyl acrylates using an oxime-
derived palladacycle/Pd(OAc)2 in water at 120 °C. Especially t-butyl
acrylate has been used for diarylation to avoid possible hydrolysis
of the ester group in the presence of inorganic bases at higher
temperature.10 As per our knowledge there is no ligand-free
heterogeneous catalyst available to serve b,b-diarylation product
through b,b-double-Heck reaction covering a large number of
substrate scopes.
Recently our group described the synthesis of solid supported
palladium(0) and rhodium(0) (SS-Pd and SS-Rh) nano/microparti-
cles as heterogeneous catalyst and their applications in cross cou-
pling, oxidation, and reduction reactions.11,13
As a part of our continuous effort to explore the potential of SS-
Pd catalyst, herein we describe a convenient methodology for
mono- and b,b-double-Heck reaction of
a,b-unsaturated esters,
amides, nitriles, and styrenes with different aryl iodides under
milder reaction condition.
Initially to search the optimum reaction condition, 4-iodotol-
uene and ethyl acrylate were taken as test substrates (Table 1).
To our delight, a combination of SS-Pd (2 mol % of Pd) and
K2CO3 (2 mmol) in DMF gave 1 in 93% yield within 6 h and con-
sidered as the best condition (Table 1, entry 7). For wider appli-
cability of the present method, 4-iodoanisole with different
acrylic ester, acrylonitrile, acrylamide, and styrene afforded good
to excellent yields of corresponding cross coupled products with
E-isomer (confirmed by 1H NMR). Different acrylic esters (Me, Et,
t
n-Bu, Bu) were explored in the similar reactions and no signifi-
cant effect of ester functionalizations was observed (Table 2, entries
1–6). Alongside, positional isomers such as 2-, 3-, and 4- substi-
tuted aryl iodides were found to have a negligible impact on
reactivity though 4-substitution gave a higher yield of desired
cinnamate derivatives (Table 2, entries 2, 5, and 7). Reaction of
4-iodoanisole with different methacrylates produced trisubsti-
tuted alkenes which is uncommon in literature12 (Table 2,
entries 8–10). Electron deficient 2- and 4-iodonitro benzenes
also afforded the corresponding products in good yields (Table 2,
entries 11–13).
q
IHBT communication no. 3314
⇑
Corresponding author. Fax: +91 1894 230433.
E-mail addresses: pdas@ihbt.res.in, pdas_nbu@yahoo.com (P. Das).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.10.062

D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
7045
Table 1
Under this milder condition, active functional groups such as
OH, CN, and CHO were found to be tolerated and gave products 15–
17 in considerable yields (Table 2, entries 14–16). 4-Iodobenzoic
acid and 4-iodoaniline also participated in Heck reaction with ethyl
acrylate to give corresponding E-cinnamates which otherwise were
rare to accomplish in previous reports. (Table 2, entries 17 and 18).
4-Bromoiodo benzene is selectively converted into 4-bromoethyl-
cinnamate 21 with excellent yield (Table 2, entry 20). Acrylonitrile,
acrylamide, and styrene derivatives were similarly found to be
tolerated and gave good conversions with different aryliodides
(Table 2, entries 21–26). 1,2- and 1,3-diiodobenzene gave 1,
2- and 1,3-diacrylobenzenes in excellent yields (Table 2, entries
27 and 28). After the completion of reaction, the catalyst was recov-
ered by filtration, washed with water and acetone, dried under
reduced pressure and used for the next cycle. The catalyst could
be recycled up to twelve runs successfully without significant loss
of activity (Fig. 1).
Synthesized cinnamate, cinnamonitrile, and stilbene derivatives
were further used for second Heck reaction to prepare correspond-
ing b,b-diarylalkenes.
Monoarylated alkenes 3 and 6 were applied for b-arylation to
produce b,b-diaryl substituted alkenes 30 and 31 in satisfactory
yield. When both electron rich and deficient cinnamates were trea-
ted with different functionalized aryliodides, b,b-double-Heck
products 32–38 were formed with satisfactory yields (Table 3, en-
tries 3–9). Tetrasubstituted olefines 39 were synthesized from the
Optimization of reaction condition for mono-Heck reaction
CO2Et
I
CO2Et
Catalyst
+
Solvent, Base
110 °C
1
Entry
Catalyst (mol %)
Solvent
Base
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Pd(OAc)2, (2)
PdCl2, (2)
Pd2(dba)3, (2)
Pd(PPh3)4, (2)
Pd/C, (2)
SS-Pd (1)
SS-Pd (2)
SS-Pd (3)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
SS-Pd (2)
—
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMA
PEG 400
Toluene
water
THF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
NaOH
Et3N
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
—
8
8
8
8
8
12
6
6
6
6
6
6
6
6
6
6
6
18
18
68
75
82
72
66
88
93
93
87
75
86
88
68
82
05
75
70
29
0
ACN
DMF
DMF
K2CO3
a
Isolated yields, reaction condition: 4-iodotoluene (1 equiv), ethyl acrylate
(2 equiv), base (2 equiv), catalyst (2 mol %).14
Table 2
SS-Pd catalyzed mono-Heck reaction of substituted aryliodides and
a,b-unsaturated compounds
R3
R3
R2
I
SS-Pd, K2CO3
R1
R1
+
R2
DMF, 6h, 110 °C
Entry
1
Aryl iodides
Olefins
Products
Yielda (%)
I
I
I
CO2Me
CO2Me
MeO
2
98
MeO
MeO
CO2Et
CO2Et
2
3
97b
MeO
MeO
3
CO2-n-Bu
CO2-n-Bu
93
4
MeO
I
CO2Me
CO2Et
CO2Me
4
5
95
OMe
OMe
5
I
CO2Et
92b
OMe
OMe
6
7
I
t
t
CO2 Bu
CO2 Bu
6
90
OMe
OMe
(continued on next page)

7046
D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
Table 2 (continued)
Entry
Aryl iodides
Olefins
CO2Et
Products
Yielda (%)
95
MeO
I
I
CO2Et
7
8
8
MeO
CO2Me
CO2Me
MeO
MeO
MeO
9
93
91
92
MeO
MeO
I
I
CO2-n-Bu
CO2-n-Bu
9
10
t
t
CO2 Bu
CO2 Bu
10
11
MeO
O2N
I
CO2Et
CO2Et
O2N
O2N
11
86b
12
13
I
CO2-n-Bu
CO2-n-Bu
12
13
14
80
82
88
O2N
I
CO2Et
CO2Et
CO2Et
NO2
NO2
14
I
I
CO2Et
HO
15
HO
CO2Et
CO2Et
CO2Et
CO2Et
NC
15
16
17
89
88
81
16
NC
I
CO2Et
OHC
HO2C
17
OHC
HO2C
I
CO2Et
18
I
CO2Et
CO2Et
H2N
18
75
19
H2N

D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
7047
Table 2 (continued)
Entry
Aryl iodides
Olefins
CO2Et
Products
Yielda (%)
CO2Et
I
19
20
92
93
20
I
CO2Et
CN
CO2Et
Br
21
Br
I
CN
MeO
21
22
23
99
75
78
22
MeO
I
CONH2
CONH2
23
I
I
Ph-4-OMe
Ph-4-OMe
MeO
24
MeO
MeO
Ph
Ph
MeO
24
25
77
75
25
I
Ph
Ph
Ph
26
I
Ph
O2N
26
27
69
27
O2N
I
CO2Et
CO2Et
CO2Et
CO2Et
84c
93c
I
I
28
EtO2C
CO2Et
28
29
I
a
Isolated yields, reaction conditions: aryliodide (1 equiv), ethyl acrylate (2 equiv), K2CO3 (2 equiv), and SS-Pd (2 mol %), only the E-isomers were isolated in all the cases.
Reaction was carried out by using 5 g of substrate.
Aryliodide (1 equiv), ethyl acrylate (4 equiv), K2CO3 (4 equiv), and SS-Pd (2 mol %), reaction time 10 h.
b
c
reaction of 11 with 4-iodoanisole in 80% yield (Table 3, entry 10).
substrate for b,b-double-Heck reaction and gave corresponding
homodiarylated alkene product 42 (Table 3, entry 14). Interest-
ingly, highly conjugated b,b-double-Heck product 43 was prepared
by the reaction of 29 with 4-iodoanisole following the same reac-
tion condition (Table 3, entry 15). Methyl and ethyl crotonates
were also tested with 4-iodoanisole for the same reaction to give
44 and 45 in excellent yields regardless of b-methyl substitution
(Table 3, entries 16 and 17).
Interestingly, when 4-methoxy cinnamate 3 was treated with com-
parably bulky aryl halide (such as 1-iodonaphthalen) the reaction
followed both cis and trans approach at intermediate steps and
produced 40 with E/Z: 52/48 (Table 3, entry 11). Although, when
naphthyl substituted acrylate 20 was treated with 4-iodoanisole
the reaction followed the major trans orientation to form a stable
intermediate and gave 40 in comparable yield with E/Z: 90/10
(Table 3, entry 12). 1,2-Bis(4-methoxyphenyl)ethane 24 coupled
efficiently with 4-iodoanisole to afford 41 in 72% yield. 3-
(4-Methoxyphenyl)acrylonitrile 22 was also found to be a suitable
b,b-Double-Heck reactions of alkenes were further investigated
in one-pot. Addition of 2.4 equiv of aryl iodide at a time increases
the formation of homocoupled diaryls and decreases the yield of

7048
D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
98
96
94
92
90
88
86
84
82
80
corresponding b,b-double-Heck products. To overcome this prob-
lem, a one pot sequential strategy was adopted. Desired b,b-dou-
ble-Heck product was produced in one-pot on addition of
another 1.2 equiv of aryl iodide after 6 hours of reaction (Table 4).
The reaction of ethyl and n-butyl acrylates with methyl and meth-
oxy substituted aryl iodides under similar condition afforded the
corresponding b,b-double-Heck products in good yields (Table 4,
entries 1–4). 4-Methoxystyrene also participated in the same reac-
tion to give 41 in satisfactory yield (Table 4, entry 5). Interestingly,
acryl amides and acrylonitriles also participated in the same reac-
tion with different aryl iodides to produce 42, 48, 49, and 50 in
good yields (Table 4, entries 6–9).
1
2
3
4
5
6
7
8
9
10
11 12
No. of runs
In summary, a ligand-free heterogeneous palladium catalyst SS-
Pd was used for mono- and b,b-double-Heck reactions of different
Figure 1. Recyclability studies of SS-Pd catalyst for compound 3.
Table 3
Heck reaction of b-substituted
a
, b-unsaturated compounds using SS-Pd
R2
R2
R3
R
I
SS-Pd, K2CO3
R3
+
DMF, 6h, 110 °C
R
R1
R1
Entry
Olefins
Aryl iodide
Products
Yielda (%)/E/Z ratio
I
MeO
CO2Et
MeO
MeO
1
3
90
30
MeO
MeO
I
I
OMe
CO2Et
2
3
6
3
78
OMe
31
MeO
CO2Et
80 E/Z::91/9
OMe
32
I
I
CO2Et
4
5
6
6
75 E/Z::90/10
OMe
33
CO2Et
78 E/Z::92/8
OMe
34

D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
7049
Table 3 (continued)
Entry
Olefins
Aryl iodide
Products
Yielda (%)/E/Z ratio
I
CO2Et
6
1
77 E/Z::77/23
MeO
MeO
35
MeO
O2N
I
I
CO2Et
7
8
9
12
14
12
75 E/Z::86/14
72 E/Z::72/28
68 E/Z::82/18
36
MeO
MeO
CO2Et
MeO
NO2
37
I
CO2Et
38
O2N
I
MeO
t
CO2 Bu
MeO
10
11
80
39
MeO
MeO
I
CO2Et
11
12
3
66 E/Z::52/48
70 E/Z::90/10
40
I
I
20
40
MeO
MeO
OMe
OMe
13
24
72
MeO
41
(continued on next page)

7050
D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
Table 3 (continued)
Entry
Olefins
Aryl iodide
Products
Yielda (%)/E/Z ratio
I
MeO
CN
MeO
MeO
14
22
92
42
MeO
MeO
I
CO2Et
15
29
70
43
CO2Et
MeO
MeO
MeO
CO2Me
I
I
CO2Me
16
95 E/Z::100/00
96 E/Z::100/00
44
MeO
MeO
CO2Et
CO2Et
17
45
a
Isolated yields; Reaction conditions: aryliodide (1 equiv), b-substituted acrylic ester/nitrile (1 equiv), K2CO3 (2 equiv), and SS-Pd (2 mol %). E/Z ratio was determined by 1
H
NMR (300 MHz).15
Table 4
by filtration and recycled up to twelve runs without significant loss
of catalytic activity.
One pot b,b-double-Heck reaction of aryliodide and
a
,b-unsaturated compounds
R'
Acknowledgments
I
R
SS-Pd, K2CO3
DMF, 12h, 110 °C
R
Authors are grateful to Dr. P. S. Ahuja, Director IHBT for provid-
ing necessary facilities during the course of the work. We gratefully
acknowledge the financial assistance from the Department of
Science and Technology (Nano Mission), New Delhi (Grant No.
SR/NM/NS-95/2009). D.S. (SRF), S. K. (JRF), A.K.S. (SRF), Bandna
(SRF), and NRG (SRF) gratefully acknowledge CSIR/UGC, New Delhi,
India for research fellowships.
R'
+
R'
Entry
R0
R
Product
Yielda (%)
1
2
3
4
5
6
7
8
9
m-OMe
p-OMe
o-OMe
p-Me
p-OMe
p-OMe
o-OMe
p-OMe
o-OMe
CO2Et
CO2Et
CO2Et
CO2nBu
p-OMe-Ph
CONH2
CONH2
CN
46
30
31
47
41
48
49
42
50
72
70
86
66
55
72
70
88
84
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
10.062.
CN
a
Isolated yields; reaction conditions: aryliodide [(1.2 equiv)ꢀ2], ethyl acrylate
(1 equiv), K2CO3 (4 equiv), and SS-Pd (3 mol %).
References and notes
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D. Sharma et al. / Tetrahedron Letters 53 (2012) 7044–7051
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J = 16.00 Hz, 1H); 13CNMR (75 MHz, CDCl3)
d 14.76, 21.81, 60.75, 117.14,
128.73, 130.01, 132.20, 140.96, 144.96, 167.50; HREIMS data: m/z Calcd for
[M+H]+ C12H15O2 191.2463, obsd 191.2460.
9. Delample, M.; Villandier, N.; Douliez, J. P.; Camy, S.; Condoret, J. S.; Pouilloux,
Y.; Barrault, J.; Jerome, F. Green Chem. 2010, 12, 804.
15. Ethyl 3,3-bis(4-methoxyphenyl)acrylate 30 (Table 3, entry 1): A mixture of (E)-
ethyl-3-(4-methoxyphenyl)acrylate
(100 mg,
0.48 mmol),
iodoanisole
10. (a) Botella, L.; Najera, C. Tetrahedron Lett. 1833, 2004, 45; (b) Botella, L.; Najera,
C. J. Org. Chem. 2005, 70, 4360.
(114 mg, 0.48 mmol), and potassium carbonate (132 mg, 0.96 mmol) was
taken in DMF (0.5 ml) and then added SS-Pd (216 mg, 2 mol % Pd). The reaction
mixture was heated at 110 °C for 6 h under nitrogen atmosphere. After
completion, the reaction mixture was treated with water (1 ml) and extracted
with ethyl acetate (3 ꢀ 5 ml). The organic layer was finally washed with brine
and dried over anhydrous Na2SO4. The crude mixture was purified by column
chromatography (EtOAc/Hexane, 3:97), which afforded ethyl 3,3-bis(4-
methoxyphenyl)acrylate 25 as a light yellow gummy liquid (135 mg, 90%
yield) 1H NMR (300 MHz, CDCl3) d 1.15–1.20 (t, J = 7.1, 3H), 3.83 (s, 3H), 3.86 (s,
11. (a) Das, P.; Sharma, D.; Shil, A. K.; Kumari, A. Tetrahedron Lett. 2011, 52, 1176;
(b) Bandna; Aggarwal, N.; Das, P. Tetrahedron Lett. 2011, 52, 4954; (c) Bandna;
Guha, N. R.; Shil, A. K.; Sharma, D.; Das, P. Tetrahedron Lett. 2012, 53, 5318–
5322; (d) Shil, A. K.; Sharma, D.; Guha, N. R.; Das, P. Tetrahedron Lett. 2012, 53,
4858; e) Guha, N. R.; Reddy, C. B.; Aggarwal, N.; Sharma, D.; Shil, A. K.; Bandna,
Das, P. Advanced Synthesis & Catalysis (Accepted), 2012.
12. (a) Beller, M.; Riermeier, T. H. Tetrahedron Lett. 1996, 37, 6535; (b) Arellano, C.
G.; Corma, A.; Iglesias, M.; Sancheza, F. Adv. Synth. Catal. 2004, 346, 1758.
13. The solution of 100 mg of NaBH4 in 30 ml of water was added to 4 g of
Amberlite IRA 900 resin (chloride form) (Across, BE) in a 100 ml flask. The
mixture was stirred for 4 h at room temperature. Then the resin was washed
with water till pH became neutral and then with acetone to remove water from
3H), 4.05–4.13 (m, 2H), 6.25 (s, 1H), 6.84–6.94 (m, 4H), 7.16–7.28 (m, 4H); 13
C
NMR (75 MHz, CDCl3) d 14.96, 56.04, 56.15, 60.76, 114.04, 114.52, 115.78,
130.80, 131.67, 131.12, 134.67, 157.15, 160.50, 161.57, 167.26; HREIMS data:
m/z Calcd. for [M+H]+ C19H21O4 313.3676 obsd. 313.3643.