N,N′-bis(2-pyridinecarboxamide)-1,2-benzene palladium complex as a new efficient catalyst for Suzuki-Miyaura coupling reaction under phosphane free conditions Dedicated to Professor Mehdi Rashidi

Article abstract of DOI:10.1016/j.ica.2014.06.039

In this article, palladium complex of N,N′-bis(2-pyridinecarboxamide) -1,2-benzene has been introduced as a new catalyst for the Suzuki-Miyaura coupling reaction of aryl halides in water. The catalyst is easily prepared from the reaction of Pd(OAc)₂ and N,N′-bis(2-pyridinecarboxamide)- 1,2-benzene ligand and has been characterized using ¹H NMR, TGA, FT-IR, solid and liquid UV-Vis spectroscopy.

Full text of DOI:10.1016/j.ica.2014.06.039

Inorganica Chimica Acta 421 (2014) 433–438
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N,N0-bis(2-pyridinecarboxamide)-1,2-benzene palladium complex
as a new efficient catalyst for Suzuki–Miyaura coupling reaction
under phosphane free conditions
⇑
⇑
Mohammad Gholinejad , Hamid R. Shahsavari
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), P.O. Box 45195-1159, Gavazang, Zanjan 45137-6731, Iran
a r t i c l e i n f o
a b s t r a c t
In this article, palladium complex of N,N0-bis(2-pyridinecarboxamide)-1,2-benzene has been introduced
as a new catalyst for the Suzuki–Miyaura coupling reaction of aryl halides in water. The catalyst is easily
prepared from the reaction of Pd(OAc)2 and N,N0-bis(2-pyridinecarboxamide)-1,2-benzene ligand and has
been characterized using 1H NMR, TGA, FT-IR, solid and liquid UV–Vis spectroscopy.
Ó 2014 Elsevier B.V. All rights reserved.
Article history:
Received 24 March 2014
Received in revised form 18 June 2014
Accepted 24 June 2014
Available online 11 July 2014
Dedicated to Professor Mehdi Rashidi
Keywords:
Palladium catalyst
Suzuki–Miyaura
Water
Phosphane free
Carbon–carbon bond
1. Introduction
Performing palladium catalyzed coupling reactions in more eco-
friendly reaction media such as water which is non-toxic, cheap and
In recent years extensive attention has been paid to the devel-
opment of transition-metal-catalyzed cross-coupling reactions in
organic synthesis [1,2]. Among the different transition metals, pal-
ladium has found wide utility because it catalyzed important car-
bon–carbon and carbon-hetero atom bond formation reactions,
under relatively mild reaction conditions [3–6]. Palladium cata-
lyzed Suzuki–Miyaura reaction which is reaction between boronic
acid derivatives and aryl derivatives, has become one of the most
widely used methods for the formation of sp2-sp2 carbon–carbon
bond [7–18].
Phosphane ligands are generally used as ligands in palladium
catalyzed Suzuki–Miyaura coupling reaction [19–22]. However,
phosphane ligands are usually toxic, unrecoverable, thermally
unstable, and their synthesis are difficult. In order to avoid men-
tioned disadvantages, in recent years, there are growing interests
in using phosphane free palladium catalyzed Suzuki–Miyaura cou-
pling reactions. Magnetite supported palladium catalysts [23–34]
and nitrogen-based ligands such as diazabutadienes [35], oximes
[36–41], N-heterocyclic carbenes, [42–48] and diimine [49] are
examples of phosphane free Suzuki–Miyaura coupling reactions.
inflammable instead of toxic and expensive organic solvent is also
interesting issue for chemists. Furthermore, using water as a solvent,
facilitate separation of desire products from the reaction phase.
Very recently, synthesis and characterization of palladium
complex of deprotonated N,N0-bis(2-pyridinecarboxamide)-1,
2-benzene has been reported [50]. The formation of palladium
complex between of N,N0-bis(2-pyridinecarboxamide)-1,2-benzene
and PdCl2 was performed in the presence of NaH as base for
deprotonating of ligand. The complex has been found to interact
with CT-DNA through an intercalative mode, which was investi-
gated by absorption, fluorescence and viscosity measurement
tools. Now in this work, we report formation of palladium complex
of N,N0-bis(2-pyridinecarboxamide)-1,2-benzene in the absence of
base and its reactivity in the Suzuki–Miyaura coupling reaction
of structurally different aryl iodides and bromides with phenylbo-
ronic acid.
2. Results and discussion
2.1. Synthesis and characterization of the complexes
We have synthesized N,N0-bis(2-pyridinecarboxamide)-1,
2-benzene ligand according to the reported method in literature
[50,51] (Scheme 1).
⇑
Tel./fax: +982433153232.
E-mail addresses: gholinejad@iasbs.ac.ir (M. Gholinejad), shahsavari@iasbs.ac.ir
(H.R. Shahsavari).
http://dx.doi.org/10.1016/j.ica.2014.06.039
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

434
M. Gholinejad, H.R. Shahsavari / Inorganica Chimica Acta 421 (2014) 433–438
O
3.5
3
NH2
NH2
NH
N
N
P(OPh)3
Pyridine
+
HO2C
N
NH
O
2.5
2
1eq
2eq
Scheme 1. Synthesis of N,N0-bis(2-pyridinecarboxamide)-1,2-benzene.
1.5
1
O
O
NH
N
N
NH
N
N
OAc
OAc
Pd(OAc)2
THF
Pd
0.5
0
NH
O
NH
O
0
0.5
1
1.5
2
Scheme 2. Complex formation between ligand and Pd(OAc)2.
L / Μ
Fig. 2. Mole ratio plot for complex formation between Pd(OAc)2 and ligand.
4
3.5
3
However, complex formation between ligand and palladium
acetate was studied without using any deprotonating base
(Scheme 2).
The structure of the synthesized palladium complex was
characterized using different techniques such as 1H NMR, TGA,
IR, and UV–Vis spectroscopy. Study of UV–Vis spectra of Pd(OAc)2,
ligand and complex showed the disappearance of characteristic
peak of Pd(OAc)2 (405 nm) and a formation of new broad absorp-
tion band (385 nm) due to the PdL complex formation (Fig. 1).
We have also studied the molar ratio of palladium with respect
to ligand by using the mole ratio method [52–54]. The results
showed that the complex formation between the Pd(OAc)2 and
ligand in THF or CH2Cl2 was in good harmony with the formation
of (PdL) complex (Fig. 2).
2.5
2
t = 10 min
Pd(OAc)2
t = 1 min
1.5
1
Ligand
0.5
0
High thermal stability of catalyst was confirmed using TGA
analysis which shows palladium complex is stable up to 250 °C
(Fig. 3). In addition, comparison of FT-IR of ligand with complex
indicates preserve of structure of ligand during the formation of
complex (see Supporting information).
340
360
380
400
420
440
460
480
500
λ / nm
1H NMR spectra difference between pyridine based ligands
and their metal complexes, is one the important methods for
Fig. 1. UV–Vis spectra of reaction between ligand and Pd(OAc)2 for formation of Pd
complex.
Fig. 3. Thermo-gravimetric (TGA) diagram of Pd Complex.

M. Gholinejad, H.R. Shahsavari / Inorganica Chimica Acta 421 (2014) 433–438
435
Fig. 4. Changes in the 1H NMR spectra of ligand and Pd complex.
1.00
0.75
0.50
0.25
0.00
Table 1
The results of the reaction of iodobenzene with phenylboronic acid in the presence of
different bases using Pd catalyst.
Pd Complex
Ligand
Pd(OAc)2
I
Catalyst (1 mol%)
+
PhB(OH)2
Base, Solvent
100 °C
Entry
Solvent
Base
Yield
1
2
3
4
5
6
7
Toluene
Toluene
Toluene
DMF
DMF
DMF
Et3N
KOH
K2CO3
Et3N
K2CO3
KOH
trace
trace
29
trace
2
trace
4
200
300
400
500
600
700
800
H2O
Et3N
8
9
H2O
H2O
H2O
H2O
dioxane
dioxane
dioxane
DMF–H2O
DMF–H2O
H2O
KOH
K2CO3
DBU
Na2CO3
Et3N
KOH
K2CO3
Et3N
K2CO3
K2CO3
87
98
7
85
trace
trace
7
12
73
λ (nm)
10
11
12
13
14
15
16
17a
Fig. 5. Normalized diffuse reflectance UV–Vis spectra of Pd(OAc)2, ligand and
palladium complex in solid-state.
characterization of complexes in the literature [55,56]. It is worth
to note that, the 1H NMR spectra of the ligand in DMSO and its pal-
ladium complex is similar, but the protons of the complex are
shifted downfield relative to the protons of the ligand which is con-
firmed successful chelation of ligand to Pd (Fig. 4).
The solid-state diffuse reflectance UV–Vis spectra of the ligand,
Pd(OAc)2 and palladium complex exhibit a pattern similar to those
seen in solution by a little shifting and it confirmed complex
formation (Fig. 5).
trace
a
Reaction in the absence of catalyst.
As demonstrated in Table 1, using K2CO3 as a base and water as
a solvent, afforded high reaction yield for the reaction of iodoben-
zene with phenylboronic acid. The optimized reaction condition
was successfully applied for the reaction of structurally different
aryl iodide and bromides.
2.2. Catalytic study
The results showed that coupling of aryl iodides with phenylbo-
ronic acid was carried out smoothly to afford good to excellent
yields of the corresponding coupled products. Reaction of aryl bro-
mides proceeded efficiently and desire coupling products were
In order to find optimized reaction conditions in Suzuki–Miyaura
coupling reaction, we have studied reaction of iodobenzene as a
model compound with phenylboronic acid in different solvents
and bases (Table 1).

436
M. Gholinejad, H.R. Shahsavari / Inorganica Chimica Acta 421 (2014) 433–438
Table 2
Reaction of structurally different aryl halides with phenylboronic acid in the presence of catalyst.
X
+
Catalyst (1 mol%)
PhB(OH)2
K2CO3 (1.5 mmol)
H2O (2 mL)
100 °C
R
R
X= Cl, Br, I
Entry
1
ArX
Time (h)
Product
Isolated yield%
97
3
I
2
3
4
5
4.5
95
93
92
82
I
MeO
Me
MeO
Me
4
2
5
I
I
O2N
O2N
I
I
6
7
3
6
91
89
S
S
I
I
Me
I
Me
8
5
90
9
15
84
85
Br
10
15
20
3
Br
Me
Me
11
12
13
83
87
81
Br
MeO
NC
MeO
NC
Br
4
Br
O2N
O2N

M. Gholinejad, H.R. Shahsavari / Inorganica Chimica Acta 421 (2014) 433–438
437
Table 2 (continued)
Entry
14
ArX
Time (h)
6
Product
Isolated yield%
84
N
Br
Br
N
15
16
24
70
6
88
Br
N
N
N
N
17
18
24
24
45
54
Cl
Cl
Cl
NC
Me
NC
Me
19
24
41
obtained in high to excellent yields. We have also studied reaction
of aryl chlorides with phenylboronic acid. However, the result
showed that the reactions were sluggish and coupling products
were obtaine d in 41–54% isolated yield (Table 2).
references, respectively, are shown in parentheses as follows: 1H
(400 or 250 MHz, TMS) and 13C (100 or 63 MHz, TMS). The chem-
ical shifts and coupling constants are in ppm and Hz, respectively.
The microanalyses were performed using a Thermofinigan Flash
EA-1112 CHNSO rapid elemental analyzer. UV–Vis spectra in
solution or solid were recorded by Ultrospec 3100 Pro, UV–Vis
spectrometer or UV–Vis–NIR Spectrometer Cary 5-E (Varian),
respectively. The chemical were obtained from Sigma or Merck
chemical companies and used without further purification. The
progress of the reactions was followed with TLC using silica gel
SILG/UV 254 plates or by GC Varian CP 3800 instrument. IR spectra
were run on a FT-IR Bruker Vector 22 spectrophotometer.
In order to get more information about active palladium spe-
cies, mercury poisoning test was carried out. The addition of
300 eq Hg(0) to the reaction mixture, did not inhibit catalytic activ-
ity which confirm that catalytic active species is ligand-bound pal-
ladium. In addition, we have studied hot filtration test for the
reaction of 4-bromoanisol and phenylboronic acid. The reaction
mixture was filtered after 1 h at the reaction temperature (20%
GC yield) and filtrate was allowed to react for 20 h. GC analysis
of the reaction after 20 h indicated 22% GC yield which confirm
that the catalyst mostly have a heterogeneous nature at the reac-
tion conditions.
4.1. Synthesis
Also, TGA and FT-IR analysis of isolated catalyst from the complete
reaction of iodobenzene with phenylboronic acid showed no appre-
ciable difference with fresh catalyst (see Supporting information).
4.1.1. General procedure for the preparation of ligand
The ligand was prepared according to the reported procedure in
the literature [49,50], which briefly will explain here. 2-pyridine-
carboxylic acid (1.23 g, 10 mmol) and 1,2 diaminobenzene (0.54 g,
5 mmol) were added to stirring pyridinic solution (10 mL). After
the addition of triphenylphosphite (2.6 mL, 10 mmol) to the solu-
tion, the reaction mixture was heated for 4 h at 80 °C and allowed
the solution stand overnight at room temperature. A pale brown
crystalline solid resulted, was washed with methanol to give long
white needles. Yield: 305, 96%; Anal. Calc. for C18H14N4O2: C, 67.9;
H, 4.4; N, 17.6. Found: C, 67.6; H, 4.2; N, 17.7%. IR (KBr, cmꢀ1):
3. Conclusions
In conclusion, in this article we have introduced palladium
complex of N,N0-bis(2-pyridinecarboxamide)-1,2-benzene as
a
new palladium catalyst for the Suzuki–Miyaura coupling reaction
of aryl halides in water. In the presence of catalyst aryl iodides
and bromides were reacted efficiently. The catalyst has been
characterized using 1H NMR, TGA, FT-IR, solid and liquid UV–Vis.
Mercury poisoning and hot filtration tests showed that the catalyst
mostly have a heterogeneous and ligand-bound palladium nature
at the reaction conditions.
m
C@O, 1671; m
N–H, 3310. 1H NMR (250 MHz, DMSO): d 10.59 (s,
2H), 8.52–8.48 (m, 2H), 8.04–8.01 (m, 2H), 7.95–7.89 (m, 1H),
7.64–7.59 (m, 2H), 7.54–7.48 (m, 2H), 7.20–7.14 (m, 2H). 13C NMR
(63 MHz, DMSO): d 163.0, 149.5, 148.7, 138.3, 131.1, 127.3, 125.9,
125.5, 122.6.
4. Experimental
4.1.2. General procedure for the preparation of the palladium complex
To a solution of ligand (95 mg, 0.3 mmol) in dry THF (10 mL)
was added Pd(OAc)2 (67 mg, 0.3 mmol) and the solution was
The 1H and 13C NMR spectra were recorded on a Bruker Avance
DPX 400 or 250 MHz spectrometer. The operating frequencies and

438
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stirred for 30 min.
separated and wash with cold THF and dried under vacuum. Yield:
A yellow solid precipitated, which was
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134, 83%; Anal. Calc. for C22H20N4O6Pd: C, 48.7; H, 3.7; N, 10.3.
Found: C, 49.1; H, 3.9; N, 10.2%. IR (KBr, cmꢀ1):
m
Pd–N, 512; mC@O
,
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m
N–H, 3421. 1H NMR (250 MHz, DMSO) d 10.71 (s, 2H), 8.64
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7.79 (d, J = 4.1 Hz, 2H), 7.67 (d, J = 4.8 Hz, 2H), 7.30 (d, J = 6.0, 2H).
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4.1.3. General experimental procedure for the Suzuki–Miyaura
reaction
Aryl halide (1 mmol), phenylboronic acid (1.5 mmol), palladium
complex (1 mol%), K2CO3 (1.5 mmol), and water (1.5 mL) were added
to 5 mL flask and mixture was stirred at 100 °C for appropriate
reaction time. The progress of the reaction to completion was mon-
itored by TLC or GC analysis. After the completion of reaction, the
aqueous layer was extracted with ethyl acetate or diethyl ether
(5 ꢁ 1 mL). Organic extracts were combined together and dried
over anhydrous Na2SO4 and purified by flash chromatography
using hexane/EtOAc to give the desired coupling product.
Acknowledgments
Authors are grateful to Institute for Advanced Studies in Basic
Sciences (IASBS) Research Council and Iran National Science Foun-
dation (INSF-grant number of 92027596) for financial support.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2014.06.039.
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