5-Nitrobenzimidazole containing Pd(II)catalyzed C[sbnd]C cross-coupling reactions: The effect of the N-substituent of the benzimidazole structure on catalyst activity

Article abstract of DOI:10.1016/j.molstruc.2019.04.101

A series of Pd(II)complexes (1a-e)were successfully synthesized by reaction of N-substituted 5-nitrobenzimidazole with [PdCl₂(CNCH₃)₂]in toluene under argon reflux condition. Their catalytic activity in the Suzuki-Miyaura

Full text of DOI:10.1016/j.molstruc.2019.04.101

Accepted Manuscript
5-Nitrobenzimidazole containing Pd(II) catalyzed C-C cross-coupling reactions:
The effect of the N-substituent of the benzimidazole structure on catalyst activity
Kenan Buldurun, İsmail Özdemir
PII:
S0022-2860(19)30510-1
10.1016/j.molstruc.2019.04.101
MOLSTR 26473
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Accepted Date:
24 September 2018
24 April 2019
Please cite this article as: Kenan Buldurun, İsmail Özdemir, 5-Nitrobenzimidazole containing Pd(II)
catalyzed C-C cross-coupling reactions: The effect of the N-substituent of the benzimidazole
structure on catalyst activity, Journal of Molecular Structure (2019), doi: 10.1016/j.molstruc.
2019.04.101
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ACCEPTED MANUSCRIPT
5-Nitrobenzimidazole containing Pd(II) catalyzed C-C cross-coupling reactions: The
effect of the N-substituent of the benzimidazole structure on catalyst activity
Kenan Buldurun1,2, İsmail Özdemir2,3
1Muş Alparslan University, Faculty of Science and Arts, Department of Chemistry, 49250-
Muş/TURKEY
2İnönü University, Catalysis Research and Application Center, 44280-Malatya/TURKEY
3İnönü University, Faculty of Science and Arts, Department of Chemistry, 44280-
Malatya/TURKEY
ABSTRACT
A series of Pd(II) complexes (1a-e) were successfully synthesized by reaction of N-
substituted 5-nitrobenzimidazole with [PdCl2(CNCH3)2] in toluene under argon reflux
condition. Their catalytic activity in the Suzuki-Miyaura and Mizoroki-Heck coupling
reactions were investigated. All these complexes were characterized by elemental analysis, 1H
NMR, 13C NMR and IR spectroscopy. The catalytic activities of N-substituted 5-
nitrobenzimidazole palladium(II) complexes were screened in Mizoroki-Heck and Suzuki-
Miyaura coupling reactions. The reactions were optimized for the most suitable temperature,
solvent and base system. The Pd(II) complexes exhibited good catalytic activity at the
Mizoroki-Heck reaction. Additionally, the Suzuki-Miyaura showed relatively excellent
activity at the coupling reaction.
Keywords: 5-Nitrobenzimidazole, Catalytic activity, Suzuki-Miyaura, Spectroscopy

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1. Introduction
Palladium-catalyzed C-C cross-coupling reactions, due to its versatile features, have
become very popular in recent years [1]. A wide variety of organic products composed of
these reactions are important substrates which are widely used for pharmaceutical applications
and various chemical industries, such as arylated olefins, asymmetric biaryls, arylalkines
[2,3].
Palladium-catalyzed C-C cross-coupling reactions are also used for agricultural
chemistry, natural products, herbicides, molecular organic materials and components for
optical device production [4-6]. C-C bond forming reactions, particularly the intense demand
for new generation products which C-C bonds are formed under mild condition, have
encouraged the scientists to produce more efficient catalysts formed under mild conditions
and to motivate them to explore more efficient catalysts market [7]. These reactions are most
advantageous among the well-known C-C bonding reactions. This is principally because they
have a wide range of functional groups including bisbenzimidazole [8], nitrogen-containing
ligands [9], carbenes [10,11] and more recently Schiff bases [12]. They also possess a light
reaction conditions, and their starting reagents are cheap and possess low toxicity [13].
Synthesized ligand structures and donor groups have a strong effect on the catalytic
performances of transition metal complexes, and therefore the ligand design has a
considerable impact on the progression of catalytic science. The ligand used to obtain these
complexes has a significant degree of structural and electronic properties, catalytic
performance and selectivity [14]. On the other hand, the ligands are determinative in the
stability of the active species and catalyst lifetime [15]. For this reason, a new environment-
friendly, stable, inexpensive and easily accessible nitrogen-based ligand class has been
developed in place of toxic, expensive and sensitive phosphine ligands. Such nitrogen-
containing ligands form Pd(II) complexes exhibiting high stability and high catalytic
performance for C-C binding reactions [16]. Thus, the development of efficient synthetic
methods that provide easy access to such heterobiarils has aroused great interest in the field of
synthetic chemistry [17]. Moreover, nitrogen-based ligands are generally non-toxic, harmless
to nature, air/moisture insensitive, easy-to-use and have superior properties compared to
certain disadvantages of conventional phosphine ligands [18]. Thus, palladium complexes
with nitrogen-ligands attract significant attention [19-22].

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Furthermore, C-C coupling reactions, particularly chelating ligands containing
benzimidazole groups, have been studied extensively in the last two decades because of the
transition metal compounds widely used as a ligand coordination chemistry of azoles [23-28].
Herein, the synthesis and characterization of five new Pd(II) complexes having aliphatic,
methyl, methoxy and only aromatic moiety bearing benzylic different types of N-substituted
5-nitrobenzimidazole ligands and their catalytic activity in Suzuki-Miyaura and Mizoroki-
Heck reactions were reported. All synthesized compounds were characterized using 1H NMR,
13C NMR and IR spectroscopy and elemental analysis. The results of the characterization
were found to support the proposed structures. The catalytic activities of newly synthesized
Pd(II) complexes in the Suzuki-Miyaura and Mizoroki-Heck coupling reactions were
investigated.
2. Experimental
The entire reactions for the preparation of Pd(II) complexes and N-coordinated 5-
nitrobenzimidazole as the ligand were carried out using the standard Schlenk techniques to
degrade the glass materials under argon gas. Chemicals were purchased from Sigma Aldrich
and Fluka. Melting points were detected in glass capillaries under air with an electrothermal-
9200 melting point apparatus. FTIR spectra were recorded by KBr pellets in the range of 400-
4000 cm-1 on a Perkin Elmer Spectrum 65 spectrophotometer at the Center Research
Laboratory located in Muş Alparslan University. 1H and 13C NMR spectra were recorded with
a Bruker Avance DPX at 300 Merkur spectrometer operated at 300 MHz in CDCl3 with
tetramethylsilane as an internal reference. Elemental analyses were recorded at the Research
Center Laboratory of Inonu University. All catalytic reactions were monitored on an Agilent
6890N GC system by GC-FID with an HP-5 column of 30 m length, 0.32 mm diameter and
0.25 mm film thickness. Column chromatography was performed using silica gel 60 (70-230
mesh). Solvent ratios are given as v/v.
2.1. General procedure to synthesis of Pd(II) complexes(1a-e)
A solution of the N-substituted 5-nitrobenzimidazole (12 mmol) and PdCl2(CH3CN)2
(6 mmol) in toluene (25 mL) were heated and refluxed for 5 h. Upon cooling to room
temperature, the precipitates (1a–e) were obtained. The obtained products were recrystallized

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from dichloromethane/diethyl ether (1:3) at room temperature, filtered off and dried under
vacuum.
Synthesis of dichloro-N-(benzyl)-5-nitrobenzimidazole palladium(II) 1a. mp.:224°C.
1H NMR (300 MHz, CDCl3) δ: 8.76 (s, 1H, NCHN), 8.22-7.21 (m, 8H, NC6H3N and
NCH2C6H4), 5.46 (s, 2H, NCH2C6H4(CH3)-2). 13C NMR (300 MHz, CDCl3) δ: 146.6
(NCHN), 110.1, 117.2, 118.9, 127.2, 128.8, 129.3, 134.3, 137.9, 143.3, (NC6H3N and
NCH2C6H4), 49.4 (NCH2C6H4(CH3)-2). IR (KBr, cm-1): 1518 (C=N). Anal. Calc. for
C28H22N6O4PdCl2: C, 49.16; H, 3.22; N, 12.29. Found: C, 49.16; H, 3.20; N, 12.28.
Synthesis of dichloro-N-(2-ethylbutane)-5-nitrobenzimidazole palladium(II) 1b. mp:
1
˃320 °C. H NMR (300 MHz, CDCl3) δ: 8.60 (s, 1H, NCHN), 8.30-7.20 (m, 3H, NC6H3N),
4.06 (s, 2H, NCH2CH(CH2CH3)2), 1.84 (m, 1H,NCH2CH(CH2CH3)2), 1.29 and 1.27 (m, 4H,
NCH2CH(CH2CH3)2), 0.90 (m, 6H, NCH2CH(CH2CH3)2). 13C NMR (300 MHz, CDCl3) δ:
147.0
(NCHN),
146.8-105.8
(NC6H3N),
48.0
(NCH2CH(CH2CH3)2),
40.1
(NCH2CH(CH2CH3)2), 22.3 (NCH2CH(CH2CH3)2), 9.5 (NCH2CH(CH2CH3)2). IR (KBr, cm-
1): 1520 (C=N). Anal. Calc. for C26H34N6O4PdCl2: C, 46.45; H, 5.06; N, 12.51. Found: C,
46.47; H, 5.04; N, 12.50.
Synthesis of dichloro-N-(2-methylcyclohexyl)-5-nitrobenzimidazole palladium(II) 1c.
mp: 236 °C. 1H NMR (300 MHz, CDCl3) δ: 9.23(s, 1H, NCHN), 8.52-7.84 (m, 3H, NC6H3N),
4.58 (d, 2H, CH2C6H11), 2.51 and 1.18 (m, 11H, CH2C6H11). 13C NMR (300 MHz, CDCl3) δ:
144.1 (NCHN), 143.8-109.8 (NC6H3N), 45.3 (CH2C6H11), 36.0-25.4 (CH2C6H11). IR (KBr,
cm-1): 1514 (C=N). Anal. Calc. for C28H34N6O4PdCl2: C, 48.31; H, 4.88; N, 12.07. Found:
C, 48.28; H, 4.86; N, 12.05.
Synthesis of dichloro-N-(3,5-dimethylbenzyl)-5-nitrobenzimidazole palladium(II) 1d.
mp: 279 °C. 1H NMR (300 MHz, CDCl3) δ: 8.81 (s, 1H, NCHN), 8.67-7.20 (m, 6H, NC6H3N
and NCH2C6H3(CH3)2-3,5), 5.65 (s, 2H, NCH2C6H3(CH3)3-3,5), 2.28 and 2.22 (s, 6H,
NCH2C6H3(CH3)2-3,5). 13C NMR (300 MHz, CDCl3) δ: 149.7 (NCHN), 144.5-110.0
(NC6H3N
and
NCH2C6H3(CH3)2-3,5),
49.01
(NCH2C6H3(CH3)3-3,5),
20.81
(NCH2C6H3(CH3)2-3,5). IR (KBr, cm-1): 1520 (C=N). Anal. Calc. for C32H30N6O4PdCl2: C,
51.93; H, 4.05; N, 11.36. Found: C, 51.93; H, 4.05; N, 11.36.
Synthesis of dichloro-N-(3,4,5-trimethoxybenzyl)-5-nitrobenzimidazole palladium(II)
1
1e. mp: 296 °C. H NMR (300 MHz, CDCl3) δ: 9.15 (s, 1H, NCHN), 8.71-6.70 (m, 5H,

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NC6H3N and NCH2C6H2(OCH3)-3,4,5), 5.55 (s, 2H, NCH2C6H2(OCH3)-3,4,5), 3.62 and 3.52
(s, 9H, NCH2C6H2(OCH3)-3,4,5). 13C NMR (300 MHz, CDCl3) δ:153.1 (NCHN), 149.1-
105.8 (NC6H3N and NCH2C6H2(OCH3)-3,4,5), 49.3 (NCH2C6H2(OCH3)-3,4,5), 60.02 and
56.1 (NCH2C6H2(OCH3)-3,4,5). IR (KBr, cm-1): 1510 (C=N). Anal. Calc. for
C34H34N6O10PdCl2: C, 47.25; H, 3.93; N,9.72. Found: C, 47.23; H, 3.91; N, 9.71.
2.2. General procedure for theMizoroki-Heck type coupling reactions
After preliminary tests at different temperatures and different bases, the optimum
condition for the reaction of aryl bromide and styrene was achieved with the use of ethanol
(solvent), K2CO3 (base), 80 ºC (temperature) and 3 h (duration). Palladium complexes (1.0
mmol%), aryl bromide (1.0 mmol), styrene (1.5 mmol), K2CO3 (2.0 mmol) and ethanol (3
mL) were added into a small Schlenk tube under atmosphere air, and the mixture was heated
at 80 °C for 3 h. Isolated yield was determined by GC.
2.3. General procedure for the Suzuki-Miyaura type coupling reactions
After preliminary testing of various bases at different temperatures, the use of ethanol
(solvent), K2CO3 (base), 80 ºC (temperature) and 3 h (duration) provided the optimum
condition for the reaction of aryl bromide and phenylboronic acid. Palladium complexes (1.0
mmol%), aryl bromide (0.2 mmol), phenylboronic acid (0.3 mmol), K2CO3 (1.2 mmol) and
ethanol (3 mL) were added in to a small Schlenk tubes under atmosphere air, and the mixture
was heated at 80 °C for 3 h. Isolated yield was determined by GC.
3. Result and discussion
Nitrogen-containing ligands have been found to be more stable against air and
moisture. They are also modular and less expensive. In recent years, a number of various
ligand design Pd(II) complexes are reported to exhibit high activity for the C-C coupling
reactions [29]. In particular, the transition metal complexes with nitrogen-donor atoms
containing the benzimidazole scaffold have been successfully utilized for the catalytic
conversion of organic compounds [30].These findings have encouraged the researchers in this
field to examine the design and catalytic properties of new metal complexes with N-
coordinated ligands [31]. All complexes are isolated from the air as stable, non-hygroscopic
solids and can be dissolved in dimethylformamide, dimethylsulfoxide, chloroform,
dichloromethane and halogenated solvents. However, they are insoluble in diethyl ether,

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petroleum ether and n-hexane solution and also did not show any decomposition symptoms
when exposed to air for days.
All compounds were synthesized in a single step, and the latter products were stable in
solution and in solid form, as seen in Scheme1.
Scheme 1 Synthesis of palladium-N-5-nitrobenzimidazole complexes
1
13
The H and C NMR of palladium complexes (1a-e) showed that the NCHN signals
1
occurred between 8.60-9.23 ppm and 146.0-153.1 ppm, respectively. The H NMR values
indicated that the NCHN signals shifted to the low area in the palladium complexes compared
to the corresponding ligand because of an electron withdrawing effect of the metal center. The
IR spectrums showed that palladium-N-5-nitrobenzimidazole complexes (1a-e) exhibited a
characteristic (NCN) band typically at the range of 1510-1520 cm-1.
Table 1
Table 2
It is of importance to determine the appropriate proportions and amounts of base and
solvent. Therefore, many different bases and solvents were examined for the Suzuki-Miyaura
reaction. At the beginning, many bases and different solvents were examined, as seen in the
(Table 1, 2). For ethanol, the coupling reaction was completed at approximately 3 h when the
most suitable base, K2CO3, was used (Table 2, entry 9). The other bases such as NaOH, KOH,
KOtBu and Cs2CO3 produced slightly lower yields (Table 1, entries 1-5). The use of DMF,
H2O, ethanol, methanol, toluene, dioxane, THF, DMF+H2O as solvents were studied (Table 2,
entries 1-9) at elevated temperature. The tests indicated that high yields were obtained using
ethanol as solvent and K2CO3 as a base. The reaction was effected at 80 °C temperature.
Table 3
Initially, the optimized conditions with arylboronic acid and various aryl halides
(Table 1, Table 2) were investigated. For the structures of 4-bromo aryl substrates containing
both electron donating (-OCH3, -CH3) and electron withdrawing (-CHO) groups, the desired
products were obtained in yields at 70-100% in the presence of catalysts of Pd(II) (1a-e)
complexes. In general, the activated bromides, 4-bromoacetophenone, 4-bromotoluene, 4-
bromobenzaldehyde (Table 3, entries1, 8, 9, 13) could couple efficiently with phenylboronic
acid 1a,1c, 1d to afford the desired products in >99% yields. After that, the disubstituted

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substrate p-bromobenzene, which provided the biaryl product in 70% yield, was obtained
under the same reaction conditions (Table 3, entry 18). The reactions of phenylboronic acid
with bromobenzene exhibited good yields of up to yield 70-87% at 80 °C (Table 3, entries 16-
20). On the other hand, the presence of electron-donating or electron-withdrawing groups in
the para-position, particularly in the para position due to the aryl bromides substrates,
significantly contributed to the increase of the reaction rates by significantly affecting the
catalyst activity. Palladium complexes (1a-e) were shown to be effective compounds for C-C
binding reactions of Suzuki-Miyaura, and the C-C coupling products were obtained in high
yield. The palladium complexes (1a-e) also promoted the transformation of biaryl in very
high yields in the condition reactions (Table 3, entries 1,8,9,13). These results showed that
five novel N-coordinated palladium complexes (1a-e) could catalyzed C-C coupling reaction.
Almost all complexes were obviously good catalyst for Suzuki-Miyaura reaction. Both
electron withdrawing releasing (p-Ar-Br) groups with phenylboronic acid provided the
corresponding products with high yields. Moreover, the results showed that both activated and
deactivated aryl bromides are efficiently converted into biaryl at these conditions. In this
regard, N-donor ligand-based Pd(II) complexes have been reported in many studies [30].
Overall, these results suggest that the steric and electronic properties of the ligand are highly
effective on the catalytic activity of the catalyst complexes.
Table 4
Table 5
Table 6
Initially, various solvents were investigated, and it was observed that the yield of 1a was
improved with ethanol (Table 5, entries 2,9). Then, other bases were examined, and the
desired coupling product 1a was obtained in high yields by employing K2CO3 as bases (Table
4, entry 4). Based on the results of other bases, such as Na2CO3, Cs2CO3, KOH, KOtBu and
NaOH, they are found to be less effective in obtaining the coupling product (Table 1, entries
1-5). Overall, the catalytic protocol using Pd(II) complexes as catalyst with K2CO3 as base in
ethanol at 80 °C was determined to be the most effective method in a high yield (Table 6,
entry 16). As attempt, no products were observed without the addition of palladium complex
(Table 4, entry 6). Once the reaction conditions were established (e.g., base, solvent and
temperature parameters), the full conversion was obtained (in Table 5, entry 10). It was found

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that the reduction of the catalyst amount used in the reaction did not have an effect on the
conversion products.
A model reaction was performed by stirring styrene with various types of aryl bromides,
such as 4-bromoacetophenone, 4-bromotoluene, 4-bromobenzene, 4-bromobenzaldehyde in
ethanol using (0.005 mmol) Pd(II) complexes at 80 °C for 3 h. Furthermore, when reactions
were performed using aryl bromides, high yields were obtained in the case of the Pd(II)
catalysts (1a-e) (Table 6, entries 5, 7, 9, 16, 18, 19, 23 and 25). When Table 6 is evaluated,
catalysts were observed to be active in the Mizoroki-Heck reaction in general. In order to
compare the catalyst performance, Pd(II) catalysts (1a-e) were tested under the same
conditions. The yield increased on the substrate having the electron-donating or electron-
withdrawing groups. It was observed that the catalyst exhibited higher conversion and yield.
Optimized reaction conditions were tested, and the Pd(II) catalysts (1a-e) were reacted with
both the electron-donating and the electron-withdrawing styrene and the aryl bromides
reaction. Aryl bromides were converted to the corresponding coupled product in high yields
(Table 6). Furthermore, increasing electron donating or electron-withdrawing on the aryl
bromides did not have much effect on catalytic activities (Table 6, entry 1-25). That is, high
yields were obtained when styrene reacted with both aryl bromides bearing electron-
withdrawing or electron-donating substituent -CHO and -COCH3, -OCH3 and -CH3 (Table 6,
entries 1-15).
All in all, several factors are effective in catalyst performance. The catalyst
performance, the molecular structure of the substrate, the electronic effects of the ligands and
complex catalyst concentration used also play an important role. On the other hand, the
reaction temperature is highly effective on the efficiency of the coupling product [4,15].
Moreover, ligand is found to have a significant impact both on the catalytic activity and
sustainability. It is observed that Pd(II) catalysts (1a-e) exhibit higher conversions and yields
[32, 33].
4. Conclusions
In this work, the preparation and characterization a series of new Pd(II) catalysts (1a-
e) and their catalytic activities for Mizoroki-Heck and Suzuki-Miyaura reactions are
presented. Catalytic experiments show that for the C-C coupling product the Pd(II) catalysts
(1a-e) can be obtained for a wide range of aryl bromide with styrene for good yields. 5-

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nitrobenzimidazole Pd(II) complexes containing aryl and aliphatic positions are also observed
to show a better activity. The results exhibit that their catalytic efficiency depends
significantly on the ligand properties. Pd(II) catalysts (1a-e) listed in Table 3, Table 6 are
determined to be highly effective compounds in the preparation of C-C coupling products
obtained by coupling phenylboronic acid and aryl bromides and styrene to aryl bromides. It is
also found that the activities of the Pd(II) complexes present in the Mizoroki-Heck coupling
reactions are relatively lower than those of the Suzuki-Miyaura coupling reactions.
Apparently, Pd(II) catalysts show a similar effectiveness in the formation of desired C-C
coupling product under optimal conditions at 80 °C in ethanol. It is expected that catalysts
such as [PdCl2(N-substituted 5-nitrobenzimidazole)2]will have environmental industrial
applications because the preparation and purification of such catalysts are extremely simple.
The observed catalytic activity demonstrates that synthesized N-coordinated 5-
nitrobenzimidazole Pd(II) catalysts (1a-e) are significantly effective for catalytic of Suzuki-
Miyaura and Mizoroki-Heck coupling reaction.
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ACCEPTED MANUSCRIPT
R
R
Toluene / 90 °C
N
N
N
+
1/2
PdCl2(CH3CN)2
N
O2N
O2N
2
Pd
Cl
Cl
1a-e
OCH3
OCH3
OCH3
N
N
N
N
N
N
N
N
N
N
O2N
O2N
O2N
O2N
O2N
2
2
2
2
2
Pd
Pd
Pd
Pd
Pd
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
1c
1d
1b
1e
1a
Scheme 1 Synthesis of palladium-N-5-nitrobenzimidazole complexes

ACCEPTED MANUSCRIPT
Highlight
 Novel Pd(II) complexes synthesized and characterized.
 The catalytic activities of newly synthesized Pd(II) complexes in the Suzuki-Miyaura
and Mizoroki-Heck coupling reactions were investigated.
 The synthesized Pd(II) complexes (1a-e) were found to exhibit good activity in
Suzuki-Miyaura and Mizoroki-Heck C-C coupling reactions.

ACCEPTED MANUSCRIPT
Table 1
Effect of bases for the Suzuki-Miyaura reaction
Conversion
Entry
Base
Time (h)
(%)
40
51
27
100
28
-
1
2
3
4
5
6
NaOH
Cs2CO3
Na2CO3
K2CO3
KOtBu
-
10
10
10
10
10
10
Reaction conditions: 4-Bromoacetophenone (0.2 mmol), phenylboronic acid (0.3 mmol), catalyst (0.001 mmol)
and base (1.2 mmol), solvent (3 mL)
Table 2
Effect of solvents for the Suzuki-Miyaura reaction
Entry
Solvents
Time (h)
Conversion
(%)
-
1
2
3
4
5
6
7
8
9
H2O
24
10
10
10
10
10
10
10
3
Ethanol
Methanol
DMF
Toluene
Dioxane
THF
100
26
12
21
80
25
16
100
DMF+H2O
Ethanol
Reaction conditions: 4-Bromoacetophenone (0.2 mmol), phenylboronic acid (0.3 mmol), catalyst (0.001 mmol)
and base (1.2 mmol), solvent (3 mL)

ACCEPTED MANUSCRIPT
Table 3
The Suzuki-Miyaura coupling reaction of aryl halides with phenylboronic acid 1a-e
B(OH)2
Pd(II) Comp.(1a-e)
R
Br
H3COC
+
EtOH, 80 °C / K2CO3
R= H, CH3, OCH3, COCH3, CHO
Entry
1
Catalyst(1a-e)
Ar-X
Product
% Conv.
100
83
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
2
H3COC
Br
3
82
H3COC
4
91
5
80
6
88
7
80
8
100
100
87
H3C
Br
H3C
9
10
11
12
13
14
15
16
17
18
19
20
84
81
100
90
H3CO
H3CO
Br
80
87
72
Br
70
82
84
Reaction conditions: 4-Bromoacetophenone (0.2 mmol), phenylboronic acid (0.3 mmol), catalyst (0.001 mmol)
and base (1.2 mmol), EtOH (3 mL)

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Table 4
Effect of bases for the Mizoroki-Heck reaction
Conversion
Entry
Base
Time (h)
(%)
42
38
30
100
31
-
1
2
3
4
5
6
NaOH
Cs2CO3
Na2CO3
K2CO3
KOtBu
-
10
10
10
10
10
10
Reaction conditions: 4-Bromobenzene (1 mmol), styrene (1.5 mmol), catalyst (% Pd(II) complexes(1a-e)) (0.005
mmol) and base (2 mmol), solvent (3 mL)
Table 5
Effect of solvents for the Mizoroki-Heck reaction
Entry
Solvents
Time (h)
Conversion
(%)
-
100
42
15
13
75
25
16
100
100
1
2
3
4
5
6
7
8
H2O
24
10
10
10
10
10
10
10
3
Ethanol
Methanol
DMF
Toluene
Dioxane
THF
DMF+H2O
Ethanol
Ethanol
9
10*
3
Reaction conditions: 4-Bromobenzene (1 mmol), styrene (1.5 mmol), catalyst (% Pd(II) complexes (1a-e))
(0.005 mmol) and base (2 mmol), solvent (3 mL),*catalyst% Pd(II) (0.001 mmol)

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Table 6
The Mizoroki-Heck coupling reaction of aryl halides with styrene 1a-e
Pd(II) Comp.(1a-e)
R
Br
+
H3COC
EtOH, 80 °C / K2CO3
R= H, CH3, OCH3, COCH3, CHO
Entry
Catalyst(1a-e)
1a
ArX
Time(h)
Yield(%)
1
3
80
2
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
82
88
70
98
93
95
80
99
72
79
68
75
60
67
100
73
95
100
100
80
90
100
78
Br
COCH3
3
4
5
6
7
Br
CH3
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Br
OCH3
Br
Br
CHO

ACCEPTED MANUSCRIPT
25
1e
3
100
aReaction conditions: R-C6H4Br-p (1 mmol), styrene (1.5 mmol), K2CO3 (2 mmol), % Pd(II) complexes (1a-e)
(0.005 mmol), EtOH (3 mL), purity of compounds is checked by GC and NMR yields are based on p-
arylbromide.
All reactions were monitored by GC. Temperature 80 °C, 3 h.