Substituted 2-(2′-pyridyl)benzimidazole palladium(II) complexes as an efficient catalytic system for Suzuki-Miyaura cross-coupling reactions

Article abstract of DOI:10.3906/kim-1505-105

A new series of N, N-type 2-(2′-pyridyl)benzimidazole ligands (2A₁, 2A₂, 3B₁, 3B₂, 3B₃, and 4C₁) and their Pd(II) complexes (5A₁, 5A₂, 6B₁, 6B₂, 6B₃, and 7C₁) were prepared and characterized by conventional spectroscopic methods and elemental analyses. The incorporation of N-coordinated benzimidazole complexes of palladium gave high catalytic activity in the Suzuki-Miyaura coupling of aryl halides substrates. After determining the best active catalyst as 5A₁, bearing the mesityl substituent on the benzimidazole ring with the Pd(II) ion, optimization studies were carried out via changing the substrate, base, time, atmosphere, and the effect of water. The DMF:H₂O (4/1) and Cs₂CO₃ as base were found to be critical for the efficiency of the reaction yield (100%).

Full text of DOI:10.3906/kim-1505-105

Turk J Chem
2015) 39: 1289 – 1299
Turkish Journal of Chemistry
(
http://journals.tubitak.gov.tr/chem/
¨
˙
⃝
c TUBITAK
Research Article
doi:10.3906/kim-1505-105
Substituted 2-(2’-pyridyl)benzimidazole palladium(II) complexes as an efficient
catalytic system for Suzuki–Miyaura cross-coupling reactions
∗
¨
Mahmut ULUSOY , Nurdal ONCEL, Emine AYTAR
Department of Chemistry, Faculty of Arts and Sciences, Harran University, S¸ anlıurfa, Turkey
Received: 27.05.2015
•
Accepted/Published Online: 29.09.2015
•
Printed: 25.12.2015
Abstract: A new series of N, N -type 2-(2’-pyridyl)benzimidazole ligands (2A
1
, 2A
2
1 2 3 1
, 3B , 3B , 3B , and 4C )
and their Pd(II) complexes (5A , 5A , 6B , 6B , 6B , and 7C ) were prepared and characterized by conventional
1
2
1
2
3
1
spectroscopic methods and elemental analyses. The incorporation of N -coordinated benzimidazole complexes of palla-
dium gave high catalytic activity in the Suzuki–Miyaura coupling of aryl halides substrates. After determining the best
active catalyst as 5A
studies were carried out via changing the substrate, base, time, atmosphere, and the effect of water. The DMF:H
4/1) and Cs CO as base were found to be critical for the efficiency of the reaction yield (100%).
1
, bearing the mesityl substituent on the benzimidazole ring with the Pd(II) ion, optimization
2
O
(
2
3
Key words: Palladium, 2-(2’-pyridyl)benzimidazole, aryl halides, phenylboronic acid, Suzuki–Miyaura
1
. Introduction
There has been a long-standing interest in the properties of palladium complexes because they are widely used
as catalysts for carbon–carbon bond forming reactions.1 These reactions are key steps in many syntheses of
organic chemicals and natural products, as well as in a variety of industrial processes.2 Important examples
for this type of catalysis are the Suzuki–Miyaura,3 Negishi,4 Kumada,5 Hiyama,6 and Stille7 reactions. The
palladium-catalyzed reaction of aryl chlorides with arylboronic acid (the Suzuki–Miyaura reaction, Scheme 1a)
or with alkenes (the Heck reaction, Scheme 1b) is one of the most common methods for C–C bond formation
and has attracted much current interest.8
−12
Scheme 1. Cross-coupling of an aryl halide: (a) the Suzuki–Miyaura and (b) Heck–Mizoroki reaction.
∗
Correspondence: ulusoymahmut@harran.edu.tr
1
289

ULUSOY et al./Turk J Chem
The Suzuki–Miyaura reaction is one of the most important carbon–carbon bond forming reactions and
has been widely used in industrial organic synthesis.13,14 Traditionally, this reaction is promoted by catalysts
based on Pd, which is a precious metal. Due to several advantages, including relative mild reaction conditions,
tolerance of a broad range of functional groups, and the compatibility towards water as solvent or cosolvent, the
Suzuki–Miyaura reaction is applicable for the preparation of, for example, fine chemicals and pharmaceuticals
on an industrial scale.1
5−17
Hence, the Suzuki–Miyaura cross-coupling reaction is one of the most widely used
methods for the construction of biaryl compounds, owing to the stability and low toxicity of the organoboranes
8−25
relative to other organometallic reagents.1
The traditional Suzuki–Miyaura reaction usually proceeds using P- and N-ligand based palladium catalysts,25
and much attention has been paid to improve the Suzuki–Miyaura reaction by designing various new ligands. Pd–
6−29
N coordinated complexes also showed good catalytic performance in Suzuki–Miyaura coupling reactions.2
However, most of these ligands are expensive, which has significantly limited their industrial applications. There-
fore, the development of efficient catalytic systems consisting of economical catalysts is still a highly desirable
goal.
We report here the synthesis and spectroscopic characterization of the Pd(II) complexes (5A1 , 5A2 ,
6
B1 , 6B2 , 6B3 , and 7C1) of different N -benzylated 2-(2’-pyridyl)benzimidazole (PBI) ligands (2A1 , 2A2 ,
B1 , 3B2 , 3B3 , and 4C1) were determined by 1 H and 13 C NMR spectra. All of the Pd(II) complexes
3
(
5A1 , 5A2 , 6B1 , 6B2 , 6B3 , and 7C1) were screened in the Suzuki–Miyaura cross-coupling reactions of
aryl halides with phenylboronic acid. The optimal catalytic conditions were investigated in detail via changing
the substrate, base, time, atmosphere, and the effect of water.
2
2
. Results and discussion
.1. Synthesis of compounds
As summarized in Scheme 2, PBI ligands (2A1 , 2A2 , 3B1 , 3B2 , 3B3 , and 4C1) were prepared in moderate
yield by one pot reaction via deprotonation of PBI using a base such as NaH or KOH, followed refluxing the 1:1
molar ratio of benzyl halides in anhydrous toluene or tetrahydrofuran (THF) (Scheme 2). Desired PBI ligands
(
(
2A1 , 2A2 , 3B1 , 3B2 , 3B3 , and 4C1) were obtained in high yields as white solids following recrystallization
70%–87%) and satisfactory spectroscopic results were acquired for all ligands. As summarized in Scheme 2, the
Pd complexes (5A1 , 5A2 , 6B1 , 6B2 , 6B3 , and 7C1) were obtained by reactions of PBI (2A1 , 2A2 , 3B1 ,
B2 , 3B3 , and 4C1) with PdCl2 (CNMe)2 in good yields as yellow solids following recrystallization. The 1
3
H
and 13 C NMR spectra with elemental analysis results support the 1:1 ratio of metal/ligand, as expected. The
multinuclear NMR spectra and elemental analysis showed that the ligands and their complexes supported the
proposed structures.
2
.2. Spectroscopic characterization
The NMR spectra of ligands (2A1 , 2A2 , 3B1 , 3B2 , 3B3 , and 4C1) and their Pd(II) complexes were
recorded in DMSO-d6 or CDCl3 at room temperature and the assignments made for the observed chemical
shifts are listed in the Experimental section. A comparison of the chemical shifts of the aromatic protons and
carbons of the PBI ligands (2A1 , 2A2 , 3B1 , 3B2 , 3B3 , and 4C1) with their Pd(II) complexes indicated
the formation of a dative M←N bond as expected and also confirmed the participation of the nitrogen atoms in
coordination for metal complexes. These aromatic protons and carbons also become nonequivalent as a result of
1290

ULUSOY et al./Turk J Chem
their different exposure to the ring current effect due to the different substituent groups, which were otherwise
identical. In the 1 H NMR spectra, the significative signal for ligands (2A1 , 2A2 , 3B1 , 3B2 , 3B3 , and 4C1)
and their Pd(II) complexes were observed at 5.50–6.40 ppm for N–CH 2 proton and at 45.2–68.7 ppm range for
N–CH2 carbon. These values and the other NMR data are in good agreement with the proposed structures.
Scheme 2. The structures of the prepared compounds.
1
291

ULUSOY et al./Turk J Chem
The IR spectra of the Pd(II) complexes are compared with those of the free ligand in order to determine
the coordination sites that may be involved in chelation. There are some guide peaks in the spectra of the
ligands, which are of good help for achieving this goal. The position and/or the intensities of these peaks are
expected to change upon chelation. Coordination of the ligands to the metal through the nitrogen atom is
expected to reduce the electron density in the azomethine link and lower the ν (C=N) absorption frequency.
−
1
The very strong and sharp bands located at 1625–1600 cm
of the azomethine of the ligands. These bands are shifted 5–10 cm
the participation of the azomethine group of these ligands in binding to the palladium ion.30,31
are assigned to the ν (C=N) stretching vibrations
−1
to a lower wavenumber, which supports
2
.3. Catalytic studies
The palladium-catalyzed reactions of aryl halides with arylboronic acids (the Suzuki–Miyaura reaction) is the
most common method for C–C bond formation.32,33 The palladium-catalyzed reactions are usually carried out
homogeneously in the presence of a base. The reactivity of the aryl halide component decreases sharply in the
order X = I > Br > Cl and electron withdrawing substituents R are required for the chlorides to react.3
2−38
The palladium complexes (5A1 , 5A2 , 6B1 , 6B2 , 6B3 , and 7C1) were tested as catalysts for the
Suzuki–Miyaura coupling reactions to give the biaryl compounds. We initially studied the reaction of phenyl-
◦
boronic acid with 4-bromoacetophenone in DMF/H2 O as a model reaction under heating to 80 C in the
presence of 1.5 mmol % of Pd(II) metal catalysts and 1.5 mmol of bases. The comparison of synthesized
catalysts at the same catalytic conditions is summarized in Table 1.
Table 1. Comparison of Pd(II) complexes as catalysts in Suzuki–Miyaura coupling reactions using 4-bromoacetophenone
with phenylboronic acid as substrates.
a
Entry Catalysts Solvent
Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
5A1
5A1
5A2
5A2
6B1
6B1
6B2
6B2
6B3
6B3
7C1
7C1
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
DMF/H2O (4:1)
1
2
1
2
1
2
1
2
1
2
1
2
99.8
100.0
85.4
90.5
98.2
97.7
98.1
99.2
97.0
94.7
96.6
96.5
0
1
2
Reaction conditions: 1.5 mmol % Pd, 1 mmol 4-bromoacetophenone, 1.5 mmol phenylboronic acid, 3 mL solvent
◦
a
(
DMF(4)/H
2
O(1)), heat (80 C), base (Cs CO ), The yields checked by GC analysis.
2
3
The synthesized metal complexes were compared in the same catalytic conditions. From the results in
Table 1, it is evident that the palladium complex that contains electron donating mesityl substituent with mono
NN type 5A1 complex is the most effective of the complexes examined. After determining the best active
1292

ULUSOY et al./Turk J Chem
Table 2. Suzuki–Miyaura coupling reactions of aryl halides with phenylboronic acid.
1
.5% 5A1
x
2
B(OH )
o
Cs CO DMF/H O, 80
C
R
R
2
3,
2
a
Tme (h) Yeld (%)
Entry
1
Catalysts
Arylhalde
Product
O
5A1
4-bromoacetophenone
4-bromoacetophenone
4-bromoanlne
1
2
1
2
99.8
100.0
86.3
95.1
O
2
3
4
5A1
5A1
5A1
NH2
4-bromoanlne
NH2
NO2
5
6
7
5A1
5A1
5A1
1-bromo-4 ntrobenzene
1-bromo-4-ntrobenzene
4-bromoansole
1
2
1
97.9
97.7
98.1
NO2
O
O
8
9
5A1
5A1
4-bromoansole
2-bromoansole
2
1
99.9
98.3
O
O
1
1
0
1
5A1
5A1
2-bromoansol
2
1
99.3
79.2
-
F
zene
-
F
1
1
1
1
1
1
1
2
3
4
5
6
7
8
5A1
5A1
5A1
5A1
5A1
5A1
5A1
2
1
2
1
2
1
2
62.3
60.2
74.5
4.2
zene
O
4-chloroacetophenone
O
4-chloroacetophenone
4-chloroansole
O
O
C
C
4-chloroansole
3.8
N
N
4-chlorobenzontrle
4-chlorobenzontrle
80.3
85.4
O
C
1
9
5A1
methyl-4-chlorobenzoate
1
73.2
O
O
C
2
2
0
1
5A1
5A1
methyl-4-chlorobenzoate
2-chlorobenzene
2
1
78.4
3.4
O
Reaction conditions: 1.5 mmol % 5A
1
,
1 mmol arylhalide, 1.5 mmol phenylboronic acid, 3 mL solvent
◦
a
(
DMF(4)/H
2
O(1)), heat (80 C), base (Cs
2
CO
3
). The yields checked by GC analysis
1
293

ULUSOY et al./Turk J Chem
catalyst, the optimization studies were carried out by changing various parameters such as temperature, time,
aryl halide, and base.
In order to find the optimum conditions, a series of experiments was performed with 4-bromoacetophenone
and phenylboronic acid, which were to be model compounds (Table 2, entries 1 and 2). The yield was increased
with increasing time from 1 to 2 h as reaction time. When we used the 4-chloroacetophenone as substrate,
moderate yields (Table 2, entries 13 and 14) were achieved, but coupling of electron-neutral 4-chlorobenzene
electron-rich 4-chloroanisole (Table 2, entries 15 and 16) was unsuccessful.39
According to Figure 1, water positively affected the reaction yield. The effect of the catalyst was examined
for the Suzuki–Miyaura cross-coupling reactions (Figure 2). It can be seen that the reaction yield is strongly
affected by the catalyst. The effect on the reactions of the bases was also investigated. As a base, Cs2 CO3
was the best choice in water–DMF (1/4) systems (Figure 3). All catalytic reactions were carried out in inert
atmosphere. Even in this atmosphere the catalyst was still effective (Figure 4).
1
1
10
00
1
1
20
00
99.8
100.0
99.8
100.0
9
0
0
0
0
80
85.4
6
4
2
0
0
0
8
7
6
66.3
5.7
3.4
0
5
A1(a)
5A1(b)
*(a)
*(b)
DMF(a)
DMF(b)
€
DMF/H O(a) DMF/H O(b)
2
2
e eect of water
€e eect of catalyst
Figure 2. The effect of catalyst.
Reaction conditions: 1.5 mmol % Pd, 1 mmol 4-
Figure 1. The effect of water.
Reaction conditions: 1.5 mmol % Pd, 1 mmol 4-
bromoacetophenone, 1.5 mmol phenylboronic acid, heat
bromoacetophenone, 1.5 mmol phenylboronic acid, 3
◦
◦
(
80 C), base (Cs
2
CO
3
). Reaction time (a) 1 h, (b) 2 h.
mL solvent (DMF, DMF/H
Cs CO ), 5A
tion time (a) 1 h, (b) 2 h.
2
O), heat (80 C), base
(
2
3
1
(catalyst), *(without catalyst). Reac-
3
3
. Experimental
.1. Materials and measurements
All reagents and solvents were of reagent-grade quality and obtained from commercial suppliers (Merck, Sigma-
Aldrich, Acros Organics, and Alfa-Aesar). 1 H NMR spectra were recorded at 25 C using an Agilent-VNMRS-
◦
1
3
400 spectrometer at 400 MHz or a Bruker Avance DRX spectrometer at 300 MHz.
C NMR spectra were
◦
recorded at 25 C on a Bruker operating at 100.56 MHz or a Bruker Avance DRX spectrometer at 75.0 MHz.
TMS was used as an internal reference for recording 1 H and 13 C NMR in DMSO-d6 or CDCl3 and coupling
constants (J) are reported in hertz. Elemental analyses were performed by using a LECO CHNS model 932
elemental analyzer. Melting points were measured in open capillary tubes with an Electrothermal 9100 melting
point apparatus and are uncorrected. FT-IR spectra were obtained from KBr pellets (3-mg sample in 300 mg of
KBr) on a PerkinElmer Spectrum RXI FT-IR Fourier transform spectrometer (4000–400 cm 1). All reactions
−
were performed using a Schlenk-type flask under nitrogen and standard high vacuum-line techniques. The
1294

ULUSOY et al./Turk J Chem
mixture was separated by centrifugation, and the liquid phase was subjected to GC (Agilent 7820A) analysis
with ethylene glycol dibutyl ether as internal standard and hydrogen as the carrier gas.
1
1
02
00
1
00.2
00
100.0
99.8
1
00.0
1
98
96
99.8
99.8
9
9.8
9.6
9.4
9.2
9
9.7
94
92
9
9.6
9
9
9
90.0
9
9.5
90
89.0
88
8
8
8
6
4
2
9
9
5A1(a)
5A1(b)
5A1*(a)
5A1*(b)
Na CO (a) Na CO (b) K CO (a) K CO (b) Cs CO (a) Cs CO (b)
2
3
2
3
2
3
2
3
2
3
2
3
Comparng the bases
€e eect of atmosphere
Figure 4. The effect of atmosphere.
Reaction conditions: 1.5 mmol % Pd, 1 mmol 4-
Figure 3. The effect of bases.
Reaction conditions: 1.5 mmol % Pd, 1 mmol 4-
bromoacetophenone, 1.5 mmol phenylboronic acid, 3 mL
bromoacetophenone, 1.5 mmol phenylboronic acid, 3
◦
◦
solvent (DMF(4)/H
2
O(1)), heat (80 C). Reaction time
mL solvent (DMF(4)/H
2
O(1)), heat (80
C), base
(
a) 1 h, (b) 2 h.
(Cs
2
CO
3
), 5A
1
(The reaction was carried out in inert
*(The reaction was carried out in air).
atmosphere), 5A
1
Reaction time (a) 1 h, (b) 2 h.
3
.2. General procedure for the Suzuki–Miyaura coupling reactions
Pd(II) complex (1.5% mmol), phenylboronic acid (1.5 mmol), aryl halides (1 mmol), base (1.5 mmol), and
solvent (3 mL) were added to a Schlenk tube under nitrogen atmosphere. The Schlenk tube was stirred at
◦
80
C for the desired hours. The reaction mixture was then cooled to room temperature, diluted with CH2 Cl2 ,
and filtered through Celite. The yield of the reaction was determined by GC (Agilent 7820A).
3
.3. General procedure for synthesis of the ligands
The ligands 2A4 and 2A 42 1 were synthesized by modification of the method in the published procedure.
0
1
The remaining ligands were synthesized as follows:
In a two-necked, 100-mL round-bottom flask equipped with a blanket of nitrogen (N2) was placed 30
mL of anhydrous toluene or tetrahydrofuran (THF) at room temperature for each ligand. KOH (0.56 g, 10.0
mmol) was added to these solutions, then a solution of 2-pyridylbenzimidazole (1.95 g, 10.0 mmol) in anhydrous
toluene (10 mL) was slowly added and stirred at reflux for 6 h. To these solutions, benzyl halides were added
such as 2,4,6-trimethylbenzyl bromide (2.13 g, 10.0 mmol) for ligand 2A1 , 2,3,4,5,6-pentamethylbenzylbromide
(
2.45 g, 10.0 mmol) for ligand 2A2 , 1,2-bis(bromomethyl)benzene (1.32 g, 5.0 mmol) for ligand 3B1 , 2,4-
bis(bromomethyl)-1,3,5-trimethylbenzene (1.53 g, 5.0 mmol) for ligand 3B2 , 1,4-bis(bromomethyl)-2,3,5,6-
tetramethylbenzene (1.60 g, 5.0 mmol) for ligand 3B3 , and 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene
(
1.33 g, 3.3 mmol) for ligand 4C1 , respectively, and then heated under reflux for 24 h. The volatiles were
evaporated in vacuum to dryness. The residue was dissolved in CH2 Cl2 and filtered via cannula on Celite. The
solution was concentrated to 15 mL and then the desired product was precipitated in 30 mL of n-hexane.
◦
For 2A1 : Color: white, yield: 85%, mp: 169–172 C. Anal. Calc. for [C22 H21 N3 ] (M.W: 327.17
1
295

ULUSOY et al./Turk J Chem
g/mol): C, 80.70; H, 6.47; N, 12.83; found: C, 80.73; H, 6.37; N, 12.84. 1 H NMR (300 MHz, CDCl3 , δ ppm);
2
6
8
.15 (s, 6H, mes-(CH 3)2); 2.26 (s, 3H, mes-CH 3); 6.22 (s, 2H, N-CH 2); 6.76 (d, J = 8.0 Hz, 1H, Ar-CH );
.83 (s, 2H, mes(CH )2); 7.03–7.07 (m, 1H, Ar-CH ); 7.20–7.35 (m, 2H, Ar-CH ); 7.85–7.89 (m, 2H, Ar-CH );
1
3
.44–8.46 (dd,J = 8.0, 8.4 Hz, 1H, Ar-CH ); 8.70–8.72 (m, 1H, Ar-CH ).
C NMR (75.48 MHz, CDCl3 , δ
ppm): 20.4 and 21.1 (mes-(CH3); 46.1 (N-CH2); 112.0; 120.1; 122.8; 123.6; 124.1; 125.7; 129.6; 129.9; 136.4;
37.3; 137.5; 137.7; 142.4; 148.6; 150.7; 151.0 (Ar-CH)
1
◦
For 2A2 : Color: white, yield: 82%, mp: 143–145 C. Anal. Calc. for [C24 H25 N3 ] (MW: 355.20
g/mol): C, 81.09; H, 7.09; N, 11.82; found: C, 80.56; H, 7.91; N, 11.53. 1 H NMR (400 MHz, CDCl3 , δ ppm);
1
.26 (s, 6H, o-(CH 3)2); 1.36 (s, 6H, m-(CH 3)2); 2.13–2.20 (s, 3H, p−CH 3); 5.50 (s, 2H, N-CH 2); 6.86 (s, 1H,
Ar-CH ); 7.11 (s, 1H, Ar-CH ); 7.26 (s, 1H, Ar-CH ); 7.35 (s, 1H, Ar-CH ); 7.49 (s, 1H, Ar-CH ); 8.46 (s, 1H,
Ar-CH ); 10.19 (s, 2H, Ar-CH ). 13 C NMR (100.56 MHz, CDCl3 , δ ppm): 17.0; 17.4; 29.6; 31.7; 34.4 and 35.2
(
CH3); 49.3 (N-CH2); 117.9; 121.2; 122.4; 125.5; 126.5; 133.8; 134.0; 137.5; 140.7; 158.0; 167.9 (Ar-CH).
◦
For 3B 1 : Color: white, yield: 84%, mp: 183–190 C. Anal. Calc. for [C32 H24 N6 ] (M.W: 492.21
1
g/mol): C, 78.03; H, 4.91; N, 17.06; found: C, 78.01; H, 4.89; N, 17.09. H NMR (400 MHz, CDCl3 , δ
ppm); 6.40 (s, 4H, N-CH 2); 6.69–6.67 (m, 2H, Ar-CH ); 7.00-7.03 (m, 2H, Ar-CH ); 7.21–7.37 (m, 8H, Ar-CH );
7
.79–7.84(m, 2H, Ar-CH ); 7.91 (d, J = 7.6 Hz, 2H, Ar-CH ); 8.47–8.50 (t, J = 6.2 Hz, 4H, Ar-CH ). 13 C NMR
100.56 MHz, CDCl3 , δ ppm): 47.1 (N-CH2); 111.0; 120,5; 123,3; 124.0; 124.2; 125.0; 126.5; 127.8; 134.5;
37.1; 137.2; 142.9; 148.7; 150.1; 150.6 (Ar-CH).
(
1
◦
For 3B 2 : Color: white, yield: 87%, mp: 214–220 C. Anal. Calc. for [C35 H30 N6 ] (MW: 534.25
g/mol): C, 78.63; H, 5.66; N, 15.72; found: C, 77.05; H, 5.93; N, 15.01. 1 H NMR (400 MHz, CDCl3 , δ ppm);
2
3
7
.02 (s, 3H, CH ); 2.60 (s, 6H, CH ); 6.22 (s, 4H, N-CH ); 6.55 (d, J = 5.2 Hz, 2H, Ar-CH ); 6.87–6.93 (m,
3 3 2
H, Ar-CH ); 7.16–7.20 (t, J = 8.2 Hz, 2H, Ar-CH ); 7.31–7.35 (m, 2H, Ar-CH ); 7.74–7.75 (m, 2H, Ar-CH );
1
3
.82–7.86 (m, 2H, Ar-CH ); 8.36–8.39 (m, 2H, Ar-CH ); 8.65–8.67 (m, 2H, Ar-CH ).
C NMR (100.56 MHz,
CDCl3 , δ ppm): 16.1 and 20.8 (CH3); 46.5 (N-CH2); 111.9; 120,5; 122,5; 123.6; 124.0; 125.6; 128.4; 129.2;
131.6; 131.7; 136.7; 137.2; 137.4; 137.7; 138.0; 143.0; 148.6; 150.7; 151.0 (Ar-CH).
◦
For 3B 3 : Color: white, yield: 70%, mp: 185–200 C. Anal. Calc. for [C36 H32 N6 ] (MW: 548.27
g/mol): C, 78.80; H, 5.88; N, 15.32; found: C, 78.97; H, 5.76; N, 15.27. 1 H NMR (400 MHz, CDCl3 , δ ppm);
2
7
(
.18 (s, 12H, (CH 3)4); 6.33 (s, 4H, N-CH 2); 6.58 (d,J = 8.4 Hz, 2H, Ar-CH ); 6.95–6.99 (m, 2H, Ar-CH );
.20–7.26 (m, 4H, Ar-CH ); 7.81 (d,J = 8.0 Hz, 2H, Ar-CH ); 7.87–7.91 (t, J = 7.8 Hz, 2H, Ar-CH ); 8.41–8.44
t, J = 8.8 Hz, 2H, Ar-CH ); 8.74 (d,J = 4.0 Hz, 2H, Ar-CH ). 13 C NMR (100.56 MHz, CDCl3 , δ ppm): 16.1;
7.2 and 20.8 (CH3); 47.6 and 49.3 (N-CH2); 112.3; 120.0; 122.7; 123.8; 125.0; 125.7; 132.0; 134.2; 135.8;
38.2; 143.1; 144.6; 149.2; 150.1; 151.2 (Ar-CH).
1
1
◦
For 4C 1 : Color: white, yield: 84%, mp: 242–245 C. Anal. Calc. for [C48 H39 N9 ] (MW: 741.33
g/mol): C, 77.71; H, 5.30; N, 16.99; found: C, 77.69; H, 5.36; N, 16.95. 1 H NMR (400 MHz, CDCl3 , δ ppm);
.26 (s, 9H, (CH 3)3); 6.31 (s, 6H, N-CH 2); 6.45 (d, J = 8.4 Hz, 2H, Ar-CH ); 6.77 (d, J = 7.6 Hz, 2H,
2
Ar-CH ); 7.17–7.36 (m, 7H, Ar-CH ); 7.46–7.52 (m, 1H, Ar-CH ); 8.37–8.44 (m, 6H, Ar-CH ); 8.63 (d, J = 4.4
Hz, 3H, Ar-CH ); 8.69 (d, J = 4.8 Hz, 3H, Ar-CH ). 13 C NMR (100.56, MHz, CDCl3 , δ ppm): 17.3 (CH3);
47.1 (N-CH2); 111.9; 120.4; 122.5; 123.8; 124.0; 125.6; 132.7; 137.3; 138.5; 143.1; 148.6 (Ar-CH).
1296

ULUSOY et al./Turk J Chem
3
.4. General procedure for the synthesis of the Pd(II) complexes
The complexes were synthesized as follows:
In a two-necked, 50-mL round-bottom flask equipped with a blanket of nitrogen (N2) was placed 15 mL
of anhydrous tetrahydrofuran (THF) at room temperature for each metal complex synthesis. The solution of 1.0
mmol of each ligand in 7 mL of anhydrous tetrahydrofuran (THF) was stirred for 20 min. Then PdCl2 (CNMe)2
(
1.0 mmol for complex 5A1 , 1.0 mmol for complex 5A2 , 2.0 mmol for complex 6B1 , 2.0 mmol for complex
B2 , 2.0 mmol for complex 6B3 , and 3.0 mmol for complex 7C1) was added to the ligand solution. Once the
6
metal salt was added, the color of reaction mixtures immediately turned to yellowish. The reaction mixtures
◦
were stirred at 60 C for 2 h. Then 25 mL of n-hexane was added to mixtures for precipitation and the crude
product was filtered off, washed with THF, and filtered off again to remove unreacted ligands. The resulting
solids were redissolved in CH2 Cl2 (5 mL) and then precipitated with diethyl ether (10 mL) to give the clear
crystal solid.
◦
For 5A1 : Color: orange, yield: 79%, mp: 288–289 C. Anal. Calc. for [C22 H21 Cl2 N3 Pd] (MW:
1
5
05.02 g/mol): C, 52.35; H, 4.19; N, 8.32; found: C = 52.01; H = 4.57; N = 7.83. H NMR (400 MHz,
DMSO-d6 , δ ppm): 2.07 (s, 6H, o-(CH 3)2); 2.25 (s,3H, p-CH3); 6.04 (s, 2H, N-CH 2); 6.67 (d, J = 8 Hz; 1H,
Ar-CH ); 6.94 (s, 2H, Ar-CH ); 7.20–7.17 (t, J = 7.4 Hz; 1H, Ar-CH ); 7.30–7.26 (t, J = 7.8 Hz, 1H, Ar-CH );
7
.83–7.80 (t,J = 6.6 Hz, 1H, Ar-CH ); 8.35–8.30 (m, 1H, Ar-CH ); 8.58 (d, J =8.4 Hz, 1H, Ar-CH ); 8.87 (d,J
8.0 Hz, 1H, Ar-CH ); 9.26 (d,J = 5.2 Hz, 1H, Ar-CH ); 13 C NMR (100.56 MHz, DMSO-d6 , δ ppm): 17.8
and 21.3 (CH3); 56.6 (N-CH2); 106.5; 112.0; 119.1; 122.5; 124.2; 124.6; 128.5; 132.7; 134.8; 135.9 and 137.6
Ar-CH).
For 5A2 : Color: yellow, yield: 82%, mp: 268–270 C. Anal. Calc. for [C24 H25 Cl2 N3 Pd] (MW: 533.05
g/mol): C, 54.10; H, 4.73; N, 7.89; found: C, 54.29; H, 5.14; N, 7.01. 1 H NMR (400 MHz, DMSO-d6 , δ ppm):
=
(
◦
2
1
6
.09 (s, 6H, o-(CH ) ); 2.18 (s,6H, m-(CH ) ); 2.25 (s, 3H,p-CH ); 6.05 (s, 2H, N-CH ); 6.35 (d, J = 8 Hz,
3 2 3 2 3 2
H, Ar-CH ); 7.06–7.10 (t, J = 8.0 Hz, 1H, Ar-CH ); 7.23–7.27 (t, J = 7.8 Hz, 1H, Ar-CH ); 7.82–7.86 (t,J =
.6 Hz, 1H, Ar-CH ); 8.34–8.38 (m, 1H, Ar-CH ); 8.73 (d, J = 8.8 Hz, 1H, Ar-CH ); 8.90 (d, J = 8.8 Hz, 1H,
Ar-CH ); 9.31 (d, J = 5.6 Hz, 1H, Ar-CH ); 13 C NMR (100.56 MHz, DMSO-d6 , δ ppm): 17.6; 17.7 and 17.9
CH3); 55.8 (N-CH2); 100.27; 102.23; 105.35; 109.40; 119.43; 127.55; 133.56; 134.47; 144.53; 148.58; 152.37
and 155.20 (Ar-CH).
(
◦
For 6B 1 : Color: yellow, yield: 86%, mp: >300 C. Anal. Calc. for [C32 H24 Cl4 N6 Pd2 ] (MW: 844.89
g/mol): C, 45.36; H, 2.86; N, 9.92; found: C, 45.88; H, 2.45; N, 9.07. 1 H NMR (400 MHz, DMSO-d6 , δ ppm);
5
.72 (s, 4H, N-CH 2); 6.59 (s, 2H, Ar-CH ); 7.08–7.10 (m, 2H, Ar-CH ); 7.36–7.61 (m, 4H, Ar-CH ); 7.71–7.84
m, 4H, Ar-CH ); 8.04–7.96 (m, 2H, Ar-CH ); 8.40–8.32 (m, 2H, Ar-CH ); 8.65 (d, J = 8.8 Hz, 1H, Ar-CH );
.99 (d, J = 8.0 Hz, 1H, Ar-CH ); 9.06 (d, J =5.2 Hz, 1H, Ar-CH ); 9.28 (d, J = 5.2 Hz, 1H, Ar-CH ). 13
NMR (100.56 MHz, DMSO-d6 , δ ppm): 45.2 and 45.6 (N-CH2); 110.8; 120.1; 122,5; 123.8; 124.0; 124.9; 125.7;
26.2; 134.8; 136.3; 137.8; 142.7; 149.5; 151.2 (Ar-CH).
(
8
C
1
◦
For 6B 2 : Color: yellow, yield: 87%, mp: >300 C. Anal. Calc. for [C35 H30 Cl4 N6 Pd2 ] (MW: 886.94
g/mol): C, 47.27; H, 3.40; N, 9.45; found: C, 46.98; H, 3.97; N, 9.62. 1 H NMR (400 MHz, DMSO-d6 , δ ppm);
.92 (s, 3H, CH 3); 2.23 (s, 6H, CH 3); 6.15 (s, 4H, N-CH 2); 6.72 (d,J = 8.4 Hz, 2H, Ar-CH ); 6.89–6.97
m, 3H, Ar-CH ); 7.14–7.20 (m, 2H, Ar-CH ); 7.51–7.57 (m, 2H, Ar-CH ); 7.72 (d, J = 8.4 Hz, 2H, Ar-CH );
1
(
1
3
7.98–8.07 (m, 2H, Ar-CH ); 8.30 (d, J = 8.0 Hz, 2H, Ar-CH ); 8.78 (d,J = 4.8 Hz, 2H, Ar-CH ).
C NMR
1
297

ULUSOY et al./Turk J Chem
(
100.56 MHz, DMSO-d6 , δ ppm): 16.8; 21.2 and 26.1 (CH3); 46.9 and 68.7 (N-CH2); 113.5; 121.3; 122.8;
124.5; 125.6; 126.7; 132.4; 133.9; 135.6; 138.2; 138.9; 139.1; 142.5; 148.7; 151.7 (Ar-CH).
◦
For 6B 3 : Color: yellow, yield: 77%, mp: 242–247 C. Anal. Calc. for [C36 H32 Cl4 N6 Pd2 ] (MW:
9
00.95 g/mol): C, 46.92; H, 4.01; N, 9.58; found: C, 47.87; H, 3.57; N, 9.30. 1 H NMR (300 MHz, DMSO-d6 ,
δ ppm); 1.82 (s, 4H, CH 3); 1.89 (s, 4H, CH 3); 2.01 (s, 4H, CH 3); 2.09 (s, 4H, CH 3); 5.76 (s, 4H, N-CH 2);
6
.46 (d,J = 9.0 Hz, 2H, Ar-CH ); 7.03–7.48 (m, 2H, Ar-CH ); 7.67–7.87 (m, 2H, Ar-CH ); 8.35–8.42 (m, 2H,
1
3
Ar-CH ); 8.61 (s, 2H, Ar-CH ); 8.73 (s, 2H, Ar-CH ); 8.86 (s, 2H, Ar-CH ); 9.28 (s, 2H, Ar-CH ).
C NMR
(
75.48 MHz, CDCl3 , δ ppm): 18.7; 20.2 and 25.6 (CH3); 46.3 and 48.9 (N-CH2); 67.8; 113.6; 121.4; 124.2;
125.3; 133.7; 136.9; 143.6; 145.0; 150.5 (Ar-CH).
◦
For 7C 1 : Color: yellow, yield: 83%, mp: 242–245 C. Anal. Calc. for [C48 H39 Cl6 N9 Pd3 ] (MW:
268.86 g/mol): C, 45.26; H, 3.09; N, 9.90; found: C, 45.34; H, 3.17; N, 9.84. 1 H NMR (400 MHz, DMSO-d6 ,
1
δ ppm); 2.13 (s, 9H, (CH 3)3); 6.18 (s, 6H, N-CH 2); 6.52 (d,J = 8.0 Hz, 2H, Ar-CH ); 6.94–6.96 (t,J = 8.0 Hz,
H, Ar-CH ); 7.12–7.26 (m, 2H, Ar-CH ); 7.31–7.45 (t,J = 8.0 Hz, 2H, Ar-C H ); 7.42–7.46 (t,J = 7.6 Hz, 2H,
2
Ar-CH ); 7.71–7.80 (m, 4H, Ar-CH ); 8.27–8.39 (m, 2H, Ar-CH ); 8.59–8.80 (m, 4H, Ar-CH ); 9.00 (d,J = 5.6
Hz, 2H, Ar-CH ); 9.18 (d,J = 4.0 Hz, 2H, Ar-CH ). 13 C NMR (100.56 MHz, DMSO-d6 , δ ppm): 17.5 (CH3);
125.1; 125.9; 127.6; 141.8 (Ar-CH).
4
. Conclusion
In the numerous catalyst optimization studies that have been published, the principal focus is often to test the
robustness of the catalytic system as a function of the reaction conditions and substrate scope. Here, a simple
method is given for the preparation of Pd(II) complexes that are coordinated by substituted PBI (mono-NN,
di-NN, and tri-NN types) ligands. These complexes were found to be active catalysts for the Suzuki–Miyaura
cross-coupling reactions using DMF/H2 O (4:1) as solvent. In order to find optimum conditions a series of
experiments was performed with 4-bromoacetophenone and phenylbronic acid as model compounds. These
simple reaction conditions allow for the cross-coupling of aryl halides with phenylbronic acid yielding biaryls in
high yields. We also showed that temperature in this system has a minimal effect on the coupling itself. Efforts
focused on identifying the effects of the base, water, time, and air in the coupling reactions.
Acknowledgments
¨
˙
¨
This work was supported by TUBITAK (TBAG Project No: 110T655) and HUBAK (Project No: 13100).
References
1
2
3
4
5
6
7
8
.
.
.
.
.
.
.
.
Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester, UK, 1995.
Weskamp, T.; B ¨o hm, V. P. W.; Herrmann, W. A. J. Organomet. Chem. 1999, 585, 348–352.
Miyaura, N.; Yamada, K.; Suzuki, A. Tetrahedron Lett. 1979, 20, 3437–3440.
Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 2719–2724.
Herrmann, W. A.; Bohm, V. P. W.; Reisinger, C. J. Organomet. Chem. 1999, 576, 23–41.
Lee, H. M.; Nolan, S. P. Org. Lett. 2000, 2, 2053–2055.
Stille, J. K. Angew. Chem. Int. Ed. Engl. 1986, 25, 508–524.
Miyaruna, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
1298

ULUSOY et al./Turk J Chem
9
. Suzuki, A. J. Organomet. Chem. 1999, 576, 147–168.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
0. Stanforth, S. P. Tetrahedron 1998, 54, 263–303.
1. Whitcombe, N. J.; Hii, K. K.; Gibson, S. E. Tetrahedron 2001, 57, 7449–7476.
2. Crisp, G. T. Chem. Soc. Rev. 1998, 27, 427–436.
3. Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58, 9633–9695.
4. Uozumi, Y. Top. Curr. Chem. 2004, 242, 77–112.
5. Torborg, C.; Beller, M. Adv. Synth. Catal. 2009, 351, 3027–3043.
6. Magano, J.; Dunetz, J. R. Chem. Rev. 2011, 111, 2177–2250.
7. Picquet, M. Platin. Met. Rev. 2013, 57, 272–280.
8. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
9. Suzuki, A. J. Organomet. Chem. 1999, 576, 147–168.
0. Suzuki, A. Chem. Commun. 2005, 4759–4763.
1. Littke, A. F.; Fu, G. C. Angew. Chem. Int. Ed. 2002, 41, 4176–4211.
2. Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. Adv. Synth. Catal. 2006, 348, 609–679.
3. Polshettiwar, V.; Decottignies, A.; Len, C.; Fihri, A. Chem. Sus. Chem. 2010, 3, 502–522.
4. Slagt, V. F.; De Vries, A. H. M.; De Vries, J. G.; Kellogg, R. M. Org. Process Res. Dev. 2010, 14, 30–47.
5. Alonso, F.; Beletskaya, I. P.; Yus, M. Tetrahedron 2008, 64, 3047–3101.
6. Baran, T.; Aciksoz, E.; Mentes, A. J. Mol. Cat. A. 2015, 407, 47–52.
7. Das, S.; Bhunia, S.; Maity, T.; Koner, S. J. Mol. Cat. A. 2014, 394, 188–197.
8. Tenchiu, A. C.; Ventouri, I. K.; Ntasi, G.; Palles, D.; Kokotos, G.; Demertzi, D. K.; Kostas, I. D. Inorg. Chim.
Acta 2015, 435, 142–146.
2
3
9. Temel, H.; Pasa, S.; Ocak, Y. S.; Yilmaz, I.; Demir, S.; Ozdemir, I. Synthetic Met. 2012, 161, 2765–2775.
0. Kılın ¸c arslan, R.; Karabıyık, H.; Ulusoy, M.; Ayg u¨ n, M.; C¸ etinkaya, B.; B u¨ y u¨ kg u¨ ng o¨ r, O. J. Coord. Chem. 2006,
5
9, 1649–1656.
3
3
3
3
3
3
3
3
3
1. Tas, E.; Aslanoglu, M.; Guler, M.; Ulusoy, M. J. Coord. Chem. 2004, 57, 583–589.
2. Littke, A. F.; Fu, G. F. Angew. Chem., Int. Ed. 2002, 41, 4176–4211.
3. Bedford, R. B.; Hazelwood, S. L.; Limmert, M. E. Chem. Commun. 2002, 2610–2611.
4. Stanforth, S. P. Tetrahedron 1998, 54, 263–303.
5. Crisp, G. T. Chem. Soc. Rev. 1998, 27, 427–436.
6. Whitcombe, N. J.; Hii, K. K.; Gibson, S. E. Tetrahedron 2001, 57, 7449–7476.
7. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
8. Suzuki, A. J. Organomet. Chem. 1999, 576, 147–168.
9. Hillier, A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang, C.; Nolan, S. P. J. Organomet. Chem. 2002, 653,
6
9–82.
0. Sahin, C.; Ulusoy, M.; Zafer, C.; Ozsoy, C.; Varlikli, C.; Dittrich, T.; Cetinkaya, B.; Icli, S. Dyes Pigments 2009,
4, 88–94.
4
4
8
¨
1. An ˘g ay, F.; C¸ elik, O.; Barlık, O.; Ulusoy, M. Acta Cryst. 2014, E70, o563–o564.
1
299