PEPPSI-Pd-NHC catalyzed Suzuki-Miyaura cross-coupling reactions in aqueous media

Article abstract of DOI:10.1016/j.tet.2019.02.062

A series of unsymmetrical 1,3-disubstituted benzimidazolium chlorides were synthesized as N-heterocyclic carbene (NHC) precursors. These compounds were used to synthesize of the PEPPSI-type palladium NHC complexes. The structures of all compounds were cha

Full text of DOI:10.1016/j.tet.2019.02.062

Accepted Manuscript
PEPPSI-Pd-NHC catalyzed Suzuki-Miyaura cross-coupling reactions in aqueous
media
Nazan Kaloğlu, İsmail Özdemir
PII:
S0040-4020(19)30242-X
https://doi.org/10.1016/j.tet.2019.02.062
TET 30185
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 31 December 2018
Revised Date: 22 February 2019
Accepted Date: 27 February 2019
Please cite this article as: Kaloğlu N, Özdemir İ, PEPPSI-Pd-NHC catalyzed Suzuki-Miyaura cross-
coupling reactions in aqueous media, Tetrahedron (2019), doi: https://doi.org/10.1016/j.tet.2019.02.062.
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ACCEPTED MANUSCRIPT
Graphical Abstract
PEPPSI-Pd-NHC Catalyzed Suzuki-Miyaura Cross-Coupling Reactions in
Aqueous Media
Nazan Kaloğlu[a,b] and İsmail Özdemir*[a,b]
aİnönü University, Faculty of Science and Arts, Department of Chemistry, 44280 Malatya, Turkey
bİnönü University, Catalysis Research and Application Center, 44280 Malatya, Turkey

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
PEPPSI-Pd-NHC Catalyzed Suzuki-Miyaura Cross-Coupling Reactions in Aqueous
Media
Nazan Kaloğlu[a,b] and İsmail Özdemir*[a,b]
aİnönü University, Faculty of Science and Arts, Department of Chemistry, 44280 Malatya, Turkey
bİnönü University, Catalysis Research and Application Center, 44280 Malatya, Turkey
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A series of unsymmetrical 1,3-disubstituted benzimidazolium chlorides were synthesized as N-
heterocyclic carbene (NHC) precursors. These compounds were used to synthesize of the
PEPPSI-type palladium NHC complexes. The structures of all compounds were characterized by
1H NMR, 13C NMR, FT-IR spectroscopy and elemental analyses. The catalytic activity of the
PEPPSI-type palladium–NHC complexes has been evaluated with respect to the Suzuki-Miyaura
cross-coupling reactions of phenyl boronic acid with various aryl halides in aqueous media.
Available online
Keywords:
2009 Elsevier Ltd. All rights reserved
.
N-Heterocyclic carbene
PEPPSI-type palladium complex
Suzuki-Miyaura cross-coupling reaction
1. Introduction
range of transition metals16,17 and begun to replace phosphine
ligands18 due to their unique properieties.19 The easy preparation
and handling of their precursors, their high modularity, and their
strong σ-donor properties, which allow them to form strong
metal-NHC bonds that prevent ligand dissociation, have rendered
them extremely popular as supporting ligands in transition metal
catalysis.20 The σ-donor properties of NHC ligands are crucial in
controlling their interaction with transition metals, and as a
consequence, to determine the selectivity and reactivity of NHCs
in transition-metal catalysis. Recently, Szostak and co-workers
have reported a simple NMR method for estimating σ-donor
Biaril motifs are important building blocks for commercially
important compounds such as various natural products,
pharmaceuticals, agrochemicals and functional materials.1-6
Therefore, the preparation of such compounds is very important
for modern organic synthesis. Transition metal-catalyzed cross-
coupling reactions have becomes one of the most conventional
methods among C-C bond forming processes for biaryls.7-10 The
development of this methodology has revolutionised synthetic
chemistry and was acknowledged with the award of a Nobel
Prize in Chemistry in 2010 for palladium-catalysed cross-
couplings in organic synthesis.11 Nowadays, the Suzuki-Miyaura
reaction is probably the most commonly used cross-coupling
process for synthesis of biaryls because of its mild reaction
conditions and high functional group tolerance.12 Moreover,
boronic acids are environmentally safer and much less toxic than
other metaloorganic compounds for example organostannanes,
and the inorganic by-products are easily removed from the
reaction mixture, making the reaction suitable for industrial
processes.13
1
properties of NHC ligands based on a straightforward H NMR
measurement of NHC ligand precursors.21 Due to this and similar
unique features, various NHC complexes have been synthesised
with different transition-metals to date and have demonstrated
excellent activities as catalysts in different organic
transformations.22-26
Since the discovery of transition-metal-catalyzed reactions,
there is a continuous effort to develop new catalyst systems
which will be effective for a wide range of products. In most of
these reactions are generally used organic solvents, most of
which are toxic, flammable, and explosive. However, due to the
environmental concerns necessity for the use of the benign
solvent water as the medium for chemical reactions is
continuously growing. The use of water as a solvent in Suzuki-
Miyaura cross-coupling reactions helps with the solvation of
Most of the early work on Suzuki-Miyaura cross-coupling
reactions focused on using tertiary phosphine as ligands and so
phosphine ligands have become an indispensable class of ligands
for the coupling of aryl chlorides.14,15 Since the discovery of N-
heterocyclic carbenes (NHCs) by Arduengo in 1991, NHCs have
become one of the most versatile class of ligands for a wide

2
Tetrahedron
these organic-insoluble materials and inorganic bases. Also,
Miyaura cross-coupling reactions of phenylboronic acid and aryl
ACCEPTED MANUSCRIPT
organoboron compounds are often quite stable to protolytic
decomposition by water. In addition to being cheap and safe
solvent,27 water has the additional advantage that the Suzuki-
Miyaura cross-coupling reactions products are often poorly
soluble in water. Thus, they can be easily separated from the
reaction mixture. This advantage, though, also turns out to be a
drawback, as the aryl halides are poorly soluble in water.28 To
overcome this problem, addition of a minumum volume of a
protic co-solvent such as alcohol should led to even faster Suzuki
coupling reactions. Thus, in recent times, there is a particular
emphasis on the development of catalyst systems that will be
effective for Suzuki-Miyaura cross-coupling reactions in aqueous
media.29
halides at mild conditions in aqueous media.
Fig. 2. PEPPSI-type palladium-NHC complexes 2a-f.
2. Results and discussion
Palladium-NHC complexes such as bis(NHC)-type (a),
pincer-type (b), allyl-type (c) and PEPPSI-type, (PEPPSI =
Pyridine Enhanced Precatalyst Preparation Stabilization and
Initiation), (d) are the well-known and the most active ones for
cross-coupling catalysis (Figure 1).30 Among them, PEPPSI-type
palladium-NHC complexes can be easily obtained and are easy to
handle in contrast to other type palladium-NHC complexes.31-35
The high activity of PEPPSI complexes in catalysis has been
based on to the presence of a loosely bound throwaway pyridine
ligand that makes way for the incoming substrate.36
2.1. Preparation of Benzimidazolium Chlorides
The four new benzimidazolium chlorides 1a, 1c, 1e and 1f were
synthesized by reacting N-(3-methoxybenzyl)benzimidazole with
alkyl chlorides in dimethylformamide (DMF) at 80 C for 36 h
o
(Scheme 1). These benzimidazolium chlorides 1b and 1d were
obtained as we previously described.16c Benzimidazolium
1
chlorides were characterized using H NMR, 13C NMR and FT-
IR spectroscopy and gave satisfactory elemental analysis. As
shown in Table 1, The FT-IR data clearly indicated that the ben
zimidazolium chlorides 1a–f exhibit a characteristic ν(NCN) band
typically between 1557-1567 cm-1. The resonances for C(2)-H
were observed as sharp singlets at δ 11.48-12.00 ppm. The13C
NMR values of NCHN resonances in 1a-f appear at the range
143.7-143.9 ppm as single signal. These NMR values are in line
with those found for other benzimidazolium chlorides of the
literature.12i, 16c, 17d, 20c, 26
2.2. Preparation of PEPPSI-type palladium–NHC complexes
The general procedure for the preparation of the PEPPSI-type
palladium–NHC complexes 2a-f, according to the method
reported by Organ,40 is shown in Scheme 1. The six new
palladium complexes 2a-f were synthesized by the reaction of the
corresponding benzimidazolium chlorides (1a-f) obtained from
PdCl2 and pyridine in the presence of K2CO3 as a base. The air
and moisture-stable PEPPSI-type palladium-NHC complexes are
yellow in colour and soluble in common organic solvents such as
acetone, dichloromethane, chloroform, DMF, ethanol and
acetonitrile. They were fully characterised by elemental analysis,
1H NMR and 13C NMR and FT-IR spectroscopy and gave
satisfactory elemental analysis. The absence, in the 13C NMR and
1H NMR spectra, of the characteristic signals of the iminocarbon
(143.7-143.9 ppm) and the acidic imino proton (11.48-12.00
ppm), which are present in the salts 1a-f, suggests the formation
of NHC-carbenes and their coordination to form PEPPSI-type
palladium-NHC complexes. In addition, the characteristic
carbene carbons in compounds 2a-f appear in the 13C NMR
spectra as deshielded singlets at between 162.8-164.5 ppm. The
FT-IR data clearly indicated that the PEPPSI-type palladium–
NHC complexes 2a-f exhibit a characteristic ν(NCN) band typically
between 1396–1410 cm−1. These NMR values are in line with
those found for other PEPPSI-type palladium-NHC complexes of
Fig. 1. Well-known different type palladium-NHC complexes.
There are many examples of the application of PEPPSI-type
complexes in the Suzuki-Miyaura reaction in aqueous medium,
in which their excellent catalytic activity and versatility are
clearly evidenced.37 In this context, recently we have also
reported to synthesis of PEPPSI-type palladium-NHC complexes
and their catalytic activity in the Suzuki-Miyaura reactions in
aqueous media.38 Here in this contribution, we report the
synthesis and structural characterizations of a series of new bulky
NHC precursors (1a-f), and their air-stable, convenient to handle
and easily accessible new PEPPSI-type palladium-NHC
complexes of the general formula [PdCl2(NHC)(pyridine)], (2a-f)
(Figure 2). These complexes stabilized over 3-methoxybenzyl -
functionalized NHC ligands and containing a “throwaway”
pyridine ligand. These precatalysts are effective for the Suzuki-

3
20c, 26a, 39
the literature.
The analytical data are in good agreement
prepared, and are summarized in Table 1.
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with the compositions proposed for all the new compounds we
Scheme 1. Synthesis of the benzimidazolium chlorides (1a-f) and the PEPPSI-type palladium-NHC complexes (2a-f).
Table 1
Physical and spectroscopic properties of new compounds.
Isolated yield
M.p.
(oC)
137-138
93-94
v(CN)
H(2) 1H NMR
(ppm)
C(2) 13C NMR
(ppm)
Compound
Molecular formula
(%)
85
78
89
82
60
63
53
55
51
45
(cm-1)
C16H17ClN2O
C18H21ClN2O2
1567
1557
1558
1558
1407
1410
1405
1410
1410
1396
11.73
11.60
143.9
143.8
143.8
143.7
163.3
162.8
163.2
164.3
164.5
164.1
1a
1c
1e
1f
C26H29ClN2O
128-129
139-140
107-108
143-144
173-174
238-239
184-185
224-225
12.00
C27H31ClN2O
11.48
C21H22Cl2N3OPd
C24H28Cl2N3OPd
C23H26Cl2N3O2Pd
C27H26Cl2N3OPd
C31H34Cl2N3OPd
C32H36Cl2N3OPd
-
-
-
-
-
-
2a
2b
2c
2d
2e
2f
2.3. Optimization of the Reaction Conditions for Suzuki-Miyaura
Coupling
EtOH or solvent mixtures such as i-PrOH/H2O (1:1; v/v), i-
PrOH/H2O (1:3; v/v), i-PrOH/H2O (3:1; v/v) were tested in the
present of K2CO3 as base at 50 C for 3 h (Table 2, entries 6-11).
o
To study the efficiency of the PEPPSI-type palladium-NHC
complexes 2a-f in Suzuki-Miyaura coupling reactions, we first
selected the complex 2c as the model catalyst, the phenylboronic
acid as model substrate and the 4-chloroacetophenone as model
coupling partner (Table 2, Eq. 1). To find the best base, different
bases (Na2CO3, K2CO3, Cs2CO3, NaOH, KOH) were tested in
When a mixed solvent of i-PrOH/H2O (1:3; v/v) was used, a good
yield was observed (Table 2, entry 10). When the reaction time
was reduced from 3 h to 2 h at 50 °C, no noticeable effect on the
yield was observed (Table 2, entry 12), but when the reaction
time was reduced from 2 h to 1 h, the conversion decreased to
63%. (Table 2, entry 13). As a result of the optimisation
experiments, a very good yield (95%) was obtained with K2CO3
base and i-PrOH/H2O (1:3; v/v) solvent system, at 50 °C for 2 h
in air (Table 2, entry 12).
o
the present of i-PrOH as solvent at 50 C for 3 h in air (Table 2,
entries 1-5). When a base of K2CO3 was used, a good yield of
coupling product was obtained (Table 2, entry 2). Then, to find
the best solvent medium, different solvents such as DMF, water,

4
Tetrahedron
ACCEPTED MANUSCRIPT
Table 2
Optimization of the Suzuki-Miyaura coupling reactions of phenylboronic acid with 4-chloroacetophenone by complex 2c.a
Entry
Solvent
Base
Yield (%)b,c
1
2
3
4
5
6
7
8
9
10
11
12d
13e
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
DMF
H2O
EtOH
Na2CO3
K2CO3
Cs2CO3
NaOH
KOH
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
50
70
40
64
52
12
8
10
70
98
65
95
63
i-PrOH / H2O (1:1; v/v)
i-PrOH / H2O (1:3; v/v)
i-PrOH / H2O (3:1; v/v)
i-PrOH / H2O (1:3; v/v)
i-PrOH / H2O (1:3; v/v)
a Reaction conditions: complex 2c (0.01 mmol, 1 mol %), 4-chloroacetophenone (1.0 mmol), phenylboronic acid (1.5 mmol), base (2.0 mmol), solvent (4 mL), 50 oC, 3 h.
b Yields (%) were calculated according to 4-chloroacetophenone by GC analysis using decane as an internal standard.
c Yields are average of two runs.
d Reaction time is 2 h.
e Reaction time is 1 h.
2.4. Suzuki-Miyaura coupling of Phenylboronic Acid with
Various Aryl Halides
is known that oxidative additions of electron-withdrawing
substrates to electron rich palladium-complexes and reductive
elimination of the product from large, sterically hindered
palladium-complexes proceed more readily. Therefore, the
presence of an NHC ligand, (eg. 1c), bearing a different second
donating group such as ether side chains on the metal may
radically increase the catalytic performance of the catalyst (eg.
2c). The chelating nature of these ligands promotes production of
highly stable complexes. The hemilabile part of such ligands is
capable of reversible dissociation to produce vacant coordination
sites, allowing complexation of substrates during the catalytic
cycle. At the same time the strong donor carbene moiety remains
connected to the metal centre. Based on these observations, the
following tests were carried out different (hetero)aryl halides (X
= Br, Cl, F) in presence of 2c catalyst (Table 4, Eq. 3).
The optimized conditions were applied to the Suzuki-Miyaura
coupling reactions of different aryl chlorides with phenylboronic
acid using the PEPPSI-type palladium-NHC complexes (2a-f) at
o
50 C for 2 h (Table 3, Eq. 2). As shown in Table 3, both
electron-rich, electron-poor and sterically hindered aryl chlorides
effectively afford the corresponding products (55–95%) in 2-3 h
at 50 oC (Table 3, entries 1-42). When the reaction of 4-
chlorobenzene was investigated, yields at between 81–90%
(Table 3, entries 1-6). The palladium-PEPPSI-NHC complex 2a-f
were further assessed in the cross-coupling of phenylboronic acid
with two electron‐rich aryl chlorides; namely, p-chlorotoluene
and p-chloroanisole. This aryl chlorides were both rapidly
o
converted into biaryls at 50 C for 2 h (yields of 83-92% and 75-
The palladium complex 2c was further assessed in the
cross-coupling of phenylboronic acid with two electron-deficient
aryl chlorides; namely, 4-cyano chlorobenzene and 4-
chlorobenzotrifluoride. These aryl chlorides were both rapidly
converted into biaryls (yields of 94% and 78% after 2 h,
respectively) (Table 4, entries 1 and 3). But, when the reaction
time was reduced from 2 h to 1 h at 50 °C, the yields decreased to
70% and 54%, respectively (Table 4, entries 2 and 4). When 4-
bromobenzaldehyde was used as the substrate, 97% yield was
observed after 1 h (Table 4, entry 6), but when the reaction time
was reduced from 1 h to 0.5 h at 50 °C, no noticeable effect on
the yield was observed (yield of %94) (Table 4, entry 6).
85%, respectively) (Table 3, entries 7-12 and 13-18). As
anticipated, somewhat lower activities were found with the two
ortho-substituted aryl chlorides; namely, o-chlorotoluene and o-
chloroanisole (yields of 65-78% and 55-65%, respectively)
(Table 3, entries 19-24 and 25-30). When these aryl chlorides
were used, the reaction time was increased from 2 h to 3 h. The
coupling of phenylboronic acid with electron-poor aryl chlorides
such as p-chloroacetophenone and p-chloronitrobenzene also
proceeds nicely. p-Chloroacetophenone and p-chloronitrobenzene
gave the phenylboronic acid with 86%-95% and 85-93% yields,
respectively at 50 oC for 2 h (Table 3, entries 31-36 and 37-42).
Although small differences in reactivities were
observed for 2a-f catalyst due to the similar nature of the NHC
moieties, it can say that the most effective catalyst in this study is
2c. We attributed these performance differences to well-
accordance electronic and steric properties of the NHC ligand. It
When the reactions of sterically hindered aryl bromides
such as o-bromotoluene and o-cyano bromobenzene were
investigated, the yield was 98% in both cases (Table 4, entries 7
and 9). As anticipated, somewhat lower activities were found

5
with the two ortho-substituted bromobenzenes o-cyano
bromobenzene (77% yield in 0.5 h) and 4-cyano bromobenzene
(72% yield in 0.5 h) (Table 4, entries 8 and 10). With
phenylboronic acid, even the sterically hindered 3-
bromoquinoline led to the expected coupling product with 98%
yield in 1h. (Table 4, entry 11). But, when the reaction time was
reduced from 1 h to 0.5 h, the yield decreased to 78% (Table 4,
entry 12). A similar trend was observed when phenylboronic acid
was reacted with the an unreactive substrate such as 3,4-
ACCEPTED MANUSCRIPT
dimethoxy fluorobenzene. For example, 3,4-dimethoxy
fluorobenzene gave yield of 43% after 2 h. (Table 4, entry 13).
But, when the reaction time was increased from 2 h to 5 h, the
yield increased to 67% (Table 4, entry 14). When the reaction
time was increased from 5 h to 10 h, 98% yield was observed in
the reaction.
Table 3
Catalytic activities of complexes (2a-f) in the Suzuki-Miyaura coupling reactions of phenylboronic acid with aryl chlorides.a
Entry
Aryl chloride
[Pd]
Biaryl product
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
2
87
86
90
83
81
88
86
83
92
88
85
90
78
75
85
79
77
81
69
65
78
71
73
75
59
55
65
57
58
60
89
86
95
92
90
94
91
89
93
87
85
92
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
a Reaction conditions: palladium 2a-f, (0.01 mmol, 1 mol%), aryl chloride (1.0 mmol), phenylboronic acid (1.5 mmol), K2CO3 (2.0 mmol), i-PrOH/H2O (1:3; v/v) (4 mL), 50 oC.
b Yields (%) were calculated according to aryl chloride by GC analysis using decane as an internal standard.

6
Tetrahedron
ACCEPTED MANUSCRIPT
Table 4
Suzuki-Miyaura cross-coupling of different aryl halides catalyzed by palladium complex 2c.a
Entry
Aryl halide
Biaryl product
Time (h)
Yield (%)b
1
2
3
4
2
1
2
1
94
70
78
54
5
6
1
0.5
1
98
77
98
72
97
94
98
78
43
67
98
7
8
0.5
1
9
10
11
12
13
14
15
0.5
1
0.5
2
5
10
a Reaction conditions: palladium 2c (0.01 mmol, 1 mol%), aryl halide (1.0 mmol), phenylboronic acid (1.5 mmol), K2CO3 (2.0 mmol), i-PrOH/H2O (1:3; v/v) (4 mL), 50 oC.
b Yields (%) were calculated according to aryl halide by GC analysis using decane as an internal standard.
In previous works, similar substrates have been
Miyaura cross-coupling reaction between the phenylboronic acid
and aryl halides. When the catalytic studies were evaluated, it
was found that all of the complexes were suitable for the Suzuki-
Miyaura cross-coupling reaction. Surprisingly, similar yields
were obtained for the coupling of each aryl halides. We can say
that there is no significant difference between these complexes on
the catalytic activity. The only significant difference between 2a-
f complexes indicates that electronic and steric properties are also
playing some role in these processes. As a result of this catalytic
reactions provides many advantages such as low catalyst loading,
very good yields, green solvent system, simple and efficient
procedure, short reaction times under an air atmosphere.
employed with higher reaction time (3 h), and higher reaction
o
temperature (80 C) has been chosen for Suzuki-Miyaura cross-
coupling reaction in presence of palladium-PEPPSI catalysts.
However, in the present work the reaction temperature was
o
reduced to 50 C, and the reaction time was shortened to 2 h for
aryl chlorides. When compared with our previous work, here, the
reaction time was shortened to 2 h and higher yields were
obtained, whereas in previous work, the reaction was carried out
in presence of 1.0 mol% palladium-PEPPSI-NHC catalyst and
K2CO3 as the base in DMF/water mixture at 80 oC.41
3. Conclusion
4. Experimental
In conclusion, six new PEPPSI-type palladium-NHC complexes
were successfully synthesized and characterized by 1H NMR, 13
C
4.1. General Methods
NMR and FT-IR spectroscopy. These palladium complexes were
used as the catalysts in the synthesis of biaryls using Suzuki-
The synthesis of NHC salts and PEPPSI-type palladium-NHC
complexes were carried out under argon using standard Schlenk

7
line techniques. Elemental analyses were performed by İnönü
4.2.3. 1-(3-Methoxybenzyl)-3-(2-methoxyethyl)benzimidazolium
Chloride (1c)
ACCEPTED MANUSCRIPT
University Scientific and Technological Research Center
(Malatya, Turkey). Melting points were measures in open
capillary tubes with an Electrothermal-9200 melting points
apparatus. IR spectra were recorded on ATR unit in the range of
400-4000 cm-1 with Perkin Elmer Spectrum 100
(1.08 g, yield 78%) 1H NMR (400 MHz, CDCl3, 25 oC): δ = 3.35
(s, 3H, CH2CH2OCH3); 3.80 (s, 3H, CH2C6H4(OCH3)-3); 3.96 (t,
2H, J = 4.7 Hz, CH2CH2OCH3); 4.87 (t, 2H, J= 4.7 Hz,
CH2CH2OCH3); 5.83 (s, 2H, CH2C6H4(OCH3)-3); 6.85-6.87,
7.03-7.11, 7.25-7.29, 7.51-7.59 and 7.82-7.84 (m, 8H, arom.
CHs, NC6H4N and CH2C6H4(OCH3)-3); 11.60 (s, 1H, NCHN)
ppm. 13C NMR (100 MHz, CDCl3, 25 oC): δ = 47.8
1
Spectrofotometer. H NMR and 13C NMR spectra were recorded
using Bruker Avance AMX and Bruker Avance III spectrometer
operating at 300, 400 and 500 MHz (1H NMR) and at 75, 100 and
125 MHz (13C NMR) in CDCl3. The NMR studies were carried
out in high-quality 5 mm NMR tubes. The chemical shifts (δ) are
reported in ppm relative to CDCl3. Coupling constants (J values)
are given in hertz. NMR multiplicities are abbreviated as follows:
s = singlet, d = doublet, t = triplet, pent = pentet, hext = hextet, m
(CH2CH2OCH3);
(CH2C6H4(OCH3)-3);
51.4
59.09
(CH2C6H4(OCH3)-3);
(CH2CH2OCH3);
55.6
70.44
(CH2CH2OCH3); 113.4, 113.8, 114.1, 114.8, 120.3, 126.9, 130.3,
131.0, 132.3, 134.2, 160.2 (arom. Cs, NC6H4N and
CH2C6H4(OCH3)-3); 143.8 (NCHN) ppm. Elemental analysis
calcd (%) for C18H21ClN2O2 (Mr = 332.13 g. mol-1): C 64.96, H
6.36, N 8.42; found (%): C 64.98, H 6.39, N 8.43.
1
= multiplet. H NMR spectra are solvents (δ = 77.16 ppm for
CDCl3). All catalytic reactions were monitored on an Agilent
6890N GC and Schimadzu 2010 Plus GC-MS system by GC-FID
with an HP-5 column of 30 m length, 0.32 mm diameter, and
0.25 ꢀm film thickness.referenced to residual protiated solvents
(δ = 7.26 ppm for CDCl3), 13C chemical shifts are reported
relative to deuteriated.
4.2.4. 1-(3-Methoxybenzyl)-3-(benzyl)benzimidazolium Chloride
(1d)
This benzimidazolium chloride was synthesized according to
published procedure.16c
4.2. General procedure for the preparation of benzimidazolium
chlorides (1a-f)
4.2.5.1-(3-Methoxybenzyl)-3-(4-tert-butylbenzyl)benzimidazolium
Chloride (1e)
N-(3-Methoxybenzyl)benzimidazole (1.0 g; 4.2 mmol) was
dissolved in degassed DMF (3 mL) and alkyl chloride (4.2 mmol)
was added at room temperature. The reaction mixture was stirred
at 80 °C for 36 h under argon. After completion of the reaction,
the solvent was removed by vacuum and diethyl ether (15 mL)
was added to obtain a white crystalline solid, which was filtered
off. The solid was washed with diethyl ether (3×10 mL) and
dried under vacuum. The crude product was recrystallized from
ethanol/diethyl ether mixture (1:3, v/v) at room temperature and,
completely dried under vacuum. All benzimidazolium chlorides
(1a-f) were isolated as air- and moisture-stable white solids and
were isolated in 78-89 % yields.
(1.57 g, yield 89%) 1H NMR (300 MHz, CDCl3, 25 oC): δ = 1.20
(s, 9H, CH2C6H4(C(CH3)3)-4); 3.74 (s, 3H, CH2C6H4(OCH3)-3);
5.75 (s, 2H, CH2C6H4(C(CH3)3)-4); 5.78 (s, 2H,
CH2C6H4(OCH3)-3); 6.78-6.82, 6.96-7.03 and 7.20-7.54 (m, 12H,
arom.
CHs,
NC6H4N,
CH2C6H4(OCH3)-3
and
CH2C6H4(C(CH3)3)-4); 12.00 (s, 1H, NCHN) ppm. 13C NMR (75
MHz, CDCl3, 25 oC): δ = 31.1 (CH2C6H4(C(CH3)3)-4); 34.6
(CH2C6H4(C(CH3)3)-4); 51.3 CH2C6H4(C(CH3)3)-4); 51.5
(CH2C6H4(OCH3)-3); 55.6 (CH2C6H4(OCH3)-3); 113.7, 114.9,
120.3, 126.3, 127.0, 128.0, 129.6, 130.4, 131.4, 134.1, 152.4,
160.2 (arom. Cs, NC6H4N, CH2C6H4(OCH3)-3 and
CH2C6H4(C(CH3)3)-4); 143.8 (NCHN) ppm. Elemental analysis
calcd (%) for C26H29ClN2O (Mr = 420.20 g. mol-1): C 74.18, H
6.94, N 6.65; found (%): C 74.20, H 6.95, N 6.67.
4.2.1. 1-(3-Methoxybenzyl)-3-(methyl)benzimidazolium Chloride
(1a)
(1.02 g, yield 85%) 1H NMR (300 MHz, CDCl3, 25 oC): δ = 3.71
(s, 3H, CH2C6H4(OCH3)-3); 4.23 (s, 3H, CH3); 5.77 (s, 2H,
CH2C6H4(OCH3)-3); 6.75-6.78, 6.96-7.03, 7.15-7.24 and 7.48-
7.68 (m, 8H, arom. CHs, NC6H4N and CH2C6H4(OCH3)-3); 11.73
4.2.6.1-(3-Methoxybenzyl)-3-(2,3,4,5,6-pentamethylbenzyl)-
benzimidazolium Chloride (1f)
1
o
(1.49 g, yield 82%) H NMR (500 MHz, CDCl3, 25 C): δ =
2.25, 2.28 and 2.31 (s, 15H, CH2C6(CH3)5-2,3,4,5,6); 3.79 (s, 3H,
CH2C6H4(OCH3)-3); 5.88 (s, 2H, CH2C6(CH3)5-2,3,4,5,6); 5.94
(s, 2H, CH2C6H4(OCH3)-3); 6.84-6.86, 6.96-6.98, 7.02-7.29 and
7.42-7.59 (m, 8H, arom. CHs, NC6H4N, CH2C6H4(OCH3)-3);
11.48 (s, 1H, NCHN) ppm. 13C NMR (125 MHz, CDCl3, 25 oC):
o
(s, 1H, NCHN) ppm. 13C NMR (75 MHz, CDCl3, 25 C): δ =
33.8 (CH3); 51.3 (CH2C6H4(OCH3)-3); 55.6 (CH2C6H4(OCH3)-3);
112.8, 113.7, 113.8, 114.7, 120.5, 127.1, 127.2, 130.3, 131.01,
132.15, 134.2, 160.2. (arom. Cs, NC6H4N and CH2C6H4(OCH3)-
3); 143.9 (NCHN) ppm. Elemental analysis calcd (%) for
C16H17ClN2O (Mr = 288.10 g. mol-1): C 66.58, H 5.93, N 9.70;
found (%): C 66.60, H 5.94, N 9.72.
δ
=
17.0, 17.1 and 17.3 (CH2C6(CH3)5-2,3,4,5,6);
48.3(CH2C6(CH3)5-2,3,4,5,6); 51.4 (CH2C6H4(OCH3)-3); 55.5
(CH2C6H4(OCH3)-3); 113.6, 113.7, 114.6, 120.1, 126.9, 127.0,
130.3, 131.5, 133.5, 133.9, 134.5, 137.3, 160.1 (arom. Cs,
NC6H4N, CH2C6H4(OCH3)-3 and CH2C6(CH3)5-2,3,4,5,6); 143.7
(NCHN) ppm. Elemental analysis calcd (%) for C26H29ClN2O
(Mr = 421.00 g. mol-1): C 74.18, H 6.94, N 6.65; found (%): C
74.20, H 6.95, N 6.67.Elemental analysis calcd (%) for
4.2.2. 1-(3-Methoxybenzyl)-3-(n-butyl)benzimidazolium Chloride
(1b)
This benzimidazolium chloride was synthesized according to
published procedure.16c

8
Tetrahedron
ACCEPTED MANUSCRIPT
1
o
C27H31ClN2O (Mr = 434.21): C 74.55, H 7.18, N 6.44; found
(0.264 g, yield 53%) H NMR (400 MHz, CDCl3, 25 C): δ =
(%): C 74.57, H 7.19, N 6.45.
3.40 (s, 3H, CH2CH2OCH3); 3.77 (s, 3H, CH2C6H4(OCH3)-3);
4.26 (t, 2H, J= 5.4 Hz, CH2CH2OCH3); 5.10 (t, 2H, J= 5.3 Hz,
CH2CH2OCH3); 6.16 (s, 2H, CH2C6H4(OCH3)-3); 6.88-6.90,
7.11-7.33 and 7.77-7.81(m, 8H, arom. CHs, NC6H4N and
CH2C6H4(OCH3)-3); 7.36-7.39, 7.58-7.60 and 9.07-9.09 (m, 3H,
4.3. General procedure for the preparation of PEPPSI-type
palladium-NHC complexes (2a-f)
Benzimidazolium chlorides (1a-f) (1.0 mmol) were converted,
with moderated yields, into the PEPPSI-type palladium-NHC
complexes (2a-f) by reaction with PdCl2 (1.0 mmol) in refluxing
NC5H5) ppm. 13C NMR (100 MHz, CDCl3, 25 C): δ = 47.8
o
(CH2CH2OCH3);
(CH2C6H4(OCH3)-3);
53.7
(CH2C6H4(OCH3)-3);
59.1 (CH2CH2OCH3);
55.6
71.3
o
pyridine in the presence of K2CO3 (5.0 mmol) as a base at 80 C
(CH2CH2OCH3); 111.2, 111.5, 113.0, 114.7, 120.3, 129.7, 134.2,
136.5, 138.0, 160.2 (arom. Cs, NC6H4N and CH2C6H4(OCH3)-3);
123.1, 124.6, 152.6 (NC5H5); 163.2 (Pd-Ccarbene) ppm. Elemental
analysis calcd (%) for C23H26Cl2N3O2Pd (Mr = 552.04 g. mol-1):
C 49.88, H 4.73, N 7.59; found (%): C 49.89, H 4.75, N 7.60.
for 16 h. Volatiles were removed in vacuo, and the residue was
washed with n-pentane (2×5 mL). The crude product was
dissolved with CH2Cl2 then filtered through a pad of celite and
silica gel (70-230 mesh) to remove the unreacted PdCl2 and
benzimidazolium chloride. Then, the crude complex was
crystallized from CH2Cl2/n-pentane mixture (1:4, v/v) at room
temperature and, completely dried under vacuum. All palladium
complexes were isolated as air- and moisture-stable yellow solids
and were isolated in 45-63 % yields.
4.3.4. Dichloro-[1-(3-methoxybenzyl)-3-(benzyl)benzimidazol-2-
ylidene](pyridine)palladium(II) (2d)
1
o
(0.264 g, yield 55%) H NMR (400 MHz, CDCl3, 25 C): δ =
3.76 (s, 3H, CH2C6H4(OCH3)-4); 6.19 (s, 2H, CH2C6H4(OCH3)-
3); 6.22 (s, 2H, CH2C6H5); 6.88-7.37 (m, 10H, arom. CHs,
NC6H4N, CH2C6H4(OCH3)-3 and CH2C6H5); 7.60-7.62, 7.71-7.75
and 9.02-9.03 (m, 3H, NC5H5) ppm. 13C NMR (100 MHz, CDCl3,
25 oC): δ = 53.7 (CH2C6H4(OCH3)-3 and CH2C5H5); 55.6
(CH2C6H4(OCH3)-3); 111.4, 113.0, 114.7, 128.1, 128.2, 128.8,
129.7, 134.7, 134.9, 136.5, 137.9, 154.3, 160.2 (arom. Cs,
NC6H4N, CH2C6H4(OCH3)-3 and CH2C6H5); 123.1, 124.5, 152.6
(NC5H5); 164.3 (Pd-Ccarbene) ppm. Elemental analysis calcd (%)
for C27H26Cl2N3OPd (Mr = 584.05 g. mol-1): C 55.36, H 4.47, N
7.17; found (%): C 55.37, H 4.48, N 7.19.
4.3.1. Dichloro-[1-(3-methoxybenzyl)-3-(methyl)benzimidazole-
2-ylidene](pyridine)palladium(II), (2a)
1
o
(0.317 g, yield 60%) H NMR (300 MHz, CDCl3, 25 C): δ =
3.66 (s, 3H, CH2C6H4(OCH3)-3); 4.30 (s, 3H, CH3); 6.04 (s, 2H,
CH2C6H4(OCH3)-3); 7.02-7.04, 7.16-7.31 (m, 10H, arom. CHs,
NC6H4N, CH2C6H4(OCH3)-3 and NC5H5); 7.67-7.71 and 8.97-
9.00 (m, 3H, NC5H5). 13C NMR (75 MHz, CDCl3, 25 C): δ =
o
35.3 (CH3); 53.5 (CH2C6H4(OCH3)-3); 55.6 (CH2C6H4(OCH3)-
3);109.9, 111.4, 112.9, 114.8, 120.3, 129.7, 134.2, 135.5, 136.5,
138.0, 160.2. (arom. Cs, NC6H4N and CH2C6H4(OCH3)-3);
123.2, 124.6, 152.5 (NC5H5)163.3 (Pd-Ccarbene) ppm. Elemental
analysis calcd (%) for C21H22Cl2N3OPd (Mr = 508.02 g. mol-1): C
49.48, H 8.24, N 4.35; found (%): C 49.50, H 8.25, N 4.36.
4.3.5.Dichloro-[1-(3-methoxybenzyl)-3-(4-tert-butyl)benzimid-
azol-2-ylidene](pyridine)palladium(II) (2e)
1
o
(0.233 g, yield 51%) H NMR (400 MHz, CDCl3, 25 C): δ =
1.29 (s, 9H, CH2C6H4(C(CH3)3)-4); 3.76 (s, 3H,
CH2C6H4(OCH3)-3); 6.26 (s, 4H, CH2C6H4(C(CH3)3)-4 and
CH2C6H4(OCH3)-3); 7.06-7.39 (m, 12H, arom. CHs, NC6H4N,
CH2C6H4(OCH3)-3 and CH2C6H4(C(CH3)3)-4); 7.56-7.58, 7.73-
7.75 and 9.00-9.03 (m, 5H, NC5H5) ppm. 13C NMR (100 MHz,
4.3.2. Dichloro-[1-(3-methoxybenzyl)-3-(n-butyl)benzimidazol-2-
ylidene](pyridine)palladium(II), (2b)
1
o
(0.343 g, yield 63%) H NMR (400 MHz, CDCl3, 25 C): δ =
1.03 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3); 1.53 (hext, J = 7.4 Hz,
4H, CH2CH2CH2CH3); 2.19 (pent,
J
=
7.4 Hz, 2H,
CDCl3, 25 oC):
δ = 31.3 (CH2C6H4(C(CH3)3)-4); 34.5
CH2CH2CH2CH3); 3.67 (s, 3H, CH2C6H4(OCH3)-3); 4.80 (t, J =
7.4 Hz, 2H, CH2CH2CH2CH3); 6.06 (s, 2H, CH2C6H4(OCH3)-3);
7.03-7.31 (m, 10H, arom. CHs, NC6H4N, CH2C6H4(OCH3)-3 and
NC5H5) ppm, 7.70 and 8.99 (m, 3H, C5H5). 13C NMR (100 MHz,
(CH2C6H4(C(CH3)3)-4); 52.9 CH2C6H4(C(CH3)3)-4); 53.1
(CH2C6H4(OCH3)-3); 55.6 (CH2C6H4(OCH3)-3); 111.3, 111.5,
112.9, 114.6, 120.2, 125.8, 127.7, 129.7, 132.0, 134.5, 136.7,
138.1, 152.0, 160.2 (arom. Cs, NC6H4N, CH2C6H4(OCH3)-3 and
CH2C6H4(C(CH3)3)-4); 123.2, 124.4, 151.2 (NC5H5); 164.5 (Pd-
Ccarbene) ppm. Elemental analysis calcd (%) for C31H34Cl2N3OPd
(Mr = 640.11 g. mol-1): C 58.00, H 5.34, N 6.55; found (%): C
58.01, H 5.35, N 6.56.
CDCl3, 25 oC):
(CH2CH2CH2CH3);
(CH2CH2CH2CH3);
δ
=
31.8
53.2
13.9 (CH2CH2CH2CH3); 20.4
(CH2CH2CH2CH3);
48.7
55.7
(CH2C6H4(OCH3)-3);
(CH2C6H4(OCH3)-3); 110.3, 111.6, 113.05, 114.7, 120.3, 120.4,
129.7, 134.4, 135.0, 136.6, 137.9, 160.2 (arom. Cs, NC6H4N and
CH2C6H4(OCH3)-3); 123.0, 124.6, 152.6 (NC5H5); 162.8 (Pd-
Ccarbene) ppm. Elemental analysis calcd (%) for C24H28Cl2N3OPd
(Mr = 550.06 g. mol-1): C 52.24, H 5.11, N 7.61; found (%): C
52.25, H 5.13, N 7.62.
4.3.6. Dichloro-[1-(3-methoxybenzyl)-3-(2,3,4,5,6-pentamethyl-
benzyl)benzimidazol-2-ylidene](pyridine)palladium(II) (2f)
(0.203 g, yield 45%) 1H NMR (00 MHz, CDCl3, 25 oC): δ = 2.33,
2.34 and 2.36 (s, 15H, CH2C6(CH3)5-2,3,4,5,6); 3.79 (s, 3H,
CH2C6H4(OCH3)-3); 6.25 (s, 2H, CH2C6(CH3)5-2,3,4,5,6); 6.35
(s, 2H, CH2C6H4(OCH3)-3); 6.88-7.38 (m, 8H, arom. CHs,
NC6H4N, CH2C6H4(OCH3)-3); 7.35-7.40, 7.76-7.82 and 8.98-
9.01 (m, 5H, NC5H5) ppm. 13C NMR (75 MHz, CDCl3, 25 oC): δ
4.3.3. Dichloro-[1-(3-methoxybenzyl)-3-(2-methoxyethyl)benz-
imidazol-2-ylidene](pyridine)palladium(II), (2c)

9
15. (a) So CM, Lau CP, Kwong FY, Org. Lett. 2007:9:2795-2798;
=
16.9, 17.3 and 17.5 (CH2C6(CH3)5-2,3,4,5,6); 51.3
ACCEPTED MANUSCRIPT
(b) Harkal S, Rataboul F, Zapf A, Fuhrmann C, Riermeier T, Monsees
A, Beller M, Adv. Synth. Catal. 2004:346:1742-1748;
(c) Littke AF, Dai C, Fu GC, J. Am. Chem. Soc. 2000:122:4020-4028.
16. (a) Couve-Bonnaire S, Carpentier JF, Mortreux A, Castanet Y,
Tetrahedron Lett. 2001:42:3689-3691;
(b) Couve-Bonnaire S, Carpentier JF, Mortreux A, Castanet Y,
Tetrahedron 2003:59:2793-2799;
(c) Kaloğlu M, Özdemir İ, Tetrahedron 2018:74:2837-2845.
17. (a) Arduengo AJ, Harlow RL, Kline M, J. Am. Chem. Soc. 1991:113:
361-363;
(CH2C6(CH3)5-2,3,4,5,6); 53.2 (CH2C6H4(OCH3)-3); 55.5
(CH2C6H4(OCH3)-3); 111.1, 111.6, 113.0, 114.5, 119.6, 120.2,
122.7, 127.8, 129.7, 133.1, 134.3, 134.5, 135.1, 135.9, 136.8,
138.0, 160.1 (arom. Cs, NC6H4N, CH2C6H4(OCH3)-3 and
CH2C6(CH3)5-2,3,4,5,6); 123.1, 124.4, 151.2 (NC5H5); 164.1 (Pd-
C
carbene) ppm. Elemental analysis calcd (%) for C32H36Cl2N3OPd
(Mr = 654.13 g. mol-1): C 58.59, H 5.53, N 6.41; found (%): C
58.60, H 5.54, N 6.43.
(b) Clavier H, Nolan SP, Chem. Commun. 2010:46:841-861;
(c) Leverett AR, McKay AI, Cole ML, Dalton Trans. 2015:44:498-
500;
4.4. General procedure for Suzuki-Miyaura cross-coupling
reaction
(d) Kaloğlu M, Gürbüz N, Sémeril D, Özdemir İ, Eur. J. Inorg. Chem.
2018:10: 1236-1243.
18. (a) Herrmann WA, Elison M, Fisher J, Köcher C, Artus GR, Angew.
Chem. Int. Ed. 1995:34:2371-2374;
Phenylboronic acid (1.5 mmol), aryl chloride (1.0 mmol), K2CO3
(2.0 mmol), PEPPSI-type palladium-NHC catalyst (0.01 mmol, 1
mol%) (2a-f) and mixture of isopropanol/water (1:3; v/v) (4 mL)
were added to a small raund bottom flask in air. The mixture was
stirred at 50 ° C for 2 h. At the end of the reaction, the cooled
solution to room temperature was extracted with a mixture of
EtOAc/n-hexane (1:5, v/v). The organic phase was separated and
dried over anhydrous MgSO4, the solution passed through the
micro silica gel column was concentrated. Product
characterizations were performed by GC. The reaction yields
were determined by GC based on aryl chloride.
(b) Scott NM, Nolan SP, Eur. J. Inorg. Chem. 2005:10:1815-1828;
(c) Wanzlick HW, Schikora E, Angew. Chem. 1960:72:494-494;
(d) Bourissou D, Guerret O, Gabbai FP, Bertrand G, Chem. Rev.
2000:100:39-92.
19. (a) Hermann WA, Angew. Chem. Int. Ed. 2002:41:1290-1309;
(b) Grasa GA, Viciu MS, Huang J, Zhang C, Trudell ML, Nolan P,
Organometallics 2002:21:2866-2873;
(c) Diez-Gonzalez S, Nolan SP, Coord. Chem. Rev. 2007: 251:874-
883.
20. (a) Cavallo L, Correa A, Costabile C, Jacobsen HJ, Organomet. Chem.
2005:690:5407-5413;
(b) Strassner T, Top. Organomet. Chem. 2004:13:1-20;
(c) Kaloğlu M, Özdemir İ, Dorcet V, Bruneau C, Doucet H, Eur. J.
Inorg. Chem. 2017:10:1382-1391;
(d) Frenkin G, Solà M, Vyboishchikov SF, J. Organomet. Chem. 2005:
690:6178-6204;
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://
(e) Radius U, Bickelhaupt FM, Coord. Chem. Rev. 2009:253: 678-686;
(f) Jacobsen H, Correa A, Poater A, Costabile C, Cavallo L, Coord.
Chem. Rev. 2009:253:687-703.
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ACCEPTED MANUSCRIPT
• A series of new benzimidazolium chlorides (1a-f) as N-heterocyclic carbene (NHC) ligand
precursors and their corresponding new PEPPSI-type palladium-NHC complexes (2a-f) were
synthesized.
• The all new compounds were fully characterized by analytical and spectral methods.
• PEPPSI-type palladium-NHC complexes were tested as promising catalyst in the synthesis of biaryls
using Suzuki-Miyaura cross-coupling reaction between the phenylboronic acid and aryl halides.