Palladium PEPPSI complexes: Synthesis and catalytic activity on the Suzuki-Miyaura coupling reactions for aryl bromides at room temperature in aqueous media

Article abstract of DOI:10.1016/j.ica.2018.04.018

A new series of palladium N-heterocyclic carbene complexes having methoxyethyl on the side chain (3a–d, 4a–e) have been synthesized and fully characterized by NMR, HRMS and IR. Next, the palladium-NHC-PEPPSI complexes 3a-e and 4a-e were used as catalyst in Suzuki-Miyaura coupling reactions were investigated for aryl bromides at room temperature in aqueous media. 3a-d and 4a-e complexes showed good catalytic activity for electron-donating or electron-drawing aryl bromides with arylboronic acid. Complex 4b exhibited higher activity compared to other analogues due to bearing more electronically donating NHC ligands.

Full text of DOI:10.1016/j.ica.2018.04.018

Accepted Manuscript
Research paper
Palladium PEPPSI complexes: synthesis and catalytic activity on the Suzuki-
Miyaura coupling reactions for aryl bromides at room temperature in aqueous
media
Nedra Touj, Nevin Gürbüz, Naceur Hamdi, Sedat Yaşar, İsmail Özdemir
PII:
S0020-1693(18)30028-8
https://doi.org/10.1016/j.ica.2018.04.018
ICA 18209
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
5 January 2018
26 February 2018
11 April 2018
Please cite this article as: N. Touj, N. Gürbüz, N. Hamdi, S. Yaşar, I. Özdemir, Palladium PEPPSI complexes:
synthesis and catalytic activity on the Suzuki-Miyaura coupling reactions for aryl bromides at room temperature in
aqueous media, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/j.ica.2018.04.018
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Palladium PEPPSI complexes: synthesis and catalytic activity on the Suzuki-Miyaura
coupling reactions for aryl bromides at room temperature in aqueous media
Nedra Touj,1,2 Nevin Gürbüz,1,3 Naceur Hamdi,2 Sedat Yaşar,*1,3 and İsmail Özdemir1,3
1İnönü University, Catalysis Research and Application Center, Faculty of science and Art,
Department of Chemistry, 44280 Malatya, Turkey
2 Research Laboratory of Environmental Sciences and Technologies (LR16ES09), Higher
Institute of Environmental Sciences and Technology, University of Carthage, Hammam-Lif,
Tunisia
3İnönü University, Faculty of Science and Art, Department of Chemistry, 44280 Malatya,
Turkey
*Corresponding author: tel:+90 422 3773735, fax:+90 4223410212,
e-mail:syasar44@gmail.com
Running Head: Benzimidazole based Pd-PEPPSI complexes and Suzuki coupling reaction
for aryl bromide substrate at room temperature
Abstract
A new series of palladium N-heterocyclic carbene complexes having methoxyethyl on the
side chain (3a-d, 4a-e) have been synthesized and fully characterized by NMR, HRMS and
IR. Next, the palladium-NHC-PEPPSI complexes 3a-e and 4a-e were used as catalyst in
Suzuki-Miyaura coupling reactions were investigated for aryl bromides at room temperature
in aqueous media. 3a-d and 4a-e complexes showed good catalytic activity for electron-
donating or electron-drawing aryl bromides with arylboronic acid. Complex 4b exhibited
higher activity compared to other analogues due to bearing more electronically donating NHC
ligands.

Keywords: Palladium N-heterocyclic carbene complex; benzimidazole; Suzuki-Miyaura
cross coupling; C-C bond formation; aqueous media
1. Introduction
The coordination chemistry of palladium has attracted a special interest in the field of
catalysis for C-C bond formations for over 40 years. For this purpose, palladium based
complexes or palladium salts are commonly used as catalyst. Cross-coupling reactions are the
most important and accepted methods to produce fine chemicals in organic synthesis and for
industry and academia. Suzuki-Miyaura reaction is one of the most beneficial and studied C-C
bond forming reactions due to its reputation which comes from use of non-toxic chemicals,
substrate tolerance, green solvents, mild reaction conditions and easy separation of product
from reaction media.[1-3] Some excellent reviews were published on this area.[4] When the
history of the Suzuki-Miyaura coupling reaction is examined, generally, phosphines have
dominated as the ligand used.[5] However, some limitations of phosphine ligands include
toxicity and sensitivity to air and moisture.[6] Therefore, to overcome these disadvantages,
development of phosphine-free catalytic system is one of the most challenging and
demanding issue in Suzuki-Miyaura cross-coupling reactions.
After 1991, N-heterocyclic carbenes (NHCs) are firmly occupied an important place in
the ancillary ligands for organometallic chemistry and homogeneous catalysis. Since this date,
NHCs have begun to replace phosphine ligands.[7-10] High thermal stability, nontoxic
chemistry, resistance to oxidation, strong σ-donor ligands ability[13] with weak π-acceptor
capability, tuneable of electronic and steric properties and easily handling are some of the
superior advantageous of NHCs.[7,11-13] The commonly used NHC ligands for transition metals
are generated from imidazolium, imidazolidinium and benzimidazolium based salts in
presence of strong bases. Herrmann et al reported well-define Pd-NHC complexes used as
effective catalysts in C-C bond formation reactions.[14] Other research groups reported well-

defined NHC-Pd complexes used successfully as effective catalyst in C-C bond formation
reaction.[15-18] Herrmann study’s encouraged Nolan[19-21] and others [22] to further investigate
Pd-NHC complex as catalysts in Suzuki-Miyaura cross-coupling. Glorius et al. succeed in the
production of sterically demanding biaryls via Suzuki-Miyaura coupling reaction at room
temperature with low catalyst loadings in high yields.[ 23] Organ’s studies take a very
important place in cross-coupling reactions.[24] They synthesized a series of Pd-PEPPSI
(PEPPSI= Pyridine-Enhanced Precatalyst Preparation, Stabilisation and Initiation) complexes
with various NHC ligands. These catalyst displayed high reactivity with wide range of
substrates and inorganic bases. Research showed that the activity of the Pd-PEPPSI
complexes was attributed to NHC ligands.[25-28] Our group also synthesized and investigated
the catalytic activity of Pd-PEPPSI type complexes in Suzuki-Miyaura cross-coupling
reactions of aryl chlorides.[29]
Carbenes are most effectively stabilized after coordinated to transition metals, and many of
them are stable in water. The properties of various transition-metal-carbene complexes in
aqueous media have been studied.[30] The use of water as a solvent in Suzuki-Miyaura cross-
coupling reactions helps with the solvation of these organic-insoluble materials and inorganic
bases. Also, organoboron compounds are often quite stable to protolytic decomposition by
water. In addition to being cheap and safe solvent,[31–33] 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.[34] 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. There are certain key challenges for development of
methodologies using water or aqueous medium as solvents.

Herein, we report the synthesis and characterization of nine new palladium-PEPPSI
complexes bearing methoxyethyl on the side chain and the catalytic activity in Suzuki-
Miyaura cross-coupling reactions at room temperature in aqueous media.
2. Experimental Section
2.1 Materials
All reactions for the preparation of benzimidazolium salts (1-2) and palladium-(NHC)-
PEPPSI complexes (3-4) were carried out under air. PdCl2, pyridine and solvents were
purchased from Sigma-Aldrich and used as obtained. Elemental analyses were performed by
ElementarVario EL III Carlo Erba 1108. The melting points of the complexes and NHC
precursors were determined using Stuart automatic melting point apparatus (SMP-40). IR
spectra were recorded with a PerkinElmer Spectrum 100 GladiATR FT/IR spectrophotometer.
13
1H, C NMR spectra were recorded in CDCl3 or DMSO-d6 solutions operating on a Bruker
Avance III HD 400 MHz NMR spectrometer and chemical shifts were reported relative to
tetramethylsilane for 1H, 13C NMR spectra as standard. Signals are quoted in parts per million
as  downfield from tetramethylsilane ( 0.00) as an internal standard. Coupling constants (J
values) are given in hertz. NMR multiplicities are abbreviated as follows: s = singlet, d =
doublet, t = triplet, m = multiplet signal. The HRMS (ESI) electrospray ionization mass
spectra were recorded on a Shimadzu LCMS-IT-Toff spectrometer in CH3CN/CHCl3. Column
chromatography was performed using silica gel 60 (70-230 mesh). Solvent ratio is given as
v/v.
2.2 General procedure for the synthesis of NHC precursors, 1a-d and 2a-e.
For
the
preparation of
benzimidazolium
salts
1a-d
and
2a-e.,
1-(2-
Methoxyethyl)benzimidazole (1 mmol) was dissolved in anhydrous dimethylformamide
(DMF), (3 mL) and alkyl halide (1.2 mmol) was added at room temperature. The reaction

mixture was stirred at 70 oC for 48 h. After completion of the reaction, the DMF 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 (3x10 mL) and dried under vacuum. The
crude product was recrystallized from dichloromethane–diethyl ether and completely dried
under vacuum to give the title compounds as white crystals.
2.2.1 1-(2-Methoxyethyl)-3-(2,3,4,5,6-penthamethylbenzyl)benzimidazolium chloride, 1a
This NHC precursor was synthesized according to published procedure.[35]
2.2.2 1-(2-Methoxyethyl)-3-(2,4,6-trimethylbenzyl)benzimidazolium chloride, 1b
This NHC was synthesized according to published procedure.[36]
2.2.3 1-(2-Methoxyethyl)-3-(3,5-dimethylbenzyl)benzimidazolium bromide, 1c
1
Yield: 92% (3.1 g); m.p.= 311.1 °C. ν(CN)= 1560.26 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.28 [s, 6H, CH2C6H3(CH3)2-3,5], 3.36 [s, 3H, CH2CH2OCH3], 3.98 [t, J = 4 Hz, 2H,
CH2CH2OCH3], 4.89 [t, J = 4 Hz, 2H, CH2CH2OCH3], 5.73 [s, 2H, CH2C6H3(CH3)2-3,5],
6.96 and 7.06 [s, 3H, CH2C6H3(CH3)2-3,5], 7.55 [m, 3H, NC6H4N], 7.82 [d, J = 8 Hz,
1H,NC6H4N], 11.40 [s, 1H, NCHN]. 13C NMR (CDCl3, 100 MHz, δ, ppm): 21.3
[CH2C6H3(CH3)2-3,5],
47.9
[CH2CH2OCH3],
51.7
[CH2C6H3(CH3)2-3,5],
59.2
[CH2CH2OCH3], 70.5 [CH2CH2OCH3], 113.5, 114.1 [NC6H4N-o], 126.1 [CH2C6H3(CH3)2-
3,5;C2,4,6], 127.0 and 127.1 [NC6H4N-m], 131.0 and 131.0 [NC6H4N-i], 132.3
[CH2C6H3(CH3)2-3,5;C1], 139.2 [CH2C6H3(CH3)2-3,5; C3,5], 142.6 [NCHN]. Anal. Calc. for
C19H23N2OBr (%): C, 60.81; H, 6.18; N, 7.46. Found (%): C, 60.88; H, 6.30; N, 7.59.
2.2.4 1-(2-Methoxyethyl)-3-(4-methylbenzyl)benzimidazolium chloride, 1d

1
Yield: 90% (2.9 g); m.p. = 302.5 °C. ν(CN)= 1557.32 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.29 [s, 3H, CH2C6H4(CH3)-4], 3.35 [s, 3H, CH2CH2OCH3], 3.95 [t, J = 4 Hz, 2H,
CH2CH2OCH3], 4.87 [t, J = 4 Hz, 2H, CH2CH2OCH3], 5.83 [s, 2H, CH2C6H4(CH3)-4], 7.10
and 7.29 [d, J = 8 Hz, 4H, CH2C6H4(CH3)-4], 7.52, 7.58, and 7.86 [d, J = 8 Hz, 4H,
NC6H4N], 11.24 [s, 1H, NCHN]. 13C NMR(CDCl3, 100 MHz, δ, ppm): 21.2 [CH2C6H4(CH3)-
4], 47.9 [CH2CH2OCH3], 51.3 [CH2C6H4(CH3)-4], 59.1 [CH2CH2OCH3], 70.1
[CH2CH2OCH3], 113.6, 114.1 [NC6H4N-o], 127.1 [NC6H4N-m], 128.4 [CH2C6H4(CH3)-
4;C2,3,5,6], 129.9 and 130.9 [NC6H4N-i], 132.2 [CH2C6H3(CH3)2-3,5;C1], 139.3
[CH2C6H4(CH3)-4;C4], 142.9 [NCHN]. Anal. Calc. for C18H21N2OCl (%): C, 68.24; H, 6.68;
N, 8.84. Found (%): C, 68.19; H, 6.75; N, 8.93%.
2.2.5 1-(2-Methoxyethyl)-3-(2,3,4,5,6-pentamethylbenzyl)-5,6-dimethylbenzimidazolium
chloride, 2a
This NHC precursor was synthesized according to published procedure.[36]
2.2.6
1-(2-Methoxyethyl)-3-(2,4,6-trimethylbenzyl)-5,6-dimethylbenzimidazolium
chloride, 2b
This NHC precursor was synthesized according to published procedure.[36]
2.2.7 1-(2-Methoxyethyl)-3-(3,5-dimethylbenzyl)-5,6-dimethylbenzimidazolium bromide,
2c
1
Yield: 89% (3.19 g); m.p. = 267.6 °C. ν(CN)= 1563.49 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.22 [s, 6H, CH2C6H3(CH3)2-3,5], 2.31 and 2.35 [s, 6H, NC6H2(CH3)2N-5,6], 3.29 [s,
3H, CH2CH2OCH3], 3.89 [t, J = 4 Hz, 2H, CH2CH2OCH3], 4.73 [t, J = 4 Hz, 2H,
CH2CH2OCH3], 5.59 [s, 2H, CH2C6H3(CH3)2-3,5], 6.90 and 6.95 [s, 3H, CH2C6H3(CH3)2-
3,5], 7.22 and 7.47 [s, 2H, NC6H2(CH3)2N-5,6], 11.05 [s, 1H, NCHN]. 13C NMR(CDCl3, 100

MHz, δ, ppm): 20.6 and 20.7 [NC6H2(CH3)2N-5,6], 21.2 [CH2C6H3(CH3)2-3,5], 47.5
[CH2CH2OCH3], 51.2 [CH2C6H3(CH3)2-3.5], 59.1 [CH2CH2OCH3], 70.3 [CH2CH2OCH3],
113.0, 113.5 [NC6H2(CH3)2N-o], 125.7 [CH2C6H3(CH3)2-3,5;C2,4,6], 130.8 and 132.6
[NC6H2(CH3)2N-i],
132.6[CH2C6H3(CH3)2-3,5;C1], 137.2 [NC6H2(CH3)2N-m],
139.1
[CH2C6H3(CH3)2-3,5;C3,5], 141.8 [NCHN]. Anal. Calc. for C21H27N2OBr (%): C, 62.53; H,
6.75; N, 6.95. Found (%): C, 62.59; H, 6.79; N, 7.13%.
2.2.8 1-(2-Methoxyethyl)-3-(4-methylbenzyl)-5,6-dimethylbenzimidazolium chloride, 2d
1
Yield: 87% (3.0 g); m.p. = 256.8 °C. ν(CN)= 1559.72 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.32 [s, 3H, CH2C6H4(CH3)-4], 2.37and 2.41 [s, 6H, NC6H2(CH3)2N-5,6], 3.36 [s, 3H,
CH2CH2OCH3], 3.95 [t, J = 4 Hz, 2H, CH2CH2OCH3], 4.78 [t, J = 4 Hz, 2H, CH2CH2OCH3],
5.72 [s, 2H, CH2C6H4(CH3)-4], 7.18 and 7,36 [d, J = 8 Hz, 4H, CH2C6H4(CH3)-4], 7.31 and
7.53 [s, 2H, NC6H2(CH3)2N-5,6], 11.23 [s, 1H, NCHN]. 13C NMR (CDCl3, 100 MHz, δ,
ppm): 20.6 and 20.7 [NC6H2(CH3)2N-5,6], 21.2 [CH2C6H4(CH3)-4], 40.2[CH2CH2OCH3],
51.0 [CH2C6H4(CH3)-4], 59.2 [CH2CH2OCH3], 70.3 [CH2CH2OCH3], 113.0, 113.5
[NC6H2(CH3)2N-o], 128.2 [NC6H2(CH3)2N-i], 130.0 [CH2C6H4(CH3)-4;C2,3,5,6], 130.8
[CH2C6H4(CH3)-4;C1], 137.2 [CH2C6H4(CH3)-4;C4], 139.1 [NC6H2(CH3)2N-m], 141.8
[NCHN]. Anal. Calc. for C20H25N2OCl (%): C, 69,65; H, 7.31; N, 8.12. Found (%): C, 69.77;
H, 7.43; N, 8.24.
2.2.9 1-(2-Methoxyethyl)-3-(4-tert-butylbenzyl)-5,6-dimethylbenzimidazolium bromide,
2e
1
Yield: 74% (2.85 g); m.p. = 255.4 °C. ν(CN)= 1559.06 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 1.29 [s, 9H, CH2C6H4(C(CH3)3)-4], 2.40 and 2.43 [s, 6H, NC6H2(CH3)2N-5,6], 3.38 [s,
3H, CH2CH2OCH3], 3.98 [t, J = 4 Hz, 2H, CH2CH2OCH3], 4.79 [t, J = 4 Hz, CH2CH2OCH3],
5.73 [s, 2H, CH2C6H4(C(CH3)3)-4], 7.34 and 7.53 [s, 2H, NC6H2(CH3)2N-5,6], 7.42 [s, 4H,

CH2C6H4(C(CH3)3)-4], 11.27 [s, 1H, NCHN]. 13C NMR (CDCl3, 100MHz, δ, ppm): 20.6 and
20.7 [NC6H2(CH3)2N-5,6], 31.2 [CH2C6H4(C(CH3)3)-4], 47.5[CH2CH2OCH3], 50.9
[CH2C6H4(C(CH3)3)-4], 59.2 [CH2CH2OCH3], 70.3 [CH2CH2OCH3], 112.9 and 113.5
[NC6H2(CH3)2N-o], 126.3 [CH2C6H4(CH3)-4;C3,5], 128.0 [CH2C6H4(CH3)-4, C2,6], 129.5 and
129.8 [NC6H2(CH3)2N-i], 130.8 [CH2C6H4(CH3)-4;C1], 137.2 [NC6H2(CH3)2N-m], 141.8
[NCHN], 152.3 [CH2C6H4(C(CH3)3)-4; C4]. Anal. Calc. for C23H31N2OBr (%): C, 64.03; H,
7.24; N, 6.49. Found (%): C, 64.11; H, 7.30; N, 6.61.
2.3 General procedure for the preparation of the palladium-PEPPSI complexes, (3a-d,
4a-e)
In air, a pressure tube was charged with PdCl2 (180 mg, 1 mmol), NHC precursors (1.1
mmol), K2CO3 (700 mg, 5 mmol) and 3 mL of pyridine. The reaction mixture was heated with
o
vigorous stirring for 12 h at 80 C then cooled to room temperature and diluted with
dichloromethane (DCM). A short silica column was used for filtration. All volatiles were
evaporated. Residue yellow solid was washed with hexane (2x10 mL) and diethyl ether (2x10
mL). The yellow solid was crystallized with DCM-Hexane (1:3) for further purification.
2.3.1
Dichloro[1-(2-methoxyethyl)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazole-2-
ylidene]pyridinepalladium(II), 3a
1
Yield: 88% (0.4 g); m.p. = 243.9 °C. ν(CN)= 1447.16 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.25 [s, 6H, CH2C6(CH3)5-2,6], 2.32 [s, 6H, CH2C6(CH3)5-3,5], 2.34 [s, 3H,
CH2C6(CH3)5-4], 3.38 [s, 3H, CH2CH2OCH3], 4.23 [t, J = 4 Hz, 2H, CH2CH2OCH3], 5.13 [t,
J = 4 Hz, 2H, CH2CH2OCH3], 6.26 [s, 2H, CH2C6(CH3)5-2,3,4,5,6], 6.44, 6.97 and 7.18 [t,
3H, NC6H4N], 7.54 [d, J = 8 Hz, 1H, NC6H4N], 7.39 [t, J = 8 Hz, 2H, NC5H5-H3,5], 7.81 [t, J
13
= 8 Hz, 1H, NC5H5-H4], 8.98 [d, J = 8 Hz, 2H, NC5H5-H2,6]. C NMR (CDCl3, 100 MHz, δ,
ppm): 16.9, 17.3 and 17.5 [CH2C6(CH3)5-2,3,4,5,6], 48.6 [CH2CH2OCH3], 51.2

[CH2C6(CH3)5-2,3,4,5,6], 59.2 [CH2CH2OCH3], 72.0 [CH2CH2OCH3], 111.3 [NC6H4N-o],
122.7 [NC5H5, C3,5], 123.0 [NC6H4N-m], 124.5 [CH2C6(CH3)5-2,3,4,5,6;C3,5], 127.8
[CH2C6(CH3)5-2,3,4,5,6;C4], 133.1 [NC6H4N-i], 134.7 [CH2C6(CH3)5-2,3,4,5,6;C2,6], 135.9
[NC5H5;C4], 138.1 [CH2C6(CH3)5-2,3,4,5,6;C1], 151.2 [NC5H5;C2,6], 163.3 [Pd-Ccarb].
HRMS(ESI), m/z=468,1243 [M+Na+H]+ (calcd for C22H28N2OPdNa:468,1217).
2.3.2
Dichloro[1-(2-methoxyethyl)-3-(2,4,6-trimethylbenzyl)benzimidazole-2-
ylidene]pyridinepalladium(II), 3b
1
Yield: 82% (0.35 g); m.p. = 215.5 °C. ν(CN)= 1448.80 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.26 [s, 9H, CH2C6H2(CH3)3-2,4,6], 3.28 [s, 3H, CH2CH2OCH3], 4.14 [t, J = 4 Hz, 2H,
CH2CH2OCH3], 5.04 [t, J = 4 Hz, 2H, CH2CH2OCH3], 6.11 [s, 2H, CH2C6H2(CH3)3-2,4,6],
6.39 and 7.47 [d, J = 8 Hz, 2H, NC6H4N], 6.86 [s, 2H, CH2C6H2(CH3)3-2,4,6], 6.89 and 7.10
[t, J = 8 Hz, 2H, NC6H4N], 7.31 [t, J = 8 Hz, 2H, NC5H5-H3,5], 7.72 [t, J = 8 Hz, 1H, NC5H5-
13
H4], 8.91 [d, J = 8 Hz, 2H, NC5H5-H2,6]. C NMR (CDCl3, 100 MHz, δ, ppm): = 20.8 and
21.1 [CH2C6H2(CH3)3-2,4,6], 48.6 [CH2CH2OCH3], 50.0 [CH2C6H2(CH3)3-2,4,6], 59.2
[CH2CH2OCH3], 72.0 [CH2CH2OCH3], 111.1 and 111.4 [NC6H4N-o], 122.8 [NC5H5;C3,5],
123.1 [NC6H4N-m], 124.5 [CH2C6H2(CH3)3-2,4,6;C3,5], 127.5 [CH2C6H2(CH3)3-2,4,6;C4],
134.7 [CH2C6H2(CH3)3-2,4,6;C2,6], 134.4 and 135.6 [NC6H4N-i], 138.2 [NC5H5;C4], 138.8
[CH2C6H2(CH3)3-2,4,6;C1], 151.3 [NC5H5;C2,6], 163.5 [Pd-Ccarb]. HRMS(ESI),
m/z=440,0914 [M+Na+H]+ (calcd for C20H24N2OPdNa:440,0904); m/z=413,0680 [M-H]-
(calcd for C20H24N2OPd:413,0845).
2.3.3
Dichloro[1-(2-methoxyethyl)-3-(3,5-dimethylbenzyl)benzimidazole-2-
ylidene]pyridinepalladium(II), 3c
1
Yield: 88% (0.32 g); m.p. = 205.5 °C. ν(CN)= 1445.58 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.21 [s, 6H, CH2C6H3(CH3)2-3,5], 3.30 [s, 3H, CH2CH2OCH3], 4.23 [m, 2H,
CH2CH2OCH3], 5.10 [d, J = 6 Hz, 2H, CH2CH2OCH3], 6.07 [m, 2H, CH2C6H3(CH3)2-3,5],

6.86 [s, 1H, NC6H4N], 7.05[m, 2H, NC6H4N], 7.48 [d, J = 8 Hz, 1H, NC6H4N], 7.15 and 7.19
[s, 3H, CH2C6H3(CH3)2-3,5], 7.28 [m, 2H, NC5H5-H3,5], 7.48 [d, J = 8 Hz, 1H, C6H4-H4],
7.67-6.72 [m, 1H, NC5H5-H4], 8.95 [m, 2H, NC5H5-H2,6]. 13C NMR (CDCl3, 100 MHz, δ,
ppm): 21.3 [CH2C6H3(CH3)2-3,5], 48.8 [CH2CH2OCH3], 53.3 [CH2C6H3(CH3)2-3,5], 59.2
[CH2CH2OCH3], 71.7 [CH2CH2OCH3], 111.2 and 111.5 [NC6H4N-o], 123.1 [NC5H5;C3,5],
124.6 [NC6H4N-m], 125.9 [CH2C6H3(CH3)2-3,5;C2,6], 129.8 [CH2C6H3(CH3)2-3,5;C4], 134.8
and 134.3 [NC6H4N-i], 135.9 [CH2C6H3(CH3)2-3,5;C1], 138.1 [NC5H5;C4], 138.4
[CH2C6H3(CH3)2-3,5;C3,5], 152.7 [NC5H5;C2,6], 163.4 [Pd-Ccarb]. HRMS(ESI),
m/z=571,6105 [M+Na-H]+ (calcd for C24H27N3OCl2PdNa:571,0385); m/z=426,0798
[M+Na+H]+ (calcd for C19H22N2OPdNa:426,0786).
2.3.4
Dichloro[1-(2-methoxyethyl)-3-(4-methylbenzyl)benzimidazole-2-
ylidene]pyridinepalladium(II), 3d
1
Yield: 86% (0.30 g); m.p. = 200.7 °C. ν(CN)= 1446.03 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.10 [s, 3H, CH2C6H4(CH3)-4], 3.30 [s, 3H, CH2CH2OCH3], 4.16 [m, 2H,
CH2CH2OCH3], 5.02 [m, 2H, CH2CH2OCH3], 6.06 [s, 2H, CH2C6H4(CH3)-4], 6.94-7.74 [m,
6H, CH2C6H4(CH3)-4,NC6H4N, NC5H5-H4], 7.10 [t, J = 8 Hz, 2H, CH2C6H4(CH3)-4], 7.38 [d,
13
J = 8 Hz, 2H, NC5H5-H3,5], 7.48 [d, J = 8 Hz, 1H, NC6H4N], 8.96 [m, 2H, NC5H5-H2,6]. C
NMR (CDCl3, 100 MHz, δ, ppm)= 21.2 [CH2C6H4(CH3)-4], 48.9 [CH2CH2OCH3], 53.54
[CH2C6H4(CH3)-4], 59.2 [CH2CH2OCH3], 71.4 [CH2CH2OCH3], 111.3 and 111.5 [NC6H4N-
o], 123.0 [NC5H5;C3.5], 124.6 [NC6H4N-m], 128.0 [CH2C6H4(CH3)-4;C2,6], 129.5
[CH2C6H4(CH3)-4;C3,5], 131.8 [NC6H4N-i], 134.2 [CH2C6H4(CH3)-4;C4], 136.0
[CH2C6H4(CH3)-4;C1], 137.9 [NC5H5;C4], 152.7 [NC5H5; C2,6], 163.1 [Pd-Ccarb].
HRMS(ESI), m/z=467,1327 [M+2H]+ (calcd for C23H25N3OPd:467,1189); m/z=464,1175 [M-
H]- (calcd for C23H25N3OPd:464,0954).

2.3.5
Dichloro[1-(2-methoxyethyl)-3-(2,3,4,5,6-pentamethylbenzyl)-5,6-
dimethylbenzimidazole-2-ylidene]pyridinepalladium(II), 4a
1
Yield: 81% (0.38 g); m.p. = 206.5 °C. ν(CN)= 1449.03 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.02 [s, 3H, CH2C6(CH3)5-4], 2.15 [s, 6H, CH2C6(CH3)5-3,5], 2.22 [s, 6H,
CH2C6(CH3)5-4 and NC6H2(CH3)2N-5,6], 2.24 [s, 3H, NC6H2(CH3)2N-5,6], 3.30 [s, 3H,
CH2CH2OCH3], 4.12 [t, J = 5.6 Hz, 2H, CH2CH2OCH3], 4.96 [t, J = 5.6 Hz, 2H,
CH2CH2OCH3], 6.04 [s, 2H, CH2C6(CH3)5-2,3,4,5,6], 6.18 and 7.18 [s, 2H, NC6H2(CH3)2N-
5,6], 7.27 [d, J = 8 Hz, 2H, NC5H5-H3,5], 7.70 [t, J = 7.2 Hz, NC5H5-H4], 8.83 [d, J = 8 Hz,
13
2H, NC5H5-H2,6]. C NMR (CDCl3, 100 MHz, δ, ppm): 16.9, 17.2 and 17.5 [CH2C6(CH3)5-
2,3,4,5,6], 20.2 and 20.4 [C6H2(CH3)2], 48.4 [CH2CH2OCH3], 50.4 [CH2C6(CH3)5-2,3,4,5,6],
59.2 [CH2CH2OCH3], 71.9 [CH2CH2OCH3], 111.3 and 111.6 [NC6H2(CH3)2N-o], 124.4
[NC5H5, C3,5], 128.2 and, 131.8 [NC6H2(CH3)2N-i], 133.0 [CH2C6(CH3)5-2,3,4,5,6;C2,6], 133.3
[CH2C6(CH3)5-2,3,4,5,6;C4], 134.1 [NC6H2(CH3)2N-m], 134.8 [CH2C6(CH3)5-2,3,4,5,6;C2,6],
135.7 [NC5H5;C4], 138.0 [CH2C6(CH3)5-2,3,4,5,6;C1], 151.2 [NC5H5;C2,6], 160.9 [Pd-Ccarb].
HRMS(ESI), m/z=494,1506 [M+Na+H]+ (calcd for C24H32N2OPdNa:494,1525).
2.3.6 Dichloro[1-(2-methoxyethyl)-3-(2,4,6-trimethylbenzyl)-5,6-dimethylbenzimidazole-
2-ylidene]pyridinepalladium(II), 4b
1
Yield: 79% (0.35 g); m.p. = 208.9 °C. ν(CN)= 1410.35 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.03 [s, 3H, CH2C6H2(CH3)3-4], 2.21and 2.26 [s, 6H, NC6H2(CH3)2N-5,6] 2.25[s, 6H,
CH2C6H2(CH3)3-2,6], 3.29 [s, 3H, CH2CH2OCH3], 4.13 [t, J = 5.6 Hz, 2H, CH2CH2OCH3],
4.96 [t, J = 5.6 Hz, 2H, CH2CH2OCH3], 6.01 [s, 2H, CH2C6H2(CH3)3-2,4,6], 6.19 [s, 1H,
NC6H2(CH3)2N-5,6], 6.85 [s, 2H, CH2C6H2(CH3)3-2,4,6], 7.19 [s, 2H, NC5H5-H3,5], 7.29 [t,J
= 8.8 Hz, 1H, NC6H2(CH3)2N-5,6], 7.71 [t,J = 8.8 Hz, 1H, NC5H5-H4], 8.89 [d, J = 8.8Hz,
2H, NC5H5-H2,6]. 13C NMR (CDCl3, 100 MHz, δ, ppm): 20.2 and 20.42 [NC6H2(CH3)2N]
20.8 and 21.1 [CH2C6H2(CH3)3-2,4,6], 48.3 [CH2CH2OCH3], 49.5 [CH2C6H2(CH3)3-2,4,6],

59.2 [CH2CH2OCH3], 71.9 [CH2CH2OCH3], 111.4 and 111.5 [NC6H2(CH3)2N-o], 124.4
[NC5H5;C3.5], 127.9 [CH2C6H2(CH3)3-2,4,6;C2,6], 132.0 [NC6H2(CH3)2N-i], 133.0
[NC6H2(CH3)2N-m], 134.2 [CH2C6H2(CH3)3-2,4,6;C4], 138.1 [CH2C6H2(CH3)3-2,4,6;C3,5],
138.2 [NC5H5;C4], 138.9 [CH2C6H2(CH3)3-2,4,6;C1], 151.3 [NC5H5;C2,6], 161.2 [Pd-Ccarb].
HRMS(ESI), m/z=637,5322 [M+2Na]+ (calcd for C27H33Cl2N3OPdNa2:637,0831);
m/z=489,1196 [M+2Na+H]+ (calcd for C22H28N2OPdNa2:489,1110); m/z=468,1246
[M+Na+H]+ (calcd for C22H28N2OPdNa:468,1217).
2.3.7 Dichloro[1-(2-methoxyethyl)-3-(3,5-dimethylbenzyl)-5,6-dimethylbenzimidazole-2-
ylidene]pyridinepalladium(II), 4c
1
Yield: 87% (0.33 g); m.p. =233.5 °C. ν(CN)= 1445.47 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 2.23 and 2.33 [s, 6H, NC6H2(CH3)2N-5,6], 2.28 [s, 6H, CH2C6H3(CH3)2-3,5], 3.39 [s,
3H, CH2CH2OCH3], 4.22 [t, J = 5.6 Hz, 2H, CH2CH2OCH3], 5.01 [t, J = 5.6 Hz, 2H,
CH2CH2OCH3], 5.95 [s, 2H, CH2C6H3(CH3)2-3,5], 6.85 [m, 1H, NC6H2(CH3)2N-5,6], 6.93 [s,
1H, NC6H2(CH3)2N-5,6], 7.20 and 7.30 [s, 3H, CH2C6H3(CH3)2-3,5], 7.33 [m, 2H, NC5H5-
H3,5], 7.76 [m, 1H, NC5H5-H4], 9.02 [m, 2H, NC5H5-H2,6]. 13C NMR (CDCl3, 100 MHz, δ,
ppm): 20.4 [NC6H2(CH3)2N], 21.3 [CH2C6H3(CH3)2-3,5], 48.6 [CH2CH2OCH3], 53.2
[CH2C6H3(CH3)2-3,5], 59.2 [CH2CH2OCH3], 71.4 [CH2CH2OCH3], 111.4 and 111.6
[NC6H2(CH3)2N-o], 124.5 [NC5H5;C3,5], 125.8 [CH2C6H3(CH3)2-3,5;C2,6], 129.7
[CH2C6H3(CH3)2-3,5;C4], 132.1, 133.0 [NC6H2(CH3)2N-i], 134.5 [NC6H2(CH3)2N-m], 135.0
[CH2C6H3(CH3)2-3,5;C1], 137.9 [NC5H5;C4], 138.3 [CH2C6H3(CH3)2-3,5;C3,5], 151.7
[NC5H5;C2,6], 160.8 [Pd-Ccarb]. HRMS(ESI), m/z=1102,3491 [2M+4Na]+ (calcd for
C52H58N6O2Pd2Na4:1102,2282); m/z=507,0180 [M]+ (calcd for C26H31N3OPd:507,1502);
m/z=509,0369 [M+2H]+ (calcd for C26H31N3OPd:509,1506).

2.3.8
Dichloro[1-(2-methoxyethyl)-3-(4-methylbenzyl)-5,6-dimethylbenzimidazole-2-
ylidene]pyridinepalladium(II), 4d
1
Yield: 75% (0.31 g); m.p. = 225.6 °C. ν(CN)= 1445.91 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm):2.21 [s, 3H, CH2C6H4(CH3)-4], 2.25 [s, 6H, NC6H2(CH3)2N-5,6], 3.32 [s, 3H,
CH2CH2OCH3], 4.14 [t, J = 6 Hz, 2H, CH2CH2OCH3], 4.95 [t, J = 6 Hz, 2H, CH2CH2OCH3],
6.04 [s, 2H, CH2C6H4(CH3)-4], 7.10 [m, 2H, CH2C6H4(CH3)-4], 7.19 and 7.22 [s, 1H,
NC6H2(CH3)2N-5,6], 7.36 [m, 2H, CH2C6H4(CH3)-4], 7.40 [m, 2H, NC5H5-H3,5], 7.68 [m,
1H, NC5H5-H4], 8.96 [m, 2H, NC5H5-H2,6]. 13C NMR (CDCl3, 100 MHz,δ, ppm): 20.3
[NC6H2(CH3)2N], 21.2 [CH2C6H4(CH3)-4], 48.5 [CH2CH2OCH3], 53.0 [CH2C6H4(CH3)-4],
59.2 [CH2CH2OCH3], 71.6 [CH2CH2OCH3], 111.5 and 111.6 [NC6H2(CH3)2N-o], 124.5
[NC5H5;C3.5], 127.9 [CH2C6H4(CH3)-4;C2,6], 129.5 [CH2C6H4(CH3)-4;C3,5], 132.2 and 132.7
[NC6H2(CH3)2N-i], 134.5 [NC6H2(CH3)2N-m], 138.0 [CH2C6H4(CH3)2-4;C4], 151.29
[CH2C6H4(CH3)-4; C1], 152.1 [NC5H5; C4], 152.7 [NC5H5;C2,6], 161.0 [Pd-Ccarb].
HRMS(ESI), m/z=560,3253 [M-3H]- (calcd for C25H29N3OPdCl2:560,0488); m/z=415,0857
[M+H]+ (calcd for C20H24N2OPd:415,1002); m/z=440,0926 [M+Na+2H]+ (calcd for
C20H24N2OPdNa:440,1056).
2.3.9 Dichloro[1-(2-methoxyethyl)-3-(4-tert-buthylbenzyl)-5,6-dimethylbenzimidazole-2-
ylidene]pyridinepalladium(II), 4e
1
Yield: 79% (0.30 g); m.p. = 174.8 °C. ν(CN)= 1448.41 cm-1. H NMR (CDCl3, 400 MHz, δ,
ppm): 1.22 [s, 9H, CH2C6H4(C(CH3)3)-4], 2.15 and 2.25 [s, 6H, NC6H2(CH3)2N-5,6], 3.31 [s,
3H, CH2CH2OCH3], 4.15 [t, J = 6 Hz, 2H, CH2CH2OCH3], 4.96 [t, J = 6 Hz 2H,
CH2CH2OCH3], 5.99 [m, 2H, CH2C6H4(C(CH3)3)-4], 6.76 [m, 1H, NC6H2(CH3)2N-5,6], 7.23
[s, 1H, NC6H2(CH3)2N-5,6],7.19 [s, 1H, CH2C6H4(C(CH3)3)-4], 7.26-7,45 [m, 4H,
CH2C6H4(C(CH3)3)-4, NC5H5-H4], 7.43 [d, J = 8.4 Hz, 2H, NC5H5-H3,5], 8.96 [m, 2H,
NC5H5-H2,6].13C NMR (CDCl3, 100 MHz,δ, ppm): 20.2 [NC6H2(CH3)2N], 31.3

[CH2C6H4(C(CH3)3)-4], 34.6 [CH2C6H4(C(CH3)3)-4], 48.5 [CH2CH2OCH3], 52.9
[CH2C6H4(C(CH3)3)-4], 59.2 [CH2CH2OCH3], 71.6 [CH2CH2OCH3], 111.5 and 111.6
[NC6H2(CH3)2N-o], 124.5 [NC5H5;C3.5], 125.7 [CH2C6H4(C(CH3)3)-4; C3,5], 127.9
[CH2C6H4(C(CH3)3)-4;C2,6], 132.2 and 132.8 [NC6H2(CH3)2N-i], 134.5 [NC6H2(CH3)2N-m],
138.0 [CH2C6H4(C(CH3)3)-4;C1], 151.3 [NC5H5;C4], 152.1 [CH2C6H4(C(CH3)3)-4;C4], 152.7
[NC5H5; C2,6], 161.0 [Pd-Ccarb]. HRMS(ESI), m/z=455,1254 [M-H]- (calcd for
C23H30N2OPd:455,1315).
2.4 General Procedure for Suzuki-Miyaura Reactions
In air, Pd-PEPPSI complex (0.5 mol %), aryl bromide (1.0 mmol), phenylboronic acid (1.2
mmol), K2CO3 (1 mmol), and 4 mL of water/i-PrOH (3:1 v/v) were added to a small round
bottom flask and the mixture stirred appropriate time. The reaction mixture was extracted
with Et2O. Products were purified by column chromatography using ethylacetate/hexane
(0.5:9.5 v/v). All coupling products obtained via Suzuki-Miyaura coupling reactions are
previously reported compounds, and were identified by comparison of our data with that
available in the literature.
3. Results and Discussion
3.1 Materials and methods
Our strategy was based on the construction of the N-heterocyclic carbene precursors bearing a
methoxyethyl which is grouped on the side chain to increase solubility in water as well as in
electron density of palladium complexes (Scheme 1). To do so, new unsymmetrical 1-
methoxyethyl-3-arylbenzimidazolium that based on precursors (1a-d and 2a-e) were prepared
according to literature.[29,35-36] Thus, the structure of 1a-d and 2a-e is shown in Scheme 1 and
the 1c, 2c and 2e compounds were also synthesised as the bromide salts due to corresponding
aryl halides which commercially available on bromides form. Concerning the treatment of 1-

(2-methoxyethyl)benzimidazole with 1.2 equivalents, it yields of different aryl halides in
o
DMF at 70 C led to the formation of corresponding NHC precursors in 74-92% yields. The
1
NHC precursors were fully characterized by H and 13C NMR, IR and elemental analysis.
1
However, the assigned structures for the NHC precursors are supported by the H NMR
spectra where the resonances for C2-H (carben carbon= C2) were observed as sharp singlet
signals at 10.96, 11.06, 11.40, 11.24, 10.01, 10.81, 11.05, 11.23 and 11.27 ppm, respectively,
for 1a-d and 2a-e. The 13C NMR data also supports the assigned structures of the NHC
precursors by C2 chemical shifts that come to resonance at 143.0, 143.7, 142.6, 143.0, 141.4,
142.3, 141.8, 141.7 and 141.8 ppm, respectively, for 1a-d and 2a-e.
Scheme 1. Synthesis of NHC precursors.
The Pd-PEPPSI complexes 3a-d and 4a-e were synthesized according to literature reported
by Organ (Scheme 2);24 and the reaction of NHC precursors with PdCl2 in pyridine at 80 oC in
the presence of excess of K2CO3 afforded the palladium PEPPSI complexes 3a-d and 4a-e in
75-88% yields.
Finally, all complexes were purified by crystallization using dichloromethane DCM/hexane
1
13
1
(1:2) and characterized by H and C NMR, HRMS and IR. For the H NMR spectra of the
palladium-NHC-PEPPSI complexes 3a-d, and 4a-e, sharp peaks in the lower field region

belonging to the acidic imino proton of benzimidazolium salts (NCHN) were not observed
between δ=10.0-12.0 ppm. Similarly, in the 13C NMR spectra, imino carbon of
benzimidazolium salts (NCHN) were not observed between δ=150-155 ppm. In the 1 H NMR
13
and C NMR spectra of the complexes 3a-d, and 4a-e, loss of the characteristic peak of the
acidic imino proton (NCHN) and imino carbon (NCHN), signal suggests the formation of the
palladium-NHC-PEPPSI complexes. The 13C{1H} N-C-N signals of 1a-c and 2a-c, which are
respectively equal to 143.0, 143.7, 142.6, 143.0, 141.4, 142.3, 141.8, 141.7 and 141.8 ppm
were shifted to 163.3, 163.5, 163.4, 163.1, 160.9, 161.2, 160.8, 161.0 and 161.0 ppm,
respectively, in 3a-d and 4a-e.
Scheme 2. Synthesis of Pd-PEPPSI complexes.
3.2 Suzuki-Miyaura cross-coupling reaction

As know from the literature, water and alcohol took very important place as solvent in the
Suzuki-Miyaura reactions. [29,34,37-41a-h]
Table 1. The optimization for the Suzuki-Miyaura reaction of 4-bromoanisolea
aEntry
1
Solvent
i-PrOH/H2O(1:3)
i-PrOH/H2O(1:3)
i-PrOH/H2O(1:3)
i-PrOH/H2O(1:3)
i-PrOH/H2O(1:3)
i-PrOH
Base
K2CO3
Na2CO3
Cs2CO3
K3PO4
KOH
Yield(%)b
80
58
2
48
3
59
4
49
5
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
75
6
H2O
45
7
DMF
53
8
EtOH
69
9
MeOH
68
10
11
12
13
14
15
16c
17d
Acetone
45
i-PrOH/H2O(1:1)
DMF/H2O(1:3)
EtOH/H2O(1:3)
MeOH/H2O(1:3)
i-PrOH/H2O(1:3)
i-PrOH/H2O(1:3)
78
49
57
50
78
65
aReaction Condition:1 mmol of 4-bromoanisole, 1.2 mmol of phenylboronic acid, 1 mmol of
base, 0,5 mol% 3a, 4 mL solvent, room temperature, 1 hour. Yields are the average of the two

runs. b Isolated yield. c Reaction performed under nitrogen atmosphere. d 3a used as catalyst,
room temperature, 1.5 h
To study the efficiency of the palladium-NHC complexes 3a-d and 4a-e in Suzuki-Miyaura
coupling reactions, we first studied the impact of the solvent and volume ratio. Then, the
cross-coupling of 4-bromoanisole (1 mmol) with phenylboronic acid (1.2 mmol) in 4 mL i-
PrOH/H2O (1:3 v/v) under air was selected as a model reaction with 3a (0.5 mol%) and
K2CO3 (1 mmol) at room temperature in air (Table 1). In the literature, water soluble
inorganic bases have been conveniently used in Suzuki-Miyaura cross-coupling reactions in
aqueous media. [29,34] Thus, the first survey of this study was screening the performance of
different inorganic bases in i-PrOH/H2O (1:3 and 1:1 v/v). Different bases led to different
activity in the present protocol for Suzuki reactions (Table 1, entries 1-5) but the most
efficient base in this condition is K2CO3, which provides a 80% isolated yield in 1h.
Comparatively, lower yields were obtained with other bases (Table 1). Therefore, we think
that this catalytic differentiation is caused by better solubility of potassium carbonate in
water.When single type of solvent such as H2O, EtOH, MeOH, DMF or i-PrOH used, lower
coupling product took place compared to product obtained via i-PrOH/H2O (1:3) solvent
system (Table 1, entries 6-11). Different solvent mixtures such as EtOH/H2O, DMF/H2O, and
MeOH/H2O (1:3 v/v), were led to lower cross-coupling product (Table 1, entries 13-15).
Morever, single type solvent and solvent/H2O mixtures (except isopropanol) led to lower
yield are also observed. This may be attributed to low solubility of base in single type solvent
as shown in (Table 1, entries 7-11) or low solubility of complex in too polar solvent or
solvent/H2O mixtures (Table 1, entries 7-15). As a result of the optimisation experiments, a
very good yield (80%) was obtained with i-PrOH/H2O (1:3 and 1:1 v/v) solvent system in
open air (Table 1, entries 1 and 12). Hence, we selected 1:3 ratio for obtaining good yields.
We are quite satisfied to report that 1-2% undesired homo-coupling product was observed in

optimization of Suzuki the coupling reaction proceeding at room temperature in open air.
Additionally, this protocol also compared to the reaction performed under nitrogen
atmosphere and the results showed that there is not any significance difference among the
yields obtained from reaction under nitrogen atmosphere (Table 1, entry 16). To show how
importance of the methoxy chain, we compared the activity of the 4c with a very similar
complex which is not bear a methoxy chain. The palladium complex which N,N-substituted
with 3,5 dimethyl benzyl group is already synthesised and published[41h] by our group (See the
paper for 3a compound). From our previous study, this complex tested in different conditions
but totally needs temperature to catalyse Suzuki coupling reaction of aryl bromides. The
reaction of complex 3a in the same catalytic condition gives lower yields in longer time at
room temperature (Table 1, entry 17). From these results, it is clear that a methoxy chain is
very important for the increase solubility of the complexes 3a-d and 4a-e.
To evaluate the scope our catalytic system, different aryl bromides were examined (Table 2).
As shown in Table 2, both electron-donating and electron-withdrawing groups bearing aryl
bromides effectively afford the corresponding products (61-97 %) in short time at room
temperature (Table 2, entries 1-6). For example, 4-bromoacetophenone afforded a good yield
in 10 min, resulting in a TOF of 1000 h-1 (Table 2, entry 2). However, -CH3 and -OCH3
Table 2. Catalytic activities of 3a-d and 4a-e complexes in the Suzuki-Miyaura coupling
reactions under optimized conditions.a
[Pd-NHC]/yield (%)b
Entry
Product
3a
3b
3c
3d
4a
4b
4c
4d
4e
1
80
82
75
54
72
93
68
88
78

2c
3
96
80
66
88
67
71
91
52
74
87
51
54
89
57
65
95
89
86
93
57
72
77
77
63
85
57
86
4
5c
6c
7d
8e
9
94
90
98
-
96
81
95
-
85
83
92
-
88
74
94
-
91
90
96
-
96
92
98
-
88
86
95
-
91
84
98
-
96
87
98
-
trace trace trace trace trace trace trace trace trace
areaction condition: 0.5 mol٪[Pd-NHC], 1 mmol p-R-C6H4Br, 1.1 mmol phenylboronic acid,
1.0 mmol K2CO3, rt, 1h. Yields are average of two runs.
b Isolated yield
c10 min.
d 1 mol%[Pd-NHC]
e 1 mmol 4-(OCH3)-C6H4Cl
substituted aryl bromides showed slightly lower activity than –NO2, and -COCH3 substituted
aryl bromides due to the high nuclophilicity of the electron donating substituents (Table 2,
entries 1,3). However, increasing the catalyst loading up to 1 mol% resulted in an increased
yield (98%) (Table 2, entry 7). Catalyst 4b and others did not show any activity when 4-
chloro anisole used as substrate (Table 2, entry 8). Trace amount products were observed with
4-chloroacetophenon used as substrate (Table 2, entry 9). This low catalytic activity of
complexes with 4-chloroaryl substrates may be attribute to low oxidative addition rate of aryl
chlorides to palladium(0) in this catalytic conditions. When the catalytic activities of the
complexes 3a-d and 4a-e are compared among themselves, the complex 4b has showed
slightly higher catalytic activity, independent from the nature of the substrate. It may be due

to well-balanced electronic and steric properties of 4b than other complexes. All tested
complexes have similar steric bulky. Thus, we think that electronic properties of the
complexes are more prevalent than steric parameters of the complexes. Also, this catalytic
system is almost equally effective for electronically rich and poor aryl bromides. Thus, our
study is pretty significant for the production of coupled product at room temperature in very
short time using green solvents with low catalyst loading (0.5 mol%) without need to any
additives such as NaX, NaSO4 etc.
These new catalysts have a different and superior advantage. The presence of a NHC
ligand bearing a second different donating group such as –OCH3 on the metal may radically
increase the catalytic performance of catalyst. The chelating nature of these ligands promote
[41i-k]
production of highly stable complexes.
The hemilable part in 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 center.
To compare the catalytic activity of our system with existing catalysts, there are a few
reports in the literature on Suzuki-Miyaura cross-couplings of aryl bromides running in our
[42-49]
catalyst system.
When considering the amount of catalyst, time, temperature and
solvent, the yield is better than the literature by our catalyst system. [41] It is believed that this
performance is due to the presence of a second donor group on the catalyst that mentioned
above. However, there are more effective catalyst reported on literature for Suzuki cross-
coupling reaction of aryl chlorides or bromides.
4. Conclusion
In summary, new palladium-NHC complexes bearing a methoxyethyl on the side chain have
been synthesised and characterised by different spectroscopic techniques. The catalytic
reactivity of these complexes in Suzuki-Miyaura cross-coupling reactions with aryl bromides

at room temperature in aqueous media. Among these complexes, complex 4b exhibited good
catalytic performance with different types of aryl bromides when other complexes showed
lower catalytic activity. The catalyst system described here has several advantages including
low catalyst loading, substrate tolerance, very good yields, room temperature, green solvents,
short reaction times and very simple procedure. These results represent a significant
improvement in the field of the C-C bond formation reactions.
Acknowledgements
This project was supported by İnönü University Research Fund (BAP:2016-195). We are also
grateful to the Technological and Scientific Research Council of Turkey TUBİTAK-
MHESRS (Tunisia) for the financial support to NedraTouj.
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Highlights
 New N-heterocyclic carben ligands bearing methoxyethyl on the side chain have been
synthesized.
 New palladium- NHC-pyridine complexes have been synthesized.
 palladium- NHC-pyridine complexes performed lovely catalytic activity at room
temperature in open air.
 With this catalyse system aryl bromides arylated under mild reaction condition.