Catalytic activities in the direct C5 arylation of novel palladium N-heterocyclic carbene complexes containing benzimidazol-2-ylidene nucleus

Article abstract of DOI:10.1016/j.ica.2014.01.015

New palladium N-heterocyclic carbene (NHC) complexes (1a-e) were synthesized in very good yields by the reaction of 1-phenyl-3- alkylbenzimidazolium salts with Pd(OAc)₂ in dimethyl sulfoxide. These synthesized complexes were fully characterized

Full text of DOI:10.1016/j.ica.2014.01.015

Inorganica Chimica Acta 413 (2014) 221–230
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Catalytic activities in the direct C5 arylation of novel palladium
N-heterocyclic carbene complexes containing benzimidazol-2-ylidene
nucleus
b
c
d
Senem Akkoç a, , Yetkin Gök , Mehmet Akkurt , Muhammad Nawaz Tahir
⇑
a Faculty of Science, Department of Chemistry, Erciyes University, 38039 Kayseri, Turkey
b Faculty of Science and Arts, Department of Chemistry, Inönü University, 44280 Malatya, Turkey
c Faculty of Science, Department of Physics, Erciyes University, 38039 Kayseri, Turkey
d Faculty of Science, Department of Physics, Sargodha University, Sargodha, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2013
Received in revised form 5 January 2014
Accepted 6 January 2014
Available online 30 January 2014
New palladium N-heterocyclic carbene (NHC) complexes (1a–e) were synthesized in very good yields by
the reaction of 1-phenyl-3-alkylbenzimidazolium salts with Pd(OAc)2 in dimethyl sulfoxide. These syn-
thesized complexes were fully characterized using elemental analyses, FT-IR, 1H NMR, 13C NMR and
LC–MS (for 1a, 1c and 1e) spectroscopy data. Also, the molecular structure of the bis[1-phenyl-3-(2-
methyl-1,4-benzodioxane)benzimidazol-2-ylidene]dibromopalladium(II) complex (1d) was structurally
characterized by single crystal X-ray diffraction study. The new PdII complexes (1a–e) were tested as cat-
alysts in the direct C5 arylation of 2-n-butylfuran, 2-n-butylthiophene and 2-n-propylthiazole with var-
ious aryl bromides at 130 °C for 1 h. Also, some experiments were carried out by using aryl chlorides in
order to be used for comparison. The results are reported herein. These complexes exhibited quite high
catalytic activities under the given conditions.
Keywords:
N-heterocyclic carbene
PdII complexes
Direct arylation
Single crystal structure
Aryl bromides
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
palladium catalysts are usually relatively inefficient. Therefore,
we synthesized Pd-NHC complexes to find more efficient cata-
Metal N-heterocyclic carbene (NHC) complexes display perfect
catalytic activities for various useful organic transformations such
as C–H bond activation, C–C and C–N cross-coupling reactions
[1–15]. Among the metal–NHC complexes, Pd-NHC complexes
have been used for certain purposes such as for catalysis and for
their biological activity as anticancer agents [4,16]. Two
approaches to perform a coupling reaction are available to gener-
ate a catalytically active species: (i) a Pd0 source combined with
an ancillary ligand to generate the catalyst in situ is employed
[17,18] and (ii) PdII complexes are mostly used as precatalysts
[19]. The Pd-NHC complexes are prepared simply both by means
of diverse salts with Pd(OAc)2 and by Ag-NHC complexes with
PdCl2(PhCN)2 or PdCl2(CH3CN)2. In the formation of palladium-
carbene, various palladium compounds can be employed, like
PdCl2 [4,20], Pd(OAc)2 [4,21–23], PdCl2(PhCN)2 [4,24] and
PdCl2(CH3CN)2 [13,25]. Among them, palladium acetate is the most
commonly used.
lysts for the direct 5-arylation of 2-n-propylthiazole, 2-n-butylfu-
ran and 2-n-butylthiophene with various aryl halides. The
catalytic activities of the synthesized PdII complexes were found
to be very high. These complexes were fully characterized
by means of elemental analyses, 1H NMR, 13C NMR, LC–MS
(for 1a, 1c and 1e) and FT-IR spectroscopies. Also, the crystal
structure of the bis[1-phenyl-3-(1,4-benzodioxane-2-methyl)
benzimidazol-2-ylidene]dibromopalladium(II) complex (1d) is re-
ported here.
2. Experimental
2.1. Materials and methods
For the preparation of 1a–e, all reactions were carried out under
argon in flame–dried glassware using standard Schlenk-type flasks
and standard high vacuum-line techniques. Solvents such as
dichloromethane and diethyl ether were of analytical grade. Prior
to their use, they were dried under P4O10 and Na in an inert atmo-
sphere, respectively. All reagents were purchased from Aldrich,
Fluka and Merck. All 1H NMR and 13C NMR analyses were
In the case of direct arylation of heteroaromatics by using
challenging aryl bromides, it was observed that ‘‘ligandless’’
⇑
Corresponding author. Tel.: +90 352 437 52 62; fax: +90 352 437 49 33.
E-mail address: senemakkoc@erciyes.edu.tr (S. Akkoç).
http://dx.doi.org/10.1016/j.ica.2014.01.015
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

222
S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
performed in CDCl3 and DMSO. The 1H NMR and 13C NMR spectra
were recorded by using a Bruker AC300P FT spectrometer operat-
ing at 300.13 MHz (1H) and 75.47 MHz (13C). Chemical shifts (d)
were given in ppm according to relative tetramethylsilane. The
coupling constants (J) were given in Hz. The FT-IR spectra were
recorded on a Mattson 1000 spectrophotometer and wave num-
bers were recorded in cmÀ1. LC–MS analyses of Pd-NHC complexes
were made using an Agilent Technologies 1100 Series LC mass
spectrometer. Melting points were measured in open capillary
tubes with an Electrothermal-9200 melting point apparatus.
Elemental analyses were performed by the Technological and
Scientific Research Council of Turkey Microlab.
imidazolium salt (0.31 g, 0.89 mmol) and Pd(OAc)2 (0.1 g,
0.45 mmol) in dimethyl sulfoxide (3–4 mL). Yield: 82%; m.p.
320–321 °C. 1H NMR (300.13 MHz, CDCl3, 25 °C, TMS): d = 5.32
(d, J: 10.86 Hz, 4 H, C6H4CHCH2); 5.82 (s, 4 H, NCH2C6H4CHCH2);
6.77 (m, 2 H, C6H4CHCH2); 7.14–8.02 (m, 26 H, Ar–H). 13C NMR
(75.47 MHz, CDCl3, 25 °C, TMS): d = 53.8 (C6H4CHCH2); 108.5
(NCH2C6H4CHCH2); 110.8 (C6H4CHCH2); 111.1, 123.4, 126.7,
127.5, 128.1, 129.1, 135.1, 137.3 and 137.7 (Ar–C); 181.2 (2-C).
FT-IR m(NCN)
: . Anal. Calc. for C44H36N4PdCl2: C,
1597.34 cmÀ1
66.22; H, 4.55; N, 7.02. Found: C, 66.29; H, 4.47; N, 7.00%.
2.1.3. Bis1-phenyl-3-(phthalimido-N-propyl)benzimidazol-2-ylidene]-
dibromopalladium(II), 1c
2.1.1. Bis[1-phenyl-3-(2-morpholinoethyl)benzimidazol-2-ylidene]-
dichloropalladium(II), 1a
1c compound, with a method similar to the one used in 1a
compound, was prepared from 1-phenyl-3-(phthalimido-N-
propyl)benzimidazolium salt (0.38 g, 0.9 mmol) and Pd(OAc)2
(0.1 g, 0.45 mmol) in dimethyl sulfoxide (3–4 mL). Yield: 85%;
m.p. 330–331 °C. 1H NMR (300.13 MHz, CDCl3, 25 °C, TMS):
d = 2.64, 3.69 and 4.97 (m, 12 H, NCH2CH2CH2N); 7.25–7.83
(m, 26 H, Ar–H). 13C NMR (75.47 MHz, CDCl3, 25 °C, TMS):
d = 26.7, 35.6 and 45.7 (NCH2CH2CH2N); 111.1, 123.4, 123.8,
124.1, 129.5, 132.1, 132.8, 134.2, 134.8 and 136.9 (Ar–C); 168.2
1-Phenyl-3-(2-morpholinoethyl)benzimidazol-2-ylidene
salt
(0.309 g, 0.9 mmol) and Pd(OAc)2 (0.1 g, 0.45 mmol) in dimethyl
sulfoxide (3–4 mL) were heated at 60 °C for 24 h, and then at
110–120 °C for 1 h. The solvent (DMSO) was then removed under
reduced pressure. The crude product was crystallized from dichlo-
romethane-hexane (2:1) at room temperature. The crystals were
filtered, washed with diethyl ether (3 Â 10 mL) and dried under
vacuum. Yield: 86%; m.p. 255–256 °C. 1H NMR (300.13 MHz,
DMSO, 25 °C, TMS): d = 2.47 [t, J: 4.0 Hz, 8 H, NCH2CH2N(CH2CH2)2-
O]; 2.87 (t, J: 6.6 Hz, 4 H, NCH2CH2NC4H8O); 3.68 [t, J: 4.0 Hz, 8 H,
NCH2CH2N(CH2CH2)2O]; 4.69 (t, J: 6.6 Hz, 4 H, NCH2CH2NC4H8O);
7.11–8.03 (m, 18 H, Ar–H). 13C NMR (75.47 MHz, DMSO, 25 °C,
TMS): d = 45.9, 54.0 and 57.8 (NCH2CH2NC4H8O); 67.1 (NCH2CH2
NC4H8O); 111.1, 123.2, 127.3, 128.1, 128.7, 129.4, 134.6, 135.3
(C@O); 173.0 (2-C). FT-IR
48H38N6O4 PdBr2 m/z: 1029.08; found (L2PdBr2-Br): 949.1. Anal.
m
(NCN): 1596.32 cmÀ1. LC–MS calcd. for
C
Calc. for C48 H38N6O4PdBr2: C, 56.02; H, 3.72; N, 8.17. Found: C,
56.11; H, 3.68; N, 8.15%.
2.1.4. Bis1-phenyl-3-(1,4-benzodioxano-2-methyl)benzimidazol-2-yli-
dene]dibromopalladium(II), 1d
and 137.9 (Ar–C); 181.7 (2-C). FT-IR
calcd. for 38H42N6O2PdCl2: m/z: 792.11; found (L2PdCl2-Cl):
m
(NCN): 1597.45 cmÀ1. LC–MS
1d compound, with a method similar to the one used in 1a com-
pound, was prepared from 1-phenyl-3-(1,4-benzodioxano-2-
methyl)benzimidazolium salt (0.34 g, 0.9 mmol) and Pd(OAc)2
(0.1 g, 0.45 mmol) in dimethyl sulfoxide (3–4 mL). Yield: 89%;
m.p. 328–329 °C. 1H NMR (300.13 MHz, CDCl3, 25 °C, TMS):
d = 3.57 (m, 4 H, NCH2CHCH2O2C6H4); 4.74 (m, 2 H, NCH2CHCH2O2
C6H4); 4.85 (m, 4 H, NCH2CHCH2O2C6H4); 6.99–7.74 (m, 26 H,
Ar–H). 13C NMR (75.47 MHz, CDCl3, 25 °C, TMS): d = 48.7, 65.7
and 71.9 (NCH2CHCH2O2C6H4); 111.0, 111.6, 117.4, 121.8, 123.6,
C
757.1. Anal. Calc. for C38H42N6O2PdCl2: C, 57.62; H, 5.34; N,
10.61. Found: C, 57.68; H, 5.25; N, 10.63%.
2.1.2. Bis1-phenyl-3-(4-vinylbenzyl)benzimidazol-2-ylidene]dichloro-
palladium(II), 1b
1b compound, with a method similar to the one used in 1a
compound, was prepared from 1-phenyl-3-(4-vinylbenzyl)benz-
Fig. 1. Molecular structure of 1d with displacement ellipsoids drawn at the 20% probability level.

S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
223
Fig. 2. The molecular packing of 1d viewed down the a-axis.
128.8, 129.6, 134.7, 136.1, 137.5, 142.4 and 143.3 (Ar–C); 182.1 (2-C).
FT-IR
(NCN): 1594.49 cmÀ1. Anal. Calc. for C44H36N4O4PdBr2: C,
2.2. General procedure for the direct C5 arylations
m
55.57; H, 3.82; N, 5.89. Found: C, 55.65; H, 3.75; N, 5.90%.
The heteroaryl derivative (2 mmol), aryl halide (1 mmol), Pd
complexes 1a–e (0.005 mmol), KOAc (1 mmol) and DMAc (2 mL)
were added into a Schlenk tube equipped with a magnetic stirring
bar. The Schlenk tube was purged several times with argon and
was placed in a preheated oil bath at 130 °C. The reactants were
stirred for 1 h (with aryl bromides) and for 20 h (with aryl chlo-
rides). The solvent was removed by heating the reaction vessel
under vacuum. The products were eluted by using an appropriate
ratio of diethyl ether/pentane (1:3). The reaction mixture was
purified by flash chromatography on silica gel. The purity of
compounds was checked by GC and NMR. Yields were based on
aryl halides (aryl bromide and aryl chloride).
2.1.5. Bis1-phenyl-3-naphthalenomethylbenzimidazol-2-ylidene]-
dichloropalladium(II), 1e
1e compound, with a method similar to the one used in 1a com-
pound, was prepared from 1-phenyl-3-naphthalenomethylbenz-
imidazolium salt (0.33 g, 0.9 mmol) and Pd(OAc)2 (0.1 g,
0.45 mmol) in dimethyl sulfoxide (3–4 mL). Yield: 83%; m.p.
294–295 °C. 1H NMR (300.13 MHz, CDCl3, 25 °C, TMS): d = 6.25
(s,
4
H, NCH2C10H7); 6.47–8.30 (m, 32 H, Ar–H). 13C NMR
(75.47 MHz, CDCl3, 25 °C, TMS): d = 49.5 (NCH2C10H7); 111.1,
112.5, 123.4, 123.8, 125.6, 125.9, 126.6, 127.3, 128.3, 128.8,
129.2, 130.6, 133.4, 133.7, 134.1, 135.2, 137.2 (Ar–C); 182.9 (2-C).
FT-IR
m
(NCN): 1500.08 cmÀ1. LC–MS calcd. for C48H36N4PdCl2 m/z:
2.2.1. 2-Acetophenyl-5-n-propylthiazole (2)
846.15; found (L2PdCl2-Cl): 811.2. Anal. Calc. for C48H36N4PdCl2:
C, 68.13; H, 4.29; N, 6.62. Found: C, 68.21; H, 4.35; N, 6.64%.
Corresponding product 2 was obtained in 85%, 51%, 50%, 88%
and 81% conversions by the reaction of 2-n-propylthiazole

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S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
N
PdBr2
N
2
O
N
N
PdCl2
N
N
N
2
1c
PdBr2
2
O
O
1b
CH=CH2
1d
O
N
X-
N
N
N
N
i) Pd(OAc)2
ii) DMSO
PdCl2
N
PdCl2
N
2
2
O
R
1a
1e
Scheme 1. The synthesis of [1-phenyl-3-alkylbenzimidazol-2-ylidene]dihalidepalladium(II) complexes (1a–e).
(0.26 g, 2 mmol), 4-bromoacetophenone (0.2 g, 1 mmol), KOAc
(0.28 g, 2 mmol), 4-bromoanisole (0.19 g, 1 mmol), KOAc (0.1 g,
(0.1 g, 1 mmol) and 1a–e (0.005 mmol).
1 mmol) and 1a–e (0.005 mmol).
2.2.2. 2-(4-Methoxyphenyl)-5-n-propylthiazole (3)
2.2.7. 2-(4-Methylphenyl)-5-n-butylthiophene (8)
Corresponding product 3 was obtained in 100%, 79%, 94%, 100%
and 100% conversions by the reaction of 2-n-propylthiazole (0.26 g,
2 mmol), 4-bromoanisole (0.19 g, 1 mmol), KOAc (0.1 g, 1 mmol)
and 1a–e (0.005 mmol).
Corresponding product 8 was obtained in 94%, 80%, 97%, 99%
and 96% conversions by the reaction of 2-n-butylthiophene
(0.28 g, 2 mmol), 4-bromotoluene (0.17 g, 1 mmol), KOAc (0.1 g,
1 mmol) and 1a–e (0.005 mmol).
2.2.3. 2-(4-Methylphenyl)-5-n-propylthiazole (4)
2.2.8. 2-Phenyl-5-n-butylthiophene (9)
Corresponding product 4 was obtained in 100%, 61%, 94%, 100%
and 81% conversions by the reaction of 2-n-propylthiazole (0.26 g,
2 mmol), 4-bromotoluene (0.17 g, 1 mmol), KOAc (0.1 g, 1 mmol)
and 1a–e (0.005 mmol).
Corresponding product 9 was obtained in 85%, 71%, 62%, 93%
and 88% conversions by the reaction of 2-n-butylthiophene
(0.28 g, 2 mmol), bromobenzene (0.16 g, 1 mmol), KOAc (0.1 g,
1 mmol) and 1a–e (0.005 mmol).
2.2.4. 2-Phenyl-5-n-propylthiazole (5)
2.2.9. 2-n-Butyl-5-acetophenylfuran (10)
Corresponding product 5 was obtained in 100%, 66%, 96%, 86%
and 89% conversions by the reaction of 2-n-propylthiazole
(0.25 g, 2 mmol), bromobenzene (0.16 g, 1 mmol), KOAc (0.1 g,
1 mmol) and 1a–e (0.005 mmol).
Corresponding product 10 was obtained in 97%, 92%, 100%, 74%
and 79% conversions by the reaction of 2-n-butylfuran (0.25 g,
2 mmol), 4-bromoacetophenone (0.2 g, 1 mmol), KOAc (0.1 g,
1 mmol) and 1a–e (0.005 mmol).
2.2.5. 2-n-Butyl-5-acetophenylthiophene (6)
2.2.10. 2-n-Butyl-5-(4-methoxyphenyl)furan (11)
Corresponding product 6 was obtained in 98%, 100%, 99%, 91%
and 96% conversions by the reaction of 2-n-butylthiophene
(0.27 g, 2 mmol), 4-bromoacetophenone (0.2 g, 1 mmol), KOAc
(0.1 g, 1 mmol) and 1a–e (0.005 mmol).
Corresponding product 11 was obtained in 92%, 54%, 87%, 86%
and 70% conversions by the reaction of 2-n-butylfuran (0.25 g,
2 mmol), 4-bromoanisole (0.19 g, 1 mmol), KOAc (0.1 g, 1 mmol)
and 1a–e (0.005 mmol).
2.2.6. 2-n-Butyl-5-(4-methoxyphenyl)thiophene (7)
2.2.11. 2-n-Butyl-5-(4-methylphenyl)furan (12)
Corresponding product 7 was obtained in 92%, 99%, 97%, 94%
and 100% conversions by the reaction of 2-n-butylthiophene
Corresponding product 12 was obtained in 88%, 70%, 91%, 95%
and 89% conversions by the reaction of 2-n-butylfuran (0.25 g,

S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
225
Table 1
2.2.14. 2-n-Butyl-5-(4-methylphenyl)thiophene (15)
Crystallographic data and collection parameters for 1d.
Corresponding product 15 was obtained in 70% conversion by
the reaction of 2-n-butylthiophene (0.25 g, 2 mmol), 4-chlorotolu-
ene (0.11 g, 1 mmol), KOAc (0.09 g, 1 mmol) and 1c (0.005 mmol).
Formula
C44H36Br2N4O4PdÁCH2Cl2ÁCH3NO
Molecular weight
Crystal size (mm)
Crystal system
Space group
a (Å)
1080.94
0.18 Â 0.20 Â 0.35
triclinic
2.2.15. 2-n-Butyl-5-acetophenylfuran (16)
ꢀ
P1
Corresponding product 16 was obtained in 78% conversion by
the reaction of 2-n-butylfuran (0.25 g, 2 mmol), 4-chloroacetophe-
none (0.16 g, 1 mmol), KOAc (0.1 g, 1 mmol) and 1a (0.005 mmol).
9.3581 (3)
12.3362 (5)
19.0523 (7)
81.881 (2)
87.575 (2)
85.186 (2)
2168.70 (14)
2
1.655
2.45
multi-scan
0.561–0.644
32335
b (Å)
c (Å)
a
(°)
b (°)
(°)
2.2.16. 2-n-Butyl-5-(4-methylphenyl)furan (17)
c
V (Å3)
Z
Corresponding product 17 was obtained in 65% conversion by
the reaction of 2-n-butylfuran (0.25 g, 2 mmol), 4-chlorotoluene
(0.13 g, 1 mmol), KOAc (0.1 g, 1 mmol) and 1d (0.005 mmol).
Calculated density (g cmÀ3)
l
(mmÀ1)
Absorption correction
Transmission factor range
Reflections measured
Rint
2.3. Crystal structure determinations
0.038
X-ray data for 1d were collected on a Bruker Kappa APEXII CCD
Mean r(I)/I
hmax
Independent reflections
Weighting scheme
diffractometer using Mo
Ka
radiation (k = 0.71073 A) at
27.1
9522
T = 296(2) K. The structure was solved by SIR-97 [26] and refined
by full-matrix least-squares refinement on F2 using SHELXL-97 [27].
w = 1/[r2(Fo2) + (0.0553P)2 + 1.3897P] where
P = (Fo2 + 2Fc2)/3
6354
All
H atoms were placed geometrically with N–H = 0.86 Å,
Reflections used in
C–H = 0.93 Å (aromatic), 0.97 Å (methylene) and 0.98 Å (methine),
and refined using a riding model with Uiso(H) = 1.2Ueq(C, N). Five
poorly fitted reflections, (001), (À1À11), (012), (À104), and
(À110), were omitted from the refinement. The ORTEP and pack-
ing diagrams (Figs. 1 and 2) of 1d were drawn using PLATON [28].
refinement [I > 2
Parameters
R(Fobs
Rw(F2)
S
r(I)]
552
)
0.046
0.121
1.02
0.001
0.64
Shift/errormax
Maximum electron density
(e ÅÀ3)
3. Results and discussion
Minimum electron density
À0.86
(e ÅÀ3)
3.1. Synthesis of palladium N-heterocyclic carbene complexes (Pd-NHC)
CCDC
894210
The synthetic route for phenyl substituted palladium complexes
described in this study is given in Scheme 1. According to the
method described in the literature, the 1-phenyl-3-alkyl
benzimidazolium salts were prepared by the quaternization of
N-phenylbenzimidazole with a variety of alkyl halides in dimethyl-
formamide (DMF) [29–31]. The Pd-NHC complexes (1a–e) were
2 mmol), 4-bromotoluene (0.17 g, 1 mmol), KOAc (0.1 g, 1 mmol)
and 1a–e (0.005 mmol).
2.2.12. 2-n-Butyl-5-phenylfuran (13)
Corresponding product 13 was obtained in 95%, 92%, 82%, 92%
and 94% conversions by the reaction of 2-n-butylfuran (0.25 g,
2 mmol), bromobenzene (0.16 g, 1 mmol), KOAc (0.1 g, 1 mmol)
and 1a–e (0.005 mmol).
Table 3
Bond Angles (°) for 1d.
Br1–Pd1–Br2
Br1–Pd1–C7
Br1–Pd1–C29
Br2–Pd1–C7
Br2–Pd1–C29
C7–Pd1–C29
C9–O1–C10
C15–O2–C16
C31–O3–C32
C37–O4–C38
C6–N1–C7
92.62 (2)
87.43 (11)
177.14 (11)
179.10 (11)
85.22 (11)
94.75 (15)
113.4 (4)
114.7 (5)
115.0 (4)
113.2 (5)
110.4 (3)
124.7 (3)
124.9 (3)
110.3 (3)
123.0 (3)
126.6 (3)
110.6 (4)
125.9 (4)
123.5 (4)
110.7 (4)
123.4 (3)
125.6 (3)
106.2 (3)
131.1 (4)
106.4 (3)
132.0 (4)
126.0 (3)
127.3 (3)
106.6 (3)
N1–C8–C9
O1–C9–C8
114.8 (3)
106.6 (4)
113.0 (5)
121.3 (4)
119.1 (4)
122.1 (4)
119.0 (4)
113.9 (6)
118.4 (3)
121.1 (4)
106.1 (3)
130.8 (4)
132.5 (4)
106.6 (4)
126.8 (3)
127.0 (3)
106.0 (3)
114.0 (4)
110.1 (5)
106.8 (4)
117.6 (5)
122.5 (5)
121.6 (5)
119.3 (5)
111.3 (5)
119.4 (4)
119.7 (4)
108.9 (6)
89.4 (15)
O1–C9–C16
O1–C10–C15
O1–C10–C11
O2–C15–C10
O2–C15–C14
O2–C16–C9
N2–C17–C18
N2–C17–C22
N4–C23–C28
N4–C23–C24
N3–C28–C27
N3–C28–C23
Pd1–C29–N3
Pd1–C29–N4
N3–C29–N4
N3–C30–C31
O3–C31–C38
O3–C31–C30
O3–C32–C33
O3–C32–C37
O4–C37–C32
O4–C37–C36
O4–C38–C31
N4–C39–C44
N4–C39–C40
Cl1–C45–Cl2
O5–C46–N5
2.2.13. 2-n-Butyl-5-acetophenylthiophene (14)
Corresponding product 14 was obtained in 60% conversion by
the reaction of 2-n-butylthiophene (0.25 g, 2 mmol), 4-chloroace-
tophenone (0.14 g, 1 mmol), KOAc (0.09 g, 1 mmol) and 1a
(0.005 mmol).
C6–N1–C8
C7–N1–C8
C1–N2–C7
Table 2
Bond lengths (Å) for 1d.
C1–N2–C17
C7–N2–C17
C28–N3–C29
C28–N3–C30
C29–N3–C30
C23–N4–C29
C23–N4–C39
C29–N4–C39
N2–C1–C6
N2–C1–C2
N1–C6–C1
N1–C6–C5
Pd1–C7–N2
Pd1–C7–N1
N1–C7–N2
Pd1–Br1
Pd1–Br2
Pd1–C7
Pd1–C29
Cl1–C45
Cl2–C45
O1–C10
O1–C9
O2–C16
O2–C15
O3–C31
O3–C32
O4–C38
O4–C37
2.4796 (5)
2.4892 (6)
2.002 (4)
1.986 (4)
1.748 (10)
1.626 (10)
1.373 (6)
1.440 (7)
1.378 (8)
1.374 (6)
1.432 (7)
1.376 (7)
1.410 (7)
1.379 (7)
O5–C46
N1–C8
N1–C7
N1–C6
N2–C17
N2–C7
1.19 (2)
1.462 (6)
1.349 (5)
1.397 (5)
1.429 (5)
1.350 (5)
1.403 (5)
1.394 (5)
1.472 (6)
1.360 (5)
1.406 (6)
1.428 (6)
1.347 (5)
1.58 (4)
N2–C1
N3–C28
N3–C30
N3–C29
N4–C23
N4–C39
N4–C29
N5–C46

226
S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
Table 4
In Pd-NHC catalysts (1a–e), direct C5 arylation of 2-n-propylthiazole by using aryl bromides.a,b,c
N
N
Pd-NHC (0.005 mmol)
R
Br
+
R
S
nPr
nPr
S
DMAc (2 mL), KOAc (1 mmol), 1 h
S
Entry
Aryl bromide
Pd-NHC
Product
Conversion (%)
1
2
3
4
5
1a
1b
1c
1d
1e
85
51
50
88
81
N
O
Br
C CH3
nPr
nPr
H3COC
2
6
7
1a
1b
1c
1d
1e
100
79
N
Br
OMe
CH3
8
94
9
10
S
100
100
MeO
3
4
11
12
13
14
15
1a
1b
1c
1d
1e
100
61
94
100
81
N
Br
Br
nPr
S
H3C
16
17
18
19
20
1a
1b
1c
1d
1e
100
66
96
86
89
N
nPr
S
H
5
a
b
c
Reaction condition: 2-n-propylthiazole (2 mmol), aryl bromide (1 mmol), Pd-NHC (1a–e) (0.005 mmol), KOAc (1 mmol), N,N-dimethylacetamide (2 mL), 130 °C, 1 h.
Product purity was checked by GC and NMR.
Conversions were calculated according to aryl bromide.
obtained by the treatment of 1-phenyl-3-alkyl benzimidazolium
salts with 1 equivalent of Pd(OAc)2 in the presence of dimethyl
sulfoxide in 82–89% yields (Scheme 1). The reaction mixture was
heated at 60 °C for 24 h and at 110–120 °C for 1 h. The air and
moisture stable Pd-NHC complexes were soluble in halogenated
solvents such as chloroform and dichloromethane. The five new
Pd-NHC complexes were characterized by spectroscopic methods
(1H NMR, 13C NMR, LC–MS and FT-IR) and elemental analysis tech-
niques which support the proposed structures. Furthermore, the
solid state structure of 1d was analyzed by single crystal X-ray dif-
fraction. The 1H NMR and 13C NMR spectra are consistent with the
proposed formulae and appear to be spectroscopically pure. The 1H
NMR spectra of the heterocyclic salts containing the benzimidazo-
lium further supported the assigned structures; the resonance for
C(2)–H was observed as sharp singlets at 11.42, 12.08, 11.21,
11.41 and 11.70 ppm for benzimidazolium salts [31,39]. The 1H
NMR spectra of the Pd-NHC complexes showed the absence of
any signal of the acidic benzimidazolium C2–H between 9 and
12 ppm. This condition indicated the successful deprotonation of
benzimidazolium salts and confirmed the formation of the ex-
pected Pd-NHC complexes. In the 13C NMR spectra, there is one sig-
nal for the carbenic carbons (NCN) at d ca. 181.7, 181.2, 173.0,
182.1 and 182.9 ppm for 1a–e, respectively. Therefore, these com-
plexes are not cis/trans mixtures. The FT-IR data for Pd-NHC com-
plexes exhibit a characteristic m(NCN) band at 1597.45, 1597.34,
1596.32, 1594.49 and 1500.08 for 1a–e, respectively. Also, the
resulting LC–MS spectrums confirmed the synthesized complexes,
too.
3.2. X-ray analysis
A single crystal of the representative complex 1d was obtained
for X-ray analysis by slow diffusion of CH2Cl2 into NH2CHO solu-
tions at ambient temperature. The lattice held organic solvent mol-
ecules, such as CH2Cl2, NH2CHO, appear in the unit cells of the
determined structure in 1d. The molecular structure of 1d was con-
firmed by single crystal X-ray structure determination; the atom-
numbering scheme is shown in Fig. 1. The palladium center in
the 1d complex is coordinated by two NHC ligands and two bromo
ligands in a cis fashion.
As shown in Fig. 1, the Pd atom of the 1d compound has a dis-
torted square-planar coordination environment defined by two
imidazole C atoms derived from a chelating 1-(2,3-dihydro-1,4-
benzodioxane-2-ylmethyl)-3-phenyl-2,3-dihydro-1H-benzimid-
azole ligand and two Br atoms. The N1/N2/C1–C7 and N3/N4/C23–
C29 benzimidazole ring systems in 1d are planar with the maxi-
mum deviations of À0.040(3) Å for N1 and À0.029(4) Å for C29,
respectively. While the benzimidazole and phenyl rings make a
dihedral angle of 61.98(18) and 66.6(2)° with each other, they
are rotated with respect to the coordination plane of the metal

S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
227
Table 5
In Pd-NHC catalysts (1a–e), direct arylation of 2-n-butylthiophene by using aryl bromides.a,b,c
Pd-NHC (0.005 mmol)
DMAc (2 mL), KOAc (1 mmol), 1 h
+
R
Br
R
nBu
nBu
S
S
Entry
Aryl bromide
Pd-NHC
Product
Conversions (%)
1
2
3
4
5
1a
1b
1c
1d
1e
98
100
99
91
96
O
nBu
Br
C CH3
S
H3COC
6
6
7
8
9
1a
1b
1c
1d
1e
92
99
97
94
100
Br
Br
OMe
CH3
nBu
S
10
MeO
H3C
7
11
12
13
14
15
1a
1b
1c
1d
1e
94
80
97
99
96
nBu
S
8
16
17
18
19
20
1a
1b
1c
1d
1e
85
71
62
93
88
Br
nBu
S
H
9
a
b
c
Reaction condition: 2-n-butylthiophene (2 mmol), aryl bromide (1 mmol), Pd-NHC (1a–e) (0.005 mmol), KOAc (1 mmol), N,N-dimethylacetamide (2 mL), 130 °C, 1 h.
Product purity was checked by GC and NMR.
Conversions were calculated according to aryl bromide.
by 83.93(11), 70.11(16)°, 76.55(13) and 70.58(18)°, respectively.
The 1,4 dioxane rings of the 2,3-dihydro-1,4-benzodioxane groups
almost adopt a distorted half-chair conformation [the puckering
parameters [32] are QT = 0.394(6) Å, h = 131.0(9)°, / = 268.1(10)°
for O1/O2/C9/C10/C15/C16 and QT = 0.453(6) Å, h = 128.9(8)°,
/ = 278.8(8)° for O3/O4/C31C32/C37/C38].
However, a few examples of couplings using deactivated aryl bro-
mides have been reported [35,36]. We achieved very good results
even though we conducted the arylation reaction for a short period
of 1 h and at a low temperature. We performed a study focusing on
the catalytic activity of direct arylation in 5 situations using 2-n-
propylthiazole, 2-n-butylthiophene and 2-n-butylfuran rings with
diverse aryl halides (4-bromoacetophenone, 4-bromoanisole, 4-
bromotoluene, bromobenzene, 4-chloroacetophenone and 4-chlo-
rotoluene). The reactions cannot proceed at 3- and 4-positions.
This is because the charge density at 3- and 4-positions are less
than charge density at 5-position. Also, C5 arylation is highly selec-
tive because 2-position (C2) is blocked. The reaction was achieved
by using Pd-NHC, aryl bromide, thiazole/thiophene/furan and
KOAc in DMAc by heating in an oil bath at 130 °C for 1 h. The de-
sired product was obtained in more than 50% yield when KOAc
was used as a base. The time of reactions which were conducted
by using aryl chlorides was limited to 20 h and lower conversions
were obtained. When the reactions were completed, the products
were purified by flash chromatography on silica gel. The purity of
the compounds was checked by using GC and NMR. The conversion
of starting material to product was determined by GC.
The molecular packing along the a-axis of 1d is shown in Fig. 2.
Weak C–HÁ Á Á
p interactions and p–p stacking interactions
[Cg6Á Á ÁCg6 (2 À x, Ày, 1 À z) = 3.842(3) Å and Cg8Á Á ÁCg8(1 À x,
1 À y, 2 À z) = 3.804(3) Å, where Cg6 and Cg8 are the centroids
of the C10–C15 and C23–C28 rings, respectively] also help in the
stabilization of the crystal packing. The crystal data and collection
parameters are listed in Table 1.
The Pd–Br bond lengths are 2.4796(5) and 2.4892(6) Å, and the
Pd–C bond lengths are 2.002(4) and 1.986(4) Å. The Br–Pd–Br and
C–Pd–C bond angles are 92.62(2) and 94.75(15)°, respectively. The
values of all bond lengths and bond angles (Tables 2 and 3) are nor-
mal and are comparable with the reported values of similar struc-
tures [33,34].
3.3. Catalytic applications of Pd-NHC complexes (1a–e) in arylation
reactions
3.3.1. In Pd-NHC catalysts, direct arylation of 2-n-propylthiazole
Miura and Nomura studied the arylation reaction of thiazoles.
The palladium-catalyzed direct arylation of arylbromides with 2-
n-propylthiazole in dimethylformamide has been described by
them [37,38]. The influence of the five new synthesized Pd-NHC
The selective C2 or C5 arylation of heteroaromatics such as thi-
azole, oxazole thiophene, pyrrole, imidazole, pyrazole, triazole,
pyridine, furan or indole has been extensively described through
palladium-catalyzed C–H bond activation in recent years [8–12].

228
S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
Table 6
In Pd-NHC catalysts (1a–e), direct C5 arylation of 2-butylfuran by using aryl bromides.a,b,c
Pd-NHC (0.005 mmol)
R
Br
+
R
nBu
nBu
DMAc (2 mL), KOAc (1 mmol), 1 h
O
O
Entry
Aryl bromide
Pd-NHC
Product
Conversion (%)
1
2
3
4
5
1a
1b
1c
1d
1e
97
92
100
74
79
O
nBu
Br
C CH3
O
H3COC
10
6
7
8
9
1a
1b
1c
1d
1e
92
54
87
86
70
Br
Br
Br
OMe
CH3
nBu
O
10
MeO
11
11
12
13
14
15
1a
1b
1c
1d
1e
88
70
91
95
89
nBu
O
H3C
12
16
17
18
19
20
1a
1b
1c
1d
1e
95
92
82
92
94
nBu
O
H
13
a
b
c
Reaction condition: 2-n-butylfuran (2 mmol), aryl bromide (1 mmol), Pd-NHC (1a–e) (0.005 mmol), KOAc (1 mmol), N,N-dimethylacetamide (2 mL), 130 °C, 1 h.
Product purity was checked by GC and NMR.
Conversions were calculated according to aryl bromide.
complexes was successively investigated in this coupling reaction.
The results in the desired product are usually very high. The ob-
tained results are given in Table 4.
The reactivity of 2-n-butylthiophene was similar to 2-n-propyl-
thiazole (Table 5). In the Pd-NHC (1a–e) catalysts, arylation
coupling products were obtained as a result of the reaction of
4-bromoacetophenone, 4-bromoanisole, 4-bromotoluene and bro-
mobenzene with 2-n-butylthiophene. When Table 5 is examined, it
is seen that the results of the arylation coupling reaction are
between 62% and 99%. The activities of the complexes are close
to each other, but the best results are obtained in the presence of
the 1d complex.
Firstly, we investigated the direct 5-arylation of 2-n-propyl-
thiazole with 4-bromoacetophenone using these five new palla-
dium complexes. A high conversion of the coupling product 2
was obtained with 4-bromoacetophenone and Pd-NHC complexes
(1a, 1d and 1e) (Table 4, entries 1–6). Then, to assure this tendency,
4-bromoanisole, 4-bromotoluene and bromobenzene were reacted
with 2-n-propylthiazole by using these five new complexes (Ta-
ble 4, entries 6–20). For this transformation, complexes 1a, 1c
and 1d were found to be effective catalysts. When Table 4 is exam-
ined, it is seen that the results of the arylation coupling reaction are
between 50 and 100. In arylation coupling reactions conducted
using 2-n-propylthiazole, it appears that higher conversions were
obtained using electron-rich rather than electron-deficient rings.
Also, for 4-bromoanisole, the best results were achieved with cat-
alysts 1a, 1d and 1e to give 3 in 100% for three complexes (Table 4,
entries 6, 9 and 10). The best conversions were obtained with cat-
alysts 1a and 1d for 4-bromotolune and 1a for bromobenzene to
give 4 and 5 in 100%.
3.3.3. In Pd-NHC catalysts, direct arylation of 2-n-butylfuran
We analyzed the reactivity of 2-n-butylfuran with four aryl bro-
mides in Pd-NHC (1a–e) catalysts for this coupling reaction and the
results are given in Table 6.
The arylation coupling conversions of aryl bromides with 2-n-
butylfuran were obtained in the Pd-NHC (1a–e) catalysts. When
Table 6 is examined, it is seen that the results of the arylation cou-
pling reaction are between 74% and 100%. In general, the catalytic
activities of the palladium complexes are quite similar, with only
small differences that can be attributed to the substituents present
on the ligands. It was observed that the 1a complex is more active
than the other complexes. Good conversions in 10 were achieved
with complexes 1a–c for the coupling with 4-bromoacetophenone.
3.3.2. In Pd-NHC catalyst, direct arylation of 2-n-butylthiophene
It should be noted that just a few examples of the direct aryla-
tion of aryl halides with 2-n-butylthiophene by using Pd-NHC
complexes have been reported [4]. We investigated the reactivity
of 2-n-butylthiophene using different aryl bromides in the pres-
ence of Pd-NHC complexes. The obtained results are given in
Table 5.
3.3.4. In Pd-NHC catalysts, direct arylation of heteroarenes by using
aryl chlorides
Finally, we investigated the reactivity of 2-n-butylfuran and
2-n-butylthiophene with aryl chlorides (4-chloroacetophenone

S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
229
Table 7
In Pd-NHC catalysts, direct arylation of heteroarenes by using aryl chlorides.a,b,c
Pd-NHC (0.005 mmol)
R
Cl
R
+
nBu
nBu
E
DMAc (2 mL), KOAc (1 mmol)
E
E: S or O
Entry
1
Aryl chloride
Pd-NHC
Product
Conversions (%)
1a
1c
1a
1d
70
72
78
69
O
C
nBu
Cl
Cl
CH3
S
H3COC
14
2
3
4
CH3
nBu
S
H3C
15
O
C
nBu
Cl
Cl
CH3
O
H3COC
16
CH3
nBu
O
H3C
17
a
b
c
Reaction condition: Heteroarene (2 mmol), aryl chloride (1 mmol), Pd-NHC (0.005 mmol), KOAc (1 mmol), N,N-dimethylacetamide (2 mL), 130 °C, 20 h.
Product purity was checked by GC and NMR.
Conversions were calculated according to aryl chloride.
X
E
R
Ar
E
X
E
R
X
E
R
Ar
Ar
Ar
XPd
XPd
Ar-Pd-X
-HPdX
E
XPd
R
R
E= O or S
Scheme 2. Stereomutation to allow elimination.
and 4-chlorotoluene) in Pd-NHC (1a, 1c and 1d) catalysts at 130 °C
for 20 h and the obtained conversions are given in Table 7.
The arylation coupling reactions conducted by using aryl chlo-
rides such as p-chloroacetophenone and p-chlorotoluene were ac-
quired by heating the mixture at 130 °C for 20 h. These reactions
were obtained in good conversions (Table 7, entries 1–4). However,
when the results of these reactions conducted using aryl chlorides
are examined, lower conversions are observed with respect to
reactions conducted using aryl bromides. In other words, they
were found to be less reactive.
4. Conclusion
To conclude, in this study, five new Pd-NHC complexes (1a–e)
which were confirmed by elemental analyses, FT-IR, LC–MS (for
1a, 1c and 1e), 1H NMR and 13C NMR were synthesized from various
1-phenyl-3-alkylbenzimidazolium salts with Pd(OAc)2 in dimethyl
sulfoxide in very excellent yields. The complex 1d was also charac-
terized by single crystal X-ray diffraction studies. We have found
out that these new palladium complexes are practical catalysts for
the direct regioselective C5 arylation of 2-n-butylfuran, 2-n-butyl-
thiophene and 2-n-propylthiazole using both electron-deficient
and electron-rich aryl halides as coupling partners. Better results
were obtained from reactions which were conducted by using aryl
bromides.
3.4. Mechanism of furan and thiophene direct arylation
A mechanism similar to that of the Heck reaction for the aryla-
tion of thiophenes and furans was suggested by Sharp [40]. Such a
mechanism would require either the stereomutation or elimina-
tion of 3–4 prior to elimination [41] (Scheme 2).
Acknowledgments
_
This work was financially supported by Inönü University Re-
_
search Fund (I.U.B.A.P. 2011/130). The authors acknowledge the

230
S. Akkoç et al. / Inorganica Chimica Acta 413 (2014) 221–230
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provision of funds for the purchase of a diffractometer and encour-
agement by Dr Muhammad Akram Chaudhary, Vice Chancellor,
University of Sargodha, Pakistan.
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[18] H. Ohta, T. Fujihara, Y. Tsuji, Dalton Trans. 3 (2008) 379.
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Appendix A. Supplementary material
[22] C. Xu, X.-Q. Hao, Z. Li, X.-M. Dong, L.-M. Duan, Z.-Q. Wang, B.-M. Ji, M.-P. Song,
Chem. Commun. 17 (2012) 34.
[23] S. Demir, I. Özdemir, H. Arslan, D. VanDerveer, J. Organomet. Chem. 696 (2011)
CCDC 894210 contains the supplementary crystallographic data
for 1d. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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