Synthesis, Characterization and Crystal Structure of New 2-Morpholinoethyl-Substituted Bis-(NHC)Pd(II) Complexes and the Catalytic Activity in the Direct Arylation Reaction

Article abstract of DOI:10.1007/s10562-017-2132-3

Abstract: This paper contains the synthesis of the new 2-morpholinoethyl substituted bis-(NHC)Pd(II) complexes and their catalytic activity in direct arylation reaction. The new bis-(NHC)Pd(II) complexes have been prepared from Ag(I)NHC complexes by using

Full text of DOI:10.1007/s10562-017-2132-3

Catal Lett
DOI 10.1007/s10562-017-2132-3
Synthesis, Characterization and Crystal Structure of New
2
-Morpholinoethyl-Substituted Bis-(NHC)Pd(II) Complexes
and the Catalytic Activity in the Direct Arylation Reaction
1
1
2
1
2
Yakup Sarı · Aydın Aktaş · Duygu Barut Celepci · Yetkin Gök · Muhittin Aygün
Received: 24 April 2017 / Accepted: 24 June 2017
©
Springer Science+Business Media, LLC 2017
Abstract This paper contains the synthesis of the new
-morpholinoethyl substituted bis-(NHC)Pd(II) complexes
and elemental analysis techniques. Molecular and crystal
structure of the complex 1a and its ligand (N-benzylbenzi-
midazole) were obtained by single crystal X-ray diffraction
method. The new bis-(NHC)Pd(II) complexes exhibit activ-
ity in the reaction after being examined as catalysts in the
direct arylation (C–H activation) reaction.
2
and their catalytic activity in direct arylation reaction. The
new bis-(NHC)Pd(II) complexes have been prepared from
Ag(I)NHC complexes by using transmetallation method.
The new bis-(NHC)Pd(II) complexes have been charac-
1
13
terized by using H NMR, C NMR, FTIR spectroscopy
*
Aydın Aktaş
aydinaktash@hotmail.com
1
2
Department of Chemistry, Faculty of Science, İnönü
University, 44280 Malatya, Turkey
Department of Physics, Faculty of Science, Dokuz Eylül
University, 35160 Buca, Izmir, Turkey
Vol.:(0
1
123456789)
3

Y. Sarı et al.
Graphical Abstract
Keywords N-Heterocyclic carbenes · Bis-(NHC)
Pd(II) · Single crystal X-ray diffraction · Direct arylation ·
Butylfuran · Butylthiophene
In recent years NHC ligands have an important place
in transition-metal chemistry due to their unique compl-
exation properties, synthetic versatility and highly adjust-
able properties [10]. Metal-NHC complexes, especially
Ag(I)-NHC complexes have attracted continuous atten-
tion [11]. They are used as suitable carbene transfer rea-
gents for other metal–carbene complexes (as Pd, Ru, Ni,
Rh, and Ir) which are not always easily found [12–16].
Also, biomedical applications of Ag-NHC complexes
such as antimicrobial, anticancer and antitumor agents
have been researched [17–19].
1
Introduction
The N-heterocyclic carbenes (NHCs) were known as
unstable and non-isolable intermediates when first dis-
covered by Wanzlick [1] and Öfele [2] in 1968. However,
after the report on the extraordinary stability, isolation,
and storability of crystalline NHC IAd by Arduengo et al.
in 1991 [3–5], numerous studies have been reported on
the NHC as ligands in organic and organometallic chem-
istry [6]. These ligands with strong σ-donor and weak
π-acceptor properties can form stable complexes with
almost all transition metals [7–9].
Pd-NHC complexes are considered to be one of the
most important classes of metal-NHC complexes. The
pioneering participation from the groups of Nolan
[20], Herrmann [21, 22], Glorious [23] and Organ [24]
have been mentioned in this topic. Metal-NHC com-
plexes have found wide application area that includ-
ing olefin metathesis, hydrosilylation, and Pd-catalyzed
1
3

Synthesis, Characterization and Crystal Structure of New 2-Morpholinoethyl-Substituted…
1
13
cross-coupling reactions [25]. Bis-(NHC)Pd(II)dihalide
complexes are efficient catalysts for different C–C and
C–N coupling reactions [26, 27]. Usually accepted that
the chelate effect revealed on their metal complexes pre-
sents extra stability for the generation of durable metal
complexes, which are extremely desirable for catalytic
applications, especially those requiring harsh reaction
conditions [28].
spectrometer. Proton ( H) and Carbon ( C) NMR spectra
were recorded using either a Varian AS 300 Merkur spec-
1
13
trometer operating at 300 MHz ( H), 75.47 MHz ( C) in
CDCl with tetramethylsilane as an internal reference. All
3
reactions were observed on an Agilent 6890 N GC system
by GC-FID with an HP-5 column of 30 m length, 0,32 mm
diameter and 0,25 μm film thickness. Column chromatog-
raphy was performed using silica gel 60 (70–230 mesh).
Elemental analyses were performed by İnönü University
Scientific and Technological Research Center (Malatya,
Turkey).
The palladium catalyzed direct arylation of isoxa-
zoles [29], the reaction of the five-membered heteroaro-
matic ring with aryl halides via C–H bond activation, has
been firstly reported by Nakamura et al in 1982 [30–39].
One of the most important methods in modern organic
chemistry is palladium-catalyzed carbon–carbon (C–C)
cross-coupling reactions since direct (C–H) arylation
has taken attention as an alternative C–C coupling reac-
tion in recent years [37, 40]. Recently, reactions of the
C–H activation via organopalladium intermediate species
have become multipurpose [41, 42]. Palladium catalytic
systems are rather widespread owing to their selectivity,
high activity, versatility, and efficiency. Also, different
catalytic systems for the C–H bond transformations have
been improved for the eco-friendly synthesis method
Single crystal X-ray diffraction data set of the com-
plex 1a and its ligand (N-benzylbenzimidazole) were col-
lected at room temperature on a Rigaku-Oxford Xcali-
bur EOS diffractometer using graphite monochromated
Mo–Kα radiation (λ=0.71073 Å). The data were collected
Pro
and integrated using CrysAlis software [55]. Utilizing
OLEX2 [56], the structures were solved by direct methods
in SHELXT [57] and refined by full-matrix least-squares
2
on F in SHELXL [58]. Anisotropic thermal parameters
were applied to all non-hydrogen atoms. Hydrogen atoms
of the ligand were found in the difference map and refined
freely. For the complex, all hydrogen atoms were placed
in geometrically idealized positions (C–H=0.93–0.97 Å,
Cl–H=1.630–1.707 Å). Crystallographic data is summa-
rized in Table 1.
[
43–45].
In recent years, numerous studies have been pub-
lished on the metal-NHC complexes containing direct
arylation, transfer hydrogenation, Suzuki–Miyaura and
Heck reactions [46–54]. Our study contains the synthe-
sis of the new series of 2-morpholinoethyl-substituted
bis-(NHC)Pd(II) complexes and their structural and
spectroscopic characterization. The structure of 1a was
confirmed by the single-crystal X-ray diffraction method.
Also, the catalytic activities of the bis-(NHC)Pd(II)
complexes have been investigated that they are more
efficient and stable catalysts for the direct arylation reac-
tions of 2-n-butylfuran and 2-n-butylthiophene with aryl
bromide.
2.1 Synthesis of bis[1-benzyl-3-(2-morpholinoethyl)
benzimidazol-2-ylidene]dichloropalladium(II), 1a
PdCl (PhCN) (0.078 g, 0.3 mmol) was added to a solution
2
2
of
chloro[1-benzyl-3-(2-morpholinoethyl)benzimidazol-
2-ylidene] silver(I) (288 mg, 0.6 mmol) in dichlorometh-
ane (20 mL). The reaction mixture was stirred for 24 h
at room temperature in the dark conditions. Then filtered
through Celite and the solvents were evaporated under
vacuum to afford the product as a light yellow solid. The
crude product was recrystallized from dichloromethane/
diethyl ether (1:3) at room temperature. Yield: 0.172 g
2
Experimental
−
1
(
70%). m.p.: 205–206°C; ν : 1452.6 cm . Anal.
(CN)
All synthesis involving bis-(NHC)Pd(II) complexes 1a–f
were carried out under an inert atmosphere in flame-dried
glassware using standard Schlenk techniques. The solvents
used were purified by distillation over the drying agents
Calc. for C H N O PdCl : C: 58.58; H: 5.65; N: 10.25.
40 46 6 2 2
1
Found: C:59.41; H: 6.13; N: 9.82. H NMR (300 MHz,
CDCI , δ, ppm); 2.42 (t, 8H, J: 4.2 Hz, –NCH CH O–);
3
2
2
3.11 (m, 4H, –NCH CH NC H O); 3.48 (m, 8H, –NCH
2
2
4
8
2
indicated and were transferred under Ar: Et O (Na/K
CH O–); 5.00 (t, 4H, J: 4.5 Hz, –NCH CH NC H O–);
2
2
2
2 4 8
1
3
alloy), CH Cl (P O ), hexane, toluene (Na).
6.18 (s, 4H, –CH C H –); 7.03–7.35 (m, 18H, Ar–H).
C
2
2
4
10
2
6
5
All other reagents were commercially available from
Aldrich Chemical Co. and used without further puri-
fication. Melting points were identified in glass capil-
laries under air with an Electrothermal-9200 melting
NMR (75 MHz, CDCI , δ, ppm); 52.1 (–NCH CH O–);
3 2 2
54.3 (–NCH CH NC H O); 58.0 (–NCH CH O–); 66.9
2
2
4
8
2
2
(–NCH CH NC H O–); 67.3 (–C H CH –); 111.0, 111.7,
2
2
4
8
6
4
2
111.9, 124.2, 128.1, 133.0, 133.2, 134.1, 134.2, 134.5, and
point apparatus. FT-IR spectra were saved in the range
137.6 (Ar–C); 181.6 (2-CH).
1
4
00–4000 cm− on Perkin Elmer Spectrum 100 FT-IR
1
3

Y. Sarı et al.
Table 1 Crystal data
and structure refinement
data of complex 1a and
N-benzylbenzimidazole
N-benzylbenzimidazole
1a
Empirical formula
Formula weight
Crystal description, colour
Crystal size (mm)
Temperature (K)
Wavelength (Å)
Crystal system
Space group, Z
a (Å)
b (Å)
c (Å)
α (°)
β ( °)
C H N
C H Cl N O Pd
1
4
12
2
41 48
4
6
2
208.26
905.05
Prismatic, colourless
0.359 × 0.286 × 0.260
294 (2)
Prismatic, colourless
0.191 × 0.171 × 0.104
293 (2)
0.71073
Triclinic
0.71073
Monoclinic
P121/n 1, 4
6.2199 (6)
8.2758 (8)
21.406 (2)
90
97.260 (10)
90
1093.05 (19)
1.266
P-1, 1
9.9679 (7)
10.6355 (7)
12.4128 (9)
73.424 (6)
72.786 (6)
62.099 (7)
1093.94 (15)
1.374
γ (°)
3
Volume (Å )
ρcalc (mg m 3)
−
μ (mm−
F (000)
1
)
0.076
440
0.709
466
θ Range for data collection (°)
3.12–28.46
3.04–25.68
Index ranges
h
−8 to 6
−12 to 6
k
−10 to 10
−12 to 12
l
−28 to 27
−15 to 14
Reflections collected
Independent reflections
Completeness
Refinement method
Data/restrains/parameters
4373
7184
1436 [R (int)=0.0259]
99.78%
Full-matrix least-squares on F
1436/0/193
3372 [R (int)=0.0369]
99.83%
2
Full-matrix least-squares on F2
3372/6/259
2
Goodness-of-fit on F
1.006
1.055
Final R indices [I>2σ(I)]
R indices (all data)
R =0.049, wR =0.087
R =0.062, wR =0.110
R =0.081, wR =0.138
1 2
1
2
1
2
R =0.096, wR =0.104
1
2
2
.2 Synthesis of Bis[1-(3-methylbenzyl)-3-(2-mor-
NMR (75 MHz, CDCI , δ, ppm); 45.7 (–C H –CH ); 52.8
3 6 4 3
pholinoethyl)benzimidazol-2-ylidene]
dichloropalladium(II), 1b
(–NCH CH O–); 53.8 (–NCH CH NC H O); 57.7 (–NCH
2 2 2 2 4 8 2
CH O–); 66.8 (–NCH CH NC H O–); 67.1 (–C H CH –);
2
2
2
4
8
6
4
2
1
10.4, 110.7, 111.5, 123.0, 127.8 128.6 and 129.3 (Ar–C);
The synthesis of 1b was carried out in the same way as that
described for 1a, but chloro[1-(3-methylbenzyl)-3-(2-mor-
pholinoethyl)benzimidazol-2-ylidene] silver(I) (296 mg,
181.8 (2-CH).
0
.6 mmol) was used instead of chloro[1-benzyl-3-(2-mor-
2.3 Synthesis of Bis[1-(4-methylbenzyl)-3-(2-mor-
pholinoethyl)benzimidazol-2-ylidene]
dichloropalladium(II), 1c
pholinoethyl)benzimidazol-2-ylidene] silver(I). Yield:
−
1
0
.188 g, (74%). m.p.: 254–256°C; ν : 1456.7 cm .
(CN)
Anal. Calc. for C H N O PdCl : C: 59.47; H: 5.94;
4
2
50
6
2
2
1
N: 9.91. Found: C: 59.61; H: 6.01; N: 9.93. H NMR
The synthesis of 1c was carried out in the same way as
that described for 1a, but chloro[1-(4-methylbenzyl)-
3-(2-morpholinoethyl)benzimidazol-2-ylidene] silver(I)
(296 mg, 0.6 mmol) was used instead of chloro[1-ben-
zyl-3-(2-morpholinoethyl)benzimidazol-2-ylidene]
(
300 MHz, CDCI , δ, ppm); 2.30 (s, 6H, –C H –CH ); 2.99
3 6 4
3
(
t, 8H, J: 4.5 Hz, –NCH CH O–); 3.36 (t, 4H, J: 7.6 Hz,
2
2
–
NCH CH NC H O); 3.64 (t, 8H, J: 4.5 Hz, –NCH
2 4 8 2
2
CH O–); 4.89 (t, 4H, J: 7.6 Hz, –NCH CH NC H O–);
2
2
2
4
8
1
3
6
.14 (s, 4H, –CH C H –); 7.03–7.39 (m, 16H, Ar–H).
C
silver(I). Yield: 0.198 g, (78%). m.p.: 249–251 °C; ν
:
(CN)
2
6
4
1
3

Synthesis, Characterization and Crystal Structure of New 2-Morpholinoethyl-Substituted…
1
1
5
9
–
3
448.1 cm− . Anal. Calc. for C H N O PdCl : C:
–NCH CH O–); 3.86 (s, 6H, –C H OCH ); 3.89 (s, 12H,
2 6 2
4
2
50
6
2
2
2
3
9.47; H: 5.94; N: 9.91. Found: C: 59.53; H: 5.88; N:
–C H (OCH ) ); 5.01 (m 4H, –NCH CH NC H O–);
6 2 3 2 2 4 8
2
1
13
.82. H NMR (300 MHz, CDCI , δ, ppm); 2.36 (s, 6H,
6.13 (s, 4H, –CH C H (OCH ) –). C NMR (75 MHz,
3
2
6 2 3 3
C H –CH ); 2.42 (t, 8H, J: 4.2 Hz, –NCH CH O–);
CDCI , δ, ppm); 52.3 (–NCH CH O–); 54.2 (–NCH CH
6
4
3
2
2
3 2 2 2 2
.11 (m, 4H, –NCH CH NC H O); 3.47 (m, 8H, –NCH
NC H O); 56.4 (–C H OCH ); 56.7 (–C H (OCH ) );
4 8 6 2 3 6 2 3 2
2
2
4
8
2
CH O–); 4.99 (t, 4H, J: 4.5 Hz, –NCH CH NC H O–);
57.8 (–NCH CH O–); 60.8 (–NCH CH NC H O–);
2 2 2 2 4 8
2
2
2
4
8
6
.20 (s, 4H, –CH C H –); 7.02–7.18 (m, 16H, Ar–H).
66.8 (–CH C H (OCH ) –); 131.1, 133.3, 133.9, 134.9,
2 6 2 3 3
2
6
4
1
3
C NMR (75 MHz, CDCI , δ, ppm); 21.2 (–C H –CH );
135.0,153.4 and 153.8 (Ar–C); 181.7 (2-CH).
3
6
4
3
5
2.1 (–NCH CH O–); 54.2 (–NCH CH NC H O); 57.6
2 2 2 2 4 8
(
–NCH CH O–); 66.8 (–NCH CH NC H O–); 67.4
2
2
2
2
4
8
(
–C H CH –); 110.4, 111.4, 111.6, 123.1, 127.7 and
2.6 Synthesis of Bis[1-butyl-3-(2-morpholinoethyl)
benzimidazol-2-ylidene]dichloropalladium(II), 1f
6
4
2
1
29.3 (Ar–C); 181.8 (2-CH).
The synthesis of 1f was carried out in the same way as that
described for 1a, but chloro[1-butyl-3-(2-morpholinoethyl)
benzimidazol-2-ylidene] silver(I) (267 mg, 1.2 mmol) was
used instead of chloro[1-benzyl-3-(2-morpholinoethyl)
benzimidazol-2-ylidene] silver(I). Yield: 0.178 g, (79%).
2
.4 Synthesis of Bis[1-(2,3,4,5,6-pentamethylbenzyl)-3
-
(2-morpholinoethyl)benzimidazol-2-ylidene]
dichloropalladium(II), 1d
−
1
The synthesis of 1d was carried out in the same way
as that described for 1a, but chloro[1-(2,3,4,5,6-
pentamethylbenzyl)-3-(2-morpholinoethyl)benzimida-
zol-2-ylidene] silver(I) (330 mg, 0.6 mmol) was used
instead of chloro[1-benzyl-3-(2-morpholinoethyl)ben-
zimidazol-2-ylidene] silver(I). Yield: 0.207 g, (72%).
m.p.: 237–238°C; ν : 1454.8 cm . Anal. Calc. for
(CN)
C H N O PdCl : C: 54.29; H: 6.70; N: 11.17. Found:
3
4
50
6
2
2
1
C: 55.48; H: 6.95; N: 10.83. H NMR (300 MHz, CDCI ,
3
δ, ppm); 1.08 (m, 6H, –(CH ) –CH ); 1.60 (m, 4H,
2
3
3
–(CH ) –CH –CH ); 2.25 (m, 4H, –CH –CH –C H );
2
2
2
3
2
2
2
5
2.67 (m, 8H, –NCH CH O–); 3.25 (m, 4H, –NCH CH
2
2
2
2
−
1
m.p.: 248–250 °C; ν
: 1456.7 cm . Anal. Calc. for
NC H O); 3.72 (m, 8H, –NCH CH O–); 4.88 (t, 4H, J:
(
CN)
4 8 2
2
C H N O PdCl : C: 62.53; H: 6.93; N: 8.75. Found:
7.8 Hz, –CH –C H ); 5.01 (t, 4H, J: 6.6 Hz, –NCH CH
5
0
66
6
2
2
2
3
7
2
2
1
13
C: 62.64; H: 7.02; N: 8.67. H NMR (300 MHz, CDCI ,
NC H O–); 7.29–7.49 (m, 8H, Ar–H).
C
3
NMR
3
4
8
δ, ppm); 2.30 (s, 6H, –C –CH ); 2.38–2.40 (s, 30H,
(75 MHz, CDCI , δ, ppm); 14 (–(CH ) –CH ); 20.5
6
3
3
2 3
–
4
3
–
C –(CH ) ); 2.42 (s 8H, –NCH CH O–); 2.60 (m,
(–(CH ) –CH –CH ); 32.2 (–CH –CH –C H ); 48.2
6
3 5
2
2
2 2 2 3 2 2 2 5
H, –NCH CH NC H O); 3.50 (s, 8H, –NCH CH O–);
(–NCH CH O–); 54.2 (–NCH CH NC H O); 58.0 (–NCH
2 2 2 4 8 2
2
2
4
8
2
2
2
.78 (m 4H, –NCH CH NC H O–); 5.12 (s, 4H,
CH O–); 58.2 (–CH –C H ); 67.4 (–NCH CH NC H O–);
2
2
4
8
2
2 3 7 2 2 4 8
1
3
CH C (CH ) –); 7.35–7.47 (m, 8H, Ar–H). C NMR
110.5, 110.8, 111.4, 122.8, 123.7, 134.2 and 134.7 (Ar–C);
2
6
3 5
(
(
75 MHz, CDCI , δ, ppm); 16.9–17.6 (–C –(CH ) ); 17.3
181.4 (2-CH).
3 6 3 4
–C –CH ); 51.3 (–NCH CH O–); 51.7 (–NCH CH
6
3
2
2
2
2
NC H O); 54.0 (–NCH CH O–); 65.8 (–NCH CH N-
4
8
2
2
2
2
C H O–); 66.8 (–C (CH ) CH –). 127.9, 133.1, 134.3,
2.7 General Method for Direct Arylation of Furan
and Thiophene with Aryl Bromides
4
8
6
3 5
2
1
34.5, 134.9 and 135.9 (Ar–C); 182.0 (2-CH).
The aryl bromide derivatives (4-bromo acetophenone,
4-bromoanisole and 4-bromo toluene) (1 mmol) and heter-
oaryl derivatives (2-n-butylfuran and 2-n-butylthiophene)
(2 mmol), KOAc (1 mmol) and bis-(NHC)Pd(II) com-
plexes 1a–f (0.003 mmol) were dissolved in N,N-dimethy-
lacetamide (DMAc) (2 mL) in a small Schlenk tube under
argon as described in the literature [46]. The reaction mix-
ture was stirred in an oil bath at 130°C for 1 h then was
cooled to room temperature and the solvent was removed
under vacuum. The obtained residue was purified by col-
umn chromatography (silica gel 60–120 mesh) by using
diethyl ether/n-hexane (1:5) as eluent to afford the pure
product. The purity of the compounds was checked by
gas chromatography (GC) and gas chromatography-mass
2
.5 Synthesis of Bis[1-(3,4,5-trimethoxybenzyl)-3
-
(2-morpholinoethyl)benzimidazol-2-ylidene]
dichloropalladium(II), 1e
The synthesis of 1e was carried out in the same way as that
described for 1a, but chloro[1-(3,4,5-trimethoxybenzyl)-
3
0
-(2-morpholinoethyl)-2-ylidene]silver(I)
(342
mg,
.6 mmol) was used instead of chloro[1-benzyl-3-(2-mor-
pholinoethyl)benzimidazol-2-ylidene] silver(I). Yield:
−
1
0
.210 g, (70%). m.p.: 225–238°C; ν : 1455.2 cm .
(CN)
Anal. Calc. for C H N O PdCl : C: 55.23; H: 5.84;
4
6
58
6
8
2
1
N: 8.40. Found: C: 55.38; H: 5.72; N: 8.21. H NMR
(
300 MHz, CDCI , δ, ppm); 2.42 (t, 8H, J: 4.2 Hz, –NCH
3
2
CH O–); 3.12 (m, 4H, –NCH CH NC H O); 3.51 (s, 8H,
2
2
2
4
8
1
3

Y. Sarı et al.
1
3
spectrometry (GC-MS). Conversions were calculated by
taking into account the conversion of aryl bromides to
products.
Pd(II) complexes in the C NMR spectra appeared highly
downfield shifted at δ 181.6, 181.8, 181.8, 182.0, 181.7 and
181.4 ppm for 1a–f, respectively. The results of the ele-
mental analysis, which is one of the analytical techniques
used to prove the synthesis of compounds, were evaluated
and it was observed that the calculated values were very
close to the found values. The FT-IR data clearly indicated
the presence of ν(CN) at 1452.6, 1456.7, 1448.1, 1456.7,
3
Results and Discussion
−
1
3
.1 Synthesis of Bis-NHCPd(II) Complexes (1a–f)
1455.2and 1454.8 cm for the new bis-(NHC)Pd(II) com-
plexes (1a–f), respectively. Also, we obtained an appropri-
ate single crystal for complex 1a.
The N-benzylbenzimidazole is synthesized by using benzi-
midazole and benzyl chloride [59, 60] (Fig. 1). The syn-
thetic route for unsymmetrically 2-morpholinoethyl-sub-
stituted bis-(NHC)Pd(II) complexes defined in this study
was illustrated in Scheme 1. The new bis-(NHC)Pd(II)
complexes 1a–f were prepared from the synthesized Ag(I)
NHC complexes via transmetallation method. The air and
moisture stable the new bis-(NHC)Pd(II) complexes were
soluble in solvents such as toluene, dichloromethane, and
chloroform. The new bis-(NHC)Pd(II) complexes 1a–f
were prepared by mixing chloro[1-alkyl-3-(2-morpholinoe-
thyl) benzimidazol-2-ylidene] silver(I) with 0.5 equivalents
of PdCl (PhCN) in dichloromethane (20 mL), then the
3.2 Direct Arylation of 2-n-butylfuran and 2-n-butylth-
iophene with Various Aryl Bromides
We carried out some experiments for the parameters of
direct arylation reaction of para-substituted aryl bromides
with 2-n-butylthiophene and 2-n-butylfuran in the presence
of 1a–f as the catalyst. The best reaction conditions con-
sisted of at the temperature: 130°C, base: KOAc, time: 1 h,
solvent: DMAc and catalyst loading: 3 mmol% in the litera-
ture [46].
2
2
reaction mixture was stirred at room temperature for 24 h in
dark condition. The new bis-(NHC)Pd(II) complexes were
obtained as a light yellow solid in 78 to 79% yield. The for-
mations of the nonsymmetrical substituted complexes were
Conversions of the products for 2-n-butylthiophene are
between 63 and 99% and for 2-n-butylfuran are between 59
and 96% (Tables 2, 3). When 4-bromoacetophenone was
used, the best conversion was obtained. However, when
we used 4-bromoanisole, it was obtained at low conversion
(Tables 2, 3).
1
13
confirmed by FT-IR, H NMR and C NMR spectroscopic
methods and elemental analysis techniques. These spectra
1
3
are consistent with the proposed formulate. In the C NMR
Initially, we investigated the binding of 2-n-butylthio-
phene with 4-bromoacetophenone, 4-bromoanisole and
spectra, the Pd–C
resonances of this new bis-(NHC)
carbene
Fig. 1 The molecular structure
of the N-benzylbenzimidazole,
showing the atom labeling. Dis-
placement ellipsoids are drawn
at the 25% probability level
1
3

Synthesis, Characterization and Crystal Structure of New 2-Morpholinoethyl-Substituted…
O
O
O
N
N
N
N
N
[PdCl (PhCN) ]
N
Ag O
2
2
2
Cl
2
AgCl
PdCl2
2
o
DCM
DCM, 25 C, 24 h
2
N
R
N
R
N
R
o
2
5 C, 24 h
1
O
O
,
,
,
,
R:
,
O
a
b
c
d
e
f
Scheme 1 Synthesis of bis-(NHC)Pd(II) Complexes 1a–f
4
-bromotoluene by using complexes 1a–f as the catalyst.
dichloromethane solvent molecule in the triclinic space
−
When the effects of 1a–f in the formation of the products
group P 1. As depicted in Fig. 2, the asymmetric unit has
one-half-molecule and it is completed with a twofold sym-
metry axis [symmetry code: 1−x, 1−y, 1−z]. The struc-
ture shows a distorted square-planar geometry in a trans
configuration around the metal center. The Pd–C bond
length [2.016 (1) Å] is compatible with the many other
trans-Pd(II) complexes, whereas it is longer than the cis-
configuration ones [62–65]. In the study of Huynh et al.,
these results show that the carbene ligands are more weakly
bound to the Pd-center in the trans-form [66]. The planes
of the N-benzylbenzimidazole are almost perpendicular
2
8
4
, 3 and 4 were analyzed, conversions of 99–91, 63–89 and
2–93% were observed respectively (Table 2). The use of
-bromoacetophenone with 2-n-butylthiophene gave the
desired coupling product for different complexes (1b, 1d,
and 1f) as catalysts in better excellent conversion than the
others, such as 95, 99 and 95%, respectively (Table 2).
Then, we investigated the binding of 2-n-butylfuran with
4
-bromoacetophenone, 4-bromoanisole, and 4-bromotolu-
ene with complexes 1a–f as the catalyst. When the effects
of 1a–f in the formation of product 5, 6 and 7 were ana-
lyzed, conversions of 86–96, 59–81 and 83–93% were
observed respectively (Table 3). The best results were
obtained when 2-n-butylthiophene with 4-bromoaceto-
phenone were used (Table 3). Finally, 2-n-butylfuran was
bound with 4-bromoanisole to give the arylated products
i
i
[74.65(2)°] to the Pd/C1/C1 /Cl/Cl plane. All other bond
lengths and angles are shown in Tables 4 and 5, mostly
consistent with the Pd(II) complex studies in the literature
[67, 68].
In the crystal structure, molecules are linked by inter-
molecular C–H⋯O hydrogen bond [H⋯O=2.46 Å,
C–O=3.353(2) Å, C–H⋯O=161°, symmetry code:
1+x, −1+y, 1+z] to form an infinite chain along the
6
in fewer conversions. When 4-bromoacetophenone and
4
-bromotoluene with 2-n-butylfuran were utilized in the
direct arylation reaction, conversions of the products (5 and
2
7
) were obtained and observed to be better than the prod-
ab plane. This hydrogen bond also generates R (16) ring
2
uct 6 (Table 3). When compared to similar studies [53, 61],
published recently, bis-(NHC)Pd(II) complexes that we
have synthesized to appear highly active catalysts.
motif (Fig. 3). Moreover, there is a strong C–H⋯pi inter-
action between the C13 atom of the morpholine ring and
the benzene ring of the benzimidazole moiety [Cg: C2/C3/
C4/C5/C6/C7; C13–Cg 3.697(3) Å, H13A⋯Cg 2.81 Å,
C13–H13A⋯Cg 152°, symmetry code: −x, 1−y, 1−z],
which is responsible for the 2D supramolecular network
and stabilization of the crystal structure.
3
.3 Structure Description of the Complex 1a
The results of the single crystal X-ray diffraction analysis
illustrate that complex 1a crystallizes with a disordered
1
3

Y. Sarı et al.
Table 2 Bis-(NHC)Pd(II) catalysed direct arylation of 2-n-butylthiophene by using aryl bromides
Pd(II)NHC (1a-f) (0.003mmol)
+
R
Br
R
DMAc (2 ml), KOAc (1mmol)
S
S
o
1
30 C, 1 h
Entry
Ar–Br
Pd(II)NHC
Product
% Conv.
91
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
95
O
O
91
Br
S
99
2
92
95
1a
1b
1c
1d
1e
1f
82
78
63
O
Br
O
S
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
89
3
82
79
1a
1b
1c
1d
1e
1f
87
82
83
Br
S
87
4
92
93
Reaction conditions: 2-n-butylthiophene (2 mmol), aryl bromide (1 mmol), bis-(NHC)Pd(II)(0.003 mmol), KOAc (1 mmol), DMAc (2 mL),
30°C, 1 h, product purity was checked by GC and NMR, conversions were calculated according to aryl bromide
1
1
3

Synthesis, Characterization and Crystal Structure of New 2-Morpholinoethyl-Substituted…
Table 3 Bis-(NHC)Pd(II) catalyzed direct arylation of 2-n-butylfuran by using aryl bromides
Pd(II)NHC (1a-f) (0.003mmol)
+
R
Br
R
DMAc (2 ml), KOAc (1mmol)
O
O
o
1
30 C, 1 h
Entry
Ar–Br
Pd(II)NHC
Product
% Conv.
96
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
93
O
O
88
Br
O
91
5
86
92
1a
1b
1c
1d
1e
1f
74
78
81
O
Br
O
O
1
0
1
2
3
4
5
6
7
8
62
6
1
1
1
1
1
1
1
1
71
59
1a
1b
1c
1d
1e
1f
93
83
87
Br
O
84
7
92
85
Reaction conditions: 2-n-Butylfuran (2 mmol), aryl bromide (1 mmol), bis-(NHC)Pd(II)(0.003 mmol), KOAc (1 mmol), DMAc (2 mL), 130°C,
h, product purity was checked by GC and NMR, conversions were calculated according to aryl bromide
1
1
3

Y. Sarı et al.
Fig. 2 The molecular structure
of the complex 1a, showing the
atom labeling. Displacement
ellipsoids are drawn at the 25%
probability level
C5
C4
C6
C3
C10
C11
C7
C2
C9 N3
O1
N2
C20
C14
C12
C15
C17
N1
C8
C13
C19
Cl1
C1
C18
Pd1
C16
C21
Cl2
i
C1
i
Cl1
Cl3
Table 4 Selected bond length
Atom
Atom
Length/Å
Atom
Atom
Length/Å
Atom
Atom
Length/Å
(
Å) of 1a
Pd1
Pd1
O1
C1
2.0156 (1)
2.3052 (2)
1.4184 (1)
1.4095 (1)
N1
N1
N1
N2
C1
C2
C8
C1
1.3467 (1)
1.3848 (1)
1.4643 (1)
1.3486 (1)
N2
N2
N3
N3
N3
C7
C14
C9
C10
C13
1.3888 (1)
1.4606 (1)
1.4419 (1)
1.4659 (1)
1.4725 (1)
Cl1
C11
C12
O1
Table 5 Selected bond angles
°) of 1a
Atom
Atom
Atom
C1
C1
N1
N2
N2
Angles (°)
Atom
Atom
Atom
Angles (°)
(
Cl1
Cl1
Pd1
Pd1
N1
Pd1
Pd1
C1
C1
C1
89.26 (1)
90.74 (1)
127.12 (1)
126.66 (1)
106.21 (1)
C1
C2
C1
C1
C9
C9
N1
N1
N2
N2
N3
N3
C8
C8
C7
C14
C10
C13
125.09 (1)
124.34 (1)
111.10 (1)
125.00 (1)
110.87 (1)
111.56 (1)
i
iSymmetry code: 1−x, 1−y, 1−z
1
3

Synthesis, Characterization and Crystal Structure of New 2-Morpholinoethyl-Substituted…
2
Fig. 3 Hydrogen bonding of the molecules in the crystal structure and formation of the R (16) ring motif [symmetry codes: (i) 1−x, 1−y, 1−z,
2
(
ii) 1+x, −1+y, 1+z, (iii) 2−x, −y, 2−z]
4
Conclusions
cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Center, 12, Union Road, Cambridge
CB2 1EZ, UK. fax: (+44) 1223-336-033, email: deposit@
ccdc.cam.ac.uk.
As a result, we reported the synthesis of the new 2-mor-
pholinoethyl substituted bis-(NHC)Pd(II) complexes 1a–f.
The bis-(NHC)Pd(II) complexes were prepared via the
Ag(I)NHC complexes transmetallation route. The catalytic
activities of this new 2-morpholinoethyl substituted bis-
Acknowledgements The authors acknowledge İnönü University
Scientific and Technology Center for the elemental analyses of the
compounds and Dokuz Eylül University for the use of the Rigaku
Oxford Xcalibur Eos Diffractometer (purchased under University
Research Grant No: 2010.KB.FEN.13).
(
NHC)Pd(II) complexes have been examined that they are
more efficient and stable catalysts for the direct arylation
reactions of 2-n-butylfuran and 2-n-butylthiophene with
aryl bromide. The crystal structures determination of the
complex 1a and its ligand (N-benzylbenzimidazole) were
performed by single crystal X-ray diffraction method. The
bis-(NHC)Pd(II) complex 1a has a distorted square planar
geometry in the trans configuration. The crystal structure is
stabilized by the intermolecular C–H⋯O hydrogen bonds
and the C–H⋯pi interaction (Tables 4, 5).
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