2-methyl-1,4-benzodioxan-substituted bis(NHC)PdX2 complexes: Synthesis, characterization and the catalytic activity in the direct arylation reaction of some 2-alkyl-heterocyclic compounds

Article abstract of DOI:10.1007/s13738-018-1512-y

Almost in all fields of chemistry, the C–C cross-coupling reactions such as the direct arylation reaction have attracted much attention and have advanced quickly in recent years due to the importance of environment-friendly properties. This study contains

Full text of DOI:10.1007/s13738-018-1512-y

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1512-y
ORIGINAL PAPER
2
-methyl-1,4-benzodioxan-substituted bis(NHC)PdX complexes:
2
Synthesis, characterization and the catalytic activity in the direct
arylation reaction of some 2-alkyl-heterocyclic compounds
Yetkin Gök · Aydın Aktaş1 · Yakup Sarı · Hülya Erdoğan
1
1
1
Received: 19 November 2017 / Accepted: 8 October 2018
©
Iranian Chemical Society 2018
Abstract
Almost in all fields of chemistry, the C–C cross-coupling reactions such as the direct arylation reaction have attracted much
attention and have advanced quickly in recent years due to the importance of environment-friendly properties. This study
contains the synthesis of the 2-methyl-1,4-benzodioxan-substituted bis(NHC)PdX complexes and their catalytic activity in
2
direct arylation reaction. The bis(NHC)PdX complexes have been prepared from the 2-methyl-1,4-benzodioxan-substituted
2
1
Ag(I)NHC complexes via transmetallation method. The bis(NHC)PdX complexes have been characterized using H NMR,
2
1
3
C NMR, FT-IR spectroscopy and elemental analysis techniques. The bis(NHC)PdX complexes have been examined as
2
catalysts in the direct arylation reactions with 2-n-butylfuran, 2-n-butylthiophene and 2-isopropylthiazole, and have dem-
onstrated excellent activity in these reactions.
Keywords N-Heterocyclic carbenes · Direct arylation · Butylfuran · Butylthiophene · 2-Isopropylthiazole
Introduction
applications [19–21] of Pd(II)NHC complexes are known,
but Pd(II)NHC complexes are more well-known for their
unique catalytic properties [22–24].
The importance of NHC ligands in organic and organome-
tallic chemistry is increasing day by day [1–4]. It is empha-
sized that the remarkable effect of NHC ligands on transition
metal catalysis is because of the strong sigma donor charac-
ter even in the oldest reviews [5–7]. It is believed that in the
cross-coupling reactions, in particular, the strong M–NHC
bond prevents the decomposition of the molecular catalysts
In recent years, formation of carbon–carbon bonds via
C–H bond activation has become a popular method for
palladium-catalyzed arylation of heteroaromatics. For this
reaction, most of the heteroaromatic compounds such as
(benzo)thiophenes, (benzo)furans, pyrroles, indoles, oxa-
zoles, imidazoles, pyrazoles or triazoles can be used [25].
In recent years important studies have been published on the
catalytic properties of palladium-based complexes [26–30].
In particular, the catalytic activities on the direct arylation
reactions of the palladium-based complexes containing NHC
ligands are becoming more and more important [31–38].
Therefore, we researched the synthesis and the characteriza-
tion of the 2-methyl-1,4-benzodioxan-substituted bis(NHC)
[
8], and stabilizes the higher oxidation states necessary in
multiple catalytic contexts.
Metal–NHC complexes are unique organometallic com-
pounds in which numerous studies have been carried out on
both catalytic activity studies and medical applications. The
NHC–palladium complexes are simply synthesized by means
of different NHC salts with Pd(OAc) [9–12] and using the
2
transmetallation method [13–15] in which Ag–NHC com-
PdX complexes. Also, we investigated the catalytic activi-
2
plexes are used as the transfer agent with PdCl (PhCN) [16]
ties of the 2-methyl-1,4-benzodioxan-substituted bis(NHC)
2
2
or PdCl (CH CN) [17, 18]. From these complexes, medical
PdX complexes in direct arylation reactions, and they dem-
2
3
2
2
onstrated quite good activity as catalysts in the direct aryla-
tion reactions with 2-n-butylfuran, 2-n-butylthiophene, and
*
Aydın Aktaş
2
-isopropylthiazole.
aydinaktash@hotmail.com
1
Department of Chemistry 44280, Faculty of Science, İnönü
University, Malatya, Turkey
Vol.:(0
1
123456789)
3

Journal of the Iranian Chemical Society
Experimental
Synthesis of dibromo-bis[1-butyl-3-(2-methyl-1,4-benzodi-
oxan)benzimidazol-2-ylidene]palladium(II), 1b
All synthesis involving bis(NHC)PdX complexes 1a–h
2
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
Using the same method for the synthesis of complex 1a,
the 1b complex was prepared from bromo[1-butyl-3-(2-
methyl-1,4-benzodioxan)benzimidazol-2-ylidene]silver(I)
(255 mg·0.50 mmol) and bis(benzonitrile)palladium(II)
chloride [PdCl2(PhCN)2] (95 mg·0.25 mmol). Yield: 79%
(180 mg). Anal. Calc. for C40H44N4O4PdBr2: C: 52.73, H:
indicated and were transferred under Ar: Et O (Na/K alloy),
2
CH Cl (P O ), hexane, toluene (Na).
2
2
4
10
All other reagents were commercially available from
Merck and Aldrich Chemical Co. and used without fur-
ther purification. Melting points were identified in glass
capillaries under air with an Electrothermal-9200 melt-
ing point apparatus. FT-IR spectra were saved in the range
1
4.87, N: 6.15. Found: C: 52.68, H: 4.82, N: 6.11. H NMR
(300 MHz, DMSO-d6) δ (ppm) = 0.97 (t, 6H, –CH2CH-
2CH2CH3, J: 6.8 Hz); 1.53 (m, 4H, –CH2CH2CH2CH3);
2.31 (m, 4H, –CH2CH2CH2CH3); 4.37 (m, 4H, –NCH-
2CHOCH2–); 5.23 (t, 4H, –NCH2CH2CH2CH3 J: 6.0 Hz);
5.34 (m, 2H, –CH2CHOCH2–); 5.38 (d, 4H, –OCHCH2O– J:
−
1
4
00–4000 cm on PerkinElmer Spectrum 100 FT-IR spec-
1
13
trometer. Proton ( H) and Carbon ( C) NMR spectra were
recorded using either a Varian AS 300 Merkur spectrom-
1
3
4.6 Hz); 7.05–7.49 (m, 16H, Ar–H). C NMR (75.47 MHz,
DMSO-d6) δ (ppm) = 14.3 (–CH2CH2CH2CH3); 20.3
(–CH2CH2CH2CH3); 32.4 (–CH2CH2CH2CH3); 47.3
(OCH2CH(CH2)O); 51.3 (–CH2CH2CH2CH3); 53.2
(OCH2CH(CH2)O); 72.4 (OCH2CH(CH2)O); 117.2, 117.4,
117.5, 121.4, 122.0, 123.3, 135.0 (Ar–C); 181.6 (2-C–Pd).
1
13
eter operating at 300 MHz ( H), 75.47 MHz ( C) in CDCl
3
with tetramethylsilane as an internal reference. All 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 chromatography was
performed using silica gel 60 (70–230 mesh). Elemental
analyses were performed by İnönü University Scientific and
Technological Research Center (Malatya, TURKEY).
Synthesis of dibromo-bis[1-(2-methoxyethyl)-3-(2-methyl-1,
4-benzodioxan) benzimidazol-2-ylidene]palladium(II), 1c
Synthesis
Using the same method for the synthesis of complex 1a, the
1
c complex was prepared from bromo[1-(2-methoxyethyl)-
Synthesis of dibromo-bis[1-methyl-3-(2-methyl-1,
3-(2-methyl-1,4-benzodioxan)benzimidazol-2-ylidene]
silver(I) (256 mg·0.50 mmol) and bis(benzonitrile)
palladium(II) chloride [PdCl (PhCN) ] (95 mg·0.25 mmol).
4-benzodioxan)benzimidazol-2-ylidene]palladium(II), 1a
2
2
Bromo[1-methyl-3-(2-methyl-1,4-benzodioxan)benzi-
midazol-2-ylidene]silver(I)) (234 mg·0.50 mmol) and
bis(benzonitrile)palladium(II) chloride [PdCl (PhCN) ]
Yield: 87%. (200 mg). Anal. Calc. for C38H40N4O6PdBr2:
C: 49.88, H: 4.41, N: 6.12. Found: C: 49.91, H: 4.42, N:
1
6.14. H NMR (300 MHz, DMSO-d6) δ (ppm) = 3.38 (s,
2
2
(
95 mg·0.25 mmol) in dichloromethane (20 mL) were
6H, –CH2CH2OCH3); 4.32 (t, 4H, –CH2CH2OCH3 J:
7.2 Hz); 4.39 (m, 4H, –NCH2CHOCH2–); 4.42 (m, 4H,
–CH2CH2OCH3 J: 7.2 Hz); 5.40 (d, 4H, –OCHCH2O–J:
4.6 Hz); 5.44 (m, 2H, –CH2CHOCH2–); 6.90–7.04
stirred for 24 h at room temperature in dark conditions.
Then, they were filtered through celite and the solvents
were evaporated under vacuum to make the product
into a white or light yellow solid. The crude product
was recrystallized from dichloromethane/diethyl ether
1
3
(m, 16H, Ar–H). C NMR (75.47 MHz, DMSO-d6) δ
(ppm) = 28.6 (–CH2CH2OCH3); 35.9 (–CH2CH2OCH3);
47.5 (OCH2CH(CH2)O); 53.4 (–CH2CH2OCH3); 58.5
(OCH2CH(CH2)O); 72.5 (OCH2CH(CH2)O); 117.5, 117.6,
117.7, 121.7, 122.1, 123.4, 134.7, 135.1, 142.3 and 143.2 2
(Ar–C); 182.4 (2-C–Pd).
(
1:3) at room temperature. Yield: 84% (174 mg). Anal.
Calc. for C H N O PdBr : C: 49.39, H: 3.90, N: 6.78.
3
4
32
4
4
2
1
Found: C: 49.47, H: 4.83, N: 6.72. H NMR (300 MHz,
DMSO-d ) δ (ppm) = 4.44 (m, 4H, –NCH CHOCH –);
6
2
2
4
.46 (s, 6H, –CH ); 5.28 (m, 4H, –OCHCH O–); 5.38
3
2
1
3
(
m, 2H, –CH CHOCH –); 6.93–7.54 (m, 16H, Ar–H).
C
Synthesis of dibromo-bis[1-(2-ethoxyethyl)-3-(2-methyl-1,4-
benzodioxan) benzimidazol-2-ylidene]palladium(II), 1d
2
2
NMR (75.47 MHz, DMSO–d ) δ (ppm) = 34.5 (–CH );
6
3
4
7.8 (OCH CH(CH )O); 53.5 (OCH CH(CH )O); 72.6
2 2 2 2
(
OCH CH(CH )O); 117.5, 117.6, 117.7, 121.7, 122.2,
Using the same method for the synthesis of com-
2
2
1
23.5, 134.9 and 143.1(Ar–C); 181.8 (2-C–Pd).
plex 1a, the 1d complex was prepared from bromo[1-
(
2-ethoxyethyl)-3-(2-methyl-1,4-benzodioxan)benzi-
midazol-2-ylidene]silver(I) (263 mg 0.50 mmol) and
bis(benzonitrile)palladium(II) chloride [PdCl (PhCN) ]
2
2
(
95 mg·0.25 mmol). Yield: 81% (234 mg). Anal. Calc.
1
3

Journal of the Iranian Chemical Society
for C H N O PdBr : C: 50.95, H: 4.70, N: 5.95.
133.9, 134.2, 135.4, 137.5, 142.2 and 143.2 (Ar–C); 182.3
(2-C–Pd).
4
0
44
4
6
2
1
Found: C: 50.89, H: 4.68, N: 6.01. H NMR (300 MHz,
DMSO-d ) δ (ppm) = 1.06 (t, 6H, –CH CH OCH CH , J:
6
2
2
2
3
6
–
.9 Hz); 3.48 (m 4H, –CH CH OCH CH ); 4.13 (m, 4H,
2 2 2 3
CH CH OCH CH ); 4.48 (m, 4H, –NCH CHOCH –); 4.71
Synthesis of dichloro-bis[1-(2,4,6-trimethylbenzyl)-3-
(2-methyl-1,4-benzodioxan) benzimidazol-2-ylidene]
palladium(II), 1g
2
2
2
3
2
2
(
m, 4H, –CH CH OCH CH ); 5.20 (d, 4H, –OCHCH O– J:
2
2
2
3
2
4
.6 Hz); 5.40 (m, 2H, –CH CHOCH –); 6.82–7.78 (m, 16H,
2 2
1
3
Ar–H). C NMR (75.47 MHz, DMSO-d ) δ (ppm)=15.3
6
(
(
–CH CH OCH CH ); 35.9 (–CH CH OCH CH ); 47.5
Using the same method for the synthesis of complex
1a, the 1g complex was prepared from chloro[1-(2,4,6-
trimethylbenzyl)-3-(2-methyl-1,4-benzodioxan)benzi-
midazol-2-ylidene]silver(I) (271 mg·0.50 mmol) and
bis(benzonitrile)palladium(II) chloride [PdCl (PhCN) ]
2
2
2
3
2
2
2
3
OCH CH(CH )O); 53.6 (–CH CH OCH CH ); 66.3
2
2
2
2
2
3
(
OCH CH(CH )O); 72.3 (–CH CH OCH CH ); 73.2
2 2 2 2 2 3
(
OCH CH(CH )O); 111.7, 112.2, 117.6, 117.8, 122.1, 122.3,
2
2
1
23.7, 134.8, 142.7 and 143.3 (Ar–C); 182.0 (2-C–Pd).
2
2
(
95 mg·0.25 mmol). Yield: 80% (195 mg). Anal. Calc. for
Synthesis of dichloro-bis[1-benzyl-3-(2-methyl-1,4-benzo-
dioxan)benzimidazol-2-ylidene]palladium(II), 1e
C H N O PdCl : C: 64.10, H: 5.38, N: 5.75. Found: C:
52 52 4 4 2
1
64.08, H: 5.35, N: 5.77. H NMR (300 MHz, DMSO-d )
6
δ (ppm)=2.31 and 2.41 (s, 18H, –CH C H (CH ) ); 4.50
2
6
2
3 3
Using the same method for the synthesis of complex 1a,
the 1e complex was prepared from chloro[1-benzyl-3-(2-
methyl-1,4-benzodioxan)benzimidazol-2-ylidene]silver(I)
(d, 4H, –OCHCH O– J: 6.6 Hz); 5.23 (d, 4H, –NCH-
2
CHOCH – J: 9.9 Hz); 5.32 (s, 4H, –CH C H (CH ) ),
2
2
2
6
2
3 3
5.48 (m, 2H, –CH CHOCH –); 6.03–7.51 (m, 20H,
2
2
1
3
(
250 mg·0.50 mmol) and bis(benzonitrile)palladium(II)
Ar–H). C NMR (75.47 MHz, DMSO-d ) δ (ppm)=21.0
6
chloride [PdCl (PhCN) ] (95 mg·0.25 mmol). Yield: 86%
and 21.2 (–CH C H (CH ) ); 47.9 (OCH CH(CH )O);
2
2
2
6
2
3 3
2
2
(
190 mg). Anal. Calc. for C H N O PdCl : C: 62.07,
51.1 (–CH C H (CH ) ); 65.1 (OCH CH(CH )O); 72.3
4
6
40
4
4
2
2 6 2 3 3 2 2
1
H: 4.53, N: 6.29. Found: C: 62.11, H: 4.56, N: 6.32. H
(OCH CH(CH )O); 110.4, 111.7, 112.1, 117.3, 117.7,
2 2
NMR (300 MHz, DMSO-d ) δ (ppm)=4.05 (d, 4H, –NCH-
121.5, 121.9, 122.2, 122.9, 123.3, 127.8, 129.7, 134.5,
6
CHOCH – J: 9.9 Hz); 4.57 (d, 4H, –OCHCH O– J: 9.9 Hz);
135.3, 138.6, 138.8, 142.3 and 143.2 (Ar–C); 182.4 (C–Pd).
2
2
2
4
.93 (m, 2H, –CH CHOCH –); 5.21 (s, 4H, –NCH C H );
2 2 2 6 5
1
3
6
.68–7.67 (m, 26H, Ar–H). C NMR (75.47 MHz, DMSO-
d ) δ (ppm) = 48.1 (OCH CH(CH )O); 52.5 (–CH C H );
Synthesis of dichloro-bis[1-(2-methyl-1,4-benzo-
dioxan)-3-(4-vinylbenzyl)benzimidazol-2-ylidene]
palladium(II), 1h
6
2
2
2
6
5
6
1
1
1
5.1 (OCH CH(CH )O); 72.6 (OCH CH(CH )O); 111.1,
2 2 2 2
17.3, 117.7, 121.5, 121.9, 122.2, 123.5, 127.4, 127.8,
28.2, 128.7, 129.1, 133.9, 134.1, 135.2, 135.4, 142.3 and
43.2 (Ar–C); 182.5(2-C–Pd).
Using the same method for the synthesis of complex 1a,
the 1h complex was prepared from chloro[1-(2-methyl-
1,4-benzodioxan)-3-(4-vinylbenzyl)benzimidazol-2-ylidene]
silver(I) (263 mg·0.50 mmol) and bis(benzonitrile)
palladium(II) chloride [PdCl (PhCN) ] (95 mg·0.25 mmol).
Synthesis of dichloro-bis[1-(4-methylbenzyl)-3-(2-methyl-1,
-benzodioxan) benzimidazol-2-ylidene]palladium(II), 1f
4
2
2
Using the same method for the synthesis of com-
Yield: 84% (198 mg). Anal. Calc. for C H N O PdCl :
50 44 4 4 2
plex 1a, the 1f complex was prepared from chloro[1-
C: 63.74, H: 4.71, N: 5.95. Found: C: 63.76, H: 4.74, N:
1
(
4-methylbenzyl)-3-(2-methyl-1,4-benzodioxan)ben-
5.92. H NMR (300 MHz, DMSO-d ) δ (ppm) = 4.07
6
zimidazol-2-ylidene]silver(I) (257 mg·0.50 mmol) and
bis(benzonitrile)palladium(II) chloride [PdCl (PhCN) ]
(d, 4H, –NCH CHOCH – J: 7.2 Hz); 4.32 (m, 2H,
2
2
–CH CHOCH –); 4.57 (d, 4H, –OCHCH O– J: 7.2 Hz);
2
2
2
2
2
(
95 mg·0.25 mmol). Yield: 90% (207 mg). Anal. Calc. for
5.23 and 5.75 (d, 4H, CH C H CH=CH , J: 7.5 Hz); 5.84
2 6 4
2
C H N O PdCl : C: 62.79, H: 4.83, N: 6.10. Found: C:
(s, 4H, CH C H CH=CH ); 6.60 (dd, 2H, C H CH=CH ,
4
8
44
4
4
2
2
6 4 2 6 4 2
1
13
6
2.82, H: 4.79, N: 6.12. H NMR (300 MHz, DMSO-d ) δ
J: 7.5 Hz); 6.74–7.67 (m, 24H, Ar–H). C NMR
6
(
ppm)=2.29 (s, 6H, –CH C H (CH )); 4.06 (d, 4H, –NCH-
(75.47 MHz, DMSO-d ) δ (ppm) = 48.3 (OCH CH(CH )
2 6 4 3
6
2
2
CHOCH – J: 10.8 Hz); 4.52 (m, 2H, –CH CHOCH –);
O); 51.4 (–CH C H CH = CH ); 65.4 (OCH CH(CH )O);
2
2
2
2
2 6 4 2 2 2
4
.96 (d, 4H, –OCHCH O– J: 10.8 Hz); 5.33 (s, 4H,
71.6 (OCH CH(CH )O); 111.3, 113.8, 115.2, 117.5, 117.8,
2 2
2
1
3
–
NCH C H (CH ); 6.32–7.59 (m, 24H, Ar–H). C NMR
123.5, 126.6, 126.8, 127.1, 127.8, 128.2, 128.7, 131.1,
2
6
4
3
(
75.47 MHz, DMSO-d ) δ (ppm)=21.2 (–CH C H (CH ));
132.2, 135.9, 136.3 and 138.4 (Ar–C and –CH=CH ); 182.1
6
2
6
4
3
2
4
8.1 (OCH CH(CH )O); 53.3 (–CH C H (CH )); 65.8
(2-C–Pd).
2
2
2
6
4
3
(
OCH CH(CH )O); 72.8 (OCH CH(CH )O); 111.1, 117.3
2
2
2
2
1
17.7, 121.5, 121.7, 122.1, 123.3, 129.4, 129.7, 132.2,
1
3

Journal of the Iranian Chemical Society
Results and discussion
the formation of the expected bis(NHC)PdX2 complexes.
1
3
In the C NMR spectra, the Pd-C
resonances of
carbene
1
3
Synthesis of bis(NHC)PdX synthetic route
this bis(NHC)PdX2 complexes in the C NMR spectra
appeared highly downfield when it shifted at δ 181.8,
2
complexes (1a–h)
1
81.60, 181.4, 182.0, 182.5, 182.3, 182.4, and 182.1 ppm
The parent 2-methyl-1,4-benzodioxan-substituted
for 1a–h, respectively. The results of the elemental analy-
sis, which is one of the most 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, 1444, 1455, 1454, 1445, 1447,
bis(NHC)PdX complexes 1a–h were synthesized using
2
the common silver carbene transfer method. The sil-
ver complexes were directly used for transmetalation to
palladium(II) in a 2/1 ratio to afford the desired bis(NHC)
PdX complexes which have been illustrated in Scheme 1.
2
−
1
The bis(NHC)PdX complexes 1a–h were prepared by
1445, and 1447 cm for the bis(NHC)PdX2 complexes
(1a–i), respectively. Crystallographic and physical data of
all compounds are summarized in Table 1.
2
mixing [PdCl (PhCN) ] with 0.5 equivalents of chloro(or
2
2
bromo)[1-alkyl(or aryl)-3-(2-methyl-1,4-benzodioxan)
benzimidazol-2-ylidene]silver(I) in dichloromethane
(
20 mL), then the reaction mixture was stirred at room
Proposed catalytic cycle for bis(NHC)PdX2 com‑
plexes
temperature for 24 h in dark conditions. The bis(NHC)
PdX complexes were obtained as a light yellow and
2
white solid in 79–89% yield. The air- and moisture-sta-
The proposed general catalytic pathway is shown in
Scheme 2. In this cycle, first the oxidative addition of the
aryl halide to the pre-activated bis(NHC)PdX2 complex
takes place. It is believed that oxidative addition occurs
more readily in the presence of the NHC complex thanks
to strong sigma donor properties [39, 40]. Then, the ligand
exchange occurs with the effect of the base. The character
of the base in this step has important due to both oxidative
addition and reductive elimination. Then, the 2-substituted
furan/thiophene molecule is added to the complex. In this
ble bis(NHC)PdX complexes were soluble in solvents
2
such as dimethylformamide and dimethylsulfoxide. The
bis(NHC)PdX complexes were less soluble in halogens
2
such as chloroform and dichloromethane. The formation of
the 2-methyl-1,4-benzodioxan-substituted complexes was
1
13
confirmed by FT-IR, H NMR and C NMR spectroscopic
methods and elemental analysis techniques. These spectra
are consistent with the proposed formulate. This condition
indicated the successful transmetallation and confirmed
Scheme 1 Synthesis of
2
-methyl-1,4-benzodioxan-
substituted bis(NHC)PdX
2
complexes 1a–h
1
3

Journal of the Iranian Chemical Society
Table 1 Physical properties of
compounds and their results of
spectroscopic analysis
13C 2-C–Pd (δ)
IR: ν(CN) (cm−1
)
Compound
Formula
Yield (%)
m.p. (°C)
1
1
1
1
1
1
1
1
a
b
c
d
e
f
C H N O PdBr
84
79
87
81
86
90
80
84
280–282
221–223
232–234
234–236
237–238
146–147
288–289
230–231
181.8
181.6
181.4
182.0
182.5
182.3
182.4
182.1
1452
1444
1455
1454
1445
1447
1445
1447
3
4
32
4
4
2
2
2
2
2
2
2
2
C H N O PdBr
4
0
44
4
4
C H N O PdBr
3
8
40
4
6
C H N O PdBr
4
0
44
4
6
C H N O PdCl
4
6
40
4
4
C H N O PdCl
4
8
44
4
4
g
h
C H N O PdCl
52 52 4 4
C H N O PdCl
5
0
44
4
4
Scheme 2 Proposed catalytic cycle for the direct C–H bond arylation for bis(NHC)PdX complexes
2
step, activation of C–H occurs at position 5. In the course of
C–H activation, the NHC ligand contributes to stabilizing of
the occurring complex. Lastly, C5-arylated furan/thiophene
product has been obtained by the result of reductive elimi-
atom provide the stability of the complex in the catalytic
cycle, while the steric bulk of the ligand facilitating reduc-
tive elimination in the catalytic cycle. Therefore, we used
ligands with different electronic and steric properties on the
nation. In this step, the steric bulk of the bis(NHC)PdX
bis(NHC)PdX complexes.
2
2
complex facilitates elimination of arylated furan/thiophene
product.
In the bis(NHC)PdX complexes, the electronic prop-
2
erties provided by the alkyl substituents attached to the N
1
3

Journal of the Iranian Chemical Society
General method for direct arylation of furan
and thiophene with aryl halides
containing the electron withdrawing substrates is higher
(Table 2).
Second, we examined the coupling of 2-n-butylthio-
phene with 4-bromoacetophenone, 4-bromoanisole, 4-bro-
motoluene and 4-bromobenzene with complexes 1a–h as
the catalyst. When the effect of 1a–h in the formation
of product 6, 7, 8 and 9 was analyzed, conversions of
89–98%, 75–97%, 74–96% and 89–98% were observed,
respectively (Table 3). The use of 4-bromoacetophenone
with 2-n-butylthiophene gave the desired coupling prod-
uct for different complexes (1c and 1d) as catalysts in
better conversion than the others, such as 98 and 98%,
respectively (Table 3). The use of 4-bromobenzene with
2-n-butylthiophene gave the desired coupling product for
different complexes (1a and 1c) as catalysts in better excel-
lent conversion than the others, such as 98% and 99%,
respectively (Table 3). The 2-n-butylthiophene was bound
with 4-bromoanisole to give the arylated products 7 in less
conversions. When 4-bromoacetophenone, 4-bromotolu-
ene and 4-bromobenzene with 2-n-butylthiophene were
utilized in the direct arylation reaction, conversions of the
products (6, 8 and 9) were obtained and observed to be
better than the product 7 (Table 3).
The heteroaryl derivatives (2-n-butylfuran, 2-n-butylthio-
phene and 2-isopropylthiazole) (2 mmol), the aryl halide
derivatives (4-chloroacetophenone, 4-chloroanisole, 4-iodo-
toluene, 4-bromoacetophenone, 4-bromoanisole, 4-bromo-
toluene and 4-bromobenzene) (1 mmol), KOAc (1 mmol)
and bis(NHC)PdX complexes 1a–h (0.003 mmol) were
2
dissolved in N,N-dimethylacetamide (DMAc) (2 mL) in a
small Schlenk tube under argon as described in the litera-
ture [9]. The reaction mixture was stirred in an oil bath at
1
30 °C for 1 h, and then was cooled to room temperature
and the solvent was removed under vacuum. The obtained
residue was purified by column chromatography (silica gel
6
0–120 mesh) 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 chroma-
tography–mass spectrometry (GC–MS). Conversions were
calculated by taking into account the conversion of aryl bro-
mides to products.
Direct arylation of 2‑n‑butylfuran, 2‑n‑butylthio‑
phene and 2‑isopropylthiazole with various aryl
bromides
Then, we investigated the coupling of 2-isopropylthi-
azole with 4-bromoacetophenone, 4-bromoanisole, 4-bro-
motoluene and 4-bromobenzene with complexes 1a–d as
the catalyst. When the effect of 1a–d in the formation of
product 10, 11, 12 and 13 was analyzed, conversions of
98–99%, 85–92%, 80–94% and 76–98% were observed,
respectively (Table 4). The use of 4-bromoacetophenone
with 2-isopropylthiazole gave the desired coupling prod-
uct for all complexes 1a–d as catalysts in better excellent
conversion than the others, such as 99%, 98%, 99%, and
99%, respectively (Table 4). When 4-bromoacetophenone,
4-bromotoluene and 4-bromobenzene with 2-isopropylthi-
azole were utilized in the direct arylation reaction, conver-
sions of the products (10, 11 and 12) were obtained and
observed to be better than the product 13 (Table 4). The
2-isopropylthiazole was bound with 4-bromoanisole to
give the arylated products 13 in less conversions (Table 4).
Then, we used the chloride substrates, which are more
difficult to bind than the bromide substrates. We exam-
ined the catalytic activities of 4-chloroacetophenone and
4-chloroanisole substrates in the presence 2-n-butylfuran
and 2-n-butylthiophene with catalysts 1d and 1h at 16 h and
130 °C. As expected from the experiment, the conversions
of coupling of 4-chloroacetophenone with 2-n-butylfuran
and 2-n-butylthiophene (product 2 and 6) are higher than the
We performed some experiments for the parameters of direct
arylation reaction of para-substituted aryl bromides with
2
-n-butylfuran, 2-n-butylthiophene and 2-isopropylthiazole
(
for 1a–d) in the presence of 1a–h as catalyst. Conversions
of the products for 2-n-butylfuran are between 59 and 99%,
for 2-n-butylthiophene are between 74 and 98%, and for
2
-isopropylthiazole are between 76 and 99% (Tables 2, 3, 4).
First, we examined the coupling of 2-n-butylfuran with
-bromoacetophenone, 4-bromoanisole, 4-bromotoluene,
4
and 4-bromobenzene using complexes 1a–h as the catalyst.
When the effect of 1a–h in the formation of the products 2,
3
, 4 and 5 was analyzed, conversions of 86–99%, 59–96%,
7
5–93% and 73–96% were observed, respectively (Table 2).
In the case of using 2-n-butylfuran with 4-bromoacetophe-
none and 4-bromobenzene, the desired coupling product is
obtained in a better conversion, whereas when the 2-n-butyl-
furan was used with 4-bromoanisole and 4-bromotoluene,
the desired coupling product is obtained in a lower conver-
sion (Table 2). In general, the conversion at the reaction that
used groups containing the electron donating substrates is
lower, while the conversion at the reaction that used groups
1
3

Journal of the Iranian Chemical Society
Table 2 Bis(NHC)
PdX complexes (1a–h)
2
catalyzed direct arylation
of 2-n-butylfuran using aryl
bromides
Entry
R
Pd(II)NHC
1a
Product
% Conv.
95
86
92
99
95
86
92
92
96
64
92
59
96
64
70
59
79
82
75
81
93
82
82
75
96
91
87
73
87
89
88
90
1
2
3
4
5
6
7
8
9
1b
1c
-
COCH
3
1d
1e
2
1f
1g
1h
1a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1b
1c
1d
1e
-
OCH
3
1f
3
1g
1h
1a
1b
1c
1d
1e
-
CH
3
4
1f
1g
1h
1a
1b
1c
-
H
1d
1e
5
1f
1g
1h
Reaction conditions 2-n-butylfuran (2 mmol), aryl bromide (1 mmol), bis(NHC)PdX2
complexes (1a–h) (0.003 mmol), KOAc (1 mmol), DMAc (2 mL), 130 °C, 1 h, product
purity was checked by GC and NMR, conversions were calculated according to aryl bro-
mide
1
3

Journal of the Iranian Chemical Society
Table 3 Bis(NHC)
PdX complexes (1a–h)
2
catalyzed direct arylation of
2
-n-butylthiophene using aryl
bromides
Entry
R
Pd(II)NHC
1a
Product
% Conv.
93
93
98
98
93
93
91
89
97
96
82
91
75
96
82
91
96
91
74
92
94
91
96
90
97
98
89
98
96
97
96
95
1
2
3
4
5
6
7
8
9
1b
1c
1d
1e
-
COCH
3
6
1f
1g
1h
1a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1b
1c
1d
1e
-
OCH
3
7
8
9
1f
1g
1h
1a
1b
1c
1d
1e
-
CH
3
1f
1g
1h
1a
1b
1c
1d
1e
-
H
1f
1g
1h
Reaction conditions 2-n-butylthiophene (2 mmol), aryl bromide (1 mmol), bis(NHC)PdX
2
(
1a–h) (0.003 mmol), KOAc (1 mmol), DMAc (2 mL), 130 °C, 1 h, product purity was
checked by GC and NMR, conversions were calculated according to aryl bromide
1
3

Journal of the Iranian Chemical Society
Table 4 Bis(NHC)
PdX complexes (1a–d)
2
catalyzed direct arylation of
2
-isopropylthiazole using aryl
bromides
Entry
R
Pd(II)NHC
Product
% Conv.
1
2
3
4
1a
1b
1c
1d
99
98
99
99
-
COCH
3
1
0
1
5
6
7
8
9
1a
1b
1c
1d
1a
1b
1c
1d
90
85
90
92
94
80
90
85
-
OCH
3
1
10
11
12
-
CH
3
12
13
14
15
16
1a
1b
1c
1d
83
76
87
98
-
H
13
Reaction conditions 2-isopropylthiazole (2 mmol), aryl bromide (1 mmol), bis(NHC)PdX (1a–
2
d) (0.003 mmol), KOAc (1 mmol), DMAc (2 mL), 130 °C, 1 h, product purity was checked by
GC, conversions were calculated according to aryl bromide
conversions of coupling of 4-chloroanisol with 2-n-butyl-
furan and 2-n-butylthiophene (product 3 and 7) (Table 5).
The use of catalyst 1h that containing aromatic substituent
gave the desired coupling product in better conversion than
the catalyst 1d that containing the aliphatic substituent. We
can say reductive elimination may be easier for aromatic
compounds. However, 4-iodotoluene, which easily bonded
with 2-n-butylfuran and 2-n-butylthiophene (product 4 and
Conclusions
Conclusively, we reported the synthesis of the 2-methyl-
1,4-benzodioxan-substituted bis(NHC)PdX complexes
2
1a–h. The bis(NHC)PdX 1a–h complexes were prepared
2
from the Ag(I)NHC complexes via transmetallation method.
The catalytic activity of this 2-methyl-1,4-benzodioxan-sub-
stituted bis(NHC)PdX complexes have been investigated
2
8
) was obtained at low temperature (80 °C) and in a short
as they are more efficient and stable catalysts for the direct
arylation reactions of 2-n-butylfuran 2-n-butylthiophene and
2-isopropylthiazole with aryl halide.
time (30 min) in the high conversion (Table 6). All the
above catalytic studies, when compared with the similar
studies in the recent [31, 35, 39–41], the bis(NHC)PdX
2
1
a–h complexes appeared to be highly active catalysts in
direct arylation reactions.
1
3

Journal of the Iranian Chemical Society
Table 5 Bis(NHC)PdX
complex (1d and 1 h)
2
catalyzed direct arylation
of 2-n-butylfuran and
2
-n-butylthiophene using aryl
chlorides
Entry
R
E
O
O
Pd(II)NHC
Product
2
% Conv.
1
2
1d
1h
93
96
-
COCH
3
3
4
O
O
1d
1h
75
81
-
OCH
3
3
6
7
5
6
S
S
1d
1h
90
94
-
COCH
3
7
8
S
S
1d
1h
71
77
-
OCH
3
Table 6 Bis(NHC)PdX
complex (1d and 1 h)
2
catalyzed direct arylation
of 2-n-butylfuran and
2
4
-n-butylthiophene using
-iodotoluene
Entry
E
O
O
Pd(II)NHC
Product
% Conv.
1
2
1d
1h
98
99
4
8
3
4
S
S
1d
1h
96
99
Acknowledgements This work was financially supported by Inönü
University Research Fund (IUBAP 2011/21) and the authors acknowl-
edge İnönü University Scientific and Technology Center for the ele-
mental analyses of the compounds.
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