N-Propylphthalimide-substituted bis-(NHC)PdX2 complexes: synthesis, characterization and catalytic activity in direct arylation reactions

Article abstract of DOI:10.1007/s11243-017-0190-4

Palladium-catalyzed direct arylation of heteroaromatics has become a popular method for producing carbon–carbon bonds via C–H bond activation. A wide diversity of heteroaromatics such as furan, thiophenes and thiazoles can be used for this reaction. This

Full text of DOI:10.1007/s11243-017-0190-4

Transit Met Chem
DOI 10.1007/s11243-017-0190-4
N‑Propylphthalimide‑substituted bis‑(NHC)PdX2 complexes:
synthesis, characterization and catalytic activity in direct
arylation reactions
Hülya Erdoğan1 · Aydın Aktaş1 · Yetkin Gök1 · Yakup Sarı1
Received: 29 July 2017 / Accepted: 23 October 2017
© Springer International Publishing AG, part of Springer Nature 2017
Abstract Palladium-catalyzed direct arylation of heteroar-
omatics has become a popular method for producing carbon–
carbon bonds via C–H bond activation. A wide diversity of
heteroaromatics such as furan, thiophenes and thiazoles can
be used for this reaction. This paper reports the synthesis of
N-propylphthalimide-substituted bis-(NHC)PdX2 complexes
(NHC = N-heterocyclic carbene), and their catalytic activ-
ity in direct arylation reactions. The complexes have been
prepared from Ag(I)NHC precursors by transmetallation
and characterized by spectroscopy and elemental analysis.
The bis-(NHC)PdX2 complexes show excellent activity as
catalysts in the direct arylation reactions of 2-n-butylfuran,
2-n-butylthiophene and 2-isopropylthiazole.
Many chemists have devoted time to the development of new
Pd-catalyzed direct arylation reactions. To date, a wide range
of electronically rich and poor (hetero)aromatic compounds
have been successfully used in palladium-catalyzed direct
arylation reactions [12–19], and this approach is one of the
most efective methods to access aryl–heteroaryl derivatives
[20–22].
Numerous studies have been carried out on the catalytic
activities of Pd(II)-based complexes containing diferent
ligands [23, 24]. In recent years, Pd–NHC complexes con-
taining N-heterocyclic carbene (NHC) ligands have attracted
great interest [25–27]. Complexes of NHC ligands have
distinctive properties such as being strong σ-donors, weak
π-acceptors and good resistance to heat, air and moisture
[28–30].
Introduction
In our work, we have investigated the synthesis and char-
acterization of bis-(NHC)PdX2 complexes. Also, we exam-
ined the catalytic activities of these complexes in direct
arylation reactions. The complexes proved to have fairly
good activity, even with low catalyst loadings, in direct
arylation reactions with 2-n-butylfuran, 2-n-butylthiophene
and 2-isopropylthiazole.
Direct arylation of aromatic and heteroaromatic C–H bonds
has become an important method of aryl C–C bond forma-
tion in organic chemistry. Some catalytic systems developed
for C–H bond transformations can allow eco-friendly syn-
thesis methods [1–6]. One of the most common methods
used for the formation of aryl–aryl bonds is by transition
metal complex-mediated reactions. Suzuki–Miyaura, Stille
and Negishi couplings are among the most important exam-
ples of these methods [7, 8].
Experimental
In recent years, palladium catalytic systems have attracted
much attention in metal-catalyzed direct arylation reactions
due to their selectivity, efciency and versatility [9–11].
All synthesis involving bis-(NHC)PdX2 complexes 1a–i
were carried out under an inert atmosphere in flame-
dried glassware using standard Schlenk techniques. The
solvents used were purifed by distillation over the dry-
ing agents indicated and were transferred under Ar: Et2O
(Na/K alloy), CH2Cl2 (P4O10), hexane, toluene (Na). All
other reagents were obtained commercially from Merck
and Aldrich, and used without further purifcation. Melting
points were measured in glass capillaries under air with an
* Aydın Aktaş
aydinaktash@hotmail.com
1
Department of Chemistry, Faculty of Science, İnönü
University, 44280 Malatya, Turkey
Vol.:(0123456789)
1 3

Transit Met Chem
Electrothermal-9200 melting point apparatus. FTIR spec-
tra were obtained in the range of 400–4000 cm−1 on a Per-
kin–Elmer Spectrum 100 FTIR spectrometer. Proton (1H)
and carbon (13C) NMR spectra were recorded using a Varian
AS 300 Merkur spectrometer operating at 300 MHz (1H)
or 75.47 MHz (13C) in CDCl3 with tetramethylsilane as an
internal reference. Reaction products were assayed 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 flm thick-
ness. Column chromatography was performed using silica
gel 60 (70–230 mesh). Elemental analyses were obtained by
the İnönü University Scientifc and Technological Research
Center (Malatya, TURKEY). Crystallographic and physical
data of all the complexes are summarized in Table 1.
Preparation of complex 1b
According to the same procedure as for complex 1a, complex
1b was prepared from bromo[1-ethyl-3-(N-propylphthalim-
ide)benzimidazol-2-ylidene]silver(I) (271 mg. 0.52 mmol).
Yield: 0.15 g (60%). Anal. Calc. for C40H38N6O4PdBr2:
C: 51.49, H: 4.11, N: 9.01. Found: C: 51.46, H: 4.09, N:
9.03. 1H NMR (300 MHz, DMSO-d6) δ (ppm) = 1.65 (m,
6H, –CH2CH3); 2.51 (m, 4H, –(C6H4)NCH2CH2CH2N–);
3.89 (m, 4H, –(C6H4)NCH2CH2CH2N–); 4.72 (m, 4H,
–CH2CH3); 4.92 (m, 4H, –(C6H4) NCH2CH2CH2N–);
7.31–7.90 (m, 16H, Ar–H). 13C NMR (75.47 MHz,
DMSO-d6) δ (ppm) = 15.2 (–CH2CH3); 28.8 (–(C6H4)
NCH2CH2CH2N–); 36.2 (–(C6H4)NCH2CH2CH2N–); 46.2
(–CH2CH3); 55.4 (–(C6H4)NCH2CH2CH2N–); 111.3, 123.5,
132.2, 132.3, 133.7, 133.8, 134.0, 134.1, 134.7 and 134.8
(Ar–C); 181.0 (2–C–Pd).
Preparation of complex 1a
A mixture of bis(benzonitrile)palladium(II) chloride
[PdCl2(PhCN)2] (0.1g, 0.26 mmol) and bromo[1-methyl-
3-(N-propylphthalimide)benzimidazol-2-ylidene]silver(I)
(0.264 g, 0.52 mmol) in dichloromethane (20 mL) was
stirred for 24 h at room temperature in the dark. The mix-
ture was fltered through celite, and the solvents were evapo-
rated under vacuum to aford the product as a white or light
yellow solid. The crude product was recrystallized from
dichloromethane/diethyl ether (1:3) at room temperature.
Yield: 0.21 g (89%). Anal. Calc. for C38H34N6O4PdBr2: C:
50.43, H: 3.79, N: 9.29. Found: C:50.47, H:3.83, N:9.26.
1H NMR (300 MHz, DMSO-d6) δ (ppm) = 2.59 (m, 4H,
–(C6H4)NCH2CH2CH2N–); 4.35 (t, 4H, –(C6H4)NCH-
2CH2CH2N– J: 7.5 Hz); 4.44 (s, 6H, –CH3); 5.01 (m, 4H,
Preparation of complex 1c
According to the same procedure as for complex 1a, com-
plex 1c was prepared from bromo[1-butyl-3-(N-propyl-
phthalimide)benzimidazol-2-ylidene]silver(I) (285 mg.
0.52 mmol). Yield: 86% (221 mg). 0.22 g (86%). Anal. Calc.
for C44H46N6O4PdBr2: C: 53.43, H: 4.69, N: 8.50. Found:
1
C: 53.39, H: 4.74, N: 8.47. H NMR (300 MHz, DMSO-
d6) δ (ppm) = 1.09 (t, 3H, –CH2CH2CH2CH3, J: 6.9 Hz);
1.55 (m, 4H, –CH2CH2CH2CH3); 2.26 (m, 4H, –CH2CH-
2CH2CH3); 2.73 (m, 4H, –(C6H4)NCH2CH2CH2N–);
3.96 (t, 4H, –(C6H4) NCH2CH2CH2N, J: 6.9 Hz); 4.81
(m, 4H, –CH2CH2CH2CH3); 4.93 (m, 4H, –(C6H4)NCH-
2CH2CH2N–); 7.27–7.89 (m, 16H, Ar–H). 13C NMR (75.47
MHz, DMSO-d6) δ (ppm) = 13.7 (–CH2CH2CH2CH3);
20.4 (–CH2CH2CH2CH3); 29.4 (–(C6H4)NCH2CH2CH2N–);
35.1 (–(C6H4)NCH2CH2CH2N–); 41.0 (–CH2CH2CH2CH3);
56.1 (–CH2CH2CH2CH3); 56.6 (–(C6H4)NCH2CH2CH2N–);
110.9, 111.2, 123.0, 123.3, 123.4, 132.1, 133.1 and 134.1
(Ar–C); 181.2 (2–C–Pd).
–(C6H4)NCH2CH2CH2N–); 7.29–7.90 (m, 16H, Ar–H). 13
C
NMR (75.47 MHz, DMSO-d6) δ (ppm) = 29.2 (–(C6H4)
NCH2CH2CH2N–); 34.7 (–CH3); 36.1 (–(C6H4)NCH-
2CH2CH2N–); 55.6 (–(C6H4)NCH2CH2CH2N–); 110.2,
110.3, 123.1, 123.2, 123.4, 132.1, 132.2, 133.8, 134.1 and
135.1 (Ar–C). 181.5 (2–C–Pd).
Table 1 Physical properties
and spectroscopic analysis of
the complexes
Compound
Formula
Yield (%)
m.p. (°C)
13C 2-C-Pd (δ)
IR: ν(CN) (cm−1
)
1a
1b
1c
1d
1e
1f
1 g
1 h
1i
C38H34N6O4PdBr2
C40H38N6O4PdBr2
C44H46N6O4PdBr2
C42H42N6O6PdBr2
C44H46N6O6PdBr2
C52H46N6O4PdCl2
C52H46N6O4PdCl2
C56H54N6O4PdCl2
C58H46N6O4PdCl2
89
60
86
75
65
81
78
87
84
228–230
244–246
218–220
292–294
248–250
204–205
254–255
276–277
225–227
181.5
181.0
181.2
181.9
181.6
182.1
181.9
182.0
182.6
1442
1464
1465
1462
1454
1432
1440
1426
1432
1 3

Transit Met Chem
Preparation of complex 1d
6.99–7.83 (m, 24H, Ar–H). 13C NMR (75.47 MHz, DMSO-
d6) δ (ppm) = 21.3 (–CH2C6H4(CH3)); 29.0 (–(C6H4)NCH-
2CH2CH2N); 36.3 (–(C6H4)NCH2CH2CH2N); 46.3 (–(C6H4)
NCH2CH2CH2N); 52.7 (–CH2C6H4(CH3)); 110.2, 111.4,
123.1, 124.7, 124.9, 128.4, 128.7, 132.1, 133.9, 134.2,
134.3, 134.5, 135.4, 135.6, 138.3 and 138.6 (Ar–C); 168.2
(C=O); 182.1(2–C–Pd).
According to the same procedure as for complex 1a, com-
plex 1d was prepared from bromo[1-(2-methoxyethyl)-
3-(N-propylphthalimide)benzimidazol-2-ylidene]silver(I)
(287 mg. 0.52 mmol). Yield: 0.19 g (75%). Anal. Calc.
for C42H42N6O6PdBr2: C: 50.80, H: 4.26, N: 8.46. Found:
1
C: 50.73, H: 5.22, N: 8.42. H NMR (300 MHz, DMSO-
d6) δ (ppm) = 3.26 (s, 6H, –CH2CH2OCH3); 3.90 (m, 4H,
–CH2CH2OCH3); 4.97 (m, 4H, –CH2CH2OCH3); 2.51
(m, 4H, –(C6H4)NCH2CH2CH2N); 4.26 (m, 4H, –(C6H4)
NCH2CH2CH2N); 4.99 (m, 4H, –(C6H4)NCH2CH2CH2N);
7.37–7.91 (m, 16H, Ar–H).13C NMR (75.47 MHz, DMSO-
d6) δ (ppm) = 29.4 (–(C6H4)NCH2CH2CH2N); 35.2
(–(C6H4)NCH2CH2CH2N); 56.6 (–(C6H4)NCH2CH2CH2N);
29.1 (–CH2CH2OCH3); 36.2 (–CH2CH2OCH3); 58.9
(–CH2CH2OCH3); 123.4, 123.5, 132.2, 132.3, 134.7 and
134.8 (Ar–C); 181.9 (2–C–Pd).
Preparation of complex 1g
According to the same procedure as for complex 1a, com-
plex 1g was prepared from chloro[1-(4-methylbenzyl)-
3-(N-propylphthalimide)benzimidazol-2-ylidene]silver(I)
(288 mg. 0.52 mmol). Yield: 0.20 g (78%). Anal. Calc. for
C52H46N6O4PdCl2: C: 62.69, H: 4.65, N: 8.44. Found: C:
62.75, H: 4.69, N: 8.48. 1H NMR (300 MHz, DMSO-d6) δ
(ppm) = 2.27 (s, 6H, –CH2C6H4(CH3)); 2.59 (m, 4H, –(C6H4)
CH2CH2CH2N–); 3.71 (t, 4H, –(C6H4)CH2CH2CH2N, J:
7.2 Hz); 4.91 (t, 4H, –(C6H4)CH2CH2CH2N–, J: 7.2 Hz);
5.96 (s, 4H, –(C6H4)CH2C6H4(CH3)); 7.02–7.86 (m, 24H,
Ar–H). 13C NMR (75.47 MHz, DMSO-d6) δ (ppm) = 21.1
(–CH2C6H4(CH3)); 28.9 (–(C6H4)CH2CH2CH2N–); 36.3
(–(C6H4)CH2CH2CH2N–); 46.1 (–(C6H4)CH2CH2CH2N–);
52.3 (–CH2C6H4(CH3)); 110.2, 110.5, 111.5, 123.0, 123.3,
127.6, 127.8, 129.3, 132.1, 132.5, 132.7, 133.9, 134.2,
134.3, 134.5, 137.3 ve 137.5 (Ar–C); 167.9 and 168.2
(C=O); 181.9 (2–C–Pd).
Preparation of complex 1e
According to the same procedure as for complex 1a,
complex 1e was prepared from bromo[1-(2-ethoxyethyl)-
3-(N-propylphthalimide)benzimidazol-2-ylidene]silver(I)
(294 mg. 0.52 mmol). Yield: 0.17 g (65%). Anal. Calc.
for C44H46N6O6PdBr2: C: 51.76, H: 4.54, N: 8.23.
1
Found: C: 51.87, H: 4.64, N: 8.27. H NMR (300 MHz,
DMSO-d6) δ (ppm) = 1.24 (t, 6H, –CH2CH2OCH2CH3,
J: 7.2 Hz); 2.64 (m 4H, –(C6H4)NCH2CH2CH2N–); 3.50
(m 4H, –CH2CH2OCH2CH3); 4.12 (m, 4H, –(C6H4)
NCH2CH2CH2N–); 4.14 (t, 4H, –CH2CH2OCH2CH3,
J: 7.2 Hz); 4.71 (m, 4H, –CH2CH2OCH2CH3); 5.15
(m, 4H, –(C6H4)NCH2CH2CH2N–); 7.28–7.91 (m,
16H, Ar–H). 13C NMR (75.47 MHz, DMSO-d6) δ
(ppm) = 15.2 (–CH2CH2OCH2CH3); 28.9 (–(C6H4)NCH-
2CH2CH2N–); 36.3 (–(C6H4)NCH2CH2CH2N–); 46.2
(–CH2CH2OCH2CH3); 66.8 (–(C6H4)NCH2CH2CH2N–);
69.8 (–CH2CH2OCH2CH3); 70.2 (–CH2CH2OCH2CH3);
109.9, 110.2, 111.6, 112.1, 123.2, 123.3, 132.1, 132.2, 133.8
and 134.1 (Ar–C); 181.6 (2–C–Pd).
Preparation of complex 1h
According to the same procedure as for complex 1a, com-
plex 1h was prepared from chloro[1-(2,4,6-trimethylbenzyl)-
3-(N-propylphthalimide)benzimidazol-2-ylidene]silver(I)
(302 mg. 0.52 mmol). Yield: 0.23 g (87%). Anal. Calc.
for C56H54N6O4PdCl2: C: 63.91, H: 5.17, N: 7.99. Found:
1
C: 64.01, H: 5.20, N: 8.04. H NMR (300 MHz, DMSO-
d6) δ (ppm) = 2.77 (m, 4H, –(C6H4)CH2CH2CH2N–);
4.16 (t, 4H, –(C6H4)CH2CH2CH2N–, J: 7.5 Hz); 5.23 (t,
4H, –(C6H4)CH2CH2CH2N–, J: 7.5 Hz); 2.27 and 2.35 (s,
18H,CH2C6H2(CH3)3); 6.18 (s, 4H, –CH2C6H2(CH3)3),
6.38–7.82 (m, 20H, Ar–H). 13C NMR (75.47 MHz, DMSO-
d6) δ (ppm) = 20.9 and 21.1 (–CH2C6H2(CH3)3); 29.0
(–(C6H4)CH2CH2CH2N); 36.3 (–(C6H4)CH2CH2CH2N);
46.3 (–(C6H4)CH2CH2CH2N); 49.6 (–CH2C6H2(CH3)3);
110.3, 111.8, 122.8, 123.2, 128.2, 129.6, 132.0, 132.2,
133.8, 134.3, 134.5, 138.2, 138.5 ve 138.9 (Ar–C); 168.1
(C=O); 182.0 (C–Pd).
Preparation of complex 1f
According to the same procedure as for complex 1a, com-
plex 1f was prepared from chloro[1-(3-methylbenzyl)-
3-(N-propylphthalimide)benzimidazol-2-ylidene]silver(I)
(288 mg. 0.52 mmol). Yield: 0.21 g (81%). Anal. Calc.
for C52H46N6O4PdCl2: C: 62.69, H: 4.65, N: 8.44. Found:
1
C: 62.65, H: 4.61, N: 8.38. H NMR (300 MHz, DMSO-
Preparation of complex 1i
d6) δ (ppm) = 2.32 (s, 6H, –CH2C6H4(CH3)); 2.81 (m,
4H, –(C6H4)NCH2CH2CH2N–); 4.19 (t, 4H, –(C6H4)
NCH2CH2CH2N, J: 7.2 Hz); 5.14 (t, 4H, –(C6H4)NCH-
2CH2CH2N, J: 7.2 Hz); 5.97 (s, 4H, –CH2C6H4(CH3));
According to the same procedure as for complex 1a, com-
plex 1i was prepared from chloro[1-naftalenomethyl-
3-(N-propylphthalimide)benzimidazol-2-ylidene] silver(I)
1 3

Transit Met Chem
(306 mg. 0.52 mmol). Yield: 0.23 g (84%). Anal. Calc. for
C58H46N6O4PdCl2: C: 65.21, H: 4.34, N: 7.87. Found: C:
65.14, H: 4.32, N: 7.85. 1H NMR (300 MHz, DMSO-d6) δ
(ppm) = 2.83 (m, 4H, (–(C6H4)CH2CH2CH2N–); 4.21 (t, 4H,
–(C6H4)CH2CH2CH2N–, J: 7.2 Hz); 5.18 (t, 4H, –(C6H4)
CH2CH2CH2N–, J: 7.2 Hz); 6.19 (s, 4H, –CH2C10H7);
6.72–7.88 (m, 30H, Ar–H). 13C NMR (75.47 MHz, DMSO-
d6) δ (ppm) = 29.1 (–(C6H4)CH2CH2CH2N–); 36.3 (–(C6H4)
CH2CH2CH2N–); 46.3 (–(C6H4)CH2CH2CH2N–); 49.5
(CH2C10H7); 110.4, 111.3, 122.3, 123.2, 125.2, 125.9, 126.2,
126.8, 128.3, 128.9, 130.3, 130.9, 132.3, 133.1, 133.9, 134.7
ve 134.8 (Ar–C); 168.3 (C=O); 182.6 (2–C–Pd).
60–120 mesh) using diethyl ether/n-hexane (1:5) as eluent
to aford the pure product. The purities of the compounds
were checked by GC and GC–MS. Conversions were cal-
culated based on the aryl bromide.
Results and discussion
Synthesis of bis‑(NHC)PdX2 parent complexes (1a–i)
The synthetic route for the N-propylphthalimide substi-
tuted bis-(NHC)PdX2 complexes is illustrated in Scheme 1.
The bis-(NHC)PdX2 complexes 1a‑i were prepared from
the corresponding N-propylphthalimide substituted Ag(I)
NHC complexes via transmetallation, as reported in the lit-
erature [32]. The bis-(NHC)PdX2 complexes were obtained
as light yellow solids in 60–89% yields. Resistant to air
and moisture, the complexes are soluble in solvents such
as DMF and DMSO, but less soluble in halogenated sol-
vents such as chloroform and dichloromethane. Forma-
tion of the N-propylphthalimide substituted complexes
was confrmed by FTIR, 1H NMR and 13C NMR spectros-
copy and by elemental analysis. The 13C NMR spectra of
the complexes reveal the Pd–C(carbene) signal as a sin-
glet between at 181.0 and 182.6 ppm [33], instead of the
Ag–C(carbene) singlet observed between 188 and 190 ppm
for the Ag(I)NHC complexes [34], confrming the successful
Procedure for arylation of furan, thiophene
and thiazole
The heteroaryl derivatives (2-n-butylfuran, 2-n-butylth-
iophene and 2-isopropylthiazole) (2 mmol), the aryl bro-
mide derivatives (4-bromo acetophenone, 4-bromoani-
sole, 4-bromotoluene and 4-bromobenzene) (1 mmol),
KOAc (1 mmol) and bis-(NHC)PdX2 complexes 1a–i
(0.003 mmol) were dissolved in N,N-dimethylacetamide
(DMAc) (2 mL) in a small Schlenk tube under argon as
described in the literature [31]. The mixture was stirred
in an oil bath at 130 °C for 1 h, then cooled to room tem-
perature, and the solvent was removed under vacuum. The
residue was purifed by column chromatography (silica gel
O
N
O
N
O
O
N
N
[PdCl2(PhCN)2]
DCM, 25 oC, 24 h
PdX2
AgX
2
2
N
R
N
R
1
O
O
CH3
C2H5
R:
a
b
c
d
e
f
g
h
i
Scheme 1 Synthesis of N-propylphthalimide substituted bis-(NHC)PdX2 complexes 1a–i. X = Cl or Br
1 3

Transit Met Chem
Table 2 Catalysis of the direct arylation of 2-n-butylfuran with aryl
bromides by complexes 1a–i (see Scheme 2)
Table 3 Catalysis of the direct arylation of 2-n-butylthiophene with
aryl bromides by complexes 1a–i (see Scheme 3)
Entry
R
Pd(II)NHC
% Conv.
Entry
R
Pd(II)NHC
% Conv.
1
2
3
4
5
6
7
8
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
1a
1b
1c
1d
1e
1f
1g
1h
1i
1a
1b
1c
1d
1e
1f
1g
1h
1i
1a
1b
1c
1d
1e
1f
1g
1h
1i
1a
1b
1c
1d
1e
1f
1g
1h
1i
77
84
93
83
94
77
84
93
97
75
96
96
88
78
93
75
84
60
61
80
89
84
99
74
80
86
84
81
74
70
85
85
76
83
80
77
1
2
3
4
5
6
7
8
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
1a
1b
1c
1d
1e
1f
1g
1h
1i
1a
1b
1c
1d
1e
1f
1g
1h
1i
1a
1b
1c
1d
1e
1f
1g
1h
1i
1a
1b
1c
1d
1e
1f
1g
1h
1i
94
93
99
97
98
94
93
92
98
81
68
72
57
78
51
68
74
57
94
76
61
76
79
93
85
98
63
98
96
99
97
95
93
96
94
91
9
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
–H
Reaction conditions 2-n-butylfuran (2 mmol), aryl bromide (1 mmol),
complexes 1a–i (0.003 mmol), KOAc (1 mmol), DMAc (2 mL),
130 °C, 1 h. Product purity was checked by GC and NMR, conver-
sions were calculated according to the aryl bromide
Reaction conditions 2-n-butylthiophene (2 mmol), aryl bromide
(1 mmol), complex 1a–i (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 the aryl bromide
+
R
Br
O
O
R
Scheme 2 The direct arylation reaction of 2-n-butylfuran with aryl bromides by complexes 1a–i
1 3

Transit Met Chem
+
R
Br
R
S
S
Scheme 3 The direct arylation reaction of 2-n-butylthiophene with aryl bromides by complexes 1a–i
2-isopropylthiazole in the presence of 1a–i as catalyst. Prod-
uct conversions for 2-n-butylfuran were between 60 and
99%, for 2-n-butylthiophene between 51 and 99%, and for
2-isopropylthiazole between 71 and 99% (Tables 2, 3 and 4).
Initially, we investigated the reactions of 2-n-butylfuran
with 4-bromoacetophenone, 4-bromoanisole, 4-bromotolu-
ene and 4-bromobenzene using complexes 1a–i as catalysts.
Conversions of 77–97%, 60–96%, 61–99% and 70–85% were
observed for R = –COCH3, –OCH3, –CH3 and –H, respec-
tively (Table 2). Generally, the conversions for substrates
containing electron-withdrawing groups were higher than
those for substituents containing electron-donating groups.
Next, we investigated the reactions of 2-n-butylthiophene
with 4-bromoacetophenone, 4-bromoanisole, 4-bromotolu-
ene and 4-bromobenzene using complexes 1a–i as catalysts.
Conversions of 92–99%, 51–81%, 61–94% and 91–99% were
observed R=–COCH3, –OCH3, –CH3 and –H, respectively
(Table 3).
Table 4 Catalysis of the direct arylation of 2-isopropylthiazole with
aryl bromides by complexes 1a–e (see Scheme 4)
Entry
R
Pd(II)NHC
% Conv.
1
2
3
4
5
6
7
8
–COCH3
–COCH3
–COCH3
–COCH3
–COCH3
–OCH3
–OCH3
–OCH3
–OCH3
–OCH3
–CH3
–CH3
–CH3
–CH3
–CH3
–H
–H
–H
–H
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
94
99
96
99
98
71
89
92
91
80
99
99
89
87
84
96
73
78
77
81
9
10
11
12
13
14
15
16
17
18
19
20
Finally, we investigated the reactions of 2-isopropylthi-
azole with 4-bromoacetophenone, 4-bromoanisole, 4-bro-
motoluene and 4-bromobenzene using complexes 1a–e as
catalysts. Conversions of 96–99%, 71–92%, 84–99% and
73–96% were observed R = –COCH3, –OCH3, –CH3 and
–H, respectively (Table 4). When compared to similar stud-
ies [32, 35] published recently, the bis-(NHC)PdX2 com-
plexes that we have synthesized in this work appear to be
highly active catalysts.
–H
Reaction conditions 2-isopropylthiazole (2 mmol), aryl bromide
(1 mmol), complex 1a–e (0.003 mmol), KOAc (1 mmol), DMAc
(2 mL), 130 °C, 1 h. Product purity was checked by GC, conversions
were calculated according to the aryl bromide
transmetallation reaction. The results of the elemental analy-
sis were in good agreement with the theoretical values. The
FTIR spectra of all of the complexes 1a–i show a strong
band at 1426–1465 cm−1 for ν(CN) (Table 1). Unfortunately,
despite all our eforts, we could not obtain a single crystal
from these new complexes for X-ray difraction studies.
Conclusions
We have reported the synthesis of N-propylphthalimide sub-
stituted bis-(NHC)PdX2 complexes from the corresponding
Ag(I)NHC complexes via transmetallation. The catalytic
activities of these N-propylphthalimide substituted bis-
(NHC)PdX2 complexes show that they are efcient and sta-
ble catalysts for the direct arylation reactions of 2-n-butyl-
furan, 2-n-butylthiophene and 2-isopropylthiazole with aryl
bromides.
Direct arylation of 2‑n‑butylfuran, 2‑n‑butylthiophene
and 2‑isopropylthiazole
We have investigated the direct arylation of para-substituted
aryl bromides with 2-n-butylfuran, 2-n-butylthiophene and
Scheme 4 The direct arylation
N
N
reaction of 2-isopropylthiazole
with aryl bromides by com-
plexes 1a–e
+ R
Br
i-Pr
S
i-Pr
S
R
1 3

Transit Met Chem
16. Ueda K, Yanagisawa S, Yamaguchi J, Itami K (2010) Angew
Chem Int Ed 49:8946
Acknowledgements This work was fnancially supported by İnönü
University Research Fund (IUBAP 2012/02) and the authors acknowl-
edge İnönü University Scientifc and Technology Center for the ele-
mental analyses of the compounds.
17. Tamba S, Fuji R, Mori A, Hara K, Koumura N (2011) Chem Lett
40:922
18. Fu HY, Chen L, Doucet H (2012) J Org Chem 77:4473
19. Reddy VP, Qiu R, Iwasaki T, Kambe N (2013) Org Lett 15:1290
20. Bheeter CB, Chen L, Soulé J-F, Doucet H (2016) Catal Sci Tech-
nol 6:2005
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