N-heterocyclic carbenes: Useful ligands for the palladium-catalysed direct C5 arylation of heteroaromatics with aryl bromides or electron-deficient aryl chlorides

Article abstract of DOI:10.1002/ejic.200901195

New Pd-N-heterocyclic carbene complexes have been prepared and employed for palladium-catalysed direct arylation of heteroaromatic derivatives by using aryl halides. These catalyst precursors promote the coupling of challenging aryl halides such, as deactivated or congested aryl bromides and also activated aryl chlorides. This procedure employs only 1 mol-% of an air-stable palladium complex. This is a practical advantage over the procedures that employ palladium attached to air-sensitive phosphane ligands, which are often used to promote the coupling of such, aryl halides.

Full text of DOI:10.1002/ejic.200901195

FULL PAPER
DOI: 10.1002/ejic.200901195
N-Heterocyclic Carbenes: Useful Ligands for the Palladium-Catalysed Direct
C5 Arylation of Heteroaromatics with Aryl Bromides or Electron-Deficient
Aryl Chlorides
Ismail Ozdemir,*[a] Yetkin Gök,[a] Özlem Özerog˘lu,[a] Murat Kalog˘lu,[a] Henri Doucet,*[b]
and Christian Bruneau[b]
Keywords: Aryl halides / Atom economy / C–H activation / Carbenes / Heteroaromatics / Palladium
New Pd–N-heterocyclic carbene complexes have been pre- also activated aryl chlorides. This procedure employs only
pared and employed for palladium-catalysed direct arylation
of heteroaromatic derivatives by using aryl halides. These
catalyst precursors promote the coupling of challenging aryl
halides such as deactivated or congested aryl bromides and
1 mol-% of an air-stable palladium complex. This is a practi-
cal advantage over the procedures that employ palladium at-
tached to air-sensitive phosphane ligands, which are often
used to promote the coupling of such aryl halides.
C2 or C5 arylation of heteroaromatics such as furans, thio-
phenes, thiazoles, oxazoles or indoles by means of a palla-
dium-catalysed C–H bond activation has been largely de-
scribed in recent years.[2–7] However, most of these reactions
were performed by using reactive aryl halides such as aryl
iodides or electron-deficient aryl bromides. Relatively few
examples of couplings using deactivated aryl bromides[8,9]
and especially aryl chlorides[10] have been reported so far.
In most cases, the couplings with such challenging sub-
strates were performed by using palladium attached to a
phosphane ligand.[8,10] A few reactions have also been per-
formed with Pd(OH)2, Pd(OAc)2 or Pd/C; however, in the
presence of such a catalyst, the substrate scope is limited,[9]
and the yields are low in some cases.[9a,9c]
Introduction
Due to their inherent biological activity, the synthesis of
arylated heterocycles continues to attract the attention of
synthetic organic chemists. Conventional methods for the
synthesis of such compounds include metal-catalysed cross-
coupling reactions such as Suzuki-, Stille-, Negishi- or
Kumada-type reactions (Scheme 1).[1] They make possible
either the coupling of aryl halides with organometallic de-
rivatives of heterocycles or the coupling of heteroaryl ha-
lides with aryl–metal derivatives. Nevertheless, these pro-
cedures require the preliminary preparation of an organo-
metallic derivative, and produce stoichiometric amounts of
metallic salts as byproducts.
Whereas the efficiency of phosphane ligands has been
explored for these couplings, the influence of carbene li-
gands remains almost unexplored.[10e,11,12] One of the ex-
amples was reported by Sames and co-workers. They de-
scribed in 2006 the use of imidazolylidene ligands of vary-
ing electronic and steric properties for the palladium-cata-
lysed direct arylation of indoles or pyrroles using bromo-
benzene or aryl iodides.[11a] They observed that an impor-
tant steric demand on the carbene ligand led to better re-
sults in terms of both rate and conversion. Fagnou and co-
workers also employed quite congested N-heterocyclic car-
bene palladium catalysts to promote intramolecular direct
arylations of arenes.[12] To the best of our knowledge, N-
heterocyclic carbene ligands have not yet been employed for
the palladium-catalysed direct arylation of furans, thio-
phenes or thiazoles.
Scheme 1.
The direct regioselective couplings of heteroaromatics
with aryl halides by means of C–H bond activation/func-
tionalisation would provide cost-effective and environmen-
tally attractive access to arylated heterocycles. The selective
˙
[a] Chemistry Department, Faculty Science and Letters, Inönü
University,
44069 Malatya, Türkiye
[b] Institut Sciences Chimiques de Rennes,
UMR 6226 CNRS-Université de Rennes “Catalyse et Or-
ganometalliques”,
N-Heterocyclic carbene (NHC) ligands show many inter-
esting properties that make them valuable as ligands in pal-
ladium or ruthenium catalysis.[13–17] A combination of their
powerful σ-donating and weak π-accepting character allows
Campus de Beaulieu, 35042 Rennes, France
Fax: +33-2-23236939
E-mail: henri.doucet@univ-rennes1.fr
1798
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N-Heterocyclic Carbenes as Ligands for Direct C5 Arylation
for the generation of a stronger bond to the metal atom reaction of [PdCl2(PhCN)2] with a silver complex of car-
than their phosphane homologues and leads to the forma- bene ligands at room temperature gave 1a and 1b in 76 and
tion of interestingly robust electron-rich metal complexes. 78% yields, respectively (Scheme 2). Complexes 2a–e were
Consequently, metal–NHC complexes tend to be air-stable, prepared in 55–89% yields by the reaction of carbene salts
easy to handle and highly active in several catalytic trans- with PdCl2 in the presence of 3-chloropyridine and a base
formations for which harsh conditions are required. N- (Scheme 3). The reaction of benzimidazolium salts with
Benzylimidazolinium and benzimidazolium salts have al- Pd(OAc)2 proceeded smoothly on heating at 60 °C for 3 h
ready been used to generate ruthenium–carbene complexes and then 110 °C for a further 2 h to give 3a–e[11c]
that have shown efficient catalytic properties in C–H bond (Scheme 4).
activation[15] and allylic substitution.[16]
“Ligandless” palladium catalysts are generally relatively
inefficient for the direct arylation of heteroaromatics by
using challenging aryl bromides or aryl chlorides.[3d,4e,9]
Therefore, the discovery of more efficient catalysts for the
direct arylation of deactivated aryl bromides or aryl chlo-
rides would provide environmentally attractive and indus-
trially viable procedures. As carbene ligands have proved to
be very useful for several palladium-catalysed reactions, we
decided to explore their potential for the direct 5-arylation
of thiophenes, furans or thiazoles.
Results and Discussion
First, we prepared a range of Pd–NHC complexes using
a variety of carbene ligands. It is known that deviations
Scheme 4.
from the accustomed structures of palladium–NHC com-
plexes can be attributed to steric rather than to electronic
factors.[14c] As the use of relatively congested carbene li-
gands had been found to be required for the direct arylation
of indoles or pyrroles[11a] or arenes,[12] we decided to em-
ploy carbenes bearing relatively bulky N-substituents. The
We initially directed our efforts towards the palladium-
catalysed direct 5-arylation of 2-n-butylfuran with 4-bromo-
anisole using these Pd–NHC complexes (Scheme 5). We
had previously observed that with this deactivated aryl bro-
mide, a low yield of 12% was obtained in the presence of
1 mol-% Pd(OAc)2 as the catalyst in the absence of li-
gand.[3c] At elevated temperature, when a high concentra-
tion of Pd(OAc)2 is employed as the catalyst precursor
(Ͼ1 mol-%), so-called “palladium black”, which is gen-
erally inactive for such catalysed reactions, is formed quite
rapidly. Consequently, in the absence of a stabilising agent
such as phosphane or carbene ligands, the conversions of
such challenging aryl bromides and the yields of coupling
products are generally not increased by using a high catalyst
loading (5–10 mol-%).
Scheme 2.
Scheme 3.
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I. Ozdemir, Y. Gök, Ö. Özeroglu, M. Kaloglu, H. Doucet, C. Bruneau
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FULL PAPER
The reaction of strongly deactivated aryl bromide, 4-bromo-
N,N-dimethylaniline with 2-n-butylfuran gave 5 in 69% in
the presence of 1 mol-% of complex 1b (Table 1, Entry 13).
It should be noted that, in the presence of Pd(OAc)2 as the
catalyst, only traces of 5 had been obtained.[3c] The cou-
pling of the congested aryl bromide, 2-bromotoluene, with
2-n-butylfuran also proceeded to give 6. However, a moder-
ate yield of 41% was obtained in the presence of catalyst 1b
due to the formation of unidentified side-products (Table 1,
Entry 16). Again, the use of Pd(OAc)2 as the catalyst gave
only traces of 6.[3c] Two functionalised furan derivatives
have also been arylated in moderate to good yields by using
4-bromoanisole or 4-bromo-N,N-dimethylaniline (Table 1,
Entries 17–28). Starting from methyl 2-methylfuran-3-
carboxylate, the use of carbene ligands substituted by a
hemilabile ether functionality on one side chain (complexes
1a and 3d) gave the highest yields (Table 1, Entries 21–26).
The direct coupling of aryl chlorides to heteroaromatics,
and especially with furans, is still a very challenging reac-
tion. To the best of our knowledge, only one example of
coupling of a furan derivative (benzofuran) with an aryl
chloride has been reported,[10b] and there is no report on
the use of Pd–N-heterocyclic carbene complexes for this re-
action. We observed that the reaction of 4-chloronitroben-
zene with three furan derivatives gave 10, 12 and 13 in good
yields (Table 2, Entries 1–4 and 6–12). On the other hand,
Scheme 5.
We examined the influence of our Pd–N-heterocyclic car-
bene complexes for this coupling reaction (Table 1, En-
tries 1–11). In all cases, the presence of such ligands on pal-
ladium was found to be beneficial. With several ligands, a
complete conversion of 4-bromomoanisole was observed.
Moreover, the yields in the target product 4 were generally
high (Table 1, Entries 2, 5 and 11). The use of a hemilabile
N-substituent[18] on the carbene in complexes 1a and 3d,
which had been found to be beneficial for some catalysed
reactions, did not improve the yield (Table 1, Entries 1, 2,
10 and 11). We also compared the efficiency of this reaction
of the complexes containing an annullated N-heterocyclic
carbene (1a, 1b and 2a–e) with complexes 3a–e. Annullated
N-heterocyclic carbenes are less electron-rich ligands than
imidazolidinylenes.[16,19] However, we did not observe sig-
nificant differences using these two types of carbene ligands
(Table 1, Entries 1–11). Then, we examined the scope and
limitations of some of these catalysts using a variety of aryl
bromides and furan derivatives (Table 1, Entries 12–28).
Table 1. Pd-catalysed direct arylation of furan derivatives by using aryl bromides (Scheme 5).[a]
[a] Conditions: [Pd] (0.01 mmol), aryl bromide (1 mmol), furan derivative (2 mmol), KOAc (2 mmol), N,N-dimethylacetamide (DMAc;
3 mL), 150 °C, 20 h, conversion of the aryl bromide determined by GC and NMR spectroscopy, isolated yields.
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N-Heterocyclic Carbenes as Ligands for Direct C5 Arylation
Table 2. Pd-catalysed direct arylation of furan derivatives by using aryl chlorides (Scheme 5).[a]
[a] Conditions: [Pd] (0.01 mmol), aryl chloride (1 mmol), furan derivative (2 mmol), KOAc (2 mmol), DMAc (3 mL), 150 °C, 20 h, conver-
sion of the aryl chloride determined by GC and NMR spectroscopy, isolated yields.
1-chloro-4-(trifluoromethyl)benzene was found to be less re- complexes 3a and 3c gave very poor yields (Table 3,
active, and 11 was obtained in only 19% yield (Table 2, En- Entries 14–18). It should be noted that no example of direct
try 5).
arylation of thiophenes with aryl halides by using
Next, we examined the reactivity of 2-n-butylthiophene Pd–N-heterocyclic carbene complexes have been reported
in the presence of these Pd–N-heterocyclic carbene com- so far.
plexes (Scheme 6, Table 3). High yields of 14 were obtained
for the coupling with 4-bromoanisole by using catalysts 1a,
1b or 3a (Table 3, Entries 1, 2 and 6). Even 4-bromo-N,N-
dimethylaniline was successfully coupled with 2-n-butyl-
thiophene in the presence of 1 mol-% of catalyst 1b to give
15 in 69% yield (Table 3, Entry 8). It should be noted that
for this reaction the use of Pd(OAc)2 without addition of
Scheme 6.
Finally, we studied the reactivity of a thiazole derivative
ligands gave no coupling product.[4e] Several complexes with these Pd–carbene complexes (Table 4). As expected,
were employed for the coupling of 1-chloro-4-nitrobenzene; good yields of product 17 were obtained in the presence of
however, only moderate yields of 16 were obtained (Table 3, 2-n-propylthiazole and 4-bromoanisole (Table 4, Entries 1–
Entries 11–18). The best yields were obtained in the pres- 6). The use of more challenging substrate 4-bromo-N,N-di-
ence of the benzimidazolylidene-containing carbene com- methylaniline reacted with 2-n-propylthiazole gave the tar-
plexes 2c, 2d and 2e, whereas imidazolidinium ligand based get compound 18 in high yield (Table 4, Entries 7 and 8).
Table 3. Pd-catalysed direct arylation of 2-n-butylthiophene by using aryl halides (Scheme 6).[a]
[a] Conditions: [Pd] (0.01 mmol), aryl halide (1 mmol), 2-n-butylthiophene (2 mmol), KOAc (2 mmol), DMAc (3 mL), 150 °C, 20 h, con-
version of the aryl halide determined by GC and NMR spectroscopy, isolated yields.
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I. Ozdemir, Y. Gök, Ö. Özeroglu, M. Kaloglu, H. Doucet, C. Bruneau
˘
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FULL PAPER
Table 4. Pd-catalysed direct arylation of 2-n-propylthiazole by using aryl halides (Scheme 7).[a]
[a] Conditions: [Pd] (0.01 mmol), aryl halide (1 mmol), 2-n-propylthiazole (2 mmol), KOAc (2 mmol), DMAc (3 mL), 150 °C, 20 h, conver-
sion of the aryl halide determined by GC and NMR spectroscopy, isolated yields.
(1 mmol) were dissolved in CH2Cl2 (20 mL) and stirred at room
temperature for 24 h. The reaction mixture was purified through a
short pad of Celite. The solvent was removed under reduced pres-
sure. The solid was washed with diethyl ether (3ϫ10 mL) and dried
under vacuum. The crude product was then crystallised from
CH2Cl2/Et2O (1:2) (Scheme 2).
We had previously observed that Pd(OAc)2 catalyses this
reaction in moderate yield.[9d] Up to 72% of product 19 was
obtained for the coupling of 1-chloro-4-nitrobenzene in the
presence of catalyst 3b (Table 4, Entry 15).
Dichloridobis[1-(2-methoxyethyl)-3-(naphthalen-1-ylmethyl)benzimid-
azol-2-ylidene]palladium(II) (1a): Yield: 0.616 g, 76 %; m.p. 237–
238 °C. 1 H NMR (300 MHz, CDCl3 ): δ = 3.46 (s, 6 H,
CH2CH2OCH3), 4.65 (m, 8 H, CH2CH2OCH3), 6.20 (s, 4 H,
CH2 C1 0 H7 ), 6.89–8.45 (m, 22 H, Ar-H) ppm. 13 C NMR
(75.7 MHz, CDCl3): δ = 47.9 49.5, 58.6, 71.8, 110.6, 111.2, 122.3,
122.9, 125.2, 125.5, 126.0, 126.8, 128.1, 128.3, 130.3, 133.2, 134.3,
135.3, 182.5 ppm. C42H40Cl2N4O2Pd (810.12): calcd. C 62.27, H
4.98, N 6.92; found C 62.28, H 4.95, N 6.89.
Conclusion
We have demonstrated that N-heterocyclic carbene li-
gands attached to a palladium(II) centre generate useful
catalyst precursors for the direct regioselective C5 arylation
of furans, thiophenes or thiazoles using some deactivated
aryl bromides. We also report the first examples of direct
arylations of heteroaromatics using aryl chlorides as cou-
pling partners in the presence of Pd–N-heterocyclic carbene
complexes. Our procedure employs only 1 mol-% of air-
stable palladium complexes.[20] This is a practical advantage
over the procedures using palladium attached to air-sensi-
tive phosphane ligands.[10b,10d,10e,10f] Finally, this procedure
is environmentally attractive, as the major byproducts are
AcOK together with HBr instead of the metal salts that
result from using more classical coupling procedures.
Bis[1,3-bis(2-phenylethyl)benzimidazol-2-ylidene]dichloridopalladi-
um(II) (1b): Yield: 0.648 g, 78 %; m.p. 278–279 °C. 1H NMR
(300 MHz, CDCl3): δ = 3.46 (m, 16 H, CH2CH2C6H5), 7.07–7.73
(m, 28 H, Ar-H) ppm. 13C NMR (75.7 MHz, CDCl3): δ = 50.4,
55.4, 112.5, 124.3, 127.1, 129.0, 129.3, 133.5, 138.1, 183.9 ppm.
C46H44Cl2N4Pd (830.19): calcd. C 66.55, H 5.34, N 6.75; found C
66.54, H 5.34, N 6.76.
Synthesis of the NHC–PdCl2–3-Chloropyridine Complexes 2a–e: In
air, a vial was charged with PdCl2 (1.0 mmol), benzimidazolidinium
salt (1.1 mmol), K2CO3 (5 mmol) and a stirrer bar. 3-Chloropyr-
idine (4.0 mL) was added and the mixture heated with vigorous
stirring at 80 °C for 16 h. After cooling to room temperature, the
reaction mixture was diluted with CH2Cl2 and filtered through a
short pad of silica gel covered with a pad of Celite eluting with
CH2Cl2 until the product was completely recovered. Most of the
CH2Cl2 was removed, and the 3-chloropyridine was then vacuum-
distilled and saved for reuse. The pure complexes 2a–e were isolated
after triturating with hexane, decanting the supernatant and drying
under high vacuum (Scheme 3).
Experimental Section
General Remarks: All chemical reactants were obtained from com-
mercial sources and used without further purification. NHC–Pd
and NHC–PdCl2–3-chloropyridine complexes were prepared ac-
cording to known methods.[16] DMAc analytical grade (99%) was
not distilled before use. KOAc (99%+) was employed. All reactions
were carried out under argon by using vacuum lines with Schlenk
tubes and oven-dried glassware. H (200 MHz) and 13C (50 MHz)
spectra were recorded in CDCl3. Chemical shifts (δ) are reported
in ppm relative to CDCl3. Flash chromatography was performed
on silica gel (230–400 mesh).
1
[1,3-Bis(naphthalen-1-ylmethyl)benzimidazol-2-ylidene]dichlorido[(3-
chloropyridine-N)palladium(II) (2a): Yield: 0.613 g, 89%; m.p. 170–
171 °C. 1H NMR (300 MHz, CDCl3): δ = 6.77 (s, 4 H, CH2Ar),
7.05–8.91 (m, 22 H, Ar-H) ppm. 13C NMR (75.7 MHz, CDCl3): δ
Synthesis of the Benzimidazol-2-ylidene–Pd Complexes 1: Benz-
imidazolin-2-ylidene–Ag complex (2 mmol) and [PdCl2(PhCN)2]
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N-Heterocyclic Carbenes as Ligands for Direct C5 Arylation
= 50.5, 115.5, 122.9, 123.6, 124.7, 125.2, 125.6, 126.0, 126.1, 126.9,
128.8, 129.0, 130.2, 130.8, 132.5, 133.8, 134.7, 138.1, 149.2, 150.3,
164.8, 197.3 ppm. C34H26Cl3N3Pd (689.37): calcd. C 59.24, H 3.80,
N 6.10; found C 59.23, H 3.82, N 6.11.
magnetic stirring bar. The Pd complex (0.01 mmol, see Tables 1–4)
and DMAc (3 mL) were added, and the Schlenk tube was purged
several times with argon. The Schlenk tube was placed in a pre-
heated oil bath at 150 °C, and the reactants were stirred for 20 h.
Then, the reaction mixture was analysed by gas chromatography to
determine the conversion of the aryl halide. The solvent was re-
moved by heating of the reaction vessel under vacuum, and the
residue was charged directly onto a silica gel column. The products
were eluted by using an appropriate ratio of diethyl ether/pentane.
Dichlorido(3-chloropyridine-N)[1-(naphthalen-1-ylmethyl)-3-
(2,3,4,5,6-pentamethylbenzyl)benzimidazol-2-ylidene]palladium(II)
(2b): Yield: 0.582 g, 82%; m.p. 135–136 °C. 1H NMR (300 MHz,
CDCl3): δ = 2.42 (m, 15 H, C6Me5), 6.33 (s, 2 H, CH2Ar), 6.71 (s, 2
H, CH2Ar), 6.80–8.91 (m, 15 H, Ar-H) ppm. 13C NMR (75.7 MHz,
CDCl3): δ = 17.7, 18.0, 18.1, 50.7, 51.8, 103.9, 111.6, 114.4, 123.4,
123.7, 126.1, 126.2, 127.2, 129.5, 135.0, 136.5, 138.5, 149.6, 150.6,
157.9, 164.0, 175.5 ppm. C35H34Cl3N3Pd (709.44): calcd. C 59.25,
H 4.83, N 5.92; found C 59.25, H 4.86, N 5.94.
2-n-Butyl-5-(4-methoxyphenyl)furan (4):[3c] The reaction of 4-bro-
moanisole (0.187 g, 1 mmol), 2-n-butylfuran (0.248 g, 2 mmol) and
KOAc (0.196 g, 2 mmol) with 1a (8.00 mg, 0.01 mmol) afforded the
corresponding product 4 in 74% (0.170 g) yield.
Dichlorido(3-chloropyridine-N)[1-(naphthalen-1-ylmethyl)-3-(2,4,6-
trimethylbenzyl)benzimidazol-2-ylidene]palladium(II) (2c): Yield:
0.600 g, 88%; m.p. 154–155 °C. H NMR (300 MHz, CDCl3): δ =
2.43 (s, 9 H), 5.57 (s, 2 H, Ar), 5.92 (s, 2 H, CH2Ar), 6.31 (s, 2 H,
CH2Ar), 6.50–8.32 (m, 15 H, Ar-H) ppm. 13C NMR (75.7 MHz,
CDCl3): δ = 20.8, 20.9, 21.0, 49.1, 50.2, 110.5, 111.2, 122.3, 122.8,
123.1, 124.7, 125.1, 126.1, 126.7, 127.5, 127.9, 128.3, 128.5, 129.1,
129.7, 130.4, 131.2, 132.5, 133.1, 133.7, 134.6, 137.6, 138.1, 138.9,
149.2, 163.8, 182.6 ppm. C33H30Cl3N3Pd (681.39): calcd. C 58.17,
H 4.44, N 6.17; found C 58.15, H 4.45, N 6.17.
2-n-Butyl-5-[4-(dimethylamino)phenyl]furan (5): The reaction of 4-
bromo-N,N-dimethylaniline (0.200 g, 1 mmol), 2-n-butylfuran
(0.248 g, 2 mmol) and KOAc (0.196 g, 2 mmol) with 1a (8.00 mg,
0.01 mmol) afforded the corresponding product 5 in 65% (0.158 g)
1
1
yield. H NMR (200 MHz, CDCl3): δ = 0.95 (t, J = 7.3 Hz, 3 H,
H3CCH2CH2CH2), 1.46 (m, 2 H, H3CCH2CH2CH2), 1.46 (m, 2 H,
H3CCH2CH2CH2), 2.69 (t, J = 7.3 Hz, 2 H, H3CCH2CH2CH2),
2.99 [s, 6 H, C6H4N(CH3)2], 6.04 (d, J = 3.2 Hz, 2 H, furan), 6.35
(d, J = 3.2 Hz, 2 H, furan), 6.75 (d, J = 8.9 Hz, Ar), 7.54 (d, J =
8.9 Hz, Ar) ppm. 13C NMR (50 MHz, CDCl3): δ = 14.3, 22.7, 28.4,
30.5, 40.8, 101.3, 111.9, 112.7, 113.6, 125.5, 126.8, 145.6, 146.5
ppm. C16H21NO (243.34): calcd. C 78.97, H 8.70, N 5.76; found C
78.95, H 8.72, N 5.77.
Dichlorido(3-chloropyridine-N)[1,3-bis(2,3,4,5,6-pentamethylbenzyl)-
benzimidazol-2-ylidene]palladium(II) (2d): Yield: 0.576 g, 79%; m.p.
340 °C (decomp). 1H NMR (300 MHz, CDCl3): δ = 2.36 (m, 30 H,
C6Me5), 6.28 (s, 4 H, CH2C6Me5), 6.40–8.87 (m, 8 H, Ar-H) ppm.
13C NMR (75.7 MHz, CDCl3): δ = 17.7, 17.9, 18.0, 51.8, 111.6,
123.0, 125.1, 128.3, 133.5, 133.6, 135.1, 136.3, 138.4, 148.0, 149.5
150.5, 159.6, 164.4, 175.6 ppm. C36H42Cl3N3Pd (729.52): calcd. C
59.27, H 5.80, N 5.76; found C 59.30, H 5.20, N 5.75.
2-n-Butyl-5-(2-methylphenyl)furan (6):[8l] The reaction of 2-bromo-
toluene (0.171 g, 1 mmol), 2-n-butylfuran (0.248 g, 2 mmol) and
KOAc (0.196 g, 2 mmol) with 1a (8.00 mg, 0.01 mmol) afforded the
corresponding product 6 in 39% (0.084 g) yield.
[5-(4-Methoxyphenyl)furan-2-yl]methyl Acetate (7):[8e] The reaction
of 4-bromoanisole (0.187 g, 1 mmol), furfuryl acetate (0.280 g,
2 mmol) and KOAc (0.196 g, 2 mmol) with 1b (8.30 mg,
0.01 mmol) afforded the corresponding product 7 in 76% (0.187 g)
yield.
[1,3-Bis(2-methoxyethyl)benzimidazol-2-ylidene]dichlorido(3-chloro-
pyridine-N)palladium(II) (2e): Yield: 0.289 g, 55 %; m.p. 104–
105 °C. 1 H NMR (300 MHz, CDCl3 ): δ = 3.36 (s, 6 H,
NCH2CH2OCH3), 5.07 (m, 8 H, NCH2CH2OCH3), 6.40–8.87 (m,
8 H, Ar-H) ppm. 13C NMR (75.7 MHz, CDCl3): δ = 48.6, 59.2,
71.7, 111.3, 123.2, 124.9, 132.7, 135.2, 138.2, 149.2, 150.3, 161.5,
186.5 ppm. C18H22Cl3N3O2Pd (525.16): calcd. C 41.17, H 4.22, N
8.00; found C 41.18, H 4.23, N 8.01.
Methyl 2-(4-Methoxyphenyl)-5-methylfuran-3-carboxylate (8):[8e]
The reaction of 4-bromoanisole (0.187 g, 1 mmol), methyl 2-meth-
ylfuran-3-carboxylate (0.280 g, 2 mmol) and KOAc (0.196 g,
2 mmol) with 1a (8.00 mg, 0.01 mmol) afforded the corresponding
product 8 in 66% (0.163 g) yield.
The complexes 3a, 3c, 3d and 3e were synthesised according to a
literature procedure.[20a]
Methyl 2-[4-(Dimethylamino)phenyl]-5-methylfuran-3-carboxylate
(9): The reaction of 4-bromo-N,N-dimethylaniline (0.200 g,
1 mmol), methyl 2-methylfuran-3-carboxylate (0.280 g, 2 mmol)
and KOAc (0.196 g, 2 mmol) with 3a (10.4 mg, 0.01 mmol) af-
forded the corresponding product 9 in 44% (0.114 g) yield. 1H
NMR (200 MHz, CDCl3): δ = 2.65 (s, 3 H, CH3), 3.00 [s, 6 H,
N(CH3)2], 3.86 (s, 3 H, OCH3), 6.59 (s, 1 H, furan), 6.75 (d, J =
8.8 Hz, 2 H, Ar), 7.54 (d, J = 8.8 Hz, 2 H, Ar) ppm. 13C NMR
(50 MHz, CDCl3): δ = 40.9, 51.7, 57.9, 102.6, 112.7, 114.5, 123.2,
125.3, 126.8, 140.8, 143.5, 164.5 ppm. C15H17NO3 (259.30): calcd.
C 69.48, H 6.61, N 5.40; found C 69.49, H 6.63, N 5.38.
Synthesis of Bis[1-(4-tert-butylbenzyl)-3-(2,4,6-trimethylbenzyl)-
imidazolin-2-ylidene]dichloridopalladium(II) (3b): A stirred solution
of 1,3-dialkylimidazolidinium salt (2 mmol) and Pd(OAc)2
(1 mmol) in DMSO (10 mL) was heated at 60 °C for 3 h and then
at 110 °C for a further 2 h, during which time the reaction solution
changed from being initially orange. The solvent was then removed
in vacuo to give pale yellow solid 3b. The crude product was crys-
tallised from CH2Cl2/Et2O (1:2). The crystals were filtered, washed
with diethyl ether (3ϫ10 mL) and dried under vacuum (Scheme 7).
1
Yield: 0.568 g, 65%; m.p. 230 °C (decomp). H NMR (300 MHz,
CDCl3): δ = 1.32 (s, 18 H, tBu), 2.41 (m, 18 H, Me), 3.18 (m, 4 H,
CH2CH2), 3.40 (m, 4 H, CH2CH2), 5.35 (s, 8 H, CH2Ar), 6.87 (s,
4 H, Ar), 7.29 (d, J = 8.4 Hz, 4 H, Ar), 7.45 (d, J = 8.4 Hz, 4 H,
Ar) ppm. 13C NMR (75.7 MHz, CDCl3): δ = 20.7, 20.9, 21.0, 54.5,
125.8, 127.5, 128.5, 129.3, 131.6, 138.1, 138.4, 151.2, 174.6 ppm.
C48H64Cl2N4Pd (874.37): calcd. C 65.93, H 7.38, N 6.41; found C
65.94, H 7.37, N 6.42.
2-n-Butyl-5-(4-nitrophenyl)furan (10):[3d] The reaction of 1-chloro-
4-nitrobenzene (0.157 g, 1 mmol), 2-n-butylfuran (0.248 g, 2 mmol)
and KOAc (0.196 g, 2 mmol) with 3a (10.4 mg, 0.01 mmol) af-
forded the corresponding product 10 in 69% (0.169 g) yield.
2-n-Butyl-5-[4-(trifluoromethyl)phenyl]furan (11):[3d] The reaction of
1-chloro-4-(trifluoromethyl)benzene (0.181 g, 1 mmol), 2-n-but-
ylfuran (0.248 g, 2 mmol) and KOAc (0.196 g, 2 mmol) with 1a
(8.00 mg, 0.01 mmol) afforded the corresponding product 11 in
19% (0.051 g) yield.
General Procedure for Direct Arylations: In a typical experiment,
the aryl halide (1 mmol), heteroaryl derivative (2 mmol) and KOAc
(2 mmol) were introduced into a Schlenk tube equipped with a
Eur. J. Inorg. Chem. 2010, 1798–1805
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1803

I. Ozdemir, Y. Gök, Ö. Özeroglu, M. Kaloglu, H. Doucet, C. Bruneau
˘
˘
FULL PAPER
[5-(4-Nitrophenyl)furan-2-yl]methyl Acetate (12):[8e] The reaction of
1-chloro-4-nitrobenzene (0.157 g, 1 mmol), (furan-2-yl)methyl ace-
tate (0.280 g, 2 mmol) and KOAc (0.196 g, 2 mmol) with 1a
(8.00 mg, 0.01 mmol) afforded the corresponding product 12 in
70% (0.183 g) yield.
Methyl 2-Methyl-5-(4-nitrophenyl)furan-3-carboxylate (13):[3d] The
reaction of 1-chloro-4-nitrobenzene (0.157 g, 1 mmol), methyl 2-
methylfuran-3-carboxylate (0.280 g, 2 mmol) with 2a (6.90 mg,
0.01 mmol) afforded the corresponding product 13 in 78%
(0.204 g) yield.
2-n-Butyl-5-(4-methoxyphenyl)thiophene (14):[4e] The reaction of 4-
bromoanisole (0.187 g, 1 mmol), 2-n-butylthiophene (0.280 g,
2 mmol) and KOAc (0.196 g, 2 mmol) with 1a (8.00 mg,
0.01 mmol) afforded the corresponding product 14 in 80%
(0.197 g) yield.
2-n-Butyl-5-[4-(dimethylamino)phenyl]thiophene (15):[4e] The reac-
tion of 4-bromo-N,N-dimethylaniline (0.200 g, 1 mmol), 2-n-butyl-
thiophene (0.280 g, 2 mmol) and KOAc (0.196 g, 2 mmol) with 1b
(8.30 mg, 0.01 mmol) afforded the corresponding product 15 in
69% (0.179 g) yield.
[1]
[2]
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2-n-Butyl-5-(4-nitrophenyl)thiophene (16): The reaction of 1-chloro-
4-nitrobenzene (0.157 g, 1 mmol), 2-n-butylthiophene (0.280 g,
2 mmol) with 2a (6.90 mg, 0.01 mmol) afforded the corresponding
product 16 in 40% (0.104 g) yield. 1H NMR (200 MHz, CDCl3):
δ = 0.98 (t, J = 7.4 Hz, 3 H, H3CCH2CH2CH2), 1.45 (m, 2 H,
H3CCH2CH2CH2), 1.75 (m, 2 H, H3CCH2CH2CH2), 2.88 (t, J =
7.4 Hz, 2 H, H3CCH2CH2CH2), 6.92 (d, J = 3.7 Hz, 1 H, thio-
phene), 7.19 (d, J = 8.9 Hz, Ar), 8.17 (d, J = 3.7 Hz, 1 H, thio-
phene), 8.23 (d, J = 8.9 Hz, Ar) ppm. 13C NMR (50 MHz, CDCl3):
δ = 14.1, 22.7, 30.5, 34.1, 122.3, 123.2, 123.6, 124.7, 135.5, 139.8,
145.4, 148.7 ppm. C14H15NO2S (261.34): calcd. C 64.34, H 5.79, N
12.24; found C 64.36, H 5.80, N 12.23.
2-(4-Methoxyphenyl)-5-n-propylthiazole (17):[9d] The reaction of 4-
bromoanisole (0.187 g, 1 mmol), 2-n-propylthiazole (0.254 g,
2 mmol) and KOAc (0.196 g, 2 mmol) with 1a (8.00 mg,
0.01 mmol) afforded the corresponding product 17 in 82%
(0.191 g) yield.
2-[4-(Dimethylamino)phenyl]-5-n-propylthiazole (18):[9d] The reac-
tion of 4-bromo-N,N-dimethylaniline (0.200 g, 1 mmol), 2-n-pro-
pylthiazole (0.254 g, 2 mmol) and KOAc (0.196 g, 2 mmol) with 1a
(8.00 mg, 0.01 mmol) afforded the corresponding product 18 in
71% (0.175 g) yield.
2-(4-Nitrophenyl)-5-n-propylthiazole (19):[9d] The reaction of 1-
chloro-4-nitrobenzene (0.157 g, 1 mmol), 2-n-propylthiazole
(0.254 g, 2 mmol) and KOAc (0.196 g, 2 mmol) with 3a (10.4 mg,
0.01 mmol) afforded the corresponding product 19 in 68%
(0.169 g) yield.
[5]
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[8]
5-(4-Cyanophenyl)-2-n-propylthiazole (20):[9d] The reaction of 4-
chlorobenzonitrile (0.138 g, 1 mmol), 2-n-propylthiazole (0.254 g,
2 mmol) and KOAc (0.196 g, 2 mmol) with 2d (7.30 mg,
0.01 mmol) afforded the corresponding product 20 in 41%
(0.094 g) yield.
Acknowledgments
We thank the Centre National de la Recherche Scientifique and
˙
“Rennes Metropole”, Inönü University Research Fund (BAP 2009/
13) and Technological and Scientific Research Council of Türkiye
˙
TÜBITAK (107T419 and 108T411) for providing financial sup-
port.
1804
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1798–1805

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Received: December 10, 2009
Published Online: March 15, 2010
Eur. J. Inorg. Chem. 2010, 1798–1805
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1805