Synthesis, characterization and catalytic behaviour of a palladium complex bearing a hydroxy-functionalized N-heterocyclic carbene ligand

Article abstract of DOI:10.1039/c3nj01281f

The synthesis of a new stable palladium(II) complex (3) featuring an unsymmetrical substituted N-heterocyclic carbene (NHC) ligand with a pendant hydroxy-functionalized group was successfully accomplished via transmetalation of the corresponding bis-NHC silver(I) complex (2). Solid-state structures of both 2 and 3 were determined by single-crystal X-ray diffraction. The catalytic behaviour of 3 in the direct regioselective arylation of furan and thiophene derivatives by using challenging aryl halides was studied, revealing that 3 was capable of promoting these environmentally attractive coupling reactions to afford arylated heterocycles in moderate to good yields.

Full text of DOI:10.1039/c3nj01281f

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Synthesis, characterization and catalytic behaviour
of a palladium complex bearing a hydroxy-
functionalized N-heterocyclic carbene ligand†‡
Cite this: New J. Chem., 2014,
38, 762
Annaluisa Mariconda,a Fabia Grisi,*a Chiara Costabile,a Salvatore Falcone,a
Valerio Bertolasib and Pasquale Longoa
The synthesis of
a new stable palladium(II) complex (3) featuring an unsymmetrical substituted
N-heterocyclic carbene (NHC) ligand with a pendant hydroxy-functionalized group was successfully
accomplished via transmetalation of the corresponding bis-NHC silver(I) complex (2). Solid-state
structures of both 2 and 3 were determined by single-crystal X-ray diffraction. The catalytic behaviour of
3 in the direct regioselective arylation of furan and thiophene derivatives by using challenging aryl
halides was studied, revealing that 3 was capable of promoting these environmentally attractive coupling
reactions to afford arylated heterocycles in moderate to good yields.
Received (in Victoria, Australia)
16th October 2013,
Accepted 27th November 2013
DOI: 10.1039/c3nj01281f
www.rsc.org/njc
complexes containing mono- and poly-ligating NHCs, pincer-
NHCs and mixed donor systems has been generated and
Introduction
N-heterocyclic carbenes (NHCs) have become ubiquitous ligands extensively utilized in homogeneous catalysis.1d,10
in organometallic chemistry, thus proving to be more than just
Our contribution in this field is mainly related to the
phosphine mimics.1 Due to their strong electronic s-donating exploration of modified NHC ligands for ruthenium olefin
properties combined with a shielding steric pattern, NHCs form metathesis catalysts.11 Recently, some of us reported on novel
stronger bonds with metal centers than phosphine ligands,2 zirconium–diamide complexes bearing alkoxide-functionalized
leading to more stable transition metal complexes with superior N-heterocyclic carbenes [NHC–O] that, in combination with
catalytic activities. The structural flexibility of NHCs renders methylaluminoxane, are able to polymerize ethylene to linear
this class of ligands exceptionally intriguing and versatile, polyethylene and propylene to highly isotactic polypropylene.12
as evidenced by numerous applications ranging from homo- Following this study, we decided to extend our investigation on
geneous catalysis to material and medicinal sciences.1,2
In the last few decades, heteroatom-functionalized NHCs
functionalized NHCs to other metal complexes.
In particular, we focused our efforts on the development of
incorporating a pendant neutral or anionic functional group NHC bearing Pd(II) complexes and the study of their catalytic
have received considerable attention in the organometallic activity. This family of palladium complexes has received a lot
chemistry due to their ability to act as chelating or pincer of academic and industry attention during the last ten years, as
ligands. Indeed, they are expected to enhance catalyst stability a result of their ability to mediate numerous organic reactions,
and to offer a key structure for the construction of stereodirecting principally cross-coupling reactions, and of their remarkable
elements for asymmetric catalysis purposes. Moreover, the intro- stability, easy handling and robustness under harsh reaction
duction of a functional group into the side chain of a NHC ligand conditions.10b,d,13 Herein, we describe the synthesis and char-
offers the possibility of anchoring the catalyst to a solid support.3–7 acterization of a new palladium(II) complex incorporating an
As a result, a huge library of early4b,c,8 and late transition9 metal hydroxy-functionalized NHC [NHC–OH]. This complex was
obtained through a synthetic strategy involving transmetalation
of the corresponding NHC–silver complex, whose detailed
a
´
Dipartimento di Chimica e Biologia, Universita di Salerno, Via Giovanni Paolo II 132,
structural analysis is also given for the first time.
I-84084 Fisciano, Salerno, Italy. E-mail: fgrisi@unisa.it
b Dipartimento di Scienze Chimiche e Farmaceutiche, Centro di Strutturistica
The catalytic behavior of the novel palladium complex has
been explored in the direct arylation of heteroaromatic deriva-
tives by using challenging aryl halides. This coupling reaction is
very attractive because arylated heterocycles represent essential
structural units of biologically relevant natural products, drugs
and agrochemicals.14 Moreover, the catalyzed regioselective
´
Diffrattometrica, Universita di Ferrara, Via L. Borsari 46, I-44121 Ferrara, Italy
† This article is dedicated to Professor Adolfo Zambelli on the occasion of his
80th birthday.
‡ Electronic supplementary information (ESI) available. CCDC 948493 and
948494. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3nj01281f
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coupling reactions of heterocycles with aryl-halides by direct resonated at 184.2 ppm as a sharp singlet. The lack of carbene–C
conversion of a C–H bond in a C–C bond,15 instead of tradi- coupling to silver suggests a fluxional behaviour of the NHC–Ag
tional methods involving the stoichiometric reaction of aryl complex 2.19 Although chemical shifts in the NMR spectra clearly
halides with organometallic derivatives of heterocycles or the indicated the formation of an NHC–Ag complex, they did not
reaction of heteroaryl halides with aryl-metal derivatives,16 are allow unambiguous distinction of whether a mono- or bis-NHC
economically and environmentally effective. So far, the effi- complex was formed.
ciency of NHC–Pd complexes has been almost unexplored for
Mass spectrometry (ESI-MS) provided fundamental data on
these couplings, whereas the discovery of more efficient cata- the structure of compounds in the gas phase. In fact, the
lysts would provide environmentally attractive and industrially maximum peak at 467 Da, associated with M + 2 at 469 Da,
viable procedures.
is attributable to [(NHC–OH)2Ag]+. On the other hand, the
elemental analysis of 2 gives a molar ratio among silver, ligand
and iodide of 1 : 1 : 1, therefore, taken together, the NMR, MS
and elemental analyses suggest that complex 2 very likely
consist of ionic structures based on [(NHC–OH)2Ag]+ cations
and [AgI2]ꢀ anions.20 As for NHC Ag(I) complexes reported up to
now, complex superstructures are frequently observed in the
solid state, especially when the NHC contains additional donor
functionalities.9d,18 Usually, with coordinating anions (X = e.g.
halides) mono-NHC Ag(I) complexes of the formula [(NHC)AgX]n
are formed, whereas bis-NHC Ag(I) complexes of the type
[(NHC)2Ag]X when X is a noncoordinating anion, such as
NO3ꢀ, OTfꢀ, BF4ꢀ, and PF6ꢀ, are obtained.18 In solution,
mono-NHC Ag(I) complexes are typically in fast equilibrium
with the respective homoleptic species, whereas bis-NHC Ag(I)
complexes are static in coordination (Scheme 2).
Results and discussion
The synthetic plan to reach the novel palladium complex is
depicted in Scheme 1. The hydroxy-functionalized imidazolium
salt (1) was easily prepared by ring opening of cyclohexenoxide
with imidazole and subsequent reaction in acetonitrile with
iodomethane.17 For coordination of the imidazolium salt 1 as
NHC to palladium, a transmetalation reaction of the corresponding
NHC–Ag complex (2) with PdCl2(CH3CN)2 was employed affording
[NHC–OH]PdCl2(CH3CN) (3) in good yield (69%).
Synthesis and characterization of the [NHC–OH]Ag complex (2)
Transmetalation has proven to be a convenient and efficient
approach to synthesise NHC–metal complexes, since NHC–Ag
complexes are generally air- and moisture-stable, easy to syn-
thesize and with a strong tendency to crystallize. The driving
force for this reaction is the precipitation of silver halide salts.18
Thus, N-methyl,N0-[(2-hydroxy-cyclohexyl)]-imidazolium iodide
1 was treated with Ag2O (1.5 : 1 molar ratio) in refluxing CH2Cl2
under exclusion of light. Ag2O particularly serves as a mild base,
reacting predominantly at the C2 position of the imidazolium
salt without deprotonation of other acidic protons. The silver
complex 2 was isolated as a white solid after filtration and
removal of the solvent under reduced pressure (57%).
Single crystals of 2 suitable for X-ray diffraction were grown
by slow evaporation of a saturated CH2Cl2 solution. The asym-
metric unit of the Ag compound is built up by four independent
[Ag(NHC)2]+ cations, two independent [Ag2I4]2ꢀ anions and two
molecules of acetonitrile.21 A selection of bond distances and
angles is shown in Table 1. Each anion is ‘‘sandwiched’’ between
two cationic complexes [Ag(NHC)2]+ by means of short AgꢁꢁꢁAg
and AgꢁꢁꢁC(carbene) interactions. The two ‘‘sandwiches’’ display
some differences as far as the anion position is concerned. In the
first arrangement, shown in Fig. 1, both the metallic centres of the
anion are involved in AgꢁꢁꢁAg interactions with the cations as well
as in AgꢁꢁꢁC1(carbene) short contacts (Table 2).
Initial structural analyses of the isolated product were
1
conducted using H and 13C NMR. The product appeared to be
spectroscopically pure and, as expected, in the 1H NMR spectrum
the C2-H signal of the imidazole ring was absent, whereas in
the 13C-NMR spectrum the characteristic coordinated carbene
The latter systems are slightly different from the previous
one because the anion is not centered between the two cations
and, accordingly, only one metallic center, Ag7, can interact
with the cationic Ag atoms and with the carbene carbons C1G
and C1H (Fig. 2).
This asymmetric arrangement produces a guest cavity
which, in the crystal, contains two molecules of acetonitrile.
In all the independent cationic Ag complexes the C1(carbene)–
Ag–C10(carbene) angles are slightly bent [C–Ag–C angle of 1571
Scheme 1 Synthesis of [NHC–OH]Pd(II) complex 3.
Scheme 2 Solution structures of mono-NHC Ag(I) complexes.
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Table 1 Selected bond distances and angles (Å and degrees) for 2
Table 2 Intermolecular short interactions (Å) for 2
Distances
O1Aꢁ ꢁ ꢁO1B
2.813(10)
2.971(11)
2.774(11)
2.751(11)
2.871(13)
2.788(10)
2.851(12)
2.992(12)
Ag1ꢁ ꢁ ꢁAg3
3.252(1)
3.239(1)
3.128(1)
3.166(1)
3.186(1)
3.276(1)
3.180(10)
3.212(9)
3.346(10)
3.074(10)
3.242(11)
3.292(11)
O1Aꢁ ꢁ ꢁO1B(1 ꢀ x,ꢀy,1ꢀz)
O1Cꢁ ꢁ ꢁO1D
Ag1ꢁ ꢁ ꢁAg4
Ag2ꢁ ꢁ ꢁAg3
Ag2ꢁ ꢁ ꢁAg4
Ag5ꢁ ꢁ ꢁAg7
Ag6ꢁ ꢁ ꢁAg7
Ag3ꢁ ꢁ ꢁC1A
Ag3ꢁ ꢁ ꢁC1C
Ag4ꢁ ꢁ ꢁC1B
Ag4ꢁ ꢁ ꢁC1D
Ag7ꢁ ꢁ ꢁC1F
Ag7ꢁ ꢁ ꢁC1G
Ag1–C1A
Ag1–C1A
C1A–N2A
Ag2–C1C
C1C–N1C
C1C–N2C
Ag6–C1E
C1E–N1E
C1E–N2E
Ag5–C1G
C1G–N1G
C1G–N2G
2.122(8)
Ag1–C1B
C1B–N1B
C1B–N2B
Ag2–C1D
C1D–N1D
C1D–N2D
Ag6–C1F
C1F–N1F
C1F–N2F
Ag5–C1H
C1H–N1H
C1H–N2H
2.102(8)
1.342(11)
1.349(11)
2.083(8)
1.367(10)
1.361(11)
2.096(11)
1.356(12)
1.344(13)
2.088(9)
1.339(11)
1.358(11)
2.132(8)
O1Cꢁ ꢁ ꢁO1E
O1Dꢁ ꢁ ꢁO1F
O1Eꢁ ꢁ ꢁO1F
1.356(11)
1.311(12)
2.089(10)
1.367(13)
1.340(12)
2.104(10)
1.360(12)
1.344(12)
O1Gꢁ ꢁ ꢁO1H
O1Gꢁ ꢁ ꢁO1H(ꢀx,2 ꢀ x,2 ꢀ z)
1.359(13)
1.362(12)
Ag3–I1
Ag3–I2
Ag3–I3
Ag7–I5
Ag7–I6
Ag7–I7
2.711(1)
2.864(1)
2.861(1)
2.720(1)
2.806(1)
2.839(1)
Ag4–I4
Ag4–I2
Ag4–I3
Ag8–I8
Ag8–I6
Ag8–I7
2.705(1)
2.833(1)
2.883(1)
2.710(1)
2.779(1)
2.838(1)
Angles
C1A–Ag1–C1B
N1A–C1A–N2A
N1B–C1B–N2B
C1E–Ag6–C1F
N1E–C1E–N2E
N1F–C1F–N2F
155.5(3)
105.0(7)
103.3(8)
158.9(4)
105.1(8)
103.9(8)
C1C–Ag2–C1D
N1C–C1C–N2C
N1D–C1D–N2D
C1G–Ag5–C1H
N1G–C1G–N2G
N1H–C1H–N2H
155.0(3)
104.4(7)
106.6(8)
157.8(4)
103.4(8)
104.7(8)
I1–Ag3–I2
I1–Ag3–I3
I2–Ag3–I3
I4–Ag4–I2
I4–Ag4–I3
I2–Ag4–I3
Ag3–I2–Ag4
Ag3–I3–Ag4
116.56(4)
134.36(4)
108.97(4)
125.04(4)
125.04(4)
109.21(4)
71.07(3)
I5–Ag7–I6
I5–Ag7–I7
I6–Ag7–I7
I8–Ag8–I6
I8–Ag8–I7
I6–Ag8–I7
Ag7–I6–Ag8
Ag7–I7–Ag8
131.53(4)
120.53(4)
107.94(7)
122.46(5)
128.59(5)
108.73(4)
71.61(3)
Fig. 2 ORTEP22 view of the latter arrangement of 2 where a [Ag2I4]2ꢀ
anion is asymmetrically ‘‘sandwiched’’ between two [Ag(NHC)]+ cations.
The thermal ellipsoids are at the 50% probability level.
70.40(3)
70.29(4)
bond between the hydroxo groups of cyclohexanol substituents.
The hydrogens of hydroxo groups of structure 2 could not be
localized. Beyond the intramolecular O–HꢁꢁꢁO hydrogen bonds the
hydroxo groups are also involved in intermolecular hydrogen bonds
between couples of cations which are, in such way, held together by
a circular hydrogen bond system as shown in Scheme 1.
The crystal is characterized by infinite ribbons built up by couples
of cations linked by O–Hꢁ ꢁ ꢁO H-bonds and inter-connected to
the anions by means of Agꢁ ꢁ ꢁAg and Agꢁ ꢁ ꢁC(carbene) short
+
interactionsꢁꢁꢁ[Ag(NHC)2]2 ꢁꢁꢁ[Ag2I4]2ꢀꢁꢁꢁ[Ag(NHC)2]+ ꢁꢁꢁ[Ag2I4]2ꢀꢁꢁꢁ
2
[Ag(NHC)2]+ ꢁ ꢁ ꢁ (Fig. 3). The intra and intermolecular distances
2
involving Ag metallic centres are in agreement with other
carbene complexes displaying similar Ag(I)d10ꢁ ꢁ ꢁAg(I)d10 closed
shell short interactions.23–26
Fig. 1 ORTEP22 view of the first arrangement of 2 where a [Ag2I4]2ꢀ anion
is ‘‘sandwiched’’ between two identical but crystallographic independent
[Ag(NHC)]+ cations. The thermal ellipsoids are at the 50% probability level.
Synthesis and characterization of the [NHC–OH]Pd complex (3)
The so-generated NHC Ag(I) complex was afterwards employed
in the reaction with PdCl2(CH3CN)2 in CH2Cl2 at room tem-
perature (1 : 1 molar ratio), following the synthetic procedure
(on average for the four cations)], with respect to the typical developed by Wang and Lin.19 Interestingly, although for NHC
linear conformation of other similar structures,23–26 in order to transfer reactions mono-NHC Ag(I) is by far the most frequently
allow the formation of an intramolecular O–Hꢁ ꢁ ꢁO hydrogen utilized, partially because the more stable bis-NHC Ag(I) complexes
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Fig. 3 Infinite ribbons in the crystal of 2 built up by couples of cations linked by OHꢁ ꢁ ꢁO H-bonds and inter-connected to the anions by means of
Agꢁ ꢁ ꢁAg and Agꢁ ꢁ ꢁC(carbene) short interactions. (i): 1 ꢀ x, ꢀy, 1 ꢀ z; (ii) ꢀx, 2 ꢀ y, 2 ꢀ z.
are believed to be less active in these reactions,9d,27 we found
that the bis-NHC Ag(I) complex 2 was capable of efficiently
transferring one carbene ligand affording the mono-NHC Pd(II)
complex 3. It is worth underlining that this synthetic approach
allowed us to successfully achieve the desired palladium complex,
whereas other methods of carbene introduction failed.28 Notably,
to the best of our knowledge compound 3 represents the first
example of mono-NHC palladium complex featuring an hydroxy-
functionalized NHC ligand. Indeed, only bis-NHC Pd(II) com-
plexes with similar modified NHC ligands have been reported
so far.29 Complex 3 was isolated as an air- and moisture-stable
pale yellow solid and fully characterized by 1D and 2D NMR, mass
spectrometry and elemental analyses.
The structural assignment of 3 was unambiguously established
by X-ray diffraction. The ORTEP22 view of the Pd complex is shown
in Fig. 4. A selection of bond distances and angles is given in Table 3.
The coordination geometry around the Pd(II) centre is essen-
tially square planar with one carbene, two chloride ligands and
one acetonitrile ligand trans to the NHC (N-heterocyclic carbene).
The coordination plane is almost perpendicular to the NHC ring,
the dihedral angle between the two planes being 86.01(6)1. This
conformation allows the formation of a O–Hꢁ ꢁ ꢁCl hydrogen
bond, O1ꢁ ꢁ ꢁCl1 = 3.263(3) Å, between the hydroxo group of the
Fig. 4 ORTEP22 view of 3 showing the thermal ellipsoids at the 50%
probability level.
cyclohexanol substituent at the NHC ring and a coordinated Cl reactions involving deactivated aryl halides have been described
atom. Bond distances between Pd1 centre and the atoms of up to now,15 and the role of NHC ligands in these challenging
ligands are in perfect agreement with those observed in other transformations is almost unexplored.33g,34 Therefore, we decided
very similar complexes.30–32
to employ our Pd(II) complex to promote the direct C5 arylation of
furans and thiophenes (see Scheme 3).
Catalytic activity
The coupling reactions were carried out by using 1 mol% of
As a preliminary study on the catalytic behaviour of 3, we have palladium and KOAc as base in DMF at 150 1C. The formation
chosen the direct regioselective coupling of heteroaromatics of the target arylated heterocycles was monitored by GC and
with aryl halides.
In recent years, numerous studies on the selective C2 or C5 results are summarized in Scheme 3.
1H NMR analyses over a period of 24 h, and the most relevant
arylation of heteroaromatics such as furans, thiophenes, thiazoles,
The reaction of deactivated aryl bromide 4-bromoanisole 4
oxazoles or indoles by means of palladium catalysed C–H bond with functionalized furan derivatives 5 and 7 proceeded to give,
activation have been reported.33 In most cases, the couplings were respectively, heterocoupled products 6 and 8 with moderate
performed by using reactive aryl halides such as aryl iodides or yields (34–40%) in 5 h. Prolonged reaction time (24 h) did not
electron-deficient aryl bromides. A limited number of coupling improve the yields, however, after this time, we observed the
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with slightly higher yields.33g Only a few examples of the
challenging direct coupling of arylchlorides to heteroaromatics
with NHC–Pd complexes are known.33g The reaction of 4-chloro-
nitrobenzene 9 with furan derivative 5, promoted by catalyst 3,
gave 10 in good yield (59%) within 3 h, whereas the reaction of 9
with furanic substrate 7 afforded 11 in lower yield (37%). More-
over, in the last case after 24 hours a decreased yield in the desired
product was registered, as a consequence of undesired secondary
reactions. It is worth to underline that for both reactions a
complete conversion of 4-chloronitrobenzene to side-products is
observed. We also examined the direct arylation of thiophenes
with aryl halides. Also this coupling reaction has been scarcely
investigated using NHC palladium catalysts up to now.33g As for
the reaction of the strongly deactivated arylbromide 4-bromo-N,N-
dimethylaniline 12 with 2-methylthiophene 13, catalyst 3 revealed
low efficiency, affording a very low yield (15%) of the arylated
thiophene derivative 14 in 2 h. Prolonged reaction time (24 h)
decreased the yield of 14, producing unidentified products and
leading to full conversion of the arylbromide 12. A better result
was obtained in the coupling of 4-chloronitrobenzene 9 with
2-methylthiophene 13, that proceeded to form the desired
product 15 with 34% yield in 5 h, in line with the results
obtained in analogous reactions promoted by similar mono-
NHC palladium complexes.33g In this case, conversion of the
aryl chloride 9 is not complete (70%).
Table 3 Selected bond distances and angles (Å and degrees) for 3
Distances
Pd1–Cl1
Pd1–C1
C1–N1
2.2999(6)
1.948(2)
1.342(2)
Pd1–C12
Pd1–N3
C1–N2
2.2979(6)
2.084(2)
1.342(2)
Angles
Cl1–Pd1–C12
C11–Pd1–N3
Cl2–Pd1–N3
N1–C1–N2
177.62(2)
90.60(6)
91.78(6)
106.0(2)
Cl1–Pd1–C1
Cl2–Pd1–C1
C1–Pd1–N3
87.92(6)
89.71(6)
178.32(7)
H-bond
O1–H1
H1ꢁ ꢁ ꢁCl1
0.79(3)
2.69(2)
O1ꢁ ꢁ ꢁCl1
3.263(3)
130(3)
O1–H1ꢁ ꢁ ꢁCl1
Conclusions
In summary, we have described an efficient synthetic route to
mono-NHC Pd(II) complexes featuring a functionalized, unsymme-
trical substituted NHC ligand. The presented complex 3, featuring
both N-hydroxy functional group and N-methyl group on the NHC,
was obtained for the first time through a transmetalation reaction of
the corresponding bis-NHC silver compound 2. Both complexes 2
and 3 were fully characterized by NMR, MS and elemental analyses.
The structures of 2 and 3 were confirmed by single-crystal X-ray
diffraction studies. The catalytic behaviour of 3 was investigated in
the attractive, direct regioselective C5 arylation of heteroaromatics
by using challenging aryl halides, where only few NHC palladium
complexes have been employed up to now. Catalyst 3 proved to be a
suitable catalyst for these coupling reactions. Although no evidence
for possible advantages of a pendant functional group on the NHC
ligand is detected, our preliminary catalytic results encourage
deeper investigation of the catalytic potential of this class of
palladium complexes, also in other cross coupling reactions,
to better recognize NHC modifications that could address further
catalyst design. Moreover, the pendant hydroxyl group on the
NHC ligand could be exploited as a good linker functionality for
catalyst immobilization onto solid supports.
Scheme 3 Direct arylation of furan and thiophene derivatives with aryl
halides promoted by 3. Reaction conditions: aryl halide (1 mmol), hetero-
aryl derivative (2 mmol), KOAc (2 mmol), 3 (0.01 mmol) and DMF (3 mL).
Experimental section
General information
nearly complete conversion of 4-bromoanisole (80–100%) to
undesired side-products. Symmetrical substituted mono-NHC All manipulations were performed under oxygen- and moisture-
palladium catalysts are reported to perform the same reactions free atmosphere in an MBraun MB 200 glove-box. All of the
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reagents were purchased from Sigma-Aldrich and were used as stirred for 24 h. The reaction mixture was monitored by gas
1
received. All the solvents were thoroughly deoxygenated and chromatography and H NMR to determine the conversion of
dehydrated under nitrogen by refluxing over suitable drying the aryl halide and the formation of the desired product.
agents. Deuterated solvents (Euriso-Top products) were degassed
Methyl 2-(4-methoxyphenyl)-5-methylfuran-3-carboxylate (6)
under a nitrogen flow and stored over activated 4 molecular
sieves. NMR spectra were recorded on a Bruker AM250 and a
Bruker AM300 operating at 250 and 300 MHz for proton and
62.5 MHz and 75 MHz for carbon spectra, respectively. The H
The reaction of 4-bromoanisole 4 (0.187 g, 1 mmol), methyl
2-methylfuran- 3-carboxylate 5 (0.280 g, 2 mmol) and KOAc
(0.196 g, 2 mmol) with Pd catalyst 3 (4 mg, 0.01 mmol) afforded
the corresponding product 6 in 40% yield in 5 h.
1
and 13C NMR chemical shifts are referenced to SiMe4 (d = 0 ppm)
using the residual proton impurities of the deuterated solvents as
internal standards. Spectra are reported as follows: chemical shift
(ppm), multiplicity and integration. Multiplicities are abbreviated as
follows: singlet (s), doublet (d), triplet (t), quartet (q), multiplet (m),
and broad (br). Elemental analyses for C, H, N were carried out on a
ThermoFinnigan Flash EA 1112 and were performed according
to standard microanalytical procedures. ESI-MS were performed
on a Waters Quattro Micro triple quadrupole mass spectrometer
equipped with an electrospray ion source.
[5-(4-Methoxyphenyl)furan-2-yl]methyl acetate (8)
The reaction of 4-bromoanisole 4 (0.187 g, 1 mmol), (furan-2-yl)-
methyl acetate 7 (0.280 g, 2 mmol) and KOAc (0.196 g, 2 mmol)
with Pd catalyst 3 (4 mg, 0.01 mmol) afforded the corresponding
product 8 in 34% yield in 5 h.
Methyl 2-methyl-5-(4-nitrophenyl)furan-3-carboxylate (10)
The reaction of 1-chloro-4-nitrobenzene 9 (0.157 g, 1 mmol) and
methyl 2-methylfuran-3-carboxylate 5 (0.280 g, 2 mmol) with
Pd catalyst 3 (4 mg, 0.01 mmol) afforded the corresponding
product 10 in 59% yield in 5 h.
Synthesis of complex 2
A 250 mL round-bottom flask was charged with molecular
sieves, 0.5 g (16 ꢂ 10ꢀ4 mol) of 1, 110 mL of CH2Cl2 and
0.244 g (10 ꢂ 10ꢀ4 mol) of Ag2O. The mixture was protected [5-(4-Nitrophenyl)furan-2-yl]methyl acetate (11)
from light and heated with vigorous stirring at 55 1C for 1.5 h.
The reaction of 1-chloro-4-nitrobenzene 9 (0.157 g, 1 mmol),
The resulting grey suspension was filtered through celite and
the volatiles removed under reduced pressure to afford 0.380 g
(57%) of the silver complex as a white solid. The crude product
was crystallized from dichloromethane at room temperature.
1H NMR (250 MHz, CD2Cl2): d 7.04 (d, 2H), 4.43 (m, 1H), 3.87
(s, 3H), 3.79 (m, 1H), 2.94 (br, 1H), 2.12–1.27 (m, 8H). 13C NMR
(62.5 MHz, CD2Cl2): d 184.2 (NCN), 122.6, 118.8, 73.8, 67.5, 39.4,
35.2, 33.7, 25.5, 25.1. ESI-MS (CH3CN, m/z): 467.36 [Ag(L)2]+.
Elem. Anal.: found (%): C 28.8, H 3.7, N 6.8. Calc. for
(furan-2-yl)methyl acetate (0.280 g, 2 mmol) and KOAc (0.196 g,
2 mmol) with Pd catalyst 3 (4 mg, 0.01 mmol) afforded the
corresponding product 11 in 37% yield in 2 h.
2-Methyl-5-(4-methoxyphenyl)thiophene (14)
The reaction of 4-bromo-N,N-dimethylaniline (0.200 g, 1 mmol),
2-methylthiophene 13 (0.200 g, 2 mmol) and KOAc (0.196 g,
2 mmol) with Pd catalyst 3 (4 mg, 0.01 mmol) afforded the
corresponding product 14 in 15% yield in 3 h.
C
10H16AgIN2O (%): C 28.9, H 3.8, N 6.7.
2-Methyl-5-(4-nitrophenyl)thiophene (15)
Synthesis of complex 3
The reaction of 1-chloro-4-nitrobenzene (0.157 g, 1 mmol) and
2-methylthiophene (0.200 g, 2 mmol) with Pd catalyst 3 (4 mg,
0.01 mmol) afforded the corresponding product 15 in 34% yield
in 5 h.
NMR spectra of new compounds and X-ray data for 2 (CCDC
948494) and 3 (CCDC 948493) are provided in the ESI.‡
0.664 g of complex 2 (16 ꢂ 10ꢀ4 mol) and 0.414 g of PdCl2-
(CH3CN)2 (16 ꢂ 10ꢀ4 mol) were dissolved in CH2Cl2 (120 mL)
and stirred at room temperature for 1.5 h. The reaction mixture
was protected from light, and subsequently filtered through
celite to afford a clear light yellow solution. The solvent was
removed under reduced pressure to give 0.200 g (69%) of a light
yellow solid. 1H NMR (300 MHz, CDCl3): d 7.00 (s, 2H), 5.37
(br, 1H), 4.74 (br, 1H), 4.27 (s, 3H), 3.74 (br, 1H), 2.72 (bs, 2H),
2.26–1.62 (m, 9H). 13C NMR (75 MHz, CD2Cl2): d 139.7 (NCN),
125.0, 120.1, 73.2, 67.6, 38.8, 35.6, 33.6, 25.6, 25, 1.4 (CH3CN).
ESI-MS (CH3CN, m/z): 323.25 [Pd(NHC)Cl]+. Elem. Anal.:
found (%): C 36.0, H 4.7, N 10.4. Calc. for C12H19PdCl2IN3O (%):
C 36.1, H 4.8, N 10.6.
Acknowledgements
The authors thank Dr Patrizia Iannece and Patrizia Oliva for
technical assistance. Financial support from the Ministero
´
dell’Universita e della Ricerca Scientifica e Tecnologica is grate-
fully acknowledged.
General procedure for direct arylations
References
In a typical experiment, the aryl halide (1 mmol), heteroaryl
derivative (2 mmol), KOAc (2 mmol), the Pd complex 3
(0.01 mmol) and DMF (3 mL) were introduced into a vial, under
nitrogen, equipped with a magnetic stirring bar. The vial was
placed in a preheated oil bath at 150 1C, and the reactants were
1 (a) C. S. J. Cazin, N-Heterocyclic Carbenes in Transition Metal
Catalysis and Organocatalysis, Springer, 2011; (b) S. P. Nolan,
N-Heterocyclic Carbenes in Synthesis, Wiley-VCH, Weinheim,
Germany, 2006; (c) F. Glorius, N-Heterocyclic Carbenes in
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 762--769 | 767

View Article Online
NJC
Transition Metal catalysis, Springer-Verlag, Berlin, Germany,
Paper
(c) A. A. Danopoulos, S. Winston and W. B. Motherwell, Chem.
Commun., 2002, 1376; (d) D. Pugh and A. A. Danopoulos, Coord.
Chem. Rev., 2007, 251, 610; (e) A. A. D. Tulloch, A. A.
Danopoulos, S. Winston, S. Kleinhenz and G. Eastham,
J. Chem. Soc., Dalton Trans., 2000, 4499; ( f ) A. A. D. Tulloch,
S. Winston, A. A. Danopoulos, G. Eastham and M. B.
Hursthouse, Dalton Trans., 2003, 699; (g) J. J. Van Veldhuizen,
J. E. Campbell, R. E. Giudici and A. H. Hoveyda, J. Am. Chem.
Soc., 2005, 127, 6877.
8 (a) W. A. Herrmann, G. M. Lobmaier and M. Elison,
J. Organomet. Chem., 1996, 520, 231; (b) C. Y. Liu,
D. Y. Chen, G. H. Lee, S. M. Peng and S. T. Liu, Organo-
metallics, 1996, 15, 1055.
9 (a) N. M. Scott and S. P. Nolan, Eur. J. Inorg. Chem., 2005,
1815; (b) K. J. Cavell and D. S. McGuinness, Coord. Chem. Rev.,
2004, 248, 671; (c) A. R. Chianese, X. W. Li, M. C. Janzen,
J. W. Faller and R. H. Crabtree, Organometallics, 2003, 22, 1663;
(d) J. C. Garrison and W. J. Youngs, Chem. Rev., 2005,
105, 3978; (e) S. Sakaguchi, K. S. Yoo, J. O’Neill, J. H. Lee,
T. Stewart and K. W. Jung, Angew. Chem., Int. Ed., 2008,
47, 9326; ( f ) A. Bartoszewicz, R. Marcos, S. Sahoo, A. K.
Inge, X. Zou and B. Martin-Matute, Chem.–Eur. J., 2012,
2007; (d) C. M. Crudden and D. P. Allen, Coord. Chem. Rev.,
2004, 248, 2247; (e) A. Correa, S. P. Nolan and L. Cavallo, Top.
Curr. Chem., 2011, 302, 131; ( f ) S. Diez-Gonzalez, N-Heterocyclic
Carbene, Royal Society Chemistry (RSC) Catalysis Series, 2011;
(g) L. Benhamou, E. Chardon, G. Lavigne, S. Bellemin-
´
Laponnaz and V. Cesar, Chem. Rev., 2011, 111, 2705.
2 (a) R. Dorta, E. D. Stevens, N. M. Scott, C. Costabile,
L. Cavallo, C. D. Hoff and S. P. Nolan, J. Am. Chem. Soc.,
2005, 127, 2485; (b) S. Diez-Gonzalez and S. P. Nolan, Coord.
Chem. Rev., 2007, 251, 874; (c) D. J. Cardin, B. Cetinkay and
M. F. Lappert, Chem. Rev., 1972, 72, 545; (d) D. C. Graham,
K. J. Cavell and B. F. Yates, J. Phys. Org. Chem., 2005, 18, 298;
(e) R. W. Hoffmann, Angew. Chem., Int. Ed., 1968, 7, 754;
( f ) C. L. Lai, W. H. Guo, M. T. Lee and C. H. Hu, J. Organomet.
Chem., 2005, 690, 5867; (g) L. Cavallo, A. Correa, C. Costabile
and H. Jacobsen, J. Organomet. Chem., 2005, 690, 5407;
(h) H. Jacobsen, A. Correa, C. Costabile and L. Cavallo,
J. Organomet. Chem., 2006, 691, 4350; (i) H. Jacobsen,
A. Correa, A. Poater, C. Costabile and L. Cavallo, Coord. Chem.
Rev., 2009, 253, 687.
3 (a) O. Ku¨hl, Funtionalised N-heterocyclic Carbene Complexes,
Wiley-VCH, Weinheim, 2010; (b) O. Ku¨hl, Chem. Soc. Rev.,
2007, 36, 592; (c) D. Pugh and A. A. Danopoulos, Coord.
Chem. Rev., 2007, 251, 610; (d) A. T. Normand and K. J.
˜
18, 14510; (g) I. Penafiel, I. M. Pastor, M. Yus, M. A.
Esteruelas and M. Olivan, Organometallics, 2012, 31, 6154;
(h) M. Benitez, E. Mas-Marza, J. A. Mata and E. Peris,
Chem.–Eur. J., 2011, 700, 132; (i) L. Ray, V. Katiyar,
S. Barman, M. J. Raihan, H. Nanavati, M. M. Shaikh and
P. Ghosh, J. Organomet. Chem., 2007, 692, 4259.
´
Cavell, Eur. J. Inorg. Chem., 2008, 2781; (e) R. Corberan,
´
E. Mas-Marza and E. Peris, Eur. J. Inorg. Chem., 2009, 1700.
4 (a) W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1291;
(b) D. Zhang, H. Aihara, T. Watanabe, T. Matsuo and 10 (a) R. B. Bedford, C. S. J. Cazin and D. Holder, Coord. Chem.
H. Kawaguchi, J. Organomet. Chem., 2007, 692, 234;
(c) H. Aihara, T. Matsuo and H. Kawaguchi, Chem. Commun.,
2003, 2204; (d) D. Zhang and H. Kawaguchi, Organometallics,
2006, 25, 5506.
Rev., 2004, 248, 2283; (b) N. Marion and S. P. Nolan, Acc.
Chem. Res., 2008, 41, 1440; (c) F. E. Hahn and M. C. Jahnke,
Angew. Chem., Int. Ed., 2008, 47, 3122; (d) E. A. B. Kantchev,
C. J. O’Brien and M. G. Organ, Angew. Chem., Int. Ed., 2007,
46, 2768.
5 Part 1: (a) J. R. Miecznikowski and R. H. Crabtree, Abstr.
Paper. Am. Chem. Soc., 2004, 228, U898; (b) D. G. Gillingham 11 (a) F. Grisi, C. Costabile, E. Gallo, A. Mariconda, C. Tedesco
and A. H. Hoveyda, Abstr. Paper. Am. Chem. Soc., 2006, 231;
(c) A. H. Hoveyda and R. R. Schrock, Chem.–Eur. J., 2001,
7, 945; (d) H. Clavier, L. Coutable, J. C. Guillemin and
M. Mauduit, Tetrahedron: Asymmetry, 2005, 16, 921; (e) Sp.
Iss. SI: H. Clavier, L. Coutable, L. Toupet, J. C. Guillemin
and M. Mauduit, J. Organomet. Chem., 2005, 690, 5237.
6 (a) E. Peris and R. H. Crabtree, Coord. Chem. Rev., 2004,
248, 2239; (b) M. C. Perry and K. Burgess, Tetrahedron: Asym-
metry, 2003, 14, 951; (c) Y. Lee and A. H. Hoveyda, J. Am. Chem.
Soc., 2006, 128, 15604; (d) J. J. Van Veldhuizen, D. G. Gillingham,
S. B. Garber, O. Kataoka and A. H. Hoveyda, J. Am. Chem. Soc.,
2003, 125, 12502; (e) J. J. Van Veldhuizen, S. B. Garber,
and P. Longo, Organometallics, 2008, 27, 4649; (b) F. Grisi,
A. Mariconda, C. Costabile, V. Bertolasi and P. Longo,
Organometallics, 2009, 28, 4988; (c) C. Costabile,
A. Mariconda, L. Cavallo, P. Longo, V. Bertolasi, F. Ragone
and F. Grisi, Chem.–Eur. J., 2011, 17, 8618; (d) V. Siano,
I. D’Auria, F. Grisi, C. Costabile and P. Longo, Cent. Eur.
J. Chem., 2011, 9, 605; (e) F. Grisi, C. Costabile, A. Grimaldi,
C. Viscardi, C. Saturnino and P. Longo, Eur. J. Org. Chem.,
2012, 5928; ( f ) A. Perfetto, C. Costabile, P. Longo,
V. Bertolasi and F. Grisi, Chem.–Eur. J., 2013, 19, 10492;
(g) A. Mariconda, F. Grisi, A. Granito and P. Longo,
Macromol. Chem. Phys., 2013, 214, 1973.
J. S. Kingsbury and A. H. Hoveyda, J. Am. Chem. Soc., 2002, 12 (a) C. Bocchino, M. Napoli, C. Costabile and P. Longo,
124, 4954; ( f ) Z. G. Wang, H. M. Sun, H. S. Yao, Q. Shen and
Y. Zhang, Organometallics, 2006, 25, 4436; (g) M. Z. Chen,
H. M. Sun, W. F. Li, Z. G. Wang, Q. Shen and Y. Zhang,
J. Organomet. Chem., 2006, 691, 2489.
7 (a) Z. G. Wang, H. M. Sun, H. S. Yao, Y. M. Yao, Q. Shen and
Y. Zhang, J. Organomet. Chem., 2006, 691, 3383;
(b) A. A. Danopoulos, A. A. D. Tulloch, S. Winston,
G. Eastham and M. B. Hursthouse, Dalton Trans., 2003, 1009;
J. Polym. Sci., Part A: Polym. Chem., 2011, 49, 862;
(b) C. Costabile, C. Bocchino, M. Napoli and P. Longo,
J. Polym. Sci., Part A: Polym. Chem., 2012, 50, 3728.
13 (a) M. G. Organ, G. A. Chass, D. C. Fang, A. C. Hopkinson
and C. Valente, Synthesis, 2008, 2776; (b) R. Jackstell,
M. G. Andreu, A. Frisch, K. Selvakumar, A. Zapf, H. Klein,
¨
A. Spannenberg, D. Rottger, O. Briel, R. Karch and M. Beller,
Angew. Chem., Int. Ed., 2002, 41, 986; (c) A. Zapf and
768 | New J. Chem., 2014, 38, 762--769
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
Paper
NJC
M. Beller, Chem. Commun., 2005, 431; (d) K. Selvakumar,
A. Zapf and M. Beller, Org. Lett., 2002, 4, 3031; (e) L. R.
presence of alkali-metal bases and subsequent reaction with
a metal precursor did not afford the desired product.
˜
Titcomb, S. Caddick, F. G. N. Cloke, D. J. Wilson and 29 (a) I. Penafiel, I. M. Pastor, M. Yus, M. A. Esteruelas,
´ ˜
M. Olivan and E. Onate, Eur. J. Org. Chem., 2011, 7174;
D. McKerrecher, Chem. Commun., 2001, 1388; ( f ) K. Arentsen,
S. Caddick, F. G. N. Cloke, A. P. Herring and P. B. Hitchcock,
Tetrahedron Lett., 2004, 45, 3511; (g) A. K. de Lewis, S. Caddick,
F. G. N. Cloke, N. C. Billingham, P. B. Hitchcock and J. Leonard,
˜
(b) I. Penafiel, I. M. Pastor and M. Yus, Eur. J. Org. Chem.,
˜
2012, 3151; (c) I. Penafiel, I. M. Pastor and M. Yus, Eur.
J. Org. Chem., 2013, 1479.
J. Am. Chem. Soc., 2003, 125, 10066; (h) Z. Jin, S. X. Guo, X. P. Gu, 30 M. V. Baker, D. H. Brown, R. A. Haque, B. W. Skelton and
L. L. Qiu, H. B. Song and J. X. Fang, Adv. Synth. Catal., 2009,
351, 1575; (i) D. R. Jensen, M. J. Schultz, J. A. Mueller and
A. H. White, J. Inclusion Phenom. Macrocyclic Chem., 2009,
65, 97.
M. S. Sigman, Angew. Chem., Int. Ed., 2003, 42, 3810; 31 C. E. Willans, K. M. Anderson, M. J. Paterson, P. C. Junk,
( j) G. D. Frey, J. Schu¨tz, E. Herdtweck and W. A. Herrmann,
Organometallics, 2005, 24, 4416; (k) Z. Jin, L. L. Qiu, Y. Q. Li,
H. B. Song and J. X. Fang, Organometallics, 2010, 29, 6578.
14 (a) M. M. Joullie, S. Berritt and E. M. Forbeck, Curr. Opin.
L. J. Barbour and J. W. Steed, Eur. J. Inorg. Chem., 2009,
2835.
32 Q.-X. Liu, H. Wang, X.-J. Zhao, Z.-Q. Yao, Z.-Q. Wang, A.-H.
Chen and X.-G. Wang, CrystEngComm, 2012, 14, 5330.
Drug Discovery Dev., 2008, 11, 829; (b) K. C. Nicolaou and 33 For some recent examples, see: (a) L. Chen, J. Roger,
J. S. Chen, Pure Appl. Chem., 2008, 80, 727.
C. Bruneau, P. H. Dixneuf and H. Doucet, Adv. Synth. Catal.,
2011, 353, 2749; (b) L. Chen, J. Roger, C. Bruneau,
P. H. Dixneuf and H. Doucet, Chem. Commun., 2011,
47, 1872; (c) C. B. Bheeter, J. K. Bera and H. Doucet,
J. Org. Chem., 2011, 76, 6407; (d) C. B. Bheeter, J. K. Bera
and H. Doucet, RSC Adv., 2012, 2, 7197; (e) K. Beydoun and
H. Doucet, ChemSusChem, 2011, 4, 526; ( f ) L. Ackermann
15 (a) D. Alberico, M. E. Scott and M. Lautens, Chem. Rev., 2007,
107, 174; (b) T. Satoh and M. Miura, Chem. Lett., 2007, 200;
(c) H. Doucet and J. C. Hierso, Curr. Opin. Drug Discovery Dev.,
2007, 10, 672; (d) I. V. Seregin and V. Gevorgyan, Chem. Soc.
Rev., 2007, 36, 1173; (e) B. J. Li, S. D. Yang and Z. J. Shi, Synlett,
2008, 949; ( f ) F. Bellina and R. Rossi, Tetrahedron, 2009,
65, 10269; (g) L. Ackermann, R. Vicente and A. R. Kapdi,
Angew. Chem., Int. Ed., 2009, 48, 9792.
16 J. J. Li and G. W. Gribble, Palladium in Heterocyclic Chemistry,
Pergamon, Amsterdam, 2000.
17 P. L. Arnold, M. Rodden, K. M. Davis, A. C. Scarisbrick,
A. J. Blake and C. Wilson, Chem. Commun., 2004, 1612.
18 I. J. B. Lin and C. S. Vasam, Coord. Chem. Rev., 2007,
251, 642.
19 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, 972.
20 M. Napoli, C. Saturnino, E. I. Cianciulli, M. Varcamonti,
A. Zanfardino, G. Tommonaro and P. Longo, J. Organomet.
Chem., 2013, 725, 46.
21 Acetonitrile molecules in the crystal come from the synthesis
of the salt 1 (see Scheme 1).
¨
and S. Barfuesser, Synlett, 2009, 808; (g) I. Ozdemir, Y. Gok,
¨
˘
˘
O. Ozeroglu, M. Kaloglu, H. Doucet and C. Bruneau, Eur.
J. Inorg. Chem., 2010, 1798; (h) F. Poˇzgan, J. Roger and
H. Doucet, ChemSusChem, 2008, 1, 404; (i) J. J. Dong,
J. Roger, F. Poˇzgan and H. Doucet, Green Chem., 2009,
11, 1832; ( j) P. Amaladass, J. A. Clement and A. K.
Mohanakrishnan, Tetrahedron, 2007, 63, 10363; (k) L.-C.
Campeau, M. Bertrand-Laperle, J.-P. Leclerc, E. Villemure,
S. Gorelsky and K. Fagnou, J. Am. Chem. Soc., 2008,
130, 3276; (l) N. Lebrasseur and I. Larrosa, J. Am. Chem.
Soc., 2008, 130, 2926; (m) S. A. Ohnmacht, P. Mamone,
A. J. Culshaw and M. F. Greaney, Chem. Commun., 2008,
1241; (n) F. Besselievre, F. Mahuteau-Betzer, D. S. Grierson
and S. Piguel, J. Org. Chem., 2008, 73, 3278.
22 M. N. Burnett and C. K. Johnson, ORTEP III, Report ORNL-6895, 34 (a) I. Ozdemir, N. Gurbuz, N. Kaloglu, O. Dogan, M. Kaloglu,
Oak Ridge National Laboratory, Oak Ridge, TN, 1996.
23 W. Chen and F. Liu, J. Organomet. Chem., 2003, 673, 5.
24 P. de Fremont, N. M. Scott, E. D. Stevens, T. Ramnial,
O. C. Lightbody, C. L. B. Macdonald, J. A. C. Clyburne, C. A.
Abernethy and S. P. Nolan, Organometallics, 2005, 24, 6301.
25 L. Busetto, M. C. Cassani, C. Femoni, A. Macchioni, R. Mazzoni
and D. Zuccaccia, J. Organomet. Chem., 2008, 693, 2579.
26 X. Y. Lu, F. Chen, W. F. Xu and X. T. Chen, Inorg. Chim. Acta,
2009, 362, 5113.
C. Bruneau and H. Doucet, Beilstein J. Org. Chem., 2013,
9, 303; (b) A. R. Martin, A. Chartoire, A. M. Z. Slawin and
S. P. Nolan, Beilstein J. Org. Chem., 2012, 8, 1637; (c) Z. Jin,
S.-X. Guo, L.-L. Qiu, G.-P. Wu and J.-X. Fang, Appl. Organomet.
Chem., 2011, 25, 502; (d) S. Demir, I. Ozdemir, H. Arslan and
Van D. Derveer, J. Organomet. Chem., 2011, 696, 2589;
(e) L. Ackermann, R. Vincente and R. Born, Adv. Synth. Catal.,
2008, 350, 741; ( f ) B. B. Toure, B. S. Lane and D. Sames,
Org. Lett., 2006, 8, 1979; (g) N. Gu¨rbu¨z, I. Ozdemir and
B. Cetinkaya, Tetrahedron Lett., 2005, 46, 2273; (h) O. Dogan,
N. Gu¨rbu¨z, I. Ozdemir, B. Cetinkaya, O. Sahin and
¨
27 (a) W. A. Hermann, S. K. Schneider, K. Ofele, M. Sakamoto
and E. Herdtweck, J. Organomet. Chem., 2004, 689, 2441;
(b) U. Hintermair, U. Englert and W. Leitner, Organometallics,
2011, 30, 3726.
¨
O. Bu¨yu¨kgu¨ngor, Dalton Trans., 2009, 7087; (i) H. Arslan,
I. Ozdemir, D. Vanderveer, S. Demir and B. Cetinkaya,
J. Coord. Chem., 2009, 62, 2591; ( j) L.-C. Campeau,
P. Thansandote and K. Fagnou, Org. Lett., 2005, 7, 1857.
28 Any attempt to prepare functionalized NHC–palladium
complexes by deprotonation of imidazolium salt 1 in the
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