Palladium Complexes with Tetrahydropyrimidin-2-ylidene Ligands: Catalytic Activity for the Direct Arylation of Furan, Thiophene, and Thiazole Derivatives

Article abstract of DOI:10.1021/om501201r

The synthesis and characterization of novel 1,3-benzyl-3,4,5,6-tetrahydropyrimidin-2-ylidene-based N-heterocyclic carbene palladium(II) complexes (1a-d) were described. The crystal structure of trans-dichlorobis[1,3-bis(4-methylbenzyl)-3,4,5,6-tetrahydrop

Full text of DOI:10.1021/om501201r

Article
pubs.acs.org/Organometallics
Palladium Complexes with Tetrahydropyrimidin-2-ylidene Ligands:
Catalytic Activity for the Direct Arylation of Furan, Thiophene, and
Thiazole Derivatives
†
†
†
‡
ahin,§
̈
̈
̇
Emine Ozge Karaca, Nevin Gurbuz, Ismail Ozdemir, Henri Doucet, Onur S
̈
̈
Orhan Buyukgungor,∥ and Bekir C
̧
etinkaya*,⊥
̈
̈
̈
̈
†Catalysis Research and Application Center, Inonu University, 44280, Malatya, Turkey
̈
̈
‡Centre de Catalyse et Chimie Verte, Institut des Sciences Chimiques de Rennes, Universite
́
de Rennes 1, 35042 Rennes, France
§Scientific and Technological Research Application and Research Center, Sinop University, 57010, Sinop, Turkey
∥Department of Physics, Ondokuz Mayıs University, 55139, Samsun, Turkey
⊥
̇
Department of Chemistry, Faculty of Science, Ege University, 35040, Bornova-Izmir, Turkey
S
* Supporting Information
ABSTRACT: The synthesis and characterization of novel 1,3-
benzyl-3,4,5,6-tetrahydropyrimidin-2-ylidene-based N-hetero-
cyclic carbene palladium(II) complexes (1a−d) were
described. The crystal structure of trans-dichlorobis[1,3-bis(4-
methylbenzyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]-
palladium(II) was presented. Pd(II) complexes 1a−d were
tested as catalysts in the direct C5 or C2 arylation of furans,
thiophenes, and thiazoles, with various aryl bromides at 150 °C
for 1 h. These complexes exhibited moderate to high catalytic
activities under the given conditions.
the preliminary synthesis of organometallic derivatives. In
INTRODUCTION
■
addition, the required organometallic nucleophilic reagents,
particularly when being functionalized, are often not
commercially available or are relatively expensive. Moreover,
these reactions provide a stoichiometric amount of side
products. In recent years, the transition-metal-catalyzed so-
called direct arylation has undergone rapid development, and it
represents a viable alternative to traditional cross-coupling
reactions with organometallic reagents.12−14 Direct arylation
reactions through cleavage of C−H bonds is considered as an
environmentally and economically more attractive strategy.15
Consequently, the procedure provides a valuable and
straightforward technique for the synthesis of biaryls.
Ohta and co-workers reported the direct 2- or 5-arylation of
furans and thiophenes, with aryl halides, in moderate to good
yields by using [Pd(PPh3)4] as the catalyst.12 Since then, the
palladium-catalyzed direct arylation of heteroaryl derivatives
with aryl halides has proved to be a powerful method for the
synthesis of a wide variety of arylated heterocycles.16−23 Only a
few examples of (NHC)Pd-catalyzed direct arylations of
heteroaromatics have been reported to date.24 In this
Intensive attention has been paid to the properties and
application of N-heterocyclic carbene (NHC) complexes of
transition metals, and the pioneering work on the coordination
chemistry of NHC ligands was independently reported by
1
2
̈
Wanzlick and Ofele in 1968 and Lappert and co-workers in
the early 1970s.3,4 The isolation of free NHC5 and utilization of
NHC complexes in catalysis6 stimulated the search further.
Among the NHCs reported, five-membered NHCs derived
from imidazol-2-lidenes, imidazolin-2-ylidenes, triazolylidenes,
and thiazolylidenes (abbreviated as 5-NHC) have been
extensively studied. In contrast, the related six-membered
NHCs (6-NHC) are relatively less developed.7 Increasing the
NHC heterocycle ring size and thus the corresponding N−
CNHC−N bond angle affords markedly different steric and
electronic properties, in comparison with those of their
traditional five-membered counterparts.8 The strong σ-donating
property of 6-NHCs makes them attractive ligand candidates
especially for the discovery of new catalytic modes and
reactions.9
Much attention has been given to the synthesis of arylated
heterocycles due to their biological or physical properties.10 In
this context, palladium-catalyzed reactions such as Stille, Suzuki,
or Negishi couplings allow the efficient synthesis of a wide
variety of bi(hetero)aryls.11 However, these couplings require
Special Issue: Mike Lappert Memorial Issue
Received: November 28, 2014
Published: May 6, 2015
© 2015 American Chemical Society
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connection, recently we have reported the C−H bond
activation by applying complexes of imidazolin-2-ylidene and
benzimidazol-2-ylidene and in situ formed metal systems for
arylation of arene and heteroaromatic compounds.25 In view of
the above information and the growing interest in catalytic
activity of palladium complexes to act as an efficient catalyst in
direct arylation reactions, in this article, we now report the
synthesis of four new (6-NHC)Pd(II) complexes (1) from 1,3-
dibenzyl-3,4,5,6-tetrahydropyrimidinium salts. All synthesized
1546, 1518, and 1515 cm−1 respectively for 1a−1d. 13C
chemical shifts, which provide a useful diagnostic tool for this
type of metal carbene complex, exhibited a singlet resonance at
193.7, 183.7, 192.4, and 192.8 ppm ascribed to the carbenic
carbon atom. This is consistent with the trans configuration of
the complexes and the increased basisity of 6-NHC ligands
relative to five-membered counterparts. The increased σ-
donation shifts the Ccarb signal to higher frequencies.
Structural Characterization of 1a. The crystals of 1a
suitable for X-ray analysis were obtained from a chloroform
solution layered with diethyl ether. The molecular structure of
complex 1a has been confirmed by X-ray single-crystal analyses.
Details of data collection and crystal structure determinations
are given in the Supporting Information.
1
compounds were characterized by H NMR, 13C NMR, IR
spectroscopy, and elemental analysis techniques, which support
the proposed structures. The molecular and crystal structure of
the complex trans-dichlorobis[1,3-bis(4-methylbenzyl)-3,4,5,6-
tetrahydropyrimidin-2-ylidene]palladium(II) was determined
by single-crystal X-ray diffraction. We examined the activity
of the synthesized palladium complexes in the direct arylation
of various heteroaromatic compounds with bromobenzene
derivatives.
The molecular structure of 1a with the atom labeling is
shown in Figure 1. The asymmetric unit contains two
RESULTS AND DISCUSSION
■
Synthesis of Palladium Carbene Complexes. Since the
first catalytic applications of palladium/NHC complexes
realized in 1995,26 numerous complexes have been synthesized
by using various methods. The reaction of Pd(OAc)2 and
imidazolium salts is one of the most frequently used reported
methods to afford palladium(II) NHC complexes. However,
this well-known methodology used to synthesize (5-NHC)Pd-
(II) complexes failed when applied to the saturated six-
membered tetrahydropyrimidinium salts, probably due to the
low acidity of the C2−H.27 The attempt to synthesize (6-
NHC)AgX, which is a versatile NHC transfer reagent,28 was
similarly unsuccessful. Finally, (6-NHC)Pd complexes (1) have
been prepared by Lappert’s procedure4 employing the in situ
formed enetetraamine, which can replace the coordinated
ligands such as Py, PPh3, and P(OMe)3. The (6-NHC)Pd
complexes (1) were obtained in 74−78% yield by reaction of
the 6-NHC dimer with 0.5 equiv of [PdCl2(PPh3)2] (Scheme
1). The 6-NHC dimer was not isolated, but generated in
Figure 1. Molecular structure of 1a showing the atom-numbering
scheme [(i) −x+1, −y+1, −z+1; (ii) −x+2, −y+2, −z+2]. Selected
bond lengths [Å] and angles [deg]: C21−Pd2 = 2.0543(17), N1−
C1−N2 = 117.53(16), C1−Pd1−Cl1 = 92.96(5), N4−C21−Pd2 =
120.68(13), C21−Pd2−Cl2ii = 89.30(5), C1−Pd1 = 2.0666(17),
Cl1−Pd1 = 2.3123(5), Cl2−Pd2 = 2.3241(5), N1−C1−Pd1 =
121.41(13), C1−Pd1−Cl1i = 87.04(5), N3−C21−Pd2 = 121.61(13).
crystallographically independent molecules. Each Pd(II) ion is
coordinated to two chlorine atoms and two carbon atoms, thus
exhibiting a distorted square-planar arrangement in a mutually
trans environment. The Pd−Ccarb distance (2.066 Å) in 1a is
longer than the corresponding bond length (2.066 Å) reported
for the trans-[PdBr2(benzimidazol-2-ylidene)2] system.24b This
longer bond length is presumably due to greater steric
interactions of 6-NHC on coordination, and this is also
consistent with the larger N−Ccarb−N angle (117.53°) in 1a.
Molecules of 1a are linked into sheets by a combination of C−
H···π interactions. Atoms C2 and C32 in the molecule at (x, y,
z) act as hydrogen-bond donors to the Cg(7) and Cg(6)
benzene rings in the molecules at (x, y, z−1) and (2−x, 2−y,
1−z), so forming zigzag chains running parallel to the [111]
and [001] directions (Figure 2). These chains are extended into
the 3D supramolecular network by C−H···π interactions.
Details of C−H···π interactions are given in the Supporting
Information.
Scheme 1. Synthesis of Palladium−Carbene Complexes
solution by deprotonation of the corresponding tetrahydropyr-
imidinium salt by KOBut at 25 °C. The ligand precursor 1,3-
dialkyl-3,4,5,6-tetrahydropyrimidinium halide was obtained
according to the literature.29
All complexes were isolated as air-stable, yellow, crystalline
solids, and they were soluble in solvents such as dichloro-
methane, chloroform, toluene, and tetrahydrofuran and
insoluble in nonpolar solvents. The new complexes were
Catalytic Studies: Direct Arylation of Heteroaromatic
Compounds via C−H Bond Activation Using 1a−1d as
Catalysts. Direct arylation of heterocycles has received
considerable interest among synthetic chemists, as it would
eliminate the need for establishing a reactive functionality prior
to C−C coupling, enabling direct elaboration and expansion of
the core motif.31−33 To the best of our knowledge, Pd-carbene
1
characterized by H and 13C NMR, elemental analysis, FTIR,
and X-ray diffraction. The formation of the Pd-NHC complexes
was confirmed by the absence of the 1H NMR resonance signal
of the tetrahydropyrimidinium C2−H. The palladium com-
plexes exhibit a characteristic ν(NCN) band typically at 1537,
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cases, only the C5-arylated products were formed. We also
performed a study on 4,5-dimethythiazole to induce direct
arylation at the C2 position using the same substrates (Table
1).
In all cases, the presence of 6-NHC ligands on palladium was
found to be profitable. The direct coupling reactions of methyl
2-methyl-3-furoate with bromobenzene, 4-bromonitrobenzene,
and 4-bromoanisole proceeded smoothly to generate the
corresponding 5-arylated methyl 2-methyl-3-furoate in good
yields (65−89%, Table 1, entries 1−3). Concerning the
electronic properties of the aryl bromide, electron-withdrawing
and electron-donating groups were tolerated. For this reaction,
complexes 1a and 1b were found to be slightly more effective
catalysts (Table 1, entries 1−3). Similar substrates have recently
been employed, by Dong et al.,34 in direct arylation with a
Pd(OAc)2 catalyst. Following the same trends as reported by
Dong, a lower yield was observed with 4-bromonitrobenzene
(Table 1, entry 2). The reaction of a strongly deactivated aryl
bromide, 4-bromoanisole, with methyl 2-methyl-3-furoate gave
the desired product in 85% yield in the presence of 1 mol % of
complex 1b (Table 1, entry 3). 2-Methyl-3-furoate has also
been arylated in moderate to good yields using bromobenzene
(Table 1, entry 1). For bromobenzene, the best results were
achieved with complex 1a in 73% yield. It is notable that in the
case of methyl 2-methyl-3-furoate decarboxylation products
were not detected.
Figure 2. Crystal structure of 1a, showing the formation of C−H···π
interactions.
complexes bearing a 3,4,5,6-tetrahydropyrimidin-2-ylidene
ligand for direct arylation of heteroaromatic compounds have
not been reported so far.
For the sake of comparison with previously reported
results24c,h we decided to use the following reaction conditions:
(6-NHC)Pd complexes (1a−1d) 1 mol %; 1 mmol of aryl
bromide, 2 mmol of heteroaryl derivative, 2 mmol of KOAc;
solvent, DMAc (N,N-dimethylacetamide); reaction temper-
ature, 150 °C; reaction time, 1 h. Under these reaction
conditions, four heterocyclic substrates were allowed to react
with aryl bromides bearing electron-donating or electron-
withdrawing groups at the para position to furnish the arylated
products in moderate to good yields (Table 1). Initially, we
focused on the direct arylation at the C5 position using methyl
2-methyl-3-furoate, 2-n-butylthiophene, and 2-n-propylthiazole.
The coupling reactions were regioselective, and in almost all
Next, we examined the reactivity of 2-n-butylthiophene using
the same coupling partners. As with methyl 2-methyl-3-furoate,
substituents on aryl bromides display a minor effect on the
reaction (Table 1, entries 4−6). The 5-arylated thiophenes
were obtained in 70−88% yields. Bromobenzene was
successfully coupled with 2-n-butylthiophene in the presence
of 1 mol % of catalyst 1a to give 2-n-butyl-5-phenylthiophene in
a
Table 1. Direct Arylation of Heteroaromatic Compounds by Using Aryl Bromides
a
Conditions: Pd-NHC (0.01 mmol), aryl halide (1 mmol), heteroaromatic compound (2 mmol), KOAc (2 mmol), DMAc (3 mL), 150 °C, 1 h,
conversion of the aryl halide determined by GC and GC-MS.
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78% yield (Table 1, entry 4). High yields of 2-n-butyl-5-(4-
methoxyphenyl)thiophene were obtained for the coupling with
4-bromoanisole using catalysts 1a and 1d (Table 1, entry 6). It
is worth noting that the use of Pd(OAc)2 without addition of
ligands gave coupling product in only 50% yield at 130 °C.35
When the aryl chloride was used, arylated products were
formed after 20 h. For example 2-n-butyl-5-(4-nitrophenyl)-
thiophene was obtained in the coupling with 4-chloronitro-
benzene using catalysts 1a−1d in 84%, 82%, 80%, and 81%
conversion, respectively.
The palladium-catalyzed direct arylation of 2-n-propylth-
iazole with aryl bromides in DMF has been described by Miura
and Nomura.36 We investigated the direct C5 arylation of 2-n-
propylthiazole with aryl bromides, and the results of these
experiments are summarized in Table 1. Selective C5 arylations
were observed using bromobenzene, 4-bromonitrobenzene, and
4-bromoanisole, resulting in 68−89% yields of products (Table
1). The reactivity of 2-n-propylthiazole was similar to 2-n-
butylthiophene. The reaction of the electron-rich aryl bromide
4-bromoanisole with methyl 2-n-propylthiazole gave the desired
product in 89% yield in the presence of 1 mol % of complex 1b
(Table 1, entry 6). Bromobenzene was successfully coupled
with 2-n-propylthiazole in the presence of 1 mol % of catalyst
1a to give 5-phenyl-2-n-propylthiazole in 77% yield (Table 1,
entry 7). High yields of 5-(4-nitrophenyl)-2-n-propylthiazole
were obtained for the coupling with 4-bromonitrobenzene
using catalyst 1b (Table 1, entry 5). Generally speaking, the
complex 1b seems to be a slightly more effective catalyst for
this reaction.
In previous works, the reaction time was chosen as 20 h for
arylation of methyl 2-methyl-3-furoate, 2-n-propylthiazole, and
2-n-propylthiazole with aryl bromides, whereas in the present
work the reaction time was shortened to 1 h and higher yields
were obtained as compared to our previous results.24c For
example bromoarenes were coupled with 2-n-butylthiophene in
the presence of imidazolin-2-ylidene-Pd complexes to give the
desired product in 10−56% yields only after 20 h,24c whereas
the use of (6-NHC)Pd complexes gave higher yields (Table 1,
entry 4).
Finally, the scope of the direct arylation reaction was
extended to 4,5-dimethylthiazole. It should be noted that no
example of direct arylation of 4,5-dimethylthiazole with aryl
bromides by using Pd−N-heterocyclic carbene complexes has
been reported so far. The reaction performed with p-substituted
aryl bromides and the results of these experiments are
summarized in Table 1, entries 10−12. Bromobenzene, 4-
bromonitrobenzene, and 4-bromoanisole gave moderate to
high yields of C2 arylation products in the presence of 1 mol %
catalysts (Table 1, entry 10). Generally, the reactivity of 4,5-
dimethylthiazole was similar to 2-n-propylthiazole. The reaction
of 4,5-dimethylthiazole with bromobenzene generated the
corresponding product in 71% yield in the presence of 1 mol
% of complex 1b (Table 1, entry 10). High yields of 4,5-
dimethyl-2-(4-methoxyphenyl)thiazole were obtained for the
coupling with 4-bromoanisole using catalysts 1a−1d (Table 1,
entry 12) with little variance between the complexes. To our
knowledge, these are the first examples applied to direct
arylations of furan, thiophene, or thiazoles by using both
electron-deficient and electron-rich aryl bromides as the
coupling partners catalyzed by [(6-NHC)PdCl2] complexes.
CONCLUSION
■
We report here the synthesis and characterization of four new
ring-expanded 6-NHC palladium complexes (1a−1d) by
thermal cleavage reaction of the enetetraamines, based on
1,3-dibenzyl-3,4,5,6-tetrahydropyrimidin-2-ylidenes. Complex
1a has been characterized by single-crystal X-ray diffraction
studies as a trans isomer. The catalytic activity of these
complexes was investigated in C5/C2 direct arylation of furan,
thiophene, and thiazole derivatives in the presence of KOAc.
Moreover, in the present study the product yield was higher
and the reaction time shorter (1 h) as compared to previous
results. The higher efficiency may be attributed to the higher σ-
donating ability of 6-NHC as compared to 5-NHC. It has to be
emphasized that this procedure is environmentally more
attractive than the classical coupling procedures. Finally, we
are currently investigating the scope and application of these
complexes as catalysts for other metal-catalyzed C−H bond
activation reactions.
EXPERIMENTAL SECTION
■
General Methods. All reactions for the preparation of
tetrahydropyrimidinium salts and palladium-(NHC) complexes (1)
were carried out under argon in flame-dried glassware using standard
Schlenk techniques. The solvents used were purified by distillation
over the drying agents indicated and were transferred under Ar: THF,
Et2O (Na/K alloy), CH2Cl2 (P4O10), hexane, toluene (Na). All
reagents were purchased from Aldrich Chemical Co. Melting points
were determined in glass capillaries under air with an Electrothermal-
9200 melting point apparatus. FT-IR spectra were recorded as KBr
pellets in the range 400−4000 cm−1 on an ATI UNICAM 1000
1
spectrometer. H NMR and 13C NMR spectra were recorded using a
Varian AS 400 Merkur spectrometer operating at 400 MHz (1H) and
100 MHz (13C) in CDCl3 and DMSO-d6 with tetramethylsilane as an
internal reference. All catalytic reactions were monitored on an Agilent
6890N GC and Schimadzu 2010 Plus GC-MS 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 Inonu
University Scientific and Technology Center.
̈
General Method for the Preparation of Palladium Com-
plexes 1a−d. A suspension of the 1,3-benzyl-3,4,5,6-tetrahydropyr-
imidinium salt (10 mmol) and potassium tert-butoxide (15 mmol) in
THF (20 mL) was stirred for 10 h. After the stirring, hexane (20 mL)
was added and the mixture filtered. The filtrate was evaporated to
dryness (ca. 4 mmol of enetetraamine formed, and the reaction was
1
monitored by H NMR). The residue was dissolved in warm toluene
(20 mL), and this was used as stock solution, owing to air and
moisture sensitivity of the alkenes formed. In the second step, a
mixture of [PdCl2(PPh3)2] (0.60 mmol) in toluene (10 mL) and the
corresponding alkene (0.60 mmol) in toluene (2.0 mL) was heated
under reflux for 2 h and then cooled to 50 °C, and hexane (10 mL)
was added. The precipitate formed was filtered off and washed with
hexane (2 × 10 mL). The yellow product was recrystallized from
CH2Cl2/Et2O (5:15 mL).
1a. Yield: 0.28 g, 74%; mp 295−296 °C. IR: ν(CN) = 1537 cm−1. 1H
NMR (CDCl3): δ 1.74 (p, J = 6 Hz, 4H, NCH2CH2CH2N), 2.31 (s,
12H, CH2C6H4(CH3)-4), 2.90 (t, J = 6 Hz, 8H, NCH2CH2CH2N),
5.36 (s, 8H, CH2C6H4(CH3)-4), 7.05 and 7.33 (d, J = 7.8 Hz, 16H,
CH2 C6 H4 (CH3 )-4). 1 3 C{H} NMR (CDCl3 ):
δ 20.6
(NCH2 CH2 CH2 N), 21. 2 (CH 2 C6 H2 (CH3 )-4), 43. 4
(NCH2CH2CH2N), 60.9 (CH2C6H4(CH3)-4), 128.3, 129.0, 133.3,
136.8 (CH2C6H4(CH3)-4), 193.7 (Pd-Ccarb). Anal. Calcd for
C40H48N4Cl2Pd: C, 63.03; H, 6.35; N, 7.35. Found: C, 62.98; H,
6.18; N, 7.33.
1b. Yield: 0.32 g, 78%; mp 2772−273 °C. IR: ν(CN) = 1546 cm−1.
1H NMR (CDCl3): δ 1.23 (t, J = 5.4 Hz, 12H, CH2C6H4(CH2CH3)-
4), 1.76 (p, J = 5.7 Hz, 4H, NCH2CH2CH2N), 2.61 (q, J = 7.8 Hz, 8H,
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CH2C6H4(CH2CH3)-4), 2.91 (t, J = 5.7 Hz, 8H, NCH2CH2CH2N),
5.55 (s, 8H, CH2C6H4(CH2CH3)-4), 7.08 and 7.36 (d, J = 8.3 Hz,
16H, CH2C6H4(CH2CH3)-4). 13C{H} NMR (CDCl3): δ 15.5
(CH2 C6H2 (CH2CH3)-4), 20.6 (NCH2CH2CH2N), 28.5
(CH2C6H2(CH2CH3)-4), 43.4 (NCH2 CH2CH2N), 61.0
(CH2 C6 H4 (CH2 CH3 )-4), 128.6, 128.8, 133.6, 143.2
(CH2C6H4(CH2CH3)-4), 183.7 (Pd-Ccarb). Anal. Calcd for
C44H56N4Cl2Pd: C, 64.58; H, 6.90; N, 6.85. Found: C, 64.59; H,
6.62; N, 6.81.
tion is available free of charge on the ACS Publications website
at DOI: 10.1021/om501201r.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: bekir.cetinkaya@ege.edu.tr.
Notes
1c. Yield: 0.30 g, 76%; mp 280−281 °C. IR ν(CN) = 1518 cm−1. 1H
NMR (CDCl3): δ 1.15 (t, J = 6.9 Hz, 24H, CH2C6H4N(CH2CH3)-4)2,
1.70 (p, J = 6 Hz, 4H, NCH2CH2CH2N), 2.89 (t, J = 6 Hz, 8H,
NCH2CH2CH2N), 3.32 (q, J = 6.9 Hz, 16H, CH2C6H4N(CH2CH3)2-
4), 5.63 (s, 8H, CH2C6H4N(CH2CH3)2-4), 6.85 and 7.38 (d, J = 8.7
Hz, 16H, CH2C6H4N(CH2CH3)2-4). 13C{H} NMR (CDCl3): δ 12.6
(CH2C6H2N(CH2CH3)2-4), 22.7 (NCH2CH2CH2N), 43.1
(NCH2CH2CH2N), 44.3 (CH2C6H2N(CH2CH3)2-4), 60.7
(CH2C6H4N(CH2CH3)2-4), 111.6, 123.3, 130.1, 147.1 (CH2C6H4N-
(CH2CH3)2-4), 192.4 (Pd-Ccarb). Anal. Calcd for C52H76N8Cl2Pd: C,
63.05; H, 7.73; N, 11.31. Found: C, 63.05; H, 7.80; N, 11.29.
1d. Yield: 0.25 g, 70%; mp 252−253 °C. IR: ν(CN) = 1515 cm−1. 1H
NMR (CDCl3): δ 1.68 (m, 4H, NCH2CH2CH2N), 2.94 (t, J = 5.4 Hz,
8H, NCH2CH2CH2N), 3.86 (s, 12H, CH2C6H4(OCH3)2-3), 3.87 (s,
12H, CH2C6H4(OCH3)2-4), 5.52 (s, 8H, CH2C6H3(OCH3)2-3,4),
6.72 and 6.81 (d, J = 8.1 Hz, 8H) and 7.32 (s, 4H, CH2C6H3(OCH3)2-
3,4). 13C{H} NMR (CDCl3): δ 20.7 (NCH2CH2CH2N), 43.2
(NCH2 CH2 CH2 N), 55.8 (CH2 C6 H2 (OCH3 )2 -3), 56.3
(CH2C6H2(OCH3)2-4), 61.0 (CH2C6H4(OCH3)2-3,4), 110.3, 111.1,
120.6, 128.9, 148.3, 149.2 (CH2C6H4(OCH3)2-3,4), 192.8 (Pd−Ccarb).
Anal. Calcd for C44H56N4O8Cl2Pd: C, 55.85; H, 5.97; N, 5.92. Found:
C, 55.87; H, 5.97; N, 5.90.
Typical Procedure for Direct Arylations. As described in refs
24c and 24h, in a typical experiment, the aryl bromide (1 mmol),
heteroarene derivative (2 mmol) (see Table 1), and KOAc (2 mmol)
were introduced in a Schlenk tube, equipped with a magnetic stirring
bar. The Pd complex (0.01 mmol) and DMAc (3 mL) were added,
and the Schlenk tube was purged several times with argon. The
Schlenk tube was placed in a preheated oil bath at 150 °C, and the
reaction mixture was stirred for 1 h. Then, the reaction mixture was
analyzed by gas chromatography to determine the conversion of the
aryl bromide and the yield of product. The solvent was removed 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
and pentane.24c,34,37
Crystal Structure Analysis. A suitable crystal of 1a was selected
for data collection, which was performed on a STOE IPDS II
diffractometer equipped with graphite-monochromatic Mo Kα
radiation at 296 K. The structures were solved by direct methods
using SHELXS-9738 and refined by full-matrix least-squares methods
on F2 using SHELXL-9739 from within the WINGX39 suite of
software. All non-hydrogen atoms were refined with anisotropic
parameters. The H atoms were located from difference maps and then
treated as riding atoms with C−H distances of 0.93−0.97 Å. The large
SD values and displacement parameters of the C23 atom were caused
by the disorder. This disorder was modeled as two different
orientations, with occupancy factors of 0.629(10) and 0.371(10),
respectively. Molecular diagrams were created using MERCURY.40
Details of data collection and crystal structure determinations are given
in Table 1. Figure 1 shows the molecular structure of 1a.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the Technological and
Scientific Research Council of Turkey TUBITAK-BOSPHO-
̇
̇
RUS (France) [109T605], TUBA, and Inonu University
̈
̈
̇
̈
Research Fund (I.U. B.A.P: 2013/51).
DEDICATION
■
This article is dedicated to the memory of Professor Michael
Franz Lappert.
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