Synthesis, characterization and catalytic activity of novel N-heterocyclic carbene-palladium complexes

Article abstract of DOI:10.1039/b906497b

The reaction of Pd(OAc)₂ with 1-(benzhydryl)-3-(alkyl) benzimidazolium salts 1a-d yields trans-bis[1-(benzhydryl)-3-(alkyl) benzimidazolin-2-ylidene]dibromopalladium(II) complexes (2a-d) which were characterized by elemental analysis, NMR spectroscopy and the molecular structures of 2b, and 2d were determined by X-ray crystallography. The catalytic activity of PdBr₂bis(benzimidazolin-2-ylidene) complexes 2a-d was evaluated in the direct arylation reaction of benzothiazole with bromobenzene derivatives.

Full text of DOI:10.1039/b906497b

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www.rsc.org/dalton | Dalton Transactions
Synthesis, characterization and catalytic activity of novel N-heterocyclic
carbene-palladium complexes†
a
a
a
b
c
c
¨
˙
¨
Oznur Dog˘an, Nevin Gu¨rbu¨z, Ismail Ozdemir,* Bekir C¸ etinkaya, Onur S¸ahin and Orhan Bu¨yu¨kgu¨ngo¨r
Received 1st April 2009, Accepted 19th June 2009
First published as an Advance Article on the web 21st July 2009
DOI: 10.1039/b906497b
The reaction of Pd(OAc)2 with 1-(benzhydryl)-3-(alkyl)benzimidazolium salts 1a–d yields
trans-bis[1-(benzhydryl)-3-(alkyl)benzimidazolin-2-ylidene]dibromopalladium(II) complexes (2a–d)
which were characterized by elemental analysis, NMR spectroscopy and the molecular structures of 2b,
and 2d were determined by X-ray crystallography. The catalytic activity of PdBr2bis(benzimidazolin-
2-ylidene) complexes 2a–d was evaluated in the direct arylation reaction of benzothiazole with
bromobenzene derivatives.
these reactions, the critical step is the C–H bond cleavage and
metallation of the aromatic ring with the transition metal complex.
We have recently shown that NHC–ruthenium(II) species in
situ generated from [RuCl2(p-cymene)]2 and monoazolium salts
under basic conditions were able to catalyze the direct arylation of
2-phenylpyridine by aryl bromides.22
We now report the synthesis of new palladium(II) com-
plexes with electron-rich carbene ligands, arising from N,N¢-
dialkylbenzimidazolium salts, upon reaction with Pd(OAc)2 pre-
cursor, and their application in catalytic C–H bond functionaliza-
tion.
Introduction
Since the first characterization of metal complexes containing
N-heterocyclic carbene (NHC) ligands by Ofele and Wanzlick
in 1968, the development of metal–NHC complexes by Lappert in
the early 1970s,3 and the isolation of the stable free NHC by the
group of Arduengo in 1991,4 much attention has been paid toward
their properties and application.
1
2
¨
NHCs show many interesting properties that make them
valuable as ligands in catalysis. A combination of their powerful
s-donating and weak p-accepting character allows for the gen-
eration of a stronger bond to the metal than their phosphine
homologues and leads to the formation of interestingly robust
electron-rich metal complexes. Consequently, metal–NHC com-
plexes tend to be air-stable, easy to handle and highly active
in several catalytic transformations where harsh conditions are
often required.5 In recent years, an exceptionally large number of
NHC complexes have emerged and have been used successfully
in many catalytic transformations, notably the C–C and C–N
cross-coupling reactions,6,7 metathesis,8 hydrosilylation,9 transfer
hydrogenation,10 and furan synthesis.11
Heteroaromatics are important structural units frequently
found in natural products,12 pharmaceutically active substances,
agrochemicals13 and organic functional materials such as liquid
crystals and fluorescent dyes.14 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. Direct transformation of a C–H bond into a
C–C bond is a relatively clean and efficient method for meeting
such goals.15 In recent years, significant progress has been made
toward the development of direct arylation of a wide variety
of substrates using Pd,16 Rh,17 Ru,18–20 and Ir21 catalysts. For
Results and discussion
Preparation of benzimidazolium salts
Dialkylbenzimidazolium salts, (1a–d) conventional functionalized
NHC precursors, were synthesized by consecutive alkylation of
1- benzhydrylbenzimidazole with alkyl halides (Scheme 1).
According to Scheme 1, the salts (1a–d) were obtained in
almost quantitative yield by quarternization of 1-benzhydryl-
benzimidazole in DMF with alkyl halides.23 The salts were air-
and moisture stable both in the solid state and in solution. The
structures of 1a–d were determined by their characteristic spec-
troscopic data and elemental analyses. 13C NMR chemical shifts
were consistent with the proposed structure, the imino carbon
appeared as a typical singlet in the 1H-decoupled mode at 142.7,
142.6, 142.4 and 153.8 ppm respectively for benzimidazolium
1
bromides 1a–d. The H NMR spectra of the benzimidazolium
salts further supported the assigned structures; the resonances for
C(2)–H were observed as sharp singlets at 10.16, 9.95, 9.43 and
9.82 ppm respectively for 1a–d. The IR data for benzimidazolium
=
salts 1a–d clearly indicate the presence of the –C N– group with a
-1
=
n(C N) vibration at 1544, 1557, 1543 and 1596 cm respectively
for 1a–d. The NMR values are similar to those found for other
aIno¨nu¨ University, Faculty of Science and Art, Department of
Chemistry, 44280, Malatya, Turkey. E-mail: iozdemir@inonu.edu.tr;
Fax: +904223410212; Tel: +904223410212
1,3-dialkylbenzimidazolium salts.23
Preparation of palladium complexes 2
bEge University, Faculty of Science, Department of Chemistry, 35100,
˙
Bornova-Izmir, Turkey
The formation of NHC–metal complexes is mainly based on
four principal routes (Scheme 2): (i) in situ deprotonation of
the corresponding azolium salts, (ii) complexation of the free
cOndokuzMayıs University, Department of Physics, 55139, Samsun, Turkey
† CCDC reference numbers 716524 & 716525. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b906497b
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7087–7093 | 7087
©

Scheme 1 Synthesis of 1,3-dialkylbenzimidazolium bromides.
Scheme 2 General preparation of NHC complexes.
stable NHC, (iii) thermal cleavage of electron rich alkenes, and
(iv) transmetallation from a silver–NHC complex.24
those recently reported for other PdBr2(N-heterocyclic carbene)2
complexes.26
The reaction of benzimidazolium salts, with the Pd(OAc)2
complex proceeded smoothly on heating at 30 ◦C for 3 h and then
120 C for a further 6 h. The PdBr2(1,3-dialkyl-benzimidazolin-
2-ylidene)2, complexes 2 as crystalline solids in 75–81% yield
(Scheme 3).
Complexes 2a–d, which were very stable in the solid state have
been characterized by analytical and spectroscopic techniques.
Palladium complexes exhibit a characteristic n(NCN) band typically
at 1557, 1606, 1616 and 1595 cm-1 respectively for 2a–d.25 13C
chemical shifts, which provide a useful diagnostic tool for metal
carbene complexes, show that Ccarb is substantially deshielded.
Values of d(13Ccarb) are in the range 182–184 ppm and are similar
to those found in other carbene complexes. These new complexes
showed typical spectroscopic signatures that were in line with
Structural characterization of 2b, and 2d. Crystals of 2b and
2d suitable for X-ray analysis were obtained from a chloroform
solution layered with diethyl ether. The molecular structures of
complexes have been confirmed by X-ray single-crystal analyses.
Colorless single-crystals of 2b and 2d suitable for data collection
were selected and performed on a STOE IPDS II diffractometer
◦
˚
with graphite monochromated Mo-Ka radiation l = 0.71069 A.
The structures were solved by direct-methods using SHELXS-
9727 and refined by full-matrix least-squares methods on F2 using
SHELXL-9728 from within the WINGX29,30 suite of software.
The parameters for data collection and structure refinement of
complexes 2b and 2d are listed in Table 1. All non-hydrogen atoms
were refined with anisotropic parameters. Hydrogen atoms bonded
7088 | Dalton Trans., 2009, 7087–7093
This journal is
The Royal Society of Chemistry 2009
©

Scheme 3 Synthesis of palladium–NHC complexes.
Table 1 Parameters for data collection and structure refinement of 2b
and 2d
2b
2d
Empirical formula
C48H48Br2N4O2Pd
C60H56Br2N4O6Pd·
2(CHCl3)
1434.04
296
Triclinic
¯
P1
Formula weight
T/K
979.12
296
Triclinic
¯
P1
8.9725(3)
10.4541(4)
12.0262(4)
81.773(3)
86.671(3)
85.751(4)
1112.08(7)
1
Crystal system
Space group
˚
a/A
10.692(5)
12.829(6)
13.904(5)
65.559(5)
88.175(5)
67.876(4)
1591.0(11)
1
1.497
1.85
724
0.44 ¥ 0.24 ¥ 0.14
1.9–26.5
36044
6603
0.050
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
r
calcd/Mg m-3
1.462
2.26
496
m/mm-1
F(000)
Crystal size/mm3
0.44 ¥ 0.29 ¥ 0.22
q Range for data collection/◦ 2.0–28.0
Reflections collected
Independent reflection
R(int)
28000
5130
0.068
Max./min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
R1 (I > 2s(I))
0.660 and 0.422
5130/38/269
1.05
0.038
0.095
0.045
0.098
0.58 and -0.67
0.702 and 0.373
6603/0/370
1.05
0.035
0.080
0.047
0.084
0.52 and -0.56
Fig. 1 ORTEP drawing of complex 2b showing 40% probability thermal
˚
ellipsoids. Selected bond lengths [A]: Pd1–Br1 = 2.4191(3), Pd1–C1 =
wR2 (I > 2s(I))
2.016(2), C1–N1 = 1.345(3), C1–N2 = 1.359(3), C2–N1 = 1.385(3),
C7–N2 = 1.396(3), C8–N2 = 1.477(3), C8–C9 = 1.520(4), C21–N1 =
1.459(3); angles [◦] : C1–Pd1–Br1 = 92.7(7), N1–C1–Pd1 = 124.6(18),
N2–C1–Pd1 = 128.6(18), N1–C1–N2 = 106.5(2), N1–C2–C3 = 131.1(3),
N2–C8–C9 = 112.4(2), C9–C8–C15 = 115.9(2), N1–C21–C22 = 112.2(3).
Symmetry code: (i) 1 - x, 1 - y, 1 - z.
R1 (all data)
wR2 (all data)
Drmax./min./e A
-3
˚
˚
to carbon were placed in calculated positions (C–H = 0.93–0.97 A)
and treated using a riding model with U = 1.2 times the U value
of the parent atom for CH, CH2 and CH3. For the structure of 2b,
the large s.u. values and displacement parameters of some atoms
in the molecule are caused by disorder of the ethoxyethyl group.
The refinement of the disordered ethoxyethyl group was made
anisotropically using PART and EADP restrictions. This disorder
was modelled as two different orientations as A and B groups
[hereafter A = O1a, C23a, C24a and B = O1b, C23b, C24b],
seen in Fig. 1, with occupancy factors of 0.504(7) and 0.496(7),
respectively. Molecular diagrams were created using ORTEP-III.31
Geometric calculations were performed with Platon.32 Molecular
structures of 2b and 2d with selected data are presented in
Figs. 1 and 2 respectively, and p ◊ ◊ ◊ ring interactions are shown in
Table 2.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7087–7093 | 7089
©

˚
Fig. 2 ORTEP drawing of complex 2d showing 40% probability thermal ellipsoids. Selected bond lengths [A]: Pd1–Br1 = 2.4232(7), Pd1–C1 =
2.020(3), C1–N1 = 1.345(3), C1–N2 = 1.359(3), C2–N1 = 1.388(3), C7–N2 = 1.405(3), C8–N2 = 1.472(3), C8–C9 = 1.520(4), C21–N1 = 1.455(3),
C21–C22 = 1.510(4); angles [◦] : C1–Pd1–Br1 = 91.0(7), N1–C1–Pd1 = 125.7(18), N2–C1–Pd1 = 128.0(18), N1–C1–N2 = 106.2(2), N1–C2–C3 =
130.9(3), N2–C8–C9 = 112.0(2), C9–C8–C15 = 115.9(2), N1–C21–C22 = 113.1(2). Symmetry code: (i) 1 - x, 1 - y, 1 - z.
Table 2 p ◊ ◊ ◊ ring interactions
Conclusions
2d
From readily available starting materials, such as 1-(benzhydryl)-
3-(alkyl)benzimidazolium salts, four novel PdBr2(1,3-dialkyl-
benzimidazolin-2-ylidene)2 complexes (2a–d) have been prepared
and characterized. Complexes 2b and 2d were characterized by
single crystal X-ray diffraction studies. The efficiency of complexes
2a–d as catalyst precursors for the arylation of benzothiazole with
aryl bromides has also been established.
C–H ◊ ◊ ◊ Cg/◦
134.97
130.29
˚
C ◊ ◊ ◊ H(I)
Cg(J)
H ◊ ◊ ◊ Cg/A
C12 ◊ ◊ ◊ H12
C19 ◊ ◊ ◊ H19
C20 ◊ ◊ ◊ H20
Cg(2)i
Cg(5)ii
Cg(5)ii
3.3235
3.2306
3.3637
124.78
Cg(2): C2–C3–C4–C5–C6–C7, Cg(5): C22–C23–C24–C25–C26–C27.
Symmetry codes: (i) -x, 2 - y, 1 - z; (ii) 1 - x, 1 - y, 1 - z.
Experimental
Direct arylation of benzothiazole via C–H bond activation. We
showed that NHC–palladium(II) species in situ generated from
Pd(OAc)2 and monoazolium salts under basic conditions were able
to catalyze the direct arylation of aldehydes by aryl halides.33,23e
Herein, we report a facile C-arylation of benzothiazole with aryl
bromides catalyzed by well defined and stable palladium-NHC
complexes. The influence of various bases such as Cs2CO3, K2CO3,
K3PO4, NaH and KOBut was studied. It was observed that the
bases Cs2CO3 and K3PO4 afforded good yields of the desired prod-
ucts. However, due to cost considerations K3PO4 was preferred
over Cs2CO3. The effect of the various solvents on the reaction
system was also examined. It was observed that nonpolar solvents
such as toluene and xylene gave low yields of product probably
due to the poor solubility of reactant and catalysts in the reaction
medium. We found that the reactions performed in NMP with
K3PO4 as the base at 130 ◦C gave better results than other bases.
Control experiments indicated that the arylation of benzothiazole
with bromobenzene did not occur in the absence of 2a. Under
these optimization conditions, bromobenzene, p-bromotoluene,
p-bromoanisole and p-bromoacetophenone, reacted cleanly with
benzothiazole in good yields (Table 3, entries 4, 6, 12 and 16).
All reactions for the preparation of benzimidazolium salts (1)
and palladium-(NHC) complexes (2) were carried out under Ar
in flame-dried glass-ware using standard Schlenk-type flasks. The
solvents used were purified by distillation over the drying agents
indicated and were transferred under Ar. 1a–d were prepared
according to known methods.23 All reagents were purchased from
Aldrich Chemical Co. 1H NMR and 13C NMR spectra were
recorded using a Varian AS 400 Merkur spectrometer operating at
400 MHz (1H), 100 MHz (13C) in CDCl3 with tetramethylsilane as
an internal reference. Chemical shifts (d) are given in ppm relative
to TMS, coupling constants (J) in Hz. Infrared spectra were
recorded as KBr pellets in the range 400–4000 cm-1 on a ATI UNI-
CAM 1000 spectrometer. Melting points were measured in open
capillary tubes with an Electrothermal-9200 melting point appa-
ratus and are uncorrected. Elemental analyses were performed by
the Turkish Research Council (Ankara, Turkey) Microlab.
Synthesis of ligands
General procedure for the preparation of the benzimidazolium
salts (1a–d). The benzimidazolium salts were prepared as
1a–c according to our previous report.23e To a solution of
7090 | Dalton Trans., 2009, 7087–7093
This journal is
The Royal Society of Chemistry 2009
©

Table 3 Arylation of benzothiazole with aryl bromides
Entry
Cat.
R
Yielda,b,c,d (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2a
2b
2c
2d
2a
2b
2c
2d
2a
2b
2c
2d
2a
2b
2c
2d
H
H
H
H
CH3
CH3
CH3
CH3
OCH3
OCH3
OCH3
OCH3
COCH3
COCH3
COCH3
COCH3
65
61
67
81
63
70
59
69
68
73
56
80
49
47
51
58
a Reaction conditions: 1.5 mmol of p-R-C6H4Br, 1.0 mmol benzothiazole, 2 mmol K3PO4, 1.5 mol Pd, 3 mL NMP. b Purity of all compounds determined
by NMR and the yield calculated based on the aryl bromide. c All reactions followed by GC. d Temperature 150 ◦C and time 30 h.
1-alkylbenzimidazoline (10 mmol) in DMF (10 mL) was slowly
added alkylbromide (10 mmol) at 25 ◦C and the resulting mixture
was stirred at 12 h at 80 ◦C. Et2O (10 mL) was added to the reaction
mixture. A white solid was precipitated in this period. The solid
was washed with diethyl ether (3 ¥ 15 mL), dried under vacuum.
The precipitate was then crystallized from EtOH/Et2O (1:2).
183.7 (Ccarbene). Anal. Calc. for C46H44O2N4Br2Pd: C, 58.04; H,
4.66; N, 5.89. Found: C, 58.07; H, 4.71; N, 5.83%.
trans-bis[1-(Benzhydryl)-3-(ethoxyethyl)benzimidazolin-2-ylid-
ene]dibromo-palladium(II)
(2b). Compound
2b
was
prepared in the same way as 2a, from 1-(benzhydryl)-3-
(ethoxyethyl)benzimidazolium bromide (1b) (0.44 g, 1 mmol) and
Pd(OAc)2 (0.11 g, 0.5 mmol) in DMSO (5 mL). Yield: 0.37 g
1-(Benzhydryl)-3-(3,4,5-trimethoxybenzyl)benzimidazolium bro-
mide (1d). Yield: 4,91 g (90%); mp 253–254 ◦C; n(CN)
=
(75%); mp 281–283 ◦C; n(CN) = 1606cm-1. H NMR (400 MHz,
1
1595.66 cm-1. H NMR (400 MHz, CDCl3): d = 3.61 (s, 3H,
CH2C6H2(OCH3)3-4), 3.74 (s, 6H, CH2C6H2(OCH3)3-3,5), 5.67
(s, 2H, CH2-(C6H2)-(OCH3)3-3,4,5), 6.90 (s, 2H, CH2-(C6H2)-
(OCH3)3-3,4,5), 7.41–8,35 (m, 15H, CH(C6H5)2, Ar), 9.82 (s,1H,2-
CH). 13C NMR (100 MHz, CDCl3): d = 51.0 (CH2C6H2(OCH3)3-
3,5), 56.7 (CH2C6H2(OCH3)3-4), 60.6 (CH2-(C6H2)-(CH3)3-3,4,5),
64.8 (CH(C6H5)2), 106.7, 115.1, 127.5, 127.6, 127.7, 127.9, 129.8,
129.9, 130.1, 132.0, 132.8, 138.3, 142.7 (Ar), 153.8 (2-CH). Anal.
Calc. for C30H29N2O3Br: C, 66.06; H, 5,36; N, 5.14. Found: C,
66.02; H, 5.39; N, 5.22%.
1
CDCl3): d = 1.04 (t, 6H, J = 6.9 Hz, OCH2CH3), 3.43 (quart.,
4H, J = 6.9 Hz, OCH2CH3), 4.12 (t, 4H, J = 6 Hz, NCH2CH2O),
4.98 (t, 4H, J = 6. Hz, CH2CH2O), 8.50 (s, 2H, CH(C6H5)2,
6.73–7.57 (m, 28H, Ar). 13C NMR (100 MHz, CDCl3): d =
15.0 (OCH2CH3), 67.9 (OCH2CH3), 66.8 (NCH2CH2O), 69.2
(NCH2CH2O), 48.2 (CH(C6H5)2), 111.4, 113.3, 122.5, 128.4,
129.0, 133.8, 135.9, 137.6 (Ar), 183.9 (Ccarbene). Anal. Calc. For
C48H48Br2N4O2Pd: C, 58.88; H, 4.94, N, 5.72. Found: C, 58.92; H,
4.99; N, 5.69%.
Synthesis of complexes trans-bis[1-(Benzhydryl)-3-(methoxy-
trans-bis[1-(Benzhydryl)-3-(2,4,6-trimethylbenzyl)benzimidazo-
lin-2-ylidene]dibromo-palladium(II) (2c). Compound 2c was pre-
pared in the same way as 2a, from 1-(benzhydryl)-3-(2,4,6-
trimethylbenzyl)benzimidazolium bromide (1c) (0.50 g, 1 mmol)
and Pd(OAc)2 (0.11 g, 0.5 mmol) in DMSO (15 mL). Yield: 0.45 g
ethyl)benzimidazolin-2-ylidene]dibromopalladium(II)
(2a). 1-
(Benzhydryl)-3-(methoxyethyl)benzimidazolium bromide (1a)
(0.42 g, 1 mmol) and Pd(OAc)2 (0.11 g, 0.5 mmol) were solved in
DMSO (15 mL). The resulting mixture was stirred for 3 h at room
temperature and then for 6 h at 120 ◦C. The solvent was removed
under reduced pressure. The solid was washed with ether (3 ¥
10 mL) and dried under vacuum. The crude product was then
crystallized from CH2Cl2/Et2O (1:2). Yield: 0.36 g (76%); mp
220–221 ◦C; n(CN) = 1557cm-1. 1H NMR (400 MHz, CDCl3): d =
3.27 (s, 6H, OCH3), 4.08 (t, 4H, J = 6 Hz, NCH2CH2O), 4.97 (t,
4H, J = 6 Hz, NCH2CH2O), 8.51 (s, 2H, CH(C6H5)2), 6.74–7.58
(m, 28H, Ar). 13C NMR (100 MHz, CDCl3): d = 59.2 (OCH3),
67.5 (NCH2CH2O), 71.5 (NCH2CH2O), 48.4 (CH(C6H5)2), 111.3,
113.5, 122.6, 127.9, 128.4, 129.0, 129.6, 133.6, 135.9, 137.6 (Ar),
(81%); mp 299–300 ◦C; n(CN)= 1616 cm-1. H NMR (400 Mhz,
1
CDCl3): d = 2.32 (s, 12H, CH2C6H2(CH3)3-2,6), 2.37 (s, 6H,
CH2C6H2(CH3)3-4), 5.93 (s, 4H, CH2-(C6H2)-(CH3)3), 6.95 (s, 4H,
CH2-(C6H2)-(CH3)3), 8.83 (s, 2H, CH(C6H5)2), 7.38–7.73 (m, 28H,
Ar). 13C NMR (100 MHz, CDCl3): d = 21.1 (CH2C6H2(CH3)3-4),
21.4 (CH2C6H2(CH3)3-2,6), 53.5 (CH2-(C6H2)-(CH3)3-2,4,6), 67.4
(CH(C6H5)2), 114.6, 114.7, 122.1, 122.4, 127.8, 128.3, 128.4, 128.8,
129.6, 134.7, 135.0, 138.0, 138.4, 153.6 (Ar), 182.0 (Ccarbene). Anal.
Calc. for C60H58Br2N4Pd: C, 65.43; H, 5.31; N, 5.09. Found: C,
65.41; H, 5.30; N, 5.07%.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7087–7093 | 7091
©

trans-bis[1-(Benzhydryl)-3-(3,4,5-trimethoxybenzyl)benzimida-
zolin-2-ylidene]dibromo-palladium(II) (2d). Compound 2d was
prepared in the same way as 2a, from 1-(benzhydryl)-3-(3,4,5-
trimethoxybenzyl)benzimidazolium bromide (1d) (0.56 g, 1 mmol)
and Pd(OAc)2 (0.11 g, 0.5 mmol) in DMSO (15 mL). The crude
product was then crystallized from CHCl3/Et2O (1:2). Yield:
Z. Naturforsch., 2007, 62b, 357–361; (f) F. E. Hahn, M. C. Jahnke
and T. Pape, Organometallics, 2007, 26, 150–154; (g) S. K. Yen, L. L.
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2006, 25, 5105–5112; H. V. Huynh, C. Holtgrewe, T. Pape, L. L. Koh
and F. E. Hahn, Organometallics, 2006, 25, 245–249; (h) F. E. Hahn,
M. C. Jahnke, V. Gomez-Benitez, D. Morales-Morales and T. Pape,
Organometallics, 2005, 24, 6458–6463.
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Nolan, Annual Rep. Prog. Chem., Sect. B, 2005, 101, 171–191; (d) N-
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8 (a) T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 2001, 34, 18–29;
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0.56 g (78%); mp 275–277 ◦C; n(CN)= 1595 cm-1. H NMR (400
1
MHz, CDCl3): d = 3.77 (s, 12H, CH2C6H2(OCH3)3-3,5), 3.89
(s, 6H, CH2C6H2(OCH3)3-4), 6.05 (s, 4H, CH2-(C6H2)-(OCH3)3-
3,4,5), 6.91 (s, 4H, CH2-(C6H2)-(OCH3)3-3,4,5), 8.64 (s, 2H,
CH(C6H5)2), 6.54–7.40 (m, 28H, Ar). 13C NMR (100 MHz,
CDCl3): d = 56.9 (CH2C6H2(CH3)3-3,5), 60.8 (CH2C6H2(CH3)3-
4), 65.9 (CH2-(C6H2)-(CH3)3-3,4,5), 67.5 (CH(C6H5)2), 105.3,
111.4, 113.6, 122.7, 122.8, 127.9, 128.4, 128.7, 129.0, 131.3,
134.6, 134.8, 137.5, 138.1 (Ar), 184.0 (Ccarbene). Anal. Calc. for
C60H56Br2N4O6Pd·2(CHCl3): C, 51.96; H, 4.01; N, 3.91. Found: C,
51.92; H, 4.02; N, 3.93%.
9 M. F. Lappert and R. K. Maskell, J. Organomet. Chem., 1984, 264,
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General procedure for the arylation of benzothiazole. The Pd–
NHC complex (% 1.5 mol), aryl bromides (1.5 mmol), benzothia-
zole (1 mmol), K3PO4 (2.0 mmol) and NMP (3 mL) were all added
to a small Schlenk tube and the mixture was heated at 150 ◦C for
30 h in an oil bath. EtOAc were added to the cold reaction mixture.
The organic phase was dried over MgSO4 and concentrated
under vacuum. The remaining residue was purified by column
chromatography on silica gel (EtOAc/hexane mixture) to yield
the arylated products. Conversion and ratios were determined by
1H NMR and by GC analyses.
˙
¨
11 (a) B. C¸ etinkaya, I. Ozdemir, C. Bruneau and P. H. Dixneuf, J. Mol.
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Acknowledgements
This work was financially supported by the Technological and
˙
Scientific Research Council of Turkey TUBITAK-CNRS (France)
˙ ¨
[TBAG-U/181 (106T716)], Ino¨nu¨ University Research Fund (I.U.
B.A.P: 2009/13) and the Faculty of Arts and Sciences, Ondokuz
Mayıs University, Turkey, for the use of the Stoe IPDS-II
diffractometer (purchased from grant no. F279 of the University
Research Fund).
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