Synthesis, characterization and catalytic properties of cis-dibromo{1,1′-di[3,4,5-trimethoxybenzyl]-3,3′- butylenedibenzimidazol-2,2′-diylidene}palladium (II)

Article abstract of DOI:10.1016/j.inoche.2011.02.001

An N-heterocyclic carbene palladium-based complex, cis-dibromo{1,1′- di[3,4,5-trimethoxybenzyl]-3,3′-butylenedibenzimidazol-2, 2′-diylidene}palladium(II), has been synthesized and characterized by elemental analysis, IR spectroscopy and ¹H- and ¹³C-NMR spectroscopy. The crystal and molecular structure of the title compound was determined by single-crystal X-ray diffraction. The title compound consists of a 1,1′-di[3,4,5-trimethoxybenzyl]-3,3′-butylenedibenzimidazole and two bromo ligands coordinated to a palladium atom in a distorted square-planar cis-system. Two benzoimidazole rings are connected to each other by a C ₄H₈ bridge. The substituted benzimidazole ligand forms a bidentate chelate with palladium, bonding via the carbene carbon atoms. There are two independent molecules A and B in the asymmetric unit. The Pd - Br bonds are 2.4675(14) and 2.4601(13) ?, and the Pd - C_carbene bonds are 1.985(9) and 1.986(9) ? for molecule A. Each A and B molecule is stabilized with intra- and inter-molecular hydrogen bonds and C - H...π interactions. The palladium-carbene complex was tested as a catalyst in the direct arylation of benzothiazole with arylbromides. The most suitable reaction conditions for the direct arylation of benzothiazole with arylbromides are NMP, K₃PO₄, Pd-NHC and 130 °C.

Full text of DOI:10.1016/j.inoche.2011.02.001

Inorganic Chemistry Communications 14 (2011) 672–675
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, characterization and catalytic properties of cis-dibromo{1,1′-di
[3,4,5-trimethoxybenzyl]-3,3′-butylenedibenzimidazol-2,2′-diylidene}palladium (II)
a
c
d
İsmail Özdemir a, Hakan Arslan b, , Serpil Demir , Don VanDerveer , Bekir Çetinkaya
⁎
a
Department of Chemistry, Faculty of Science and Art, İnönü University, Malatya, TR-44280, Turkey
Department of Chemistry, Faculty of Arts and Science, Mersin University, Mersin, TR-33343, Turkey
b
c
Department of Chemistry, Clemson University, Clemson, SC-29634, USA
d
Department of Chemistry, Faculty of Science, Ege University, Bornova-İzmir, TR-35100, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
An N-heterocyclic carbene palladium-based complex, cis-dibromo{1,1′-di[3,4,5-trimethoxybenzyl]-3,3′-
butylenedibenzimidazol-2,2′-diylidene}palladium(II), has been synthesized and characterized by elemental
analysis, IR spectroscopy and 1H- and 13C-NMR spectroscopy. The crystal and molecular structure of the title
compound was determined by single-crystal X-ray diffraction. The title compound consists of a 1,1′-di[3,4,5-
trimethoxybenzyl]-3,3′-butylenedibenzimidazole and two bromo ligands coordinated to a palladium atom in
a distorted square-planar cis-system. Two benzoimidazole rings are connected to each other by a C4H8 bridge.
The substituted benzimidazole ligand forms a bidentate chelate with palladium, bonding via the carbene
carbon atoms. There are two independent molecules A and B in the asymmetric unit. The Pd―Br bonds are
2.4675(14) and 2.4601(13)Å, and the Pd―Ccarbene bonds are 1.985(9) and 1.986(9)Å for molecule A. Each A
and B molecule is stabilized with intra- and inter-molecular hydrogen bonds and C―H…π interactions. The
Received 1 April 2010
Accepted 5 February 2011
Available online 12 February 2011
Keywords:
N-heterocyclic carbenes
Bidentate palladium complexes
Crystal structure
Arylation of benzothiazole
Palladium catalyst
palladium–carbene complex was tested as
a catalyst in the direct arylation of benzothiazole with
arylbromides. The most suitable reaction conditions for the direct arylation of benzothiazole with
arylbromides are NMP, K3PO4, Pd–NHC and 130 °C.
© 2011 Elsevier B.V. All rights reserved.
Heteroaryl groups directly connected by single Csp2―Csp2 bonds
to heteroaryl moieties are present as core structures in many
biologically active compounds, naturally-occurring substances, agro-
chemicals, and optical and photochromic materials in polymer science
[1,2]. The most useful method to prepare for these important
derivatives is the metal-catalyzed cross-coupling of aryl halides
with heteroaryl derivatives [3]. A viable solution could be the use of
palladium(II) complexes with suitable ligands, which should increase
the stability of the catalyst under reaction conditions without
negatively affecting its reactivity. One type of ligand would be an N-
heterocyclic carbene.
N-heterocyclic carbene (NHC) ligands appear particularly suited to
this purpose, in that it is known that their palladium(II) complexes
possess a high thermal and hydrolytic stability, even under strongly
acidic conditions [4].
Recently, our research group has focused on N-heterocyclic
carbene derivative ligands and their metal complexes for synthesis,
characterization, crystal structure and catalytic activity [5–14]. In this
contribution, we pursue further our previous work on the chelating
biscarbene palladium(II) complex. Bis(benzimidazolium) salt as the
NHC precursor, was synthesized by treatment of 1-substituted
benzimidazole with 1,4-dibromobuthane according to the literature
[10]. Because of the 1,4-butylene linker group is more flexible than the
other more commonly used bridges such as methylene, o-xylylene
etc. [15] we select 1,4-butylene group as a bridge/linker group. The
reaction of the bis(benzimidazolium) salt with Pd(OAc)2 in dimethyl
sulfoxide resulted in the Palladium–NHC complex (2) as a crystalline
solid (Scheme 1) [16]. The spectroscopically pure 2, which is very
stable in the solid state, was characterized by analytical and
spectroscopic techniques [16]. The FT-IR spectroscopy, 1H- and 13C–
NMR spectroscopy, and elemental analysis data of the title compound
confirm the proposed structure [16,17]. The crystal structure of this
new complex [17,18], as well as its applications in the direct arylation
of benzothiazole with arylbromides [19] is described.
The complex exhibits signals slightly upfield in comparison with
the parent carbene precursor (1); as expected, the C2–H signal is
absent. Correspondingly, the 13C–NMR spectrum of the title com-
pound shows the characteristic coordinated carbene signal at
173.8 ppm, which is in the typical range observed for Pd–NHC
complexes. The IR data for the Pd–carbene complex clearly indicate
the presence of the C―N group with a νCN vibration at 1462 cm−1
.
The molecular structure of the title compound was confirmed by
the result of a single crystal X-ray structure determination. The
molecular structure of 2, with the atom-numbering scheme, is shown
⁎
Corresponding author. Tel.: +90 532 7073122; fax: +90 324 3610047.
E-mail address: hakan.arslan.acad@gmail.com (H. Arslan).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.02.001

İ. Özdemir et al. / Inorganic Chemistry Communications 14 (2011) 672–675
673
Scheme 1. Synthesis of palladium-NHC complex.
in Fig. 1. Selected bond lengths and angles are listed in the caption of
Fig. 1 [20]. The asymmetric unit of the title compound contains two
crystallographically independent molecules A and B. There is very
little difference between the bond lengths and angles of these
molecules.
The coordination geometry around the palladium atom is square
planar, with Ccarben and Br atoms cis to each other. There is a small
amount of distortion of the square plane towards a tetrahedron. The
palladium atom is displaced slightly at a distance of 0.018 Å from the
coordination plane defined by the C1–C12–Br1–Br2 atoms. The Br1–
Pd1–Br2 angle of 94.74(5)° and the C1–Pd–C12 angle of 93.3(4)°
agree well with values reported for structures of the type cis-PdL2X2
(L: Carben derivative ligands) [21–23].
(6) and 2.4622(6)] in {1,1′-dibenzyl-3,3′-ethylenediimidazolin-2,2′
diylidene}palladium(II) dibromide [21], follow a similar trend to
those in the title compound. In addition, the Pd―Br bond distances
are shorter than the platinum complex, (1,1′-dimethyl-3,3′-methy-
lene-4-diimidazolin-2,2′-diylideneplatinum(II) dibromide) (2.4976
(11) and 2.4883(13)Å) [26].
The Pd―Ccarben bond in the title complex is somewhat shorter
than the average of 1.997 0.019 Å calculated for 14 Pd–Ccarben
distances in 9 Pd–NHC complexes reported to the Cambridge
Structural Database [24]. The corresponding Pd―Ccarben bond length
values [1.959(6)–1.993(2)] in the compounds {1,1′-di(4-methoxy-
benzyl)-3,3′-ethylenediimidazolin-2,2′diylidene}palladium(II) dibro-
mide, {1,1′-di(3-methoxybenzyl)-3,3′-ethylenediimidazolin-2,2′
diylidene}palladium(II) dibromide, {1,1′-di(4-fluorobenzyl)-3,3′-
ethylenediimidazolin-2,2′diylidene}palladium(II) dibromide, {1,1′-
dibenzyl-3,3′-ethylenediimidazolin-2,2′diylidene}palladium(II)
dibromide, and {1,1′-di(1-naphthalenemethyl)-3,3′-ethylenediimi-
dazolin-2,2′diylidene}palladium(II) dibromide [21], [1.980(8)–1.994
(8)] in the compounds diiodo(methylenebis(imidazo[1,5-a]-pyridine-
3-ylidene))palladium(II) and dibromo(methylenebis(imidazo[1,5-a]-
pyridine-3-ylidene))palladium(II) [22], and [1.983(5) and 1.971(5)Å]
in dibromo(1,1′-dimethyl-3,3′-methylenediimidazoline-2,2′-diyli-
dene)palladium(II) [25] follow a similar trend to those in the title
compound. In addition, the Pd–Ccarben distances are also slightly
shorter than the other Pd―Ccarben single bonds; 1-(o-methoxyben-
zyl)-3-tert-butylimidazol-2-ylidene)2PdCl2 (2.036(5)Å) [27], trans-
{3-(2-((2,6-diisopropylphenyl)-imino)propyl)-1-methylimidazol-2-
ylidene}PdCl2, (2.037(1)Å) [28], [(κ1−nPrCNCHPh)2PdCl2], (2.067(10)
Å) [29], bis(1-(benzoxazolin-2-yl)-3-mesitylimidazol-2-ylidene)
diiodo palladium(II) (2.016(5)Å) [30], and bis(1,3-bis-(2,4,6-tri-
methylbenzyl)benzimidazol-2-ylidene)palladium(II) chloride (2.035
(2)Å) [12]. The Pd―Ccarben bond lenght values (Pd1–C12, 1.985(9)
and Pd1–C1, 1.986(9)Å) differ, but are only slightly greater than those
in the similar platinum complex [1.963(10) and 1.950(10)Å] [30].
The benzimidazole ring is almost planar and the maximum
deviations from planarity are −0.030(8)Å for atom N1 and 0.034
(10)Å for atom C13. The dihedral angle of two benzimidazole
moieties is 89.7(3)°. In addition, the benzoimidazole moiety (N1,N2,
C1–C7) forms dihedral angles of 82.8(4)° and 8.6(4)° with the mean
planes through the 3,4,5-trimethoxybenzyl rings (C20:C25) and (C30:
C35), respectively.
The Pd―Br bond in the title complex is somewhat shorter than the
average of 2.484 0.023 Å calculated for 44 Pd–Br distances in 22
palladium–NHC complexes reported in the Cambridge Structural
Database [24]. The corresponding Pd―Br bond length values [2.4580
The crystal structure of the title compound is stabilized by
intermolecular C―H…Br and C―H…O; and by intramolecular
C―H…N and C―H…O van der Waals contact which link the
molecules into a three-dimensional molecular network (Fig. 2) [31].
In addition, the packing is stabilized by C―H…π interactions [31].
The arylation reaction of thiazoles has been studied by Miura and
Nomura. They have described that the palladium catalyzed direct
arylation of thiazole with aryl bromides in DMF [32,33]. We describe
here successively the reactions of substituted bromobenzene deriva-
tives with benzothiazole. Initially, the direct arylation of benzothia-
zole with bromobenzene was chosen as a model reaction and the roles
of various reaction parameters on the yield for the coupling of
bromobenzene with benzothiazole in the presence of 1.5 mol% Pd
catalyst were investigated. The influence of various organic and
Fig. 1. The molecular structure of cis-dibromo{1,1′-di[3,4,5-trimethoxybenzyl]-3,3′-
butylenedibenzimidazol-2,2′-diylidene}palladium(II). Thermal ellipsoids are shown at
the 50% probability level. Pd1–C12 1.985(9), Pd1–C1 1.986(9), Pd1–Br2 2.4601(13),
Pd1–Br1 2.4675(14), N1–C1 1.339(12), N1–C2 1.419(11), N1–C19 1.474(11), N2–C1
1.340(11), N2–C7 1.420(12), N2–C8 1.460(11), N3–C12 1.377(11), N3–C13 1.395(13),
N3–C11 1.445(12), N4–C12 1.309(11), N4–C18 1.390(12), N4–C29 1.437(11) Å, C12–
Pd1–C1 93.3(4), C12–Pd1–Br2 84.7(3), C1–Pd1–Br2 177.7(2), C12–Pd1–Br1 178.9(3),
C1–Pd1–Br1 87.3(3), Br2–Pd1–Br1 94.74(5), C1–N1–C2 110.8(7), C1–N1–C19 125.6
(7), C2–N1–C19 123.6(7), C1–N2–C7 110.9(7), C1–N2–C8 125.1(7), C7–N2–C8 123.9
(7), C12–N3–C13 108.9(8), C12–N3–C11 125.8(8), C13–N3–C11 124.9(8), C12–N4–C18
111.4(7), C12–N4–C29 126.5(7), C18–N4–C29 122.1(8), N1–C1–N2 106.8(7), N1–C1–
Pd1 128.1(6), N2–C1–Pd1 125.1(7), N2–C8–C9 113.0(8), C10–C9–C8 114.3(7), C9–
C10–C11 114.3(9), N3–C11–C10 111.0(8), N4–C12–N3 107.5(8), N4–C12–Pd1 128.3
(6), N3–C12–Pd1 124.2(7), N1–C19–C20 113.4(7), N4–C29–C30 115.5(8)o.

674
İ. Özdemir et al. / Inorganic Chemistry Communications 14 (2011) 672–675
Fig. 2. Packing diagram for 2 complex.
inorganic bases such as K3PO4, Cs2CO3, KOtBu, and K2CO3 was studied
for the standard reaction (Table 1, entries 1–4). It was observed that
the all bases afforded good yields of the desired product. However,
due to cost considerations K3PO4 was preferred. The effect of various
solvents on the reaction system was also studied (Table 1, entries 4–
7). It was observed that N-methylpyrrolidone was effective in
providing higher conversions whereas solvents like toluene, DMF,
dioxane showed lower conversions. Finally, we studied the influence
of a higher reaction temperature. At 150 °C instead of 130 °C, some
side-products were also formed. Then using the most suitable reaction
conditions (NMP, K3PO4, Pd–NHC, 130 °C) we examined the scope and
limitation of this reaction with a variety of aryl bromides. Table 1
summarizes the results obtained for these reactions. We have
demonstrated how to produce higher yields for the Pd–NHC catalyzed
direct arylation of benzothiazole (Table 1, entry 9). The presence of
electron donating substituents appears to have a minor effect on the
reaction yields. Bromobenzenes with electron donating groups, such
as p-bromoanisole and p-bromotoluene, took longer reaction times
(Table 1, entries 8 and 9) compared with bromobenzene. Without a
catalyst, the blank reaction indicated that the arylation of benzotia-
zole with bromobenzene gave products from the aryl bromide
substrate.
Table 1
Palladium catalyzed direct arylation of benzothiazole and aryl bromidesa.
Entry
1
R
Base
Solvent
NMP
Time(h)
20
Product
Yield (%)
21
H
K2CO3
2
3
4
5
6
7
8
H
Cs2CO3
KOtBu
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
NMP
20
20
20
20
20
20
24
20
25
58
10
23
35
65
H
NMP
N
S
H
NMP
H
DMF
H
Toluene
Dioxane
NMP
H
N
CH3
CH3
S
N
9
OCH3
K3PO4
K3PO4
NMP
NMP
24
20
74
53
OCH3
COCH3
S
N
10
COCH3
S
a
Reaction conditions: 1.5 mmol of R–C6H4Br, 1.0 mmol of benzothiazole, 1.5 mol%Pd catalyst, 130 °C. Purity of compounds was checked by NMR and yields are based on
benzothiazole. All reactions were monitored by GC and GC-MS.

İ. Özdemir et al. / Inorganic Chemistry Communications 14 (2011) 672–675
675
(2008). SHELXTL Version 6.10, Acta Cryst. A64, 112–122.] by direct and
conventional Fourier methods. Full-matrix least-squares refinement was [Shel-
drick, G. M. (2008). SHELXTL Version 6.10, Acta Cryst. A64, 112–122.] based on F2.
Apart from hydrogen all atoms were refined anisotropically; hydrogen atom
coordinates were calculated at idealized positions and refined using a riding
model. Further details concerning data collection and refinement are given in
reference [18]. PLATON [A.L.Spek (2010) PLATON, A Multipurpose Crystallo-
graphic Tool, Utrecht University, Utrecht, The Netherlands] was used to
determine that a void of 373 Å3 was present. SQUEEZE [described in: P.V.D.
Sluis and A.L. Spek, Acta Cryst., A46 (1990) 194] was applied and it determined
that the void contained approximately 7 electrons indicating a very small amount
of diffuse solvent. Molecular graphics is prepared with OLEX2 Software [20].
[18] Empirical formula: C38H42Br2N4O6Pd; Formula weight: 916.98; Temperature: 153
(2) K; Wavelength: 0.71073 Å; Crystal system: Monoclinic; Space group: P2(1)/c;
Unit cell dimensions: a=21.295(4) Å, b=11.711(2) Å, c=32.873(7) Å, α=90 °,
β=102.80(3) °, γ=90 °; Volume: 7994(3) Å3; Z: 8; Calculated density: 1.524 Mg/
In conclusion, we have designed and synthesized a novel air stable
palladium-N-heterocyclic carbene complex. The molecular and crystal
structure of the palladium complex was elucidated. The complex is
found to exhibit good catalytic activity in the direct arylation of
benzothiazole with arylbromides.
Acknowledgement
This work was financially supported by the Technological and
Scientific Research Council of Turkey TUBİTAK-CNRS (France) [TBAG-
U/181 (106T716)] and İnönü University Research Fund (İ.Ü. B.A.P:
2009/10 and 2009/13).
m3; Absorption coefficient: 2.512 mm-1
; F(000): 3696; Crystal size:
0.34×0.12×0.04 mm; Theta range for data collection: 2.25 to 25.05 °; Limiting
indices: -25≤h≤22, -10≤k≤13, -39≤l≤39; Reflections collected/unique:
44107/13678 [R(int)=0.0893]; Completeness to theta: 25.05 (96.7%); Absorption
correction: REQAB (multi-scan); Max. and min. transmission: 0.9062 and 0.4822;
Refinement method: Full-matrix least-squares on F2; Data/restraints/parameters:
13678/0/931, Goodness-of-fit on F2: 1.019; Final R indices [IN2σ(I)]: R1=0.0809,
wR2=0.2029; R indices (all data): R1=0.1290, wR2=0.2352; Largest diff. peak
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(NHC) complex were carried out under argon in flame-dried glassware using
standard Schlenk techniques. Chemicals were obtained from Sigma Aldrich and
Fluka. (Scheme 1). 1.0 mmol of bis(benzimidazolium) salt and Pd(OAc)2 (0.22 g,
1.0 mmol) were dissolved in 5 mL DMSO and stirred at room temperature for 2 h,
afterwards the mixture was heated for 5 h at 50 °C and later 2 h at 90 °C and 0.5 h
120 °C. The volatile compounds were removed in vacuum and the precipitate was
washed twice with 5 mL THF. The complex was recrystallized by dichloro-
methane:diethyl ether (1:3) at room temperature. Cis-dibromo{1,1’-di[3,4,5-
trimethoxybenzyl]-3,3’-butylenedibenzimidazol-2,2’-diylidene}palladium (II),
Yield: 0.62 g (68%). M.p.: 204-205 °C, υ(CN): 1462 cm-1 1H NMR (399.9 MHz,
.
CDCl3) d=7.50-7.13 (m, 4H, NC6H4N), 7.41(d, 2H, J=8.1 Hz, NC6H4N), 7.06 (d,
2H, J=8.1 Hz, NC6H4N), 6.48 (s, 4H, CH2C6H2(OCH3)3-3,4,5), 6.15 (d, 2H,
J = 15.6 Hz, CH2C6H2(OCH3)3-3,4,5), 5.16 (d, 2H, J = 15.6 Hz, CH2C6H2
(OCH3)3-3,4,5), 5.95 and 4.68 (m, 4H, -CH2CH2CH2CH2-), 3.81 (s, 6H, CH2C6H2
(OCH3)3-3,4,5), 3.61 (s, 12H, CH2C6H2(OCH3)3-3,4,5), 2.32 and 1.51 (m, 4H,
-CH2CH2CH2CH2-). 13C NMR (100.5 MHz, CDCl3) d=173.8 (Ccarbene), 153.7, 137.6,
134.1, 133.7, 130.5, 123.9, 111.9, 110.3, 104.4 and 102.2 (NC6H4N and CH2C6H2
(OCH3)3-3,4,5), 60.9 (CH2C6H2(OCH3)3-3,4,5), 56.2 (CH2C6H2(OCH3)3-3,4,5), 56.0
(CH2C6H2(OCH3)3-3,4,5), 44.1 (-CH2CH2CH2CH2-), 24.6 (-CH2CH2CH2CH2-). Anal.
Calc. for C38H42N4O6PdBr2: C, 49.77; H, 4.62; N, 6.11. Found: C, 49.65; H, 4.74; N,
6.24%.
[31] D-H..X, D-H Å, H-X Å, D-X Å, D-H-X °: C6-H6..Br2i, 0.96, 2.86, 3.799(10), 167; C8-
H8B..Br2i, 0.96, 2.91, 3.620(10), 131; C11'-H11C..O3ii, 0.96, 2.59, 3.434(13), 147; C14-
H14..Br1'iii, 0.96, 2.87, 3.561(12), 130; C25-H25..O5iv, 0.96, 2.48, 3.410(13), 163;
C36'-H36D..Br2v, 0.96, 2.90, 3.414(13), 115; C36'-H36E..Br2'vi, 0.96, 2.85, 3.623(11),
138; C37-H37B..O4vii, 0.96, 2.51 3.430(14), 161; C38-H38B..Br2iv; 0.96, 2.84, 3.540
(10), 130;C37'-H37D..O4', 0.96, 2.31, 2.888(19), 118; C10-H10B..N2, 0.96, 2.60, 2.963
(13), 103; C37-H37A..O6, 0.96, 2.57, 3.081(13), 113; C35'-H35'..N4', 0.96, 2.52, 2.865
(13), 101; C21-H21..N1, 0.96, 2.55, 2.894(13), 101; C4-H4..Cg4viii, 0.96, 2.73, 3.649
(12), 161; C19'-H19D..Cg14ix, 0.96, 2.68, 3.566(11), 153; C29-H29A..Cg5ix, 0.96, 2.48,
3.337(11), 148; C37'-H37E..Cg11x, 0.96, 2.99, 3.469(14), 112; C38'-H38D..Cg11ix,
0.96, 2.97, 3.708(14), 135. Cg4: C13- C14-C15-C16-C17-C18; Cg5: C20-C21-C22-
C23-C24-C25; Cg11: C2'-C3'-C4'-C5'-C6'-C7'; Cg14:C30'-C31'-C32'-C33'-C34'-C35'.
Symmetry codes: i, -x, -1/2+y, 1/2-z; ii, 1-x, -y, 1−z; iii, 1-x, 1/2+y, 1/2-z; iv, -x, 1-y,
1-z; v, 1+x, y, z; vi, x, 1+y, z; vii, -x, 2-y, 1-z; viii; x, -1+y, z; ix; x, y, z; x; 1-x, 1/2+y,
1/2-z.
[17] Melting point was determined in glass capillaries under air with an Electrother-
mal-9200 melting point apparatus. FT-IR spectra were recorded as KBr pellets in
the range 400–4000 cm-1 with a ATI UNICAM 1000 spectrometer. The elemental
analyses were performed at TUBITAK (Ankara, Turkey) Microlab. 1H- and 13C-
NMR spectra were recorded with a Varian AS 400 Merkur spectrometer operating
at 400 MHz (1H) (13C) in CDCl3 with tetramethylsilane as an internal reference.
Coupling constants (J values) are given in hertz. NMR multiplicities are
abbreviated as follows: s=singlet, d=doublet, t=triplet and m=multiplet
signal. Single crystal X-ray data were collected on a Rigaku AFC8S Mercury CCD
diffractometer [Molecular Structure Corporation & Rigaku (2006). CrystalClear,
MSC, The Woodlands, Texas, USA, and Rigaku Corporation, Tokyo, Japan] using
monochromated Mo–Kα radiation. The structure was solved [Sheldrick, G. M.
[32] S. Pivsa-Art, T. Satoh, Y. Kawamura, M. Miura, M. Nomura, Bull. Chem. Soc. Jpn 71
(1998) 467.
[33] A. Yokooji, T. Okazawa, T. Satoh, M. Miura, M. Nomura, Tetrahedron 59 (2003)
5685.