Synthesis, physico-chemical, structure and supramolecular properties of pinacolophanes: Versatile synthetic precursors to stilbenophanes

Article abstract of DOI:10.1080/10610278.2010.544954

Novel pinacolophanes tethered by methyl and ethyl chains were synthesised and characterised. The stereochemistry of these small-sized cyclophanes was determined by NMR spectral data as well as by single-crystal X-ray analysis. Intramolecular hydrogen bond

Full text of DOI:10.1080/10610278.2010.544954

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Supramolecular Chemistry
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Synthesis, physico-chemical, structure and
supramolecular properties of pinacolophanes: versatile
synthetic precursors to stilbenophanes
a
a
a
Hossein Reza Darabi , Mohammad Hashemi Karouei , Mohammad Jafar Tehrani , Kiomars
a
a
b
Aghapoor , Mitra Ghasemzadeh & Bernhard Neumüller
a
Nano & Organic Synthesis Lab, Chemistry & Chemical Engineering Research Centre of Iran ,
Pajoohesh Boulevard, km 17, Karaj Hwy, Tehran, 14968-13151, Iran
b
Fachbereich Chemie der Philipps-Universität Marburg , Hans-Meerwein-Strasse, 35032,
Marburg, Germany
Published online: 15 Apr 2011.
To cite this article: Hossein Reza Darabi , Mohammad Hashemi Karouei , Mohammad Jafar Tehrani , Kiomars Aghapoor ,
Mitra Ghasemzadeh & Bernhard Neumüller (2011) Synthesis, physico-chemical, structure and supramolecular properties
of pinacolophanes: versatile synthetic precursors to stilbenophanes, Supramolecular Chemistry, 23:6, 462-469, DOI:
10.1080/10610278.2010.544954
To link to this article: http://dx.doi.org/10.1080/10610278.2010.544954
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Supramolecular Chemistry
Vol. 23, No. 6, June 2011, 462–469
Synthesis, physico-chemical, structure and supramolecular properties of pinacolophanes:
versatile synthetic precursors to stilbenophanes
a
Hossein Reza Darabi *, Mohammad Hashemi Karouei , Mohammad Jafar Tehrani , Kiomars Aghapoor ,
a
a
a
a
Mitra Ghasemzadeh and Bernhard Neum u¨ ller
b
a
Nano & Organic Synthesis Lab, Chemistry & Chemical Engineering Research Centre of Iran, Pajoohesh Boulevard, km 17,
Karaj Hwy, Tehran 14968-13151, Iran; Fachbereich Chemie der Philipps-Universit a¨ t Marburg,
Hans-Meerwein-Strasse, 35032 Marburg, Germany
b
(
Received 26 July 2010; final version received 29 October 2010)
Novel pinacolophanes tethered by methyl and ethyl chains were synthesised and characterised. The stereochemistry of these
small-sized cyclophanes was determined by NMR spectral data as well as by single-crystal X-ray analysis. Intramolecular
hydrogen bondings in the crystal structure of the molecules play an important role in holding their configuration, while the
intermolecular hydrogen bondings lead to a designed arrangement of the molecules. The stereoselective transformation of
pinacolophanes to stilbenophanes in improved yield is also reported.
Keywords: pinacolophanes; pinacol coupling; X-ray structure; molecular tectonics; stilbenophanes
1
.
Introduction
because the synthesis of them using the McMurry reaction
suffered from the difficulty in purification. Therefore,
improvement of the synthesis of 3 was desired.
The design and synthesis of cyclophanes possessing
rigidly defined cavities and shape-persistent structures
attract current interest in view of supramolecular
chemistry (1). Stilbenophanes, cyclophanes containing
stilbene moieties, with well-defined cavities are intriguing
molecules from both physico-chemical and supramolecu-
lar points of view (2–11).
Pinacolophanes 2, cyclophanes containing pinacol
moieties, are possible intermediates in the alkene-forming
process for the synthesis of the corresponding stilbeno-
phanes 3 (Scheme 1). Exploration of the new strategy for
stilbenophanes 3 synthesis, therefore, begins with
investigations on the synthesis of 2 as key precursors.
On the other hand, the physico-chemical, supramolecular
properties of 2 together with their potentially application
in asymmetric syntheses (11, 19) attracted our interest.
Here, we report on the synthesis of cis- and trans-
pinacolophanes 2. To the best of our knowledge, only the
trans-isomers 2 have been synthesised and characterised
In this context, we have synthesised a series of ortho-
stilbenophanes 3, possessing stilbene unit and alkyl chains,
to study their structure, conformation and supramolecular
properties (12–16). Their conformation is depended on the
alkyl chain length and Z/E stereochemistry of the olefins.
We have also studied the supramolecular properties of
3
example, a saddle-shaped stilbenophane forms inclusion
and their related compounds (12, 14, 16). As the best
(
20). In order to establish with great certainty the
þ
stereochemistry of each isomer, the X-ray crystal structure
of the cyclic diols 2 was determined. The generation of
H-bonded molecular networks in their solid state
introduces 2 as new molecular tectons. Finally, we report
an effective synthesis of 3 from 2 in improved yields.
complex with Ag ion, which can be confirmed by both
NMR and theoretical analyses (12).
On the other hand, stilbenophanes 3 could serve as key
precursors in synthetic approaches to the corresponding
tolanophanes by bromination/dehydrobromination method
(
13, 18).
To understand the novel supramolecular properties of
more deeply, development of its practical synthesis has
2.
Results and discussion
3
2.1 Synthesis and characterisation of pinacolophanes 2
become an important problem of the study.
Stilbenophanes 3 have been prepared from the
McMurry coupling of the corresponding dialdehydes 1,
which are usually the mixtures of geometric isomers (12–
The starting material for the pinacol coupling, the
bis(carbaldehydes) 1a–b, was obtained from the reaction
of 2-hydroxybenzaldehyde with the diiodomethane and 1,2-
dibromoethane, respectively, under reflux conditions (21).
1
7). However, the availability of 3 has been unsatisfactory,
*Corresponding author. Email: darabi@ccerci.ac.ir
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2011 Taylor & Francis
DOI: 10.1080/10610278.2010.544954
http://www.informaworld.com

Supramolecular Chemistry
463
HO
Reflux
OH
O
O
O
n
O
n
CHO OHC
trans-2
trans-3
TiCl -Zn
4
RT
HO
OH
O
n O
Reflux
1
, (n = 1, 2)
O
O
O
O
n
n
cis-2
cis-3
Scheme 1. The chemoselectivity of the titanium-induced macrocyclisation of the bis-carbaldehyde 1 at different reaction temperatures.
As shown in Scheme 2, the intramolecular pinacol
coupling of 1 with low-valent titanium (LVT), prepared
protons are not equivalent. The stereochemical assignment
deduced from NMR is in agreement with the X-ray
structure analysis of molecules 2 (22, 23).
from TiCl and Zn in tetrahydrofuran (THF) (14, 22), at
4
room temperature gave a mixture of trans- and cis-isomers
of 2.
2.2 The molecular structure of pinacolophanes 2
The cis- and trans-isomers of 2 could be rapidly
isolated in useful yields by column chromatography.
The trans-2a and cis-2a can be separated from the product
mixtures by column chromatography in 25 and 40%
yields, respectively, as fine colourless needles. In a similar
manner, trans-2b and cis-2b were also prepared from the
corresponding dicarbaldehyde 1b in 25 and 50% yields,
respectively (Scheme 2).
The structures of compounds trans-2a, cis-2a and cis-2b
were confirmed by X-ray diffraction studies. The ORTEP
drawing and crystal data are shown in Figure 1 and Table 1,
1
respectively. According to the Mo-Ka radiation, the
Flack parameter for trans-2a and cis-2b could not be
calculated accurately, in case of cis-2b with a large
standard deviation, 20.2(6). The cis configuration of the
molecules can be described as ‘open scallop’.
1
13
The H and C NMR spectra of the cis- and
trans-isomers of 2 are in accord with the symmetry of these
molecules. The aromatic protons appear as two doublets and
two triplets, while non-aromatic protons of trans-2 and cis-2
appear in different patterns. In 2a, the benzylic protons of
trans-isomer (unlike in cis-isomer) appear as two doublets,
because of their different positions relative to the etheric
oxygen (5.7 and 5.4 ppm), but the methylene protons of both
isomers are observed as a singlet around 5.5 ppm.
As shown in Table 1, trans-2a crystallises in the
orthorhombic space group P2 2 2 , cis-2a in the monoclinic
1 1 1
space group P2 /c and cis-2b in the orthorhombic space
1
group Pna21.
2.2.1 The molecular structure of trans-2a
Although the Mo-Ka radiation of the absolute structure
could not be refined, the planar trans-2a possesses a meso-
configuration.
In contrast to 2a, the benzylic protons of both isomers
b appeared as one sharp singlet, while the methylene
2
HO
OH
CHO OHC
HO
TiCl -Zn
4
RT
OH
O
O
O
O
O
n
O
n
n
1
1
a; n = 1
b; n = 2
trans-2a; n = 1
trans-2b; n = 2
cis-2a; n = 1
cis-2b; n = 2
Scheme 2. Synthesis of pinacolophanes 2.

4
64
H.R. Darabi et al.
Figure 1. ORTEP drawing of trans-2a (left), cis-2a (middle, major specimen) and one of the crystallographic molecules in cis-2b
right).
(
As shown in Figure 1, two intramolecular H bridges fix
an exo-conformation (O1· · ·O4: 3.03(8), O2· · ·O1: 3.22(8)
˚
A) and lead to an angle of 158 between the two phenylene
rings. While one benzylic proton is towards the centre of a
molecule with a short intramolecular CZH· · ·O bond
˚
facing oxygen atom (2.43 A), the other one is directed out
having a short hydrogen bond with the neighbouring
arrangement with dihedral angles in the range of
1048–1228. There are four crystallographic independent
asymmetric molecules (shown in blue, green, red and
violet) in tetrameric unit and all of them are meso, which
are connected via hydrogen bonds to each other (Figure 3).
This tetramer forms further hydrogen bonds to neighbours.
A very short intramolecular O2ZH2· · ·O1 interaction
between hydrogen of a hydroxyl group with the oxygen
atom of the neighbouring hydroxyl group (O2· · ·O1
˚
hydroxyl group (2.28 A).
The crystal packing of trans-2a includes four
molecules in which pinacol units overlap each other not
only in a face-to-face interaction, but also in an edge-to-
face interaction. The intermolecular H bonding forms
˚
2.62(3) A) is observed.
The crystal packing of cis-2b includes 16 molecules
per unit cell, in which four asymmetric molecules are
connected via strong hydrogen bonding. As shown in
Figure 3(A) and (B), two molecules (shown in blue and
violet) are in a back-to-back arrangement having one
highly short intermolecular H-bond interaction
˚
columns along [100] (O1· · ·O2a: 2.95(7) A (Figure 2).
2
.2.2 The molecular structure of cis-2a
˚
The molecule of cis-2a possesses approximate Cs-
symmetry (Figure 1). The phenyl rings are in a face-to-
face configuration with a dihedral angle of about 938.
There is a disorder in the molecule. The sequences
C71/O31/H1/O41/H3/C81 and O31/C15/C41 as shown in
Figure 1 belong to the major specimen (occupation
parameter 0.65). The bridge C6-C71-C81-C9 as well as
the bridge of the minor specimen C6-C72-C82-C9 exhibits
a twist-conformation concerning the corresponding OH-
(O1ZH1· · ·O2 ¼ 2.00 A).
In contrast, two other asymmetric molecules (shown in
red and green) are in a nearly face-to-face interaction
without any intermolecular H-bond interaction. However,
both red and green molecules have a short H-bond
˚
interaction with the violet (H· · ·O ¼ 2.21 and 2.03 A,
respectively) and also with the blue (H· · ·O ¼ 1.92 and
˚
2.36 A, respectively). Therefore, the molecules in crystal
are arranged in a designed shape, which is resulted from
the various intra- and intermolecular hydrogen bondings of
the molecules (Figure 3(C) and (D)).
groups.
(
A short intramolecular OZH· · ·O bond
˚
O2· · ·O1 ¼ 2.81(2) A) and two short intermolecular
˚
hydrogen bonds O1ZH1· · ·O2a (O1· · ·O2a ¼ 2.78(2) A)
˚
and O2ZH3· · ·O41a (O2· · ·O41a ¼ 2.84(9) A) were
found. The first one stabilises the twist-configuration and
the latter ones are responsible for the connection of the
molecules in the unit cell.
2
.3 The stereoselective transformation of 2–3
Pinacolophanes 2 may serve as key intermediates in
synthetic approaches to the corresponding stilbenophanes
In the crystal structure of cis-2a, the molecules are
stacked in columns along [010] connected by various
CZH· · ·O and OZH· · ·O hydrogen bonds (Figure 2).
3
. Although a variety of 3 have been prepared using the
McMurry coupling reactions as a key step (12–18), the
route was flawed by the difficulty in purification and the
need for sophisticated procedures.
Exploration of the new strategy for stilbenophanes
synthesis begins with investigations using pinacolo-
phanes 2 as starting materials. Treatment of cis- and
trans-isomer 2 with LVT, generated by the reaction of
2
.2.3 The molecular structure of cis-2b
The molecules of 2b have an approximate C -symmetry
s
(
Figure 1). The phenyl rings have a face-to-face

Supramolecular Chemistry
465
s
u
a
b
g
m

4
66
H.R. Darabi et al.
Figure 2. View of the packing of trans-2a (left) and cis-2a (right) along a- and b-axes, respectively, via hydrogen-bonded network.
titanium(IV) chloride with zinc in THF, led to the
high yield formation of pure cis- and trans-isomer 3,
respectively (Scheme 3).
solvent (THF) (12, 15). Notably, the yields of cis- and
trans-isomer 3a were significantly improved as compared
with those in the previous procedures (12–16). The
products 3 were readily obtained in almost pure forms
simply by a flash chromatographic filtration through
silica gel.
As shown in Table 2, the overall yield of each isomer
in this two-step sequence is higher than those previously
reported for the direct McMurry coupling of 1 in the same
Figure 3. Crystal structure of 2b: hydrogen-bonded network in tetrameric unit with four asymmetric molecules (A and B); Arrangement
of molecules in the crystallographic direction along a-axis (C) and c-axis (D). Hydrogen atoms have been omitted for clarity.

Supramolecular Chemistry
467
Table 2. A comparison between the present work and the
previous procedure for the preparation of 3.
converted into the stilbenophanes 3 with high stereo-
selectivity and improved yield with an easier work-up.
Product (%)
Synthetic method
trans-3a
cis-3a
trans-3b
cis-3b
4. Experimental section
McMurry of 1
Present work
1 (15)
20
2 (15)
30
25 (12)
23
20 (12)
48
4.1 General
All reactions were carried out under nitrogen (Schlenk
conditions). Unless otherwise noted, all chemicals were
obtained from commercial sources and used as received
without further purification. Solvents were purified and
dried by using common methods. Column chromatog-
raphy was carried out using Merck silica gel 60, 70-230
mesh ASTM. NMR spectra were recorded on a Bruker
The success of this new procedure will expand the
range and availability of 3 that can be prepared for the
studies aimed at elucidating their properties.
DRX-500 spectrometer in CDCl using TMS as an internal
3
standard.
3
.
Conclusion
The smallest members of pinacolophanes 2a–b were
synthesised by intramolecular reductive coupling in the
presence of LVT at room temperature. The cis- and
trans-configuration of products was confirmed by both
4.1.1 General procedure for the preparation of pinaco-
lophanes 2. Anhydrous THF (100 ml) was added to Zn
dust (2.2 g, 34 mmol) under an argon atmosphere. TiCl4
(3 ml, 27 mmol) was added to the mixture at 08C, and the
black suspension thus obtained was warmed to room
temperature and then refluxed for 2 h. A solution of
dialdehyde 1 (10 mmol) in THF (50 ml) was added
dropwise to the above black reaction mixture at room
temperature, and the resulting mixture was stirred for an
additional 12 h. The reaction mixture was quenched with
10% aqueous K CO (30 ml). The organic layer was
1
H NMR and X-ray structure analyses. The self-assembly
between hydroxyl groups via hydrogen bonding gen-
erates H-bonded networks that were structurally charac-
terised by X-ray diffraction studies on single crystals.
The different interactions between the 1,2-dihydroxy
type in pinacols 2 as tectons with different locations of
H-bond sites in cis- and trans-configuration lead to
different arrangements, in the crystal, which is due to the
tetragonal angles of 1,2-dihydroxy groups in the
molecules. Furthermore, the pinacolophanes 2 are easily
2
3
separated, and the aqueous suspension was extracted with
diethyl ether. The combined organic layers were dried over
anhydrous MgSO , filtered and evaporated to afford a
4
HO
TiCl -Zn, reflux
OH
4
O
O
O
n
O
n
trans-2a; n = 1
trans-2b; n = 2
trans-3a; n = 1; (80%)
trans-3b; n = 2; (90%)
HO
OH
TiCl -Zn, reflux
4
O
O
O
O
n
n
cis-2a; n = 1
cis-2b; n = 2
cis-3a; n = 1; (75%)
cis-3b; n = 2; (95%)
Scheme 3. The synthesis of pure isomers 3 from the corresponding isomers 2.

4
68
H.R. Darabi et al.
syrupy liquid, which was purified by chromatography on
silica gel using a 1:1 mixture of ethyl acetate and hexane to
afford pure cis- and trans-isomers 2.
3 mmol) was added to the mixture at 08C, and the black
suspension thus obtained was warmed to room tempera-
ture and then refluxed for 2 h. A solution of cis- or trans-
isomers 2 (0.36 mmol) in THF (10 ml) was added dropwise
to the above black reaction mixture at room temperature.
The reaction mixture was stirred at reflux temperature.
After disappearance of the substrate (TLC), the reaction
mixture was treated with aqeous. K CO (10%) and stirred
1
4
NMR (300 MHz, CDCl , 258C): d 2.99 (br s, 2H), 5.36 (d,
.1.1.1 Pinacolophane trans-2a. Colourless solid,
H
3
1
H, J ¼ 12 Hz), 5.55 (br s, 2H), 5.74 (d, 1H, J ¼ 12 Hz),
2
3
1
3
6
NMR (75 MHz, CDCl , 258C): d 73.2, 122.6, 124.5, 127.6,
.91 (d, 2H), 7.09 (t, 2H), 7.19 (t, 2H), 7.48 (d, 2H);
C
open to the atmosphere, until oxidation of the titanium was
completed (off-white suspension). The organic layer was
separated, and the aqueous suspension was extracted with
diethyl ether. The combined organic layers were dried over
3
1
2
3
28.4, 132.2, 133.5, 158.1; MS(EI), m/z (rel. intensity, %)
þ
21
58 (M , 5), 136 (100); n (KBr, cm ): 3535 (OH, sh),
477 (OH, br), 3055, 2956, 1600, 1580; anal. calcd for
anhydrous MgSO , filtered and evaporated. A flash
4
C H O : C, 69.76; H, 5.46. Found: C, 69.97; H, 5.22.
15 14 4
column chromatography on silica gel (ethyl acetate:hex-
ane; 1:8) afforded pure cis- or trans-isomers 3.
We have already reported the spectral data of
stilbenophanes 3 (12, 15).
1
4
NMR (300 MHz, CDCl , 258C): d 3.26 (s, 2H), 5.45 (s,
.1.1.2 Pinacolophane cis-2a. Colourless solid,
H
3
2
7
1
H), 5.54 (s, 2H), 6.83 (d, 2H), 6.98 (t, 2H), 7.16 (t, 2H),
1
.28 (d, 2H); C NMR (75 MHz, CDCl , 258C): d 70.1,
3
1
4.1.2.1 Stilbenophane trans-3a. Colourless solid,
NMR (300 MHz, CDCl , 258C): d 5.12 (d, 1H), 5.43 (d,
H
3
01.4, 121.6, 125.6, 129.5, 130.1, 134.9, 156.0; MS(EI),
þ
3
m/z (rel. intensity, %) 258 (M , 5), 136 (100); n (KBr,
2
cm ): 3473 (OH, sh), 3354, 3300 (OH, br), 3018, 2935,
1H), 5.49 (s, 2H), 6.88 (d, 2H), 6.95 (t, 2H), 7.19 (t, 2H),
13
7.25 (d, 2H), C NMR (75 MHz, CDCl ) d 153.96,
1
3
2
H, 5.46. Found: C, 69.89; H, 5.62.
885, 1604, 1584; anal. calcd for C H O : C, 69.76;
5 14 4
128.40, 125.14, 121.56, 121.27, 117.09, 90.30, 76.23;
MS(EI), m/z (rel. intensity, %) 224 (20), 223 (90), 210
1
(80), 181 (60), 152 (50).
1
4
NMR (300 MHz, CDCl , 258C): d 3.15 (s, 2H), 4.18
.1.1.3 Pinacolophane cis-2b. Colourless solid,
H
1
.1.2.2 Stilbenophane cis-3a. Colourless solid, H NMR
4
3
(
300 MHz, CDCl , 258C): d 5.02 (s, 1H), 5.05 (s, 1H) 6.90
3
(
ddd, 2H, J ¼ 12 Hz), 4.42 (ddd, 2H, J ¼ 12 Hz), 5.81 (s,
13
(
d, 2H), 6.93 (t, 2H), 7.14 (t, 2H), 7.37 (d, 2H), C NMR
2
H), 6.76 (d, 2H), 6.89 (t, 2H), 7.05 (t, 2H), 7.42 (d, 2H);
C NMR (75 MHz, CDCl , 258C): d 70.2, 70.7, 118.0,
1
3
(75 MHz, CDCl ) d 145.91, 130.30, 127.17, 126.02,
3
3
124.48, 123.49, 123.46, 121.02, 120.79, 117.50, 117.44,
115.14, 111.03, 103.30, 73.98; MS(EI) m/z (rel. intensity,
%) 224 (10), 210 (90), 152 (5), 135 (15).
1
intensity, %) 272 (M , 20), 254 (15), 149 (50), 120 (100),
23.4, 128.3, 128.6, 133.0, 155.5; MS(EI), m/z (rel.
þ
2
6 (95); n (KBr, cm ): 3421 (OH, sh), 3320 (OH, br),
1
7
3
C, 70.57; H, 5.92. Found: C, 70.25; H, 6.11.
068, 3034, 2982, 2875, 1581; anal. calcd for C H O :
4
1
6
16
1
4.1.2.3 Stilbenophane trans-3b. Colourless solid,
NMR (300MHz, CDCl , 258C): d 4.22 (s, 4H), 6.81 (s,
2
H
3
13
H), 6.95 (m, 4H), 7.02 (dd, 2H), 7.13 (td, 2H). C NMR
1
4
NMR (300 MHz, CDCl , 258C): d 2.96 (s, 4H), 4.22 (dd,
.1.1.4 Pinacolophane trans-2b. Colourless solid,
H
(
500MHz, CDCl ) d 71.6, 120.2, 123.1, 128.2, 129.9, 130.0,
3
31.4, 156.1; MS(EI), m/z (rel. intensity, %) 266 (M , 45).
3
þ
1
4
H, J ¼ 18 Hz), 4.42 (dd, 4H, J ¼ 18 Hz), 5.39 (s, 4H),
1
3
6
NMR (75 MHz, CDCl , 258C): d 71.0, 76.1, 118.8, 123.7,
.82 (d, 4H), 6.91 (t, 4H), 7.10 (t, 4H), 7.23 (d, 4H);
C
1
4.1.2.4 Stilbenophane cis-3b. Colourless solid, H NMR
3
1
2
29.2, 129.3, 133.5, 156.5; MS(EI), m/z (rel. intensity, %)
þ
(
300 MHz, CDCl , 258C): d 4.16 (s, 4H), 7.05 (s, 2H), 7.13
3
72 (M , 45), 254 (15), 149 (55), 121 (100), 105 (15); n
13
m, 4H), 7.20 (td, 2H), 7.33 (dd, 2H). C NMR (75 MHz,
(
CDCl ) d 73.2, 122.6, 124.5, 127.6, 128.4, 132.2, 133.5,
158.1; MS(EI), m/z (rel. intensity, %) 266 (M , 45), 181
(34), 165 (56), 55 (100).
2
1
KBr, cm ): 3530 (OH, sh), 3400 (OH, br), 3062, 2940,
(
3
2881, 1600, 1583; anal. calcd for C H O : C, 70.57;
H, 5.92. Found: C, 70.85; H, 6.22.
þ
1
6
16
4
Supporting Information
4.1.2 General procedure for the stereoselective trans-
formation of the pinacolophanes 2 to stilbenophanes 3.
X-ray structure analyses trans-2a, cis-2a and cis-2b and
NMR, mass and IR spectra of all of pinacolophanes 2 and
stilbenophanes 3 are available online.
Anhydrous THF (30 ml) was added to Zn dust (0.4 g,
6
mmol) under an argon atmosphere. TiCl4 (0.35 ml,

Supramolecular Chemistry
469
Note
(11) Rojanathanes, R.; Tuntulani, T.; Bhanthumnavin, W.;
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1.
Further details can be obtained free of charge on application
to the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: þ44 (0)1223
(
(
(
(
12) Darabi, H.R.; Azimzadeh Arani, M.; Motamedi, A.;
Firouzi, R.; Herges, R.; Mohebbi, A.R.; Nasseri, S.;
N a¨ ther, C. Supramol. Chem. 2009, 21, 632–637.
13) Darabi, H.R.; Jadidi, K.; Mohebbi, A.R.; Faraji, L.;
Aghapoor, K.; Shahbazian, S.; Azimzadeh Arani, M.;
Nasseri, S.M. Supramol. Chem. 2008, 20, 327–333.
14) Darabi, H.R.; Mirza-Aghayan, M.; Ali-Saraie, L.;
Bolourtchian, M.; Neum u¨ ller, B.; Ghassemzadeh, M.
Supramol. Chem. 2003, 15, 55–58.
3
36033; Email: deposit@ccdc.cam.ac.uk) quoting the
depository nos. CCDC 776726 (trans-2a), 776727 (cis-2a)
and 776728 (cis-2b).
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2