Synthesis, crystal structure and complexation with dibenzylammonium ion of a novel class of crownophanes containing bridged fragments of fluorenone and stilbene

Article abstract of DOI:10.1016/j.tetlet.2004.02.061

Two representatives of a novel class of crownophanes containing fragments of fluorenone and stilbene bridged by units of diethylene glycol and triethylene glycol, respectively, have been synthesized. The crystal structure and complexation behavior of thes

Full text of DOI:10.1016/j.tetlet.2004.02.061

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 2927–2930
Synthesis, crystal structure and complexation with
dibenzylammonium ion of a novel class of crownophanes containing
bridged fragments of fluorenone and stilbene
Nikolay G. Lukyanenko,a,* Tatiana I. Kirichenko,a Alexander Yu. Lyapunov,a
Catherine Yu. Kulygina,a Yurii A. Simonov,b Marina S. Fonarib
and Mark M. Botoshanskyc
aDepartment of Fine Organic Synthesis, A.V. Bogatsky Physico-Chemical Institute, National Academy of Sciences of Ukraine,
Lustdorfskaya doroga 86, 65080 Odessa, Ukraine
bInstitute of Applied Physics, Academy of Sciences of Moldova, Academy Str., 5 MD 2028, Chisinau, Moldova
cDepartment of Chemistry, Technion-Israel Institute of Technology, Technion City, 32000 Haifa, Israel
Received 3 December 2003; revised 5 February 2004; accepted 13 February 2004
Abstract—Two representatives of a novel class of crownophanes containing fragments of fluorenone and stilbene bridged by units of
diethylene glycol and triethylene glycol, respectively, have been synthesized. The crystal structure and complexation behavior of
these crownophanes were studied. They form much stronger complexes with dibenzylammonium hexafluorophosphate (log Ka value
in CH3CN is equal to 3.92 0.06 and 4.40 0.05, respectively) than benzocrown ethers. This makes them an attractive alternative
for benzocrown ethers as components in supramolecular synthesis.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Crownophane-type macrocycles incorporating rigid
aromatic moieties bridged by flexible polyether chains
have attracted considerable attention due to their
excellent ability to bind inorganic and organic cations
and neutral substrates strongly and selectively. Such
synthetic receptors provide a controlled means for
studying the fundamentals of non-covalent intermolec-
ular forces in nature and open new routes for the
development of sensors, catalysts, switches and other
molecular devices. They can also be used as platforms
for the design of supramolecular systems (e.g., rotaxanes
and catenanes).1–7
With the purpose of obtaining potentially photo-
switchable crownophanes with high binding affinity for
electron-deficient guests, we were intrigued by bisphe-
nols 18 and 49 (Scheme 1) as the aromatic blocks for the
construction of a new family of large cyclophanes. Bis-
phenol 1 was selected based on the following: (i) it is a
highly polarized p electron-rich extended aromatic sys-
tem where the carbonyl oxygen can act as a sensor that
recognizes an electron-deficient guest, directs it towards
the macrocyclic host cavity and stabilizes the complexes
because of electrostatic interactions, (ii) being a power-
ful H-acceptor, the carbonyl oxygen is capable of strong
hydrogen bonding of the substrate often dominating the
processes of molecular recognition and self-assembly
that are essential in the formation of supramolecular
systems, (iii) fluorenone and its derivatives have good
luminescence properties that are important for the
development of sensitive fluorescence-based chemosen-
sors, and finally yet importantly, (iv) the carbonyl group
of the fluorenone fragment can be converted into a
variety of functional groups that would allow for fine-
tuning of the binding behavior of the crownophanes.
Photoresponsive crownophanes that change properties
under the external action of light are of particular
interest because of their potential application in photo-
switchable devices for detection of organic and inor-
ganic species and as building blocks of supramolecular
systems similar to the photocontrollable rotaxanes.6
Keywords: Crownophane; Fluorenone; Stilbene; Complexation;
Dibenzylammonium hexafluorophosphate.
On the other hand, derivatives of bisphenol 4 such as
other stilbenoid compounds can undergo a variety of
* Corresponding author. Tel.: +380-482-655042; fax: +380-482-6520-
12; e-mail: ngl@farlep.net
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.02.061

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N. G. Lukyanenko et al. / Tetrahedron Letters 45 (2004) 2927–2930
photochemical transformations, such as trans-to-cis
isomerization, cis-stilbene ring closure to form phen-
anthrene and [2+2] cycloaddition of trans-stilbene to
give cyclobutanes.10 If a stilbene fragment is incorpo-
rated into a crownophane, the photoreversible isomeri-
zation process of trans-to-cis and vice versa should be
accompanied by large structural modifications of the
macrocycle that alter its binding properties and can be
used as a function key to photoswitching.
bonate at 80–85 ꢁC for 30 h gave the diols 2a12 and 2b11
in 78% and 77% yields, respectively. Conversion of these
diols into ditosylates 3a12 and 3b11 was achieved in 88%
and 84% yields using p-toluenesulfonyl chloride in a
mixture of chloroform and dioxane in the presence of
triethylamine at 0–20 ꢁC. Further reaction of 3a and 3b
with bisphenol 4 in DMF in the presence of anhydrous
potassium carbonate as the base at 80–85 ꢁC for 50 h
gave after work-up and chromatographic purification
over silica gel, the crownophanes 5a and 5b in 21% and
31% yields, respectively.13
Recently, we described the preparation and the prop-
erties of crownophanes with two bridged fluorenone
fragments.11 Here, we report for the first time the syn-
thesis, complexation behavior and crystal structure of
crownophanes containing bridged moieties of fluore-
none and stilbene.
The single-crystal structures of 5a and 5b were deter-
mined by X-ray crystallography,14 and their computer-
generated drawings are shown in Figure 1.
In both crownophanes 5a and 5b, the stilbene fragment
adopts the thermodynamically stable E-configuration.
Crownophane 5a possesses an elongated cavity of
effective dimensions ca. 4 · 14 A. The macrocycle is self-
filling, with planar moieties of fluorenone and stilbene
The synthetic pathway leading to cyclophanes 5a and 5b
is shown in Scheme 1. Reaction of bisphenol 1 with
chlorohydrins of diethylene glycol or triethylene glycol
in DMF in the presence of anhydrous potassium car-
ꢀ
Scheme 1. Synthesis of crownophanes 5a and 5b.
Figure 1. Solid-state structure of crownophanes 5a and 5b.

N. G. Lukyanenko et al. / Tetrahedron Letters 45 (2004) 2927–2930
2929
aligned parallel to each other with proximal partial
overlapping with the interplanar distances being in the
of the obtained experimental values (4 · 30 points) were
used for joint computer processing. The data were
treated using the nonlinear least squares fitting program
SIRKO.21 The experimental data fit best with a 1:1
complexation model. The logarithm of equilibrium
constants was found to be 3.92 0.06 and 4.40 0.05 for
the complexes of 5a and 5b, respectively. The stability of
these complexes is much higher with respect to the
complexes of salt 6 with benzocrown ethers, which are
used extensively for designing remarkable supramolec-
ular systems.20 For comparison, the logarithms of
association constants of 6 with dibenzo[24]crown-819
and tribenzo[27]crown-922 in CD3CN are 2.62 and 2.43,
respectively.
ꢀ
range 3.255–3.678 A and with an interplanar angle equal
to 3.8ꢁ. This geometry is consistent with the conven-
tional parallel p–p stacking.15 In crownophane 5b, the
stilbene moiety is not planar; the angle of twist between
the benzene rings is 13.1ꢁ. The planar fluorenone frag-
ment and the stilbene unit are arranged in a T-shaped
mode with an interplanar angle of 77.4ꢁ to afford
opportunity for attractive C–Hꢀ ꢀ ꢀp interactions. The
closest distances of two carbon atoms of the stilbene
ꢀ
moiety from a fluorenone plane, 3.512 and 3.670 A, are
in good agreement with those cited for such interac-
tions.15;16 These interactions can determine the confor-
mation of flexible organic molecules in the solid state
but are disfavored in solution by entropic factors due to
the restricted internal mobility.
Using a large set of studied pseudorotaxanes and
rotaxanes it was shown that the fundamental driving
force responsible for the threading interaction is the
formation of the strong hydrogen bonds between the
NH2þ acidic protons and the oxygen atoms of the crown
ether.20 The highly polarized carbonyl group of the
fluorenone fragment in crownophanes 5a and 5b is a
more powerful H-acceptor than the ether oxygen atoms
of crown ethers. This is probably the origin of the high
affinity of these crownophanes to ammonium salt 6.
Additionally, complexes of crownophanes can be sta-
bilized by ion–dipole interactions between the positively
charged nitrogen atom of the guest and the carbonyl
oxygen atom of the host and by p–p intermolecular
interactions between the aromatic parts of the guest and
host.
Generally, the self-filling of the crownophane cavity in
the solid state is not a serious hindrance for complexa-
tion since the cavity dimensions in solution can vary
over rather wide limits in accord with the steric
requirements of the substrate, owing to mobility of the
flexible oligo(ethyleneoxy) bridges.17;18 However, the
energy gain of complexation should be sufficient to
compensate for the energy loss during the initial process
of enlargement of the self-filling cavity.
In order to obtain information regarding the binding
ability of the newly synthesized crownophanes 5a and
5b, we investigated their complexation with dibenzyl-
ammonium hexafluorophosphate 6.
In this letter, we have demonstrated the first synthesis
and crystal structure of new types of crownophanes 5a
and 5b that form very stable complexes with dibenzyl-
ammonium ions and most likely with the other sec-
ondary ammonium salts. This feature makes them an
attractive alternative for benzocrown ethers as compo-
nents in supramolecular synthesis. Furthermore, these
compounds are potentially photoresponsive macrocyclic
hosts. In fact, estimations derived from AM1 calcula-
tions23 indicate that pseudorotaxane-like inclusion
complexes of salt 6 with crownophanes 5a and 5b that
possess cis-stilbene fragments are significantly more
stable than complexes with crownophanes having trans-
stilbene fragments, by 10.0 and 13.2 kcal/mol, respec-
tively.
This salt was selected as a test guest compound because
of its ability to form the pseudorotaxane-like complexes
with a variety of the large crown ethers containing
aromatic fragments.19;20 The structure of such crown
ethers is similar to the framework of crownophanes,
since each of them contains rigid aromatic moieties
bridged by flexible polyether chains. Due to this, their
complexing ability should probably be similar, also.
This fact makes crownophanes 5a and 5b likely candi-
dates for the formation of pseudorotaxanes with sec-
ondary ammonium salts.
Investigations of the binding properties of crowno-
phanes containing bridged fluorenone and stilbene
moieties and their dependence on stilbene fragment
configuration are in development with respect to
photoreversible self-assembly and supramolecular syn-
thesis.
The stability constants of the complexes formed between
ammonium salt 6 and crownophanes 5a and 5b have
been determined by spectrophotometric titration in
acetonitrile at 25 ꢁC. The UV absorption bands of the
crownophanes decrease in intensity with increased salt
concentration. The complexation of guest 6 with hosts
5a and 5b was monitored by measuring the absorbance
of solutions where the molar ratio of guest increases
with respect to the host over the range 0.1:1 to 50:1
during the titration. The absorbance measurements were
carried out at four wavelengths simultaneously and sets
Acknowledgements
The diffraction data were collected at the Department of
Chemistry, Technion, Haifa, through the cooperation of
Prof. M. Kaftory whom we thank.

2930
N. G. Lukyanenko et al. / Tetrahedron Letters 45 (2004) 2927–2930
70 eV, m=z (%) 564 (100, Mþ), 282 (8), 212 (20). UV–vis,
References and notes
CH3CN, kmax (log e) 271 (4.97), 310 (4.47), 334 (4.36), 468
(2.46). Anal. calcd for C35H32O7: C, 74.45; H, 5.71. Found:
C, 74.28; H, 5.94. Crownophane 5b: 31%; mp 170–171 ꢁC.
1H NMR (300 MHz; CDCl3; d, ppm; J, Hz) 3.70–3.83 (m,
12H), 3.84–3.95 (m, 8H), 4.15 (t, 4H, J ¼ 4:52), 6.62 (s,
2H), 6.76 (d, 1H, J ¼ 2:18), 6.80 (d, 5H, J ¼ 8:72), 6.93 (d,
2H, J ¼ 2:49), 6.99 (d, 2H, J ¼ 8:41), 7.15 (d, 4H,
J ¼ 8:71). 13C NMR (75.5 MHz; CDCl3; d, ppm; J, Hz)
67.5, 67.8, 69.5, 69.9, 70.9, 71.1, 110.4, 114.9, 120.4, 120.5,
125.8, 127.2, 130.4, 135.8, 137.3, 158.1, 159.0, 193.3; EI-
MS, 70 eV, m=z (%) 652 (100, Mþ), 326 (5), 212 (11). UV–
vis, CH3CN, kmax (log e) 271 (4.94), 308 (4.48), 334 (4.37),
468 (2.62). Anal. calcd for C39H40O9: C, 71.76; H, 6.18.
Found: C, 71.55; H, 6.01.
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14. X-ray quality single crystals were obtained by slow
evaporation of C6H6 and MeCN solutions of 5a and 5b,
respectively. Measurements were made on a Nonius CCD
diffractometer with graphite monochromatized Mo-Ka
7. Blanco, M.-J.; Jimenez, M. C.; Chambron, J.-C.; Heitz,
V.; Linke, M.; Sauvage, J.-P. Chem. Soc. Rev. 1999, 28,
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ꢀ
radiation (k ¼ 0:71073 A). The structures were solved by
direct methods and refinement, based on F 2, was made by
full-matrix least-squares techniques. All non-hydrogen
atoms were refined isotropically and hydrogen atoms were
placed in geometrically calculated positions and refined
with temperature factors 1.2 times those of their bonded
atoms. Crystal data for 5a: C35H32O7, 564.63, triclinic, P1,
ꢀ
a ¼ 9:390ð2Þ,
b ¼ 11:625ð2Þ,
c ¼ 14:118ð3Þ A,
a ¼
3
ꢀ
79:49ð2Þꢁ, b ¼ 83:21ð2Þꢁ, c ¼ 68:51ð2Þꢁ, V ¼ 1407:7ð5Þ A ,
Z ¼ 2, qcalcd ¼ 1:332 g cmꢁ3, l ¼ 0:092 mmꢁ1, F ð000Þ ¼
596, 2hmax ¼ 50:70ꢁ (ꢁ11 6 h 6 10, ꢁ13 6 k 6 13, ꢁ16 6
l 6 16). Final residuals (for 380 parameters) were
R1 ¼ 0:0565 and wR2 ¼ 0:1289 for 2444 reflections with
I > 2rðIÞ, and R1 ¼ 0:1394 and wR2 ¼ 0:1544, GOF ¼
0.905 for all 4997 data. Residual electron density was
12. Diol 2a and ditosylate 3a were obtained following the
method described for compounds 2b and 3b, respec-
1
tively.11 2a: 78%; orange crystals; mp 117.5–119.5 ꢁC. H
NMR (300 MHz; CDCl3; d, ppm; J, Hz) 1.97 (br s, 2H),
3.65–3.72 (m, 4H), 3.74–3.82 (m, 4H), 3.84–3.92 (m, 4H),
4.14–4.21 (m, 4H), 6.97 (dd, 2H, J ¼ 2:18, 8.09), 7.17 (d,
2H, J ¼ 2:18), 7.29 (d, 2H, J ¼ 8:09). Anal. calcd for
C21H24O7: C, 64.94; H, 6.23. Found: C, 65.19; H, 6.29. 3a:
88%; orange crystals; mp 110–112 ꢁC. 1H NMR (300 MHz;
CDCl3; d, ppm; J, Hz) 2.42 (s, 6H), 3.73–3.83 (m, 8H),
4.07 (t, 4H, J ¼ 4:52), 4.21 (t, 4H, J ¼ 4:82), 6.95 (dd, 2H,
J ¼ 2:18, 8.10), 7.12 (d, 2H, J ¼ 2:18), 7.27–7.36 (m, 6H),
7.80 (d, 4H, J ¼ 8:09). Anal. calcd for C35H36O11S2: C,
60.33; H, 5.21. Found: C, 60.47; H, 5.41.
0.356 and )0.183 eAꢁ3. Crystal data for 5b: C39H40O9,
ꢀ
652.74, triclinic, P1, a ¼ 11:051ð2Þ, b ¼ 11:342ð2Þ, c ¼
ꢀ
15:295ð3Þ A, a ¼ 69:81ð2Þꢁ, b ¼ 74:90ð2Þꢁ, c ¼ 68:74ð2Þꢁ,
V ¼ 1656:6ð5Þ A , Z ¼ 2, qcalcd ¼ 1:308 g cmꢁ3
,
l ¼
3
ꢀ
0:092 mmꢁ1, F ð000Þ ¼ 692, hmax ¼ 50:70ꢁ (ꢁ13 6 h 6 13,
ꢁ12 6 k 6 11, ꢁ17 6 l 6 17). Final residuals (for 434
parameters) were R1 ¼ 0:0577 and wR2 ¼ 0:1142 for 2444
reflections with I > 2rðIÞ, and R1 ¼ 0:2261 and wR2 ¼
0:1616, GOF ¼ 0.661 for all 5201 data. Residual electron
13. General procedure. A solution of 4 (5.52 g, 10 mmol) and
the appropriate ditosylate (3a or 3b, 10 mmol) in dry DMF
(400 mL) was added dropwise over 10 h to a stirred
suspension of K2CO3 (5.52 g, 40 mmol) in DMF (600 mL)
under argon at 80 ꢁC and heating was maintained for a
further 40 h. The reaction mixture was filtered and the
filtrate was evaporated to dryness in vacuo. The residue
and solid obtained after the first filtration were combined,
washed with methanol and filtered. The air-dried solid was
extracted with toluene using a Soxhlet extractor for 40 h.
The toluene extract was filtered and the solid residue was
extracted with hot toluene several times until complete
extraction of the product. The solvent was removed from
the combined toluene extracts under reduced pressure and
the residue was subjected to column chromatography
(SiO2, CHCl3/MeOH, 100:1), to afford pure 5a or 5b as
orange crystals after crystallization from toluene or
MeCN, respectively. Crownophane 5a: 21%; mp 196–
197 ꢁC. 1H NMR (300 MHz; CDCl3; d, ppm; J, Hz) 3.79–
3.90 (m, 8H), 3.92 (t, 4H, J ¼ 4:25), 4.30 (t, 4H, J ¼ 4:25),
6.43 (s, 2H), 6.61 (br s, 2H), 6.73 (dd, 2H, J ¼ 2:18, 8.09),
6.77 (d, 4H, J ¼ 8:72), 7.00 (d, 4H, J ¼ 8:41), 7.13 (d, 2H,
J ¼ 8:40). 13C NMR (75.5 MHz; CDCl3; d, ppm; J, Hz)
67.4, 68.4, 69.3, 69.6, 110.8, 115.7, 119.1, 119.9, 125.6,
126.9, 130.5, 135.9, 136.0, 157.1, 158.7, 193.2; EI-MS,
density was 0.233 and )0.225 eAꢁ3. The CIF files with
ꢀ
data for 5a and 5b have been deposited, CDCC reference
codes 201313 and 201314.
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