Bis(oxofluorenediyl)oxacyclophanes: Synthesis, crystal structure and complexation with paraquat in the gas phase

Article abstract of DOI:10.1002/chem.200400870

The first three representatives of the new family of oxacyclophanes incorporating two 2,7-dioxyfluorenone fragments, connected by [-CH ₂CH₂O-]_m spacers (m=2-4), have been synthesized. The yield of the smallest oxacyclophane (m = 2) is considerably higher with respect to the larger ones (m = 3 and m = 4), which are formed in comparable yields. Molecular modeling and NMR spectra analysis of the model compounds suggest that an essential difference in oxacyclophanes yields is caused by formation of quasi-cyclic intermediates, which are preorganized for macrocyclization owing to intramolecular π-π stacking interactions between the fluorenone units. The solid-state structures of these oxacyclophanes exhibit intra- and intermolecular π-π stacking interactions that dictate their rectangular shape in the fluorenone backbone and crystal packing of the molecules with the parallel or T-shape arrangement. The crystal packing in all cases is also sustained by weak C-H...O hydrogen bonds. FAB mass spectral analysis of mixtures of the larger oxacyclophanes (m = 3 and m = 4) and a paraquat moiety revealed peaks corresponding to the loss of one and two PF ₆^- counterions from the 1:1 complexes formed. However, no signals were observed for complexes of the paraquat moiety with the smaller oxacyclophane (m=2). Computer molecular modeling of complexes revealed a pseudorotaxane-like incorporation of the paraquat unit, sandwiched within a macrocyclic cavity between the almost parallel-aligned fluorenone rings of the larger oxacyclophanes (m = 3 and m = 4). In contrast to this, only external complexes of the smallest oxacyclophane (m = 2) with a paraquat unit have been found in the energy window of 10 kcal mol^-1.

Full text of DOI:10.1002/chem.200400870

Bis(oxofluorenediyl)oxacyclophanes: Synthesis, Crystal Structure and
Complexation with Paraquat in the Gas Phase
[
a]
[a]
[a]
Nikolay G.Lukyanenko,* Tatiana I.Kirichenko, Alexander Yu Lyapunov,
[
a]
[b]
[b]
Alexander V.Mazepa, Yurii A.Simonov, Marina S.Fonari, and
[
c]
Mark M.Botoshansky
À
Abstract: The first three representa-
tives of the new family of oxacyclo-
phanes incorporating two 2,7-dioxy-
fluorenone fragments, connected by
renone units. The solid-state structures
of these oxacyclophanes exhibit intra-
and intermolecular p–p stacking inter-
actions that dictate their rectangular
shape in the fluorenone backbone and
crystal packing of the molecules with
the parallel or T-shape arrangement.
The crystal packing in all cases is also
sustained by weak CÀH···O hydrogen
to the loss of one and two PF6 coun-
terions from the 1:1 complexes formed.
However, no signals were observed for
complexes of the paraquat moiety with
the smaller oxacyclophane (m=2).
Computer molecular modeling of com-
plexes revealed a pseudorotaxane-like
incorporation of the paraquat unit,
sandwiched within a macrocyclic cavity
between the almost parallel-aligned
fluorenone rings of the larger oxacyclo-
phanes (m=3 and m=4). In contrast
to this, only external complexes of the
smallest oxacyclophane (m=2) with a
paraquat unit have been found in the
[
-CH CH O-] spacers (m=2–4), have
2 2 m
been synthesized. The yield of the
smallest oxacyclophane (m=2) is con-
siderably higher with respect to the
larger ones (m=3 and m=4), which
are formed in comparable yields. Mo-
lecular modeling and NMRspectra
analysis of the model compounds sug-
gest that an essential difference in oxa-
cyclophanes yields is caused by forma-
tion of quasi-cyclic intermediates,
which are preorganized for macrocycli-
zation owing to intramolecular p–p
stacking interactions between the fluo-
bonds. FAB mass spectral analysis of
mixtures of the larger oxacyclophanes
(m=3 and m=4) and
a paraquat
moiety revealed peaks corresponding
Keywords: crown compounds
·
À1
energy window of 10 kcalmol .
cyclophanes · fluorenones · host–
guest systems · macrocycles
Introduction
In the design and synthesis of new molecular receptors, cy-
clophanes play an important role as versatile host com-
pounds that are capable of entrapping molecular guests
within the central cavity or sandwiching them between host
[
a] Prof. N. G. Lukyanenko, Dr. T. I. Kirichenko, A. Y. Lyapunov,
Dr. A. V. Mazepa
[1]
Department of Fine Organic Synthesis
A. V. Bogatsky Physico-Chemical Institute
National Academy of Sciences of Ukraine
Lustdorfskaya doroga 86, 65080 Odessa (Ukraine)
Fax : (+38)482-340-803, (+38)482-652-012
E-mail: ngl@farlep.net
molecules in the crystal lattice. Host compounds are com-
monly designed by using rigid building blocks in order to
stabilize a hollow ring conformation. Recently, oxacyclo-
phane-type macrocycles incorporating rigid aromatic moiet-
ies bridged by flexible polyethers chains have attracted con-
siderable attention. Such compounds successfully couple
properties of classical crown ethers and cyclophanes. This
feature makes them excellent receptors both for ionic and
[
b] Dr. Y. A. Simonov, Dr. M. S. Fonari
Institute of Applied Physics Academy of Sciences of Moldova
Academy str., 5 MD 2028, Chisinau (Moldova)
[
c] Dr. M. M. Botoshansky
Department of Chemistry
Technion—Israel Institute of Technology
Technion City, 32000 Haifa (Israel)
[2]
neutral guests.
As a powerful recognition tool utilized to guide the com-
plexation and the synthesis of supramolecular species, vari-
ous types of noncovalent intermolecular interactions can be
used. These are, specifically, hydrogen bonds, stacking, elec-
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
262
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DOI: 10.1002/chem.200400870
Chem. Eur. J. 2005, 11, 262 – 270

FULL PAPER
trostatic, hydrophobic, and charge-transfer interactions, as
large oxacyclophanes namely bis(oxofluorenediyl)oxacyclo-
phanes. Bisphenol 1 was selected for the following reasons:
[3]
well as metal coordination. Nevertheless, the electrostatic
interactions play a dominant role, and in the case in which
polar subsystems are included into the macrocyclic host
framework, it is possible to identify the total stabilization
1) It is a highly polarized p-electron-rich extended aromatic
system, in which the carbonyl group can act as a sensor
that recognizes an electron-deficient guest, can direct it
towards the macrocyclic host cavity and can stabilize the
complexes because of electrostatic interactions.
2) It is a powerful hydrogen-bond acceptor; the carbonyl
oxygen atom is capable to form strong hydrogen bonds
with the substrate, which is often the dominating factor
in molecular recognition and self-assembly of supra-
molecular systems.
3) Fluorenone and its derivatives have good luminescence
properties that are important for the development of
sensitive fluorescence-based chemosensors.
4) Finally, the carbonyl group of the fluorenone fragment
can be converted into a variety of functional groups; this
allows for finetuning of the binding behavior of the oxa-
cyclophanes.
[4]
energy within the limits of the electrostatic energy term.
Therefore, the introduction of extended aromatic moieties
containing polar groups and well-developed, polarized p-
electron systems into the framework of macrocyclic hosts
seems a reasonable approach to enhance such interactions.
Most of the investigations in this direction are based on the
synthesis of polar receptors that contain appropriately posi-
tioned hydroxy or carboxy groups in a rigid macrocyclic
[1b,5]
framework.
The other polar groups, especially the car-
bonyl groups, can serve as hydrogen-bond acceptors and
play an essential role in the determination of the binding
ability of the hosts, the three-dimensional chemical struc-
ture, and the properties of their complexes.
One of the most significant advances in the field of supra-
molecular chemistry resulted from the quest for effective
hosts for the complexation of 1,1’-dialkyl-4,4’-bipyridinium
[6]
salts (paraquats). During the 1980s Stoddart et al. discov-
ered that large bisarylene crown ethers, in particular, com-
bine into pseudorotaxanes (mechanically threaded struc-
tures without bulky end groups) with paraquat units with as-
In a preliminary communication, we discussed briefly the
preparation and some structural features of oxacyclophane
[9]
12. Here we report: 1) the preparation of the first three
representatives of the bis(oxofluorenediyl)oxacyclophanes,
2) the X-ray structural analysis of the oxacyclophanes, and
3) the complexation of the oxacyclophanes with 1,1’-dimeth-
yl-4,4’-bipyridinium bis(hexafluorophosphate) (paraquat) in
the gas phase.
2
3
À1 [6]
sociation constants about 10 –10 m . This research initiat-
ed the synthesis of a variety of pseudorotaxanes, rotaxanes,
[7]
catenanes, and polyrotaxanes.
The structure of bisarylene crown ethers is similar to the
framework of oxacyclophanes, since each of them contains
rigid aromatic moieties bridged by flexible polyethers
chains. Therfore, their complexing ability should also be
similar. In addition, it is apparent that the binding ability of
the oxacyclophanes that contain polar groups can be appre-
ciably augmented by attractive electrostatic interactions be-
tween the macrocyclic host and the positively charged guest.
With the purpose of obtaining the macrocyclic receptors
that potentially possess high intrinsic affinity to electron-de-
ficient guests, we were interested in 2,7-dioxy-9H-fluoren-9-
Results and Discussion
Synthesis: The synthetic pathway leading to the oxacyclo-
phanes 11–13 is shown in Scheme 1. Reaction of bisphenol 1
with the chlorohydrins of di-, tri-, or tetraethylene glycol in
DMF in the presence of anhydrous potassium carbonate at
80–858C for 40 h afforded the diols 5–7, respectively. Con-
version of these diols into bistosylates 8–10 was achieved in
good yields (70–88%) by using p-toluenesulfonyl chloride in
[8]
one (1) as an aromatic block for synthesis of new family of
Scheme 1. Synthesis of the bis(oxofluorenediyl)oxacyclophanes 11–13.
Chem. Eur. J. 2005, 11, 262 – 270
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
263

N. G. Lukyanenko et al.
a mixture of chloroform and dioxane in the presence of tri-
ethylamine at 0–208C. Further macrocyclization reaction of
the obtained bistosylates with bisphenol 1 in DMF in the
presence of anhydrous potassium carbonate as the base at
effort to obtain experimental evidence of this assumption
we have synthesized acyclic compounds 15 and 17
(Figure 1). As shown in Table 1, all the fluorenone proton
1
signals in the H NMRspectra are subject to a slight, but
80–858C for 40 h, under high dilution conditions, gave after
noticeable upfield shifts (0.02–0.06 ppm) in comparison with
workup and chromatographic purification over silica gel, the
oxacyclophanes 11–13 in 53, 27, and 30% yields, respective-
ly. We did not gain any appreciable increase in yields of bis-
1
[a]
[b]
[c]
Table 1. Selected H NMRspectroscopic data
[d and Dd values in
ppm] for the oxacyclophanes 11–13 and the model compounds 15 and 17
(
oxofluorenediyl)oxacyclophanes by using cesium carbonate
in [D ]DMSO at 298 K.
6
as the base instead of potassium carbonate, despite the fact
that the cesium cation promotes formation of many macro-
cyclic systems (cesium effect).
The yield of the oxacyclophane 11 is much higher with re-
spect to oxacyclophanes 12 and 13, which are formed in
comparable yields. To find out why the yields of oxacyclo-
phanes differ so considerably, an extensive Monte Carlo
conformational search for the imaginary model compounds
[d]
[d]
[d]
Ha
Hb
Hc
d
Dd
d
Dd
d
Dd
[10]
11
12
6.66
6.78
6.84
7.12
7.05
7.16
À0.39
À0.27
À0.21
À0.04
6.85
6.80
6.84
6.92
7.01
6.94
À0.16
À0.21
À0.17
À0.02
7.17
7.11
7.18
7.23
7.48
7.29
À0.31
À0.37
À0.30
À0.06
13
15
17
17
[
e]
[e]
1
[
a] H NMRspectra were recorded at 300 MHz. [b] The values reported
14–16 (Figure 1) was performed with the MMFF force field
correspond to the centroids of the multiplets. [c] Dd values were obtained
as the difference between chemical shifts of the appropriate protons of
the reference compound 17 and the compounds 11–13, and 15. [d] The
protons mentioned are depicted on the structural formula in Figure 1.
[
3
e] In CDCl .
those of 17; this shift undoubtedly arises from the mutual
shielding effect of the fluorenone components (Table 1).
Such shielding effect reveals an appreciable population in
solution of the conformation of compound 15 in which two
fluorenone fragments are closely located with almost paral-
lel alignment (shown in Figure 1). This is in a fairly good
agreement with the hypotheses made about the geometry of
intermediate A.
In solution, oxacyclophanes conformations coexist in a dy-
namic equilibrium, with relative populations determined by
their respective energies. Since the H NMRspectra of 11–
Figure 1. Schematic representation of the intermediate A and chemical
formulas of the model compounds 14–17.
1
1
3 in [D ]DMSO show only a single set of proton signals,
6
[11]
as implemented in the Spartan 02 program package. It re-
sulted in minimal energy conformations of these com-
pounds, which in all cases have an almost parallel arrange-
ment of the partially overlapping fluorenone moieties with
the interplanar distances between them equal to 3.66–
fast conformational exchange on the NMRtimescale is
taking place in the solutions of these compounds. A Monte
Carlo conformational search (MMFF force field, Spartan
02) indicates that the most stable conformers of oxacyclo-
phanes 11–13 are the anti and syn forms, differing in the
mutual orientation of the carbonyl groups (Figure 2). Insig-
3.69 Š. This geometry is commensurate with conventional
parallel p–p stacking interactions between the aromatic
units that stabilize a minimal energy conformations of the
[3d]
compounds 14–16. We can therefore assume that the es-
sential difference in the yields of the oxacyclophanes 11–13
is caused by the formation of the quasi-cyclic intermediate
(
A), which is preorganized for macrocyclization owing to
the intramolecular p–p stacking interactions between the
fluorenone units (Figure 1). According to the entropic crite-
rion, the probability of such self-organizing should be more
for molecules with the shortest length of the bridge connect-
ing two fragments of a fluorenone. The increase in bridge
length and, hence, degrees of freedom of a molecule makes
formation of an intermediate (A) less entropically favorable,
owing to restriction of internal mobility of a molecule. This
is apparently the cause of the lower yields of the oxacyclo-
phanes 12 and 13 relative to that of oxacyclophane 11. In an
Figure 2. Chemical formula of the paraquat 18 and schematic representa-
tion of the syn- and anti-forms of the oxacyclophanes 11–13.
nificant energy differences between these conformers, 0.01,
À1
0.10, and 0.48 kcalmol for 11, 12, and 13, respectively,
infer that they are almost equally populated, at least in
vacuo. Analysis of CPK molecular models indicates that
264
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Bis(oxofluorenediyl)oxacyclophanes
FULL PAPER
these conformers can be inter-
converted at rotation of the flu-
orenone units around their long
axis. The calculated (HF/3-
21G*) energy barrier associated
with this dynamic process in the
oxacyclophane 11, for example,
À1
is only 9 kcalmol . Compari-
1
son of the H NMRspectra of
11–13 with that of the model
compound 17 indicates signifi-
cant upfield shifts (Dd lies be-
tween À0.16 and À0.39 ppm)
for
all
aromatic
protons
(
Table 1); these shifts are a
result of the shielding effects
exerted by the fluorenone units.
This reveals that in the aver-
aged conformations of oxacy-
clophanes 11–13 in solution, the Figure 3. Top view (left) and side view (right) for the solid-state structure of the oxacyclophanes a) 11, b) 12,
and c) 13. There are CÀH···O hydrogen bonds between the CH
polyether loops. Their respective geometries are C···O, H···O, CH···O, 3.12, 2.45 Š, 1258 for 11; 3.17, 2.41 Š,
348 for 12; and 3.00, 2.51 Š, 1118 for 13.
groups and proximal oxygen atoms of the
fluorenone units are predomi-
nantly parallel and closely lo-
cated, as observed in the calcu-
lated and solid-state structures.
2
1
[3]
tions between them. However, the corresponding fluore-
none–fluorenone separation of 3.08 Š in 13 clearly indicates
the absence of the intramolecular p–p stacking. In com-
pounds 11 and 12, the overlap of the aromatic systems is im-
mediately apparent, being approximately the same in the
both molecules (Figure 3, left column). A similar molecular
shape has been found in the macrocycles that incorporate
X-ray crystallography: The cavity size, the shape, the rigidi-
ty, the nature of the binding sites and intra- and intermolec-
ular interactions govern the binding power of a host. To in-
vestigate these parameters, crystal structures of the oxacy-
clophanes have been studied. Single crystals suitable for X-
ray crystallography were grown by crystallization of com-
pound 11 from nitrobenzene or by slow concentration of the
solutions of oxacyclophanes 12 and 13 in acetonitrile and di-
oxane, respectively. In all cases the initial concentrations of
[12]
hydroquinol, or biphenyl units bridged by the oxyethylene
[13]
chains of the same length, while in the case of the anthra-
cene backbone the elongated shape of the molecule is dis-
À4
À5
[14]
11–13 were in the range 10 –10 m, because of their very
torted. In compound 13, the parallel arrangement of the
low solubility. The molecular geometry of oxacyclophanes
and their packing in the crystal are stabilized by the combi-
nation of intra- and intermolecular CÀH···O hydrogen-bond-
fluorenone units is retained; however, one of them is consid-
erably displaced with respect to the other in order to opti-
mize the dipole–dipole interactions between the carbonyl
groups. The oxacyclophane 13 exists in the crystals with a
sigmoid edge profile reminiscent of that in bis(5-carbome-
thoxy-1,3-phenylene)[32]crown-10 in which the aromatic
ing, p–p stacking interactions between the fluorenone units,
and CÀH···p interactions between the appropriately oriented
hydrogen atoms of the methylene groups and the p-elec-
tron-rich aromatic moieties. The oxacyclophanes studied
have crystallographic centers of symmetry located in the
center of macrocycles owing to an antiparallel arrangement
of the fluorenone units (Figure 3). Their planarity is extend-
ed to include three oxygen atoms attached to the aromatic
moiety (one carbonyl group oxygen atom and two ether
ones). The fused aromatic rings of the fluorenone backbone
form a practically planar system. The macrocycles are self-
filling, with two fluorenone units aligned parallel to each
other about the crystallographic center of symmetry. The
fluorenone backbone, with the distance of 9.62 Š between
two attached ether oxygen atoms, dictates the rectangular
shape of the macrocycle 11, while 12 and 13 have S-shaped
structures. The fluorenone units are positioned at interpla-
nar distances of 3.53 Š in 11 and 3.45 Š in 12; these distan-
ces correspond to the intramolecular p–p stacking interac-
[15]
rings are parallel, but do not overlap spatially.
The
common feature of 11–13 is the availability of two weak in-
version-related intramolecular CÀH···O interactions be-
tween the CH groups and proximal oxygen atoms of the
2
polyether loops (Figure 3, right column). The corresponding
C···O separations range from 3.00 to 3.17 Š and are respon-
sible for the formation of two intramolecular six-membered
pseudorings. The short CÀH···O intramolecular interactions
that are found to fill the cavity are typical for classic crown
ethers, although in the case of [18]crown-6 and its deriva-
tives they act across the cavity and define the elongated
[16]
shape of the molecule.
The oxacyclophanes 11–13 have
centrosymmetric C conformations, described by an appro-
i
priate sequences of torsion angles of the crown ether
[17]
loops. The crystal packing in 11–13 is dictated by weak in-
termolecular CÀH···O hydrogen bonds and p–p stacking in-
Chem. Eur. J. 2005, 11, 262 – 270
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265

N. G. Lukyanenko et al.
¯
teractions that obey P1 symmetry in 11 and 13 and P2 /c
and 3.39, 2.47 Š, 1708 in 13, respectively. These interactions
are responsible for the tapes running along b direction both
1
symmetry in 12 (Figure 4). The molecules of 11 and 13 are
packed in a similar way into thick layers in which the surfa-
ces are formed by the aromatic fluorenone backbones (Fig-
ure 4a and c). The layer organization is controlled predomi-
in 11 and 13. The OCH groups form the weaker CÀH···O
2
2
2
bonds that are in the bc plane and close the layered R (8)
rings that are built on the methylene group hydrogen atom
[18]
and the neighboring oxygen atom. These hydrogen bonds
have C···O, H···O distances and CH···O angles equal to 3.46,
2
.62 Š, 1468 in 11 and 3.60, 2.71 Š, 1538 in 13. The packing
of the layers is governed by the p–p stacking interactions
between the partially overlapping fluorenone units. The in-
terlayer separation is 3.37 Š in 11 and 3.53 Š in 13. The
molecules of 12 are packed to form the chevron-like sheets
(
Figure 4b). The adjacent rows are oriented to optimize T-
type edge-to-face interactions between the aromatic compo-
nents with the dihedral angle of 1038 between the planes of
[19]
inclined fluorenone moieties. These sheets are also inter-
connected into a three-dimensional grid through CÀH···O
hydrogen bonds, with respective geometries of C···O, H···O,
CH···O, 3.55, 2.59 Š, 1708 and 3.42, 2.49 Š, 1608.
Complexation studies: A very low solubility of the oxacyclo-
phanes 11–13 in usual organic solvents restricts application
of NMRspectroscopy for investigations of their complexa-
tion in solutions. The [D ]DMSO was the only solvent suita-
6
ble for NMRexperiments. Because this medium weakens or
[20]
suppresses the formation of complexes,
we did not ob-
serve pronounced induced changes in the chemical shifts of
the protons of the hosts 11–13 or the guest 18 in NMRspec-
tra for the samples of their mixtures. A convenient way to
explore the binding ability of macrocyclic hosts is mass spec-
trometry, which gives the opportunity to study host–guest
chemistry as a purely bimolecular interaction in the absence
[21]
of solvents and other interfering species.
Therefore, the
complexation of the oxacyclophanes 11–13 with 1,1’-dimeth-
yl-4,4’-bipyridinium bis(hexafluorophosphate) (18; Figure 2)
in the gas phase was analyzed by fast atom bombardment
mass spectrometry (FAB-MS). The separate samples of
equimolar amounts of paraquat 18 and compounds 11, 12,
or 13 dissolved in a DMF/m-nitrobenzyl alcohol mixture
(
1:1) were subjected to FAB-MS analysis. In the cases of
both 12 and 13, peaks were observed in the mass spectra
À
that correspond to the loss of one and two PF6 counterions
from the formed 1:1 complexes (Table 2). This fragmenta-
tion pattern has been observed in many pseudorotaxanes
[6b,22]
and catenanes derived from paraquat derivatives.
How-
ever, no signal was observed which indicated that a complex
had been formed with compound 11.
Figure 4. The part of one of the sheets sustained by the hydrogen bonds
presented in the solid-state structure of the oxacyclophanes a) 11, b) 12,
and c) 13.
6
Table 2. FAB-MS data for the complexes of 11–13 with 18·2PF .
+
[a]
+[b]
+[b]
[b,c]
[
M]
[MÀPF
6
]
[MÀ2PF
6
]
Host
nantly by two types of CÀH···O hydrogen bonds, differing
1
1
1
1
2
3
[1040]
[1128]
[1216]
–
–
565 (100)
653 (100)
741 (100)
by the oxygen atoms involved in these interactions. The car-
bonyl group oxygen atom interacts with hydrogen atoms of
alkyl or aryl groups of the translated oxacyclophane mole-
cules. The respective geometries of these CÀH···O hydrogen
bonds are C···O, H···O, CÀH···O, 3.23, 2.54 Š, 1298 in 11,
983 (5)
1071 (7)
838 (2)
926 (2)
[
a] The peaks corresponding to the molecular ion of the complexes were
not observed. [b] The peaks intensities are shown in parentheses.
[c] Peaks corresponding to the protonated oxacyclophanes.
266
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Bis(oxofluorenediyl)oxacyclophanes
FULL PAPER
Inspection of CPK models revealed that the paraquat 18
could be easily accommodated inside the macrocycles 12
and 13, but also that there are significant steric restrictions
on its penetration into the cavity of the macrocycle 11. Fur-
ther computer modeling (a Monte Carlo conformational
search in conjunction with the MMFF force field; semiem-
the ether oxygen atoms of the macrocycle (Figure 5a). The
calculated stabilization energy values of the complexes
11·18, 12·18, and 13·18 are 31.9, 33.1, and 43.8 kcalmol , re-
À1
spectively. The larger stabilization energy of the 13·18 com-
plex with respect to the 12·18 is in agreement with the rela-
+
tive intensities of [MÀPF ] peaks in their FAB mass spec-
6
[23]
pirical AM1 single-point energy calculations)
that in the most stable structures of the complexes 12·18 and
3·18 the oxacyclophanes possess anti-conformations. The
indicated
tra. Nevertheless, the complex 11·18 is not formed despite
the fact that its stabilization energy in vacuo is similar to
that of the 12·18. Many publications demonstrate that in
FABMS the signals are generated by direct desorption of
1
macrocycles cavities are tightly filled by compound 18,
which is located at the averaged distances of 4.0 and 3.9 Š
between the centroids of the fluorenone units and paraquat
for the 12·18 and 13·18, respectively. These distances are ap-
propriate for p–p stacking interactions (Figure 5b and c).
The oxygen atoms of the carbonyl groups are directed to-
wards the paraquat 18 at averaged distances from its cent-
roid of 3.8 and 3.7 Š for the complexes 12·18 and 13·18, re-
spectively. This immediately indicates the considerable
dipole–charge interactions between the carbonyl groups of
the fluorenone moieties and the paraquat that are undoubt-
edly an important stabilization component of the complexes.
The structures of the complexes 12·18 and 13·18 are addi-
tionally stabilized by CÀH···O interactions between the
[21]
the complex ions preformed in the condensed phase. The
formation of host–guest complexes in the condensed phase
implies the solvation of both counterparts and hence the
possible modification of a variety of noncovalent interac-
tions between them. Therefore, the calculated values of the
stabilization energy of the complexes do not necessarily re-
flect complexation in solution closely enough. The protic
and highly polar DMF/m-nitrobenzyl alcohol matrix used in
our experiments is a medium in which hydrogen bonds and
electrostatic interactions responsible for complex formation
become weak or even destroyed. Probably the competing
salvation effect is strong enough to prevent formation of an
external complex of the oxacyclophane 11, while the forma-
tion of the less-solvated inclusion complexes of the oxacy-
clophanes 12 and 13 are permitted.
acidic hydrogen atoms of paraquat methyl groups and the
oxygen atoms of the polyether loops of the oxacyclophanes
1
1
2 and 13. In a general way the calculated structure of the
2·18 is similar to that described for the pseudorotaxane-like
complexes of paraquat with bisarylene crown ethers in the
Conclusion
[6b]
solid state, for example with bis-p-phenylene[34]crown-10,
[24]
while the 13·18 has a “hot dog” structure.
In contrast,
We have reported the synthesis of a new family of macrocy-
clic receptors, bis(oxofluorenediyl)oxacyclophanes, contain-
ing two fragments of 2,7-dioxyfluorenone bridged by the di-,
tri-, and tetraethylene glycol units. An essential feature of
these oxacyclophanes is the presence within the macrocyclic
framework of highly polarized, p-electron-rich, extended ar-
omatic systems of the fluorenone that can stabilize the com-
plexes as a result of electrostatic interactions and hydrogen
only the external complex of the syn-conformer of oxacyclo-
phane 11 with the paraquat 18 was found in the energy
À1
window of 10 kcalmol . The most stable structure of the
11·18 is held together by electrostatic interactions between
two carbonyl groups of 11 and one of the nitrogen atoms of
+
1
8 (C=O···N distances are 3.1 and 3.3 Š) and by hydrogen
bonding involving the hydrogen atoms of the bipyridine and
Figure 5. Calculated structures and stabilization energy (DE) of the complexes of paraquat 18 with oxacyclophanes a) 11, b) 12, and c) 13. The DE values
are the difference between the energies of the global minima of the complexes Ecomplex and the energies of the global minima of the free host and guest
E
host and Eguest, respectively (DE=EcomplexÀEhostÀEguest).
Chem. Eur. J. 2005, 11, 262 – 270
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
267

N. G. Lukyanenko et al.
+
bond formation with the substrate. These interactions are
often the dominating factors of molecular recognition and
self-assembly of supramolecular systems. As a result they
make bis(oxofluorenediyl)oxacyclophanes attractive macro-
cyclic receptors for ionic and neutral species and as compo-
nents in supramolecular synthesis. Future work will focus on
exploring the ability of this macrocycle to act as a host for
organic guest molecules.
(273); MS (EI): m/z (%): 564 (14) [M] , 388 (2), 212 (10), 45 (100); ele-
mental analysis calcd (%) for C29
C 61.87, H 6.94.
40
H O11 (564.6): C 61.69, H 7.14; found:
General procedure for the preparation of the bistosylates 8–10: A so-
lution of p-toluenesulfonyl chloride (14.30 g, 75 mmol) in dry dioxane
30 mL) was added dropwise to solution of 5–7 (30 mmol) and triethyl-
amine (9.11 g, 90 mmol) in chloroform over 2 h at 0–58C. The solution
was allowed to warm to RT and stirring was continued for 30 h. An equal
volume of chloroform was added to the slurry and the mixture was suc-
cessively washed with 5% aqueous HCl, 10% aqueous ammonia, water,
(
4
and brine, and dried over MgSO . After evaporation of the solvent,
crude product was extracted with hot isopropyl alcohol. Pure bistosylates
were isolated on cooling solution.
Experimental Section
2
-{2-{{7-{2-{2-{[(4-methylphenyl)sulfonyl]oxy}ethoxy}ethoxy}-9-oxo-9H-
fluoren-2-yl}oxy}ethoxy}ethyl 4-methylbenzenesulfonate (8): Orange-red
General: Chlorohydrins (2) and (3), and triethylene glycol bistosylate are
commercially available and were used as received. 2,7-Dioxy-9H-fluoren-
1
solid (18.37 g, 88%); m.p. 110–1128C; H NMR(CDCl
3
): d=2.42 (s,
[
8]
[25]
[26]
6H), 3.73–3.83 (m, 8H), 4.07 (t, J=4 Hz, 4H), 4.21 (t, J=4 Hz, 4H), 6.95
9
-one (1), chlorohydrin (4),
2,7-dimethoxy-9H-fluoren-9-one (17)
[27]
(
(
dd, J=2, 8 Hz, 2H), 7.12 (d, J=2 Hz, 2H), 7.27–7.36 (m, 6H), 7.80 ppm
d, J=8 Hz, 4H); IR(KBr): n˜ =1700 cm (C=O); UV/Vis (dioxane):
and 2-hydroxy-7-methoxy-9H-fluoren-9-one
were prepared as de-
À1
scribed. Thin-layer chromatography (TLC) was carried out on aluminum
sheets coated with silica gel 60F (Merck 5554). The plates were inspected
l
max(e)=272 (91636), 301 (7958), 314 (7615), 464 nm (373); MS (EI): m/z
+
by UV light and, if required, developed in I
2
vapor. Column chromatog-
(%): 696 (5) [M] , 524 (26), 497 (7), 282 (10), 212 (31); elemental analy-
raphy was carried out by using silica gel (Acros 0.060–0.200 mm). Melting
sis calcd (%) for C35
5.41.
36 11 2
H O S (696.8): C 60.33, H 5.21; found: C 60.47, H
1
points were determined in open capillaries and are uncorrected. All
H
1
3
and C NMRspectra were recorded on Varian VXR-300 (300 MHz and
5.5 MHz, respectively) spectrometer. All chemical shifts are quoted in
2-{2-{2-{{7-{2-{{-{2-{[(4-methylphenyl)sulfonyl]oxy}ethoxy}ethoxy}ethoxy}-
9-oxo-9H-fluoren-2-yl}oxy}ethoxy}ethoxy}ethyl 4-methylbenzenesulfo-
7
1
ppm on the d scale with TMS or residual solvent as an internal standard.
The coupling constants are expressed in Hz. Infrared spectra were re-
corded on a Specord 75IRinstrument. Electronic absorption spectra
were obtained on a Specord M40 spectrophotometer in the 200–900 nm
range, in quartz cells with 1 cm path length. Electron impact (EI) mass
spectra were recorded on a MX-1321 spectrometer at 70 eV. Fast atom
nate (9): Orange solid (19.75 g, 84%); m.p. 68–708C; H NMR(CDCl 3):
d=2.43 (s, 6H), 3.57–3.75 (m, 12H), 3.79–3.87 (m, 4H), 4.08–4.21 (m,
8H), 6.97 (dd, J=2, 8 Hz, 2H), 7.15 (d, J=2 Hz, 2H), 7.29 (d, J=8 Hz,
2H), 7.33 (d, J=8 Hz, 4H), 7.80 ppm (d, J=8 Hz, 4H); IR(KBr): n˜ =
À1
1700 cm (C=O); UV/Vis (dioxane): lmax(e)=225 (52742), 272 (139197),
301 (12700), 314 (12173), 469 nm (518); MS (FAB): m/z (%): 785 (100)
+
bombardment (FAB) mass spectrometry was performed on
070EQ mass spectrometer, equipped with a xenon primary atom beam,
and an m-nitrobenzyl alcohol matrix was utilized.
General procedure for the preparation of the diols 5–7: Bisphenol 1
a
VG
[M+H] ; elemental analysis calcd (%) for C H O S (784.9): C 59.68,
3
9
44 13 2
7
H 5.65; found: C 59.56, H 5.47.
2
-{2-{2-{2-{{7-{2-{2-{2-{2-{[(4-methylphenyl)sulfonyl]oxy}ethoxy}ethoxy}-
ethoxy}ethoxy}-9-oxo-9H-fluoren-2-yl}oxy}ethoxy}ethoxy}ethoxy}ethyl 4-
methylbenzenesulfonate (10): Dark red viscous oil, solidified on standing
(
16.98 g, 80 mmol) was added to suspension of freshly ground K
2 3
CO
1
(
66.34 g, 480 mmol) and NaI (24.00 g, 160 mmol) in dry DMF (400 mL)
(18.31 g, 70%); H NMR(CDCl 3): d=2.43 (s, 6H), 3.60 (s, 8H), 3.62–
under argon. After stirring for 1 h at 608C, chlorohydrin 2, 3, or 4
240 mmol) was added and the temperature was raised to 808C. Stirring
and heating were continued for 35 h. After cooling to room temperature,
the reaction mixture was filtered and the residue was washed with DMF
3.76 (m, 12H), 3.85 (t, J=4 Hz, 4H), 4.11–4.20 (m, 8H), 6.97 (dd, J=2,
8 Hz, 2H), 7.15 (d, J=2 Hz, 2H), 7.28 (d, J=8 Hz, 2H), 7.33 (d, J=8 Hz,
4H), 7.79 ppm (d, J=8 Hz, 4H); IR(KBr): n˜ =1700 cm (C=O); UV/
(
À1
Vis (dioxane): lmax(e)=229 (25270), 272 (90783), 302 (7635), 314 (7516),
+
(
50 mL). The filtrate was evaporated to dryness in vacuo. The residue
was dissolved in chloroform, and the solution was washed consequently
with 5% aqueous NaOH, water and brine, dried over MgSO , and evapo-
464 nm (439); MS (FAB): m/z (%): 873 (100) [M+H] ; elemental analy-
sis calcd (%) for C H O S (872.9): C 59.16, H 6.00; found: C 58.98, H
4
3
52 15 2
4
5.83.
rated in vacuo. The residue was purified by recrystallization from isopro-
pyl alcohol for 5 and 6, and from ethanol/diethyl ether for 7.
General procedure for the preparation of the oxacyclophanes 11–13: A
solution of 1 (2.12 g, 10 mmol) and the appropriate bistosylate 8–10
(10 mmol) in dry DMF (400 mL) was added dropwise over 10 h to a stir-
2
,7-Bis[2-(2-hydroxyethoxy)ethoxy]-9H-fluoren-9-one (5): Red solid
1
(
3
24.21 g, 78%); m.p. 117–1198C; H NMR(CDCl ): d=1.97 (brs, 2H),
2 3
red suspension of K CO (5.52 g, 40 mmol) in DMF (600 mL) under
3
4
8
2
.65–3.72 (m, 4H), 3.74–3.82 (m, 4H), 3.84–3.92 (m, 4H), 4.14–4.21 (m,
argon at 808C; heating was then maintained for a further 40 h. The reac-
tion mixture was filtered, and the filtrate was evaporated to dryness in
vacuo. The residue and solid obtained after the first filtration were com-
bined, washed with cold methanol, and filtered. The air-dried solid was
extracted with toluene by 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,
the residue washed with a small amount of acetone and then subjected to
H) 6.97 (dd, J=2, 8 Hz, 2H), 7.17 (d, J=2 Hz, 2H), 7.29 ppm (d, J=
À1
Hz, 2H); IR(KBr): n˜ =1700 cm (C=O); UV/Vis (CH
3
OH): lmax(e)=
+
70 (100000), 469 (269); MS (EI): m/z (%): 388 (44) [M] , 300 (7), 212
(388.4): C
(
35), 45 (100); elemental analysis calcd (%) for C21
H
24
O
7
6
4.94, H 6.23; found: C 65.19, H 6.29.
2
,7-Bis{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}-9H-fluoren-9-one (6): R ed
1
solid (29.32 g, 77%); m.p. 91–928C; H NMR(CDCl
3
): d=2.18 (brs,
2
4
7
H), 3.63 (t, J=4 Hz, 4H), 3.68–3.82 (m, 12H), 3.87 (t, J=4 Hz, 4H),
.17 (t, J=4 Hz, 4H), 6.97 (dd, J=2, 8 Hz, 2H), 7.17 (d, J=2 Hz, 2H),
column chromatography (SiO
cyclophanes.
2 3
, CHCl /MeOH, 100:1), to afford pure oxa-
À1
.28 ppm (d, J=8 Hz, 2H); IR(KBr): n˜ =1700 cm (C=O); UV/Vis
(
(
(
CH
41) [M] , 432 (3), 344 (3), 212 (11), 45 (100); elemental analysis calcd
%) for C25 (476.5): C 63.01, H 6.77; found: C 62.82, H 6.65.
,7-Bis{2-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}ethoxy}-9H-fluoren-9-
3
OH): lmax(e)=270 (88261), 473 nm (336); MS (EI): m/z (%): 476
Oxacyclophane 11: Dark red crystals (2.98 g, 53%); m.p. 296—2988C
+
1
(
decomp); H NMR([D
6
]DMSO): d=3.81 (t, J=3 Hz, 8H), 4.09 (t, J=
32 9
H O
3
Hz, 8H), 6.66 (brs, 4H), 6.84 (dd, J=2, 8 Hz, 4H), 7.16 ppm (d, J=
1
3
2
8 Hz, 4H); C NMR(CF
137.5, 140.7, 160.9, 200.3 ppm; IR(KBr): n˜ =1700 cm (C=O); UV/Vis
(dioxane): lmax(e)=264 (119785), 302 (11201), 314 (10843), 473 nm
3
COOD): d=69.9, 71.9, 115.8, 123.1, 123.6,
1
À1
one (7): Orange solid (36.09 g, 80%); m.p. 61–638C; H NMR(CDCl
d=2.07 (brs, 2H), 3.61 (t, J=4 Hz, 4H), 3.65–3.77 (m, 20H), 4.17 (t, J=
4
2
3
):
+
Hz, 4H), 4.28 (t, J=4 Hz, 4H), 6.97 (dd, J=2, 8 Hz, 2H), 7.17 (d, J=
(507); MS (EI): m/z (%): 564 (100) [M] , 282 (7), 239 (8), 212 (11); ele-
À1
Hz, 2H), 7.28 ppm (d, J=8 Hz, 2H); IR(KBr): n˜ =1700 cm (C=O);
mental analysis calcd (%) for C34
72.26, H 5.25.
H
28
O
8
(564.6): C 72.33, H 5.00; found: C
3
UV/Vis (CH OH): lmax(e)=270 (77664), 300 (6725), 312 (6287), 469 nm
268
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 262 – 270

Bis(oxofluorenediyl)oxacyclophanes
FULL PAPER
Oxacyclophane 12: Red crystals
Table 3. Crystal data, data collection, and refinement parameters of oxacyclophanes 11, 12, and 13.
12 13
(
1.76 g, 27%); m.p. 197—1998C;
1
1
1
H NMR([D
8
4
6
]DMSO): d=3.65 (s,
H), 3.75 (t, J=4 Hz, 8H), 4.04 (t, J=
Hz, 8H), 6.80 (brs, 4H), 6.82 (brd,
formula
C
564.56
34
H
28
O
8
C
652.67
38
H
36
O
10
42 44 12
C H O
740.77
À1
M
r
[gmol
]
dimensions [mm]
T [K]
0.36ꢁ0.35ꢁ0.12
293(2)
0.35ꢁ0.18ꢁ0.05
293(2)
0.20ꢁ0.15ꢁ0.04
293(2)
J=8 Hz, 4H), 7.11 ppm (d, J=8 Hz,
1
3
4
7
1
1
l
3
3
H); C NMR(CF COOD): d=67.6,
crystal system
space group
a [Š]
b [Š]
c [Š]
triclinic
P1
monoclinic
triclinic
P1
0.5, 71.2, 111.1, 121.8, 123.0, 135.7,
39.6, 159.4, 198.8 ppm; IR(KBr): n˜ =
700 cm (C=O); UV/Vis (dioxane):
max(e)=264 (123029), 302 (11591),
14 (10895), 470 nm (459); MS (EI):
m/z (%): 652 (100) [M] , 580 (16), 326
¯
¯
P2
1
/c
À1
7.933(2)
8.747(2)
11.170(2)
94.04(2)
109.24(2)
112.12(3)
661.0(3)
1
8.372(2)
23.230(4)
8.660(2)
90.0
113.53(2)
90.0
1544.2(6)
2
1.404
8.009(1)
8.531(1)
14.059(3)
102.33(3)
99.68(3)
91.39(2)
923.3(3)
1
+
a [8]
b [8]
(
14), 212 (18); elemental analysis calcd
%) for C38 10 (652.7): C 69.93, H
.56; found: C 69.77, H 5.69.
Oxacyclophane 13: Orange crystals
2.22 g, 30%); m.p. 176—1778C;
g [8]
V [Š ]
(
36
H O
3
5
Z
À3
1
calc [gcm
]
1.418
1.01
1.332
0.98
(
À1
m [cm
]
1.02
1
H NMR([D
H), 3.75 (brs, 8H), 3.99 (brs, 8H),
.84 (brs, 8H), 7.18 ppm (d, J=8 Hz,
H); C NMR(CDCl ): d=68.1, 69.7,
3
0.8, 71.1, 110.0, 120.4, 120.7, 135.8,
6
]DMSO): d=3.59 (s,
F(000)
296
688
392
8
6
4
7
1
1
l
3
q range [8]
index range (h,k,l)
reflns collected
independent reflns
reflns observed [I>2s(I)]
parameters
2.0–26.4
Æ9, 10, 13
8319
2642
1399
2.7–27.8
Æ10, 29, 11
11986
3422
1468
218
2.5–25.3
Æ9, 10, 16
8681
3257
1707
1
3
37.4, 159.1, 193.2 ppm; IR(KBr): n˜ =
À1
700 cm (C=O); UV/Vis (dioxane):
190
245
max(e)=263 (134464), 270 (119107),
02 (12685), 314 (11934), 468 nm
R
1
[I>2s(I)]
0.0496
0.0999
0.930
0.162
À0.163
0.0546
0.1237
0.819
0.280
À0.306
0.0512
0.1052
0.955
0.200
À0.193
2
2
wR (F )
goodness-of-fit
D1max [eŠ
D1min [eŠ
(
576); MS (EI): m/z (%): 740 (100)
+
[
M] , 369 (5), 238 (17), 212 (21); ele-
mental analysis calcd (%) for
12 (740.8): C 68.10, H 5.99;
À3
]
À3
]
42 44
C H O
found: C 68.34, H 6.22.
Compound 15: A solution of 2-hy-
droxy-7-methoxy-9H-fluoren-9-one (2.40 g, 10.6 mmol) in dry DMF
20 mL) was added to suspension of freshly ground K CO (2.92 g,
1.2 mmol) in dry DMF (20 mL) under argon. After stirring at 608C for
0 min, a solution of triethyleneglycol bistosylate (2.29 g, 5 mmol) in dry
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK;
fax: (+44)1223-336-033; or deposit@ccdc.cam.ac.uk).
(
2
2
2
3
DMF (20 mL) was added to the mixture over 30 min, and the tempera-
ture was raised to 808C. Stirring and heating were continued for 12 h.
After cooling to room temperature, the reaction mixture was filtered and
the residue was washed with a small amount of DMF. The filtrate was
evaporated in vacuo, the residue was dissolved in chloroform, and the so-
lution was washed consequently with 5% aqueous NaOH, water, and
Acknowledgement
The diffraction data were collected at the Department of Chemistry,
Technion, The Haifa, through the cooperation of Professor Menahem
Kaftory whom we would like to acknowledge.
brine, dried over MgSO
due was subjected to column chromatography (SiO
4
, and evaporated at reduced pressure. The resi-
, CHCl /MeOH,
00:1) to afford pure 15 as bright red crystals (1.66 g, 58%). M.p. 150–
2
3
1
1
4
7
2
1
3
50.58C; H NMR(CDCl ): d=3.76 (s, 4H), 3.82 (s, 6H), 3.85–3.90 (m,
H), 4.11–4.17 (m, 4H), 6.87–6.96 (m, 4H), 7.10–7.14 (m, 4H), 7.21–
.26 ppm (m, 4H); MS (EI): m/z (%): 566 (100) [M] , 340 (17), 283 (16),
53 (37), 226 (76), 211 (31); elemental analysis calcd (%) for C34
566.6): C 72.07, H 5.34; found: C 72,13, H 5.38.
+
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H O
(
X-ray crystallographic data for 11, 12, and 13: Table 3 provides a summa-
ry of the crystallographic data for compounds 11–13. Data were collected
at a room temperature on a Nonius Kappa CCD diffractometer equipped
with graphite monochromated MoKa radiation by using f–w scans with a
sample-to-detector distance of 29 mm. Unit cell parameters were ob-
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3
[
28]
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[
2] a) S. Inokuma, S. Sakaki, J. Nishimura, Top. Curr. Chem. 1994, 172,
8
7–118; b) S. Tsuzuki, H. Houjou, Y. Nagawa, M. Goto, K. Hirata-
[
28]
LEPACK. The structure solution and refinement proceeded similarly
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James, C. J. Ward, J. Chem. Soc. Perkin Trans. 1 2000, 3155–3184;
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3] For papers and reviews on these noncovalent interactions, see:
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kins, J. Urch, J. Chem. Soc. Perkin Trans. 2 2001, 651–669; d) E. A.
[
29]
for all structures using SHELX97 program package.
All structures
2
were solved by direct methods (SHELXS-97) and refined on F by full-
matrix least-squares techniques (SHELXL-97). The geometrically con-
strained hydrogen atoms were placed in calculated positions with isotrop-
ic temperature factors (1.2 times the carbon temperature factor) and re-
fined as riding atoms.
[
CCDC 239347, 204895, and 239346 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge via
Chem. Eur. J. 2005, 11, 262 – 270
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1
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[
[
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aryl-Caryl-O-Cmethylene
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[
[
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Received: September 11, 2004
Published online: November 18, 2004
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