Synthesis of podands bearing aromatic end groups and complex formation with tropylium tetrafluoroborate in 1,2-dichloroethane

Article abstract of DOI:10.1002/(SICI)1099-1395(199907)12:7<557::AID-POC155>3.0.CO;2-T

A series of podands bearing phenyl, naphthyl and anthryl end groups were prepared and characterized. UV-visible spectrophotometry was used to investigate the host-guest chemistry of the podands in complexation with tropylium tetrafluoroborate in 1,2-dichloroethane. The results, are discussed and compared with those for previously studied systems containing crown ethers. The stability constants for these open-chain polyethers are in the range 5,1-8,4 dm³ mol^-1, except for the podand having anthryl end groups [1,12 bis(anthryl-9)-2,5,8,11-tetraoxadodecane], which gives a 10-fold increase in the stability constant. Copyright

Full text of DOI:10.1002/(SICI)1099-1395(199907)12:7<557::AID-POC155>3.0.CO;2-T

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 12, 557–563 (1999)
Synthesis of podands bearing aromatic end groups and
complex formation with tropylium tetra¯uoroborate in
1,2-dichloroethane
Markku LaÈmsaÈ, Kirsi Raitamaa and Jouni Pursiainen*
Department of Chemistry, University of Oulu, Linnanmaa, P.O. Box 333, FIN-90571 Oulu, Finland
Received 2 October 1998; revised 15 December 1998; accepted 15 December 1998
ABSTRACT: A series of podands bearing phenyl, naphthyl and anthryl end groups were prepared and characterized.
UV–visible spectrophotometry was used to investigate the host–guest chemistry of the podands in complexation with
tropylium tetrafluoroborate in 1,2-dichloroethane. The results are discussed and compared with those for previously
studied systems containing crown ethers. The stability constants for these open-chain polyethers are in the range 5.1–
8.4 dm3 mol 1, except for the podand having anthryl end groups [1,12-bis(anthryl-9)-2,5,8,11-tetraoxadodecane],
which gives a 10-fold increase in the stability constant. Copyright 1999 John Wiley & Sons, Ltd.
KEYWORDS: molecular recognition; p–p stacking; podands; tropylium tetrafluoroborate
INTRODUCTION
number of tropyliophanes, which have the tropylium ion
as a part of the molecular skeleton, and other macrocyclic
compounds containing tropylium ion have been synthe-
sized.8–10
Crown ethers and their acyclic analogues, podands,1 are
of wide interest because of their tendency to form
complexes with cations and uncharged organic mol-
ecules. The research on crown ethers and podands has
mostly focused on their complexation with alkali metals,
alkaline earth metals and ammonium cations, but
complexation has also been demonstrated with diazo-
nium, hydronium, acylium and hydrazinium species.2
Recently, investigations in host–guest chemistry have
focused on molecular recognition and the potential of p–
p interactions to secure strong and selective binding for
organic molecules. We have demonstrated that p–p
stacking and cation–p interactions play a significant role
in the host–guest complexation between benzene-sub-
stituted crown ethers and electron-deficient aromatic
carbenium ions such as tropylium3,4 and pyridinum.5
Tropylium ion has been shown to be an ideal guest for
investigation of p–p interactions. It is a monocharged
organic cation containing an even number of electrons
and as such represents a new type of guest in host–guest
chemistry. That tropylium ion is an effective p-acceptor
is exemplified by the successful synthesis of many
intramolecular and intermolecular charge-transfer com-
plexes with aromatic hydrocarbons.6,7 In addition, a large
The capability of podands for complex formation with
organic molecules depends on several factors, including
the number and nature of the donor atoms, ring size,
substituents and topological and conformational proper-
ties.1 The selectivity and binding efficiency of podand
molecules can be improved by adding functional groups
in terminal position(s), while their wrap-around cap-
ability can be modified through substitution of the
polyether chain. The aromatic end groups should be
such as to allow p–p stacking interaction with aromatic
guests. Likewise, enlargement of the aromatic surface in
podands would be expected to improve and strengthen
the complexation with an aromatic guest.
Here we report the synthesis and characterization of a
series of podands bearing aromatic substituents at both
ends of the oligoether chain. The capability of the
podands for complexation with an organic guest was
studied with tropylium tetrafluoroborate in 1,2-dichloro-
ethane (DCE) by UV–visible absorption spectrophoto-
metry. An important aim of the study was to determine
the influence of the macrocyclic effect, donor atoms and
aromatic substituents on the complexation of aromatic
cations. A comparison between crown ethers and
podands was undertaken as it was expected to be
informative for the development of new tweezer-type
hosts capable of p–p binding with cationic organic
molecules.
*Correspondence to: J. Pursiainen, Department of Chemistry,
University of Oulu, Linnanmaa, P.O. Box 333, FIN-90571 Oulu,
Finland.
E-mail: pursi@cc.oulu.fi
Copyright 1999 John Wiley & Sons, Ltd.
CCC 0894–3230/99/070557–07 $17.50

¨ ¨
M. LAMSA, K. RAITAMAA AND J. PURSIAINEN
558
tropylium tetrafluoroborate was followed by absorption
RESULTS AND DISCUSSION
changes in the UV–visible spectra. Except for P9, a
yellow–orange colour developed spontaneously upon the
addition of podand to a solution of tropylium tetrafluoro-
borate in dry DCE. The anthracene-substituted podand
P9 behaved differently; its addition to a solution of
tropylium ion in DCE induced the development of
intense red colour. The electronic spectrum of the
substituted podands in the presence of tropylium ion
exhibited a broad wavelength absorption at 300–600 nm.
For example, the addition of 3-methoxybenzene-sub-
stituted podand (P3) to DCE solutions containing
tropylium salt led to the appearance of a new absorption
band with maximum at about 465 nm, not found in the
spectrum of either tropylium tetrafluoroborate or P3. The
intensity of the new band increased with the incremental
additions of podand. The band is indicative of a charge-
transfer interaction and the formation of a molecular
complex between tropylium ion and the podand (Fig. 1).
The substantial hypsochromic (blue) shift from 468 to
435 nm accompanying the change from DCE to MeCN as
solvent (Fig. 2) is in accordance with the solvent
sensitivity of a charge-transfer band.
Synthesis
Our aim was to prepare acyclic analogues of previously
investigated benzene-substituted crown ethers, which
contain multiple binding sites bearing aromatic substi-
tuents. In particular, we were interested in the introduc-
tion of large aromatic substituents at the end of the
acyclic polyether chain. We applied the ‘end group
concept’11 to imitate the structure of crown ethers
substituted with benzene or other aromatic groups. In
essence, this is the recognition that when conformation-
ally flexible systems are rigidified, they become stronger
complexing agents and form more ordered crystals.
Aromatic groups were introduced into the terminal
positions by the Williamson ether synthesis (Scheme
1). The reactants were dichlorinated or ditosylated
glycols were prepared from the respective glycols and
commercially available aromatic alcohols. The 4-(ben-
zyloxy)phenyl-substituted podands P5 and P6 are also
precursors for the dibenzo-substituted crown ethers
2B28C8 and 2B34C10, respectively.12
Several combinations of bases and solvents tested in
the preparation of an anthracene-substituted podand from
chlorinated or tosylated glycols and 2-aminoanthracene
or 2-hydroxyanthracene, but without success. However, a
reaction between 9-(hydroxymethyl)anthracene and
triethylene glycol ditosylate in the presence of sodium
hydride led to the anthracene-substituted podand 1,12-
bis(9-anthryl)-2,5,8,11-tetraoxadodecane (P9).
The method of continuous variation, or Job’s meth-
od,13 was used to confirm the stoichiometry of the
complex. As can be seen in Fig. 3, the occurrence of a
maximum at a mole fraction of 0.5 implies that only one
complex (1:1) was present under the conditions used.
Typical double-reciprocal plots for the podand–tropy-
lium ion complexes revealed a linear relationship for the
entire range of concentrations tested. This was further
evidence for the 1:1 stoichiometry of the complexes in
solution. Values for the stability constants K and molar
absorptivities of complex "C in DCE for podand–
tropylium ion complexes were calculated by the Rose
and Drago method.3,14 Results are given in Table 1.
Properties of complexes
The complexation behaviour of the podands in DCE with
Scheme 1.
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 557–563 (1999)

COMPLEXATION OF PODANDS WITH TROPYLIUM TETRAFLUOROBORATE
559
Figure 2. Absorption spectra of P3±tropylium tetra¯uoro-
borate complex in DCE and MeCN solutions at 25°C. The
change of solvent from DCE to MeCN is accompanied by a
hypsochromic shift (33 nm)
Figure 1. Absorption spectra of tropylium tetra¯uoroborate
3
(2.0 Â 10 M) in DCE solutions at 25°C in the presence of
increasing amounts of P3: (1) 0, (2) 0.006, (3) 0.012, (4)
0.024, (5) 0.036, (6) 0.048 and (7) 0.06 M
The data in Table 1 suggest that stepwise extension of
the polyether chain does not lead to an enhancement of
the binding of the tropylium ion. Likewise, the values of
the stability constant generally responded only slightly to
changes in the aromatic substituent. Again, the anthra-
cene-substituted podand P9 constitutes an exception; the
value of the stability constant of P9 (85.5 Æ 4.3
dm3 mol 1) is 10 times larger than the values for the
other podands studied. The number of oxygen atoms
involved in the complexation with tropylium ion
has an impact on the stability of the complexes. Com-
parison of the K values3 of 0.7 Æ 0.1 dm3 mol 1 for 1,4-
diphenoxybutane–tropylium (1,4-diPhBu) and 1.5 Æ 0.2
Figure 3. Job plot for P3±tropylium tetra¯uoroborate in DCE
at 25°C, ꢀ = 425 nm
Table 1. Stability constants, molar absorptivities of complexes and free energies of binding for the interaction of podands with
tropylium ion in 1,2-dichloroethane solution at 25°Ca
"
C
1
1
1
Podand
ꢀmax (nm)
K (dm3 mol
)
(dm3 mol 1 cm
)
DG° (kJ mol
)
r2
P1
P2
P3
P4
P5
P6
P7
P8
410
425
465
475
460
450
470
430
502
435
425
425
423
7.6 Æ 1.0
5.9 Æ 2.3
5.1 Æ 0.7
5.2 Æ 0.5
7.7 Æ 1.7
6.7 Æ 1.2
7.1 Æ 0.4
8.4 Æ 3.3
86.2 Æ 4.6
128.5 Æ 4.1
662 Æ 43
726 Æ 199
791 Æ 82
573 Æ 43
710 Æ 123
909 Æ 108
1408 Æ 69
1447 Æ 353
1765 Æ 31
1575 Æ 18
1060 Æ 13
—
5.01
4.42
4.05
4.06
5.05
4.73
4.85
5.28
11.05
12.04
13.91
—
0.9966
0.9719
0.9995
0.9997
0.9977
0.9969
0.9999
0.9809
0.9995
—
P9
2B18C6b
2B24C8b
1,4-DiPhBuc
1,8-DiPhOcc
273.5 Æ 13.8
0.7 Æ 0.1
—
—
—
1.5 Æ 0.2
—
—
a
Values were calculated from the absorbance at selected wavelength by the method of Rose and Drago, Eqn. (1). Crown ethers are included for
comparison.
b Ref. 3.
c
Ref. 4.
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 557–563 (1999)

¨ ¨
M. LAMSA, K. RAITAMAA AND J. PURSIAINEN
560
1
dm3 mol for 1,8-diphenoxyoctane–tropylium (1,8-di-
PhOc) in DCE at 25°C with our present K values shows
that the stability of the complexes increases with
increasing number of oxygen donors in the acyclic chain
(Table 1). The length of the carbon chain in 1,8-
diphenoxyoctane is the same as in P2, and equal to the
length of the opened macrocycle of 12-crown-4 or half of
the length of opened macrocycle of 24-crown-8. The
crown ethers dibenzo-24-crown-8 (2B24C8) and diben-
zo-30-crown-10 (2B30C10) are the cyclic counterparts of
the podands P1 and P2, and the stability constants of 274
1
1
dm3 mol for 2B24C8–tropylium3 and 418 dm3 mol
for 2B30C10–tropylium complexes3 in DCE at 25°C
demonstrate that the steric factors and macrocyclic nature
of the host molecule play an important role in the
complexation of tropylium ion (Table 1).
Figure 4. Calculated (RHF-AM1) minimum energy confor-
mation of P1±tropylium ion complex
The x-ray crystal structure of the solid 1:1 complex
formed between 2B24C8 and tropylium tetrafluoroborate
has revealed that the electron-deficient tropylium ring is
inserted into the cavity of the macrocycle between two
adjacent benzene rings.15 The data in Table 1 indicate
that the acyclic host molecules are not able to form a
cleft-like cavity stable enough for tropylium cation. The
wrap-around capability of podands has been exploited in
many metal ion complexes.16 In these podand–metal
complexes, cations are surrounded by oxygen atoms and
the addition of suitable end groups enhances the ligand
rigidity sufficiently to permit the isolation of the
complexes. Because of the size and nature of tropylium
ion, a similar wrap-around phenomenon is not encoun-
tered in the podand–tropylium ion systems studied here.
The flexibility of the polyether chain and the weakness of
the p-stacking interaction in the absence of a well shaped
cavity result in relatively weak binding between the
podands and tropylium ion. Substitution of the benzene
rings and increase in the aromatic surface from benzene
to naphthalene both have only a minimal effect on the
stability of the complexes. This observation provides
further evidence that the p–p interaction, face-to-face or
edge-to-face, cannot contribute with full efficacy to the
tropylium complexation with acyclic hosts. The sizeable
stability constant of P9 shows that the structural factors
of the ligands are of considerable importance in the
podand–tropylium ion complexation. Multiple binding is
important in the molecular recognition of both neutral
and charged organic molecules and the requirements of
steric and functional complementarity and spatial
preorganization of the host compound are correspond-
ingly high.17 The attachment of anthracene to the
polyether chain via the methyl group in position 9 and
the area of the aromatic surface differentiate P9 from the
other podands studied. Evidently the spatial preorganiza-
tion and therefore the p–p interaction also have a greater
effect on the stability of the P9–tropylium complex than
on the stability of the other podand complexes in the
present study.
podands with tropylium ion, we carried out semiempi-
rical RHF-AM1 calculations for the P1–tropylium sys-
tem using Gaussian 94.18 As a starting point we took the
crystal structure of the 2B24C8–tropylium tetrafluoro-
borate complex.4 The cyclic structure of the crown ethers
was broken by removing one of the polyether chains and
the counter ion was also taken away. Figure 4 shows the
geometry-optimized structure of the P1-tropylium ion
complex. Dotted lines indicate the possible interactions.
Similar characteristics were also displayed by the
optimized
1,7-bis(phenyl)-1,4,7-trioxaheptane–tropy-
lium and 1,7-bis(3-methoxyphenyl)-1,4,7-trioxaheptane–
tropylium cation structures derived from the unsatis-
factorily solved structure of the 2B18C6–tropylium
tetrafluoroborate complex.4 The observed edge-to-face
interaction between the aromatic units in the calculated
structures differs from the interaction in the crystal
structures of the complexes formed between dibenzo-
crown ethers and tropylium cation, where the face-to-
face stacking is observed.4 The calculated structures
emphasize the importance of the interactions between
oxygen atoms in the podand framework and tropylium
cation. The lower stability constant of the 1,8-diphenox-
yoctane (two oxygen atoms) than P1 (four oxygen atoms)
complexes in DCE solution (Table 1) agrees well with the
importance of direct interactions between oxygen atoms
and the tropylium ion. Additionally, we have previously
observed by fast atom bombardment mass spectrometry
that tropylium ions form complexes in the gas phase with
acyclic polyethers without aromatic substituents in the
polyether chain.19
CONCLUSIONS
The intermolecular interactions in the complexation of
organic guest molecules are essentially weaker than those
in the complexation of metal ions. Among the non-
covalent intermolecular forces that contribute to the
complex formation between podand and tropylium ion
are cooperative interactions, such as aromatic–aromatic
In an attempt to shed light on the complexation of
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 557–563 (1999)

COMPLEXATION OF PODANDS WITH TROPYLIUM TETRAFLUOROBORATE
561
p–p interaction between the electron-rich and electron-
deficient aromatic units, CH— O hydrogen bonding
between the polyether oxygen atoms and the tropylium
hydrogen atoms and electrostatic cation–p interactions
between the p-face of an aromatic system and the positive
charge of tropylium ion. The same forces also play a
significant role in self-assembly processes where large
ordered nanometre-scale structures are formed in a
selective way from relatively small molecular com-
pounds. Recently, podands and their complexation
capability have been utilized in supramolecular chem-
istry, most notably in the preparation of rotaxanes and
pseudorotaxanes.20
mixture was allowed to cool to room temperature. The
mixture was partitioned between dichloromethane and
water. The organic layer was separated and washed with
5% NaOH solution, water and brine and dried over
MgSO4. Evaporation gave the crude product, which was
subjected to further purification.
1,10-Diphenyl-1,4,7,10-tetraoxaundecane (P1). The
compound was prepared in 75% yield by literature
method.23 White crystals; m.p. 43°C (lit. 43.5–45°C);23
1H NMR (CDCl3, 25°C), ꢁ 7.22–7.32 (4H, aryl, m),
6.87–6.92 (6H, aryl, m), 4.13 (4H, a-CH2, t, J = 4.37 Hz),
3.87 (4H, b-CH2, J = 4.6 Hz, t), 3.76 (4H, g-CH2, s); 13
C
NMR (CDCl3, 25°C), ꢁ 68.1, 70.5, 71.6, 115.4, 121.5,
‡
130.1; EI MS (70 eV), m/z 302 [M ]; HRMS (EI),
calculated 302.1518, observed 302.1512.
EXPERIMENTAL
Materials and methods. The starting materials were
purchased from commercial sources and used without
further purification, unless mentioned otherwise. Aceto-
nitrile (MeCN) (Fluka, Buchs, Switzerland) and 1,2-
dichloroethane (DCE) (Lab-Scan, Dublin, Ireland) were
dried and distilled according to literature procedures.21
1,8-Dichloro-3,6-dioxaoctane and 1,11-dichloro-3,6,9-
trioxaundecane were prepared by a literature method22
from triethylene glycol (Fluka) and tetraethylene glycol
(Fluka), respectively. Thin-layer chromatography (TLC)
was carried out on aluminium plates coated with silica
gel. Compounds were detected by UV radiation measure-
ment. Flash column chromatography was performed on
1,13-Diphenyl-1,4,7,10,13-pentaoxatridecane
(P2).
1,11-Dichloro-3,6,9-trioxaundecane was converted to
the title product and isolated as a colourless oil in 84%
1
yield by distillation. B.p. 151°C (0.1 mmHg); H NMR
(CDCl3, 25°C), ꢁ 7.21–7.31 (4H, aryl, m), 6.81–6.98
(6H, aryl, m), 4.12 (4H, a-CH2, m), 3.87 (4H, b-CH2, m),
3.87 (8H, g-Z-CH2, m); 13C NMR (CDCl3, 25°C), ꢁ 68.2,
70.5, 71.4, 115.5, 121.6, 130.1, 159.8; EI MS (70 eV), m/
‡
‡
z 346 [M ]; CI (NH3) MS, m/z 365 [M ‡ NH3] ; HRMS
(EI), calculated 346.4224, observed 346.1777.
1,10-Bis(4-methoxyphenyl)-1,4,7,10-tetraoxaunde-
cane (P3). Recrystallization from EtOH afforded the title
compound as a white crystalline solid in 96% yield. M.p.
70°C; 1H NMR (CDCl3, 25°C), ꢁ 6.78 (8H, aryl, s), 5.18
(4H, a-CH2, m), 3.60–3.80 (6H, OCH3, 4H, 8H, g-Z-CH2,
m); 13C NMR (CDCl3, 25°C), ꢁ 43.4, 56.5, 71.3, 72.1,
1
silica gel with the solvents specified. H and 13C NMR
spectra were recorded on a Bruker AM200 spectrometer.
NMR chemical shifts are reported in ppm downfield from
internal tetramethylsilane (TMS). The coupling constants
are expressed in Hz. Electron ionization (EI) and fast
atom bombardment (FAB) mass spectra were obtained
using a Kratos MS 80 mass spectrometer operating with
the DART data system. Ultraviolet–visible (UV–visible)
spectra were recorded with a Philips PU 8740 spectro-
photometer and matched glass cells of 10 mm pathlength.
The cell containing the solution was maintained within to
Æ0.05°C of a set temperature by circulating water from a
thermostated bath through a double-walled cell insert.
The temperature inside the cell was monitored with a
digital thermometer. Small amounts of the compounds
were accurately weighed with a Perkin-Elmer AD-2
autobalance. Elemental analysis was carried out with a
Perkin-Elmer 2400 apparatus. Melting points (m.p.) were
determined with a Thermopan microscope (Reichert,
Vienna, Austria) melting-point apparatus and are un-
corrected.
‡
115.6, 116.7, 150.2, 154.4; EI MS (70 eV), m/z 362 [M ],
‡
CI (NH3) MS, m/z 380 [M ‡ NH3] ; HRMS (EI),
calculated 362.1729, observed 362.1712.
1,13-Bis(4-methoxyphenyl)-1,4,7,10,13-pentaoxatri-
decane (P4). Subjection of the colourless oil to silica gel
column chromatography with EtOAc–n-hexane (1:1) as
1
the eluent afforded P4 in 82% yield. H NMR (CDCl3,
25°C), ꢁ 6.78–6.88 (8H, aryl, m), 4.06 (4H, a-CH2, t,
J = 4.8 Hz), 3.82 (4H, b-CH2, t, J = 4.8 Hz), 3.75 (6H,
OCH3, s), 3.70 (8H, g-Z-CH2, m); 13C NMR (CDCl3,
25°C), ꢁ 56.3, 68.7, 70.5, 71.3, 71.4, 115.2, 153.6, 154.5;
‡
EI MS (70 eV), m/z 406 [M ]; HRMS (EI), calculated
406.1991, observed 406.1966.
1,8-Bis[(4-benzyloxy)phenoxy]-3,6-dioxaoctane (P5). 4-
Benzyloxyphenol (Aldrich, Milwaukee, WI, USA) was
used as a starting material. The crude product was
recrystallized from CH2Cl2–Et2O affording a white
General procedure for the synthesis of substituted
podands P1±P8. A mixture of NaOH (2.04 g, 0.051 mol),
aromatic alcohol (0.05 mol) and dichloroglycol
(0.025 mol) was stirred and heated at reflux in 20 ml of
H2O–EtOH (1:1) for 16–24 h, after which the reaction
1
crystalline solid in 28% yield. M.p. 110°C; H NMR
(CDCl3, 25°C), ꢁ 7.30–7.40 (10H, aryl, m), 6.81–6.91
(8H, aryl, m), 5.00 (4H, CH2, s), 4.08 (4H, a-CH2, t,
J = 4.8 Hz), 3.83 (4H, b-CH2, J = 4.8 Hz, t), 3.74 (4H, g-
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 557–563 (1999)

¨ ¨
M. LAMSA, K. RAITAMAA AND J. PURSIAINEN
562
CH2, s); 13C NMR (CDCl3, 25°C), ꢁ 68.8, 70.6, 71.4,
compound as a light yellow crystalline solid in 23%
yield. M.p. 73°C; H NMR (CDCl3, 25°C), ꢁ 8.39 (6H,
1
71.5, 116.3, 116.5, 128.2, 128.6, 129.2, 153.9; EI MS
‡
(70 eV), m/z 514 [M ]; HRMS (EI), calculated 514.2355,
aryl, d, J = 10.5 Hz), 7.97 (4H, aryl, dd, J = 9.4 Hz), 7.38–
7.55 (8H, aryl, m), 3.72–3.78 (4H, a-CH2, m), 3.63–3.67
(4H, b-CH2, m), 3.63 (4H, g-CH2, s); 13C NMR (CDCl3,
25°C), ꢁ 66.0, 70.2, 71.4, 71.6, 125.1, 125.6, 126.8,
observed 514.2359.
1,11-Bis[(4-benzyloxy)phenoxy]-3,6,9-trioxaundecane
(P6). The white solid was obtained after recrystallization
‡
129.0, 129.5, 129.6, 132.1; EI MS (70 eV), m/z 530 [M ],
1
from CH2Cl2–Et2O, yield 88%. M.p. 84°C; H NMR
HRMS (EI), calculated 530.2457, observed 530.2420.
(CDCl3, 25°C), ꢁ 7.30–7.43 (10H, aryl, m), 6.80–6.91
(8H, aryl, m), 5.00 (4H, CH2, s), 4.07 (4H, a-CH2, t,
J = 4.8 Hz), 1.98 (4H, a-CH2, t, J = 4.8 Hz), 3.70 (8H, g-
-CH2, m); 13C NMR (CDCl3, 25°C), ꢁ 68.1, 69.8, 70.6,
70.7, 70.8, 115.6, 115.7, 127.5, 127.9, 128.5, 137.3,
1,3,5-Cycloheptatrienylium tetra¯uoroborate. Tropy-
lium salt was prepared according to literature proce-
dures;25 m.p. 203°C (decomp.); 1H NMR (CD3CN,
30°C), ꢁ 9.24 (7H, s).
‡
153.1; EI MS (70 eV), m/z 558 [M ]; HRMS (EI),
calculated 558.2617, observed 558.2614.
Complexation studies. Stability constant determina-
tion by UV±visible spectrophotometry. The stability
constant for 1:1 complexation was defined by a method
described in detail elsewhere.3 The absorption measure-
ments were made immediately after the mixing of podand
and tropylium solutions. The Rose–Drago equation:
1,10-Dinaphthalene-1,4,7,10-tetraoxaundecane (P7).
Evaporation gave the solid, which was recrystallized
from CH2Cl2–Et2O in 37% yield. M.p. 77–78°C; H
NMR (CDCl3, 25°C), ꢁ 7.66–7.77 (6H, aryl, m), 7.27–
7.48 (4H, aryl, m), 7.09–7.22 (4H, aryl, m), 4.23 (4H, a-
CH2, m), 3.91 (4H, b-CH2, m), 3.57–3.80 (4H, g-CH2,
m); 13C NMR (CDCl3, 25°C), ꢁ 67.5, 69.8, 70.6, 71.0,
106.8, 119.0, 123.6, 126.3, 126.8, 127.6, 129.1, 129.4,
1
1
A
A0
CDCAꢀ"C "A†
ˆ
CA CD ‡
ꢀ1†
K
"
C
"
A
A0
A
‡
where A0 is the absorbance of pure acceptor solution, A is
the absorbance of the acceptor–donor solution, CA and
CD are the initial concentrations of acceptor and donor,
and "C and "A are the molar absorptivities of complex and
acceptor in solution, respectively, contains two unknown
constants, K and "C, which were evaluated by an iteration
method with a PC implementing the SigmaPlot 4.0
program.26 The program relies on a least-squares
procedure with the Marquardt–Levenberg algorithm.27
The errors in K and "C were evaluated numerically by
standard deviations of single K and "C values usually
obtained from 6–10 measurements.
134.5, 136.3, 156.7; EI MS (70 eV), m/z 402 [M ];
HRMS (EI), calculated 402.1831, observed 402.1813.
1,13-Dinaphthalene-1,4,7,10,13-pentaoxatridecane
(P8). Evaporation gave the white solid, which was
recrystallized from CH2Cl2–Et2O in 76% yield. M.p.
1
44–46°C; H NMR (CDCl3, 25°C), ꢁ 7.65–7.78 (6H,
aryl, m), 7.26–7.48 (4H, aryl, m), 7.09–7.21 (4H, aryl,
m), 4.23 (4H, a-CH2, m), 3.91 (4H, b-CH2, m), 3.57–3.80
(10H, g-Z-CH2, m); 13C NMR (CDCl3, 25°C), ꢁ 67.4,
69.7, 70.7, 70.8, 106.8, 119.0, 123.6, 126.3, 126.7, 127.6,
‡
129.0, 129.3, 134.5, 156.7; EI MS (70 eV), m/z 446 [M ];
HRMS (EI), calculated 446.2093, observed 446.2105.
1,12-Bis(anthryl-9)-2,5,8,11-tetraoxadodecane (P9). At
room temperature, to a solution of 9-hydroxymethylan-
thracene (1.12 g, 5.36 mmol) (Aldrich) in dry DMF
(40 ml) was added dropwise with stirring NaH 0.28 g
(5.5 mmol, 50% in mineral oil, washed previously with n-
pentane) in dry DMF (10 ml). Stirring was continued for
30 min after completion of the addition. A dry DMF
solution (10 ml) of triethylene glycol ditosylate24 (1.23 g,
2.68 mmol) was then introduced dropwise. The reaction
mixture was warmed for 18 h at 80°C before cooling to
room temperature. The excess of NaH was quenched by
the addition of a few drops of water, then the solvent was
removed in vacuo and the residue was partitioned
between water (30 ml) and dichloromethane (40 ml).
The organic layer was washed twice with 2 M HCl, water
and brine and dried over MgSO4. Evaporation gave the
crude product, which was subjected to silica gel column
chromatography with EtOAc–n-hexane (1:1) as the
eluent. Recrystallization from EtOH afforded the title
Acknowledgements
We thank Mrs Pa¨ivi Joensuu for the mass spectra.
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