Novel 4,4′-bipyridinium-based cationic mono- and bicyclic cyclophanes

Article abstract of DOI:10.1002/ejoc.200390183

The intra-annularly functionalised tetracationic cyclophanes 3a-b were synthesised from the corresponding m-terphenyl dibromides and 4,4′-bipyridine by a simple quaternisation methodology. An intra-annularly linked tetracationic cyclophane 10 was synthesised in three steps and it possesses a concave structure and novel intramolecular CT interactions. Synthesis of the tetracationic cyclophanes 13, 16a and 16b containing carbonyl groups was accomplished from the corresponding carbonyl dibromides and 4,4′-bipyridine. Sixfold coupling of a tricarbonyl tribromide with 4,4′-bipyridine afforded a rare hexacationic cyclophane 18. The cyclophanes 3a and 3c form CT complexes with a bis(1H-indol-3-yl)-(phenyl)methane compound while the cyclophane 13 forms CT complexes with 1,4-dimethoxybenzene and indole. Electrochemical parameters were obtained for all the cyclophanes. They exhibit two sets of redox peaks and most of them are quasireversible. The smallest-cavity cyclophane 13 has the lowest reduction potentials in the series. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200390183

FULL PAPER
Novel 4,4Ј-Bipyridinium-Based Cationic Mono- and Bicyclic Cyclophanes
Perumal Rajakumar*[a] and Kannupal Srinivasan[a]
Keywords: Charge transfer / Cyclophanes / Electrochemistry / N ligands
The intra-annularly functionalised tetracationic cyclophanes
3a−b were synthesised from the corresponding m-terphenyl
forded a rare hexacationic cyclophane 18. The cyclophanes
3a and 3c form CT complexes with a bis(1H-indol-3-yl)-
dibromides and 4,4Ј-bipyridine by a simple quaternisation (phenyl)methane compound while the cyclophane 13 forms
methodology. An intra-annularly linked tetracationic cyclo- CT complexes with 1,4-dimethoxybenzene and indole. Elec-
phane 10 was synthesised in three steps and it possesses a trochemical parameters were obtained for all the cyclo-
concave structure and novel intramolecular CT interactions.
phanes. They exhibit two sets of redox peaks and most of
Synthesis of the tetracationic cyclophanes 13, 16a and 16b
them are quasireversible. The smallest-cavity cyclophane 13
containing carbonyl groups was accomplished from the cor- has the lowest reduction potentials in the series.
responding carbonyl dibromides and 4,4Ј-bipyridine. Sixfold ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
coupling of a tricarbonyl tribromide with 4,4Ј-bipyridine af- Germany, 2003)
Introduction
Results and Discussion
Mechanically interlocked compounds such as rotaxanes
and catenanes are increasingly attracting synthetic chemists’
attention because of their ability to provide the basic ele-
ments for constructing nanoscale devices in the future.[1]
The Stoddart cyclophane, cyclobis(paraquat-p-phenylene),
derived from p-xylenyl dibromide and 4,4Ј-bipyridine, has
been employed for the construction of a number of rotax-
anes and catenanes based on its ability to form inclusion
complexes with π-electron-rich aromatic molecules.[2] Re-
placement of either the bipyridinium recognition sites or
the p-phenylene spacers of the Stoddart cyclophane with
other recognition sites or aromatic spacers has led to novel
tetracationic cyclophanes with potential applications.[3] We
are interested in incorporating m-terphenyl building blocks
into cyclophane structures[4] because such cyclophanes pos-
sess noncollapsible rigid cavities with intra-annular func-
tionality. Furthermore, the cavities of such cyclophanes
would be large and could form complexes with large elec-
tron-rich guest molecules. Introduction of carbonyl groups
into the aromatic spacers would be more promising because
we could study the effect of the electron-deficient carbonyl
groups on the complexing ability of such cyclophanes.
Herein we report syntheses and electrochemical properties
of some novel tetra- and hexacationic cyclophanes
possessing mono- and bicyclic structures incorporating the
4,4Ј-bipyridinium building unit.
Cyclophanes with m-Terphenyl Spacers
The synthetic methodology employed for the syntheses
of these cyclophanes closely parallels that reported pre-
viously by the Hünig[5] and Stoddart[6] groups. Heating one
equivalent of one of the m-terphenyl dibromides[7] 1aϪd
with five equivalents of 4,4Ј-bipyridine in acetonitrile under
reflux afforded a mixture of dicationic precyclophanes
2aϪd and tetracationic cyclophanes 3aϪd in 66Ϫ82% over-
all yields after counterion exchange with NH4PF6. The for-
mation of tetracationic cyclophanes may be attributable to
the angular nature of the m-terphenyl dibromides, which
favoured the [2ϩ2] macrocyclisation. Analysis of the 1H
NMR spectra of these mixtures revealed that about
10Ϫ50% of the tetracationic cyclophanes 3aϪd were pre-
sent along with the dicationic precyclophanes 2aϪd. With-
out separation, the mixtures were heated under reflux with
a slight excess of a m-terphenyl dibromide under high di-
lution conditions to afford the tetracationic cyclophanes
3aϪd in 16Ϫ25% yields after column chromatography and
counterion exchange. One-pot syntheses were also carried
out by heating equimolar mixtures of 1aϪd and 4,4Ј-bipyri-
dine in acetonitrile under reflux under high dilution con-
ditions, and this method gave the tetracationic cyclophanes
3aϪd in yields similar to the two-step procedure
(Scheme 1). All the cyclophanes were thoroughly character-
ised by spectroscopic and analytical data.
MOPAC calculations (PM3) indicated the cavity size of
˚
[a]
3a was 12.8 ϫ 13.2 A, which was further confirmed by
Department of Organic Chemistry, University of Madras,
XRD studies.[8] The ORTEP plot of the crystal structure of
3a is shown in Figure 1. The centrosymmetric macrocyclic
tetracation as a whole assumes a chair-like conformation.
Guindy Campus,
Chennai-600 025, Tamil Nadu, India
Fax: (internat.) ϩ 91Ϫ44Ϫ2352494
E-mail: perumalrajakumar@hotmail.com
1277
Eur. J. Org. Chem. 2003, 1277Ϫ1284  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/03/0407Ϫ1277 $ 20.00ϩ.50/0

P. Rajakumar, K. Srinivasan
FULL PAPER
Scheme 1. Reagents and conditions: i) 4,4Ј-bipyridine (5 equiv.), CH3CN, reflux, 30 h, then NH4PF6, CH3CN, 66Ϫ82%; ii) 1aϪd, CH3CN,
reflux, 48 h, then NH4PF6, H2O; afforded 3a (25%), 3b (19%), 3c (16%) and 3d (27%); iii) 4,4Ј-bipyridine (1 equiv.), CH3CN, reflux, 48 h,
then NH4PF6, H2O; afforded 3a (18%), 3b (22%), 3c (15%) and 3d (28%)
Two hexafluorophosphate anions are inserted into the
We were also interested in replacing one of the p-phenyl-
cavity of the tetracation and the other two anions are ene spacers of the Stoddart cyclophane with a m-terphenyl
situated away from the cavity. Four water molecules are unit for the comparison of their complexation behaviours.
partly inserted into the cavity. The two outer rings of the Thus, the cyclophanes 5a and 5b were synthesised by heat-
m-terphenyl unit are twisted from the central ring by 24.7° ing an equimolar mixture of the bispyridinium salt 4 and
and 18.9°, respectively, and this flexibility allows the forma- 1a/1d under reflux (Scheme 2).
tion of these cyclophanes without the use of any templates
in better yields as compared with that of the Stoddart cyclo-
phane.
Scheme 2. Reagents and conditions: i) 1a/1d, CH3CN, reflux, 48 h,
then NH4PF6, H2O; afforded 5a (23%) and 5b (27%)
By connecting two m-terphenyl units through their 2Ј-
positions with a tethering unit, followed by linking the
outer rings with bipyridinium moieties, it is possible to con-
struct bicyclic cyclophanes. The novelty of the resulting bi-
cyclic cyclophanes is twofold. If the tethering unit con-
necting the two m-terphenyl units is long enough, then the
cyclophane can be expected to possess a concave nature
and, hence, can undergo an umbrella inversion process.
Furthermore, if the unit used for the intra-annular connec-
tion is electron rich, the cyclophane will have two peripheral
electron-deficient layers and an electron-rich middle layer
like a capacitor and, hence, can show novel CT interactions.
Figure 1. ORTEP plot of the crystal structure of 3a; the coun-
terions and water molecules are omitted for clarity
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Eur. J. Org. Chem. 2003, 1277Ϫ1284

Novel 4,4Ј-Bipyridinium-Based Cationic Mono- and Bicyclic Cyclophanes
FULL PAPER
Cyclophanes with Aromatic Carbonyl Spacers
To introduce carbonyl groups into the structures of the
tetracationic cyclophanes, the carbonyl dibromides 11, 14a
and 14b were chosen to provide the aromatic spacers. These
dibromides were prepared by the FriedelϪCrafts acylation
of the corresponding aromatic acid chlorides with toluene
followed by twofold radical bromination with NBS. Reac-
tion of five equivalents of 4,4Ј-bipyridine with one equiva-
lent of dibromides 11, 14a and 14b in refluxing acetonitrile
gave the dicationic precyclophanes 12, 15a and 15b in 68,
80 and 77% yields, respectively, after counterion exchange.
These precyclophanes were then heated under reflux with a
slight excess of the dibromides 11, 14a and 14b to give the
tetracationic cyclophanes 13, 16a and 16b containing car-
bonyl groups in 16, 12 and 14% yields, respectively, after
column chromatography and counterion exchange
(Scheme 4).
A bicyclic cyclophane 18 with a fascinating tris(paraquat)
cage was derived from the tricarbonyl tribromide 17 as
shown in Scheme 5. This hexacationic cyclophane was ob-
tained in 3% yield by a sixfold coupling of two equivalents
of the tribomide 17 with three equivalents of 4,4Ј-bipyri-
dine, followed by column chromatography and counterion
exchange. It is noteworthy to mention that such cyclo-
phanes with hexacationic cage are rare in the literature.
Such cyclophanes in general cannot be detected by mass
spectrometry.[9] 1H NMR and 13C NMR spectra, however,
supported the proposed cage structure for the cyclophane
18.
Scheme 3. Reagents and conditions: i) NaH, DMF, 80 °C, 48 h,
22%; ii) NBS, Bz2O2, CCl4, reflux, 40 h, 80%; iii) 4,4Ј-bipyridine (2
equiv.), CH3CN, reflux, 24 h, then NH4PF6, H2O, 60%
Complexation Studies
We investigated the complexation behaviour of the cyclo-
phanes 3aϪd with several electron-rich guest molecules like
1,4-dimethoxybenzene, 1,4-bis(2-hydroxyethoxy)benzene,
Synthesis of an intra-annularly linked bicyclic cyclophane indole, ferrocene and TTF. The association, however, was
10 is outlined in Scheme 3. Reaction of the sodium salt gen- much too weak to be measured by either UV/Vis or 1H
erated from 1,4-bis(2-hydroxyethoxy)benzene (6) and NaH NMR spectroscopic techniques. Even when one of the p-
with two equivalents of m-terphenyl acid chloride 7 in phenylene spacers of the Stoddart cyclophane was replaced
DMF gave the diester 8 in 22% yield. Fourfold radical bro- by a m-terphenyl spacer, as in the case of cyclophanes 5a
mination of 8 using NBS and Bz2O2 in CCl4 afforded the and 5b, formation of CT complexes could not be detected
tetrabromide 9 in 80% yield. Heating two equivalents of by UV spectroscopy. This phenomenon is due to the large
4,4Ј-bipyridine with one equivalent of 9 under reflux gave cavity size that nullifies the πϪπ stacking interactions be-
the bicyclic cyclophane 10 in 60% yield after column chro- tween the complementary aromatic units of the host and
matography and counterion exchange.
the guest.[10] These cylophanes, however, formed CT com-
MOPAC calculations (PM3) indicated a concave struc- plexes with electron-rich guest molecules of larger size. For
ture for the cyclophane 10 with the hydroquinone ring con- example, while mixing an equimolar solution of 3a with
stituting the bottom portion. Its 1H NMR spectrum bis(1H-indol-3-yl)(phenyl)methane in MeCN, a deep red
showed an upfield change in chemical shift of δ ϭ 0.54 ppm colour developed with a CT band centred around 497 nm
for the hydroquinone protons as compared with the hydro- (ε ϭ 1667 Ϫ1cmϪ1) with an association constant (Ka) of
quinone protons in 9 and, hence, there should be intramo- 12 Ϫ1 (determined by BenesiϪHildebrand method[11]).
lecular CT interactions between the hydroquinone unit and Similarly, the CT complexes of the cyclophane 3c with
the bipyridinium moieties. We tried to investigate the um- bis(1H-indol-3-yl)(phenyl)methane gave a value of Ka of 18
brella inversion process of the cyclophane 10 by variable- Ϫ1 at 492 nm (ε ϭ 1111 Ϫ1cmϪ1). The formation of CT
1
temperature H NMR spectroscopy. The inversion process, complexes was also studied for the cyclophane 13, which
1
however, was too fast on the H NMR time scale and no has a relatively smaller cavity. It formed CT complexes with
coalescence was observed between the temperatures of 22 smaller electron-rich guest molecules, like 1,4-dimeth-
°C and 140 °C in DMSO.
oxybenzene and indole with association constants of 0.46
Eur. J. Org. Chem. 2003, 1277Ϫ1284
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P. Rajakumar, K. Srinivasan
FULL PAPER
Scheme 4. Reagents and conditions: i) 4,4Ј-bipyridine (5 equiv.), CH3CN, reflux, 30 h, then NH4PF6, CH3CN; afforded 12 (68%), 15a
(80%) and 15b (78%); ii) 11, CH3CN, reflux, 48 h, then NH4PF6, H2O, 16%; iii) 14a/14b, CH3CN, reflux, 48 h, then NH4PF6, H2O;
afforded 16a (12%) and 16b (14%)
Scheme 5. Reagents and conditions: i) 4,4Ј-bipyridine (3 equiv. for 2 equiv. of 17), CH3CN, reflux, 72 h, then NH4PF6, H2O, 3%

Ϫ1and 0.62 Ϫ1, respectively. The smaller magnitudes of shown in Table 1. Among the cyclophanes containing m-
these values of Ka could be due to the loss of rigidity of the terphenyl spacers, the cyclophanes 3a, 3d and 10 showed
cavities of the host molecules as well as the minimised two reversible one-electron redox processes (for which we
πϪπ stacking interactions resulting from the presence of found the difference between anodic and cathodic peaks
carbonyl groups.
∆Ep ϭ 74 mV vs. Ag/AgCl in DMSO at room temperature)
as compared with ferrocene. The quasireversibility of the
second redox process of the cylophane 3b, and both the
first and second redox processes of the cyclophane 3c, may
be due to the nature of the intra-annular functional groups.
The cyclophanes 5aϪb showed two sets of quasireversible
peaks because of the presence of nonidentical spacers.
Electrochemical Properties
All the cyclophanes exhibited two sets of redox waves
that are characteristic of paraquat derivatives. The electro-
chemical parameters obtained for the cyclophanes are
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Eur. J. Org. Chem. 2003, 1277Ϫ1284

Novel 4,4Ј-Bipyridinium-Based Cationic Mono- and Bicyclic Cyclophanes
FULL PAPER
and were uncorrected. IR spectra were recorded on Nicolet Impact
400 FT-IR and FTIR-8300 spectrophotometers. 1H and 13C NMR
spectra were recorded on Jeol 400 MHz, Bruker 300 MHz and
Bruker ARX 200 MHz spectrometers. The FAB-MS spectra were
recorded on a Jeol SX 102/DA-6000 mass spectrometer. Ultra-
violet-Visible (UV) spectra were recorded on a Shimadzu 260 spec-
Table 1. The electrochemical parameters obtained for the cyclo-
phanes in DMSO at 25 °C
Cyclo- E1pc
E1pa
E11/2
∆E1p E2pc
E2pa
E21/2
∆E2p
phane[a] (mV) (mV) (mV) (mV) (mV) (mV) (mV) (mV)
3a
3b
3c
Ϫ365 Ϫ287 Ϫ326 78
Ϫ364 Ϫ278 Ϫ321 86
Ϫ381 Ϫ245 Ϫ313 136
Ϫ392 Ϫ326 Ϫ359 66
Ϫ375 Ϫ252 Ϫ314 123
Ϫ381 Ϫ256 Ϫ319 125
Ϫ384 Ϫ310 Ϫ347 74
Ϫ375 Ϫ166 Ϫ271 209
Ϫ343 Ϫ270 Ϫ307 73
Ϫ355 Ϫ235 Ϫ295 120
Ϫ505 Ϫ296 Ϫ401 209
Ϫ733 Ϫ659 Ϫ696 74
Ϫ849 Ϫ653 Ϫ751 196
Ϫ907 Ϫ641 Ϫ774 266
Ϫ758 Ϫ694 Ϫ726 64
Ϫ759 Ϫ640 Ϫ700 119
Ϫ777 Ϫ648 Ϫ713 129
Ϫ755 Ϫ669 Ϫ712 86
Ϫ778 Ϫ563 Ϫ671 215
Ϫ871 Ϫ764 Ϫ818 107
Ϫ746 Ϫ598 Ϫ672 148
Ϫ835 Ϫ773 Ϫ784 102
trophotometer. Elemental analyses were performed on
a
PerkinϪElmer 240B elemental analyzer. Electrochemical studies
were carried out on a CH Instruments electrochemical analyzer.
3d
5a
5b
10
13
16a
16b
18
General Procedure for the Synthesis of Dicationic Precyclophanes:
A solution of the dibromide (2.50 mmol) in dry CH3CN (25 mL)
was added dropwise with stirring to a solution of 4,4Ј-bipyridine
(12.5 mmol) in refluxing dry CH3CN (20 mL) for 6 h under nitro-
gen. The reaction mixture was heated under reflux for further 24 h
and then cooled to room temperature. The precipitated solid was
filtered and washed thoroughly with diethyl ether (20 mL) and
CHCl3 (20 mL). The residue was suspended in CH3CN (20 mL),
solid NH4PF6 (1.00 g) was added, and the mixture was stirred for
30 min and then filtered. The solvent was removed under vacuum;
the residue was washed thoroughly with H2O and then dried to
give the dicationic precyclophane.
[a]
E1 and E2 are the cathodic peak potentials of the first and
pc
pc
second redox processes respectively. E1 and E2 are the anodic
pa
pa
peak potentials of the first and second redox processes respectively.
E1 and E2 are the averages of the cathodic and anodic peak
1/2
1/2
potentials of the first and second redox processes respectively. ∆E1
p
and ∆E2p are the differences between the cathodic and anodic peak
potentials of the first and second redox processes respectively.
Dicationic Precyclophane 2a: From 1a (1.04 g) and 4,4Ј-bipyridine
(1.95 g), the product (1.50 g, 82%) was obtained as a yellow solid,
which contained about 10% of 3a as revealed by 1H NMR spec-
troscopy. The product was used in the next step without separation
or further characterisation.
Among the cyclophanes containing aromatic carbonyl spa-
cers, all the redox processes, except the first redox process
of 16a, were quasireversible because of the presence of car-
bonyl groups. For the cyclophane 13, both the first and se-
cond redox potentials were shifted to less-negative poten-
tials as compared to other cyclophanes. The electrostatic
repulsion between the two positively charged bipyridinium
units is maximised in 13 because it has the smallest cavity
size in the series. This repulsion was decreased significantly
upon reduction and, hence, the ability to accept electrons is
greatest for 13.[12]
Dicationic Precyclophane 2b: From 1b (1.24 g) and 4,4Ј-bipyridine
(1.95 g), the product (1.43 g, 71%) was obtained as a yellow solid,
which contained about 45% of 3b as revealed by 1H NMR spec-
troscopy. The product was used in the next step without separation
or further characterisation.
Dicationic Precyclophane 2c: From 1c (1.15 g) and 4,4Ј-bipyridine
(1.95 g), the product (1.28 g, 66%) was obtained as a yellow solid,
which contained about 25% of 3c as revealed by 1H NMR spec-
troscopy. The product was used in the next step without separation
or further characterisation.
Conclusions
Dicationic Precyclophane 2d: From 1d (1.18 g) and 4,4Ј-bipyridine
(1.95 g), the product (1.35 g, 69%) was obtained as a yellow solid,
which contained about 50% of 3d as revealed by 1H NMR spec-
troscopy. The product was used in the next step without separation
or further characterisation.
Based on Hünig and Stoddart methodology, we have pre-
pared novel mono- and bicyclic tetra- and hexacationic
cyclophanes. Because of their large cavity sizes, the cyclo-
phanes 3a and 3c form CT complexes only with large elec-
tron-rich guest molecules like bis(1H-indol-3-yl)(phenyl)-
methane. The cyclophane 13, however, which has a smaller
cavity, is able to form CT complexes with smaller electron-
rich guest molecules like 1,4-dimethoxybenzene and indole.
The concave cyclophane 10 and the hexacationic cage cyclo-
phane 18 are of interest because of their attractive struc-
tural features. The electrochemical parameters have been
determined for all the cyclophanes. They exhibit two sets of
redox peaks and most of them are quasireversible because
of the presence of functional groups. The reduction poten-
tials are lowest for the smallest-cavity cyclophane 13.
Dicationic Precyclophane 12: From 11 (0.92 g) and 4,4Ј-bipyridine
(1.95 g), 12 (1.16 g, 68%) was obtained as a colourless solid after
recrystallisation from acetone/H2O (9:1). M.p. 244 °C. IR (KBr):
1
ν˜ ϭ 1642 cmϪ1 (CϭO). H NMR (200 MHz, CD3CN): δ ϭ 5.85
(s, 4 H, CH2), 7.60 (d, J ϭ 8.0 Hz, 4 H, Ar-H), 7.83Ϫ7.87 (m, 8
H, Ar-H & bipy-3Ј-H), 8.35 (d, J ϭ 6.2 Hz, 4 H, bipy-3-H),
8.85Ϫ8.88 (m, 8 H, bipy-2 & 2Ј-H) ppm. 13C NMR (50 MHz,
CD3CN): δ ϭ 64.2, 118.1, 122.6, 127.0, 128.3, 129.8, 131.3, 137.9,
141.9, 145.8, 151.6, 195.7 ppm. MS (FAB): m/z ϭ 665 [Mϩ Ϫ PF6].
C35H28F12N4OP2 (810.57): calcd. C 51.86, H 3.48, N 6.91; found
C 51.72, H 3.50, N 7.12.
Dicationic Precyclophane 15a: From 14a (1.18 g) and 4,4Ј-bipyri-
dine (1.95 g), 15a (1.82 g, 80%) was obtained as a colourless solid
after recrystallisation from acetone/H2O (9:1). M.p. Ͼ 208 °C
(dec.). IR (KBr): ν˜ ϭ 1642 cmϪ1 (CϭO). 1H NMR (400 MHz,
[D6]DMSO): δ ϭ 6.02 (s, 4 H, CH2), 7.74 (d, J ϭ 7.8 Hz, 4 H, Ar-
H), 7.84Ϫ7.86 (m, 8 H, Ar-H), 8.01 (d, J ϭ 4.9 Hz, 4 H, bipy-3Ј-
H), 8.65 (d, J ϭ 6.3 Hz, 4 H, bipy-3-H), 8.86 (d, J ϭ 4.9 Hz, 4 H,
Experimental Section
General Remarks: Melting points were determined by the open
capillary tube method using a Toshniwal melting point apparatus
Eur. J. Org. Chem. 2003, 1277Ϫ1284
1281

P. Rajakumar, K. Srinivasan
bipy-2Ј-H), 9.36 (d, J ϭ 6.4 Hz, 4 H, bipy-2-H) ppm. 13C NMR 122.4, 126.5, 127.8, 129.3, 130.0, 134.0, 138.4, 141.6, 146.3, 151.4,
FULL PAPER
(100 MHz, [D6]DMSO): δ ϭ 62.8, 122.3, 126.3, 129.3, 130.0, 130.8,
153.5, 170.3 ppm. MS (FAB): m/z
C62H48F24N4O4P4 (1492.95): calcd. C 49.88, H 3.24, N 3.75; found
ϭ Ϫ 2PF6].
1202 [Mϩ
137.5, 139.1, 140.2, 141.3, 145.9, 151.2, 153.4, 195.1 ppm. MS
(FAB): m/z ϭ 769 [Mϩ Ϫ PF6]. C42H32F12N4O2P2 (914.67): calcd. C 50.01, H 3.12, N 3.66.
C 55.15, H 3.53, N 6.13; found C 55.43, H 3.70, N 6.05.
Tetracationic Cyclophane 3d: From the dicationic precyclophane 2d
(642 mg, 0.35 mmol, based on the amount of 2d present in the mix-
ture) and 1d (190 mg), 3d (463 mg, 27%, based on the amount of
2d present) was obtained as a colourless solid. M.p. Ͼ 300 °C
(dec.). IR (KBr): ν˜ ϭ 1724 cmϪ1 (CϭO). 1H NMR (400 MHz,
[D6]DMSO): δ ϭ 2.97 (s, 6 H, CH3), 5.97 (s, 8 H, CH2), 7.36Ϫ7.63
(m, 22 H, Ar-H), 8.74 (d, J ϭ 6.4 Hz, 8 H, bipy-3-H), 9.47 (d, J ϭ
5.9 Hz, 8 H, bipy-2-H) ppm. 13C NMR (100 MHz, [D6]DMSO):
δ ϭ 51.7, 63.3, 127.4, 128.7, 129.0, 129.6, 130.5, 131.9, 133.9, 138.9,
Dicationic Precyclophane 15b: From 14b (1.18 g) and of 4,4Ј-bipyri-
dine (1.95 g), 15b (1.77 g, 77%) was obtained as a colourless solid
after recrystallisation from acetone/H2O (9:1). M.p. Ͼ 195 °C
(dec.). IR (KBr): ν˜ ϭ 1642 cmϪ1 (CϭO). 1H NMR (200 MHz,
CD3CN): δ ϭ 5.78 (s, 4 H, CH2), 7.51Ϫ8.01 (m, 16 H, Ar-H &
bipy-3Ј-H), 8.26 (d, J ϭ 5.8 Hz, 4 H, bipy-3-H), 8.73Ϫ8.82 (m, 8
H, bipy-2 & 2Ј-H) ppm. 13C NMR (50 MHz, CD3CN): δ ϭ 64.1,
118.0, 122.5, 127.0, 128.3, 129.6, 129.8, 131.4, 134.4, 138.0, 138.8,
140.6, 141.9, 145.8, 151.8, 195.5 ppm. MS (FAB): m/z ϭ 769 [Mϩ
Ϫ PF6]. C42H32F12N4O2P2 (914.67): calcd. C 55.15, H 3.53, N 6.13;
found C 55.22, H 3.65, N 6.15.
141.0, 146.0, 149.3, 169.0 ppm. MS (FAB): m/z ϭ 1230 [Mϩ
Ϫ
2PF6]. C64H52F24N4O4P4 (1521.00): calcd. C 50.54, H 3.45, N 3.68;
found C 50.23, H 3.35, N 3.82.
One-Pot Synthesis of the Tetracationic Cyclophanes 3aϪd: A mix-
ture of the m-terphenyl dibromides 1aϪd (0.72 mmol) and 4,4Ј-
bipyridine (0.72 mmol) was heated under reflux for 48 h in dry
CH3CN (150 mL). The reaction mixture was then cooled to room
temperature and the solvent was reduced to one-fifth of its volume
under vacuum. The residue was purified as outlined in the general
procedure above. The yields of 3aϪd obtained by this method were
18, 22, 15 and 28%, respectively. The cyclophanes 3aϪd obtained
by this method were identical in all respects with those obtained
by the two-step procedure.
General Procedure for the Synthesis of Tetracationic Cyclophanes:
The dicationic precyclophane (0.35 mmol) was heated under reflux
with a slight excess of the corresponding dibromide (0.40 mmol) in
CH3CN (250 mL) for 48 h. The reaction mixture was cooled to
room temperature and the solvent was reduced to one-fifth of its
volume under reduced pressure. The precipitated solid was col-
lected, dried and purified by column chromatography over SiO2
using CH3OH/H2O/satd. aq. NH4Cl (6:3:1) as eluent. The cyclo-
phane-containing fractions were combined and the solvent was
evaporated under vacuum. The residue was dissolved/suspended in
H2O (50 mL) and solid NH4PF4 (0.25 g) was added, then the pre-
cipitate was filtered, washed thoroughly with H2O and dried to give
the pure tetracationic cyclophane.
Tetracationic Cyclophane 5a: From 4 (247 mg) and 1a (166 mg), 5a
(101 mg, 23%) was obtained as a pale yellow solid. M.p. Ͼ 300 °C.
1H NMR (400 MHz, [D6]DMSO): δ ϭ 5.90 (s, 4 H, CH2), 5.97 (s,
4 H, CH2), 7.54Ϫ7.76 (m, 16 H, Ar-H), 8.68 (d, J ϭ 5.4 Hz, 8 H,
bipy-3 & 3Ј-H), 9.47 (m, 8 H, bipy-2 & 2Ј-H) ppm. 13C NMR
(100 MHz, [D6]DMSO): δ ϭ 63.2, 63.6, 125.8, 127.1, 127.2, 128.1,
128.9, 129.7, 129.9, 130.2, 134.1, 135.5, 140.3, 141.6, 145.6, 145.8,
Tetracationic Cyclophane 3a: From the dicationic precyclophane 2a
(334 mg, 0.35 mmol, based on the amount of 2a present in the mix-
ture) and 1a (166 mg, 0.40 mmol), 3a (158 mg, 25%, based on the
amount of 2a present) was obtained as a pale yellow solid. Single
crystals suitable for X-ray studies were grown by vapour diffusion
of iPr2O into a solution of 3a in acetonitrile. M.p. Ͼ 210 °C (dec.).
1H NMR (400 MHz, [D6]DMSO): δ ϭ 6.03 (s, 8 H, CH2),
7.60Ϫ8.03 (m, 24 H, Ar-H), 8.81 (d, J ϭ 5.9 Hz, 8 H, bipy-3-H),
9.63 (d, J ϭ 5.9 Hz, 8 H, bipy-2-H) ppm. 13C NMR (100 MHz,
[D6]DMSO): δ ϭ 63.2, 125.0, 126.6, 127.3, 127.8, 129.5, 129.8,
133.7, 136.5, 140.0, 145.7, 149.1 ppm. MS (FAB): m/z ϭ 1114 [Mϩ
Ϫ 2PF6]. C60H48F24N4P4·3H2O (1458.98): calcd. C 49.39, H 3.73,
N 3.84; found C 49.50, H 3.64, N 3.80.
148.7, 148.9 ppm. MS (FAB): m/z
ϭ Ϫ 2PF6].
962 [Mϩ
C48H40F24N4P4·2H2O (1288.77): calcd. C 44.73, H 3.44, N 4.35;
found C 44.78, H 3.42, N 4.40.
Tetracationic Cyclophane 5b: From 4 (247 mg) and 1d (190 mg), 5b
(124 mg, 27%) was obtained as a pale yellow solid. M.p. Ͼ 300 °C.
IR (KBr): ν˜
ϭ
1729 cmϪ1 (CϭO). 1H NMR (400 MHz,
[D6]DMSO): δ ϭ 3.41 (s, 3 H, CH3), 5.87 (s, 4 H, CH2), 5.95 (s, 4
H, CH2), 7.24 (d, J ϭ 7.8 Hz, 4 H, Ar-H), 7.46Ϫ7.52 (m, 6 H, Ar-
H), 7.63 (t, J ϭ 7.3 Hz, 1 H, Ar-H), 7.77 (s, 4 H, xyl-H), 8.65Ϫ8.67
(m, 8 H, bipy-3 & 3Ј-H), 9.43 (d, J ϭ 6.8 Hz, 4 H, bipy-2-H),
9.49 (d, J ϭ 6.4 Hz, 4 H, bipy-2Ј-H) ppm. 13C NMR (100 MHz,
[D6]DMSO): δ ϭ 49.2, 61.3, 61.6, 125.1, 125.3, 126.1, 126.5, 127.0,
127.3, 128.0, 128.3, 131.8, 132.3, 133.5, 136.9, 138.9, 143.6, 143.8,
Tetracationic Cyclophane 3b: From the dicationic precyclophane 2b
(505 mg, 0.35 mmol, based on the amount of 2b present in the mix-
ture) and 1b (173 mg), 3b (283 mg, 19%, based on the amount of
2b present) was obtained as a pale yellow solid. M.p. Ͼ 230 °C
146.8, 166.3 ppm. MS (FAB): m/z
ϭ Ϫ 2PF6].
1020 [Mϩ
1
(dec.). H NMR (400 MHz, [D6]DMSO): δ ϭ 6.01 (s, 8 H, CH2),
C50H42F24N4O2P4 (1310.77): calcd. C 45.82, H 3.23, N 4.27; found
C 45.51, H 3.32, N 4.35.
7.06Ϫ7.67 (m, 22 H, Ar-H), 8.78 (d, J ϭ 6.4 Hz, 8 H, bipy-3-H),
9.56 (d, J ϭ 6.4 Hz, 8 H, bipy-2-H) ppm. 13C NMR (100 MHz,
[D6]DMSO): δ ϭ 63.5, 127.9, 128.5, 128.9, 129.8, 131.3, 135.6,
138.3, 143.5, 145.5, 148.3, 149.6 ppm. MS (FAB): m/z ϭ 1272 [Mϩ
Ϫ 2PF6]. C60H46Br2F24N4P4·H2O (1580.74): calcd. C 45.59, H 3.06,
N 3.54; found C 45.52, H 3.16, N 3.51.
Tetracationic Cyclophane 13: From 12 (284 mg) and 11 (147 mg),
13 (75 mg, 16%) was obtained as a white solid. M.p. Ͼ 275 °C
(dec.). IR (KBr): ν˜ ϭ 1642 cmϪ1 (CϭO). 1H NMR (200 MHz,
CD3CN): δ ϭ 5.87 (s, 8 H, CH2), 7.35 (d, J ϭ 7.8 Hz, 8 H, Ar-H),
7.67 (d, J ϭ 7.8 Hz, 8 H, Ar-H), 8.34 (d, J ϭ 6.0 Hz, 8 H, bipy-3-
H), 8.89 (d, J ϭ 6.0 Hz, 8 H, bipy-2-H) ppm. 13C NMR (50 MHz,
CD3CN): δ ϭ 64.7, 118.0, 128.2, 128.8, 131.1, 138.2, 138.9, 146.8,
Tetracationic Cyclophane 3c: From the dicationic precyclophane 2c
(421 mg, 0.35 mmol, based on the amount of 2c present in the mix-
ture) and 1c (184 mg), 3c (188 mg, 16%, based on the amount of
2c present) was obtained as a pale yellow solid. M.p. Ͼ 192 °C
195.8 ppm. MS (FAB): m/z
ϭ
1018 [Mϩ
Ϫ
2PF6].
C50H40F24N4O2P4 (1308.76): calcd. C 45.89, H 3.08, N 4.28; found
C 45.66, H 3.03, N 4.19.
1
(dec.). IR (KBr): ν˜ ϭ 3415 (OϪH), 1711 (CϭO) cmϪ1. H NMR
(400 MHz, [D6]DMSO): δ ϭ 6.02 (s, 8 H, CH2), 7.35Ϫ7.68 (m, 22
H, Ar-H), 8.80 (d, J ϭ 6.4 Hz, 8 H, bipy-3-H), 9.59 (d, J ϭ 6.4 Hz,
Tetracationic Cyclophane 16a: From 15a (320 mg) and 14a
8 H, bipy-2-H) ppm. 13C NMR (100 MHz, [D6]DMSO): δ ϭ 63.1, (189 mg), 16a (65 mg, 12%) was obtained as a colourless solid. M.p.
1282
Eur. J. Org. Chem. 2003, 1277Ϫ1284

Novel 4,4Ј-Bipyridinium-Based Cationic Mono- and Bicyclic Cyclophanes
FULL PAPER
Ͼ 248 °C (dec.). IR (KBr): ν˜ ϭ 1642 cmϪ1 (CϭO). 1H NMR above to give 10 (183 mg, 60%) as a pale red solid. M.p. Ͼ 215 °C
(400 MHz, CD3CN/[D6]DMSO): δ ϭ 6.58 (s, 8 H, CH2), 8.28Ϫ8.56
(m, 24 H, Ar-H), 9.10 (d, J ϭ 5.9 Hz, 8 H, bipy-3-H), 9.83 (dis-
(dec.). IR (KBr): ν˜ ϭ 1725 cmϪ1 (CϭO). 1H NMR (400 MHz,
[D6]DMSO): δ ϭ 3.67 (distorted t, 4 H, OCH2), 3.88 (distorted t,
torted d, 8 H, bipy-2-H) ppm. 13C NMR (100 MHz, CD3CN/ 4 H, OCH2), 5.97 (s, 8 H, CH2), 6.08 (s, 4 H, hq-H), 7.23Ϫ8.05
[D6]DMSO): δ ϭ 62.6, 117.0, 125.9, 128.8, 129.4, 130.4, 138.1,
(m, 22 H, Ar-H), 8.62 (d, J ϭ 5.9 Hz, 8 H, bipy-3-H), 9.52 (d, J ϭ
5.9 Hz, 8 H, bipy-2-H) ppm. 13C NMR (100 Mz, [D6]DMSO): δ ϭ
63.1, 63.3, 64.9, 115.2, 116.1, 122.2, 126.2, 126.9, 128.0, 129.0,
133.7, 138.8, 141.4, 145.3, 148.6, 150.2, 168.2 ppm. MS (FAB):
m/z ϭ 1509 [Mϩ Ϫ PF6]. C72H58F24N4O6P4·3H2O (1709.17): calcd.
C 50.60, H 3.77, N 3.28; found C 50.56, H 3.75, N 3.33.
139.9, 145.3, 153.6, 194.7 ppm. MS (FAB): m/z ϭ 1226 [Mϩ
Ϫ
2PF6]. C64H48F24N4O4P4 (1516.97): calcd. C 50.67, H 3.19, N 3.69;
found C 5.53, H 3.27, N 3.47.
Tetracationic Cyclophane 16b: From 15b (320 mg) and 14b
(189 mg), 16b (73 mg, 14%) was obtained as a colourless solid. M.p.
1
Ͼ 260 °C. IR (KBr): ν˜ ϭ 1642 cmϪ1 (CϭO). H NMR (400 MHz,
Bicyclic Cyclophane 18: A mixture of the tricarbonyl tribromide 17
(300 mg, 0.45 mmol) and 4,4Ј-bipyridine (105 mg, 0.67 mmol) was
heated under reflux for 72 h in dry CH3CN (300 mL). The reaction
mixture was then cooled to room temperature and the solvent was
reduced under vacuum to one-fifth of its volume. The precipitated
product was purified by column chromatography in the manner
described above to give 18 (15 mg, 3%) as a pale yellow solid. M.p.
Ͼ 235 °C (dec.). IR (KBr): ν˜ ϭ 1642 cmϪ1 (CϭO). 1H NMR
(400 MHz, [D6]DMSO): δ ϭ 5.96 (s, 12 H, CH2), 7.69 (d, J ϭ
7.8 Hz, 12 H, Ar-H), 7.86 (d, J ϭ 7.81 Hz, 12 H, Ar-H), 8.01 (s, 6
H, Ar-H), 8.61 (d, J ϭ 5.9 Hz, 12 H, bipy-3-H), 9.32 (d, J ϭ 5.4 Hz,
12 H, bipy-2-H) ppm. 13C NMR (100 Mz, [D6]DMSO): δ ϭ 62.6,
122.5, 126.2, 129.1, 130.7, 137.3, 139.2, 141.7, 145.8, 153.0, 193.9.
C90H66F36N6O6P6 (2197.32): calcd. C 49.20, H 3.03, N 3.82; found
C 49.34, H 3.25, N 3.63.
[D6]DMSO): δ ϭ 6.03 (s, 8 H, CH2), 7.77Ϫ7.79 (m, 14 H, Ar-H),
7.98 (d, J ϭ 7.4 Hz, 8 H, Ar-H), 8.27 (s, 2 H, Ar-H), 8.74 (d, J ϭ
5.9 Hz, 8 H, bipy-3-H), 9.51 (d, J ϭ 5.9 Hz, 8 H, bipy-2-H) ppm.
13C NMR (100 MHz, [D6]DMSO): δ ϭ 61.1, 125.4, 127.2, 127.4,
128.3, 128.5, 132.1, 134.8, 135.5, 136.6, 144.0, 147.4, 192.5 ppm.
MS (FAB): m/z ϭ 1226 [Mϩ Ϫ 2PF6]. C64H48F24N4O4P4·H2O
(1534.99): calcd. C 50.08, H 3.28, N 3.65; found C 50.02, H 3.34,
N 3.61.
Diester 8: The m-terphenylcarbonyl chloride 7 Ϫ obtained from of
the corresponding acid[7] (5.58 g, 18.48 mmol) and SOCl2 (1.35 mL;
18.48 mmol) using 4Ϫ5 drops of pyridine Ϫ was added in three
portions to the disodium salt of 1,4-bis(2-hydroxyethoxy)benzene
[from
6 (1.50 g, 7.56 mmol) and NaH (60% in oil; 0.76 g,
18.94 mmol)] in anhydrous DMF (100 mL) under nitrogen. The
mixture was stirred at 80 °C for 48 h and then the DMF was
evaporated under reduced pressure. The residue was dissolved in
CH2Cl2 (2 ϫ 100 mL), washed with water (2 ϫ 100 mL), dried
(Na2SO4) and then the solvents were evaporated to give a dark red
solid. Column chromatography (SiO2; hexane/EtOAc, 9:1, v/v) gave
8 (1.28 g, 22%) as a white solid. M.p. 170 °C. IR (KBr): ν˜ ϭ 1732
cmϪ1 (CϭO). 1H NMR (300 MHz, CDCl3): δ ϭ 2.32 (s, 12 H,
CH3), 3.63 (t, J ϭ 4.0 Hz, 4 H, OCH2), 4.17 (t, J ϭ 4.0 Hz, 4 H,
OCH2), 6.66 (s, 4 H, hq-H), 7.12 (d, J ϭ 6.4 Hz, 8 H, Ar-H),
7.30Ϫ7.34 (m, 12 H, Ar-H), 7.46 (t, J ϭ 6.5 Hz, 2 H, Ar-H) ppm.
13C NMR (75 MHz, CDCl3): δ ϭ 21.4, 63.1, 66.0, 115.5, 128.6,
128.9, 129.2, 129.5, 132.7, 137.4, 137.8, 140.5, 153.0, 169.6 ppm.
MS (FAB): m/z ϭ 766 [Mϩ]. C52H46O6 (766.94): calcd. C 81.44, H
6.04; found C 81.50, H 6.02.
Determination of Association Constants by UV/Vis Spectroscopy
(Benesi؊Hildebrand Method): In a typical experiment, an aliquot
(3.5 mL) of a standard stock solution of the cyclophane in MeCN
was placed in a quartz cuvette. A known amount of the electron-
rich guest molecule was added by incremental amounts and
changes in the absorbance of the CT band were recorded. A plot
of [concentration of cyclophane]/absorbance vs. 1/[concentration of
guest] was linear. From the slope and the intercept, the values of
Ka and ε were evaluated. The plots were linear suggesting that the
predominant species in solution was a 1:1 complex.
Electrochemical Measurements: Electrochemical experiments were
carried out in nitrogen-purged DMSO solutions at room tempera-
ture. The solutions for electrochemistry were held at a concen-
tration in the range of 10Ϫ3  of the electroactive species. TBAPF6
(0.1 ) was included as a supporting electrolyte. A glassy carbon
electrode was used as the working electrode; its surface was rou-
tinely polished with a 0.05-µm alumina/water slurry on a felt sur-
face prior to use. All potentials were recorded against a saturated
Ag/AgCl electrode and a platinum wire was used as a counter elec-
trode. The potential range was cycled from 0 to Ϫ1.2 V at a scan
rate of 50 mV/s for all samples.
Tetrabromide 9: NBS (381 mg, 2.14 mmol) was added in four equal
portions at 4 h intervals to a solution of 8 (400 mg, 0.52 mmol) in
CCl4 heated at reflux. Each portion was immediately followed by
the addition of Bz2O2 (a few mg). After heating under reflux for a
total of 40 h, the mixture was cooled and the precipitated succinim-
ide removed by filtration. The residue obtained after evaporation
of the solvent was chromatographed (SiO2; hexane/CH2Cl2, 1:1,
v/v) and the final product was recrystallised (hexane/CH2Cl2) to
give 9 (452 mg, 80%) as a pale yellow solid. M.p. 106 °C. IR (KBr):
ν˜ ϭ 1729 cmϪ1 (CϭO). 1H NMR (400 MHz, CDCl3): δ ϭ 3.56
(distorted t, 4 H, OCH2), 4.07 (distorted t, 4 H, OCH2), 4.37 (s, 8
Acknowledgments
K. S. thanks CSIR, India, for financial support. The authors thank
Dr. K. Chinnakali, Department of Physics, Anna University, for
XRD studies; Dr. K. Pandian, Department of Chemistry, Univer-
sity of Madras, P. G. Extension Centre, Vellore, for discussions on
electrochemistry; RSIC, Madras, for NMR spectra; and RSIC,
Lucknow, for FAB-MS.
H, CH2), 6.61 (s, 4 H, hq-H), 7.25Ϫ7.50 (m, 22 H, Ar-H) ppm. 13
C
NMR (100 MHz, CDCl3): δ ϭ 33.2, 63.3, 65.7, 115.3, 128.3, 128.5,
128.9, 129.4, 132.3, 137.0, 139.7, 140.4, 152.7, 169.0 ppm. MS
(FAB): m/z ϭ 1083 [Mϩ ϩ 1]. C52H42Br4O6 (1082.53): calcd. C
57.70, H 3.91; found C 57. 55, H 3.74.
Bicyclic Cyclophane 10: A mixture of the tetrabromide 9 (200 mg,
0.185 mmol) and 4,4Ј-bipyridine (58 mg, 0.37 mmol) was heated
under reflux for 24 h in dry CH3CN (100 mL). The reaction mix-
ture was then cooled to room temperature and the solvent was
reduced to one-fifth of its volume under vacuum. The precipitated
product was purified by column chromatography as described
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P. Rajakumar, K. Srinivasan
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Received August 17, 2002
[O02470]
1284
Eur. J. Org. Chem. 2003, 1277Ϫ1284