Sulfonamide carbazole receptors for anion recognition

Article abstract of DOI:10.1039/c1ob06126g

Carbazole-based receptors functionalized with two sulfonamide groups have been synthesized and their properties as anion receptors have been evaluated. The receptor with bis(trifluoromethyl)aniline groups has shown a very high affinity for halide ions, especially remarkable as only two hydrogen bonds are formed in the complexes. ¹H NMR and fluorescence titrations have been carried out and binding constants up to 7.9 × 10⁶ M ^-1 have been reached. X-ray structures have been obtained and a modelling study has shown the possible reasons for the large affinity of these compounds for halide anions. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1ob06126g

View Online / Journal Homepage / Table of Contents for this issue
Organic &
Biomolecular
Chemistry
Dynamic Article Links
Cite this: Org. Biomol. Chem., 2011, 9, 8321
www.rsc.org/obc
PAPER
Sulfonamide carbazole receptors for anion recognition†
a
a
a,b
Angel L. Fuentes de Arriba, Mar´ıa G. Turiel, Luis Simo´n, Francisca Sanz,c Juan F. Boyero,d
´
Francisco M. Mun˜iz,e Joaqu´ın R. Mora´na and Victoria Alca´zar* f
Received 8th July 2011, Accepted 14th September 2011
DOI: 10.1039/c1ob06126g
Carbazole-based receptors functionalized with two sulfonamide groups have been synthesized and their
properties as anion receptors have been evaluated. The receptor with bis(trifluoromethyl)aniline groups
has shown a very high affinity for halide ions, especially remarkable as only two hydrogen bonds are
formed in the complexes. 1H NMR and fluorescence titrations have been carried out and binding
constants up to 7.9 ¥ 106 M-1 have been reached. X-ray structures have been obtained and a modelling
study has shown the possible reasons for the large affinity of these compounds for halide anions.
from 3,6-di-tert-butyl-9H-carbazole-1,8-disulfonic acid. Because
Introduction
the NHs are not directly linked to the carbazole platform, the
geometry of these clefts is different from the ones previously
reported.13 The ability of these compounds to accommodate
The design and synthesis of receptors for anion recognition
through hydrogen bonds is an active field in research.1 Amides,2
ureas and thioureas,3 guanidines4 and sulfonamides,5 among
others, have shown their potential as hydrogen-bond donors
and many anion receptors have included them. The directional
character of H-bonds makes an effective binding to the anions
feasible when a number of H-bond donor groups are properly
positioned on a molecular platform. Calixarenes,6 xanthenes,7
anthracenes,8 binaphthyls,9 chromenones10 and carbazoles11 are
only a few examples of frameworks that have been used to build
molecular clefts for anion recognition.
1
different anions has been studied by H NMR and fluorescence
titrations. X-ray structures of the pure receptors and some of their
complexes have been obtained and the use of these compounds as
fluorescent sensors has also been explored.
Results and discussion
Synthesis
Since the pioneering work of Jurczak,12 much attention has been
focused on the 1,8-diamino-3,6-dichlorocarbazole as a versatile
building block for the synthesis of anion receptors. Simple func-
tionalization of the two amine side arms provides a preorganized
binding site, which can be further stabilized by the hydrogen bond
coming from the central NH of the carbazole.13
Compounds 1 and 2 were prepared starting from the readily
available 3,6-di-tert-butyl-9H-carbazole14 (3) using straightfor-
ward procedures. The starting material shows high solubility in
common organic solvents and due to the fact that positions 3 and
6 are substituted, sulfonation with chlorosulfonic acid in CH2Cl2
afforded the desired 3,6-di-tert-butyl-9H-carbazole-1,8-disulfonic
acid in good yield (96%). The reaction of the acid (4) with PCl5
yielded the corresponding sulfonyl chloride (5), which was reacted
with the corresponding amines to afford the desired compounds
(Scheme 1).
Herein we report the synthesis and evaluation of the H-bond
properties of two novel sulfonamide carbazole receptors derived
aDepartamento de Qu´ımica Orga´nica, Universidad de Salamanca, Plaza de
los Ca´ıdos 1-5, E-37008, Salamanca, Spain
bDepartamento de Ingenier´ıa Qu´ımica, Universidad de Salamanca, Plaza de
los Ca´ıdos 1-5, E-37008, Salamanca, Spain
1H NMR and fluorescence titrations
cServicio de Rayos X, Universidad de Salamanca, Plaza de los Ca´ıdos 1-5,
E-37008, Salamanca, Spain
1H NMR titrations in CDCl3 were performed to explore the anion
complexation properties of the carbazole based receptors. As
expected, receptor 2 derived from 3,5 bis(trifluoromethyl)aniline
showed a better affinity for the guests due to the H-bond
activation by the CF3 electron-withdrawing groups,15 and this
compound was chosen to carry out the main part of the
assays.
dDepartamento de Qu´ımica Anal´ıtica, Universidad de Salamanca, Plaza de
los Ca´ıdos 1-5, E-37008, Salamanca, Spain
eInstituto de Cera´mica y Vidrio, CSIC, Kelsen 5, E-28049, Madrid, Spain
f
Departamento de Ingenier´ıa Qu´ımica Industrial y Medio Ambiente, Univer-
sidad Polite´cnica de Madrid, Jose´ Gutie´rrez Abascal 2, E-28006, Madrid,
Spain. E-mail: valcazar@etsii.upm.es; Fax: +34 915618618; Tel: +34
913363203
1
† Electronic supplementary information (ESI) available: Copies of NMR,
IR and MS spectra of the compounds, selected binding curves, X-ray
characterization data and modelling studies. CCDC reference numbers
832821–832825. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1ob06126g
The association constants are collected in Table 1. In all H
NMR measurements the concentration of the host was kept
constant (c = 2.5 ¥ 10-3 M) and increasing amounts of the guest
were added until saturation was reached.
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8321–8327 | 8321
©

View Online
methods carried out at much lower concentrations. Fluorescence
quenching titration curves of carbazole 2 (10 mM) with halides
allowed calculation of an association constant of 4.2 ¥ 105 M-1 for
iodide (ESI Fig. S15–S16†). However, for bromide and chloride no
binding curves could be obtained at this host concentration (ESI
Fig. S17†) and more dilute solutions were then prepared (5 mM,
1 mM and 0.1 mM). While the association constant between 2 and
TEABr was determined to be 1.1 ¥ 106 M-1 (ESI Fig. S19†), the
high affinity of receptor 2 for chloride did not allow measurement
of an absolute constant and a competitive titration18 was run,
yielding an association constant of 7.9 ¥ 106 M-1 (ESI Fig. S20†).
On the other hand, 1H NMR titrations for chloride and bromide
in the more competitive solvent DMSO-d6 afforded, as expected,
lower values of the association constants (Ka = 210 M-1 for
chloride vs. Ka = 25 M-1 for bromide) but the selectivity trend was
maintained. We also evaluated the binding ability of the receptor
2 towards DMSO in CDCl3, affording an association constant
of 710 M-1, much lower than that reported for halides (Table 1,
entries 2–3). Although receptor 2 bound halides preferentially over
DMSO, with DMSO as solvent, the large molar DMSO : halide
ratio strongly reduced the halide association constants (ESI Fig.
S22–S24†).
Scheme 1 Synthesis of receptors 1 and 2.
Table 1 Association constants (M-1) of the complexes formed by re-
ceptors 1 and 2 and several anions (added as tetrabutyl or tetraethyl
ammonium salts) at 298 K in CDCl3. Errors estimated to be £ 10%
Oxoanions such as hydrogen sulfate, m-nitrobenzoate and
perchlorate were also tested, but in all cases H NMR titrations
Entry
Anion
Compound 1
Compound 2
1
(Table 1, entries 5, 6 and 7) revealed a strong decrease in affinity
compared to the halide ions. Again, small shifts for the carbazole
NH were observed during the titrations while sulfonamide NHs
(Ddsat = 1.31 ppm) seemed to play the main role in binding (ESI
Fig. S25†).
Titration with dihydrogen phosphate caused broadening of
the carbazole and sulfonamide NH resonances, precluding an
accurate determination of the association constant from these
data. However, upfield shifts of the aromatic H-4¢ resonance (Dd =
-0.28 and -0.35 ppm upon addition of 1 and 2 equiv., respectively)
suggested strong binding, although the data could not be fitted to a
binding isotherm as has already been reported by other authors.19
Further evidence of phosphate binding came from the fact that
receptor 2 was capable of extracting monohydrogen phosphate
(as its diammonium salt) from an aqueous solution, when 18-
crown-6-ether was present in the organic phase.
With the more basic anion acetate, the NH resonances disap-
peared completely during the titration, which might indicate de-
protonation. Although the 3,5-bis(trifluoromethyl)phenyl proton
resonances were visible along the titration, the data could not be
fitted adequately to a binding model. In the fluorescence study
(l = 350 nm), the intrinsic blue fluorescence of the receptor 2 was
quenched on addition of acetate; this effect is quite similar to that
observed with added tetrabutylammonium hydroxide, and could
be attributed to the basic character of the anions that deprotonates
the receptor. Treatment with p-TsOH regenerated, in both cases,
the initial fluorescence.
1
2
3
4
5
6
7
8
9
Fluoride
Chloride
Bromide
Iodide
Hydrogen sulfate
m-Nitrobenzoate
Perchlorate
Dihydrogen phosphate
Acetate
—
2.2 ¥ 104a
7.9 ¥ 106b
1.1 ¥ 106c
4.2 ¥ 105c
8.8 ¥ 104a
2.9 ¥ 104a
3.7 ¥ 104
4.5 ¥ 103
—
—
—
—
—
—
2.4 ¥ 103a
d
d
a Measured by 1H NMR titration. b Measured by competitive fluorescence
titration with bromide. c Measured by fluorescence. d Data could not be
fitted to a 1 : 1 or 1 : 2 binding stoichiometry.
1H NMR spectra did not provide evidence for the direct
participation of the carbazole NH in the stability of the complexes.
The chemical shift of the NH for the free receptors (singlet at
10.21 ppm for compound 1 and at 10.37 ppm for compound 2)
did not change upon addition of the guests. On the contrary,
sulfonamide NH protons were strongly involved in binding as
evidenced by the large complexation induced shifts (up to 3.33 ppm
for compound 1 and 1.74 ppm for compound 2). Also, the aromatic
protons of the bis(trifluoromethyl)aniline unit were shifted during
the titration (Ddsat = -0.34 ppm for H-4¢) allowing us to estimate
the association constants either by the sulfonamide NH or CH
resonances (ESI Fig. S13†).
1H NMR titration of receptor 2 with tetrabutylammonium
fluoride in CDCl3 yielded an association constant of 2.2 ¥ 104 M-1
for the 1 : 1 complex. In the more polar solvent DMSO-d6, a
large excess of fluoride (10 : 1 anion to receptor ratio) led to
deprotonation16 with concomitant formation of the species [HF2]-,
as evidenced by 1H NMR (ESI Fig. S21†).
The association constants collected in Table 1 show the higher
affinity of receptor 2 for the halides chloride, bromide and iodide,
compared to the tested oxoanions. These results are unusual,
and to our knowledge this preference has not been previously
reported for H-bond anion receptors.20 If the carbazole NH is
not engaged in hydrogen bonding with the anions (as pointed out
For the rest of the halides (Cl-, Br- and I-), although the data
indicated a very tight 1 : 1 binding in deuterochloroform (ESI
Fig. S14†), the association constants could not be accurately
1
1
determined by H NMR.17 Thus, the interaction of receptor 2
by the H NMR data), the complexes with receptor 2 seem to
with these three halides was studied by fluorescence titration
be stabilized only by two hydrogen bonds with the sulfonamide
8322 | Org. Biomol. Chem., 2011, 9, 8321–8327
This journal is
The Royal Society of Chemistry 2011
©

View Online
NHs. On the other hand, the well-known Schreiner’s thiourea,
with two hydrogen-bond donors, bound carboxylates with larger
preference than halides as expected (Ka = 1.4 ¥ 104 M-1 for TBA
m-nitrobenzoate vs. Ka = 8.9 ¥ 103 M-1 for TEACl, ESI Fig. S26†).
Therefore, to try to understand the reasons for this uncommon
preference, X-ray analysis and modelling studies were carried out.
Fig. 3–5 (ESI Fig. S29–S31†) show the geometry of the
complexes with chloride, bromide and iodide.
X-ray analysis
Slow evaporation of methylene chloride from a methylene chlo-
ride/cyclohexane solution of pure receptors allowed us to obtain
crystals suitable for X-ray analysis (Fig. 1 and 2, ESI Fig. S27–
S28†).
Fig. 3 X-ray crystal structure of 2·TEACl. Tetraethylammonium counter
cation was omitted for clarity.
Fig. 1 X-ray structure of compound 1.
Fig. 4 X-ray crystal structure of 2·TEABr. Tetraethylammonium counter
cation was omitted for clarity.
Fig. 2 X-ray structure of compound 2.
X-ray diffraction analysis showed very similar conformations
for both compounds. The central carbazole NH forms two
intramolecular H-bonds, with NHcarbazole ◊ ◊ ◊ Osulfonamide distances of
˚
˚
˚
˚
2.949 A and 2.995 A for receptor 1 and 2.828 A and 3.031 A for
receptor 2. In both structures the distances between the two sulfon-
amide NHs of the side arms is too large (Nsulfonamide ◊ ◊ ◊ Nsulfonamide
6.676 A) for the simultaneous formation of two H bonds with an
=
Fig. 5 The X-ray crystal structure of 2·TBAI. Tetrabutylammonium
˚
counter cation was omitted for clarity.
anion.
The structures of the complexes formed between receptor 2
and tetraalkylammonium halides (chloride, bromide and iodide)
were also solved by X-ray diffraction. Crystals of the 1 : 1
anion–receptor complexes were obtained by slow evaporation of
CH2Cl2 from a methylene chloride/cyclohexane solution contain-
ing equimolar amounts of host and guest. However, attempts
to grow crystals of the complexes with oxoanions, under the
aforementioned conditions, were unsuccessful. Slow evaporation
of the solvent from solutions of receptor 2 and m-nitrobenzoate,
perchlorate, hydrogen sulphate or phosphate did not yield crystals
of the complexes, affording only crystals of the pure receptor.
Crystals of the complexes revealed a similar pattern with all the
anions inside the carbazole cleft. The structures show that each
halide is bound by two H-bonds, almost symmetrically disposed,
with the sulfonamide NHs. The NHsulfonamide ◊ ◊ ◊ X (X = halide)
˚
˚
˚
lengths are 3.138 A and 3.169 A for the chloride, 3.290 A and
˚
˚
˚
3.294 A for the bromide and 3.464 A and 3.535 A for the iodide
(Table 2).
The complexes are further stabilized by two interactions with
the aromatic CHs in positions 2¢, with distances CH ◊ ◊ ◊ X varying
˚
˚
˚
from 3.580 A for the chloride to 3.654 A for bromide and 3.769 A
for iodide. Searches of the Cambridge Structural Database21 reveal
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8321–8327 | 8323
©

View Online
˚
Table 2 Distances (A) from the X-ray structures of receptor 2 and their
with the oxygen atoms. But the explanation for the higher affinity
for chloride (Ka = 7.9 ¥ 106 vs. 2.9 ¥ 104 and 2.4 ¥ 103) cannot
rely only on this reason. A comparison between the computed
structures with chloride and perchlorate allows us to establish
another difference: as it is shown in Fig. 7, complexation with
the oxoanion requires a more pronounced conformational change
in the cleft reducing the Nsulfonamide ◊ ◊ ◊ Nsulfonamide distance by more
complexes with halides (Cl, Br, I)
(N ◊ ◊ ◊ N)sulfonamide NHsulfonamide ◊ ◊ ◊ X CH ◊ ◊ ◊ X NHcarbazole ◊ ◊ ◊ X
2
6.676
—
—
—
2·TEACl 5.363
3.138/3.169
3.290/3.294
3.464/3.535
3.580
3.654
3.769
3.845
3.963
4.106
2·TEABr 5.555
2·TBAI
5.853
˚
than 0.3 A compared to the complex with chloride. This effect is
enlarged at the top of the cleft where the separation between the
that such interactions between substituted benzene rings and
anions (halides and oxoanions) are very common in the solid state.
In addition, in full agreement with the 1H NMR data, the
carbazole NH does not contribute to the binding as evidenced by
˚
carbons of the trifluoromethyl groups is reduced by more than 1 A:
˚
˚
(C ◊ ◊ ◊ C)CF3 = 5.9 A (complex with chloride) and (C ◊ ◊ ◊ C)CF3 = 4.4 A
(complex with perchlorate), provoking steric hindrance between
˚
the fluorine atoms (distance F ◊ ◊ ◊ F = 2.8 A).
˚
˚
the distances NHcarbazole ◊ ◊ ◊ X in the range from 3.845 A to 4.106 A.
The fact that the pyrrole NH is not involved in the recognition
event is outstanding compared to other known X-ray structures
for complexes between chloride and carbazole receptors22 where
this interaction is always one of the dominant ones.
Further stabilization of the complexes by anion–p interactions
between halides and carbazole rings were not observed in the solid
state (ESI Fig. 32†).
While the X ray analysis showed a good coincidence between
receptor and halide geometries, it did not explain why oxoanions
were not as suitable for this cleft, therefore a modelling study was
started.
Modelling studies
A modelling study using the program Gaussian0323 revealed the
possible reasons for the lower affinity of receptor 2 for oxoanions.
Models of the complex of receptor 2 with chloride showed an
almost perfect match with the X-ray structure (Fig. 6). The halide
is bound in the complex by two H-bonds with the sulfonamide
Fig. 7 Overlay of the optimized complex structures (B3LYP/6-31G**)
between receptor 2 and TEACl (in grey) and TEAClO4 (in green). In the
perchlorate association complex, steric hindrance can be observed between
the trifluoromethyl groups.
˚
NHs (NHsulfonamide ◊ ◊ ◊ Cl distance of 3.2 A). The computed distances
˚
for the intramolecular H-bonds (NHcarbazole ◊ ◊ ◊ Osulfonamide = 2.9 A)
˚
and for the interactions CH ◊ ◊ ◊ X (3.7 A) are in excellent agreement
Conclusions
with the X-ray diffraction measurements.
The readily available sulfonamide carbazole receptor 2 has shown
a remarkably high affinity for halide anions, with the largest
1
binding constant for chloride. According to the H NMR data
and supported by the X-ray structures, it is proposed that the
complexes are stabilized by two H- bonds via the sulfonamide
NHs and the other two CH ◊ ◊ ◊ X interactions. In any case, the
carbazole NH seems not to be involved in binding, keeping the
same two intramolecular H-bonds already present in the free
receptors. Surprisingly, oxoanions are not as good guests as halides
for receptor 2.
The conformational change associated with complex formation
might be responsible for this behaviour. The two sulfonamide NH
groups are far apart in the receptors and must be brought closer
upon complexation. As modelling studies suggest, carboxylates
and other oxoanions form complexes where the conformational
change is more relevant. On the contrary, the larger halides are
able to set two H-bonds with minor changes in the conformation,
and so the binding process is more favoured.
Fig. 6 Optimized structure of the complex between receptor 2 and TEACl
(B3LYP/6-31G** level of theory).
In the case of oxoanions such as perchlorate or benzoate,
where the oxygen atom has to be bound in the cleft, the
calculated structures are quite similar to the one with chloride,
˚
with respect to H-bond lengths: NHsulfonamide ◊ ◊ ◊ Operchlorate = 3.0 A;
˚
˚
NHsulfonamide ◊ ◊ ◊ Obenzoate = 2.9 A; NHcarbazole ◊ ◊ ◊ Osulfonamide = 2.9 A for
both complexes. Taking into account the larger van der Waals
radius for Cl (175 pm) versus O (152 pm), the H-bonds for the
complex with the halide seem to be stronger than those formed
Experimental
3,6-Di-tert-butyl-9H-carbazole-1,8-disulfonic acid (4). 3,6-di-
tert-butyl-9H-carbazole14 3 (10.0 g, 35.82 mmol) was dissolved
8324 | Org. Biomol. Chem., 2011, 9, 8321–8327
This journal is
The Royal Society of Chemistry 2011
©

View Online
in CH2Cl2 (200 cm3) in a three necked flask equipped with a
magnetic stirrer, a pressure-equalising dropping funnel and under
argon atmosphere. The reaction mixture was cooled down to
46%); mp 121–124 ◦C; (Found: 50,03; H, 3.74; N, 4.73; S, 7.23.
C36H31F12N3O4S2 requires C, 50.17; H, 3.63; N, 4.88; S, 7.44);
n
max(film/cm-1) 3436, 3227, 1619, 1151, 989 and 898; dH (200 MHz,
0
◦C in an ice bath. Then, a solution of chlorosulfonic acid
CDCl3) 1.41 (18H, s), 7.58 (2H, s), 7.73 (4H, s), 8.00 (2H, d, J 1.8),
8.42 (2H, d, J 1.8), 9.69 (2H, s, NH), 10.22 (1H, s, NH); dC (50
MHz, CDCl3) 31.7, 35.2, 118.3, 119.1, 119.3, 123.0 (q, 1JCF 271.9
(4.9 cm3, 35.82 mmol) in methylene chloride (30 cm3) was added
dropwise with vigorous stirring. Once the addition was complete,
the mixture was stirred for another half an hour and the reaction
was monitored through 1H NMR analysis of an aliquot. If starting
material was still present, a few drops of chlorosulfonic acid in
methylene chloride was added to the dropping funnel and stirring
was continued until the reaction was complete. Then, the solvent
was partially evaporated under reduced pressure until a solid
began to precipitate. The reaction mixture was cooled down and
the solid was filtrated to afford the crude disulfonic acid, which
was used without further purification in the next step (15.13 g,
96%), mp 104–107 ◦C; (Found: C, 54.26; H, 5.75; N, 3.28; S,
14.55. C20H25NO6S2 requires C, 54.65; H, 5.73; N, 3.19; S, 14.59);
2
Hz), 123.9, 125.5, 125.7, 133.2 (q, JCF 33.8 Hz), 133.8, 138.3,
144.3; MS (ESI-) m/z 860.4.
Acknowledgements
The authors thank the Spanish Direccio´n General de In-
vestigacio´n, Ciencia
y Tecnolog´ıa (DGI-CYT) (CTQ2010-
19906/BQU) and the UE (European Re-integration Grant
PERG04-GA-2008-239244) for their support in this work. The
Spanish Ministerio de Educacio´n (MEC) is acknowledged for the
fellowship (A. L. F. A.). The authors are also grateful to Dr Mar
Lo´pez Blanco and Dr Ce´sar Raposo.
n
max(film/cm-1) 3448, 1755, 1625, 1158 and 1054; dH (200 MHz,
CD3OD) 1.47 (18H, s), 7.96 (2H, d, J 2), 8.30 (2H, d, J 2); dC (50
MHz, CD3OD) 31.2, 34.5, 119.1, 121.8, 124.2, 126.3, 134.0, 142.1;
MS (ESI-) m/z 218.6.
Notes and references
3,6-Di-tert-butyl-N1,N8 -dibutyl-9H -carbazole-1,8-disulfona-
mide (1). The disulfonic acid 4 (2.0 g, 4.55 mmol) was suspended
in CH2Cl2 (10 cm3) and cooled down in an ice bath. Then, PCl5
(3.0 g, 14.4 mmol) was added and the reaction mixture was stirred
until evolution of gas ceased. The ice bath was then removed
and the reaction was stirred at room temperature until no more
bubbles could be observed. 1H NMR analysis of an aliquot
showed no starting material. Then, the solvent was removed under
reduced pressure to afford the corresponding sulfonyl chloride (5),
which was used in the next reaction without further purification.
Compound 5 (1.0 g, 2.1 mmol) in methylene chloride (10 cm3)
was treated with an excess of n-butylamine (1 cm3, 10.5 mmol)
and the mixture was stirred at room temperature. The reaction
was monitored by TLC. Once the reaction was complete, the
solvent was removed under reduced pressure and the crude residue
was treated with 2 N HCl and extracted with ethyl acetate. The
combined organic layers were dried over sodium sulphate, and the
solvent was evaporated. Chromatography with CH2Cl2/EtOAc
(95 : 5) afforded the pure compound 1 (1.04 g, 90%); mp 166–
169 ◦C; (Found: C, 61.45; H, 7.73; N, 7.40; S, 11.30. C28H43N3O4S2
requires C, 61.17; H, 7.88; N, 7.64; S, 11.66); nmax(film/cm-1) 3409,
1755, 1606, 1333, 1145 and 736; dH (200 MHz, CDCl3) 0.72 (6H,
t, J 6.8), 1.09–1.25 (4H, m), 1.28–1.39 (4H, m), 1.41 (18H, s), 2.91
(4H, q, J 6.8), 6.35 (2H, t, J 6.8, NH), 7.97(2H, d, J 1.8), 8.35
(2H, d, J 1.8), 10.19 (1H, s, NH); dC (50 MHz, CDCl3) 13.6, 19.8,
31.2, 32.1, 35.2, 42.7, 121.6, 121.6, 124.6, 125.1, 134.1, 143.0; MS
(ESI-) m/z 548.5, 584.5 (M + Cl)-.
1 For more recent reviews, see: themed issue on Supramolecular Chem-
istry of Anionic Species, Chem. Soc. Rev., 2010, 39; J. L. Sessler, P.
A. Gale and W.-S. Cho, Anion Receptor Chemistry, Royal Society of
Chemistry, Cambridge, UK, 2006; G. W. Bates and P. A. Gale, Struct.
Bonding, 2008, 129, 1; Z. Zhang and P. R. Schreiner, Chem. Soc. Rev.,
2009, 38, 1187; C. Caltagirone and P. A. Gale, Chem. Soc. Rev., 2009,
38, 520; P. A. Gale, S. E. Garc´ıa-Garrido and J. Garric, Chem. Soc.
Rev., 2008, 37, 151; P. Prados and R. Quesada, Supramol. Chem., 2008,
20, 201; P. A. Gale and R. Quesada, Coord. Chem. Rev., 2006, 250,
3219; P. A. Gale, Acc. Chem. Res., 2006, 39, 465; N. Gimeno and R.
Vilar, Coord. Chem. Rev., 2006, 250, 3161; J. Yoon, S. K. Kim, N. J.
Singh and K. S. Kim, Chem. Soc. Rev., 2006, 35, 355; M. A. Hossain,
Curr. Org. Chem., 2008, 12, 1231; E. A. Katayev, P. J. Melfi and J. L.
Sessler, Modern Supramolecular Chemistry, 2008, 315; R. Vilar, Eur. J.
Inorg. Chem., 2008, 357; S. Kubik, Chem. Soc. Rev., 2009, 38, 585; P.
Dydio, D. Lichosyt and J. Jurczak, Chem. Soc. Rev., 2011, 40, 2971;
V. Amendola, M. Bonizzoni, D. Esteban-Gomez, L. Fabbrizzi, M.
Licchelli, F. Sancenon and A. Taglietti, Coord. Chem. Rev., 2006, 250,
1451; V. Amendola, D. Esteban-Gomez, L. Fabbrizzi and M. Licchelli,
Acc. Chem. Res., 2006, 39, 343; P. A. Gale, Amide- and Urea-Based
Anion Receptors in Encyclopedia of Supramolecular Chemistry, ed. J. L.
Atwood and J. W. Steed, Marcel Dekker, New York, 2004, 31.
2 P. Pia˛tek and J. Jurczak, Chem. Commun., 2002, 2450; P. A. Gale,
S. Camiolo, C. P. Chapman, M. E. Light and M. B. Hursthouse,
Tetrahedron Lett., 2001, 42, 5095; J. J. Park, Y.-H. Kim, C. Kim
and J. Kang, Tetrahedron Lett., 2011, 52, 2759; I. I. Stoikov, A. A.
Yantemirova, R. V. Nosov, I. K. Rizvanov, A. R. Julmetov, V. V.
Klochkov, I. S. Antipin, A. I. Konovalov and I. Zharov, Org. Biomol.
Chem., 2011, 9, 3225; M. Kinsella, P. G. Duggan, J. Muldoon, K.
S. Eccles, S. E. Lawrence and C. M. Lennon, Eur. J. Org. Chem.,
2011, 1125; A. Dorazco-Gonzalez, H. Hoepfl, F. Medrano and A.
K. Yatsimirsky, J. Org. Chem., 2010, 75, 2259; M. Arunachalam and
P. Ghosh, Chem. Commun., 2009, 5389; N. Bernier, S. Carvalho, F. Li,
R. Delgado and V. Felix, J. Org. Chem., 2009, 74, 4819; B. Jimenez, E.
Calle and C. Caballero, Sensors, 2009, 9, 1534; X.-F. Shang, H. Lin, Z.-
S. Cai and H.-K. Lin, J. Heterocycl. Chem., 2008, 45, 1329; T. Zielinski,
P. Dydio and J. Jurczak, Tetrahedron, 2008, 64, 568; H. Nelissen, F. M.
Hubertus and D. K. Smith, Chem. Commun., 2007, 3039; T. Zielinski
and J. Jurczak, Tetrahedron, 2005, 61, 4081; S. Kumar, H. Singh and
R. Sharma, J. Indian Chem. Soc., 2003, 80, 1111; M. Chmielewski
and J. Jurczak, Tetrahedron Lett., 2004, 45, 6007; S. O. Kang, J. M.
Llinares, D. Powell, D. Vandervelde and K. Bowman-James, J. Am.
Chem. Soc., 2003, 125, 10152; K. Navakhun, P. A. Gale, S. Camiolo,
M. E. Light and M. B. Hursthouse, Chem. Commun., 2002, 2084; M.
Arunachalam and P. Ghosh, Org. Lett., 2010, 12, 328; V. Amendola,
M. Boiocchi, L. Fabbrizzi and A. Palchetti, Chemistry, 2004, 11,
120; K. Choi and A. D. Hamilton, J. Am. Chem. Soc., 2003, 125,
10241.
N1,N8-Bis(3,5-bis(trifluoromethyl)phenyl)-3,6-di-tert-butyl-9H-
carbazole-1,8-disulfonamide (2). The disulfonic acid 4 was trans-
formed into the sulfonyl chloride 5 following the same procedure
described for the synthesis of compound 1. Compound 5 (1.32 g,
2.78 mmol) and 3,5-(bis(trifluoromethyl)aniline (1.9 g, 8.29 mmol)
were heated in pyridine (4 cm3) at 90 ◦C for 2 h. The reaction was
monitored by TLC. The solvent was evaporated and the residue
was treated with 2 N HCl and extracted with EtOAc. The com-
bined organic layers were dried (Na2SO4) and chromatography
(CH2Cl2/EtOAc, 95 : 5) yielded the desired compound 2 (1.10 g,
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8321–8327 | 8325
©

View Online
3 V. Amendola, L. Fabbrizzi and L. Mosca, Chem. Soc. Rev., 2010, 39,
3889; A.-F. Li, J.-H. Wang, F. Wang and Y.-B. Jiang, Chem. Soc. Rev.,
2010, 39, 3729; P. R. Edwards, J. R. Hiscock, P. A. Gale and M. E. Light,
Org. Biomol. Chem., 2010, 8, 100; C. K. De, E. G. Klauber and D. Seidel,
J. Am. Chem. Soc., 2009, 131, 17060; W.-X. Liu, R. Yang, A.-F. Li, Z.
Li, Y.-F. Gao, X.-X. Luo, Y.-B. Ruan and Y.-B. Jiang, Org. Biomol.
Chem., 2009, 7, 4021; D. Meshcheryakov, F. Arnaud-Neu, V. Boehmer,
M. Bolte, J. Cavaleri, V. Hubscher-Bruder, I. Thondorf and S. Werner,
Org. Biomol. Chem., 2008, 6, 3244; D. E. Gomez, L. Fabbrizzi, M.
Licchelli and E. Monzani, Org. Biomol. Chem., 2005, 3, 1495; B. Vesna,
N. Bregovic, K. Mlinaric-Majerski and N. Basaric, Tetrahedron, 2011,
67, 3846; A. Aldrey, C. Nunez, V. Garcia, R. Bastida, C. Lodeiro and
A. Macias, Tetrahedron, 2010, 66, 9223; C. Jia, B. Wu, S. Li, Z. Yang,
Q. Zhao, J. Liang, Q.-S. Li and X.-J. Yang, Chem. Commun., 2010, 46,
5376; J. P. Clare, A. Statnikov, V. Lynch, A. L. Sargent and J. W. Sibert,
J. Org. Chem., 2009, 74, 6637; I. Ravikumar, P. S. Lakshminarayanan,
M. Arunachalam, E. Suresh and P. Ghosh, Dalton Trans., 2009, 4160;
C. M. G. dos Santos, T. McCabe, G. Watson, P. E. Kruger and T.
Gunnlaugsson, J. Org. Chem., 2008, 73, 9235; M. Hamon, M. Menand,
S. Le Gac, M. Luhmer, V. Dalla and I. Jabin, J. Org. Chem., 2008, 73,
7067; L. Pescatori, A. Arduini, A. Pochini, F. Ugozzoli and A. Secchi,
Eur. J. Org. Chem., 2008, 109; C. Perez-Casas and A. K. Yatsimirsky, J.
Org. Chem., 2008, 73, 2275; P. S. Lakshminarayanan, I. Ravikumar, E.
Suresh and P. Ghosh, Chem. Commun., 2007, 5214; F. M. Pfeffer, P. E.
Kruger and T. Gunnlaugsson, Org. Biomol. Chem., 2007, 5, 1894; J. A.
Tovilla, R. Vilar and A. J. P. White, Chem. Commun., 2005, 4839; D. A.
Jose, D. K. Kumar, B. Ganguly and A. Das, Tetrahedron Lett., 2005, 46,
5343; B. P. Hay, T. K. Firman and B. A. Moyer, J. Am. Chem. Soc., 2005,
127, 1810; T. Gunnlaugsson, A. P. Davis, J. E. O’Brien and M. Glynn,
Org. Biomol. Chem., 2005, 3, 48; C. R. Bondy, P. A. Gale and S. J. Loeb,
J. Am. Chem. Soc., 2004, 126, 5030; M. F. d. l. Torre, E. G. Campos,
S. Gonzalez, J. R. Moran and M. C. Caballero, Tetrahedron, 2001, 57,
3945; B. H. M. Snellink-Ruel, M. M. G. Antonisse, J. F. J. Engbersen,
P. Timmerman and D. N. Reinhoudt, Eur. J. Org. Chem., 2000, 165; H.
Boerrigter, L. Grave, J. W. M. Nissink, L. A. J. Chrisstoffels, J. H. van
der Maas, W. Verboom, F. de Jong and D. N. Reinhoudt, J. Org. Chem.,
1998, 63, 4174; S. Nishizawa, P. Buehlmann, M. Iwao and Y. Umezawa,
Tetrahedron Lett., 1995, 36, 6483; D. R. Turner, M. J. Paterson and J.
W. Steed, J. Org. Chem., 2006, 71, 1598; X. He, F. Herranz, E. C.-C.
Cheng, R. Vilar and V. W.-W. Yam, Chem.–Eur. J., 2010, 16, 9123; D.
A. Jose, D. K. Kumar, B. Ganguly and A. Das, Org. Lett., 2004, 6,
3445.
4 B. P. Orner and A. D. Hamilton, J. Inclusion Phenom. Macrocyclic
Chem., 2001, 41, 141; P. Blondeau, M. Segura, R. Pe´rez-Ferna´ndez and
J. de Mendoza, Chem. Soc. Rev., 2007, 36, 198; P. S. Dieng and C. Sirlin,
Int. J. Mol. Sci., 2010, 11, 3334; V. Kra´l, F. P. Schmidtchen, K. Lang
and M. Berger, Org. Lett., 2002, 4, 51; A. J. Ayling, S. Broderick, J.
P. Clare, A. P. Davis, M. N. Pe´rez-Paya´n, M. Lahtinen, N. J. Nissinen
and K. Rissanen, Chem.–Eur. J., 2002, 8, 2197; F. P. Schmidtchen,
A. Gleich and A. Schummer, Pure Appl. Chem., 1989, 61, 1535; F. P.
Schmidtchen and M. Berger, Chem. Rev., 1997, 97, 1609; L. J. Lawless,
A. G. Blackburn, A. J. Ayling, M. N. Pe´rez-Paya´n and A. P. Davis, J.
Chem. Soc., Perkin Trans. 1, 2001, 1329.
5 O. Mammoliti, S. Allasia, S. Dixon and J. D. Kilburn, Tetrahedron,
2009, 65, 2184; V. Amendola, M. Boiocchi, L. Fabbrizzi and A.
Palchetti, Chem.–Eur. J., 2005, 11, 120; V. Amendola, L. Fabbrizzi,
L. Mosca and F.-P. Schmidtchen, Chem.–Eur. J., 2011, 17, 5972; C.
Caltagirone, G. W. Bates, P. A. Gale and M. E. Light, Chem. Commun.,
2008, 61; M. V. Lopez, M. R. Bermejo, M. E. Vazquez, A. Taglietti,
G. Zaragoza, R. Pedrido and M. Martinez-Calvo, Org. Biomol. Chem.,
2010, 8, 357; O. B. Berryman, C. A. Johnson II, L. N Zkaharov, M. M.
Haley and D. W. Johnson, Angew. Chem., Int. Ed., 2008, 47, 117; T.-P.
Lin, C.-Y. Chen, Y.-S. Wen and S.-S. Sun, Inorg. Chem., 2007, 46, 9201;
Y. Wu, X. Peng, J. Fan, S. Gao, M. Tian, J. Zhao and S. Sun, J. Org.
Chem., 2007, 72, 62; S.-i. Kondo, T. Suzuki, T. Toyama and Y. Yano,
Bull. Chem. Soc. Jpn., 2005, 78, 1348; S.-i. Kondo, T. Suzuki and Y.
Yano, Tetrahedron Lett., 2002, 43, 7059; A. P. Davis, J. J. Perry and R.
P. Williams, J. Am. Chem. Soc., 1997, 119, 1793; Y. Morzherin, D. M.
Rudkevich, W. Verboom and D. N. Reinhoudt, J. Org. Chem., 1993, 58,
7602.
Schatz and H. Schmaderer, Eur. J. Org. Chem., 2006, 1899; T. Pinter,
S. Jana, R. J. M. Courtemanche and F. Hof, J. Org. Chem., 2011, 76,
3733; A. Lascaux, S. Le Gac, J. Wouters, M. Luhmer and I. Jabin, Org.
Biomol. Chem., 2010, 8, 4607; I. Dinares, C. G. de Miguel, N. Mesquida
and E. Alcalde, J. Org. Chem., 2009, 74, 482; J. L. Sessler, P. A. Gale
and J. W. Genge, Chem.–Eur. J., 1998, 4, 1095.
7 B. C. Hamann, N. R. Branda and J. Rebek, Tetrahedron Lett., 1993,
34, 6837; K. P. Xiao, P. Buhlmann, S. Nishizawa, S. Amemiya and Y.
Umezawa, Anal. Chem., 1997, 69, 1038; F. M. Mun˜iz, V. Alca´zar, L.
Simo´n, C. Raposo, E. Calle and J. R. Mora´n, Eur. J. Org. Chem., 2009,
1009; V. Alca´zar, M. Segura, P. Prados and J. de Mendoza, Tetrahedron
Lett., 1998, 39, 1033.
8 D. E. Gross, V. Mikkilineni, V. M. Lynch and J. L. Sessler, Supramol.
Chem., 2010, 22, 135; K. Ghosh and G. Masanta, New J. Chem., 2009,
33, 1965; S. J. Brooks, C. Caltagirone, A. J. Cossins, P. A. Gale and
M. E. Light, Supramol. Chem., 2008, 20, 349; W. Huang, H. Lin, Z.
Cai and H. Lin, Talanta, 2010, 81, 967; S. K. Kim, N. J. Singh, S. J.
Kim, K. M. K. Swamy, S. H. Kim, K.-H. Lee, K. S. Kim and J. Yoona,
Tetrahedron, 2005, 61, 4545; K. Ghosh and G. Masanta, Chem. Lett.,
2006, 35, 414.
9 K. M. K. Swamy, N. J. Singh, J. Yoo, S. K. Kwon, S.-Y. Chung, C.-H.
Lee and J. Yoon, J. Inclusion Phenom. Macrocyclic Chem., 2010, 66,
107; E. Martinborough, T. M. Denti, P. P. Castro, T. B. Wyman, C. B.
Knobler and F. Diederich, Helv. Chim. Acta, 1995, 78, 1037; L. Yang,
S. Qin, X. Su, F. Yang, J. You, C. Hu, R. Xie and J. Lan, Org. Biomol.
Chem., 2010, 8, 339; K. Tsubaki, H. Tanaka, H. Morikawa and K.
Fuji, Tetrahedron, 2003, 59, 3195; J. Reeder, P. P. Castro, C. B. Knobler,
E. Martinborough, L. Owens and F. Diederich, J. Org. Chem., 1994,
59, 3151; S. Sambasivan, D.-S. Kim and K. H. Ahn, Chem. Commun.,
2010, 46, 541; K. Ghosh and T. Sen, J. Phys. Chem. B, 2011, 115, 8597.
10 C. Raposo, M. Almaraz, M. Mart´ın, V. Weinrich, M. L. Mussons, V.
Alca´zar, M. C. Caballero and J. R. Mora´n, Chem. Lett., 1995, 759; C.
Raposo, N. Pe´rez, M. Almaraz, M. L. Mussons, M. C. Caballero and
J. R. Mora´n, Tetrahedron Lett., 1995, 36, 3255; C. Raposo, M. Crego,
M. L. Mussons, M. C. Caballero and J. R. Mora´n, Tetrahedron Lett.,
1994, 35, 3409; S. Gonza´lez, R. Pela´ez, F. Sanz, M. B. Jime´nez, J. R.
Mora´n and M. C. Caballero, Org. Lett., 2006, 8, 4679.
11 C.-X. Jiao, C.-G. Niu, S.-Y. Huan, Q. Shen, Y. Yang, G.-L. Shen and
R.-Q. Yu, Talanta, 2004, 64, 637; M. Yu, H. Lin and H. Lin, Supramol.
Chem., 2008, 20, 357; D. Curiel, M. Ma´s-Montoya, G. Sa´nchez, R.
A. Orenes, P. Molina and A. Ta´rraga, Org. Biomol. Chem., 2010, 8,
4811; P. A. Gale, J. R. Hiscock, C. Z. Jie, M. B. Hursthouse and M.
E. Light, Chem. Sci., 2010, 1, 215; P. A. Gale, Chem. Commun., 2008,
4525; T. Wang, Y. Bai, L. Ma and X.-P. Yan, Org. Biomol. Chem., 2008,
6, 1751; A. K. Mahapatra, G. Hazra and P. Sahoo, Beilstein J. Org.
Chem., 2010, DOI: 10.3762/bjoc.6.12; P. Pia˛tek, V. M. Lynch and J. L.
Sessler, J. Am. Chem. Soc., 2004, 126, 16073; Y. Kato, M. M. Conn and
J. Rebek Jr., Proc. Natl. Acad. Sci. U. S. A., 1995, 92, 1208; F. Han, L.
Chi, X. Liang, S. Ji, S. Liu, F. Zhou, Y. Wu, K. Han, J. Zhao and T. D.
James, J. Org. Chem., 2009, 74, 1333; J. R. Hiscock, C. Caltagirone, M.
E. Light, M. B. Hursthouse and P. A. Gale, Org. Biomol. Chem., 2009,
7, 1781.
12 M. J. Chmielewski, M. Charon and J. Jurczak, Org. Lett., 2004, 6, 3501.
13 N. Ahmed, I. Geronimo, I.-C. Hwang, N. J. Singh and K. S. Kim,
Chem.–Eur. J., 2011, DOI: 10.1002/chem.201100243T; D. E. Gross,
V. Mikkilineni, V. M. Lynch and J. L. Sessler, Supramol. Chem.,
2010, 22, 135; D. Thangadurai, N. J. Singh, I.-C. Hwang, J. W.
Lee, R. P. Chandran and K. S. Kim, J. Org. Chem., 2007, 72,
5461; J. R. Hiscock, P. A. Gale, C. Caltagirone, M. B. Hursthouse
and M. E. Light, Supramol. Chem., 2010, 22, 647; T. D. Thangadurai,
N. J. Singh, I.-C. Hwang, J. W. Lee, R. P. Chandran and K. S. Kim, J.
Org. Chem., 2007, 72, 5461.
14 X. Yang, R. Lu, F. Gai, P. Xue and Y. Zhan, Chem. Commun., 2010,
46, 1088.
15 P. R. Schreiner and A. Wittkopp, Chem.–Eur. J., 2003, 9, 407; Z. Zhang
and P. R. Schreiner, Chem. Soc. Rev., 2009, 38, 1187.
16 T. Gunnlaugsson, P. E. Kruger, P. Jensen, J. Tierney, H. D. P. Ali and
G. M. Hussey, J. Org. Chem., 2005, 70, 10875; Q. Li, Y. Guo, J. Xu and
S. Shao, J. Photochem. Photobiol., B, 2011, 103, 140.
17 L. Fielding, Tetrahedron, 2000, 56, 6151.
6 H. Gala´n, M. T. Murillo, R. Quesada, E. C. Escudero-Ada´n, J.
Benet-Buchholz, P. Prados and J. de Mendoza, Chem. Commun.,
2010, 46, 1044; R. Joseph and C. P. Rao, Chem. Rev., 2011,
DOI: 10.1021/cr1004524; V. Stastny, P. Lhota´k, V. Michlova´, I. Stibor
and J. Sykora, Tetrahedron, 2002, 58, 7027; T. Fahlbusch, M. Frank, J.
18 J. P. Clare, A. J. Ayling, J.-B. Joos, A. L. Sisson, G. Magro, M. N. Pe´rez-
Paya´n, T. N. Lambert, R. Shukla, B. D. Smith and A. P. Davis, J. Am.
Chem. Soc., 2005, 127, 10739.
19 J. R. Hiscock, C. Caltagirone, M. E. Light, M. B. Hursthouse and P.
A. Gale, Org. Biomol. Chem., 2009, 7, 1781.
8326 | Org. Biomol. Chem., 2011, 9, 8321–8327
This journal is
The Royal Society of Chemistry 2011
©

View Online
˚
20 From the references cited herein, selected data for association constants
for benzoate versus chloride: 77000 versus 35000, in P. Pia˛tek, V. M.
Lynch and J. L. Sessler, J. Am. Chem. Soc., 2004, 126, 16073; 21 000
versus 11 100, in M. Kinsella, P. G. Duggan, J. Muldoon, K. S. Eccles,
S. E. Lawrence and C. M. Lennon, Eur. J. Org. Chem., 2011, 1125; 658
versus 15, in J. R. Hiscock, P. A. Gale, C. Caltagirone, M. B. Hursthouse
and M. E. Light, Supramol. Chem., 2010, 22, 647; 1230 versus 12, in M.
J. Chmielewski, M. Charon and J. Jurczak, Org. Lett., 2004, 6, 3501;
5670 versus 102, in J. R. Hiscock, C. Caltagirone, M. E. Light, M. B.
Hursthouse and P. A. Gale, Org. Biomol. Chem., 2009, 7, 1781; 15 135
versus 437, in D. Curiel, M. Ma´s-Montoya, G. Sa´nchez, R. A. Orenes,
P. Molina and A. Ta´rraga, Org. Biomol. Chem., 2010, 8, 4811; 1600
versus 50 in D. E. Gross, V. Mikkilineni, V. M. Lynch and J. L. Sessler,
Supramol. Chem., 2010, 22, 135.
to 2.302 A”; ref. 11: T. Wang, Y. Bai, L. Ma and X.-P. Yan, Org. Biomol.
Chem., 2008, 6, 1751“stabilized by two hydrogen bonds with N–H ◊ ◊ ◊ Cl
˚
˚
distances of 2.262 A and 2.307 A”.
23 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, J. A. Montgomery, T. Vreven Jr., K. N. Kudin, J. C.
Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci,
M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E.
Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D.
Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-
Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W.
Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A.
Pople, in Gaussian 03 Revision D.03, Gaussian, Inc, Wallingford CT,
2004.
21 B. P. Hay and V. S. Bryantsev, Chem. Commun., 2008, 2417.
22 For crystal structures of complexes between carbazole receptors and
chloride, see for example: ref. 12: M. J. Chmielewski, M. Charon and J.
Jurczak, Org. Lett., 2004, 6, 3501 “the strongest hydrogen bonds to Cl
˚
stem from NHs of the carbazole 2.22–2.33 A”; ref. 11: D. Curiel, M.
Ma´s-Montoya, G. Sa´nchez, R. A. Orenes, P. Molina and A. Ta´rraga,
˚
Org. Biomol. Chem., 2010, 8, 4811 “N–H ◊ ◊ ◊ Cl, ranging from 2.265 A
This journal is
The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 8321–8327 | 8327
©