Sulfonamide-imines as selective fluorescent chemosensors for the fluoride anion

Article abstract of DOI:10.1039/b916040j

Two new sulfonamide-type fluorescent chemosensors in organic media are reported. The two receptors, [N,N′-bis(2-tosylaminobenzylidene)-1,2- diaminoethane and N,N′-bis(2-tosylaminobenzylidene)-1,3-diamino-2- propanol], display marked changes in the fluores

Full text of DOI:10.1039/b916040j

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Sulfonamide-imines as selective fluorescent chemosensors for
the fluoride anion†
Miguel Va´zquez Lo´pez,*a Manuel R. Bermejo,*a M. Eugenio Va´zquez,b Angelo Taglietti,c
Guillermo Zaragoza,d Rosa Pedridoa and Miguel Mart´ınez-Calvoa
Received 5th August 2009, Accepted 15th October 2009
First published as an Advance Article on the web 24th November 2009
DOI: 10.1039/b916040j
Two new sulfonamide-type fluorescent chemosensors in organic media are reported. The two receptors,
[N,N¢-bis(2-tosylaminobenzylidene)-1,2-diaminoethane and N,N¢-bis(2-tosylaminobenzylidene)-
1,3-diamino-2-propanol], display marked changes in the fluorescence emission intensities as a result of
deprotonation by basic anions, and show high selectivity for fluoride over other inorganic anions, such
as acetate or dihydrogenphosphate. These results suggest that the presence of the imine group as an
intramolecular H-bond acceptor enhances the selectivity of these sensors compared to previous
examples in the literature. The deprotonation mechanism has been demonstrated by
spectrophotometric and spectrofluorimetric titrations as well as by NMR spectroscopy. The X-ray
structures of both receptors are also discussed.
promote the deprotonation of N–H receptors,10,12 making these
two anions the most significant complication for the construction
of specific receptors for the fluoride ion.13
Herein we describe two new examples of sulfonamide-based
fluorescent chemosensors (Scheme 1, H2La and H3Lb) that are
capable of detecting fluoride anions in CH3CN solution. These
compounds show high sensitivity and, at the same time, display
exceptional selectivity without interference from acetate or phos-
phate.
Introduction
The importance of inorganic anionic analytes in numerous
biological and chemical processes has stimulated the search for
improved molecular recognition and sensing of these species.1 The
monitoring of fluoride anions is of particular interest due to their
fundamental role in dental care and in osteoporosis treatment, as
well as their significant contribution to environmental pollution.2
Although a number of sensors for fluoride anions have been
reported,3 there is still a need for simple and easily accessible
receptors with improved optical response and specificity.
Most of the fluoride chemosensors described in the literature are
neutral H-bond donor receptors based on N–H proton transfer
from the donor unit to the acceptor component.4 These systems
include ureas,5 thioureas,6 amides,7 sulfonamides8 and pyrroles,9
with the fluoride acting as an acceptor. The more acidic the
donor, the stronger the receptor-anion interaction and, in a
limiting situation, exceptionally acidic donor moieties may suffer
deprotonation on interaction with strongly basic anionic species.10
For fluoride ions the deprotonation process is also favoured due
to the formation of the particularly stable HF2- dimer.11 However,
highly basic inorganic anions such as CH3CO2- or H2PO4- can also
Experimental section
General information
Chemicals and solvents of the highest commercial grade available
were used without further purification. FAB mass spectra were
recorded on a Micromass Autospec spectrometer, employing
m-nitrobenzyl alcohol as the matrix. Elemental analyses were
performed on a Carlo Erba EA 1108 analyzer. NMR spectra
were recorded on a Bruker DPX-250 using CD3CN as solvent.
UV/Vis spectra were recorded on HP 8452A or on Jasco V-630
spectrometers. Fluorescence emission spectra were recorded on a
Jobin-Ivon Fluoromax-3 spectrometer. Titrations were performed
on 1 or 2 mL samples of solutions of the receptors (10 or 40 mM) in
CH3CN, by addition of CH3CN stock solutions of the appropriate
anion in the form of tetrabutylammonium salts.
The structure determination of H3Lb was performed at low
temperature with a Bruker Appex II CCD diffractometer, using
graphite-monochromated Mo-Ka radiation from a fine focus
sealed tube source. Intensities were corrected for absorption
(SADABS). The structures were successfully solved by direct
methods (SIR97),14 which gave the positions of most of the
non-hydrogen atoms. The remaining atoms were identified by
successive Fourier difference synthesis. Refinements were carried
out on F2 by full-matrix least-squares techniques using SHELXL-
97.15 The positions of all H atoms were calculated geometrically
and a riding model was used in their refinement except for those H
aDepartamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, Universidad
de Santiago de Compostela, 15782, Santiago de Compostela, Spain. E-mail:
miguel.vazquez.lopez@usc.es, manuel.bermejo@usc.es
bDepartamento de Qu´ımica Orga´nica, Facultad de Qu´ımica, Universidad de
Santiago de Compostela, 15782, Santiago de Compostela, Spain
cDipartimento di Chimica Generale, Universita` di Pavia, 27100 Pavia, Italy
dServicio de Difraccio´n de Rayos X, Edificio CACTUS, Universidad de
Santiago de Compostela, 15782 Santiago de Compostela, Spain
† Electronic supplementary information (ESI) available: Crystallographic
data for H3Lb, selected bond distances and angles for H3Lb, 1H NMR
titrations of H2La and H3Lb with fluoride ions and spectrophotomet-
ric and spectrofluorimetric titrations of H2La with OH-, acetate and
dihydrogenphosphate ions and of H3Lb with OH-, fluoride, acetate
and dihydrogenphosphate ions. CCDC reference number 746892. For
ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/b916040j
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 357–362 | 357
©

View Article Online
Scheme 1 a) TABO;13 b) H2La; c) H3Lb
atoms involved in the intramolecular and intermolecular hydrogen
Results and discussion
bonds, which were found in a difference electron-density map and
then refined with their coordinates riding on the corresponding
carrier heteroatom.
N,N¢-Bis(2-tosylaminobenzylidene)-1,2-diaminoethane (H2La,
Scheme 1) was prepared by a modification of a previously
reported method.16 The first step involved the N-tosylation of
2-aminobenzyl alcohol with tosyl chloride in CH2Cl2 in the
presence of NEt3 to give tosylamidobenzyl alcohol (I).16
Subsequent oxidation of the OH group in I with g-MnO2 afforded
2-tosylaminobenzaldehyde (II).16,17a The final step involved the
condensation between aldehyde II and 1,2-diaminoethane in
chloroform.17b,18 Likewise, N,N¢-bis(2-tosylaminobenzylidene)-
1,3-diamino-2-propanol (H3Lb Scheme 1) was synthesized
following a reported procedure.16
The acidity and poor hydrogen-bonding donor ability of the
sulfonamide group made it easy to deprotonate with basic accep-
tors. In the TABO chemosensor recently reported by Peng’s group
(Scheme 1),13 the acidity is enhanced by a strong intramolecular
H-bond between the N–H fragment of the sulfonamide group
and the nitrogen atom of the adjacent benzimidazole moiety. This
feature allows fluoride and even acetate (which is a little less basic)
to deprotonate the amide group with comparable effectiveness.
We envisaged that the replacement of the benzimidazole moiety
of the TABO receptor by a weaker H-bond acceptor unit like
Synthesis
2-Tosylaminobenzyl alcohol (I). Triethylamine (1.7 mL,
12.2 mmol) was added to a solution of 2-aminobenzyl alcohol
(1.5 g, 12.2 mmol) in CH2Cl2 (100 mL). The mixture was heated
◦
at 30 C and tosyl chloride (2.5 g, 13.1 mmol) was added to the
mixture after the alcohol had completely dissolved. The reaction
mixture was heated under reflux for 8 h. The resulting red solution
was filtered through Celite and washed with aqueous HCl (pH =
4; 3 ¥ 100 mL). The combined organic fractions were dried over
Na2SO4 and partially concentrated under reduced pressure at
25 ◦C. The product was precipitated with Et2O. The resulting pale
yellow solid was recrystallized from CH2Cl2. Yield: 75%. Mass
spectrometry (ESI): m/z = 278.1 [I + H]+.16
2-Tosylaminobenzaldehyde (II). g-MnO2 (0.552 g, 6.3 mmol)
was added to a solution of 2-tosylaminobenzyl alcohol (0.440 g,
1.6 mmol) in dry CH2Cl2 (50 mL) under argon. The suspension
was stirred at r.t. for 15 h and then filtered through Celite. The
filtrate was partially concentrated on a rotatory evaporator at
25 ◦C and the product was precipitated with Et2O. The resulting
pale yellow solid was recrystallized from CH2Cl2. Yield: 78%. Mass
spectrometry (ESI): m/z = 276.1 [II + H]+.16,17a
=
the imine group (C N) would diminish the acidity of the N–H
donor fragment of the sulfonamide moiety, resulting in increased
selectivity between fluoride and acetate ions.
X-ray studies
N,N¢-Bis(2-tosylaminobenzylidene)-1,2-diaminoethane (H2La).
1,2-Diaminoethane (0.030 mL, 0.45 mmol) was added to a solu-
tion of tosylaminobenzaldehyde (0.25 g, 0.91 mmol) in chloroform
(25 mL). The mixture was heated under reflux and the volume of
the solution was reduced to about 5 mL over a period of 4 h
in a Dean–Stark trap. The resulting bright yellow solution was
filtered through a thin Celite bed and concentrated under reduced
pressure at 40 ◦C. The product was precipitated with methanol as
a bright yellow solid and this was collected by filtration, washed
with Et2O and dried in vacuo. Yield: 95%. Anal. Found: C, 62.65;
H, 5.14; N, 9.59; S, 10.38; Calc. for C30H30N4O5S2: C, 62.72; H,
5.05; N, 9.75; S, 10.76. Found: Mass spectrometry (FAB): m/z =
575.3 [H2L1 + H]+. 1H NMR data (see ESI†). lmax (e, CH3CN) =
220 (35984 M-1 cm-1), 264 (10350), 316 (2986) nm.17b,18
Yellow crystals of H2La were formed by slow evapora-
tion at room temperature of a solution of the receptor in
chloroform.17b H2La exhibits two strong intramolecular H-
bonding N(amide)–H ◊ ◊ ◊ N(imine) interactions, one on each of the
2-tosylaminobenzylidene moieties (Fig. 1). The distances between
˚
these N atoms are 2.705(3) and 2.681(3) A for N1 ◊ ◊ ◊ N2 and
˚
N3 ◊ ◊ ◊ N4, respectively (H1A ◊ ◊ ◊ N2 = 1.84 A and H4A ◊ ◊ ◊ N3 =
˚
1.80 A). It is also worth mentioning that intermolecular H-bonds
or aromatic interactions between neighboring molecules were not
observed in the crystal cell.
Single crystals of H3Lb suitable for X-ray diffraction studies
were formed by slow evaporation of a CH3CN solution of the
receptor at room temperature. The main crystallographic data and
bond distances are listed in the ESI.† There are two independent
358 | Org. Biomol. Chem., 2010, 8, 357–362
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 1 Structural parameter of the hydrogen-bonded interactions
Distance Distance
Donor–H ◊ ◊ ◊ Acceptor (A) D–H (A) H ◊ ◊ ◊ A (A) D ◊ ◊ ◊ A (D–H ◊ ◊ ◊ A)
Distance
˚
Angle (◦)
˚
˚
N(1)–H(1 N) ◊ ◊ ◊ N(2)
N(4)–H(4 N) ◊ ◊ ◊ N(3)
O(5)–H(5O) ◊ ◊ ◊ O(2)a
N(5)–H(5 N) ◊ ◊ ◊ N(6)
N(8)–H(8 N) ◊ ◊ ◊ N(7)
0.84(3)
0.84(4)
0.89(3)
0.86(4)
0.85(3)
2.02(3)
1.92(4)
1.91(3)
1.90(4)
1.96(3)
1.79(2)
2.661(4)
2.642(4)
2.686(4)
2.657(4)
2.650(5)
2.686(4)
133(3)
144(4)
145(4)
146(4)
138(3)
163(5)
O(10)–H(10O) ◊ ◊ ◊ O(9)b 0.93(4)
Symm Code: a (0.5 - x, 0.5 + y, 1.5 - z). b (1.5 - x, -0.5 + y, 1.5 - z).
intermolecular hydrogen bonds leads to the formation of zig-zag
1D supramolecular chains (Fig. 3) along the b-direction.
Recently, Gale et al. have reported the X-ray structures of
some deprotonated sulfonamide receptors.8b Unfortunately, all the
attempts to obtain single crystals of any of the two anion-sensor
complexes described herein were unsuccessful.
Fig. 1 ORTEP representation of the crystal structure of receptor H2La.17b
H atoms, except for those involved in intramolecular hydrogen bonds, have
been omitted for clarity. Thermal ellipsoids are at 30% of probability.
molecules with opposite chirality in the asymmetric unit of the
crystal cell of H3Lb, giving rise to nearly identical intra- and
intermolecular hydrogen-bonding interactions, and therefore we
will only discuss one of them.
The structure (Fig. 2) reveals the formation of the symmetrical
Schiff base, with the two tosylamide arms oriented in opposite
directions in order to minimize the steric repulsions.
The arrangement of the two 2-tosylaminobenzylidene moieties
of H3Lb is also highly conditioned by two strong intramolecu-
lar N(amide)–H ◊ ◊ ◊ N(imine) H-bonds. Moreover, there are also
hydrogen-bonding interactions between adjacent molecules, which
are connected through the oxygen atoms of the tosyl groups and
the OH group of the aliphatic spacer (Table 1). The network of
Anion binding studies
The interaction of H2La and H3Lb with various anions was
systematically studied by UV/Vis and fluorescence emission
titrations, which were performed in CH3CN by addition of a
standard solution of the corresponding tetraalkylammonium salt
of the anion to a solution of the receptor.
The absorption spectrum of H2La in CH3CN has three bands
with maxima at 220, 264 and 316 nm. Titration of this ligand with
fluoride anions resulted in a bathochromic shift of the spectra
with an isosbestic point at 236 nm and the formation of a new
absorption band with a maximum at 361 nm (Fig. 4).
Fig. 2 ORTEP representation of the structures of the two independent molecules of the receptor H3Lb founded in the asymmetric unit of the crystal cell.
H atoms (except for those involved in inter or intramolecular hydrogen bonds) have been omitted for clarity. Thermal ellipsoids are at 50% of probability.
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 357–362 | 359
©

View Article Online
Fig. 5 Spectrofluorimetric titration of a CH3CN solution 10 mM in H2La
with a standard solution of fluoride ions. Inset: fluorescence intensity at
454 nm vs. concentration of fluoride ions (lex = 313 nm).
fluorescence emission increased markedly (Fig. 5).13 This new
fluorescence emission band matches well with the band formed
in the presence of tetrabutylammonium hydroxide, suggesting
that it can be ascribed to the deprotonated anion (La)2-. The
fluorescence titration profile at 454 nm presents a slow increase
at low concentrations of fluoride, resulting form the displacement
experimented by the emission band. As with the UV titrations,
we observed that CH3CO2- and H2PO4- only induced comparable
signal changes at much higher concentrations than fluoride, and
Fig. 3 Stick representation of part of the crystal cell of the receptor H3Lb,
showing the intermolecular H bonds established between the tosyl O atoms
and the OH group of the aliphatic spacer in adjacent molecules.
none of the other anions investigated (HSO4 , Cl-, Br-, I- or NO3 )
induced any noticeable fluorescence emission changes.
-
-
The UV/Vis and fluorescence emission titrations were repeated
with the receptor H3Lb, which contains a 2-propanol spacer. This
moiety was selected because it was found that the hydroxyl group
encourages the formation of an intermolecular H-bond between
neighbouring molecules through the oxygen atoms of the tosyl
groups.18,19 Furthermore, we were interested in studying the effect
that these intermolecular interactions could have on the acidity of
the N–H donor fragments of the receptor. The participation of the
OH group of H3Lb in intermolecular H-bonding was confirmed
by the X-ray data, as indicated above (Fig. 3).
H3Lb has a similar UV spectrum to H2La in MeCN. As with
H2La, the addition of fluoride anions induce a bathochromic shift
resulting from the formation of the anionic species (HLb)2-, as
demonstrated by the coincidence of the emission spectrum in
the presence of tetrabutylammonium hydroxide. Once again, only
CH3CO2- and H2PO4- were able to deprotonate the receptor H3Lb
but these gave only a residual response. The fluorescence response
of H3Lb also parallels the observations discussed previously for
H2La. H3Lb displayed very weak fluorescence emission at 509 nm
(lex = 313 nm) in CH3CN. The addition of fluoride resulted in
the appearance of a strong fluorescence emission band at 461 nm
that progressively increased with the addition of the salt and the
formation of the deprotonated anion species (HLb)2-. Once again,
CH3CO2 and H2PO4 induce similar spectral changes, but with
much less sensitivity. The difference in the behaviour of H3Lb in
the presence of different anions is clearly distinguishable by the
fluorescence intensity, not only quantitatively in the fluorimeter
but also under a hand-held UV lamp (lex = 365 nm), as shown in
Fig. 6.
Fig. 4 Spectrophotometric titration of a CH3CN solution 40 mM in H2La
with a standard solution of fluoride ions. Inset: absorbance at 361 nm vs.
concentration of fluoride ions.
The new band at 361 nm matches well with the absorption band
formed in the presence of tetrabutylammonium hydroxide and can
be assigned to the deprotonated anion (La)2-. Analogous titrations
were also carried out with CH3CO2 , H2PO4 , HSO4 , Cl-, Br-, I-
-
-
-
-
and NO3 . However, the receptor H2La could only be deprotonated
at very high concentrations of CH3CO2 and H2PO4 . Changes in
the spectra were not observed on the addition of any of the other
anions.
-
-
-
-
Spectrofluorimetric titrations of H2La with the same series
of anions were also carried out in CH3CN. H2La shows very
weak fluorescence, with an emission band centered at 510 nm
(lex = 313 nm). As expected, the addition of fluoride anions
induced a significant blue shift of this band (454 nm) and the
360 | Org. Biomol. Chem., 2010, 8, 357–362
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 2 Log KD for H2La and H3Lb interaction with anions
a
b
log KD
log KD
Anion
H2La
H3Lb
H2La
H3Lb
F-
CH3CO2
H2PO4
8.652 0.03
5.915 0.07
4.284 0.12
8.911 0.05
6.203 0.09
4.497 0.08
8.406 0.09
5.841 0.12
4.017 0.09
8.669 0.06
6.048 0.08
4.486 0.10
-
-
a From UV/Vis titration spectra. b From fluorescence titration spectra.
HF + F- ꢀ HF2
(2)
-
The overall equilibrium, with a stoichiometry of 1 : 4 for HnL-
fluoride interactions, can be obtained combining eqn (1) and (2):13
HnL + 4F- ꢀ H(n-2)L2- + 2HF2
(3)
-
This two-step equilibrum can also be applied to the N–H
-
deprotonation processes promoted by the anions CH3CO2 and
H2PO4 , which can also form relatively stable dimers.10,12,13
-
The UV/Vis and fluorescence emission titration data were fitted
to the above model using the SPECFIT/32TM programme.21 The
corresponding KD values are compiled in Table 2. These KD
values demonstrate that receptors H2La and H3Lb can selectively
detect fluoride ions by a fluorogenic “OFF/ON” response with
high sensitivity and selectivity. Previously reported sulfonamide
chemosensors do not display this level of selectivity.
Fig. 6 Relative fluorescence intensities of 10 mM solutions of receptors
H2La (lem = 454 nm) and H3Lb (lem = 461 nm) in the presence of 20 equiv. of
F-, CH3CO2- and H2PO4- in CH3CN (lex = 313 nm). Bottom, fluorescence
visual features of the interaction of inorganic anions with receptor H3Lb
in CH3CN solution (10 mM) under a UV lamp (lex = 365 nm); from left
to right: +20 equiv. of CH2CO2-; +20 equiv. of H2PO4-; free receptor;
+20 equiv. of F-.
Conclusions
In summary, we have developed a new family of fluorescent
sulfonamide chemosensors for fluoride ions in organic media.
These systems are based on the deprotonation of the amide donor
fragments in the presence of highly basic inorganic anions. The
presence of the imine group as an intramolecular H-bond acceptor
enhances the selectivity of these sensors compared to previous
examples in the literature. The equilibrium constants for fluoride
anions are two orders of magnitude larger than those calculated
for acetate, and four orders of magnitude larger than those
for dihydrogenphosphate. The deprotonation mechanism has
beendemonstrated by spectrophotometric andspectrofluorimetric
titrations as well as by NMR spectroscopy. The X-ray structures
of both receptors are also discussed.
Finally, we observed that the presence of an OH group in the
aliphatic spacer of the receptor causes a slight increase in the
equilibrium constants. We believe that this effect could be due to
hydrogen bonding interactions between the tosyl O atoms and the
OH group and the influence of these interactions on the donor
properties of the N-H fragments of the receptor. We are currently
studying this interaction as a means to modulate the affinity (and
selectivity) of this class of chemosensors.
NMR studies
The 1H NMR spectra in CD3CN of H2La and H3Lb show obvious
changes on addition of fluoride ions. In both spectra the NH
signal (13.11 ppm for H2La and 13.25 for H3Lb) rapidly disappears;
the imine proton signal shifts downfield and the aromatic proton
signals shift slightly when F- ions are added. These observations
further confirm that the fluoride anion causes deprotonation of
the amide groups of both receptors.
Equilibrium constants
From the data collected, it is clear that the changes in the NMR,
UV/Vis and emission spectra of H2La and H3Lb in MeCN in
the presence of F- are a consequence of the deprotonation of the
sensors and the formation of the anionic species (La)2- and (HLb)2-.
The deprotonation process of the N–H fragments of H2La and
H3Lb promoted by fluoride anions follow the acid–base reaction
equilibrium below:13
Acknowledgements
HnL + 2F- ꢀ H(n - 2)L2- + 2HF (KD)
(1)
The Galician Directorate-General for Research and Development
(DXID) (PGIDIT06PXIB209055PR) and the Spanish Ministry
for Science and Innovation (MCI) (CTQ2006-01339) funded this
work. M. V. L. thanks the Spanish MCI for a Ramo´n y Cajal
-
Moreover, considering the particularly high stability of the HF2
dimer,11 it can be suggested that the following dimer formation
process occurs in the subsequent step:20
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 357–362 | 361
©

View Article Online
grant. M. E. V. also thanks the Spanish MCI for a Ramo´n y Cajal
grant. M. V. L. dedicates this work to his newborn and second
son, Gabriel.
8 (a) M. A. Hossain, S. O. Kang, J. M. Llinares, D. Powell and K.
Bowman- James, Inorg. Chem., 2003, 42, 5043; (b) C. Caltagirone, G. W.
Bates, P. A. Gale and M. E. Light, Chem. Commun., 2008, 61; (c) S.
Valiyaveettil, J. F. J. Engbersen, W. Verboom and D. N. Reinhoudt,
Angew. Chem., Int. Ed. Engl., 1993, 32, 900; (d) S. Kondo, T. Suzuki
and Y. Yano, Tetrahedron Lett., 2002, 43, 7059; (e) A. J. Ayling, M. N.
Pe´rez-Paya´n and A. P. Davis, J. Am. Chem. Soc., 2001, 123, 12716.
9 J. L. Sessler, M. J. Cyr, V. Lynch, E. McGhee and J. A. Ibers, J. Am.
Chem. Soc., 1990, 112, 2810.
10 (a) M. Boiocchi, L. Del Boca, D. Esteban-Go´mez, L. Fabbrizzi, M.
Licchelli and E. Monzani, Chem.–Eur. J., 2005, 11, 3097; (b) R. M.
Duke, J. E. O’Brien, T. McCabe and T. Gunnlaugsson, Org. Biomol.
Chem., 2008, 6, 4089.
References
1 (a) Supramolecular Chemistry of Anions ed. A. Bianchi, K. Bowman-
James, E. Garc´ıa-Espan˜a, Wiley-VCH, New York, 1997; (b) P. D. Beer,
Acc. Chem. Res., 1998, 31, 71; (c) C. R. Bondy and S. J. Loeb, Coord.
Chem. Rev., 2003, 240, 77; (d) P. A. Gale and R. Quesada, Coord.
Chem. Rev., 2006, 250, 3219; (e) C. Suksai and T. Tuntulani, Chem.
Soc. Rev., 2003, 32, 192; (f) C. Bowman-James, Acc. Chem. Res., 2005,
38, 671; (g) T. Gunnlaugsson, M. Glynn, G. M. Tocci, P. E. Kruger and
F. M. Pfeffer, Coord. Chem. Rev., 2006, 250, 3094; (h) V. Amendola, D.
Esteban Go´mez, L. Fabbrizzi and M. Licchelli, Acc. Chem. Res., 2006,
39, 343; (i) R. Mart´ınez-Ma´n˜ez and F. Sanceno´n, Chem. Rev., 2003,
103, 4419; (j) J. L. Sessler and J. M. Davis, Acc. Chem. Res., 2001, 34,
989; (k) M. Berger and F. P. Schmidtchen, Chem. Rev., 1997, 97, 1609.
2 (a) B. Moss, Chem. Ind., 1996, 407; (b) J. M. Tomich, D. Wallace, K.
Henderson, K. E. Mitchell, G. Radke, R. Brandt, C. Ambler, A. J.
Scott, J. Grantham, L. Sullivan and T. Iwamoto, Biophys. J., 1998, 74,
256; (c) S. Matsuo, K. Kiyomiya and M. Kurebe, Arch. Toxicol., 1998,
72, 798; (d) D. Briancon, Rev. Rhum, 1997, 64, 78.
11 S. Gronert, J. Am. Chem. Soc., 1993, 115, 10258.
12 D. Esteban Go´mez, L. Fabbrizzi, M. Licchelli and E. Monzani, Org.
Biomol. Chem., 2005, 3, 1495.
13 Y. Wu, X. Peng, J. Fan, S. Gao, M. Tian, J. Zhao and S. Sun, J. Org.
Chem., 2007, 72, 62.
14 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacov-
azzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and R. Spagna,
J. Appl. Crystallogr., 1999, 32, 115.
15 G. M. Sheldrick, SHELX97, Programs for Crystal Structure Analysis,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
16 M. Va´zquez Lo´pez, G. Zaragoza, R. Pedrido, G. Rama and M. R.
Bermejo, Inorg. Chem. Commun., 2008, 11, 995.
3 (a) M. Va´zquez, L. Fabbrizzi, A. Taglietti, R. M. Pedrido, A. M.
Gonza´lez-Noya and M. R. Bermejo, Angew. Chem., Int. Ed., 2004, 43,
1962; (b) T. Gunnlaugsson, P. E. Kruger, P. Jensen, J. Tiemey, H. D. P.
Ali and G. M. Hussey, J. Org. Chem., 2005, 70, 10875; (c) M. Boiocchi,
L. D. Boca, D. E. Go´mez, L. Fabbrizzi, M. Licchelli and E. Monzani,
J. Am. Chem. Soc., 2004, 126, 16507.
17 (a) J. Mah´ıa, M. A. Maestro, M. Va´zquez, M. R. Bermejo, A. M.
Gonza´lez and M. Maneiro, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 1999, 55, 2158; (b) J. Mah´ıa, M. A. Maestro, M. Va´zquez,
M. R. Bermejo, A. M. Gonza´lez and M. Maneiro, Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun., 2000, 56, 347.
18 A. M. Garc´ıa-Deibe, J. S. Matalobos, M. Fondo, M. Va´zquez and M. R.
Bermejo, Inorg. Chim. Acta, 2004, 357, 2561.
4 T. Steiner, Angew. Chem., Int. Ed., 2002, 41, 48.
5 A. B. Descalzo, K. Rurack, H. Weisshoff, R. Martinez-Ma´n˜ez, M. D.
Marcos, P. Amoros, K. Hoffmann and J. Soto, J. Am. Chem. Soc., 2005,
127, 184.
6 T. Gunnlaugsson, A. P. Davis, G. M. Hussey, J. Tierney and M. Glynn,
Org. Biomol. Chem., 2004, 2, 1856.
7 P. A. Gale, Chem. Commun., 2005, 3761.
19 M. Va´zquez Lo´pez, G. Zaragoza, M. Otero, R. Pedrido, G. Rama and
M. R. Bermejo, Cryst. Growth Des., 2008, 8, 2083.
20 V. Amendola, M. Boiocchi, L. Fabbrizzi and A. Palchetti, Chem.–
Eur. J., 2005, 11, 5648.
21 H. Gampp, M. Maeder, C. J. Meyer and A. D. Zuberbuehler, Talanta,
1985, 32, 1133.
362 | Org. Biomol. Chem., 2010, 8, 357–362
This journal is
The Royal Society of Chemistry 2010
©