Naked eye detection of anions by alkynyl-ruthenium exo-receptors: Selective recognition of fluoride anion

Article abstract of DOI:10.1039/b503698d

Alkynyl-ruthenium complexes bearing terminal hydrogen-bonding receptors act as efficient anion sensors exhibiting large guest-induced colour changes and show unexpectedly high selectivity to fluoride ions. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b503698d

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Naked eye detection of anions by alkynyl-ruthenium exo-receptors:
selective recognition of fluoride anion{
Jean-Luc Fillaut,*a Julien Andrie`s,a Lo¨ıc Toupetb and Jean-Pierre Desvergnec
Received (in Cambridge, UK) 14th March 2005, Accepted 13th April 2005
First published as an Advance Article on the web 29th April 2005
DOI: 10.1039/b503698d
the metal and the remote groups through the p-conjugated
path,11,12 even weak second-sphere interactions are expected to
provoke the discernable changes required for efficient colorimetric
sensing.
Alkynyl-ruthenium complexes bearing terminal hydrogen-
bonding receptors act as efficient anion sensors exhibiting large
guest-induced colour changes and show unexpectedly high
selectivity to fluoride ions.
We report herein a series of anion sensors possessing hydrogen
bonding recognition sites at the remote end of alkynyl-ruthenium
derivatives. These ruthenium-acetylide based sensors were applied
to the colorimetric detection of F2, AcO2 and H2PO42 anions at a
low analyte concentration and shed new light on electrostatic
repulsive effects as a mean to discriminate these anionic species.
Compounds 4a,b and 5a were obtained starting from the corres-
ponding acetylenic units bearing thiazolidinedione, rhodanine and
barbituric acid moieties 2a,b and 3a{ via a two step procedure
(Scheme 1).13 Compound 5b was obtained by a Knoevenagel
condensation of thiobarbituric acid with trans-(dppe)2Ru(Cl)-
(CMC–C6H4–CHO).14 Compounds 4–5 are characterised by strong
absorption bands due to a dp(Ru) A p*(CMCR) metal-to-ligand
charge transfer transition in the visible region (4a lmax 5 490 nm in
Recognition of anions by colorimetric sensors is a research area of
importance due to the paramount role of these species in the
environment, biology, etc.1–5 Although the incorporation of
transition metal subunits has led to several strategies in this field,6
transition metal s-acetylide complexes have rarely been considered
as potential sensors for small molecules and ionic species.7–10 As
these organometallic systems, which possess an almost linear
M–CMC–R structure, allow efficient electronic coupling between
methylene chloride; emax 5 2.5 6 104 dm3 mol21cm21; 5a lmax
5
590 nm; emax 5 4.0 6 104 dm3 mol21 cm21).
The structure of the model compound 7 indicates the planarity
of the conjugated ligand and reveals the absence of steric
constraints around the terminal organic receptor moiety (Fig. 1).{
Instantaneous colour changes were observed upon addition of
2
F2, AcO2 or H2PO4 anions (Fig. 2) to 4 or 5. Conversely no
detectable colour change is observed even upon addition of large
excesses of HSO42, Cl2 , Br2 and NO32. Not surprisingly, the
colour of a methylene chloride solution of the model compound 7,
Scheme 1 Reagents and conditions a) [(dppe)2RuCl]+TfO2, 4-ethynyl-
benzaldehyde
1,
(5Z)-5-(4-ethynylbenzylidene)-1,3-thiazolidine-2,4-
dione 2a or (5Z)-5-(4-ethynylbenzylidene)-2-thioxo-1,3-thiazolidin-4-one
2b (1.1 equiv.), CH2Cl2; b) t-BuOK, THF; c) [(dppe)2RuCl]+TfO2, 5-(4-
ethynylbenzylidene)pyrimidine-2,4,6-trione 3a (1.1 equiv.), THF; d) NEt3,
CH2Cl2; e) 5-[(5-ethynylthien-2-yl)methylene]-1,3-dimethyl-pyrimidine-
2,4,6-trione 6 f) thiobarbituric acid, THF, EtOH, reflux, 1 week.
Fig. 1 ORTEP view of
7 showing 50% probability displacement
{ Electronic supplementary information (ESI) available: details of
synthetic, X-ray crystallographic and spectroscopic experiments. See
http://www.rsc.org/suppdata/cc/b5/b503698d/
˚
ellipsoids and the atom numbering. Selected bond lengths (A), bond
angles (deg): Ru1–C1 1.977(2); C1–C2 1.204(3); C2–C3 1.406(3); C10–O2
1.214(4); Ru1–C1–C2 177.2(2); C1–C2–C3 174.0(3).
*jean-luc.fillaut@univ-rennes1.fr
2924 | Chem. Commun., 2005, 2924–2926
This journal is ß The Royal Society of Chemistry 2005

View Article Online
Table 1 Affinity constants for compounds 4 and 5 (M21) with
anionic substrates in dichloromethane at 22 uC
Anion
4a
4b
5a
5b
F2
log K1
log K1?K2
AcO2
log K1
log K1?K2
H2PO4
5.2 ¡ 0.1 6.7 ¡ 0.2
5.0 ¡ 0.1 7.1 ¡ 0.4
4.2 ¡ 0.1a
10.6 ¡ 0.1
4.7 ¡ 0.1a
11.2 ¡ 0.1
4.0 ¡ 0.1
7.1 ¡ 0.2
4.6 ¡ 0.1
8.8 ¡ 0.2
2
log K1
log K1?K2
a
4.2 ¡ 0.1 ndb
3.4 ¡ 0.1
4.4 ¡ 0.1
7.6 ¡ 0.3
ndc
b
Maximal values.
Non-determined because of competitive
c
deprotonation. The second equilibrium was suppressed during the
fitting process because of the very low concentration of
[5a.(H2PO4)2]22
.
estimated based on 1:1 (host–guest) binding models for complexes
4–5. The calculated K1 (Table 1) values for F2, AcO2 and
2
H2PO4 anions are qualitatively in agreement with their basicity.
Fig. 2 Colour changes induced by the addition of anions (10 eq.) or
piperidine (20 eq.) to complexes 4a (a), 4b (b), 5a (c) and 5b (d) (6.7 6
1025 M solutions in methylene chloride). Anions were added in the form
of their tetrabutylammonium salts.
These values confirm that complexes 4 with a sole binding site are
definitely not selective. The plots for 5a,b suggest that the
stoichiometry of the host–guest complexes is not simply 1:1.
Since there are two potential binding sites in 5a and 5b, it is
reasonable to assume a 1:2 stoichiometry for the corresponding
host–guest complexes.
which bears a dimethylbarbituric moiety, was not affected by the
addition of anionic species whatever they are.15 On the other hand,
The first complexation of F2 and AcO2 anions leads to
association constants of rather close values (5a log K1 # 4)
indicating that differences in their intrinsic basicity and electro-
negativity are not dominant. The selectivity of 5a and 5b with
respect to these anions results from the considerable differences in
the K2 values (5a F2 log K2 # 6; AcO2 log K2 # 3). Thus, the
discrimination between fluoride and other anions by 5a and 5b is
mainly due to their relative capability to achieve 1:2 host–guest
complexes. This suggests that the discrimination between AcO2
and F2 results from modifications of the density of charge in the
exo-receptor because of the complexation of a first anionic species.
As carbonyl (or thiocarbonyl) groups face approaching anions, we
assume that electrostatic repulsions20–22 exerted by these groups
over antagonist groups (CLO; PLO) are enhanced by the
complexation of a first anion to receptors 5 and disfavor
subsequent binding of oxoanions. F2 is thus the anion which
presents the most suitable characteristics (electronegativity and
size) to establish a strong H-bond interaction with the remaining
–NH binding site of the receptors [5.A2].
2
the changes observed upon addition of F2, AcO2 and H2PO4
anions to complexes 4–5 are fully reversed upon addition of water
which presumably competes with these anions.
Sensors 4a and 4b which contain only one recognition site,
proved to be inefficient at distinguishing between AcO2 and F2.
Complete colour changes are observed for 4a upon addition of
6 equiv. of F2 or 10 equiv. of AcO2 (4a: lmax 5 490 nm; emax
2.5 6 104 dm3 mol21cm21; [4a.F2] and [4a.AcO2]: lmax 5 415 nm;
max 5 2.3 6 104 dm3 mol21cm21). The presence of a thiocarbonyl
5
e
unit in 4b results in a higher sensitivity of the sensors and in the
lack of discrimination between the anions. The complete colour
change of the methylene chloride solution of 4b occurs upon
addition of 2 equiv. of AcO2 as well as 2 equiv. of F2, (4b:
lmax 5 550 nm; emax 5 2.6 6 104 dm3 mol21cm21; [4b.F2] and
[4b.AcO2]: lmax 5 465 nm; emax 5 2.2 6 104 dm3 mol21cm21).
More striking results were obtained upon addition of anions to
5a and 5b, as these compounds exhibit unexpectedly high
selectivity to fluoride ions, even in the presence of other anions.
Thus, 5a undergoes a blue (lmax 5 590 nm; emax 5 4.0 6
104 dm3 mol21cm21) to orange fluoride anion-induced colour
change (lmax 5 480 nm; emax 5 2.6 6 104 dm3 mol21cm21). Even
if they result from ‘‘incipient proton-transfer reactions’’16 these
colour changes differ from those observed in the deprotonation
process as monitored by addition of piperidine in methylene
chloride, (lmax 5 340 nm; emax 5 2.2 6 104 dm3 mol21cm21).17
Complete colour change is effected upon the addition of 4 equiv.
In summary, alkynyl-ruthenium derivatives linked to non pre-
organized receptors provide an unexplored class of anion receptors
that are adapted to the visual detection of anions in methylene
chloride. Additionally, compounds 4–5 consist of receptors where
carbonyl units face the complexed anions resulting in an
unprecedented model of discrimination between anionic species.
Financial support from ‘‘la Re´gion Bretagne’’ for a PhD grant
to J. A. and from the CNRS is gratefully acknowledged.
2
of F2 to 5a. Colour changes upon addition of AcO2 or H2PO4
Jean-Luc Fillaut,*a Julien Andrie`s,a Lo¨ıc Toupetb and
Jean-Pierre Desvergnec
anions require significantly larger amounts of these salts (5a:
260 equiv. of AcO2 or more than 1000 equiv. H2PO42).
aInstitut de Chimie de Rennes, Laboratoire «Organome´talliques et
Catalyse: Chimie et Electrochimie Mole´culaires», UMR 6509 CNRS,
Universite´ de Rennes 1, Campus de Beaulieu, 35042, Rennes cedex,
France. E-mail: jean-luc.fillaut@univ-rennes1.fr; Fax: 33 22323 6939;
Tel: 33 22323 5952
Various stoichiometries were tested and rationalized with respect
to the quality of the fitting parameters and the physical significance
of the calculated spectra.18,19 The equilibrium constants were first
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 2924–2926 | 2925

View Article Online
bLaboratoire de la Physique de la Matie`re Condense´e, UMR 6626
CNRS, Universite´ de Rennes 1, Campus de Beaulieu, 35042, Rennes
cedex, France. E-mail: loic.toupet@univ-rennes1.fr; Fax: 33 22323 6717;
Tel: 33 22323 6497
9 V. W. W. Yam, R. P. L. Tang, K. M. C. Wong and K. K. Cheung,
Organometallics, 2001, 20, 4476.
10 Q. Z. Yang, L. Z. Wu, H. Zhang, B. Chen, Z. X. Wu, U. P. Zhang and
C. H. Tung, Inorg. Chem., 2004, 43, 5195.
11 N. J. Long and C. K. Williams, Angew. Chem. Int. Ed., 2003, 42,
2586.
12 C. E. Powell and M. G. Humphrey, Coord. Chem. Rev., 2004, 248,
725.
cLaboratoire de Chimie Organique et Organome´tallique, UMR 5802
CNRS, Universite´ Bordeaux 1, 351, Cours de la Libe´ration, 33405,
Talence cedex, France. E-mail: jp.desvergne@lcoo.u-bordeaux1.fr;
Fax: 33 55684 6646; Tel: 33 55684 6283
13 D. Touchard, P. Haquette, S. Guesmi, L. LePichon, A. Daridor,
L. Toupet and P. H. Dixneuf, Organometallics, 1997, 16, 3640.
14 J.-L. Fillaut, J. Perruchon, P. Blanchard, J. Roncali, S. Golhen,
M. Allain, A. Migalsaka-Zalas, I. V. Kityk and B. Sahraoui,
Organometallics, 2005, 24, 687.
15 Comparative studies carried out with thienyl and phenyl based alkynyl
derivatives didn’t permit to detect significant differences in the general
behaviour of the corresponding complexes as far as the molecular
recognition is concerned.
Notes and references
{ Crystal data. C65H57ClN2O3RuS, M 5 1206.59, triclinic, a 5 10.9596(2),
˚
b 5 14.6367(4), c 5 18.5586(6) A, a 5 78.498(1), b 5 81.692(1),
3
˚
¯
c 5 77.416(1)u, V 5 2831.2(1) A , T 5 293 K, space group P1, Z 5 2,
l(MoKa) 5 0.71073 A, m 5 5.23 cm21, 63203 reflections measured. 15716
˚
independent reflections from which 11629 with I . 2.0s(I). R 5 0.040,
Rw 5 0.0101. CCDC 243761. See http://www.rsc.org/suppdata/cc/b5/
b503698d/ for crystallographic data in CIF or other electronic format.
16 T. Steiner, Angew. Chem. Int. Ed., 2002, 41, 48.
17 J. L. Fillaut, M. Price, A. L. Johnson and J. Perruchon, Chem.
Commun., 2001, 739.
1 P. D. Beer and P. A. Gale, Angew. Chem. Int. Ed., 2001, 40, 487.
2 J.-P. Desvergne and A. W. Czarnik, Chemosensors of Ion and Molecular
Recognition, Kluwer, Dordrecht, 1997.
18 (a) R. A. Binstead, SPECFIT: Spectrum Software Associates,
Chapell Hill, NC, 1996; (b) H. Gampp, M. Maeder, C. J. Meyer and
A. D. Zuberbu¨hler, Talanta, 1985, 32, 257.
3 P. A. Gale, Coord. Chem. Rev., 2000, 199, 181.
19 K. A. Connors, Binding Constants: The Measurement of Molecular
Complex Stability, John Wiley & Sons, Inc, New York, 1987.
20 W. L. Jorgensen and J. Pranata, J. Am. Chem. Soc., 1990, 112,
2008.
21 J. Pranata, S. G. Wierschke and W. L. Jorgensen, J. Am. Chem. Soc.,
1991, 113, 2810.
22 C. Schmuck and U. Machon, Chem. Eur. J., 2005, 11, 1109.
4 R. Martinez-Manez and F. Sancenon, Chem. Rev., 2003, 103, 4419.
5 C. Suksai and T. Tuntulani, Chem. Soc. Rev., 2003, 32, 192.
6 P. D. Beer and E. J. Hayes, Coord. Chem. Rev., 2003, 240, 167.
7 J. D. Lewis and J. N. Moore, Dalton Trans., 2004, 1376.
8 X. X. Lu, C. K. Li, E. C. C. Cheng, N. Y. Zhu and V. W. W. Yam,
Inorg. Chem., 2004, 43, 2225.
2926 | Chem. Commun., 2005, 2924–2926
This journal is ß The Royal Society of Chemistry 2005