A novel fluoride ion colorimetric chemosensor

Article abstract of DOI:10.1021/ol801153d

(Figure Presented) A novel phosphonium derivative of naphthalene was synthesized by the reaction of 1,8-dibromomethylnaphthalene with triphenylphosphine, which only showed a distinct color change when treated with fluoride ions.

Full text of DOI:10.1021/ol801153d

ORGANIC
LETTERS
2
008
Vol. 10, No. 14
931-2934
A Novel Fluoride Ion Colorimetric
Chemosensor
2
Hyoung Min Yeo, Byung Ju Ryu, and Kye Chun Nam*
Department of Chemistry and Institute of Basic Science, Chonnam National UniVersity,
3
00 Yongbong-Dong, Bukgu, Gwangju 500-757, Korea
kcnam@chonnam.ac.kr
Received April 11, 2008
ABSTRACT
A novel phosphonium derivative of naphthalene was synthesized by the reaction of 1,8-dibromomethylnaphthalene with triphenylphosphine,
which only showed a distinct color change when treated with fluoride ions.
Anion recognition is an area of growing interest in supramo-
lecular chemistry due to its important role in a wide range
of environmental, clinical, chemical, and biological applica-
tions, and considerable attention has been focused on the
design of host molecules that are able to selectively recognize
Even though some receptor compounds for fluoride ions
8
have been reported, there is a paucity of reports on selective
9
,10
naked eye chemosensors for fluoride.
nitronaphthalene urea, as a signal unit for fluoride, have been
Nitrophenyl and
11–13
reported as chromogenic chemosensors,
but a naphtha-
1,2
and sense anion species. Color changes that can be detected
by the naked eye are widely used as signals for events owing
to the inexpensive equipment required or no equipment at
lene triphenylphosphonium ligand for the anion remains to
be developed.
3
–5
all.
(
8) (a) Dusemund, C.; Sandanayake, K. R. A. S.; Shinkai, S. J. Chem.
Among the biologically important anions, fluoride is of
Soc., Chem. Commun. 1995, 333. (b) Yamamoto, H.; Ori, A.; Ueda, K.;
Dusemund, C.; Shinkai, S. Chem. Commun. 1996, 407. (c) Scherer, M.;
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B.; Oh, K. S.; Gong, Y. J.; Lee, J. W.; Yoon, J.; Lee, H. C.; Kim, K. S. J.
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6
particular interest due to its established role in dental care
7
and osteoporosis.
(
1) Supramolecular Chemistry of Anions; Bianchi, E., Bowman-James,
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(
.
10.1021/ol801153d CCC: $40.75  2008 American Chemical Society
Published on Web 06/24/2008

In pursuit of a selective fluoride ion chemosensor, a
naphthalene phosphonium derivative 5 was synthesized, and
1
its anion binding properties were investigated by H NMR,
UV-vis spectroscopy, color changes, and X-ray structural
analysis. To our knowledge, it is the first report of a
1
4
colorimetric chemosensor based on phosphonium ions.
Using a previously reported method, 1,8-naphthalene
bicarboxylic dianhydride 1 was reduced to the corresponding
1
5
alcohol 2 and following bromination with PBr
3
produced
16
3
4
in high yield. Treatment with triphenylphosphine yielded
1
7
-
,
and the bromide ions were replaced with PF
(Scheme 1).
6
by a
simple reaction with NaPF
6
Scheme 1. ynthesis of
,8-Bis(triphenylphosphoniomethyl)naphthalene
1
3
1
Figure 1. S P NMR spectra of ligand 5 (a) and on the addition of
Dihexafluorophosphate 5
-
F
(b).
The UV-vis experiments were carried out in a DMSO
-
5
solution. A receptor solution (3 × 10 M) was treated with
the representative anions such as tetrabutylammonium (TBA)
fluoride, chloride, bromide, hydrogen sulfate, and dihydrogen
-
phosphate. When compound 5 forms a complex with F , a
new peak appears at 447 nm. However, a bathochromic shift
of other ions was observed with a small change as shown in
Figure 2. Figure S22 explains the absorption titration data
1
The H NMR spectrum of 5 showed a doublet at δ 5.65
ppm (J ) 16.2 Hz) for the methylene protons due to the
coupling of the phosphorus atom and a mixture of multiplets
at δ 7.01 to δ 7.69 ppm for the phenyl and naphthalene
aromatic protons. To investigate the selectivity, a series of
anions such as tetrabutylammonium (TBA) fluoride, chloride,
bromide, iodide, perchlorate, hydrogen sulfate, and dihy-
6
drogen phosphate were treated with ligand 5 in DMSO-d ,
as shown in Figure S1. The most obvious spectral changes
were observed when fluoride ions were treated. A methylene
peak at δ 5.65 ppm, as a doublet, disappeared, and several
aromatic peaks at δ 7-8 ppm were moved to multiplets at
δ 7.6 ppm; however, no noticeable changes were observed
with bromide, iodide, hydrogen sulfate, and perchlorate.
However, similar changes were observed when 5 was treated
with dihydrogen phosphate ions: the aromatic signals became
broad, and the doublets at δ 5.65 ppm disappeared.
5
Figure 2
.
SAbsorption spectra of compound 5 (3.0 × 10- M) on
the additions of tetrabutylammonium fluoride, chloride, bromide,
-
4
Dh yMd rSo Og e. n sulfate, and dihydrogen phosphate (3.0 × 10 M) in
The binding properties of 5 toward anions were also
3
1
31
investigated using P NMR spectroscopy. The P NMR
spectrum of ligand 5 showed an interesting feature (Figure
-
for 5 with F . From the absorption titration, the association
1
). In the presence of fluoride ions, the phosphorus signal
-
constant of complex 5 with F was observed to be 1.38 ×
shifts from δ 24.238 to δ 26.776 ppm, 2.538 ppm downfield,
but in the presence of chloride ions, only a 0.385 ppm upfield
shift was observed (Figure S3).
4
-1
1
0 M .
A color change was easily observed on mixing the ligand
and anions, as shown in Figure 3. A receptor solution was
simply treated with various anions such as tetrabutylammo-
nium (TBA) fluoride, chloride, bromide, dihydrogen phos-
phate, and hydrogen sulfate, for which noticeable color
changes were observed. In particular, the colorless ligand
(
14) Hamdi, A.; Nam, K. C.; Ryu, B. J.; Kim, J. S.; Vicens, J.
Tetrahedron Lett. 2004, 45, 4689.
(
(
(
15) Beyler, R. E.; Sarett, L. H. J. Am. Chem. Soc. 1952, 74, 1406.
16) Carpino, L. A. J. Am. Chem. Soc. 1963, 85, 2144.
17) Mitchell, R. H.; Sondheimer, F. Tetrahedron 1968, 24, 1397.
2932
Org. Lett., Vol. 10, No. 14, 2008

Table 1. Distance between Methylene Carbons and Anions in
1
8
the Ligand
the counteranion
PF6-
carbon-anion
distance (Å)
C11-P3
C11-P4
C30-P3
C30-P4
C11-Br1
C11-Br2
C30-Br1
C30-Br2
C11-Cl1
C11-Cl2
C30-Cl1
C30-Cl2
8.888
15.012
9.639
14.973
7.966
3.669
9.505
3.623
7.890
3.514
9.404
3.472
Br-
4
Figure 3
.
SColor changes of ligand 5 (3.0 × 10- M) on the
Cl-
additions of tetrabutylammonium (TBA) fluoride, chloride, bromide,
Dd i Mh y Sd Or o.gen phosphate, and hydrogen sulfate (3.0 × 10 M) in
-3
solution became markedly orange when fluoride ions were
added to compound 5 in DMSO, but no color changes were
observed on the additions of chloride, bromide, and hydrogen
sulfate ions. A pale yellow color appeared on the addition
of dihydrogen phosphate ions.
The crystal structure of the ligand revealed the unsym-
metrical location of the two anions (Table 2). One stayed
close to the middle of the two phosphorus atoms, whereas
the other was positioned slightly outside of the phosphorus
atoms (Figures 4, S5, and S6). Two anions may be able to
bromides and 3.514 and 3.472 Å between the methylene
carbons and the chlorides. The X-ray structure for fluoride
is not currently available, but a short distance would be
expected.
Recently, colorimetric changes due to the deprotonation
-
19
of NH have been utilized as sensors for F . It is reported
-
that F is sufficiently basic to deprotonate NH, which can
1
cause usually long wavelength color change. The H NMR
experiments also support the deprotonation process. In our
case, a new triplet, which corresponds to the formation of
2
0
FHF, was observed at around 16 ppm (Figure S19). From
the UV-vis titration (Figures S22 and S23), the new
absorption peak appeared at 447 nm on the addition of 2
equiv of fluoride, and then the absorption maxima shifted to
4
07 nm as further aliquots of fluoride were added. We
interpreted this behavior as the fluoride binding to the
receptor, and further additions of fluoride trigger deproto-
2
1
nation. A similar spectral change was observed when
t
treated with 100 equiv of KO Bu. But, when treated with 1
t
equiv of KO Bu, the intensity of the new peak was quite
low and the color change was not observed, indicating the
ligand 5 as an effective colorimetric chemosensor for fluoride
ions (Figures S20 and S21).
In conclusion, a new phosphonium derivative of naphtha-
lene was synthesized by the reaction of 1,8-dibromometh-
Figure 4. SCrystal structure of the ligand with two chloride ions.
Table 2. Crystal Data and Structure Refinement for the Ligand
with Two Chloride Ions
hydrogen bond with the methylene protons, depending on
the anion species, especially a small anion, such as the
fluoride ion. The distance between the methylene carbon and
empirical formula
formula weight
crystal system
space group
unit cell dimensions
C50 H43 Cl2 N P2
790.69
triclinic
P1j
the anions showed an interesting feature. Large anions such
-
as PF
6
were reasonably distant from the methylene carbons.
a ) 11.2692(11) Å, R ) 108.221(2)°
b ) 13.1613(13) Å, ꢀ ) 98.803(3)°
c ) 14.7442(14) Å, γ ) 93.853(2)°
0.944
Table 1 shows 8.888 and 9.639 Å between the methylene
-
carbons and phosphorus atoms of the two PF
6
, but 3.669
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
and 3.623 Å between the methylene carbons and the
R1 ) 0.0720, wR2 ) 0.1157
R1 ) 0.1662, wR2 ) 0.1556
(
18) Crystallographic data for the structure reported in this article have
-
3
been deposited with the Cambridge Crystallographic Data Centre, CCDC
largest diff. peak and hole 0.581 and -0.365 e.Å
-
NO 676782 for chloride, 676783 for bromide, and 676784 for PF6 .
Org. Lett., Vol. 10, No. 14, 2008
2933

ylnaphthalene with triphenylphosphine, which only showed
a distinct color change when treated with fluoride ions. The
high selectivity for fluoride can be attributed to the acidity
of the methylene protons and the small size of fluoride ions.
Acknowledgment. The NMR spectra were obtained at the
Korea Basic Science Institute, Kwangju, Korea. This work
was supported by the Korea Science and Engineering
Foundation (KOSEF) grant funded by the Korea government
(MOST) (No. R01-2007-000-20245-0).
(
19) (a) Gunnlaugsson, T.; Kruger, P. E.; Jensen, P.; pfeffer, F. M.;
Supporting Information Available: Spectroscopic data
Hussey, G. M. Tetrahedron Lett. 2003, 44, 8909. (b) Camiolo, S.; Gale,
P. A.; Hursthouse, M. B.; Light, M. E. Org. Biomol. Chem. 2003, 1, 741.
1
for ligand 5, H NMR titration spectra, and X-ray structure
(
c) Gale, P. A. Acc. Chem. Res. 2006, 39, 465.
20) Xu, Z.; Kim, S.; Kim, H. N.; Han, S. J.; Lee, C.; Kim, J. S.; Qian,
X.; Yoon, J. Tetrahedron Lett. 2007, 48, 9151.
21) Caltagirone, C.; Bates, G. W.; Gale, P. A.; Light, M. E. Chem.
Commun. 2008, 61.
-
-
-
6
for Cl , Br , PF , and their data. This material is available
(
free of charge via the Internet at http://pubs.acs.org.
(
OL801153D
2934
Org. Lett., Vol. 10, No. 14, 2008