Detecting Anions in Aqueous Media
FULL PAPER
media. The optimization of the molecular structure of the
cationic azaborines is now under way in our laboratory with
the aim to detect fluoride ions as well as other biologically
important anions, such as the azide ion, in 100% water.
Experimental Section
Bis(trimethylammonio)azaborine diiodide 1a: MeI (1.5 mL, 24 mmol)
was added to a solution of azaborine 7 (550 mg, 1.1 mmol) in THF
(30 mL), and the mixture was stirred at 558C for three days. The result-
ing precipitate was filtered off, washed with THF, and dried in vacuo to
give 1a as a yellow solid (0.70 g, 83%). M.p. 117–1188C (decomp);
1H NMR (400 MHz, CD2Cl2): d=0.96 (d, J=6.6 Hz, 12H), 1.36 (d, J=
6.8 Hz, 6H), 2.18 (sept, J=6.6 Hz, 2H), 3.01 (sept, J=6.8 Hz, 1H), 3.91
(s, 18H), 4.23 (s, 3H), 7.15 (s, 2H), 7.96 (d, J=3.4 Hz, 2H), 8.09 (d, J=
9.6 Hz, 2H), 8.74 ppm (dd, J=9.6, 3.4 Hz, 2H); 1H NMR (400 MHz,
D2O): d=0.98 (d, J=6.8 Hz, 12H), 1.37 (d, J=7.2 Hz, 6H), 2.30 (sept,
J=6.8 Hz, 2H), 3.08 (sept, J=7.2 Hz, 1H), 3.62 (s, 18H), 4.22 (s, 3H),
7.40 (s, 2H), 8.14 (d, J=10.0 Hz, 2H), 8.23 (d, J=3.6 Hz, 2H), 8.27 ppm
(dd, J=10.0, 3.6 Hz, 2H);13C NMR (126 MHz, CD3OD): d=24.9, 25.1,
35.9, 37.1, 37.6, 58.4, 120.5, 121.6, 122.0, 127.1, 128.7, 129.4, 141.3, 147.8,
151.3, 152.7 ppm; 11B NMR (128 MHz, CD2Cl2): d=53.7 ppm; low-reso-
lution (LR)MS (FAB+): m/z: 638 ([MÀI]+); elemental analysis calcd
(%) for C34H50BI2N3·1.5H2O: C 51.53, H 6.74, N 5.30; found: C 51.73, H
6.77, N 5.08.
Bis(methyldiphenylphosphonio)azaborine diiodide 2a: MeI (1.5 mL,
24 mmol) was added to a CH2Cl2/THF (2:3 v/v, 50 mL) solution of aza-
borine 8 (1.0 g, 1.3 mmol) and the mixture was stirred at 528C for 21 h.
The solvents were removed under reduced pressure, and the crude mate-
rial was purified by re-precipitation from CH2Cl2 and Et2O to give aza-
borine 2a as
a pale yellow solid (0.89 g, 65%). M.p. 334–3358C
(decomp); 1H NMR (400 MHz, CD2Cl2): d=0.66 (d, J=6.8 Hz, 12H),
1.28 (d, J=6.8 Hz, 6H), 1.92 (sept, J=6.8 Hz, 2H), 2.87 (sept, J=6.8 Hz,
Figure 6. The UV/Vis (a) and fluorescence (b) spectral changes of 2a
upon adding aqueous NaCN in H2O containing HEPES (0.5m) and
NaOH (pH 7.0) at 298 K. [2a]=4.1ꢁ10À6 m. lex =369 nm.
1
1H), 3.03 (d, JPH =13.2 Hz, 6H), 4.32 (s, 3H), 6.77 (s, 2H), 7.48–7.58 (m,
16H), 7.67–7.75 (m, 6H), 8.28 (dd, J=9.2, 2.4 Hz, 2H), 8.50 ppm (ddd,
J=11.4, 9.2, 2.4 Hz, 2H); 13C{1H} NMR (126 MHz, CD2Cl2): d=10.3 (d,
J=57.6 Hz), 23.5 (s), 23.7 (s), 33.9 (s), 34.9 (s), 37.0 (s), 108.7 (d, J=
93.9 Hz), 118.6 (d, J=89.7 Hz), 118.6 (d, J=12.3 Hz), 119.4 (s), 128.0 (d,
J=9.8 Hz), 129.9 (d, J=13.0 Hz), 132.5 (d, J=10.6 Hz), 134.7 (s), 136.5
(d, J=12.9 Hz), 144.8 (d, J=10.6 Hz), 148.8 (s), 149.2 (s), 149.5 ppm (s)
(one signal corresponding to B–CACTHNUTRGNE(UNG Tip) carbon could not be observed);
13C{1H} NMR (126 MHz, CD3OD): d=9.38 (d, J=57.0 Hz), 25.0 (s), 25.2
(s), 35.8 (s), 36.9 (s), 37.9 (s), 111.5 (d, J=92.9 Hz), 120.5 (d, J=12.0 Hz),
121.1 (s), 121.3 (d, J=88.9 Hz), 129.6 (d, J=10.5 Hz), 131.6 (d, J=
12.9 Hz), 134.5 (d, J=10.6 Hz), 135.1 (s), 136.3 (d, J=2.5 Hz), 137.9 (d,
J=12.6 Hz), 146.7 (d, J=10.5 Hz), 150.7 (s), 151.1 (d, J=2.4 Hz),
151.6 ppm (s); 31P NMR (162 MHz, CD2Cl2): d=21.1 ppm; 11B NMR
(128 MHz, CD2Cl2): d=56.3 ppm; LRMS (FAB+): m/z: 920 ([MÀI]+);
elemental analysis calcd (%) for C54H58BI2NP2·2H2O: C 59.85, H 5.77, N
1.29; found: C 60.00, H 5.79, N 1.32.
Figure 7. The photograph of the solution of 2a in DMSO/H2O solution
(3:1 v/v) upon adding various anions (100 equivalents) under 370-nm UV
lamp irradiation.
These dicationic azaborines showed enhanced Lewis acid-
ity compared with the parent azaborine owing to the strong
electron-withdrawing properties of the cationic functionali-
ties. This was determined from a complex formation study
with fluoride and cyanide ions in organic solvents as well as
in aqueous solvents. In addition, bisphosphonioazaborine ex-
hibited a higher complex formation ability with the cyanide
ion than with the fluoride ion in an aqueous solvent system,
and complexation with the cyanide ion could be monitored
by optical spectroscopy.
Acknowledgements
This work was partly supported by Grants-in-Aid for The Global COE
Program for Chemical Innovation and for Scientific Research from the
Ministry of Education, Culture, Sports, Science, and Technology of Japan
(T.K.). We thank the Tosoh Finechem Corporation for the generous gifts
of alkyllithiums.
Chem. Rev. 2003, 103, 4419; c) S. W. Thomas III, G. D. Joly, T. M.
These results indicate that the introduction of cationic
functional groups into the azaborine framework is an effec-
tive way to develop optical anion sensors for use in aqueous
Chem. Eur. J. 2009, 15, 5056 – 5062
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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