Ambident chemosensors based on benzo[h]chromen-2-one

Article abstract of DOI:10.1134/S1070428007120172

Schiff bases derived from 7-hydroxy-4-methyl-2-oxobenzo[h]chromene-8- carbaldehyde in solution exist as equilibrium mixtures of benzoid and quinoid tautomers. The fraction of the quinoid tautomer increases with rise in solvent polarity. The Schiff base containing a benzo-15-crown-5 fragment on the nitrogen atom was shown to be a new ambident chemosensor capable of selectively binding transition metal cations via reaction at the o-hydroxyaldehyde imine fragment and alkaline-earth metals via host-guest interaction with the crown ether moiety. This compound exhibits a pronounced sensor activity toward Mg ²⁺ and Ba²⁺ ions and is a selective naked-eye fluorescent chemosensor for Cu²⁺ and Co²⁺ ions.

Full text of DOI:10.1134/S1070428007120172

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 12, pp. 1836–1841. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © L.G. Minyaeva, R.V. Tyurin, V.V. Mezheritskii, A.V. Tsukanov, E.N. Shepelenko, A.D. Dubonosov, V.A. Bren’, V.I. Minkin, 2007,
published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 12, pp. 1832–1836.
Ambident Chemosensors Based on Benzo[h]chromen-2-one
L. G. Minyaevaa, R. V. Tyurina, V. V. Mezheritskiia, A. V. Tsukanova, E. N. Shepelenkob,
A. D. Dubonosovb, V. A. Bren’a, b, and V. I. Minkina, b
a Institute of Physical and Organic Chemistry, Rostov State University,
pr. Stachki 194/2, Rostov-on-Don, 344090, Russia
e-mail: mezher@ipoc.rsu.ru
b South Research Center, Russian Academy of Sciences, Rostov-on-Don, Russia
Received April 9, 2007
Abstract—Schiff bases derived from 7-hydroxy-4-methyl-2-oxobenzo[h]chromene-8-carbaldehyde in solution
exist as equilibrium mixtures of benzoid and quinoid tautomers. The fraction of the quinoid tautomer increases
with rise in solvent polarity. The Schiff base containing a benzo-15-crown-5 fragment on the nitrogen atom was
shown to be a new ambident chemosensor capable of selectively binding transition metal cations via reaction at
the o-hydroxyaldehyde imine fragment and alkaline-earth metals via host–guest interaction with the crown
ether moiety. This compound exhibits a pronounced sensor activity toward Mg2+ and Ba2+ ions and is a selec-
tive naked-eye fluorescent chemosensor for Cu2+ and Co2+ ions.
DOI: 10.1134/S1070428007120172
Chemosensors are abiotic systems including a re-
ceptor fragment which is capable of selectively inter-
acting with a substrate, a signaling fragment, and
a linker connecting them [1–3]. If a fluorescent sig-
naling fragment is present, bridging moiety may be
lacking, and sensor properties originate as a rule from
the CHEQ effect (Chelation Enhanced Fluorescence
Quenching) [4]. Most frequently, crown ether [5–7]
and o-hydroxyaldehyde imine [8, 9] receptors are used.
However, only a few data are available on compounds
having both these fragments in a single molecule
[10–13], while their combination with a fluorophoric
heterocyclic signaling system is almost unknown. With
a view to obtain ambident CHEQ chemosensors cap-
able of selectively interacting with both alkaline-earth
and transition metals, in the present work we made
Scheme 1.
HO
Me
HO
Me
HO
Me
O
Ph
N
PhN=CHOEt
HCl
O
O
O
O
O
O
I
II
III
HO
Me
R
N
RNH2
O
O
IVa–IVd
O
O
O
R = Ph (15N) (a), PhCH2 (b), i-Pr (c),
(d).
O
O
1836

AMBIDENT CHEMOSENSORS BASED ON BENZO[h]CHROMEN-2-ONE
1837
Scheme 2.
HO
Me
O
H
O
Me
O
R
N
R
N
O
O
A
IVa–IVd
B
an attempt to synthesize benzo[h]chromen-2-one deriv-
atives containing an o-hydroxyaldehyde moiety in the
naphthalene fragment. This work continues our studies
on the design of ortho- and peri-fused heterocyclic
systems on the basis of naphthalene-1,5-diol [14].
Reactions of crown ether derivative IVd with alkali
and alkaline-earth metal cations are accompanied by
considerable displacement of tautomeric equilibrium
toward benzoid complexes V (Scheme 3), as was re-
ported previously for Schiff bases of the benzofuran
series [22, 23]. The intensity of the absorption maxi-
mum at λ 480 nm (corresponding to the quinoid tauto-
mer) in the electronic spectra decreases by ~15% for
alkali metals and 25% for alkaline-earth metals. Addi-
tion of a transition metal acetate to a solution of IVd in
dimethyl sulfoxide induces a blue shift of the long-
wave absorption maximum (Δλ ≈ 10–30 nm) as a re-
sult of formation of chelates VI (Scheme 3) [24].
The reaction of previously reported 7-hydroxy-
4-methylbenzo[h]chromen-2-one (I) [15] with ethyl
N-phenylformimidate turned out to be the most suc-
cessful for the introduction of an aldehyde function-
ality into the ortho position with respect to the hydroxy
group. We thus obtained Schiff base II in 83% yield,
and acid hydrolysis of II smoothly afforded aldehyde
III. Condensation of III with primary amines gave the
corresponding Schiff bases IVa–IVd (Scheme 1).
In the 1H NMR spectrum of o-hydroxyaldehyde III,
signals from protons in the formyl and hydroxy groups
appeared as sharp singlets at 10.1 and 12.6 ppm.
Therefore, we presumed that compound III in CDCl3
at room temperature exists exclusively in the hydroxy-
aldehyde form. Schiff bases IVa–IVd in solution give
rise to equilibrium between the benzoid (A) and quin-
oid (B) tautomers that absorb at λ 420 and 490 nm,
respectively [16–18] (Scheme 2). The fraction of the
quinoid form decreases as the solvent polarity rises
(Fig. 1). The effect of the substituent on the nitrogen
atom changes depending on the solvent nature. In non-
polar solvents, the fraction of the quinoid tautomer
increases in the series Ph < PhCH2 < Me2CH, whereas
the reverse order is observed in polar solvents (e.g., in
DMSO).
Crown ether-containing Schiff base IVd showed
a high sensitivity for copper(II) and cobalt(II) ions.
Acetonitrile and dimethyl sulfoxide solutions of IVd
exhibit strong fluorescence with its maximum at
λ 530 nm upon excitation at λexcit 480 nm. Addition of
D
0.8
1
0.7
0.6
2
0.5
0.4
The NH and CH protons in crown ether-containing
1
derivative IVd resonate in the H NMR spectrum as
2
0.3
broadened singlets, indicating fast proton exchange
[19]. 15N-Labeled Schiff base IVa in dimethyl sulfox-
ide characteristically displayed splitting of the labile
proton due to coupling with 15N (J = 50.1 Hz), which
corresponded to an A/B ratio of 44:56 [20, 21]. On the
basis of the electronic absorption and 1H NMR spectra
we calculated the molar absorption coefficient for the
quinoid tautomer (εB = 2.63×104 l mol–1 cm–1) and pa-
rameters of tautomeric equilibria for Schiff bases IVa–
IVd assuming that the coefficient εB weakly depends
on the solvent and substituent nature (see table) [17].
1
0.2
0.1
300
350 400
450 λ, nm
Fig. 1. Electronic absorption spectra of Schiff base IVa in
(1) DMSO and (2) toluene; c = 2.5×10–5 M.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

MINYAEVA et al.
Spectral parameters of Schiff bases IVa–IVd and parameters of the tautomeric equilibrium A
1838
B
Compound
no.
Electronic absorption spectrum, λmax, nm
(ε×10–4 , l mol–1 cm–1)
Fraction of
tautomer B, %
ΔGo293
,
kJ/mol
Solvent
K0 ([B]/[A])
Toluene 342 (1.52), 425 (1.33), 477 (0.56), 510 (0.54)
DMSO 307 (3.28), 477 (1.48), 508 (1.52)
19.8
56.3
0.247
1.288
3.4
–0.6–
IVa
IVb
IVc
IVd
Toluene 390 (0.68), 412 (0.80), 453 (0.60), 476 (0.60)
DMSO 299 (4.48), 453 (1.32), 476 (1.32)
22.8
50.2
0.295
1.008
3.0
0–0.02–
Toluene 298 (2.96), 390 (0.64), 412 (0.76), 453 (0.80), 478 (0.80)
DMSO 298 (4.20), 450 (1.20), 475 (1.20)
30.4
45.6
0.437
0.838
2.0
0.4
Toluene 357 (1.20), 425 (1.88), 483 (0.56), 514 (0.54)
DMSO 450 (1.10), 480 (1.20), 510 (0.88)
19.8
33.5
0.247
0.504
3.4
1.7
by considerably weaker variations in the fluorescence
intensity. Addition of magnesium or barium perchlo-
rate to a solution of chemosensor IVd in acetonitrile
induces fluorescence quenching by a factor of 3.4 or
2.9, respectively (Fig. 3). Nevertheless, this effect is
sufficient to detect Mg2+ and Ba2+ ions in solution.
Thus we have synthesized a novel ambident fluo-
rescent chemosensor capable of selectively binding
different metal ions, transition metal cations (due to
copper(II) or cobalt(II) acetate leads to a pro-
nounced CHEQ effect: the fluorescence intensity de-
creases by a factor of 39 and 33, respectively, without
appreciable shift of the emission maximum (Fig. 2).
The change in the emission intensity is readily detected
visually, so that Schiff base IVd may be used as naked-
eye sensor for qualitative express analysis of Cu(II)
and Co(II) ions in solution. Reactions of IVd with al-
kali and alkaline-earth metal cations are accompanied
Scheme 3.
HO
Me
O
O
Me
O
N
NH
O
O
O
O
Mn+
Mn+
O
O
O
O
O
O
O
O
V, A
V, B
Mn+ –Mn+
Mn+ –Mn+
HO
N
Me
O
O
Me
O
NH
O
O
O
O
O
O
O
O
O
O
O
O
IVd, A
IVd, B
M/2
O
Me
O
M2+
M2+
N
O
O
O
O
O
O
VI
Mn+ = Li+, Na+, K+, Cs+, Mg2+, Ca2+, Ba2+; M2+ = Zn2+, Cu2+, Pb2+, Cd2+, Co2+.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

AMBIDENT CHEMOSENSORS BASED ON BENZO[h]CHROMEN-2-ONE
1839
40
30
20
10
0
the presence of o-hydroxyaldehyde imine fragment),
and alkaline-earth metal ions (due to crown ether
receptor). Crown ether-containing Schiff base IVd is
characterized by pronounced sensitivity for Mg2+ and
Ba2+ ions and is an efficient selective naked-eye fluo-
rescent chemosensor for Cu2+ and Co2+ ions.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Varian
Zn2+
Cu2+
Hg2+
Pb2+
Cd2+
Co2+
Unity-300 spectrometer at 300 MHz using the residual
solvent signal as reference (CHCl3, δ 7.25 ppm;
DMSO, δ 2.50 ppm). The electronic absorption spectra
were measured on a Specord M-40 spectrophotometer,
and the luminescence spectra, on a Hitachi 650-60
spectrofluorimeter. The IR spectra were obtained on
a Specord 75IR instrument from samples dispersed in
mineral oil.
Fig. 2. Relative changes in the fluorescence intensity of
Schiff base IVd in DMSO (c = 2.5×10–5 M) upon addition
of transition metal ions (c = 2.5×10–4 M).
7-Hydroxy-4-methyl-8-[phenyl(15N)iminometh-
yl]benzo[h]chromen-2-one (IVa). A mixture of 0.1 g
(0.4 mmol) of o-hydroxyaldehyde III and 0.04 ml
(0.4 mmol) of (15N)aniline in 5 ml of dioxane was
heated for 30 min under reflux. The precipitate was
filtered off, recrystallized from dimethylformamide,
washed with alcohol, and dried in air. Yield 0.065 g
(50%), mp 265–267°C. IR spectrum, ν, cm–1: 3390,
7-Hydroxy-4-methyl-8-(phenyliminomethyl)-
benzo[h]chromen-2-one (II). A mixture of 0.45 g
(2 mmol) of 7-hydroxy-4-methylbenzo[h]chromen-2-
one [15] and 0.6 ml of ethyl N-phenylformimidate in
5–7 ml of o-dichlorobenzene was heated for 2 h under
reflux. The mixture was cooled, and the yellow–orange
precipitate (0.45 g) was filtered off and washed with
petroleum ether. The filtrate was diluted with petrole-
um ether to isolate an additional portion (0.1 g) of the
product. Overall yield 0.55 g (83%), mp 266–267°C
(from DMF). IR spectrum, ν, cm–1: 3447, 1714, 1640,
1620. 1H NMR spectrum (CDCl3), δ, ppm: 2.61 s (3H,
4-CH3), 6.42 s (1H, 3-H), 7.28–7.52 m (6H, Harom),
7.64 d (1H, 10-H, J9,10 = 8.7 Hz), 7.80 d (1H, 5-H,
J5,6 = 8.9 Hz), 8.36 d (1H, 9-H, J9,10 = 8.7 Hz), 8.58 d
(1H, N=CH, JCH, NH = 5.3 Hz), 15.20 br.s (1H,
N···H···O). Found, %: C 76.77; H 4.34; N 4.57.
C21H15NO3. Calculated, %: C 76.59; H 4.55; N 4.25.
1
1714, 1620, 1590. H NMR spectrum, δ, ppm: in
CDCl3: 2.58 s (3H, 4-CH3), 6.42 s (1H, 3-H), 7.28–
7.52 m (6H, Harom), 7.63 d (1H, 10-H, J9,10 = 8.7 Hz),
7.80 d (1H, 5-H, J5,6 = 9.0 Hz), 8.35 d (1H, 9-H, J9,10
=
8.7 Hz), 8.57 d (1H, 15N=CH, JCH,NH = 1.7 Hz),
15.20 br.s (1H, 15N···H···O); in DMSO-d6: 2.56 s (3H,
4-CH3), 6.55 s (1H, 3-H), 7.27–7.64 m (6H, Harom),
7.78 d (1H, 10-H, J9,10 = 8.6 Hz), 8.24 d (1H, 9-H,
15
J9,10 = 8.6 Hz), 9.10 d (1H, N=CH, JCH,NH = 6.9 Hz),
1
15.21 d (1H, 15N···H···O, JHN = 50.1 Hz). Found, %:
C 76.67; H 4.34; N 4.57. C21H15NO3. Calculated, %:
C 76.36; H 4.54; N 4.54.
8-Benzyliminomethyl-7-hydroxy-4-methyl-
benzo[h]chromen-2-one (IVb). A mixture of 0.1 g
(0.4 mmol) of o-hydroxyaldehyde III, 3 ml of dioxane,
7-Hydroxy-4-methyl-2-oxobenzo[h]chromene-8-
carbaldehyde (III). Dilute hydrochloric acid (1:1), 3–
5 ml, was added to 0.3 g (0.9 mmol) of Schiff base II
in 50 ml of dioxane, and the mixture was heated for
30 min on a boiling water bath. The mixture was
cooled and diluted with water, and the precipitate was
filtered off, Yield 0.23 g (76%), mp 290–292°C (de-
comp.; from DMF). IR spectrum, ν, cm–1: 3100, 1700,
1680, 1630, 1600. 1H NMR spectrum (CDCl3), δ, ppm:
2.61 s (3H, 4-CH3), 6.50 s (1H, 3-H), 7.72 d (2H, 6-H,
3
2
1
0
Li+
Na+
K+
Cs+ Mg2+ Ca2+ Ba2+
10-H, J5,6 = J9,10 = 8.9 Hz), 8.11 d (1H, 5-H, J5,6
=
8.9 Hz), 8.31 d (1H, 9-H, J9,10 = 8.9 Hz), 10.10 s (1H,
CHO), 12.60 s (1H, OH). Found, %: C 70.57; H 4.27.
C15H10O4. Calculated, %: C 70.86; H 3.93.
Fig. 3. Relative changes in the fluorescence intensity of
Schiff base IVd in acetonitrile (c = 2.5×10–5 M) upon addi-
tion of alkali and alkaline-earth metal ions (c = 2.5×10–4 M).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

MINYAEVA et al.
1840
and 3 ml of acetonitrile was heated to the boiling point.
The hot solution was filtered from the undissolved
material, 0.04 ml (~0.4 mmol) of benzylamine was
added to the filtrate, and the mixture was heated under
reflux until a solid began to separate (~10 min). The
mixture was cooled, and the precipitate, 0.08 g
(~60%), was filtered off and purified by column chro-
matography on Silokhrom using chloroform as eluent.
Yield 0.065 g (48%), mp 216–217°C. IR spectrum, ν,
6.83–6.98 m (3H, Harom), 7.40 d (1H, 6-H, J5,6 =
8.9 Hz), 7.61 d (1H, 5-H, J5,6 = 8.9 Hz), 7.81 d (1H,
10-H, J9,10 = 8.9 Hz), 8.33 d (1H, 9-H, J9,10 = 8.9 Hz),
8.55 s (1H, =CH), 15.27 br.s (1H, OH). Found, %:
C 66.70; H 6.07; N 2.58. C29H31NO8. Calculated, %:
C 66.78; H 5.99; N 2.69.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 05-03-32470), by the Ministry of Education and
Science of the Russian Federation (project nos. RNP.-
2.2.2.2.5592, RNP.2.1.1.4939), by the President of the
Russian Federation (project no. NSh-4849.2006.3),
and by the Program “Development of Monitoring
Technologies, Ecosystem Modeling, and Forecasting
while Exploring Natural Resources under Arid Climate
Conditions” of the Earth Science Division, Russian
Academy of Sciences.
1
cm–1: 3420, 1727, 1633, 1620. H NMR spectrum
(DMSO-d6), δ, ppm: 2.49 s (3H, 4-CH3), 4.84 s (2H,
NCH2), 6.53 s (1H, 3-H), 7.16 d (1H, 6-H, J5,6
=
9.0 Hz), 7.30 d (1H, 5-H, J5,6 = 9.0 Hz), 7.32–7.46 m
(5H, Harom), 7.66 d (1H, 10-H, J9,10 = 8.6 Hz), 8.18 d
(1H, 9-H, J9,10 = 8.6 Hz), 8.54 d (1H, N=CH, JCH,NH
=
6.5 Hz), 13.57 br.s (1H, N···H···O). Found, %:
C 76.65; H 5.34; N 4.44. C22H17NO3. Calculated, %:
C 76.97; H 4.96; N 4.08.
7-Hydroxy-8-isopropyliminomethyl-4-methyl-
benzo[h]chromen-2-one (IVc). A mixture of 0.06 g
(0.2 mmol) of o-hydroxyaldehyde III and 0.02 ml
(0.2 mmol) of isopropylamine in 10 ml of alcohol was
heated for 10 min under reflux. The mixture was
cooled and diluted with water, the precipitate (0.04 g)
was filtered off, and most part of the filtrate was
evaporated to isolate an additional portion (0.02 g) of
the product. The fractions were combined and purified
by chromatography on aluminum oxide using chloro-
form as eluent. Yield 0.05 g (50%), mp 207–208°C. IR
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