Imidazo-benzo-15-crown-5 ethers bearing arylthienyl and bithienyl moieties as novel fluorescent chemosensors for Pd2+ and Cu2+

Article abstract of DOI:10.1016/j.tet.2011.06.106

Novel fluorescent ionophores bearing imidazo-arylthienyl or imidazo-bithienyl π-conjugated bridges functionalized with one or two fused benzo-15-crown-5 ethers as receptor units are reported. The sensing ability of the compounds in the presence of metalli

Full text of DOI:10.1016/j.tet.2011.06.106

Tetrahedron 67 (2011) 7106e7113
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Imidazo-benzo-15-crown-5 ethers bearing arylthienyl and bithienyl moieties
as novel fluorescent chemosensors for Pd2þ and Cu2þ
,
c
,
a,
*
Rosa M.F. Batista a, Elisabete Oliveira b, Susana P.G. Costa a, Carlos Lodeiro b , M. Manuela M. Raposo
*
a Centre of Chemistry, Univeristy of Minho, Campus Gualtar, 4710-057 Braga, Portugal
b REQUIMTE, Department of Chemistry, FCT-UNL, 2829-516 Monte de Caparica, Portugal
c BIOSCOPE Group, Faculty of Science, Physical-Chemistry Department, Campus Ourense, University of Vigo, 32004 Ourense, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 June 2011
Received in revised form 29 June 2011
Accepted 30 June 2011
Available online 6 July 2011
Novel fluorescent ionophores bearing imidazo-arylthienyl or imidazo-bithienyl
p-conjugated bridges
functionalized with one or two fused benzo-15-crown-5 ethers as receptor units are reported. The
sensing ability of the compounds in the presence of metallic cations (Liþ, Naþ, Kþ, Ca2þ, Zn2þ, Cu2þ, Ni2þ
,
Pd2þ, and Hg2þ) and fluoride ion was studied in MeCN/DMSO solutions by absorption and emission
spectroscopy. The experimental results indicate that all compounds could act as selective fluorimetric
sensors for Cu2þ and Pd2þ and also for the fluoride ion, in the case of the bis-substituted crown ether
derivatives.
Dedicated to the Centenary of the Portu-
guese Chemical Society
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Crown ethers
Arylthiophene
Bithiophene
Imidazole
Fluorescent chemosensors
CHEQ effect
Pd2þ
Cu2þ
Fꢀ
1. Introduction
fluorescence signal, thereby taking advantage of the intrinsic se-
lectivity of communication of fluorescence via two experimental
The development of artificial receptors for the sensing and
recognition of environmentally and biologically important ionic
species is currently of great interest. Highly selective anion1 or
cation2 sensing is imperative for many areas, including environ-
mental, biological, clinical, and waste management applications.
The potential for progress in the development of fluorescent
sensors can be explained by the distinct advantages offered by
fluorescence detection in terms of sensitivity, selectivity, response
time, local observation, etc. Typically, an auxochrome generating
the fluorescence signal is combined with an analyte-responsive
receptor via a saturated or unsaturated spacer. The sensing prop-
erties of such systems depend on the receptor-controlled (chem-
ical) selectivity and the analyte-mediated (spectroscopic) signaling
selectivity as well as sensitivity. Suitable fluorescent reporters
must efficiently transduce a binding event into a measurable
parameters, excitation and emission wavelength, and its high
sensitivity.1c,d,3
Crown ether derivatives occupy a special place among receptors
and are widely used in the design of new chemosensors based on
their unique ability to coordinate the cations of alkaline metals,
their fairly high selectivity and accessibility. In addition to alkaline
metals, crown ethers are also effective complexing reagents for the
cations of alkaline-earth metal ions and transition metal ions.4 On
the other hand, hydrogen-bond donors, such as pyrrole/cal-
ixpyrrole, (thio)urea, dipyrrolylquinoxalines, indolocarbazoles, and
(benzo)imidazole usually act as anion binding sites and the acidity
of the NH proton of the imidazole can be tuned by changing the
electronic properties of the imidazole substituents.5 Recently,
2,4,5-triaryl(heteroaryl)-imidazole-based chromophores have re-
ceived increasing attention due to their interesting optical prop-
erties. For example, one of the most interesting applications is as
fluorescent chemosensors.6aec The development of chemosensors
for the sensing of transition metal ions is one of the most active
research fields with great potential for environmental and
* Corresponding authors. Tel.: þ351 253 604381; fax: þ351 253 604382; e-mail
address: mfox@quimica.uminho.pt (M.M.M. Raposo).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.06.106

R.M.F. Batista et al. / Tetrahedron 67 (2011) 7106e7113
7107
physiological applications, in particular Cu2þ-sensitive systems.7
Even though great achievement in the field of colorimetric and/or
fluorescent chemosensors for Cu2þ has been obtained,8 there is still
a demand to develop new indicators with improved properties,
especially fluorescent sensors with high efficiency in the visible
nitrobenzo-15-crown-5 ether were used in the synthesis of
imidazo-benzocrown ethers 3e5, using the synthetic methodology
described above in order to evaluate the influence of the different
p-conjugated bridges on the optical and sensing properties of the
new compounds (Scheme 1).
R
S
O
O2N
H2N
O
O
OHC
O
1a R = H
+
1b R = CHO
O
Na2S2O4 / DMSO / 80 oC
CHO
S
OHC
S
2
1a
2
1b
O
O
O
S
H
N
N
N
S
O
O
O
O
O
O
S
NH
N
H
3
N
O
O
O
O
5
H
O
O
N
S
O
O
N
N
O
O
NH
O
O
4
O
O
O
O
Scheme 1. Synthesis of imidazo-benzocrown ether derivatives 3e5.
spectra and with specific selectivity toward Cu2þ over other com-
petitive metal ions. Also, due to the widespread application of Pd2þ
as catalyst in organic synthesis is important the development of
novel systems for its easy detection specially because a high level of
residual palladium (typically 300e2000 ppm) is often found in the
resultant products, which thus may be a health hazard.9
Compounds 3e5 were obtained in moderate to good yields
(53e78%) and their structures were unambiguously confirmed by
their analytical and spectral data (Table 1). Aldehyde precursors
were commercially available (1a) or synthesized as reported pre-
viously by some of us (1b, 2).6d,13
Table 1
We have demonstrated that oligothiophene and arylthiophene
derivatives, electronically connected to recognition sites, are effi-
Yields, IR, 1H NMR, UVevis absorption, and fluorescence data for imidazo-
benzocrown ethers 3e5
cient
p-conjugated bridges for the fluorimetric and/colorimetric
Compd
Yield
(%)
IR
n
dH
UVevis
Fluorescence
sensing of certain anions (e.g., Fꢀ, CNꢀ) and cations (Hþ, Naþ, Pd2þ
,
(cmꢀ1
)
(ppm)c
Cu2þ, Zn2þ, Hg2þ, Ni2þ).5d,6c,10 Following our current interests on
colorimetric and fluorimetric chemosensors provided with het-
erocyclic moieties,5d,6c,10,11 three novel heterocyclic systems con-
taining arylthiophene (3 and 4) or bithiophene (5) bridges and one
or two imidazo-benzocrown ether binding moieties were designed
and synthesized.
lmax
(nm)d
lem
Stokes’
shift (nm)
fF
(nm)d
3
4
5
64
78
53
3443a
3449a
3451b
d
360
395
415
447
500
568
87
105
135
0.76
0.50
0.10
13.45
12.76
a
For the NH stretching band (recorded in Nujol).
For the NH stretching band (recorded in KBr).
For the NH proton of the imidazole ring (in DMSO-d6).
b
c
d
In MeCN/DMSO (99:1) solution.
2. Results and discussion
2.1. Synthesis
2.2. Photophysical study of imidazo-benzocrown ether
derivatives 3e5
The electronic absorption and emission spectra of compounds
3e5 were obtained in MeCN/DMSO (99:1) solution (Table 1). The
comparison of the absorption maxima of compounds 3 and 4 re-
veals the influence of the introduction of a second imidazo-
benzocrown ether moiety as the longest wavelength transition
was shifted from 360 to 395 nm, due to more extensive electron
delocalization. When comparing compounds 4 and 5, which differ
Recently the application of a mild and versatile method for 2-
benzimidazole synthesis, was reported through a one-step re-
action involving Na2S2O4 reduction of o-nitroanilines in the pres-
ence of pyridyl and quinolyl aldehydes12 in DMSO. To the best of
our knowledge, this is the first time that this synthetic methodol-
ogy is applied to arylthiophene and bithiophene aldehydes and an
o-nitroaminobenzocrown ether derivative. Therefore, formyl-
arylthiophenes 1a,b, diformyl-bithiophene 2, and 40-amino-50-
in the electronic nature of the p-conjugated bridge, it can be seen

7108
R.M.F. Batista et al. / Tetrahedron 67 (2011) 7106e7113
that compound 5 shows a higher intramolecular charge transfer
efficiency due to the substitution of a phenyl for a thiophene ring.
The same trend was observed in the emission spectra for related
compounds.14 The study of the fluorescence properties of com-
pounds 3e5 showed that they are strongly emissive, with relative
fluorescence quantum yields ranging from 0.10 to 0.76 (Fig. 1).
Ca2þ, Zn2þ, Cu2þ, Ni2þ, Pd2þ, and Hg2þ) in MeCN/DMSO (99:1)
solutions. Having in mind our recent results concerning the
sensing properties of imidazo-anthraquinone derivatives bear-
ing thiophene moieties,5d compounds 3e5 were also studied as
chemosensors for the Fꢀ anion. It is known the acidity of the
NH proton of the imidazole ring can also be tuned by changing
the electronic properties of the
p-conjugated bridge and our
results for the signal of NH appearing downfield in the 1H NMR
spectra indicated high acidity and strong hydrogen bonding
ability.
I
norm. /a.u.
1
0.03
A
Abs 3
Abs 4
Abs 5
Due to the presence of protonable imidazo units, all reported
compounds were studied in the presence of Hþ, by titration with
a solution of methanesulphonic acid in MeCN/DMSO (99:1). In
general, the absorption spectra of all compounds were slightly af-
fected, showing a red-shift of 10 nm. Regarding the emission
spectra, for 3 the intensity of the emission was practically un-
affected upon addition of 50 equiv of acid, whereas addition of the
same amount of acid to 4 induced a 50% quenching, and 5 showed
a remarkable 70% increase in fluorescence intensity and a 20 nm
blue shift. This effect can be probably due to the different aromatic
bridge present in 4 and 5, bearing spacers of different planarity
between both imidazo-benzo units.18 At the same time, the pro-
tonation at the nitrogen of the imidazo group resulted in a partial
quenching.18b (Fig. 2).
0.0225
0.015
0.0075
0
0.8
Emis. 3
Emis. 4
Emis. 5
0.6
0.4
0.2
0
300
400
500
600
700
800
Wavelength/nm
Fig. 1. Absorption and emission spectra of compounds 3e5 in MeCN/DMSO (99:1),
T¼298 K, [3]¼5.0ꢁ10ꢀ7 M, [4]¼5.5ꢁ10ꢀ7 M, [5]¼4.3ꢁ10ꢀ7
lexc4¼395 nm; lexc5¼415 nm).
M
(
lexc3¼360 nm,
Fig. 2. Spectrofluorimetric titration of compounds 4 (A) and 5 (B) in MeCN/DMSO (99:1) solutions as a function of added CH4SO3. The insets show the normalized fluorescence
intensity at 500 nm and 535 nm, respectively ([4]¼4.30ꢁ10ꢀ7 M, lexc¼395 nm; [5]¼5.10ꢁ10ꢀ7 M, lexc¼415 nm).
Our results revealed a decrease in the relative fluorescence
quantum yield when a second imidazo-benzocrown was in-
troduced (3 compared to 4), due to the azomethine nitrogens that
contribute to the heavy atom effect concomitant with the in-
creased degree of conjugation,15 or when a thiophene replaced
a phenyl ring (4 compared to 5), with the heavy atom induced
spin-orbit coupling by the sulfur atoms giving rise to a very effi-
cient intersystem crossing mechanism, that lowers the emis-
sion.14,16 In the latter case, the decrease was larger pointing to the
better quenching process produced by the sulfur atom present in
the thiophene when compared to the nitrogen present in the
imidazole.
For all compounds, the fluorescence intensity was quenched
upon addition of fluoride ion. For compound 3, 4000 equiv were
necessary to reach a plateau, while compounds 4 and 5 required the
addition of 200 and 260 equiv, respectively. Compound 4 appears to
be the most acidic, a fact also confirmed by the 1H NMR NH signal
appearing downfield (when compared to 5). A blue shift in the
emission band was observed at the same time for all the compounds
(Fig. 3). This quenching effect can be understood as a PETeffect from
the lone pair of electrons located at the deprotonated imidazole ring.
The sensing ability of compounds 3e5 was evaluated through
interaction with metal ions, such as alkaline (Naþ, Liþ, and Kþ),
alkaline-earth (Ca2þ), and transition and post-transition metal
cations (Zn2þ, Cu2þ, Ni2þ, Pd2þ, and Hg2þ) in MeCN/DMSO (99:1) by
spectrophotometric and spectrofluorimetric titrations.
2.3. Spectrophotometric and spectrofluorimetric titrations
with proton, metallic cations and fluoride anion
The addition of up to 2000 equiv of Naþ, Liþ, and Kþ metal ions
practically does not induce spectral changes, producing only a 10%
quenching of the fluorescence emission. However, in compound 5
the addition of the same amount of Naþ resulted in a blue shift in
Compounds 3e5 were also evaluated as chemosensors in
the presence of Hþ and several metal cations (Liþ, Naþ, Kþ,

R.M.F. Batista et al. / Tetrahedron 67 (2011) 7106e7113
7109
Fig. 3. Absorption and fluorescence spectra of MeCN/DMSO (99:1) solutions of 3 (A), 4 (B), and 5 (C) and fluorescence titration as a function of Bu4NF added. The insets show the
normalized fluorescence intensity at 447 nm (3), 496 nm (4), and 568 nm (5) ([3]¼5.13ꢁ10ꢀ7 M, lexc¼360 nm; [4]¼4.30ꢁ10ꢀ7 M, lexc¼395 nm; [5]¼5.10ꢁ10ꢀ7 M, lexc¼415 nm).
the emission band and an intensity increase of 20% reaching a pla-
teau (Fig. 4). It is well known that the benzo-15-crown-5-ether
quelating unit is used specifically for Naþ sensing. However, our
results suggest that the high delocalized charge presented in these
conjugated systems could modulate the interaction with the crown
ether resulting in small changes in the ground state, as well as in
the excited state.
atom from the imidazole ring and the sulfur atoms in compounds 4
and 5, both perfectly designed to produce a chelate ring.
The quenching effect observed could be attributed to an energy
transfer quenching of the
p* emissive state through low-lying
metal-centered unfilled d-orbitals for Pd2þ and Cu2þ, and to an
intersystem crossing mechanism due to the heavy atom effect.19
Taking into account the non coordinative counterions used for
ꢀ
In general, the interaction of compounds 3e5 with Zn2þ, Ni2þ, and
Hg2þ show a very small blue shift, between 10 and 15 nm, in the ab-
sorption band. In the case of Zn2þ that normally produces a CHEF
(chelation enhancement of fluorescence) effect with polyamine sys-
tems, it was observed a 40e50% quenching of emission in all cases.
Similar findings had been published for compounds bearing a co-
ordinative aromatic nitrogen atom.17 Concerning Ni2þ andHg2þ, itwas
observed the same quenching effect of about 50% with compound 4.
The strongest interaction observed for the new compounds
all metal complexes, (CF3SO3 or BF4ꢀ) the hypothesis of 2:1 M/L
molar ratio could be perfectly predicted as acetonitrile can act as
a secondary ligand. The stoichiometry of the complexes was
obtained through Job’s plot, and for example, for ligand 3 the
stoichiometry 1:2 L:M was deduced in the presence of Pd2þ (Fig. 7).
The complexation constants of compounds 3e5, were obtained
from the spectroscopic titrations using the Hypspec program.20 The
highest constant for Pd2þ ions was obtained for compound 3
(log Kass¼11.07ꢂ0.01) and the value decreased for the other two host
systems in the sequential order 3>4>5. In the case of Cu2þ, similar
values were obtained for all systems (from log Kass¼10.32ꢂ0.01 to
log Kass¼10.93ꢂ0.01). For both metal ions, the experimental values
suggest the formation of a dinuclear complex. The study of the in-
teraction with fluoride ion indicated a mononuclear species,
exhibiting lower constant values in all cases (Table 2).
reported was found in the presence of Pd2þ and Cu2þ
.
A CHEQ (chelation enhancement of the quenching) effect in the
fluorescence emission for these both metals was observed (Figs. 5
and 6). Moreover, a blue shift was observed when Cu2þ was
added to ligand 5 (Fig. 6). The stronger interaction was detected for
compound 4 in the presence of Cu2þ, where only 25 equiv are
enough to quench the emission. In the case of compounds 3 and 5,
up to 40 and 60 equiv were necessary, respectively.
3. Conclusions
Insets of Fig. 5 show the metal ion titration followed at the
maximum of the emission band. Inspection of these figures shows
that compound 3 and 5 are totally quenched upon the addition of
15 equiv of Pd2þ, while in compound 4, 40 equiv to obtain the same
quenching effect were necessary. In summary, compounds 3 and 5
appear to be quenched more efficiently by Pd2þ while compound 4
by Cu2þ. This result turns out from the involvement of the nitrogen
In conclusion, novel imidazo-benzocrown ether-based iono-
phores 3e5 bearing arylthienyl and bithienyl p-conjugated bridges
were synthesized in moderate to good yields and evaluated as fluo-
rimetric sensors. Selectivity and sensitivity for Cu2þ and Pd2þ was
observed for all systems. Moreover, systems 4 and 5 proved to be
efficient proton and also basic anion sensors, due to changes in
emission after deprotonation of the imidazole NH by the fluoride ion.

7110
R.M.F. Batista et al. / Tetrahedron 67 (2011) 7106e7113
I norm / a.u.
1
I norm / a.u.
0.03
A
B
0.033
A
0.0275
4
3
1
A
0.025
4Li ; 4K
4Na
3Li ; 3Na
0.8
0.6
0.8
3K
0.02
0.015
0.01
0.005
0
0.022
0.6
0.4
0.2
3Ca
3Zn
4Ca
4Zn
0.0165
0.011
0.4
0.2
0
0.0055
0
300
400
500
600
700
240 320 400 480 560 640
Wavelength / nm
Wavelength/nm
I norm / a.u.
0.03
C
1
A
5Na
0.025
0.02
0.015
0.01
0.005
0
5
0.8
0.6
0.4
0.2
0
5Li ; 5K
5Zn
5Ca
300 400 500 600 700 800 900
Wavelength / nm
Fig. 4. Absorption and fluorescence spectra of MeCN/DMSO (99:1) solutions of 3 (A), 4 (B), and 5 (C) after addition of 2000 equiv of NaBF4; LiBF4; KBF4; Ca(CF3SO3)2 and Zn(CF3SO3)2
in CH3CN ([3]¼5.13ꢁ10ꢀ7 M, lexc¼360 nm; [4]¼4.30ꢁ10ꢀ7 M, lexc¼395 nm; [5]¼5.10ꢁ10ꢀ7 M, lexc¼415 nm).
I
/a.u.
I
/a.u.
1
norm.
0.03
A
0.025
0.025
A
I
/ a.u.
I
/a.u.
A
B
1
1
1
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
447 nm
500 nm
0.02
0.015
0.01
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
0.02
0
5
10 15 20 25 30
[Pd ]/[3]
0
20 40 60 80 100
[Pd ]/[4]
0.015
0.01
0.005
0.005
300 400 500
600 700 800
280 350 420 490 560 630 700
Wavelength/nm
Wavelength/nm
I
norm. /a.u.
0.03
I
/a.u.
1
C
A
1
568 nm
0.8
0.025
0.6
0.4
0.2
0
0.8
0.02
10 15 20 25 30 0.6
5
0
[Pd ]/[5]
0.015
0.01
0.4
0.2
0
0.005
300 400 500 600 700 800 900 1000
Wavelength/nm
Fig. 5. Absorption spectra of MeCN/DMSO (99:1) solutions of 3 (A), 4 (B), and 5 (C) and fluorescence titration as a function of added Pd(CH3CN)4BF4. The insets show the normalized
fluorescence intensity at 447 nm (3), 500 nm (4), and 568 nm (5) (T¼298 K; [3]¼5.13ꢁ10ꢀ7 M, lexc¼360 nm; [4]¼5.10ꢁ10ꢀ7 M, lexc¼395 nm; [5]¼4.30ꢁ10ꢀ7 M, lexc¼415 nm).

R.M.F. Batista et al. / Tetrahedron 67 (2011) 7106e7113
7111
I norm. /a.u.
I norm. /a.u.
1
0.02
A
I
/a.u.
I
A
0.033
B
1
1
0.8
A
0.6
0.4
0.2
0
447 nm
0.015
500 nm
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
0.02475
0.4
0.2
0
0
20 40 60 80 100
[Cu ]/[3]
0.01
0.005
0
0
5
10 15 20 25 30 35
[Cu ]/[4]
0.0165
0.00825
300 350 400 450 500 550 600 650 700
Wavelength/nm
300 400 500 600 700 800 900 1000
Wavelength/nm
I
norm. /a.u.
1
0.03
A
I
/a.u.
1
C
0.8
0.6
0.4
0.2
0
0.025
0.02
568 nm
0.8
0.6
0.4
0.2
0
0
50 100150200250300
[Cu ]/[5]
0.015
0.01
0.005
300 400 500 600 700 800 9001000 1100
Wavelength/nm
Fig. 6. Absorption and fluorescence spectra of MeCN/DMSO (99:1) solutions of 3 (A), 4 (B), and 5 (C) as a function of added Cu(CF3SO3)2. The insets show the normalized fluo-
rescence intensity at 447 nm (3), 500 nm (4), and 568 nm (5) ([3]¼5.13ꢁ10ꢀ7 M, lexc¼360 nm; [4]¼4.30ꢁ10ꢀ7 M, lexc¼395 nm, [5]¼5.10ꢁ10ꢀ7 M, lexc¼415 nm).
4. Experimental
0.6
4.1. Synthesis general
A
360nm
Progress of the reaction was monitored by thin layer chroma-
tography (0.25 mm thick precoated silica plates: Merck Fertigplatten
0.4
Kieselgel 60 F254), while purification was effected by silica gel col-
umn chromatography (Merck Kieselgel 60; 230e400 mesh). NMR
spectra were obtained on a Varian Unity Plus Spectrometer at an
operating frequency of 300 MHz for 1H and 75.4 MHz for 13C or
a Bruker Avance III 400 at an operating frequency of 400 MHz for 1H
and 100.6 MHz for 13C, using the solvent peak as internal reference.
The solvents are indicated in parenthesis before the chemical shift
0.2
0
values (d relative to TMS). Mps were determined on a Gallenkamp
apparatus and are uncorrected. Infrared spectra were recorded on
a BOMEM MB 104 spectrophotometer. Mass spectrometry analyses
were performed at the C.A.C.T.I.-Unidad de Espectrometria de Masas
of the University of Vigo, Spain. Elemental analysis was carried out
on a Leco CHNS-932.
4-Amino-5-nitrobenzo-15-crown-5 was purchased from
Aldrich and used as received. The synthesis of 2-(40-formylphenyl)-
thiophene, 2-formyl-5-(40-formylphenyl)-thiophene and 5,50-
diformyl-2,20-bithiophene has been described elsewhere.6d,13
0
0.2
0.4
0.6
0.8
1
1.2
2+
Molar Fraction Pd
Fig. 7. Job’s plot of compound 3 in the presence of Pd2þ
.
Table 2
Association constants for benzocrown ethers 3e5 in the presence of Fꢀ, Pd2þ, and
Cu2þ in MeCN/DMSO (99:1)
Compd
Guest
log Kass (M:L)
3
Fꢀ
3.27ꢂ0.01 (1:1)
10.32ꢂ0.01 (2:1)
11.07ꢂ0.01 (2:1)
4.09ꢂ0.01 (1:1)
10.78ꢂ0.01 (2:1)
9.72ꢂ0.03 (2:1)
4.10ꢂ0.02 (1:1)
10.93ꢂ0.01 (2:1)
10.60ꢂ0.01 (2:1)
4.2. General procedure for the synthesis of compounds 3e5
Cu2þ
Pd2þ
Fꢀ
A solution of 4-amino-5-nitrobenzo-15-crown-5 and the for-
mylated precursor (molar ratio 1:1 for the synthesis of compound 3
and molar ratio 2:1 for the preparation of compounds 4 and 5) in
DMSO (3 mL) was treated with Na2S2O4 (3 equiv), dissolved in
a small volume of water, and heated at 80 ꢃC with stirring for 15 h.
The mixture was then cooled to room temperature and the product
4
5
Cu2þ
Pd2þ
Fꢀ
Cu2þ
Pd2þ

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R.M.F. Batista et al. / Tetrahedron 67 (2011) 7106e7113
precipitated during neutralization with NH4OH 5 M. The precipitate
was filtered, washed with water and diethyl ether and dried to give
the expected product.
were used without previous purification. CH4SO3 was used to
change the acidity conditions of the MeCN/DMSO solutions. Lu-
minescence quantum yields were measured using a solution of
quinine sulfate in sulfuric acid (0.1 M) as standard [fF¼0.54].22 All
measurements were conducted at 298 K.
4.2.1. Crown ether 3. Yellow solid (64%). Mp: 291.5e293.0 ꢃC. IR
(Nujol)
n 3443, 2923, 2855, 1639, 1609, 1464, 1377, 1293, 1256, 1219,
1209, 1173, 1139, 1081, 1050, 1008, 983, 945, 849, 826 cmꢀ1. 1H NMR
Acknowledgements
(DMSO-d6)
d
3.63 (s, 8H, 4ꢁ CH2), 3.82 (s, 4H, 2ꢁ CH2), 4.13 (s, 4H,
ˇ
2ꢁ CH2), 7.19e7.22 (m, 3H, 400-H, 4-H and 5-H), 7.67 (dd, 1H, J¼4.5
and 0.9 Hz, 500-H), 7.71 (dd, 1H, J¼2.7 and 0.9 Hz, 300-H), 7.93 (d, 2H,
J¼8.7 Hz, 20-H and 60-H), 8.13 (d, 2H, J¼8.7 Hz, 30-H and 50-H). 13C
~
Thanks are due to the Fundac¸ ao para a Ciencia e Tecnologia
(Portugal) and FEDER for financial support through the Centro de
Química and Centro de Física-Universidade do Minho, and Pro-
ject PTDC/QUI/66250/2006 (FCOMP-01-0124-FEDER-007428),
Ph. D. grant to R.M.F.B. (SFRH/BD/36396/2007) and Postdoctoral
grant to E.O. (SFRH/BPD/72557/2010). The NMR spectrometer
Bruker Avance III 400 is part of the National NMR Network and
was purchased within the framework of the National Program
for Scientific Re-equipment, contract REDE/1517/RMN/2005 with
funds from POCI 2010 (FEDER) and FCT. C.L. thanks Xunta de
Galicia, Spain, for the Isidro Parga Pondal Research Program.
NMR (DMSO-d6)
d
68.71 (2ꢁ CH2), 68.99 (2ꢁ CH2), 69.71 (2ꢁ CH2),
70.52 (2ꢁ CH2), 97.93 (C4 and C5), 124.12 (C40), 125.42 (C300), 126.04
(C20 and C60), 127.39 (C500), 127.61 (C30 and C50), 128.14 (C3a and
C5a), 128.97 (C400), 136.53 (C10), 141.99 (C200), 147.06 (C2), 148.16
(C4a and C4b). MS (FAB) m/z (%): 467 ([MþH]þ, 60), 466 (Mþ, 17),
308 (13), 307 (40), 289 (17), 155 (32), 154 (100). HRMS: (FAB) m/z
(%) for C25H27N2O5S; calcd 467.1641; found 467.1654.
4.2.2. Crown ether 4. Brown solid (78%). Mp: 246.5e248.9 ꢃC. IR
(Nujol)
n
3449, 2930, 2842, 1633, 1593, 1467, 1378, 1284, 1121,
1053, 938, 844, 811, 722 cmꢀ1
.
1H NMR (DMSO-d6) 3.65 (s, 16H,
Supplementary data
4ꢁ CH2), 3.82 (s, 8H, 2ꢁ CH2), 4.11 (s, 8H, 2ꢁ CH2), 7.14 (s, 2H, 4-H
and 5-H), 7.18 (s, 2H, 4-H and 5-H), 7.71 (d, 1H, J¼4.0 Hz, 300-H),
7.87 (d, 2H, J¼8.8 Hz, 20-H and 60-H), 7.92 (d, 1H, J¼4.0 Hz, 400-H),
8.27 (d, 2H, J¼8.4 Hz, 30-H and 50-H), 13.45 (br s, 1H, NH). 13C
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2011.06.106. These data in-
clude MOL files and InChIKeys of the most important compounds
described in this article.
NMR (DMSO-d6)
d
68.46 (4ꢁ CH2), 68.52 (4ꢁ CH2), 69.13 (4ꢁ
CH2), 69.65 (2ꢁ CH2), 69.73 (2ꢁ CH2), 125.40, 125.69, 126.89,
127.22, 128.62, 133.76, 134.20, 143.41, 145.38, 145.84, 146.22,
148.81. MS (FAB) m/z (%): 795 ([MþNa]þ, 100), 773 ([MþH]þ, 21),
636 (12), 517 (10). HRMS: (FAB) m/z (%) for C40H45N4O10S; calcd
773.2856; found 773.2866.
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1H NMR (DMSO-d6) 3.63 (s, 16H, 8ꢁ
CH2), 3.82 (s, 8H, 4ꢁ CH2), 4.08 (s, 8H, 4ꢁ CH2), 6.99 (s, 2H, 2ꢁ 4-H),
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