Cu(II)- and Hg(II)-induced modulation of the fluorescence behavior of a redox-active sensor molecule

Article abstract of DOI:10.1021/ic000827u

Here, we report on a fluorescent 1,2,4-thiadiazole derivative (oxidized form) and its reduced form, the corresponding iminoyl thiourea. The thiadiazole displays a strong modulation of its fluorescence behavior, selectively upon addition of Cu(II), while the iminoyl thiourea functions as a chemodosimeter for Hg(II). Additionally, the Cu(II)-thiadiazole complex is characterized by HRMS, and the Hg(II)-induced desulfurization of the iminoyl thiourea is monitored by mass spectrometry.

Full text of DOI:10.1021/ic000827u

Inorg. Chem. 2001, 40, 641-644
641
Cu(II)- and Hg(II)-Induced Modulation of the Fluorescence Behavior of a Redox-Active
Sensor Molecule
†
†
,†
‡
Gunther Hennrich, Wolfgang Walther, Ute Resch-Genger,* and Helmut Sonnenschein
Federal Institute for Materials Research and Testing, Richard-Willstaetter-Strasse 11,
1
0
2489 Berlin, Germany, and Institute of Nonclassical Chemistry, Permoserstrasse 15,
4303 Leipzig, Germany
ReceiVed July 24, 2000
Here, we report on a fluorescent 1,2,4-thiadiazole derivative (oxidized form) and its reduced form, the corresponding
iminoyl thiourea. The thiadiazole displays a strong modulation of its fluorescence behavior, selectively upon
addition of Cu(II), while the iminoyl thiourea functions as a chemodosimeter for Hg(II). Additionally, the Cu(II)-
thiadiazole complex is characterized by HRMS, and the Hg(II)-induced desulfurization of the iminoyl thiourea is
monitored by mass spectrometry.
5
Introduction
lecular assemblies, usually with a structurally well developed
6
receptor unit being part of a fluoroionophore system. Recently,
we reported on a redox-switchable fluoroionophore combining
a high selectivity for Hg(II) with a high signal output, i.e.,
fluorescence enhancement. In this system a simple 1,2,4-
thiadiazole was attached via a methylene spacer to an anthracene
fluorophore in a way that allowed photoinduced electron transfer
PET) from the receptor to the fluorophore unit to occur. It is
known from the literature that selective binding of heavy metal
and transition metal cations is achieved by receptors containing
sulfur or nitrogen heteroatoms. Previously, we have shown
the complexation behavior of redox-switchable 1,2,4-thiadiazole/
iminoyl thiourea ionophores.
While the design of fluorogenic receptors for metal cations
such as alkaline and alkaline earth metal cations as well as,
more recently, for the d metal cation Zn(II) is a well-
established field in supramolecular chemistry, still a great deal
of effort is invested in the construction of devices that are able
10
7
1
2
to signal the presence of heavy and transition metal cations.
(
Considering the growing interest in molecules capable of
performing logic operations, special attention has to be focused
on the importance of heavy and transition metal cations in such
devices serving as molecular switches.3
Most of the known molecular systems that monitor these
cations selectively, especially strongly quenching paramagnetic
Cu(II) or the heavy metal cation Hg(II), exploit the mechanism
8
,9
1
0
Following this modular approach, a structurally more simple
1,2,4-thiadiazole/iminoyl thiourea redox system with a naphthyl
fluorophore was synthesized (Figure 1). Both forms, the
heterocyclic thiadiazole 1 (oxidized form) and the ring-opened
4
of complexation-induced fluorescence quenching (CHEQ).
Only a very few systems have been reported in which com-
plexation of Cu(II) or Hg(II) results in an enhancement of the
fluorescence. In most cases, to suppress the interaction of the
quenching metal ions and the fluorophore, considerable synthetic
effort had to be made to obtain chemically demanding supramo-
(
4) Kr a¨ mer, R. Angew. Chem. 1998, 110, 804-806; Angew. Chem., Int.
Ed. 1998, 37, 772-773. Yoon, J.; Ohler, N. E.; Vance, D. H.;
Aumiller, W. D.; Czarnik, A. W. Tetrahedron Lett. 1997, 38, 3845-
3
848. Torrado, A.; Walkup, G. K.; Imperiali, B. J. Am. Chem. Soc.
†
Federal Institute for Materials Research and Testing.
Institute of Nonclassical Chemistry.
1998, 120, 609-610. Bernardo, M. A.; Pina, F.; Escuder, B.; Garcia-
Espa n˜ a, E.; Godino-Salido, M. L.; LaTorre, J.; Luis, S. V.; Ramirez,
J. A.; Soriano, C. J. Chem. Soc., Dalton Trans. 1999, 915-921.
‡
(
1) Chemosensors of Ion and Molecule Recognition; Desvergne, J. P.,
Czarnik, A. W., Eds.; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1997; pp 75-90. de Silva, A. P.; Gunaratne, H. Q. N.;
Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J.
T.; Rice, T. E. Chem. ReV. 1997, 97, 1515-1567. Koike, T. Chem.
Soc. ReV. 1998, 27, 179-184. Kubo, K.; Ishige, R.; Kubo, J.; Sakurai,
T. Talanta 1999, 48, 181-187.
(5) Inuoe, M. B.; Medrano, F.; Inoue, M.; Raitsimring, A.; Fernando, Q.
Inorg. Chem. 1997, 36, 2335-2340. Grandini, P.; Mancin, F.; Tecilla,
P.; Scrimin, P.; Tonellato, U. Angew. Chem. 1999, 111, 3247-3250.
(6) Gosh, P.; Bharadwaj, P. K.; Roy, J.; Gosh, S. J. Am. Chem. Soc. 1997,
119, 11903-11909. Talanova, G. G.; Elkarim, N. S. A.; Talanov, V.
S.; Bartsch, R. A. Anal. Chem. 1999, 71, 3106-3109. Rurack, K.;
Kollmannsberger, M.; Resch-Genger, U.; Daub, J. J. Am. Chem. Soc.
2000, 122, 968-969.
(
2) Kido, H.; Szurdoki, F.; Gustin, M. S.; Hammock, B. D. In Metals
and Genetics; Sarkar, A., Ed.; Kluwer Academic/Plenum Publishers:
New York, 1999; pp 101-115. Alfimov, M. V.; Gromov, S. P.;
Fedorov, Y. V.; Fedorova, O. A.; Vedernikov, A. I.; Churakov, A. I.;
Kuz’mina, L. G.; Howard, J. A. K.; Bossmann, S.; Braun, A.; Woerner,
M.; Sears, D. F., Jr.; Saltiel, J. J. Am. Chem. Soc. 1999, 121, 4992-
(7) Hennrich, G.; Sonnenschein, H.; Resch-Genger, U. J. Am. Chem. Soc.
1999, 121, 5073-5074.
(8) Chae, M. Y.; Czarnik, A. W. J. Am. Chem. Soc. 1992, 114, 9704-
9705. Dujols, V.; Ford, F.; Czarnik, A. W. J. Am. Chem. Soc. 1997,
119, 7386-7387.
5000.Wang, F.; Schwabacher, A. W. J. Org. Chem. 1999, 64, 8922-
928. Bergonzi, R.; Fabbrizzi, L.; Licchelli, M.; Mangano, C. Coord.
8
(9) Guillon, E.; Dechamps-Olivier, I.; Mohamadou, A.; Barbier, J.-P.
Inorg. Chim. Acta 1998, 268, 13-19. Sandor, M.; Geistmann, F.;
Schuster, M. Anal. Chim. Acta 1999, 388, 19-26. Cattrall, R. W.;
Gregorio, C. C.; Webster, R. D. Anal. Chem. 1997, 69, 3353-3359.
Bernardo, M. A.; Pina, F.; Garcia-Espa n˜ a, E.; LaTorre, J.; Luis, S.
V.; Llinares, J. M.; Ramirez, J. A.; Soriano, C. Inorg. Chem. 1998,
37, 3935-3942.
Chem. ReV. 1998, 70, 31-46.
(
3) Beer, P. D.; Gale, P. A.; Cheng, G. Z. Cood. Chem. ReV. 1999, 185-
1
86, 3-36. Amendola, V.; Fabbrizzi, L.; Linati, L.; Mangano, C.;
Pallavinci, P.; Zema, M. Chem. Eur. J. 1999, 12, 3679-3688.
Fabbrizzi, L.; Licchelli, M.; Pallavinci, P. Acc. Chem. Res. 1999, 32,
8
46-853. de Silva, A. P.; Dixon, I. M.; Gunaratne, H. Q. N.;
Gunnlaugsson, J. T.; Maxwell, P. R. S.; Rice, T. E. J. Am. Chem.
Soc. 1999, 121, 1393-1394.
(10) Hennrich, G.; Sonnenschein, H.; Resch-Genger, U. Eur. J. Org. Chem.
2000, 3, 539-542.
1
0.1021/ic000827u CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/11/2001

642 Inorganic Chemistry, Vol. 40, No. 4, 2001
Hennrich et al.
Figure 1. Oxidized form 1: 3-phenyl-5-(1-aminonaphthyl)-1,2,4-
thiadiazole. Reduced form 2: N-iminobenzyl-N′-(R-naphthyl)-thiourea.
Table 1. Spectroscopic Data of the Free Compounds 1, 2, and 3
(
Φ
ꢀ, Extinction Coefficient; Ex, Excitation Wavelength in nm;
f
, Fluorescence Quantum Yield)a
fluorescence
em/nm (ex)
220 (4.66), 243 (4.48), 319 (3.95) 405 (350)
217 (4.74), 305 (4.22)
223 (4.81), 309 (4.29)
absorption
ex/nm (log10 ꢀ)
λ
λ
Φ
f
-
-
-
3
3
3
1
2
3
1.9 × 10
334, 412* (290) 5.1 × 10
368 (290)
5.9 × 10
a
-5
(*) Broad shoulder, weakly fluorescent.
Figure 2. Fluorescence behavior of 1 (c ) 3.65 × 10 M in
4 2
acetonitrile, excitation at 350 nm) upon addition of Cu(ClO ) ;
measurement after 48 h: (a) free 1; (b) 0.1 equiv of Cu(II); (c) 0.3
equiv of Cu(II); (d) 0.5 equiv of Cu(II); (e) 2 equiv of Cu(II). Inset:
iminoyl thiourea 2 (reduced form), can be converted into each
other by chemical oxidation or reduction, respectively. There-
fore, the system presented can be considered as a two-faced
molecule containing binding sites that differ in geometry and
electron-donating capacity, depending on the redox state.
In this paper, we study the influence of different heavy metal
and transition metal cations on the fluorescence behavior of 1
and 2 by optical spectroscopy accompanied by mass spectro-
scopic measurements. Mass spectroscopy has proved to be a
powerful tool in the study of host-guest interactions. Here,
it offers the opportunity to monitor the chemical processes
occurring in solution in a concentration range similar to that
used for the fluorometric studies. Furthermore, all the metal-
cation-containing solutions investigated are accessible by this
method, whereas with NMR spectroscopy the paramagnetism
9, 1 + 0.5 equiv of Cu(II), time-dependent fluorescence enhancement.
of Ca(II) gives a slightly enhanced (2-fold) fluorescence
intensity. No spectral shifts are observed. The cation-induced
changes in the UV/vis spectrum of 1 are negligible.
Remarkably, a drastic Cu(II)-induced modulation of the
fluorescence of 1 is found (Figure 2). Upon addition of Cu(II)
in the sub-parts per billion concentration region, i.e., 0.05-0.5
equiv (0.18-1.8 µM) of 1, the probe’s fluorescence is switched
on immediately, accompanied by a red shift of the emission
maximum from 405 nm for the free thiadiazole derivative 1 to
1
1
4
42 nm in the presence of 0.5 equiv Cu(II), successively.
The strongest fluorescence enhancement (FE) is observed for
a metal-to-ligand concentration ratio (Cu(II):1) of 1:2. The
increase of the emission intensity is time dependent, varying
additionally with the concentration of 1. Immediately after
addition of 0.5 equiv of Cu(II), a 4-fold fluorescence enhance-
ment is obtained, and an approximately constant signal is
reached after 6 h (inset, Figure 2). The final FE is 46-fold, the
fluorescence quantum yield of the Cu(II)-1 complex being
of Cu(II) would lead to severe problems. Due to the relatively
low association constants expected12 and the difficulties in
obtaining suitable crystals for X-ray analysis, we used high-
resolution mass (HRMS) and IR spectroscopy for complex
characterization.
Results and Discussion
0
.088.
Synthesis. Compound 2 was prepared under mild conditions
in 56% yield by reacting benzamidinium hydrochloride with
Increasing the concentration of Cu(II) results in the occurrence
of a new broad and structureless band with a global maximum
located at 531 nm. This behavior is also dependent on the
concentration of 1 and is consistent with the formation of
1
-naphthylisothiocyanate in the presence of sodium hydrogen
carbonate. Using 1-naphthylisocyanate in the presence of
triethylamine, the urea 3 as a reference compound for 2 was
obtained in the same manner. 2 can be easily converted into
the 1,2,4-thiadiazole 1 by oxidation with iodine. The back-
1
4
intermolecular excimers. The excimer complex displays an
enhanced fluorescence compared to the fluorescence of the free
monomeric compound 1. Upon a further increase of the metal
ion concentration, gradual dynamic fluorescence quenching is
observed.
reduction of 1, leading to the thiourea 2, can be achieved with
zinc in glacial acetic acid.13
Spectroscopic Studies. The absorption and fluorescence
properties of free 1, 2, and 3 are listed in Table 1. The spectra
in acetonitrile were recorded in the concentration range between
Mass spectrometry proved the formation of a 1:2 Cu(II)
complex by its characteristic isotopic pattern and high resolution
of the mass signal at m/z 667, using samples with concentrations
of the same order of magnitude as those employed for the
spectroscopic studies. For both metal-to-ligand ratios investi-
gated, i.e., 1:1 and 1:2, the same 1:2 Cu(II)-1 complex was
found as the only complex species. Also in mass spectroscopy,
time-dependent complex formation can be observed from a time-
dependent variation of the peak intensities of 1 and the complex.
Hence, also the complex displaying excimer emission exists in
a 1:2 stoichiometry. The different fluorescence behavior is
-
5
-5
1
.1 × 10 and 3.9 × 10 for 1, 2, and 3.
Addition of various bivalent cations (Ca(II), Hg(II), Mg(II),
Ni(II), and Pb(II)) in a 1-100-fold excess (complete complex-
ation) has only minor effects on the fluorescence behavior of
the 1,2,4-thiadiazole 1. The emission of weakly fluorescent
compound 1 is quenched by Ni(II) and Pb(II), while addition
(
11) Vincenti, M. J. Mass Spectrom. 1995, 30, 925-939.
(
12) da Silva, A. S.; de Silva, M. A. A.; Carvalho, C. E. M.; Antunes, O.
A. C.; Herrera, J. O. M.; Brinn, I. M.; Mangrich, A. S. Inorg. Chim.
Acta 1999, 292, 1-6. Maekawa, M.; Munakata, M.; Kuroda-Sowa,
T.; Suenaga, Y.; Sugimoto, K. Inorg. Chim. Acta 1999, 290, 153-
(14) Parker, D.; Williams, J. A. G. J. Chem. Soc., Perkin Trans. 1995,
1305-1314. Beeby, A.; Parker, D.; Williams, J. A. G. J. Chem. Soc.,
Perkin Trans. 1996, 1565-1579.
158.
(13) See ref 10 and citations therein.

Redox-Switchable Fluorescent Probe for Metal Cations
Inorganic Chemistry, Vol. 40, No. 4, 2001 643
Although a slow complexation of Hg(II) by urea 3 can be
1
6
assumed, the formation of a complex species could not be
confirmed by mass spectrometry. Upon addition of Hg(II) (2
equiv) to 2 in acetonitrile solution, a signal at m/z 290 appears
+
rapidly, attributed to the molecular ion [3 + H] , while the peak
+
at m/z 304 (molecular ion [2 - H] ) decreases. At higher values,
various ion peaks with weak intensities are found which are
attributed to the presence of cluster ions only; i.e., there is no
evidence for the formation of a Hg(II) complex.
Also for the iminoyl thiourea 2, the fluorometric response
upon addition of various cations proved to be very selective
1
7
for Hg(II). A 100-fold excess (complete complexation) of
Ca(II) and Ni(II) results in a modest enhancement (40% and
20% respectively) of the emission intensity at 334 nm. Addition
of 100 equiv of Cu(II) yields a weakly fluorescent excimer band
at 519 nm. Again, the effects observed in the absorption spectra
are negligible.
-
5
Figure 3. Fluorescence enhancement of 2 (c ) 1.94 × 10 M in
acetonitrile, excitation at 290 nm) upon addition of Hg(ClO
4 2
) ;
measurement after 48 h: (a) free 2; (b) 0.1 equiv of Hg(II); (c) 10
equiv of Hg(II); (d) 1 equiv of Hg(II).
Conclusion
We synthesized a structurally simple redox-switchable mo-
lecular sensing system which exists in two structurally different
forms. Each form is capable of signaling selectively the strongly
fluorescence quenching cations Cu(II) respectively Hg(II) by
drastic fluorescence enhancement. A fluorescent 1:2 Cu(II)-1
complex is obtained, displaying a FE factor of 46. Switching
on the fluorescence is achieved immediately after addition of
the respective metal cation, although gaining a full, constant
signal requires a long period of time, making the system less
attractive for analytical applications. The iminoylthiourea 2
functions as a chemodosimeter, reporting selectively the pres-
ence of Hg(II) by a 34-fold fluorescence enhancement. The
signaling mechanism for both forms, i.e., the Cu(II)-1 complex
formation or the chemical reaction of 2, is revealed in solution
by means of mass spectroscopy.
Figure 4. Desulfurization of the iminoylthiourea 2 by Hg(II) leading
to the corresponding urea 3.
therefore attributed to different coordination modes within the
complex due to various possible binding sites and conformers.
To reveal more details about the exact mode of the Cu(II)
coordination, IR spectroscopic measurements were performed
in addition to the UV/vis and MS studies. By comparison of
the spectral position and shape of the vibrational bands of the
free ligand 1 with those of the Cu(II) complex, obtained as an
amorphous solid, it can be seen that Cu(II) coordination by 1
takes place to the NH group and additionally to the thiadiazole
ring, most likely to the N4-nitrogen.15
Upon addition of Hg(II) to a solution of 2, a red shift and an
increase in the naphthalene emission are observed immediately,
after 48 h finally yielding a band at 368 nm with a 34-fold
enhanced fluorescence intensity while the emission band at
initially 334 nm has disappeared almost completely (Figure 3).
Simultaneously, the absorption maximum of 2 at 305 nm is
shifted to 295 nm. This time-dependent effect, reaching constant
signal intensities after 48 h, is significant with amounts of Hg(II)
exceeding 0.1 equiv (1.9 µmol). An excess of Hg(II) (>1 equiv)
leads to an initial fluorescence enhancement, followed by a
subsequent bimolecular quenching. The fluorescence of 2 is
quenched completely after 48 h upon addition of a 100-fold
excess (1.9 mmol) of Hg(II).
Experimental Section
General Methods. All the reagents and solvents, which were of
the highest purity commercially available, were obtained from Aldrich
and Merck, respectively. The reaction progress was monitored by
analytical thin-layer chromatography (TLC), performed with plastic
silica gel plates 60 F254 (5735, Merck). Column chromatography was
carried out with silica gel 60 (7731, Merck). The purity of 1 and 2 was
checked by HPLC. Nuclear magnetic resonance data were recorded
on a UNITY plus-500 spectrometer with chemical shifts reported in
4
parts per million (Me Si as internal standard, J in hertz, coupling
constants taken directly from the obtained spectra). IR spectra were
determined in KBr with a Perkin-Elmer model 1600 instrument. Melting
points were determined using a Boetius apparatus and are uncorrected.
Fluorescence and UV/Vis Spectroscopy. Absorption spectra were
recorded on a Carl Zeiss SPECORD M400 spectrometer. A Spectronic
Instruments Inc. 8100 fluorescence spectrometer was employed for the
fluorescence studies. Emission measurements were performed in a four-
sided 1 cm quartz cell at room temperature in a right angle geometry
and are corrected for the spectral response of the detection system.
This behavior is due to the desulfurization of the thiocarbonyl
function by the thiophilic Hg(II) cation, leading to the N-imi-
nobenzyl-N′-(R-naphthyl)-urea 3 (Table 1 and Figure 4). Free
-2
-3
Standard solutions (10 -10 M) for titration experiments were
prepared using spectroscopic grade acetonitrile and dried metal per-
chlorates. Appropriate dilution was carried out using volumetric pipets.
The spectra in acetonitrile were recorded at concentrations of 3.9 ×
3
displays strongly enhanced fluorescence upon addition of Hg-
(II). The enhancement of the emission intensity proceeds slowly
and is accompanied by a hypsochromic shift of the absorption
band from 309 to 291 nm. After 48 h the fluorescence quantum
-
5
-5
-5
10 M for 1, 1.51 × 10 M for 2, and 1.10 × 10 M for 3. The
-
3
-1
yield has increased from 5.9 × 10 for free 3 to 1.7 × 10 .
fluorescence quantum yields were determined using quinine sulfate as
standard (Φ
adjusted to 0.1-0.2 at the excitation wavelength.
) 0.55)18 with absorbances of the solutions of 1, 2, and
f
3
(
15) Due to the difficulties of making an unequivocal assignment of the
-
1
various peaks in the region between 1600 and 1200 cm to the
respective vibrational transitions, we restrict ourselves to only noting
the significant differences in the spectra of free 1 and the Cu(II)
complex in this area. See also: Kurzer, F. J. Chem. Soc., Perkin Trans.
(16) Richter, R.; Sieler, J.; Beyer, L.; Lindqvist, O.; Andersen, L. Z. Anorg.
Allg. Chem. 1986, 522, 171-183.
(17) Desulfurization of 2 occurs also with Ag(I), leading to a 30-fold
fluorescence enhancement.
1
1985, 311-314.

644 Inorganic Chemistry, Vol. 40, No. 4, 2001
Hennrich et al.
Mass Spectrometry. All the mass spectra were acquired on a MAT
5 (Finnigan MAT, Bremen) high-resolution sector field mass spec-
(CDCl
3
) 8.8 (1 H, br s, NH), 8.13-7.25 (12 H, m, PhsH, NaphsH);
3
9
δ
C
(CDCl ) 183.85 (sCsS), 169.76 (sNsCdNs), 135.23, 134.56,
trometer with electrospray ionization (API-II). Typical, optimized values
for some parameters were the following: capillary voltage, 2.8 kV;
capillary temperature, 230 °C; capillary/skimmer voltage, 50 V; sheath/
auxiliary gas, 4/0.2 L/min air. The acetonitrile dissolved samples were
flow-injected by using a 20 µL sample loop with methanol as the mobile
phase at a flow rate of 200 µL/min. The exact masses of the ions were
determined by peak matching with polypropylene glycols at a resolution
of 5000-6000.
132.91, 129.97, 128.75, 128.39, 127.84, 127.54, 127.07, 126.98, 126.91,
125.78, 121.08, 119.07 (PhsC, NaphsC). IR: νmax 3157s (NH), 1630w
-
(CdN). HRMS: calculated for [C18
302.0748; error 1.5 ppm. TLC: R
Bis-(3-phenyl-5-(1-aminonaphthyl)-1,2,4-thiadiazole)-Cu(II) Com-
H
13
N
4
S-H] , 302.0752; found,
f
) 0.63 n-Hex-EE (4:1 v/v).
-
4
plex. (a) In Solution. A solution of 1 (c ) 3.65 × 10 M) in
acetonitrile was treated with 2 equiv of Cu(ClO ) and left for 48 h
4 2
before the measurement. HRMS: calculated for [C H N S Cu],
36
24
6 2
Materials. N-Iminobenzyl-N′-(r-naphthyl)-thiourea (2). A mixture
of 1-naphthylisothiocyanate (185 mg, 1.0 mmol), benzamidine hydro-
chloride (156 mg, 1.0 mmol), and sodium hydrogen carbonate (140
mg) was stirred overnight in dioxane (20 mL) at room temperature.
The resulting solid was filtered off and washed with dioxane. The filtrate
was concentrated in vacuo. The remaining yellow oil was treated with
diethyl ether and n-hexane to give a yellow solid. Recrystallization
from acetonitrile-ethanol (4:1 v/v) gave pale yellow crystals. Yield
667.0700; found, 667.0700; error -0.6 ppm.
b) As a Solid. To a solution of 1 (100 mg, 0.33 mmol) in ethyl
acetate (8 mL) was added copper(II) triflate (58 mg, 0.16 mmol). Slow
evaporation of the solvent afforded the Cu(II) complex after 6 d as a
(
brown, amorphous solid. IR:
νmax 3164br (NH), 1611s (CdN).
HRMS: calculated for [C36
error 1.5 ppm.
H N S Cu], 669.0956; found, 669.0945;
26 6 2
N-Iminobenzyl-N′-(r-naphthyl)-urea (3). Benzamidinium hydro-
chloride (1.0 g, 6.4 mmol) and 1-naphthylisocyanate (1.1 g, 6.4 mmol)
were refluxed in dioxane (50 mL) and triethylamine (5 mL) for 2.5 h.
The resulting solid was filtered off, and the filtrate was concentrated
in vacuo. Treating the remaining yellow oil with chloroform-petroleum
ether (4 mL, 1:1 v/v) and leaving it overnight in the refrigerator led to
the precipitation of colorless crystals which were filtered off and
recrystallized from acetonitrile. Yield 380 mg (41%), mp 138 °C. Anal.
1
71 mg (56%), mp 160-164 °C. Anal. Calcd for C18
H, 4.92; N, 13.77. Found: C, 70.82; H, 4.86; N, 13.54. NMR: δ
CDCl ) 11.6 (1 H, br s, NH), 10.8 (1 H, br s, NH), 8.05-7.25 (12 H,
m, Ph-H, Naph-H), 6.5 (1H, br s, NH); δ (DMSO-d ) 186.71 (sCd
S), 162.30 (sCdNs), 139.49, 134.64, 131.82, 128.96, 128.44, 128.21,
15 3
H N S: C, 70.82;
H
(
3
C
6
1
28.06, 127.61, 124.66, 123.86, 123.53, 122.48 (PhsC, NaphsC);.
+
MS (ESI): m/z (relative intensity) 304 ([M - H] , 100), 256, 240,
2
28. TLC: R
3
f
) 0.16 n-Hex-EE (4:1 v/v).
Calcd for C18
H, 5.07; N, 14.23. NMR: δ
.04-7.47 (13 H, m, PhsH, NaphsH, sNH), 6.21 (1 H, br s, NH);
(CDCl ) 165.90 (sCdO), 164.11 (sCdNs), 135.43, 134.14,
H
15
N
3
O: C, 70.74; H, 5.19; N, 14.53. Found: C, 70.64;
-Phenyl-5-(1-aminonaphthyl)-1,2,4-thiadiazole (1). To a suspen-
H
(CDCl ) 9.96 (1 H, br s, NaphsNH),
3
sion of 2 (146 mg, 0.5 mmol) in chloroform (20 mL) was added a
saturated chloroformic iodine solution dropwise until no further
decolorization was observed. NaOH (1 N, 20 mL) was added, the
suspension was stirred for 10 min, and the phases were separated. The
8
δ
C
3
133.42, 131.82, 128.80, 128.62, 126.97, 125.97, 125.83, 124.66, 121.03,
1
+
19.16 (PhsC, NaphsC). MS (FAB): m/z (relative intensity) 290 ([M
organic layer was dried (MgSO
give a yellow solid. Recrystallization from 2-propanol yielded pure 1
as colorless crystals. Yield 126 mg (83%), mp 152 °C. NMR: δ
4
), and the solvent was evaporated to
+
H] , 100), 169, 144, 121. TLC: R
f
) 0.15 n-Hex-EE (4:1 v/v).
H
Acknowledgment. We gratefully acknowledge financial
support by the Deutsche Forschungsgemeinschaft.
(
18) Testa, A. C. Fluorescence News 1969, 4, 1-3. Olmsted, J., III. J.
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