5-[2-(Methylthio)ethyl]-3-phenyl-2-thioxoimidazolidin-4-one and its complexes with transition metals (CoII, NiII, and Cu II). Synthesis and electrochemical investigation

Article abstract of DOI:10.1007/s11172-007-0057-5

The reaction of 5-[2-(methylthio)ethyl]-3-phenyl-2-thioxoimidazolidin-4-one (LH) with salts MCl₂? xH₂O (M = Co, Ni, Cu; x = 2, 6) afforded the [M(L)Cl]_n complexes of Ni^II, Co ^II, and Cu^II.

Full text of DOI:10.1007/s11172-007-0057-5

Russian Chemical Bulletin, International Edition, Vol. 56, No. 2, pp. 351—355, February, 2007
351
5ꢀ[2ꢀ(Methylthio)ethyl]ꢀ3ꢀphenylꢀ2ꢀthioxoimidazolidinꢀ4ꢀone
and its complexes with transition metals (CoII, NiII, and CuII).
Synthesis and electrochemical investigation
E. K. Beloglazkina,ꢀ A. G. Majouga, A. А. Moiseeva, М. G. Tsepkov, and N. V. Zyk
Department of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Eꢀmail: bel@org.chem.msu.ru
The reaction of 5ꢀ[2ꢀ(methylthio)ethyl]ꢀ3ꢀphenylꢀ2ꢀthioxoimidazolidinꢀ4ꢀone (LH) with
salts MCl2•хH2O (M = Co, Ni, Cu; x = 2, 6) afforded the [M(L)Cl]n complexes of NiII, CoII,
and CuII. The electrochemical behavior of the LH ligand and its complexes was studied using
the cyclic voltammetry and rotating disk electrode techniques. The structures of the syntheꢀ
sized compounds were determined by the data of UV—Vis and IR spectroscopy, mass specꢀ
trometry, and electrochemical characteristics.
Key words: 2ꢀthioxoimidazolidinꢀ4ꢀone, 2ꢀthiohydantoine, nickel(II) complexes, cobalt(II)
complexes, copper(II) complexes, cyclic voltammetry, rotating disk electrode technique.
Scheme 1
Complexes of transition metals, in particular,
nickel(II),1 cobalt(II),2 and copper(II),3 with organic
S,Nꢀcontaining ligands attrack attention as models of
metal enzymes and electroactive catalysts. Among promꢀ
ising organic ligands are, e.g., thioꢀsubstituted imidꢀ
azolones. We have earlier4—7 synthesized the CoII, NiII,
and CuII complexes with a series of 5ꢀ(pyridylmethylꢀ
idene)ꢀsubstituted 2ꢀthioxoimidazolidinꢀ4ꢀones (2ꢀthioꢀ
hydantoines). Particular representatives of these comꢀ
pounds are able to reversibly electrochemically reduce5
and catalyze alkene epoxidation.6,7 In the present work,
we synthesized a series of the complexes of 5ꢀ[2ꢀ(methylꢀ
thio)ethyl]ꢀsubstituted 2ꢀthiohydantoine and determined
their structures.
plexes 2—4 is formed upon the addition of an equivalent
amount of triethylamine (Scheme 2).
Results and Discussion
Scheme 2
Synthesis of 5ꢀ[2ꢀ(methylthio)ethyl]ꢀ3ꢀphenylꢀ2ꢀ
thioxoimidazolidinꢀ4ꢀone (1) and its complexes with the
CoII, NiII, and CuII salts. The most convenient method
for the synthesis of 2ꢀthiohydantoines are the reactions of
amino acids with aryl or alkyl isothiocyanates.8 Ligand 1
(hereinafter LH) was synthesized by the reaction of pheꢀ
nyl isothiocyanate with methionine in a pyridine—water
mixture in the presence of sodium hydroxide, affording
substituted thiourea, whose ring closure with target prodꢀ
uct formation was carried out by the treatment with hydroꢀ
chloric acid (Scheme 1).
x = 2 (M = Cu), 6 (M = Co, Ni); M = Co (2), Ni (3), Cu (4)
According to elemental analysis data, the composition
of the synthesized compounds corresponds to the simꢀ
plest molecular formula M(L)Cl. Nevertheless, a monoꢀ
meric structure for them seems improbable because of
geometric concepts. This elemental composition is posꢀ
sible for dimeric coordination compounds with bridging
No changes occur upon reflux of ligand 1 with metal
chloride hydrates in EtOH; however, a precipitate of comꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339—343, February, 2007.
1066ꢀ5285/07/5602ꢀ0351 © 2007 Springer Science+Business Media, Inc.

352
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
Beloglazkina et al.
chlorine atoms of types I and II (similar structures with
fourꢀmembered metallacycles have been described earꢀ
lier9,10), for dimeric structure III with the bridging thiolate
sulfur atoms (see Refs 10 and 11), and for polymeric
structures, e.g., IV.
Unfortunately, we failed to synthesize complexes 2—4
as crystals appropriate for Xꢀray diffraction analyꢀ
sis. Therefore, the structures of complexes 2—4 were
ascribed on the basis of the spectral and electrochemiꢀ
cal data.
Electronic and IR spectroscopy. The results of studyꢀ
ing ligand 1 and complexes 2—4 by electronic and IR specꢀ
troscopy are presented in Table 1.
In the IR spectra of the synthesized complexes, the
absorption band of the С=S group is shifted to higher
frequencies compared to an analogous band of the free
ligand (see Table 1), which makes it possible to reject
structure II, where the sulfur atom of the C=S group is
not involved in coordination. The absorption band of the
N—Н group observed for the free ligand is absent in the
IR spectra of the complexes. This confirms that the
N(1) atom in the complex is deprotonated.
The electronic spectra of complexes 2—4 contain one
or two bands in the UV region, which are similar to those
in the UV spectrum of ligand 1 and correspond, most
likely, to the π—π*ꢀ and n—π*ꢀtransitions in the organic
fragment. The spectra of the complexes contain also lowerꢀ
absorption bands in the visible spectral region. For cobalt
complex 2, the shape of the spectrum agrees with the
tetrahedral or distorted tetrahedral coordination environꢀ
ment of the metal ion.12,13 One should assume either
planarꢀsquare geometry or a structure intermediate beꢀ
tween planar square and tetrahedron of the coordination
environment of NiII for nickel complex 3 (because abꢀ
sorption bands of noticeable intensity at 600—700 nm are
absent).13,14 The electronic spectrum of copper complex 4
contains a lowꢀintensity band at 710—720 nm, which is
also characteristic of tetrahedral complexes.13,14 Thereꢀ
fore, based on the data of optical spectroscopy, we can
ascribe structures with a distorted tetrahedral environꢀ
Table 1. Results of studying compounds 1—4 by IR and electronic spectroscopy
Comꢀ
pound
IR, ν/cm–1
C=C (Ph)
Electronic spectrum,
λ/nm (logε)
N—Н
3180
C=O
1745
C=S
Other bands
1
2
3
4
1595, 1435,
1360
1150,
1170
1183
755, 720,
705
740, 710,
690
740, 720,
690
760, 705
296 (3.90), 323 (2.15)
—
—
—
1720
1720
1750
1595, 1485,
1455, 1375
1600, 1485,
1460, 1375
1600, 1510,
1520, 1465,
1380
271 (3.95), 307 (3.54),
625 (2.0)
268 (3.94), 403 (1.90)
1183
1205
287 (3.98), 323 (2.22),
714 (1.22)

Metal complexes of 2ꢀthioxoimidazolidinꢀ4ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
353
Scheme 3
ment of metal ions to the synthesized complexes of
ligand 1. In them coordination occurs, most likely, to the
deprotonated N(1) atom of the thiohydantoine fragment
and thionic sulfur atom.
Mass spectrometry. The mass spectral characteristics
of the cobalt and nickel complexes (2 and 3) differ subꢀ
stantially from those of the copper complex 4. In the mass
spectra of positive ions obtained by the ionization of comꢀ
plexes 2 and 3, the highest intensity belongs to the fragꢀ
mentation ion with m/z 209 corresponding, most likely,
to the [1 – MeСН=С=О] fragment. These complexes are
mostly characterized by the presence of intense peaks
with m/z 302 and 324 in the mass spectra. No peaks with
m/z 302 and 324 are observed in the mass spectrum of
compound 4, and the maximum intensity belongs to the
peak with m/z 235 (presumably [PhNH—CH=S]CuCl+);
the peak with m/z 591 is also observed
([(1)2Cu2Cl2 – PhNCS + 2 H]+). The intensity ratio in
isotopic clusters of the peaks agrees with the performed
assignment.
For copper complex 4, taking into account the peak
with m/z 591 (see above) corresponding to an ion conꢀ
taining two chlorine atoms, one can propose the dimeric
structure with the bridging chlorine atoms of type I or II.
According to the IR spectral data (see Table 1) that conꢀ
firm the participation of the thionic sulfur atom in coorꢀ
dination with the metal, structure I should be preferred.
For compounds 2 and 3, the dimeric structure with the
bridging sulfur atoms of type III or polymeric structure
seems to be most probable.
at the potentials about –1.1 V (oneꢀelectron reduction)
and 1.1—1.5 V (twoꢀelectron oxidation), respectively.
Comparing these data with the results obtained for substiꢀ
tuted thiohydantoine 1, we can mention that the oxidaꢀ
tion of the latter is easier and its reduction is much more
difficult than those in the case of pyridylmethylideneꢀ
substituted 2ꢀthiohydantoines. This difference can be exꢀ
plained by the acceptor character of the pyridylmethylꢀ
idene substituent in position 5 of earlier studied 2ꢀthioꢀ
hydantoines and the donor character of the 2ꢀ(methylꢀ
thio)ethyl group in the case of ligand 1.
The first step of oxidation of complexes 2—4 proceeds
at potentials of 0.84—1.01 V, and the second step occurs
at potentials of 1.31—1.41 V. In the first step, deprotonated
Note that the addition of twofold excess MeI to soluꢀ
tions of complexes 2—4 in DMF changes the color of the
solution from yellowꢀbrown to dark brownꢀred. Accordꢀ
ing to available published data,15,16 this can be related to
the alkylation of the ligand to the sulfur atom, changing
the coordination environment of the metal. In this case,
the alkylation occurs only in the case of the complexes
containing no bridging sulfur atoms. Thus, the experiꢀ
ment allows one to reject structure III. The polymeric
structure of complexes 2 and 3 is confirmed by the results
of electrochemical investigation (see below).
Table 2. Electrochemical reduction (ERed) and oxidation (E Ox
)
potentials of compounds 1—4 measured vs. Ag/AgCl/KCl(sat.)
by the CV (Ep is the peak potential) and RDE (E1/2 is the halfꢀ
wave potential) methods on the GC electrodea
Red
Red
Ox
Ox
Comꢀ
pound
Ep
E1/2
Ep
E1/2
V
Thus, based on the spectral data, we can assume that
the cobalt and nickel complexes (2 and 3) have polymeric
structures, and copper complex 4 is dimeric with the strucꢀ
ture of type I (Scheme 3).
1
2
–1.96, –2.50
–0.78, –1.47, –0.72, –1.40,
–2.07/0.04b
–0.77, –1.53,
–1.96
0.36/056c,
0.05/0.16,
–0.54,
–0.93/0.12b,
–2.01
–2.14, –2.55
1.14
,1.01,
1.31
1.23
,1.07,
1.41
–2.10
–0.77, –1.97
3
4
1.30
1.24
Electrochemical investigation. The electrochemical beꢀ
havior of ligand 1 and complexes 2—4 was studied by the
cyclic voltammetry (CV) and rotating disk electrode
(RDE) techniques on a glassy carbon (GC) electrode in
DMF against a 0.05 M solution of Bu4NClO4. The potenꢀ
tials of electrochemical oxidation and reduction are given
in Table 2.
We have earlier17 shown that the first steps of reducꢀ
tion and oxidation of 5ꢀ(pyridylmethylidene)ꢀ3ꢀphenylꢀ
2ꢀthiohydantoines proceed irreversibly to the C=S bond
0.53c, 0.12,
–0.62, –1.28,
–1.96
1.36
,1.19,
1.44
a DMF, 0.05 M solution of Bu4NClO4; peak potentials in reꢀ
verse scan of the CV curves are given after slash.
b Peak of oxidative desorption of M0.
c Initial potential of 0.7 V.

354
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
Beloglazkina et al.
i/µA
organic ligand 1 is oxidized, probably, similarly to the
process described in Ref. 5. The second oxidation step
corresponds in potential to the oxidation of the coordiꢀ
nated chloride anions.17
–20
Compared to the CV curve of the free ligand, the
CV curves of the cobalt and nickel complexes (2 and 3)
exhibit three reduction peaks with less negative potentials
(for example, –0.77, –1.47, and –2.07 V for complex 2),
which correspond, most likely, to the transitions
A
0
20
40
II
I
M
→ M → M0 (M = Co, Ni)
B
and to the reduction of the anionic organic ligand. Note
that complex 2 decomposes to form metallic cobalt when
the potential of the third cathodic redox potential is
achieved, which is indicated by the appearance of a black
film of Co0 on the electrode surface and the oxidative
desorption peak in the reverse scan of the CV curve at
Ep = 0.04 V (Fig. 1).
A´
1
0
–1
Fig. 2. Cyclic voltammogram of complex 4 (DMF, 10–3 mol L–1
on the glassy carbon electrode.
–2 E/V
)
Binuclear copper complex 4 is reduced through the
formation of mixedꢀvalent complexes, which is confirmed
by the appearance of four additional reduction peaks in the
CV curve compared to that of the free ligand (Scheme 4).
Copper(I)ꢀcontaining reduction products A and B are
rather stable in time and do not decompose with formaꢀ
tion of the free metal under the conditions of CV curve
recording (sweep rate 200 mV s–1). However, product C
that formed by electrolysis at the potential of the third
peak (Ep = –0.54 V) decomposes gradually, most likely,
resulting in the destruction of the complex. As a result,
the peak of oxidative desorption of zeroꢀvalent copper is
observed in the reverse anodic scan of the CV curve (see
Fig. 2, peak B). When the potential of the fourth reducꢀ
tion peak is achieved, the desorption peak becomes more
intense and is identified in the reverse scan without elecꢀ
trolysis, which indicates the fast decomposition of the
complex. The reduction peaks of ligand 1 are observed at
more negative potential values.
Scheme 4
Note that for this series of compounds the experiꢀ
ments on the RDE are impeded by the strong adsorption
of both the initial compounds and reduction (or oxidaꢀ
tion) products on the electrode surface, which results in
the formation of nonꢀconducting films. This is indicated
by the current decrease in the RDE curves and very low
current values (1/9—1/12 е).
Under the experimental conditions, compound 4 and
product B interact, most likely, with each other giving
compound А. This is confirmed by the fact that in the
CV curve the intensity of the reverse peak of the first
reduction wave (Fig. 2, peak A´) is higher than the intenꢀ
sity of the forward peak (peak A).
Generalizing the results of electrochemical investigaꢀ
tion, we can conclude that the primary reduction of all
the complexes studied proceeds to the metal and the oxiꢀ
dation occurs to the coordinated thiohydantoine anion.
The electrochemical data also confirm structural similarꢀ
ity of complexes 2 and 3 and the dimeric structure of
copper complex 4.
i/µA
–20
–10
0
10
20
Experimental
1
0
–1
–2 E/V
The course of the reactions and individual character of the
products were monitored by TLC on a stationary silica gel layer
(Silufol). H NMR spectra were recorded on a VarianꢀXRꢀ400
Fig. 1. Cyclic voltammogram of complex 2 (DMF, 10–3 mol L–1
on the glassy carbon electrode.
)
1

Metal complexes of 2ꢀthioxoimidazolidinꢀ4ꢀone
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
355
instrument with a working frequency of 400 MHz in CDCl3.
IR spectra were measured on a URꢀ20 instrument in Nujol and
on an IR200 FTꢀIR spectrometer (TermoNicolet) with a resoꢀ
lution of 4 cm–1. Mass spectra of laser ionization of positive ions
were obtained on a Vision 2000 timeꢀofꢀflight mass spectromꢀ
eter with an N2 laser (radiation wavelength 336 nm).
Et3N (0.075 g, 0.75 mmol). The yield was 0.08 g (55%),
m.p. 266 °C. Calculated (%): C, 39.56; H, 3.60; N, 7.69.
С
12H13N2OS2•CuCl. Found (%): C, 39.85; H, 3.75; N, 7.66.
This work was financially supported by the Council on
Grants of the President of the Russian Federation (Proꢀ
gram of State Support for Young Candidates of Science,
Grant MKꢀ2460.2006.3).
A PIꢀ50ꢀ1.1 potentiostat connected to a PRꢀ8 programmer
was used for electrochemical investigation. Working electrodes
were glassy carbon (d = 2 mm), platinum (d = 3 mm), and gold
(d = 2 mm) disks. The supporting electrolyte was a 0.05 M
solution of Bu4NClO4 in DMF, the reference electrode was
Ag/AgCl/KCl(sat.), and the counter electrode was the platinum
References
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,
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5ꢀ[2ꢀ(Methylthio)ethyl]ꢀ3ꢀphenylꢀ2ꢀthioxoimidazolidinꢀ4ꢀ
one (1) was synthesized according to a described procedure.8
A 2 M solution of NaOH was added to a solution of Lꢀmethionꢀ
ine (2 g, 0.013 mol) in a water—pyridine (1 : 1) mixture (20 mL)
to pH 9, and this pH value was maintained constant during the
whole reaction. The mixture was heated to 40 °C, phenyl
isothiocyanate (1.81 g, 0.013 mol) was added, and the mixture
was stirred for 1 h at 40 °С with periodical pH measurement.
Pyridine and excess isothiocyanate were removed by the extracꢀ
tion of the reaction mixture with an equal volume of benzene.
Concentrated HCl (3 mL) was added to the aqueous fraction,
and the mixture was refluxed for 2 h. The reaction mixture was
concentrated by evaporating to 1/2 volume under reduced presꢀ
sure and cooled down to 20 °С. The pale yellow precipitate that
formed was filtered off and recrystallized from MeOH. The yield
was 2.93 g (85%), m.p. 133—134 °С (cf. Ref. 8: m.p. 133 °С).
Synthesis of complexes 2—4 (general procedure). Ligand 1
was dissolved in minimum hot EtOH, and 1 equiv. of a metal
salt dissolved in minimum EtOH was added. Triethylamine
(1 equiv.) was added to the boiling mixture, and reflux was
continued for 10 h. The mixture was cooled to ~20 °C, and the
precipitate that formed was filtered off.
Complex 2. Dark brown complex 2 was synthesized from
ligand 1 (0.20 g, 0.75 mmol), CоCl2•6H2O (0.08 g, 0.75 mmol),
and Et3N (0.075 g, 0.75 mmol). The yield was 0.08 g
(57%), m.p. 282 °C (with decomp.). Calculated (%): C, 40.06;
H, 3.64; N, 7.79. С12H13N2OS2•CoCl. Found (%): C, 39.38;
H, 4.22; N, 7.18.
Complex 3. Yellow complex 3 was synthesized from ligand 1
(0.20 g, 0.75 mmol), NiCl2•6H2O (0.08 g, 0.75 mmol), and Et3N
(0.075 g, 0.75 mmol). The yield was 0.09 g (64%), m.p. 317 °C
(with decomp.). Calculated (%): C, 40.06; H, 3.64; N, 7.79.
С12H13N2OS2•NiCl. Found (%): C, 39.89; H, 3.99; N, 7.57.
Complex 4. Brown complex 4 was synthesized from ligand 1
(0.20 g, 0.75 mmol), CuCl2•2H2O (0.06 g, 0.75 mmol), and
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Received June 26, 2006;
in revised form November 24, 2006