5-(Pyridylmethylidene)-substituted 2-thiohydantoins and their complexes with CuII, NiII, and CoII: Synthesis, electrochemical study, and adsorption on the cystamine-modified gold surface

Article abstract of DOI:10.1007/s11172-006-0371-3

A series of Cu^II, Ni^II, and Co^II complexes with 5-(pyridylmethylidene)-substituted 2-thiohydantoins (L) were synthesized by the reactions of the corresponding organic ligands with MCl ₂?nH₂O. The resu

Full text of DOI:10.1007/s11172-006-0371-3

Russian Chemical Bulletin, International Edition, Vol. 55, No. 6, pp. 1015—1027, June, 2006
1015
5ꢀ(Pyridylmethylidene)ꢀsubstituted 2ꢀthiohydantoins and their complexes
with CuII, NiII, and CoII: synthesis, electrochemical study, and adsorption
on the cystamineꢀmodified gold surface
E. K. Beloglazkina,ꢀ A. G. Majouga, I. V. Yudin, N. A. Frolova, N. V. Zyk,
V. D. Dolzhikova, A. A. Moiseeva, R. D. Rakhimov, and K. P. Butin†
Department of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Eꢀmail: bel@org.chem.msu.ru
A series of CuII, NiII, and CoII complexes with 5ꢀ(pyridylmethylidene)ꢀsubstituted
2ꢀthiohydantoins (L) were synthesized by the reactions of the corresponding organic ligands
with MCl2•nH2O. The resulting complexes have the composition LMCl2 (M = Cu or Ni) or
L2MCl2 (M = Co). The reactions with N(3)ꢀunsubstituted thiohydantoins afford complexes
containing fourꢀmembered metallacycles, in which the metal ion is coordinated by the S and
N(3) atoms of the thiohydantoin ligand. The reactions of N(3)ꢀsubstituted thiohydantoins give
complexes in which the S and N(1) atoms are involved in coordination. Study by IR spectroꢀ
scopy demonstrated that the pyridine nitrogen atom is not involved in coordination. Based on
the results of electrochemical study of the ligands and complexes by cyclic voltammetry and
calculation of their frontier orbitals by the PM3(tm) method, the mechanism of oxidation and
reduction of these compounds was proposed. In the first reduction and oxidation steps, the
metal atom in the copper and nickel complexes remains, apparently, intact, and these proꢀ
cesses occur with the involvement of the ligand fragments, viz., the coordinated thiohydantoin
ligand and chloride anion, respectively. In the cobalt complexes, the first reduction step occurs
at the ligand; the first oxidation state, at the metal atom. Measurements of the contact angle
of aqueous wetting and electrochemical study demonstrated that carboxyꢀcontaining
2ꢀthiohydantoins and their complexes can be adsorbed on the cystamineꢀmodified gold surꢀ
face. The structures of the complexes on the surface differ from the structures of these comꢀ
plexes in solution.
Key words: 5ꢀ(pyridylmethylidene)ꢀ2ꢀthiohydantoins; CuII, NiII, and CoII complexes; cyꢀ
clic voltammetry; quantum chemical calculations by the PM3(tm) method; adsorption.
2ꢀThiohydantoins (4ꢀoxoimidazolidineꢀ2ꢀthiones) exꢀ
hibit anticonvulsant, antibacterial, antiviral, and antiꢀ
thrombotic activities.1—4 It is known5 that coordination
with transition metal ions sometimes increases antiviral
and antitumor activities of such drugs.
resulting complexes contain fourꢀmembered metallaꢀ
cycles.
Hydantoin or thiohydantoin molecules containing a
fragment with an additional donor atom can form cheꢀ
late12—16 or surpamolecular17 complexes in which the
metal atom is coordinated by one or two thiohydantoin
ligands in the neutral or deprotonated form. The factors
responsible for the composition of the complexes and the
charge of the thiohydantoin ligand remain unknown. For
example, the reactions of 5ꢀ[(Z )ꢀ2ꢀpyridyl]hydantoin
(LH) with NiII and CuII salts under the same condiꢀ
tions give13 the chelate complexes [LNi(H2O)4]Cl and
(LH)CuCl2(H2O)2, respectively (structures of these comꢀ
plexes are presented below), whereas the reactions with
copper(II) chloride in the presence of melamine (MA)
produce the supramolecular complex CuL2(MA)2, in
which chelating coordination bonds between two nitroꢀ
gen atoms (of the pyridine and hydantoin fragments) and
2ꢀThiohydantoin molecules contain the thioamide
fragment and can undergo the thioneꢀthiol tautomerism
(NH—C=S
N=C—SH)6 due to which they can be
coordinated to metal ions through the lone electron pairs
of the nitrogen or sulfur atoms, or both. The resulting
complexes can contain 2ꢀthiohydantoins as either neutral
ligands or monoanions.5—12
Complexes of hydantoins and thiohydantoins
with CuII,9,10 FeIII 9,10 CoII,9,10 NiII,9,10 MnII,9 CsI,7
,
PtII,5 TlIII 6,8 HgII,8,10 ZnII,10 CdII,10 VIII, VIV,
,
and VV (see Ref. 11) have been synthesized. Most of the
† Deceased.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 978—990, June, 2006.
1066ꢀ5285/06/5506ꢀ1015 © 2006 Springer Science+Business Media, Inc.

1016
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
Beloglazkina et al.
the CuII ions are combined with binding of MA through
hydrogen bonds.17
Scheme 1
R = 2ꢀpyridyl (1), 3ꢀpyridyl (5), 4ꢀpyridyl (8)
These complexes are of practical interest because the
introduction of a transition metal ion into supramolecular
crystalline systems imparts the optical, conducting, and
magnetic properties of this ion to the complexes. As a
result, such materials hold promise as materials in nonꢀ
linear optics and as conductors and ferromagnets.
The aim of the present study was to synthesize a series
of 5ꢀ(pyridylmethylidene)ꢀsubstituted 2ꢀthiohydantoins,
investigate their complexation with CoII, NiII, and
CuII salts and the electrochemical behavior of the resultꢀ
ing ligands and complexes, and examine their adsorption
on the cystamine ((H2NCH2CH2S)2)ꢀmodified gold
surface.
data,13,18,19 we assigned the Z configuration to these comꢀ
pounds.
The synthesis of 3ꢀphenylꢀ5ꢀ(pyridylmethylidene)ꢀ2ꢀ
thiohydantoins 3, 6, and 9 has been documented earꢀ
lier.20 Thiohydantoins 2, 4, and 7 containing the methyl
or 4ꢀcarbethoxyphenyl substituent at position 3 were synꢀ
thesized according to analogous procedures (Scheme 2).
Scheme 2
Results and Discussion
Synthesis of ligands. We synthesized 5ꢀ(pyridylmethylꢀ
idene)ꢀsubstituted 2ꢀthiohydantoins 1—9 and studied
these compounds in complexation reactions with nickel,
cobalt, and copper chlorides. The structures of compounds
1—9 are given below.
R = Me (2), 4ꢀEtO2CC6H4 (4, 7);
R´ = 2ꢀpyridyl (2, 4), 3ꢀpyridyl (7)
Carbethoxyꢀcontaining thiohydantoins 4 and 7 were
hydrolyzed to prepare the corresponding acids 10 and 11
(Scheme 3). The resulting compounds containing saltꢀ
forming groups were used to modify the gold surface (see
below).
R = H (1, 5, 8), Me (2), Ph (3, 6, 9), 4ꢀEtO2CC6H4 (4, 7)
5ꢀ(Pyridylmethylidene)ꢀsubstituted thiohydantoins 1,
5, and 8 containing no substituents at the N(3) atom
were synthesized by condensation of 2ꢀthiohydantoin
with the corresponding pyridinecarbaldehydes in a glyꢀ
cine—Na2CO3 buffer solution (Scheme 1).
Scheme 3
Earlier,13 the Z configuration of the C=C bond in
compound 1 has been established by Xꢀray diffraction.
Compounds 5 and 8, which we prepared for the first time,
are also formed as one geometric isomer. Based on the
criteria developed from 1H NMR spectroscopic
R = 2ꢀpyridyl (10), 3ꢀpyridyl (11)

2ꢀThiohydantoin metal complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
1017
Table 1. Characteristics of the complexes of 5ꢀ(pyridylmethylꢀ
idene)ꢀsubstituted thiohydantoins with MCl2•6H2O (M = Co,
Ni, or Cu)
Synthesis of complexes. Copper(II), nickel(II), and
cobalt(II) complexes with compounds 1—9 were syntheꢀ
sized by refluxing mixtures of the corresponding ligands
and metal chlorides in aqueous dioxane (Scheme 4). The
compositions and the melting points of the complexes
based on ligands 1, 3, 6, 7, and 9 are given in Table 1. In
other cases, crystalline complexes were not isolated. Howꢀ
ever, coordination apparently occurs with other ligands as
well because mixing of their solutions with metal chloride
solutions is accompanied by a change in the color.
Liꢀ
Compoꢀ Yield Color M.p.
Found
Calculated
(%)
N
gand sition
of the
(%)
/°C
C
H
complex
1
6
1•NiCl2
55
55
64
Yellow 276 33.07 2.22 12.94
33.92 2.13 12.80
Brown 266 43.10 2.81 9.87
43.27 2.64 10.10
Yellow 317 44.10 2.37 10.20
(decom.) 43.80 2.68 10.22
Green 282 51.20 2.89 10.80
(decom.) 50.80 3.10 11.68
Crimꢀ 269 44.46 3.23 8.57
6•CuCl2
6•NiCl2
Scheme 4
(6)2•CoCl2• 57
•H2O
7•CuCl2
7
9
62
74
52
43
son
44.32 3.10 8.61
7•NiCl2•
•2MeCN
9•CuCl2
Yellow 273 39.31 3.02 10.33
39.22 3.12 10.40
Brown 310 43.05 2.85 9.76
43.27 2.64 10.10
Yellow >300 43.63 2.71 10.14
43.80 2.68 10.22
9•NiCl2
(9)2CoCl2• 50
•H2O
Yellow 310 50.12 3.45 11.34
50.80 3.10 11.68
coordinated by the N and S atoms of two different ligands
(see, for example, Refs 20 and 21), or fourꢀmembered
metallacycles analogous to those described above. Howꢀ
ever, complexes containing fourꢀmembered metallacycles
were isolated in all cases (see Scheme 4). Therefore, the
presence and character of the pyridylmethylidene subꢀ
stituent at position 5 of the thiohydantoin ring has no
significant effect on complexation, and the presence or
the absence of a substituent at the N(3) atom of the
thiohydantoin fragment and the nature of the complexꢀ
forming metal play the decisive role.
In the IR spectra of all the complexes with pyridylꢀ
containing ligands under consideration, the C=S absorpꢀ
tion band (1190—1210 cm–1) is shifted to higher frequenꢀ
cies compared to that in the spectra of the free ligands
(1145—1170 cm–1) (Table 2). This is evidence that the
sulfur atom is involved in coordination in all complexes.
The N—H absorption band in the complexes with the
3ꢀ and 4ꢀpyridylꢀcontaining ligands is also shifted comꢀ
pared to that of the free ligands (see Table 2). Conseꢀ
quently, the N(3) atom is also presumably involved in
coordination. By contrast, the position of the ν(N(1)—H)
band in the spectrum of the nickel complex with 2ꢀpyridylꢀ
containing ligand 1 is virtually identical to that in the
spectrum of the starting ligand, whereas the ν(N(3)—H)
band is shifted by 120 cm–1 (see Table 2). This is evidence
for coordination through the N(3) atom.
n = 2 (M = Cu), 6 (M = Ni, Co); R = Ph (6, 9), 4ꢀEtO2CC6H4 (7);
Py = 2ꢀpyridyl (1), 3ꢀpyridyl (6, 7), 4ꢀpyridyl (9)
The resulting copper and nickel complexes have the
composition LMCl2 (sometimes, with the inclusion of
one or two MeCN or H2O molecules). The cobalt comꢀ
plexes have the composition L2MCl2 (see Table 1).
The structural formula of the complex compounds
were established by electronic and IR spectroscopy and
are presented in Scheme 4. According to the published
data, chelate NꢀpyridylꢀNꢀhydantoinꢀcoordinated comꢀ
plexes would be expected to be formed with 2ꢀpyridylꢀ
containing ligands 1—4 (see above). For the steric reaꢀ
sons, 3ꢀpyridylꢀ (5—7) and 4ꢀpyridylꢀcontaining (8 and 9)
ligands would be expected to form either polynuclear
(bridged) N,Sꢀcomplexes, in which each metal atom is
The positions of the absorption bands in the IR specꢀ
tra of the starting ligands at ~1500 and ~1610 cm–1 correꢀ

1018
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
Beloglazkina et al.
Table 2. Results of electronic and IR spectroscopic studies of 5ꢀ(pyridylmethylidene)ꢀ2ꢀthiohydantoins and their complexes
Compound
IR, ν/cm–1
Electronic spectrum, λ/nm
(ε•10–4/L mol–1 dm–1
)
N(1)—H N(3)—H
C=O
C=C
Py
C=S
1
3160
3180 br
3200
3330
3270
3080
3260
3200
—
3280
3400
—
—
—
3170
—
—
1760, 1720
1750, 1710
1760
1745
1750, 1710
1760
1660
1650
1650
1665
1650
1660
1670
1650
—
1620, 1475
1620, 1475
1610, 1480
1590, 1495
—
1620, 1480
1610, 1500
1610, 1500
—
1170
1195
1160
1170
1160
1165
1145
1190
—
—
—
—
—
—
—
—
1•NiCl2
2
3
4
5
6
1740
1745
—
6•CuCl2
6•NiCl2
—
448 (3.62), 670 (1.75),
674 (1.75), 689 (1.74)
445 (4.27), 608 (2.17),
672 (2.32)
—
(6)2•CoCl2•H2O
3300 br
—
1740
1655
1610, 1500
1190
7
3290
3160
3060
3155
3180
3190
—
—
—
3250
—
—
1750, 1700
1740, 1720
1740, 1725
1740
1650
1655
1655
1650
1660
1645
1610, 1495
1610, 1495
1610, 1495
1615, 1495
1610, 1500
1605, 1500
1165
1185
1180
1165
1160
1190
—
—
—
—
7•CuCl2
7•NiCl2•2MeCN
8
9
1750
1735
—
9•CuCl2
440 (4.07), 568 (1.02),
635 (1.32)
9•NiCl2
3165
—
—
1740
1740
1645
1650
1610, 1500
1610, 1495
1210
1190
432 (3.67), 598 (1.94),
607 (1.94), 666 (1.98)
440 (4.15), 666 (1.60),
674 (1.60), 682 (1.60)
(9)2•CoCl2•H2O
3450 br,
3180
sponding to stretching vibrations of the pyridine ring22,23
are virtually identical to those in the spectra of the correꢀ
sponding complexes. This indicates that the pyridine niꢀ
trogen atom in all complexes is not involved in coordinaꢀ
tion; otherwise (according to the published data23—25),
these bands should be shifted to higher wavenumbers
5ꢀbenzylideneꢀ2ꢀthiohydantoins in aqueous or alcoholic
media at a dropping mercury electrode was documented
in several publications,28—30 but the only voltammetric
Scheme 5
by ~15 cm–1
.
The electronic spectra of the cobalt complexes with
3ꢀ and 4ꢀpyridylꢀcontaining ligands 6 and 9 show an inꢀ
tense absorption band in the visible region at ~440 nm,
which is apparently assigned to the metal—ligand charge
transfer, and two or three mediumꢀintensity bands at
600—680 nm (see Table 2). These spectral patterns are
consistent with the octahedral coordination environꢀ
ment.26,27 Analogous spectra of the nickel and copper
complexes with ligands 6 and 9 have, along with absorpꢀ
tion bands at 440—450 nm, three lowꢀintensity bands
at 660—690 nm, which is typical of tetrahedral comꢀ
plexes.24,27 Based on the results of optical spectroscopy, it
can be concluded that the cobalt complexes with ligands
6 and 9 correspond to the structure B (see Scheme 4),
whereas the structures A and C should be apparently asꢀ
signed to the nickel and copper complexes with 3ꢀphenylꢀ
substituted and 3ꢀunsubstituted ligands, respectively.
Electrochemical study of 5ꢀ(pyridylmethylidene)ꢀsubꢀ
stituted 2ꢀthiohydantoins and their complexes with CuII,
NiII, and CoII. Ligands. Polarographic reduction of
Ar = Ph, 4ꢀNO2C6H4, 4ꢀClC6H4, 4ꢀMeOC6H4,
4ꢀHOC6H4, 4ꢀMe2NC6H4

2ꢀThiohydantoin metal complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
1019
study of arylꢀsubstituted 5ꢀbenzylideneꢀ2ꢀthiohydantoins
in an aprotic medium was published.31
According to the published data,31 oxidation of 5ꢀarylꢀ
ideneꢀ2ꢀthiohydantoins affords a biradical, which reacts
with solvents with recovery of the starting compound.
Reduction of 5ꢀarylideneꢀ2ꢀthiohydantoins gave thiol A,
which was isolated as the reaction product after preparaꢀ
tive electrolysis (Scheme 5).31
A similar mechanism of oxidation and reduction can
be proposed for the pyridylꢀsubstituted thiohydantoins
under consideration. To validate this hypothesis, we perꢀ
We studied the electrochemical behavior of ligands 1
and 3—9 and their complexes with metal chlorides by
cyclic voltammetry (CV) and using a rotating disk elecꢀ
trode (RDE) at glassyꢀcarbon (GC) and Pt electrodes
and, in some cases, at an Au electrode in DMF solutions.
The electrochemical oxidation and reduction potentials
are given in Table 3.
Table 3. Electrochemical reduction potentials (ERed) and oxidation potentials (EOx) of 5ꢀ(pyridylmethylidene)ꢀ2ꢀthiohydantoins and
their complexes measured relative to Ag/AgCl/KCl(satur.) by the CV (Ep is the peak potential) and RDE (E1/2 is the halfꢀwave
potential) methods at a glassyꢀcarbon electrodea
Red
Red
Ox
Ox
Red
Red
Ox
Ox
Comꢀ
pound
Ep
E1/2
Ep
E1/2
Comꢀ
pound
Ep
E1/2
Ep
E1/2
V
V
1
–1.16, –1.80, –1.11 (2),
1.60 1.50 (1)
6•NiCl2
–1.24b, –1.90, –1.10 (1),
1.12 1.10 (2)
1.17 1.52
–2.38, –2.80
–1.80 (1),
–2.81
–2.43, –2.75
–1.43 (2),
–1.88 (<1)
1•NiCl2
–1.10b, –1.73, –1.05 (1),
1.20, 1.21 (1),
1.62 1.59 (2)
1.34 1.36 (1)
8
–0.95, –1.44 f, –0.93 (1),
–1.73, –2.21, –1.72 (1),
–2.45, –2.68
–1.73 (1)
–1.04d, –1.28, –1.04 (1),
–2.82
–2.40 (0.6)
c
c
(1)2•CoCl2
–1.76, –2.42
–1.42e,
–1.76e
9
–0.85, –1.41 f, –0.81 (1),
–1.51 f, –1.64, –1.62 (1),
–1.99 f, –2.69 –2.08 (0.59)
–0.84, –1.34, 0.54 (1),
1.13 1.13,
1.51
3
–1.16, –1.70, –1.02 (1),
–2.27, –2.78 –1.70 (1)
–1.19d, –1.63, –1.15 (1),
0— 1.08 (2)
1.30 1.25 (1)
9•CuCl2
1.30 1.25 (2)
,
(3)2•CoCl2
–1.60, –1.90
–0.48 (0.25)g,h
–0.84 (0.7),
–1.34 (0.5),
–1.63 (0.6),
–2.01 (0.3)
–1.86, –2.44
–1.47 (1.5),
–1.80 (0.3)
5
–1.30, –1.84, –1.27 (1),
–1.97, –2.51, –1.90 (1)
–2.83
–1.01d, –1.68, –0.97 (1),
–1.91, –2.38, –1.71 (1)
–2.87
1.52 1.32 (1)
9•NiCl2
–0.90 f, –1.14, –0.84 (1),
1.12 1.10 (2)
1.35 1.35 (2)
c
(5)2•CoCl2
6
1.21, 1.30 (1)
1.56
–1.64, –2.36
–1.07 (0.8),
–1.51 (1.8)
(9)2•CoCl2• –0.92e, –1.70, –0.85 (1),
–1.21, –1.84, –1.14 (1),
1.53 1.38 (1)
•H2O
–2.00
–1.65 (1)
–2.37, –2.77
–1.84 (1.5),
–2.54 (1.3)
0.50 (1),
–0.52 (0.5)g,h, 1.27
–1.17 (1),
CuCl2•2H2O +0.45/+0.58h, +0.50 (1)h
–0.51/–0.16
0—
.—
6•CuCl2
0.44/0.52,
–1.19 f,
–1.57f,
0.52, 1.22 (2)
NiCl2•6H2O –1.32/+0.16
CoCl2•6H2O –0.86,
–1.21/+0.35
–1.30 (2)
–1.30
1.20 1.00 (2)
1.53, 1.50 (1),
1.70 1.70 (1)
–1.82, –2.13, –1.36 (0.9),
–2.52 –1.84 (1)
a The number of electrons transferred in this step, which was determined on a rotating disk electrode by comparing with the oneꢀ
electron oxidation wave of ferrocene, is given in parentheses; the peak potentials on reverse scans in the CV curves are given after
a slash.
b Radical anions are stable at a glassyꢀcarbon electrode; reduction at platinum or gold electrodes was accompanied by deposition of
free metal.
c The complex was not isolated; the in situ formation in DMF from equimolar amounts of the ligand and MCl2•nH2O was confirmed
by electrochemical methods.
d In the case of accumulation at the potential of the first reduction wave, cobalt metal is deposited on a glassyꢀcarbon electrode; in the
case of reduction at Pt or Au electrodes, elimination of Cо occurs without accumulation.
e After this peak, the curve drops, which is indicative of adsorption of the product on the electrode.
f Lowꢀintensity peak.
g The peak is weakly pronounced and is not always reproduced.
h The initial potential is +0.7 V.

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Beloglazkina et al.
formed semiempirical quantum chemical calculations of
the frontier orbitals by the PM3 method32 for compounds
1, 3, 5, 6, 8, and 9. The results of calculations demonꢀ
strated that the character of the highest occupied molecuꢀ
lar orbitals (HOMO) and the lowest unoccupied molecuꢀ
lar orbitals (LUMO) in the molecules of these compounds
are independent of the nature of the pyridyl fragment (2ꢀ,
3ꢀ, or 4ꢀpyridyl) and the substituent at the N(3) atom
(Fig. 1). According to calculations, the orbitals of the
conjugated Michael πꢀsystem of the carbonyl group and
the C=C bond, as well as the orbitals of the C=S bond,
make the major contribution to LUMO (see Fig. 1), which
is consistent with the mechanism of reduction proposed
earlier.31 However, the orbitals of the lone pairs of the
sulfur atoms make the major contribution to HOMO (see
Fig. 1, a—f ). Consequently, initial oxidation should also
occur at the C=S fragment. In addition, the proposed31
scheme of oxidation is inapplicable in the case of 3ꢀsubꢀ
stituted ligands because the N(3) atom in the resulting
radical cation does not contain a hydrogen atom, which
can be abstracted.
5ꢀ(Pyridylmethylidene)ꢀsubstituted 2ꢀthiohydantoins
are successively reduced in four oneꢀelectron steps,
4ꢀpyridylꢀsubstituted compounds being more readily reꢀ
duced, whereas 3ꢀpyridylꢀsubstituted compounds being
most difficult to reduce (see Table 3 and Fig. 2). The first
a
b
c
d
e
f
g
h
Fig. 1. Frontier orbitals of 5ꢀ(pyridylmethylidene)ꢀsubstituted 2ꢀthiohydantoins 1 (a, b), 3 (c, d), 5 (e, f ) and the product of their
reduction, viz., thiol A (g, h), calculated by the PM3(tm) method (see Schemes 5 and 6): HOMO (a, c, e, g) and LUMO (b, d, f, h).

2ꢀThiohydantoin metal complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
1021
nisms of electrooxidation of these two groups of comꢀ
pounds should be different. Presumably, the radical catꢀ
ion that is generated in the first oxidation step is unstable.
In the case of Nꢀunsubstituted ligands, this radical cation
is stabilized as a result of proton abstraction from the
N(3) atom, but elimination of the Ar+ cation from the
radical cations of compounds 3, 6, or 9 is unlikely to
occur. In the latter case, twoꢀelectron oxidation can imꢀ
mediately give rise to the sulfenium cation (Scheme 6). It
should be noted that Xꢀray diffraction study20 demonꢀ
strated that the plane of the Ph group at the N(3) atom in
5ꢀ(pyridylmethylidene)ꢀsubstituted 2ꢀthiohydantoins is
virtually orthogonal to the plane of the pyrimidine ring
and, consequently, this group cannot stabilize the catꢀ
ionic or radical center at the adjacent nitrogen atom.
Earlier,31 reduction of 5ꢀarylidenethiohydantoins to
thiol A (see Scheme 5) has been documented. For 5ꢀ(pyriꢀ
dylmethylidene)ꢀsubstituted 2ꢀthiohydantoins, we obꢀ
served four oneꢀelectron reduction waves. According to
quantum chemical calculations, LUMO of thiol of type A
(see Scheme 6) is localized on the conjugated πꢀsystem of
the carbonyl group (see Fig. 1, g, h) and the C=C bond,
and reduction of thiol should occur at this fragment. As
5 µA
1
5
2
1
0
–1
–2
E/V
Fig. 2. Cyclic voltammograms of compounds 1 and 5.
oxidation step of these compounds is oneꢀelectron irreꢀ
versible (in the case of 3ꢀunsubstituted compounds 1, 5,
and 8) or twoꢀelectron irreversible (in the case of 3ꢀsubꢀ
stituted compounds 3, 6, and 9). Therefore, the mechaꢀ
Scheme 6

1022
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
Beloglazkina et al.
a result, fourꢀelectron reduction of the starting compound
affords, apparently, alcohol B.
sity on the potential scan from zero to the anodic region.
However, initial reduction followed by oxidation leads to
a considerable increase in the intensity of this peak.
The fact that the reduction curves of the free ligands
are similar to those of their complexes, apparently, indiꢀ
cates that reduction of the complexes of this structural
type occurs at the ligand rather than at the metal atom.
This assumption is also evidenced by the fact that reducꢀ
tion of the complexes occurs more readily than reduction
of the corresponding ligands. Coordination to the posiꢀ
tively charged metal atom should decrease the electron
density on the ligand molecule and lead to reduction at
less negative potentials.
Analysis of the CV curves of all the complexes under
study revealed the following characteristic features. First,
the reduced forms of the complexes with 3ꢀsubstituted
ligands 3, 6, and 9 are less stable than the corresponding
complexes with 3ꢀunsubstituted ligands 1, 5, and 8. For
all complexes of the former group, the first reduction
peak is followed by a peak of oxidative desorption of a
zeroꢀvalent metal from the electrode surface, whereas
these peaks are absent for the complexes of the latter
group (Fig. 4). Second, the reduced forms of the comꢀ
plexes of 3ꢀ and 4ꢀpyridylꢀsubstituted ligands with CoCl2
are less stable than the corresponding complexes with
NiCl2 and CuCl2. After the first reduction step of the
cobalt complexes, cobalt metal is deposited on the elecꢀ
trode surface, whereas the radical anions of the nickel and
copper complexes are stable.
For all the compounds under consideration, a peak at
+0.7 V is observed on the reverse potential scan after the
second or third reduction wave. This peak, apparently,
corresponds to oxidation of the thiol group and additionꢀ
ally confirms the formation of thiol.
Therefore, the following mechanism of electrooxiꢀ
dation and reduction of 5ꢀ(pyridylmethylidene)ꢀsubstiꢀ
tuted 2ꢀthiohydantoins can be proposed based on the exꢀ
perimental and calculated data (see Scheme 6).
Complexes. Cyclic voltammograms of all the complexes
under study are similar to the CV curves of the free ligands
(Fig. 3). Like the corresponding ligands, the 3ꢀunsubꢀ
stituted complexes undergo oneꢀelectron oxidation,
whereas the 3ꢀsubstituted complexes undergo twoꢀelecꢀ
tron oxidation. However, the peaks in the cathodic region
of the CV curves of the cobalt complexes are shifted to
more positive potentials compared to the free ligands,
whereas these shifts for the nickel and copper complexes
are insignificant and the reduction potentials of the latter
complexes are close to those for the corresponding ligands
(see Table 3 and Fig. 3). The CV curves of the complexes
differ also from the corresponding data for the starting
ligands in that they have an oxidation peak of the coordiꢀ
nated chloride ion at 1.1—1.2 V. This peak has low intenꢀ
5 µA
Apparently, reduction of the complexes starts with the
electron transfer to the ligand fragment followed by the
slow electron density transfer to the metal atom (Scheme 7
for M = Cu and Ni; Py = 3ꢀ or 4ꢀpyridyl). The resulting
complex of the neutral ligand with MI dissociates to form
a
1
5 µA
1
0
–1
–2
E/V
5 µA
2
b
1
0
–1
–2
E/V
1
0
–1
–2
E/V
Fig. 3. Cyclic voltammograms of ligand 5 (solid line) and its
complex with CoCl2 (dashed line) (a), ligand 6 (solid line) and
its complex with NiCl2 (dashed line) (b).
Fig. 4. Cyclic voltammograms of the cobalt complexes with
ligands 3 (1) and 5 (2).

2ꢀThiohydantoin metal complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
1023
the zeroꢀvalent metal, the ligand, and chloride anions
(hence, at the potential of the first wave, the intensity of
the peaks of oxidative desorption of metal and oxidation
of chloride anions at 1.1—1.2 V increases). Apparently,
the radical anion C of the complexes with 3ꢀphenylꢀsubꢀ
stituted ligands (see Scheme 7) is less stable because the
Ph group (inductive acceptor), which is orthogonal to the
plane of the thiohydantoin ring, destabilizes the radical
center in the ligand fragment. The structures of the radiꢀ
cal anions of the 3ꢀunsubstituted complexes are, apparꢀ
ently, similar to the structure of the radical anion C, i.e.,
the electron density transfer to metal occurs more slowly.
that the electrode surface is blocked by an adsorbed elecꢀ
trolysis product because of poor solubility of copper(I)
compounds.20
The structures of the cobalt complexes with ligands 6
and 9 differ from those of the other complexes. According
to calculations, the d orbitals of the metal atom in these
complexes also make a contribution to singly occupied
molecular orbitals (SOMO) as opposed to the copper and
nickel complexes (Fig. 5, a—c). This is, apparently, reꢀ
sponsible for the fact that reduction occurs more readily
and the reduced forms are less stable.
The complexes can be oxidized at either the coordiꢀ
nated chloride anion (which is consistent with the calcuꢀ
lated data, see Fig. 5) or the metal atom to the MIII state,
which is stabilized by the donor ligand.
Scheme 7
We compared the CV curves of oxidation of the comꢀ
plexes and starting metal chlorides. Anodic oxidation of
CoCl2•6H2O at a rotating disk electrode gives rise to two
oneꢀelectron waves (see Table 3), one of which is, apparꢀ
ently, associated with the CoII → CoIII transition, whereas
another wave is attributed to oxidation of one of the
ligands, for example, of the water molecule
III
III
[Cl2Co —OH2]+ – e → 1/2 [Cl2Co —O]2 + 2 H+
or chloride ions20
–
3 [CoCl2]+ – 2 e → 3 Co+ + 2 Cl3
.
In the anodic branch of the polarization curves of the
cobalt complexes with ligands 5, 6, and 9, the first peak is
shifted to less positive potentials by ~400 mV compared to
the starting ligands and CoCl2•6H2O (see Fig. 3, a and
Table 3). Complexation of the metal ion with a donor
ligand should facilitate oxidation at the metal atom but
hinder oxidation at the ligand. Hence, this peak should be
assigned to the CoII → CoIII transition. Therefore, the
first reduction step of the cobalt complexes presumably
occurs at the ligand, whereas the first oxidation step ocꢀ
curs at the metal atom.
The copper complexes with ligands 6 and 9 give the
weakly pronounced, sometimes irreproducible, second
reduction peak at –0.5 V (CuI → Cu0). Suppression of
this peak can, in principle, be a consequence of the fact
a
b
The first oxidation potentials of the nickel complexes
with ligands 1, 6, and 9 are less positive than the oxidation
potentials of the corresponding ligands and are higher
than the oxidation potential of NiCl2•6H2O (see Table 3).
Therefore, this process cannot be oxidation at the metal
atom; otherwise, the donor ligand would facilitate reꢀ
duction.
c
d
No oxidation peaks of CuCl2•2H2O, which could corꢀ
respond to the formation of copper(III), are observed in
the anodic region up to +1.7 V. By contrast, a twoꢀelecꢀ
tron peak is observed at 1.22—1.25 V for the copper comꢀ
plexes, which rejects the hypothesis of oxidation at the
metal. As in the case of the nickel complexes, the potenꢀ
tial of this peak is less positive than the potential of the
first oxidation peak of the ligands (see Table 3). Apparꢀ
ently, oxidation of the copper and nickel complexes ocꢀ
Fig. 5. Frontier orbitals of the complexes 5•NiCl2 (a, b),
5•CuCl2 (c), and (6)2•CoCl2•H2O (d): HOMO (a), LUMO (b),
and SOMO (c, d) calculated by the PM3(tm) method (chlorine
atoms in Fig. 5, d are omitted).

1024
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
Beloglazkina et al.
curs at the coordinated chloride anions, which is conꢀ
firmed by the calculated data. The HOMOs of these comꢀ
plexes are localized primarily on the chlorine atoms (see
Fig. 5, c). Therefore, the metal atom in the copper and
nickel complexes remains intact in the first reduction and
oxidation steps, and these processes occur at the ligand
fragments, viz., the coordinated thiohydantoin ligand and
the chloride anion, respectively.
Adsorption. We examined adsorption of thiohydantoin
ligands and their metal complexes on the gold surface.
Selfꢀorganized monolayers containing transition metal
atoms involved in complexes are of interest from the point
of view of their practical use in catalytic reactions on the
surface33 and for the design of ionꢀselective electrodes.34
The gold surface was modified according to a twoꢀ
step procedure (Scheme 8). Initially, a selfꢀorganized
monolayer of cystamine (12) containing terminal amino
groups35 was prepared on the gold surface. Then this
monolyaer was treated with a solution of carboxyꢀsubstiꢀ
tuted thiohydantoin 10 or 11. We expected that the surꢀ
face reaction producing a salt would give rise to a bilayer
analogous to that described earlier36 and containing the
donor thiohydantoin fragments on the outer side.
increase in the hydrophilicity of the surface upon the salt
formation with carboxyꢀcontaining thiohydantoins.
The possibility of adsorption of compounds 10 and 11
and the complexes with ligand 11 on the gold surface was
studied also by electrochemical methods. A bilayer on a
gold electrode was prepared according to an approach
analogous to the aboveꢀdescribed twoꢀstep procedure (see
Scheme 8). The data for the adsorbed ligands and comꢀ
plexes were compared with the electrochemical characꢀ
teristics obtained for solutions of the corresponding comꢀ
pounds. The results are given in Table 4.
Di(2ꢀaminoethyl) disulfide (12), which is either
adsorbed on a gold electrode or is present in solution, is
reduced at ~–0.9 V and is oxidized at ~–1.65 V. Howꢀ
ever, reduction becomes quasireversible in the case of
formation of a monolayer (see Table 4). The formation of
a bilayer leads to a change in the redox characteristics of
the adsorbed compound (see Table 4 and Fig. 6). The
second surface modification can, in principle, involve the
following two competitive processes: the formation of a
bilayer as a result of the surface salt formation reaction
and the displacement of cystamine from the monolayer
with thiohydantoin that is present in solution. In this
case, thiohydantoin can be adsorbed on the surface
through the thione sulfur atom. However, the treatment
Scheme 8
Table 4. Electrochemical reduction potentials (ERed) and oxidaꢀ
tion potentials (EOx) of compounds 10—12 and their complexes
with metal chlorides at Pt (in solution) and Au (in the adsorbed
state) electrodes (MeCN, a 0.05 M Bu4NBF4 solution, relative
to Ag/AgCl/KCl(satur.), 20 °C)
Red
Ox
Compound
Ep
Ep
V
12 (solution)
12 (monolayer)
10 (solution)
–0.97/0.00, 1.62/0.93а
–1.37
–0.88/–0.62b, 1.65/0.80с
–1.56
–1.03/–0.51, 1.53/0.87
–1.71/–1.63
12 + 10 (bilayer)
11 (solution)
–1.37
1.66/1.43
–0.82/–0.51, 1.50/0.82
–1.24/–1.08,
–1.78/–1.68
12 + 11 (bilayer)
–0.96/–0.58 1.61/0.82d
12 + 11 (bilayer) + СuCl2•2H2O –0.74/–0.53 1.64/0.85b,е
12 + 11 (bilayer) + NiCl2•6H2O –0.93, –1.46 1.39/0.78 f
12 + 11 (bilayer) + CoCl2•6H2O –0.99/–0.52 1.71/0.80b
a The intensity ratio between the direct and reverse peaks (Id : Ir)
In each step of this modification, the aqueous wetting
angle was measured and CV curves were recorded.
is 3 : 1.
b Id : Ir = 2 : 1.
The contact angle after the modification of the cystaꢀ
mine plate was 50 1°, which agrees with the known data
(55 4° for a gold film deposited onto the glass surface).37
After the second modification, the contact angle decreases
to 35 1°, which is, in our opinion, associated with an
c Id : Ir = 5 : 1.
d Id : Ir = 4 : 1.
e On the reverse scan, two reduction peaks of free copper chloꢀ
ride are observed in the cathodic region at +0.40 and –0.64 V.
f Id : Ir = 8 : 1.

2ꢀThiohydantoin metal complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
1025
potentials compared to the starting ligand are observed.
However, the formation of the complex was reliably esꢀ
tablished based on the appearance of two reduction peaks
of free copper chloride after the anodic peak in the caꢀ
thodic branch of the CV curve. Apparently, the structures
of the complexes formed on the surface differ from those
in solution because their redox characteristics are subꢀ
stantially different (cf. Tables 3 and 4; Figs 3, 4, and 7).
Presumably, in the case of formation of a closeꢀpacked
layer of the thiohydantoin ligands on the electrode surꢀ
face, coordination of the metal ion occurs only through
the nitrogen atom of the pyridine fragment directed outꢀ
ward, whereas the nitrogen and sulfur atoms of the
thiohydantoin ligands located inside the layer are not inꢀ
volved in coordination at all. This can account for the fact
that we failed to prepare complexes with metal salts for
2ꢀpyridylꢀcontaining compounds 10 fixed on the surface,
whereas 3ꢀpyridylꢀsubstituted ligand 11, in which the pyꢀ
ridine nitrogen atom is more accessible for coordination
from the outer side of the bilayer, forms such complexes.
1
0
–1 E/V
2 µA (solid line)
5 µA (dashed line)
Fig. 6. Cyclic voltammograms of a monolayer of cystamine 12
on the gold electrode surface (solid line) and a bilayer of 12 + 11
(dashed line).
Experimental
Commercial 2ꢀthiohydantoin and di(2ꢀaminoethyl) disulꢀ
fide (Acros) were used without additional purification. 3ꢀPheꢀ
nylꢀsubstituted 2ꢀthiohydantoins and their 5ꢀpyridylmethylꢀ
idene derivatives 3, 6, and 9 were synthesized according to a
of the cystamineꢀmodified surface of the gold electrode
with a solution of thiohydantoin 7 does not lead to changes
in the voltammetric curve, which is evidence for the former
mechanism.
1
known procedure.20 The H NMR spectra were measured on a
VarianꢀVXRꢀ400 instrument at 400 MHz. The IR spectra were
recorded on an URꢀ20 instrument in Nujol mulls. The EI mass
spectra were obtained on a JMSꢀD300 GLCꢀmass spectrometer
equipped with a JMAꢀ2000 computer and an HPꢀ5890 chroꢀ
matograph.
After soaking of the bilayerꢀmodified electrode in a
solution containing MCl2•6H2O, the formation of comꢀ
plexes occurs on the surface, which is confirmed by the
observed changes in the CV curves (see Table 4 and Fig. 7).
For example, the nickel complex with compound 11 fixed
on the surface is oxidized more readily than the correꢀ
sponding ligand by 0.32 V, and reduction becomes a twoꢀ
step process. For the copper complex with the same ligand,
no considerable changes in the oxidation and reduction
Quantum chemical calculations were performed by the
semiempirical SCF PM3 method,33 which was extended by inꢀ
cluding the parameters for all firstꢀrow transition metals and
selected secondꢀ and thirdꢀrow transition metals (HyperChem
program package, HyperCube Inc., USA). Geometry optimizaꢀ
tion of the molecules was carried out with a gradient of no
higher than 10 kal Å–1 mol–1 as the convergence criterion.
The contact angle was measured with the use of silicon
plates containing a vacuumꢀdeposited gold layer (layer thickꢀ
ness was 50 10 nm, the plate size was 5×5 mm) purchased from
HTꢀMDT. In the first modification step, the plates were soaked
in a 10–3 M cystamine solution in ethanol for 1 day, washed
several times with ethanol, and dried. Then the aqueous wetting
angle was measured on a MG horizontal microscope equipped
with a goniometer (drop volume was 0.01 mL, the measurement
accuracy was 1°). The surface was further modified by treatꢀ
ment with a 10–3 M solution of thiohydantoin 11 in ethanol
analogously to the first step. The contact angle was determined
as the average of four measurements.
2 µA
1
0
–1
E/V
Electrochemical measurements were performed on a
PIꢀ50ꢀ1.1 potentiostat. Glassyꢀcarbon (d = 2 mm), platinum
(d = 3 mm), or gold (d = 1 mm) disks were used as the working
electrodes, a 0.05 M Bu4NClO4 solution in DMF served as the
supporting electrolyte, and Ag/AgCl/KCl(satur.) was used as
the reference electrode. The potential scan rates were 200 mV s–1
Fig. 7. Cyclic voltammograms of the surfaceꢀadsorbed complex
12 + 11 + CuCl2•2H2O (solid line) and the complex 7•CuCl2
in an MeCN solution (dashed line).

1026
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
Beloglazkina et al.
(CV) and 20 mV s–1, 2800 min–1 (RDE). All measurements
were carried out under argon. The samples were dissolved in the
preꢀdeaerated solvent. Dimethylformamide (highꢀpurity grade)
was purified by refluxing followed by successive vacuum distillaꢀ
tion over anhydrous CuSO4 and P2O5.
To obtain a bilayer on a gold electrode, a monolayer of
di(2ꢀaminoethyl) disulfide (12) was prepared, and the electrode
was soaked in its 10–3 M solution in EtOH for 1 day. Then the
electrode was washed with ethanol and kept in a solution of acid
10 or 11 for 1 day to obtain a bilayer. The electrode with the
bilayer was again successively washed with water, a supporting
solution, and acetone and dried in air at ~20 °C. Then the
CV curve was recorded. To prepare a surfaceꢀbound complex,
the electrode was immersed in a solution of the corresponding
metal salt in MeCN, soaked in this solution for one day, washed,
and dried. Then the CV curve was recorded.
5ꢀ[(Z )ꢀ4ꢀPyridylmethylidene]ꢀ2ꢀthioxoimidazolidinꢀ4ꢀone
(8). The yield was 88%, m.p. >315 °C. Found (%): C, 52.11;
H, 3.75; N, 19.95. C9H7N3OS. Calculated (%): C, 52.68;
1
H, 3.41; N, 20.48. H NMR (CDCl3), δ: 6.39 (s, 1 H, =CH);
7.63 (d, 2 H, βꢀHPy, β´ꢀHPy, J = 6.2 Hz); 8.59 (d, 2 H, αꢀHPy
α´ꢀHPy, J = 6.3 Hz); 12.5 (br.s, 2 H, NH).
,
3ꢀSubstituted 5ꢀ(pyridylmethylidene)ꢀ2ꢀthiohydantoins 2
and 4 (general procedure). 3ꢀSubstituted 2ꢀthiohydantoin
(1 equiv.) was dissolved in a 2% ethanolic solution of KOH
(1.2 equiv.) with vigorous stirring. After complete dissolution of
2ꢀthiohydantoin, pyridinecarbaldehyde (1 equiv.) was added
dropwise and the reaction mixture was stirred for 12 h. The
precipitate was filtered off and dissolved in water. The solution
was neutralized with vigorous stirring with dilute HCl to pH 7.
The precipitate that formed was filtered off and recrystallized
from a 3 : 1 EtOH—DMF mixture.
3ꢀSubstituted 2ꢀthiohydantoins (general procedure). Glycine
(1 equiv.) was dissolved in a 1 : 1 water—pyridine mixture. Then
a 2 M sodium hydroxide solution was added to pH 9, and this pH
was maintained until the reaction was completed. The reaction
mixture was warmed to 40 °C. At this temperature, isothioꢀ
cyanate (1.5 equiv.) was added. The reaction mixture was stirred
at 40 °C for 1 h, pH being monitored from time to time. Pyridine
and excess isothiocyanate were separated by extraction with an
equal volume of benzene. Then concentrated HCl (3 mL) was
added to the aqueous phase. The reaction mixture was refluxed
for 2 h, concentrated to 1/2 of the initial volume, and cooled to
~20 °C. The paleꢀyellow precipitate that formed was filtered off
and recrystallized from methanol.
3ꢀMethylꢀ5ꢀ[(Z )ꢀ2ꢀpyridylmethylidene]ꢀ2ꢀthioxoimidazolꢀ
idinꢀ4ꢀone (2). The yield was 73%, m.p. 230 °C. Found (%):
C, 54.91; H, 4.06; N, 19.21. C10H9N3OS. Calculated (%):
C, 54.79; H, 4.11; N, 19.18. 1H NMR (CDCl3), δ: 3.23 (s, 3 H,
Me); 6.72 (s, 1 H, =CH); 7.39 (dd, 1 H, γꢀHPy, J1 = 4.8 Hz, J2 =
1.2 Hz); 7.74 (d, 1 H, β´ꢀHPy, J = 7.8 Hz); 7.89 (dd, 1 H, βꢀHPy
J1 = 7.7 Hz, J2 = 2.2 Hz); 8.75 (d, 1 H, αꢀHPy, J = 3.9 Hz).
,
3ꢀ(4ꢀCarbethoxyphenyl)ꢀ5ꢀ[(Z )ꢀ2ꢀpyridylmethylidene]ꢀ2ꢀ
thioxoimidazolidinꢀ4ꢀone (4). The yield was 70%, m.p. 279 °C.
Found (%): C, 61.14; H, 4.19; N, 13.20. C18H15N3O3S. Calcuꢀ
1
lated (%): C, 61.18; H, 4.28; N, 13.11. H NMR (CDCl3), δ:
1.40 (t, 3 H, Me, J = 6.8 Hz); 4.40 (q, 2 H, OCH2, J = 6.8 Hz);
7.21 (s, 1 H, =CH); 7.40 (d, 2 H, βꢀHPh, J = 8.2 Hz); 7.50 (t,
1 H, γꢀHPy, J = 8.3 Hz); 7.78 (t, 1 H, βꢀHPy, J = 4.2 Hz); 8.20
(d, 2 H, αꢀHPh, J = 8.0 Hz); 8.70 (d, 1 H, β´ꢀHPy, J = 4.2 Hz);
8.81 (d, 1 H, αꢀHPy, J = 8.4 Hz); 11.97 (br.s, 1 H, NH).
3ꢀMethylꢀ2ꢀthioxoimidazolidinꢀ4ꢀone. The yield was 62%,
m.p. 140 °C (cf. lit data38: m.p. 140 °C).
3ꢀ(4ꢀCarbethoxyphenyl)ꢀ2ꢀthioxoimidazolidinꢀ4ꢀone. The
yield was 72%, m.p. 176 °C. Found (%): C, 54.47; H, 4.50;
N, 10.53. C12H12N2O3S. Calculated (%): C, 54.55; H, 4.55;
3ꢀ(4ꢀCarbethoxyphenyl)ꢀ5ꢀ[(Z)ꢀ3ꢀpyridylmethylidene]ꢀ2ꢀ
thioxoimidazolidinꢀ4ꢀone (7). A mixture of 4ꢀcarbethoxyphenyl
isothiocyanate (2.07 g, 0.01 mol), glycine (0.75 g, 0.01 mol),
and pyridineꢀ3ꢀcarbaldehyde (1.07 g, 0.01 mol) in glacial acetic
acid (10 mL) was refluxed with stirring for 3 h and then cooled.
The precipitate that formed was filtered off, washed with water,
and recrystallized from a 3 : 1 EtOH—DMF mixture. The yield
was 2.53 g (71%), m.p. 284 °C. Found (%): C, 61.12; H, 4.22;
N, 13.28. C18H15N3O3S. Calculated (%): C, 61.18; H, 4.28;
1
N, 10.60. H NMR (CDCl3), δ: 1.40 (m, 5 H, Me, CH2); 4.40
(q, 2 H, OCH2, J = 7.0 Hz); 7.44 (d, βꢀHAr, J = 8.2 Hz); 8.19 (d,
2 H, αꢀHAr, J = 8.0 Hz); 11.98 (br.s, 1 H, NH). IR, ν/cm–1
3280, 1750, 1710, 1650. MS, m/z (Irel (%)): 264 [M]+ (9).
:
3ꢀUnsubstituted 5ꢀ(pyridylmethylidene)ꢀ2ꢀthiohydantoins 1,
5, and 8 (general procedure). A mixture of 2ꢀthioxotetrahydroꢀ
4Hꢀimidazolꢀ4ꢀone, Na2CO3, and glycine (1 equiv. each) was
dissolved with stirring in a minimum volume of refluxing water
and added to a solution of pyridinecarbaldehyde (1 equiv.). The
reaction mixture was stirred for 1 h and cooled to ~20 °C. The
precipitate that formed was filtered off and successively washed
with water and diethyl ether.
1
N, 13.11. H NMR (CDCl3), δ: 1.40 (t, 3 H, Me, J = 6.9 Hz);
4.40 (q, 2 H, CH2, J = 6.9 Hz); 7.15 (s, 1 H, =CH); 7.39 (d, 2 H,
βꢀHPh, J = 8.2 Hz); 7.43 (d, 1 H, γꢀHPy, J = 8.1 Hz); 7.50 (d,
2 H, αꢀHPh, J = 7.9 Hz); 8.17 (t, 1 H, βꢀHPy, J = 8.0 Hz); 8.51
(d, 1 H, αꢀHPy, J = 4.8 Hz); 8.84 (s, 1 H, α´ꢀHPy); 11.95 (br.s,
1 H, NH). 13C NMR (CDCl3), δ: 0.56, 47.88, 95.54, 101.87,
110.27, 114.47, 115.55, 116.126, 122.94, 135.94, 137.56.
Hydrolysis of the ester group in 3ꢀ(4ꢀcarbethoxyphenyl)ꢀ5ꢀ
[(Z )ꢀpyridylmethylidene]ꢀ2ꢀthioxoimidazolidinꢀ4ꢀones 4 and 7
(general procedure). Compound 4 or 7 (0.34 g, 0.001 mol) was
dissolved in a 1 : 3 MeOH—H2O mixture (20 mL) and then a
15% KOH solution was added with stirring to pH 8—9. The
reaction mixture was stirred at ~20 °C for 12 h. Then acetic acid
was added with cooling to ~5 °C to neutral pH and stirred
for 1 h. The precipitate that formed was filtered off and washed
with water.
5ꢀ[(Z )ꢀ2ꢀPyridylmethylidene]ꢀ2ꢀthioxoimidazolidinꢀ4ꢀone
(1). The yield was 92%, m.p. 260—262 °C. Found (%): C, 52.49;
H, 3.35; N, 20.30. C9H7N3OS. Calculated (%): C, 52.68;
1
H, 3.41; N, 20.48. H NMR (CDCl3), δ: 7.23 (s, 1 H, =CH);
7.48 (t, 1 H, γꢀHPy, J = 8.3 Hz); 7.78 (t, 1 H, βꢀHPy, J = 4.2 Hz);
8.69 (d, 1 H, β´ꢀHPy, J = 4.2 Hz); 8.81 (d, 1 H, αꢀHPy, J = 8.4
Hz); 12.30 (br.s, 2 H, NH). MS, m/z (Irel (%)): 205 [M]+ (28).
5ꢀ[(Z )ꢀ3ꢀPyridylmethylidene]ꢀ2ꢀthioxoimidazolidinꢀ4ꢀone
(5). The yield was 90%, m.p. 297 °C. Found (%): C, 52.40;
H, 3.33; N, 20.35. C9H7N3OS. Calculated (%): C, 52.68;
1
H, 3.41; N, 20.48. H NMR (CDCl3), δ: 6.49 (s, 1 H, =CH);
7.43 (dd, 1 H, γꢀHPy, J1 = 4.1 Hz, J2 = 8.1 Hz); 8.17 (d, 1 H,
βꢀHPy, J = 8.0 Hz); 8.52 (d, 1 H, αꢀHPy, J = 4.8 Hz); 8.84 (s,
1 H, α´ꢀHPy); 12.33 (br.s, 2 H, NH). MS, m/z (Irel (%)):
205 [M]+ (23).
3ꢀ(4ꢀCarboxyphenyl)ꢀ5ꢀ[(Z )ꢀ2ꢀpyridylmethylidene]ꢀ2ꢀ
thioxoimidazolidinꢀ4ꢀone (10). The yield was 95%, m.p. 288 °C.
Found (%): C, 62.69; H, 3.28; N, 12.87. C16H11N3O3S. Calcuꢀ
lated (%): C, 62.77; H, 3.38; N, 12.92. 1H NMR (DMSOꢀd6), δ:

2ꢀThiohydantoin metal complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 6, June, 2006
1027
7.23 (s, 1 H, =CH); 7.44 (d, βꢀHAr, J = 8.2 Hz); 7.50 (t, 1 H,
βꢀHPy, J = 4.1 Hz); 7.78 (t, 1 H, γꢀHPy, J = 8.3 Hz); 8.20 (d,
2 H, αꢀHAr, J = 8.0 Hz); 8.69 (d, 1 H, β´ꢀHPy, J = 4.2 Hz); 9.59
13. M. M. Chowdhry, A. Burrows, D. M. Mingos, A. J. White,
and D. J. Williams, J. Chem. Soc., Chem. Commun.,
1995, 1521.
14. J. S. Casas, E. E. Castellano, M. D. Couce, N. Playa,
A. Sanchez, J. Sordo, J. M. Varela, and J. Zukermanꢀ
Schpector, J. Coord. Chem., 1999, 47, 299.
15. J. Casas, A. Castineiras, N. Playa, A. Sanchez, J. Sordo,
J. Varela, and E. VazquezꢀLopez, Polyhedron, 1999, 18, 3653.
16. A. G. Majouga, E. K. Beloglazkina, S. Z. Vatsadze, A. A.
Moiseeva, F. S. Moiseev, K. P. Butin, and N. V. Zyk,
Mendeleev Commun., 2005, 48.
17. M. M. Chowdhry, D. M. Mingos, A. J. White, and D. J.
Williams, J. Chem. Soc., Chem. Commun., 1996, 899.
18. A. G. Majouga, E. K. Beloglazkina, S. Z. Vatsadze, N. A.
Frolova, and N. V. Zyk, Izv. Akad. Nauk, Ser. Khim., 2004,
2734 [Russ. Chem. Bull., Int. Ed., 2004, 53, 2850].
19. S.ꢀF. Tan, K.ꢀP. Ang, and Y.ꢀF. Fong, J. Chem. Soc., Perkin
Trans. 2, 1986, 1941.
(d, 1 H, αꢀHPy, J = 8.4 Hz); 11.95 (br.s, 1 H, NH). IR, ν/cm–1
:
3380, 3280, 1745, 1730, 1600.
3ꢀ(4ꢀCarboxyphenyl)ꢀ5ꢀ[(Z )ꢀ3ꢀpyridylmethylidene]ꢀ2ꢀ
thioxoimidazolidinꢀ4ꢀone (11). The yield was 91%, m.p. 295 °C.
Found (%): C, 62.71; H, 3.31; N, 12.88. C16H11N3O3S. Calcuꢀ
lated (%): C, 62.77; H, 3.38; N, 12.92. 1H NMR (DMSOꢀd6), δ:
7.20 (s, 1 H, =CH); 7.36 (d, 2 H, βꢀHPh, J = 8.2 Hz); 7.43 (d,
1 H, γꢀHPy, J = 4.1 Hz); 7.49 (d, 2 H, αꢀHPh, J = 7.9 Hz); 8.19
(d, 1 H, βꢀHPy, J = 8.0 Hz); 8.51 (d, 1 H, αꢀHPy, J = 4.8 Hz);
8.86 (s, 1 H, α´ꢀHPy); 11.95 (br.s, 1 H, NH). IR, ν/cm–1: 3370,
3290, 1740, 1730, 1600.
Synthesis of complexes from 5ꢀ[(Z )ꢀpyridylmethylidene]ꢀ2ꢀ
thioxoimidazolidinꢀ4ꢀones (general procedure). 5ꢀ[(Z )ꢀPyridylꢀ
methylidene]ꢀ2ꢀthioxoimidazolidinꢀ4ꢀone (0.7 mmol) was disꢀ
solved in a minimum volume of hot 1,4ꢀdioxane, and a solution
of a metal salt (0.35 mmol in a minimum volume of water in the
case of ligands 1—3, 5, 6, 8, and 9 or 0.7 mmol in a minimum
volume of MeCN in the case of ligands 4 and 7) was added. The
reaction mixture was refluxed for 10 h and cooled to ~20 °C.
The precipitate that formed was filtered off and successively
washed with water, ethanol, and diethyl ether.
20. E. K. Beloglazkina, S. Z. Vatsadze, A. G. Majouga, N. A.
Frolova, R. B. Romashkina, N. V. Zyk, A. A. Moiseeva, and
K. P. Butin, Izv. Akad. Nauk, Ser. Khim., 2005, 2679 [Russ.
Chem. Bull., Int. Ed., 2005, 54, 2771].
21. A. G. Majouga, Ph. D. (Chem.) Thesis, M. V. Lomonosov
Moscow State University, Moscow, 2005, 131 pp. (in
Russian).
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ
32845), the Program "Russian Universities" (Grant
05.03.046), and the Presidium of the Russian Academy of
Sciences (Program "Theoretical and Experimental Studꢀ
ies of the Nature of Chemical Bonds and Mechanisms of
Chemical Reactions and Processes").
22. N. Goswami and D. M. Eichhorn, Inorg. Chem., 1999,
38, 4329.
23. D. Zhu, Y. Xu, Y. Mei, Y. Sci, C. Tu, and X. You, J. Mol.
Struct., 2001, 559, 119.
24. L. Zhang, L. Liu, D. Jia, and K. Yu, Struct. Chem., 2004,
15, 327.
25. M. Bakiler, I. V. Masliv, and S. Akyuz, J. Mol. Struct., 1999,
476, 21.
26. I. KuzniarskaꢀBiernacka, A. Bartecki, and K. Kurzak, Polyꢀ
hedron, 2003, 22, 997.
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Received September 19, 2005;
in revised form January 12, 2006