Formation of CuI(CH3CN)4ClO4 in the reactions of copper(II) perchlorate with acetonitrile in the presence of sulfur-containing organic compounds

Article abstract of DOI:10.1134/S1070363209070172

Cu(ClO₄)₂?6H₂O was shown to react with 2,2?-[propane-1,3-diylbis(thio-2-phenylnemethylidene]-bis(3-pyridylamine) (I) or (5Z)-2-ethoxycarbonylmethyl-(2-pyridylmethylidene)-3,5-dihydro-4H- imidazol-4-one (II) in the presence of CH₃CN with the reduction of copper(II) to copper(I) and the formation of the tetrahedral complex Cu ^I(CH₃CN)₄ClO₄ (III). In the course of the reaction the organic ligands I and II were oxidized to the corresponding sulfoxides.

Full text of DOI:10.1134/S1070363209070172

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 7, pp. 1504–1508. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © Е. K. Beloglazkina, A.V. Shimorsky, A.G. Mazhuga, О.V. Shilova, V.А. Tafeenko, N.V. Zyk, 2009, published in Zhurnal Obshchei
Khimii, 2009, Vol. 79, No. 7, pp. 1147–1151.
Formation of CuI(CH3CN)4ClO4 in the Reactions
of Copper(II) Perchlorate with Acetonitrile
in the Presence of Sulfur-Containing Organic Compounds1
Е. K. Beloglazkina, A. V. Shimorsky, A. G. Mazhuga,
О. V. Shilova, V. А. Tafeenko, and N. V. Zyk
Faculty of Chemistry, Moscow State University, Vorob’evy gory 1, Moscow, 119992 Russia
e-mail: bel@org.chem.msu.ru
Received June 25, 2008
Abstract—Cu(ClO4)2·6H2O was shown to react with 2,2'-[propane-1,3-diylbis(thio-2-phenylnemethylidene]-
bis(3-pyridylamine) (I) or (5Z)-2-ethoxycarbonylmethyl-(2-pyridylmethylidene)-3,5-dihydro-4Н-imidazol-4-
one (II) in the presence of CH3CN with the reduction of copper(II) to copper(I) and the formation of the
tetrahedral complex CuI(CH3CN)4ClO4 (III). In the course of the reaction the organic ligands I and II were
oxidized to the corresponding sulfoxides.
DOI: 10.1134/S1070363209070172
Spontaneous reduction of copper(II) during com-
plexation with organic ligands is described in a series
of papers [1–12]. In most cases the question which
compound acted as a donor of electrons was not
discussed, although in some papers the suggestions
were made of participation of the solvent in the redox
process or of occurrence of a photochemical reaction
(see, for example, [6, 9]). On the other hand, in some
cases the spontaneous reduction of the metal ion
cannot be explained invoking only these factors, for
example, when using the solvents incapable of
oxidation [5, 6]. In these cases, it is reasonable to
assume that the organic ligand used acts as a reducing
agent.
oxygen) or hydrolyzed to sulfoxide. Note that although
under conventional conditions free sulfides are very
slowly oxydized by the air oxygen, such a process
catalyzed by the copper salts was described for
oxidation of sulfur-containing macrocycles [13]. It is
also noteworthy that in active centers of the most of
mononuclear [14, 15] and binuclear [16] copper-
containing enzymes the metal atom is coordinated just
by the donor sulfur atoms (thioether or thiolate) and
nitrogen atoms (usually imidazole). Such copper-
containing enzymes (hemocyanins, thyrosinases, etc.)
are capable to react with oxygen [17] and in the course
of the reaction the exchange of electrons between the
copper ion and the ligand occurs. Since sulfur itself is
a soft donor, in a number of cases its coordination with
soft Cu(I) turns out to be preferable as compared to
coordination with more hard Cu(II); therefore the
exchange of electrons between the metal and the ligand
occurs in the complex.
Several examples were published of the formation
of copper(I) complexes upon interaction of copper(II)
salts with organic sulfides, containing, as a rule,
additional nitrogen donor atoms and representing
tetradentate ligands (see references above). In most
cases, the oxidation product was not isolated but it
might be assumed that during the reaction the one-
electron oxidation of the thioether group by the Cu(II)
ion occurred with the formation of the sulfur-centered
radical-cation, which is further oxidized (by the air
When investigating the reactions of complexing of
sulfur-containing organic ligands with copper(II)
perchlorate in the presence of acetonitrile we have
found that the main product of the reaction of
compounds I and II (see scheme below) with Cu
(ClO4)2·6Н2О was the tetrahedral copper(I) complex
Cu(CH3CN)4ClO4 (III) earlier characterized by X-ray
structural analysis [18, 19].
1 Dedicated to academician B.A. Trofimov on the occasion of his
70th birthday.
1504

FORMATION OF CuI(CH3CN)4ClO4 IN THE REACTIONS OF COPPER(II) PERCHLORATE
1505
In the present work we tried to formulate the factors
that make the reduction of copper(II) to copper(I) the
predominat process in the complexing with organic
ligands. Based on our data and those available from the
literature, the structural criteria making the ligand
capable of reducing copper(II) to copper(I) during
complexing can be suggested.
Upon mixing the solutions of copper(II) perchlorate
and ligand I or II complex III was formed as colorless
crystals whose structure was proved by X-ray analysis.
The complex is stable in solution and in crystalline
form in the absence of air, but gradually decomposes
turning green when stored in air.
With this, the orhanic ligand suffers oxidation at the
sulfur atom to the corresponding sulfoxide and
hydrolysis, perhaps, catalyzed by the copper salt and,
apparently, occurring by the action of the crystal-
We have found that complex III was the major
product of the reaction of ligands I or II with cop-
per(II) perchlorate at room temperature.
S
S
S
S
O
+
NCCl3
Cu
ClO4_
+
Cu(ClO4)2 6H2O
N
N
CH3CN
CH3CN
N
N
CH3CN/EtOH
or CH3CN
20oC
NCCH3
N
N
N
N
III
68%
I
S
S
O
O
O
IV
Ph
Ph
N
O
O
O
N
S
S
O
O
Cu(ClO4)2 6H2O
CH3CN/EtOH
or CH3CN
OEt
OEt
N
N
N
III
56%
+
20oC
N
II
Ph
N
O
S
O
O
OH
N
N
V
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

1506
BELOGLAZKINA et al.
lization water present in the starting copper salt. As
organic products of the reaction, we have isolated
dialdehyde IV and acid V, respectively.
the metal ion during the reaction of complexing must
be to a large extent determined by the used organic
ligand. Several structural requirements to the ligand
capable of being a donor in such a reaction can be
formulated. Three factors should be taken into account:
Note that we have for the first time observed the
redox reaction during complexing copper(II) salt with
bidentate organic ligand. This refutes the conclusion
made in [7] that the presence of the tetradentate
macrocyclic ligand is necessary for the reduction
process CuII → CuI to occur. We succeeded in showing
that the process of this type could proceed upon the
interaction not only with acyclic but even with a
bidentate ligand.
(1) Correlation between the geometry of the
complex and the copper ion oxidation state. For Cu(I)
complexes (d10) the tetrahedral or trigonal coordination
is preferable, while for Cu(II) complexes (d9) more
typical is the octahedral, trigonal bypyramidal, square
planar or tetrahedral geometry [20, 21].
On this basis, it should be assumed that to favor the
CuII → CuI transition during the process of
complexing, the ligand must not be conformationally
rigid and the coordination surrounding of the copper
ion could become tetrahedral. An indirect confirmation
of this assumption is the fact that the reduction of
copper(II) to copper(I), similar to that we observed,
occurs in complexing with conformationally flexible
macrocyclic ligands [4]. The assumption is also
corroborated by the fact that ligand IV containing
between the sulfur atoms a shorter bridge consisting of
two carbon atoms does not give complex III when
introduced in the reaction under conditions similar to
those for the reaction “I + Cu(ClO4)2·6Н2О:”
It is noteworthy that when copper(II) chloride is
introduced in the reaction instead of the corresponding
perchlorate, complex III is not formed. Apparently,
this is due to the fact that chloride ion, as a strong
electron-donor, coordinates directly with the copper
ion, whereas non-nucleophilic perchlorate ion locates
on the outer sphere of the complex. This is consistent
with the preferred coordination of the soft copper(I)
atom with soft sulfur atom of the thioether ligand,
whereas the hard copper(II) atom is preferred for
coordination with hard donor, chloride anion.
Apart from the counterion in the employed cop-
per(II) salt, the possibility of spontaneous reduction of
S
S
III
N
N
N
N
IV
Note also that in natural mononuclear copper-
containing enzymes (for example, plastocyanin [14]
and azurine [15]) the active center containing two
imidazole, thiolate and thioether donor atoms, can
easily change its geometry, and in the form that
stabilizes Cu(I) the coordination surrounding of copper
represents a distorted tetrahedron.
ligands of similar structure differing only by the type
of the donor system (N4 or N2S2); the process of
reduction CuII → CuI occurred only in the case of the
N2S2 ligands, while for the ligands of the N4 type the
Cu(II) complex was formed [5].
(3) Donor ability of the ligand. Strong electron-
donor ligands must stabilize higher oxidation state of
the central metal atom [in our case, Cu(II)], whereas
weakly donating or π-acceptor ligands (such as
sulfides or nitriles) preferably stabilize a lower oxida-
tion state [Cu(I)].
(2) HSAB princile. Harder ligands (that is, charged,
or containing the donor nitrogen or oxygen atoms
rather than sulfur atoms) must better stabilize the hard
Cu(II) cation. Soft uncharged sulfide ligands must
better stabilize the soft Cu(I) cation.
To summarize, it can be assumed that upon
complexing of copper(II) salts with organic ligands,
the formation of copper(I) complexes can be anticipa-
This assumption is proved by investigation of
complexing reactions with conformationally flexible
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

FORMATION OF CuI(CH3CN)4ClO4 IN THE REACTIONS OF COPPER(II) PERCHLORATE
1507
ted in the cases when organic reagent has the following
structural features. (1) Bidentate ligand or tetradentate
ligand with conformational flexibility sufficient for
making the coordination surrounding of the copper ion
tetrahedral. (2) The presence of a soft sulfide donor
atom in the ligand. (3) Non-nucleophilic counterion in
the starting inorganic salt.
in the range 14–16°: a = 24.223(3), b = 8.442(3),
с = 20.716(1) Å, V = 4236.2(2), space group Pna2i,
Z = 12. Correction for extinction was made by the use
of ω-scanning [23]. The massive of experimental data
was treated by the use of the package of programs
WinGX [24]. All further calculations were performed
using the SHELX97 program package [25]. The crystal
structure was determined by the direct method with
subsequent refinement of positional and thermal
parameters for all non-hydrogen atoms by a full-matrix
least-squares method in the anisotropic approximation.
Hydrogen atoms were placed in the geometrically
calculated positions by the use of the rider model.
Final R factor = 0.0056 from 2624 reflections with
intensity I > 2а(I).
Besides, in the reactions we studied, it turned out
that it is necessary to use a nitrile-containing solvent
(MeCN; when carrying out the reaction in EtOH the
Cu(II) complexes are formed [22]). This can be
understood since in the course of the redox reaction the
sulfide group of the ligand oxidizes to the sulfoxide
group (evidently, the source of the oxygen atom is the
air oxygen since no formation of III is observed when
performing the reaction in an argon atmosphere); the
arising donor atom S(IV) is harder than the initial S(II)
atom, and, therefore, apparently it is less strongly
bound to the soft Cu(I) atom and is substituted in the
coordination sphere by the soft nitrile ligand.
2,2'-[Propane-1,3-diylbis(thio-2-phenylnemethyl-
idene]bis(3-pyridylamine) (I). In 15 ml of EtOH
948 mg (3 mmol) of 1,5-bis(2-formylphenyl)-1,5-di-
thiapentane and 564 mg (6 mmol) of 3-aminopyridine
was dissolved, refluxed for 15 h, filtered, and the
solvent was removed to obtain 980 mg (2.1 mmol,
1
Based on the data obtained and available in the
literature it can be assumed that it is the ligand that
acts as a source of electrons for the metal ion
reduction. These reactions simulate one of the studies
of the process of electron transfer in copper-containing
enzymes, where the ligand acts as a mediator of
electron transfer from molecular oxygen. Electron
transfer from ligand to metal requires a decrease in the
energy of the transition state for the CuII → CuI
process, which is possible on the condition of
conformational flexibility and softness of the ligand.
70%) of brown oil. H NMR (CDC13): 9.02, 9.01 s
(2Н), 8.49 m (4Н), 8.12 m (2Н), 7.50 m (2Н) 7.34 m
(8Н), 3.03, 3.02 t (4Н, J 7.0 Hz), 1.93 m (2Н). IR
spectrum (film): 1680, 1620, 1590, 1580, 1445, 1420.
MS EI (m/z, %): 467 (М–Н+, 2.5).
5-Pyridylmethylidene-3-phenyl-2-carbethoxy-
methylthiotetrahydro-4Н-imidazol-4-one (II).To 0.3 g
(1 mmol) of 3-phenyl-5(7)-2-pyridylmethyl-idene)-2-
thioxotetrahydro-4Н-imidazol-4-one 10 ml of water,
10 ml of ethanol, and 15% aqueous solution of KOH
(0.063 g, 1 mmol) was added. After complete dis-
solution, 0.178 g (1 mmol) of ethyl bromoacetate was
added and stirred for 3 h. The precipitate formed was
filtered off, washed with ethanol, diethyl ether and
dried in the air to obtain 0.364 g (93%) of compound
EXPERIMENTAL
The reactions were monitored and the individuality
of the products was checked by the method of thin
layer chromatography on the fixed silica gel (Silufol).
1H NMR spectra were registered on a Varian-XR-400
instrument with working frequency 400 MHz in
CDCl3. IR spectra were recorded on a UR-20
instrument in thin film or mineral oil. Electron impact
mass spectra were registered on a JMS-D300 mass
spectrometer (direct injection, ion source temperature
150ºС, energy of ionizing electrons 70 eV, accelerating
voltage 3 kV).
1
II. Н NMR (CDC13): 8.81 d (1Н J 7.8 Hz), 8.71 d
(1Н, J 4.0), 7.80 d. t (1Н, J 7.7, 1.5 Hz), 7.45 m (4Н),
7.28 m (ЗН), 4.28 q (2Н, J 7.0, СН2), 4.10 s (2Н,
СН2), 1.31 t (ЗН, СН3, J 7.0 Hz). Found, %: С 62.01;
Н 4.32; N 11.63. C19H17N3SO3. Calculated, %: С 62.11;
Н 4.66; N 11.44.
Reaction of Сu(ClO4)2·6Н2О with ligand I. 103 mg
(0.22 mmol) of compound I and 81.4 mg (0.22 mmol)
of Cu(ClO4)2·6H2O was refluxed in 2 ml of the mixture
ethanol–acetonitrile (1:1) or CH3CN in the course of
1 h, cooled to 0°С, the precipitated crystals (36 mg,
yield 50%) were filtered off. IR spectrum (film, ν, cm–1):
1680, 1645, 1625, 1590, 1565 (С=N). Found, %: C
28.67, H 3.43, N 15.80. C8H12N4CuClO4. Calculated,
Light-green crystals of compound III were
analyzed on an automatic single-crystal diffractometer
CAD-4 (κ, МоKα = 0.71073, graphite monochromator,
ω-scanning). Parameters of the unit cell were
determined and refined from 25 reflections for angles
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

1508
BELOGLAZKINA et al.
6. Benzekri, A., Cartier, С., Latour, J.-M., Limosin, D.,
Rey, P., and Verdaguer, M., Inorg. Chim. Acta, 1996,
vol. 252, p. 413.
%: C 29.36; H 3.67; N 17.13. After the mother liquor
was cooled to –20°С 38 mg (55%) of compound IV
1
was crystallized. Н NMR (CDC13): 10.20, 10.15 s
7. Nickless, D.E., Powers, M.J., and Urbach, F.L., Inorg.
Chem., 1983, vol. 22, p. 3210.
(2Н, СНО), 7.86 m (4Н), 7.52 m (2Н), 7.40 m (2Н)
7.33 m (8Н), 3.10, 3.12 t (4Н, J 7.0 Hz), 2.11 m (2Н).
IR spectrum (vaseline oil, ν, cm–1): 1700, 1650, 1210,
1065 (S=O). Found, %: С 64.84; Н 5.02. C17H16S2O2.
Calculated, %: С 64.56; Н 5.06.
8. Latour, J.M., Limosin, D., and Rey, P., J. Chem. Soc,
Chem. Commun., 1985, p. 464.
9. Verheijdt, P.I., Hassnoot, J.G., and Reedijk, J., Inorg.
Chim. Acta, 1983, vol. 76, p. L43.
Reaction of Сu(ClO4)2·6Н2О with ligand II. To
the solution of 52 mg (0.14 mmol) of compound II in
2 ml of CH2Cl2 3 ml of CH3CN was added for layer
separation. Then the solution of 50 mg (0.14 mmol) of
Cu(ClO4)2·6H2O in 2 ml of CH3CN was slowly added.
The reaction mixture was firmly closed and allowed to
stay until the crystalline precipitate formed. The
precipitate was filtered off, the solution filtered
through the column with silica gel of 4–5 cm height.
Solvent was removed, the obtained green oil was
purified by TLC (eluent ethyl acetate:methanol 2:1) to
obtain 11 mg (23%) of compound V as a white
crystalline compound. IR spectrum (mineral oil): 3450
br, 1740, 1715, 1635, 1185, 995 (S=O). Found, %: С
56.38; Н 4.02; N, 11.35. C17H13N3SO4. Calculated, %: С
57.46; Н 3.66; N 11.83.
10. Mandal, S.K., Woon, T.C., Tompson, L.K., New-
lands, M.J., and Gage, E.J., Aust. J. Chem., 1986, vol. 39,
p. 1007.
11. Kitawara, U.S., Munakata, M., and Higashi, A., Inorg.
Chim. Acta, 1984, vol. 84, p. 79.
12. Sakurai, T., Kimura, M., and Nakahara, A., Bull. Chem.
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13. Musker, W.K., Acc. Chem. Res., 1980, vol. 13, p. 1040.
14. Colman, P.M., Freeman, H.C., Guss, J.M., Murata, M.,
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Nature, 1978, vol. 272, p. 319.
15. Adman, E.T., Stenkamp, R.E., Sieker, L.C., and Jen-
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ACKNOWLEDGMENTS
18. Hemmerich, P. and Sigwart, G., Experientia, 1963,
vol. 12, p. 488.
This work was financially supported by RFBR
(grant no. 07-03-00584-а), Foundation for Support of
National Science, and Grant for support of talented
students, aspirants, and young scientists of the
Lomonosov Moscow State University, 2007.
19. Soregh, C., Kierkegaard, P., and Norrestam, R., Acta
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