Ferrocenes conjugated with thiophene, carbazole, and pyrimidine fragments: Synthesis and properties

Article abstract of DOI:10.1134/S1070427210080215

Ferrocenyl-containing chalcones containing π-excessive heterocyclic fragments capable of electrochemical polymerization (carbazole, thiophene, 2,4-ethylenedioxythiophene) were prepared by the Claisen-Schmidt reaction. 2,4,6-Trisubstituted pyrimidines deri

Full text of DOI:10.1134/S1070427210080215

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 8, pp. 1435−1439. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © G.G. Abashev, A.D. Antuf’eva, A.Yu. Bushueva, P.G. Kudryavtsevd, I.V. Osorgina, R.V. Syutkin, E.V. Shklyaeva, 2010, published
in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 8, pp. 1330−1334.
Ferrocenes Conjugated with Thiophene, Carbazole,
and Pyrimidine Fragments: Synthesis and Properties
G. G. Abasheva,b, A. D. Antuf’evac, A. Yu. Bushuevaa,b, P. G. Kudryavtsevd,
I. V. Osorginab, R. V. Syutkina,b, and E. V. Shklyaevab,c
a Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, Perm, Russia
b Natural Science Institute, Perm State University, Perm, Russia
c Perm State University, Perm, Russia
d Trivektr Research and Production Enterprise, Limited Liability Company, Perm, Russia
Received March 10, 2010
Abstract—Ferrocenyl-containing chalcones containing π-excessive heterocyclic fragments capable of
electrochemical polymerization (carbazole, thiophene, 2,4-ethylenedioxythiophene) were prepared by the Claisen–
Schmidt reaction. 2,4,6-Trisubstituted pyrimidines derived from them were synthesized.
DOI: 10.1134/S1070427210080215
The properties of ferrocene and its derivatives
attract steady interest of researchers in many fields of
organic and organometallic chemistry. Wide range of
studies of applied properties of ferrocene is due to its
specific physical and chemical properties: unusually
high (for organometallic compounds) thermal stability,
high vapor pressure, low toxicity, good solubility in
organic solvents, and diverse chemical transformations.
The use of electrochemical properties of ferrocene is
based on readiness and reversibility of one-electron
redox processes. The ferrocene–ferricenium cation
system is one of the most highly reversible redox
systems. Thanks to this property, this redox couple
has found wide practical use: as reversible electrodes
in analytical chemistry and as electron-transfer agent
in various systems (primarily in biochemical studies)
[1, 2]. Recently there has been growing interest in the
use of ferrocene-containing organic compounds in such
fields as nonlinear optics [3] and chemosensorics [4]. It
was also shown that compounds containing a ferrocene
fragment can penetrate through cell membranes [5].
At the same time, it is known that such heterocycles
as pyrrole, thiophene, and pyrimidine are widely used
in fabrication of conducting and electroluminescent
materials [6]. A combination of the properties of
ferrocene and such heterocycles could lead to new
unique properties of materials, i.e., nonlinear optical,
magnetic, or electrochemical properties.
From acetylferrocene I and diacetylferrocene VIII
preparedinadvance,wesynthesizedferrocene-containing
chalcones containing unsubstituted thiophene (V, IX)
and carbazole (VI) fragments, described previously
[7], and 3,4-ethylenedioxythiophene fragment (VII)
(Scheme 1). The Claisen–Schmidt condensation used
in our study can be performed by diverse procedures.
We used either refluxing of a mixture of aldehyde and
ketone in 2% aqueous alkali solution (chalcones V, VII,
IX) or heating in a 10% solution of KOH in methanol
(chalcone VI). Relatively recently a procedure was
described for preparing chalcone VI without solvent
[8]. All the compounds obtained have bright color: red
(V–VII, X) or violet (IX).
The chalcones prepared were subsequently used
for synthesizing ferrocene-substituted pyrimidines
by cyclization with guanidine sulfate in aqueous
solution [9] or with guanidine nitrate in dioxane [10]
in the presence of alkali. Under these conditions,
1435

1436
ABASHEV et al.
we successfully synthesized previously unknown
pyrimidine X (Scheme 2). The two other chalcones, VI
and VII, cyclize under these conditions with a very low
yield.
Then, by the reaction of 2-amino-6-(thiophen-2-
yl)-4-ferrocenylpyrimidine X with 2,5-dimethoxy-
tetrahydrofuran in acetic acid, we synthesized previously
unknown substituted pyrimidine XI containing as
Scheme 1.
I
NaOH, 2%
NaOH, 2%
2 h, refluxing
2 h, refluxing
KOH, MOH
10 %
2 h, refluxing
IV
II
V
III
VI
VII
NaOH, 2%
2 h, refluxing
VIII
IX
Scheme 2.
CH3COOH,
2,5-dimethoxyTHF
2 h, refluxing
V
X
XI
H2O2
refluxing
[(NH2)2 CNH]2 • H2SO4
EtOH, NaOH 40%
refluxing
refluxing
Xa
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FERROCENES CONJUGATED WITH THIOPHENE, CARBAZOLE, AND PYRIMIDINE FRAGMENTS 1437
substituents three π-excessive fragments: ferrocene,
anodic oxidation, Е2 , is observed. It corresponds to the
ра
thiophene, and pyrrole (Scheme 2).
formation of a radical cation by oxidation of heterocyclic
fragments present in the structure (carbazole, thiophene,
pyrrole). For chalcone VI, the potential of this peak
is 1304 mV, and this compound polymerizes under
the conditions of cyclic voltammetry. The potential of
the peak of the polymerization onset, Eonset, for this
compound is 1047 mV, and in the process a bright violet
film is formed on the electrode surface. Polymerization
of pyrimidines X and XI under the above-indicated
conditions was not observed, but on replacement of
the solvent used (acetonitrile) by a mixture of boron
trifluoride etherate and methylene chloride (3 : 2) [11]
compound XI containing simultaneously ferrocene,
pyrimidine, pyrrole, and thiophene rings also appeared
to be capable of electrochemical polymerization.
All the compounds obtained were studied by
cyclic voltammetry. Measurements were performed
in a three-electrode cell with Ag/АgCl reference
electrode, glassy carbon working electrode, and Pt wire
auxiliary electrode. The conditions of electrochemical
measurements were identical in all the cases: supporting
electrolyte Еt4NClO4, сsup = 0.1 M; сmonomer = 1 ×
10–3 M; Vscan = 100 mV s–1; absolute CH3CN as
solvent. We showed that all the compounds under
these conditions showed stable reversible oxidation of
the ferrocene fragment to the ferricenium fragment.
For the convenience of comparison, under the same
conditions we recorded the cyclovoltammograms of
unsubstituted ferrocene. The peak potentials Ер for the
1
1
transitions Fc2+ → Fc3+ (Е ра) and Fc3+ → Fc2+ (Е
)
The structure of X was confirmed by single crystal
X-ray diffraction. The compound crystallizes in the
tetragonal system, space group I41; unit cell parameters:
a = 21.5709(8), b = 21.5709(8), c = 13.4184(7) Å; α =
β = γ = 90°; unit cell volume V = 6243.63 Å3.
рс
were 488 and 384 mV, respectively (see table). The peak
potentials for the compounds synthesized are given in
the table. For the convenience of comparison of the
electron-donor properties of the compounds prepared,
we also present the values of ΔЕр and Ер . As seen from
the table, the half-wave potentials of the compounds
There are short S···S contacts in the structure. The
thiophene, pyrimidine, and one of the cyclopentadiene
rings in the structure of the molecule are coplanar.
½
synthesized are shifted toward more positive values
relative to unsubstituted ferrocene (432 mV). This may
be due to delocalization of the electron density in the
conjugated systems. Delocalization of the electron
density is more efficient in the case of chalcones,
especially of dichalcone IX, which leads to the highest
EXPERIMENTAL
The 1H NMR spectra were recorded with
a Mercury plus300 device, internal reference HMDS.
Electrochemical studies were performed with an
IPC-compact device equipped with an EM-04
electrochemical sensor. The results were processed with
the IPC-compact 8.60F program. Mass-spectrometric
analysis was performed with an Agilent Technologies
6890N/5975B gas chromatograph–mass spectrometer
(HP-5ms column, 30 × 0.25 mm, 0.25 μm, carrier gas
He, ionization by electron impact, 70 eV).
half-wave potential Ер : 951 mV. For all the compounds
½
prepared, except dichalcone IX, the second peak of
Redox potentials of the compounds obtained
a
Е1
Е1
ΔЕр
Ер
½
ра
рс
Ferrocene
Е2ра, mV
mV
484
708
700
706
1008
605
634
381
634
610
655
894
529
572
103
74
432
634
655
655
951
567
603
Acetylferrocene I was prepared by acetylation of
ferrocene with acetic anhydride in the presence of
orthophosphoric acid [13]. Diacetylferrocene was
isolated as by-product.
V
VI
VII
IX
X
1393
1304
1584
90
51
9-Ethyl-9H-carbazole-3-carbaldehyde III was
prepared by the procedure similar to that described
in [14]. To a solution of 4.46 g (0.02 mol) of
N-ethylcarbazole and 1.90 g (0.026 mol) of DMF in
40 ml of chlorobenzene, we added dropwise with stirring
6.13 g (0.04 mol) of POCl3. The reaction mixture was
stirred at 65–70°С for 5 h, cooled to room temperature,
114
76
1290
1198
XI
62
a
∆Ер
Е
= Ер – ——.
р
½
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010

1438
ABASHEV et al.
and poured into 200 ml of water, after which the product
was extracted with methylene chloride. The organic
layers were combined and washed with water and
aqueous NaHCO3 solution. The solvent was evaporated,
and the viscous residue was washed with hexane and
recrystallized from ethanol. White crystals. Yield 73%,
ferrocene), 4.57 br.s (2Н, ferrocene), 4.89 br.s (2Н,
ferrocene), 6.93 and 6.88 d (1Н, СН=, J 15.0), 7.08 t
(1Н, thiophene, J 3.6), 7.33 d (1Н, thiophene, J 3.6),
7.39 d (1Н, thiophene, J 4.5), 7.86 and 7.91 d (1Н, СН=,
J 15.0).
3-(3,4-Ethylenedioxythiophen-2-yl)-1-ferrocenyl-
propenone VII was prepared by the procedure similar
to that for V. Red-orange crystals, yield 75%, mp 178–
1
mp 86–88°С. Н NMR spectrum (CDCl3, δ, ppm, J,
Hz): 1.42 t (2Н, СН3, J 7.2); 4.31 q (3Н, СН2, J 7.2);
7.29 t (1Н, carbazole, J 8.1); 7.40, 7.43 d (1Н, carbazole,
J 8.1); 7.5 t (1Н, carbazole-С6, J 8.1); 7.95, 7.98 dd (1Н,
carbazole, J 8.4); 8.10 , 8.11 d (1Н, carbazole, J 8.4);
8.55 s (1Н, carbazole); 10.05 s (1Н, СНО).
1
180°С. Н NMR spectrum (CDCl3, δ, ppm, J, Hz):
4.2br.s(5H,Fc),4.25m(2Н,СН2О),4.35m(2Н,СН2О),
4.54 t (2Н, Fc, J 1.8), 4.87 t (2Н, Fc, J 1.8), 6.45 s (1Н,
thiophene), 6.87 and 6.92 d (1Н, СН=, J 15.3), 7.78 and
7.83 d (1Н, СН=, J 15.6). Mass spectrum, m/z: М+ 380
(100%). C19H16FeO3S. M 380.23.
3,4-Ethylenedioxythiophene-2-carbaldehyde
IV was prepared by the procedure similar to that
described in [15]. To a solution of 7.1 g (0.05 mol)
of 3,4-ethylenedioxythiophene in 50 ml of dry
1,2-dichloroethane we added dropwise with stirring
and cooling with cold water 3.7 g (0.05 mol) of dry
dimethylformamide and then (over a period of 0.5 h)
7.67 g (0.05 mol) of POCl3. After adding the reactants,
the mixture was stirred for 15 min at room temperature
and then for 5–6 h at approximately 80°С, after which it
was cooled with ice-cold water, 10 ml of Н2О was added
dropwise, and the mixture was stirred for 30 min and
poured into cold water; the layers were separated. The
organic layer was washed with water and evaporated;
a small amount of the target product was obtained. To
the aqueous layer, ~50 ml of concentrated HCl was
added, and the mixture was left overnight. The product
precipitated in the form of slightly colored needles.
It was filtered off, and the filtrate was treated with an
additional ~15-ml portion of HCl and allowed to stand
for 3 h, after which an additional crop of the aldehyde
was filtered off. Yield about 90%, mp 155°С. 1H NMR
spectrum (CDCl3, δ, ppm): 4.25–4.28 m (2Н, СН2О),
4.34–4.37 m (2Н, СН2О), 6.79 s (1Н, thiophene), 9.90
(1Н, СНО).
3-(N-Ethylcarbazol-3-yl)-1-ferrocenylpropenone
VI. A mixture of 0.558 g (0.0025 mol) of N-ethyl-
3-carbaxolecarbaldehyde and 0.62 g (0.0027 mol)
of acetylferrocene was stirred in 20 ml of refluxing
methanol containing 0.7 g (0.0125 mol) of KОН for
3 h. After cooling, a half of the solvent was removed,
the residue was poured into water, the mixture was
extracted with CH2Cl2, the combined organic layers
were washed with water, the solvent was removed, and
the solid residue was separated on a column packed
with silica gel (eluent hexane : acetone = 4 : 1). Red
crystalline substance, yield 68%, mp 197–199°С.
1Н NMR spectrum (CDCl3, δ, ppm, J, Hz): 1.46 t (3Н,
СН3, J 6.9), 4.23 s (3H, Fc), 4.36–4.43 q (2H, CH2, J
6.9), 4.58 br.s (2H, Fc), 4.97 br.s (2H, Fc), 7.16 and 7.21
d (1Н, CH=, J 15.9), 7.25–7.31 m (3H, carbazole), 7.41
and 7.44 d (1H, carbazole, J 8.4), 7.50 t (1H, carbazole,
J 8.4), 7.77 and 7.80 d (1H, carbazole, J 9.6), 8.00 and
8.05 d (1H, CH=, J 15.9), 8.15 and 8.17 d (H, carbazole,
J 7.2), 8.36 s (1Н, carbazole).
1,1'-Di[3-(thiophen-2-yl)prop-2-enoyl]ferrocene
IX. A mixture of 2.7 g (0.01 mol) of diacetylferrocene
and 2.24 g (0.02 mol) of 2-thiophenecarbaldehyde
in 500 ml of a 2% NaOH solution was refluxed for
2 h. After the reaction completion and cooling, the
precipitate that formed was filtered off, washed with
a large amount of water, and recrystallized from
chlorobenzene. Decomposes at temperatures higher
than 200°C. 1Н NMR spectrum (CDCl3, δ, ppm, J, Hz):
4.57 br.s (4Н, ferrocene), 4.86 br.s (4Н, 2 thiophene),
6.84 t (2Н, 2 thiophene, J 3.6), 6.96–7.36 m (6Н, 4Н
thiophene + 2Н =СН), 7.84 and 7.89 d (2Н, 2=СН, J
14.8).
1-Ferrocenyl-3-(thiophen-2-yl)propenone
V.
A mixture of 0.74 g (0.0066 mol) of thiophene-2-
carbaldehyde and 1.5 g (0.0066 mol) of acetylferrocene
in 150 ml of a 2% NaOH solution was refluxed for
2 h. The precipitate formed on cooling was filtered off
and washed with a large amount of cold water. The
product purity was checked by TLC (eluent methylene
chloride). If necessary, the product was purified by
column chromatography on silica gel (eluent CH2Cl2).
Red-violet crystals, yield about 67%, mp 75–76°С.
1Н NMR spectrum (CDCl3, δ, ppm, J, Hz): 4.20 s (5Н,
2 - A m i n o-4-ferrocenyl-6-(thiophen-2-yl)
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010

FERROCENES CONJUGATED WITH THIOPHENE, CARBAZOLE, AND PYRIMIDINE FRAGMENTS 1439
pyrimidine X. A mixture of 2.1 g of 1-ferrocenyl-
3-(thiophen-2-yl)propenone (0.0062 mol), 1.53 g of
guanidine sulfate, and 5 ml of a 50% aqueous KOH
solution in 50 ml of ethanol was stirred and then refluxed
for 1 h. Then, under the same conditions, 3 ml of Н2О2
was added in small portions over a period of 1 h. After
that, the reaction mixture was poured into cold water.
The precipitate was filtered off, dried, and purified by
columnchromatography(eluentCH2Cl2),withcollection
of the last fraction. Red-violet crystals. Yield 55%, mp
199–200°С. 1Н NMR spectrum (CDCl3, δ, ppm, J, Hz):
4.09 br.s (5Н, ferrocene), 4.45 t (2Н, ferrocene, J 1.8),
4.94 t (2Н, ferrocene, J 1.8), 5.06 br.s (2H, NH2), 7.02 s
(1H, pyrimidine), 7.14 t (1Н, thiophene, J 3.6), 7.45
and 7.47 dd (1Н, thiophene, J 5.1), 7.73 and 7.74 dd
(1Н, thiophene, J 3.6). Mass spectrum, m/z: М+ 361.1
(100.0%). C18H15FeN3S2. M 361.1.
of Organic Synthesis, Ural Branch, Russian Academy of
Sciences, Yekaterinburg) for performing single crystal
X-ray diffraction analysis of the compounds prepared.
The study was financially supported by the
Analytical Departmental Target Program of the Russian
Ministry for Education and Science “Development of
the Scientific Potential of Higher School.”
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1
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New ferrocene-containing pyrimidines were
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The authors are grateful to P.A. Slepukhin (Institute
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 83 No. 8 2010