Push-pull 2-ferrocenyl-4-hydroxythiazoles: A novel method of the construction of the thiazole ring

Article abstract of DOI:10.1016/j.jorganchem.2008.04.043

The title compounds were obtained by cyclization of ferrocenyl thioimidates in the presence of sodium ethoxide. They were transformed into the corresponding 4-acetoxy-derivatives in reaction with acetic anhydride/pyridine. The structure of 4-acetoxy-5-(ethoxycarbonyl)-2-ferrocenylthiazole was determined by X-ray diffraction. The EFISH measurements revealed significant second-order nonlinear properties of 4-acetoxy-2-ferrocenyl-5-(4-nitrophenyl)ferrocenylthiazole (μβ = 250 × 10^-48 esu at 1907 nm).

Full text of DOI:10.1016/j.jorganchem.2008.04.043

Journal of Organometallic Chemistry 693 (2008) 2982–2986
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
‘‘Push–pull” 2-ferrocenyl-4-hydroxythiazoles: A novel method of the construction
of the thiazole ring
b
c
Anna Wrona a, Janusz Zakrzewski a, , Lucjan Jerzykiewicz , Keitaro Nakatani
*
a Department of Organic Chemistry, University of Lodz, 90-136 Lodz, Narutowicza 68, Poland
b Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroclaw, Poland
c Laboratoire de Photophysique et Photochimie Supramoleculaires et Macromoleculaires (PPSM, CNRS UMR 8531), Ecole Normale Superieure de Cachan,
61, Avenue du Président Wilson, 94235 Cachan Cédex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The title compounds were obtained by cyclization of ferrocenyl thioimidates in the presence of sodium
ethoxide. They were transformed into the corresponding 4-acetoxy-derivatives in reaction with acetic
anhydride/pyridine. The structure of 4-acetoxy-5-(ethoxycarbonyl)-2-ferrocenylthiazole was determined
by X-ray diffraction. The EFISH measurements revealed significant second-order nonlinear properties of
Received 14 February 2008
Received in revised form 18 April 2008
Accepted 28 April 2008
Available online 6 May 2008
4-acetoxy-2-ferrocenyl-5-(4-nitrophenyl)ferrocenylthiazole (
l
b = 250 ꢀ 10ꢁ48 esu at 1907 nm).
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Ferrocene
Thiazole
Cyclization
X-ray structure
NLO
EFISH
1. Introduction
2-ferrocenyl-4-hydroxythiazoles with electron-withdrawing sub-
stituents at C-5.
Ferrocenyl thiazoles have attracted interest as electroactive li-
gands [1], selective ion-sensing [2] and biologically active com-
pounds [3]. In our opinion they are also promising candidates for
nonlinear optical (NLO) chromophores. Indeed, taking into account
earlier results obtained for purely organic thiazole compounds [4],
‘‘push–pull” ferrocenyl thiazoles are expected to exhibit large sec-
ond-order NLO properties. Continuing our research program de-
voted to ferrocene-based NLO chromophores [5] we became
interested in synthesis and study of 2-ferrocenyl thiazoles having
electron-accepting groups at C-4 or C-5. Here we report on the no-
vel method of the synthesis of the thiazole ring, leading to
2. Results and discussion
In our earlier paper [6] we described the S-alkylation of N-(eth-
oxycarbonyl)ferrocenecarbothioamide 1 yielding thioimidates 2a–
2c (Scheme 1). Now we have found that these compounds treated
with excess of sodium ethoxide in ethanol at r.t. afford, after acid-
ification, the 2-ferrocenyl-4-hydroxythiazoles 3a–3c in >90% iso-
lated yield.
In the case of reaction of 2a and 2b intense violet or red color-
ation of the reaction mixtures before acidification was observed,
assignable to the strongly conjugated anions of 3a and 3b (e.g. 5).
N
O-
N
N
O-
O
Fe+
Fe
Fe
S
S
S
O-
N+
O
O-
O-
N+
O-
N+
O-
5
* Corresponding author. Tel.: +48 42 665 5333; fax: +48 42 665 5258.
E-mail address: janzak@uni.lodz.pl (J. Zakrzewski).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.043

A. Wrona et al. / Journal of Organometallic Chemistry 693 (2008) 2982–2986
2983
H
N
COOEt
N
COOEt
+
R
Br
Fe
Fe
S
S
R
2a-c
1. EtO-Na+
2. H+
1
N
OH
N
Ac2O / Py
OAc
Fe
Fe
S
S
R
R
3a-c
4a-b
(a) R = C6H4-p- NO2
(b) R = C6H4-p- CN
(c) R = COOEt
Scheme 1. Synthesis of ferrocenylthiazoles by cyclization of thioimidates 2a–2c.
Table 1
Compounds 3a and 3b are red solids insoluble in most organic sol-
vents except pyridine. In their 13C NMR spectra, measured in this
solvent, the signals of the thiazolyl C-4 and C-2 appear at 160–
165 ppm (in the spectrum of (15N)-3a these signals are splitted into
doublets with J (15Nꢂ13C) = 2–3 Hz. The signals of C-5 appear at
ꢃ104 ppm. The 15N NMR spectrum of (15N)-3a displays the signal
of the thiazolyl nitrogen in the expected region [7], at ꢁ88 ppm
(relative to external, neat CH3NO2).
Selected geometrical parameters (Å, °) for 3c
C1–C2
C1–C5
C2–C3
C3–C4
C4–C5
C1–C6
S1–C6
S1–C8
C7–C8
N1–C7
N1–C6
C8–C9
O1–C9
O2–C9
O3–C7
1.433(7)
1.438(7)
1.410(7)
1.416(7)
1.413(7)
1.445(7)
1.729(5)
1.727(5)
1.375(7)
1.368(6)
1.322(6)
1.439(7)
1.330(6)
1.234(6)
1.350(6)
C2–C1–C6
C5–C1–C6
C2–C1–C5
C1–C6–S1
N1–C6–C1
N1–C6–S1
C8–S1–C6
C6–N1–C7
O1–C9–C8
O2–C9–C8
O3–C7–N1
C9–C8–S1
C7–C8–S1
125.8(4)
127.1(4)
107.0(4)
121.2(4)
123.7(4)
115.1(4)
89.7(2)
109.5(4)
113.4(4)
122.1(4)
116.2(4)
124.9(4)
108.6(4)
S1–C8–C9–O2
S1–C8–C9–O1
C7–C8–C9–O2
C2–C1–C6–N1
C2–C1–C6–S1
177.6(4)
ꢁ2.3(6)
3.0(8)
3.0(8)
ꢁ176.4(4)
In the solid state molecules 3c form centrosymmetric dimers with bifurcated intra-
and intermolecular hydrogen bonds (Fig. 2 and Table 2).
The treatment of 3a–3b with acetic anhydride in pyridine affor-
ded acetates 4a–4b which were much better soluble in organic sol-
vents like dichloromethane, acetone or THF.
Compound 3c is soluble in dichloromethane or chloroform. Its
structure was confirmed by spectroscopic and analytical data as
Fig. 1. Molecular view of 3c with atom labeling scheme. Ellipsoids represent 50%
probability.

2984
A. Wrona et al. / Journal of Organometallic Chemistry 693 (2008) 2982–2986
Table 2
well as by single crystal X-ray diffraction (Fig. 1, Table 1). The
0
Hydrogen bonds in dimers of 3c
lengths of the C7–O3 and C7–C8 bonds (1.350(6) ÅA and
0
1.375(6) ÅA, respectively) are in accord with the 4-hydroxythiazole
structure and exclude tautomeric structure of
D–H–A
Distance (Å)
D–H
Angle (°)
D
2-thiazolin-4-one.
H–A
D–A
D–H–A
The hydroxythiazole form is the sole existing in solution of 3c in
CDCl3 as indicated by the presence of the signal of the OH proton
at ꢃ10 ppm in the 1H NMR spectrum of this compound. The thia-
zole ring is practically coplanar with the Cp ring (angle C2–C1–
C6–S1 = ꢁ176.4(4)° and C5–C1–C6–S1 = 7.6(7)°) and the ester
group (angle S1–C8–C9–O2 = 177.6(4)°, C7–C8–C9–O2 = 3.0(8)°
and S1–C8–C9–O2 = ꢁ2.3(6)°).
O3–H3–O2
O3–H3–O20
0.80(8)
0.80(8)
2.19(8)
2.27(8)
2.860(5)
2.874(5)
142.(7)
132.(7)
(i) 2ꢁx, ꢁy, 1ꢁz.
(RC(@S)NH2 reacts with R0–CH(X)–COOEt and the cyclization occurs
via formation of the C(5)–N bond. In our method RC(@S)NHCOOOEt
reacts with R0CH2X and the cyclization occurs via formation of the
C(4)–C(5) bond. Therefore, these two methods can be considered
as complementary.
Since ferrocenyl ‘‘push–pull” compounds are considered as effi-
cient second-order NLO chromophores [12] we have studied elec-
trochemistry, linear and nonlinear optical properties of 4a. The
data are gathered in Table 3 along with the data for (E)-Fc-
CH@CH–C6H4–NO2-(p) (7) taken from the literature [13],
respectively.
Cyclic voltammetry of 4a in CH2Cl2 reveals a reversible Fe(II)/
Fe(III) ferrocenic couple with the redox potential shifted anodically
with respect to that of 7. This means that replacement of the eth-
ylenic bond in the (E)-CH@CH–Ph–NO2-(p) group by the acetoxy-
thiazole nucleus brings about stronger electron withdrawal from
the ferrocene moiety. The electronic absorption spectrum confirms
the ‘‘push-pull” character of 4a. Two bands observed in the visible
In the solid state molecules 3c form centrosymmetric dimers
with bifurcated intra- and intermolecular hydrogen bonds (Fig. 2;
Table 2).
In the literature there are only scarce data concerning 4-
hydroxythiazoles. These compounds were synthesized mainly by
reaction of thioamides with
a-bromoesters or a-haloacid halides
(Hantzsch synthesis) or -mercaptoacids with nitriles [8]. Interest-
a
ingly, some compounds of this class exhibited biological activity
(inhibition of 5-lipoxygenase) [8b,8c].
Formation of 3a–3c can be understood assuming that 2a–2c are
deprotonated by sodium ethoxide with formation of carboanions 6
stabilized by sulfur [9] and electron-accepting group R. This anion
undergoes cyclization via nucleophilic attack on the COOEt group.
The presence of a strong electron accepting group is necessary as
indicated by the failure of cyclization of the compound 2 when
R = C6H4–COOEt-(p). To our knowledge only one example of the
similar type of cyclization, involving nucleophilic attack of a sulfur-
and carbonyl group-stabilized carbanion on the nitrile group lead-
ing to the 4-aminothiazole ring has been reported [10].
region can be assign to
bands show solvatochromic behavior similar to that reported for
p–
p* and MLCT transitions [13,14]. These
7 (Table 4).
O
Compound 4a is thermally stable up to 250 °C (TGA data) and
displays slightly better transparency than 7. Finally, the EFISH
(electric field-induced second harmonic generation) measure-
N
OEt
ments at 1907 nm gave the value of lb higher than that reported
Fe
S
for 7 (moreover, it should be noticed that the value reported for
the latter compound is stronger dispersion-enhanced because of
a shorter incident wavelength).
R
6
In conclusion, we have developed an efficient route to ‘‘push–
pull” ferrocenyl thiazoles via unprecedented cyclization of depro-
tonated ferrocenyl thioimidates. Preliminary experiments con-
firmed potential of these compounds for the second-order
nonlinear optics.
It is of interest to compare our cyclization method with the classical
Hantzsch 4-hydroxythiazole synthesis [8,11]. In the latter method
Fig. 2. Centrosymmetric dimers formed by 3c in the solid state. Ellipsoids represent 50% probability.

A. Wrona et al. / Journal of Organometallic Chemistry 693 (2008) 2982–2986
2985
Table 3
Electrochemical, linear and nonlinear optical properties of 4a and 7
3.2. Synthesis of 4a–4b
Compound CVa Electronic transitionsb
EFISHc
Acetic anhydride (24 l, 0.25 mmol) was added to a solution of
3a–3b (0.25 mmol) in pyridine (200 l) and stirred at r.t. overnight.
The reaction mixture was diluted by adding water (10 ml). The
solution was extracted with dichloromethane and the organic ex-
tracts were dried (MgSO4) and the solvent evaporated. The crude
product was purified on silica gel column which was eluted with
CH2Cl2.
E1/2 (mV)
(
p
ꢁ
p*) kmax (nm)
max, Mꢁ1 cmꢁ1
(MLCT) kmax (nm)
max, Mꢁ1 cmꢁ1
lb
(
D
Ep, mV)
(e
)
(
e
)
(10ꢁ48 esu)
4a
7
200 (90)
354 (54000)
363d
498 (13200)
511d
250
55 (100)d
140e
a
In CH2Cl2 vs. ferrocene/ferrocenium.
In CHCl3.
In CHCl3 at 1907 nm.
Data taken from [13a] (values of emax are not given).
In CHCl3 at 1064 nm. Value calculated using values of
b
c
Spectroscopic and analytical data: 4a. 1H NMR (200 MHz,
CDCl3): d 2.39 (s, 3H, CH3), 4.21 (s, 5H, Cp), 4.51 (t, J = 1.9 Hz, 2H,
Cp), 4.90 (t, J = 1.9 Hz, 2H, Cp), 7.72 (d, J = 8.9 Hz, 2H, Ar), 8.25 (d,
J = 8.9 Hz, 2H, Ar). 13C NMR (50 MHz, CDCl3): d 168.1 (CO), 146.5
(SCN), 136.8 (COC), 136.4 (Ar), 127.5 (Ar), 124.4 (Ar), 118.2 (Ar),
103.4 (CAr), 70.9 (Cp), 70.6 (Cp), 67.8 (Cp), 21.1 (CH3); IR (CHCl3,
cmꢁ1): 1786 (CO), 1514, 1341 (NO2). MS (EI): 448 (M+), HRMS:
Found: 448.018018, Calc. for C21H16SFeN2O4: 448.018079. 4b. 1H
NMR (200 MHz, CDCl3): d 2.37 (s, 3H, CH3), 4.19 (s, 5H, Cp), 4.49
(t, J = 1.7 Hz, 2H, Cp), 4.88 (t, J = 1.7 Hz, 2H, Cp), 7.65 (d,
J = 8.5 Hz, 2H, Ar), 7.67 (d, J = 8.5 Hz, 2H, Ar). 13C NMR (50 MHz,
CDCl3): d 168.2 (CO), 166.8 (SCN), 135.1 (COC), 134.9 (Ar), 132.7
(Ar), 127.5 (Ar), 118.6 (Ar), 118.4 (CN), 110.9 (CAr), 70.8 (Cp),
70.5 (Cp), 68.9 (Cp), 67.8 (Cp), 21.0 (CH3) IR (CHCl3, cmꢁ1): 2227
(C„N), 1782 (CO). Anal. Calc. for C22H16SFeN2O2: C, 61.70, H,
3.77, N, 6.54, S, 7.49. Found: C, 62.03, H, 3.69, N, 6.75, S, 7.31%.
d
e
l
and b from Refs.
[13a,13b], respectively.
Table 4
Solvatochromism of 4a and 7
Compound
CHCl3
THF
MeOH
kmax (nm)
kmax (nm)
kmax (nm)
(e
max, Mꢁ1 cmꢁ1
)
(e
max, Mꢁ1cmꢁ1
)
(e )
max, Mꢁ1 cmꢁ1
4a
7
354 (54000)
498 (13200)
363a
353 (52000)
483 (13000)
360a
351 (52600)
488 (13000)
358a
511a
503a
502a
a
Data taken from Ref. [13a] (values of emax are not given).
3. Experimental
4. X-ray diffraction measurements
All reactions were carried out under argon. The solvents were
purified according to standard procedures. Chromatographic sepa-
ration was performed on Silica gel Merck 60 (230–400 mesh
ASTM). Complexes 2a–2c were synthesized as previously described
[6]. Labeled (15N)-3a was synthesized from (15N)-1, obtained using
The crystals of 3c suitable for X-ray diffraction study was grown
from layered dichloromethane–pentane. The crystal was mounted
on a glass fiber and then flash-frozen to 100 K (Oxford Cryosystem-
Cryostream Cooler). Preliminary examination and intensities data
(
15N)-ethoxycarbonylisothiocyanate (prepared from KSC15N and
collections were carried out on a Kuma KM4CCD
j-axis diffractom-
eter with graphite-monochromated Mo K radiation [16]. The data
a
ClCOOEt) according to the published procedure [15]. NMR spectra
were recorded in CDCl3 on VARIAN GEMINI 200BB (200 MHz for
1H) spectrometer and referenced to internal TMS. IR spectra were
recorded on a FT-IR NEXUS (Thermo Nicolet) spectrometer.
were corrected for Lorentz, polarization and absorption effects. The
structures were solved by direct methods and refined by the full-
matrix least-squares method on all F2 data using the SHELXTL soft-
ware [17]. Carbon bonded hydrogen atoms were included in calcu-
lated positions and refined in the riding mode using SHELXTL default
3.1. Synthesis of 3a–3c
Solution of 2a–2c (0.25 mmol) in ethanol (5 ml) containing so-
dium ethoxide (0.5 mmol) was stirred 5 min at r.t. and acidified
with diluted aqueous HCl. The red precipitate was filtered off,
washed with cold aqueous ethanol and dried in vacuo.
Table 5
The crystal and structure refinement data for 3c
Formula
M
C16H15FeNO3S
357.20
Spectroscopic and analytical data: 3a. 1H NMR (200 MHz,
C5D5N): d 4.19 (s, 5H, Cp), 4.47 (s, 2H, Cp), 5.06 (s, 2H, Cp), 8.15
(d, J = 8.7 Hz, 2H, Ar), 8.30 (d, J = 8.5 Hz, 2H, Ar). 13C NMR
(50 MHz, C5D5N): d 166.6(SCN), 162.8 (COH), 141.0 (Ar), 128.5
(Ar), 125.7 (Ar), 124.5 (Ar), 104.3 (CAr), 78.6 (Cp), 71.1 (Cp), 70.9
(Cp), 68.2 (Cp). IR (KBr, cmꢁ1): 3442 (OH), 1507, 1331 (NO2), MS
(EI): 406 (M+), HRMS: Found: 406.007454, Calc. for C19H14SFeN2O3:
406.0074536. 3b. 1H NMR (200 MHz, C5D5N): d 4.17 (s, 5H, Cp),
4.44 (s, 2H, Cp), 5.03 (s, 2H, Cp), 7.73 (d, J = 8.5 Hz, 2H, Ar), 8.07
(d, J = 8.5 Hz, 2H, Ar). 13C NMR (50 MHz, C5D5N): d 164.9 (SCN),
161.3 (COH), 138.1 (Ar), 132.2 (Ar), 125.6 (Ar), 119.4 (Ar), 107.1
(CN), 103.9 (CAr), 78.6 (Cp), 71.1 (Cp), 70.9 (Cp), 68.2 (Cp). Anal.
Calc. for C20H14SFeN2O: C, 62.19, H, 3.65, N, 7.25, S, 8.30. Found:
C, 62.04, H, 3.75, N, 7.68, S, 8.19%. 3c 1H NMR (200 MHz, CDCl3):
d 1.38 (t, J = 7.1 Hz, 3H, CH2CH3), 4.15 (s, 5H, Cp), 4.36 (q,
J = 7.1 Hz, 2H, CH2CH3), 4.50 (t, J = 1.7 Hz, 2H, Cp), 4.92 (t,
J = 1.7 Hz, 2H, Cp). 13C NMR (50 MHz, CDCl3): d 173.4 (CO), 169.9
(SCN), 165.8 (COH), 94.0 (CCO), 71.3 (Cp), 70.6 (Cp), 69.8 (Cp),
68.3 (Cp), 61.4 (CH2), 14.3 (CH3) IR (CHCl3, cmꢁ1): 3432 (OH),
1659 (CO). Anal. Calc. for C16H15SFeNO3: C, 53.80, H, 4.23, N,
3.92, S, 8.98. Found: C, 53.67, H, 4.29, N, 3.72, S, 9.05%.
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
triclinic
P1
7.822(5)
10.231(5)
10.602(5)
64.64(1)
76.94(1)
71.88(1)
724.4(7)
2
1.638
1.196
100(2)
0.71073
ꢀ
b
c
V (Åꢁ3
)
Z
Dx (gcmꢁ3
)
l
(mmꢁ1
)
T (K)
k (Å)
Index ranges
Number of data collected
Number of unique data
Rint
ꢁ9 6 h 6 7, ꢁ12 6 k 6 11, ꢁ12 6 l 6 12
7939
2547
0.041
2516
204
0.0719
0.1134
ꢁ0.681
0.408
Number of I > 2
Number of parameters
R1 [I > 2 (I)]
wR2 (all data)
r(I) data
r
D
D
qmin (e Åꢁ3
qmax (e Åꢁ3
)
)

2986
A. Wrona et al. / Journal of Organometallic Chemistry 693 (2008) 2982–2986
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The principle of EFISH technique is described elsewhere [18,19].
In order to avoid the reabsorption of the generated second har-
monics the data were recorded using the 1907 nm, 10 ns incident
laser pulses. The compound was dissolved in chloroform at various
concentrations (0–5 mM). The centrosymmetry of the solution was
broken by dipolar orientation of the chromophores with a high
voltage pulse (ꢃ5 kV on 2 mm during 5
ls) Calibration of the cell
was made by monitoring the second harmonic generation by a ser-
ies of solutions of 2-methyl-4-nitroaniline (
l
b = 71 ꢀ 10ꢁ48 esu).
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Supplementary material
CCDC 668118 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.ccdc.ca-
m.ac.uk/data_request/cif.
Acknowledgment
(b) J.C. Calabrese, L.-T. Cheng, J.C. Green, S.R. Marder, W. Tam, J. Am. Chem.
Soc. 113 (1991) 7227.
The financial support from the Polish Ministry of Science and
Higher Education (Grant PBZ-KBN-118/T09/2004) is gratefully
acknowledged.
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