Synthesis of two new thioesters bearing ferrocene: Vibrational characterization and ab initio calculations. X-ray crystal structure of S-(2-methoxyphenyl)ferrocenecarbothioate

Article abstract of DOI:10.1016/j.poly.2009.11.006

Structural and conformational properties of S-benzyl ferrocenecarbothioate (I) and S-(2-methoxyphenyl) ferrocenecarbothioate (II) are analyzed using data obtained from X-ray diffraction, vibrational data and theoretical calculations. According to chemical quantum calculations, the synperiplanar and antiperiplanar forms are found as the first and second more stable conformations, respectively, for the title compounds. The geometric parameters and normal modes of vibration were calculated using a density functional theory method (B3LYP) and the 6-31+G** basis set for all atoms except for iron. For this atom the calculations were carried out with the Lanl2dz basis set. The calculated parameters are in good agreement with the corresponding X-ray diffraction values. The combined experimental and theoretical approach allows a consistent assignment for most of the fundamental modes.

Full text of DOI:10.1016/j.poly.2009.11.006

Polyhedron 29 (2010) 827–832
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Polyhedron
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Synthesis of two new thioesters bearing ferrocene: Vibrational
characterization and ab initio calculations. X-ray crystal structure
of S-(2-methoxyphenyl)ferrocenecarbothioate
Isabel C. Henao Castañeda a,d,1, Carlos O. Della Védova a,b, Oscar E. Piro c, Nils Metzler-Nolte e, Jorge L. Jios a,
*
a Laboratorio de Servicios a la Industria y al Sistema Científico (UNLP-CIC-CONICET), Departamento de Química, Facultad de Ciencias Exactas,
Universidad Nacional de La Plata, 47 esq. 115, 1900 La Plata, Argentina
b CEQUINOR (UNLP-CONICET), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 esq. 115, 1900 La Plata, Argentina
c Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata and Institute IFLP (CONICET, CCT-La Plata), C.C. 67, 1900 La Plata, Argentina
d Departamento de Farmacia, Facultad de Química Farmacéutica, Universidad de Antioquia, calle 67 No Medellín, Colombia
e Lehrstuhl für Anorganische Chemie I, Bioanorganische Chemie, Fakultät für Chemie und Biochemie, Ruhr-Universität Bochum, Universitätsstrasse150, D-44801 Bochum, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Structural and conformational properties of S-benzyl ferrocenecarbothioate (I) and S-(2-methoxyphenyl)
ferrocenecarbothioate (II) are analyzed using data obtained from X-ray diffraction, vibrational data and
theoretical calculations. According to chemical quantum calculations, the synperiplanar and antiperipla-
nar forms are found as the first and second more stable conformations, respectively, for the title com-
pounds. The geometric parameters and normal modes of vibration were calculated using a density
functional theory method (B3LYP) and the 6-31+G** basis set for all atoms except for iron. For this atom
the calculations were carried out with the Lanl2dz basis set. The calculated parameters are in good agree-
ment with the corresponding X-ray diffraction values. The combined experimental and theoretical
approach allows a consistent assignment for most of the fundamental modes.
Received 18 August 2009
Accepted 10 November 2009
Available online 13 November 2009
Keywords:
Metallocenes
Ferrocenecarbothioates
X-ray single crystal analysis
Vibrational analysis
Conformation analysis
Density functional calculations
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
cules [6,7]. Beside, some substances containing the –C(O)–S– moi-
ety such as acetiamine are used as vitamin-B1 source [8]. Antiviral
In a previous paper we reported the vibrational and conforma-
tional analysis of aromatic thioester compounds [1]. In anticipation
of a subsequent structure–activity relationship study and with the
aim to obtain a deeper and general insight on the conformational
and vibrational properties of thiol esters compounds of the type
X–C(O)S–Y, we report in this work the spectroscopic and structural
study of two new and close related compounds, S-benzyl ferro-
cenecarbothioate (I) and S-(2-methoxyphenyl) ferrocenecarbothio-
ate (II) (see Fig. 1). Only a few examples of other closely related
ferrocenyl containing thiol esters have been described in the liter-
ature. Of these, the synthesis of the isomeric S-ferrocenemethyl
benzenecarbothioate [2] and S-(p-methylphenyl)ferrocenecarbo-
thioate [3] compounds are worth mentioning. Our interest in the
conformational and vibrational properties of thioesters is also
due of their structural connection with biological system such as
acetyl coenzyme A, malonyl coenzyme A, the complement system
in different organisms [4,5] and several human endogenous mole-
activity against HIV-1 virus [9,10] and in vitro anti-cancer activity
[11–14] were found in some thioester compounds. Also, the inclu-
sion of the ferrocene moiety in the title compounds may be of
interest since ferrocene itself exhibits interesting properties as
anti-anemic or cytotoxic agent and it have been conjugated with
well-known medicines like antibiotic, anti-inflammatory, antineo-
plastic and antimalarial drugs [15].
Thiol esters (sulfenyl carbonyl compounds) generally present
planar conformation around the
the possibility of conformational equilibrium between synperipla-
nar ( (O–C–S–Y) = 0°) and antiperiplanar ( (O–C–S–Y) = 180°)
s (O–C–S–Y) dihedral angle, with
s
s
conformations. The synperiplanar form was found the most stable
conformation for both organic and inorganic molecules [16]. More-
over, in a previous work we have found that the +anticlinal confor-
mation is present as second most stable conformation [1].
In this paper we report the crystal structure of the S-benzyl fer-
rocenecarbothioate (I). Furthermore, the infrared and Raman spec-
tra of the title compounds were recorded. The conformational
energies, the geometric parameters and IR and Raman intensities
and vibrational frequencies were calculated by the B3LYP method
using the 6-31G** basis set for hydrogen, carbon, oxygen and sulfur
nuclei, and Lanl2dz for iron. The calculated spectra afford a basis
* Corresponding author. Fax: +54 221 4714527.
E-mail address: jljios@quimica.unlp.edu.ar (J.L. Jios).
Predoctoral fellow of the Consejo Nacional de Investigaciones Científicas
Técnicas, CONICET, Argentina.
1
y
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.11.006

828
I.C. Henao Castañeda et al. / Polyhedron 29 (2010) 827–832
numerically for absorption with PLATON [20]. The structure was
CH3
O
solved by direct and Fourier methods with SHELXS [21] and its
non-H atom refined by full-matrix least-squares with SHELXL [22].
The hydrogen atoms were positioned stereo-chemically and re-
fined with the riding model. Crystal data and structure refinement
parameters are summarized in Table 1.
TB
S
S
Fe
Fe
TP
O
O
I
II
The infrared spectra were recorded in KBr pellets in the range of
4000 and 400 cmÀ1 on a Thermo-Nicolet IR200 FT-IR spectrometer
(2 cmÀ1 resolution). The Raman spectra were measured using a FT
Bruker IFS85 spectrometer (spectral resolution 4 cmÀ1) between
3500 and 150 cmÀ1. The 1064-nm radiation line of an Nd/YAG laser
has been used for excitation. The samples were handled in Pyrex
capillaries at room temperature.
Quantum chemical calculations were carried out with GAUSSIAN
03 [23] program package, implemented on a personal computer.
The geometric structures for the more stable conformers were sub-
sequently calculated using the B3LYP method with 6-31G** and
Lanl2dz basis set. The same method was used to determine the fre-
quencies of the normal modes of vibration. Assignment of vibra-
tional modes was obtained by visual inspection of displacement
vectors. The calculations have been performed for molecules in
vacuum and therefore environmental effects were not considered.
Fig. 1. Structure of the studied compounds and labeling of the phenyl rings.
for the assignments of the experimental infrared and Raman bands.
The comparison between theoretical and experimental parameters
assists in the determination of intra- or inter-molecular interac-
tions of the free molecules or in the packed molecules,
respectively.
2. Experimental
S-benzyl- and S-(2-methoxyphenyl)ferrocenecarbothioate were
synthesized as follows: ferrocenoyl chloride [17] (1.15 g, 5 mmol)
was dissolved in dry pyridine (1 ml) and stirred mechanically at
20 °C. Then 6 mmol of S-benzyl- or S-(2-methoxyphenyl) hydrosul-
fide were added and the reaction mixture was kept at 20–22 °C
with stirring under Ar for 2 h. The product was treated with dichlo-
romethane, the organic layer washed with HCl 1 M, filtered
through magnesium sulfate anhydrous and dried in vacuum. The
product was recrystallized from petroleum ether (fraction 40–60).
The 1H (250.13 MHz) and 13C (62.98 MHz) NMR spectra of com-
pound I and II were measured at 298 K on a Bruker AC 250 spec-
trometer. The compounds were dissolved in CDCl3. Chemical
shifts, d, are given in ppm relative to TMS (d = 0 ppm) and are ref-
erenced by using the residual undeuterated solvent signal. Cou-
pling constants, J, are reported in Hz, multiplicities being marked
as: singlet (s), broad singlet (br.s), doublet (d), double double dou-
blet (ddd), triplet (t), double triplet (dt) or multiplet (m).
3. Results and discussion
3.1. Synthesis and NMR characterization
3.1.1. S-benzyl ferrocenecarbothioate (I)
Orange–red solid; yield 85%; m.p. 76–77 °C; 1H NMR (CDCl3,
250 MHz, 25 °C): d = 7.25–7.23 (m, 5H, C6H5), 4.85 (t, J = 2 Hz, 2H,
H21, H24), 4.47 (t, J = 2 Hz, 2H, H22, H23), 4.24 (s, 2H, CH2), 4.15 (s,
5H, C5H5) ppm; 13C RMN (CDCl3, 62.98 MHz, 25 °C): d = 193.0
(C@O), 128.9 (C3, C5), 128.5 (C2, C6), 127.1 (C4), 123.9 (C1), 79.0
(C25), 71.8 (C21, C24), 70.5 (C5H5), 68.9 (C22, C23), 32.7 (CH2) ppm.
Single crystals of I suitable for X-ray structural analysis were
obtained by slow evaporation from an acetonitrile solution. Dif-
fraction data were collected on an Enraf–Nonius CAD4 equipment
3.1.2. S-(2-methoxyphenyl) ferrocenecarbothioate (II)
Orange–red solid, yield 87%; m.p. 125.0–126.0 °C; 1H NMR
(CDCl3, 250 MHz, 25 °C): d = 7.47 (dd, J = 7.5 and 1.5 Hz, 1H, H6),
7.43 (ddd, J = 8, 8 and 2 Hz, 1H, H4), 7.02 (dt, J = 8 and 1 Hz, 1H,
H5), 7.00 (br.d, J = 8 Hz, 1H, H3), 4.94 (t, J = 2 Hz, 2H, H21, H24),
4.50 (t, J = 2 Hz, 2H, H22, H23), 4.32 (s, 5H, C5H5), 3.88 (s, 3H, CH3)
ppm; 13C RMN (CDCl3, 62.98 MHz, 25 °C): d = 190.7 (C@O), 159.7
(C2), 137.4 (C6), 131.5 (C4), 121.0 (C5), 115.8 (C1), 111.4 (C3), 78.9
(C25), 71.8 (C21, C24), 70.7 (C5H5), 69.1 (C22, C23), 55.8 (CH3) ppm.
(graphite monochromate Cu Ka radiation, k = 1.54184 Å) with EX-
PRESS [18] and reduced with XCAD4 [19]. The data were corrected
Table 1
Crystal data and structure refinement results for C18H16FeOS (I).
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C18H16FeOS
336.22
296(2)
3.2. Crystal structure analysis
triclinic
ꢀ
P1
The S-benzyl ferrocenecarbothioate (I) belongs to a series of
compounds with the general formula X–C(O)S–Y. It presents syn-
periplanar conformation around the dihedral angle of the sulfenyl
carbonyl moiety –C(O)–S–. A value of 0° would be expected for the
5.986(1)
b (Å)
9.947(1)
c (Å)
13.268(1)
a
(°)
83.813(7)
b (°)
89.02(1)
dihedral angle
s (O–C–S–Y) according to the reported study on the
c
(°)
75.11(1)
759.0(2)
2, 1.471
9.197
Volume (Å3)
conformational transferability of sulfenyl carbonyl compounds
[24]. In this work, a marked deviation of 14.5° from the planarity
Z, calculated density (Mg/m3)
Absorption coefficient (mmÀ1
F(0 0 0)
)
was found for the corresponding dihedral angle
(see Table 2 and Fig. 2). This value is also larger than experimental
data found for the dihedral angle (O–C–S–C) in similar molecules.
s (O–C8–S–C7)
348
Crystal size (mm)
h Range data collection (°)
Index ranges
Reflections collected/unique
Observed reflections [I > r(I)]
0.28 Â 0.20 Â 0.08
s
3.35–67.91
0 ꢀ h ꢀ 6, À11 ꢀ k ꢀ 11, À15 ꢀ l ꢀ 15
2959/2672 [R(int) = 0.0512]
2294
Values of 4.89–5.40°, 4.5°, and 2.0° [25], 1.43° [26] and 0.6–3.7°
[27] were reported for the syn form of thioester compounds. This
deviation is attributed to the packing effect, since computational
study showed a planarity around the sulfenyl carbonyl function
for the free molecule (see below). Such packing arrangement, al-
lows a short intra-molecular distance of 2.35 Å between the car-
bonyl oxygen atom and the hydrogen H7b bonded to carbon C7
(see Fig. 2). This hydrogen atom and the atoms of the sulfenyl
Refinement method
Full-matrix least-squares on F2
2672/0/191
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.069
Final R-index [I > 2
r
(I)]e
R1 = 0.0572, wR2 = 0.1446
R1 = 0.0707, wR2 = 0.1612
0.759 and À0.598
R indices (all data)
Largest peak and hole (e AÀ3
)

I.C. Henao Castañeda et al. / Polyhedron 29 (2010) 827–832
829
Table 2
Selecteda homologous experimental (X-ray diffraction) and calculated (B3LYP/6-31G** and Lanl2dz) intra-molecular bond distances (Å) and angles (°) of S-benzyl
ferrocenecarbothioate (I) and S-(2-methoxyphenyl) ferrocenecarbothioate (II).
I
II
I
II
Experimental
Calculated
Calculated
Experimental
Calculated
Calculated
Bond distances (Å)
C(1)–C(6)
C(1)–C(2)
C(1)–C(7)
C(1)–S
C(7)–S
C(8)–O
C(8)–S
1.372(9)
1.375(8)
1.493(7)
1.40
1.40
1.51
1.40
1.41
C(8)–C(25)
C(21)–C(22)
C(21)–C(25)
C(22)–C(23)
C(23)–C(24)
C(24)–C(25)
1.462(6)
1.408(7)
1.418(6)
1.411(7)
1.417(7)
1.427(7)
1.47
1.42
1.44
1.43
1.42
1.44
1.48
1.42
1.44
1.43
1.42
1.44
1.78
1.825(5)
1.204(6)
1.768(5)
1.85
1.22
1.81
1.21
1.83
Bond angles
C(6)–C(1)–C(2)
C(6)–C(1)–C(7)
C(2)–C(1)–C(7)
O–C(8)–C(25)
C(22)–C(21)–C(25)
C(21)–C(22)–C(23)
C(22)–C(23)–C(24)
C(23)–C(24)–C(25)
C(21)–C(25)–C(24)
C(8)–C(25)–Fe
117.8(6)
120.6(6)
121.6(5)
126.4(5)
108.1(4)
108.5(4)
107.9(4)
107.8(4)
107.6(4)
120.5(3)
118.81
120.72
120.47
121.14
107.89
108.29
108.35
107.72
107.75
122.57
119.60
C(8)–S–C(7)
C(8)–S–C(1)
C(6)–C(1)–S
C(2)–C(1)–S
C(1)–C(7)–S
O–C(8)–S
C(25)–C(8)–S
C(21)–C(25)–C(8)
C(24)–C(25)–C(8)
98.5(3)
99.38
101.04
119.29
121.04
123.62
107.93
108.25
108.32
107.77
107.73
123.57
112.1(4)
119.4(4)
114.1(4)
122.8(4)
129.2(4)
113.97
122.29
114.56
123.11
129.04
122.64
113.73
122.99
129.23
Torsion angles
C(1)–C(7)–S–C(8)
C(1)–S–C(8)–C(25)
C(2)–C(1)–C(7)–S
C(2)–C(1)–S–C(8)
C(6)–C(1)–S––C(8)
C(3)–C(2)–C(1)–C(7)
C(3)–C(2)–C(1)–S
C(5)–C(6)–C(1)–C(7)
C(5)–C(6)–C(1)–S
C(6)–C(1)–C(7)–S
80.6
90.85
S–C(8)–C(25)–C(24)
O–C(8)–C(25)–C(21)
O–C(8)–C(25)–C(24)
C(8)–C(25)–C(24)–Fe
C(8)–C(25)–Fe–C(24)
C(8)–C(25)–C(21)–Fe
C(7)–S–C(8)–O
C(1)–S––C(8)–O
C(7)–S–C(8)–C(25)
S–C(8)–C(25)–C(21)
1.5
À7.1
4.67
À0.44
4.67
0.85
À176.34
117.50
À124.45
À117.71
179.33
À105.3
À90.15
À178.4
113.1
À124.1
À113.9
14.5
À176.22
116.17
À124.18
À116.58
5.63
À68.93
113.91
178.8
À177.2
73.4
179.72
À179.71
89.80
À177.84
0.33
177.21
À165.4
À172.25
À179.55
172.9
À178.15
a
A complete list of the data in Table 2 is included as Supplementary data.
from 121.7 to 122.6 and 99.8 to 100.6, respectively. The required
geometric arrangement for this attractive intra-molecular effect
force C7 to deviate from planarity. Similar interaction is not possi-
ble in the previously reported aromatic thioesters of the type X–
C(O)–S–Ar in which the dihedral angle of the O@C–S–C moiety ap-
proach to zero.
The bond distances around the sulfenyl carbonyl moiety in the
general structure X–C(O)–S–Y deserves further analysis. The dis-
tances C8–S and C8–O are 1.77 Å and 1.20 Å, respectively, and
are in agreement with the corresponding bond distances reported
in the literature: C–S (1.77–1.79 Å) and C@O (1.18–1.21 Å). How-
ever, the bond distances X–C (C8–C25) and S–Y (S–C7) are 1.46 Å
and 1.83 Å, respectively. Values reported in the literature are
slightly longer for the first bond (X–C: 1.49–1.50 Å); and markedly
shorter for the last bond (S–Y: 1.76–1.78 Å). In the previously re-
ported structures, the carbon of the S–Y bond belongs to a sp2-
hybridized atom, whereas in the title compound, the sp3-hybrid-
ized C7 enables as expected, a lengthening of the S–Y bond.
Fig. 2. Molecular diagram of S-benzyl ferrocenecarbothioate (I), showing the
labeling of the non-H atoms, except for H7b, and their displacement ellipsoids at
the 50% probability level.
carbonyl moiety, –S–C@O, are all involved in a plane that enable a
hydrogen bond interaction in solid state. The strength of this inter-
action could be classified between weak and moderate taking into
account the short interatomic HÁÁÁO distance mentioned above.
Moreover, the calculated bond angles O–C8–S and C8–S–C7 for
the free molecule (122.3 and 99.4, respectively) are larger than
the experimental ones (119.4 and 98.5, respectively. See Table 2).
The decrease of these angles in solid state is consistent with a more
effective H bond interaction. Further evidence can be found by
comparing the bond angles for close related compounds in which
this hydrogen bond was not possible or not detected. The O–C8–
S and C8–S–C7 bond angles in these compounds are larger, ranging
3.3. Computational study
The experimental and calculated geometric parameters for
compounds I and II are shown together in Table 2 to facilitate
the comparison. The potential energy curves around the sulfenyl-
carbonyl moiety were calculated for the dihedral angles
s O–C8–
S–C7 and O1–C8–S–C1 for compounds I and II, respectively and
s
are depicted in Fig. 3. These curves show two minima being the
synperiplanar rotamer the conformer of lowest energy, in concor-
dance with most of the thioester compounds. In contrast with
our previous results the second minimum is located in the anti-
periplanar instead of +anticlinal conformation. The antiperiplanar

830
I.C. Henao Castañeda et al. / Polyhedron 29 (2010) 827–832
conformer is higher in energy with differences of 9 Kcal/mol and
6 Kcal/mol for compounds I and II, respectively.
3.4. Vibrational analysis
Compounds I and II present 105 and 108 normal modes of
vibration, respectively. In Table 3 are shown the calculated and ob-
served (IR and Raman) vibration mode wavenumbers and intensi-
ties. A tentative assignment of the experimental spectra is also
proposed. For convenience in the assignments description of Ta-
ble 3, the phenyl rings of the compounds I and II are symbolized
as TB and TP, respectively (see Fig. 1). The patterns of the ring
modes TP(k) and TB(k) for k = 1–34 are included as Supplementary
data.
The calculated and observed wavenumbers are in good agree-
ment and is illustrated in Fig. 4 by comparing the simulated and
the experimental IR spectra and the experimental Raman obtained
for compound I.
Fundamental bands corresponding to C@O stretching mode are
at 1626 cmÀ1 and 1670 cmÀ1 for compounds I and II, respectively.
The region of the stretching frequency in compound II is similar to
those reported for the S-(2-methoxyphenyl) 4-substituted-ben-
zenecarbothioates (1678–1671 cmÀ1). The change in the hybrid-
ization of the carbon atom linked to the sulfur atom in the S–Y
portion expressed by the lengthening of this bond seems to be
responsible for the red shift in compound I with respect to both
Fig. 3. Potential energy curve as a function of the torsion angle (s) of the O–C8–S–
C7 (compound I) and O–C8–S–C1 (compound II), calculated with the HF/6-31G level
of approximation.
Table 3
Selected data of calculated (B3LYP/6-31+G**) and experimental (IR and Raman) wavenumbers (cmÀ1), relative intensities and tentative assignments for I and IIa,b
.
Calculated
I
Calculated
II
Assignmentc
IR
Raman
IR
Raman
1746 vs,s
1488 w,w
1653 vs
1444 m
1651 m
1443 w
1779 vs,s
1669 vs
1674 m
m
m
m
m
(C@O)
1488 w,m
1317 vs,vw
1275 vs,m
1248 vw,vw
C8–C25
C2–O2
C8–C25
1276 m
1243 vs
ovl
1276 vw
1243 m
1214 vw
1274 vs,vw
1247 vw,vw
1229 vw,vw
1136 vw,vw
sh
1200 w
1105 w
1219 w
1204 w
1105 s
d O–C8–C25
C7–C1
ring breathing (CP + SCP)
(C1–S)
m
1137 vw,w
1061 vw,vw
965 w,vw
832 w,vw
823 vs,w
1106 vw
1106 s
m
969 w,vw
828 w,vw
830 w,vw
822 vw,vw
786 vw,vw
948 m
812 vs
822 sh
952 w
822 w
773 w
686 w
574 w
944 w
ovl
818 vs
944 vw
ovl
d i.p. (S–C8–C25)
d o.o.p. CH (CP+SCP) i.ph.
m
m
d i.p. (S–C7–C1)
m
m
d i.p. (C1–S–C8–C25)
d i.p. (C7–S–C8–C25)
d o.o.p. (S–C8–C25–C24)
d S–C1–C6
S–C8
(C7–C1)
767 m
686 m
573 m
700 vw,vw
598 vw,vw
696 vw
599 vw
(S–C1)
S–C7)
680 vw,w
599 vw
583 vw,vw
557 vw,vw
557 vw,vw
479 vw,vw
464 w,vw
484 w
454 vw
489 vw
454 vw
459 w,vw
477 s
d CP–Fe–SCP
470 vw,vw
448 vw,vw
423 vw,vw
365 vw,vw
354 vw,vw
340 vw,vw
311 vw,vw
278 vw,vw
264 vw,vw
207 vw,vw
180 vw,vw
166 vw,vw
131 vw,vw
482 w
438 w
397 w
335 s
453 vw,vw
448 vw,vw
415 vw,vw
355 vw,vw
d CP–Fe–SCP
m as CP–Fe–SCP
d as (O1@C8–S)
Ring tilt CP–SCP
d o.o.p. (C1–C7–S)
ring tilt CP–SCP
d (C2–C1–C7–S)
m s (CP-Fe–SCP)
d C21–C25–C8–O)
ring tilt CP–SCP
s (O1–C8–S–C)
ovl
397 vw
325 vs
340 vw,vw
ovl
304 vs
277 w
260 vw
209 w
179 w
164 w
281 vw,vw
266 vw,vw
202 v
200 vw,vw
173 vw,vw
275 vw
200 vw
ovl
167 vw
ring tilt CP–SCP
d (C25–C24–C8–S)
a
A complete list of the data in this Table is included as Supplementary data.
Intensities have been classified semi-quantitatively in terms of very strong (vs), strong (s), medium (m), weak (w) and very weak (vw). For the calculated band wave
b
numbers, the first and the second intensity symbols are separated by points and refer to IR and Raman intensity, respectively. Shoulder and overlapping bands have been
denoted by (sh) and (ovl), respectively.
c
d, deformation; m, stretching; s, torsion; q, rocking; s, symmetric; as, antisymmetric; wag, wagging; i.p., in plane; o.o.p., out of plane; CP, cyclopentadienyl ring; SCP,
substituted cyclopentadienyl ring.

I.C. Henao Castañeda et al. / Polyhedron 29 (2010) 827–832
831
S (compound II) stretching vibrations were assigned to the bands
at 686 cmÀ1 (IR and Raman) for compound I and 692 cmÀ1 (IR)
and 696 cmÀ1 (Raman) for compound II. The S–C8–C25 antisym-
metric stretching was assigned to the bands at 948 cmÀ1 (IR) and
953 cmÀ1 (Raman) for compound I and at 944 cmÀ1 (IR and Ra-
man) for compound II.
200
(a)
The bands found at 599 cmÀ1 in the IR and Raman spectra of
compound I were assigned to the C7–S–C8–C25 in plane deforma-
tion mode, while the corresponding band in compound II (C1–S–
C8–C25) appears at lower frequencies: 573 cmÀ1 (IR) and
574 cmÀ1 (Raman). The Raman bands at 397 cmÀ1 in both com-
pounds were assigned to the O1–C8–S antisymmetric deformation
mode.
0
Most of the vibrational modes corresponding to the ferrocene
system are active in the Raman spectra. The ring breathing normal
mode was assigned to the bands at 1105 cmÀ1 (IR) and 1106 cmÀ1
(Raman) for compound I and 1106 cmÀ1 (IR and Raman) for com-
pound II. Strong and very strong Raman bands at 335 cmÀ1 and
325 cmÀ1 for compounds I and II, respectively, were assigned to
the ring tilt of the ferrocene system. Weak Raman bands at 209
and 164 cmÀ1 for compound I and 200 and 167 cmÀ1 for com-
pound II were also assigned to the same mode. The analysis of
the cyclopentadienyl–Fe–cyclopentadienyl stretching modes de-
serves further analysis. The bands at 277 and 275 cmÀ1 in com-
pounds I and II, respectively were assigned to the symmetric
stretching mode and the band at 438 cmÀ1 found in the Raman
spectra of compound I was assigned to the antisymmetric mode.
The corresponding band for compound II is overlapping.
(b)
0.6
0.4
0.2
0.0
4000 3500 3000 2500 2000 1500 1000
500
wavenumbers cm-1
Fig. 4. Calculated (a) and experimental (b) IR spectra of S-benzyl ferrocenecarbo-
thioate (I).
4. Conclusions
Following with our studies on conformational and structural
properties around the –C(O)–S– moiety in thioester compounds
we have arrived to a good agreement with the evidence from
experimental and theoretical data. The predominant syn conforma-
tion is now extended to two new compounds I and II. The crystal
structure of the S-benzyl ferrocenothioate (I) shows a synperipla-
nar conformation around the sulfenyl carbonyl moiety with a dihe-
compound II and others reported S-aryl benzenecarbothioates. In
the last class of compounds, the 2-methoxyphenyl group bonded
to the sulfur atom generates new resonance forms as is depicted
in Fig. 5, such as (iv) that preclude the resonance form (iii), rein-
force the weight of the form (i) and consequently produce a blue
shift frequency. Furthermore, the form (iv) can explain the short-
ening of the S–Y bond in S-arylbenzenecarbothioates respect to
the compound I. A complementary explanation regarding to the
lengthening of S–Y bond in compound I was already stated in the
crystal structure analysis.
Vibrational bands around the sulfenyl carbonyl group constitute
the most interesting bands to be analyzed here. The bands found at
698 cmÀ1 (IR and Raman) in compound I and 692 cmÀ1 (IR) and
688 cmÀ1 (Raman) in compound II were assigned to the out-of-
plane deformation of the carbonyl group. This mode results shifted
to higher frequencies in comparison with the corresponding vibra-
tion of S-(2-methoxyphenyl) 4-substituted-benzenecarbothioates
(from 636 to 642 cmÀ1). The ferrocenyl moiety exerts a red shift ef-
fect of about 50 cmÀ1. The most intense IR band for compound (II)
at 1243 cmÀ1 was assigned to the C8–C25 stretching mode. For
compound (I) this normal mode was assigned to the bands at
1246 cm-1 (IR) and 1247 cm-1 (Raman). The S–C8 stretching band
shows a strong absorption at 822 and 818 cmÀ1 in the IR spectrum
of compound I and II, respectively. The C7–S (compound I) and C1–
dral angle
predicted planarity (
s
O–C–S–Y = 14.5°. This marked deviation from the
= 0°) is attributed to the establishment of a
s
new plane due to an intramolecular hydrogen bond interaction:
C@OÁ Á ÁH–C7.
Acknowledgments
The authors acknowledge the Consejo Nacional de Investigaci-
ones Científicas y Técnicas (CONICET), Comisión de Investigaciones
Científicas de la Provincia de Buenos Aires (CIC), Facultad de Cien-
cias Exactas (UNLP), Agencia Nacional de Promoción Científica y
Técnica (ANPCYT), Fundación Antorchas, Alexander von Humboldt
Foundation, DAAD (Deutscher Akademischer Austauschdienst,
Germany). ICHC specially acknowledges the CONICET for the doc-
toral scholarship to Latin-American students.
CODV specially acknowledges the DAAD, which generously
sponsors the DAAD Regional Program of Chemistry of the Republic
X
X
X
X
C+
O
S+
O
S
O
S+
O
S
OMe
OMe
OMe
OMe
-
i
ii
iii
iv
Fig. 5. Resonance forms in S-aryl thioesters.

832
I.C. Henao Castañeda et al. / Polyhedron 29 (2010) 827–832
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Appendix A. Supplementary data
CCDC 722639 contains the supplementary crystallographic data
for S-(2-methoxyphenyl)ferrocenecarbothioate. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
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033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
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