Synthesis, spectral characterization and electrochemical properties of (2-alkylthiobenzoyl)ferrocenes. Crystal structures of 2-methylthio, 2-ethylthio and 2-isopropylthio derivatives

Article abstract of DOI:10.1016/j.poly.2010.04.034

The one-pot synthesis of seven new (2-alkylthiobenzoyl)ferrocenes has been achieved by Friedel-Crafts acylation of ferrocene with acid chlorides generated in situ from the corresponding carboxylic acids and phosphorous trichloride. The obtained compounds

Full text of DOI:10.1016/j.poly.2010.04.034

Polyhedron 29 (2010) 2311–2317
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, spectral characterization and electrochemical properties
of (2-alkylthiobenzoyl)ferrocenes. Crystal structures of 2-methylthio, 2-ethylthio
and 2-isopropylthio derivatives
a
b
b
c
a,
-
*
´
´
´
´
´
Zoran Ratkovic , Sladana B. Novakovic , Goran A. Bogdanovic , Dejan Šegan , Rastko D. Vukicevic
a Department of Chemistry, Faculty of Science, University of Kragujevac, R. Domanovi´ca 12, 34000 Kragujevac, Republic of Serbia
b
ˇ
Vinca Institute of Nuclear Sciences, Laboratory of Theoretical Physics and Condensed Matter Physics, P.O. Box 522, 11001 Belgrade, Republic of Serbia
c Faculty of Chemistry, University of Belgrade, P.O. Box 158, 11001 Belgrade, Republic of Serbia
a r t i c l e i n f o
a b s t r a c t
Article history:
The one-pot synthesis of seven new (2-alkylthiobenzoyl)ferrocenes has been achieved by Friedel–Crafts
acylation of ferrocene with acid chlorides generated in situ from the corresponding carboxylic acids and
phosphorous trichloride. The obtained compounds were characterized by spectroscopic data (UV, IR, 1H
and 13C NMR), whereas their electrochemical properties have been investigated by cyclic voltammetry.
The single-crystal X-ray structure determinations for three of them are also reported. Each of the three
derivatives exhibits the intramolecular C–H. . .O interaction which involves the donor from the cyclo-
pentadienyl (Cp) ring and the carbonyl oxygen as acceptor. This interaction favors the coplanar arrange-
ment of the two moieties. The angles between the vectors coinciding the C–O bonds and the
corresponding Cp planes are all below 6.4°. Conventional hydrogen bonds do not exist in any of the
three crystal structures but some weak intermolecular interactions of the C–H. . .O, C–H. . .S and C–
Received 27 March 2010
Accepted 30 April 2010
Available online 23 May 2010
Keywords:
Ferrocene
2-Alkylthiobenzoic acids
(2-Alkylthiobenzoyl)ferrocenes
Cyclic voltammetry
Crystal structure
H. . .p types have been found and analyzed in detail. Different geometrical parameters for these crystal
C–H. . .p interactions
structures as well as for 22 similar ones extracted from Cambridge Structural Database (CSD) have been
compared and analyzed.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
The most frequently used method in functionalization of ferro-
cene is Friedel–Crafts acylation, discovered by Woodward at the
There is no other example among unnatural compounds that
has captured the attention of chemists so intensively as ferrocene
and its derivatives. It is the consequence of several unique features
of ferrocenes. First of all, ferrocene itself is a commercially avail-
able and relatively cheap compound which could be easily func-
tionalized to derivatives that are very appreciated for their
outstanding stability in both aqueous and non-aqueous media.
The iron core of ferrocenes is able to exist in both Fe2+ or Fe3+ mak-
ing them to possess very interesting redox properties. Ferrocenes
have applications in numerous fields, particularly in those such
as organic synthesis, catalysis, electrochemical, electronic absorp-
tion and nonlinear optical materials [1,2]. Although the earliest
attempts to apply ferrocene derivatives in medicine were discour-
aging [3,4], chemists did not abandon this idea, and nowadays
many ferrocene derivatives have been biologically evaluated
against certain diseases. These investigations have showed that
many ferrocenyl compounds display interesting cytotoxic, antitu-
mor, antimalarial, and antimicrobial activity [5–14].
early days of ferrocene [15]. The products of this reaction, the cor-
responding ferrocenyl ketones, are also known as the compounds
which are susceptible to many easily achievable transformations.
Their carbonyl group allows for introducing of heteroatoms like
nitrogen, sulfur or phosphorus in the form of a certain nucleophilic
functional group. It is particularly useful to introduce an additional
heteroatom in the same time when acylating ferrocene, using acyl
halides containing the corresponding functional groups. This
methodology is, however, limited by the fact that nucleophilic
functional groups form complexes with Lewis acids preventing
thus the necessary acylating complex formation. Several years
ago we improved above mentioned Woodward’s acylation of ferro-
cene and showed that both carboxylic acid chlorides and the Lewis
catalyst can be generated in situ, making, thus, the synthesis of
acylferrocenes much shorter [16–18]. Following this procedure
we recently prepared and characterized several acylferrocenes
containing sulfur in the side chain [19]. The present paper deals
with the continuation of these investigations, and we wish to re-
port herein on the synthesis of seven new (2-alkylthio)benzoylfer-
rocenes (1a–g, Fig. 1). The distance between the carbonyl group
and the sulfur atom in these bifunctional molecules makes them
* Corresponding author. Tel.: +381 34 300 268; fax: +381 34 335 040.
E-mail address: vuk@kg.ac.rs (R.D. Vukic´evic´).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.04.034

´
Z. Ratkovic et al. / Polyhedron 29 (2010) 2311–2317
2312
corresponding ketone. After evaporation of the solvent, remains
colored oil which solidified after standing to deep red–orange sol-
ids (except in the case of 1c).
2.2.1. (2-Methylthiobenzoyl)ferrocene (1a)
65%; m.p. 95–96 °C; red crystals; IR (KBr):
1674, 1562, 1463, 1412, 1317, 1272, 1255, 1062, 1046, 897, 743,
711, 694, 652 and 551 cm–1 1H NMR (200 MHz, CDCl3): d = 2.45
m = 3061, 2921, 2648,
;
(s, 3H), 4.29 (s, 5H), 4.56 (t, 2H, J = 1.78 Hz), 4.79 (t, 2H, J =
1.78 Hz,), 7.17 (m, 1H), 7.33–7.43 (m, 2H) and 7.59 ppm (m, 2H);
13C NMR (200 MHz, CDCl3): d = 16.3, 69.8, 71.2, 72.5, 78.6, 123.7,
126.4, 128.3, 130.4, 138.3, 138.6 and 199.5 ppm.
Fig. 1. (2-alkylthiobenzoyl)ferrocenes.
2.2.2. (2-Ethylthiobenzoyl)ferrocene (1b)
interesting for different synthetic purposes, particularly as a poten-
tial starting material for synthesis of bidentate sulfur containing
ligands.
The synthesis of ketones 1a–g has been achieved by introducing
at once both the carbonyl group and sulfur atom into the target
molecule. The obtained compounds are well characterized by spec-
tral data and cyclovoltammetric measurements, whereas single-
crystal X-ray structure determinations for three of them (1a, b,
and d) are also performed.
53%; m.p. 103–104 °C; red crystals; IR (KBr):
2922, 1642, 1582, 1444, 1374, 1294, 1255, 1041, 1030, 856, 756,
700, 694, 652 and 498 cmÀ1 1H NMR (200 MHz, CDCl3): d = 1.29,
m = 3092, 2967,
;
(t, 3H, J = 7.34 Hz), 2.94 (q, 2H, J = 7.34 Hz,), 4.29 (s, 5H), 4.55 (t,
2H, J = 1.93 Hz), 4.77 (t, 2H, J = 1.94 Hz), 7.17–7.42 (m, 3H), and
7.52–7.57 ppm (m, 1H); 13C NMR (200 MHz, CDCl3): d = 13.8,
27.7, 69.9, 71.1, 72.5, 78.8, 124.5, 128.2, 128.6, 130.1, 136.1,
140.4 and 199.9 ppm.
2.2.3. (2-Propylthiobenzoyl)ferrocene (1c)
2. Experimental
25%; red–orange oil; IR (KBr):
m = 3434, 3110, 2961, 2927, 1639,
1584, 1462, 1442, 1399, 1292, 1042, 855, 824, 747 and 488 cmÀ1
;
1H NMR (200 MHz, CDCl3): d = 0.99 (t, 3H, J = 7.3 Hz,), 1.66 (hx, 2H,
J = 7.3 Hz,), 2.89 (t, 2H, J = 7.3 Hz,), 4.29 (s, 5H), 4.55 (t, 2H, J = 2 Hz),
4.77 (t, 2H, J = 2 Hz), 7.2–7.24 (m, 1H), 7.38–7.42 (m, 2H) and 7.52–
7.56 ppm (m, 1H); 13C NMR (200 MHz, CDCl3): d = 13.5, 22.1, 35.7,
69.9, 71.1, 72.5, 78.9, 124.4, 128.2, 128.7, 130.1, 136.4, 140.4 and
199.9 ppm.
2.1. General
All chemicals were commercially available and used as re-
ceived, except that the solvents were purified by distillation. S-
Alkylthiosalicylic acids were synthesized by alkylation of thiosali-
cylic acid (Merck), following the procedure described elsewhere
[20]. Chromatographic separations were carried out using silica
gel 60 (Merck, 230–400 mesh ASTM), whereas silica gel 60 on Al
plates, layer thickness 0.2 mm (Merck), was used for TLC. IR spectra
were recorded on Perkin–Elmer Spectrum One FT-IR spectrometer
with a KBr disc. UV measurements were performed on a Perkin–El-
mer Lambda 35 double-beam UV–Vis spectrophotometer in CH2Cl2
as the solvent. NMR spectra were recorded on a Varian Gemini
(200 MHz) spectrometer, using CDCl3 as the solvent and TMS as
the internal standard. Chemical shifts are expressed in d (ppm).
Electrochemical measurements were performed by using a CH
Instruments (Austin, TX) potentiostat CHI760b Electrochemical
Workstation. A standard three-electrode cell (5 mL) equipped with
a platinum disk (d = 2 mm), a platinum wire and a silver wire im-
mersed in 0.1 M LiClO4 solution in CH3CN as the working, counter
and reference electrode, respectively.
2.2.4. (2-Isopropylthiobenzoyl)ferrocene (1d)
40%; m.p. 80–81 °C; red crystals; IR (KBr):
1642, 1584, 1462, 1442, 1375, 1292, 1106, 1041, 1003, 850, 824,
749, 704, 657 and 486 cmÀ1 1H NMR (200 MHz, CDCl3): d = 1.26
m = 3095, 2962, 2924,
;
(d, 6H, J = 6.7 Hz), 3.45 (h, 1H, J = 6.7 Hz), 4.29 (s, 5H), 4.54 (t,
2H, J = 1.97 Hz), 4.73 (t, 2H, J = 1.97 Hz) and 7.24–7.54 ppm (m,
4H); 13C NMR (200 MHz, CDCl3): d = 22.8, 37.8, 69.8, 71, 72.4,
78.9, 125.2, 127.8, 129.8, 131.1, 134.6, 142.0 and 200.2 ppm.
2.2.5. (2-Butylthiobenzoyl)ferrocene (1e)
26%; m.p. 65–66 °C; red–orange crystals; IR (KBr):
2928, 1639, 1584, 1463, 1442, 1375, 1292, 1106, 1041, 1003,
855, 824, 749, 703, 667 and 486 cmÀ1 1H NMR (200 MHz, CDCl3):
m = 2956,
;
d = 0.88 (t, 3H, J = 7.32 Hz), 1.37–1.71 (m, 4H), 2.91 (t, 2H,
J = 7.31 Hz), 4.29 (s, 5H), 4.55 (t, 2H, J = 1.95 Hz), 4.77 (t, 2H,
J = 1.95 Hz), 7.18–7.41 (m, 3H) and 7.51–7.55 ppm (m, 1H); 13C
NMR (200 MHz, CDCl3): d = 13.5, 21.9, 30.7, 33.2, 69.8, 71.1, 72.5,
78.8, 124.2, 128.1, 128.3, 130.1, 136.5, 140.0 and 199.8 ppm.
2.2. General procedure for the synthesis of compounds 1a–g
The solution of the corresponding carboxylic acid 3a–g
(1 mmol), ferrocene (186 mg, 1 mmol) and PCl3 (ꢀ0.1 mL, 1 mmol,)
in 50 mL of CH2Cl2 was stirred overnight at room temperature in a
two necked round-bottom bottle, supplied with a reflux condenser
protected from air moisture with the CaCl2 tube. Anhydrous AlCl3
(200 mg, 1.5 mmol) was added to this mixture which immediately
become dark-violet, and stirring was continued for additional 4 h.
The resulting mixture was then poured into a cold KOH solution
(50 mL, 1 mol/L). The red–orange organic layer was separated
whereas the aqueous one was extracted with an additional portion
of CH2Cl2 (30 mL). The collected organic layers were washed with
water, brine and water successively. After drying over anhydrous
Na2SO4, the solvent was evaporated, and the residue was purified
by column chromatography (SiO2/light petroleum, then toluene
or toluene/ethyl acetate 9:1). The first fraction (light yellow) was
unconsumed ferrocene and second one (orange or red) was the
2.2.6. (2-Cyclohexylthiobenzoyl)ferrocene (1f)
22%; m.p. 92 °C; red–orange crystals; IR (KBr):
1639, 1583, 1443, 1374, 1290, 1262, 1176, 1106, 1040, 998, 854,
822, 750, 702, 656 and 483 cmÀ1 1H NMR (200 MHz, CDCl3):
m = 2926, 2851,
;
d = 1.15–2.05 (m, 10H), 3.18 (m, 1H), 4.28 (s, 5H), 4.55 (t, 2H, J =
1.97 Hz), 4.72 (t, 2H, J = 1.97 Hz) and 7.24–7.53 ppm (m, 4H); 13C
NMR (200 MHz, CDCl3): d = 25.6, 26.0, 33.1, 46.4, 69.9, 71.1, 72.5,
79.1, 125.3, 127.9, 129.7, 131.3, 134.1, 142.3 and 200.4 ppm; Anal.
Calc. for C23H24FeOS (404.35): C, 68.32; H, 5.98; Fe, 13.81; O, 3.96;
S, 7.93. Found: C, 68.31; H, 5.97%.
2.2.7. (2-Benzylthiobenzoyl)ferrocene (1g)
20%; m.p. 118–119 °C; red–orange crystals; IR (KBr):
2852, 1636, 1583, 1494, 1441, 1374, 1292, 1176, 1106, 1041,
m = 2922,

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Z. Ratkovic et al. / Polyhedron 29 (2010) 2311–2317
1026, 854, 825, 748, 701, 656 and 484 cmÀ1
;
1H NMR (200 MHz,
of the materials for publication: PLATON [25], PARST [26] and ORTEPIII
[27].
CDCl3): d = 4.12 (s, 2H), 4.28 (s, 5H), 4.55 (t, 2H, J = 1.96 Hz), 4.75
(t, 2H, J = 1.97 Hz), 7.12–7.45 (m, 3H) and 7.53–7.58 ppm (m,
1H); 13C NMR (200 MHz, CDCl3): d = 38.9, 69.9, 71.1, 72.5, 78.8,
125.1, 127.1, 128.2, 128.4, 129, 129.8, 130.1, 135.6, 136.9, 140.7
and 199.9 ppm; Anal. Calc. for C24H20FeOS (412.32): C, 69.91; H,
4.89; Fe, 13.54; O, 3.88; S, 7.78. Found: C, 69.87; H, 4.93%.
3. Results and discussion
3.1. Synthesis
Present investigations we started by submitting ferrocene to the
reaction with an equimolar mixture of thiosalicylic (2-mercapto-
benzoic) acid (2) and phosphorus trichloride in the presence of alu-
minum trichloride. Encouraged by our earlier finding that salicylic
acid can be used in a one-pot synthesis of (2-hydroxybenzoyl)fer-
rocene [18,28], we expected to obtain (2-mercaptobenzoyl)ferro-
cene. However, the reaction failed to give the desired product,
and we decided to continue the investigations by S-alkylation of
acid 2 (Scheme 1), hoping that the alkylthio group will not hinder
the reaction, in contrast to the unprotected SH group. Applying the
known procedure [20], we obtained the corresponding S-alkylthio-
salicylic acids 3a–g and, then, submitted them to the reaction with
phosphorus trichloride. The obtained intermediate chlorides (4a–
g) have not been isolated and purified, but treated in situ with alu-
minum trichloride and ferrocene resulting in the corresponding
sulfur containing ferrocenyl ketones 1a–g (20–65%; Scheme 1).
2.3. X-ray data collection and structure refinement for compounds 1a,
1b and 1d
Crystal data and experimental details for the three ferrocene
derivatives are summarized in Table 1. The diffraction data were
collected on an Enraf–Nonius CAD4 diffractometer [21] by using
graphite-monochromated Mo K
a
(0.71073 Å) radiation at
293(2) K. The data were corrected for Lorentz and polarization ef-
fects [22]. Crystal structures were solved by direct methods with
the program SHELXS97 [23a] and refined on the F2 by full-matrix
least-square method with SHELXL97 [23b] both incorporated in
WINGX [24] program package.
All H atoms were placed at geometrically calculated positions
with the C–H distances fixed to 0.93 from Csp2 and 0.96, 0.97
and 0.98 Å from methyl, methylene and methine Csp3, respectively.
The corresponding isotropic displacement parameters of the
hydrogen atoms were equal to 1.2 Ueq and 1.5 Ueq of the parent
Csp2 and Csp3, respectively. The software used for the preparation
3.2. Spectral characterization
NMR and IR spectral data of the synthesized new compounds
1a–g clearly confirm their structures. Thus, the IR spectra of all
compounds contain the intensive bond at 1636–1642 cmÀ1, which
is attributed to the carbonyl group. On the other hand, in 1H NMR
spectra of all compounds three signals appear at the same position
– at 4.29 (s), 4.55 (t) and 4.80 (t) ppm. They correspond to the five
protons of unsubstituted cyclopentadienyl ring and two proton
pairs of monosubstituted cyclopentadienyl ring, respectively. All
these spectra also contain multiple signals at 7.17–7.60 ppm, cor-
responding to the four protons of an ortho-disubstituted benzene
ring. The multiplicity and the intensity of other signals appearing
in these spectra exactly depict the specific structures of the corre-
sponding compounds.
Table 1
Crystallographic data for 1a, 1b and 1d.
1a
1b
1d
Empirical formula
Formula weight
Color
T (K)
Crystal size (mm)
C
18H16FeOS
C19H18FeOS
350.26
deep red
293(2)
C20H20FeOS
363.26
deep red
293(2)
336.22
deep red
293(2)
0.25 Â 0.14 Â 0.33 Â 0.20 Â 0.28 Â 0.18 Â 0.12
0.10
monoclinic
P21
0.15
monoclinic
C2/c
Crystal system
Space group
Lattice constants
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
7.7062(13)
12.624(4)
8.063(2)
90.00
102.37(2)
90.00
766.2(3)
2
1.457
25.323(12)
7.767(5)
20.315(11)
90.00
124.56(4)
90.00
3291(3)
8
1.414
11.694(9)
10.274(3)
15.068(12)
90.00
105.18(5)
90.00
1741(14)
4
1.386
The common signals in all 13C NMR spectra belong to the car-
bons of unsubstituted cyclopentadienyl ring (at 70.0 ppm), two
methylene carbon pairs of monosubstituted cyclopentadienyl ring
(at 71.50 and 72.6 ppm), one quaternary carbon atom of the same
ring (at 78.80 ppm) and one carbonyl carbon (at 200 ppm). The sig-
nals of the phenyl carbons of all the compounds, however, differ
slightly but noticeably.
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
Dcalc
,
q
(g cmÀ3
)
h range for data
2.59–27.97
1.95–25.98
1.81–25.97
All synthesized compounds 1a–g in UV spectra exhibit absorp-
tion maximum at almost the same wave length (about 475 nm) as
it is showed by Fig. 2.
collection (°)
Absorption coefficient
1.115
1.042
0.987
(mmÀ1
)
F(0 0 0)
348
700
756
Reflections collected
Independent
reflections
1739
1623
5567
3031
3583
3451
3.3. Molecular geometry and intermolecular interactions in the crystal
structures of compounds 1a, 1b and 1d
Parameters
187
199
208
Goodness-of-fit (GOF)
R1 [I > 2r(I)]
0.985
0.0400
1.008
0.0371
0.938
0.0517
With the aim to compare the geometrical features of com-
pounds 1a, 1b and 1d (Fig. 3) to those of the similar structures,
Scheme 1. Synthesis of (2-alkylthiobenzoyl)ferrocenes 1a–g.

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Z. Ratkovic et al. / Polyhedron 29 (2010) 2311–2317
2314
Fig. 2. UV spectra of compounds 1a–1g in dichoromethane (1 Â 10À3 mol LÀ1).
the Cambridge Structural Database (CSD) [29] was used. We ex-
tracted 22 crystal structures [30–46] from CSD which comprise
at least one structural fragment (benzoylferrocene moiety) shown
in Fig. 4. The list of CSD refcodes and references of these 22 crystal
structures are given in Supplementary material (Table 1S).
The cyclopentadienyl rings in 1a, 1b and 1d adopt a nearly
eclipsed geometry. The values of the torsion angles C10–Cg1–
Cg2–C1 (which relate the substituted C10 and corresponding,
eclipsed C1 atoms through centroids of the Cp rings, Cg1 and
Cg2) are 2.9, 9.0 and 15.7° in 1a, 1b and 1d, respectively, indicating
an increasing deviation from the regular eclipsed conformation in
the same order. This is the major difference considering the geom-
etry of the ferrocene units in the three derivatives. The same C10–
Cg1–Cg2–C1 torsion angle was analyzed for 22 crystal structures
extracted from CSD. Distribution of the torsion angle values is gi-
ven in the Supplementary material (Fig. 1S) indicating the range
from 0 to 16° as the most frequent.
The C–C bonds within the Cp rings are consistent; it should be
noticed however, that in all three compounds the C–C bonds with-
in the substituted rings, Cp1 (average values: 1.418, 1.421 and
1.418 Å in 1a, 1b and 1d, respectively) are slightly longer than in
the unsubstituted rings, Cp2 (average values: 1.408, 1.392 and
1.400 Å in 1a, 1b and 1d, respectively). The longest bonds in Cp1
are C6–C10 and C9–C10 which are placed in the vicinity of the car-
bonyl substituent bonded to C10 atom (Fig. 3). The pairs of Cp1 and
Cp2 rings show only small mutual tilting as evidenced from the
corresponding Cp1/Cp2 dihedral angles which are all below 3.1°.
There is a very slight difference in the distances of the Fe atom
from the least-square planes of the Cp rings and in each of the
cases the metal is positioned closer to the substituted ring Cp1
for approximately 0.01 Å. The scatterplot in the Supplementary
material (Fig. 2S) compares the distances between the Fe atom
and the least-square planes of Cp1 and Cp2 in 22 extracted crystal
structures. It can be noticed that in the majority of structures, this
difference is below 0.015 Å and only in two cases exceeds the value
of 0.02 Å.
Fig. 3. Crystal structures and atom-numbering scheme of compounds 1a (a), 1b (b)
and 1d (c). Displacement ellipsoids are drawn at the 40% probability level.
Special attention was devoted to the spatial position of the car-
bonyl group with regard to the rest of molecule (in all analyzed
crystal structures this group is bonded to the same structural frag-
ments, ferrocene moiety and phenyl ring). In the present deriva-
tives the carbonyl moiety, C11–O1, is almost coplanar with Cp1
ring. The angle between the vector coinciding the C11–O1 bond
and the Cp1 plane is equal to 1.4°, 6.4° and 5.0° in 1a, 1b and 1d,
respectively. This coplanar position is supported by rather bent
intramolecular C6–H. . .O1 contact which is present in all these
compounds (Table 2). The angle between the carbonyl vector and
Fig. 4. Fragment used in CSD search.
the phenyl fragment is on the other hand much larger and equal
to 48.1°, 76.0° and 77.0°. The scatterplot in Fig. 3S displays a dispo-
sition of this vector (V1) with regard to the corresponding Cp1
(Cp1/V1) and Ph (Ph/V1) planes in 22 similar crystal structures. It

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Z. Ratkovic et al. / Polyhedron 29 (2010) 2311–2317
Table 3
is evident that in almost all crystal structures the carbonyl moie-
ties are preferable coplanar to Cp1 rings. The maximal deviations
from the Cp1 planes are always below 20°, at the same time, the
deviation angles from Ph rings can exceed 65°. The values corre-
sponding to the three present derivatives, (also assigned in scatter-
plot), indicate that the deviations of the carbonyl groups from the
Ph rings are larger in compounds 1b and 1d than in all other struc-
tures. The different behavior i.e. the better co-planarity of the car-
bonyl group with Ph ring instead of Cp1 is observed only in one
crystal structure, RUVHEV [30]. This crystal structure however con-
tains rather strong competing intramolecular hydrogen bond
which engages the carbonyl to the neighboring hydroxyl group
and probably influences its final position.
It should be also emphasized that in the present crystal struc-
tures C10–C11 bond which attaches the carbonyl moiety to Cp1
ring is always shorter in comparison to C11–C12 toward the Ph
ring (Table 3). The same relation between the two bond lengths
is also found in the 22 crystal structures extracted from CSD
(Fig. 4S) with only one exception, the coordination polymer IKAZOJ
[31]. The shorter length of the C10–C11 bond is probably a conse-
Selected bond lengths (Å) and bond angles (°) in crystal structures of 1a, 1b and 1d.
1a
1b
1d
O1–C11
C10–C11
C11–C12
S1–C17
S1–C18
C18–C19
C18–C20
O1–C11–C10
O1–C11–C12
C6–C10–C11
C9–C10–C11
C11–C12–C13
C11–C12–C17
C17–S1–C18
1.226(6)
1.485(10)
1.499(8)
1.766(6)
1.796(9)
1.226(3)
1.424(4)
1.514(4)
1.757(3)
1.807(3)
1.470(6)
1.225(4)
1.468(5)
1.511(5)
1.781(4)
1.836(5)
1.491(6)
1.528(6)
122.8(4)
119.5(4)
107.9(5)
126.1(4)
120.3(5)
120.9(4)
101.3(4)
119.7(6)
119.9(6)
107.9(6)
129.1(7)
121.3(5)
119.1(5)
103.0(4)
122.2(3)
119.4(3)
106.8(3)
125.9(3)
118.8(2)
121.3(3)
104.5(2)
C–H groups from the neighboring Cp rings (see Fig. 5S in the Sup-
plementary material). In that way the Ph ring acts as a acceptor
in the intermolecular C–H. . . interactions to the neighboring Cp
p
p
rings. The perpendicular distance of the H atom from the plane
of the phenyl ring (Hperp. . .Ph) in these interactions is shorter than
3.05 Å what could be accepted as satisfactory for the existence of
quence of p-electron delocalization existing between the Cp1 ring
and the carbonyl group. In addition to the previously mentioned
intramolecular C–H. . .O interaction this delocalization can contrib-
ute to the coplanar arrangement of the two moieties.
C–H. . .
p Hperp. . .Ph = 3.03 Å, (i)
interactions [1a: C6–H6. . .Phi,
= Àx + 1, y À 1/2, Àz + 2; 1b: C8–H8. . .Phi, Hperp. . .Ph = 3.04 Å, and
C4–H4. . .Phi, Hperp. . .Ph = 2.71 Å, (i) = Àx + 1/2, Ày + 1/2, Àz + 1;
1d: C8–H8. . .Phi, Hperp. . .Ph = 2.92 Å, (i) = Àx + 1, Ày + 2, Àz].
In the centrosymmetrical crystal structures 1b and 1d above
The orientation of the phenyl rings with regard to the Cp1 could
be considered as a main geometrical dissimilarity between the de-
scribed (S-alkylbenzoyl)ferrocene derivatives. In compound 1a
which has the smallest, S-methyl, substituent the dihedral angle
between the least-square planes of the Ph and Cp1 rings is
46.8(3)°. This is larger than found in two crystal structures describ-
ing unmodified Benzoylferrocene (ZZZHCY01 [32a] and ZZZHCY02
[32b]) where this angle is equal to 37.7° and 38.3°. In S-ethyl and S-
isopropyl derivatives the Ph moiety becomes more perpendicularly
positioned making the dihedral angles of 82.4(1)° and 80.2(2)°.
The three crystal structures lack in typical hydrogen bonding
donors, thus, despite the presence of the carbonyl oxygen acceptor,
the crystal packing is stabilized only by weak C–H. . .O, C–H. . .S and
described intermolecular C–H. . .
cules into pairs, while in the non-centrosymmetrical structure
1a the C–H. . . interactions assemble the molecules into chain
p interactions relate the mole-
p
extended in b direction. The similar structural motif was also ob-
served in several other crystal structures such as: TIDXOU [33],
YARRUE [34], ZZZHCY01 [32a], ZZZHCY02 [32b], CIXNED [35]
and COCKOV [36]. The 1a, 1b and 1d crystal structures are also
stabilized by additional C–H. . .
p interactions where C–H groups
of the phenyl moieties interact with the cyclopentradienyl
p sys-
tem [1a: C16–H16. . .Cp1ii, Hperp. . .Cp1 = 3.04 Å, (ii) = Àx, y + 1/2,
C–H. . .p interactions (Table 2S). The different types of C–H donors,
Àz + 2; 1d: C13–H13. . .Cp2ii,
H
perp. . .Cp2 = 2.88 Å, (ii) Àx + 1,
Cp in 1a, Cp and Ph in 1b and Cp, Ph and alkyl in 1d are engaged in
interactions to carbonyl groups. The C–H. . .O interaction in 1a and
1b which can be considered as the shortest involve Cp hydrogens
and connect the corresponding molecules into chains with clear
directional preferences along the c and b axis, respectively. It is,
however, interesting to point out to particular structural motif
which seems to characterize each of these crystal structures.
Namely, in the crystal arrangements of 1a, 1b and 1d, the Ph ring
is positioned in a nearly perpendicular orientation to some of
Ày + 1, Àz], as well as the C–H. . .
p interactions where alkyl C–H
groups interact with both type of
p systems [1a: C18–
H18a. . .Cp2iii, Hperp. . .Cp2 = 2.78 Å, (iii) = xÀ1, y, z + 1 and C18–
H18c. . .Cp1ii,
Hperp. . .Cp1 = 2.50 Å;
1b:
C18–H18b. . .Cp2ii,
H
perp. . .Cp2 = 2.98 Å, (ii) = x + 1/2, Ày + 1/2, z + 1/2; 1d: C20–
H20c. . .Phiii,
H
perp. . .Ph = 3.00 Å, (iii) = Àx + 2, y + 1/2, Àz + 1/2
and C20–H20a. . .Cp2iv, Hperp. . .Cp2 = 3.03 Å, (iv) = x + 1, Ày + 3/2,
z + 1/2].
Table 2
Geometrical parameters for intra- and intermolecular C–H. . .A (A = O and S) interactions in crystal structures of 1a, 1b and 1d. All H atoms are placed at geometrically calculated
positions.
D–H. . .A
D–H (Å)
H. . .A (Å)
D. . .A (Å)
D–H. . .A (°)
Symmetry codes
1a
C6–H6. . .O1
C4–H4. . .O1
C7–H7. . .O1
C5–H5. . .S1
C15–H15. . .S1
0.93
0.93
0.93
0.93
0.93
2.72
2.60
2.67
3.13
3.07
2.872(8)
3.190(8)
3.482(9)
3.859(7)
3.871(7)
89.6
123.7
146.1
136.5
145.5
x, y, z
x, y, z À 1
Àx + 1, y À 1/2, Àz + 2
x, y, z À 1
Àx, y + 1/2, Àz + 2
1b
1d
C6–H6. . .O1
C1–H1. . .O1
C13–H13. . .O1
C15–H15. . .S1
0.93
0.93
0.93
0.93
2.83
2.43
2.61
3.07
2.883(3)
3.211(5)
3.498(4)
3.826(4)
86.4
141.4
161.1
139.3
x, y, z
Àx + 1/2, y + 1/2, Àz + ½
Àx + 1/2, y + 1/2, Àz + ½
x, y + 1, z
C6–H6. . .O1
C7–H7. . .O1
C15–H15. . .O1
C19–H19b. . .O1
C4–H4. . .S1
0.93
0.93
0.96
0.93
0.93
2.87
2.76
2.79
2.76
3.07
2.978(6)
3.317(6)
3.298(6)
3.669(7)
3.994(6)
87.2
119.6
115.0
158.5
171.1
x, y, z
Àx + 1, y + 1/2, Àz + 1/2
x, Ày + 3/2, À1/2 + z
x + 1/2, y + 1/2, Àz + 1/2
Àx + 1, Ày + 2, Àz

´
Z. Ratkovic et al. / Polyhedron 29 (2010) 2311–2317
2316
Table 4
exhibit a reversible one-electron redox couple at almost the same
potential.
Three new crystal structures are characterized by single-crystal
Electrochemical data of compounds 1a–g.
Compounds
Epa (mV)a
Epc (mV)a
E1/2 (mV)b
D
E (mV)c
X-ray analysis and their geometrical parameters are compared to
additional 22 crystal structures of benzoylferrocenes extracted
from Cambridge Structural Database. Special attention was de-
voted to spatial position of the carbonyl group with regard to the
rest of the molecule (ferrocene moiety and phenyl ring). It was
found that in almost all crystal structures the carbonyl moiety is
preferable coplanar to Cp1 ring. Except in one case, the maximal
deviations of the C–O (carbonyl) vector from the Cp1 plane are al-
ways below 20°, at the same time, the deviation angles from Ph
rings are above 20° and can exceed 65°. It should be also empha-
sized that in all crystal structures the C–C bond which attaches
the carbonyl moiety to Cp1 ring is always shorter (more than
0.03 Å in average) in comparison to C–C bond toward the Ph ring.
Analysis of intermolecular interactions shown that Cp and Ph rings
1a
1b
1c
1d
1e
1f
383
383
383
384
380
389
383
310
307
309
308
306
303
311
346.5
345
346
346
343
346
347
73
76
74
76
74
86
72
1g
Epa and Epc anodic and cathodic peak potentials, respectively, at 100 mV sÀ1
E1/2 = (Epa + Epc)/2.
E = Epa À Epc.
.
a
b
c
from benzoylferrocene can act as a
interactions.
p acceptors in the C–H. . .p
Acknowledgements
This work was supported by the Ministry of Science and Tech-
nological Development of the Republic of Serbia (Grants 142042
and 142010).
Appendix A. Supplementary data
CCDC 771043, 771044 and 771045 contain the supplementary
crystallographic data for 1a, 1b and 1d. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cam-bridge CB2 1EZ, UK; fax: (+44) 1223–336-033;
or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at doi:10.1016/
j.poly.2010.04.034.
Fig. 5. Cyclovoltammograms of compound 1a and ferrocene at Pt disc in 0.1 M
LiClO4 in acetonitrile at v = 0.1 V/s.
3.4. Electrochemistry
Cyclic voltammetry in acetonitrile containing 0.1 mol/L lithium
perchlorate as a supporting electrolyte has been used for the eval-
uation of electrochemical properties of the synthesized com-
pounds 1a–g. All ketones exhibit a reversible one-electron redox
couple at almost the same potential. Oxidation waves appear at
380–389 mV, whereas the reduction ones at 303–311 mV, and
we attributed them to the oxidation of the ferrocene unit by
the forward potential sweep, and reduction of the obtained ferric-
inium ion at the beck potential sweep. These potentials are
slightly more positive than that of the unsubstituted ferrocene,
as a consequence of the presence of an electron-withdrawing acyl
group (see Table 4).
As the representative example we give the voltammogram of
compound 1e (solid line, Fig. 5) together with the voltamogram
of ferrocene (dashed line, Fig. 5). The difference between anodic
and cathodic peak potentials is close to the theoretical value and
independent of the scan rate v. Both, anodic and cathodic peak cur-
rents are proportional to the square root of the scan rate (see
Fig. 6S in the Supplementary material), and their ratio is indepen-
dent of the scan rate, indicating a diffusion-controlled process.
References
[1] A. Togni, T. Hayashi, Ferrocenes: Homogenous Catalysis, Organic Synthesis,
Material Science, VCH, Weinheim, Germany, 1995.
[2] A. Togni, R.L. Haltermann, Metallocenes, Wiley-VCH, Weinheim, Germany,
1998.
[3] B. Loev, M. Flores, J. Org. Chem. 26 (1961) 3595.
[4] F.D. Popp, S. Roth, J. Kirby, J. Med. Chem. 6 (1963) 83.
[5] C. Biot, G. Glorian, L.A. Maciejewski, J.S. Brocard, J. Med. Chem. 40 (1997) 3715.
[6] D. Osella, M. Ferrali, P. Zanello, F. Laschi, M. Fontani, C. Nervi, G. Cavigiolio,
Inorg. Chim. Acta 306 (2000) 42.
[7] G. Jaouen, S. Top, A. Vessières, R. Alberto, J. Organomet. Chem. 600 (2000) 23.
[8] D.R. van Staveren, N. Metzler-Nolte, Chem. Rev. 104 (2004) 5931.
[9] E.W. Neuse, J. Inorg. Organomet. Polym. 15 (2005) 3.
[10] C.S. Allardyce, A. Dorcier, C. Scolaro, P.J. Dyson, Appl. Organomet. Chem. 19
(2005) 1.
[11] G. Jaouen, W. Beck, M.J. McGlinchey, in: G. Jaouen (Ed.), Bioorganometallics:
Biomolecules, Labeling, Medicine, Wiley-VCH, Weinheim, 2006.
[12] M.F.R. Fouda, M.M. Abd-Elzaher, R.A. Abdelsamaia, A.A. Labib, Appl.
Organomet. Chem. 21 (2007) 613.
[13] O. Payen, S. Top, A. Vessières, E. Brulé, M.-A. Plamont, M.J. McGlinchey, H.
Müller-Bunz, G. Jaouen, J. Med. Chem. 51 (2008) 1791.
[14] I. Damljanovic´, M. Vukic´evic´, N. Radulovic´, R. Palic´, E. Ellmerer, Z. Ratkovic´,
´
´
´
M.D. Joksovic, R.D. Vukicevic, Bioorg. Med. Chem. Lett. 19 (2009) 1093.
[15] R.B. Woodward, M. Rosenblum, M. Whiting, J. Org. Chem. 74 (1952) 3458.
´
´
´
´
´
´
[16] R.D. Vukicevic, M. Vukicevic, Z. Ratkovic, S. Konstantinovic, Synlett (1998)
1329.
4. Conclusions
[17] M.D. Vukic´evic´, Z.R. Ratkovic´, A.V. Teodorovic´, G.S. Stojanovic´, R.D. Vukic´evic´,
Tetrahedron 58 (2002) 9001.
[18] R.D. Vukic´evic´, D. Ilic´, Z. Ratkovic´, M. Vukic´evic´, Monats. Chem. 132 (2001)
625.
[19] D. Ilic´, I. Damljanovic´, D. Stevanovic´, M. Vukic´evic´, N. Radulovic´, V. Kahlenberg,
G. Laus, R.D. Vukic´evic´, Polyhedron 29 (2010) 1863.
[20] R.J. Irving, W.C. Fernelius, J. Phys. Chem. 60 (1956) 1427.
[21] Enraf-Nonius CAD4 Software, Version 5.0, Enraf-Nonius, Delft, The
Netherlands, 1989.
In conclusion, we showed that (2-alkylthiobenzoyl)ferrocenes
can be synthesized by a one-pot acylation procedure from the cor-
responding 2-alkylthiobenzoic acids, phosphorus trichloride and
ferrocene without isolation of the intermediate acid chlorides.
The seven new sulfur containing ketones – ferrocene derivatives
– were well characterized by spectral data (IR, NMR and UV). As
the cyclovoltammetric measurements showed, these ketones
[22] CAD-4 Express Software, Enraf-Nonius, Delft, The Netherlands, 1994.

´
2317
Z. Ratkovic et al. / Polyhedron 29 (2010) 2311–2317
[23] (a) G.M. Sheldrick, SHELXS97. Program for the Solution of Crystal Structures,
University of Göttingen, Germany, 1997;
[34] T.V. Baukova, L.G. Kuzmina, N.V. Dvortsova, Russ. J. Inorg. Chem. 37 (1992)
1497.
(b) G.M. Sheldrick, SHELXS97. Program for the Refinement of Crystal Structures,
University of Göttingen, Germany, 1997.
[35] G. Li, Z.-F. Li, J.-X. Wu, C. Yue, H.-W. Hou, J. Coord. Chem. 61 (2008)
464.
[24] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[25] (a) A.L. Spek, Acta Crystallogr. A46 (1990) C34;
[36] G. Li, C. Yue, J. Wu, L. Wang, H. Hou, React. Inorg., Met.-Org., Nano-Met. Chem.
37 (2007) 267.
(b) A.L. Spek, PLATON
University, Utrecht, The Netherlands, 1998.
[26] M. Nardelli, PARST, J. Appl. Crystallogr. 28 (1995) 659.
[27] L.J. Farrugia, ORTEPIII for Windows – J. Appl. Crystallogr. 30 (1997) 565.
[28] G. Eminovic´, M. Vukic´evic´, Z. Ratkovic´, D. Ilic´, R.D. Vukic´evic´, Synlett (2003)
2416.
,
A
Multipurpose: Crystallographic Tool, Utrecht
[37] S.Z. Ahmed, G. Ferguson, C. Glidewell, J. Organomet. Chem. 585 (1999) 331.
[38] K. Heinze, M. Schlenker, Eur. J. Inorg. Chem. (2004) 2974.
[39] W. Figueroa, M. Fuentealba, C. Manzur, A.I. Vega, D. Carrillo, J.R. Hamon, C.R.
Chim. 8 (2005) 1268.
[40] J.F. Gallagher, G. Ferguson, S.Z. Ahmed, C. Glidewell, A. Lewis, Acta Crystallogr.
C53 (1997) 1772.
[29] F.H. Allen, Acta Crystallogr. B58 (2002) 380.
[30] C. Glidewell, S.Z. Ahmed, J.F. Gallagher, G. Ferguson, Acta Crystallogr. C53
(1997) 1775.
[31] G. Li, H. Hou, L. Li, X. Meng, Y. Fan, Y. Zhu, Inorg. Chem. 42 (2003) 4995.
[32] (a) I.R. Butler, W.R. Cullen, S.J. Rettig, J. Trotter, Acta Crystallogr. C44 (1988)
1666;
[41] M. Erben, A. Ruzicka, J. Vinklarek, V. Stava, D. Vesely, Acta Crystallogr. E63
(2007) m3067.
[42] A.C. Benyei, C. Glidewell, P. Lightfoot, B.J.L. Royles, D.M. Smith, J. Organomet.
Chem. 539 (1997) 177.
[43] Y.J. Wu, X.L. Cui, Y.H. Liu, H.Z. Yuan, X.A. Mao, J. Organomet. Chem. 543 (1997)
63.
(b) J.C. Barnes, W. Bell, C. Glidewell, R.A. Howie, J. Organomet. Chem. 385
(1990) 369.
[33] G. Li, Z.-F. Li, J.-X. Wu, L. Zhu, H.-W. Hou, Chin. J. Inorg. Chem. 23 (2007) 975.
[44] K. Heinze, M. Beckmann, J. Organomet. Chem. 691 (2006) 5576.
[45] Y.Y. Dou, Y.F. Xie, L.F. Tang, Appl. Organomet. Chem. 22 (2008) 25.
[46] G. Calvarin, D. Weigel, Acta Crystallogr. B27 (1971) 1253.