Antibacterial 3-(arylamino)-1-ferrocenylpropan-1-ones: Synthesis, spectral, electrochemical and structural characterization

Article abstract of DOI:10.1016/j.jorganchem.2011.08.016

Syntheses of fourteen new 3-(arylamino)-1-ferrocenylpropan-1-ones have been achieved in good to excellent yields by an aza-Michael addition of different arylamines to acryloylferrocene. The reaction was performed by microwave (MW) irradiation (500 W/5 min

Full text of DOI:10.1016/j.jorganchem.2011.08.016

Journal of Organometallic Chemistry 696 (2011) 3703e3713
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Antibacterial 3-(arylamino)-1-ferrocenylpropan-1-ones: Synthesis, spectral,
electrochemical and structural characterization
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Ivan Damljanovic , Dragana Stevanovic , Anka Pejovic , Mirjana Vukicevic , Sladjana B. Novakovic ,
d
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*
Goran A. Bogdanovic , Tatjana Mihajlov-Krstev , Niko Radulovic , Rastko D. Vukicevic
Department of Chemistry, Faculty of Science, University of Kragujevac, R. Domanovica 12, 34000 Kragujevac, Serbia
Department of Pharmacy, Faculty of Medicine, University of Kragujevac, S. Markovica 69, 34000 Kragujevac, Serbia
Vinca Institute of Nuclear Sciences, Laboratory of Theoretical Physics and Condensed Matter Physics, PO Box 522, 11001 Belgrade, Serbia
Department of Biology and Ecology, Faculty of Science and Mathematics, University of Nis, Visegradska 33, 18000 Nis, Serbia
Department of Chemistry, Faculty of Science and Mathematics, University of Nis, Visegradska 33, 18000 Nis, Serbia
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a r t i c l e i n f o
a b s t r a c t
Article history:
Syntheses of fourteen new 3-(arylamino)-1-ferrocenylpropan-1-ones have been achieved in good to
excellent yields by an aza-Michael addition of different arylamines to acryloylferrocene. The reaction was
performed by microwave (MW) irradiation (500 W/5 min) of a mixture of reactants and montmorillonite
K-10, without a solvent. The obtained compounds were spectrally and electrochemically (cyclic vol-
tammetry) fully characterized, whereas single-crystal X-ray analysis has been performed for three of
them. In a microdilution assay, all of the compounds were shown to have a broad-spectrum effect on
Gram-negative and -positive bacteria, although the degree of inhibition varied. A notable activity was
observed for all compounds in inhibiting the growth of an important human pathogen Staphylococcus
aureus.
Received 22 June 2011
Received in revised form
17 August 2011
Accepted 18 August 2011
Keywords:
3-(Arylamino)-1-ferrocenylpropan-1-ones
Mannich bases
Acryloylferrocene
Montmorillonite K-10
Microwave irradiation
Antibacterial activity
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
many applications of Mannich bases and their derivatives, however,
the most important ones are surely those applied in synthesis of
Derivatives of ferrocene are of widespread interest in many
fields of chemistry, such as organic synthesis [1], coordination
chemistry [2], material sciences [1,3,4] and, nowadays, medicinal
chemistry [5e10]. This is the consequence of several unique
features of these compounds, such as the easiness of derivatization,
the outstanding stability in both, aqueous and non-aqueous media,
very interesting redox properties, etc. Multifunctional derivatives
of this metallocene are particularly valuable, and in this regard
pharmaceuticals [11,13e15]. The most famous synthetic approach
to Mannich bases is, of course, the Mannich reaction [11,12,16]
which, however, has many disadvantages. Drastic reaction condi-
tions and long reaction times (causing many side reactions) are the
main ones [11,12,16]. Furthermore, the use of primary amines in this
reaction is not suitable, since the obtained products are also good
substrates of the same reaction that continues up to the substitu-
tion of both hydrogen atoms of the amine group giving, thus,
tertiary amines containing two 3-oxo-groups. A very good alter-
native to the Mannich reaction is the aza-Michael addition e the
Mannich bases (Mannich ketones;
b-aminoketones) containing
a ferrocene unit might be very interesting.
In general, Mannich bases are versatile synthetic building
blocks, which can easily be converted into a range of useful deriv-
atives, such as 1,3-aminoalcohols and products of the substitution
of the amino group with some other nucleophile [11,12]. Among
conjugate addition of amines to the olefinic bond of a,b-unsatu-
rated carbonyls [17]. There are several advantages of this reaction,
such as the mild reaction conditions and the possibility to
synthesize secondary Mannich bases. A plethora of catalytic
systems have been developed for this reaction up to date [18e39].
While the addition of aliphatic amines to Michael acceptors
proceeds readily (even without a catalyst [40,41]), aromatic ones
did not undergo this reaction easily because of its lower nucleo-
philicity, particularly when mild conditions and environmental
friendly catalysts were used [22,29,31,36,39].
* Corresponding author.
** Corresponding author. Fax: þ381 34 33 50 40.
ꢀ
E-mail addresses: nikoradulovic@yahoo.com (N. Radulovic), vuk@kg.ac.rs
ꢀ
ꢀ
(R.D. Vukicevic).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.016

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According to the best of our knowledge, there is only one
previous report on the addition of amines to some -unsaturated
acylferrocenes [31], where the authors described the reaction of
several chalcone-type ferrocenes with aliphatic amines under mild
conditions (ultrasound irradiation and water as the solvent). The
mixture of reagents in the presence of 100 mg of montmorillonite
a
,b
K-10 (500 W, 5 and 10 min), and this resulted in an increase of the
yield of 5a up to 55%. Experiments with the increased amount of
the catalyst (up to 500 mg) did not affect the yield significantly.
Since only small amounts of the starting ketone 3 have been
recovered (up to 10%) from the above performed experiments, we
concluded that this compound underwent a certain side reaction
(most probably some kind of polymerization, because a very polar
dark product, which was neither isolated nor identified, formed
during the runs). This side product may be the result of multiple
corresponding
b-aminoketones were obtained in high yields.
However, the reaction failed when aromatic amines wereused as the
Michael-donors. In continuation of our permanent interest in the
synthesis of ferrocene derivatives containing more than one
heteroatom in the side chain(interesting fromthe both the synthetic
and medicinal chemistry points of view) [42e48], herewith we wish
to report on a suitable synthesis of a series of 3-(arylamino)-1-
ferrocenylpropan-1-ones by the addition of various aromatic
amines to 1-ferrocenylprop-2-en-1-one (acryloylferrocene).
Michael additions of the formed b-aminoketones to more mole-
cules of acryloylferrocene, perhaps even leading through tertiary
amines to quaternary ammonium salts that would be expected to
behave in this way. In order to (statistically) suppress this, the
following experiments were performed using a double amount of
the amine 4a. The target compound e b-aminoketone 5a e was
2. Results and discussion
obtained in 85% yield, regardless the reaction time (5 or 10 min).
Then the same reaction conditions (1 mmol of acryl-
oylferrocene/2 mmol of arylamine/100 mg of montmorillonite K-
10/500 W/5 min) were applied to the reaction of the ketone 3 with
the another thirteen substrates 4ben. The corresponding Mannich
bases 5ben were obtained in good to excellent yields (see Table 1)
and were fully spectrally characterized (see below).
As it can be seen from the data listed in Table 1, the lowest yields
of the corresponding Mannich bases were achieved when amines
4e, 4l and 4n were used. In the case of 4e the steric nature (bulk-
iness) of the substrate is the most likely reason for it, whereas the
lowered nucleophilicity of the amino group of the two nitroanilines
causes the decrease in the yields of 4l and 4n. In order to try to
improve the yields in these cases, we performed experiments
having a prolonged time of exposure of the reactants and the
catalyst to MW irradiation. However, not even doubling the reac-
tion time to 10 min did not cause an increase in obtained yields.
Again, the unconsumed amines were recovered almost quantita-
tively and almost no ketone 3, further strengthening the notion of
multiple Michael additions.
2.1. Synthesis
The primary goal of our study was to find and optimize
a procedure for the synthesis of 3-(arylamino)-1-ferrocenylpropan-
1-ones with particular attention paid to finding mild enough
conditions for the reaction to proceed with an acceptable yield and
making use of an environmental friendly catalyst. Knowing that the
application of environmentally benign catalysts such as clay [36]
and mild reaction conditions [31,39] does not make possible the
addition of aromatic amines to Michael acceptors (contrary to
aliphatic ones), we expected that the simultaneous use of mont-
morillonite K-10 (as a solid acidic catalyst) and microwave irradi-
ation would improve the outcome of this approach. It turned out
that this idea was quite correct, and that the corresponding Man-
nich bases were obtained in good to almost quantitative yields.
Our investigations began by the preparation of the intended
Michael acceptor e acryloylferrocene (3, Scheme 1). This was
achieved by FriedeleCrafts acylation of ferrocene (1) with 3-
chloropropanoic acid chloride in the presence of AlCl3 as the
Lewis acid catalyst [49], and the subsequent dehydrohalogenation
of the obtained (3-chloropropionyl)ferrocene (2) by means of
potassium acetate [50].
2.2. Spectral characterization
Intense absorption bands were present in the IR spectra of the
obtained 3-(N-arylamino)propanones 5 for the C]O (at around
1660 cmꢀ1) and secondary NH groups (3340e3390 cmꢀ1, sharp).
The 1H NMR spectra contained typical signals for a mono-
substituted ferrocene (two triplets at w4.76 and 4.50 ppm, and a
singlet at w4.12 ppm) and were also characterized by the presence
of two multiplet signals for the protons of the O]CeCH2eCH2eN
grouping, which were positioned in the region of 3.25e3.83 and
2.97e3.12 ppm (generally in agreement with a previous report
[51]). An interesting feature of the 1H NMR spectra was the occur-
rence of coupling of the NH protons with those of the adjacent CH2
group. The NeCH2 signals appeared as either sharp or somewhat
broadened quartets in a number of cases (the ortho- and meta-
substituted anilines with an electron-withdrawing group) from
accidental equivalence of the vicinal HNeCH2 and CH2eCH2
couplings (J ca. 6 Hz). Such a coupling was not observed for the
benzene analogs where the CH2 group bonded to amino showed
little indication of coupling to the NH protons, so NH exchange
must have been rapid on the NMR time scale [52] as also seems to
be the case with compounds 5aee,h,n in the current study. The
proton of the secondary amino group was a broadened signal at
3.6e4.8 ppm, typical of NH protons of anilines in CDCl3 solution,
In order to optimize the synthesis of the title compounds (5aen,
Scheme 1), aniline (4a) was used as the test substrate for the
addition to the conjugated enone e acryloylferrocene (3). Thus,
when ketone 3 (1 mmol) and amine 4a (1 mmol) were irradiated in
a microwave oven (500 W, 5 min) without a catalyst or solvent, and
after the usual work-up and flash chromatography (silica gel/
toluene, then n-hexaneeethyl acetate 9:1), the pure
b-amino-
ketone 5a (Scheme 1) was obtained in 37% yield. The same result
was achieved by a prolongation of the reaction time to 10 min. The
next two experiments we performed by irradiating the same
with the only exception for compound 5l, an o-nitroaniline (ca. d 8)
that had, as expected, an NH signal downfield of this range. The
broadening has several sources: partially averaged coupling to
neighboring protons, intermolecular exchange with other NH
Scheme 1. Synthesis of 3-(arylamino)-1-ferrocenylpropan-1-ones: (i) AlCl3, CH2Cl2, r.t.
(ii) CH3COOK, ethanol, reflux, 2.5 h. (iii) solvent-free, montmorillonite K-10, MW,
500 W, 5 min.

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Table 1
Structures of the newly prepared 3-(arylamino)-1-ferrocenylpropan-1-ones (5aen) and corresponding starting amines (4aen), as well as the yield of the reactions.
Run
Amine
Product
Yielda
5a
4a
4b
1
85%
5b
5c
2
3
89%
80%
4c
5d
5e
4d
4e
4
5
95%
59%
4f
5f
6
7
98%
89%
5g
4g
5h
5i
4h
4i
8
9
83%
93%
5j
4j
10
11
87%
93%
5k
4k
4l
5l
12
64%
(continued on next page)

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I. Damljanovic et al. / Journal of Organometallic Chemistry 696 (2011) 3703e3713
Table 1 (continued )
Run
Amine
Product
Yielda
5m
5n
4m
13
87%
4n
14
64%
a
Isolated yields based on the starting enone.
protons, and partially coalesced coupling to the quadrupolar 14N
nucleus (I ¼ 1), which usually has a short T1. The labile NH protons
were identified by shaking the CDCl3 solutions of the compounds
with a drop of D2O, which resulted in the disappearance of the NH
signals and in the transformation of the mentioned quartets
(NHeCH2) to the corresponding triplets, thus corroborating the
existence of such NHeCH2 coupling. It appears that this slow
chemical exchange is more pronounced for the more acidic NH
protons and those involved in intramolecular hydrogen bonding
(the proximity of the electron-withdrawing groups, halogens and
the nitro group, in ortho- and meta-positions).
The aromatic protons in the positions ortho to the amino group
of the aniline fragment afford diagnostic signals from their high
field disposition (at 6.6e6.8 ppm). 13C NMR spectra also corrobo-
rate the structure of these ferrocene derivatives. Signals at ca. 78.7,
72.4, 69.8 and 69.2 can be attributed to the ferrocene moiety while
the other characteristic signals, one at about 200 ppm and two
about 38 ppm, are those corresponding to the carbonyl- and
methylene carbons, respectively.
the resulting orientation of the C14-phenyl ring are quite different
for compound 5l. The C12eC13eN1eC14 torsion angle describes
this difference (74.2(6), 68.7(8) and ꢀ175.7(6)ꢁ for 5j, 5m and 5l,
respectively). The orientation of the phenyl ring with respect to the
ferrocenyl unit is well illustrated in Supplementary material
(Fig. A1). This conformational particularity of the structure 5l
could be explained by the formation of the N1eH.O2 intra-
molecular hydrogen bond (Fig. 1c) which does not exist in 5j and
5m.
The only significant H-bond donor in all three crystal structures
is the N1eH group. In 5j and 5m, adjacent molecules form
centrosymmetric dimers by hydrogen bonding between N1eH and
O1. Geometry of these dimers for both crystal structures is very
similar (see Fig. A2 in Supplementary material). In 5l, the N1eH
does not participate in any intermolecular H-bonding. Geometrical
parameters for the selected intra- and intermolecular interactions
are given in Table 3.
2.4. Electrochemistry
2.3. X-ray crystal structure of 5j, 5l and 5m
Cyclic voltammetry in acetonitrile containing 0.1 mol/l lithium
perchlorate as the supporting electrolyte has been used for the
evaluation of electrochemical properties of the compounds 5aen.
The voltammogram of compound 5a is presented here (Fig. 2) as
Most of the synthesized compounds were crystal substances,
suitable for X-ray crystal structure analysis. Herein, we present the
structures of 5j, 5l and 5m compounds (Fig. 1aec).
a
representative example, whereas the data of the other
compounds are listed in Table 4. As it can be seen from the
summarized data, all of the synthesized -aminoketones exhibited
The cyclopentadienyl rings (Cp) of the title compounds 5j and
5m are close to an eclipsed geometry. The C1eCg1eCg2eC6 torsion
angle is 9.5(5)ꢁ in 5j and 11.3(5)ꢁ in 5m (Cg1 and Cg2 are centroids
of the corresponding Cp rings). In 5l, the Cp rings are more eclipsed
and the C1eCg1eCg2eC6 torsion angle is ꢀ4.0(4)ꢁ. In all three
compounds the Cp rings within the ferrocenyl units are almost
parallel with interplanar angles 1.1(4), 2.3(4) and 0.7(5)ꢁ for 5j, 5m
and 5l, respectively. The Cg1eCg2 distance (3.295, 3.309 and
b
two well defined oxidation waves on the forward potential sweep
(O1, at 0.650e0.693 V and O2, at 0.693e1.373 V, respectively) and
one reduction wave on the back potential sweep (R1, at
0.592e0.620 V). As depicted in Fig. 2B for 5a, the reduction peak R1
appeared also when the potential was reversed after O1. Since the
difference between the values of these two potentials is close to the
theoretical one, O1 and R apparently belong to a reversible redox
couple, appearing due to the presence of the ferrocene nucleus.
Their position lays more than 200 mV higher than that of the
unsubstituted ferrocene (see Fig. A3 in the Supplementary
material), as expected for ferrocene derivatives possessing an
electron-withdrawing group conjugated to the cyclopentadienyl
ring(s). Both the anodic (O1) and cathodic (R1) peak currents are
proportional to the square root of the scan rate (as depicted for 5a,
Fig. A4 in Supplementary material), and their ratio is independent
of the scan rate, indicating a diffusion-controlled process.
ꢁ
ꢂ
3.301 A) and the Cg1eFeeCg2 angle (178.5, 177.4 and 178.5 ) are
also very similar for all crystal structures.
The C1]O1 carbonyl group lies approximately in the plane of
the
substituted
Cp
ring
with
the
O1eC11eC1eC5
angle ꢀ4.5(8), ꢀ3.2(8) and ꢀ6.9(9)ꢁ for the three compounds,
respectively. Bond lengths and angles show expected values
(Table 2). The C1eC11eC12eC13eN1 fragment, although consisted
of single bonds, adopts a similar conformation in all three mole-
cules (Fig.1aec). The C1eC11eC12eC13 and the C11eC12eC13eN1
torsion
angles
are
ꢀ167.5(4)/74.4(6),
ꢀ164.4(4)/67.4(7)
and ꢀ179.2(5)/71.8(7)ꢁ for 5j, 5m and 5l, respectively. However,
regardless of this similarity, the directionality of N1eC14 bond and
The second oxidation wave (O2) is due to an irreversible
oxidation of the aniline unit of these molecules. A study of the

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3707
Table 2
cyclovoltammetry of N-alkylanilines [53e55] showed that these
Selected bond lengths and angles for 5j, 5m and 5l.
compounds undergo irreversible anodic oxidation, producing
a single oxidation wave on the first scan. Upon reversal of the scan
three cathodic waves are obtained (at the potentials between 0.2
and 0.5 V). In the subsequent anodic scans three anodic waves
appeared at the corresponding potentials, making up together with
the cathodic ones three reversible couples. It was demonstrated
that they belong to the products obtained from the species formed
by the anodic oxidation of anilines [53e55]. We assumed that the
lack of such type of waves in the cyclovoltammograms of
compounds 5aen is a consequence of their accidental overlapping
with the waves belonging to the ferrocene unit. In order to confirm
5j
5m
5l
ꢂ
Bond lengths (A)
O1eC11
N1eC14
N1eC13
C1eC11
C11eC12
C12eC13
C16eCl
CeN2
1.223(6)
1.380(8)
1.440(7)
1.462(7)
1.497(7)
1.519(7)
1.731(6)
1.220(6)
1.358(7)
1.454(7)
1.457(8)
1.514(8)
1.523(8)
1.218(6)
1.351(8)
1.452(8)
1.459(8)
1.507(8)
1.519(8)
1.470(8)
1.217(7)
1.237(7)
1.440(9)
1.237(7)
1.223(7)
N2eO2
N2eO3
Bond angles (ꢁ)
O1eC11eC1
O1eC11eC12
C1eC11eC12
C11eC12eC13
N1eC13eC12
C14eN1eC13
122.3(5)
120.4(5)
117.2(5)
113.7(4)
113.6(5)
122.8(5)
122.3(6)
121.4(5)
116.3(5)
112.7(5)
113.8(5)
123.3(5)
121.6(5)
120.4(6)
117.9(5)
113.2(5)
109.6(5)
124.6(6)
it, 4-(phenylamino)butan-2-one (6) was synthesized and its elec-
trochemical properties investigated by cyclic voltammetry subject
to the same conditions. As depicted in Fig. 3, this compound
exhibited only one oxidation wave in the first cycle (Fig. 3A, solid
curve), but three in the second one (curve b). However, when
acetylferrocene was added, these waves overlapped with the
electrode response of acetylferrocene (curve c), and we find this to
be sufficient evidence to back up the above statements.
2.5. Biology
Medicinal chemists are open to the inclusion of ferrocene into
their drug design strategies because of the novelty introduced by its
presence. Previous workers [56e58] have found that certain
Mannich bases possessed in vitro antimicrobial activity. Chatten
et al. [59] have shown that besides the difference in amine moieties,
the substituents in phenyl ketones also exert an influence on
Table 3
ꢂ ꢁ
Geometrical parameters (A, ) of hydrogen bonds and selected CeH.O interactions
for 5j, 5m and 5l. The CeH.O interactions are given if H.O distance is shorter than
ꢁ
ꢂ
2.7 A and CeH.O angle is larger than 100 .
DeH.A
DeH
D.A
H.A
DeH.A
5j
C4eH4.N1i
N1eH1N.O1ii
C7eH7.Cl1iii
0.93
0.91(6)
0.93
3.559(7)
3.020(7)
3.625(13)
2.69
2.14(6)
2.87
156
164(4)
139
Symmetry codes: (i) x ꢀ 1, þy þ 1, þz; (ii) ꢀx þ 1, ꢀy þ 1, ꢀz þ 1; (iii) ꢀx þ 1,
ꢀy þ 1, ꢀz þ 2
5m
C9eH9.O2i
0.93
0.93
0.73(4)
0.93
3.443(10)
3.272(10)
3.142(7)
3.388(7)
2.66
2.65
2.46(5)
2.64
143
125
156(5)
138
C4eH4.O3i
N1eH1N.O1ii
C19eH19.O1ii
Symmetry codes: (i) ꢀx þ 1, ꢀy þ 1, ꢀz þ 1; (ii) ꢀx þ 2, ꢀy þ 1, ꢀz
5l
N1eH1N.O1i
N1eH1N.O2i
C6eH6.O2i
0.76(8)
0.76(8)
0.93
0.93
0.93
2.984(8)
2.625(8)
3.469(10)
2.662(11)
3.352(7)
3.373(9)
3.130(8)
2.70(8)
2.01(7)
2.63
2.34
2.57
105(6)
139(7)
150
100
142
C16eH16.O3i
C2eH2.O1ii
C9eH9.O3iii
C12eH12a.O1iv
0.93
0.97
2.67
2.44
133
128
Fig. 1. The molecular structure of 5j (a), 5m (b) and 5l (c; N1eH.O2 is labeled by
dashed lines) with the atom numbering scheme. Displacement ellipsoids are drawn at
the 50% probability level.
Symmetry codes: (i) x,y,z; (ii) x þ 1, þy, þz; (iii) ꢀx þ 1, þy þ 1/2, ꢀz ꢀ 1/2; (iv)
x þ 1/2, ꢀy þ 1/2 þ 2, ꢀz

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3708
Fig. 2. Cyclic voltammograms of 5a at the glassy carbon electrode (2 mm diameter) by a 0.1 V sꢀ1 scan rate in a 0.1 M acetonitrile solution of LiClO4: A) up to 1.5 V (dashed curve e
the electrolyte, solid curve e first scan, dotted curve e second scan) and B) up to 0.75 V (solid curve e first scan, dotted curve e second scan).
activities. These observations together with the fact that ferrocene
is widely regarded as a substitute for the aromatic benzene ring
prompted the preparation and testing of the antibacterial activity of
Mannich products containing a ferrocene system as a part of the
ketone moiety. The minimum inhibitory concentration (MIC) of the
synthesized compounds 5aen was measured against growth of six
bacteria (three Gram-positive and three Gram-negative) that were
chosen to represent the major types of bacteria associated with
human disease. The results of these studies and those of minimal
bactericidal activity (MBC) are presented in Table 5 as the averages
of multiple determinations. The tested bacteria were generally
sensitive to these compounds, and as shown in Table 5, the values of
MIC for compounds 5aen varied between 0.02 and 12.50 mg/ml.
Growth inhibition of the bacteria was observed for all of the
compounds early in the incubation period but the test organism
overgrew the inhibition zones within 48 h as reflected in the high
differences in the obtained MIC and MBC values. The best results
(Table 5) were obtained against a Gram-negative bacterium and an
important human pathogen, Staphylococcus aureus (MIC values
0.02e0.10 mg/ml), but most of the compounds exhibited activity at
least one hundred fold lower than Tetracycline against both Gram-
positive and negative bacteria (although the latter seem to be more
susceptible to the compounds). Infections caused by Pseudomonas
aeruginosa are often difficult to treat chemotherapeutically because
of the unusually high resistance of the organism to most antimi-
crobial drugs [60,61] and because resistance to other drugs may
evolve rapidly [61]. Therefore, it was not surprising that this
organism was the most resistant to nearly all of the compounds
studied. When comparing the activity of the herein synthesized
Mannich bases, in general, compounds having an electron-acceptor
functionality (5fen) appeared not to be more or less effective in
inhibiting the growth of all bacteria than compounds possessing
a electron-donating substituent or no substituent at all (5aee). A
similar stands for the sets of three regioisomeric compounds
(differing only in the position of the substituent on the benzene
ring), e.g. 5bed, since they had a mutually very similar antibacterial
effect as well. It was tempting to assume that the steric effects could
prevent the ortho isomers from interacting with the receptor of the
test organisms, however, the differences in potency usually
ascribed to substituents at the various positions in the benzene ring
have not been found. The other parts of the molecule seem to have
a much more important contribution to the activities observed.
Some Mannich bases derived from the corresponding acetophe-
nones (analogous to the currently prepared ferrocene derivatives)
were found to possess significant antimicrobial activity [62] (e.g. in
a disk diffusion assay [62], 1-phenyl-3-(phenylamino)propan-1-
one, the analog of compound 5a, inhibited the growth of Escher-
ichia coli with a zone of 15 mm in diameter, while at the same dose
per disk the antibiotic ofloxacin had a zone of 22 mm). Since
ferrocene is electron donating (spara
ꢀ0.18 compared to
ferrocene
spara phenyl 0.01) and electron donation to the ketone can occur, one
can take this as a possible cause of the decrease in activity in the
case of the metallocene containing compounds.
Table 4
Peak potentials obtained by cyclic voltammetry of the Mannich bases 5aen at the
glassy carbon electrode (2 mm diameter) by a 0.1 V sꢀ1 scan rate in a 0.1 M aceto-
nitrile solution of LiClO4.
3. Conclusion
In conclusion, we described herein an easily performable
procedure for the synthesis of N-aryl-3-amino-1-ferrocenylpropan-
1-ones via an aza-Michael addition of the corresponding aromatic
amines to acryloylferrocene in good to excellent yields. We
unambiguously showed that both, the catalyst (montmorillonite
K-10) and the microwave irradiation play an important role in this
synthesis. The procedure requires short reaction times, and
employs an environmentally friendly, as well as cheap catalyst.
Compound
O1 (mV)
O2 (mV)
R (mV)
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
665
653
653
693
662
647
644
638
647
647
662
659
650
653
851
803
784
693
830
992
983
861
1031
1007
952
1373
1166
1361
620
598
613
604
604
601
595
598
595
595
610
595
610
592
A trait worth noting of the 1H NMR spectra of the synthesized
b-
aminoketones, possessing electron-withdrawing substituents in
the ortho- and meta-positions of the aniline moiety of the mole-
cules, was the occurrence of coupling of the NH protons with those
of the adjacent CH2 group, indicating a slow NH exchange on the
NMR time scale. The NeCH2 signals appeared as quartets from

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I. Damljanovic et al. / Journal of Organometallic Chemistry 696 (2011) 3703e3713
3709
Fig. 3. Cyclic voltammograms of 3 mM solution of 4-(phenylamino)butan-2-one (6) at the glassy carbon electrode (2 mm diameter) by a 0.1 V sꢀ1 scan rate in a 0.1 M acetonitrile
solution of LiClO4: A) without acetylferrocene (solid curve e first scan, dotted curve e second scan) and B) with 3 mM acetylferrocene (first scan).
accidental equivalence of the vicinal HNeCH2 and CH2eCH2
couplings. Such coupling that appears to be in connection with the
acidity and/or intramolecular hydrogen bonding was not observed
for the benzene analogs or for the compounds having electron-
donating or para-electron-withdrawing substituents.
of inhibition varied. A notable exception to the generally medium-
low activity is shown by the fact that all compounds inhibited best
S. aureus. The introduction of either an electron-donating or
acceptor group in the ortho position to the phenyl resulted in no
alteration in activity.
The structure of three compounds was unequivocally corrobo-
rated by single-crystal X-ray analysis. Besides some conformational
similarity in molecular structure of all three compounds, two of
them with NO2 substituent at the phenyl ring show different
orientation of the phenyl ring regarding to the rest of molecule. The
ferrocene compound with NO2 in the ortho position forms strong
NeH.O intramolecular hydrogen bond while other two
compounds use the same NeH donor group for formation of
geometrically similar centrosymmetric dimers.
4. Experimental section
4.1. General remarks
All chemicals were commercially available and used as received,
except that the solvents were purified by distillation. Chromato-
graphic separations were carried out using silica gel 60 (Merck,
230e400 mesh ASTM), whereas silica gel 60 on Al plates, layer
thickness 0.2 mm (Merck) was used for TLC. Melting points
(uncorrected) were determined on a Mel-Temp capillary melting
All of the compounds appeared to have broad-spectrum effect
on Gram-negative and Gram-positive bacteria, although the degree
Table 5
Minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) of the synthesized Mannich bases 5aen.
Compound (mg/ml)
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
T
Gram (ꢀ) bacterial strains
Escherichia coli ATCC 25922
MIC
MBC
0.78
25.00
0.39
25.00
0.39
25.00
0.39
25.00
0.78
25.00
0.78
25.00
0.78
25.00
0.20
25.00
0.39
25.00
0.78
25.00
0.39
25.00
0.39
12.50
1.56
25.00
0.39
25.00
1.56
1.56
Salmonella enterica ATCC 13076
MIC
MBC
0.78
12.50
6.25
50.00
1.56
25.00
1.56
12.50
0.78
12.50
1.56
12.50
12.50
50.00
0.20
12.50
0.78
12.50
1.56
12.50
0.39
12.50
0.39
12.50
0.78
12.50
0.39
12.50
3.12
3.12
Pseudomonas aeruginosa ATCC 27853
MIC
MBC
1.56
25.00
0.78
25.00
1.56
12.50
3.12
25.00
3.12
12.50
3.12
25.00
3.12
25.00
3.12
25.00
1.56
25.00
3.12
25.00
3.12
25.00
1.56
25.00
1.56
25.00
0.78
25.00
3.12
3.12
Gram (þ) bacterial strains
Staphylococcus aureus ATCC 6538
MIC
MBC
0.02
3.12
0.02
3.12
0.10
6.25
0.02
3.12
0.02
3.12
0.05
3.12
0.10
6.25
0.02
3.12
0.10
6.25
0.10
6.25
0.05
3.12
0.10
6.25
0.10
6.25
0.02
3.12
0.09
0.09
Bacillus cereus ATCC 10876
MIC
MBC
0.39
25.00
1.56
50.00
3.12
50.00
0.10
12.50
1.56
25.00
0.39
12.50
0.39
12.50
0.78
25.00
0.78
25.00
0.78
25.00
0.39
12.50
0.39
25.00
0.39
12.50
0.39
12.50
1.56
1.56
Clostridium perfringens ATCC 19404
MIC
MBC
0.39
12.50
0.20
12.50
0.20
12.50
0.20
12.50
0.20
12.50
0.20
25.00
0.39
6.25
0.39
6.25
0.20
12.50
0.20
12.50
0.20
12.50
0.39
12.50
0.39
12.50
0.20
12.50
1.56
1.56
T, Tetracycline (
mg/ml).

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I. Damljanovic et al. / Journal of Organometallic Chemistry 696 (2011) 3703e3713
3710
points apparatus, model 1001. The 1H and 13C NMR spectra of the
samples in CDCl3 were recorded on a Varian Gemini (200 MHz)
4.3.2. 1-Ferrocenyl-3-(o-tolylamino)propan-1-one (5b)
m.p. 112 ꢁC; IR: nmax (KBr)/cmꢀ1 3393, 3098, 2918, 1668, 1603,
spectrometer. Chemical shifts are expressed in
d (ppm), relative to
1503, 1457, 1408, 1260, 1068, 826, 754; 1H NMR (200 MHz, CDCl3)
residual solvent protons as the internal standard (CDCl3: 7.26 ppm
for 1H and 77 ppm for 13C). Cyclic voltammetry experiments were
performed at room temperature under argon in a three-electrode
cell using an Autolab potentiostat (PGSTAT 302N). The working
electrode was a glassy carbon disk (2 mm diameter). The counter
electrode was a platinum wire, and a silver wire was used as the
reference electrode. IR measurements were carried out with a Per-
kineElmer FTIR 31725-X spectrophotometer. Microanalysis of
carbon, hydrogen and nitrogen was carried out with a Carlo Erba
1106 microanalyser; their results agreed favorably with the calcu-
lated values. The reactions (microwave assisted syntheses) were
performed by placing the teflon quivet with the reagents without
a solvent in a closed reactor equipped with pressure and temper-
ature control units and irradiating inside the cavity of a MicroSynth
(Milestone) according to the following parameters: power 500 W,
5 min.
d
7.25e6.98 (m, 2H, Ar), 6.76e6.59 (m, 2H, Ar), 4.76 (t, J ¼ 1.9 Hz, 2H,
Fc), 4.49 (t, J ¼ 1.9 Hz, 2H, Fc), 4.14 (brs, 1H, NH), 4.10 (s, 5H, Fc),
3.69e3.54 (m, 2H, NeCH2), 3.04 (t, J ¼ 6.0 Hz, 2H, COeCH2), 2.13 (s,
3H, CH3); 13C NMR (50 MHz, CDCl3)
d 203.5 (CO), 145.6 (Ar), 130.2
(Ar), 127.0 (Ar), 122.4 (Ar), 117.0 (Ar), 109.5 (Ar), 78.7 (Fc), 72.3 (Fc),
69.7 (Fc), 69.1 (Fc), 38.6 (NeC), 38.1 (CeC), 17.4 (CH3); Anal. Calcd.
(C20H21FeNO): C, 69.18; H, 6.10; N, 4.03; Found: C, 69.19; H, 6.13; N,
3.99.
4.3.3. 1-Ferrocenyl-3-(m-tolylamino)propan-1-one (5c)
m.p. 121 ꢁC; IR: nmax (KBr)/cmꢀ1 3349, 3082, 2934, 1655, 1603,
1457, 1404, 1281, 1265, 1106, 826, 773; 1H NMR (200 MHz, CDCl3)
d
7.18e6.92 (m, 1H, Ar), 6.59e6.48 (m, 3H, Ar), 4.75 (t, J ¼ 1.9 Hz, 2H,
Fc), 4.48 (t, J ¼ 1.9 Hz, 2H, Fc), 4.13 (brs, 1H, NH), 4.11 (s, 5H, Fc), 3.55
(t, J ¼ 6.1 Hz, 2H, NeCH2), 2.99 (t, J ¼ 6.1 Hz, 2H, COeCH2), 2.27 (s,
3H, CH3); 13C NMR (50 MHz, CDCl3)
d 2034 (CO), 147.6 (Ar), 138.9
(Ar), 129.1 (Ar), 118.3 (Ar), 113.8 (Ar), 110.1 (Ar), 78.7 (Fc), 72.2 (Fc),
69.7 (Fc), 69.1 (Fc), 38.6 (NeC), 38.1 (CeC), 21.5 (CH3); Anal. Calcd.
(C20H21FeNO): C, 69.18; H, 6.10; N, 4.03; Found: C, 69.17; H, 6.07; N,
4.04.
4.2. Acryloylferrocene (3)
Anhydrous AlCl3 (2.0 g, 15 mmol) was suspended in a cooled
solution (an ice bath) of 2.8 g (15 mmol) of ferrocene (1) and 1.9 g
(15 mmol) of 3-chloropropionyl chloride in 100 ml of dry
dichloromethane, and the obtained mixture stirred for 5 h. The
mixture was quenched with water (100 ml), filtered off (Buchner
funnel), and the organic layer was separated. The water layer was
extracted with two additional 30 ml portions of dichloromethane,
the combined organic layers were washed with saturated solution
of NaHCO3 and the solvent distilled off. The crude product was re-
dissolved in toluene, passed through a short column of silica, and
the toluene evaporated. The solid residue was placed in a solution
of 1.5 g of CH3COOK in 100 ml of ethanol and refluxed for 2.5 h.
After that the ethanol was evaporated, the residue extracted with
dichloromethane and the obtained solution dried over anhydrous
Na2SO4. Flash chromatography (SiO2/toluene) gave 2.41 g
(w10.5 mmol; w67% based on ferrocene) of pure acryloylferrocene
(3). The spectral data of 3 were in agreement with the literature
ones [63].
4.3.4. 1-Ferrocenyl-3-(p-tolylamino)propan-1-one (5d)
m.p. 73 ꢁC; IR: nmax (KBr)/cmꢀ1 3351, 3090, 2918, 1656, 1618,
1521, 1456, 1401, 1273, 1070, 824, 807; 1H NMR (200 MHz, CDCl3)
d
6.99 (d, J ¼ 8.2 Hz, 2H, Ar), 6.57 (d, J ¼ 8.4 Hz, 2H, Ar), 4.74 (t,
J ¼ 1.9 Hz, 2H, Fc), 4.47 (t, J ¼ 1.9 Hz, 2H, Fc), 4.10 (s, 5H, Fc), 4.06
(brs, 1H, NH), 3.53 (t, J ¼ 6.1 Hz, 2H, NeCH2), 2.98 (t, J ¼ 6.1 Hz, 2H,
COeCH2), 2.22 (s, 3H, CH3); 13C NMR (50 MHz, CDCl3)
d 203.4 (CO),
145.3 (Ar), 129.7 (Ar), 126.5 (Ar), 113.1 (Ar), 78.7 (Fc), 72.2 (Fc), 69.7
(Fc), 69.0 (Fc), 38.9 (NeC), 38.1 (CeC), 20.2 (CH3); Anal. Calcd.
(C20H21FeNO): C, 69.18; H, 6.10; N, 4.03; Found: C, 69.20; H, 6.10; N,
4.05.
4.3.5. 1-Ferrocenyl-3-(mesitylamino)propan-1-one (5e)
m.p. 86 ꢁC; IR: nmax (KBr)/cmꢀ1 3378, 3094, 2940, 1655, 1485,
1456, 1376, 1310, 1243, 1021, 821; 1H NMR (200 MHz, CDCl3)
d 6.82
(s, 2H, Ar), 4.77 (t, J ¼ 1.8 Hz, 2H, Fc), 4.48 (t, J ¼ 1.8 Hz, 2H, Fc), 4.18
(s, 5H, Fc), 3.62 (brs, 1H, NH), 3.25 (t, J ¼ 5.7 Hz, 2H, NeCH2), 2.97 (t,
J ¼ 5.7 Hz, 2H, COeCH2), 2.31 (s, 6H, o-CH3), 2.22 (s, 3H, p-CH3); 13
C
4.3. General procedure for the synthesis of Mannich bases 5aen
NMR (50 MHz, CDCl3) d 203.9 (CO), 143.3 (Ar), 131.2 (Ar), 130.0 (Ar),
129.2 (Ar), 78.7 (Fc), 72.2 (Fc), 69.7 (Fc), 69.1 (Fc), 43.1 (NeC), 39.7
(CeC), 20.5 (p-CH3), 18.1 (o-CH3); Anal. Calcd. (C22H25FeNO): C,
70.41; H, 6.71; N, 3.73; Found: C, 70.40; H, 6.70; N, 3.75.
Acryloylferrocene (3, 1 mmol), the corresponding amine (4aen,
2 mmol) and 100 mg of montmorillonite K-10 were well mixed and
irradiated in a microwave oven for 5 min at (500 W). The reaction
mixture was extracted with dichloromethane (30 ml), the solvent
evaporated and the crude product purified by flash chromatog-
raphy (SiO2). Amines were eluted with toluene, whereas ketone 3
and the target Mannich bases 5aen were separated by using of
a mixed solvent (n-hexane/ethyl acetate ¼ 9:1, v/v) as the eluent. In
all cases the complete excess of the amines was recovered. The
spectral data of compounds 5aen follow.
4.3.6. 1-Ferrocenyl-3-(2-fluorophenylamino)propan-1-one (5f)
m.p. 89 ꢁC; IR: nmax (KBr)/cmꢀ1 3383, 3096, 2903, 1665, 1619,
1529, 1402, 1261, 1190, 824, 735; 1H NMR (200 MHz, CDCl3)
d
7.13e6.50 (m, 4H, Ar), 4.77 (t, J ¼ 1.8 Hz, 2H, Fc), 4.50 (t, J ¼ 1.8 Hz,
2H, Fc), 4.37 (brs, 1H, NH), 4.12 (s, 5H, Fc), 3.71e3.48 (brq, 2H,
NeCH2), 3.02 (t, J ¼ 6.1 Hz, 2H, COeCH2); 13C NMR (50 MHz, CDCl3)
d
202.9 (CO),151.7 (JCF ¼ 238.8 Hz, Ar),136.2 (JCF ¼ 11.5 Hz, Ar),124.5
(JCF ¼ 3.4 Hz, Ar), 116.7 (JCF ¼ 7.0 Hz, Ar), 114.6 (JCF ¼ 18.5 Hz, Ar),
111.9 (JCF ¼ 3.3 Hz, Ar), 78.7 (Fc), 72.4 (Fc), 69.7 (Fc), 69.1 (Fc), 38.2
(NeC), 38.1 (CeC); Anal. Calcd. (C19H18FFeNO): C, 64.98; H, 5.17; N,
3.99; Found: C, 64.99; H, 5.20; N, 4.01.
4.3.1. 1-Ferrocenyl-3-(phenylamino)propan-1-one (5a)
m.p. 106 ꢁC; IR: nmax (KBr)/cmꢀ1 3358, 3085, 2933, 1655, 1603,
1515, 1498, 1456, 1401, 1274, 1069, 825, 746, 695; 1H NMR
(200 MHz, CDCl3)
d 7.30e7.10 (m, 2H, Ar), 6.78e6.58 (m, 3H, Ar),
4.76 (t, J ¼ 1.9 Hz, 2H, Fc), 4.49 (t, J ¼ 1.9 Hz, 2H, Fc), 4.21 (brs, 1H,
4.3.7. 1-Ferrocenyl-3-(3-fluorophenylamino)propan-1-one (5g)
m.p. 124 ꢁC; IR: nmax (KBr)/cmꢀ1 3362, 3098, 2945, 1654, 1622,
1499, 1457, 1399, 1261, 1154, 1072, 840, 823, 755, 686; 1H NMR
NH), 4.11 (s, 5H, Fc), 3.57 (t, J ¼ 6.1 Hz, 2H, NeCH2), 3.01 (t,
J ¼ 6.1 Hz, 2H, COeCH2); 13C NMR (50 MHz, CDCl3)
d 203.4 (CO),
147.6 (Ar), 129.2 (Ar), 117.4 (Ar), 112.9 (Ar), 78.7 (Fc), 72.3 (Fc), 69.7
(Fc), 69.1 (Fc), 38.5 (NeC), 38.0 (CeC); Anal. Calcd. (C19H19FeNO): C,
68.49; H, 5.75; N, 4.20; Found: C, 68.51; H, 5.71; N, 4.23.
(200 MHz, CDCl3) d 7.20e7.01 (m, 1H, Ar), 6.48e6.28 (m, 3H, Ar),
4.77 (t, J ¼ 1.9 Hz, 2H, Fc), 4.51 (t, J ¼ 1.9 Hz, 2H, Fc), 4.39 (brs, 1H,
NH), 4.12 (s, 5H, Fc), 3.63e3.46 (brq, 2H, NeCH2), 3.01 (t, J ¼ 6.0 Hz,

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3711
2H, COeCH2); 13C NMR (50 MHz, CDCl3)
d
203.3 (CO), 164.2
J ¼ 1.9 Hz, 2H, Fc), 4.50 (t, J ¼ 1.9 Hz, 2H, Fc), 4.36 (brs, 1H, NH), 4.12
(s, 5H, Fc), 3.61e3.46 (brq, 2H, NeCH2), 3.00 (t, J ¼ 6.0 Hz, 2H,
(JCF ¼ 242.8 Hz, Ar), 149.5 (JCF ¼ 10.6 Hz, Ar), 130.4 (JCF ¼ 10.2 Hz,
Ar), 108.9 (JCF ¼ 2.3 Hz, Ar), 103.8 (JCF ¼ 21.6 Hz, Ar), 99.3
(JCF ¼ 25.3 Hz, Ar), 78.6 (Fc), 72.4 (Fc), 69.8 (Fc), 69.1 (Fc), 38.4
(NeC), 37.8 (CeC); Anal. Calcd. (C19H18FFeNO): C, 64.98; H, 5.17; N,
3.99; Found: C, 64.95; H, 5.17; N, 4.00.
COeCH2); 13C NMR (50 MHz, CDCl3)
d 203.2 (CO), 148.8 (Ar), 135.0
(Ar), 130.2 (Ar), 117.2 (Ar), 112.2 (Ar), 111.4 (Ar), 78.6 (Fc), 72.4 (Fc),
69.7 (Fc), 69.1 (Fc), 38.3 (NeC), 37.8 (CeC); Anal. Calcd.
(C19H18ClFeNO): C, 62.07; H, 4.93; N, 3.81; Found: C, 62.05; H, 4.96;
N, 3.80.
4.3.8. 1-Ferrocenyl-3-(4-fluorophenylamino)propan-1-one (5h)
m.p. 127 ꢁC; IR: nmax (KBr)/cmꢀ1 3399, 3102, 2911, 1664, 1521,
1461, 1400, 1219, 1050, 818, 785; 1H NMR (200 MHz, CDCl3)
4.3.11. 3-(4-Chlorophenylamino)-1-ferrocenylpropan-1-one (5k)
m.p. 51 ꢁC; IR: nmax (KBr)/cmꢀ1 3344, 3092, 2933, 1658, 1596,
1509, 1493, 1456, 1396, 1273, 1088, 1066, 824, 799; 1H NMR
d
6.97e6.82 (m, 2H, Ar), 6.66e6.54 (m, 2H, Ar), 4.76 (t, J ¼ 1.9 Hz,
2H, Fc), 4.51 (t, J ¼ 1.9 Hz, 2H, Fc), 4.12 (brs, 1H, NH), 4.12 (s, 5H, Fc),
(200 MHz, CDCl3) d 7.19e7.01 (m, 2H, Ar), 6.65e6.50 (m, 3H, Ar),
3.52 (t, J ¼ 6.0 Hz, 2H, NeCH2), 3.00 (t, J ¼ 6.0 Hz, 2H, COeCH2); 13
C
4.75 (t, J ¼ 1.9 Hz, 2H, Fc), 4.50 (t, J ¼ 1.9 Hz, 2H, Fc), 4.24 (brs, 1H,
NMR (50 MHz, CDCl3)
d
203.4 (CO), 155.9 (JCF ¼ 235.1 Hz, Ar), 144.1
NH), 4.11 (s, 5H, Fc), 3.52 (t, J ¼ 6.0 Hz, 2H, NeCH2), 2.98 (t,
(JCF ¼ 1.5 Hz, Ar), 115.7 (JCF ¼ 22.3 Hz, Ar), 113.9 (JCF ¼ 7.4 Hz, Ar),
103.8 (JCF ¼ 21.6 Hz, Ar), 99.3 (JCF ¼ 25.3 Hz, Ar), 78.7 (Fc), 72.4 (Fc),
69.8 (Fc), 69.1 (Fc), 39.3 (NeC), 37.9 (CeC); Anal. Calcd.
(C19H18FFeNO): C, 64.98; H, 5.17; N, 3.99; Found: C, 65.00; H, 5.21;
N, 3.97.
J ¼ 6.0 Hz, 2H, COeCH2); 13C NMR (50 MHz, CDCl3)
d 203.3 (CO),
146.2 (Ar), 129.0 (Ar), 121.8 (Ar), 113.9 (Ar), 78.6 (Fc), 72.4 (Fc), 69.7
(Fc), 69.1 (Fc), 38.7 (NeC), 37.8 (CeC); Anal. Calcd. (C19H18ClFeNO):
C, 62.07; H, 4.93; N, 3.81; Found: C, 62.10; H, 4.94; N, 3.79.
4.3.12. 1-Ferrocenyl-3-(2-nitrophenylamino)propan-1-one (5l)
m.p. 96 ꢁC; IR: nmax (KBr)/cmꢀ1 3377, 3116, 2935, 1661, 1617,
1568, 1508, 1457, 1399, 1263, 1238, 1149, 823, 743; 1H NMR
4.3.9. 3-(2-Chlorophenylamino)-1-ferrocenylpropan-1-one (5i)
m.p. 108 ꢁC; IR: nmax (KBr)/cmꢀ1 3418, 3096, 2921, 1675, 1599,
1504, 1456, 1410, 1325, 1256, 1025, 823, 750; 1H NMR (200 MHz,
(200 MHz, CDCl3) d 8.42e8.11 (m, 2H, NH and Ar), 7.60e7.40 (m, 1H,
CDCl3)
d
7.33e7.10 (m, 2H, Ar), 6.82e6.55 (m, 2H, Ar), 4.77 (t,
Ar), 6.96 (d, J ¼ 8.5 Hz, 1H, Ar), 6.75e6.59 (m, 1H, Ar), 4.80 (t,
J ¼ 1.9 Hz, 2H, Fc), 4.53 (t, J ¼ 1.9 Hz, 2H, Fc), 4.17 (s, 5H, Fc), 3.76 (q,
J ¼ 6.6 Hz, 2H, NeCH2), 3.12 (t, J ¼ 6.6 Hz, 2H, COeCH2); 13C NMR
J ¼ 1.9 Hz, 2H, Fc), 4.77 (brs, 1H, NH), 4.50 (t, J ¼ 1.9 Hz, 2H, Fc), 4.12
(s, 5H, Fc), 3.64 (q, J ¼ 6.1 Hz, 2H, NeCH2), 3.03 (t, J ¼ 6.2 Hz, 2H,
COeCH2); 13C NMR (50 MHz, CDCl3)
d
202.7 (CO), 143.5 (Ar), 129.3
(50 MHz, CDCl3) d 201.5 (CO), 145.0 (Ar), 136.1 (Ar), 126.9 (Ar), 115.3
(Ar), 127.8 (Ar), 119.4 (Ar), 117.3 (Ar), 110.9 (Ar), 78.7 (Fc), 72.4 (Fc),
69.8 (Fc), 69.2 (Fc), 38.1 (NeC), 38.1 (CeC); Anal. Calcd.
(C19H18ClFeNO): C, 62.07; H, 4.93; N, 3.81; Found: C, 62.03; H, 4.94;
N, 3.78.
(Ar), 113.4(Ar), 78.3 (Fc), 72.5 (Fc), 69.7 (Fc), 69.1 (Fc), 38.3 (NeC),
37.6 (CeC); Anal. Calcd. (C19H18FeN2O3): C, 60.34; H, 4.80; N, 7.41;
Found: C, 60.30; H, 4.81; N, 7.41.
4.3.13. 1-Ferrocenyl-3-(3-nitrophenylamino)propan-1-one (5m)
m.p. 91 ꢁC; IR: nmax (KBr)/cmꢀ1 3329, 3098, 2956, 1656, 1620,
1526, 1456, 1347, 1265, 1238, 826, 782; 1H NMR (200 MHz, CDCl3)
4.3.10. 3-(3-Chlorophenylamino)-1-ferrocenylpropan-1-one (5j)
m.p. 121 ꢁC; IR: nmax (KBr)/cmꢀ1 3353, 3086, 2930, 1654, 1596,
1487, 1456, 1400, 1275, 1248, 1073, 822, 758; 1H NMR (200 MHz,
d
7.60e7.40 (m, 2H, Ar), 7.36e7.21 (m, 1H, Ar), 7.36e7.21 (m, 1H, Ar),
CDCl3)
d 7.14e7.00 (m, 1H, Ar), 6.72e6.45 (m, 3H, Ar), 4.76 (t,
6.98e6.85 (m, 1H, Ar), 4.78 (t, J ¼ 1.9 Hz, 2H, Fc), 4.71 (brs, 1H, NH),
Table 6
Crystallographic data for 5j, 5m and 5l.
Identification code
5j
5m
5l
Empirical formula
Formula weight
C19H18ClFeNO
367.64
C19H18FeN2O3
378.20
C19H18FeN2O3
378.20
Color, crystal shape
Crystal size (mm3)
Temperature (K)
Dark-orange, prism
0.32 ꢂ 30 ꢂ 25
293(2)
Dark-orange, plate
0.36 ꢂ 0.31 ꢂ 0.10
293(2)
Dark-orange, prism
028 ꢂ 0.25 ꢂ 0.23
293(2)
ꢂ
Wavelength (A)
0.71073
0.71073
0.71073
Crystal system
Space group
Triclinic
P ꢀ 1
Triclinic
P ꢀ 1
Orthorhombic
P212121
Unit cell dimensions
ꢂ
a (A)
7.5449(7)
9.7317(8)
12.5382(11)
88.912(7)
76.107(8)
69.330(12)
833.96(13)
9.109(3)
9.659(2)
11.242(3)
65.53(3)
72.79(2)
84.94(4)
859.3(4)
5.8295(7)
13.6390(18)
21.231(4)
90
90
90
ꢂ
b (A)
ꢂ
c (A)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
3
ꢂ
V (A )
1688.0(4)
Z
2
2
4
Dcalc (Mg/m3)
1.464
1.067
3.03e28.97
1.462
0.898
2.98e28.92
1.488
0.914
3.14e29.03
m
(mmꢀ1
)
q
range for data collection (ꢁ)
Reflections collected
6698
5930
5237
Independent reflections, Rint
3803, 0.0458
99.6
3877, 0.1109
99.7
3564, 0.0470
99.8
Completeness (%) to
q
¼ 26.32ꢁ
Refinement method
Full-matrix least-squares on F2
3803/0/212
Full-matrix least-squares on F2
3877/0/230
Full-matrix least-squares on F2
3564/0/230
Data/restraints/parameters
Goodness-of-fit on F2
1.090
0.992
1.052
Final R1/wR2 indices [I > 2
s
(I)]
0.0889/0.1997
0.0853/0.1856
0.0683/0.1349

ꢀ
I. Damljanovic et al. / Journal of Organometallic Chemistry 696 (2011) 3703e3713
3712
4.53 (t, J ¼ 1.9 Hz, 2H, Fc), 4.13 (s, 5H, Fc), 3.70e3.54 (brq, 2H,
NeCH2), 3.05 (t, J ¼ 5.9 Hz, 2H, COeCH2); 13C NMR (50 MHz, CDCl3)
range 0.01e50.00 mg/ml (the diluting factor 2). The bacterial
inoculum was added to all wells containing the compounds in
appropriate concentrations and the plates were incubated at 37 ꢁC
during 24 h. Tetracycline served as a positive control, while the
solvent (10% DMSO(aq)) was used as a negative control. The DMSO
solvent controls did not produce any measurable inhibition of the
test organisms. Replicate tests performed with a specific dilution of
a test compound on any given day were in excellent agreement and
results obtained with a specific dilution of any given compound on
different days were generally in close agreement. One non-
inoculated well, free of the antimicrobial agents, was also
included to ensure medium sterility.
d
203.3 (CO), 148.6 (Ar), 147.6 (Ar), 129.8 (Ar), 119.2 (Ar), 111.9 (Ar),
105.9 (Ar), 78.4 (Fc), 72.6 (Fc), 69.8 (Fc), 69.2 (Fc), 38.4 (NeC), 37.7
(CeC); Anal. Calcd. (C19H18FeN2O3): C, 60.34; H, 4.80; N, 7.41;
Found: C, 60.32; H, 4.84; N, 7.43.
4.3.14. 1-Ferrocenyl-3-(4-nitrophenylamino)propan-1-one (5n)
m.p. 189e190 ꢁC; IR: nmax (KBr)/cmꢀ1 3356, 3107, 2907, 1653,
1604, 1501, 1471, 1319, 1115, 832, 754; 1H NMR (200 MHz, CDCl3)
d
8.09 (d, J ¼ 9.2 Hz, 2H, Ar), 6.61 (d, J ¼ 9.2 Hz, 2H, Ar), 4.79 (t,
J ¼ 1.9 Hz, 2H, Fc), 4.58 (t, J ¼ 1.9 Hz, 2H, Fc), 4.14 (s, 5H, Fc), 3.74
(brs, 1H, NH), 3.66 (t, J ¼ 6.1 Hz, 2H, NeCH2), 3.07 (t, J ¼ 6.1 Hz, 2H,
Bacterial growth was visualized by adding 20 ml of 0.5% (w/w)
COeCH2). 13C NMR (50 MHz, CDCl3)
d
204.0 (CO), 153.5 (Ar), 137.5
triphenyltetrazolium chloride (TTC) aqueous solution [72]. Minimal
inhibitory concentration (MIC) was defined as the lowest concen-
tration of the compounds 5aen that inhibited visible growth (red
colored pellet on the bottom of the wells after the addition of TTC),
while minimal bactericidal concentration (MBC) was defined as the
lowest concentration of the compound that killed 99.9% of bacterial
cells. To determine MBC, broth was taken from each well without
any visible growth and inoculated in Mueller Hinton agar (MHA) for
24 h at 37 ꢁC.
(Ar), 126.8 (Ar), 111.0 (Ar), 78.3 (Fc), 73.2 (Fc), 70.1 (Fc), 69.5 (Fc),
38.0 (NeC), 38.0 (CeC); Anal. Calcd. (C19H18FeN2O3): C, 60.34; H,
4.80; N, 7.41; Found: C, 60.33; H, 4.82; N, 7.38.
4.4. X-ray crystallography
Single-crystal diffraction data for 5j, 5l and 5m were collected
on a Oxford Diffraction Xcalibur Sapphire3 Gemini diffractometer
ꢂ
equipped with Mo K
a
radiation (
l
¼ 0.71073 A) at room tempera-
ture. Data were processed with CrysAlis software [64] with multi-
scan absorption corrections applied using SCALE3 ABSPACK [64].
All three crystal structures were solved with SHELXS [65] and
refined using SHELXL [65].
4.5.3. Statistical analysis
All experiments were done in quantiplicate and mean values are
presented. In order to evaluate statistically any significant differ-
ences among mean values, a one-way ANOVA test was used. p
values less than 0.05 (p < 0.05) were used as the significance level.
The H1n atom attached to N1 was located by difference Fourier
synthesis and refined isotropically. All other H atoms were placed at
geometrically calculated positions with the CeH distances fixed to
Acknowledgment
2
ꢂ
0.93 from C(sp ); 0.97 and 0.98 A from methylene and methine
C(sp3), respectively. The corresponding isotropic displacement
parameters of the hydrogen atoms were equal to 1.2Ueq and 1.5Ueq
of the parent C(sp2) and C(sp3), respectively.
This work was supported by the Ministry of Education and
Science of the Republic of Serbia (grant 172034).
A summary of crystallographic data is given in Table 6.
Figures were produced using ORTEP-3 [66] and MERCURY, Version
2.4 [67]. The software used for the preparation of the materials for
publication: WinGX [68], PLATON [69], PARST [70].
Appendix. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2011.08.016.
4.5. Biology
Appendix A. Supplementary data
4.5.1. Test microorganisms
CCDC 827956, 827957 and 821837 contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
The synthesized Mannich bases 5aen were tested against
a panel of microorganisms (American Type Culture Collection
strains), including Gram-positive S. aureus ATCC 6538, Bacillus
cereus ATCC 10876, Clostridium perfringens ATCC 19404, Gram-
negative Salmonella enterica ATCC 13076, E. coli ATCC 25922 and
P. aeruginosa ATCC 27853. Bacterial strains were maintained on
Nutrient agar at optimal temperature of 37 ꢁC at the Microbiology
Laboratory (Department of Biology, Faculty of Science and Mathe-
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