Dinuclear heptacoordinate dibutyltin (IV) complexes derived from Schiff bases and dicarboxylates: Synthesis, cytotoxicity, and antioxidant activity

Article abstract of DOI:10.1016/j.jorganchem.2013.03.038

The synthesis of dinuclear dibutyltin (IV) complexes 1a-4d, prepared in one pot by the reaction of 2-amino-4-R-phenol (R = H, Me, Cl, NO₂), 2-pyridinecarboxaldehyde, dicarboxylic (2,5-pyridinedicarboxylic, terephthalic, isophthalic, and oxalic)

Full text of DOI:10.1016/j.jorganchem.2013.03.038

Journal of Organometallic Chemistry 738 (2013) 10e19
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Dinuclear heptacoordinate dibutyltin (IV) complexes derived from Schiff bases
and dicarboxylates: Synthesis, cytotoxicity, and antioxidant activity
Alejandro Ramírez-Jiménez, Rolando Luna-García, Armando Cortés-Lozada, Simón Hernández,
*
Teresa Ramírez-Apan, Antonio Nieto-Camacho, Elizabeth Gómez
Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México 04510, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of dinuclear dibutyltin (IV) complexes 1ae4d, prepared in one pot by the reaction of
Received 28 January 2013
Received in revised form
22 March 2013
2-amino-4-R-phenol (R
¼
H, Me, Cl, NO2), 2-pyridinecarboxaldehyde, dicarboxylic (2,5-pyridine-
dicarboxylic, terephthalic, isophthalic, and oxalic) acids and dibutyltin oxides, is described. The com-
plexes were characterized using IR, MS and 1H, 13C and 119Sn NMR techniques. The molecular structures
of complexes 1a, 1c and 4c were established using X-Ray diffraction, and these complexes exhibited a
distorted pentagonal-bipyramidal (BPT) geometry in which the equatorial plane consisted of three ox-
ygen atoms and two nitrogen atoms, and the butyl groups occupied the axial positions. The cytotoxicity
of the terephthalic acid derivatives 1aed in HCT-15 colon cancer, MCF7 breast cancer and PC3 prostate
cancer cell lines was investigated in vitro. The antioxidant activity of these complexes was also measured
using the DPPH (1,1-diphenyl-2-picrylhydrazyl) assay.
Accepted 25 March 2013
Keywords:
Diorganotin(IV)
Carboxylates
119Sn NMR
X-ray
Ó 2013 Elsevier B.V. All rights reserved.
Cytotoxicity
Antioxidant activity
1. Introduction
picolinoacylhydrazone, which exhibit supramolecular structures
with 1D chains or 2D networks [19]. The Schiff base ligands
Organotin(IV) complexes have been widely investigated
because of their structural diversity and possible applications
as cytotoxic, anti-inflammatory, antimicrobial, cardiovascular,
insecticidal, and antifungal agents [1e5]. Several ligands have
been reported to lead to a variety of complexes, including
monomeric, dimeric, trimeric, tetrameric and polymeric com-
plexes with different geometries and coordination modes [6e10].
Special attention has been devoted to Schiff Base ligands, which
form organotin complexes with different structural arrangements
and interesting biological activities [11-12]. Carboxylates are also
important from the biochemical point of view due to their anti-
proliferative properties [13e17]. Additionally, numerous studies
have been undertaken concerning the types of coordination
geometries assumed by these complexes. Some examples of
dinuclear organotin complexes are the molecular adducts of dio-
rganotin dichloride with N-(2-oxidearylideneaminoacidato) [18]
and the dinuclear diorganotin(IV) derivatives of pyruvic acid
containing an ONO donor system also afford dinuclear tin(IV)
complexes with five- or six-coordinative geometries depending
on the type of substituent bonded to the metal center [20],
whereas bifunctional tridentate ligands form three classes of
organotin(IV) complexes: diorganotin, triorganotin and dinuclear
organotin derivatives [21]. Although a number of reports of this
class of compounds have been described, few examples of dinu-
clear organotin complexes containing mixed ligands have been
described. Thus, we recently reported the synthesis of a series of
mononuclear organotin(IV) complexes with mixed ligand. In that
study, we demonstrated that penta- or heptacoordinated com-
plexes can be obtained depending on the reaction conditions and
the stoichiometry [22]. As part of our interest in this type of
complexes, in this report, we describe the synthesis of dinuclear
heptacoordinated dibutyltin(IV) complexes containing mixed li-
gands and dicarboxylates. In an in vitro study, complexes 1ae
d exhibited varied antiproliferative activities against three cell
lines. These complexes also exhibited antioxidant activity in the
DPPH (1,1-diphenyl-2-picrylhydrazyl) assay; specifically, com-
plexes 1b (IC50 ¼ 9.24
active than
-tocopherol (IC50 ¼ 31.74
positive control.
m
M) and 1c (IC50 ¼ 9.24
mM) were more
M), which was used as a
a
m
* Corresponding author. Tel.: þ52 55 56224506.
E-mail address: eligom@unam.mx (E. Gómez).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.038

A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
11
Table 1
2. Results and discussion
Assignment of characteristic FT-IR vibrations (cmꢀ1).
The complexes were obtained in a one-step reaction from 2-
pyridinecarboxaldehyde, 2-amino-4-R-phenol (R ¼ H, CH3, Cl,
NO2), di-n-butyltin(IV) oxide and the corresponding dicarboxylic
acid in a 2:2:2:1 M ratio (Scheme 1). The compounds were isolated
in yields ranging from 53 to 93%.
Compound
nasym
nsym
dn
1a
1b
1c
1d
2a
2b
2c
2d
3a
1567
1556
1548
1561
1564
1545
1545
1560
1639
1607
1637
1612
1639
1616
1648
1372
1387
1369
1400
1379
1381
1379
1387
1345
1373
1346
1371
1347
1373
1355
1381
1459
1467
1460
1489
195a
169a
179a
161a
185a
164a
166a
173a
2.1. FTIR analysis
294b
234a
291b
241a
291b
243a
293b
e
180c
173c
181c
151c
The infrared spectra (FTIR) of complexes 1ae4d exhibited bands
in the region of 1588e1612 cmꢀ1 that were assigned to the C]N
stretching vibrations of the different complexes. These bands are
3b
3c
3d
shifted to lower energies compared with the n(N]C) stretch of the
Schiff base ligand [12,22]. This shift has been attributed to the
donation of the lone pair of the azomethine nitrogen to the tin atom
[11]. The absence of the carboxylic acid and phenol OH groups
resulted in the deprotonation of the ligand and the formation of a
SneO bond. The spectra of complexes 1aed and 2aed exhibited
two different absorption bands in the range of 1371 cmꢀ1 to
1560 cmꢀ1, which correspond to the nsym(COOꢀ) and nasym(COOꢀ)
vibrational modes of the carboxyl groups, respectively. The energy
difference between the asymmetric and symmetric carboxylate
stretching vibrations is in the range of 160e195 cmꢀ1, which is
attributed to the formation of a chelating carboxylate with aniso-
bidentate coordination (see Table 1) [23]. However, the spectra for
the 2,5-pyridinedicarboxylic acid derivatives 3aed exhibited two
different bands in the ranges of 1648 to 1607 and 1371e1345 cmꢀ1
that were assigned to the nasym(COOꢀ) and nsym(COOꢀ) vibrations.
4a
4b
4c
4d
1639
1640
1641
1640
Carboxylate coordination mode (a) anisobidentate, (b) monodentate (c) bidentate.
The energy difference between the asymmetric and symmetric
carboxylate stretching vibrations indicated that the carboxylates
are coordinated to metal center in both the monodentate and
anisobidentate coordination modes. These Dn values are similar to
those of the monomeric complex and the 2,5-pyridine tin carbox-
ylates previously described, which verifies the presence of the two
4
18
R
3
17
5
R
2
N
O
O
O
19
N
Bu
N
16
Bu
O
Bu
N
Bu
15
O
O
O
O
Sn
Bu
17
Sn
N
Sn
Bu
O
O
Sn
Bu
N
16
O
Bu
N
9
O
15
N
14
10
2a
14
2b
2c
2d
1a
13
R
1b
1c
1d
12
R
Terephthalic acid
Isophthalic acid
O
R
NH2
OH
H
2 n-Bu2SnO
+
+
N
a) R = H
b) R = CH3
c) R = Cl
d) R = NO2
Oxalic acid
2,6-pyridinedicarboxilic acid
4
3
O
3
17
18
5
4
21
2
2
16
R
Bu
19
R
N
O
O
Bu
O
O
Bu
Bu
N
5
N
15
22
O
O
O
7
20
Sn
Bu
Sn
Sn
Sn
Bu
N
N
O
N
O
N
7
O
O
Bu
N
Bu
9
14
N
9
14
13
10
10
13
12
R
12
4a
4b
4c
4d
3a
3b
3c
3d
R
Scheme 1.

12
A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
coordination modes [6,7,22]. The spectra of the oxalic acid de-
rivatives 4aed exhibit a nasym(COOꢀ) stretching frequency at
approximately 1640 cmꢀ1, and the nsym(COOꢀ) mode appears in the
range of 1459e1489 cmꢀ1, which is shifted to a higher energy
relative to those observed for complexes 2ae3d. The Dn value (in
the range of 170e180 cmꢀ1) and the band shift of nsym(COOꢀ)
indicate that the carboxylate group coordinates to the metal center
in a bidentate fashion [23] (Table 1).
All complexes exhibited four signals in the range of 13.4e32.6 ppm
corresponding to the butyl groups. This result reveals that the two
butyl moieties bonded to the tin atom are equivalent, as was
observed in the proton NMR spectra. Thus, for complexes 1a,1b and
2b, it was also possible to measure the coupling constant 1J(13Ce119/
117Sn) using these values, and the Lockhart equation [24] was used
to calculate the CeSneC bond angles, which were determined to be
167.1, 166.2 and 168.9ꢁ for complexes 1a, 1b and 2b, respectively.
As was observed for complexes 3aed, multiple signals for the
ligand fragments coordinated to the metal were observed because
of the presence of two different coordination modes for the 2,5-
pyridinedicarboxylate fragment. Compounds 4aed exhibited sig-
nals for only half of the molecule.
2.2. Mass spectrometry (FABþ)
The mass spectrometry data showed the molecular ions only for
complexes 1aec, 2aed, 3a,3ced, and 4c with a low relative abun-
dance; however, for all complexes, the [M ꢀ Bu]þ ion and the
fragment ions corresponding to the subsequent loss of the butyl
and the carboxylate groups [Mþ ꢀ PyCOOꢀ] were also observed.
The fragmentation pattern exhibited the characteristic natural
isotopic profile in which 120Sn is the most abundant isotope. To
confirm the formation of the dinuclear complexes, a comparative
analysis of the isotopic distribution of the [M ꢀ 57 ꢀ 1]þ ion with
the calculated isotopic patterns was performed, and a quantitative
similitude was observed.
2.5. 119Sn NMR
Typical signals in the range of ꢀ347 to ꢀ367 ppm for hepta-
coordinated tin were observed in the 119Sn NMR spectra of com-
pounds 1ae2d. However, in the case of compounds 3aed, two
signals were observed, one in the range of ꢀ333 to ꢀ357 ppm and
the other in the range of ꢀ414 to ꢀ441 ppm, indicating two
different chemical environments around the tin atom. The first
signal appears in the same region as those observed for the ter-
ephthalic and isophthalic derivatives, which allowed us to suc-
cessfully assign the signals for each tin atom. For the oxalate
derivatives 4aec, signals with chemical shifts between ꢀ413.6
and ꢀ415.6 were detected, and these signals are shifted to lower
frequencies compared with those of compounds 1ae2d, which
strongly suggests a different coordination environment.
2.3. 1H NMR
The 1H NMR spectra of the dinuclear derivatives containing
terephthalic and isophthalic acids exhibited signals corresponding
to symmetrical species. The 1H NMR spectra of the derivatives of
terephthalic acid (1aed) exhibited a single signal between 8.21 and
8.30 ppm corresponding to the aromatic hydrogen H-15. For the
complexes containing isophthalic acid derivatives (2aed), two
doublets signals at approximately 9.1 and 7.5 ppm were detected
for protons H-15 and H-18, respectively (the numbering followed in
all molecules is indicated in the Supplementary material). The
aliphatic region contained only one triplet signal corresponding to
the methyl hydrogens of the butyl groups bonded to the tin atom
because of the magnetic equivalence of these groups.
For complexes 3aed, the proton NMR spectra exhibited two
groups of signals in the aromatic region for the two metal frag-
ments due to the non-symmetry of 2,5-pyridinedicarboxylate. The
chemical shifts for one of these groups of signals are similar to
those of the monomeric species that were described previously,
which strongly indicates the presence of a heptacoordinated tin
heterocyclic ring species in which the carboxylate group is coor-
dinated in a monodentate fashion [22]. In this case, the aliphatic
region exhibited two triplet signals for the methyl hydrogens of the
butyl groups attached to the metal, thus corroborating the presence
of two different chemical environments around the tin atoms in the
bimetallic complex. The complete assignment of the individual
signals was performed based on the results of 2D experiments.
The 1H NMR spectra of complexes 4aec exhibited only one
triplet signal arising from the methyl hydrogens of the butyl groups
bonded to the metal, as was observed for complexes 1ae2d, thus
confirming the symmetry in the molecule. Because complex 4d was
not soluble in common solvents, we were unable to characterize
this complex using NMR spectroscopy.
2.6. X-ray diffraction
The molecular structures of compounds 1a, 1c and 4c were
established using X-ray diffraction. The details of the crystallo-
graphic data and a summary of the data parameters for the three
complexes are given in Table 2. Selected bond lengths are listed in
Table 3, and bond angles were included as Supplementary material.
The unit cell of 1c consists of two halves of crystallographically
independent but chemically equivalent molecules. An examination
of the molecular structures of these compounds reveals that the
two tin atoms are equivalent due to the presence of an inversion
center in the molecule; the geometry is a distorted pentagonal
bipyramid (BPT) (Figs. 1e3). The equatorial plane consists of three
oxygen atoms from the phenoxide and the carboxylate groups, two
nitrogen atoms from the azomethine and one nitrogen from the
pyridine ring. The butyl groups occupy the axial positions and form
a CeSneC angle of 167.2(1) to 170.6(3)ꢁ. These values are in
agreement with those calculated from the NMR solution data
(166.2e168.9ꢁ), indicating that the geometries of these species are
similar. The atoms in the equatorial plane exhibit N(1)eSneN(2)
and N(2)eSne(O1) angles in the range of 66.4e78.4ꢁ.
The Sn(1)eO(1) bond lengths are slightly shorter than the van
der Waals radii, whereas the SneO(3) bond lengths are slightly
longer than that found in complexes containing chelating carbox-
ylates [25].The O / Sn bond distances in complexes 1a and 1c are
ꢀ
2.519(3) and 2.493(4)/2.528(4) A, respectively; these values are
similar to those of the complexes described in the literature that
possess an OeSn coordination bond [26]. The O / Sn bond length
for 4c (Sn(1)eO(3)) is 2.405(3), which is shorter than those of
complexes 1a and 1c. This difference may be attributed to the
formation of five-membered rings and the presence of a bidentate
coordination mode of the carboxylate ligand, which is in contrast
with that observed for compounds 1a and 1c in which the
carboxylate forms four-membered rings, as evidenced from the IR
spectra.
2.4. 13C NMR
The molecular symmetry of complexes 1ae2d is also evident
from the 13C NMR spectra. For the terephthalic acid derivatives
(1ae1d), three signals for the ipso carbon C-16, the ortho carbon C-
15 and the carboxylate carbon C-17 were observed. In the case of
complexes 2aed, the isophthalate moieties gave rise to four signals
for the ipso (C-16), ortho (C-15 and C-17) and meta (C-18), carbons.

A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
13
Table 2
cell line, complex 1d exhibited better cytotoxicity than complexes
1a and 1b did, whereas complex 1a exhibited lower cytotoxicity. It
is evident that compound 1c displayed higher values of cytotoxicity
against MCF7 breast cancer cells than it did against the PC3 prostate
and HCT15 colon cell lines, Apparently, the effect of the substituent
on the aromatic rings plays a role in the inhibition mechanism,
which has also been observed in the heptacoordinate tin com-
pounds derived from pyridine Schiff bases [12]. Although the tested
complexes 1aed exhibited higher cytotoxicity against MCF7 breast
cancer cells they are less cytotoxic than the tetra-n-butyltin-bis-
3,6-dioxaheptanoato and -bis,3,6,9-trioxadecanoato-distannoxane
dimers previously described [15].
Crystallographic data for compounds 1a, 1c and 4c.
Complex
1a
1c
4c
Formula
C48H58N4O6Sn2 C48H56Cl2N4O6Sn2 C42H52Cl2N4O6Sn2
1024.36
Formula weight
1093.25
1017.16
(g molꢀ1
)
Crystal size (mm)
0.392 ꢂ 0.154
ꢂ 0.126
Red
Monoclinic
P21/n
10.003(1)
18.985(2)
12.273(1)
90ꢁ
95.245(2)
90ꢁ
2320.9(4)
2
1.466
0.204 ꢂ 0.108
ꢂ 0.044
Red
Triclinic
P-1
9.988(1)
13.186(2)
19.128(2)
98.760(2)
93.039(2)
104.782(2)
2396.1(5)
2
0.35 ꢂ 0.22 ꢂ 0.18
Color
Red
Trigonal
R-3
25.3606(11)
25.3606(11)
20.6259(18)
90ꢁ
90ꢁ
120
Crystal system
Space group
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(o)
(o)
(o)
2.8. Antioxidant activity
3
ꢀ
V (A )
11488.5(12)
9
1.323
The antioxidant activity of ligands L1eL4 and complexes 1ae
d against the stable free radical 1,1-diphenyl-2-picrylhydrazyl
(DPPH) was investigated, as shown in Table 5. The reduction
capability of the DPPH radicals was determined from the decrease
in its absorbance at 517 nm, which can be induced by antioxidants
[27]. The inhibitory effect of the ligands and their corresponding
Sn(IV) complexes on OH increased with increases in the sample
concentration. All of the complexes exhibited a stronger effect than
the free ligands did. Complexes 1aec were also more active than
Z
Dcalc. (g/cm3)
No. of collected
reflections
1.449
25,901
25,291
32,002
No. of independent 4246 (0.0636)
8761 (0.0492)
8761
4698 (0.0786)
4698
reflections (Rint
No. of observed
reflections
)
4246
No. of parameters
290
563
338
Ra
Rw
0.0305
0.0412
0.962
0.0445
0.0593
1.062
0.0464
0.0702
0.962
b
were
a-tocopherol and quercetin, which were used as positive
GOF
controls. These results agree with those of previous studies [28,29]
in which the metal center increased the antioxidant activity in
comparison with the free ligand, as was observed for L1eL3
(Table 5). The nitro derivative 1d did not exhibit activity;
conversely, complex 1b exhibited the highest activity.
P
P
a
R ¼ jjFoj ꢀ jFcjj/ jFoj.
P
P
b
Rw(Fo)2 ¼ [ w(Fo2 ꢀ F2c)2/ wFo4]1/2
.
2.7. Cytotoxic studies
3. Conclusions
The cytotoxic activity of complexes 1aed was assessed using
three tumor cell lines. Table 4 shows the IC50 values using HCT-15
colon cancer, MCF7 breast cancer and PC3 prostate cancer cell
lines. All of the complexes exhibited higher cytotoxicity than the
positive control did. In the MCF7 cell line, compound 1c was shown
to be more cytotoxic than complexes 1a,1b, and 1d were. In the PC3
cell line, compounds 1a and 1b exhibited the poorest cytotoxic
properties. A substantial improvement is evident with complex 1d,
which exhibited an IC50 value in the micromolar range; thus,
complex 1d is approximately four orders of magnitude more
cytotoxic than compounds 1a and 1b are. In the HCT15 colon cancer
Dinuclear heptacoordinated species with different crystal
structures were obtained. This observation reveals that 2,5-
pyridinedicarboxylates give rise to two coordination modes in the
molecule. In this case, the preferred structure was observed to
include a pyridine nitrogen coordinated to the metal center. The
terephthalic and isophthalic acids gave rise to an anisobidentate
coordination; however, the oxalic acid derivatives were coordi-
nated in a bidentate mode. The cytotoxicity assay showed that all of
the complexes display different antitumor activities against the
tumor cells tested. Complex 1d exhibited the highest cytotoxic
activity against PC3 prostate and HCT15 colon cell lines; however,
for the MCF7 breast cancer cells, complex 1b exhibited the best
cytotoxicity. The antioxidant activity experiments showed that
these complexes possess high antioxidant activity that is capable of
stabilizing a radical molecule. These complexes are also more active
than are the ligands, indicating that the metal center increases the
activity.
Table 3
ꢁ
ꢀ
Bond lengths (A) and angles ( ) for complexes 1a, 1c and 4c.
Bond lengths
1a
1c
4c
Sn(1)eO(1)
Sn(2)eO(4)
Sn(1)eN(2)
Sn(2)eN(4)
Sn(1)eN(1)
Sn(2)eN(3)
Sn(1)eO(2)
Sn(2)eO(6)
Sn(1)eO(3)
Sn(2)eO(5)
Sn(1)eC(19)
Sn(2)eC(45)
Sn(1)eC(15)
Sn(2)eC(41)
N(2)eC(7)
2.106(2)
2.134(3)
2.109(3)
2.347(3)
2.356(3)
2.493(4)
2.528(4)
2.479(3)
2.571 (3)
2.303(3)
2. 276(3
2.128(5)
2.128(4)
2.128(4)
2.141(4)
1.274(6)
1.275(5)
1.253(5)
1.272(5)
1.272(5)
2.254(5)
2.162(3)
2.339(2)
2.519(3)
2.288(2)
2.595(2)
2.129(3)
2.121(3)
1.273(3)
1.272(3)
1.247(3)
2.370(4)
2.539(4)
2.261(3)
2.405(3)
2.117(6)
2.107(6)
1.281(5)
1.246(5)
4. Experimental
2-Aminophenol, 2-amino-4-methylphenol, 2-amino-4-chloro-
phenol, 2-amino-4-nitrophenol, 2-pyridinecarboxaldehyde, oxalic
acid, 2,5-pyridinedicarboxylic acid, terephthalic acid, isophthalic
acid, and dibutyltin oxide were obtained from the Aldrich Chemical
Co. The 1H, 13C and 119Sn NMR spectra were recorded using a JEOL
Eclipse þ300 instrument. The reported chemical shifts (ppm) are
relative to (CH3)4Si, and the coupling constants are quoted in Hertz
(Hz). The melting points were measured using a Fisher Johns
apparatus and are uncorrected. The mass spectra were obtained
using a JEOL JMS-AX505 HA mass spectrometer operating in posi-
tive mode. The elemental analysis was obtained using an Exeter
Analytical CE-440 instrument. The IR spectra were recorded on a
N(4)eC(33)
C(23)eO(2)
C(49)eO(5)
C(23)eO(3)
C(49)eO(6)

14
A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
Fig. 1. Perspective view of the molecular structure of complex 1a, ORTEP (Thermal ellipsoids at 30% of probability).
Bruker Tensor 27 instrument. The X-Ray crystallographic studies
were performed using a Bruker Smart Apex CCD diffractometer
4.1. Reduction of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH)
ꢀ
with a l(Mo-K ¼ 0.71073 A graphite monochromator at T ¼ 293 K.
A test was carried out on 96-well microplates. A 50
the solution of the test compound was mixed with 150
m
L aliquot of
L of an
M). This
a
)
All structures were solved using direct methods using a SHELXS
[30] program, all non-hydrogen atoms were refined anisotropically
using full-matrix, least squares techniques. All hydrogen atoms
were placed in idealized positions based on the hybridization with
thermal parameters fixed at 1.2 times (for eCH) and 1.5 times (for e
CH3) the value of the attached atom. The structure solutions and
refinements were performed using SHELXTL v 6.10. [31]. Com-
pound 4c possesses disordered butyl groups, which were modeled
in two and three major contributors. The ratio of the site occupa-
tional factor (SOF) for butyl groups was 0.66/0.44 and 0.43/0.35/
0.22, respectively.
m
ethanolic solution of DPPH (final concentration 100
m
mixture was incubated at 37 ꢁC for 30 min, and the absorbance was
then measured at 515 nm using a microplate reader ELx 808. The %
inhibition of each compound was determined by comparison with a
100 mM DPPH ethanolic blank solution.
The ligands (L1eL4) that were used to compare the antioxidant
activity with the corresponding complexes were prepared as
follows.
The corresponding aminophenol and 2-pyridinecarboxaldehyde
in a 1:1 ratio were added to a solution of 30 mL of ethanol for L1 or
toluene for L2eL4. The reaction mixture was refluxed for 4 h for L1
and for 8 h for L2eL4. The solvent was then evaporated under low
A cell culture assay for cytotoxicity activity was carried out as
described previously [32].
Fig. 2. Perspective view of the molecular structure of complex 1c, ORTEP (Thermal ellipsoids at 30% of probability).

A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
15
Fig. 3. Perspective view of the molecular structure of complex 4c ORTEP (Thermal ellipsoids at 30% of probability, the minor component of the disordered butyl group was omitted
for clarity).
pressure to yield yellow solids for L1, L3, L4 with melting points
(m.p.) of 102e106 ꢁC, 103e104 ꢁC and 205e207ꢁ, respectively. A
brown solid was obtained for L2 with a m.p. of 133e135 ꢁC.
15 mL of methanol, 0.261 g (1.045 mmol) of di-n-butyltin(IV) oxide
and 0.086 g (0.523 mmol) of terephthalic acid were added. The re-
action mixture was stirred at room temperature for 1 h until a
precipitate was observed. The mixture was then filtered to give
0.4502 g (0.427 mmol, 82% yield) of a red solid, m.p. 230 ꢁC (dec); IR
4.2. Complex 1a
(KBr, cmꢀ1): 1556 (nasymCO2), 1387 (nsymCO2), 1598 (
n
C]N); 1H NMR
(CD2Cl2, 300 MHz)
d
: 0.60 (12H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.97e
To a solution of 0.2 mL (2.090 mmol) of 2-pyridinecarbo-
xaldehyde in 30 mL of methanol, 0.228 g (2.090 mmol) of 2-
aminophenol, 0.520 g (2.090 mmol) of di-n-butyltin(IV) oxide and
0.174 g (1.045 mmol) of terephthalic acid were added. The reaction
mixture was refluxed for 4 h After cooling at room temperature, a
precipitate was observed. This precipitate was then filtered to yield
0.996 g (0.975 mmol, 93% yield) of a red solid, m.p. 250 ꢁC (dec); IR
1.50 (24H, m, Sn(CH2)3CH3), 2.30 (6H, s, CH3), 6.95 (2H, d, J ¼ 8.5 Hz,
H-13), 7.14 (2H, dd, J ¼ 8.5, 1.7 Hz, H-12), 7.40 (2H, s, H-10), 7.58 (2H,
ddd, J ¼ 7.6, 5.0, 1.0 Hz, H-3), 7.84 (2H, d, J ¼ 7.7 Hz, H-5), 8.04 (2H,
ddd, J ¼ 7.7, 7.6, 1.5 Hz, H-4), 8.21 (4H, s, H-15), 8.83 (2H, s, H-7), 9.21
(2H, d, J ¼ 5.0 Hz, H-2); 13C NMR (CD2Cl2, 75 MHz)
d: 13.6 (C-d), 20.7
(CH3), 26.6 (C-g), 27.9 (C-
b
), 32.0 (1J119Sn/117Sne13C ¼ 1020/965 Hz, C-
(KBr, cmꢀ1): 1567 (nasymCO2), 1372 (nsymCO2), 1586 (
n
C]N); 1H NMR
: 0.60 (12H, t, J ¼ 7.2 Hz, Sn(CH)2CH3), 0.99e1.45
a), 116.3 (C-10), 121.5 (C-13), 125.6 (C-11), 126.9 (C-3), 127.2 (C-5),
129.7 (C-15), 130.1 (C-9), 135.1 (C-12), 136.9 (C-16), 139.6 (C-4), 143.3
(CDCl3, 300 MHz)
d
(C-7), 148.8 (C-6), 149.7 (C-2), 162.4 (C-14), 175.1 (C-17); 119Sn NMR
(24H, m, Sn(CH2)3CH2), 6.68 (2H, ddd, J ¼ 8.3, 7.0, 1.2 Hz, H-11), 7.19
(2H, dd, J ¼ 8.5, 1.2 Hz, H-13), 7.31 (2H, ddd, J ¼ 8.5, 7.0, 1.4 Hz, H-12),
7.54 (2H, dd, J ¼ 8.3, 1.4 Hz, H-10), 7.61 (2H, ddd, J ¼ 7.5, 5.0, 0.8 Hz,
H-3), 7.79 (2H, d, J ¼ 7.7 Hz, H-5), 8.04 (2H, ddd, J ¼ 7.7, 7.5,1.7 Hz, H-
4), 8.30 (4H, s, H-15), 8.78 (2H, s, H-7), 9.25 (2H, d, J ¼ 5.0 Hz, H-2);
(CD2Cl2, 112 MHz)
d
: ꢀ351.7; MS (FABþ) [m/z] (%): [Mþ, 1053] (2);
[(M ꢀ Bu)þ, 997] (10), [445] (100); Anal. Calc. for C50H62O6N4Sn2: C
57.06, H 5.94, N 5.32, Found: C 57.01, H 5.96, N 5.33.
13C NMR (CDCl3, 75 MHz)
d
: 13.6 (C-
d
), 26.3 (C-
g), 27.6 (C-b), 31.8
4.4. Complex 1c
(1J119Sn/117Sne13C ¼ 1030/975 Hz, C-
a),115.9 (C-10),116.0 (C-13),122.4
(C-11),126.2 (C-3),126.7 (C-5),129.7 (C-15),130.3 (C-9),133.6 (C-12),
136.3 (C-16), 139.1 (C-4), 142.7 (C-7), 148.6 (C-6), 149.7 (C-2), 164.3
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarbo-
xaldehyde in 15 mL of methanol, 0.151 g (1.051 mmol) of 2-
amino-4-chlorophenol, 0.261 g (1.045 mmol) of di-n-butyltin(IV)
oxide and 0.087 g (0.523 mmol) of terephthalic acid were added.
The reaction mixture was stirred for 2 h at room temperature until
a precipitate was observed, which was then filtered to give 0.455 g
(0.427 mmol, 80% yield) of a red solid, m.p. 214e217 ꢁC; IR (KBr,
(C-14), 175.5 (C-17); 119Sn NMR (CDCl3, 112 MHz)
d: ꢀ347.7; MS
(FABþ) [m/z] (%): [Mþ, 1026] (1); [(M ꢀ Bu)þ, 969] (15), [431] (100);
Anal. Calc. for C48H58O6N4Sn2: C 56.28, H 5.71, N 5.47, Found: C
56.05, H 5.65, N 5.48.
cmꢀ1): 1548 (nasymCO2), 1369 (nsymCO2), 1591 (
n
C]N); 1H NMR
4.3. Complex 1b
(CD2Cl2, 300 MHz)
1.38 (24H, m, (CH2)3CH3), 7.00 (2H, d, J ¼ 9.0 Hz, H-13), 7.25 (2H, dd,
d
: 0.68 (12H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.97e
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxa-
ldehyde and 0.129 g (1.045 mmol) of 2-amino-4-methylphenol in
Table 5
Table 4
Antioxidant activity IC50
mM of ligands L1-L4 and complexes 1aed.
IC50 mM of complexes 1aed.
Compound
IC50
(
m
M)
Complex
IC50(mM)
Complex
PC3
HCT15
MCF-7
L1
L2
L3
L4
26.29 ꢃ 2.89
21.10 ꢃ 2.37
36.26 ꢃ 2.59
30.22 ꢃ 0.72
10.89 ꢃ 0.47
31.74 ꢃ 1.04
1a
1b
1c
1d
21.18 ꢃ 2.68
9.24 ꢃ 1.12
1a
1b
1c
1d
8.6 ꢃ 0.7
6.5 ꢃ 0.7
4.3 ꢃ 0.5
0.7 ꢃ 0.01
3.7 ꢃ 0.1
1.5 ꢃ 0.1
25.8 ꢃ 3.7
3.3 ꢃ 0.2
7.1 ꢃ 0.4
2.0 ꢃ 0.2
2.7 ꢃ 0.2
14.02 ꢃ 3.14
114.91 ꢃ 20.04
2.6 ꢃ 0.1
1.0 ꢃ 0.1
Quercetine
a-tocopherol
Cis-platin
15.90 ꢃ 2.1
13.48 ꢃ 0.7

16
A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
J ¼ 9.0, 2.4 Hz, H-12), 7.57 (2H, d, J ¼ 2.4 Hz, H-10), 7.67 (2H, ddd,
J ¼ 7.8, 4.8, 0.9 Hz, H-3), 7.82 (2H, d, J ¼ 7.8 Hz, H-5), 8.09 (2H, ddd,
J ¼ 7.8, 7.8,1.5 Hz, H-4), 8.21 (4H, s, H-15), 8.80 (2H, s, H-7), 9.23 (2H,
4-methylphenol, 0.262 g (1.045 mmol) of di-n-butyltin(IV) oxide
and 0.086 g (0.523 mmol) of isophthalic acid were added. The re-
action mixture was stirred for 1 h 30 min until a precipitate was
d, J ¼ 4.8 Hz, H-2); 13C NMR (CD2Cl2, 75 MHz)
d
: 13.6 (C-
d
), 26.6 (C-
observed. The mixture was then filtered to give 0.478
(0.454 mmol, 87% yield) of a red solid, m.p. 226e230 ꢁC; IR (KBr,
cmꢀ1): 1545 (nasymCO2), 1381 (nsymCO2), 1604 ( C]N); 1H NMR
(CDCl3, 300 MHz)
: 0.59 (12H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.97e
g
g
), 27.9 (C-b), 32.2 (C-a), 116.4 (C-10), 120.6 (C-11), 123.0 (C-13),
127.1 (C-3), 127.7 (C-5), 129.8 (C-15), 131.0 (C-9), 133.4 (C-12), 136.7
(C-16), 139.8 (C-4), 144.8 (C-7), 148.4 (C-6), 150.0 (C-2), 163.2 (C-14),
n
d
175.4 (C-17); 119Sn NMR (CD2Cl2, 112 MHz)
d
: ꢀ355.2; MS (FABþ)
1.42 (24H, m, Sn(CH2)3CH3), 3.30 (6H, s, AreCH3), 7.09 (2H, d,
J ¼ 8.7 Hz, H-13), 7.14 (2H, dd, J ¼ 8.7, 1.5 Hz, H-12), 7.35 (2H, s, H-
10), 7.50 (1H, d, J ¼ 7.7 Hz, H-18), 7.62 (2H, dd, J ¼ 7.5, 5.3 Hz, H-3),
7.81 (2H, d, J ¼ 7.7 Hz, H-5), 8.06 (2H, ddd, J ¼ 7.7, 7.5, 1.7 Hz, H-4),
8.39 (2H, dd, J ¼ 7.7, 1.7 Hz, H-17), 8.78 (2H, s, H-7), 9.12 (1H, s, H-
[m/z] (%): [(M ꢀ H)þ, 1093] (2); [(M ꢀ Bu)þ, 1037] (10), [465] (100);
Anal. Calc for C48H56O6N4Sn2Cl2: C 52.73, H 5.16, N 5.12, Found: C
52.09, H 5.15, N 4.95.
4.5. Complex 1d
15), 9.32 (2H, d, J ¼ 5.3 Hz, H-2); 13C NMR (CDCl3, 75 MHz)
d: 13.4
(C-d), 20.6 (CH3), 26.2 (C-g), 27.4 (C-b
), 31.8 (1J119Sn/117Sne
13C
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxa-
ldehyde in 15 mL of methanol, 0.162 g (1.05 mmol) of 2-amino-4-
nitrophenol, 0.262 g (1.045 mmol) of di-n-butyltin(IV) oxide and
0.087 g (0.525 mmol) of terephthalic acid were added. The reaction
mixture was stirred for 1 h 40 min until a precipitate was observed,
which was then filtered to give 0.510 g (0.457 mmol, 87% yield) of a
red solid, m.p. 217 ꢁC; IR (KBr, cmꢀ1): 1561 (nasymCO2), 1400
¼ 1045.3/1008.4 Hz, C-
a), 115.7 (C-10), 121.8 (C-13), 125.0 (C-11),
125.9 (C-3), 126.4 (C-5), 127.5 (C-18), 129.6 (C-9), 131.7 (C-15), 133.1
(C-16), 133.5 (C-17), 134.9 (C-12), 139.1 (C-4), 141.7 (C-7), 148.5 (C-
6), 149.7 (C-2), 162.4 (C-14), 175.4 (C-19); 119Sn NMR (CDCl3,
112 MHz)
d
: ꢀ355.1; MS (FABþ) [m/z] (%): [Mþ, 1054] (1);
[(M ꢀ Bu)þ, 997] (10), [445] (100); Anal. Calc. for C50H62O6N4Sn2: C
57.06, H 5.94, N 5.32, Found: C 57.09, H 5.96, N 5.37.
(
nsymCO2), 1590 (n d: 0.61 (12H, t,
C]N); 1H NMR (CD2Cl2, 300 MHz)
J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.99e1.38 (24H, m, Sn(CH2)3CH3), 7.06 (2H,
d, J ¼ 9.4 Hz, H-13), 7.76 (2H, ddd, J ¼ 7.7, 5.0, 0.9 Hz, H-3), 7.98 (2H,
d, J ¼ 7.7 Hz, H-5), 8.18 (2H, ddd, J ¼ 7.7, 7.7,1.5 Hz, H-4), 8.20 (2H, dd,
J ¼ 9.4, 2.6 Hz, H-12), 8.25 (4H, s, H-15), 8.60 (2H, d, J ¼ 2.6 Hz, H-10),
9.06 (2H, s, H-7), 9.30 (2H, d, J ¼ 5.0 Hz, H-2); 13C NMR (CD2Cl2,
4.8. Complex 2c
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxal-
dehyde in 15 mL of methanol, 0.151 g (1.051 mmol) of 2-amino-4-
chlorophenol, 0.261 g (1.045 mmol) of di-n-butyltin(IV) oxide and
0.087 g (0.523 mmol) of isophthalic acid were added. The reaction
mixture was stirred for 45 min until a precipitate was observed. The
mixture was then filtered to give 0.424 g (0.389 mmol, 74% yield) of
a red solid, m.p. 207e212 ꢁC; IR (KBr, cmꢀ1): 1545 (nasymCO2), 1379
75 MHz) d: 13.5 (C-d), 26.5 (C-g), 27.9 (C-b), 32.6 (C-a), 113.9 (C-13),
121.5 (C-12), 127.9 (C-3), 128.4 (C-5), 128.6 (C-10), 129.8 (C-9), 129.9
(C-15), 136.4 (C-11), 136.7 (C-16), 140.3 (C-4), 147.3 (C-7), 147.8 (C-6),
150.2 (C-2), 170.0 (C-14), 176.0 (C-17); 119Sn NMR (CD2Cl2, 112 MHz)
d
: ꢀ366.9; MS (FABþ) [m/z] (%): [(M ꢀ Bu ꢀ 1)þ, 1058] (10), [476]
(nsymCO2), 1600 (n d: 0.60 (12H, t,
C]N); 1H NMR (CDCl3, 300 MHz)
(100); Anal. Calc. for C48H56O10N6Sn2: C 51.73, H 5.06, N 7.54, Found:
C 51.23, H 5.13, N 7.04.
J ¼ 7.2 Hz, Sn(CH2)3CH3), 1.01e1.41 (24H, m, Sn(CH2)3CH3), 7.11 (2H,
d, J ¼ 9.0 Hz, H-13), 7.25 (2H, dd, J ¼ 9.0, 2.5 Hz, H-12), 7.50 (1H, d,
J ¼ 7.8 Hz, H-18), 7.53 (2H, d, J ¼ 2.7 Hz, H-10), 7.68 (2H, dd, J ¼ 7.2,
5.1 Hz, H-3), 7.85 (2H, d, J ¼ 7.8 Hz, H-5), 8.10 (2H, ddd, J ¼ 7.8, 7.2,
1.5 Hz, H-4), 8.38 (2H, dd, J ¼ 7.8,1.5 Hz, H-17), 8.76 (2H, s, H-7), 9.10
(1H, s, H-15), 9.34 (2H, d, J ¼ 5.1 Hz, H-2); 13C NMR (CD2Cl2, 75 MHz)
4.6. Complex 2a
To a solution of 0.2 mL (2.090 mmol) of 2-pyridinecarbox-
aldehyde in 30 mL of methanol, 0.228 g (2.090 mmol) of 2-
aminophenol, 0.520 g (2.090 mmol) of di-n-butyltin(IV) oxide and
0.174 g (1.045 mmol) of isophthalic acid were added. The reaction
mixture was refluxed for 1 h. After cooling at room temperature, a
precipitate was observed, which was filtered to give 0.931 g
(0.908 mmol, 87% yield) of an orange solid, m.p. 242e245 ꢁC; IR
d: 13.5 (C-d), 26.2 (C-g), 27.5 (C-b), 32.0 (C-a), 115.8 (C-10), 120.4 (C-
11), 123.2 (C-13), 126.5 (C-3), 126.8 (C-5), 127.6 (C-18), 130.4 (C-15),
131.8 (C-9), 133.2 (C-16), 133.3 (C-12), 133.3 (C-17), 139.3 (C-4),
143.2 (C-7), 148.1 (C-6), 149.9 (C-2), 163.2 (C-14), 175.7 (C-19); 119Sn
NMR (CDCl3, 112 MHz)
d
: ꢀ357.8; MS (FABþ) [m/z] (%): [(M þ H)þ,
1095] (0.2); [(M ꢀ Bu)þ, 1037] (3), [465] (100); Anal. Calc. for
C48H56O6N4Sn2Cl2: C 52.73, H 5.16, N 5.12, Found: C 52.03, H 5.17, N
4.91.
(KBr, cmꢀ1): 1564 (nasymCO2), 1379 (nsymCO2), 1586 (
n
C]N); 1H NMR
: 0.59 (12H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.98e1.42
(CDCl3, 300 MHz)
d
(24H, m, Sn(CH2)3CH3), 6.67 (2H, ddd, J ¼ 8.2, 7.0, 1.2 Hz, H-11), 7.18
(2H, dd, J ¼ 8.4, 1.2 Hz, H-13), 7.31 (2H, ddd, J ¼ 8.4, 7.0, 1.5 Hz, H-12),
7.50 (1H, d, J ¼ 7.6 Hz, H-18), 7.54 (2H, dd, J ¼ 8.2, 1.5 Hz, H-10), 7.64
(2H, ddd, J ¼ 7.6, 5.0, 1.0 Hz, H-3), 7.81 (2H, d, J ¼ 7.7 Hz, H-5), 8.06
(2H, ddd, J ¼ 7.7, 7.6, 1.7 Hz, H-4), 8.39 (2H, dd, J ¼ 7.6, 1.5 Hz, H-17),
8.80 (2H, s, H-7), 9.12 (1H, t, J ¼ 1.5 Hz, H-15), 9.35 (2H, d, J ¼ 5.0 Hz,
4.9. Complex 2d
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxal-
dehyde in 15 mL of methanol, 0.162 g (1.05 mmol) of 2-amino-4-
nitrophenol, 0.262 g (1.045 mmol) of di-n-butyltin(IV) oxide and
0.087 g (0.525 mmol) of isophthalic acid were added. The reaction
mixture was stirred for 2 h until a precipitate was observed. The
mixture was then filtered to give 0.473 g (0.424 mmol, 81% yield) of
a red solid, m.p. 208e211 ꢁC; IR (KBr, cmꢀ1): 1560 (nasymCO2), 1387
H-2); 13C NMR (CDCl3, 75 MHz)
32.0 (C-
d
: 13.6 (C-
d), 26.3 (C-g), 27.6 (C-b),
a
), 115.8 (C-10), 115.9 (C-13), 122.3 (C-11), 126.2 (C-3), 126.5
(C-5), 127.6 (C-18), 130.3 (C-15), 131.8 (C-9), 133.2 (C-12), 133.5 (C-
16), 133.6 (C-17), 139.1 (C-4), 142.2 (C-7), 148.5 (C-6), 149.9 (C-2),
164.5 (C-14), 175.6 (C-19); 119Sn NMR (CDCl3, 112 MHz)
d
: ꢀ347.7;
(nsymCO2), 1592 (n d: 0.61 (12H, t,
C]N); 1H NMR (CDCl3, 300 MHz)
MS (FABþ) [m/z] (%): [Mþ, 1026] (2); [(M ꢀ Bu ꢀ 1)þ, 968] (5), [431]
(100); Anal. Calc for C48H58O6N4Sn2: C 56.28, H 5.71, N 5.47, Found: C
55.95, H 5.61, N 5.45.
J ¼ 7.2 Hz, Sn(CH2)3CH3),1.00e1.40 (24H, m, Sn(CH2)3CH3), 7.16 (2H,
d, J ¼ 9.4 Hz, H-13), 7.56 (1H, d, J ¼ 7.7 Hz, H-18), 7.80 (2H, ddd,
J ¼ 7.4, 5.1, 0.7 Hz, H-3), 8.04 (2H, d, J ¼ 7.7 Hz, H-5), 8.22 (2H, ddd,
J ¼ 7.7, 7.4, 1.5 Hz, H-4), 8.23 (2H, dd, J ¼ 9.4, 2.6 Hz, H-12), 8.42 (2H,
dd, J ¼ 7.7, 1.2 Hz, H-17), 8.65 (2H, d, J ¼ 2.6 Hz, H-10), 9.09 (2H, s, H-
7), 9.12 (1H, d, J ¼ 1.2 Hz, H-15), 9.41 (2H, d, J ¼ 5.1 Hz, H-2); 13C
4.7. Complex 2b
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxa-
ldehyde in 15 mL of methanol, 0.129 g (1.045 mmol) of 2-amino-
NMR (CDCl3, 75 MHz) d: 13.4 (C-d), 26.1 (C-g), 27.6 (C-b), 32.4 (C-a),
113.6 (C-13), 121.7 (C-12), 127.4 (C-18), 127.8 (C-3), 128.5 (C-5,10),

A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
17
129.3 (C-15), 131.9 (C-9), 132.7 (C-16), 133.6 (C-17), 136.3 (C-11),
139.9 (C-4), 146.2 (C-7), 147.6 (C-6), 150.2 (C-2), 169.9 (C-14), 176.3
100), 121.6 (C-13), 122.1 (C-130), 124.0 (C-11), 124.8 (C-110), 125.6 (C-
17), 125.7 (C-3), 125.9 (C-30), 126.2 (C-5), 126.7 (C-50), 129.6 (C-9),
129.7 (C-9), 132.5 (C-19), 134.5 (C-12), 135.1 (C-120), 138.8 (C-4),
139.2 (C-40), 141.0 (C-7), 141.4 (C-70), 148.4 (C-6), 148.5 (C-60), 149.3
(C-2), 149.9 (C-20), 151.1 (C-20), 151.7 (C-16), 162.0 (C-14), 163.0 (C-
140), 166.9 (C-22), 172.5 (C-121); 119Sn NMR (CDCl3, 112 MHz)
(C-19); 119Sn NMR (CDCl3,112 MHz)
d
: ꢀ369.3; MS (FABþ) [m/z] (%):
[Mþ, 1116] (1); [(M ꢀ Bu ꢀ 1)þ, 1058] (4), [476] (100); Anal. Calc. for
C48H56O10N6Sn2: C 51.73, H 5.06, N 7.54, Found: C 51.29, H 5.16, N
7.34.
d
: ꢀ333.2, ꢀ438.3; MS (FABþ) [m/z] (%): [(M ꢀ Bu)þ, 998] (6), [445]
4.10. Complex 3a
(100); Anal. Calc. for C49H61O6N5Sn2: C 55.87, H 5.84, N 6.65, Found:
C 55.77, H 5.81, N 6.59.
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxa-
ldehyde in 30 mL of methanol, 0.114 g (1.045 mmol) of 2-
aminophenol, 0.260 g (1.045 mmol) of di-n-butyltin(IV) oxide and
0.090 g (0.582 mmol) of 2,5-pyridinedicarboxylic acid were added.
The reaction mixture was refluxed for 1 h 30 min, which was fol-
lowed by the distillation of 10 mL of solvent. After cooling at room
temperature, a precipitate was observed, which was filtered to give
0.400 g (0.389 mmol, 74% yield) of an orange solid, m.p. 237e
242 ꢁC; IR (KBr, cmꢀ1): 1639, 1607 (nasymCO2), 1345, 1373 (nsymCO2),
4.12. Complex 3c
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxald-
ehyde in 15 mL of methanol, 0.152 g (1.051 mmol) of 2-amino-4-
chlorophenol, 0.262 g (1.045 mmol) of di-n-butyltin (IV) oxide
and 0.088 g (0.523 mmol) of 2,5-pyridinedicarboxylic acid were
added. The reaction mixture was stirred for 50 min until a pre-
cipitate was observed. The mixture was then filtered to give 0.404 g
(0.370 mmol, 71% yield) of a red solid, m.p. 224e228 ꢁC (dec); IR
1590 (
n
C]N); 1H NMR (CDCl3, 300 MHz)
d
: 0.49 (6H, t, J ¼ 7.1 Hz,
Sn(CH2)3CH3), 0.62 (6H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.84e1.57 (24H,
m, Sn(CH2)3CH3), 6.64 (1H, ddd, J ¼ 8.3, 6.9, 1.2 Hz, H-11), 6.71 (1H,
ddd, J ¼ 8.1, 7.2, 1.2 Hz, H-110), 7.20 (1H, dd, J ¼ 8.4, 1.2 Hz, H-13),
7.31 (1H, dd, J ¼ 8.5, 1.2 Hz, H-130), 7.32 (2H, ddd, J ¼ 8.4, 6.9, 1.2 Hz,
H-12), 7.34 (2H, ddd, J ¼ 8.5, 7.2, 1.4 Hz, H-120), 7.57 (1H, dd, J ¼ 8.3,
1.5 Hz, H-10), 7.57 (1H, ddd, J ¼ 7.3, 5.2, 1.1 Hz, H-3), 7.58 (1H, dd,
J ¼ 8.1, 1.4 Hz, H-100), 7.67 (1H, ddd, J ¼ 7.6, 4.9, 1.0 Hz, H-30), 7.74
(1H, d, J ¼ 7.6 Hz, H-5), 7.87 (1H, d, J ¼ 7.8 Hz, H-50), 8.04 (1H, ddd,
J ¼ 7.6, 7.3, 1.7 Hz, H-4), 8.10 (1H, ddd, J ¼ 7.8, 7.6, 1.5 Hz, H-40), 8.57
(1H, d, J ¼ 7.8, H-17), 8.81 (1H, s, H-7), 8.82 (1H, dd, J ¼ 7.8,1.9 Hz, H-
20), 8.88 (1H, s, H-7’b), 9.30 (1H, d, J ¼ 5.2 Hz, H-2), 9.84 (1H, d,
(KBr, cmꢀ1): 1639, 1616 (nasymCO2), 1347, 1373 (nsymCO2), 1590 (
N); 1H NMR (CDCl3, 300 MHz)
: 0.49 (6H, t, J ¼ 7.2 Hz,
nC]
d
Sn(CH2)3CH3), 0.62 (6H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.8e1.6 (24H, m,
Sn(CH2)3CH3), 7.14 (1H, d, J ¼ 9.3, Hz, H-13), 7.14 (1H, d, J ¼ 9.3, Hz,
H-130), 7.25 (1H, dd, J ¼ 9.3, 2.4 Hz, H-120), 7.29 (1H, dd, J ¼ 9.3,
2.6 Hz, H-12), 7.55 (1H, d, J ¼ 2.4 Hz, H-100), 7.57 (1H, d, J ¼ 2.6 Hz,
H-10), 7.67 (1H, dd, J ¼ 6.6, 5.1 Hz, H-30), 7.69 (1H, dd, J ¼ 7.2, 4.8 Hz,
H-3), 7.76 (1H, d, J ¼ 7.5 Hz, H-50), 7.89 (1H, d, J ¼ 7.5 Hz, H-5), 8.03
(1H, ddd, J ¼ 7.5, 6.6, 1.5 Hz, H-40), 8.13 (1H, ddd, J ¼ 7.5, 7.2, 1.5 Hz,
H-4), 8.57 (1H, d, J ¼ 8.1 Hz, H-18), 8.75 (1H, s, H-70), 8.81 (1H, dd,
J ¼ 8.1,1.8 Hz, H-17), 8.82 (1H, s, H-7), 9.28 (1H, d, J ¼ 4.8 Hz, H-2),
9.84 (1H, d, J ¼ 5.1 Hz, H-20), 10.28 (1H, s, H-20); 13C NMR (CDCl3,
J ¼ 4.9 Hz, H-20), 10.34 (1H, s, H-15); 13C NMR (CDCl3, 75 MHz)
d:
13.4 (C-
31.6 (C-
d), 13.6 (C-
d
), 26.2 (C-
g
), 26.3 (C-
g
), 27.5 (C-
b
), 27.8 (C-
b
),
75 MHz)
d: 13.5 (C-
d
), 13.6 (C-
d), 26.2 (C-g), 26.3 (C-g), 27.6 (C-b),
a
), 32.6 (C-
a
), 114.9 (C-10), 116.0 (C-100), 116.1 (C-13), 116.4
27.8 (C- ), 31.6 (C-
b
a
), 32.7 (C-a
), 115.0 (C-10), 116.0 (C-100), 116.2 (C-
(C-130), 122.2 (C-11), 122.5 (C-110), 125.0 (C-17), 126.0 (C-3), 126.1
(C-30), 126.5 (C-5), 126.9 (C-50), 130.2 (C-9), 130.4 (C-90), 132.6 (C-
19), 133.1 (C-12), 133.8 (C-120), 138.9 (C-4), 139.3 (C-40), 141.2 (C-18),
142.1 (C-7), 143.2 (C-70), 148.4 (C-6), 148.5 (C-60), 149.6 (C-2), 150.0
(C-20), 151.3 (C-20), 151.8 (C-16), 164.1 (C-14), 165.1 (C-140), 166.9 (C-
13), 116.4 (C-130), 122.2 (C-11), 122.5 (C-110), 125.0 (C-17), 126.0 (C-
3), 126.1 (C-30), 126.5 (C-5), 126.9 (C-50), 130.2 (C-9), 130.5 (C-90),
132.6 (C-19), 133.1 (C-12), 133.8 (C-120), 139.0 (C-4), 139.4 (C-40),
141.2 (C-18), 142.1 (C-7), 143.2 (C-70), 148.4 (C-6), 148.6 (C-60), 149.6
(C-2), 150.0 (C-20), 151.3 (C-20), 151.9 (C-16), 164.1 (C-14), 165.1 (C-
140), 166.9 (C-22), 172.7 (C-21); 119Sn NMR (CDCl3, 112 MHz)
22), 172.7 (C-21); 119Sn NMR (CDCl3, 112 MHz)
d: ꢀ335.8, ꢀ440.7;
MS (FABþ) [m/z] (%): [Mþ, 1027] (1); [(M ꢀ Bu)þ, 970] (5), [431]
(100); Anal. Calc. for : C47H57O6N5Sn2 C 55.05, H 5.60, N 6.83,
Found: C 54.91, H 5.56, N 6.82.
d
: ꢀ335.0, 439.8; MS (FABþ) [m/z] (%): [Mþ, 1095] (2); [(M ꢀ Bu)þ,
1038] (10), [465] (100); Anal. Calc for C47H55O6N5Sn2Cl2: C 51.59, H
5.07, N 6.40, Found: C 51.02, H 5.05, N 6.07.
4.11. Complex 3b
4.13. Complex 3d
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxal-
dehyde in 15 mL of methanol, 0.129 g (1.045 mmol) of 2-amino-
4-methylphenol, 0.261 g (1.045 mmol) of di-n-butyltin(IV) oxide
and 0.088 g (0.523 mmol) of 2,5-pyridinedicarboxylic acid were
added. The reaction mixture was stirred for 1 h until a precipitate
was observed. The mixture was then filtered to give 0.475 g
(0.450 mmol, 91% yield) of a red solid, m.p. 242 ꢁC (dec); IR (KBr,
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxal-
dehyde in 15 mL of methanol, 0.162 g (1.05 mmol) of 2-amino-4-
nitrophenol, 0.262 g (1.045 mmol) of di-n-butyltin (IV) oxide and
0.087 g (0.525 mmol) of 2,5-pyridinedicarboxylic acid were added.
The reaction mixture was stirred for 1 h 40 min until a precipitate
was observed. The mixture was then filtered to give 0.510 g
(0.457 mmol, 87% yield) of a red solid, m.p. 217 ꢁC (dec); IR (KBr,
cmꢀ1): 1637, 1612 (nasymCO2), 1346, 1371 (nsymCO2), 1612 (
1H NMR (CDCl3, 300 MHz)
: 0.49 (6H, t, J ¼ 7.1 Hz, Sn(CH2)3CH3),
0.61 (6H, t, 7.2 Hz, Sn(CH2)3CH3), 0.82e1.56 (24H, m,
n
C]N);
cmꢀ1): 1648 (nasymCO2), 1355, 1381 (nsymCO2), 1589 (
n
C]N); 1H
d
NMR (CDCl3, 300 MHz)
d: 0.51 (6H, t, J ¼ 6.9 Hz, Sn(CH2)3CH3), 0.64
J
¼
(6H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.86e1.56 (24H, m, Sn(CH2)3CH3),
7.17 (1H, d, J ¼ 9.4 Hz, H-13), 7.21 (1H, d, J ¼ 9.4 Hz, H-130), 7.73 (1H,
dd, J ¼ 7.0, 5.4 Hz, H-3), 7.82 (1H, dd, J ¼ 7.0, 5.1 Hz, H-30), 7.98 (1H,
d, J ¼ 7.6 Hz, H-5), 8.14 (1H, d, J ¼ 7.7 Hz, H-50), 8.15 (1H, ddd, J ¼ 7.6,
7.0, 1.5 Hz, H-4), 8.27 (1H, ddd, J ¼ 7.7, 7.0, 1.5 Hz, H-40), 8.28 (2H, dd,
J ¼ 9.4, 2.6 Hz, H-12), 8.62 (1H, d, J ¼ 8.0 Hz, H-18), 8.68 (1H, d,
J ¼ 2.6 Hz, H-10), 8.73 (1H, d, J ¼ 2.4 Hz, H-100), 8.86 (1H, dd, J ¼ 8.0,
1.9 Hz, H-17), 9.10 (1H, s, H-7), 9.22 (1H, s, H-70), 9.37 (1H, d,
J ¼ 5.4 Hz, H-2), 9.89 (1H, d, J ¼ 5.1 Hz, H-20), 10.28 (1H, d, J ¼ 1.9 Hz,
Sn(CH2)3CH3), 2.32 (6H, s, AreCH3), 7.12 (1H, d, J ¼ 8.7 Hz, H-13),
7.15e7.20 (3H, m, H-130, 12,120), 7.37 (1H, s,10), 7.39 (1H, s,100), 7.55
(1H, ddd, J ¼ 7.6, 5.2, 0.8 Hz, H-3), 7.64 (1H, dd, J ¼ 6.9, 5.1 Hz, H-30),
7.73 (1H, d, J ¼ 7.7 Hz, H-5), 7.85 (1H, d, J ¼ 7.7 Hz, H-50), 7.99 (1H,
ddd, J ¼ 7.7, 7.6, 1.5 Hz, H-4), 8.09 (1H, ddd, J ¼ 7.7, 6.9, 1.4 Hz, H-40),
8.56 (1H, d, J ¼ 8.0 Hz, H-17), 8.77 (1H, s, H-7), 8.81 (1H, dd, J ¼ 8.0,
1.8 Hz, H-18), 8.85 (1H, s, H-70), 9.28 (1H, d, J ¼ 5.2 Hz, H-2), 9.83
(1H, d, J ¼ 5.1 Hz, H-20), 10.32 (1H, s, H-20); 13C NMR (CDCl3,
75 MHz)
27.4 (C-
d
: 13.3 (C-
d
), 13.4 (C-
d
), 20.7 (CH3), 26.1 (C-
g
), 26.2 (C-
g
),
H-20); 13C NMR (DMSO-d6, 75 MHz)
), 25.5 (C- ), 27.0 (C- ), 27.1 (C- ), 31.5 (C-
d
: 12.9 (C-
d
),13.0 (C-
d), 25.4 (C-
b
), 27.6 (C-
b
), 31.3 (C-
a
), 32.4 (C- ), 115.7 (C-10), 115.9 (C-
a
g
g
b
b
a), 32.1 (C-a
), 114.0 (C-

18
A. Ramírez-Jiménez et al. / Journal of Organometallic Chemistry 738 (2013) 10e19
13), 120.3 (C-12), 120.6 (C-120), 124.5 (C-17), 126.8 (C-3), 127.3 (C-3),
127.3 (C-5), 127.4 (C-50), 128.0 (C-10), 128.7 (C-100), 129.3 (C-9),
129.5 (C-90), 131.8 (C-19), 135.0 (C-11), 136.0 (C-110), 139.6 (C-4),
140.0 (C-40), 140.8 (C-18), 147.1 (C-7), 147.4 (C-70), 148.5 (C-6), 148.8
(C-60), 149.0 (C-2), 149.8 (C-20), 150.1 (C-20), 151.0 (C-16), 165.6 (C-
14), 168.7 (C-140), 169.6 (C-22), 172.3 (C-21); 119Sn NMR (DMSO-d6,
0.047 g (0.523 mmol) of oxalic acid were added. The reaction
mixture was stirred for 1 h, and the solvent was then eliminated
under vacuum. The solid was crystallized from CH2Cl2/Hexane to
give 0.351 g (0.345 mmol, 66% yield) of an orange solid, m.p. 247e
250 ꢁC (dec); IR (KBr, cmꢀ1): 1641 (nasymCO2), 1460 (nsymCO2), 1588
(
n
C]N); 1H NMR (CD2Cl2, 300 MHz)
d
: 0.61 (6H, t, J ¼ 7.2 Hz,
112 MHz)
d
: ꢀ356.8, ꢀ447.6; MS (FABþ) [m/z] (%): [Mþ, 1117] (1);
Sn(CH2)3CH3), 0.97e1.38 (12H, m, Sn(CH2)3CH3), 7.00 (1H, d,
J ¼ 9.0 Hz, H-13), 7.25 (1H, dd, J ¼ 9.0, 2.4 Hz, H-12), 7.57 (1H, d,
J ¼ 2.4 Hz, H-10), 7.67 (1H, ddd, J ¼ 7.8, 4.8, 0.9 Hz, H-3), 7.82 (1H, d,
J ¼ 7.8 Hz, H-5), 8.09 (1H, ddd, J ¼ 7.8, 7.8, 1.5 Hz, H-4), 8.80 (1H, s,
[(M Bu
ꢀ
ꢀ
1)þ, 1059] (7), [476] (100); Anal. Calc. for
C47H55O10N7Sn2: C 50.61, H 4.97, N 8.79, Found: C 50.01, H 5.00, N
8.49.
H-7), 9.23 (1H, d, J ¼ 4.8 Hz, H-2); 13C NMR (CD2Cl2, 75 MHz)
d: 13.6
4.14. Complex 4a
(C-d), 26.6 (C-g), 28.2 (C-b), 32.4 (C-a), 116.3 (C-10), 119.9 (C-11),
123.0 (C-13), 127.0 (C-3), 127.5 (C-5), 131.2 (C-9), 133.4 (C-12), 139.5
To a solution of 0.2 mL (2.090 mmol) of 2-pyridinecarboxal-
dehyde in 30 mL of methanol, 0.228 g (2.090 mmol) of 2-
aminophenol, 0.520 g (2.090 mmol) of di-n-butyltin(IV) oxide
and 0.094 g (1.045 mmol) of oxalic acid were added. The reaction
mixture was stirred for 1 h until a precipitate was observed, and it
was then filtered to give 0.920 g (0.968 mmol, 93% yield) of an
orange solid, m.p. 253e257 ꢁC (dec); IR (KBr, cmꢀ1): 1639
(C-4), 145.1 (C-7), 148.5 (C-6), 150.9 (C-2), 163.8 (C-14); 119Sn
NMR (CD2Cl2, 112 MHz)
(0.2); [(M
C42H52O6N4Sn2Cl2: C 49.51, H 5.11, N 5.50, Found: C 51.54, H 5.30, N
5.34.
d
: ꢀ414.9; MS (FABþ) [m/z] (%): [Mþ, 1018]
ꢀ
Bu)þ, 961] (0.6), [465] (100); Anal. Calc. for
4.17. Complex 4d
(nasymCO2), 1459
(nsymCO2), 1590
(n
C]N); 1H NMR (CDCl3,
300 MHz)
d
: 0.59 (6H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.97e1.30 (12H,
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxal-
dehyde in 15 mL of methanol, 0.162 g (1.051 mmol) of 2-amino-
4-nitrophenol, 0.262 g (1.045 mmol) of di-n-butyltin(IV) oxide and
0.047 g (0.525 mmol) of oxalic acid were added. The reaction
mixture was stirred for 15 min until a precipitate was observed. The
mixture was then filtered to give 0.400 g (0.345 mmol, 74% yield) of
a yellow solid, m.p. 265 ꢁC (dec); IR (KBr, cmꢀ1): 1640 (nasymCO2),
m, Sn(CH2)3CH3), 6.68 (1H, ddd, J ¼ 8.2, 7.0, 1.2 Hz, H-11), 7.26 (1H,
ddd, J ¼ 8.4, 7.0,1.4 Hz, H-12), 7.31 (1H, dd, J ¼ 8.4,1.2 Hz, H-13), 7.52
(1H, dd, J ¼ 8.2, 1.4 Hz, H-10), 7.54 (1H, ddd, J ¼ 7.5, 5.0, 1.0 Hz, H-3),
7.75 (1H, d, J ¼ 7.7 Hz, H-5), 8.04 (1H, ddd, J ¼ 7.7, 7.5, 1.7 Hz, H-4),
8.78 (1H, s, H-7), 9.63 (1H, d, J ¼ 5.0 Hz, H-2); 13C NMR (CDCl3,
75 MHz) d: 13.5 (C-d), 26.3 (C-g), 27.9 (C-b), 31.8 (C-a), 115.3 (C-10),
1489 (nsymCO2), 1588 (
n
C]N); MS (FABþ) [m/z] (%): [(M ꢀ Bu ꢀ 1)þ,
115.9 (C-13), 122.4 (C-11), 126.1 (C-3), 126.4 (C-5), 130.4 (C-9), 133.3
(C-12), 138.9 (C-4), 142.8 (C-7), 148.6 (C-6), 150.9 (C-2), 164.9 (C-14),
982] (1), [476] (100); Anal. Calc. for C42H52O10N6Sn2: C 48.58, H
5.05, N 8.09, Found: C 48.24, H 5.14, N 7.87.
169.9 (C-15); 119Sn NMR (CDCl3, 112 MHz)
d
: ꢀ415.6; MS (FABþ) [m/
z] (%): [(M ꢀ Bu ꢀ 1)þ, 892] (3), [431] (100); Anal. Calc. for
C42H54O6N4Sn2: C 53.19, H 5.74, N 5.91, Found: C 51.43, H 5.65, N
5.60.
Acknowledgments
The authors are grateful for financial support from DGAPA
(IN200911) and thank Rocío Patiño, Eréndira García, Javier Pérez
and Luis Velasco for their technical support with the IR, elemental
analysis, and mass spectrometry experiments.
4.15. Complex 4b
To a solution of 0.1 mL (1.045 mmol) of 2-pyridinecarboxal-
dehyde in 15 mL of methanol, 0.130 g (1.045 mmol) of 2-amino-
4-methylphenol, 0.262 g (1.045 mmol) of di-n-butyltin(IV) oxide
and 0.048 g (0.523 mmol) of oxalic acid were added. The reaction
mixture was stirred for 5 min until a precipitate was observed and
then filtered. To separate the tin oxide from the remainder of the
reaction mixture, the solid was dissolved in CH2Cl2 and filtered
again. The solution was dried to yield 0.267 g (0.275 mmol, 53%
yield) of a red solid, m.p. 265e268 ꢁC; IR (KBr, cmꢀ1): 1640
Appendix A. Supplementary material
CCDC 870877, 870878 and 870879 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.
(nasymCO2), 1467
(nsymCO2), 1604 (n
C]N); 1H NMR (CD2Cl2,
300 MHz)
d
: 0.61 (6H, t, J ¼ 7.2 Hz, Sn(CH2)3CH3), 0.97e1.26 (12H,
Appendix B. Supplementary material
m, Sn(CH2)3CH3), 2.30 (3H, s, AreCH3), 6.90 (1H, d, J ¼ 8.5 Hz, H-13),
7.11 (1H, dd, J ¼ 8.5, 1.9 Hz, H-12), 7.36 (1H, d, J ¼ 1.9 Hz, H-10), 7.59
(1H, ddd, J ¼ 7.6, 5.1, 1.0 Hz, H-3), 7.78 (1H, d, J ¼ 7.7 Hz, H-5), 8.04
(1H, ddd, J ¼ 7.7, 7.6, 1.7 Hz, H-4), 8.79 (1H, s, H-7), 9.54 (1H, d,
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.03.038.
J ¼ 5.1 Hz, H-2); 13C NMR (CD2Cl2, 75 MHz)
d: 13.6 (C-d), 20.7 (CH3),
References
26.7 (C-g), 28.2 (C-b), 32.3 (C-a), 116.1 (C-10), 121.7 (C-13), 124.8 (C-
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