Synthesis, crystal structures and, antibacterial and antiproliferative activities in vitro of palladium(II) complexes of triphenylphosphine and thioamides

Article abstract of DOI:10.1016/j.ica.2010.06.015

Palladium(II) complexes with triphenylphosphine (PPh₃) and thioamides of the general formulae, [Pd(L)₂(PPh₃) ₂]Cl₂ and [Pd(L)₂(PPh₃)₂] have been prepared and characterized by elemental analysis, IR and NMR ( ¹H, ¹³C and ³¹P) methods, and two of them (trans-[Pd(PPh₃)₂(Dmtu)₂]Cl₂· (H₂O)(CH₃OH)_0.5 (1) and trans-[Pd(PPh ₃)₂(Mpy)₂] (2)) by X-ray crystallography; where L = thiourea (Tu), methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), 2-mercaptopyridine (Mpy), 2-mercaptopyrimidine (Mpm) and thionicotinamide (Tna). The spectral data of the complexes are consistent with the sulfur coordination of thioamides to palladium(II). The crystal structures of the complexes show that (1) has ionic character consisting of [Pd(PPh₃)₂(Dmtu)₂]⁺² cations and uncoordinated Cl^- ions, while (2) is a neutral complex with Mpy behaving as anionic thiolate ligand. The coordination environment around palladium in (2) is nearly regular square-planar, while in (1) the trans angles show significant distortions from 180°. The complexes were screened for antibacterial effects, brine shrimps lethality bioassay and antitumor activity. These complexes showed significant activities in most of the cases against the tested bacteria as compared to that of a standard drug. Their antitumor activity against prostate cancer cells (PC3) is comparable with doxorubicin, together with no cytotoxic effects in brine shrimps lethality bioassay study.

Full text of DOI:10.1016/j.ica.2010.06.015

Inorganica Chimica Acta 363 (2010) 3261–3269
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, crystal structures and, antibacterial and antiproliferative activities
in vitro of palladium(II) complexes of triphenylphosphine and thioamides
c
a
Shafqat Nadeem a, Michael Bolte b, Saeed Ahmad c, , Tahira Fazeelat , Syed Ahmed Tirmizi ,
*
Muhammad Khawar Rauf a, Samina A. Sattar d,e, Sadia Siddiq d,e, Abdul Hameed f, Syed Zeeshan Haider f
a Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
b Institut für Anorganische Chemie, J.W. Goethe-Universität Frankfurt Max-von-Laue-Strasse 7, 60438 Frankfurt/Main, Germany
c Department of Chemistry, University of Engineering and Technology, Lahore 54890, Pakistan
d International Center for Chemical Sciences, H.E.J. Research Institute of Chemistry, University of Karachi, Karachi, Pakistan
e Dr. Panjwani Center for Molecular Medicine and Drug Research, University of Karachi, Karachi, Pakistan
f Microbiology Research Laboratory, Department of Biological Sciences, Quaid-i-Azam University, Islamabad, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium(II) complexes with triphenylphosphine (PPh3) and thioamides of the general formulae,
[Pd(L)2(PPh3)2]Cl2 and [Pd(L)2(PPh3)2] have been prepared and characterized by elemental analysis, IR
and NMR (1H, 13C and 31P) methods, and two of them (trans-[Pd(PPh3)2(Dmtu)2]Cl2ꢀ(H2O)(CH3OH)0.5
(1) and trans-[Pd(PPh3)2(Mpy)2] (2)) by X-ray crystallography; where L = thiourea (Tu), methylthiourea
(Metu), N,N0-dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), 2-mercaptopyridine (Mpy), 2-mer-
captopyrimidine (Mpm) and thionicotinamide (Tna). The spectral data of the complexes are consistent
with the sulfur coordination of thioamides to palladium(II). The crystal structures of the complexes show
that (1) has ionic character consisting of [Pd(PPh3)2(Dmtu)2]+2 cations and uncoordinated Clꢁ ions, while
(2) is a neutral complex with Mpy behaving as anionic thiolate ligand. The coordination environment
around palladium in (2) is nearly regular square-planar, while in (1) the trans angles show significant dis-
tortions from 180°. The complexes were screened for antibacterial effects, brine shrimps lethality bioas-
say and antitumor activity. These complexes showed significant activities in most of the cases against the
tested bacteria as compared to that of a standard drug. Their antitumor activity against prostate cancer
cells (PC3) is comparable with doxorubicin, together with no cytotoxic effects in brine shrimps lethality
bioassay study.
Received 19 February 2010
Received in revised form 27 May 2010
Accepted 8 June 2010
Available online 15 June 2010
Keywords:
Palladium(II) complexes
Triphenylphosphine
Thioamides
Thiolate
Antitumor activity
Antibacterial activity
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
duce side effects of platinum drugs [8–16]. Special attention in this
regard has been given to palladium(II) complexes [17–29], since
Platinum compounds are among the most efficacious metal-
based anticancer agents [1–7]. However, for the reasons of severe
side effects, drug resistance and the limited spectrum of tumors
[1–7], there has been a wide spread search for related complexes
(e.g., of Pd, Ru and Au) that are able to improve effectiveness and re-
the coordination geometry and complex forming processes of palla-
dium(II) are very similar to those of platinum(II) [17,21,26]. How-
ever, Pt(II) complexes are thermodynamically and kinetically more
stable than those of Pd(II). Pd(II) complexes undergo aquation and li-
gand exchange reactions 105 times faster than the corresponding
Pt(II) analogues. This kinetic lability leads to the lower antitumor
activity of cis-[Pd(en)Cl2] and cis-[Pd(DACH)2Cl2] when compared
to the analogous Pt(II) complexes [15,17,30–33]. The palladium(II)
complexes dissociate readily in solutionleading to very reactive spe-
cies that are unable to reach their pharmacological targets such as
DNA [15,17,30–33]. This rapid aquation and formation of very reac-
tive species could be overcome if palladium(II) complexes are stabi-
lized by bulky ligands and suitable leaving groups [17]. As a result,
some palladium complexes with aromatic N-containing ligands
e.g., 1,10-phenanthroline and derivatives of pyridine, quinoline
and pyrazole [18–20,34,35], thiosemicarbazones [25,26,36] and
Abbreviations: G (+), gram positive; G (ꢁ), gram negative; ATCC, American Type
Culture Collection; DSM, Deutsch Sammlung von Mikroorganismen; DMSO, dime-
thysulfoxide; MTT, 3-(4,5-dimethylthiazole-2-yl) -2,5- diphenyltetrazolium bro-
mide; DMEM, Dulbacco’s Modified Eagle Medium; FBS, foetal bovine serum; ELIZA,
Enzyme Linked Immuno Sorbent Assay; IC50, inhibitory concentration 50%; LD50
,
lethal dose 50%; PPh3, triphenylphosphine; L, ligand; Tu, thiourea; MeTu, meth-
ylthiourea; DMTu, dimethylthiourea; TMTu, tetramethylthiourea; Imt, imidazoli-
dine-2-thione; MPy, mercaptopyridine; MPm, mercaptopyrimidine; Tna,
thionicotinamide; PC3, prostate cancer -3.
* Corresponding author. Tel.: +92 333 5248570.
E-mail address: saeed_a786@hotmail.com (S. Ahmad).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.06.015

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S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
triphenylphosphine [37] have shown very promising antitumor
properties. Antiproliferative activities of some palladacycles have
also been reported [24,32].
is a considerable potential for further testing of some of the com-
plexes as antitumor agents, while data of brine shrimps lethality
bioassay showed no toxicity to normal cells in vitro. The structures
of the ligands used in this study are shown in Scheme 1.
Although for platinum-based anticancer drugs it is generally ac-
cepted that DNA is the primary intracellular target [1–7], the DNA
binding studies of palladium complexes showed that their reactiv-
ity depends on the ligand environment of Pd(II) [15,17,38–42]. The
results of several studies indicated the changes in structure of DNA
on Pd binding but the correlations between the structure and the
mode of interaction could not be established [31,39,41]. Since
Pd(II) can react with many biological molecules of the body, they
exhibit high toxicity [30].
2. Experimental
2.1. Chemicals
Palladium(II) chloride was purchased from Degussa AG 40474,
Dusseldorf, Germany. Thiourea (Tu), methylthiourea (Metu),
N,N0-dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), 2-mer-
captopyridine (Mpy), 2-mercaptopyrimidine (Mpm) and thionicoti-
namide (Tna) were purchased from ACROS Organics, Belgium.
Triphenylphosphine (PPh3) was obtained from Alfa Aesar, USA.
As the biological activity of a complex strongly depends on the
nature of the ligands and on the metal coordination pattern, the re-
cent research has been directed to synthesis and evaluation of com-
plexes with biologically interesting ligands with the aim of
widening spectrum of complex activity [17,30,43]. These findings
have stimulated investigation of palladium(II) complexes with thi-
ones and thiolate ligands because of their relevance to the biological
systems [24–29,43,44]. Most of the palladium(II) complexes with
thioamide ligands show a square-planar geometry in which these li-
gands act as terminal S bonded [29,45–50], bidentate chelating [24–
26,28,29,49–54] or bidentate bridging [55–57]. It appears from
these studies that thiourea derivatives and thioamides with satu-
rated rings bind to Pd(II) in neutral thione form [45–48], while the
unsaturated heterocyclic thiones (being electron-rich) such as mer-
captopyridine and mercaptopyrimidine prefer to coordinate to
Pd(II) as anionic thiolate ligands [28,29,49–54]. Furthermore, in
the thione form, thioamides usually bind through sulfur atom only
behaving as a monodentate ligand [45–48]. We are interested in
investigating the structural chemistry and biological properties of
Pd–thione complexes and in this regard we have already reported
the spectroscopic and structural characterization of a number of
palladium(II) complexes with thiones [45,46,58]. In this paper we
present the synthesis and characterization of new palladium(II)
complexes containing triphenylphosphine and a number of thioam-
ides as ligands including the crystal structures of two of them. It is
interesting to note that in one of them, trans-[Pd(PPh3)2(Dmtu)2]-
Cl2ꢀ(H2O)(CH3OH)0.5 (1), the thioamide ligand coordinates in neutral
thione form while in the other, trans-[Pd(PPh3)2(Mpy)2] (2), it be-
haves as an anionic thiolate ligand. The synthesized complexes have
been screened for antibacterial and antitumor activities including
brine shrimps lethality bioassay study. The results showed signifi-
cant antibacterial activity as compared to the standard drugs indi-
cating their potential for future antibacterial agents. Data
obtained on human prostate cancer cells (PC3) indicated that there
2.2. Synthesis of the complexes
Potassium tetrachloropalladate(II) was prepared as described in
the literature; by the reaction of palladium chloride with an excess
of potassium chloride [45]. The complexes were prepared by add-
ing 2 equiv. of triphenylphosphine in 15 mL acetonitrile to a solu-
tion of K2[PdCl4] (0.326 g) in 15 mL of water followed by addition
of 2 equiv. of thioamides in 15 mL methanol. The mixture was stir-
red for 15 min before addition of thioamides and for further half an
hour after their addition. For the complexes of Tu, Metu, Dmtu and
Tmtu, yellow colored; for Tna light brown and, for Mpy and Mpm,
light orange colored solutions were obtained. The resulting solu-
tions were filtrated and filtrates were kept at room temperature
for crystallization for 3–5 days. As a result yellow powders were
obtained. Crystals of 1 and 2 were grown by slow evaporation of
acetonitrile/methanol solutions at room temperature. The experi-
mental yield of the products was around 50–60%. The elemental
analyses and melting points (m.p.) of the complexes are given in
Table 1.
2.3. Measurements
Elemental analysis was carried out on a Leco CHNS-932 Leco
Corporation USA. Melting point was recorded on an Electrothermal
IA 9000 Series, Essex SS2 5PH UK. FT-IR spectra were recorded on a
Thermo Nicolet Nexus 6700 USA. The 1H and 13C NMR spectra of
the ligands and their complexes in DMSO-d6 (Tmtu complex in
CDCl3) were obtained on Bruker Avance 300 MHz NMR spectrom-
eter operating at frequencies of 300.00 MHz and 75.47 MHz,
CH3
CH3
N
CH3
N
CH3
N
CH3
N
H2N
NH2
H2N
N
C
S
C
S
H
H
C
S
H
H3C
C
S
CH3
Thiourea
N-Methylthiourea N,N -Dimethylthiourea
Tetramethylthiourea
S
P
NH
N
NH
2
NH
N
S
S
2-Mercaptopyridine 2-Mercaptopyrimidine
Thionicotinamide
Triphenylphosphine
Scheme 1. Structures of the ligands used in the study.

S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
3263
Table 2
respectively, at 300 K. The spectral conditions were: 32 K data
Crystal data and details of the structure refinement for 1 and 2.
points, 1.822 s acquisition time, 2.00 s pulse delay and 6.00 ls
pulse width. The 13C chemical shifts were measured relative to
TMS.
Compound
1
2
Empirical formula
Formula weight
C
42.50H50Cl2N4O1.50P2PdS2 C46H38N2P2PdS2
944.23
851.26
0.29 ꢂ 0.13 ꢂ 0.13
Crystal dimensions (mm3)
T (K)
0.31 ꢂ 0.25 ꢂ 0.22
173(2)
173(2)
monoclinic, P(2)
1/n
2.4. X-ray structure determination
ꢀ
Crystal system, space group
triclinic, P1
The orange crystals were mounted in random orientation on a
glass fiber on a STOE IPDS-II two circle diffractometer [59]
a (Å)
b (Å)
c (Å)
11.8147(8)
14.3401(9)
14.9106(9)
96.059(5)
107.053(5)
107.168(5)
2255.9(2)
2
9.9971(9)
15.2220(12)
12.9921(12)
90
97.355(7)
90
equipped with graphite monochromated Mo
Ka radiation
a
(°)
(k = 0.71073 Å). An empirical absorption correction was performed
using the MULABS option in PLATON [60]. The structures were solved
by direct methods using SHELXS-97 and refined with full-matrix
least-squares on F2 with SHELXL-97 [61]. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were located in a
difference map but refined using a riding model. Table 2 summa-
rizes the crystal data and refinement details. For molecular graph-
ics XP from the SHELXTL suite [62] was used.
b (°)
c
(°)
V (Å3)
1960.8(3)
4
Z
F(0 0 0)
974
872
Density (calculated)
1.390
1.442
(g/dm3)
Index ranges, hkl
ꢁ14:13, ꢁ17:16, 0:17
ꢁ11:11, ꢁ17:17,
ꢁ15:15
Absorption coefficient
0.731
0.697
(mmꢁ1
)
2h range (°)
Completeness to h = 25.00°
Reflections collected
1.46–25.02
100.0%
17 567
2.45–25.01
100.0%
9934
2.5. Antibacterial activities
The antibacterial activity of all synthesized metal complexes
has been investigated against four bacteria, two G (+) i.e. Staphylo-
coccus aureus ATCC 25923, Bacillus subtilis DSM 3256 (Germany), and
two G (ꢁ) bacterial strains i.e. Escherichia coli ATCC 25922, and
Pseudomonas aeruginosa ATCC 10197 by the agar well diffusion
method [63–65]. Nutrient agar was purchased from OXOID, Eng-
land. Imipenum was used as standard antibiotic, which is b-lactam
antibiotic effective against G (+) as well as G (ꢁ) bacteria. Three
milligrams of the test samples (ligands and complexes) were dis-
solved in 1 ml of DMSO. Two to three milliliters nutrient broth
(0.8 g/100 mL) was prepared in distilled water with pH 7 and
was autoclaved at 121 °C, 15 psi pressure and for 20 min. Fresh cul-
tures grown in 24 h on nutrient broth at pH 7 were used for sensi-
tivity testing. To compare the turbidity of bacterial cultures
McFarland BaSO4 solution was used as turbidity standard. To per-
form antibacterial assay, nutrient agar medium was prepared by
dissolving 2 g/100 mL in distilled water with pH 7 and the medium
was autoclaved. A 25 mL of the nutrient agar medium was poured
in Petri plate’s 9 cm diameter and allowed to solidify. Using sterile
cotton swabs lawns of test cultures were prepared on labeled
plates. Four wells per plate were prepared with the help of sterile
Unique reflections, [R(int)
]
7961 [0.0539]
7961/2/523
0.8557 and 0.8051
3441 [0.0882]
3441/0/242
0.9148 and
0.8234
Data/restraints/parameters
Maximum, minimum
transmission
Goodness-of-fit (GOF) on F2 0.867
0.853
Final R indices [I > 2
r
(I)]
R1 = 0.0275,
wR2 = 0.0641
R1 = 0.0381,
wR2 = 0.0663
1.205 and ꢁ0.564
R1 = 0.0597,
wR2 = 0.1335
R1 = 0.0967,
wR2 = 0.1423
1.355 and ꢁ1.063
R indices (all data)
Largest difference in peak
and hole (e Åꢁ3
)
standard antibiotic imipenum with zone inhibition of 21, 18, 16
and 18 mm, respectively, which were taken as 100%.
2.6. In vitro antiproliferative activity
In order to assess the cancer chemotherapeutic potential of the
complexes, cytotoxicity assays were performed using brine
shrimps (Artemia salina) and human prostrate cancer cell line
(PC-3). For brine shrimp lethality bioassay 2 mg complexes were
dissolved in 2 mL DMSO and using this solution, diluted solutions
cork borer (2 mm). Using micropipette, 30 lL of test solution were
poured in respective labeled wells. Now, these Experimental plates
were incubated for 24 h and average of zones of inhibition (%) of
three replicates were measured and compared with the zone of
with concentrations of 5, 50 and 500 lg/mL were transferred to
vials with each concentration run in triplicate (3 vials/concentra-
tion). The brine shrimp eggs were hatched in artificial sea water
Table 1
Elemental analyses, m.p., and % yield, of [Pd(L)2(PPh3)2]Cl2 complexes.
Complexes
Found (calculated) (%)
M.p. (°C)
Yield (%)
C
H
N
S
[Pd(Tu)2(PPh3)2]Cl2
55.43
(53.43)
54.45
(54.46)
55.32
(54.49)
57.71
(57.17)
63.74
(64.90)
57.74
(57.06)
58.89
4.67
(4.48)
4.36
(4.80)
5.01
(4.49)
5.44
(5.63)
4.25
(4.47)
4.25
(4.14)
4.41
6.60
(6.56)
6.02
(6.35)
6.23
(5.98)
5.72
(5.80)
3.19
(3.29)
6.69
(6.05)
5.69
7.29
(7.51)
7.18
(7.27)
7.10
(6.84)
6.48
(6.64)
6.88
(7.52)
6.89
(6.92)
6.49
235–238
160–162
205–206
258–260
191–194
176–178
198–200
60
65
70
65
65
60
60
[Pd(Metu)2(PPh3)2]Cl2
[Pd(Dmtu)2(PPh3)2]Cl2ꢀ(H2O)(CH3OH)0.5
[Pd(Tmtu)2(PPh3)2]Cl2
[Pd(Mpy)2(PPh3)2]
[Pd(Mpm)2(PPh3)2]Cl2
[Pd(Tna)2(PPh3)2]Cl2
(58.93)
(4.33)
(5.73)
(6.56)

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S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
Table 3
Selected IR absorption (cmꢁ1) for thioamides and their palladium(II) triphenylphosphine complexes.
Species
m(C@S)
m
(N ꢁ H)
d(N ꢁ H)
m
(C ꢁ N)
m(Pd–S)
Tu
730
697
634
619
641
633
622
690
739
746
624
697
698
694
3156, 3365
3144, 3265
3163, 3245
3120, 3283
3203
1604
1618
1624
1634
1552
1592
1473
1481
1488
1568
1521
1521
1491
1476
1487
1478
1491
1534
1468
1476
[Pd(Tu)2(PPh3)2]Cl2
Metu
[Pd(Metu)2(PPh3)2]Cl2
Dmtu
298
319
320
320
327
297
330
[Pd(Dmtu)2(PPh3)2]Cl2ꢀ(H2O)(CH3OH)0.5
3159
Tmtu
[Pd(Tmtu)2(PPh3)2]Cl2
Mpy
[Pd(Mpy)2(PPh3)2]
Mpm
[Pd(Mpm)2(PPh3)2]Cl2
Tna
[Pd(Tna)2(PPh3)2]Cl2
3176
3432
3153
3428
3180
3431
1578
1577
1602
1560
1675
1600
(pH adjusted at 7.4) at room temperature under constant aeration
for 48 h. After 2-days of hatching and maturation, 30 larvae were
placed in a vial containing 5 mL of artificial sea water. Test com-
pounds in different concentrations (5, 50 and 500 ppm) were
added to the vials before making up the final volume to 5 ml with
sea water. The vials were maintained under illumination at
28 1 °C for 24 h and supplemented other vials with DMSO and
reference cytotoxic drug serving as negative and positive controls,
respectively. The data was analyzed with Finney computer pro-
gram to determine LD50 values with 95% confidence intervals
[66–70].
Cytotoxicity towards human prostate cancer cell line (PC3) was
evaluated by means of MTT (Tetrazolium salt reduction) assay [71].
For cytotoxic assay the tests and reference samples were dissolved
in DMSO with the concentration of 1 mg/mL. The cells were grown
in DMEM (Dulbacco’s Modified Eagle Medium) containing 10% FBS
and 2% antibiotic (penicillin and streptomycin) and maintained at
37 °C with 5% CO2 level for 24 h in flask. Briefly 1 ꢂ 105 cells/mL
were plated in a 96 well flat-bottom micro plates for 24 h incuba-
in Table 3. A low frequency shifts in the
730 cmꢁ1 and high frequency shifts in
m
(C@S) band at 622–
m
(C–N) bands indicate that
coordination occurs through sulfur atoms of thione forms of the li-
gands in the solid state [32(a,b)]. The absorptions at 297–320 cmꢁ1
were attributed to the
m(Pd–S) vibrations. A characteristic peak due
to
m
(P–CPh) around 1090 cmꢁ1 indicated the presence of PPh3 in the
complexes. For Dmtu complexes, m(O–H) vibrations were also ob-
served at 3530 and 3448 cmꢁ1 indicating the presence of water
and methanol in the complex.
The 1H, 13C and 31P NMR chemical shifts are given in Table 4. In 1H
NMR spectra of the complexes of thiones the N–H signal of thiones
become less intense upon coordination and shifted downfield from
their positions in free ligands. The deshielding of the N–H proton is
related to an increase of the
pelectron density in the C–N bond upon
complexation [45]. In 13C NMR upfield shifts are observed in the
>C@S resonance of ligands by (ꢃ2.8 to 10 ppm) on its complexation
with palladium(II). The upfield is attributed to the lowering of dou-
ble bond character in the >C@S bond and a shift of N ? C electron
density producing a partial double bond character in the C–N bond,
as observed in other metal complexes of thiones [45,72–74]. Among
these complexes, [Pd(Mpy)2(PPh3)2]Cl2 with the most significant
shift in C-2 was found to be the most stable.
tion to allow for cell attachment. A 50 lL MTT solution (3-(4,5-
dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide) (2 mg/
mL) was added to the well, 4 h before the end of incubation. After
aspiration of medium and reagents overnight, 100
l
L DMSO was
The resonances of triphenylphosphine ring carbons of the com-
plexes were observed in the regions of 128–134 ppm. The carbon
atoms, C(–P), C-2, C-3 and C-4 of free triphenylphosphine resonate
at 137.2, 133.6, 128.5 and 128.7 ppm, respectively. In complexes
the C–P resonance shifted upfield by about 3–4 ppm (in case of
Tmtu by 8 ppm), while the other resonances remained almost
unshifted. Upfield shifts in the C–P resonance compared to free
Ph3P are consistent with its coordination to metal center [47].
The C(–P), C-2 and C-3 resonances were in the form of doublets
(or broad singlets), while C-4 appeared as a sharp singlet. However,
in the Tmtu complex, [Pd(Tmtu)2(PPh3)2]Cl2, these resonances (ex-
cept C-4) appear as triplets (instead of doublets) showing that the
two phosphorus atoms are nonequivalent and will follow an
AA0XX0 spin system (Fig. 1). The simple triplet appearance arises
added and mixed thoroughly for 15 min to dissolve the Formazan
crystals. The inhibition of cell growth induced by the tested com-
plexes was detected by measuring the absorbance of each well at
570 nm using an ELISA plate reader. Mean absorbance of at least
three independent experiments for each drug dose was expressed
as a percentage of the untreated control well absorbance and plot-
ted vs. drug concentration. IC50 value represent the drug concen-
tration suitable to reduce the mean absorbance at 570 nm to 50%
compared to the untreated control wells. Doxorubicin was used
in this assay as positive controls for prostrate cancer cells.
3. Results and discussion
3
due to the fact that 2J(31P–31P) ꢄ J(31P–13C) and the inner lines
The complexes were prepared by means of the two-step reac-
tion of K2[PdCl4] with PPh3 and selected thiones in the molar ratio
of 1:2:2 in water–methanol–acetonitrile media. The elemental
analyses of the resulting products correspond to the compositions
[(Ph3P)2Pd(thione)2] and [(Ph3P)2Pd(thione)2]Cl2. The analysis of
the starting Pd-PPh3 complex corresponds to the formula,
[Pd(PPh3)2Cl2].
of the AB spectrum are so close together that they cannot be re-
solved while the intensity of the outer lines lies below the detec-
tion limit.
In the 31P NMR the 31P resonance in the complexes is significantly
downfield shifted compared to free Ph3P as observed in the other
palladium(II) complexes of triphenylphosphine [54]. A downfield
shift in 31P resonance of the complexes is related to the donation of
electron pair on phosphorus to metal that reduces the shielding at
phosphorus nucleus. It was further observed that the 31P NMR spec-
tra of Tu, Mpy and Mpm complexes displayed single resonances,
while for Metu, Dmtu and Tmtu complexes another less intense res-
3.1. Spectroscopic studies
Selected IR spectroscopic vibrational bands for the free ligands
and their palladium(II)–triphenylphosphine complexes are given

S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
3265
Table 4
1H, 13C and 31P chemical shifts of thioamides and their palladium(II)–triphenylphosphine complexes in DMSO-d6 (Tmtu complex in CDCl3).
Species
NꢁH
C-2
C-3
C-4
C-5
C-6
31P
PPh3
Tu
ꢁ5.5
6.98, 7.25
183.81
[Pd(Tu)2(PPh3)2]Cl2
Metu
[Pd(Metu)2(PPh3)2]Cl2
7.67, 8.08
6.95, 7.45, 7.65
7.75, 7.94
178.66
181.10, 184.10
172.07
22.3
19.8
29.90, 31.10
30.02
31.21
Dmtu
7.38
7.74
3.08a
3.11a
182.70
179.38
193.42
190.10
177.69
167.36
181.90
174.1
151.59
197.92b
153.75
182.64b
30.75
31.27
42.05
44.50
133.22
132.50
[Pd(Dmtu)2(PPh3)2]Cl2ꢀ(H2O)(CH3OH)0.5
19.9
23.3
25.9
26.0
Tmtu
[Pd(Tmtu)2(PPh3)2]Cl2
Mpy
[Pd(Mpy)2(PPh3)2]
Mpm
[Pd(Mpm)2(PPh3)2]Cl2
Tna
113.04
116.83
155.0
156.31
134.87
137.49
139.14
109.96
114.40
123.06
137.91
139.82
155.0
156.31
147.61
9.77, 10.12
10.25
135.31
133.32
[Pd(Tna)2(PPh3)2]Cl2
132.20
124.29
150.70
25.64, 42.27
a
Signals due to CH3 protons.
Value for C@S resonance.
B
Table 5
Selected bond lengths (Å) and bond angles (°) of 1 and 2.
and 175.14 (5)°, respectively. The bond lengths at palladium (Ta-
ble 5) agree well with the values reported for the corresponding
distances in other palladium(II) complexes [29,45–57,76–78]. The
carbon atoms in N–C@S or N@C–S moieties of the ligands are
sp2-hybridized.
In the crystal structure of complex (1), N–H hydrogen atoms of
Dmtu and those of water molecules are hydrogen bonded with Clꢁ
ions. All N–H bonded hydrogen atoms are involved in hydrogen
bonding. Hydrogen bonding details are listed in Table 6.
Complexes Bond lengths
Bond Angles
(1)
Pd(1)–S(1)
Pd(1)–S(2)
Pd(1)–P(1)
Pd(1)–P(2)
P(1)–C(21)
P(1)–C(31)
2.3234(6)
2.3362(5)
2.3530(6)
2.3605(5)
1.8155(16) S(2)–Pd(1)–P(2)
1.822(3) P(1)–Pd(1)–P(2)
S(1)–Pd(1)–S(2)
S(1)–Pd(1)–P(1)
S(2)–Pd(1)–P(1)
S(1)–Pd(1)–P(2)
149.018(16)
91.62(2)
86.757(19)
87.539(19)
92.629(18)
177.272(16)
(2)
Pd(1)–
2.3376(19) P(1)#1–Pd(1)–P(1)
180.0
P(1)#1
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–
2.3376(19) P(1)#1–Pd(1)–S(1)
2.3374(19) P(1)–Pd(1)–S(1)
2.3374(19) P(1)#1–Pd(1)–
S(1)#1
94.37(7)
85.63(7)
85.63(7)
3.3. Antibacterial studies
S(1)#1
The antibacterial activities of the palladium(II) triphenylphos-
phine complexes have been determined against four strains of bac-
teria (S. aureus (ATCC 25923), B. subtilis (DSM 3256), E. coli (ATCC
25922), and P. aeruginosa (ATCC 10197) and the results are shown
in Table 7. Significant antibacterial activities were observed as
compared to a standard drug. The mercaptopyridine complex
exhibits a very good activity against three bacteria B. subtilis,
E. coli and P. aeruginosa comparable with standard drug imipenum
while it has significant activity against S. aureus. The complexes of
methylthiourea, tetramethylthiourea and mercaptopyrimidine ex-
hibit also showed good activity against all of these four bacteria.
The complexes of thiourea, dimethylthioure and imidazolidine-2-
thione have shown moderate activity. While those of, tetramethyl-
thiourea and thionicotinamide are inactive against all bacteria, that
suggests that bacteria have high resistance against these two
complexes.
P(1)–C(11)
P(1)–C(31)
P(1)–C(21)
1.812(8)
1.839(7)
1.846(8)
P(1)–Pd(1)–S(1)#1
S(1)–Pd(1)–S(1)#1
94.37(7)
180.00(9)
Symmetry transformations used to generate equivalent atoms: #1 x, y, z ꢁ 1.
onance appeared around 26.5 ppm, which is probably due to the
existence of another isomeric (cis) form in solution. Also in the spec-
tra of [Pd(Dmtu)2(PPh3)2]Cl2 and [Pd(Tna)2(PPh3)2]Cl2, a resonance
at 42 ppm was also observedthatmay bedue toformationof Ph3P@S
[75].
3.2. Crystal structures description
The structures of complex cations of 1 and 2 are shown in Figs. 2
and 3, respectively. The selected bond distances and bond angles
are listed in Table 5. The crystal structure of (1) consists of
[Pd(PPh3)2(Dmtu)2]+2 cations and uncoordinated Clꢁ ions along
with one molecule of water and half of methanol. The complex
(2) is neutral in which Mpy binds as an anionic thiolate ligand.
The Pd atom in (1) adopts a distorted square-planar geometry,
while in (2) the coordination environment around Pd is nearly reg-
ular square-planar. In both structures, thioamide ligands (N,N0-
dimethylthiourea and 2-mercaptopyridine) behave as S-donors
and are binding in a terminal mode. The two thioamides as well
as two triphenylphsophine molecules are bound in a trans fashion.
The corresponding cis S–Pd–P angles varying from 87.19 (4)°–
91.20 (4)° and the trans S–Pd–S angles and P–Pd–P of 159.49 (5)°
3.4. Brine shrimp lethality bioassay
Palladium(II)–triphenylphosphine complexes of thioureas and
heterocyclic thiones showed considerable cytotoxic activity in
the brine shrimp (Artemia salina) lethality bioassay. The refer-
ence drug Etoposide was used as positive control with the dose
of 7.4625 lg/mL. Lethal dose 50 (LD50) values of reference and
test samples observed after 24 h are shown in Table 8. All the
tested complexes have been proven to be non-toxic to brine
shrimps because brine shrimps showed resistance to all these
compounds even when the concentration was increased to 100
times.

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S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
Fig. 1. 13C{1H} NMR spectrum of Ph3P region of [(Ph3P)2Pd(Tmtu)2]Cl2 (showing triplets for 13C–31P coupling due to non equivalent phosphorus atoms).
Fig. 2. Molecular structure of [Pd(Dmtu)2(PPh3)2]Cl2ꢀ(CH3OH)0.5ꢀH2O. (1).
3.5. In vitro cytotoxicity studies on human prostate cancer cells
curves obtained after 72 h exposure by means of MTT test, are
shown in Table 9. The data shows that some of the studied com-
pounds particularly [Pd(Tu)2(PPh3)2]Cl2, [Pd(Dmtu)2(PPh3)2]Cl2
and [Pd(Mpm)2(PPh3)2]Cl2 exhibit significant in vitro cytotoxic
activity, i.e. 18.30 1.22, 5.80 0.57, 8.17 0.47, respectively, as
The cytotoxic effect of compounds were assessed and compared
to that of doxorubicin on human prostate cancer cell line. Inhibi-
tion concentration IC50 values, calculated from the dose-survival

S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
3267
Fig. 3. Molecular structure of [Pd(Mpy)2(PPh3)2] (2).
Table 6
compared to doxorubicin which has IC50 of 0.912 0.12. Similar
activity in vitro was already observed for some thioamide com-
plexes of palladium(II) and platinum(II) [21,24,25,29,44,79].
In this study we have shown that K2PdCl4 react with triphenyl-
phosphine and then thiones to form the complexes of the types,
[PdL2(PPh3)2]Cl2 and [PdL2(PPh3)2] in which the ligands coordinate
through sulfur atom in thione or thiolate forms. In this way, it pro-
vides useful information about the nature of Pd–S bonding in Pd–
thione complexes. The complexes exhibit significant antibacterial
and antitumor activity (against prostate cancer cells) showing
the potential for further testing as antibacterial/antitumor agents.
Hydrogen bond distances (Å) and angles (ꢁ) for (1).
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
2.44(3)
Dꢀ ꢀ ꢀA
3.191(2)
3.1798(17) 150(2)
3.1724(19) 164(2)
3.209(2)
\D–Hꢀ ꢀ ꢀA
157(2)
N(1)–H(1)ꢀ ꢀ ꢀCl(1)
N(2)–H(2)ꢀ ꢀ ꢀCl(2)
N(3)–H(3)ꢀ ꢀ ꢀCl(1)
N(4)–H(4)ꢀ ꢀ ꢀCl(2)#1
O(1W)–H(1WA)ꢀ ꢀ ꢀCl(2)
0.79(3)
0.774(18) 2.49(2)
0.85(3)
0.79(3)
2.35(2)
2.49(3)
151(2)
173(3)
172(4)
0.824(10) 2.515(11) 3.335(2)
O(1W)–H(1WB)ꢀ ꢀ ꢀCl(1)#2 0.820(10) 2.560(12) 3.373(2)
Symmetry transformations used to generate equivalent atoms: #1 x, y, z ꢁ 1; #2
ꢁx + 1, ꢁy + 2, ꢁz + 1.
Table 7
Antibacterial activities of palladium(II) triphenylphosphine of thioamides complexes.
Name of complexes/std./ligands
Staphylococcus aureus
Bacillus subtilis
Escherichia coli
Pseudomonas aeruginosa
(ATCC 25923)
(DSM 3256)
(ATCC 25922)
(ATCC 10197)
Microorganism (% zone of inhibition of std. drugs, ligands and complexes)
Imipenum
Tu
100 (21)
0
100 (18)
0
100 (16)
13
100 (18)
0
[Pd(Tu)2(PPh3)2]Cl2
Metu
[Pd(Metu)2(PPh3)2]Cl2
Dmtu
38
0
52
10
43
0
10
52
50
19
29
0
39
17
67
11
56
11
0
95
95
45
53
0
38
45
57
13
38
0
13
100
100
63
72
19
45
33
50
11
56
0
11
83
85
45
42
0
[Pd(Dmtu)2(PPh3)2]Cl2ꢀ(H2O)(CH3OH)0.5
Tmtu
[Pd(Tmtu)2(PPh3)2]Cl2
Mpy
[Pd(Mpy)2(PPh3)2]
Mpm
[Pd(Mpm)2(PPh3)2]Cl2
Tna
[Pd(Tna)2(PPh3)2]Cl2
38
39
38
0
Concentration of the standard drug (Imipenum) = 10
Concentration of sample = 3 mg/mL.
lg/disc.

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S. Nadeem et al. / Inorganica Chimica Acta 363 (2010) 3261–3269
Table 8
Brine shrimps lethality bioassay of palladium(II) triphenylphosphine complexes of thioamides.
Compounds
Dose (
l
g/mL)
No. of survivors/no. of shrimps
LD50
(lg/mL)
Etoposide
[Pd(Tu)2(pph3)2]Cl2
100
100
100
100
100
100
100
100
10
10
10
10
10
10
10
10
1
1
1
1
1
1
1
1
7.4625
24/30
18/30
18/30
20/30
25/30
19/30
22/30
25/30
22/30
20/30
22/30
24/30
22/30
23/30
27/30
26/30
25/30
27/30
26/30
26/30
26/30
[Pd(Metu)2(pph3)2]Cl2
[Pd(Dmtu)2(PPh3)2]Cl2ꢀ(H2O)(CH3OH)0.5
[Pd(Tmtu)2(pph3)2]Cl2
[Pd(Mpy)2(pph3)2]
[Pd(Mpm)2(pph3)2]Cl2
[Pd(Tna)2(pph3)2]Cl2
361.269
374.270
804.680
185.728
666.910
287.105
Table 9
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Acknowledgements
Financial support from Pakistan Council for Science and Tech-
nology, Islamabad, Pakistan is gratefully acknowledged. The
in vitro cytotoxicity screening and brine shrimps lethality bioassay
studies were carried out by Prof. Dr. Iqbal Chaudhary in the labora-
tory of Dr. Panjwani Center for Molecular Medicine and Drug Re-
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