Diazoketiminato Complexes of Platinum(II) and Palladium(II
[(HL1NH)Pt(acac)]: [(HL1NH)Pt(dmso)Cl] (50 mg, 0.1 mmol) was
dissolved in 40 mL of methanol and acetylacetone (10 mg,
0.38 mmol) was added. The mixture was then heated to reflux for
4 h to afford a blue solution. Evaporation of the solvent gave a
dark blue residue, which was purified by chromatography on a sil-
ica gel (60–120 mesh) column with toluene as eluent. Evaporation
of the solvent gave [(HL1NH)Pt(acac)] as a dark blue solid. Yield:
32.10 mg (65%). C17H17N3O2Pt (490.36): calcd. C 41.55, H 3.48,
N 8.53; found C 41.60, H 3.46, N 8.56.
arrangement with weak intermolecular interactions. Inter-
estingly, the delocalized diazoketiminato chelates [(HLnNH)-
Pt(dmso)Cl] and [(HLnNH)Pt(acac)] exhibit reversible one-
electron reductions in their cyclic voltammograms. This
electron-transfer property has been attributed to a ligand-
centered reversible azo (–N=N–) reduction by EHMO cal-
culations. The results of an in vitro study of the cytotoxicity
of [(HL1NH)Pt(dmso)Cl] against the HeLa cell line are
interesting in terms of dose dependence and apoptotic
pattern of cell death. Further biological experiments are un-
derway to compare the relative activities with cisplatin.
[(HL2NH)Pt(acac)] and [(HL3NH)Pt(acac)]: These compounds
were prepared following the same procedure as for [(HL1NH)Pt-
(acac)] but with [(HL2NH)Pt(dmso)Cl] (52 mg, 0.1 mmol) and
[(HL3NH)Pt(dmso)Cl] (54 mg, 0.1 mmol). Yield: 35.05 mg (70%,
for the HL2NH complex C18H19N3O2Pt) and 36.24 mg (70%, for
the HL3NH complex C17H16ClN3O2Pt).
Experimental Section
C18H19N3O2Pt (504.36): calcd. C 42.85, H 3.79, N 8.29; found C
42.82, H 3.76, N 8.32.
C17H16ClN3O2Pt (524.86): calcd. C 38.83, H 3.08, N 8.05; found
C 38.86, H 3.04, N 8.00.
Materials: The solvents used in the reactions were of reagent grade
(E. Merck, Kolkata, India) and were purified and dried by reported
procedures.[14] Platinum chloride, dimethyl sulfoxide, and acetyl-
acetone were purchased from the same company. Potassium tetra-
chloroplatinate and sodium tetrachloropalladate were prepared by
a reported procedure. Trypan blue, propidium iodide, and Annexin
V-FITC were obtained from Aldrich. HeLa cells were collected
from NCCS, Pune, India. The ligands 2-(phenylazo)aniline
(HL1NH2), 2-(p-tolylazo)aniline (HL2NH2), and 2-(p-chlorophen-
ylazo)aniline (HL3NH2) were prepared following the reported pro-
cedures.[14,15,18]
[(HL1NH)PdCl]2: A solution of HL1NH2 (100 mg, 0.5 mmol) in
5 mL of dmso was added to a solution of Na2PdCl4 (150 mg,
0.5 mmol) in 5 mL of dmso. The mixture was stirred for 4 h at
60 °C and a dark pink solid was obtained upon evaporation of
dmso. Pure [{(HL1NH)PdCl}2]was obtained from the pink solid by
chromatography on a silica gel (60–120 mesh) column with toluene
as the eluent. Solid [{(HL1NH)PdCl}2] was obtained upon evapo-
ration of the eluent. Yield: 188.80 mg (55%). C24H20Cl2N6Pd2
(1352.5): calcd. C 42.59, H 2.95, N 12.42; found C 42.54, H 3.01,
N 12.38.
Physical Measurements: Microanalysis (C,H,N) was performed
using a Perkin–Elmer 240C elemental analyzer. Infrared spectra
were recorded with a Perkin–Elmer L120-00A FT-IR spectrometer
with the samples prepared as KBr pellets. Electronic spectra were
recorded with a Shimadzu UV- 2401 PC spectrophotometer. 1H
NMR spectra were obtained with Bruker 500 RPX and Bruker 300
DPX spectrometers in CDCl3 using TMS as the internal standard.
Electrochemical measurements were performed using a PAR Versa-
stat II potentiostat with a platinum disk working electrode, a plati-
num wire auxiliary electrode, and an aqueous saturated calomel
electrode (SCE) as reference, (0.1 ) Bu4NClO4 as supporting elec-
trolyte, in acetonitrile. Electrochemical measurements were carried
out under a dinitrogen atmosphere at 298 K and were uncorrected
for junction potentials. Cytotoxicity was measured with a Fluores-
cence Microscope (Olympus BX40, Tokyo, Japan), FACS Calibur
(BD Biosciences) and the Cell Quest (Bekton Dickinson) software
package.
Synthesis of [(HL1NH)Pt(dmso)Cl]: A solution of 2-(phenylazo)-
aniline (HL1NH2; 100 mg, 0.5 mmol) in 5 mL of dmso was added
to a solution of K2PtCl4 (207 mg, 0.5 mmol) in 5 mL of the same
solvent. The mixture was stirred for 5 h at 60 °C and a dark pink
solid was obtained upon evaporation of dmso. Pure [(HL1NH)-
Pt(dmso)Cl] was obtained from the pink solid by chromatography
on a silica gel (60–120 mesh) column with toluene as the eluent.
Solid [(HL1NH)Pt(dmso)Cl] was obtained by evaporating the elu-
ent. Yield: 115.25 mg (45%). C14H16ClN3OPtS (504.9): calcd. C
33.25, H 3.18, N 8.34; found C 33.27, H 3.16, N 8.31.
Reaction of HL1NHCH2Ph with Na2PdCl4:
A solution of
HL1NHCH2Ph (110 mg, 0.52 mmol) in 5 mL of dmso was added
to a solution of Na2PdCl4 (150 mg, 0.52 mmol) in 5 mL of dmso.
The mixture was stirred for 4 h at 60 °C and a dark brown solid
was obtained upon evaporation of dmso. Pure [(HL1NHCH2Ph)-
PdCl] was obtained from the brown solid by chromatography on a
silica gel (60–120 mesh) column with a toluene/acetonitrile mixture
(90:10 v/v) as eluent. Solid [(L1NHCH2Ph)PdCl] was obtained
upon evaporation of the eluent. Yield: 119.99 (55%).
Reaction of HL1NHCH2Ph with K2PtCl4:
A solution of
HL1NHCH2Ph (110 mg, 0.52 mmol) in 5 mL of dmso was added
to a solution of K2PtCl4 (215 mg, 0.52 mmol) in 5 mL of dmso.
The mixture was stirred for 5 h at 60 °C and a dark pink solid was
obtained upon evaporation of dmso. Pure [(HL1NH)Pt(dmso)Cl]
was isolated by chromatography on a silica gel (60–120 mesh) col-
umn with toluene as the eluent. Solid [(HL1NH)Pt(dmso)Cl] was
obtained upon evaporation of the eluent. Yield: 130.76 mg (50%).
Viability Assay. Trypan Blue Exclusion Test: HeLa cells were treated
with 4, 8, 12, and 16 µ solutions of complex in dmso.[28] The cells
(10 µL suspension) were then placed on cover slips at the required
dilution and each cover slip was placed cell-side down onto a slide
containing a drop of 0.125% Trypan Blue dye (wt/vol in sterile
isotonic saline). The excess dye solution was removed by applying
gentle pressure with gauze at the edges of the cover slip. The slides
were viewed within ten minutes with a light microscope at a magni-
fication of 40ϫ and 50–100 cells counted. Viable cells remained
unstained, while the nuclei of nonviable cells were stained blue.
[(HL2NH)Pt(dmso)Cl] and [(HL3NH)Pt(dmso)Cl]: These com-
plexes were prepared following the same procedure as for
[(HL1NH)Pt(dmso)Cl] but with HL2NH2 (106 mg, 0.5 mmol) and
HL3NH2 (116 mg, 0.5 mmol). Yield: 104.27 mg (40%, for the
HL2NH2 complex C15H18ClN3OPtS) and 121.62 mg (45%, for the
Differentiation Between Apoptosis and Necrosis by FACS: To distin-
HL3NH2 complex C14H15Cl2N3OPtS). C15H18ClN3OPtS (518.9): guish between apoptosis and necrosis treated or untreated cells
calcd. C 34.71, H 3.41, N 8.12; found C 34.68, H 3.46, N 8.09.
C14H15Cl2N3OPtS (539.4): calcd. C 31.10, H 2.80, N 7.82; found
C 31.14, H 2.78, N 7.78.
(1ϫ106 in each case) were harvested, in a double labeling system,
and PI and Annexin V Fluos (Boehringer Mannheim) added di-
rectly to the culture medium or to the cell suspension. The mixture
Eur. J. Inorg. Chem. 2007, 4272–4281
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Pratihar, Jahar Lal
