Battle et al.
was removed by filtration, washed with water, and dried. Yield
pic)]. To the best of our knowledge, there have been no
reports of such compounds in the literature other than in
patents covering both platinum(II) and platinum(IV) ana-
logues of cis-[PtCl2(NH3)(2-pic)].12,13 Here we describe the
successful preparation and characterization of one platinum-
(IV) analogue of cis-[PtCl2(NH3)(2-pic)] and studies that
show that most such compounds are unstable.
1.15 g, 2.1 × 10-3 mol, 53%.
Cis-[PtI2(NH3)(2-pic)] (1.15 g, 2.1 × 10-3 mol) was suspended
in water (50 mL) and stirred with 2.0 stoichiometric equivalents
of AgNO3 (0.70 g, 4.1 × 10-3 mol) in the dark at room temperature
for 6 h. The silver iodide that precipitated from solution was
removed by filtration, and the filtrate was treated with dropwise
additions of 1 M HCl to remove any remaining Ag+. This step
was repeated until all the Ag+ was removed. An excess of KCl
(0.56 g, 7.4 × 10-3 mol) was added, and the mixture was stirred
at room temperature. After 3 h, a yellow-green precipitate of cis-
[PtCl2(NH3)(2-pic)] formed. The solid was collected, washed with
cold water, ethanol, and ether, and placed in a desiccator. Yield
0.43 g, 1.1 × 10-3 mol, 55% (29% based on cis-[PtCl2(NH3)2]).
Experimental Section
Instrumentation and Materials. All compounds used were of
technical grade. Potassium tetrachloroplatinate(II) was obtained
from Aithaca Chemical Corp. Pyridine and 2-picoline(2-methylpy-
ridine) were obtained from Aldrich. Tetraethylammonium chloride-
1-water was obtained from Merck, and all compounds were used
without further purification. Hydrogen peroxide (30%) was obtained
from Ajax Chemicals and stored in the dark at 5 °C. Diffuse
reflectance infrared Fourier transform spectra (DRIFTS) of the
complexes were obtained on a Bio-Rad FTS-7 spectrophotometer
over the range 400-4000 cm-1 using a KBr background and matrix.
Elemental analysis (C, H, N) was conducted by the Microanalytical
Service of the Australian National University, Canberra. Electro-
chemical measurements were carried out using a BAS 100W
system. Glassy carbon working electrodes, Ag/AgCl reference
electrodes, and platinum wire auxiliary electrodes were used. The
solutions were degassed prior to measurements using argon gas,
which had previously been passed through an oxygen trap. The
supporting electrolyte was tetraethylammonium chloride at a
concentration of 0.1 M, and the concentration of the complexes
was 2 mM. Cisplatin (cis-[PtCl2(NH3)2]) was prepared as previously
described.14
Method 3. This synthesis was adapted and modified from the
method previously described by Davies et al.17 K2[PtCl4] (0.50 g,
1.2 × 10-3 mol) was dissolved in DMF (25 mL) and stirred. One
stoichiometric equivalent of 2-picoline (0.12 mL, 1.2 × 10-3 mol)
was added slowly, and the mixture was stirred at 50 °C in the dark
for 6 h. The mixture changed to a dull orange color, and KCl
precipitated from the solution. The KCl was removed by filtration
and the DMF removed from the filtrate via rotary evaporation.
Diethyl ether was added in excess to the remaining thick orange
oil, and K[PtCl3(2-pic)] preciptated as a buff-colored solid. This
solid was collected, washed with ether, and dried in a desiccator.
Yield 0.43 g, 1.1 × 10-3 mol, 91%.
K[PtCl3(2-pic)] (0.43 g, 1.1 × 10-3 mol) was suspended in water
(20 mL) and stirred. KI (0.38 g, 2.3 × 10-3 mol, 2.1 stoichiometric
equivalents) was added, and the mixture was stirred for 3 h. The
very dark brown precipitate that formed was removed by filtration
and suspended in water. Ammonia (30%, 0.20 mL, 1.7 × 10-3
mol, 1.5 stoichiometric equivalents) was added to the stirring
precipitate, and the reaction was watched closely until the precipitate
changed from dark brown to yellow. The solid was filtered from
the mixture before the yellow color turned green (indicating the
formation of an aquated species and a loss of yield). The yellow
solid, cis-[PtI2(NH3)(2-pic)] was washed with water and ether. Yield
0.45 g, 8.1 × 10-4 mol, 73%. Dry cis-[PtI2(NH3)(2-pic)] (0.45 g,
8.1 × 10-4 mol) was converted to the chloride as described in
Method 2. Yield 0.18 g, 4.8 × 10-4 mol, 59%.
Synthesis of cis-Amminedichloro(2-picoline)platinum(II).
Method 1. This synthesis was adapted and modified from the
method previously described for cis-amminedichloropyridineplati-
num(II) by Abrams et al.15
cis-[PtCl2(NH3)2] (1.17 g, 3.9 × 10-3 mol) was used to synthesize
[Et4N][PtCl3(NH3)] dissolved in water (20 mL). One stoichiometric
equivalent of 2-picoline (0.38 mL, 3.9 × 10-3 mol) was added
slowly, and the mixture was stirred at room temperature in the dark
for 72 h. A gray-green precipitate resulted, which was removed by
filtration and washed with water. This solid was resuspended in
water and stirred at 80 °C until dissolution was complete. The
solution was filtered, the solvent removed, and the resulting cis-
[PtCl2(NH3)(2-pic)] was collected as a dull yellow solid. Yield 0.35
g, 9.3 × 10-4 mol, 24%.
Method 4. This synthesis was adapted and modified from the
method previously described by Danzeisen et al.18 K2[PtCl4] (0.49
g, 1.2 × 10-3 mol) was dissolved in water (10 mL) and stirred at
room temperature. Five stoichiometric equivalents of KI (0.98 g,
5.9 × 10-3 mol) were added, and the solution was stirred in the
dark until all the solid had dissolved. One stoichiometric equivalent
of 2-picoline (0.12 mL, 1.2 × 10-3 mol) was added slowly while
stirring, and the mixture was stirred in the dark, at room temperature,
for 12 h. The dark brown precipitate that formed was separated by
filtration and suspended in water. Slow addition of 1.5 stoichio-
metric equivalents of 30% ammonia (0.21 mL, 1.8 × 10-3 mol)
followed, and the reaction was watched closely until the brown
precipitate turned yellow. The yellow solid cis-[PtI2(NH3)(2-pic)]
was collected, washed with cold water and ether, and dried in a
desiccator. Yield 0.52 g, 9.3 × 10-4 mol, 79%. cis-[PtI2(NH3)(2-
pic)] (0.51 g, 9.3 × 10-4 mol) was converted to the chloride as
described in Method 2. Yield 0.21 g, 5.5 × 10-4 mol, 60%. IR
(KBr, cm-1) 3195 s, 3065 w, 1610 s, 1566 m, 1479 vs, 1452 m,
Method 2. This synthesis was adapted and modified from the
method previously described by Kelland.16 cis-[PtCl2(NH3)2] (1.17
g, 3.9 × 10-3 mol) was used to synthesize [(Et)4N][PtCl3(NH3)],
dissolved in water (20 mL) as in Method 1. Water (20 mL) was
added and the solution stirred before adding 2.1 stoichiometric
equivalents of potassium iodide (1.36 g, 8.2 × 10-3 mol). The clear
orange solution was stirred in the dark at room temperature until it
turned red. Then, 1.1 stoichiometric equivalents of 2-picoline (0.40
g, 4.3 × 10-3 mol) was added slowly, and the mixture stirred until
a light brown precipitate of cis-[PtI2(NH3)(2-pic)] formed. The solid
(12) Wong, E. S. Y.; Giandomenico, C. M. U.S. Patent No. 68949049,
2001.
(13) Wong, E. S. Y.; Giandomenico, C. M. U.S. Patent No. 6,413,953,
2002.
(14) Dhara, S. C. Indian J. Chem. 1970, 8, 193-194.
(15) Abrams, M. J.; Giandomenico, C. M.; Vollano, J. F.; Schwartz, D. A.
Inorg. Chim. Acta 1987, 131, 3-4.
(17) Davies, M. S.; Diakos, C. I.; Messerle, B. A.; Hambley, T. W. Inorg.
Chem. 2001, 40, 3048-3054.
(18) Danzeisen, O. F.; Rotter, H. W.; Thiele, G. Z. Anorg. Allg. Chem.
1998, 624, 763-768.
(16) Kelland, L. R.; Barnard, C. D. J. Drugs Future 1998, 23, 1062-1065.
6318 Inorganic Chemistry, Vol. 45, No. 16, 2006