4776 Organometallics, Vol. 28, No. 16, 2009
Dub et al.
EtOH/HBr (30 mL þ 2 mL) mixture and filtered through Celite.
Ethene gas was flushed through the obtained solution during
4 h; then nBu4PBr (163 mg, 0.482 mmol) was added, and the
resulting mixture was stirred under an ethene flush for 1 h. The
pure yellow-orange (nBu4P)[PtBr3(C2H4)] was obtained after
solvent evaporation, washing with water (4 ꢁ 6 mL), recrystal-
lization from dichloromethane/diethyl ether, washing with pen-
tane, and finally drying in vacuo. Yield: 160 mg (46%). The
spectroscopic data of this material were identical to those of the
product of method A.
Synthesis of (nBu4P)[PtBr3(PhNH2)] (3). To a solution of
K2PtCl4 (260 mg, 0.626 mmol) in water (12 mL), adjusted to
pH=2 by addition of CH3COOH, was added KBr (6.71 g, 90
equiv), and the resulting mixture was stirred for 3 h at room
temperature. Aniline (57 μL, 0.626 mmol) in 0.5 mL of EtOH
was then added drop by drop, and the obtained mixture was
stirred for 1 h, resulting in the formation of a yellow-orange
precipitate. To this mixture was added a solution of nBu4PBr
(212 mg, 0.626 mmol) in dichloromethane (7 mL), and the
resulting biphasic system was vigorously stirred for 20 min
and transferred into the separating funnel. Then the red organic
phase was separated. Following solvent evaporation and re-
crystallization from dichloromethane/diethyl ether, red crystals
of pure (nBu4P)[PtBr3(PhNH2)] were obtained in 41% yield
(202 mg).
Synthesis of trans-PtBr2(PhNH2)(C2H4) (4). Method A. From
K2PtCl4. To an aqueous solution (6 mL) of K2PtCl4 (100 mg,
0.241 mmol) was added KBr (2.580 g, 90 equiv), and the
resulting solution was stirred for 3 h at room temperature.
The solvent was then evaporated under reduced pressure, and
K2PtBr4 was extracted by three equal portions of a EtOH/HBr
mixture (total volume: 15 mL of EtOH þ 1 mL of concentrated
aqueous HBr) and filtered through Celite. The resulting solution
was flushed with ethylene for 5 h; then the solvent was evapo-
rated to dryness. Dissolution in water (7 mL) followed by
addition of an ethanol solution of aniline (22 μL, 0.241 mmol
in 0.5 mL) resulted in an immediate precipitation of a yellow
powder. After 1 h of stirring, the solid was filtered, washed with
water, and dried. It was then redissolved in the minimum
amount of dichloromethane (ca. 3 mL), and the solution was
filtered and evaporated to dryness. Yield: 49% (56 mg). The
compound is unstable in DMSO-d6, yielding a mixture of
products (195Pt resonances at δ -3306, -3495, -3578, -3733
with approximate relative ratio of 1:6:1:3 from signal in-
tegration). The resonance at δ -3578 is identical to that
obtained by dissolution of 2 and tentatively assigned to
[PtBr3(DMSO-d6)]- (see above). The compound slowly changes
color toward black when kept in air for several days as a solid.
Storage under argon is recommended.
Method B. From Zeise’s Salt. An aqueous solution (8 mL) of
Zeise’s salt (200 mg, 0.543 mmol) and KBr (3.228 g, 50 equiv)
was stirred under an ethene flush for 20 h at room temperature.
An aniline (50 μL, 0.543 mmol) solution in EtOH (1 mL) was
then added dropwise, yielding a yellow precipitate. After stirring
for 1 h at room temperature, the precipitate was filtered, washed
with water, and dried in vacuo. Subsequent washing with
pentane and drying in vacuo affords yellow trans-[PtBr2(C2H4)-
(PhNH2)] in 73% yield (189 mg). The spectroscopic data of this
material were identical to those of the product of method A.
Synthesis of cis-PtBr2(PhNH2)(C2H4) (5), from K2PtCl4. To
an aqueous solution (5 mL) of K2PtCl4 (100 mg, 0.241 mmol),
adjusted to pH=2 by the addition of CH3COOH, was added
KBr (2.58 g, 90 equiv), and the resulting mixture was stirred for 3
h at room temperature. Aniline (22 μL, 0.241 mmol) in 0.5 mL of
EtOH was then added dropwise, and the resulting mixture was
stirred for 1 h, yielding a small amount of yellow precipitate.
After filtration, the resulting red solution was flushed with
ethene for 4 h, yielding a yellow-green precipitate, which was
then filtered. The precipitate was washed with water and dried in
vacuo. Yield: 48 mg (42%).
Synthesis of cis-PtBr2(PhNH2)2 (6). To a solution of K2PtCl4
(1000 mg, 2.409 mmol) in water (40 mL) was added KBr (25.8 g,
90 equiv), and the resulting mixture was stirred for 3 h at room
temperature. A solution of aniline (440 μL, 4.818 mmol) in 2 mL
of EtOH was then added dropwise. The mixture was stirred for
3 h and filtered. The pale yellow precipitate was washed
sequentially with water, EtOH, and Et2O and then dried in
vacuo. Yield: 1.23 g (94%). The compound is not stable
in DMSO. Upon dissolving the compound in DMSO-d6,
the formation of new 195Pt NMR resonances (a major peak
at δ -3495 and a minor one at δ -3306) was observed. They are
tentatively attributed to [PtBr2(DMSO)(PhNH2)] and
[PtBr2(DMSO)2], respectively.
X-ray Crystallography. Single crystals of 1, 2, and 3 suitable
for the X-ray study were prepared as follows: to a suspension of
the compound in Et2O at the reflux temperature was added
dichloromethane dropwise until a homogeneous system formed.
The solution was then filtered while hot and kept at -20 °C
overnight. In the case of 1, the solution was then further
concentrated to approximately one-third of its original volume
and kept at -20 °C during two weeks, yielding large (ca. 3 mm)
deep-red crystals. Crystals of 4 were prepared in the same
manner as 2 and 3, albeit using a pentane/Et2O combination.
The crystals of 5 were prepared by slow evaporation of a
saturated acetone solution. A single crystal of each compound
was mounted under inert perfluoropolyether on the tip of a glass
fiber and cooled in the cryostream of a Bruker APEX2 CCD
diffractometer. Data were collected using monochromatic Mo
KR radiation (λ=0.71073). The structures were solved by direct
methods (SIR97)66 and refined by least-squares procedures on
F2 using SHELXL-97.67 All H atoms attached to carbon were
introduced in calculations in idealized positions and treated as
riding models. The drawing of the molecules was realized with
the help of ORTEP32.68 Crystal data and refinement para-
meters are given in the Supporting Information (Table S10).
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication nos. CCDC 725742-725747. Copies
of the data can be obtained free of charge on application to the
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: (þ44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
Computational Details. All geometry optimizations were per-
formed with the Gaussian03 suite of programs69 using the
B3LYP functional, which includes the three-parameter gradi-
ent-corrected exchange functional of Becke70 and the cor-
relation functional of Lee, Yang, and Parr, which includes both
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(67) Sheldrick, G. M. SHELXL97, Program for Crystal Structure
€
€
Refinement; University of Gottingen: Gottingen, Germany, 1997.
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(69) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
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Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
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Dub, Pavel A.
