cis-to-trans isomerization promoted by pyridine as a crucial step for the selective preparation of trans-Pt(SAr)(CI)(PAr′3)2

Article abstract of DOI:10.1021/ic051780l

The general strategy for the syntheses of trans-Pt(SAr)(CI) (PAr′₃)₂ (1) (Ar = Ph, C₆H ₄-2-Me, C₆H₄-3-OMe C₆H ₄-2-F, etc.; Ar′ = Ph, C₆H₄-4-OMe, C ₆H₄-4-Me, and C₆H₄-4-CF₃) by the reaction of cis-PtCl₂(PAr′₃)₂ with ArSH has been developed. The mechanistic investigation suggested that isomerization of cis-1 into trans-1 promoted by the combined use of C ₆H₆ as a solvent and pyridine as a base was the key to the successful preparation of 1.

Full text of DOI:10.1021/ic051780l

Inorg. Chem. 2006, 45, 1399−1404
cis-to-trans Isomerization Promoted by Pyridine as a Crucial Step for
the Selective Preparation of trans-Pt(SAr)(Cl)(PAr
′
)
3 2
Fumikazu Yamashita, Hitoshi Kuniyasu,* Jun Terao, and Nobuaki Kambe*
Department of Molecular Chemistry & Frontier Research Center, Graduate School of
Engineering,Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received October 14, 2005
The general strategy for the syntheses of trans-Pt(SAr)(Cl)(PAr
′
)
(1) (Ar
)
Ph, C6H4-2-Me, C6H4-3-OMe C6H4-
3
2
2-F, etc.; Ar′ ) Ph, C6H4-4-OMe, C6H4-4-Me, and C6H4-4-CF3) by the reaction of cis-PtCl2(PAr with ArSH has
′
)
3 2
been developed. The mechanistic investigation suggested that isomerization of cis-1 into trans-1 promoted by the
combined use of C6H6 as a solvent and pyridine as a base was the key to the successful preparation of 1.
Introduction
also showed that the reaction of trans-Pd(SPh)(CO2Me)-
(PCy3)2 with 1-octyne yielded (Z)-(n-C6H13)(PhS)CdC(H)-
(CO2Me).4 These results indicated that the C-S or C-C
bond-forming reductive eliminations from Pd(II) or Pt(II)
were generally much faster than the insertion of unsaturated
organic compounds into the S-M (M ) Pd, Pt) bonds.5 To
our knowledge, direct evidence of the insertion of unsaturated
compounds into S-Pd or S-Pt bond when a catalytically
active substrate was employed has not yet been provided.6,7
We have expected that complexes with general formula Pt-
(SAr)(Cl)(PAr′3)2 (1) would be versatile as substrates for
scrutinization of the insertion processes because complex 1
would be thermodynamically more stable than the corre-
sponding Pd complexes,8 and the anticipated Pt(II) com-
plexes, formed by the insertion of unsaturated molecules into
S-Pt bond, would resist further reactions, such as the C-Cl
bond-forming reductive elimination. However, with respect
to the syntheses of platinum complexes with general formula
Unveiling the reactivity of transition metal complexes
having ArS-M (M ) Pd or Pt) bonds toward unsaturated
compounds is of critical importance for understanding and
developing catalytic reactions using the S-X bond (X )
typical element or functional group) activations1 because
many of them can involve the insertion of unsaturated organic
molecules into S-M bonds. However, clear-cut investigation
of the insertion process has been generally hampered by the
successive reactions. For instance, we have reported that the
reaction of Pd(SAr)2(PPh3)(CNAr) with (ArS)2 (Ar ) C6H4-
4-Me) produced ArSCdNAr(SAr) and Pd(SAr)2(PPh3)n and
that the reaction of Pt(SAr)(Ph)(PPh3)2 (Ar ) C6H4-4-Br)
with 1-octyne produced Pt(n-C6H13CCH)(PPh3)2 and (Z)-
(n-C6H13)(ArS)CdC(H)(Ph).2,3 In both cases, possible in-
termediates, thioimidoyl palladium or vinyl platinum, pro-
duced by the insertion of ArNC into S-Pd or 1-octyne into
S-Pt, were not detected at all. Furthermore, Tanaka et al.
(4) Hua, R.; Takeda, H.; Onozawa, S.-y.; Abe, Y.; Tanaka, M. J. Am.
Chem. Soc. 2001, 123, 2899.
* To whom correspondence should be addressed. E-mail:
kuni@chem.eng.osaka-u.ac.jp (H.K.); kambe@chem.eng.osaka-u.ac.jp (N.K.).
(1) For reviews, see: (a) Kuniyasu, H. In Catalytic Heterofunctionaliza-
tion; Togni, A., Gru¨tzmacher, H., Eds.; Wiley-VCH: Zu¨rich, 2001; p
217. (b) Ogawa, A. In Main Group Metals in Organic Synthesis;
Yamamoto, H., Oshima, K., Eds.; Wiley-VCH: Weinheim, Germany,
2004; p 813. (c) Kondo, T.; Mitsudo, T. Chem. ReV. 2000, 100, 3205.
(d) El Ali, B. Alper, H. In Handbook of Organopalladium Chemistry
for Organic Synthesis; Negishi, E., Ed.; Wiley: New York, 2002;
Chapter VI.6; p 2333. (e) Ogawa, A. In Handbook of Organopalladium
Chemistry for Organic Synthesis; Negishi, E., Ed.; Wiley: New York,
2002; Chapter VII.6; p 2841. (f) Han, L.; Tanaka, M. Chem. Commun.
1999, 395. (g) Beletskaya, I.; Moberg, C. Chem. ReV. 1999, 99, 3435.
(2) Kuniyasu, H.; Sugoh, K.; Su, M. S.; Kurosawa, H. J. Am. Chem. Soc.
1997, 119, 4669.
(5) Beletskaya et al. have been reported on the mechanism of Pd- and
Pt-catalyzed addition of diselenide to alkynes. However, no definitive
evidence of the formation of vinyl platinum generated by the insertion
of alkyne into Se-Pt bond has been provided. (a) Ananikov, V. P.;
Beletskaya, I. P.; Aleksandrov, G. G.; Eremenko, I. L. Organometallics
2003, 22, 1414. (b) Ananikov, V. P.; Kabeshov, M. A.; Beletskaya, I.
P. Dokl. Chem. 2003, 390, 112.
(6) We have reported that DMAD, which is generally inactive as a
substrate of catalytic S-X activation, inserted into the S-Pd bond of
Pd(SAr)2(DPPE) to produce vinyl palladium. Sugoh, K.; Kuniyasu,
H.; Kurosawa, H. Chem. Lett. 2002, 106.
(7) Koelle et al. have reported that the reaction of [Cp*Ru(SBu-t)]2 with
methyl propiolate formed a binuclear vinyl Ru-complex. Koelle, U.;
Rietmann, C.; Tjoe, J.; Wagner, T.; Englert, U. Organometallics 1995,
14, 703.
(8) Jones, W. D.; Reynolds, K. A.; Sperry, C. K.; Lachicotte, R. J.;
Godleski, S. A.; Valente, R. R. Organometallics 2000, 19, 1661.
(3) Sugoh, K.; Kuniyasu, H.; Sugae, T.; Ohtaka, A.; Takai, Y.; Tanaka,
A.; Machino, C.; Kambe, N.; Kurosawa, H. J. Am. Chem. Soc. 2001,
123, 5108.
10.1021/ic051780l CCC: $33.50
Published on Web 01/11/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 3, 2006 1399

Yamashita et al.
1.27 times larger than that of the internal standard under 1H-coupled
conditions where the PD time was set for 70 s, roughly five times
longer than the relaxation time T1 of PPh3 (ca. 13.5 s).)
Attempted Synthesis of trans-1a (run 1 of Table 2). cis-PtCl2-
(PPh3)2 (cis-2a) (7.9 mg, 0.010 mmol), SdP(C6H4-4-Me)3 (3.0 mg,
0.009 mmol as an internal standard), C6D6 (0.5 mL), PhSH (3a,
1.2 mg, 0.012 mmol), and Et3N (5.0 mg, 0.05 mmol) were mixed
in a Pyrex NMR tube. Then the reaction was monitored by 31P and
1H NMR spectra. The 31P NMR spectrum showed the formation
of 1, only very limited examples of related complexes, such
as Pt(SAr)(Cl)(PPh3)2 (Ar ) C6H2-2,4,6-i-Pr3),9a Pt(SCF3)-
(Cl)(PPh3)2,9b and Pt(SPy)(Cl)(PPh3),9c-9e have been docu-
mented. These publications made us feel that possible
dimerization, polymerization, and disproportionation can be
significant drawbacks in the preparation and handling 1.10
Herein, we wish to report on our discovery that complex 1
is actually quite selectively prepared as a thermodynamically
stable complex using pertinent reaction conditions. The key
to our success was employment of benzene, as the solvent,
and pyridine, which acted not only as a base but also as a
cis-to-trans isomerization catalyst.11
of cis-Pt(SPh)(Cl)(PPh3)2 (cis-1a) [δ 21.6 (JP-P ) 17 Hz, JPt-P
)
2676 Hz), 20.1 (JP-P ) 17 Hz, JPt-P ) 3840 Hz)] and cis-4a [δ
23.8 (s, JPt-P ) 2880 Hz)] in 8 and 55% yields, respectively after
1h. Other reactions shown in Table 2 except for run 8 were carried
out and the yields of the products were calculated similarly.
Synthesis of trans-1a (run 8 of Table 2): General Procedure
for Preparation of 1. cis-2a (347 mg, 0.44 mmol), C6H6 (20 mL)
and pyridine (0.16 mL, 2.0 mmol) were combined in a dry three-
necked flask equipped with an additional flask. Then the C6H6 (3
mL) solution of PhSH (0.40 mmol) was added dropwise to the
solution, and resultant reaction mixture was stirred for a total of 2
h. Then the reaction mixture was filtered; hexane (100 mL) was
added into the filtered solution, and the resultant solid was filtered,
washed over hexane, and dried under vacuo. It was then purified
by PTLC using benzene as an eluent to give the desired trans-1a
as a yellow solid (247 mg, 71%).
Experimental Section
1
General Comments. H and 31P NMR spectra in benzene-d6
solution were recorded with a JEOL JNM-AL-400 (400 MHz)
spectrometer, and their chemical shifts were recorded relative to
Me4Si and 85% (aq) H3PO4. IR spectra were measured with a
Perkin-Elmer Model 1600 spectrometer. Combustion analyses were
performed in the Instrumental Analysis Center of the Faculty of
Engineering, Osaka University. Melting points were determined on
a Yanaco MICRO melting point apparatus. Preparative TLC was
carried out using Wakogel B-5F silica gel using benzene as an
eluent. X-ray crystal data for trans-1i were collected with a Rigaku
RAXIS-RAPID Imaging Plate diffractometer, and its ORTEP
drawing in Figure 1 was shown with 50% probability ellipsoids.
The platinum complexes cis-Pt(Cl)2(PR3)2 (cis-2) and trans-Pt(Cl)2-
(PPh3)2 (trans-2a) were prepared according to the literature.12a-c
The authentic platinum complex cis-Pt(SPh)2(PPh3)2 (cis-4a) was
also synthesized according to the literature,13 and its stereochemistry
has been unambiguously identified by X-ray crystallographic
analysis. The chemical shift and coupling constant of trans-Pt(SPh)2-
(PPh3)2 (trans-4a) in 31P NMR spectra was determined by using
the isomerization of cis-4a to trans-4a. The platinum complex trans-
Pt(SC6H4-4-OMe)2(PPh3)2 (4b) was prepared according to the
literature.10b Thiols (3), pyridine, NEt3, PPh3, C6D6, C6H6, and CD2-
Cl2 were commercially obtained and employed without any further
purification. The 31P NMR spectra were measured using standard
1H-gated decoupled conditions to calculate the yields of 1a and 4a
shown in Table 2 with SdP(C6H4-4-Me)3 as an internal standard.
The values may contain ca. 30% errors from the difference in
Other platinum complexes shown in Tables 4 and 5 were
prepared and isolated in a similar manner.
trans-Pt(SPh)(Cl)(PPh3)2 (1a). Yellow solid. mp: 212-213 °C.
1H NMR (400 MHz, C6D6): δ 7.94-7.88 (m, 12 H), 7.28 (dd, J
) 8.0 Hz, J ) 1.6 Hz, 2 H), 6.98-6.95 (m, 18 H), 6.67-6.61 (m,
3 H). 31P NMR (160 MHz, C6D6): δ 24.4 (s, JPt-P ) 2745 Hz). IR
(KBr): 3054, 1578, 1481, 1469, 1434, 1384, 1311, 1186, 1158,
1096, 1024, 998, 741, 705, 691, 522, 513, 414 cm-1. Anal. Calcd
for C42H35ClP2PtS: C, 58.37; H, 4.08. Found: C, 58.08; H, 4.00.
trans-Pt(SC6H4-2-Me)(Cl)(PPh3)2 (1b). Yellow solid. mp: 201-
202 °C. 1H NMR (400 MHz, C6D6): δ 8.33 (d, J ) 7.6 Hz, 1 H),
7.90-7.88 (m, 12 H), 6.97-6.96 (m, 18 H), 6.80 (t, J ) 7.2 Hz,
1 H), 6.67 (t, J ) 7.2 Hz, 1 H), 6.53 (d, J ) 6.8 Hz, 1 H), 1.86 (s,
3 H). 31P NMR (160 MHz, C6D6): δ 24.5 (s, JPt-P ) 2751 Hz). IR
(KBr): 3054, 1582, 1480, 1455, 1434, 1186, 1158, 1096, 1060,
1027, 998, 854, 742, 705, 692, 522, 513, 428 cm-1. Anal. Calcd
for C43H37ClP2PtS: C, 58.80; H, 4.25. Found: C, 58.64; H, 4.25.
trans-Pt(SC6H4-3-OMe)(Cl)(PPh3)2 (1c). Yellow solid. mp:
1
sensitivity to NOE by H irradiation between complexes and the
1
192-193 °C. H NMR (400 MHz, C6D6): δ 7.95-7.90 (m, 12
internal standard. (The integrals of trans-1a and trans-4a were both
H), 7.04-6.97 (m, 19 H), 6.75 (m, 1 H), 6.61 (t, J ) 7.6 Hz, 1 H),
6.40 (d, J ) 7.6 Hz, 1 H), 3.26 (s, 3 H). 31P NMR (160 MHz,
C6D6): δ 24.6 (s, JPt-P ) 2745 Hz). IR (KBr) 3462, 3048, 2988,
2830, 2354, 1581, 1480, 1467, 1435, 1310, 1276, 1239, 1218, 1183,
1097, 1071, 1046, 998, 857, 743, 706, 692, 540, 522, 513, 500
cm-1. Anal. Calcd for C43H37ClOP2PtS: C, 57.75; H, 4.17.
Found: C, 57.97; H, 4.21.
(9) (a) Chen, Q.; Boeheim, F.; Dabrowiak, J.; Zubieta, J. Inorg. Chim.
Acta 1994, 216, 83. (b) Dixon, K. R.; Moss, K. C.; Smith, M. A. S.
J. Chem. Soc., Dalton Trans. 1973, 1528. (c) Narayan, S.; Jain, V. K.
Transition Met. Chem. 1999, 24, 409. (d) Nakatsu, Y.; Nakamura,
Y.; Matsumoto, K.; Ooi, S. Inorg. Chim. Acta 1992, 196, 81. (e)
Umakoshi, K.; Sasaki, Y. Inorg. Chem. 1997, 36, 4296.
(10) (a) Rauchfuss, T. B.; Shu, J. S.; Roundhill, D. M. Inorg. Chem. 1976,
15, 2096. (b) Zanella, R.; Ros, R.; Graziani, M. Inorg. Chem. 1973,
12, 2736. (c) Boschi, T.; Crociani, B.; Toniolo, L.; Belluco, U. Inorg.
Chem. 1970, 9, 532. (d) Benefiel, A.; Roundhill, D. M.; Fultz, W. C.;
Rheingold, A. L. Inorg. Chem. 1984, 23, 3316.
(11) For the ability of pyridine for isomerization catalyst, see: (a) Tudor,
D. M.; Becker, J. J.; White, S. P.; Gagne´, R. M. Organometallics 2000,
19, 4376. (b) Basolo, F.; Chatt, J.; Gray, H. B.; Pearson, R. G.; Shaw,
B. L. J. Chem. Soc., Dalton Trans. 1974, 1377. (c) Tanaka, H.; Isobe,
K.; Kawaguchi, S. Inorg. Chim. Acta 1981, 54, L201. (d) Cattalini,
L.; Martelli, M. J. Am. Chem. Soc. 1969, 91, 312. (e) Anderson, G.
K.; Cross, R. J. J. Chem. Soc. ReV. 1980, 9, 185.
trans-Pt(SC6H4-4-OMe)(Cl)(PPh3)2 (1d). Yellow solid. mp:
1
214-216 °C. H NMR (400 MHz, C6D6): δ 7.94-7.91 (m, 12
H), 7.09 (d, J ) 8.0 Hz, 2 H), 6.99-6.98 (m, 18 H), 6.31 (d, J )
8.4 Hz, 2 H), 3.25 (s, 3 H). 31P NMR (160 MHz, C6D6): δ 24.6 (s,
JPt-P ) 2773 Hz). IR (KBr): 3056, 2358, 2340, 1485, 1434, 1280,
1234, 1182, 1096, 1028, 826, 746, 693, 627, 580, 523, 511, 440
cm-1. Anal. Calcd for C43H37ClOP2PtS: C, 57.75; H, 4.17.
Found: C, 57.68; H, 4.12.
(12) Both cis-2a and trans-2a can be selectively prepared in pure form.
(a) Cavinato, G.; Toniolo, L. Inorg. Chim. Acta 1981, 52, 39. (b)
Jensen, K. A. Z. Anorg. Allegm. Chem. 1936, 229, 225. (c) Rahn, J.
A.; Baltusis, L.; Nelson, J. H. Inorg. Chem. 1990, 29, 750.
trans-Pt(SC6H4-2-F)(Cl)(PPh3)2 (1e). Yellow solid. mp: 211-
212 °C. H NMR (400 MHz, C6D6): δ 8.00 (t, J ) 8.8 Hz, 1 H),
1
7.92-7.84 (m, 12 H), 7.00-6.91 (m, 18 H), 6.55-6.51 (m, 1 H),
(13) Lai, R. D.; Shaver, A. Inorg. Chem. 1981, 20, 477.
6.48-6.42 (m, 1 H), 6.29-6.24 (m, 1 H). 31P NMR (160 MHz,
1400 Inorganic Chemistry, Vol. 45, No. 3, 2006

SelectiWe Preparation of trans-Pt(SAr)(Cl)(PAr′3)2
Table 1. Crystallographic Data for trans-1i
C6D6): δ 24.5 (s, JPt-P ) 2717 Hz). IR (KBr): 3054, 2350, 1957,
1587, 1558, 1480, 1460, 1435, 1310, 1250, 1210, 1185, 1159, 1096,
1070, 1028, 998, 870, 810, 742, 706, 691, 618, 596, 522, 513, 499,
458, 430 cm-1. Anal. Calcd for C42H34ClFP2PtS: C, 57.18; H, 3.88.
Found: C, 58.20; H, 3.82.
formula
fw
T (°C)
λ (Å)
space group
a (Å)
b (Å)
C43H36BrCl3P2PtS
1028.12
23.0
0.71069
P1h (No. 2)
11.6513(5)
12.5267(8)
14.5392(8)
76.714(2)
88.574(2)
79.061(3)
2027.3(2)
2
trans-Pt(SC6H4-4-Cl)(Cl)(PPh3)2 (1f). Yellow solid. mp: 219-
220 °C. 1H NMR (400 MHz, C6D6): δ 7.89-7.84 (m, 12 H), 7.05
(d, J ) 8.0 Hz, 2 H), 6.96-6.95 (m, 18 H), 6.61 (d, J ) 8.8 Hz,
2 H). 13C NMR (CD2Cl2, 100 MHz): δ 134.3 (t, J ) 6.0 Hz),
130.3 (s), 129.9 (s), 128.8 (t, J ) 28.4 Hz), 127.7 (s), 127.2 (t, J
) 5.5 Hz), 126.6 (s), 125.8 (s). 31P NMR (160 MHz, C6D6): δ
24.3 (s, JPt-P ) 2718 Hz). IR (KBr): 3422, 3049, 2356, 1618, 1570,
1480, 1468, 1434, 1306, 1184, 1092, 1028, 1008, 998, 818, 808,
752, 743, 704, 692, 540, 523, 512, 488, 418 cm-1. Anal. Calcd for
C42H34Cl2P2PtS: C, 56.13; H, 3.81. Found: C, 55.85; H, 3.81.
trans-Pt(SC6H4-3-Cl)(Cl)(PPh3)2 (1 g). Yellow solid. mp: 217-
218 °C. 1H NMR (400 MHz, C6D6): δ 7.91-7.86 (m, 12 H), 7.38
(m, 1 H), 7.01-6.97 (m, 18 H), 6.89-6.86 (m, 1 H), 6.65-6.62
(m, 1 H), 6.29 (t, J ) 8.0 Hz, 1 H). 31P NMR (160 MHz, C6D6):
δ 24.4 (s, JPt-P ) 2706 Hz). IR (KBr) 3494, 3056, 2361, 2341,
1652, 1571, 1480, 1450, 1436, 1392, 1308, 1182, 1098, 1074, 1028,
999, 856, 776, 742, 706, 691, 676, 638, 523, 513, 500 cm-1. Anal.
Calcd for C42H34Cl2P2PtS: C, 56.13; H, 3.81. Found: C, 55.94;
H, 3.88.
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calcd (g/cm3)
1.684
47.94
µ (cm-1
)
R indices [I > 2σ(I)]a
R1
0.0403
0.114
wR2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
2
2
2
1594, 1570, 1500, 1483, 1460, 1440, 1404, 1289, 1253, 1180, 1100,
1029, 825, 800, 719, 648, 536, 507, 452, 433, cm-1. Anal. Calcd
for C49H49ClO6P2PtS: C, 55.60; H, 4.67. Found: C, 56.03; H, 4.68.
trans-Pt(SC6H4-4-Me)(Cl)[P(C6H4-4-CF3)3]2 (1m). Yellow solid.
1
mp: 214-215 °C. H NMR (400 MHz, C6D6): δ 7.65-7.60 (m,
12 H), 7.23 (d, J ) 8.0 Hz, 12 H), 6.80 (d, J ) 8.4 Hz, 2 H), 6.42
(d, J ) 8.4 Hz, 2 H), 1.99 (s, 3 H). 31P NMR (160 MHz, C6D6):
δ 24.0 (s, JPt-P ) 2837 Hz). IR (KBr) 1610, 1486, 1398, 1325,
trans-Pt(SC6H4-2-Cl)(Cl)(PPh3)2 (1h). Yellow solid. mp: 212-
214 °C. 1H NMR (400 MHz, C6D6): δ 8.26 (d, J ) 7.6 Hz, 1 H),
7.89-7.87 (m, 12 H), 6.98-6.96 (m, 18 H), 6.71 (d, J ) 7.6 Hz,
1 H), 6.61 (t, J ) 7.2 Hz, 1 H), 6.41 (t, J ) 7.6 Hz, 1 H). 31P NMR
(160 MHz, C6D6): δ 24.5 (s, JPt-P ) 2715 Hz). IR (KBr) 3424,
3050, 1892, 1570, 1480, 1433, 1309, 1273, 1240, 1185, 1158, 1096,
1170, 1129, 1063, 1017, 831, 808, 706, 599, 527, 444, 417 cm-1
.
Anal. Calcd for C49H31ClF18P2PtS: C, 45.75; H, 2.43. Found: C,
45.82; H, 2.54.
X-ray Crystallography. The crystal was mounted on a glass
capillary. Data collection was performed on a Rigaku RAXIS-
RAPID Imaging Plate diffractometer (Mo KR, λ ) 0.71069 Å)
with graphite-monochromated Mo KR radiation. The structure was
solved by heavy-atom Patterson methods, expanded using Fourier
techniques, and refined with full-matrix least-squares. All non-
hydrogen atoms and hydrogen atoms were refined anisotropically
and isotropically, respectively. All calculations were performed by
using the teXsan crystallographic software program package. A
summary of the fundamental crystal data and experimental param-
eters for the structure determination of complex trans-1i is given
in Table 1.
1033, 998, 850, 740, 692, 660, 618, 540, 520, 452, 435, 417 cm-1
.
Anal. Calcd for C42H34Cl2P2PtS: C, 56.13; H, 3.81. Found: C,
55.84; H, 3.75.
trans-Pt(SC6H4-4-Br)(Cl)(PPh3)2 (1i). Yellow solid. mp: 209-
210 °C. 1H NMR (400 MHz, C6D6): δ 7.88-7.83 (m, 12 H), 6.99
(d, J ) 8.4 Hz, 2 H), 6.96-6.94 (m, 18 H), 6.74 (d, J ) 8.4 Hz,
2 H). 31P NMR (160 MHz, C6D6): δ 24.3 (s, JPt-P ) 2714 Hz). IR
(KBr): 3050, 1573, 1480, 1464, 1434, 1382, 1308, 1184, 1097,
1027, 1004, 844, 806, 752, 743, 704, 692, 540, 523, 512, 483, 462,
442 cm-1. Anal. Calcd for C42H34BrClP2PtS: C, 53.48; H, 3.63.
Found: C, 54.04; H, 3.60.
trans-Pt(SC6H4-2-i-Pr)(Cl)(PPh3)2 (1j). Yellow solid. mp: 196-
197 °C. 1H NMR (400 MHz, C6D6): δ 8.47 (d, J ) 7.2 Hz, 1 H),
7.92-7.87 (m, 12 H), 6.97-6.96 (m, 18 H), 6.82-6.74 (m, 2 H),
6.70-6.68 (m, 1 H), 2.98 (quint, J ) 6.8 Hz, 1 H), 0.99 (d, J )
6.8 Hz, 6 H). 31P NMR (160 MHz, C6D6): δ 24.5 (s, JPt-P ) 2757
Hz). IR (KBr): 3436, 3048, 2951, 2860, 1580, 1481, 1480, 1461,
1434, 1358, 1310, 1274, 1186, 1158, 1096, 1071, 1051, 1029, 999,
840, 744, 730, 691, 618, 522, 512, 462, 431 cm-1. Anal. Calcd for
C45H41ClP2PtS: C, 59.63; H, 4.56. Found: C, 59.42; H, 4.52.
trans-Pt(SC6H4-4-Me)(Cl)[P(C6H4-4-Me)3]2 (1k). Yellow solid.
mp: 215-217 °C. 1H NMR (400 MHz, C6D6): δ 7.94 (q, J ) 5.6
Hz, 12 H), 7.30 (d, J ) 8.0 Hz, 2 H), 6.88 (d, J ) 7.6 Hz, 12 H),
6.54 (d, J ) 8.0 Hz, 2 H), 2.04 (s, 3 H), 1.95 (s, 18 H). 31P NMR
(160 MHz, C6D6): δ 23.0 (s, JPt-P ) 2734 Hz). IR (KBr): 3424,
3018, 2918, 2863, 1598, 1560, 1498, 1482, 1448, 1396, 1310, 1189,
1098, 1020, 799, 708, 644, 631, 612, 522, 478 cm-1. Anal. Calcd
for C49H49ClP2PtS: C, 61.15; H, 5.13. Found: C, 60.98; H, 5.10.
trans-Pt(SC6H4-4-Me)(Cl)[P(C6H4-4-OMe)3]2 (1l). Yellow solid.
Synthesis of the Mixture of cis-1a and cis-4a. cis-PtCl2(PPh3)2
(158 mg, 0.2 mmol), C6H6 (20 mL), and 5 N NaOH(aq) (0.12 mL)
were added to a dry three-necked flask equipped with an additional
flask. Then the C6H6 (2 mL) solution of PhSH (0.0224 g 0.2 mmol)
was added gradually, and the resultant reaction mixture was stirred
for a total of 30 min. Then the reaction mixture was filtered; hexane
(100 mL) was added to the filtered solution, and the resultant solid
was filtered, washed over methanol, ether, and hexane, and dried
in vacuo to yield a solid (35 mg) containing cis-1a and cis-4a in a
ratio of 36/64.
Reaction of cis-1a-Containing 4a with Bases (Table 3). cis-
1a-containing 4a (4.0 mg, 0.0016 mmol of cis-1a and 0.0028 mmol
of cis-4a), SdP(C6H4-4-Me)3 (1.7 mg, 0.0051 mmol as an internal
standard), C6D6 (0.5 mL), and pyridine (0.9 mg, 0.010 mmol) were
mixed in a Pyrex NMR tube. The 31P NMR spectrum taken after
20 min showed complete isomerization of cis-1a to trans-1a. The
reactions using other additives shown in Table 2 were carried out
and monitored by NMR spectroscopy in a similar manner.
Synthesis of Authentic cis-4a. cis-PtCl2(PPh3)2 (316 mg, 0.40
mmol) and toluene (25 mL) were added in a dry three-necked flask
equipped with an additional flask. Then the ether (8 mL) solution
of PhSH (97 mg, 0.88 mmol) and NEt3 (178 mg, 1.76 mmol) was
1
mp: 105-107 °C. H NMR (400 MHz, C6D6): δ 7.99-7.95 (m,
12 H), 7.42 (d, J ) 8.0 Hz, 2 H), 6.68 (d, J ) 8.0 Hz, 12 H), 6.57
(d, J ) 7.6 Hz, 2 H), 3.17 (s, 18 H), 2.02 (s, 3 H). 31P NMR (160
MHz, C6D6): δ 21.1 (s, JPt-P ) 2708 Hz). IR (KBr): 2930, 2835,
Inorganic Chemistry, Vol. 45, No. 3, 2006 1401

Yamashita et al.
Table 2. Reaction of 2a with 3a in the Presence of Basea
Scheme 1. Possible Reaction Routes for the Reaction of 2a with 3a
run
2a
cis
trans
cis
cis
cis
cis
trans
cis
base
Et3N
Et3N
Et3N
1a (%)b (cis/trans)
4a (%)b (cis/trans)
1
2
8 (100/0)
13 (0/100)
7 (0/100)
30 (93/7)
34 (94/6)
93 (0/100)
93 (0/100)
71f (0/100)
81 (34/66)
55 (100/0)
38 (76/24)
44 (100/0)
38 (100/0)
36 (100/0)
6 (0/100)
7 (0/100)
-
3c
4d
5d
6
KOH
NaOH
pyridine
pyridine
pyridine
pyridine
7
8e
9g
solubility is much higher than that of cis-2a to produce cis-
4a as a major product (through path a and b in Scheme 1).
On the other hand, when trans-2a was employed instead of
cis-2a, 13% of trans-1a and 38% of 4a (cis/trans ) 76/24)
were produced (run 2).14 Among these three complexes, the
formation of trans-1a and trans-4a can be accounted for by
the stereoselective substitution of ArS for the Cl atom of
trans-2a and trans-1a (through path c and d in Scheme 1).
Because trans-2a isomerizes into cis-2a in solution15 and
the trans-effect of PPh3 is stronger than that of Cl,16 the
formation of cis-4a through the paths e, a, and then b would
become the major route. No yield improvement was achieved
in the presence of 5 equiv of PPh3 (run 3), even though the
fact that no formation of cis-1a was confirmed suggested
that PPh3 somewhat catalyzed the isomerization of cis-1a to
trans-1a (vide infra). While the yields of 1a slightly increased
when KOH (aq) and NaOH (aq) were employed as bases, a
considerable amount of 4a was produced as a byproduct in
both cases (runs 4 and 5). In stark contrast, a dramatic change
occurred when pyridine was selected. Both reactions em-
ploying cis-2a and trans-2a produced trans-1a highly
selectively in 93% yields (runs 6 and 7). This can be
reasonably explained by the assumption that the the isomer-
ization of cis-1a into trans-1a (path f in Scheme 1) is facilely
promoted by the presence of pyridine. That is, when cis-2a
was employed as a starting complex, the kinetic product cis-
1a generated through path a was converted into trans-1a,
whose reactivity toward 3a (path d) is significantly lower
than that of cis-2a because of the weaker trans-effect of SAr
than that of PPh3 of cis-2a.16 On the other hand, when trans-
2a was employed, as predicted by the result of the reaction
using Et3N as a base (run 2), cis-2a can be generated via
path e and would react with 3a to produce cis-1a. However,
if cis-1a was rapidly isomerized to trans-1a by the effect of
pyridine, again, trans-1a is selectively produced. Complex
1a was isolated in a 71% yield from the preparative scale of
the reaction after purification by PTLC (run 8). The choice
cis
8 (100/0)
a Unless otherwise noted, 2a (0.010 mmol), 3a (0.012 mmol), SdP(C6H4-
4-Me)3 (internal standard) and base (0.05 mmol) in C6D6 (0.5 mL) at 25
°C for 1 h. b Yields were tentatively determined from 31P{1H} NMR spectra.
c PPh3 (0.05 mmol). d Aqueous 5 N. e 0.40 mmol scale. f Isolated yield.g In
CD2Cl2 (0.5 mL).
added gradually, and the resultant reaction mixture was stirred for
a total of 6 h. Then the solvent was removed by evaporation, and
the yellow residue was dissolved in 20 mL of CH2Cl2. This solution
was extracted with 200 mL of water and dried over anhydrous
MgSO4. After the solvent was removed by evaporation, the resultant
solid was recrystallized from CH2Cl2/ether to give cis-4a as a yellow
solid (227 mg, 60%).
Isomerization of cis-4a into trans-4a. 4a (5.1 mg, 0.0054
mmol), SdP(C6H4-4-Me)3 (2.6 mg, 0.0077 mmol as an internal
standard), and C6D6 (0.5 mL) were mixed in a Pyrex NMR tube.
The 31P NMR spectrum taken after 42 h showed that the ratio of
cis-4a/trans-4a was 96/4.
cis-4a. 31P NMR (160 MHz, C6D6): δ 23.8 (s, JPt-P ) 2880
Hz).
trans-4a. 31P NMR (160 MHz, C6D6): δ 23.4 (s, JPt-P ) 2823
Hz).
Solubility of cis-2a in C6D6. Because of the low solubility of
cis-2a, the sample containing cis-2a (6.7 mg, 0.0085 mmol) and
SdP(C6H4-4-Me)3 (2.7 mg, 0.0080 mmol as an internal standard)
in C6D6 (0.5 mL) was accumulated for 12 h by 31P NMR
spectroscopy at 25 °C. Thus, the solubility of cis-2a was calculated
to be ca. 1.6 × 10-4 mmol in 0.5 mL of C6D6.
Dimerization of 4b into 4b′. 4b (5.0 mg, 0.0050 mmol), Sd
P(C6H4-4-Me)3 (1.7 mg, 0.0050 mmol as an internal standard), and
C6D6 (0.5 mL) were combined in a Pyrex NMR tube. The solution
was heated at 60 °C, and the reaction was monitored by 31P NMR
spectra. The spectrum taken after 6 h showed the ratio of 4b/[Pt-
(SC6H4-4-OMe)2(PPh3)]2 (4b′) was 51/49.
4b. 31P NMR (160 MHz, C6D6): δ 23.3 (s, JPt-P ) 2889 Hz).
4b′ (syn/anti mixture). 31P NMR (160 MHz, C6D6): δ 21.1 (s,
JPt-P ) 3398 Hz), 19.9 (s, JPt-P ) 3367 Hz).
Results and Discussion
First, the reactions of Pt(Cl)2(PPh3)2 (2a) with PhSH (3a)
(1.2 equiv) in the presence of some bases (5 equiv) were
monitored by 31P NMR spectra (Table 2). When the reaction
of cis-2 with 3a was carried out using Et3N as a base in
C6D6 (0.5 mL), cis-Pt(SPh)(Cl)(PPh3)2 (1a) and cis-Pt(SPh)2-
(PPh3)2 (4a) were obtained in 8 and 55% (92% based on
3a) yields, respectively after 1 h (run 1).13 Given that the
solubility of cis-2a is significantly low (1.6 × 10-4 mmol
in 0.5 mL of C6D6 at 25 °C), this result indicated that 3a
dominantly reacted with in situ generated cis-1a, whose
(14) trans-4a is thermodynamically more stable than cis-4a; however,
isomerization from cis-4a to trans-4a was very sluggish in C6D6 (cis/
trans ) 96/4 from cis-4a at 25 °C after 42 h).
(15) When trans-2a, whose purity was checked in CDCl3 with a 31P NMR
spectrum, was dissolved in C6D6, a mixture of 2a with cis/trans )
10/90 was detected in solution. (a) Redfield, D. A.; Nelson, J. H. Inorg.
Chem. 1973, 12, 15. (b) Harvey, J. N.; Heslop, K. M.; Orpen, A. G.;
Pringle, P. G. Chem. Commun. 2003, 278.
(16) (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV.
1973, 10, 335. (b) Chan, L. T.; Chen, H.-W.; Fackler, J. P., Jr.; Masters,
A. F.; Pan, W.-H. Inorg. Chem. 1982, 21, 4291. (c) Tu, T.; Zhou,
Y.-G.; Hou, X.-L.; Dai, L.-X.; Dong, X.-C.; Yu, Y.-H.; Sun, J.
Organometallics 2003, 22, 1255.
1402 Inorganic Chemistry, Vol. 45, No. 3, 2006

SelectiWe Preparation of trans-Pt(SAr)(Cl)(PAr′3)2
Table 3. cis-to-trans Isomerization of 1a in the Presence of Additivesa
Table 5. Syntheses of 1 with Various Phosphine Ligandsa
run
cis-2
PR3
trans-1
yield (%)b
run
solvent
additive
time
cis/trans
1
2b
2c
2d
2e
2f
P(C6H4-4-Me)3
P(C6H4-4-OMe)3
P(C6H4-4-CF3)3
PMePh2
1k
1l
1m
1n
1o
53
37
80
35d
1
2
3
4
5
C6D6
C6D6
C6D6
C6D6
CD2Cl2
pyridine
none
NEt3
PPh3
pyridine
20 min
1 h
1 h
20 min
20 min
0/100
100/0
100/0
57/43
90/10
2c
3
4
5
e
P(OEt)3
-
a cis-2 (0.40 mmol), 3k (0.42 mmol), and pyridine (2.0 mmol) in C6H6
(20 mL) at 25 °C for 2 h. b Isolated yield after PTLC. c A mixture of trans-
1l/cis-2c/trans-4l ) 87/4/9 was obtained as a crude reaction mixture. d NMR
yield. e Complicated mixture.
a cis-1a (0.0016 mmol containing 0.0028 mmol of cis-4a) and additive
(0.01 mmol) in solvent (0.5 mL).
Table 4. Syntheses of 1 with Various Functional Groupsa
run
3
Ar
1
yield (%)b
1
2
3
3b
3c
3d
3e
3f
3 g
3h
3i
C6H4-2-Me
C6H4-3-OMe
C6H4-4-OMe
C6H4-2-F
C6H4-4-Cl
C6H4-3-Cl
C6H4-2-Cl
C6H4-4-Br
C6H4-2-i-Pr
1b
1c
1d
1e
1f
1g
1h
1i
55
88
49
59
66
87
58
80
57
4
5c
6
7d
8
9
3j
1j
a cis-2a (0.40 mmol), 3 (0.42 mmol), and pyridine (2.0 mmol) in C6H6
(20 mL) at 25 °C for 2 h. b Isolated yield after PTLC. c A mixture of trans-
1f/trans-4f ) 98/2 was obtained as a crude reaction mixture. d A mixture
of trans-1h/cis-2a/trans-4h ) 92/4/4 was obtained as a crude mixture.
of solvent is also crucial for the selective formation of trans-
1a. The reaction of cis-2a with 3a using pyridine as a base
performed in CD2Cl2 yielded a mixture of 1a (81%, cis/trans
) 34/66) and cis-4a (8%) (run 9).
The cis-1a-containing cis-4a prepared by reprecipitation
from the reaction mixture using NaOH as a base (run 5 in
Table 2) was subjected to a solution of pyridine (run 1 in
Table 3) to obtain more conclusive evidence for the cis-to-
trans isomerization by pyridine. As expected, complete
isomerization into trans-1a was confirmed after 20 min at
25 °C. On the other hand, in the absence of base or in the
presence of Et3N, no isomerization took place after 1 h (runs
2 and 3). It must be noted that PPh3, which is generally
considered to be a good catalyst for the cis-to-trans isomer-
ization of transition-metal complexes showed much inferior
activity (cis/trans ) 57/43, run 4). Furthermore, in ac-
cordance with the data of run 9 in Table 2, the isomerization
was very sluggish in CD2Cl2 even in the presence of pyridine
(run 5). Although the role of pyridine in C6D6 was not cleared
at the moment, pyridine, which is much less bulky than PPh3
and shows stronger affinity for the Pt(II) complex than NEt3,
would coordinate to vacant coordination site of cis-1 and
facilitate the isomerization.11a
Figure 1. Molecular structure of trans-1i (thermal ellipsoids set at 50%
probability). Solvent molecule (CH2Cl2) omitted for clarity.
isolated in moderate to good yields (runs 1-9; 49-88% in
Table 4) using the present protocol. Crystals of 1i (Ar )
C6H4-4-Br) suitable for X-ray crystallographic analyses were
obtained from a CH2Cl2/hexane solution, and its ORTEP
diagram is shown in Figure 1. The present method was also
applicable to platinum complexes with moieties other than
PPh3. The corresponding 1 complexes with P(C6H4-4-Me)3,
P(C6H4-4-OMe)3, and P(C6H4-4-CF3)3 as ligands were also
synthesized and successfully isolated in 53, 37, and 80%
yields, respectively (runs 1-3 in Table 5). The reaction using
cis-PtCl2(PMePh2)2 (cis-2e) formed the desired product trans-
Pt(SAr)(Cl)(PMePh2)2 (trans-1n), albeit in a low yield (run
4), while the reaction of cis-Pt(Cl)2[P(OEt)3]2 (cis-2f) with
3k gave a complicated mixture (run 5).
The generality of the present method for the syntheses of
1 by the reactions of cis-2 with 3 is shown in Tables 4 and
5. trans-1 platinum complexes with various substituents such
as Me, OMe, F, Cl, Br, and i-Pr in Ar were all successfully
Although the vulnerability of complex 1 to disproportion-
ation and polymerization8,10 was implicated in the papers
dealing with the preparation of platinum complexes with an
S-Pt-Cl fragment,9 all 1 complexes prepared by the present
Inorganic Chemistry, Vol. 45, No. 3, 2006 1403

Yamashita et al.
methodology were actually quite stable in C6D6 solution even
at 60 °C for 6 h. On the other hand, dithiolate complex trans-
Pt(SC6H4-4-OMe)2(PPh3)2 (4b) was converted into a mixture
of 4b and its dimeric form, [Pt(SC6H4-4-OMe)2(PPh3)]2 (4b′),
in a ratio of 51/49 under the same conditions. This fact can
be rationalized by assuming that the high electronegativity
of the trans-Cl ligand made a significant contribution toward
preventing dimerization and polymerization by decreasing
the basicity of the lone pairs on SAr group.8
Sonogashira reactions.17 The utility of 1 for the examination
of the insertion of unsaturated molecules into the S-Pt bond
is now under investigation.
Acknowledgment. We thank the Instrumental Analysis
Center, Faculty of Engineering, Osaka University, for
elemental analysis.
Supporting Information Available: X-ray crystallographic data
file (CIF) for trans-1i, 1H and 31P NMR spectra of trans-1e, trans-
1i, and trans-1l, and 31P NMR spectra of crude reaction mixtures
of run 5 and run 7 in Table 4 and run 2 in Table 5. This material
is available free of charge via the Internet at http://pubs.acs.org.
Conclusion
In conclusion, the general synthetic procedure of trans-
Pt(SAr)(Cl)(PAr′3)2 has been established by taking advantage
of pyridine as a cis-to-trans isomerization catalyst. This study
also indicated that the participation of pyridine not only as
a base but also as an isomerization catalyst must be taken
into consideration when thinking about the reaction mech-
anisms of some catalytic reactions such as Heck and
IC051780L
(17) (a) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009.
(b) Klingelho¨fer, S.; Heitz, W.; Greiner, A.; Oestreich, S.; Fo¨rster,
S.; Antonietti, M. J. Am. Chem. Soc. 1997, 119, 10116. (c) Sono-
gashira, K. In Handbook of Organopalladium Chemistry for Organic
Synthesis; Negishi, E., Ed.; Wiley: New York, 2002; Chapter III.2.8.1,
p 493.
1404 Inorganic Chemistry, Vol. 45, No. 3, 2006