Cis and trans isomers of Pt(SiHAr2)2(PR3)2 (R = Me, Et) in the solid state and in solutions

Article abstract of DOI:10.1021/om980939h

Summary: trans-Pt(SiHPh₂)₂(PMe₃)₂ (1) is prepared from the reaction of H₂SiPh₂ with cis-PtEt₂(PMe₃)₂ and is characterized by X-ray crystallography. Dissolution of 1 in THF-d₈ or CD₂Cl₂ causes its isomerization into cis-Pt(SiHPh₂)²(PMe₃)₂, which is equilibrated to 1 in the solutions. Temperature-dependent ¹H NMR spectra of a mixture of the isomers provided thermodynamic parameters for the trans to cis isomerization, ΔH° = 5.7(3) kJ mol^-1 and ΔS° = 6.7(7) J mol^-1K^-1 in CD₂Cl₂ and ΔH° = 3.8(2) kJ mol^-1 and ΔS° = 3.5(6) J mol^-1K^-1 at 298 K in THF-d₈, respectively. The reactions of H₂SiAr₂ with Pt(PEt₃)₄ give cis-Pt(SiHAr₂)₂(PEt₃)₂ (2, Ar = C₆H₅; 3, Ar = C₆H₄F-p), which are considerably more stable than the trans isomers in CD₂Cl₂ (ca. 96:4 in an equilibrated CD₂Cl₂ solution of Pt(SiHPh₂)₂(PEt₃)₂ at room temperature).

Full text of DOI:10.1021/om980939h

Organometallics 1999, 18, 1349-1352
1349
Cis a n d Tr a n s Isom er s of P t(SiHAr 2)2(P R3)2 (R ) Me, Et)
in th e Solid Sta te a n d in Solu tion s
Yong-J oo Kim,* J ong-Il Park, and Sang-Chul Lee
Department of Chemistry, Kangnung National University, Kangnung 210-702, Korea
Kohtaro Osakada,* Makoto Tanabe, J un-Chul Choi, Take-aki Koizumi, and
Takakazu Yamamoto*
Research Laboratory of Resources Utilization, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama 226-8503, J apan
Received November 18, 1998
Summary: trans-Pt(SiHPh2)2(PMe3)2 (1) is prepared from
the reaction of H2SiPh2 with cis-PtEt2(PMe3)2 and is
characterized by X-ray crystallography. Dissolution of
1 in THF-d8 or CD2Cl2 causes its isomerization into cis-
Pt(SiHPh2)2(PMe3)2, which is equilibrated to 1 in the
num complexes and alkyl- or hydrido(organosilyl)-
platinum(II) complexes bearing two phosphine ligands
(4) Hydrido(silyl)platinum(II) complexes: (a) Baird, M. C. J . Inorg.
Nucl. Chem. 1967, 367. (b) Eaborn, C.; Pidcock, A.; Ratcliff, B. J .
Organomet. Chem. 1972, 43, C5. (c) Eaborn, C.; Tune, D. J .; Walton,
D. R. M. J . Chem. Soc., Dalton Trans. 1973, 2255. (d) Eaborn, C.;
Ratcliff, B.; Pidcock, A. J . Organomet. Chem. 1974, 65, 181. (e) Azizian,
H.; Dixon, K. R.; Eaborn, C.; Pidcock, A.; Shuaib, N. M.; Vinaixa, J . J .
Chem. Soc., Chem. Commun. 1982, 1020. (f) Latif, L. A.; Eaborn, C.;
Pidcock, A. P.; Weng, N. S. J . Organomet. Chem. 1994, 474, 217. (g)
Ebsworth, E. A. V.; Marganian, V. M.; Reed, F. J . S. J . Chem. Soc.,
Dalton Trans. 1978, 1167. (h) Koizumi, T.; Osakada, K.; Yamamoto,
T. Organometallics 1997, 16, 6014. (i) Mitchell, G. P.; Tilley, T. D. J .
Am. Chem. Soc. 1998, 120, 7635.
(5) Halogeno(silyl)platinum(II) and alkoxo(silyl)platinum com-
plexes: (a) Yamashita, H.; Hayashi, T.; Kobayashi, T.; Tanaka, M.;
Goto, M. J . Am. Chem. Soc. 1988, 110, 4417. (b) Yamashita, H.;
Tanaka, M.; Goto, M. Organometallics 1993, 12, 988. (c) Chang, L. S.;
J ohnson, M. P.; Fink, M. J . Organometallics 1989, 8, 1369. (d)
Goikhman, R.; Aizenberg, M.; Shimon, L. J . W.; Milstein, D. J . Am.
Chem. Soc. 1996, 118, 10894.
1
solutions. Temperature-dependent H NMR spectra of a
mixture of the isomers provided thermodynamic param-
eters for the trans to cis isomerization, ∆H° ) 5.7(3) kJ
mol-1 and ∆S° ) 6.7(7) J mol-1K-1 in CD2Cl2 and ∆H°
) 3.8(2) kJ mol-1 and ∆S° ) 3.5(6) J mol-1K-1 at 298
K in THF-d8, respectively. The reactions of H2SiAr2 with
Pt(PEt3)4 give cis-Pt(SiHAr2)2(PEt3)2 (2, Ar ) C6H5; 3,
Ar ) C6H4F-p), which are considerably more stable than
the trans isomers in CD2Cl2 (ca. 96:4 in an equilibrated
CD2Cl2 solution of Pt(SiHPh2)2(PEt3)2 at room temper-
ature).
(6) Other mononuclear silylplatinum complexes: (a) Pham, E. K.;
West, R. J . Am. Chem. Soc. 1989, 111, 7667. (b) Pham, E. K.; West, R.
Organometallics 1990, 9, 1517. (c) Levy, C. J .; Puddephatt, R. J .; Vittal,
J . J . Organometallics 1994, 13, 1559 (d) Levy, C. J .; Vittal, J . J .;
Puddephatt, R. J . Organometallics 1996, 15, 2108. (e) Shimada, S.;
Tanaka, M.; Honda, K. J . Am. Chem. Soc. 1995, 117, 8289.
In tr od u ction
Platinum complexes with organosilyl ligands1-7 have
been widely studied because the complexes are often
involved as crucial intermediates in Pt complex cata-
lyzed synthetic reactions such as hydrosilylation of
alkenes,8 bissilylation of alkenes and dienes,9 and
dehydrocoupling of organosilanes to form Si-Si or Si-C
bonds.10 Most of the mononuclear bis(organosilyl)plati-
(7) Dinuclear Pt complexes with bridging silyl or silylene ligands:
(a) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.; Pugh, N.
J .; Spencer, J . L.; Stone, F. G. A.; Woodward, P. J . Chem. Soc., Dalton
Trans. 1980, 659. (b) Ciriano, M.; Green, M,; Howard, J . A. K.; Proud,
J .; Spencer, J . L.; Stone, F. G. A.; Tsipis, C. A. J . Chem. Soc., Dalton
Trans. 1978, 801. (c) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W.
J . J . Am. Chem. Soc. 1988, 110, 4068. (d) Zarate, E. A.; Tessier-Youngs,
C. A.; Youngs, W. J . J . Chem. Soc., Chem. Commun. 1989, 577. (e)
Anderson, A. B.; Shiller, P.; Zarate, E. A.; Tessier-Youngs, C. A.;
Youngs, W. J . Organometallics 1989, 8, 2320. (f) Braunstein, P.; Knorr,
M.; Hirle, B.: Reinhard, G.; Schubert, U. Angew. Chem., Int. Ed. Engl.
1992, 31, 1583. (g) Knorr, M.; Braunstein, P.; Tiripicchio, A.; Ugozzoli,
F. Organometallics 1995, 14, 4910. (h) Knorr, M.; Hallauer, E.; Huch,
V.; Veith, M.; Braunstein, P. Organometallics 1996, 15, 3868. (i)
Braunstein, P.; Knorr, M. J . Organomet. Chem. 1995, 500, 21.
(8) Reviews: (a) Ojima, I. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989;
Chapter 25. (b) Speier, J . L. Adv. Organomet. Chem. 1979, 17, 407. (c)
Cundy, C. S.; Kingston, B. M.; Lappert, M. F. Adv. Organomet. Chem.
1973, 11, 253. (d) Comprehensive Handbook on Hydrosilylation;
Marciniec, B., Ed.; Pergamn Press: Oxford, 1992.
(9) (a) Yamamoto, K.; Okinoshima, H.; Kumada, M. J . Organomet.
Chem. 1971, 27, C31. (b) Hayashi, T.; Kobayashi, T.; Kawamoto, A.
M.; Yamashita, H.; Tanaka, M. Organometallics 1990, 9, 280. (c) Tsuji,
Y.; Lago, R. M.; Tomohiro, S.; Tsuneishi, H. Organometallics 1992,
11, 2353. (d) Sakaki, S.; Ogawa, M.; Musashi, Y. J . Organomet. Chem.
1997, 535, 25. See also: Tamao, K.; Hayashi, T.; Kumada, M. J .
Organomet. Chem. 1976, 114, C19. Tamao, K.; Okazaki, S.; Kumada,
M.; J . Organomet. Chem. 1978, 146, 87. Sakurai, H.; Kamiyama, Y.;
Nakadaira, Y. J . Am. Chem. Soc. 1975, 97, 931. Sakurai, H.; Eriyama,
Y.; Kamiyama, Y.; Nakadaira, Y. J . Organomet. Chem. 1984, 264, 229.
Seyferth, D.; Goldman, E. W.; Escudie´, J . J . Organomet. Chem. 1984,
271, 337. Kobayashi, T.; Hayashi, T.; Yamashita, H.; Tanaka, M. Chem.
Lett. 1989, 467. Ito, Y.; Suginome, M.; Murakami, M. J . Org. Chem.
1991, 56, 1948. Pan, Y.; Mague, J . T.; Fink, M. J . Organometallics
1992, 11, 3495.
(1) Bis(silyl)platinum(II) complexes: (a) Chatt, J .; Eaborn, C.;
Ibekwe, S. J . Chem. Soc., Chem. Commun. 1966, 700. (b) Chatt, J .;
Eaborn, C.; Kapoor, P. N. J . Chem. Soc. (A) 1970, 881. (c) Chatt, J .;
Eaborn, C.; Ibekwe, S. D.; Kapoor, P. N. J . Chem. Soc. (A) 1970, 1343.
(d) Holmes-Smith, R. D.; Stobart, S. R.; Cameron, T. S.; J ochem, K. J .
Chem. Soc., Chem. Commun. 1981, 937. (e) Kobayashi, T.; Hayashi,
T.; Yamashita, H.; Tanaka, M. Chem. Lett. 1988, 1411. (f) Kobayashi,
T.; Hayashi, T.; Yamashita, H.; Tanaka, M. Chem. Lett. 1989, 467. (g)
Yamashita, H.; Kobayashi, T.; Hayashi, T.; Tanaka, M. Chem. Lett.
1990, 1447. (h) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics
1992, 11, 3227. (i) Grundy, S. L.; Holmes-Smith, R. D.; Stobart, S. R.;
Williams, M. A. Inorg. Chem. 1991, 30, 3333. (j) Heyn, R. H.; Tilley,
T. D. J . Am. Chem. Soc. 1992, 114, 1917. (k) Michalczyk, M. J .; Recatto,
C. A.; Calabrese, J . C.; Fink, M. J . J . Am. Chem. Soc. 1992, 114, 7955.
(l) Sakaki, S.; Ieki, M. J . Am. Chem. Soc. 1993, 115, 2373. (m) Ozawa,
F.; Kamite, J . Organometallics 1997, 17, 55630. (n) Gehrhus, B.;
Hitchcock, P. B.; Lappert, M. F.; Maciejewski, H. Organometallics 1997,
17, 55599.
(2) Alkyl(silyl)platinum(II) complexes: (a) Ozawa, F.; Hikida, T.;
Hayashi, T. J . Am. Chem. Soc. 1994, 116, 2844. (b) Ozawa, F.; Hikida,
T. Organometallics 1996, 15, 4501. (c) Ozawa, F.; Hikida, T.; Hasebe,
K.; Mori, T. Organometallics 1998, 17, 1018. (d) Gilges, H.; Kickelbick,
G.; Schubert, U. J . Organomet. Chem. 1997, 548, 57. (e) Gilges, H.;
Schubert, U. Organometallics 1998, 17, 4760.
(3) Silyl(germyl)platinum(II) complexes: Glockling, F.; Hooton, K.
A. J . Chem. Soc. (A) 1967, 1066.
10.1021/om980939h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 03/04/1999

1350 Organometallics, Vol. 18, No. 7, 1999
Notes
F igu r e 1. ORTEP drawing of trans-Pt(SiHPh2)2(PMe3)2
(1) (50% probability). The molecule has a crystallographic
point of symmetry at the Pt center position. Atoms with
asterisks are crystallographically equivalent to those hav-
ing the same number without asterisks. Selected bond
lengths (Å) and angles (deg): Pt-P1 2.287(2), Pt-Si1
2.407(2), P1-Pt-P1* 180.0, P1-Pt-Si1 86.97(8), P1*-Pt-
Si1 93.03(8), Si1-Pt-Si1* 180.0.
1
F igu r e 2. Temperature-dependent change of the H NMR
spectra (phenyl hydrogen region) of the equilibrated mix-
ture of cis- and trans-Pt(SiHPh2)2(PMe3)2 in THF-d8.
favor cis structure of the square-planar coordination.
There have been only a few exceptional complexes such
as trans-PtH(SiXH2){P(C6H11)3}(X ) H, Cl)4g and trans-
PtMe(SiPh3)L2 (L ) PMe2Ph, PMePh2),2a-c the latter of
which are readily turned, upon reaction with CO, into
the thermodynamically more stable cis isomer. Prefer-
ential cis geometry of the bis(organosilyl)platinum
complexes was attributed to a large trans effect of the
organosilyl ligand,1a while precise determination of
relative thermodynamic stability between cis and trans
isomers has not been reported so far. Here we report
isolation and crystal structure of trans-Pt(SiHPh2)2-
(PMe3)2 as well as its trans-cis isomerization in solu-
tions.
not only of 1 but also of its isomer generated in the
solution. The isomer is assigned to cis-Pt(SiHPh2)2-
(PMe3)2 on the basis of a larger J (HPt) of the SiH
hydrogen signal (74 Hz) and a smaller J (PtP) (1659 Hz)
value than 1 (J (HPt) ) 25 Hz, J (PtP) ) 2402 Hz) as
well as the J (PtP) similar to those of already reported
cis-Pt(SiR3)2(PR′3)2 type complexes.1c,d,h Although a
benzene-d6 solution of Pt(SiHPh2)2(PMe3)2 contains
1
almost equal amounts of trans and cis isomers, the H
NMR spectra of the complex in THF-d8 and in CD2Cl2
exhibit the presence of a larger amount of the cis isomer
than 1 (ca. 77:23 in CD2Cl2 and 74:26 in THF-d8 at 25
1
°C). The H NMR spectra of the mixture at -50 to 10
°C in THF-d8 show a temperature-dependent change in
relative peak intensities between the isomers, as de-
picted in Figure 2, indicating that the cis and trans
isomers are equilibrated as shown in eq 2. The equili-
Resu lts a n d Discu ssion
H2SiPh2 reacts with cis-PtEt2(PMe3)2 in a 2:1 molar
ratio to give trans-Pt(SiHPh2)2(PMe3)2 (1) at room
temperature accompanied by evolution of ethane. Com-
bration of the trans and cis form of Pt(SiHPh2)2(PMe3)2
is observed also in CD2Cl2, whereas a benzene solution
of the complex shows negligible temperature-dependent
change in the signal intensity possibly due to slow
isomerization and/or a small ∆G° of the reaction in
benzene. Figure 3 summarizes the equilibrium con-
stants of the reaction in the temperature range -50 to
10 °C, which provides the thermodynamic parameters
of ∆H° ) 5.7(3) kJ mol-1 and ∆S° ) 6.7(7) J mol-1 K-1
in CD2Cl2 and ∆H° ) 3.8(2) kJ mol-1 and ∆S° ) 3.5(6)
J mol-1 K-1 at 298 K in THF-d8, respectively.
plex 1 is isolated by recrystallization of the product and
characterized by X-ray crystallography. The molecule
has a square-planar coordination around the Pt center
with two mutually trans SiHPh2 ligands, as shown in
Figure 1. The Pt-Si bond is elongated (2.407(2) Å) by a
large trans influence of an SiHPh2 ligand at the trans
position. The reactions of diorganosilanes with dialky-
lpalladium and -platinum complexes with phosphine
ligands also gave bis(organosilyl) complexes of the group
1
10 metals but with cis geometry.11,12 The H and 31P-
{1H} NMR spectra of 1 in benzene-d6 contain signals
Trans-cis isomerization of square-planar organopal-
ladium(II) and -platinum(II) complexes has been re-
ported to occur via dissociation of auxiliary phosphine
ligands and ensuing isomerization of three-coordinated
intermediates or an associative pathway involving Ber-
ry’s pseudorotation.13-15 Addition of PMe3 to a CD2Cl2
(10) (a) Yamamoto, K.; Okinoshima, H.; Kumada, M. J . Organomet.
Chem. 1970, 23, C7. (b) Uchimaru, Y.; Mouneer, A.; Sayed, M. E.;
Tanaka, M. Organometallics 1993, 12, 2065. (c) Uchimaru, Y.; Brandl,
P.; Tanaka, M.; Goto, M. J . Chem. Soc., Chem. Commun. 1993, 744.
(11) Eaborn, C.; Pidcock, A.; Ratcliff, B. J . Organomet. Chem. 1974,
66, 23.
(12) Schubert, U.; Mu¨ller, C. J . Organomet. Chem. 1989, 373, 165.

Notes
Organometallics, Vol. 18, No. 7, 1999 1351
F igu r e 4. ORTEP drawing of cis-Pt(SiHPh2)2(PEt3)2 (2)
(50% probability). Selected bond lengths (Å) and angles
(deg): Pt-P1 2.362(3), Pt-P2 2.355(3), Pt-Si1 2.374(3),
Pt-Si2 2.359(3), P1-Pt-P2 103.9(1), P1-Pt-Si1 87.9(1),
P1-Pt-Si2 157.1(1), P2-Pt-Si1 156.6(1), P2-Pt-Si2
94.0(1), Si1-Pt-Si2 80.7(1). Selected bond lengths (Å) and
angles (deg) of 3: Pt-P1 2.373(3), Pt-P2 2.356(3), Pt-Si1
2.355(3), Pt-Si2 2.369(3), P1-Pt-P2 99.4(1), P1-Pt-Si1
94.74(9), P1-Pt-Si2 165.48(9), P2-Pt-Si1 162.2(1), P2-
Pt-Si2 88.7(1), Si1-Pt-Si2 79.91(9).
F igu r e 3. van’t Hoff plots of isomerization of 1 to cis-Pt-
(SiHPh2)2(PMe3)2 (a) in THF-d8 and (b) in CD2Cl2.
solution of Pt(SiHPh2)2(PMe3)2 (PMe3:Pt ) ca. 1:1) led
to broadening of the 31P{1H} NMR signals. Although the
1H NMR signal of SiH hydrogens of the trans and cis
isomers lost P-H coupling, neither broadening nor
coalescence of the signals was observed at the temper-
ature range -30 to 30 °C. Thus, the trans-cis isomer-
ization is not significantly accelerated by addition of
PMe3 and probably does not involve the associative
pathway.
Although isolation of cis-Pt(SiHPh2)2(PMe3)2 as single
crystals was not feasible, cis-Pt(SiHAr2)2(PEt3)2 (2, Ar
) C6H5, 3; Ar ) C6H4F-p) were obtained from the
reaction of H2SiAr2 with Pt(PEt3)4, as shown in eq 3 and
characterized by X-ray crystallography and NMR spec-
troscopy. Figure 4 depicts the molecular structure of 2,
plexes as well as their equilibrium in solutions. cis-Pt-
(SiHPh2)2(PEt3)2 is much more stable than the trans
isomer. Use of PMe3 as the auxiliary ligand has resulted
in a reduction of difference in thermodynamic stability
between the cis and trans isomers and enabled isolation
and full characterization of 1 having the trans structure.
Exp er im en ta l Section
Gen er a l Meth od s. All manipulations of the complexes
were carried out using standard Schlenk techniques under
argon or nitrogen atmosphere. cis-PtEt2(PMe3)2 and Pt(PEt3)4
were prepared according to the literature method.16 NMR
spectra (1H, 400 MHz; 31P, 160 MHz; 13C, 100 MHz) were
recorded on a J EOL EX-400 spectrometer. Peak positions of
the 31P NMR were referenced to external 85% H3PO4. Elemen-
tal analyses were carried out with a Yanaco MT-5 CHN
autocorder and with a Yanaco YS-10 ion chromatograph.
P r ep a r a tion of tr a n s-P t(SiHP h 2)2(P Me3)2 (1). To a hex-
ane (6 mL) solution of cis-PtEt2(PMe3)2 (522 mg, 1.3 mmol)
was added H2SiPh2 (498 mg, 2.7 mmol) at room temperature.
A colorless solid began to precipitate after 1 h. Stirring of the
reaction mixture was continued for 12 h. The resulting solid
was collected by filtration, washed with hexane, and dried in
vacuo. Recrystallization from toluene-hexane gave 1 as color-
less crystals (827 mg, 90%). The NMR data were obtained in
a mixture of 1 and its cis isomer (ca. 50:50 in benzene-d6, 23:
77 in CD2Cl2, and 26:74 in THF-d8 at 25 °C). 1H NMR
(benzene-d6, 25 °C): δ 0.95 (br, PMe3 (cis)), 1.16 (br, PMe3
(trans), J (PtH) ) 29 Hz), 5.29 (t, SiH (trans), J (PH) ) 13 Hz,
J (PtH) ) 25 Hz), 5.60 (apparent triplet due to multispin
system, SiH (cis), J (PtH) ) 74 Hz), 7.13-7.22 (m, meta (trans
and cis) and para (cis)), 7.30 (t, para (trans), J (HH) ) 7 Hz),
7.88 (d, ortho (cis), J (HH) ) 7 Hz), 7.94 (d, ortho (trans), J (HH)
) 7 Hz); (CD2Cl2, 25 °C) δ 1.29 (br, PMe3 (trans)), 1.35 (br,
PMe3 (cis)), 4.81 (t, SiH (trans), J (PH) ) 13 Hz, J (PtH) not
determined due to overlapping with the signal of cis isomer),
4.90 (apparent triplet due to multispin system, SiH (cis),
J (PtH) ) 76 Hz), 7.14 (m, meta and para (cis)), 7.27 (t, para
(trans), J ) 7 Hz), 7.32 (t, meta (trans), J ) 7 Hz), 7.52 (m,
ortho (cis)), 7.67 (d, ortho (trans), J ) 7 Hz); (THF-d8, 25 °C)
δ 1.36 (br, PMe3 (cis and trans)), 4.90 (SiH (trans), J not
which has a distorted square-planar coordination around
the metal center with two diphenylsilyl ligands at cis
positions. Complex 3 has similar cis coordination around
the Pt center. The NMR spectra of 2 and 3 contain the
signals of their trans isomers in a small intensity. The
1H NMR signal ratios of the trans- and cis-Pt(SiHPh2)2-
(PEt3)2 are 4:96 to 6:94 in the temperature range -30
to 25 °C. Precise equilibrium constants and thermody-
namic parameters were not obtained due to small peak
intensity of the signal of the trans isomer.
The present study has provided crystallographic
results of cis- and trans-Pt(SiHAr2)2(PR3)2 type com-
(13) Anderson, G. K.; Cross, R. J . Chem. Soc. Rev. 1980, 9, 185.
(14) (a) Ozawa, F.; Ito, T.; Nakamura, Y.; Yamamoto, A. J . Orga-
nomet. Chem. 1979, 168, 375. (b) Ozawa, F.; Ito, T.; Yamamoto, A. J .
Am. Chem. Soc. 1980, 102, 6457. (c) Ozawa, F.; Ito, T.; Nakamura, Y.;
Yamamoto, A. Bull. Chem. Soc. J pn. 1981, 54, 1868. (d) Tatsumi, K.;
Hoffmann, R.; Yamamoto, A.; Stille, J . K. Bull. Chem. Soc. J pn. 1981,
54, 1857. (e) Alibrandi, G.; Scolaro, L. M.; Romeo, R. Inorg. Chem. 1991,
30, 4007. (f) Minniti, D. Inorg. Chem. 1994, 33, 2631. (g) Casado, A.
L.; Casares, J . A.; Espinet, P. Organometallics 1997, 16, 5730.
(15) Bis(triorganostanyl)platinum complexes and hydrido(triarylsi-
lyl)platinum complexes with two phosphine ligands were reported to
undergo rapid intramolecular exchange of the two stannyl or two
phosphine ligands via a tetrahedral transition state. Although the
transition state may also cause intramolecular cis-trans isomerization,
the trans-cis isomerization was not observed in the complexes. See:
ref 4e and Obora, Y.; Tsuji, Y.; Nishiyama, K.; Ebihara, M.; Kawamura,
T. J . Am. Chem. Soc. 1996, 118, 10922.
(16) (a) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59,
411. (b) Yoshida, T.; Matsuda, T.; Otsuka, S. Inorg. Synth. 1990, 28,
122.

1352 Organometallics, Vol. 18, No. 7, 1999
Notes
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Deta ils of Refin em en t of 1-3
1
2
3
chemical formula
C
30H40P2PtSi2
C36H52P2PtSi2
797.59
C36H48F4P2PtSi2
869.59
fw
713.52
cryst syst
monoclinic
C2/c (No. 15)
23.027(5)
8.957(4)
triclinic
P1h (No. 2)
12.168(4)
16.896(6)
9.952(4)
90.12(3)
113.75(2)
92.97(3)
1869(1)
2
triclinic
P1h (No. 2)
11.581(2)
16.895(2)
9.866(1)
96.63(1)
93.39(1)
86.28(1)
1910.9(5)
2
space group
a, Å
b, Å
c, Å
15.943(6)
R, deg
â, deg
108.51(2)
γ, deg
V, Å3
3117(1)
4
Z
µ, cm-1
47.41
39.61
38.95
F(000)
1424
808
872
Dcalcd, g cm-3
crystal size, mm × mm × mm
2θ range, deg
no. of unique reflns
no. of used reflns (I g 3σ(I))
no. of variables
R (Fo)a
1.521
1.418
1.512
0.5 × 0.7 × 0.9
5.0-55.0
3804
0.5 × 0.6 × 0.8
5.0-50.0
5785
0.3 × 0.4 × 0.6
5.0-55.0
6734
2459
160
0.032
0.036
4366
370
0.045
0.042
5942
406
0.044
0.058
Rw (Fo)a
a
Weighting scheme, [{σ(Fo)}2]-1
.
estimated due to overlapping with the SiH signal of trans
isomer), 5.00 (br, SiH (cis), J (PtH) ) 75 Hz), 7.04 (m, meta
and para (cis)), 7.20 (t, para (trans), J (HH) ) 7 Hz), 7.26 (t,
meta (trans), J (HH) ) 7 Hz), 7.49 (d, ortho (cis), J (HH) ) 7
Hz), 7.64 (d, ortho (trans), J (HH) ) 7 Hz). 13C{1H} NMR (CD2-
Cl2, 25 °C): δ 18.6 (br, P(CH3)3), 127.2 (ortho (cis), J (PtC) )
29 Hz), 127.5 (para (cis)), 127.6 (ortho (trans), J (PtC) ) 22
Hz), 137.2 (meta (cis), J (PC) ) 13 Hz), 143.1 (ipso (cis), J (PC)
and J (PtC) not determined); (benzene-d6, 25 °C) δ 18.0 (br,
P(CH3)3), 127.3 (para (cis and/or trans), 137.3 (meta (trans),
J (PtC) ) 15 Hz), 137.5 (meta (cis), J (PC) ) 13 Hz), 143.2 (ipso
(cis), J (PC) ) 16 Hz), 145.3 (ipso (trans), J (PtC) ) 24 Hz).
Several signals were not observed due to overlapping with
those of the solvent or low peak intensity. 31P{1H} NMR
(benzene-d6, 25 °C): δ -24.0 (trans, J (Pt-P) ) ca. 2400 Hz),
-17.0 (cis, J (PtP) ) ca. 1640 Hz); (CD2Cl2, 25 °C) δ -22.8
(trans, J (Pt-P) ) 2402 Hz), -15.8 (cis, J (PtP) ) 1659 Hz).
Anal. Calcd for C30H40P2Si2Pt: C, 50.48; H, 5.65. Found: C,
50.17; H, 5.53.
P r ep a r a tion of cis-P t(SiHAr 2)(P Et3)2 (2, Ar ) P h ; 3, Ar
) C6H4F -p). To a pentane (5 mL) solution of Pt(PEt3)4 (1.39
g, 2.1 mmol) was added H2SiPh2 (777 mg, 4.2 mmol) at room
temperature. The yellow solution turned colorless within a
short time, and a colorless solid was soon generated on stirring.
After 3 h the resulting solid product was collected by filtration,
washed with pentane, and dried in vacuo (1.54 g, 93%). The
NMR spectrum of the product contained signals of trans and
cis isomers in a 6:94 ratio. Recrystallization from toluene-
hexane afforded single crystals of cis-Pt(SiHPh2)2(PEt3)2 (2).
1H NMR (benzene-d6): δ 0.75-0.82 (m, 18H, J (PH) ) 16 Hz,
J (HH) ) 7 Hz, P-CH2-CH3, (cis and trans)), 1.58-1.66 (m,
12H, P-CH2-CH3, (cis)), 1.86-1.88 (m, 12H, P-CH2-CH3
(trans)), 5.46 (t, 2H, SiH (trans), J (PH) ) 11 Hz), 5.70
(apparent triplet due to multispin system, 2H, Si-H (cis),
J (PH) ) 16 Hz, J (PtH) ) 69 Hz), 7.12-7.20 (m, 12H, meta
and para (cis) and meta (trans)), 7.30 (t, 4H, para (trans),
J (HH) ) 7 Hz), 7.80 (d, 8H, J (HH) ) 7 Hz, ortho (cis)), 7.96
(d, 8H, J (HH) ) 7 Hz, ortho (trans)). 13C{1H} NMR (benzene-
d6, signals of cis form): δ 8.6 (CH3, J (PtC) ) 15 Hz), 18.2 (CH2,
dd, J (PC) ) 13 and 2 Hz), 127.2 (ortho), 127.4 (para), 137.4
(meta, J (PtC) ) 20 Hz), 143.3 (ipso, J (PC) ) 4 Hz). 31P{1H}
NMR (benzene-d6): δ 15.7 (cis, J (PtP) ) 1710 Hz) and 6.77
(trans, J (PtP) ) 2441 Hz). Anal. Calcd for C36H52P2Si2Pt: C,
54.18; H, 6.56. Found: C, 53.80; H, 6.28.
meta), 7.52 (dd, 8H, J (HH) ) 8 Hz, J (FH) ) 7 Hz, ortho). 31P-
{1H} NMR (benzene-d6): δ 15.3 (cis, J (PtP) ) 1694 Hz) and
6.6 (trans, J (PtP) ) 2418 Hz). Anal. Calcd for C36H48F4P2Si2-
Pt: C, 49.70; H, 5.56; F, 8.74. Found: C, 49.65; H, 5.65; F, 8.44.
Equ ilibr iu m Con sta n ts Mea su r em en t. A sealable NMR
tube was charged with complex 1 (ca. 25 mg). CD2Cl2 (ca. 0.40
mL) was vacuum transferred to the tube. After three freeze-
pump-thaw cycles the tube was sealed. The NMR spectra
were recorded at -50, -30, -10, and 10 °C. Molar ratios of 1
and its cis isomer in equilibrated mixtures were determined
by comparison of the peak area of the ortho phenyl hydrogens.
K ) [1]/[cis-Pt(SiHPh2)(PMe3)2] ) 0.105 (-50 °C), 0.136 (-30
°C), 0.173 (-10 °C), and 0.198 (10 °C). Equilibrium constants
in THF-d8 were estimated similarly; K ) 0.198 (-50 °C), 0.235
(-30 °C), 0.277 (-10 °C), and 0.302 (10 °C).
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of 1-3 suit-
able for X-ray diffraction study were obtained by recrystalli-
zation from toluene-pentane and mounted in glass capillary
tubes under argon. Intensities were collected for Lorentz and
polarization effects on a Rigaku AFC-5R automated four-cycle
diffractometer by using Mo KR radiation (λ ) 0.71069 Å) and
the ω-2θ scan method, and an empirical absorption correction
(Ψ scan) was applied. Calculations were carried out by using
a program package TEXSAN on a DEC Micro VAX-II com-
puter. Atomic scattering factors were obtained from the
literature.17 A full-matrix least-squares refinement was used
for non-hydrogen atoms with anisotoropic thermal parameters.
Positions of the SiH hydrogens were determined by the
difference Fourier technique, while the other hydrogens were
located by assuming the ideal geometry. The hydrogens were
included in the structure calculation without further refine-
ment of the parameters. Crystallograhic data and details of
refinement are summarized in Table 1.
Ack n ow led gm en t. This work was supported by the
Basic Science Research Institute Program (No. BSRI-
97-3440), Korean Ministry of Education, and by a Grant-
in-Aid for Scientific Research (No. 09940229) and for
Scientific Research on Priority Areas (“Inter-element
Linkage”, No. 09239212) from the Ministry of Educa-
tion, Science, Sports, and Culture, J apan.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data of 1-3. This material is available free of charge via the
Internet at http://pubs.acs.org.
Complex 3 was prepared analogously (86%). 1H NMR
(benzene-d6, signals of cis form): δ 0.71 (td, 18H, J (PH) ) 15
Hz, J (HH) ) 7 Hz, P-CH2-CH3), 1.53 (m, 12H, P-CH2-CH3),
5.45 (apparent triplet due to multispin system, 2H, J (PtH) )
69 Hz, Si-H), 6.86 (dd, 8H, J (HH) ) 8 Hz, J (FH) ) 8 Hz,
OM980939H
(17) International Tables for X-ray Crystallography; Kynoch: Bir-
mingham, England, 1974; Vol. 4.