Synthesis and crystal structures of platinum (II) complexes with phosphine sulfide: Cis-Dichloro[dimethylsulfoxide](triphenylphosphine sulfide) platinum (II) and (-)-cis-dichloro[(S)-methyl-p-tolylsulfoxide](triphenylphosphine sulfide) platinum (II)

Article abstract of DOI:10.1016/j.ica.2005.12.007

The addition of triphenylphosphine sulfide (Ph₃PS) to bis-sulfoxide platinum (II) complexes [Pt(Me₂SO)₂Cl ₂] and (-)-[Pt(Me-p-TolSO)₂Cl₂] yields mixed ligand complexes [Pt(Ph₃PS)(Me₂SO)Cl₂] (1) and (-)-[Pt(Ph₃PS)(Me-p-TolSO)Cl₂] (2), which are effective catalysts for hydrosilylation reaction. These mixed-ligand complexes were obtained in crystal state and analyzed by X-ray diffraction, ¹H, ³¹P and ¹⁹⁵Pt NMR; 2 was also studied by circular dichroism spectroscopy. Both complexes exist in CDCl₃ solution as a dynamic equilibrium of two geometric isomers with an approximate 1:10 ratio, but only cis-isomer is obtained on crystallization. The X-ray structures of the complexes have classical geometry, and phosphine sulfide and sulfoxides are coordinated via sulfur. The new structural data for simple platinum-Ph ₃PS coordination bond, unaffected by chelation or bridging, were evaluated. The lengths of this bond are 2.300(4) ? in 1 and 2.305(3) ? in 2, respectively. PtSP angle equals 105.7(2)° in 1 and 104.05(13)° in 2, the PtSP plane is almost perpendicular to the coordination plane. The static trans-influence of Ph₃PS is estimated to be strong and close to that of S-coordinated Me₂SO. The complex 2 exhibits strong circular dichroism at a wavelength below 330 nm, caused both by inherent Me-p-TolSO stereogenic center and induced asymmetry of Ph₃PS.

Full text of DOI:10.1016/j.ica.2005.12.007

Inorganica Chimica Acta 359 (2006) 1031–1040
www.elsevier.com/locate/ica
Synthesis and crystal structures of platinum (II)
complexes with phosphine sulfide:
cis-Dichloro[dimethylsulfoxide](triphenylphosphine sulfide)
platinum (II) and (ꢀ)-cis-dichloro[(S)-methyl-p-tolylsulfoxide]-
(triphenylphosphine sulfide) platinum (II)
a,
b
b
c
Alexej N. Skvortsov *, Alexander N. Reznikov , Dimitry A. de Vekki , Adam I. Stash ,
c
b
b
Vitaly K. Belsky , Vitaly N. Spevak , Nickolaj K. Skvortsov
a
Department of Biophysics, St. Petersburg State Polytechnical University, Polytechnicheskaja st. 29, St. Petersburg 195251, Russia
b
St. Petersburg State Institute of Technology (Technical University), Moskowsky pr. 26, St. Petersburg 190013, Russia
c
X-ray Laboratory, L.Ya. Karpov Institute of Physical Chemistry, Vorontsovo Pole St. 10, Moscow 103064, Russia
Received 30 April 2005; received in revised form 23 November 2005; accepted 4 December 2005
Available online 10 January 2006
Abstract
The addition of triphenylphosphine sulfide (Ph3PS) to bis-sulfoxide platinum (II) complexes [Pt(Me2SO)2Cl2] and (ꢀ)-[Pt(Me-p-Tol-
SO)2Cl2] yields mixed ligand complexes [Pt(Ph3PS)(Me2SO)Cl2] (1) and (ꢀ)-[Pt(Ph3PS)(Me-p-TolSO)Cl2] (2), which are effective catalysts
for hydrosilylation reaction. These mixed-ligand complexes were obtained in crystal state and analyzed by X-ray diffraction, 1H, 31P and
195Pt NMR; 2 was also studied by circular dichroism spectroscopy. Both complexes exist in CDCl3 solution as a dynamic equilibrium of
two geometric isomers with an approximate 1:10 ratio, but only cis-isomer is obtained on crystallization. The X-ray structures of the
complexes have classical geometry, and phosphine sulfide and sulfoxides are coordinated via sulfur. The new structural data for simple
˚
platinum–Ph3PS coordination bond, unaffected by chelation or bridging, were evaluated. The lengths of this bond are 2.300(4) A in 1 and
˚
2.305(3) A in 2, respectively. PtSP angle equals 105.7(2)ꢀ in 1 and 104.05(13)ꢀ in 2, the PtSP plane is almost perpendicular to the coor-
dination plane. The static trans-influence of Ph3PS is estimated to be strong and close to that of S-coordinated Me2SO. The complex 2
exhibits strong circular dichroism at a wavelength below 330 nm, caused both by inherent Me-p-TolSO stereogenic center and induced
asymmetry of Ph3PS.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Phosphine sulfide; Triphenylphosphine sulfide; Sulfoxide; Platinum complexes; Optical activity; Hydrosilylation
1. Introduction
the second contains chiral methyl-p-tolylsulfoxide (Me-p-
TolSO, 1-methylsulfinyl-4-methylbenzene) as a ligand.
The complexes were synthesized from respective bis-sulfox-
ide complexes and Ph3PS and were subject to spectroscopic
and structural studies. The newly prepared complexes
arouse particular interest, because they display high cata-
lytic activity in hydrosilylation reactions. Sulfur-containing
ligands are rarely used for the preparation of transition
metal-based homogeneous catalysts as they are believed
to reduce the catalytic activity up to full suppression of
The present study is dedicated to synthesis and charac-
terization of neutral platinum (II) complexes with triphe-
nylphosphine sulfide (Ph3PS) and sulfoxide ligands. The
first compound contains dimethylsulfoxide (Me2SO), while
*
Corresponding author. Tel.: +7 812 552 79 64; fax: +7 812 552 79 61.
E-mail addresses: skvor@mail.cytspb.rssi.ru, skvor@phmf.spbstu.ru
(A.N. Skvortsov).
0020-1693/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.12.007

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A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
catalytically active centers. However, our studies of Pt(II)
complexes with sulfoxide ligands as potent catalysts in
hydrosilylation of olefins [1–3], vinylsiloxanes [4], ketones
[5–7] and aromatic azomethins [8] have shown that these
complexes can exhibit high catalytic activity. Some of the
sulfoxide Pt(II) complexes could act as photoinduced cata-
lysts; hence efficient catalysis is triggered by UV-irradiation
[9]. The test of the new phosphine sulfide sulfoxide plati-
num (II) complexes as catalysts in the reaction of 1-heptene
with methyldichlorosilane and in the reaction of acetophe-
none with diphenylsilane [5] showed that under comparable
conditions these compounds exhibit even higher catalytic
activity than the symmetric bis-sulfoxide complexes. E.g.,
in the reaction of acetophenone with diphenylsilane at
70 ꢀC and catalyst concentration 0.3 mM, 50% conversion
was reached in 19 min for phosphine sulfide sulfoxide cat-
alyst versus 80 min for bis-sulfoxide catalyst. The final con-
versions in these systems exceeded 80% [5]. In the reaction
of selected aromatic azomethins with methyldichlorosilane,
catalyzed by phosphine sulfide sulfoxide platinum (II) com-
plexes, the desired product content exceeded 99% [8]. It has
been shown previously, that the stereogenic center of Me-p-
TolSO is retained upon coordination to platinum, but its
absolute configuration is inverted [10–15]. So the chiral
sulfoxide phosphine sulfide complex attracts interest for
two reasons. On the first hand, it may be a potential cata-
lyst for asymmetric hydrosilylation. On the other hand,
Me-p-TolSO proved to be a very useful chiral label for
studying ligand exchange at concentrations, relevant to cat-
alytic systems, by circular dichroism (CD) spectroscopy
and optical rotation measurements [16–18].
The structure of the complexes under study also has gen-
eral implication. In contrast to phosphines and phosphine
oxides, the information on coordination compounds, con-
taining phosphine sulfide ligands is relatively scarce and
discrete. The atom of sulfur incorporated in phosphine sul-
fide molecules R3PS is in low oxidation state. All sulfur
compounds in lower oxidation states are known to be effi-
cient donors for the majority of heavier metals. In Pear-
son’s terms they are soft bases, and this favors the
formation of stable donor–acceptor compounds with soft
acids. It is not surprising, then, that phosphine sulfides
form stable coordination complexes with heavier metals:
gold [19–21], platinum [22,23], iridium [24], palladium
[25–28], rhodium [29–32,24], ruthenium [33], niobium
[34,35], molybdenum [36] and indium [37,38]. The struc-
tural data were also reported for complexes with copper
[39–44], silver [45–48], aluminium [49], and diiodine [50–
52]. Some related structural data also exist on organome-
tallic compounds of manganese, palladium, platinum,
and iridium, containing coordinated phosphine sulfide. In
all reported cases, coordination of phosphine sulfide was
found to occur via sulfur atom, with phosphorus–sulfur-
metal angle ranging from 91ꢀ [42] to 117ꢀ [29]. Yet, the
majority of the structures, studied by X-ray analysis up
to date, contain phosphine sulfide as a functional group
of a chelating ligand, or belong to organometallic com-
pounds. The mode of coordination in such structures is
masked by chelation effects, and influence of metal–carbon
bonds, so the information on ligand properties of «simple»
phosphine sulfides is even more scant. The present study
gives representative example of triphenylphosphine sulfide
structure as a ligand in classical platinum (II) coordination
compounds. The presence of two different S-donor ligands
in the same complex allows us to compare their binding
properties. As the structural data for sulfoxide mixed
ligand platinum complexes are numerous and well charac-
terized [11–15,50–58], the relative static trans- and cis-
effects of phosphine sulfide may be estimated.
2. Experimental
2.1. Materials and physical measurements
2.1.1. The reagents
Acetone, dimethyl sulfoxide, chloroform, and methylene
chloride were obtained from ‘‘Merck’’ and used without
purification. Triphenylphosphine was obtained from
‘‘Merck’’ and purified by recrystallization from 4:1 metha-
nol–chloroform mixture in argon atmosphere. Triphenyl-
phosphine sulfide (Ph3PS) was synthesized from
triphenylphosphine and equimolar amount of elemental sul-
fur by standard procedure. The chiral sulfoxide (+)-(R)-Me-
p-TolSO was synthesized by the method described in the
literature [59]. The enantiomeric purity of the obtained
compound exceeded 96% as judged by optical rotation.
1
2.1.2. H, 31P{1H}, and 195Pt{1H} NMR spectra
The 1H, 31P{1H}, and 195Pt{1H} NMR spectra were
recorded on a Bruker AC-200 instrument operating at
1
200.13, 81.01, and 43.03 MHz. Selected H and 195Pt{1H}
spectra were recorded on a Bruker AM-500 spectrometer,
operating at 500.13 and 107.51 MHz, respectively. The
spectra were recorded from CDCl3 saturated solutions in
standard 5 mm NMR tubes. Typical parameters for 1H
experiments: 40ꢀ pulses, 8 K data points; resolution,
0.61 Hz; 50–100 scans. No internal standard was used for
1
1H spectra, the H chemical shifts in ppm from TMS were
calculated from deuterium lock frequency. Typical param-
eters for 31P NMR spectra: 8 K data points; resolution
1.0 Hz; 1000–1500 scans. Typical parameters for 195Pt
experiments: 32 K data points; resolution 0.5–3.8 Hz;
1200–1500 scans. Chemical shifts are reported in ppm rela-
tive to 85% H3PO4 (31P{1H}) and aqueous Na2PtCl6
(
195Pt{1H}) as respective external standards. The
1
200.13 MHz H NMR signals of protons coupled to 195Pt
and distorted by effects of 195Pt chemical shift anisotropy
were analyzed by accurate numeric method, that yields cor-
rect value of J
[60]. E.s.d.s for calculated coupling
1H–195Pt
constants are given in parentheses.
2.1.3. The UV–Vis properties
Absorption spectra were obtained on scanning spectro-
photometer Specord-M40 (Karl Zeiss). Optical rotations

A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
1033
20
20
½aꢁD were measured with polarimeter 241MC (Perkin–
for purity by optical polarimetry: ½aꢁD in CH2Cl2 ꢀ220ꢀ. A
sample of [Pt(Me-p-TolSO)2Cl2] (0.05 g, 0.087 mmol) was
placed in a flask with a reflux condenser and a mixer.
Two equivalents of Ph3PS (0.051 g, 0.17 mmol) and 4 ml
of methylene chloride were added. The system was heated
at reflux and mixed for 5 h, the initial reagents dissolved
completely. The formed solution was cooled and mixed
with hexane. A yellow precipitate was formed. The precip-
itate was collected on Shott filter and dried. Then the pre-
cipitate was redissolved in a small volume of 1:1 mixture of
acetone and methylene chloride. When the solvent partially
evaporated, yellow-green crystals formed. Yield 0.05 g,
80% initial platinum. The product is soluble in chloroform,
methylene chloride, less soluble in acetone, insoluble in
Elmer), using 10 cm cells. Circular dichroism (CD) spectra
were recorded with dichrograph Mark-V (Jobin-Yvon).
(+)-D-10-camphorsulfonic acid was used as calibration
standard for CD measurements. Crystals of complex
{Pt(Ph3PS)[(S)-Me-p-TolSO]Cl2} from the same prepara-
tion as the crystal used for X-ray studies were dissolved
in methylene chloride in concentration 5 · 10ꢀ4 M. The
round fused silica quartz cell with optical pathlengths
1 cm (in wavelength region 350–700 nm) and 0.1 cm
(220–350 nm region) were used. Absorbance of solvent
and optical activity of cell walls were accounted for. The
quantitative spectra of solutions were recorded from 3
independently prepared samples and the magnitudes of e
and De presented below are median values.
20
hexane. Melting point 204 ꢀC. ½aꢁD in CH2Cl2 ꢀ121ꢀ. Anal.
Calc. for C26H25Cl2OPPtS2: C, 43.70; H, 3.52; Cl 10.63; Pt
29.25; S 4.81. Found: C, 43.66; H, 3.47, Cl 10.60; Pt 29.27;
S 4.85%. The NMR spectra of CDCl3 solution of 2 also
show the presence of two distinct species 2a and 2b with
2.2. Synthesis of complexes
2.2.1. Synthesis of 1: [Pt(Ph3PS)(Me2SO)Cl2]
1
A sample of platinum dimethyl sulfoxide complex cis-
[Pt(Me2SO)2Cl2] (0.11 g, 0.26 mmol), synthesized from
K2PtCl4 and 2 equivalents of Me2SO, was placed in a
round-bottomed flask with a reflux condenser with 10 ml
of acetone. A calculated amount of Ph3PS (0.156 g,
0.53 mmol) was added, and the mixture was heated at reflux
to the full dissolution of the precipitate and the formation of
yellow solution. After removal of the solvent, we obtained
0.226 g of a yellow residue. The residue was redissolved in
small volume of 1:1 mixture of acetone and methylene chlo-
ride. When the solvent partially evaporated, yellow crystals
formed. Yield 0.12 g, 70% initial platinum. The product is
soluble in chloroform, methylene chloride, less soluble in
acetone, insoluble in ethanol and hexane. Melting point
164–165 ꢀC. Anal. Calc. for C20H21Cl2OPPtS2: C, 37.62;
H, 3.32; Cl, 10.33; Pt 28.43; S 9.35. Found: C, 37.34; H,
3.21; Cl, 10.33; Pt 28.45; S 9.38%. The NMR spectra of
CDCl3 solution of 1 display the presence of two distinct spe-
cies 1a and 1b with 11:1–13:1 molar ratio. Both of them are
consistent with the proposed compound structure. Some of
the peaks of minor species 1b are overlapped with stronger
1a resonances. So some quantities could not be calculated
for 1b, and only reliable values are listed. 1H NMR d,
10:1–12:1 molar ratio. H NMR d, ppm: 2a 2.43 s (3H,
3
CH3); 3.21 t (3H, SCH3), JH–Pt 20.6(3) Hz; 7.91 d (2H,
Ha[Tol]), 7.28 d (2H, Hb[Tol]), 3J 8.1 Hz; 7.86 m (6H,
Ha[Ph3PS]), JH–P 13.7 Hz, 7.50 m (6H, Hb[Ph3PS]), JH–P
3
4
3.5 Hz; 7.61 m (3H, Hc[Ph3PS]), Ja–b 7.8 Hz, Jb–c
3
3
4
7.9 Hz, Ja–c 1.3 Hz; 2b 2.41 s (3H, CH3); 3.26 t (3H,
SCH3), JH–Pt 21.5(5) Hz; 7.9 d (2H, Ha[Tol]); 7.83 m
3
(6H, Ha[Ph3PS]), JH–P 14 Hz, 7.4 m (6H, Hb[Ph3PS]),
3
4JH–P 3.6 Hz; 7.59 m (3H, Hc[Ph3PS]), Ja–b 7.9 Hz, Jb–c
3
3
7.9 Hz. 195Pt{1H} d, ppm: 2a ꢀ3342 d, JPt–P 115(3) Hz.
2
1
The meaningful regions of 500 MHz H NMR spectrum
of 2 in CDCl3 are presented as supplementary material,
Fig. S1 and S2.
2.3. X-ray crystallography on the compounds 1 and 2
Crystals of complexes, suitable for X-ray analysis were
obtained from the solutions of the compounds in a 1:1
vol. mixture of acetone and methylene chloride by evapo-
rating the solvent gradually.
2.3.1. X-ray crystal structure determination for cis-
[Pt(Ph3PS)(Me2SO)Cl2]
A yellow crystal of 1, 0.50 · 0.12 · 0.12 mm, was used for
analysis. The X-ray diffraction data were obtained with
Enraf-Nonius CAD4 diffractometer with Nb b-filtered Mo
3
ppm: 1a 3.09 t (6H, CH3), JH–Pt 20.7(2) Hz; 7.92 m (6H,
Ha[Ph3PS]), JH–P 13.6 Hz, 7.53 m (6H, Hb[Ph3PS]), JH–P
3
4
3.5 Hz; 7.63 m (3H, Hc[Ph3PS]), 3Ja–b 7.9 Hz, Jb–c 7.8 Hz,
3
4Ja–c 1.2 Hz; 1b 3.24 t (6H, CH3), JH–Pt 22.6(8) Hz;
Ka source (0.71073 A). The h/2h scan with 2hmax = 50ꢀ was
3
˚
7.86 m (6H, Ha[Ph3PS]), JH–P 13.8 Hz; 7.59 m (3H,
used. The intensities of three selected reflections, each
monitored for 60 min showed a decay less than 0.2% during
the experiment. The temperature of the crystals was
(293 2) K. The compound crystallizes in P21nb ortho-
3
Hc[Ph3PS]), Ja–b 7.6 Hz, Jb–c 8 Hz. 31P{1H} d, ppm: 1a
3
3
40.2 t, JPt–P 116(1). 195Pt{1H} d, ppm: 1a ꢀ3326 d, JPt–P
2
2
116(2) Hz; 1b ꢀ3232 d, 2JPt–P 86(5) Hz.
rhombic space group. The unit cell parameters are:
˚
2.2.2. Synthesis of 2: (ꢀ)-{Pt(Ph3PS)[(S)-Me-p-
TolSO]Cl2}
Chiral platinum methyl p-tolyl sulfoxide complex (ꢀ)
-cis-{Pt[(S)-Me-p-TolSO]2Cl2]} was synthesized from
K2PtCl4 and (+)-(R)-Me-p-TolSO as described earlier
[13], purified by recrystallization from acetone and checked
a = 9.090(2),
b = 15.256(3),
c = 16.596(3) A,
V =
2301.5(8) A , Z = 4, qcalc = 1.843 g cmꢀ3, F(000) = 1232.
The data were collected in h k l range 0–10, 0–18, 0–19;
1487 reflections with I > 2r(I) were measured. X-ray absorp-
tion, l = 65.88 cmꢀ1, was accounted for. Non-hydrogen
atoms were refined anisotropically by full-matrix least-
3
˚

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A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
squares method on F. The hydrogen atoms were added at
arbitrary positions and refined isotropically. Final
R = 0.032, Rw = 0.080 for all observed reflections.
configuration, and atom numbering scheme for (ꢀ)-
{Pt(Ph3PS)[(S)-Me-p-TolSO]Cl2} (2) are presented in
Fig. 2.
The platinum atom in both structures is in the square
planar environment. The sulfoxides and phosphine sulfides
in both structures are coordinated via sulfur. The coordina-
tion planes of 1 and 2 are almost undistorted square pla-
nar, deviation of atoms from coordination plane is less
2.3.2. X-ray crystal structure determination for (ꢀ)-cis-
{Pt(Ph3PS)[(S)-Me-p-TolSO]Cl2}
A yellow-green crystal of 2, 0.45 · 0.25 · 0.23 mm, was
analyzed with a Syntex P-1 diffractometer with Nb b-fil-
˚
˚
tered Mo Ka source (0.71073 A). The h/2h scan with
than 0.05 A. The three angles of coordination plane in 1
2hmax = 50ꢀ was used. The intensities of three selected
reflections showed a decay less than 0.3% during the whole
experiment. The temperature of the crystals was
(293 2) K. Complex 2 crystallizes in P212121 orthorhom-
differ from right angles by less than 0.5ꢀ, so the coordina-
tion plane of 1 has almost classical geometry. In slightly
less regular structure of 2 the coordination plane is twisted
by about 5ꢀ.
bic space group. The unit cell parameters are: a = 9.817(2),
The lengths of platinum–ligand bonds indirectly indicate
the mutual influence of ligands. The platinum–chloride
bonds are rather long, as was expected for complexes with
sulfoxide, exhibiting very strong static trans- and cis-influ-
ences. The two chloride ligands in complex 1 have compa-
rable Pt–Cl distances. In 2 the chloride ligand Cl1 trans to
Ph3PS is even more withdrawn from the coordination cen-
ter, while the Pt–Cl2 bond trans to sulfoxide is longer in 1
than in 2. The latter fact is consistent with stronger trans-
influence of Me2SO as compared to Me-p-TolSO. It may
be concluded that trans-influence of Ph3PS is stronger than
that of Me-p-TolSO and comparable to that of Me2SO,
which has almost the strongest trans-influence in platinum
complexes. The static cis-influence of Ph3PS could also be
estimated. It was shown that in [Pt(Me2SO)LCl2] series of
3
˚
˚
b = 14.555(3), c = 18.769(4) A, V = 2681.8(10) A , Z = 4,
q
calc = 1.770 g cmꢀ3
,
F(000) = 1392. The data were
collected in h k l range 0–11, 0–16, 0–20; 2280 reflections
with I > 2r(I) were measured. X-ray absorption, l =
56.64 cmꢀ1, was accounted for. Non-hydrogen atoms were
refined anisotropically by full-matrix least-squares method
on F. The position of hydrogen atoms was determined
from difference syntheses and refined isotropically. Final
R = 0.032, Rw = 0.080 for all observed reflections. Abso-
lute structure was determined by Flack method, the calcu-
lated absolute structure factor is ꢀ0.010(13). Calculation of
geometry properties and illustrations was made with pro-
gram PLATON [61].
˚
3. Results and discussion
complexes, Pt–S distance (dPt–S(O), A) increase in the fol-
lowing order of ligands L: NH3 (2.186), H2O (2.194), 2-
methylpyridine (2.200), pyridine and pyrimidine (2.209),
benzonitrile (2.215), MeCN (2.220), C2H4 (2.223), Me2SO
(2.234, 2.248) [54–57]. The values of dPt–S(O) for the com-
plex 1 are close to those in the complex with benzonitrile.
So we conclude that static cis-influence of Ph3PS is of the
same level than that of nitriles.
3.1. Synthesis of complexes
The mixed-ligand sulfoxide phosphine sulfide platinum
(II) complexes were synthesized from bis-sulfoxide com-
plexes and phosphine sulfide. The reaction occurs by the
displacement of one of sulfoxide ligands in the initial com-
plex. Our attempts to synthesize bis-phosphine sulfide plat-
inum complexes failed. No substitution of the second
sulfoxide ligand occurs even if phosphine sulfide is taken
The two structures show the same positioning of Ph3PS
with respect to coordination plane and sulfoxide ligand,
though sulfoxide and rings positions, and packing are dif-
ferent. The RMS fit of coordination planes of the two
structures, displaying this fact, is presented in Fig. 3. Thus,
we believe that the mode of Ph3PS coordination is gov-
erned only by specific properties of poorly studied triphe-
nylphosphine sulfide–platinum bond. In 1 and 2 Ph3PS
coordinates in such way that the plane, containing PtSP
angle is almost perpendicular to coordination plane (the
interfacial angle is 89.3(2)ꢀ for 1 and 89.78(14)ꢀ for 2). Such
position was not observed in platinum complexes, studied
earlier [22,23,62–64], probably because PS group in those
compounds was a part of the chelating ligand. The PtS1P
angle itself is 105.7(2)ꢀ in 1 and 104.05(13)ꢀ in 2. This angle
is rather variable in Ph3PS complexes with different electro-
philes, ranging from 102.5ꢀ in untypical copper(I) complex
[39] to 116–117ꢀ in niobium(V) complexes [34,35]. Yet, for
most complexes with platinum metals and gold it ranges
from 103ꢀ to 106ꢀ. The difference in the coordination prop-
erties of the sulfur atoms in sulfoxides and Ph3PS is
1
in over 5-fold excess. The example of H NMR spectrum
of the fresh product of the reaction of cis-[Pt(Me2SO)2Cl2]
with 5-fold excess of Ph3PS is provided as supplementary
material, Fig. S3 and S4. Only the two mixed ligand com-
plexes are formed. The initial bissulfoxide complex is
totally consumed in the reaction. We do not propose any
precise pathway of the reaction, as the mixed ligand
product is subject to fast cis–trans isomerization in CDCl3
(discussed in detail below).
3.2. X-ray structures
The X-ray analysis of the obtained crystals definitely
shows that both complexes have cis-geometry in crystal
state. The bond lengths and angles for the structures are
listed in Table 1. The molecular structure, and atom num-
bering scheme for cis-[Pt(Ph3PS)(Me2SO)Cl2] (1) are pre-
sented in Fig. 1. The molecular structure, absolute

A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
1035
Table 1
Selected structural parameters for cis-[Pt(Ph3PS)(Me2SO)Cl2] and cis-[Pt(Ph3PS)(Me-p-TolSO)Cl2] complexes
cis-[Pt(Ph3PS)
cis-{Pt(Ph3PS)
Ph3PS
(R)-Me-p-TolSO
(Me2SO)Cl2]
[(S)-Me-p-TolSO]Cl2}
(data from Ref. [66])
(data from Ref. [67])
˚
Bonds (A)
Pt–Cl(1)
Pt–Cl(2)
Pt–S(1)
Pt–S(2)
S(1)–P
2.316(5)
2.315(3)
2.300(4)
2.214(3)
2.026(6)
1.452(17)
1.778(18)
1.74(3)
2.322(3)
2.311(3)
2.305(3)
2.216(3)
2.018(4)
1.470(10)
1.76(2)
1.791(11)
1.788(10)
1.788(8)
1.799(10)
1.9529(8)
S(2)–O
1.493(10)
1.797(7)
1.796(13)
S(2)–C(19)
S(2)–C(20)
P–C(1)
P–C(7)
P–C(13)
1.811(14)
1.822(17)
1.815(15)
1.8220(16)
1.8115(17)
1.8188(16)
Angles (ꢀ)
Cl(1)–Pt–Cl(2)
Cl(1)–Pt–S(1)
Cl(1)–Pt–S(2)
Cl(2)–Pt–S(1)
Cl(2)–Pt–S(2)
S(1)–Pt–S(2)
Pt–S(1)–P
89.48(15)
177.63(16)
89.75(16)
89.56(15)
176.02(15)
91.06(16)
105.7(2)
118.3(6)
110.0(6)
109.0(8)
107.4(9)
108.7(11)
102.3(10)
113.9(6)
106.0(6)
114.4(6)
110.1(7)
105.5(7)
106.8(7)
89.22(11)
176.17(11)
92.69(11)
89.14(9)
177.37(10)
89.07(10)
104.05(13)
117.0(4)
111.3(7)
111.5(4)
107.9(8)
106.2(5)
101.7(8)
116.4(3)
106.0(3)
113.6(5)
109.8(5)
105.2(5)
105.5(4)
Pt–S(2)–O
Pt–S(2)–C(19)
Pt–S(2)–C(20)
O–S(2)–C(19)
O–S(2)–C(20)
C(19)–S(2)–C(20)
S(1)–P–C(1)
S(1)–P–C(7)
S(1)–P–C(13)
C(1)–P–C(7)
C(1)–P–C(13)
C(7)–P–C(13)
106.5(3)
105.5(3)
97.6(3)
113.19(7)
113.02(7)
111.97(7)
103.61(8)
107.38(8)
107.11(8)
Dihedral angles (ꢀ)
Pt–S(1)–P–C(13)
S(2)–Pt–S(1)–P
ꢀ85.8(6)
ꢀ90.7(2)
4.9(8)
ꢀ92.3(4)
ꢀ90.22(14)
27.5(5)
S(1)–Pt–S(2)–O
O–S(2)–C(20)–C(21)
26.1(12)
5.0(15)
Estimated standard deviations are given in parenthesis.
reflected in the lengths of Pt–S bonds. These are markedly
different, which is indicative of stronger bond between
Pt(II) and sulfoxides as compared to phosphine sulfide
and suggests lower donor power of the latter. The lengths
of platinum–triphenylphosphine sulfide bonds are
Pt(II) < [Fe2I4] ꢃ Mo(V) < Nb(V) < I2. The P–S–A (A –
acceptor atom) angle increases in the order Pt(II) ꢂ
Au(I) ꢂ I2 < [Fe2I4] ꢂ Al(III) ꢂ Cu(I) < Mo(V) < Nb(V).
(The comparison is based on 3 complexes of Au(I) [19–21],
2 complexes of Pt(II) studied in the present work, 3 Nb(V)
complexes [34,35], 3 diiodine adducts [50–52], and unique
examples for the other metals: Cu [44], Al [49], Mo [36],
and Fe [65]).
The coordinated phosphine sulfide ligand undergoes
structural changes, as compared to the free molecule [66]
(see Table 1). The P–S bond becomes longer, while P–C
bonds shorten. The phosphorus atom becomes more tetra-
hedral on coordination: the S–P–C angles decrease, while
C–P–C angles become wider. The same trends are observed
for Ph3PS coordinated to various nucleophiles. They are
caused by withdraw of electrons from sulfur and weaken-
ing of the P–S bond. These structural changes are more
profound in Me2SO complex. Formally Ph3PS has C3v
symmetry. But in fact local threefold symmetry of phos-
˚
2.300(4) and 2.305(3) A in 1 and 2, respectively. It is longer
than analogous bond trans to chloride in dichloro-(1-(diph-
enylphosphino)-8-(diphenylthiophosphoryl)naphthalene-
˚
P,S)-platinum(II) (2.286 A) [22] but it is significantly
shorter than the bond trans to phosphine sulfide in trans-
bis(2-(diphenylthiophosphinyl)-N-(diphenylphosphino)ani-
˚
line-P,S)-platinum (2.343 A) [23]. In platinum organic
compounds [62,63] and complex with phosphine sulfide
as a bridging ligand [64] the analogous bond is much longer
˚
(>2.4 A). The evaluated data for platinum–Ph3PS bond
may be compared to other Ph3PS bonds with different elec-
trophiles, known up to date. If we exclude organometallic
compounds, the length of Ph3PS–electrophile bond
increases in the following order Au(I) < Cu(I) < Al(III) ꢂ

1036
A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
Fig. 3. RMS fit of coordination planes in crystal structures of cis-
[Pt(Ph3PS)(Me2SO)Cl2] (bold line) and (ꢀ)-cis-{Pt(Ph3PS)[(S)-Me-p-Tol-
˚
SO]Cl2} (thin line). RMS difference 0.073 A for atoms in coordination
plane.
Fig. 1. Crystal structure of cis-[Pt(Ph3PS)(Me2SO)Cl2] (50% probability
ellipsoids).
The sulfoxide ligands in both structures are classically S-
coordinated. The relative position of substituents at the
sulfur atom in chiral sulfoxide in 2 is retained, so that abso-
lute configuration of Me-p-TolSO is inverted. This fact was
previously observed in a number of structures of platinum
complexes with Me-p-TolSO [11–15], and may be consid-
ered as a general rule. The platinum–sulfoxide bond
lengths, structural changes in sulfoxide ligands (contraction
of S–O and S–C bonds and flattening of ‘‘sulfoxide pyra-
mid’’) and position of S–O bond of Me2SO in the coordi-
nation plane of 1 are in accordance with general trends
for S-coordinated sulfoxides [53]. Our previous X-ray stud-
ies [13–15] show that S–O bond of Me-p-TolSO also tends
to enter coordination plane, but this tendency is not so pro-
nounced. The negatively charged oxygen atom of sulfoxide
in both structures points away from the cis-chloride ligand,
like in most of the neutral sulfoxide platinum complexes
with cis-geometry [53–56]. Though partial conjugation
between the aromatic system and the electrons of the S–
O bond makes the coplanar position of this bond more
favorable [68], the S–O bond is not coplanar to tolyl ring
in the structure of 2. This described conjugation is of inter-
est, because it significantly affects chiroptic properties of
Me-p-TolSO and its complexes. As we noticed in our pre-
vious work [15], the conjugation of S–O bond with tolyl
ring could be easily overridden by crystal packing require-
ments and thus it is not necessarily observed in X-ray struc-
tures of complexes with Me-p-TolSO.
Fig. 2. Crystal structure and absolute configuration of (ꢀ)-cis-
{Pt(Ph3PS)[(S)-Me-p-TolSO]Cl2} (50% probability ellipsoids).
phorus in most of the known structures of free and coordi-
nated Ph3PS is not realized, distinct single plane of symme-
try could be observed instead. Therefore, the two lone pairs
at sulfur are not equivalent. In the studied structures, the
positioning of the plane of Ph3PS approximate symmetry
with respect to coordination plane is given by the torsion
angle Pt–S1–P–C13, which is close to 90ꢀ. We suggest that
the rotation of unhindered Ph3PS with respect to P–S bond
in 1 and 2 is caused by selective coordination through a cer-
tain sulfur lone pair. The structural characteristics of aro-
matic rings in both structures are fairly typical (taking
standard deviations into account). None of the rings is
coplanar with P–S bond.
The packing of complexes shows no peculiar intermolec-
ular contacts or prominent stacking interaction.
3.3. NMR and isomerization of complexes
The discussed complexes are interesting from the view-
point of their catalytic activity in hydrosilylation reactions.
According to modern concepts of catalytic action of plati-
num complexes in hydrosilylation reaction, the ligands are

A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
1037
dynamically exchanged in the catalytic cycle [4,69]. So the
isomerization and ligand exchange of the complexes is of
particular interest.
all the other protons are more deshielded than in the corre-
sponding minor species 1b and 2b (the difference in H
1
chemical shifts of 1a and 1b is larger, than in 2a and 2b,
it is consistent with stronger p-acceptor properties of
Me2SO as compared to Me-p-TolSO). The 195Pt chemical
The CDCl3 solutions of both studied sulfoxide phos-
phine sulfide complexes invariably contain two species, a
major form and a minor one, as evidenced by NMR spectra.
3
shift of 1b is larger than in 1a. The JH–Pt coupling con-
1
According to H NMR, both species are fully consistent
stants are significantly larger in minor species as compared
to major species. According to the trends listed above, such
properties suggest that the major species is a trans- isomer,
while the minor is a cis- one. The fact, that only minor cis-
isomer is obtained on crystallization, should not be very
annoying. The complex could gradually isomerize towards
less soluble form, while the latter crystallizes out.
with the proposed structure of mixed-ligand complexes
(Fig. S1–S4). The difference in chemical shifts and Pt–H
coupling constants of the two species, calculated from
200 MHz spectra by accurate method [60], is significant
(Fig. S5). So these species are not conformational isomers.
The observed proportion of isomers is about 10:1 and varies
slightly in different preparations. On crystallization only
cis-isomer is isolated, as confirmed by X-ray analysis.
Nevertheless, even the fresh CDCl3 solution of the crystals
contains both isomers; its NMR spectrum does not change
notably with time. Thereby, we suggest that the solutions
of complexes 1 and 2 are true equilibrium mixtures of cis-
and trans-isomers. The rates of isomerization of the com-
plexes should be relatively high, as it should be faster than
crystallization–dissolution process. Yet the isomerization
rates are slow on NMR scale: there is no detectable broad-
ening of resonance peaks by chemical exchange.
But there is still one controversial fact concerning
195Pt–31P coupling constants for complex 1. These con-
stants should be significantly larger in cis-isomer, just like
3JPt–H constants. The major species 1a displays significantly
3
larger (116 2 Hz) JPt–P constant than 1b (86 5 Hz),
which is contrary to the assumption that 1a is trans-
[Pt(Ph3PS)(Me2SO)Cl2]. The data for 2 are unfortunately
absent: we could not detect the 195Pt{1H} signal of 2b
because of its low concentration.
Our attempts to prepare systems, enriched with minor
isomer, were by now unsuccessful. Attempts to substitute
the solvent for more polar one (water or alcohol), caused
decomposition of complexes. So our assignment of major
species in CDCl3 solution to trans-[Pt(Ph3PS)(RR0SO)Cl2]
should be considered tentative.
As the equilibrium settles fast as compared to dissolu-
tion, we have by now no trustworthy method to assign
major and minor species to cis- and trans-isomers. The gen-
eral trends that describe the influence of geometry on
chemical shifts and coupling constants give controversial
results. It is well known, that sulfoxide is a strong p-accep-
tor. Phosphine sulfide is also supposed to be a good p-
acceptor, based on its electronic structure and strong static
trans-influence. This fact has a direct relation to chemical
shifts. It is generally considered, that the back donation
of p-electrons to p-acceptor causes the decrease in overall
deshielding of the ligand protons. On the contrary the
coordination center is slightly deshielded by p-bonding.
When two p-acceptors are in trans-position to each other,
they have to share the same orbitals of coordination center.
So the combined action of two p-bonds on chemical shifts
is weaker in trans-complexes. Hence, Pt(II) complexes with
cis-position of two p-acceptors exhibit larger (less negative)
There are some hints for the mechanism of isomeriza-
1
tion from the 500 MHz H NMR spectra of 2. The thor-
ough analysis of the spectrum (Fig. S1) reveals small
traces of uncoordinated sulfoxide (d 2.69, 2.36 ppm) and
two species with S-coordinated sulfoxide (d 3.46, 2.43;
3.54, 2.46 ppm). The content of traces is about 1% of the
total sulfoxide content. The S-coordinated traces were
attributed to cis- and trans-{Pt[(S)-Me-p-TolSO]2Cl2}
based on the chemical shift values. This fact hints for the
dissociation of small amount of free sulfoxide from the
complex. The free sulfoxide boosts ligand exchange and
aids the isomerization.
3.4. Optical activity of (ꢀ)-{Pt(Ph3PS)[(S)-Me-p-
1
195Pt chemical shifts and smaller H chemical shifts than
TolSO]Cl2}
the respective trans-isomers. The SCH3 group of S-coordi-
nated sulfoxides is one of known exceptions: it is affected
both by r-donor and p-acceptor items and its H chemical
shift is larger in cis-isomers [15,55–58].
The strong circular dichroism (CD) of enantiomerically
pure Me-p-TolSO and complexes that contain Me-p-TolSO
ligand is caused by stereogenic sulfur center. Generally,
asymmetric sulfoxides display two electronic transitions
of S–O group that fall in the 200–260 nm region. These
bands are very broad and overlap significantly with each
other and higher energy transitions, so the UV-spectrum
is not very informative. However, in chiral sulfoxides these
transitions are optically active and show circular dichroism
with opposite sign. This results in a characteristic two-band
CD spectrum [15]. Partial conjugation of the electrons of
tolyl ring and S–O group makes Me-p-TolSO strongly
asymmetric [68]. So absorption and CD of its S–O bands
1
Another important trend states that neutral cis-com-
plexes of platinum (II) display stronger 195Pt-ligand spin
coupling, than trans-complexes. For sulfoxide complexes
3
the most indicative is JPt–H coupling constant of SCH3
group. In all the neutral sulfoxide complexes, studied by
us previously [11–15], as well as in other sulfoxide com-
3
plexes [55–58], this rule is obeyed: typical value of JPt–H
is 20–21 Hz for trans-isomers and 22–24 Hz for cis-isomers.
In major species 1a and 2a the SCH3 group protons are
less deshielded upon coordination (Figs. S1, S3, S5), while

1038
A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
become far more intensive, than that of aliphatic sulfoxides
[70]. For (+)-Me-p-TolSO the CD of the low-energy S–O
band is strongly positive (Fig. 4, dotted line).
As noted above, Me-p-TolSO coordinates to platinum
(II) via sulfur with the retention of the relative position
of substituents at the sulfur atom, and the inversion of
absolute configuration. Previously, we studied a series of
for {PtL[(S)-Me-p-TolSO]Cl2} complexes (Fig. 4, solid
line). The two peaks of opposite sign, corresponding to
S-coordinated sulfoxide, are readily recognized in far-UV
region. But the CD band at 270 nm is positive and a new
negative band is observed at 290 nm. We suggest that such
appearance of CD spectrum is caused by ligand–ligand
interaction. Chiral Me-p-TolSO behaves as the first type
of Moffit classification for optically active chromophores
[72]. Both electronic and magnetic transition dipoles of
such chromophores have significantly non-zero values.
The low-energy electronic transitions of nearby Ph3PS
ligand lie in the same region, as that of the low-energy
Me-p-TolSO transition. If dipole–dipole interaction is
effective, both transitions should be shifted on energy scale
and become exciton-coupled. As one of the initial transi-
tions is optically active, both exciton-coupled transitions
become optically active (induced optical activity). Usually
such transitions have the opposite sign of CD. We should
keep in mind yet, that dipole–dipole interaction and
induced optical activity could be averaged toward zero by
rotation of interacting chromophores with respect to each
other. But configuration of Ph3PS shown by the crystal
structure of 2 almost eliminates the possibility of such aver-
aging. The Ph3PS ligand is very unlikely to rotate through
its coordination bond for steric reasons. The rotation of
Me-p-TolSO only is not enough for effective averaging.
Besides in cis-isomer Me-p-TolSO rotation is also strongly
hindered by Ph3PS. So we suggest that two peaks of oppo-
site sign at 270 and 290 nm are caused by coupling of opti-
cally active Me-p-TolSO transitions to lower energy
transition of Ph3PS.
platinum
complexes
(ꢀ)-{PtL[(S)-Me-p-TolSO]Cl2},
L = Py, Bu3P, NH3, NH2Me [15]. We noticed that coordi-
nation via sulfur causes the change of sign of CD bands.
The usual spectral pattern of CD spectra of such complexes
in CH2Cl2 solutions displays three distinct regions. A
strong negative low-energy S–O CD band with a peak at
240–245 nm is observed in far-UV region. Only a rising
slope of its positive high energy counterpart may be
observed in CH2Cl2. Intermediate negative CD band is
located at 270–275 nm. It was attributed to electronic tran-
sitions of tolyl ring. Its intensity is sensitive to the nature of
non-chiral ligands; it increases if a bulky ligand is present
in cis to Me-p-TolSO. Low energy bands of d–d transitions
stretch to the visible region and respond for the color of the
complexes. They are highly dependent on ligand nature
and complex geometry [71], but their induced CD is very
weak.
The CD spectrum of (ꢀ)-cis-{Pt(Ph3PS)[(S)-Me-p-Tol-
SO]Cl2} is more complicated than the expected pattern
Adding various nucleophiles to 2 causes ligand substitu-
tion and change in circular dichroism. The coupled value of
the optical rotation ½aꢁ2D0 also change, this effect was used by
us to monitor reactions in models of catalytic systems. The
strongest nucleophiles substitute for chiral sulfoxide. The
free (+)-Me-p-TolSO, released into solution can be easily
and quantitatively identified by its strong positive CD
and optical rotation [10,16–18].
4. Conclusion
The phosphine sulfide complexes of platinum (II) can be
prepared from bis-sulfoxide complexes and equimolar
amount of phosphine sulfide. Yet only mixed ligand com-
plexes are formed even with excess phosphine sulfide. The
newly synthesized complexes are potent catalysts in hydro-
silylation reaction. Triphenylphosphine sulfide (Ph3PS)
sulfoxide platinum (II) complexes exist as a mixture of rap-
idly turning cis- and trans-isomers in chloroform solution,
but crystallize out as cis-isomer. The equilibrium ratio of
isomers in chloroform solution is approximately 1:10.
The geometry of major isomer was not established because
of NMR data controversies, and this subject needs further
investigation. The crystal structures of cis-isomers are clas-
sical platinum (II) complexes. They give the excellent exam-
ple of simple coordination of phosphine sulfide to
Fig. 4. The UV and CD spectra of (ꢀ)-{Pt(Ph3PS)[(S)-Me-p-TolSO]Cl2}
(solid line) and (+)-Me-p-TolSO (dotted line) at 20 ꢀC in CH2Cl2.

A.N. Skvortsov et al. / Inorganica Chimica Acta 359 (2006) 1031–1040
1039
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Acknowledgement
This work was supported by the Russian Foundation
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Crystallographic data (excluding structure factors) for
the structures of complexes 1 and 2 in this paper have been
deposited with the Cambridge Crystallographic Data Cen-
tre as supplementary publication Nos. CCDC 241253 and
241252, respectively. Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44 0 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk). Supple-
mentary data associated with this article can be found, in
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