Carbon-phosphorous bond cleavage on a platinum centre. Crystal structure of sym-cis-[Pt(μ-PPh2)(PPh2CH2CH 2S-P,S)]2

Article abstract of DOI:10.1016/S0020-1693(03)00227-5

The complex [Pt(dppet-P,S)₂] (Hdppet=PPh₂CH ₂CH₂SH) that had been synthesized previously from K ₂PtCl₄ and Hdppet in the presence of base with moderate yields (ca. 50%), has been prepared i

Full text of DOI:10.1016/S0020-1693(03)00227-5

Inorganica Chimica Acta 353 (2003) 280Á283
/
www.elsevier.com/locate/ica
Note
CarbonÁ
/
phosphorous bond cleavage on a platinum centre.
Crystal structure of sym-cis-[Pt(m-PPh2)(PPh2CH2CH2SÁ
/
P,S)]2
a
a,
b,
Josep Duran , Alfonso Polo *, Julio Real *, Angel Alvarez-Larena ,
c
´
´
J. Francesc Piniella c
a Departament de Qu´ımica, Universitat de Girona. Campus de Montilivi s/n, E-17071 Girona, Spain
b Departament de Qu´ımica, Universitat Auto`noma de Barcelona, E-08193, Cerdanyola, Barcelona, Spain
c Servei de Difraccio´ de Raigs-X, Universitat Auto`noma de Barcelona, E-08193, Cerdanyola, Barcelona, Spain
Received 13 November 2002; accepted 28 February 2003
Abstract
The complex [Pt(dppetÁ
the presence of base with moderate yields (ca. 50%), has been prepared in high yield (ca. 95%) in the absence of base. [Pt(dppetÁ
P,S)2] is stable in the air, in the presence of acid (2 M HCl) and in refluxing toluene, but in the sun light it turns into binuclear sym-
cis-[Pt(m-PPh2)(dppetÁP,S)]2 (1). The crystal structure of 1 revealed a non-crystallographically planar Pt2P4S2 core with open m-PÁ
PtÁP(dppet) angles (102, 1048) and similar m-PÁ
ligand.
# 2003 Elsevier B.V. All rights reserved.
/
P,S)2] (HdppetꢀPPh2CH2CH2SH) that had been synthesized previously from K2PtCl4 and Hdppet in
/
/
/
/
˚
Pt distances of 2.311(4), 2.318(5), 2.302(5), 2.324(5) A, little influenced by the trans
/
/
Keywords: Platinum; Phosphinothiolate; Phosphide; Crystal structures
1. Introduction
best prepared in acidic conditions rather than in basic
conditions. This observation prompted us to study the
case of platinum, i.e., the synthesis and stability of
phosphinothiolate complexes of platinum in acid con-
ditions.
The stability of ligands is an important factor in any
practical application of metal complexes [1]. In the case
of phosphinothiols, it has been reported that this ligands
may decompose into phosphine sulphides, as in certain
conditions there is cleavage of the carbonÁ/sulphur bond
and formation of the strong phosphorousÁ
[2]:
/sulphur bond
2. Results and discussion
PMe(Ph)CH2CH2SH 0 SꢀPMe(Ph)CH2CH3
2.1. Synthesis
Phosphinothiols are also subjected to oxidation, first
on phosphorous but also on sulphur. Furthermore,
thiolates are basic and this constitutes a difference
with the important class of diphosphine ligands, which
are obviously less basic, for any application in acidic
media. However, we have reported that some palladi-
um(II) phosphinothiolate complexes, such as the bische-
The bischelate [Pt(dppet)2] is perhaps the simplest
phosphinothiolate complex of platinum [4,5], it can be
prepared in reproducible low yields (ca. 50%) from
K2PtCl4 or PtCl2 and the ligand in the presence of bases
such as NEt3. The use of a base seems necessary to
remove the proton from the weakly acidic thiol, but the
presence of a base throughout the synthesis favours the
oxidation of both the phosphorous and the sulphur.
Basic conditions are commonly used in the synthesis of
late [Pd(dppet)2] (HdppetꢀPPh2CH2CH2SH) [3], are
/
* Corresponding authors. Fax: ꢁ
E-mail addresses: alfons.polo@udg.es (A. Polo), juli.rcal@uab.es (J.
Real).
/34-93-581 3101.
platinum thiolates and even dithiolates [6Á
/
8], but it is
difficult to decide if this responds to the actual need for
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00227-5

J. Duran et al. / Inorganica Chimica Acta 353 (2003) 280Á
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283
281
a base or to the idea that the thiol sulphur will not form
complexes unless the proton is removed previously.
The direct, base free reaction of K2PtCl4 with the
phosphinothiol Hdppet afforded [Pt(dppet)2] in high
yield, always above 85%. Apparently, the phosphi-
nothiolato chelate forms a very strong bond to platinum
and the presence of HCl and excess chloride is no
problem. Also, the acidic conditions seem beneficial for
the stability of the ligand. The spectroscopic data,
specifically the large coupling constant of phosphorous
to platinum (1JPÁPt
ꢀ2811 Hz), together with the strong
/
preference of platinum for a cis-P,P coordination,
should support a cis-P,P structural assignment as
reported [5], although other authors have assumed a
trans structure [4,11Á13]. Chemical shifts for cis- and
/
trans-P,P complexes of this type can be very similar, as
shown in the case of the comparable palladium com-
plexes [Pd(sp)2] (Hspꢀ
/
PPh2(6-RÁ
/
C6H3Á
/
2-SH, RꢀH,
/
SiMe3) that exist in both cis and trans forms [9,10].
Bischelate [Pt(dppet)2] showed high stability, it is
stable in hydrochloric acid (2 M), in air as a solid or
in solution for moderate periods of time, and in
refluxing toluene. However, when solutions of
[Pt(dppet)2] were allowed to stand in the sun light, the
formation of crystals was observed. This was a new
material, as it was only sparingly soluble or insoluble in
all tested solvents and its elemental analysis did not
correspond to [Pt(dppet)2], but to a composition high in
phosphorous and low in sulphur: P2PtS. It later proved
to be the phosphido-bridged binuclear [Pt(m-
Fig. 1. ORTEP plots of sym-cis-[Pt(m-PPh2)(dppetÁ
above projection carbon atoms have been represented by small circles
(all non-hydrogen atoms have been refined anisotropically), below all
/
P,S)]2, in the
carbon atoms (except C1Á/C4) have been omitted, all for the sake of
clarity.
PPh2)(dppetÁP,S)]2 (1).
/
In this new complex the ligand diphenylphosphido
has formed by cleavage of the phosphorousÁcarbon
/
bond of dppet ligand and loss of the C2H4S fragment.
The thiolate sulphur, a group that usually forms strong
bonds to transition metals, has been effectively displaced
from the coordination sphere of platinum by the
bridging phosphide.
Scheme 1. Structural possibilities of phosphido complexes relevant to
the discussion.
2.2. Crystal structure
note that in the distribution of bridging versus terminal
coordination positions, two ligands (the phosphido
PR2ꢂ and the thiolato RSꢂ groups) with a strong
preference to form bridges between transition metal ions
are competing, the result is that the phosphide phos-
phorous takes the bridging position and structure E is
not observed [3].
The structure of 1 consists of discrete molecules of
sym-cis-[Pt(m-PPh2)(dppetÁ
/
P,S)]2 as depicted in Fig. 1.
Comparable bridging phosphido structures with nega-
tive (X) and neutral terminal ligands (PR3), be them
trans geometries of
18].
open or chelate tend to adopt sym Á
/
type A (see Scheme 1), rather than type C [14Á
/
The six phenyl rings on phosphorous P1, P2 and P3
are accommodated on the same side, overcoming the
steric interactions by adopting conformations in some
However, binuclear 1 is unique in that it prefers a cis
structure (D) rather than the apparently less sterically
encumbered trans configuration (B). It is interesting to

282
J. Duran et al. / Inorganica Chimica Acta 353 (2003) 280Á283
/
cases (notably phenyl groups on P2, see Fig. 1) almost
perpendicular to the core plane. Also, the interfering
phenyl rings on P2 and P3 are almost parallel to each
Table 1
Crystallographic data for complex 1
Formula
M
C52H48P4Pt2S2
1251.08
293(2)
other. The angles P1Á
P2ÁPt2ÁP3 (1028) are large compared to the angles
formed by the less bulky thiolato ligand: S1ÁPt1ÁP4
(948) and S2ÁPt2ÁP4 (958). This deformation can be
compared to that of cis-[Pd(PPh2(C6H4Á2-S))2], where a
similar effect was observed [9]. As this congestion could
be avoided by adopting the more common sym Átrans
geometry, it must be assumed that the sym Ácis arrange-
ment is caused by electronic factors.
/
Pt1Á
/
P2 (1048, see Table 2) and
/
/
T (K)
Crystal system
Space group
Unit cell dimensions
monoclinic
P21/c
/
/
/
/
/
˚
a (A)
9.572(10)
21.437(9)
23.716(9)
93.16(6)
4
˚
b (A)
˚
c (A)
/
b (8)
/
Z
V (A )
3
˚
4859(6)
1.710
6.004, 0.999, 0.705
Bridging phosphido phosphorous to platinum(II)
distances trans to sulphur in 1 are only very slightly
shorter than those trans to the phosphine-type phos-
phorous of ligand dppet, which seems exceptional as
phosphorous should exert a larger trans influence. The
consequences of the lower trans influence of chloride are
important in comparable platinum complexes (see Table
Dcalc (g cmꢂ3
)
m (mmꢂ1), Tmax, Tmin
Crystal dimensions (mm3)
Data/restraints/parameters
Goodness-of-fit
0.07ꢃ
/
0.04ꢃ0.04
/
8521/0/445
0.850
R(Fo) [I ꢀ
/
2s(I)] a
0.0751
0.1618
Rw(Fo2) (all data) b
a
R(Fo)ꢀ
/
SjjFojꢂ
/
jFcjj/SjFoj.
Fc2)2/S w(Fo2)2]1/2
3), making m-PÁ/Pt distances very different.
Rw(Fo2)ꢀ[S w(Fo2ꢂ
/
/
.
b
3. Experimental
weeks, after which time a crop of small yellow prismatic
crystals had formed. The crystals were isolated by
3.1. Materials and measurements
filtration and washed with ethyl ether (3ꢃ10 ml). The
/
yield was 52 mg (28%) of 1. Elemental Anal. Found
(Calc. for C52H48P4Pt2S2): C, 49.53 (49.92); H, 4.13
(3.87); P, 9.53 (9.90); Pt, 30.85 (31.18); S, 4.88 (5.13)%.
Compound 1 was insoluble in organic solvents; other
platinum phosphido complexes such as [PtCl(m-
PHMes)(PH2Mes)] [16] are also insoluble.
Conventional oxygen-free synthetic methods have
been employed in order to prevent the oxidation of the
ligand. The solid complexes are air stable but the
solutions were kept under nitrogen atmosphere. 31P
NMR spectra are reported in the d scale and referred to
external 85% H3PO4. Elemental analyses (C, H and S)
were performed with a Carlo Erba CHNS EA-1108.
Phosphorous content was determined after mineraliza-
tion by a colorimetric method on phosphomolybdova-
nadate, at the S.A.Q. of the U.A.B. Platinum content
was determined by repeated cycles of mineralization
with conc. HNO3 in a heated crucible and ignition at
temperatures over 900 8C (open crucible), which gave
platinum metal. The ligand Hdppet was prepared as
described [19]. The synthesis of [Pt(dppet)2] in basic
conditions was done as reported [5], using triethylamine,
sodium hydroxide and potassium tert-butoxyde, the
yields ranged from 40 to 60% of a dull yellow material.
The preparation of [Pt(dppet)2] in acidic conditions was
done in the same way but omitting the base, the yields
were reproducibly higher and ranged from 85 to 98%, of
Table 2
˚
Selected bond lengths (A) and bond angles (8) for 1
Bond lengths
Pt(1)Á
Pt(1)Á
Pt(1)Á
Pt(1)Á
P(1)Á
P(1)Á
P(1)Á
P(2)Á
P(2)Á
S(1)Á
S(2)Á
/
P(1)
P(2)
P(4)
S(1)
2.287(5)
2.311(4)
2.318(5)
2.324(5)
1.827(9)
1.836(8)
1.847(17)
1.812(11)
1.854(9)
1.776(19)
1.80(2)
Pt(2)Á
Pt(2)Á
Pt(2)Á
Pt(2)Á
/
P(3)
P(2)
P(4)
S(2)
2.292(5)
2.302(5)
2.324(5)
2.316(5)
1.82(2)
/
/
/
/
/
/
/
C(21)
C(11)
C(1)
P(3)Á
P(3)Á
P(3)Á
P(4)Á
P(4)Á
C(1)Á
C(3)Á
/
C(4)
/
/
C(61)
C(51)
C(81)
C(71)
1.831(15)
1.850(12)
1.835(11)
1.839(10)
1.52(2)
/
/
/
C(41)
C(31)
/
/
/
/
C(2)
/
C(2)
a bright yellow material with 31P{1H} NMR (121.4
/
C(3)
/
C(4)
1.54(3)
1
MHz, CD2Cl2, r.t.) d 61.7, J(PÁ
/
Pt)ꢀ
/
2811 Hz.
Bond angles
Pt(2)ÁP(2)Á
P(1)ÁPt(1)Á
P(1)ÁPt(1)Á
P(2)ÁPt(1)Á
P(1)ÁPt(1)Á
P(2)ÁPt(1)Á
P(4)ÁPt(1)Á
/
/
Pt(1)
P(2)
P(4)
P(4)
S(1)
S(1)
S(1)
103.45(17)
104.30(16)
176.50(15)
76.86(16)
84.38(17)
170.77(17)
94.66(17)
Pt(1)Á
P(3)ÁPt(2)Á
P(3)ÁPt(2)Á
P(2)ÁPt(2)Á
P(3)ÁPt(2)Á
P(2)ÁPt(2)Á
S(2)ÁPt(2)Á
/
P(4)Á
/
Pt(2)
P(2)
S(2)
S(2)
P(4)
P(4)
102.54(17)
102.17(18)
85.8(2)
/
/
/
/
3.2. Preparation of [Pt(m-PPh2)(dppetÁ
/
P,S)]2 (1)
/
/
/
/
/
/
/
/
171.94(18)
175.16(19)
76.91(16)
95.24(18)
A solution of [Pt(dppet)2] (200 mg, 0.29 mmol) in
dichloromethane (ca. 100 ml) and n-buthylether (ca. 40
ml) was prepared under nitrogen in a side arm flask. The
stoppered flask was allowed to rest in the sun for 6
/
/
/
/
/
/
/
/
/
/
/
/
P(4)

J. Duran et al. / Inorganica Chimica Acta 353 (2003) 280Á
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283
283
Table 3
Representative m-phosphido phosphorousÁ
/
platinum(II) distances relevant to trans influence effects
˚
Pt) [A] trans to P
˚
Pt) [A] trans to Cl or S
d(m-PÁ
/
d(m-PÁ
/
Ref., CSD code
[Pt(m-PPh2)(dppetÁ
/
P,S)]2
2.318(5), 2.324(5)
2.316(2), 2.330(2)
2.312(1)
2.311(4), 2.302(5)
2.243(2), 2.255(2)
2.247(1)
This work
[PtCl(m-PPh(CH2)3PCy2)]2
[PtCl(m-PPh(CH2)3PCy2)]2
[PtCl(m-PHMes)(PEt3)]2
[PtCl(m-PHMes)(PPh3)]2
[PtCl(m-PPh2)(PHPh2)]2
[Pt(m-PPh2)(dppe)]22ꢁ
[14], BOPPEB20
[14], CIBDAS10
[16], ZUQWOX
[16], ZUQWUD
[15], BEXYAE
[15], BEXYEI
[16], ZUQXAK
2.323(2)
2.318(2)
2.265(2)
2.268(2)
2.260(3)
2.329(3)
2.362(3), 2.335(3)
2.356(2)
[Pt(m-PHMes)(dppe)]22ꢁ
[2] P.-H. Leung, A.C. Willis, S.B. Wild, Inorg. Chem. 31 (1992) 1406.
[3] N. Brugat, A. Polo, A. Alvarez-Larena, J.F. Piniella, J. Real
Inorg. Chem. 38 (1999) 4829.
3.3. X-ray crystallography
All crystals of 1 were very small yellow prisms. Data
collection and determination of the unit cell on the
selected specimen was performed on a Enraf Nonius
[4] G. Schwarzenbach, Chem. Zvesti 19 (1965) 200.
[5] M. Kita, T. Yamamoto, K. Kashiwabara, J. Fujita, Bull. Chem.
Soc. Jpn. 65 (1992) 2272.
[6] R.D. Lay, A. Shaver, Inorg. Chem. 20 (1981) 477.
[7] A.K. Fazlur-Rahman, G. Verkade, Inorg. Chem. 31 (1992) 5331.
[8] J. Fornie´s-Ca´mer, A. Aaliti, N. Ruiz, A.M. Masdeu-Bulto´, C.
Claver, C.J. Cardin, J. Organomet. Chem. 530 (1997) 199.
[9] J. Real, E. Prat, A. Polo, A. Alvarez-Larena, J.F. Piniella, Inorg.
Chem. Commun. 3 (2000) 221.
CAD 4 diffractometer, operating with graphite-mono-
˚
0.71069 A) at 293(2)
chromated Mo Ka radiation (lꢀ
/
K. The u range was 1Á
from 0 to 25 and l from 0 to 28, using the v Á
/
258, with h from ꢂ
/
11 to 11, k
2u scan
/
method. The crystal structure was solved by direct
methods using the SHELXS-86 program [20] and refined
by full-matrix least-squares methods on F2 for all
reflections with SHELXL-97 [21]. The function minimised
[10] N. Brugat, J. Duran, A. Polo, J. Real, A. Alvarez-Larena, J.F.
Piniella, Tetrahedron: Asymmetry 13 (2002) 569.
[11] D.M. Roundhill, S.G.N. Roundhill, W.B. Beaulieu, U. Bagchi,
Inorg. Chem. 19 (1980) 3365.
2
2 2
was
(0.0825P)2], with Pꢀ
S w(jFoj ꢂ
/
jFcj )
where
(Fo2ꢁ2Fc2)/3. Non-hydrogen
wꢀ
/
1/[s2(Fo2)ꢁ
/
[12] A. Benefiel, D.M. Roundhill, Inorg. Chem. 25 (1986) 4027.
[13] J.S. Kim, J.H. Reibenspies, M.Y. Darensbourg, J. Am. Chem.
Soc. 118 (1996) 4115.
/
/
atoms were refined anisotropically and phenyl rings
were refined as rigid groups. Hydrogen atoms were
included in calculated positions. Crystallographic data
are collected in Table 1 and selected distances and angles
in Table 2.
[14] R. Glaser, D.J. Kountz, R.D. Waid, J.C. Gallucci, D.W. Meek, J.
Am. Chem. Soc. 106 (1984) 6324.
[15] A.J. Carty, F. Hartstock, N.J. Taylor, Inorg. Chem. 21 (1982)
1349.
[16] I.V. Kourkine, M.B. Chapman, D.S. Glueck, K. Eichele, R.E.
Wasylischen, G.P.A. Yap, L.M. Liable-Sands, A.L. Rheingold,
Inorg. Chem. 35 (1996) 1478.
[17] L.R. Falvello, J. Fornie´s, J. Go´mez, E. Lalinde, A. Mart´ın, M.T.
Moreno, J. Sacristan, Chem. Eur. J. 5 (1999) 474.
[18] E. Alonso, J.M. Casas, F.A. Cotton, X. Feng, J. Fornie´s, C.
Fortun˜o, M. Tomas, Inorg. Chem. 38 (1999) 5034.
[19] J. Chatt, J.R. Dilworth, J.A. Schmutz, J.A. Zubieta J. Chem.
Soc., Dalton Trans. (1979) 1595.
Acknowledgements
This work was financially supported by the M.E.C.
(Spain) through project BQU2002-04070-C02.
[20] G.M. Sheldrick, in: G.M. Sheldrick, C. Kruger, R. Goddard
¨
(Eds.), SHELXS-86, Crystallographic Computing 3, Oxford Uni-
References
versity Press, Oxford, UK, 1985, pp. 175Á
[21] G.M. Sheldrick, SHELXL-97, Program for X-ray Crystal Structure
Refinement, University of Gottingen, Gottingen, Germany, 1997.
/
178.
[1] P.W.N.M. van Leeuwen, Appl. Catal. A 212 (2001) 61.
¨
¨