Antisymbiosis. Preferential coordination of anionic oxygen versus neutral sulfur donor atoms of methylsulfanyl- or methylsulfinyl-acetato, 2-benzoato and 2-phenolato to the cis-PtII(PPh3)2 and Pt II(dppe) residues

Article abstract of DOI:10.1016/j.ica.2004.09.039

The interaction of an excess of the title ligands L^- with the cis-Pt(phos)₂ moieties gives compounds a-b cis-[Pt(L-O) ₂(phos)₂] (a, phos = P(Ph)₃; b, phos = 1/2 dppe), in which O- is preferred to S-coordination. Such preference is confirmed by the fact that the same products are obtained by reaction of excess of L ^- with the previously reported a-d complexes [Pt(L-O,S)(phos) ₂]⁺, (c, phos = PPh₃, d, phos = 1/2 dppe), for which chelate ring opening occurs with rupture of Pt-S rather than Pt-O bonds. Compound a can be obtained also by oxidative addition of HL to [Pt(PPh ₃)₃]. The Pt-O bonds in compounds a-d are stable towards substitution by Me₂SO, pyridine and tetramethylthiourea. Substitution of L's occurs with N,N′-diethyldithiocarbamate, which forms a very stable chelate with Pt(II). Thiourea and N,N′-dimethylthiourea also react, because they give rise to cyclometallated products [Pt(phos)₂(NRC(S) NHR)]⁺ (R = H, CH₃), with one ionised thioamido group, as revealed by an X-ray investigation of [Pt(PPh₃)₂(NHC(S) NH₂)]⁺. The preference of O versus S coordination, as well as the stability of the Pt-O bonds, are discussed in terms of antisymbiosis.

Full text of DOI:10.1016/j.ica.2004.09.039

Inorganica Chimica Acta 358 (2005) 555–564
www.elsevier.com/locate/ica
Antisymbiosis. Preferential coordination of anionic oxygen
versus neutral sulfur donor atoms of methylsulfanyl- or
methylsulfinyl-acetato, 2-benzoato and 2-phenolato to the
cis-PtII(PPh3)2 and PtII(dppe) residues
a
Laura Battan , Serena Fantasia , Mario Manassero
a
b,
*
,
a,
b
Alessandro Pasini *, Mirella Sansoni
a
Dipartimento di Chimica Inorganica, Metallorganica e Analitica, via Venezian 21, 20133 Milano, Italy
Dipartimento di Chimica Strutturale e Stereochimica Inorganica, via Venezian 21, 20133 Milano, Italy
b
Received 13 May 2004; accepted 22 September 2004
Available online 21 November 2004
Abstract
The interaction of an excess of the title ligands Lꢀ with the cis-Pt(phos)2 moieties gives compounds a–b cis-[Pt(L-O)2(phos)2] (a,
phos = P(Ph)3; b, phos = 1/2 dppe), in which O- is preferred to S-coordination. Such preference is confirmed by the fact that the
same products are obtained by reaction of excess of Lꢀ with the previously reported a–d complexes [Pt(L-O,S)(phos)2]+, (c,
phos = PPh3, d, phos = 1/2 dppe), for which chelate ring opening occurs with rupture of Pt–S rather than Pt–O bonds. Compound
a can be obtained also by oxidative addition of HL to [Pt(PPh3)3]. The Pt–O bonds in compounds a–d are stable towards substi-
tution by Me2SO, pyridine and tetramethylthiourea. Substitution of Lꢀs occurs with N,N0-diethyldithiocarbamate, which forms a
very stable chelate with Pt(II). Thiourea and N,N0-dimethylthiourea also react, because they give rise to cyclometallated products
[Pt(phos)2(NRC(S)NHR)]+ (R = H, CH3), with one ionised thioamido group, as revealed by an X-ray investigation of
[Pt(PPh3)2(NHC(S)NH2)]+. The preference of O versus S coordination, as well as the stability of the Pt–O bonds, are discussed
in terms of antisymbiosis.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Antisymbiosis; Platinum phosphine complexes; Pt–O bonds
1. Introduction
design and synthesis of complexes with particular prop-
erties and reactivity, and is useful in fields as different as
catalysis, catalysis poisoning, biochemistry and pharma-
cology [1–9]. For instance, the major drawbacks of cis-
platin chemotherapy are toxicity and resistance, both
arising, inter alia, from the binding of platinum to sulfur
rich proteins [5,6], a cisplatin analogue with low affinity
for sulfur would therefore be highly desirable.
A detailed knowledge of the principles which rule the
affinity between metal ions and donor atoms allows the
*
Corresponding authors. Tel.: +39 0250314381; fax: +39
The affinity of a metal ion M for a ligand Z is ruled
by the hard–soft acid–base (HSAB) principle (some-
times called symbiosis [10]), however if other ligands
0250314405.
E-mail addresses: mario.manassero@unimi.it (M. Manassero),
alessandro.pasini@unimi.it (A. Pasini).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.039

556
L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
are present, in a complex of schematic formula A–M–Z,
the nature of the ‘‘ancillary’’ ligand A influences the
affinity of M for Z, especially if A and Z are trans to
each other, and such influence can sometimes reverse
the order of affinity dictated by the HSAB principle.
This latter behaviour was termed antisymbiosis and
was defined as ‘‘the preference of a hard donor ligand
trans to a soft ligand bound to a soft metal centre’’
[11–14] or ‘‘the destabilisation of a soft ligand trans to
another soft ligand bound to a soft metal centre’’ [13–
18].
In this paper, we wish to describe the results of
some studies on Pt(II) phosphine complexes with the
hybrid [19,20] ligands L depicted in Scheme 1. These
ligands are particularly suitable to study antisymbiosis,
because a metal centre can discriminate between two
donor sites of different nature, a hard anionic oxygen
and a soft neutral sulfur atom. In previous works,
we found that when the ancillary ligands are amino
groups, the stable species are [Pt(am)2(L-O,S)]+
(am = NH3 or 1/2 ethylenediamine) [21–24], even in
the presence of an excess of Lꢀ. On the contrary, in
the case of the cis-PtII(phos)2 moiety, not only the che-
late complexes [Pt(L-O,S)(phos)2]+ can be obtained
only with the ligands with the thioether group, sa, sb
and sph [24], but also excess of saꢀ or sbꢀ gives the
bi-substituted O-coordinated [Pt(L-O)2(phos)2] [25] (a,
b). Here, we want to discuss in detail these latter re-
sults. Numbering of compounds and abbreviations
are reported in Scheme 1.
2. Experimental
2.1. General
Elemental analyses (C, H, and N) were performed at
the Microanalytical Laboratory, the University of Mila-
no. IR (KBr pellets) spectra were recorded on JASCO
FT/IR-5300. 1H and 31P NMR spectra (CDCl3 solu-
tions) were recorded on a Bruker Advance DRX 300.
d values (ppm) are versus external Me4Si and H3PO4,
respectively. FAB+ mass spectra were obtained, from
4-nitrobenzyl alcohol, on a VCA Analytical 7070 EQ,
with xenon as the FAB source; isotopic cluster abun-
dance was checked by computer simulation.
All chemicals were of reagent grade. The synthesis of
the ligands [21,22], [Pt(NO3)2(phos)2] and [Pt(L-
O,S)(phos)2]NO3 [24], has been described previously.
[Pt(PPh3)3] [26] and [Pt(dppe)2] [27] were obtained fol-
lowing the literature procedures.
Dihydrogen evolution, during the oxidative addition
reactions, was checked by a gas chromatography-mass
spectroscopy technique as described in [28].
O
-
O
O
-
-
O
S
O
S
S
CH3
CH3
CH3
-
2-(methylsulfanyl)benzoate, sb-
2-(methylsulfanyl)phenolate, sph-
-
(methylsulfanyl)acetate, sa
-
-
O
O
O
O
O
O
S
CH3
O
S
O
S
CH3
CH3
2-(methylsulfiyil)phenolate, soph-
2-(methylsulfinyl)benzoate, sob-
(methylsulfinyl)acetate, soa-
CH3
(O)
(O)
+
phos
phos
phos
O
S
S
CH3
CH3
Pt
Pt
phos
O
O
S
O
[Pt(L-O,S)(phos2]+
c (phos = PPh3); d (phos = 1/2 dppe)
cis-[Pt(L-O)2(phos)2]
a (phos = PPh3;b (phos = 1/2 dppe)
Numbering of phosphine compounds
+
[
[Pt(L-O) (phos)
Pt(L-O,S)(phos)2]
]
2
2
L
L
(phos)2 sa
soa
2a
2b
sb
3a
3b
sob
4a
4b
sph soph
sa
1c
1d
soa
2c*
2d*
sb
3c
3d
sob
4c*
4d
sph soph
(PPh3)2
5a§
6c§
5c
1a
6a
dppe
5b*
6d§
5d
1b
6b
* Not obtained. § Detected through NMR, but not isolated in the solid state.
Scheme 1.

L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
557
2.2. Synthesis of cis-[Pt(L-O)2(phos)2] (a–b type
compounds)
the white product was obtained by the addition of di-
isopropyl ether.
The same procedure was employed for 2a, 3a, 4a and
6a, which were obtained in 80–90% yields. In the case of
the reaction with Hsph, compound 5a was identified as a
minor component of the reaction mixture by 31P NMR,
together with 5c.
2.2.1. Reaction of [Pt(NO3)2(phos)2] with excess Lꢀ:
synthesis of bis-(methylsulfinylacetato-O){bis(diphenyl-
phosphine)ethane}platinum(II) (2b)
Potassium methyl-sulfinylacetate was prepared by
evaporating to dryness, under reduced pressure, a solu-
tion of 0.678 g of Hsoa (0.54 mmol) in 5.3 ml of 0.1
mol Lꢀ1 aqueous KOH. The residue was treated with
0.136 g (0.21 mmol) of [Pt(dppe)(NO3)2], 10 mL of
CH2Cl2 and refluxed for 8 h. The filtered solution was
concentrated and treated with di-isopropyl ether yield-
ing 0.131 g (74%) of a white precipitate. Anal. Calc.
for C32H36O7P2PtS2:C, 45.0; H, 4.2. Found: C, 44.9,
H, 4.1%. IR: 1645, 1338 cmꢀ1 (COO); 1028 cmꢀ1
2.3. Reactivity
2.3.1. Reaction of the phosphine complexes with pyridine:
[(methylsulfanyl)benzoato-O]bis-(triphenylphosphine)-
(pyridine)platinum(II) nitrate, 7a(NO3)
A CH2Cl2 solution (20 mL) of equimolar amounts of
pyridine (0.006 g) and [Pt(PPh3)2(sb-O,S)[NO3 (0.071 g,
0.076 mmol) was heated at 30 ꢁC for 2 h. The product
was obtained as a CH2Cl2 solvate by concentration
and addition of di-isopropyl ether. Yield: 84%
(0.065 g). Anal. Calc. for C49.25H42.5Cl0.5N2O5P2PtS
(7a(NO3).1/4 CH2Cl2): C, 56.3; H, 4.6; N, 2.5. Found:
C, 56.4; H, 4.4; N, 2.7%. IR: 1623, 1334 cmꢀ1 (COO).
1H NMR: 2.18 (CH3S); 8.73 (JPt–H, 30–9 Hz, a hydro-
gen of py). 31P NMR: 5.10, (d, JPP 21.2Hz; JPtp, 3391
Hz, trans to N); 7.59 (d; JPtP, 3688 Hz, trans to O).
1
(SO). H NMR: 2.44 (CH3S). 31P NMR: 32.4.
The other a–b compounds were prepared by the same
procedure, starting from either cis-[Pt(NO3)2(PPh3)2] or
[Pt(dppe)(NO3)2]. 5a was obtained only as a minor com-
ponent in the reaction mixture and could not be iso-
lated. Reaction of cis-[Pt(dppe)(NO3)2] with excess
Ksph gave only 5d. Analyses and spectral data are re-
ported in the supplementary material.
Reaction of 0.060
(sb-O,S)]NO3 with 0.006 g of pyridine gave 0.054 g
(83%) of bis-[(diphenylphosphine)ethane](methyl
sulfanylbenzoato)(pyridine)platinum(II) nitrate,
g (0.072 mmol) [Pt(dppe)
2.2.2. Reaction of the chelate [Pt(L-S,O)(PPh3)2]NO3
with Lꢀ: synthesis of cis-bis(methylsulfanylacetato-O)-
bis(triphenylphosphine)platinum(II) (1a)
7b(NO3). Anal. Calc. for C39H36N2O5P2PtS: C, 51.8;
H, 4.3; N, 3.3. Found: C, 51.9; H, 4.1; N, 3.2%. IR:
Potassium methylsulfanylacetate was prepared as
above from 3.4 mL of aqueous 0.1 mol Lꢀ1 KOH and
0.036 g (0.34 mmol) of methylsulfanylacetic acid. An
equimolar amount of [Pt(PPh3)2(sa-O,S)]NO3 (0.300 g
dissolved in in 40 mL of CH2Cl2) was added to the res-
idue. The slurry was refluxed for 8 h, filtered and con-
centrated to 3 mL under reduced pressure. The white
product was obtained by addition of di-isopropyl ether.
Yield: 88%, 0.278 g. Anal. Calc. for C42H40O4P2PtS2: C,
54.2; H, 4.3. Found: C, 54.0; H, 4.1%. IR: 1637, 1330
1
1625, 1338 cmꢀ1 (COO). H NMR: 2.21 (CH3S); 8.43
(JPtp, 29.0 Hz). 31P NMR: 35.07 (d, JPP, 7.0 Hz; JPtP
3519 Hz, trans to O), 35.43 (d; JPtP, 3406, trans to N).
Complexes a and b, as well as the other c–d, failed to
,
react under the same conditions.
2.3.2. Reactions of the phosphine complexes with
dimethylsulfoxide
These reactions were carried out by dissolving 1 mL
of Me2SO and 0.08 mmol of either a–b or c–d complexes
in 15 mL of CH2Cl2 and boiling the solution for 8 h. In
all cases, concentration and addition of di-isopropyl
ether gave the unreacted starting material.
1
cmꢀ1 (COO). H NMR: 1.89 (CH3S). 31P NMR: 6.54
(JPtP, 3817 Hz).
Compounds 3a, 1b and 3b were obtained in the same
way in 80–90% yields.
2.3.3. Reactions of a–d complexes with sodium
diethyldithiocarbamate
2.2.3. Oxidative addition reactions of HL to [Pt(PPh3)3]:
alternative synthesis of compounds a. cis-bis(methyl-
sulfanylacetato-O)bis(triphenylphosphine)platinum(II)
(1a)
A solution of 0.051 g of methylsulfanylacetic acid
(0.48 mmol) in 5 mL of CH2Cl2 was added to a cold
(ice bath) solution of 0.235 g of [Pt(PPh3)3] (0.24 mmol)
in 20 mL of CH2Cl2, under a nitrogen atmosphere. The
yellow colour faded within a few minutes and the col-
ourless solution was kept in the cold for two hours, con-
centrated under reduced pressure, and 0.206 g (92%) of
These reactions were performed by treating, at room
temperature, ethanol solutions of complexes a–d with a
slight excess of Na(Et2NCS2) Æ 3H2O. After 2 h, addition
of di-isopropyl ether gave the Lꢀ salts of 8a, or 8b as
oily products which were used as such for spectral char-
acterisation. Analytically pure samples were obtained in
80–90% yield by the addition of a water solution of
Na(BF4) to ethanol solutions of the products.
[Pt(Et2NCS2)(PPh3)2](BF4), 8a(BF4): FAB+: m/z 867.
(calc. for [Pt(Et2NCS2)(PPh3)2]+, 867).

558
L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
[Pt(dppe)(Et2NCS2)](BF4), 8b4(BF4): FAB+, m/z, 741
11a(NO3) Æ H2O. Anal. Calc. for C49H51N3O6P2PtS2:
C, 53.5; H, 4.7; N, 3.8. Found: C, 53.4; H, 4.6; N,
(calc. for [Pt(dppe)(Et2NCS2)]+, 741). Analyses and
spectral data are reported in the supplementary
material.
1
4.1%. H NMR: 2.32 (CH3S of sb); 3.01 (CH3 of tmtu).
31P NMR: 5.53 (d, JP–P, 19.0 Hz; JPtP, 3624, trans to O);
18.78 (d; JPtP, 3258 Hz, trans to S). FAB+ MS: 1019
(calc. 1019).
2.3.4. Reaction of a–d complexes with thiourea or
N,N0-dimethylthiourea
bis-(triphenylphosphine)[thioureato-(N,S]}
num(II) tetrafuroborate, 9a(BF4).
11b(NO3) Æ H2O. Anal. Calc. for C39H39N3O6P2PtS2:
C, 48.4; H, 4.0; N, 4.4. Found: C, 48.7; H, 4.2; N,
plati-
1
4.6%. H NMR: 2.30 (CH3S of sb); 2.96 (CH3 of tmtu).
31P NMR: 34.23 (d, JP–P, 6.0 Hz; JPtP, 3530Hz, trans to
O); 48.41 (d; JPtP, 3041, trans to S).
An ethanol solution (15 mL) of 0.070 g (0.066 mmol)
of [Pt(PPh3)2(sb-O)2] and 0.050 g of thiourea was stirred
at room temperature for one hour. Concentration to
drops and addition of di-isopropyl ether gave a white
product, which was crystallised as the BF4 salt by the
addition of 0.011 g of NaBF4 in 15 mL of water. Yield:
88%, 0.051 g. Anal. Calc. for C37H33BF4N2P2PtS: C,
50.4; H, 3.8; N, 3.2%. Found: C, 50.5; H, 3.9; N, 3.4.
31P NMR: 11.55 (d, JPP, 20.0 Hz; JPtP, 3360 Hz),
14.70 (d; JPtP, 3240 Hz). FAB+: m/z, 794 (calc. for
[Pt(NHSCNH2)(PPh3)2]+ 794).
The same procedure was used for all a–d complexes.
The dppe d derivatives gave decomposition products,
with the exception of bis-{(diphenylphosphine)eth-
ane}{thioureato-(N,S)}platinum(II), which precipitated
spontaneously from the reaction mixture as the sb salt.
9b(sb) in 60% yield. Anal. Calc for C35H34N2O2P2PtS2:
C, 50.3; H, 4.1; N, 3.4. Found: C, 50.5; H, 4.0; N,
3.4%. 31P NMR: 38.33 (d, JPP, 7.2 Hz; JPtP, 3220 Hz);
41.37 (d, JPtP, 3203 Hz). FAB+: m/z 668 (calc. for
[Pt(dppe)(NHCSNH2)]+, 668.
2.3.6. Reactions of the [Pt(en)(L-O,S)]+ complexes
with sodium diethyldithiocarbamate
The reaction of equimolar amounts of [Pt(en)(sa-
O,S)]NO3 [22] and Na(dttc) Æ 3H2O (0.096 g and 51.5
g, respectively, 0.227 mmol) was performed in 20 mL
of water, at room temperature. The readily formed yel-
low solid was filtered off and was found to be [Pt(dttc)2]
by comparison with an authentic sample. All [Pt(en)(L-
O,S)]NO3 complexes behaved in a similar way.
2.3.7. Reaction of [Pt(en)(sa-O,S)]NO3 with thiourea:
synthesis of (ethylenediamine) {methylsulfanyl-acetato-
(S)}(thiourea)platinum(II) nitrate hydrate, [Pt(en)-
(sa-S)(tu)]NO3 Æ H2O
This compound was obtained by mixing 0.111 g
(0.263 mmol) of [Pt(en)(sa-O,S)]NO3 with an equimolar
amount of thiourea (0–020 g) in 20 mL of water. After 4
h at room temperature the solution was concentrated to
2 mL under reduced pressure, addition of ethanol (6
mL) and di-isopropyl ether (15 mL) gave 0.046 g
(35%) of a white solid. Anal. Calc. for C6H19N5O6PtS2:
C, 13.9; H, 3.7; N, 13.6. Found: C, 13.7; H, 3.7; N,
13.9%. IR: 1595 cmꢀ1 (masym uncoordinated CO2ꢀ),
The reactions with N,N0-dimethylthiourea were per-
formed in a similar way. 10a(BF4): Anal. Calc for
C39H37BF4N2P2PtS: C, 51.5; H, 4.1; N, 3.1. Found:
1
51.4; H, 4.2; N, 3.0%. H NMR: 2.16 (d, JP–H, 3.9 Hz;
JPt–H, 30.7 Hz; CH3Nꢀ); 2.78 (d, JH–H, 4.39 Hz;
CH3NH); 8.15 (d, JH–H, 4.39 Hz; NH). 31P NMR:
1
1384 cmꢀ1 (ionic NO3ꢀ). H NMR: 2.45 (s, JPt–H 44.8
Hz, CH3S); 3.60 (b, JPt–H about 51 Hz, CH2S); 2.7
(mt,b, JPt–H about 40 Hz).
12.11 (d, JP–P, 22.9 Hz; JPt–P, 3319 Hz); 16.85 (d; JPt–P
3220 Hz).
,
10b(NO3). Anal. Calc for C29H31N3O3P2PtS: C, 45.9;
1
2.3.8. (Ethylenediamine)bis(thiourea)platinum(II)
nitrate methylsulfanylacetate, [Pt(en)(tu)2]NO3 sa
Reaction of [Pt(en)(sa-S)(tu)] (0.016 g, 0.034 mmol)
with 0.003 g (0.016 mmol) of thiourea in 10 mL of water
gave, after 3 h, and concentration under reduced pressure,
[Pt(en)(tu)2](NO3)(sa), which was characterised by spec-
troscopy. IR, 1560 cmꢀ1 (free CO2ꢀ of sa), 1384 cmꢀ1 (io-
nic NO3). 1H MNR: d, 2.06 (s, CH3S of free saꢀ); 3.12 (s,
CH2 of saꢀ); 2.84 (b, JPt–H 40.7 Hz, CH2 of en).
H, 4.1; N, 5.5. Found: C, 45.6; H, 4.4; N, 5.4%. H
NMR: 2.65 (d, JP–H, 4.1 Hz; JPt–H, 37.2 Hz; CH3Nꢀ);
2.92 (br, CH3NH); 8.25 (br, NH). 31P NMR: 37.42 (d,
JP–P, 7.5 Hz; JPtP, 3105 Hz); 45.05 (d; JPtP, 3235 Hz).
2.3.5. Reaction of complexes a–d with
tetramethylthiourea
Solutions of the complexes (typically 0.1 mmol in 30
mL of CH2Cl2) and an excess of tetramethylthiourea
(tmtu) were left at room temperature for 2–6 h. Com-
plexes a–b were recovered unreacted; 1c, 1d, 5c and 5d
reacted slowly, with some decomposition, while 3c and
3d gave analytically pure cis-[Pt(PPh3)2(sb-O)(tmtu)]
(NO3), 11a and [Pt(dppe)(sb-O)(tmtu)](NO3), 11b,
respectively, by the addition of di-isopropyl ether to
the concentrated solutions.
2.4. X-ray data collections and structure determinations
Crystal data are summarised in Table 1; other exper-
imental details are listed in the supporting information.
The diffraction experiments were carried out on a Bru-
ker SMART CCD area-detector diffractometer at room
temperature. Crystals of 9a(NO3) gave a good diffrac-

The structures were solved by direct methods (
S
H
E
L
XS)
[33] and refined by full-matrix least-squares using all
L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
559
Table 1
Crystallographic data
2
reflections and minimising the function RwðF 2o ꢀ kF c2Þ
Compound
3a Æ H2O
9aNO3
(refinement on F2). Anisotropic thermal factors were re-
fined for all the non-hydrogen atoms. The three hydro-
gen atoms bonded to N(1) and N(2) in 9a(NO3) were
refined with fixed isotropic thermal factors. The hydro-
gen atoms of the water molecule in 3a Æ H2O were ne-
glected. The remaining hydrogen atoms were placed in
Formula
M
C52H46O5P2PtS2
1072.11
C37H33N3O3P2PtS
856.80
Color
colourless
monoclinic
P21/c
colourless
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
˚
a (A)
19.708 (2)
11.792 (1)
21.733 (2)
90
12.969 (1)
23.550 (2)
13.019 (1)
90
˚
˚
b (A)
their ideal positions (C–H = 0.97 A), with the thermal
parameter B 1.10 times that of the carbon atom to which
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
they are attached, and not refined. In the final Fourier
ꢀ3
93.73 (1)
90
118.66 (1)
90
˚
maps, the maximum residuals were 3.44(45) e A at
ꢀ3
3
˚
˚
˚
˚
1.05 Afrom Pt and 2.34(21) e A at 0.89 Afrom Pt
for 3a Æ H2O and 9aNO3, respectively. CCDC nos.
231102 and 231103 contain the supplementary crystallo-
graphic data for this paper.
U (A )
Z
5040.0 (9)
4
2152
3489.1 (4)
4
1696
F(000)
Dc (g cmꢀ3
T (K)
)
1.413
293
1.631
293
Crystal
dimensions (mm)
l(Mo Ka) (cmꢀ1
0.141 · 0.215 · 0.519 0.141 · 0.338 · 0.423
)
30.0
42.5
3. Results and discussion
Min. and max.
transmiss.
3.1. Syntheses of a and b type compounds
These compounds were obtained by the following
reactions, whose outcome shows also the preference of
Factors
Scan mode
0.476–1.00
x
0.30
0.416–1.00
x
0.30
Frame width (ꢁ)
Time per frame (s)
No. of frames
Detector-sample
distance (cm)
h-Range
15
25
2þ
2450
4.00
2450
4.00
the PtðphosÞ
fragment for O, rather than S donor
atoms (see Scheme 2):
2
3–23
full sphere
3–27
full sphere
1. Substitution of labile ligands of Pt-phosphine
complexes
cis-[Pt(NO3)2(phos)2] + 2 KL
Reciprocal space
explored
No. of reflections
(total; independent)
Rint
48195, 7274
57643, 10646
! [Pt(L-O)2(phos)2] + 2 KNO3
0.0925
0.115, 0.126
0.0362
0.056, 0.073
2. Reaction of excess Lꢀ with the chelate c–d complexes
[Pt(L-O,S)(phos)2]+ + KL ! [Pt(L-O)2(phos)2] + K+
only the sa, sb and sph c–d derivatives are available
[24,25].
Final R2 and
R2w indicesa
(F2, all reflections)
Conventional
R1 index
0.053
4487
0.029
7975
3. An alternative route to compound a is the oxidative
addition of HL to a Pt(0) derivative
[I > 2r(I)]
Reflections
[Pt(PPh3)3] + 2
HL ! cis-[Pt(L-O)2(phos)2] + H2
with I > 2r(I)
No. of variables
Goodness of fitb
559
1.25
433
1.04
Formation of dihydrogen, confirmed by gas mass
spectroscopy [28], suggests an intermediate hydrido-
PtII species, which upon reaction with a second mole
of HL yields the product and H2. We were unable to
detect such intermediate.
2
2 1=2
a
R2 ¼ ½Rðj F 2o ꢀ kF c2 j =RF o2ꢁ; R2w ¼ ½Rw=ðF o2 ꢀ kF c2Þ =RwðF 2oÞ ꢁ
.
2
1=2
2
b
½RwðF 2o ꢀ kF c2Þ =ðNo ꢀ NvÞꢁ
,
where w ¼ 4F 2o=rðF o2Þ , rðF 2oÞ ¼
½r2ðF o2Þ þ ðpF o2Þ2ꢁ1=2, No is the number of observations, Nv the number
of variables, and p, the ignorance factor, = 0.04 for both 3a Æ H2O and
9aNO3.
All ligands L gave the bi-substituted O-coordinated
compounds [Pt(L-O)2(phos)2]; 5a was obtained only in
traces, 5b was not obtained.
tion, whereas crystals of 3a Æ H2O gave a diffraction of
poor quality and within a h range limited to 21ꢁ. No
crystal decay was observed, hence no time-decay correc-
tion was needed. The collected frames were processed
with the software SAINT [29] and an empirical absorp-
tion correction was applied (SADABS) [30] to the col-
lected reflections. The calculations were performed
using the Personal Structure Determination Package
[31] and the physical constants tabulated therein [32].
3.2. Spectroscopic evidence for O-coordination of L in a
and b compounds
Infrared spectra. The carboxylato stretching frequen-
cies of compounds 1a–4a and 1b–4b are as expected
for unidentate carboxylato groups [34]. Stretching fre-
quencies of the sulfoxide groups in 2a, 4a, 2b and 4b

560
L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
phos
phos
ONO2
ONO2
Pt
+ L-,
+ 2 L-
only for sa-, sb- and sph-
(O)
SCH3
+ L-
not for L- = sph
+
Pt
phos
phos
phos
phos
O
O
O
Pt
S
CH3
SCH3
(O)
(
-
,
-
, )
1a 6a 1b 4b 6b
( , , , , , , , )
1c 3c 5c 6c 1d 3d 5d 6d
Me2SO,
or py
py
tmtu
dmso
no reaction
phos
phos
+
Pt
SCH3
O
no reaction
py
only for sb
(7a and 7b)
+
phos
phos
11a
O
SCH3
Pt
SC(NMe2)2
and
11b
+
Pt
Nadttc
Et
phos
phos
S
Nadttc
C
N
S
8b
Et
, or
8a
tu, or dmtu
tu, or dmtu
+
Pt
phos
phos
S
C
NHR
(R = CH )
10b
NR
, or
, or (R = H);
9a 9b
10a
3
Scheme 2.
are similar to those of the free anions Lꢀ, showing that
these groups are not involved in coordination.
charged Lꢀs are more tightly bound to Pt in the latter,
with consequent lowering of the Pt–P bond strength.
Compare literature data: JPt–P trans to carboxylato are
3700–3800 Hz in [Pt(dppe)(malonato-O,O0)] [36] and
3400–3500 Hz in [Pt(dppe)(phosphine)(carboxylato-
O)]+ [39].
1
In H NMR spectra, the d values of the SCH3 pro-
tons are similar to those of free Lꢀ and show neither
P–H nor Pt–H coupling, which instead we always ob-
served in the case of S-coordination of these ligands to
PtII [21–24].
Phosphorus-31 NMR spectra display one singlet,
with Pt satellites, showing equivalence of the two P
atoms. Pt–P coupling constants of 1–4, a–b are around
3600–3800 Hz, close to the values reported for cis-
[Pt(PPh3)2(RCOO-O)2] [35] and [Pt(dppe)(malonato-
O,Oꢀ)] [36]. JPt–P of the phenolato complexes 5 and 6,
are lower, as observed in similar cases [24,37,38]: alkoxo
groups are strong r donors which compete more effec-
tively with a trans phosphine [38]. The Pt–P coupling
constants in (neutral) compounds a and b are higher
than those of P trans to the carboxylato groups in (cat-
ionic) c and d, presumably because the negatively
3.3. Structure of [Pt(PPh3)2(sb-O)2]. H2O (3a Æ H2O)
O-coordination was confirmed for 3a by an X-ray
structure determination. Crystals of the monohydrate
were obtained by slow diffusion of cyclohexane into a
CH2Cl2 solution. Although the crystals were of poor
quality (see Section 2), we report this structure as a final
proof of O-coordination of Lꢀs in these complexes. An
ORTEP [40] view of the complex is shown in Fig. 1,
whose caption reports relevant bond lengths and angles.
The metal is four coordinate with two cis-triphenylphos-
phine and two cis, O-coordinated sb anions.

L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
561
3.5. Structure of [Pt(NHCSNH2)(PPh3)2]NO3,
9a(NO3)
A proof for cyclometallation of thiourea was ob-
tained by the X-ray structure determination of 9a. To
our knowledge, the only reported structures of cyclo-
metallated thioureato Pt–phosphine complexes [44,45]
are all derivatives of N-substituted thiourea
RNHCSNRꢀ and not of unsubstituted thiourea
NH2CSNHꢀ.
Crystals were obtained by cyclohexane diffusion into
a CHCl3 solution of the product of the reaction of
3c(NO3) with tu. The stꢀructure consists of the packing
of 9a cations and NO3 anions in a 1:1 molar ratio.
An ORTEP view of the cationic complex is shown in
Fig. 2, selected bond distances and angles are reported
in the Figure caption. Two cis phosphines, the sulfur
atom and the NHꢀ group of tu, complete the coordina-
tion set, which is planar with a slight square pyramidal
distortion, maximum distances from the best plane
˚
being +0.066(1) Afor Pt and ꢀ0.076(3) for S. The Pt–
P(1) bond (trans to S) is longer than Pt–P(2) and, is in
a range normal for PPh3 trans to S (thiourea) [44–46].
The Pt–S and Pt–N bond distances are also comparable
to those of N-substituted thioureato complexes, showing
that substitution at the N position of thiourea does not
affect the bonding ability of the deprotonated thioamido
group in an appreciable way.
Fig. 1. ORTEP view of [Pt(PPh3)2(sb-O)2]. H2O (3a Æ H2O). Selected
bond distances (A) and angles (ꢁ): Pt–P(1), 2.227(3); Pt–P(2), 2.269(3);
Pt–O(1), 2.049(6); Pt–O(2), 2.080(6). P(1)–Pt–P(2), 98.1(1); P(1)–Pt–
O(1), 173.9(2); P(1)–Pt–O(2), 90.6(2); P(2)–Pt–O(1), 85.3(2); P(2)–Pt–
O(2), 171.2(2); O(1)–PtO(2), 85.9(2).
˚
3.4. Stability and reactivity studies
Having observed the preference of the cis-PtII(phos)2
moieties for O rather than S donor atoms, shown by the
above results, we wanted to look at the stability of such
Pt–O bonds in the presence of other ligands, by per-
forming the reactions summarised in Scheme 2.
Compounds a–b are recovered unreacted in the pres-
ence of either Me2SO or pyridine. As for c–d, only 3c
and 3d reacted, and only with pyridine, yielding [Pt(L-
O)(phos)2(py)]+ (7a and 7b).
Substitution of the Pt–O bonds was achieved only
with reagents capable of forming stable chelate rinꢀgs
with Pt(II). Thus, N,N0 diethyldithiocarbamate (dttc )
reacts with all compounds a–d yielding the known
[41,42] [Pt(dttc)(phos)2]+, 8a and 8b. Moreover, also
thiourea (tu) and N,N0-dimethylthiourea react with
compounds a–d forming the cyclometallated derivatives
[Pt(phos)2(NRCSNHR)]+ (R = H, 9a and 9b or
R = CH3, 10a and 10b), with a deprotonated thioamido
group, characterised by comparison of spectral data
with those of similar complexes [43–45]. Tetrame-
thylthiourea (tmtu), which does not form cyclometalla-
tion under these conditions, reacts only with 3c and 3d
giving [Pt(phos)2(sb-O)(tmtu)]+, 11a and 11b, again with
retention in the Pt–O bonds.
˚
Fig. 2. ORTEP view of 9a(NO3). Selected bond distances (A) and
angles (ꢁ): Pt–S, 2.363(1); Pt–P, 2.291(1); Pt–P(2), 2.251(1); Pt–N(1),
2.058(2). S–Pt-P(1), 160.40(2); S–Pt–P(2), 97.86(3); S–Pt–N(1), 68.94;
P(1)–Pt–P(2), 100.37(3); P(1)–Pt–N(1), 92.66(8); P(2)–Pt–N(1),
166.79(8).

562
L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
S
S
Et2N
Pt
NEt2
S
S
dttc-
NH2
NH2
(O)
Me
S
C
H2N
H2N
S
Pt
O
Me(O)S O-
GMP
no reaction for sph
(O)
Me
(O)
Me
H2N
H2N
S
(O)
O
H2N
H2N
Me
S
O
stable
for sa
Pt
H2N
H2N
S
O
Pt
S
C(NH2)2
NH2
GMP(N7)
Pt
S
O
usually slow
S
C
Me (O)
order of reactivity
sob>soa>soph>sb
GMP
NH2
veryunstable,
isolated only for sa
H2N
H2N
S
C(NH2)2
C(NH2)2
GMP(N7)
GMP(N7)
2+
Pt
H2N
H2N
Pt
S
these reactions occur
also with sa
Scheme 3.
3.6. Comparison with the reactivity of [Pt(en)2(L-
O,S)]+
chelate ring is overcome by the preference for O-
coordination.
The reactivity of these complexes [21–24] is summar-
ised in Scheme 3, which reports also the reactions with
dttcꢀ and thiourea, performed for comparison purposes.
The [Pt(L-O,S)(NH3)2]+ derivatives are not included,
since they easily lose the amino ligands [24] and are
therefore unsuitable for comparison.
A first difference with the phosphine complexes is
that upon reaction with nucleophiles (Nu), like
GMP, tu, as well as an excess of Lꢀ, chelate ring
opening of L occurs at the Pt–O bond, with formation
of [Pt(en)(L-S)(Nu)]. In these species, the Pt–S bonds
are little reactive, thus, for instance, cyclometallation
of tu does not occur. A second difference is the high
stability of the chelate ring of Lꢀs in the en complexes:
the bi-substituted species [Pt(en)(L-S)2] can be ob-
served in solution, but are little stable, they lose one
L giving the chelate [Pt(en)(L-O,S)]+ [23]. On the con-
trary, in the phosphine complexes, the stability of the
4. Conclusions
By using the ligands presented here, we have shown
that if the PtII(phos)2 fragment has the possibility of
choosing between O and S coordination, the former is
preferred. The Pt–O bonds thus formed are reluctant
to substitution, since they react only with reagents which
form very stable chelate rings with PtII.
Among the factors which can contribute to the pref-
erence of such a cis-PtO2P2 coordination set, one can
envisage steric requirements: O-coordination of Lꢀs is
less sterically demanding than S-coordination, a factor
that is more important with phenylphosphine than with
en complexes. Steric hindrance has indeed been pro-
posed [17] to be the origin of O-coordination of Me2SO
in cis-[Pt(Me2SO-O)2(PPh3)2]2+, but in the case of the
less sterically demanding [Pt(Me2SO)2(PMe3)2] the re-

L. Battan et al. / Inorganica Chimica Acta 358 (2005) 555–564
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Crystallographic data have been deposited with the
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1
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