Influence of the terminal ligands on the redox properties of the {Pt 2(μ-S)2} core in [Pt2(Ph 2X(CH2)2XPh2)2(μ-S) 2] (X = P or As) complexes and on their reactivity towards metal centres, protic acids and organic electrophiles

Article abstract of DOI:10.1039/b502196k

In order to explore possible ways for modulating the unusually rich chemistry shown by complexes of formula [L₂Pt(μ-S) ₂PtL₂] we have studied the influence of the nature of the terminal ligand L on the chemical properties of the {Pt₂(μ-S) ₂} core. The systematic study we now report allows comparison of the behaviour of [Pt₂(dpae)₂(μ-S)₂] (dpae = Ph₂As(CH₂)₂AsPh₂) (1) with the already reported analogue [Pt₂(dppe)₂(μ-S)₂] (dppe = Ph₂P(CH₂)₂PPh₂). Complex 1 as well as the corresponding multimetallic derivatives [Pt(dpae){Pt ₂(dpae)₂(μ-S)₂}](BPh₄) ₂ 2, [M{Pt₂(dpae)₂(μ-S)₂} ₂]X₂ (M = Cu^II, X = BF₄ 3; M = Zn^II, X = BPh₄ 4; M = Cd^II, X = ClO₄ 5; M = Hg^II, X = Cl 6 or X₂ = Cl_1.5[HCl ₂]_0.5 6′) have been characterized in the solid phase and in solution. Comparison of structural parameters of 1 and 3-6′ with those of the corresponding phosphine analogues, together with the results of the electrochemical study for 1, allow us to conclude that replacement of dppe by dpae causes a decrease in basicity of the {Pt₂(μ-S)₂} core. The study of the reactivity of 1 towards CH₂Cl₂ and protic acids has led to the structural characterization of [Pt(dpae)(S ₂CH₂)] 9 and [PtCl₂(dpae)] 10. Moreover, comparison with the reactivity of [Pt₂(dppe)₂(μ-S) ₂] indicates that the stability of the intermediate species as well as the nature of the final products in both multistep reactions are sensitive to the nature of the terminal ligand. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b502196k

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F U L L P A P E R
Influence of the terminal ligands on the redox properties of the
{Pt2(l-S)2} core in [Pt2(Ph2X(CH2)2XPh2)2(l-S)2] (X = P or As)
complexes and on their reactivity towards metal centres, protic acids
and organic electrophiles
Fernando Novio, Rube´n Mas-Balleste´, Iluminada Gallardo, Pilar Gonza´lez-Duarte,*
Agust´ı Lledo´s* and Neus Vila
Departament de Qu´ımica, Universitat Auto`noma de Barcelona, E-08193, Bellaterra, Barcelona,
Spain. E-mail: Pilar.Gonzalez.Duarte@uab.es, agusti@klingon.uab.es; Fax: (+34)935813101;
Tel: (+34)935811363
Received 15th February 2005, Accepted 28th June 2005
First published as an Advance Article on the web 11th July 2005
In order to explore possible ways for modulating the unusually rich chemistry shown by complexes of formula
[L2Pt(l-S)2PtL2] we have studied the influence of the nature of the terminal ligand L on the chemical properties of the
{Pt2(l-S)2} core. The systematic study we now report allows comparison of the behaviour of [Pt2(dpae)2(l-S)2]
(dpae = Ph2As(CH2)2AsPh2) (1) with the already reported analogue [Pt2(dppe)2(l-S)2] (dppe = Ph2P(CH2)2PPh2).
Complex 1 as well as the corresponding multimetallic derivatives [Pt(dpae){Pt2(dpae)2(l-S)2}](BPh4)2 2,
[M{Pt2(dpae)2(l-S)2}2]X2 (M = CuII, X = BF4 3; M = ZnII, X = BPh4 4; M = CdII, X = ClO4 5; M = HgII, X = Cl 6
or X2 = Cl1.5[HCl2]0.5 6ꢀ) have been characterized in the solid phase and in solution. Comparison of structural
parameters of 1 and 3–6ꢀ with those of the corresponding phosphine analogues, together with the results of the
electrochemical study for 1, allow us to conclude that replacement of dppe by dpae causes a decrease in basicity of
the {Pt2(l-S)2} core. The study of the reactivity of 1 towards CH2Cl2 and protic acids has led to the structural
characterization of [Pt(dpae)(S2CH2)] 9 and [PtCl2(dpae)] 10. Moreover, comparison with the reactivity of
[Pt2(dppe)2(l-S)2] indicates that the stability of the intermediate species as well as the nature of the final products in
both multistep reactions are sensitive to the nature of the terminal ligand.
energy as well as the ligand to metal charge transfer are highly
Introduction
dependent on the nature of the donor atom, P or As.15
The high nucleophilicity of the bridging sulfido ligands of
We herein report the synthesis, structural characterization
the {Pt2S2} core in [L2Pt(l-S)2PtL2] compounds accounts
and electrochemical behaviour of [Pt2(dpae)2(l-S)2] 1, where
for their rich reaction chemistry in the presence of a wide
dpae denotes 1,2-bis(diphenylarsino)ethane, and its reactivity
range of electrophilic species.1,2 In this context, we ex-
plored by means of experimental data and theoretical cal-
towards the same chemical species as those already studied
with [Pt2(dppe)2(l-S)2] under similar experimental conditions. A
comparative analysis of both sets of results shows that the change
of the donor atom, P or As, in comparable terminal ligands can
be taken as a good strategy for modulating the nucleophilicity
of the {Pt2S2} core.
culations the redox properties of complexes [Pt2(P∩P)2(l-S)2],
where P∩P = 1,2-bis(diphenylphosphino)ethane (dppe) or 1,3-
bis(diphenylphosphino)propane (dppp),3 their reactivity to-
wards organic electrophiles,4 protic acids5 and metal centres,6
as well as the influence of the {Pt2S2} core on the reactivity
of organic or inorganic Lꢀ ligands in [MLꢀy{L2Pt(l3-S)2PtL2}x]z
aggregates.7 Remarkably, all reported studies on the chemistry
of the {Pt2S2} core have been carried out using [L2Pt(l-S)2PtL2]
compounds where the terminal ligands are unidentate (L) or
bidentate (L2) phosphines.
Experimental
Materials and methods
All the manipulations were carried out at room temperature
under an atmosphere of pure dinitrogen, and conventionally
dried and degassed solvents were used throughout. These were
Purex Analytical Grade from SDS. Complex [PtCl2(dpae)] was
obtained by replacing dppe with dpae in the procedure reported
for the synthesis of the dppe analogue.6b
Elemental analyses were performed on a Carlo-Erba CHNS
EA-1108 analyzer. Microanalytical data for 2 have been omitted
because those referring to the carbon content were unsatisfac-
tory, as already reported in some related phosphine platinum
complexes.7a All complexes have been characterized by ESI-MS,
NMR and, when single crystals were available, by X-ray diffrac-
tion data. The ESI-MS measurements were performed on a VG
Quattro Micromass Instrument. The experimental conditions
were as follows: 10 ll of sample injected at 15 ll min−1; capillary-
counter electrode voltage, 4.5 kV; lens-counter electrode voltage
1.0 kV; cone potential, 55 V; source temperature, 90 ◦C; m/z
range, 300 to 1600. The carrier was a 1 : 1 acetonitrile/water
mixture or methanol containing formic acid (1%–20%).
Transition metal complexes containing phosphine ligands
have been the objects of intense study.8 Interest in this family of
complexes has been mainly fuelled by the diverse coordination
features offered by phosphine ligands, by the possibility of
tuning their steric and electronic properties, and by the use of
phosphine complexes in various catalytic reactions.9 Remark-
ably, whereas the first metal complexes containing arsine ligands
were reported well over 100 years ago, the development of arsine
coordination chemistry has received much less attention than its
phosphine analogue.10 The suitability of 31P nuclei for NMR
studies and the toxicity of some arsine precursors could account
for the great prevalence of phosphine complexes and also for the
scarce number of comparative studies between the phosphine
and arsine families.11 Notwithstanding this, it has been reported
that replacement of phosphine ligands by their arsine analogues
affects the acid–base,12 catalytic13 and redox14 properties of the
corresponding metal complexes. In addition, theoretical data
have revealed that the M–X (X = P or As) bond dissociation
2 7 4 2
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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of a blue solid. This suspension was kept at 4 ◦C for 30 min
and the solid filtered off, washed with diethyl ether and dried
under vacuum. Yield 84% (Found: C, 40.20; H, 3.21; S, 4.10.
Calc. for C104H96As8B2CuF8Pt4S4: C, 40.41; H, 3.13; S, 4.15%).
Slow evaporation of a saturated solution (1 : 1 ethanol/acetone
mixture) of the solid afforded violet X-ray quality crystals of the
title compound.
1
Table 1 1H NMR, 13C–{ H} NMRa and ESI-MS data for complexes
1–7 and 9–12
Compound
m/z
Calcd MW d Haliph (ppm)
1 [Pt2(dpae)2S2]
1426.7b 1426.9
1052.4c 2107.0
1458.9c 2917.4
1459.7c 2919.2
1484.4c 2966.4
1528.2c 3054.4
2.21
2.59
2 [Pt3(dpae)3S2]2+
3 [Cu{Pt2(dpae)2S2}2]2+
4 [Zn{Pt2(dpae)2S2}2]2+
5 [Cd{Pt2(dpae)2S2}2]2+
6 [Hg{Pt2(dpae)2S2}2]2+
9 [Pt(dpae)(S2CH2)]e
10 [PtCl2(dpae)]
2.41
2.39
2.45
[Zn{Pt2(dpae)2(l-S)2}2](BPh4)2 4.
A solution of ZnCl2
(0.010 g, 0.07 mmol) in 10 ml of CH3CN was added to a solution
of 1 (0.200 g, 0.14 mmol) in the same solvent (100 ml) and
the mixture stirred for 1 h. The resultant pale yellow solution
was filtered through Celite. NaBPh4 (0.050 g, 0.14 mmol) was
added to the filtrate and the NaCl thus formed filtered off and
the filtrate concentrated to 5 ml. Then, addition of diethyl ether
resulted in the appearance of a pale yellow solid. This suspension
7 [Pt2(dpae)2(l-S)(l-SCH2Cl)]+ 1476.5
1475.5
759.5
752.3
760.2b
716.4d
2.39
2.55
2.38
2.43
11 [Pt2(dpae)2(l-S3(CH2)2)]2+
12 [Pt2(dpae)2(l-S)(l-SH)]+
744.1c 1486.4
f
1426.7
1427.9
a Solvents in NMR measurements: 1, 2, 9, 10, 11, 12 in d6-DMSO;
4, 5, 6 in CD3Cl. b m/z = M + 1. c m/z = M/2. d Mass of fragment
[PtCl(dpae)]+. e dH(SCH2) = 6.06 ppm; 3JPt–H(SCH2) = 40.2 Hz;
dC(SCH2) = 44.6 ppm. f dH(SCH2) = 4.16 ppm; 3JPt–H(SCH2) = 66.6 Hz;
dC(SCH2) = 23.5 ppm.
◦
was kept at 4 C for 30 min and the solid filtered off, washed
with diethyl ether and dried under vacuum. Yield 80% (Found:
C, 50.21; H, 3.72; S, 3.47. Calc. for C152H136As8B2Pt4S4Zn·4H2O:
C, 50.30; H, 3.99; S, 3.53%). Crystallization of 4 from a 1 : 1
ethanol/acetone mixture gave pale yellow crystals suitable for
X-ray diffraction.
1H and 13C–{ H} NMR spectra were recorded from samples
1
in (CD3)2SO, CDCl3 or CD3OD solutions at room temperature,
unless otherwise indicated, using a Bruker AC250 spectrometer.
1H and 13C chemical shifts are relative to SiMe4. ESI-MS and
[Cd{Pt2(dpae)2(l-S)2}2](ClO4)2 5. Cd(ClO4)2·6H2O (0.035 g,
0,07 mmol) was added to a CH3CN solution (100 ml) containing
1 (0.200 g, 0.14 mmol). After 1 hour of stirring the solution was
concentrated to 5 ml to which addition of diethyl ether resulted
in the appearance of a pale yellow solid. This suspension was
1H and 13C–{ H} NMR data for the synthesized complexes 1–
1
6, 9, 10 as well as for the detected species 7, 11 (Scheme 3)
and 12 (Scheme 4) are given in Table 1. 113Cd–{ H} (300 MHz,
1
◦
kept at 4 C for 30 min and the solid filtered off, washed with
1
(CD3)2SO) and 199Hg–{ H} (500 MHz, CD3OD) NMR spectra
diethyl ether and dried under vacuum. Yield 80% (Found: C,
39.90; H, 3.12; S, 4.19. Calc. for C104H96As8CdCl2O8Pt4S4: C,
39.46; H, 3.06; S, 4.05%). Crystals suitable for X-ray diffraction
were obtained by slow evaporation of 5 in a 1 : 1 ethanol/acetone
mixture.
were recorded at 66.5 and 89.5 MHz, respectively. 113Cd chemical
shifts are relative to external 0.1 mol dm−3 Cd(NO3)2 aqueous
solutions, 199Hg to external HgMe2 in D2O. The 113Cd–{ H} and
1
199Hg–{ H} spectra were simulated on a Pentium-200 computer
1
using the gNMR V4.0.1 program.16
[Hg{Pt2(dpae)2(l-S)2}2]Cl2 6. A solution of HgCl2 (0.019 g,
0.07) in 10 mL of CH3CN was added to a CH3CN solution
(100 ml) containing 1 (0.200 g, 0.14 mmol). After 1 h of stirring
the pale green solution was concentrated. Addition of diethyl
ether resulted in the appearance of a pale yellow solid. This
Further characterization of 3 in CH3CN solution was per-
formed by means of EPR (Bruker ESP 300, at room temperature
or at 113 K) and UV-Vis-NIR (SHIMADZU UV-3101PC, 200–
1500 nm) measurements.
In order to achieve a pure product with maximum yield in
the synthesis of 1, 2, 9 and 10 the reaction time was fixed after
monitoring the reaction by 1H NMR.6
◦
suspension was kept at 4 C for 30 min and filtered. The solid
was washed with diethyl ether and dried under vacuum. Yield
80% (Found: C, 40.50; H, 3.22; S, 3.99. Calc. for C104H96As8Cl2-
HgPt4S4: C, 39.97; H, 3.10; S, 4.10). Slow evaporation of a
concentrated solution of 6 in a 1:1 ethanol/acetone mixture
afforded yellow crystals of [Hg{Pt2(dpae)2(l-S)2}2]Cl1.5[HCl2]0.5
(6ꢀ). The presence of the [Cl–H–Cl]− anion as counterion is
precedented in bis(aminophosphine) complexes of platinum.17
Preparations
[Pt2(dpae)2(l-S)2] 1. [PtCl2(dpae)] (0.250 g, 0.33 mmol) was
added to a suspension of Na2S·9H2O (0.150 g, 0.62 mmol) in
benzene (75 ml) and the mixture stirred at room temperature for
8 h. The excess of Na2S·9H2O, the NaCl formed, and the unre-
acted [PtCl2(dpae)] were filtered off. Removal of the solvent from
the filtrate under vacuum yielded an orange solid. Yield 80%
(Found: C, 43.26; H, 3.45; S, 5.02. Calc. for C52H48As4Pt2S2: C,
43.77; H, 3.39; S, 4.49%). X-Ray quality crystals were obtained
by slow evaporation of a saturated solution of 1 in benzene.
[Pt(dpae)(S2CH2)] 9. CH2Cl2 (0.5 ml, 7.8 mmol) and
[PtCl2(dpae)] (0.100 g, 0.13 mmol) were subsequently added to a
suspension of Na2S·9H2O (0.080 g, 0.33 mmol) in benzene. After
6 h of stirring the excess of Na2S·9H2O and the NaCl formed
were filtered off. The filtrate was concentrated to dryness giving a
yellow solid. Yield 70% (Found: C, 43,30; H, 3.60; S, 8,21. Calc.
for C27H26As2PtS2: C, 42.70; H, 3.45; S, 8.44%). Crystallization
of 9 from acetonitrile yielded yellow X-ray quality crystals.
[Pt3(dpae)3(l3-S)2](BPh4)2 2. [PtCl2(dpae)] (0.106 g,
0.14 mmol) was added stepwise to a CH3CN solution of
1 (0.200 g, 0.14 mmol) and the mixture stirred at room
temperature for 24 h. The resulting solution was filtered
through Celite. Addition of NaBPh4 (0.096 g, 0.28 mmol) to
the filtrate caused formation of NaCl that was filtered off. The
solvent was removed from the filtrate under vacuum to yield
the title compound as a yellow solid. Yield 75%. X-Ray quality
crystals were obtained by slow evaporation of a saturated
solution of 2 in DMSO.
[PtCl2(dpae)] 10. To a solution of [PtCl2(cod)] (0.190 g,
0.51 mmol) in CH2Cl2 (50 ml) solid dpae (0.250 g, 0.51 mmol)
was added and the mixture stirred at room temperature for 3 h.
Then, the suspension was filtered and the solid was washed
with diethyl ether and vacuum dried. Yield 88% (Found: C,
41.76; H, 3.15. Calc. for C26H24As2Cl2Pt: C, 41.51; H, 3.21%).
Recrystallization from acetone gave colourless crystals of 10
suitable for X-ray diffraction.
[Cu{Pt2(dpae)2(l-S)2}2](BF4)2 3. A solution of Cu(BF4)2·
6H2O (0.024 g, 0.07 mmol) in 10 ml of CH3CN was added
to a solution of 1 (0.200 g, 0.14 mmol) in the same solvent
(100 ml) and the mixture stirred for 1 h. The resultant blue
solution was filtered through Celite and the filtrate concentrated
to 5 ml. Addition of diethyl ether resulted in the appearance
Reactivity of 1 towards non-metallic electrophiles
Protic acids. To analyze the evolution of 1 in the presence
of protons as a function of time as well as the corresponding re-
action pathway an already published procedure was followed.5b
In this case controlled amounts of either concentrated or 2 M
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
2 7 4 3

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solutions of HCl or HClO4 were added with stirring at room
temperature to a solution of 1 in 5–10 ml of CH3CN. An aliquot
of this solution was removed at different times, evaporated to
dryness and the solid obtained characterized by 1H NMR in d6-
DMSO and by ESI-MS data. The moles of acid added ranged
between 1 and 40 times those of 1, whose initial concentration
usually was 3.5 mM. Under these experimental conditions the
reaction of 1 with protons progresses too rapidly to enable the
analysis of the influence of the time variable. Overall, the nature
and relative amounts of the reaction products are mainly deter-
mined by the number of equivalents added of HCl or HClO4.
Organic electrophiles. The reaction of 1 with CH2Cl2 was
followed similarly to that of the [Pt2(dppe)2(l-S)2] analogue.4
Thus, aliquots taken at different times from a 1.4 mM solution
of 1 in CH2Cl2 at room temperature were evaporated to dryness,
1
and the 1H and 13C–{ H} NMR (both in d6-DMSO), as well as
the ESI-MS spectra of the solid residue were recorded. These
data showed that after 15 min of exposure to CH2Cl2 compound
1 has fully evolved to 9 and 10. After 12 h the concentration of
9 shows a significant decrease with the concomitant formation
of a new species, probably [Pt2(dpae)2(l-S3(CH2)2)]Cl2 (11), only
partially characterized. After several weeks, the initial solution
contains mainly 10 and 11 with a small amount of 9.
In order to confirm that 11 comes from the reaction of 9 with
CH2Cl2 a pure sample of 9 (0.050 g, 0.07 mmol) was added
with stirring to CH2Cl2 (5 ml). After 30 days the solution was
evaporated to dryness, the solid residue dissolved in toluene and
the filtered solution concentrated to yield a pale yellow solid.
Characterization of this solid by 1H and 13C NMR and by ESI-
MS data indicated that it consists of a mixture of 9 and 11 at a
15 : 85 mole ratio.
Oxidation of 1 with 4-nitrobenzenediazonium tetrafluoroborate
A
solution of 4-nitrobenzenediazonium tetrafluoroborate
(0.017 g, 0.07 mmol) in CH3CN was added dropwise to a CH3CN
solution of 1 (0.100 g, 0.07 mmol) in an ice/water bath and
the mixture stirred for 10 min. The solution was filtered and
the filtrate concentrated to dryness giving a brown solid. This
was dissolved in methanol, and addition of NaBPh4 (0.032 g,
0.09 mmol) to the solution afforded a yellow solid that was fil-
tered off, washed with diethyl ether and vacuum dried. 1H NMR
and ESI-MS data are fully consistent with the isolated solid
being the already characterized complex 2 with an 85% yield.
Electrochemical measurements
Cyclic voltammograms were carried out at room temperature
in an electrochemical conical cell which can be used for three
electrodes. For cyclic voltammetry experiments, the working
electrode was in all cases a glassy carbon disc of 0.5 mm
diameter. This was polished by using a 1 lm diamond paste.
The counter electrode was a platinum disc of 1 mm diameter.
All the potentials are reported vs. an aqueous saturated calomel
electrode isolated from the working electrode compartment by
a salt bridge. The cyclic voltammetry apparatus was composed
of a home-built-solid-state amplifier potentiostat with positive
feedback iR drop compensation and a Tacussel GSTP 4
generator. The voltammograms were displayed on a Tektronix
(2212). Electrolyses were carried out in the same electrochemical
cell as the cyclic voltammetry experiments using a PAR 273A
potentiostat. A graphite rod was used as the working electrode
and a platinum wire as a counter electrode isolated from the
anodic compartment.
X-Ray crystallographic characterization of complexes 1–6ꢀ, 9
and 10
A summary of crystal data, data collection, and refinement
parameters for the structural analyses of the title complexes
is given in Table 2. Measurements of diffraction intensity data
2 7 4 4
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3

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◦
˚
Table 3 Selected distances (A) and angles ( ) for [Pt2(dpae)2(l-S)2] (1)
were collected on a Bruker SMART CCD-1000 area-detector
and [Pt2(dppe)2(l-S)2].6a Average values are given in parentheses
diffractometer with grafite-monochromated Mo-Ka radiation
˚
(k = 0.71073 A). Absorption correction was carried out by
[Pt2(dpae)2(l-S)2] (1)
[Pt2(dppe)2(l-S)2]
semiempirical methods based on redundant and symmetry-
equivalent reflections with the aid of the SADABS program.18
Cell parameters were obtained from a least-squares fit on the
observed setting angles of all significant intensity reflections.
The structures were resolved by direct methods and refined by
full-matrix least-squares based on F2, with the aid of SHELX-
97 software.19 All non-hydrogen atoms were anisotropically
refined except for the lightest atoms in 5. Hydrogen atoms
were included at geometrically calculated positions with thermal
parameters derived from the parent atoms. Molecular graphics
are represented by Ortep-3 for Windows.
Pt–S
2.332
2.319
2.333
2.315
(2.324)
2.351
2.371
2.353
2.367
(2.360)
3.101
3.252
2.358
2.341
2.344
2.355
(2.349)
2.232
2.254
2.238
2.254
(2.245)
3.134
3.292
Pt–Xb
S–S
Pt–Pt
In compound 4 the solvent molecules appear to be highly
disordered thus hampering the reliable modelling of its position
and distribution. Therefore, the SQUEEZE function20 was used
to eliminate from the measured intensity data the contribution of
the electron density in the disordered solvent region and thus the
solvent-free data was employed in the final refinement. The unit
S–Pt–S
X–Pt–Xb
ha
83.65
83.70
(83.67)
86.22
85.38
(85.80)
139.75
83.62
83.73
(83.67)
86.64
85.81
(86.22)
140.18
cell contains four cavities located at (−0.052, −0.052, 0.000) and
3
˚
symmetry-related positions. The volume of each cavity is 840 A
and contains 390 electrons.
a Dihedral angle between two {PtS2} planes. b X = As in dpae and P in
CCDC reference numbers 262977 (1), 262978 (10), 262979 (3),
262980 (4), 262981 (6ꢀ), 263121 (9), 263122 (5) and 263123 (2).
See http://dx.doi.org/10.1039/b502196k for crystallographic
data in CIF or other electronic format.
dppe.
Computational details
Calculations were performed with the GAUSSIAN 98 series
of programs.21 Density functional theory (DFT) was applied
with the B3LYP functional.22 Effective core potentials (ECP)
were used to represent the innermost electrons of the platinum
atom23a as well as the electron core of the As and S atoms.23b The
basis set for Pt was that associated with the pseudopotential,
with a standard double-f LANL2DZ contraction.21 The basis
set for the As and S atoms was that associated with the pseu-
dopotential, with a standard double-f LANL2DZ contraction21
supplemented with a set of d-polarization functions.24 A 6-31G
basis set was used for the C and H atoms.25 Solvent effects were
taken into account by means of polarizable continuum model
(PCM) calculations26 using standard options of PCM and cavity
keywords.21 Free solvation energies were calculated with CH2Cl2
(e = 8.93) or CH3CN (e = 36.64) as solvent, keeping the geometry
optimised for the isolated species (single-point calculations).
Fig. 1 Molecular structure of complex 1 with key atoms labelled and
50% probability ellipsoids.
˚
ligands, (d(Pt–S) = 2.398 A for [Pt2(H2P(CH2)2PH2)2(l-S)2] and
˚
d(Pt–S) = 2.375 A for [Pt2(H2As(CH2)2AsH2)2(l-S)2]). Calculated
structural parameters are given in Table 8.
Results and discussion
Theoretical and experimental structural data indicate that
the longer Pt–X distance for X = As (if compared to X = P)
entails a weaker Pt–X interaction and, as a consequence, a lower
trans influence, which is evidenced by the decrease in the Pt–S
distances. This trend has also been observed in the literature for
the set of complexes cis-[PtCl2(XPh3)2]27 and cis-[PtCl2(XEt3)2]28
(X = P, As), where the Pt–Cl distances are lower for X = As.
Molecular structure of [Pt2(dpae)2(l-S)2] (1)
The synthetic procedure followed to obtain metalloligand 1 was
similar to that of [Pt2(dppe)2(l-S)2].6a In the present case, the
observed sensitivity of the chemical shift corresponding to the
arsine CH2 groups with regard to the nature of the complex
1
species allowed the reaction to be monitored by H NMR and
thus enabled determination of the optimum reaction time for a
Compound [Pt2(dpae)2(l-S)2] (1) as metalloligand to metal
centres
maximum yield. Complex 1 has been characterized by ESI-MS
1
and H NMR data (Table 1). X-Ray diffraction of 1 (Fig. 1)
constitutes the first example of a complex of formula [Pt2L4(l-
S)2] (L = phosphine) to be structurally characterized.
The reaction of 1 with [PtCl2(dpae)] and NaBPh4 afforded
the trinuclear complex [Pt3(dpae)3(l3-S)2](BPh4)2 (2), and with
various divalent cations led to pentanuclear species of general
formula [M{Pt2(dpae)2(l-S)2}2]2+ (M = Cu 3, Zn 4, Cd 5, and
Hg 6), by similar procedures to those already described for the
corresponding phosphine analogues.6 Complexes 2–6 have been
characterized by ESI-MS and 1H NMR data (Table 1) and X-ray
diffraction (Tables 4 and 5).
The EPR spectrum of 3 in CH3CN solution at room tem-
perature displays a signal at giso = 2.062 and the hyperfine
coupling constant to the copper ion (I = 3/2) Aiso is 58.5 ×
10−4 cm−1. The electronic spectrum of this complex in the same
Comparison between the geometric parameters of
[Pt2(dppe)2(l-S)2] and [Pt2(dpae)2(l-S)2] (1) (Table 3) provides
the first evidence of the effect of replacing phosphorus by arsenic
as donor atom. One difference between the structures consists
of an increase in the Pt–X distances when X = As with respect
to that observed for X = P. An additional structural variation
˚
is observed in the Pt–S distances that average 2.349 A in
˚
[Pt2(dppe)2(l-S)2] and 2.324 A in [Pt2(dpae)2(l-S)2] (1). Similar
variations have been found by means of DFT calculations using
H2P(CH2)2PH2 (dhpe)3 and H2As(CH2)2AsH2 (dhae) as model
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
2 7 4 5

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◦
ꢀ
˚
Table 4 Selected distances (A) and angles ( ) for complexes 3–6
3 (M = Cu)
4 (M = Zn)
5 (M = Cd)
6ꢀ (M = Hg)
M–S
Pt–S
2.351(3), 2.331(4)
2.327(4), 2.325(4)
2.347(4), 2.343(3)
2.340(3), 2.326(3)
2.347(3), 2.332(3)
2.352(4), 2.338(4)
2.371(15), 2.364(15)
2.366(14), 2.364(14)
2.367(16), 2.357(14)
2.369(17), 2.360(14)
2.378(3), 2.378(3)
2.377(3), 2.377(3)
2.352(3), 2.353(2)
2.353(2), 2.352(3)
2.350(2), 2.346(3)
2.350(2), 2.346(3)
2.361(11), 2.357(11)
2.361(11), 2.357(11)
2.354(11), 2.347(12)
2.354(11), 2.347(12)
2.573(4), 2.570(4)
2.569(4), 2.560(3)
2.349(3), 2.352(3)
2.337(4), 2.339(4)
2.357(4), 2.338(4)
2.346(4), 2.349(4)
2.355(17), 2.356(17)
2.360(2), 2.358(2)
2.344(15), 2.356(16)
2.357(17), 2.347(16)
2.458(3), 2.466(3)
2.783(3), 2.902(3)
2.337(3), 2.349(3)
2.353(3), 2.374(3)
2.354(3), 2.378(3)
2.332(3), 2.346(3)
2.353(12), 2.369(13)
2.364(13), 2.382(12)
2.364(13), 2.369(12)
2.369(12), 2.371(13)
Pt–As
S–M–S a
81.52(12), 81.85(13)
108.30(13), 147.76(14)
146.84(14), 106.97(13)
81.75(11), 81.30(12)
81.24(11), 81.28(12)
85.24(5), 85.16(5)
82.72(13), 82.62(14)
135.49(9), 135.49(9)
114.49(8), 114.49(8)
83.87(10), 83.84(10)
83.87(10), 83.84(10)
85.97(4), 85.97(4)
76.00(11), 75.62(12)
117.32(12), 146.16(12)
148.01(12), 110.30(12)
84.36(13), 84.70(12)
84.34(13), 84.67(12)
86.44(6), 85.52(8)
73.82(9), 71.22(8)
111.37(9), 168.75(9)
133.10(8), 112.90(9)
84.77(10), 83.43(9)
83.73(10), 84.50(9)
85.20(4), 85.55(4)
84.96(4), 84.88(4)
b
S–M–Sꢀ
S–Pt–S
As–Pt–As
85.35(7), 84.99(5)
85.87(4), 85.87(4)
86.33(5), 85.55(6)
a The two S atoms belong to the same {Pt2S2} core. b The two S atoms belong to different {Pt2S2} cores.
◦
data are consistent with the 113Cd and 199Hg NMR features found
for the dppe analogue.6b
˚
Table 5 Selected distances (A) and angles ( ) for complexes 2, 9 and 10
Complex 2
The structure of 2 that consists of discrete trinuclear
[Pt3(dpae)3(l-S)2]2+ cations (Fig. 2) can be described similarly to
that of the previously reported dppe analogue.6b The structure
of the cations in complexes 3, 4 and 5 can be considered as
formed by two [Pt2(dpae)2(l-S)2] metalloligands linked through
sulfur to the heterometal Cu, Zn or Cd, which shows a distorted
tetrahedral coordination (Fig. 3). In 3 for each cation there are
Pt(1)–S(1)
Pt(2)–S(1)
Pt(3)–S(1)
Pt(1)–As(1)
Pt(2)–As(3)
Pt(3)–As(5)
S(1)–S(2)
2.335(11)
2.343(11)
2.326(11)
2.351(6)
2.350(7)
2.355(6)
3.052
Pt(1)–S(2)
Pt(2)–S(2)
Pt(3)–S(2)
Pt(1)–As(2)
Pt(2)–As(4)
Pt(3)–As(6)
Pt(1)–Pt(2)
Pt(2)–Pt(3)
2.365(11)
2.360(12)
2.367(12)
2.360(6)
2.361(6)
2.363(6)
3.048(5)
3.061(5)
Pt(1)–Pt(3)
3.168(5)
−
two BF4 anions, one ethanol and one water molecule. One
of the anions is disordered over three different positions with
populations of 0.50, 0.25 and 0.25, respectively. In 5, one of the
two perchlorate anions is disordered in two different positions,
each with 50% population.
S(1)–Pt(1)–S(2)
S(1)–Pt(3)–S(2)
80.96(4)
81.13(4)
S(1)–Pt(2)–S(2)
As(1)–Pt(1)–As(2)
As(5)–Pt(3)–As(6)
80.91(4)
84.59(18)
85.12(19)
As(3)–Pt(2)–As(4) 85.68(17)
h a = 120.00
Complex 9
Pt(1)–S(1)
Pt(1)–As(1)
S(1)–C(1)
S(1)–S(2)
2.291(3)
2.367(10)
1.875(16)
2.932
Pt(1)–S(2)
Pt(1)–As(2)
S(2)–C(1)
2.304(2)
2.375(10)
1.969(17)
S(1)–C(1)–S(2)
Pt(1)–S(1)–C(1)
S(1)–Pt(1)–S(2)
99.40(7)
89.60(5)
79.31(11)
As(1)–Pt–As(2)
Pt(2)–S(2)–C(1)
85.19(3)
91.60(5)
Complex 10
Pt(1)–Cl(1)
Pt(1)–As(1)
2.336(14)
2.333(7)
Pt(1)–Cl(2)
Pt(1)–As(2)
2.344(13)
2.335(7)
Cl(1)–Pt(1)–Cl(2)
90.23(5)
As(1)–Pt(1)–As(2)
86.36(2)
a Dihedral angle between two {PtS2} planes.
solvent shows a very broad band with maximum intensity at
m1 = 8550 cm−1 (1170 nm, e = 720 dm3 mol−1 cm−1), a band at
m2 = 17360 cm−1 (576 nm, e = 5300 dm3 mol−1 cm−1) and a very
strong absorption between 27000–50000 cm−1 (360–200 nm, e >
30000 dm3 mol−1 cm−1). The magnetic and spectroscopic features
of complex 3, which are very close to those found for the dppe
analogue, are consistent with a distorted tetrahedral geometry
about the heterometal and confirm that it is a copper(II) rather
than a copper(I) ion.6a
Fig. 2 Structure of the cation in complex 2 with 50% probability
displacement ellipsoids and selected atoms labels.
Comparison between the structure of phosphine and arsine
containing pentametallic cations (Table 6) provides further
evidence of the influence of the nature of the donor atom,
P or As, on the chemical properties of the {Pt2S2} core.
Thus, the longer M–S distances observed in the pentanuclear
[M{Pt2(dpae)2(l-S)2}2]2+ cations indicate a minor coordinating
ability for the {Pt2(l-S)2} core. These findings corroborate that
1
Concerning complexes 5 and 6, the 113Cd–{ H} NMR spec-
1
trum of 5 in d6-DMSO and the 199Hg–{ H} NMR spectrum of
6 in CD3OD display a quintet centred at d = 467 ppm and
−1048 ppm respectively, as expected if disregarding the less
intense bands of the theoretical splitting due to coupling with
four platinum nuclei (2JPt–Cd = 213 Hz, 2JPt–Hg = 330 Hz). These
2 7 4 6
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3

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◦
2+
˚
Table 6 Comparison of average bond lengths (A) and angles ( ) for analogue [M{Pt2(Ph2X(CH2)2XPh2)2(l-S)2}] complexes, X = As, P
M = Cu (3)
X = As
M = Cua
X = P
M = Zn (4)
X = As
M = Znb,c
X = P
M = Cd (5)
X = As
M = Cdb
X = P
M = Hg (6ꢀ)
M = Hgb
X = P
X = As
M–S
Pt–S
Pt–X
S–S
2.333
2.341
2.365
3.052
3.178
2.314
2.365
2.252
3.084
3.099
2.378
2.350
2.369
3.140
3.129
2.386
2.372
2.262
3.117
3.096
2.568
2.346
2.354
3.155
3.154
2.557
2.371
2.244
3.188
3.107
2.652 d
2.353
2.368
3.152
3.192
2.590
2.370
2.247
3.178
3.125
Pt–Pt
S–M–S e
81.68
127.46
81.39
85.18
127.3
51.4
83.59
125.20
81.92
85.95
119.7
60.0
82.67
124.99
83.85
85.92
127.0
70.2
81.60
125.85
82.20
85.60
120.2
67.0
75.81
130.46
84.52
85.96
135.0
56.1
77.11
128.61
84.47
85.80
124.5
66.4
72.52
131.53
84.10
85.14
132.8
56.0
75.60
130.71
84.20
86.58
125.3
53.0
f
S–M–Sꢀ
S–Pt–S
X–Pt–X
h g
x h
ꢀ
a Ref. 6a. b Ref. 6b. c Poorly diffracting crystals. d In 6 the two short and two long Hg–S distances average 2.462 and 2.842 A, respectively. e The two
S atoms belong to the same{Pt2S2} core. f The two S atoms belong to different{Pt2S2} cores. g Dihedral angle between two {PtS2} planes. h Dihedral
angle between two {MS2} planes.
˚
Fig. 4 Structure of the cation in complex 6ꢀ with 50% probability
displacement ellipsoids and selected atoms labels. Phenyl rings are
Fig. 3 Structure of the cation in complex 5 with 50% probability
omitted for clarity. Dotted lines denote the two longest Hg · · · S
displacement ellipsoids and selected atoms labels.
distances.
the changes in the electronic structure associated with the
substitution of phosphorus by arsenic entail a decrease in the
availability of the electron density on the sulfur atoms, which is
evidenced by weaker M–S interactions.
widening of the signals with decreasing temperature is consistent
with the occurrence at room temperature of the dynamic process
depicted in Scheme 1.
An additional consequence of the electronic effects accom-
panying the replacement of phosphorus by arsenic in com-
pounds [L2Pt(l-S)2PtL2] is provided by the molecular struc-
ture of the corresponding [Hg{L2Pt(l-S)2PtL2}2]2+ derivative,
which shows an essentially tetrahedral environment about Hg
in [Hg{Pt2(dppe)2(l-S)2}2]2+6b but linear with two secondary
Hg · · · S interactions in [Hg{Pt2(dpae)2(l-S)2}2]2+ (Fig. 4). On
the other hand, the X-ray analysis of 6ꢀ shows that the charge
of the latter cation is compensated by 1.5 Cl− and 0.5 [HCl2]−
anions whose association with the water and ethanol molecules
via hydrogen bonding gives rise to two different units.
Scheme 1
Redox properties
1
The 199Hg–{ H} NMR data at room temperature for complex
In order to explore the redox behaviour of 1, as well as
the influence of the terminal ligands on the electron-donor
properties of the {Pt2S2} core in complexes [L2Pt(l-S)2PtL2], we
performed electrochemical measurements and DFT calculations
following the same methodology as already reported for the
[Pt2(dppe)2(l-S)2] analogue.3
1
6 displays one quintet centred at −1048 ppm. The H NMR
spectrum at room temperature shows only one signal including
all the CH2 groups of the terminal ligand (Table 1), thus
indicating a greater symmetry in solution than that observed
in the solid-phase structure.
This apparent inconsistency can be attributed to fast fluxion-
ality of the cation of 6 in solution as shown in Scheme 1. In
In the anodic scan, cyclic voltammograms of 1 in CH3CN,
DMF and DMSO/0.1 M nBu4NBF4 show two consecutive and
well-defined chemically irreversible oxidation waves at low scan
rates (Fig. 6a). At relatively high scan rates (from 10 V s−1), the
two oxidation waves become reversible with E◦ values of 0.15
1
order to corroborate this hypothesis, variable temperature H
NMR and 199Hg NMR spectra were recorded (Fig. 5). Despite
not being able to determine the temperature of coalescence, the
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
2 7 4 7

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1
Fig. 5 VT 199Hg–{ H} and 1H NMR spectra recorded for a solution of 6 in CD3OD.
shows a one-electron process for each wave (in comparison with
the oxidation of tris-4-bromophenylamine in the same medium).
Variation in the shape of the voltammograms with scan rate
suggests the presence of chemical reactions coupled with both
the first and second oxidation waves. A minor oxidation wave ap-
pears at 0.33 V in DMF (Fig. 6). The main traits of the oxidation
processes are similar for the [Pt2(dppe)2(l-S)2] analogue.3
The nature of the products obtained after the chemical
evolution of the monooxidized species [Pt2(dpae)2(l-S)2]+ was
elucidated from electrolysis up to 1 F at a slightly more positive
1
potential than the first peak potential of 1 and subsequent H
NMR and ESI-MS measurements in the resulting solution.
Spectroscopic data showed that regardless of the solvent used
trimetallic species 2 is the major product obtained (89% yield).
To corroborate that the monooxidized species evolves to 2,
complex 1 was made to react at a 1 : 1 molar ratio with the one-
electron oxidant 4-nitrobenzenediazonium tetrafluoroborate.
The presence of 2 in the final solution was confirmed by 1H NMR
and ESI-MS data. The former data allowed estimation of a 91%
reaction yield. In addition, the redox features of the compound
formed by the total electrolysis of 1 were fully consistent with
those obtained from pure complex 2. The cyclic voltammogram
of 2 in CH3CN, DMF and DMSO/0.1 M nBu4NBF4, shows two
irreversible one-electron reduction waves at −1.49 and −2.20 V
(Fig. 7).
Fig. 6 Cyclic voltammetry of 1 (3.0 mM) in DMF/0.1 M nBu4NBF4
at 293 K. Glassy carbon working disc electrode (0.5 mm diameter).
The scan is within the potential range: −0.60/1.60/−0.60. Scan rate: a)
1.0 V s−1 or b) 10.0 V s−1
.
and 0.86 V, respectively, in DMF (Fig. 6b). The experimental
standard potentials in all solvents studied are summarized in
Table 7. Analysis of peak intensity, at low and high sweep rates
Table 7 Comparison of the standard potentials, E◦, found for [Pt2
(dpae)2(l-S)2] (1) and [Pt2(dppe)2(l-S)2]a with those calculated for the
corresponding model compoundsb
Exp. vs SCE/V
Compounds
Calc. vs SCE/V
CH3CN
DMF
DMSO
Fig. 7 Cyclic voltammetry of 2 (3.0 mM) in DMF/0.1 M nBu4NBF4
at 293 K. Glassy carbon working disc electrode (0.5 mm diameter). The
scan is within the potential range: −0.60/−2.60/−0.60 V. Scan rate
[Pt2(dpae)2(l-S)2]b
M → M+
−0.16
0.63
0.14
0.34
0.84
0.15
0.33
0.86
0.15
0.35
0.84
1.0 V s−1
.
M+ → M2+
[Pt2(dppe)2(l-S)2]b
M → M+
These results show that the electrochemical oxidation of 1
follows the mechanism depicted in Scheme 2. The monooxidized
species [Pt2(dpae)2(l-S)2]+ resulting from single electron removal
from complex 1 partially evolves at a slow rate to trimetallic
species 2. In addition, [Pt2(dpae)2(l-S)2]+ is capable of being
further oxidized to [Pt2(dpae)2(l-S)2]2+ at a more positive
potential.
−0.20
0.59
0.02
0.25
0.92
0.06
0.30
1.01
—
—
—
M+ → M2+
a Ref. 3, except for data obtained in DMF. b Calculations performed with
dhae or dhpe model ligands in CH3CN.
2 7 4 8
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3

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◦
Table 8 Calculated geometrical parameters (bond distances in A, and angles in ) for the series of complexes [Pt2(dhae)2(l-S)2]n+ (n = 0, 1, 2)
˚
Pt · · · Pt
S · · · S
Pt–S
Pt–As
Pt–S–Pt
S–Pt–S
As–Pt–As
h b
[Pt2(dhae)2(l-S)2]a
[Pt2(dhae)2(l-S)2]+
[Pt2(dhae)2(l-S2)]2+
3.397 (3.252)
3.403
3.528
3.211 (3.101)
2.952
2.075
2.375 (2.325)
2.367
2.434
2.436 (2.360)
2.439
2.427
91.3 (88.8)
91.9
92.9
85.1 (83.7)
77.2
50.4
85.6 (85.3)
85.3
85.4
152.3 (139.8)
133.8
106.5
a Experimental values for complexes with dpae ligand, or the corresponding average, are given in parenthesis. b Dihedral angle between two {PtS2}
planes.
Comparison of theoretical and experimental data obtained
from the phosphine and arsine analogue complexes gives further
insight into the role of the terminal ligands in the electronic
features of the {Pt2(l-S)2} core. Irrespective of the solvent used,
the first oxidation potential is higher for the dpae containing
complex, which indicates a greater reluctance of 1 to be
oxidised than its phosphine analogue. These results together
with the longer M–S distances in [M{Pt2L4(l-S)2}2]2+ complexes
with L2 = dpae if compared to L2 = dppe are consistent with
a decrease in the basicity of the sulfur atoms in the {Pt2(l-S)2}
core when it is bound to terminal dpae ligands. However, despite
the first oxidation of [Pt2L4(l-S)2] occurs at higher potentials
for L2 = dpae, the second oxidation process is more favourable
Scheme 2
for the dpae containing complex. The latter observation can
be attributed to the stabilization provided by dpae to the final
Theoretical calculations of the energetic and structural fea-
disulfide containing complex [Pt2L4(l-S2)]2+, in agreement with
tures corresponding to the species obtained from 1 (Table 8)
a recent theoretical report.29
Additional evidence for the influence of the nature of L on
indicate that after two consecutive monoelectronic oxidations
2+
the {Pt2(l-S)2} core evolves into {Pt2(l-S2)} , which contains
the electronic features of the {Pt2(l-S)2} core arise from the
a bridging disulfide ligand (Scheme 2). Moreover, DFT results
different redox properties observed for the trimetallic complexes
allow the determination of theoretical redox potentials whose
degree of concordance with the experimental data (Table 7) is
[Pt3(dppe)3(l3-S)2]2+ and [Pt3(dpae)3(l3-S)2]2+. Thus, whereas
comparable to that found for the [Pt2(dppe)2(l-S)2] analogue.3
Despite the limitations inherent to the solvent used the
observed and calculated differences between the oxidation
potentials associated to M → M+ and M+ → M2+ are fairly
coincident. The methodology used also allows a thermodynamic
estimation of the possible evolution pathways for [Pt2L4(l-S)2]+.
The results obtained are fully consistent with the reaction that
involves the concomitant formation of monometallic [PtL2(S2)]
and trimetallic [Pt3L6(l-S)2]2+ species according to:
cyclic voltammetry measurements on the former species show
a bielectronic irreversible reduction at −2.10 V (in DMF at
0.1 V s−1),30 under the same conditions the latter displays two
monoelectronic irreversible reductions at −1.49 V and −2.20 V
(Fig. 7).
Reactivity of [Pt2(dpae)2(l-S)2] (1) towards non-metallic
electrophiles
The series of 1H NMR and ESI-MS data recorded as a function
of time for the reaction of 1 with CH2Cl2 (Fig. 8) leads to
the multistage pathway shown in Scheme 3. The first step of
the reaction involves monoalkylation of the {Pt2S2} core to
yield [Pt2(dpae)2(l-S)(l-SCH2Cl)]Cl (7), which possibly evolves
to [Pt2(dpae)2(l-S2CH2)]Cl2 (8) to finally afford a mixture of
[Pt(dpae)(S2CH2)] (9) and [PtCl2(dpae)] (10). Complexes 9 and
10 have been characterized by 1H NMR and ESI-MS (Table 1)
as well as by X-ray diffraction data (Table 5 and Fig. 9 and 10).
2 [Pt2(dpae)2(l-S)2]+ → [Pt3(dpae)3(l3-S)2]2+ + [Pt(dpae)(S2)]
DG = −90.7 kJ mol−1
In addition, [Pt(dpae)(S2)] could be responsible for the
oxidation that follows the first monoelectronic oxidation of the
{Pt2(l-S)2} core in 1 (calculated standard potential, 0.17 V;
experimental value 0.33 V).
Fig. 8 Evolution of 1 in CH2Cl2 as a function of time monitored by 1H NMR. Spectra of the different aliquots were recorded in d6-DMSO. The
signal at ca. 2.1 ppm is probably due to acetone impurity.
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
2 7 4 9

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Scheme 3
Fig. 9 Structure of complex 9 with 50% probability displacement
ellipsoids and selected atoms labels.
Fig. 10 Structure of complex 10 with 50% probability displacement
ellipsoids and selected atoms labels.
Within this context, it seems that replacement of dppe by dppp
in [PtL2(S2CH2)] has the same effect as changing dppe for dpae.
Following the methodology already used in the theoretical
study of the reactivity of [Pt2(dppe)2(l-S)2] with CH2Cl2, DFT
calculations have been performed in order to compare the
energetic profiles of the reaction pathway corresponding to
arsine or phosphine containing compounds (Table 9). Similarly
to the results reported for dppe and dppp, the differences found
in the evolution of [Pt2(dppe)2(l-S)2] and [Pt2(dpae)2(l-S)2] (1) in
CH2Cl2 do not find translation in the calculated thermodynamic
values. Hence, it is reasonable to conclude that the differences
observed arise from a combination of thermodynamic and
kinetic factors.
While ESI-MS measurements gave evidence for the formation
of 7 (m/z = 1476.5), both 7 and 8 could not be detected by 1H
NMR.
The pattern of evolution of the {Pt2S2} core and the elusive
nature of the alkylated intermediate species compare well with
the behaviour of the phosphine analogue [Pt2(dppe)2(l-S)2] upon
exposure to CH2Cl2.4 It is worth noting that [Pt2L4(l-S)(l-
SCH2Cl)]Cl could be detected by NMR techniques for L2 =
dppe and dppp but it is elusive if L2 = dpae, thus indicating a
greater reactivity of this species with arsine ligands.
One main difference in the reactivity of complexes [L2Pt(l-
S)2PtL2] refers to the stability of [PtL2(S2CH2)] in CH2Cl2 with
time. Thus, this complex evolves spontaneously to [Pt2L4(l-
S3(CH2)2)]Cl2 after several weeks in the presence of CH2Cl2
if L2 = dpae, but no evolution was observed for L2 = dppe.
However, an analogous product to [Pt2(dpae)2(l-S3(CH2)2)]Cl2
(11) (Table 1) was fully characterized for dppp as terminal ligand.
The set of reactions triggered by the protonation of the {Pt2(l-
S)2} core in complex [Pt2(dppe)2(l-S)2] has been the object of
recent studies.5b The final products of this multistep process
depend on the coordinating ability of the conjugate base of the
protic acid. Thus, protonation with HCl leads to the formation
Table 9 Calculated reaction energies (kJ mol−1) corresponding to the evolution of [Pt2(dhae)2(l-S)2] and [Pt2(dhpe)2(l-S)2]a in CH2Cl2
Reaction
L = dhae
L = dhpe
[Pt2L4(l-S)2] + CH2Cl2 → [Pt2L4(l-S)(l-SCH2Cl)]Cl
[Pt2L4(l-S)(l-SCH2Cl)]Cl → [Pt2L4(l-S2CH2)]Cl2
[Pt2L4(l-S2CH2)]Cl2 → [PtCl2L2] + [PtL2(l-S2CH2)]
Total
+6.7
+180.2
−287.6
−100.7
+6.7
+185.6
−296.4
−104.1
a Ref. 4
2 7 5 0
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3

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of a mixture of [PtCl2(dppe)] and [Pt3(dppe)3(l3-S)2]Cl2, but only
to [Pt3(dppe)3(l3-S)2](ClO4)2 if HClO4 is the source of protons.
Present results obtained on the reactivity of 1 towards the
same protic acids (Fig. 11) evidence a comparable behaviour
for the arsine analogue, [Pt2(dpae)2(l-S)2] (1), as depicted in
Scheme 4.
form from the evolution of a diprotonated [Pt2(dpae)2(l-SH)2]2+
species that was undetected among these reactions. On the other
hand, addition of two or more equivalents of HClO4 or HCl
results in the total conversion of 1 to 2. Remarkably, addition
of an excess of HCl over 30 equivalents causes formation of the
monometallic complex [PtCl2(dppe)] (10), which coexists with 2
in the final solution.
Despite the fact that the reaction of [L2Pt(l-S)2PtL2] in the
presence of protic acids leads eventually to complexes of formula
[PtCl2L2] and [Pt3L6(l-S)2]2+, L2 = dppe or dpae, some differ-
ences observed during this evolution deserve consideration. The
first one refers to the different stability of the monoprotonated
species [Pt2L4(l-S)(l-SH)]+, which rapidly evolves to the final
products if L2 = dpae, but instead, for L2 = dppe, the same
reaction requires a significant excess of acid. This different
stability is consistent with the fact that only [Pt2(dppe)2(l-S)(l-
SH)]+ has been isolated and structurally characterized by X-ray
diffraction.
The second difference refers to the preference for the forma-
tion of [PtCl2L2] over [Pt3L6(l-S)2]2+ as a result of the reaction of
[L2Pt(l-S)2PtL2] with HCl. Thus, for L2 = dppe, [PtCl2(dppe)]
is usually the major product. In contrast, the reaction of 1
with HCl yields the trimetallic compound 2 almost exclusively.
These findings indicate that the type of cleavage undergone
by the {Pt2(l-SH)2} ring in the intermediate diprotonated
species formed in the reaction of [L2Pt(l-S)2PtL2] with HCl
(Scheme 4) occur differently. The breakage of this ring is
preferentially symmetrical for L2 = dpae and asymmetrical for
dppe. As already discussed,5b an asymmetric cleavage leads to
an equimolar mixture of [PtCl2L2] and [PtL2(SH)2], while if it
occurs symmetrically it leads to two [PtClL2(SH)] species that
eventually give rise to the trinuclear [Pt3L6(l-S)2]2+ complex.
DFT calculations have allowed comparison of the thermo-
dynamic feasibility for the formation of [PtCl2L2] or [Pt3L6(l-
S)2]2+ as a function of L2 = dppe or dpae (Table 10). However, no
Fig. 11 Evolution of 1 with HCl as a function of the number of
equivalents of acid added. Monitored by 1H NMR in d6-DMSO
solution.
Addition of one equivalent of acid (HCl or HClO4) to
a solution of 1 in acetonitrile affords a mixture consisting
of monoprotonated [Pt2(dpae)2(l-S)(l-SH)]+(12) and trinuclear
[Pt3(dpae)3(l3-S)2]2+ (2) species coexisting with unaltered start-
ing complex 1. Unlike 2, which had been isolated (Tables 1 and 5)
and thus could be easily identified in solution, 12 could only be
characterized by means of ESI-MS and 1H NMR data (Table 1).
Moreover, on the basis of previous results5b complex 2 should
Scheme 4
Table 10 Calculated energies (kJ mol−1) corresponding to the reaction of [Pt2(dhae)2(l-S)2] and [Pt2(dhpe)2(l-S)2]5b with HCl in CH3CN solution
Reaction
L = dhae
L = dhpe
[Pt2L4(l-S)2] + HCl → [Pt2L4(l-S)(l-SH)]Cl
−10.45
+73.15
−19.65
+71.9
[Pt2L4(l-S)(l-SH)]Cl + HCl → [Pt2L4(l-SH)2]Cl2
(+62.7)a
−223.6
(+52.25)a
−232.8
[Pt2L4(l-SH)2]Cl2 + 2HCl → 2[PtCl2L2] + 2SH2
(−160.9)a
−81.9b
(−180.6)a
−78.2b
3[Pt2L4(l-SH)2]Cl2 → 2[Pt3L6(l3-S)2]Cl2 + 2SH2+ 2HCl
(−19.2)a
(−25.9)a
a Relative energy per dimer {Pt2}. b Per mol of [Pt2L4(l-SH)2]Cl2.
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
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significant differences have been found in the thermodynamics of
these processes. Thus, as already observed for the reaction with
CH2Cl2, not only thermodynamic but also kinetic factors have to
be taken into account in order to explain the differences observed
in the reaction of [Pt2(dppe)2(l-S)2] and [Pt2(dpae)2(l-S)2] (1)
with HCl. Notwithstanding this, the calculations reflect a subtle
decrease in the basicity of 1 with respect to [Pt2(dppe)2(l-S)2],
the reaction energy of the first protonation being 9.2 kJ mol−1
less favourable in the case of 1. This decrease in basicity of the
{Pt2S2} core when it is bound to arsine ligands is consistent with
the electrochemical properties of 1 as well as with the structural
features of the corresponding metal derivatives.
Acknowledgements
This research was supported by the Ministerio de Educacio´n
y Ciencia (MEC, Spain, Grants CTQ2004–01463, BQU2003–
05457 and BQU2002–04110–CO2–02). FNV is indebted to
MEC for a pre-doctoral scholarship. We are grateful to Dr J.
Vidal from ICMAB and Dr J. Sola from UAB for the EPR
measurements, Dr A. L. Llamas and Dr B. Dacun˜a from USC
for crystal structure determination, R. Gesto from USC for Hg
NMR measurements, and F. Ca´rdenas from UB for Cd NMR
measurements.
Overall, comparison of the structural parameters of the
pentanuclear derivatives and the electrochemical data obtained
for complexes [L2Pt(l-S)2PtL2], L2 = dppe and dpae, indicate
that the sulfur atoms of the {Pt2S2} core are less basic with
the diarsine than with the diphosphine terminal ligands. On this
basis, the first functionalization of the {Pt2S2} ring by reaction of
[L2Pt(l-S)2PtL2] with CH2Cl2 or protic acids, i.e. the formation
of [Pt2L4(l-S)(l-SCH2Cl)]Cl or [Pt2L4(l-S)(l-SH)]+, should be
less favoured for L = arsine. However, the previous reactions
proceed extensively and rapidly in all cases, and thus the previous
order of basicity cannot be corroborated. Notwithstanding this,
the species first formed by activation of the {Pt2(l-S)2} core, via
alkylation or protonation, seem to be more reactive if diarsine
is the terminal ligand.
References
1 P. Gonza´lez-Duarte, A. Lledo´s and R. Mas-Balleste´, Eur. J. Inorg.
Chem., 2004, 3585.
2 S.-W. A. Fong and T. S. A. Hor, J. Chem. Soc., Dalton Trans., 1999,
639.
3 R. Mas-Ballest
A. Lledo´s, C. Me´gret and D. de Montauzon, Dalton Trans., 2004,
706.
e´, M. Capdevila, P. Gonza´lez-Duarte, M. Hamidi,
4 R. Mas-Balleste´, M. Capdevila, P. A. Champkin, W. Clegg, R. A.
Coxall, A. Lledo´s, C. Me´gret and P. Gonza´lez-Duarte, Inorg. Chem.,
2002, 41, 3218.
5 (a) G. Aullo´n, M. Capdevila, W. Clegg, P. Gonza´lez-Duarte, A.
Lledo´s and R. Mas-Balleste´, Angew. Chem. Int. Ed., 2002, 41, 2776;
(b) R. Mas-Balleste´, G. Aullo´n, P. A. Champkin, W. Clegg, C.
Me´gret, P. Gonza´lez-Duarte and A. Lledo´s, Chem. Eur. J., 2003, 9,
5023.
6 (a) M. Capdevila, Y. Carrasco, W. Clegg, R. A. Coxall, P. Gonza´lez-
Duarte, A. Lledo´s, J. Sola and G. Ujaque, Chem. Commun., 1998, 597;
(b) M. Capdevila, Y. Carrasco, W. Clegg, R. A. Coxall, P. Gonza´lez-
Duarte, A. Lledo´s and J. A. Ram´ırez, J. Chem. Soc., Dalton Trans.,
1999, 3103.
7 (a) R. Mas-Balleste´, P. A. Champkin, W. Clegg, P. Gonza´lez-
Duarte, A. Lledo´s and G. Ujaque, Organometallics, 2004, 23, 2522;
(b) R. Mas-Balleste´, W. Clegg, A. Lledo´s and P. Gonza´lez-Duarte,
Eur. J. Inorg. Chem., 2004, 3223.
8 J. H. Downing and M. B. Smith, in Comprehensive Coordination
Chemistry II, ed. J. A. McCleverty and T. J. Meyer, Elsevier
Pergamon, Amsterdam, 2003, vol. 1, ch. 12, pp. 253–296.
9 (a) P. W. N. M. van Leeuwen, P. C. J. Kamer, J. N. H. Reek and P.
Dierkes, Chem. Rev., 2000, 100, 2741; (b) P. B. Dias, M. E. Minas
de Piedade and J. A. Martinho Simoes, Coord. Chem. Rev., 1994,
135/136, 737; (c) J. R. Sowa, Jr. and R. J. Angelici, Inorg. Chem.,
1991, 30, 3534; (d) C. A. Tolman, Chem. Rev., 1977, 77, 313.
10 W. Levason and G. Reid, in Comprehensive Coordination Chemistry
II, ed. J. A. McCleverty and T. J. Meyer, Elsevier Pergamon,
Amsterdam, 2003, vol. 1, ch. 16, pp. 377-389.
Conclusion
All data presented in this work reveal that the substitution of
phosphorus by arsenic as donor atom in complexes of formula
[Pt2(Ph2X(CH2)2XPh2)2(l-S)2] is a main factor influencing the
chemical features of the {Pt2S2} core. Thus, from a structural
point of view, the lower trans influence of the arsine ligand
entails a decrease in the Pt–S distance in [Pt2(dpae)2(l-S)2]
with respect to that observed for [Pt2(dppe)2(l-S)2]. This effect
also implies an increase of the M–S distances in complexes
[M{Pt2L4(l-S)2}2]2+ (M = Cu, Zn, Cd) when the diarsine dpae
is used as terminal ligand instead of the diphosphine dppe. The
latter findings show that the metalloligand [Pt2L4(l-S)2] has a
weaker interaction with the heterometal M when L2 = diarsine,
and account for the distinct coordination geometries observed
for the mercury centre in [Hg{Pt2L4(l-S)2}2]2+ for L2 = dppe,
dpae.
11 (a) A. Cingolani, Effendy, J. V. Hanna, M. Pellei, C. Pettinari, C.
Santini, B. W. Skelton and A. H. White, Inorg. Chem., 2003, 42,
4938; (b) G. Ferguson, Y. Li, A. J. McAlees, R. McCrindel and K.
Xiang, Organometallics, 1999, 18, 2428; (c) N. Kuznik and O. F.
Wendt, J. Chem. Soc., Dalton Trans., 2002, 3074.
12 J. R. Sowa, Jr., V. Zanotti, G. Facchin and R. J. Angelici, J. Am.
Chem. Soc., 1992, 114, 160.
13 (a) R. B. Bedford, C. S. J. Cazin, S. J. Coles, T. Gelbrich, M. B.
Hursthouse and V. J. M. Scordia, Dalton Trans., 2003, 3350; (b) C.
Amatore, A. Bucaille, A. Fuxa, A. Jutand, G. Meyer and A. N.
Ntepe, Chem. Eur. J., 2001, 7, 2134; (c) V. Farina, B. Krishnan, D. R.
Marshall and G. P. Roth, J. Org. Chem., 1993, 58, 5434.
14 (a) R. A. Cipriano, W. Levason, R. A. S. Mould, D. Plechter
and M. Webster, J. Chem. Soc., Dalton Trans., 1990, 2609; (b) W.
Levason, S. R. Preece and C. S. Frampton, Polyhedron, 1996, 15,
2719; (c) N. R. Champness, W. Levason, S. R. Preece, M. Webster
and C. S. Frampton, Inorg. Chim. Acta, 1996, 244, 65; (d) N. J.
Holmes, W. Levason and M. Webster, J. Chem. Soc., Dalton Trans.,
1997, 4223; (e) B. D. Yeomans, D. G. Humphrey and G. A. Heath,
J. Chem. Soc., Dalton Trans., 1997, 4153.
Additional evidence for the decrease in basicity of the {Pt2(l-
S)2} core associated to the use of arsines as terminal ligands
comes from its electrochemical characterization. Hence, the first
monoelectronic oxidation observed for [Pt2L4(l-S)2] complexes
appears at a slightly higher potential if L2 = diarsine, thus
indicating a major resistance to oxidation. In contrast, the
second monoelectronic oxidation appears at lower potentials
when L2 = diarsine, which indicates that the final dioxidized
product is more stabilized by diarsine than by diphosphine
ligands. If assuming that the dioxidized product contains a
bridging disulfide ligand, the extra stabilization provided by
diarsines is consistent with recent theoretical findings.
A different chemical evolution of [Pt2L4(l-S)2] in the presence
of CH2Cl2 or protons has also been observed depending on L2 =
dppe or dpae. According to the above mentioned data, the
first functionalization of the {Pt2(l-S)2} core by means of
its reaction with CH2Cl2 or protic acids, i.e. the formation
of [Pt2L4(l-S)(l-SH)]+ or [Pt2L4(l-S)(l-SCH2Cl)]+, should be
less favourable for L2 = dpae. However, further evolution of
these monofunctionalized species is boosted if arsine is used as
terminal ligand.
15 A. Y. Timoshkin, A. V. Suvorov, H. F. Bettinger and H. F. Schaefer,
III, J. Am. Chem. Soc., 1999, 121, 5687.
16 P. H. M. Budzeelar, gNMR V4.0.1, Cherwell Scientific Publishing
Ltd., Oxford, UK, 1997.
17 A. Habtemariam, B. Watchman, B. S. Potter, R. Palmer, S. Parsons,
A. Parkin and P. J. Sadler, J. Chem. Soc., Dalton Trans., 2001,
1306.
Overall, the rich and diverse chemistry of [Pt2(P∩P)2(l-
S)2] complexes has been extended by taking advantage of the
influence of the terminal ligands on the reactivity of the {Pt2S2}
core.
18 G. M. Sheldrick, SADABS, Area-Detector Absorption Correction.
Siemens Industrial Automation Inc., Madison, WI, 1996.
2 7 5 2
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3

View Article Online
19 G. M. Sheldrick, SHELX-97 (SHELXS-97 and SHELXL-97),
Programs for Crystal Structure Analysis, Institu¨t fu¨r Anorganische
Chemie der Universita¨t Go¨ttingen, Germany, 1998.
F. J. Delvin, C. F. Chabalowski and M. J. Frisch, J. Phys. Chem.,
1994, 98, 11623.
23 (a) P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299; (b) W. R.
Wadt and P. J. Hay, J. Chem. Phys., 1985, 82, 284.
24 A. Ho¨llwarth, M. Bo¨hme, S. Dapprich, A. W. Ehlers, A. Gobbi, V.
Jonas, K. F. Ko¨hler, R. Stegman, A. Veldkamp and G. Frenking,
Chem. Phys. Lett., 1993, 208, 237.
25 W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys., 1972, 56,
2257.
26 (a) C. Amovilli, V. Barone, R. Cammi, E. Cance`s, M. Cossi, B.
Mennucci, C. S. Pomelli and J. Tomasi, Adv. Quant. Chem., 1998,
32, 227; (b) J. Tomasi and M. Persico, Chem. Rev., 1994, 94,
2027.
20 P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A, 1990, 46,
194; A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7.
21 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, R. E.
Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels,
K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M.
Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford,
J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma,
D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman,
J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong,
J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S. Replogle and
J. A. Pople, Gaussian98 (Revission A.7), Gaussian Inc., Pittsburgh,
PA, 1998.
27 S. Otto and M. H. Johansson, Inorg. Chim. Acta, 2002, 329,
135.
28 S. Otto and A. J. Muller, Acta Crystallogr., Sect. C, 2001, 57,
1405.
29 G. Aullo´n, M. Hamidi, A. Lledo´s and S. Alvarez, Inorg. Chem., 2004,
43, 3702.
22 (a) C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785;
30 K. Matsumoto, K. Takahashi, M. Ikuzawa, H. Kimoto and S. Okeya,
Inorg. Chim. Acta, 1998, 281, 174.
(b) A. D. Becke, J. Chem. Phys., 1993, 98, 5648; (c) P. J. Stephens,
D a l t o n T r a n s . , 2 0 0 5 , 2 7 4 2 – 2 7 5 3
2 7 5 3