Stable diplatinum complexes with functional thiolato bridges from dialkylation of [Pt2(μ-S)2(P-P)2] [P-P = 2 × PPh3, Ph2P(CH2)3PPh 2]

Article abstract of DOI:10.1039/b707526j

The normally robust monoalkylated complexes [Pt₂(-S)(-SR) (PPh₃)₄]⁺ can be activated towards further alkylation. Dialkylated complexes [Pt₂(-SR)₂(P-P) ₂]²⁺ (P-P = 2 × PPh₃, Ph ₂P(CH₂)₃PPh₂) can be stabilized and isolated by the use of electron-rich and aromatic halogenated substituents R [e.g. 3-(2-bromoethyl)indole and 2-bromo-4′-phenylacetophenone] and 1,3-bis(diphenylphosphino)propane [Ph₂P(CH₂) ₃PPh₂ or dppp] which enhances the nucleophilicity of the {Pt₂(-S)₂} core. This strategy led to the activation of [Pt₂(-S)(-SR)(PPh₃)₄]⁺ towards R-X as well as isolation and crystallographic elucidation of [Pt₂(- SC₁₀H₁₀N)₂(PPh₃)₄] (PF₆)₂ (2a), [Pt₂(-SCH₂C(O)C ₆H₄C₆H₅)₂(PPh ₃)₄](PF₆)₂ (2b), and a range of functionalized-thiolato bridged complexes such as [Pt₂(-SR) ₂(dppp)₂](PF₆)₂ [R = -CH ₂C₆H₅ (8a), -CH₂CHCH₂ (8b) and -CH₂CN (8c)]. The stepwise alkylation process is conveniently monitored by Electrospray Ionisation Mass Spectrometry, allowing for a direct qualitative comparison of the nucleophilicity of [Pt ₂(-S)₂(P-P)₂], thereby guiding the bench-top synthesis of some products observed spectroscopically. The Royal Society of Chemistry.

Full text of DOI:10.1039/b707526j

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Stable diplatinum complexes with functional thiolato bridges from
dialkylation of [Pt2(l-S)2(P–P)2] [P–P = 2 × PPh3, Ph2P(CH2)3PPh2]†
Siew Huay Chong,a William Hendersonb and T. S. Andy Hor*a
Received 18th May 2007, Accepted 11th July 2007
First published as an Advance Article on the web 2nd August 2007
DOI: 10.1039/b707526j
The normally robust monoalkylated complexes [Pt2(l-S)(l-SR)(PPh3)4]+ can be activated towards
further alkylation. Dialkylated complexes [Pt2(l-SR)2(P–P)2]2+ (P–P = 2 × PPh3, Ph2P(CH2)3PPh2) can
be stabilized and isolated by the use of electron-rich and aromatic halogenated substituents R [e.g.
3-(2-bromoethyl)indole and 2-bromo-4ꢀ-phenylacetophenone] and 1,3-bis(diphenylphosphino)propane
[Ph2P(CH2)3PPh2 or dppp] which enhances the nucleophilicity of the {Pt2(l-S)2} core. This strategy led
to the activation of [Pt2(l-S)(l-SR)(PPh3)4]+ towards R–X as well as isolation and crystallographic
elucidation of [Pt2(l-SC10H10N)2(PPh3)4](PF6)2 (2a), [Pt2(l-SCH2C(O)C6H4C6H5)2(PPh3)4](PF6)2 (2b),
and a range of functionalized-thiolato bridged complexes such as [Pt2(l-SR)2(dppp)2](PF6)2 [R =
–CH2C6H5 (8a), –CH2CHCH2 (8b) and –CH2CN (8c)]. The stepwise alkylation process is conveniently
monitored by Electrospray Ionisation Mass Spectrometry, allowing for a direct qualitative comparison
of the nucleophilicity of [Pt2(l-S)2(P–P)2], thereby guiding the bench-top synthesis of some products
observed spectroscopically.
have been isolated and structurally identified, they are assisted
Introduction
by the use of an overhead spacer R–R across the S · · · S
The “butterfly-look-alike” metalloligand [Pt2(l-S)2(PPh3)4] (1) is
bridge, such as [Pt2(l-SCnH2nS)(PPh3)4](PF6)2 (n = 2 and 4)
best known as a precursor to multimetallic materials.1 Recently,
and [Pt2(l-SCH2C6H4CH2S)(P–P)2](PF6)2 [P–P = 2 × PPh3 and
Ph2P(CH2)3PPh2 (dppp)].4,7 In this paper, we shall present some
new findings on the activation of the monoalkylated complexes,
the synthetic approach to “unsupported” doubly bridged thiolato
complexes of Pt(II), and describe the conditions under which they
can be stabilized and isolated.
there has been an emerging interest in its applied coordination
chemistry as a magnet for organic electrophiles,2 activation of ro-
bust C–X bonds,3 and as a templating agent for organochalcogen
compounds such as dithiacyclophane,4 etc. Underpinning these
applications lies a versatile strategy—transformation of [Pt2S2]
to [Pt2(SR)2]2+ via [Pt2(S)(SR)]+ with R being an organic moiety
or metalloorganic fragment. This seemingly trivial conversion,
especially towards organic nucleophiles, is plagued with problems
due to the poor affinity of cationic (and electrophilic) [Pt2(l-S)(l-
SR)]+ towards another electrophile RX. The tendency for a dica-
tionic complex [Pt2(l-SR)2(PR3)4]2+2X− to disintegrate into two
mononuclear components viz. [Pt(SR)2(PR3)2] and [PtX2(PR3)2]
is also thermodynamically overwhelming. This problem is also
associated with the misintepretation of [Pt2(l-SMe)2(PPh3)4]2+2I−
from the reaction of 1 and MeI, which was later identified as
[Pt2(l-S)(l-SMe)(PPh3)4]+I−.5
It is therefore not surprising that amidst the large array
of [Pt2S2]-based complexes and aggregates known, there are
very few doubly bridged thiolato complexes which have been
prepared by dialkylation of 1, with the exception of [Pt2(l-
SCH3)2(PPh3)4](PF6)2 which has recently been reported by our
group.2a Some have been identified under Electrospray Ionisation
Mass Spectrometry (ESI-MS) conditions6 but they have not
been synthesized as laboratory-scale products. For those that
Results and discussion
Reactivity of [Pt2(l-S)2(PPh3)4] (1) towards halides containing
aromatic and electron-rich substituents—syntheses of dialkylated
[Pt2(l-SR)2(PPh3)4]2+ products
The dimethylation of [Pt2(l-S)2(PPh3)4] (1) with dimethyl sul-
fate (Me2SO4)2a to give [Pt2(l-SCH3)2(PPh3)4](PF6)2 is the first
example of a double-alkylation reaction on the {Pt2(l-S)2}
system, giving [Pt2(l-SR)2(PPh3)4]2+ (2) with doubly bridging
thiolates. The diprotonated derivative [Pt2(l-SH)2(PPh3)4]2+ is
detected by mass spectrometry (ESI-MS),8 although detailed
protonation studies on [Pt2(l-SH)2(Ph2P(CH2)nPPh2)2] (n = 2
or 3) by Gonza´lez-Duarte et al.9 have shown that such dipro-
tonated species are unstable in solution. However, the selenide
analogue [Pt2(l-SeH)2(PPh3)4][ClO4]2 has been isolated and crys-
tallographically characterized.10 Attempts to prepare complexes
2 with excess monohalide, RX is hindered by the deactivation
of the unsubstituted sulfide in [Pt2(l-S)(l-SR)(PPh3)4]+ (3) due
to the positive charge on the monocation. This is exemplified
in the reaction of 1 with 3-bromopropionitrile and ethyl 3-
bromopropionate, which results in the rapid and exclusive forma-
tion of [Pt2(l-S)(l-SCH2CH2CN)(PPh3)4]+ (3a) and [Pt2(l-S)(l-
SC2H4CO2CH2CH3)(PPh3)4]+ (3b), respectively. Both 3a and 3b
remain stable to further alkylation even in the presence of excess
aDepartment of Chemistry, National University of Singapore, 3, Science
Drive 3, Singapore, 117543, Singapore. E-mail: andyhor@nus.edu.sg;
Fax: +(65) 6873 1324; Tel: +(65) 6874 2663
bDepartment of Chemistry, University of Waikato, Private Bag 3105,
Hamilton, New Zealand
† CCDC reference numbers 647935–647939. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b707526j
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Table 1 Principal ions observed in the ESI-MS-monitored reactions of
[Pt2(l-S)2(PPh3)4] (1) with reactive monoalkylating halides
alkyl halides. Single-crystal X-ray diffraction analyses of the PF6
salt of 3a and 3b confirmed the presence of mixed thiolate–sulfide
bridges (Fig. 1). The {Pt2(l-S)2} butterflies of both structures
are inevitably bent with dihedral angles (h) between the two
PtS2 planes of 144◦ (3a) and 157◦ (3c), compared with 168◦ in
the parent complex 1.11 A larger degree of bending is expected
in order to accommodate the bridge substituent and minimize
its repulsion with the terminal PPh3. Alkylation of the sulfide
bridges lengthens the Pt–S bond, as evidenced in the longer Pt–
Reaction time
a
Alkylating agents
Observed ions (m/z, %)
1 h
3 h
1 d
3c (1647, 100), 2a (896, 45)
2a (896, 100), 3c (1647, 10)
2a (895, 100)
˚
SCH2CH2CN (Pt(2)–S(1) = 2.3525 A) length relative to that of
1 h
1 d
2b (946, 100)
˚
Pt–S (Pt(2)–S(2) = 2.345 A). The thiolate ligand adopts an exo
2b (946, 100), 4 (1711, 19)
conformation, pointing away from the bulky triphenylphosphines.
Noticeably, the thiolate ligand in 3a appears to hover above
the unsubstituted sulfide thus causing steric hindrance. This
could provide another explanation for the resistance of the
unsubstituted sulfide towards further alkylation. An ESI-MS
study using weak monofunctional alkylating agents6 such as
n-butyl chloride, Me2NCH2CH2Cl·HCl, bromoethylphthalimide,
1 h
3 d
1 week
3d (1651, 100), 2c (901, 10)
3d (1651, 100), 2c (900, 86)
2c (900, 100), 3d (1652, 33)
=
PhNHCOCH2Cl, and hydrazones such as PhC( NNHAr)CH2Br
=
and CH3C( NNHAr)CH2Cl, all pointed to selective monoalky-
a Refers to the reaction time at which an aliquot from the reaction mixture
is analyzed by ESI-MS.
lation of the {Pt2(l-S)2} core.
reaction of 1 with 3-(2-bromoethyl)indole is monitored by ESI-
MS, (Table 1) it clearly demonstrates a stepwise alkylation from the
first hour of reaction and that both sulfur sites are susceptible to
attack, as evidenced by the peaks [Pt2(l-S)(l-SC10H10N)(PPh3)4]+
(3c) (m/z 1647, 100%) and [Pt2(l-SC10H10N)2(PPh3)4]2+ (2a)
(m/z 896, 45%). The dialkylated 2a becomes the predominant
species after 3 h of reaction and 3c is barely noticeable in the
ESI mass spectrum, suggesting complete dialkylation. Likewise,
the reaction of 1 with a similar substrate, that is, 2-bromo-
4ꢀ-phenylacetophenone (BrCH2C(O)C6H4C6H5), a halide that
possesses aromatic (biphenyl), p-conjugated functionalities,
results in dialkylation, which proceeds to completion within
an hour to give [Pt2(l-SCH2C(O)C6H4C6H5)2(PPh3)4]2+ (2b)
(m/z 946, 100%). The monoalkylated species, [Pt2(l-S)(l-
SCH2C(O)C6H4C6H5)(PPh3)4]+ is absent in the mass spectrum,
pointing to a faster rate of reaction. Not only does the ESI-MS
provide a simple technique to follow the course of reaction, it
also identifies the formation of possible side product(s). This is
illustrated by the identification of a phosphine-displaced complex
[Pt2(l-SCH2C(O)C6H4C6H5)2(PPh3)3Br]+ (4) (m/z 1711, 19%)
after 1 d of reaction.
Fig.
1 50% thermal ellipsoid representation of the cations of
[Pt2(l-S)(l-SCH2CH2CN)(PPh3)4](PF6) (3a) and [Pt2(l-S)(l-SC2H4CO2-
CH2CH3)(PPh3)4](PF6) (3b). The phenyl rings of PPh3 and hydrogen atoms
are omitted for clarity.
Further alkylation of 3 can be achieved by using a powerful
methylating agent (Me2SO4) to give the mixed thiolato bridging
The stability of novel complexes 2a and 2b may be en-
hanced by the p–p interaction between the two sets of aro-
matic substituents on each bridging sulfide. When an alkyl
halide containing less aromatic substituents is used, such
as 2-bromo-2ꢀ-methoxyacetophenone, BrCH2C(O)C6H4(OCH3),
the tendency for dialkylation is noticeably lower. Under
such circumstances, the monoalkylated species, [Pt2(l-S)(l-
SCH2C(O)C6H4(OCH3))(PPh3)4]+ (3d) (m/z 1651, 100%) becomes
the predominant species, even after 3 d of reaction. Although
the dialkylated product [Pt2(l-SCH2C(O)C6H4(OCH3))2(PPh3)4]2+
(2c) (m/z 901, 10%) starts to form in the first hour, it becomes
the major product (m/z 900, 100%) after 1 week. The complex 3d
(m/z 1652, 33%) however remains present, as observed in the mass
spectrum, thus demonstrating incomplete dialkylation. Scheme 1
summarizes the reaction of 1 with these reactive halides.
complex [Pt2(l-SR)(l-SCH3)(PPh3)4]2+ [R
=
–CH2C6H5,
–CH2CHCH2, –C5H10CO2CH2CH3, –C2H4CO2CH2CH3,
–
CH2CH2CN, –C2H4CH(O)2C2H4 and –C2H4SC6H5]. This is
however limited to the introduction of the methyl substituent.2a
General dialkylation of 1 to [Pt2(l-SR)2(PPh3)4]2+ (2) is achieved
by the choice of an appropriate alkylating agent.6 Reactive alkyl
halides such as allyl bromide and methyl chloroacetate lead to the
stepwise formation of [Pt2(l-SCH2CHCH2)2(PPh3)4]2+ and [Pt2(l-
SCH2CO2CH3)2(PPh3)4]2+ upon prolonged reactions. Reactive
halides that contain aromatic and electron-rich substituents
generally give successful reactions. This is also demonstrated
by the use of 3-(2-bromoethyl)indole, which is an aromatic,
heterocyclic compound with
a highly electron delocalized
structure at the fused rings (fused benzene and pyrrole). When the
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unaffected by the variation and degree of functionalization about
1
the sulfur bridges. The 31P{ H} NMR spectrum of 2a is consistent
with the symmetrical nature of the molecule, displaying a singlet
at dP = 19.6 ppm with the associated satellites, 1JPt–P = 2926 Hz for
1
all the chemically equivalent phosphine groups. Similar 31P{ H}
NMR characteristics are observed in complex 2b—a singlet is
observed at dP = 20.0 ppm (1JPt–P = 3117 Hz). The stronger
Pt–P coupling in 2b is consistent with a higher electronegativity
or greater share of electron density in its p-conjugated biphenyl
structure, which also supports a faster dialkylation of 1 with 2-
bromo-4ꢀ-phenylacetophenone.
Enhancing the nucleophilicity of {Pt2(l-S)2} by replacing terminal
PPh3 with chelating Ph2P(CH2)3PPh2 ligands—syntheses of
dialkylated [Pt2(l-SR)2(dppp)2]2+ products
In a study of the reaction of [Pt2(l-S)2(Ph2P(CH2)nPPh2)2] [n = 3,
dppp (5); n = 2, dppe (6)] in CH2Cl2, it is shown that nucleophilic
behaviour is highly dependent on the nature of the phosphines.3a
The complex [Pt2(l-S)2(dppp)2] (5) is expected to be more basic
than 1 because the more efficient electron donation of dppp should
render the trans-sulfide more electron-rich and nucleophilic. The
lower steric demand of dppp compared to 2 × PPh3 is also expected
to provide more room for the incoming electrophile. The sulfide
in 5 could provide a more facile route to the second alkylation
and hence formation of dithiolato bridges even with the use of
simple monohalides. Formation of [Pt2(l-SR)2(dppp)2]2+ (8) from
5 through [Pt2(l-S)(l-SR)(dppp)2]+ (7) is therefore expected to
occur.
Indeed, when 5 and 1 are compared directly (ESI-MS) in their
reactions with benzyl bromide, the higher reactivity of the former is
immediately evident from the clean formation of the dibenzylated,
[Pt2(l-SCH2C6H5)2(dppp)2]2+ (8a) (m/z 731, 100%) within 1 d of
reaction (Scheme 2). Similar reaction with 1 proceeds much slower
over 2 d and gives [Pt2(l-S)(l-SCH2C6H5)(PPh3)4]+ (3e) as the
major species, and the dialkylated product being the minor species.
Scheme 1 Dialkylation reactions of [Pt2(l-S)2(PPh3)4] (1) with reactive
halides containing aromatic, electron-rich substituents.
We have reported earlier the synthetic applications of
ESI-MS.6,12 This is also applicable to the successful syn-
theses of both diplatinum bis(l-thiolate) complexes as the
PF6 salts, i.e. [Pt2(l-SC10H10N)2(PPh3)4](PF6)2 (2a) and [Pt2(l-
SCH2C(O)C6H4C6H5)2(PPh3)4](PF6)2 (2b) in good isolated yields
(90% and 98%, respectively). The single crystal X-ray diffraction
analysis of complex 2a (Fig. 2) shows the two indole-substituted
thiolate bridging ligands in a syn–exo conformation, pointing
away from the sterically bulky PPh3 ligands. The two aromatic
(fused benzene and pyrrole) rings are oriented perpendicular to
each other, and separated at a distance where steric repulsion is
averted. The complex has a C2 symmetry at the molecular centre,
with a bent {Pt2(l-S)2} ring hinged at a dihedral angle of 140◦,
which is similar to that observed in mono- and other dialkylated
complexes. The extent of hinging in the {Pt2(l-S)2} ring seems to be
Scheme 2 Comparison of the reaction rates of complexes 1 and 5 with
benzyl bromide. A faster reaction rate is observed when the dppp ligand
is used in place of PPh3. Dialkylation is completed in the reaction of 5
while the monoalkylated [Pt2(l-S)(l-SCH2C6H5)(PPh3)4]+ (3e) remains as
the major species in the reaction of 1.
Fig.
2
A 50% thermal ellipsoid representation of the cation of
[Pt2(l-SC10H10N)2(PPh3)4](PF6)2 (2a). The phenyl rings of PPh3 and
hydrogen atoms are omitted for clarity.
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Table 2 Ionic species observed in the ESI-MS-monitored reactions of [Pt2(l-S)2(dppp)2] (5) with monoalkylating halides.
Reaction timea and
conditions
Alkylating agent
Observed ions (m/z, %)
1 d
[Pt2(l-SCH2C6H5)2(dppp)2]2+ (8a) (731, 100); [Pt2(l-SCH2C6H5)2(dppp)2]2+Br− (1541, 28)
1 h
5 h
1 h
[Pt2(l-SCH2CHCH2)2(dppp)2]2+ (8b) (681, 100); [Pt2(l-S)(l-SCH2CHCH2)(dppp)2]+ (7b) (1319, 25);
[Pt2(l-SCH2CHCH2)2(dppp)2]2+Br− (1440, 10)
8b (680.5, 100); [Pt2(l-SCH2CHCH2)2(dppp)2]2+Br− (1440, 17)
[Pt2(l-SCH2CN)2(dppp)2]2+ (8c) (679, 100); [Pt2(l-SCH2CN)2(dppp)2]2+Br− (1439, 45)
4 h
[Pt2(l-S)(l-SC2H4CO2CH2CH3)(dppp)2]+ (7d) (1379, 100); [Pt2(l-SC2H4CO2CH2CH3)2(dppp)2]2+ (8d)
(740, 29)
1 d
4 d
1 week
8d (740, 100); 7d (1379, 65); [Pt2(l-SC2H4CO2CH2CH3)2(dppp)2]2+Br− (1560, 10)
8d (740, 100); 7d (1379, 9); [Pt2(l-SC2H4CO2CH2CH3)2(dppp)2]2+Br− (1561, 24)
8d (740, 100)
1 h, 60 ◦
1 d, 60 ◦
C
C
7d (1380, 100); 8d (740, 16)
8d (740, 100); 7d (1379, 30); [Pt2(l-SC2H4CO2CH2CH3)2(dppp)2]2+Br− (1560, 26)
8d (740, 100); 7d (1380, 5); [Pt2(l-SC2H4CO2CH2CH3)2(dppp)2]2+Br− (1561, 30)
[Pt2(l-S)(l-SC5H10CO2CH2CH3)(dppp)2]+ (7e) (1421, 100); [Pt2(l-SC5H10CO2CH2CH3)2(dppp)2]2+ (8e)
(783, 8)
2 d, 60◦C
5 h
1 d
7e (1421, 100); 8e (782, 45)
3 d and 60 ◦C for 2 d 8e (782, 100); [Pt2(l-SC5H10CO2CH2CH3)2(dppp)2]2+Br− (1645, 46)
a Refers to the reaction time at which an aliquot from the reaction mixture is analyzed by ESI-MS.
Other side products, such as [Pt2(l-SCH2C6H5)2(PPh3)3Br]+ (9)
and the phosphonium ion [Ph3PCH2C6H5]+ (10) are also observed.
Use of dppp also suppresses the problem of phosphine displace-
ment (as in 9). Reactions towards other monohalides give similar
conclusions. The ESI-MS data are summarized in Table 2.
The complex [Pt2(l-SCH2C6H5)2(dppp)2](PF6)2 8a, isolated in
81% yield, represents the first isolated doubly-bridged dithiolato
complex [Pt2(l-SR)2(dppp)2]2+ arising from alkylation of 5. The
related diprotonated species, [Pt2(l-SH)2(dppp)2]2+ is unstable
in solution and decomposes to mononuclear complexes.9 The
1
31P{ H} NMR spectrum of 8a is typical of a symmetrical structure
and displays a singlet at dP = −0.7 ppm with the associated
satellites for the Pt–P coupling, 1JPt–P = 2733 Hz for the chemically
equivalent phosphine groups. Confirmation of its identity by an
X-ray diffraction study (Fig. 3) also shows that the two benzyl
thiolate ligands adopt a syn–exo conformation, pointing away
from the diphosphines. The central {Pt2(l-S)2} ring is hinged
with a dihedral angle of 141◦, a modest increase from the parent
complex, 5 (h = 135◦),3a accompanied by a slight lengthening of
Fig.
3 A 50% thermal ellipsoid representation of the cation of
[Pt2(l-SCH2C6H5)2(dppp)2](PF6)2 (8a). The phenyl rings of dppp and
hydrogen atoms are omitted for clarity.
suggests that the stability of the dialkylated products depend not
only on the peripheral phosphine or the basicity of the counter
anion, but also the nature of the alkyl substituent.
Successful reactions have also been achieved with allyl bromide,
bromoacetonitrile, ethyl 3-bromopropionate and ethyl 6-bromo-
hexanoate, resulting in the formation of [Pt2(l-SCH2CHCH2)2-
(dppp)2]2+ (8b) (m/z 680.5, 100%), [Pt2(l-SCH2CN)2(dppp)2]2+
(8c) (m/z 679, 100%), [Pt2(l-SC2H4CO2CH2CH3)2(dppp)2]2+
(8d) (m/z 740, 100%) and [Pt2(l-SC5H10CO2CH2CH3)2(dppp)2]2+
(8e) (m/z 782, 100%), respectively. As before, the chelating effect
˚
˚
the Pt · · · Pt distance to 3.333 A (from 3.235 A in 5). It is worth
pointing out that although 5 reacts with CH2Cl23a and protic acid8
leading to fragmentation of the {Pt2(l-SR)2} core, examination of
the Pt–S bonds in 8a gives no indication that the Pt–S bonds are
weakened by the dialkylation. A comparison with the molecular
structure of [Pt2(l-S)(l-SCH2C6H5)(PPh3)4](PF6) (3e) (Fig. 4) is
made: the Pt–S(CH2C6H5) bond lengths in the monoalkylated 3e
˚
(Pt(1)–S(1) = 2.3667(13) A) and dibenzylated, 8a (Pt(1)–S(1) =
˚
˚
2.370(3) A and Pt(1)–S(2) = 2.372(3) A) are comparable. This
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and suitable, but in this group, there are many more singly-bridging
[M–l2-S–M] than doubly bridging [M–(l2-S)2–M] sulfides. The
former tends to alkylate to give [M–l2-SR–M]+ but there is little
tendency for a second alkylation to take place. Forceful alkylation
would only lead to the collapse of the complex and release of
R2S. There is also a more facile competitive pathway—alkylation
of the metal giving metal alkyls. The {M2(l-S)2} core is hence
the most convenient template for dithiolato bridged complexes.
Such complexes could provide an entry to other organometallic
complexes.15a Unfortunately, such a core is known to be highly
basic and nucleophilic, and many such complexes could not be
isolated. Hence the [Pt2(l-S)2(PR3)4] or [Pt2(l-S)2(P–P)2] series are
among the very few dinuclear doubly bridging sulfide complexes
that can be isolated and prepared in good yield. Its high shelf-
life and resistance towards (aerial) oxidation or hydrolysis thus
makes this a unique complex and a useful addition to pre-existing
methodology for accessing a range of Pt sulfide-based materials.
Fig.
4
A 50% thermal ellipsoid representation of the cation of
[Pt2(l-S)(l-SCH2C6H5)(PPh3)4](PF6) (3e). The phenyl rings of PPh3 and
hydrogen atoms are omitted for clarity.
Conclusion
of dppp helps to preserve the phosphine and protect it from
displacement by free bromide (Table 2). The free bromide, however,
appears in an ion pair with the dialkylated [Pt2(l-SR)2(dppp)2]2+
complexes giving [{Pt2(l-SR)2(dppp)2}Br]+. Reaction with bro-
moacetonitrile proceeds with completion almost immediately
(within an hour at r.t.) to give the dialkylated species as the sole
product. The other reactions are slower, such that the stepwise
alkylation can be followed by ESI-MS changes. While the reaction
withallyl bromide is completedin5h atr.t., those withlonger chain
halides containing ester fun◦ctionalities are slower and require
heating at approximately 60 C for 2 d in order for dialkylation
to be complete. Preparation of the ESI mass spectrometrically
observed species is straightforward and results in reasonably good
yields, which is illustrated in the preparation of the dialkylated
complexes, [Pt2(l-SCH2CHCH2)2(dppp)2](PF6)2 (8b) (80% yield)
and [Pt2(l-SCH2CN)2(dppp)2](PF6)2 (8c) (71% yield).
We have found a simple solution to a long-standing problem. The
method developed herein allows us to bypass the use of thiolato
substrates16 such as [Pt(SR)2(PR3)2] which are generally prepared
from the repulsive thiols RSH or their salts.17 The alternative of
using 1 or 5 as a precursor also has other advantages such as its
easy preparation from cheap and readily available Na2S by a one-
pot method. Another key benefit is that the current methodology
is generally applicable to a large variety of aliphatic, aromatic
and heterocyclic halides. Using the mononuclear thiolato route
would be problematic because this would require the subsequent
preparation of the [Pt(SR)2(PR3)2] that makes use of functional
thiols that are unstable and may be difficult to access. Isolation
of the complexes described suggests that we could design and
incorporate different functionalities on the alkyl residue such as
nitrile, ester, allyl, benzyl, indolyl and ketone, etc. The syntheses
herein therefore could provide a pathway to functional thiolates
for different applications. In addition, our method potentially
paves the way to prepare hetero-dithiolated complexes, [Pt2(l-
SR)(l-SRꢀ)(dppp)2]2+ (where R = Rꢀ = CH3). Details of such
syntheses will be reported in due course. Our current effort is
hence directed at anchoring the {Pt2(l-S)2} moiety on a solid
support by thiolato spacers thus expanding the current use of
thiolates in homogeneous catalysis,16a,18 molecular electronics,16b,19
and medicine,20 etc.
The use of dppp to enhance the sulfide reactivity and rate
towards alkylation has an opposite effect to that used by
Henderson et al.13 on AsPh3 and Gonza´lez-Duarte et al.14 on
Ph2As(CH2)2AsPh2 (dpae); the latter ligands tend to reduce the
basicity of the {Pt2(l-S)2} core. With this knowledge, we are now
in a better position to tune and control the reactivity of the sulfide
bridge towards a range of Lewis acids or electrophiles and direct
the product outcome, be it mono- or dithiolate formation, and tri-
or tetrametallic aggregate formation.
Although alkylation of the l-sulfido ligands is an established
concept,15 it is ironic that such a seemingly straightforward and
powerful reactivity has resulted in only a few synthetically useful
methods in the preparation of thiolate bridged complexes. There
are a few main reasons. The majority of sulfide complexes in
the literature have l3 or capping sulfide, which has very poor
nucleophilicity towards R–X. These are not suitable precursors for
thiolate complexes. The l2 bridging sulfide is much more reactive
Experimental
Methods and materials
All manipulations were carried out at room temperature, unless
otherwise stated, under an atmosphere of nitrogen. Solvents used
were generally analytical grade (Tedia), dried and deoxygenated
before used. [Pt2(l-S)2(PPh3)4] (1) was synthesized by metathesis
of cis-[PtCl2(PPh3)2] with Na2S·9H2O (Riedel-de Hae¨n) in benzene
suspension, followed by filtration, and washing with water to
remove soluble sodium salts. ESI-MS (80% MeOH–20% H2O):
m/z 1503 [M + H+]. [Pt2(l-S)2(dppp)2] (5) was synthesized
according to published methods.3a ESI-MS (80% MeOH–20%
H2O): m/z 1279 [M + H]+. The following chemicals were used as
4012 | Dalton Trans., 2007, 4008–4016
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supplied from Aldrich: allyl bromide, benzyl bromide, bromoace-
tonitrile, 3-bromopropionitrile, 3-(2-bromoethyl)indole, 2-bromo-
4ꢀ-phenylacetophenone, 2-bromo-2ꢀ-methoxyacetophenone, and
ammonium hexafluorophosphate. Ethyl 3-bromopropionate and
ethyl 6-bromohexanoate were obtained from TCI.
[Pt2(l-SC10H10N)2(PPh3)4](PF6)2
(2a). 3-(2-Bromoethyl)-
indole (79.2 mg, 0.353 mmol, 7 equiv.) was introduced into
an orange suspension of 1 (79.2 mg, 0.053 mmol) in methanol
(35 mL). The mixture was stirred for 4 h to give a pale yellow
solution, followed by the addition of excess NH4PF6 (20.0 mg,
0.123 mmol). Deionized water (70 mL) was added to induce
precipitation. Pale yellow powder of 2a (98.6 mg, 90%) was
obtained after washing with water (100 mL) and diethyl ether
Elemental analyses were performed on a Perkin-Elmer PE
1
2400 CHNS elemental analyzer. H and 13C NMR spectra were
recorded at 25 ◦C on a Bruker ACF 300 spectrometer (at 300 and
75.47 MHz, respectively) with Me4Si as internal standard. The
31P NMR spectra were recorded at 25 ◦C at 121.50 MHz with
85% H3PO4 as external reference. Electrospray mass spectra were
obtained in the positive-ion mode with a Finnigan/MAT LCQ
mass spectrometer coupled with a TSP4000 HPLC system and the
crystal 310 CE system. The mobile phase was 80% methanol–20%
H2O (flow rate: 0.4 mL min−1). The capillary temperature was
150 ◦C. Peaks were assigned from the m/z values and from the
isotope-distribution patterns.
(100 mL) using vacuum suction filtration. 31P{ H} NMR
1
(CD2Cl2): dP = 19.6 ppm (s, 1JPt–P = 2926 Hz); 1H NMR (CD2Cl2):
dH = 1.64–1.70 (br m, 4 H; 2SCH2), 2.02 (br s, 4 H; 2SCH2CH2),
=
6.53 (s, 2 H; 2C CHNH), 6.81–6.84 (br d, J = 7.9 Hz, 4 H;
2C6H4), 7.00 (br t, J = 7.1 Hz, 4 H; 2C6H4), 7.22–7.49 (m, 60
=
H; 12C6H5), 8.62 (s, 2 H; 2C CHNH); ESI-MS (MeOH–H2O):
m/z (%): 895.5 ([M]2+, 100), 1935 (15, [M]2+[PF6]−); elemental
analysis: calcd (%) for Pt2S2C92H80P6F12N2 (2081.74): C 53.08,
H 3.87, N 1.35, S 3.08; found (%): C 52.80, H 4.02, N 1.39,
S 2.86. Pale yellow crystals of [Pt2(l-SC10H10N)2(PPh3)4](PF6)2
suitable for X-ray crystallographic analysis were obtained from
dichloromethane–methanol.
Syntheses
[Pt2(l-S)(l-SCH2CH2CN)(PPh3)4](PF6) (3a). 3-Bromopro-
pionitrile (20.0 lL, 32.3 mg, 0.241 mmol, 12 equiv.) and
compound 1 (29.9 mg, 0.020 mmol) in methanol (10 mL) gave
a yellow solution within 10 min. After stirring for 2.25 h,
excess NH4PF6 (15.0 mg, 0.092 mmol) was added, turning the
solution into a yellow suspension. Deionized water (30 mL)
was used to complete the precipitation. The yellow precipitate
was washed with deionized water (100 mL) and diethyl ether
(100 mL) using vacuum suction filtration to yield a bright
[Pt2(l-SCH2C(O)C6H4C6H5)2(PPh3)4](PF6)2 (2b). 2-Bromo-
4ꢀ-phenylacetophenone (65.0 mg, 0.236 mmol, 6 equiv.) was
introduced into an orange suspension of 1 (59.7 mg, 0.040 mmol)
in methanol (22 mL). Solubilization occurred after 5 min and the
dark yellow solution was left to stir overnight. Excess NH4PF6
(20.0 mg, 0.123 mmol) was added, resulting in a light yellow
suspension. Deionized water (50 mL) was added to complete
precipitation. Yellowish–orange powder of 2b (84.8 mg, 98%)
was obtained after washing with water (100 mL) and diethyl
1
yellow powder of 3a (29.4 mg, 87%). 31P{ H} NMR (CDCl3):
1
1
dP = 24.6 ppm (br s, JPt–P(1) = 3319 Hz, JPt–P(2) = 2579 Hz);
1H NMR (CD2Cl2): dH = 1.80 (t, J = 7.5 Hz, 2 H; CH2CN),
1.97 (br s, 2 H; SCH2), 7.09–7.40 ppm (m, 60 H; 12C6H5);
ESI-MS (MeOH–H2O): m/z (%): 1557 ([M]+, 100); elemental
analysis: calcd (%) for Pt2S2C75H64P5F6N (1702.47): C 52.91,
H 3.80, N 0.82, S 3.77; found (%):C 52.67, H 3.65, N 0.81, S
4.04. Yellow crystals of [Pt2(l-S)(l-SCH2CH2CN)(PPh3)4](PF6)
suitable for X-ray crystallographic analysis were obtained from
dichloromethane–methanol.
1
ether (100 mL) using vacuum suction filtration. 31P{ H} NMR
(CD2Cl2): dP = 20.0 ppm (s, 1JPt–P = 3117 Hz); 1H NMR (CD2Cl2):
dH = 2.08 (br s, 4 H; 2SCH2), 7.06–7.79 (m, 18 H; 2C6H4C6H5),
7.06–7.79 ppm (m, 60 H; 12C6H5); ESI-MS (MeOH/H2O):
m/z (%): 946 ([M]2+, 100); elemental analysis: calcd (%) for
Pt2S2C100H82P6F12O2 (2183.83): C 55.00, H 3.78, S 2.94; found
(%): C 54.89, H 3.17, S 2.56.
[Pt2(l-SCH2C6H5)2(dppp)2](PF6)2
(8a). Benzyl
bromide
[Pt2(l-S)(l-SC2H4CO2CH2CH3)(PPh3)4](PF6) (3b). Ethyl 3-
bromopropionate (50.0 lL, 63.0 mg, 0.348 mmol, 10 equiv.)
and compound 1 (50.8 mg, 0.034 mmol) in methanol (20 mL)
gave a yellow solution after 10 min. The mixture was stirred
for 2.5 h, followed by the addition of excess NH4PF6 (15.0 mg,
0.092 mmol), which turned the solution into a yellow suspension.
Deionized water (50 mL) was used to complete the precipitation.
Yellow powder of 3b (48.4 mg, 82%) was obtained by washing
with deionized water (100 mL) and diethyl ether (100 mL) using
(40.0 lL, 57.5 mg, 0.336 mmol, 9 equiv.) was added to a bright
yellow solution of 5 (49.5 mg, 0.039 mmol) in methanol (18 mL).
The mixture was left to stir overnight until the reaction reached
completion (ESI-MS (MeOH–H2O): m/z (%): 730.2 (100, [M]2+),
1540.9 (36, [M]2+Br−)). Excess NH4PF6 (20.0 mg, 0.123 mmol)
was then added to the pale yellow solution. Deionized water
(40 mL) was used to induce precipitation. Pale yellow powder
of 8a (55.1 mg, 81%) was obtained by washing with deionized
water (100 mL) and diethyl ether (100 mL) using vacuum suction
1
1
1
vacuum suction filtration. 31P{ H} NMR (CD2Cl2): dP = 24.7 ppm
filtration. 31P{ H} NMR (CD2Cl2): dP = −0.7 ppm (s, JPt–P
=
(br s, 1JPt–P(1) = 3280 Hz, 1JPt–P(2) = 2596 Hz); 1H NMR (CD2Cl2):
dH = 1.24 (t, J = 7.2 Hz, 3 H; OCH2CH3), 1.62 (t, J =
8.6 Hz, 2 H; CH2CO), 2.35 (br s, 2 H; SCH2), 3.98–4.06 (q, J =
7.2 Hz, 2 H; OCH2), 7.06–7.43 ppm (m, 60 H; 12C6H5); ESI-
MS (MeOH–H2O): m/z (%): 1604 ([M]+, 100); elemental analysis:
calcd (%) for Pt2S2C77H69P5F6O2 (1749.52): C 52.86, H 3.98, S
3.67; found (%): C 52.78, H 3.95, S 3.54. Orange crystals of
[Pt2(l-S)(l-SC2H4CO2CH2CH3)(PPh3)4](PF6) suitable for X-ray
crystallographic analysis were obtained from dichloromethane–
methanol.
2733 Hz); 1H NMR (CD2Cl2): dH = 1.95 (br s, 4 H; 2SCH2), 2.90
(br s, 8 H; 2PC3H6P), 3.35 (br s, 4 H; 2PC3H6P), 6.44–6.46 (d,
J = 6.2 Hz, 4 H; 2CH2C6H5), 6.98–7.05 (m, 6 H; 2CH2C6H5),
7.29–7.76 ppm (m, 40 H; 8C6H5); ESI-MS (MeOH–H2O): m/z
(%): 730.5 ([M]2+, 100), 1606.0 (15, [M]2+[PF6]−); elemental
analysis: calcd (%) for Pt2S2C68H66P6F12 (1751.36): C 46.63, H
3.80, S 3.66; found (%): C 46.99, H 3.85, S 3.23. Pale yellow
crystals of [Pt2(l-SCH2C6H5)2(dppp)2](PF6)2 suitable for X-ray
crystallographic analysis were obtained from dichloromethane–
methanol.
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[Pt2(l-SCH2CHCH2)2(dppp)2](PF6)2 (8b). Allyl bromide
(40.0 lL, 55.9 mg, 0.462 mmol, 11 equiv.) was added to a bright
yellow solution of 5 (54.7 mg, 0.043 mmol) in methanol (18 mL).
The mixture was stirred for 5 h until tbe reaction reached
completion (ESI-MS (MeOH–H2O): m/z (%): 680.2 (100, [M]2+),
1439.7 (35, [M]2+Br−)). Excess NH4PF6 (20.0 mg, 0.123 mmol) was
then added, resulting in a light yellow suspension. Deionized water
(40 mL) was used to complete precipitation. Pale yellow powder
of 8b (56.3 mg, 80%) was obtained by washing with deionized
water (100 mL) and diethyl ether (100 mL) using vacuum suction
100), 1505 ([M]2+[PF6]−, 55); elemental analysis: calcd (%) for
Pt2S2C60H62P6F12 (1651.25): C 43.64, H 3.78, S 3.88; found (%): C
43.29, H 3.55, S 3.32.
[Pt2(l-SCH2CN)2(dppp)2](PF6)2 (8c). A procedure similar to
the above was employed. Bromoacetonitrile (40.0 lL, 68.9 mg,
0.574 mmol, 15 equiv.) was added into a bright yellow solution
of 5 (47.1 mg, 0.037 mmol) in methanol (20 mL). The mixture
was stirred for 2 h followed by the addition of excess NH4PF6
(20.0 mg, 0.123 mmol), resulting in a light yellow suspension.
Deionized water (40 mL) was used to complete precipitation. Pale
yellow powder of 8c (42.9 mg, 71%) was obtained by washing
with deionized water (100 mL) and diethyl ether (100 mL) using
1
1
filtration. 31P{ H} NMR (CD2Cl2): dP = 0.7 ppm (s, JPt–P
=
1
2726 Hz); H NMR (CD2Cl2): dH = 1.96 (br m, 4 H; 2SCH2),
2.83–2.95 (br m, 12 H; 2PC3H6P), 4.64 (m, 2 H; 2CHCHaHb), 4.74
(m, 2 H; 2CHCHaHb), 4.79 (m, 2 H; 2SCH2CH), 7.35–7.76 ppm
(m, 40 H; 8C6H5); ESI-MS (MeOH–H2O): m/z (%): 680 ([M]2+,
1
vacuum suction filtration. 31P{ H} NMR (CD2Cl2): dP = 0.8 ppm
1
(s, JPt–P = 2775 Hz); 1H NMR (CD2Cl2): dH = 2.04 (br m,
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for complexes 3a, 3b, 2a, 8a and 3e
[Pt2(l-S)(l-SCH2CH2CN)(PPh3)4](PF6) (3a)
Pt(2)–P(3)
Pt(2)–P(4)
2.2884(19)
2.2981(16)
Pt(2)–S(1)
Pt(2)–S(2)
2.3525(18)
2.345(5)
Pt(1)–S(1)
Pt(1)–S(2)
2.3371(16)
2.388(5)
S(1)–C(1)
1.882(13)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(2)–Pt(2)
S(1)–Pt(1)–S(2)
89.82(6)
88.78(18)
84.28(12)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–S(1)
P(1)–Pt(1)–S(2)
98.12(5)
93.62(6)
171.61(12)
P(2)–Pt(1)–S(1)
P(2)–Pt(1)–S(2)
C(1)–S(1)–Pt(1)
168.17(6)
171.61(12)
102.2(4)
C(1)–S(1)–Pt(2)
101.6(4)
144
ha
[Pt2(l-S)(l-SC2H4CO2CH2CH3)(PPh3)4](PF6) (3b)
Pt(1)–P(1)
Pt(1)–P(2)
2.3002(15)
2.2794(14)
Pt(1)–S(1)
Pt(1)–S(1A)
2.3458(14)
2.3313(14)
Pt(2)–S(1)
2.3312(14)
S(1)–C(1)
1.821(11)
157
Pt(1)–S(1)–Pt(2)
S(1)–Pt(1)–S(2)
P(1)–Pt(1)–P(2)
95.70(5)
81.59(6)
99.76(5)
P(1)–Pt(1)–S(1)
P(1)–Pt(1)–S(2)
P(2)–Pt(1)–S(1)
87.32(5)
168.86(5)
172.79(5)
P(2)–Pt(1)–S(2)
C(1)–S(1)–Pt(1)
C(1)–S(1)–Pt(2)
91.30(5)
109.2(3)
103.3(4)
ha
[Pt2(l-SC10H10N)2(PPh3)4](PF6)2 (2a)
Pt(1)–P(1)
Pt(1)–P(2)
2.2929(13)
2.3105(15)
Pt(1)–S(1)
Pt(1)–S(2)
2.3498(13)
2.3812(12)
Pt(2)–S(1)
Pt(2)–S(2)
2.3689(12)
2.3533(12)
S(1)–C(1)
S(2)–C(11)
1.830(6)
1.839(6)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(2)–Pt(2)
S(1)–Pt(1)–S(2)
90.42(5)
90.04(4)
81.89(4)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–S(1)
P(1)–Pt(1)–S(2)
97.69(5)
94.18(5)
175.43(5)
C(1)–S(1)–Pt(1)
C(1)–S(1)–Pt(2)
103.5(2)
109.20(19)
ha
140
[Pt2(l-SCH2C6H5)2(dppp)2](PF6)2 (8a)
Pt(1)–P(1)
Pt(1)–P(2)
2.286(3)
2.289(3)
Pt(1)–S(1)
Pt(1)–S(2)
2.370(3)
2.372(3)
Pt(2)–S(1)
Pt(2)–S(2)
2.361(3)
2.376(3)
S(1)–C(1)
S(2)–C(8)
1.836(13)
1.843(11)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(2)–Pt(2)
S(1)–Pt(1)–S(2)
89.58(10)
89.18(9)
83.50(9)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–S(1)
P(1)–Pt(1)–S(2)
90.37(11)
92.51(10)
170.88(10)
C(1)–S(1)–Pt(1)
C(1)–S(1)–Pt(2)
108.2(5)
105.5(4)
ha
141
[Pt2(l-S)(l-SCH2C6H5)(PPh3)4](PF6) (3e)
Pt(1)–P(1)
Pt(1)–P(2)
2.3011(14)
2.2671(13)
Pt(1)–S(1)
Pt(1)–S(2)
2.3667(13)
2.3209(13)
Pt(2)–S(1)
Pt(2)–S(2)
2.3594(13)
2.3363(13)
S(1)–C(1)
1.850(6)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(2)–Pt(2)
S(1)–Pt(1)–S(2)
89.96(4)
91.66(5)
81.45(5)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–S(1)
P(1)–Pt(1)–S(2)
98.71(5)
87.69(5)
168.81(5)
P(2)–Pt(1)–S(1)
P(2)–Pt(1)–S(2)
C(1)–S(1)–Pt(1)
172.61(5)
92.30(5)
100.13(19)
C(1)–S(1)–Pt(2)
105.0(2)
140
ha
a
h = Dihedral angle between the two PtS2 planes.
4014 | Dalton Trans., 2007, 4008–4016
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Table 4 Crystallographic data for complexes 3a, 3b, 2a, 8a and 3e
Complex
3a
3b
2a·1.5CH2Cl2·CH3OH
8a·4CH2Cl2
3e·2CH2Cl2·2CH3OH
Formula
M
C75H64F6NP5Pt2S2 C77H69F6O2P5Pt2S2
C94.5H87Cl3F12N2OP6Pt2S2 C72H74Cl8F12P6Pt2S2 C83H79Cl4F6O2P5Pt2S2
1702.42
Monoclinic
P2(1)/c
23.038(3)
12.9432(17)
23.952(3)
90
1749.47
Monoclinic
C2/c
17.5679(16)
19.0008(16)
21.5327(19)
90
2241.13
Triclinic
P1
2091.03
Triclinic
P1
1981.41
Triclinic
P1
Crystal system
Space group
¯
¯
¯
˚
a/A
13.1226(5)
17.2989(7)
21.3799(8)
89.893(10)
87.216(10)
72.929(10)
4633.7(3)
2
13.5578(11)
24.083(2)
27.457(2)
112.135(2)
101.057(2)
94.877(2)
8027.4(11)
4
13.5370(11)
14.0622(12)
24.080(2)
81.118(2)
85.273(2)
61.710(2)
3987.7(6)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
110.173(3)
90
90.508(3)
90
3
˚
V/A
4465.0(5)
4
1.687
7187.4(11)
4
1.617
Z
qcalcd/g cm−3
1.606
1.730
1.650
l/mm−1
4.412
4.119
3.323
3.988
3.853
Temperature/K
Reflections measured
Independent reflections 15 395
223(2)
46 800
223(2)
24 358
8243
183(2)
61 431
21 244
223(2)
105 953
36 850
223(2)
51 960
18 308
Rint
0.0584
865
0.0449
0.1127
0.969
0.0574
448
0.0435
0.1244
0.985
0.0365
1117
0.044
0.1336
1.075
2.943, −1.384
0.0897
1864
0.082
0.2457
1.050
5.711, −2.565
0.0486
949
0.0475
0.1265
1.043
3.732, −1.801
Parameters
R (F, F2 > 2r)
Rw (F2, all data)
Goodness of fit on F2
Max., min. electron
density/e A
1.781, −0.846
2.377, −0.593
−3
˚
−
4 H; 2SCH2), 2.54–3.01 (br m, 12 H; 2PC3H6P), 7.12–7.51 ppm
(m, 40 H; 8C6H5); ESI-MS (MeOH–H2O): m/z (%): 679 ([M]2+,
100), 1503 ([M]2+[PF6]−, 70); elemental analysis: calcd (%) for
Pt2S2C58H56N2P6F12 (1649.19): C 42.24, H 3.42, N 1.70, S 3.89;
found (%): C 42.42, H 3.71, N 1.16, S 3.84.
one titled cation and one PF6 anion in the asymmetrical unit.
There are also two dichloromethane and two methanol solvent
molecules. Restraints were applied in the refinement of 3a, 3b and
8a. Restraints to the bond lengths and thermal parameters of the
atoms were used for atoms involved in disorder and in structures
for which the data quality needs to be improved. Upon application
of restraints, the bond distances and thermal parameters became
better and the R values were not increased.
X-Ray crystal structure determination and refinement†
The selected bond lengths and angles for complexes 3a, 3b, 2a,
8a and 3e are given in Table 3. All measurements were made on
a Bruker AXS SMART APEX diffractometer equipped with a
Acknowledgements
We acknowledge the National University of Singapore for finan-
cial support and S. H. Chong thanks NUS for a Kiang Ai Kim
Graduate Research Scholarship. We are grateful to L. L. Koh and
G. K. Tan for assistance in the X-ray single-crystal crystallographic
data collection and analyses.
˚
CCD area detector by using Mo-Ka radiation (k = 0.71073 A).
The software SMART21 was used for the collection of data frames,
for indexing reflections, and to determine lattice parameters;
SAINT21 was used for the integration of the intensity of the
reflections and for scaling; SADABS22 was used for empirical
absorption correction; and SHELXTL23 was used for space group
and structure determination, refinements, graphics, and structure
reporting. The structure was refined by full-matrix least squares on
F2 with anisotropic thermal parameters for non-hydrogen atoms.
A summary of crystallographic parameters for the data collections
and refinements is given in Table 4.
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