Tuning the sulfur-heterometal interaction in organolead(IV) complexes of [Pt2(μ-S)2(PPh3)4]

Article abstract of DOI:10.1016/j.jorganchem.2007.07.010

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with Ph₃PbCl, Ph₂PbI₂, Ph₂PbBr₂ and Me₃PbOAc result in the formation of bright yellow to orange solutions containing the cations [Pt₂(μ-S)₂(PPh₃)₄PbR₃]⁺ (R₃ = Ph₃, Ph₂I, Ph₂Br, Me₃) isolated as PF₆^- or BPh₄^- salts. In the case of the Me₃Pb and Et₃Pb systems, a prolonged reaction time results in formation of the alkylated species [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (R = Me, Et). X-ray structure determinations on [Pt₂(μ-S)₂(PPh₃)₄PbMe₃]PF₆ and [Pt₂(μ-S)₂(PPh₃)₄PbPh₂I]PF₆ have been carried out, revealing different coordination modes. In the Me₃Pb complex, the (four-coordinate) lead atom binds to a single sulfur atom, while in the Ph₂PbI adduct coordination of both sulfurs results in a five-coordinate lead centre. These differences are related to the electron density on the lead centre, and indicate that the interaction of the heterometal centre with the {Pt₂S₂} metalloligand core can be tuned by variation of the heteroatom substituents. The species [Pt₂(μ-S)₂(PPh₃)₄PbR₃]⁺ display differing fragmentation pathways in their ESI mass spectra, following initial loss of PPh₃ in all cases; for R = Ph, loss of PbPh₂ occurs, yielding [Pt₂(μ-S)₂(PPh₃)₃Ph]⁺, while for R = Me, reductive elimination of ethane gives [Pt₂(μ-S)₂(PPh₃)₃PbMe]⁺, which is followed by loss of CH₄.

Full text of DOI:10.1016/j.jorganchem.2007.07.010

Journal of Organometallic Chemistry 692 (2007) 4933–4942
www.elsevier.com/locate/jorganchem
Tuning the sulfur–heterometal interaction in organolead(IV)
complexes of [Pt2(l-S)2(PPh3)4]
a
a,
a
b,
*
Kristina Pham , William Henderson *, Brian K. Nicholson , T.S. Andy Hor
a
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
b
Received 15 May 2007; accepted 11 July 2007
Available online 14 July 2007
Abstract
Reactions of [Pt2(l-S)2(PPh3)4] with Ph3PbCl, Ph2PbI2, Ph2PbBr2 and Me3PbOAc result in the formation of bright yellow to orange
solutions containing the cations [Pt2(l-S)2(PPh3)4PbR3]+ (R3 = Ph3, Ph2I, Ph2Br, Me3) isolated as PF6ꢀ or BPh4ꢀ salts. In the case of the
Me3Pb and Et3Pb systems, a prolonged reaction time results in formation of the alkylated species [Pt2(l-S)(l-SR)(PPh3)4]+ (R = Me, Et).
X-ray structure determinations on [Pt2(l-S)2(PPh3)4PbMe3]PF6 and [Pt2(l-S)2(PPh3)4PbPh2I]PF6 have been carried out, revealing differ-
ent coordination modes. In the Me3Pb complex, the (four-coordinate) lead atom binds to a single sulfur atom, while in the Ph2PbI adduct
coordination of both sulfurs results in a five-coordinate lead centre. These differences are related to the electron density on the lead cen-
tre, and indicate that the interaction of the heterometal centre with the {Pt2S2} metalloligand core can be tuned by variation of the het-
eroatom substituents. The species [Pt2(l-S)2(PPh3)4PbR3]+ display differing fragmentation pathways in their ESI mass spectra, following
initial loss of PPh3 in all cases; for R = Ph, loss of PbPh2 occurs, yielding [Pt2(l-S)2(PPh3)3Ph]+, while for R = Me, reductive elimination
of ethane gives [Pt2(l-S)2(PPh3)3PbMe]+, which is followed by loss of CH4.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Platinum complexes; Lead complexes; Sulfide ligands; Crystal structures; Electrospray mass spectrometry
1. Introduction
related selenide complex [Pt2(l-Se)2(PPh3)4] [7], leading to
the isolation and characterisation of a range of new
Pt2SnE2 trimetallic aggregates. In this paper we report
the extension of this methodology to adducts formed
between [Pt2(l-S)2(PPh3)4] and organolead(IV) com-
pounds. To date, only adducts of (inorganic) lead(II) have
been described; reaction of [Pt2(l-S)2(PPh3)4] and
Pb(NO3)2 gave [Pt2(l-S)2(PPh3)4Pb(NO3)2] which with
NH4PF6 gave [Pt2(l-S)2(PPh3)4Pb(NO3)]PF6, with both
complexes characterised by X-ray crystallography[8]. The
related complex [Pt2(l-S)2(dppf)2] [dppf = 1,10-bis(diph-
enylphosphino)ferrocene] forms a similar lead(II) adduct
[Pt2(l-S)2(dppf)2Pb(NO3)](NO3) [9] and lead(II) adducts
of [Pt2(l-S)2(PPh3)4] have been examined theoretically [10].
In a series of recent papers we have been applying the
technique of electrospray ionisation mass spectrometry
(ESI MS) to probe the coordination chemistry of the met-
alloligand [Pt2(l-S)2(PPh3)4] [1–4]. This methodology
allows the rapid screening of reaction systems on a small
scale, with promising systems then being investigated on
a more traditional macroscopic scale for full characterisa-
tion [5]. Because the ESI technique involves soft ionisation,
solution ions are transferred in an essentially intact state
into the gas phase, so such an MS-directed synthetic meth-
odology gives a good picture of solution speciation.
Using this methodology we have previously investigated
organo-tin(IV) adducts of [Pt2(l-S)2(PPh3)4] [6] and of the
2. Results
*
Corresponding authors. Tel.: +64 7 838 4656; fax: +64 7 838 4219.
The reaction of [Pt2(l-S)2(PPh3)4] with Ph3PbCl in meth-
E-mail addresses: w.henderson@waikato.ac.nz (W. Henderson),
andy.hor@nus.edu.sg (T.S.A. Hor).
anol rapidly led to the formation of a clear, bright yellow
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.010

4934
K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
solution which was shown by ESI MS to contain solely the
triphenyllead(IV) adduct [Pt2(l-S)2(PPh3)4PbPh3]+ (m/z
1941). From this solution, solid products 1a and 1b were
readily isolable in good yields by addition of NH4PF6 or
NaBPh4, respectively. The complexes give satisfactory
microanalytical data and are stable and soluble in polar
solvents such as dichloromethane and chlorofoꢀrm. The cat-
ion could also be isolated as its N(SO2C2F5)2 salt 1c, as
orange-yellow crystals; the presence of the anion in this
derivative was confirmed by negative-ion ESI MS. The
reaction of [Pt2(l-S)2(PPh3)4] with 0.5 mol equivalents of
hexaphenyldilead (Ph3Pb–PbPh3) also results in the forma-
tion of [Pt2(l-S)2(PPh3)4PbPh3]+. Using this route, com-
plex 1a was isolated in 77% yield, and the product had
identical ESI MS and 31P–{1H} NMR spectroscopic prop-
erties to 1a prepared from Ph3PbCl. The mechanism by
which this reaction occurs is unknown, but Ph3Pb–PbPh3
has been well established as a source of Ph3PbR com-
pounds through Pb–Pb bond cleavage [11]. In contrast,
no reaction was observed between [Pt2(l-S)2(PPh3)4] and
PbPh4 in refluxing methanol.
(l-SMe)(PPh3)4]+, was easily identified by comparison of
its spectral parameters with an authentic sample of
[Pt2(l-S)(l-SMe)(PPh3)4]I prepared according to the litera-
ture procedure [14], and found to have the same chemical
shifts and 1J(PtP) coupling constants as reported [2591
and 3220 Hz for phosphines trans to S and SMe, respec-
tively]. The second component gave a single 31P resonance
1
[d 17.3, J(PtP) 3101 Hz] indicating a symmetrical struc-
ture. The complex cis-[Pt(SMe)2(PPh3)2] can be ruled out
on the basis of its reported 31P NMR data [d 25.5,
1J(PtP) 2862 Hz] [16], but it is possible that the product
is the trans isomer of [Pt(SMe)2(PPh3)2]. The neutral com-
plex [Pt(SMe)2(PPh3)2] would be expected to show a low
ionisation efficiency in the ESI mass spectrum, however
the mass spectrum of the crude product did show a very
low intensity ion at m/z 766, assigned to [Pt(SMe)-
(PPh3)2]+, an ion that might be expected to be observed
for such a complex.
The reaction of [Pt2(l-S)2(PPh3)4] with Et3PbOAc was
also investigated by ESI MS, and found to parallel that
of the methyl system, giving the species [Pt2(l-S)2-
(PPh3)4PbEt3]+ at m/z 1797. However, conversion to the
(previously unreported) ethylated derivative [Pt2(l-S)-
(l-SEt)(PPh3)4]+ at m/z 1532 occurred more rapidly. The
relative reactivity of the methyl and ethyl systems was
subsequently compared by the competitive reaction of
[Pt2(l-S)2(PPh3)4] with 0.5 molar equivalents of each of
Me3PbOAc and Et3PbOAc in methanol. The starting mate-
rials quickly dissolved (<1 min) to produce a clear, bright
yellow solution that contained equal amounts of [Pt2-
(l-S)2(PPh3)4PbMe3]+ and [Pt2(l-S)2(PPh3)4PbEt3]+ as
the base peaks in the ESI mass spectrum. This was then
followed by the slower conversion to the species [Pt2-
(l-S)(l-SR)(PPh3)4]+, with the ethyl derivative being
formed significantly more rapidly. Noteworthy in this
reaction system was the observation of a (low intensity)
species at m/z 1769, tentatively assigned to the mixed-alkyl
species [Pt2(l-S)2(PPh3)4PbMe2Et]+, though interestingly
[Pt2(l-S)2(PPh3)4PbMeEt2]+ was not observed.
The reaction of [Pt2(l-S)2(PPh3)4] with Me3PbOAc in
methanol was more complex, and the products formed
were dependent on the reaction time. A clear, bright yellow
solution rapidly formed, and after a short reaction time (ca.
1 h), ESI MS showed the expected parent ion [Pt2(l-
S)2(PPh3)4PbMe3]+ (m/z 1755) as essentially the sole spe-
cies >m/z 400. A low intensity ion was observed at m/z
562, assigned to [(Me3Pb)2OAc]+; this species has been
observed previously in the ESI mass spectrum of Me3Pb-
OAc [5]. The trimethyllead adduct was isolated as its
ꢀ
PF6 salt 2, by addition of excess NH4PF6 to the filtered
reaction solution; satisfactory microanalytical data were
1
obtained. The H NMR spectrum of the complex shows
the PbCH3 groups as a singlet at d 1.16, showing coupling
to 207Pb of 61.5 Hz. This value can be compared to 68 and
63 Hz for Me3PbBr and Me3PbI, respectively [12]. The 31P–
{1H} NMR spectrum showed a single resonance at d 23.2
with coupling to 195Pt of 2944 Hz.
When the reaction between [Pt2(l-S)2(PPh3)4] and
Me3PbOAc was monitored by ESI MS, [Pt2(l-S)2(PPh3)4-
PbMe3]+ was observed to form rapidly, followed by a
much slower conversion to a species at m/z 1518, which
was assigned to the mono-methylated species [Pt2(l-S)-
(l-SMe)(PPh3)4]+, confirmed by examination of the high
resolution isotope pattern. This species is well-known from
early studies on [Pt2(l-S)2(PPh3)4]; it has been synthesised
from the reaction of [Pt2(l-S)2(PPh3)4] with MeI in diethyl
ether, [13,14], and has been generated in situ on a (MS-
monitored) micro-scale by reaction of [Pt2(l-S)2(PPh3)4]
with a range of methylating agents, such as MeI, MeBr,
Me2SO4, and MeP(O)(OMe)2 [15]. After 9 days, ESI MS
of the reaction mixture showed predominantly [Pt2(l-S)-
(l-SMe)(PPh3)4]+, which was isolated as a crude hexaflu-
orophosphate salt by addition of NH4PF6 to the filtered
reaction mixture. The 31P–{1H} NMR spectrum of this
product showed two components. The first, [Pt2(l-S)-
The observation of the alkylated species [Pt2(l-S)-
(l-SR)(PPh3)4]+ (R = Me, Et) in reactions between
[Pt2(l-S)2(PPh3)4] and R3PbOAc indicates that the R3Pb+
group is acting as an alkylating agent. Heavy element
organometallics have previously been reported to act as
alkylating or arylating agents [17], including PbMe4 [18]
and trimethyllead species [19]. In contrast, prolonged reac-
tion (>1 week) between [Pt2(l-S)2(PPh3)4] and either
Ph3PbCl or Pb2Ph6 produced no phenylated derivative.
Diaryl-lead(IV) halide systems have also been investi-
gated; the reaction of [Pt2(l-S)2(PPh3)4] with Ph2PbI2
yielded an orange solution, containing predominantly
[Pt2(l-S)2(PPh3)4PbPh2I]+ at m/z 1991 together with [Pt2-
(l-S)2(PPh3)4PbPh2]2+ at m/z 932. The dicationic nature
of the latter ion was confirmed by its isotope distribution
pattern. In this system, the soft iodide anion has a tendency
to remain coordinated to the soft lead(IV) centre. On pre-
cipitation of the product with excess NH4PF6, an orange

K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
4935
solid was obtained which gave good elemental microana-
lytical data for the iodo complex [Pt2(l-S)2(PPh3)4-
PbPh2I]PF6 (3). The 31P–{1H} NMR spectrum showed a
single sharp peak at d 16.2, showing coupling to 195Pt of
3068 Hz. However, the ESI MS spectrum (in methanol)
of the isolated orange solid showed a roughly equal mix-
ture of [Pt2(l-S)2(PPh3)4PbPh2I]+ and [Pt2(l-S)2(PPh3)4-
PbPh2]2+. It is feasible that in a polar solvent (such as
methanol) some dissociation occurs due to the low concen-
tration of iodide in the polar solvent. Consistent with this,
addition of a small quantity of aqueous NaI solution to the
methanol analyte solution resulted in complete conversion
to the iodo complex [Pt2(l-S)2(PPh3)4PbPh2I]+. Recrystal-
lisation of the iodo complex 3 by vapour diffusion of
diethyl ether into a dichloromethane solution gave a
homogenous sample of orange blocks of the complex suit-
able for an X-ray diffraction study, which confirmed its for-
mulation, as described in the following section. Analysis of
one crystal by ESI MS again showed the iodo complex as
the base peak, but with [Pt2(l-S)2(PPh3)4PbPh2]2+ still
observed (50% relative intensity).
behaviour in ESI MS analysis, giving both [Pt2(l-S)2-
(PPh3)4PbPh2Br]+ (m/z 1944) and [Pt2(l-S)2(PPh3)4-
PbPh2]2+ (m/z 932). Likewise, reaction of [Pt2(l-S)2(PPh3)4]
with Ph2PbBr2 followed by addition of a large excess of
KSCN yielded a yellow solid which analysed as the thiocy-
anato derivative [Pt2(l-S)2(PPh3)4PbPh2SCN]SCN (5) on
the basis of ESI MS (product cation at m/z 1922), 31P–
1
{1H} NMR [d 15.74, J(PtP) 3091] and elemental analysis.
3. X-ray structure determinations on [Pt2(l-S)2(PPh3)4-
PbMe3]PF6 (2) and [Pt2(l-S)2(PPh3)4PbPh2I]PF6 (3)
The structure of the cation of the trimethyllead derivative
2 is illustrated in Fig. 1. It consists of the usual P4Pt2S2 core
with the Me3Pb+ group attached to one of the two S atoms.
There is no significant interaction with the other S atom, as
˚
evidenced by the longer Pb–S distance [3.835(1) A c.f.
˚
2.611(1) A for the bonded one] and by the symmetrical
geometry around the Pb atom (C–Pb–C angles essentially
equal at 115.0 1.6ꢁ). For comparison, Me3PbSMe has a
˚
Pb–S distance of 2.588 A and C–Pb–C angles of 117 2ꢁ
[20]. The Pt–S distances to the lead-bonded S atom average
In a similar manner, reaction of [Pt2(l-S)2(PPh3)4] with
Ph2PbBr2 gave a yellow solution which furnished the anal-
ogous bromo complex [Pt2(l-S)2(PPh3)4PbPh2Br]PF6 (4)
on addition of NH4PF6. This complex showed similar
31P NMR spectroscopic parameters to the iodo complex
[d 16.1, 1J(PtP) 3087 Hz], and also showed analogous
˚
˚
2.374 A, while those to the two-coordinate S are 2.329 A.
It is noteworthy that in the 31P–{1H} NMR spectrum of this
complex, a single sharp resonance was observed at room
temperature, suggesting that the complex is fluxional in
solution, with the PbMe3 group hopping between S centres.
C(2)
C(3)
C(1)
Pb(1)
S(2)
P(3)
Pt(2)
Pt(1)
P(1)
S(1)
P(2)
P(4)
Fig. 1. Structure of the cation of [Pt2(l-S)2(PPh3)4PbMe3]PF6 (2), showing the atom labelling scheme. For clarity, only the ipso carbon atoms of the six
PPh3 ligands have been shown.

4936
K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
Upon cooling to 223 K, the spectrum remained essentially
unchanged, suggesting a very facile exchange process.
In contrast, the structure of the Ph2IPb+ analogue 3
shown in Fig. 2 has the lead atom interacting with both
S atoms, though not equally. The Pb–S(1) distance is short
at 2.567(2) A, while Pb–S(2) is 2.879(2) A. This results in a
five-coordinate Pb atom with pseudo trigonal bipyramidal
coordination, the I and S(2) atoms occupying the axial
positions [I–Pb–S(2) angle 156.6ꢁ]. A similar arrangement
was also found for the corresponding Me2ClSn+ and
(PhCH2)2BrSn+ analogues [1]. Related systems are known
in the literature, for example the complex [Ph2Pb(dmit)]
examples of derivatives of (Ph3P)4Pt2S2 in the Cambridge
Crystallographic Database (May 2006 version), most of
these having the equivalent dihedral angle in the range
123–147ꢁ with a mean value of 134ꢁ (excluding the parent
complex with an angle of 168ꢁ [24], and two unusual
examples with two AuCl or AgCl groups attached to the
S atoms, with angles of 180ꢁ [25]). However there does
not seem to be any particular pattern to variations in this
fold-angle in terms of the number or type of groups
attached to the sulfur atom(s), so it appears it is a flexible
parameter determined by intramolecular and crystal
packing interactions and is not a consequence in 2 and 3
of differing Pb coordination.
˚
˚
(H2dmit = 4,5-dimercapto-1,3-dithiole-2-thione),
which
adds iodide to give [Ph2Pb(dmit)I]ꢀ; the same product is
formed from Ph2PbI2 and (Et4N)2[Zn(dmit)2] [21].
4. Electrospray mass spectrometry study
˚
The Pb–I distance of 2.9208 A in 3 is longer than the
equivalent in a four-coordinate R3Pb–I compound (2.849
A study of the cone voltage-induced fragmentation of
the organolead(IV) adducts [Pt2(l-S)2(PPh3)4PbMe3]+
and [Pt2(l-S)2(PPh3)4PbPh3]+ has been carried out, in
order to explore differences in fragmentation pathways
imposed by the different organic groups. A number of stud-
ies have previously concerned the ESI MS analysis of
organolead complexes. In an early study, the ESI MS
behaviour of Me3PbCl and Et3PbCl were studied and
yielded the parent [R3Pb]+ cations under low fragmenta-
tion conditions.[26] At a fragmentor voltage of 100 V, the
most abundant fragment ions were formed by loss of R–
R, while at 150 V, the bare lead cation [Pb]+ was observed.
˚
A) [22] but is similar to a pseudo-five-coordinate equivalent
˚
with an intramolecular coordinated –NMe2 group (2.956 A)
[23]. Presumably it would take little to remove the I atom and
convert 3 into the dication [Pt2(l-S)2(PPh3)4PbPh2]2+ with a
Ph2Pb group symmetrically attached to both S atoms. This is
consistent with the observation that the ‘parent’ [Pt2(l-S)2-
(PPh3)4PbPh2I]+ cation readily loses iodide in ESI MS anal-
ysis, giving [Pt2(l-S)2(PPh3)4PbPh2]2+
.
One significant difference between 2 and 3 is the dihedral
angle formed by the two P2PtS2 planes in each cation,
138.1ꢁ for 2 and 126.3ꢁ for 3. There are approximately 70
C(15)
C(25)
C(16)
C(14)
C(26)
C(22)
I(1)
C(11)
C(24)
C(21)
C(13)
C(23)
Pb(1)
C(12)
S(1)
P(3)
Pt(1)
P(2)
S(2)
Pt(2)
P(4)
P(1)
Fig. 2. Structure of the cation of [Pt2(l-S)2(PPh3)4PbPh2I]PF6 (3), showing the atom labelling scheme. For clarity, only the ipso carbon atoms of the six
PPh3 ligands have been shown.

K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
4937
Similar results have been observed for Me3PbOAc [5].
Aryllead(IV) carboxylates have also been studied [27] and
ESI has been used in the ‘bare metal’ or ‘elemental’ mode,
for the quantitative analysis of organolead compounds
[28]. A study of diphenyl lead(IV) thiosemicarbazonate
complexes found that fragmentation by loss of two phenyl
groups occurred first, giving product ions in which the
Pb–S bond is retained [29].
loss of an additional PPh3 from [Pt2(l-S)2(PPh3)3Ph]+,
and at even higher voltages such as 140 V the base peak
is an ion at m/z 977 is formed by elimination of PhH from
[Pt2(l-S)2(PPh3)2Ph]+.
Contrasting behaviour was observed in the fragmenta-
tion of the trimethyllead ion [Pt2(l-S)2(PPh3)4PbMe3]+
when analysed under comparable conditions; a series of
spectra for 2 at increasing cone voltage are shown in
Fig. 4. The ion [Pt2(l-S)2(PPh3)4PbMe3]+ was the only major
peak observed at low to moderate cone voltages (e.g. 50 V,
Fig. 4a). In comparable behaviour to [Pt2(l-S)2(PPh3)4-
PbPh3]+, at higher cone voltages (e.g. 90 V, Fig. 4b) the first
fragment ion formed was [Pt2(l-S)2(PPh3)3PbMe3]+ at m/z
1493, formed by simple loss of a PPh3 ligand. At this cone
voltage, an ion at m/z 1463 was also observed; this ion
became the base peak at 120 V, Fig. 4c. The loss of 30 Da
clearly indicates fragmentation by loss of ethane, and the
ion at m/z 1463 is assigned to [Pt2(l-S)2(PPh3)3PbMe]+. This
is similar to the fragmentation process for [Me3Pb]+ itself
[26], and analogous loss of ethane from cationic dimethyl
derivatives of gold(III) and thallium(III) has been previously
reported [30]. It is at this point that the fragmentation path-
ways of [Pt2(l-S)2(PPh3)3PbMe3]+ and [Pt2(l-S)2(PPh3)3-
PbPh3]+ have clearly diverged. When the cone voltage is
further increased to 140 V (Fig. 4d), the base peak now
becomes an ion at m/z 1185. Examination of the high resolu-
tion isotope pattern shows that this ion has the formula
[Pt2(l-S)2(PPh3)2Pb–H]+, formed by loss of CH4 and PPh3
from [Pt2(l-S)2(PPh3)3PbMe]+; this ion may contain a cyclo-
metallated PPh3 ligand.
Positive-ion ESI mass spectra for [Pt2(l-S)2(PPh3)4-
PbPh3]PF6 (1a) in dichloromethane–methanol solution
are shown in Fig. 3. At low cone voltages, e.g. up to
50 V (Fig. 3a), the parent ion [Pt2(l-S)2(PPh3)4PbPh3]+
(m/z 1941) dominates. Increasing the cone voltage to
80 V begins to effect fragmentation, with an ion at m/z
1679 being formed initially, and assigned to the species
[Pt2(l-S)2(PPh3)3PbPh3]+, formed by dissociation of a
PPh3 ligand; at 100 V (Fig. 3b) this is the base peak. For-
mation of another ion at m/z 1317 is also observed, becom-
ing the base peak at a cone voltage of 120 V (Fig. 3c). This
ion is assigned as the phenylated species [Pt2(l-S)2(PPh3)3-
Ph]+, which may contain a l-SPh group, and presumably
formed by loss of neutral PbPh2 from [Pt2(l-S)2(PPh3)3-
PbPh3]+. The parent species [Pt2(l-S)2(PPh3)4Ph]+, which
is presumably [Pt2(l-S)(l-SPh)(PPh3)4]+, has been gener-
ated by reaction of [Pt2(l-S)2(PPh3)4] with phenylating
agents such as PhBr and [Ph2I]Cl [15]. Loss of isotopi-
cally-rich Pb has a noticeable effect in compressing the iso-
tope envelope of the ion [Pt2(l-S)2(PPh3)3Ph]+, compared
to lead-containing ions. At 120 V, an ion at m/z 1055 is
assigned to the species [Pt2(l-S)2(PPh3)2Ph]+, formed by
Fig. 3. Positive-ion ESI mass spectra of the complex [Pt2(l-S)2(PPh3)4PbPh3]PF6 (1a), at cone voltages of (a) 20 V, (b) 100 V and (c) 120 V.

4938
K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
Fig. 4. Positive-ion ESI mass spectra of the complex [Pt2(l-S)2(PPh3)4PbMe3]PF6 (2), at cone voltages of (a) 50 V, (b) 90 V, (c) 120 V and (d) 140 V.
Interestingly, a single crystal of [Pt2(l-S)2(PPh3)4PbMe3]-
PF6 (obtained by slow crystallisation from CH2Cl2-Et2O)
showed, in addition to the dominant parent ion at m/z
1755, a low intensity ion at m/z 1503, assigned as [Pt2(l-S)2-
(PPh3)4H]+. A likely explanation of this is that the free sul-
fide centre can be protonated, destabilising the complex,
resulting in the extrusion of Me3Pb+ and formation of the
protonated species [Pt2(l-S)2(PPh3)4H]+. The monodentate
their electron-withdrawing effect strengthening the Pt–P
bonds [6]. In this work, the values of 1J(PtP) for the lead(IV)
adducts [PbPh2Br (3087 Hz) > PbPh2I (3068 Hz) > PbPh3
(3013 Hz) > PbMe3 (2944 Hz)] follow the expected trend
and confirm that the PbMe3 group is the weakest Lewis
acid. For the weaker Lewis acids PbMe3 and PbEt3 the
electronic requirements of the lead atom are readily satisfied
by coordination to a single sulfide donor, while for the
stronger Lewis acid PbPh2I+, both sulfides are coordinated
(one more strongly than the other in the solid state), giving a
five-coordinate lead centre.
+
+
+
nature of the {Pt2S2} metalloligand towards the PbMe3
fragment could promotes such a process, compared to a
bidentate system (as in the PbPh2I+ derivative).
Exchange reactions have also been explored using ESI
MS. Methanolic solutions of [Pt2(l-S)2(PPh3)3PbMe3]+
with added Ph3PbCl, and of [Pt2(l-S)2(PPh3)3PbPh3]+ with
added Me3PbOAc were prepared, and analysed by ESI MS.
In the former system complete exchange of the organolead
groups occurred, yielding [Pt2(l-S)2(PPh3)3PbPh3]+, but no
reaction was observed for the latter system.
It is noteworthy that alkylation reactions occur for [Pt2-
(l-S)2(PPh3)3PbMe3]+, (through Pb–C bond cleavage) and
more rapidly for [Pt2(l-S)2(PPh3)3PbEt3]+, but arylation
does not occur at all for [Pt2(l-S)2(PPh3)3PbPh3]+ nor for
[Pt2(l-S)2(PPh3)3PbPh2I]+. Although the structure of
+
PbPh3 adduct has not been determined, it would not be
unreasonable to suggest that it has an analogous structure
to the PbPh2I+ adduct, with a five-coordinate lead.
Increased steric bulk at Pb and the lack of availability of
a free sulfide could account for the lack of arylation reac-
tivity in the PbPh3 and Ph2PbX (X = Br, I) systems. ESI
MS observations indicate that Ph3Pb+ forms a more stable
solution adduct with the {Pt2S2} metalloligand than does
Me3Pb+, consistent with stronger bonding to the more
5. Discussion
The metalloligand [Pt2(l-S)2(PPh3)4] readily forms
adducts with chemically soft lead(IV) species by displace-
ment of halide ligands, analogous to the organo-tin(IV) sys-
+
tems [6]. The mode of binding of a PbR3 fragment to the
+
{Pt2S2} metalloligand core appears to depend on the Lewis
acidity of the lead moiety. A study of the variation in
1J(PtP) coupling constants in a series of organo-tin(IV)
adducts of [Pt2S2(PPh3)4] found that the stronger Lewis
strongly Lewis acidic PbPh3 fragment, which interacts
with both sulfur donors.
A possible mechanism that accounts for the alkylation
process is shown in Scheme 1, and involves intramolecular
attack of the free sulfide group at a Pb–CH2 carbon, resulting
1
acids result in observation of higher J(PtP) values, due to

K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
4939
+
R
Ph P
3
S
Ph P
3
S
Ph P Pt
3
CH
CH
2
+
Ph P Pt
3
Pb
Ph P Pt
3
+
[Pb(CH R) ]
2 2
2
Ph P Pt
3
S
Ph P
3
CH
2
R
S
Ph P
3
CH R
2
R
R = H or CH3
Scheme 1.
in transfer of the alkyl group from Pb to S. Presumably,
PbR2 is generated in this process. Simple divalent organo-
lead compounds are known to be unstable with respect to
lead(IV) [31], and PbR2 would not be expected to be detected
in the ESI mass spectrum due to the anticipated lack of an
ionisation pathway. To account for the greater reactivity in
the ethyl system, it is possible that the lead centre would be
more electron-rich than in the methyl case (due to the posi-
tive inductive effect of the additional Me groups), so that
chloroform solution of either iodine or bromine (2 mol
equiv.) to a chloroform solution of Ph4Pb. The product
was isolated by reduction in the volume of the solution
and addition of petroleum spirits, giving yellow (Ph2PbI2)
or white (Ph2PbBr2) microcrystals.
7. Synthesis of [Pt2(l-S)2(PPh3)4PbPh3]PF6 (1a)
A suspension of [Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol)
and Ph3PbCl (71 mg, 0.150 mmol) in methanol (30 mL)
was stirred at room temperature, resulting in the rapid for-
mation of a clear, bright yellow solution. After stirring for
24 h, the solution was filtered to remove a trace of insoluble
matter, and to the filtrate was added NH4PF6 (100 mg,
0.613 mmol), resulting in the formation of a yellow micro-
crystalline solid. After stirring for 10 min water (10 mL)
was added to complete precipitation. The product was iso-
lated by filtration, washed with water (10 mL) and dried
under vacuum to give 1a (198 mg, 71%) as a bright yellow
solid. M.p. decomp. >300 ꢁC. Anal. Calc. for C90H75F6P5-
PbPt2S2: C, 51.8; H, 3.6. Found: C, 51.6; H, 3.6%. 31P–
+
the Pb–S bond is further weakened, the PbEt3 group is a
poorer Lewis acid still, and alkyl transfer occurs more rap-
idly. The observation that a key mass spectrometric frag-
mentation of [Pt2(l-S)2(PPh3)3PbMe3]+ is via elimination
of Me–Me, but analogous loss of Ph–Ph is not observed
for [Pt2(l-S)2(PPh3)3PbPh3]+ is also consistent with the pres-
ence of weaker Pb–C(alkyl) bonds.
6. Experimental
General experimental procedures were as described in
recent publications from these laboratories [1–4]. ESI mass
spectra were recorded on a VG Platform II instrument in
positive-ion mode, using methanol as the mobile phase.
Reaction solution aliquots were diluted with methanol
prior to analysis, while isolated salts were dissolved in sev-
eral drops of CH2Cl2 before diluting with MeOH to give a
total solid concentration of ca. 0.1 mg mLꢀ1. Confirmation
of species was facilitated by comparison of observed and
calculated isotope distribution patterns, the latter obtained
from the Isotope program [32]. Reported m/z values are for
the most intense peak in the isotope distribution envelope.
Elemental analyses were obtained by the Campbell Micro-
analytical Laboratory at the University of Otago, Dunedin,
New Zealand.
1
{1H} NMR, d 21.8 [s, J(PtP) 3013]. ESI MS m/z 1941,
[Pt2(l-S)2(PPh3)4PbPh3]+ (100%).
8. Synthesis of [Pt2(l-S)2(PPh3)4PbPh3]BPh4 (1b)
Following the synthesis of 1a, complex 1b was prepared
analogously, replacing NH4PF6 by NaBPh4 (150 mg,
0.439 mmol), resulting in the immediate formation of a
light yellow precipitate; no water was added in this case.
Following filtration and washing with cold methanol, com-
plex 1b was obtained (201 mg, 67%). Anal. Calc. for
C114H95BP4PbPt2S2: C, 60.6; H, 4.2. Found: C, 60.3; H,
4.5%.
The compounds triphenyllead chloride (Aldrich), trim-
ethyllead acetate (Aldrich), triethyllead acetate (Aldrich),
tetraphenyllead (Aldrich), hexaphenyldilead (Aldrich),
sodium tetraphenylborate (BDH), potassium thiocyanate
(BDH), Li[N(SO2C2F5)2] (3M) and ammonium hexaflu-
orophosphate (Aldrich) were used as received. The com-
pound [Pt2(l-S)2(PPh3)4] was prepared by the literature
procedure [13]. Diphenyllead diiodide and diphenyllead
dibromide were prepared by the dropwise addition of a
9. Synthesis of [Pt2(l-S)2(PPh3)4PbPh3]N(SO2C2F5)2 (1c)
Following the general procedure for 4a, Complex 1c was
isolated in 52% yield by addition of LiN(SO2C2F5)2 to the
filtered reaction solution, and was obtained as small
orange-yellow crystals. The presence of the cation and
anion were confirmed by positive- and negative-ion
[N(SO2C2F5)2ꢀ, m/z 380] ESI MS, respectively.

4940
K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
10. Synthesis of [Pt2(l-S)2(PPh3)4PbPh3]PF6 (1a) from
Pb2Ph6
after ca. 10 min. A positive-ion ESI mass spectrum showed
[Pt2(l-S)2(PPh3)4PbPh2I]+ as the dominant species. After fil-
tration, solid NH4PF6 (200 mg, 1.227 mmol) was added to
the filtrate, giving an orange solid, which was filtered off,
washed with water, and dried to give 3 (198 mg, 70%). Anal.
Calc. for C84H70F6IP5PbPt2S2: C, 47.2; H, 3.3. Found: C,
47.2; H, 3.5%. A positive-ion ESI mass spectrum in metha-
nol showed a mixture of [Pt2(l-S)2(PPh3)4PbPh2I]+ (m/z
1991) and [Pt2(l-S)2(PPh3)4PbPh2]2+ (m/z 932). 31P–{1H}
NMR, d 16.23 [s, 1J(PtP) 3068]. Recrystallisation by vapour
diffusion of diethyl ether into a dichloromethane solution of
the complex yielded bright orange crystals of 3, shown by the
X-ray structure determination to be the Æ3CH2Cl2 solvate.
These lose solvent upon standing in air when removed from
the mother liquor.
A suspension of [Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol)
and Pb2Ph6 (59 mg, 0.067 mmol) in methanol (30 mL) was
stirred at room temperature, giving a clear, bright yellow
solution after several hours. ESI MS showed predomi-
nantly the [Pt2(l-S)2(PPh3)4PbPh3]+ cation. After stirring
for 36 h, the solution was filtered, and NH4PF6 (100 mg,
0.613 excess) added to the stirred filtrate, giving a yellow
precipitate. After addition of water (30 mL), the product
was filtered off, washed with water (10 mL), and dried
under vacuum to give 1a (215 mg, 77%), which was spec-
troscopically identical to the sample of 1a prepared from
Ph3PbCl.
11. Synthesis of [Pt2(l-S)2(PPh3)4PbMe3]PF6 (2)
14. Synthesis of [Pt2(l-S)2(PPh3)4PbPh2Br]PF6 (4)
Following the general method for 1a (from Ph3PbCl), a
suspension of [Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol) with
Me3PbOAc (73 mg, 0.234 mmol) in methanol (30 mL) was
stirred at room temperature, rapidly giving a bright yellow
solution which was stirred for 1.5 h. Filtration, followed
by addition of NH4PF6 (100 mg, 0.613 mmol) to the filtrate
gave a bright yellow microcrystalline solid (199 mg, 79%).
Anal. Calc. for C75H69F6P5PbPt2S2: C, 47.4; H, 3.7. Found:
C, 47.6; H, 3.8%. ESI MS m/z 1755, [Pt2(l-S)2(PPh3)4-
[Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol) and Ph2PbBr2
(75 mg, 0.144 mmol) in methanol (30 mL) was stirred at
room temperature for 40 min., giving a clear yellow-orange
solution. After filtration, solid NH4PF6 (200 mg, 1.227
mmol) was added to the filtrate, giving a yellow-orange
precipitate, which was filtered, washed with water, and
dried to give 4 (195 mg, 70%). Anal. Calc. for C84H70BrF6-
P5PbPt2S2: C, 48.3; H, 3.4. Found: C, 48.1; H, 3.3%. ESI
MS: [Pt2(l-S)2(PPh3)4PbPh2Br]+ (m/z 1944, 70%) and
[Pt2(l-S)2(PPh3)4PbPh2]2+ (m/z 932, 100%).31P–{1H}
1
PbMe3]+ (100%). 31P–{1H} NMR, d 23.2 [s, J(PtP) 2944].
2
1
1H NMR, 1.16 [s, Pb–Me, J(207PbH) 61.5] and 7.35–7.05
NMR, d 16.14 [s, J(PtP) 3087].
(m, Ph). Recrystallisation by vapour diffusion of diethyl
ether into a dichloromethane solution gave bright yellow
blocks.
15. Synthesis of [Pt2(l-S)2(PPh3)4PbPh2(SCN)]SCN (5)
When this reaction was repeated using a longer reaction
time (>24 h), ESI MS of the isolated product, which had a
slightly oily consistency, showed the presence of a substan-
tial quantity of [Pt2(l-S)(l-SMe)(PPh3)4]+ at m/z 1518.
[Pt2(l-S)2(PPh3)4] (281 mg, 0.187 mmol) and Ph2PbBr2
(113 mg, 0.218 mmol) in methanol (30 mL) was stirred at
room temperature for 1 h. To the resulting clear yellow-
orange solution was added KSCN (500 mg, large excess),
resulting in the rapid deposition of a yellow precipitate.
The mixture was stirred for 22 h, and the yellow product
filtered, washed with water (2 · 10 mL) and dried under vac-
uum to give 5 (310 mg, 84%). Anal. Calc. for C86H70N2-
P4PbPt2S4: C, 52.1; H, 3.6; N, 1.4. Found: C, 51.1; H, 3.4;
N, 1.4%. 31P–{1H} NMR, d 15.73 [s, 1J(PtP) 3091].
12. Synthesis of crude [Pt2(l-S)(l-SMe)(PPh3)4]PF6 using
Me3PbOAc
A mixture of [Pt2(l-S)2(PPh3)4] (100 mg, 0.067 mmol)
with Me3PbOAc (36 mg, 0.116 mmol) in methanol (30 mL)
was stirred, while being monitored periodically by positive-
ion ESI MS. After 9 days, the dominant species observed
was [Pt2(l-S)(l-SMe)(PPh3)4]+ at m/z 1518. The resulting
light yellow solution was filtered to remove a trace of insolu-
ble matter, and to the filtrate was added NH4PF6 (150 mg,
0.920 mmol), giving a light yellow precipitate. Water
(10 mL) was added to assist precipitation, and the solid
was filtered off, washed with 10 mL water, and dried under
vacuum to give crude [Pt2(l-S)(l-SMe)(PPh3)4]PF6 (62 mg).
16. X-ray crystallography
X-ray intensity data were collected on a Bruker CCD
diffractometer using standard procedures and software.
Empirical absorption corrections were applied (SADABS
[33]). Structures were solved by direct methods and devel-
2
oped and refined on Fo using the SHELX programmes [34]
operating under WINGX [35]. Hydrogen atoms were
included in calculated positions.
13. Synthesis of [Pt2(l-S)2(PPh3)4PbPh2I]PF6 (3)
17. Structure of [Pt2(l-S)2(PPh3)4PbMe3]PF6 (2)
A suspension of [Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol)
and Ph2PbI2 (110 mg, 0.179 mmol) in methanol (30 mL) was
stirred at room temperature, giving a clear orange solution
Yellow prismatic crystals were obtained from CH2Cl2/
Et2O.

K. Pham et al. / Journal of Organometallic Chemistry 692 (2007) 4933–4942
4941
Table 1
(Rint 0.0305) used after correction for absorption (Tmax, min
0.350, 0.229). Crystal dimensions 0.32 · 0.26 · 0.24 mm3.
Selected bond parameters for [Pt2(l-S)2(PPh3)4PbMe3]PF6 (2) and [Pt2(l-
S)2(PPh3)4PbPh2I]PF6 (3)
2
Refinement on Fo converged at R1 0.0466 [I > 2r(I)]
(2)
(3)
and wR2 0.1198 (all data), GoF 1.026. The atoms of the
three solvent molecules showed relatively high Uiso values
suggesting they were not firmly held in the lattice, and
˚
Bond lengths (A)
Pt(1)–S(1)
Pt(1)–S(2)
Pt(2)–S(1)
Pt(2)–S(2)
Pt–P (av)
Pb(1)–S(1)
Pb(1)–S(2)
Pb(1)–I(1)
Pb(1)–C(1)
Pb(1)–C(2)
Pb(1)–C(3)
2.323(1)
2.377(1)
2.335(1)
2.372(1)
2.292(1)
3.835(1)
2.611(1)
2.374(2)
2.351(2)
2.371(2)
2.362(2)
2.299(2)
2.567(2)
2.879(2)
2.9208(6)
2.217(8)
2.222(8)
3
˚
residual De peaks of <5 e A near the I atom suggested that
this also was not completely ordered. The structure of 3 is
illustrated in Fig. 2, with selected bond parameters summa-
rised in Table 1.
Acknowledgements
2.203(3)
2.209(3)
2.210(3)
We thank the University of Waikato and the National
University of Singapore (NUS) for support of this work.
We also thank Kelly Kilpin for recording the NMR spec-
tra, and Dr. Tania Groutso (University of Auckland) for
collection of the X-ray data sets of 2 and 3.
Angles (ꢁ)
P(1)–Pt(1)–P(2)
P(3)–Pt(2)–P(4)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(2)–Pt(2)
Pt(1)–S(2)–Pb(1)
Pt(2)–S(2)–Pb(1)
Pt(1)–S(1)–Pb(1)
Pt(2)–S(1)–Pb(1)
C(1)–Pb(1)–C(2)
C(1)–Pb(1)–C(3)
C(2)–Pb(1)–C(3)
C(1)–Pb(1)–I(1)
C(2)–Pb(1)–I(1)
S(1)–Pb(1)–I(1)
S(2)–Pb(1)–I(1)
100.69(2)
103.17(2)
93.35(2)
91.06(2)
101.38(2)
99.84(2)
97.44(7)
102.43(7)
86.23(6)
86.95(6)
83.42(5)
81.81(5)
90.21(5)
88.68(5)
114.4(3)
Appendix A. Supplementary material
CCDC 645598 and 645599 contain the supplementary
crystallographic data for 2 and 3. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.jorganchem.2007.07.010.
113.3(1)
114.3(1)
116.6(1)
96.5(2)
99.6(2)
89.32(4)
156.60(4)
Dihedral angle (ꢁ)
P2Pt(1)S2/P2Pt(2)S2
138.1
126.3
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˚
ꢀ
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