Reactions of [Pt2(μ-S)2(PPh3)4] with Group 6 and 7 metal carbonyls; Crystal structure of the apparently unsaturated heterometallic complex [Pt2Re(μ3-S)2(PPh3) 4(CO)3]+

Article abstract of DOI:10.1016/S0022-328X(99)00640-3

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] (1) with a mixture containing [Re₂(CO)₁₀], Me₃NO·2H₂O and MeOH at room temperature affords an oxidative methoxylation complex, [Pt₂Re₂(μ-OMe)₂(μ₃-S) ₂(PPh₃)₄(CO)₆] (2), and a Pt-Re heterometallic salt, [Pt₂Re(μ₃-S)₂(PPh₃) ₄(CO)₃]⁺[Re₃(μ ₃-OMe)(μ-OMe)₃(CO)₉]^- (3a). The core of the cation of 3a comprises a {Pt₂ReS₂} trigonal bipyramidal 'cluster' with weak Pt-Re bonding interactions and an apparently unsaturated Re(I) atom. The [BF₄]^- salt of this cation, 3b, can be prepared by the reaction of 1 with [Re(CO)₅(H₂O)][BF₄], and the Mn analogue, [Pt₂Mn(μ₃-S)₂(PPh₃) ₄(CO)₃][BF₄] (4), can be similarly synthesised using [Mn(FBF₃)(CO)₅]. Addition of 1 to [M(I)₂(CO)₃(NCMe)₂] (M=Mo, W) is accompanied by iodide migration to give the salts [Pt₂M(μ₃-S)₂I(PPh₃) ₄(CO)₄][M(I)₃(CO)₄] (M=Mo, 5; W, 6a). With [Mo(CO)₄(NCMe)₂], 1 undergoes reductive carbonylation and desulfurization to give [Pt₂(μ-S)(PPh₃)₃(CO)] (7). The above reactions represent the first examples of 1 as a metalloligand towards carbonyl complexes of the less electron-rich transition metals, and demonstrate that addition reactions of 1 can be complicated by ligand dissociation, ligand migration, or reductive desulphurization. The crystal structures of compounds 3a and 3b were determined.

Full text of DOI:10.1016/S0022-328X(99)00640-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 595 (2000) 276–284
Reactions of [Pt2(m-S)2(PPh3)4] with Group 6 and 7 metal
carbonyls; crystal structure of the apparently unsaturated
heterometallic complex [Pt2Re(m3-S)2(PPh3)4(CO)3]+
Huang Liu a, Chenghua Jiang a, Jeremy S.L. Yeo a, Kum Fun Mok a, Ling Kang Liu b,
T.S. Andy Hor a,1, Yaw Kai Yan c,*
a Department of Chemistry, Faculty of Science, National Uni6ersity of Singapore, Kent Ridge, Singapore 119260, Singapore
b Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan, ROC
c Di6ision of Chemistry, National Institute of Education, Nanyang Technological Uni6ersity, 469 Bukit Timah Road, Singapore 259756, Singapore
Received 1 September 1999; received in revised form 27 September 1999; accepted 4 October 1999
Abstract
Reaction of [Pt2(m-S)2(PPh3)4] (1) with a mixture containing [Re2(CO)10], Me3NO·2H2O and MeOH at room temperature
affords an oxidative methoxylation complex, [Pt2Re2(m-OMe)2(m3-S)2(PPh3)4(CO)6] (2), and a PtꢀRe heterometallic salt, [Pt2Re(m3-
S)2(PPh3)4(CO)3]+[Re3(m3-OMe)(m-OMe)3(CO)9]− (3a). The core of the cation of 3a comprises a {Pt2ReS2} trigonal bipyramidal
‘cluster’ with weak PtꢀRe bonding interactions and an apparently unsaturated Re(I) atom. The [BF4]− salt of this cation, 3b, can
be prepared by the reaction of 1 with [Re(CO)5(H2O)][BF4], and the Mn analogue, [Pt2Mn(m3-S)2(PPh3)4(CO)3][BF4] (4), can be
similarly synthesised using [Mn(FBF3)(CO)5]. Addition of 1 to [M(I)2(CO)3(NCMe)2] (M=Mo, W) is accompanied by iodide
migration to give the salts [Pt2M(m3-S)2I(PPh3)4(CO)4][M(I)3(CO)4] (M=Mo, 5; W, 6a). With [Mo(CO)4(NCMe)2], 1 undergoes
reductive carbonylation and desulfurization to give [Pt2(m-S)(PPh3)3(CO)] (7). The above reactions represent the first examples of
1 as a metalloligand towards carbonyl complexes of the less electron-rich transition metals, and demonstrate that addition
reactions of 1 can be complicated by ligand dissociation, ligand migration, or reductive desulphurization. The crystal structures
of compounds 3a and 3b were determined. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Platinum; Sulfide; Rhenium; Tungsten; Metalloligand; Heterometallic
1. Introduction
Multinuclear aggregates with three to six metal centres
have been synthesised by the reaction of 1 with a
variety of electron-rich (d8 and d10) metal fragments,
e.g. Cu(I), Ag(I), Au(I), Pd(II), Pt(II), and Rh(I) [1–6].
There was no apparent initiative for similar experimen-
tation to be carried out with the earlier metals as 1 was
not expected to behave differently towards these metals.
Using some representative Group 6 ([Mo(I)2(CO)3-
(NCMe)2], [W(I)2(CO)3(NCMe)2], and [Mo(CO)4(NC-
Me)2]) and Group 7 ([Re2(CO)10], [Re(CO)5(H2O)][BF4]
and [Mn(FBF3)(CO)5]) metal carbonyls as substrates,
we demonstrate, however, that in the course of the
formation of heterometallic Lewis acid/base adducts
with 1, complications such as ligand dissociation and
migration, ion-pair formation or reductive desulfur-
ization can occur, which lead to some unexpected prod-
ucts. This is best illustrated by the reactions of 1 with
Extensive studies have shown that [Pt2(m-S)2(PPh3)4]
(1) is a versatile precursor in the rational synthesis of
heterometallic multinuclear platinum sulfide complexes
[1–7]. The nucleophilicity and adjustable orientations
of the sulfur lone pairs in 1 make the complex a
powerful Lewis base that supports a wide variety of
coordination geometries of the heterometals.
* Corresponding author. Fax: +65-469-89-52.
E-mail address: ykyan@nie.edu.sg (Y.K. Yan)
1 Also corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00640-3

H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
277
[M(I)2(CO)3(NCMe)2] (M=Mo, W) and [Re2(CO)10]/
Me3NO, which lead to the isolation of [Pt2MI-
(PPh3)4(CO)4(m3-S)2][M(I)3(CO)4] and [Pt2Re(m3-S)2-
[Re2(CO)10]ꢀMe3NOꢀMeOH mixture has been dis-
cussed in our earlier work [9,10].
Complex 3a displays a conductivity in MeOH solu-
tion typical of that of a 1:1 electrolyte in MeOH [11].
Its 31P{1H}-NMR spectrum indicates that the phos-
phine groups are Pt-bound and chemically equivalent.
(PPh3)4(CO)3][Re3(m3-OMe)(m-OMe)3(CO)9],
respec-
tively. The formation of these heterometallic salts from
ligand migration suggests that the metalloligand chem-
istry of 1 is rich and that the current view of its
reactivity being confined to direct adduct formation is
too simplistic.
1
The H-NMR spectrum shows the phenyl peaks in the
7.2–7.5 ppm region. Two singlets attributed to the
m-OCH3 and m3-OCH3 protons are also observed at
4.25 and 4.52 ppm, respectively. The integration ratio
of ca. 20:3:1 confirms the presence of four PPh3 ligands
and three m-OCH3 groups per m3-OCH3 group.
2. Results and discussion
2.1. Reaction of [Pt2(v-S)2(PPh3)4] (1) with Group 7
metal carbonyls
2.2. Crystal structure of [Pt2Re(v3-S)2(PPh3)4(CO)3]-
[Re3(v3-OMe)(v-OMe)3(CO)9] (3a)
Oxidative decarbonylation of [Re2(CO)10] by Me3NO
in the presence of MeOH at room temperature (r.t.)
followed by the addition of 1 results in [Pt2Re2(m-
OMe)2(m3-S)2(PPh3)4(CO)6] (2) and [Pt2Re(m3-S)2-
(PPh3)4(CO)3][Re3(m3-OMe)(m-OMe)3(CO)9] (3a). The
identity of 2, which can be thought of as comprising
two Re(CO)3 units bridged by two methoxo groups and
one dithio ligand [Pt2(m-S)2(PPh3)4], is deduced from its
spectroscopic data, and by the analogy between its
synthesis procedure and that of the analogous diphos-
phine-bridged complexes [Re2(m-OMe)2(m-PP)(CO)6]
(PP=diphosphine) [8].
Single-crystal X-ray diffraction analysis revealed 3a
to be a salt with a heterometallic RePt2 cation and a
homometallic trirhenium anion (Figs. 1 and 2). The
cation is best viewed as a sulfide-bicapped heterometal-
lic {Pt2Re} triangle in a trigonal bipyramidal frame-
work. It is a 48-electron aggregate with an apparently
unsaturated 16-electron, five-coordinate Re(I) core. Al-
though the quality of the structural data is not suffi-
ciently high to allow a detailed bonding analysis, some
geometrical characteristics are significant and worthy of
,
mention. While the Pt···Pt separation (3.275(5) A) is
typically non-bonding [12], the Pt···Re distances
,
(3.067(6) and 3.099(6) A) are within the range for weak
bonding (cf. the PtꢀRe bond lengths of [PtRe3(CO)14(m-
,
H)3] [13] fall in the range of 2.769(1) to 3.067(1) A).
With the Pt and Re atoms in close contact, we can
propose a donation of two electrons from the totally
The IR (wCO) spectrum of complex 2 is very similar to
1
those of the latter [8]. Its H-NMR spectrum shows a
complex resonance at 7.19–7.46 ppm, which is at-
tributed to the phenyl protons of the PPh3 ligands, and
a singlet signal at 4.22 ppm, which is assigned to the
bridging methoxo protons. The integration ratio of ca.
10:1 confirms the presence of four PPh3 ligands per two
methoxo groups. The 31P{1H} spectrum shows a sharp
signal at 17.5 ppm which is flanked symmetrically by a
pair of characteristic 195Pt satellites (1J(31Pꢀ195Pt)=
3255 Hz). This is consistent with the presence of Pt-
bonded phosphines that are chemically equivalent. That
complex 2 is a non-electrolyte in solution is also consis-
tent with its proposed formula. Complex 2 is likely to
be formed via direct attack of 1 on the intermediate
[Re2(CO)8(m-OMe)2], the presence of which in the
Fig. 1. Structure of the cation of [Pt2Re(m3-S)2(PPh3)4(CO)3][Re3(m-
,
OMe)3(m3-OMe)(CO)9] (3a). Key bond lengths (A): Pt(1)···Re(4)
3.099(6), Pt(2)···Re(4) 3.067(6), Pt(1)ꢀS(1) 2.38(2), Pt(1)ꢀS(2) 2.31(2),
Pt(2)ꢀS(1) 2.38(2), Pt(2)ꢀS(2) 2.38(2), Re(4)ꢀS(1) 2.40(2), Re(4)ꢀS(2)
2.40(2).

278
H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
dppm)3]+, where the Re atom achieves its 18-electron
configuration by accepting electrons from the three
PtꢀPt bonds of the [Pt3(m-dppm)3] fragment [14].
It is nevertheless peculiar that the Re(I) centre
chooses to opt for a coordination sphere with three
strong ReꢀCO bonds and two strong ReꢀS bonds, plus
two weak PtꢀRe interactions, rather than the expected
octahedral configuration of {Re(CO)4(SꢀS)} [SꢀS=
Pt2(m-S)2(PPh3)4]. This coordinative unsaturation of the
Re centre may reflect the steric demand of the bulky
metallo ligand 1 on the Re(I) core.
The anion in 3a, [Re3(m3-OMe)(m-OMe)3(CO)9]−, has
previously been structurally characterised as its [NEt4]+
salt [15]. It consists of a Re3 triangle held together by
one face-capping and three edge-bridging methoxo
groups, with no ReꢀRe bonds.
Fig. 2. Structure of the anion of [Pt2Re(m3-S)2(PPh3)4(CO)3][Re3(m-
OMe)3(m3-OMe)(CO)9] (3a).
2.3. Mechanism for the formation of compound 3a
Whilst the precise mechanism for the formation of 3a
is unknown, the cation possibly arises from the dis-
placement of the methoxide group and one CO ligand
of [Re(CO)4(OMe)] by [Pt2(m-S)2(PPh3)4]. The presence
of the intermediate [Re(CO)4(OMe)] in the [Re2-
(CO)10]ꢀMe3NOꢀMeOH reaction mixture has been pre-
viously discussed [16]. The [Re3(m3-OMe)(m-OMe)3-
(CO)9]− anion would then be formed from the aggrega-
tion of the free methoxide with three [Re(CO)4(OMe)]
fragments, with concomitant loss of CO. There is no
Fig. 3. Proposed donation of electron density from the PtꢀS s-bonds
to the empty dz orbital of Re in the cation [Pt2Re(m3-
2
S)2(PPh3)4(CO)3]+
.
evidence that
mechanistically.
2
and 3a are directly related
2.4. Synthesis and crystal structure of
[Pt2Re(v3-S)2(PPh3)4(CO)3][BF4] (3b)
The poor quality of the structural data for 3a is due
mainly to poor crystal quality and disorder in the
[Re3(m3-OMe)(m-OMe)3(CO)9]− anion. Despite repeated
attempts, we were unable to grow better crystals of 3a.
Attempts were thus made to exchange the [Re3(m3-
OMe)(m-OMe)3(CO)9]− anion with [PF6]−, with the
hope that the hexafluorophosphate salt of [Pt2Re(m3-
S)2(PPh3)4(CO)3]+ would be easier to crystallise. More-
over, replacing the disordered [Re3(m3-OMe)(m-OMe)3-
(CO)9]− anion, which contains three very heavy Re
atoms, by an anion comprising much lighter atoms,
should improve the refinement of the atomic coordi-
nates of the [Pt2Re(m3-S)2(PPh3)4(CO)3]+ cation, which
is the focus of our attention. We have not been able,
however, to prepare the hexafluorophosphate salt of
[Pt2Re(m3-S)2(PPh3)4(CO)3]+ by metathesis with
[NH4][PF6].
Fig. 4. Structure of the cation of [Pt2Re(m3-S)2(PPh3)4(CO)3][BF4]
(3b).
symmetric linear combination of s(PtꢀS) orbitals to the
empty dz orbital of Re (Fig. 3). This effectively gives
2
rise to an 18-electron Re(I) centre. The local geometry
of Re(I) can hence be described as a ‘piano stool’ with
the carbonyls serving as the three legs and Pt2S2 as the
seat. This explanation of bonding in 3a is analogous to
that proposed for the cluster [Pt3{m3-Re(CO)3}(m-
An alternative strategy was to synthesise the te-
trafluoroborate salt of [Pt2Re(m3-S)2(PPh3)4(CO)3]+ by
reacting [Pt2(m-S)2(PPh3)4] with [Re(CO)5(H2O)][BF4].
This strategy turned out to be successful, and gave a

H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
279
52% yield of [Pt2Re(m3-S)2(PPh3)4(CO)3][BF4] (3b) as
red–orange crystals.
competition for Re d-orbital interaction between S(2)
and the carbonyl group trans to it {C(3)ꢀO(3)}. Corre-
spondingly, the ReꢀC(3) bond is also the longest of the
three ReꢀCO bonds (Table 1). The average ReꢀCO
The crystal structure of 3b (Fig. 4) confirms the
deductions regarding the [Pt2Re(m3-S)2(PPh3)4(CO)3]+
cation drawn from the crystal structure of 3a. In addi-
tion, the better quality of the structural data for 3b
allows a more detailed analysis of the geometry of the
cation. The {Pt2S2} ring is hinged at an angle of 130°
,
bond length (1.862(1) A) is much shorter than that in
I
,
other fac-{Re (CO)3} units (ca. 1.90 A) [15,17]. The
range of IR wCO frequencies for 3b (2012–1896 cm−1
)
is; however, similar to that for the complexes [Re2(m-
OR)2(m-dppf)(CO)6] [R=H, Me, Et, Ph; dppf=1,1%-
bis(diphenylphosphino)ferrocene] (2027–1887 cm−1),
which also contain fac-{ReI(CO)3} units [9,15]. These
observations suggest that the ReꢀCO backbonding in
3b is quite strong, and that the Re atom is not electron
deficient.
Judging from the ReꢀPt and ReꢀS distances, the
Pt(1)ꢀS(1) bond is the nearest PtꢀS bond to the Re
atom, and is expected to interact most strongly with it.
Correspondingly, the Pt(1)ꢀS(1) bond is the longest of
the PtꢀS bonds (Table 1). This is consistent with the
proposed donation of electron density from the PtꢀS
bonds to the Re atom.
,
(between two PtS2 planes). The Pt···Pt (3.255 A) and
,
S···S (3.080 A) distances are typically non-bonding [12].
The Pt···Re distances are unequal, with the Re atom
,
significantly closer to Pt(1) (3.0668(9) A) than Pt(2)
,
(3.1678(8) A). This is probably due to repulsion be-
tween Pt(2) and the carbonyl group {C(1)ꢀO(1)}. Both
the Pt···Re distances are, however, short enough to be
consistent with the proposed weak Pt···Re bonding
interaction.
,
The ReꢀS(2) bond [2.452(3) A] is slightly longer than
,
the ReꢀS(1) bond (2.437(3) A), probably due to the
Table 1
,
Selected bond lengths (A) and angles (°) for compound 3b
2.5. Reaction of [Pt2(v-S)2(PPh3)4] (1) with
[Mn(FBF3)(CO)5]
Bond lengths
Pt(1)ꢀRe(1)
Pt(2)ꢀRe(1)
Pt(1)ꢀS(1)
Pt(1)ꢀS(2)
Pt(2)ꢀS(1)
Pt(2)ꢀS(2)
Re(1)ꢀS(1)
Re(1)ꢀS(2)
3.0668(9)
3.1678(8)
2.384(3)
2.355(4)
2.359(4)
2.368(3)
2.437(3)
2.452(3)
Re(1)ꢀC(1)
Re(1)ꢀC(2)
Re(1)ꢀC(3)
C(1)ꢀO(1)
C(2)ꢀO(2)
C(3)ꢀO(3)
1.834(1)
1.856(1)
1.895(1)
1.230(1)
1.209(1)
1.168(1)
Reaction of 1 with [Mn(FBF3)(CO)5], generated in
situ by the reaction of AgBF4 with MnBr(CO)5, af-
forded a blue–violet product analysed as [Pt2Mn(m3-
S)2(PPh3)4(CO)3][BF4]·2H2O (4). The 31P-NMR and IR
(wCO) spectra of compound 4 are very similar to those
of 3b, its Re analogue. Compound 4 is rather air-sensi-
tive in solution, however, decomposing within 1 day at
r.t. to a yellow product, which is presently unidentified.
Bond angles
S(1)ꢀPt(1)ꢀS(2)
S(1)ꢀPt(2)ꢀS(2)
Pt(1)ꢀS(1)ꢀPt(2)
Pt(1)ꢀS(2)ꢀPt(2)
Pt(1)ꢀRe(1)ꢀPt(2)
S(1)ꢀRe(1)ꢀS(2)
C(1)ꢀRe(1)ꢀPt(1)
C(2)ꢀRe(1)ꢀPt(1)
C(3)ꢀRe(1)ꢀPt(1)
C(1)ꢀRe(1)ꢀPt(2)
C(2)ꢀRe(1)ꢀPt(2)
C(3)ꢀRe(1)ꢀPt(2)
81.1(1)
81.3(1)
86.7(1)
87.1(1)
62.91(2)
78.1(1)
155.1(4)
106.1(5)
118.2(5)
93.9(5)
140.0(6)
133.8(5)
C(1)ꢀRe(1)ꢀS(1)
C(2)ꢀRe(1)ꢀS(1)
C(3)ꢀRe(1)ꢀS(1)
C(1)ꢀRe(1)ꢀS(2)
C(2)ꢀRe(1)ꢀS(2)
C(3)ꢀRe(1)ꢀS(2)
C(1)ꢀRe(1)ꢀC(2)
C(1)ꢀRe(1)ꢀC(3)
C(2)ꢀRe(1)ꢀC(3)
O(1)ꢀC(1)ꢀRe(1)
O(2)ꢀC(2)ꢀRe(1)
O(3)ꢀC(3)ꢀRe(1)
121.7(6)
152.8(5)
95.3(5)
109.2(4)
94.8(5)
166.8(6)
85.5(8)
84.0(7)
86.0(7)
176(1)
2.6. Reaction of [Pt2(v-S)2(PPh3)4] (1) with Group 6
metal carbonyls
Reactions of 1 with [M(I)2(CO)3(NCMe)2] (M=Mo,
W) in a 1:1 molar ratio in THF are sluggish and leave
behind substantial portions of 1 unreacted. In a molar
ratio of 1:2, the reactions take place readily to give
clear red–brown solutions from which [Pt2M(m3-
S)2I(PPh3)4(CO)4][M(I)3(CO)4] (M=Mo, 5; W, 6a) can
be isolated. These are examples of high-coordinate
M(II) complexes, which have been well-studied by
Baker [18–20] and other researchers [21–26]. Attempts
to grow single crystals of compounds 5 and 6a suitable
for X-ray diffraction studies have been unsuccessful.
The identities of these compounds can, however, be
deduced from their spectroscopic, conductivity and ele-
mental analysis data (see Section 3). The molar conduc-
tivities of 5 and 6a are consistent with the compounds
being 1:1 electrolytes [11]. Both 5 and 6a show eight
terminal carbonyl absorption bands in the range 1868–
2063 cm−1 in their IR spectra (Table 2). The large
number of carbonyl bands over a large absorption
175(1)
178(2)
Table 2
Infrared carbonyl absorption data (KBr discs) of complexes 5, 6a and
6b
Complex
w(CO) (cm−1
)
[Pt2Mo(m3-S)2I(PPh3)4(CO)4]+
[Mo(I)3(CO)4]− (5)
-
2063(s), 2034(m), 2010(vs),
1983(s), 1942(s), 1926(vs),
1881(s), 1870(s)
[Pt2W(m3-S)2I(PPh3)4(CO)4]+
[W(I)3(CO)4]− (6a)
-
2062(s), 2018(m, sh), 2000(vs),
1986(vs), 1960(m), 1923(vs),
1911(s), 1868(s)
[Pt2W(m3-S)2I(PPh3)4(CO)4][PF6] 2067(m), 2000(vs), 1961(m),
(6b) 1927(s)

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H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
Scheme 1.
1,5,9,13-tetrathiacyclohexadecane (Me8[16]aneS4) to
form [MI(CO)3{h3-(Me8[16]aneS4)}][M(I)3(CO)4] (M=
Mo, W) [18a].
region is consistent with a salt with carbonyls on both
the cation and anion. The isomorphic nature of both
complexes is indicated by their similar IR bands. The
absence of nitrile absorptions in the w(CꢁN) region
(2200–2400 cm−1) confirms the complete substitution
of the MeCN ligands. Anion exchange can be carried
out on 6a with NH4PF6 in MeOH solution to give
[Pt2W(m3-S)2I(PPh3)4(CO)4][PF6] (6b) as a red–brown
precipitate. Similar treatment of 5 with NH4PF6, how-
ever, did not yield any precipitate of [Pt2Mo(m3-S)2I-
(PPh3)4(CO)4][PF6]. The presence of the uncoordinated
[PF6]− anion in 6b is verified by a strong IR band at
837 cm−1. Compared to the eight carbonyl absorptions
of 6a, only four CO bands remain in the IR spectrum
of 6b. This is consistent with the presence of four
carbonyl groups in both cation and anion of 6a, respec-
tively. The 31P{1H}-NMR spectra of 5 and 6a, which
give a single resonance with characteristic 195Pt cou-
pling, indicate that the phosphines are Pt-coordinated
and chemically equivalent, as they would be if the
[Pt2(m-S)2(PPh3)4] ligand is coordinated to the Group 6
metal as a chelate via the two sulfur atoms. Elemental
analysis data for 5, 6a and 6b are all in good agreement
with the proposed formulae of the compounds. Further
support for the proposed identities of 5 and 6a is
obtained from the analogy between the reactions lead-
ing to these compounds and the reaction of [M(I)2-
(CO)3(NCMe)2] with 3,3,7,7,11,11,15,15-octamethyl-
The proposed mechanism for the formation of 5 and
6a is shown in Scheme 1. Addition of 1 to [M(I)2(CO)3-
(NCMe)2] gives an addition product that rapidly ionises
through iodide dissociation in a donor solvent. Iodide
substitution of the labile MeCN on [M(I)2(CO)3(NC-
Me)2] yields an ion pair which adds CO (from
[M(I)2(CO)3(NCMe)2]) to give the final products. This
is analogous to the mechanism proposed for the reac-
tion of [M(I)2(CO)3(NCMe)2] with Me8[16]aneS4 to
form [MI(CO)3{h3-(Me8[16]aneS4)}][M(I)3(CO)4] (M=
Mo, W) [18a]. With an 18-electron capped octahedral
MoII/WII, no PtꢀPt or Mo/WꢀPt bond is envisaged for
the cations of compounds 5 and 6a.
Complexes 5 and 6a are air-stable solids, but their
solutions (in MeOH or acetone) are stable only when
stored under argon. The complexes decompose readily
in CH2Cl2 to regenerate 1, which subsequently reacts
with CH2Cl2 to give [Pt2(m-S)(m-SCH2Cl)(PPh3)4]Cl and
finally [Pt(SCH2Cl)2(PPh3)2] [27]. The latter is verified
by 31P{1H}-NMR analysis.
Complex 1 does not give the expected product,
[Pt2Mo(m3-S)2(PPh3)4(CO)4] with [Mo(CO)4(NCMe)2].
Instead, [Pt2(m-S)(PPh3)3(CO)] (7) [28,29] is formed (in
15% yield), and no Mo-containing product can be
isolated.

H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
281
Calc. for C80H66O8P4Pt2Re2S2: C, 45.6; H, 3.1; P, 5.9;
Re, 17.7; S, 3.0. Found: C, 45.2; H, 3.0; P, 5.5; Re,
17.2; S, 2.9%. w(CO) (CH2Cl2) 2007 s, 1993 m, 1914 m
(sh), 1887 vs, 1879 s (sh) cm−1. lH (acetone-d6) 4.22 (s,
6H, m-OCH3) and 7.19–7.46 (m, 60H, Ph); lP (acetone-
1
d6) 17.5 (t, J(31Pꢀ195Pt)=3255 Hz); for 3a·Et2O: Anal.
Calc. for C92H82O17P4Pt2Re4S2: C, 39.7; H, 3.0; P, 4.4;
Pt, 14.0; Re, 26.8; S, 2.3. Found: C, 39.6; H, 3.0; P, 4.5;
Pt, 12.9; Re, 24.7; S, 2.2%. \m (10−3 M, MeOH) 74
ohm−1 cm2 mol−1. w(CO) (acetone) 2011 w, 2004 s,
1916 m, 1893 vs, 1876 sh cm−1. lH (acetone-d6) 4.25 (s,
9H, m-OCH3), 4.52 (s, 3H, m3-OCH3) and 7.2–7.5 (m,
Formation of 7 from 1 signifies a reductive desulfurisa-
tion reaction, which has been discussed elsewhere [28].
The different behaviour of 1 towards [Mo(I)2(CO)3-
(NCMe)2] and [Mo(CO)4(NCMe)2] suggests that the
oxidation state of the heterometal is an important
factor governing the reaction pathway.
1
60H, Ph); lP (acetone-d6) 17.5 (t, J(31Pꢀ195Pt)=3263
Hz).
3. Experimental
3.3. Synthesis of [Pt2Re(PPh3)4(CO)3(v3-S)2][BF4] (3b)
Solid [Pt2(m-S)2(PPh3)4] (0.089 g, 0.06 mmol) was
3.1. Materials and methods
added with stirring to
a solution of [Re(CO)5-
All reactions were performed under argon. All sol-
vents were analytical grade and were distilled and de-
gassed by argon before use. [Pt2(m-S)2(PPh3)4] [30],
[M(I)2(CO)3(NCMe)2] (M=Mo, W) [19a] and [Mo-
(CO)4(NCMe)2] [31] were synthesised according to liter-
ature methods. Elemental analyses were conducted in
the Microanalytical Laboratory in the Department of
Chemistry of the National University of Singapore.
Infrared spectra were taken on a Perkin–Elmer 1600
FTIR spectrophotometer. Conductivity was measured
(H2O)][BF4] [32] (0.024 g, 0.06 mmol) in acetone (30
cm3). The orange suspension dissolved to give a clear
orange solution after 4 h. Stirring was continued for 1
day to ensure complete reaction. The acetone solution
was allowed to vaporise slowly in air. After 2 days,
reddish-orange crystals of 3b appeared (yield 0.057 g,
52%). Anal. Calc. for C75H60F4O3P4Pt2ReS2: C, 48.4;
H, 3.3; P, 6.7; Pt, 21.0; Re, 10.0; S, 3.5. Found: C, 47.5;
H, 3.0; P, 6.2; Pt, 20.7; Re, 11.2; S, 3.9%. w(CO)
(acetone) 2012 s, 1916 m, 1896 m cm−1. lP (acetone-d6)
17.4 (t, 1J(PꢀPt) 3257 Hz). The carbon analysis was
consistently lower than the calculated value, despite
satisfactory agreement for the other elemental analyses,
possibly due to the formation of a small amount of
refractory carbides (rhenium, platinum or boron car-
bides) during combustion analysis.
1
by using a STEM Conductivity 1000 meter. H- and
31P{1H}-NMR spectra were run on a Bruker ACF 300
spectrometer at 298 K. Chemical shifts are quoted in
ppm downfield of Me4Si and 80% H3PO4, respectively.
3.2. Syntheses of [Pt2Re2(PPh3)4(CO)6(v-OMe)2(v3-S)2]
(2) and [Pt2Re(PPh3)4(CO)3(v3-S)2][Re3(CO)9-
(v-OMe)3(v3-OMe)] (3a)
3.4. Reaction of [Pt2(v-S)2(PPh3)4] (1) with
[Mn(FBF3)(CO)5]
A solution of Me3NO·2H2O (0.062 g, 0.56 mmol) in
THF–MeOH (1:1, 20 cm3) was transferred with stirring
into a solution of Re2(CO)10 (0.151 g, 0.23 mmol) in
THF (10 cm3) at r.t. After 4 h complex 1 (0.075 g, 0.05
mmol, as a solid) was introduced into the reaction
mixture. The suspension dissolved in a period of 30 min
to give a clear golden-yellow solution. Stirring was
continued for 3 h to ensure complete reaction. All
solvent was removed under vacuum and the residue was
crystallized in ether–hexane. In 3–4 days a small
amount of yellowish brown clumps of tiny crystals of 2
was formed on the wall of the flask (yield 0.010 g, 10%
based on Pt) together with a chrome-yellow precipitate
of 3a·at the bottom of the flask (yield 0.029 g, 21%
based on Pt). Crystals of 2 were manually separated
from the precipitate of 3a. The latter was then recrys-
tallised from ether–hexane to give orange crystals.
Both 2 and 3a are air sensitive in solution. For 2: Anal.
Solid AgBF4 (0.015 g, 0.08 mmol) was added to a
stirred solution of MnBr(CO)5 (0.016 g, 0.06 mmol) in
CH2Cl2 (30 cm3). The mixture was shielded from light
and allowed to react for 3 h, after which it was filtered
under argon into another Schlenk flask. The CH2Cl2
solvent was removed from the yellow filtrate under
vacuum, and the residue was redissolved in 30 cm3 of
acetone. Solid [Pt2(m-S)2(PPh3)4] (0.087 g, 0.06 mmol)
was then added to the acetone solution, giving an
orange suspension. The suspension turned dark green a
few minutes later and eventually grey after 5 h. The
mixture was stirred for a total of 24 h and then filtered.
The blue–violet filtrate was concentrated under vacuum
and treated with deionised water to precipitate the
product. The blue–violet powder formed was washed
with deionised water, followed by ether, and dried by

282
H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
suction. It was analysed as [Pt2Mn(m3-S)2(PPh3)4-
(CO)3][BF4]·2H2O (4) (0.033 g, 31%). Anal. Calc. for
C75H64BF4O5P4Pt2MnS2: C, 51.0; H, 3.7. Found: C,
50.8; H, 3.6%. w(CO) (acetone) 2010 vs, 1931 m, 1908 m
red–brown precipitate which was separated by filtra-
tion and purified by recrystallisation from acetone–
ether to yield 5 (0.128 g, 53%). Anal. Calc. for C80H60-
I4Mo2O8P4Pt2S2: C, 39.6; H, 2.5; I, 20.9; Mo, 7.9; P,
5.1; Pt, 16.1; S, 2.6. Found: C, 39.6; H, 2.9; I, 19.0; Mo,
8.2; P, 4.9; Pt, 17.1; S, 2.8%. \m (10−3 M, MeOH) 93
ohm−1 cm2 mol−1. lP (acetone-d6) 19.7 (t, 1J(PꢀPt)
=3200 Hz).
1
cm−1. lp (acetone-d6) 18.8 (t, J(PꢀPt)=3258 Hz).
3.5. Synthesis of [Pt2Mo(v3-S)2I(PPh3)4(CO)4]-
[Mo(I)3(CO)4] (5)
Solid [Pt2(m-S)2(PPh3)4] (0.15 g, 0.1 mmol) was added
to a stirred solution of Mo(I)2(CO)3(NCMe)2 (0.103 g,
0.2 mmol) in THF (20 cm3). The solid dissolved imme-
diately to give a clear red–brown solution. After stir-
ring further for 30 min to ensure complete reaction, the
solution was filtered and the filtrate was concentrated
to ca. 10 cm3. Addition of hexane gave rise to a
3.6. Synthesis of [Pt2W(v3-S)2I(PPh3)4(CO)4]X
(X=[W(I)3(CO)4]−, 6a; [PF6]−, 6b)
Complex 6a was prepared in a manner analogous
to
5 by reacting 1 (0.15 g, 0.1 mmol) with
[W(I)2(CO)3(NCMe)2] (0.121 g, 0.2 mmol) in THF (20
cm3) (yield 0.112 g, 43%). Anal. Calc. for
C80H60I4O8P4Pt2S2W2: C, 36.9; H, 2.3; I, 19.5; P, 4.8;
Pt, 15.0; S, 2.5. Found: C, 37.4; H, 2.5; I, 19.6; P, 4.2;
Pt, 14.5; S, 2.2%. \m (10−3 M, MeOH) 108 ohm−1 cm2
Table 3
1
mol−1. lP (acetone-d6) 19.6 (t, J(PꢀPt)=3249 Hz).
Crystallographic data for compounds 3a and 3b
[Pt2W(m3-S)2I(PPh3)4(CO)4][PF6] 6b was prepared
(isolated as a red–brown precipitate) by treating a
solution of 6a in MeOH with excess NH4PF6. Anal.
Calc. for C76H60F6IO4P5Pt2S2W: C, 44.1; H, 2.9.
3a
3b
Chemical
formula
M
C88H72O16P4Pt2Re4S2
C78H66BF4O4P4Pt2ReS2
Found: C, 43.8; H, 2.5%. w(PF−6 ) (KBr) 837 vs cm−1
.
2708.55
Crystal system Monoclinic
1918.50
Monoclinic
P21/n
Space group
Unit cell di-
mensions
P21/c
3.7. Reaction of 1 with [Mo(CO)4(NCMe)2]
Mo(CO)6 (0.037 g, 0.14 mmol) was refluxed in
CH3CN (10 cm3) for 3 h to give a clear light brown
solution of [Mo(CO)4(NCMe)2]. After the solution was
cooled to r.t., 1 (0.15 g, 0.1 mmol) was added as a solid
and the mixture stirred for 10 h to give a clear brown
solution from which [Pt2(m-S)(PPh3)3(CO)] (7) (yield
0.019 g, 15%) was isolated by adding diethyl ether (50
cm3) to facilitate precipitation. The complex was iden-
tified by its IR and 31P-NMR spectra [28,29].
,
a (A)
19.05(2)
18.187(3)
28.34(1)
96.93(3)
9745(9)
4
293(2)
8.07
0.19×0.19×0.25
17.054(4)
23.826(4)
18.452(4)
102.33(2)
7325(2)
4
295(2)
5.66
0.17×0.33×0.60
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
T (K)
v (mm−1
Crystal
dimensions
(mm)
)
Radiation
Graphite-monochro-
mated Mo–Ka
q–2q
Graphite-monochro-
mated Mo–Ka
q–2q
3.8. X-ray crystallography of complex 3a
Scan mode
Absorption
corrections
Min, max
transmission
Diffractometer Nonius
None
„-Scans
Single crystals of complex 3a were obtained by slow
diffusion of hexane vapour into a solution of 3a in
Et2O. Several crystals from different crystal-growing
experiments were investigated, all of which were of
irregular shape and did not diffract well. The crystal
used for data collection gave only ca. 30% observed
reflections with I\2.5|(I) (see Table 3).
The 3548 reflections with I\2.5|(I) were used for
structure solution and refinement. The structure was
solved by direct methods and difference Fourier maps.
Structure refinement was hampered by the small num-
ber of observed reflections and disorder of the anion.
The structure was refined to the isotropic convergence
stage with only Pt, Re, S and P atoms allowed an-
isotropic motion. The refinement was performed with
rigid-group constraints for each of the 12 phenyl rings
N/A
0.269, 0.996
Siemens P4
50.0
−1–19,
−1–28,
−21–21
14 637
Max 2q (°)
hkl Ranges
44.9
−20–20,
0–19,
0–30
13 182
Reflections
measured
Unique reflec- 12 727 (0.083,
12 625 (0.062,
tions (Rint
)
based on F)
based on F2)
b
R1 a, wR
0.105, 0.119 (Rw) c
[I\2.5|(I)]
0.057, 0.125 [I\2|(I)]
a R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ.
b wR=[Sw(Fo2−Fc2)2/Sw(F2o)2]1/2
.
c Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwꢀFoꢀ ]
.
2 1/2

H. Liu et al. / Journal of Organometallic Chemistry 595 (2000) 276–284
283
(excluding hydrogen atoms) of the cation, and the
Acknowledgements
{Re3(m-OC)3(m3-OC)} fragment of the anion. In addi-
tion, the CO groups of the anion were constrained to
shift simultaneously in the x, y and z directions. The
Re3 anion was disordered (ca. 90:10) with a second Re3
anion. The major Re3 cluster was modelled with an
occupancy of 0.90 for each of the Re atoms and an
occupancy 1.00 for each of the carbon and oxygen
atoms. The minor Re3 cluster was modelled with only
three Re-atoms each with an occupancy of 0.10. An
attempt to introduce hydrogen atoms in idealized posi-
tions did not improve the R-value.
This work was supported by the National University
of Singapore (NUS) (RP 950695) and the National
Institute of Education, Singapore (RP 15/95 YYK).
H.L. and C.J. thank NUS for the award of a research
scholarship. The authors acknowledge Professor Z. Lin
of the Hong Kong University of Science and Technol-
ogy for helpful discussions.
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,
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