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M.B. Dinger et al. / Journal of Organometallic Chemistry 560 (1998) 169–181
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dimethylthiourea and silver(I) oxide was undertaken
and, as predicted, 1d was the only product formed. The
1H-NMR of complex 1d shows both the predicted
195Pt–1H and 31P–1H couplings to the methyl group
closest to the metal centre.
Complexes containing v-sulfido and -selenido bridges
between transition-metal centres have attracted consid-
erable interest for their structures [12], nucleophilicity
towards alkylation [13], catalytic activities [14] and
ability to act as ‘metallo-ligands’ towards other metal
centres, building up unusual sulfido-bridged coordina-
tion assemblies [15–17]. A large number of complexes
containing the dimeric metal(II)-sulfido/selenido unit
M(v-S,Se)2M units (M=Pd or Pt) are known [18–20],
and these units have been employed in syntheses of a
diverse range of heterobimetallic complexes [21]. A
review describing the chemistry of platinum sulfide
polynuclear complexes has recently been published [22].
To the best of our knowledge the isoelectronic gold(III)
group, Au(v-S)2Au, has been described only once pre-
viously, in the mixed gold(I)–gold(III) anion
[Au4Cl6S2]2−
[30] which highlighted the difference between palladium
and platinum systems. Sulfide-bridged platinum and
palladium dinuclear complexes have also been prepared
by C–S bond fission reactions involving propylene
sulfide [31] or thiols [32], respectively. Carbon–sulfur
and carbon–selenium bond cleavage reactions are of
interest for the formation of metal–sulfide and –se-
lenide solid-state materials having interesting optical
and electronic properties [33].
2.2. X-ray structure analysis of 4a
Crystals of compound 4a suitable for an X-ray struc-
ture determination were obtained by layering benzene
onto a chloroform solution of 4a at 4°C. The com-
pound crystallised in the rare cubic space group Pn-3n.
The molecular structure of the core of the aggregate is
shown in Fig. 1(a) together with the atom numbering
scheme. The cation lies on a two-fold axis so there are
effectively only two distinct gold ‘monomer’ units,
those formed by Au(1)/Au(2) and Au(3)/Au(3%), and
these will be subsequently referred to as monomers 1
and 2, respectively. Monomer 1 is depicted in Fig. 1(b),
and selected bond lengths and angles are presented in
Table 1.
The aggregate consists of an assembly of three Au(v-
S)2Au units (with each gold ligated by a cyclometallated
N,N-dimethylbenzylamine ligand), with the two sulfur
atoms coordinated to two of three silver(I) ions. The
three silver ions are in turn bound by two v3-chloride
ligands, above and below the plane defined by the three
silvers. The gold monomer units are pivoted at right
angles to the silver core, giving butterfly angles between
least-squares planes drawn through Au–S–Au–S and
Ag–S–S–Ag of 89.8(1) and 90.0(1)° for monomers 1
and 2, respectively. The silver atoms themselves are
coordinated in a very distorted tetrahedral configura-
tion, with an average S–Ag–S angle of 131.3(4)°, Cl–
Ag–S angle of 107.4(5)° and Cl–Ag–Cl averaging
89.5(4)°.
5
[23], isolated from the reaction between [AuCl(CO)],
Na(SBut) and 15-crown-5 (1,4,7,10,13-pentaoxacy-
clopentadecane). The molecular structure of 5 shows
the gold(III) sulfide ring coordinating to two –AuCl
units. Two X-ray crystal structures of anions containing
the related Au(v-Se)2Au unit, in [(SCH2CH2S)Au(v-
Se)2Au(SCH2CH2S)]2− [24] and [(Se4)Au(v-Se)2Au
(Se4)]2− [25] have been reported, though full details on
the former compound have not yet appeared. Examples
of gold(III) dimeric complexes containing bridging thio-
late ligands, of the type Au(v-SR)2Au are also known
[26].
The formation of the sulfide aggregates from
dimethylthiourea presumably results in the formation
of dimethyl carbodiimide as a by product, which may
be hydrolysed under the reaction conditions to give
N,N%-dimethylurea, though no attempts were made to
identify any by-product(s) formed. Desulfurisation re-
actions of thioureas by metal aggregates are well-docu-
mented in the literature [27–29], though we are aware
of only one related desulfurisation reaction of a
thiourea by a mononuclear complex under mild reac-
tion conditions. Okeya and co-workers recently re-
ported the desulfurisation of a thiourea ligand by
palladium(II), forming the sulfide-bridged dimeric com-
plex 6
In contrast to the isoelectronic four-membered Pt–
S–Pt-S ring systems with sulfido bridges, which have a
strong propensity to adopt hinged structures [12], the
monomer units in 4a are essentially flat, with no atom
deviating from the least-squares drawn through N(1),
C(11), Au(1), S(1), S(2), Au(2), C(21) and N(2) by more
˚
˚
than 0.080(9) A above, and 0.08(1) A below the plane