Cationic gold(I) phosphanyl thiolates: Aurophilic interactions in the solid state and in solution

Article abstract of DOI:10.1002/ejic.200700798

The aggregation states in solution of gold(I) cationic complexes of the formula [Au₂(StBu)(L₂)][BF₄] (L = PMe ₃, PEt₃, PtBu3, PPh₃; L₂ = dppm, dppe) were studied by MS (ESI) and DOSY spectroscopy. These compounds are tetranuclear in the solid state with a core of four gold centres bound together by aurophilic interactions and bridging thiolato groups. Some of these tetranuclear systems are maintained intact in solution depending on the phosphane steric properties or denticity. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700798

FULL PAPER
DOI: 10.1002/ejic.200700798
Cationic Gold(I) Phosphanyl Thiolates: Aurophilic Interactions in the Solid
State and in Solution
Federica Balzano,[a] Angela Cuzzola,[a] Pietro Diversi,*[a] Fabio Ghiotto,[b] and
Gloria Uccello-Barretta[a]
Keywords: Gold / Sulfur / Thiolates / Aurophilicity / Aggregation / ESI MS / NMR spectroscopy
The aggregation states in solution of gold(I) cationic com-
plexes of the formula [Au2(StBu)(L2)][BF4] (L = PMe3, PEt3,
PtBu3, PPh3; L2 = dppm, dppe) were studied by MS (ESI) and
DOSY spectroscopy. These compounds are tetranuclear in
the solid state with a core of four gold centres bound together
by aurophilic interactions and bridging thiolato groups. Some
of these tetranuclear systems are maintained intact in solu-
tion depending on the phosphane steric properties or dentic-
ity.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
It is well known that many gold(I) complexes in the solid
state adopt structures in which polynuclear systems are sta-
bilized by the presence of relatively short Au···Au distances
(aurophilic interactions).[1] In particular, cationic gold(I)
phosphanyl thiolates [Au2(SR)(L2)][BF4] (L = phosphane),
prepared by Bruce and coworkers by chemical oxidation
of the corresponding neutral phosphanyl thiolates
[Au(SR)(L)], exist in the solid state as oligomers; most of
these structures have a core of four gold atoms associated
by aurophilic interactions.[2] It is not clear if such structures
survive in solution or are cleaved to give dinuclear species
(there is no conclusive evidence on this point in the litera-
ture) (Figure 1). We recently prepared a series of related
compounds with the formula [Au2(SR)(L2)][BF4] (R =
CMe3, CH2CMe3, CH2CHMe2, CPh3; L = PMe3, PMe2Ph,
PMePh2, PPh3) and [Au2(SR)(dppe)][BF4] [dppe = 1,2-
bis(diphenylphosphanyl)ethane] by following the synthetic
strategy of Bruce.[3] In the solid state, the aurophilic interac-
tions build up a structure of four gold atoms with pairs of
atoms bound by bridging thiolato ligands, which, at least in
the cases studied by X-ray analysis, are generally arranged
in an almost perfect square or in an unprecedented zig–zag
sequence in the case of [Au2(StBu)(dppe)][BF4]. The correct
formulation for these complexes in the solid state is there-
fore [Au4(SR)2(L4)][BF4]2.
Figure 1. Di- and tetranuclear structural formulae of 2.
It would be certainly important for a better understand-
ing of the properties and the reactivities of these systems to
establish whether the aurophilic interactions unsupported
by bridging thiolato groups exist only in the solid state or
may survive in the presence of a solvent. Indeed, because
of the low energy of such interactions (5–15 kcalmol–1),[2e]
an equilibrium dimer/monomer can be postulated, which is
possibly influenced by the nature of the solvent (polarity,
chemical affinity for the metal centre, etc.) and/or the na-
ture of the phosphane and/or thiolato ligands.
In the literature there is only a limited number of studies
estimating the presence of aurophilic interactions in solu-
tion, and most of them concern AuI–AuI intramolecular
contacts often assisted by the presence of a bidentate phos-
phane.[4] In these cases, the authors demonstrated the par-
tial survival of the Au–Au bonding interactions by using 1H
and 31P VT NMR, UV/Vis and EXAFS spectroscopy.
There are a few scattered reports also for the study of the
intermolecular interactions in solution: the complexes
[Au2(dppm)(CH2)2S(O)NMe2][BF4] [dppm = 1,1-bis(di-
[a] Dipartimento di Chimica e Chimica Industriale dell’Università
di Pisa,
Via Risorgimento 35, 56126 Pisa, Italy
E-mail: div@dcci.unipi.it
[b] Scuola Normale Superiore,
Piazza dei Cavalieri 7, 56126 Pisa, Italy
phenylphosphanyl)methane],
[Au2(dmpm)(CH2)2S(O)-
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Cationic Gold(I) Phosphanyl Thiolates: Aurophilic Interactions
NMe2][BF4] [dmpm = 1,1-bis(dimethylphenylphosphanyl)- Mass Spectrometry Studies
methane][5] and {[(PPh3)Au]2Cl}[SbF6],[6] all of which crys-
tallize as dimers because of the formation of two AuI–AuI
The analyses were carried out in methanol solution. As
intermolecular bonds, were shown by electronic spec-
troscopy to maintain at least in part their dimeric structure.
Recently, diphosphane gold complexes with Au–Au con-
tacts were studied by EXAFS spectroscopy.[4a]
explained above, the gold(I) complexes here investigated
may exist in solution as monocationic dinuclear species
and/or as dicationic tetranuclear species. The analysis of the
isotopic cluster of the molecular ion is crucial to assess the
cationic charge: in fact the [Au4(StBu)2(PR3)4]2+ ion, in ad-
dition to the peak corresponding to m/z = M/2, presents
other minor peaks at m/z = M/2 + n/2 (n = 1, 2, 3, etc.)
due to the minor isotopes of carbon, sulfur and hydrogen),
whereas [Au2(StBu)(PR3)2]+ shows signals at M/2+n (n = 0,
1, 2, 3, etc.). Figures 2–6 report the MS (ESI) spectrum of
each complex with the corresponding attributions and the
enlargement of the isotopic cluster of the molecular ion.
In the case of 2a, the isotopic cluster (Figure 2b) is rather
resolved and allows us to conclude that the dicationic tetra-
nuclear structure observed in the solid state is largely main-
tained in solution. The MS–MS spectrum of the molecular
ion does not give further information on the aggregation
state. However it is interesting to note that, under more
severe experimental conditions [declustering potential (DP)
at 120 V], the isotopic cluster of the molecular peak reveals
that the dinuclear species arose at the expense of the tetra-
nuclear species (Figure 2c). The Au6 species responsible for
the peak at m/z = 921 most probably formed in the ioniza-
tion step.
In consideration of the above, to obtain information on
the aggregation state in dissolved cationic phosphanyl thio-
lates, we began a study of the homogeneous series of gold(I)
derivatives with the formula [Au2(StBu)(L2)][BF4] (L =
PMe3 2a, PEt3 2b, PtBu3 2c, PPh3 2d; L2 = dppm 2e, dppe
2f) by using MS (ESI) and DOSY (Diffusion Ordered Spec-
troscopY). MS (ESI) was recently used for the characteriza-
tion of supramolecular organometallic assemblies.[7] DOSY
NMR techniques, although very promising,[8a,8b] have not
attracted much attention so far[8c,8d] for applications in or-
ganometallic and inorganic chemistry in solution. Here we
report some conclusions obtained during these studies.
Results and Discussion
Synthesis
Complexes 2a–f were all prepared by chemical oxidation
of corresponding thiolates 1a–f with [FeCp2]BF4. Com-
In the case of 2b, the isotopic cluster is poorly resolved
pounds 1b,c, 1e, 2b,c and 2e have not been reported before, (Figure 3b). It is therefore difficult to draw specific conclu-
and their preparation and characterization can be found in sions, but in consideration of the NMR spectroscopic re-
the Experimental Section. The X-ray structures of 2d[9] and sults (vide infra) we suggest that only the dinuclear specie
2f[3b] are reported in the literature; for the other thiolates is present in solution. The m/z = 1005 peak may be derived
with monodentate phosphanes we assume that they exist in from the aggregation of the dinuclear species during the
the solid state in the usual four-membered square planar ionization process. The MS–MS spectrum does not give any
arrangement.
additional evidence.
Figure 2. a) MS (ESI+) of 2a; b) enlargement of the isotopic cluster at m/z = 635 at DP = 20 V and c) at DP = 120 V.
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F. Balzano, A. Cuzzola, P. Diversi, F. Ghiotto, G. Uccello-Barretta
FULL PAPER
Finally, complexes 2e,f containing diphosphanes are
present in solution as tetranuclear dications, as was predict-
able because the diphosphane holds the two dinuclear units
firmly together. In the particular case of 2f, the isotopic
cluster is poorly resolved (Figure 6b) and the MS–MS spec-
trum of the ion at m/z = 881 shows a small peak at m/z =
1167 (Figure 6c). Because a species with more gold atoms
than the precursor ion is unlikely to form on fragmentation,
the presence of a fragment ion at greater m/z values con-
firms the tetranuclear nature of 2f.
Figure 3. a) MS (ESI+) of 2b; b) enlargement of the isotopic cluster
at m/z = 719.3.
Alternatively, the mass spectrum recorded for 2c shows
a fairly well-resolved isotopic cluster (Figure 4b), which in-
dicates that only the monocharged dinuclear species is pres-
ent. The peak at m/z = 1174 is due to an adduct probably
formed during the ionization process.
Figure 6. a) MS (ESI+) of 2f; b) enlargement of the isotopic cluster
at m/z = 881.7; c) MS–MS spectrum of the ion at m/z = 881.
From these data it is clear that the ability of 2a–2d to
maintain totally or partially the aurophilic interactions in
solution seems to depend largely on the steric hindrance of
the phosphane (then on its cone angle, which is in the order
PMe3 ϽPEt3 ϽPPh3 ϽPtBu3).[10] In the case of 2e and 2f it
is the chelating phosphane, in addition to the thiolato li-
gand, that binds together the four gold atoms, indepen-
dently of the survival of the aurophilic interactions.
Figure 4. a) MS (ESI+) of 2c; b) enlargement of the isotopic cluster
at m/z = 887.3.
Similar conclusions can be drawn for 2d from the analy-
sis of its mass spectrum (Figure 5).
NMR Spectroscopy
The average diffusion coefficients can be related to
hydrodynamic radii rH by means of the Stokes–Einstein
equation [Equation (1)].
(1)
where k is the Boltzmann constant, T is the absolute tem-
perature, η the viscosity and c is a numerical factor, which
usually approximates to 6 for large-size molecules.
A more accurate estimation of hydrodynamic radius rЈH
can be obtained[11] by Equation (2), where the c factor is
expressed as a function of the solvent-to-solute ratio of ra-
Figure 5. a) MS (ESI+) of 2d; b) enlargement of the isotopic cluster
at m/z = 1007.4.
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Cationic Gold(I) Phosphanyl Thiolates: Aurophilic Interactions
dii on the basis of the model proposed by Wirtz and co- to those obtained from X-ray or PM3 calculations. In the
workers[12] and where rsolv is the van der Waals radius of the case of 1f, which is known to be stable in solution as disso-
solvent.
ciative processes are unlikely, excellent agreement was ob-
tained by the introduction of the Wirtz correction [Equa-
tion (2), Table 1), that is, by considering the solvent-to-sol-
ute ratio of the radii. However, the corrected hydrodynamic
radii of neutral monophosphane derivatives 1a–d were also
slightly lower, which suggests a dissociative equilibrium.
Actually, like traditional NMR measurements, DOSY tech-
niques, in the presence of rapid exchange, show only one
peak resulting from the weighted average of the signals of
each species involved. Because it is well known that gold(I)
compounds are often involved in rapid phosphane exchange
reactions,[20] it is probable that this is the reason for the
observed discrepancy between the observed and calculated
radii.
(2)
Valentini et al.[13] used DOSY measurements to deter-
mine the diffusion coefficients of some iron and palladium
compounds, whose structures in the solid state were known.
They obtained the hydrodynamic radii by using the Stokes–
Einstein equation and compared these results to the radii
of greatest steric hindrance obtained from crystallographic
parameters, rR (rotating the molecule around its geometric
centre), and they found very good consistency. The tech-
nique was also exploited for the characterization of inter-
mediates in organometallic reactions involving copper,[14]
ruthenium,[15] platinum[8b] and zirconium[16] complexes. Fi-
nally, some papers report the use of this methodology to
study the aggregation state in solution of organolithium[17]
and ruthenium complexes.[8c,11]
We then proceeded with the NMR investigation of the
series of cationic clusters 2a–f. X-ray structures in the solid
[3]
state are known only for [Au4(StBu)2(dppe)2][BF4]2
(which we assume remains tetranuclear in solution) and for
[Au4(StBu)2(PPh3)4][BF4]2;[10] for the other complexes we
used data from published structures of similar model com-
pounds or alternatively we performed PM3 calculations
using the ArgusLab program.[21] As the only limitation we
assumed that the S–Au–P angle had to be as close as pos-
sible to 180°. Analysis of the models of 2a–d shows that the
radii of greatest steric hindrance of the di- and tetranuclear
species do not differ too much (ca 1 or 2 Å), as the only
difference in size between the two species is in the third
dimension with the assumption that the other two remain
roughly constant. In spite of that, the NMR spectroscopic
results shown in Table 2 are fairly consistent and point to
the same conclusions reached by MS (ESI) spectrometry:
the corrected hydrodynamic radius of 2a is consistent with
a tetranuclear species, whereas for 2b it is intermediate be-
tween that of the dinuclear and the tetranuclear species,
which indicates that both structures are present in solution
(probably involved in rapid equilibrium).
For dppm and dppe derivatives 2e,f, as expected, the ra-
dii are nicely consistent with those predicted for the tetranu-
clear species. Complexes 2c,d gave, in contrast, even smaller
rЈH values than those predicted for the dinuclear species
from the X-ray structure data, so they probably undergo
some dissociation of the phosphane (as is likely from the
literature concerning phosphane gold(I) phosphanyl deriva-
tives and from basicity considerations in particular) or even
further disruption of the remaining Au–Au interactions.
Finally, to acquire information on the influence of the
solvent on the equilibrium involving di- and tetranuclear
species, we made some measurements in deuterated meth-
anol and acetone for comparison with the results obtained
in dichloromethane. We chose to study triethylphosphane
derivative 2b, which, as reported above, was found to exist
as a mixture of the di- and tetranuclear species, and dppe
complex 2f for comparison (Table 3).
Several correction factors[17b,18] for the equation, both se-
miempirical and theoretical have been proposed, by taking
into account the dimensions and the nonspherical form of
the particle, concentration and so on, but they have been
used only rarely as an internal standard is preferred. Some
authors[8,19] suggested the use of tetramethylsilane (TMS)
as an internal standard to avoid the problems derived from
the change in the viscosity due to the variation of the con-
centration after the addition of the solute to be analyzed
and from the temperature.
The spectra were generally performed in deuterated
dichloromethane, but in some cases also in methanol and
acetone in order to study the influence of the solvent. As
the internal standard for viscosity we adopted TMS and all
diffusion coefficients were corrected with respect to it.
To test the reliability of the method, our preliminary
study was directed towards thiolato phosphanyl compounds
1a–f, as there is no evidence of aurophilic interactions in
the solid state and presumably all the more so in solution
(Table 1).
Table 1. D (ϫ1010 m2 s–1) and r [Å] values for 1a–f in CD2Cl2 at
298 K.
[a]
[b]
D
rH
rЈH
4.2
r[c]
r[d]
[Au(StBu)(PMe3)] (1a)
[Au(StBu)(PEt3)] (1b)
[Au(StBu)(PtBu3)] (1c)
[Au(StBu)(PPh3)] (1d)
[Au2(StBu)2(dppm)] (1e)
[Au2(StBu)2(dppe)] (1f)
14.6
12.6
12.2
10.4
7.3
3.4
4.0
4.1
4.9
7.0
7.0
4.8
5.4
5.5
6.1
–
4.8
5.1
5.2
6.2
6.8
–
4.7
4.8
5.4
7.4
7.4
7.2
7.4[e]
[a] Calculated by using Equation (1), c = 6, T = 298 K, η (CD2Cl2,
298 K) = 0.433ϫ10–3 kgm–1 s–1. [b] Calculated by using Equa-
tion (2). [c] Calculated from X-ray structure data. [d] Calculated
from the minimized gas-phase structure (PM3/AM1). [e] See ref.[3]
The results for complex 2b in acetone are fairly consis-
The values of the hydrodynamic radii, calculated by em- tent with a dinuclear monocation formulation, which most
ploying Equation (1) with c = 6, were all lower with respect probably means that the equilibrium observed in dichloro-
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F. Balzano, A. Cuzzola, P. Diversi, F. Ghiotto, G. Uccello-Barretta
FULL PAPER
Table 2. D (ϫ1010 m2 s–1) and r [Å] for 2a–f in CD2Cl2 at 298 K.
[a]
[b]
D
rH
rЈH
r[c] Au2
r[c] Au4
r[d] Au2
r[d] Au4
Aggregation degree
[Au2(StBu)(PMe3)2][BF4] (2a) 8.7
[Au2(StBu)(PEt3)2][BF4] (2b) 9.3
[Au2(StBu)(PtBu3)2][BF4] (2c) 9.1
[Au2(StBu)(PPh3)2][BF4] (2d) 7.6
[Au2(StBu)(dppm)][BF4] (2e) 6.1
5.8
5.5
5.6
6.7
8.3
8.2
6.3
6.0
6.1
7.1
8.6
8.6
4.8
5.4
6.8
8.1[e]
–
6.0
7.3
7.9
9.1[e]
8.4
9.1
4.8
5.7
6.8
8.4
–
5.9
7.2
7.8
8.9
8.6
–
tetranuclear
di- and tetranuclear
dinuclear
dinuclear
tetranuclear
tetranuclear
[Au2(StBu)(dppe)][BF4] (2f)
6.1
–
–
[a] Calculated by using Equation (1), c = 6, η (CD2Cl2, 298 K) = 0.433ϫ10–3 kgm–1 s–1. [b] Calculated by using Equation (2). [c] Calcu-
lated from X-ray structure data under the assumption of a spherical shape. [d] Calculated from the minimized gas-phase structure (PM3).
[e] See ref.[9]
Table 3. D (ϫ1010 m2 s–1) and rH [Å] values for 2b and 2f in (CD3)2CO and CD3OD.
[a]
[b]
[c]
[d]
Solvent
D
rH
rЈH
r Au2
r Au4
[Au2(StBu)(dppe)][BF4] (2f)
[Au2(StBu)(dppe)][BF4] (2f)
[Au2(StBu)(PEt3)2][BF4] (2b)
[Au2(StBu)(PEt3)2][BF4] (2b)
(CD3)2CO
CD3OD
(CD3)2CO
CD3OD
8.1
5.1
14.7
9.1
8.9
7.9
4.9
4.4
9.2
9.1
9.1
8.1
5.4
4.8
5.4–5.7
5.4–5.7
[a] Calculated by using Equation (1), c = 6, T = 298 K, ηMeOH (298 K) = 0.544ϫ10–3 kgm–1 s–1, ηacetone (298 K) = 0.306ϫ10–3 kgm–1 s–1.
[b] Calculated by using Equation (2). [c] Calculated from the minimized gas-phase structure (PM3). [d] From X-ray data.[21]
methane is completely shifted towards the rupture of the the repulsion between the two monocharged unities con-
unsupported aurophilic bonds. In methanol, 2b shows a nected by aurophilic interactions, and, as a consequence,
hydrodynamic radius that is even lower with respect to that the dinuclear is preferred to the tetranuclear structure.
expected for a dinuclear species; thus, some other dissoci- Moreover, apart from diphosphane derivatives 2e,f, the aur-
ative process favoured by the polar protic solvent can be ophilic interactions are maintained (at least partially) only
invoked. Actually, methanol seems to promote other disso- when relatively small ligands (trimethyl- and triethylphos-
ciative processes even in the case of complex 2f, which, how- phane) are present. Obviously the solvent plays an impor-
ever, maintains its tetranuclear structure in acetone as in tant role: the polarity and the affinity for gold may deter-
dichloromethane.
mine the aggregation state, as shown by triethylphosphane
derivative 2b, which completely loses its tetranuclear struc-
ture in a polar solvent like acetone and methanol, whereas
it maintains the dimeric structure in part in the less-polar
solvent dichloromethane.
Finally, this work, in addition to the existing literature,
shows that NMR and MS techniques may be very useful in
the assessment of the degree of aggregation in solution of
coordination systems, and they can provide better under-
standing of the reactivity of species that may exist in a
supramolecular aggregation.
Conclusions
Table 4 shows our conclusions on the aggregation state
of the cationic gold complexes [Au2(StBu)(L2)][BF4] (2a–2f)
on the basis of MS and NMR experiments.
Table 4. Evaluation of the degree of aggregation of 2a–f in solution
by MS (ESI) and DOSY techniques.
Complex MS (MeOH) DOSY (CD2Cl2) Phosphane cone angle [°]
2a
2b
2c
2d
2e
2f
tetranuclear
dinuclear
dinuclear
dinuclear
tetranuclear
tetranuclear
tetranuclear
di- and tetranuclear
dinuclear
118
132
182
145
–
Experimental Section
dinuclear
tetranuclear
tetranuclear
Chemicals: All manipulations and reactions were carried out under
an atmosphere of nitrogen or argon by using standard techniques.
All solvents were used without any further purification.
[Au(SCMe3)]n was prepared according to the literature.[22]
–
In spite of the fact that DOSY spectroscopy and MS
Physical Measurements: 1H and 31P NMR spectra were recorded
with a Varian Gemini 200 instrument working at 200 MHz. DOSY
experiments were performed with a Varian INOVA600 spectrome-
(ESI) are performed under rather different conditions (con-
centration, solvent, etc.), the results are on the whole highly
consistent. The main conclusion is that some of the com-
plexes of 2 exist in a tetranuclear form even in dilute solu-
tions, which shows that aurophilic interactions, although
not as strong as covalent bonds, are able to maintain the
solid state architecture even in solution. Another conclu-
sion seems to be that the survival in solution of the auro-
philic interactions depends upon the steric hindrance of the
1
ter operating at 600 MHz for H by using a 5 mm broadband in-
verse probe with z axis gradient; and the sample temperature was
maintained at 25 °C. They were carried out by using a stimulated
echo sequence with self-compensating gradient schemes, a spectral
width of 8000 Hz and 64 K data points. Typically, a value of 100 ms
was used for Δ, 1.0 ms for δ and g was varied in 30 steps (16 tran-
sients each) to obtain an approximately 90–95% decrease in the
phosphane, because the greater the cone angle, the greater resonance intensity at the largest gradient amplitudes. The base-
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Cationic Gold(I) Phosphanyl Thiolates: Aurophilic Interactions
lines of all arrayed spectra were corrected prior to processing the
data. After data acquisition, each FID was apodized with 1.0 Hz
line broadening and Fourier transformed. The data were processed
with the DOSY macro (involving the determination of the reso-
nance heights of all the signals above a preestablished threshold
and the fitting of the decay curve for each resonance to a Gaussian
function) to obtain pseudo-two-dimensional spectra with NMR
chemical shifts along one axis and calculated diffusion coefficients
along the other. Centesimal analysis were carried out in the microa-
nalysis laboratory of Dipartimento di Scienze Farmaceutiche
dell’Università di Pisa. The mass spectra were obtained with an
Applied Biosystems-MDS Sciex API 4000 triple quadrupole mass
spectrometer (Concord, ON, Canada), equipped with Turbo-V Ion-
Spray (TIS) source. The operative parameters are as follows: ion-
spray voltage (IS), 5.0 kV; gas source 1 (GS1), 25; gas source 2
(GS2), 25; turbo temperature (TEM), 0 °C; entrance potential
(EP), 10 V; declustering potential (DP), 20 V; scan range, 300–
1500 m/z. MS–MS product ions were produced by collision-in-
duced dissociation (CID) of selected precursor ions in the LINAC
collision cell (Q2) and mass-analyzed in the second mass filter (Q3).
Additional experimental conditions for MS–MS product ions spec-
tra included: collision (CAD) gas, nitrogen; CAD gas pressure,
4 mPa; collision energy (CE), ramp from 5 to 130 eV (step = 2);
collision cell exit potential (CXP), 15 V. Each sample for MS (ESI)
was prepared diluting 1:100 with methanol a 5 mgmL–1 dichloro-
methane solution of the target compound and was infused by a
syringe pump Harvard Mod. 22 (Harvard Apparatus, Holliston,
MA, USA). Melting points were obtained by using a Mel Temp II
(Laboratory Devices, USA) equipped with a mercury thermometer
as detector of the temperature.
Complex 1e: Pale yellow microcrystals from toluene/pentane solu-
tion. Yield: 0.444 g (93%). H NMR (200 MHz, CDCl3, 25 °C): δ
1
= 1.52 (s, 18 H, SCMe3), 2.38 (s, 2 H, PCH2), 7.2–7.8 (br. m, 20
1
H, PPh2) ppm. H NMR (200 MHz, CD2Cl2, 25 °C): δ = 1.46 (s,
18 H, SCMe3), 3.62 (s, 2 H, PCH2), 7.3–7.8 (br. m, 20 H, PPh2)
ppm. 31P NMR (200 MHz, CDCl3, 25 °C): δ = 30.11 (s), 28.27 (s)
ppm. C33H40Au2P2S2 (956.69): calcd. C 41.43, H 4.21; found C
41.40, H 4.16.
Complex 1f: MS (ESI+): m/z (%) = 881 [Au4(StBu)2(dppe)2]++
(100%), 993 [Au2(StBu)2(dppe) + Na]+ (25), 1024 [Au5(StBu)3-
(dppe)2]++ (58), 1033 (not assigned, 23), 1167 [Au3(StBu)2(dppe)]+
(25).
Reaction of [Au(StBu)(L)] (L = PMe3, PEt3, PtBu3, PPh3) with
[FeCp2][BF4]. Formation of [Au2(StBu)(L2)][BF4] (2a–d): All com-
plexes were prepared according to the literature.[3]
Complex 2a: MS (ESI+): m/z (%) = 349 (85) [Au(PMe3)2]+, 635
(100) [Au4(StBu)2(PMe3)4]2+, 921 (14) [Au6(StBu)4(PMe3)4]2+. MS–
MS 635: m/z (%)= 273 (65) [Au(PMe3)]+, 349 (62) [Au(PMe3)2]+,
579 (100) [Au4(SH)2(PMe3)4]2+ or [Au2(SH)(PMe3)2]+, 635 (30)
[Au4(StBu)2(PMe3)4]2+
.
Complex 2b: White microcrystals from dichloromethane solution.
Yield: 0.157 g (71%). 1H NMR (200 MHz, CD2Cl2, 25 °C): δ =
2
3
1.59 (s, 18 H, SCMe3), 1.23 (dt, JP,H = 19.1 Hz, JH,H = 7.7 Hz,
3
3
24 H, PCH2), 1.94 (dq, JP,H = 9.9 Hz, JH,H = 7.7 Hz, 36 H,
1
PCCH3) ppm. H NMR (200 MHz, C6D6, 25 °C): δ = 1.55 (s, 18
H, SCMe3), 0.88 (dt, 2JP,H = 19.1 Hz, 3JH,H = 7.7 Hz, 24 H, PCH2),
1.61 (dq, JP,H = 9.9 Hz, JH,H = 7.7 Hz, 36 H, PCCH3) ppm. 31P
NMR (200 MHz, CD2Cl2, 25 °C): δ = 37.93 (s) ppm. 31P NMR
(200 MHz, C6D6, 25 °C): δ = 38.36 (s) ppm. MS (ESI+): m/z (%)
= 433 (14) [Au(PEt3)2]+, 719 (100) [Au4(StBu)2(PEt3)4]2+, 1005
[Au3(StBu)2(PEt3)2]+. MS–MS 719: m/z (%) = 315 (100) [Au-
(PEt3)]+, 433 (67) [Au(PEt3)2]+, 663 (72) [Au4(SH)2(PEt3)4]2+ or
3
3
Reaction of [Au(StBu)]n with L (L = PMe3, PEt3, PtBu3, PPh3).
Formation of [Au(StBu)(L)] (1a–d): The complexes were all pre-
pared according to the literature method.[3] Compounds 1b,c have
not been described before.
[Au2(SH)(PEt3)2]+, 719 (6) [Au4(StBu)2(PEt3)4]2+
. C16H39Au2-
BF4P2S: calcd. C 23.84, H 4.88; found C 23.65, H 4.76.
Complex 1a: MS (ESI+): m/z (%) = 349 (45) [Au(PMe3)2]+, 363
(15) [Au(StBu)(PMe3) + H]+, 635 (100) [Au4(StBu)2(PMe3)4]2+, 761
(15) not assigned, 921 (29) [Au3(StBu)2(PMe3)2]+, 997 (15)
[Au3(StBu)2(PMe3)3]+.
Complex 2c: Light grey microcrystals from dichloromethane solu-
1
tion. Yield: 0.810 g (88%). H NMR (200 MHz, CD2Cl2, 25 °C): δ
3
= 1.61 (s, 18 H, SCMe3), 1.54 (d, JP,H = 13.9 Hz, 108 H, PtBu)
ppm. 31P NMR (200 MHz, CD2Cl2, 25 °C): δ = 92.74 (s) ppm. MS
Complex 1b: Small silver flakes from pentane solution. Yield:
(ESI+): m/z (%)
=
601 (6) [Au(PtBu3)2]+, 887 (100)
1
0.153 g (80%). M.p. 43 °C. H NMR (200 MHz, CD2Cl2, 25 °C): δ
[Au2(StBu)(PtBu3)2]+, 1173 (6) [Au3(StBu)2(PtBu3)2]+. MS–MS
887: m/z (%) = 231 (16) [Au(PH3)]+, 287 (52) [Au(PH2tBu3)]+, 343
(49) [Au(PHtBu2)]+, 399 (43) [Au(PtBu3)]+, 489 (16) not assigned,
493 (14) [Au2(SH)(PH3)2]+, 549 (54) [Au2(SH)(PH3)(PH2tBu)]+,
572 (32) not assigned, 606 (32) [Au2(SH)(PH3)(PHtBu2)]+, 629 (25)
2
3
= 1.19 (dt, JP,H = 18.3 Hz, JH,H = 7.7 Hz, 6 H, PCH2), 1.45 (s, 9
H, SCMe3), 1.83 (dq, 3JP,H = 9.3 Hz, 3JH,H = 7.7 Hz, 9 H, PCCH3)
ppm. 1H NMR (200 MHz, C6D6, 25 °C): δ = 0.63 (dt, JP,H
=
2
3
3
18.3 Hz, JH,H = 7.7 Hz, 9 H, PCH2), 0.90 (dq, JP,H = 9.3 Hz,
3JH,H = 7.7 Hz, 6 H, PCCH3), 1.93 (s, 9 H, SCMe3) ppm. 31P NMR
not
assigned,
647
(16)
not
assigned,
662
(100)
(200 MHz, CD2Cl2, 25 °C):
δ =
38.64 (s) ppm. 31P NMR
[Au2(SH)(PH3)(PtBu3)]+, 685 (67) not assigned, 703 (83) not as-
signed, 718 (84) [Au2(SH)(PH2tBu)(PtBu3)]+, 741 (31) not assigned,
759 (36) not assigned, 775 (54) [Au2(SH)(PHtBu2)(PtBu3)]+, 831
(46) [Au2(SH)(PtBu3)2]+, 887 (22) [Au2(StBu)(PtBu3)2]+.
C28H63Au2BF4P2S (974.56): calcd. C 34.51, H 6.52; found C 34.63,
H 6.71.
(200 MHz, C6D6, 25 °C): δ = 38.36 (s) ppm. C10H24AuPS (404.31):
calcd. C 29.71, H 5.98; found C 29.77, H 5.92.
Complex 1c: White microcrystals from toluene/pentane solution.
Yield: 1.040 g (70%). M.p. 154 °C. 1H NMR (200 MHz, CD2Cl2,
3
25 °C): δ = 1.46 (s, 9 H, SCMe3), 1.51 (d, JP,H = 13.2 Hz, 27 H,
PCMe3) ppm. 1H NMR (200 MHz, C6D6, 25 °C): δ = 1.93 (s, 9 H,
Complex 2d: MS (ESI+): m/z (%) = 721 [Au(PPh3)2]+, 1007 (100)
[Au2(StBu)(PPh3)2]+, 1293 (7%) [Au3(StBu)(PPh3)2]+. MS–MS
1007: m/z (%) = 185 (25) [PPh2]+, 459 (85) [Au(PPh3)]+, 721 (100)
3
SCMe3), 1.07 (d, JP,H = 13.2 Hz, 27 H, PCMe3) ppm. 31P NMR
(200 MHz, CD2Cl2, 25 °C):
δ =
92.58 (s) ppm. 31P NMR
(200 MHz, C6D6, 25 °C): δ = 91.46 (s) ppm. MS (ESI+): m/z (%)
= 361 (15) not assigned, 489 (62) [Au(StBu)(PtBu3)4 + H]+, 512
(16) [Au(StBu)(PtBu3)4 + Na]+, 548 (27) not assigned, 887 (100)
[Au2(StBu)(PtBu3)2]+. C16H36AuPS (488.47): calcd. C 39.34, H
7.43; found C 39.12, H 7.38.
[Au(PPh3)2]+,
[Au2(StBu)(PPh3)2 + H]+.
951
(35)
[Au2(SH)(PEt3)2]+,
1008
(15)
Reaction of [Au2(StBu)2(L2)] (L2 = dppm, dppe) with [FeCp2][BF4].
Formation of [Au4(StBu)2(L2)2][BF4]2 (2e,f): The complexes were
prepared according to the literature.[3]
Reaction of [Au(StBu)]n with L2 (L2 = dppm, dppe). Formation of
[Au2(StBu)2(L2)] (1e,f): Complexes 1f,e were prepared according to Complex 2e: Yellow microcrystals from dichloromethane solution.
a literature procedure described for 1f.[3]
Yield: 0.235 g (87%). 1H NMR (200 MHz, CD2Cl2, 25 °C): δ =
5561
Eur. J. Inorg. Chem. 2007, 5556–5562
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org

F. Balzano, A. Cuzzola, P. Diversi, F. Ghiotto, G. Uccello-Barretta
FULL PAPER
2
gunas, Dalton Trans. 2004, 3459–3467; c) H. de la Riva, A. Pin-
tado-Alba, M. Nieuwenhuyzen, C. Hardacre, M. C. Lagunas,
Chem. Commun. 2005, 4970–4972; d) T. L. Stott, M. O. Wolf,
B. O. Patrick, Inorg. Chem. 2005, 44, 620–627; e) A. Deák, T.
Megyes, G. Tárkányi, P. Király, L. Biczók, G. Pálimkás, P. J.
Stang, J. Am. Chem. Soc. 2006, 128, 12668–12670.
[5] D. F. Feng, S. S. Tang, C. W. Liu, I. J. B. Lin, Organometallics
1997, 16, 901–909.
1.54 (s, 18 H, SCMe3), 4.35 (t, JP,H = 12.0 Hz, 4 H, PCH2), 7.2–
7.6 (br. m, 40 H, PPh2) ppm. 31P NMR (200 MHz, CD2Cl2, 25 °C):
δ = 31.28 (br. s), 34.18 (br. s) ppm. MS (ESI+): m/z (%) = 581
(9) [Au2(dppm)2]2+, 867 (100) [Au4(StBu)2(dppm)2]2+, 1019 (95) not
assigned, 1153 (50) [Au3(StBu)2(dppm)]+. MS–MS 867: m/z (%) =
185 (30) [PPh2]+, 397 (31) not assigned, 795 (100) not assigned, 811
(35) [Au4(SH)2(dppm)2]2+, 840 (9) [Au4(SH)(StBu)(dppm)2]2+, 868
(13) [Au4(StBu)2(dppm)2]2+. C58H62Au4B2F8P4S2 (1908.63): calcd.
C 36.50, H 3.27; found C 36.88, H 3.19.
[6] A. Hamel, N. W. Mitzel, H. Schmidbaur, J. Am. Chem. Soc.
2001, 123, 5106–5107.
[7] a) P. Wang, G. R. Newkome, C. Wesdemiotis, Int. J. Mass
Spectrom. 2006, 255–256, 86–92; b) S. Watase, T. Kitamura, N.
Kanehisa, M. Shizuma, M. Nakamoto, Y. Kai, S. Yanagida,
Chem. Lett. 2003, 32, 1070–1071.
[8] a) P. S. Pregosin, P. G. Anil Kumar, I. Fernandez, Chem. Rev.
2005, 105, 2977–2998; b) Y. Cohen, L. Avram, L. Frish, Angew.
Chem. Int. Ed. 2005, 44, 520–554; c) C. Zuccaccia, G. Bellachi-
oma, G. Cardaci, A. Macchioni, Organometallics 2000, 19,
4663–4665; d) T. Megyes, H. Jude, T. Grosz, I. Bakò, T. Rad-
nai, G. Tarkanyi, G. Palinkas, P. J. Stang, J. Am. Chem. Soc.
2005, 127, 10731–10738.
[9] A. Sladek, H. Schmidbaur, Chem. Ber. 1995, 128, 907–909.
[10] a) C. A. Tolman, Chem. Rev. 1977, 77, 313–348; b) Md. M.
Rahman, H. Ye Liu, A. Prock, W. P. Giering, Organometallics
1987, 6, 650–658.
[11] D. Zuccaccia, A. Macchioni, Organometallics 2005, 24, 3476–
3486.
Complex 2f: MS (ESI+): m/z (%) = 595 [Au2(dppe)2]2+, 738 (9) not
assigned, 881 (100) [Au4(StBu)2(dppe)2]2+, 1024 (17) [Au5(StBu)3-
(dppe)2]2+, 1167 (42) [Au3(StBu)2(dppe)]+. MS–MS 882: m/z (%)
= 596 (2) [Au2(dppe)2]2+, 825 (30) [Au4(SH)2(dppe)2]2+, 882 (100)
[Au4(StBu)2(dppe)2]2+, 1167 (2) [Au3(StBu3)2(dppe)]+.
Acknowledgments
We thank Ceramvetro Gold s.r.l., Florence (Italy) for the generous
gift of gold. The work was supported by the Istituto di Chimica dei
Composti Organometallici del Consiglio Nazionale delle Ricerche
(ICCOM-CNR).
[1] a) F. Scherbaum, A. Grohmann, B. Huber, C. Krüger, H.
Schmidbaur, Angew. Chem. Int. Ed. Engl. 1988, 27, 1602; b) H.
Schmidbaur, Gold. Bull. 1990, 23, 11–21; c) H. Schmidbaur,
Chem. Soc. Rev. (London) 1995, 24, 391–401; d) H. Schmid-
baur, Gold Bull. 2000, 33, 3–10.
[2] a) J. Chen, T. Jiang, G. Wei, A. A. Mohamed, C. Hom-
righausen, J. A. Krause Bauer, A. E. Bruce, M. R. M. Bruce, J.
Am. Chem. Soc. 1999, 121, 9225–9226; b) A. A. Mohamed,
A. E. Bruce, M. R. M. Bruce, Met.-Based Drugs 1999, 6, 233–
238; c) A. A. Mohamed, H. E. Abdou, J. Chen, A. E. Bruce,
M. R. M. Bruce, Comments Inorg. Chem. 2002, 23, 321–334; d)
[12] a) A. Gierer, K. Z. Wirtz, Naturforsch., Teil A 1953, 8, 522; b)
A. Spernol, K. Z. Wirtz, Naturforsch., Teil A 1953, 8, 532.
[13] M. Valentini, P. S. Pregosin, H. Ruegger, Organometallics 2000,
19, 2551–2555.
[14] A. Pichota, P. S. Pregosin, M. Valentini, M. Worle, D. Seebach,
Angew. Chem. Int. Ed. 2000, 39, 153–156.
[15] M. Valentini, P. S. Pregosin, H. Ruegger, J. Chem. Soc. Dalton
Trans. 2000, 4507–4510.
[16] a) N. E. Schlörer, E. J. Cabrita, S. Berger, Angew. Chem. Int.
Ed. 2002, 41, 107–109; b) S. Beck, A. Geyer, H. H. Brintzinger,
Chem. Commun. 1999, 2477–2478.
A. A. Mohamed, J. Chen, A. E. Bruce, M. R. M. Bruce, J. A. [17] a) I. Keresztes, P. G. Williard, J. Am. Chem. Soc. 2000, 122,
Krause Bauer, D. T. Hill, Inorg. Chem. 2003, 42, 2203–2205; e)
J. Chen, A. A. Mohamed, H. E. Abdou, J. A. Krause Bauer,
J. P. Fackler Jr, A. E. Bruce, M. R. M. Bruce, Chem. Commun.
2005, 1575–1577; f) a related tetragold neutral thiolate was re-
ported: W. J. Hunks, M. C. Jennings, R. J. Puddephatt, Inorg.
Chem. 2000, 39, 2699–2702.
10228–10229; b) I. Fernandez, E. Martinez-Viviente, F. Breher,
P. S. Pregosin, Eur. J. Inorg. Chem. 2005, 11, 1495–1506.
[18] J. T. Edward, J. Chem. Educ. 1970, 47, 261–270.
[19] E. J. Cabrita, S. Berger, Magn. Reson. Chem. 2001, 39, S 142–
148.
[20] a) M. J. Mays, P. A. Vergnano, J. Chem. Soc. Dalton Trans.
1979, 1112–1115; b) C. B. Colburn, W. E. Hill, C. A. McAuliffe,
R. V. Parish, J. Chem. Soc. Chem. Commun. 1979, 218–219; c)
S. Al-Baker, W. E. Hill, J. Chem. Soc. Dalton Trans. 1986,
1297–1300.
[21] M. A. Thompson, ArgusLab 4.0.1, Planaria Software LLC, Se-
attle, WA http://www.arguslab.com.
[22] G. A. Bowmaker, B. C. Dobson, J. Chem. Soc. Dalton Trans.
1981, 267–270.
[3] a) P. Diversi, F. Balzano, A. Cuzzola, F. Ghiotto, G. Uccello
Barretta, P. Salvadori, Atti del XXII Convegno SCI 2006, INO-
P-91, Firenze, September 2006; b) A. Battisti, O. Bellina, P.
Diversi, S. Losi, F. Marchetti, P. Zanello, Eur. J. Inorg. Chem.
2007, 865–875.
[4] a) R. Narayanaswamy, M. A. Young, E. Parkhurst, M. Ouel-
lette, M. E. Kerr, D. M. Ho, R. C. Elder, A. E. Bruce, M. R. M.
Bruce, Inorg. Chem. 1993, 32, 2506–2517; b) A. Pintado-Alba,
H. de la Riva, M. Nieuwhuyzen, D. Bautista, P. R. Raithby,
H. A. Sparkes, S. J. Teat, J. M. Lopez-de-Luzuriaga, M. C. La-
Received: July 27, 2007
Published Online: October 24, 2007
5562
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5556–5562