A Series of Homoleptic Linear Trimethylsilylchalcogenido Cuprates, Argentates and Aurates Cat[Me3SiE-M-ESiMe3] (M = Cu, Ag, Au; E = S, Se)

Article abstract of DOI:10.1021/acs.inorgchem.0c02808

The syntheses and XRD molecular structures of a complete series of silylsulfido metalates Cat[M(SSiMe3)2] (M = Cu, Ag, Au) and corresponding silylselenido metalates Cat[M(SeSiMe3)2] (M = Cu, Ag, Au) comprising lattice stabilizing organic cations (Cat = Ph4P+ or PPN+) are reported. Much to our surprise these homoleptic cuprates, argentates, and aurates are stable enough to be isolated even in the absence of any strongly binding phosphines or N-heterocyclic carbenes as coligands. Their metal atoms are coordinated by two silylchalcogenido ligands in a linear fashion. The silyl moieties of all anions show an unexpected gauche conformation of the silyl substituents with respect to the central axis Si-[E-M-E]-Si in the solid state. The energetic preference for the gauche conformation is confirmed by quantum chemical calculations and amounts to about 2-6 kJ/mol, thus revealing a rather shallow potential mainly depending on electronic effects of the metal. Furthermore, 2D HMQC methods were applied to detect the otherwise nonobservable NMR shifts of the 29Si and 77Se nuclei of the silylselenido compounds. Preliminary investigations reveal that these thermally and protolytically labile chalcogenido metalates are valuable precursors for the precipitation of binary coinage metal chalcogenide nanoparticles from organic solution and for coinage metal cluster syntheses.

Full text of DOI:10.1021/acs.inorgchem.0c02808

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A Series of Homoleptic Linear Trimethylsilylchalcogenido Cuprates,
Argentates and Aurates Cat[Me3SiE−M−ESiMe3] (M = Cu, Ag, Au; E =
S, Se)
̈
Jannick Guschlbauer, Tobias Vollgraff, Xiulan Xie, Florian Weigend, and Jorg Sundermeyer*
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ABSTRACT: The syntheses and XRD molecular structures of a complete series of silylsulfido
metalates Cat[M(SSiMe3)2] (M = Cu, Ag, Au) and corresponding silylselenido metalates
Cat[M(SeSiMe3)2] (M = Cu, Ag, Au) comprising lattice stabilizing organic cations (Cat =
Ph4P+ or PPN+) are reported. Much to our surprise these homoleptic cuprates, argentates, and
aurates are stable enough to be isolated even in the absence of any strongly binding
phosphines or N-heterocyclic carbenes as coligands. Their metal atoms are coordinated by
two silylchalcogenido ligands in a linear fashion. The silyl moieties of all anions show an
unexpected gauche conformation of the silyl substituents with respect to the central axis Si−
[E−M−E]−Si in the solid state. The energetic preference for the gauche conformation is
confirmed by quantum chemical calculations and amounts to about 2−6 kJ/mol, thus revealing a rather shallow potential mainly
depending on electronic effects of the metal. Furthermore, 2D HMQC methods were applied to detect the otherwise nonobservable
NMR shifts of the 29Si and 77Se nuclei of the silylselenido compounds. Preliminary investigations reveal that these thermally and
protolytically labile chalcogenido metalates are valuable precursors for the precipitation of binary coinage metal chalcogenide
nanoparticles from organic solution and for coinage metal cluster syntheses.
commonly used as biocides, not harmful to mammals but
deadly to microorganisms.8 In contrast, molecular gold(I)
thiolato complexes are used as metalo pharmaceuticals in
commercially established drugs, e.g. for the therapy of
arthritis.9
INTRODUCTION
■
Species containing highly thiophilic group 11 metal centers M
(M = CuI, AgI, AuI) and chalcogenolate ligands [ER]− (E = S,
Se, Te; R = organic moiety) constitute a class of compounds
mainly dominated by oligomeric cluster or coordination
polymer structural motifs.1 On the other hand, hydrosulfide
[SH]− complexes of transition metals are of interest as a class
of its own, but only very few examples of hydrosulfide
complexes are known for the coinage metals.2 The few existing
are stabilized by strongly binding coligands; homoleptic
hydrosulfide complexes are unknown. The self-assembly of
such partially coligand masked polynuclear chalcogen com-
plexes via higher aggregated oligomers and clusters, finally, to
nanocrystals can be considered a general trend and aim.3
Recently, less aggregated, molecular chalcogenide compounds,
again typically stabilized by strongly binding coligands such as
N-heterocyclic carbenes (NHC) or chelating tert.-amines,
came into focus of interest: They serve as molecular models
for reactive sites of solid state materials, e.g. [(NHC−Cu)2(μ2-
S)])4 as a molecular variant of Cu2S, they serve as molecular
building blocks such as [(tmeda)Zn(SSiMe3)2]5 in the step-by-
step bottom-up synthesis of chalcogenide materials, e.g. ZnS,
or they provide biomimetic model systems for metalloproteins
such as the tetranuclear [4Cu:2S] cluster in the active site of
N2O reductase.6 Understanding structure property relations in
metalloproteins and other bioactive compounds is challenging:
While copper represents the second most abundant transition
metal found in organisms, after iron,7 silver compounds are
Let us focus on the much less investigated, nonbiogenic class
of complexes containing trimethylsilylchalcogenido ligands
[ESiMe3]− (E = S, Se, Te). From a chemical point of view they
are hybrids of organochalcogenolato [ER]− and hydro-
chalcogenido [EH]− functional molecules with respect to
their labile bonds and potential transformations: Such
complexes can be used as a starting point for the preparation
of coinage metal chalcogenido clusters of higher complexity or
for nanoparticles10 being of interest due to their photo-
luminescence behavior.11,12 The cleavage of the E−Si linkage
can be performed with suitable desilylating agents, such as
metal acetates or acetato complexes, or by thermally induced
intra- or intermolecular elimination of E(SiMe3)2.5,10,11 The
E−R cleavage barriers grow with increasing sterical demand of
the silylchalcogenide or alkylchalcogenolate ligand. Polynuclear
compounds such as Au4[EC(SiMe3)3]4 (E = S, Se, Te)13 and
Received: September 21, 2020
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also mononuclear complexes like R3PAuSSi(SiMe3),14
R3PAuTeC(SiMe3),13 and Ph3PAuSC(SiMe3)14 are known
examples of reasonable stability at room temperature. The
latter has been reported to be of use for the synthesis of
Scheme 1. Synthesis of the Title Compounds
Cat[M(ESiMe3)2]
15
16
clusters Au108S24(PPh3)16 and Au70S20(PPh3)12 when
treated with borohydridesrather strong E−R cleavage agents
compared to e.g. acetates. However, to date, mononuclear
neutral compounds containing a coinage metal attached E−
SiMe3 group were made accessible only by applying strongly
binding amine, phosphine, or N-heterocyclic carbene auxiliary
ligands. While the phosphine compounds of the type [R3P−
M−ESiMe3] are quite difficult to handle,17 the NHC analogues
[NHC−M−ESiMe3] and related cyclic alkyl(amino)carbenes
(CAAC) [CAAC−M−ESiMe3] are of reasonable stability for
using them in selective bottom-up syntheses of defined ternary
clusters with tunable optical properties.11,18,19 Finally, NHC
masked coinage metal silylchalcogenido complexes have been
used as precursors for the preparation of coinage metal
chalcogenide materials M2E.20 These materials are receiving
growing interest due to their negligible toxicity and their
potential to act as e.g. IR emitters and superionic conductors.21
Linearly coordinated organchalcogenolato metalates of the
type [M(ER)2]− (M = Cu, Ag, Au; E = S, Se, Te; R = bulky
organic ligand) were chosen as the lead structural motif of this
study.1,23 In these anions, intermolecular charge repulsion in
combination with bulky organic groups and robust E−C bonds
are often preventing higher aggregation, but even these anionic
complexes can form higher-coordinated or higher-charged
polynuclear coinage metalates.23
Recently, we discovered a class of thermally and protolyti-
cally metastable homoleptic silylchalcogenido metalates Cat-
[M(ESiMe3)4] (M = Ga, In; E = S, Se)22a and Cat[M-
(ESiMe3)3] (M = Sn, Zn; E = S, Se).22b They have proven to
act as precursors in a solution based low temperature synthesis
of ternary and quaternary chalcogenide materials CuInS2 and
Cu2ZnSnS4, which are members of the PV absorber material
classes CIGS and CZTS, respectively.22 Encouraged by these
results, we were motivated to target so far unknown
[M(ESiMe3)2]− (M = Cu, Ag, Au, E = S, Se) precursors for
materials synthesis. The challenge was to isolate such thermally
and protolytically labile homoleptic complexes with coinage
metals having an intrinsically higher lattice energy in the form
of their metal chalcogenides compared to the metals of our
previous studies. An economically attractive aspect with
respect to potential applications seemed to be that the
targeted metastable molecular precursors might not rely on
strongly binding, expensive, and difficult to recycle PR3 or
NHC coligands. A principal aim is that these building blocks
for materials synthesis should be accessible in any element
combination Cu/Ag/Au−S/Se.
are extracted into diethyl ether, thus being separated from
LiCl. The highest yields 84−86% achieved after crystallization
are obtained with the Ph4P+ cation for 1−3. However, use of
PPN+ was indicated in some cases in order to get single crystals
suitable for XRD analysis. These thermally metastable
compounds can be handled at ambient temperature for some
time, and they can be stored at −30 °C under inert gas for an
extended period of time.
By following this low-temperature approach, the complete
series of homologues 1−6 displaying two reactive ESiMe3
moieties was isolated and fully characterized. Even small
deviations from this protocol lead to darkening of the reaction
mixture and brown-black precipitates. If such side products or
unreacted starting material are not desirable, it is beneficial to
quench mechanistically plausible partially substituted inter-
mediates [Cl−M−ESiMe3]− at low temperature by a second
equivalent of LiESiMe3 in THF; otherwise, there is a certain
risk (or chance!) of eliminating Me3SiCl, if the solution is
warming up prior to the second substitution step. All
kinetically stabilized molecular products Cat[M(ESiMe3)2]
(M = Cu, Ag, Au, E = S, Se) are colorless and crystalline
compounds. Any compounds possibly forming upon elimi-
nation of Me3Si−X (X = Cl, ESiMe3) from thermally unstable,
plausible intermediates [Cl−M−ESiMe3]− or from metastable
final products [Me3Si−M−ESiMe3]−, e.g. hypothetical poly-
anionic clusters Catn[(ME)n(MESiMe3)m] or simply their
decomposition products M2E, Cat2E and Me3SiX, are expected
to change drastically in their optical absorption and emission
spectra. The perspective to isolate crystalline intermediates on
this decay path into the thermodynamically most stable
crystalline phases should be followed up in future research:
A trigger for desired or undesired desilylation reactions seems
to be the presence or absence of excess of weakly solvated ionic
chloride Cat[Cl] in the reaction mixture.
XRD Structures. All title compounds crystallize in the
̅
triclinic space group P1, 1 with two (Figure 1) and 2−6 with
four ion pairs per unit cell (Figure 2, Figure 3, Figure S1,
Figure S2, and Figure 4, respectively).
1 reveals only one crystallographically independent anion
per unit cell, while 2−6 contain two independent anions.
Structural parameters such as E−M−E or Si−E−E−Si dihedral
angles of crystallographically independent anions are summar-
ized in Table 1. The largest differences between two
independent anions are observed in silylsulfido-argentate 2.
While structurally comparable linearly coordinated cuprates
and argentates with silylthiolate moieties [Cu(SSiPh3)2]−25 and
RESULTS AND DISCUSSION
■
Synthesis. The principle strategy to synthesize the title
compounds follows the route established in our previous
reports for other homoleptic silylchalcogenido metalates
(Scheme 1). First, an organic cation chloride Cat[Cl] is
added to the metal chlorides, here [MCl]n (M = Cu, Ag, Au),
in order to chop up the solid compound and to yield molecular
chlorometalates, Cat[MCl2] in this case. Without the need to
isolate these intermediates, 2 equiv of LiESiMe324 are added in
THF at −78 °C. After slowly warming the reaction mixture to
ambient temperature and removal of all volatiles in vacuo, the
rather lipophilic salts comprising large, nonpolarizing cations
[Ag(SSiR3 )2 ]− (R
= bis(diisopropyl)phenolate
(OC12H17))26,27 are known, the title compounds comprise
the first structurally characterized silylselenido cuprates or
argentates and silylchalcogenido aurates.
By analyzing and comparing the observed torsion angles
α(Si−E−E−Si), it became evident that all molecular structures
B
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Figure 1. Molecular structure of Ph4P[Cu(SSiMe3)2] (1). Hydrogen
atoms are neglected for clarity. Ellipsoids are shown at 50% level.
Selected bond lengths (Å) and angles (deg) of the anion in 1: Cu1−
S1 2.1412(6), Cu1−S2 2.1475(6), S1−Si1 2.1081(8), S2−Si2
2.1129(7), S1−Cu1−S2 176.63(2), Cu1−S1−Si1 100.34(2), Cu1−
S2−Si2 97.14(2), Si1−S1−S2−Si2 48.86(3).
Figure 3. Molecular structure of PPN[Au(SSiMe3)2] (3-PPN).
Hydrogen atoms are neglected for clarity. Ellipsoids are shown at
50% level. Selected bond lengths (Å) and angles (deg) of the two
crystallographically inequivalent anions in the reduced cell in 3: Au1−
S1 2.289(1), Au1−S2 2.308(1), S1−Si1 2.107(2), S2−Si2 2.112(2),
S1−Au1−S2 178.79(4), Au1−S1−Si1 103.80(5), Au1−S2−Si2
94.71(5), Si1−S1−S2-Si2 62.15(6),Au2−S3 2.299(1), Au2−S4
2.2985(9), S3−Si3 2.119(1), S4−Si4 2.119(1), S3−Au2−S4
176.52(3), Au2−S3−Si3 100.38(5), Au2−S4−Si4 102.44(4), Si3−
S3−S4−Si4 77.21(5).
Figure 2. Molecular structure of Ph4P[Ag(SSiMe3)2] (2). Hydrogen
atoms are neglected for clarity. Ellipsoids are shown at 50% level.
Selected bond lengths (Å) and angles (deg) of the crystallographically
inequivalent anions in the reduced cell in 2: Ag1−S1 2.341(1), Ag1−
S2 2.356(1), S1−Si1 2.111(1), S2−Si2 2.108(2), S1−Ag1−S2
171.70(4), Ag1−S1−Si1 106.28(5), Ag1−S2−Si2 98.59(5), Si1−
S1−S2−Si2 51.27(7), Ag2−S3 2.357(1), Ag2−S4 2.368(1), S3−Si3
2.118(2), S4−Si4 2.099(2), S3−Ag2−S4 175.56(4), Ag2−S3−Si3
100.07(5), Ag2−S4−Si4 98.19(6), Si3−S3−S4−Si4 27.82(7).
Figure 4. Molecular structure of PPN[Au(SeSiMe3)2] (6-PPN).
Hydrogen atoms are neglected for clarity. Ellipsoids are shown at 50%
level. Selected bond lengths (Å) and angles (deg) of the crystallo-
graphically inequivalent anions in the reduced cell in 6: Au1−Se1
2.3980(6), Au1−Se2 2.4015(6), Se1−Si1 2.255(1), Se2−Si2
2.256(1), Se1−Au1−Se2 175.46(2), Au1−Se1−Si1 101.36(3),
Au1−Se2−Si2 97.68(3), Si1−Se1−Se2−Si2 75.21(4), Au2−Se3
2.3956(7), Au2−Se4 2.4139(6), Se3−Si3 2.258(1), Se4−Si4
2.255(1), Se3−Au2−Se4 176.14(3), Au2−Se3−Si3 100.79(3),
Au2−Se4−Si4 90.29(3), Si3−Se3−Se4−Si4 72.49(4).
of 1−6 display their E-silyl substituent in a quasi-gauche
conformation with respect to the linear E−(M)−E axis. First,
this seemed to be unexpected, as for steric reasons such
molecules might have favored an anti-conformation as
observed in the aforementioned structurally characterized
[Cu(SSiPh3)2]−,25 [Ag(SSiR3)2]−,26,27 and the 1-adamanylth-
iolato-cuprate [Cu(SAd)2]−.28 On the other hand organo-
29
thiolates [Cu(StBu)2]− and [Au(SeCF3)2]− 30 also show this
quasi-gauche conformation.
DFT Calculations. For a deeper insight into the
phenomenon connected with the gauche-like conformation,
the variation of Si−E−E−Si torsion angle was investigated in
density functional calculations employing TURBOMOLE31
with the TPSS functional32 and dhf-TZVP basis sets.33
Structure optimizations were carried out keeping α fixed at
−10, 0, 10, ..., 0.270° and optimizing all other coordinates.
This was done for M = Cu, Ag, Au and E = S, Se in
[M(ESiMe3)2]− as well as for the model compound [Cu-
(SCl)2]−. The resulting energy curves are shown in Figure 5.
The experimentally observed preference of torsional angles
in the range of about 100° and 250° is visible also in the
calculated energy curves, but it is not very large. The maximum
difference amounts to 6 kJ/mol and is found between α = 0°
and α = 100° for [Cu(SeSiMe3)2]−. For a given M, the results
for S and Se are very similar. The impact of the choice of M to
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Table 1. Comparison of Structural Parameters of Homologue Cuprates, Argentates, and Aurates Ph4P[Cu(SSiMe3)2] (1),
Ph4P[Ag(SSiMe3)2] (2), PPN[Au(SSiMe3)2] (3-PPN), PPN[Cu(SeSiMe3)2] (4-PPN), PPN[Ag(SeSiMe3)2] (5-PPN), and
PPN[Au(SeSiMe3)2] (6-PPN)
Anion (M/E)
M−E (Å)
E−Si (Å)
E−M−E (deg)
176.63(2)
171.70(4)−175.56(4)
178.79(4)−176.52(3)
174.16(2)−174.98(3)
174.66(3)−175.29(2)
175.46(2)−176.14(3)
M−E−Si (deg)
Si−E−E−Si (deg)
1 (Cu/S)
2 (Ag/S)
3 (Au/S)
4 (Cu/Se)
5 (Ag/Se)
6 (Au/Se)
2.1412(6)−2.1475(6)
2.341(1)−2.368(1)
2.289(1)−2.308(1)
2.2613(7)−2.2836(6)
2.4487(6)−2.4745(6)
2.3956(7)−2.4139(6)
2.1081(8)−2.1129(7)
2.099(2)−2.118(2)
2.107(2)−2.119(1)
2.247(1)−2.2561(8)
2.247(2)−2.256(2)
2.255(1)−2.258(1)
97.14(2)−100.34(2)
98.19(6)−106.28(5)
94.71(5)−103.80(5)
88.30(3)−101.97(3)
87.93(4)−101.79(4)
90.29(3)−101.36(3)
48.86(3)
27.82(7)−51.82(7)
62.15(6)−77.21(5)
75.97(3)−77.45(3)
73.82(5)−74.75(6)
72.49(4)−75.21(4)
Figure 6. Orbital energies of the highest occupied MOs as a function
of the torsional angle Cl−S−S−Cl, α, of [Cu(SCl)2]−. Orbitals are
plotted for α = 0° (left) and α = 90° (right). The numbers in the
diagram (−0.246 etc.) denote the sum of the Mulliken overlap
population between Cu and the two S atoms (negative numbers
indicate antibonding character).
Figure 5. Energy as a function of the torsional angle Si−E−E−Si, α,
of [M(ESiMe3)2]− and Cl−E−E−Cl for [Cu(SCl)2]−, respectively.
Energies are given relative to the eclipsed configuration (0°). For
[Cu(SCl)2]−, the energies are divided by a factor of 2.
the shape of the curves is larger. The energy difference between
α = 0° and α = 100° decreases from Cu via Au to Ag, which is
in line with the sequence of the accessibility of the d shell for
chemical bonds and thus points to a rationalization involving
angle-dependent (π-type) interactions of the d(M) orbitals and
the p(E) orbitals. Due to the smallness of the energetic
preference of α = 100°, the net effect is expected to be small
for all compounds. We thus first discuss the electronic
structure of the model compound [Cu(SCl)2]−, which shows
a similar shape for E(α), but with energy differences between α
= 0° and α = 100° being twice as large as that for
[Cu(SeSiMe3)2]−. A Walsh-type diagram for the nine highest
occupied MOs and angles between 0° and 90° is shown in
Figure 6.
For HOMO, HOMO−1, and HOMO−6 a significant
influence of α on the orbital energies is observed. For α =
0°, the HOMO is a strongly antibonding combination
(Mulliken overlap population OP = −0.246 between Cu and
S) of dxz(Cu) and px(S); HOMO−1 is a very weakly bonding
combination of dxy(Cu) and px(S). For α = 90°, both orbitals
are essentially nonbonding, which in sum increases the overlap
and thus the bond strength. This is enhanced by HOMO−6
(dyz(Cu) with pz(S)), which changes from nonbonding to
weakly bonding, accompanied by a lowering of the orbital
energy. For this model compound, the preference of α = 90°
thus is rationalized by the change of the π interactions in these
three MOs, in particular by the decrease of the antibonding
character of the HOMO, and reflected by an increase (α = 90°
vs α = 0°) of OP by 0.180 for the sum of these MOs. When
summing over all MOs, the OP changes by 0.121 (from 1.143
to 1.264), which shows that the dominant changes indeed arise
from the three MOs listed above. For completeness we note
that the interaction between Cu and the two Cl atoms is
weakly antibonding and only slightly dependent from α:
OP(0°) = −0.134, OP(90°) = −0.152.
For the original compound [Cu(SSiMe3)2]− matters are by
far less obvious (shown in the Supporting Information, Figure
S5). As in the case of the model compound, the antibonding
character of the HOMO, which is similar to that of the model
compound, is reduced, but this stabilization is compensated by
changes in several other MOs. As a consequence, the OPs
between Cu and the two S atoms are identical for α = 90° and
α = 0°, 1.195. Here, π interactions between Cu and S alone do
not rationalize the (slight) energetic preference for α = 90°. An
explanation rather may be found in the neighbor next neighbor
interactions and further in effects of electron correlation, which
are beyond the one-electron picture of orbital considerations.
This is supported by the fact that in DFT, where these effects
are included, the energy difference between α = 0° and α = 90°
is 5.6 kJ/mol, whereas at Hartree−Fock level, where such
effects are neglected, it is only 2.3 kJ/mol.
So far, the influence of the counterions was neglected. For a
rough estimation of this effect we exemplarily calculated the
equilibrium structure of [Cu(SeSiMe3)2]− in the presence of
one PPN+ unit at the DFT level. The coordinates were taken
from the X-ray structure and kept fixed for PPN+ as well as for
the Cu atom. For the optimized structure, the gauche-type
D
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conformation is maintained (α = 95.2°). The eclipsed
conformer, which was obtained by additionally fixing α at 0°,
is higher in energy by 9.2 kJ/mol. This is close to the above
value for the gas phase, 6 kJ/mol, and also close to the
difference of single-point energies for the two structures with
PPN+ being removed, 7.1 kJ/mol. So, the (small) relative
stability of the gauche conformation compared to the eclipsed
one is not significantly affected by the presence of PPN+
despite relatively strong ionic interaction between PPN+ and
[Cu(SeSiMe3)2]− amounting to 194 kJ/mol.
NMR Spectroscopy. Silylsulfido metalates 1−3 were
investigated by 1H, 13C, and 29Si NMR spectroscopy in
THF[d8] at ambient temperature. The 1H NMR signals for the
metalate anions range from 0.12 ppm for the argentate 2 to
0.13 ppm for both, the aurate 3-Ph4P and the cuprate 1. The
13C NMR signals range from 7.4 ppm for the aurate 3-Ph4P to
8.6 ppm for the argentate 2, while the chemical shift for the
cuprate 1 is at 8.3 ppm. A trend is observed in 29Si NMR
spectra showing an increasingly pronounced low field shift with
growing molecular weight. It ranges from 5.2 ppm for the
cuprate 1 to 7.7 ppm for the aurate 3-Ph4P (Figure 7).
1
Figure 8. H−29Si-HMQC NMR (99.4 MHz, THF[d8]) spectra of
the silylselenido metalates 4-Ph4P, 5-Ph4P, and 6-Ph4P at 273 K.
1
Figure 9. H−77Se-HMQC NMR (500.2 MHz, THF[d8]) spectra of
the silylselenido metalates 4-Ph4P, 5-Ph4P, and 6-Ph4P at 273 K.
Figure 7. 29Si NMR (59.7 MHz for 1 and 2, 99.4 MHz for 3,
THF[d8]) spectra of the Ph4P[Cu(SSiMe3)2] (1, top row),
Ph4P[Ag(SSiMe3)2] (2, middle row), and Ph4P[Au(SSiMe3)2] (3-
Ph4P, bottom row).
protolytic and thermal reactivity differs drastically. In sharp
contrast to organothiolates, all of the title compounds
spontaneously precipitate monovalent coinage metal chalco-
genides from THF or other organic solutions, when methanol
or traces of water are added. Diffusion of protic reactants into
colorless solutions of e.g. Ph4P[Ag(SSiMe3)2] (2) in THF
leads to the formation of a brown-black nanocrystalline
dispersion containing Ag2S (Scheme 2, eqs 1 and 2). S-
While 1H and 13C NMR spectra were routinely recorded for
the silylselenido metalates 4−6, detection of 29Si and the 77Se
signals turned out to be very difficult. We therefore applied
two-dimensional 1H−29Si-HMQC34 and 1H−77Se-HMQC
methods at 0 °C utilizing the gradient selective coherence
transfer from the proton to the corresponding heteronuclei. At
Scheme 2. Postulated Protic Decay Paths of Silylsulfido
Cuprates, Argentates, and Aurates; Cat = Organic Cation
1
0 °C, the H NMR shifts of the silylselenido metalate anions
are quite similar, ranging from 0.27 ppm for the cuprate 4-
Ph4P as well as 0.31 ppm for the aurate 6-Ph4P, and 0.30 ppm
for the argentate 4-Ph4P. However, clear identification is
possible by the 29Si NMR shifts that are accessible by the 2D-
NMR method quite easily. The 29Si NMR shifts range from 0.2
ppm for the cuprate 4-Ph4P to 2.4 ppm for the aurate 6-Ph4P,
while the signal for the argentate 5-Ph4P is at 1.6 ppm (Figure
8).
Desilylation with formation of RO−SiMe3 (R = organyl or H)
is occurring. As plausible intermediate Ph4P[Ag(SH)2] is not
stable at room temperature, it is believed to further condense
with loss of H2S. Products of the composition “Ph4P[(AgS)]”
are not known so far, but they might be stabilized by
nucleation and condensation with nc-Ag2S forming in statu
nascendi (eq 3). Anionic clusters of the formal composition
Catn[(AgS)n(Ag2S)m] might be envisaged, but were not
isolated and characterized so far under such protic reaction
conditions represented by Scheme 2:
1
The specific 77Se NMR signals in H−77Se-HMQC NMR
spectra of selenidometalates 4-Ph4P, 5-Ph4P, and 6-Ph4P also
allow an identification. The most high-field shifted 77Se NMR
signal (−502.2 ppm) is observed for the argentate 5-Ph4P,
while the aurate 6-Ph4P shows the most low-field shifted signal
(−377.9 ppm). The 77Se NMR signal of the cuprate 4-Ph4P is
at −469.4 ppm (Figure 9).
Preliminary Study on Reactivity of [M(ESiMe3)2]−
Representatives. While silylchalcogenido metalates of the
coinage metals turned out to be similar to organochalcogeno-
lato metalates with respect to their structural features, their
Addition of MeOH to Ph4P[Ag(SSiMe3)2] leads to the
release of H2S as indicated by a weak evolution of gas and
spontaneous precipitation of a black precipitate, which after 3
E
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h of aging was centrifuged and washed with MeOH. Upon
annealing at 140 °C for 3 days, essentially phase pure
microcrystalline Ag2S was identified via PXRD (JCPDS: 14-
0072; see supplement, Figure S6). Future studies will have to
focus on soluble fractions and the question of whether partially
silylated anionic clusters Catn[(AgS)n(AgSSiMe3)m] might be
formed as intermediates on the way toward the thermody-
namic sink Ag2S.
An indication that this is not pure speculation was gained
from controlled thermolysis studies under strictly aprotic
conditions: The DSC-TGA curve of Ph4P[Cu(SSiMe3)2] (1)
under inert gas reveals a defined melting point at 91 °C (see
supplement, Figure S3). Decomposition of this molten ionic
liquid starts at an onset temperature of Tonset = 179.2 °C. At
this temperature, the robust cations remain intact according to
31P NMR studies; the anion however starts to decompose prior
to cation under elimination of volatile (Me3Si)2S. Controlled
thermolysis of the molten salt 1 in a Schlenk tube at 180 °C for
2 min under 10−2 mbar dynamic vacuum led to an orange-
yellow waxy solid. This residue was dissolved in the smallest
amount of DMF and layered with twice the volume of diethyl
ether. After a few days, red single crystals were obtained. An
XRD analysis revealed that these were identical with literature-
known (Ph4P)4[Cu12S8].35 The composition of this cubocta-
hedral cluster can formally be envisaged as
Catn[(CuS)n(Cu2S)m] with n = 4 and m = 4 (in accord with
Scheme 3, eq 3). In our synthesis, cluster nucleating anionic
conformation is confirmed by quantum chemical calculations
and amounts to about 2−6 kJ/mol, thus revealing a rather
shallow potential mainly depending on electronic effects of the
metal. Furthermore, 2D HMQC methods were applied to
detect the otherwise nonobservable NMR shifts of the 29Si and
77Se nuclei of the silylselenido compounds 4-Ph4P, 5-Ph4P,
and 6-Ph4P. We are convinced that metastable metalates of the
type introduced here will be valuable precursors for controlled
multinary coinage metal chalcogenide cluster or nanoparticle
syntheses from organic solution. Prospective veins of gold to
investigate are thermally induced, chloride induced, or strong
ligand phosphine/NHC induced Me3Si−X elimination,
nucleation, and condensation reaction paths of 1−6. The
nature of more or less polarizing, weakly coordinating organic
+
cations (Cat) and/or the periferically remaining −SiR3
substituent (R = alkyl, aryl) in their compensation of
accumulating negative cluster charge upon growth will
probably be triggering the existing range of products.
EXPERIMENTAL SECTION
■
All preparative operations were conducted by using standard Schlenk
techniques and freshly dried solvents. All solvents were dried
according to common procedures36 and passed through columns of
aluminum oxide, R3-11G-catalyst (BASF), or stored over molecular
sieves (3 or 4 Å). Other reagents were used as received unless stated
otherwise. S(SiMe3)2 and Se(SiMe3)2 were prepared analogously
according to the literature known synthesis of S(SiMe3)2;37 LiESiMe3
are known precursors for the introduction of E−SiMe3 moieties.24 We
prepared these compounds in a slightly simplified way, as described in
the Experimental Section.
Scheme 3. Postulated Thermal Decay Paths of
Cat[Cu(SSiMe3)2] and Nucleation of Cat4[Cu12S8] (Cat =
Ph4P)
Elemental analyses (C, H, N, S) were carried out by the service
department for routine analysis with a vario MICRO cube
(Elementar). Samples for the elemental analysis were weighted into
tin capsules inside a nitrogen filled glovebox. 1H and proton
decoupled 13C NMR spectra were recorded in automation with a
Bruker Avance II 300 spectrometer; 29Si and 77Se NMR spectra were
recorded by the service department for NMR analyses with a Bruker
Avance III HD 300, DRX 400, or Avance III 500 spectrometer. All
spectra were recorded at ambient temperature, unless stated
building blocks “Ph4P[(CuS)]” might have formed via selective
thermal elimination of (Me3Si)2S at 1. The literature synthesis
of (Ph4P)4[Cu12S8] via complex redox reaction of
CuCl2(H2O)2 with 3 equiv of [EtS]− in methanol, followed
by cooling to −78 °C and addition of Li2S and slow warming
of the mixture in the presence of Ph4P[Br], offers even more
room for speculations about any cluster nucleation mechanism.
The thermally and protolytically labile nature of the E−Si
bonds in these molecular precursors 1−6 provides new
perspectives for ligand L controlled formation of dispersions
of LCuxAgyAuzSnSem nanoparticles from homogeneous organic
precursor solutions under adjustable protolytic conditions
difficult to provide with other molecular precursors. On the
other hand, detailed studies on thermal decay paths under
aprotic conditions are opening perspectives to isolate and
characterize new family members of unprecedented anionic
chalcogenido clusters of these elements in future.
1
otherwise. H and 13C NMR spectra were calibrated using residual
proton signals of the solvent (THF[d8]: δH 3.58 and 1.72 ppm, δC
67.21 and 25.31 ppm). 29Si NMR spectra were referenced externally
(SiMe4: δSi0.00 ppm) just as 77Se NMR spectra (Me2Se δSe0.00 ppm).
The XRD data collection was performed on a Stoe Stadivari
diffractometer or a Bruker D8 Quest diffractometer. Details of data
collection and refinement are given in the Supporting Information.
New data sets were deposited under CCDC codes 1940489−
1940503.
Only one representative synthesis procedure of Ph4P[Cu-
(SSiMe3)2] (1) is described here. For all other representative
compounds 2−6, selected analytical data are given. The complete
data and a general synthetic procedure of all compounds are given in
the Supporting Information.
Ph4P[Cu(SSiMe3)2] (1). A mixture of Ph4P[Cl] (0.122 g, 0.32
mmol, 1.00 equiv) and CuCl (0.032 g, 0.32 mmol, 1.00 equiv) was
suspended in thf (10 mL) and stirred for 18 h at room temperature to
obtain a suspension of Ph4P[CuCl2]. In a separate flask a solution of
S(SiMe3)2 (0.119 g, 0.67 mmol, 2.1 equiv) in thf (5 mL) was stirred
at 0 °C and treated with a 2.9 M solution of n-BuLi in hexane (0.22
mL, 0.64 mmol, 2.0 equiv). The pale-yellow reaction mixture was
stirred for 30 min at 0 °C and for an additional 30 min at room
temperature. All volatiles were removed in fine vacuum until LiSSiMe3
is obtained as a colorless waxy solid, and the remaining excess of
S(SiMe3)2 is removed quantitatively. The residue is diluted in THF
(10 mL) and added dropwise to the previously prepared suspension
of Ph4P[CuCl2] at −78 °C. The reaction mixture was slowly allowed
to reach room temperature within 18 h. All volatiles were removed in
CONCLUSION
■
We described the syntheses and XRD molecular structures of
homoleptic silylsulfido and silylselenido cuprates, argentates,
and aurates [M(SSiMe3)2]− (M = Cu (1), Ag (2), Au (3)) and
[M(SeSiMe3)2]− (M = Cu (4), Ag (5), Au (6)) comprising
Ph4P+ or PPN+ cations. All metalate anions exhibit a linear
coordination with a gauche-like Si−[E−M−E]−Si conforma-
tion in the solid state. The energetic preference for the gauche
F
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Article
fine vacuum, and the residue was suspended and extracted with
diethyl ether (60 mL) and filtrated. The filtrate was stored at −30 °C
to obtain the target compound as colorless blocks. The mother liquor
can be reused for a second extraction cycle to obtain 1 as colorless
AUTHOR INFORMATION
■
Corresponding Author
̈
Jorg Sundermeyer − Fachbereich Chemie and Materials
Science Center, Philipps-Universität Marburg, 35043
Marburg, Germany; orcid.org/0000-0001-8244-8201;
Email: JSU@staff.uni-marburg.de
1
crystals with a yield of 0.168 g (0.27 mmol, 84%). H NMR (300.3
MHz, THF[d8]): δ = 7.93−7.83 (m, 20 H, (H5C6)4P+), 0.13 (s, 18 H,
[Cu(SSi(CH3)3)2]−) ppm. 13C NMR (75.5 MHz, THF[d8]): δ =
4
3
136.1 (d, JPC = 3.2 Hz, [(HC(CH2)2(CH2)2C)4P]+)), 135.6 (d, JPC
= 10.4 Hz, [(HC(CH2)2(CH2)2C)4P]+), 131.3 (d, JPC = 13.2 Hz,
2
Authors
[(HC(CH2)2(CH2)2C)4P]+), 118.9 (d, JPC = 98.3 Hz, [(HC-
1
Jannick Guschlbauer − Fachbereich Chemie and Materials
Science Center, Philipps-Universität Marburg, 35043
Marburg, Germany
Tobias Vollgraff − Fachbereich Chemie and Materials Science
Center, Philipps-Universität Marburg, 35043 Marburg,
Germany
Xiulan Xie − Fachbereich Chemie and Materials Science
Center, Philipps-Universität Marburg, 35043 Marburg,
Germany
Florian Weigend − Fachbereich Chemie and Materials Science
Center, Philipps-Universität Marburg, 35043 Marburg,
Germany; Karlsruhe Institute of Technology (KIT), Institute
of Nanotechnology, 76344 Eggenstein-Leopoldshafen,
Germany; orcid.org/0000-0001-5060-1689
(CH2)2(CH2)2C)4P]+), 8.3 (s, [Cu(SSi(CH3)3)2]−) ppm. 29Si NMR
(59.7 MHz, THF[d8]): δ = 5.2 (s) ppm. Anal. calcd for
C30H38Cu1P1S2Si2: C, 58.7; H, 6.2; S, 10.5. Found: C, 58.6; H, 5.8;
S, 10.3.
Ph4P[Ag(SSiMe3)2] (2). 29Si NMR (59.7 MHz, THF[d8]): δ = 5.2
ppm. Anal. calcd for C30H38AgPS2Si2: C, 54.8; H, 5.8; S, 9.8. Found:
C, 54.7; H, 5.8; S, 10.3.
PPN[Au(SSiMe3)2] (3-PPN). 29Si NMR (99.4 MHz, THF[d8]): δ
= 7.6 ppm. Anal. calcd for C42H48AuNP2S2Si2: C, 53.3; H, 5.1; N, 1.5;
S, 6.8. Found: C, 53.0; H, 5.2; N, 1.7; S, 6.7.
Ph4P[Cu(SeSiMe3)2] (4-Ph4P). 29Si NMR (99.4 MHz, THF[d8]):
δ = 0.23 ppm. Extended measurement times were needed to obtain a
1D-29Si NMR spectrum. It was not possible to obtain a 1D-77Se NMR
signal. For convenient detection of 29Si and 77Se NMR signals,
29Si/1H- and 77Se/1H-HMQC measurements were performed:
29Si/1H-HMQC NMR (99.4 MHz/500.2 MHz, THF[d8]): δ = H
1
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c02808
0.27/29Si 0.2 ppm. 77Se/1H-HMQC NMR (95.4 MHz/500.2 MHz,
THF[d8]): δ = H 0.28/77Se −469.4 ppm.
1
Ph4P[Ag(SeSiMe3)2] (5-Ph4P). 29Si NMR (99.4 MHz, THF[d8],
273 K): δ = 1.59 (b) ppm. 77Se NMR (95.4 MHz, THF[d8], 273 K):
δ = −501.5 (b) ppm. Extended measurement times were needed to
obtain a 1D-29Si- and 1D-77Se NMR spectrum. For a more convenient
detection of 29Si and 77Se NMR signals, 29Si/1H- and 77Se/1H-
HMQC measurements were performed: 29Si/1H-HMQC NMR (99.4
Author Contributions
J.G. concept, synthesis of all compounds, and writing the first
draft; T.V. all XRD analyses; X.X. correlated HMQC NMR
experiments; F.W. quantum chemical calculations; J.S. general
concept, writing and editing the final version. All authors have
given approval to the final version of the manuscript.
MHz/500.2 MHz, THF[d8]): δ = H 0.27/29Si 1.6 ppm. 77Se/1H-
1
HMQC NMR (95.4 MHz/500.2 MHz, THF[d8]): δ = H 0.29/77Se
1
Funding
−502.2 ppm. Anal. calcd for C30H38AgPSe2Si2: C, 47.9; H, 5.1.
DFG (SPP 1708 ‘Material Synthesis near room Temperature’).
Found: C, 47.5; H, 4.9.
Ph4P[Au(SeSiMe3)2] (6-Ph4P). 29Si NMR (99.4 MHz, THF[d8],
273 K): δ = 2.4 (b) ppm. 77Se (95.4 MHz, THF[d8], 273 K): δ =
−377.1 (b) ppm. Extended measurement times were needed to obtain
broad 1D-29Si NMR and 1D-77Se NMR signals. For the convenient
detection of 29Si and 77Se NMR signals, 29Si/1H- and 77Se/1H-
HMQC measurements were performed: 29Si/1H-HMQC NMR (99.4
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Deutsche Forschungsgemeinschaft, DFG, and its
priority program SPP 1708 ‘Material Synthesis near room
Temperature’ for financial support. We thank Bertram Peters
for his instruction and support with respect to PXRD
measurements.
1
MHz/500.2 MHz, THF[d8]): δ = H 0.27/29Si 2.4 ppm. 77Se/1H-
1
HMQC NMR (95.4 MHz/500.2 MHz, THF[d8]): δ = H 0.31/77Se
−377.3 ppm. Anal. calcd for C30H38AuPSe2Si2: C, 42.9; H, 4.6.
Found: C, 42.5; H, 4.5.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c02808.
■
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