Capping nido-Nonagermanide Clusters with M-PPh3 and Dynamics in Solution: Synthesis and Structure of closo-[(Me3Si)3Si]3Et[Ge9 M](PPh3) (M = Ni, Pt)

Article abstract of DOI:10.1021/acs.organomet.8b00459

In this work, cluster expansion of nine-atomic germanium clusters with nickel and platinum atoms is reported. The compounds [(Me₃Si)₃Si]₃Et[Ge₉Ni](PPh₃) and [(Me₃Si)₃Si]₃Et[Ge₉Pt](PPh₃) are characterized by NMR spectroscopy, elemental analysis, and single crystal X-ray structure analysis. The latter represents the first intermetalloid Ge-Pt cluster with a platinum atom as part of a deltahedron. So far, only one compound of this type has been reported for the homologous Pd. Hence, with these new compounds, metal-coordinated deltahedral Ge₉ clusters are now known for the whole triad of group 10 elements. The cluster compounds are accessible by treating [(Me₃Si)₃Si]₃EtGe₉ with η²-ethylene-bis-(triphenylphosphine)-nickel(0) and η²-ethylene-bis-(triphenylphosphine)-platinum(0), respectively, in toluene. The crystal structure determination reveals ten-vertex-closo-[Ge₉M]-cluster cores (M = Ni, Pt) bearing five exo-bonded ligands. Unlike the nine-vertex-cluster [(Me₃Si)₃Si]₃EtGe₉, the penta-functionalized platinum containing cluster compound [(Me₃Si)₃Si]₃Et[Ge₉Pt](PPh₃) does not show fluctuating behavior in solution over a wide temperature range on the NMR time scale, whereas the [(Me₃Si)₃Si]₃Et[Ge₉Ni](PPh₃) shows highly dynamic processes in solution at ambient temperature.

Full text of DOI:10.1021/acs.organomet.8b00459

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Capping nido-Nonagermanide Clusters with M‑PPh3 and Dynamics
in Solution: Synthesis and Structure of closo-
[(Me3Si)3Si]3Et[Ge9M](PPh3) (M = Ni, Pt)
Sabine Frischhut,† Felix Kaiser,‡ Wilhelm Klein,† Markus Drees,§ Fritz E. Kuhn,‡
̈
,†
̈
and Thomas F. Fassler*
†Lehrstuhl fu
Lichtenbergstraße 4, 85747 Garching, Germany
̈
r Anorganische Chemie mit Schwerpunkt Neue Materialien, Fakultat fur Chemie, Technische Universitat Munchen,
̈ ̈
̈ ̈
‡Professur fu
Germany
§Lehrstuhl fu
̈
r Molekulare Katalyse, Fakultat fur Chemie, Technische Universitat Munchen, Lichtenbergstraße 4, 85747 Garching,
̈ ̈
̈ ̈
̈
r Anorganische und Metallorganische Chemie, Fakultat fur Chemie, Technische Universitat Munchen,
̈ ̈
̈ ̈
Lichtenbergstraße 4, 85747 Garching, Germany
S
* Supporting Information
ABSTRACT: In this work, cluster expansion of nine-atomic
germanium clusters with nickel and platinum atoms is
reported. The compounds [(Me3Si)3Si]3Et[Ge9Ni](PPh3)
and [(Me3Si)3Si]3Et[Ge9Pt](PPh3) are characterized by
NMR spectroscopy, elemental analysis, and single crystal X-
ray structure analysis. The latter represents the first
intermetalloid Ge-Pt cluster with a platinum atom as part of
a deltahedron. So far, only one compound of this type has
been reported for the homologous Pd. Hence, with these new
compounds, metal-coordinated deltahedral Ge9 clusters are
now known for the whole triad of group 10 elements. The cluster compounds are accessible by treating [(Me3Si)3Si]3EtGe9
with η2-ethylene-bis-(triphenylphosphine)-nickel(0) and η2-ethylene-bis-(triphenylphosphine)-platinum(0), respectively, in
toluene. The crystal structure determination reveals ten-vertex-closo-[Ge9M]-cluster cores (M = Ni, Pt) bearing five exo-bonded
ligands. Unlike the nine-vertex-cluster [(Me3Si)3Si]3EtGe9, the penta-functionalized platinum containing cluster compound
[(Me3Si)3Si]3Et[Ge9Pt](PPh3) does not show fluctuating behavior in solution over a wide temperature range on the NMR time
scale, whereas the [(Me3Si)3Si]3Et[Ge9Ni](PPh3) shows highly dynamic processes in solution at ambient temperature.
synthesis of [{(Me3Si)3Si}3Ge9]− is carried out by reacting the
Zintl phase K4Ge9 with chlorotris(trimethylsilyl)silane in a
INTRODUCTION
[Ge9]4− Zintl clusters show multifaceted reactivity toward
■
heterogeneous reaction in acetonitrile. This synthesis route
transition metal compounds. By reacting [Ge9]4− with diverse
provides access to the stable Zintl anion [{Me3Si)3Si}3Ge9]−,
transition metal complexes, endohedrally filled cluster species
hosting transition metals in the cluster’s center, as well as
cluster compounds with exohedrally bonded transition metals,
which is highly soluble in acetonitrile, thf, and toluene.5 The
reactivity of the three-fold silylated cluster compound
[{(Me3Si)3Si}3Ge9]− has been studied intensively in recent
are accessible.1 Therefore, such clusters are candidates to study
years, including variation of silyl ligands and the accompanied
cluster growth mechanisms for the formation of intermetalloid
steric effects. New silylated cluster compounds emerged, such
clusters. The manifold reaction schemes, including stepwise
addition and insertion of transition metal atoms to deltahedral
as [{(Me3Si)2(Ph3Si)Si}3Ge9]−,6 [{(Me3Si)3Si}2{(Me3Si)2-
(Ph3Si)Si}Ge9]−,7 and [{HtBu2Si}3Ge9]−.8 Also, the introduc-
cages, flanked by disproportionation reactions allow for the
synthesis of a large variety of compounds.2
tion of specific functionalities to the Ge9 clusters via the silyl
According to the Wade−Mingos rules, [Ge9]4− represents a
ligand has been shown by the synthesis of [{(Me3Si)3Si}2-
{Ph2((CH2)nCHCH2)Si}Ge9]− and [{Ph2((CH2)nCH
nido-cluster containing 22 skeleton-bonding electrons.3 The
CH2)Si}3Ge9]−.9 The silyl ligands can also be formally
cluster can be dissolved in highly polar solvents by extraction
from the binary Zintl phases A4Ge9 (A = K, Rb), e.g., NH3(liq)
or ethylenediamine. The transfer of Ge9 Zintl cluster
exchanged by other substituents as is shown in [{(Me3Si)3-
Si}2PtBu2Ge9].10 Stannyl-decorated Zintl anions were realized
in [(SniPr3)3Ge9]−.11 More and more attention has been
compounds into less polar and more convenient solvents was
achieved by the silylation of the [Ge9]4− Zintl clusters with
chloro-silanes. The first representative was reported by Schnepf
Received: July 4, 2018
et al. through metastable Ge(I)Br,4 and an even more facile
© XXXX American Chemical Society
A
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Scheme 1. Reaction of [(Me3Si)3Si]3EtGe9 with η2-Ethylene-bis-(triphenylphosphine)-platinum(0)/η2-Ethylene-bis-
(triphenylphosphine)-nickel(0) in Toluene Yields [(Me3Si)3Si]3Et[Ge9Ni](PPh3) (1)/[(Me3Si)3Si]3Et[Ge9Pt](PPh3) (2)
drawn on the three-fold silylated Ge9 cluster compounds, as
they represent excellent starting materials for follow-up
reactions in Zintl cluster chemistry. For example, the three-
fold silylated cluster compound [{(Me3Si)3Si}3Ge9]− can
undergo nucleophilic substitution reactions with XSnPh3,
XSnnBu3, XR′, or Cl(CO)R′ (with X = halide and R′ =
organic substituent) to form neutral cluster compounds, which
show dynamic behavior in solution.12
phine)-nickel(0) and η2-ethylene-(bis-triphenylphosphine)-
platinum(0), in toluene (Scheme 1), respectively. Both
compounds crystallize from n-hexane solutions at −32 °C
and are investigated by NMR spectroscopy, elemental analysis,
and single crystal X-ray diffraction.
RESULTS AND DISCUSSION
■
Reactions of [(Me3Si)3Si]3EtGe9 with tetrakis(triphenylphos-
phine)nickel(0) or tetrakis(triphenylphosphine)platinum(0) in
analogy to the recently published procedure for the respective
palladium species20 leads to the decomposition of [(Me3Si)3-
Si]3EtGe9, as monitored in the 1H NMR spectra of the reaction
solutions. Consequently, the reactions were carried out with
the more readily reactive η2-ethylene-bis-(triphenylphos-
phine)-nickel(0) and -platinum(0) complexes where the
ethylene ligand is easier to replace. The reaction at room
temperature in toluene resulted in the formation of the desired
products [(Me3Si)3Si]3Et[Ge9M](PPh3) with M = Ni (1) and
Pt (2). The products were extracted with hexane from the solid
after removal of toluene, and recrystallized from the hexane
solutions at −32 °C.
Also, [R3Ge9]− (R = silyl ligands) readily reacts with late
transition metal halides in metathesis reactions. For example,
the linkage of two [{(Me3Si)3Si}3Ge9]− entities can be realized
in [{Me3Si)3Si}3Ge9MGe9{Si(SiMe3)3}3]n− for various metals
(M = Cu, Ag, Au, n = 1; M = Zn, Cd, Hg, n = 0), where the
cluster cores are coordinated to the metal center in an η3-
fashion.13 With [{(Si(SiMe3)3)3Ge9}Cu{Ge9(Si(SiMe3)3)3}-
CuPPh3]14 and [(CuPiPr3)4{Ge9(SiPh3)2}2],15 also larger
entities have been reported. Remarkably, the latter contains
two CuPiPr3 entities serving as linker by cluster coordination
in both Cu-η1 and Cu-η2 fashion. Additionally, each Ge9 cluster
core coordinates to one CuPiPr3 entity via the Cu atom in an
η4 fashion.
Just recently, also the first N-heterocyclic carbene (NHC)
adducts of Ge9 Zintl clusters were reported with [NHCDippM-
(η3-Ge9[{Si(SiMe3)3}3)] (M = Cu, Ag, Au) and, thus, for the
first time combined NHC and Zintl cluster chemistry, which
gave access to several new structures.10,16
Cluster expansions have been realized at bare Ge9 clusters
with Zn, Cu, Sn, Pd and also for the heavier homologues Sn9
with Zn, Cd, Ir, Cr, Mo, W, Ag, Cu, Au, and for Pb9 with Cr,
Mo, W atoms.1b,16d,17
Similarly, nido-cluster core expansion has been achieved for
[{Me3Si)3Si}3Ge9]−, resulting in closo-[[{Me3Si)3Si}3Ge9M-
(CO)3]− for M = Cr, Mo, W. The transition metal is
introduced into the polyhedral arrangement, forming a
distorted bicapped square antiprismatic [MGe9] core.18
With Pd complexes, introduction of three Pd atoms into the
cluster scaffold of [(SniPr3)3Ge9]−, followed by merging with a
second [(SniPr3)3Ge9]− unit, was observed.11,19 Just recently,
the first example of a cluster expansion of a neutral Ge9 cluster,
which carries five external ligands [(Me3Si)3Si]3EtGe9Pd-
(PPh3), was reported. The compound with a closo-[PdGe9]
core is accessible by the reaction of [(Me3Si)3Si]3EtGe9 with
[Pd(PPh3)4].20
Single crystal X-ray diffraction of crystals of 1 and 2
unequivocally revealed the formation of a distorted CS-
symmetric bicapped square-antiprismatic closo-[MGe9] core
bearing the M atom as a vertex of the square of the antiprism
and five ligands that radially point away from the cluster core
(Figure 1). The compounds crystallize in the triclinic space
̅
group P1 with one symmetry-independent cluster. The cluster
possesses pseudo-Cs symmetry with an approximate mirror
plane through the atoms Ni1/Pt1, Ge1, Ge3, Ge6, and Ge8. A
triphenylphosphine ligand is coordinated to the Ni/Pt atom
which itself coordinates to the five Ge vertices Ge1, Ge2, Ge3,
Ge4, and Ge5 of the cluster core. In particular, two hypersilyl
groups are bound to the neighboring and opposingly
positioned Ge atoms of the square of the antiprism (Ge1
and Ge3).
Both capping atoms bear ligands, namely, the ethyl
functionality at the Ge2 atom neighboring the Ni/Pt atom
and one of the three hypersilyl groups binds to the Ge6 atom.
The Ge−Ge bond lengths within the cluster core in 1 and 2 lie
in the range of 2.4682(6)−2.8020(6) Å and 2.4756(8)−
2.8885(9) Å, respectively, with Ge1−Ge2 and Ge4−Ge5 being
the shortest and longest, respectively. The Ge−Ge bond
lengths in 1 appear slightly shorter than the reported ones for
the heavier Pd homologue; the Ge−Ge bond lengths in the Pt
derivative 2 are similar to those in the lighter Pd homologue.20
The distances Ge4−Ge9 and Ge5−Ge7 appear elongated (1:
3.2429(7) Å and 3.3244(7) Å, 2: 3.2303(9) Å and 3.3053(9)
In this work, the related closo-[MGe9] cluster derivatives of
the lighter homologue M = Ni and the heavier homologue M =
Pt are presented. [(Me3Si)3Si]3Et[Ge9Ni](PPh3) (1) and
[(Me3Si)3Si]3Et[Ge9Pt](PPh3) (2) were obtained by reaction
of [(Me3Si)3Si]3EtGe9 with η2-ethylene-(bis-triphenylphos-
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2.476 Å in 1 is smaller compared to the average Pd−Ge
distance of 2.577 Å and the average Pt−Ge distance of 2.592 Å
in 2. The latter two are rather similar due to similar atom radii
of Pd and Pt.21 The shorter Ni−Ge distances lead to a stronger
distortion of the closo-cluster core accompanied by a
compression of the Ge−Ge distances.
1
The H NMR spectrum of the platinum cluster 2 shows all
expected signals at r.t. including the phenyl groups of the
phosphine ligands in the range of 7.90−6.99 ppm, the ethyl
group, which shows the two expected signals at 2.66 and 2.36
ppm with an integral ratio of 2:3, and two sharp signals at 0.65
and 0.26 ppm in a 1:2 integrals ratio for the three hypersilyl
groups. According to the approximate CS symmetry of the
polyhedron, two hypersilyl groups are chemically equivalent
(Figure 2).
Even at elevated temperatures up to 90 °C, 2 does not show
a change in its nondynamic behavior, as is revealed by
temperature-resolved NMR studies (Figure S15, Supporting
Information). Thus, the two signals for the hypersilyl groups
remain virtually unchanged throughout a wide temperature
range.
1
The H NMR spectrum of 1 at r.t. shows broad signals in
the region of the H atoms of the hypersilyl ligands at 0.61 and
0.27 ppm, and the ethyl group at 2.86 and 2.25 ppm. The large
line widths hint for a dynamic process in solution (Figure S5).
Temperature-dependent NMR spectra of 1 show sharp signals
at lower temperature up to 0 °C (Figures 2 and 3). The
hypersilyl ligands appear as two signals in a 1:2 ratio as
expected for a CS-symmetric cluster. Upon warming to 25 °C,
the signals for the hypersilyl and the ethyl ligand progressively
broaden and are visually shifted at 25 °C. When further heated
up to 80 °C, sharp signals for the hypersilyl ligands at 0.52 and
Figure 1. Molecular structures of 1 (a, b) and 2 (c, d). (a/c) The
[MGe9]-cluster cores are depicted as polyhedrons. All hydrogen
atoms as well as CH3 groups on hypersilyl moieties are omitted for
clarity. (b/d) The two squares of the underlying quadratic antiprism
of the [MGe9]-polyhedra are highlighted in red. All ellipsoids are
shown at a probability level of 50%. Ge - blue, Si - green, C - gray, P -
purple, Ni - turquoise, Pt - brown.
1
0.29 ppm in a 1:2 ratio appear in the H NMR spectrum
Å), compared to the shorter distances Ge4−Ge5 and Ge7−
Ge9 (1: 2.7638(6) Å and 2.7785(6) Å, 2: 2.8885(9) Å and
2.7497(9) Å), resulting in a considerably distorted “square”,
formed by the Ge4-Ge5-Ge7-Ge9 atoms. This has already
been observed for neutral, functionalized Ge9 Zintl
clusters.12a,20 As expected, the average Ni−Ge distance of
(Figure 3a). Also, a new signal set for the ethyl ligand at 2.60
and 1.90 ppm appears with an integrals ratio of 2:3 which still
does not show the expected multiplicity at 80 °C (Figure 3b).
The signal set of the bound triphenylphosphine ligand does
not significantly change in the described temperature range;
Figure 2. 1H NMR spectrum of dissolved crystals of compound 2, recorded in [D6]benzene at r.t. The regions of the phenyl and ethyl groups are
shown enlarged. The signals of the hypersilyl groups are marked with “hyp”; the signals of hexane are marked with “hex”.
C
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Figure 3. Variable temperature 1H NMR study of crystals of 1 in [D8]toluene in the range from −40 to 80 °C and subsequent cooling to −40 °C.
(a) The signals of the hypersilyl ligands (“hyp”) are shown. (b) The signals of the ethyl ligand (“Et”) are shown.
however, after increasing time of heating, a signal of low
Scheme 2. Two Feasible CS-Symmetric Isomers of 1′ and 1′′
intensity corresponding to free PPh3 appears (Figure S7).
Subsequent cooling to −40 °C leads to the same sharp signal
sets as before warming (Figure 2 and Figure S6). Yet, the very
Which Can Be Achieved Based on 1 by the Formal
Exchange of Vertices
1
weak signal of free PPh3 remains visible in the H NMR
spectrum, which hints at slow and irreversible PPh3 abstraction
of 1. Remarkably, compound 1 is the major component again
after heating to 80 °C and subsequent cooling. Variable
temperature 31P NMR studies also reveal dynamic temper-
ature-dependent processes in solution (Figure S8, Supporting
Information).
Hence, the clusters 1 and 2 do not show the fluctuating
behavior as is observed for [(Me3Si)3Si]3EtGe9 in solution at
r.t., since the silyl ligands are not all identical. Nevertheless, 1
shows a different dynamic process in solution at r.t., whereby
the CS-symmetry of 1 remains unchanged. This can be
concluded from the signal set of two signals for the hypersilyl
ligands as well as the corresponding integrals ratio of 1:2 at
1
temperatures above 60 °C in the temperature-dependent H
NMR spectrum.
Isomerization resulting from rotation of the ethyl group in 1
is feasible, but the reason for the lack of rotational isomerism in
2 in the analogous Pt complex remains unclear. Therefore, we
also take constitutional isomerism into account. Scheme 2
shows the two at elevated temperatures possibly formed
isomers 1′ and 1′′, which fulfill the CS-symmetry.
isomerization of 1 most likely proceeds according to a
diamond-square-diamond (DSD) rearrangement mechanism.
Such cluster rearrangement processes have been described for
boranes and carboranes,22 which are structurally and electroni-
cally related to the Ge9 clusters. Isomerizations analogous to
the formation of 1′′ out of 1 are already reported in the
literature for closo-[Sn9Mo(CO)3]4−, where the corresponding
η4- and η5-structures show a dynamic equilibrium.17g
The formation of the closo-[MGe9] cluster core (M = Ni, Pt)
of 1 and 2 is, similarly to [(Me3Si)3Si]3Et[Ge9Pd](PPh3),
believed to be initiated by an M(PPh3) entity capping the
triangular face Ge2-Ge4-Ge5 of the nido-Ge9 cluster core,
followed by a cluster-opening displacement of the ethyl-
functionalized Ge2 vertex.20
On the basis of quantum chemical DFT calculations, the
energy difference between the two isomers 1 and 1′, where the
position of the Ge2-ethyl fragment is changed with the only
ligand-free adjacent Ge8-vertex, is only as high as +7.6 kcal/
mol (energy difference between the Pt-analogous isomers 2
and 2′: +8.1 kcal/mol). Retention of the CS-symmetry in 1
would also be given when the fragments Ni-PPh3 and Ge2-
ethyl undergo a formal positional change to form the isomer
1′′. Here, the energy difference of the isomers 1 and 1′′ is +7.2
kcal/mol (energy difference between the Pt-analogous isomers
2 and 2′′: +9.2 kcal/mol). The energy differences for the
isomerization of 1 and 2 are in the same range; however, we do
not have any information about transition states. The
Currently, investigations on follow-up reactions are ongoing
in our laboratories. Among others, the behavior of the PPh3
ligand and its exchangeability for other ligands is of particular
interest to us.
D
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(geometry, absolute energy) can be found in the Supporting
Information.
CONCLUSION
■
Synthesis of η2-Ethylene-bis-(triphenylphosphine)-nickel-
(0). The product was synthesized according to a literature
procedure.28 Ni(acac)2 (1.00 g, 3.89 mmol) and PPh3 (2.04 g, 7.78
mmol) are dissolved in diethyl ether, and a stream of ethylene gas is
passed through the suspension at 0 °C. AlEt3 (469 mg, 4.11 mmol)
dissolved in 6.5 mL of hexanes is added over a period of 30 min and
stirred for 5 h. The canary yellow precipitate is filtered off with a
Schlenk frit, washed three times with diethyl ether, and dried in a
vigorous stream of ethylene. The product is isolated as a canary yellow
solid. The analytical data match those reported in the literature.
Synthesis of [(SiMe3)Si]3Ge9Et. The compound [(SiMe3)3Si]3-
Ge9Et was synthesized according to a modified literature procedur-
e.12a A solution of chlorotris(trimethylsilyl)silane (357 mg, 1.26
mmol) in 12 mL of acetonitrile is added to K4Ge9 (341 mg, 0.42
mmol). The reaction solution is stirred for 21 h at r.t. and filtered over
a glass fiber filter. Bromoethane (156 μL, 2.10 mmol) dissolved in 2
mL acetonitrile is added dropwise under vigorous stirring. A brown
precipitate is formed; the suspension is stirred for 5 h and then set
aside to allow the precipitate to settle down. The supernatant is
decanted, and the precipitate is washed three times with a total
amount of 24 mL of acetonitrile. The residue is dried in vacuo and
characterized by NMR spectroscopy (see the Supporting Informa-
tion).
In this work, we were able to complete the triad of the
compounds [(Me3Si)3Si]3Et[Ge9M](PPh3) with M = Ni-Pt.
The deltahedral Ge9 Zintl cluster compounds [(Me3Si)3Si]3-
Et[Ge9M](PPh3) [M = Ni (1), M = Pt (2)] are synthesized by
reaction of [(Me3Si)Si]3EtGe9 with η2-ethylene-bis-(triphenyl-
phosphine)-nickel(0) or η2-ethylene-bis-(triphenylphosphine)-
platinum(0). Both compounds 1 and 2 are characterized in
solution by NMR spectroscopy as well as in the solid state by
elemental analysis and single crystal X-ray diffraction. The
nickel derivative 1 shows a strongly distorted closo-[NiGe9]
cluster core and most likely undergoes a framework rearrange-
ment in solution at r.t., if compared to the closo-[MGe9] cluster
cores of the heavier homologues.
Further investigating the neutral deltahedral Ge9 Zintl
cluster compounds in follow-up reactions is of special interest
as neutral, functionalized cluster compounds can be used to
build up higher cluster aggregates. After saturating the whole
coordination sphere of the neutral Zintl cluster compound
[(Me3Si)Si]3EtGe9, new interesting structures might be
available.
Synthesis of [(SiMe3)Si]3Et[Ge9Ni](PPh3) (1). The obtained
brown solid of [(SiMe3)3Si]3Ge9Et (150 mg, 0.11 mmol) and η2-
ethylene-bis-(triphenylphosphine)-nickel(0) (65 mg, 0.11 mmol) are
dissolved in 3.2 mL of toluene and stirred for 2 h at r.t. After filtration
over a glass fiber filter, the solvent is removed. The residue was
extracted with hexane to give a dark-brown solution which was filtered
again. After concentration, the solution is stored at −32 °C for
crystallization. After 5 days, brown block-shaped crystals of 1 (yield:
27%) suitable for X-ray structure analysis formed. For NMR
spectroscopic investigations, crystals of 1 were separated from the
mother liquor, washed with acetonitrile, dried in vacuo, and dissolved
in a deuterated solvent.
EXPERIMENTAL SECTION
■
General. All manipulations were carried out under a purified argon
atmosphere using standard Schlenk techniques. The Zintl phase with
the nominal composition K4Ge9 was synthesized heating a
stoichiometric mixture of the elements K and Ge (99.999%,
Chempur) at 650 °C for 46 h in a stainless steel autoclave.23 The
solvents acetonitrile, toluene, and hexane were dried over molecular
sieve in a solvent purification system MB-SPS. cis-Dichloro-bis-
(triphenylphosphine)-platinum(II) (Sigma-Aldrich), ethylene
(≥99.5%, Sigma-Aldrich), chlorotris(trimethylsilyl)silane (≥95.0%,
TCI Chemicals), and bromoethane (98%, Sigma-Aldrich) were used
as received. Ni(acac)2 was sublimed in vacuo (10−3 mbar, 160 °C),
PPh3 was recrystallized twice from hot ethanol, and diethyl ether was
saturated with ethylene by vigorously passing a stream of ethylene gas
through the liquid over a period of 10 min. The deuterated solvents
[D6]benzene and [D8]toluene were purchased from Deutero GmbH
and stored over molecular sieves (3 Å) for at least 1 day.
1H NMR (400 MHz, [D8]toluene, 233 K): δ (ppm) 7.76 (m, 6H,
phenyl), 7.03 (m, superimposed with signal of toluene, phenyl), 7.951
3
(m, superimposed with signal of toluene, phenyl), 2.86 (q, 2H, J =
3
7.6 Hz, CH2), 2.36 (t, 3H, J = 7.6 Hz, CH3), 0.65 (s, 27H, SiCH3),
0.28 (s, 54H, SiCH3); 31P{1H} NMR (162 MHz, [D8]toluene, 233
K): δ (ppm) 50.99; elemental analysis calcd for 1·0.5 hex (%): C
33.55, H 6.08, Ni 3.28; found: C 33.23, H 6.08, Ni 3.7.
Electron-Dispersive X-ray (EDX) Analysis. The elemental
composition in the single crystals of 1 and 2 which were used to
determine the crystal structure was analyzed with a Hitachi TM-1000
tabletop microscope.
Elemental Analysis. Elemental analysis was performed by the
microanalytical laboratory at the Department of Chemistry of the
Synthesis of η2-Ethylene-bis-(triphenylphosphine)-
platinum(0). The compound was synthesized according to a
modified literature procedure.29cis-Dichloro-bis-(triphenylphos-
phine)-platinum(II) (2.03 g, 2.57 mmol) is suspended in a mixture
of 25 mL of dichloromethane and 25 mL of ethanol, cooled to 5 °C,
and ethylene is vigorously passed through the stirred suspension via
cannula. NaBH4 (0.48 g, 12.6 mmol) is added in portions within a
period of 10 min, and the solution is stirred at 5 °C for 30 min. 85 mL
of ethanol is added, the suspension is stirred for 5 min, and the
ethylene stream is turned off. The white precipitate is filtered off,
washed with water, ethanol, and pentanes, and slowly dried on air.
1.82 g (2.43 mmol, 95%) of η2-ethylene-bis-(triphenylphosphine)-
platinum(0) is isolated as a white solid. The analytical data match
those reported in the literature.29,30
̈
̈
Technische Universitat Munchen. The elements C and H were
determined with a combustion analyzer (elementar vario EL, Bruker
Corp.). Platinum was determined photometrically with tin(II)
chloride at 404 nm. Nickel was determined by atomic absorption
spectroscopy.
NMR Spectroscopy. All NMR spectra were recorded on a
BRUKER Avance Ultrashield AV400 spectrometer. The signals were
referenced to the residual proton signal of the deuterated solvents
[D6]benzene (δ = 7.16 ppm) and [D8]toluene (δCH3 = 2.09 ppm).
The chemical shifts are given in δ values in parts per million (ppm).
Variable temperature 31P NMR studies were performed on a
BRUKER AV500 cryo spetrometer. Crystals of 1 were dissolved in
the deuterated solvent at −78 °C.
DFT Calculations. All calculations have been carried out with the
software package Gaussian 09.24 The level of theory contains the
gradient approximated functional PBE25 and the def2-SV(P)26 basis
set for all elements except Pt. For the latter element, the Dresden-
Stuttgart ECP27 has been used. All optimized structures have been
proved by frequency analysis, if we have a ground state (NImag = 0)
or a transition state (NImag = 1). All energy values are unscaled ΔG
values. Detailed information about the calculated structures
Synthesis of [(SiMe3)Si]3Et[Ge9Pt](PPh3) (2). [(SiMe3)3Si]3-
Ge9Et (150 mg, 0.11 mmol) and η2-ethylene-bis-(triphenylphos-
phine)-platinum(0) (79 mg, 0.11 mmol) are dissolved in 3.2 mL of
toluene and stirred for 3.5 h at r.t. The reaction solution is filtered
over a glass fiber filter. After solvent-removal from the red-brown
filtrate in vacuo, the product is extracted with 2 mL of hexane. After
filtration, the solution is concentrated in vacuo and stored at −32 °C
for crystallization. Red-brown plates of 2 (yield: 32%) suitable for X-
ray structure analysis formed within 4 weeks. For NMR spectroscopic
investigations, crystals of 2 were separated from the mother liquor,
washed with acetonitrile, dried in vacuo, and dissolved in a deuterated
solvent.
E
DOI: 10.1021/acs.organomet.8b00459
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1H NMR (400 MHz, [D6]benzene, 298 K): δ (ppm) 7.88 (m, 6H,
phenyl), 7.09 (m, 6H, phenyl), 7.01 (m, 3H, phenyl), 2.66 (q, 2H, 3J
= 7.6 Hz, CH2), 2.36 (t, 3H, 3J = 7.6 Hz, CH3), 0.65 (s, 27H, SiCH3),
The presence of the elements Si, Ge, P, and Pt or Ni in the
measured single crystal was confirmed by EDX.
1
1
0.26 (s, 54H, SiCH3); H H COSY (400 MHz, [D6]benzene, 298
K): δ (ppm)/δ (ppm) 7.88/7.09 (phenyl), 2.65/2.37 (3J, CH2/CH3);
13C{1H} NMR (101 MHz, [D6]benzene, 298 K): δ (ppm) 140.8 (s,
phenyl), 140.4 (s, phenyl), 134.8 (s, phenyl), 134.7 (s, phenyl), 129.9
(s, phenyl), 129.8 (s, phenyl), 128.3 (superimposed with signal of
C6D6, revealed by HMBC and HSQC, phenyl), 47.7 (t, CH2), 16.1
(q, CH3), 3.1 (q, SiCH3); 1H 13C HSQC (400 MHz, 101 MHz,
[D6]benzene, 298 K): δ (ppm)/δ (ppm) 7.88/134.4, 7.89/128.0,
7.09/134.4, 7.09/129.6, 7.09/128.0, 7.01/129.6, 2.66/47.3 (1J, CH2/
CH2), 2.66/15.70 (2J, CH2/CH3), 2.36/47.35 (2J, CH3/CH2), 2.36/
15.70 (1J, CH3/CH3), 0.65/2.72 (1J, SiCH3/SiCH3), 0.26/2.74 (1J,
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00459.
Further details on the crystal structures of 1 and 2, as
well as NMR spectra are provided (PDF)
Cartesian coordinates (XYZ)
Accession Codes
1
SiCH3/SiCH3); H 13C HMBC (400 MHz, 101 MHz, [D6]benzene,
CCDC 1812801 and 1812802 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
298 K): δ (ppm)/δ (ppm) 7.88/134.6, 7.88/129.9, 7.11/140.7, 7.10/
134.7, 7.09/128.4, 7.00/134.8, 2.65/16.5, 2.36/47.7, 0.65/3.2, 0.26/
3.3; 31P{1H} NMR (162 MHz, [D6]benzene, 298 K): δ (ppm) 37.79
(s, PtPPh3); 29Si NMR (79 MHz, 298 K): −9.08 (s, Si[Si(CH3)3]3),
−9.83 (s, Si[Si(CH3)3]3), −87.04 (s, Si[Si(CH3)3]3), −94.66 (s,
Si[Si(CH3)3]3); elemental analysis calcd for 2·1.5 hex (%): C 33.42,
H 6.11, Pt 9.69; found: C 32.84, H 5.80, Pt 9.6.
X-ray Data Collection and Structure Determination. A few
crystals were transferred from the mother liquor into perfluoropo-
lyalkylether under a cold N2 stream. A single crystal was fixed on a
glass fiber and positioned in a 150 K (compound 1) or 100 K
(compound 2) cold N2 stream. The single crystal intensity data were
recorded on a Stoe StadiVari diffractometer (Mo Kα radiation (λ =
0.71073), Pilatus 300 K detector), by using the X-Area software
package.31 The crystal structure was solved by Direct Methods using
the SHELX software.32 The positions of the hydrogen atoms were
calculated and refined using a riding model. All non-hydrogen atoms
were treated with anisotropic displacement parameters. Solvent
molecules appear partially disordered in the crystal structure of 2.
Crystallographic details of compounds 1 and 2 are listed in Table 1.
CCDC 1812801 (1) and CCDC 1812802 (2) contain the
supplementary crystallographic data.
AUTHOR INFORMATION
Corresponding Author
*Fax: +49-89-289-13186. E-mail: Thomas.Faessler@lrz.tu-
muenchen.de.
■
ORCID
Wilhelm Klein: 0000-0002-6351-9921
Fritz E. Kuhn: 0000-0002-4156-780X
̈
̈
Thomas F. Fassler: 0000-0001-9460-8882
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank B.Sc. Kevin Frankiewicz for preparation of
reaction solutions and Maria Weindl for performing temper-
ature-dependent NMR studies. S.F. and F.K. are further
grateful to the Fonds der Chemischen Industrie for their
fellowships. This work was supported by funding from
TUM.solar in the context of the Bavarian Collaborative
Research Project “Solar Technologies Go Hybrid” (SolTech).
Table 1. Crystallographic Details of Compounds 1·1.5 hex
and 2·1.5 hex
1·1.5 hex
2·1.5 hex
formula
fw (g·mol−1
C56H122Ge9NiPSi12
1875.60
C56H122Ge9PtPSi12
2011.98
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