Attempted Synthesis of a Homocyclic Bis(silyl)silylene Leads to the Formation of a Tricyclo[3,1,1,12,4]octasilane

Article abstract of DOI:10.1021/acs.organomet.9b00507

The reduction of 1,1-dibromo-cyclopentasilane with a mildly reducing magnesium(I) dimer [{(MesNacnac)Mg-}₂] was examined, which gave rise to the formation of endocyclic disilene 1. The formation of 1 was further confirmed by a trapping experiment with MeOH. Additionally, 1 was found to dimerize slowly to 1-dimer. Furthermore, the formation of the homocyclic silylene was demonstrated by performing the reduction in the presence of Et₃SiH as a trapping agent. To prevent the 1,2-trimethylsilyl shift, which causes a rapid degradation of the silylene, a second synthetic strategy was established. Therefore, two different tetrasilanes 4 and 5 were synthesized. Compounds 4 and 5 were subsequently reacted with 2.1 equiv of trifluoromethanesulfonic acid to corresponding bis(trifluoromethanesulfonates) 6 and 7. 1,4-Dihalo-tetrasilanes 8a,b and 9 as well as hexasilanes 10 and 11 were obtained by a subsequent nucleophilic substitution of the triflate substituent with X^- (X = Cl^-, Br^-, or R₃Si^-). Dianionic species 12 and 13 were synthesized by the reaction of corresponding hexasilanes 10 and 11 with 2.1 equiv of KOt-Bu. Surprisingly, the salt metathesis reaction of dianionic compound 13 does not lead to the formation of the expected 1,1-halocyclopentasilanes. Instead the formation of cyclobutasilane 14 was observed. The reaction of 9 with lithium led again to the formation of 14 alongside with the formation of cyclohexasilane 15. Interestingly, 14 underwent a ring-opening formation by the reaction with gaseous HCl in the presence of AlCl₃ and compound 16 was formed. The reduction of 16 allowed straightforward access to 17 as a structurally complex hitherto unknown tricyclic polysilane.

Full text of DOI:10.1021/acs.organomet.9b00507

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Attempted Synthesis of a Homocyclic Bis(silyl)silylene Leads to the
Formation of a Tricyclo[3,1,1,12,4]octasilane
Michael Haas,*,†,‡ Andreas Knoechl,‡ Tanja Wiesner,‡ Ana Torvisco,‡ Roland Fischer,‡
and Cameron Jones*,†
†School of Chemistry, Monash University, P.O. Box 23, Melbourne, Victoria 3800, Australia
‡Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9, Graz A-8010, Austria
S
* Supporting Information
ABSTRACT: The reduction of 1,1-dibromo-cyclopentasilane
with a mildly reducing magnesium(I) dimer [{(MesNacnac)-
Mg−}2] was examined, which gave rise to the formation of
endocyclic disilene 1. The formation of 1 was further
confirmed by a trapping experiment with MeOH. Addition-
ally, 1 was found to dimerize slowly to 1-dimer. Furthermore,
the formation of the homocyclic silylene was demonstrated by
performing the reduction in the presence of Et3SiH as a
trapping agent. To prevent the 1,2-trimethylsilyl shift, which
causes a rapid degradation of the silylene, a second synthetic
strategy was established. Therefore, two different tetrasilanes 4
and 5 were synthesized. Compounds 4 and 5 were
subsequently reacted with 2.1 equiv of trifluoromethanesul-
fonic acid to corresponding bis(trifluoromethanesulfonates) 6 and 7. 1,4-Dihalo-tetrasilanes 8a,b and 9 as well as hexasilanes 10
and 11 were obtained by a subsequent nucleophilic substitution of the triflate substituent with X− (X = Cl−, Br−, or R3Si−).
Dianionic species 12 and 13 were synthesized by the reaction of corresponding hexasilanes 10 and 11 with 2.1 equiv of KOt-Bu.
Surprisingly, the salt metathesis reaction of dianionic compound 13 does not lead to the formation of the expected 1,1-
halocyclopentasilanes. Instead the formation of cyclobutasilane 14 was observed. The reaction of 9 with lithium led again to the
formation of 14 alongside with the formation of cyclohexasilane 15. Interestingly, 14 underwent a ring-opening formation by
the reaction with gaseous HCl in the presence of AlCl3 and compound 16 was formed. The reduction of 16 allowed
straightforward access to 17 as a structurally complex hitherto unknown tricyclic polysilane.
act as ligands in transition metal complexes, or in the activation
of small molecules, even without coordination to a metal.
Chart 1 depicts the most important examples.
INTRODUCTION
■
In 1964, Skell and Goldstein reported on the first evidence for
the existence of a silylene. They investigated the reduction of
dichlorodimethylsilane with sodium−potassium vapor in the
gas phase at increased temperature.1 Since this groundbreaking
discovery, many working groups examined the formation and
the chemical behavior of this extremely reactive species.
Nevertheless, all attempts to isolate and characterize a stable
silylene failed until 1994. In this year Denk, West, and co-
workers succeeded in the isolation of the first stable N-
heterocyclic silylene, which resulted in a boost to modern
silicon chemistry.2 In the two decades since this fundamental
discovery, significant advances have been made in the synthesis
of this compound class. Today, many working groups in
academia and in the industry closely investigate silylenes as
possible catalysts, as intermediates during the synthesis of
polysilanes, as well as stoichiometric reagents.3 The isolated
silylenes can be categorized into five subclasses (see Charts
1−5). Starting from the pioneer work of Denk and West et al.,
a huge variety of N-heterocyclic silylenes have been published
in literature.2,4−11 The chemistry of N-heterocyclic silylenes
has been well-developed, and this class of silylenes is found to
The subclass of base-stabilized silylenes is inextricably
connected to two very important silicon chemists, namely,
Filippou and Roesky. Both published almost simultaneously
regarding such silylenes (see Chart 2).12,13 Filippou et al. were
also able to stabilize silylenes of the type NHC → SiCl(Aryl)
(Aryl = C6H3-2,6-Mes2).14 In analogy, Cui et al. synthesized an
aminochlorosilylene of the type NHC → SiCl{N(Me3Si)-
Dipp}.15
Carbocyclic silylenes and base-stabilized silylenes are far less
common in literature. The reason for this destabilization is the
missing π-donation from the flanking N atoms, bearing lone
pairs. To the best of our knowledge, only three carbocyclic
silylenes have been published so far. Kira et al. reported on the
first carbocyclic silylene.16 Similar to the “Kira Silylene”,
Iwamoto et al. prepared another silylene of this class,17 and
more recently, Driess and co-workers reported on the synthesis
Received: July 28, 2019
© XXXX American Chemical Society
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Chart 1. Examples of N-Heterocyclic Silylenes
Chart 4. Examples of Silylenes Bearing π-Coordinated
Substituents
the reduction of the Si(IV) precursor SiBr3{N(SiMe3)(Dipp)}
with 2 equiv of the lithium boryl reagent Li{B(NDippCH)2} to
afford the desired silylene.23 More recently, Jones and Aldridge
succeeded in the isolation and characterization of the first
stable diaminosilylene, which ends a long quest for the
synthesis of this substance class24 (Chart 5).
Chart 2. Examples of Base-Stabilized Silylenes12,13
Chart 5. Examples of Acyclic Silylenes
of aromatic phosphorus ylide-stabilized carbocyclic silylene
(see Chart 3).18
Generally speaking, a silylene with a small singlet−triplet
gap, ΔES−T, and a drastic decrease of the HOMO−LUMO
gap, enables the facile activation of small molecules (e.g.,
dihydrogen, acetone, oxygen, ammonia, etc.) Unfortunately, up
to now all reported silylenes are not capable of activating CH4,
another very important small molecule. Therefore, a further
reduction of the singlet−triplet gap is essential. The holy grail
of silylene chemistry would be the isolation of a stable triplet
silylene and the investigation of the reactivity of this molecule.
In 1999, Apeloig et al. summarized in a theoretical paper that
there are two key ingredients needed for a ground-state triplet
silylene:25 (I) Electropositive substituents such as silyl groups
Chart 3. Examples of Carbocyclic Silylenes
attached to the silylene moiety. (II) Steric control of ΔES−T
:
The singlet state is continuously destabilized relative to the
triplet state upon widening the R−Si−R angle (schematically
explained in Figure 1)
Notably, there were already two examples of transient triplet
silylenes reported by the groups of Sekiguchi and Gasper.26,27
Recently, Inoue et al. published a paper on the synthesis of an
Silylenes bearing π-coordinated substituents were the first
isolable silylenes and a milestone in silicon chemistry. A
hypercoordinated electron-rich nucleophilic silylene was
published by Jutzi et al. in 1986.19,20 Moreover, Jutzi and co-
worker succeeded in the isolation of the first heteroleptic
silylene: Si(2,6-Trip2-C6H3)(η3-C5Me5) [Trip = 2,4,6-
iPr3C6H2]. Additionally, Inoue et al. published a silylene
bearing a π-coordinated substituent with interesting reactivities
(see Chart 4).
Acyclic two-coordinate silylenes are the rarest silicon(II)
species. Until 2012, they had only been observed as transient
species during photochemical experiments. The isolation of
acyclic silylenes was independently reported by Power et al.
and the groups of Jones, Mountford, Aldridge, and
Kaltsoyannis. Power et al. described the reduction of the
Si(IV) precursor SiBr2(SArMe6)2 [ArMe6 = C6H3-2,6-(C6H2-
2,4,6-Me3)2 with a mildly reducing Mg(I)−Mg(I) complex to
yield :Si(SArMe6)2.21,22 Aldridge and Jones’ approach employs
Figure 1. Effects required for the conversion of a singlet to a triplet
silylene. The σ-to-p promotion energy ΔES−T depends on the p
character of σ, which increases with increasing R−Si−R bond angle
and with decreasing electronegativity of R.
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Scheme 1. Reduction of the 1,1-Dibromo-cyclopenta-silane with [{(MesNacnac)Mg−}2]
Figure 2. INEPT 29Si NMR spectra of the dimerization process of 1.
acyclic bis(silyl)silylene.28 Following their findings and the
predictions of Apeloig, an ideal precursor for the synthesis of a
triplet silylene would be a homocyclic 1,1-dihalocyclopolysi-
lane. To date, two working groups have attempted to
synthesize a homocyclic silylene and failed. Both working
groups used the same starting material for their manipulations:
1,1-dihalo-3,3,4,4-tetramethyl-2,2,5,5-tetrakis(trimethylsilyl)-
cyclopentasilane. For the synthesis of the homocyclic silylene
Xiao et al. used potassium graphite as reducing reagent and
only observed the formation of decomposition products, which
indicates the formation of a possible silylene intermediate.29
However, no NMR spectroscopic data were recorded during
the reaction. Hassler et al. reported a 29Si NMR spectroscopic
shift for the silylene at δ +735 ppm, but they were neither able
to isolate the compound nor to detect its decomposition
products.30 KC8 as the reducing agent was probably too harsh
for this reactive molecule. Therefore, we investigated the
reduction of 1,1-dibromo-3,3,4,4-tetramethyl-2,2,5,5-tetrakis-
(trimethylsilyl)cyclopenta-silane with the mildly reducing
magnesium(I) dimer [{(MesNacnac)Mg−}2] (MesNacnac =
[(MesNCMe)2CH]−, Mes = mesityl). We also examined a
new synthetic strategy toward alternative 1,1-dihalo-cyclo-
pentasilanes, which leads to the formation of a hitherto
unknown tricyclo[3,1,1,12,4]octasilane, 17.
RESULTS AND DISCUSSION
■
Reduction with Magnesium(I) Dimer [{(MesNacnac)-
Mg−}2]. Treatment of 1,1-dibromo-cyclopentasilane in
benzene solution at room temperature with equimolar
amounts of the reduction agent results in the formation of
endocyclic disilene 1 (see Scheme 1). Instead of the expected
homocyclic silylene, we propose a very fast 1,2-trimethylsilyl-
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shift which led to the formation of 1. This disilene was
obtained with remarkable selectivity. The obtained benzene
solution could be used directly for further derivatizations or
stored at −70 °C for prolonged periods (usually weeks).
Analytical and spectroscopic data that strongly support the
structural assignment are given in the Experimental Section,
together with experimental details. Surprisingly, the 29Si NMR
spectroscopic chemical shifts of the two silicon atoms forming
the Si−Si double bond are significantly shifted to a higher field
in comparison to other examples of this compound class.
Strohmann and Kaupp calculated the 29Si NMR spectroscopic
shift tensors for symmetrically and unsymmetrically substituted
disilenes.31 They found that the chemical shifts in symmetri-
cally substituted disilenes may be understood to a large extent
from the energy denominators of the perturbation expression.
Interestingly, they also showed that the very different shifts for
the two silicon nuclei in unsymmetrically substituted systems
are mainly due to the spatial extent and orientation of the
occupied and unoccupied molecular orbitals, as sampled by the
matrix elements of nuclear magnetic moments at both silicon
sites. As 1 also contains an unsymmetrically substituted
disilene, we think that this effect is also present for this
compound.
benzene/Et3SiH solution and again equimolar amounts of
the magnesium(I) dimer were added slowly. The expected
trapping product of silylene 3 was obtained in a very selective
fashion (see Scheme 3).
Crystals of 3 of sufficient quality for single-crystal X-ray
crystallography were obtained. The molecular structure is
depicted in Figure 3, along with selected bond distances and
At room temperature, a slow dimerization to 1-dimer
occurs. This dimerization was monitored by 29Si NMR
spectroscopy and is depicted in Figure 2. The same
dimerization process was also observed by Xiao et al. but
was significantly faster and less selective. Unfortunately, all
attempts to crystallize 1 failed. Concentration of the reaction
solution in vacuo, in order to facilitate crystallization, also
caused extensive dimerization. However, definite proof for the
proposed structure of 1 was obtained after derivatization.
Upon the addition of MeOH to a freshly prepared benzene
solution of 1, the corresponding methanol trapping product, 2,
was formed (see Scheme 2). The product was subsequently
Figure 3. ORTEP representation for compound 3. Thermal ellipsoids
are depicted at the 50% probability level. Hydrogen atoms, except the
hydride, are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg) with estimated standard deviations: Si(1)−Si(2)
2.357(3), Si(2)−Si(3) 2.373(3), Si(2)−Si(6) 2.353(3), Si(2)−Si(7)
2.357(3), Si(3)−Si(4) 2.350(3), Si(4)−Si(5) 2.362(3), Si(5)−Si(9)
2.356(3), Si(5)−Si(8) 2.345(3), Si(5)−Si(1) 2.368(3), Si(10)−Si(1)
2.356(3), Si(1)−Si(2)−Si(3) 105.36(10), Si(4)−Si(3)−Si(2)
105.25(10), Si(3)−Si(4)−Si(5) 107.31(10), Si(2)−Si(1)−Si(5)
108.06 (10).
bond and dihedral angles. Compound 3 crystallized in the
monoclinic space group P121/c1 with unexceptional bond
lengths and angles. The unit cell contains 24 molecules (see
the Supporting Information).
Scheme 2. Reaction of 1 with MeOH
The trapping experiment with Et3SiH demonstrated that our
reducing agent was a good choice for this highly reactive
silylene, but the fast 1,2-trimethylsilyl shift prevented the
isolation of the silylene. Therefore, we set out to develop a new
synthetic approach to 1,1-dihalo-cyclopentasilanes. Conse-
quently, all four trimethylsilyl groups should be replaced by
organic groups in order to prevent the silyl migration. For
organic groups, we chose phenyl and tert-butyl groups, as these
groups are easily accessible and should have enough steric
protection for the silylene.
isolated by silica gel chromatography. Analytical and
spectroscopic data clearly support the structure of 1 and 2
(for details, consult the Experimental Section).
In order to prove the intermediate formation of the silylene,
a trapping experiment with Et3SiH was performed. Accord-
ingly, 1,1-dibromo-cyclopentasilane was dissolved in a
Synthesis of 1,1,1,4,4,4-Hexaphenyltetramethyl-tet-
rasilane (4) and 1,4-Di-tert-butyl-1,1,4,4-tetra′-phenyl-
Scheme 3. Reduction of the 1,1-Dibromo-cyclopentasilane with Magnesium(I) Dimer [{(MesNacnac)Mg−}2] in the Presence
of Et3SiH
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Scheme 4. Synthesis of 4 and 5
tetramethyltetrasilane (5). Compounds 4 and 5 were
prepared by the reaction of 1,2-dichloro-1,1,2,2-tetramethyldi-
slane with the corresponding silyl-lithium compound (triphe-
nylsilyl-lithium for 4 and tert-butyldiphenylsilyl-lithium for 5).
Compound 4 was previously reported by Kumada et al.,32 but
the NMR chemical shifts were not correctly assigned. Air-
stable and crystalline target compounds 4 and 5 were obtained
in isolated yields of >75% (see Scheme 4). Analytical and
spectroscopic data that well support the structural assignment
are given in the Experimental Section, together with
experimental details. The molecular structures of 4 and 5, as
determined by single-crystal X-ray crystallography, are
included in the Supporting Information.
Synthesis of 12 and 13. Disilanides 12 and 13 are
obtained by the potassium tert-butoxide mediated desilylation
of 10 and 11 in the presence of 18-crown-6 (see Scheme 6).
Scheme 6. Reaction of 10 and 11 with KOt-Bu
Reactivity of 4 and 5. Subsequently, 4 and 5 were reacted
with 2.1 equiv of trifluoromethansulfonic acid to correspond-
ing bis-triflates 6 and 7. 1,4-Dihalo-tetrasilanes 8a,b and 9 as
well as hexasilanes 10 and 11 were obtained by a subsequent
nucleophilic substitution of the triflate substituent with X− (X
= Cl−, Br−, or R3Si−). Air-stable and crystalline target
compounds 8a,b and 10 were obtained in isolated yields of
>72% (see Scheme 5). Compounds 7, 9, and 11 have two
Although the synthesis of 12 has been described before by
Klausen et al.,33 we established a new strategy to the
compound, which is more substituent tolerant and also enables
the preparation of 13. Compounds 12 and 13 are obtained as
deeply colored solids, which were used without further
purification for reactions with electrophiles. The low solubility
of 13 prevented complete characterization, but during the
synthesis of 13 crystals of quality sufficient for single-crystal X-
ray crystallography were obtained. The molecular structure is
depicted in Figure 4 along with selected bond distances and
Scheme 5. Reaction of 4 and 5 with
Trifluoromethansulfonic Acid and Subsequent Nuleophilic
Substitutions
Figure 4. ORTEP representation for compound 13. Thermal
ellipsoids are depicted at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg) with estimated standard deviations: Si(1)−K(1)
3.6181(6), Si(1)−Si(2) 2.3947(6), Si(2)−Si(1)−K(1) 106.837(18),
∑αSi(1) 313.
bond and dihedral angles. Compound 13 crystallized in the
triclinic space group P1 with unexceptional bond lengths and
̅
angles. The unit cell contains one molecule (see the
Supporting Information). In contrast to the crystal structure
of 12,33 the structure of 13 shows it to be a contact ion pair
with a Si1−K1 bond distance of 3.62 Å and Si1 is pseudo-
pyramidal.
The next reaction step was the attempted ring-closure
reaction to the corresponding cyclopentasilanes. Therefore, 12
and 13 were reacted with selected electrophiles (e.g., HSiCl3,
SiCl4, SiBr4 or GeCl4). According to Scheme 7, potassium
disilanide 12 reacts with all the above-mentioned electrophiles
chiral centers each and were obtained in isolated yields >60%.
This leads to the formation of two pairs of diastereomers for
each compound. Analytical and spectroscopic data that
perfectly support the structural assignments are given in the
Experimental Section together with experimental details. The
molecular structures of 6, 7, 8b, and 9, as determined by
single-crystal X-ray crystallography, are included in the
Supporting Information.
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Scheme 7. Attempted Ring-Closure Reactions of 12 and 13
Figure 5. ORTEP representation for compound 14. Ther-mal
ellipsoids are depicted at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg) with estimated standard deviations: Si(1)−Si(2)
2.3755(5), Si(1)−Si(1)#1 2.3469(8), Si(2)−Si(2)#1 2.4317(8),
Si(1)#1−Si(1)−Si(2) 90.135(13), Si(1)−Si(2)−Si(2)#1 88.120(13).
under the formation of uncharacterized polymeric materials.
We assume that 12 undergoes a linear polymerization instead
of the desired ring-closure reaction.
Instead of the desired cyclopentasilanes, 13 undergoes a
ring-closure reaction to cyclobutasilane 14. The reaction of 13
with electrophiles (e.g., HSiCl3, SiCl4, SiBr4 or GeCl4)
presumably involves an initial halogen−metal exchange step,
resulting in the formation of 13-X, which undergoes a
intramolecular salt metathesis reaction to give 14 (Scheme 7).
Reaction of 1,4-Dihalo-tetrasilanes 8a,b and 9 with
Lithium Metal. The generation of silyl-lithium compounds
from the corresponding chlorosilanes is well-known strategy in
silicon chemistry.34 Therefore, we reacted 1,4-dihalo-tetrasi-
lanes 8a,b and 9 with an excess of lithium metal in THF to
obtain the corresponding disilanides. The reactions of 8a,b
with lithium in THF lead to complete degradation of the
polysilanes to uncharacterized materials. The reactivity of 9
with lithium closely resembles that found for the reaction of 13
with electrophiles. Again, instead of the desired cyclo-
pentasilanes, 9 undergoes a ring-closure reaction to cyclo-
butasilane 14 and cyclohexasilane 15 (Scheme 8). While the
Figure 6. ORTEP representation for compound 15. Ther-mal
ellipsoids are depicted at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg) with estimated standard deviations: Si(1)−Si(2)
2.3625(4), Si(1)−Si(3) 2.3688(4), Si(3)−Si(2)# 2.3608(4), Si(2)−
Si(1)−Si(3) 107.414(15), Si(2)#−Si(3)−Si(1) 114.432(16), Si(3)
#−Si(2)−Si(1) 109.205(15).
Scheme 8. Reaction of 9 with Lithium in THF
along with selected bond distances and bond and dihedral
angles. Compound 14 crystallized in the monoclinic space
group C2/c with unexceptional bond lengths and angles for
cyclobutasilanes. The unit cell contains four molecules (see the
Supporting Information). Cyclobutasilane 14 exclusively forms
the trans isomer, which is caused by the locking effect of the
tert-butyl group. Compound 15 crystallized in the monoclinic
space group P121/n1 with unexceptional bond lengths and
angles for cyclohexasilanes. The unit cell contains two
molecules (see the Supporting Information). Again, 15 forms
exclusively the trans isomer, which is again caused by the
locking effect of the tert-butyl group.
Reactivity of 14. To examine the chemical properties of
14, we reacted the compound with gaseous HCl in the
presence of catalytic amounts of AlCl3. The reaction was found
to be extremely fast, and the expected dearylation took place.
However, we also observed ring scission of the cyclobutasilane,
mechanism for the formation of 14 can be easily explained by
an intramolecular salt metathesis reaction of the monosilanide,
the mechanism for the formation of side product 15 is
unknown. We assume that under these conditions silyl groups
are abstracted and that the formation of this cyclohexasilane is
thermodynamically favored. Analytical and spectroscopic data
that support the structural assignment are given in the
Experimental Section, together with experimental details. The
molecular structures of 14 and 15, as determined by single-
crystal X-ray crystallography, are depicted in Figures 5 and 6,
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and compound 16 was cleanly formed (see Scheme 9). Again,
a diastereomeric mixture was obtained, which could not be
Å. Both cyclotetrasilane moieties exhibit a twisted ring
conformation with endocyclic bond angles close to 85°.
CONCLUSION
Scheme 9. Reaction of 14 with Gaseous HCl in the Presence
of AlCl3 and Subsequent Reduction with KC8
■
In summary, we investigated the reduction of 1,1-dibromo-
cyclopentasilane with the mildly reducing magnesium(I) dimer
[{(MesNacnac)Mg−}2], which gave rise to the formation of an
endocyclic disilene 1. The formation of 1 was further
confirmed by trapping with MeOH. Moreover, 1 dimerizes
slowly to 1-dimer. Additionally, the formation of the
homocyclic silylene was demonstrated by performing the
reduction in the presence of Et3SiH as trapping agent. In order
to prevent the 1,2-trimethylsilyl shift, a second synthetic
strategy was established. Accordingly, two different tetrasilanes
4 and 5 were synthesized. Compounds 4 and 5 were then
reacted with 2.1 equiv of trifluoromethanesulfonic acid to
corresponding bis(trifluoromethanesulfonates) 6 and 7. 1,4-
Dihalo-tetrasilanes 8a,b and 9, as well as hexasilanes 10 and 11,
were obtained by a subsequent nucleophilic substitution of the
triflate substituent with X− (X = Cl−, Br−, or R3Si−).
Disilanides 12 and 13 are obtained by the potassium tert-
butoxide mediated desilylation of 10 and 11 in the presence of
18-crown-6. Surprisingly, the salt metathesis reaction of
dianionic compound 13 does not led to the expected 1,1-
halocyclopentasilanes. Instead, the formation of cyclobutasi-
lane 14 was observed. The reaction of 9 with lithium led again
to the formation of 14, alongside the formation of cyclo-
hexasilane 15. Additionally, 14 underwent a ring scission by
the reaction with gaseous HCl in the presence of AlCl3 and
compound 16 was formed. The reaction of 16 with KC8
allowed straightforward access to 17 as a structurally complex,
hitherto unknown tricyclic polysilane.
separated. Analytical and spectroscopic data that support the
structural assignment are given in the Experimental Section
together with experimental details.
Reduction of 16. Kabe et al. showed that the reduction of
1,2-di-tert-butyl-1,1,2,2-tetrachlordisilane leads to the forma-
tion of polycyclic silanes.35 Therefore, we set out to examine
the reduction of 16 with 4.1 equiv of KC8. Surprisingly, we
found the exclusive formation of 17 as a structurally complex
hitherto unknown tricyclic polysilane. The structure of 17 was
confirmed by single-crystal X-ray diffraction analysis (see
Figure 7). Compound 17 crystallized in the tetragonal space
̅
group P421c. The unit cell contains 12 molecules (see the
Supporting Information). The compound appears to be
completely unstrained as all Si−Si bond lengths were ∼2.4
EXPERIMENTAL SECTION
■
All experiments were performed under a nitrogen atmosphere using
standard Schlenk techniques. Solvents were dried using a column
solvent purification system.36 Ph3SiCl (95%) Et3SiH (98%), t-
BuPh2SiCl (95%), and 18-crown-6 were used without any further
1
purification. MeOH was dried over molecular sieves prior to use. H,
13C, and 29Si NMR spectra were recorded on either a Varian INOVA
300 spectrometer or on a Bruker Avance III 400 in C6D6 or CDCl3
solutions and referenced versus TMS using the internal 2H-lock signal
of the solvent. HRMS spectra were run on a Kratos Profile mass
spectrometer. Infrared spectra were obtained on a Bruker Alpha-P
Diamond ATR Spectrometer from the solid sample. Melting points
were determined using Stuart SMP50 apparatus and are uncorrected.
Elemental analyses were carried out on a Hanau Vario Elementar EL
apparatus.
Reduction of 1,1-Dibromo-3,3,4,4-tetramethyl-2,2,5,5-
tetra-kis(trimethylsilyl)-cyclopentasilane. First, 50 mg of 1,1-
dibromo-3,3,4,4-tetramethyl-2,2,5,5-tetrakis(trimethylsilyl)-cyclopen-
tasilane (0.076 mmol) was dissolved in 5 mL of benzene. The
solution was then slowly added to a suspension of freshly prepared
magnesium(I) dimer[{(MesNacnac)Mg−}2] (55 mg, 0.076 mmol) in
4 mL of benzene. The mixture was stirred for 20 min. At this time,
reaction control by NMR spectroscopy showed the conversion of the
starting material to the endocyclic disilene. Volatiles were then
removed in vacuo, and the residue was extracted with n-hexane (2 ×
15 mL). After removal of the solvent, a colorless oil was obtained.
Yield: 30 mg (79%) of 1 containing small amounts of the dimer and
ligand of the magnesium dimer. 1: 29Si NMR (C6D6, TMS, ppm):
−7.82, −9.00, −10.88, −11.91 (Si(CH3)3); −22.64, −37.31 (Si-
(CH3)2); −50.70, −58.96 (endo SiSi); −126.26 (Siq). 13C NMR
(C6D6, TMS, ppm): 2.79, 2.37, 1.42, 0.22 (Si(CH3)3); −1,34, −2.34,
−4.77, −5.23 (Si−(CH3)2). 1H NMR (C6D6, TMS, ppm): 0.13, 0.06,
0.04, 0.04 (s, each 9H, Si(CH3)3); 0.12, 0.11, 0.09, 0.08 (s, each 3H,
Figure 7. ORTEP representation for compound 17. Thermal
ellipsoids are depicted at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg) with estimated standard deviations: Si(1)−Si(2)
2.341(2), Si(1)−Si(4) 2.411(2), Si(1)−Si(7) 2.437(2), Si(2)−Si(3)
2.424(2), Si(3)−Si(4) 2.337(2), Si(3)−Si(5) 2.439(2), Si(6)−Si(5)
2.339(2), Si(6)−Si(7) 2.418(2), Si(5)−Si(8) 2.419(2), Si(8)−Si(7)
2.336(2), Si(2)−Si(1)−Si(4) 84.89(8), Si(2)−Si(1)−Si(7) 97.20(8),
Si(4)−Si(1)−Si(7) 114.74 (8), Si(1)−Si(2)−Si(3) 84.10(8), Si(2)−
Si(3)−Si(5) 114.55(9), Si(4)−Si(3)−Si(2)84.68(8), Si(4)−Si(3)−
Si(5) 96.02(8), Si(6)−Si(7)−Si(1) 115.71(9), Si(8)−Si(7)−Si(1)
96.29(8), Si(8)−Si(7)−Si(6) 84.89(7).
G
DOI: 10.1021/acs.organomet.9b00507
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Organometallics
Article
Si(CH3)2. IR (neat): 2050 (w), 1658 (w), 1620 (m), 1552 (m), 1510
(m), 1476 (m), 1447 (m), 1392 (s), 1371 (s), 1236 (s), 1194 (m),
1139 (m), 1084 (w), 1008 (m), 827 (s), 776 (s), 683 (s), 624 (s),
silylene trapping product 3. Volatiles were removed in vacuo, and the
residue extracted with n-hexane (3 × 15 mL). After removal of the
solvents, a solid residue was obtained. The solid residue was dissolved
in pentane and filtered through silica gel giving white crystals of 3.
Yield: 265 mg (81%) of analytically pure white crystals. 3: mp: 145−
147 °C. Anal. Calcd for C22H64Si10: C, 43.35; H, 10.58%. Found: C,
43.38; H, 10.52%. 29Si NMR (C6D6, TMS, ppm): −8.10, −8.43
(Si(CH3)3); −21.82 (Si(C2H5)3; −25.58 (Si(CH3)2); −115.34(SiH);
−130.32 (Siq). 13C NMR (C6D6, TMS, ppm): 9.16, 6.90 (Si(C2H5)3;
+
586 (s) cm−1. HRMS Calcd for (C16H48Si9 ) (M+): 492.1679. Found:
492.1674.
Reduction of 1,1-Dibromo-3,3,4,4-tetramethyl-2,2,5,5-
tetrakis(trimethylsilyl)-cyclopentasilane. First, 50 mg of 1,1-
dibromo-3,3,4,4-tetramethyl-2,2,5,5-tetrakis(trimethylsilyl)-cyclopen-
tasilane (0.076 mmol) was dissolved in 5 mL of benzene. The
solution was then slowly added to a suspension of freshly prepared
magnesium(I) dimer (55 mg, 0.076 mmol) in 4 mL of benzene. The
mixture was stirred for 20 min. At this time, reaction control by NMR
spectroscopy showed the conversion of the starting material to the
endocyclic disilene. The reaction solution was further stirred at room
temperature to allow a dimerization of the endocyclic disilene (usually
5−7 days, control by NMR spectroscopy). After complete
dimerization, all volatiles were then removed in vacuo, and the
residue were extracted with n-hexane (2 × 15 mL). After removal of
the solvents, a solid residue was obtained. The obtained crude
product was recrystallized from acetone, giving white crystals of 1-
dimer. Yield: 23 mg (61%) of analytically pure white crystals. 1-
dimer: mp: 155−157 °C. Anal. Calcd for C32H96Si18: C, 38.96; H,
9.81%. Found: C, 38.99; H, 9.79%. 29Si NMR (CDCl3, TMS, ppm):
−6.03, −6.68, −8.67, −8.75 (Si(CH3)3); −17.80, −26.02 (Si(CH3)2);
−47.35 (Siq(Si(CH3)3)2); −82.17, 98.59 (Siq(Si(CH3)3)). 13C NMR
(C6D6, TMS, ppm): 6.78, 6.34, 5.36, 5.20 (Si(CH3)3); 4.66, 2.24,
1.50, 0.98 (Si(CH3)2). 1H NMR (C6D6, TMS, ppm): 0.62, 0.48, 0.36
(s, each 6H, Si(CH3)2); 0.41 (s, 24H, Si(CH3)2 and Si(CH3)3); 0.28
(s, 18H, Si(CH3)3); 0.26 (s, 36H, Si(CH3)3). IR (neat): 1511 (w),
1400 (w), 1357 (w), 1233 (m), 1174 (m), 1058 (m), 828 (s), 772
(s), 734 (m), 683 (w), 657 (w), 623 (m), 416 (m), cm−1. HRMS
Calcd for (C32H96Si18+) (M+): 984.3359. Found: 984.3364.
1
3.80, 2.77 (Si(CH3)3); −1,87, −2.11 (Si(CH3)2). H NMR (C6D6,
TMS, ppm): 3.18 (s, 1H, SiH); 1.12 (t, 9H, Si−CH2−CH3); 0.97 (q,
6H, Si−CH2−CH3); 0.42, 0.41 (s, each 6H, Si(CH3)2); 0.37, 0.36 (s,
each 9H, Si(CH3)3. IR (neat): 2037 (m), 1460 (w), 1441 (w), 1396
(m), 1260 (m), 1237 (s), 1079 (m), 1011 (m), 822 (s), 796 (s), 777
(s), 724 (s), 679 (s), 652 (s), 637 (s), 615 (s), 573 (m) cm−1. HRMS
Calcd. for (C22H64Si10+) (M+): 608.2701. Found: 608.2707.
Synthesis of 1,1,1,4,4,4-Hexaphenyltetramethyltetrasilane
(4). A solution of (Ph)3SiLi in 150 mL of THF was freshly prepared
from 10.00 g of (Ph)3SiCl (33.92 mmol) and 0.95 g of Li (135.66
mmol) and was slowly added to a solution of 3.50 g (18.65 mmol) of
1,2-dichlorotetramehtyldisilane in 300 mL of toluene at −30 °C. The
mixture was allowed to warm to room temperature and stirred for
another 30 min, then subjected to aqueous work up with 10% sulfuric
acid. After removal of the solvents, a solid residue was obtained. The
obtained crude product was recrystallized from acetone, giving white
crystals of 4. Yield: 10.28 g (95%) of analytically pure white crystals.
4: mp: 177−179 °C. Anal. Calcd for C40H42Si4: C, 75.65; H, 6.67%.
Found: C, 75.65; H, 6.69%. 29Si NMR (C6D6, TMS, ppm): −16.24
(SiPh3); −43.56 (Si(CH3)2). 13C NMR (C6D6, TMS, ppm): 136.16,
135.87, 129.09, 128.02 (Aryl−C); −3.46 (Si−(CH3)2). 1H NMR
(C6D6, TMS, ppm): 7.61−7.59 (m, 10H, Ph−H); 7.17−7.15 (m,
20H, Ph−H); 0.27 (s, 12H, Si(CH3)2). IR (neat): 3072 (w), 3016
(w), 2948 (w), 2891 (w), 1482 (w), 1426 (m), 1098 (m), 832 (m),
781 (m), 736 (m), 696 (s), 521 (s), 481 (s), 436 (m) cm−1. HRMS
Reduction of 1,1-Dibromo-3,3,4,4-tetramethyl-2,2,5,5-
tetrakis(trimethylsilyl)-cyclopentasilane and Subsequent
Trapping with MeOH. First, 350 mg of 1,1-dibromo-3,3,4,4-
tetramethyl-2,2,5,5-tetrakis(trimethylsilyl)-cyclopentasilane (0.54
mmol) was dissolved in 20 mL of benzene. The solution was then
slowly added to suspension of freshly prepared magnesium(I)
dimer[{(MesNacnac)Mg−}2] (390 mg, 0.55 mmol) in 40 mL of
benzene. The mixture was stirred for 20 min. At this time, reaction
control by NMR spectroscopy showed the conversion of the starting
material to the endocyclic disilene 1. Subsequently, 5 mL of MeOH
was added via a syringe. The reaction solution was stirred for an
additional 12 h to ensure complete conversion. Volatiles were
removed in vacuo, and the residue extracted with n-hexane (3 × 15
mL). After removal of the solvents, a colorless oil was obtained. The
resulting solution was filtered through silica gel with pentane as the
mobile phase, affording pure 2. Yield: 245 mg (87%) of colorless oil.
2: Anal. Calcd for C17H52OSi9: C, 38.87; H, 9.98%. Found: C, 38.92;
H, 10.01%. 29Si NMR (C6D6, TMS, ppm): 15.74 (OSi); −7.74,
−8.83, −10.75, −13.64 (Si(CH3)3); −32.43, −38.25 (Si(CH3)2);
−117.76(HSi); −132.25 (Siq). 13C NMR (C6D6, TMS, ppm): 55.03
(OCH3), 3.58, 2.63, 2.49, 0.81 (Si(CH3)3); −1,52, −2.07, −4.70,
−4.87 (Si(CH3)2). 1H NMR (C6D6, TMS, ppm): 3.09 (s, 3H,
OCH3); 3.03 (s, 1H, SiH); 0.14, 0.12, 0.10, 0.05 (s, each 9H,
Si(CH3)3); 0.24, 0.16, 0.11, 0.08 (s, each 3H, Si(CH3)2. IR (neat):
2950 (w), 2925 (w), 2841 (w), 1608 (w), 1590 (w) 1592 (w), 1529
(w), 1508 (w), 1459 (m), 1387 (w), 1367 (m), 1284 (m), 1253 (m),
1183 (m), 1120 (s), 1073 (s), 955 (w), 862 (m), 840 (m), 791 (s),
755 (s), 682 (s), 566 (s), 518 (m), 464 (s) cm−1. HRMS Calcd for
+
Calcd. for (C40H42Si4 ) (M+): 634.2364. Found: 634.2365.
Synthesis of 1,4-Di-tert-butyl-1,1,4,4-tetraphenyltetrame-
thyltetrasilane (5). A solution of t-Bu(Ph)2SiLi in 150 mL of
THF was freshly prepared from 10.00 g of t-Bu(Ph)2SiCl (36.38
mmol) and 1.02 g of Li (145.53 mmol) and was slowly added to a
solution of 4.07 g (20.00 mmol) of 1,2-dichlorotetramehtyldisilane in
300 mL of toluene at −30 °C. The mixture was allowed to warm to
room temperature and stirred for another 30 min, then subjected to
aqueous work up with 10% sulfuric acid. After removal of the solvents,
a solid residue was obtained. The obtained crude product was
recrystallized from acetone, giving white crystals of 5. Yield: 8.12 g
(75%) analytically pure white crystals. 5: mp: 177−179 °C. Anal.
Calcd for C36H50Si4: C, 72.65; H, 8.47%. Found: C, 72.64; H, 8.43%.
29Si NMR (CDCl3, TMS, ppm): −8.30 (SiPh2t-Bu); −42.95
(Si(CH3)2). 13C NMR (CDCl3, TMS, ppm): 136.70, 136.66,
128.73, 127.60 (Aryl−C); 29.45 (C(CH3)3); 20.91 (C(CH3)3);
1
−1.88 (Si−(CH3)2). H NMR (CDCl3, TMS, ppm): 7.54−7.51 (m,
8H, Ph−H); 7.38−7.28 (m, 12H, Ph−H); 1.05 (s, 18H C(CH3)3);
0.03 (s, 12H, Si(CH3)2). IR (neat): 3067 (w), 3050 (w), 2965 (w),
2925 (w), 2885 (w), 2852 (w), 1460 (w), 1426 (m), 1239 (m), 1092
(m), 837 (m), 786 (s), 736 (s), 690 (s), 600 (s), 515 (s), 470 (s)
+
cm−1. HRMS Calcd for (C36H50Si4 ) (M+): 594.2990. Found:
594.2996.
Synthesis of 1,1,4,4-Tetraphenyltetramethyltetrasilane-1,4-
bis(trifluoromethane-sulfonate) (6). First, 10.00 g of 4 (15.74
mmol) was dissolved in 100 mL of toluene, and the solution was
cooled to −80 °C. Subsequently, 2.92 mL of trifluoromethansulfonic
acid (33.06 mmol) were slowly added and stirred for an additional 10
min at −80 °C. The mixture was allowed to warm to room
temperature and stirred for another 120 min. At this time, reaction
control by NMR spectroscopy showed clean conversion of the
starting material to the desired bis(trifluoromethanesulfonate). After
removal of the solvent, a solid residue was obtained. The obtained
crude product was recrystallized from a mixture of toluene and
pentane (1:3), giving white crystals of 6. Yield: 11.65 g (95%) of
analytically pure white crystals. 6: mp: 73−75 °C. Anal. Calcd for
+
(C17H52OSi9 ) (M+): 524.1942. Found: 524.1940.
Reduction of 1,1-Dibromo-3,3,4,4-tetramethyl-2,2,5,5-
tetrakis(trimethylsilyl)-cyclopentasilane in the Presence of
Et3SiH. First, 350 mg of 1,1-dibromo-3,3,4,4-tetramethyl-2,2,5,5-
tetrakis(trimethylsilyl)-cyclopentasilane (0.54 mmol) was dissolved in
10 mL of benzene and 10 mL of Et3SiH. The solution was then slowly
added to a suspension of 390 mg of freshly prepared magnesium(I)
dimer[{(MesNacnac)Mg−}2] (0.55 mmol) in 40 mL of benzene. The
mixture was stirred for 20 min. At this time, reaction control by NMR
spectroscopy showed the conversion of the starting material to
H
DOI: 10.1021/acs.organomet.9b00507
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
C30H32F6O6S2Si4: C, 46.25; H, 4.14%. Found: C, 46.30; H, 4.17%.
29Si NMR (C6D6, TMS, ppm): 18.81 (SiPh2OfT); −42.50
(Si(CH3)2). 19F NMR (C6D6, TMS, ppm): −76.72 (SiPh2OfT).
13C NMR (C6D6, TMS, ppm): 135.13, 131.92, 131.79, 128.89 (Aryl−
C); 121.19 (q, JFC = 318 Hz); 5.01 (Si−(CH3)2). H NMR (C6D6,
TMS, ppm): 7.54−7.51 (m, 8H, Ph−H); 7.08−7.103 (m, 12H, Ph−
H); 0.30 (s, 12H, Si(CH3)2). IR (neat): 1603 (w), 1472 (w), 1387
(s), 1364 (m), 1240 (m), 1209 (s), 1194 (s), 1155 (s), 1012 (m), 985
(s), 915 (s), 857 (m), 838 (s), 815 (m), 792 (m), 769 (w), 726 (m),
699 (w), 629 (s), 610 (s),568 (m) cm−1.
Synthesis of 1,4-Dibromo-1,1,4,4-tetraphenyltetramethyl-
tetrasilane (8b). First, 10.00 g of 4 (15.74 mmol) was dissolved in
100 mL of toluene, and the solution was cooled to −80 °C.
Subsequently, 2.92 mL of trifluoromethansulfonic acid (33.06 mmol)
was slowly added, and the solution was stirred for an additional 10
min at −80 °C. The mixture was allowed to warm to room
temperature and stirred for another 120 min. At this time, reaction
control by NMR spectroscopy showed clean conversion of the
starting material to the desired bis(trifluoromethanesulfonate). To
this solution were added 30 mL of DME and 13.67 g of LiBr (157.45
mmol), and the solution was stirred for 16 h at room temperature to
ensure complete conversion to 8b. After removal of the solvents in
vacuo, the remaining off-white solid was dissolved in heptane and
filtered over dry Celite, and the solvent was stripped off again. The
obtained crude product was recrystallized from pentane, giving white
crystals of 8b. Yield: 7.26 g (72%) of analytically pure white crystals.
8b: mp: 104−106 °C. Anal. Calcd for C28H32Br2Si4: C, 52.49; H,
5.03%. Found: C, 52.53; H, 5.04%. 29Si NMR (C6D6, TMS, ppm):
4.39 (SiPh2Br); −40.41 (Si(CH3)2). 13C NMR (C6D6, TMS, ppm):
1
1
Synthesis of 1,4-Di-tert-butyl-1,4-diphenyltetramethyl-tet-
rasilane-1,4-bis(trifluoro-methanesulfonate) (7). First, 10.00 g
of 5 (16.80 mmol) was dissolved in 100 mL of toluene, and the
solution was cooled to −80 °C. Subsequently, 3.11 mL of
trifluoromethansulfonic acid (35.28 mmol) was slowly added and
stirred for an additional 10 min at −80 °C. The mixture was allowed
to warm to room temperature and stirred for another 120 min. At this
time, reaction control by NMR spectroscopy showed clean conversion
of the starting material to the desired bis(trifluoromethanesulfonate).
After removal of the solvents a solid residue was obtained, which
contained clean 7 as diastereomeric mixture. Yield: 11.18 g (90%) of
an analytically pure diastereomeric mixture. The obtained product
was recrystallized from pentane, giving white crystals of one
diastereomer. Yield: 4.35 g (35%) of analytically pure white crystals.
7(meso-diastereomer): mp: 125−127 °C. Anal. Calcd for
C26H40F6O6S2Si4: C, 42.26; H, 5.46%. Found: C, 42.31; H, 5.50%.
29Si NMR (C6D6, TMS, ppm): 30.53 (Si−Pht-BuOfT); −40.61
1
135.31, 134.49, 130.56, 128.56 (Aryl−C); −4.32 (Si−(CH3)2). H
NMR (C6D6, TMS, ppm): 7.49−7.47 (m, 8H, Ph−H); 6.92−6.90
(m, 12H, Ph−H); 0.16 (s, 12H, Si(CH3)2). IR (neat): 3067 (w),
2953 (w), 2919 (w), 2880 (w), 2852 (m), 1471 (w), 1431 (w), 1358
(w), 1109 (m), 951 (s), 815 (m), 736 (m), 702 (s), 600 (s), 492 (w)
+
cm−1. HRMS Calcd for (C28H32Br2Si4 ) (M+): 637.9948. Found:
637.9952
Synthesis of 1,4-Di-tert-butyl-1,4-dichloro-1,4-diphenyl-tet-
ramethyltetrasilane (9). First, 10.00 g of 5 (16.80 mmol) was
dissolved in 100 mL of toluene, and the solution was cooled to −80
°C. Subsequently, 3.11 mL of trifluoromethansulfonic acid (35.28
mmol) were slowly added and stirred for an additional 10 min at −80
°C. The mixture was allowed to warm to room temperature and
stirred for another 120 min. At this time, reaction control by NMR
spectroscopy showed clean conversion of the starting material to the
desired bis(trifluoromethanesulfonate). To this solution 30 mL DME
and 7.12 g of LiCL (168.03 mmol) were added and stirred for 16h at
room temperature to ensure complete conversion to 9. Then the
reaction solution was subjected to an aqueous work up with 10%
sulfuric acid. After removal of the solvents a solid residue was
obtained, which contained clean 9 as diastereomeric mixture. Yield:
7.91 g (92%) of analytically pure 9 as diastereomeric mixture. The
obtained product was recrystallized from pentane, giving white
crystals of one diastereomer. Yield: 3.29 g (42%) of analytically pure
9(SS-RR-diastereomer) as white crystals. 9(SS-RR-diastereomer):
mp: 84−86 °C. Anal. Calcd for C24H40Cl2Si4: C, 56.32; H, 7.88%.
Found: C, 56.34; H, 7.92%. 29Si NMR (CDCl3, TMS, ppm): 19.93
(Si−Pht-BuCl); −40.17(Si(CH3)2). 13C NMR (CDCl3, TMS, ppm):
135.08, 134.35, 129.76, 127.90 (Aryl−C); 26.86 (C(CH3)3); 23.38
(C(CH3)3); −2.86, −3.85 (Si−(CH3)2). 1H NMR (CDCl3, TMS,
ppm): 7.61−7.58 (m, 4H, Ph−H); 7.55−7.37 (m, 6H, Ph−H); 0.97
(s, 18H C(CH3)3); 0.35 (s, 6H, Si(CH3)2); 0.05 (s, 6H, Si(CH3)2).
IR (neat): 2959 (w), 2931 (w), 2891 (w), 2857 (w), 1460 (w), 1426
(w), 1358 (w), 1245 (m), 1188 (w), 1103 (w), 1007 (w), 837 (m),
786 (m), 736 (m), 696 (m), 645 (m), 600 (m), 521 (s), 498 (s), 447
(Si(CH3)2). 19F NMR (C6D6, TMS, ppm): −76.29 (Si−Pht-BuOfT).
13C NMR (C6D6, TMS, ppm): 133.40, 132.41, 130.72, 128.28 (Aryl−
1
C); 121.42 (q, JFC = 318 Hz); 26.13 (C(CH3)3); 23.69 (C(CH3)3);
−2.44, −3.32 (Si−(CH3)2). 1H NMR (C6D6, TMS, ppm): 7.61−7.59
(m, 3H, Ph−H); 7.14−7.11 (m, 7H, Ph−H); 0.87 (s, 18H C(CH3)3);
0.39 (s, 6H, Si(CH3)2); 0.28 (s, 6H, Si(CH3)2). IR (neat): 1587 (w),
1473 (w), 1426 (w), 1379 (s), 1363 (m), 1240 (m), 1197 (s), 1151
(s), 1109 (m), 1007 (m), 965 (s), 842 (m), 816 (w), 787 (s), 740
(m),698 (s), 622 (s), 562 (w), 541 (m), 503 (m), 461 (s) cm−1.
7(SS-RR-diastereomer): 29Si NMR (C6D6, TMS, ppm): 30.74 (Si−t-
BuPhOfT); −40.11(Si(CH3)2). 19F NMR (C6D6, TMS, ppm):
−76.28 (Si−t-BuPhOfT). 13C NMR (C6D6, TMS, ppm): 133.74,
1
133.18, 131.04, 128.59 (Aryl−C); 121.44 (q, JFC = 318 Hz); 26.24
(C(CH3)3); 23.45 (C(CH3)3); −2.28, −3.33 (Si−(CH3)2). 1H NMR
(C6D6, TMS, ppm): 7.52−7.49 (m, 3H, Ph−H); 7.14−7.11 (m, 7H,
Ph−H); 0.87 (s, 18H C(CH3)3); 0.61 (s, 6H, Si(CH3)2); 0.18 (s, 6H,
Si(CH3)2).
Synthesis of 1,4-Dichloro-1,1,4,4-tetraphenyltetramethyl-
tetrasilane (8a). First, 10.00 g of 4 (15.74 mmol) was dissolved in
100 mL of toluene, and the solution was cooled to −80 °C.
Subsequently, 2.92 mL of trifluoromethansulfonic acid (33.06 mmol)
was slowly added and stirred for an additional 10 min at −80 °C. The
mixture was allowed to warm to room temperature and stirred for
another 120 min. At this time, reaction control by NMR spectroscopy
showed clean conversion of the starting material to the desired
bis(trifluoromethanesulfonate). To this solution were added 30 mL of
DME and 6.67 g of LiCl (157.45 mmol), and the solution was stirred
for 16 h at room temperature to ensure complete conversion to 8a.
Then, the reaction solution was subjected to an aqueous work up with
10% sulfuric acid. After removal of the solvents, a solid residue was
obtained. The obtained crude product was recrystallized from
pentane, giving white crystals of 8a. Yield: 7.99 g (92%) of analytically
pure white crystals. 8a: mp: 74−76 °C. Anal. Calcd for C28H32Cl2Si4:
C, 60.95; H, 5.85%. Found: C, 61.00; H, 5.90%. 29Si NMR (C6D6,
TMS, ppm): 7.14 (SiPh2Cl); −40.98 (Si(CH3)2). 13C NMR (C6D6,
TMS, ppm): 135.04, 134.48, 130.32, 128.31 (Aryl−C); −5.00 (Si−
(CH3)2).1H NMR (C6D6, TMS, ppm): 7.60−7.57 (m, 8H, Ph−H);
7.41−7.39 (m, 12H, Ph−H); 0.22 (s, 12H, Si(CH3)2). IR (neat):
3055 (w), 3021 (w), 2999 (w), 2953 (w), 2891 (w), 1477 (w), 1426
(m), 1245 (m), 1103 (s), 837 (m), 786 (s), 736 (s), 690 (s), 526 (s),
+
(m) cm−1. HRMS Calcd for (C24H40Cl2Si4 ) (M+): 510.1584. Found:
510.1579. 9(meso-diastereomer): 29Si NMR (C6D6, TMS, ppm):
19.79 (Sit-BuPhCl); −40.23(Si(CH3)2).
Synthesis of 1,2,2,5,5,6-Hexaphenyl-1,1,3,3,4,4,6,6-octame-
thylhexasilane (10). First, 10.00 g of 4 (15.74 mmol) was dissolved
in 100 mL of toluene, and the solution was cooled to −80 °C.
Subsequently, 2.92 mL of trifluoromethansulfonic acid (33.06 mmol)
was slowly added, and the solution was stirred for an additional 10
min at −80 °C. The mixture was allowed to warm to room
temperature and stirred for another 120 min. At this time, reaction
control by NMR spectroscopy showed clean conversion of the
starting material to the desired bis(trifluoromethanesulfonate). To
this a solution of PhMe2SiLi in 100 mL of THF (freshly prepared
from 5.64 g of PhMe2SiCl (33.06 mmol) and 2.30 g of Li (330.65
mmol)) were slowly added. Then, the reaction solution was subjected
to an aqueous work up with 10% sulfuric acid. After removal of the
+
504 (s), 453 (s) cm−1. HRMS Calcd for (C28H32Cl2Si4 )(M+):
550.0958. Found: 550.0960.
I
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solvents, a colorless oil was obtained. Subsequently, the oil was
chromatographed on silica gel with pentane as eluent, to give 427 mg
(94%) of analytically pure 10 as a colorless oil. 10: Anal. Calcd for
C44H54Si6: C, 70.33; H, 7.24%. Found: C, 70.35; H, 7.26%. 29Si NMR
(CDCl3, TMS, ppm): −18.95 (SiMe2Ph); −36.66 (SiPh2); −38.65
(Si(CH3)2). 13C NMR (C6D6, TMS, ppm): 139.14, 136.32, 135.62,
134.27, 128.67, 128.48, 127.85, 127.71 (Aryl−C); −1.69, −2.75
13 in standard solvents for NMR spectroscopy failed, but the product
was characterized by X-ray diffraction.
Reaction of 12 with Electrophiles (e.g., HSiCl3, SiCl4, SiBr4,
or GeCl4). First, 300 mg of 12 (0.28 mmol) was dissolved in 10 mL
of toluene, and the solution was cooled to −30 °C. To this was slowly
added a solution (0.30 mmol) of the electrophile. During the
addition, the reaction mixture went from a dark red color to colorless.
Volatiles were removed in vacuo, and the residue was extracted with n-
hexane (3 × 15 mL). After removal of the solvents, in all cases a
slightly yellow oil was obtained, and the reaction gave rise to an
uncharacterized polymer.
1
(Si(CH3)2 and Si(CH3)2Ph). H NMR (C6D6, TMS, ppm): 7.62−
7.60 (m, 8H, Ph−H); 7.50−7.40 (m, 22H, Ph−H); 0.63 (s, 12H,
Si(CH3)2Ph); 0.17 (s, 12H, Si(CH3)2). IR (neat): 3067 (w), 3050
(w), 3016 (w), 2948 (w), 2891 (w), 1426 (m), 1245 (m), 1098 (m),
832 (s), 803 (s), 781 (s), 730 (s), 696 (s), 645 (m), 498 (m), 464
Reaction of 13 with Electrophiles (e.g., HSiCl3, SiCl4, SiBr4,
or GeCl4). First, 300 mg of 13 (0.29 mmol) was dissolved in 10 mL
of toluene, and the solution was cooled to −30 °C. To this was slowly
added a solution (0.30 mmol) of the electrophile. During the
addition, the reaction mixture went from a dark orange color to
colorless. Volatiles were removed in vacuo, and the residue was
extracted with n-hexane (3 × 15 mL). After removal of the solvents, in
all cases a solid residue was obtained. The obtained crude product was
recrystallized from acetone, giving white crystals of 14. Yield: 105 mg
(83% with HSiCl3 as electrophile); 84 mg (66% with SiCl4 as
electrophile); 93 mg (74% with SiBr4 as electrophile); 45 mg (35%
with GeCl4 as electrophile) of analytically pure 14 as white crystals.
14: mp: 160−161 °C. Anal. Calcd for C24H40Si4: C, 65.38 H, 9.14%.
Found: C, 65.36; H, 9.12%. 29Si NMR (C6D6, TMS, ppm): −0.73
(SiPht-Bu); −30.34 (Si(CH3)2). 13C NMR (C6D6, TMS, ppm):
138.08, 137.09, 134.68, 128.83 (Aryl−C); 29.85 (C(CH3)3); 22.00
(C(CH3)3); −2.43, −4.28 (Si−(CH3)2). 1H NMR (C6D6, TMS,
ppm): 7.69−7.66 (m, 4H, Ph−H); 7.37−7.35 (m, 6H, Ph−H); 0.89
(s, 18H C(CH3)3); 0.49, 0.47 (s, each 6H Si(CH3)2). IR (neat): 3063
(w), 2918 (w), 2881 (w), 2846 (m), 1458 (w), 1425 (w), 1400 (w),
1356 (w), 1298 (w), 1260 (w), 1240 (w), 1184 (w), 1091 (w), 1065
(w), 1026 (w), 1003 (w), 960 (w), 938 (w), 844 (m), 826 (m), 814
(m), 799 (m), 780 (m), 745 (w), 732 (s), 699 (s), 687 (s), 664 (m),
642 (m), 584 (m), 514 (w), 488 (m), 463 (s), 450 (s), 410 (s), 395
+
(m) cm−1. HRMS Calcd for (C44H54Si6 ) (M+): 750.2841. Found:
750.2841.
Synthesis of 2,5-Di-tert-butyl-1,2,5,6-tetraphenyl-
1,1,3,3,4,4,6,6-octamethylhexasilane (11). First, 10.00 g of 5
(16.80 mmol) was dissolved in 100 mL of toluene, and the solution
was cooled to −80 °C. Subsequently, 3.10 mL of trifluoromethan-
sulfonic acid (35.29 mmol) was slowly added, and the solution was
stirred for an additional 10 min at −80 °C. The mixture was allowed
to warm to room temperature and stirred for another 120 min. At this
time, reaction control by NMR spectroscopy showed clean conversion
of the starting material to the desired bis(trifluoromethanesulfonate).
To this was slowly added a solution of PhMe2SiLi in 100 mL of THF
(freshly prepared from 6.02 g of PhMe2SiCl (35.29 mmol) and 2.47 g
of Li (352.90 mmol)). Then, the reaction solution was subjected to
aqueous work up with 10% sulfuric acid. After removal of the solvents,
a colorless oil was obtained. The obtained crude product was
recrystallized from ethanol, giving white crystals of 11 as a
diastereomeric mixture. Yield: 7.17 g (60%) of analytically pure 11
as white crystals. 11: mp: 122−125 °C. Anal. Calcd for C40H62Si6: C,
67.53; H, 8.78%. Found: C, 67.50; H, 8.83%. 29Si NMR (CDCl3,
TMS, ppm): −19.12, 19.25 (SiPht-Bu); −20.75, 21.24 (SiMe2Ph);
−36.65, 36.82 (Si(CH3)2). 13C NMR (CDCl3, TMS, ppm): 140.92,
137.20, 137.14, 136.91, 136.85, 134.57, 128.54, 128.24, 127.78,
127.51 (Aryl−C); 31.19 (C(CH3)3); 22.08, 22.06 (C(CH3)3); 0.76,
+
(m), 383 (m) cm−1. HRMS Calcd for (C24H40Si4 ) (M+): 440.2207.
Found: 440.2201.
1
0.72, 0.69, 0.18, 0.06, −0.02, −0.05 (Si(CH3)2 and Si(CH3)2Ph). H
Reaction of 8a,b with Lithium. First, 0.30 mmol of 8a,b was
dissolved in 15 mL of THF, and the solution was cooled to −30 °C.
To this was slowly added 1.50 mmol of lithium band. The solutions
were allowed to warm to room temperature and stirred for an
additional 15 h. At this time, reaction control by NMR spectroscopy
showed the formation of an uncharacterized polymer.
NMR (CDCl3, TMS, ppm): 7.55−7.52 (m, 4H, Ph−H); 7.40−7.38
(m, 4H, Ph−H); 7.31−7.26 (m, 12H, Ph−H); 1.03, 1.02 (s, 18H
C(CH3)3); 0.50, 0.47 (s, each 6H, Si(CH3)2 and Si(CH3)2Ph); 0.21,
0.13, 0.12, 0.05 (s, each 4H, Si(CH3)2 and Si(CH3)2Ph). IR (neat):
3072 (w), 2953 (m), 2925 (m), 2891 (m), 2857 (m), 1465 (w), 1426
(m), 1358 (w), 1245 (m), 1103 (m), 1047 (m), 832 (s), 809 (s), 781
Reaction of 9 with Lithium. First, 500 mg (0.98 mmol) of 9 was
dissolved in 25 mL of THF, and the solution was cooled to −30 °C.
To this was slowly added solution 30 mg (4.21 mmol) of lithium
band. The solution was allowed to warm up to room temperature and
stirred for additional 15 h. At this time, reaction control by NMR
spectroscopy showed clean conversion of the starting material to two
main products. Then, the reaction solution was subjected to an
aqueous work up with 10% sulfuric acid. After removal of the solvents,
a colorless oil was obtained. Subsequently, the oil was chromato-
graphed on silica gel with pentane as eluent, to give 223 mg (52%) of
analytically pure 14 as white crystals alongside 74 mg (27%) of
analytically pure 15 as white crystals. 15: mp: 279−281 °C. Anal.
Calcd for C28H52Si6: C, 60.35 H, 9.41%. Found: C, 60.40; H, 9.44%.
29Si NMR (CDCl3, TMS, ppm): −25.57 (SiPht-Bu); −39.82-
(Si(CH3)2). 13C NMR (CDCl3, TMS, ppm): 137.71, 137.68,
128.48, 127.22 (Aryl−C); 31.07 (C(CH3)3); 24.51 (C(CH3)3);
(s), 730 (s), 696 (s), 645 (s), 588 (m), 464 (s), 396 (m) cm−1
.
+
HRMS Calcd for (C40H62Si6 ) (M+): 710.3467. Found: 710.3475.
Reaction of 10 with KOt-Bu. First, 5.00 g of 10 (6.65 mmol) was
dissolved in 50 mL of Et2O, and the solution was cooled to −30 °C.
To this was slowly added a solution of 1.57 g (13.97 mmol) of KOt-
Bu and 3.70 g (13.97 mmol) of 18-crown-6 dissolved in 100 mL of
Et2O. During the addition, the reaction mixture went from colorless
to a dark red color, and a red precipitate began to form. The reaction
mixture was stirred overnight for 15 h. The red precipitate was
isolated and washed with diethyl ether (100 mL). The red powder
was dried under vacuum to yield 12. Yield: 6.42 g (89%) of
1
analytically pure 12 as red crystals. H and 29Si NMR spectra are
consistent with the reported spectra.29 12 contains a small amount of
uncoordinated 18-crown-6. 12: 29Si NMR (C6D6, TMS, ppm):
−36.68 (K−SiPh2); −38.64 (Si(CH3)2). 1H NMR (C6D6, TMS,
ppm): 8.02 (d, 8H, Ph−H); 7.09 (t, 8H, Ph−H); 6.87 (t, 4H, Ph−
H); 2.90 (s, 58H, (−(CH2−CH2−O)−)6; 0.41 (s, 12H, Si(CH3)2).
Reaction of 11 with KOt-Bu. First, 5.00 g of 11 (7.03 mmol) was
dissolved in 50 mL of Et2O, and the solution was cooled to −30 °C.
To this was slowly added a solution of 1.66 g (14.76 mmol) of KOt-
Bu and 3.90 g (14.76 mmol) of 18-crown-6 dissolved 100 mL of
Et2O. During the addition, the reaction mixture went from colorless
to a dark orange color, and an orange precipitate began to form. The
reaction mixture was stirred overnight for 15 h. The orange precipitate
was isolated and washed with diethyl ether (100 mL). The orange
powder was dried under vacuum to yield 13. All attempts to dissolve
1
−1.16, −2.70 (Si−(CH3)2). H NMR (CDCl3, TMS, ppm): 7.55−
7.52 (m, 4H, Ph−H); 7.28−7.26 (m, 6H, Ph−H); 0.97 (s, 18H
C(CH3)3); 0.51, 0.03 (s, each 12H Si(CH3)2). IR (neat): 3068 (w),
3042 (w), 2960 (m), 2936 (m), 2884 (m), 2846 (m), 1458 (m), 1424
(m), 1400 (m), 1358 (m), 1303 (m), 1245 (m), 1186 (m), 1092 (m),
1010 (m), 999 (m) 983 (m), 836 (s), 796 (s), 751 (s), 734 (s), 700
(s), 684 (s), 650 (s), 636 (s), 583 (m), 489 (s), 451 (m), 423 (m),
+
406 (m), 383 (m) cm−1. HRMS Calcd for (C28H52Si6 ) (M+):
556.2685. Found: 556.2690.
Reaction of 14 with Gaseous HCl. First, 300 mg of 14 (0.68
mmol) was dissolved in 10 mL of benzene. To this solution was
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added a catalytic amount of AlCl3, and subsequently gaseous HCl was
bubbled through the solution for 3 min (predried with an AlCl3
drying tower). Volatiles were removed in vacuo, and the residue was
extracted with n-hexane (3 × 15 mL). After removal of the solvent,
285 mg (98%) of analytically pure 16 (16 was recovered as a
diastereomeric mixture, which could not be separated) as colorless oil
was obtained. 16: Anal. Calcd for C12H30Cl4Si4: C, 33.64 H, 7.06%.
Found: C, 33.63; H, 7.04%. 29Si NMR (C6D6, TMS, ppm): 20.28,
20.19 (SiClt-Bu); 14.56, 13.64 (SiCl(CH3)2). 13C NMR (C6D6, TMS,
ppm): 28.64, 28.61 (C(CH3)3); 24.69, 24.10 (C(CH3)3); 4.90, 4.87,
positions. In some tough cases of disorder, anisotropic Uij-values of
the atoms were restrained (ISOR) to behave more isotropically. In
compound 7, the constraints EXYZ and EADP were used in modeling
disorder of one of the trifluoromethanesulfonate (OfT) groups to
make the ADP values of the disordered atoms more reasonable.
Disordered positions were refined using 80/20 split positions. The
distances between atom pairs were restrained to possess the same
value using the SADI instruction. In some tough cases of disorder,
anisotropic Uij-values of the atoms were restrained (ISOR) to behave
more isotropically. Despite multiple attempts to model the anisotropic
behavior for the positional disorder of the fluorine atoms in the
disordered OfT group, the main axis ADP ratio for one of the fluorine
atoms remained high. However, the residual electron density was well
below acceptable values. Compound 17 was refined as a 2-component
twin. The contributions of the two twin components refined to
0.808(8)/0.192(4). Table S1 contains crystallographic data and
details of measurements and refinement for all compounds.
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as
CCDC 1942705−1942715.
1
4.57, 4.41 (Si−(CH3)2). H NMR (C6D6, TMS, ppm): 1.12 (s, 18H
C(CH3)3); 0.65, 0.60 (s, each 6H Si(CH3)2). IR (neat): 2956 (m),
2931 (m), 2894 (m), 2861 (m), 1461 (m), 1397 (w), 1362 (m), 1246
(s), 1179 (w), 1003 (w), 975,35 (m), 936 (w), 838 (s), 799 (s), 771
(s), 697 (w), 672 (m), 626 (w), 605 (m), 514 (s), 480 (s), 464 (s),
+
429 (s), 387 (m) cm−1. HRMS Calcd for (C12H30Cl4Si4 ) (M+):
426.0179. Found: 426.0182.
Reaction of 16 with KC8. First, 360 mg (2.66 mmol) of KC8 were
suspended in 10 mL of Et2O, and the solution was cooled to −80 °C.
To this solution was slowly added 300 mg of 16 (0.70 mmol)
dissolved in 10 mL of Et2O, and the solution was stirred for an
additional 20 min at −80 °C. The mixture was allowed to warm up to
room temperature and stirred for another 6 h. At this time, reaction
control by NMR spectroscopy showed clean conversion of the
starting material to 17. Volatiles were removed in vacuo, and the
residue was extracted with n-hexane (3 × 15 mL). After removal of
the solvent, a solid residue was obtained. The obtained crude product
was recrystallized from acetone, giving white crystals of 17. Yield: 173
mg (86%) of analytically pure 17 as white crystals. 17: mp: 269−271
°C. Anal. Calcd for C24H60Si8: C, 50.27 H, 10.55%. Found: C, 50.31;
H, 10.56%. 29Si NMR (CDCl3, TMS, ppm): −23.83 (SitBu); −44.22
(Si(CH3)2). 13C NMR (CDCl3, TMS, ppm): 33.78 (C(CH3)3); 26.56
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00507.
■
S
NMR spectra and X-ray data (PDF)
Accession Codes
CCDC 1942705−1942715 contain the supplementary crys-
tallographic 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.
1
(C(CH3)3); 6.09, 4.11 (Si(CH3)2). H NMR (CDCl3, TMS, ppm):
1.21 (s, 36H C(CH3)3); 0.69, 0.64 (s, each 12H Si(CH3)2). IR
(neat): 3650 (w), 2925 (m), 2883 (m), 2848 (s), 1457 (m), 1390
(w), 1357 (m), 1234 (m), 1161 (m), 929 (w), 1005 (m), 832 (s), 801
(s), 744 (m), 728 (m), 652 (s), 582 (m), 383 (m) cm−1. HRMS
+
Calcd for (C20H51Si8 ) (M+ − t-Bu): 515.2145. Found: 515.2150.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: michael.haas@tugraz.at (M.H.).
*E-mail: cameron.jones@monash.edu (C.J.).
■
X-ray Crystallography. All crystals suitable for single-crystal X-
ray diffractometry were removed from a vial or Schlenk flask and
immediately covered with a layer of silicone oil. A single crystal was
selected, mounted on a glass rod on a copper pin, and placed in a cold
N2 stream. XRD data collection for compound 3, 6, 7, 9, 13, and 17
was performed on a Bruker APEX II diffractometer with use of an
Incoatec microfocus sealed tube of Mo Kα radiation (λ= 0.71073 Å)
and a CCD area detector. Empirical absorption corrections were
applied using SADABS or TWINABS.37,38
ORCID
Michael Haas: 0000-0002-9213-940X
Ana Torvisco: 0000-0002-6203-7330
Roland Fischer: 0000-0001-9523-5010
Cameron Jones: 0000-0002-7269-1045
XRD data collection for compounds 5, 8b, and 14 was carried out
with a Rigaku Xtalab Synergy Dualflex using a graphite mono-
chromator with either MoKα radiation (λ = 0.71073 Å) or Cu Kα
radiation (λ = 1.54180 Å); XRD data collection for 4 used the MX1
beamline of the Australian Synchrotron (λ = 0.71090 Å). The
software package Blu-Ice39 was used for synchrotron data acquisition,
while the program XDS40 was employed for synchrotron data
reduction. The structures were solved with either the use of direct
methods or the intrinsic phasing option in SHELXT and refined by
the full-matrix least-squares procedures in SHELXL.41−43 or Olex2.44
The space group assignments and structural solutions were evaluated
using PLATON.45,46 Non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were located in either a difference map or
calculated positions corresponding to standard bond lengths and
angles. Disorder was handled by modeling the occupancies of the
individual orientations using free variables to refine the respective
occupancy of the affected fragments (PART).47 Three of the six
independent molecules in compound 3 show positional disorder of
the silicon hydrogen bonds in the Et3Si−SiH moiety and were refined
using split positions, 70/30, 60/40, and 85/15 respectively.
Disordered positions for the ethyl groups in one of the Et3SiH
moiety were refined using 50/50 split positions. Disordered positions
for two of the ring −SiMe2 moieties were refined using 60/30 split
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
M.H. thanks the FWF (Vienna, Austria) for financial support
(project number J 3999-N34). C.J. acknowledges financial
support from the Australian Research Council. Part of this
research was undertaken on the MX1 beamline at the
Australian Synchrotron, Victoria, Australia.
REFERENCES
■
(1) Skell, P. S.; Goldstein, E. J. Dimethylsilene: CH3SiCH3. J. Am.
Chem. Soc. 1964, 86, 1442−1443.
(2) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. v.;
Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. Synthesis and
Structure of a Stable Silylene. J. Am. Chem. Soc. 1994, 116, 2691−
2692.
(3) Blom, B.; Driess, M. Recent Advances in Silylene Chemistry:
Small Molecule Activation En-Route Towards Metal-Free Catalysis.
In Functional Molecular Silicon Compounds II; Scheschkewitz, D., Ed.;
K
DOI: 10.1021/acs.organomet.9b00507
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Structure and Bonding Series; Springer: Berlin, 2014; Vol. 156, pp
85−123.
(25) Holthausen, M. C.; Koch, W.; Apeloig, Y. Theory Predicts
Triplet Ground-State Organic Silylenes. J. Am. Chem. Soc. 1999, 121,
2623−2624.
(26) Sekiguchi, A.; Tanaka, T.; Ichinohe, M.; Akiyama, K.; Tero-
Kubota, S. Bis(tri-tert-butylsilyl)silylene: triplet ground state silylene.
J. Am. Chem. Soc. 2003, 125, 4962−4963.
̈
(4) Gehrhus, B.; Lappert, M. F.; Heinicke, J.; Boese, R.; Blaser, D.
Synthesis, structures and reactions of new thermally stable silylenes. J.
Chem. Soc., Chem. Commun. 1995, 116, 1931−1932.
̈
(5) Driess, M.; Yao, S.; Brym, M.; van Wullen, C.; Lentz, D. A new
(27) Sekiguchi, A.; Tanaka, T.; Ichinohe, M.; Akiyama, K.; Gaspar,
P. P. Tri-tert-butylsilylsilylenes with alkali metal substituents ((t)-
Bu3Si)SiM (M = Li, K): electronically and sterically accessible triplet
ground states. J. Am. Chem. Soc. 2008, 130, 426−427.
(28) Reiter, D.; Holzner, R.; Porzelt, A.; Altmann, P. J.; Frisch, P.;
Inoue, S. Disilene-Silylene Interconversion: A Synthetically Accessible
Acyclic Bis(silyl)silylene. J. Am. Chem. Soc. 2019, 141, 13536−13546.
(29) Xiao, X.-Q.; Zhao, H.; Xu, Z.; Lai, G.; He, X.-L.; Li, Z.
Reduction of the dihalocyclopentasilanes. A quest for a homocyclic
silylene. Chem. Commun. 2013, 49, 2706−2708.
(30) Mueller, S. K.; Dzambaski, A.; Altenhuber, N.; Torvisco, A.;
Hassler, K.; Flock, M. Synthesis and characterization of 1,1-
dihalogenated cyclopentasilanes. J. Mol. Struct. 2015, 1099, 197−203.
(31) Auer, D.; Strohmann, C.; Arbuznikov, A. V.; Kaupp, M.
Understanding Substituent Effects on 29Si Chemical Shifts and
Bonding in Disilenes. A Quantum Chemical Analysis. Organometallics
2003, 22, 2442−2449.
type of N-heterocyclic silylene with ambivalent reactivity. J. Am. Chem.
Soc. 2006, 128, 9628−9629.
(6) So, C.-W.; Roesky, H. W.; Magull, J.; Oswald, R. B. Synthesis
and Characterization of [PhC(NtBu)2]SiCl: A Stable Monomeric
Chlorosilylene. Angew. Chem. 2006, 118, 4052−4054.
(7) Kong, L.; Zhang, J.; Song, H.; Cui, C. N-Aryl substituted
heterocyclic silylenes. Dalton Trans. 2009, 5444−5446.
̈
(8) Zark, P.; Schafer, A.; Mitra, A.; Haase, d.; Saak, W.; West, R.;
Muller, T. Synthesis and reactivity of N-aryl substituted N-
̈
heterocyclic silylenes. J. Organomet. Chem. 2010, 695, 398−408.
(9) Junold, K.; Baus, J. A.; Burschka, C.; Tacke, R. Bis[N,N′-
diisopropylbenzamidinato(−)]silicon(II): A Silicon(II) Compound
with Both a Bidentate and a Monodentate Amidinato Ligand. Angew.
Chem. 2012, 124, 7126−7129.
(10) Sen, S. S.; Roesky, H. W.; Stern, D.; Henn, J.; Stalke, D. High
yield access to silylene RSiCl (R = PhC(NtBu)2) and its reactivity
toward alkyne: synthesis of stable disilacyclobutene. J. Am. Chem. Soc.
2010, 132, 1123−1126.
(11) Kosai, T.; Ishida, S.; Iwamoto, T. A Two-Coordinate Cyclic
(Alkyl)(amino)silylene: Balancing Thermal Stability and Reactivity.
Angew. Chem., Int. Ed. 2016, 55, 15554−15558.
(12) Ghadwal, R. S.; Roesky, H. W.; Merkel, S.; Henn, J.; Stalke, D.
Lewis base stabilized dichlorosilylene. Angew. Chem., Int. Ed. 2009, 48,
5683−5686.
(32) Kumada, M.; Ishikawa, M.; Sakamoto, S.; Maeda, S.
Triphenylsilyllithium-catalyzed disproportionation of α,α,α,ω,ω,ω-
hexaphenylpolymethylpolysilanes to permethylated cyclopolysilanes
and hexaphenyldisilane. J. Organomet. Chem. 1969, 17, 223−229.
(33) Marro, E. A.; Press, E. M.; Purkait, T. K.; Jimenez, D.; Siegler,
M. A.; Klausen, R. S. Cooperative Noncovalent Interactions Induce
Ion Pair Separation in Diphenylsilanides. Chem. - Eur. J. 2017, 23,
15633−15637.
(13) Filippou, A. C.; Chernov, O.; Schnakenburg, G. SiBr2(Idipp): a
stable N-heterocyclic carbene adduct of dibromosilylene. Angew.
Chem., Int. Ed. 2009, 48, 5687−5690.
(34) Tamao, K.; Kawachi, A. Silyl Anions. Adv. Organomet. Chem.
1995, 38, 1−58.
(35) Luo, J.; Yan, E.-H.; Zhao, H.; Xiao, X.-Q.; Li, Z. Synthesis,
structure and reactivity of sterically demanding oligosilanylmagnesium
compounds. Polyhedron 2015, 102, 233−238.
(14) Filippou, A. C.; Chernov, O.; Blom, B.; Stumpf, K. W.;
Schnakenburg, G. Stable N-heterocyclic carbene adducts of
arylchlorosilylenes and their germanium homologues. Chem. - Eur. J.
2010, 16, 2866−2872.
(36) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Safe and Convenient Procedure for Solvent
Purification. Organometallics 1996, 15, 1518−1520.
(15) Cui, H.; Cui, C. Silylation of N-heterocyclic carbene with
aminochlorosilane and -disilane: dehydrohalogenation vs. Si−Si bond
cleavage. Dalton Trans. 2011, 40, 11937−11940.
(37) Bruker APEX2 and SAINT; Bruker AXS, Inc.: Madison, WI,
2012.
(16) Kira, M.; Ishida, S.; Iwamoto, T.; Kabuto, C. The First Isolable
Dialkylsilylene. J. Am. Chem. Soc. 1999, 121, 9722−9723.
(17) Abe, T.; Tanaka, R.; Ishida, S.; Kira, M.; Iwamoto, T. New
isolable dialkylsilylene and its isolable dimer that equilibrate in
solution. J. Am. Chem. Soc. 2012, 134, 20029−20032.
(38) Blessing, R. H. An empirical correction for absorption
anisotropy. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995, 51,
33−38.
(39) McPhillips, T. M.; McPhillips, S. E.; Chiu, H.-J.; Cohen, A. E.;
Deacon, A. M.; Ellis, P. J.; Garman, E.; Gonzalez, A.; Sauter, N. K.;
Phizackerley, R. P.; et al. Blu-Ice and the Distributed Control System:
software for data acquisition and instrument control at macro-
molecular crystallography beamlines. J. Synchrotron Radiat. 2002, 9,
401−406.
(18) Asay, M.; Inoue, S.; Driess, M. Aromatic ylide-stabilized
carbocyclic silylene. Angew. Chem., Int. Ed. 2011, 50, 9589−9592.
(19) Jutzi, P.; Kanne, D.; Kruger, C. Decamethylsilicocen - Synthese
̈
und Struktur. Angew. Chem. 1986, 98, 163−164.
́
(20) Jutzi, P.; Leszczynska, K.; Neumann, B.; Schoeller, W. W.;
(40) Kabsch, W. Automatic processing of rotation diffraction data
from crystals of initially unknown symmetry and cell constants. J.
Appl. Crystallogr. 1993, 26, 795−800.
Stammler, H.-G. 2,6-(Trip)2H3C6(Cp*)Si: a stable monomeric
arylsilicon(II) compound. Angew. Chem., Int. Ed. 2009, 48, 2596−
2599.
(41) Sheldrick, G. M. Phase annealing in SHELX-90: direct methods
for larger structures. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990,
46, 467−473.
(21) Rekken, B. D.; Brown, T. M.; Fettinger, J. C.; Tuononen, H.
M.; Power, P. P. Isolation of a stable, acyclic, two-coordinate silylene.
J. Am. Chem. Soc. 2012, 134, 6504−6507.
(22) Green, S. P.; Jones, C.; Stasch, A. Stable magnesium(I)
compounds with Mg−Mg bonds. Science 2007, 318, 1754−1757.
(23) Protchenko, A. V.; Birjkumar, K. H.; Dange, D.; Schwarz, A. D.;
Vidovic, D.; Jones, C.; Kaltsoyannis, N.; Mountford, P.; Aldridge, S. A
stable two-coordinate acyclic silylene. J. Am. Chem. Soc. 2012, 134,
6500−6503.
(24) Protchenko, A. V.; Schwarz, A. D.; Blake, M. P.; Jones, C.;
Kaltsoyannis, N.; Mountford, P.; Aldridge, S. A generic one-pot route
to acyclic two-coordinate silylenes from silicon(IV) precursors:
synthesis and structural characterization of a silylsilylene. Angew.
Chem., Int. Ed. 2013, 52, 568−571.
(42) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
(43) Sheldrick, G. M. SHELXT - integrated space-group and crystal-
structure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015,
71, 3−8.
(44) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. OLEX2: a complete structure solution, refinement
and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341.
(45) Spek, A. L. Single-crystal structure validation with the program
PLATON. J. Appl. Crystallogr. 2003, 36, 7−13.
(46) Spek, A. L. Structure validation in chemical crystallography.
Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65, 148−155.
L
DOI: 10.1021/acs.organomet.9b00507
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(47) Muller, P.; Herbst-Irmer, R.; Spek, A. L.; Schneider, T. R.;
̈
Sawaya, M. R. Crystal Structure Refinement; Oxford University Press,
2006.
M
DOI: 10.1021/acs.organomet.9b00507
Organometallics XXXX, XXX, XXX−XXX