Partial halogenation of cyclic and branched perhydropentasilanes

Article abstract of DOI:10.1021/ic300214y

The perhydropentasilanes (H₃Si)₄Si and Si ₅H₁₀ were chlorinated with SnCl₄ to give chlorohydropentasilanes without destruction of the Si-Si backbone. Tetrachloroneopentasilane (ClH₂Si)₄Si (2) was prepared in high yield from (H₃Si)₄Si and 3.5 equiv of SnCl ₄, while Si₅H₁₀ and an equimolar amount of SnCl₄ afforded a mixture of ～60% of ClSi₅H₉ (1) with polychlorinated cyclopentasilanes and unreacted starting material, which could not be separated by distillation. The selective monochlorination of Si₅H₁₀ was achieved starting from MesSi₅Cl ₉ (3; Mes = 2,4,6-trimethylphenyl) or TBDMP-Si₅Cl ₉ (4; TBDMP = 4-tert-butyl-2,6-dimethylphenyl). 3 or 4 was successfully hydrogenated with LiAlH₄ to give MesSi₅H ₉ (6) or TBDMP-Si₅H₉ (7), which finally gave 1 along with aryl-H and Si₅H₁₀ after treatment with an excess of liquid anhydrous HCl. All compounds were characterized by standard spectroscopic techniques. For Si-H derivatives, the coupled ²⁹Si NMR spectra were analyzed in detail to obtain an unequivocal structural assignment. The molecular structures of 2-4 were further confirmed by X-ray crystallography.

Full text of DOI:10.1021/ic300214y

Article
pubs.acs.org/IC
Partial Halogenation of Cyclic and Branched Perhydropentasilanes
Harald Stueger,*,† Thomas Mitterfellner,† Roland Fischer,† Christoph Walkner,† Matthias Patz,‡
and Stephan Wieber‡
†Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9, A-8010 Graz, Austria
‡Creavis, Technologies & Innovation, Evonik Industries AG, Paul Baumannstrasse 1, D-45764 Marl, Germany
S
* Supporting Information
ABSTRACT: The perhydropentasilanes (H3Si)4Si and Si5H10 were chlorinated with SnCl4
to give chlorohydropentasilanes without destruction of the Si−Si backbone. Tetrachlor-
oneopentasilane (ClH2Si)4Si (2) was prepared in high yield from (H3Si)4Si and 3.5 equiv of
SnCl4, while Si5H10 and an equimolar amount of SnCl4 afforded a mixture of ∼60% of
ClSi5H9 (1) with polychlorinated cyclopentasilanes and unreacted starting material, which
could not be separated by distillation. The selective monochlorination of Si5H10 was
achieved starting from MesSi5Cl9 (3; Mes = 2,4,6-trimethylphenyl) or TBDMP-Si5Cl9 (4;
TBDMP = 4-tert-butyl-2,6-dimethylphenyl). 3 or 4 was successfully hydrogenated with
LiAlH4 to give MesSi5H9 (6) or TBDMP-Si5H9 (7), which finally gave 1 along with aryl-H
and Si5H10 after treatment with an excess of liquid anhydrous HCl. All compounds were
characterized by standard spectroscopic techniques. For Si−H derivatives, the coupled 29Si
NMR spectra were analyzed in detail to obtain an unequivocal structural assignment. The
molecular structures of 2−4 were further confirmed by X-ray crystallography.
of selected higher silicon hydrides with the primary target to
elaborate possible pathways to doped single-source precursors
for silicon film deposition is one of our main research interests.
Although the synthesis and physical properties of linear8 and
cyclic higher silicon hydrides9 are well documented, their
chemistry is literally unexplored. This is mainly due to their
unpleasant properties such as their pyrophoric character upon
exposure to air or their thermodynamic and kinetic instability
and also due to the lack of suitable synthetic methods for
hydrosilane derivatization. Some scattered reports on chemical
transformations involving higher silicon hydrides include partial
halogenation of di-, tri-, and tetrasilanes with BX3, HX/AlX3,
AgX, SnX4, HgX2, or X2 (X = Cl, Br, I).10 These methods
usually afford product mixtures that are difficult or even
impossible to separate and frequently could only be analyzed
after further derivatization of the initial products. More
recently, Hassler et al. described the synthesis of a whole
series of halohydrodi- and trisilanes by halodephenylation of
properly substituted phenyldi- and trisilanes.11 The challenge of
this method, however, is preparation of the starting materials.
Redistribution reactions of Si2H6 or Si3H8 under the influence
of MSiH3 (M = Na, K) to give sodium and potassium silanides
containing branched oligosilanyl anions such as (H3Si)3Si− are
also described.12 A recent patent claims the synthesis of
mixtures of ClSi6H11 and Cl2Si6H10 by the reaction of Si6H12
with chlorinating agents like AgCl, HgCl2, or SnCl4.7a In our
laboratories, it was demonstrated some years ago that
functionalized linear or branched hydrosilane skeletons,
INTRODUCTION
■
Solution-based deposition and processing techniques for silicon
are of particular interest because they allow significant
reduction of processing costs compared to standard vacuum-
based approaches. Further advantages of solution methods
include suitability for large-area and flexible substrates,
increased material utilization efficiency, and lower-temperature
processing.1 Open-chained SinH2n+2 or cyclic SinH2n silicon
hydrides are potential precursors in this context because they
are liquid at room temperature for n ≥ 3 and carbon- and
oxygen-free and decompose to a-Si:H upon heating to 300 °C
and higher. In a pioneering paper, Shimoda et al. describe the
fabrication of a thin-film transistor using solution-processed
silicon films deposited by pyrolysis of liquid hydrosilane
oligomers, which were made by photooligomerization of
cyclopentasilane Si5H10.2 Later studies revealed that cyclo-
3
hexasilane Si6H12 or neopentasilane (H3Si)4Si,4 which are
more easily accessible than Si5H10, can be used as precursors
equally well.5 n- or p-doped silicon films can also be made using
this method if the hydrosilane precursor is mixed with
appropriate dopants like P4 or B10H14 prior to photo-
oligomerization.6 The initial studies, however, reported a
potential nonuniform dopant distribution within the resulting
semiconductor film, which may lead to suboptimal electrical
properties. In order to overcome this problem, it has been
suggested to use hydrosilane precursors for silicon film
deposition, which contain one or more heteroatom dopants
covalently linked to the Si−Si backbone (single-source
precursors).7 To the best of our knowledge, compounds of
this type have not been described in the literature so far.
Therefore, the detailed investigation of the chemical properties
Received: January 29, 2012
Published: May 22, 2012
© 2012 American Chemical Society
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SinHm−xClx, with n > 3, can be assembled stepwise from
properly substituted mono- and disilanes employing multistep
synthetic procedures.13 Now we present novel approaches to
the preparation of previously unknown partially chlorinated
perhydropentasilanes containing the cyclo- or neopentasilane
skeleton.
residue, which is highly pyrophoric upon exposure to air. In
order to enable quantitative analysis, the crude mixture of
partially chlorinated cyclopentasilanes was reacted with n-BuLi
at −70 °C to give the corresponding n-butyl derivatives
(Scheme 1) with higher thermal and hydrolytic stability.
According to gas chromatography (GC)/mass spectrometry
(MS) analysis performed after aqueous workup and removal of
the solvents at 25 °C and 0.05 mbar, n-BuSi5H9 (∼60%) had
been formed as the major product along with n-Bu2Si5H8
(∼35%) and minor amounts of n-Bu3Si5H7 (<2%) and residual
Si5H10 (<5%). However, pure ClSi5H9 (1) could not be isolated
by distillation or recondensation because of insufficiently
different boiling points of the single components present in
the crude product mixture.
The treatment of Si5H10 with 5 equiv of SnCl4 produces
Si5Cl10 and HSi5Cl9 in an approximate molar ratio of 1:1
instead of the expected product Si5H5Cl5 (Scheme 1). The high
chlorine content in the final products is easily understood,
taking into account the ability of HCl to chlorinate Si−H bonds
especially in the presence of Lewis acids.10c,d
RESULTS AND DISCUSSION
■
Chlorination of Si5H10 with SnCl4. Because of the
outstanding reactivity of Si−halogen bonds in nucleophilic
substitution reactions, chlorosilanes are widely used as
intermediates in the synthesis of functionalized polysilane
backbones. The selective introduction of halo substituents into
molecules like Si5H10 and (H3Si)4Si, therefore, might create
reactive sites suitable for further derivatization. Ebsworth et al.
observed that SnCl4 is an excellent reagent for chlorination of
di- and trisilanes.10j When roughly equimolar proportions of
SnCl4 and Si2H6 or Si3H8, respectively, were condensed
together and allowed to warm to room temperature, a mixture
of mono- and dichlorinated compounds was formed along with
SnCl2 and HCl. Products resulting from disubstitution at a
single Si atom or Si−Si bond scission have not been detected.
In close analogy to these findings, we observed that a pentane
solution of Si5H10 reacts with an equimolar amount of SnCl4,
according to Scheme 1.
SnCl4
Si5H10 ⎯⎯⎯⎯⎯⎯→⎯ Si5H10−xClx
−SnCl2
(1)
(2)
−HCl
Si5H10 ⎯H⎯⎯→Cl Si5H10−xClx
−H2
Scheme 1. Chlorination of Cyclopentasilane Si5H10 with
SnCl4
HCl, which is formed as a primary product from Si5H10 and
SnCl4 (eq 1), acts as an additional chlorinating agent under the
influence of the Lewis acid SnCl4 (eq 2), giving rise to the
formation of further Si−Cl bonds. The coupled 29Si NMR
spectrum of the reaction mixture obtained after stirring Si5H10
with a 5-fold excess of SnCl4 for 160 h showed a singlet at −2.7
ppm, which is easily assigned to Si5Cl10.14 Additional lines at
1
−27.9 ppm (doublet, JSi−H = 248.5 Hz), 1.1 ppm (doublet,
3
2JSi−H = 8.2 Hz), and −3.0 ppm (doublet, JSi−H = 7.3 Hz)
match data previously reported for Si5Cl9H.15 Shorter reaction
times or reduced amounts of SnCl4 lead to the formation of
complicated mixtures of chlorohydrocylopentasilanes without
any noticeable selectivity; longer reaction times and a larger
excess of SnCl4 increase the relative amount of Si5Cl10.
Chlorination of (H3Si)4Si with SnCl4. The treatment of
(H3Si)4Si with 1 equiv of SnCl4 did not result in the exclusive
formation of (H3Si)3SiSiH2Cl. Just as observed in the
analogous reaction of Si5H10, mono- and polychlorinated
products were formed along with unreacted starting material.
1
The H NMR spectrum of the reaction mixture obtained after
stirring equimolar amounts of (H3Si)4Si and SnCl4 at room
temperature for 120 h showed four different SiH3 and four
different SiH2Cl proton environments between 3.9 and 4.1 ppm
and 5.4 and 5.7 ppm, respectively, which is in accordance with
the formation of (H3Si)3SiSiH2Cl, (H3Si)2Si(SiH2Cl)2, H3SiSi-
(SiH2Cl)3, and (ClH2Si)4Si (2).
After 12 h at room temperature, SnCl4 had been completely
consumed and the solid SnCl2 was easily removed by filtration.
The 1H NMR spectrum of the resulting solution was consistent
with the formation of a mixture of mono- and polychlorinated
cyclopentasilanes Si5H10−xClx. At least four broad and poorly
resolved signals appeared in the typical range for −SiClH−
protons between 5.0 and 5.3 ppm,13c while the SiH2 region
showed a superposition of several broad bands between 3.1 and
3.4 ppm, together with the sharp Si5H10 signal near 3.3 ppm.
Removal of the solvent at reduced pressure afforded a liquid
When we reacted (H3Si)4Si with 3.5 equiv of SnCl4, exactly
one H atom per SiH3 group was exchanged with chlorine and
tetrakis(chlorosilyl)silane (2) was formed (Scheme 2). Because
of the chlorinating ability of the byproduct HCl already
mentioned above, less than the stoichiometric amount of SnCl4
was necessary to achieve complete conversion. Significantly
increased reaction times gave rise to formation of a higher
chlorinated byproduct such as Cl2HSiSi(SiH2Cl)3.
In the 29Si NMR spectrum of a mixture obtained after stirring
(H3Si)4Si and SnCl4 in a molar ratio of 1:3.5 in pentane for 72
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Scheme 2. Chlorination of Neopentasilane (H3Si)4Si with
SnCl4
Figure 1. Molecular structure of 2 in the crystal (50% thermal
probability ellipsoids). Selected bond lengths (Å) and angles (deg)
with estimated standard deviations: Si1−Si2 2.346(1), Si2−Cl1
2.074(1); Si2−Si1−Si2 111.4(1), 111.4(1), 111.4(1), 105.7(1),
105.7(1), Cl1−Si2−Si1 108.8(1).
whereas only the S4 conformer of 2 is observed in the solid
state. If the molecule is viewed along the 4-fold rotoinversion
axis of symmetry passing through Si1, all Cl atoms are oriented
in the same direction relative to Si2.
Selective Monofunctionalization of Si5H10. Because
pure 1 was not accessible by direct halogenation of Si5H10
with SnCl4, we developed an alternative preparative approach
using protective groups (Scheme 3). In the first step, one
h at room temperature and removal of solid SnCl2, only two
signals at −24.6 and −124.9 ppm appeared, while the signals of
(H3Si)4Si at −89.6 and −165.9 ppm16 disappeared. The
1
observed 29Si and H chemical shift values, splitting patterns,
and Si−H coupling constants are completely in line with the
exclusive formation of 2, as depicted in Scheme 2. In the
coupled 29Si NMR spectrum, the resonance line at −24.6 ppm
1
exhibited triplet splitting with JSi−H = 236.9 Hz, while the
Scheme 3. Selective Monofunctionalization of
Cyclopentasilane Si5H10
signal at −124.9 ppm was split into nine lines with a coupling
constant of 2JSi−H = 12.6 Hz. 1H NMR data were also consistent
with the formation of one distinct product. Besides the signals
of the solvent, only one line at 4.85 ppm appeared, which is
shifted to lower field by 1.4 ppm compared to (H3Si)4Si.12a
Chlorohydrooligosilanes described in the literature exhibit 29Si
NMR signals for ClH2Si groups between −24 and −32 ppm
with unusually large coupling constants JSi−H > 225 Hz.13b,17
1
Downfield-shifted β-Si resonances in hydrosilanes upon
chlorination are also evident. For 2, the signal of the central
Si atom is shifted tremendously by 41 ppm to lower field
relative to unsubstituted (H3Si)4Si.
Pure 2 could be isolated by crystallization from the crude
reaction mixture at −70 °C as a moisture-sensitive but
nonpyrophoric liquid in ∼50% yield. Crystals of 2 suitable
for single-crystal X-ray crystallography could be grown at −70
°C using an optical heating and crystallization device (OHCD)
laser system. A graphical representation of the molecular
structure is given in Figure 1, along with key bond lengths and
angles.
Compound 2 crystallizes in the tetragonal space group I4.
̅
The Si−Si distance of 2.346 Å is slightly longer than the Si−Si
bond length of 2.332 Å observed for (H3Si)4Si in the gas
phase.12f The Si−Cl bond length of 2.074 Å is close to the Si−
Cl distance in H3SiCl (2.06 Å),18 which is markedly shorter
than the Si−Cl bond length of 2.16 Å estimated from the sum
of the covalent radii of silicon and chlorine. The tetrahedral
geometry around Si1 is slightly distorted with Si−Si−Si bond
angles of 111.4° and 105.7°. It is interesting to compare the
structure of 2 with the structure of its carbon analogue
(ClH2C)4C. Gaseous (ClH2C)4C has been studied by electron
diffraction19 and showed small, but significant, deviations of the
C atom framework from a tetrahedral arrangement, just as
observed for the silicon skeleton of 2 in the crystal. However,
two conformers with D2d and S4 symmetry, respectively, were
detected in equal amounts for (ClH2C)4C in the gas phase,
aromatic side group was attached to the cyclopentasilane ring
by reacting Si5Cl10 with appropriate aryllithium compounds in
order to protect one of the Si−Cl bonds during the subsequent
hydrogenation step. Substituted aromatics like mesityl (Mes =
2,4,6-trimethylphenyl) or 4-tert-butyl-2,6-dimethylphenyl
(TBDMP) were better suited for this purpose than
unsubstituted phenyl rings because they greatly facilitate
crystallization of the resulting arylnonachlorocyclopentasilanes.
Thus, pure MesSi5Cl9 (3) and (TBDMP)Si5Cl9 (4) crystallized
at −30 °C in >85% yield from the crude product mixtures,
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obtained after Si5Cl10 had been reacted with 1 equiv of MesLi
or TBDMPLi. PhSi5Cl9 (5) synthesized under similar
conditions from Si5Cl10 and PhLi, however, was reluctant to
crystallize and, therefore, could not be isolated in a pure state.
In all cases, it was necessary to perform the reaction strictly
under ether-free conditions. Traces of ethers readily react with
Si5Cl10 to give undesired byproducts.
The treatment of 3 and 4 with LiAlH4 in diethyl ether
afforded the corresponding hydrocyclopentasilanes MesSi5H9
(6) and (TBDMP)Si5H9 (7). Analytically pure samples of 6
and 7 were obtained after removal of all volatile components at
0.05 mbar and 25 °C. GC/MS analysis of the resulting colorless
and moderately air-sensitive oils exhibits just one signal with
M+ ions at m/e 268 and 310, respectively, and other ions
consistent with the proposed structures.
Figure 2. Molecular structure of 3 in the crystal (50% thermal
probability ellipsoids). Selected bond lengths (Å), angles (deg), and
torsion angles (deg) with estimated standard deviations: Si1−Si2
2.365(1), Si1−Si5 2.353(1), Si2−Si3 2.367(1), Si3−Si4 2.360(1),
Si4−Si5 2.352(1), Si1−C1 1.867(2), Si1−Cl1 2.123(1), Sin−Cl
(mean) 2.050; Si5−Si1−Si2 98.7(1), Si1−Si2−Si3 103.2(1), Si4−
Si3−Si2 106.4(1), Si5−Si4−Si3 103.4(1), Si4−Si5−Si1 103.8(1);
Si1−Si2−Si3−Si4 24.7(1), Si2−Si3−Si4−Si5 5.4(1), Si3−Si4−Si5−
Si6 33.8(1), Si4−Si5−Si1−Si2 48.7(1), Si5−Si1−Si2−Si3 44.3(1).
Finally, the aryl protective groups of 6 or 7 were easily
1
removed with HCl. According to H and 29Si NMR analysis,
the colorless highly air-sensitive liquid obtained after stirring a
pentane solution of 6 with an excess of anhydrous liquid HCl at
−95 °C and removal of pentane and residual HCl at reduced
pressure contained 1, mesitylene, and up to 30% Si5H10 formed
as a byproduct. Once again, it was not possible to isolate pure 1
by fractional condensation because of insufficiently different
boiling points of the single components present in the crude
product mixture.
Compounds 3−7 were characterized by usual spectroscopic
techniques and by elemental analysis, the corresponding data
can be found in the Experimental Section. The fully coupled
29Si NMR spectra of the monofunctionalized cyclopentasilanes
1, 6, and 7 show characteristic splitting patterns due to
extensive 29Si−1H coupling, which greatly facilitates structural
assignment. All chemical shifts and coupling constants were
consistent with the proposed structures. Furthermore, excellent
agreement with literature data of open-chained hydrosilanes
containing aryl or chloro substituents was observed.11a,13a,17a,20
The −arylSiH− and −ClSiH− resonances exhibit doublet
splitting and characteristic low-field shifts relative to the triplets
arising from the endocyclic −SiH2− groups. The exceptionally
large value of 1J(29Si−1H) = 231.3 Hz observed for the −SiHCl
group in 1 is typical for silicon hydrides bearing electronegative
substituents.21 Additionally, all signals exhibit significant line
broadening due to extensive long-range coupling. The complex
endocyclic spin systems, however, prevent resolution of the
individual resonance lines, which is frequently observed in
open-chained silicon hydrides.16
Figure 3. Molecular structure of 4 in the crystal (50% thermal
probability ellipsoids). Selected bond lengths (Å), angles (deg), and
torsion angles (deg) with estimated standard deviations: Si1−Si2
2.339(1), Si1−Si5 2.359(1), Si2−Si3 2.361(1), Si3−Si4 2.367(1),
Si4−Si5 2.359(1), Si1−C1 1.862(2), Si1−Cl1 2.085(1), Si2−5−Cl
(mean) 2.043; Si5−Si1−Si2 99.2(1), Si1−Si2−Si3 105.2(1), Si4−Si3−
Si2 106.2(1), Si5−Si4−Si3 103.1(1), Si4−Si5−Si1 104.1(1); Si1−
Si2−Si3−Si4 20.1(1), Si2−Si3−Si4−Si5 9.2(1), Si3−Si4−Si5−Si1
35.1(1), Si4−Si5−Si1−Si2 47.0(1), Si5−Si1−Si2−Si3 40.7(1).
5
q =
z 2
∑
i
i=1
zi = perpendicular out‐of‐plane deviations of atom i
from a least‐squres plane through the ring
(3)
Values for q for 3 and 4 are summarized in Table 1, together
with literature data for Si5Br10 and Si5I10. Because of the
presence of the sterically demanding aromatic side groups, 3
and 4 are significantly more puckered than Si5Br10 and Si5I10.
The molecular structures of 3 and 4 as determined by single-
crystal X-ray crystallography are depicted in Figures 2 and 3
together with selected bond lengths and angles.
The average Si−Si bond distances of ∼2.36 Å within the Si5
rings of 3 and 4 are close to the values reported for Si5Br10
(2.35 Å), Si5I10 (2.36 Å),22 and Si6Cl12 (2.34 Å).23 The Si−Cl
bond lengths within the SiCl2 units are ∼2.05 Å, while the Si1−
Cl1 bond is significantly elongated to 2.12 Å in 3 and to ∼2.08
Å in 4. The cyclopentasilane rings adopt conformations close to
the envelope form with dihedral angles ∠Si2−Si3−Si4−Si5 of
5.4° for 3 and 9.2° for 4. Intermediate conformations closer to
the envelope than the twist form have been observed earlier for
the cyclopentasilanes Si5Br10 and Si5I10. The conformations of
five-membered rings are frequently described in terms of a
puckering amplitude q (eq 3):
Table 1. Summary of Five-Membered-Ring Parameters for
Halocyclopentasilanes
22
22
3
4
Si5Br10
Si5I10
a
zi
Si1
Si2
Si3
Si4
Si5
0.478
−0.339
0.183
0.446
−0.294
0.049
0.065
−0.249
0.346
0.064
−0.249
0.348
0.093
0.212
−0.300
0.138
−0.300
0.137
−0.415
0.747
−0.413
0.709
a
q
0.543
0.544
a
For definitions of zi and q, see eq 3.
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synthesized as previously reported. 1H (299.95 MHz) and 29Si
(59.59 MHz) NMR spectra were recorded on a Varian INOVA 300
spectrometer in a C6D6 solution and referenced versus tetramethylsi-
lane (TMS) using the internal 2H-lock signal of the solvent. MS
spectra were run either on a HP 5971/A/5890-II GC/MS coupling
[HP 1 capillary column, length 25 m, diameter 0.2 mm, 0.33 μm
poly(dimethylsiloxane)] or on a Kratos Profile mass spectrometer
equipped with a solid probe inlet. Melting points were determined
using a Buechi 535 apparatus and are uncorrected. Elemental analyses
were carried out on a Hanau Vario Elementar EL apparatus.
Reaction of Si5H10 with SnCl4 (1:1). A total of 2.84 g (10.9
mmol) of SnCl4 dissolved in 40 mL of pentane was slowly added to a
solution of 1.64 g (10.9 mmol) of Si5H10 in 40 mL of pentane at −30
°C. After stirring at room temperature overnight and removal of the
white precipitate, the resulting solution was cooled to −70 °C and 6.8
mL of a 1.6 M solution of n-BuLi (10.9 mmol) in hexane was added.
After stirring for an additional 1 h at room temperature, the resulting
mixture was cooled to −30 °C and hydrolyzed with 20 mL of
deoxygenated 10% H2SO4. Drying over Na2SO4 and removal of the
solvents in vacuo afforded 1.3 g of a clear and colorless liquid
containing n-BuSi5H9 and n-Bu2Si5H8 in a approximate molar ratio of
2:1 along with minor amounts of n-Bu3Si5H7 and residual Si5H10
according to GC/MS analysis.
CONCLUSION
■
In conclusion, we have successfully demonstrated that the
perhydropentasilanes (H3Si)4Si and Si5H10 can be chloro-
functionalized without destruction of the Si−Si backbone. The
selectivity of higher silicon hydrides in the chlorination reaction
with SnCl4 has been shown to be strongly dependent on the
molecular structure of the hydrosilane substrate and on the
stoichiometric ratio of the reactants. Thus, tetrachloroneopen-
tasilane 2 could be prepared in high yield from (H3Si)4Si and
3.5 equiv of SnCl4, while Si5H10 and an equimolar amount of
SnCl4 afforded mixtures of 1 with polychlorinated cyclo-
pentasilanes and unreacted starting material, which could not
be separated by distillation. In order to selectively mono-
functionalize Si5H10, a multistep synthetic procedure using
bulky Mes or TBDMP protective groups had to be applied.
Additional studies concerning chemical transformations involv-
ing 1 and 2 are currently in progress.
EXPERIMENTAL SECTION
■
All experiments were performed under a nitrogen atmosphere using
standard Schlenk techniques. Solvents were dried using a column
solvent purification system.24 SnCl4 (99%) and n-BuLi (1.6 M in
hexane) were used as purchased. Solid LiAlH4 was dissolved in diethyl
ether and filtered prior to use, and anhydrous HCl (99.8%) was passed
through AlCl3 to remove traces of moisture. Si5H10,9a Si5Cl10,25
Si(SiH3)4,4a ether-free PhLi,26 MesLi,27 and TBDMPLi28 were
n-BuSi5H9. MS [m/e (relative intensity)]: 206 (71%, M+).
n-Bu2Si5H8. MS [m/e (relative intensity)]: 262 (80%, M+).
n-Bu3Si5H7. MS [m/e (relative intensity)]: 318 (88%, M+).
Reaction of Si5H10 with SnCl4 (1:5). A total of 7.35 g (28.2
mmol) of SnCl4 dissolved in 50 mL of pentane was slowly added to a
solution of 0.84 g (5.6 mmol) of Si5H10 in 50 mL of pentane at −30
°C. After stirring at room temperature for 160 h, the resulting mixture
was filtered and concentrated in vacuo. The coupled 29Si NMR
spectrum of the resulting sticky residue was consistent with the
formation of an approximately 1:1 mixture of Si5Cl10 and Si5Cl9H.
29Si NMR (C6D6, TMS, ppm): −2.7 (s, Si5Cl10, SiCl2),14 1.1 (d,
Table 2. Crystallographic Data and Structure Refinement for
2−4
2
3
4
2
3JSi−H = 8.2 Hz, Si5Cl9H, SiCl2), −3.0 (d, JSi−H = 7.3 Hz, Si5Cl9H,
empirical formula Cl4H8Si5
C9H11Cl9Si5
578.68
C12H17Cl9Si5
620.76
SiCl2), −27.9 (d, JSi−H = 248.5 Hz, Si5Cl9H, SiClH).15
1
fw
290.31
tetragonal, I4
Reaction of Si(SiH3)4 with SnCl4 (1:1). A total of 3.40 g (13.2
mmol) of SnCl4 was added via a syringe to a solution of 2.00 g (13.2
mmol) of Si(SiH3)4 in 30 mL of pentane at 0 °C. After stirring at room
temperature for 120 h, the resulting mixture was filtered and
cryst syst, space
group
monoclinic, P2(1)
/c
triclinic, P1
̅
̅
unit cell dimens
a = 9.182(3) Å
b = 9.182(3) Å
c = 7.035(2) Å
α = 90°
a = 11.8326(8) Å
b = 22.1445(2) Å
c = 8.6689(6) Å
α = 90°
β = 92.067(2)°
γ = 90°
a = 9.2711(3) Å
b = 11.4701(4) Å
c = 13.3919(5) Å
α = 66.415(1)°
β = 84.353(1)°
γ = 84.666(1)°
1296.56(8)
1
concentrated in vacuo. H and 29Si NMR data of the resulting liquid
residue were consistent with the formation of (H3Si)3SiSiH2Cl,
(H3Si)2Si(SiH2Cl)2, H3SiSi(SiH2Cl)3, and (ClH2Si)4Si along with
unreacted Si(SiH3)4.
β = 90°
29Si NMR (INEPT dec, C6D6, TMS, ppm): 18.7, −21.0, −23.1,
−25.1 (SiH2Cl), −90.3, −93.5, −96.5, −99.3 (SiH3). 1H NMR (C6D6,
TMS, ppm): 5.61, 5.56, 5.51, 5.47 (s, SiH2Cl), 4.03, 3.99, 3.96, 3.94 (s,
SiH3).
γ = 90°
593.1(3)
volume [Å3]
2270.0(3)
Z, calcd density [ 2, 1.626
4, 1.693
2, 1.590
g·cm−3
]
abs coeff [mm−1
]
1.439
292
1.368
1152
1.203
624
Synthesis of Tetrachloroneopentasilane (2). A total of 7.50 g
(28.8 mmol) of SnCl4 was added via a syringe to a solution of 2.20 g
(14.4 mmol) of Si(SiH3)4 in 30 mL of pentane at 0 °C. After stirring at
room temperature for 12 h, another 5.60 g (21.6 mmol) of SnCl4 was
added, and the resulting mixture was stirred for 48 h. Subsequent
filtration and concentration in vacuo afforded a colorless liquid residue
containing residual pentane, 2, and minor amounts of byproduct
F(000)
cryst size [mm]
θ range [deg]
limiting indices
1.34 × 0.25 × 0.25 0.60 × 0.41 × 0.32 0.64 × 0.59 × 0.56
3.14−29.69
−12 ≤ h ≤ 11,
−12 ≤ k ≤ 12,
−9 ≤ l ≤ 8
2.52−28.00
2.677−33.338
−15 ≤ h ≤ 15, −26 −12 ≤ h ≤ 12, −14
≤ k ≤ 29, −11 ≤
l ≤ 11
≤ k ≤ 15, −18 ≤
l ≤ 18
1
according to H and 29Si NMR spectroscopy. Crystallization of the
reflns collected/
unique
793/773 [R(int) = 5473/4950 [R(int) 6869/6411 [R(int)
0.0218] = 0.0661] = 0.0273]
99.7 99.9 99.5
crude material from pentane at −70 °C gave 2.0 g (48%) of pure 2.
completeness to
Bp: 36−38 °C (0.01 mbar). Anal. Found: H, 2.70. Calcd for
θ [%]
1
Cl4H8Si5: H, 2.78. 29Si NMR (C62D6, TMS, ppm): −24.6 (t, JSi−H
=
max and min
transmn
0.698−0.656
793/0/29
1.112
0.645−0.515
5473/0/210
1.051
0.5522−0.5131
6869/0/240
1.124
1
236.9 Hz, SiH2Cl), −124.9 (m, JSi−H = 12.6 Hz, SiSi4). H NMR
(C6D6, TMS, ppm, rel intens): 4.85 (s, SiH2Cl). HRMS. Calcd for
[Cl4H6Si5]•* (M+ − 2H): m/e 285.8070. Found: m/e 285.8092.
Synthesis of Nonachloromesitylcyclopentasilane (3). A total
of 5.60 g (44.2 mmol) of ether-free mesityllithium was added to a
solution of 21.90 g (44.2 mmol) of Si5Cl10, and the resulting mixture
was stirred for 6 days at room temperature. After filtration of the salts
and concentration of the solution, 12.50 g (48%) of pure 3 could be
isolated after crystallization at −30 °C.
data/restraints/
param
GOF on F2
final R indices [I R1 = 0.0182, wR2 R1 = 0.0282, wR2 R1 = 0.0224, wR2
> 2σ(I)]
= 0.0407
= 0.0799
= 0.0568
R indices (all
data)
R1 = 0.0192, wR2 R1 = 0.0319, wR2 R1 = 0.0249, wR2
= 0.0411
= 0.0815
= 0.0584
largest diff peak
0.287 and −0.222 0.672 and −0.483
0.641 and −0.279
and hole
Mp: 55−58 °C. Anal. Found: C, 18.16; H, 1.81. Calcd for
[e·A−3
]
C9H11Cl9Si5: C, 18.68; H, 1.92. 29Si NMR (C6D6, TMS, ppm): 3.3 (s,
6177
dx.doi.org/10.1021/ic300214y | Inorg. Chem. 2012, 51, 6173−6179

Inorganic Chemistry
Article
SiCl2), 2.0 (s, SiCl2), −17.9 (s, MesSiCl). 1H NMR (C6D6, TMS, ppm,
rel intens): 6.53 (s, 2 H, CH aromatic), 2.48 (s, 6 H, o-CH3), 1.95 (s, 3
H, p-CH3). MS [m/e (relative intensity)]: decomposes prior to
evaporation.
Synthesis of (4-tert-Butyl-2,6-dimethylphenyl)-
nonachlorocyclopentasilane (4). 4 was synthesized according to
the procedure followed for compound 3 with 4.22 g (25.1 mmol) of
ether-free 4-tert-butyl-2,6-dimethylphenyllithium and 12.40 g of Si5Cl10
(25.1 mmol). Yield: 17.70 g (49%).
Mp: 124−28 °C. Anal. Found: C, 23.68; H, 2.73. Calcd for
C12H17Cl9Si5: C, 23.22; H, 2.76. 29Si NMR (C6D6, TMS, ppm): 3.2 (s,
SiCl2), 2.0 (s, SiCl2), −18.0 (s, arylSiCl). 1H NMR (C6D6, TMS, ppm,
rel intens): 6.85 (s, 2 H, CH aromatic), 2.49 (s, 6 H, o-CH3), 1.14 (s, 9
H, C(CH3)3). MS [m/e (relative intensity)]: decomposes prior to
evaporation.
Mo Kα (λ = 0.71073 Å) radiation. Crystals of 2 were grown in situ on
the same diffractometer by using the OHCD29 setup equipped with a
CO2 laser (λ = 10640 nm) in combination with an Oxford cryostream
cooling system set to a temperature of 150 K.
Data were integrated with SAINT,30 and empirical methods as
implemented in SADABS31 were used to correct for absorption effects.
Structures were solved with direct methods using SHELXS-97.
SHELXL-97 was used for refinement against all data by full-matrix
least-squares methods on F2.32 All non-H atoms were refined with
anisotropic displacement parameters. H atoms of compounds 3 and 4
were refined isotropically on calculated positions using the riding
model implemented in SHELXL-97. H atoms attached to Si in
compound 2 were located at the Fourier difference map and refined
without constraints. The X-ray diffraction crystallographic data are
summarized in Table 2. The files CCDC 863713 (2), 863714 (3), and
863715 (4) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.ac.
uk/conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax +44
1223 336033; e-mail deposit@ccdc.cam.ac.uk).
Synthesis of Nonachlorophenylcyclopentasilane (5). Synthe-
sized according to the procedure followed for compound 3 with 5.54 g
of ether-free PhLi (66 mmol) and 24.24 g of Si5Cl10 (49 mmol). After
removal of the solvent, 24.50 g of a slightly yellow oil was obtained
containing 5 and unreacted Si5Cl10 from which pure 5 could not be
separated.
29Si NMR (dec, C6D6, TMS, ppm): −2.7 (Si5Cl10, SiCl2),14 2.0,
−1.0 (Si5Cl9Ph, SiCl2), −18.1 (Si5Cl9Ph, SiClPh).
ASSOCIATED CONTENT
* Supporting Information
X-ray crystallographic data of 2−4 in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
■
S
Synthesis of Mesitylcyclopentasilane (6). A total of 27.6 mL of
a 2.3 M solution of LiAlH4 (64.0 mmol) in diethyl ether was slowly
added to a solution of 12.40 g (21.4 mmol) of 3 in 200 mL of pentane
at 0 °C. After the resulting mixture was stirred overnight at room
temperature and aqueous workup with 100 mL of deoxygenated 10%
H2SO4, drying over Na2SO4, and removal of the solvents and volatile
components in vacuo (0.05 mbar, 25 °C), 5.30 g (91%) of
spectroscopically pure 6 was obtained as a colorless and slightly
viscous liquid that decomposed during distillation at 0.05 mbar and 70
°C.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: harald.stueger@tugraz.at. Tel: +43 316 87332111.
Fax: +43 316 87332102.
Notes
Bp: 70 °C dec (0.05 mbar). Anal. Found: C, 40.58; H, 7.60. Calcd
The authors declare no competing financial interest.
for C9H20Si5: C, 40.23; H, 7.50. 29Si NMR (C6D6, TMS, ppm): −82.1
1
1
(d, JSi−H = 185.6 Hz, MesSiH), −102,2 (t, JSi−H = 194.0 Hz, SiH2),
REFERENCES
1
1
■
−106.8 (t, JSi−H = 194.7 Hz, SiH2). H NMR (C6D6, TMS, ppm, rel
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(m, 8 H, SiH2), 2.33 (s, 6 H, o-CH3), 2.08 (s, 3 H, p-CH3). MS [m/e
(relative intensity)]: 268 (40%, M+).
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