Synthesis of Wiberg's tetrasilatetrahedrane (tBu3Si) 4Si4 by a one-pot procedure

Article abstract of DOI:10.1021/om900763y

A one-pot synthesis of the tetrasilatetrahedrane (tBu₃Si) ₄Si₄ was achieved by the reaction of HSiCl₃ and Na[SitBu₃]. In this reaction the silane tBu₃SiH was obtained along with (tBu_3<

Full text of DOI:10.1021/om900763y

Organometallics 2009, 28, 6835–6837 6835
DOI: 10.1021/om900763y
Synthesis of Wiberg’s Tetrasilatetrahedrane (tBu3Si)4Si4 by a One-Pot
Procedure
€
€
Frank Meyer-Wegner, Stefan Scholz, Inge Sanger, Frauke Schodel, Michael Bolte,
Matthias Wagner, and Hans-Wolfram Lerner*
€
Institut fu€r Anorganische Chemie, Goethe-Universitat Frankfurt am Main, Max-von-Laue-Strasse 7, 60438
Frankfurt am Main, Germany
Received September 1, 2009
Summary: A one-pot synthesis of the tetrasilatetrahedrane
(tBu3Si)4Si4 was achieved by the reaction of HSiCl3 and
Na[SitBu3]. In this reaction the silane tBu3SiH was obtained
along with (tBu3Si)4Si4 and tBu3SiSitBu3. The tetrasilatetra-
hedrane (tBu3Si)4Si4 was also obtained via a one-pot approach
by treatment of Cl3SiSiCl3 or Cl3SiSiCl2SiCl3 with Na-
[SitBu3]. In the reaction of HSiCl3 with Na[SitBu3], two
molecules of the tetrasilatetrahedrane (tBu3Si)4Si4 crystallize
together with one molecule of tBu3SiSitBu3 and one molecule
of benzene. Single crystals suitable for X-ray diffraction
composed of one molecule of (tBu3Si)4Si4 and two molecules
of benzene were obtained by recrystallization from benzene.
The only known examples with tetrasilatetrahedrane struc-
tures, (tBu3Si)4Si4 (1)8 and (Dis2MeSi)4Si4 (Dis=CH(SiMe3)2)
(2),9 were reported in 1993 by Wiberg et al. and 10 years later in
2003 by Sekiguchi and co-workers.
While tetrasilatetrahedrane 1 is stable toward water, air,
light, and temperature (decomposition >300 °C), it seems to
be sensitive toward oxidizing agents. It was found that,
when using equimolar equivalents of reactants, treatment
of 1 with iodine yields quantitatively the cyclotetrasilene 3
(Scheme 1).10 No reaction could be observed between 1 and
M[SitBu3] (M=Li, Na, K).11 However, 2 can be reduced with
KC8 in Et2O, which results in the selective cleavage of the
exocyclic Si-Si bond without degradation of the tetrahe-
drane core, as shown in Scheme 1.9
The tetrasilatetrahedrane 1 was prepared by Wiberg and
co-workers in a six-step sequence, and its structure was
determined by X-ray diffraction.8,12 We present here a one-
pot synthesis of the tetrasilatetrahedrane 1 by the reaction of
HSiCl3 with Na[SitBu3]. In addition, Na[SitBu3] also reacts
with Cl3SiSiCl3 and Cl3SiSiCl2SiCl3, respectively, which give
1 in a one-pot procedure.
Introduction
In 1978, Maier and co-workers reported the first synthesis
and determination of the molecular structure of tetra(tert-
butyl)tetrahedrane, which is a very strained cage compound
with a highly symmetrical structure and unusual bonding
nature.1 Since 1988, the chemistry of stable, small-cage
compounds consisting of the heavier group 14 elements
(Si, Ge, and Sn) has been extensively studied. It has been
shown that compounds RnEn with tetrahedral (A), trigonal-
prismatic (B), or cubic polyhedra En (C) of carbon homo-
logues E are accessible only by using sterically demanding
groups R (Chart 1).2,3 Evidently, less sterically demanding
substituents do not prevent transformation of the core into
less strained compounds.4,5 Substances with polyhedral
structure of type A, B, and C have been synthesized for
E=Si and Ge,2,3 whereas for E=Sn only those of type B6 and
C7 but not of type A are known.
Results and Discussion
Surprisingly, the reaction of 1 molar equiv of Na[SitBu3]
with one of HSiCl3, as shown in Scheme 2, is quite different
from the reactions of tri-tert-butylsilanides M[SitBu3] (M=Li, Na,
11,13
K) with organyl-substituted chlorosilanes RnSiCl4-n
.
Treatment of HSiCl3 with Na[SitBu3] in 1:1 molar ratio in
benzene resulted in an immediate reaction, and the mixture
quickly became heterogeneous.14 The 29Si NMR spectrum
showed that the silanide had been completely consumed, and
new signals appeared that could be assigned to the tetra-
silatetrahedrane 1, the disilane tBu3SiSitBu3, and the silane
tBu3SiH. The formation of these products suggested to us the
mechanism, as shown in Scheme 2: (i) First Na[SitBu3]
deprotonates HSiCl3. (ii) Then, in a second step, transient
*Corresponding author. Fax: þ49-69798-29260. E-mail: lerner@
chemie.uni-frankfurt.de.
(1) Maier, G. Angew. Chem., Int. Ed. 1988, 27, 309.
(2) Wiberg, N.; Power, P. P. Molecular Clusters of Main Group
€
Elements; Driess, M., Noth, H., Eds.; Wiley-VCH: Weinheim, 2004; p 188.
(3) Sekiguchi, A.; Nagase, S. The Chemistry of Organic Silicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; John Wiley & Sons Ltd.:
New York, 1998; Vol. 2, p 119.
(4) Nagase, S. Angew. Chem., Int. Ed. 1989, 28, 329.
(5) Nagase, S. Polyhedron 1991, 10, 1299.
€
(6) Wiberg, N.; Lerner, H.-W.; Noth, H.; Ponikwar, W. Angew.
€
(10) Wiberg, N.; Auer, H.; Noth, H.; Knizek, J.; Polborn, K. Angew.
Chem., Int. Ed. 1998, 37, 2869.
(11) Lerner, H.-W. Coord. Chem. Rev. 2005, 249, 781. Wiberg, N.;
€
Amelunxen, K.; Lerner, H.-W.; Schuster, H.; Noth, H.; Krossing, I.; Schmidt-
Amelunxen, M.; Seifert, T. J. Organomet. Chem. 1997, 542, 1. Lerner,
€
€
Chem., Int. Ed. 1999, 38, 1103.
H.-W.; I. Sanger, I.; Schodel, F.; Polborn, K.; Bolte, M.; Wagner, M. Z.
Naturforsch. 2007, 62b, 1285.
(12) Wiberg, N.; Finger, C. M. M.; Auer, H.; Polborn, K. J. Orga-
(7) Sita, L. R.; Kinoshita, I. Organometallics 1990, 9, 2865. Wiberg,
€
N.; Lerner, H.-W.; Wagner, S.; Noth, H.; Seifert, T. Z. Naturforsch. 1999,
54b, 877.
nomet. Chem. 1996, 521, 377.
(8) Wiberg, N.; Finger, C. M. M.; Polborn, K. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1054.
(9) Ichinohe, M.; Toyoshima, M.; Kinjo, R.; Sekiguchi, A. J. Am.
Chem. Soc. 2003, 125, 13328.
(13) Wiberg, N. Coord. Chem. Rev. 1997, 163, 217.
(14) Reaction of HSiCl3 with K[Si(SiMe3)3] gives the cyclotrisilane
[(Me3Si)2Si]3 : Klinkhammer, K. W. Thesis, University of Stuttgart,
Germany, 1998.
r
2009 American Chemical Society
Published on Web 10/23/2009
pubs.acs.org/Organometallics

6836 Organometallics, Vol. 28, No. 23, 2009
Meyer-Wegner et al.
Chart 1. Polyhedral Structures of Carbon Homologues
Scheme 2. Synthesis of Tetrasilatetrahedrane 1 from HSiCl3 and
Na[SitBu3]
Scheme 1. Chemical Properties of Tetrasilatetrahedranes
1 and 2
Scheme 3. Synthesis of Tetrasilatetrahedrane 1 from Reactions
of Na[SitBu3] with Cl3SiSiCl3 and Cl3SiSiCl2SiCl3
NaSiCl3 undergoes NaCl elimination to form dichlorosily-
lene SiCl2. (iii) Reaction of SiCl2 with Na[SitBu3] and
dimerization of the (tBu3Si)SiCl thus formed gives the dis-
ilene (tBu3Si)ClSidSiCl(SitBu3). (iv) Dehalogenation15 of
the disilene by reaction with Na[SitBu3] finally gives the
tetrasilatetrahedrane 1, the disilane tBu3SiSitBu3, and NaCl.
It is interesting to note that the cluster buildup takes place in
the presence of unreacted HSiCl3. Therefore deprotonation
of HSiCl3 must be much slower than cluster formation with
Na[SitBu3]. Filtration and slow concentration of the filtrate
resulted in deposition of X-ray quality crystals that con-
tained two molecules of 1, one molecule of tBu3SiSitBu3, and
one molecule of benzene.16 The tetrasilatetrahedrane 1 could
be separated from tBu3SiSitBu3 by HPLC or by its precipita-
tion when acetonitrile was added to a tBuOMe solution of 1
and tBu3SiSitBu3.
liberation of SiCl2 had taken place. The dichlorosilylene SiCl2
that had been formed apparently underwent an insertion
reaction into Cl3SiSiCl2SiCl3 to give perchlorinated neopenta-
silane Si(SiCl3)4. We had verified that the degradation
of Cl3SiSiCl2SiCl3 in the presence of catalytic amounts of
donors, such as amines, in the first step gives dichlorosilylene
SiCl2 and hexachlordisilane Cl3SiSiCl3 and ultimately
produces Si(SiCl3)4.19
Reaction of nucleophilic reagents with chlorine-substi-
tuted polysilanes has received renewed interest in recent
years. We have investigated the reaction of Cl3SiSiCl3 with
Na[SitBu3]. When Cl3SiSiCl3 in benzene was treated with 2
molar equiv of Na[SitBu3], the reaction mixture underwent a
color change to orange-yellow. Three products were formed:
the tetrasilatetrahedrane 1, the disilane tBu3SiSitBu3, and
the chlorosilane tBu3SiCl, as shown in Scheme 3. Due to
hydrolysis11 and oxidation17 of Na[SitBu3], small amounts of
tBu3SiH and Na[OSitBu3] also were formed. Tetrasilatetra-
hedrane 1 could be separated from tBu3SiSitBu3 by multiple
recrystallization. Single crystals composed of one molecule
of 1 and two molecules of benzene were isolated by recrys-
tallization from benzene.18
The trisilane Cl3SiSiCl2SiCl3 reacts with 4 molar equiv of
Na[SitBu3], surprisingly forming the same products that had
been formed in the 1:1 HSiCl3/Na[SitBu3] reaction. After 1 h,
the trisilane had been completely consumed, as determined
by 29Si NMR spectroscopy. In the 29Si NMR spectrum of the
reaction mixture resonances due to the tetrasilatetrahedrane
1, the disilane tBu3SiSitBu3, the chlorosilane tBu3SiCl, and
hexachlordisilane Cl3SiSiCl3 as well as polychlorosilanes
such as the neopentasilane Si(SiCl3)4 were observed. Ob-
viously, a degradation reaction of Cl3SiSiCl2SiCl3 with
Experimental Section
General Procedures. All experiments were carried out under
dry nitrogen or argon with strict exclusion of air and moisture
using standard Schlenk techniques or a glovebox. Na[SitBu3]11
was prepared according to a literature procedure. Benzene was
distilled from sodium/benzophenone prior to use.
The NMR spectra were recorded on a Bruker AM 250, a
Bruker DPX 250, a Bruker Avance 300, and a Bruker Avance
400 spectrometer.
Synthesis of 1 from HSiCl3 and Na[SitBu3]. To a solution of
HSiCl3 (195 mg, 1.44 mmol) in 5 mL of benzene was added a
solution of Na[SitBu3] (320 mg, 1.40 mmol) in 5 mL of benzene.
The resulting orange-yellow solution quickly became cloudy.
After 1 h, the 29Si NMR spectrum showed that the silanide
Na[SitBu3] had been completely consumed, and new signals
appeared that could be assigned to the tetrasilatetrahedrane 1
(δ 52.7, δ 243.7; 6.2%20), the disilane tBu3SiSitBu3 (δ 35.0;
13.8%20), the silane tBu3SiH (δ 17.2, 10.8%20), and the remain-
ing HSiCl3 (δ -6.2, 69.4%20). Due to interference of the signals
of the tetrasilatetrahedrane 1 and the disilane tBu3SiSitBu3 in
the 1H NMR spectrum (δ 1.36), the progress of the reaction was
monitored by 29Si NMR spectroscopy. After the reaction
mixture had been filtered and the filtrate had been left to stand
at ambient temperature for one day, X-ray quality crystals that
consist of two molecules of 1, one molecule of tBu3SiSitBu3, and
(15) Dehalogenation of (tBu3Si)BrSidSiBr(SitBu3) with Na[SitBu3]
results in the formation of the tetrasilatetrahedrane 1; see ref 12.
(16) Structural details: CCDC 744853.
(17) Lerner, H.-W.; Scholz, S.; Bolte, M. Organometallics 2002, 21,
3827.
(18) Structural details: CCDC 744852.
(19) Donor-induced degradation of Cl3SiSiCl2SiCl3 leads to forma-
tion of Si(SiCl3)4, and in the presence of the silylene trapping agents 2,3-
dimethyl-1,3-butadiene gives the [4þ1] cycloadduct (δ(29Si) 36.1):
€
Meyer-Wegner, F.; Nadj, A.; Tullmann, S.; Bolte, M.; Holthausen,
M. C.; Wagner, M.; Lerner, H.-W. Unpublished results.
(20) Integral ratio of the signals in the 29Si NMR spectrum.

Note
Organometallics, Vol. 28, No. 23, 2009 6837
one molecule of benzene could be obtained from the filtrate.16
These crystals were dissolved with tBuOMe (10 mL). After
treatment of the solution with acetonitile (6 mL) pure 1 was
precipitated from this solution. Pure 1 could also be obtained by
HPLC carried out on normal stationary phase (Nucleosil, 5 μm,
tBu3SiSitBu3 was achieved by multiple recrystallizations. Single
crystals of the composition of one molecule of 1 and two
molecules of benzene were isolated by recrystallization from
benzene.18 Yield: 31 mg (26%). For selected data for 1 see above.
Synthesis of 1 from Cl3SiSiCl2SiCl3 and Na[SitBu3]. A solu-
tion of Cl3SiSiCl2SiCl3 (124 mg, 0.34 mmol) and Na[SitBu3] (284mg,
1.28 mmol) in 10 mL of benzene in 1:4 molar stoichiometry was
stirred for one day at ambient temperature. The 29Si NMR
spectrum of the reaction solution showed resonances due to the
tetrasilatetrahedrane 1 (δ 52.7, δ -243.7; 8.2%20), the disilane
tBu3SiSitBu3 (δ 35.0; 38.9%20), the chlorosilane tBu3SiCl (δ
33.5; 13.2%20), the hexachlorodisilane Cl3SiSiCl3 (δ -6.5;
38.1%20), the perchloroneopentasilane Si(SiCl3)4 (δ 3.5, δ
-82.0; 7.3%20), and other chlorine-substituted polysilanes
(2.3%20) ((Cl3Si)3SiSiCl2SiCl3 (δ 5.9, 3.7, -4.1, -80.5) and
(Cl3Si)3SiCl (δ -0.3, -32.2)). After filtering, single crystals
composed of two molecules of 1, one molecule of tBu3SiSitBu3,
and one molecule of benzene were isolated. Yield: 37 mg (31%).
For selected data for 1 see above.
1
250 ꢀ 20 mm; eluent heptane). Yield: 44 mg (48%). H NMR
(250.1 MHz, C6D6): δ 1.36 (s, 54H, tBu). 13C NMR (62.9 MHz,
C6D6): δ 25.3 (CCH3), 31.7 (CCH3). 29Si NMR (79.5 MHz,
C6D6): δ 52.7 (SitBu3), -243.7 (Si-SitBu3). The spectroscopic
data are in agreement with those reported in ref 12.
Synthesis of 1 from Cl3SiSiCl3 and Na[SitBu3]. A mixture of
Cl3SiSiCl3 (315 mg, 1.14 mmol), Na[SitBu3] (596 mg, 2.68 mmol),
and 10 mL of benzene was stirred for 2 h at ambient tempera-
ture. After 2 h, we observed in the 29Si NMR spectrum of
the reaction solution the resonances that could be assigned to
the tetrasilatetrahedrane 1 (δ 52.7, δ -243.7; 5.6%20), the
disilane tBu3SiSitBu3 (δ 35.0; 20.6%20), the chlorosilane tBu3-
SiCl (δ 33.5; 6.8%20), Cl3SiSiCl3 (δ -6.5; 62.5%20), and other
Si-containing compounds (tBu3SiH, Na[OSitBu3], etc.
(4.5%20)). After filtration, cocrystals composed of two mole-
cules of 1, one molecule of tBu3SiSitBu3, and one molecule of
benzene were grown from the filtrate at ambient temperature.
Purification of the tetrasilatetrahedrane 1 and separation from
Acknowledgment. We are grateful to the University of
Frankfurt for financial funding and the Chemetall GmbH
for a gift of tert-butyllithium.