Syntheses of functionalized oligosilanes

Article abstract of DOI:10.1007/s00706-006-0463-7

A number of differently substituted isotetra- and isoheptasilanes were synthesized. Springer-Verlag 2006.

Full text of DOI:10.1007/s00706-006-0463-7

Monatshefte f€ur Chemie 137, 613–625 (2006)
DOI 10.1007/s00706-006-0463-7
Syntheses of Functionalized Oligosilanes#
Roland Fischer1, Judith Baumgartner1, Guido Kickelbick2,
Karl Hassler1;ꢀ, and Christoph Marschner1;ꢀ
1
Institute of Inorganic Chemistry, University of Technology, 8010 Graz, Austria
2
Institute of Materials Chemistry, Vienna University of Technology, 1060 Vienna, Austria
Received December 2, 2005; accepted February 6, 2006
Published online April 28, 2006 # Springer-Verlag 2006
Summary. A number of differently substituted isotetra- and isoheptasilanes were synthesized.
Keywords. Silicon; Isotetrasilanes; Crystal Structure.
Introduction
The chemistry of exactly defined molecular structures with oligosilane backbones
has experienced an enormous development within the last few years. This is in part
a result of the development of methods facilitating the introduction of multiple
functional groups under conditions preserving silicon–silicon bonds. In the current
account we would like to disclose the syntheses of a number of key intermediates
for the building of extended structures like cage molecules and polysilane dendri-
mers [1]. These can be obtained starting from isotetra- and=or isoheptasilanes,
which bear functional groups either in a reactive form like halides or masked like
phenyl groups, which allow the easy conversion into leaving groups. Recent studies
from our laboratory showed that even the trimethylsilyl group can be considered
as a masked functional group which can be easily substituted by potassium with
potassium tert-butoxide [2].
The reactions which can be used for synthesis and manipulation of these mole-
cules can be categorised into Si–Si bond forming reactions and functional group
generating or manipulating reactions. The most frequently used method to obtain
polysilanes is the Wurtz type coupling. Disadvantages of this reaction are the
relatively harsh reaction conditions (alkali metals) and an intrinsic restriction to
symmetric products. However, for the synthesis of larger quantities of starting ma-
terials this is often the method of choice. An attractive alternative is the salt
elimination reaction between a silylanion and a silyl electrophile (usually either
ꢀ
Corresponding authors. E-mail: christoph.marschner@tugraz.at, karl.hassler@tugraz.at
Dedicated to Prof. Ulrich Schubert (TU Wien) on the occasion of his 60th birthday
#

614
R. Fischer et al.
halide or triflate). The additional flexibility provided by this reaction is gained at
the expense of the separate generation of nucleophiles and electrophiles. A few
other synthetic methods for the formation of polysilanes comprise transition metal
catalysis of hydrosilanes [3] and coupling of silyl radicals [4].
The second important class of reactions deals with the conversion of the
products of the just mentioned building reactions. Introduction of halides or tri-
flates can be accomplished most easily either via protodesilylation reaction of a
phenylsilane or by halogenation of a hydrosilane with CX4, CX3H, or phosphorus
pentahalides. For the generation of silylanions also a number of different methods
are known, the most convenient, however, is still cleavage of disilanes with
lithium.
Results and Discussion
For our purposes we frequently use methylated isotetrasilanes as starting materials.
Tris(trimethylsilyl)methylsilane (1), which is the parent compound of this struc-
tural type, can easily be obtained for example by Wurtz type reaction of trichloro-
methylsilane with three equivalents of chlorotrimethylsilane in the presence of
alkali metals [5]. In order to functionalize the trimethylsilyl groups AlCl3 catalyzed
reaction with hydrogen chloride, acetyl chloride, or trimethylchlorosilane is
required (2a) [6]. However, this can be a very capricious reaction, which frequently
requires long reaction times.
Phenylation of 2a with phenyllithium gives a mixture of the mono-, double-,
and triple phenylated products 3, 4, and 5. As they can not be separated easily by
crystallisation or distillation, the reaction mixture was subjected to reduction with
lithium aluminum hydride which results in a mixture of 5 and hydrosilanes 6 and 7
which can be separated by distillation. Pure 3 and 4 then can be obtained by
reaction of 7 and 6 with PCl5.

Syntheses of Functionalized Oligosilanes
615
Because of the above mentioned difficulties, the introduction of phenyl groups
into the isotetrasilane early on is an attractive strategy. The Wurtz type reaction to
the corresponding isotetrasilane 5 with three dimethylphenylsilyl groups, however,
often does not give clean reactions as frequently partial silylation of phenyl groups
[7] occurs. Sometimes it is even accompanied by the formation of neopentasilane 8
[8]. Whereas these problems can be avoided for the preparation of 5 by a salt
elimination reaction between three equivalents of dimethylphenylsilyllithium and
trichloromethylsilane the analogous reaction of tetrachlorosilane with four equiva-
lents of dimethylphenylsilyllithium gives 8 only in poor yield [8]. The obtained
isotetrasilane 5 can be converted easily into the respective trichloride 2a by reac-
tion with trifluoromethanesulphonic acid [9] and subsequent treatment with LiCl.
Alternatively, reaction of 5 in neat HBr at ꢁ70ꢂC leads to the respective tribromide
2b [11]. Both trihalides can be reduced to the corresponding trihydrosilane 9 [8,
11] using lithium aluminum hydride.
The just outlined procedure can also be applied for the introduction of
difunctional silyl groups. Reaction between three equivalents of methyldiphenyl-
silyllithium and trichloromethylsilane in this case leads to the formation of
tris(methyldiphenylsilyl)methylsilane (10) [10]. This compound can be converted
either to the hexabromide 11 [11] employing reaction with HBr or to the half-
functionalised 12 by addition of three equivalents of trifluoromethanesulfonic acid.
Compound 12 is obtained as a mixture of two diastereomers [12]. Compounds 11
and 12 again can be converted to the respective hydroisotetrasilanes 13 and 14 by
reaction with lithium aluminum hydride.
The so far described chemistry provides access to isotetrasilane units with
either one or two reactive residues on the terminal silyl groups as well as the
possibility to activate only one or two silyl groups. In the following section it will

616
R. Fischer et al.
be shown that these compounds can be used to produce more extended polysilanes
in a selective way. For example, reaction of two equivalents 4 with Li leads to the
formation of tetraphenyloctasilane 15 [13]. The respective tetrachlorooctasilane 16
can be obtained by the above mentioned treatment with trifluoromethanesulfonic
acid and LiCl.
Reaction of the trihalides 2a or 2b with three equivalents of methyldiphenyl-
silyllithium leads to the formation of isoheptasilane 17. Again this very stable
compound can be activated by treatment at low temperature with neat HBr to
give the hexabromide 18, which subsequently can be reduced to the hexahydro-
silane 19.
The same reaction sequence starting from trichloride 2a can also be carried out
using tert-butyldiphenylsilylpotassium as the silylation reagent in the first step
leading to structurally similar compounds 20 and 21.
X-Ray Crystallography
Compounds 5, 8, 10, 17, and 20 were subjected to single crystal X-ray diffraction
analysis. Isotetrasilane 5 (Fig. 1) appears as an almost C3 symmetric propeller

Syntheses of Functionalized Oligosilanes
617
ꢂ
˚
Fig. 1. Molecular structure of 5 with selected bond distances [A] and angles [ ] with estimated
standard deviations. Si(1)–Si(2) 2.3362(18), Si(1)–Si(4) 2.3371(19), Si(1)–Si(3) 2.3390(19),
Si(2)–Si(1)–Si(4) 110.51(7), C(1)–Si(1)–Si(3) 107.97(16), Si(2)–Si(1)–Si(3) 112.11(7), Si(4)–
Si(1)–Si(3) 111.00(7)
ꢂ
˚
Fig. 2. Molecular structure of 8 with selected bond distances [A] and angles [ ] with estimated
standard deviations: Si(2)–Si(1A) 2.3693(13), Si(2)–Si(3) 2.3718(12), Si(1A)–Si(2)–Si(1) 106.72(7),
Si(1A)–Si(2)–Si(3) 105.77(4), Si(1)–Si(2)–Si(3) 110.49(3), Si(3)–Si(2)–Si(3A) 117.22(7)

618
R. Fischer et al.
ꢂ
˚
Fig. 3. Molecular structure of 10 with selected bond distances [A] and angles [ ] with estimated standard
deviations: Si(1)–Si(3) 2.3692(9), Si(1)–Si(4) 2.3707(10), Si(1)–Si(2) 2.3712(11), Si(3)–Si(1)–Si(4)
120.35(4), C(1)–Si(1)–Si(2) 106.24(8), Si(3)–Si(1)–Si(2) 106.65(3), Si(4)–Si(1)–Si(2) 111.70(4)
shaped molecule with not much steric interaction between the three side-chains. As
a consequence Si–Si bond lengths in the molecule are relatively short (2.33–
˚
2.34 A). The angles around the central silicon atom reflect the slightly larger steric
demand of the dimethylphenylsilyl group displaying Si–Si–Si bond angles
between 110.5 and 112.1ꢂ. The corresponding neopentasilane 8 (Fig. 2) with four
dimethylphenylsilyl substituents experiences more steric strain. Si–Si bond lengths
˚
are elongated to 2.37 A, which is longer than in tetrakis(trimethylsilyl)silane
˚
(2.346(1) A) [14]. Two dimethylphenylsilyl groups are arranged in a way that
the phenyl moieties point away from the center of the molecule. This allows for
a relatively small angle of 106.7ꢂ between these groups. The remaining dimethyl-
phenylsilyl substituents accommodate the phenyl in a way closer to the central
silicon atom thus widening the bond angle to 117.2ꢂ. For compound 10 (Fig. 3)
a propeller shaped arrangement as was found for 5 does not seem to be possible for
˚
steric reasons. Si–Si bond lengths are close to 2.37 A and the tetrahedron around
Si(2) is severely distorted with fairly different Si–Si–Si angles of 106.6, 111.7, and
120.4ꢂ. Compound 17 (Fig. 4) again shows the propeller shaped arrangement. The
terminal methyldiphenylsilyl groups, however, display different spatial orienta-
˚
tions. All Si–Si bond lengths are close to 2.36 A. Si–Si–Si angles around the
central silicon atom Si(3) are ranging from 109.1 to 112.3ꢂ. In order to accom-
modate the disilanyl branches around the central silicon atom the bond angles of

Syntheses of Functionalized Oligosilanes
619
ꢂ
˚
Fig. 4. Molecular structure of 17 with selected bond distances [A] and angles [ ] with estimated
standard deviations: Si(1)–Si(2) 2.3519(10), Si(2)–Si(3) 2.3581(9), Si(3)–Si(6) 2.3576(9), Si(3)–
Si(4) 2.3661(8), Si(4)–Si(5) 2.3590(11), Si(6)–Si(7) 2.3572(8), Si(1)–Si(2)–Si(3) 117.43(4), Si(6)–
Si(3)–Si(2) 109.11(4), Si(6)–Si(3)–Si(4) 112.30(3), Si(2)–Si(3)–Si(4) 111.69(3), Si(5)–Si(4)–Si(3)
117.82(3), Si(7)–Si(6)–Si(3) 117.13(4)
the trisilanyl units are all widened to values close to 117ꢂ. For compound 20 (Fig. 5)
two independent molecules with similar structural features are found in the asym-
metric unit. Again the molecule exhibits the propeller shaped arrangement with
symmetry close to C3. As was found before for 17, the bond angles around the
central silicon atom are close to a perfect tetrahedron. The higher steric demand of
the tert-butyl groups of 20 in comparison to the methyl groups in 17 forces the
bond angles of the trisilanyl units to be widened to close to 120ꢂ. The higher steric
˚
strain also causes an elongation of the Si–Si bonds to values close to 2.38 A.
Experimental
All reactions were carried out under an atmosphere of dry Ar or N2. Solvents were dried over Na=K
alloy and distilled freshly before use. HBr was dried over P2O5. PhMe2SiLi [15], Ph2MeSiLi [16], 1,2-
di-tert-butyl-1,1,2,2-tetraphenyldisilane [17] and 2a [6] were prepared using known procedures.
1H, 13C, and 29Si NMR spectra were recorded either on a Bruker MSL 300 or on Varian INOVA
300 or 500 spectrometers. Samples for 29Si spectra were either dissolved in C6D6 or in cases of
reaction samples measured with a D2O capillary in order to provide an external lock frequency signal.
To compensate for the low isotopic abundance of 29Si the INEPT pulse sequence was used for the
amplification of the signal [18].

620
R. Fischer et al.
ꢂ
˚
Fig. 5. Molecular structure of 20 with selected bond distances [A] and angles [ ] with estimated
standard deviations (only one of two independent molecules shown): Si(1)–Si(2) 2.376(2), Si(2)–
Si(3) 2.374(2), Si(3)–Si(4) 2.376(2), Si(3)–Si(6) 2.379(2), Si(4)–Si(5) 2.385(2), Si(6)–Si(7)
2.387(2), Si(3)–Si(2)–Si(1) 122.72(9), Si(2)–Si(3)–Si(4) 109.35(9), Si(2)–Si(3)–Si(6) 109.21(9),
Si(4)–Si(3)–Si(6) 109.59(8), Si(3)–Si(4)–Si(5) 118.82(9), Si(3)–Si(6)–Si(7) 118.60(9)
IR spectra were measured with a Perkin Elmer 883 instrument. GC=MS were recorded on a HP
5890=II gas chromatograph with HP 5971=A MSD, a HP1 (cross-linked methyl silicone) column,
and He as carrier gas. High resolution mass spectra were obtained on a Kratos Profile instrument.
Elemental analyses (C, H) were carried out using a Heraeus Elementar vario EL instrument, the results
were in good agreement with the calculated values.
Tris(bromodimethylsilyl)methylsilane (2b, C7H21Br3Si4)
In a 50cm3 flask equipped with a reflux condenser cooled to ꢁ75ꢂC 5.00g 5 (11.1 mmol) were placed.
The flask was cooled to ꢁ80ꢂC and about 20 cm3 HBr were condensed onto the material. After the
condensation was complete the bath was removed and the HBr was allowed to reflux for 3 h. After
removal of all volatiles in vacuum, n-pentane was distilled onto the residue to dissolve the product. At
1
ꢁ35ꢂC 4.70g 2b (10.3 mmol, 92%) were obtained as colourless crystals. H NMR (C6D6): ꢀ ¼ 0.78
(s, 18H), 0.34 (s, 3H) ppm; 29Si NMR (toluene): ꢀ ¼ 19.7, ꢁ72.9ppm.
Bis(chlorodimethylsilyl)dimethylphenylsilylmethylsilane (3, C13H26Cl2Si4)
and Chlorodimethylsilylbis(dimethylphenylsilyl)methylsilane (4, C19H31ClSi4)
To a solution of 30.0 g 2a (92.8mmol) in 500 cm3 petrol ether, cooled to ꢁ70ꢂC, a solution of
90.0mmol phenyllithium in 300 cm3 diethyl ether (prepared from 14.1g bromobenzene and excess

Syntheses of Functionalized Oligosilanes
621
Li) was added slowly over a period of 2 h. After separation from the salts by filtration, the solvents
were removed by evaporation in vacuum and replaced by 300cm3 diethyl ether. A solution of approx.
100 mmol LiAlH4 in 200 cm3 diethyl ether was added slowly at ꢁ30ꢂC. The reaction mixture was
refluxed for a couple of hours and then added dropwise to 1000cm3 aqueous 1 N H2SO4 at 0ꢂC. The
organic phase was separated and dried (Na2SO4) overnight. Diethyl ether was then removed, and the
oily residue, which contained (HMe2Si)MeSi(SiMe2Ph)2 (6) and (HMe2Si)2MeSi(SiMe2Ph) (7) besides
some 5 was subjected to fractional distillation. Details relating to the properties of 6 and 7 are given
below.
To a solution of 5.6 g 6 (15.5 mmol) in 50cm3 petrol ether at 0ꢂC 3.2 g PCl5 (15.5 mmol) were
added, and the reaction mixture was stirred for 2 h. The solvent and PCl3 were then removed by
evaporation in vacuum and the residue was purified by fractional distillation using a short column. At
135ꢂC and 0.05mbar 4.6g 4 (72.8%) were obtained as a viscous, oily liquid which solidified slowly
upon standing. 29Si NMR: ꢀ ¼ þ30.9, ꢁ15.0, ꢁ85.9ppm.
The reaction with PCl5 was also used for the preparation of (ClMe2Si)2MeSi(SiMe2Ph) (3) in an
analogous way: 3.2 g 7 (10.8mmol) were treated with 4.5 g PCl5 (21.6mmol) and the fractional dis-
tillation gave 3.1 g 3 (78.5%) at 100–110ꢂC=0.05mbar. 29Si NMR: ꢀ ¼ þ28.9, ꢁ16.1, ꢁ78.8ppm.
Tris(dimethylphenylsilyl)methylsilane (5, C25H36Si4)
A solution of 7.00 g methyltrichlorosilane (46.9 mmol) in 120 cm3 diethylether was cooled to ꢁ70ꢂC.
Dimethylphenylsilyllithium (prepared from 25.0g dimethylphenylchlorosilane (146.5mmol) and 6.0 g
lithium powder) in 200 cm3 THF was added slowly. The reaction was allowed to warm up to room
temperature, stirred for another 12 h and poured on 2 N H2SO4=ice. The aqueous layer was extracted
several times with toluene, dried (Na2SO4), and the solvent removed in vacuum. The remaining residue
was dissolved in n-pentane and cooled to ꢁ70ꢂC whereupon crystallisation occurred and pure 12.6g
5 (60%) were obtained as colourless crystals. 1H NMR (CDCl3): ꢀ ¼ 7.31 (m, 15H), 0.23 (s, 21H) ppm;
13C NMR (CDCl3): ꢀ ¼ 140.53, 134.06, 128.63, 127.96, ꢁ1.53, ꢁ11.40 ppm; 29Si NMR (toluene):
þ
ꢀ ¼ ꢁ15.5, ꢁ86.1 ppm; EIMS: m=z (rel.int.%) ¼ 448 (5, Mþ ), 313 (12, (M-SiMe2Ph)
ꢃ
ꢃ), 236 (40,
þ
þ
ꢃ).
ꢃ
(M-SiMe2Ph2) ), 135 (100, (SiMe2Ph)
Dimethylsilylbis(dimethylphenylsilyl)methylsilane (6, C19H32Si4) and Bis(dimethylsilyl)
(dimethylphenylsilyl)methylsilane (7, C13H28Si4)
The synthesis of 6 by partial phenylation of 2a and subsequent reduction with LiAlH4 was described
above. Compounds 6 and 7 were also obtained via an alternative route by reaction of 5 with one or two
equivalents of CF3SO3H, which proceeded selectively with formation of (TfOMe2Si)MeSi(SiMe2Ph)2
and (TfOMe2Si)2MeSi(SiMe2Ph) (TfO ¼ ꢁOSO2CF3).
To a solution of 20.0 g 5 (44.6 mmol) in 100cm3 toluene, cooled to ꢁ50ꢂC either 6.7 g (44.6mmol)
or 13.4 g (89.2 mmol) CF3SO3H were added dropwise at that temperature. After complete addition, the
reaction mixtures were allowed to warm up to room temperature and stirred for 2 h. They were then
again cooled down to ꢁ30ꢂC, and stoichiometric solutions of LiAlH4 in diethyl ether were added
slowly. After stirring for 2 h at rt, the reaction mixtures were added dropwise to 1000 cm3 2 N H2SO4.
The organic phases were then subjected to the work-up procedures as described above. Typically,
achieved yields were 80–90%. 29Si NMR: (TfOMe2Si)MeSi(SiMe2Ph)2: ꢀ ¼ þ53.0, ꢁ16.4, ꢁ85.0ppm;
TfOMe2Si)2MeSi(SiMe2Ph): ꢀ ¼ þ48.4, ꢁ15.4, ꢁ85.5ppm; 6 (HMe2Si)MeSi(SiMe2Ph)2: ꢀ ¼ ꢁ15.4,
ꢁ34.4, ꢁ87.3ppm; 7 (HMe2Si)2MeSi(SiMe2Ph): ꢀ ¼ ꢁ15.3, ꢁ34.5, ꢁ80.0ppm.
Tetrakis(dimethylphenylsilyl)silane (8)
Compound 8 was prepared as described in Ref. [8] by the reaction of phenyldimethylchlorosilane and
SiCl4 with Li in a yield of less than 10%. An alternative reaction attempt with phenyldimethylsilyl-
lithium and SiCl4 did not give an improved yield. Detailed spectroscopic data were recorded and single
1
crystals suitable for X-ray structure analysis were grown from acetone. H NMR (C6D6): ꢀ ¼ 7.22–
7.30 (m, 8H), 7.10–7.18 (m, 12H), 0.41 (s, 24H) ppm; 13C NMR (C6D6): ꢀ ¼ 140.9, 134.7, 128.7,
128.0, 1.5 ppm; 29Si NMR (C6D6): ꢀ ¼ ꢁ12.8, ꢁ129.7 ppm.

622
R. Fischer et al.
Tris(dimethylsilyl)methylsilane (9, C7H24Si4)
A solution of 4.00g 2b (7.00 mmol) in 100 cm3 diethyl ether was cooled to 0ꢂC and 4.4cm3 2.4 M
LiAlH4 (10.56mmol) solution in diethyl ether were added dropwise. After complete addition the
reaction was stirred at ambient temperature for another 16h after which the solution was cautiously
(!) added dropwise to a mixture of diethyl ether=ice=2 N H2SO4. The aqueous layer was saturated with
NaCl and extracted twice with diethyl ether. The combined organic phases were dried (Na2SO4) and
evaporated to leave 1.35 g 9 (6.1mmol, 87%) as a colourless oil. 1H NMR (C6D6): ꢀ ¼ 3.92 (m, 3H),
0.23 (s, 18H), 0.21 (s, 3H) ppm; 29Si NMR (C6D6): ꢀ ¼ ꢁ35.2 (d, J ¼ 195 Hz), ꢁ88.9ppm.
Tris(methyldiphenylsilyl)methylsilane (10, C40H42Si4)
A solution of 6.20g methyltrichlorsilane (41.2mmol) in 150 cm3 ether was cooled to ꢁ70ꢂC. Methyl-
diphenylsilyllithium (prepared from 30.0g methyldiphenylchlorosilane (128.9mmol) and 6.0 g Li) in
200 cm3 THF was added dropwise. The reaction was allowed to warm up to room temperature, and
was heated to reflux for another 24 h. The solution was poured on 2 N H2SO4=ice and the aqueous
layer extracted several times with ether, dried (Na2SO4), and the solvent removed in vacuum. The
remaining residue was dissolved in n-pentane and after crystallisation at ꢁ70ꢂC 8.6 g 10 (33%) were
obtained as colourless crystals. 1H NMR (CDCl3): ꢀ ¼ 7.33 (m, 12H), 7.21 (m, 18H), 0.55 (d, J ¼ 2 Hz,
3H), 0.32 (d, J ¼ 2 Hz, 9H) ppm; 13C NMR (CDCl3): ꢀ ¼ 137.6, 135.3, 129.0, 128.0, ꢁ3.0, ꢁ8.5 ppm;
29Si NMR (C6D6): ꢀ ¼ ꢁ17.3, ꢁ84.90 ppm.
Tris(dibromomethylsilyl)methylsilane (11, C4H12Br6Si4)
Under the same conditions as described above for the synthesis of 2b 2.50 g 10 (3.94 mmol) were
converted to 11. After crystallisation from n-pentane at ꢁ35ꢂC 1.82g 11 (2.79 mmol, 71%) were
obtained as colourless crystals. 1H NMR (C6D6): ꢀ ¼ 1.33 (s, 9H), 0.51 (s, 3H) ppm; 29Si NMR (C6D6):
ꢀ ¼ 14.6, ꢁ59.4ppm.
Tris(methylsilyl)methylsilane (13, C4H18Si4)
The reaction of 1.50 g 11 (2.30 mmol) with 2.9 cm3 2.4 M LiAlH4 (6.96 mmol) solution in diethyl ether
was carried out in the same way as described above for the synthesis of 9. After work-up 0.38 g 13
(2.14 mmol, 92%) were obtained as a colourless oil. 1H NMR (C6D6): ꢀ ¼ 3.58 (m, 6H), 0.28 (s, 3H),
0.21 (s, 9H) ppm; 29Si NMR (C6D6): ꢀ ¼ ꢁ62.1 (t, J ¼ 185 Hz), ꢁ90.9ppm.
Tris(methylphenylsilyl)methylsilane (14, C22H30Si4)
To a solution of 0.60 g 10 (0.74 mmol) in 5 cm3 toluene at 0ꢂC 0.355g CF3SO3H (2.36.1 mmol) were
added dropwise. After stirring for 16 at rt complete conversion to 12 was detected by 29Si NMR
spectroscopy. 12 (as a mixture of two diasteromers): 29Si NMR (C6D6): ꢀ ¼ 31.3, 30.5, 30.4, 30.1,
ꢁ82.3 ppm. After the addition of 5 cm3 diethyl ether the mixture was cooled to 0ꢂC and 0.6 cm3 of a
2.0 M LiAlH4 (1.20 mmol) solution in diethyl ether was added dropwise. After work-up of the reaction
in a way analogous to the preparation of 9, 0.21 g 13 (0.52 mmol, 70%) were obtained as a colourless
solid. 29Si NMR (C6D6): ꢀ ¼ ꢁ31.6, ꢁ88.3ppm; EIMS: m=z (rel.int.%) ¼ 406 (3, Mþ
ꢃ), 284 (74), 239
C
1H3028Si4 calcd 406.14246, found 406.14232.
22
12
(77), 135 (76), 105 (100); HRMS:
2,5-Bis(dimethylphenylsilyl)-1,6-diphenyldecamethylhexasilane (15, C38H62Si8)
To a solution of 7.2 g 4 (17.7 mmol) in 100 cm3 toluene 2.0 g Na (87 mmol) were added and the
mixture was refluxed for 24h. After filtration the solvent was removed in vacuum and the remaining
residue distilled at 0.01 mm Hg. The fraction from 230 to 250ꢂ consisted of 4.2 g pure 15 (63.8%).
29Si NMR (toluene): ꢀ ¼ ꢁ15.3, ꢁ33.6, ꢁ80.5ppm.
2,5-Bis(chlorodimethylsilyl)-1,6-dichlordecamethylhexasilane (16, C14H42Cl4Si8)
To a solution of 3.9 g 15 (5.2mmol) in 50cm3 toluene 3.8 g CF3SO3H (25.1mmol) were added
dropwise maintaining ꢁ30ꢂC. After completion, all volatiles were removed in vacuum and the residue

Syntheses of Functionalized Oligosilanes
623
was dissolved in 50cm3 diethyl ether. An ample excess of dry LiCl (approx 1–2 g) was added at room
temperature, and the reaction mixture was stirred overnight. Diethyl ether was then removed in vacuum
and 50cm3 petrol ether was added. Lithium salts were separated by filtration, the solvent was removed
by evaporation in vacuum, and the oily residue was subjected to a fractional distillation using a short,
air-cooled column. At 150–170ꢂC (0.05 mbar), 1.7 g (57%) pure 16 solidified. The residue also
contained 16, but all attempts to obtain crystals failed. 29Si NMR (toluene): 16: ꢀ ¼ 28.6, ꢁ34.7,
ꢁ74.0 ppm; ((TfOMe2Si)2MeSiSiMe2)2: 29Si NMR: (Toluene) ꢀ ¼ þ49.3, ꢁ34.8, ꢁ79.9ppm.
Tris(2,2-diphenyltrimethyldisilanyl)methylsilane (17, C46H60Si7)
Starting with 40.1g 2a (124 mmol) and 37.9g diphenylmethylsilyllithium (185mmol) the same pro-
1
cedure as described for 5 was followed yielding 48.6 g 17 (97%) as colourless crystals. H NMR
(C6D6): ꢀ ¼ 7.52 (m, 12H), 7.14 (m, 18H), 0.64 (s, 9H), 0.23 (s, 18H), 0.13 (s, 3H) ppm; 13C NMR
(C6D6): ꢀ ¼ 138.2, 135.8, 128.8, 128.6, ꢁ1.2, ꢁ2.8, ꢁ7.0 ppm; 29Si NMR (C6D6): ꢀ ¼ ꢁ18.4, ꢁ39.2,
ꢁ69.0 ppm; EIMS: m=z (rel.int.%) ¼ 611 (Mþ–Ph2MeSi, 7) 553 (3), 487 (5), 457 (9), 415 (11), 313
(14), 197 (100), 135 (63).
Tris(2,2-dibromotrimethyldisilanyl)methylsilane (18, C10H30Br6Si7)
Compound 17 (2.90 g, 3.58 mmol) was treated with about 15cm3 HBr as described above for 2a. After
crystallisation from n-pentane 2.90g 18 (3.51 mmol, 98%) were obtained as colourless crystals.
1H NMR (C6D6): ꢀ ¼ 1.01 (s, 9H), 0.46 (s, 3H), 0.35 (s, 18H) ppm; 13C NMR (C6D6): ꢀ ¼ 10.1,
ꢁ2.0, ꢁ8.4 ppm; 29Si NMR (toluene): ꢀ ¼ 25.7, ꢁ29.7, ꢁ75.8ppm.
Tris(1,1,2-trimethyldisilanyl)methylsilane (19, C10H36Si7)
As described above for 9 a solution of 1.80g 18 (2.18 mmol) in 20cm3 diethyl ether was treated with
8.7 cm3 1.5 M LiAlH4 (13.0 mmol) solution in diethyl ether. After work-up 0.68g 19 (1.92 mol, 88%)
were obtained as a colourless oil. 1H NMR (C6D6): ꢀ ¼ 3.80 (m, 6H), 0.32 (s, 18H), 0.28 (s, 3H), 0.14
(s, 9H) ppm; 13C NMR (C6D6): ꢀ ¼ ꢁ2.5, ꢁ10.5, ꢁ11.1ppm; 29Si NMR (C6D6): ꢀ ¼ ꢁ39.9, ꢁ61.8
þ
12
ꢃ), 307 (29), 247 (42), 233 (83), 155
C
1H3628Si7 calcd 352.12019, found
10
(t, J ¼ 184 Hz), ꢁ77.0ppm; EIMS: m=z (rel.int.%) ¼ 352 (3, M
(31), 125 (34), 73 (100); IR (neat): ꢁꢀ¼ 2113cmꢁ1; HRMS:
352.12023.
Tris(2,2-diphenyl-2-tert-butyl-dimethyldisilanyl)methylsilane (20, C55H78Si7)
To ice cold Na (6.0g, 348 mmol)=K (24.0g, 614 mmol) alloy suspended in 500 cm3 diethyl ether
64.0g 1,2-di-tert-butyl-1,1,2,2-tetraphenyldisilane (134mmol) were added over a period of 4 h. The
stirring was continued for 12h. To remove excess alloy, 5 cm3 Hg were slowly added at 0ꢂC. The
solution was transferred into a dropping funnel and added to 28.6g ice cold 2a (88 mmol) in 400cm3
diethyl ether over a period of 3 h. Stirring was continued for 12h at rt and another 6 h at reflux. After
cooling to rt the mixture was diluted with toluene and poured onto ice cold 10% H2SO4. After several
extractions of the aqueous layer with toluene, the combined organic layers were dried (Na2SO4), and
the solvent was removed in vacuum. The remaining residue was treated with ether and 43.2 g pure 20
(52%) were obtained as white crystals. 29Si NMR (toluene): ꢀ ¼ ꢁ8.4, ꢁ36.8, ꢁ52.4ppm.
Tris(2,2-dibromo-2-tert-butyl-dimethyldisilanyl)methylsilane (21, C19H48Br6Si7)
A sealed glass tube charged with 9.8g 20 (10.5 mmol) and 10cm3 HBr (262mmol) was first kept at
ꢁ50ꢂC for 5 h, because the protodearylation with HBr is exothermic. Then the tube was placed in a
refrigerator at ꢁ30ꢂC for a week. By this time, all 20 was dissolved in the benzene, which had been
formed. The tube was opened under N2, and the excess of HBr and benzene were removed in vacuum.
The crystalline residue was dissolved in n-pentane. At ꢁ70ꢂC 6.2 g pure 21 (62%) were obtained as
1
colourless needles. H NMR (C6D6): ꢀ ¼ 1.17 (s, 27H), 0.78 (s, 3H) 0.64 (s, 18H) ppm; 13C NMR
(C6D6): ꢀ ¼ 26.9, 26.1, 0.6, ꢁ7.3 ppm; 29Si NMR (toluene): ꢀ ¼ 34.9, ꢁ26.1, ꢁ66.9ppm; HRMS:
1H4879Br628Si7 calcd 945.72411, found 945.72412.
12
C
19

624
R. Fischer et al.
Table 1. Crystallographic data
5
8
10
17
20
Empirical formula
Mw
C
25H36Si4
C32H44Si5
569.12
C40H42Si4
635.10
C46H60Si7
809.57
C55H78Si7
935.80
448.90
Temperature=K
˚
Wavelength=A
243(1)
293(2)
213(1)
213(1)
100(2)
0.71073
0.40ꢄ0.05ꢄ0.05
monoclinic
P2(1)=c
15.650(3)
20.166(4)
8.8766(18)
90
0.71073
0.70ꢄ0.50ꢄ0.40
monoclinic
C2=c
0.71073
0.58ꢄ0.43ꢄ0.28
triclinic
P-1
0.71073
0.47ꢄ0.43ꢄ0.28
monoclinic
C2=c
0.71073
0.50ꢄ0.35ꢄ0.05
monoclinic
P2(1)=c
32.910(7)
13.956(3)
25.287(5)
90
Size=mm
Crystal system
Space group
˚
a=A
˚
b=A
16.4476(2)
9.93780(10)
22.30910(10)
90
10.634(2)
12.445(3)
14.973(3)
77.44(3)
75.32(3)
76.46(3)
1837.0(7)
2
20.297(4)
20.089(4)
25.972(5)
90
˚
c=A
ꢂ=ꢂ
ꢃ=ꢂ
ꢄ=ꢂ
96.80(3)
90
110.8940(10)
90
105.69(3)
90
104.58(3)
90
3
˚
V=A
2781.8(10)
4
3406.70(6)
4
10195(4)
8
11241(4)
4
Z
ꢅ
calc=(g=cm3)
1.072
1.110
1.148
1.055
1.106
Absorption
coefficient=mmꢁ1
0.223
0.228
0.188
0.215
0.203
F(000)
ꢆ range=ꢂ
968
1224
676
3472
4048
1.65<ꢆ<23.29
12332=3996
1.95<ꢆ<20.82
1785=1785
1.71<ꢆ<24.71
12748=6236
1.52<ꢆ<24.71
35126=8691
1.68<ꢆ<23.26
67674=16123
Reflections
collected=unique
Completeness to ꢆ=%
Absorption correction
Data=restraints=
parameters
99.7
99.8
99.3
99.9
99.8
SADABS
3996=0=270
none
SADABS
6236=0=401
SADABS
8691=0=488
SADABS
16123=0=1149
1785=0=169
Goodness of fit on F2
Final R indices
[I>2ꢇ(I)]
0.968
1.128
1.060
1.047
1.028
R1 ¼ 0.0634,
wR2 ¼ 0.1231
R1 ¼ 0.1230,
wR2 ¼ 0.1441
0.192=ꢁ0.204
R1 ¼ 0.0548,
wR2 ¼ 0.1500
R1 ¼ 0.0568,
wR2 ¼ 0.1530
0.424=ꢁ0.334
R1 ¼ 0.0431,
wR2 ¼ 0.1170
R1 ¼ 0.0498,
wR2 ¼ 0.1221
0.300=ꢁ0.182
R1 ¼ 0.0447,
wR2 ¼ 0.1233
R1 ¼ 0.0537,
wR2 ¼ 0.1290
0.359=ꢁ0.180
R1 ¼ 0.0822,
wR2 ¼ 0.1704
R1 ¼ 0.1390,
wR2 ¼ 0.1958
0.329=ꢁ0.317
R indices (all data)
Largest diff.
3
peak=hole=(e =A )
ꢁ
˚
X-Ray Structure Analysis
Crystals were mounted onto the tip of a glass fibre, and data collection was performed on BRUKER-
AXS SMART 1000 or SMART APEX CCD diffractometers (Table 1). Data were reduced to F02 and
corrected for absorption effects with SAINT [19] and SADABS [20]. All structures were solved by
direct methods and refined by full-matrix least-squares method (SHELXL97) [21].
Acknowledgement
This study was supported by the Austrian Science Foundation (FWF) through projects S7902
(C.M.), Y120 (C.M.) and P15366 (K.H.). The Wacker AG, Burghausen, provided generous gifts
of chlorosilanes.
References
[1] Baumgartner J, Fischer R, Kickelbick G, Hassler K, Marschner C (2004) Chem Eur J 10: 1021
[2] a) Marschner C (1998) Eur J Inorg Chem 221; b) Kayser C, Fischer R, Baumgartner J, Marschner
C (2002) Organometallics 21: 1023

Syntheses of Functionalized Oligosilanes
625
[3] For a review of transition metal catalyzed methods of silicon–silicon bond formation see: Gray
GM, Corey JY (2000) In: Jones RG, Ando W, Chojnowski J (eds) Silicon-Containing Polymers,
Kluwer Academic Publishers, p 401
[4] Wiberg N, Schuster H, Simon A, Peters K (1986) Angew Chem 98: 100
[5] Gilman H, Holmes JM, Smith CL (1965) Chem & Ind (London) 848
[6] Kollegger G, Hassler K (1995) J Organomet Chem 485: 233
[7] Gilman H, Harrell RL, Smith CL, Shina K (1966) J Organomet Chem 5: 387
[8] Gilman H, Smith CL (1966) J Organomet Chem 6: 665
[9] Uhlig W (1992) J Organomet Chem 421: 189
[10] Notheis C, Brendler E, Thomas B (1998) In: Auner N, Weis J (eds) Organosilicon Chemistry III:
From Molecules to Materials, Verlag Chemie, Weinheim, p 307
[11] Herzog U, Roewer G (1997) J Organomet Chem 527: 117
[12] Marschner C, Hengge E (1998) In: Auner N, Weis J (eds) Organosilicon Chemistry III: From
Molecules to Materials, Verlag Chemie, Weinheim, p 333
[13] a) Hassler K, Kollegger GM, Siegl H, Klintschar G (1997) J Organomet Chem 533: 51;
b) Watanabe A, Nanjo M, Sunaga T, Sekiguchi A (2001) J Phys Chem A 105: 6436
[14] Heine A, Herbst-Irmer R, Sheldrick GM, Stalke D (1993) Inorg Chem 32: 2694
[15] George MV, Peterson DJ, Gilman H (1960) J Am Chem Soc 82: 403
[16] Gilman H, Lichtenwalter GD (1958) J Am Chem Soc 80: 608
[17] Reiter B, Hassler K (1994) J Organomet Chem 467: 21
[18] a) Morris GA, Freeman R (1979) J Am Chem Soc 101: 760; b) Helmer BJ, West R (1982)
Organometallics 1: 877
[19] SAINTPLUS: Software Reference Manual, Version 5.054 (1997–1998) Bruker-AXS, Madison,
WI
[20] a) Blessing RH (1995) Acta Crystallogr A 51: 33; b) SADABS (1998) Bruker-AXS, Madison,
WI
[21] Sheldrick GM (1998) SHELX97 Programs for Crystal Structure Analysis (Release 97-2),
€
€
€
Universitat Gottingen, Gottingen (Germany). Crystallographic data (excluding structure factors)
for the structures of 5, 8, 10, 17 and 20 reported in this paper were deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC-179568 for 5, CCDC-
179567 for 8, CCDC-179569 for 10, CCDC-179571 for 17, and CCDC-216733 for 20. Copies of
the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internat.) þ44-1223=336-033; E-mail: deposit@chemcrys.
cam.ac.uk]