Multiple silyl exchange reactions: A way to spirooligosilanes

Article abstract of DOI:10.1021/om900287c

Tetrakis(dimethylphenylsilyl)silane can be obtained in a one-pot reaction by treating tris(trimethylsilyl)silylpotassium with excess dimethylphenylfiuorosilane. This silyl exchange process works also with pentamethylfiuorodisilane to give tetrakis(pentame

Full text of DOI:10.1021/om900287c

Organometallics 2009, 28, 4065–4071 4065
DOI: 10.1021/om900287c
Multiple Silyl Exchange Reactions: A Way to Spirooligosilanes
Johann Hlina, Christian Mechtler, Harald Wagner, Judith Baumgartner, and
Christoph Marschner*
€
Institut fu€r Anorganische Chemie, Technische Universitat Graz, Stremayrgasse 16, A-8010 Graz, Austria
Received April 16, 2009
Tetrakis(dimethylphenylsilyl)silane can be obtained in a one-pot reaction by treating tris-
(trimethylsilyl)silylpotassium with excess dimethylphenylfluorosilane. This silyl exchange process
works also with pentamethylfluorodisilane to give tetrakis(pentamethyldisilanyl)silane. The use
of 1,4-difluorooctamethyltetrasilane produces cyclic compounds such as 1,1-bis(trimethylsilyl)-
octamethylcyclopentasilane or even spirocyclic ones such as hexadecamethylspiro[4.4]nonasilane.
Introduction
over the past few years.2,3 These compounds are highly
reactive and require bulky substituents at the silicon atom
for stabilization. In addition, their preparation frequently
requires starting materials that are difficult to obtain. None-
theless, 1,1-dilithiosilanes serve as fascinating synthetic
building blocks and have been used to obtain a number of
novel compounds with highly interesting bonding situa-
tions.4 They are, for example, perfectly suitable to generate
double bonds of silicon to other atoms in salt elimination
reactions with 1,1-dihalides. In addition, they can be reacted
either with two electrophiles or with chains containing
leaving groups in the terminal positions, to obtain chains
or silacyclic compounds. The use of tetralithiosilane as the
synthetic equivalent of a 4-fold negatively charged silicon
reagent has been reported but for some reason never adopted
for synthetic purposes.5
One way to circumvent the concurrent existence of several
negative charges on a silicon atom is the use of the Wurtz-
type coupling protocol. The consecutive reduction of halide
substituents to negative charges allows for the synthesis of
high molecular weight polysilanes.6 In this regard, the reac-
tion of SiCl4 with 4 equiv of Me3SiCl in the presence of
lithium corresponds to the hypothetical reaction of SiLi4
with 4 equiv of Me3SiCl.7 However, this protocol is not very
tolerant of functional groups, and even phenyl groups
are frequently reduced under the conditions of the Wurtz
Salt elimination reactions of negatively charged species
with electrophiles are among the workhorses of organic and
inorganic synthesis. They are especially important in
branches of organoelement chemistry where multiple bonds
and thus the associated addition chemistry are not readily
accessible. This is particularly true for the field of organo-
silicon chemistry, where salt elimination reactions of oligo-
silylpotassium compounds with silicon and numerous other
element halides have helped us tremendously to expand the
field of polysilane chemistry.1
Compounds with multiple electrophilic functionalities are
very common. Silanes with one, two, three, or four leaving
groups (e.g., halide substituents) at the same atom are quite
abundant. From a synthetic point of view, such reagents are
regarded as bearing one, two, three, or four formal positive
charges, as they can participate in as many salt elimination
reactions. Contrasting this, compounds with several formal
negative charges at one atom are not very common. A few
examples of 1,1-dilithiosilanes, which can be considered as
reagents with two formal negative charges, were reported
*Corresponding author. Tel: þþ43-316-873-8209. Fax: þþ43-316-
873-8701. E-mail: christoph.marschner@tugraz.at.
(1) For a comprehensive review covering the chemistry from our
laboratory, concerning oligosilylpotassium compounds see: Marschner,
C. Organometallics 2006, 25, 2110–2125.
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1999, 121, 10231–10232. (b) Tokitoh, N.; Hatano, K.; Sadahiro, T.; Okazaki,
R. Chem. Lett. 1999, 931–932. (c) Kira, M.; Iwamoto, T.; Yin, D.;
Maruyama, T.; Sakurai, H. Chem. Lett. 2001, 910–911. (d) Bravo-
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Ed. 2005, 44, 739-743.
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5884. (b) Hong, J.-H.; Boudjouk, P.; Castellino, S. Organometallics 1994,
13, 3387–3389. (c) Bankwitz, U.; Sohn, H.; Powell, D. R.; West, R. J.
Organomet. Chem. 1995, 499, C7–C9. (d) West, R.; Sohn, H.; Bankwitz, U.;
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r
2009 American Chemical Society
Published on Web 07/02/2009
pubs.acs.org/Organometallics

4066 Organometallics, Vol. 28, No. 14, 2009
Hlina et al.
Scheme 2. Substituent Exchange Reaction of Phenyl- and Phe-
nylethynylbis(trimethylsilyl)silylpotassium
Scheme 1. Tris(trimethylsilyl)silylpotassium Exchange Reaction
of All Trimethylsilyl against Dimethylphenylsilyl Groups Termi-
nated by Potassium Fluoride Elimination
coupling reaction.8 Its use for the synthesis of oligosilanes of
slightly higher structural complexity is therefore usually
associated with very disappointing yields.9 Imitating the
Wurtz-type coupling in more controlled ways, we have
developed stepwise strategies that make use of trimethylsilyl
groups as masked negative charges that are successively
released at the same silicon atom.1,10
Scheme 3. Synthesis of Tetrakis(pentamethyldisilanyl)silane (5)
Results and Discussion
A recent observation suggested a way to avoid the men-
tioned stepwise procedure. We found that the reaction of
trimethylsilyl-substituted silylpotassium compounds with an
excess of dimethylphenylfluorosilane (Scheme 1) yielded
tetrakis(dimethylphenylsilyl)silane (1) in almost quantitative
yield. The alternative synthetic access to this compound via
Wurtz-type coupling of dimethylphenylchlorosilane with
SiCl4 and lithium is much less clean due to side reactions
associated with reductive silylation of the phenyl groups.11
The use of oligosilylpotassium compounds other than tris-
(trimethylsilyl)silylpotassium provided some insight into the
nature of this process. Reaction of bis(trimethylsilyl)methyl-
silylpotassium with excess dimethylphenylfluorosilane shut
down the multiple exchange and resulted in exclusive salt
elimination, yielding bis(trimethylsilyl)(dimethylphenylsilyl)-
methylsilane (2). Introducing a phenyl or phenylethynyl group
to the charge-bearing silicon atom showed the exchange mecha-
nism to be operational, and phenyltris(dimethylphenylsilyl)-
silane (3) and phenylethynyltris(dimethylphenylsilyl)silane (4)
were obtained (Scheme 2).
Scheme 4. Generation of Tris(pentamethyldisilanyl)silylpotas-
sium (6)
Scheme 5. Access to Tetrakis(dimethylphenylsilyl)germane (7)
and -stannane (8)
tris(pentamethyldisilanyl)silylmercury compounds,13 could be
obtained conveniently by treatment of tetrakis(pentamethyldi-
silanyl)silane (5) with potassium tert-butoxide (Scheme 4).14
Also the question whether the exchange reaction is limited
to silyl anions was addressed. Reactions of dimethylphe-
nylfluorosilane with the analogous tris(trimethylsilyl)germyl-
potassium15 and -stannylpotassium16 compounds led to ess-
entially the same results, but proceeded more sluggishly
compared to the silyl case (Scheme 5). The formation of
tetrakis(dimethylphenylsilyl)stannane (8) required additional
portions of potassium tert-butoxide to proceed to completion.
When 1,4-difluorooctamethyltetrasilane was used instead
of dimethylphenylfluorosilane, 1 equiv of the fluorosilane
reacted with tris(trimethylsilyl)silylpotassium to give the
known 1,1-bis(trimethylsilyl)octamethylcyclopentasilane17
(9) (Scheme 6).
Changing the fluorosilane component from dimethylphenyl-
fluorosilane to pentamethylfluorodisilane allowed the conveni-
ent synthesis of the star-type oligosilane tetrakis(pentameth-
yldisilanyl)silane (5) (Scheme 3), so far only accessible by
photolysis of the tris(pentamethyldisilanyl)silyl radical.12
The corresponding tris(pentamethyldisilanyl)silyl anion
6, which was prepared previously from the respective
(8) (a) Beineke, T. A.; Martin, L. L. J. Organomet. Chem. 1969, 20,
65–73. (b) Puranik, D. B.; Fink, M. J. J. Chem. Cryst. 1994, 24, 293–299. (c)
Reyx, D.; Martins, J. M.; Campistron, I.; Huet, F. Bull. Soc. Chim. Fr. 1994,
131, 1007–1014. (d) Harloff, J.; Popowski, E.; Fuhrmann, H. J. Organomet.
Chem. 1999, 592, 136–146.
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6115. (b) Bock, H.; Keim, W.; Kira, M.; West, R. J. Am. Chem. Soc. 1979,
101, 7667–7670.
(10) Fischer, R.; Konopa, T.; Ully, S.; Baumgartner, J.; Marschner,
C. J. Organomet. Chem. 2003, 685, 79–92.
(11) (a) Gilman, H.; Smith, C. L. J. Organomet. Chem. 1966, 6, 665–
668. (b) Fischer, R.; Baumgartner, J.; Kickelbick, G.; Hassler, K.; Marschner,
C. Monatsh. Chem. 2006, 137, 613–625.
(12) (a) Bravo-Zhivotovskii, D.; Yuzefovich, M.; Bendikov, M.;
Klinkhammer, K.; Apeloig, Y. Angew. Chem. 1999, 111, 1169–1171.
Angew. Chem., Int. Ed. Engl. 1999, 38, 1100-1102. (b) Apeloig, Y.; Bravo-
Zhivotovskii, D.; Yuzefovich, M.; Bendikov, M.; Shames, A. Appl. Magn.
Reson. 2000, 18, 425–434.
(14) Marschner, C. Eur. J. Inorg. Chem. 1998, 221–226.
(15) Fischer, J.; Baumgartner, J.; Marschner, C. Organometallics
2005, 24, 1263–1268.
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Chim. Acta 2005, 358, 3174–3182.
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Article
Organometallics, Vol. 28, No. 14, 2009 4067
Scheme 6. Synthesis of 1,1-Bis(trimethylsilyl)octamethylcyclo-
pentasilane (9)
Scheme 9. Synthesis of Spiro[5.4]decasilane 13
the 4-position was replaced by methyl (12), the reaction gave
the expected spirosilane 13 (Scheme 9).
Scheme 7. Synthesis of Hexadecamethylspiro[4.4]nonasilane (11)
Mechanistic Considerations
The described silyl exchange reactions are certainly based
on equilibration processes. The fact that trimethylfluorosi-
lane, which is rather volatile, is formed facilitates the process.
We assume that the reaction proceeds via a pentacoordinate
transition state. In cases where the incoming nucleophile is
stabilized, either by three silyl groups or by two silyl and one
additional phenyl or phenylethynyl group, it seems likely
that the leaving fluoride attacks a silyl group in β-position,
similar to the Peterson olefination20 reaction (Scheme 10). A
fluorosilane is thus released and the negative charge remains
at the same silicon atom. The alternative salt elimination
process leading to the formation of potassium fluoride seems
to be less favorable. Nevertheless, once the salt elimination
reaction takes place, it terminates the exchange process. To
rule out the involvement of external fluoride attack, the
hypothetical reaction of tetrakis(trimethylsilyl)silane with
excess dimethylphenylfluorosilane was carried out in the
presence of variable amounts of potassium fluoride, with
and without crown ether present. No conversion was ob-
served in any case.
Scheme 8. One-Pot Synthesis of Hexadecamethylspiro[4.4]non-
asilane (11) Starting from Tris(trimethylsilyl)silylpotassium
Certain oligosilanes are difficult to prepare in a stepwise
manner. An occasion where the availability of a 1,1-dianio-
nic silicon atom would be particularly useful is the synthesis
of spirocyclic oligosilanes.18 Preliminary synthetic attempts
to obtain compounds containing the spiro[4.4]nonasilane
skeleton with two cyclopentasilane units were based on
reactions of 1,4-dianionic tetrasilanes with SiCl4.19 However,
likely for steric reasons, only two or three of the required four
bonds were formed during the salt elimination reactions.
When 1,1-bis(trimethylsilyl)octamethylcyclopentasilane (9)
was converted to the corresponding silylpotassium com-
pound 10 by reaction with potassium tert-butoxide14 and
then treated with 1 equiv of 1,4-difluorooctamethyltetra-
silane, the synthesis of hexadecamethylspiro[4.4]nonasilane
(11) was achieved (Scheme 7).
As we have observed multiple exchange reactions with
monofluorosilanes, it could be expected that the spirosilane
11 would form directly from tris(trimethylsilyl)silylpotas-
sium by reacting with 2 equiv of 1,4-difluorooctamethylte-
trasilane. This was indeed the case (Scheme 8), but the
reaction was not as clean and the yield was substantially
lower compared to the stepwise protocol.
Crystal Structure Analyses
Compounds 5, 6, 7, and 11 could be subjected to crystal
structure analysis. Nonasilane 5 (Figure 1) crystallizes in the
monoclinic space group P2(1)/c. The quality of the crystals
was unfortunately not very good. Nevertheless, a basic
description of the structure is possible. The geometry around
the central silicon atom is distorted tetrahedral with bond
angles ranging from 104.8° to 116.3°. The Si-Si bond
distance connecting the pentamethyldisilanyl unit with the
˚
widest bond angles is consequently the shortest (2.352 A).
The other distances to the central atom are 2.367, 2.370, and
˚
2.385 A. The sterically less encumbered bonds to the periph-
eral trimethylsilyl groups are all in the range between 2.35
˚
and 2.36 A.
Compound 6 (Figure 2) is interesting, as it allows a direct
comparison to the respective silyllithium compound (Me3-
SiMe2Si)3SiLi, which has been described to show an unusual
umbrella effect.13 This effect was associated with torsional
angles of about 35.7° for the segment Li-Si-SiMe2-SiMe3.
The analogous angles for K-Si-SiMe2-SiMe3 of 6 were
found to be between 66° and 70°. The reason for the less
pronounced back-bending seems to be the larger spatial
demand of the crown ether. In (Me3SiMe2Si)3SiLi, lithium
and the negatively charged silicon atoms are both tetracoor-
dinate. Thus, a staggered conformation around the Si-Li
bond allows the trimethylsilyl groups to reach over into
Attempts to extend this strategy to the synthesis of spirosi-
lanes of other ring sizes and substitution pattern were met with
different success. The reaction of 1,4,4-tris(trimethylsilyl)octa-
methylcyclohexasilanylpotassium did not lead to the forma-
tion of the expected spiro[5.4]decasilane. NMR spectroscopic
evidence hints to dodecamethylcyclohexasilane as the major
product. When, however, one of the trimethylsilyl groups in
(18) The only reported example of a spirocyclic oligosilane is octa-
methylspiro[2.2]pentasilane, which is not stable at ambient conditions:
Boudjouk, P.; Sooriyakumaran, R. J. Chem. Soc., Chem. Commun.
1984, 777–778.
(19) Hlina, J. Diploma Thesis, TU Graz, 2008.
(20) Peterson, D. J. J. Org. Chem. 1968, 33, 780–784.

4068 Organometallics, Vol. 28, No. 14, 2009
Hlina et al.
Scheme 10. Supposed Reaction Mechanism of the Silyl Exchange Process
Figure 3. Molecular structure and numbering of 7. Selected
˚
bond lengths [A] and bond angles [deg] with SDs: Ge(1)-Si(2)
2.3945(7), Ge(1)-Si(1) 2.3996(7), Si(1)-C(2) 1.875(2), Si(2)-
Ge(1)-Si(2A) 107.56(3), Si(2)-Ge(1)-Si(1) 105.75(3), Si(2A)-
Ge(1)-Si(1) 109.70(3), Si(2A)-Ge(1)-Si(1A) 105.75(3), Si(1)-
Ge(1)-Si(1A) 118.03(3).
Figure 1. Molecular structure and numbering of 5. Selected
˚
bond lengths [A] and bond angles [deg] with SDs: Si(1)-C(1)
1.877(7), Si(1)-Si(2) 2.360(3), Si(2)-Si(3) 2.367(3), Si(3)-Si(6)
2.352(2), Si(3)-Si(8) 2.370(3), Si(3)-Si(4) 2.385(3), Si(6)-Si(3)-
Si(2) 116.31(10), Si(6)-Si(3)-Si(8) 113.04(10), Si(2)-Si(3)-Si(8)
108.66(10), Si(6)-Si(3)-Si(4) 106.51(10), Si(2)-Si(3)-Si(4)
104.82(10), Si(8)-Si(3)-Si(4) 106.73(10).
the areas between the THF molecules. For the case of 6
the potassium atom is surrounded by the crown ether.
Conformational changes would not open space for the tri-
methylsilyl groups. Consequently, these groups avoid ap-
proaching the vicinity of the potassium atom. Even if the
˚
Si-K bond is approximately 0.9 A longer than the Si-Li
distance, the trimethylsilyl groups of 6 have to be accommo-
dated in an approximate C3 symmetric arrangement closer to
the neighboring wing. This causes a substantial elongation of
the involved Si-Si bonds. While for (Me3SiMe2Si)3SiLi
˚
rather common values of ca. 2.36 A for the LiSi-SiMe2 bond
˚
and 2.35 A for the Me2Si-SiMe3 units were found, these
values increase to 2.40 and 2.39 A, respectively, in 6.
˚
As expected, the structure of the tetrasilylated germane 7
(Figure 3) is isomorphous to the corresponding (Me2PhSi)4-
Si.11b Both crystallize in the space group C2/c with the cell
parameters of 7 being slightly enhanced. The Si-Si bond
˚
lengths of (Me2PhSi)4Si were found to be 2.37 A, and also the
˚
Si-Ge bond distances of 2.394 and 2.400 A for 7 are
common for this type of compounds.21
The structure of the spirocyclic nonasilane 11 (Figure 4)
does not appear to be very strained. Bond distances
˚
between silicon atoms range from 2.33 to 2.36 A, which
is quite typical and indicative of not much steric interac-
tion. The two five-membered rings are both exhibiting
envelope conformation. They share a silicon atom, which
is part of the envelope’s fold. The two envelope planes are
at an angle of about 70°. As both flaps open to the same
side in angles of 41° and 43°, a transoid aligned pentasilane
Figure 2. Molecular structure and numbering of 6. Selected
˚
bond lengths [A] and bond angles [deg] with SDs: K(1)-O(1)
2.885(5), K(1)-Si(1) 3.673(3), O(1)-C(12) 1.431(10), Si(1)-Si-
(4) 2.382(3), Si(1)-Si(6) 2.390(3), Si(1)-Si(2) 2.398(3), Si(2)-C
(13) 1.935(8), Si(4)-Si(1)-Si(6) 100.61(10), Si(4)-Si(1)-Si(2)
100.14(11), Si(6)-Si(1)-Si(2) 99.70(11), Si(4)-Si(1)-K(1)
118.22(9), Si(6)-Si(1)-K(1) 115.70(9), Si(2)-Si(1)-K(1)
119.11(9).
(21) A search for the structural unit Si3Ge in the Cambridge Crystal-
lographic Database using Conquest Version 1.10 provided an average
˚
˚
value of 2.377 A and a median value of 2.398 A for the Si-Ge distance.

Article
Organometallics, Vol. 28, No. 14, 2009 4069
˚
Figure 4. Molecular structure and numbering of 11. Selected bond lengths [A] and bond angles [deg] with SDs: Si(1)-Si(2) 2.3456(15),
Si(1)-Si(6) 2.3504(14), Si(1)-Si(5) 2.3612(15), Si(2)-C(1) 1.871(4), Si(2)-Si(3) 2.3299(16), Si(2)-Si(1)-Si(6) 112.65(6), Si(2)-Si(1)-
Si(9) 114.87(6), Si(6)-Si(1)-Si(9) 101.22(6), Si(2)-Si(1)-Si(5) 100.57(6), Si(6)-Si(1)-Si(5) 114.47(6), Si(9)-Si(1)-Si(5) 113.71(7).
Table 1. Crystallographic Data for Compounds 5, 6, 7, and 11
5
6
7
11
empirical formula
Mw
temperature [K]
size [mm]
cryst syst
Si9C20H60
553.49
100(2)
0.33 ꢀ 0.20 ꢀ 0.14
monoclinic
P2(1)/c
11.329(2)
13.412(3)
23.939(5)
90
93.40(3)
90
3631.1(2)
4
1.012
KO6Si7C27H69
725.55
100(2)
0.44 ꢀ 0.34 ꢀ 0.30
monoclinic
P2(1)/n
12.684(3)
18.764(4)
19.958(4)
90
97.66(3)
90
4708(2)
4
1.024
GeSi4C32H44
613.62
100(2)
0.40 ꢀ 0.32 ꢀ 0.22
monoclinic
C2/c
16.389(3)
9.6252(2)
22.329(5)
90
111.02(3)
90
3287.9(2)
4
1.240
1.097
1296
Si9C16H48
493.35
100(2)
0.28 ꢀ 0.23 ꢀ 0.20
monoclinic
P2(1)/n
10.447(2)
18.580(4)
16.570(3)
90
101.64(3)
90
3150(2)
4
1.040
space group
˚
a [A]
˚
b [A]
˚
c [A]
R [deg]
β [deg]
γ [deg]
3
˚
V [A ]
Z
F
calc [g cm-3
]
absorp coeff [mm-1
F(000)
]
0.337
1224
0.320
1584
0.381
1080
θ range [deg]
1.70 < θ < 24.00
23 620/5688
99.8
5688/0/282
1.18
1.50 < θ < 26.41
35 049/9578
99.0
9578/0/387
0.93
1.95 < θ < 26.35
12 483/3340
99.7
3340/0/172
1.13
1.67 < θ < 26.38
24 901/6427
99.8
6427/0/242
1.04
reflns collected/unique
completeness to θ [%]
data/restraints/params
goodness of fit on F2
final R indices [I > 2σ(I)]
R1 = 0.099, wR2 = 0.167 R1 = 0.091, wR2 = 0.216 R1 = 0.036, wR2 = 0.082 R1 = 0.068, wR2 = 0.163
R1 = 0.140, wR2 = 0.184 R1 = 0.195, wR2 = 0.269 R1 = 0.039, wR2 = 0.084 R1 = 0.098, wR2 = 0.180
R indices (all data)
largest diff peak/hole [e /A ] 0.58/-0.57
-
3
˚
0.04/-0.02
0.84/-0.25
1.38/-0.33
segment, which includes the joint silicon, the two flaps,
and the other fold atoms, is observed with torsional angles
of 164° and 167°.
Experimental Section
General Remarks. All reactions involving air-sensitive com-
pounds were carried out under an atmosphere of nitrogen or
argon using either Schlenk techniques or a glovebox. Solvents
were dried using a column solvent purification system.22 Potas-
sium tert-butanolate was purchased from Merck.
Conclusion
1H (300 MHz), 13C (75.4 MHz), 29Si (59.3 MHz), and 119Sn
(111.8 MHz) NMR spectra were recorded on a Varian INOVA
300 spectrometer. If not noted otherwise, samples for NMR
spectra were dissolved in deuterated benzene. In the case of
reaction control by means of 29Si NMR spectroscopy aliquots
were 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.23
Elemental analysis was carried out using a Heraeus Vario
Elementar instrument (in cases of bad carbon values WO3 was
added to facilitate complete combustion and to suppress silicon
carbide formation).
The attempted salt elimination reaction of tris(trimethyl-
silyl)silylpotassium with excess dimethylphenylfluorosilane
was unexpectedly accompanied by the exchange of all
trimethylsilyl for dimethylphenylsilyl groups. The thus ob-
tained tetrakis(dimethylphenylsilyl)silane is not easily pre-
pared by Wurtz-type coupling. The silyl exchange reaction
was found to be dependent on the presence of charge-
stabilizing substituents on the silylpotassium species. Reac-
tion of methylbis(trimethylsilyl)silylpotassium with excess
dimethylphenylfluorosilane gave the salt elimination product
methyl(dimethylphenylsilyl)bis(trimethylsilyl)silane, exclu-
sively. Tris(trimethylsilyl)silylpotassium could be reacted
with excess pentamethylsilylfluorodisilane to give tetrakis-
(pentamethyldisilanyl)silane.
X-ray Structure Determination. For X-ray structure analyses
crystals were mounted onto the tip of glass fibers, and data
The use of 1,4-difluorooctamethyltetrasilane provided a
unique opportunity to utilize this exchange reaction to
obtain spirocyclic oligosilanes, first examples of which have
been obtained this way.
(22) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(23) (a) Morris, G. A.; Freeman, R. J. Am. Chem. Soc. 1979, 101, 760–
762. (b) Helmer, B. J.; West, R. Organometallics 1982, 1, 877–879.

4070 Organometallics, Vol. 28, No. 14, 2009
Hlina et al.
collection was performed with a Bruker-AXS SMART APEX
CCD diffractometer using graphite-monochromated Mo KR
29Si NMR: δ -16.2, -76.2.31 Anal. Calcd for C30H38Si4 (510.96):
C 70.52, H 7.50. Found: C 70.59, H 7.62.
2
˚
radiation (0.71073 A). Data were reduced to Fo and corrected
Tris(dimethylphenylsilyl)phenylethynylsilane (4). The reaction
was carried out as described above for the synthesis of 1 with
dimethylphenylfluorosilane (265 mg, 1.72 mmol) in toluene
(30 mL) and phenylethynylbis(trimethylsilyl)silylpotassium
(0.29 mmol) in THF (8 mL). Compound 4 (95 mg, 61%) was
obtained as a slightly brown oil. 1H NMR: δ 7.17 (m, 15H), 7.01
(m, 5H), 0.37 (s, 18H). 29Si NMR: δ -15.7, -99.9. Anal. Calcd
for C32H38Si4 (534.99): C 71.84, H 7.16. Found: C 70.91, H 7.12.
Tetrakis(pentamethyldisilyl)silane (5). The reaction was car-
ried out according to the synthesis of 1 with pentamethylfluor-
odisilane (416 mg, 2.77 mmol) in toluene (3 mL) and tris-
(trimethylsilyl)silylpotassium (0.461 mmol) in THF (3 mL).
Complete conversion was reached after 16 h. After recrystalliza-
tion of the white residue from 2-propanol at -30 °C compound 5
(130 mg, 51%) was obtained as colorless crystals. Mp: 54-
55 °C. 1H NMR: δ 0.38 (s, 24H), 0.22 (s, 36H). 13C NMR: δ 0.4;
-0.2. 29Si NMR: δ -14.0; -38.4; -110.9. UV-vis (pentane,
for absorption effects with SAINT24 and SADABS,25 respec-
tively. Structures were solved by direct methods and refined
by full-matrix least-squares method (SHELXL97).26 All non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were located in calculated
positions to correspond to standard bond lengths and angles.
All ORTEP plots (Figures 1-4) were drawn with 30% prob-
ability thermal ellipsoids, and all hydrogen atoms were omitted
for clarity. Crystallographic data (excluding structure factors)
for the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Center as supplemen-
tary publication no. CCDC-666916 (5), 666914 (6), 666915 (7),
and 695767 (11). Copies of the data can be obtained free of charge
at http://www.ccdc.cam.ac.uk/products/csd/request/.
The following compounds were synthesized according to
the reported procedures: dimethylphenylfluorosilane,27 methylbis-
(trimethylsilyl)silylpotassium,28 phenylbis(trimethylsilyl)silylpotass-
ium,28 pentamethylfluorosilane,29 tris(trimethylsilyl)silylpotassium,14
1,4-difluorooctamethyltetrasilane,30 1,1-bis(trimethylsilyl)octamet-
hylcyclopentasilane,17c tris(trimethylsilyl)germylpotassium,15 tris-
(trimethylsilyl)stannylpotassium,16 and 1,1,4-tris(trimethylsilyl)non-
amethylcyclohexasilane.10
Tetrakis(dimethylphenylsilyl)silane (1). To a solution of di-
methylphenylfluorosilane (4.499 g, 29.16 mmol) in toluene
(50 mL) was added tris(trimethylsilyl)silylpotassium [generated
in situ from tetrakis(trimethylsilyl)silane (1.127 g, 3.514 mmol)
and KOtBu (394 mg, 3.51 mmol)] in THF (10 mL) over a period
of 10 min. The resulting yellow solution was stirred for 5 days
until complete conversion was detected. All volatile components
(solvents and silylfluorides) were removed under vacuum. The
residue was dissolved in diethyl ether and washed with dilute
sulfuric acid. After drying over Na2SO4 the product crystallized
from the ethereal solution, which was allowed to slowly evapo-
rate. Compound 1 was obtained as a colorless crystalline
material (1.88 g, 93%) with spectroscopic properties in accor-
dance with published values.11b
Methylbis(trimethylsilyl)dimethylphenylsilylsilane (2). To a
solution of dimethylphenylfluorosilane (983 mg, 6.37 mmol) in
toluene (10 mL) was added methylbis(trimethylsilyl)silylpotas-
sium (1.40 mmol) in THF (3 mL) over a period of 10 min. After
stirring for 24 h the precipitate was removed by filtration, and
after removal of all volatiles 2 (443 mg, 98%) was obtained as a
colorless oil. 1H NMR: δ 7.46 (m, 2H), 7.18 (m, 3H), 0.44 (s, 6H),
0.11 (s, 18H). 13C NMR: δ 134.0, 133.9, 128.6, 128.0, 0.3, -1.3,
-12.8. 29Si NMR: δ -12.6, -16.1, -87.5. Anal. Calcd for
C15H32Si4 (324.76): C 55.48, H 9.93. Found: C 54.91, H 9.99.
Phenyltris(dimethylphenylsilyl)silane (3). The reaction was car-
ried out according to the procedure described for 1 using dimethyl-
phenylfluorosilane (794 mg, 5.15 mmol) in toluene (10 mL)
and phenylbis(trimethylsilyl)silylpotassium (1.40 mmol) in THF
(5 mL). Compound 3 (497 mg, 90%) was obtained as a colorless oil.
1H NMR: δ 7.60 (m, 2H), 7.36 (m, 9H), 7.13 (m, 9H), 0.37 (s, 18H).
13C NMR: δ 140.2, 137.4, 134.5, 129.0, 128.1, 128.0, 128.0, -0.4.
λ
max (ε)): 211 nm (4.0 ꢀ 104), 222 nm (2.8 ꢀ 104). Anal. Calcd for
C20H60Si9 (553.46): C 43.40, H 10.93. Found: C 43.17; H 10.86.
Tris(pentamethyldisilanyl)silylpotassium 18-crown-6 (6). Com-
3
pound 5 (169 mg, 0.305 mmol), KOtBu (34 mg, 0.30 mmol), and
18-crown-6 (81 mg, 0.31 mmol) were dissolved in benzene
(3 mL) and stirred overnight at rt. Removal of benzene under
vacuum was followed by dissolving the residue in toluene (3 mL)
and pentane (0.3 mL). Compound 6 (201 mg, 92%) was
obtained as red crystals after cooling to -35 °C. 1H NMR:
δ 3.17 (s, 24H, 18-crown-6), 0.68 (s, 18H), 0.45 (s, 27H). 13C
NMR: δ 69.8 (18-crown-6), 4.4, 0.3. 29Si NMR: δ -16.1, -33.8,
-181.2.
Tetrakis(dimethylphenylsilyl)germane (7). The reaction was
carried out according to the synthesis of 1 with dimethylphenyl-
fluorosilane (533 mg, 3.45 mmol) and tris(trimethylsilyl)germyl-
potassium (0.42 mmol). After 48 h some additional KOtBu
(23 mg, 0.21 mmol) was added. Complete conversion was
reached after another 48 h. Compound 7 (75 mg, 29%) was
obtained after recrystallization from ether at 0 °C as colorless
crystals. Mp: 107-112 °C. 1H NMR: δ 7.25 (m, 20H), 0.41 (s,
24H). 13C NMR: δ 141.4, 134.4, 128.7, 128.0, 1.9. 29Si NMR:
δ -8.2. Anal. Calcd for C32H44GeSi4 (613.64): C 62.63, H 7.23.
Found: C 62.35, H 7.37.
Tetrakis(dimethylphenylsilyl)stannane (8). To a solution of
dimethylphenylfluorosilane (648 mg, 4.20 mmol) in THF/dieth-
yl ether (ca. 1:1, 5 mL) was added tris(trimethylsilyl)stannylpo-
tassium [generated in situ from tetrakis(trimethylsilyl)stannane
(173 mg, 0.420 mmol) and KOtBu (49 mg, 0.44 mmol)] in THF
(4 mL over a period of 2 min. After 24 h additional KOtBu
(49 mg, 0.44 mmol) was added. Another 24 h later, the forma-
tion of 8 as the only tin-containing species was unambiguously
verified by multinuclear NMR spectroscopy, alongside forma-
tion of tetramethyl-1,3-diphenyldisiloxane and tert-butyl (di-
methylphenylsilyl) ether. 1H NMR (C6D6): δ 7.25 (m, 20H), 0.44
3
(s, 24H, J1H-117/119Sn = 20.9/21.5 Hz). 13C NMR (C6D6):
δ 140.6, 133.6, 128.6, 128.0, 2.0 (2J13C-117/119Sn = 39/41 Hz). 29Si
NMR (C6D6): δ -11.5 (1J29Si-117/119Sn = 323/339 Hz). 119Sn NMR
(C6D6): δ -634.5 (1J29Si-119Sn = 339 Hz, 2J13C-119Sn = 41 Hz).
1,1-Bis(trimethylsilyl)octamethylcyclopentasilane (9). To a so-
lution of 1,4-difluorooctamethyltetrasilane (140 mg, 0.516 mmol) in
toluene (2 mL) was slowly added tris(trimethylsilyl)silylpotassium
(0.491 mmol) in THF (2 mL). After stirring for 14 h the reaction
mixture was poured onto 0.5 M H2SO4/water/ice and extracted
several times with ether. The combined organic layers were dried
with Na2SO4 and the solvent was removed under vacuum. NMR
analysis revealed the formation of 1,1-bis(trimethylsilyl)octa-
methylcyclopentasilane (NMR data in accordance with published
(24) SAINTPLUS: Software Reference Manual, Version 6.45;
Bruker-AXS: Madison, WI, 1997-2003.
(25) Blessing, R. H. Acta Crystallogr. A 1995, 51, 33-38: SADABS:
Version 2.1; Bruker AXS, 1998.
(26) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112–122.
(27) Kunai, A.; Sakurai, T.; Toyoda, E.; Ishikawa, M. Organometal-
lics 1996, 15, 2478–2482.
(28) Kayser, C.; Fischer, R.; Baumgartner, J.; Marschner, C. Orga-
nometallics 2002, 21, 1023–1030.
(29) Kumada, M.; Yamaguchi, M.; Yamamoto, Y.; Nakajima, J.;
Shiina, K. J. Org. Chem. 1956, 21, 1264–1268.
(30) (a) Boberski, W. G.; Allred, A. L. J. Organomet. Chem. 1974, 74,
205–208. (b) Stanislawski, D.; West, R. J. Organomet. Chem. 1980, 204,
307–314. (c) Tamao, K.; Akita, M.; Kumada, M. J. Organomet. Chem. 1983,
254, 13–22.
(31) For 29Si NMR data of compound 3 see: Notheis, C.; Brendler,
E.; Thomas, B. Organosilicon Chem. III-From Molecules to Materials;
Auner, N., Weis, J., Eds.; Wiley-VCH: New York, 1997; pp 307-311.

Article
Organometallics, Vol. 28, No. 14, 2009 4071
values: refs 17b,c) as the main product along with some tris
(trimethylsilyl)(40-fluorooctamethyltetrasilanyl)silane.
8-Trimethylsilylheptadecamethylspiro[5.4]decasilane (13). To a
solution of 1,4-difluorooctamethyltetrasilane (35 mg, 0.13 mmol)
in toluene (5 mL) was added slowly 1,4-bis(trimethylsilyl)non-
amethylcyclohexasilan-1-ylpotassium (12) [prepared from 1,1,4-
tris(trimethylsilyl)heptamethylcyclohexasilane (65 mg, 0.13 mmol)
and KOtBu (15 mg, 0.13 mmol) in THF (2 mL); 29Si NMR δ (D2O-
capillary): -2.0, -10.0, -27.7, -39.9, -81.1, -188.5]. After stirring
for 14 h the reaction mixture was poured onto 0.5 M H2SO4/water/
ice and extracted several times with ether. The combined organic
layers were dried with Na2SO4 and the solvent was removed under
vacuum. 13 was obtained as a highly viscous oil (36 mg, 48%). 1H
NMR δ (C6D6): 0.37 (s, 6H), 0.35 (s, 6H), 0.32 (s, 6H), 0.29 (s, 6H),
0.28 (s, 6H), 0.24 (s, 6H), 0.21 (s, 9H), 0.20 (s, 3H), 0.19 (s, 6H), 0.19
(s, 6H). 29Si NMR δ (C6D6): -9.5, -26.0, -30.2, -32.4 (2 signals),
-38.9 (2 signals), -41.2, -42.1, -82.3, -127.5. Anal. Calcd for
C20H60Si11 (609.63): C 39.40, H 9.92. Found: C 38.92, H 9.97.
Trimethylsilyloctamethylcyclopentasilylpotassium (10). A mix-
ture of 1,1-bis(trimethylsilyl)octamethylcyclopentasilane (900 mg,
2.21 mmol) and KOtBu (261 mg, 2.32 mmol) was dissolved in
THF (15 mL). The yellow solution was stirred for 3 h until
complete anion formation was detected. 29Si NMR data were in
close agreement with the previously prepared crown ether adduct
of 10:32 -3.4, -23.6, -23.6, -184.9.
Hexadecamethylspiro[4.4]nonasilane (11). To a solution of
1,4-difluorooctamethyltetrasilane (616 mg, 2.28 mmol) in
toluene (50 mL) was slowly added compound 10 (2.21 mmol)
in THF (15 mL). After stirring for 14 h the reaction mixture
was poured onto 0.5 M H2SO4/water/ice and extracted several
times with ether. The combined organic layers were dried with
Na2SO4 and the solvent was removed under vacuum. After
recrystallization from 2-propanol/heptane/DME 11 was ob-
tained as colorless crystals (985 mg, 90%). Mp: 88-91 °C.
UV-vis (pentane, λmax (ε)): 190 nm (5.0 ꢀ 104), 237(s) nm
(1.5 ꢀ 104), 282(s) nm (3.8 ꢀ 103). 1H NMR δ (CDCl3): 0.31 (s,
24H), 0.19 (s, 24H). 13C NMR δ (CDCl3): -1.2, -6.2. 29Si
NMR δ (C6D6): -28.3, -41.6, -130.2. Anal. Calcd for
Acknowledgment. This study was supported by the
Austrian Science Fund (FWF) via the projects Y-120,
P-18538, and P-19338.
C
16H48Si9 (493.32): C 38.95, H 9.81. Found: C 38.37, H 9.64.
Supporting Information Available: X-ray crystallographic
information in CIF format is available free of charge via the
Internet at http://pubs.acs.org.
(32) Fischer, J. Ph.D. Thesis, TU Graz, 2005.