Cyclic and bicyclic methylpolysilanes and some oligosilanylene-bridged derivatives

Article abstract of DOI:10.1021/om901104h

A number of novel cyclo- and bicyclosilanes connected by linear silanylene chains have been prepared and characterized by X-ray crystallography and NMR spectroscopy. The UV absorption properties of all compounds were studied and found to show low-energy absorption maxima red-shifted compared to acyclic compounds with comparable chain lengths. Synthesis of the new polysilanes was accomplished using silyl anions as key intermediates, which allow a stepwise controlled setup.

Full text of DOI:10.1021/om901104h

2660 Organometallics 2010, 29, 2660–2675
DOI: 10.1021/om901104h
Cyclic and Bicyclic Methylpolysilanes and Some Oligosilanylene-Bridged
Derivatives
Andreas Wallner, Johann Hlina, Tina Konopa, Harald Wagner,
Judith Baumgartner,* and Christoph Marschner*
€
Institut fu€r Anorganische Chemie, Technische Universitat Graz, Stremayrgasse 16,
A-8010 Graz, Austria
€
Ulrich Florke
€
Anorganische und Analytische Chemie, Universitat Paderborn,
Warburger Strasse 100 D-33098 Paderborn, Germany
Received December 22, 2009
A number of novel cyclo- and bicyclosilanes connected by linear silanylene chains have been prepared
and characterized by X-ray crystallography and NMR spectroscopy. The UV absorption properties of all
compounds were studied and found to show low-energy absorption maxima red-shifted compared to
acyclic compounds with comparable chain lengths. Synthesis of the new polysilanes was accomplished
using silyl anions as key intermediates, which allow a stepwise controlled setup.
Introduction
easy and direct entry to cyclopolysilanes of different ring sizes in
excellent yields, it also facilitates straightforward, further deri-
vatization of the molecules.
The chemistry of cyclopolysilanes started with Kipping’s
work on phenylated rings in the early 1920s,1 but it took almost
another thirty years before the first permethylated cyclohexa-
silane was described.2 Even today, the initial synthetic approach
used for cyclosilane preparation, the Wurtz-type coupling of
dihalosilanes with alkali metals, is still often the preferred
method. Wurtz-type conditions were also investigated with
respect to their potential for the cross coupling of diorganodi-
chlorosilanes and organotrichlorosilanes to obtain bicyclic oligo-
silanes. Nevertheless, this preparative method suffers from some
serious drawbacks such as the harsh conditions, which permit
only starting materials with very robust substituents (usually
alkyl and aryl groups), the sometimes disappointingly low
yields,3 and the limitation to certain ring sizes, depending on
the steric properties of the substituents. We and Kira’s group
have recently reported on the syntheses of cyclic and also
bicyclic polysilanes4 by a stepwise construction approach, using
dianionic polysilanes.5 Not only does this method permit an
The main interest in polysilanes stems from their unique
properties due to electron delocalization in their σ-bond
scaffold, which is not confined to acyclic polysilanes.6 The
UV absorption properties of polysilanes via the catenated
silicon framework were discovered in the 1960s.7 The pheno-
menon of a bathochromic shift behavior with increasing
chain length was explained as σ-σ* transitions of the poly-
silane chain and was found to be strongly dependent on the
Si-Si backbone conformation.8 Thus, the thermochromic
behavior of the UV absorption bands in polysilanes9 can be
explained as change of conformation in the backbone. It is
the common understanding today that anti-conformational
€
(6) (a) Hengge, E.; Stuger, H. In The Chemistry of Organic Silicon
Compounds; Rappoport, E.; Apeloig, Y., Eds.; Wiley: Chichester, 1998,; Vol
2, Chapter 37. (b) Hengge, E.; Janoschek, R. Chem. Rev. 1995, 95, 1495–
1526.
(7) (a) Kumada, M.; Tamao, K. Adv. Organomet. Chem. 1968, 6, 19–
117. (b) Gilman, H.; Atwell, W. H.; Schwebke, G. L. Chem. Ind. (London)
1964, 1063. Gilman, H.; Atwell, W. H.; Schwebke, G. L. J. Organomet.
Chem. 1964, 2, 369–371. (c) Sakurai, H.; Kumada, M. Bull. Chem. Soc. Jpn.
1964, 37, 1894–1895. (d) Hague, D. N.; Prince, R. H. Chem. Ind. (London)
1964, 1492.
*Corresponding authors. Tel: þþ43-316-873-8209. Fax: þþ43-316-873-
8701. E-mail: baumgartner@tugraz.at; christoph.marschner@tugraz.at.
(1) (a) Kipping, F. S.; Sands, J. E. J. Chem. Soc. 1921, 119, 830–847.
(b) Kipping, F. S. J. Chem. Soc. 1924, 125, 2291.
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6115. (b) Bock, H.; Keim, W.; Kira, M.; West, R. J. Am. Chem. Soc. 1979,
101, 7667–7670. (c) Jenkner, P. K.; Hengge, E.; Czaputa, R.; Kratky, C. J.
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r
pubs.acs.org/Organometallics
Published on Web 05/27/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 12, 2010 2661
Scheme 1. Synthesis of Cyclotetrasilane Compounds 1, 2, and 3
units of polysilanes extend the σ-conjugated system and afford
the first absorption maximum at longer wavelengths, while syn-
conformational units lead to rupture of the conjugation and
afford the first absorption maximum at shorter wavelengths.10
Theoretical studies, especially from Michl’s group, pointed out
that the conformational behavior of linear alkanes is different
from saturated chain polymers in general.11 For an improved
description of conformational behavior Michl and West pro-
posed a new systematic nomenclature.12
In more recent times several attempts were made to control
the conformational properties of polysilanes. The applied
strategies range from the introduction of chiral side-chains13
to the incorporation of the polysilane into a rigid frame-
work,14,15 and from the inclusion of alkylated polysilanes into
cyclodextrines16 to the use of pentacoordination of silicon
atoms.17 Work from our group18,19 and others20 featured the
use of bulky end-groups such as the tris(trimethylsilyl)silyl unit
in order to align methylated polysilane chains.
A recently published study showed that the UV absorption
behavior of partially trimethylsilyl substituted methylcyclo-
silanes is considerably different from that of the permethylated
cyclosilanes of the same ring size. To some extent it seems as if
the permethylated silanylene segments between the trimethyl-
silyl attachment points behave like acyclic transoid-oriented
chains.4c The current study is therefore concerned with the
intention to study molecules containing cyclic or even bicyclic
oligosilane units but also polysilanylene chains of different
length, which can serve as connections between the cyclosilanes.
Results and Discussion
Synthesis of New Cyclosilanes. Some years ago weprepared
four-membered heterocyclosilanes starting from 1,1,3,3-tetra-
kis(trimethylsilyl)-1,3-dipotassiodimethyltrisilane.5b With the
same 1,3-dianion also the formation of cyclotetrasilane 1 was
possible by treatment with dichlorodimethylsilane (Scheme 1).
The treatment of 1 with 1 equiv of potassium tert-butoxide pro-
vided the respective anionic compound 2 in a clean reaction.5b
Further derivatization to compounds such as 3 is thus easily pos-
sible (Scheme 1). Attempts to convert 1to the respective dianionic
compound by reaction with 2 equiv of potassiumtert-butoxide in
the presence of crown ether were not successful. Also the reaction
of 3 with 1 equiv of potassium tert-butoxide failed. In both cases
mixtures of acyclic compounds together with traces of the
expected materials were observed. Related ring-opening behavior
was observed before in the reaction of 1,1,2,2-tetrakis(trimethyl-
silyl)tetramethylcyclotetrasilane with potassium tert-butoxide.5b
Recently, we synthesized a series of octamethylcyclohexa-
silanes containing two bis(trimethylsilyl)silylene units in either
1,2,21 1,3,21 or 1,44a orientation. The synthesis of a cyclohexa-
silane with three bis(trimethylsilyl)silylenes in 1,3,5 orientation
was another goal. This compound was already reported by
Blinka and West as the product of Al(Fe)Cl3-catalyzed re-
arrangement of permethylated cyclododecasilane.22 Our own
attempts to obtain the compound by a related reaction from an
isomeric starting material revealed that this process exclusively
leads to cyclopentasilanes.23 We therefore decided to obtain
(10) Plitt, H. S.; Downing, J. W.; Raymond, M. K.; Balaji, V.; Michl,
J. J. Chem. Soc., Faraday Trans. 1994, 90, 1653–1662.
(11) Neumann, F.; Teramae, H.; Downing, J. W.; Michl, J. J. Am.
Chem. Soc. 1998, 120, 573–582.
(12) Michl, J.; West, R. Acc. Chem. Res. 2000, 33, 821–823.
(13) Fujiki, M. J. Organomet. Chem. 2003, 685, 15-34, and refer-
ences therein.
(14) (a) Tamao, K.; Tsuji, H.; Terada, M.; Asahara, M.; Yamaguchi,
S.; Toshimitsu, A. Angew. Chem., Int. Ed. 2000, 39, 3287–3290. (b) Tsuji,
H.; Terada, M.; Toshimitsu, A.; Tamao, K. J. Am. Chem. Soc. 2003, 125,
7486–7487. (c) Tsuji, H.; Fukazawa, A.; Yamaguchi, S.; Toshimitsu, A.;
Tamao, K. Organometallics 2004, 23, 3375–3377. (d) Mallesha, H.; Tsuji,
H.; Tamao, K. Organometallics 2004, 23, 1639–1642. (e) Fukazawa, A.;
Tsuji, H.; Tamao, K. J. Am. Chem. Soc. 2006, 128, 6800–6801.
(15) (a) Mazieres, S.; Raymond, M. K.; Raabe, G.; Prodi, A.; Michl,
J. J. Am. Chem. Soc. 1997, 119, 6682–6683. (b) Krempner, C.; Reinke, H.
Organometallics 2007, 26, 2053–2057.
(16) (a) Okumura, H.; Kawaguchi, Y.; Harada, A. Macromol. Rapid
Commun. 2002, 23, 781–785. (b) Okumura, H.; Kawaguchi, Y.; Harada, A.
Macromolecules 2003, 36, 6422–6429. (c) Sakamoto, T.; Naruoka, T.; Kira,
M. Chem. Lett. 2003, 32, 380–380. (d) Sanji, T.; Yoshiwara, H.; Sakurai, H.;
Tanaka, M. Chem. Commun. 2003, 1506–1507. (e) Sanji, T.; Kato, N.; Kato,
M.; Tanaka, M. Angew. Chem., Int. Ed. 2005, 44, 7301–7304. (f) Sanji, T.;
Kato, M.; Tanaka, M. Macromolecules 2005, 38, 4034–4037.
(17) (a) El-Sayed, I.; Hatanaka, Y.; Muguruma, C.; Shimada, S.;
Tanaka, M.; Koga, N.; Mikami, M. J. Am. Chem. Soc. 1999, 121, 5095–
5096. (b) El-Sayed, I.; Hatanaka, Y.; Onozawa, S.; Tanaka, M. J. Am. Chem.
Soc. 2001, 123, 3597–3598. (c) Hatanaka, Y. J. Organomet. Chem. 2003,
685, 207–217.
(18) (a) Marschner, C.; Baumgartner, J.; Wallner, A. Dalton Trans.
2006, 5667–5674. (b) Wallner, A.; Wagner, H.; Baumgartner, J.; Marschner,
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€
metallics 2005, 24, 750–761.
(20) (a) Krempner, C.; Kockerling, M. Organometallics 2008, 27,
346–352. (b) Jaeger-Fiedler, U.; Kockerling, M.; Ludwig, R.; Wulf, A.;
Krempner, C. Angew. Chem., Int. Ed. 2006, 45, 6755–6759. (c) Reinke, H.;
Krempner, C. J. Organomet. Chem. 2003, 685, 134–137.
(21) Wallner, A.; Holbling, M.; Baumgartner, J.; Marschner, C.
€
Silicon Chem. 2005, 3, 175–185.
€
(22) Blinka, T. A.; West, R. Organometallics 1986, 5, 128–133.
(23) Wagner, H.; Wallner, A.; Fischer, J.; Flock, M.; Baumgartner,
J.; Marschner, C. Organometallics 2007, 26, 6704–6717.

2662 Organometallics, Vol. 29, No. 12, 2010
Scheme 2. Synthesis of Undecamethylcyclohexasilanyl-Containing Compounds 8 and 11
Wallner et al.
the compound utilizing oligosilanyl dianion chemistry.
The initial idea was to obtain the compound by reaction
by Al(Fe)Cl3-catalyzed rearrangement of permethylated
cyclododecasilane.22
of
a suitable 1,5-dianionic precursor with dichloro-
dimethylsilane. The thus required synthesis of 1,1,1,3,3,5,
5,5-octakis(trimethylsilyl)tetramethylpentasilane (5) was
achieved by reaction of 2 equiv of tris(trimethylsilyl)silyl-
potassium with bis(trifluoromethylsulfonyloxydimethylsilyl)bis-
(trimethylsilyl)silane (eq 1). The latter was obtained from the
reaction of bis(trimethylsilyl)bis(phenyldimethylsilyl)silane (4)
with 2 equiv of triflic acid.
Attempts to convert 6 to the respective oligosilyl anions by
reaction with potassium tert-butoxide revealed that these reac-
tions are not clean. It was possible to obtain the monoanion,
which slowly undergoes a back-biting process. Attempts to
achieve formation of a dianion by addition of 2 equiv of
potassium tert-butoxide and 18-crown-6 failed. This failure is
somewhat surprising considering the fact that the formation of
dianions was easily possible with 1,1,3,3- and 1,1,4,4-tetrakis-
(trimethylsilyl)octamethylcyclohexasilanes.4a,c
Synthesis of Connected Ring Systems. With a number of
cyclo- and bicyclosilane building blocks in hand we set out to
prepare a number of oligosilane compounds containing both
cyclic and acyclic structure elements. The selective formation
of polysilanyl mono- and dianions enabled the stepwise
synthesis of well-defined oligosilanes.25
While it was possible to obtain a 1,5-dipotassium com-
pound starting from 1,1,1,5,5,5-hexakis(trimethylsilyl)hexa-
methylpentasilane,5a the reaction of 5 with even 1 equiv of
potassium tert-butoxide led to the formation of 1 and tris-
(trimethylsilyl)silylpotassium (eq 2). A similar back-biting
process was observed before in the reaction of 1,1,1,6,6,6-
hexakis(trimethylsilyl)octamethylhexasilane with potassium
tert-butoxide, which led to the formation of 1,1-bis(trimethyl-
silyl)octamethylcyclopentasilane.24
Reaction of the monopotassium compound 7, which was
obtained from 1,1,1,4,4,4-hexakis(trimethylsilyl)tetramethyl-
tetrasilane (16), with undecamethylcyclohexasilanyl bromide
led to the formation of 1,1,4,4,4-pentakis(trimethylsilyl)-1-
undecamethylcyclohexasilanyltetramethyltetrasilane (8)
(Scheme 2). In a similar way the reaction of the 1,4-dipotassium
compound 9 with 2 equiv of undecamethylcyclohexa-
silanyl bromide gave 1,1,4,4-tetrakis(trimethylsilyl)-1,4-bis-
(undecamethylcyclohexasilanyl)-2,2,3,3-tetramethyltetra-
silane (11) (Scheme 2). An alternative (slightly lower yielding)
route to 11 arose from the coupling of 2 equiv of the mono-
potassium compound derived from 104a with dichlorotetra-
methyldisilane (Scheme 2).
A change of strategy, employing the ditriflate-neopen-
tasilane building block that was used for the synthesis of 5,
allowed the synthesis of 6 utilizing 1,1,3,3-tetrakis(tri-
methylsilyl)-1,3-dipotassiodimethyltrisilane (eq 3). While
the identity of 6 was confirmed unambiguously by single-
1
crystal structure analysis, its H and 29Si NMR spectro-
scopic properties are not in agreement with reported
data.22 This provided final proof that 6 was not formed
Reactions of 2 equiv of the monopotassium derivative of 12
with 1,2-, 1,4-, or 1,6-dichloropermethylsilanes gave the di-,
(24) Mechtler, C.; Zirngast, M.; Gaderbauer, W.; Wallner, A.;
Baumgartner, J.; Marschner, C. J. Organomet. Chem. 2006, 691, 150–
158.
(25) Marschner, C. Organometallics 2006, 25, 2110–2125.

Article
Organometallics, Vol. 29, No. 12, 2010 2663
Scheme 3. Synthesis of Di-, Tetra-, and Hexasilanylene-Linked Bis[1,4,4-tris(trimethylsilyl)octamethylcyclohexasilanyl]
Compounds 13, 14, and 15
Scheme 4. Synthesis of Di- and Tetrasilanylene-Linked Bis{[2.2.2]bicyclooctasilanyl} Compounds 20 and 21
Scheme 5. Synthesis of Di- and Tetrasilanylene-Linked Bis{[2.2.1]bicycloheptasilanyl} Compounds 23 and 24
Scheme 6. Synthesis of Di- and Tetrasilanylene-Linked Bis(cyclotetrasilanyl) 25 and 26
tetra-, and hexasilanylene-linked bis[1,4,4-tris(trimethylsilyl)-
octamethylcyclohexasilanyl] compounds 13, 14, and15, respec-
tively (Scheme 3).
In an analogous manner 2 equiv of the monopotassium
derivative of 19 with 1,2- and 1,4-dichloropermethylsilanes
gave the di- and tetrasilanylene-linked bis{[2.2.2]bicyclo-
octasilanyl} compounds 20 and 21 (Scheme 4).
The cyclotetrasilane 1 crystallizes in the triclinic space
group P1. In 1 (Figure 1), as already shown for similar
compounds,5b there is only a slight difference between
˚
˚
endocyclic Si-Si (2.37 A) and exocyclic Si-SiMe3 (2.35 A)
bond lengths. For 2 (Figure 2) all Si-Si distances are
shortened for the exocyclic to 2.33 A, and the endocyclic
˚
˚
are in the range 2.35 to 2.37 A.
Similarly to the synthesis of 20 and 21, the monopotassium
derivative of 22 could be utilized to obtain di- and tetra-
silanylene-linked bis{[2.2.1]bicycloheptasilanyl} compounds
23 and 24 (Scheme 5).
For the introduction of four-membered rings 2 equiv of
compound 2 was reacted with 1,2- and 1,4-dichloroper-
methyldi- and -tetrasilanes (Scheme 6).
The two starting materials 4 and 5 crystallize in the triclinic
space group P1 and in the monoclinic space group P2(1)/c,
respectively. In tetrakis(trimethylsilyl)silane the Si-Si bonds
˚
are 2.34 A long and the bond angles (Si-Si-Si) are 109.3°
and 109.7°.26 Exchanging two methyl groups for phenyl in 4
˚
(Figure 3) elongates the Si-Si bonds to 2.36 A and increases
the bond angles between the central silicon and the two
Crystal Structure Analyses. On previous occasions we have
seen that the conformations of highly branched oligosilanes are
very similar in solid state and in solution.18a Hence it was espe-
cially interesting to obtain crystals from compounds containing
connected ring systems, but we succeeded only in 11, 13, and 14.
SiMe2Ph groups to 112.6°. In 5 all Si-Si bond distances are
€
(26) Dinnebier, R. E.; Dollase, W. A.; Helluy, X.; Kummerlen, J.;
Sebald, A.; Schmidt, M. U.; Pagola, S.; Stephens, P. W.; van Smaalen, S.
Acta Crystallogr. B 1999, 55, 1014–1029.

2664 Organometallics, Vol. 29, No. 12, 2010
Wallner et al.
The distances in this series of coordinating carbon and
˚
potassium atoms can range from as small as 2.89 A up to
˚
3.6 A; thus here we are in this range with 3.3 A.
˚
The six-membered ring 6 crystallizes in the orthorhombic
space group Pna2(1), bearing two independent molecules in
the asymmetric unit. The ring exhibits a twisted boat con-
˚
formation with Si-Si bond lengths between 2.35 and 2.39 A
within the ring and also for the exocyclic bonds (Figure 5).
The bond angles between all quaternary silicon atoms
(Si6-Si1-Si2, Si2-Si3-Si4, Si4-Si5-Si6) are widened to
about 117°.
Compound 8 crystallizes in the monoclinic space group
P2(1). The cyclohexasilane part adopts a not quite regular
chair conformation with ring bond angles between 108.1°
and 116.5° (Figure 6). Si-Si bond lengths are between 2.33
˚
˚
and 2.38 A within the ring and between 2.36 and 2.40 A along
the backbone.
Compound 11 crystallizes in the triclinic space group P1
with an inversion center between the two dimethylsilylene
spacer silicon atoms. Again, the Si-Si bond lengths along the
Figure 1. Molecular structure and numbering of 1 with 30%
probability thermal ellipsoids. Hydrogen atoms are omitted for
˚
clarity. Selected bond lengths [A] and bond angles [deg] with esti-
˚
backbone are slightly elongated (between 2.39 and 2.40 A)
compared to the ring distances. The cyclohexasilane part
shows bond angles between 104.2° and 114.3°, and the rings
adopt a trans position to each other (Figure 8). In analogy
with the parent molecule of dodecamethylcyclohexasilane29
8 and 11 show all the cyclohexasilanyl units to exhibit chair
conformations, with the sterically more demanding substit-
uents occupying the equatorial positions. The structures of 8
and 11 are quite illustrative with respect to the conforma-
tional possibilities of the compounds (Figure 11). As can be
seen in Figure 6 (lower part) molecule 8 contains two
transoid-aligned chain segments. One segment consists of a
hexasilane unit, which is present in a similar conformation to
that found for 16.30 The second segment is a pentasilane unit,
which includes a trisilane moiety from the cyclohexasilane
and two silicon atoms from the bis(trimethylsilyl)silyl section.
The two segments are oriented perpendicular to each other.
For compound 11 a different conformation was found. Here
the two undecamethylcyclohexasilanyl rings are oriented in a
way to extend the aligned chain, which is similar to what has
been observed for 16, by addition of a trisilanyl unit (Figure 8,
bottom).
mated standard deviations: Si(1)-Si(3) 2.3463(10), Si(1)-Si(4)
2.3465(12), Si(1)-Si(2) 2.3664(9), Si(1)-Si(2A) 2.3681(8), Si(2)-
C(1) 1.879(2), Si(3)-Si(1)-Si(4) 109.90(4), Si(3)-Si(1)-Si(2)
116.33(4), Si(4)-Si(1)-Si(2) 114.25(4), Si(2)-Si(1)-Si(2A)
89.03(4), Si(2A)-Si(1)-Si(2)-Si(1A) 0.0.
˚
in a normal range between 2.36 and 2.39 A, but the steric
strain of the two trimethylsilyl groups at the central silicon
increases the bond angles along the silicon backbone from
the ideal 109.5° to 127.8° (Si2-Si3-Si4) and 129.0° (Si4-
Si5-Si6). The bond angles around the central silicon atom in
the chain are in a range between 104.0° and 113.6°, whereas
these angles around the central silicon atoms of the two
terminal tris(trimethylsilyl)silyl groups are between 101.9°
and 120.1° around Si2 and 103.5° and 121.9° around Si6.
These strong deviations lead to a bending of the silicon
backbone, shown in Figure 4 (lower part).
The crown ether adducts of 10 and 2 crystallize in the
monoclinic space groups P2(1)/n and P2(1)/c, respectively.
10 is the first example of a trisilylated silyl anion with an
attached cyclosilanyl substituent. The ring exhibits a perfect
chair conformation with the metalated silicon atom in the
expected equatorial position (Figure 7). Si-Si bond dis-
tances within the molecule are fairly short, mostly around
The comparison of the two compounds 13 and 14 (Figures 9
and 10) is also interesting. Si-Si bond distances are in the range
between 2.34 and 2.38 A, and the bond angles are unexcep-
˚
˚
˚
˚
2.34 A. The Si-K distances of 3.52 A for 10 and 3.55 A for 2
fall into the range 3.45 to 3.60 A found in the other
tional. Again the transoid alignment of the main chain extends
into the cyclohexasilanyl units. Like the parent compound
1,1,4,4-tetrakis(trimethylsilyl)octamethylcyclohexasilane31 all
the six-membered rings in both molecules adopt a twist con-
formation. The interesting feature that distinguishes the struc-
tures of 13 and 14 is that the transoid alignment of 13 includes
two additional ring atoms (Figure 9, bottom right), while for
compound 14 the participation of only one additional atom is
found (Figure 10, bottom). The explanation for this somewhat
strange finding is that the rings in 13 and 14 do not feature the
˚
characterized cases of oligosilyl potassium crown-ether
adducts.27 The introduction of a negative charge onto a ring
atom, as in 2 (Figure 2), causes a folding of the previously
planar ring of 1 (Figure 1) by 20°. A folding by 31° was also
found comparing the planar ring of octakis(trimethylsilyl)-
cyclotetrasilane to the heptakis(trimethylsilyl)cyclotetra-
silanyl sodium DME adduct.5b The packing pattern of 2
shows a band-shaped supramolecular arrangement with
a coordination of the potassium atom toward a methyl
group (C32) of a neighboring molecule. This motif is pre-
dominant in cases of silyl potassium crown ether adducts.28
(29) Carrell, H. L.; Donohue, J. Acta Crystallogr. B 1972, 28, 1566–1571.
(30) (a) Lambert, J. B.; Pflug, J. L.; Allgeier, A. M.; Campbell, D. J.;
Higgins, T. B.; Singewald, E. T.; Stern, C. L. Acta Crystallogr. Sect. C:
Cryst. Struct. Commun. 1995, 51, 713–715. (b) Whittaker, S. M.; Brun,
M.-C.; Cervantes-Lee, F.; Pannell, K. H. J. Organomet. Chem. 1995, 499,
247–252.
(31) Fischer, R.; Konopa, T.; Ully, S.; Wallner, A.; Baumgartner, J.;
Marschner, C. In Organosilicon Chemistry VI. From Molecules to
Materials; Auner, N.; Weis, J., Eds.; Wiley-VCH: Weinheim, 2005; pp
355-360.
(27) (a) Kayser, C.; Fischer, R.; Baumgartner, J.; Marschner, C.
Organometallics 2002, 21, 1023–1030. (b) Jenkins, D. M.; Teng, W.;
Englich, U.; Stone, D.; Ruhlandt-Senge, K. Organometallics 2001, 20,
4600–4606.
(28) (a) Likhar, P. R.; Zirngast, M.; Baumgartner, J.; Marschner, C.
Chem. Commun. 2004, 1764–1765. (b) Baumgartner J. Unpublished results.

Article
Organometallics, Vol. 29, No. 12, 2010 2665
Figure 2. Molecular structure and numbering of 2 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
˚
Selected bond lengths [A] and bond angles [deg] with estimated standard deviations: Si(1)-Si(5) 2.325(2), Si(1)-Si(3) 2.347(2),
Si(1)-Si(2) 2.350(2), Si(1)-K(1) 3.5531(18), Si(2)-C(26) 1.889(5), Si(2)-Si(4) 2.367(2), Si(3)-Si(4) 2.359(2), Si(4)-Si(7) 2.333(2),
Si(4)-Si(6) 2.334(2), K(1)-C(32A) 3.331(5), Si(3)-Si(1)-Si(2) 84.56(7), Si(3)-Si(1)-K(1) 137.75(7), Si(2)-Si(1)-K(1) 123.96(6),
Si(1)-Si(2)-Si(4) 91.93(8), Si(1)-Si(3)-Si(4) 92.20(7), Si(3)-Si(4)-Si(2) 83.92(7), C(32A)-K(1)-Si(1) 160.21(11), Si(3)-Si(1)-
Si(2)-Si(4) 20.40(7).
UV Spectroscopy. The influence of the six-membered rings
on the UV absorption properties of compounds 8 and 11 can
be estimated from the comparison with 1,1,1,4,4,4-hexakis-
(trimethylsilyl)tetramethyltetrasilane (16) in Figure 12.
The replacement of one trimethylsilyl group of 16 by the
cyclohexasilanyl unit in 8 induces a bathochromic shift of the
low-energy absorption (maximum at 261 nm (ε=4.8ꢀ 104) anda
shoulder at 281 nm). This trend is further enforced by the addition
of another ring in compound 11 (maximum at 270 nm (ε = 3.6 ꢀ
104) and two shoulders at 241 and 286 nm). The sharp bands of 16
are replaced by broader bands for 8and 11. These can be attributed
to a higher degree of conformational flexibility as the cyclohexa-
silanyl units might undergo fast conformational changes.
Figure 13 compares the UV spectra of the di-, tetra-, and
hexasilanylene-linked bis[1,4,4-tris(trimethylsilyl)octamethyl-
cyclohexasilanyl] compounds 13, 14, and 15 with the respective
tris(trimethylsilyl)silyl-terminated analogues (16, 17, 18). Com-
pound 13, with two silicon atoms between the cyclic building
blocks, exhibits two different bathochromic shifted maxima
at longer wavelengths, 265 nm (ε = 3.8 ꢀ 104) and 289 nm (ε =
3.6 ꢀ 104), compared to the linear compound 16. The bath-
ochromic shift may be interpreted by the extension of the
transoid-aligned segments into the cyclic parts. Compound 14,
with four silicon atoms as spacers, shows only one strongly
Figure 3. Molecular structure and numbering of 4 with 30%
probability thermal ellipsoids. Hydrogen atoms are omitted for
˚
clarity. Selected bond lengths [A] and bond angles [deg] with
estimated standard deviations: Si(1)-Si(4) 2.3494(10), Si(1)-
Si(5) 2.3520(13), Si(1)-Si(2) 2.3529(8), Si(1)-Si(3) 2.3604(9),
Si(2)-C(7) 1.8750(19), Si(4)-Si(1)-Si(5) 109.22(4), Si(4)-
Si(1)-Si(2) 108.51(3), Si(5)-Si(1)-Si(2) 108.62(4), Si(4)-Si(1)-
Si(3) 106.01(4), Si(5)-Si(1)-Si(3) 111.80(4), Si(2)-Si(1)-Si(3)
112.56(4).
bathochromic shifted maximum at 297 nm (ε = 5.5 ꢀ 104)
comparable to 1,1,1,6,6,6-hexakis(trimethylsilyl)octa-
methylhexasilane (17) (Figure 13). The one narrow band of 17
indicates one predominant conformation, and the same seems to
be true for 14. The six-membered rings should maintain their
trans position (Figure 5) also in solution. An additional shoulder
at 273 nm may be attributed to a less abundant conformer. The
two maxima of 1,1,1,8,8,8-hexakis(trimethylsilyl)dodecamethyl-
octasilane (18) show the limit of the conformational control
gained by tris(trimethylsilyl)silyl units as end-groups.18 The
steric demand of these groups is not sufficient to conforma-
tionally confine a spacer consisting of six dimethylsilylene
same twist conformation. Switching of 14 to the second twist
conformer would cause the same extension of alignment as was
found for 13.

2666 Organometallics, Vol. 29, No. 12, 2010
Wallner et al.
Figure 4. Molecular structure and numbering of 5 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
˚
Selected bond lengths [A] and bond angles [deg] with estimated standard deviations: Si(1)-C(1) 1.884(3), Si(1)-Si(2) 2.3790(11),
Si(2)-Si(3) 2.3899(11), Si(3)-Si(4) 2.3874(11), Si(4)-Si(5) 2.3742(11), Si(5)-Si(6) 2.3857(11), Si(6)-Si(7) 2.3584(11), Si(1)-Si(2)-
Si(3) 101.89(4), Si(2)-Si(3)-Si(4) 127.82(4), Si(3)-Si(4)-Si(5) 108.13(4), Si(4)-Si(5)-Si(6) 129.01(4), Si(5)-Si(6)-Si(7) 112.12(4).
units tooneconformer. This can be seen bythe occurrence ofa
second band in the UV spectrum. The comparable compound
15 shows a bathochromic maximum at 303 nm (ε1 =7.3 ꢀ
104 M-1cm-1) and a shoulder around 290 nm (Figure 13),
which also indicates the existence of two conformers in
solution. The crystal structures of 13 and 14 show that both
compounds have transoid-aligned octasilane segments. How-
ever, the conformational change of the two twist conformers
would extend the segment of 14 by two silicon atoms. This
process is facile,21,32 and it is therefore likely that all ring
conformers are present in solution. At the same instance it is
also valid to expect conformers of 12 in solution, which
contain the other twist conformers and thus have shortened
transoid-aligned segments.
Compounds 20 and 21 differ from 13 and 14 by the
introduction of the tetramethyldisilanylene bridge sections,
which generates a [2.2.2]bicyclooctasilane cage and thus
locks the conformation of the cyclohexasilane system. This
seems to result in mainly one conformer existing in solution,
as only one low-energy band can be observed in each of the
UV spectra (Figure 14) of 20 (288 nm) and 21 (299 nm). The
positions of these absorption maxima do not differ substan-
tially from those for 13 and 14.
Compounds 23 and 24 are very similar to 20 and 21 in a sense
that the [2.2.2]bicyclooctasilane units are replaced by [2.2.1]-
bicycloheptasilane entities. The reason for this change was that it
can be expected that the [2.2.1]bicycloheptasilane might allow
conjugation over the dimethylsilylene bridge unit. However, the
spectra of 23 and 24 (Figure 15) are fairly similar to those of 20
and 21. The low-energy absorption band of 23 (290 nm) is
somewhat broader compared to the spectrum of 20.
Changing from the cyclohexasilane units to cyclotetra-
silanyl moieties changes the UV absorption behavior in an
unexpected way (Figure 16). The comparison with the acyclic
reference compounds 16 and 17 shows that the bands at
255 nm (25) and 275 nm (26) correspond to transoid-aligned
hexa- and octasilanyl fragments composed of the spacer and
the attached isotetrasilanyl units. The more astonishing
feature of both 25 and 26 is an absorption band around
323 nm. This particular band is not found in the spectrum of
compound 1, which is shown for comparison (Figure 16).
Conclusion. A number of compounds where cyclosilanes
are connected with silanylene spacers of different lengths
(32) Tekautz, G.; Binter, A.; Hassler, K.; Flock, M. ChemPhysChem
2006, 7, 421–429.

Article
Organometallics, Vol. 29, No. 12, 2010 2667
contain two additional silylene units, the cyclosilane-con-
taining compounds exhibit bathochromic shift behavior. The
comparison of the low-energy absorption maxima of the 1,4,4,-
tris(trimethylsilyl)cyclohexasilanyl-, the [2.2.2]bicyclooctasilanyl-,
and the [2.2.1]bicycloheptasilanyl-connected compounds shows
no marked differences. The non-bicyclic compounds exhibit
additional bands that can be attributed to conformational flexi-
bility in the cyclohexasilane unit. Although a longer transoid-
aligned segment was expected for the compounds containing the
[2.2.1]bicycloheptasilanyl unit, no clear bathochromic shift was
observed. A possible explanation for this arises from a compar-
ison of the UV spectra of 19 and 22. It was assumed that 22,
which contains one transoid-aligned pentasilane unit, would
exhibit a clearly red-shifted absorption behavior compared to
19. However, the spectrum of 22 is rather similar to that of 19,
with the expected pentasilanes absorption around 250 nm only
visible as a shoulder.
Surprisingly, it was found that the structurally very similar
compounds containing the 1,3,3-tris(trimethylsilyl)tetra-
methylcyclotetrasilanyl units show the most bathochromic
shifted bands. The fact that both compounds of this type
show the low-energy band at about the same wavelength,
irrespective of the spacer unit, suggests that this particular
band is associated with the cyclotetrasilane unit. Absorption
at comparatively low energy is also known for peralkylated
cyclotetrasilanes.33
Experimental Section
General Remarks. All reactions involving air-sensitive com-
pounds were carried out under an atmosphere of dry nitrogen or
argon using either Schlenk techniques or a glovebox. Solvents
were dried using a column solvent purification system.34 Potass-
ium tert-butanolate was purchased exclusively from Merck. All
other chemical were bought from different suppliers and were
used without further purification.
Figure 5. Molecular structure and numbering of 6 with 30%
probability thermal ellipsoids. Hydrogen atoms are omitted for
˚
clarity. Selected bond lengths [A] and bond angles [deg] with
estimated standard deviations: Si(1)-Si(2) 2.3767(16), Si(1)-Si(6)
2.3823(16), Si(2)-Si(3) 2.3594(16), Si(2)-Si(7) 2.3711(17), Si(3)-
Si(4) 2.3456(14), Si(4)-Si(5) 2.3544(14), Si(5)-Si(6) 2.3864(15),
Si(2)-Si(1)-Si(6) 117.67(7), Si(3)-Si(2)-Si(1) 113.90(6), Si(4)-
Si(3)-Si(2) 117.06(6), Si(3)-Si(4)-Si(5) 108.32(6), Si(3)-Si(4)-
Si(9) 108.26(7), Si(5)-Si(4)-Si(9) 107.90(6), Si(4)-Si(5)-Si(6)
116.62(6), Si(1)-Si(6)-Si(5) 117.25(6).
1H (300 MHz), 13C (75.4 MHz), and 29Si (59.3 MHz) NMR
spectra were recorded on a Varian Unity INOVA 300. Samples for
29Si spectra were either dissolved in deuterated solvents 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.35 If not noted otherwise, the used
solvent was C6D6 and all samples were measured at rt.
were synthesized. Due to their cyclic nature, the cyclosilane
parts of these molecules have only restricted conformational
freedom. On the basis of our recent studies concerning the
alignment of methylated polysilane chains using bulky end-
groups such as the tris(trimethylsilyl)silyl group, we decided
to study the use of cyclosilanes for this purpose. As these also
consist of catenated silicon atoms, it was expected that the
conjugation of the polysilane chain would be extended into
the cyclosilane. As can be seen in Figure 17 a transoid-aligned
dodecasilane chain would be present in compound 24,
whereas only decasilane units might be expected for 11, 14,
and 21. Comparison of UV absorption behavior of the
obtained compounds with the respective tris(trimethylsilyl)-
silyl-terminated ones is interesting. It shows that in almost all
cases the introduction of a cyclosilane unit causes a marked
bathochromic shift. Compared to the tris(trimethylsilyl)silyl-
terminated compounds, the substances with the 1,4,4,-tris-
(trimethylsilyl)cyclohexasilanyl and the [2.2.2]bicycloocta-
silanyl units would be expected to contain two additional
silylene units in the transoid-aligned segment. If the positions
of the absorption maxima are compared to the tris-
(trimethylsilyl)silyl-terminated compounds with spacers that
Elementary analysis was carried out using a Heraeus Vario
Elementar EL apparatus. In cases of low carbon values, which is
attributed to the formation and incomplete combustion of
silicon carbide, the combustion time was raised to 30 s.
UV-vis absorption spectra were recorded on a Perkin-Elmer
Lambda 35 spectrometer in spectroscopy grade pentane or heptane
solutions.
X-ray Structure Determination. For X-ray structure analyses
the crystals were mounted onto the tip of glass fibers, and data
collection was performed with a Bruker-AXS SMART APEX
CCD diffractometer using graphite-monochromated Mo
2
˚
KR radiation (0.71073 A). The data were reduced to Fo and
corrected for absorption effects with SAINT36 and SADABS,37
respectively. Structures were solved by direct methods and
(33) West, R. Pure Appl. Chem. 1982, 1041–1050.
(34) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(35) (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.
(36) SAINTPLUS: Software Reference Manual, Version 6.45; Bruker-
AXS: Madison, WI, 1997-2003.
(37) Blessing, R. H. Acta Crystallogr. Sect. A 1995, 51, 33-38:
SADABS: Version 2.1; Bruker AXS, 1998.

2668 Organometallics, Vol. 29, No. 12, 2010
Wallner et al.
Figure 6. (Top) Molecular structure and numbering of 8 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for
˚
clarity. Selected bond lengths [A] and bond and torsional angles [deg] with estimated standard deviations: Si(1)-C(1) 1.910(5),
Si(1)-Si(6) 2.3614(19), Si(1)-Si(2) 2.3790(19), Si(6)-Si(1)-Si(2) 104.45(7), Si(6)-Si(1)-Si(7) 111.47(7), Si(2)-Si(1)-Si(7) 122.36(7),
Si(3)-Si(2)-Si(1) 110.23(7), Si(4)-Si(3)-Si(2) 116.50(8), Si(3)-Si(4)-Si(5) 108.04(8), Si(6)-Si(5)-Si(4) 109.84(7), Si(5)-Si(6)-Si(1)
111.72(7), Si(15)-Si(7)-Si(8) 105.26(7), Si(15)-Si(7)-Si(14) 107.33(7), Si(8)-Si(7)-Si(14) 108.91(7), Si(15)-Si(7)-Si(1) 111.60(7),
Si(8)-Si(7)-Si(1) 111.70(7), Si(14)-Si(7)-Si(1) 111.73(7), Si(9)-Si(8)-Si(7) 116.22(7), Si(10)-Si(9)-Si(8) 113.88(7), Si(13)-Si(10)-
Si(11) 111.82(7), Si(13)-Si(10)-Si(9) 113.57(7), Si(11)-Si(10)-Si(9) 114.35(7), Si(13)-Si(10)-Si(12) 104.83(7), Si(11)-Si(10)-Si(12)
105.26(7), Si(9)-Si(10)-Si(12) 105.98(7). (Bottom) Wireframe model with transoid-aligned segments highlighted.
Figure 7. Molecular structure and numbering of 10 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
˚
Selected bond lengths [A] and bond angles [deg] with estimated standard deviations: K(1)-O(1) 2.806(7), K(1)-Si(7) 3.523(3), Si(1)-C(1)
1.913(8), Si(1)-Si(6) 2.344(3), Si(1)-Si(7) 2.346(3), Si(1)-Si(2) 2.362(3), Si(6)-Si(1)-Si(7) 108.31(11), Si(6)-Si(1)-Si(2) 105.26(12),
Si(7)-Si(1)-Si(2) 127.62(12), Si(3)-Si(2)-Si(1) 112.66(12), Si(4)-Si(3)-Si(2) 114.80(12), Si(5)-Si(4)-Si(3) 110.80(13), Si(4)-Si(5)-
Si(6) 110.63(13), Si(5)-Si(6)-Si(1) 115.57(12), Si(8)-Si(7)-Si(9) 100.98(12), Si(8)-Si(7)-Si(1) 101.15(11), Si(9)-Si(7)-Si(1) 109.74(12).

Article
Organometallics, Vol. 29, No. 12, 2010 2669
Figure 8. (Top) Molecular structure and numbering of 11 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for
˚
clarity. Selected bond lengths [A] and bond and torsional angles [deg] with estimated standard deviations: Si(1)-C(1) 1.904(5),
Si(1)-Si(2) 2.369(2), Si(1)-Si(6) 2.385(2), Si(2)-Si(1)-Si(6) 104.15(8), Si(2)-Si(1)-Si(7) 115.45(8), Si(6)-Si(1)-Si(7) 118.28(8),
Si(3)-Si(2)-Si(1) 112.90(8), Si(4)-Si(3)-Si(2) 111.89(9), Si(5)-Si(4)-Si(3) 108.98(9), Si(4)-Si(5)-Si(6) 114.28(9), Si(5)-Si(6)-Si(1)
111.15(8), Si(9)-Si(7)-Si(10) 107.87(8), Si(9)-Si(7)-Si(8) 115.17(8), Si(10)-Si(7)-Si(8) 106.84(8), Si(9)-Si(7)-Si(1) 110.68(8),
Si(10)-Si(7)-Si(1) 106.22(8), Si(8)-Si(7)-Si(1) 109.60(8). (Bottom) Wireframe model with transoid-aligned segment highlighted.
Figure 9. (Top) Molecular structure and numbering of 13 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
˚
Selected bond lengths [A] and bond and torsional angles [deg] with estimated standard deviations: Si(1)-C(1) 1.884(8), Si(1)-Si(2) 2.388(3),
Si(2)-Si(8) 2.350(3), Si(8)-Si(2)-Si(3) 109.30(12), Si(8)-Si(2)-Si(7) 107.36(11), Si(3)-Si(2)-Si(7) 107.71(11), Si(8)-Si(2)-Si(1)
109.04(12), Si(3)-Si(2)-Si(1) 105.46(11), Si(7)-Si(2)-Si(1) 117.77(12), Si(4)-Si(3)-Si(2) 115.20(11), Si(3)-Si(4)-Si(5) 112.27(12),
Si(6)-Si(5)-Si(10) 110.40(12), Si(6)-Si(5)-Si(9) 110.21(12), Si(10)-Si(5)-Si(9) 105.38(12), Si(6)-Si(5)-Si(4) 110.81(11), Si(10)-Si(5)-
Si(4) 108.35(11), Si(9)-Si(5)-Si(4) 111.53(12), Si(7)-Si(6)-Si(5) 113.38(12), Si(6)-Si(7)-Si(2) 115.33(11). (Bottom left) Polysilane
skeleton with methyl groups omitted for clarity. (Bottom right) Wireframe model with transoid-aligned segment highlighted.

2670 Organometallics, Vol. 29, No. 12, 2010
Wallner et al.
Figure 10. (Top) Molecular structure and numbering of 14 with 30% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
˚
Selected bond lengths [A] and bond and torsional angles [deg] with estimated standard deviations: Si(1)-C(1) 1.889(6), Si(1)-Si(2) 2.372(3),
Si(3)-Si(2)-Si(1) 116.96(10), Si(9)-Si(3)-Si(4) 112.15(10), Si(9)-Si(3)-Si(2) 109.56(10), Si(4)-Si(3)-Si(2) 109.02(9), Si(9)-Si(3)-Si(8)
108.06(9), Si(4)-Si(3)-Si(8) 109.21(9), Si(2)-Si(3)-Si(8) 108.78(10), Si(5)-Si(4)-Si(3) 112.87(9), Si(4)-Si(5)-Si(6) 116.02(9), Si(11)-
Si(6)-Si(5) 110.82(9), Si(11)-Si(6)-Si(10) 107.72(10), Si(5)-Si(6)-Si(10) 106.31(9), Si(11)-Si(6)-Si(7) 108.74(9), Si(5)-Si(6)-Si(7)
109.90(9), Si(10)-Si(6)-Si(7) 113.33(9), Si(8)-Si(7)-Si(6) 113.23(9), Si(7)-Si(8)-Si(3) 116.44(9). (Middle) Polysilane skeleton with methyl
groups omitted for clarity. (Bottom) Wireframe model with transoid-aligned segment highlighted.
Crystallographic data (excluding structure factors) for the
structures of compounds 2, 4, 5, 6, 7, 8, 10, 11, 13, and 14
reported in this paper have been deposited with the Cambridge
Crystallographic Data Center as supplementary publication
nos. CCDC 741866 (2), 741864 (4), 741865 (5), 741867 (6),
741863 (7), 663890 (8), 663889 (10), 663891 (11), 663893 (13),
and 663892 (14). Copies of the data can be obtained free of
charge at http://www.ccdc.cam.ac.uk/products/csd/request/.
1,1,4,4,4-Pentakis(trimethylsilyl)tetramethyltetrasilanylpotas-
sium 18-crown-6 (7),39 1,1,4,4-tetrakis(trimethylsilyl)tetramethyl-
Figure 11. (Top) 2-D representation of the polysilane backbone of
the conformer found in the crystal structure of compound 8
(highlighted bonds indicate transoid-aligned segments). (Bottom)
On the left side another possible conformer of 8 where the transoid
alignment extends from the chain into the ring in the same way as
found for 11; on the right the transoid-aligned chain elements are
highlighted.
3
tetrasilanyldipotassium (18-crown-6)2 (9),39,40 bis(trimethylsilyl)
3
undecamethylcyclohexasilanylsilanylpotassium 18-crown-6 (10),4a
3
1,4,4-tris(trimethylsilyl)octamethylcyclohexasilanylpotassium 18-
3
crown-6 (12),4a 1,1,1,4,4,4-hexakis(trimethylsilyl)tetramethyltetra
silane (16),41 1,1,1,6,6,6-hexakis(trimethylsilyl)octamethylhexasilane
(17),19 1,1,1-trimethylsilyldodecamethylbicyclo[2.2.2]octasilanyl-
potassium 18-crown-6 (19),4a diphenylbis(trimethylsilyl)silane,42
refined by full-matrix least-squares method (SHELXL97).38 All
non-hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms were placed in calculated positions to
correspond to standard bond lengths and angles. All diagrams were
drawn with 30% probability thermal ellipsoids, and hydrogen atoms
were omitted for clarity. Unfortunately, the obtained crystal quality
of some substances was poor. This fact is reflected by quite high
R and low θ values (Tables 1 and 2).
3
decamethyl-1,4,-bis(trimethylsilyl)bicyclo[2.2.1]heptasilane,4,43
(39) Kayser, C.; Kickelbick, G.; Marschner, C. Angew. Chem., Int.
Ed. 2002, 41, 989–992.
(40) Fischer, J.; Gaderbauer, W.; Baumgartner, J.; Marschner, C.
Heterocycles 2006, 67, 507–510.
(41) Whittaker, S. M.; Brun, M. C.; Cervantes-Lee, F.; Pannell, K. H.
J. Organomet. Chem. 1995, 499, 247–252.
(42) Jackson, R. A.; Rhodes, C. J. J. Organomet. Chem. 1987, 336, 45–48.
(43) Fischer, J.; Baumgartner, J.; Marschner, C. Science 2005, 310, 825.
(38) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112–122.

Article
Organometallics, Vol. 29, No. 12, 2010 2671
Figure 12. Comparison of the UV spectra of 8, 11, and 16. Spectrum of tris(trimethylsilyl)silylundecamethylcyclohexasilane (10)
shown for comparison.
Figure 13. Comparison of UV spectra of methylated isotetrasilanyl and 1,4,4-tris(trimethylsilyl)cyclohexasilanyl units connected with
compounds with disilanylene (16, 13), tetrasilanylene (17, 14), and hexasilanylene spacers (18, 15). Spectrum of 1,1,4,4-tetrakis-
(trimethylsilyl)octamethylcyclohexasilane (12) shown for comparison.
bromoundecamethylcyclohexasilane,44 1,4-dichlorooctamethyl-
tetrasilane,45 2,2-dimethyl-1,1,3,3-tetrakis(trimethylsilyl)trisilanyl
mmol) in toluene (40 mL) at 0 °C. The reaction mixture remained
colorless during the whole addition process, and a white pre-
cipitate was formed. Stirring was continued for 5 h at rt, and then
the reaction mixture was subjected to an aqueous workup with
ice/diethyl ether/0.5 M H2SO4. Compound 1 was obtained as a
colorless solid, which was further purified by recrystallization
from diethyl ether/acetone (380 mg, 95%). Mp: 183-187 °C.
dipotassium (18-crown-6)2,5b and 1,6-dichlorododecamethylhexa-
3
silane46 were prepared according to reported procedures.
Aqueous workup was performed by pouring the reaction
mixture on aqueous H2SO4 (0.5 or 2 M). After separation of
the layers the aqueous layer was extracted twice with the organic
solvent. The combined organic layers were first washed with a
saturated aqueous sodium hydrogen carbonate solution and
then dried over sodium sulfate.
NMR (δ in ppm): 1H (CDCl3) 0.22 (s, 36H), 0.50 (s, 12H); 13
C
(CDCl3) 2.5, 3.2; 29Si (CDCl3) -8.2 (Me3Si), -25.5 (Me2Si),
-95.0 (Siq). Anal. Calcd for C16H48Si8 (465.24): C 41.31, H 10.40.
Found: C 41.08, H 10.44. UV absorption: λ1 = 217 nm (ε1 =
5.4 ꢀ 104 [M-1 cm-1]), λ2 = 238 nm (ε2 = 2.0 ꢀ 104 [M-1 cm-1]),
λ3 = 253 nm (ε3 = 9.3 ꢀ 103 [M-1 cm-1]).
1,1,3,3-Tetrakis(trimethylsilyl)tetramethylcyclotetrasilane (1).
A solution of dimethyl-1,1,3,3-tetrakis(trimethylsilyl)trisilanyl-
dipotassium (18-crown-6)2 (0.860 mmol) in toluene (20 mL)
3
was added slowly to dichlorodimethylsilane (122 mg, 0.946
1,3,3-Tris(trimethylsilyl)tetramethylcyclotetrasilanylpotassium
3
18-crown-6 (2) and 1,1,3-Tris(trimethylsilyl)pentamethylcyclo-
tetrasilane (3). A solution of 1 (150 mg, 0.322 mmol) in toluene
(12 mL) was treated with potassium tert-butoxide (38 mg, 0.338
mmol) and 18-crown-6 (89 mg, 0.338 mmol). After 2 h the
reaction was complete [NMR (δ in ppm): 1H 0.62 (s, 18H), 0.65
(s, 9H), 0.96 (s, 12 H); 29Si δ -5.9 (Me3SiSiK), -10.7 (Me3SiSi),
-26.0 (Me2Si); -98.6 (Siq); -136.8 (SiK)]. This reaction mixture
(44) Mitter, F. K.; Pollhammer, G. I.; Hengge, E. J. Organomet.
Chem. 1986, 314, 1–5.
€
(45) (a) Stadelmann, B. Thesis, Technische Universitat Graz, 1994.
(b) Chernyavskii, A. I.; Yu. Larkin, D.; Chernyavskaya, N. A. Russ. Chem.
Bull. 2002, 51, 175–180. (c) Levitsky, M. M.; Zavin, B. G.; Chernyavskii,
A. I.; Erokhin, V. V. Russ. Chem. Bull. 1999, 49, 1789–1790.
(46) Gilman, H.; Inoue, S. J. Org. Chem. 1964, 29, 3418–3419.

2672 Organometallics, Vol. 29, No. 12, 2010
Table 1. Crystallographic Data for Compounds 1, 2, 4, 5, and 6
Wallner et al.
1
2
4
5
6
empirical formula
Mw
temperature [K]
size [mm]
cryst syst
C
465.26
16H48Si8
C25H62KO6Si7
694.48
100(2)
0.40 ꢀ 0.28 ꢀ 0.25
monoclinic
P2(1)/c
10.366(2)
19.171(4)
21.170(4)
90
96.37(3)
90
4207(2)
C22H40Si5
444.99
100(2)
C28H84Si13
786.12
100(2)
0.40 ꢀ 0.30 ꢀ 0.25
monoclinic
P2(1)/n
9.740(2)
31.897(6)
16.617(3)
90
94.52(3)
90
5146(2)
C48H144Si24
1395.79
100(2)
0.40 ꢀ 0.36 ꢀ 0.30
orthorhombic
Pca21
24.391(5)
19.863(4)
18.147(4)
90
90
90
8792(3)
4
1.055
0.368
3072
150(2)
0.35 ꢀ 0.28 ꢀ 0.22
0.32 ꢀ 0.28 ꢀ 0.20
triclinic
P1
triclinic
P1
9175(2)
space group
˚
a [A]
9.119(2)
9.407(2)
9.870(2)
76.07(3)
81.57(3)
65.31(3)
746(2)
1
1.036
0.361
256
˚
b [A]
9.561(2)
18.183(4)
75.97(3)
81.92(3)
62.00(3)
1366(2)
2
1.082
0.268
484
˚
c [A]
R [deg]
β [deg]
γ [deg]
3
˚
V [A ]
Z
F
4
1.096
0.356
1508
4
1.015
0.342
1736
calc [g cm-3
]
absorp coeff [mm-1
F(000)
]
θ range
2.13 < θ < 26.35
5952/3004
98.4
3004/0/117
1.11
R1 = 0.037,
wR2 = 0.089
R1 = 0.040,
wR2 = 0.092
0.36/-0.18
1.43 < θ < 25.00
29 669/7384
99.7
7384/0/364
1.15
R1 = 0.082,
wR2 = 0.173
R1 = 0.115,
wR2 = 0.188
0.65/-0.44
2.31 < θ < 26.37
710 973/5496
98.6
5496/0/254
1.03
R1 = 0.039,
wR2 = 0.097
R1 = 0.048,
wR2 = 0.103
0.60/-0.21
1.28 < θ < 26.38
40 646/10 494
99.7
10 494/0/398
1.08
R1 = 0.054,
wR2 = 0.104
R1 = 0.078,
wR2 = 0.111
0.54/-0.31
1.67 < θ < 28.35
72 642/20 647
96.5
20 647/1/650
1.04
R1 = 0.0566
wR2 = 0.1154
R1 = 0.0790
wR2 = 0.1231
0.56/-0.33
reflns collected/unique
completeness to θ [%]
data/restraints/params
goodness of fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
-
3
largest diff peak/hole [e /A ]
˚
Table 2. Crystallographic Data for Compounds 8, 10, 11, 13, and 14
8
10
11
13
14
empirical formula
Mw
temperature [K]
size [mm]
cryst syst
C30H90Si15
872.37
100(2)
0.52 ꢀ 0.40 ꢀ 0.25
monoclinic
P2(1)
15.993(3)
9.880(2)
18.665(4)
90
107.97(3)
90
2795(2)
C29H75KO6Si9
811.80
100(2)
0.42 ꢀ 0.32 ꢀ 0.28
monoclinic
P2(1)/n
10.144(2)
21.284(4)
22.641(5)
90
96.56(3)
90
4856(2)
C38H114Si20
1133.09
100(2)
C19H57Si10
566.55
100(2)
0.40 ꢀ 0.32 ꢀ 0.26
monoclinic
C2
16.160(3)
10.545(2)
22.036(4)
90
106.59(3)
90
3599(2)
C42H126Si22
1249.41
100(2)
0.48 ꢀ 0.30 ꢀ 0.22
monoclinic
P2(1)/n
9.4839(2)
24.749(5)
16.970(3)
90
93.36(3)
90
3977(2)
0.32 ꢀ 0.20 ꢀ 0.18
triclinic
P1
9.946(2)
space group
˚
a [A]
˚
b [A]
13.658(3)
15.241(3)
105.86(3)
99.83(3)
111.00(3)
1774(6)
1
1.060
0.378
622
˚
c [A]
R [deg]
β [deg]
γ [deg]
3
˚
V [A ]
Z
F
2
1.037
0.361
960
4
1.110
0.364
1768
4
1.046
0.373
1244
2
1.044
0.371
1372
calc [g cm-3
]
absorp coeff [mm-1
F(000)
]
θ range
1.34 < θ < 25.00
20 169/9710
99.8
9710/1/437
0.98
R1 = 0.058,
wR2 = 0.127
R1 = 0.074,
wR2 = 0.133
0.57/-0.31
1.32 < θ < 23.00
28 805/6750
100
6750/0/423
1.12
R1 = 0.107,
wR2 = 0.211
R1 = 0.151,
wR2 = 0.237
0.88/-0.41
1.71 < θ < 26.37
14 250/7139
98.6
7139/0/281
0.96
R1 = 0.081,
wR2 = 0.154
R1 = 0.146,
wR2 = 0.176
0.57/-0.37
1.93 < θ < 24.50
12 583/5908
99.9
5908/1/282
1.10
R1 = 0.086,
wR2 = 0.149
R1 = 0.108,
wR2 = 0.158
0.49/-0.48
1.46 < θ < 25.00
28 357/6993
99.8
6993/0/310
0.85
R1 = 0.069,
wR2 = 0.111
R1 = 0.200,
wR2 = 0.142
0.45/-0.41
reflns collected/unique
completeness to θ [%]
data/restraints/params
goodness of fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
-
3
largest diff peak/hole [e /A ]
˚
was added dropwise slowly to dimethyl sulfate (41 mg, 0.322
mmol) in diethyl ether at 0 °C. After stirring for 3 h at rt an
aqueous workup was carried out to yield a colorless oil of 3
(98 mg, 75%). NMR (δ in ppm): 1H 0.22(s, 9H), 0.29(s, 9H), 0.31
(s, 9H), 0.38(s, 3H), 0.44(s,6H), 0.52 (s,6H); 29Si -8.3 (Me3SiSi),
-8.9 (Me3SiSi), -11.9 (Me3SiSiMe), -25.1 (Me2Si), -50.0
(Me3SiSiMe), -102.9 (Me3SiSi). Anal. Calcd for C14H42Si7
(407.08): C 41.31, H 10.40. Found: C 40.98, H 10.32.
Bis(dimethylphenylsilyl)bis(trimethylsilyl)silane (4). To an
ice bath cooled solution of diphenylbis(trimethylsilyl)silane
(163 mg, 0.487 mmol) in toluene (2 mL) was added trifluoro-
methanesulfonic acid (146 mg, 0.976 mmol). The cooling bath
was removed and stirring continued overnight. After 29Si NMR
indicated complete conversion [NMR (δ in ppm): 29Si δ þ38.8
(TfOSi), -12.2 (Me3SiSi)] the solution was cooled to -78 °C
and a solution of dimethylphenylsilyllithium (prepared from
finely cut lithium wire (32 mg, 4.6 mmol) and dimethylphenyl-
chlorosilane (167 mg, 0.976 mmol) in THF) was added dropwise
in a way that the triflate solution was allowed to warm when the
solution stopped decolorizing. After complete addition stirring
was continued for 16 h at rt. After aqueous workup colorless
crystals of 4 (149 mg, 68%) were obtained. Mp: 364-368 °C.
NMR (δ in ppm): 1H 7.42 (m, 4H), 7.17(m, 6H), 0.43 (s, 12H),
0.17 (s, 18H); 29Si -9.6 (Me3SiSi), -13.2 (Me2PhSiSi), -132.8
(Me3SiSi). Anal. Calcd for C22H40Si5 (444.98): C 59.38, H 9.06.
Found: C 59.17, H 8.98.

Article
Organometallics, Vol. 29, No. 12, 2010 2673
Figure 14. Comparison of UV spectra of methylated isotetrasilanyl and [2.2.2]bicyclooctasilanyl units connected with disilanylene (16, 20)
and tetrasilanylene spacers (17, 21). Spectrum of 1,4-bis(trimethylsilyl)dodecamethylbicyclo[2.2.2]heptasilane (19) shown for comparison.
Figure 15. Comparison of UV spectra of methylated isotetrasilanyl and [2.2.1]bicycloheptasilanyl units connected with disilanylene (16, 23)
and tetrasilanylene spacers (17, 24). Spectrum of 1,4-bis(trimethylsilyl)decamethylbicyclo[2.2.1]heptasilane (22) shown for comparison.
Figure 16. Comparison of UV spectra of methylated isotetrasilanyl and 1,3,3-tris(trimethylsilyl)octamethylcyclotetrasilanyl units
connected with disilanylene (16, 25) and tetrasilanylene spacers (17, 26). Spectrum of 1,1,3,3-tetrakis(trimethylsilyl)octamethyl-
cyclotetrasilane (1) shown for comparison.

2674 Organometallics, Vol. 29, No. 12, 2010
Wallner et al.
C24H72Si12 (697.85): C 41.31, H 10.40. Found: C 40.88, H 10.44. UV
absorption: λ1 =203nm(ε1 =2.3ꢀ 105 [M-1 cm-1]), λ2 =239nm
(ε2 = 6.1 ꢀ 103 [M-1 cm-1]).
1,1,4,4,4-Pentakis(trimethylsilyl)-1-undecamethylcyclohexa-
silanyltetramethyltetrasilane (8). To a solution of bromounde-
camethylcyclohexasilane (209 mg, 0.508 mmol) in benzene
(10 mL) at rt was added a solution of 1-potassium-1,1,4,4,4-
pentakis-(trimethylsilyl)tetramethyltetrasilane (427 mg, 1 equiv)
(7) in benzene (10 mL). The reaction mixture remained colorless
during the whole addition process, and a white precipitate was
formed. After complete addition the reaction mixture was stirred
for 2 h and then subjected to an aqueous workup with heptane/
0.5 M H2SO4. After drying with sodium sulfate the solvent was
removed, yielding a colorless solid of 8 (370 mg, 84%). Mp:
1
156-159 °C. NMR (δ in ppm): H 0.66 (s, 6H), 0.61 (s, 6H),
0.54 (s, 3H), 0.49 (s, 6H), 0.43 (s, 18H), 0.43 (s, 6H), 0.35 (s, 27H),
0.26 (s, 6H), 0.25 (s, 6H), 0.23 (s, 6H); 13C 4.7, 3.8, 3.2, 2.0, -1.4,
-2.1, -2.6, -4.3, -5.2, -5.9, -6.5. 29Si (D2O cap) -9.2 (Me3Si),
-9.3 (Me3Si), -25.9 (Me2Si), -29.9 (Me2Si), -34.5 (Me2Si),
-38.6 (Me2Si), -43.5 (Me2Si), -67.9 (MeSi), -113.1 (Me3SiSi),
-126.2 (Me3SiSi). Anal. Calcd for C30H90Si15 (872.33): C 41.31,
H 10.40. Found: C 41.62, H 10.39. UV absorption: λ1 = 209 nm
(ε1 = 5.2 ꢀ 104 [M-1 cm-1]), λ2 = 261 nm (ε2 = 4.8 ꢀ 104
[M-1 cm-1]), shoulder 281 nm.
1,1,4,4-Tetrakis(trimethylsilyl)-1,4-bis(undecamethylcyclohexa-
silanyl)tetramethyltetrasilane (11). The same procedure as described
for 8 was used with bromoundecamethylcyclohexasilane (966 mg,
2.34 mmol) and 9 (1.253 g, 1.172 mmol). Compound 11 was ob-
tained as a colorless solid (710 mg, 53%). Mp: 218-223 °C. NMR
(δ in ppm): 1H 0.75 (s, 6H), 0.57 (s, 6H), 0.49 (s, 12H), 0.44 (s, 12H),
0.43 (s, 36H), 0.39 (s, 18H), 0.27 (s, 12H), 0.23 (s, 12H); 29Si (D2O
cap) -9.4 (Me3Si), -26.8 (Me2Si), -34.2 (Me2Si), -38.5 (Me2Si),
-43.6 (Me2Si), -67.6 (MeSi), -111.2 (Me3SiSi). Anal. Calcd for
C38H114Si20 (1133.04): C 40.28, H 10.14. Found: C 39.95, H 9.87.
UV absorption: λ1 = 210 nm (ε1 =4.8ꢀ 104 [M-1 cm-1]),λ2 =270
nm (ε2 = 3.6 ꢀ 104 [M-1 cm-1]), shoulder 241 nm, 286 nm.
1,2-Bis[10,40,40-tris(trimethylsilyl)octamethylcyclohexasilanyl]-
tetramethyldisilane (13). The same procedure as described for 8
was used with 12 (1.17 g, 1.45 mmol) and 1,2-dichlorotetra-
methyldisilane (136 mg, 0.732 mmol) and a reaction time of 18 h.
Compound 13 was obtained as a colorless solid (713 mg, 87%).
Mp: 227-231 °C. NMR (δ in ppm): 1H 0.68 (s, 12H), 0.51
(s, 12H), 0.47 (s, 12H), 0.43 (s, 24H), 0.41 (s, 18H), 0.34 (s, 36H);
29Si -8.1 (Me3Si), -8.6 (Me3Si), -9.2 (Me3Si), -26.6 (Me2Si),
-37.7 (Me2Si), -38.1 (Me2Si), -119.8 (Me3SiSi), -132.1 (Me3-
SiSi). Anal. Calcd for C38H114Si20 (1133.03): C 40.28, H 10.14.
Found: C 39.97, H 10.07. UV absorption: λ1 = 210 nm (ε1 =
11.3 ꢀ 104 [M-1cm-1]), λ2 = 265 nm (ε2 = 3.8 ꢀ 104 [M-1 cm-1]),
λ3 = 289 nm (ε3 = 3.6 ꢀ 104 [M-1 cm-1]).
Figure 17. 2-D representations of the polysilane backbones of
11 and the compounds with the tetrasilanylene spacers high-
lighting the best achievable all-transoid-aligned conformation.
1,1,1,3,3,5,5,5-Octakis(trimethylsilyl)-2,2,4,4-tetramethylpenta-
silane (5). To a solution of bis(trimethylsilyl)bis(dimethylphenyl-
silyl)silane (4) (2.05 g, 4.65 mmol) in toluene (10 mL) at 0 °C was
added trifluoromethylsulfonic acid (1.39 g, 9.29 mmol). After
removal of the ice bath stirring was continued for 16 h to achieve
complete conversion [NMR (δ in ppm): 29Si þ5.9 (TfOSiMe2),
-9.9 (Me3SiSi), -131.1 (Me3SiSi)]. After cooling the solution to
0 °C again tris(trimethylsilyl)silylpotassium (9.29 mmol) in THF
(10 mL) was added dropwise. A precipitate was observed, and
stirring was continued at rt for 10 h. Aqueous workup was followed
by drying over sodium sulfate and removal of the solvent. The
residue was sublimed at 70 °C/0.7 mbar and crystallized from
pentane to give 5 (1.050 g, 29%) as colorless crystals. Mp: 170-
171 °C. NMR (δ in ppm): 1H 0.76 (s, 12H, SiMe2), 0.44 (s, 18H,
SiMe3), 0.38 (s, 54H, SiMe3); 13C 7.8 (SiMe2), 5.1 [(Me3Si)2Si],
4.4 [(Me3Si)3Si]. 29Si -9.4 [(Me3Si)3Si], -9.8 [(Me3Si)2Si], -23.7
(Me2Si), -94.0 [(Me3Si)2Si], -116.8 [(Me3Si)3Si]. Anal. Calcd for
C28H84Si13 (786.08): C 42.78, H 10.77. Found: C 42.31, H 10.56.
1,1,3,3,5,5-Hexakis(trimethylsilyl)-2,2,4,4,6,6-hexamethylcyclo-
hexasilane (6). To an ice cold solution of 4 (984 mg, 1.78 mmol) in
toluene (45 mL) was added dropwise trifluoromethanesulfonic acid
(534 mg, 3.56 mmol). The stirring was continued at rt for 4 h, and
after complete conversion (controlled by NMR) the solution was
diluted with toluene (20 mL) and cooled to 0 °C again. At this
temperature 2,2-dimethyl-1,1,3,3-tetrakis(trimethylsilyl)trisilanyl-
1,4-Bis[10,40,40-tris(trimethylsilyl)octamethylcyclohexasilanyl]-
octamethyltetrasilane (14). The same procedure as described for
8 was used with 12 (754 mg, 0.931 mmol) and 1,4-dichloro
octamethyltetrasilane (140 mg, 0.462 mmol) and a reaction time
of 18 h. Compound 14 was obtained as a colorless solid (490 mg,
85%). Mp: 209-214 °C. NMR (δ in ppm): 1H 0.60 (s, 12H), 0.52
(s, 12H), 0.49 (s, 12H), 0.46 (s, 12H), 0.43 (s, 18H), 0.39 (s, 18H),
0.34 (s, 30H), 0.32 (12H); 29Si -8.2 (Me3Si), -8.6 (Me3Si), -9.0
(Me3Si), -29.2 (Me2Si), -34.7 (Me2Si), -37.9 (Me2Si), -38.4
(Me2Si), -121.7 (Me3SiSi), -132.1 (Me3SiSi). Anal. Calcd for
C42H126Si22 (1249.35): C 40.38, H 10.16. Found: C 40.24, H 9.73.
UV absorption: λ1 = 209 nm (ε1 = 10.9 ꢀ 104 [M-1 cm-1]), λ2 =
297 nm (ε2 = 5.5 ꢀ 104 [M-1 cm-1]), shoulder 273 nm.
dipotassium (18-crown-6)2 [obtained from hexakis(trimethylsilyl)-
3
1,6-Bis[10,40,40-tris(trimethylsilyl)octamethylcyclohexasilanyl]-
dodecamethylhexasilane (15). The same procedure as described
for 8 was used with 12 (418 mg, 0.516 mmol) and 1,6-dichloro-
dodecamethylhexasilane (108 mg, 0.257 mmol) and a reaction
time of 12 h. Compound 15 was obtained as a colorless solid (347
mg, 99%). Mp: 207-212 °C. NMR (δ in ppm): 1H 0.58 (s, 12H),
0.50 (s, 12H), 0.49 (s, 12H), 0.46 (s, 12H), 0.44 (s, 12H), 0.43
(s, 24H), 0.39 (s, 18H), 0.34 (s, 36H); 13C 4.7, 3.9, 3.8, 2.2, -0.1,
2,2-dimethyltrisilane (984 mg, 1.78 mmol), KOtBu (399 mg, 3.55
mmol), 18-crown-6 (940 mg, 3.55 mmol)] in toluene (55 mL) was
added dropwise, and the stirring was continued for another 12 h at
rt. After subjecting the mixture to an aqueous workup the obtained
residue was recrystallized from ethyl acetate, yielding 6 as a white
crystalline solid (360 mg, 29%). Mp: 329-332 °C. NMR (δin ppm):
1H NMR (CDCl3) 0.32 (s, 54H), 0.52(s, 18H);13C(CDCl3) 4.9, 5.1;
29Si (CDCl3) -7.6 (Me3Si), -31.1 (Me2Si), -124.1. Anal. Calcd for

Article
Organometallics, Vol. 29, No. 12, 2010 2675
-0.4, -0.6, -2.4, -3.1; 29Si -8.2 (Me3Si), -8.5 (Me3Si), -9.0
(Me3Si), -30.0 (Me2Si), -35.3 (Me2Si), -35.7 (Me2Si), -37.9
(Me2Si), -38.5 (Me2Si), -122.2 (Me3SiSi), -132.2 (Me3SiSi).
Anal. Calcd for C46H138Si24 (1365.65): C 40.46, H 10.18. Found:
C 40.73, H 9.94. UV absorption: λ1 = 303 nm (ε1 = 7.3 ꢀ 104
[M-1 cm-1]), λ2 = 218 nm (ε2 = 1.1 ꢀ 105 [M-1 cm-1]).
1,2-Bis(40-trimethylsilyldodecamethylbicyclo[2.2.2]octasilanyl)-
tetramethyldisilane (20). The same procedure as described for 8
was used with 19 (297 mg, 0.381 mmol) and 1,2-dichlorotetra-
methyldisilane (36 mg, 0.192 mmol), a reaction time of 4 h, and
aqueous workup with toluene/0.5 M H2SO4. Compound 20 was
obtained as a colorless solid (181 mg, 89%). Mp: >300 °C. NMR
(δ in ppm): 1H (CDCl3) 0.46 (s, 12H), 0.36 (s, 36H), 0.32 (s, 36H),
0.28 (s, 18H); 13C (CDCl3) 3.7, 1.9, -0.1, -0.8; 29Si (CDCl3) 0.1
(Me3Si), -26.0 (Me2Si), -37.2 (Me2Si), -37.9 (Me2Si), -121.8
(SiSi), -131.5 (Me3SiSi). Anal. Calcd for C34H102Si20 (1072.90):
C 38.06, H 9.58. Found: C 38.01, H 9.76. UV absorption: λ1 =
209 nm (ε1 = 9.1 ꢀ 104 [M-1 cm-1]), λ2 = 288 nm (ε2 = 5.0 ꢀ
104 [M-1 cm-1]).
1,4-Bis(40-trimethylsilyldodecamethylbicyclo[2.2.2]octasilanyl)-
octamethyltetrasilane (21). The same procedure as described for 8
was used with 19 (270 mg, 0.353 mmol) and 1,4-dichloroocta-
methyltetrasilane (52 mg, 0.171 mmol) and a reaction time of
18 h. Compound 21 was obtained as a colorless solid (200 mg,
98%). Mp: >300 °C. NMR (δ in ppm): 1H 0.58 (s, 12H), 0.49 (s,
12H), 0.48 (s, 36H), 0.41 (s, 36H), 0.33 (s, 18H); 29Si (D2O-cap)
-5.8 (Me3Si), -26.1 (Me2Si), -36.6 (Me2Si), -37.1 (Me2Si),
-37.7 (Me2Si), -122.1 (SiSi), -130.9 (Me3SiSi). Anal. Calcd for
C38H114Si22 (1189.21): C 38.38, H 9.66. Found: C 37.91, H 9.52.
UV absorption: λ1 = 208 nm (ε1 = 9.1 ꢀ 104 [M-1 cm-1]), λ2 =
299 nm (ε2 = 4.8 ꢀ 104 [M-1 cm-1]).
(s, 18H); 13C 3.4, 1.6, 0.9, -0.1, -0.7, -1.1, -1.6, -3.6. 29Si -5.5
(Me3Si), -14.4 (Me2Si), -25.2 (Me2Si), -31.7 (Me2Si), -31.9
(Me2Si), -38.7 (Me2Si), -119.2 (Me3SiSi), -123.5 (Me2Si)4Si.
Anal. Calcd for C34H102Si20 (1040.73): C 38.06, H 9.58. Found:
C 37.66, H 9.60. UV absorption: λ1 = 219 nm (ε1 = 6.1 ꢀ 104
[M-1 cm-1]), λ2 = 300 nm (ε2 = 5.1 ꢀ 104 [M-1 cm-1]).
1,2-Bis[1,3,3-tris(trimethylsilyl)tetramethylcyclotetrasilanyl]-
tetramethyldisilane (25). A solution of 1,3,3-tris(trimethylsilyl)-
tetramethylcyclotetrasilanylpotassium 18-crown-6 (0.430 mmol) in
3
benzene (2 mL) was slowly added (within 15 min) to a stirred
solution of 1,2-dichlorotetramethyldisilane (0.226 mmol) in benzene
(5 mL). The resulting clear and colorless reaction mixture was stirred
for 2 h. The solution was poured into a mixture of H2SO4 (0.5 M
solution) and diethyl ether. After separation of the layers the
aqueous phase was extracted several times with diethyl ether,
and the combined organic layers were dried over sodium sulfate.
After removal of solvent 25 was obtained as a white solid (185 mg,
96%).
1
NMR (δ in ppm): H 0.70 (s, 12H), 0.65 (s, 12H), 0.61 (s,
12H), 0.22 (s, 18H), 0.35(s, 18H), 0.34 (s, 18H). 13C 4.2, 3.6, 3.5,
3.4, 3.0, 1.0; 29Si -7.8, -8.5, -9.0, -24.2, -28.8, -90.6, -95.7.
Anal. Calcd for C30H90Si16 (900.40): C 40.02, H 10.07. Found:
C 39.73, H 10.17. UV absorption: λ1 = 255 nm (ε1 = 3.7 ꢀ
104 [M-1 cm-1]), λ2 = 292 nm (ε1 = 7.4 ꢀ 103 [M-1cm-1]), λ3 =
325 nm (ε1 = 9.2 ꢀ 103 [M-1 cm-1]).
1,4-Bis[1,3,3-tris(trimethylsilyl)tetramethylcyclotetrasilanyl]-
octamethyltetrasilane (26). A solution of 1,3,3-tris(trimethyl-
silyl)tetramethylcyclotetrasilanylpotassium 18-crown-6 (0.430
3
mmol) in benzene (2 mL) was slowly added (within 15 min) to a
stirred solution of 1,4-dichlorooctamethyltetrasilane (69 mg,
0.23 mmol) in benzene (5 mL). During the addition a white
precipitate was formed. The resulting colorless reaction mix-
ture was stirred for 2 h. Then the solution was poured into a
mixture of H2SO4 (0.5 M solution) and diethyl ether. The layers
were separated, the aqueous phase was extracted several times
with diethyl ether, and combined organic layers were dried over
sodium sulfate. After removing the solvent a white solid was
obtained (193 mg, 88%), which was insoluble in C6D6 and only
slightly soluble in CDCl3.
1,2-Bis(40-trimethylsilyldecamethylbicyclo[2.2.1]heptasilanyl)-
tetramethyldisilane (23). At rt a mixture of 1,4-bis(trimethylsilyl)-
decamethylbicyclo[2.2.1]heptasilane (22) (309 mg, 0.627 mmol),
potassium tert-butoxide (74 mg, 0.659 mmol), and 18-crown-6
(174 mg, 0.659 mmol) was dissolved in benzene (10 mL). The
solution immediately turned yellow, and complete conversion was
achieved after 2 h [NMR (δ in ppm): 1H 3.13 (s, 24H), 0.69 (s, 6H),
0.67(s, 12H), 0.62(s, 6H), 0.49(s, 9H), 0.47(s, 6H);29Si 1.0 (Me3Si),
-8.1 (Me2Si), -18.8 (Me2Si), -27.9 (Me2Si), -113.6 (Me3SiSi),
-177.7 (KSi)]. Using the obtained solution the same procedure as
described for 8 was followed with 1,2-dichlorotetramethyldisilane
(62 mg, 0.329 mmol) to give 23 (285 mg, 95%) as a colorless solid.
Mp: >300 °C. NMR (δ in ppm): 1H 0.59 (s, 12H), 0.54 (s, 12H),
0.50 (s, 12H), 0.45 (s, 12H), 0.41 (s, 12H), 0.40 (s, 12H), 0.34 (s, 18H).
13C 4.5, 4.4, 2.6, 2.2, 1.2, 1.1, -0.7; 29Si -5.3 (Me3Si), -14.1 (Me2Si),
-26.8 (Me2Si), -31.4 (Me2Si), -31.6 (Me2Si), -80.6 (Me3SiSi),
-118.5 (Me2SiSi). Anal. Calcd for C30H90Si18 (956.58): C 37.67,
H 9.48. Found: C 37.52, H 9.48. UV absorption: λ1 = 219 nm (ε1 =
5.4 ꢀ 104 [M-1 cm-1]), λ2 = 290 nm (ε2 = 3.2 ꢀ 104 [M-1 cm-1]).
1,4-Bis(40-trimethylsilyldecamethylbicyclo[2.2.1]heptasilanyl)-
octamethyltetrasilane (24). The same procedure as described for
23 employing 22 (404 mg, 0.559 mmol) and 1,4-dichloroocta-
methyltetrasilane (90 mg, 0.296 mmol) was used. Compound 24
(273 mg, 91%) was obtained as a colorless solid. Mp: 248-
NMR (δ in ppm): 1H (CDCl3) 0.56 (s, 12H), 0.55 (s, 12H), 0.53
(s, 12H), 0.41 (s, 12H), 0.29 (s, 18H), 0.26 (s, 18H), 0.26 (s, 18H);
13C (CDCl3) 3.9, 3.4, 3.4, 3.3, 2.8, 2.5, 1.0; 29Si (CDCl3) -7.6,
-8.2, -8.7, -23.7, -28.5, -37.6, -90.9, -95.3. Anal. Calcd
for C34H102Si18 (1016.71): C 40.17, H 10.11. Found: C 39.66,
H 10.00. UV absorption: λ1 = 274 nm (ε1 = 3.1 ꢀ 104
[M-1 cm-1]), λ2 = 325 nm (ε1 = 1.3 ꢀ 104 [M-1 cm-1]), shoulder
296 nm.
Acknowledgment. This study was supported by the
€
Austrian Fonds zur Forderung der Wissenschaften
(FWF) via the projects Y-120 and P-18538.
Supporting Information Available: X-ray crystallographic
information in CIF format and copies of H NMR spectra of
1
1
253 °C. NMR (δ in ppm): H 0.59 (s, 12H), 0.54 (s, 12H), 0.50
all new compounds are available free of charge via the Internet
at http://pubs.acs.org.
(s, 12H), 0.45 (s, 12H), 0.43 (s, 12H), 0.41 (s, 12H), 0.40 (s, 12H), 0.34