Synthesis and properties of bridgehead-functionalized permethylbicyclo[2.2. 2]octasilanes

Article abstract of DOI:10.1021/om400184y

A series of previously unknown bridgehead-functionalized bicyclo[2.2.2]octasilanes, Me₃Si-Si₈Me₁₂-X, X-Si₈Me₁₂-X, and X-Si₈Me₁₂-Y [X, Y = -SiMe_nPh_3-n (n = 1, 2) (2, 3, 10), -SiMe₂Fc (Fc = ferrocenyl) (4, 11, 13, 14), -COR (R = Me, tBu) (6, 7, 12), COOMe (8), COOH (9)], have been prepared by the reaction of the silanides Me ₃Si-Si₈Me₁₂^-K⁺ or K ^+-Si₈Me₁₂^-K⁺ with proper electrophiles and fully characterized. The molecular structures of 2, 3, 4, 6, 8, 9, 10, and 13 as determined by single-crystal X-ray diffraction analysis exhibit a slightly twisted structure of the bicyclooctasilane cage. Endocyclic bond lengths, bond angles, and dihedral angles are not influenced considerably by the substituents attached to the bridgehead silicon atoms. Due to σ(SiSi)/π(aryl) conjugation, a 20-30 nm bathochromic shift of the longest wavelength UV absorption band relative to Me₃Si-Si ₈Me₁₂-SiMe₃ (1) is evident in the UV absorption spectra of the phenyl and ferrocenyl derivatives. Otherwise, UV absorption data do not support the assumption of aryl/aryl or aryl/C=O interaction via the σ(SiSi) bicyclooctasilane framework.

Full text of DOI:10.1021/om400184y

Article
pubs.acs.org/Organometallics
Terms of Use
Synthesis and Properties of Bridgehead-Functionalized
Permethylbicyclo[2.2.2]octasilanes
Harald Stueger,* Bernd Hasken, Uwe Gross, Roland Fischer, and Ana Torvisco Gomez
Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9, A-8010 Graz, Austria
S
* Supporting Information
ABSTRACT: A series of previously unknown bridgehead-function-
alized bicyclo[2.2.2]octasilanes, Me3Si-Si8Me12-X, X-Si8Me12-X, and X-
Si8Me12-Y [X, Y = −SiMenPh3−n (n = 1, 2) (2, 3, 10), −SiMe2Fc (Fc =
ferrocenyl) (4, 11, 13, 14), −COR (R = Me, tBu) (6, 7, 12), COOMe
(8), COOH (9)], have been prepared by the reaction of the silanides
Me3Si-Si8Me12−K+ or K+−Si8Me12−K+ with proper electrophiles and
fully characterized. The molecular structures of 2, 3, 4, 6, 8, 9, 10, and
13 as determined by single-crystal X-ray diffraction analysis exhibit a
slightly twisted structure of the bicyclooctasilane cage. Endocyclic
bond lengths, bond angles, and dihedral angles are not influenced
considerably by the substituents attached to the bridgehead silicon
atoms. Due to σ(SiSi)/π(aryl) conjugation, a 20−30 nm bathochromic
shift of the longest wavelength UV absorption band relative to Me3Si-
Si8Me12-SiMe3 (1) is evident in the UV absorption spectra of the phenyl and ferrocenyl derivatives. Otherwise, UV absorption
data do not support the assumption of aryl/aryl or aryl/CO interaction via the σ(SiSi) bicyclooctasilane framework.
Wurtz-type coupling has also been applied to the synthesis of
polysilanes with bicyclic or cage-like structures.9 In many cases,
however, poor yields and severe problems in the course of the
isolation of the desired reaction products were encountered.
Thus, tetradecamethylbicyclo[2,2,2]octasilane (1-Me2) has
been prepared for the first time in <5% yield by West using
Na/K condensation of Me3SiCl2/MeSiCl3 mixtures.10 In order
to enhance the selectivity of the coupling reaction Kira et al.
reacted two equivalents of (ClMe2Si)3SiMe with lithium metal
and obtained 1-Me2 in 19% yield.11 Recent achievements in the
chemistry of α,ω-oligosilanyldianions mainly by Marschner et
al. finally enabled the synthesis of bis(trimethylsilyl)-
dodecamethylbicyclo[2.2.2]octasilane (1) and a whole series
of related oligosilane cycles and cages in excellent yields.12
Furthermore, it has been reported that 1-Me2 and 1 can be
functionalized selectively at the bridgehead Si atoms to give 1-
K, 1-K2, 1-MeX, and 1-X2 (X = Cl, Br) (compare Scheme 1),
which represent valuable synthons for further derivatization. In
a small-scale experiment Kira et al. obtained 1-Ph from 1-MeCl
and PhLi in 58% yield.13 Nucleophilic substitution reactions of
1-MeCl, however, turned out to be of limited scope because
neither scale-up to preparative amounts nor the synthesis of
bicyclo[2.2.2]octasilanes bearing functional aromatic side
groups such as p-PhCN or p-PhCF3 could be accomplished
successfully.14 The reaction of 1-K and 1-K2 with various C or
Si electrophiles to the corresponding bridgehead-functionalized
cages, on the other hand, gave quite satisfactory results.15
INTRODUCTION
■
Oligo- and polysilanes have been extensively studied due to
their chemical stability and due to their unique electronic
properties, which more or less can be related to the extensive
delocalization of σ-electrons along the silicon skeleton (σ-
delocalization).1 σ-Delocalization within cyclic Si−Si frame-
works is particularly well established,2 giving rise to pronounced
substituent effects on the properties of the Si−Si backbone such
as long-wavelength UV absorption up to the visible range,3
room-temperature photoluminescence,4 nonlinear optical be-
havior,5 and photochemical activity.6 Furthermore, σ-con-
jugated cyclopolysilane bridges have been shown to be better
mediators for electronic effects in bichromophoric covalently
linked donor−bridge−acceptor (D-br-A) compounds as
compared to their open-chained counterparts.7
Wurtz-type coupling of diorganodihalosilanes with alkali
metals is still the most prominent way for the synthesis of
cyclopolysilanes. Due to the harsh reaction conditions,
however, this method gives reasonable yields only when simple
alkyl or aryl groups are attached to silicon. In order to introduce
alternative substituents, the resulting peralkyl- or perarylcyclo-
polysilanes have to be further functionalized, which is most
frequently achieved by selective chlorodemethylation or
chlorodephenylation followed by treatment of the resulting
organochloropolysilanes with proper nucleophiles. Using this
approach a variety of functional groups such as OR, SR, NR2,
PR2, transition metal fragments MLn, and many others have
already been attached to cyclopolysilane backbones with
excellent success.8
Received: March 6, 2013
Published: August 7, 2013
© 2013 American Chemical Society
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we now would like to report on the synthesis of previously
unknown bicyclo[2.2.2]octasilanes with phenyl, ferrocenyl, and
carbonyl side groups and on the investigation of substituent
effects within the target compounds using mainly UV
absorption spectroscopy and X-ray crystallography.
Scheme 1
RESULTS AND DISCUSSION
■
It has been demonstrated earlier that polysilanyl alkali metal
compounds such as (Me3Si)3SiM (M = K, Li) smoothly react
with various electrophiles to give functional silanes (Me3Si)3SiX
with substituents X such as H, alkyl, SiR3, GeR3, COR, COOR,
or COOH attached to the central silicon atom.17 In the present
study we used a similar approach to synthesize the
corresponding bridgehead-functionalized bicyclo[2.2.2]-
octasilanes 2−12 starting from the potassium silanides 1-K
and 1-K2.
For 1-Ph Kira et al. observed dual fluorescence from the
locally excited (LE) and the intramolecular charge transfer
(ICT) state even in nonpolar solvents and, thus, were able to
demonstrate that bicyclo[2,2,2]octasilane cages can get
involved in charge transfer processes.13 In contrast to cyclic
and open-chained permethyloligosilanes, for which the first
visible transition is of σ→σ* character, TD-DFT calculations
published by Marschner and Ottoson recently assigned the
longest wavelength UV absorption band in 1 to σ→π* type
electron transitions.16 The authors of this study further suggest
that the electronic structure within bicyclo[2.2.2]octasilane
cages may result in charge transport characteristics that are
different from those of linear oligosilanes. Therefore, we found
it highly desirable to improve the understanding of the impact
of various substituent groups on the properties of the Si−Si
bond system within the bicyclo[2.2.2]octasilane cage. Herein
As depicted in Scheme 2, 1-K can easily be silylated with
PhMe2SiCl, Ph2MeSiCl, or FcMe2SiCl (Fc = ferrocenyl) in
toluene solution at −70 °C to give the air-stable and crystalline
compounds 2, 3, and 4, respectively, in yields of >70%. With a
4-fold excess of Me2SiCl2 the SiMe2Cl-substituted product 5
was obtained, which may be used for further derivatization by
nucleophilic substitution at the silicon−chlorine bond. Treat-
ment of 1-K with equimolar amounts of ClCOR (R = Me, tBu)
or ClCOOMe, furthermore, allowed for the synthesis of the
acyl- and methylcarboxybicyclo[2.2.2]octasilanes 6−8. The
corresponding carboxylic acid 9 finally could be obtained by
carbonation of 1-K with CO2 followed by acid hydrolysis of the
Scheme 2
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Scheme 3
primarily formed potassium carboxylate. 6−9 are stable against
air and moisture but slowly decompose within several weeks
upon storage at room temperature under formation of
polymeric products of unidentified composition, which also
applies to the acyl and diacyl bicyclo[2.2.2]octasilanes 12 and
14 mentioned below.
Scheme 4
The reaction of 1-K2 with two equivalents of PhMe2SiCl,
FcMe2SiCl, or ClCOtBu also proceeded straightforwardly and
yielded the symmetrically disubstituted species 10, 11, and 12,
respectively (Scheme 3).
If 4 was stirred with a 1.1 molar excess of KOtBu in DME for
40 min at room temperature, the Me3Si group was split off
selectively and the potassium silanide 4-K was cleanly formed.
The 29Si NMR spectrum of the resulting reaction solution
exhibits a resonance line at −177.62 ppm, which is easily
assigned to the negatively charged bridgehead silicon atom,
while the signals of the SiSiMe3 moiety at −6.11 (SiMe3) and
−130.67 (SiSiMe3) had disappeared. Subsequent addition of
1.1 equivalents of PhMe2SiCl or ClCOtBu at −70 °C finally
afforded the asymmetrically disubstituted cages 13 and 14
(Scheme 4).
In a similar manner 7 reacted with KOtBu to give the silanide
7-K with δ29Si = −180.69 ppm for the silicon atom bearing the
negative charge, which could be converted to 12 by addition of
another equivalent of ClCOtBu (Scheme 5). The reaction of 8
with KOtBu finally afforded a product mixture of unidentified
composition instead of the silanide 8-K. The 29Si NMR spectra
of the resulting reaction solution showed numerous signals that
could not be assigned unambiguously.
All previously unknown compounds were fully characterized
by spectroscopic means and elemental analyses. Analytical data
(compare Experimental Section) are consistent with the
proposed structures in all cases. For compounds 3, 6, 7 and
12 elemental analyses did not give satisfactory results very likely
due to incomplete combustion. In all cases, however, proper
29Si NMR chemical shift data of the bicyclooctasilane core
are summarized in Table 1. The asymmetrically substituted
compounds exhibit two 29Si resonance lines for the SiMe2
groups, while only one signal appears in the same range of the
29Si spectra of the symmetrical species 10−12. 29Si chemical
shift values near −39 ppm were found for the SiMe2 groups,
which are not significantly influenced by the nature of the
substituents X.
1
HRMS data were obtained. Additionally H- and 29Si NMR
spectra of 3, 6, 7 and 12 are displayed in the Supporting
Information in order to demonstrate the purity of the
compounds.
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Single crystals suitable for X-ray structure analysis could be
grown from compounds 2, 3, 4, 6, 8, 9, 10, and 13. The
obtained molecular structures are depicted in Figures 1−7
together with selected bond distances, bond angles, and
dihedral angles.
Scheme 5
Table 1. δ29Si Chemical Shift Data of the
Bicyclo[2,2,2]octasilane Core in 1−14 (CDCl3 solution, vs
ext. TMS, ppm)
Figure 1. ORTEP diagram for compound 2. Thermal ellipsoids are
depicted at the 50% probability level. Hydrogen atoms are omitted for
clarity. The crystals contain two independent molecules (2, 2′) in the
asymmetric unit. Selected bond lengths [Å] and bond and torsional
angles [deg] with estimated standard deviations: 2: Si−Si (mean)
2.351, Si(1)−C(1) 1.892(2), Si−Cmethyl (mean) 1.883, Si−Si−Si
(mean) 109.6, C(1)−Si(1)−Si(2) 109.47(5), Si(2)−Si(3)−Si(4)−
Si(5) −18.92(3), Si(2)−Si(7)−Si(6)−-Si(5) −18.98(3), Si(2)−
Si(8)−Si(9)−Si(5) −18.79(3), Si(2)−Si(1)−C(1)−C(2) −79.0(1),
Si(2)−Si(1)−C(1)−C(6) 98.8(1). 2′: Si−Si (mean) 2.351, Si(11)−
C(24) 1.884(2), Si−Cmethyl (mean) 1.884, Si−Si−Si (mean) 109.7,
C(24)−Si(11)−Si(12) 109.47(5), Si(15)−Si(16)−Si(17)−Si(12)
−16.32(3), Si(15)−Si(14)−Si(13)−Si(12) −16.24(3), Si(12)−
Si(18)−Si(19)−Si(15) −18.40(3), Si(12)−Si(11)−C(24)−C(25)
−85.3(1), Si(12)−Si(11)−C(24)−C(29) 92.7(1).
SiMe2
−38.3
SiSiMe3−nRn
−130.2
−129.57
−131.00; −129.04
−131.45; −128.37
−130.67; −128.90
−127.89
−130.48; −125.01
−129.78
SiCOR′ Si″+K″
a
1
b
b
b
1-K
2
−33.73; −39.61
−37.89; −38.26
−37.76; −38.18
−38.12; −38.31
−34.32, −39.67
−38.21; −38.42
−38.05; −39.76
−37.76; −38.09
−33.05; −40.06
−38.09; −39.19
−38.12; −39.22
−37.90
−178.63
3
4
4-K
5
−177.62
6
7
−130.82
−75.68
7-K
8
−73.86
−76.68
−76.72
−180.69
−129.63
−129.61
−129.73
−129.12
The phenyl compounds 2 and 3 crystallize in the triclinic
9
space group P1 and orthorhombic space group Pca2(1),
10
11
12
13
14
̅
respectively, with two independent molecules in the asym-
metric unit. 2, 4, 10, and 13 exhibit a roughly perpendicular
arrangement of the plane of the aromatic rings relative to the
adjacent Si−Si bond with torsional angles Csp2−Csp2−Si−Si not
far from 90°. Deviation from perpendicularity is much larger in
compound 3, which can be ascribed to the steric bulk of the
two phenyl rings attached to the same silicon atom. In general a
perpendicular geometry is frequently observed within the
fragment phenyl−Si−Si because it provides the basis for
effective σ(Si−Si)−π(phenyl) overlap. A study of the
absorption spectra of conformationally constrained aryldisilanes
thus demonstrated that a torsion angle between the phenyl ring
plane and the Si−Si bond of 90° effects in maximum σ−π
conjugation.18 Similar conformational dependence of UV
absorption and emission properties was also observed when
the 1,2-diphenyldisilane moiety was conformationally con-
strained by incorporation into cyclic structures.19
−38.14
−37.59
−37.89; −38.09
−37.54, −38.10
−76.88
−76.00
−129.28; −129.55
−129.59
a
b
Taken from ref 12b. Measured in DME.
δ29Si values for the bridgehead Si atoms close to the ones
observed for the corresponding (Me3Si)3SiX compounds were
measured near −130 ppm for the silyl derivatives and −77 ppm
for the acyl- and carboxy-substituted species. It is interesting to
note that the silanides 1-K, 4-K, and 7-K exhibit a marked low-
field shift of the 29Si signal assigned to the tertiary Si atom
bearing the negative charge by 15.1−18.2 ppm as compared to
(Me3Si)3SiK (δ29Si in DME solution = −195.83 ppm),17a which
probably reflects the improved ability for delocalization of the
negative charge within the Si−Si framework of the
bicyclooctasilane cage. Furthermore, the 1H NMR spectra
feature two SiMe2 signals for the unsymmetrical species and
only one signal for the symmetrical ones, which allows us to
conclude that both methyl groups attached to each silicon atom
of the bicyclooctasilane moiety are magnetically equivalent due
to the symmetric structure of the polysilane cage.
The sum of the bond angles around the carbonyl C atom in
6, 8, and 9 is close to 360° and reflects the trigonal planar
geometry within the SiRCO moiety. Carbonyl CO bond
lengths between 1.19 and 1.23 Å were measured, approximately
the same as that found in simple organic ketones, carboxylic
acids, and esters.20 Silicon carbonyl group bond lengths at
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Figure 2. ORTEP diagram for compound 3. Thermal ellipsoids are depicted at the 50% probability level. Hydrogen atoms are omitted for clarity.
The crystals contain two independent molecules (3, 3′) in the asymmetric unit. Selected bond lengths [Å] and bond and torsional angles [deg] with
estimated standard deviations: 3: Si−Si (mean) 2.355, Si(1)−C(2) 1.889(3), Si(1)−C(8) 1.876(3), Si−Cmethyl (mean) 1.887, Si−Si−Si (mean)
109.6, C(2)−Si(1)−Si(2) 112.30(9), C(8)−Si(1)−Si(2) 113.60(9), Si(2)−Si(3)−Si(4)-Si(5) −17.22(5), Si(2)−Si(7)−Si(6)−Si(5) −18.95(5),
Si(2)−Si(8)−Si(9)−Si(5) −18.59(5), Si(2)−Si(1)−C(2)−C(3) −55.5(5), Si(2)−Si(1)−C(2)−C(7) 128.1(2), Si(2)−Si(1)−C(8)−C(9)
−123.3(2), Si(2)−Si(1)−C(8)−C(13) 60.1(3). 3′: Si−Si (mean) 2.354, Si(11)−C(30) 1.890(3), Si(11)−C(36) 1.881(3), Si−Cmethyl (mean)
1.888, Si−Si−Si (mean) 109.8, C(30)−Si(11)−Si(12) 113.33(9), C(36)−Si(11)−Si(12) 109.3(1), Si(15)−Si(14)−Si(13)−Si(12) −14.11(5),
Si(15)−Si(16)−Si(17)−Si(12) −18.43(6), Si(15)−Si(19)−Si(18)−Si(12) −17.16(6), Si(12)−Si(11)−C(30)−C(31) −68.7(2), Si(12)−Si(11)−
C(30)−C(35) 114.6(2), Si(12)−Si(11)−C(36)−C(37) 117.7(3), Si(12)−Si(11)−C(36)−C(41) −61.1(3).
Figure 4. ORTEP diagram for compound 10. Thermal ellipsoids are
depicted at the 50% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and bond and torsional angles [deg]
with estimated standard deviations: Si−Si (mean) 2.352, Si(1)−C(1)
1.886(2), Si(10)−C(21) 1.882(1), Si−Cmethyl (mean) 1.886, Si−Si−Si
(mean) 109.6, C(1)−Si(1)−Si(2) 109.86(5), C(21)−Si(10)−Si(5)
110.12(4), Si(2)−Si(3)−Si(4)−Si(5) 15.63(2), Si(5)−Si(6)−Si(7)−
Si(2) 15.97(2), Si(2)−Si(8)−Si(9)−Si(5) 18.87(2), Si(2)−Si(1)−
C(1)−C(2) 83.9(1), Si(2)−Si(1)−C(1)−C(6) −94.9(1), Si(5)−
Si(10)−C(21)−C(22) 80.0(1), Si(5)−Si(10)−C(21)−C(26)
−100.6(1).
Figure 3. ORTEP diagram for compound 4. Thermal ellipsoids are
depicted at the 50% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and bond and torsional angles [deg]
with estimated standard deviations: Si−Si (mean) 2.349, Si(1)−C(18)
1.862(2), Si−Cmethyl (mean) 1.884, Si−Si−Si (mean) 109.6, Si(2)−
Si(1)−C(18) 108.67(5), Si(2)−Si(3)−Si(4)-Si(5) −13.31(3), Si(2)−
Si(7)−Si(6)−Si(5) −17.74(3), Si(2)−Si(8)−Si(9)−Si(5) −17.75(3),
Si(2)−Si(1)−C(18)−C(19) −86.1(1), Si(2)−Si(1)−C(18)−C(22)
89.4(1).
The silacarboxylic acid 9 afforded crystals of proper quality
only from 2-propanol. The resulting crystals belong to the
1.92−1.94 Å are considerably elongated, the average Si−C(sp3)
bond length was calculated from 19 169 individual XRD
experimental values to be 1.860 Å.21 Significantly elongated Si−
C bond distances in acyl silanes have been observed earlier,22
and it has been suggested that this lengthening of the silicon
carbonyl group bond can be ascribed not only to contributions
of canonical forms with single C−O bonds (Scheme 6,
structure A), but also to a resonance structure without a
formal bond between the metalloid atom and the carbonyl
carbon (Scheme 6, structure B).23 According to a more recent
study, finally, the situation is best described by structure C with
a dative bond between a negatively charged carbon and a
positively charged silicon atom.24
triclinic space group P1 with two molecules in the unit cell,
̅
which are connected to dimers via hydrogen bridges by two
molecules of 2-propanol (compare Figure 7).
There is only a minor impact of the substituents attached to
the bridgehead silicons on the structure of the bicyclooctasilane
core. In line with structural data of bicyclo[2,2,2]octasilanes
published earlier13,15b the compounds investigated in this study
exhibit a slightly twisted structure of the bicyclooctasilane cage
with nonparallel −Si2Me4− bridges in order to minimize steric
repulsion. Endocyclic dihedral angles Sibridgehead−Si−Si−
Sibridgehead range from 14.1° to 22.4°. Si−Si−Si bond angles
close to the ideal tetrahedral angle between 105.8° and 111.5°
and Si−Si bond lengths between 2.34 and 2.37 Å were
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rationalized if one assumes σ−π type hyperconjugative
interactions between the aromatic π- and the SiSi σ-
electrons.27,28 In the case of open-chained permethyloligosi-
lanes the most striking red shift was found upon introduction of
the first phenyl group, while a second phenyl substituent is
much less effective. Thus, Me3SiSiMe2SiMe3 exhibits a first
absorption maximum at 216 nm,29 which is shifted to 240 nm
3 0
in PhMe2 SiSiMe2 SiMe3
and to 243 nm in
PhMe2SiSiMe2SiMe2Ph.31 In line with this observation the
absorption spectrum of 3 displays a 5 nm red shift of the first
absorption maximum relative to 2, while 10 and 11 show
identical λmax values as compared to 2 and 4, respectively.
Apparently the σ−π conjugated bond system within 2 and 4 is
not extended further by the presence of the second aryl group,
which makes any electronic coupling of the aromatic
substituents via the bicyclooctasilane cage rather unlikely.
UV absorption spectra of the carbonyl derivatives 6−7 and
12 are depicted in Figure 9. The weak low-energy absorption
bands in the spectra of compounds 6, 7, and 12 centered near
370 nm are typical for acylsilanes and can be assigned to
symmetry-forbidden local n→π* transitions within the CO
group. The position and intensity of these absorption maxima
are nearly unaffected by the structure of the attached
oligosilanyl moiety and compare closely with the values
estimated for (Me3Si)3SiCOR or Me3SiCOR.32 In general it
is well established that β-silyl groups exert only little influence
on the energies of n→π* transitions in acyl silanes.33 Otherwise
the spectra are rather featureless. In the UV part strong maxima
around 210 nm appear, which cannot be assigned without
ambiguity either to carbonyl π→π* or electron transitions
within the polysilane skeleton. The silyl carboxylate 8 and the
silyl carboxylic acid 9 exhibit a continuously rising absorption
below 300 nm without any detectable maxima above 205 nm,
which is characteristic for related systems.17c,34 Obviously in
these species the carboxyl n→π* absorption band that is found
at 245 and 243 nm in the spectra of Me3SiCOOMe and
Me3SiCOOH,35 respectively, is completely masked by the
polysilanyl absorption in the near-UV region.
Figure 5. ORTEP diagram for compound 13. Thermal ellipsoids are
depicted at the 50% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and bond and torsional angles [deg]
with estimated standard deviations: Si−Si (mean) 2.353, Si(1)−C(1)
1.866(3), Si(10)−C(27) 1.885(3), Si−Cmethyl (mean) 1.888, Si−Si−Si
(mean) 109.7, C(1)−Si(1)−Si(2) 107.90(9), C(27)−Si(10)−Si(8)
110.21(9), Si(2)−Si(3)−Si(6)−Si(8) −15.80(5), Si(2)−Si(4)−
Si(7)−Si(8) −17.74(5), Si(2)−Si(5)−Si(9)−Si(8) −14.84(5),
Si(2)−Si(1)−C(1)−C(2) −84.4(2), Si(2)−Si(1)−C(1)−C(5)
−93.3(2), Si(8)−Si(10)−C(27)−C(28) 90.2(2), Si(8)−Si(10)−
C(27)−C(32) −87.6(3).
observed. The average Si−Si bond distance of 2.35 Å is typical
for Si−Si single bonds in cyclopolysilanes25 and agrees well
with the Si−Si covalent bond length of 2.34 Å.
UV absorption spectra of 1−14 have been recorded in order
to estimate the extent of interactions between the bridgehead
substituents with the bicyclooctasilane Si−Si bond system. UV
absorption data are summarized in Table 2.
Figure 8 compares the absorption spectrum of 1 with the
spectra of the phenyl- and ferrocenyl-substituted compounds 2,
3, 4, 10, 11, and 13. The ferrocenylsilanes 4, 11, and 13 show
characteristic weak absorption bands near 460 and 330 nm,
which arise from local transitions within ferrocene.26 All spectra
exhibit additional bands in the near UV region. For 1 a typical
shoulder appears at 240 nm, which previously has been
assigned to σ→π* type electron transitions involving the σ-SiSi
skeleton.16 In the spectra of 2 and 4 this band is shifted
considerably to the red by 20 and 30 nm, respectively. This
behavior is usually observed when aromatic side groups are
attached to permethylated oligosilane frameworks and is easily
As shown in Figure 10, finally, the absorption spectrum of 14
resembles the calculated sum spectrum of compounds 4 and 7,
which contain the separate chromophores. The spectrum of 14,
Figure 6. ORTEP diagram for compounds 6 and 8. Thermal ellipsoids are depicted at the 50% probability level. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and bond and torsional angles [deg] with estimated standard deviations: 6: Si−Si (mean) 2.353, C(1)−O(1)
1.231(4), Si(1)−C(1) 1.917(4), Si−Cmethyl (mean) 1.880, Si−Si−Si (mean) 109.1, O(1)−C(1)−C(2) 116.4(4), O(1)−C(1)−Si(1) 121.3(3),
C(2)−C(1)−Si(1) 122.1(3), Si(1)−Si(2)−Si(3)−Si(4) −22.38(6), Si(4)−Si(5)−Si(6)−Si(1) −19.06(6), Si(4)−Si(8)−Si(7)−Si(1) −19.00(6). 8:
Si−Si (mean) 2.354, C(1)−O(1) 1.201(2), C(2)−O(2) 1.447(2), C(1)−O(2) 1.357(2), Si(1)−C(1) 1.935(2), Si−Cmethyl (mean) 1.885, Si−Si−Si
(mean) 109.0, O(1)−C(1)−O(2) 121.5(1), O(1)−C(1)−Si(1) 126.9(1), O(2)−C(1)−Si(1) 111.6(1), Si(1)−Si(2)−Si(3)−Si(4) 19.15(3), Si(4)−
Si(5)−Si(6)−Si(1) 21.61(3), Si(4)−Si(8)−Si(7)−Si(1) 18.49(3), Si(1)−C(1)−O(2)−C(2) −178.7(1).
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Figure 7. ORTEP diagram for compound 9. Thermal ellipsoids are depicted at the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and bond and torsional angles [deg] with estimated standard deviations: Si−Si (mean) 2.347, C(1)−O(1) 1.194(6),
C(1)−O(2) 1.311(6), Si(1)−C(1) 1.942(5), Si−Cmethyl (mean) 1.880, O(2)−O(4) 2.661(8), O(1)−O(4) 2.807(8), Si−Si−Si (mean) 109.2,
O(1)−C(1)−O(2) 122.2(4), O(1)−C(1)−Si(1) 123.2(4), O(2)−C(1)−Si(1) 114.5(3), Si(1)−Si(2)−Si(3)−Si(4) −16.60(8), Si(4)−Si(5)−
Si(6)−Si(1) −17.02(9), Si(4)−Si(8)−Si(7)−Si(1) −20.57(9).
Scheme 6
Table 2. Absorption Data for 1−14 (n-hexane solution, c = 4
× 10−5; 10−3 mol·L−1)
λmax, abs (nm) (ε (L·mol−1·cm−1))
a
1
240sh (16 000)
2
240sh (19 000), 260sh (8200)
265sh (10 500)
3
4
268 (14 900), 330sh (185), 458 (280)
213 (62 000), 265sh (6000), 359 (140), 372 (190), 387 (160)
212 (46 500), 370 (170)
6
7
8
only end absorption
9
only end absorption
10
11
12
13
14
258 (26 700)
Figure 8. Absorption spectra of 1 and aryl-substituted bicyclo[2,2,2]-
octasilanes (n-hexane solution; c = 4 × 10−5 M; inset c = 10−3 M): (···,
gray) 1;15b (−··−, red) 2; (---, blue) 3; (, green) 4; (  ,
purple) 10; (−·−, magenta) 11; (− − −, black) 13.
268 (27 000), 325 (400), 458 (570)
232 (22 200), 371 (410)
260 (14 300), 332 (172), 457 (290)
270sh (15 000), 333 (260), 371 (240), 384 (237), 456 (315)
a
Taken from ref 15b.
(Me3Si)3SiCOR, the UV absorption spectra of the CO
derivatives 6−9 are rather featureless and, thus, do not allow
drawing even qualitative conclusions concerning interactions
between σ(SiSi) and CO group orbitals. Due to σ(SiSi)/
π(aryl) conjugation, the absorption spectra of the phenyl and
ferrocenyl derivatives show the expected bathochromic shift of
the first UV absorption band relative to 1. Attachment of
another aryl substituent to the second terminal Me3Si group,
however, did not lead to further bathochromic shifts as
observed in open-chained systems of comparable size. This
allows us to conclude that there is no direct conjugational type
interaction of the two aryl groups via the bicyclo[2,2,2]-
octasilane skeleton, which can be rationalized using steric
arguments. It has earlier been shown that cisoid conformations
do not extend the conjugation within σ(SiSi) oligosilane
skeletons.36 Because the conjugation path going from one aryl
group to the other via the octasilane cage contains one cisoid
fragment, it is not surprising that conjugation between the two
aryl groups leading to an extended conjugated system does not
occur. This assumption is further supported by the observation
therefore, seems to fulfill the classical expectation for
nonconjugatively connected chromophores.
CONCLUSIONS
■
In summary, we have elaborated synthetic approaches toward
bridgehead-functionalized permethylbicyclo[2,2,2]octasilanes.
Starting from the corresponding 1-potassium and 1,4-
dipotassium silanides previously unknown mono- and difunc-
tional derivatives with COR, COOR, COOH, and SiMenRm (R
= Ph, Fc) attached to the bridgehead silicon atoms have been
prepared successfully and fully characterized. In the crystalline
state all compounds investigated in this study exhibit a slightly
twisted structure of the bicyclooctasilane cage, which turned
out to be remarkably insensitive toward the nature of the
substituents attached to the bridgehead silicon atoms.
Except for the n→π* absorption bands of the acyl silanes 6
and 7 centered near 370 nm, which exhibit nearly constant
excitation energies as compared to Me3SiCOR or
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coupling (HP 1 capillary column, length 25 m, diameter 0.2 mm, 0.33
μm poly(dimethylsiloxane)) or on a Kratos Profile mass spectrometer
equipped with a solid probe inlet. Infrared spectra were obtained on a
Bruker Alpha-P Diamond ATR spectrometer from the solid sample.
UV−visible spectra were recorded in n-hexane solution, c = 4 × 10−5
and 10−3 mol·L−1, respectively, on a Perkin-Elmer Lambda 35
spectrometer. Positions of absorption maxima and shoulders were
obtained directly from the experimental spectra; absorptivity values ε
were determined at the position of the maxima using Lambert−Beer’s
law. Melting points were determined using a Buchi 535 apparatus and
̈
are uncorrected. Elemental analyses were carried out on a Hanau Vario
Elementar EL apparatus.
Synthesis of Dodecamethyl-4-(trimethylsilyl)-1-
(dimethylphenylsilyl)bicyclo[2.2.2]octasilane (2). A solution of
1-K in 5 mL of DME was freshly prepared from 275 mg (0.5 mmol) of
1 and 62 mg (0.55 mmol) of KOtBu. After removal of the volatile
components in vacuo at room temperature the resulting residue was
taken up in 10 mL of toluene, cooled to −70 °C, and slowly added to a
solution of 102 mg (0.6 mmol) of PhMe2SiCl in 20 mL of toluene.
Subsequently the mixture was stirred for another 30 min and finally
allowed to warm to room temperature. After aqueous workup with 100
mL of 10% sulfuric acid the organic layer was separated and dried over
Na2SO4, and the solvent was stripped off with a rotary evaporator.
Drying in vacuo (0.02 mbar) and crystallization from pentane by
evaporation of the solvent at room temperature afforded 210 mg
(69%) of white and crystalline 2.
Figure 9. Absorption spectra of CO-substituted bicyclo[2,2,2]-
octasilanes (n-hexane solution; c = 4 × 10−5 M; inset c = 10−3 M).
(−·−, green) 6; (, red) 7; (−··−, blue) 8; (···, black) 9; (---,
magenta) 12.
Mp: 131−133 °C. Anal. Found: C, 44.12; H, 8.86. Calcd for
C23H56Si10: C, 45.02; H, 9.20. 29Si NMR (CDCl3, TMS, ppm): −6.05
(SiMe3); −10.54 (SiMe2Ph); −37.89, −38.26 (SiMe2); −129.04
(SiSiMe2Ph); −131.00 (SiSiMe3). 13C NMR (CDCl3, TMS, ppm):
141.50, 133.98, 128.40, 127.67 (C5H6); 3.55 (Si(CH3)3); 1.70
(Si(CH3)2Ph); −1.17, −1.31 (Si(CH3)2). 1H NMR (CDCl3, TMS,
ppm, rel int): 7.32−7.55 (5H, m, (C6H5); 0.55 (6H, s, Si(CH3)2Ph);
0.25 (18H, s, Si(CH3)2); 0.22 (9H, s, Si(CH3)3); 0.20 (18H, s,
Si(CH3)2). HRMS: calcd for [C23H56Si10]+• (M+) 612.2075; found
612.2104.
Synthesis of Dodecamethyl-4-(trimethylsilyl)-1-
(methyldiphenylsilyl)bicyclo[2.2.2]octasilane (3). The procedure
followed was that used for 2 with 715 mg (1.3 mmol) of 1, 160 mg
(1.4 mmol) of KOtBu, and 333 mg (1.4 mmol) of Ph2MeSiCl.
Crystallization of the crude product from diethyl ether/ethanol (1:1)
by evaporation of the solvents at room temperature afforded 670 mg
(76%) of white and crystalline 3.
Mp: 136−138 °C. 29Si NMR (CDCl3, TMS, ppm): −6.08 (SiMe3);
−11.81 (SiMePh2); −37.76, −38.18 (SiMe2); −128.37 (SiSiMePh2);
−131.45 (SiSiMe3). 13C NMR (CDCl3, TMS, ppm): 138.91, 135.18,
128.71, 127.67 (C5H6); 3.48 (Si(CH3)3); 0.90 (SiCH3Ph2); −1.41
1
Figure 10. Comparison of absorption spectra of 4, 7, and 14 with the
calculated sum of the spectra of 4 and 7. (A) UV part; n-hexane
solution; c = 4 × 10−5 M; (B) visible part; c = 10−3 M, (, green) 4;
(− − −, blue) 7; (−··−) 14; (···) 4 + 7.
(×2, Si(CH3)2). H NMR (CDCl3, TMS, ppm, rel int): 7.62−7.33
(10H, m, (C6H5); 0.82 (3H, s, SiCH3Ph2); 0.26 (18H, s, Si(CH3)2);
0.23 (9H, s, Si(CH3)3); 0.20 (18H, s, Si(CH3)2). HRMS: calcd for
[C28H58Si10]+• (M+) 674.2231; found 674.2265.
Synthesis of 1-(Ferrocenyldimethylsilyl)dodecamethyl-4-
(trimethylsilyl)bicyclo[2.2.2]octasilane (4). To a solution of 1-K
in 10 mL of DME (freshly prepared from 2.76 g (5 mmol) of 1 and
0.62 g (5.5 mmol) of KOtBu) was slowly added a solution of 1.45 g
(5.2 mmol) of FcSiMe2Cl in 50 mL of DME at −50 °C. Subsequently
the mixture was stirred for another 30 min and finally allowed to warm
to room temperature. After aqueous workup with 10% sulfuric acid the
organic layer was separated and dried over Na2SO4, and the volatile
components were stripped off with a rotary evaporator. Drying in
vacuo (0.02 mbar) and crystallization from diethyl ether/acetone (1:1)
by evaporation of the solvents at room temperature afforded 2.83 g
(78%) of orange and crystalline 4.
Mp: 186−187 °C. Anal. Found: C, 44.35; H, 8.28. Calcd for
C27H61FeSi10: C, 44.95; H, 8.38. 29Si NMR (CDCl3, TMS, ppm):
−6.11 (SiMe3); −11.45 (SiMe2Fc); −38.12, −38.31 (SiMe2); −128.90
(SiSiMe2Fc); −130.67 (SiSiMe3). 13C NMR (CDCl3, TMS, ppm):
74.92, 73.37, 70.75 (C5H4−SiMe2); 68.17 (C5H5); 3.51 (Si(CH3)3);
1.95 (Si(CH3)2Fc); −1.27, −1.34 (Si(CH3)2). 1H NMR (CDCl3,
TMS, ppm, rel int): 4.35, 4.10 (4H, b, Si(C5H4)); 4.17 (5H, s, C5H5);
that the absorption spectrum of 14 resembles the calculated
sum spectrum of compounds 4 and 7 and, thus, seems to fulfill
the classical expectation for nonconjugatively connected
chromophores.
EXPERIMENTAL SECTION
■
All experiments were performed under a nitrogen atmosphere using
standard Schlenk techniques. Solvents were dried using a column
solvent purification system.37 KOtBu (97%), MeCOCl (99%),
tBuCOCl (99%), and ClCOOMe (98%) were used as purchased;
Me2SiCl2 (98%) was distilled prior to use. Commercial CO2 was dried
by passing through P2O5. PhMe2SiCl,38 Ph2MeSiCl,39 FcMe2SiCl,40 1-
12b
1
K, and 1-K2 were synthesized as previously reported. H (299.95
MHz), 13C (75.43 MHz), and 29Si (59.59 MHz) NMR spectra were
recorded on a Varian INOVA 300 spectrometer in C6D6 solution and
referenced versus TMS using the internal 2H-lock signal of the solvent.
Mass spectra were run either on an HP 5971/A/5890-II GC/MS
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0.51 (6H, s, Si(CH3)2(C5H4)); 0.23 (18H, s, Si(CH3)2); 0.21 (9H, s,
Si(CH3)3); 0.17 (18H, s, Si(CH3)2). HRMS: calcd for
[C27H60Si10Fe]+• (M+) 720.1739; found 720.1785.
−129.63 ppm (SiSiMe3). 13C NMR (CDCl3, TMS, ppm): 187.77
(COOCH3); 49.13 (COOCH3); 3.57 (Si(CH3)3); −1.32, −3.05
(Si(CH3)2). 1H NMR (CDCl3, TMS, ppm, rel int): 3.63 (3H, s,
COOCH3); 0.33 (18H, s, Si(CH3)2); 0.31 (18H, s, Si(CH3)2); 0.25
(9H, s, Si(CH3)3). IR (neat): ν(CO) = 1662 (m) cm−1. HRMS:
calcd for [C17H48O2Si9]+• (M+) 536.1578; found 536.1600.
Synthesis of Dodecamethyl-4-trimethylsilylbicyclo[2,2,2]-
octasilanyl-1-carboxylic Acid (9). A solution of 1-K in 10 mL of
DME (freshly prepared from 3.31 g (6 mmol) of 1 and 740 mg (6.6
mmol) of KOtBu) was slowly added at −70 °C to a saturated solution
of CO2 in diethyl ether, which has been obtained by slowly bubbling
thoroughly dried CO2 through 150 mL of diethyl ether at −70 °C for
20 min. Subsequently the mixture was stirred for another 30 min at
−70 °C and finally allowed to warm to room temperature. After
aqueous workup with 100 mL of 2% sulfuric acid the organic layer was
separated and dried over Na2SO4, and the volatile components were
removed with a rotary evaporator. Subsequent drying at 0.02 mbar
afforded 301 mg (96%) of pure 9 as a white, moderately air-stable
powder. Crystals suitable for X-ray structure analysis were obtained
after recrystallization from 2-propanol by evaporation of the solvent at
room temperature.
Mp: 163−165 °C (dec). Anal. Found: C, 36.08; H, 8.28. Calcd for
C16H46O2Si9: C, 36.72; H, 8.86. 29Si NMR (CDCl3, TMS, ppm):
−5.49 (SiMe3); −38.12, −39.22 (SiMe2); −76.72 (SiCOOH),
−129.61 ppm (SiSiMe3). 13C NMR (CDCl3, TMS, ppm): 193.10
(COOH); 3.58 (Si(CH3)3); −1.31, −3.07 (Si(CH3)2). 1H NMR
(CDCl3, TMS, ppm, rel int): 0.36 (18 H, s, Si(CH3)2); 0.32 (18H, s,
Si(CH3)2); 0.25 (9H, s, Si(CH3)3). IR (neat): ν(O−H) = 3200−2500
(m) cm−1; ν(CO) = 1631 (m) cm−1. HRMS: calcd for
[C16H45O2Si9]+• ([M − H]+) 521.1343; found 521.1346.
S y n t h e s i s o f 1 , 4 - B i s ( d i m e t h y l p h e n y l s i l y l ) -
dodecamethylbicyclo[2.2.2]octasilane (10). A solution of 1-K2
in 10 mL of toluene (freshly prepared from 276 mg (0.5 mmol) of 1,
123 mg (1.1 mmol) of KOtBu, and 291 mg (1.1 mmol) of 18-crown-
6) was slowly added to a solution of 170 mg (1.0 mmol) of PhMe2SiCl
in 40 mL of toluene at −70 °C. Subsequently the mixture was stirred
for another 30 min at −70 °C and finally allowed to warm to room
temperature. After aqueous workup with 100 mL of 3% sulfuric acid
the organic layer was separated and dried over Na2SO4, and the
solvent was stripped off with a rotary evaporator. Drying in vacuo
(0.02 mbar) and crystallization from pentane by evaporation of the
solvent at room temperature afforded 220 mg (65%) of colorless and
crystalline 10.
Synthesis of 1-(Chlorodimethylsilyl)dodecamethyl-4-
(trimethylsilyl)bicyclo[2.2.2]octasilane (5). A solution of 1-K in
5 ml of DME was freshly prepared from 2.21 g (4 mmol) of 1 and 0.42
g (4.2 mmol) of KOtBu. After removal of the volatile components in
vacuo at room temperature the resulting residue was taken up in 5 mL
of toluene, cooled to −70 °C, and slowly added to a solution of 2.06 g
(16 mmol) of Me2SiCl2 in 20 mL of toluene. Subsequently the mixture
was stirred for another 30 min and finally allowed to warm to room
temperature. After removal of the volatile components in vacuo (0.02
mbar) the solid residue was taken up with 20 mL of heptane and
filtered over Celite. Removal of the solvent from the filtrate and drying
in vacuo at room temperature afforded 2.13 g (93%) of pure 5 as
colorless crystals.
Mp: 155−157 °C (dec). Anal. Found: C, 35.72; H, 8.78. Calcd for
C17H51ClSi10: C, 35.70; H, 8.99. 29Si NMR (CDCl3, TMS, ppm):
33.27 (SiMe2Cl); −6.13 (SiMe3); −38.21, −38.42 (SiMe2); −125.01
(SiSiMe2Cl); −130.48 (SiSiMe3). 13C NMR (CDCl3, TMS, ppm):
1
8.24 (Si(CH3)2Cl); 3.37 (Si(CH3)3); −1.34, −1.66 (Si(CH3)2). H
NMR (CDCl3, TMS, ppm, rel int): 0.58 (6H, s, Si(CH3)2Cl); 0.37,
(18H, s, Si(CH3)2); 0.31 (18H, s, Si(CH3)2); 0.26 (9H, s, Si(CH3)3).
MS: calcd for [C17H51ClSi10]+• (M+) 570.2; found 570.3.
S y n t h e s i s o f 1 - A c y l - 4 - ( t r i m e t h y l s i l y l ) -
dodecamethylbicyclo[2.2.2]octasilane (6). A solution of 1-K in
10 mL of DME (freshly prepared from 2.21 g (4 mmol) of 1 and 0.49
g (4.4 mmol) of KOtBu) was slowly added to a solution of 0.33 g (4.2
mmol) of MeCOCl in 40 mL of diethyl ether at −80 °C. Subsequently
the mixture was stirred for an additional hour at −80 °C and finally
allowed to warm to room temperature. After aqueous workup with 100
mL of 2% sulfuric acid the organic layer was separated and dried over
Na2SO4, and the solvent was stripped off with a rotary evaporator. The
resulting oily residue was chromatographed (toluene/heptane, 10:1,
silica gel) to give 6 (0.88 g, 42%) as a white solid. Crystals suitable for
X-ray structure analysis could be grown from acetone solution by
evaporation of the solvent at room temperature.
Mp: 60 °C (dec). 29Si NMR (CDCl3, TMS, ppm): −5.65 (SiMe3);
−38.05, −39.76 (SiMe2); −72.68 (SiCOMe), −129.78 ppm (SiSiMe3).
13C NMR (CDCl3, TMS, ppm): 244.06 (COCH3); 42.69 (COCH3);
1
3.48 (Si(CH3)3); −1.38, −2.78 (Si(CH3)2). H NMR (CDCl3, TMS,
ppm, rel int): 2.30 (3H, s, COCH3); 0.34 (18H, s, Si(CH3)2); 0.30
(18H, s, Si(CH3)2); 0.24 (9H, s, Si(CH3)3). IR (neat): ν(CO) =
1632 (m) cm−1. HRMS: calcd for [C17H48OSi9]+• (M+) 520.1628;
found 520.1653.
Mp: 181−182 °C. Anal. Found: C, 49.72; H, 8.17. Calcd for
C28H58Si10: C, 49.78; H, 8.65. 29Si NMR (CDCl3, TMS, ppm): −10.60
(SiMe2Ph); −37.90 (SiMe2); −129.73 (SiSiMe2Ph). 13C NMR
(CDCl3, TMS, ppm): 141.42, 133.94, 128.39, 127.66 (C6H5); 1.64
Synthesis of 1-Trimethylacyl-4-(trimethylsilyl)-
dodecamethylbicyclo[2.2.2]octasilane (7). The procedure fol-
lowed was that used for 6 with 825 mg (1.5 mmol) of 1, 179 mg (1.6
mmol) of KOtBu, and 192 mg (1.6 mmol) of tBuCOCl. Yield: 740 mg
(88%) of a colorless solid, which gave 520 mg (61%) of pure and
crystalline 7 after recrystallization from acetone by evaporation of the
solvent at room temperature.
1
(Si(CH3)2Ph); −1.36 (Si(CH3)2). H NMR (CDCl3, TMS, ppm, rel
int): 7.53−7.31 (10H, m, (C6H5); 0.54 (12H, s, Si(CH3)2Ph); 0.17
(36H, s, Si(CH3)2). HRMS: calcd for [C28H58Si10]+• (M+): 674.2231;
found: 647.2247.
Synthesis of 1,4-Bis(ferrocenyldimethylsilyl)-
dodecamethylbicyclo[2.2.2]octasilane (11). The procedure fol-
lowed was that used for 10 with 1.00 g (1.8 mmol) of 1, 0.43 g (3.8
mmol) of KOtBu, 1.15 g (3.8 mmol) of 18-crown-6, and 1.15 g (4.1
mmol) of FcMe2SiCl. Crystallization of the crude product from diethyl
ether by evaporation of the solvent at room temperature afforded 320
mg (20%) of orange and crystalline 11.
Mp: 290 °C (dec). Anal. Found: C, 47.92; H, 7.02. Calcd for
C36H68Fe2Si10: C, 48.39; H, 7.67. 29Si NMR (CDCl3, TMS, ppm):
−11.40 (SiMe2Fc); −38.14 (SiMe2); −129.12 (SiSiMe2Fc). 13C NMR
(CDCl3, TMS, ppm): 74.61, 73.16, 70.51 (C5H4−SiMe2), 67.92
(C5H5); 1.92 (Si(CH3)2Fc); −1.39 (Si(CH3)2). 1H NMR (CDCl3,
TMS, ppm, rel int): 4.31, 4.05 (8H, b, C5H4-SiMe2); 4.14 (10H, b,
C5H5); 0.51 (12H, s, Si(CH3)2Fc); 0.13 (36H, s, Si(CH3)2). HRMS:
calcd for [C36H66Si10Fe2]+• (M+) 890.1561; found 890.1549.
S y n t h e s i s o f 1 , 4 - B i s ( t r i m e t h y l a c y l ) -
dodecamethylbicyclo[2.2.2]octasilane (12). Method a: The
procedure followed was that used for 10 with 276 mg (0.5 mmol)
of 1, 123 mg (1.1 mmol) of KOtBu, 291 mg (1.1 mmol) of 18-crown-
Mp: 202−204 °C (dec). 29Si NMR (CDCl3, TMS, ppm): −5.83
(SiMe3); −37.76, −38.09 (SiMe2); −75.68 (SiCOtBu), −130.82 ppm
(SiSiMe3). 13C NMR (CDCl3, TMS, ppm): 247.64 (COtBu); 48.41
(COCMe3); 24.67 (C(CH3)3); 3.46 (Si(CH3)3); −1.19, −1.90
(Si(CH3)2). 1H NMR (CDCl3, TMS, ppm, rel int): 1.04 (9H, s,
C(CH3)3); 0.32 (18H, s, Si(CH3)2); 0.30 (18H, s, Si(CH3)2); 0.24
(9H, s, Si(CH3)3). IR (neat): ν(CO) = 1622 (m) cm−1. HRMS:
calcd for [C20H54OSi9]+• (M+) 652.2098; found 562.2119.
Synthesis of 1-Methylcarboxy-4-(trimethylsilyl)-
dodecamethylbicyclo[2.2.2]octasilane (8). The procedure fol-
lowed was that used for 6 with 550 mg (1.0 mmol) of 1, 123 mg (1.1
mmol) of KOtBu, and 470 mg (5 mmol) of ClCOOMe.
Recrystallization of the resulting resinous residue from ethanol by
evaporation of the solvent at room temperature afforded 490 mg
(89%) of white and crystalline 8.
Mp: 60 °C (dec). Anal. Found: C, 37.26; H, 8.40. Calcd for
C17H48O2Si9: C, 38.00; H, 9.00. 29Si NMR (CDCl3, TMS, ppm):
−5.52 (SiMe3); −38.09, −39.19 (SiMe2); −76.68 (SiCOOMe),
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6, and 132 mg (1.1 mmol) of ClCOtBu. Crystallization of the crude
product from acetone at −30 °C afforded 140 mg (48%) of white and
crystalline 12.
Si(CH3)2Fc); 0.28, 0.20 (36H, s, Si(CH3)2). IR (neat): ν(CO) =
1621 cm−1 (m). HRMS: calcd for [C29H60FeOSi9]+• (M+) 732.1919;
found 732.1945.
X-ray Crystallography. For X-ray structure analysis suitable
crystals were mounted onto the tip of glass fibers using mineral oil.
Data collection was performed on a Bruker Kappa Apex II CCD
diffractometer at 100 K for compounds 2, 3, 4, 6, 8, 10, and 13 and
200 K for compound 9 using graphite-monochromated Mo Kα (λ =
0.71073 Å) radiation. Details of the crystal data and structure
refinement are provided as Supporting Information. The SHELX
version 6.1 program package was used for the structure solution and
refinement.41 Absorption corrections were applied using the SADABS
program.42 All non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were included in the
refinement at calculated positions using a riding model as
implemented in the SHELXTL program. Crystallographic data
(excluding structure factors) have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications CCDC-
923021 (2), CCDC-923023 (3), CCDC-923022 (4), CCDC-923018
(6), CCDC-923020 (8), CCDC-923019 (9), CCDC-923017 (10),
and CCDC-923016 (13). Copies of the data can be obtained free of
charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax (internat.) +44-1223/336-033; e-mail
deposit@ccdc.cam.ac.uk).
Method b: 282 mg (0.5 mmol) of 7 was stirred with 62 mg (1.1
mmol) of KOtBu in 10 mL of DME for 40 min at room temperature.
At this time 29Si NMR analysis revealed quantitative formation of the
silanide 7-K. The resulting red solution was slowly added to a solution
of 66 mg (0.55 mmol) of ClCOtBu in 10 mL of diethyl ether at −70
°C. Subsequently the mixture was stirred for another 30 min at −70
°C and finally allowed to warm to room temperature. After stirring for
an additional 2 h aqueous workup was accomplished by addition of
100 mL of 3% sulfuric acid, separation of the organic layer, drying over
Na2SO4, and removal of the solvent with a rotary evaporator.
Crystallization of the oily residue from acetone/pentane (1:1) by
evaporation of the solvents at room temperature afforded 90 mg
(32%) of 12.
7-K: 29Si NMR (DME/D2O, TMS, ppm): −33.05; −40.06 (SiMe2);
−73.86 (SiCOtBu); −180.69 (SiK).
12: Mp: 218−219 °C (dec). 29Si NMR (CDCl3, TMS, ppm):
−37.59 (SiMe2); −76.88 (SiCOtBu). 13C NMR (CDCl3, TMS, ppm):
247.09 ((COC(CH3)3), 48.45 (COC(CH3)3), 24.63 (COC(CH3)3),
−1.88 (Si(CH3)2). 1H NMR (CDCl3, TMS, ppm, rel int): 1.04 (18H,
s, C(CH3)3), 0.34 (36H, s, Si(CH3)3). IR (neat): ν(CO) = 1621
cm−1 (m). HRMS: calcd for [C22H54O2Si8]+• (M+) 574.2278; found
574.2303.
ASSOCIATED CONTENT
S y n t h e s i s o f 1 - ( F e r r o c e n y l d i m e t h y l s i l y l ) - 4 -
(dimethylphenylsilyl)dodecamethylbicyclo[2.2.2]octasilane
(13). A 360 mg (0.5 mmol) sample of 4 was stirred with 62 mg (0.55
mmol) of KOtBu in 5 mL of DME for 40 min at room temperature. At
this time 29Si NMR analysis of the resulting red solution revealed
quantitative formation of the silanide 4-K. The resulting red solution
was slowly added to a solution of 940 mg (0.55 mmol) of PhMe2SiCl
in 10 mL of diethyl ether at −70 °C. Subsequently the mixture was
stirred for another 30 min at −70 °C and finally allowed to warm to
room temperature. After stirring for an additional 2 h aqueous workup
was accomplished by addition of 100 mL of 3% sulfuric acid,
separation of the organic layer, drying over Na2SO4, and removal of
the solvent with a rotary evaporator. Crystallization of the oily residue
from acetone at −30 °C afforded 310 mg (80%) of red and solid 13.
The product can be purified further by column chromatography
(hexane, silica gel). Yield: 230 mg (59%).
■
S
* Supporting Information
1H and 29Si NMR spectra of 3, 6, 7, and 12. Tables and CIF
files giving crystal, collection, and refinement data for the
structures of compounds 2, 3, 4, 6, 8, 10, and 13. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Tel: +43/316/873-32111. Fax: +43/316-32102. E-mail:
harald.stueger@tugraz.at.
■
Notes
The authors declare no competing financial interest.
4-K: 29Si NMR (DME/D2O, TMS, ppm): 6.58 (Me3Si-OtBu);
−11.71 (SiMe2Fc); −34.32, −39.67 (SiMe2); −127.89 (SiSiMe2Fc);
−177.62 (SiK).
ACKNOWLEDGMENTS
We thank the FWF (Wien, Austria) for financial support
(project number P21271-N19).
■
13: Mp: 153−156 °C. Anal. Found: C, 48.71; H, 7.55. Calcd for
C32H62FeSi10: C, 49.05; H, 7.98. 29Si NMR (CDCl3, TMS, ppm):
−10.59 (SiMe2Ph); −11.60 (SiMe2Fc); −37.89, −38.09 (SiMe2);
−129.28, −129.55 (SiSiMe2Ph, SiSiMe2Fc). 13C NMR (CDCl3, TMS,
ppm): 141.52, 133.96, 128.38, 127.66 (C6H5); 75.23, 73.85, 71.02
(C5H4−SiMe2); 68.42 (C5H5); 1.95, 1.65 (Si(CH3)2Ph, Si(CH3)2Fc);
−1.34, −1.36 (Si(CH3)2). 1H NMR (CDCl3, TMS, ppm, rel int):
7.54−7.32 5H, (m, (C6H5)); 4.18 (5H, b, (C5H5)); 4.35, 4.10 (4H, b,
(C5H4)-SiMe2); 0.55 (12H, b, Si(CH3)2Ph, Si(CH3)2Fc); 0.18, (36H,
b, Si(CH3)2). HRMS: calcd for [C32H62Si10Fe]+• (M+) 782.1896;
found 782.1866.
Synthesis of 1-(Ferrocenyldimethylsilyl)-4-(trimethylacyl)-
dodecamethylbicyclo[2.2.2]octasilane (14). The procedure fol-
lowed was that used for 13 with 360 mg (0.5 mmol) of 4, 62 mg (0.55
mmol) of KOtBu, and 66 mg (0.55 mmol) of ClCOtBu. After removal
of the solvents, washing of the crude product with acetone, and drying
in vacuo (0.02 mbar) 280 mg (78%) of pure 14 was obtained as an
orange powder.
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