Oligosilanylsilatranes

Article abstract of DOI:10.1021/acs.organomet.5b00404

Oligosilanes with attached silatranyl units were obtained by reactions of potassium oligosilanides with a silatranyl triflate. Interaction between Si and N atoms was observed in the ²⁹Si NMR spectra (upfield-shifted SiO₃ resonances) and in the solid-state structures (Si-N distances between 2.29 and 2.16 ?). The Si-N interaction can be "switched off" either by protonation of the nitrogen lone pair or by potassium silanide formation caused by trimethylsilyl group cleavage in the presence of potassium tert-butoxide. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00404

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pubs.acs.org/Organometallics
Oligosilanylsilatranes
Mohammad Aghazadeh Meshgi,† Judith Baumgartner,‡ and Christoph Marschner*,†
‡
†Institut fur Anorganische Chemie der Technischen Universitat Graz and Institut fur Chemie, der Karl Franzens Universitat Graz,
Stremayrgasse 9, 8010 Graz, Austria
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Oligosilanes with attached silatranyl units were
obtained by reactions of potassium oligosilanides with a
silatranyl triflate. Interaction between Si and N atoms was
observed in the 29Si NMR spectra (upfield-shifted SiO3
resonances) and in the solid-state structures (Si−N distances
between 2.29 and 2.16 Å). The Si−N interaction can be “switched off” either by protonation of the nitrogen lone pair or by
potassium silanide formation caused by trimethylsilyl group cleavage in the presence of potassium tert-butoxide.
preference for transoid arrangements of chains. This con-
formation is of some importance, as it is known to facilitate the
delocalization of σ-bonding electrons.21 In addition to
conformational properties, also electronic factors such as
substituent electronegativity22−26 and hypercoordination27,28
can influence the optical absorption properties. We therefore
were interested in introducing silyl substituents into oligosi-
lanes, which have a weakened Si−Si bond.
Synthesis. One issue that has to be dealt with when
hypercoordinate entities are incorporated into oligosilanes is
the choice of which group should be used. We decided that the
plain silatrane consisting of a silicon atom with a triethanol-
amine ligand would serve best as a starting point.
In principle there are two ways to prepare a silatranyl-
substituted oligosilane. Either the silatrane silicon atom is
introduced first and then the triethanolamine unit is attached or
the silatranyl unit is prepared first and is then attached as a
whole to the oligosilane. After some experiments we found
both strategies possible but concentrated on the second one,
which proved to be more general and gave better yields in our
hands.
For the attachment of the silatrane unit the obvious way to
proceed seemed to be reaction of a silatrane with a suitable
leaving group with a silanyl anion. While we found that
reactions with silatranyl chloride 1 are a possible option, it
turned out that the use of the respective triflate 2 gave better
yields. Synthesis of silatranyl triflate 2 was accomplished by
reaction of silatranyl chloride29 1 with trimethylsilyl triflate
(Scheme 1).30
INTRODUCTION
■
Due to the four valence electrons that group 14 elements
possess, they exhibit a strong prevalence for tetravalent
compounds. However, even for carbon, compounds with
both diminished (lower) and higher coordination sphere are
known. As carbon is a rather small atom, hypervalent
coordination states usually lead to steric interactions between
substituents. Therefore, such situations are typically not stable
but only represent intermediates or transition states, such as in
SN2 reactions.1−3
For the heavier elements silicon, germanium, and tin the
situation is somewhat different. While they share the electronic
situation of carbon, their atomic radii are larger and therefore
they can more easily accommodate additional substituents.
Today, numerous stable penta- and hexacoordinate compounds
are known for silicon,4−8 germanium,7−9 and tin.10−12 In
particular, the so-called atrane molecules (silatranes, germa-
tranes, and stannatranes), substances which feature the heavy
group 14 element with a trialkanolamine ligand N-
[(CR1R2)nO]3ER (E = Si, Ge), have been studied to quite
some extent. In many cases it was found that hypercoordination
has a profound influence on the bond located trans to the
nitrogen atom.
Interestingly, a survey of known sila- and germatranes with
different triethanolamine substituents reveals that, despite the
large variety of attached groups R which have been studied,
almost no compounds of atranes with bonds to other heavy
group 14 elements exist.13,14 Only very recently Zaitsev et al.
published a first study addressing compounds where an atrane
unit is attached to a heavy group 14 oligomer unit.15 In the
current account we want to present our activities concerning
the synthesis and chemistry of silatranyl-substituted oligosi-
lanes.
Reaction of silatranyl triflate 2 with tris(trimethylsilyl)silyl
potassium31 gave the expected neopentasilane 3 in an
acceptable yield of 51% (Scheme 2). In an analogous way
also the related compounds 4 and 5 were obtained.
With the reaction of isotetrasilanides and 2 being established,
the question arose whether 2-trisilanides would also react the
same way. During the course of our studies on oligosilanyl
RESULTS AND DISCUSSION
■
In recent years we have put some effort into the investigation of
conformational properties of oligosilanes.16−20 In particular,
compounds with bulky end groups such as the tris-
(trimethylsilyl)silyl unit were found to exhibit a strong
Received: May 12, 2015
© XXXX American Chemical Society
A
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For a proper comparison of the UV-absorption properties of
oligosilanes with and without silatranyl units it was desirable to
obtain derivatives of 2,2,5,5-tetrakis(trimethylsilyl)-
Scheme 1. Synthetic Access to Silatranyl Triflate 2
decamethylhexasilane.20 Reaction of the respective silanide
33,34
(Me3Si)3Si(Me2Si)2Si(K)(SiMe3)2
with 2 did not proceed
to 16 with a satisfactory yield due to the increased steric bulk of
the anion. However, reaction of the anion 10, which was
already substituted with silatranyl, with 1-chloro-3,3-bis-
(trimethylsilyl)heptamethyltetrasilane 1519 allowed the isola-
tion of compound 16 (Scheme 4). Following the same strategy,
the 2,5-disilatranylhexasilane compound 17 was obtained by
reaction of 2 equiv of 10 with 1,2-dichlorotetramethyldisilane
(Scheme 4). Although silanide 10 is sterically more demanding
than tris(trimethylsilyl)silyl potassium it can react with another
equivalent of 2 to give neopentasilane 18 containing two
silatranyl units (Scheme 2).
Scheme 2. Formation of Oligosilanylsilatranes using Salt
Elimination Reactions
The fact that the silatrane nitrogen atom donates electron
density to the silicon diminishes its basicity. For a number of
silatranes, in particular ones with electronegative substituents, it
has been shown that protonation occurs preferentially at one of
the oxygen atoms, which also exhibit a stronger kinetic
basicity.35,36 Theoretical calculations predict, however, that for
a silylated silatrane protonation should occur preferentially at
the nitrogen atom.35 To estimate the degree of the nitrogen
donation on the Si−Si bond of 3, it was treated with
trifluoromethanesulfonic acid to protonate the nitrogen lone
pair and thus switch off the Si−N interaction. The obtained
ammonium salt 19·OTf forms cleanly and the shut-off Si−N
interaction is visible in the NMR spectra and the solid-state
structure (Scheme 5). While protonation with the extremely
strong trifluoromethanesulfonic acid (pKa = −14)37 could be
expected, an attempt to achieve protonation with excess acetic
acid (pKa = 4.76)37 failed completely. Reaction of 3 with
trichloroacetic acid (pKa = 0.65)37 was not complete with a
stoichiometric amount of Cl3CCO2H, but a 5-fold excess gave
19·TCA. Other than an osmium complex with a silatranyl
ligand,38,39 19·OTf seems to be the only structurally
characterized example of a silatrane protonated at the nitrogen
atom.
NMR Spectroscopy. The compounds of this study were
characterized by multinuclear NMR spectroscopy (Table 1).
The proton spectra of the neutral compounds (3−9, 16−18) in
CDCl3 exhibit the typical pattern of two triplets (3JH−H =5.6
Hz) for the two methylene groups of the silatrane unit with
chemical shifts of ca. 3.65 ppm for the O-CH2 units and 2.72
ppm for the neighboring N-CH2 moieties. It is interesting to
note that a relatively strong solvent effect is observed for the
proton spectra, which shall be exemplified for compound 3, for
which the methylene resonances OCH2/CH2N were found at
3.65/2.72 ppm in CDCl3 and 3.30/1.83 ppm in C6D6. The
respective 13C resonances of the neutral compounds, which are
also all very similar, were found around 58.5 ppm for the O-
CH2 and 51.9 ppm for the N-CH2 units (in both CDCl3 and
anions, on several occasions the reactivity of 2-trisilanides
differed substantially from that of isotetrasilanides.32 However,
for the case of the reactions with 2, the use of a series of 2-
trisilanides occurred smoothly. Reaction of 2 with methylbis-
(trimethylsilyl)silyl potassium gave 6 in a respectable yield of
75%, reflecting the better steric accessibility of the silanide
(Scheme 2). With sterically more demanding silanides carrying
ethyl, isopropyl, and phenyl the reactions also proceeded to 7−
9; however, these reactions gave less satisfying yields (Scheme
2).
Given the access to this series of oligosilanylsilatranes, we
wanted to find out whether these compounds could be used as
building blocks. Therefore, compound 3 was reacted with
potassium tert-butoxide to cleanly obtain compound 10, which
is the product of trimethylsilyl abstraction (Scheme 3). An
analogous reaction was carried out with compound 5 to give
11. In every case attack of the butoxide was selective for a
trimethylsilyl group. When the same reaction was attempted
with the alkylated oligosilanylsilatranes 6 and 7, again the
expected silatranylsilanides 12 and 13 were formed. However,
in these cases the reactions were not as clean and also attack at
the silatranyl unit was observed, yielding the bis(trimethylsilyl)-
alkylsilyl potassium species and the silatranyl tert-butyl ether as
side products. For the methylated substrate 6 the ratio between
the silanide 12 and the silatranyl ether was about 2:1, whereas
for the sterically somewhat better shielded ethylated compound
7 the ratio of 13 to the silatranyl ether was about 8:1. The
phenylated compound 9, however, displayed a clean reaction
with potassium tert-butoxide to selectively afford silanide 14.
Scheme 3. Formation of Silatranyl Oligosilanides by Trimethylsilyl Abstraction
B
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Scheme 4. Synthesis of Larger Silatranylated Oligosilanes 16 and 17
reflecting a stronger degree of hypercoordination, which is
consistent with what is observed in the solid-state structures
(vide infra). Silatranes, where the attached silyl group bears
only methyl and phenyl groups such as Me3Si, Me2PhSi, and
MePh2Si,13 which are less electron donating than the
(Me3Si)2SiR groups reported here, allow an even higher degree
of hypercoordination and therefore shift even further upfield to
values of −64.0, −67.0, and −69.0 ppm, respectively.13
Interestingly, the chemical shift for the geminal disilatranylsi-
lane 18 of −46.8 ppm indicates a substantially diminished
degree of hypercoordination. The chemical shift of the
respective resonance of 19 at −22.8 ppm shows the effect of
a silatranyl unit with Si−N interaction turned off by
protonation of the nitrogen lone pair. For the silyl anions
10−14 a downfield shift of the silatranyl resonance can be
expected. Indeed, a shift from −52.6 ppm for 3 to −11.8 ppm
for the respective anion 10 is observed, which reflects not only
the expected downfield shift of a silyl group in a position α to a
negatively charged atom but also the fact that the Si−N
interaction is turned off in these compounds, as is also clearly
visible in the solid-state structures (vide infra). Another point
worth mentioning is that the 29Si NMR resonances of the
negatively charged silicon atoms in compounds 10 (−210.5
ppm) and 11 (−215.7 ppm) appear at considerably higher field
in comparison to (Me3Si)3SiK (−191.1 ppm).41 Compounds
11 and 14 are chiral silanides, and 11 is particularly interesting,
as the tert-butyldimethysilyl group has two diastereotopic
methyl groups which allow determination of the configurational
stability of the chiral silanide. Given the additional coordination
Scheme 5. Protonation of Silatrane 3 with
Trifluoromethanesulfonic Acid or Trichloroacetic Acid
C6D6). For the silyl anions 10−14 (in C6D6) the proton
resonances shift considerably to lower field to values around
3.80 ppm for the methylene groups attached to oxygen atoms
and 2.84 ppm for the amino-substituted atoms. The anionic
compounds exhibit also slightly diminished coupling constants
between the methylene groups. As can be expected, 29Si NMR
spectroscopy provides the most direct insight into the
electronic situation of the compounds involved in this study
(Table 1).
To understand the influence exerted by the nitrogen atom on
the silicon atom in the silatranyl unit, comparison with the
chemical shift of a related trialkoxysilylated oligosilane is
required. The chemical shift of the MeO3Si group of
(MeO3Si)4Si40 is −35 ppm, and thus the more shielded
chemical shift of ca. −53 ppm found for 3−5, 16, and 17
should reflect the degree of hypercoordination (interaction
between Si and N). The respective chemical shifts of
compounds 6−9, with more electronegative alkylsilyl sub-
stituents, are further shifted to values close to −57 ppm, thus
Table 1. NMR Spectroscopic Data of Oligosilanyl Silatranes
29Si
compd
SiMe3
−9.9
SiO3
Siq
−133.9
other
13C OCH2/CH2N
1H OCH2/CH2N
a
a
3
−52.6
58.6/52.2
3.65/2.72
b
b
58.6/51.5
3.30/1.83
a
a
4
−9.3
−9.7
−54.0
−51.5
−57.8
−56.6
−56.6
−56.6
−11.8
−11.0
−14.9
−15.0
−19.4
−53.8
−53.2
−46.8
−22.8
−132.2
−136.8
−88.0
−78.4
−69.6
−15.0, −40.0
4.0 (tBuMe2Si)
58.4/51.9
3.66/2.73
a
a
5
58.7/52.1
3.65/2.72
a
a
6
−12.9
−13.2
−13.5
−13.1
−3.2
−3.0
−5.1
−6.2
−7.7
58.3/51.8
3.69/2.74
a
a
7
58.3/51.9
3.66/2.71
a
a
8
58.5/52.0
3.67/2.73
a
a
9
−76.2
58.1/51.6
3.75/2.76
b
b
10
11
12
13
14
16
17
18
19
−210.5
−215.7
−144.0
−125.1
−113.0
−128.6/−129.3
−129.5
−135.5
−141.1
61.0./54.3
3.86/2.84
b
b
11.3
61.0/54.2
3.81/2.82
b
b
60.9./54.2
3.76/2.80
b
b
61.0./54.3
3.88/2.88
b
b
61.1/54.2
3.84/2.81
a
a
−9.2/−9.6
−9.2
−9.5
−30.6/−30.8 (Me2Si),
−31.2
58.5/51.8
3.66/2.73
b
b
58.8/51.5
3.36/1.90
b
b
59.4/52.7
3.68/2.71
b
b
−9.7
56.4/53.1
3.34/2.64
a
b
Measured in CDCl3. Measured in C6D6.
C
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Figure 1. UV spectra of compounds 16 and 17 and of [(Me3Si)3SiMe2Si]2 and [Me(Me3Si)2SiMe2Si]2 in pentane.
to the silatranyl oxygen, an increased configurational stability
might be possible. However, at ambient temperature two
different methyl resonances could not be observed either in the
1H or in the 13C NMR spectrum. Therefore, it has to be
concluded that at room temperature pyramidal inversion of
silanide 11 is fast on the NMR time scale.
and therefore all-transoid hexasilane conformers with trime-
thylsilyl end groups are presumably contributing to the
hexasilane absorption band.
C o n v e r s e l y , f o r 2 , 5 - b i s ( t r i m e t h y l s i l y l ) -
dodecamethylhexasilane, where two trimethylsilyl groups are
exchanged for methyl groups, the hexasilane band shows a
bathochromic shift of 7 nm to an absorption maximum of 263
nm. This behavior is consistent with the typically observed
trend of electron-withdrawing substituents causing a bath-
ochromic shift of the absorption maxima and electron-donating
groups being responsible for contrasting behavior.43
Crystal Structure Analysis. Compounds 3, 5−7, 9−11,
14, and 17−19 of this study were subjected to single-crystal
XRD analysis. For compound 3 (Figure 2) it was found to be
impossible to conduct the measurement at 100 K, as the
crystals at this temperature lost structural integrity. At 200 K
UV Spectroscopy. The UV absorption spectra of the
silatranes 3, 5−9, and 18 exhibit the expected absorption bands
associated with the trisilane segment around 210 nm only as
badly recognizable shoulders. Compound 4, containing a
tetrasilane unit, showed an absorption maximum at 223 nm.
For a meaningful comparison to other oligosilanes it is essential
to have compounds with well-resolved absorption bands and a
number of compounds with similar structures. Compounds 16
and 17, with one and two silatranyl units, meet these
requirements and are therefore best suited to estimate the
influence of the siltranyl units on the property of σ-bond
electron delocalization. In order to compare these to
structurally related compounds UV spectra of 2,2,5,5-tetrakis-
(trimethylsilyl)decamethylhexasilane42 and 2,5-bis-
(trimethylsilyl)dodecamethylhexasilane33 are also shown in
Figure 1.
In the branched oligosilanes with hexasilane units as the
longest chain segments the effect of the silatranyl units in
comparison to that of trimethylsilyl groups is not very
pronounced. For compound 16, containing one silatranyl
group, the longest wavelength absorption band (254 nm)
shows a 2 nm hypsochromic shift. The same band is shifted
further toward blue by another 2 nm for compound 17. While
the molecular structure of 17 in the solid state indicates the
silatranyl units as part of the all-transoid hexasilane conformer,
it needs to be pointed out that for 16 and 17 in solution
rotation of the bulky tris(silyl)silyl group is likely to be facile
the structure was solved in the triclinic space group P1.
̅
Crystals of the more asymmetric compound 5 (Figure 3)
were not sensitive to low temperature and crystallize in the
trigonal space group R3. Both trimethylsilyl groups and also the
̅
tert-butyldimethylsilyl group showed some disorder. The
methylated and ethylated isotetrasilanes 6 (Figure 4) and 7
(Figure 5) both crystallize in the orthorhombic space group
Pcca, with the latter compound exhibiting somewhat elongated
axes. For 7 some disorder of the ethyl CH3 group can be found.
The phenylated compound 9 (Figure 6) crystallizes in the
orthorhombic space group Pca21 with two crystallographically
independent molecules in the asymmetric unit. The silanides
10 (Figure 7) and 11 (Figure 8) both crystallize in the
monoclinic space group P21/n. For compound 10 some
disorder in the silatranyl unit was found. For the phenylated
silanide 14 (Figure 9), crystallizing in the triclinic space group
P1, an additional benzene molecule was found in the
̅
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Figure 4. Molecular structure of 6 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−O(3)
1.670(2), Si(1)−O(1) 1.673(2), Si(1)−O(2) 1.682(2), Si(1)−N(1)
2.167(3), Si(1)−Si(2) 2.3523(13), Si(2)−C(7) 1.908(3), Si(3)−C(8)
1.871(4), N(1)−C(1) 1.474(4); O(3)−Si(1)−O(1) 117.43(12),
O(1)−Si(1)−O(2) 120.09(12), C(1)−N(1)−C(4) 113.7(2).
Figure 2. Molecular structure of 3 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−O(1)
1.650(3), Si(1)−N(1) 2.292(4), Si(1)−Si(2) 2.3509(18), Si(2)−Si(3)
2.3351(18), Si(3)−C(13) 1.863(5), N(1)−C(1) 1.462(6), N(1)−
C(5) 1.461(5), O(1)−C(2) 1.420(5), C(1)−C(2) 1.522(6); C(1)−
N(1)−C(5) 114.4(4), C(2)−O(1)−Si(1) 123.4(3), C(4)−O(2)−
Si(1) 123.9(3), C(6)−O(3)−Si(1) 123.6(3).
Figure 5. Molecular structure of 7 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−O(1)
1.671(3), Si(1)−N(1) 2.182(3), Si(1)−Si(2) 2.3443(15), Si(2)−C(7)
1.907(4), Si(2)−Si(4) 2.3341(17), N(1)−C(2) 1.473(5), O(1)−C(1)
1.409(5); O(1)−Si(1)−O(3) 117.49(14), O(1)−Si(1)−O(2)
120.03(15), O(1)−Si(1)−N(1) 82.58(13), Si(4)−Si(2)−Si(1)
113.38(6), C(6)−N(1)−C(4) 114.1(3).
Figure 3. Molecular structure of 5 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(5)−C(13)
1.883(7), Si(5)−Si(1) 2.3510(18), Si(6)−C(23) 1.885(7), Si(1)−
Si(4) 2.3456(12), Si(1)−Si(2) 2.346(1), Si(2)−O(1) 1.661(2),
Si(2)−N(1) 2.283(3), O(1)−C(2) 1.376(4), N(1)−C(1) 1.446(5),
C(1)−C(2) 1.393(5); O(3)−Si(2)−O(2) 117.55(15), O(3)−Si(2)−
O(1) 116.97(15), O(2)−Si(2)−O(1) 117.83(12), C(5)−N(1)−C(1)
114.4(4).
values with respect to this are the Si−N distance and the bond
between the silatranyl unit and the oligosilane (Table 2).
For the chlorosilatrane 1 the Si−N distance has been
determined to be 2.023 Å.5 For the isotetrasilanyl-substituted
compounds 3 (Figure 2) and 5 (Figure 3) elongated distances
of 2.293(3) and 2.283(2) Å consistent with the more electron
donating and sterically much more demanding character of the
attached silyl substituents were found. For compounds 6
(Figure 4), 7 (Figure 5), and 9 (Figure 6) the smaller size of
the attached group but also its more electronegative character
of the alkyl and aryl substituents cause a shortening of the Si−
N distances to values of 2.167(3), 2.182(4), and 2.162(5) Å.
The respective value for a PhMe2Si-substituted silatrane was
found to be even shorter: 2.153(2) Å.13
asymmetric unit. Compound 17 (Figure 10) crystallizes in the
monoclinic space group P21/c with two crystallographically
independent half-molecules in the asymmetric unit, for which
the second halves are generated by a center of inversion. Also
for 17 a disordered silatranyl unit was found. The disilatrane 18
(Figure 11) crystallizes in the monoclinic space group C2/c.
The silatranylium triflate 19 (Figure 12), which crystallizes in
the monoclinic space group P21/c, shows three crystallo-
graphically independent ion pairs in addition to half a molecule
of benzene on a special position in the asymmetric unit. The
hydrogen attached to the nitrogen atom of 19 was detected in
the experimental electron density map.
The Si−SiO3 distances of 3, 5−7, and 9 are 2.351(2),
2.346(1), 2.352(1), 2.344(2), and 2.383(2) Å, respectively,
which are rather typical Si−Si bond lengths observed in
oligosilanes. Along with the silanide formation, which causes a
localization of negative charge on the silicon atom trans to the
The number of structures determined in the course of this
study allows a fair assessment of the influence of the silatranyl
unit on the oligosilane structure. The most important structural
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Figure 6. Molecular structure of 9 (thermal ellipsoid plot drawn at the
30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−C(3)
1.910(6), Si(1)−Si(4) 2.342(2), Si(5)−Si(6) 2.383(2), Si(5)−C(9)
1.904(6), Si(6)−O(4) 1.662(5), Si(6)−O(6) 1.674(5), Si(6)−O(5)
1.682(5), Si(6)−N(2) 2.176(6), N(1)−C(26) 1.496(8), N(2)−C(32)
1.486(8), O(1)−C(25) 1.430(8); O(4)−Si(6)−O(6) 119.7(3),
O(4)−Si(6)−O(5) 118.4(3), O(6)−Si(6)−O(5) 117.3(3), C(36)−
N(2)−C(32) 114.2(5).
Figure 8. Molecular structure of 11 (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−Si(4)
2.2947(12), Si(1)−Si(2) 2.3276(13), Si(1)−Si(3) 2.3391(14), Si(1)−
K(1) 3.6321(13), Si(2)−C(19) 1.878(4), Si(4)−O(8) 1.656(2),
Si(4)−K(1) 3.8618(15), O(5)−C(8) 1.430(3), N(1)−C(18)
1.430(4); O(8)−Si(4)−O(9) 105.61(12), O(8)−Si(4)−O(7)
106.14(12), Si(1)−K(1)−Si(4) 35.49(2), C(18)−N(1)−C(14)
119.8(3).
Figure 7. Molecular structure of 10 (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): O(7)−Si(1)
1.659(4), O(7)−K(1) 3.197(5), O(8)−C(15) 1.407(7), O(8)−Si(1)
1.684(4), Si(1)−Si(2) 2.3080(18), Si(2)−K(1) 3.3634(16), N(1)−
C(16) 1.430(7); Si(1)−O(7)−K(1) 97.9(2), C(14)−N(1)−C(16)
119.9(6), C(14)−N(1)−C(17) 122.1(6), C(16)−N(1)−C(17)
117.4(5).
Figure 9. Molecular structure of 14 (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−C(22)
1.9141(17), Si(1)−Si(3) 2.3087(7), Si(1)−K(1) 3.5722(9), Si(3)−
O(9) 1.6642(12), Si(4)−C(19) 1.8841(19), K(1)−O(7) 2.9983(12),
N(1)−C(16) 1.441(2), O(1)−C(1) 1.421(2); O(9)−Si(3)−K(1)
145.02(5), C(16)−N(1)−C(18) 120.35(14), C(16)−N(1)−C(13)
119.81(14), C(18)−N(1)−C(13) 119.59(14), Si(3)−O(7)−K(1)
111.86(5).
nitrogen, an interaction between silicon and nitrogen is no
longer observable in compounds 10, 11, and 14. The Si−N
distances are between 3.10 and 3.18 Å. Along with this shut-off
Si−N interaction Si−SiO3 bond distances of 2.308(2),
2.295(1), and 2.3088(8) Å for 10, 11, and 14 are substantially
shorter than those in the neutral compounds 3, 5, and 9,
indicating nondisturbed Si−Si bonds. The structural motif of
the silanides 10, 11, and 14 is different from the usual
potassium silanide crown ether complexes. Typically the
position of the potassium atom in the solid-state structure is
that of a tetrahedral substituent. Complexes 10, 11, and 14
show a distortion of the potassium position in order to
coordinate to one of the silatrane oxygen atoms. A similar
coordination situation was observed for the case of (Me3Si)2Si-
(K)OMe.44 This coordination behavior is taken to an extreme
by Krempner’s silanides (MeOMe2Si)3SiK45 and
(MeOCH2CH2OMe2Si)3SiK,46 where the potassium ion only
coordinates to the alkoxy groups. However, the Si−K distances
of 10, 11, and 14 are comparable to what was observed for
(Me3Si)3SiK·18-crown-641 and also the distances between
potassium and the silatranyl oxygen are only slightly elongated
in comparison to K−O distances of the crown ether. The
structural properties of compound 17 were expected to be close
to those of 3 and 5. However, the Si−N distances of the two
crystallographically independent molecules of 17 are 2.223(4)
and 2.209(4) Å and thus are significantly shorter, while the Si−
SiO3 bond distances are comparable to those of 3 and 5. The
two independent molecules exhibit all-transoid hexasilane
conformations, with the silatranyl silicon atoms being starting
and ending points of this particular conformational subunit.
F
DOI: 10.1021/acs.organomet.5b00404
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Organometallics
Article
Figure 12. Molecular structure of 19 (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−Si(5)
2.3072(12), Si(1)−Si(3) 2.3439(13), Si(2)−C(26) 1.868(4), Si(5)−
O(11) 1.637(2), N(1)−C(18) 1.503(4), O(9)−S(3) 1.447(2),
O(10)−C(13) 1.414(4), S(3)−C(12) 1.824(4), F(8)−C(12)
1.338(4); Si(5)−Si(1)−Si(3) 105.74(5), Si(5)−Si(1)−Si(4)
107.83(5), O(11)−Si(5)−O(10) 106.94(12), C(18)−N(1)−C(16)
116.8(3).
Figure 10. Molecular structure of 17 (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−Si(2)
2.3504(18), Si(2)−O(1) 1.657(4), Si(2)−N(1) 2.223(4), Si(3)−C(9)
1.872(7); O(2)−Si(2)−O(3) 117.5(2), N(1)−Si(2)−Si(1)
177.79(14), C(4)−N(1)−C(2) 115.2(6).
CONCLUSION
■
Although silatranes are a substance class that has been known
for some time, almost no examples exist with silyl substituents.
Our interest in the chemistry and properties of oligosilanes led
us to investigate possibilities to attach silatranyl units to
oligosilanes. While reactions of potassium oligosilanides with
chlorosilatrane did not give the expected compounds in
satisfactory yields, it was found that analogous reactions with
a silatranyl triflate give the oligosilanylated silatranes in
acceptable yields.
29Si NMR spectroscopy clearly suggests a Si−N interaction,
as indicated by upfield-shifted SiO3 resonances. In addition, the
solid-state structures with Si−N distances between 2.29 and
2.16 Å are supportive of this. Weakening of the Si−Si bond
trans to the Si−N interaction, however, becomes only obvious
upon comparing the Si−Si distances of structurally related
compounds with the Si−N interaction either active or “turned
off” by protonation of the nitrogen lone pair. Accordingly, the
weakening of the (Me3Si)3Si−Si bond by the silatrane effect
accounts to an elongation of about 0.05 Å.
Attempts to submit the obtained oligosilanlysilatranes to
further silanide formation by reaction with potassium tert-
butoxide were successful. By single-crystal XRD analysis and
multinuclear NMR spectroscopy it was found that upon
silanide formation again the silatrane Si−N interaction is
turned off. The obtained silanides can be used as building
blocks for the construction of more extended oligosilane
systems or for the preparation of a geminal disilatranylsilane.
Figure 11. Molecular structure of 18 (thermal ellipsoid plot drawn at
the 30% probability level). All hydrogen atoms are omitted for clarity.
Selected bond lengths (in Å) and angles (in deg): Si(1)−Si(3)
2.3343(5), Si(1)−Si(2) 2.3416(5), Si(2)−O(2) 1.6512(10), Si(3)−
C(9) 1.8728(15), N(1)−C(6) 1.4574(17), O(1)−C(1) 1.4232(17);
Si(3)−Si(1)−Si(2) 108.594(17), O(2)−Si(2)−O(3) 116.47(5),
C(6)−N(1)−C(2) 115.79(12), C(6)−N(1)−C(4) 115.73(11),
C(2)−N(1)−C(4) 116.37(11).
Then again, in accordance with what was found by NMR
spectroscopy for the geminal disilatrane 18, the respective Si−
N distance for 18 is 2.421(1) Å, being the longest of the neutral
silatranyloligosilanes, but still the Si−SiO3 bond distance is in
the same range as for all the other neutral compounds. For the
protonated silatrane 19 no interaction between silicon and
nitrogen can be detected; the Si−N distances for the three
crystallographically independent molecules are around 3.39 Å
(Table 2), which is even longer than those for the silanide cases
of 10, 11, and 14. Accordingly, the Si−SiO3 bond distances are
shortened (2.301(1)/2.304(1)/2.307(1) Å) to about the same
extent that was detected for 10, 11, and 14. The triflate
counterions are situated above the silatrane close to the
protonated nitrogen with H−O distances between 1.73(2) and
1.76(2) Å.
EXPERIMENTAL SECTION
■
General Remarks. All reactions involving air-sensitive compounds
were carried out under an atmosphere of dry nitrogen or argon using
either Schlenk techniques or a glovebox. Reagent grade CHCl3 was
used for the synthesis of chlorosilatrane 1. All other solvents were
dried using a column-based solvent purification system.47 Ethyltris-
(trimethylsilyl)silane,31 isopropyltris(trimethylsilyl)silane,48 phenyltris-
(trimethylsilyl)silane,48 2,2-bis(trimethylsilyl)octamethyltetrasilane,42
(tert-butyldimethylsilyl)tris(trimethylsilyl)silane,31 1-chloro-3,3-bis-
(trimethylsilyl)heptamethyltetrasilane,19 and 1,2-dichlorotetramethyl-
disilane49,50 were prepared according to previously published
procedures. Methyltris(trimethylsilyl)silane51 was prepared similarly
to ethyltris(trimethylsilyl)silane31 by reaction of tris(trimethylsilyl)silyl
G
DOI: 10.1021/acs.organomet.5b00404
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Article
Table 2. Compilation of Structural Data Derived by Single-Crystal XRD Analysis of 3, 5−7, 9−11, 14, and 17−19
compd
dSi··N (Å)
dSi−SiO (Å)
dSi−SiMe (Å)
dSi−R (Å)
∠
(deg)
Me3SiSiR
3
3
3
2.292(3)
2.283(2)
2.167(3)
2.182(4)
2.162(5)
3.134(4)
3.184(3)
3.103(2)
2.351(2)
2.346(1)
2.352(1)
2.344(2)
2.383(2)
2.308(2)
2.295(1)
2.335(2)−2.341(2)
2.341(1)−2.346(1)
2.339(1)/2.346(1)
2.334(2)/2.356(2)
2.342(2)−2.358(2)
2.312(2)/2.318(2)
2.328(1)
5
2.351(3)
6
1.908(3)
7
1.907(5)
9
1.904(6)/1.911(7)
3.363(2)
10
11
14
17
18
19
103.42(7)
104.65(5)
100.25(5)
2.339(1)/3.632(1)
1.914(2)/3.5722(8)
2.358(2)-2.369(2)
2.3088(8)
2.3431(8)
2.223(4)/2.209(4)
2.421(1)
2.350(2)/2.342(2)
2.3415(5)
2.343(2)−2.346(2)
2.3343(5)
3.394(3)/3.389(3)/3.397(3)
2.301(1)/2.304(1)/2.307(1)
2.339(1)−2.351(1)
potassium with dimethyl sulfate. All other chemicals were obtained
from different suppliers and used without further purification.
1H (300 MHz), 13C (75.4 MHz), 19F (282.2 MHz), and 29Si (59.3
MHz) NMR spectra were recorded on a Varian INOVA 300
chloroform (40 mL) in a 250 mL three-neck flask with condenser. The
reaction mixture was stirred and heated for 6 h to reflux. After all
volatiles were removed under vacuum, the residue was washed with
chloroform and 1-chlorosilatrane (7.10 g, 0.0339 mol, 82%) was
obtained as a white powder with spectroscopic properties in
1
spectrometer and are referenced to tetramethylsilane (TMS) for H,
13C, and 29Si and to CFCl3 for 19F. In the case of reaction samples a
D2O capillary was used to provide an external lock frequency signal.
To compensate for the low isotopic abundance of 29Si, the INEPT
pulse sequence52,53 was used for the amplification of the signal.
Elemental analysis was carried out using a Heraeus VARIO
ELEMENTAR instrument. GC/MS analyses were carried out on a
Agilent 7890A (capillary column HP-5MS; 30 m × 0.250 mm; film
0.25 μm) with an Agilent 5975C mass spectrometer.
accordance with reported data.60 NMR (δ ppm, CDCl3): H, 3.97
1
(t, J = 5.9 Hz, 6H, OCH2), 3.01 (t, J = 5.9 Hz, 6H, NCH2); 29Si,
−85.9.
Silatranyl Triflate (2). A slurry of 1-chlorosilatrane (2.00 g, 9.54
mmol, 1.00 equiv) and trimethylsilyl triflate (4.24 g, 19.07 mmol, 2.00
equiv) in toluene (1 mL) was strongly stirred and heated for 72 h to
65 °C. The progress of the reaction was monitored by 1H NMR
spectroscopic analysis of the peaks of trimethylsilyl triflate and the
formed trimethylchlorosilane. Compound 2 was obtained as an air-
sensitive white powder (2.92 g, 9.50 mmol, 99%) after removing
volatiles under vacuum. NMR (δ ppm, DMSO-d6): 1H, 3.84 (t, J = 5.9
Hz, 6H, OCH2), 3.13 (t, J = 5.9 Hz, 6H, NCH2); 13C, 118.33 (q, J =
318 Hz, CF3), 57.52 (OCH2), 50.69 (NCH2); 29Si, −97.1; 19F, −77.45.
Anal. Calcd for C7H12F3NO6SSi (323.31): C, 26.00; H, 3.74; N, 4.33;
S, 9.92. Found: C, 25.73; H, 3.54; N, 4.20; S, 9.69.
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 Kα radiation
2
(0.71073 Å). The data were reduced to Fo and corrected for
absorption effects with SAINT54 and SADABS,55 respectively. The
structures were solved by direct methods and refined by full-matrix
least-squares methods (SHELXL97).56 If not noted otherwise, all non-
hydrogen atoms were refined with anisotropic displacement
parameters and all hydrogen atoms were located in calculated
positions to correspond to standard bond lengths and angles.
Crystallographic data (excluding structure factors) for the structures
of compounds 3, 5−7, 9−11, 14, and 17−19 reported in this paper
have been deposited with the Cambridge Crystallographic Data Center
as supplementary publication nos. CCDC 1062942 (3), 1062948 (5),
1062943 (6), 1062944 (7), 1062946 (9), 1062945 (10), 1062951
(11), 1062947 (14), 1062941(17), 1062949 (18), and 1062950 (19).
Data can be obtained free of charge at http://www.ccdc.cam.ac.uk/
products/csd/request/.
Tris(trimethylsilyl)silatranylsilane (3). Tetrakis(trimethylsilyl)-
silane (2.00 g, 6.23 mmol) and KOtBu (734 mg, 6.54 mmol) in THF
(5 mL) were stirred for 14 h. After the formation of the organosilyl
anion was confirmed by means of NMR spectroscopy, the solvent was
removed and toluene was added (5 mL). To a solution of this
compound was added a suspension of 2 (2.22 g, 6.85 mmol) in
toluene (2 mL) dropwise within 2 h. After 12 h the precipitate was
removed by filtration and washed with pentane (3 mL) and then the
solvent was removed. After sublimation (40 °C, 1 mbar) and
recrystallization with hexane colorless crystalline 3 (1.35 g, 51%)
was obtained. Mp: 144−146 °C. NMR (δ ppm, CDCl3): 1H, 3.65 (t, J
= 5.6 Hz, 6H, OCH2), 2.72 (t, J = 5.6 Hz, 6H, NCH2), 0.15 (s, 27H,
Me3Si); 13C, 58.56 (OCH2), 52.15 (NCH2), 2.20 (Me3Si); 29Si, −9.9
Figures of solid-state molecular structures were generated using
Ortep-3 as implemented in WINGX57 and rendered using POV-Ray
3.6.58
1
(Me3Si), −52.6 (SiO3), −133.9 (Siq). NMR (δ ppm, C6D6): H, 3.30
(t, J = 5.6 Hz, 6H, OCH2), 1.83 (t, J = 5.6 Hz, 6H, NCH2), 0.53 (s,
27H, Me3Si); 13C, 58.55 (OCH2), 51.53 (NCH2), 2.77 (Me3Si). Anal.
Calcd for C15H39NO3Si5 (421.91): C, 42.70; H, 9.32; N, 3.32. Found:
C, 43.29; H, 8.62; N, 3.25. MS (70 eV) m/z (%): 423(3) [M− + H],
N(CH2CH2OSiMe3)3. To a solution of triethanolamine (10.0 g,
0.067 mol) in dichloromethane (100 mL) in a 500 mL two-neck flask
was added triethylamine (30.0 g, 0.301 mol), and the mixture was
cooled to 0 °C in an ice bath. Within 1 h trimethylchlorosilane (25.5 g,
0.234 mol) was added dropwise to the flask. After the ice bath was
removed, the reaction mixture was warmed to room temperature with
stirring over 2 h. The reaction mixture was then added slowly to water
(100 mL), and the organic phase was separated from the aqueous
layer, which was washed twice with small portions of dichloromethane.
The combined organic phases were dried over Na2SO4. The organic
solvent was removed under vacuum, and a pale yellow oil (18.0 g,
0.049 mol, 73%) was obtained as the product with spectroscopic
properties in accordance with reported data.59 NMR (δ ppm, CDCl3):
1H, 3.51 (t, J = 6.8 Hz, 6H, OCH2), 2.59 (t, J = 6.8 Hz, 6H, NCH2),
0.00 (s, 27H, SiMe3); 13C, 61.05 (OCH2), 57.59 (NCH2), −0.69
(Me3Si); 29Si, 17.6.
+
406(4) [M+ − Me], 278(3) [(SiMe3)3SiSiH3 ], 249(1) [(Si-
+
Me3)3SiH], 232(2) [Si4Me8 ], 174(100) [N(CH2CH2O)3Si+],
+
+
147(1) [N(CH2CH2O)3 ], 73(13) [SiMe3 ].
1,1-Bis(trimethylsilyl)-1-silatranylpentamethyltrisilane (4).
The same procedure as for 9 was used, with 2,2-bis(trimethylsilyl)-
octamethyltetrasilane (435 mg, 1.15 mmol), KOtBu (135 mg, 1.21
mmol), and 2 (408 mg, 1.26 mmol). After recrystallization from
diethyl ether/acetonitrile 1/1 colorless crystalline 4 (320 mg, 58%)
was obtained. Mp: 78−79 °C. NMR (δ ppm, CDCl3): 1H, 3.66 (t, J =
5.6 Hz, 6H, OCH2), 2.73 (t, J = 5.6 Hz, 6H, NCH2), 0.19 (s, 6H,
Me2Si), 0.17 (s, 18H, (Me3Si)2Si), 0.09 (s, 9H, Me3Si); 13C, 58.41
(OCH2), 51.85 (NCH2), 2.60 ((Me3Si)2-Si), −1.24 (Me3Si), −2.01
(Me2Si); 29Si, −9.3 ((Me3Si)2Si), −15.0 (Me3Si-SiMe2), −40.0
(Me3Si-SiMe2), −54.0 (SiO3), −132.2 (Siq). Anal. Calcd for
C17H45NO3Si6 (480.06): C, 42.53; H, 9.45; N, 2.92. Found: C,
Silatranyl Chloride (1). A mixture of N(CH2CH2OSiMe3)3 (14.0
g, 0.0383 mol) and SiCl4 (7.00 g, 0.0412 mol) was dissolved in
H
DOI: 10.1021/acs.organomet.5b00404
Organometallics XXXX, XXX, XXX−XXX

Organometallics
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42.43; H, 8.94; N, 2.70. MS (70 eV) m/z (%): 464(10) [M+ − Me],
406(100) [M+ − SiMe3], 290(3) [Si5C10H30+], 174(50) [N-
(Siq). Anal. Calcd for C18H35NO3Si4 425.82: C, 50.77; H, 8.28; N,
3.29. Found: C, 49.84; H, 7.86; N, 3.19. MS (70 eV) m/z (%): 425(4)
[M+], 410(4) [M+ − Me], 352(2) [M+ − SiMe3], 309(11)
+
+
(CH2CH2O)3Si+], 131(3) [NC6H13O2 ], 73(10) [SiMe3 ]. UV: λ
223 nm (ε = 1.85 × 104 M−1 cm−1).
[(SiMe3)2SiSiO3C4H11+], 279(3) [(SiMe3)2SiSiO3C2H5 ], 253(4)
+
[(SiMe3)2SiSiO3H3+], 193(2) [Me4Si3O3H+], 174(100) [N-
(tert-Butyldimethylsilyl)bis(trimethylsilyl)silatranylsilane (5).
The same procedure as for 3 was used, with (tert-butyldimethylsilyl)-
tris(trimethylsilyl)silane (500 mg, 1.38 mmol), KOtBu (162 mg, 1.45
mmol), and 2 (490 mg, 1.51 mmol). After recrystallization from
hexane colorless crystalline 5 (268 mg, 42%) was obtained. Mp: 124−
+
+
(CH2CH2O)3Si+], 135(6) [Si3O3H3 ], 73(3) [SiMe3 ].
Bis(trimethylsilyl)silatranylsilyl Potassium 18-Crown-6 (10).
A solution of 3 (50 mg, 0.12 mmol), KOtBu (14 mg, 0.12 mmol), and
18-crown-6 (33 mg, 0.12 mmol) in benzene (1 mL) was stirred. After
14 h NMR spectroscopic analysis showed full conversion to 10. By
addition of benzene (1 mL) pale orange crystals (77 mg, >99%)
suitable for X-ray analysis could be obtained. NMR (δ ppm, C6D6):
1H, 3.86 (t, J = 5.1 Hz, 6H, OCH2), 3.30 (s, 24H, 18-cr-6), 2.84 (t, J =
5.1 Hz, 6H, NCH2), 0.78 (s, 18H, 2 Me3Si); 13C, 70.23 (18-cr-6),
60.96 (OCH2), 54.26 (NCH2), 7.18 (Me3Si); 29Si, −3.2 (Me3Si),
−11.8 (SiO3), −210.5 (Siq). MS (70 eV) m/z (%) (after treatment
with ethyl bromide): 377(6) [M+], 362(8) [M+ − Me], 304(3) [M+ −
1
126 °C. NMR (δ ppm, CDCl3): H, 3.65 (t, J = 5.4 Hz, 6H, OCH2),
2.72 (t, J = 5.4 Hz, 6H, NCH2), 0.93 (s, 9H, (Me3C), 0.18 (s, 18H, 2
Me3Si), 0.12 (s, 6H, Me2Si); 13C, 58.68 (OCH2), 52.09 (NCH2),
27.98 (Me3C), 18.43 (Me3C), 2.77 (Me3Si), −1.61 (Me2Si); 29Si, 4.0
(tBuMe2Si), −9.7 (Me3Si), −51.5 (SiO3), −136.8 (Siq). Anal. Calcd
for C18H45NO3Si5 (463.99): C, 46.60; H, 9.78; N, 3.02. Found: C,
46.78; H, 8.99; N, 3.05. MS (70 eV) m/z (%): 463(3) [M+], 448(8)
[M+ − Me], 406(15) [M+ − tBu], 290(2) [tBuSi4Me8H], 174(100)
+
[N(CH2CH2O)3Si+], 73(10) [SiMe3 ].
+
SiMe3], 174(100) [N(CH2CH2O)3Si+], 130(3) [NC6H12O2 ], 73(6)
+
Bis(trimethylsilyl)methylsilatranylsilane (6). The same proce-
dure as for 3 was used, with methyltris(trimethylsilyl)silane (1.50 g,
5.70 mmol), KOtBu (672 mg, 5.98 mmol), and 2 (2.03 g, 6.27 mmol)
After sublimation (34 °C, 1 mbar) and recrystallization from hexane
colorless crystalline 6 (1.16 g, 75%) was obtained. Mp: 109−111 °C.
NMR (δ ppm, CDCl3): 1H, 3.69 (t, J = 5.6 Hz, 6H, OCH2), 2.74 (t, J
= 5.6 Hz, 6H, NCH2), 0.09 (s, 18H, 2 Me3Si), 0.03 (s, 3H, MeSi); 13C,
58.33 (OCH2), 51.79 (NCH2), −0.03 (2 Me3Si), −12.66 (MeSi); 29Si,
−12.9 (Me3Si), −57.8 (SiO3), −88.0 (SiMe). Anal. Calcd for
C13H33NO3Si4 (363.75): C, 42.93; H, 9.14; N, 3.85. Found: C,
43.20; H, 8.56; N, 3.72. MS (70 eV) m/z (%): 364(4) [M+], 348(5)
[SiMe3 ].
(tert-Butyldimethylsilyl)trimethylsilylsilatranylsilyl Potassi-
um 18-Crown-6 (11). The same procedure as for 10 was used,
with 5 (50 mg, 0.107 mmol), KOtBu (13 mg, 0.133 mmol), and 18-
crown-6 (30 mg, 0.113 mmol). After crystallization using heptane pale
yellow crystalline 11 (74 mg, >99%) was obtained. NMR (δ ppm,
C6D6): 1H, 3.81 (t, J = 5.0 Hz, 6H, OCH2), 3.28 (s, 24H, CH2O), 2.82
(t, J = 5.0 Hz, 6H, NCH2), 1.19 (s, 9H, (CH3)3C), 0.71 (s, 9H,
(CH3)3Si), 0.70 (s, 6H, (CH3)2Si); 13C, 70.06 (18-cr-6), 60.97
(OCH2), 54.23 (NCH2), 29.22 (Me3C), 19.22 (Me3C), 7.37
((Me3Si)Si), 1.95 ((Me2Si)Si); 29Si, 11.3 (tBuMe2Si), −3.0 (Me3Si),
−11.0 (SiO3), −215.7 ((Me3Si)Si). MS (70 eV) m/z (%) (after
treatment with ethyl bromide): 419(3) [M+], 404(6) [M+ − Me],
362(22) [M+ − tBu], 246(3) [Si3C11H30+], 174(100) [N-
+
[M+ − Me], 309(39) [Me(SiMe3)2SiSiO3C3H8 ], 294(13) [Me-
+
+
(SiMe3)2SiSiO3C2H5 ], 279(10) [Me(SiMe3)2SiSiO3CH2 ], 260(3)
+
[N(CH2CH2O)3SiSi2Me2 ], 193(5) [Me4Si3O3H+], 174(100) [N-
+
+
(CH2CH2O)3Si+], 132(3) [Si3O3 ], 73(9) [SiMe3 ].
+
+
(CH2CH2O)3Si+], 130(3) [NC6H12O2 ], 73(8) [SiMe3 ].
Bis(trimethylsilyl)ethylsilatranylsilane (7). The same procedure
as for 3 was used, with ethyltris(trimethylsilyl)silane (600 mg, 2.17
mmol), KOtBu (255 mg, 2.27 mmol), and 2 (772 mg, 2.39 mmol).
After sublimation (38 °C, 1 mbar) and recrystallization from hexane
colorless crystalline 7 (205 mg, 25%) was obtained. Mp: 109−111 °C.
NMR (δ ppm, CDCl3): 1H, 3.66 (t, J = 5.6 Hz, 6H, OCH2), 2.71 (t, J
= 5.6 Hz, 6H, NCH2), 1.05 (t, J = 7.9 Hz, 3H, CH2CH3), 0.72 (q, J =
7.3 Hz, 2H, CH2CH3), 0.10 (s, 18H, 2 Me3Si); 13C, 58.34 (OCH2),
51.86 (NCH2), 12.79 (CH2CH3), 0.73 (2 Me3Si), −0.02 (CH2CH3);
29Si, −13.2 (Me3Si), −56.6 (SiO3), −78.4 (SiEt). Anal. Calcd for
C14H35NO3Si4 377.78: C, 44.51; H, 9.34; N, 3.71. Found: C, 44.96; H,
9.08; N, 3.57. MS (70 eV) m/z (%): 377(5) [M+], 362(7) [M+ − Me],
Trimethylsilylmethylsilatranylsilyl Potassium 18-Crown-6
(12). A solution of 6 (200 mg, 0.55 mmol), KOtBu (63 mg, 0.56
mmol), and 18-crown-6 (150 mg, 0.56 mmol) in C6D6 (2 mL) was
stirred. After 14 h observation by NMR spectroscopy showed a
mixture of the three products 12, bis(trimethylsilyl)methylsilyl
potassium.18-crown-6, and N(CH2CH2O)3SiOtBu. 12: NMR (δ
1
ppm, C6D6): H, 3.76 (t, J = 4.4 Hz, 6H, OCH2), 3.26 (s, 24H, 18-
cr-6), 2.80 (t, J = 4.4 Hz, 6H, NCH2), 0.52 (s, 9H, Me3Si), 0.45 (s, 3H,
MeSi); 13C, 70.03 (CH2O), 60.91 (OCH2), 54.17 (NCH2), 4.06
(Me3SiSi), −9.24 (CH3Si); 29Si, −5.1 (Me3Si), −14.9 (SiO3), −144.0
(Siq). MS (70 eV) m/z (%) (after treatment with ethyl bromide):
318(1) [M+ − H], 304(10) [M+ − Me], 290(3) [M+ − Et], 276(3)
[N(CH2CH2O)3SiSi2C3H10+], 246(10) [M+ − SiMe3], 218(41)
+
+
309(13) [Et(SiMe3)2SiSiO3C2H6 ], 294(4) [Et(SiMe3)2SiSiO3CH3 ],
+
+
279(3) [Et(SiMe3)2SiSiO3 ], 193(3) [Me4Si3O3H+], 174(100) [N-
[N(CH2CH2O)3SiSiCH4 ], 193(8) [Me4Si3O3H+], 174(100) [N-
+
+
+
+
(CH2CH2O)3Si+], 130(3) [NC6H12O2 ], 73(7) [SiMe3 ].
(CH2CH2O)3Si+], 149(4) [NC6H15O3 ], 130(4) [NC6H12O2 ],
73(7) [SiMe3 ].
+
Bis(trimethylsilyl)isopropylsilatranylsilane (8). The same
procedure as for 3 was used, with isopropyltris(trimethylsilyl)silane
(500 mg, 1.28 mmol), KOtBu (147 mg, 1.31 mmol), and 2 (453 mg,
1.40 mmol). After recrystallization from hexane colorless crystalline 8
(283 mg, 56%) was obtained. Mp: 118−120 °C. NMR (δ ppm,
CDCl3): 1H, 3.67 (t, J = 5.6 Hz, 6H, OCH2), 2.73 (t, J = 5.6 Hz, 6H,
NCH2), 1.34 to 1.18 (m, 1H, CH), 1.12 (d, J = 6.4 Hz, 6H, Me2CH),
0.14 (s, 18H, 2 Me3Si); 13C, 58.48 (OCH2), 52.03 (NCH2), 23.30
(Me2CH), 11.05 (Me2CH), 1.40 (Me3Si); 29Si, −13.5 (Me3Si), −56.6
(SiO3), −69.6 (SiiPr). Anal. Calcd for C15H37NO3Si4 391.19: C, 45.98;
H, 9.52; N, 3.57. Found: C, 45.22; H, 8.98; N, 3.52. MS (70 eV) m/z
Trimethylsilylethylsilatranylsilyl Potassium 18-Crown-6 (13).
A solution of 7 (50 mg, 0.13 mmol), KOtBu (15 mg, 0.14 mmol), and
18-crown-6 (36 mg, 0.14 mmol) in benzene (1 mL) was stirred. After
14 h observation by NMR spectroscopy showed conversion to the
three products 13, bis(trimethylsilyl)ethylsilyl potassium 18-crown-6,
and N(CH2CH2O)3SiOtBu. 13: NMR (δ ppm, C6D6): 1H, 3.88 (t, J =
5.2 Hz, 6H, OCH2), 3.27 (s, 24H, 18-cr-6), 2.88 (t, J = 5.2 Hz, 6H,
NCH2), 1.68 (t, J = 7.5 Hz, 3H), 1.41 (q, J = 7.8 Hz, 2H), 0.74 (s, 9H,
Me3Si); 13C, 70.08 (CH2O), 60.95 (OCH2), 54.29 (NCH2), 19.42
(CH3CH2), 4.85 (Me3SiSi), 2.68 (CH3CH2); 29Si, −6.2 (Me3Si),
−15.0 (SiO3), −125.1 (Siq). MS (70 eV) m/z (%) (after treatment
with ethyl bromide): 333(1) [M+], 318(8) [M+ − Me], 304(4) [M+ −
Et], 290(3) [N(CH2 CH2 O)3 SiSi2 Me4 + ], 276(3) [N-
(CH2CH2O)3SiSi2C3H10+], 260(11) [M+ − SiMe3], 246(3) [N-
+
(%): 391(5) [M+], 376(7) [M+ − Me], 202(2) [iPrSi3Me5 ], 174(100)
+
+
[N(CH2CH2O)3Si+], 130(2) [NC6H12O2 ], 73(8) [SiMe3 ].
Bis(trimethylsilyl)phenylsilatranylsilane (9). The same proce-
dure as for 3 was used, with tris(trimethylsilyl)phenylsilane (2.00 g,
6.16 mmol), KOtBu (712 mg, 6.34 mmol), and 2 (2.19 g, 6.77 mmol).
After recrystallization using hexane colorless crystalline 9 (700 mg,
+
+
(CH2CH2O)3SiSiC3H8 ], 232(42) [N(CH2CH2O)3SiSiC2H6+],
+
218(2) [N(CH2CH2O)3SiSiCH4 ], 204(3) [N(CH2CH2O)3SiSiH2 ],
1
174(100) [N(CH2CH2O)3Si+], 130(4) [NC6H12O2+], 73(5)
27%) was obtained. Mp: 161−163 °C. NMR (δ ppm, CDCl3): H,
+
7.65 (m, 2H, Ph), 7.23 (m, 3H, Ph), 3.75 (t, J = 5.6 Hz, 6H, OCH2),
2.76 (t, J = 5.6 Hz, 6H, NCH2), 0.17 (s, 18H, 2 Me3Si); 13C, 136.91
(Ph), 129.07 (Ph), 127.03 (Ph), 126.40 (Ph), 58.14 (OCH2), 51.62
(NCH2), 0.54 (Me3Si); 29Si, −13.1 (Me3Si), −56.6 (SiO3), −76.2
[SiMe3 ].
Trimethylsilylphenylsilatranylsilyl Potassium 18-Crown-6
(14). A solution of 9 (50 mg, 0.12 mmol), KOtBu (14 mg, 0.12
mmol), and 18-crown-6 (32 mg, 0.12 mmol) in benzene (1 mL) was
I
DOI: 10.1021/acs.organomet.5b00404
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
stirred. After 14 h observation by NMR spectroscopy showed
quantitative conversion to 14. By addition of benzene (1 mL) yellow
crystals (77 mg, >99%) suitable for X-ray analysis were obtained.
NMR (δ ppm, C6D6): 1H, 8.13 (d, 2H, Ph), 7.02 (m, 3H), 3.84 (t, J =
5.0 Hz, 6H, OCH2), 3.20 (s, 24H, CH2O), 2.81 (t, J = 5.0 Hz, 6H,
NCH2), 0.69 (s, 9H, Me3Si); 13C, 157.75 (Ph), 137.61 (Ph), 126.19
(Ph), 121.69 (Ph), 70.15 (18-cr-6), 61.14 (OCH2), 54.17 (NCH2),
4.58 (Me3Si); 29Si, −7.7 (Me3Si), −19.4 (SiO3), −113.0 (Siq). MS (70
eV) m/z (%) (after treatment with ethyl bromide): 366(5) [M+ −
Me], 308(10) [M+ − SiMe3], 280(31) [N(CH2CH2O)3SiSiPhH+],
6H, OCH2), 2.64 (s, 6H, NCH2), 0.25 (s, 27H, (Me3)3Si); 13C, 121.52
(q, J = 319 Hz, CF3), 56.44 (OCH2), 53.13 (NCH2), 2.11 (Me3SiSi);
29Si, −9.7 (Me3Si), −22.8 (SiO3), −141.1 ((Me3Si)2Si); 19F, −77.85.
Tris(trimethylsilyl)silatranyliumsilane Trichloroacetate (19·
TCA). To a solution of 3 (30 mg, 0.07 mmol) in C6D6 (0.5 mL) was
added trichloroactic acid (60 mg, 0.37 mmol). 1H NMR spectroscopic
monitoring showed quantitative conversion to 19·TCA. NMR (δ ppm,
C6D6): 1H, 10.73 (bs, 5H, NH and Cl3CCO2H), 3.49 (s, 6H, OCH2),
2.72 (s, 6H, NCH2), 0.26 (s, 27H, (Me3)3Si); 29Si, −9.7 (Me3Si),
−23.2 (SiO3), −141.1 ((Me3Si)2Si).
+
253(4) [PhSi3O3C3H8 ], 174(100) [N(CH2CH2O)3Si+], 135(7)
+
+
[Si3O3H3 ], 73(3) [SiMe3 ].
ASSOCIATED CONTENT
* Supporting Information
■
2,5,5-Tris(trimethylsilyl)-2-silatranyldecamethylhexasilane
(16). 3 (350 mg, 0.75 mmol) and KOtBu (87 mg, 0.77 mmol) were
dissolved in THF (2 mL). After 14 h the formation of the silyl anion
10 was confirmed by means of NMR spectroscopy; the solvent was
removed, and benzene was added (3 mL). This solution was added
dropwise to 1-chloro-3,3-bis(trimethylsilyl)heptamethyltetrasilane
(300 mg, 0.75 mmol) in toluene (3 mL) at 0 °C within 1 h. After
12 h the solvent was removed, the residue treated with pentane, and
the insoluble parts were filtered off. The solvent was again removed,
and recrystallization with diethyl ether/acetonitrile (1/1) afforded
colorless crystalline 16 (354 mg, 66%). Mp: 130−136 °C. NMR (δ
S
Tables, figures, and CIF files containing crystallographic
information for compounds 3, 5−7, 9−11, 14, and 17−19
and NMR spectra for 9−14, 18, and 19. The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/acs.organomet.5b00404.
AUTHOR INFORMATION
Corresponding Author
*E-mail for C.M.: christoph.marschner@tugraz.at.
■
1
ppm, CDCl3): H, 3.66 (t, J = 5.56 Hz, 6H, OCH2), 2.73 (t, J = 5.61
Hz, 6H, NCH2), 0.39 (s, 6H, Me2Si), 0.35 (s, 6H, Me2Si), 0.24 (s,
27H, 3 Me3Si), 0.20 (s, 18H, 2 Me3Si); 13C, 58.50 (OCH2), 51.84
(NCH2), 3.52 (Me3Si), 2.97 (Me3Si), 0.53 (Me2Si), 0.40 (Me2Si);
29Si, −9.2 (Me3Si), −9.6 (Me3Si), −30.6 (Me2Si), −30.8 (Me2Si),
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
−53.8 (SiO3), −128.6 (Siq), −129.3 (Sq). Anal. Calcd for
C25H69NO3Si10 (712.68): C, 42.13; H, 9.76; N, 1.97. Found: C,
41.66; H, 9.65; N, 1.73. UV: λ 254 nm (ε = 5.45 × 104 M−1 cm−1).
2,5-Bis(trimethylsilyl)-2,5-disilatranyldecamethylhexasilane
(17). The same procedure as for 3 was used, with 3 (500 mg, 1.19
mmol), KOtBu (137 mg, 1.22 mmol), and dichlorotetramethyldisilane
(116 mg, 0.62 mmol). Recrystallization with diethyl ether/acetonitrile
(1/1) afforded colorless crystalline 17 (200 mg, 41%). Mp: 244−248
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Support for this study was provided by the Austrian Fonds zur
Forderung der wissenschaftlichen Forschung (FWF) via the
project P-26417 (C.M.).
̈
1
°C. NMR (δ ppm, C6D6): H, 3.36 (t, J = 5.6 Hz, 12H, OCH2), 1.90
(t, J = 5.6 Hz, 12H, NCH2), 0.84 (s, 12H, (CH3)2Si), 0.61 (s, 36H,
(CH3)3SiSi); 13C, 58.75 (OCH2), 51.49 (NCH2), 3.54 ((Me3Si)2Si),
0.56 (Me2Si); 29Si, −9.2 ((Me3Si)3Si), −31.2 (Me2Si), −53.2 (SiO3),
−129.5 ((Me3Si)3Si). MS (70 eV) m/z (%): 799(1) [M+ − Me],
640(1) [N(CH2 CH2 O)3 SiSi8 O3 C1 3 H3 8 + ], 464(11) [N-
(CH2CH2O)3SiSi5C10H30+], 406(100) [N(CH2CH2O)3SiSi4C8H24+],
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DOI: 10.1021/acs.organomet.5b00404
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