Wagner-Meerwein-Type Rearrangements of Germapolysilanes - A Stable Ion Study

Article abstract of DOI:10.1021/acs.organomet.5b00431

(Chemical Equation Presented). The rearrangement of tris(trimethylsilyl)silyltrimethylgermane 1 to give tetrakis(trimethylsilyl)germane 2 was investigated as a typical example for Lewis acid catalyzed Wagner-Meerwein-type rearrangements of polysilanes and polygermasilanes. Direct ²⁹Si NMR spectroscopic evidence is provided for several cationic intermediates during the reaction. The identity of these species was verified by independent synthesis and NMR characterization, and their transformation was followed by NMR spectroscopy.

Full text of DOI:10.1021/acs.organomet.5b00431

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Article
pubs.acs.org/Organometallics
Wagner−Meerwein-Type Rearrangements of Germapolysilanes - A
Stable Ion Study
Lena Albers,† Mohammad Aghazadeh Meshgi,§ Judith Baumgartner,*,‡ Christoph Marschner,*,§
and Thomas Muller*,†
̈
†Institut fur Chemie, Carl von Ossietzky Universitat Oldenburg, Carl von Ossietzky-Strasse 9-11, D-26129 Oldenburg, Federal
̈
̈
Republic of Germany
‡Institut fur Chemie, Karl Franzens Universitat Graz, Stremayrgasse 9, 8010 Graz, Austria
§Institut fur Anorganische Chemie, Technische Universitat Graz, Stremayrgasse 9, 8010 Graz, Austria
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: The rearrangement of tris(trimethylsilyl)silyl-
trimethylgermane 1 to give tetrakis(trimethylsilyl)germane 2
was investigated as a typical example for Lewis acid catalyzed
Wagner−Meerwein-type rearrangements of polysilanes and
polygermasilanes. Direct 29Si NMR spectroscopic evidence is
provided for several cationic intermediates during the reaction.
The identity of these species was verified by independent
synthesis and NMR characterization, and their transformation
was followed by NMR spectroscopy.
The description of this process as being a silicon variation of
the Wagner−Meerwein rearrangement suggests the presence of
cationic intermediates.4,5 However, despite the fact that the
chemistry of silyl cations has experienced immense popularity
in recent years,8 experimental evidence for polysilanyl-
substituted silyl cations and their possible involvement in
rearrangement or fragmentation reactions is indeed rather
scarce. Lambert and co-workers reported on the formation of
tris(trimethylsilyl)silylium, (Me3Si)3Si+, most probably in the
form of its arene complexes; the obtained 29Si NMR spectra
suggest, however, substantial decomposition of the material.9
Structural aspects and the question of aromaticity and
homoaromaticity had been the focus in several publications
of the Sekiguchi group concerning some cyclic polysilasilyl
cations.10,11 Sekiguchi and co-workers also demonstrated the
occurrence of a degenerated intramolecular 1,3-methyl shift
occurring in a dialkyloligosilanylsilyl cation.12 Interestingly, in
none of these reports were parallels drawn between the subject
of study and the likely involvement of similar species in the sila-
Wagner−Meerwein rearrangement. During our own exper-
imental studies of the Wagner−Meerwein rearrangement in
oligosilanes,13 we found that for germylsilanes a particular
preference exists for the formation of products in which the
germanium atoms occupy central positions in the oligosilane
frameworks.14 A deeper insight was provided by a computa-
tional study of the fundamental reaction of germylsilane 1 to
INTRODUCTION
■
Despite the most interesting properties and the widespread
potential use of oligo- and polysilanes, synthetic access to this
class of compounds is mainly limited to the Wurtz-type
coupling reaction, in which the Si − Si chain is built up in a
reductive process using silicon halides and alkali metals.1 Up to
date alternative methods for the synthesis of oligosilanes such
as dehydrocoupling of hydrosilanes2 or electrochemically
mediated Si−Si bond forming processes3 do not reach the
prominence of the Wurtz-type coupling. While this process
works fairly well for the preparation of dialkylated linear
polysilane polymers and small cyclosilanes, it does not provide
satisfactory access to compounds of even slightly enhanced
structural complexity. In particular, the generation of well-
defined polycyclic molecules in acceptable yields has proven to
be very challenging by this method.1 Regarding the potential
for such materials being useful for technical applications, there
is intrinsic interest in novel approaches that open the possibility
to develop new synthetic tools for the preparation of open
chain, cyclic, and polyhedral compounds with silicon containing
backbones. Pioneering work by the group of Kumada and
Ishikawa,4 further developed by the groups of West,5 Markl,6a
̈
and Pannell,6b revealed that the Lewis acid catalyzed Wagner−
Meerwein-type rearrangement of oligosilanes is a powerful
method to create structures of higher complexity. The high
yield synthesis of an all-silicon analogue of adamantane from a
structural isomer, reported previously by two of us, is certainly
one of the more spectacular examples for the potential of this
synthetic methodology.7
Received: May 21, 2015
© XXXX American Chemical Society
A
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give germane 2 (reaction 1, Scheme 1). The results of density
functional theory (DFT) calculations suggested an exothermic
[R3Si(arene)] [B(C6F5)4] (R = Me, Et, iPr; arene = C6H5CH3,
C6H6, C6H5Cl), 10,8 and used arenes as solvents. In the past, it
was shown8 that the combination of arene solvents and weakly
coordinating anions is suitable for the detection of highly
reactive silylium ions. In order to allow the NMR spectroscopic
detection of the postulated cationic intermediates, we tested at
first the stoichiometric reaction between germylsilane 1 and
triethylsilyl benzenium borate, [Et3Si(C6D6))] [B(C6F5)4], 10a.
The reaction in benzene at 6 °C was completed after 2 h and
resulted in a biphasic reaction mixture that is typical for
solutions of tetrakis(pentafluorophenyl)borates in aromatic
hydrocarbons.8 29Si NMR spectra obtained from the ionic
phase showed many signals, which indicated the formation of a
complicated reaction mixture. The 29Si NMR analysis of the
second, nonpolar layer showed the presence of at least nine
different neutral compounds. These nine compounds were
identified by GC/MS spectrometry and NMR spectroscopy as
the expected germane 2, three different methylethylsilanes, and
a series of silylated germanes 11 and 12 (Scheme 3 and
Scheme 1. Rearrangement of Germylsilane 1 to Silylgermane
2 Using Lewis Acids
multistep rearrangement via several isomeric silyl- and germyl
cations 3−8 (Scheme 2). According to this investigation, the
isomerization occurs via consecutive 1,2-silyl and 1,2-methyl
shifts with an overall barrier of less than 50 kJ mol−1.14
Scheme 3. Stoichiometric Reaction between Triethylsilyl
Benzenium Borate 10a and Silylgermane 1 in Benzene at T =
6°C
Scheme 2. Suggested Isomerization Cascade of Germylium
Ion 3 to Silylium Ion 814
Supporting Information for details). Noteworthy, germanes 11
and 12, which all have cation 8 as a common intermediate, are
substituted with a different number of ethyl groups. When the
same reaction was performed with tri-iso-propylsilyl toluenium
borate, [iPr3Si(C7D8)][B(C6F5)4], 10b, only two side products
An experimental investigation on the course of the principal
reaction 1 would greatly benefit from the simplicity of the
reactants, proposed intermediates, and products and from the
straightforward interpretation of their NMR spectra. The close
chemical relationship between silicon and germanium suggests
that conclusions drawn from a mechanistic study of reaction 1
will be of significance also in the case of polysilanes. Here, we
report on a 29Si NMR investigation of the exemplary reaction 1,
which provides direct evidence for cationic intermediates in the
sila-Wagner−Meerwein rearrangement and for the clean
transformation of the incipient germyl cation 3 into the
product-forming silyl cation 8 at low temperatures along a
cascade of isomeric cations 4−7 (Scheme 2).
i
i
were detected, namely, (Me3Si)3GeSiMe2 Pr and Pr3SiMe.
Finally, when trimethylsilyl toluenium borate [Me3Si(C7D8)]
[B(C6F5)4], 10c, was applied as reaction partner, only the
expected rearrangement product 2 and tetramethylsilane were
identified in the nonpolar phase (see Supporting Information).
Although with all three silylarenium borates 10 the clean
production of cationic species at room temperature was not
achieved, the results of these stoichiometric reactions indicate
that the initial step of the rearrangement reaction is cation
formation by cleavage of either a Ge−C- or Si−C bond. Judged
from the calculated bond strengths, the cleavage of a Ge−C
bond is preferred over that of a Si−C bond (De(Ge−C) = 305
kJ mol−1; (De(Si−C) = 347 kJ mol−1).14 This clearly supports
our initial assumption that the first cationic intermediate
formed should be germyl cation 3 which undergoes a
rearrangement reaction to give silyl cation 8. Furthermore,
the results suggest that the terminating step consists in back
transfer of an alkyl group to the rearranged cation which yields
besides germane 2 the alkylated products 13 (Scheme 4). The
multiple substitution5 in the case of the ethyl substituted silyl
arenium ion demonstrates the ease of alkyl group exchange
under the applied conditions, which is only limited by the steric
requirements of the exchanging groups.
RESULTS AND DISCUSSION
■
As a starting point for our experimental investigation, we tested
additional cationic Lewis acids as stoichiometric reagents or
catalysts for the rearrangement of model compound 1. The idea
behind using a cationic Lewis acid is to introduce weakly
coordinating anions such as the tetrakis(pentafluorophenyl)-
borate, [B(C6F5)4]−,15 which will be beneficial for the
stabilization of the postulated cationic intermediates. Indeed,
we found that already 4 mol % of trityl borate [Ph3C][B-
(C6F5)4], 9, induces the complete transformation of germylsi-
lane 1 into the symmetric germane 2 in dichloromethane at
room temperature (Scheme 1).16 For the generation of
stoichiometric amounts of the postulated cationic intermediates
in the rearrangement reaction shown in Scheme 1, we switched
to the even more electrophilic trialkylsilyl arenium borates,
In contrast to the reaction at room temperature, the reaction
of silylgermane 1 with tri-iso-propylsilyl toluenium borate, 10b,
in toluene-d8 at −20 °C yielded cleanly a single ionic
compound as indicated by only two resonances that were
detected in the 29Si NMR spectra of the ionic phase. The NMR
B
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Scheme 4. Reaction of Silylgermane 1 with Different Triakylsilyl Arenium Borates 10 at r.t. (Borate Anion Not Shown)
Scheme 5. Formation of Silyl Toluenium Ion 8(C7D8) from Different Precursor Compounds
Table 1. Experimental and Calculated 29Si NMR Chemical Shifts of Solvent Complexes of Germylium Ions 3 and 7 and Silylium
a
Ion 8
compound
δ29Si (Siq)
δ29Si (SiMe3)
δ29Si (Si+Me2)
δ29Si (SiMe2)
(−13)
[3(C7D8)]
7(C7D8)]
−87.9 (−93)
−7.9 (−7)
(8; −13)
−2.4 (0)
−1.5 (0)
8(C7D8)]
98.1 (108)
b
[8(ClC6D5)]
154.3 (157)
a
b
Calculated values for the nondeuterated compounds at GIAO/M06-L/6-311G(2d,p)//M06-2X/6-311+G(d,p) are in parentheses. Calculated for
the chloronium ion structure [8−Cl-C6H5]. Chloronium ions are the dominating species when silyl cations are generated in chlorinated arenes; see
ref 22.
data (δ29Si = −87.9 (Siq) and δ29Si = −7.9 (SiMe3), integral
ratio in the 29Si{1H} inverse gated experiment, 1:3) is
consistent with the structure of germyl toluenium ion
3(C7D8). This assignment was supported by the fact that the
same cationic species was formed by the conventional Bartlett
Condon Schneider hydride transfer17 reaction of hydridoger-
mane 14 with trityl borate 9 (Scheme 5). In addition, the
results of quantum mechanical calculations18,19 of 29Si NMR
chemical shifts for an optimized molecular structure of 3(C7H8)
predict values that are very close to the experiment (see Table
1).
characteristic for silyl arenium ions.8 The 29Si NMR chemical
shifts of these cationic species are reported to be very sensitive
to changes of the solvent due to the replacement of the arene
molecule attached to the silicon atom. Indeed, the 29Si NMR
chemical shift of the low field resonance varies significantly with
the arene solvent from δ29Si = 98.1 in toluene-d8 to δ29Si =
154.3 in chlorobenzene-d5 (see Table 1).22 On the basis of
these results, the two new 29Si NMR signals were tentatively
assigned to silyl toluenium ion 8(C7D8). This assignment was
supported by its independent synthesis by hydride transfer
reaction from the appropriate silane 15 (see Scheme 5 and
Figure 2) and by quantum mechanical calculations of the 29Si
NMR chemical shifts of optimized molecular structures of
arene complexes of 8 (see Table 1). According to the NMR
results, solutions of the silyl toluenium borate [8(C7D8)][B-
(C6F5)4] in toluene at T = −20 °C are stable for at least 3 days.
When the temperature of the NMR probe was gradually raised
in steps of 10 °C, already at T = −10 °C new signals in the 29Si
NMR spectrum appeared, and exposure of the NMR sample to
temperatures of about +20 °C resulted in complete
decomposition of cation 8(C7D8) (see Supporting Information,
Figure S21).23 The thermal instability of arenium borate
[8(C7D8)][B(C6F5)4] in solution prevents its isolation in
Interestingly, already after 2 h at −20 °C two new 29Si NMR
resonances were detected in both cases (δ29Si = −2.4 and
+98.1, integral ratio in the 29Si{1H} inverse gated experiment,
3:1; see Figure 1 and Supporting Information).20 Over time,
the intensity of the new signals increased significantly while the
original 29Si NMR signals of germyl cation 3(C7D8) vanished
(see Figure 1), thereby confirming the clean conversion of
silylgermyl toluenium ion 3(C7D8) into a new cationic species
in toluene at −20 °C. The new high field signal appears in the
typical region for trimethylsilyl groups attached to germa-
nium,21 but the measured chemical shift is not specific. More
informative is the low field resonance at δ29Si = 98.1, which is
C
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predicted stability sequence for the free silylium and germylium
ions (see Figure S22, Supporting Information). In particular,
the silyltoluenium ion 8(C7H8) is predicted to be the most
stable along the complete reaction sequence, and the overall
reaction 3(C7H8) → 8(C7H8) is found to be exothermic by 44
kJ mol−1. Experimentally, however, no indications for the
cationic intermediates 4−7 or for the related arenium ions were
detected. In order to test our mechanistic proposal, we decided
to generate one specific cation along the reaction cascade,
shown in Scheme 2, and to monitor its rearrangement.
Therefore, we subjected silylgermane 16 to the hydride transfer
reaction in toluene in an attempt to generate the corresponding
germyltoluenium 7(C7D8) (Scheme 5). This last step of the
reaction sequence, 7(C7H8) → 8(C7H8), is predicted by the
calculations to be exothermic by 15 kJ mol−1 (Figure S22,
Supporting Information). 29Si{1H} NMR spectra recorded after
15 min at −20 °C showed no signals expected for cation
7(C7H8) (compare Figure S19c (Supporting Information) and
calculated values in Table 1), but the characteristic resonances
for silyltoluenium 8(C7D8) already dominated. In agreement
with the computational results, this experiment shows that
germyltoluenium ion 7(C7D8) undergoes a fast 1,2-shift of the
trimethylsilyl group to form the more stable cation 8(C7D8).
Obviously, the barrier for this rearrangement is rather low
and in a similar range as the 18 kJ mol−1 that is predicted for
the transformation of the free cations 7 → 8 (Figure S22,
Supporting Information),14 and therefore, germyltoluenium ion
7(C7D8) cannot be detected even at temperatures as low as
−20 °C.
CONCLUSIONS
■
We were able to synthesize polysilanyl-substituted silyl and
germyl cations, such as silyl cation 8 and germyl cation 3 in the
form of their arene complexes at low temperatures using the
weakly coordinating [B(C6F5)4]− anion. The cation synthesis
was done using either the stoichiometric reaction of germa-
oligosilanes with a cationic Lewis acid such as tri-iso-
propylsilyltoluenium, or, in a more regio-controlled way, by
the standard hydride transfer reaction between hydrido-silanes
and -germanes with the trityl cation. The cationic species were
identified by low-temperature NMR spectroscopy supported by
the results of quantum mechanical NMR chemical shift
calculations. Applying these techniques, we were able to verify
several silyl- and germyl cations and their solvent complexes as
intermediates in the sila-Wagner−Meerwein rearrangement of
silagermane 1 (eq 1, Scheme 1) and to provide strong evidence
for their clean interconversion at low temperatures. We are
convinced that this reaction is archetypical for many synthetic
useful Lewis acid catalyzed skeletal rearrangements in
polysilanes and polygermasilanes. Additional stable ion studies
for sila-Wagner−Meerwein rearrangement of oligosilanes of
higher complexity are currently under investigation in our
laboratory to identify general rules and reaction patterns.
Figure 1. 99 MHz 29Si{1H} NMR spectra (toluene-d8, 253 K) of the
rearrangement of germyl toluenium ion 3(C7D8) (•) to silyl
i
toluenium 8(C7D8) (*) (↓ Pr3SiMe). (a) Spectrum 2 h after the
addition of [iPr3Si(C7D8)][B(C6F5)4]; (b) after 9 h; (c) after 25 h; (d)
after 120 d at 210 K.
Figure 2. 99 MHz 29Si{1H} NMR spectrum (toluene-d8, 253 K) of
silyl toluenium ion 8(C7D8) at 253 K in toluene synthesized by
hydride transfer from silane 15.
substance and additional characterization. These NMR experi-
ments demonstrated the clean conversion of silylgermyl
toluenium ion 3(C7D8) to germylsilyl toluenium 8(C7D8) in
toluene at −20 °C. According to our previous computational
study, this sila-variant of the Wagner−Meerwein rearrangement
is expected to proceed via several cationic intermediates (see
Scheme 2).14 Additional DFT computations at the B3LYP/6-
311+G(d,p) level of theory18,19 indicated that complexation of
the formed silyl and germyl cations with the arene solvent has
no significant influence on the calculated reaction coordinate.
The calculated relative energies of the toluene complexes of
cations 3−8 reveal only slight modifications of the previously
EXPERIMENTAL SECTION
■
All manipulations of air- and moisture-sensitive compounds were
carried out under argon or nitrogen atmosphere using Schlenk
techniques or a standard glovebox (Braun Unilab). Glassware was
dried in an oven at 120 °C and evacuated prior to use. The solvents
tetrahydrofuran (THF), dimethoxyethane (DME), n-pentane, ben-
zene, and toluene were dried over sodium and distilled under nitrogen
atmosphere. Chlorobenzene was dried over CaCl2 and stored over
molecular sieves. Deuterated benzene and toluene were stored over
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molecular sieves after drying over sodium. Dichlorodimethylgermane,
chlorodimethylsilane, triethylsilane, tri-iso-propylsilane and trimethyl-
chlorosilane were obtained from commercial suppliers, and the silanes
were dried over molecular sieves. Sodium methanolate was prepared
by addition of sodium to an excess of abs. methanol. After all sodium
was consumed, the solvent was removed in vacuo. Triphenylmethyl
tetrakis(pentafluorophenyl) borate 9 ([Ph3C][B(C6F5)4]) was pre-
pared according to a modified literature procedure.24 Tetrakis-
(trimethylsilyl)silane,25 tetrakis(trimethylsilyl)germane26 2, tris-
(trimethylsilyl)silylpotassium,27 tris(trimethylsilyl)germylpotassium,28
tris(trimethylsilyl)silyltrimethylgermane29 1, chloropentamethyldisi-
lane,30 and trimethylsilane31 were synthesized according to reported
procedures. GC-MS spectra were performed on a Thermo Focus
DSQ. NMR spectra were recorded on Bruker Avance 500, Avance III
500 and Varian Inova 300 spectrometers. 1H NMR spectra were
calibrated against the residual proton signal of the solvent as internal
reference (benzene-d6/δ1H(C6D5H) = 7.20; toluene-d8/δ1H(CD2H)
= 2.08; chloroform-d1/δ1H(CHCl3) = 7.24; chlorobenzene-d5/δ1H-
(C6D4HCl) = 7.14) and 13C NMR spectra by using the central line of
the solvent signal (benzene-d6/δ13C(C6D6) = 128.0, toluene-d8/
δ13C(C6D5CD3) = 20.4, chloroform-d1/δ13C(CDCl3) = 77.0, chlor-
obenzene-d5/δ13C(C6D5Cl) = 134.2). 29Si{1H} NMR spectra were
calibrated against an external standard (29Si(Me2SiHCl) = 11.1 versus
tetramethylsilane (TMS)). The 29Si{1H} NMR inverse gated spectra
were recorded with a relaxation delay D1 = 10 s. On the basis of our
experiences, at −20 °C this delay is long enough to allow a reliable
integration of the peaks. The 29Si{1H} INEPT spectra were recorded
with delays D3 = 8.4 ms and D4 = 31.3 ms. IR spectra were recorded
on a Bruker Tensor 27 instrument. Analysis values for carbon show
often too low values, which we attribute to the formation and
incomplete combustion of silicon carbide, although vanadium
pentoxide as combustion aid was used.
2SiMe3-OMe], 73.0 (100) [Me3Si+]. No satisfactory combustion
analysis was available due to contamination with the chloride side-
product.
Tris(trimethylsilyl)silyldimethylgermane (14). A solution of
0.62 g (1.62 mmol) tris(trimethylsilyl)silyldimethylmethoxygermane
18 in 30 mL of THF and a suspension of 0.062 g (1.62 mmol) of
LiAlH4 in 50 mL of THF were cooled to 0 °C with an ice bath. The
solution of silagermane 18 was added to the LiAlH4 suspension and
the reaction mixture was stirred for 20 min at 0 °C before it was
allowed to warm to room temperature and stirred for another 20 min.
The mixture was slowly added to ice cold 2 M sulfuric acid. The
phases were separated, and the aqueous phase was extracted two times
with 50 mL of diethyl ether. The combined organic phases were dried
over sodium sulfate and filtered, and the solvent was removed under
reduced pressure. The product was crystallized from ethanol as a waxy,
1
colorless solid (0.38 g, 1.09 mmol, 67%). H NMR (499.87 MHz,
3
305.0 K, C6D6, δ ppm): 0.30 (s, 27H, (CH3)3Si), 0.50 (d, JH,H = 4.2
3
Hz, 6H, (CH3)2Ge), 4.04 (sept, JH,H = 4.2 Hz, 1H, GeH). 13C{1H}
NMR (125.69 MHz, 305.0 K, C6D6, δ ppm): −2.3 ((CH3)2Ge), 2.5
((CH3)3Si). 29Si{1H} NMR (99.31 MHz, 305.0 K, C6D6, δ ppm):
−128.3 (((CH3)3Si)3Si), −9.4 (((CH3)3Si)3Si). Mass required for
C11H34GeSi4: 352.1. Mass found GC/MS: 351.1 (0.1) [M+-H], 337.1
(0.6) [M+-Me-H], 278.0 (30) [M+-SiMe3-H], 189.1 (13) [M+-2SiMe3-
Me-H], 174.0 (4) [M+-SiMe3-GeMe2H], 73.1 (100) [Me3Si+]. IR
(ATR, neat): νGe−H 1982 cm−1. Anal. found/calcd. for C11H34GeSi4: C
37.63/37.60, H 10.67/9.75.
Tris(trimethylsilyl)germyldimethylsilane (15).34 Solutions of
2.99 mmol tris(trimethylsilyl)germylpotassium28 in 30 mL of DME
and of 0.6 mL (excess, 5.52 mmol) of chlorodimethylsilane in 30 mL
of DME were cooled to 0 °C with an ice bath. The germylpotassium
compound was slowly added to the chlorosilane solution during 1 h.
The ice bath was allowed to warm to room temperature overnight.
The reaction mixture was then hydrolyzed with 1 M sulfuric acid. The
organic layer was separated, and the aqueous phase was extracted with
10 mL of diethyl ether. The combined organic phases were dried over
sodium sulfate, and the filtrate was concentrated to 5 mL under
reduced pressure. The product was crystallized by adding 2 mL of
acetonitrile as a colorless, waxy solid (0.847 g, 80.6%). 1H NMR
(499.87 MHz, 305.0 K, CDCl3, δ ppm):34 0.22 (s, 27H, (CH3)3Si),
0.27 (d, 3JH,H = 4.2 Hz, 6H, (CH3)2Si), 4.12 (sept, 3JH,H = 4.2 Hz, 1H,
SiH). 13C{1H} NMR (125.71 MHz, 305.0 K, CDCl3, δ ppm): −1.4
((CH3)2Si), 3.1 ((CH3)3Si). 29Si INEPT NMR (99.31 MHz, 305.0 K,
CDCl3, δ ppm): −29.8 (dsept, 1JSi,H = 180.5 Hz, 2JSi,H = 7.0 Hz, SiH),
−4.7 ((CH3)3Si). Mass required for C11H34GeSi4: 352.1. Mass found
GC/MS: m/z (%) = 351.1 (0.3) [M+-H], 337.1 (2.5) [M+-Me-H],
278.1 (64) [M+-SiMe3-H], 189.9 (22) [M+-2SiMe3-Me-H], 174.0 (2)
[M+-SiMe3-GeMe2H], 73.0 (100) [Me3Si+]. IR (ATR, neat): νSi−H
2085 cm−1. Anal. found/calcd. for C11H34GeSi4: C 36.31/37.60, H
9.98/9.75.
Dimethoxydimethylgermane (17). This compound was pre-
pared according to slightly modified literature procedures.32 NaOMe
(2.84 g) (3.5 eq., 52.57 mmol) was suspended in 40 mL of pentane,
and 1.74 mL (15.00 mmol) of dichlorodimethylgermane was slowly
added with a syringe. The mixture was stirred overnight at room
temperature. The excess of NaOMe and formed NaCl were separated
from the solution by using a centrifuge (20 min, 2000 rpm), and then
the product-containing pentane solution was decanted using a Teflon
tube. The salts were washed with 10 mL of pentane and again
centrifuged and decanted. The pentane solutions were combined, and
the product was separated from the solvent by fractionated distillation
1
(bp.: 118 °C at normal pressure (1.45 g, 58%). H NMR (500.13
MHz, 297.9 K, C6D6, δ): 0.30 (s, 6H, (CH3)2Ge), 3.54 (s, 6H,
Ge(OCH3)2). 13C{1H} NMR (125.77 MHz, 298.1K, C6D6, δ): −2.9
((CH3)2Ge), 51.6 (Ge(OCH3)2). Mass required for C4H12GeO2:
166.0. Mass found GC/MS: 164.9 (0.5) [M+-H], 150.8 (100) [M+-
Me], 135.9 (72) [M+-OMe], 120.9 (88) [M+-OMe-Me], 104.9 (84)
[M+-OMe-2Me].
Tris(trimethylsilyl)pentamethyldisilanylgermane (19). A sol-
ution of 1.37 mmol tris(trimethylsilyl)germylpotassium·18-crown-628
in 3 mL of benzene was added dropwise to a solution of 0.25 g (1.51
mmol) of chloropentamethyldisilane30 in 3 mL of benzene. After 5 h,
the solution mixture was quenched with 1 M sulfuric acid, and the
phases were separated. The aqueous phase was extracted with pentane,
and the combined organic phases were dried over sodium sulfate and
filtered, and the solvent was removed under reduced pressure. The
product was obtained as colorless crystals by crystallization from
Tris(trimethylsilyl)silyldimethylmethoxygermane (18). A sol-
ution of 4.50 mmol tris(trimethylsilyl)silylpotassium27 in 40 mL of
pentane and a solution of 0.75 g (4.50 mmol) of dimethoxydime-
thylgermane 17 in 10 mL of pentane were cooled to 0 °C. The silyl
potassium compound was added dropwise to the germane solution.
The ice bath was allowed to warm to room temperature overnight.
The reaction mixture was then hydrolyzed with 1 M hydrochloric acid.
The organic layer was separated and dried over sodium sulfate. The
solvent was removed under reduced pressure, and the product was
purified by Kugelrohr distillation (0.62 g, 36%). Because of the use of
hydrochloric acid, about 14% of the corresponding germyl chloride
was formed as a byproduct, which was detected in the GC
1
methanol/diethyl ether 1:2 (0.42 g, 73%). H NMR (299.94 MHz,
298.0 K, C6D6, δ ppm): 0.22 (s, 9H, Si(CH3)2Si(CH3)3), 0.36 (s, 27H,
((CH3)3Si)3Ge), 0.40 (s, 6H, Si(CH3)2Si(CH3)3). 13C{1H} NMR
(75.43 MHz, 298.0 K, C6D6, δ ppm): −0.8 (Si(CH3)2Si(CH3)3), −0.4
(Si(CH3)2Si(CH3)3), 4.0 (((CH3)3Si)3Ge). 29Si{1H} INEPT NMR
(59.59 MHz, 295.0 K, C6D6, δ ppm): −34.0 (Si(CH3)2Si(CH3)3),
−15.5 (Si(CH3)2Si(CH3)3), −5.2 (((CH3)3Si)2Ge). Mass required for
C14H42GeSi5: 424.1. Mass found GC/MS: m/z (%) = 424 (1) [M+];
408 (1) [M+-Me-H]; 351 (3) [M+-SiMe3]; 278 (10) [M+-2SiMe3];
259 (1) [GeSi3C7H17+]; 243 (1) [GeSi3C6H13+]; 219 (3) [Ge-
Si2C6H17+]; 203 (11) [M+-3SiMe3-2H]; 187(8)[M+-3SiMe3-Me-4H];
1
chromatograms and NMR spectra. H NMR (499.87 MHz, 305.0 K,
C6D6, δ ppm): 0.34 (s, 27H, (CH3)3Si), 0.60 (s, 6H, (CH3)2Ge), 3.54
(s, 3H, CH3OGe). 13C{1H} NMR (125.69 MHz, 305.0 K, C6D6, δ
ppm): 2.6 ((CH3)3Si), 4.1 ((CH3)2Ge), 52.6 (CH3OGe). 29Si{1H}
INEPT NMR (99.31 MHz, 305.0 K, C6D6, δ ppm): −124.6
(((CH3)3Si)3Si), −9.9 (((CH3)3Si)3Si). Mass required for
C12H36GeOSi4: 382.1. Mass found GC/MS: 367.2 (1) [M+-Me],
351.2 (0.5) [M+-OMe], 278.0 (8) [M+-SiMe3-OMe], 205.1 (13) [M+-
E
DOI: 10.1021/acs.organomet.5b00431
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
+
+
+
147 (7) [GeSiMe3 ]; 131 (35) [SiMe3SiMe2 ]; 73 (100) [SiMe3 ].
Anal. found/calcd. for C14H42GeSi5 C 39.33/39.70, H 9.50/9.99.
Bis(trimethylsilyl)pentamethyldisilanylgermane (16). A mix-
ture of 0.21 g (0.49 mmol) of germapolysilane 19, 0.062 g (0.51
mmol) of KOtBu, and 0.134 g (0.51 mmol) of 18-crown-6 ether was
dissolved in 2 mL of benzene. After the complete formation of
germylpotassium compound 20 was confirmed by NMR spectroscopy,
the solution was added to a stirred mixture of 10 mL of degassed
diethyl ether and 20 mL of degassed 2 M sulfuric acid cooled with an
ice bath. The phases were separated, the aqueous phase was extracted
with degassed diethyl ether, and the combined organic phases dried
over sodium sulfate. The solvents were removed under reduced
pressure, and the product was obtained as a colorless oil (0.15 g, 91%).
The compound is sensitive to oxygen and should be stored under
argon at −20 °C.
precooled solution of the named trialkylsilyl arenium borate 10a−c.
The reaction mixture was stirred for 2 h at the specified temperature
and then allowed to warm to room temperature. The polar phase and
the nonpolar phase were each transferred to separate NMR tubes to be
analyzed independently. In the following reactions, the NMR spectra
of the polar phase showed too may signals to be analyzable, but the
compounds in the nonpolar phase were identified by NMR and GC/
MS spectroscopy (see Figures S8−11 in the Supporting Information
for details).
Rearrangement of Tris(trimethylsilyl)silyldimethylgermyl
Toluenium Borate (3(C7D8)[B(C6F5)4]) to Tris(trimethylsilyl)-
germyldimethylsilyl Toluenium Borate (8(C7D8)[B(C6F5)4])
Starting from Silagermane (1). To a solution of 0.18 g (0.50
mmol) of tris(trimethylsilyl)silyltrimethylgermane 1 in 1 mL of
toluene-d8 cooled to −20 °C, 1 equiv of tri-iso-propylsilyl toluenium
borate 10b was slowly added via a Teflon tube. The mixture was
stirred for 1 h at −20 °C. The brown polar phase and the light yellow
nonpolar phase were each transferred to separate NMR tubes at −20
°C and stored at −60 °C overnight until the NMR spectra were
recorded the next morning. The polar phase contained borates
[3(C7D8)][B(C6F5)4] and [8(C7D8)][B(C6F5)4]). The nonpolar
phase contained methyl-triiso-propylsilane and the rearrangement
Germylpotassium Compound 18-Crown-6 (20). 1H NMR
(299.94 MHz, 298.0 K, C6D6, δ ppm): 0.39 (s, 9H (Si(CH3)2)Si-
(CH3)3), 0.59 (s, 18H ((CH3)3Si)2GeK), 0.64 (s, 6H, Si(CH3)2Si-
(CH3)3), 3.25 (s, 24H, CH2O). 13C{1H} NMR (75.43 MHz, 295.0 K,
C6D6, δ ppm): 0.0 (Si(CH3)2Si(CH3)3), 3.5 (Si(CH3)2Si(CH3)3), 8.5
(((CH3)3Si)2GeK), 70.0 (CH2O). 29Si{1H} INEPT NMR (59.59
MHz, 295.0 K, C6D6, δ ppm): −33.0 (Si(CH3)2Si(CH3)3), −16.6
(Si(CH3)2Si(CH3)3), −3.4 (((CH3)3Si)2GeK). Mass required for
C13H38GeSi4 after ethyl bromide derivatization: 380.1. Mass found
after ethyl bromide derivatization GC/MS: m/z (%) = 380 (1)[M+];
365 (1) [M+-Me]; 350 (3) [M+-Et-H]; 307 (1) [M+-SiMe3]; 292 (1)
[M+-SiMe3-Me]; 277 (3) [M+-SiMe3-2Me]; 262 (1) [M+-SiMe3-
3Me]; 234 (3) [M+-2SiMe3]; 219 (8) [M+-2SiMe3-Me]; 203 (17)
[M+-2SiMe3-2Me-H]; 187 (6) [M+-2SiMe3-3Me-2H]; 159 (4) [M+-
1
product 2. Polar phase H NMR (499.87 MHz, 253.0 K, C7D8, δ
+
ppm): −0.15 (((CH3)3Si)3GeSi(CH3)2 ), 0.07 (((CH3)3Si)3GeSi-
+
+
(CH3)2+), 0.12 (((CH3)3Si)3SiGe(CH3)2 ), 0.28 (((CH3)3Si)3SiGe-
(CH3)2 ). 13C{1H} NMR (125.71 MHz, 253.0 K, C7D8, δ ppm): 1.6
+
+
(((CH3)3Si)3SiGe(CH3)2 ), 2.5 (((CH3)3Si)3GeSi(CH3)2 ), 5.5
+
+
(((CH3)3Si)3GeSi(CH3)2 ), 12.1 (((CH3)3Si)3SiGe(CH3)2 ). 29Si-
{1H} NMR (99.31 MHz, 253.0 K, C7D8, δ ppm): −87.9
+
3SiMe3-H]; 145 (10) [M+-3SiMe3-Me]; 131 (33) [GeSiC2H5 ]; 115
+
+
(((CH3)3Si)3SiGe(CH3)2 +), −7.9 (((CH3)3Si)3SiGe(CH3)2 ), −2.4
+
(9) [GeSiCH+]; 73 (100) [SiMe3 ].
+
(((CH3)3Si)3GeSi(CH3)2 ), 98.1 (((CH3)3Si)3GeSi(CH3)2 ) (see
Bis(trimethylsilyl)pentamethyldisilanylgermane (16). 1H
NMR (499.87 MHz, 305.1 K, C6D6, δ ppm):): 0.22 (s, 9H,
Si(CH3)2Si(CH3)3), 0.35 (s, 18H, ((CH3)3Si)2Ge), 0.40 (s, 6H,
Si(CH3)2Si(CH3)3), 2.25 (s, 1H, GeH). 13C{1H} NMR (125.71 MHz,
305.0 K, CDCl3, δ ppm): −1.7 (Si(CH3)2Si(CH3)2), −1.6 (Si-
(CH3)3Si(CH3)2), 3.1 (((CH3)3Si)2Ge). 29Si{1H} NMR (99.31 MHz,
305.0 K, C6D6, δ ppm): −34.3 (Si(CH3)2Si(CH3)3), −16.2 (Si-
(CH3)2Si(CH3)3), −5.7 (((CH3)3Si)2Ge). Mass required for
C11H34GeSi4: 352.1. Mass found GC/MS: 335 (2) [M+-Me-2H];
278 (27) [M+-SiMe3-H]; 263 (2) [M+-SiMe3-Me-H]; 203 (13) [M+-
2SiMe3-2H]; 189 (10) [M+-2SiMe3-Me-2H]; 173 (2) [M+-2SiMe3-
Figures S12a−c in the Supporting Information). Nonpolar phase
1H NMR (499.87 MHz, 305.0 K, C7D8, δ ppm): −0.17 (s,
3
((CH3)2CH)3SiCH3), 0.26 (s, ((CH3)3Si)4Ge), 0.86 (sept, JH,H
7.3 Hz, ((CH3)2CH)3SiCH3), 0.97 (d, JH,H
=
3
= 7.3 Hz,
((CH3)2CH)3SiCH3). 13C{1H} NMR (127.71 MHz, 305.0 K, C7D8,
δ ppm): −10.1 (((CH3)2CH)3SiCH3), 3.5 (((CH3)3Si)4Ge), 11.8
(((CH3)2CH)3SiCH3), 18.8 (((CH3)2CH)3SiCH3). 29Si{1H} NMR
(99.31 MHz, 305.0 K, C7D8, δ ppm): −5.1 (((CH3)3Si)4Ge), 9.0
(((CH3)2CH)3SiCH3) (see Figures S13a−d in the Supporting
Information).
Rearrangement of Tris(trimethylsilyl)silyldimethylgermyl
toluenium Borate (3(C7D8)[B(C6F5)4]) to Tris(trimethylsilyl)-
germyldimethylsilyl Toluenium Borate (8(C7D8)[B(C6F5)4])
Starting from Hydrogen Substituted Silagermane (14). tris-
(trimethylsilyl)silyldimethylgermane 14 (0.14 g (0.40 mmol)) and
0.37 g (0.40 mmol) of triphenylmethyl tetrakis(pentafluorophenyl)-
borate were each dissolved in 1 mL of toluene-d8 and cooled to −20
°C. Silagermane 14 was slowly added to the borate salt via a Teflon
tube, and the mixture was stirred at −20 °C for 1.5 h. The brown polar
phase and the light yellow nonpolar phase were each transferred to
NMR tubes at −20 °C. The NMR spectra were recorded at −20 °C.
The polar phase contained borates [3(C7D8)][B(C6F5)4] and
[8(C7D8)][B(C6F5)4]). The nonpolar phase contained triphenyl-
2Me-2H]; 131 (24) [SiMe3SiMe2 ]; 115 (14) [Si2C4H11+]; 73 (100)
+
+
[SiMe3 ]. IR (ATR, neat) νGe−H 1951 cm−1. Anal. found/calcd. for
C11H34GeSi4 C 38.85/37.60, H 9.41/9.75.
General Preparation of Trialkylsilyl Arenium Borates (10a−
d).33 Triphenylmethyl tetrakis(pentafluorophenyl)borate was dis-
solved in 3 mL of the indicated solvent, and the silane was added.
The formation of two phases could be observed, and the biphasic
reaction mixture was vigorously stirred for 30 min. The upper,
nonpolar phase was removed, and the lower, polar phase was washed
with 2 mL of the used solvent, and again the nonpolar phase was
removed. The polar phase was dried under reduced pressure for 30
min and then dissolved in the respective deuterated solvent.
Triethylsilyl Benzenium Borate (10a). Triphenylmethyl tetrakis-
(pentafluorophenyl)borate (0.50 g (0.54 mmol)) was dissolved in 3
mL of benzene, and 0.14 mL (1.6 eq., 0.87 mmol) of triethylsilane was
added.
Tri-iso-propylsilyl Toluenium Borate (10b). Triphenylmethyl
tetrakis(pentafluorophenyl)borate (0.46 g (0.50 mmol)) was dissolved
in 3 mL of toluene, and 0.11 mL (1.1 eq., 0.55 mmol) of triiso-
propylsilane was added.
Trimethylsilyl Toluenium Borate (10c). Triphenylmethyl
tetrakis(pentafluorophenyl)borate (0.46 g (0.50 mmol)) was dissolved
in 3 mL of toluene, and 0.06 mL (1.1 eq., 0.55 mmol) of
trimethylsilane was added.
1
methane and the rearrangement product 2. Polar phase H NMR
(499.87 MHz, 253.0 K, C7D8, δ ppm): −0.15 (((CH3)3Si)3GeSi-
+
+
(CH3)2+), 0.07 (((CH3)3Si)3SiGe(CH3)2+), 0.12 (((CH3)3Si)3GeSi-
(CH3)2 ), 0.28 (((CH3)3Si)3SiGe(CH3)2 ). 13C{1H} NMR (125.71
+
MHz, 253.0 K, C7D8, δ ppm): 1.6 (((CH3)3Si)3SiGe(CH3+)2 ), 2.4
+
(((CH3)3Si)3GeSi(CH3)2 ), 5.5 (((CH3)3Si)3GeSi(CH3)2 ), 12.1
+
(((CH3)3Si)3SiGe(CH3)2 ). 29Si{1H} NMR (99.31 MHz, 253.0 K,
C7D8,
δ
ppm): −87.9 (((CH3)3Si)3SiGe(CH3)2+), −7.9
+ +
(((CH3)3Si)3SiGe(CH3)2+), −2.4 ((CH3)3Si)3GeSi(CH3)2 )), 98.1
(((CH3)3Si)3GeSi(CH3)2 ) (see Figures S14a−c and S15a−b in the
1
Supporting Information). Nonpolar phase H NMR (499.87 MHz,
305.0 K, C7D8, δ ppm): 0.30 (s, ((CH3)3Si)4Ge), 5.38 (s, Ph3CH),
6.98−7.09 (m, Ph3CH). 13C{1H} NMR (127.71 MHz, 305.0 K, C7D8,
δ ppm): 3.5 ((CH3)3Si)4Ge), 57.1 (Ph3CH), 125.4 (Ph3CH), 128.3
(Ph3CH), 129.2 (Ph3CH), 144.3 (Ph3CH). 29Si{1H} NMR (99.31
General Procedure for the Rearrangement of Tris-
(trimethylsilyl)silyltrimethylgermane (1) with Trialkylsilyl Are-
nium Borates (10a−c). A solution of 0.18 g (0.50 mmol) of
silagermane 1 in 1 mL of the named deuterated solvent was added to a
F
DOI: 10.1021/acs.organomet.5b00431
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
MHz, 305.0 K, C7D8, δ ppm): −5.1 ((CH3)3Si)4Ge) (see Figures
S16a−c in the Supporting Information).
ASSOCIATED CONTENT
■
S
* Supporting Information
Tris(trimethylsilyl)germyldimethylsilyl Toluenium Borate
(8(C7H8)[B(C6F5)4]) from Silane 15. Tris(trimethylsilyl)germyl-
dimethylsilane 15 (0.18 g (0.50 mmol)) and 0.46 g (0.50 mmol) of
triphenylmethyl tetrakis(pentafluorophenyl)borate were both dis-
solved in 1 mL of toluene-d8 and cooled to −20 °C. Germylsilane
15 was slowly added to the borate salt via a Teflon tube, and the
mixture was stirred at −20 °C for 1.5 h. The brown polar phase and
the light yellow nonpolar phase were each transferred to separate
NMR tubes at −20 °C and stored at −60 °C overnight until the NMR
spectra were recorded the next morning. The polar phase contained
borate [8(C7D8)][B(C6F5)4]. The nonpolar phase contained
Experimental and theoretical characterization, including the
preparation of all compounds of interests and computational
details. The Supporting Information is available free of charge
on the ACS Publications website at DOI: 10.1021/
acs.organomet.5b00431.
AUTHOR INFORMATION
■
Corresponding Authors
*(J.B.) E-mail: baumgartner@tugraz.at.
*(C.M.) E-mail: christoph.marschner@tugraz.at.
*(T.M.) E-mail: thomas.mueller@uni-oldenburg.de.
1
triphenylmethane and the rearrangement product 2. Polar phase H
NMR (499.87 MHz, 253.0 K, C7D8,
δ ppm): −0.15
(((CH3)3Si)3GeSi(CH3)2+), 0.12 (((CH3)3Si)3GeSi(CH3)2+).
Notes
13C{1H} NMR (125.71 MHz, 253.0 K, C7D8, δ ppm): 2.5
The authors declare no competing financial interest.
+
+
(((CH3)3Si)3GeSi(CH3)2 ), 5.5 (((CH3)3Si)3GeSi(CH3)2 ). 29Si{1H}
NMR (99.31 MHz, 253.0 K, C7D8, δ ppm): −2.4 (((CH3)3Si)3GeSi-
ACKNOWLEDGMENTS
+
+
■
(CH3)2 ), 98.1 (((CH3)3Si)3GeSi(CH3)2 ) (see Figures S17a−c in the
1
This work was supported by the ERA-chemistry program
(DFG-Mu1440/8-1, FWF-I00669) and by Carl von Ossietzky
University Oldenburg. The simulations were performed at the
HPC Cluster HERO (High End Computing Resource
Oldenburg), located at the University of Oldenburg (Germany)
and funded by the DFG through its Major Research
Instrumentation program (INST 184/108-1 FUGG) and the
Ministry of Science and Culture (MWK) of the Lower Saxony
State.
Supporting Information). Nonpolar phase H NMR (499.87 MHz,
305.0 K, C7D8, δ ppm): 0.29 (s, ((CH3)3Si)4Ge), 5.38 (s, Ph3CH),
6.98−7.10 (m, Ph3CH). 13C{1H} NMR (125.69 MHz, 305.0 K, C7D8,
δ ppm): 3.5 (((CH3)3Si)4Ge), 57.2 (Ph3CH), 125.4 (Ph3CH), 128.3
(Ph3CH), 129.2 (Ph3CH), 144.3 (Ph3CH). 29Si{1H} NMR (99.31
MHz, 305.0 K, C7D8, δ ppm): −5.1 (((CH3)3Si)4Ge) (see Figure
S18a−c in the Supporting Information).
Tris(trimethylsilyl)germyldimethylsilyl-phenylchloronium
Borate (8(C6D5Cl)[B(C6F5)4]) from Silane 15. Tris(trimethylsilyl)-
germyldimethylsilane 15 (0.09 g (0.25 mmol)) and 0.23 g (0.25
mmol) of triphenylmethyl tetrakis(pentafluorophenyl)borate were
both dissolved in 0.5 mL of chlorobenzene-d5 and cooled to −20
°C. Germylsilane 15 was slowly added to the borate salt via a Teflon
tube, and the mixture was stirred at −20 °C for 1.5 h. The brown
solution was transferred into a NMR tube at −20 °C and stored at
−60 °C overnight until the NMR spectra were recorded the next
morning. The mixture contained borate [8(C6D5Cl)][B(C6F5)4], the
rearrangement product 2, and triphenylmethane. 29Si{1H} NMR
(99.31 MHz, 253.0 K, C6+D6Cl, δ ppm): −5.1 (((CH3)3Si)4Ge), −1.4
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(((CH3)3Si)3GeSi(CH3)2 ), 154.3 (((CH3)3Si)3GeSi(CH3)2 ).
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(8(C7D8)[B(C6F5)4]) from Germane 16. Bis(trimethylsilyl)-
pentamethyldisilanylgermane 16 (0.11 g (0.32 mmol)) and 0.29 g
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1
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̈
rearrangement product 2. Polar phase H NMR (499.87 MHz, 253.0
K, C7D8, δ ppm): −0.16 (((CH3)3Si)3GeSi(CH3)2+), 0.12
(9) (a) Lambert, J. B.; Zhang, S. J. Chem. Soc., Chem. Commun. 1993,
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+
(((CH3)3Si)3GeSi(CH3)2 ). 13C{1H} NMR (125.71 MHz, 253.0 K,
+
C7D8, δ ppm): 2.5 (((CH3)3Si)3GeSi(CH3)2 ), 5.5 (((CH3)3Si)3GeSi-
metallics 1996, 15, 5495−5501. (d) Ottosson, C.-H.; Szabo,
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́
K. J.;
+
(CH3)2 ). 29Si{1H} NMR (99.31 MHz, 253.0 K, C7D8, δ ppm): −2.4
+
+
(((CH3)3Si)3GeSi(CH3)2 )), 98.2 (((CH3)3Si)3GeSi(CH3)2 )) (see
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1
Figures S19a−c in the Supporting Information). Nonpolar phase H
NMR (499.87 MHz, 305.0 K, C7D8, δ ppm): 0.30 (s, ((CH3)3Si)4Ge),
5.38 (s, Ph3CH), 6.98−7.10 (m, Ph3CH). 13C{1H} NMR (125.69
MHz, 305.0 K, C7D8, δ ppm): 3.5 ((CH3)3Si)4Ge), 57.1 (Ph3CH),
125.4 (Ph3CH), 128.2 (Ph3CH), 129.1 (Ph3CH), 144.3 (Ph3CH).
29Si{1H} NMR (99.31 MHz, 305.0 K, C7D8, δ ppm): −5.1
(((CH3)3Si)4Ge) (see Figure S20a−c in the Supporting Information).
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Chem. Soc. 2005, 127, 9978−9979. (b) Igarashi, M.; Ichinohe, M.;
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