Direct alkoxysilylation of alkoxysilanes for the synthesis of explicit alkoxysiloxane oligomers

Article abstract of DOI:10.1016/j.jorganchem.2012.05.033

Direct alkoxysilylation, which is a powerful tool to provide explicit alkoxysiloxanes, is developed and its versatility is investigated. Siloxane pentamers Si[OSiR¹(OMe)₂]₄ having various functional groups (R¹ = methyl, vinyl, phenyl, chloropropyl and n-butyl groups) were successfully obtained by direct alkoxysilylation of Si(OR)₄ (R = t-Bu, CHPh₂). Thus, the versatility of the reaction is confirmed on organic functional groups R¹. Functional group tolerance of the reaction is discussed on the basis of electronegativity of the R¹ groups. Alkoxysilylation of Si(Ot-Bu)₂(OMe) ₂ and Si(Ot-Bu)(OMe)₃ selectively gives trimer (MeO) ₂Si[OSiMe(OMe)₂]₂ and dimer (MeO) ₃SiOSiMe(OMe)₂, respectively. Thus, the feasibility on siloxane structure is also confirmed. Various siloxane compounds are synthesized by this newly developed reaction for the first time.

Full text of DOI:10.1016/j.jorganchem.2012.05.033

Journal of Organometallic Chemistry 716 (2012) 26e31
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Direct alkoxysilylation of alkoxysilanes for the synthesis of explicit alkoxysiloxane
oligomers
,
Ryutaro Wakabayashi a b, Misa Tamai a, Kazufumi Kawahara a, Hiroki Tachibana a, Yutaka Imamura c,
,b,
Hiromi Nakai c, Kazuyuki Kuroda a
*
a Department of Applied Chemistry, Waseda University, Ohkubo-3, Shinjuku-ku, Tokyo 169-8555, Japan
b Kagami Memorial Research Institute for Materials Science and Technology, Waseda University, Nishiwaseda-2, Shinjuku-ku, Tokyo 169-0051, Japan
c Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Direct alkoxysilylation, which is a powerful tool to provide explicit alkoxysiloxanes, is developed and its
versatility is investigated. Siloxane pentamers Si[OSiR1(OMe)2]4 having various functional groups
(R1 ¼ methyl, vinyl, phenyl, chloropropyl and n-butyl groups) were successfully obtained by direct
alkoxysilylation of Si(OR)4 (R ¼ t-Bu, CHPh2). Thus, the versatility of the reaction is confirmed on organic
functional groups R1. Functional group tolerance of the reaction is discussed on the basis of electro-
negativity of the R1 groups. Alkoxysilylation of Si(Ot-Bu)2(OMe)2 and Si(Ot-Bu)(OMe)3 selectively gives
trimer (MeO)2Si[OSiMe(OMe)2]2 and dimer (MeO)3SiOSiMe(OMe)2, respectively. Thus, the feasibility on
siloxane structure is also confirmed. Various siloxane compounds are synthesized by this newly devel-
oped reaction for the first time.
Received 13 March 2012
Received in revised form
16 May 2012
Accepted 20 May 2012
Keywords:
Alkoxysilanes
Siloxanes
Nonhydrolytic synthesis
Solegel processes
Lewis acids
Ó 2012 Published by Elsevier B.V.
1. Introduction
[9e16]. Otherwise, their molecular weight, siloxane structure and
compositions cannot be regulated. Silanols have a strong tendency
Construction of siloxane framework under a controlled manner
is a common issue in materials chemistry. Siloxane bond accounts
for main component of silicone, silsesquioxane, silica, silicate and
zeolite. Properties of these materials strongly depend on the
siloxane structures. Therefore, synthetic methodologies for silox-
anes are explored and developed by many researchers until now.
Explicit siloxane compounds are useful as “molecular building
blocks” for the precise assembly of siloxane framework in above
synthetic methodologies [1e13].
Alkoxysilyl group is quite valuable functional group for their
utility to siloxane formation, such as solegel process, nonhydrolytic
solegel process and PierseRubinsztajn reaction. Preparation of
nano- and meso-structured silica-based hybrid materials is
demonstrated by the use of discrete alkoxysiloxane oligomers
(explicit siloxane compounds having alkoxy groups).
to self-condense, thus they usually require stabilization by intro-
ducing bulky functional groups [15e17]. It is difficult to develop
synthetic approaches to silicates for the purposes explored here
because the reactions are quite complicated, involving the
competitive formation and dissociation of siloxane bonds in water.
To solve this problem, we have developed a nonhydrolytic reaction
to synthesize discrete alkoxysiloxane oligomers [18]. It is accom-
plished by optimizing nonhydrolytic solegel process generally for
preparing amorphous silica and other inorganic oxides [19e24].
Specific alkoxysilanes [Si(Ot-Bu)4 or Si(OCHPh2)4] are used instead
of silanols or silicates. These unusual alkoxysilanes can release
stable carbocations and enable formation of discrete alkoxysiloxane
oligomer in the presence of BiCl3 as Lewis acid catalyst. In addition,
their large steric hindrance makes them more stable than
conventional alkoxysilanes (ethoxysilanes and methoxysilanes)
toward hydrolysis.
In spite of their advantages, the number of actual discrete
alkoxysiloxane oligomers and synthetic routes to them is quite
limited, because silanols or silicates are required as their precursors
However, the alkoxysilylation reaction is examined only with
chlorosilanes having SieH group in previous communication.
Application of the reaction with other functional groups is highly
desirable because silica-organic hybrid materials introduce various
functional groups to materials that can be used as catalysts and
adsorbents for example. Previously, we demonstrated the synthesis
* Corresponding author. Department of Applied Chemistry, Waseda University,
Ohkubo-3, Shinjuku-ku, Tokyo 169-8555, Japan. Fax: þ81 3 5286 3199.
E-mail address: kuroda@waseda.jp (K. Kuroda).
0022-328X/$ e see front matter Ó 2012 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.jorganchem.2012.05.033

R. Wakabayashi et al. / Journal of Organometallic Chemistry 716 (2012) 26e31
27
BiCl3 cat.
-SiOR + ClSiR1(OR2)2
R = tBu, -CHPh2
-SiOSiR1(OR2)2
R1 = H, Me, Ph, -CH=CH2, -(CH2)3Cl, n-Bu
R2 = Me, Et
R1
Si
MeO
R1
Si
OMe
OMe
R1
Si
MeO
OMe
OMe
MeO
OMe
O
O
O
O
MeO
Si
OMe
Si
O
R1
R1
O
O
OMe
Si
Si
R1
Si
Si
MeO
MeO
OMe
Si
OMe
OMe
MeO
OMe
R1
MeO
Scheme 1. Synthesis of discrete alkoxysiloxane oligomers by direct alkoxysilylation
reaction.
of Si[OSiH(OMe)2]4 and Si[OSiH(OEt)2]4 [18]. Therefore, our inter-
ests are focused whether functional groups can be successfully
introduced to oligomers by the reaction. Moreover, the ratio of
organic groups to Si is also required to control functional group
content in the resulting silica-organic hybrid materials, thus we
also synthesized oligomers having other T/Q ratios (amount of
organic group in hybrid materials). (Silicone nomenclature:
Tn ¼ R1Si(OSi)n(OH)3ꢀn; Qn ¼ Si(OSi)n(OH)4ꢀn.)
Herein we report the functional group tolerance on the
synthesis of discrete alkoxysiloxane oligomers (Scheme 1). In
contrast to previous syntheses using silanols or silicates, the reac-
tion proposed here can realize the synthesis of discrete alkox-
ysiloxane oligomers having various functional groups together with
siloxane structures.
Fig. 1. 29Si NMR spectra of crude Si[OSiR1(OMe)2]4 before distillation (solvent: CDCl3)
(the product was filtered through celite pad and removed solvents and excess chlor-
osilanes up to 40 ꢁC under vacuum): (a) R1 ¼ Me (1); (b) R1 ¼ eCH]CH2 (2);
(c) R1 ¼ Ph (3); (d) R1 ¼ e(CH2)3Cl (4); (e) R1 ¼ n-Bu (5).
2. Results and discussion
spectra were recorded after solvent evaporation and filtration
through a celite pad but that no further purification was conducted.
Each 29Si NMR spectrum in Fig. 1 shows signals due to Q4 {Si
[OSiR1(OMe)2]4} and T1 {Si[OSiR1(OMe)2]4}. The chemical shift of T0
and T1 is known to be affected by R1 groups [26,27]. Compounds
R1Si(OMe)3 (shown as T0 signals in Fig. 1) are impurities formed by
the synthesis of ClSiR1(OMe)2. They are also formed by quenching
the reaction by adding pyridine and methanol. Although a Q3 signal
(ca. ꢀ100 ppm, OSi(OSi)3) and small T1 signal besides main T1
2.1. Synthesis of alkoxysiloxane oligomers Si[OSiR1(OMe)2]4 to
investigate functional group (R1) tolerance
To investigate functional group tolerance in alkoxysilylation, Si
[OSiR1(OMe)2]4 compounds containing various functional groups
R
1 were synthesized (Scheme 2 top).
Fig. 1 shows the 29Si NMR spectra of the crude products of
compounds Si[OSiR1(OMe)2]4 (1e5). Please note that these NMR
R1
Si
O
MeO
OMe
R1 = H, Me, Ph,
-CH=CH2,
OMe
Si
O
MeO
Si
MeO
Si
O
R1
-(CH2)3Cl, n-Bu
R1
O
OMe
Si
OMe
R1
MeO
ClSiR1(OMe)2
R1 = Me (1), -CH=CH2 (2), Ph (3),
-(CH2)3Cl (4), n-Bu (5)
Si(OR)4
BiCl3 cat.
MeCN/hexane
R1=OMe
Si(OMe)4
t
OMe
Si
(R = Bu, -CHPh2)
OMe
O
MeO
MeO
Si
OMe
O
OMe
Si
MeO
OMe
n
(mixture)
Scheme 2. Synthesis of Si[OSiR1(OMe)2]4 with various R1 groups.

28
R. Wakabayashi et al. / Journal of Organometallic Chemistry 716 (2012) 26e31
appears at Fig. 1(b), Si[OSiR1(OMe)2]4 is undoubtedly the main
2.3. Utility for forming siloxane structure
product by complete alkoxysilylation of Si(Ot-Bu)4 or Si(OCHPh2)4.
A
Q3 signal (Fig. 1(b)) implies the formation of (MeO)Si
We examined the synthesis of other siloxane structures to
extend the utility of the reaction. Compounds having other T/Q
ratios can also be useful for solegel processing to control the
properties of silica-based hybrids. Scheme 3 shows the synthetic
procedure used for (MeO)2Si[OSiMe(OMe)2]2 (6) and (MeO)3SiO-
SiMe(OMe)2 (7) from a reactant composed of Si(Ot-Bu)2(OMe)2 and
Si(Ot-Bu)(OMe)3.
The reactant was synthesized by adding a controlled amount of
t-BuOH and MeOH to SiCl4 in the presence of triethylamine as an
acid scavenger. The 29Si NMR spectrum of the reactant (Fig. 3a)
[OSiR1(OMe)2]3 through partial transesterification between
diphenylmethoxy and methoxy groups competitive to siloxane
formation. The 13C NMR spectra (see Supplementary data for
details) only show the signals due to R1 group and methoxy groups
(around ca. 50 ppm), which show the selective silylation of tert-
butoxy or diphenylmethoxy groups and retention of methoxy
groups with all R1 groups. The 1H NMR spectra also support the
results of 13C NMR spectra (see Supplementary data for details). The
formation of these compounds was demonstrated via high-
resolution MS measurements (see Experimental section). On the
basis of these results, the oligomers Si[OSiR1(OMe)2]4 were
successfully obtained with R1 ¼ methyl (1), vinyl (2), phenyl (3),
chloropropyl (4) and n-butyl (5) groups.
shows the signals at
assigned to Si(Ot-Bu)(OMe)3 and Si(Ot-Bu)2(OMe)2 respectively.
d
¼ ꢀ83.0 and ꢀ88.0 ppm. These signals can be
These assignments are based on the fact that the signal of Si(OMe)4
and Si(Ot-Bu)4 appears at around
d
¼ ꢀ78.0 and ꢀ98.0 ppm [14,18].
All oligomers, except 3, were isolated by vacuum distillation (see
Experimental section; isolated yields: 35% (1), 10% (2), 69% (4), 32%
(5)). Although the formation of Si[OSiR1(OMe)2]4 with R1 ¼ Ph (3) is
suggested by the same analyses above, its isolation was unsuc-
cessful because of its high boiling point for vacuum distillation and
its potential reactivity toward silica in flash chromatography. On
the other hand, branched oligomer Si[OSiR1(OMe)2]4 was not
obtained at all when R1 ¼ OMe (Scheme 2 bottom), and a mixture of
linear alkoxysiloxane oligomers was formed as mentioned in our
previous report [18].
Thus the exchange of one methoxy group with one tert-butoxy
group should cause a shift upfield by 5 ppm in 29Si NMR
measurements. Similar shifts of signals in 29Si NMR measurements
were also observed for transesterification between Si(OMe)4 and
other silicon alkoxides [18,31].
The 29Si NMR spectrum of the product (Fig. 3b) shows signals
assigned to (MeO)2Si[OSiMe(OMe)2]2 (Q2) and (MeO)3SiOSi-
Me(OMe)2 (Q1) at ꢀ93.7 and ꢀ85.9 ppm, respectively. There are
three signals around ꢀ48 ppm, showing T1 species of methyl-
alkxoysilanes (MeSi(OSi)(OR00)2): R00 ¼ H or Me [26]. These T1
signals can be assigned to targeted compounds ((MeO)2Si[OSi-
Me(OMe)2]2 (ꢀ47.7 ppm), (MeO)3SiOSiMe(OMe)2 (ꢀ47.5 ppm)) and
a small amount of by-product {[(MeO)2MeSi]2O} (ꢀ47.9 ppm). The
13C and 1H NMR measurements show the signals arising from
methoxy and methyl groups (see Supplementary data for details).
EI-MS measurements also confirm the formation of (MeO)2Si[OSi-
Me(OMe)2]2 and (MeO)3SiOSiMe(OMe)2. These data indicate that
alkoxysilylation of tert-butoxy groups in the precursors proceeds in
a manner similar to the synthesis of Si[OSiR1(OMe)2]4 (Scheme 3).
These results show the utility of the reaction in the synthesis of
targeted siloxane structures. In these experiments, the electron
densities of Si and O in Si(Ot-Bu)(OMe)3 and Si(Ot-Bu)2(OMe)2
should be similar to those of Si(Ot-Bu)4. Thus, the reaction proceeds
similarly to alkoxysilylation of Si(Ot-Bu)4.
2.2. Discussion of functional group tolerance
We investigated the effect of R1 group on the reaction using ab
initio calculations with Spartan’08 software [28]. As mentioned
above, functional group R1 ¼ OMe is the only functional group
that is unsuccessful for direct alkoxysilylation targeting Si
[OSiR1(OMe)2]4. The steric and electronic effects are considered to
explain the differences arising from the R1 group in the synthesis.
Fig. 2 shows the molecular structures of ClSiR1(OMe)2 optimized at
the B3LYP/6-31G** level in order to compare the size of functional
groups. The size of methoxy group seems similar to that of vinyl
group and larger functional groups are successful for the reaction.
Therefore, the size of R1 group should not be a primary factor.
On the other hand, the group electronegativity study with 1H
NMR shows that the methoxy group is the most electron with-
drawing of all the R1 groups used in this study [29]. These data are
also consistent with electron density analyses at the B3LYP/6-31G**
level (Table S1: see Supplementary data for details). These results
suggest that R1 group should be less electron withdrawing than
methoxy group.
3. Conclusion
We have demonstrated direct alkoxysilylation reaction which is
a powerful tool for the synthesis of molecular building block in
solegel process. Our method does not require preparing unstable
intermediates like silanols, thus it is applicable for the synthesis of
discrete alkoxysiloxane oligomers that have not been synthesized
before. Seven new branched alkoxysiloxane oligomers were
obtained in good yields by utilizing this reaction. The reaction offers
utility for a wide variety of alkoxysilylations of alkoxysilanes except
for trialkoxysilylation (R1 ¼ OMe). The experiments and molecular
simulation indicate that silicon atom in the trialkoxysilyl group has
This feasibility is similar to that of PierseRubinsztajn reaction
which forms siloxane bond from hydrosilane and alkoxysilane with
B(C6F5)3 catalyst. It is said that hydrosilanes containing two or more
electron withdrawing functional groups are inert to siloxane
formation [30], which shows the similarity between nonhydrolytic
solegel process and PierseRubinsztajn reaction.
Fig. 2. Molecular structures of ClSiR1(OMe)2 for comparing the size of functional group R1 (white: H; gray: C; red: O; yellow: Si; green: Cl). Structure optimization was performed at
the B3LYP/6-31G** level with Spartan’08 software (Wavefunction Inc.) [11]. (For interpretation of the references to color in this figure legend, the reader is referred to the web
version of this article.)

R. Wakabayashi et al. / Journal of Organometallic Chemistry 716 (2012) 26e31
29
acetonitrile (MeCN, anhydrous, >99.5%, Kanto Chemical), bismuth
trichloride (BiCl3, >98.0%, Kanto Chemical), tert-butyl alcohol (t-
BuOH, >99.0%, Kanto Chemical), methanol (>99.8%, dehydrated,
Wako Pure Chemical), triethylamine (>99.0%, Wako Pure Chemical)
and pyridine (>99.5%, dehydrated, Wako Pure Chemical) were used
as received without further purification.
Me
MeO
OMe
Si
O
Si
OMe
MeO
Ot-Bu
O
Si
Me
OMe
Si
Si
MeO
OMe
(6)
MeO
MeO
Ot-Bu
ClSiMe (OMe)2
OMe
BiCl3 cat.
MeCN/hexane
4.2. Instruments
Me
Si
MeO
OMe
Liquid-state 1H, 13C and 29Si NMR spectra were obtained on JEOL
ECX-500 and JEOL Lambda-500 spectrometers with the resonance
frequencies of 500 MHz, 126 MHz and 99 MHz, respectively.
Chemical shifts for 1H, 13C and 29Si NMR were referenced to tetra-
methylsilane at 0 ppm. The repetition time between each pulse for
29Si NMR was 10 s. In order to obtain quantitative spectra, a trace
amount of Cr(acac)3 was added to a sample solution to reduce the
29Si spin-lattice relaxation time (T1). EI mass analysis was carried
out with a JEOL JMS-GCmateII instrument. FAB mass analysis was
carried out with a JEOL JMS-SX102A instrument.
MeO
Ot-Bu
O
OMe
Si
MeO
OMe
(7)
Scheme 3. Alkoxysilylation of Si(Ot-Bu)2(OMe)2 and Si(Ot-Bu)(OMe)3 for the synthesis
of a mixture composed of (MeO)2Si[OSiMe(OMe)2]2 (6) and (MeO)3SiOSiMe(OMe)2 (7).
low electron density due to strong electron withdrawing effects of
the alkoxy groups. The synthesis of discrete alkoxysiloxane oligo-
mers is achieved with the other functional groups. In combination
with functional group tolerance, the synthesis of oligomers having
other T/Q ratios has also been accomplished. We believe that the
reaction is quite useful to prepare siloxane compounds of use in the
preparation of functional siloxane-based materials.
4.3. Synthesis of alkoxysiloxane oligomer Si[OSiR1(OMe)2]4
(R1 ¼ Me) (1)
In all the oligomer syntheses described here, the syntheses
become much easier than those reported previously [18]. Bismuth
chloride is used as a catalyst for both chloroalkoxysilane synthesis
and direct alkoxysilylation. The by-products in both reactions are
the same alkyl chloride (RCl) and easily removed. Methyltri-
chlorosilane (MeSiCl3, 11.7 mL, 100 mmol) was slowly added to an
acetonitrile (20 mL) solution of BiCl3 (0.3 mg, 1 mmol) and MTBE
(24 mL, 200 mmol) in a 200 mL Schlenk flask at 0 ꢁC [25]. The molar
ratio was MeSiCl3/MTBE/BiCl3 ¼ 1:2:0.01. The mixture was stirred
overnight at r.t. and a crude chlorodimethoxymethylsilane (ClSi-
Me(OMe)2) solution was obtained. Although a certain amount of
MeSi(OMe)3 was present in the solution, the solution was used
without further purification because the compound does not
contain SiCl groups and does not affect the next alkoxysilylation. An
acetonitrile solution (40 ꢁC) of Si(OCHPh2)4 (7.6 g, 10 mmol) was
added to the crude chloroalkoxysilane solution. The mixture was
stirred for 3 h at r.t. Then, excess amounts of pyridine and methanol
were added to deactivate the Lewis acid and to convert remained
SiCl groups to SiOMe groups. The solvents, excess MeSi(OMe)3 were
removed under reduced pressure. Compound 1 was also obtained
from Si(Ot-Bu)4 instead of Si(OCHPh2)4. Hexane was used as
a solvent instead of acetonitrile at that time. Compound 1 was
isolated by vacuum distillation (1.8 g (3.5 mmol), yield 35%). 1:
4. Experimental section
4.1. General
All reactions were carried out under N2 atmosphere. Chlor-
osilanes, such as methyltrichlorosilane (MeSiCl3, >95.0%), vinyl-
trichlorosilane (CH2]CHSiCl3, >98.0%), phenyltrichlorosilane
(PhSiCl3, >98.0%), 3-chloropropyltrichlorosilane (Cl(CH2)3SiCl3,
>97.0%), n-butyltrichlorosilane (n-BuSiCl3, >98.0%) and tetra-
chlorosilane (SiCl4, >98.0%) were purchased from Tokyo Chemical
Industry. Tetrakis(diphenylmethoxy)silane (Si(OCHPh2)4) and tet-
ra(tert-butoxy)silane (Si(Ot-Bu)4) were synthesized according to
our previous report [18]. Other chemicals, including tert-butyl
methyl ether (MTBE, t-BuOMe, anhydrous, 99.8%, SigmaeAldrich),
Colorless liquid. 1H NMR (500 MHz, CDCl3)
3.56 ppm (s, 24H); 13C NMR (128 MHz, CDCl3):
d
¼ 0.16 (s, 12H),
d
¼ 50.1, ꢀ7.0 ppm;
29Si NMR (99 MHz, CDCl3)
d
¼ e48.1 (4Si, T1), ꢀ110.7 ppm (1Si, Q4);
HRMS (EI, 70 eV) calcd. for C11H33O12Siþ5 [MꢀMe]þ:497.0818;
found: 497.0811.
4.4. Synthesis of alkoxysiloxane oligomer Si[OSiR1(OMe)2]4
(R1 ¼ eCH]CH2) (2)
Compound 2 was synthesized according to the manner similar
to 1. Vinyltrichlorosilane (CH2]CHSiCl3) was used instead of
methyltrichlorosilane in the synthesis of 1. The compound was
isolated by vacuum distillation (0.55 g (1.0 mmol), yield 10%). 2:
Colorless liquid. 1H NMR (500 MHz, THF-d8)
d
¼ 3.52 (s, 24H),
5.84e6.08 ppm (m, 12H); 13C NMR (128 MHz, THF-d8)
d
¼ 50.5,
130.3, 137.1 ppm; 29Si NMR (99 MHz, THF-d8)
d
¼ ꢀ64.6 (4Si,
Fig. 3. 29Si NMR spectra of: (a) the reactant, a mixture of Si(Ot-Bu)2(OMe)2 and Si(Ot-
T1), ꢀ111.1 ppm (1Si, Q4); HRMS (EI, 70 eV) calcd. for C14H33O12Siþ5
Bu)(OMe)3; (b) the product, a mixture of (MeO)2Si[OSiMe(OMe)2]2 (6) and (MeO)3
-
SiOSiMe(OMe)2 (7).
[MꢀCH]CH2]þ: 533.0818; found: 533.0814.

30
R. Wakabayashi et al. / Journal of Organometallic Chemistry 716 (2012) 26e31
4.5. Synthesis of alkoxysiloxane oligomer Si[OSiR1(OMe)2]4
spectra. Si(Ot-Bu)2(OMe)2 and Si(Ot-Bu)(OMe)3 were subsequently
alkoxysilylated with the following procedure. Into a dried 200 mL
Schlenck flask, BiCl3 (0.3 g), acetonitrile (20 mL), methyltri-
chlorosilane (11.7 mL) were added. The flask was cooled to 0 ꢁC and
MTBE (24 mL) was slowly added. The mixture was stirred for
overnight and the mixture composed of Si(Ot-Bu)2(OMe)2 and
Si(Ot-Bu)(OMe)3 (2.15 g) was added. The mixture was stirred for
3 h, then pyridine (4.5 mL) and methanol (8.9 mL), were added at
(R1 ¼ Ph) (3)
Compound 3 was synthesized according to the manner similar
to 1. Phenyltrichlorosilane (PhSiCl3) was used instead of methyl-
trichlorosilane in the synthesis of 1. A hexane (10 mL) solution of
Si(Ot-Bu)4 (3.2 g, 10 mmol) was used instead of an acetonitrile
solution of Si(OCHPh2)4. The reaction time was 1 day after the
addition of Si(Ot-Bu)4. See Supplementary data for NMR spectra of
crude product. Formation of 3 was also estimated with high-
resolution MS measurement: HRMS (FAB) calcd. for C31H41O11Si5þ
[MꢀMeO]þ: 729.1495; found: 729.1484.
0
ꢁC. The solvent and excess alkoxysilanes were removed under
reduced pressure. The mixture was filtered over a celite pad with
hexane. The crude product (1.9 g) was obtained after evaporation of
hexane. See the 29Si NMR spectrum shown as Fig. 3. See
Supplementary data for 13C and 1H NMR spectra. Formations of
titled compounds were also estimated with MS measurements:
HRMS for 6 (EI, 70 eV) calcd. for C7H21O8Siþ3 [MꢀMeO]þ 317.0544;
found: 317.0538. HRMS for 7 (EI, 70 eV) calcd. for C5H15O5Si2þ
[MꢀMeO]þ 211.0458; found: 211.0456.
4.6. Synthesis of alkoxysiloxane oligomer Si[OSiR1(OMe)2]4
(R1 ¼ e(CH2)3Cl) (4)
Compound 4 was synthesized according to the manner similar
to 1. 3-Chloropropyltrichlorosilane (Cl(CH2)3SiCl3) was used instead
of methyltrichlorosilane in the synthesis of 1. A hexane (10 mL)
solution of Si(Ot-Bu)4 (3.2 g, 10 mmol) was used instead of a warm
acetonitrile solution of Si(OCHPh2)4. The reaction time was 3 h after
the addition of Si(Ot-Bu)4. The compound was isolated by Kugel-
rohr distillation (5.4 g (6.9 mmol), yield 69%). 2: Yellowish liquid. 1H
Acknowledgments
We thank Prof. R. Laine (University of Michigan) for his
comments which have greatly improved the manuscript We also
thank Dr. T. Shibue and Mr. N. Sugimura (MCCL, Waseda University)
for the help in NMR and MS measurements. This work was sup-
ported in part by a Grant-in-Aid for Scientific Research (No.
23245044) and the Global COE program “Practical Chemical
Wisdom” from MEXT, Japan. K. Kawahara is grateful for financial
support provided through a Grant-in-Aid for JSPS Fellow from
MEXT. K. Kuroda also acknowledges the support by Elements
Science and Technology Project “Functional Designs of Silicon-
Oxygen-Based Compounds by Precise Synthetic Strategies” from
MEXT, Japan.
NMR (500 MHz, CDCl3)
d
¼ 0.78e0.81 (m, 8H), 1.87e1.93 (m, 8H),
3.51e3.54 (t, 8H), 3.57 ppm (s, 24H); 13C NMR (128 MHz, CDCl3)
d
¼ 8.2, 26.3, 47.3, 50.3 ppm; 29Si NMR (99 MHz, CDCl3)
d
¼ ꢀ51.3
(4Si, T1), ꢀ111.2 (1Si, Q4): HRMS (FAB) calcd. for C19H45O11Cl4Siþ5
[MꢀMeO]þ: 729.0562; found: 729.0591.
4.7. Synthesis of alkoxysiloxane oligomer Si[OSiR1(OMe)2]4 (R1 ¼ n-
Bu) (5)
Compound 5 was synthesized according to the manner similar
to 1. n-Butyltrichlorosilane (n-BuSiCl3) was used instead of meth-
yltrichlorosilane in the synthesis of 1. A hexane (10 mL) solution of
Si(Ot-Bu)4 (3.2 g, 10 mmol) was used instead of a warm acetonitrile
solution of Si(OCHPh2)4. The reaction time was 3 h after the addi-
tion of Si(Ot-Bu)4. The compound was isolated by Kugelrohr
distillation 2.1 g (3.2 mmol, yield 32%). Colorless liquid. 1H NMR
Appendix A. Supplementary material
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.jorganchem.2012.05.033.
(500 MHz, CDCl3)
d
¼ 0.65e0.68 (m, 8H), 0.88e0.91 (t, 12H),
References and notes
1.32e1.45 (m, 16H), 3.56 ppm (s, 24H); 13C NMR (128 MHz, CDCl3)
d
¼ 10.4, 13.7, 24.9, 26.3, 50.2. 29Si NMR (99 MHz, CDCl3)
¼ ꢀ50.2
d
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