Synthesis of Dodecaallylhexasilacyclohexane and Its Convertibility

Article abstract of DOI:10.1002/zaac.201800171

Dodecaallylhexasilacyclohexane 4, which would be a stable precursor for a variety of hexasilacyclohexane derivatives, was synthesized by the reaction of [pedeta·SiH₂Cl]₂[Si₆Cl₁₂·2Cl] (1) with allylmagnesium bromide. In addition, an effective synthetic route of dodecachlorohexasilacyclohexane 3 from trichlorosilane was found. Deallylmethoxylation of 4 with catalytic amount of iodine and methanol yielded dodecamethoxyhexasilacyclohexane 5 almost quantitatively, but was found to be highly sensitive toward water. Herein, we report the first spectroscopical and structural data of 5.

Full text of DOI:10.1002/zaac.201800171

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201800171
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Synthesis of Dodecaallylhexasilacyclohexane and Its Convertibility
Yamato Omatsu,[a] Yoshiyuki Mizuhata,*[a,b] and Norihiro Tokitoh*[a,b]
Dedicated to Professor Dr. Alexander Filippou on the Occasion of his 60th Birthday
Abstract. Dodecaallylhexasilacyclohexane 4, which would be a stable allylmethoxylation of 4 with catalytic amount of iodine and methanol
precursor for a variety of hexasilacyclohexane derivatives, was synthe-
sized by the reaction of [pedeta·SiH Cl] [Si Cl12·2Cl] (1) with allyl-
magnesium bromide. In addition, an effective synthetic route of do-
yielded dodecamethoxyhexasilacyclohexane 5 almost quantitatively,
but was found to be highly sensitive toward water. Herein, we report
the first spectroscopical and structural data of 5.
2
2
6
decachlorohexasilacyclohexane 3 from trichlorosilane was found. De-
atom bond formation with easy activation by Brønsted acids.[6]
We conceived that the introduction of allyl groups to
Introduction
Hexasilacyclohexane derivatives, six-membered cyclic oli-
gosilanes, are investigated for a long time from the viewpoint
of their σ conjugation, unique structures and characteristic re-
actions.[ Such cyclic oligosilanes are generally prepared by
reductive condensation of dihalosilanes with alkali or transi-
tion metals. However, these synthetic procedures have some
difficulties, as such as low yield and low reproducibility. More-
over, the common synthetic approach, the reaction of dihalo-
silane with lithium, results in various ring-size products de-
pending on the substituents on the silicon atom. For example, a
four-membered ring compound is preferentially obtained from
diisopropyldichlorosilane,[2] whereas six-membered ring si-
lanes are majorly produced in the case of dimethyldichloro-
silane.[ To develop the chemistry of hexasilacyclohexane de-
rivatives, more effective synthetic route is required.
2–
[
Si Cl ·2Cl] derivatives, which can be obtained with com-
6 12
paratively high yield, enables us to create various functional
hexasilacylcohexane derivatives.
1]
Herein, we report the attempts to introduce allyl groups to
2–
[
Si Cl ·2Cl] compounds 1 and 2. As results, we have suc-
6 12
ceeded in the synthesis and conversion of dodecaallylhexasila-
cyclohexane 4. During the course of this study, we have
achieved
the
NMR
spectral
investigation
of
[
Ph P] [Si Cl ·2Cl] (2) and found an effective synthetic route
4
2
6
12
to dodecachlorohexasilacyclohexane Si Cl (3).
6
12
Results and Discussion
3]
Taking facile and high-yield preparation into account, we
2
–
selected [Ph P] [Si Cl ·2Cl] (2) as a [Si Cl ·2Cl] source
In 2001, Boudjouk and co-workers reported the first synthe-
sis of a hexasilacylcohexane with planar and inverse sandwich
structure, [pedeta·SiH Cl] [Si Cl ·2Cl] (1) from trichlorosi-
4
2
6
12
6
12
and prepared it from trichlorosilane and tetraphenylphosphon-
ium chloride by following the reported procedures (Scheme 1,
upper part).[ Since no spectroscopic data have been reported
for compound 2, because of its low solubility in organic sol-
vents, we measured solid-state NMR spectra (Figure 1). The
2
2
6
12
5a]
lane and N,N,NЈ,NЈ,NЈЈ-pentaethyldiethylenetriamine (PED-
ETA).[4] This reaction is one of the selective synthetic route of
six-membered silicon rings. After this report, several
2
9
2
–
Si NMR chemical shift (δ = –21.2 ppm) was comparable to
[
Si Cl ·2Cl] compounds having different cations have been
6 12
[
7]
[
5]
that of [nBu N] [Si Cl ·2Cl] in CD Cl (δ = –21.7 ppm).
4 2 6 12 2 2
synthesized. Unfortunately, those have not been fully charac-
terized spectroscopically owing to their low solubility in com-
mon organic solvents. In addition, their reactivity is less
known. Hence, more investigation on their properties is de-
manded.
On the one hand, allylsilanes typically have enough stability
under air and are widely used as reagents for silicon–hetero-
*
Prof. Dr. Y. Mizuhata
E-Mail: mizu@ boc.kuicr.kyoto-u.ac.jp
Homepage: http://oec.kuicr.kyoto-u.ac.jp/~tokitohlab/index-e.html
Prof. Dr. N. Tokitoh
*
E-Mail: tokitoh@boc.kuicr.kyoto-u.ac.jp
[
[
a] Institute for Chemical Research
Kyoto University
Gokasho, Uji, Kyoto 611–0011, Japan
b] Integrated Research Consortium on Chemical Sciences
Gokasho, Uji, Kyoto 611–0011, Japan
Scheme 1. Synthesis of compounds 2 and 3.
Z. Anorg. Allg. Chem. 2018, 644, 930–934
930
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Two signals were observed in the 35Cl NMR spectrum, indicat- reports, this synthetic route of 3 from trichlorosilane via 2 is
ing two types of chlorine atoms, i.e., the bonded and coordi- the most effective way from the viewpoint of reaction time,
nated Cl atoms.
total yield, and safety. Unfortunately, the reaction of 2 with
allylmagnesium bromide gave a complicated reaction mixture
(
Scheme 2, upper part). The reaction of 3 with an allyllithium
reagent led to 4 (19% yield) and tetraallylsilane (16% yield)
Scheme 2, lower part) together with the cleavage of Si–Si
bonds.
Next, we investigated the allylation reaction of compound 1
Scheme 3). Compound 1 was treated with excess amount of
(
(
allylmagnesium bromide for 5 h. Recrystallization of the crude
mixture from hexane afforded compound 4 as a colorless solid
in 51% yield. Compound 4 has enough stability to the air with-
Figure 1. Solid-state 29Si (left) and 35Cl (right) NMR spectra of 2.
1
13
1
out polymerization due to the allyl-groups. In the H, C{ H},
and 29Si NMR spectra, all allyl substituents and silicon atoms
Next, we attempted the introduction of allyl groups to com-
pound 2. However, the reaction of 2 with allylmagnesium
bromide was found to give a complicated mixture including
triphenylphosphine and a small amount of dodecaallylhexasila-
cyclohexane (4) (Scheme 2, upper part).[ The yield could not
be improved in spite of attempts under various reaction condi-
29
are observed equally. A Si NMR signal (δ = –36.0 ppm) of
in C D is shifted to lower field with respect to that of do-
4
6
6
[11]
decamethylhexasilacyclohexane (δ = –42 ppm).
8]
tions. This is probably due to the electrophilic character of
+
the phosphorus atom in the cation part (Ph P ), preventing the
4
reaction of the allyl nucleophile with the Si centers.
Scheme 3. Synthesis of 4 using 1.
In order to reveal substituent-convertibility, compound 4
was treated with 13 equiv. of methanol and catalytic amount
of iodine on the basis of the reaction conditions of deallylalk-
[12]
oxylation reported previously (Scheme 4). The reaction pro-
1
ceeded quantitatively as judged by H NMR spectroscopy, giv-
ing dodecamethoxyhexasilacyclohexane (5) as a colorless solid
in 98% yield. According to a previous report, compound 5,
synthesized from 3, showed reasonable elemental analysis re-
1
[13]
sults but multiple peaks in the H NMR spectrum.
In our
experiment, on the one hand, only one signal was observed
1
29
both in the H and Si NMR spectra. As judged by these
differences, compound 5 in the previous report is considered
to have contained several side-products, such as cyclic oligosi-
lanes with four-, five- or seven-membered silicon ring. Com-
Scheme 2. Attempted synthesis of compound 4 using 2 or 3.
In order to synthesize 4, dodecachlorohexasilacyclohexane
3, a cation-free hexasilacyclohexane derivative, would be a
pound 5 is highly reactive towards H O to decompose into
2
suitable precursor. There are mainly two synthetic routes to
obtain 3. One is dephenylchlorination of dodecaphenylhexa-
silacyclohexane (Si Ph ), which is given from diphenyldi-
methanol and unidentified compounds. Single crystals of 5
were obtained by recrystallization from hexane solution.
Hence, we have succeeded in the first identification of 5 spec-
troscopically and structurally.
6
12
chlorosilane with lithium in extremely low yield and low re-
producibility.[ The other is chlorination of hexasilacyclohex-
ane prepared by reduction of 1 with lithium aluminum hydride.
In this case, the problems are the generation of a pyrophoric
9]
gas (SiH ) during the reduction and the usage of chlorine gas
4
for the chlorination.[4,10] Wagner and co-workers recently re-
ported the reaction of [nBu N] [Si Cl ·2Cl] with AlCl to
4
2
6
12
3
give 3 in moderate yield.[ This synthetic approach is much
securer than two routes mentioned above. However, it takes
quite long reaction time to obtain [nBu N] [Si Cl ·2Cl] in
5b]
Scheme 4. Synthesis of 5 from 4.
4
2
6
12
also low yield.
Solid-state molecular structures of 4 (Figure 2)[8] and 5 (Fig-
We found that the reaction of 2 with 2 equiv. of AlCl gave 3 ure 3) were determined by X-ray diffraction studies. Both 4
3
in 65% yield (Scheme 1, lower part). Compared with previous and 5 have a chair-type structure as well as general hexasila-
Z. Anorg. Allg. Chem. 2018, 930–934
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© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
cyclohexane derivatives. Comparison of average Si–Si bond longer than those of Si Cl . The sums of the interior angles
6
12
lengths and the sum of the interior angles of Si ring is shown of 4 and 5 are similar to those of Si Me and Si Cl (3).
6
6
12
6
12
in Table 1, together with those of Si Me and 3, which we
6
12
reanalyzed based on the data measured at the same temperature
as 4 and 5 (–170 °C). The Si–Si bond lengths of 4 are slightly Conclusions
longer than those of Si Me and shorter than those of Si Ph
6
12
6
12
av. 2.39 Å).[14]
We have succeeded in the synthesis of per-allyl-substituted
(
The bond-shortening would be caused by the
electron-donating effect of the substituents on the silicon
atoms. The observed Si–Si bond lengths of 5 are slightly
Si compound 4, which has a high substituent-convertibility
6
with methoxy groups, and we achieved the first identification
of dodecamethoxy compound 5 in terms of both spectral and
structural aspects.
Experimental Section
General Methods: All manipulations were carried out in an argon
atmosphere using either Schlenk line techniques or glove boxes. All
solvents were purified by standard methods and/or the Ultimate Sol-
[
15]
vent System, Glass Contour Company.
Remaining tiny amounts of
water and oxygen in deuterated solvents were removed by bulb-to-
bulb distillation from potassium mirror or molecular sieves 4A prior
1
13
31
29
to use. H (300 MHz), C (75 MHz), P (121 MHz), Si (59.6 MHz)
NMR spectra in solvents were measured on a JEOL JNM AL-300
spectrometer. Solid-state NMR spectra were measured with a Bruker
Avance III 800US Plus NMR spectrometer. A signal arising from re-
sidual C
6
D
5
H (δ =7.16 ppm) in the C
6
D
6
was used as an internal stan-
(δ =128 ppm) for the
(δ =0.0 ppm) was
1
dard for the H NMR spectra, and that of C
6 6
D
1
3
C NMR spectra. The signal arising from SiMe
4
used as an external standard for the 29Si NMR spectra. High-resolution
Figure 2. Molecular structure of 4 in the solid state. All hydrogen
atoms are omitted for clarity; displacement ellipsoids are depicted at
the 50% probability level. Selected bond lengths /Å: Si1–Si2
mass spectrometry data were obtained with a JEOL JMS-700 MStation
(
JURC, Institute for Chemical Research, Kyoto University) or with a
®
Bruker Daltonics micrOTOF focus-Kci with an IonSence DART -SVP
ion source. All melting points were determined with a Büchi Melting
Point Apparatus M-565 and are uncorrected. Elemental analyses were
carried out at the Microanalytical Laboratory (Institute for Chemical
Research) of Kyoto University.
2.3510(5), Si2–Si3 2.3499(6), Si1–Si3* 2.3600(5).
Synthesis of 4: To a diethyl ether solution (4.0 mL) of 1 (1.51 g,
1
.2 mmol) and lithium chloride (756 mg, 18 mmol) was added a di-
ethyl ether solution of allylmagnesium bromide (1.2 m, 15 mL,
8 mmol) at –78 °C. After stirring for 1 h at the same temperature and
for 4 h at room temperature, the reaction mixture was quenched with
4
saturated NH Cl aq., extracted with hexane and dried with Na SO .
1
4
2
The organic layer was concentrated using a rotary evaporator, giving
a crude mixture. Recrystallization of the mixture in a freezer for 8 h
afforded colorless crystals. The crystals were washed with acetonitrile
and dried under reduced pressure, giving compound 4 (397 mg,
1
0
.61 mmol) in 51% yield. M.p.: 128–130 °C. H NMR (C
6
D
6
, room
Figure 3. Molecular structure of 5 in the solid state. All hydrogen
atoms and disordered part are omitted for clarity; displacement ellip-
soids are depicted at the 50% probability level. Selected bond lengths /
Å: Si1–Si2 2.3572(7), Si2–Si3 2.3567(7), Si1–Si3* 2.3612(7), Si1–O1
1
1
2
temperature): δ = 2.06 (d, J = 8.0 Hz, CHCH Siϫ24), 4.95 (dd, J =
2
1
2
1
7, J = 2.4 Hz, CH
CH CHCH ϫ12), 5.94 (sext, J = 8.0 Hz, CH
, room temperature): δ = 20.4, 114, 136. Si NMR (C
room temperature): δ = –36. DART-TOF MS (positive): m/z calcd. for
2 2
CHCH ϫ12), 5.03 (dd, J = 17, J = 2.4 Hz,
1
2 2
CHCH
ϫ12). 13C{ H}
1
2
2
2
9
1
.646(2), Si1–O2 1.643(2), Si2–O3 1.646(2), Si2–O4 1.645(2), Si3– NMR (C
6
D
6
6 6
D ,
O5 1.649(2), Si3–O6 1.644(2).
Table 1. Average of Si–Si bond lengths and the sum of the interior angles of six-membered silicon ring.
4
5
Si
6
Me12 a)
3
Av. Si–Si bond length /Å
Range /Å
The sum of interior angles /°
Range /°
2.35
2.36
2.34
2.33
2.3499(6)–2.3600(5)
662
110.34(2)–110.46(2)
2.3567(7)–2.3612(7)
663
110.30(3)–111.11(3)
2.3372(2)–2.3445(2)
670
110.75(5)–112.85(6)
2.331(1)–2.336(1)
676
111.26(7)–115.06(7)
6
a) Si Me12 was synthesized from 3 with methylmagnesium bromide.
Z. Anorg. Allg. Chem. 2018, 930–934
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6
Table 2. Crystallographic data for 3, 4, 5, and Si Me12.
3
4
5
Si
6
Me12
36Si
Empirical formula
Formula weight
Temperature /K
Crystal color
Crystal size /mm
Crystal system
Space group
a /Å
b /Å
c /Å
α /°
β /°
Cl12Si
6
C
36
H60Si
6
C
12
H
36
O12Si
6
C
12
H
6
593.94
103(2)
661.38
103(2)
colorless
540.95
103(2)
colorless
348.95
103(2)
colorless
colorless
0.08ϫ0.05ϫ0.03
monoclinic
C2/c (no. 15)
17.3650(18)
9.6145(8)
13.2554(15)
90
110.233(13)
90
2076.5(4)
4
0.25ϫ0.20ϫ0.20
0.20ϫ0.12ϫ0.05
0.12ϫ0.12ϫ0.03
monoclinic
C2/c (no. 15)
17.8271(4)
10.0471(2)
13.8530(3)
90
109.059(3)
90
2345.21(10)
4
triclinic
triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
9.6036(2)
10.8060(3)
11.4686(3)
108.617(2)
100.558(2)
109.4770(10)
1005.91(5)
1
8.9516(2)
9.0862(2)
9.7437(2)
108.613(2)
112.939(2)
100.705(2)
646.52(3)
1
γ /°
V /Å3
Z
D
μ /mm
–3
calc /g·cm
1.900
1.926
1.092
0.230
1.389
0.373
0.988
0.345
–
1
θ range /°
Reflections collected
3.276 to 25.246
11416
2.192 to 25.248
13609
2.530 to 25.249
8520
2.360 to 25.248
15692
Independent reflections
1870
3620
2330
2127
R
int
0.1000
0
82
99.3
0.0351
0
190
99.5
1.031
0.0115
0
164
99.4
1.060
0.0179
0
88
99.8
No. of restraints
No. of parameters
Completeness to θ
Goodness of fit
1.042
1.115
R
1
[I Ͼ 2σ(I)]
wR [I Ͼ 2σ(I)]
(all data)
wR (all data)
Largest diff. peak /e·Å
0.0467
0.0932
0.0769
0.1052
0.717
–0.438
0.0319
0.0843
0.0342
0.0860
0.454
0.0343
0.0961
0.0359
0.0967
0.512
0.0204
0.0575
0.0211
0.0580
0.293
–0.109
2
R
1
2
3
3
Largest diff. hole /e·Å
–0.164
–0.463
+
C
36
H
61Si
6
: 661.3383 ([M + H] ); found: 661.3342. C36
H
60Si
6
: calcd.
Single-crystal X-ray Diffraction Analysis of 5: Single crystals of 5
were obtained from a hexane solution. Compound 5 crystallizes in the
triclinic space group P1, containing 0.5 molecule per asymmetric unit.
C 65.38; H 9.14%; found: C 65.12; H 9.15%.
¯
Synthesis of 5: To a dichloromethane solution (5.0 mL) of compound
(330 mg, 0.50 mmol) and iodine (13 mg, 50 μmol) was added meth-
anol (262 μL, 6.5 mmol) at room temperature. After stirring for 6 h,
compound 4 was completely consumed as judged by the H NMR
spectrum. The reaction mixture was concentrated under reduced pres-
sure, giving compound 5 (264 mg, 0.49 mmol, 98% yield) as a white
solid. M.p.: 154 °C (dec.). H NMR (C
6 6
D , room temperature): δ = 53.4 ppm. Si
NMR (C , room temperature): δ = –9.18 ppm. FABMS: m/z calcd.
A slipped disorder (Si4–Si6 and O7-C12) was observed. The major/
minor occupancy ratios changed among the crystals, and the highest
ratio observed was 0.94:0.06. For the minor part of the disorder, EADP
functions were used between all atoms of the minor part and the corre-
sponding atoms of the major part. Due to the low occupancy of the
minor part, the accuracy of the bond lengths and angles for the minor
part is relatively poor. Therefore, structural parameters are discussed
with respect to the major part.
4
1
1
6
D
6
, room temperature): δ =
.76 (s); 13C{ H} NMR (C
1
29
3
6 6
D
O
+
for C11
H
O
O
33
12Si
11Si
12Si
6
: 525.0588; ([M – Me] ); found: 525.0584, calcd. for Crystallographic data (excluding structure factors) for the structures in
+
C
C
11
H
H
33
6
:
509.0639;
([M–OMe] );
found:
509.0638.
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-1839740 (3), CCDC-1553273 (4), CCDC-1839739
12
36
6
: calcd. C 26.65; H 6.71%; found: C 27.39; H 6.64%.
X-ray Diffraction Studies: Suitable crystals were mounted in Fom-
blin Y oil on a glass fiber. Low-temperature (103 K) data were col-
lected with a RIGAKU Saturn70 CCD system with VariMax Mo Op-
®
(
6
5), and CCDC-1839741 (Si Me12) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk)
tics using Mo-K
α
radiation (λ = 0.71075 Å) with φ- and ω-scans. An
empirical absorption correction was applied to the diffraction data
[
16]
[17]
using SCALE3 ABSPACK
for 3, 5, and Si
6
Me12 and MULABS
Acknowledgements
[
18]
for 4. Structures were solved by direct methods using SHELXT and
refined against F on all data by full-matrix least-squares with
SHELXL-2016/6.[ All non-hydrogen atoms were refined anisotropi-
2
This work was supported by JSPS KAKENHI (Grant Nos.
JP16H04110, JP18H01963, JP24109013, JP25288021, and
19]
cally. All hydrogen atoms were refined using a riding model. The iso- JP26410044), Integrated Research Consortium on Chemical Science
tropic displacement parameters of all hydrogen atoms were fixed to
.2 times the Ueq value of the atoms they are linked to (1.5 times for
methyl groups). Details of the data quality and a summary of the resid-
ual values of the refinements for all structures are contained within
Table 2.
(IRCCS) and Kyoto University Research Coordination Alliance
(KURCA). This study was also supported by the Joint Usage/Research
Center (JURC, Institute for Chemical Research (ICR), Kyoto Univer-
sity) by providing access to a Bruker Avance III 800US Plus NMR
spectrometers. We are grateful for computation time, which was pro-
1
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
vided by the Super Computer System (ICR, Kyoto University). Ele-
mental analyses were carried out at the Microanalytical Laboratory
ICR, Kyoto University).
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[
(
[
Keywords: Allylsilane; Oligosilane; Hexasilacyclohexane;
Cyclohexasilane; Halosilane
29.
[
10] X. Dai, D. L. Schulz, C. W. Braun, A. Ugrinov, P. Boudjouk, Or-
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